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048213063 | summary | The invention relates to a system comprising an X-ray source, an elongate detector tube and a slit diaphragm between the X-ray source and the detector tube, the slit-shaped aperture of the diaphragm extending parallel with the longitudinal axis of the detector tube and the detector tube including at least one cathode extending in the longitudinal direction of the tube and at least one anode located opposite to the cathode and likewise extending in the longitudinal direction of the tube, the tube being evacuated and, during operation, an electrical field being established between the cathode and the anode. Such an elongate X-ray detector tube is disclosed in Dutch patent application 79,00878 and is particularly suited for use in slit radiography. It is known from the article "Computerized dual-energy imaging: a technical description" by J. Coumans et al in Medicamundi, Vol. 27, No. 3, 1982, to produce so-called dual-energy X-ray images by alternately operating an X-ray source at two different high voltage levels, for example 70 and 120 kVp. The alternate application of the two voltages to the X-ray source results in the generation of X-ray beams having mutually different "energetic centers of gravity", in other words, mutually different hardnesses. By successively irradiating the object to be examined, such as the body of a patient, with X-radiation having a first energetic center of gravity, and X-radiation having a second energetic center of gravity, it is possible to so process, for example by means of a computer, the resultant X-ray images that, for example, only tissue and no bones are imaged, permitting the imaging of tissue located behind, for example, ribs. This is the result of the fact that different materials in, for example, the human body exhibit different absorption to X-radiation of different hardnesses. The use of different levels for the high voltage supply of an X-ray source entails the drawback that the irradiation has to be performed at two successive points of time, while the interval between these points of time must not be too long as otherwise movements of the object under examination can result in errors when processing the images obtained by means of the different X-ray beams. In slit radiography, as described in, for example, U.S. patent application No. 06/648,707, filed on Sept. 7, 1984, mechanical scanning is required for obtaining a complete image of a patient, while the scanning time for a total image height of 0.4 m is approximately 1 second. This scanning time is so long that a subsequent second scan, at a different X-ray source voltage, inevitably leads to a changed geometry of the image of the patient, which is unacceptable. It is an object of the invention to provide facilities permitting the application of the so-called dual energy image processing techniques to slit radiography, without the need for switching the anode voltage of the X-ray source. To this end, in accordance with the invention in a system of the above type a filter is mounted near the slit diaphragm in the path between the X-ray source and the detector tube, which filter intercepts a portion of the X-ray beam emitted by the source over the entire length of the slit-shaped aperture and blocks relatively low energy X-radiation in this beam portion, and the cathode is provided with an X-ray detection layer consisting of two essentially parallel strips extending in the longitudinal direction of the tube, one of these strips receiving the radiation passed by the filter and the other of the strips receiving the unfiltered radiation. The one strip preferably is of considerably greater thickness than the other strip. The invention is based on the insight that, in slit radiography, the local exposure time is considerably less than the canning time for the complete image. The local exposure time is the time required by a flat fan X-ray beam for passing a point of the patient. This beam is obtained by means of the slit diaphragm between the X-ray source and the patient, which diaphragm only allows X-radiation to be incident, after passing through the patient, on the detector tube within a spatial angle defined by the strip-like detector seen from the focal point of the X-ray source. When this slit diaphragm is thought to be divided into two narrower, superimposed slits of equal length, which slits need, in general, not be equally narrow, the original X-ray beam may be regarded to be composed of two superimposed, even flatter fan subbeams each incident on an associated narrow strip of the detector. The mechanical scanning thus results in two images, with a time difference of less than 0.1 second between the instants at which the same points of the patient are recorded. It is known that the radiation is hardened by placing a plate of suitable thickness of, for example, Pb or Cu in an X-ray beam, which means that lower energy radiation, i.e. radiation of lower frequencies, is attenuated to a higher degree than higher energy radiation, i.e. radiation of higher frequencies. Matter acts as a high pass filter upon X-radiation passing therethrough. Low pass filters for X-radiation cannot be realized in actual practice. In accordance with the invention, such a high pass filter is so mounted at the slit diaphragm in the X-ray beam path that it intercepts a portion of the flat fan X-ray beam, which portion actually constitutes one of the aforesaid subbeams. The passage of this subbeam through the filter results in a shift of the "energetic center of gravity" to a higher energy relative to that of the subbeam which passes through the slit diaphragm without being filtered. Furthermore, in accordance with a preferred embodiment of the invention the detector is so arranged that the strip on which the unfiltered beam is incident, predominantly absorbs soft radiation and optimally passes hard radiation while the strip on which the filtered beam is incident, optimally absorbs the radiation hardened by the filter. In this manner, the spacing between the "energetic centers of gravity" with which the beams act on the detector, can be increased even further. To achieve the detector characteristics desired, the strip of the detector on which the filtered beam is incident, is of considerably greater thickness than the other strip. If the detector includes an X-ray screen, besides the thickness of the screen also the screen material of one strip can be selected to differ from that of the other strip. For example, screen material consisting of atoms of low atomic number will predominantly absorb soft radiation. |
050158651 | abstract | A sterile surgical garment having a forward and rearward portion. A forwardly positioned outer layer of substantially the same size and shape as that of the forward portion secured at the bottom edge of the forward portion. Cooperable fasteners secure the unattached portion of the outer layer to the forward portion. X-ray-protective material is removably positioned between the forward portion and the outer layer. A second embodiment is disclosed wherein the X-ray-protective material is removably secured within a removable case. The case is attached to the forward portion by cooperable fasteners. |
description | This application claims Paris convention priority from EP 13 159 569.6 filed Mar. 15, 2013, the entire disclosure of which is hereby incorporated by reference. The invention relates to an x-ray analyzing system for x-ray scattering analysis comprising: an x-ray source for generating a beam of x-rays propagating along a transmission axis, at least one hybrid slit with an aperture which defines the shape of the cross-section of the x-ray beam, a sample on which the x-ray beam shaped by the hybrid slit is directed, and an x-ray detector for detecting x-rays originating from the sample, wherein the hybrid slit comprises at least three hybrid slit elements, each hybrid slit element comprising a single crystal substrate bonded to a base with a taper angle α≠0, the single crystal substrates of the hybrid slit elements limiting the aperture. Such an x-ray analyzing system is known from WO 2011 086 191 A1. X-ray measurements, in particular x-ray diffraction (XRD) and small angle x-ray scattering (SAXS) measurements are used for chemical analysis and structural analysis of samples in a variety of applications. In particular in SAXS measurements using laboratory sources it is important to have a high photon flux and a low background. The photon flux is important to have short data acquisition times and the low background is important since the scattering signal is often very low. The aperture of the slit defines the size and shape of the beam cross-section and the divergence of the beam which are important parameters for the achievable resolution. By directing x-rays to an aperture of a slit of polycrystalline material parasitic diffraction can happen, which results in a decreased signal to noise ratio. In order to limit the divergence of the x-ray beam it is known to use three aperture slits within the optical path of the x-ray beam. However, this results in a reduction of the photon flux and therefore in an increased measurement time. Li Youli; Beck Roy; Huang Tuo; et al. (Scatterless hybrid metal-single-crystal slit for small angle x-ray scattering and high resolution x-ray diffraction; JOURNAL OF APPLIED CRYSTALLOGRAPHY Volume: 41 Pages: 1134-1139 (2008)) suggested the use of hybrid slits where the edges are made of single crystals such as Germanium or Silicon. The hybrid slits comprise a metal base on which a rectangular single crystal substrate is mounted, wherein the single crystal substrates of the hybrid slit elements limiting the aperture. Parasitic scattering due to total reflection and scattering at grain boundaries can be avoided. The introduction of hybrid slits has made it possible to use only two slits (square pinholes) and still have a low background. WO 2011 086 191 A1 discloses an x-ray analyzing system for SAXS measurements using hybrid slits comprising two sets of two hybrid slit elements being arranged opposite with respect to each other to form a rectangular or square aperture. In SAXS measurements the resolution is determined by the smallest achievable scattering angle which in turn depends on the size of the cross-section of the direct beam which is blocked by an appropriate beamstop. Since the minimal beamstop size is determined by the distance from the center to the outermost point of the beam cross-section, the resolution of the x-ray analyzing system known from WO 2011 086 191 A1 is limited by the dimensions of the hybrid slit elements. It is the object of the invention to suggest an x-ray analyzing system with improved resolution and signal to noise ration. In accordance with the invention this object is achieved in that the hybrid slit elements are staggered with an offset along the transmission axis. The x-ray beam is directed on the sample, whereby the edges of the single crystal substrates of the hybrid slit limits the cross-section of the x-ray beam generated by the x-ray source. Therefore the hybrid slit elements are positioned circumferential around the transmission axis with their basis facing away from the transmission axis and their single crystal substrates facing towards the transmission axis. Due to the inventive staggered arrangement of the hybrid slit elements the single crystal substrates are positioned at different positions along the transmission axis (offset in z-direction), in which the single crystal substrates may overlap (seen in projection along the transmission axis) without obstructing each other. Thus the size of the aperture of the hybrid slit can be chosen independently of the size of the hybrid slit elements and the shape of the aperture can be chosen independently of the size if the aperture by selecting an appropriate number of hybrid slit elements. Preferably the offset between corresponding parts of the single crystal substrates complies with the dimension of the single crystal substrates in direction of the transmission axis. The offset of the hybrid slit elements then depends on the thickness of the single crystal substrates. By staggering the hybrid slit elements a polygonal cross-section with a high number of edges can be realized which—in spite of the high number of edges—shows a small size. The bases of the hybrid slit elements are preferably made of high density metal; the single crystal substrates are of high quality in order to ensure a minimum number of material defects (perfect single crystal), preferably the single crystal substrates made of Ge, Si are used. The hybrid slit, the sample and the detector are preferably positioned along the transmission axis, whereby the sample is positioned between the hybrid slit and the detector. The hybrid slit is positioned within the optical path of the beam between the x-ray source and the sample. It is also possible to displace the detector perpendicular to the optical path in order to measure a wider angular range. In this case the direct beam (beam passing the hybrid slit without being scattered) is directed to the edge of the detector. In a preferred embodiment the hybrid slit elements are arranged to form a polygon with n edges viewed in projection along the transmission axis, with n>4, in particular n≥8. Preferably the shape of the cross-section of the beam defined by the aperture is a regular polygon. The higher the number of edges in the polygon, the better it approximates a circle and, thus, the higher the photon flux that will pass it. Due to the increased photon flux the number of slits and thus the size of the analyzing system can be reduced. For a negligible offset of the single crystal substrates the shape of the aperture of the hybrid slit is also a regular polygon and the distances of the single crystal substrates to the transmission axis is the same for all single crystal substrates. With regard of a non-negligible offset the distances d of the single crystal substrates vary in dependence of the position of the single crystal substrates along the transmission axis (Δd=OS tan(2θ) with Δd=difference of distances to transmission axis, 2θ=divergence angle, OS=offset between neighboring single crystal substrates). In a special embodiment of the inventive x-ray analyzing system the hybrid slit elements are movable perpendicular to the transmission axis, in particular radial. The size and/or shape of the aperture of the hybrid slit can be varied by varying the radial position of the hybrid slit elements. Since opposing hybrid slit elements do not obstruct each other opposing hybrid slit elements can form a pair and the hybrid slit elements are staggered pairwise. I.e. opposing hybrid slit elements are positioned at the same z-position. Thereby the dimension of the hybrid slit can be reduced. In a preferred embodiment the x-ray analyzing system is a small angle x-ray diffraction analyzing system comprising a beamstop which is positioned between the hybrid slit and the detector for blocking incident x-rays. For SAXS measurements the detector is positioned close to the transmission axis of the x-ray source in order to detect signals of big nanoparticles. The beamstop is positioned between the sample under investigation and the detector. The beamstop prevents any portion of the direct beam from hitting the detector, which could otherwise saturate the detector and make measurements of the diffracted x-ray energy more difficult. Therefore the beamstop has to be large enough to cover the area that can be hit by the direct beam. On the other hand the scattering angle should be as small as possible and therefore the beamstop is chosen as small as possible. Preferably the radial positions and the positions along the transmission axis of the hybrid slit elements are chosen to optimize the photon flux of the detected scattered x-rays. Because of the divergence of the x-ray-beam the radial positions of the single hybrid slit elements depend on their respective positions along the transmission axis. In order to optimize the photon flux, the cross-section of the x-ray beam passing the hybrid slit should resemble the shape and size of the beamstop (usually circular). Most preferably the x-ray source is a laboratory source, e.g. a sealed tube, a rotating anode, a microsource, or a metal-jet source. Laboratory sources show a large divergence which lead to flux losses. In combination with a laboratory source the inventive x-ray analyzing system leads to significant photon flux increase (compared to state of the art x-ray analyzing systems) while the background is still low. The taper angle is preferably larger than the beam divergence, in particular α>10°. The beam defining single crystal substrate is oriented far from any Bragg peak position with respect to the incident beam in order to inhibit abnormal transmission. In addition the taper angle should be chosen wide enough in order to inhibit surface scattering from the slit. In a highly preferred embodiment two hybrid slits are provided, wherein the slits are positioned and spaced apart from each other along the transmission axis. Additionally a further slit can be provided, in particular a circular pinhole. The two hybrid slits are preferably separately adjustable in order to adapt the beam cross-section to the requirements of the sample. The present invention also relates to the use of an inventive apparatus as described above, for optimizing the photon flux in SAXS measurements, in particular using a laboratory source. Further advantages can be extracted from the description and the enclosed drawing. The features mentioned above and below can be used in accordance with the invention either individually or collectively in any combination. The embodiments mentioned are not to be understood as exhaustive enumeration but rather have exemplary character for the description of the invention. The invention is shown in the drawing. FIG. 1 shows an embodiment of an inventive x-ray analyzing system 1, e.g. for SAXS measurements. The x-ray analyzing system 1 comprises an x-ray source 2, in particular a laboratory source, emitting an x-ray beam XB along a transmission axis 3. The x-ray beam XB may be prepared by a beam forming element 4 which collects the emitted x-rays, generates a beam of a defined divergence and monochromatism which is then directed to two aperture slits 5a, 5b. The aperture slits 5a, 5b are arranged at a distance along the transmission axis 3 and limit the size of the cross-section of the x-ray beam XB which is directed to a sample 6. The aperture slit 5b (hybrid slit) which is positioned near the sample 6 comprises several hybrid slit elements 7, which are arranged circumferentially around the transmission axis 3. Each hybrid slit element 7 comprises a single crystal substrate 8 bonded to a base 9 (FIG. 2b). The single crystal substrate 8 is inclined with a taper angle α with respect to the x-ray beam XB (see FIG. 2c). Due to the tilted arrangement of the single crystal substrates 8 the size and shape of the cross-section of the beam XB is defined by sharp edges 12 of the single crystal substrates 8 facing the transmission axis 3. By using hybrid slit elements 7 with single crystal substrates 8 parasitic scattering due to grain boundaries and defects can be avoided. In addition, parasitic scattering due to total reflection can be reduced by choosing the taper angle α of the single crystal substrates 8 wider than the angle of total reflection. The x-ray beam XB is directed to the sample 6 which is positioned at a distance from the hybrid slit 5b in direction of the transmission axis 3. Scattered x-rays are detected by an x-ray detector 10 (here: position-sensitive area detector) positioned at a distance from the sample 6 in direction of the transmission axis 3. In order to prevent the detector 10 of being saturated, the direct beam XB is blocked by a beamstop 11 positioned between the sample 6 and the detector 10, wherein the transmission axis 3 hits the beamstop 11 at its center. The size of the polygonal hybrid slit 5b and the size of the beamstop 11 are chosen such, that the most divergent rays 13 (indicated by thin black lines in FIG. 2) of the direct beam XB pass the hybrid slit 5b and the sample 6 is blocked by the beamstop 11. Usually one wants to have the scattering angle 2θ as small as possible and therefore the beamstop 11 should be chosen as small as possible. FIG. 2a shows a preferred embodiment of the hybrid slit 5b with eight hybrid slit elements 4. The single crystal substrates 8 of the hybrid slit elements 7 form an octagonal inner contour. Generally for a hybrid slit 5b with a polygonal aperture with n edges at least n hybrid slit elements 7 are required. According to the invention the hybrid slit elements 7 are staggered with an offset along the transmission axis 3. The staggered arrangement of the hybrid slit elements 7 enables an overlapping arrangement of the hybrid slit elements 7. Thus, small aperture slit sizes can be achieved independently of the size of the single crystal substrates 8 (length l of the aperture edges are not limited to the length L of the single crystal substrates 8—see FIG. 2b, 2c). The offset between two neighboring hybrid slit elements 7 preferably corresponds to the thickness (dimension in direction of the transmission axis 3) of the according single crystal substrate 8 (neighboring single crystal substrates 8 are in contact or nearly in contact with each other). In contrast to the known hybrid slits, an increased number of hybrid slit elements 7 can be provided to form the aperture slit 5b by staggering the hybrid slit elements 7. Thus, the photon flux can be increased by approximating a circular shape, wherein at the same time parasitic scattering can be reduced by using tilted single crystal substrates 8. Yet, the number of hybrid slit elements is limited by the maximal length of the hybrid slit 5b which can be integrated in the x-ray analyzing system. The aperture slit 5a which is positioned between the source 2 and the hybrid slit 5b can be a circular pinhole, since this increases the total area of the slits and therefore also increases the photon flux. It is almost entirely the hybrid slit 5b that determines the background and therefore only hybrid slit 5b needs to be polygonal, however, both aperture slits 5a, 5b can be polygonal hybrid slits as it will in all cases increase the photon flux, as shown in the following: For a given size of the beamstop 11 with radius R the maximum diameter of the polygonal hybrid slit 5b is pre-determined, since the beamstop 11 has to be able to stop all x-rays that pass the hybrid slit 5b. FIG. 3 shows the cross-section of an x-ray beam that has passed an octagonal hybrid slit configuration 5b. The maximum diameter of the cross-section is 2R. The higher the number of edges in the polygonal hybrid slit, the better it approximates a circle and, thus, the higher the photon flux that will pass it. The area of a polygon with n sides is: A = 1 2 nR 2 sin ( 2 π n ) for a square, n=4 the equation gives A=2R2 and for an octagon A=2.82843 R2. For n infinitely large, the polygon approaches a circle for which A=R2π. The gain factor in photon flux for using a circular slit for aperture slit 5a and an octagonal hybrid slit for aperture slit 5b is 1.414 and thus 41.4% compared to using a circular slit for aperture slit 5a and a square hybrid slit for aperture slit 5b. The gain factor in photon flux for using a circular slit for aperture slit 5a and an octagonal hybrid slit for aperture slit 5b compared to using two square hybrid slits is 2.221 and thus 122.1%. In experiments gain factors very close to the predicted values have been determined. The hybrid slit elements 7 can be installed to be movable along the direction of the transmission axis 3 and/or along a radial direction (perpendicular to the transmission axis 3). The latter enables to create different sized and/or shaped hybrid slits 5b in order to adapt the hybrid slit 5b to different applications with different sized beamstops 11. Please note that in order to produce a symmetric cross-section of the x-ray beam different hybrid slit elements 7 have to be arranged at different distances to the transmission axis 3 due to the divergence of the x-ray beam XB and the staggered arrangement of the hybrid slit elements 7. Since the hybrid slit elements 7 are preferable staggered close to each other, the differences of the distances of the hybrid slit elements 7 to the transmission axis 3 are small and not shown in FIG. 2a. Correspondingly, for changing the size but keeping the shape of the aperture of the hybrid slit 5b, the different hybrid slit elements 7 have to be moved by different distances depending on their position along the transmission axis 3, i.e. the further the hybrid slit element 7 are away from the x-ray source 2, the further it has to be moved radially. The inventive staggered arrangement of hybrid slit elements 7 provides more flexibility concerning size and shape of the aperture of the hybrid slit 5b. A multitude of hybrid slit elements 7 can be used to form a polygonal aperture with a high number of edges, in particular with more than four edges, wherein the length of the edges of the aperture is smaller than the length of the single crystal substrates 8. Thus, the photon flux for a given beamstop size can be increased or the beamstop size can be reduced and the resolution of the x-ray analyzing system 1 can be increased for a given photon flux. 1 x-ray analyzing system 2 x-ray source 3 transmission axis 4 beam forming element 5a aperture slit 5b aperture slit/hybrid slit 6 sample 7 hybrid slit elements 8 single crystal substrate 9 base 10 x-ray detector 11 beamstop 12 sharp edges of the single crystal substrates 13 most divergent x-rays of the x-ray beam 2θ scattering angle α taper angle XB x-ray beam |
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abstract | An exemplary thinned-down betavoltaic device includes an N+ doped silicon carbide (SiC) substrate having a thickness between about 3 to 50 microns, an electrically conductive layer disposed immediately adjacent the bottom surface of the SiC substrate; an N− doped SiC epitaxial layer disposed immediately adjacent the top surface of the SiC substrate, a P+ doped SiC epitaxial layer disposed immediately adjacent the top surface of the N− doped SiC epitaxial layer, an ohmic conductive layer disposed immediately adjacent the top surface of the P+ doped SiC epitaxial layer, and a radioisotope layer disposed immediately adjacent the top surface of the ohmic conductive layer. The radioisotope layer can be 63Ni, 147Pm, or 3H. Devices can be stacked in parallel or series. Methods of making the devices are disclosed. |
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052710521 | summary | TECHNICAL FIELD OF THE INVENTION This invention pertains to a nuclear reactor control system which employs the use of an enriched boric acid solution in which the boron-10 isotope to boron-11 isotope ratio is greater than 19.8:80.2 as is found in naturally occurring boron acid solutions. This invention also pertains to operating a nuclear reactor plant utilizing an enriched boric acid solution for its primary reactor coolant solution during power operations and a natural boric acid solution for refueling functions in which the amount of make-up enriched boric acid solution needed for the reactor coolant system after refueling is minimized. BACKGROUND OF THE INVENTION A nuclear reactor must be provided with a system to control the reactor output. A number of ways of controlling the excess reactivity that is consciously designed into a nuclear power reactor core are known. These include the use of neutron absorbing control rods that can be inserted into or withdrawn from the reactor core, the adjustment of moderator temperature which changes the density and therefore both the fast neutron moderation and the thermal neutron absorption rates of the hydrogen in the light water coolant/moderator, and the use of solid and dissolved neutron absorbing poison materials incorporated either directly in the reactor core lattice (as burnable poison rods or fuel pellet coatings) or dissolved in the primary coolant/moderator as a "chemical shim". The chemical shim is commonly a boric acid solution. Systems employing such a boric acid solution for control of the nuclear reactor are discussed in Loose U.S. Pat. No. 3,380,889 and Gramer et al. U.S. Pat. No. 3,666,626. These coolant systems utilize natural boric acid solutions, which contain a maximum boron-10 (B-10) to boron-11 (B-11) atomic ratio of 19.8:80.2. The prior art has refined processes for concentrating the natural boric acid solutions used as chemical shims in reactor coolant systems. This concentration is necessary due to the need for a highly concentrated solution of neutron capturing compounds at the start of the reactor cycle and to compensate for the loss of B-10 material (nuclei) during the reactor cycle, and to minimize waste water streams containing radioactive wastes. Van der Schoot U.S. Pat. No. 4,073,683 discloses an ion exchange system to reconcentrate a natural boric acid solution while also producing a dilute natural boric acid solution to control the reactivity in the reactor core. Brown et al. U.S. Pat. No. 4,225,390 discloses a joint ion exchange and evaporative system to control the reactivity of the reactor core wherein the chemical shim is also natural boric acid. U.S. Pat. No. 4,225,390 also discloses how to load follow the reactor using a natural boric acid solution. These processes deal with "concentrating" a solution of natural boric acid, that is, they raise or lower the amount of natural boric acid in a solution, but do not disclose how to operate a nuclear reactor which utilizes "enriched" boric acid as the primary reactor coolant. The term "enriched" refers to a boric acid solution in which the B-10 to B-11 atomic ratio is above the naturally occurring ratio of 19.8:80.2. It is known that the B-10 isotope is the only isotope in boron-based poisons that contributes materially to the absorption of excess thermal or near thermal neutrons in reactor configurations. This is due to its relatively large neutron capture cross section in the thermal range. Also, it is known that the presence of any of the boron-based poison compounds in a typical power generating nuclear reactor leads to known deleterious effects, such as corrosion and wear, on other material components of the reactor core and of the associated nuclear steam supply system. Therefore, it follows that marked advantages over the prior art reactor coolant systems containing a chemical shim could be obtained if the B-10 to B-11 isotope ratio could be raised, thereby allowing a significant reduction in the total quantity of the boron-based poison material in the primary reactor coolant system at all times during power operations. Such a system would allow for the control of the nuclear reactor and also would be less deleterious on the physical components constituting the nuclear reactor. SUMMARY OF THE INVENTION The invention provides a pressurized water reactor coolant system (RCS) which differs from prior systems in that it contains a boric acid solution which is enriched in the boron-10 isotope to control the excess reactivity that is consciously designed into a nuclear power reactor core. This boric acid solution--referred to herein as EBA--is enriched in the boron-10 isotope and has a B-10 to B-11 atomic isotope ratio in excess of the natural ratio of 19.8:80.2. An EBA solution is preferred as a reactor coolant system solution since such a solution allows for a lower overall boric acid concentration in the reactor coolant system. This lower overall boric acid concentration means that a lower amount of lithium hydroxide is necessary to control the pH in the reactor coolant system. Such a reactor coolant system has a milder chemistry than those of the prior art and allows for a lower minimum temperature to be kept in the boric acid storage system. The lower concentration of the boric acid and the lithium hydroxide may lead to prolonged life for the components constituting the nuclear reactor coolant system. Therefore it is an object of the present invention to provide an apparatus for controlling the excess reactivity of a nuclear reactor utilizing an EBA solution in the reactor coolant system during the power producing operation of the core cycle. It is also an object of this invention to provide a process in which a nuclear reactor can be operated employing a reactor coolant system containing an EBA solution and minimizing the intermixing between the reactor coolant system and the refueling water system which contains a natural boric acid solution. The inventive nuclear reactor control system comprises a nuclear reactor which has a primary reactor coolant solution circulating through the reactor core. The coolant solution is comprised of an isotopically enriched boron-10 boric acid, or EBA, solution. The EBA solution has a boron-10 to boron-11 atomic isotope ratio of greater than 19.8:80.2, and as great as 95:5 at the start of the reactor cycle. The inventive control system employs a refueling water storage system containing a natural boric acid solution. This storage tank is connected to the reactor vessel and employed during a refueling operation. The control system design of the present invention is operated during the normal power operation mode by diverting a quantity of the primary reactor coolant which is an EBA solution from the coolant system to a boron-10 storage system. When the reactivity of the reactor core diminishes, the boric acid concentration of the EBA solution is decreased and enriched boric acid is stored in the boron-10 storage system. At the end of the reactor core cycle the concentration of boron-10 in the coolant solution is near 0-10 ppm. Therefore, most of the boron-10 material is in the boron-10 storage system. The inventive process for operating the EBA solution coolant system also provides that minimal mixing of the EBA solution and the refueling water solution will occur during and after refueling. During the refueling, the refueling water storage tank solution of natural boric acid--referred to herein as NBA--mixes with the reactor coolant solution (containing 0-10 ppm boron-10) in the reactor coolant system. After refueling, and when the fuel rods have been replaced, the vessel is closed. The boric acid solution in the reactor coolant system is then replaced with enriched boric acid. The invention provides for an apparatus and procedure to reduce the dilution of the EBA solution during this replacement step. The replacement of the boric acid solution in the reactor coolant system with the enriched boric acid is accomplished in the following manner. The solution within the refueling canal is drained via the drain system to the refueling water storage tank. A portion of the solution still within the reactor vessel and the reactor coolant system is drained to a tank. The remaining solution in the reactor vessel and the reactor coolant system is displaced by the replacement EBA solution, preferably under plug flow conditions to minimize intermixing. The reactor is now in a condition to begin the next cycle. A preferred method of minimizing the intermixing of the refueling water storage solution and the EBA solution is provided. Once the solution in the refueling canal is transferred via the drain system to the refueling water storage tank, then a portion of the remaining solution in the vessel is drained to the reactor hold-up tank by means of the residual heat removal system (RHR system). This RHR system is connected to the reactor coolant loop which connects the reactor vessel to the steam generation system. After an amount of the reactor coolant is drained from the reactor coolant system via the RHR system, and most preferably to a level such that the minimum amount of coolant is left in the reactor vessel to maintain core cooling and shutdown margin, displacement may begin. The displacement with the EBA solution is preferably carried out by employing the RHR system piping to both direct the incoming EBA solution and the outgoing remaining vessel coolant solution. The displacement can be monitored by use of temperature sensitive devices since the temperature of the incoming EBA solution is significantly cooler than the exiting vessel solution. Monitoring may also be accomplished by a B-10 isotope analyzer. The EBA solution for displacing the solution in the reactor vessel following refueling can be supplied by directing a heated solution through the ion exchange resins or by utilizing the concentrated EBA solution from the evaporative system. A make-up supply of EBA solution can be supplied to the reactor coolant system to compensate for EBA dilution during this displacement process. |
abstract | A collimator for an X-ray testing machine and a method for adjusting the collimator with the aid of a detection system disposed in the collimator that includes at least two spatially separate detection devices, disposed and spacing one behind the other. |
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claims | 1. A method for deconvolving far-field optical images for improved image resolution, comprising:positioning a near-field optical probe source at specific regions of an object to be imaged which correspond to specific pixels in far-field imaging modalities;moving the probe source with respect to a surface of the object to obtain associated detailed near-field information on the relative heights of point sources on the surface and detailed information on borders of the object;obtaining far-field optical image data corresponding to the object through a lens simultaneously with obtaining said near field information;moving the object to be imaged with respect to said lens with nanometric precision using a scanned probe microscope;recording said far-field optical data and any additional information the scanned probe microscope can provide on height, optical or other parameters of the object from at least one near-field image;determining the point spread function (PSF) of the far-field imaging lens using the near-field information;incorporating the recorded near-field information from the scanned probe microscope with said far-field data in deconvolution algorithms for added precision of the far-field imaging to obtain a deconvolved super-resolution image of the object to be imaged. 2. The method of claim 1, wherein obtaining said super-resolution image includes obtaining the point spread function of the lens with only atomic force topography information. 3. The method of claim 1, wherein obtaining said near-field optical data includes scanning said object with subwavelength resolution to define optical contrast points on said object. 4. The method of claim 1, wherein the far-field image is recorded by non-linear optical imaging. 5. The method of claim 2, wherein the far-field image is recorded by non-linear optical imaging. 6. The method of claim 3, wherein the far-field image data is recorded by non linear optical imaging. 7. A method for deconvolving far-field optical images for improved image resolution, including:producing a set of integrated and correlated near and far-field images; andvalidating the correlation of the images by a scanned probe microscope. 8. The method of claim 7, further including:computing the error between a deconvolved optical image and one or more points of an image obtained by the scanned probe microscope; andcomputing a newly deconvolved image based on the computed error. 9. The method of claim 8, wherein the deconvolved image is computed using a closed loop algorithm in which the error is checked and minimized between computed data and actual highly accurate data obtained from scanned probe microscopy. 10. The method of claim 8, wherein optical deconvolution is aided by correlated data sets from other microscopes simultaneously imaging the object at higher resolution than optical imaging. 11. A method for deconvolving far-field optical images for improved image resolution, comprising:combining atomic force microscope imaging of an object with near-field scanned probe optical imaging to provide two images of the object;altering a parameter associated with the scanned probe imagery in the near field optical image, andcorelating the images by data from the atomic force microscope. 12. A method for deconvolving far-field optical images for improved image resolution, comprising:incorporating a scanned probe device into any optical microscope with an image recording modality and without obstructing any of the imaging modes of the optical microscope;recording completely integrated image data sets from the scanned probe microscope and from the optical microscope in a computer; andproviding associated software including a deconvolution algorithm in the computer for deconvolution of the image data sets to provide corresponding images. 13. The method of claim 12, wherein deconvolution is iterative, utilizing the error between a prior deconvolved image and scanned data. |
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053612841 | claims | 1. An apparatus adapted for removable insertion into a fluid heat exchanger of a pressurized water reactor containing a corrosive medium, comprising an elongated, sealed tube and means for creating a corrosion condition onthe exterior of the tube, characterized in that the means for creating a corrosion condition comprises: first means for providing heat to the tube at a first axial position within the tube and for pressurizing the interior of the tube with a gas; second means for retaining the corrosive medium in contact with the exterior surface of the tube proximate to the first axial position; and mounting means for remountably attaching the apparatus to a port of the heat exchanger such that the first axial position of the tube extends into the corrosive medium. third means for providing a first signal indicative of a first corrosion condition of the exterior surface of the tube proximate to the first axial position. third means for providing a first signal indicative of a first corrosion condition of the exterior surface of the tube proximate to the first axial position. a gas inlet port for pressurizing the interior of the tube with a pressurized gas; a heater for providing heat to the tube at a first axial position within the tube; a structure for retaining the corrosive medium in contact with the exterior surface of the tube proximate to the first axial position; probe means for providing a first signal indicative of a first corrosion condition of the exterior surface of the tube proximate to the first axial position and to the structure. inserting a portion of the sealed tube comprising the second means within the heat exchanger; pressurizing the interior of the tube to a first pressure; heating the exterior surface of the tube proximate to the first axial position to a first temperature; providing the first signal indicative of the first corrosion condition with the probe after the pressuring and heating steps. pressurizing the interior of the tube to a first pressure; heating the exterior surface of the tube proximate to the first axial position to a first temperature; and providing the signal indicative of the corrosion condition with the third means. first means for providing heat to the tube at a first axial position within the tube and for pressurizing the interior of the tube with a gas; second means for retaining the corrosive medium in contact with the exterior surface of the tube proximate to the first axial position; and third means for providing a signal indicative of a corrosion condition of the exterior surface of the tube proximate to the first axial position. 2. The apparatus at claim 1, characterized in that the first means comprises a gas inlet port for connection to a source of pressurized gas. 3. The apparatus of claim 2, characterized in that the second means comprises a member having a first surface proximate to the exterior surface of the tube forming a crevice between the first surface and the exterior surface of the tube. 4. The apparatus of claim 3, characterized in that the means for creating a corrosion condition further comprises: 5. The apparatus of claim 2, characterized in that the second means comprises a consolidated, porous material disposed adjacent to the exterior surface of the tube. 6. The apparatus of claim 5, characterized in that the means for creating a corrosion condition further comprises: 7. An apparatus adapted for removable insertion into a fluid heat exchanger of a pressurized water reactor containing a corrosive medium, comprising an elongated sealed tube and means for predicting corrosion of the heat exchanger tubes, characterized in that the means for predicting corrosion comprises: 8. The apparatus of claim 7, characterized in that the structure comprises a consolidated, porous material. 9. The apparatus of claim 8, characterized in that the consolidated, porous material comprises a metal oxide powder. 10. The apparatus of claim 9, characterized in that the metal oxide is a member of the group consisting of aluminum oxide, zirconium oxide and iron oxide. 11. The apparatus of claim 7, characterized in that the first signal indicative of a corrosion condition is a member of the group of signals consisting of potential noise, current noise, coupling current, zero-resistance current, ac impedance and electrochemical potential. 12. A method of predicting corrosion of exterior surfaces of heat exchange tubes within an active pressurized water reactor heat exchanger with an apparatus adapted for removable insertion within the heat exchanger comprising an elongated sealed tube, first means for heating the tube at a first axial position within the tube and for pressurizing the interior of the tube with a gas, second means for retaining a corrosive sludge in contact with the exterior surface proximate to the first axial position, and a probe for providing a first signal indicative of a first corrosion condition of the exterior surface proximate to the first axial position, comprising the steps of: 13. The method of claim 12, characterized in that the first pressure is at least about a pressure within the heat exchange tubes of an active steam generator heat exchanger connected to the pressurized water reactor. 14. The method of claim 12, characterized in that the first temperature is at least about a temperature at the exterior surfaces of the heat exchange tubes of an active steam generator heat exchanger connected to the pressurized water reactor. 15. The method of claim 12, characterized in that the first signal indicative of the first corrosion condition is a member of the group of signals consisting of potential noise, current noise, coupling current, zero-resistance current, ac impedance and electrochemical potential. 16. A method of accelerating corrosion of surfaces contacting a corrosive medium with an apparatus adapted for removable insertion within a fluid reservoir containing the corrosive medium, comprising an elongated sealed tube, first means for providing heat to the tube at a first axial position within the tube and for pressurizing the interior of the tube with a gas, second means for retaining a corrosive sludge in contact with an exterior surface proximate to the first axial position, and third means for providing a signal indicative of a corrosion condition of the exterior surface of the tube proximate to the first axial position, comprising the steps of: first inserting a portion of the apparatus comprising the second means within the fluid reservoir; 17. The method of claim 16, characterized in that the first pressure is at least about a pressure within the heat exchanger tubes of an operating pressurized water reactor. 18. The method of claim 16, characterized in that the first temperature is at least about a temperature found within the heat exchanger tubes of an operating pressurized water reactor. 19. An apparatus adapted for removable insertion within a fluid reservoir containing a corrosive medium, comprising an elongated, sealed tube and means for creating a corrosion condition on an exterior of the tube, the means for creating a corrosion condition comprising: 20. The apparatus of claim 19, characterized in that the second means comprises a consolidated, porous material disposed adjacent to the exterior surface of the tube. 21. The apparatus of claim 19, characterized in that the second means comprises a member having a first surface proximate to the exterior surface of the tube and forming a crevice between the first surface and the exterior surface of the tube. |
048511870 | description | Referring now to the figures of the drawings in detail and first, particularly, to FIGS. 1-3 thereof, there is seen an angle element 2 having two legs 3 and 4 which are at right angles to one another and have equal lengths. Walls 5 and 6 are located on the same side of the legs 3 and 4. The walls 5 and 6 are at right angles to one another and to a top crosspiece 40 of the legs 3 and 4. In the top cross-piece 40, the walls 5 and 6 form an elongated L-shaped profile 7 which is at right angles to the legs 3 and 4, while at the ends of the legs 3 and 4 they are shaped into a rigid, outwardly protruding support knob 8. On the outside of the L-shaped profile 7, an elongated leaf spring 9 is disposed on each of the two walls 5 and 6 in the direction of the L-shaped profile 7. One end of each leaf spring 9 is rigidly secured by a screw or transverse pin 10 to the angle element 2 at the upper end of the L-shaped profile 7. The other end of each leaf spring 9 is guided freely so as to slide in a slot 12 on the outside of the lower end of the L-shaped profile 7. The leaf springs 9 are bent at three transverse lines 11 in such a way that the leaf springs 9 curve outward away from the outside of the L-shaped profile 7. The top crosspiece 40 of the legs 3 and 4 also has a through bore 13 formed therein at right angles to the two legs 3 and 4, that is parallel to the walls 5 and 6. A screw bolt 14 is displaceable and rotatable about the longitudinal axis thereof in the bore 13. The bore 13 has a smaller diameter on the underside of the angle element 2 than on the top and a shoulder 16 is thereby formed. One end of the screw bolt 14 on the top of the angle element 2 has a bolt head 15, which has a larger diameter than the bore 13 at the shoulder 16. The bolt head 15 is associated with the shoulder 16 of the bore 13 for support on the angle element 2. A spring washer 18 yielding in the longitudinal direction of the screw bolt 14 is also loosely located on the screw bolt 14 between the bolt head 15 and the shoulder 16 in the bore 13 of the angle element 2, and a recess 22 is provided in the angle element 2 for the spring washer 18. The other end of the screw bolt 14 at the underside of the angle element 2 is provided with a thread 21. An expansion shaft 23 of reduced diameter is located between the thread 21 and the bolt head 15. The thread 21 of the screw bolt 14 can be screwed on the top of a head plate of the nuclear reactor fuel assembly of FIG. 4 with a corner bolt. The bolt head 15 also has an annular recess or constriction location 41 in the outer surface thereof between the two ends thereof, which is formed by a coaxial bolt head shaft 42 of reduced diameter and is located in the bore 13 in the top of the angle element 2. In the angle element 2, the screws 10 with which the leaf springs 9 are firmly screwed to the angle element 2, are disposed radially relative to the bolt head shaft 42 in a common plane, which is perpendicular to the longitudinal axis of the screw bolt 14. One end of each of the two screws 10, which serve as transverse pins, protrudes or in other words extends freely between the two ends of the bolt head 15 into the annular recess or constriction location 41 in the bolt head, while the other end is secured to the angle element 2. The screws act as retaining structures for the screw bolt 14 at that location, in order to prevent the bolt head 15 from being able to slide out of the bore 13 in the direction of the longitudinal axis thereof toward the top of the angle element 2. This occurs due to the fact that the screws form a stop for the end of the bolt head 15 with the screw bolt 14 on the underside of the angle element 2. However, the bolt head shaft 42 is constructed in such a way as to be long enough to assure sufficient play for the bolt head 15 way spacing from the ends of the two screws 10. In this way, the spring washer 18 can be pressed into place in such a way that one end thereof rests flush on the shoulder 16 whenever the other end of the bolt head 15 has a diameter larger than the bolt head shaft 42. The two screws 10 are hexagonal socket screws, for example, having screw heads 50 on the ends of the screws 10 located on the outside of the angle element 2. The ends of the screws also have crimped edges 51, which are bent into a depression 52 on the outside of the angle element 2 in order to secure the screw 10 against rotation in the depression 52. As shown in FIG. 4, in which identical elements are provided with the same reference numerals as in FIGS. 1-3, the fuel assembly for a boiling water nuclear reactor has an elongated square fuel assembly box 30, which is provided with a crossbar 31 inside a corner at the upper end thereof. Fuel rods 32 and 33 filled with nuclear fuel are disposed beside one another inside the fuel assembly box 30, with longitudinal axes parallel to the longitudinal direction of the fuel assembly box 30. The upper ends of the fuel rods 32, which are adjacent the inside of the fuel assembly box 30, are guided through ducts or leadthroughs 34 in a head plate 35 inside the fuel assembly box 30 and screwed in the ducts 34. The upper ends of other fuel rods 33 filled with nuclear fuel are merely loosely guided in ducts in the head plate 35. All of the fuel rods 32 and 33 are supported against the head plate 35 by helical springs 36. In the same manner, the lower ends of the fuel rods 32 and 33 are guided in ducts in a bottom plate inside the fuel assembly box 30 which is not shown in FIG. 4 and the fuel rods 32 are once again screwed firmly in place. A corner bolt 37 having a longitudinal axis parallel to the longitudinal direction of the fuel assembly box 30 and to the longitudinal axes of the fuel rods 32 and 33, is located on top of the head plate 35, in a corner of the fuel assembly box 30. The crossbar 31, which is located inside a corner of the fuel assembly box 30, rests on the upper end of the corner bolt 37. The top crosspiece 40 of the angle element 2 rests on the outside of the crossbar 31 in such a way that the fuel assembly box 30 is fitted in a play-free manner with the edge thereof between the walls 5 and 6 of the angle element 2 and in particular in the L-shaped profile 7. The screw bolt 14 engages an opening or duct in the crossbar 31 and the threaded part 22 thereof is screwed firmly in a threaded bore in the corner bolt 37. A hoop-like handle 38 for the gripper of a fuel assembly loading machine is also disposed on the top of the head plate 35. In a boiling water nuclear reactor, as described in German Published, Non-Prosecuted Application DE-OS No. 28 24 265, corresponding to U.S. Pat. No. 4,304,635 and in German Published, Non-Prosecuted Application DE-OS No. 30 27 562, four fuel assemblies at a time are disposed as shown in FIG. 4 in a square grid opening of a transverse grid, which is the so-called upper core grid. Each of the fuel assemblies is thus located in one corner of the opening, in such way that the corners of the fuel assembly boxes 30 are located with the angle elements 2 in the center of the opening, where leaf springs 9 of laterally adjacent fuel assemblies are supported against one another, two at a time. The fuel assembly boxes of the four fuel assemblies located in the same opening of the core grid form a gap-like interstice with a + or cross-shaped cross section, in which an elongated control rod, which also has a + or cross-shaped cross section, is inserted from the lower ends of the four fuel assemblies. When the four fuel assemblies are loaded into or unloaded from the openings of the core grid, expansion forces acting upon the screw bolt 14 in the longitudinal direction and exceeding a threshold value can at worst cause the screw bolt 14 to break at the expansion shaft 23 between the thread 21 and the bolt head 15 having a lesser diameter which is provided for this purpose, so that in this case there will be no loose part of the bolt to travel into the gap-like interstice between the fuel assembly boxes where it could hinder the control rod. This is because the thread 21 remains screwed into the corner bolt 37, while the rest of the screw bolt 14 including the spring washer 18 continues to be retained in captive fashion on the angle element 2, because of the screws 10 forming a stop for the bolt head 15 and because of the recess 22 for the spring washer 18. If the screw bolt 14 on the radiation-exposed fuel assembly is to be replaced after use in the boiling water reactor, all that is required is to unscrew the screws 10, after bending the crimped edge or rim 51 open and out of the outside of the angle element 2, thus freeing the bolt head 15 and the screw bolt 14 as well. |
summary | ||
042636540 | summary | BACKGROUND OF THE INVENTION The present invention relates to a system for determining normal operating values of plant data which sequentially change in the transient operational mode, for example, during the start-up or shut-down operation of a plant. In order to determine whether or not a plant is operating normally, it is a required task for the plant operator to compare the present values of main plant data with their normal operating values. Especially, such a determination is important during any transient operational mode of the plant, since the plant status sometimes becomes unstable at such times. In the transient operational mode, the values of the main plant data change broadly. For example, during the start-up operation of a nuclear power plant, plant data such as the reactor pressure, the reactor power, the main steam flow, and the feedwater flow are known to change in a range from 0 to 100 percent. Therefore, the operator of the plant must determine the normal values of plant data in response to the present plant status before making a comparison between the present values and the normal values. The normal value corresponds to a plant data operating value of the plant when the plant is properly operating during an operating step thereof. Even for the experienced operator, great effort and skill are required to determine the normal values of the plant data which are changing over such a wide range of values during the transient operational mode. It is possible to determine the normal values of plant data by repeatedly analyzing the dynamic characteristic of the plant. However, such a method consumes considerable time and requires the use of rather complicated apparatus. It is, therefore, generally undesirable. SUMMARY OF THE INVENTION A main object of the present invention is to provide a system for determining the normal values of plant data in a reasonably short time and with apparatus of simple construction. In order to achieve such an object, the present invention is characterized by provision of a system for determining the normal values of plant data which comprises first means for determining the present plant status in response to at least one type of plant data changing with the operation of the plant and second means for determining at least one normal value of plant data in response to the plant status derived from said first means. |
046845046 | summary | CROSS REFERENCE TO RELATED APPLICATION Reference is hereby made to the following copending application dealing with related subject matter and assigned to the assignee of the present invention: "Nuclear Reactor" by Harry M. Ferrari et al, assigned U.S. Ser. No. 732,220 and filed May 9, 1985. BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates generally to fuel assemblies for nuclear reactors and, more particularly, is concerned with a bow resistant fuel assembly structure for non-control rod locations of the reactor core. 2. Description of the Prior Art The cores of nuclear reactors conventionally include a plurality of fuel assemblies. In a typical pressurized water nuclear reactor (PWR), all fuel assemblies are geometrically alike. Each fuel assembly includes a multiplicity of fuel rods held in an organized array by grids spaced along the fuel assembly length. The grids are attached to a plurality of control rod guide thimbles. Top and bottom nozzles of the fuel assembly are secured to opposite ends of the control rod guide thimbles which extend above and below the opposite ends of the fuel rods. The guide thimbles together with the top and bottom nozzles rigidly attached thereto compose the structural skeleton of the fuel assembly. To control the fission process created by nuclear fuel contained in the fuel rods, typically a number of control rods are reciprocally positioned for movement in the guide thimbles of the fuel assembly. However, not all of the fuel assembly locations of a reactor core use control rods. Only about one-third of the fuel assemblies are in control rod locations. But since heretofore all PWR fuel assemblies have been constructed to be alike geometrically, this means that the fuel assemblies for control rod locations have been the same as those for non-control rod locations. A departure from this prior practice of constructing all PWR fuel assemblies alike has been proposed recently. As described and illustrated in the patent application cross-referenced above, a separate fuel assembly design for non-control rod locations includes a bottom nozzle, a number of longitudinally extending structural members which contain a burnable poison and a top nozzle. It also includes a number of grids which are axially spaced and attached to the longitudinal structural members and support an array of fuel rods. The top and bottom nozzles are attached to the longitudinal structural members by screw thread connections or other suitable rigid attaching means. An instrumentation tube is located in the center of the assembly and is supported by the top and bottom nozzles and by the grids. One important difference in this non-control rod fuel assembly over the conventional control rod fuel assembly lies in the design of the longitudinal structural members which interconnect the top and bottom nozzles to form the structural skeleton of the assembly. In the conventional PWR assembly, the structural members are the hollow guide thimble tubes which are open at the top and closed at the bottom (except for small holes for coolant flow). These tubes are positioned within the fuel assembly to align with the control rods. During reactor operation, the control rods move reciprocally in the tubes. On the other hand, in the non-control rod fuel assembly intended for use in non-control rod core locations, the structural member also in the form of tubes do not receive control rods. Therefore, different functional as well as structural use can be made of the tubes. Functionally, this non-control rod structural member contains burnable absorber material. Burnable absorbers, such as a suitable compound of boron, are used in modern reactors to provide an additional means for controlling reactivity especially at the beginning of life of the nuclear fuel. Structurally, the elongated tube of the structural member is closed at each end by end plugs which are welded to the tube. The tube and end plug material is preferably Zircaloy-4. A spring holds the absorber material in place in the tube and provides a plenum for accumulation of helium gas which is released when a neutron interacts with a boron atom. To assemble the non-control rod structural members into the fuel assembly, the tubes must be empty and open at one end. After the grids are bulge fitted to the tubes, the absorber material and spring are loaded into the tubes and the remaining one end plugs welded in place. The fuel rods are then loaded and the top and bottom nozzles are bolted on. In the non-control rod fuel assembly, there are eight absorber structural members whereas the conventional control rod fuel assembly has twenty-four guide thimbles. Thus, there are sixteen more fuel rods per non-control rod fuel assembly which has the benefits described in the above cross-referenced application. The use of non-control rod fuel assemblies in PWRs having the design described above has created an opportunity to possibly overcome an important problem which has been present for a long time and affects the overall performance of PWR fuel assemblies: fuel assembly bow. There appears to be a definite relationship between the magnitude of fuel assembly bow and compressive stresses in the guide thimbles. Unfortunately, there is no readily apparent method of appreciably reducing the compressive stresses in the guide thimbles of control rod fuel assemblies which are in control rod core locations. However, for fuel assemblies in non-control rod core locations and designed as described above, an opportunity would appear to exist to find a way of greatly reducing the compressive stresses in the longitudinal structural members. SUMMARY OF THE INVENTION The present invention provides an improved longitudinal structural member for the non-control rod fuel assembly designed to satisfy the aforementioned needs. In the non-control rod fuel assembly described above and more completely disclosed in the cross-referenced patent application, axial force from the top nozle hold-down spring is transmitted from the top nozzle adapter plate to the top end plug of the longitudinal structural member, through its cladding tube to the bottom end plug and then to the bottom nozzle adapter plate. The cladding tube is thus placed in a state of compression which will result in permanent fuel assembly bow. The present invention improves the design of the longitudinal structural member so as to greatly reduce or counteract the deleterious effects of compressive stresses on its cladding tube. Basically, the solution involves preloading the cladding tube of the structural member in tension. Preloading the tube of a free standing structure of this type in tension means that the central part of it must be loaded in compression. Also, the material loaded in compression must not be subject to thermal or irradiation induced creep or the structure will creep to a permanently bowed position. Thus, the center portion must be made of a creep resistant material. Ceramic materials which are very creep resistant can be used. Therefore, the improvement of the present invention envisions a unique arrangement for applying a compressive load on the ceramic material, such preferably being in a stacked pellet form, so that the cladding tube can be preloaded in tension. Accordingly, the present invention is set forth in a fuel assembly for use at non-control rod locations of a nuclear reactor core. The fuel assembly includes top and bottom nozzles and a plurality of longitudinal structural members extending between and attached to the nozzles for forming the assembly into an integral unitary structure. At least certain of the structural members includes an elongated hollow cladding tube extending between the top and bottom nozzles and means secured to opposite ends of the tube for hermetically sealing the tube and attaching it to the top and bottom nozzles. The present invention relates to the improvement which comprises: (a) a quantity of irradiation-induced creep resistant material disposed within the tube; and (b) pretensioning means positioned within the tube for applying a predetermined compressive load to the creep resistant material therein and reacting the load so as to preload the tube in a state of pretension having a magnitude sufficient to substantially counteract an axial load typically transmitted through the unitary structure of the fuel assembly and thereby greatly reduce the compressive stress in the tube of the structural member. More particularly, the creep resistant material is a ceramic material, such as zirc oxide, in pellet form. The ceramic pellets are coated with a burnable absorber material. Also, the pretensioning means can be either of two embodiments. In one embodiment, the pretensioning means is an elongated bellows type device positioned within the tube between the stack of creep resistant pellets and one of the tube ends. The interior of the bellows type device is pressurized to create a predetermined axial force therein which places the creep resistant pellets in compression and the tube in the state of pretension. Additionally, the remainder of the tube can be pressurized. In an alternative embodiment, the pretensioning means is an arrangement of belleville springs positioned within the tube between the stack of creep resistant pellets and one of the tube ends so as to create the predetermined axial force therein which places the creep resistant material in compression and the tube in the state of pretension. The belleville springs in the arrangement thereof are both stacked in parallel and in series. These and other advantages and attainments of the present invention will become apparent to those skilled in the art upon a reading of the following detailed description when taken in conjunction with the drawings wherein there is shown and described an illustrative embodiment of the invention. |
description | This application claims the benefit under 35 U.S.C. § 119 to U.S. Provisional Application Ser. No. 62/731,683 filed Sep. 14, 2018, and titled MONOCHROMATIC X-RAY FILTER, which is herein incorporated by reference in its entirety. Traditional diagnostic radiography uses x-ray generators that emit X-rays over a broad energy band. A large fraction of this band contains x-rays which are not useful for medical imaging because their energy is either too high to interact in the tissue being examined or too low to reach the X-ray detector or film used to record them. The x-rays with too low an energy to reach the detector are especially problematic because they unnecessarily expose normal tissue and raise the radiation dose received by the patient. It has long been realized that the use of monochromatic x-rays, if available at the appropriate energy, would provide optimal diagnostic images while minimizing the radiation dose. To date, no such monochromatic X-ray source has been available for routine clinical diagnostic use. Monochromatic radiation has been used in specialized settings. However, conventional systems for generating monochromatic radiation have been unsuitable for clinical or routine commercial use due to their prohibitive size, cost and/or complexity. For example, monochromatic X-rays can be copiously produced in synchrotron sources utilizing an inefficient Bragg crystal as a filter or using a solid, flat target x-ray fluorescer but these are very large and not practical for routine use in hospitals and clinics. Monochromatic x-rays may be generated by providing in series a target (also referred to as the anode) that produces broad spectrum radiation in response to an incident electron beam, followed by a fluorescing target that produces monochromatic x-rays in response to incident broad spectrum radiation. The term “broad spectrum radiation” is used herein to describe Bremsstrahlung radiation with or without characteristic emission lines of the anode material. Briefly, the principles of producing monochromatic x-rays via x-ray fluorescence are as follows. Thick Target Bremsstrahlung In an x-ray tube electrons are liberated from a heated filament called the cathode and accelerated by a high voltage (e.g., ˜50 kV) toward a metal target called the anode as illustrated schematically in FIG. 1. The high energy electrons interact with the atoms in the anode. Often an electron with energy E1 comes close to a nucleus in the target and its trajectory is altered by the electromagnetic interaction. In this deflection process, it decelerates toward the nucleus. As it slows to an energy E2, it emits an X-ray photon with energy E2−E1. This radiation is called Bremsstrahlung radiation (braking radiation) and the kinematics are shown in FIG. 2. The energy of the emitted photon can take any value up to the maximum energy of the incident electron, Emax. As the electron is not destroyed it can undergo multiple interactions until it loses all of its energy or combines with an atom in the anode. Initial interactions will vary from minor to major energy changes depending on the actual angle and proximity to the nucleus. As a result, Bremsstrahlung radiation will have a generally continuous spectrum, as shown in FIG. 3. The probability of Bremsstrahlung production is proportional to Z2, where Z is the atomic number of the target material, and the efficiency of production is proportional to Z and the x-ray tube voltage. Note that low energy Bremsstrahlung X-rays are absorbed by the thick target anode as they try to escape from deep inside causing the intensity curve to bend over at the lowest energies, as discussed in further detail below. Characteristic Line Emission While most of the electrons slow down and have their trajectories changed, some will collide with electrons that are bound by an energy, BE, in their respective orbitals or shells that surround the nucleus in the target atom. As shown in FIG. 4, these shells are denoted by K, L, M, N, etc. In the collision between the incoming electron and the bound electron, the bound electron will be ejected from the atom if the energy of the incoming electron is greater than BE of the orbiting electron. For example, the impacting electron with energy E>BEK, shown in FIG. 4, will eject the K-shell electron leaving a vacancy in the K shell. The resulting excited and ionized atom will de-excite as an electron in an outer orbit will fill the vacancy. During the de-excitation, an X-ray is emitted with an energy equal to the difference between the initial and final energy levels of the electron involved with the de-excitation. Since the energy levels of the orbital shells are unique to each element on the Periodic Chart, the energy of the X-ray identifies the element. The energy will be monoenergetic and the spectrum appears monochromatic rather than a broad continuous band. Here, monochromatic means that the width in energy of the emission line is equal to the natural line width associated with the atomic transition involved. For copper Kα x-rays, the natural line width is about 4 eV. For Zr Kα, Mo Kα and Pt Kα, the line widths are approximately, 5.7 eV, 6.8 eV and 60 eV, respectively. The complete spectrum from an X-ray tube with a molybdenum target as the anode is shown in FIG. 5. The characteristic emission lines unique to the atomic energy levels of molybdenum are shown superimposed on the thick target Bremsstrahlung. X-Ray Absorption and X-Ray Fluorescence When an x-ray from any type of x-ray source strikes a sample, the x-ray can either be absorbed by an atom or scattered through the material. The process in which an x-ray is absorbed by an atom by transferring all of its energy to an innermost electron is called the photoelectric effect, as illustrated in FIG. 6A. This occurs when the incident x-ray has more energy than the binding energy of the orbital electron it encounters in a collision. In the interaction the photon ceases to exist imparting all of its energy to the orbital electron. Most of the x-ray energy is required to overcome the binding energy of the orbital electron and the remainder is imparted to the electron upon its ejection leaving a vacancy in the shell. The ejected free electron is called a photoelectron. A photoelectric interaction is most likely to occur when the energy of the incident photon exceeds but is relatively close to the binding energy of the electron it strikes. As an example, a photoelectric interaction is more likely to occur for a K-shell electron with a binding energy of 23.2 keV when the incident photon is 25 keV than if it were 50 keV. This is because the photoelectric effect is inversely proportional to approximately the third power of the X-ray energy. This fall-off is interrupted by a sharp rise when the x-ray energy is equal to the binding energy of an electron shell (K, L, M, etc.) in the absorber. The lowest energy at which a vacancy can be created in the particular shell and is referred to as the edge. FIG. 7 shows the absorption of tin (Sn) as a function of x-ray energy. The absorption is defined on the ordinate axis by its mass attenuation coefficient. The absorption edges corresponding to the binding energies of the L orbitals and the K orbitals are shown by the discontinuous jumps at approximately 43.4 keV and 29 keV, respectively. Every element on the Periodic Chart has a similar curve describing its absorption as a function of x-ray energy. The vacancies in the inner shell of the atom present an unstable condition for the atom. As the atom returns to its stable condition, electrons from the outer shells are transferred to the inner shells and in the process emit a characteristic x-ray whose energy is the difference between the two binding energies of the corresponding shells as described above in the section on Characteristic Line Emission. This photon-induced process of x-ray emission is called X-ray Fluorescence, or XRF. FIG. 6B shows schematically X-ray fluorescence from the K shell and a typical x-ray fluorescence spectrum from a sample of aluminum is shown in FIG. 8. The spectrum is measured with a solid state, photon counting detector whose energy resolution dominates the natural line width of the L-K transition. It is important to note that these monoenergetic emission lines do not sit on top of a background of broad band continuous radiation; rather, the spectrum is Bremsstrahlung free. Some embodiments include a monochromatic x-ray source comprising an electron source configured to generate electrons, a primary target arranged to receive electrons from the electron source to produce broadband x-ray radiation in response to electrons impinging on the primary target, and a secondary target comprising at least one layer of material capable of producing monochromatic x-ray radiation in response to absorbing incident broadband x-ray radiation emitted by the primary target. Some embodiments include a carrier configured for use with a broadband x-ray source comprising an electron source and a primary target arranged to receive electrons from the electron source to produce broadband x-ray radiation in response to electrons impinging on the primary target, the carrier comprising a distal portion having an aperture that allows x-ray radiation to exit the carrier, and a proximal portion comprising a secondary target having at least one layer of material capable of producing fluorescent x-ray radiation in response to absorbing incident broadband x-ray radiation, and at least one support on which the at least one layer of material is applied, the at least one support including a cooperating portion that allows the proximal portion to be coupled to the distal portion. According to some embodiments, a carrier configured for use with a broadband x-ray source comprising an electron source and a primary target arranged to receive electrons from the electron source to produce broadband x-ray radiation in response to electrons impinging on the primary target is provided. The carrier comprising a housing configured to be removably coupled to the broadband x-ray source and configured to accommodate a secondary target capable of producing monochromatic x-ray radiation in response to incident broadband x-ray radiation, the housing comprising a transmissive portion configured to allow broadband x-ray radiation to be transmitted to the secondary target when present, and a blocking portion configured to absorb broadband x-ray radiation. Some embodiments include a carrier configured for use with a broadband x-ray source comprising an electron source and a primary target arranged to receive electrons from the electron source to produce broadband x-ray radiation in response to electrons impinging on the primary target, the carrier comprising a housing configured to accommodate a secondary target that produces monochromatic x-ray radiation in response to impinging broadband x-ray radiation, the housing further configured to be removably coupled to the broadband x-ray source so that, when the housing is coupled to the broadband x-ray source and is accommodating the secondary target, the secondary target is positioned so that at least some broadband x-ray radiation from the primary target impinges on the secondary target to produce monochromatic x-ray radiation, the housing comprising a first portion comprising a first material substantially transparent to the broadband x-ray radiation, and a second portion comprising a second material substantially opaque to broadband x-ray radiation. Some embodiments include a monochromatic x-ray device comprising an electron source configured to emit electrons, a primary target configured to produce broadband x-ray radiation in response to incident electrons from the electron source, a secondary target configured to generate monochromatic x-ray radiation via fluorescence in response to incident broadband x-ray radiation, and a housing for the secondary target comprising an aperture through which monochromatic x-ray radiation from the secondary target is emitted, the housing configured to position the secondary target so that at least some of the broadband x-ray radiation emitted by the primary target is incident on the secondary target so that, when the monochromatic x-ray device is operated, monochromatic x-ray radiation is emitted via the aperture having a monochromaticity of greater than or equal to 0.7 across a field of view of at least approximately 15 degrees. According to some embodiments, monochromatic x-ray radiation emitted via the aperture has a monochromaticity of greater than or equal to 0.8 across a field of view of at least approximately 15 degrees. According to some embodiments, monochromatic x-ray radiation emitted via the aperture has a monochromaticity of greater than or equal to 0.9 across a field of view of at least approximately 15 degrees. According to some embodiments, monochromatic x-ray radiation emitted via the aperture has a monochromaticity of greater than or equal to 0.95 across a field of view of at least approximately 15 degrees. Some embodiments include a monochromatic x-ray device comprising an electron source configured to emit electrons, a primary target configured to produce broadband x-ray radiation in response to incident electrons from the electron source, and a secondary target configured to generate monochromatic x-ray radiation via fluorescence in response to incident broadband x-ray radiation, wherein the device is operated using a voltage potential between the electron source and the primary target that is greater than twice the energy of an absorption edge of the secondary target. According to some embodiments, the device is operated using a voltage potential between the electron source and the primary target that is greater than three times the energy of an absorption edge of the secondary target. According to some embodiments, the device is operated using a voltage potential between the electron source and the primary target that is greater than four times the energy of an absorption edge of the secondary target. According to some embodiments, the device is operated using a voltage potential between the electron source and the primary target that is greater than five times the energy of an absorption edge of the secondary target. Some embodiments include a monochromatic x-ray device comprising an electron source comprising a toroidal cathode, the electron source configured to emit electrons, a primary target configured to produce broadband x-ray radiation in response to incident electrons from the electron source, at least one guide arranged concentrically to the toroidal cathode to guide electrons toward the primary target, and a secondary target configured to generate monochromatic x-ray radiation via fluorescence in response to incident broadband x-ray radiation. According to some embodiments, the at least one guide comprises at least one first inner guide arranged concentrically within the toroidal cathode. According to some embodiments, the at least one guide comprises at least one first outer guide arranged concentrically outside the toroidal cathode. Some embodiments include a monochromatic x-ray component for producing monochromatic x-ray radiation from broadband x-ray radiation, the monochromatic x-ray component comprising a housing configured to be positioned proximate a broadband x-ray source, at least one first target arranged to receive broadband x-ray radiation emitted from the broadband x-ray source when the housing is positioned proximate the broadband x-ray source, the at least one first target configured to produce first monochromatic x-ray radiation in response to the received broadband x-ray radiation, and at least one second target to receive at least some of the first monochromatic x-ray radiation produced by the at least one first target when the at least one second target is positioned within the monochromatic x-ray component, the at least one second target configured to produce second monochromatic x-ray radiation in response to the received first monochromatic x-ray radiation. Some embodiments include a monochromatic x-ray component for producing monochromatic x-ray radiation from broadband x-ray radiation, the monochromatic x-ray component comprising a housing configured to be positioned proximate a broadband x-ray source, at least one first target arranged to receive broadband x-ray radiation emitted from the broadband x-ray source when the housing is positioned proximate the broadband x-ray source, the at least one first target configured to produce first monochromatic x-ray radiation in response to the received broadband x-ray radiation, and a receptacle configured to accommodate at least one second target, the at least one second target configured to receive at least some of the first monochromatic x-ray radiation produced by the at least one first target and produce second monochromatic x-ray radiation in response to the received first monochromatic x-ray radiation when the at least one second target is positioned within the receptacle. A monochromatic x-ray source comprising a broadband x-ray source configured to emit broadband x-ray radiation, a monochromatic x-ray component coupled to the broadband x-ray source, the monochromatic x-ray component comprising at least one first target arranged to receive broadband x-ray radiation emitted from the broadband x-ray source and configured to produce first monochromatic x-ray radiation in response to the received broadband x-ray radiation, and at least one second target to receive at least some of the first monochromatic x-ray radiation produced by the at least one first target when the at least one second target is positioned within the monochromatic x-ray component, the at least one second target configured to produce second monochromatic x-ray radiation in response to the received first monochromatic x-ray radiation. Some embodiments include a monochromatic x-ray source comprising a broadband x-ray source configured to emit broadband x-ray radiation, a monochromatic x-ray component coupled to the broadband x-ray source, the monochromatic x-ray component comprising at least one first target arranged to receive broadband x-ray radiation emitted from the broadband x-ray source and configured to produce first monochromatic x-ray radiation in response to the received broadband x-ray radiation, and a receptacle configured to accommodate at least one second target, the at least one second target configured to receive at least some of the first monochromatic x-ray radiation produced by the at least one first target and produce second monochromatic x-ray radiation in response to the received first monochromatic x-ray radiation when the at least one second target is positioned within the receptacle. Some embodiments include a method of generating monochromatic x-ray radiation, the method comprising receiving broadband x-ray radiation by at least one first target, generating first monochromatic x-ray radiation by the at least one first target in response to the received broadband x-ray radiation, receiving at least some of the first monochromatic x-ray radiation generated by the at least one first target by at least one second target, and generating second monochromatic x-ray radiation by the at least one second target in response to the received first monochromatic x-ray radiation. As discussed above, conventional x-ray systems capable of generating monochromatic radiation to produce diagnostic images are typically not suitable for clinical and/or commercial use due to the prohibitively high costs of manufacturing, operating and maintaining such systems and/or because the system footprints are much too large for clinic and hospital use. As a result, research with these systems are limited in application to investigations at and by the relatively few research institutions that have invested in large, complex and expensive equipment. Cost effective monochromatic x-ray imaging in a clinical setting has been the goal of many physicists and medical professionals for decades, but medical facilities such as hospitals and clinics remain without a viable option for monochromatic x-ray equipment that can be adopted in a clinic for routine diagnostic use. The inventor has developed methods and apparatus for producing selectable, monochromatic x-radiation over a relatively large field-of-view (FOV). Numerous applications can benefit from such a monochromatic x-ray source, in both the medical and non-medical disciplines. Medical applications include, but are not limited to, imaging of breast tissue, the heart, prostate, thyroid, lung, brain, torso and limbs. Non-medical disciplines include, but are not limited to, non-destructive materials analysis via x-ray absorption, x-ray diffraction and x-ray fluorescence. The inventor has recognized that 2D and 3D X-ray mammography for routine breast cancer screening could immediately benefit from the existence of such a monochromatic source. According to some embodiments, selectable energies (e.g., up to 100 kev) are provided to optimally image different anatomical features. Some embodiments facilitate providing monochromatic x-ray radiation having an intensity that allows for relatively short exposure times, reducing the radiation dose delivered to a patient undergoing imaging. According to some embodiments, relatively high levels of intensity can be maintained using relatively small compact regions from which monochromatic x-ray radiation is emitted, facilitating x-ray imaging at spatial resolutions suitable for high quality imaging (e.g., breast imaging). The ability to generate relatively high intensity monochromatic x-ray radiation from relatively small compact regions facilitates short, low dose imaging at relatively high spatial resolution that, among other benefits, addresses one or more problems of conventional x-ray imaging systems (e.g., by overcoming difficulties in detecting cancerous lesions in thick breast tissue while still maintaining radiation dose levels below the limit set by regulatory authorities, according to some embodiments). With conventional mammography systems, large (thick) and dense breasts are difficult, if not impossible, to examine at the same level of confidence as smaller, normal density breast tissue. This seriously limits the value of mammography for women with large and/or dense breasts (30-50% of the population), a population of women who have a six-fold higher incidence of breast cancer. The detection sensitivity falls from 85% to 64% for women with dense breasts and to 45% for women with extremely dense breasts. Additionally, using conventional x-ray imaging systems (i.e., broadband x-ray imaging systems) false positives and unnecessary biopsies occur at unsatisfactory levels. Techniques described herein facilitate monochromatic x-ray imaging capable of providing a better diagnostic solution for women with large and/or dense breasts who have been chronically undiagnosed, over-screened and are most at risk for breast cancer. Though benefits associated with some embodiments have specific advantages for thick and/or dense breasts, it should be appreciated that techniques provided herein for monochromatic x-ray imaging also provide advantages for screening of breasts of any size and density, as well as providing benefits for other clinical diagnostic applications. For example, techniques described herein facilitate reducing patient radiation dose by a factor of 6-26 depending on tissue density for all patients over conventional x-ray imaging systems currently deployed in clinical settings, allowing for annual and repeat exams while significantly reducing the lifetime radiation exposure of the patient. Additionally, according to some embodiments, screening may be performed without painful compression of the breast in certain circumstances. Moreover, the technology described herein facilitates the manufacture of monochromatic x-ray systems that are relatively low cost, keeping within current cost constraints of broadband x-ray systems currently in use for clinical mammography. Monochromatic x-ray imaging may be performed with approved contrast agents to further enhance detection of tissue anomalies at a reduced dose. Techniques described herein may be used with three dimensional 3D tomosynthesis at similarly low doses. Monochromatic radiation using techniques described herein may also be used to perform in-situ chemical analysis (e.g., in-situ analysis of the chemical composition of tumors), for example, to improve the chemical analysis techniques described in U.S. patent application Ser. No. 15/825,787, filed Nov. 28, 2017 and titled “Methods and Apparatus for Determining Information Regarding Chemical Composition Using X-ray Radiation,” which application is incorporated herein in its entirety. Conventional monochromatic x-ray sources have previously been developed for purposes other than medical imaging and, as a result, are generally unsuitable for clinical purposes. Specifically, the monochromaticity, intensity, spatial resolution and/or power levels may be insufficient for medical imaging purposes. The inventor has developed techniques for producing monochromatic x-ray radiation suitable for numerous applications, including for clinical purposes such as breast and other tissue imaging, aspects of which are described in further detail below. The inventor recognized that conventional monochromatic x-ray sources emit significant amounts of broadband x-ray radiation in addition to the emitted monochromatic x-ray radiation. As a result, the x-ray radiation emitted from such monochromatic x-ray sources have poor monochromaticity due to the significant amounts of broadband radiation that is also emitted by the source, contaminating the x-ray spectrum. The inventor has developed techniques for producing x-ray radiation with high degrees of monochromaticity (e.g., as measured by the ratio of monochromatic x-ray radiation to broadband radiation as discussed in further detail below), both in the on-axis direction and off-axis directions over a relatively large field of view. Techniques described herein enable the ability to increase the power of the broadband x-ray source without significantly increasing broadband x-ray radiation contamination (i.e., without substantially reducing monochromaticity). As a result, higher intensity monochromatic x-ray radiation may be produced using increased power levels while maintaining high degrees of monochromaticity. The inventor has further developed geometries for secondary targets (i.e., fluorescent target arranged to emit monochromatic radiation in response to incident broadband x-ray radiation) that significantly increase monochromatic x-ray intensity, allowing for decreased exposure times without degrading image quality or increasing power levels. According to some embodiments, secondary targets are constructed using one or more layers of secondary target material, instead of using solid secondary targets as is conventionally done. According to some embodiments, a monochromatic x-ray device is provided that is capable of producing monochromatic x-ray radiation having characteristics (e.g., monochromaticity, intensity, etc.) that enable exposure times of less than 20 seconds, according to some embodiments, exposure times of less than 10 seconds and, according to some embodiments, exposure times of less than ? seconds for mammography. According to some embodiments, a monochromatic x-ray device is provided that emits monochromatic x-rays having a high degree of monochromaticity (e.g., at 90% purity or better) over a field of view sufficient to image a target organ (e.g., a breast) in a single exposure to produce an image at a spatial resolution suitable for diagnostics (e.g., a spatial resolution of a 100 microns or better). Following below are more detailed descriptions of various concepts related to, and embodiments of, monochromatic x-ray systems and techniques regarding same. It should be appreciated that the embodiments described herein may be implemented in any of numerous ways. Examples of specific implementations are provided below for illustrative purposes only. It should be appreciated that the embodiments and the features/capabilities provided may be used individually, all together, or in any combination of two or more, as aspects of the technology described herein are not limited in this respect. FIG. 9 illustrates a two dimensional (2D) schematic cut of a conventional x-ray apparatus for generating monochromatic x-rays via x-ray fluorescence. The x-ray apparatus illustrated in FIG. 9 is similar in geometry to the x-ray apparatus illustrated and described in U.S. Pat. No. 4,903,287, titled “Radiation Source for Generating Essentially Monochromatic X-rays,” as well as the monochromatic x-ray source illustrated and described in Marfeld, et al., Proc. SPIE Vol. 4502, p. 117-125, Advances in Laboratory-based X-ray Sources and Optics II, Ali M. Khounsayr; Carolyn A. MacDonald; Eds. Referring to FIG. 9, x-ray apparatus 900 comprises a vacuum tube 950 that contains a toroidal filament 905 that operates as a cathode and primary target 910 that operates as an anode of the circuit for generating broadband x-ray radiation. Vacuum tube 950 includes a vacuum sealed enclosure formed generally by housing 955, front portion 965 (e.g., a copper faceplate) and a window 930 (e.g., a beryllium window). In operation, electrons (e.g., exemplary electrons 907) from filament 905 (cathode) are accelerated toward primary target 910 (anode) due to the electric field established by a high voltage bias between the cathode and the anode. As the electrons are decelerated by the primary target 910, broadband x-ray radiation 915 (i.e., Bremsstrahlung radiation as shown in FIG. 3) is produced. Characteristic emission lines unique to the primary target material may also be produced by the electron bombardment of the anode material provided the voltage is large enough to produce photoelectrons. Thus, broadband x-ray radiation (or alternatively broad spectrum radiation) refers to Bremsstrahlung radiation with or without characteristic emission lines of the primary target. The broadband radiation 915 emitted from primary target 910 is transmitted through window 930 of the vacuum enclosure to irradiate secondary target 920. Window 930 provides a transmissive portion of the vacuum enclosure made of a material (e.g., beryllium) that generally transmits broadband x-ray radiation generated by primary target 910 and blocks electrons from impinging on the secondary target 920 (e.g., electrons that scatter off of the primary target) to prevent unwanted Bremststralung radiation from being produced. Window 930 may be cup-shaped to accommodate secondary target 920 outside the vacuum enclosure, allowing the secondary target to be removed and replaced without breaking the vacuum seal of x-ray tube 950. In response to incident broadband x-ray radiation from primary target 910, secondary target 920 generates, via fluorescence, monochromatic x-ray radiation 925 characteristic of the element(s) in the second target. Secondary target 920 is conical in shape and made from a material selected so as to produce fluorescent monochromatic x-ray radiation at a desired energy, as discuss in further detail below. Broadband x-ray radiation 915 and monochromatic x-ray radiation 925 are illustrated schematically in FIG. 9 to illustrate the general principle of using a primary target and a secondary target to generate monochromatic x-ray radiation via fluorescence. It should be appreciated that broadband and monochromatic x-ray radiation will be emitted in the 4π directions by the primary and secondary targets, respectively. Accordingly, x-ray radiation will be emitted from x-ray tube 950 at different angles θ relative to axis 955 corresponding to the longitudinal axis through the center of the aperture of x-ray tube 950. As discussed above, the inventor has recognized that conventional x-ray apparatus for generating monochromatic x-ray radiation (also referred to herein as monochromatic x-ray sources) emit significant amounts of broadband x-ray radiation. That is, though conventional monochromatic sources report the ability to produce monochromatic x-ray radiation, in practice, the monochromaticity of the x-ray radiation emitted by these conventional apparatus is poor (i.e., conventional monochromatic sources exhibit low degrees of monochromaticity. For example, the conventional monochromatic source described in Marfeld, using a source operated at 165 kV with a secondary target of tungsten (W), emits monochromatic x-ray radiation that is approximately 50% pure (i.e., the x-ray emission is approximately 50% broadband x-ray radiation). As another example, a conventional monochromatic x-ray source of the general geometry illustrated in FIG. 9, operating with a cathode at a negative voltage of −50 kV, a primary target made of gold (Au; Z=79) at ground potential, and a secondary target made of tin (Sn; Z=50), emits the x-ray spectra illustrated in FIG. 10A (on-axis) and FIG. 10B (off-axis). As discussed above, x-ray radiation will be emitted from the x-ray tube at different angles θ relative to the longitudinal axis of the x-ray tube (axis 955 illustrated in FIG. 9). Because the on-axis spectrum and the off-axis spectrum play a role in the efficacy of a monochromatic source, both on-axis and off-axis x-ray spectra are shown. In particular, variation in the monochromaticity of x-ray radiation as a function of the viewing angle θ results in non-uniformity in the resulting images. In addition, for medical imaging applications, decreases in monochromaticity (i.e., increases in the relative amount of broadband x-ray radiation) of the x-ray spectra at off-axis angles increases the dose delivered to the patient. Thus, the degree of monochromaticity of both on-axis and off-axis spectra may be an important property of the x-ray emission of an x-ray apparatus. In FIG. 10A, on-axis refers to a narrow range of angles about the axis of the x-ray tube (less than approximately 0.5 degrees), and off-axis refers to approximately 5 degrees off the axis of the x-ray tube. As shown in FIGS. 10A and 10B, the x-ray spectrum emitted from the conventional monochromatic x-ray source is not in fact monochromatic and is contaminated with significant amounts of broadband x-ray radiation. In particular, in addition to the characteristic emission lines of the secondary target (i.e., the monochromatic x-rays emitted via K-shell fluorescence from the tin (Sn) secondary target resulting from transitions from the L and M-shells, labeled as Sn Kα and Sn Kβ in FIGS. 10A and 10B, respectively), x-ray spectra 1000a and 1000b shown in FIGS. 10A and 10B also include significant amounts of broadband x-ray radiation. Specifically, x-ray spectra 1000a and 1000b include significant peaks at the characteristic emission lines of the primary target (i.e., x-ray radiation at the energies corresponding to K-shell emissions of the gold primary target, labeled as Au Kα and Au Kβ in FIGS. 10A and 10B), as well as significant amounts of Bremsstrahlung background. As indicated by arrows 1003 in FIGS. 10A and 10B, the Sn Kα peak is only (approximately) 8.7 times greater than the Bremsstrahlung background in the on-axis direction and approximately 7 times greater than the Bremsstrahlung background in the off-axis direction. Thus, it is clear from inspection alone that this conventional monochromatic x-ray source emits x-ray radiation exhibiting strikingly poor monochromaticity, both on and off-axis, as quantified below. Monochromaticity may be computed based on the ratio of the integrated energy in the characteristic fluorescent emission lines of the secondary target to the total integrated energy of the broadband x-ray radiation. For example, the integrated energy of the low energy broadband x-ray radiation (e.g., the integrated energy of the x-ray spectrum below the Sn Kα peak indicated generally by arrows 1001 in FIGS. 10A and 10B), referred to herein as Plow, and the integrated energy of the high energy broadband x-ray radiation (e.g., the integrated energy of the x-ray spectrum above the Sn Kβ peak indicated generally by arrows 1002 in FIGS. 10A and 10B), referred to herein as Phigh, may be computed. The ratio of the integrated energy of the characteristic K-shell emission lines (referred to herein as Pk, which corresponds to the integrated energy in the Sn Kα and the Sn Kβ emissions in FIGS. 10A and 10B) to Plow and Phigh provides a measure of the amount of broadband x-ray radiation relative to the amount of monochromatic x-ray radiation emitted by the x-ray source. In the example of FIG. 10A, the ratio Pk/Plow is 0.69 and the ratio Pk/Phigh is 1.7. In the example of FIG. 10B, the ratio Pk/Plow is 0.9 and the ratio Pk/Phigh is 2.4. Increasing the ratios Plow and Phigh increases the degree to which the spectral output of the source is monochromatic. As used herein, the monochromaticity, M, of an x-ray spectrum is computed as M=1/(1+1/a+1/b), where a=Pk/Plow, b=Pk/Phigh. For the on-axis x-ray spectrum in FIG. 10A produced by the conventional x-ray apparatus, M=0.33, and for the off-axis x-ray spectrum in FIG. 10B produced by the conventional x-ray apparatus, M=0.4. As such, the majority of the energy of the x-ray spectrum is broadband x-ray radiation and not monochromatic x-ray radiation. The inventor has developed techniques that facilitate generating an x-ray radiation having significantly higher monochromaticity, thus improving characteristics of the x-ray emission from an x-ray device and facilitating improved x-ray imaging. FIG. 11A illustrates an x-ray device 1100 incorporating techniques developed by the inventor to improve properties of the x-ray radiation emitted from the device, and FIG. 11B illustrates a zoomed in view of components of the x-ray device 1100, in accordance with some embodiments. X-ray device 1100 comprises a vacuum tube 1150 providing a vacuum sealed enclosure for electron optics 1105 and primary target 1110 of the x-ray device. The vacuum sealed enclosure is formed substantially by a housing 1160 (which includes a front portion 1165) and an interface or window portion 1130. Faceplate 1175 may be provided to form an outside surface of front portion 1165. Faceplate 1175 may be comprised of material that is generally opaque to broadband x-ray radiation, for example, a high Z material such as lead, tungsten, thick stainless steel, tantalum, rhenium, etc. that prevents at least some broadband x-ray radiation from being emitted from x-ray device 1100. Interface portion 1130 may be comprised of a generally x-ray transmissive material (e.g., beryllium) to allow broadband x-ray radiation from primary target 1110 to pass outside the vacuum enclosure to irradiate secondary target 1120. In this manner, interface portion 1130 provides a “window” between the inside and outside the vacuum enclosure through which broadband x-ray radiation may be transmitted and, as result, is also referred to herein as the window or window portion 1130. Window portion 1130 may comprise an inner surface facing the inside of the vacuum enclosure and an outer surface facing the outside of the vacuum enclosure of vacuum tube 1150 (e.g., inner surface 1232 and outer surface 1234 illustrated in FIG. 12). Window portion 1130 may be shaped to form a receptacle (see receptacle 1235 labeled in FIG. 12) configured to hold secondary target carrier 1140 so that the secondary target (e.g., secondary target 1120) is positioned outside the vacuum enclosure at a location where at least some broadband x-ray radiation emitted from primary target 1110 will impinge on the secondary target. According to some embodiments, carrier 1140 is removable. By utilizing a removable carrier 1140, different secondary targets can be used with x-ray system 1100 without needing to break the vacuum seal, as discussed in further detail below. However, according to some embodiments, carrier 1140 is not removable. The inventor recognized that providing a hybrid interface portion comprising a transmissive portion and a blocking portion facilitates further reducing the amount of broadband x-ray radiation emitted from the x-ray device. For example, FIG. 11C illustrates an interface portion 1130′ comprising a transmissive portion 1130a (e.g., a beryllium portion) and a blocking portion 1130b (e.g., a tungsten portion), in accordance with some embodiments. Thus, according to some embodiments, interface portion 1130′ may comprise a first material below the dashed line in FIG. 11C and comprise a second material different from the first material above the dashed line. Transmissive portion 1130a and blocking portion 1130b may comprise any respective material suitable for performing intended transmission and absorption function sufficiently, as the aspect are not limited for use with any particular materials. According to some embodiments, the location of the interface between the transmissive portion and the blocking portion (e.g., the location of the dashed line in FIG. 11C) approximately corresponds to the location of the interface between the transmissive portion and the blocking portion of the carrier when the carrier is inserted into the receptacle formed by the interface portion. According to some embodiments, the location of the interface between the transmissive portion and the blocking portion (e.g., the location of the dashed line in FIG. 11C) does not correspond to the location of the interface between the transmissive portion and the blocking portion of the carrier when the carrier is inserted into the receptacle formed by the interface portion. A hybrid interface component is also illustrated in FIG. 28A, discussed in further detail below. In the embodiment illustrated in FIGS. 11A and 11B, secondary target 1120 has a conical geometry and is made of a material that fluoresces x-rays at desired energies in response to incident broadband x-ray radiation. Secondary target may be made of any suitable material, examples of which include, but are not limited to tin (Sn), silver (Ag), molybdenum (Mo), palladium (Pd), or any other suitable material or combination of materials. FIG. 19 illustrates the x-ray spectra resulting from irradiating secondary target cones of the four exemplary materials listed above. Secondary target 1120 provides a small compact region from which monochromatic x-ray radiation can be emitted via fluorescent to provide good spatial resolution, as discussed in further detail below. The inventor has appreciated that removable carrier 1140 can be designed to improve characteristics of the x-ray radiation emitted from vacuum tube 1150 (e.g., to improve the monochromaticity of the x-ray radiation emission). Techniques that improve the monochromaticity also facilitate the ability to generate higher intensity monochromatic x-ray radiation, as discussed in further detail below. In the embodiment illustrated in FIGS. 11A and 11B, removable carrier 1140 comprises a transmissive portion 1142 that includes material that is generally transmissive to x-ray radiation so that at least some broadband x-ray radiation emitted by primary target 1110 that passes through window portion 1130 also passes through transmissive portion 1142 to irradiate secondary target 1120. Transmissive portion 1142 may include a cylindrical portion 1142a configured to accommodate secondary target 1120 and may be configured to allow the secondary target to be removed and replaced so that secondary targets of different materials can be used to generate monochromatic x-rays at the different characteristic energies of the respective material, though the aspects are not limited for use with a carrier that allows secondary targets to be interchanged (i.e., removed and replaced). Exemplary materials suitable for transmissive portion 1142 include, but are not limited to, aluminum, carbon, carbon fiber, boron, boron nitride, beryllium oxide, silicon, silicon nitride, etc. Carrier 1140 further comprises a blocking portion 1144 that includes material that is generally opaque to x-ray radiation (i.e., material that substantially absorbs incident x-ray radiation). Blocking portion 1144 is configured to absorb at least some of the broadband x-ray radiation that passes through window 1130 that is not converted by and/or is not incident on the secondary target and/or is configured to absorb at least some of the broadband x-ray radiation that might otherwise escape the vacuum enclosure. In conventional x-rays sources (e.g., conventional x-ray apparatus 900 illustrated in FIG. 9), significant amounts of broadband x-ray radiation is allowed to be emitted from the apparatus, corrupting the fluorescent x-ray radiation emitted by the secondary target and substantially reducing the monochromaticity of the emitted x-ray radiation. In the embodiments illustrated in FIGS. 11A, 11B, 12, 13A-C and 17A-C, the transmissive portion and the blocking portion form a housing configured to accommodate the secondary target. According to some embodiments, blocking portion 1144 includes a cylindrical portion 1144a and an annular portion 1144b. Cylindrical portion 1144a allows x-ray radiation fluoresced by the secondary target 1120 in response to incident broadband x-ray radiation from primary target 1110 to be transmitted, while absorbing at least some broadband x-ray radiation as discussed above. Annular portion 1144b provides a portion providing increased surface area to absorb additional broadband x-ray radiation that would otherwise be emitted by the x-ray device 1100. In the embodiment illustrated in FIGS. 11A and 11B, annular portion 1144b is configured to fit snugly within a recess in the front portion of the x-ray tube to generally maximize the amount of broadband x-ray radiation that is absorbed to the extent possible. Annular portion 1144b includes an aperture portion 1144c that corresponds to the aperture through cylindrical portions 1144b and 1142a to allow monochromatic x-ray radiation fluoresced from secondary target 1120 to be emitted from x-ray device 1100, as also shown in FIGS. 13B and 17B discussed below. Exemplary materials suitable for blocking portion 1144 include, but are not limited to, lead, tungsten, tantalum, rhenium, platinum, gold, etc. In the embodiment illustrated FIGS. 11A and 11B, carrier 1140 is configured so that a portion of the secondary target is contained within blocking portion 1144. Specifically, as illustrated in the embodiment shown in FIGS. 11A and 11B, the tip of conical secondary target 1120 extends into cylindrical portion 1144b when the secondary target is inserted into transmissive portion 1142 of carrier 1140. The inventor has appreciated that having a portion of the secondary target contained within blocking portion 1144 improves characteristics of the monochromatic x-ray radiation emitted from the x-ray device, as discussed in further below. However, according to some embodiments, a secondary target carrier may be configured so that no portion of the secondary target is contained with the blocking portion of the carrier, examples of which are illustrated FIGS. 13A-C discussed in further detail below. Both configurations of carrier 1140 (e.g., with and without blocking overlap of the secondary target carrier) provide significant improvements to characteristics of the emitted x-ray radiation (e.g., improved monochromaticity), as discussed in further detail below. As illustrated in FIG. 12, carrier 1240 (which may be similar or the same as carrier 1140 illustrated in FIGS. 11A and 11B) is configured to be removeable. For example, carrier 1240 may be removeably inserted into receptacle 1235 formed by interface component 1230 (e.g., an interface comprising a transmissive window), for example, by inserting and removing the carrier, respectively, in the directions generally indicated by arrow 1205. That is, according to some embodiments, carrier 1240 is configured as a separate component that can be inserted into and removed from the x-ray device (e.g., by inserting removeable carrier 1240 into and/or removing the carrier from receptacle 1235). As shown in FIG. 12, carrier 1240 has a proximal end 1245 configured to be inserted into the x-ray device and a distal end 1247 from which monochromatic x-ray radiation is emitted via aperture 1244d through the center of carrier 1240. In the embodiment illustrated in FIG. 12, cylindrical blocking portion 1244a is positioned adjacent to and distally from cylindrical transmissive portion 1242a. Annular blocking portion 1244b is positioned adjacent to and distally from block portion 1244a. As shown, annular blocking portion 1244b has a diameter D that is larger than a diameter d of the cylindrical blocking portion 1244a (and cylindrical transmissive portion 1242a for embodiments in which the two cylindrical portions have approximately the same diameter). The distance from the extremes of the proximal end and the distal end is labeled as height H in FIG. 12. The dimensions of carrier 1240 may depend on the dimensions of the secondary target that the carrier is configured to accommodate. For example, for an exemplary carrier 1240 configured to accommodate a secondary target having a 4 mm base, diameter d may be approximately 4-5 mm, diameter D may be approximately 13-16 mm, and height H may be approximately 18-22 mm. As another example, for an exemplary carrier 1240 configured to accommodate a secondary target having a 8 mm base, diameter d may be approximately 8-9 mm, diameter D may be approximately 18-22 mm, and height H may be approximately 28-32 mm. It should be appreciated that the dimensions for the carrier and the secondary target provided are merely exemplary, and can be any suitable value as the aspect are not limited for use with any particular dimension or set of dimensions. According to some embodiments, carrier 1240 may be configured to screw into receptacle 1235, for example, by providing threads on carrier 1240 capable of being hand screwed into cooperating threads within receptacle 1235. Alternatively, a releasable mechanical catch may be provided to allow the carrier 1240 to be held in place and allows the carrier 1240 to be removed by applying force outward from the receptacle. As another alternative, the closeness of the fit of carrier 1240 and receptacle 1235 may be sufficient to hold the carrier in place during operation. For example, friction between the sides of carrier 1240 and the walls of receptacle 1235 may be sufficient to hold carrier 1240 in position so that no additional fastening mechanism is needed. It should be appreciated that any means sufficient to hold carrier 1240 in position when the carrier is inserted into the receptacle may be used, as the aspects are not limited in this respect. As discussed above, the inventor has developed a number of carrier configuration that facilitate improved monochromatic x-ray radiation emission. FIGS. 13A and 13B illustrate a three-dimensional and a two-dimensional view of a carrier 1340, in accordance with some embodiments. The three-dimensional view in FIG. 13A illustrates carrier 1340 separated into exemplary constituent parts. In particular, FIG. 13A illustrates a transmissive portion 1342 separated from a blocking portion 1344. As discussed above, transmissive portion 1342 may include material that generally transmits broadband x-ray radiation at least at the relevant energies of interest (i.e., material that allows broadband x-ray radiation to pass through the material without substantial absorption at least at the relevant energies of interest, such as aluminum, carbon, carbon fiber, boron, boron nitride, beryllium oxide, silicon, silicon nitride, etc. Blocking portion 1344, on the other hand, may include material that is generally opaque to broadband x-ray radiation at least at the relevant energies of interest (i.e., material that substantially absorbs broadband x-ray radiation at least at the relevant energies of interest, such as lead, tungsten, tantalum, rhenium, platinum, gold, etc. In this way, at least some broadband x-ray radiation emitted by the primary target is allowed to pass through transmissive portion 1342 to irradiate the secondary target, while at least some broadband x-ray radiation emitted from the primary target (and/or emitted from or scattered by other surfaces of the x-ray tube) is absorbed by blocking portion 1344 to prevent unwanted broadband x-ray radiation from being emitted from the x-ray device. As a result, carrier 1340 facilitates providing monochromatic x-ray radiation with reduced contamination by broadband x-ray radiation, significantly improving monochromaticity of the x-ray emission of the x-ray device. In the embodiments illustrated in FIGS. 13A-C, blocking portion 1344 includes a cylindrical portion 1344a and annular portion 1344b having a diameter greater than cylindrical portion 1344a to absorb broadband x-ray radiation emitted over a wider range of angles and/or originating from a wider range of locations to improve the monochromaticity of the x-ray radiation emission of the x-ray device. According to some embodiments, transmissive portion 1342 and blocking portion 1344 may be configured to couple together or mate using any of a variety of techniques. For example, the transmissive portion 1342, illustrated in the embodiment of FIG. 13A as a cylindrical segment, may include a mating portion 1343a at one end of the cylindrical segment configured to mate with mating portion 1342b at a corresponding end of cylindrical portion 1344a of blocking portion 1344. Mating portion 1343a and 1343b may be sized appropriately and, for example, provided with threads to allow the transmissive portion 1342 and the blocking portion 1344 to be mated by screwing the two portion together. Alternatively, mating portion 1343a and 1343b may be sized so that mating portion 1343a slides over mating portion 1343b, or vice versa, to couple the two portions together. It should be appreciated that any mechanism may be used to allow transmissive portion 1342 and blocking portion 1344 to be separated and coupled together. According to some embodiments, transmissive portion 1342 and blocking portion 1344 are not separable. For example, according to some embodiments, carrier 1340 may be manufactured as a single component having transmissive portion 1342 fixedly coupled to blocking portion 1344 so that the portions are not generally separable from one another as a general matter of course. Transmissive portion 1342 may also include portion 1325 configured to accommodate secondary target 1320. For example, one end of transmissive portion 1342 may be open and sized appropriately so that secondary target 1320 can be positioned within transmissive portion 1342 so that, when carrier 1340 is coupled to the x-ray device (e.g., inserted into a receptacle formed by an interface portion of the vacuum tube, such as a transmissive window or the like), secondary target 1320 is positioned so that at least some broadband x-ray radiation emitted from the primary target irradiates secondary target 1320 to cause secondary target to fluoresce monochromatic x-rays at the characteristic energies of the selected material. In this way, different secondary targets 1320 can be positioned within and/or held by carrier 1340 so that the energy of the monochromatic x-ray radiation is selectable. According to some embodiments, secondary target 1320 may include a portion 1322 that facilitates mating or otherwise coupling secondary target 1320 to the carrier 1340. For example, portions 1322 and 1325 may be provide with cooperating threads that allow the secondary target to be screwed into place within the transmissive portion 1342 of carrier 1340. Alternatively, portions 1322 and 1325 may be sized so that the secondary target fits snuggly within transmissive portion and is held by the closeness of the fit (e.g., by the friction between the two components) and/or portion 1322 and/or portion 1325 may include a mechanical feature that allows the secondary target to held into place. According to some embodiments, a separate cap piece may be included to fit over transmissive portion 1342 after the secondary target has been inserted into the carrier and/or any other suitable technique may be used to allow secondary target 1320 to be inserted within and sufficiently held by carrier 1340, as the aspects are not limited in this respect. In the embodiment illustrated in FIG. 13B, secondary target 1320 is contained within transmissive portion 1342, without overlap with blocking portion 1344. That is, the furthest extent of secondary target 1320 (e.g., the tip of the conical target in the embodiment illustrated in FIG. 13B) does not extend into cylindrical portion 1344a of the blocking portion (or any other part of the blocking portion). By containing secondary target 1320 exclusively within the transmissive portion of the carrier, the volume of secondary target 1320 exposed to broadband x-ray radiation and thus capable of fluorescing monochromatic x-ray radiation may be generally maximized, providing the opportunity to generally optimize the intensity of the monochromatic x-ray radiation produced for a given secondary target and a given set of operating parameters of the x-ray device (e.g., power levels of the x-ray tube, etc.). That is, by increasing the exposed volume of the secondary target, increased monochromatic x-ray intensity may be achieved. The front view of annular portion 1344b of blocking portion 1334 illustrated in FIG. 13B illustrates that annular portion 1344b includes aperture 1344c corresponding to the aperture of cylindrical portion 1344a (and cylindrical portion 1342) that allows monochromatic x-rays fluoresced from secondary target 1320 to be emitted from the x-ray device. Because blocking portion 1344 is made from a generally opaque material, blocking portion 1344 will also absorb some monochromatic x-rays fluoresced from the secondary target emitted at off-axis angles greater than some threshold angle, which threshold angle depends on where in the volume of the secondary target the monochromatic x-rays originated. As such, blocking portion 1344 also operates as a collimator to limit the monochromatic x-rays emitted to a range of angles relative to the axis of the x-ray tube, which in the embodiments in FIGS. 13A-C, corresponds to the longitudinal axis through the center of carrier 1340. FIG. 13C illustrates a schematic of carrier 1340 positioned within an x-ray device (e.g., inserted into a receptacle formed by an interface portion of the vacuum tube, such as exemplary window portions 1130 and 1230 illustrated in FIGS. 11A, 11B and 12). Portions 1365 correspond to the front portion of the vacuum tube, conventionally constructed of a material such as copper. In addition, a cover or faceplate 1375 made of a generally opaque material (e.g., lead, tungsten, tantalum, rhenium, platinum, gold, etc.) is provided having an aperture corresponding to the aperture of carrier 1340. Faceplate 1375 may be optionally included to provide further absorption of broadband x-ray to prevent spurious broadband x-ray radiation from contaminating the x-ray radiation emitted from the x-ray device. According to some embodiments, exemplary carrier 1340 may be used to improve monochromatic x-ray emission characteristics. For example, FIGS. 14A and 14B illustrate the on-axis x-ray spectrum 1400a and off-axis x-ray spectrum 1400b resulting from the use of carrier 1340 illustrated in FIGS. 13A, 13B and/or 13C. As shown, the resulting x-ray spectrum is significantly improved relative to the on-axis and off-axis x-ray spectra shown in FIGS. 10A and 10B that was produced by a conventional x-ray apparatus configured to produce monochromatic x-ray radiation (e.g., conventional x-ray apparatus 900 illustrated in FIG. 9). As indicated by arrow 1403 in FIG. 14A, the on-axis Sn Kα peak is approximately 145 times greater than the Bremsstrahlung background, up from approximately 8.7 in the on-axis spectrum illustrated in FIG. 10A. The off-axis Sn Kα peak is approximately 36 times greater than the Bremsstrahlung background as indicated by arrow 1403 in FIG. 14B, up from approximately 7.0 in the off-axis spectrum illustrated in FIG. 14B. In addition, the ratios of Pk (the integrated energy of the characteristic K-shell emission lines, labeled as Sn Kα and Sn Kβ in FIGS. 14A and 14B) to Plow (the integrated energy of the low energy x-ray spectrum below the Sn Kα peak, indicated generally by arrows 1401 in FIGS. 14A and 14B) and Phigh (the integrated energy of the high energy spectrum above the Sn Kβ peak, indicated generally by arrows 1402) are 21 and 62, respectively, for the on-axis spectrum illustrated in FIG. 14A, up from 0.69 and 1.7 for the on-axis spectrum of FIG. 10A. The ratios Pk/Plow and Pk/Phigh are 12.9 and 22, respectively, for the off-axis spectrum illustrated in FIG. 14B, up from 0.9 and 2.4 for the off-axis spectrum of FIG. 10B. These increased ratios translate to an on-axis monochromaticity of 0.94 (M=0.94) and an off-axis monochromaticity of 0.89 (M=0.89), up from an on-axis monochromaticity of 0.33 and an off-axis monochromaticity of 0.4 for the x-ray spectrum of FIGS. 10A and 10B, respectively. This significant improvement in monochromaticity facilitates acquiring x-ray images that are more uniform, have better spatial resolution and that deliver significantly less x-ray radiation dose to the patient in medical imaging applications. For example, in the case of mammography, the x-ray radiation spectrum illustrated in FIGS. 10A and 10B would deliver four times the mean glandular dose to normal thickness and density breast tissue than would be delivered by the x-ray radiation spectrum illustrated in FIGS. 14A and 14B. FIG. 14C illustrates the field of view of the conventional x-ray source used to generate the x-ray spectrum illustrated in FIGS. 10A and 10B along with the field of view of the x-ray device used to generate the x-ray spectrum illustrated in FIGS. 14A and 14B. The full width at half maximum (FWHM) of the conventional x-ray apparatus is approximately 30 degrees, while the FWHM of the improved x-ray device is approximately 15 degrees. Accordingly, although the field of view is reduced via exemplary carrier 1340, the resulting field of view is more than sufficient to image an organ such as the breast in a single exposure at compact source detector distances (e.g., approximately 760 mm), but with increased uniformity and spatial resolution and decreased radiation dose, allowing for significantly improved and safer x-ray imaging. FIG. 15 illustrates the integrated power ratios for the low and high energy x-ray radiation (Pk/Plow and Pk/PHigh) as a function of the viewing angle θ and FIG. 16 illustrates the monochromaticity of the x-ray radiation for the conventional x-ray apparatus (1560a, 1560b and 1660) and the improved x-ray apparatus using exemplary carrier 1340 (1570a, 1570b and 1670). As shown by plots 1570a, 1570b and 1670, monochromaticity decreases as a function of viewing angle. Using carrier 1340, monochromatic x-ray radiation is emitted having a monochromaticity of at least 0.7 across a 15 degree field of view and a monochromaticity of at least 0.8 across a 10 degree field of view about the longitudinal axis. As shown by plots 1560a, 1560b and 1660, monochromaticity of the conventional x-ray apparatus is extremely poor across all viewing angles (i.e., less than 0.4 across the entire field of view). The inventor has appreciated that further improvements to aspects of the monochromaticity of x-ray radiation emitted from an x-ray tube may be improved by modifying the geometry of the secondary target carrier. According to some embodiments, monochromaticity may be dramatically improved, in particular, for off-axis x-ray radiation. For example, the inventor recognized that by modifying the carrier so that a portion of the secondary target is within a blocking portion of the carrier, the monochromaticity of x-ray radiation emitted by an x-ray device may be improved, particularly with respect to off-axis x-ray radiation. FIGS. 17A and 17B illustrate a three-dimensional and a two-dimensional view of a carrier 1740, in accordance with some embodiments. Exemplary carrier 1740 may include similar parts to carrier 1340, including a transmissive portion 1742 to accommodate secondary target 1720, and a blocking portion 1744 (which may include a cylindrical portion 1744a and annular portion 1744b with an aperture 1744c through the center), as shown in FIG. 17A. However, in the embodiment illustrated in FIGS. 17A-C, carrier 1740 is configured so that, when secondary target 1720 is positioned within transmissive portion 1742, a portion of secondary target 1720 extends into blocking portion 1744. In particular, blocking portion includes an overlap portion 1744d that overlaps part of secondary target 1720 so that at least some of the secondary target is contained within blocking portion 1744. According to some embodiments, overlap portion 1744d extends over between approximately 0.5 and 5 mm of the secondary target. According to some embodiments, overlap portion 1744d extends over between approximately 1 and 3 mm of the secondary target. According to some embodiments, overlap portion 1744d extends over approximately 2 mm of the secondary target. According to some embodiments, overlap portion 1744d extends over less than 0.5 mm, and in some embodiments, overlap portion 1744d extends over greater than 5 mm. The amount of overlap will depend in part on the size and geometry of the secondary target, the carrier and the x-ray device. FIG. 17C illustrates carrier 1740 positioned within an x-ray device (e.g., inserted in a receptacle formed at the interface of the vacuum tube), with a faceplate 1775 provided over front portion 1765 of a vacuum tube (e.g., vacuum tube 1150 illustrated in FIG. 11A). According to some embodiments, exemplary carrier 1740 may be used to further improve monochromatic x-ray emission characteristics. For example, FIGS. 18A and 18B illustrate the on-axis x-ray spectrum 1800a and off-axis x-ray spectrum 1800b resulting from the use of carrier 1740 illustrated in FIGS. 17A-C. As shown, the resulting x-ray spectrum are significantly improved relative to the on-axis and off-axis x-ray spectrum produced the conventional x-ray apparatus shown in FIGS. 10A and 10B, as well as exhibiting improved characteristics relative to the x-ray spectra produced using exemplary carrier 1340 illustrated in FIGS. 13A-C. As indicated by arrow 1803 in FIG. 18A, the on-axis Sn Kα peak is 160 times greater than the Bremsstrahlung background, compared to 145 for the on-axis spectrum in FIG. 14A and 8.7 for the on-axis spectrum illustrated in FIG. 10A. As indicated by arrow 1803 in FIG. 18B, the off-axis Sn Kα peak is 84 times greater than the Bremsstrahlung background, compared to 36 for the off-axis spectrum in FIG. 14B and 7.0 for the off-axis spectrum illustrated in FIG. 10B. The ratios of Pk (the integrated energy of the characteristic K-shell emission lines, labeled as Sn Kα and Sn Kβ in FIGS. 18A and 18B) to Plow (the integrated energy of the low energy x-ray spectrum below the Sn Kα peak, indicated generally by arrows 1801 in FIGS. 18A and 18B) and Phigh (the integrated energy of the high energy spectrum above the Sn Kβ peak, indicated generally by arrows 1802) are 31 and 68, respectively, for the on-axis spectrum illustrated in FIG. 18A, compared to 21 and 62 for the on-axis spectrum of FIG. 14A and 0.69 and 1.7 for the on-axis spectrum of FIG. 10A. The ratios Pk/Plow and Pk/Phigh are 29 and 68, respectively, for the off-axis spectrum of FIG. 18B, compared to 12.9 and 22, respectively, for the off-axis spectrum illustrated in FIG. 14B and 0.9 and 2.4 for the off-axis spectrum of FIG. 10B. These increased ratios translate to an on-axis monochromaticity of 0.96 (M=0.96) and an off-axis monochromaticity of 0.95 (M=0.95), compared to an on-axis monochromaticity of 0.94 (M=0.94) for x-ray spectrum of FIG. 14A and an off-axis monochromaticity of 0.89 (M=0.89) for the x-ray spectrum of FIG. 14B, and an on-axis monochromaticity of 0.33 and an off-axis monochromaticity of 0.4 for the x-ray spectra of FIGS. 10A and 10B, respectively. Referring again to FIGS. 15 and 16, the stars indicate the on-axis and off-axis low energy ratio (1580a) and high energy ratio (1580b), as well as the on-axis and off-axis monochromaticity (1680), respectively, of the x-ray radiation emitted using exemplary carrier 1640. As shown, the x-ray radiation exhibits essentially the same characteristics on-axis and 5 degrees off-axis. Accordingly, while exemplary carrier 1740 improves both on-axis and off-axis monochromaticity, use of the exemplary carrier illustrate in FIGS. 17A-C exhibits a substantial increase in the off-axis monochromaticity, providing substantial benefits to x-ray imaging using monochromatic x-rays, for example, by improving uniformity, reducing dose and enabling the use of higher x-ray tube voltages to increase the mononchromatic intensity to improve the spatial resolution and ability differentiate small density variations (e.g., small tissue anomalies such as micro-calcifications in breast material), as discussed in further detail below. Using carrier 1740, monochromatic x-ray radiation is emitted having a monochromaticity of at least 0.9 across a 15 degree field of view and a monochromaticity of at least 0.95 across a 10 degree field of view about the longitudinal axis. It should be appreciated that the exemplary carrier described herein may be configured to be a removable housing or may be integrated into the x-ray device. For example, one or more aspects of the exemplary carriers described herein may integrated, built-in or otherwise made part an x-ray device, for example, as fixed components, as the aspects are not limited in this respect. As is well known, the intensity of monochromatic x-ray emission may be increased by increasing the cathode-anode voltage (e.g., the voltage potential between filament 1106 and primary target 1100 illustrated in FIGS. 11A and 11B) and/or by increasing the filament current which, in turn, increases the emission current of electrons emitted by the filament, the latter technique of which provides limited control as it is highly dependent on the properties of the cathode. The relationship between x-ray radiation intensity, cathode-anode voltage and emission current is shown in FIG. 20, which plots x-ray intensity, produced using a silver (Ag) secondary target and a source-detector distance of 750 mm, against emission current at a number of different cathode-anode voltages using two different secondary target geometries (i.e., an Ag cone having a 4 mm diameter base and an Ag cone having a 8 mm diameter base). Conventionally, the cathode-anode voltage was selected to be approximately twice that of the energy of the characteristic emission line of the desired monochromatic x-ray radiation to be fluoresced by the secondary target as a balance between producing sufficient high energy broadband x-ray radiation above the absorption edge capable of inducing x-ray fluorescence in the secondary target to produce adequate monochromatic x-ray intensity, and producing excess high energy broadband x-ray radiation that contaminates the desired monochromatic x-ray radiation. For example, for an Ag secondary target, a cathode-anode potential of 45 kV (e.g., the electron optics would be set at −45 kV) would conventionally be selected to ensure sufficient high energy broadband x-rays are produced above the K-edge of silver (25 keV) as illustrated in FIG. 21 to produce the 22 keV Ag K monochromatic x-ray radiation shown in FIG. 19 (bottom left). Similarly, for a Sn secondary target, a cathode-anode potential of 50 kV would conventionally be selected to ensure sufficient high energy broadband x-rays are produced above the K-edge of tin (29 keV) as illustrated in FIG. 21 to produce the 25 keV Sn K monochromatic x-ray radiation shown in FIG. 19 (bottom right). This factor of two limit on the cathode-anode voltage was conventionally followed to limit the high energy contamination of the monochromatic x-rays emitted from the x-ray apparatus. The inventor has recognized that the techniques described herein permit the factor of two limit to be eliminated, allowing high cathode-anode voltages to be used to increase mononchromatic x-ray intensity without significantly increasing broadband x-ray radiation contamination (i.e., without substantial decreases in monochromaticity). In particular, techniques for blocking broadband x-ray radiation, including the exemplary secondary target carriers developed by the inventors can be used to produce high intensity monochromatic radiation while maintaining excellent monochromaticity. For example, FIG. 22 illustrates the on-axis monochromaticity 2200a and the off-axis monochromaticity 2200b for a number of cathode-anode voltages (primary voltage) with a Sn secondary target using exemplary carrier 1740 developed by the inventor. Similarly, FIG. 23 illustrates the on-axis monochromaticity 2300a and the off-axis monochromaticity 2300b for a number of cathode-anode voltages (primary voltage) with an Ag secondary target using exemplary carrier 1740 developed by the inventor. As shown, a high degree of monochromaticity is maintained across the illustrated range of high voltages, varying by only 1.5% over the range illustrated. Thus, higher voltages can be used to increase the monochromatic x-ray intensity (e.g., along the lines shown in FIG. 20) without substantially impacting monochromaticity. For example, monochromatic x-ray radiation of over 90% purity (M>0.9) can be generated using a primary voltage up to and exceeding 100 KeV, significantly increasing the monochromatic x-ray intensity. According to some embodiments, a primary voltage (e.g., a cathode-anode voltage potential, such as the voltage potential between filament 1106 and primary target 1110 of x-ray tube 1150 illustrated in FIGS. 11A and 11B) greater than two times the energy of the desired monochromatic x-ray radiation fluoresced from a given target is used to generate monochromatic x-ray radiation. According to some embodiments, a primary voltage greater than or equal to approximately two times and less than or equal to approximately three times the energy of the desired monochromatic x-ray radiation fluoresced from a given target is used to generate monochromatic x-ray radiation. According to some embodiments, a primary voltage greater than or equal to approximately three times and less than or equal to approximately four times the energy of the desired monochromatic x-ray radiation fluoresced from a given target is used to generate monochromatic x-ray radiation. According to some embodiments, a primary voltage greater than or equal to approximately four times and less than or equal to approximately five times the energy of the desired monochromatic x-ray radiation fluoresced from a given target is used to generate monochromatic x-ray radiation. According to some embodiments, a primary voltage greater than or equal to five times greater the energy of the desired monochromatic x-ray radiation fluoresced from a given target is used to generate monochromatic x-ray radiation. In each case, x-ray radiation having monochromaticity of greater than or equal to 0.9, on and off axis across the field of view may be achieved, though it should be appreciated that achieving those levels of monochromaticity is not a requirement. The inventor has recognized the geometry of the x-ray tube may contribute to broadband x-ray radiation contamination. The inventor has appreciated that the electron optics of an x-ray tube may be improved to further reduce the amount of broadband x-ray radiation that is generated that could potentially contaminate the monochromatic x-rays emitted from an x-ray device. Referring again to FIGS. 11A and 11B, x-ray device 1100 includes electron optics 1105 configured to generate electrons that impinge on primary target 1110 to produce broadband x-ray radiation. The inventor has developed electron optics geometry configured to reduce and/or eliminate bombardment of surfaces other than the primary target within the vacuum enclosure. This geometry also reduces and/or eliminates parasitic heating of other surfaces that would have to be removed via additional cooling in conventional systems. As an example, the geometry of electron optics 1105 is configured to reduce and/or eliminate bombardment of window portion 1130 and/or other surfaces within vacuum tube 1150 to prevent unwanted broadband x-ray radiation from being generated and potentially emitted from the x-ray tube to degrade the monochromaticity of the emitted x-ray radiation spectrum. In the embodiment illustrated in FIGS. 11A and 11B, electron optics 1105 comprises a filament 1106, which may be generally toroidal in shape, and guides 1107, 1108 and/or 1109 positioned on the inside and outside of the toroidal filament 1106. For example, guides 1107, 1108, 1109 may be positioned concentrically with the toroidal filament 1106 (e.g., an inner guide 1107 positioned within the filament torus and an outer guides 1108 and 1109 positioned around the filament torus) to provide walls on either side of filament 1106 to prevent at least some electrons from impinging on surfaces other than primary target 1110, as discussed in further detail below. According to some embodiments, electronic optics 105 is configured to operate at a high negative voltage (e.g., 40 kV, 50 kV, 60 kV, 70 kV, 80 kV, 90 kV or more). That is, filament 1106, inner guide 1107 and outer guides 1108, 1109 may all be provided at a high negative potential during operation of the device. As such, in these embodiments, primary target 1110 may be provided at a ground potential so that electrons emitted from filament 1106 are accelerated toward primary target 1110. However, the other components and surfaces of x-ray tube within the vacuum enclosure are typically also at ground potential. As a result, electrons will also accelerate toward and strike other surfaces of x-ray tube 1150, for example, the transmissive interface between the inside and outside of the vacuum enclosure (e.g., window 1130 in FIGS. 11a and 11b). Using conventional electron optics, this bombardment of unintended surfaces produces broadband x-ray radiation that contributes to the unwanted broadband spectrum emitted from the x-ray device and causes undesirable heating of the x-ray tube. The inventor appreciated that this undesirable bombardment of surfaces other than primary target 1110 may be reduced and/or eliminated using inner guide 1107 and outer guides 1108 and/or 1109 that provide a more restricted path for electrons emitted by filament 1106. According to some embodiments, guides 1107-1109 are cylindrical in shape and are arranged concentrically to provide a restricted path for electrons emitted by filament 1106 that guides the electrons towards primary target 1110 to prevent at least some unwanted bombardment of other surfaces within the vacuum enclosure (e.g., reducing and/or eliminating electron bombardment of window portion 1130). However, it should be appreciated that the guides used in any given implementation may be of any suitable shape, as the aspects are not limited in this respect. According to some embodiments, guides 1107, 1108 and/or 1109 comprise copper, however, any suitable material that is electrically conducting (and preferably non-magnetic) may be used such as stainless steel, titanium, etc. It should be appreciated that any number of guides may be used. For example, an inner guide may be used in conjunction with a single outer guide (e.g., either guide 1108 or 1109) to provide a pair guides, one on the inner side of the cathode and one on the outer side of the cathode. As another example, a single inner guide may be provided to prevent at least some unwanted electrons from bombarding the interface between the inside and outside of the vacuum tube (e.g., window portion 1130 in FIGS. 11A and 11B), or a single outer guide may be provide to prevent at least some unwanted electrons from bombarding other internal surface of the vacuum tube provides. Additionally, more than three guides may be used to restrict the path of electrons to the primary target to reduce and/or eliminate unwanted bombardment of surfaces within the vacuum enclosure, as the aspects are not limited in this respect. FIGS. 24A and 24B illustrate a cross-section of a monochromatic x-ray source 2400 with improved electron optics, in accordance with some embodiments. In the embodiment illustrated, there is a 80 kV is the potential between the cathode and the anode. Specifically, a tungsten toroidal cathode 2406 is bias at −80 kV and a gold-coated tungsten primary target 2410 is at a ground potential. A copper inner guide 2407 and an outer copper guides 2408 and 2409 are also provided at −80 kV to guide electrons emitted from the cathode to prevent at least some electrons from striking surfaces other than primary target 2410 to reduce the amount of spurious broadband x-ray radiation. Monochromatic x-ray source 2400 uses a silver secondary target 2420 and a beryllium interface component 2430. FIG. 24B illustrates the electron trajectories between the toroidal cathode and the primary target when the monochromatic x-ray source 2400 is operated. FIGS. 25 and 26 illustrate the locus of points where the electrons strike primary target 2410, demonstrating that the guides prevent electrons from striking the interface component 2430 in this configuration. FIG. 27 illustrates a monochromatic x-ray source including a hybrid interface component having transmissive portion of beryllium and a blocking portion of tungsten that produces monochromatic x-ray radiation of 97% purity (M=0.97) when combined with other techniques described herein (e.g., using the exemplary carriers described herein). FIG. 28 illustrates an alternative configuration in which the cathode is moved further away from the primary target, resulting in divergent electron trajectories and reduced monochromaticity. The monochromatic x-ray sources described herein are capable of providing relatively high intensity monochromatic x-ray radiation having a high degree of monochromaticity, allowing for relatively short exposure times that reduce the radiation dose delivered to a patient undergoing imaging while obtaining images with high signal-to-noise ratio. Provided below are results obtained using techniques described herein in the context of mammography. These results are provided to illustrate the significant improvements that are obtainable using one or more techniques described herein, however, the results are provided as examples as the aspects are not limited for use in mammography, nor are the results obtained requirements on any of the embodiments described herein. FIG. 29 illustrates a mammographic phantom (CIRS Model 011a) 2900 used to test aspects of the performance of the monochromatic x-ray device developed by the inventor incorporating techniques described herein. Phantom 2900 includes a number of individual features of varying size and having different absorption properties, as illustrated by the internal view of phantom 2900 illustrated in FIG. 29. FIG. 30 highlights some of the embedded features of phantom 2900, including the linear array of 5 blocks, each 1 cm thick and each having a composition simulating different densities of breast tissue. The left most block simulates 100% glandular breast tissue, the right most, 100% adipose (fat) tissue and the other three have a mix of glandular and adipose with ratios ranging from 70:30 (glandular:adipose) to 50:50 to 30:70. All 5 blocks are embedded in the phantom made from a 50:50 glandular to adipose mix. The total thickness of the phantom is 4.5 cm. FIG. 30 also shows a schematic description of the imaging process in one dimension as the x-ray beam enters the phantom, passes through the blocks and the phantom on their way to the imaging detector where the transmitted x-ray intensity, is converted into an integrated value of Gray counts. (The intensity in this case is the sum of the x-ray energies reaching each detector pixel. The electronics in each pixel convert this energy sum into a number between 0 and 7000, where 7000 represents the maximum energy sum allowable before the electronics saturate. The number resulting from this digital conversion is termed a Gray count). The data shown by the red horizontal line in a) of FIG. 30 is the x-ray intensity, B, measured through the background 50:50 glandular-adipose mixture. The data shown by the black curve is the x-ray intensity, W, transmitted through the 50:50 mix and the 1 cm blocks. The varying step sizes represent different amounts of x-ray absorption in the blocks due to their different compositions. Plot b) in FIG. 30 defines the signal, S, as W-B and plot c) of FIG. 30 defines the contrast as S/B. The figure of merit that is best used to determine the detectability of an imaging system is the Signal-to-Noise Ratio, SNR. For the discussion here, the SNR is defined as S/noise, where the noise is the standard deviation of the fluctuations in the background intensity shown in plot a) of FIG. 30. Images produced using techniques described herein and may with 22 keV x-rays and 25 keV x-rays and presented herein and compared to the SNR values with those from a commercial broad band x-ray mammography machine. Radiation exposure in mammographic examinations is highly regulated by the Mammography Quality Standards Act (MQSA) enacted in 1994 by the U.S. Congress. The MQSA sets a limit of 3 milliGray (mGy) for the mean glandular dose (mgd) in a screening mammogram; a Gray is a joule/kilogram. This 3 mGy limit has important ramifications for the operation of commercial mammography machines, as discussed in further detail below. Breast tissue is composed of glandular and adipose (fatty) tissue. The density of glandular tissue (ρ=1.03 gm/cm−3) is not very different from the density of adipose tissue (ρ=0.93 gm/cm−3) which means that choosing the best monochromatic x-ray energy to optimize the SNR does not depend significantly on the type of breast tissue. Instead, the choice of monochromatic energy for optimal imaging depends primarily on breast thickness. A thin breast will attenuate fewer x-rays than a thick breast, thereby allowing a more significant fraction of the x-rays to reach the detector. This leads to a higher quality image and a higher SNR value. These considerations provide the major rationale for requiring breast compression during mammography examinations with a conventional, commercial mammography machine. Imaging experiments were conducted the industry-standard phantom illustrated in FIG. 29, which has a thickness of 4.5 cm and is representative of a typical breast under compression. Phantom 2900 has a uniform distribution of glandular-to-adipose tissue mixture of 50:50. The SNR and mean glandular dose are discussed in detail below for CIRS phantom images obtained with monochromatic energies of 22 keV and 25 keV. Experiments were also conducted with a double phantom, as illustrated in FIG. 32, to simulate a thick breast under compression with a thickness of 9 cm. The double phantom also has a uniform distribution of glandular-to-adipose tissue mixture of 50:50. The SNR and mean glandular dose are presented for the double phantom using a monochromatic energy of 25 keV. The high SNR obtained on this model of a thick breast demonstrates that monochromatic x-rays can be used to examine women with reduced compression or no compression at all, since, typically, a compressed breast of 4.5 cm thickness is equivalent to an uncompressed breast of 8-9 cm thickness, as discussed in further detail below. The experiments demonstrate that the mean glandular dose for the monochromatic measurements is always lower than that of the commercial machine for the same SNR. Stated in another way, the SNR for the monochromatic measurements is significantly higher than that of the commercial machines for the same mean glandular dose. Thus, monochromatic X-ray mammography provides a major advance over conventional broadband X-ray mammographic methods and has significant implications for diagnosing breast lesions in all women, and especially in those with thick or dense breast tissue. Dense breasts are characterized by non-uniform distributions of glandular tissue; this non-uniformity or variability introduces artifacts in the image and makes it more difficult to discern lesions. The increased SNR that monochromatic imaging provides makes it easier to see lesions in the presence of the inherent tissue variability in dense breasts, as discussed in further detail below. FIG. 31 illustrates images of phantom 2900 obtained from a monochromatic x-ray source described herein using monochromatic Ag K (22 keV) and Sn K (25 keV) x-rays and an image from a conventional commercial mammography machine that uses broad band emission, along with respective histograms through the soft tissue blocks. The image from the commercial machine is shown in (a) of FIG. 31. The SNR for the 100% glandular block is 8.4 and the mean glandular dose (mgd) is 1.25 mGy (1 Gy=1 joule/kgm). Image (b) in FIG. 31 illustrates a monochromatic image using 22 keV x-rays and image (c) in FIG. 31 was obtained with 25 keV X-rays. The mean glandular doses for the 100% glandular block measured with 22 keV is 0.2 mGy and that measured with 25 keV is 0.08 mGy, and the SNR values are 8.7 for both energies. To achieve the same SNR as the commercial machine, the monochromatic system using 22 keV delivers a dose that is 6.7 times lower and using 25 keV delivers a dose that is 15 times lower. The dose reduction provided by the monochromatic X-ray technology offers significantly better diagnostic detectability than the conventional broad band system because the SNR can be increased by factors of 3 to 6 times while remaining well below the regulatory dose limit of 3 mGy for screening. For example, the SNR value for the 22 keV images would be 21.8 at the same dose delivered by the commercial machine (1.25 mGy) and 32 for a dose of 2.75 mGy. Similarly, using the 25 keV energy, the SNR values would be 34 and 51 for mean glandular doses of 1.25 mGy and 2.75 mGy, respectively. This significantly enhanced range in SNR has enormous advantages for diagnosing women with dense breast tissue. As mentioned earlier, such tissue is very non-uniform and, unlike the uniform properties of the phantoms and women with normal density tissue, the variability in glandular distribution in dense breast introduces artifacts and image noise, thereby making it more difficult to discern lesions. The higher SNR provided by techniques describe herein can overcome these problems. The monochromatic x-ray device incorporating the techniques described herein used to produce the images displayed here is comparable in size and footprint of a commercial broadband x-ray mammography system, producing for the first time low dose, high SNR, uniform images of a mammographic phantom using monochromatic x-rays with a degree of monochromaticity of 95%. In fact, conventional monochromatic x-ray apparatus do not even approach these levels of monochromaticity. To simulate thick breast mammography, a model for thick breast tissue was created by placing two phantoms on top of each other (total thickness 9.0 cm), the 18-220 ACR Mammography Accreditation Phantom (3200) placed on top of the CIRS Model 011A phantom (2900), as shown in FIG. 32. For this series of experiments, 25 keV x-rays were selected to optimize the transmission while maintaining good contrast in the soft tissue represented by the 1 cm array of blocks embedded on the CIRS phantom. The images for the 25 keV monochromatic x-rays are compared to the images obtained from the same commercial broad band mammography machine used in the previous experiment. The resulting images are displayed in FIG. 33, along with the histograms of the contrast through the soft tissue blocks. The image quality for the thick breast tissue is superior to anything obtainable with current commercial broad band systems. The dose delivered by the commercial machine is 2.75 mGy and only achieves a SNR of 3.8 in the 100% glandular block. The monochromatic image in FIG. 33 has a SNR=7.5 for a dose of 0.43 mGy. The dose required for the commercial broad band X-ray system to reach a SNR of 8.5, the accepted value of radiologists for successful detection in thinner 4.5 cm thick tissue would be 14 mGy, 11 times higher than the commercial dose used to image normal density breast tissue (1.25 mGy). This is prohibitively high and unsafe for screening and 4.7 times higher than the regulated MQSA screening limit. On the other hand, the required dose from the monochromatic system to achieve a SNR=8.5 is only 0.54 mGy, 26 times lower than that required by the commercial machine. The dose required using monochromatic x-rays is safe, more than 5 times lower than the regulatory limit, and still 2.5 times lower than the dose for normal thickness, 4.5 cm breasts using the commercial broad band x-ray mammography machine. Comparing the monochromatic X-ray and the commercial broad band X-ray machines at close to the maximum allowed exposure (2.75 mGy), the monochromatic technology provides 5 times higher SNR. The above discussion is summarized schematically in FIG. 34. The measurements on the 9 cm thick breast phantom show that the monochromatic techniques described herein facilitate elimination of breast compression during mammography screening. A 4.5 cm compressed breast could be as thick at 9 cm when uncompressed. Whereas the commercial machine loses sensitivity as the breast thickness increases because it cannot increase the dose high enough to maintain the SNR and still remain below the regulated dose limit, the monochromatic x-ray system very easily provides the necessary SNR. As an example, of a monochromatic mammography procedure, a woman may lie prone on a clinic table designed to allow her breasts to extend through cutouts in the table. The monochromatic x-ray system may be designed to direct the x-rays parallel to the underside of the table. The table also facilitates improved radiation shielding for the patient by incorporating a layer of lead on the underside of the table's horizontal surface. The inventor has recognized that the spatial resolution of the geometry of the monochromatic x-ray device described herein is excellent for mammographic applications. According to some embodiments, the monochromatic x-ray system has a source-to-detector distance of 760 mm, a secondary target cone with a 4 mm base diameter and 8 mm height, and an imaging detector of amorphous silicon with pixel sizes of 85 microns. This exemplary monochromatic x-ray device using the techniques described herein can easily resolve microcalcifications with diameters of 100-200 microns in the CIRS and ACR phantoms. FIGS. 35 and 36 illustrate images and associated histograms obtained using this exemplary monochromatic x-ray radiation device compared to images obtained using the same commercial device. The microcalcifications measured in the double ACR-CIRS phantom (stacked 2900 and 3200 phantoms) experiments described earlier using the monochromatic 25 keV x-ray lines have a SNR that is 50% higher than the SNR for the commercial machine and its mean glandular dose (mgd) is 6 times lower for these images. If one were to make the monochromatic SNR the same as that measured in the commercial machine, then the monochromatic mean glandular does (mgd) would be another factor of 2 times smaller for a total of 11 times lower. Simple geometric considerations indicate that the effective projected spot size of the secondary cone is 1-2 mm. FIG. 37 illustrates histograms of the measured intensity scans through line-pair targets that are embedded in the CIRS phantom. The spacing of the line-par targets ranges from 5 lines per mm up to 20 lines per mm. The top four histograms show that the scans for 18 keV, 21 keV, 22 keV and 25 keV energies using a 4 mm secondary cone described briefly above can discern alternating intensity structure up to 9 lines per mm which is consistent with a spatial resolution FWHM of 110 microns. The 18 keV energy can still discern structure at 10 lines per mm. The bottom histogram in FIG. 37 is an intensity scan through the same line-pair ensemble using a commonly used commercial broad band mammography system. The commercial system's ability to discern structure fails beyond 8 lines per mm. This performance is consistent with the system's modulation transfer function (MTF), a property commonly used to describe the spatial frequency response of an imaging system or a component. It is defined as the contrast at a given spatial frequency relative to low frequencies and is shown in FIG. 38. The value of 0.25 at 9 lines/mm is comparable to other systems with direct detector systems and better than flat panel detectors. According to some embodiments, the exemplary monochromatic system described herein was operated with up to 2000 watts in a continuous mode, i.e., the primary anode is water-cooled, the high voltage and filament current are on continuously and images are obtained using a timer-controlled, mechanical shutter. The x-ray flux data in FIG. 20 together with the phantom images shown in FIGS. 31 and 33 provide scaling guidelines for the power required to obtain a desired signal to noise for a specific exposure time in breast tissue of different compression thicknesses. Using a secondary material of Ag, 4 mm and 8 mm cone assemblies are compared for a compressed thickness of 4.5 cm and 50:50 glandular-adipose mix) in FIG. 39. The power requirements for a compressed thickness of 9 cm (50:50 glandular-adipose mix) as defined by experiments described above are compared in FIG. 40 for the 4 mm, 8 mm cones made from Sn. The results indicate that a SNR of 8.5 obtained in a measurement of the 100% glandular block embedded in the CIRS phantom of normal breast density compressed to 4.5 cm can be achieved in a 5 second exposure expending 9.5 kW of power in the primary using the 4 mm cone (FIG. 39 top); 3.7 kW are needed if one uses the 8 mm cone (FIG. 39 bottom). In both of these cases, the source-to-detector (S-D) is 760 mm. If 2 sec are required, 9.2 kW are needed if an 8 mm cone is used or a 4 mm cone can be used at a source-to-detector (S-D) distance of 471 mm instead of 760 mm. Since the spatial resolution dependence is linear with S-D, then moving the 4 mm cone closer to the sample will only degrade the spatial resolution by 1.6 times, but it will still be better than the 8 mm cone at 760 mm. In general, there is a trade-off between spatial resolution and exposure time that will determine whether the 4 mm or 8 mm embodiments at the two source-to-detector distances best suit an application. This data serves as guides for designing monochromatic x-ray sources and do not exclude the possibilities for a variety of other target sizes and source-to-detector distances. For thick breast tissue compressed to 9 cm, the dependency of the SNR on power is shown in FIG. 40. A 7 sec exposure can produce a SNR of 8.5 at 11 kW using a 4 mm Sn cone at a source-to-detector distance of 471 mm or with a 8 mm cone at 760 mm. Conventional broad band commercial mammography systems would have to deliver a 14 mGy dose to achieve this same SNR whereas the monochromatic system at 25 keV would only deliver 0.54 mGy, a factor of 26 times lower and still 2.3 times lower than the conventional dose of 1.25 mGy delivered by a commercial machine in screening women with normal density breast tissue compressed to 4.5 cm. The inventor has recognized the importance of maximizing the monochromatic X-ray intensity in a compact x-ray generator for applications in medical imaging. Increased intensity allows shorter exposures which reduce motion artifacts and increase patient comfort. Alternatively, increased intensity can be used to provide increased SNR to enable the detection of less obvious features. There are three basic ways to increase the monochromatic flux: 1) maximizing fluorescence efficiency through the geometry of the target, 2) enhance the total power input on the primary in a steady state mode and 3) increase the total power input on the primary in a pulsed mode. The inventor has developed techniques to increase monochromatic flux corresponding to each. With respect to improving fluorescence efficiency (which involves increasing the amount of fluorescent x-ray produced by a secondary target and/or decreasing the amount of fluorescent x-rays absorbed by the secondary target) via the geometry of the target, in analyzing the x-ray fluorescence phenomenon, the inventor recognized that conventional solid secondary targets contribute to inefficiency in producing monochromatic fluorescent x-ray flux emitted from the secondary target. In particular, broadband x-rays incident on a secondary target (e.g., the secondary targets described in the foregoing) are described by the Bremsstrahlung spectrum and characteristic lines emitted from the primary target. For example, FIG. 21 illustrates the spectrum 2100 emitted by a gold (Au) primary target (anode) for a 100 kVp cathode-anode voltage, including Bremsstrahlung emission 2100c and characteristic gold L and K-shell emissions 2100a and 2100b, respectively. Also illustrated in FIG. 21 are the K-absorption edges 2110a and 2110b for Ag (25 keV) and Sn (29 keV), respectively. The horizontal arrows 2115a and 2115b extending from the respective absorption edge energy to 100 keV illustrate photons in spectrum 2100 with energies above the respective absorption edges that are therefore candidates for inducing x-ray fluorescence from Ag and Sn targets, respectively. As discussed in the foregoing, fluorescence occurs when photons are absorbed by an atom and electrons are ejected from the atom. As vacancies in the inner shell of the atom are filled by electrons from the outer shells, a characteristic fluorescent x-ray whose energy is the difference between the two binding energies of the corresponding shells (i.e., the difference between the binding energy of the outer shell from which an electron left and the binding energy of the inner shell in which a vacancy was filled) is emitted from the atom. The probability that a photon will be absorbed by secondary target material decreases approximately with the third power of the photon energy, thus the absorption length in the secondary target increases with photon energy. For example, 63% of 40 keV photons will be absorbed in the first 60 microns of Ag, whereas 170 microns and 360 microns are required to absorb 63% of 60 keV and 80 keV photons, respectively. The inventor has recognized that due to the fall off in the probability of absorption and the increase in absorption length as a function of photon energy, conventional solid secondary targets exhibit significantly reduced fluorescent x-ray flux because the secondary target itself absorbs a significant amount of the fluorescent x-rays that are generated in the interior of the secondary target. FIG. 41 schematically illustrates this principle. In particular, in FIG. 41, two exemplary x-ray photons 4115a and 4115b are incident on a solid secondary target 4120. For example, x-rays 4115a and 4115b may be emitted from a primary target bombarded with electrons from a cathode of the primary stage of the x-ray source illustrated in FIG. 9 (e.g., x-rays 915 emitted by primary target 910 in response to electrons 907 emitted from cathode 905). With reference to the example spectrum illustrated in FIG. 21, x-rays 4115a and 4115b may be those emitted from a primary target comprising a gold surface and, therefore, exemplary x-rays 4115a and 4115b having energies above the absorption edge of the primary target material (e.g., above absorption edge 2110a for silver and above absorption edge 2110b for tin) and are therefore both candidates for producing fluorescent x-rays characteristic of the secondary target material. As shown in FIG. 41, x-ray photon 4115a is absorbed near the surface of secondary target 4120, allowing fluorescent x-ray 4125a produced by the absorption event to escape secondary target 4120 before being absorbed (e.g., x-ray photon 4115a may be relatively close to the absorption edge of the secondary target material and therefore have a higher likelihood of being absorbed near the surface). As a result, fluorescent x-ray 4125a contributes to the monochromatic x-ray flux emitted from the secondary target and that can be utilized to perform imaging. That is, because the original absorption event occurred close to the surface of secondary target 4120, monochromatic fluorescent x-ray 4125a exits secondary target 4120. On the other hand, x-ray photon 4115b penetrates further into secondary target 4120 before being absorbed (e.g., x-ray photon 4115b may have an energy further away from the absorption edge of the secondary target material and therefore have a lower probability of being absorbed near the surface). As a result of being absorbed in the interior of the secondary target, fluorescent x-ray 4125b is absorbed by secondary target 4120 and prevented from contributing to the monochromatic x-ray flux emitted from the secondary target and available for imaging. That is, because the original absorption event occurred deeper in the interior of secondary target 4120, monochromatic fluorescent x-ray 4125b is absorbed before it can exit secondary target 4120. The inventor has appreciated that the geometry of conventional solid secondary targets in fact prevents significant amounts of fluorescent x-rays from exiting the secondary target and contributing to the available monochromatic x-ray flux, and has recognized that different geometries would allow substantial increases in monochromatic x-ray flux to be emitted from the secondary target. Accordingly, the inventor has developed secondary target geometries that substantially reduce the probability that monochromatic x-rays fluoresced by the secondary target will be absorbed by the secondary target, thereby increasing the monochromatic x-ray flux emitted from the secondary target and available to perform imaging. According to some embodiments, the geometry of the secondary target increases the probability that an original absorption event occurs at or near a surface of the secondary target. For example, according to some embodiments, the number of opportunities an x-ray photon has to be absorbed near a surface of the secondary target is increased. As another example, according to some embodiments, the number of opportunities an x-ray photon has to be absorbed within an interior of the secondary target sufficiently distant from a surface of the secondary target is reduced and/or eliminated. The inventor has recognized that the above benefits may be achieved by using a secondary target comprising one or more layers of material instead of as a solid bulk target as is conventionally done. A layer refers herein to material provided as, for example, a sheet, foil, coating, film or veneer that can be applied, deposited or otherwise produced to be relatively thin, as opposed to conventional solid targets that are provided as bulk material. According to some embodiments, a secondary target comprises a plurality of layers, each providing an opportunity for incident x-rays to be absorbed at or near a surface of the secondary target, some illustrative examples of which are discussed in further detail below. FIG. 42 illustrates a cross-section of a secondary target configured to increase monochromatic x-ray flux emitted from the secondary target, in accordance with some embodiments. In the example illustrated in FIG. 42, secondary target 4220 may be substantially the same shape and size as solid target 4120 illustrated in FIG. 41. However, instead of being constructed as a solid target (e.g., as bulk material), secondary target 4220 is constructed as a conical shell 4220a of secondary target material. The term shell is used herein to refer to one or more layers that form a given geometry (e.g., a conical shell, frustoconical shell, cylindrical shell, etc.). A shell may be open or closed and may be provided in any suitable form (e.g., as a foil, sheet, coating, film, veneer or other material layer), examples of which are described in further detail below. Exemplary secondary target 4220 may be of foil construction of the desired secondary target material. The term “foil” refers herein to a thin layer of material that can be provided according to a desired geometry, further examples of which are discussed below. As a result of the layered nature of secondary target 4220 (e.g., via the foil construction), interior 4222 of secondary target 4220 provides substantially unobstructed transmission paths for x-rays that penetrate through the layers of the conical shell. For example, interior 4222 may be air or may include material substantially transparent to x-ray radiation (e.g., interior may include a substrate to support the secondary target material layer(s) (e.g., foil), or may be a substrate on which secondary target material is otherwise applied such via sputtering or other coating or deposition techniques, as discussed in further detail below.). As with x-ray 4115a illustrated in FIG. 41, x-ray 4215a undergoes an initial (also referred to as an original or first) absorption event at or near the surface of secondary target 4220 and, as a result, fluorescent x-ray 4225a is emitted from the secondary target before it can be absorbed (i.e., before a second absorption event occurs). In the exemplary embodiment illustrated in FIG. 42, x-ray 4215a is absorbed within the material thickness of conical shell 4220a. Also, like x-ray 4115b illustrated in FIG. 41, x-ray 4215b penetrates into an interior of secondary target 4220. However, because interior 4222 is made of subject matter substantially transparent to x-rays (e.g., air, plastic, carbon fiber, etc.), x-ray 4215a is transmitted through the interior and undergoes an initial absorption event at or near another surface of secondary target 4220 (i.e., a layer of material on the other side of conical shell 4220a) instead of in the interior of the secondary target, as was the case with conventional solid secondary target 4120 illustrated in FIG. 41. Specifically, x-ray 4215 is transmitted through one layer of conical shell 4220a and interior 4222 and is absorbed by a layer of material on the other side of conical shell 4220a. As a result of this initial absorption event occurring at or near a surface of secondary target 4220, fluorescent x-ray 4225c produced in response to this absorption event exits secondary target 4220 and contributes to the monochromatic flux emitted from the secondary target. The inventor has recognized that the thickness of the material layers of the secondary target impacts the efficiency of fluorescent x-ray production. While any thickness for a secondary target layer that increases the fluorescent x-ray flux relative to a solid secondary target may be suitable, the thickness of material layers can be generally optimized by considering the physics of x-ray transmission and absorption. FIG. 43 illustrates schematically an x-ray absorption and fluorescence event in connection with a layer of material having a thickness, t. In reference to FIG. 43, the intensity of x-rays transmitted through a thin layer of material (e.g., foil), Itransmit, can be expressed as follows: I transmit = I incident ( E incident ) e - μ ( E incident ) t cos ( θ ) ( 1 ) In equation (1), Eincident is the energy of the incident x-ray, μ is the absorption coefficient at energy Eincident, t is the thickness of the secondary target layer, and θ is the apex angle of the layer relative to the vertical direction. The amount of x-rays absorbed in the material layer, Iabsorb, is expressed below in equation (2) as follows: I absorb = I incident - I transmit = I incident [ 1 - e - μ ( E incident ) t cos ( θ ) ] ( 2 ) The absorbed x-rays will produce fluorescent x-rays characteristic of the absorbing material of the secondary target as discussed above. The amount of fluorescent x-rays that originate at the location, t/cos(θ), and escape from the secondary target is expressed below in equations (3) and (4) as follows: I escape = F ɛ I absorb e - μ ( E F ) t sin ( θ ) ( 3 ) I escape = F ɛ I incident [ 1 - e - μ ( E incident ) t cos ( θ ) ] e - μ ( E F ) t sin ( θ ) ( 4 ) In equations (3) and (4), FE is the efficiency of the fluorescent x-ray production. Accordingly, there is a thickness, t of the layer of material that maximizes the intensity of the escaping fluorescent x-rays. This can be normalized to the ratio, Iescape/Iincident Fε, as shown below in equation (5) as follows: I escape I incident F ɛ = [ 1 - e - μ ( E incident ) t cos ( θ ) ] e - μ ( E F ) t sin ( θ ) ( 5 ) Using the equations above, plots 4400a and 4400b illustrated in FIGS. 44A and 44B, respectively, were obtained. Plots 4400a and 4400b show fluorescent x-ray emission (i.e., fluorescent x-ray intensity exiting a layer of secondary target material) as a function of material thickness at a number of exemplary incident x-ray photon energies, using silver (Ag) and tin (Sn) as the secondary target material layer, respectively. Specifically, plot 4400a illustrates fluorescent x-ray emission as a function of the thickness of a layer of Ag material arranged with an apex angle of 14 degrees relative to the vertical (i.e., θ=14 degrees) for exemplary primary x-ray energies of 40 keV, 50 keV, 60 keV, 80 keV and 100 keV. Similarly, plot 4400b fluorescent x-ray emissions for the same arrangement (geometry) but using instead a layer of Sn material. As demonstrated by plots 4400a and 4400b, each curve at the different primary x-ray energies exhibits a peak corresponding to the optimal thickness for the corresponding material layer. As shown, the optimal thickness at each exemplary energy is within a relatively narrow range. In particular, the optimal thickness for each energy ranges between 17 and 19 microns for the Ag layer and between 24 and 25 microns for the Sn layer. Accordingly, the inventor has appreciated that selecting thicknesses within these ranges for a secondary target provides excellent fluorescent x-ray emission characteristics over a wide range of incident x-ray energies. It should be appreciated, however, that thicknesses outside the optimal range may also be used, as the aspects are not limited to selecting values within any particular range, let alone the optimal range for the particular secondary target material. That said, choosing thicknesses within the optimal range may produce secondary targets having better fluorescent x-ray emission characteristics, some examples of which are discussed in further detail below. Accordingly, the thickness of the layer(s) of secondary target material may be chosen based on the material type, the operating parameters of the monochromatic x-ray source and/or the intended application of the monochromatic x-rays. For example, the fluorescent emission vs. thickness curve for uranium has a peak corresponding to the optimal thickness of approximately 60 microns, but the characteristic curve is broader than the characteristic curves for Ag and Sn illustrated in FIGS. 44A and 44B, providing a much larger range of thicknesses exhibiting significantly improved fluorescent x-ray emission characteristics. As another example, molybdenum has a characteristic peak in its emission vs. thickness curve of approximately 13 microns. The choice of material thickness may also be based on the operating parameters of the monochromatic x-ray source. For example, thicker material layers may be preferable when using higher power devices to convert more of the higher energy x-rays emitted. Thus, exemplary secondary target material layers can range from 5 microns or less (e.g., down to micron) up to 200 microns or more. Typical secondary target material thicknesses for mammography diagnostic applications may range from approximately 10 microns or less to 50 microns or more, as an example. Secondary target material thickness may also be selected based on the number of material layers provided (e.g., material thickness may be reduced and additional layers added) to obtain desired fluorescent x-ray emission characteristics. FIG. 45A illustrates an exemplary secondary target 4520 similar in geometry to secondary target 4220 illustrated in FIG. 42. In particular, secondary target 4520 is a conical shell of Sn having a total enclosed angle of 28 degrees (i.e., two times the apex angle of 14 degrees (θ=14°) relative to the vertical), a width of 4 millimeters at its base (b=4 mm) and a material thickness of 25 microns (t=25 μm). Secondary target 4520 (and 4520′ in FIG. 45B) are oriented with the apex at the distal side of the secondary target and the base at the proximal side of the target. The terms “distal” and “proximal” refer herein to ends or sides closer to and farther away from the exit aperture of the monochromatic source (e.g., exit aperture 4544 illustrated in FIG. 45B). Accordingly, the distal side or distal end of a secondary target is the side that is closer to the exit aperture than the opposing side, which is referred to as the proximal side or proximal end. In FIG. 45A, the distal end of secondary target 4520 is indicated by arrow 4247 and the proximal end of secondary target 4520 is indicated by arrow 4245. Similarly, the terms “distally” and “proximally” refer herein to relative directions towards and away from the exit aperture (e.g., in the directions indicated by arrows 4247 and 4245, respectively). The fluorescent x-ray emission from the exemplary secondary target illustrated in FIG. 45A was both simulated and measured experimentally, the results of which are illustrated in FIGS. 46 and 47, respectively. Specifically, for the simulation, x-ray fluorescence was computed using the equations above based on a model of a monochromatic x-ray source used to produce actual x-ray fluorescent emissions for the corresponding experiment discussed below. Additionally, fluorescent x-ray emissions were simulated (i.e., determined computationally) in the same manner for a conventional solid Sn secondary target of the same dimensions (i.e., a solid cone of tin having an apex angle of 14 degrees and a base of 4 mm). The simulated fluorescent x-ray emissions from the Sn foil secondary target (e.g., secondary target 4520) and the solid Sn target are illustrated in FIG. 46 discussed in further detail below. To obtain experimental measurements, a conical shell secondary target 4520′ was constructed using Sn foil having the approximate dimensions of secondary target 4520a illustrated in FIG. 45A. Specifically, an approximately 25 micron thick Sn foil conical shell was formed having a base width of approximately 4 mm and an apex angle of approximately 14 degrees, as illustrated schematically by secondary target 4520′ illustrated in FIG. 45B. The Sn foil secondary target was positioned within a carrier and inserted into a monochromatic x-ray source (i.e., a monochromatic x-ray source as embodied by the aspects of the exemplary monochromatic x-ray sources described herein). Specifically, as illustrated schematically in FIG. 45B, a Sn foil target 4520′ was positioned within carrier 4540 and inserted into a beryllium window 4530 that interfaces with the primary stage of a monochromatic x-ray source comprising primary target 4510 (gold plated tungsten) and cathode 4506 formed by a toroidal filament. The monochromatic x-ray source was operated by using 80 kV between the cathode 4506 and primary target 4510 with an emission current of 0.33 mA. Fluorescent x-rays emitted from the monochromatic source were detected using a cadmium telluride (CdTe) photon counting detector. Additionally, the same experiment was performed to obtain x-ray fluorescent measurements using a conventional sold Sn target having a base of 4 mm. As mentioned above, the simulations were performed using a model of the same physical system (i.e., the same monochromatic x-ray source and detector) and operational parameters employed to obtain actual fluorescent x-ray emission measurements to compare simulated results to actual measurements. FIGS. 46 and 47 illustrate the fluorescent x-ray emissions obtained via the simulations and actual experiments discussed above, respectively. Specifically, simulated emissions 4625a and 4625b show the simulated Kα and Kβ fluorescent x-ray emissions for the Sn conical shell secondary target (i.e., secondary target 4520 illustrated schematically in FIG. 45A), respectively. Simulated emissions 4625a′ and 4625b′ show the simulated Kα and Kβ fluorescent x-ray emissions for the Sn solid cone secondary target, respectively. Similarly, measured emissions 4725a and 4725b show the actual Kα and Kβ fluorescent x-ray emissions measured for the Sn conical shell secondary target (i.e., secondary target 4520′ illustrated schematically in FIG. 45B), respectively, and measured emissions 4725a′ and 4725b′ show the actual Kα and Kβ fluorescent x-ray emissions measured for the Sn solid cone secondary target, respectively. As shown, the simulated and measured fluorescent x-ray emissions for the Sn conical shell secondary target are significantly increased relative to the corresponding emissions for the Sn solid cone secondary target. Notably, the simulated and experimental results are in substantial agreement, demonstrating the veracity of the simulations. It should be appreciated that the dimension of the secondary target discussed above is merely exemplary and can be chosen as desired. For example, the maximum diameter of the secondary target (e.g., the diameter of the base of secondary target 4220) can be chosen based on the requirements of the monochromatic x-ray source. In particular, the larger the secondary target the greater the monochromatic x-ray flux that can be produced. However, the larger the secondary target, the larger the “spot size” of the fluorescent x-ray source, resulting in decreased spatial resolution of the resulting images. As such, there is typically a trade-off in increasing or decreasing the size of the secondary target (i.e., the larger the secondary target the greater the fluorescent x-ray intensity and the smaller the secondary target the better the resulting spatial resolution, all other operating parameters held the same. Thus, for applications in which fluorescent x-ray intensity may be more important than optimal spatial resolution, larger secondary targets may be preferred, for example, secondary targets having a maximum diameter of 8 mm, 10 mm, 15 mm or larger. By contrast, for applications in which spatial resolution is paramount, smaller secondary targets may be preferred, for example, secondary targets having a maximum diameter of 4 mm, 2 mm, 1 mm or smaller. As depicted in the drawings herein, the maximum diameter refers to the width of the secondary target at its maximum (e.g., in a direction orthogonal to the longitudinal axis of the secondary target). For example, the maximum diameter for a conical, cylindrical or spiral shell corresponds to the diameter of the shell at its base, whether the base is oriented distally or proximally. According to some embodiments, a secondary target has a maximum diameter of less than or equal to approximately 10 mm and greater than or equal to approximately 8 mm, according to some embodiments, a secondary target has a maximum diameter of less than or equal to approximately 8 mm and greater than or equal to approximately 6 mm, according to some embodiments, the secondary target has a maximum diameter of less than or equal to approximately 6 mm and greater than or equal to approximately 4 mm, according to some embodiments, the secondary target has a maximum diameter of less than or equal to approximately 4 mm and greater than or equal to approximately 2 mm, and according to some embodiments, the secondary target has a maximum diameter of less than or equal to approximately 2 mm and greater than or equal to approximately 1 mm. According to other embodiments, a secondary target has a maximum diameter of greater than 10 mm and according to other embodiments a secondary target has a maximum diameter of less than 1 mm. It should be appreciated that the above dimensions are merely exemplary and larger or smaller secondary targets may be used, as the aspects are not limited in this respect. Additionally, the size of a secondary target can be varied in other ways, for example, by changing the height (i.e., the maximum dimension in a direction parallel to the longitudinal axis) to base aspect ratio (e.g., height to maximum diameter ratio). A change in the aspect ratio generally has a corresponding change to the apex angle. Thus it should be appreciated that different apex angles may be selected as desired, ranging from 0 degrees (i.e., vertical layers) to 90 degrees (i.e., a horizontal layers), as the aspects are not limited in this respect. According to some embodiments, a secondary target has an aspect ratio (e.g., using any of the exemplary diameters discussed above) of between 1:2 and 1:1, according to some embodiments, the secondary target has as aspects ratio between 1:1 and 2:1, according to some embodiments, the secondary target has an aspect ratio of between 2:1 and 3:1, according to some embodiments, the secondary target has an aspect ratio of between 3:1 and 4:1, according to some embodiments, the secondary target has an aspect ratio of between 4:1 and 5:1, according to some embodiments, the secondary target has an aspect ratio of between 5:1 and 6:1, according to some embodiments, the secondary target has an aspect ratio of between 6:1 and 7:1, and according to some embodiments, the secondary target has an aspect ratio of between 7:1 and 8:1. It should further be appreciated that the above aspect ratios are exemplary and other aspects ratios may be chosen, as the aspects are not limited in this respect. As demonstrated above, using a layer of secondary target material instead of a solid target may significantly increase fluorescent x-ray flux, as demonstrated by the above simulations and experiments. However, the inventor has appreciated that even at the optimal thickness for the secondary target material, some fraction of incident x-rays will pass through the secondary target without being absorbed by the secondary target, and the potential of producing a monochromatic x-rays from these transmitted x-rays is therefore lost. For example, FIG. 48 illustrates a conical shell secondary target 4820 similar or the same as secondary target 4220 illustrated in FIG. 42. As shown, while some of the incident x-rays are converted to fluorescent x-rays, a number of incident primary x-rays pass through the secondary target without being absorbed. As a result, the potential of generating monochromatic fluorescent x-rays from these transmitted x-rays is lost (e.g. incident x-rays 4815a-f emitted from a primary targeted are transmitted through secondary target 4820 without being absorbed). The inventor has recognized that more of the available incident x-rays (e.g., broadband x-rays emitted from a primary target) can be converted to monochromatic fluorescent x-rays by including additional layers of secondary target material, thereby providing additional opportunities for x-rays to undergo an initial absorption event near a surface of the secondary target. More particularly, the inventor has recognized that using multiple layers of secondary target material increases the total absorption probability of incident x-rays while maintaining short path lengths for the resulting fluorescent x-rays to exit the secondary target. This multiple layer geometry also makes it possible to take better advantage of higher energy x-rays present in the incident broadband spectrum (i.e., the higher energy photons in the Bremsstralung spectrum) which would ordinarily be absorbed deep inside a solid secondary target where the resulting fluorescent x-rays have a very low probability of escaping (i.e., exiting the secondary target to contribute to the monochromatic x-ray flux). According to some embodiments, a plurality of nested layers of secondary target material is used to increase monochromatic x-ray flux emission from the secondary target. FIGS. 49A and 49B illustrate cross-sections of exemplary secondary targets comprising nested conical shells providing a plurality of layers of secondary target material to increase the probability of an absorption event occurring at or near a surface of the secondary target material. In particular, secondary target 4920 comprises an outer conical shell 4920a and an inner conical shell 4920b, both formed substantially in the shape of a cone in the embodiment illustrated in FIGS. 49A and 49B. By nesting a plurality of shells, additional layers of secondary target material is disposed in the transmission paths of x-rays incident on the secondary target, increasing the number of opportunities for, and thus the probability that, an incident x-ray will undergo an initial absorption event in one of the plurality of layers of secondary target material. Because each of the plurality of layers is relatively thin (e.g., within the optimal range for the corresponding material), the number of initial absorption events occurring at or near a surface of the secondary target material is increased, thereby increasing the amount of monochromatic x-ray flux that exits the secondary target. According to some embodiments, each of the plurality of layers has a thickness that falls within an optimal range, for example, a thickness that generally maximizes fluorescent x-ray emission for the respective type of material used, as determined in the manner discussed above. However, it should be appreciated that the thickness of the plurality of layers may be outside the optimal range and can be of any thickness, as the aspects are not limited in this respect. Additionally, the plurality of layers may have the same, substantially the same or different thicknesses. For example, in the embodiment illustrated in FIGS. 49A and 49B, outer conical shell 4920a and inner conical shell 4920b may be constructed having the same thickness (or substantially the same thickness) or may be constructed having different thicknesses, as the aspects are not limited in this respect. As discussed above, using nested conical shells increases the probability that incident x-rays will be absorbed by the secondary target. For example, comparing FIG. 48 and FIG. 49A, broadband x-rays 4815a, 4815c, 4815d, 4815e and 4815f that were transmitted through secondary target 4820 were absorbed by secondary target 4920 and, more specifically, by inner conical shell 4920b, thereby producing additional fluorescent x-rays with the potential of exiting the secondary target 4920. However, the inventor recognized that while the layers of secondary target material provide additional opportunities for broadband x-rays to undergo an initial absorption event, the additional layers also present further opportunities for the resulting fluorescent x-rays to be absorbed before exiting the secondary target. For example, as illustrated in FIG. 49B, broadband x-rays 4815d and 4815e, which were transmitted through secondary target 4820 but absorbed by inner conical shell 4920b, produce fluorescent x-rays 4925d and 4925e that are absorbed by the material layers of secondary target 4920 before exiting the secondary target. That is, because the distal end of the exemplary nested conical shells illustrated in FIGS. 42, 48 and 49 are generally closed, some amount of fluorescent x-rays will be absorbed and prevented from exiting the secondary target. Thus, though broadband x-rays 4815d and 4815e underwent an initial absorption event at or near a surface of secondary target 4920 (i.e., at or near the surface of inner conical shell 4920b), the resulting fluorescent monochromatic x-rays 4925d and 4925e were absorbed by inner conical shell 4920b and outer conical shell 4920a, respectively, before exiting secondary target 4920. To facilitate a further increase in the fluorescent x-ray flux exiting a secondary target, the inventor has developed geometries that decrease the probability that fluorescent x-rays will be absorbed by second target material before exiting the secondary target and contributing to the monochromatic x-ray flux. According to some embodiments, a secondary target is constructed to have one or more openings in at least one layer of secondary target material to allow fluorescent x-rays to exit the secondary target unimpeded (i.e., without having to be pass through further material layers). For example, the distal end of the secondary target may be opened or partially opened to allow unobstructed transmission of at least some fluorescent x-rays produced in response to initial absorption events of incident x-rays. According to some embodiments, one or more conical shells may be inverted to reduce obstructions to fluorescent x-ray transmission (e.g., one or more conical shell may be arranged with its apex on the proximal side of the secondary target). According to some embodiments, cylindrical or spiral shells are provided to generally open the distal end of the secondary target. Some illustrative examples of secondary targets with open geometries are discussed in further detail below. FIG. 50A illustrates a secondary target 5020 comprising nested shells 5020a and 5020b, wherein outer shell 5020a is constructed as a frustoconical shell open at the distal end to provide unimpeded transmission paths for an increased number of fluorescent x-rays produced at layers internal to the secondary target (e.g., produced as a result of broadband x-ray absorption by inner conical shell 5020b). Compared with the exemplary fluorescent x-rays absorbed by secondary target 4920 illustrated in FIGS. 49A and 49B, fluorescent x-ray 4925e exits secondary target 5020 unimpeded via the open distal end of frustoconical shell 5020a, instead of being absorbed by the outer shell (e.g., outer conical shell 4920a of secondary target 4920 illustrated in FIGS. 49A and 49B), thereby increasing the fluorescent x-ray flux emitted by secondary target 5020. However, fluorescent x-ray 4925d is still absorbed by inner conical shell 5020b. FIG. 50B illustrates a secondary target 5020′ in which both the inner and outer shells (e.g., inner shell 5020b′ and outer shell 5020a) are frustoconical, providing at least some unimpeded transmission paths from the inside of both shells and thereby reducing the probability that fluorescent monochromatic x-rays will be absorbed by the secondary target. For example, fluorescent x-ray 4925d, which is illustrated as being absorbed by inner conical shell 5020b in FIG. 50a, exits unimpeded via the opening at the distal end of inner frustoconical shell 5020b′. Accordingly, by opening one or more nested shells, the probability that fluorescent x-rays are absorbed by the secondary target can be reduced. It should be appreciated, however, that frustoconical shells reduce the probability of fluorescent x-ray absorption but also reduce the surface area of the secondary target available for initial absorption events of incident x-rays (e.g., broadband x-rays emitted by the primary target), thus potentially reducing the number of fluorescent x-rays produced by the secondary target. The inventor has appreciated that by inverting one or more conical shells of a secondary target, the amount of unimpeded transmission paths can be increased without a corresponding loss in surface area. FIG. 51 illustrates a secondary target 5120 in which an outer shell has been inverted to decrease the probability that fluorescent x-rays produced by the layers of secondary target material will also be absorbed by those layers. In particular, secondary target 5120 is constructed using an inner conical shell 5120b (e.g., a conical shell similar in geometry to the exemplary inner conical shells illustrated in FIGS. 49A, 49B and 50A). Outer shell 5120a is formed by a conical or frustoconical shell that is inverted relative to inner conical shell 5120b, thereby providing unimpeded transmission paths for an increased number of fluorescent x-rays produced by secondary target 5120 (e.g., produced in response to absorbing broadband x-rays from a primary target.) By inverting outer shell 5120a (e.g., by orienting the outer shell so that the apex-side of the shell is at or toward the proximal end of the secondary target instead of the distal end), the probability of fluorescent x-ray absorption can be decreased without reducing the surface area of the secondary target available to absorb primary x-rays (e.g., broadband x-rays emitted by a primary target). Thus, the generally “W” shaped geometry of exemplary secondary target 5120 facilitates significantly increasing the fluorescent x-ray intensity emitted by the secondary target, as demonstrated in further detail below. FIG. 52 illustrates a secondary target 5220 in which both the inner and outer shells have been inverted so that the apex-side of the respective shells are oriented toward the proximal end of the secondary target. Specifically, secondary target 5220 is constructed using inner conical shell 5220b having its apex directed toward the proximal end of the secondary target (i.e., generally inverted relative to the orientation of inner conical shell 5120b of secondary target 5120) and outer shell 5220a also oriented towards the proximal end in the direction of outer shell 5120a of exemplary secondary target 5220. As another variation using an open geometry, FIG. 53 illustrates a secondary target 5320 in which both outer shell 5320a and inner shell 5320b have a generally conical shape and are oriented with their respective apexes directed towards the proximal end of the secondary stage. It is noted that while the exemplary secondary targets illustrated in FIGS. 51, 52 and 53 have two nested shells, any number of shells may be used, including a single shell (e.g., the single conical shell of exemplary secondary target 4520b illustrated in FIG. 45B may be inverted so that its apex is directed toward the proximal end of the secondary target instead of toward the distal end, with the base optional opened). Based on the insight provided by the inventor, numerous other open geometries are also possible. For example, FIGS. 54A-C illustrate exemplary secondary targets formed from generally cylindrical shells. In particular, exemplary secondary targets 5420 and 5420′ are constructed using an outer cylindrical shell 5420a and inner cylindrical shell 5420b open at the distal end to decrease the probability of fluorescent x-rays produced from initial absorption of broadband x-rays being absorbed by the secondary target. FIG. 54B illustrates a top down view of secondary targets 5420 and 5420′ showing outer cylindrical shell 5420a and inner shell 5420b. As further illustrated, secondary target 5420 illustrated in FIG. 54A includes secondary target material at the proximal end of the secondary target (e.g., the inner and outer shells may be closed or substantially closed at the proximal end), while secondary target 5420′ illustrated in FIG. 54C is open at the proximal end. As discussed above in connection with conical or frustoconical shells, any number of cylindrical shells may be used to construct the secondary target, as the aspects are not limited in this respect. As another generally open geometry variation, FIGS. 55A-C illustrate secondary targets constructed using a spiral geometry. In particular, secondary target 5520 illustrated in FIG. 55A comprises cylindrical spiral 5520a and secondary target 5520′ illustrated in FIG. 55C comprises conical spiral 5520a′. While a conical spiral is illustrated in FIG. 55C, a frustoconical (not shown) spiral may be more easily manufactured. FIG. 54B illustrates a top down view of a cross-section of secondary targets 5520 and 5520′ showing the characteristic spiral geometry of the secondary targets. As with the number of nested shells, a spiral geometry can have any number of turns to provide a desired number of layers of secondary target material to provide sufficient opportunity for incident broadband radiation to undergo an initial absorption event at or near a surface of the secondary target (i.e., sufficient opportunity to be absorbed by one of the layers of material forming the secondary target), as the aspects are not limited in this respect. A number of the exemplary secondary targets described in the foregoing include secondary target material on the proximal side of the secondary target (e.g., side 4220c of secondary target 4220 illustrated in FIG. 42). However, as an alternative, the proximal side of the secondary target may be left open and/or generally free of secondary target material. For example, FIGS. 56-59 illustrate secondary targets 5620, 5720, 5820 and 5920 that are substantially open on the proximal side of the secondary target. This may simplify construction of the secondary target. As also discussed in the foregoing, a plurality of layers may be used to increase the probability that broadband x-rays will be absorbed and any number of layers may be employed. For example, FIGS. 60A-C and 61A-C illustrate secondary targets configured with different number of layers of secondary target material using a conical geometry and an inverted conical geometry, respectively. In particular, FIG. 60A illustrates a single conical shell secondary target 6020 in which x-rays passing through the secondary target (e.g., along axis 6053 orthogonal to the longitudinal axis 6055 of the monochromatic x-ray source) typically encounter two layers of secondary target material. Secondary target 6020′ illustrated in FIG. 60B is constructed of two nested conical shells and therefore provides four layers of secondary target material for x-rays passing through the target, and secondary target 6020″ illustrated in FIG. 60C is constructed from three nested conical shells presenting six layers of secondary target material that provide opportunities for broadband x-rays to be absorbed. Similarly, FIGS. 61A-C illustrate secondary targets constructed using an open (e.g., inverted shell) geometry. In particular, secondary target 6120 illustrated in FIG. 61A is constructed using a generally “W” shape, providing four layers of secondary target material to absorb incident broadband x-rays (e.g., secondary target 6120 comprises four separate layers in the direction orthogonal to the longitudinal axis of the secondary target so that many (if not most) incident x-rays will have four opportunities to undergo an initial absorption event). Secondary targets 6120′ and 6120″ illustrated in FIGS. 61B and 61C, respectively, are constructed with nested inverted conical shells, both providing six layers of secondary target material capable of absorbing incident broadband x-ray radiation. Referring to FIG. 55C, secondary target 5520′ constructed using a spiral geometry provides seven layers of secondary target material capable absorbing primary x-rays emitted from a primary target to produce fluorescent x-rays. As discussed above, the secondary targets illustrated herein are exemplary and any number of layers may be used to construct a secondary target, as the aspects are not limited in this respect. Increasing the number of layers may facilitate converting more high energy incident x-rays to fluorescent x-rays. As illustrated by the exemplary secondary targets illustrated in FIGS. 60A-C and 61A-C, each successive shell has a different apex angle (e.g., by virtue of having different aspect ratios). This change in apex angle is more clearly illustrated by exemplary secondary targets 6220 and 6220′ in FIGS. 60D and 60E, where a relatively wide apex angle is used to construct the generally conical shells. In particular, outer shell 6220a of exemplary target 6220 illustrated in FIG. 60D has an apex angle of approximately 60 degrees while inner shell 6220b has an apex angle of approximately 30 degrees. A progression from relatively large apex angle to smaller apex angle can also be seen by the decreasing apex angles of outer, middle and inner shells 6220a′, 6220b′ and 6220c′ of exemplary secondary target 6220′ illustrated in FIG. 60E. FIG. 60F illustrates an exemplary secondary target 6220″ with a plurality of nested shells in which the apex angle is substantially the same for both outer shell 6220a″ and inner shell 6220b″. It should be appreciated that a secondary target can be constructed to have any desired apex angle or apex angles depending on the geometry of the one or more shells, including the boundary angles of 0 degrees (i.e., vertical layer(s) resulting, for example, by the cylindrical shells illustrated in FIGS. 54A-C or by lining up planar layers of secondary material layers in the horizontal direction) and 90 degrees (i.e., horizontal layer(s) resulting, for example, by rotating the cylindrical shells illustrated in 54A-C by 90 degrees or by stacking planar layers of secondary target material in the vertical direction with a desired amount of spacing between the successive layers). It should be appreciated that varying the apex angle applies to other geometries as well, including the “W” shaped geometries illustrated in FIGS. 61A-C. To illustrate the efficacy of using layered secondary targets, FIG. 62 shows the monochromatic fluorescent x-ray flux output emitted from secondary targets using a number of different geometries relative to the monochromatic fluorescent x-ray flux emitted from a conventional solid cone secondary target. The monochromatic fluorescent x-ray intensity shown in FIG. 62 was simulated using silver (Ag) as the secondary target material and the layered secondary targets were simulated with each layer formed by a 17 micron thick Ag foil. As shown in FIG. 62, monochromatic fluorescent x-ray flux emitted by solid conical secondary target 6220A was normalized to one. Secondary target 6220B, comprising a single conical shell, produced twice the monochromatic fluorescent x-ray intensity and secondary target 6220C, comprising nested conical shells, produced 2.5 times the monochromatic fluorescent x-ray intensity as conventional solid secondary target 6220A. Secondary target 6220D, comprising inverted nested shells in a generally “W” shaped geometry provided a factor of 3.2 times the monochromatic fluorescent x-ray flux compare to the conventional solid cone secondary target 6220A. The increase in monochromatic fluorescent x-ray intensity produced using techniques described herein has a significant impact on the power requirements of the x-ray source, reducing the input power required at the primary cathode-anode stage to produce the same monochromatic x-ray flux at the output of a monochromatic x-ray source, as discussed in further detail below. The secondary target material provided in the exemplary geometries discussed in the foregoing may be provided on a support or substrate to provide a secondary target that can be relatively easily handled and positioned to form the secondary stage of a monochromatic x-ray source. FIGS. 63A and 63B illustrate an exemplary support secondary target material, in accordance with some embodiments. In the example illustrated in FIGS. 63A and 63B, a support 6322 for nested conical shells of secondary target material is provided comprising an outer support 6322a for outer conical shell 6320a and an inner support 6322b for inner conical shell 6320b. Outer support 6322a includes a substrate 6324a and inner support 6322b includes a substrate 6324b on which secondary target material (e.g., a metallic fluorescer) can be applied to form inner and outer nested conical shells, respectively. Support 6322 (e.g., inner and outer supports 6322a and 6322b) may be made of any suitable material, for example, a generally low atomic number material that is sufficiently transparent to both incident broadband x-rays and fluorescent x-rays produced by the secondary target. For example, the support can be constructed using carbon fiber, nylon, polyethylene, boron nitride, aluminum, silicon or any other suitable material. The support for the secondary target material (e.g., support 6322) may be manufactured using any suitable technique, for example, 3D-printing, machining, material growth, casting, molding, etc. Moreover, secondary target material may be applied to the substrate surfaces of the secondary target support in any suitable manner. For example, thin foil may be attached or otherwise affixed to the substrate(s) of the support to form the secondary target (e.g., to form inner and outer conical nested foils). Alternatively, if free-standing foils are not the optimum choice, for example, secondary target material may be applied using any suitable deposition technique, such as evaporation, sputtering, epitaxial growth, electroplating or any other suitable material deposition process. For example, some secondary target material may be difficult to produce in thin-foil form, but can be readily deposited using deposition techniques commonly used in semiconductor and MEMS fabrication. Thus, deposition methods make it possible to utilize materials for the secondary target that are not available as free-standing thin foils or not easily machineable, e.g. antimony, tellurium which are useful for x-ray mammography. Higher Z materials, which are applicable, but not limited to cardiac or thorasic imaging, can be made from rare earth elements (e.g., dysprosium, holmium) or higher Z elements (e.g., tantalum, tungsten, platinum or depleted uranium). The exemplary support illustrated in FIGS. 63A and 63B may be constructed using hollow conical supports 6322a and 6322b, though the support could also be formed using solid pieces of support material or a combination of solid and hollow support pieces. As illustrated in FIG. 63B, outer support 6322a comprises (in addition to substrate portion 6324a on which secondary target material is applied) base portion 6324c having a groove or other interlocking portion 6324d and a platform portion 6324e that together cooperate with inner support 6322b to allow the inner support to be correctly positioned and snapped into place. In particular, platform 6324e engages with base portion 6324f of inner support 6322b to limit how far the inner support 6322b can be inserted into the outer support 6322a in the direction indicated by arrow 6355. In addition, cooperating portion 6324g engages with the interlocking portion 6324d of base 6324c to snap the inner support to the outer support to nest inner conical shell 6320b within outer conical shell 6320a, thereby forming a nested conical shell secondary target. It should be appreciated that the support may be formed from a single integrated piece of material, or may provide a substrate on which to apply secondary target material in other ways, as the aspects are not limited in this respect. FIGS. 64 and 65 illustrate two exemplary secondary targets arranged within a carrier positioned within a window of a monochromatic x-ray source. Specifically, carrier 6440 may be the same or similar to any of the carriers described herein that, when housing a secondary target, forms the secondary stage of a monochromatic x-ray source. It should be appreciated that carrier 6440 may utilize any of the techniques described herein. For example, carrier 6440 may include a blocking portion 6444 and a transmissive portion 6442 in which the secondary target is positioned (e.g., exemplary secondary targets 6420 and 6520). The blocking portion may comprise material that blocks x-ray radiation so that substantially all of the x-rays emitted from the monochromatic x-ray source exit via exit aperture 6544c, details of which were described in the foregoing. Transmissive portion 6442 may be constructed of material that is generally transparent to x-rays, as also discussed in detail herein. It should be appreciated that carrier 6440 may be removable from the first stage of the monochromatic x-ray source or may be provided as integrated components of the monochromatic x-ray source that are not generally removable. Moreover, it should be appreciated that layered secondary targets (e.g., exemplary secondary targets 6420 and 6520) can be employed in a monochromatic x-ray source in other ways without using the exemplary carriers described herein. In FIGS. 64 and 65, exemplary carrier 6440 is shown positioned within window 6430 that provides an interface to the primary stage of the monochromatic x-ray source and, more particularly, to primary target 6410 and cathode 6406. In FIG. 64, secondary target 6420 is constructed using a nested conical shell geometry, for example, any of the geometries illustrated in FIGS. 49A-B, 50A-B, 60A-C, etc. In FIG. 65, secondary target 6520 is constructed using an inverted or “W” shaped geometry, for example, any of the open geometries illustrated in FIGS. 51-53, 61A-C, etc. Referring to FIG. 65, the inverted geometry of secondary target 6520 may allow for advantageous modification to the carrier by, for example, eliminating the need for at least part of the carrier of the secondary stage. In particular, because the maximum dimension of secondary target 6520 (or other inverted geometries) is at the distal end of the secondary target, the distal end can be supported by the distal end of the carrier (e.g., a blocking portion of the carrier). As a result, the transmissive portion (e.g., transmissive portions 1342 and 1742 illustrated in FIGS. 13A-C and 17A-C, respectively) can be eliminated in some embodiments, removing material that can potentially interact with primary x-rays from the primary target, fluorescent x-rays from the secondary target, or both. In particular, the support or substrate on which secondary material is applied may also provide the proximal portion of the carrier that connects to or couples with the distal end of the carrier (e.g., the blocking portion in embodiments in which such techniques are used). For example, FIGS. 66A and 66B illustrate a carrier 6640 for a layered secondary target 6620 having an inverted geometry in which the maximal diameter of the target is on the distal side of the secondary target. Carrier 6640 includes a distal portion 6644 comprising an exit aperture 6644c through which fluorescent x-rays are emitted from the monochromatic x-ray source. Distal portion may be constructed in any suitable manner and, for example, may be constructed of blocking material as described in the foregoing. Carrier 6640 also comprises proximal portion 6642 comprising secondary target 6620. Specifically, the secondary target itself generally forms the proximal portion of carrier 6640. For example, as illustrated in FIG. 66B, proximal portion 6642 may comprise an outer support 6642 on which secondary target material is applied to form outer shell 6620a and an inner support 6642b on which secondary target material is applied to form inner shell 6620b. It should be appreciated that supports 6642a and 6642b may be constructed using any of the techniques described herein (e.g., 3D printing, machining, casting, etc.) and may be formed using any of the materials described herein (e.g., relatively low atomic number material that is substantially transparent to x-ray radiation.). Similarly, secondary target material may be applied using any technique described herein to form the layers of secondary target (e.g., to form exemplary outer shell 6620a and inner shell 6620b illustrated in FIGS. 66A and 66B). The distal and proximal portions of carrier 6640 may include cooperating portions that allow the two portions to be coupled. For example, distal portion 6644 may include a cooperating portion 6644d and proximal portion 6642 may include a cooperating portion 6642d that can be removably coupled (e.g., snapped together) so that different secondary targets can be coupled to the distal portion 6644 of carrier 6640. Thus, in the exemplary carrier 6640 illustrated in FIGS. 66A and 66B, the secondary target 6620 is part of the proximal portion as opposed to being a separate component from the transmissive portion of the carrier. As discussed above, the intensity of monochromatic x-ray emission may also be increased by varying the operating parameters of the first stage of the monochromatic source, for example, by increasing the cathode-anode voltage (e.g., the voltage potential between filament 6406 and primary target 6410 illustrated in FIGS. 64 and 65) and/or by increasing the filament current which, in turn, increases the emission current of electrons emitted by the filament. To further illustrate the monochromatic x-ray flux increase using layered secondary targets, FIG. 67 plots x-ray intensity against emission current at a number of different cathode-anode voltages using three different secondary target types: 1) an Ag solid cone having a 4 mm diameter base (see lines 65a, 65b and 65c); 2) an Ag solid cone having a 8 mm diameter base (see lines 67a, 67b and 67c); and 3) a thin foil “W” shaped target having a base diameter of 4 mm, i.e., the diameter at the distal end of the inverted shell (see lines 69a, 69b and 69c). As shown, the “W” shaped geometry of the layered secondary target produces substantially more fluorescent x-ray flux at the same cathode-anode voltage and, in fact, produces a higher fluorescent x-ray flux at 60 kVp than the 4 mm solid cone produces at 100 kVp. The layered secondary target (i.e., the 4 mm “W” shaped target) also produces more monochromatic x-ray flux than the 8 mm solid cone at 60 kVp despite the larger surface area of the 8 mm solid cone. Accordingly, layered secondary targets provide significant advances over conventional secondary targets with respect to fluorescent x-ray intensity production. More specifically, the curves in FIG. 67 show that the layered secondary target having a “W” shaped geometry for a 4 mm diameter conical base provides an intensity that is 25% larger than the intensity from the 8 mm diameter solid cone. Since the 4 mm diameter cone provides better spatial imaging resolution than the 8 mm solid cone, the “W” shaped geometry provides increased fluorescent x-ray intensity while maintaining the spatial imaging resolution of the 4 mm diameter solid cone. To increase the power and further decrease the exposure times, power levels of 10 kW-50 kW may be used. The projected power requirements for the layered secondary target with “W” shaped geometry embodiment is compared to the power requirements of the solid conical targets illustrated in FIGS. 68-71, which solid conical target were examined and compared to a commercial machine in FIGS. 39 and 40. FIG. 39 illustrated the power requirements for a 4.5 cm compressed breast and FIG. 40 the requirements for a 9 cm compressed breast. As shown in FIGS. 68-71, power requirements for the layered secondary target (“W” shaped geometry) is significantly reduced from the solid secondary targets to achieve the same signal-to-noise ratio, which was already a significant improvement over commercial machines. FIGS. 68 and 69 illustrate the improvements for a 4.5 cm compressed breast and FIGS. 70-71 the improvements for a 9 cm compressed breast. As discussed above, to increase the power and further decrease the exposure times, power levels of 10 kW-50 kW may be used. For example, an electron beam in high power commercial medical x-ray tubes (i.e., broadband x-ray tubes) has approximately a 1×7 mm fan shape as it strikes an anode that is rotating at 10,000 rpm. Since the anode is at a steep angle to the electron beam, the projected spot size in the long direction as seen by the viewer is reduced to about 1 mm. For an exposure of 1 sec, once can consider the entire annulus swept out by the fan beam as the incident surface for electron bombardment. For a 70 mm diameter anode, this track length is 210 mm, so the total incident anode surface area is about 1400 mm2. For the monochromatic system using a conical anode with a 36 mm diameter and a truncated height of 6 mm, the total area of incidence for the electrons is 1000 mm2. Therefore, it should be straightforward to make a 1 sec exposure at a power level that is 70% of the power of strong medical sources without damaging the anode material; 100 kW is a typical power of the highest power medical sources. Assuming a very conservative value that is 50% of the highest power, an anode made of a composite material operating at 50 kW should be achievable for short exposures. This is more power than is needed for thick and/or dense breast diagnostics but offers significant flexibility if reducing the effective size of the secondary cone becomes a priority. A one second exposure at 50 kW generates 50 kJ of heat on the anode. If the anode is tungsten, the specific heat is 0.134 J/g/K. To keep the temperature below 1000° C. in order not to deform or melt the anode, the anode mass needs to be at least 370 gm. An anode of copper coated with a thick layer of gold would only have to be 130 gm. These parameters can be increased by at least 2-3 times without seriously changing the size or footprint of the source. For repeat exposures or for longer exposures, the anode in this system can be actively cooled whereas the rotating anode system has to rely on anode mass for heat storage and inefficient cooling through a slip-ring and slow radiative transfer of heat out of the vacuum vessel. The monochromatic x-ray systems described above can be actively cooled with water. According to some embodiments, the primary anode material can be chosen to maximize the fluorescent intensity from the secondary. In the tests to date, the material of the primary has been either tungsten (W) or gold (Au). They emit characteristic K emission lines at 59 keV and 68 keV, respectively. These energies are relatively high compared to the absorption edges of silver (Ag; 25.6 keV) or tin (Sn; 29 keV) thereby making them somewhat less effective in inducing x-ray fluorescence in the Ag or Sn secondary targets. These lines may not even be excited if the primary voltage is lower than 59 keV. In this situation only the Bremsstrahlung induces the fluorescence. Primary material can be chosen with characteristic lines that are much closer in energy to the absorption edges of the secondary, thereby increasing the probability of x-ray fluorescence. For example, elements of barium, lanthanum, cerium, samarium or compounds containing these elements may be used as long as they can be formed into the appropriate shape. All have melting points above 1000° C. If one desires to enhance production of monochromatic lines above 50 keV in the most efficient way, higher Z elements are needed. For example, depleted uranium may be used (K line=98 keV) to effectively induce x-ray fluorescence in Au (absorption edge=80.7 keV). Operating the primary at 160 kV, the Bremsstrahlung plus characteristic uranium K lines could produce monochromatic Au lines for thorasic/chest imaging, cranial imaging or non-destructive industrial materials analysis. For many x-ray imaging applications including mammography, the x-ray detector is an imaging array that integrates the energies of the absorbed photons. All spectroscopic information is lost. If a spectroscopic imager is available for a particular situation, the secondary target could be a composite of multiple materials. Simultaneous spectroscopic imaging could be performed at a minimum of two energies to determine material properties of the sample. Even if an imaging detector with spectral capability were available for use with a broad-band source used in a conventional x-ray mammography system for the purpose of determining the chemical composition of a suspicious lesion, the use of the spectroscopic imager would not reduce the dose to the tissue (or generically the sample) because the broad band source delivers a higher dose to the sample than the monochromatic spectrum. Contrast-enhanced mammography using monochromatic x-ray radiation is superior to using the broad band x-ray emission. It can significantly increase the image detail by selectively absorbing the monochromatic X-rays at lower doses. The selective X-ray absorption of a targeted contrast agent would also facilitate highly targeted therapeutic X-ray treatment of breast tumors. In the contrast enhanced digital mammographic imaging conducted to date with broad band x-ray emission from conventional x-ray tubes, users try to take advantage of the increased absorption in the agent, such as iodine, by adjusting the filtering and increasing the electron accelerating voltage to produce sufficient x-ray fluorescence above the 33 keV K absorption edge of iodine. FIG. 72 shows the mass absorption curves for iodine as a function of x-ray energy. The discontinuous jumps are the L and K absorption edges. The contrast media will offer greater absorption properties if the broad band spectra from conventional sources span an energy range that incorporates these edges. As a result, detectability should improve. Monochromatic radiation used in the mammographic system discussed here offers many more options for contrast-enhanced imaging. Ordinarily, one can select a fluorescent target to produce a monochromatic energy that just exceeds the iodine absorption edge. In this sense, the monochromatic x-ray emission from the tube is tuned to the absorption characteristics of the contrast agent. To further improve the sensitivity, two separate fluorescent secondary targets may be chosen that will emit monochromatic X-rays with energies that are below and above the absorption edge of the contrast agent. The difference in absorption obtained above and below the edge can further improve the image contrast by effectively removing effects from neighboring tissue where the contrast agent did not accumulate. Note that the majority of x-ray imaging detectors currently used in mammography do not have the energy resolution to discriminate between these two energies if they irradiate the detector simultaneously; these two measurements must be done separately with two different fluorescent targets in succession. This is surely a possibility and is incorporated in our system. Since the contrast agent enhances the x-ray absorption relative to the surrounding tissue, it is not necessary to select a monochromatic energy above the K edge to maximize absorption. For example, FIG. 72 shows that the absorption coefficient for the Pd Kα 21.175 keV energy, which is below the K edge, is comparable to the absorption coefficient of the Nd Kα 37.36 keV energy which is above the K edge. As long as the atoms of the contrast agent are sufficiently heavier (atomic number, Z>45) than the those in the surrounding tissue (C, O, N, P, S; Z<10 and trace amounts of Fe, Ni, Zn, etc., Z<30), the monochromatic x-ray technique increases the potential choices for contrast agents in the future. The secondary targets of Pd, Ag and Sn are perfect options for this application. Using monochromatic energies below the absorption edge of iodine, for example, takes better advantage of the quantum absorption efficiency of a typical mammographic imaging detector. The absorption at 37 keV (above the iodine edge) is about 2 times lower than at 22 keV (below the edge). The lower energy may also prove to have better detectability in the surrounding tissue simultaneously. FIG. 73 shows a linear set of 3 drops of Oxilan 350, an approved iodine contrast agent manufactured by Guerbet superimposed on the the ACR phantom. The amount of iodine in each of the drops ˜1 mg iodine. The inventor has recognized alternative techniques for generating monochromatic x-rays that can, according to some embodiments, make use of existing broadband x-ray sources (e.g., conventional broadband x-rays tubes). For example, according to some embodiments, a monochromatic x-ray attachment may be fitted, attached or otherwise coupled to a conventional broadband x-ray source and/or may be provided to operate in conjunction with a conventional broadband x-ray source that is modified to accept the monochromatic x-ray attachment. In this manner, widely used broadband x-ray equipment (e.g., widely available broadband x-ray tubes used for medical, industrial or other applications) may be leveraged to produce a monochromatic x-ray source. As a result, existing broadband x-ray products can be retrofitted with little or no modification to the existing broadband x-ray source. Additionally, existing and/or conventional broadband x-ray source may be manufactured to include and/or may be augmented with a monochromatic x-ray component to convert a broadband x-ray source to a monochromatic x-ray source. It should be appreciated, however, that aspects of a monochromatic x-ray component may be used with any broadband x-ray source and are not limited for use with any particular existing and/or conventional broadband x-ray source. Further details of some embodiments of a monochromatic x-ray component configured to couple with a broadband x-ray source are described below, including with reference to FIGS. 74, 75A-75B, 76A-76B, 79A-79B and 80A-80B. FIG. 74 illustrates schematically concepts related to using a monochromatic x-ray component provided external to a broadband x-ray source to produce monochromatic x-rays, in accordance with some embodiments. Monochromatic x-ray source 7400 comprises broadband x-ray source 7450 and monochromatic x-ray component 7460. Broadband x-ray source 7450 may be a conventional x-ray source (e.g., a conventional x-ray tube maintained under vacuum pressure) configured to produce broadband x-rays, for example, for use in medical or industrial applications, as discussed in further detail below. The inventor has recognized that broadband x-rays sources, such as the conventional broadband x-ray source illustrated in FIG. 74, may be augmented with a monochromatic x-ray component to convert broadband x-rays emitted by the broadband x-ray source to monochromatic x-rays. For example, exemplary monochromatic x-ray component 7460 provides an attachment that can be provided external to the vacuum tube of broadband x-ray source 7450 to receive broadband x-rays emitted from the x-ray tube and to convert the broadband x-rays to monochromatic x-rays to form, together, a monochromatic x-ray source 7400. In the embodiment illustrated in FIG. 74, monochromatic x-ray component 7460 comprise two stages of x-ray production; a first stage that converts broadband x-rays to monochromatic x-rays of a first energy and a second stage that converts monochromatic x-rays to monochromatic x-rays at a second energy level. To perform the first stage conversion, a first stage secondary target 7410 is positioned in transmission paths of broadband x-rays 7415 emitted from broadband x-ray source 7450. First stage secondary target 7410 is configured to, in response to incident broadband x-rays, emit monochromatic x-rays 7425a via the fluorescence phenomena discussed in the foregoing. To perform the second stage conversion, a second stage secondary target 7420 is positioned to receive monochromatic x-rays 7425a emitted by first stage secondary target 7410. Second stage secondary target 7420 is configured to, in response to incident x-rays, emit monochromatic x-rays 7425b. In this manner, monochromatic x-ray component 7460 may be used to augment a broadband x-ray source to produce a monochromatic x-ray source that produces desired monochromatic x-rays. The geometry illustrated in FIG. 74 allows for a relatively compact monochromatic x-ray source to be provided by using a two stage monochromatic x-ray conversion technique. By using a relatively compact second stage secondary target (e.g., a cone or shell having a base of between 1 mm and 10 mm), divergent x-rays from the first stage secondary target are converted and emitted from a relatively small focal point, providing monochromatic x-ray flux suitable for imaging applications (i.e., producing intense, focused monochromatic x-ray flux suitable for imaging application, as discussed in the foregoing). In particular, the geometry of the first stage and second stage targets facilitates imaging for reasons discussed above in connection with the geometry of the primary and secondary targets described in the foregoing. Thus, it should be appreciated that any of the dimensions and arrangements, sizes, power levels, relative distances, source-to-detector distances, etc., may be applied to the monochromatic x-ray components described herein. Various embodiments using the general geometry schematically illustrated in FIG. 74 are discussed in further detail below. FIG. 75A illustrates components of a monochromatic x-ray source 7500, in accordance with some embodiments. Monochromatic x-ray source 7500 comprises broadband x-ray source 7550 and monochromatic x-ray component 7560. Broadband x-ray source 7550 may be a conventional x-ray source configured to produce broadband x-rays or may be a broadband x-ray source of any design, whether conventional or not. For example, broadband x-ray source 7550 may be a broadband x-ray source configured for use in medical applications typical in radiology, such as mammography, cardiography, orthopedics, oncology or other medical x-ray applications. Broadband x-ray source 7550 may alternatively be an x-ray source configured for industrial applications such as for inspection applications (e.g., inspection of industrial structures such as bridges, buildings or other infrastructure to detect defects, cracking, points of failure or other indicators bearing on the structures integrity). As such, broadband x-ray source 7550 may operate at power levels ranging from, for example, 500 W to 100 KW depending on the particular application and application requirements. Broadband x-ray source 7550 comprises a vacuum tube 7555 that maintains an internal space 7557 under vacuum conditions. Internal space 7557 may contain components of typical broadband x-ray sources, such as an electron source (e.g., a filament that functions as a cathode) coupled to a power source, and a primary target (e.g., anode) that emits broadband x-rays in response to electrons incident on the primary target. The details of broadband x-ray source 7550 are not illustrated because exemplary monochromatic x-ray components described herein are intended to be agnostic to the specific internal configuration and geometry of the broadband x-ray source that it is designed to augment and/or supplement, and the aspects of the monochromatic x-ray components are not limited for use with any particular broadband x-ray source implementation. Broadband x-ray source 7550 emits broadband x-rays 7515 via aperture 7558. Thus, the components of monochromatic x-ray source 7500 from the line denoted by arrow 7559 in the direction of the arrow may be an existing and/or conventional x-ray broadband source (e.g., a standalone and independently functioning broadband x-ray tube). It should be appreciated, however, that the broadband x-ray source 7550 need not be an existing or conventional broadband source, but may be any broadband x-ray source, including an x-ray broadband source manufactured specifically to be coupled to or to be integral with monochromatic x-ray component 7560, as the aspects are not limited in this respect. Monochromatic x-ray component 7560 is configured to attached, affix or otherwise couple to broadband x-ray source 7550 to receive broadband x-rays 7515 emitted by broadband x-ray source 7550 and to emit monochromatic x-rays 7525b in response, including positioning the monochromatic x-ray component proximate the broadband x-ray source with or without physical connection or contact between the monochromatic x-ray component and the broadband x-ray source. Accordingly, the monochromatic x-ray component need only be positioned next to or sufficiently near the broadband x-ray source to receive broadband x-rays, thereby coupling (e.g., via the broadband x-rays) the monochromatic x-ray source to the broadband x-ray source. For example, monochromatic x-ray component 7560 may be configured as an attachment 7565 that fits to the front face of broadband x-ray source 7550 where broadband x-rays are emitted. In this manner, emitted broadband x-rays are captured by monochromatic x-ray component 7560 for conversion to monochromatic x-rays. Alternatively, monochromatic x-ray component 7560 may be configured to be positioned proximate (e.g., next to, adjacent or sufficiently near) broadband x-ray source 7550 with or without physical attachment or contact between the components. In the embodiment illustrated in FIG. 75A, monochromatic x-ray component 7560 comprises a housing 7565 configured to attach to broadband x-ray tube 7555 and is adapted to couple to the particular broadband x-ray source 7550 for which it is designed to augment for production of monochromatic x-rays. Housing or attachment 7565 of the monochromatic x-ray component contains a first stage secondary target 7510 arranged to receive at least some broadband x-rays 7515 emitted by broadband x-ray source 7550 and is configured to emit monochromatic x-rays 7525a in response to incident broadband x-rays via the fluorescence properties discussed in detail in the foregoing. First stage secondary target may be constructed from any suitable material including, for example, rhodium (Rh), palladium (Pd), silver (Ag), tin (Sn), antimony (Sb), tellurium (Te), lanthanum (La), cerium (Ce), neodymium (Nd), samarium (Sm), tantalum (Ta), tungsten (W), rhenium (Re), gold (Au), provided the energy of the characteristic monochromatic x-ray radiation emitted from the target sufficiently exceeds absorption edge(s) of the second stage secondary target. Housing 7565 also includes a receptacle 7530 configured to accommodate a second stage secondary target 7520 that, when inserted into receptacle 7530, is positioned to receive at least some monochromatic x-rays 7525a emitted by first stage secondary target 7510 and is configured to emit monochromatic x-rays 7525b responsive to incident monochromatic x-rays 7525a. First stage secondary target 7510 may be arranged in a geometry similar to primary target 910 illustrated in FIG. 9 and, more particularly, arranged so that there is a conically shaped space formed by the surface of the first secondary target 7510 into which second secondary target 7520 can be positioned. However, there are key distinctions between secondary stage target 7510 and primary target 910 illustrated in FIG. 9. First, because secondary target 7510 is configured to convert broadband x-rays to monochromatic x-rays (as opposed to generating broadband x-rays from an incident electron beam), secondary target 7510 should be of a material suitable for generating monochromatic x-rays at a desired and/or suitable energy, as discussed in further detail below. Second, unlike primary target 910, secondary target 7510 is positioned outside the vacuum seal of broadband x-ray tube 7555 (i.e., secondary target 7510 is located external to broadband x-ray tube 7555). More generally, in the embodiment illustrated in FIG. 75, because monochromatic x-ray component 7560 may be adapted to attach to an existing broadband x-ray source, components of the monochromatic x-ray component (e.g., attachment 7565, first and second stage secondary targets 7510 and 7520, receptacle 7530, etc.) are arranged external to the vacuum tube of broadband x-ray source 7550 (e.g., at atmospheric pressure). Secondary target 7520 of the second stage of x-ray conversion may be similar or the same as any of the exemplary secondary targets discussed herein. In particular, secondary target 7520 may be a solid secondary target (e.g., manufactured as bulk material) or may be formed using any of the layered geometries described herein (e.g., any of the geometries discussed in connection with FIGS. 42-66). Second stage secondary target made be made of any suitable material including, but not limited to molybdenum (Mo), rhodium (Rh), palladium (Pd), silver (Ag), tin (Sn), antimony (Sb), tellurium (Te), lanthanum (La), cerium (Ce), neodymium (Nd), samarium (Sm), tantalum (Ta), tungsten (W), rhenium (Re), gold (Au), etc., provided the characteristic energy of monochromatic x-ray radiation emitted from the first stage secondary target exceeds one or more absorption edges of the selected material so that fluorescent events can occur. Additionally, though secondary target 7520 is illustrated in FIG. 75 as being positioned within receptacle 7530 without a carrier or holder, secondary target 7520 may be arranged within receptacle 7530 via a removable carrier, as illustrated in FIG. 79A, 79B. In particular, a removable carrier that includes any one or more features of the removable carriers described herein may be used to house secondary target 7520, as discussed in further detail in connection with FIGS. 79A, 79B. Alternatively, any one or more of the features of a removable carrier (e.g., transmissive portions, blocking portions, etc.) may be provided as part of receptacle 7530 instead of as a removable component (e.g., one or more features of a removable carrier may be integrated with or manufactured as a generally permanent aspect of receptacle 7530, as discussed in further detail below in connection with FIGS. 80A-80B. Receptacle 7530 is configured to accommodate secondary target 7520 and/or a carrier for holding and positioning secondary target 7520. Accordingly, in this manner, a monochromatic x-ray component may be coupled to a broadband x-ray source to produce a monochromatic x-ray source. FIG. 75B illustrates components of a monochromatic x-ray source, in accordance with some embodiments. Monochromatic x-ray source 7500′ may be similar in many respects to exemplary monochromatic x-ray source 7500 discussed above in connection with FIG. 75A. However, monochromatic x-ray component 7560′ additionally includes filter 7562 formed from material that blocks broadband x-rays below a desired threshold (e.g., x-rays energies below an absorption edge of the first stage secondary target material). By absorbing broadband x-rays with insufficient energy to cause a fluorescent event in the first stage secondary target, these lower energy x-rays can be prevented from interacting with the attachment and/or potentially exiting the monochromatic x-ray source via aperture 7568 (or otherwise leaking from the monochromatic x-ray source), which would otherwise result in a reduction in the monochromaticity of the emitted x-rays. Additionally, a blocking component 7566 (e.g., a lead shield) is provided to absorb broadband x-rays having transmission paths generally aligned with aperture 7568 to prevent such x-rays from being emitted from monochromatic x-ray source 7500′. According, filter 7562 and blocking component 7566 may be used to improve the monochromaticity of the x-rays emitted from monochromatic x-ray source FIG. 76A illustrates components of a monochromatic x-ray source utilizing a monochromatic x-ray attachment coupled to a broadband x-ray tube to generate monochromatic x-rays, in accordance with some embodiments. In particular, monochromatic x-ray source 7600 comprises a broadband x-ray tube 7650 configured to emit broadband x-rays via aperture 7758. Broadband x-ray tube 7650 may be, for example, an existing and/or conventional x-ray tube used for medical or industrial applications, or may be a broadband x-ray source specifically manufactured to be a back-end source of broadband x-rays for a monochromatic x-ray device. Monochromatic x-ray source 7600 further comprises monochromatic x-ray component 7660 configured to attach and/or couple to broadband x-ray tube 7650 to receive broadband x-rays emitted from the broadband x-ray source and in turn emit monochromatic x-rays 7625 using a two stage conversion process. In the embodiment illustrated in FIG. 76A, exemplary broadband x-ray tube 7650 is provided under vacuum conditions and comprises a cathode 7652 (e.g., a circular filament) capable of producing an electron beam that accelerates via a voltage differential between cathode 7652 and anode 7654, as shown by the labeled electron trajectory. Anode 7654 may be, for example, a tungsten anode held at a high voltage that operates as a primary target to produce broadband x-rays in response to the impinging electron beam. As discussed above, due to the deceleration of electrons in the anode (primary target 7654), broadband x-rays produced by primary target 7654 will include x-rays at characteristic tungsten emission lines as well as Bremsstrahlung x-ray radiation, which are emitted from broadband x-ray source 7650 via aperture 7658. As shown in FIG. 76A, monochromatic x-ray attachment 7660 is provided external to broadband x-ray tube 7650 and is configured to attach, affix or otherwise couple to broadband x-ray tube 7650 outside the vacuum seal of the x-ray tube. Exemplary monochromatic x-ray attachment 7660 comprises a first stage secondary target 7610 configured to receive at least some broadband x-ray radiation emitted from broadband x-ray tube 7650 and, in response to incident broadband x-rays, produce monochromatic x-rays at an energy characteristic of the target material. When monochromatic x-ray attachment 7660 is coupled to broadband x-ray tube 7650, first stage secondary target 7610 forms a generally conical space about aperture 7658 in transmission paths of broadband x-rays emitted from the broadband x-ray tube 7650. Incident broadband x-rays then interact with first stage secondary target 7610 such that monochromatic x-rays are emitted from the target via fluorescence. Monochromatic x-ray attachment 7660 further comprises second stage secondary target 7620 positioned to receive monochromatic x-rays emitted by first stage secondary target 7610. In particular, in the embodiment illustrated in FIG. 76A, second stage secondary target 7620 may positioned within the conical space formed in part by first stage secondary target 7610. Incident monochromatic x-rays from first stage secondary target 7610 may then interact with second stage secondary target 7620 such that monochromatic x-rays 7625 at an energy characteristic of the target material are emitted via fluorescence via aperture 7668. To improve monochromaticity of the emitted monochromatic x-rays, exemplary monochromatic x-ray attachment 7660 comprises filter 7662 formed from material that blocks broadband x-rays below a desired threshold as discussed above in connection with exemplary monochromatic x-ray component 7560′ illustrated in FIG. 75B. Additionally, a blocking component 7666 (e.g., a lead shield) may be provided to absorb broadband x-rays having transmission paths aligned with aperture 7668, thus preventing such x-rays from being emitted from the monochromatic x-ray source 7600. FIG. 76B illustrates a simulation of x-ray production of monochromatic x-ray source 7600, including broadband x-rays produced and emitted by broadband x-ray tube 7650, first stage monochromatic x-rays emitted by the first stage monochromatic x-ray target (e.g., target 7610) of monochromatic x-ray attachment 7660, and second stage monochromatic x-rays 7625 emitted by the second stage secondary target (e.g., target 7620). It should be appreciated that to employ the two stage conversion described herein, the first stage secondary target material and the second stage secondary target material are chosen to permit the appropriate fluorescence effect. Specifically, the first stage secondary target may be selected such that monochromatic x-ray radiation emitted by the first stage secondary target has energy that exceeds one or more absorption edges of the second stage secondary target so that fluorescent events can occur. Suitable combinations of first stage and second stage secondary targets include, but are not limited to: tungsten (W) as a first stage secondary target in combination with any element with an atomic number less than or equal to 68 as a second stage secondary target; tellurium (Te) as a first stage secondary target in combination with any element with an atomic number less than or equal to 48 as a second stage secondary target; tin (Sn) as a first stage secondary target in combination with any element with an atomic number less than or equal to 46 as a second stage secondary target; rhodium (Rh) as a first stage secondary target in combination with any element with an atomic number less than or equal to 42 as a second stage secondary target, etc. It should be appreciated that any combination in which the characteristic energies of the first stage secondary target exceed those of the second stage secondary target may be used, as the aspects are not limited for use with any particular combination of secondary targets. The x-ray spectrum resulting from a simulation using tin (Sn) as a first stage secondary target and molybdenum (Mb) as a second stage secondary target is illustrated in FIG. 77A. The actual x-ray spectrum measured using the exemplary geometry discussed in connection with FIG. 76A for a Sn first stage secondary target and a Mb second stage secondary target is shown in FIG. 77B. FIGS. 78A and 78B illustrate x-ray spectra results measured using a tin and molybdenum secondary target combination and a tin and palladium secondary target combination, respectively. As illustrated in FIGS. 77A-77B and 78A-78B, the x-ray spectra include generally undesirable flux both from the broadband x-ray source and the first stage secondary target that reduces the monochromaticity of the x-rays emitted from the monochromatic source, some of which can be eliminated by providing a thicker filter 7662 and/or strategically arranged blocking portions. In particular, as discussed in the foregoing, monochromaticity of emitted x-rays can be significantly improved using aspects of a carrier, either implemented as a removable housing or integrated in and/or with a receptacle adapted to accommodate a secondary target (e.g., a second stage secondary target). FIGS. 79A-79B and FIGS. 80A-80B illustrate exemplary embodiments employing techniques described herein to improve the monochromaticity of a monochromatic x-ray source provided by augmenting a broadband x-ray source with a monochromatic x-ray component. It should be appreciated that some applications may not require the high level of monochromaticity afforded by the various techniques described herein, and aspects of a monochromatic x-ray component add-on or attachment are not limited for use with any particular technique or combination of techniques that improve monochromaticity. FIGS. 79A and 79B illustrate exemplary components of a monochromatic x-ray source having a removable carrier configured to house a second stage secondary target and adapted to be inserted into the receptacle of a monochromatic x-ray component used to augment a broadband x-ray source to produce monochromatic x-rays, in accordance with some embodiments. Monochromatic x-ray source 7900 may include components that are similar or the same as monochromatic x-ray source 7500 illustrated in FIG. 75. For example, exemplary monochromatic source 7900 comprises a broadband x-ray source 7950 and a monochromatic x-ray component 7960 coupled thereto to receive broadband x-ray radiation and responsively generate monochromatic x-rays 7925b. Monochromatic x-ray component 7960 comprises first stage secondary target 7910 arranged in the transmission path of broadband x-rays emitted from broadband x-ray source 7950 to generated monochromatic x-rays in response to incident broadband x-rays. In the exemplary embodiment illustrated in FIGS. 79A and 79B, a removable carrier 7940 is provided to house second stage secondary target 7920 and is configured to be inserted into receptacle 7930 of monochromatic x-ray component 7960. Exemplary carrier may comprise a transmissive portion 7942 that includes material that is generally transmissive to x-ray radiation so that at least some monochromatic x-ray radiation emitted by first stage secondary target 7910 that passes through receptacle 7930 also passes through transmissive portion 7942 to irradiate second stage secondary target 7920. Exemplary carrier 7940 further comprises a blocking portion 7944 that includes material that is generally opaque to x-ray radiation (i.e., material that substantially absorbs incident x-ray radiation). Blocking portion 7944 is configured to absorb at least broadband x-ray radiation emitted from broadband x-ray source 7960 and/or monochromatic x-ray radiation emitted from first stage secondary target 7910. Exemplary blocking portion 7944 may include a cylindrical portion 7944a (which may or may not overlap a portion of second stage secondary target 7920) and annular portion 7944b having a diameter greater than cylindrical portion 7944a to absorb x-ray radiation emitted over a wider range of angles and/or originating from a wider range of locations to improve the monochromaticity of the x-ray radiation emission of the monochromatic x-ray source 7900. Aperture 7944c in blocking portion 7944 corresponds to an aperture of transmissive portion 7942 to allow monochromatic x-rays fluoresced from second stage secondary target 7920 to be emitted from the monochromatic x-ray component 7960. FIG. 79A illustrates removable carrier 7940 prior to insertion into receptacle 7930 and FIG. 79B illustrates removable carrier 7940 after it has been inserted into receptacle 7930 so that second stage secondary target 7920 is positioned to receive monochromatic x-rays emitted by first stage secondary target 7910. Exemplary carrier 7940 may include any one or more of the features discussed herein. In particular, transmissive portion 7942 and blocking portion 7944 may be similar to or the same as, and may include any one or combination of the features of the transmissive and blocking portions described herein, including with reference to FIGS. 11A-C, 12, 13A-C and 17A-C. According to some embodiments, a removable carrier is formed primarily, substantially or entirely from generally transmissive material (e.g., some embodiments of removable carrier may not include blocking material so that portion 7944 may be formed from transmissive material), as the aspects are not limited in this respect. Alternatively, features of carrier 7940 may be integrated into receptacle 7930, as discussed in connection with FIGS. 80A and 80B, as the aspects are not limited for use with removable carriers. FIGS. 80A and 80B illustrate exemplary components of a monochromatic x-ray source, in accordance with some embodiments. Monochromatic x-ray sources 8000A and 8000B may include components that are similar or the same as monochromatic x-ray source 7500, 7500′ and 7900 illustrated in FIGS. 75A, 75B and 79A-79B, respectively. For example, exemplary monochromatic sources 8000A and 8000B comprise a broadband x-ray source 8050 and a monochromatic x-ray component 8060 coupled thereto to receive broadband x-ray radiation and responsively generate monochromatic x-rays 8025b. As shown, monochromatic x-ray component 8060 comprises first stage secondary target 8010 arranged in transmission paths of broadband x-rays emitted from broadband x-ray source 8050 to generated monochromatic x-rays in response to incident broadband x-rays. In the embodiments illustrated in FIGS. 80A and 80B, one or more aspects of a carrier are integrated on, with or within the monochromatic x-ray component. For example, a blocking portion 8044A may be attached, affixed or otherwise coupled to the monochromatic x-ray attachment to provide blocking capabilities of spurious x-ray radiation. Blocking portion 8044A may be removable or may be permanently affixed to monochromatic x-ray component 8060A. For example, blocking portion 8044A may be configured to removably engage with receptacle 8030 so that blocking portion 8044A is separable from receptacle 8030 to, for example, insert and/or replace the second stage secondary target 8020. Blocking portion 8044B may be provided generally as part of the outer portion or wall of the monochromatic x-ray component as an integrated portion of the monochromatic x-ray component 8000B. It should be appreciated that other arrangements are possible, such as blocking portions formed as layers of or within other components or otherwise arranged to facilitate x-ray blocking to improve the monochromaticity of the monochromatic x-ray source. As discussed above, according to some embodiments, the monochromatic x-ray source does not include blocking portions, as the aspects of a monochromatic x-ray component or attachment is not limited in this respect. Thus, any of the techniques described herein to improve monochromaticity and/or intensity of emitted monochromatic x-rays may be applied to the monochromatic x-ray components in the same or substantially the same manner to improve the characteristics of the monochromatic x-ray emission. Having thus described several aspects and embodiments of the technology set forth in the disclosure, it is to be appreciated that various alterations, modifications, and improvements will readily occur to those skilled in the art. Such alterations, modifications, and improvements are intended to be within the spirit and scope of the technology described herein. For example, those of ordinary skill in the art will readily envision a variety of other means and/or structures for performing the function and/or obtaining the results and/or one or more of the advantages described herein, and each of such variations and/or modifications is deemed to be within the scope of the embodiments described herein. Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific embodiments described herein. It is, therefore, to be understood that the foregoing embodiments are presented by way of example only and that, within the scope of the appended claims and equivalents thereto, inventive embodiments may be practiced otherwise than as specifically described. In addition, any combination of two or more features, systems, articles, materials, kits, and/or methods described herein, if such features, systems, articles, materials, kits, and/or methods are not mutually inconsistent, is included within the scope of the present disclosure. All definitions, as defined and used herein, should be understood to control over dictionary definitions, definitions in documents incorporated by reference, and/or ordinary meanings of the defined terms. The indefinite articles “a” and “an,” as used herein in the specification and in the claims, unless clearly indicated to the contrary, should be understood to mean “at least one.” The phrase “and/or,” as used herein in the specification and in the claims, should be understood to mean “either or both” of the elements so conjoined, i.e., elements that are conjunctively present in some cases and disjunctively present in other cases. Multiple elements listed with “and/or” should be construed in the same fashion, i.e., “one or more” of the elements so conjoined. Other elements may optionally be present other than the elements specifically identified by the “and/or” clause, whether related or unrelated to those elements specifically identified. Thus, as a non-limiting example, a reference to “A and/or B”, when used in conjunction with open-ended language such as “comprising” can refer, in one embodiment, to A only (optionally including elements other than B); in another embodiment, to B only (optionally including elements other than A); in yet another embodiment, to both A and B (optionally including other elements); etc. As used herein in the specification and in the claims, the phrase “at least one,” in reference to a list of one or more elements, should be understood to mean at least one element selected from any one or more of the elements in the list of elements, but not necessarily including at least one of each and every element specifically listed within the list of elements and not excluding any combinations of elements in the list of elements. This definition also allows that elements may optionally be present other than the elements specifically identified within the list of elements to which the phrase “at least one” refers, whether related or unrelated to those elements specifically identified. Thus, as a non-limiting example, “at least one of A and B” (or, equivalently, “at least one of A or B,” or, equivalently “at least one of A and/or B”) can refer, in one embodiment, to at least one, optionally including more than one, A, with no B present (and optionally including elements other than B); in another embodiment, to at least one, optionally including more than one, B, with no A present (and optionally including elements other than A); in yet another embodiment, to at least one, optionally including more than one, A, and at least one, optionally including more than one, B (and optionally including other elements); etc. Also, the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having,” “containing,” “involving,” and variations thereof herein, is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. In the claims, as well as in the specification above, all transitional phrases such as “comprising,” “including,” “carrying,” “having,” “containing,” “involving,” “holding,” “composed of,” and the like are to be understood to be open-ended, i.e., to mean including but not limited to. Only the transitional phrases “consisting of” and “consisting essentially of” shall be closed or semi-closed transitional phrases, respectively. |
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046997539 | abstract | The responses of a nuclear reactor refueling machine to commands from a detachable control console are simulated to allow operation of the console for testing and operator training with the console removed from the machine. A simulator, which is connected to the console by the same input and output leads which normally connect the console to the refueling machine, includes a single pulse generator driven by a single three phase A-C motor to simulate movement of the refueling machine bridge, trolley and hoist. The motor drive signals generated on separate console output leads are all connected to the single simulator motor, while the brake release signals energize relays which switch the pulse signals generated by the single pulse generator to the console input leads corresponding to the selected refueling machine component drive motor. The portable simulator also contains relays which simulate engagement and disengagement of fuel assembly and control rod cluster grippers and a device for coupling portions of the refueling machine mast to the hoist. In addition, a number of circuits are provided for testing various control console functions. |
description | The present invention relates generally to transmission electron microscopy, and more specifically, to transmission electron microscopy analyzing a sample using two low-voltage electron beams. Electron microscopy provides an electron beam to a sample to analyze characteristics of the sample. Relatively high-energy electrons, such as between 10-20 keV may be emitted from an electron gun. The electrons travel through a condenser and an objective lens and are slowed by a sample bias or potential. At the surface of the sample, the electrons may have a low energy level, such as between near 0 eV-100 eV, and may interact with the surface of the sample and in a region within the sample that is close to the surface. The electrons backscatter and re-accelerate to the relatively high-energy level. The electrons may be projected onto an imaging plane, and patterns generated by the electrons may provide information regarding the sample, and in particular regarding a surface region of the sample. Exemplary embodiments include a first electron beam source configured to provide a first electron beam to a surface region of a sample, a second electron beam source configured to provide a second electron beam to pass through the sample, the second electron beam having an initial energy level less than an initial energy level of the first electron beam, and a receiving unit configured to analyze the first electron beam and the second electron beam to obtain information about the sample. Additional exemplary embodiments include a system including an electron microscopy assembly and an imaging unit. The electron microscopy assembly is configured to provide a first electron beam to a surface of a sample without passing through the sample and to pass a second electron beam through the sample, the second electron beam having an initial energy level less than an initial energy level of the first electron beam. The imaging unit is configured to analyze the sample based on the first electron beam and the second electron beam. Further exemplary embodiments include an electron microscopy assembly. The electron microscopy assembly includes a first electron beam source configured to generate a first electron beam to travel in a first direction to contact a surface region of the sample and to scatter from the surface region of the sample and travel in a second direction opposite the first direction. The electron microscopy assembly further includes an imaging unit configured to receive the first and second low-voltage electron beams to generate data corresponding to the sample. Additional features and advantages are realized through the techniques of the present invention. Other embodiments and aspects of the invention are described in detail herein and are considered a part of the claimed invention. For a better understanding of the invention with the advantages and the features, refer to the description and to the drawings. Transmission electron microscopy of organic materials, including biological materials, is notoriously difficult due to radiation damage caused by high-energy electrons. In exemplary embodiments, a first low-voltage electron beam is provided to detect characteristics on a surface of a sample and a second low-voltage electron beam is provided to pass through the sample and detect characteristics inside the sample. FIG. 1 illustrates a block diagram of an electron microscopy apparatus 100 according to an embodiment of the present disclosure. The apparatus 100 includes a first electron source 101 configured to provide a first electron beam, first magnetic deflection unit and optics 102 to modify characteristics of the first electron beam, a filter 103 to filter the first electron beam, a cathode objective lens 104 to focus the first electron beam, and a sample 105. The sample 105 may include a substrate having holes formed therein, and a material of interest may be provided in the holes. The sample is electrically biased relative to the objective lens so as to reduce the energy of the electrons beam generated by electron source 101, to an energy range of about 0 eV-100 eV. The system 100 is configured such that the electron source 101 emits the first electron beam at a high energy level, such as between 15 keV and 20 keV, and when the first electron beam reaches the sample 105, the electron beam has a low energy level, such as between about 0 eV and 100 eV. One or more of the first optics and magnetic deflector 102, the filter 103, the cathode objective lens 104, and a potential of the sample 105 may reduce an energy level of the first electron beam between the electron source 101 and the sample 105. The magnetic deflector and optics 102 may include one or more of lenses, deflectors, and a magnet to focus and divide or redirect the first electron beam. The lenses may include, for example, a gun lens and a condenser lens. The magnet may be a prism array or an electron beam deflector configured to deflect the first electron beam from a first path from the electron source 101 to a second path toward the sample 105. In one embodiment, the magnet deflects the first electron beam by an angle of about ninety degrees)(90°. The filter 103 may include an aperture through which the first electron beam passes to cause only portions of the electron beam within predetermined height, length, radial dimensions, or energy to pass through to the sample 105. The cathode objective lens 104 may alter a magnification of an image generated by the electron beam and an energy level of the electron beam. The sample 105 may be maintained at a potential similar to that of the electron source 101, such as between 15 kV and 20 kV. The first electron beam, or at least a portion of the first electron beam, may scatter at the surface of the sample 105 and reflect back to the cathode objective lens 104, filter 103 and first magnetics and/or optics 102. The surface of the sample may include an outer surface and a region just below the outer surface. The electron beam may pass through second magnetics and optics 107 and to a receiving unit 108 configured to receive the first electron beam, detect image patterns generated by the first electron beam, and output signals corresponding to the detected patterns. The receiving unit 108 may include an imaging unit to generate an image of the detected image patterns. In one embodiment, the second magnetics and/or optics 107 includes one or more projection lenses. The second magnetics and/or optics 107 may also include one or more contrast apertures, mirror arrays, and magnets. For example, in one embodiment the electron beam exits the first magnetics and optics 102 in one direction and is diverted into another direction by a magnet or prism into a direction corresponding to an electron mirror or mirror array. The mirror or mirror array may be an electrostatic element. The first electron beam may be reflected from the mirror or mirror array back to the magnet or prism, and the magnet or prism may redirect the beam through one or more projection lenses toward the receiving unit 108. The apparatus 100 further includes a low-voltage electron source 106 configured to generate a second electron beam having a low energy level, such as between around 0 eV (but not including 0 eV) and around 100 eV. For example, in one embodiment the low-voltage electron source 106 generates an electron beam having an energy level of about 5 eV. The second electron beam is of such an energy level that it passes through the sample 105 toward the first magnetics and optics 102. In other words, whereas the electron beam from the electron source 101 is deflected or scattered from a surface or surface region of the sample 105, obtaining surface information of the sample 105, the beam from the low-voltage electron source 106 passes through the sample 105. Both beams are directed by the first magnetics and optics 102 and the second magnetics and/or optics 107 to the receiving unit 108. Both beams may be directed at the sample at the same time, or in one embodiment, either the first electron beam generated by source 101 or the second electron beam generated by source 106 is directed at the sample, while the other beam is not directed at the sample, or is turned off. In other words, data can be obtained with first electron beam alone, or with the second electron beam alone, or data can be obtained by both the first and second electron beams simultaneously. In addition, embodiments of the present disclosure encompass a first electron beam having a portion scatter or reflect from the surface of the sample 105, while a portion is absorbed in or passes through the sample 105. The portion of the first beam that is scattered or reflected may be analyzed to analyze the sample 105, and the portion that is absorbed or passes through the sample 105 may not be analyzed. In addition, embodiments of the present disclosure encompass a second electron beam having a portion pass through the sample 105, while a portion is absorbed in or is scattered at a surface of the sample 105. The portion of the second beam that passes through the sample 105 may be analyzed to analyze the sample 105, and the portion that is absorbed or scattered by the sample 105 may not be analyzed Once the second electron beam from the low-voltage electron source 106 has passed through the sample 105, the energy level of the second electron beam may be increased to a high-voltage energy level. For example, in one embodiment, the energy level of the second electron beam is increased by one or more of the magnetics and optics 102, the filter 103, the cathode objective lens 104, and a voltage potential of the sample 105, to reach an energy level near the energy level of the first electron beam. According to embodiments of the present disclosure, the apparatus 100 including first and second magnetics/optics 102 and 107 and the low-voltage electron source 106 may generate images of the sample 105 having a resolution of about 1 nm, and the second electron beam from the low-voltage electron source 106 does not damage the sample 105. Although FIG. 1 illustrates an electron microscopy apparatus 100 having a particular configuration of magnetics and optics 102 and 107 and a receiving unit 108, embodiments of the present disclosure may be implemented in any electron microscopy apparatus capable of passing a low-voltage electron beam through a sample and generating data about the sample from the electron beam. Examples of electron microscopy apparatuses in which the low-voltage electron beam may be provided include a low-energy electron microscope (LEEM), Photo Electron Emission Microscope (PEEM), or any other suitable microscope. FIG. 2 illustrates a low-voltage electron source portion 200 according to embodiments of the present disclosure. The low-voltage electron source portion 200 corresponds to the region A of FIG. 1. The low-voltage electron source portion 200 includes an objective cathode lens 210 and an electron source assembly 220. The objective lens 210 includes a lens 211 including an entrance aperture 212. The objective lens 210 may decelerate an electron beam moving toward the sample 230 and may accelerate an electron beam moving from the sample 230 to the objective lens 210. In particular, the sample 230 may be maintained at a negative potential, while the entrance aperture 212 of the objective lens 210 facing the sample may be maintained at a ground potential. Accordingly, electrons leaving the sample 230 may be accelerated towards the objective lens 210. Alternatively the sample may be held at or near ground potential, while the objective lens 210 including the aperture 212 is held at a positive high potential, so that the electrons are accelerated towards the objective lens 210. The electron beam assembly 220 includes a holder 221, which may be an electrically insulating holder, such as a ceramic holder. The electron beam assembly further includes an electron source 222 and a sample mount 223 onto which the sample 230 is mounted. As discussed above, in embodiments of the present disclosure, the electron source 222 is a low-voltage electron source configured to generate a low-voltage electron beam E having an energy level between about 0 eV (but not including 0 eV) and 100 eV. The electron beam E passes through the sample 230 and interacts with the sample 230 to generate patterns in the electron beam that may be detected by a receiving unit, such as the receiving unit 108 of FIG. 1, to obtain data about the sample 230 and/or generate an image corresponding to the sample 230. FIG. 3 illustrates a system 300 according to an embodiment of the present disclosure. The system includes an electron microscope assembly 310 in communication with a computer 320. For example, the electron microscope assembly may correspond to the electron microscopy apparatus 100 of FIG. 1. The computer 320 includes a control unit 321 and an analysis unit 322. The control unit 321 may include a processor, memory, logic, and other circuitry to control operation of the electron microscope assembly 310. For example, the control unit 321 may operate according to a program stored in memory and executed by a processor or according to manual user controls to control voltage levels of one or more electron beams, transmission times, transmission durations, lens positions, sample positions, receiving unit positions, or any other characteristic of the electron microscope assembly 310 for controlling operation of the electron microscope assembly 310. The analysis unit 322 may receive data from the electron microscope assembly 310, such as from a receiving unit 108, as illustrated in FIG. 1, configured to detect patterns in one or more electron beams and transmit corresponding signals to the computer 320. The analysis unit 322 may include computer programs executed by a processor, as well as manual controls, to control analysis, storage, and display of the data from the receiving unit 108. The analysis unit 322 may include, for example, an imaging unit to generate an image of the sample based on the detected patterns in the electron beams. Although FIG. 3 illustrates a block diagram of a system 300 according to embodiments of the present disclosure for purposes of description, it is understood that embodiments may include additional features not illustrated in FIG. 3, such as I/O hardware, wired communication interfaces, wireless communication interfaces, storage devices, display units, user interfaces, and other functional units. FIG. 4 illustrates a method according to an embodiment of the present disclosure. In block 401, a sample is provided in an electron microscopy assembly. The sample may include a substrate having holes formed therein, and a material of interest may be provided in the holes. In block 402, a first electron beam is provided to the sample. In one embodiment, the first electron beam is controlled to have a voltage potential that is low relative to the voltage potential of the sample. For example, the first electron beam may have a potential between around 15 keV and 20 keV when emitted from an electron source and may have a potential reduced to between around 0 eV and 100 eV when the first electron beam reaches the sample. The first electron beam, or at least a portion of the first electron beam, may be reflected, deflected, or scattered at the surface of the sample, or at a surface region of the sample. Any portion of the first electron beam that passes through the sample may not be utilized for analysis of the sample. In block 403, a low-voltage electron beam is provided to the sample and it passes through the sample, or at least a portion of the low-voltage electron beam passes through the sample. The low-voltage electron beam may have an energy level between about 0 eV and 100 eV and may be provided to the sample from a side opposite the first electron beam. Embodiments of the present disclosure encompass a low-voltage electron beam having a portion pass through the sample and a portion scatter upon contacting the sample. The portion that passes through the sample may be used for analysis of the sample, and the portion that scatters may be disregarded. The low-voltage electron beam and/or the first electron beam may be received by a receiving unit in block 404. The receiving unit may be a device capable of detecting electron energy and generating signals based on the detected electron energy. When the first beam interacts with the surface of the sample, patterns may be generated in the first beam corresponding to characteristics of the surface region of the sample. Likewise, when the low-voltage beam passes through the sample, patterns may be generated in the low-voltage electron beam corresponding to characteristics in the sample. The receiving unit may be configured to detect the patterns in the first electron beam and the low-voltage electron beam, and my generate signals based on the detected patterns. Although FIG. 4 describes a low-voltage electron beam being analyzed by the receiving unit, it is understood that the term “low-voltage electron beam” refers to the voltage at which the electron beam was generated and is used to distinguish the low-voltage electron beam from the first electron beam. Upon passing through the sample, the energy level of the low-voltage electron beam may be increased to a relatively higher voltage, such as a same voltage as the first electron beam. In block 405, the signals may be analyzed to obtain sample information, such as images, composition data, physical features, or other information about the sample. Analyzing the signals may include generating an image based on the signals, and the image may include an image of the sample. FIG. 5 illustrates a block diagram of a system 500 for controlling and analyzing data of an electron microscopy assembly 540 according to embodiments of the present disclosure. The methods described herein can be implemented in hardware, software (e.g., firmware), or a combination thereof. In an exemplary embodiment, the methods described herein are implemented in hardware as part of the microprocessor of a special or general-purpose digital computer, such as a personal computer, workstation, minicomputer, or mainframe computer. The system 500 therefore includes general-purpose computer 501 as illustrated in FIG. 5. In an exemplary embodiment, in terms of hardware architecture, as shown in FIG. 5, the computer 501 includes a processor 505 including a plurality of execution units, an error detection unit, a dispatch rules adjustment unit, and an instruction dispatch unit. The computer 501 further includes memory 510 coupled to a memory controller 515, and an electron microscopy assembly 540 communicatively coupled via a local input/output controller 535. The input/output controller 535 can be, for example but not limited to, one or more buses or other wired or wireless connections, as is known in the art. The input/output controller 535 may have additional elements, which are omitted for simplicity, such as controllers, buffers (caches), drivers, repeaters, and receivers, to enable communications. Further, the local interface may include address, control, and/or data connections to enable appropriate communications among the aforementioned components. The processor 505 is a hardware device for executing software, particularly that stored in storage 520, such as cache storage, or memory 510. The processor 505 can be any custom made or commercially available processor, a central processing unit (CPU), an auxiliary processor among several processors associated with the computer 501, a semiconductor based microprocessor (in the form of a microchip or chip set), a macroprocessor, or generally any device for executing instructions. The memory 510 can include any one or combination of volatile memory elements (e.g., random access memory (RAM, such as DRAM, SRAM, SDRAM, etc.)) and nonvolatile memory elements (e.g., ROM, erasable programmable read only memory (EPROM), electronically erasable programmable read only memory (EEPROM), programmable read only memory (PROM), tape, compact disc read only memory (CD-ROM), disk, diskette, cartridge, cassette or the like, etc.). Moreover, the memory 510 may incorporate electronic, magnetic, optical, and/or other types of storage media. Note that the memory 510 can have a distributed architecture, where various components are situated remote from one another, but can be accessed by the processor 505. The instructions in memory 510 may include one or more separate programs, each of which comprises an ordered listing of executable instructions for implementing logical functions. In the example of FIG. 5, the instructions in the memory 510 a suitable operating system (OS) 511. The operating system 511 essentially controls the execution of other computer programs and provides scheduling, input-output control, file and data management, memory management, and communication control and related services. In an exemplary embodiment, a conventional keyboard 550 and mouse 555 can be coupled to the input/output controller 535. The system 500 can further include a display controller 525 coupled to a display 530. In an exemplary embodiment, the system 500 can further include a network interface 560 for coupling to a network 565. The network 565 can be an IP-based network for communication between the computer 501 and any external server, client and the like via a broadband connection. The network 565 transmits and receives data between the computer 501 and external systems. In an exemplary embodiment, network 565 can be a managed IP network administered by a service provider. The network 565 may be implemented in a wireless fashion, e.g., using wireless protocols and technologies, such as WiFi, WiMax, etc. The network 565 can also be a packet-switched network such as a local area network, wide area network, metropolitan area network, Internet network, or other similar type of network environment. The network 565 may be a fixed wireless network, a wireless local area network (LAN), a wireless wide area network (WAN) a personal area network (PAN), a virtual private network (VPN), intranet or other suitable network system and includes equipment for receiving and transmitting signals. If the computer 501 is a PC, workstation, intelligent device or the like, the instructions in the memory 510 may further include a basic input output system (BIOS) (omitted for simplicity). The BIOS is a set of essential software routines that initialize and test hardware at startup, start the OS 511, and support the transfer of data among the hardware devices. The BIOS is stored in ROM so that the BIOS can be executed when the computer 501 is activated. When the computer 501 is in operation, the processor 505 is configured to execute instructions stored within the memory 510, to communicate data to and from the memory 510, and to generally control operations of the computer 501 pursuant to the instructions. In an exemplary embodiment, where execution unit error detection and dispatch rules adjustment is implemented in hardware, the dispatch rules adjustment methods described herein can be implemented with any or a combination of the following technologies, which are each well known in the art: a discrete logic circuit(s) having logic gates for implementing logic functions upon data signals, an application specific integrated circuit (ASIC) having appropriate combinational logic gates, a programmable gate array(s) (PGA), a field programmable gate array (FPGA), etc. As described above, embodiments for controlling and analyzing data from an electron microscopy assembly can be embodied in the form of computer-implemented processes and apparatuses for practicing those processes. An embodiment may include a computer program product 600 as depicted in FIG. 6 on a computer readable/usable medium 602 with computer program code logic 604 containing instructions embodied in tangible media as an article of manufacture. Exemplary articles of manufacture for computer readable/usable medium 602 may include floppy diskettes, CD-ROMs, hard drives, universal serial bus (USB) flash drives, or any other computer-readable storage medium, wherein, when the computer program code logic 604 is loaded into and executed by a computer, the computer becomes an apparatus for practicing the invention. Embodiments include computer program code logic 604, for example, whether stored in a storage medium, loaded into and/or executed by a computer, or transmitted over some transmission medium, such as over electrical wiring or cabling, through fiber optics, or via electromagnetic radiation, wherein, when the computer program code logic 604 is loaded into and executed by a computer, the computer becomes an apparatus for practicing the invention. When implemented on a general-purpose microprocessor, the computer program code logic 604 segments configure the microprocessor to create specific logic circuits. In some embodiments, when the first and second electron beams have the same energy at the sample, the part of first beam that is reflected from the sample is complementary to the part of the second beam that passes through the sample. In addition, a part of the first and second electron beams may be absorbed by the sample, but when the first and second electron beams have the same electron energy at the sample, the absorbed parts will be the same for both beams. In some embodiments, a total beam intensity of the first beam may be determined by setting the sample potential such that all electrons in the second electron beam are reflected, without the electrons from the first electron beam touching the sample. By a comparison of the intensities of the first and second electron beams arriving at the sample with identical electron energy, and with the intensity of the first electron beam when it is fully reflected, the reflected, transmitted, and absorbed parts of the electron beams at that energy can be determined. As will be appreciated by one skilled in the art, aspects of the present invention may be embodied as a system, method or computer program product. Accordingly, aspects of the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment (including firmware, resident software, micro-code, etc.) or an embodiment combining software and hardware aspects that may all generally be referred to herein as a “circuit,” “module” or “system.” Furthermore, aspects of the present invention may take the form of a computer program product embodied in one or more computer readable medium(s) having computer readable program code embodied thereon. Any combination of one or more computer readable medium(s) may be utilized. The computer readable medium may be a computer readable signal medium or a computer readable storage medium. A computer readable storage medium may be, for example, but not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any suitable combination of the foregoing. More specific examples (a non-exhaustive list) of the computer readable storage medium would include the following: an electrical connection having one or more wires, a portable computer diskette, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or Flash memory), an optical fiber, a portable compact disc read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the foregoing. In the context of this document, a computer readable storage medium may be any tangible medium that can contain, or store a program for use by or in connection with an instruction execution system, apparatus, or device. A computer readable signal medium may include a propagated data signal with computer readable program code embodied therein, for example, in baseband or as part of a carrier wave. Such a propagated signal may take any of a variety of forms, including, but not limited to, electro-magnetic, optical, or any suitable combination thereof. A computer readable signal medium may be any computer readable medium that is not a computer readable storage medium and that can communicate, propagate, or transport a program for use by or in connection with an instruction execution system, apparatus, or device. Program code embodied on a computer readable medium may be transmitted using any appropriate medium, including but not limited to wireless, wireline, optical fiber cable, RF, etc., or any suitable combination of the foregoing. Computer program code for carrying out operations for aspects of the present invention may be written in any combination of one or more programming languages, including an object oriented programming language such as Java, Smalltalk, C++ or the like and conventional procedural programming languages, such as the “C” programming language or similar programming languages. The program code may execute entirely on the user's computer, partly on the user's computer, as a stand-alone software package, partly on the user's computer and partly on a remote computer or entirely on the remote computer or server. In the latter scenario, the remote computer may be connected to the user's computer through any type of network, including a local area network (LAN) or a wide area network (WAN), or the connection may be made to an external computer (for example, through the Internet using an Internet Service Provider). Aspects of the present invention are described above with reference to flowchart illustrations and/or block diagrams of methods, apparatuses, systems and computer program products according to embodiments of the disclosure. It will be understood that blocks of the flowchart illustrations and/or block diagrams, and combinations of blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions/acts specified in the flowchart and/or block diagram block or blocks. These computer program instructions may also be stored in a computer readable medium that can direct a computer, other programmable data processing apparatus, or other devices to function in a particular manner, such that the instructions stored in the computer readable medium produce an article of manufacture including instructions which implement the function/act specified in the flowchart and/or block diagram block or blocks. The computer program instructions may also be loaded onto a computer, other programmable data processing apparatus, or other devices to cause a series of operational steps to be performed on the computer, other programmable apparatus or other devices to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide processes for implementing the functions/acts specified in the flowchart and/or block diagram block or blocks. The flowchart and block diagrams in the Figures illustrate the architecture, functionality, and operation of possible implementations of systems, methods and computer program products according to various embodiments of the present invention. In this regard, each block in the flowchart or block diagrams may represent a module, segment, or portion of code, which comprises one or more executable instructions for implementing the specified logical function(s). It should also be noted that, in some alternative implementations, the functions noted in the block may occur out of the order noted in the figures. For example, two blocks shown in succession may, in fact, be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved. It will also be noted that some blocks of the block diagrams and/or flowchart illustration, and combinations of blocks in the block diagrams and/or flowchart illustration, can be implemented by special purpose hardware-based systems that perform the specified functions or acts, or combinations of special purpose hardware and computer instructions. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one more other features, integers, steps, operations, element components, and/or groups thereof. The corresponding structures, materials, acts, and equivalents of all means or step plus function elements in the claims below are intended to include any structure, material, or act for performing the function in combination with other claimed elements as specifically claimed. The description of the present invention has been presented for purposes of illustration and description, but is not intended to be exhaustive or limited to the invention in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the invention. The embodiment was chosen and described in order to best explain the principles of the invention and the practical application, and to enable others of ordinary skill in the art to understand the invention for various embodiments with various modifications as are suited to the particular use contemplated. While the preferred embodiment to the invention had been described, it will be understood that those skilled in the art, both now and in the future, may make various improvements and enhancements which fall within the scope of the claims which follow. These claims should be construed to maintain the proper protection for the invention first described. |
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description | Table I is a listing of absorbing layer thicknesses. Referring now to FIG. 1, the essential principle of operation for the devices of the present invention is illustrated. FIG. 1 is a conceptual cross section view of a single neutron detector comprising a means for detecting neutrons 10 stacked on an absorbing layer 11. The absorbing layer 11, being composed of a first material that absorbs protons, such as titanium, is stacked on a hydrogenous substrate 12. Hydrogenous substrate 12 is composed of a second material having hydrogen atoms interacting with an unknown source of neutrons, indicated by box 13. When a single neutron detector is placed in a field of a neutron spectrum, the incident neutrons, indicated by arrow 14, from suspected neutron source 13 interact with hydrogen atoms within hydrogenous substrate 12. This interaction produces proton recoils that travel in fairly straight lines, one of which is indicated by arrow 15, through the absorber layer 11 and the detector means 10. Scattered neutrons, indicated by arrow 16, are deflected away from the hydrogenous substrate 12. Detector means 10 is connected to a data processing means, indicated by box 17, and a ground 18. The data processing means 17 includes a means for proton distribution. Using several detector means 10 with each absorbing layer 11 having a different thickness allows protons with energies and corresponding ranges greater than the thickness of a particular absorbing layer 11 to reach detector means 10 and produce proton counts. The amount of absorber layers 11 and their thickness can be selected to correspond to ranges of protons from a low value for 1 MeV and larger thicknesses of 250 MeV. Hydrogenous substrate 12 converts part of the kinetic neutron energy to energy of the recoil protons 15 and the detector means 10 detects protons passing through the absorbing layer 12. This approach is demonstrated by considering the energy transfer behavior of neutrons and protons. The maximum energy a neutron of energy En can transfer to a proton Ep (max) equals En (1,2). For this example, assume an absorbing layer 11 thickness of d. For monoenergetic neutrons (En), the number of recoil protons reaching detecting means 10 and producing proton counts decreases as energy En decreases. The number of protons will eventually equal zero when the range of maximum energy recoil protons becomes smaller than d. Recoil particles due to elastic scattering do occur in the higher atomic number non-hydrogenous absorber but, except for very high En, they do not contribute to the counts due to their small range and the unfavorable quantum energy transfer in elastic scattering. Having a system with K units, each with a different d and exposing them to a neutron spectrum, one obtains data which consist of K counts or count rate values Ci(di) i=1, 2, . . . K where for dixe2x88x921 less than di less than di+1, Cixe2x88x921 (dixe2x88x921 greater than Ci greater than Ci+1. From these numbers one can unfold the incident spectrum of neutrons. The detector means 10 can be of any shape or configuration and can be any type of solid state device. The inventors herein have employed a depleted n/p diode used to measure alpha particles, which was relatively insensitive to beta particles because of their low LET (Linear Energy Transfer) values as a detector means 10. Spectroscopic grade detectors are not required for this device since only event counting is required and data describing the energy spectrum are not needed. In considering the thicknesses of absorbing layers 11 and the ranges of protons to be measured, an energy range of 1 to 250 MeV was selected to match the expected neutron spectrum distribution. One solution to achieve this objective is to fabricate an instrument that converts a distribution of neutrons to one of recoil protons, which are charged particles that can be easily counted. By employing 12 detector means 10 within a given chamber, the recoil protons are essentially sorted into 12 bins where they can be readily counted. Said absorber layers 11 can be constructed of aluminum for detecting the lower energy levels or tantalum for the higher values. The hydrogenous substrate 12 for each detector means 10 could be constructed of polyethylene. The data processing means 17 and its means for proton distribution provides a hitherto unavailable capability to determine a proton distribution pattern to construct a neutron spectrum indicating the spectrum of neutrons from an unknown source of neutrons 13. In operation, results of a spectral measurement are a set of pairs from the detector means 10 and the absorbing layer 11 that allows protons with energies and corresponding ranges greater than the absorbing layer 11""s thickness to reach the detector means 10 and produce proton recoil counts. One data processing means 17 successfully employed by the present inventors is a 3-dimensional Monte Carlo Adjoint Transport code, NOVICE, which is described in Jordan, T., xe2x80x9cNovice, A Radiation Transport and Shielding Codexe2x80x9d, Experimental and Mathematical Physics Consultant, Report EMP. L 82.001, January 1982. FIG. 2 is a chart showing plots of counts in the detector versus proton energy with different thicknesses indicated as a parameter on the curves, and these results were obtained using the NOVICE program and a flat spectrometer 20 depicted in FIG. 6, which will be described below. The FIG. 2 plots are counts in the detector versus proton energy with the aluminum and tantalum thicknesses indicated as a parameter on the curves. In this preliminary assessment of the feasibility of neutron monitor with multiple neutron detectors, an incident neutron spectrum and the subsequent unfolding software were not included in the code""s run. The proton recoil spectrum was assumed to exist in the converter material of hydrogenous substrate 12. The separation or resolution of proton energy shown in FIG. 2 provides useful information about detecting 12 ranges of neutron energy. The flat configuration of monitor 20, depicted in FIG. 6, along with the use of tantalum for the absorber layers 11 and for the chamber 21 make it too heavy for spacecraft or other airborne applications. Using a data processing device with the NOVICE computer software to analyze the monitor revealed other more useful potential configurations for neutron spectrometers, which were modeled and analyzed by the computer. One configuration suggested by the FIG. 2 NOVICE results is a pentagon dodecahedron, which allows for a full measurement range because of its 12 surfaces, each supporting a detector-absorber pair with different absorber layer thicknesses. FIGS. 3A and 3B, are perspective drawings depicting a detector means 41 stacked on a pentagonal absorbing layer 42 and a dodecahedron neutron spectrometer monitor 40, respectively. Referring now to FIG. 3A, which depicts a perspective view of a neutron detector comprising a detector means 41 stacked on an absorbing layer 42. Absorbing layer 42 is composed of a first material that absorbs protons, such as titanium. By placing this assembly on an appropriate hydrogenous substrate, a neutron detector is provided. Referring now to FIG. 3B, dodecahedron neutron spectrometer monitor 40 is depicted with 11 of 12 of the absorbing layers 42 with varying thicknesses stacked on a surface facet of a solid dodecahedron substrate 43, which provides the hydrogenous substrate. Dodecahedron substrate 43 is shown partially exposed without one absorbing layer for illustrative purposes. FIG. 4 is a front view drawing of the dodecahedron neutron spectrometer monitor 40 with all absorbing layers 51-62, respectively, covering each of the 12 facets of substrate 43 and representative dimensions. For the sake of clarity, only one detector means 42 is shown stacked on absorbing layer 54, with 11 other detector means 42 for the other 11 absorbing layers 51-53 and 55-62, respectively, not shown. Each of the 12 absorbing layers 51-62 are constructed with a varying thickness and are stacked on a surface facet of the solid dodecahedron substrate 43. Substrate 43 is composed of a hydrogenous material, such as polyethylene, having hydrogen atoms and functions as a neutron converter when interacting with said absorbing layers 51-62 in the presence of an unknown energy distribution, indicated by box 44, which emits incident neutrons, indicated by arrow 63. In operation, said hydrogenous substrate 43 converts said neutrons to recoil protons and each of said detector means 42 detects recoil protons passing through each absorbing layer 51-62, respectively. Each absorbing layer 51-62, respectively has a different thickness, as depicted in FIG. 5, to absorb neutron energies from 1 to 250 MeV. Returning now to FIG. 4, the hydrogenous substrate 43 is housed in a concentrically hollow spherical chamber, indicated by broken line 45. Each detector means 42 is coupled to a means for data processing, indicated by box 46, outside the spherical chamber 45, which provides a count of recoil protons to a means for proton distribution, not shown, residing within said data processing means 46. The means for proton distribution determines a proton distribution pattern to construct a neutron spectrum pattern indicating the spectrum of neutrons from said suspected source of neutron radiation 44. FIG. 4 also includes representative dimensions. Each absorbing layer 51-62 is pentagonally shaped in this embodiment, with each side 2.03 cm in length. Each of said detector means 42 are circular and 0.5xe2x80x3 wide and 0.015xe2x80x3 thick. Covered hydrogenous substrate 43 is 4.47 cm in height and housed concentrically within hollow spherical chamber 45. Hydrogenous substrate 43 was fabricated from a solid block of Lucite(trademark). The hollow spherical chamber 45 is composed of titanium in this embodiment with an inner diameter of 10.8 cm and a wall thickness of 2.5 cm. Each of said 12 absorbing layers 51-62 is composed of titanium in this embodiment with a varying thickness ranging from 0.00105 cm to 2.4217 cm, as described in Table I below. Detector means 42 can be constructed from a depleted n/p diode. It should be understood to those skilled in the art that these dimensions are merely representative and numerous other choices of dimensions are possible. FIG. 5 is a perspective drawing of hydrogenous substrate 43, using like numerals for similar structural elements, illustrating a number of absorbing layers with a varying thickness. In this drawing, covered hydrogenous substrate 43 is shown removed from the hollow spherical shell 45 to better illustrate each absorbing layer having a different thickness. Referring back to FIG. 2, which is the chart showing plots of counts in the detector versus proton energy with different thicknesses indicated as a parameter on the curves from the NOVICE program. Those plots from the FIG. 6 flat spectrometer 20, which will be described shortly, are based on using aluminum and tantalum as absorber material. These results suggested using titanium as the preferred absorber material for the FIG. 4 absorbing layers 51-62 for all energy levels, because titanium is lighter than tantalum and its neutrons do not generate nuclear interactions. Only elastic scattering takes place. The proton energy resolution from this embodiment is also relatively good. The FIG. 2 results also indicate that aluminum absorbers produced a slightly better energy resolution for the lower range of energies, 1 to 10 MeV. The size of this dodecahedron configuration is small and light in weight and very practical for a spacecraft application. In order to insure that an unknown neutron spectrum has an isotropic distribution, the spectrometer 40 can also be located at the center of a titanium sphere with a diameter of 3 inches. FIG. 6 is a perspective conceptual drawing of the flat embodiment of the present invention""s neutron spectrometer monitor 70. Monitor 70 comprises a group of the FIG. 1 neutron detector means 10 arranged in a chamber 71. As described above, having several detector means 10 stacked onto absorbing layers, not shown, each having a different thickness, allows protons with energies and corresponding ranges greater than the thickness of each absorbing layer to reach the detector means 10 and produce proton counts. FIG. 6 depicts 12 detector means 10 which correspond to 12 energy bins and thus detect protons with ranges corresponding to energies from 1 MeV up to 250 MeV. The floor of chamber 71 serves as the hydrogenous substrate. Monitor 70 is placed in proximity to an unknown source of neutrons, shown as box 76. Detecting means 10 is coupled to a means for data processing, indicated by box 77, and provides a separate count of recoil protons for each different thickness employed in the absorbing layers. The data processing means 77 transmits the count of recoil protons to a means for proton distribution, not shown, residing within the data processing means 77. The means for proton distribution determines a proton distribution pattern to construct a neutron spectrum pattern indicating the spectrum of neutrons from the suspected concentration of neutrons 76. Bulkhead output connector 72 on the chamber 71 allows correction of voltage to the detector as well as correction of output counts to counting instruments. In the flat configuration, said chamber 71 is shown in a rectangular shape, and its walls 78, lid, not shown, and unit compartments 79 can be composed of tantalum. Each detector means 10 in the egg-crate-like structure is numbered lxe2x80x2-12xe2x80x2, respectively, to correspond with readings shown in the FIG. 2 chart. Detector means 7xe2x80x2 is depicted with representative dimensions of 2 cm in width and 2 cm in length. A gap 80 between detector means 11xe2x80x2 and 12xe2x80x2 is 0.471 cm. The thickness of each wall 78 is 1 cm and its height is about 3 cm. The chamber 71 is depicted as 15 cm in length and 5.41 cm in width. These dimensions are merely representative and numerous other choices of dimensions are possible, however, it is critical that each absorber layer is constructed with a different thickness according to the minimum and maximum energies of neutrons in the spectrum. Similarly, the materials used for constructing the absorber layers, detector means 10 and chamber 71 can also be varied according to the minimum and maximum energies of neutrons in the spectrum. It is to be understood that details concerning materials, shapes and dimensions are merely illustrative, and that other combinations of materials, shapes and dimensions can also be advantageously employed and are considered to be within the contemplation of the present invention. We also wish it to be understood that we do not desire to be limited to the exact details of construction shown and described. It will be apparent that various structural modifications may be made without departing from the spirit of the invention and the scope of the appended claims. |
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claims | 1. A charged particle beam irradiation apparatus comprising:an irradiation section configured to irradiate an irradiated body with a charged particle beam;a multi-leaf collimator configured to set an irradiation range of the charged particle beam which is irradiated from the irradiation section;an imaging section that is provided so as to be able to advance and retreat with respect to an irradiation axis of the charged particle beam which is irradiated from the irradiation section, between the irradiation section and the multi-leaf collimator, and directly images an opening portion of the multi-leaf collimator; anda drive section configured to move the imaging section between an imaging position corresponding to an irradiation area which includes the irradiation axis of the charged particle beam and a retreated position away from the irradiation area. 2. The charged particle beam irradiation apparatus according to claim 1, wherein the imaging section is mounted on amounting bracket that can advance and retreat with respect to the irradiation axis of the charged particle beam,the drive section moves the mounting bracket between the imaging position and the retreated position, anda shield wall for protecting the imaging section from the charged particle beam is provided closer to the side of the irradiation axis of the charged particle beam than the imaging section in the mounting bracket when the mounting bracket is at the retreated position. 3. The charged particle beam irradiation apparatus according to claim 2, wherein a light source section configured to irradiate light to the opening portion of the multi-leaf collimator is further mounted on the mounting bracket. 4. The charged particle beam irradiation apparatus according to claim 3, wherein the light source section is mounted on the mounting bracket so as to be located on the irradiation axis of the charged particle beam when the mounting bracket is at the imaging position. |
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abstract | A light water reactor for generating power that utilizes circulation of a primary coolant at saturation pressure to cool a nuclear core and transfer heat from the core to a secondary coolant through one or more heat exchangers of a condensing steam generator. The secondary coolant, once heated can drive power generation equipment, such as steam turbines or otherwise, before being condensed and returned to the one or more heat exchangers. |
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summary | ||
062953346 | summary | This application is based on Japanese Patent Applications No. HEI-9-115871 and No. HEI-9-115872 both filed on May 6, 1997 and No. HEI-10-45506 filed on Feb. 26, 1998, the entire contents of which are incorporated herein by reference. BACKGROUND OF THE INVENTION a) Field of the Invention The present invention relates to a transmission system for synchrotron light (SR light), and more particularly to an SR light transmission system capable of giving an intensity distribution to SR light in a cross sectional plane perpendicular to its optical axis and to an SR light transmission system for irradiating a certain area by swinging up and down a transporting direction of the SR light using a swinging mirror. b) Description of the Related Art PA1 An output window made of a beryllium thin film is formed in a window flange 37 which is hermetically mounted on an output end of the outgoing vacuum duct 30. SR light entering the outgoing vacuum duct 30 transmits through the output window formed in the window flange 37 and is radiated to the outside of the vacuum duct 30. An X-ray stepper 50 is disposed facing the window flange 37. The X-ray stepper 50 holds a semiconductor substrate 51 at the position where SR light radiated from the window flange 37 is applied. An exposure mask 52 is supported in front of the semiconductor substrate 51. With reference to FIG. 1, the structure of a conventional X-ray exposure system will be described. Reference to FIG. 1 is also made when embodiments of the invention are described later. The X-ray exposure system comprises an SR light generator unit 1, an SR light transmission unit 10 and an X-ray stepper 50. The SR light generator unit 1 comprises a vacuum room 2 and an electron beam circular orbit 3 formed therein. SR light is radiated from electrons moving along the circular orbit 3. This SR light is output from a beam output port of the vacuum room 2. The SR light transmission unit 10 has an incoming vacuum duct 11, a mirror box 12 and an outgoing vacuum duct 30. Incoming opening 13 and outgoing opening 14 are formed in the wall of the mirror box 12. The incoming vacuum duct 11 hermetically communicates the beam output port of the SR light generator unit 1 with the incoming opening 13. In the vacuum duct 11, a vacuum shielding valve (not shown), an SR light shielding shutter (not shown) and the like are mounted. The input port of the outgoing vacuum duct 30 is hermetically coupled to the outgoing opening 14. A reflection mirror 15 is disposed in the mirror box 12 and supported by a mirror swinging mechanism 16. SR light entering the mirror box 12 via the incoming opening 13 is reflected by the mirror 15 and enters the outgoing vacuum duct 30 via the outgoing opening 14. The mirror 15 is disposed such that its incidence plane contains an optical center axis of incidence SR light and a normal to a reflection plane at the reflection point and such that an angle between the optical center axis and the reflection plane is about 1 to 2.degree., i.e., such that the incidence angle is about 89 to 88.degree.. The swinging mechanism 16 swings the mirror 15 a long an axis vertical to the incidence plane and passing the reflection point of SR light, i.e., a horizontal rotary shaft is used as a swing axis. As the mirror 15 swings, reflected SR light is swung up and down. The swing axis may be set to a position different from the reflection point of SR light. Although SR light is irradiated omnidirectionally in the horizontal plane, it only has a spread of about +/-1 mrad (mili-radian) in the vertical plane. By swinging the mirror 15, SR light is swung in the vertical direction so that SR light can be applied to a broad surface area of the semiconductor substrate 51. SR light diverges in the horizontal direction. This SR light is therefore converged in the horizontal direction to make it parallel light fluxes, so that SR light radiated from the light source can be more efficiently used. If the intensity of X-ray is increased, the X-ray exposure time can be shortened. In order to converge SR light in the horizontal direction, as the mirror 15 shown in FIG. 1, a cylindrical mirror or a toroidal mirror is used. A substantial focal length of a cylindrical mirror or toroidal mirror changes with an incidence angle of SR light. As the mirror 15 is swung, the incident angle changes and the focal length with respect to the horizontal plane changes with the incidence angle correspondingly. As the focal length changes, an energy density of SR light on the surface of the semiconductor substrate 51 changes. It is therefore difficult to uniformly apply X-rays to the surface of the semiconductor substrate 51. SR light reflected by a cylindrical mirror or a toroidal mirror has a shape extending along generally a circular line in the cross sectional plane (cross beam section) perpendicular to the optical axis. Therefore, an SR light radiation area on the exposure surface of the semiconductor substrate 51 also has a shape extending along generally a circular line. SR light can be applied to a broad area by moving this radiation area in the radial direction passing through a center point of the circular line. A length of the circular radiation area cut along a straight line parallel to the motion direction of the area becomes longer at a position more remote from the center of the radiation area in the horizontal direction. In addition, the exposure amount on the exposure plane obtained by swinging the mirror and moving such an exposure area in the vertical direction on the exposure plane becomes larger at a position more remote from the center of the exposed area. It is therefore difficult to uniformly expose the exposure plane by using SR light having a circular radiation area. SUMMARY OF THE INVENTION It is an object of the present invention to provide an SR light transmission system capable of improving an exposure performance of an exposure apparatus using SR light. It is another object of the present invention to provide a synchrotron radiation light transmission system capable of making a distribution of exposure amounts in an exposure area nearly uniform. According to one aspect of the present invention, there is provided a synchrotron radiation light transmission system, comprising: a mirror box formed with an incoming opening and an outgoing opening through which synchrotron radiation light having a horizontally elongated cross section passes; a mirror disposed in the mirror box for reflecting the synchrotron radiation light; and a swinging mechanism for supporting the mirror so as to allow the synchrotron radiation light entering the mirror box via the incoming opening to be reflected by the mirror and to change a travelling direction in a vertical plane and for swinging the mirror to change a change angle of the travelling direction, wherein a swing axis is on a cross line, or on its extension, between an incidence plane of the synchrotron radiation light and a tangential plane of the mirror at a reflection point and also on an incidence side of the synchrotron radiation light from the reflection point, the reflection point of the synchrotron radiation light moves on a reflection plane of the mirror as the mirror swings, and the mirror is swung so that an incidence angle becomes larger as a distance between a light source of the synchrotron radiation light and the reflection point becomes longer. If the mirror is a cylindrical surface mirror, a toroidal mirror, a conical surface mirror or the like, a focal length in the horizontal plane changes with an incidence angle of synchrotron radiation light. A change in the focal length is compensated by changing the position of the reflection point to thereby form suitable reflected SR light. According to another aspect of the present invention, there is provided a synchrotron radiation light transmission system, comprising: a mirror box formed with an incoming opening and an outgoing opening through which synchrotron radiation light having a horizontally elongated cross section passes; a light source for making the synchrotron radiation light incident upon the incoming opening of the mirror box; a mirror disposed in the mirror box for reflecting the synchrotron radiation light; and a swinging mechanism for supporting the mirror so as to allow the synchrotron radiation light entering the mirror box via the incoming opening to be reflected by the mirror and to change a travelling direction in a vertical plane and for swinging the mirror to change a change angle of the travelling direction, wherein a reflection point on the mirror of the synchrotron radiation light moves on a reflection plane of the mirror as the mirror swings, the mirror is swung so that an incidence angle becomes larger as a distance between a light source of the synchrotron radiation light and the reflection point becomes longer, and a distance between the reflection point of the synchrotron radiation light and a swing axis of the mirror is not shorter than a distance between the reflection point and the light source. As the swing radius is set longer than the distance between the reflection point and light source, the energy density of synchrotron radiation light on the exposure plane can be made more uniform. According to another aspect of the present invention, there is provided a synchrotron radiation light transmission system comprising: an optical system for transmitting synchrotron radiation light; and a thin film disposed in an optical path of the synchrotron radiation light, made of material capable attenuating the synchrotron radiation light, and formed so that an optical path length in the thin film of the synchrotron radiation light transmitting through the thin film is not uniform in an in-plane of the thin film. Since the optical path length in the thin film of synchrotron radiation light is different at each point in the in-plane of the thin film, the synchrotron radiation light can be attenuated by different amounts at respective points in the in-plane of the thin film. According to a further aspect of the present invention, there is provided a synchrotron radiation light transmission system, comprising: a mirror box formed with an incoming opening and an outgoing opening through which synchrotron radiation light having a horizontally elongated beam cross section passes; a mirror disposed in the mirror box for reflecting the synchrotron radiation light; a duct coupled to the outgoing opening of the mirror box for defining a hollow space through which the synchrotron radiation light output from the outgoing opening passes; and a thin film mounted at an output port of the duct for attenuating and transmitting the synchrotron radiation light, wherein an optical path length in the thin film of the synchrotron radiation light transmitting through the thin film is made different in each point in an in-plane of the thin film to change an attenuation amount of the synchrotron radiation light in the in-plane. Since the transmission optical path length of the thin film is different at each point, the attenuation amount of synchrotron radiation light also become different. By controlling the transmission optical path length distribution, a desired intensity distribution of the synchrotron radiation light transmitted through the thin film can be obtained. As above, an attenuation amount distribution of SR light can be provided in a plane perpendicular to the optical axis. If the invention is applied to X-ray exposure using SR light, uniform exposure is possible by attenuating SR light so as to compensate for a variation of SR light intensities in the beam cross section. |
042242584 | claims | 1. A method of producing spherical particles of uniform size of a nuclear fuel or breeder material from drops of a water solution of nitrates of uranium, plutonium or thorium or mixtures of two or more of said nitrates, in which method said solution is subdivided into drops with the aid of a vibrator, and said drops are caused to fall into a water solution of ammonia after passing through a first space occupied by a gas medium free of ammonia for a sufficient distance for the formation of spherical drops and then passing through a second space containing ammonia gas for fixing the spherical shape of the drops by surface hardening, and after immersion in the ammonia solution the resulting oxide spheres are dried and sintered, comprising the improvement which consists in that: the ammonia gas is introduced into said second space in a stream directed at the drops of said solution in a direction oblique to their direction of movement and with a component of motion in the direction movement of said drops of said solution. said supply conduit system for the ammonia gas comprises at least one nozzle (11,13) so disposed with respect to said nozzle (2) of said second container (15) that the ammonia gas is introduced into said volume of space (6) overlying said ammonia solution (5) in said first container (1,12) in a stream directed at the drops of said solution formed by said nozzle (2,2') of said second container (15,16) in a direction oblique to the direction of movement of said drops at the place of meeting them and with a component of motion in their said direction of movement. 2. A method as defined in claim 1 in which at the place of incidence on said drops the direction of flow of ammonia gas forms an angle with the direction of movement of said drops which lies in the range from 30.degree. to 60.degree.. 3. A method as defined in claim 1 in which the velocity of flow of said ammonia gas is between 10 and 20 times as great as the average velocity of movement of said drops. 4. A method as defined in any of the preceding claims in which said ammonia gas is supplied to said second space in a plurality of streams directed at said drops, and in which the places of incidence of the respective streams are spaced from each other along the path of the drops. 5. An apparatus for the production of spherical particles of uniform size of a nuclear fuel or breeder material from drops of a water solution of nitrates of uranium, plutonium or thorium or mixtures of two or more of said nitrates, comprising a first container (1) for a precipitation bath of a water solution of ammonia and an overlying volume of a gaseous ammonia phase, at least one second container (15) for said nitrate solution equipped with a nozzle for dispensing drops of said solution, and a supply conduit system for the ammonia gas, and further comprising the improvement which consists in that: 6. An apparatus as defined in claim 5 in which said nozzle of said supply conduit system for the ammonia gas is so disposed that the ammonia gas stream impinges upon the succession of drops of said solution so as to form an angle in the range from 30.degree. to 60.degree. with the path of said drops at the place of incidence on said path. 7. An apparatus as defined in claim 5, in which supply conduit system for the ammonia gas has two nozzles (11,13) arranged one behind the other in the direction of movement of said drops which nozzles are so disposed that the places of the incidence on said drops of the respective ammonia gas streams produced by said nozzles are spaced from each other along the path of movement of said drops. 8. An apparatus as defined in claim 5, 6, or 7 in which said nozzles (11,13) of said supply conduit system for the introduction of ammonia gas are constituted as flat nozzles with the long dimension of their respective opening cross-sections disposed perpendicularly to the plane in which the axes respective nozzle for the ammonia gas of said nozzle for said solution lie. |
summary | ||
056339038 | summary | BACKGROUND OF THE INVENTION FIELD OF THE INVENTION The invention relates to a method for dismantling bulky parts of pressure-vessel fittings of a nuclear plant into transportable part-sizes, which includes inserting a bulky part into an open transport container with the bulky part projecting by a predeterminable amount above an end surface of the transport container, supporting a separating device on the end surface of the transport container and fixing the separating device relative to the transport container, and separating the bulky part above the end surface. A method of that type is known from Published East German Application DD 222 997 A1. There, an absorber element being formed of a plurality of absorber rods is drawn out of a fuel assembly of a pressurized-water reactor into a transfer container. A ceiling is provided with a plurality of transfer wells, into each of which an ultimate-storage container that is open at the top is inserted. A separating device which is set down at the end surface of the ultimate-storage container has a top side on which the transfer container having the absorber element rests. The absorber element is then moved a predeterminable amount into the ultimate-storage container and is sheared off through the use of the separating device. Positioned underneath the ceiling is a transport container, into which the loaded ultimate-storage container is inserted. The method according to Published East German Application DD 222 997 A1 requires a very deep water tank, since disposed above the separating device is the transfer container which is at least 4 m long and above which a sufficient water covering of several meters is still necessary for shielding reasons. Furthermore, the provision of a plurality of containers (transfer, ultimate-storage and transport containers) is required. German Published, Non-Prosecuted Patent Application DE 40 31 153 A1 discloses an installation for the comminution of fuel-element cans. The fuel-element can is introduced into an introduction well and is supported on the bottom of a slide-guide chamber. A shearing slide detaches part of the fuel-element can and pushes the detached part to an ejection device. A container is disposed underneath the ejection device and receives the detached part. SUMMARY OF THE INVENTION It is accordingly an object of the invention to provide a method for dismantling bulky parts of pressure-vessel fittings of a nuclear plant, which overcomes the hereinafore-mentioned disadvantages of the heretofore-known methods of this general type and which makes do with few containers and with a small water-tank depth. With the foregoing and other objects in view there is provided, in accordance with the invention, a method for dismantling bulky parts of pressure-vessel fittings of a nuclear plant into transportable parts of smaller sizes, which comprises a) setting down a bottom part of an open transport container on a bottom of a water tank; inserting a bulky part into the bottom part of the open transport container; moving a casing part of the open transport container over the inserted bulky part like a sleeve until the casing part contacts the bottom part and the bulky part projects a predeterminable amount above an end surface of the casing part; connecting the casing part to the bottom part; supporting a separating device on the end surface of the transport container and fixing the separating device relative to the transport container; and separating the bulky part above the end surface of the casing part with the separating device. Thus, the transport container, which is necessary in any case at a later time, serves for receiving the bulky part during the separating operation, so that a complicated holding device for the bulky part and the separating device supported on the transport container are dispensed with. Furthermore, there is no need to lift the bulky part above the end surface of the transport container, thereby always guaranteeing a sufficient water covering. Other features which are considered as characteristic for the invention are set forth in the appended claims. Although the invention is illustrated and described herein as embodied in a method for dismantling bulky parts of pressure-vessel fittings of a nuclear plant, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims. The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings. |
059088842 | claims | 1. A radiation shielding material comprising: powder of material of high radiation absorptivity mainly having specific gravity not smaller than 12, and vulcanized rubber so that said radiation shielding material has elastic deformability for withstanding stress caused by bending, strength for withstanding heat and chemical cleaning, and a radiation shielding ability, wherein a Fisher sub-sieve sizer particle size of said powder of material of high radiation absorptivity is not larger than 50 .mu.m and, wherein said powder of material of high radiation absorptivity is a mixture powder containing powder having a particle size not smaller than 4 .mu.m but not larger than 100 .mu.m in a range of from 60% by weight to 95% by weight, and powder having a particle size smaller than 4 .mu.m in a range of from 5% by weight to 40% by weight. dispersing powder of material of high radiation absorptivity mainly having specific gravity not smaller than 12 into unvulcanized rubber in advance; and vulcanizing and forming said unvulcanized rubber into vulcanized rubber having a predetermined shape, strength for withstanding heat and chemical cleaning, deformability and flexibility for withstanding stress caused by bending and radiation shielding ability, wherein powder having a Fisher sub-sieve sizer particle size not larger than 50 .mu.m is used as said powder of material of high radiation absorptivity, and 2. A radiation shielding material according to claim 1, wherein said powder of material of high radiation absorptivity contains at least one member selected from the group consisting of tungsten, tungsten compounds, and tungsten radical alloys. 3. A radiation shielding material according to claim 1, wherein a content of said powder of material of high radiation absorptivity is more than 80% by weight and up to 99% by weight. 4. A radiation shielding material according to claim 1, wherein said vulcanized rubber is vulcanized fluoro rubber. 5. A radiation shielding material according to claim 1, wherein said vulcanized rubber has electrical conductivity. 6. A radiation shielding material according to claim 1, wherein said powder of material of high radiation absorptivity has .gamma.-ray absorption coefficient (cm.sup.-1) in the range of about 0.7 to 1.2 when the energy of .gamma.-rays is 1.5 MeV. 7. A method of producing a radiation shielding material comprising the steps of: 8. A method for producing a radiation shielding material according to claim 7, wherein said unvulcanized rubber is unvulcanized fluoro rubber. 9. A method for producing a radiation shielding material according to claim 7, wherein an electrical conductivity addition agent is mixed in said unvulcanized rubber and said unvulcanized rubber is vulcanized and formed into a predetermined shape. 10. A method for producing a radiation shielding material according to claim 9, wherein carbon powder is added as said electrical conductivity addition agent. 11. A method for producing a radiation shielding material according to claim 7, wherein at least one member selected from the group consisting of peroxides, and polyols is used as a vulcanizing agent. 12. A method for producing a radiation shielding material according to claim 7, wherein said powder of material of high radiation absorptivity has .gamma.-ray absorption coefficient (cm.sup.-1) in the range of about 0.7 to 1.2 when the energy of .gamma.-rays is 1.5 MeV. |
abstract | A respiration phantom that may be used to perform quality assurance on a radiation delivery system. The respiration phantom includes a human-like skeletal structure, at least one deformable component, and a respiration actuator. The deformable component is positionable at least partially internal to the human-like skeletal structure, has a shape resembling an organ of a human anatomy, and attenuates radiation substantially similarly to the organ of the human anatomy. The respiration actuator is positioned to deform the deformable component with a respiration-like motion. |
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046506330 | description | DETAILED DESCRIPTION The invention as described herein, is employed with a water cooled and moderated nuclear reactor of the boiling water type, an example of which is illustrated in simplified schematic form in FIG. 1. Such a reactor system includes a pressure vessel 10 containing a nuclear fuel core 11 submerged in a coolant-moderator such as lightwater, the normal water level being indicated at 12. A shroud 13 surrounds the core 11, and a coolant circulation pump 14 pressurizes a lower chamber 16 from which coolant is forced upward through the core 11. A part of the water coolant is converted to steam which passes through seperators 17 which are inside a dryer seal skirt 9, dryers 18, and thence through a steam line 19 to a utilization device such as a turbine 21. A portion of the steam is diverted from turbine 21 through preheaters 92 and 93 in a feedwater flowline 26. Condensate formed in a condenser 22, along with any necessary make-up water, is returned as feedwater to the vessel 10 by a condensate pump 30, a subsequent feedwater pump 23 and through a control valve 24 in the feedwater line 26. A plurality of control rods 27, containing neutron absorber material, are provided to control the level of power generation and to shutdown the reactor when necessary. Such control rods 27 are selectively insertable among the fuel assemblies of the core under control of a control rod control system 28. For proper reactor operation, it is necessary to maintain the water level in vessel 10 within predetermined upper and lower limits. A general approach to such water level control will now be discussed. A first aspect of such control is a comparison between the steam outflow from the vessel with the feedwater in-flow. A signal proportional to the steam flow rate is provided by a steam flow sensor 29, which may be a differential pressure transmitter that senses the differential pressure from a pair of spaced pressure taps in a flow measuring device 31 placed in the steam line 19. Similarly, a signal proportional to the feedwater flow rate is provided by a sensor 32 which may be in the form of a differential pressure transmitter connected to a flow measuring device 33 in the feedwater line 26. The signals from flow sensors 29 and 32 are transmitted to a feedwater control system 34 wherein one is subtracted from the other. A difference of zero indicates that outflow and inflow are the same and the water level will remain constant. If the difference is other than zero, a signal corresponding in sign and proportional in amplitude to the difference is applied to valve controller 36, which adjusts the valve 24 in a manner to bring steam outflow and feedwater inflow toward balance. This arrangement provides rapid correction and normally maintains vessel water level within the bounds of a relatively narrow deadband. However, it does not sense or control the position of the water level in the vessel. Thus, a second aspect of water level control is the provision of an upper water level pressure tap 37 and a lower water level pressure tap 38 which provide signals from which the position of the water level can be determined. The pressure taps 37 and 38 communicate with the interior of the vessel 10 and are connected to a differential pressure transmitter 39 which converts the difference in pressure at taps 37 and 38 to an output signal indicative of the position of the water level 12. This signal is applied to the feedwater control system 34 and is employed therein to modify the control signal to valve controller 36 whereby the valve 24 is controlled to adjust the feedwater flow rate and thereby maintain the position of the water level 12 within the prescribed upper and lower normal operating limits. (Although not shown here for clarity of drawing, it is noted that the usual system employs two or more sets of pumps 23 and 30, valves 24, and controllers 36 connected in parallel. See FIG. 2.) If for some reason, such as component failure, the water level control system 34 fails to maintain the water level within normal limits, the water level may become excessively low or high. A level detector 40 is provided to detect an excessively low, out-of-limits water level, and to produce a signal OL.sub.1. Similarly, a level detector 41 is provided to detect an excessively high water level and to produce a signal OL.sub.h. These signals are received by a Reactor Protection System 42, which responds to an out-of-limits condition by signaling the control rod control system 28 to insert the control rods and scram the reactor. These and other water level control systems, to which the present invention can advantageously be applied, are set forth in detail in U.S. Pat. No. 4,302,288, incorporated above. Referring to FIG. 2, an overview of a typical condensate delivery system is shown. Elements used for active control of feedwater temperature or pressure are schematically depicted. Condenser 22 collects condensate from a power turbine and from preheaters 92 and 93. Condensate is delivered to three condensate pumps 30 through a one into three manifold 150. The condensate is delivered as feedwater through the condensate pumps, and its temperature is raised by passing it through preheaters 92. The preheaters utilize steam extracted from the power turbine. The feedwater is then brought into a 3 into 2 manifold 151 for delivery to two feedwater pumps 23. Preheaters 93 are provided after the outputs of the feedwater pumps. If the condensate delivery system incorporates motor driven feedwater pumps, flow control valves 24 are incorporated in each flow line immediately after the last preheat stage. A two into one manifold 152 then delivers the feedwater to the reactor vessel. As noted above, a typical condensate delivery system comprises a plurality of centrifugal pumps. The use of groups of pumps connected in parallel provides benefits of redundancy in case one pump fails. Polyphase electrical motors and/or steam driven turbines are utilized to provide motive force to the various pumps. Where turbines are used, flow control means for steam delivered to those turbines can be substituted for flow control means 24 in the feedwater flow lines. Condensate is typically at a temperature of 10.degree.-20.degree. F. above ambient temperature and at a pressure of 20-25 inches of mercury. The condensate pumps boost the pressure of the feedwater to approximately 700 psig. Preheaters 92 raise the water temperature to about 375.degree. F. The feedwater pumps then boost the water pressure to about 1075 psig. All of the above figures are for normal operation and under certain circumstances can be expected to vary. In FIG. 3, a preferred embodiment of the present invention is set forth. The condensate delivery system is depicted as having only two inline pumps for the sake of clarity. The positions of manifolds 150, 151 and 152 are shown. Each feedwater pump in a condensate delivery system will have a pump system protection system. Accordingly, each flow control valve 24 is independently controlled. Feedwater flowline 26 comprises the various pumps, pipes and valves used to connect condenser 22 to the reactor vessel 10. Condenser 22 is directly connected to the condensate pump 30. The condensate pump leads into the feedwater pump 23. The feedwater pump 23 communicates with the pressure vessel 10 through the flow control valve 24. The pumps 23 and 30 typically are centrifugal pumps. Drive motors 50 and 52 drive the condensate and feedwater pumps respectively. Generally, a three phase, non-synchronous induction type motor is used. The flow control valve 24 is adapted to be selectively positioned by valve controller 36. Preheaters 92 and 93 use steam diverted from the turbine 21 to raise the temperature of the feedwater being introduced to the reactor vessel. Preheater 92 heats water flowing in the feedwater line 26 between the condensate pump 30 and the feedwater pump 23. Preheater 93 heats water received from the feedwater pump. A temperature sensor 56 and a pressure sensor 58 are provided in the intake 54 of the feedwater pump 23. Each sensor develops an electrical signal proportional to the value of the physical condition measured. The temperature signal is thus proportional to the temperature of the feedwater in the pump intake. The pressure signal is proportional to the water pressure in the pump intake. The water temperature during normal operation is typically 375.degree. F., although it will be lower when the reactor system is not operating at full power. Normal water pressure in the intake is about 700 psig. The temperature signal and the pressure signal are processed by appropriate circuitry in a subcooling processor 60. The subcooling processor may include a microprocessor adapted to perform a table lookup operation. The temperature signal and the pressure signal are processed by individual analog to digital converters. Subcooling values for the matrix of discrete pressures and temperatures are provided in memory. The microprocessor determines the appropriate address in memory from the temperature and pressure indications and thus generates a subcooling level indication. A digital to analog converter processes the subcooling indication from the accessed memory register. A signal value, correlated with the subcooling of the water in the pump intake, is thus provided. The correlated signal is transmitted to the non-inverting terminal of a summer 62. The subcooling function is non-analytic and is depicted graphically in FIG. 5. The limit signal generator 64 receives the temperature signal from the feedwater pump intake. The limit signal generator is a function generator which matches the measured temperature to a required predetermined value of subcooling needed to prevent cavitation in the feedwater pump at that temperature. Such subcooling values are provided from test data supplied by the manufacturer. A representative set of values is depicted graphically in FIG. 5. The circuit can be realized with a calibrated constant current source and a summing node. A particular quantity of subcooling required at a given temperature implies a certain minimum pressure for that temperature. A signal proportional to the subcooling required is transmitted to the inverting input terminal of the summer 62. Summer 62 develops a signal proportional to the subcooling margin of feedwater entering the feedwater pump 23. A negative signal indicates a negative margin and the consequent possibility of cavitation. This signal is transmitted to a subcooling limit trigger 98. Subcooling limit trigger 98 generates a constant valued, positive "on" signal should the subcooling determined by subcooling processor 60 be less than the minimum required; that is should the signal from summer 62 be negative with respect to ground reference. This occurs when the subcooling processor 60 generates a signal smaller than the required subcooling signal from subcooling generator 64. The limit trigger can be realized using a Schmitt trigger with following inverter. Any signal generated by limit trigger 98 is transmitted to a first input terminal of an OR GATE 80. The output signal from OR GATE 80 is applied to a valve position control signal generator 84 for control of flow control valve 24, as described hereinafter. As mentioned above, three phase induction motors may be used provide motive force to the pumps in the feedwater flow line. Such motors draw electrical current at a constant voltage and frequency and convert it to mechanical power and torque in response to the load imposed on the motor. Such motors are adapted to draw increasing current to produce increasing mechanical power and torque throughout their useful operating range. Such motors also include power limit switches, which disconnect the motor from its supply lines should electrical power consumption rise above a predetermined limit. The electrical power consumption of the motor is given by the relation: EQU P=(3).sup.1/2 Cos .phi.V.sub.11 I.sub.b where Cos .phi. is the inphase component of the current drawn (power factor) PA1 V.sub.11 is line to line voltage PA1 I.sub.b is branch current The power factor, Cos .phi., in the operational area of the motor can be treated as a constant for operating values of interest here. Also, the line to line voltage is assumed to be constant. Thus, I.sub.b varies almost directly with power consumed and this is correlated with the load driven by the motor. Current drawn is monitored as an indication of power consumed. Other conditions could be monitored as such an indication, e.g., motor rotational velocity, or power could be calculated by monitoring the above values and using the above relationship. However, a current monitor provides a reliable, easily resolvable, and relatively inexpensive indicator. Accordingly, a current transformer 66 is applied to one of the three power input lines 68 of a drive motor 52. This is proportional to the total power as the time average current drawn in any one of the three lines of a symetrical motor is equal to that drawn on any one other line. A signal proportional to that of current drawn is induced in the current transformer and transmitted to a current scaler 61, which reduces that signal to a signal appropriately scaled to the subsequent limit trigger 70. The scaled current is introduced to the inverting terminal of trigger 70. A second signal, a steady current limit signal from a calibrated current source, is provided to the non-inverting terminal of limit trigger 70 from current limit generator 65. Should the indicative signal from the current scaler 61 exceed the current limit signal, the limit trigger 70 will produce a fixed, positive valued output signal. This signal is transmitted to a second input terminal of OR GATE 80. OR GATE 80 operates conventionally and transmits a signal to an integrator 82 in the valve position control signal generator 84 in response to either indication signal. The valve position control signal generator 84 receives and sums input signals from both an existing water level control system 34, such as described hereinbefore, and the pump system protection system. The signal from the water level control system 34 is introduced to the valve position control signal generator 84 through a signal limiter 88 which limits a positive indication (i.e., an indication to begin opening the flow control valve) to a predetermined maximum value. Such a limiter can be built using an operational amplifier with a resistive negative feedback loop. The integrator 82 produces an output signal which increases with time for as long as an output signal is received from OR GATE 80. Integrator 82 can be realized using an operational amplifier with capacitive feedback. The output signals from signal limiter 88 and integrator 82 are introduced, respectively, to the positive and negative terminals of a summing amplifier 90. Summer 90 generates the actual valve position control signal which is applied to valve controller 36. Integrator 82 and limiter 88 are provided so that when conflicting demands are made by the respective systems, i.e. the pump system protection system and the water level control system, the pump system protection system eventually prevails. This arrangement maintains pump operation in case of a heavy demand for feedwater flow. A time delay shutdown trigger may be incorporated, as a backup shutdown device, into the aforedescribed pump system protection system. The subcooling margin signal generated by summer 62 is transmitted to an analog to digital converter 113. A/D 113 provides the data input to time delay calculator 105 which is adapted to transmit a trip signal to relay 104 which, in turn, can cut off power to drive motor 52 under circumstances to be described below. Calculator 105 incorporates a microprocessor programmed to trigger a timing mechanism should the subcooling margin become negative and fall below a first minimum value, for example -10 BTU/LBM. As subcooling initially falls through the first minimum, the timer begins a 30 second countdown, which, should it come to completion, will cause a trip signal to be transmitted to relay 104. A series of secondary minimums are provided in memory, which if passed result in set quantities of time being subtracted from the aforesaid timer. For example, if the subcooling margin falls below -20 BTU/LBM, 10 seconds are subtracted from the running timer. If the subcooling margin falls to -30 BTU/LBM, 15 additional seconds are subtracted from the timer. A sudden decline in subcooling from a safe positive level to -30 BTU/LBM allows the pump protection system a maximum of 5 seconds to restore satisfactory operating margins. The timer is stopped and reset should subcooling margin recover to a predetermined minimum, for example, -5 BTU/LBM. Referring now to FIG. 4, a second preferred embodiment of the invention will be discussed. The specific embodiment of the invention depicted is a primarily analog realization of the invention. As before, a pressure sensor 58 and a temperature sensor 56 are introduced to the inlet of a feedwater pump 23. The signal generated by the temperature sensor is transmitted to a saturation pressure function generator 161. The saturation pressure function generator 161 is a one input function generator which generates a signal proportional to what the pressure sensor 58 would generate if the water were saturated at that temperature. Function generator 161 is realized with a calibrated current source and a summing node. Accordingly, the signal generated by function generator 161 is equal to or less than the signal produced by pressure sensor 58. The saturation pressure signal is subtracted from actual pressure at summer 160. The resulting pressure difference signal is the pressure margin which is correlated with pump inlet subcooling. The pressure difference signal, from junction 160, is introduced to the positive terminal of a summer 162. Function generator 164 provides a temperature dependent, required pressure difference signal which correlates with adequate subcooling at each operating temperature. Function generator 164 is a one input generator and may be realized as a calibrated current source and summing node. The signal generated by function generator 164 is transmitted to the negative terminal of summer 162. Should the value of the difference signal fall below the signal from function generator 164, the signal from summer 162 will become negative. Again a subcooling limit trigger 98 is provided to generate a fixed, positive valued control signal should summer 162 generate a negative valued signal, indicative of an inadequate pressure margin needed to assure an adequate subcooling margin. The depicted condensate delivery system utilizes a steam driven turbine 132 to drive the feedwater pump 23. Control of flow through the flowline 26 is effected through control of the motive force driving turbine 132. Control is achieved by controlling the quantity of steam introduced to turbine 132. A flow control valve 124 is included in the steam to turbine delivery line for this purpose. Valve controller 84 performs the same function in the embodiment in FIG. 4 as in the previously discussed embodiment of FIG. 3. The signal produced is applied through a summer 138 to a valve position controller 136, which controls steam flow to turbine 132 by positioning flow control valve 124 according to the demands of the water level control and pump protection systems. Accordingly, a demand for increased feedwater flow will result in opening of the steamflow control valve 124. An overriding signal that pump cavitation is threatened results in progressive repositioning of valve 124 to reduce steam flow. Such variation in steam flow controls turbine energization and thereby controls feedwater flow through pump 23. The reduced flow through the pump allows the condensate pumps to restore pressure to the pump inlet reducing the danger of pump cavitation. As in the case of the embodiment of FIG. 3, a time delay shutdown trigger may be incorporated as a backup shutdown device in the embodiment of FIG. 4. An analog to ditigal converter converts the pressure margin signal from summer 162 into a digital input for time delay calculator 105, which is the same as calculator 105 described for FIG. 3. Note, however, that pressure margin levels are substituted for subcooling margins as minimum trigger levels for the timer. Trip generator 204 is connected to receive a trip signal from calculator 105. On receipt of a trip signal, trip generator 204 develops a valve position signal of sufficient magnitude to dominate all other inputs to summer 138. The resulting signal from 138 is transmitted to valve position 136 and closure of flow control valve 124 is effected. A turbine cannot draw power in a manner analogous to an electrical motor. Accordingly, it is not necessary to monitor the power consumed by the turbine. The power monitoring aspect of the invention is not used in the second embodiment. It will be understood that the analog based embodiment described immediately above may be substituted for the microprocessor based embodiment described in relation to the motor driven feedwater pump. Likewise, the microprocessor based embodiment can be applied to a turbine driven pump system. The operation of the invention is hereinafter elaborated upon with reference to FIGS. 1, 2, 3, 4, and 5, as appropriate. FIRST EXAMPLE Consider the first preferred embodiment. Condensate is collected in condenser 22 at approximately atmospheric pressure. The condensate pump 30 boosts pressure to approximately 700 psig. The feedwater pump 23 further boosts this to approximately 1075 psig for reintroduction to the pressure vessel. Suppose water temperature at the feedwater pump inlet is 375.degree. F. Flow is controlled through the aforementioned flow control valve 24. This is normal operation. Required subcooling is about 75 BTU/LBM. Suppose that the water level control system detects a steam flow greatly in excess of feedwater flow. This condition may be a consequence, for example, of a leak in the feedwater line upstream from the feedwater flow measuring device 33. If not responded to, it portends a coming reduction in water level within the reactor vessel. Accordingly, the water level control system transmits a signal to the valve position control signal operator which generates a command to the valve position controller to begin opening the valve to increase feedwater flow. Increasing flow is associated with decreasing pressure at the inlet of the feedwater pump. System operating conditions will begin to move downward on the curve denoted "MARGIN" in FIG. 5. As flow increases, the load on the motor 52 driving the pump 23 increases. Consequently, current drawn by the drive motor 52 increases. As can be observed from FIG. 5, subcooling will decrease as pressure falls (water temperature remains constant). Should the point marked "minimum" be crossed, a signal will be provided by the feedwater pump system protection system through control signal generator 84 to valve controller 36 to move valve 24 toward its closed position maintaining the minimum subcooling necessary to prevent pump cavitation. Likewise, if current drawn by motor 52 becomes excessive, a signal will be generated to close the valve 24 to reduce flow and thereby reduce load. Integrator 82 assures that these signals dominate the signal from the water level control system. EXAMPLE 2 Suppose operation of the same plant as above, but under partial power. Referring to FIG. 5, an exemplary partial power operating point is so labeled. If the condensate delivery system is operating normally, feedwater pump inlet pressure will be uneffected from the full power operating point. However, pump inlet temperature will be substantially reduced. The system would be operating with approximately 225 BTU/LBM subcooling. The required minimum subcooling would be about 70 BTU/LBM. A prior art pressure trigger would trigger a motor shutdown at a pressure, which would yield subcooling of about 155 BTU/LBM. A variety of causes could result in a rapid reduction in feedwater pump inlet gauge pressure below the 375 psig level at which pressure triggers have been set to activate. A failure of a condensate pump could reduce pressure below the previously employed pressure trigger level but not put the pump into actual danger of cavitation. The condensate delivery system could tolerate one condensate pump failure and remain operational. An unnecessary reactor scram would be avoided. In the exemplary embodiments of the invention described above and shown in FIGS. 4 and 5, the invention is shown as applied to a condensate delivery system in a nuclear power reactor. It will be readily apparent that the invention is not so limited and that it may be used as a reliable method and apparatus to protect pumps used in various settings, e.g. hydraulics. Various substitutions and modifications may also be made in the types of components used. While certain embodiments of the present invention have been disclosed herein, it will be clear that numerous modifications, variations, substitutions, changes and full and partial equivalents will now occur to persons skilled in the art without departing from the spirit and scope of the invention herein. Accordingly, it is intended that the invention be limited only by the spirit and scope of the appended claims. |
description | The present application claims the benefit of U.S. Provisional Application No. 60/712,694, entitled “Large-Field Scanning of Charged Particles,” filed Aug. 30, 2005, by inventor Kirk J. Bertsche, the disclosure of which is hereby incorporated by reference. 1. Field of the Invention The present invention relates generally to charged-particle beam apparatus. 2. Description of the Background Art Charged-particle beam apparatus utilize particles such as electrons, protons or ions. Such apparatus include, for example, scanning electron microscopes (SEMs), electron beam inspection/review tools, electron beam metrology tools, and various other apparatus. One embodiment relates to a charged-particle beam apparatus. The apparatus includes at least a source for generating the charged-particle beam, a first deflector, and a second deflector. The first deflector is configured to scan the charged-particle beam in a first dimension. The second deflector is configured to deflect the scanned beam such that the scanned beam impinges telecentrically (perpendicularly) upon a surface of a target substrate. Another embodiment relates to a method of electron beam inspection. A primary electron beam is generated and scanned in a first dimension. The scanned beam is deflected such that it impinges telecentrically upon a surface of a target substrate. Another embodiment relates to a method of electron beam lithography. A primary electron beam is generated and scanned in a first dimension. The scanned beam is controllably blocked so as to generate a programmed pattern. The scanned beam is also deflected such that it impinges telecentrically upon a surface of a target substrate. Other embodiments are also disclosed. For some applications, it is desirable to scan a charged-particle beam over a large distance in at least one dimension. This may be done with a relatively large working distance (similar to the scan size) between deflectors and target, as in a typical cathode ray tube (CRT). An example of such a configuration is shown in FIG. 1. FIG. 1 is a schematic diagram depicting an apparatus 100 which deflects a charged-particle beam over a large distance. The left side of FIG. 1 is a cross-section showing the xz-plane of the column, while the right side of FIG. 1 is a cross-section showing the yz-plane of the column. The optic axis of the column lies along the z-direction. The components shown in FIG. 1 are generally in a vacuum environment within a column structure. The apparatus 100 may include other well-known components which are not discussed below. A primary or incident electron beam 101 is generated using an electron gun (or other type of electron source) 102 and gun lenses 104. Other column components 106 may include, for example, blanker, aperture, DC align, and DC and dynamic stigmator components. A main lens 108 may then focus the beam 101, and the beam 101 may be deflected across a large angular range using a scan deflector 110. The scan deflector 110 may be implemented as an electrostatic deflector in one embodiment, or may be implemented as a magnetic deflector in another embodiment. In the configuration shown in FIG. 1, the scan deflector 110 scans the beam 101 along the x-direction. Depicted on the left side of FIG. 1 are two example trajectories: the beam as undeflected 101-a and going straight down the optic axis of the column; and the beam as deflected 101-b at an angle in the negative x-direction. The scanned beam 101 impinges upon a substrate surface 114. However, the apparatus 100 of FIG. 1 has the drawback and disadvantage in that the beam 101 of charged particles does not land perpendicularly onto the surface of the target substrate 112. In other words, the configuration of FIG. 1 is not “telecentric.” This non-perpendicular (non-telecentric) landing is visible, for example, in the trajectory 101-b of the beam when it is deflected far from the optical axis of the column. With this condition, topography of the target will cause shadowing which is dependent on scan position, and there may also be variations in the yield of scattered electrons. A second disadvantage is that with the large working distance, electric fields at the target substrate cannot be varied over a large range. Furthermore, the scattered electrons (secondary electrons and/or backscattered electrons) in such a system tend to spread over a large area. This makes the scattered electron detection system (not shown) complex and large. The complex and large detection system may typically limit the detection speed and the possibilities for energy or spatial resolution. Therefore, it is highly desirable to improve the scanning of charged-particle beams over large fields. In particular, it is highly desirable to overcome the above discussed drawbacks and limitations. The present application discloses techniques to substantially improve large-field scanning of charged particles. Depending on the particular application, one or more of these techniques may be combined together. FIG. 2 is a schematic diagram depicting an apparatus which deflects a charged-particle beam over a large distance in a telecentric manner in accordance with an embodiment of the invention. The left side of FIG. 2 is a cross-section showing the xz-plane of the column, while the right side of FIG. 2 is a cross-section showing the yz-plane of the column. The optic axis of the column lies along the z-direction. The components shown in FIG. 2 are generally in a vacuum environment within a column structure. The apparatus 200 may include other well-known components which are not discussed below. A primary or incident electron beam 201 is generated using an electron gun (or other type of electron source) 202 and gun lenses 204. Other column components 206 may include, for example, blanker, aperture, DC align, and DC and dynamic stigmator components. A main lens 208 may then focus the beam 201, and the beam 201 may be deflected across a large angular range using a scan deflector 210. The scan deflector 210 may be implemented as an electrostatic deflector in one embodiment, or may be implemented as a magnetic deflector in another embodiment. In the configuration shown in FIG. 2, the scan deflector 210 scans the beam 201 along the x-direction. Depicted on the left side of FIG. 2 are two example trajectories: the beam as undeflected 201-a and going straight down the optic axis of the column; and the beam as deflected 201-b at an angle in the negative x-direction. In this apparatus 200, the scanned beam 201 passes through a slot along the x-direction in a collector plate of the secondary electron detector 212. The detector 212 is thus configured to allow the beam 201 to be scanned along one-dimension while also functioning to collect secondary electrons emitted from the substrate 218. The beam 201 is then deflected for a second time by a linear deflector. Here, the linear deflector comprises a magnetic scanner 214. The magnetic scanner 214 is configured so as not to deflect the undeflected beam 201-a traveling along the optic axis of the column. The greater the angle of the deflected beam 201-b, the greater the second deflection by the magnetic scanner 214 so as to re-orient the beam perpendicularly with respect to the surface of the substrate 218. In one embodiment, the magnetic scanner 214 may be comprised of two long coils, with or without pole pieces. The magnetic field from the magnetic scanner 214 is oriented in the short direction (i.e. across the slot). If pole pieces are used, they are preferably laminated rather than solid to avoid eddy currents. Electric field strength at the surface of the substrate 218 may be controlled by a Wehnelt electrode 216. The Wehnelt electrode 216 comprises a long slotted charge-control electrode which is a short distance above the surface of the substrate 218. The Wehnelt electrode 216 provides for control over the electric fields at the substrate surface while allowing a large scan in one dimension. The Wehnelt electrode 216 also provides for the option of one-dimensional focusing of the secondary electrons emitted from the substrate 218. In accordance with an alternate embodiment, the apparatus may be configured without the detector 212, such that the scattered electrons may instead be collected at a combined Wehnelt electrode/detector assembly at 216. In another alternate embodiment, such a detector may be omitted altogether, and the substrate current may instead be used to provide a signal for forming an image of the substrate. FIG. 3 is a schematic diagram depicting an apparatus 300 which deflects a charged-particle beam over a large distance in a telecentric manner in accordance with another embodiment of the invention. The left side of FIG. 3 is a cross-section showing the xz-plane of the column, while the right side of FIG. 3 is a cross-section showing the yz-plane of the column. The optic axis of the column lies along the z-direction. The components shown in FIG. 3 are generally in a vacuum environment within a column structure. The apparatus 300 may include other well-known components which are not discussed below. A primary or incident electron beam 301 is generated using an electron gun (or other type of electron source) 302 and gun lenses 304. Other column components 306 may include, for example, blanker, aperture, DC align, and DC stigmator components. A main lens 308 may then focus the beam 301, and the beam 301 may be deflected across a large angular range using a scan deflector 310. The scan deflector 310 may be implemented as an electrostatic deflector in one embodiment, or may be implemented as a magnetic deflector in another embodiment. In the configuration shown in FIG. 3, the scan deflector 310 scans the beam 301 along the x-direction. Depicted on the left side of FIG. 3 are two example trajectories: the beam as undeflected 301-a and going straight down the optic axis of the column; and the beam as deflected 301-b at an angle in the negative x-direction. In this apparatus 300, the scanned beam 301 is deflected for a second time by a linear deflector 312. Here, the linear deflector 312 comprises a magnetic scanner or an electric comb deflector. The linear deflector 312 is configured or operated so as not to deflect the undeflected beam 301-a traveling along the optic axis of the column. The greater the angle of the deflected beam 301-b, the greater the second deflection by the linear deflector 312 so as to re-orient the beam perpendicularly with respect to the surface of the substrate 318. In one embodiment, the linear deflector 312 may be implemented as a magnetic scanner comprised of two long coils, with or without pole pieces. The magnetic field from the magnetic scanner is oriented in the short direction (i.e. along the y-direction). If pole pieces are used, they are preferably laminated rather than solid to avoid eddy currents. In another embodiment, the linear deflector 312 may be implemented as an electric comb deflector. Such an electric comb deflector is described further below in relation to FIG. 7. After the second deflection, the beam 301 may pass through an electric secondary electron (SE) separator 314. The SE separator 314 is configured to separate secondary electrons 319 emitted from the surface, such that the secondary electrons 319 are directed away from the primary beam 301 and towards the secondary electron detection system. The SE separator 314 separates the secondary electrons 319 from the primary beam 301 before the secondary electrons 319 reach the linear deflector 312. Such separation is particularly advantageous if the linear deflector 312 comprises a magnetic scanner because otherwise the secondary electrons 319 may be deflected in a wrong direction by the magnetic scanner. An implementation of the SE separator 314 is discussed further below in relation to FIG. 4. Electric field strength at the surface of the substrate 318 may be controlled by a Wehnelt electrode 316. The Wehnelt electrode 316 may comprise a long slotted charge-control electrode which is a short distance above the surface of the substrate 318. The Wehnelt electrode 316 provides for control over the electric fields at the substrate surface while allowing a large scan in one dimension. A positive potential may be applied to the Wehnelt electrode 316 with respect to the substrate 318 so as to accelerate the secondary electrons 319 away from the substrate. The Wehnelt electrode 316 may also provide one-dimensional focusing (in the y-dimension) of the secondary electrons 319 emitted from the substrate 318. Furthermore, an additional electrode or electrodes (not depicted) may be positioned further from the substrate 318 than the Wehnelt electrode 316. The additional electrode(s) may have a positive potential with respect to the substrate and may be used for better control of fields at the substrate surface than the use of the Wehnelt electrode 316 alone. For example, a “saddle field” may be formed, giving no electric field at the substrate surface directly under the slot, but with an approximately linearly increasing field strength as distance increases from the substrate surface. The secondary electron detection system may include, for example, a de-scanner 320 and a detector 322. The de-scanner 320 may be configured to deflect the secondary electrons along the x-direction in such a way that the secondary electrons converge upon the position of the detector 322. Alternatively, the secondary electron detection system may comprise an array detector which includes a series of detector elements along the x-direction so as to detect the secondary electrons without necessarily needing the de-scanner 320. FIG. 4 is a detailed view including an implementation of the secondary electron separator 314. Here, the separator 314 is shown as implemented as an electric separator including three pairs of electrodes 402-a, 402-b, and 402-c, the electrodes being oriented lengthwise in the x-direction. The first pair of electrode 402-a is shown with a negatively-charged (relatively negative potential) left electrode and a positively-charged (relatively positive potential) right electrode. The second pair of electrode 402-b is shown with a positively-charged (relatively positive potential) left electrode and a negatively-charged (relatively negative potential) right electrode. The third pair of electrode 402-c is shown with a negatively-charged (relatively negative potential) left electrode and a positively-charged (relatively positive potential) right electrode. Preferably, the potentials on the electrodes are adjusted so that the primary electron beam 301 (which is of higher energy) is only slightly deflected and impacts perpendicularly upon the surface of the substrate 318. However, because the secondary electrons 319 are emitted in the reverse direction at much lower energies, the secondary electrons 319 are substantially deflected by the separator 314 such that their trajectories are bent away from the optic axis and towards the detection system. In the particular implementation illustrated in FIG. 4, the secondary electrons 319 may be deflected between the second 402-b and third 402-c electrode pairs such that they travel into the de-scanner device 320. FIG. 5 shows simulated electric fields and secondary electron trajectories in an electric separator. The simulated separator of FIG. 5 includes two pairs of electrodes 502-a and 502-b. Secondary electrons 319 emitted from the surface of the substrate 318 travel through a slotted Wehnelt 316 and to the bottom pair of electrodes 502-b. The trajectories of the secondary electrons 319 are deflected (bent) so that the secondary electrons 319 leave the optic axis of the column and are directed to between the right electrode of the bottom pair 502-b and the right electrode of the top pair 502-a. This simulation shows that the secondary electron beam separator 314 of FIG. 3 may be successfully configured. FIG. 6 is a schematic diagram depicting an apparatus which utilizes both a static magnetic field and an electric deflector in accordance with another embodiment of the invention. The left side of FIG. 6 is a cross-section showing the xz-plane of the column, while the right side of FIG. 6 is a cross-section showing the yz-plane of the column. The optic axis of the column lies along the z-direction. The components shown in FIG. 6 are generally in a vacuum environment within a column structure. The apparatus 600 may include other well-known components which are not discussed below. A primary or incident electron beam 601 is generated using an electron gun (or other type of electron source) 602 and gun lenses 604. Other column components 606 may include, for example, blanker, aperture, DC align, and DC and dynamic stigmator components. A main lens 608 may then focus the beam 601, and the beam 601 may be deflected across a large angular range using a scan deflector 610. The scan deflector 610 may be implemented as an electrostatic deflector in one embodiment, or may be implemented as a magnetic deflector in another embodiment. In the configuration shown in FIG. 6, the scan deflector 610 scans the beam 601 along the x-direction. Depicted on the left side of FIG. 6 are two example trajectories: the beam as undeflected 601-a and going straight down the optic axis of the column; and the beam as deflected 601-b at an angle in the negative x-direction. The scanned beam 601 is then deflected for a second time by an elongated Wien filter 614. The elongated Wien filter 614 comprises an electric “comb” deflector, where the electric field is along the slot direction (i.e. along the x-direction), combined with a static magnetic deflector, where the magnetic field is across the slot direction (i.e. along the y-direction). The electric comb deflector is configured or operated so as not to deflect the undeflected beam 601-a traveling along the optic axis of the column. The greater the angle of the deflected beam 601-b, the greater the second deflection by the electric comb deflector so as to re-orient the beam perpendicularly with respect to the surface of the substrate 618. Electric field strength at the surface of the substrate 618 may be controlled by a Wehnelt electrode 616. The Wehnelt electrode 616 may comprise a long slotted charge-control electrode which is a short distance above the surface of the substrate 618. The Wehnelt electrode 616 provides for control over the electric fields at the substrate surface while allowing a large scan in one dimension. A positive potential may be applied to the Wehnelt electrode 616 with respect to the substrate 618 so as to accelerate the secondary electrons 619 away from the substrate. The Wehnelt electrode 616 may also provide one-dimensional focusing (in the y-dimension) of the secondary electrons 619 emitted from the substrate 618. Furthermore, an additional electrode or electrodes (not depicted) may be positioned further from the substrate 618 than the Wehnelt electrode 616. The additional electrode(s) may have a positive potential with respect to the substrate and may be used for better control of fields at the substrate surface than the use of the Wehnelt electrode 616 alone. For example, a “saddle field” may be formed, giving no electric field at the substrate surface directly under the slot, but with an approximately linearly increasing field strength as distance increases from the substrate surface. The elongated Wien filter 614 may be configured to deflect the secondary electrons 619 so as to effectively de-scan their positions such that the secondary electrons 619 converge at a point which is offset along the slot dimension from the electron source. In other words, the Wien filter 614 may de-scan the secondary electrons such that they enter a fixed detection system. As illustrated in FIG. 6, the detection system may comprise a de-scanner 620, an entry slot 621, an energy analyzer 622, and a segmented detector 623. The de-scanner 620 may be configured to deflect the secondary electrons 619 so that they enter the entry slot 621 at a uniform position and/or angle. The energy analyzer 622 receives the secondary electrons passing through the entry slot 621. The energy analyzer 622 may be configured to disperse the electrons with an electric or magnetic field so that their position is dependent on their energy. A segmented detector (or a detector array) 623 may receive the dispersed electrons so as to provide an energy spectrum of the detected secondary electrons. FIG. 7 is a schematic diagram depicting an electric comb deflector 700 in accordance with an embodiment of the invention. The electric comb deflector 700 is shown in plan view (the view in the xy plane of FIG. 3, for example). The electric comb deflector 700 includes two rows of electrodes 702-a and 702-b. A position in the plane of the primary electron beam 704 is shown in between the two rows of electrodes 702-a and 702-b. Electric charges may be controllably applied to the electrodes in each row such that dipole electric fields E 706 are in the vicinity of the primary electron beam 704. As shown, the general idea is to have the electrodes 708 nearest to the electron beam position 704 to have a neutral (or near neutral) charge, the electrodes 710 on the side towards the optic axis (“X”) 707 in relation to the electron beam position 704 to be positively charged, and the electrodes 712 on the side away from the optic axis 707 in relation to the electron beam position 704 be negatively charged. This results in an electric field E 706 pointed away from the optic axis 707 and in the application of electrostatic force F which bends the trajectory of the negatively-charged electron beam 704. As the electron beam 704 is scanned to and from along the x-dimension, the charges on the electrodes 702-a and 702-b are adjusted in position and strength so as to bend the electron beam 704 by an appropriate amount. In other words, the electrostatic potentials applied to the electrodes 702 are scanned with the beam 704. Preferably, the applied potentials are of a strength so as to achieve telecentric impingement of the electron beam 704 onto the substrate. Of course, when the electron beam 704 is positioned at the optic axis 707, no deflection is needed. In the absence of a magnetic field, no electric field E 706 need by generated by the electric comb deflector 700 at this position. If the electric comb deflector 700 is part of an elongated Wien filter (as in FIG. 6), the field E 706 generated by the electric comb deflector 700 at this position will create a force on the electron beam 704 equal and opposite to the magnetic force, so that the electron beam 704 has no net deflection. Alternatively, in some situations, it may be possible for the electric comb deflector's electrostatic potentials to be static. For example, a quasi-parabolic potential profile may be applied along the slot dimension (the x-dimension). The above-discussed techniques may be used with a single electron source, or with a linear array of sources. For a linear array of sources, it is preferable to deflect the charged-particle beams from all the sources simultaneously and to detect secondary electrons on separate detectors corresponding to the sources. If a smaller spot size of the primary beam is needed in the above-discussed systems, lenses elongated in the slot dimension may be used to provide additional focusing. These can be of the electric “comb lens” or the magnetic “slider lens” variety. A magnetic “slider lens” is described, for example, in U.S. Pat. No. 6,633,366 to de Jager et al. Possible applications for the above-discussed techniques include, for example, electron beam inspection and electron beam lithography. In the case of electron beam inspection, the secondary electrons, the backscattered electrons, and/or the substrate current may be used as the detected signal. The wafers or other substrates being inspected may be translated in a direction perpendicular to the linear scan provided by the above-described apparatus. In other words, if the scan is along the x-dimension, the wafers or other substrates may be translated along the y-dimension. In the case of electron beam lithography, detection of the secondary electrons is not needed. The primary electron beam may be controllably blocked so as to generate a programmed pattern. In the above description, numerous specific details are given to provide a thorough understanding of embodiments of the invention. However, the above description of illustrated embodiments of the invention is not intended to be exhaustive or to limit the invention to the precise forms disclosed. One skilled in the relevant art will recognize that the invention can be practiced without one or more of the specific details, or with other methods, components, etc. In other instances, well-known structures or operations are not shown or described in detail to avoid obscuring aspects of the invention. While specific embodiments of, and examples for, the invention are described herein for illustrative purposes, various equivalent modifications are possible within the scope of the invention, as those skilled in the relevant art will recognize. These modifications can be made to the invention in light of the above detailed description. The terms used in the following claims should not be construed to limit the invention to the specific embodiments disclosed in the specification and the claims. Rather, the scope of the invention is to be determined by the following claims, which are to be construed in accordance with established doctrines of claim interpretation. |
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abstract | The invention concerns an illumination system for wavelengths less than 193 nm, especially for EUV-lithography with |
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046648747 | summary | CROSS REFERENCE TO RELATED APPLICATIONS Reference is hereby made to the following copending applications dealing with related subject matter and assigned to the assignee of the present invention: 1. "Nuclear Reactor Fuel Assembly With A Removable Top Nozzle" by John M. Shallenberger et al, assigned U.S. Ser. No. 644,758 and filed Aug. 27, 1984. 2. "Locking Tube Removal and Replacement Tool And Method In A Reconstitutable Fuel Assembly" by John M. Shallenberger et al, assigned U.S. Ser. No. 670,418 and filed Nov. 9, 1984. 3. "Top Nozzle Removal And Replacement Fixture And Method In A Reconstitutable Fuel Assembly" by John M. Shallenberger et al, assigned U.S. Ser. No. 670,729 and filed Nov. 13, 1984. 4. "Locking Tube Insertion Fixture And Method In A Reconstitutable Fuel Assembly" by John M. Shallengerger et al, assigned U.S. Ser. No. 689,696 and filed Jan. 8, 1985. 5. "Locking Tube Removal Fixture And Method In A Reconstitutable Fuel Assembly" by John M. Shallenberger et al, assigned U.S. Ser. No. 695,762 and filed Jan. 28, 1985. 6. "Reusable Locking Tube In A Reconstitutable Fuel Assembly" by John M. Shallenberger et al, assigned U.S. Ser. No. 719,108 and filed Apr. 2, 1985. BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates generally to fuel assemblies for nuclear reactors and, more particularly, is concerned with an insertion and removal fixture and method for installing and removing a reusable locking tube into and from a releasable locking position in a removable top nozzle of a reconstitutable fuel assembly. 2. Description of the Prior Art In most nuclear reactors, the reactor core is comprised of a large number of elongated fuel assemblies. Conventional designs of these fuel assemblies include a plurality of fuel rods and control rod guide thimbles held in an organized array by grids spaced along the fuel assembly length and attached to the control rod guide thimbles. Top and bottom nozzles on opposite ends of the fuel assembly are secured to the guide thimbles which extend slightly above and below the ends of the fuel rods. At the top end of the fuel assembly, the guide thimbles are attached in passageways provided in the adapter plate of the top nozzle. The guide thimbles may each include an upper sleeve for attachment to the top nozzle. During operation of such fuel assembly in a nuclear reactor, a few of the fuel rods may occasionally develop cracks along their lengths resulting primarily from internal stresses, thus establishing the possibility that fission products having radioactive characteristics may seep or otherwise pass into the primary coolant of the reactor. Such products may also be released into a flooded reactor cavity during refueling operations or into the coolant circulated through pools where the spent fuel assemblies are stored. Since the fuel rods are part of the integral assembly of guide thimbles welded to the top and bottom nozzles, it is difficult to detect and remove the failed rods. Until recently, to gain access to these rods it was necessary to remove the affected assembly from the nuclear reactor core and then break the welds which secure the nozzles to the guide thimbles. In so doing, the destructive action often renders the fuel assembly unfit for further use in the reactor because of the damage done to both both the guide thimbles and the nozzle which prohibits rewelding. In view of the high costs associated with replacing fuel assemblies, considerable interest has arisen in reconstitutable fuel assemblies in order to minimize operating and maintenance expenses. The general approach to making a fuel assembly reconstitutable is to provide it with a removable top nozzle. One reconstitutable fuel assembly construction, devised recently, is illustrated and described in the first U.S. patent application cross-referenced above. It incorporates an attaching structure for removably mounting the top nozzle on the upper ends of the control rod guide thimbles. The attaching structure includes a plurality of outer sockets defined in an adapter plate of the top nozzle, a plurality of inner sockets with each formed on the upper end of one of the guide thimbles, and a plurality of removable locking tubes inserted in the inner sockets to maintain them in locking engagement with the outer sockets. Each outer socket is in the form of a passageway through the adapter plate which has an annular groove. Each inner socket is in the form of a hollow upper end portion of the guide thimble having an annular bulge which seats in the annular groove when the guide thimble end portion is inserted in the adapter plate passageway. A plurality of elongated axial slots are provided in the guide thimble upper end portion to permit inward elastic collapse of the slotted portion so as to allow the larger bulge diameter to be inserted within and removed from the annular circumferential groove in the passageway of the adapter plate. In such manner, the inner socket of the guide thimble is inserted into and withdrawn from locking engagement with the outer socket. The locking tube is inserted from above the top nozzle into a locking position in the hollow upper end portion of the guide thimble forming the inner socket. When inserted in its locking position, the locking tube retains the bulge of the inner socket in its expanded locking engagement with the annular groove and prevents the inner socket from being moved to a compressed releasing position in which it could be withdrawn from the outer socket. In such manner, the locking tubes maintain the inner sockets in locking engagement with the outer sockets and thereby the attachment of the top nozzle on the upper ends of the guide thimbles. Furthermore, due to the vibration forces and the like, it is desirable to secure the locking tubes in their locking positions. For such purpose, suitable means, such as a pair of bulges, are formed in the upper portion of each locking tube after insertion in its locking position which bulges fit into the circumferential bulge in the upper end portion of the guide thimble. Prior to removal of the top nozzle from, and after its replacement back on, the fuel assembly, the locking tubes must be removed from and replaced back at their locking positions. Tools and fixtures for accomplishing either removal or replacement of each locking tube, either individually one at a time or all simultaneously, are illustrated and described in the second through fifth U.S. patent applications cross-referenced above. In carrying out reconstitution of the fuel assembly, it is the common practice to discard the old locking tubes having the above construction because of the presence of partially collapsed bulges thereon which are produced by deformation upon removal of the locking tubes. Then, a full complement of new locking tubes are installed on the guide thimble upper ends and secured thereon by formation of a pair of new bulges. This practice had a number of disadvantages in terms of the large inventory of locking tubes which must be maintained, the provision which must be made for disposal of discarded irradiated locking tubes, the requirement for producing new bulges in the newly installed locking tubes and the need for inspection of the new bulges. In order to substantially eliminate the above-mentioned disadvantages, a reusable locking tube as illustrated and disclosed in the sixth U.S. patent application cross-referenced above was recently originated. However, in order to fulfill the objectives of the reusable locking tube as a viable solution to the problems associated with the prior locking tube, a need does exist for means to effectively and efficiently carry out removal and replacement of the reusable locking tube from and into the top nozzle so as to enhance commercial acceptance thereof. SUMMARY OF THE INVENTION The present invention together with other components, some of which comprise the invention disclosed and claimed in the third U.S. patent application cross-referenced above, provides a system of remote-operated, submersible equipment designed to satisfy the aforementioned needs. The equipment is operable to remove and subsequently remount or replace the locking tubes and top nozzle of a reconstitutable fuel assembly, such as the one disclosed in the sixth U.S. patent application cross-referenced above, at a reactor plant. After the locking tubes and top nozzle have been removed, the upper ends of the fuel rods are exposed from the top of the reconstitutable fuel assembly. Thus, access to the fuel rods is gained for any of a variety of purposes: inspecting them for failure, removing and replacing failed rods, transferring partially spent fuel rods from one assembly to another, and/or rearrangement of fuel rods to attain better uranium utilization in the reactor core. Once inspection, removal, replacement and/or rearrangement of the fuel rods is completed, the top nozzle is placed back on the upper ends of the guide thimbles and the locking tubes replaced in their locking positions. The present invention provides a fixture and method operable to simultaneously remove and subsequently reinstall a full complement of reusable locking tubes, such as the one disclosed in the sixth cross-referenced application, into and from a releasable locking position in a removable top nozzle of a reconstitutable fuel assembly. Components of the fixture remove and replace the reusable locking tubes in a manner which provides positive locking tube engagement and disengagement. With the fixture of the present invention mounted on the removable top nozzle of an irradiated fuel assembly to be reconstituted, the locking tubes can be withdrawn from the removable top nozzle/guide thimble joints and held within the confines of the top nozzle just above the adapter plate in accurate alignment for subsequent reinsertion. Time required to accomplish either removal or replacement of all locking tubes securing a removable top nozzle after placement of the fixture onto the top nozzle is very short, approximately one to two minutes. Accordingly, the present invention sets forth for use with a reconstitutable fuel assembly including a top nozzle with an adapter plate having at least one passageway, at least one guide thimble with an upper end portion and an attaching structure having a hollow locking tube for releasably locking the upper end portion of the guide thimble within the passageway of the top nozzle adapter plate, a fixture and method for inserting and removing the locking tube into and from a locking position in the top nozzle. The fixture includes: (a) locking tube engaging means being circumferentially expandable and collapsible; (b) actuating means receivable through the locking tube engaging means and being movable between disengaged and engaged positions relative to the locking tube engaging means for causing the latter to respectively assume circumferentially collapsed and expanded conditions; (c) aligning means interconnecting the actuating means and the locking tube engaging means so as to limit movement of the actuating means along a predetermined linear path between upper and lower limits relative to the locking tube engaging means, the actuating means when located at one of the limits being disposed at its disengaged position in which the tube engaging means is caused to assume its circumferentially collapsed condition in which it is disposed away from a lower end of the locking tube, the actuating means when located at the other of the limits being disposed at its engaged position in which the tube engaging means is caused to assume its circumferentially expanded condition in which it is disposed against the lower end of the locking tube; (d) biasing means interengaging the actuating and locking tube engaging means so as to bias the actuating means for movement relative to the tube engaging means so as to dispose the actuating means at its engaged position and other limit, the biasing means being yieldable for allowing the actuating means to move relative to the tube engaging means so as to dispose the actuating means at its disengaged position and one limit; and (e) operating means supporting the actuating means and being releasably lockable on the top nozzle for disposing the actuating means and therewith the locking tube engaging means, via its interconnection by the aligning means to the actuating means, through the locking tube in the top nozzle, the operating means being operable for moving the actuating means to its disengaged position and one limit to cause the locking tube engaging means to assume the circumferentially collapsed condition for facilitating disposing of the actuating means and the tube engaging means through the locking tube, the operating means also being operable for moving the actuating means to its engaged position and other limit to cause the locking tube engaging means to assume the circumferentially expanded condition for facilitating removal of the locking tube from its locking position, the operating means further being operable when the actuating means is at its engaged position and other limit and said tube engaging means is in its circumferentially expanded condition to move the actuating means and tube engaging means together away from the top nozzle and withdraw the locking tube from its locking position. More particularly, the locking tube engaging means includes a lower traveling plate, and at least one hollow flexure tube attached to and projecting downwardly from the lower plate. The flexure tube has an axially segmented sleeve portion which terminates in a lower segmented rim, with the rim being expandable to a first outside diameter greater than an inside diameter of the locking tube and collapsible to a second outside diameter less than the inside diameter of the locking tube. The actuating means includes an upper traveling plate disposed above the lower plate, and at least one actuating rod attached to and projecting downwardly from the upper plate and through the flexure tube. The actuating rod has a shaft portion which terminates in a lower enlarged nose disposed below the segmented rim of the flexure tube such that movement of the actuating rod to its engaged position forcibly inserts its enlarged nose into the segmented rim sufficiently to expand the same to its first outside diameter size wherein the segmented rim will engage the lower end of the locking tube, whereas movement of the actuating rod to its disengaged position withdraws its enlarged nose from the segmented rim sufficiently to allow contraction of the same to its second outside diameter size wherein the segmented rim will fit through the locking tube. Further, the operating means includes a mounting plate, and a central shaft supporting the upper traveling plate from the mounting plate and being operable for moving the upper plate toward and away from the lower plate and thereby moving the actuating rod between its disengaged position and one limit and its engaged position and other limit and for moving the upper and lower traveling plates together and thereby moving the actuating rod and the flexure tube together toward and away from the locking tube in the top nozzle. Also, the aligning means is a pair of elongated pins extending between and interconnecting the mounting plate and the upper and lower traveling plates. Each of the pins has a lower element on a lower end which defines the maximum limit of movement of the upper plate away from the lower plate. The method for inserting and removing the locking tubes into and from their locking positions includes the operative steps of: (a) positioning a pair of upper and lower plates adjacent the adapter plate of the top nozzle such that a plurality of elongated flexure tubes, being attached to the lower plate and receiving a plurality of actuating rods attached to the upper plate, extend through the locking tubes; (b) moving the upper plate upwardly to a maximum displacement away from the lower plate so as to forcibly insert the enlarged lower noses of the actuating rods into the segmented lower rims of the flexure tubes sufficiently to expand the rims so that they engage the lower ends of the locking tubes; and (c) once the upper plate has been moved to its maximum displacement away from the lower plate, moving the upper and lower plates together so as to move the flexure tubes relative to the top nozzle and cause withdrawal of the locking tubes from their locking positions. The method further includes the steps of: (d) after removal and replacement of the top nozzle, positioning the upper and lower plates, being disposed at their maximum displacement away from one another, adjacent the adapter plate of the top nozzle so as to place the locking tubes engaged on the flexure tubes back into their locking positions; (e) moving the upper plate toward the lower plate so as to withdraw the enlarged lower noses of the actuating rods from the segmented lower rims of the flexure tubes sufficiently to allow contraction of the rims so that they disengage from the lower ends of the locking tubes; and (f) moving the upper and lower plates away from the top nozzle so as to withdraw the flexure tubes and actuating rods through the locking tubes. These and other advantages and attainments of the present invention will become apparent to those skilled in the art upon a reading of the following detailed description when taken in conjunction with the drawings wherein there is shown and described an illustrative embodiment of the invention. |
claims | 1. A method for treating protective products manufactured by polyvinyl alcohol (PVA) so as to treat radioactive materials attached on the PVA protective products by a dissolution-concentration tank, the method comprising:a liquid waste pyrolysis/oxidation step for pyrolyzing and oxidizing organic matter in a filtrate treated by the dissolution-concentration tank at a high temperature;a catalytic oxidation step for treating organic matter existing in an untreated gas discharged from the pyrolysis/oxidation step;an exhaust cooling step for collecting and cooling waste heat in the oxidized organic matter gas;a condensed water collecting step for collecting condensed water generated from the exhaust cooling step;anda condensed water discharging step for filtering particulates in finally discharged condensed water and discharging the condensed water to a plant liquid release system (LRS). 2. The method of claim 1, wherein the method further comprises, before the liquid waste pyrolysis/oxidation step:a dissolving/concentrating step for dissolving and concentrating the PVA protective products;a concentrate first filtering step for separating particulates existing in the PVA concentrate by a filter;anda second filtering step. 3. The method of claim 2, wherein in the concentrate first filtering step, large-size particles are removed by the filter and a pump rotating at high speed is used to sufficiently mix the organic matter with an oxidant, thereby oxidizing the PVA solution. 4. The method of claim 1, wherein in the liquid waste pyrolysis/oxidation step, a pyrolysis/oxidation reactor is operated at a temperature in order to oxidize the PVA solution. 5. The method of claim 1, wherein in the catalytic oxidation step, a catalytic oxidation reactor is operated at a temperature in order to oxidize the PVA solution. 6. The method of claim 1, wherein in the catalytic oxidation step, a catalyst comprising platinum (Pt), palladium (Pd), and alumina (Al2O3) is used. 7. An apparatus for treating PVA protective products according to the method of claim 1, the apparatus comprising:a pyrolysis/oxidation reactor for liquid waste, in which organic matter in a filtrate treated by the dissolution-concentration tank is pyrolyzed and oxidized at a high temperature;a catalytic oxidation reactor for treating organic matter existing in an untreated gas among gas treated in the pyrolysis/oxidation reactor;a heat exchanger for collecting and cooling waste heat in the oxidized organic matter gas; anda condensed water storage tank for collecting condensed water generated from the heat exchanger. 8. The method of claim 1, further comprising:a radioactivity concentration analyzing step of a PVA solution whose radioactive materials are removed, and a concentrate storing step; anda disposal step for treating a concentrated non-radioactive PVA solution. 9. The method of claim 2, wherein a multi-reactor is connected to a heater tank for heating an inside of the multi-reactor in the PVA dissolving/concentrating step. 10. The method of claim 9, wherein the heater tank heats the multi-reactor while PVA of the protective products is firstly dissolved in a solution within the multi-reactor. 11. The method of claim 10, wherein the solution comprising PVA dissolved therein is concentrated so as to minimize a generation amount of liquid-state waste to be self-disposed. 12. The method of claim 9, wherein the heater tank allows purified water whose ionic particles are removed to indirectly heat the multi-reactor via a heating jacket. 13. The method of claim 12, wherein the purified water contained in the heater tank is formed into vapor of 100-130° C. by a heater. 14. The method of claim 9, wherein in the multi-reactor, during first dissolution of PVA, hydrogen peroxide and iron salt are introduced for causing a Fenton reaction, and hydroxyl radicals generated from the Fenton reaction facilitate dissolution of PVA. 15. The method of claim 9, wherein in the multi-reactor, during first dissolution of PVA, when 70 to 95% of PVA material is dissolved, hydrogen peroxide and an iron salt solution are introduced to cause a Fenton reaction. 16. The method of claim 14, wherein the hydrogen peroxide is introduced in an amount of 0.3 to 1 LH2O2/kgPVAprotective-clothes, and the iron salt solution is introduced in an amount of 0.1 to 0.5 Liron-salt-solution/kgPVAprotective-clothes. 17. The method of claim 14, wherein the iron salt solution is formed by introducing 6.25 mL of H2SO4 and 2.18 g of FeSO47H2O in a 500 mL volumetric flask, and filling distilled water up to 500 mL of the volumetric flask, followed by a purifying process for one hour. 18. The method of claim 2, wherein in the first filtering step, a filter with a diameter of 1 to 80 μm is used to firstly remove radioactive nuclides contained in the concentrate. 19. The method claim 2, wherein in the first filtering step and the second filtering step, a filter with a diameter of 0.2 to 80 μm is used to filter the concentrate. 20. The method of claim 8, wherein the disposal step for treating the PVA solution is carried out by any one of a concentrate self-disposal process or a concentrate dried-product incineration disposal process. |
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description | FIG. 1 shows a radiation source indicated by reference number 1, and a filter which is generally indicated by reference number 2. The processing organ that is used in the apparatus for, for example, extreme ultraviolet lithography, is not shown. This processing organ is located at the side of the filter 2 facing away from the radiation source 1. The filter 2 comprises a number of plates 3 positioned in a radial direction from the radiation source 1. It is possible to position said plates in a honeycomb construction, or as a plurality of concentric cones as shown in FIG. 3. FIGS. 1 and 2 show that in the direction of radiation from the source 1, the plates are positioned such as to be evenly distributed next to one another. The proximal end 4 of the filter 2 is at a distance X from the radiation source 1, which distance is selected depending on the pressure and the type of buffer gas in which the radiation source 1, the processing organ (not shown), and also the filter 2, are placed. If the apparatus is used for extreme ultraviolet lithography, the buffer gas is preferably krypton having a pressure of 0.5 Torr, and the value of X may be 5 cm. The length of the plates of the filter is indicated by L. The value of L is selected depending on the pressure of the buffer gas and the form of the filter 2. The value of L, that is to say the length of the filter, is at least 1 cm. In FIG. 1, this value is approximately 10 cm. The thickness of the plates 3 may be, for example, 0.1 mm, and the spacing between the plates at the side nearest the radiation source 1, may be approximately 1 mm. This may result in an optical transparency of the filter 2, which is determined by the formula d d + d f xc3x97 100 xe2x80x83 % in which d=the distance between two plates of the filter at the proximal side of the filter; and df=the thickness of a plate of the filter. The effectiveness of the filter can be promoted if the surface of the plates 3 is slightly roughened. When the apparatus is used for extreme ultraviolet lithography, radiation is used having a wavelength of 13.5 nanometers. Various inert gasses may be used as buffer gas, such as helium and krypton which, compared with other gasses have the lowest absorption coefficient at this wavelength. Krypton is better able to meet the requirements of the present application because the atomic mass of krypton is more compatible with that of the atomic- and microparticles emitted by the radiation source, which augments the inhibition of said undesirable particles. The krypton gas used is maintained at a pressure of at least several mTorr. It should be noted that taken over a distance of 20 cm at a pressure of 0.5 Torr, the optical transparency of krypton for the desired radiation is approximately 90%. The filter used in the apparatus is comprised of copper plates (other materials are also possible) which have a length of 7 cm and are positioned at 2 cm from the radiation source. At a plate thickness of 0.2 mm and with the plates being spaced at approximately 0.8 mm at the side of the radiation source, the filter will have a geometrical transparency of approximately 80%. The effectiveness of the filter was measured at room temperature and at a temperature of approximately xe2x88x9290xc2x0 C. At both these temperatures the effectiveness of the filter was shown to be very high, almost 100. It will be clear to the person skilled in the art that the various dimensions of the filter forming part of the apparatus according to the invention, as well as the distance from the filter to the radiation source, has to be determined in practice on the basis of the above-mentioned inter-relating ratios. It is therefore possible to apply diverse variations to the above description, without departing from the idea of the invention as specified in the appended claims. It will be appreciated by those skilled in the art that changes could be made to the embodiments described above without departing from the broad inventive concept thereof. It is understood, therefore, that this invention is not limited to the particular embodiments disclosed, but it is intended to cover modifications within the spirit and scope of the present invention as defined by the appended claims. |
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046541853 | description | DETAILED DESCRIPTION Referring now to FIG. 1, a nuclear reactor 1 includes a pressure vessel 3, generally of cylindrical shape having an outer pressure resistant wall 5 that is closed at its bottom by a bottom wall 7 of hemispherical contour. The vessel is closed at the top by a flanged dome-shaped head 9, which is secured, such as by bolts, to the top edge 11 of the pressure resistant wall 5, preferably seated in a channel 13 about the wall 5. The pressure resistant wall 5 has a plurality of inlet nozzles 15 and a plurality of outlet nozzles 17 distributed about its periphery, with four of each of such nozzles usually provided. A nuclear core 19 is supported in the lower region of the vessel 3, the core being supported in spaced relationship to bottom wall 7 by an outer barrel 21, the outer barrel 21 having a flange 23 which rests on a ledge 25 in the inner surface of the pressure resistant wall 5. The core 19 includes a series of fuel assemblies 27 and thimbles 29 for receiving control rods (not shown), which are mounted between a lower core plate 31 and upper core plate 33. The control rods, as is known, may contain rod clusters of high or low absorption cross-section for neutrons, and water displacement rod clusters, and serve to reduce the thermal power of the reactor, or otherwise control the same, or to shut down the reactor. In the upper region of the vessel 3, the upper internals 35 and a calandria 37 are provided. The upper internals 35 include vertical guides 39 for control rods and vertical guides 41 for water displacement rods. The calandria 37 has a lower horizontal support plate 43 and an upper horizontal support plate 45, with a series of generally vertical hollow members 47 therebetween. The hollow members 47, generally of circular cross-section, are secured by welds to the upper horizontal support plate 45, and pass through the lower hollow support plate 43. The lower and upper horizontal support plates 43 and 45 are generally circular, with the hollow members 47 substantially uniformly spaced therebetween. The plates 43 and 45 are surrounded by a shell 49. The shell 49 is situated within an inner barrel 51, which inner barrel also contains the upper internals 35, that is supported by a flange 53 that rests on flange 23 of the outer barrel 21. Shell 49 also has a flange 55 about the top edge thereof which rests on flange 53 of inner barrel 51. The shell 49 has openings 57 therein which communicate with openings 59 in the inner barrel 51, which openings 59 in turn communicate with openings 61 in outer barrel 21, which finally communicate with the outlet nozzles 17. Inner barrel 51 supports the upper core plate 33 and horizontal plates 63 are provided along the inner barrel 51. The core 19, upper internals 35 and calandria 37 are mounted generally coaxially within the vessel 3, while the shell 49, inner barrel 51 and outer barrel 21 are also mounted generally coaxially therein. An annulus 65 between the outer barrel 21 and the pressure resistant wall 5 provides for communication between the inlet nozzles 15 and the lower end of the core 9. Drive rods 67 from the control rods extend through head penetrating adaptors 69 in the dome-shaped head and then through the hollow members 47 of the calandria 37. The drive rod mechanisms 71 may be contained within an enclosure formed by walls 73 and a cover (not shown), the walls welded to the outer end 75 of the dome-shaped head 9. Coolant enters through inlet nozzles 15 and flows downwardly through annulus 65 to bottom wall 7 and then upwardly through the core 19, upper internals 35 and into the calandria 37, from which it flows transversely to and outwardly from the outlet nozzles 17. Joints between the openings 57 in shell 49, openings 59 in inner barrel 51 and openings 61 in outer barrel 21 are provided to form pressure-tight seals at the outlet nozzles 17 so that there is minimal or no bypass flow of coolant from the annulus 65 directly to the outlet nozzles 17. In the arrangement described, an area of unused open space 77 is present in the dome-shaped head 9, into which some coolant will flow from the calandria 37. Because of the existence of this open space 77 long drive shafts are required, which are usually of two-piece assemblies. Since there is some flow of coolant through space 77, flow shrouds are best used to protect the drive shafts. Such flow of coolant into the space 77 also requires the use of more coolant in the reactor than would be required without the presence of such a space. Referring now to FIGS. 2 and 3, the improved deep beam head 81 of the present invention is illustrated. A calandria 37 is disposed in the upper region of the pressure vessel 3 of an improved nuclear reactor 82. The reactor 82 comprises the components of reactor 1 aforedescribed, except in the region above the inlet nozzles 15 and outlet nozzles 17, such as the upper internals 35 with control rod guides 39, displacement rod guides 41, and horizontal plates 63, above the core (not shown), all of which are supported in outer barrel 21 and inner barrel 51. The calandria 37 contains a lower horizontal support plate 43, upper horizontal support plate 45, hollow members 47, and outer shell 49. The upper support plate 45, as shown, is in the form of a sealing plate 83 which, at its outer periphery 85, rests on the top edge 11 of the pressure resistant wall 5, and seals the top opening of the pressure vessel 3. A ring member 87 is provided about the upper periphery of the sealing plate 83, and is secured to the outer pressure resistant wall 5 such as by bolts 89 which pass through apertures 91 in the ring member 87 and apertures 93 in the sealing plate 83, and are fixed in the pressure resistant wall 5, with nuts 95 securing the ring member 87, through the bolts 89, to the pressure resistant wall 5. A plurality of spaced reinforcing members 97 are provided atop of the sealing plate 83, the reinforcing members 97 extending across the sealing plate and being secured to the ring member 87 such as by welds 99. A plurality of transverse cross-members 101 atop the sealing plate 83 extend across the sealing plate 83 and are secured, as by welds 103, to the reinforcing members 97, with the end portion of said plurality of cross-members also secured to the ring member 87 by welds 105. As illustrated in the drawings, the reinforcing members 97 and transverse cross-members 101 may have a raised central portion relative to the end portions thereof to provide additional strength. The number of reinforcing members 97 and cross-members 101 used may vary dependent upon their thickness and heighth and, as indicated in FIG. 4 may extend across the sealing plate 83 between each row of drive rod mechanisms, every other row of drive rod mechanisms, or less frequently. The specific quantity of such reinforcing members and cross-members would be that sufficient to provide the resistance to pressure of the sealing member needed for a particular reactor design. For example, with a sealing plate of a thickness of about six inches, reinforcing members and cross-members of a heighth of about 12-15 inches and a thickness of about two inches could be used between every other row of drive mechanisms. An enclosure may be provided to enclose the drive rod mechanisms 71, the enclosure having vertical walls 107, with the vertical walls 107 secured by welds 109 to the ring member 87. Securing means, such as bolts 111, with the heads thereof disposed in a recess 113 in the underside of the sealing plate 83, are provided to secure the ring member 87 and sealing plate 83 together. Since the reinforcing members 97 and cross-members 101 are secured to each other and to the ring member 87, but not to the sealing plate 83, the calandria 37 is readily separable from the same by removal of the bolts 111. An O-ring 115 is also provided between the top edge 11 of the pressure vessel wall 5 and the flange 85 of the sealing plate 83 to provide a seal therebetween. Welds 117 are also used to seal the drive mechanism system to the sealing plate 83 and preclude any leakage therebetween. The incorporation of the sealing plate 83 and upper horizontal support plate 45 as a single unit provides a number of advantages. The elimination of the open space between the upper support plate of the calandria and the dome-shaped head conventionally used enables the use of simpler, shorter one piece drive rod assemblies instead of two piece drive assemblies. Also, there is no need for flow shrouds to protect the drive rods, as is generally needed where the upper open area is present with coolant passing therethrough. Alignment problems are also reduced since the calandria upper support plate with the hollow members and the mechanism pressure housing are unitary. Concerns about buckling of long drive rod assemblies during drive mechanism actuation are eliminated since shorter assemblies can be used. The construction enables the use of mechanism housings of the same length, due to removal of a dome-shaped head, resulting in economies of scale. Also, the primary coolant water volume in the reactor is reduced since no open space for primary coolant is present above the calandria between the conventional upper horizontal support plate of the calandria and the conventional dome-shaped head. Maintenance and disassembly of the reactor is improved by the present construction. The calandria, since it is secured to the ring member 87 by bolts 111 through the sealing plate 83, is removable with the vessel head, exposing the upper internals 35 of the reactor for maintenance or inspection. Also, because shorter drive rods are usable, a smaller pit for storage of the upper internals could be used. By avoiding the open space normally present between the calandria and the conventional dome-shaped head, the length of the pressure vessel 3 is reduced, which improves the strength of the same and reduces machining necessary. Also, a smaller containment vessel could be used to contain the reactor. The shorter construction would reduce the required containment and crane height. In addition, the seismic capability is improved because of the overall shorter length of the reactor and the ability to weld the vertical walls 107 of the enclosure, or internals head package shroud, directly to the ring member 87. There is thus provided a deep beam head for a nuclear reactor which, by being formed as a part of a calandria in the upper portion of the reactor, provides benefits that are not achievable when the conventional dome-shaped heads are used on such reactors. |
claims | 1. A transmission electron microscope (TEM) comprising:a high-voltage source configured to supply a high voltage to two high-voltage outputs and and to supply a control signal to a controller output, wherein the control signal is indicative of at least one of a deviation of the supplied high voltage from a reference voltage and temporal fluctuations of the supplied high voltage;an acceleration electrode configured and arranged to accelerate electrons of an electron beam to a kinetic energies corresponding to the high voltage, wherein the acceleration electrode is electrically connected to one of the two high-voltage outputs;a focusing lens configured and arranged to focus the electron beam onto a location in an object plane, wherein the focusing lens is arranged in a beam path of the electron beam system downstream of the acceleration electrode;an energy-dispersive component configured and arranged to deflect electrons of different kinetic energies differently, wherein the energy-dispersive component is arranged in the beam path downstream of the object plane;a detector arranged in the beam path downstream of the energy-dispersive component; anda controller connected to the controller output of the high-voltage source, wherein at least one of the following holds:(a) the controller is configured to control a beam deflector, which is arranged in the beam path downstream of the energy-dispersive component and upstream of the detector, such that a deflective effect of the beam deflector on the electron beam changes in dependence on the control signal supplied by the high-voltage source;(b) the controller is configured to control a monochromator, which is arranged in the beam path upstream of the focusing lens, such that only electrons of the electron beam having a kinetic energies from within an adjustable energy interval are allowed to traverse the monochtomator and such that a central energy of the energy interval changes in dependence on the control signal supplied by the high-voltage source;(c) the controller is configured to control the energy-dispersive component such that a dispersion by the energy-dispersive component changes in dependence on the control signal supplied by the high-voltage source;(d) the controller is configured to collect a plural intensity distributions detected by the detector and to accumulate the plural intensity distributions, wherein the intensity distributions are offset relative to one another by an amount which is determined in dependence on the control signal supplied by the high-voltage source; and(e) the controller is configured to control an actuator configured to displace the detector in a direction transverse to the beam path in dependence on the control signal supplied by the high-voltage source. 2. A method of operating a transmission electron microscope, the method comprising:generating a high voltage;accelerating electrons of an electron beam to a kinetic energies which correspond to the high voltage;directing the electron beam onto an object;measuring intensities of the electrons of the electron beam having interacted with the object in dependence on the kinetic energy of the electrons;detecting deviations of the generated high voltage from a reference voltage; andperforming at least one of:(a) deflecting the electron beam between the object and a detector in dependence on the detected deviations of the generated high voltage;(b) monochromatizing the electron beam such that the kinetic energies of the electrons of the electron beam are in a selected energy interval, and changing the selected energy interval in dependence on the detected deviations;(c) changing a dispersion of an energy-dispersive component traversed by the electron beam in dependence on the detected deviations;(d) repeatedly measuring intensities of the electrons of the electron beam having interacted with the object in dependence on the kinetic energies of the particles, wherein the measured intensities of plural measurements are corrected with respect to the kinetic energies of the electrons in dependence on the detected deviations and wherein the corrected intensities are accumulated to form an accumulated spectrum; and(e) displacing a detector used for measuring the intensities of the electrons relative to the object in dependence on the detected deviations. |
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044118589 | summary | BACKGROUND OF THE INVENTION This invention relates to analysis of fuel rod performance in a nuclear power plant reactor and more particularly to the monitoring of power density in a nuclear power reactor for analysis of fuel rod performance. Fuel rod failure is a costly factor in nuclear power plant operation and has created a need for the development of an on-line, fuel failure avoidance system through which (a) the state of all fuel rods is continuously monitored, (b) the data obtained by monitoring is analyzed, and (c) fuel rod failure forecasts are generated as a result of such analysis. The foregoing analysis function of such failure avoidance systems has involved the creation of a failure model from which to calculate the expected frequency of fuel failure in commercial nuclear power plant reactors. One such failure model developed is based on the concept of fuel rod failure resulting primarily from pellet-clad interaction. Experiments have shown that pellet-clad interaction failures occur either during rapid increases in power, referred to as "power shocks", or within a few hours thereafter. The power shocks produce thermal expansion, fission gas release, and shape distortion of the fuel pellets causing clad strain and longitudinal cracks in the fuel rod cladding. Pellet deformation also results in axial localization of strain at pellet joints. Other factors associated with pellet clad interaction are also believed to be responsible for fuel rod failure, but all such factors are consequences of power shocks. Accurate and continuous monitoring of fuel rod power density is therefore essential in order to enable detection of power shocks and through a failure model as aforementioned to furnish a power utility operator with the information necessary to control power distribution by control rod movement and/or coolant flow rate control in a boiling water reactor or by control rod movement and/or boron concentration control in the moderator of a pressure water reactor. The power density of the reactor has been monitored through sensors located in the fuel rod assembly. One type of sensor heretofore utilized for such purpose has been of the thermal neutron flux type. Although such neutron flux sensors provide power measurement signals that exhibit a rapid response to changes in local power density, they are unsatisfactory from two other important standpoints. First, the power measurement signal of a neutron flux sensor is not directly related to the linear heat generation rate of the fuel rod so that various calibration and correction factors must be introduced in order to approximate the rather complex relationship involved. Second, the neutron flux sensor has an emitter subject to burn-out. According to prior copending application Ser. No. 888,881, filed Mar. 21, 1978 now U.S. Pat. No. 4,298,430 owned in common with the present application, a local power density sensor is disclosed, which provides a signal output which is directly related to the linear heat generation rate for the fuel rods to enable more accurate determination of this parameter as compared to measurement by neutron flux sensors. Further, the sensor disclosed in the aforementioned prior patent is of the gamma radiation heat generating type which has no emitter subject to burn-out. However, the gamma ray sensor does not have a rapid signal response to changes in power as in the case of a neutron flux sensor which is in conflict with the requirement for real time local fuel power measurements in a fuel failure avoidance system. It is therefore an important object of the present invention to provide a method of furnishing a nuclear power utility operator with real time, yet accurate, knowledge of local fuel power rate in the reactor core to enable operation of the power plant within adequate margins with respect to those operational parameters determined from local power measurements. An additional object is to provide a power monitoring system for the fuel rods of the nuclear power reactor which benefits from the use of a gamma ray type of sensor. SUMMARY OF THE INVENTION In accordance with the present invention, a plurality of gamma ray sensors of the type disclosed in the aforementioned prior patent, provide input analog signals processed through two parallel paths to produce two separate power shape readouts that may be compared. One of the signal processing lines, generally known in the art, is of the precision type including a process computer into which various model parameters and correction factors are introduced from data storage to supply precision information to the utility operator from which fuel failure avoidance decisions may be made in the operation of the power plant. The other signal processing line directly converts the analog signals into a power readout as a function of local fuel power rates of fuel rods adjacent to the sensors by calibration of the analog signals. According to certain embodiments, both of the signal processing lines include a dynamic filter assembly through which a signal deconvolution process is performed in order to modify the readouts so as to compensate for delays caused by slow signal response of the sensors to changes in power. A continuous readout from the direct signal processing line may be compared with the precision readout of the signal processing line in parallel therewith to provide updated corrective calibration the continuous readout. The continuous readout will provide the utility operator with information necessary to avoid plant shutdown during interruptions in the precision readout arising from computer downtime caused by updating of its data storage or other causes. |
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055531067 | claims | 1. A residual stress improving method for members in reactor pressure vessel, comprising: a first step of ejecting, toward a first region in a surface of members in reactor pressure vessel submerged in reactor water, a water jet in the form of a high speed submerged water jet at temperature lower than any temperatures of said reactor water and said members in reactor pressure vessel from a nozzle to impinge against said first region in water environment; and a second step of stopping the impingement of said water jet against said first region, allowing said first region to be heated again. 2. A residual stress improving method for members in reactor pressure vessel according to claim 1, wherein said second step comprises moving said nozzle while ejecting said water jet from said nozzle such that said water jet impinges toward a second region different from said first region of members in reactor pressure vessel. 3. A residual stress improving method for members in reactor pressure vessel according to claim 1, wherein said second step comprises stopping the ejection of said water jet from said nozzle. 4. A residual stress improving method for members in reactor pressure vessel according to claim 1, 2 or 3, wherein an initial ejection speed of said water jet from said nozzle is not less than 100 m/s, but not larger than 700 m/s. 5. A residual stress improving method for members in reactor pressure vessel according to claim 1, 2 or 3, wherein an initial ejection speed of said water jet from said nozzle is not less than 200 m/s, but not larger than 400 m/s. 6. A residual stress improving method for members in reactor pressure vessel according to claim 1, 2 or 3, wherein an initial ejection speed of said water jet from said nozzle is not less than 250 m/s, but not larger than 350 m/s. 7. A residual stress improving method for members in reactor pressure vessel according to claim 1, 2 or 3, wherein a source of said water jet is low temperature water obtained by cooling said reactor water and pumping the same under pressure. 8. A residual stress improving method for members in reactor pressure vessel according to claim 1, 2 or 3, wherein a source of said water jet is low temperature water prepared outside the reactor and pumped under pressure. 9. A residual stress improving method for members in reactor pressure vessel according to claim 1, 2 or 3, wherein a source of said water jet is low temperature pure water prepared outside the reactor plant and pumped under pressure. 10. A residual stress improving method for members in reactor pressure vessel according to claim 1, 2 or 3, wherein said water jet is high speed jet water including cavitation bubbles. 11. A residual stress improving method for members in reactor pressure vessel according to claim 1, 2 or 3, wherein said nozzle is a an elbow-shaped nozzle for ejecting said high speed submerged water jet at a predetermined angle with respect to the inflow direction of high pressure water supplied to said nozzle. |
abstract | The invention comprises a semi-vertical patient positioning, alignment, and/or control method and apparatus used in conjunction with charged particle or proton beam radiation therapy of cancerous tumors. Patient positioning constraints are used to maintain the patient in a treatment position, including one or more of: a seat support, a back support, a head support, an arm support, a knee support, and a foot support. One or more of the positioning constraints are movable and/or under computer control for rapid positioning and/or immobilization of the patient. The system optionally uses an X-ray beam that lies in substantially the same path as a proton beam path of a particle beam cancer therapy system. The generated image is usable for: fine tuning body alignment relative to the proton beam path, to control the proton beam path to accurately and precisely target the tumor, and/or in system verification and validation. |
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047568666 | summary | BACKGROUND OF THE INVENTION It has been proposed to tag all commercially produced explosives with a unique material that can be easily identified. Vapor taggants of considerable cleverness have been investigated. However, they have two strikes against them, namely the required cooperation of explosives manufacturers (common to any taggant program; explosives manufacturers are particularly resistant to introducing any substance that reduces the performance or reliability of the explosive), and the ease with which the system can be circumvented by appropriately sealing the bomb. This second drawback can be circumvented if a taggant is used that can be detected by its nuclear properties, or by some other penetrating probe. I have previously suggested that explosives or detonators that have been partially deuterated are easily detected by irradiation with 4 MeV gammas. This takes advantage of the fact that deuterium has the second lowest threshold for (gamma,n), and has the additional advantage that explosive performance is not sacrificed, since deuterated X has the same chemistry as ordinary X. The estimated cost is of the order of 10 cents per detonator or stick of dynamite. This scheme is adaptable to area searches (when everyone has been evacuated), where, with the longer integration time permitted, it is possible to search a whole airplane at once. Unfortunately, all tagging schemes have the distinct disadvantage that they have no applicability to scenarios that are driven by forces of international terrorism. With almost no exceptions, all explosives current in use contain large amounts of nitrogen, typically between 20% and 35% by weight. Although there are some common articles that also contain nitrogen (animal products and some synthetics), they generally have nitrogen present in lower concentrations and being generally more spread out. A known method exploits the nuclear reaction produced by the capture of slow neutrons by nitrogen nuclei, giving off an unusually high energy (10.8 MeV) gamma ray that is easily detected by scintillation detectors. The parcel to be examined passes through a shielded enclosure in which it is subject to slow neutrons while being examined for gamma emission. In order to "see" whether the source of gamma rays is compact (a bomb) or spread out (a nylon sweater), a number of detectors are used to form a crude image of the gamma emitting object, i.e., the shape of the nitrogen-containing material. It must always be crude, since slow neutrons do not go on straight lines but diffuse through the package being examined. As additional related prior art, I discovered .sup.12 N and observed its then record-holding short half life (12 ms) in about 1949. The decay of this isotope produces back to back 511 keV annihilation radiation. Nitrogen 12, Physical Review, 1949. The reaction .sup.14 N(gamma, 2n).sup.12 N was seen by Panofsky et al. in about 1952. This reaction has received little, if any, attention since discovery in so far as I am aware. SUMMARY OF THE INVENTION This apparatus and method exploits that reaction whose cross-section includes the production of 511 keV annihilation radiation from the decay of an exceedingly short-lived isotope of nitrogen produced by irradiating ordinary nitrogen with high energy x-rays of about 40 MeV. This takes advantage of the fact that the x-ray source emanating from a microtron is a narrow beam, which can be electrically scanned over the parcel in order to image the nitrogen inside. This allows high resolution imaging of the contents of parcels by an improvement on the method of "positron emission tomography." This disclosed apparatus and method appears to make possible the determination of the mass of nitrogen in each two inch cube of the bag's volume, in two seconds, with the ability to re-examine the bag in 16 seconds, and similarly determine the mass of nitrogen in each one inch cube of the bag. If that potential can be realized, I do not see any way in which ordinary explosives could be undetected, in amounts sufficient to cause appreciable damage to a commercial aircraft. Advantages and Disadvantages The advantages of this method are: (1) Detection cannot be prevented by encapsulating, sealing, or wrapping the explosive, since detection does not depend on a sample of vapor given off by the explosive; (2) Detection cannot be prevented by shielding the explosive against neutrons or x-rays; (3) Detection does not depend on taggants that must be included when the explosive is manufactured; (4) All currently used explosives can be detected; (5) Photographic or x-ray film will not be fogged; (6) The systems are fast - as little as 1 to 2 seconds per package. The disadvantages of this method are: (1) Nitrogen is not unique to explosives, therefore compact concentrations of nitrogen (for example, a six-inch cube of nylon) will cause false alarms; (2) The apparatus is large (perhaps as large as a small room) and expensive (more than $100K); (3) Exotic nitrogen-free explosives will escape detection. |
abstract | An irradiation system includes a radiation source for providing a radiation beam at a controlled power level. A product location system provides product so that the radiation beam impinges on the product. A sensor system measures an intensity of the radiation beam that passes through the product, and a control system adjusts the power level of the radiation beam based on the intensity of the radiation beam that passes through the product. |
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061455830 | abstract | A device for inspecting the interior of steam generators capable of visually inspecting interior of tubes in steam generators, including upper portions steam generator tubes, tops and bottoms of support plates, wrapper-to-support plate welds, and other internal structures. |
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063317117 | summary | FIELD OF THE INVENTION This invention relates to lithography and more specifically to a method and apparatus for correcting variations in features formed by scanning lithography where the variations are measurable and of low frequency and are dependent on the feature's location on the substrate. BACKGROUND Lithography is a well known field and includes both electron beam and photolithography. A typical application of lithography is for defining patterns onto photo or electron sensitive resist coated on a substrate The substrate is typically a semiconductor wafer or a reticle blank for semiconductor fabrication. The lithography process defines a pattern on the resist which is then developed and used for subsequent etching or other steps. Lithography includes using a reticle (mask) in which a beam of for instance light is directed through a mask which defines the pattern in order to image the pattern onto the substrate; and also scanning where a beam, for instance of electrons or light, is directed in a raster or vector scan onto the resist. The scanned beam is turned on and off in order to expose or not expose various portions of the resist. In lithography an important goal is uniformity of each instance of an identical feature defined by the lithography process. The features are the elements imaged onto the substrate. There can be systematic variations in feature sizes that are determined by the feature's location on the substrate and which arise from a variety of causes. To simplify this description, it will refer to the feature as the critical dimension with the smallest tolerance for deviation from the designed value. Sources of such systematic variations are, for instance, imperfections in the "optical" components (optical lenses or electrostatic/electromagnetic lenses) of the lithography machine ("tool") that contribute to the intra-field uniformity of features; resist sensitivity at different positions on a substrate caused for example by inhomogeneities of the baking process which typically occurs after exposure or after the application of resist; and radial inhomogeneities from variations in resist thickness and/or induced by process steps such as resist development or chrome etching. Since it is to be understood (see above) that scanning lithography is typically used not only to fabricate semiconductor devices by direct writing, but also to fabricate the reticles used in photolithography, the problems with such variations are essentially the same in both cases. It is known that a reproducible low spatial frequency variation dependent on the substrate location in critical dimension features can be caused by the above described effects. After these low frequency "signatures" have been characterized, for instance by experimentation, it is possible to compensate for the resulting error in the image by modifying the pattern (image) data. This modifying the pattern data of course is only available in the beam write (scanning) lithography regime mentioned above, where the data is the information defining the pattern which is used to control the scanning. Unfortunately because the pattern data is generally not radially symmetric and the pattern grid (the raster or vector scan grid) is not commensurate with the systematic critical dimension variation, correction for such low frequency errors requires selecting a finer (smaller) data address grid. For a raster scan system, this causes the write times to increase proportionately to the inverse square of the ratio of the data address grids. To better explain this, consider as an example a reproducible radial variation in critical dimensions observed experimentally from the center to the edge of a mask (for use in semiconductor fabrication) which is being written, for instance, by electron beam lithography. Assume the largest differences in critical dimensions observed from the radial variation are 50 nanometers (nm) the original data address grid (spacing between pixel which define the pattern) is 30 nm and the goal is to have no more than a 10 nm radial error in critical dimension features. To meet this average error criteria, the data would have to be refractured on a 10 nm grid, with the pattern data vertices adjusted appropriately to compensate for the radial effect. Ignoring the (additionally adverse) increase in the number of geometrical figures created by the radial perturbation to the pattern data the exposure time would increase nine (30 nm/10 nm).sup.2 times due to the reduction of the data address grid size alone. In other words, it would take at least nine times longer to write such a mask given the finer address grid when compensating for a radial error. This very substantial reduction in throughput is undesirable since it increases fabrication cost proportionately. The reference to the geometrical figures is that typically physical features written on a mask are divided into a number of sub-shapes, for instance, squares, rectangles, etc. for ease of data processing. This further division would increase the number of figures required to describe all patterns which now depend on their location of the substrate. In other words, the data must be redescribed as a single pattern for the substrate. This brute force approach to overcoming the above-mentioned systematic variations is not economical and hence unsatisfactory. It would be better to compensate for such errors without refracturing the data and therefore substantially increasing the fabrication time. It is to be understood that the technical problem here expressed in terms of patterning a mask also applies to direct writing of features on a wafer or other substrate. SUMMARY In accordance with this invention, in a scanning (raster or vector) lithography tool a relatively weak intensity diffuse secondary exposure beam (typically of electrons or light) is used to modify the main scanning exposure of the target in small dose increments, dependent on the positional coordinates of the target carrying the resist to be exposed. This approach can be implemented on lithography scanning exposure tools which use either light or charged particle (e.g., electron) exposure systems and is independent of the lithography tool pattern generator architecture, that is whether it is raster or vector scan. Because the exposure from the secondary weaker intensity beam is additive to the more intense primary exposure, relative critical dimension control can be made in fine increments. The secondary exposure beam is typically Gaussian, i.e., of lower intensity at its edges than at its center. Through selection of the intensity and spot size of the secondary exposure, sub-nanometer relative critical dimension increments are possible. Because the effects to be compensated for, as described above, change slowly over the area of the target substrate, the secondary exposure can be efficiently performed at a large address grid size which is independent of the pattern address data. This secondary exposure corrects for the above-noted variations without requiring the primary exposure to be done at a smaller data address. This overcomes the above-mentioned throughput problem with the prior art brute force approach. Thus to the extent that critical dimension uniformity is critical to crevice performance and low frequency spatial errors associated with the location on the target substrate are identified as being systematic, this method efficiently compensates for these errors. This allows cost reductions for a given minimum critical dimension error. |
052251543 | summary | BACKGROUND OF THE INVENTION The present invention relates to a fuel assembly for a nuclear reactor, and more particularly to a fuel assembly structural member, made of zirconium (Zr) alloys, such as a fuel cladding tube, a spacer, a channel box or the like. Structural members of a fuel assembly for a nuclear reactor are generally made of zirconium alloy. FIG. 2 is a schematic cross-sectional view showing a fuel assembly for a BWR (boiling water reactor). The fuel assembly is composed of a number of fuel rods 1 each having fuel pellets in a cladding tube, a spacer 2 for retaining the fuel rods at a predetermined interval, a channel box 3 for encasing the fuel rods and the spacer, an upper tie plate 4 and a lower tie plate 5 for holding upper and lower ends of the fuel rods 1, and a handle 6 for transportation of the assembly as a whole. The fuel cladding tubes 11, the spacer 2 and the channel box 3 of these structural members are made of zirconium alloy and are assembled by welding. FIGS. 3 to 5 show welded portions of the fuel rods 1, the spacer 2 and the channel box 3. As shown in FIG. 3, end plugs 13 are mounted at welded portions 8 on both ends of each fuel cladding to be 11. As shown in FIGS. 4A to 4D, spacers 2 are classified into two types, i.e., a lattice type and a circular type. The welded portions 8 of the lattice type spacer 2 are joint portions between spacer bars 21 and a spacer band 22, lattice points 23 at each of which the spacer bars 21 intersect with each other, and an overlapped portion of the spacer band 22, as shown in FIGS. 4a and 4B. On the other hand, the welded portions 8 of the circular spacer are contact points of spacer rings 25, contact portions between the spacer rings 25 and a spacer band 22, and an overlapped portion of the spacer band 22, as shown in FIGS. 4C and 4D. FIG. 5 shows a shape and welded portions 8 of the channel box 3. The channel box 3 is manufactured by coupling and welding two U-shaped, bent members 31 together, so that two weld lines 8 extends longitudinally. As described above, any one of the structural members has the welded portions. The zirconium alloy members are used in the reactor water that is held at a high temperature and a high pressure. In general, the zirconium alloy has a high anti-corrosion and a small neutron absorption cross section. These properties of the zirconium alloy are suitable fuel assembly structural members for a nuclear reactor. The well known alloy are as follows: zircaloy-2 (Sn: 1.2 to 1.7%, Fe: 0.7 to 0.2%, Cr: 0.05 to 0.15%, Ni: 0.03 to 0.08, Zr: remainder); zircaloy-4 (Sn: 1.2 to 1.7%, Fe: 0.18 to 0.24%, Cr: 0.05 to 0.15%, Zr: remainder); Zr-1.0% Nb alloy; Zr-2.5% Nb alloy; Zr-3.5% Sn-0.8% Nb-0.8% Mo alloy (Excel alloy); Zr-1.0% Sn-1.0% Nb-0.2 to 0.5% Fe alloy; Zr-Nb (0.5 to 5%) Sn-(0 to 3.0%)-any one (up to 2.0%) of Fe, Ni, Cr, Ta, Pd, Mo and W; and the like. It should be noted that, in the description, by weight is represented simply by % except for the case where it is necessary to distinguish these expressions. When the so-called zircaloy, i.e., Zr-Sn-Fe-Cr-(Ni) alloy is used in a boiling water nuclear reactor, there occurs a local oxidation (hereinafter referred to as nodular corrosion). The generation of the nodular corrosion causes a thickness of normal portions of the structural member to be decreased, and at the same time, causes hydrogen generated in accordance with the corrosion reaction to be absorbed into the members, resulting in embrittlement of the members. Since the corrosion phenomenon is developed in accordance with a lapse of time, it is considered that the corrosion of the members is a factor for determining a service life of the fuel assembly under the operational condition of high degree of burn-up in which these members are used for a long period of time. Also, the hydrogen absorption of this alloy is higher than that of Zr-2.5% Nb alloy. Japanese Patent Unexamined Publication No. 58-22364 shows a heat treatment for quenching members from a temperature of .alpha.+.beta. phase or .beta. phase in order to prevent the nodular corrosion. However, even with this method, it is impossible to prevent the nodular corrosion. In a Zr-Nb alloy containing Nb, if the amount of Nb is increased, the mechanical strength is increased so that the hydrogen absorptivity is lower than that of the zircaloy. In addition, the local corrosion called "nodular corrosion" does not occur. However, as shown in "proceedings of the International Symposium on Environmental Degradation of Materials in Nuclear Power Systems Water Reactors", Myrtle Beach, S.C., August 22-25, pp. 274-294, since the corrosion property in the weld zone and heat-affected zone thereof is low, there is a problem in using the alloy for the welding structural members. Also, a ductility of the alloy is low so that the alloy is inferior in deformability against impact loads and the like. Japanese Patent Unexamined Publication No. 61-170552 shows a method for producing a plate member and a tubular member made of high corrosion resistance Zr alloy containing Nb of 0.5 to 2.0%, Sn of 1.5% or less and Fe of 0.25% or less. In order to assemble this alloy as a fuel structural member, it is necessary to weld the high corrosion resistance plate and tubular members, so that the anti-corrosion property of the weld zone will be again degraded. U.S. Pat. No. 3,121,034 shows a method for improving the weldability under the condition that a cold rolling reduction is 50 to 60% and the final heat treatment is performed at a temperature of 550.degree. to 600.degree. C. for 1 to 240 hours, by using Zr-0.5 to 5% Nb alloy, Zr-0.5 to 5% Nb-0 to 3% Sn alloy or quarternary alloy of Zr-0.5 to 5% Nb-0 to 3 Sn-0 to 2% any one of Fe, Ni, Cr, Ta, Pd, Mo and W. However, it would be difficult to perform an intensive working of several tens of percents for the weld structural member. Japanese Patent Unexamined Publication 47-28594 shows a method for improving an anti-corrosion property by annealing a Zr-Nb alloy member after welding. However, according to the disclosure of the foregoing literature, even if such a heat treatment is performed, the property of the welded portions is not improved. On the other hand, with respect to the fuel structural member of multi-layers, Japanese Patent Unexamined Publication Nos. 54-45495, 54-59660, 55-164396, 56-76088, 58-195485, 58-199836 and 58-216988 show a method in which a Zr liner layer is provided on an inner surface of a tube to thereby prevent a stress corrosion cracking due to a mutual effect between uranium dioxide and plutonium oxide pallets and the inner surface of the tube. However, this method has no effect for improving the corrosion resistance property of the outer surface of the tube. In the foregoing prior art techniques, there is no total consideration for properties needed in the structural members for fuel of high degree of burn-up, such as an corrosion resistance property of weld zone, an corrosion resistance property of non-welded portions, a tensile property, and resistivity against hydrogen embrittlement. These properties have been incompatible with each other. SUMMARY OF THE INVENTION Accordingly, an object of the invention is to provide a fuel assembly for a nuclear reactor, having structural members that are provided with sufficient properties needed in structural members for fuel of high degree of burn-up, such as an corrosion resistance property of weld zone, an corrosion resistance property of non-welded portions, a tensile property and resistance against hydrogen embrittlement. Also, another object of the invention is to provide a method for producing such a fuel assembly and members therefor. These and other objects are attained by adopting tubular members and plate members of three-layer structure having a high ductility material in an inner side and a high strength and high corrosion resistance material in an outer side for fuel structural members. According to the present invention, there is provided a fuel assembly for a nuclear reactor, comprising a fuel cladding tube of three-layer structure having an outer surface layer in contact with reactor water of a nuclear reactor which outer surface layer is made of a Zr-based alloy containing Nb, Sn and Mo, an inner surface layer in contact with nuclear fuel which inner surface layer is made of pure zirconium, and an intermediate layer made of a high ductility alloy which is higher in ductility than the outer surface layer and which is higher in strength than the inner surface layer . |
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claims | 1. Canister for transporting and/or storing radioactive materials, said canister comprising a lateral body extending around a longitudinal axis of said canister, said lateral body forming a cavity for housing radioactive materials and comprising an inner metal shell and an outer metal shell, the two shells being concentric and forming jointly an annular space inside which is housed a radiological protection device forming a barrier against gamma radiation, said radiological protection device comprising at least one first and one second metal radiological protection components adjacent along a circumferential direction of the canister,characterised in thatsaid first component is supported against the outer shell and at a distance from said inner shell, whereas said second component is supported against the inner shell and at a distance from said outer shell, andin that said first and second components are in contact with each other along an interface taking, in section along any plane orthogonal to the longitudinal axis and crossing this interface, the form of a straight line segment defining with a radial straight line crossing it at its centre an acute angle (A),wherein the first and second components are distinct, andwherein the contact force between said first and second components at the interface radially constrains the first and second components against the outer shell and inner shell, respectively. 2. Canister according to claim 1, characterised in that said angle (A) is between 30 and 60°. 3. Canister according to claim 1, characterised in that said interface is flat. 4. Canister according to claim 1, characterised in that it comprises at least one first metal radiological protection component as well as two second metal radiological protection components arranged on either side of said first component along the circumferential direction, said first component being in contact with each of the two second components along respectively two interfaces each taking, in section along any plane orthogonal to the longitudinal axis and crossing this interface, the shape of a straight line segment defining with a radial straight line crossing it at its centre an acute angle (A), the two straight line segments being respectively supported by two straight lines coming closer to each other going radially towards the interior and intercepting between the two radial straight lines. 5. Canister according to claim 1, characterised in that it comprises at least one second metal radiological protection component as well as two first metal radiological protection components arranged on either side of said second component along the circumferential direction, said second component being in contact with each of the two first components along respectively two interfaces each taking, in section along any plane orthogonal to the longitudinal axis and crossing this interface, the shape of a straight line segment defining with a radial straight line crossing it at its centre an acute angle, the two straight line segments being respectively supported by two straight lines coming closer to each other going radially towards the exterior and intercepting between the two radial straight lines. 6. Canister according to claim 1, characterised in that it comprises a plurality of first and second metal radiological protection components, laid out alternately along the circumferential direction. 7. Canister according to claim 6, characterised in thateach first radiological protection component has a section, along any plane orthogonal to the longitudinal axis, of overall trapezium shape, the large base of which is supported against the outer shell and the small base at a distance from the inner shell,in that each second radiological protection component has a section, along any plane orthogonal to the longitudinal axis, of overall trapezium shape, the large base of which is supported against the inner shell and the small base at a distance from the outer shell, andin that the faces of the first and second components defining the sides of trapeziums are in two by two contact, so as to form said interfaces. 8. Canister according to claim 7, characterised in that for each trapezium, the large base is intercepted, locally at its centre, orthogonally by a radial straight line. 9. Canister according to claim 7, characterised in that each trapezium is isosceles. 10. Canister according to claim 7, characterised in that the large base of each trapezium is straight or arc of circle shape of diameter identical to that of the shell surface that it contacts. 11. Canister according to claim 7, characterised in that for each trapezium, the ratio of lengths between the large base and the small base is between 3 and 8. 12. Canister according to claim 6, characterised in that each of said plurality of first and second components is maintained only by contacts in the annular space. 13. Canister according to claim 12, characterised in that it comprises tightening means housed in said annular space, making it possible to constrain said plurality of first and second components along the circumferential direction. 14. Canister according to claim 12, characterised in that each of said plurality of first and second components takes the form of a prism with trapezoidal base. 15. Canister according to claim 6, characterised in that each of said plurality of first components or each of said plurality of second components is assembled fixedly to its associated shell, and in that each of the plurality of other components is maintained only by contacts in the annular space. 16. Canister according to claim 15, characterised in that each of the plurality of components assembled fixedly to its associated shell has a section reducing in a given direction of the longitudinal direction (X) of the canister, and in that each of the plurality of other components has a section increasing in said given direction of the longitudinal direction. 17. Method for producing a canister according to claim 1, wherein each first and second metal radiological protection component are inserted into said annular space, then a tightening is carried out making it possible to constrain these components along the circumferential direction. |
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046438467 | description | PREFERRED EMBODIMENT OF THE INVENTION The present invention will now be described in more detail with reference to a preferred embodiment of the present invention. Referring to FIG. 1 illustrating an example of a process flow according to the present invention, radioactive sodium 2, supplied through a conduit 1 or by means of a metal drum, is stored in a sodium storage vessel 3, heated appropriately, and delivered to a sodium-mercury mixer 5 by the pressure of an inert gas which is supplied through an inert gas conduit 4. In this sodium-mercury mixer 5, the radioactive sodium heated at around 180.degree. C. and mercury 10 drawn out of the bottom of an amalgam decomposition tower or denuding tower 8, which will be described below, or purified mercury 25 supplied from a mercury purifying means 24 are mixed to form a radioactive sodium amalgam 6 containing about 0.2 to 0.3% by weight of sodium. The sodium amalgam 6 is then transported to the denuding tower 8 through a mercury pump 7 to be reacted with a trace amount of water supplied from a conduit 9, so that the sodium amalgam is decomposed to produce mercury 10 and a solution 11 containing about 50% by weight of radioactive sodium hydroxide in the bottom portion of the tower 8. An inert gas may be introduced optionally for safety through a conduit 12. The mercury 10 drawn out of the bottom of the denuding tower 8 is supplied to the sodium-mercury mixer 5 as described above. The radioactive sodium hydroxide solution 11, which is floating on the layer of the mercury 10, is tentatively stored in a storage vessel 14 through a conduit 13, and then delivered to a mixer 15 to be mixed with an appropriate amount of vitrifiable substance, e.g. glass 16 as a solidifying material. The mixture is heated in a heat-melting furnace 17, in which the sodium hydroxide solution is heat-dried and at the same time the resulting solid sodium hydroxide is confined in a vitrified body 18. The vitrified body thus obtained is then taken out of the furnace. The vitrifiable substances include, for example, silicate compounds, aluminum oxide, magnesium oxide, and mixtures thereof. A melting point depressant such as B.sub.2 O.sub.3 may be added in order to lower the melting point of these vitrifiable substances. Considering the safety in the treatment or the soundness of the vitrified body, dilution of the alkalinity of the radioactive sodium hydroxide, which is strongly alkaline, or addition of an acid to the radioactive sodium hydroxide to form a salt such as sodium nitrate, sodium sulfate, or sodium carbonate, may be conducted before the melt-solidification with the vitrifiable substance 16 to form the vitrified body 18. The vitrified body 18 may be formed by either a continuous or a batch method. The exhaust gas discharged from the heat-melting furnace 17 contains water. This water is recycled to the denuding tower 8 through a conduit 19 to be reacted with radioactive sodium amalgam as described above. The water and mercury contained in the exhaust gas discharged from the denuding tower 8 are supplied to a recovery tower 20, which is cooled with cooling water, to be separated from each other for recovery, and returned to the denduing tower 8. The exhaust gas discharged from the recovery tower 20, therefore, contains only hydrogen and a trace amount of mercury entrained with the exhaust gas. In order to deprive the exhuast gas of this trace amount of mercury, the exhaust gas is passed through a mercury removal tower 21 packed with an adsorbent, for example, a chelate resin over a certain residence time, whereby the mercury is adsorbed by the adsorbent. The exhaust gas is discharged from the mercury-removal tower 21, optionally through a HEPA filter to remove the radioactive substances, to the outer atmosphere. Since the final exhaust gas comprises hydrogen alone, the amount of the water to be supplied through the conduit 9 to the denuding tower 8 will be satisfactory if it corresponds to the amount of the exhaust hydrogen. Radioactive corrosion materials, for example, metals such as cobalt, manganese, or iron and oxides thereof, may sometimes be entrained with the radioactive sodium 2 as impurities to contaminate the radioactive sodium amalgam 6. In that case, a part of the sodium amalgam 6 containing the radioactive impurities supplied from the mercury pump 7 is delivered through a branch pipe 23 shown by a dotted line in FIG. 1 to a mercury purifying means 24 where it is heated to form vaporzied mercury and a residue containing radioactive impurities. The vaporized mercury is then supplied to the sodium-mercury mixer 5 as purified mercury 25. The impurities-containing residue is supplied through a conduit 26 and the mixer 15 into the heat-melting furnace 17, to be incorporated, for example, in the vitrified body 18 together with the radioactive sodium hydroxide supplied from the denuding tower 8. The detail of the vitrification process using glass is as described above. Plastics, cement, or other known solidifying materials can of course be used. When using these materials, sodium hydroxide is supplied from the storage vessel 14 of FIG. 1 to a neutralizing means 27 shown in FIG. 3, where the sodium hydroxide is neutralized with an appropriate amount of an acid. The sodium hydroxide thus neutralized is then supplied to an agitator 29, together with the impurities separated in the mercury purifying means 24 and transported through the conduit 26. Plastics, cement, asphalt, or other solidifying material are simultaneously supplied from a solidifying material feeder 28 to the agitator 29. The radioactive sodium hydroxide or its salt is thus filled and solidified in these solidifying materials and stored in a solidified body container 30. As understood from the above description, radioactive sodium is tentatively amalgamated and then converted into radioactive sodium hydroxide suitable for solidification in the present invention. The treatment method of the present invention is therefore advantageous in that the reaction can be very easily controlled and radioactive substances can be safely and securely treated in small facilities. Moreover, there are no fear of leakage or scattering of the radioactive sodium, because the sodium is, whether it is in the form of solution, slurry, or solid, or whether it is neutralized or converted into a salt by the addition of an acid, solidified with a solidifying material and confined in a stable solidified body. In the present invention, the mercury obtained by reacting the radioactive sodium amalgam with water is recycled to the preceding step of forming sodium amalgam, and the water contained in the exhaust gas generated during the heat-melting of the radioactive sodium hydroxide with the vitrifying material is recycled to the step of the reaction of the sodium amalgam with water. Since the material balance in the use of mercury and water as described above can be favorably adjusted in the present invention, the process can be carried out in a closed circuit. Those which are discharged outside by the method of the present invention comprise hydrogen and the solidified body alone. Thus, the amount of the water to be supplied will be sufficient if it can make up the discharged hydrogen. The radioactive corrosion materials entrained with the radioactive sodium can be simultaneously treated by the method of the present invention. The present invention thus provides a remarkably excellent method of advantageously treating radioactive sodium. It is evident that radioactive sodium can be treated by the above-described closed circuit process also in the case where cement or other solidifying materials are used in place of glass, by heat-drying the radioactive sodium hydroxide preliminarily and recycling the formed water to the denuding tower 8 through the conduit 19 in the same manner as described above. The present invention will be more readily understood by the following example. According to the process flow shown in FIG. 1, sodium amalgam was prepared it the sodium-mercury mixer 5 and reacted with water in the denuding tower 8, whereby a solution containing about 50% by weight of radioactive sodium hydroxide and mercury were obtained. The mercury was recycled to the sodium-mercury mixer 5, while the radioactive sodium hydroxide solution was heat-melted, afer an appropriate amount of silicon dioxide was added thereto, at about 1200.degree. C. in the microwave heat-melting furnace 17, yielding sodium silicate in the form of a stable vitrified body. The reaction is represented by the following formula: EQU SiO.sub.2 +2NaOH=Na.sub.2 SiO.sub.3 +H.sub.2 O The obtained vitrified body is represented by the formula: xR.sub.2 O.zSiO.sub.2.xR.sub.2 O.yRO.zSiO.sub.2, wherein R stands for B, Al, Li, Na, or other ordinary glass components elements, and x, y and z for the proportions of the respective oxide components. The water formed in the heat-melting furnace 17 was recycled to the denuding tower 8. An example of the material balance is shown in FIG. 2. As understood from the Figure, a favorable balance was realized. While the invention has been described with respect to specific embodiments, it is to be understood that variations and modification thereof may be made by those skilled in the art without departing from the scope of the invention. |
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claims | 1. A ray beam guiding apparatus, comprising:a ray beam guiding box which has substantially fan-shaped top and bottom surfaces, defines an inner space, and has open wide and narrow ends;an engaging member joined to the narrow end of the ray beam guiding box;a first collimator mounted to the ray beam guiding box adjacent to the narrow end and for adjusting a profile of the ray beam in a first direction and a second direction perpendicular to the first direction;a second collimator having a calibration slit or grill and mounted to the ray beam guiding box adjacent to the wide end;an adjusting member connecting the engaging member and a ray generator for emitting rays and for adjusting a distance between the ray generator and the ray beam guiding box;wherein the ray beam guiding box comprises:a lower box body, including:a substantially fan-shaped bottom plate,first and second side plates extending upwardly from two sides of the bottom plate and perpendicular to the bottom plate, andan extension plate portion extending from the wide end of the ray beam guiding box and lying in the same plane as that of the bottom plate, in which a detector support with a detector array is disposed on the extension plate portion; andan upper cover covering a top of the lower box body. 2. The ray beam guiding apparatus according to claim 1, wherein a ray shielding layer is disposed inside the ray beam guiding box, and a through aperture is formed at a substantial center of the ray beam guiding box so as to penetrate through the bottom plate and the upper cover. 3. The ray beam guiding apparatus according to claim 2, further comprising:a first boss disposed on the bottom plate adjacent to the narrow end, and for engaging and mounting a first calibration member having a calibration slit;a second boss disposed on the bottom plate adjacent to the wide end, and for engaging and mounting a second calibration member having a calibration slit, in which the through aperture is located between the first and second bosses and the first and second calibration members being cooperated to calibrate the ray beam emitted from the ray generator and passing through the ray beam guiding box; anda third boss disposed on the extension plate portion and for engaging the detector support and adjust a distance between the detector support and a target spot of the ray generator, wherein the detector support has a support body and a detector arm moveable with respect to the support body. 4. The ray beam guiding apparatus according to claim 3, wherein the first collimator comprises:first and second sliding stoppers which are engaged in a first slide groove formed in the ray beam guiding box, and slidable along the first slide groove in the first direction so as to adjust a first distance therebetween; andthird and forth sliding stoppers which are engaged in a second slide groove formed in the ray beam guiding box, and slidable along the second slide groove in the second direction so as to adjust a second distance therebetween. 5. The ray beam guiding apparatus according to claim 4, wherein the first collimator further comprises:a first graduator connected to the first and second sliding stoppers to adjust sliding of the first and second sliding stoppers along the first slide groove; anda second graduator connected to the third and forth sliding stoppers to adjust sliding of the third and forth sliding stoppers along the second slide groove. 6. The ray beam guiding apparatus according to claim 5, further comprising:a first adjusting screw disposed on the adjusting plate to adjust a position of the ray generator with respect to the ray beam guiding box in the first direction; anda second adjusting screw disposed on the adjusting plate to adjust a position of the ray generator with respect to the ray beam guiding box in the second direction. 7. A ray inspection system comprising the ray beam guiding box according to claim 1. |
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description | The present invention relates to a dedicated alternate injection system to mitigate the effects of a single aircraft impact on a nuclear power plant, such as but not limited to a boiling water reactor plant or a pressurized water reactor plant. Based on proposed and/or amended regulations from the Nuclear Regulatory Commission (NRC), it is desirable and/or required for nuclear power plants to have the ability to withstand the impact of a large, commercial aircraft on the plant. Nuclear power plants can include light water reactors, such as, boiling water reactors and pressurized water reactors. FIG. 1 is a sectional view of a boiling water nuclear reactor pressure vessel 10 with parts cut away to expose the interior thereof. The reactor pressure vessel 10 has a generally cylindrical shape and is closed at one end by a bottom head 12 and at its other end by a removable top head 14. A sidewall 16 extends from the bottom head 12 to the top head 14. A cylindrically shaped core shroud 20 surrounds a reactor core 22. The shroud 20 is supported at one end by a shroud support 24 and includes a removable shroud head 26 at the other end. An annulus 28 is formed between the shroud 20 and the sidewall of the vessel 16. Heat is generated within the core 22, which includes fuel bundles 36 of fissionable material. Water circulated up through the core 22 is at least partially converted to steam. Steam separators 38 separate steam from water, which is re-circulated. Residual water is removed from the steam by steam dryers 40. The steam exits the reactor pressure vessel 10 through a steam outlet 42 near the vessel top head 14 and is commonly used to drive a turbine generator for the production of electricity. The fuel bundles 36 are aligned by a lower core plate 50 located at the base of the core 22. A top guide 52 aligns the fuel bundles 36 as they are lowered into the core 22. Core plate 50 and top guide 52 are supported by the core shroud 20. The amount of heat generated in the core 22 is regulated by inserting and withdrawing control blades 44 of neutron absorbing material in a cruciform shape for BWRs (and cylindrical rods for PWRs). The control rod guide tubes 46 below the lower core plate 50, align the vertical motion of the control blades 44 during insertion and withdrawal. Hydraulic control rod drives 48, which extend through the bottom head 12, effect the insertion and withdrawal of the control blades 44. The reactor pressure vessel 10 is housed in a containment building (not shown). The containment building is constructed of several feet thick reinforced concrete and steel liner. This containment building is referred to as the primary containment. The primary containment itself is housed in a reinforced concrete structure, referred to as the secondary containment or the reactor building. The reactor building houses safety systems needed to mitigate an accident in the reactor pressure vessel. A potential means of compliance with the proposed and/or amended NRC regulations is to design and build all safety-related structures with walls and other openings which are strong enough to withstand the impact of an aircraft. Various analyses have shown that to withstand an aircraft impact, the walls would need to be several feet thicker than the existing design. The existing safety-related structures in a nuclear power plant include the secondary containment (e.g., the reactor building), the control building (e.g., the main control room) and structures that contain the safety grade water systems, such as but not limited to the service water system (e.g., service water building). Modifying these existing safety-related structures, or building new safety-related structures, to withstand an aircraft impact would be very costly. Thus, there is a need and desire to provide a means of mitigating the effects of a single commercial aircraft impact on a nuclear power plant, which is cost effective. The present invention provides a cost-effective means of mitigating the effects of a single commercial aircraft impact on a nuclear power plant which can be utilized with the current design of the safety-related systems and structures, and requires minimal or no modification to these existing systems and structures. In an aspect, the present invention provides an alternate feedwater injection system to at least partially mitigate the effects of an aircraft impact on a light water nuclear reactor. The light water nuclear reactor is positioned in a reactor building. The light water nuclear reactor includes a reactor core and a primary system. The alternate feedwater injection system includes a water storage tank, an injection point into the primary system, and a pump capable to transfer water from the water storage tank to the injection point and ultimately to the reactor core. The water storage tank, pump and injection point are located external to the reactor building and are outside of an identified aircraft impact area or are inside the identified aircraft impact area and provided with a means of protection from the aircraft impact. In another aspect, the present invention provides a suppression pool venting system for a nuclear power plant. The suppression pool venting system is located in a primary containment. The suppression pool venting system includes a primary vent system and an alternate secondary vent system. Each of the primary and secondary vent systems includes a vent path from the suppression pool to atmosphere. Each of the vent paths includes a rupture disc. The rupture disc automatically ruptures at a predetermined set point to vent the primary containment when the primary containment pressure reaches the predetermined set point. The present invention relates to an alternate feedwater injection system (AFIS) for use in a nuclear power plant. The AFIS of the present invention is operable to mitigate the effects resulting from a single commercial aircraft impact on a nuclear power plant. In such an event, the AFIS is capable to provide cooling flow to the fuel in the nuclear reactor. The AFIS is suitable for use in a variety of nuclear reactor designs. In particular, the AFIS of the present invention can be employed in light water reactors. Thus, the AFIS of the present invention can be employed in boiling water reactors (BWRs) and advanced boiling water reactors (ABWRs), and with appropriate modifications can be utilized in pressurized water reactors (PWRs) and advanced pressurized water reactors (APWRs). For ease of description, the present invention will be disclosed herein in reference to an ABWR. The AFIS is positioned in a location external to the exiting safety-related structures and outside an identified aircraft impact area. As previously indicated, safety-related structures in a nuclear power plant include secondary containment (e.g., the reactor building), control building (e.g., main control room) and safety-grade water system structures (e.g., the service water building). The reactor building houses safety systems for operation of the nuclear reactor. The main control room houses the instrumentation and controls to monitor and control operation of the nuclear reactor. The service water structure houses the cooling water circulated from an ultimate hat sink used in cooling support components. The AFIS can be located in an underground structure, such as, a bunker, or it can be in an above-ground structure. The AFIS includes piping, valves, at least one pump and a water source to supply the pump. The at least one pump, valves and associated piping can be located in a pump house. The at least one pump is operable to deliver water from the AFIS to the primary system, and ultimately to the reactor core of the nuclear power plant. The location of the AFIS is at a sufficient distance from the reactor building such that a simultaneous impact on the existing reactor building and the pump house of the AFIS is precluded. Further, the water and power sources for the AFIS pump are also located a sufficient distance from the reactor building such that a simultaneous impact on the existing reactor building and the water and power sources are precluded. The water source can be any type of container that is sized to store an adequate amount of water supply for the AFIS pump(s). In one embodiment, the water source is a demineralized water storage tank. The tank is connected to the pump by inlet piping and the pump is connected to the reactor of the nuclear power plant by discharge piping. The piping can be positioned underground or can be positioned above-ground with sufficient means of protection from the aircraft impact. The size and material of the piping can vary. In one embodiment, the piping is approximately 6 inches in diameter and is constructed of carbon steel. The injection point of the AFIS positioned at various locations in the primary system. In one embodiment, the injection point is located in the feedwater piping. Various conventional means known in the art can be used to protect the injection point from physical, fire and shock damage which could result from the aircraft impact. Water from the water source is provided to the AFIS pump and the AFIS pump is capable of injecting water into the primary system at the reactor operating pressure and with sufficient flow rate to allow the nuclear fuel in the reactor core to remain covered by water and to preclude the fuel from overheating. When the AFIS is not in use, the existing containment isolation valves in the nuclear power plant are typically sufficient to provide isolation of the AFIS. In one embodiment, check valve(s) and/or motor-operated valve(s) may be included in the AFIS piping, for example, upstream of the injection point, to isolate the AFIS when not employed. These valves are either positioned outside the predetermined/identified impact and fire zones or a protection means is employed to protect them from the aircraft impact. In an ABWR, following reactor scram, steam is generated in the reactor core due to decay heat, and the steam is discharged through existing safety relief valves (SRVs) to a suppression pool. In one embodiment, the SRV can be modified to include a normally de-energized solenoid with DC power supply from the pump house. Further, for nitrogen supply to the valve, a connection point outside the reactor building is provided to allow for use of a portable nitrogen bottle. With the addition of the DC power and nitrogen supply, the SRV can be maintained in the open position, to allow a depressurization of the reactor below the operating pressure. The discharge of steam to the suppression pool causes the temperature of the suppression pool to increase. The suppression pool is positioned in the primary containment and therefore, the decay heat is retained in the primary containment and the pressure in the primary containment will gradually increase. The primary containment pressure can be relieved by a vent system. For example, an existing rupture disc will open to discharge steam to the atmosphere to automatically relieve the pressure when the containment pressure reaches a pre-determined pressure set point. Typically, the vent system will relieve the pressure in about 24 hours after the aircraft impact. The vent path typically includes at least one isolation valve to allow termination of the steam discharge to the atmosphere, if so desired. In one embodiment, it is contemplated that the existing suppression pool vent system may be damaged by the aircraft impact and therefore, venting of the suppression pool may be restricted or precluded. In accordance with the present invention, in an embodiment wherein capability of the existing primary suppression pool vent system is restricted or precluded, an alternate secondary vent system is added for venting capability. The alternate vent system includes vent piping which is routed above-ground a sufficient distance from the installed vent system such that both vent systems would not be within the effected zone of the aircraft impact. To assure that the alternate vent system is used as a secondary vent system or as a back-up, the rupture disc set point for the alternate vent system can be at a higher pressure than the set point of the existing (e.g., primary) vent path rupture disc. Offsite radioactivity release as a result of venting is expected to be minimal. There is no expectation of fuel damage and short-lived activity is anticipated to decay in the suppression pool and the water in the suppression pool will provide scrubbing. A limited set of instrumentation is protected from the aircraft impact area which provides indication in the pump room to allow implementation of the operator actions in the event of an aircraft impact. In one embodiment, indication is also provided in the control room. These instruments are: a reactor pressure vessel water level; a reactor pressure vessel pressure; suppression pool pressure; and suppression pool water level. The instrumentation is located in the reactor building, but protected from the impact of the aircraft strike by being placed in a room which is structured to be protected from fire, shock or physical damage resulting from the aircraft impact. The power supply to the instrumentation is provided from the pump house by cables routed underground. If any portion is located above ground, it includes a protection means to protect it from fire. In the event of an aircraft impact, the operator initiates the AFIS from the pump house such that the AFIS delivers water to the injection point of the primary system to ultimately cool the nuclear fuel in the reactor core. In one embodiment, at least thirty minutes are available for the operator to initiate the injection flow. In this embodiment, it is contemplated that there would be at least limited advance warning of the approaching aircraft to allow operator actions, such as, reactor scram and dispatching of personnel to the pump house. In another embodiment, if the control of the AFIS is available in the control room, the injection flow is initiated from the control room. The pump house, pump, piping and valves, instrumentation, and alternate vent system are not required to be safety grade. The seismic design or safety classification of these structures and systems is to ensure that the addition of these structures and systems do not degrade the design of the existing safety or seismically designed systems. The power source to the pump house can be non-1E and the water source to the pump house can be non-safety. A common pump house can serve a nuclear plant site having multiple reactor units, provided that the effected zone of the aircraft impact does not include more than one reactor to the extent that multiple reactors need to rely on the AFIS to provide cooling flow. In one embodiment, an AFIS is designed to mitigate the following damage that may result from aircraft impact of a nuclear power plant: loss of all safety division cabling in the reactor building as a result of fire; loss of all instrumentation to the control room as a result of fire; loss of control room due to fire and shock; degradation of the ultimate heat sink (UHS) capacity due to physical and fire damage; loss of all 1E and non-1E power distribution due to fire spreading simultaneously in the reactor building and the turbine building; and inaccessibility of reactor and control buildings to execute post impact recovery actions due to physical damage and fire/extreme temperatures. FIG. 2 shows an alternate feedwater injection system 1 that is designed in accordance with an embodiment of the present invention to mitigate the damage from the impact of a single aircraft. In this embodiment, as shown in FIG. 2, the pump house 10 of the AFIS 1 is an above-ground structure housing a pump 20. The water source 30 for the pump 20 is a demineralized water tank which is located near the pump house 10. The pump house 10 and the water tank 30 are positioned such as to preclude simultaneous impact of the pump house 10 and the water tank 30, and the reactor building 40. In one embodiment, the pump house 10 and the water tank 30 are located behind an ultimate heat sink basin (not shown). Piping 50, from the discharge of pump 20, is routed through the reactor service water tunnel 60 to the reactor building 40 for each of a Unit A and a Unit B at a multiple-unit nuclear power plant site. Above ground, the piping 50 is routed in the steam tunnel 70 and the injection point 80 is provided through the feedwater line 90 for injection into the reactor vessel (not shown). Further, as shown in FIG. 2, a first motor-operated valve 15 is positioned in the piping 50 downstream of the pump 20 discharge, in the pump house 10. A second motor-operated valve 25 is positioned in the piping 50 located in the reactor service water tunnel 60 to control flow to the reactor. In one embodiment, the second valve 25 is located in the pump room. The power source for the pump 20 and the motor operated valves 15,25 is provided by a non-safety power supply (not shown) which is expected to remain available following the aircraft impact. A similar power supply (not shown) is provided for a second nuclear unit and can be employed as the backup power supply for the impacted nuclear unit. The preferred power supply is from the Unit A gas turbine generator bus with the back-up power supply from the Unit B gas turbine generator bus. A means can be provided for manually switching power from the one power supply to the back-up power supply. The pump 20 can be started locally from the pump house 10. In an embodiment, the pump can also be remotely started from the control room (not shown). In a further embodiment, it is contemplated that injection of water from the AFIS can be initiated within thirty minutes of an aircraft impact to prevent fuel uncovery in the reactor core (not shown). FIG. 3 shows a suppression pool venting system (SPVS) 100 in accordance with an embodiment of the present invention. The SPVS 100 is positioned in the reactor building 40. The reactor pressure vessel 110 and the suppression pool 120 are located in the primary containment 130. The primary containment 130 is located in the reactor building 40. The SPVS 100 includes an existing vent system 140 having a vent path 145 and rupture discs 150 positioned therein. One of the rupture discs 150, which is located in close proximity to the stack 158, is used to prevent debris from entering the vent path 145. The rupture discs 150 automatically fail when the pressure of the suppression pool 120 reaches a predetermined set point and the pressure of the primary containment 130 is relieved by venting steam to the stack 158 and into the atmosphere 190. The one of the rupture discs, which is located in close proximity to the stack 158, fails (i.e., blows) at a very low pressure. In addition, the existing vent path 145 includes valves 155 which are normally left open and can be utilized to terminate the vent flow to the stack 158, as desired. In addition to this existing vent system 140, the SPVS 100 also includes an alternate vent system 160. The alternate vent system 160 includes valves 170 and rupture discs 175 positioned in the alternate vent piping 180. The valves 170 are normally left open and can be utilized to terminate the vent flow, as desired. The alternate vent system 160 is capable of depressurizing the suppression pool 120 located in the primary containment 130 by discharging steam through the vent piping 180 and into the atmosphere 190. Since the alternate vent system 160 is used as a secondary vent system or as a back-up, the rupture disc set point for the rupture disc 175 may be at a higher pressure than the rupture disc set point for the rupture disc 150 in the existing (e.g., primary) vent system 140. While specific embodiments of the invention have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular embodiments disclosed are meant to be illustrative only and not limiting as to the scope of the invention which is to be given the breath of the appended claims and any and all equivalents thereof. |
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claims | 1. A method of charged particle beam processing, comprising:providing an ion beam system having a first gas supply and a second gas supply, the first and second gas supplies being selectively connected to the plasma chamber of an ion source for producing ions of a first type or ions of a second type, respectively, the ion beam system including focusing optics for forming a beam of ions extracted from the plasma chamber;selectively causing a gas from the first gas supply to enter the plasma chamber; andprocessing a work piece using a beam of ions of the first type extracted from the plasma chamber;selectively causing a gas from the second gas supply to enter the plasma chamber;processing the work piece using a beam of ions of the second type extracted from the plasma chamber, in which the work piece is not removed from the vacuum chamber and the vacuum chamber is not exposed to atmosphere between processing the work piece using the beam of ions of a first type and processing the work piece using the beam of ions of a second type. 2. The method of claim 1 in which the ion source comprises a RF-excited, impedance matched plasma chamber for receiving an ion species and extracting an ion beam from the plasma chamber. 3. The method of claim 2 in which the impedance matched plasma chamber is coupled to impedance matching circuitry that is adjustable to vary an amount of power transferred to the plasma for a particular selected ion species. 4. The method of claim 1 in which processing a work piece using a beam of ions of the first type includes directing a beam having a submicron spot size toward the work piece and in which processing a work piece using a beam of ions of the second type includes locally directing a beam having a submicron spot size toward the work piece. 5. The method of claim 1 in which processing a work piece using a beam of ions of the first type includes processing the work piece using a Gaussian shaped ion beam. 6. The method of claim 1 in which processing a work piece using a beam of ions of a first type or processing a work piece using a beam of ions of a second type includes processing the work piece by one of the following processes:depositing material using ion beam induced deposition or direct material deposition;removing material using ion beam sputtering or chemically-enhanced ion beam etching;forming an image of the work piece using ion beam imaging; oranalyzing the composition of the work piece using secondary ion mass spectroscopy. 7. The method of claim 1 in which processing a work piece using a beam of ions of a first type or processing a work piece using a beam of ions of a second type includes directing a beam of inert ions or a beam of reactive ions at the work piece. 8. The method of claim 1 in which processing a work piece using a beam of ions of the first type or processing a work piece using a beam of ions of the second type includes directing a beam of ions to deposit a material on the work piece surface. 9. The method of claim 8 in which directing a beam of ions to deposit a material on the work piece surface includes directing a beam of ions that include atoms other than those to be deposited and that decompose to deposit the atoms of the desired deposit material. 10. The method of claim 8 in which directing a beam of ions to deposit a material on the work piece surface includes directing a beam of ions that include atoms only of the material to be deposited. 11. The method of claim 1 in which processing a work piece using a beam of ions of a first type includes directing a beam comprising ions of at least two chemical compositions or in which locally processing a work piece using a beam of ions of a second type includes directing a beam comprising ions of at least two chemical compositions. 12. The method of claim 1 in which processing a work piece using a beam of ions of a first type or processing a work piece using a beam of ions of a second type includes directing a gas toward the work piece from a gas injection system, the gas comprising a precursor gas that decomposes in the presence of the ion beam to deposit a material onto the work piece surface or an etch-enhancing gas that reacts in the presence of the ion beam to remove material from the surface. 13. An ion beam system, comprising:a plurality of source gas connections for connecting multiple source gases to a vessel that encloses a region of plasma;a vessel enclosing the region of plasma;an antenna in proximity to the vessel, the antenna excited by an RF electrical source to induce ionization of the plasma;circuitry that couples the antenna to the electrical source to substantially reduce oscillations in the ionized plasma; andan extraction mechanism to extract the ionized plasma into a beam. 14. The system of claim 13, further comprising charged particle beam optics for focusing the beam into a Gaussian shape. 15. The system of claim 13, wherein the source gas connections selectively couples a source of an inert gas or a source of a reactive gas to the plasma chamber. 16. The system of claim 13, wherein the source gas connections selectively couples to the vessel a first gas used for deposition and a second gas used for etching. 17. The system of claim 13, wherein a gas coupled to the vessel comprises a source that decomposes on the work piece surface to deposit a material or a gas that combined with the material on the surface to form a volatile reaction product, thereby etching the surface, or that forms a non-volatile reaction product that remains on the surface. 18. The system of claim 13, wherein the system exhibits an energy spread that is less than about 4 eV. 19. The system of claim 13, further comprising a focusing mechanism that produces a beam of high brightness exceeding 1000 A/cm2/sr. 20. The system of claim 13, wherein an extracted beam exhibits an extracted beam energy of about 8 keV or greater. 21. The system of claim 13, wherein an extracted beam exhibits a current exceeding about 50 nano-amperes and is focused to a spot size of less than 200 nanometers. 22. The system of claim 13, wherein the beam formed from a selected gas is focused to a submicron spot size. 23. An ion beam system for treatment of a specimen, comprising:an organometallic gas coupled to a plasma chamber;a plasma chamber to which the organometallic gas is coupled;a helical antenna positioned around the plasma chamber and excited to ionize the organometallic gas within the plasma chamber;circuitry in a network comprising the antenna to impedance-match a source of excitation to the antenna; andan extraction mechanism for extracting an ionized organometallic beam for deposition of the metal of the beam onto a specimen. 24. The system of claim 23, wherein the circuitry comprises a capacitance in series with a parallel combination of a capacitance and the helical antenna. 25. The system of claim 23, wherein the organometallic gas is tungsten hexacarbonyl. 26. The system of claim 23, wherein the beam is focused to a submicron spot size. 27. A method for producing an ion beam, comprising:providing a plurality of different gas sources to be individually and sequentially selected to be coupled to a plasma chamber;providing circuitry coupled to an antenna to reduce modulation of a plasma potential;selectively coupling to the plasma chamber a first one of the plurality of different gases and then at least a second one of the plurality of gases;applying RF power to an antenna that couples energy to the selected gas within the chamber to induce ionization of a gas to produce an ion plasma; andextracting an ionized beam from a region of extraction in proximity to the antenna. 28. The method of claim 27, wherein one selected gas is used for etching and another selected gas is used for deposition. 29. The method of claim 27, wherein the circuitry is adjustable to vary an amount of power transferred to the plasma for a particular selected gas. |
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048184748 | description | For a better understanding of the invention, it is merely pointed out that the assemblies constituting the core of pressurized water nuclear reactors are essentially constituted by a framework or structure which supports and positions a bundle or group of fuel rods. The structure generally comprises a lower end fitting, an upper end fitting and intermediate grids or gratings, said components being connected by guide tubes. The latter also serve to receive mobile rods belonging to grapnels fulfilling various functions, such as the checking of the fission reaction in the reactor core. The fuel rods supported by the structure have a can, in which is located a stack of nuclear fuel pellets, the can being sealed at its ends by plugs. Generally, the pressurized water reactor assemblies have a square section and are positioned in vertically juxtaposed manner in order to form the reactor core. In order to permit the realization of the inventive control or management process, said assemblies are dismantlable. More specifically, the upper end fitting can be separated from the remainder of the structure in order to ensure the replacement of the fuel rods. Such dismantlable assemblies are known. As stated hereinbefore, assemblies of the AFA type belong to this category. However, it is also possible to use other dismantlable assembly types. According to the invention, the assemblies constituting the core of a pressurized water reactor are of two types. A first type of assembly is constituted by rods containing uranium dioxide UO.sub.2 pellets. These assemblies are identical to those presently used in most pressurized water reactors and they e.g. form approximately two thirds of the reactor core. A second type of assembly e.g. forming the final third of the reactor core uses a fuel produced by the recycling of the plutonium produced in the uranium dioxide assemblies after irradiation. More specifically, the rods of these assemblies contain mixed uranium and plutonium oxide pellets UO.sub.2 --PuO.sub.2. In order to take account of the juxtapositioning of the assemblies of both types in the reactor core and in order to prevent the formation of hot points, the mixed uranium and plutonium oxide assemblies are produced in a special way, illustrated in FIG. 1a. In order to simplify figs. 1a and 1b, no account is taken of the construction of the previously described assemblies. The hatched areas correspond to fuel rod systems all constructed in the same way within each zone and the framework or structure is not shown. Thus, each of these mixed oxide assemblies, such as assembly 10 in FIG. 1a comprises, during the initial loading of the core, several concentric zones in which the plutonium concentration of teh mixed oxide pellets contained in the rods differs. More specifically, this concentration decreases from the centre of the assembly towards its peripherary, the concentration being uniform within each zone. In the embodiment shown in exemplified manner in FIG. 1a, assembly 10 comprises three concentric zones with different plutonium concentrations. Thus, from the centre of the assembly towards its peripherary, are provided a central zone 12, an intermediate zone 14 and a peripheral zone 16. The dimensions of zones 12, 14 and 16 are determined in such a way that each of them contains the same number of rods. During the initial loading of the reactor illustrated in FIG. 1a, the central zone 12 is filled with identical new rods C.sub.1 containing mixed UO.sub.2 --PuO.sub.2 oxide pellets, whereof the plutonium concentration is higher than in zones 14 and 16. In said zone 12, the initial plutonium concentration can e.g. be approximately 4%. In the same way, the plutonium concentration of the mixed UO.sub.2 --PuO.sub.2 oxide pellets located in rods C.sub.2 filling the intermediate zone 14 is higher than the plutonium concentration of the pellets located in the rods C.sub.3 filling the peripheral zone 16. In the aforementioned example, the initial concentrations in zones 14 and 16 can be respectively close to 3% and 2%. When an irradiation cycle is ended, e.g. after approximately one year following the first loading of the core, the plutonium concentration in each of the zones 12, 14 and 16 of the mixed uranium and plutonium oxide assemblies 10 has dropped. More specifically, the plutonium concentration of rods C.sub.1 located in central zone 12 is then very close to the initial concentration in the intermediate zone 14 (approximately 3% in the aforementioned example). In the same way, the plutonium concentration of the rods C.sub.2 in intermediate zone 14 has become close to the initially existing concentration in peripheral zone 16 (approximately 2% in the present example). Finally, the plutonium concentration of rods C.sub.3 in the peripheral zone 16 has also dropped to well below its initial value. According to the invention and as is very diagrammatically illustrated in FIG. 1b, each of the mixed uranium-plutonium oxide assemblies 10 is then dismantled and the following operations are performed: discharge of rods C.sub.3 located in peripheral zone 16 (arrow F.sub.1 in FIG. 1b), PA1 transfer of rods C.sub.2 from intermediate zone 14 into peripheral zone 16 (arrow F.sub.2), PA1 transfer of rods C.sub.1 from central zone 12 into intermediate zone 14 (arrow F.sub.3), and PA1 loading of new rods C.sub.4 into central zone 12 (arrow F.sub.4). The new rods C.sub.4 introduced into the central zone 12 of assemblies 10 are all identical and contain mixed UO.sub.2 --PuO.sub.2 oxide pellets with a uniform plutonium concentration. which is identical to the plutonium concentration which initially existed in central zone 12. In the aforementioned example, said concentration is approximately 4%. It should be noted that the concentration is below the mean value of the plutonium concentrations in the rods of a mixed oxide assembly managed solely in a conventional way. Thus, in the present example, this mean value would be approximately 4.5%, whereas the plutonium concentration of rods C.sub.1 and then C.sub.4 placed in central zone 12 is approximately 4%. At the end of each irradiation cycle, the aforementioned operations are repeated. Thus, according to the invention, there is a management or control of the position of the rods within the mixed oxide assemblies 10. This is carried out in such a way that, apart from the initial loading of the reactor, a single type of rod containing mixed UO.sub.2 --PuO.sub.2 oxide pellets has to be introduced into the assemblies. Thus, there is a considerable reduction in manufacturing costs compared with a traditional management, in which there would be a complete replacement of assembly 10. Thus, throughout the life of the reactor, it would be necessary to manufacture several rod types corresponding to each of the zones of assemblies 10. Obviously, the invention is not limited to the embodiment described, in which each of the assemblies 10 is subdivided into three concentric zones. Thus, the number of zones is equal to the number of irradiation cycles undergone by the uranium dioxide assemblies. Thus, the mixed uranium-plutonium oxide assemblies can also be formed from two, or at least four concentric zones, as a function of the number of cycles. The principle of the internal management or control of these assemblies still remains the same. Thus, at the end of each cycle, the rods contained in the peripheral zone are discharged and the rods contained in the other zones are transferred towards the outside of the assembly into the zone adjacent to that which they previously occupied. The central zone, which is consequently freed, is then filled with new rods having a single plutonium enrichment. As has already been stated, the inventive management of the distribution of the rods within mixed UO.sub.2 --PuO.sub.2 oxide assemblies is added to the overall management of the assemblies within the reactor core. The principle of this overall management remains unchanged compared with that normally used in pressurized water nuclear reactors. It is merely pointed out that the invention tends to simplify this overall management, because the average properties of the mixed UO.sub.2 --PuO.sub.2 oxide assemblies constituting e.g. approximately one third of the core assemblies, evolves very little over a period of time. Thus, these assemblies are to a certain extent restored to a new state at the end of each cycle, whereas conventional uranium dioxide assemblies are only replaced after three successive irradiation cycles. The process for the management of rods within mixed oxide assemblies according to the invention also makes it possible to successively pass each of the rods into the different zones of said assemblies. Therefore, when these rods are discharged, they have a very similar irradiation. This feature makes it possible to envisage a better use of the fuel compared with the mixed oxide assemblies which would remain in the core for three successive cycles. Thus, in view of the fact that the neutron multiplication factor as a function of the plutonium content increases ever more slowly when said content rises, the plutonium concentration in the rods introduced during each cycle into the central zone of the mixed oxide assemblies is below the mean value of the concentration in a mixed oxide assembly which would remain in the core for several successive cycles. For example, if said mean value is approximately 4.5%, a concentration of close to 4% would be adequate. Finally, it should be noted that the invention makes it possible to reuse the framework of the mixed oxide assemblies for a number of cycles which is only dependent on the ageing of said framework. This feature also helps to reduce manufacturing costs. |
summary | ||
050842293 | summary | FIELD OF THE INVENTION This invention relates to an apparatus for testing a specimen under a high temperature heat transient, and more particularly, relates to such an apparatus which is capable of rapid heating and cooling rates under vacuum conditions to prevent oxidation of the specimen and/or release of entrained gases. DESCRIPTION OF THE PRIOR ART It has been important to perform rapidly repeatable heat transient tests on fuel elements for nuclear power plants. These test are used to determine the state of the fuel cells (elements), i.e., the change in the composition of a fuel element as it is used during the fission process. Typically, a sample number of fuel elements are tested from a "bank" of fuel elements loaded at the same time. In the past, a sampling of fuel elements to be tested have been removed by robot from reactor and placed into a sealed "Hot Cell" testing area. The sampling of fuel elements are then subjected to high temperatures and the gaseous materials released by the fuel elements are analyzed. Each fuel element tested is raised to a critical heat temperature, i.e., the temperature before the sample begins to change state. Once it reaches this temperature it must be rapidly cooled before it can be further handled. This has been a rather cumbersome and time consuming process which required a substantial area (floor space) of the reactor. Furthermore, the movement of the fuel elements out of the hot cell area creates a handling problem, which in and of itself adds to the time and expense of testing. What is desired is testing apparatus for testing in situ in the hot cell. An object of this invention is to provide an in situ critical heat test apparatus for fuel elements. A second object of this invention is to provide this test apparatus with a remotely controlled and powered induction flux heating furnace. A further object of this invention is to provide this test apparatus with structure to draw off the gaseous materials released when the fuel element is heated and to permit the examining of these gaseous materials at a separate location. Another object of this invention is to provide this test apparatus with a rapid temperature reduction of hot fuel elements. A still further object of this invention is to provide this apparatus with structure to permit rapid heating and cooling rates under vacuum conditions to prevent oxidation of the specimen and/or release of entrained gases. SUMMARY OF THE INVENTION The objects of this invention are realized in an in situ test apparatus for testing irradiated fuel elements and corrosion coupons within a hot cell to simulate conditions in a nuclear reactor. A specimen, which has been welded to thermocouple wires and attached to a riser clamp at its lower end and a furnace cap at its upper end, is placed by robot apparatus in a quartz heating tube located within the hot cell. A specimen riser clamp rests upon a movable metal pin which is sealed inside the quartz heating tube. The furnace cap rests on the upper portion of the tube and closes the apparatus. The quartz heating tube is coupled to an evacuation pipe having a valve which, when opened, allows access through the evacuation pipe to a vacuum pump system. All gas present in the apparatus is evacuated before the apparatus is put into use. Gaseous materials released during the test are collected by a remote apparatus which measures the fission gas collected. An induction coil around the quartz furnace tube generates heat in the specimen by electrically induced EMF energy. A remote radio frequency generator is used to provide the power to the induction wires. After the specimen has been heated for a desired time, the metal pin supporting the specimen riser clamp is magnetically removed. The specimen drops into a cooling chamber or quench chamber which is filled with water. This chamber cools the specimen. The quench chamber is supplied with water from a reservoir. The flow of water is controlled with a valve in a circulation tube connecting the reservoir and the quench chamber. Cooling water is circulated from the quench chamber by a remotely controlled circulation pump which pumps the water from the quench chamber to the reservoir. Because the specimens may be highly irradiated, all operations are capable of being performed in a hot cell by slave manipulators. A welding station and an inspection station are located with the hot cell for making up specimens. A welder power supply, temperature recorder, radio frequency generator, pump control and fission gas collection apparatus are all located outside the hot cell, being connected through the cell wall at one of four cell plugs. |
054901871 | abstract | A method for enhancing the diffusion of gas bubbles or voids attached to impurity precipitates, and biasing their direction of migration out of the host metal (or metal alloy) by applying a temperature gradient across the host metal (or metal alloy). In the preferred embodiment of the present invention, the impurity metal is insoluble in the host metal and has a melting point lower than the melting point of the host material. Also, preferably the impurity metal is lead or indium and the host metal is aluminum or a metal alloy. |
description | This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2015-028871, filed on Feb. 17, 2015, the entire contents of which are incorporated herein by reference. An embodiment of the present invention relates to a method for manufacturing a core barrel and a core barrel. In a pressure vessel of a pressurized water reactor, there is provided a core barrel (also referred to as a “reactor core tank”) holding a reactor core including a fuel assembly. The core barrel has a function to support a weight of the fuel assembly and a function to position the fuel assembly. In a conventional pressurized water reactor, the fuel assembly is placed on a lower core plate, a lower core support plate is provided under the lower core plate, and the lower core plate is attached to the lower core support plate through a lower core support column. With this configuration, the fuel assembly is supported by the lower core support plate constituting the core barrel. The above-described lower core support column is fastened to the lower core plate and the lower core support plate with bolts or the like. With this arrangement, the fuel assembly may be damaged when the bolt is broken. In order to address this issue, a structure has been conceived in which a lower core support plate and a lower core plate are integrated so that the lower core support plate has a function of the lower core plate and in which a fuel assembly is placed on the lower core support plate. FIG. 5 shows an example of a core barrel used in such a structure. A core barrel 50 shown in FIG. 5 includes a flange 51 to be attached to a reactor pressure vessel, an upper barrel 52 extending downward from the flange 51, a nozzle 53 provided on the upper barrel 52, an middle barrel 54 extending downward from the upper barrel 52, a lower barrel 55 extending downward from the middle barrel 54, the above-described lower core support plate 56 connected to the lower end part of the lower barrel 55. In the above members, the lower core support plate 56 has a placement surface 57 on which a fuel assembly is to be placed. The upper barrel 52, the middle barrel 54, and the lower barrel 55 are made, as shown in FIG. 6, by bended plate-shaped members in a cylindrical shape and by welding the bended members to one another, and on the respective curbed members, there are formed an upper barrel vertical weld line 58, an middle barrel vertical weld line 59, and a lower barrel vertical weld line 60. Further, as shown in FIG. 5, between the flange 51 and the upper barrel 52 is formed a flange circumferential weld line 61, between the upper barrel 52 and the middle barrel 54 is formed an upper barrel circumferential weld line 62, between the middle barrel 54 and the lower barrel 55 is formed an middle barrel circumferential weld line 63, and between the lower barrel 55 and the lower core support plate 56 is formed a lower core support plate circumferential weld line 64. As described above, the core barrel is made in a welded can structure. However, if the weld line is faced to the fuel assembly, radiation emitted from the fuel assembly may cause, in some cases, stress corrosion cracking, thermal embrittlement, and irradiation embrittlement. For this reason, in the form in which a fuel assembly is supported through a lower core plate and a lower core support column by a lower core support plate, a core barrel manufactured by forging is known to reduce weld lines facing the fuel assembly. In the process of manufacturing the core barrel shown in FIG. 5, first the lower core support plate 56 is machined to form the placement surface 57 and fuel alignment pin holes (not shown) in which fuel alignment pins for positioning the fuel assembly are to be inserted. Subsequently, the lower barrel 55 is welded to the lower core support plate 56. Then, the flange 51, the upper barrel 52, and the middle barrel 54 are welded to the lower barrel 55. A high accuracy is generally required in a holding position of each fuel assembly in a reactor core. Therefore, it is desirable that a flatness of the placement surface 57 of the lower core support plate 56 and the positions or the shapes of the fuel alignment pin holes should have high accuracy. However, lower core support plate circumferential weld line 64 is formed at a position close to the placement surface 57 of the lower core support plate 56. Therefore, due to influence of the welding when the lower core support plate circumferential weld line 64 is formed, it may happen that the accuracies of the flatness of the placement surface 57 or the fuel alignment pin holes which are already formed by machining cannot satisfy required values. In this case, it can be difficult to secure the accuracy of the position of each fuel assembly. A method for manufacturing a core barrel according to an embodiment is a method for manufacturing a core barrel which is to be disposed in a reactor pressure vessel of a pressurized water reactor and is to hold a reactor core including a fuel assembly. The method for manufacturing a core barrel includes the welding one end part of a short ring to a lower core support plate; and machining the lower core support plate to which the short ring is welded. The machining of the lower core support plate includes: forming a placement surface on which the fuel assembly is to be placed; and forming a fuel alignment pin hole, in which a fuel alignment pin for positioning the fuel assembly is to be inserted. After the machining of the lower core support plate, a main body barrel is welded to the other end part of the short ring, where the main body barrel covers the reactor core including the fuel assembly to be placed on the placement surface. In addition, the core barrel according to the embodiment is to be disposed in a pressure vessel of a pressurized water reactor and is to hold a reactor core including a fuel assembly. The core barrel includes: a lower core support plate having a placement surface on which the fuel assembly is to be placed and having a fuel alignment pin hole in which a fuel alignment pin for positioning the fuel assembly is to be inserted; a main body barrel which covers the reactor core including the fuel assembly to be placed on the placement surface of the lower core support plate; and a short ring one end part of which is welded to the lower core support plate and the other end part of which is welded to the main body barrel. Hereinafter, with reference to the drawings, a core barrel and a method for manufacturing a core barrel in the embodiment of the present invention will be described. First, with reference to FIG. 1, a schematic configuration of a pressurized water reactor will be described. As shown in FIG. 1, a pressurized water reactor 1 includes a reactor pressure vessel 2 in a cylindrical shape having a central axial line extending in the vertical direction (top-and-bottom direction in FIG. 1), a coolant inlet nozzle 3 and a coolant outlet nozzle 4 provided in the reactor pressure vessel 2, and a core barrel 20 disposed in the reactor pressure vessel 2. Of the above components, on the core barrel 20 is provided a nozzle 34, and the nozzle 34 communicates with the coolant outlet nozzle 4 so that mixing with coolant flowing from the coolant inlet nozzle 3 is prevented. The core barrel 20 contains and holds a reactor core 5 including a fuel assembly 5a. The core barrel 20 has a lower core support plate 21 to be described later, and the fuel assembly 5a of the reactor core 5 is placed on the lower core support plate 21. Coolant flows from a pipe (not shown) outside the reactor pressure vessel 2 through the coolant inlet nozzle 3 into the reactor pressure vessel 2. The coolant having flown in flows downward in a down corner 6 formed between a side wall of the reactor pressure vessel 2 and the core barrel 20, and the direction of the flow is changed to upward by a flow skirt 7 provided in the lower part of the reactor pressure vessel 2. Then the coolant flows through the flow holes 24 (see FIG. 3) of the lower core support plate 21 into the reactor core 5. The coolant having flown into the reactor core 5 cools the fuel, so that the temperature of the coolant is raised; and the coolant flows from the reactor core 5 and flows through the nozzle 34 and the coolant outlet nozzle 4 out to a pipe (not shown) outside the reactor pressure vessel 2. In the upper part of the reactor pressure vessel 2, there is disposed a control rod drive mechanism 8, and control rods can be inserted into the reactor core 5 so as to control the output of the reactor and stop the reaction in the reactor at a time of emergency. Further, in the upper part of the reactor pressure vessel 2, there is disposed an lower core support plate 9, and the reactor core 5 is held from above. Next, with reference to FIG. 2, the core barrel 20 in the present embodiment will be described. As shown in FIG. 2, the core barrel 20 has the lower core support plate 21 on which the fuel assembly 5a is to be placed, and a main body barrel 30 which covers the reactor core 5 including the fuel assembly 5a to be placed on the lower core support plate 21. Of the above components, the lower core support plate 21 is made of a plate-shaped member, and the main body barrel 30 (each barrel to be described later) is made by members in a cylindrical shape, for example, by bended plate-shaped members into a cylindrical shape and by welding the members to one another. As shown in FIG. 2 and FIG. 3, the lower core support plate 21 has: a placement surface 22 on which the fuel assembly 5a is to be placed; fuel alignment pin holes 23 in which fuel alignment pins 10 for positioning the fuel assembly 5a; and the flow holes 24 through which the coolant flows. The placement surface 22, the fuel alignment pin holes 23, and the flow holes 24 are formed when the lower core support plate 21 is machined. Further, on the outer side, in the radial direction, of the placement surface 22, there is provided a junction part 25 to which a lower end part of a short ring 37 to be described later is welded. The main body barrel 30 has: a flange 31 which is to be attached to the reactor pressure vessel 2; an upper barrel 32 extending downward from the flange 31; and a lower barrel 33 extending downward from the upper barrel 32. Of the above components, on the upper barrel 32, the nozzle 34 is provided. The flange 31, the upper barrel 32, and the lower barrel 33 are welded to one another; between the flange 31 and the upper barrel 32, there is formed a flange circumferential weld line 35; and between the upper barrel 32 and the lower barrel 33, there is formed an upper barrel circumferential weld line 36. The lower core support plate 21 and the lower barrel 33 are coupled through the short ring 37. More specifically, one end part of the short ring 37 (lower end part) is welded at the junction part 25 of the lower core support plate 21, and the other end part (upper end part) of the short ring 37 is welded to the lower barrel 33. Between the lower core support plate 21 and the short ring 37, there is formed a lower core support plate circumferential weld line 38, and between the short ring 37 and the lower barrel 33, there is formed a lower barrel circumferential weld line 39. The short ring 37 according to the present embodiment is formed in a ring shape having an axial direction length (length in the top-and-bottom direction in FIG. 2) shorter than the lower barrel 33, and the term “short ring” are used to represent a ring having such an axial direction length that the lower core support plate 21 can be machined after the short ring 37 is welded to the lower core support plate 21. More specifically, the short ring 37 preferably has such an axial direction length that a tool of a machining device can reach the lower core support plate 21 from an opening 40 in the upper end part of the short ring 37 after the short ring 37 is welded to the lower core support plate 21 and that the lower core support plate 21 can be machined with an intended accuracy. Such an axial direction length of the short ring 37 is preferably about 300 mm, for example. With this arrangement, it is possible to perform accurately, with the common machining device, a machining process by extending the tool to the lower core support plate 21 through the opening 40 in the upper end part of the short ring 37. In addition, since the axial direction length of the short ring 37 is made to be about 300 mm, the lower barrel circumferential weld line 39 can be located away from the lower core support plate 21, and it is possible to prevent or reduce deformation of the lower core support plate 21 when the short ring 37 and the lower barrel 33 are welded to each other or when the lower barrel circumferential weld line 39 is subjected to a heat treatment. Next, an operation of the above configured present embodiment will be described. Here, a method for manufacturing the core barrel 20 will be described. First, the lower end part of the short ring 37 is welded to the junction part 25 of the lower core support plate 21 (step S1). In this case, bevels (not shown) are formed on the lower end part of the short ring 37 at the junction part 25 of the lower core support plate 21, and welding is performed with the lower end part of the short ring 37 at the junction part 25 of the lower core support plate 21 butted against each other. By this process, the lower core support plate circumferential weld line 38 is formed. Subsequently, the formed lower core support plate circumferential weld line 38 is subjected to a dimensional stabilization heat treatment (step S2). This treatment releases a residual stress in the lower core support plate circumferential weld line 38. Note that the dimensional stabilization heat treatment may be performed in a method commonly performed as a heat treatment after welding. Next, the lower core support plate 21 is machined to form the placement surface 22, the fuel alignment pin holes 23, and the flow holes 24 (step S3). In this step, the lower core support plate 21 and the short ring 37 are fully machined to form the placement surface 22, the fuel alignment pin holes 23, and the flow holes 24 in final forms with intended accuracies. Since the residual stress in the lower core support plate circumferential weld line 38 is already released by the dimensional stabilization heat treatment in the above-described step S2, release of residual stress due to the machining process is prevented or reduced in step S3. With this arrangement, the accuracy of the machining process is successfully improved. Note that the machining process can be performed by using a machining device having a tool which reaches the lower core support plate 21 from the opening 40 in the upper end part of the short ring 37. In addition, the final shapes mean a situation in which the lower core support plate 21 and the short ring 37 are in the same shapes as when the core barrel 20 is completed. Next, the lower barrel 33 of the main body barrel 30 which covers the reactor core 5 is welded to the upper end part of the short ring 37 (step S4). More specifically, bevels (not shown) are formed on the lower end part of the lower barrel 33 and the upper end part of the short ring 37, and welding is performed with the lower end part of the lower barrel 33 and the upper end part of the short ring 37 butted against each other. By this process, the lower barrel circumferential weld line 39 is formed. In this step, since the lower barrel circumferential weld line 39 is formed at a position away from the lower core support plate 21, deformation of the lower core support plate 21 due to the welding of the lower barrel 33 and the short ring 37 can be prevented or reduced. After that, the formed lower barrel circumferential weld line 39 is subjected to a dimensional stabilization heat treatment (step S5). This treatment releases a residual stress in the lower barrel circumferential weld line 39. In this step, since the residual stress in the lower core support plate circumferential weld line 38 has been released in the above step S2, deformation of the lower core support plate 21 can be prevented or reduced at the time of the heat treatment in step S5. In addition, since the lower barrel circumferential weld line 39 is formed at a position away from the lower core support plate 21 as described above, deformation of the lower core support plate 21 due to the dimensional stabilization heat treatment of the lower barrel circumferential weld line 39 can be prevented or reduced. Note that the process of welding the flange 31 and the upper barrel 32 to each other and the process of welding the upper barrel 32 and the lower barrel 33 to each other may be performed in step S5, or may be performed before or after step S5. In any of the cases, the formed flange circumferential weld line 35 and upper barrel circumferential weld line 36 are preferably subjected to a dimensional stabilization heat treatment similar to the above steps S2 and S5. As described above, according to the present embodiment, since the lower core support plate 21 to which the lower end part of the short ring 37 is welded is machined, the placement surface 22 on which the fuel assembly 5a is to be placed and the fuel alignment pin holes 23 in which the fuel alignment pins 10 for positioning the fuel assembly 5a are inserted are formed in the lower core support plate 21, and the lower barrel 33 of the main body barrel 30 is then welded to the upper end part of the short ring 37. Thus, it is possible to locate the lower barrel circumferential weld line 39, which is to be formed after the placement surface 22 and the fuel alignment pin holes 23 are formed by machining, away from the lower core support plate 21. Therefore, it is possible to prevent or reduce deformation of the lower core support plate 21 due to the welding after the machining of the lower core support plate 21. As a result, it is possible to improve the shape accuracy of the lower core support plate 21, on which the fuel assembly 5a is to be placed, whereby the positional accuracy of the fuel assembly 5a can be improved. Further, according to the present embodiment, the core barrel 20 can be made by welding a plate-shaped member as the lower core support plate 21 to members in a cylindrical shape such as the short ring 37 and the main body barrel 30. Thus, it is possible to manufacture the core barrel 20 at a lower cost than by a forging process. Further, according to the present embodiment, after the lower core support plate circumferential weld line 38 formed between the short ring 37 and the lower core support plate 21 is subjected to a heat treatment, the lower core support plate 21 is subjected to a machining process. Thus, it is possible to release a residual stress in the lower core support plate circumferential weld line 38 before the lower core support plate 21 is subjected to the machining process. Therefore, it is prevented that the stress is released when the lower core support plate 21 is subjected to the machining process, whereby the accuracy of the machining process can be improved. With the above-described embodiment, it is possible to improve the shape accuracy of the lower core support plate, on which the fuel assembly is to be placed, whereby it is possible to improve the positional accuracy of the fuel assembly. While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions. |
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abstract | A new radiography method which utilizes contrast enhancement mechanisms with highly collimated X-ray beams without optics to achieve high imaging resolution and improve the time resolution is disclosed. This invention includes irradiating the object with an unmonochromatized beam, specifically highly collimated synchrotron radiation, and detecting an unmonochromatized beam image after the unmonochromatized beam has passed through the object. With compact design, a system for imaging an object with very high resolution, X-ray radiography with a wide range of X-ray sources, such as synchrotron radiation, without any sophisticated X-ray optics is also disclosed. This invention may achieve real-time images with micrometer resolution. |
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description | This invention relates generally to CT imaging systems, and more particularly to methods and apparatus for reducing a radiation dose applied to an object or person being imaged. In some known CT imaging system configurations, an x-ray source projects a fan-shaped beam which is collimated to lie within an X-Y plane of a Cartesian coordinate system and generally referred to as an “imaging plane”. The x-ray beam passes through an object being imaged, such as a patient. The beam, after being attenuated by the object, impinges upon an array of radiation detectors. The intensity of the attenuated radiation beam received at the detector array is dependent upon the attenuation of an x-ray beam by the object. Each detector element of the array produces a separate electrical signal that is a measurement of the beam intensity at the detector location. The intensity measurements from all the detectors are acquired separately to produce a transmission profile. In third generation CT systems, the x-ray source and the detector array are rotated with a gantry within the imaging plane and around the object to be imaged such that the angle at which the x-ray beam intersects the object constantly changes. A group of x-ray attenuation measurements, i.e., projection data, from the detector array at one gantry angle is referred to as a “view”. A “scan” of the object comprises a set of views made at different gantry angles, or view angles, during one revolution of the x-ray source and detector. In an axial scan, the projection data is processed to construct an image that corresponds to a two-dimensional slice taken through the object. One method for reconstructing an image from a set of projection data is referred to in the art as the filtered backprojection technique. This process converts the attenuation measurements from a scan into integers called “CT numbers” or “Hounsfield units” (HU), which are used to control the brightness of a corresponding pixel on a cathode ray tube display. To reduce the total scan time, a “helical” scan may be performed. To perform a “helical” scan, the patient is moved while the data for the prescribed number of slices is acquired. Such a system generates a single helix from a fan beam helical scan. The helix mapped out by the fan beam yields projection data from which images in each prescribed slice may be reconstructed. Reconstruction algorithms for helical scanning typically use helical weighing algorithms that weight the collected data as a function of view angle and detector channel index. Specifically, prior to a filtered backprojection process, the data is weighted according to a helical weighing factor, which is a function of both the gantry angle and detector angle. The weighted data is then processed to generate CT numbers and to construct an image that corresponds to a two-dimensional slice taken through the object. To further reduce the total acquisition time, multi-slice CT has been introduced. In multi-slice CT, multiple rows of projection data are acquired simultaneously at any time instant. When combined with helical scan mode, the system generates a single helix of cone beam projection data. Similar to the single slice helical, weighting scheme, a method can be derived to multiply the weight with the projection data prior to the filtered backprojection algorithm. Significant dose reduction can be achieved by using a bowtie filter to shape the intensity profile of the x-ray beam in the X-axis. Also, different shaped bowties can be advantageously used. For example, one shape can be used for the head or a small body, yet another shape for a pediatric head and another shape for a large body or flat. A large selection of shapes would be useful to best fit each patient and patient anatomy. However, manufacturing an imaging system with a large number of bowtie filters can significantly increase the overall cost of the imaging system because of the volume required to accommodate and move each of the filters. The present invention, in one aspect, therefore provides a filter assembly for a computed tomographic imaging system. The filter assembly includes first and second endplates at opposite ends of the filter assembly. Also provided is a first moveable subassembly that includes at least a first x-ray filter and which is configured to move along an axis perpendicular to the first endplate between the first the second endplates. A second moveable subassembly is also provided that includes at least a second x-ray filter. The second moveable subassembly is configured to move along an axis perpendicular to the second endplate between the first and second endplates. The first moveable subassembly and the second moveable subassembly are independently movable to provide at least a small bowtie x-ray filter, a large bowtie x-ray filter, a medium bowtie x-ray filter, a flat filter, and a closed position for a radiation source positioned in a fixed position relative to the filter assembly. In another aspect, the present invention provides a computed tomographic (CT) imaging system. The CT imaging system includes a rotatable gantry having a gantry opening and an x-ray filter assembly on the rotatable gantry. The CT imaging system also includes a radiation source configured to direct a fan beam of radiation towards an object in the gantry opening through the x-ray filter assembly and a detector array on the rotatable gantry configured to acquire projection data representative of radiation passing through the object. The CT imaging system is configured to reconstruct an image of the object utilizing the acquired projection data. Also, the filter assembly further includes first and second endplates at opposite ends of the filter assembly. Also provided is a first moveable subassembly that includes at least a first x-ray filter and which is configured to move along an axis perpendicular to the first endplate between the first the second endplates. A second moveable subassembly is also provided that includes at least a second x-ray filter. The second moveable subassembly is configured to move along an axis perpendicular to the second endplate between the first and second endplates. The first moveable subassembly and the second moveable subassembly are independently movable to provide at least a small bowtie x-ray filter, a large bowtie x-ray filter, a medium bowtie x-ray filter, a flat filter, and a closed position for a radiation source positioned in a fixed position relative to the filter assembly. In yet another aspect, the present invention provides a method for filtering a radiation source of a computed tomographic (CT) imaging system for scanning a region of an object using the CT imaging system. The method includes passing a fan beam of the radiation source between first and second endplates at opposite ends of a filter assembly. The filter assembly has a first moveable subassembly that includes at least a first x-ray filter configured to move along an axis perpendicular to the first endplate and the fan beam between the first and second endplates. The filter assembly also has a second moveable subassembly comprising at least a second x-ray filter configured to move along an axis perpendicular to the second endplate and the fan beam between the first and second endplates. The method further includes moving at least one of the first moveable subassembly or the second moveable subassembly to interpose a small bowtie x-ray filter, a large bowtie x-ray filter, a medium bowtie x-ray filter, a flat filter, or a closed position between the radiation source and the object. Significant dose reduction is achievable by using bowtie filters to shape the intensity profile of the x-ray beam in the X-axis of a CT imaging system. It will be appreciated that configurations of the present invention advantageously accommodate multiple bowtie filters within a given volume. These filters can be accommodated economically and, in at least some CT configurations, without significant configuration changes. Various configurations of the present invention not only accommodate multiple filter configurations but also provide the ability to conveniently change filter configurations. As used herein, an element or step recited in the singular and proceeded with the word “a” or “an” should be understood as not excluding plural said elements or steps, unless such exclusion is explicitly recited. Furthermore, references to “one embodiment” of the present invention are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features. Also as used herein, the phrase “reconstructing an image” is not intended to exclude embodiments of the present invention in which data representing an image is generated but a viewable image is not. However, many embodiments generate (or are configured to generate) at least one viewable image. Referring to FIGS. 1 and 2, a multi-slice scanning imaging system, for example, a Computed Tomography (CT) imaging system 10, is shown as including a gantry 12 representative of a “third generation” CT imaging system. Gantry 12 has a radiation source 14 (such as an x-ray tube, which is also called an x-ray source herein) that projects a beam of radiation, such as x-rays 16, toward a detector array 18 on the opposite side of gantry 12. Detector array 18 is formed by a plurality of detector rows (not shown) including a plurality of detector elements 20 which together sense the projected x-rays that pass through an object, such as a medical patient 22 between array 18 and source 14. Each detector element 20 produces an electrical signal that represents the intensity of an impinging x-ray beam and hence can be used to estimate the attenuation of the beam as it passes through object or patient 22. During a scan to acquire x-ray projection data, gantry 12 and the components mounted therein rotate about a center of rotation 24. FIG. 2 shows only a single row of detector elements 20 (i.e., a detector row). However, multi-slice detector array 18 includes a plurality of parallel detector rows of detector elements 20 such that projection data corresponding to a plurality of quasi-parallel or parallel slices can be acquired simultaneously during a scan. Rotation of components on gantry 12 and the operation of x-ray source 14 are governed by a control mechanism 26 of CT system 10. Control mechanism 26 includes an x-ray controller 28 that provides power and timing signals to x-ray source 14 and a gantry motor controller 30 that controls the rotational speed and position of components on gantry 12. A data acquisition system (DAS) 32 in control mechanism 26 samples analog data from detector elements 20 and converts the data to digital signals for subsequent processing. An image reconstructor 34 receives sampled and digitized x-ray data from DAS 32 and performs high-speed image reconstruction. The reconstructed image is applied as an input to a computer 36, which stores the image in a storage device 38. Image reconstructor 34 can be specialized hardware or computer programs executing on computer 36. Computer 36 also receives commands and scanning parameters from an operator via console 40 that has a keyboard. An associated cathode ray tube display 42 (or any other suitable type of display, such as a liquid crystal display or plasma display) allows the operator to observe the reconstructed image and other data from computer 36. The operator supplied commands and parameters are used by computer 36 to provide control signals and information to DAS 32, x-ray controller 28, and gantry motor controller 30. In addition, computer 36 operates a table motor controller 44, which controls a motorized table 46 to position patient 22 in gantry 12. Particularly, table 46 moves portions of patient 22 through gantry opening 48. In one embodiment, computer 36 includes a device 50, for example, a floppy disk drive, CD-ROM drive, DVD drive, magnetic optical disk (MOD) device, or any other digital device including a network connecting device such as an Ethernet device for reading instructions and/or data from a computer-readable medium 52, such as a floppy disk, a CD-ROM, a DVD or another digital source such as a network or the Internet, as well as yet to be developed digital means. In another embodiment, computer 36 executes instructions stored in firmware (not shown). Computer 36 is programmed to perform functions described herein, and as used herein, the term computer is not limited to just those integrated circuits referred to in the art as computers, but broadly refers to computers, processors, microcontrollers, microcomputers, programmable logic controllers, application specific integrated circuits, and other programmable circuits, and these terms are used interchangeably herein. Although the specific embodiment mentioned above refers to a third generation CT system, the methods described herein equally apply to fourth generation CT systems (stationary detector-rotating x-ray source) and fifth generation CT systems (stationary detector and x-ray source). Additionally, it is contemplated that the benefits of the invention accrue to imaging modalities other than CT. Additionally, although the herein described methods and apparatus are described in a medical setting, it is contemplated that the benefits of the invention accrue to non-medical imaging systems such as those systems typically employed in an industrial setting or a transportation setting, such as, for example, but not limited to, a baggage scanning system for an airport or other transportation center. In some configurations of the present invention and referring to FIG. 3, a filter assembly 100 is provided in an efficient packaging design to provide multiple “bowtie” filters shapes and profiles. Filter assembly 100 includes a first endplate 102 and a second endplate 104 at opposite ends of filter assembly 100. Also included are a first moveable subassembly 106 that includes at least a first x-ray filter 108. First moveable subassembly 106 is configured (for example, in a manner described in more detail below) to move along an axis z perpendicular to first endplate 102 and in a region between first endplate 102 and second endplate 104. Similarly, second moveable subassembly 110 includes at least a second x-ray filter 112. Second moveable subassembly 110 is configured (for example, in a manner similar to that of first moveable subassembly 106) to move along an axis z (e.g., the same axis z as subassembly 106) perpendicular to second endplate 104. Second moveable subassembly 110 is also configured to move in a region between first endplate 102 and second endplate 104. First and second moveable subassemblies 106 and 110 are not required to move through the entire region between endplates 102 and 104, and in fact, the ranges of movement of subassemblies 106 and 110 are each limited in some configurations. In some configurations, subassemblies 106 and 110 are independently moveable to provide a plurality of filters, depending upon which of subassemblies 106 or 110, or both, is positioned within x-ray beam 16. In some configurations, first moveable subassembly 106 and second moveable subassembly 110 are independently moveable to provide at least a small bowtie x-ray filter 108, a large bowtie x-ray filter 114, a medium bowtie x-ray filter 112, a flat filter 118, and a closed position 120. All of these filters are provided for radiation source 14, which is positioned in a fixed position relative to filter assembly 100. Also in some configurations, first moveable subassembly 106 includes a small bowtie filter 108 and a large bowtie filter 114, and second moveable subassembly 110 includes a medium bowtie filter 112. Also, at least one flat filter 118 is configurable (for example, by movement of one or more of subassemblies 106 or 110) to overlap a portion of one of bowtie filters 108 and 114 of first moveable subassembly 106 in at least one position in a range of movement of first moveable subassembly 106 and second moveable subassembly 110. In some configurations, filter assembly 100 includes flat filter 118 and a second flat filter 122. In an exemplary embodiment, second flat filter 122 is a titanium plate, and flat filter plate 118 is a tungsten plate. The one or more bowtie filters 108, 114 of first moveable subassembly 106 can comprise a combination of aluminum and graphite machined parts and copper. The one or more bowtie filters 112 of second moveable subassembly 110 can comprise aluminum and graphite machined parts. To move subassemblies 106 and 110, some configurations of the present invention provide a first stepper motor 130 with a lead screw drive 132 that is configured to move first moveable subassembly 106 and a second stepper motor 134 with a lead screw drive 136 that is configured to move second movable subassembly 110. Hollow tubing 138, 140, such as hollow metal tubing, is provided between first endplate 102 and second endplate 104. Wires or cables 142, 144 are run inside the hollow tubing to carry electrical signals to at least one of stepper motors 130 or 134. One or more position encoders 146, 148 can be provided in some configurations with a feedback control (which can be provided, for example, by computer 36 or by a separate feedback control, not shown in the figures) to provide a home position reference and position feedback. Wires or cables for position encoders 146 and 148 can also be run through hollow tubing 138, 140. It will thus be recognized that a plurality of bowtie shapes and filters are available using filter assembly 100. In some configurations and referring to FIG. 8, filter assembly 100 is fitted into a base assembly 200, which is mounted on gantry 12. X-ray tube 14 produces an x-ray beam that passes through opening 202 to form a fan beam 16, which is further shaped by filter assembly 100 before passing out an opposite side of base assembly 202 and into gantry opening 48. By moving first moveable subassembly 106 and/or second moveable subassembly 110 into various positions, a plurality of bowtie and other filter shapes can be imparted to fan beam 16. For example, and referring to FIG. 5, a closed position 120 is provided in which flat plate 118 is interposed in front of x-ray fan beam 16, completely blocking x-rays from reaching an object 22. This position is useful, for example, during x-ray tube warm up. In some configurations and referring to FIG. 9, an air position is provided into which first subassembly 106 and second subassembly 110 can be moved so that a clear path is provided through gap 150 in filter assembly 100 for x-ray beam 16. In yet another position and referring to FIG. 10, small bowtie filter 108 is interposed in the x-ray path. A patient's head can advantageously be imaged in this position, for example. In some configurations, in the position shown in FIG. 10, flat filter 118 overlaps large filter 114 to advantageously permit assembly 100 to provide a plurality of filter positions in a restricted volume allocated for assembly 100. In yet another position and referring to FIG. 11, large filter 114 is interposed in the x-ray path. This position can advantageously be used for imaging entire bodies, for example. In still another position and referring to FIG. 12, flat filter 118 is interposed in the x-ray path, represented as gap 152 in FIG. 12. This position can advantageously be used for imaging a large body, for example. In yet another position and referring to FIG. 13, a medium bowtie filter 112 is interposed in the x-ray path. This position can advantageously be used in pediatric imaging, for example. In some configurations, in this position, flat filter 118 also overlaps large filter 114. Stepper motors 130 and 134 with lead screws 132 and 136, respectively, are used to drive the filters. A filter home switch (not shown in the Figures) is used to provide an absolute position reference and/or a home position reference. Incremental encoders 146 and 148 are used for position feedback. Lead nuts 170, which are pressed into or otherwise affixed on or into first subassembly 106 and second subassembly 110 also form part of the drive mechanisms. The use of flat strips of titanium and tungsten for the large body (flat) filter and closed position rather than an aluminum and graphite combination helps to define an overlap, as shown in FIGS. 6 and 7. The use of separate motors 130, 134 and encoders 146, 148 as part of the drive mechanism poses a challenge for cable routing. Because a printed circuit collimator control board is located close to a filter subassembly in some configurations, wires or cables 142 and 144 are routed back to front out of the X-Ray beam using, for example, stainless steel tubes 138 and 140. These tubes are used (in some configurations, in addition to other hardware 180) to connect endplates 102 and 104 to one another as well as for cable routing. (Additional hardware 180 also serves as a rail on which subassemblies 106 and 110 are guided in their movement.) Tubing 138 and 140 is positioned away from the x-ray beam to ensure that no artifacts are generated. Subassemblies 106 and 110 can be moved independently of one another or simultaneously to reduce or minimize filter positioning time. In some configurations of the present invention, filter assembly 100 is used in an imaging system 10 having a rotatable gantry 12 having a gantry opening 48. X-ray filter assembly 100 is mounted on rotatable gantry 12. Radiation source 14 is configured to direct a fan beam 16 of radiation towards an object or patient 22 in gantry opening 48 through x-ray filter assembly 100. Detector array 18 is on rotatable gantry 12 and is configured to acquire projection data representative of radiation passing through object 22, and imaging system 10 is configured to reconstruct an imaging of object 22 using the acquired projection data. In some configurations, a method for filtering a radiation source 14 of a computed tomographic (CT) imaging system for scanning a region of an object 22 using a CT imaging system 10. The method includes passing a fan beam 16 of the radiation source between first and second endplates 102 and 104 of a filter assembly 100. Filter assembly 100 has a first moveable subassembly 106 comprising at least a first x-ray filter 108 configured to move along an axis z perpendicular to first endplate 102 and also perpendicular to a plane of fan beam 16 between first and second endplates 102 and 104. Filter assembly 100 also has a second moveable subassembly 110 comprising at least a second x-ray filter 112 configured to move along an axis z perpendicular to second endplate 104 and a plane of fan beam 16 between first and second endplates 102 and 104. The method further comprises moving at least one of first moveable subassembly 106 or second moveable subassembly 110 to interpose a small bowtie x-ray filter, a large bowtie x-ray filter, a medium bowtie x-ray filter, a flat filter, or a closed position between the radiation source and the object. In some configurations, the method further comprises overlapping at least one flat filter on the second moveable subassembly over a portion of a bowtie filter of the first moveable subassembly. It will be appreciated that configurations of the present invention facilitate compact packaging of a plurality of filters. Moreover, filters are interchangeable with a minimum of design changes. Also, configurations of the present invention are easy to implement and cost effective. While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims. |
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046831045 | claims | 1. Device for the inspection of fuel rods combined into fuel rod bundles in a fuel element of a nuclear reactor, comprising a frame for supporting a fuel element including a base plate, a cover plate and four supports in the form of four first leadscrew drive mechanisms, two mutually parallel second leadscrew drive mechanisms attached to and extending transversely to said first leadscrew drive mechanism, a third leadscrew drive mechanism jointly supported by and extending transversely to said second leadscrew drive mechanism, and an accessory carrier mechanism disposed on said third leadscrew drive mechanism and movable in a plurality of levels for entering gaps between fuel rods of the fuel element. 2. Device according to claim 1, wherein each of said leadscrew drive mechanism includes a respective support plate attached to another of said mechanisms. 3. Device according to claim 1, wherein said first leadscrew drive mechanisms each have an end surface and a motor having a flange, said cover plate being held between said end faces and said flanges. |
summary | ||
claims | 1. A method of repairing a shroud support, comprising the steps of:setting each of support apparatuses on each upper end of a plurality of control rod drive mechanism housings attached to a bottom of a reactor pressure vessel, in said reactor pressure vessel;positioning horizontally a rail guide member rotatably attached to each of said support apparatus by rotating said rail guide member in an axial direction of said reactor pressure vessel;setting a rail on each of said rail guide members;moving each of said rails, which include said rail on which said repair device is set and said rail on which said repair device is not set, toward an inner surface of said reactor pressure vessel along each said rail guide member, said rails setting on each of said rail guide members;setting a plurality of said moved rails along a weld of said shroud support in a reactor pressure vessel over either an entire perimeter on an inner circumference of said reactor pressure vessel or a part of said entire perimeter; andperforming repair operation of said weld of said shroud support by a repair device that is moved along said plurality of rails set along said weld of said shroud support. 2. The method of repairing a shroud support according to claim 1, wherein said setting of said rails comprises the steps of:setting a support base on each upper end of said part of said plurality of control rod drive mechanism housings;performing said set of said support apparatus by setting said support apparatus on said support base; setting a rail push-out apparatus on each of said support apparatuses; andperforming the movement of each of said rails by pushing out each of said rails by each of said set rail push-out apparatuses, said repair device being set on said rail positioning below said weld of said shroud support. 3. The method of repairing a shroud support according to claim 1, wherein said repair operation is performed under an air atmosphere. 4. The method of repairing a shroud support according to claim 1 further comprising the steps of:attaching support arms to each of support apparatuses;performing said set of each of said rails by setting a bent rail on each of said rail guide members;performing said movement of each of said rails by moving each of said bent rails, which include said bent rail on which said repair device is set and said bent rail on which said repair device is not set, toward an inner surface of said reactor pressure vessel along each said rail guide member;spreading each of said bent rails; andsupporting each of said spread rails by said support arms attached to each of said support apparatuses. 5. The method of repairing a shroud support according to claim 4, wherein said setting of said rails comprises the steps of:setting a rail push-out apparatus on each of said support apparatuses;performing the movement of each of said rails by pushing out each of said rails by each of said set rail push-out apparatuses, said repair device being set on said rail positioning below said weld of said shroud support; andperforming said spreading of said bent rail by an upward curvature formed on top of each of said support arms when said bent rail is moved by said rail push-out apparatus. |
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058870440 | description | DETAILED DESCRIPTION OF THE INVENTION Zirconium was selected to be alloyed with the Pu because of the fabrication, reprocessing, and irradiation experience obtained thus far with U--Pu--Zr fuel. Zirconium is the component of the U--Pu--Zr fuel alloy that raises the alloy solidus temperature and provides resistance against fuel cladding chemical interaction (FCCI) and dimensional stability during irradiation (see G. L. Hofman and L. C. Walters, "Metallic Fast Reactor Fuels" in Materials Science and Technology, vol. 10A, pp. 1-43. Furthermore, the IFR pyrochemical reprocessing scheme was developed for U--Pu--Zr fuel and, thus, can accommodate Pu and Zr fuel constituents (see J. P. Ackerman, "Chemical Basis for Pyrochemical Reprocessing of Nuclear Fuel,". I&EC Research, 29, (1991), pp. 141-145). The composition of the Pu--Zr fuel alloy was determined on the basis of desired alloy solidus and liquidus temperatures. The solidus temperature of Pu--28Zr is approximately 1090.degree. C., which is above the peak 2.sigma. fuel temperature for an off-normal event in a PRISM-like ALMR. PRISM is a proposed commercial ALMR design that utilizes the IFR metal fuel cycle disclosed in 1988 in Seattle, Wash. (R. C. Berglund, F. E. Tippets, L. N. Salerno, "PRISM, A Safe, Economic, and Testable Liquid Metal Fast Breeder Reactor Plant," Proc. Int'l Topical Meeting on Safety of Next Generation Power Reactors). The liquidus temperature must be sufficiently low to facilitate injection casting of fuel slugs; the Pu--28Zr liquidus temperature of approximately 1325.degree. C. meets this criterion. Eliminating U-238 from a fast reactor removes the component of U--Pu--Zr fuel that provides most of the negative doppler reactivity feedback and neutron absorption necessary for maintaining a sufficiently low burnup swing. Therefore, in addition to Zr, it is desirable to alloy with an element which will act as a neutron poison and compensate for these neutronic effects. Hafnium (Hf) has a large resonance capture cross-section and in the fuel system will: 1) alloy well with Pu--Zr because it is chemically similar to Zr; PA1 2) provide negative Doppler reactivity feedback which otherwise decreases to nearly zero when the U-238 is removed from a metal-fueled core; PA1 3) act as a fixed absorber requiring a higher plutonium inventory in the core. Because the plutonium destruction rate is fixed by the thermal power of the core, this should lead to a smaller burnup reactivity loss rate. Hf can be incorporated into the fuel alloy, perhaps replacing some of the Zr in Pu--28Zr, and/or in a sheath that surrounds the Pu--Zr fuel slug. Incorporating Hf in the fuel alloy will provide a better coupling between the Hf Doppler feedback and fuel temperatures than would be obtained with Hf present only in the sheath. Hf and Zr have essentially the same atomic radii and very similar chemical behavior. The thermal conductivities of the two elements are essentially the same and the heat capacities are nearly the same. Therefore, the two elements should have similar effects on thermophysical properties of the fuel alloy. In addition, Hf and Zr have similar free energies of formation for many compounds (e.g. the tetrachlorides), so the two elements should behave similarly in the pyrochemical reprocessing scheme. The addition of Hf to the Pu--Zr alloy should not significantly alter the thermophysical properties of the base alloy. The Pu--Zr and Pu--Hf phase diagrams shown in FIGS. 1(a) and 1(b) indicate that the two alloy systems contain similar phases at the Pu-rich end. However, as the composition of Pu decreases, the .alpha.-to-.beta. (or .alpha..sub.Zr -to.sub.-.epsilon. in the Pu--Zr system) temperatures and the liquidus temperatures are higher in the Pu--Hf system than in the Pu--Zr system because the corresponding temperatures are higher for Hf than for Zr. Similarly, a Pu--28(Zr, Hf) alloy should have a higher liquidus temperature than Pu--28Zr, which will raise the temperature required for injection casting. Also, note that solubility of Hf in Pu (10 at. % in the .delta. and .epsilon. phases) is much less than that of Zr (up to 70 at. % in .delta.-Pu and totally miscible in .epsilon.-Pu). Because of this, Hf is not able to raise the solidus temperature of Pu--Hf as can Zr in Pu--Zr. Thus, the solidus temperature in Pu--Hf is 765.degree. C. or less. Therefore, a Pu--Zr--Hf fuel alloy requires sufficient Zr to maintain the alloy solidus temperature at an acceptable value. Although this invention uses Pu--28(Zr, Hf) for purposes of illustration, the invention extends to other compositions also. Determining the amounts of Hf to be placed in the fuel alloy will require consideration of the Hf/Pu atom ratio required for desirable reactor performance, acceptable casting conditions, phase equilibria at operating temperatures, and alloy solidus temperatures. To estimate the thermal conductivity, enthalpy and specific heat of Pu--28Zr, experimental data for the thermal conductivity of a variety of U--Zr alloys and for the Pu-1 wt % Al alloy were used. These data are shown in FIG. 2. The Pu--1Al alloy is delta phase-stabilized, as is expected for the Pu--28Zr alloy. The atomic radii of Zr and Al are very similar, so the thermal conductivity of Pu--1Zr was assumed to be equivalent with increasing Zr content for the U--Zr alloy and was used to extrapolate the thermal conductivity of Pu--1Zr to Pu--28Zr; This projected thermal conductivity for Pu--28Zr is shown as the lowest curve in FIG. 2. Also shown in FIG. 2 is the known thermal conductivity of the ternary alloy U--15Pu--7Zr. The thermal conductivity of U--15Pu--7Zr is similar to, but greater than, the conductivity of U--20Pu--10Zr which is routinely irradiated in EBR-II. The projected thermal conductivity of Pu--28Zr is roughly half of that of U--15Pu--7Zr at 600.degree. C. While low for a metallic fuel alloy, initial calculations of thermal performance indicate this fuel thermal conductivity would be acceptable. The specific heat of Pu--28Zr is needed for evaluating transient behavior of the fuel. Because no data on the thermodynamic properties of Pu--28Zr are available, the enthalpy of Pu--28Zr as a function of temperature was estimated to yield an estimate of the specific heat. The Pu--28Zr alloy was assumed to be an ideal solution, and the enthalpy of the solution was computed as the mole-fraction-weighted sum of the elemental molar enthalpies of Pu and Zr obtained from the literature. Thermodynamic data generated in this manner retains phase transition discontinuities present in the elemental specific heats that will likely not exist at different temperatures. When this procedure was applied to the estimation of the specific heat of Pu--28Zr, the calculated specific heat was fairly constant, varying from 32.1 to 34.8 J/mol-K over 375.degree. to 1075.degree. C. This specific heat is similar to that of the U--Zr alloys reported in the literature. The density of Pu--28Zr can be estimated by multiplying the reported densities of .delta.-Pu (15.9 g/cm.sup.3) and .alpha.-Zr (6.5 g/cm.sup.3) by the respective atom fractions and summing, resulting in a value of 11.2 g/cm.sup.3. The same method results in a value of 10.3 g/cm.sup.3 for Pu--36Zr (Pu-60 at . % Zr), which agrees with a reported measured value. Hardness measurements for rolled Pu--36Zr are much less (at .about.100 DPH) than for homogenized U--20Pu--10Zr (at .about.420 DPH). The softness of the Pu--Zr alloy was attributed to the retained .delta. (FCC) phase. Because the Pu--Zr alloy is so much softer than U--Pu--Zr, it should have much less tensile strength--at least at lower temperatures. Mechanical properties at fuel operating temperatures will be more similar. Data concerning the irradiation performance of Pu--Zr is scarce, but the general fuel performance of the Pu--Zr alloy can be inferred from experience with other metallic fuel alloys. Heavily cold-rolled specimens made of Zr-5 wt. % Pu and Zr-7 wt. % Pu were shown to have poor dimensional stability (length changes of 200-500%) under irradiation to 1.3 at . % burnup at temperatures of 410.degree.-530.degree. C. However, the microstructure of those specimens indicated they existed as a solid solution of Pu in .alpha.-Zr; thus, the specimens had a hexagonal close-packed crystal structure. The high amount of cold work and the anisotropic structure (inducing preferred grain orientation) are likely reasons for the dimensional instability of these alloys under irradiation. An as-cast Pu--28Zr fuel slug will exist in a non-equilibrium (at room temperature) FCC .delta. phase. Upon heating to reactor temperatures, the Pu--Zr phase diagram (FIG. 1a) indicates that the .delta. phase and the BCC .epsilon. phase of Pu and the BCC .beta. phase of Zr) will become stable; thus the fuel will consist mainly of symmetric (cubic) phases. Such fuel will not contain the preferred orientation present in heavily cold rolled .alpha.-phase samples, so dimensional instability in Pu--28Zr fuel slugs is not expected. Reported swelling measurements of Zr-40 at . % Pu made after irradiation to 0.83 at . % burnup indicate that Pu--Zr irradiated in the delta phase is relatively stable. Reported examination of irradiated U--Pu--Zr has revealed radial regions that are depleted and enriched in Zr as compared to the as-cast composition. If Zr depleted fuel material contacts cladding material, then enhanced interdiffusion of fuel and cladding constituents may result. In addition, fuel regions enriched in Pu may experience locally high power density and, thus, locally high temperatures; a reduction in Zr would also lower the solidus temperature in that region of the fuel, reducing the margin to onset of fuel melting. According to the model presently used to explain this behavior, differences in Zr solubility (along the temperature gradient) in the matrix phase of multi-phase zones provide the driving force for Zr migration into the .gamma. phase region in the center of the fuel pin, see D. L. Porter, C. E. Lahm, and R. G. Pahl, "Fuel Constituent Redistribution during the Early Stages of U--Pu--Zr Irradiation," Met. Trans. A. 21A, (1990), pp. 1871-1876. The phase diagram in FIG. 1a shows that Pu--28Zr will have no such multi-phase zones (except for, perhaps, a very small region of .epsilon.+.delta.), so the current model would predict no Pu or Zr migration. The Pu--Hf phase diagram (FIG. 1b) also indicates that, in accordance with the current model as discussed above, Pu--Hf alloys are vulnerable to Hf migration which could lead to Pu-enriched regions of the fuel. The .delta. and .epsilon. phases of Pu--Hf form the matrix for Hf compositions less than about 50 at. %, and these phases have increasing solubility of Hf with temperature. Thus, a Hf concentration (i.e. activity) gradient is established across the radius of the fuel element after it attains operating temperatures. It is believed that Hf would diffuse down the concentration gradient, dissolving .alpha.-Hf in the higher temperature portion of the matrix phase and precipitating .alpha.-Hf in the lower temperature portion. This would deplete the high temperature region of the fuel slug (the center) of Hf and enrich the low temperature region. Should it be found that Hf does migrate radially, but Zr does not, then the retained Zr in the Hf-depleted regions will maintain a sufficiently high solidus temperature. The design of the proposed fuel element was guided by three important criteria. First, the dimensions of the fuel element should resemble those of the reference ALMR U--Pu--Zr fuel as much as possible. Second, the Pu content of the proposed fuel element should be similar to that of the reference. Third, fabrication techniques for the Pu-burning fuel elements should be very similar to those for the reference elements. Meeting these criteria will facilitate conversion of an ALMR from a conventional fuel design to that of a pure burner or vice versa. As discussed, Pu--Zr--Hf must contain enough dissolved Zr to maintain a high solidus temperature. Thus, Hf cannot displace a large amount of Zr from the base Pu--28Zr alloy, nor can it displace much Pu if the fuel is to maintain power densities similar to those of U--Pu--Zr fuels. To incorporate additional Hf into the fuel element, a Hf--Zr sheath around the fuel alloy is proposed, see FIG. 3. The Pu--Zr (or Pu--Zr--Hf) fuel alloy 10 is injection cast into Hf--Zr molds 15 that will remain intact with the fuel slug 10. The sheathed-fuel will eliminate disposable quartz mold waste and should reduce axial fuel swelling to values less than would be obtained with unsheathed fuel, reducing that component of the burnup reactivity swing during a reactor cycle. The molds 15 are separated from the cladding 20 by an alkali metal 25, such as Na. By way of example, the fuel slug 10 may have an inner core O.D. of 0.127 inches or an outer core O.D. of 0.139". The sheath/mold may have an O.D. of 0.216" and inner core I.D. of 0.127" and outer core I.D. of 0.139". The fuel slug 10 may be Pu--28Zr % or Pu--28(Zr, Hf) or other alloys of Pu, Zr and Hf. Generally Hf should be present in an amount not greater than 10% by weight of the combined amount of Pu, Zr, Hf in the fuel and sheath combined. Alternatively, the fuel slug 10 can be Pu, Zr and the sheath 15 can be Hf--Zr, where Hf may be 74 wt % and Zr 26 wt %. The actual sheath inner diameter (or fuel slug outer diameter) and Hf contents of the fuel and sheath will be determined from neutronics calculations known to those of ordinary skill in this art that determine the Hf/Pu atom ratio necessary for desirable reactor performance. The sheath outer diameter and cladding 20 inner diameter shown were selected to retain the same radial plenum as conventional IFR fuel elements (which typically have a 75% smeared fuel density); this amount of radial clearance between fuel and cladding can sufficiently accommodate fuel swelling in U--Zr and U--Pu--Zr alloys. HT9, the reference cladding for the IFR concept, is the recommended cladding material of stainless steel. HT9 has excellent swelling resistance and has exhibited good performance characteristics with U--Pu--Zr fuels. Moreover, a large performance database applicable to fast-reactor environments already exists. The fuel can be fabricated using techniques that are currently used in the production of EBR-II fuel with remotely operated equipment similar to that which has been built for the fuel cycle demonstration in the IFR program. The fuel alloy could be melted in a vacuum induction furnace and injection cast into tubes of the Hf--Zr alloy sealed at one end. The sheathed fuel slug 10, 15 will then be sheared to length and sealed in the HT9 cladding 20 along with sodium 25 used to provide a thermal bond between fuel and cladding. Experience has shown that casting into Zr molds requires melt temperatures less than 1500.degree. C., so the fuel alloy liquidus temperatures must be at least 150.degree. C. below that point (i.e. about 500.degree. C. below the melting or solidus temperature of the sheath material) to allow for superheating of the melt. The Hf--Zr phase diagram indicates that the liquidus temperature of Hf--26Zr is approximately 200.degree. C. higher than the melting temperature of Zr, so additional margin is attained by including Hf in the sheath material. The Pu--28Zr liquidus temperature of approximately 1325.degree. C. is sufficiently low to preclude problems with casting into Hf--Zr molds. The fuel alloy Hf content that can be successfully cast into a Hf--Zr mold will depend on the solidus temperature of the mold material and thus on the Hf content in the Hf--Zr alloy. Based on the estimated thermal properties of the Pu--28Zr fuel alloy, a thermal analysis was performed for a fuel element design similar to that shown in FIG. 3. The dimensions are similar to those expected in an ALMR, except that the fuel is the standard EBR-II length of 34.3 cm (13.5 in). The fuel element is from a 37-pin experimental subassembly to be irradiated in row 4 of EBR-II designed for a total coolant flow rate of 355 liters min (94 gal/min) of sodium. The fuel element is expected to operate with a beginning-of-life (BOL) average and peak pin power of 312 W/cm and 355 W/cm, respectively (9.5 and 10.8 kW/ft). As shown in Table 1, under the anticipated nominal conditions of pin power and subassembly flow rate, the peak fuel centerline temperature is expected to reach about 726.degree. C., while the peak cladding temperature reaches about 477.degree. C. Based on current experience with U--Pu--Zr fuel elements clad in HT9, neither temperature condition is considered aggressive. FIG. 4 shows how the fuel centerline temperature varies along the length of the element under the anticipated nominal conditions as well as .+-.20% deviations from the nominal power-to-flow ratio (P/F). TABLE 1 ______________________________________ Peak Temperatures from the Steady-State Analysis. Peak Temperature (.degree.C.) P/F.sup.a - 20% P/F.sup.a P/F.sup.a + 20% ______________________________________ Coolant 439 455 472 Clad O.D. 443 461 479 Clad I.D. 455 477 498 Sheath O.D. 461 484 507 Sheat I.D. 516 551 587 Fuel Center 665 726 785 ______________________________________ Experiments in EBR-II require thermal analyses of the experiment response to both anticipated and unlikely off-normal reactor events. These include both reactivity insertion and loss-of-flow events, and the power and flow variations with time for these events have been documented for EBR-II. The transient behavior of the Pu--28Zr fuel element during unlikely reactivity insertion and unlikely loss-of-flow events in EBR-II was calculated beginning from the nominal steady-state condition and is shown in FIGS. 5 and 6, respectively. The calculations indicate that the fuel temperatures remain well below the solidus temperature of Pu--28Zr, so these off-normal events pose no safety concerns for this fuel design. The temperature calculations shown are based on estimated thermal properties; thus, the uncertainty associated with these temperatures are unknown, but must be regarded as high. Furthermore, these calculations are for BOL conditions. During irradiation the fuel will develop porosity and undergo restructuring leading to a degradation of the fuel thermal conductivity and an increase in fuel temperatures. However, the thermal safety margin for this fuel design should be similar to that of U--20Pu--10Zr fuel currently irradiated in EBR-II. Thus, no thermal operational concerns are expected for this fuel design. Two important aspects of fuel element performance that must be observed with this alloy are fuel-cladding chemical interaction (FCCI) and axial fuel elongation due to swelling. Interdiffusion of fuel and cladding constituents in U--Pu--Zr fuel elements clad in HT9 can result in the formation of compositions in the fuel that have lower melting temperatures than the fuel alloy itself and in the formation of interaction zones that penetrate into the cladding and are considered wastage. Such interaction can ultimately lead to premature cladding failure. However, the relatively high composition of Zr (50 at. %) should be sufficient to prevent formation of low-melting-temperature compositions of Pu and Fe (which form a eutectic near 10 at. % Pu at 410.degree. C.) and should mitigate the penetration of fuel constituents into the cladding. Because the Pu--Hf phase diagram indicates that Hf is much less soluble in the .delta. and .epsilon. phases of Pu is Zr, a Pu--28(Zr, Hf fuel alloy could have two-phase regions stable at reactor operating temperatures. If the alloy had too little Zr, then the matrix phase in some regions of the fuel would consist of .delta. or .epsilon. Pu with little Hf or Zr in solution. These high-Pu phases could then interact with the cladding if fuel-cladding contact occurred. So, a sufficient Zr content in Pu--Zr--Hf such as >10 wt % will be necessary to limit potential FCCI. While there has been disclosed what is considered to be the preferred embodiment of the present invention, it is understood that various changes in the details may be made without departing from the spirit, or sacrificing any of the advantages of the present invention. |
claims | 1. A method of encapsulating a hazardous waste material or components thereof, the method comprising: adding the hazardous waste material to a settable composition, the composition comprising a calcium carbonate, a caustic magnesium oxide and an additive, and wherein the additive is an organic acid selected from the group consisting of citric acid, lemon acid, acetic acid, glycolic acid, oxalic acid, and other di or poly carboxylic acids, tartaric acid, salicylic acid, ethylenediamine tetra acetic acid (EDTA) and other tetra acids; forming a slurry; and allowing the slurry to set to encapsulate the hazardous waste material or components thereof, the additive accelerating the formation of strong binding agents and assisting the recrystallisation of the composition to make it set. 2. A method of encapsulating as defined in claim 1 , wherein the additive is present between 0.01% and 10% by weight of the total composition. claim 1 3. A method of encapsulating as defined in claim 1 , wherein the organic acid is present between 0.01% to 10% by weight of the total composition. claim 1 4. A method of encapsulating as defined in claim 3 , wherein the organic acid assists in carbonisation of caustic magnesium oxide to recrystallise the composition into a set material that encapsulates the hazardous waste material. claim 3 5. A method of encapsulating as defined in claim 4 , wherein the additive acts as a ligand to form complexes around the hazardous waste material or components thereof, helping to trap the hazardous waste material or components thereof in the set material. claim 4 6. A method of encapsulating as defined in claim 1 , wherein the settable composition further comprises an inorganic salt. claim 1 7. A method of encapsulating as defined in claim 6 , wherein the inorganic salt is a metal salt selected from the group consisting of aluminum sulphate, magnesium sulphate and sodium chloride. claim 6 8. A method of encapsulating as defined in claim 7 , wherein the inorganic salt is present between 0.1%-5% by weight of the total composition. claim 7 9. A method of encapsulating as defined in claim 1 , wherein the hazardous waste material or components thereof is in the form of a powder having a mean particle size falling within the range of 0.01 mm to 5.0 mm. claim 1 10. A method of encapsulating as defined in claim 9 , wherein the mean particle size falls within the range of 0.1 mm to 1.0 mm. claim 9 11. A method of encapsulating as defined in claim 1 , wherein the caustic magnesium oxide of the settable composition is selected from the group consisting of: claim 1 (a) a magnesium composition which comprises magnesium carbonate and a decarbonated magnesium; (b) a magnesium carbonate which has been treated by heating to liberate carbon dioxide thereby forming a composition which is partially calcined; (c) a synthetic blend formed by mixing calcium carbonate with preformed caustic magnesium oxide, the preformed magnesium oxide being prepared by heating magnesium carbonate to partially drive off carbon dioxide until a desired level of calcination is obtained; and (d) a magnesium deficient dolomite heated to form a composition comprising calcium carbonate and caustic magnesium oxide, and to which is added additional caustic magnesium oxide. 12. A method of encapsulating as defined in claim 11 , wherein the caustic magnesium oxide has between 2%-50% of the carbon dioxide retained within the magnesium carbonate. claim 11 13. A method of encapsulating as defined in claim 1 , wherein the settable composition further comprises a sulphate additive present between 0.01% and 20% by weight of the total composition; and claim 1 wherein the sulphate is selected from the group consisting of sulphuric acid, a metal sulphate, magnesium sulphate and aluminum sulphate. 14. A method of encapsulating arsenic or components thereof, the method comprising: adding to the arsenic or components thereof a sulphate, an iron chloride and/or an alkaline agent, and water forming a slurry; mixing the slurry with a settable composition, the composition comprising a calcium carbonate, a caustic magnesium oxide and an additive, and wherein the additive is an organic acid selected from the group consisting of citric acid, lemon acid, acetic acid, glycolic acid, oxalic acid, and other di or poly carboxylic acids, tartaric acid, salicylic acid, ethylenediamine tetra acetic acid (EDTA) and other tetra acids; and allowing the composition to set to encapsulate the arsenic or components thereof, the additive accelerating the formation of strong binding agents and assisting in the recrystallisation of the composition to make it set. 15. A method of encapsulating as defined in claim 14 , wherein said sulphate added to the arsenic or components thereof is aluminium sulphate. claim 14 16. A method of encapsulating as defined in claim 14 , wherein said alkaline agent added to the arsenic or components thereof is a carbonate. claim 14 17. A method of encapsulating as defined in claim 16 , wherein said iron chloride added to the arsenic or components thereof is ferric chloride. claim 16 18. A method of encapsulating mercury or components thereof, the method comprising: adding the mercury or components thereof to a settable composition, the settable composition comprising a calcium carbonate, a caustic magnesium oxide and an additive, and wherein the additive is an organic acid selected from the group consisting of citric acid, lemon acid, acetic acid, glycolic acid, oxalic acid, and other di or poly carboxylic acids, tartaric acid, salicylic acid, ethylenediamine tetra acetic acid (EDTA) and other tetra acids; forming a slurry; and allowing the slurry to set to encapsulate the mercury or components thereof, the additive accelerating the formation of strong binding agents and assisting the recrystallisation of the composition to make it set. 19. A method of encapsulating nickel and chromium or components thereof, the method comprising: adding the nickel and chromium or components thereof to a settable composition, the settable composition comprising a calcium carbonate, and caustic magnesium oxide and an additive, and wherein the additive is an organic acid selected from the group consisting of citric acid, lemon acid, acetic acid, glycolic acid, oxalic acid, and other di or poly carboxylic acids, tartaric acid, salicylic acid, ethylenediamine tetra acetic acid (EDTA) and other tetra acids; forming a slurry; and allowing the slurry to set to encapsulate the nickel and chromium or components thereof, the additive accelerating the formation of strong binding agents and assisting the recrystallisation of the composition to make it set. 20. A method of encapsulating radioactive materials, the method comprising: adding the radioactive materials to a settable composition, the settable composition comprising a calcium carbonate, a caustic magnesium oxide, and an additive, and wherein the additive is an organic acid selected from the group consisting of citric acid, lemon acid, acetic acid, glycolic acid, oxalic acid, and other di or poly carboxylic acids, tartaric acid, salicylic acid, ethylenediamine tetra acetic acid (EDTA) and other tetra acids; forming a slurry; and allowing the slurry to set to encapsulate the radioactive materials therein, the additive accelerating the formation of strong binding agents and assisting the recrystallisation of the composition to make it set. 21. A method of encapsulating as defined in claim 20 , wherein the settable composition further comprises lead or a lead compound. claim 20 |
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description | 1. Field of the Invention The invention relates to an apparatus and method for detecting optical signals, and particularly to an apparatus and method for detecting two-dimension optical image signals. 2. Description of the Related Art FIG. 1 shows a systematic view of a general apparatus for fluorescence signals detection. A sampling light beam L1′ passes an excitation filter or a monochromator 110. The filter or monochromator 110 lets the excitation laser L1 pass through and irradiate the labeled sample 120 in the testing zone. The labeled sample 120 is excitated to radiate fluorescence. The emission light L2 passes a second filter or a monochromator 112 where unneeded noise light is removed. Then, a monochromical emission is detected by a photodetector 130. There are two technical manners for detecting fluorescence signals. The first manner is to apply laser as an excitation light and apply a photomultiplier tube (PMT) to detect the received signal and form a two-dimensional image. The second manner is to apply white light of mercury lamp or xenon lamp and to use a high-resolution camera, such as a CCD (charge-coupled device) camera, to take the fluorescence picture for further image analysis through an image analyzer. The laser and photomultiplier tube detection system mainly follows the structure of an optical microscope. As shown in FIG. 2, a laser source 202 provides a laser beam to be separated by a dichroic mirror 210 and focused in the testing zone. The labeled sample 220 in the testing zone is excited to radiate fluorescence. The dichroic mirror 210 separates the excitation laser and the emission light into different paths. The light source is focused by lens into a spot. The size of the spot determines the resolution of the detection system. However, the size of the spot is restricted by the optical limitation of diffraction and the wavelength of the incident light. Furthermore, since the detection signal is processed with pixel of the focused spot, a precise moving device with displacement resolution higher than the optical resolution is required for obtaining a two-dimensional scanning. The precise device increases the hardware cost. The single point scanning also increases the imaging time and slows the operation. There have been many prior devices for detecting fluorescence signals. For example, U.S. Pat. No. 5,719,391 discloses a fluorescence imaging system including an objective entrance pupil and a two-dimensional moving system. U.S. Pat. No. 5,780,857 discloses a scanning system with both laser and white light beams. U.S. Pat. Nos. 6,355,934, 6,471,916, 6,603,537, 6,628,385, 6,646,271 and 6,664,537 also disclose other derivative devices. Most of them are laser and photomultiplier tube systems using dichroic mirrors to separate the incidence excitation laser and the emission light. When omitting the dichroic mirror, the optical design may sacrifice the wholeness of entrance aperture of the received emission light. The other detection devices with CCD cameras mainly use white light sources. However, the white light source occupies much space and generates a lot of heat that cause trouble and difficulty of system design. The system also requires two filters, in which one removes the excessive wavelength light in the incidence beam; the other removes the noise in the emission light. A dichroic mirror is also required to separate the incidence light and the emission light. U.S. Pat. No. 6,630,063 discloses a fluorescence signal detection system applying capillary electrophoresis. The system also uses a laser beam refracted by lens and formed into scanning beams through a galvanometer. However, instead of two-dimensional scanning, it is only applicable to one-dimensional scanning. Accordingly, the present invention is directed to an optical detection apparatus and method thereof applying a one-dimensional scanning laser beam and a one-dimensional moving carrier to achieve two-dimensional fluorescence signal detection, so as to solve the problems and restrictions of prior arts. In one aspect, the optical detection apparatus and method thereof according to the invention does not use dichroic mirror so as to simplify the optical design and save cost. In another aspect, the optical detection apparatus and method thereof according to the invention is applicable to the field of biochips for reading the signals. The biochips include micro-array chips, micro fluidic chips, DNA chips, protein arrays, tissue arrays, Lab-on-a-chip and other kinds of glass or polymer slides. In yet another aspect, the optical detection apparatus and method thereof according to the invention has both abilities to detect the signals for fluorescence labelling signals and the colorimetric signals. In order to achieve the aforesaid objects, the optical detection apparatus according to the invention, applicable for detecting the image signals of a labeled sample and includes a laser module, a scan module, a carrier and a light receiver. The laser module provides excitation light and then transmits the excitation light, and the scan module continuously reflects the excitation light and then introduces the excitation light to provide a linear scanning light by changing a reflection angle. The carrier moves the scan module in a direction nonparallel to a direction of the linear scanning light so as to provide a two-dimensional testing zone. In this case, the preferred direction, in which the carrier moves, is perpendicular to the direction of the linear scanning light. The labeled sample placed in the testing zone is excited by the excitation light and generates emission light to be received by the light receiver. Therefore, the light receiver acquires the image signals of the labeled sample according to the emission light. The scan module is as a polygonal mirror and a motor, or as a galvanometer which includes a reflective mirror and a driving unit. Moreover, the polygonal mirror includes a polyhedron rotor having poly reflective surfaces, or is formed with mirrors. The polyhedron rotor having poly reflective surfaces may be made of a polyhedron rotor and scanning mirrors embedded thereon. Further, the laser module can be a laser generator or an array with many laser generators, such as an array of laser diodes. Moreover, the laser module further includes a collimation and coupling lenses connected to the laser generator(s). When the laser module includes a laser generator and a collimation and coupling lenses, the laser generator generates laser beam, and then the laser beam is collimated and guided by a collimation and coupling lenses. When the laser module includes many laser generators and a collimation and coupling lenses, the laser generators generate laser beams with different wavelengths, respectively; and then the laser beams are coupled into the excitation light by a collimation and coupling lenses. Furthermore, the laser generator(s) can be carried by the carrier or steadfastly installed. When the laser generator(s) is/are steadfastly installed, the laser module further includes a mirror, which is carried by the carrier to move with the scan module, for reflecting the excitation light from the collimation and coupling lenses to the scan module. The emission light emitted from the labeled sample can be guided to the light receiver via at least one mirror. The light receiver has an image-sensing module, such as a charge-coupled device (CCD). A cooling element can be applied to reduce the dark current of the CCD. The optical detection apparatus according to the invention further includes a light generator used to illuminate the labeled sample evenly so as to help detecting the colorimetric image signals of the labeled sample. Further, the optical detection method according to the invention comprises the following steps. First, provide linear scanning light at a tilt angle. Then, move the linear scanning light in a direction nonparallel to linear direction of the linear scanning light to form a two-dimensional testing zone. Further, illuminate and excite a labeled sample in the testing zone to emit emission light. And, receive the emission light and form image signal of the labeled sample according to the emission light. Moreover, the preferred direction, in which the linear scanning light is moved, is perpendicular to the linear direction. In the step of providing the linear scanning light at a tilt angle, there are steps of generating excitation light, and continuously reflecting the excitation light with change of the reflection angle to form the linear scanning line. The optical detection method according to the invention further comprises a step of guiding the emission light via at least a mirror into a receiving portion according to the emission light. In other words, the testing zone, the mirror and the light receiver are serially arranged in an emission light path. As shown in FIG. 3A, an optical detection apparatus according to a first embodiment of the invention is illustrated. In this case, a light module 310 generates excitation light L1 scanning in Y-axis, and the light module 310 is carried by a carrier 320 to move in a direction nonparallel to Y-axis, so as to achieve two-dimensional scanning. The preferred direction is along X-axis. In other words, the excitation light L1 scanning in Y-axis and moving along X-axis is combined to produce a two-dimensional testing zone in which a labeled sample 330 is placed. The labeled sample 330 excited by the linear scanning light to emit emission light L2. A light receiver 340 receives the emission light L2 and processes to form image signals of the labeled sample 330. In this case, the labeled sample is a test sample labeled with or having fluorescent compounds, or colorimetric compounds. The fluorescent compounds may be fluorescent groups, quantum dot particles, other dye particles or an antibody conjugated with indocarbocyanine dyes or fluorescent proteins, etc., such as fluorescein, rhodamine, dichlorofluorescein, hexachlorofluorescein, tetramethylrhodamine, indocarbocyanine dyes, Texas Red, ethidium bromide, chelated lanthanides, phycoerythrin, GFP, avidin fluorescein (FITC), IgG- phycoerythrin (PE), anti-fluorescein (FITC), IgG2a PE-Cy5, TRITC (tetramethylrhodamine-5-isothiocyanate), and the like. The indocarbocyanine dyes may be Cy3, Cy5, Cy5.5, or Cy7, etc. The fluorescent proteins may be R-PE, or B-PE, etc. The colorimetric compounds may be colorimetric enzymes such as alkaline phosphatase (AP) or horseradish peroxidase (HRP). The light module 310 includes a laser module 312 and a scan module 314. The laser module 312 provides excitation light L1 to the scan module 314. The scan module 314 continuously reflects and introduces the excitation light L1, and provides a linear scanning light in Y-axis by changing of the reflection angle. The carrier 320 moves the light module 310 in a direction nonparallel to Y-axis, such as along X-axis, so as to achieve two-dimensional scanning as shown in FIG. 3B. The scan module 314 includes a polygonal mirror 3141 and a motor 3142 as shown in FIG. 3C. Moreover, the polygonal mirror 3141 includes a polyhedron rotor having poly reflective surfaces, or is formed with mirrors. The polyhedron rotor having poly reflective surfaces may be made of a polyhedron rotor and scanning mirrors embedded thereon. The scan module 314 receives the excitation light L1, and continuously reflects and introduces the excitation light L1 to provide a linear scanning light in Y-axis by rotating the polygonal mirror 3141, which is formed that the poly reflective surfaces or poly-mirrors arrange on the polyhedron rotor. As each reflective surface or mirrors rotates and passes through the excitation light L1, it reflects and introduces the excitation light L1 to form a Y-axis scanning light that makes up one part of the continuous one-dimensional scanning light. In other words, the polygonal mirror 3141 rotated by the motor 3142 continuously reflects and introduces the excitation light L1 into a Y-axis scanning light caused by each reflective surface or mirrors which arrange on the polyhedron rotor rotated by the motor. With reference to FIG. 3D, the scan module 314 is as a galvanometer as disclosed in U.S. Pat. Nos. 6,630,063 and 6,819,468. The laser module 312 generates excitation light L1 passing through the galvanometer and formed into Y-axis scanning light. The galvanometer comprises a reflective mirror 3143 and a driving unit 3144. The reflective mirror 3143 has one reflective surface. The driving unit 3144 drives the reflective mirror 3143 so that the reflective mirror 3143 oscillates and simultaneously reflects the excitation light L1 to form a Y-axis scanning light that makes up one part of the continuous one-dimensional scanning light. The emission light L2 emitted by the labeled sample 330 can be guided by at least a mirror 350 (or mirrors 350-1, 350-2) to the light receiver 340. The mirror 350 or mirrors 350-1, 350-2 guide the emission light L2 to any suitable position in the apparatus where the light receiver 340 locates so as to compact the apparatus to a smaller size as shown in FIGS. 3E to 3H. The excitation light L1 is reflected by the scan module 314 and passed to the testing zone in a tilt angle, so that the excitation light L1 passes aside the mirror 350 or mirrors 350-1. The laser module 312 can be a laser generator to generate excitation light L1 and pass the light directly to the scan module 314 without turning. Then, the scan module 314 reflects the excitation light L1 to the testing zone for Y-axis scanning. In other words, the laser module can be a larger size laser generator to generate the direct light path to the scan module, thereby further compact the apparatus. As shown in FIG. 3H, the laser module 312 can be a laser generator 3121 connected with a collimation and coupling lenses 3122. The laser generator 3121 generates excitation light L1 passing via the collimation and coupling lenses 3122 to the scan module 314. Then, the scan module 314 reflects the excitation light L1 to the testing zone for Y-axis scanning. The laser generator 3121 can be a tubular laser. The laser module 312 may have an array of laser generators, which generate the laser beams with different wavelengths, respectively, and a collimation and coupling lenses to couple the laser beams into the excitation light. Besides, the laser module 312 may be an array of the same laser generators for providing the linear scanning light, and the laser generators may be laser diodes. Further, a collimation and coupling lens is used to collimate the scanning light to the testing zone. Furthermore, the laser generator(s) cannot be installed on the carrier, that is, the laser module(s) is/are steadfastly installed. It assumed that the laser module includes a laser generator for generating the excitation light. In this case, the laser generator 3121 is steadfastly installed, and the laser module further includes a mirror 3123 which is installed on the carrier 320 to move with the scan module 314 and to reflect the excitation light L1 to the scan module 314, as shown in FIGS. 3I and 3J. Moreover, the excitation light generated by the laser generator(s) can be collimated and guided by the collimation and coupling lenses (not shown in FIGS. 3I and 3J) first, and then be reflected by the mirror. As shown in FIG. 3K, a light generator 360 is mounted upon the testing zone to provide illumination to the labeled sample so that the apparatus can also be used for detecting the colorimetric image of the labeled sample. The light generator 360 has light-emitting diodes suitably arranged for even illumination through studies of optical simulation. In other words, the labeled sample with colorimetric compounds, such as colorimetric enzymes, is illuminated by the light generator 360, so as to enable the light receiver 340 to form the colorimetric image according to the light from the labeled sample. In this case, the light generator may be a light emitting diode (LED). The carrier 320 includes an actuator for providing nonparallel to Y-axis scanning movement of the excitation light L1. Moreover, the preferred scanning movement is X-axis scanning movement. The actuator can be a stepping motor, gear AC/DC motor, linear motor, a screw or a ballscrew system, but is not limited to these devices. The light receiver 340 includes an image lens, a filter and an image-sensing module. The image lens receives the emission light L2, passes it through the filter to get a certain wavelength light for the image-sensing module to form image signals of the labeled sample corresponding to the emission light. The filter can be mechanically replaced according to characteristics of the fluorescence image. The image-sensing module can be a charge-coupled device (CCD). A cooling element can be applied to reduce the dark current of the CCD and increase the signal-to-noise ratio. Therefore, the optical detection apparatus of the invention has both functions of detection for the image signals by fluorescence labelling and colorimetric. That is, the laser module may be used for detecting the fluorescence image and a portion of the colorimetric images, and the light generator, such as the LED, may be used for detecting another portion of the colorimetric images. Further, the light receiver is used for receiving the emission light from the labeled sample in both above detection modes. The invention further includes a detecting method comprising the following steps. First, provide linear excitation light with a tilt angle. Then, move the linear excitation light in a direction perpendicular to the linear direction of the linear excitation light to form a testing zone. Further, illuminate and excite a labeled sample in the testing zone to get an emission light. And, receive the emission light and form the image signals of the labeled sample corresponding to the emission light to acquire an image. That is, the tilt angle means that the light path of the linear excitation light and that of the emission light are different from each other. In the step of providing linear excitation light with a tilt angle, there are steps of generating excitation light and forming scanning lines by continuously reflecting the excitation light with change of reflection angle of a scan module. The excitation light can be directly passed to the scan module, or collimated by a collimator before being passed to the scan module. There is at least a mirror to reflect the emission light to a light receiver. The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims. |
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abstract | Provided is a nuclear reactor system and method therefor, for increasing the speed of conversion of a radionuclide to a stable nuclide to reduce radionuclide concentration using thermal neutrons produced by reducing the velocity of fast neutrons, while simultaneously subjecting fast-neutron-induced thermal energy of a primary cooling material to heat exchange with a secondary cooling material in a heat exchanger (7), and feeding the energy to a turbine system to generate power, the system having a nuclear reactor container (1) comprising a first container (11), and a second container (12), a plurality of metal fuel assemblies (22) and a liquid metal, which is the primary cooling material, being disposed in the first container, and the second cooling material capable of dual use as a neutron moderator and a MA radioactivity-extinguishing assembly or FP-extinguishing assembly (24) being loaded in the second container. |
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description | 1. Field Example embodiments generally relate to apparatuses and methods for controlling movement of components. The controlling may involve, for example, allowing, limiting, and/or preventing movement. The components may be integrated components. Example embodiments also relate to nuclear reactor plants and to apparatuses and methods for controlling movement of components in the nuclear power plants. 2. Description of Related Art A reactor pressure vessel (“RPV”) of a boiling water reactor (“BWR”) may have a generally cylindrical shape and may be closed at both ends (e.g., by a bottom head and a removable top head). A top guide may be spaced above a core plate within the RPV. A core shroud, or shroud, may surround the core and may be supported by a shroud support structure. The shroud may have a generally cylindrical shape and may surround both the core plate and the top guide. There may be a space or annulus located between the cylindrical RPV and the cylindrically shaped shroud. In a BWR, hollow tubular jet pumps positioned within the annulus provide the required reactor core water flow. The upper portion of a jet pump, known as the inlet mixer, may be laterally positioned and supported by related art jet pump restrainer brackets. The restrainer brackets may support the inlet mixer by attaching to the adjacent jet pump riser pipe. The lower portion of a jet pump, known as the diffuser, may be coupled to the inlet mixer by a slip joint. The slip joint between the inlet mixer and a collar of the diffuser may have an operating clearance that accommodates relative axial thermal-expansion movement between the upper and lower portions of the jet pump. The operating clearance also may permit leakage flow from the driving pressure inside the jet pump. Excessive leakage flow may cause oscillating motion in the slip joint, known as flow induced vibration (“FIV”) or slip joint leakage flow induced vibration (“SJLFIV”), which may be a source of detrimental vibration excitation in the jet pump assembly. While related art jet pump restrainer brackets may provide system stiffness that mitigates vibration of system components, SJLFIV may still occur between the inlet mixer and diffuser. The slip joint leakage rate may increase due, for example, to single loop operation, increased core flow, and/or jet pump crud deposition. Thermal and pressure displacements of the shroud and RPV may diminish alignment interaction loads in the jet pump assembly that are beneficial in restraining vibration, such as a lateral force in the slip joint. The resultant increased vibration levels and corresponding vibration loads on the piping and supports may cause jet pump component degradation from wear and fatigue. High levels of FIV may be possible in certain jet pump designs at some abnormal operational conditions having increased leakage rates. Therefore, it may be desirable to provide a jet pump assembly that has a lateral load in the slip joint area to maintain the stiffness of the interface between the inlet mixer and diffuser to prevent oscillating motion and suppress FIV. Related art apparatuses and methods are discussed, for example, in U.S. Pat. No. 4,285,770 to Chi et al. (“the '770 patent”); U.S. Pat. No. 6,394,765 B1 to Erbes et at (“the '765 patent”); U.S. Pat. No. 6,438,192 B1 to Erbes et at (“the '192 patent”); U.S. Pat. No. 6,450,774 B1 to Erbes et at (“the '774 patent”); and U.S. Pat. No. 6,587,535 B1 to Erbes et al. (“the '535 patent”). The disclosures of the '192 patent, the '535 patent, the '765 patent, the '770 patent, and the '774 patent are incorporated in this application by reference in their entirety. Related art apparatuses and methods also are discussed, for example, in U.S. Patent Application Publication Nos. 2008/0031741 A1 to Torres (“the '741 publication”); 2010/0242279 A1 to Sprague et at (“the '279 publication”); 2010/0329412 A1 to Ellison et al. (“the '412 publication”); 2011/0052424 A1 to Bass et al. (“the '424 publication”); 2011/0135049 A1 to Wroblewski et at (“the '049 publication”); and 2011/0176938 A1 to DeFilippis et al. (“the '938 publication”). The disclosures of the '049 publication, the '279 publication, the '412 publication, the '424 publication, the '741 publication, and the '938 publication are also incorporated in this application by reference in their entirety. Additionally, related art apparatuses and methods also are discussed, for example, in U.S. patent application Ser. No. 12/982,280 to Sprague et al. entitled “Method and Apparatus for a Jet Pump Three Point Slip Joint Clamp” (“the '280 application”). The disclosure of the '280 application is likewise incorporated in this application by reference in its entirety. Moreover, related art apparatuses and methods are discussed, for example, in World Intellectual Property Organization (“WIPO”) International Publication No. WO 2011/035043 A1. Example embodiments may provide apparatuses and methods for controlling movement of a first component integrated with a second component. Example embodiments also may provide apparatuses and methods for controlling movement of components in a nuclear power plant. In example embodiments, an apparatus for controlling movement of a first component integrated with a second component may include a first clamp configured to engage the first component, a second clamp configured to engage the second component, and/or a plurality of connectors configured to connect the first and second clamps. The connectors may allow movement of the first clamp relative to the second clamp in a first direction between the first and second clamps. The connectors may limit movement of the first clamp relative to the second clamp in a second direction perpendicular to the first direction. In example embodiments, the connectors may allow linear movement of the first clamp relative to the second clamp in the first direction. In example embodiments, the connectors may limit linear movement of the first clamp relative to the second clamp in the second direction. In example embodiments, the connectors may limit rotational movement of the first clamp relative to the second clamp about an axis defined in the first direction. In example embodiments, the connectors may prevent linear movement of the first clamp relative to the second clamp in the second direction. In example embodiments, the connectors may prevent rotational movement of the first clamp relative to the second clamp about an axis defined in the first direction. In example embodiments, the first clamp may include two or more first clamp sections. In example embodiments, the two or more first clamp sections may be connected together using a plurality of first clamp bolts. In example embodiments, the first clamp may include two or more first clamp sections and/or the second clamp may include two or more second clamp sections. In example embodiments, the two or more first clamp sections may be connected together using a plurality of first clamp bolts and/or the two or more second clamp sections may be connected together using a plurality of second clamp bolts. In example embodiments, an apparatus for controlling movement of components in a nuclear power plant, the nuclear power plant including a reactor pressure vessel and a jet pump assembly within the reactor pressure vessel, may include a first clamp configured to engage the jet pump assembly, a second clamp configured to engage the jet pump assembly, and/or a plurality of connectors configured to connect the first and second clamps. The connectors may allow movement of the first clamp relative to the second clamp in an axial direction of the jet pump assembly. The connectors may limit movement of the first clamp relative to the second clamp in a direction perpendicular to the axial direction of the jet pump assembly. In example embodiments, the first clamp may be configured to engage an inlet mixer of the jet pump assembly. In example embodiments, the second clamp may be configured to engage a diffuser of the jet pump assembly. In example embodiments, the connectors may allow linear movement of the first clamp relative to the second clamp in the axial direction of the jet pump assembly. In example embodiments, the connectors may limit linear movement of the first clamp relative to the second clamp in the direction perpendicular to the axial direction of the jet pump assembly. In example embodiments, the connectors may limit rotational movement of the first clamp relative to the second clamp about the axial direction of the jet pump assembly. In example embodiments, an apparatus for controlling movement of components in a nuclear power plant, the nuclear power plant including a reactor pressure vessel and a jet pump assembly within the reactor pressure vessel, may include a first clamp configured to engage an inlet mixer of the jet pump assembly, a second clamp configured to engage a diffuser of the jet pump assembly, and/or a plurality of connectors configured to connect the first and second clamps. The first clamp, second clamp, and connectors may allow movement of the inlet mixer relative to the diffuser in an axial direction of the jet pump assembly. The first clamp, second clamp, and connectors may limit movement of the inlet mixer relative to the diffuser in a direction perpendicular to the axial direction of the jet pump assembly. In example embodiments, the first clamp, second clamp, and connectors may allow linear movement of the inlet mixer relative to the diffuser in the axial direction of the jet pump assembly. In example embodiments, the first clamp, second clamp, and connectors may limit linear movement of the inlet mixer relative to the diffuser in the direction perpendicular to the axial direction of the jet pump assembly. In example embodiments, the first clamp, second clamp, and connectors may limit rotational movement of the inlet mixer relative to the diffuser about the axial direction of the jet pump assembly. In example embodiments, a method for controlling movement of a first component integrated with a second component may include engaging the first component with a first clamp, engaging the second component with a second clamp, and connecting the first and second clamps using a plurality of connectors. The connectors may allow movement of the first clamp relative to the second clamp in a first direction between the first and second clamps. The connectors may limit movement of the first clamp relative to the second clamp in a second direction perpendicular to the first direction. These and other features and advantages of this invention are described in, or are apparent from, the following detailed description of various example embodiments of the apparatuses and methods according to the invention. Example embodiments will now be described more fully with reference to the accompanying drawings. Embodiments, however, may be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. Rather, these example embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope to those skilled in the art. In the drawings, the thicknesses of layers and regions are exaggerated for clarity. It will be understood that when an element is referred to as being “on,” “connected to,” “electrically connected to,” or “coupled to” to another component, it may be directly on, connected to, electrically connected to, or coupled to the other component or intervening components may be present. In contrast, when a component is referred to as being “directly on,” “directly connected to,” “directly electrically connected to,” or “directly coupled to” another component, there are no intervening components present. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. It will be understood that although the terms first, second, third, etc., may be used herein to describe various elements, components, regions, layers, and/or sections, these elements, components, regions, layers, and/or sections should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer, and/or section from another element, component, region, layer, and/or section. For example, a first element, component, region, layer, and/or section could be termed a second element, component, region, layer, and/or section without departing from the teachings of example embodiments. Spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “upper,” and the like may be used herein for ease of description to describe the relationship of one component and/or feature to another component and/or feature, or other component(s) and/or feature(s), as illustrated in the drawings. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting of example embodiments. As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural fog ills as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises,” “comprising,” “includes,” and/or “including,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which example embodiments belong. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and should not be interpreted in an idealized or overly formal sense unless expressly so defined herein. It should also be noted that in some alternative implementations, functions and/or acts noted may occur out of the order noted in the figures. For example, two figures shown in succession may in fact be executed substantially concurrently or may sometimes be executed in the reverse order, depending upon the functionality and/or acts involved. Reference will now be made to example embodiments, which are illustrated in the accompanying drawings, wherein like reference numerals may refer to like components throughout. FIG. 1 is a perspective view of related art BWR jet pump assembly 100. Major components of jet pump assembly 100 include riser pipe 102, inlet mixers 104, and diffusers 106. Inlet mixers 104 insert into respective diffusers 106. The interface between inlet mixer 104 and associated diffuser 106 is slip joint 108. Jet pump restrainer brackets 110 may be used to stabilize movement of inlet mixers 104. This stabilization may reduce SJLFIV of and leakage at slip joint 108. As may be seen, the body of inlet mixer 104 generally has a smaller diameter than the body of associated diffuser 106. FIG. 2 is a detailed view of related art slip joint 208. The interface between inlet mixer 204 and associated diffuser 206 is slip joint 208. It should be noted that bottom portion 204a of inlet mixer 204 inserts into upper crown 206a of diffuser 206. Guide ears 206b of diffuser 206 typically assist with proper insertion by guiding bottom portion 204a into upper crown 206a as inlet mixer 204 is lowered onto diffuser 206. FIG. 3 is a cross-sectional view of related art slip joint 308. The interface between inlet mixer 304 and associated diffuser 306 is slip joint 308. As before, bottom portion 304a of inlet mixer 304 inserts into upper crown 306a of diffuser 306. Distal end 304b of inlet mixer 304 rests in upper crown 306a of diffuser 306 to form slip joint 308. SJLFIV may occur in slip joint 308 when tolerances between distal end 304b of inlet mixer 304 and upper crown 306a of diffuser 306 are inconsistent and/or excessive. Additionally, leakage may occur at the interface, as water may leak between distal end 304b of inlet mixer 304 and upper crown 306a of diffuser 306 and out of slip joint 308. FIG. 4 is a detailed view of first clamp section 402 of first clamp 400 (shown in FIG. 7) in accordance with example embodiments. First clamp section 402 may include body 404, offsets 406, channels 408, end portions 410, and/or through holes 412. Body 404 may include inner edge 414, outer edge 416, top surface 418, and/or bottom surface 420. First clamp 400 may be designed for installation on an associated diffuser. As a result, first clamp section 402 may be physically larger and/or have a larger radius of curvature than a clamp section designed for installation on an associated inlet mixer. First clamp 400 may include two first clamp sections 402 joined together to substantially encircle the associated diffuser. In the alternative, first clamp 400 may include a single-piece clamp. However, the use of a single-piece clamp may require installation prior to or together with installation of the associated inlet mixer and/or diffuser, or at least partial disassembly of an already installed inlet mixer and/or diffuser. In the alternative, first clamp 400 may include more than two clamp sections. Modification of first clamp 400 to include a single-piece clamp or more than two clamp sections would be understood by a person having ordinary skill in the art (“PHOSITA”). Although not required, first clamp sections 402 of first clamp 400 may be substantially identical. Such an arrangement would facilitate manufacture, supply, installation, and replacement of first clamp 400. A cross-section of body 404 may be square, rectangular, or some other shape. Modification of body 404 to a desired cross-sectional shape would be understood by a PHOSITA. A diffuser may include two or more guide ears (e.g., four guide ears). The guide ears may be evenly spaced around the periphery of the diffuser. The guide ears may assist in the integration of an inlet mixer with an associated diffuser. For example, this assistance may be particularly beneficial when attempting to remotely insert an inlet mixer into a diffuser, where the interface between the inlet mixer and the diffuser forms a slip joint. As shown in FIG. 4, first clamp section 402 may include offsets 406. Offsets 406 in first clamp section 402 may provide clearance for guide ears of the associated diffuser. If the guide ears are evenly spaced around the periphery of the diffuser, then offsets 406 may be evenly spaced around first clamp 400. Modification of first clamp sections 402 so that offsets 406 may be evenly spaced around first clamp 400 would be understood by a PHOSITA. Positioning of the guide ears of the associated diffuser in offsets 406 may help to prevent movement of first clamp section 402 in the vertical direction (toward the associated inlet mixer) and/or may help to prevent rotation of first clamp section 402 about an axial direction of the associated diffuser. As shown in FIG. 4, first clamp section 402 may include channels 408. Channels 408 may extend completely through body 404 (e.g., from top surface 418 to bottom surface 420). In the alternative, channels 408 may extend only partly through body 404. Modification of body 404 so that channels 408 extend completely through or only partly through body 404 would be understood by a PHOSITA. As shown in FIG. 4, first clamp section 402 may include two channels 408. In the alternative, first clamp section 402 may include only one channel 408 or more than two channels 408. Modification of first clamp section 402 to include only one channel 408 or more than two channels 408 would be understood by a PHOSITA. As shown in FIG. 4, channels 408 may be disposed within body 404 of first clamp section 402 (i.e., between inner edge 414 and outer edge 416). In the alternative, for example, channels 408 may be disposed on inner edge 414 of body 404 (e.g., so that inner edge 414 includes a portion of channel 408) and/or outer edge 416 of body 404 (e.g., so that outer edge 416 includes a portion of channel 408). Modification of first clamp section 402 so that channels 408 are disposed on inner edge 414 and/or outer edge 416 would be understood by a PHOSITA. As shown in FIG. 4, channels 408 may have a cruciform shape. Channels 408 may have one or more other shapes, as well, such as, for example, triangular, rectangular, circular, tear drop, or dovetail. Modification of channels 408 to include one or more other shapes would be understood by a PHOSITA. As discussed above, first clamp 400 may include two first clamp sections 402 joined together to substantially encircle the associated diffuser. First clamp sections 402 may be disposed around an associated diffuser so that end portions 410 of one first clamp section 402 may near or in contact with end portions 410 of another first clamp section 402. First clamp sections 402 may be connected together at end portions 410 using a plurality of first clamp bolts 422 (shown in FIG. 7) and through holes 412. First clamp sections 402 also may be connected together at end portions 410 using lock nuts, ratchets, and the like, as would be understood by a PHOSITA. Tightening of the first clamp bolts may provide a sufficient grip between first clamp 400 and the associated diffuser so as to prevent movement of first clamp 400 in the vertical direction (e.g., either toward or away from the associated inlet mixer) and/or about an axial direction of the associated diffuser. Positioning of the guide ears of the associated diffuser in offsets 406 also may help to prevent movement of first clamp 400 in the vertical direction (toward the associated inlet mixer) and/or may help to prevent rotation of first clamp 400 about an axial direction of the associated diffuser. First clamp sections 402 may be connected together using other types of connections and/or connectors. First clamp sections 402 may be hinged together, for example, on one side. End portions 410 may include, for example, male and/or female dovetail joints. Modification of first clamp sections 402 so that they may be connected together using other types of connections and/or connectors would be understood by a PHOSITA. Interaction of first clamp 400 with connectors and a second clamp with be discussed in detail below. FIG. 5 is a detailed view of second clamp section 502 of second clamp 500 (shown in FIG. 7) in accordance with example embodiments. Second clamp section 502 may include body 504, channels 508, end portions 510, and/or through holes 512. Body 504 may include inner edge 514, outer edge 516, top surface 518, and/or bottom surface 520. Second clamp 500 may be designed for installation on an associated inlet mixer. As a result, second clamp section 502 may be physically smaller and/or have a smaller radius of curvature than a clamp section designed for installation on an associated diffuser. Second clamp 500 may include two second clamp sections 502 joined together to substantially encircle the associated inlet mixer. In the alternative, second clamp 500 may include a single-piece clamp. However, the use of a single-piece clamp may require installation prior to or together with installation of the associated inlet mixer and/or diffuser, or at least partial disassembly of an already installed inlet mixer and/or diffuser. In the alternative, second clamp 500 may include more than two clamp sections. Modification of second clamp 500 to include a single-piece clamp or more than two clamp sections would be understood by a PHOSITA. Although not required, second clamp sections 502 of second clamp 500 may be substantially identical. Such an arrangement would facilitate manufacture, supply, installation, and replacement of second clamp 500. A cross-section of body 504 may be square, rectangular, or some other shape. Modification of body 504 to a desired cross-sectional shape would be understood by a PHOSITA. As shown in FIG. 5, second clamp section 502 may include channels 508. Channels 508 may extend completely through body 504 (i.e., from top surface 518 to bottom surface 520). In the alternative, channels 508 may extend only partly through body 504. Modification of body 504 so that channels 508 extend completely through or only partly through body 504 would be understood by a PHOSITA. As shown in FIG. 5, second clamp section 502 may include two channels 508. In the alternative, second clamp section 502 may include only one channel 508 or more than two channels 508. Modification of second clamp section 502 to include only one channel 508 or more than two channels 508 would be understood by a PHOSITA. As shown in FIG. 5, channels 508 may be disposed on outer edge 516 of body 504 (e.g., so that outer edge 516 includes a portion of channel 508). In the alternative, for example, channels 508 may be disposed within body 504 of second clamp section 502 (i.e., between inner edge 514 and outer edge 516) and/or on inner edge 514 of body 504 (e.g., so that inner edge 514 includes a portion of channel 508). Modification of second clamp section 502 so that channels 508 are disposed within body 504 and/or on inner edge 514 would be understood by a PHOSITA. As shown in FIG. 5, channels 508 may have a cruciform shape. Channels 508 may have one or more other shapes, as well, such as, for example, triangular, rectangular, circular, tear drop, or dovetail. Modification of channels 508 to include one or more other shapes would be understood by a PHOSITA. As discussed above, second clamp 500 may include two second clamp sections 502 joined together to substantially encircle the associated inlet mixer. Second clamp sections 502 may be disposed around an associated inlet mixer so that end portions 510 of one second clamp section 502 may near or in contact with end portions 510 of another second clamp section 502. Second clamp section 502 may be connected together at end portions 510 using a plurality of second clamp bolts 522 (shown in FIG. 7) and through holes 512. Second clamp sections 502 also may be connected together at end portions 510 using lock nuts, ratchets, and the like, as would be understood by a PHOSITA. Tightening of the second clamp bolts may provide a sufficient grip between second clamp 500 and the associated inlet mixer so as to prevent movement of second clamp 500 in the vertical direction (i.e., either toward or away from the associated diffuser) and/or about an axial direction of the associated inlet mixer. Second clamp sections 502 may be connected together using other types of connections and/or connectors. Second clamp section 502 may be hinged together, for example, on one side. End portions 510 may include, for example, male and/or female dovetail joints. Modification of second clamp sections 502 so that they may be connected together using other types of connections and/or connectors would be understood by a PHOSITA. FIG. 6A is a perspective view of connector 600 in accordance with example embodiments. Connectors 600 may be configured to connect first clamp 400 and second clamp 500. Connectors 600 may be configured to connect first clamp sections 402 and second clamp sections 502. Connectors 600 may have a cross-section similar to channels 408 and/or channels 508. FIG. 6B is a cross-sectional view of connector 600 in accordance with example embodiments. Connectors 600 may have a cruciform shape including, for example, main body 602 and transepts 604. Connectors 600 may have one or more other shapes, as well, such as, for example, triangular, rectangular, circular, tear drop, or dovetail. Modification of connectors 600 to include one or more other shapes would be understood by a PHOSITA. Modification of connectors 600 to have a cross-section similar to channels 408 and/or channels 508 also would be understood by a PHOSITA. One or more connectors 600 may be fixed to first clamp section 402. For example, when first clamp section 402 includes two channels 408, one connector 600 may be fixed to first clamp section 402 in one channel 408 and/or another connector 600 may be fixed to first clamp section 402 in the other channel 408. Connectors 600 may be fixed to first clamp sections 402 by welding, for example, or one or more other methods so that connectors 600 do not move relative to first clamp sections 402. Methods for fixing connectors 600 to first clamp sections 402 would be understood by a PHOSITA. One or more connectors 600 may be fixed to second clamp section 502. For example, when second clamp section 502 includes two channels 508, one connector 600 may be fixed to second clamp section 502 in one channel 508 and/or another connector 600 may be fixed to second clamp section 502 in the other channel 508. Connectors 600 may be fixed to second clamp sections 502 by welding, for example, or one or more other methods so that connectors 600 do not move relative to second clamp sections 502. Methods for fixing connectors 600 to second clamp sections 502 would be understood by a PHOSITA. As would be understood by a PHOSITA, materials used in and fabrication processes for first clamp 400, second clamp 500, and/or connectors 600 may be selected so as to minimize galvanic corrosion, intergranular stress corrosion cracking (“IGSCC”), activation by neutron and gamma flux, and/or other problems associated with nuclear plants. Thus, the materials might include, for example, stainless steels (e.g., type 304 stainless steel, type 316 stainless steel), molybdenum alloys, and/or titanium alloys. FIG. 7 is a cross-sectional view of jet pump assembly 700 according to example embodiments. Jet pump assembly 700 may include inlet mixer 704 and diffuser 706. The interface between inlet mixer 704 and diffuser 706 is slip joint 708. Bottom portion 704a of inlet mixer 704 may be inserted into upper crown 706a of diffuser 706 to integrate inlet mixer 704 with diffuser 706. Distal end 704b of inlet mixer 704 may rest in upper crown 706a of diffuser 706 to form slip joint 708. In FIG. 7, first clamp 400 may include two first clamp sections 402 joined together to substantially encircle diffuser 706. First clamp sections 402 may be connected together at end portions 410 using a plurality of first clamp bolts 422. First clamp sections 402 may be disposed so that offsets 406 accommodate guide ears 706b of diffuser 706. Channels 408 may extend completely through first clamp sections 402. In FIG. 7, second clamp 500 may include two second clamp sections 502 joined together to substantially encircle inlet mixer 704. Second clamp sections 502 may be connected together at end portions 510 using a plurality of second clamp bolts 522. Channels 508 may extend completely through second clamp sections 502. In FIG. 7, connectors 600 may be fixed to first clamp 400 so that connectors 600 may not move relative to first clamp 400. Connectors 600 may not be fixed to second clamp 500 so that connectors 600 may move relative to second clamp 500. In FIG. 7, connectors 600 may allow movement of first clamp 400 relative to second clamp 500 in a first direction between first clamp 400 and second clamp 500. The allowed movement of first clamp 400 relative to second clamp 500 may be linear movement. The first direction may be, for example, an axial direction of inlet mixer 704, an axial direction of diffuser 706, and/or an axial direction of jet pump assembly 700. The allowed movement may relate, for example, to thermal expansion of inlet mixer 704, diffuser 706, and/or other related components. In example embodiments, connectors 600 may be fixed to second clamp 500 and may not be fixed to first clamp 400. In example embodiments, one or more connectors 600 may be fixed to first clamp 400 and may not be fixed to second clamp 500, while one or more other connectors 600 may be fixed to second clamp 500 and may not be fixed to first clamp 400. In these embodiments as well, connectors 600 may allow movement of first clamp 400 relative to second clamp 500 in the first direction between first clamp 400 and second clamp 500. In FIG. 7, connectors 600 may limit and/or prevent movement of first clamp 400 relative to second clamp 500 in a second direction perpendicular to the first direction. The limited and/or prevented movement of first clamp 400 relative to second clamp 500 may be linear movement. The limited and/or prevented movement of first clamp 400 relative to second clamp 500 may be rotational movement about an axis defined in the first direction. The axis may be, for example, an axis of inlet mixer 704, an axis of diffuser 706, and/or an axis of jet pump assembly 700. The limited and/or prevented movement may relate, for example, to oscillating motion, FIV, and/or turbulent flow internal to jet pump assembly 700. In FIG. 7, first clamp 400, second clamp 500, and/or connectors 600 may allow movement of inlet mixer 704 relative to diffuser 706 in an axial direction of inlet mixer 704, an axial direction of diffuser 706, and/or an axial direction of jet pump assembly 700. The allowed movement of inlet mixer 704 relative to diffuser 706 may be, for example, linear movement. The allowed movement may relate, for example, to thermal expansion of inlet mixer 704, diffuser 706, and/or other related components. In FIG. 7, first clamp 400, second clamp 500, and/or connectors 600 may limit and/or prevent movement of inlet mixer 704 relative to diffuser 706 in a direction perpendicular to an axial direction of inlet mixer 704, an axial direction of diffuser 706, and/or an axial direction of jet pump assembly 700. The limited and/or prevented movement of inlet mixer 704 relative to diffuser 706 may be linear movement. The limited and/or prevented movement of inlet mixer 704 relative to diffuser 706 may be rotational movement about an axial direction of inlet mixer 704, an axial direction of diffuser 706, and/or an axial direction of jet pump assembly 700. The limited and/or prevented movement may relate, for example, to oscillating motion, FIV, and/or turbulent flow internal to jet pump assembly 700. The arrangement in FIG. 7 may maintain stiffness of slip joint 708 to prevent oscillating motion and/or suppress FIV, while simultaneously allowing thermal expansion of inlet mixer 704, diffuser 706, and/or other related components. FIG. 8 is a flowchart of a method for controlling movement of a first component integrated with a second component according to example embodiments. As shown in S800 of FIG. 8, a first clamp may engage the first component. As related to FIGS. 7 and 8, first clamp 400 may engage diffuser 706. As shown in S802 of FIG. 8, a second clamp may engage the second component. As related to FIGS. 7 and 8, second clamp 500 may engage inlet mixer 704. As shown in S804 of FIG. 8, the first and second clamps may be connected using a plurality of connectors. As related to FIGS. 7 and 8, connectors 600 may connect first clamp 400 and second clamp 500. In FIG. 8, engaging the first component with a first clamp (S800), engaging the second component with a second clamp (S802), and connecting the first and second clamps using a plurality of connectors (S804) may be performed in any order. As related to FIGS. 7 and 8, for example, first clamp 400 and second clamp 500 may be connected using connectors 600. Then first clamp 400 may engage diffuser 706, followed by second clamp 500 engaging inlet mixer 704. In the alternative, second clamp 500 may engage inlet mixer 704, followed by first clamp 400 engaging diffuser 706. Or first clamp 400 may engage diffuser 706 at the same time that second clamp 500 engages inlet mixer 704. In another example, first clamp 400 may engage diffuser 706 at the same time that second clamp 500 engages inlet mixer 704. Then first clamp 400 and second clamp 500 may be connected using connectors 600. As related to FIGS. 7 and 8, one or more connectors 600 may be fixed to first clamp 400 prior to first clamp 400 engaging diffuser 706. Similarly, one or more connectors 600 may be fixed to second clamp 500 prior to second clamp 500 engaging inlet mixer 704. For example, all connectors 600 may be fixed to first clamp 400 prior to first clamp 400 engaging diffuser 706, all connectors 600 may be fixed to first clamp 400 prior to second clamp 500 engaging inlet mixer 704, and/or all connectors 600 may be fixed to first clamp 400 prior to connectors 600 connecting first clamp 400 and second clamp 500. In another example, one or more connectors 600 may be fixed to second clamp 500 prior to second clamp 500 engaging inlet mixer 704, one or more connectors 600 may be fixed to second clamp 500 prior to first clamp 400 engaging diffuser 706, and/or one or more connectors 600 may be fixed to second clamp 500 prior to connectors 600 connecting first clamp 400 and second clamp 500. As related to FIGS. 7 and 8, once first clamp 400 engages diffuser 706, second clamp 500 engages inlet mixer 704, and first clamp 400 and second clamp 500 are connected using connectors 600, connectors 600 may allow movement of first clamp 400 relative to second clamp 500 in a first direction between first clamp 400 and second clamp 500 and/or may allow movement of inlet mixer 704 relative to diffuser 706 in the first direction. That movement may be, for example, linear movement of inlet mixer 704 relative to diffuser 706. The first direction may be, for example, an axial direction of jet pump assembly 700, inlet mixer 704, and/or diffuser 706. The first direction may be, for example, vertical. As related to FIGS. 7 and 8, once first clamp 400 engages diffuser 706, second clamp 500 engages inlet mixer 704, and first clamp 400 and second clamp 500 are connected using connectors 600, connectors 600 may limit and/or prevent movement of first clamp 400 relative to second clamp 500 in a second direction perpendicular to the first direction and/or may limit and/or prevent movement of inlet mixer 704 relative to diffuser 706 in the second direction. That movement may be, for example, linear movement of inlet mixer 704 relative to diffuser 706. That movement may be, for example, rotational movement of inlet mixer 704 relative to diffuser 706 about an axis defined in the first direction. The second direction may be, for example, horizontal (e.g., defining a horizontal plane). While example embodiments have been particularly shown and described, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims. |
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055880363 | description | DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 is a block diagram showing an X-ray CT apparatus according to the embodiment of the present invention. Referring to FIG. 1, a subject, i.e. a patient, 1 lies on a bed 2 which is movable horizontally and vertically by a known drive means. The X-ray CT apparatus comprises an X-ray tube 3, which irradiates an X-ray to the patient 1 and an X-ray detector 4, which detects the irradiated X-ray. The X-ray tube 3 and the X-ray detector 4 are mounted on a gantry or frame 5 which can be turned around a predetermined axis of rotation. The X-ray CT apparatus of the embodiment is also equipped with a high-voltage generator 6 for generating high voltage to be applied to the X-ray tube 3, a high-voltage controller 7 for controlling the high-voltage generator 6, a bed drive unit 8 for driving the bed 2 and a bed controller 9 for controlling the bed drive unit 8. The X-ray CT apparatus of this embodiment is further equipped with a gantry drive unit 10 for rotating the gantry 5 around a predetermined axis of rotation and a gantry controller 11 for controlling the gantry drive unit 10. The X-ray CT apparatus of the embodiment still further comprises a main controller 12, which controls the high-voltage controller 7, the bed controller 9, and the gantry controller 11. A monitor 13 for displaying a desired image and a sub-monitor 13a for displaying the radiographing conditions are also equipped, and these monitors 13 and 13a are also operatively connected to the main controller 12. The main controller 12 indirectly controls the X-ray tube 3, the bed 2, and the gantry 5 so that the X-ray tube 3 irradiates a predetermined X-ray. The bed 2 moves to a predetermined position or at a predetermined speed, and the gantry 5 rotates at a predetermined rotational speed or at a predetermined tilt angle. The X-ray CT apparatus of this embodiment further comprises an exposure information file 14, in which exposure information data is stored as a disk or the like, and the main controller 12 is designed to set radiographing conditions according to past exposure information data stored in the exposure information file 14 and controls the bed 2, the X-ray tube 3, and the gantry 5 in accordance with the set radiographing conditions. The exposure information data may be directly inputted into the controller 12 through an on-line system. In the above meanings, the main controller 12 comprises the following elements as shown in FIG. 2. The main controller 12 comprises a central processing unit (CPU) 112a, a scan control element 112b giving instructions to the high voltage control 7, the bed drive controller 9 and the gantry controller 11, a display control element 112c giving instructions to the monitor 13 and the sub-monitor 13a, and an input/output control element 112d for the exposure information file 14. These elements 112b, 112c and 112d are operatively connected to the CPU 112a. An input control element 112e may be disposed between the CPU 112a and the display control element 112c. The functions of the controller 12 including these elements will be made more clear hereinafter with reference to the flowchart of FIG. 3. The exposure information file 14 stores exposure information, including the ID of a patient, the name of the patient, the date of exposure, scan mode, the number of the scans, a radiographed area, a scan speed, a tube voltage, a tube current, a slicing width, a reconstruction function, a posture of the patient, a direction of inserting the patient, a direction of observation, a use of a contrast medium, a type of voice, a relative table position, a tilt angle, a pause time between scans, and a scan pitch. The tilt angle refers herein to the angle of the tilt of the gantry 5 from a predetermined reference axis (the vertical direction when the X-ray CT apparatus is normally disposed). A zero tilt angle, for example, indicates that the slice plane is set in a direction perpendicular to the body axis of a patient. The scan pitch refers to the distance between adjoining slices. The main controller 12 is capable of converting, out of the exposure information, the data showing the slice-related information, that is, the number of slices, the tilt angle and the scan pitch (hereinafter referred to totally as "slice information data"), into graphic data (hereinafter referred to as "slice information image data"), which can be displayed on a scanographic image in a superimposed manner, and the desired slice information image data is inversely converted to the slice information data. The operation of the X-ray CT apparatus of the present invention will be described hereunder. FIGS. 3A and 3B are flowcharts showing the procedure for setting radiographing conditions by using the X-ray CT apparatus, in which the flowchart of FIG. 3A represents the case requiring no scanographing operation and FIG. 3B represents the case requiring the scanographing operation. First, with reference to FIG. 3A, identification (ID) number and name of a subject such as patient are entered at a step S1, and past exposure information data corresponding to the ID No. and the name of the patient is indexed by the main controller 12 from an exposure information file stored in the information exposure file 14 at step S2. In the next step S3, it is confirmed whether the past exposure information is indexed or not. In the case of "YES", the indexed information is displayed on the display sub-monitor 13a (step S4) as numerical data, and in the case of "NO", the radiographing conditions are manually set (step S5). In a step S6, it is confirmed whether the radiographing conditions are set by utilizing the displayed exposure information or not. In the case of "YES", the set radiographing conditions are set and stored in the file 14 in a step S9, and in this operation, when it is required to modify the numerical data of the radiographing conditions, such modification or correction will be done in a step S7 before the step S9. In the step S6, in the case of "NO", it is confirmed whether the indexing is to be carried out continuously or not (step S8), and in the case of "NO", the radiographing conditions are manually set as referred to in the step S5. In the case of "YES", the step returns to the step S2 to again carry out the indexing of the another past exposure information of the same patient from the stored exposure information file and continue the same operations as those described above. In the final step S10, the scanning operation is carried out under the set and stored radiographing conditions under the controlling of the main controller 12 through the high voltage controller 7, the bed controller 9 and the gantry controller 11 for controlling the setting conditions of the high voltage generator 6 for the X-ray tube 3, the patient bed 2 and the gantry 4. On the other hand, in the case where a previous scanographing is required for setting radiographing position and range of the patient, the operation will be performed in accordance with the flowchart of FIG. 3B. With reference to FIG. 3B, identification (ID) number and name of a subject such as patient are entered at a step S101 and a scanographing is preliminarily performed for setting the position and the region of the patient to be radiographed in the next step S102. The thus obtained scanographic image is displayed on the monitor 13 at a step S103. In parallel to these steps S102 and S103, other steps S202 and S203, which corresponding to the step S2 and S3 are performed, that is, the past exposure information data corresponding to the ID No. and the name of the patient are indexed by the main controller 12 from an exposure information file stored in the information exposure file 14 at the step S202. In the next step S203, it is confirmed whether the past exposure information is indexed or not. In the case of "YES", the information from the Step S103 is combined, and a slice information from the indexed exposure data is converted to a slice information image data in a step S104 by the main controller 12 and the indexed information is displayed (step S105) as numerical data on the sub-monitor 13a and slice information image data on the monitor 13 by superimposing it on the scanographic image. In connection with this step, FIG. 4A shows the slice information image data 22, which is displayed in a superimposed manner on the scanographic image 23 on the monitor 13. At this point, no relationship of relative position has been established between the slice information image and the scanographic image on the monitor. FIG. 4C shows the numerical data 21 displayed on the sub-monitor 13a. In the step S203, in the case of "NO", the radiographing conditions are manually set (step S106). In a step S107, it is confirmed whether the radiographing conditions are set by utilizing the displayed exposure information on the sub-monitor 13a or not. In the case of "YES", the radiographing conditions are set and stored in a step S111. However, this step S111 will be done through the following steps S108 to S110 in a case where it is required to modify or correct the numerical data of the radiographing conditions of the displayed exposure information regarding such as the tube current, tube voltage, scanning speed, etc., the modification is performed in a step S108. In this modification, if, for example, a touch-panel type EL display is used as the sub-monitor 13a, a switch 24 may be installed beside the section where the numerical data 21 to be modified is displayed, and the new numerical data can be set by pressing the switch 24. Furthermore, in a case of requiring the modification or correction of the slice information image data, the radiographing operation is performed with a desired tilt angle. This is performed in a step S109, and the modified or corrected slice information image data is inversely converted into the slice information (step S110). This step S110 will be performed in the case of no modification for inversely converting the data to the slice information. In the step S109, reference is to be made to FIG. 4B showing one mode of modifying the slice information image data. As is apparent from the comparison with FIG. 4A, the whole slice information image has been moved on the monitor with respect to the scanographic image, and next, the modified data is inversely converted as mentioned above. In the step S107, in the case of "NO", it is confirmed whether the indexing is to be carried out continuously or not (step S113), and in the case of "NO", the radiographing conditions are manually set as referred to in the step S106. In the case of "YES", the step returns to the step S202 to again carry out the indexing of the past exposure information of the same patient from the stored exposure information file and continue the same operations as those described above. In the final step S112, the scanning operation is carried out under the set and stored radiographing conditions under the controlling of the main controller 12 through the high voltage controller 7, the bed drive controller 9 and the gantry controller 11 for controlling the setting conditions of the high voltage of the X-ray tube 3, the patient bed 2 and the gantry 4. In the above operation steps, in a preferred embodiment of the present invention, a plurality of past exposure information data of one patient are stored in the file with respect to the respective portions to be exposed in a predetermined file position in a manner such that when a new information is stored, the oldest information is automatically vanished, and accordingly, the same numbers of the past exposure information data are stored in accordance with the passing of time. As described above, the X-ray CT apparatus of the present invention is designed to automatically set the radiographing conditions in accordance with the past exposure information. This achieves higher examination efficiency and reduced burden on the operator. Further, in the above embodiment, the whole slice information image data are moved as one mode of modifying the slice information image data, but it is needless to say that there is no need to move the slice information image data if the slice happens to be set at the desired radiographing point. Furthermore, only the tilt angle of a particular slice may be modified or the scan pitch of a particular section may be modified. In the embodiment described above, the exposure information file is provided separately from the main controller, but it may alternatively be provided in a disk inside the main controller. Moreover, a single exposure information file may be configured so that it may be shared by a plurality of X-ray CT apparatuses through, for example, a network. |
claims | 1. An X-ray fluoroscopic apparatus, that collects an X-ray fluoroscopic radiograph including a specific region of a subject and detects a position of the specific region, and sends a therapeutic beam irradiation signal to a radiation irradiation device while tracking a movement of said specific region, said X-ray fluoroscopic apparatus, further comprising:an X-ray tube;an X-ray detector that detects an X-ray that is irradiated from said X-ray tube and transmits through said subject;an irradiation area projection element that generates a projection area denoting a therapeutic beam irradiation area by performing a virtual fluoroscopic projection simulating a geometric fluoroscopic condition between said X-ray tube and said X-ray detector relative to an initial set of CT image data based on said therapeutic beam irradiation area registered in said CT image data of said subject generated when an initial therapy planning is created;a specific region projection element that generates a specific projection area denoting a specific regional area by performing a virtual fluoroscopic projection simulating a geometric fluoroscopic condition between said X-ray tube and said X-ray detector relative to said initial set of CT image data based on the specific region registered on said CT image data of said subject generated when said therapy planning is created;a superimposition element that both superimposes the projection area denoting said therapeutic beam irradiation area onto said X-ray fluoroscopic radiograph, and superimposes the specific projection area denoting said specific-regional area to said X-ray fluoroscopic radiograph at said specific-regional position detected based on said X-ray fluoroscopic radiograph; anda gating element that sends the therapeutic beam irradiation signal to the radiation irradiation apparatus when the projection area denoting the specific-regional area superimposed onto the X-ray fluoroscopic radiograph by said superimposition element are placed in the projection area denoting the therapeutic beam irradiation area superimposed to the X-ray fluoroscopic radiograph by the superimposition element. 2. The X-ray fluoroscopic apparatus, according to claim 1, further comprising:an image display element that displays the X-ray fluoroscopic radiograph and the projection area denoting said therapeutic beam irradiation area superimposed on said X-ray fluoroscopic radiograph by said superimposition element and the projection area denoting said specific-regional area superimposed to said X-ray fluoroscopic radiograph by said superimposition element. 3. The X-ray fluoroscopic apparatus, according to claim 1, further comprising:a template area selection element that selects an area including said specific region from said X-ray fluoroscopic radiograph;a template generation element that generates a template indicating said specific region from the area including said specific region selected by said template area selection element; anda position detection element that detects a position of said specific region relative to said fluoroscopic radiograph by performing template matching by using the template generated by using said X-ray fluoroscopic radiograph and said template generation element. 4. The X-ray fluoroscopic apparatus, according to claim 3, wherein:said template area selection element selects an area including said specific region from said X-ray fluoroscopic radiograph by a DRR (digital reconstructed radiography) image generated by one of a step of:performing the virtual fluoroscopic projection simulating a geometric fluoroscopic condition between said X-ray tube and said X-ray detector relative to said CT image data; andmachine learning learned using an X-ray fluoroscopic radiograph obtained by an X-ray fluoroscopy of said subject in advance. 5. The X-ray fluoroscopic apparatus, according to claim 4, wherein:said machine learning that is one selected from the group consisting of:a support vector machine, a decision tree, a boosting and a neural network. 6. The X-ray fluoroscopic apparatus, according to claim 3, further comprising:a DRR image generation element that generates a DRR image including said specific region by performing a virtual fluoroscopic projection simulating a geometric fluoroscopic condition between said X-ray tube and said X-ray detector relative to CT image data of said subject generated when a therapy planning is created; andan image display element that displays an image including said specific region selected by said template area selection element and an image obtained by superimposing a projection area denoting said specific region generated by said specific region projection element to a DRR image generated by said DRR image generation element. 7. The X-ray fluoroscopic apparatus, according to claim 1, further comprising:a DRR image generation element that generates a DRR image including said specific region by performing a virtual fluoroscopic projection simulating a geometric fluoroscopic condition between said X-ray tube and said X-ray detector relative to CT image data of said subject generated when said initial therapy planning is created; andan image display element that displays said X-ray fluoroscopic radiograph and an image obtained by superimposing a projection area denoting said specific region generated by said specific region projection element to a DRR image generated by said DRR image generation element. 8. The X-ray fluoroscopic apparatus, according to claim 6, wherein:said CT image data is a four-dimensional CT image data, further comprising:a group of three-dimensional CT image data including said specific region relative to a plurality of continuous breathing phases of said subject; andsaid DRR image generation element generates a DRR image including said specific region based on CT image data of phases in association with said X-ray fluoroscopic radiograph. 9. The X-ray fluoroscopic apparatus, according to claim 1, further comprising:said CT image data is a four-dimensional CT image data, further comprising:a group of three-dimensional CT image data including said specific region relative to a plurality of continuous breathing phases of said subject; andsaid specific region projection element generates a projection area denoting said specific region based on CT image data of phases in association with said X-ray fluoroscopic radiograph. 10. An x-ray fluoroscopic apparatus, comprising:an X-ray tube;an X-ray detector that detects an X-ray that is irradiated from said X-ray tube and transmits through a subject; wherein:said X-ray fluoroscopic apparatus collects an X-ray fluoroscopic radiograph including a specific region of said subject and detects a position of the specific region, and sends a therapeutic beam irradiation signal to a radiation irradiation device while tracking a movement of said specific region;a specific region projection element that generates a projection area denoting said specific-regional area by performing a virtual fluoroscopic projection simulating a geometric fluoroscopic condition between said X-ray tube and said X-ray detector relative to an initial set of CT image data of said subject based on said specific region registered on said CT image data of said subject generated when an initial therapy planning is created;a DRR image generation element that generates a DRR image including said specific region by performing a virtual fluoroscopic projection simulating a geometric fluoroscopic condition between said X-ray tube and said X-ray detector relative to CT image data of said subject generated when said initial therapy planning is created;a template area selection element that selects an area including said specific region from said X-ray fluoroscopic radiograph;an image display element that displays an image of an area including said specific region in said X-ray fluoroscopic radiograph selected by said template area selection element, and an image obtained by superimposing a projection area denoting said specific region generated by said specific region projection element to a DRR image generated by said DRR image generation element;a template generation element that generates a template indicating said specific region from an area including said specific region selected by said template area selection element; anda position detection element that detects a position of said specific region relative to said fluoroscopic radiograph by performing template matching by using said X-ray fluoroscopic radiograph and a template generated by said template generation element. 11. The X-ray fluoroscopic apparatus, according to claim 10, wherein:said template area selection element selects a DRR image generated by a step of performing a virtual fluoroscopic projection simulating a geometric fluoroscopic condition between said X-ray tube and said X-ray detector relative to said CT image data, or selecting an area including said specific region from said X-ray fluoroscopic radiograph by machine learning learned using an X-ray fluoroscopic radiograph obtained by an initial X-ray fluoroscopy of said subject in advance. 12. The X-ray fluoroscopic apparatus, according to claim 11, wherein:said machine learning that is one selected from the group consisting of:a support vector machine, a decision tree, a boosting and a neural network. |
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047388188 | description | DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 illustrates schematically a pressurized water reactor (PWR) nuclear PWR plant to which the invention is applied. The PWR includes a nuclear reactor vessel 1 having a reactor core 3 in which controlled fission reactions produce heat. Reactor coolant in the form of light water is circulated in a primary loop 5, which includes the reactor core 3, a hot leg conduit 7, a steam generator 9, a cold leg conduit 11, and a reactor coolant pump 13. The coolant is circulated within the steam generator 9 through thousands of u-shaped tubes 15, immerged in water which is converted to steam by the heat carried by the reactor coolant. Temperature sensors 17 in the hot and cold leg 7 and 11 are used to generate an average coolant temperature, T.sub.avg, which among other things, is used to control the power generated by the reactor. Steam from the steam generator 9 circulates in a secondary loop 19 which includes a steam header 21 which conducts the steam to a steam turbine 23. The turbine 23 utilizes the steam to drive a generator 25 which produces electricity. Steam exhausted from the turbine is condensed in condenser 27 and the condensate is returned to the steam generator 9 as feedwater through a conduit 29 by a main feedwater pump 31, which together with a supply of make up water 33, an air operated control valve 35, and a motor operated main feedwater isolation valve 37, constitute the main feedwater system 39. The steam header 21 includes a pressure relief valve 41 and a motor operated main steam isolation valve 43. A steam dump system includes a conduit 45 which diverts steam around the turbine to the condenser under the control of a compressed air driven steam dump valve 47. The steam dump system provides a means for dissipating excess heat such as in the event of a turbine trip, and the relief valve relieves excessive steam pressure. In view of the importance of the secondary loop being able to absorb the heat generated by the reactor, a backup system for the main feedwater system is provided in the form of an auxiliary feedwater system 49 which includes an auxiliary feedwater pump 51 which pumps water from an auxiliary feedwater supply tank 53 through a check valve 55 into the feedwater conduit 29. The level of feedwater in the steam generator 9 is measured by a level measuring system 57 and typically feedwater flow in the main system is controlled to maintain the feedwater at a programmed level. While FIG. 1 shows only one steam generator 9 for clarity, a typical power plant has one to four steam generators 9, each provided with heated coolant from the one reactor through its own primary loop, and all supplying steam to the one turbine-generator combination. The main feedwater system usually includes two main feedwater pumps 31 in parallel, either of which is sufficient to provide feedwater for all of the steam generators. Likewise, the auxiliary feedwater system 49 includes multiple pumps 51 in parallel which inject feedwater into the conduit 29 for each steam generator. Separate feedwater flow control valves 35, main feedwater isolation valves 37, and auxiliary feedwater check valves 55, as well as steam relief valves 41 and steam isolation valves 43, are provided for each steam generator. A single steam dump line 45 with valve 47 connected to the common portion of steam header 21 dumps steam for all of the steam generators. Feedwater flow to each steam generator is controlled by a three element controller such as the controller 59 shown schematically in FIG. 2. The three elements of control are steam generator water level, feedwater flow and steam flow. A programmer 61 establishes a programmed level for the feedwater as a function of nuclear power which is a measure of the load imposed on the steam generator. The programmed level signal is compared in summer 63 with a signal representative of the actual feedwater level in the steam generator as measured by the measuring system 57 to generate a level error signal. The programmed level signal and the measured level signal are passed through lag units 65 and 67 respectively which reduce noise, and in the case of the programmed level signal, smoothes out changes in the set point due to changes in nuclear power. The level error signal is applied to a PID controller 73 which applies proportional control action through block 75, and integral and derivative control action through block 77, to the applied signal. The feedwater level signal thus generated is combined in summer 79 with a feedwater flow signal, and a steam flow signal to generate a three element signal to which proportional and integral control action is applied in PI controller 83 to generate a feedwater flow control signal. This signal is compared with a control signal generated, in a manner to be discussed below, as a function of reactor coolant temperature in an Auctioneer Low unit 85 which selects the signal of smallest magnitude as the active control signal to modulate the feedwater control valve 35. The active control signal selected by the Auctioneer Low unit 85 is compared with the output from PI Controller 83 in a summer 89, with the difference multiplied by a proportionality factor in unit 91 and summed with the level error signal in the summer 93 in the PID controller 73. The Auctioneer Low unit 85, summer 89, amplifier 91 and the associated connections, are new components added by the present invention, to be discussed below, to a conventional three element controller for the feedwater control valve 35. Such a controller regulates the flow of feedwater to the steam generator to maintain the steam generator feedwater inventory at the programmed level with dynamic compensation which takes into account any mismatch between steam flow and feedwater flow. The scheme described above provides good control of the feedwater to the steam generator, but it is subject to conditions which can give rise to undesirable actuation of the auxiliary feedwater system. In the event a reactor trip followed by a turbine trip, the pressure rises in the steam generator. The interruption of steam flow also causes the steam voids, which typically account for about one-third of the water volume in the steam generator, to collapse, thereby rapidly lowering the water level. The increased pressure actuates the steam dump which reinitiates steaming to reestablish the voids and thereby raise the level somewhat. The dumping of steam however, leads to a low level signal which activates the main feedwater system. The cool feedwater supplied to the steam generator has the potential for lowering T.sub.avg, the average temperature of the reactor coolant in the primary loops, to an extent which could reduce the shutdown margin of the reactor to an unacceptable extent as explained above. To prevent this from occurring, the main feedwater isolation valve 37 is closed when T.sub.avg is lowered to a preselected value. A circuit effecting this is shown in FIG. 3 wherein the simultaneous occurrence of a reactor trip signal and a Low T.sub.avg signal sets a flip-flop 90 through an AND gate 92. The flip-flop 90, which is reset manually, activates the main feedwater isolation logic 94 to close isolation valves 37. Termination of main feedwater flow, with continued operation of the steam dump, leads to a low-low level indication which automatically activates the auxiliary feedwater system. As previously mentioned, it is undesirable to unnecessarily challenge such a safety system. In addition, the auxiliary feedwater is colder and the system does not provide automatic control of the water level as the main feedwater system does, and therefore, can also potentially reduce the shutdown margin to an undesirable level. The effect of the above described scenario, that is, a reactor trip followed by a turbine trip which leads to actuation of the auxiliary feedwater system, on the key system parameters in a PWR at full power, which does not incorporate the invention, is illustrated in FIGS. 4a-f. As seen by FIG. 4a the nuclear power initially drops rapidly and then more slowly falls to zero power. FIG. 4b illustrates that the steam pressure rises rapidly when the turbine trips and steam flow is terminated, until the steam dump opens and the pressure falls to the no load pressure. Steam flow, as shown in FIG. 4c, falls from a nominal fractional value of 1.0 at a full power to zero when the turbine trips, rises as the dump system takes effect, and then falls off to zero. FIG. 4d shows that T.sub.avg of the reactor coolant falls below the Low T.sub.avg set point which results in isolation of the main feedwater system. T.sub.avg then increases somewhat before gradually falling off below the no load value. The feedwater flow, as indicated by FIG. 4e, drops initially due to a mismatch with steam flow which is terminated by shut down of the turbine, increases with activation of the steam dump, and then is cut to zero with the closing of the main feedwater isolation valves as a result of the drop in T.sub.avg. FIG. 4f illustrate the effect of this transient on steam generator level. The level drops with the collapse of the voids when steam flow ceases upon tripping of the turbine, recovers to some extent initially with activation of the steam dump and then falls rapidly when the main feedwater isolation valve closes until the low-low limit is reached and the auxiliary feedwater system is activated to raise the level again. We have determined that in order to avoid auxiliary feedwater operation, the main feedwater system must be kept in operation after reactor trip while avoiding a primary coolant excessive cool down. This is achieved by the following: A. The low primary t.sub.avg set point, which triggers isolation of the main feedwater system, is lowered to a value below the no load temperature. It will be noticed from FIG. 4d that in the conventional feedwater control system, the Low T.sub.avg set point is above the no load temperature. As this function is not used in any accident analysis, lowering the set point does not require any reanalysis. The only verification to be performed is to assure that the design transient "reactor trip without inadvertent cooldown" is not exceeded, or to assess the acceptability of small deviations. Lowering of the T.sub.avg set point below the no load temperature will avoid main feedwater isolation when going from full load to no load conditions. B. The low-low steam generator level reactor trip set point is assumed to be lowered to a value below the initial dip in level caused by the termination of steam flow. In order to gain the maximum margin on auxiliary feedwater start on low-low steam generator level, it can be necessary, depending upon plant, and more importantly, steam generator design to: (a) lower the low-low level set point; PA1 (b) filter the level signal to reduce the magnitude of the transient; PA1 (c) delay the auxiliary feedwater start by a time interval which will allow the level to recover from the critical dip caused by termination of steam flow; PA1 (d) start the auxiliary feedwater system on a wide range signal (normally the low-low level signal is generated by narrow range instrumentation which provides accurate measurement but only in the expected range of steam generator level. In some steam generator designs, the lowered set point may be out of the range of the narrow range instrumentation and the wide range signal may have to be used); PA1 (e) demonstrate acceptability of the above by appropriate accident reanalysis: PA1 (f) upon detection of a reactor trip, overriding the high feedwater flow demand induced by the low steam generator level with a flow demand program based upon primary temperature measurement. PA1 (a) the steam dump flow does not deplete steam generator inventory to the extent that the low-low level is reached; PA1 (b) feedwater flow is gradually reduced as no load temperature is reached. PA1 (c) feedwater flow is interrupted (in control mode) slightly below no load temperature and before the new low primary temperature set point is reached; PA1 (d) the feedwater flow demand at no load exceeds decay heat level at the time this temperature is reached. Excessive cooldown, as well as a steam generator low-low level signal, are avoided by the additions to the feedwater control system shown in FIG. 5. The T.sub.avg signals for each of the primary loops generated from the temperature sensors 17 are auctioneered low with the lowest signal selected. Dynamic compensation is applied to the selected T.sub.avg signal by lead-lag unit 95 to speed up the response. The compensated T.sub.avg signal is then utilized to generate a T.sub.avg programmed feedwater flow control signal in programmer 97. An exemplary program is illustrated in FIG. 6. This program is selected such that: Returning to FIG. 5, application of this T.sub.avg programmed flow control signal to the Auctioneer Low unit 85 of FIG. 2 is controlled by an analog gate 99. The gate 99 is controlled by a flip-flop 101 which is set by a reactor trip signal. A reactor trip sets the flip-flop 101 to turn on analog gate 99 to apply the T.sub.avg programmed flow control signal to the Auctioneer Low unit 85 which selects the smaller of this signal and the conventional, level programmed flow control signal for positioning the main feedwater control valve 35. As the primary temperature goes down, the T.sub.avg programmed flow control signal will be lower in magnitude and will thus be selected to control main feedwater flow. Hence, the Auctioneer Unit 85 permits the steam generator level to recover slowly in the automatic mode without excessive cooldown. Once set by a reactor trip signal, the flip-flop 101 keeps the analog gate 99 turned on in order to allow resetting the reactor trip breakers and a quick restart if plant conditions permit. With this arrangement, no operator action is required to control steam generator level and primary temperature while the restart is being attempted. The flip-flop 101 can be reset through an OR gate 103 by a manual signal or automatically when the steam generator level is at the programmed value. In the latter case, the feedwater flow demand is zero and there is, no risk of plant undercooling. With the flip-flop reset, the analog gate applies a high level signal to the Auctioneer Low Unit 85 so that the conventional flow control signal is selected as the active signal. When the primary temperature program loop is active and is actually limiting the feedwater flow, the feedwater control loop is open and the steam generator level control system will eventually integrate the steam generator level error signal to a full open demand. As a result, the Auctioneer Low Unit 85 will select the signal from the primary temperature, T.sub.avg, program loop even when the no load steam generator level has been reestablished, thereby producing a steam generator overfilled condition. Moreover, when the reactor trip breakers are reset, and the limited T.sub.avg programmed flow control signal is cut off by the analog switch and replaced by a high level signal, there will be a step demand when the Auctioneer Low Unit switches back to the level programmed flow control signal which has been integrated up to the full demand level. To avoid these problems, the steam generator level control system integral and derivative terms are slaved to the primary temperature, T.sub.avg, loop signal whenever the T.sub.avg programmed flow control signal is active and its demand is below the proportional value opening demand from the steam generator level control system. This is accomplished in the system shown in FIG. 2 by the feedback provided from the output of the Auctioneer Low Unit 85. This signal is compared with the level programmed flow control signal appearing at the output of PI controller 83. When the Auctioneer Low Unit 85 selects the level programmed signal, there is no feedback since the two signals applied to the summer 89 are the same. With the T.sub.avg programmed signal selected, the feedback forces the level programmed signal to track the T.sub.avg programmed signal. With this arrangement, when the reactor trip breakers are reset or when steam generator level reaches the programmed value, and the system reverts to level control, the feedwater flow demand will initially remain the same; and will thereafter be corrected in accordance with the level program as required. Thus, a bumpless transfer is effected between the two programs. Techniques for effecting bumpless transfer between two control signals are known and can be accomplished by other arrangements than the preferred form shown in FIG. 2. A suitable circuit for avoiding startup of the auxiliary feedwater system on a low-low level signal generated by the initial dip in level by filtering the level signal, as prescribed by item B(b) above, is illustrated in FIG. 7. As shown, the level signal generated by the level measuring system 57 is applied to a low pass filter 105 which has a bandwidth below the frequency of the dip in level resulting from momentary interruption in steam flow following a reactor trip. A comparator 107 compares the filtered level signal with the low-low set point signal to generate a signal which activates an auxiliary feedwater start logic circuit 109 to turn on the auxiliary feedwater pumps 51 when the filtered level falls below the set point value. As shown in FIG. 8, the level signal from the steam generator level measuring system 57 can be alternately delayed by a delay circuit 111 as suggested in paragraph B(c) above for an interval which permits the level to recover from the initial dip following reactor trip. The delay circuit 111 in effect only exhibits a change in output when the change in input persists for the preselected interval of time. As in the case of the filtered level signal, the delayed signal is compared in a comparator 107 with the low-low set point to actuate the auxiliary feedwater start logic 109 when the level falls below the set point value for the prescribed time period. The level signal may be both filtered and delayed where necessary to prevent auxiliary feedwater start-up on the initial dip following a reactor trip; however, careful analysis is required to assume that adequate protection is provided. A reactor trip from full power with the invention is illustrated by FIGS. 9 through 11. As shown in FIG. 9, feedwater flow drops rapidly following the trip as steamflow is terminated by the turbine trip, and then increases rapidly in response to the collapse of the voids and resultant sudden decrease in level. After the steam dump opens and the level recovers to some extent, another dip occurs in the flow, and then under the T.sub.avg program, the flow steadily decreases until an equilibrium flow for the decay heat is reached. FIG. 10 plots primary T.sub.avg, which as can be seen, falls rapidly, passing through the previous Low T.sub.avg set point, which would have isolated the main feedwater system, before decreasing more slowly and leveling off at the no load temperature. With the invention, T.sub.avg does not threaten the new Low T.sub.avg set point. FIG. 11 illustrates steam generator level following the reactor trip. The level falls rapidly from about 58% of nominal value at the time of the trip due to collapse of the voids, recovers to about 42% when the steam dump opens and steam flow is reestablished, and then falls as steam is dumped before the feedwater flow exceeds the steam losses and the level slowly climbs to the no load value of about 60%. As can be seen from the plot, a comfortable margin is maintained between the minimum level reached of about 23% nominal and the low-low level set point of about 12% at which the auxiliary feedwater system is started. The steam generator level characteristic is plant specific, but the plot shown is typical. If the low-low level set point can not be lowered sufficiently for safety reasons, other steps mentioned above may be adequate to avoid actuating the auxiliary feedwater system such as delaying, if possible, the actuation so that the level has an opportunity to recover from a momentary dip. With the present invention, excessive primary cooldown and starting of the auxiliary feedwater system following a reactor trip are avoided. While specific embodiments of the invention have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular arrangements disclosed are meant to be illustrative only and not limiting as to the scope of the invention which is to be given the full breadth of the appended claims and any and all equivalents thereof. |
summary | ||
abstract | A method of suppressing deposition of radionuclides on components of a nuclear power plant comprises forming a ferrite film by contacting a first chemical including iron (II) ions, a second chemical for oxidizing the iron (II) ions to iron (III) ions, and a third chemical for adjusting the pH of a processing solution containing a mixture of the first and second chemicals to be 5.5 to 9.0 with the metal member surface in a time period from a finishing stage in decontamination step of removing contaminants formed on the surface of metal member composing the nuclear power plant, and suppressing deposition of radionuclides on the metal member by the ferrite film. |
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description | This application is a continuation of U.S. application Ser. No. 15/075,497, filed Mar. 21, 2016, which is a continuation of U.S. application Ser. No. 13/502,946, filed Apr. 19, 2012 (now U.S. Pat. No. 9,289,624, issued Mar. 22, 2016), which is a continuation of PCT Application No. PCT/EP2010/065707, filed Oct. 19, 2010, which claims priority to European Application No. 09173989.6, filed Oct. 23, 2009, all of which are incorporated herein by reference. The present invention relates to a charged particle therapy apparatus used for radiation therapy. More particularly, this invention relates to a rotatable gantry designed for receiving a charged particle beam in a direction substantially along a rotation axis of the gantry, for transporting and for delivering said beam to a target to be treated. Radiotherapy using charged particles (e.g. protons, carbon ions, . . . ) has proven to be a precise and conformal radiation therapy technique where a high dose to a target volume can be delivered while minimizing the dose to surrounding healthy tissues. In general, a particle therapy apparatus comprises an accelerator producing energetic charged particles, a beam transport system for guiding the particle beam to one or more treatment rooms and, for each treatment room, a particle beam delivery system. One can distinguish between two types of beam delivery systems, fixed beam delivery systems delivering the beam to the target from a fixed irradiation direction and rotating beam delivery systems capable of delivering beam to the target from multiple irradiation directions. Such a rotating beam delivery system is further named gantry. The target is generally positioned at a fixed position defined by the crossing of the rotation axis of the gantry and the central treatment beam axis. This crossing point is called isocenter and gantries of this type capable of delivering beams from various directions to the isocenter are called isocentric gantries. The gantry beam delivery system comprises devices for shaping the beam to match the target. There are two major techniques used in particle beam therapy to shape the beam: the more common passive scattering techniques and the more advanced dynamic radiation techniques. An example of a dynamic radiation technique is the so-called pencil beam scanning (PBS) technique. In PBS a narrow pencil beam is magnetically scanned across a plane orthogonal to the central beam axis. Lateral conformity in the target volume is obtained by adequate control of the scanning magnets. Depth conformity in the target volume is obtained by adequate control of the beam energy. In this way, a particle radiation dose can be delivered to the entire 3D target volume. The particle beam energies required to have sufficient penetration depth in the patient depend on the type of particles used. For example, for proton therapy, proton beam energies are typically ranging between 70 MeV and 250 MeV. For each required penetration depth the beam energy needs to be varied. The energy spread of the beam should be limited as this directly influences the so-called distal dose fall-off. However, not all accelerator types can vary the energy. For fixed energy accelerators (e.g. a fixed isochronous cyclotron) typically an energy selection system (ESS) is installed between the exit of the accelerator and the treatment room as shown in FIGS. 1, 2 and 3. Such an energy selection system is described by Jongen et al. in “The proton therapy system for the NPTC: equipment description and progress report”, Nuc. Instr. Meth. In Phys. Res. B 113 (1996) 522-525. The function of the Energy Selection System (ESS) is to transform the fixed energy beam extracted from the cyclotron (e.g. 230 MeV or 250 MeV for protons) into a beam having an energy variable between the cyclotron fixed energy down to a required minimum energy (for example 70 MeV for protons). The resulting beam must have a verified and controlled absolute energy, energy spread and emittance. The first element of the ESS is a carbon energy degrader which allows to degrade the energy by putting carbon elements of a given thickness across the beam line. Such an energy degrader is described in patent EP1145605. As a result of this energy degradation, there is an increase in emittance and energy spread of the beam. The degrader is followed by emittance slits to limit the beam emittance and by a momentum or energy analysing and selection device to restore (i.e. to limit) the energy spread in the beam. A layout of such a known energy selection system 10 is shown in FIG. 1 together with a stationary, fixed energy accelerator 40 (in this example a cyclotron). After the degrader and emittance limiting slits, the beam passes through a 120° achromatic bend made up of two groups of two 30° bends. To meet the specification for the distal fall off, the momentum spread or the energy spread in the beam is limited by a slit placed at the center of the bend. The beam is focused by quadrupoles before the bend and between the two groups of two 30° bending magnets so that the emittance width of the beam is small and the dispersion is large at the position of the slit. The entire beam line starting at the energy degrader 41 up to the treatment isocenter 50 forms an optical system that is achromatic, i.e. a beam-optical system which has imaging properties independent from momentum (dispersionless) and independent from its transverse position. The beam line can be divided in multiple sections and each section is forming itself an achromat. As shown in FIG. 2, the first section is the ESS 10 followed by an achromatic beamline section that brings the beam up to the entrance point of a treatment room. In the case of a gantry treatment room, this entrance point is the entrance point or coupling point of the rotating gantry 15. The gantry beam line is then forming a third achromatic beam line section. In the case of a single treatment room particle therapy configuration, as shown in FIG. 3, the beam line comprises two achromatic beam line sections: a first section is the ESS 10 that brings the beam up to the gantry entrance point and the second achromatic section corresponds to the rotating gantry 15 beam line. At the gantry entrance point, the beam must have the same emittance in X and Y in order to have a gantry beam optics solution that is independent from the gantry rotation angle. The X and Y axis are perpendicular to each other and to the central beam trajectory. The X axis is in the bending plane of the dipole magnets. A disadvantage of the use of such a degrader and energy analyser is that this device requires a relative large space area as shown in FIG. 1 and hence a large building footprint is required. The installation of an ESS results also in an extra equipment cost. The present invention aims to provide a solution to overcome at least partially the problems of the prior art. It is an objective of the present invention to provide a charged particle therapy apparatus that has a reduced size and that can be built at a reduced cost when compared to the prior art particle therapy apparatus. The present invention is set forth and characterized by the appended claims. In the prior art particle therapy configurations as shown for example in FIGS. 1 to 3, the functionalities of limiting the momentum spread (or energy spread, which is equivalent) and the emittance of the beam is performed by a separate device, namely with the energy selection system (ESS) 10, which is installed between the stationary accelerator 40 and the rotating gantry 15. As shown on FIG. 1, a first element of the ESS is an energy degrader 41 which is used to degrade the energy of the particle beam of the fixed-energy accelerator 40. With the present invention, a rotatable gantry beam delivery system is provided having a gantry beam line configuration which fulfills multiple functions: The known function of transporting, bending and shaping an entering particle beam in such a way that a particle treatment beam can be delivered at a gantry treatment isocenter for use in particle therapy; The additional function of limiting the energy spread of the entering particle beam to a selected maximum value. With the present invention, the ESS functionality of limiting the energy spread or momentum spread of the beam to a selected value is performed by the gantry system itself. Hence the size and cost of a particle therapy facility can be reduced. In the context of the present invention, the momentum spread is defined as the standard deviation of the momentums of the particles at a given location and is expressed as a percentage of the average momentum of all particles at this location. Whatever the location of the means for limiting the momentum spread in the gantry, these means are preferably designed for limiting said momentum spread to 10%, more preferably to 5%, and even more preferably to 1% of the average momentum of all particles. Preferably, the gantry also fulfills a second additional function of limiting the transverse beam emittance of the entering particle beam to a selected maximum value, which further reduces cost and size of the particle therapy facility. More preferably, the gantry according to the invention also comprises a collimator installed in-between the gantry entrance point and a first quadrupole magnet in the gantry. This collimator is used for reducing the emittance of the beam before the beam is arriving at the first magnet in the gantry beam line. In an alternative preferred embodiment, the above mentioned collimator is installed outside of the gantry, i.e. in-between the energy degrader and the entrance point of the gantry. According to the invention, a particle therapy apparatus is also provided comprising a stationary particle accelerator, an energy degrader and a rotatable gantry having means to limit the momentum spread of the beam. Preferably said gantry also comprises means to limit the emittance of the beam. Alternatively, a particle therapy apparatus is provided comprising a stationary particle accelerator, an energy degrader, a rotatable gantry comprising means to limit the momentum spread of the beam and a collimator installed in-between said energy degrader and said gantry for limiting the emittance of the beam. More preferably, said gantry comprises additional means to limit the emittance of the beam. The present invention will now be described in detail in relation to the appended drawings. However, it is evident that a person skilled in the art may conceive several equivalent embodiments or other ways of executing the present invention. The drawings described are only schematic and are non-limiting. In the drawings, the size of some of the elements may be exaggerated and not drawn on scale for illustrative purposes. A exemplary particle therapy configuration according to the invention is shown in FIG. 4. In this example, the rotatable gantry according to the invention is coupled with a stationary-, fixed energy-particle accelerator 40 to form a single room particle therapy apparatus 100. An example of a particle accelerator for protons is a superconducting synchrocyclotron which has a compact geometry (e.g. with an extraction radius of 1.2 m). The gantry according to the invention is installed in the gantry room and a shielding wall (e.g. a 1.7 m thick concrete wall) separates the gantry room from the accelerator room. An energy degrader 41 is installed between the accelerator 40 and a gantry entrance point 45 (coupling point). This energy degrader 41 is positioned within the accelerator room just in front of the shielding wall 52 separating the accelerator room from the gantry room. The gantry entrance point 45 is located after the degrader 41 and is an entrance window for the beam line of the gantry. This entrance window 45 is the first part of a gantry beam line section where the beam is entering the gantry in a direction substantially along the rotation axis of the gantry. The rotation axis of the gantry is indicated by a horizontal dash-dotted line passing through the isocentrer 50 and the entrance point 45. As shown in FIG. 4, there is no momentum or energy analyser device installed between the degrader and the gantry entrance point as is the case in the prior art systems (FIGS. 1 to 3). Similar as in the prior art configurations shown in FIGS. 1 to 3, there is a short beam line section between the exit of the accelerator and the degrader 41, where for example two quadrupole magnets 44 are installed for transporting and focusing the beam into a small spot (for example between 0.5 mm and 2 mm one sigma) at the energy degrader. The energy degrader 41 is for example a rapidly adjustable, servo controlled, rotating, variable thickness, cylinder of degrading material (as disclosed in EP1145605). The distance between the exit of the accelerator and the degrader can be about 2 m. Other types of energy degrading systems, e.g. lateral moving wedge shaped based degraders can be used as well. The energy degrader currently used by the applicant has at its entrance an integrated horizontal-vertical beam profile monitor which allows measurement of the size and position of the beam spot and, through a control system algorithm, means for automatic tuning of the up-stream beam optics. Hence, the beam at the degrader 41 can be well defined, for example, the beam is focused into a small waist with a half width not exceeding 2 mm in both planes. With these input beam conditions, the output emittance of the beam degraded in energy is dominated by multiple scattering in the degrader and is relatively independent from the input conditions. The resulting beam after energy degradation can be considered as a diverging beam from a virtual waist in X and Y at the degrader with a given size and divergence. The two orthogonal coordinate axis X and Y are perpendicular (transverse) to the central beam trajectory. The emittances in X and Y (also called “transverse emittances”) can be considered to be substantially identical at this point. The larger the energy reduction introduced by the degrader, the larger will be the transversal emittance in X and Y and the larger will be the momentum spread of the degraded beam. The embodiment of the invention is a gantry configuration comprising means 43 to limit the momentum spread of the incoming beam. A beam entering the gantry comprising particles having an average momentum value and a momentum spread. To limit the momentum spread of the incoming beam, a pair of momentum analysing slits 43 are installed in the gantry. These momentum analysing slits 43 are preferably located at a position along the beam path where the particles of the beam are dispersed according to their momentum. More preferably, these slits are installed at a position where the nominal dispersion is larger than the nominal beam size. The nominal dispersion is defined as a transversal displacement of a particle whose momentum differs by 1% (one percent) of an average momentum P of all particles of the beam. The nominal beam size is defined as the one sigma beam size value in X of a mono-energetic particle beam having the average momentum P. Suppose that the nominal dispersion is 2.5 cm: this means that a particle having a momentum P′=1.01. P will be displaced by 2.5 cm in X from a particle having momentum P. In this example, a particle having a momentum P′=0.99. P will also be displaced in X by 2.5 cm but having an X coordinate with an opposite sign. The momentum limiting slits can for example be installed at a position where the nominal beam size in X is between 0.2 cm and 1 cm and the nominal dispersion in X is between 1 cm and 3 cm. By opening or closing the slits, the maximum momentum spread that is required (selected) can be obtained. One can for example select to limit the maximum momentum spread to 0.5% of the average momentum by adjusting the slits correspondingly. If one wants to limit the maximum momentum spread to 0.4% of the average momentum, then one has to close the pair of momentum slits more. For this purpose a calibration curve can be established, defining the slit opening as function of the required momentum spread. In the configuration of FIG. 4, the nominal dispersion is large in comparison with the beam size at a position in-between gantry quadrupole magnet number seven and the second dipole magnet 48 and hence this is a preferred position to install the momentum spread limiting slits. These slits can for example be installed just before the second dipole magnet 48. The exact position can vary depending on the detailed gantry configuration. Instead of using a pair of slits as means for reducing the momentum spread of the beam, other means can be used as well. For example one can use apertures or collimators with various diameters which can be put in the beam line, preferably at the above discussed positions. In the example shown in FIG. 4, a gantry for delivering scanning beams at the treatment isocenter 50 is presented and the beam line of this gantry comprises three dipole magnets 47,48,49 and seven quadrupole magnets 44. In this gantry configuration, scanning magnets 46 are installed upstream of the last dipole magnet 49. Between the gantry entrance point 45 and the first dipole magnet and in between the first and second dipole magnet there are respectively, two and five quadrupole magnets. Preferably, in addition to the means 43 to limit the momentum spread of the beam, also means 42 to limit the transverse beam emittance can be installed in the gantry 15. For this purpose, two pairs of slits (in X and Y) limiting the beam divergence can for example be installed in-between the second quadrupole magnet and the first dipole magnet 47. Hence, by limiting the divergence of the beam, the transverse beam emittance, which is proportional to the beam divergence, is limited. The first two quadrupoles installed in the gantry in-between the entrance point 45 and the first dipole magnet 47 serve to focus the divergent beam, originating from the degrader, before the beam reaches the divergence limiting slits. To what extent the beam emittance needs to be reduced will depend on what the maximum emittance the gantry can accept to efficiently transport the beam and it will also depend on what the beam requirements are at the treatment isocenter (such as for example the beam size required at the treatment isocenter). Acceptable beam emittances and beam sizes may depend on the technique used for shaping the beam (e.g. pencil beam scanning or passive scattering). The example given in FIG. 4 is for a scanning beam delivery system. For a pencil beam proton scanning system the beam emittance can for example be limited to 7.5 Pi mm mrad in both X and Y. For practical beam tuning purposes, just in front, downstream, of the divergence limiting or emittance limiting slits, a beam profile monitor can be installed (not shown on FIG. 4). Instead of using a pair of slits in X and Y as means for reducing the divergence of the beam, other means can be used as well. For example one can use apertures or collimators with various diameters which can be put in the beam line. If the energy reduction of the beam is very large (e.g. reduction of 250 MeV protons down to 70 MeV), the emittance and divergence of the beam becomes very large and the diameter of the beam, just before the first quadrupole magnet in the gantry, can become larger than the diameter of the beam line pipe. For this purpose a collimator (not shown in FIG. 4) can furthermore be installed upstream of the first quadrupole magnet in the gantry 15 to cut off already a part of the beam. This collimator can be installed in the gantry 15 in-between the entrance point 45 and the first quadrupole magnet of the gantry. Alternatively, such a collimator can be installed outside the gantry, i.e. in-between the degrader and the entrance point 45 of the gantry 15. When such a collimator for limiting the emittance of the beam is installed in either of the two positions mentioned above, in an alternative gantry embodiment the means 42 for limiting the emittance can be omitted. When a particle beam hits divergence and/or momentum limiting slits, neutrons are produced. To limit the neutron radiation at the level of the treatment isocenter 50 where the patient is positioned, adequate shielding need to be provided. As neutrons are mainly emitted in the direction of the beam, one can install just after the first dipole magnet, across the axis of rotation of the gantry, a neutron shielding plug 51 to shield the neutrons produced on means to limit the emittance of the beam installed upstream of the first dipole magnet 47. As the neutrons are mainly emitted in the direction of the beam, neutrons produced at the momentum limiting slits 43 are not directing to the patient. Nevertheless, a local neutron shielding (not shown on FIG. 4) can be installed around the momentum limiting slits 43 in order to reduce overall neutron background radiation. In order not to overload FIG. 4, details of the mechanical construction of the gantry have been omitted on purpose. Examples of such mechanical elements not shown on FIG. 4 are: two spherical roller bearings for rotating the gantry by at least 180° around the patient, a gantry drive and braking system, a drum structure for supporting a cable spool, a counterweight needed to get the gantry balanced in rotation, . . . . When designing a gantry for particle therapy, several beam optical conditions need to be fulfilled. At the gantry entrance point 45 the beam must have identical emittance parameters in X and Y in order to have a gantry beam optics solution that is independent from the gantry rotation angle. As discussed above, these conditions are naturally fulfilled when placing the energy degrader just in front of the gantry entrance point. In addition, the following beam optical conditions need to be met: 1. The gantry beam-optical system must be double achromatic, i.e. the beam imaging properties must be independent from momentum (dispersionless) and independent from position. 2. The maximum size of the beam (one sigma) inside the quadrupoles should preferably not exceed 2 cm in order to keep a reasonable transmission efficiency in the gantry.There is also a third condition that however can vary depending on the technique used for shaping the beam as discussed above. For a scanning system this third condition can be described as follows: 3. At the isocenter 50 the beam must have a small waist, of substantially identical size in X and Y.For a scattering system, required beam sizes can be specified more upstream of the isocenter (for example at the exit of the last bending magnet) and the acceptable beam sizes for scattering are in general larger than for scanning (for example 1 cm at the exit of the last bending magnet)In addition to these three conditions (1 to 3), new requirements are introduced resulting from the current invention: 4. At the position of the energy spread limiting slits 43, the nominal dispersion in X should preferably be large in comparison with the nominal beam size in X (for examples of values see discussion above).Preferably, a gantry according to the invention also comprises means to limit the emittance of the beam. This results in an additional requirement: 5. At the position of the emittance limiting slits 42, the beam must have beam optical parameters (size and divergence) in X and Y that allow to cut the divergence. This means for example that the beam must have a reasonable size (e.g. 0.5 cm to 2 cm, one sigma). The gantry configuration shown in FIG. 4 is based on a beam optical study performed with the beam optics “TRANSPORT” code (PSI Graphic Transport Framework by U. Rohrer based on a CERN-SLAC-FERMILAB version by K. L. Brown et al.). The beam envelopes in X and Y in the gantry beam line for an entering proton beam of 170 MeV are shown in FIG. 5 as an example. The beam envelopes are plotted for the X direction and Y direction in the lower panel and upper panel, respectively. In this example the emittance of the final beam is 12.5 Pi mm mrad. This corresponds to a situation where the divergence of the incoming beam has been limited to 6 mrad in X and Y. The beam transported through the system can then be considered as a beam starting at the degrader with a small beam spot of 1.25 mm and a divergence of 6 mrad. With this beam optics a beam size at the treatment isocenter of 3.2 mm (one sigma value) is obtained which is an adequate value for performing pencil beam scanning. The positions of the quadrupole magnets and dipole magnets are shown on FIG. 5. The transversal positions of the dipole magnets (the vertical gaps) are not shown on scale in this figure and the purpose is only to indicate their position along the central trajectory. Especially the gap in X an Y of the last bending magnet 49 are much larger than on the scale of FIG. 5 as a large opening is needed because the scanning magnets are positioned upstream of this dipole magnet and a large scanning area need to be covered at isocenter. The position of the scanning magnets along the beam path is indicated by a vertical line. The dotted line represents the nominal dispersion in X of the beam. As shown, just before the second dipole magnet 48 a large nominal dispersion value is obtained and this is the position where the momentum limiting slits 43 are preferably installed. The position along the central beam trajectory of the momentum limiting slits 43 is indicated by a vertical line on FIG. 5. The nominal beam size in X at the momentum limiting slits is about 0.23 cm while the nominal dispersion in X at this position is about 2.56 cm, hence obtaining a good momentum separation of the incoming beam. Preferably, also divergence limiting slits 42 are used. A good position for these slits 42 is indicated on FIG. 5 by a vertical line. At this position, the beam size in X and Y is about 1.8 cm and 0.6 cm, respectively. This beam optical solution presented fulfills the conditions of a double achromat. In the example shown in FIG. 4 and FIG. 5, a three dipole gantry configuration was used with dipole bending angles of respectively 36°, 66° and 60°. However, the invention is not limited to a specific gantry configuration for what concerns number of dipoles or bending angles of the dipoles. The invention is neither limited to the number of quadrupole magnets and the relative positions of the quadrupoles with respect to the dipole magnets. As a second example, the invention has been applied to a conical two dipole large throw gantry. This corresponds to the gantry configuration shown on FIG. 2 and FIG. 3. These large throw gantries have been built by the applicant and are discussed by Pavlovic in “Beam-optics study of the gantry beam delivery system for light-ion cancer therapy”, Nucl. Instr. Meth. In Phys. Res. A 399 (1997) on page 440. In these gantries a first 45° dipole magnet bends the beam away from the axis of rotation of the gantry and the beam then further follows a second straight beam line section before entering the second 135° dipole magnet which is bending and directing the beam essentially perpendicular to the axis of rotation. The straight beam line section between the gantry entrance point and the first 45° dipole magnet comprises, in the original gantry design, four quadrupole magnets (FIG. 2 is a configuration having only two quadrupole magnets installed in this beam line section), and the second straight section between the first and second dipole magnet comprises five quadrupole magnets. With this gantry the distance between the exit of the last bending magnet and the treatment isocenter is 3 m and the beam shaping elements configured in a so-called nozzle are installed upstream of the last bending magnet. This nozzle uses either the passive scattering technique or the scanning technique for shaping the beam conform the treatment target. The scanning magnets are part of the nozzle and are hence installed downstream of the last gantry dipole magnet. A beam optical analysis has been performed for this two dipole gantry configuration. The same conditions and requirements as discussed above have been respected. The resulting beam envelopes in this gantry are shown in FIG. 6 for a proton beam of 160 MeV. The beam envelopes are plotted for the X direction and Y direction in the lower panel and upper panel, respectively. The positions along the central beam path of the 45° dipole magnet 67, the 135° dipole magnet 68 and the various quadrupole magnets 44 are indicated in FIG. 6. Also here the energy degrader is installed just before the entrance window of the gantry and, as an example, in this calculation the divergence was cut at 8 mrad and the emittance of the final beam is 10 Pi mm mrad both in X and Y. The beam envelope as shown in FIG. 6 starts at the gantry entrance window and the beam has a size of 1.25 mm (one sigma value). In this gantry configuration the first straight section between the entrance window and the first 45° gantry bending magnet 67, comprises four quadrupole magnets 44. Divergence limiting devices 42 are installed in between the second and third quadruople magnet and are indicated by a vertical line on FIG. 6. The momentum spread limiting slits 43 are installed at a position where the nominal dispersion in X is large compared to the nominal beam size. The dotted line on FIG. 6 represents the nominal dispersion in X of the beam. The position of the momentum spread limiting slits 43 are indicated by a vertical line on FIG. 6. At this position the nominal dispersion is about 2.6 cm in X and the nominal beam size in X (one sigma value) is about 0.6 cm which is adequate for analysing the incoming beam according to momentum and limiting the momentum spread to a given value by setting the slits at the corresponding position. The beam envelope shown in FIG. 6 is a tuning solution for a nozzle using the scanning technique (the scanning magnets are installed downstream of the 135° dipole magnet but are not shown on FIG. 6). This gantry configuration used in this beam optics study also comprises two quadrupole magnets installed upstream of the 135° last dipole magnet 68 as indicated on FIG. 6. With this tuning solution, a double waist in X and Y is obtained at isocenter having a beam size of 4 mm (one sigma value), which is suitable for performing pencil beam scanning. This beam optical solution fulfills the conditions of a double achromat. A particle therapy apparatus 100 can be formed by combining a stationary, fixed energy particle accelerator, an energy degrader and a rotatable gantry according to the invention, i.e. a rotatable gantry comprising means for limiting the energy spread or momentum spread of the beam and preferably also comprising means for limiting the emittance of the beam. As shown on FIG. 4, which is an example of a proton therapy apparatus, a compact geometry can be obtained and the building footprint that is needed to install this apparatus is smaller than with a separate energy selection system. Although the embodiments described are focusing on proton gantries, the invention is not limited to proton gantries. The person skilled in the art can easily apply the elements of the invention, i.e. means for analysing the beam (limiting the emittance and limiting the energy spread), to gantries for use with any type of charged particles such as e.g. a gantry for carbon ions or other light ions. Gantries for particle therapy have been designed since many years and, in combination with stationary, fixed energy particle accelerators, a separate energy selection system was always installed in the beam line between the accelerator and the gantry. According to the present invention a new gantry configuration is provided comprising means for limiting the energy spread or momentum spread of the beam and preferably also comprising means for limiting the emittance of the beam. Hence the gantry itself comprises functionalities of the standard prior art energy selection system. By designing a gantry with these means to analyse the beam as described, a more compact particle therapy apparatus can be built. |
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description | This application is a continuing application of U.S. application Ser. No. 11/753,966, filed May 25, 2007, which claims priority under 35 U.S.C. §119 to Japanese Patent Application No. 2006-146042, filed May 26, 2006, the entire disclosure of which are herein expressly incorporated by reference. 1. Field of the Invention The present invention relates to a method and apparatus for correcting coordinates so as to arrange a sample in a field of view in a review apparatus for moving a sample stage onto the specified coordinates to review the sample. More particularly, the present invention relates to an apparatus for deciding a position for review based on information of a position of a defect detected by a higher-level checking apparatus like an SEM (Scanning Electron Microscope) based defect review apparatus. 2. Background Art In semiconductor manufacturing, it is important to find defects appearing during a manufacturing process in early phases and take measures against the defects in order to ensure yield enhancement. In recent years, even slight defects have nonnegligible effects on yields as semiconductors become smaller, hence making the size of defects to be reviewed smaller. An SEM-based defect review apparatus is an apparatus for reviewing such slight defects. The apparatus generally reviews defects based on positions of the defects detected by an optical checking apparatus. In this way, before the SEM-based defect review apparatus reviews in detail the defects detected by the checking apparatus, the checking apparatus executes the defect detecting processing as preprocessing. So the detecting apparatus is herein defined as a “higher-level” apparatus. A defect is reviewed manually using the SEM-based defect review apparatus as follows: a sample stage is moved onto coordinates outputted by the higher-level checking apparatus for image pickup at a low magnification (in a wide field of view); after a position of the defect is confirmed visually, the sample stage is moved such that the defect position is in the middle of the field of view; and a defective image is picked up at a high magnification (in a small field of view). These steps have been automated as the ADR (Automatic Defect Review). In the ADR, a defect appearing in a field of view of an image at a low magnification is detected using image processing, and then a sample stage is moved such that the detected defect is in the middle of the field of view to pick up a high magnification image at a relevant magnification for review of details of the defect. From the perspective of the image processing, a low magnification image is preferably magnified to fully magnify the defect for the review. However, a too high magnification may cause the defect to be out of the view field if a deviation of the position is substantial. Because of this, ADR configuration has a difficulty in setting a parameter of a magnification for a low magnification image, so that user experience is needed for the setting. This is not preferable since the ADR steps depend on user's skill based on the user experience. To address the above problem, JP Patent Publication (Kokai) No. 2001-338601 (2001) proposes a method of efficiently performing a task of setting a magnification for a low magnification image including: a function of visualizing a deviation between a defect position outputted by a higher-level checking apparatus and a defect position detected in the ADR by displaying the deviation as a vector on a wafer map; a function of correcting a coordinate system such that the deviation is minimum; and a function of optimizing the magnification for the low magnification image depending on the amount of the detected deviation. These functions can visualize a deviation, optimize a correction table, and optimize a magnification for a low magnification image. However, if there are a plurality of higher-level checking apparatuses, or if different deviation tendencies are shown depending on, for example, check conditions or a deviation tendency changes over time even in the case of that there is only a single checking apparatus, the optimal correction result cannot be obtained using a single correction table. In view of the foregoing, an object of the present invention is to provide a method and an apparatus for correcting coordinates so as to arrange a sample in a field of view properly and quickly in a review apparatus for moving a sample stage onto the specified coordinates to review the sample. To solve the above problems, the present invention is mainly characterized in that a plurality of coordinate correction tables are retained, correction effectiveness of the coordinate correction tables in review is evaluated, and the review is performed using an optimal correction table. More specifically, the present invention relates to a review apparatus for moving a sample stage onto coordinates (a defect position on a wafer), for example, previously calculated by a checking apparatus so as to review the sample. The review apparatus according to the present invention identifies a combination of the checking apparatus calculating a coordinate value and a condition (for example, a check mode) to calculate the coordinates. Based on the identified combination of said apparatus and said calculation condition, one of a plurality of coordinate correction tables is selected that are provided in correspondence to the combination of said checking apparatus and the calculation condition of said coordinates. Then, the coordinates calculated by said checking apparatus are corrected according to said selected coordinate correction tables. In this way, an optimal correction result can be obtained quickly and properly compared to the conventional case that correction table switching depends on a checking apparatus ID. Furthermore, the present invention relates to a review apparatus for moving a sample stage onto coordinates (a defect position on a wafer), for example, previously calculated by a checking apparatus so as to review the sample, including: a plurality of coordinate correction tables to correct a deviation between a pre-calculated coordinate value and a sample position on said review apparatus; and coordinate correction table evaluation means for evaluating accuracy of the correction according to said plurality of coordinate correction tables. Based on the result of the evaluation by said table evaluation means, one of said plurality of coordinate tables is chosen for use to correct said pre-calculated coordinate value. In this way, even when the coordinate correction table selected based on the combination of the checking apparatus ID and the check mode is no longer optimal due to change over time, a more suitable table can be used to correct the above amount of deviation. Other features of the present invention will become apparent in the following best embodiment and the attached drawings to practice the present invention. According to the present invention, an optimal coordinate correction table can be automatically selected for use from a plurality of coordinate correction tables. This can reduce phenomena in that a reviewed object is out of a field of view because a coordinate correction table is not a proper one. Further, using an optimal correction table, the amount of a deviation can be reduced and a review magnification to identify a defect position can be increased. This makes possible to improve defect detection performance by increasing a low magnification (a magnification to detect a defect position) particularly in the ADR. Referring to the attached drawings, embodiments of the present invention will be described below. A review apparatus according to a first embodiment prepares a plurality of coordinate correction tables to switch to one of the coordinate correction tables statically depending on a checking apparatus and its check mode. On the other hand, a review apparatus according to a second embodiment prepares a plurality of coordinate correction tables to always switch dynamically to one of the coordinate correction tables evaluated as an optimal one by performing the evaluation in parallel to the review, thereby obtaining a better correction result. FIG. 1 is a cross-sectional view of configuration of an SEM-based semiconductor defect review apparatus (a review apparatus) according to an embodiment of the present invention. The SEM-based defect review apparatus in FIG. 1 consists of an electron gun 101, a lens 102, a deflector 103, an objective lens 104, a sample 105, a stage 106, a secondary particle detector 109, an electro-optic system control unit 110, an A/D converting unit 111, a stage control unit 112, a central control unit 113, an image processing unit 114, a display 115, a keyboard 116, a storage device 117, a mouse 118 and the like. An electron beam 107 emitted by the electron gun 101 converges on the lens 102, is deflected on the deflector 103, converges on the objective lens 104 and then is radiated onto the sample 105. Secondary particles 108 such as secondary electrons or reflected electrons are generated from the sample 105 radiated with the electron beam 107 depending on a form or materials of the sample. The generated secondary particles 108 are detected by the secondary particle detector 109 and converted into digital signals by the A/D converting unit 111 to form an SEM image. The produced SEM image is subjected to image processing such as defect detection executed by the image processing unit 114. The lens 102, the deflector 103 and the objective lens 104 are controlled by the electro-optic system control unit 110. A sample is positioned on the stage 106 controlled by the stage control unit 112. The central control unit 113 interprets an input from the keyboard 116, the mouse 118 or the storage device 117 to control the electro-optic system control unit 110, the stage control unit 112, the image processing unit 114 and the like, and outputs details of the processing on the display 115 and to the storage device 117 as necessary. The storage device 117 stores coordinate correction tables and a control program illustrated in flowcharts in FIGS. 4 and 6 as described below. FIG. 2 is a diagram of network connection between higher-level checking apparatuses and a review apparatus according to the embodiment of the present invention. A network (201) connects to a checking apparatus (ID: 1) (202), a checking apparatus (ID: 2) (203), a checking apparatus (ID: 3) (204) and a review apparatus (205). The network 201 can also connects to a plurality of review apparatuses. A review apparatus connects to a storage device (206). The storage device can be integrated into the review apparatus or separated from the review apparatus for the network connection. The storage device saves coordinate correction tables (207, 208 and 209) corresponding to the checking apparatuses. The storage device switches to an optimal coordinate correction table based on an ID of a checking apparatus when the review is executed. In FIG. 2, the coordinate correction tables correspond to the checking apparatuses one-to-one. For example, a coordinate correction table A is selected when the checking apparatus (ID: 1) is used to detect a defect, a coordinate correction table B is selected when the checking apparatus (ID: 2) is used to detect a defect, and a coordinate correction table C is selected when the checking apparatus (ID: 3) is used to detect a defect. Since the checking apparatuses correspond to the coordinate correction tables one-to-one as described in the above, one of the checking apparatuses sends information of a defect position and a checking apparatus ID to at least a review apparatus, and the review apparatus selects a coordinate correction table corresponding to the checking apparatus ID. FIG. 3 is a drawing illustrating processing in the case of different tendencies of deviations of detected coordinates depending on check modes of higher-level checking apparatuses. Hereinafter, a check mode means a manner to detect a defect including, for example, a mode to detect a defect by exposing light onto a wafer at an angle, a mode to detect a defect by looking a wafer from the above and the like (such as a mode to detect a defect by scanning a wafer on XY coordinates or a mode to detect a defect by scanning a wafer on rotating coordinates). FIG. 3A is one example of display of differences between coordinate values detected by the higher-level checking apparatus and coordinate values detected by the review apparatus using vectors (also disclosed in JP Patent Publication (Kokai) No. 2001-338601 (2001)). FIG. 3A shows that, for example, when a position is farther apart from the center of the wafer, the deviation tends to be larger toward the wafer periphery in a check mode 1 (301), while a deviation toward the left tends to be larger in the left side of the wafer in a check mode 2 (302). In such instances, when the coordinate correction table switching depends on only an ID of a checking apparatus, it is difficult to obtain good correction results in both of the check modes because of different tendencies of deviations on coordinates depending on check modes. In view of the above difficulty, this embodiment has a function of switching to a coordinate correction table depending on a check mode of the checking apparatus in addition to the function of switching to a coordinate correction table based on a checking apparatus ID. Although an instance of different deviation tendencies depending on check modes is assumed herein, the different deviation tendencies depending on check modes may be due to a defect position identify algorithm of a checking apparatus or operation of a sample stage of the checking apparatus. Furthermore, the accuracy may decrease in detecting a defect position by a checking apparatus over time, so that the apparatus generally needs to be maintained regularly. FIG. 3B illustrates a function of switching to a correction table depending on a check mode (a condition for a checking apparatus to detect a defect and calculate coordinates of the defect). A checking apparatus (304) and a review apparatus (308) connect to a network 303. The review apparatus connects to a storage device (309). The storage device can be integrated into the review apparatus or separated from the review apparatus for the network connection. The checking apparatus 304 sends coordinates of a detected defect and information of a check mode together to the review apparatus. The information of a check mode includes, for example: information of a mode to detect a defect by exposing light onto a wafer at an angle, a mode to detect a defect by looking a wafer from the above and the like (such as a mode to detect a defect by scanning a wafer on XY coordinates or a mode to detect a defect by scanning a wafer on rotating coordinates) as described in the above; information of sensitivity of the checking apparatus in the detection; information of a serial number of the detecting apparatus and the like. The review apparatus 308 receives the information of a check mode from the checking apparatus 304 and determines a check mode of the checking apparatus from the information. Then, the review apparatus 308 switches to one of the coordinate correction tables (310, 311 and 312) based on the determined check mode. The coordinate correction tables are configured to perform coordinates correction optimally for any of the check modes. For example, the tables are used to obtain a deviation between coordinates actually detected in a check mode of the checking apparatus and coordinates detected by the review apparatus by a statistically process. As described in the above, the correction table switching depends on a pre-determined check mode of a pre-determined checking apparatus, enabling to obtain a good correction result in an instance with different deviation tendencies depending on the check modes. As described above, the review apparatus according to the first embodiment selects a coordinate correction table statically in correspondence to a check mode of the checking apparatus. That is, a checking apparatus and a check mode uniquely decide a coordinate correction table. However, because of temporal changes or the like in the apparatus, a coordinate correction table decided uniquely depending on a check mode is not always an optimal table. Although periodical maintenance is effective to the temporal changes as described above, its steps must be extremely complicated. To address the above problem, according to a second embodiment, even if a checking apparatus and/or a review apparatus change with a certain tendency over time, a plurality of coordinate correction tables are prepared in correspondence to the temporal changes, or a plurality of coordinate correction tables are prepared in correspondence only to a plurality of check modes to always switch dynamically to a coordinate correction table evaluated as an optimal one by performing the evaluation in parallel to the review, thereby obtaining a better correction result. The system configuration (FIG. 2) and the configuration of the review apparatus (FIG. 3) are similar to those of the first embodiment, and therefore will not be further described herein. FIG. 4 is a flowchart illustrating a function of automatically switching to a coordinate correction table. This function is operated by the central control unit 113 unless otherwise noted. The coordinate correction table switching is automatic herein although a user can set for the coordinate correction table switching. That is, this embodiment is characterized in that a deviation tendency is evaluated based on a coordinate value outputted by a checking apparatus and a coordinate value of a sample position detected in the review to switch to an optimal coordinate correction table in the review. In FIG. 4, at the start of the review (401), a coordinate correction table in its initial setting is in use (402). The coordinate correction table in its initial setting can be configured as any table, or configured based on a previous processing result as described below (see FIG. 6). During the review (403 to 409), if the coordinate correction table selecting function is enabled (the function is ON) (404), evaluation values of the coordinate correction tables are calculated (405), a maximum evaluation value is further calculated (406), and a coordinate correction table with the maximum evaluation value is selected (407). These processes allow for review using an optimal coordinate correction table even if a tendency differs from a default coordinate correction table. An equation (1) is an exemplary formula of calculating an evaluation value E of a coordinate correction table. The evaluation value is defined so as to be higher for a smaller deviation amount D after the correction by a coordinate correction table. Generally, a review order is often decided such that the amount of stage movement is minimum to improve throughput. In that case, samples will be reviewed from the closest sample in order. [ Formula 1 ] E n = 1 ∑ i = 1 n W i D i ( 1 ) Since deviation tendencies are local in most cases, close samples often have similar deviation tendencies. A value is effective that is evaluated by weighting the tendency of the closest deviation in the case of a review order with the minimum distance of a movement. In that case, an increasing function of a weighting coefficient W for the review order is effective. For example, it is effectual to ignore the deviation amount previous to closer points. Alternatively, in the case of a sufficient calculation cost including a processing time, the weighting function can be effectually a function of a distance between a review point to calculate an evaluation value and a review point with the previously calculated deviation amount. FIG. 5 shows one example of switching to a coordinate correction table with considering the weight coefficient described in the above. In FIG. 5A, there are seven review points on a wafer. A point on the wafer indicates checked coordinates (x0, y0) outputted by a checking apparatus, and also indicates detected coordinates (x, y) detected by the review apparatus as shown by the head of the arrow. Two coordinate correction tables are evaluated herein and coordinates corrected according to the tables are correction coordinates 1 (x1, y1) and correction coordinates 2 (x2, y2). For simplicity, a correcting equation for the correction tables are simplified to calculate the correction coordinates 1 by the equation (2) and the correction coordinates 2 by the equation (3):[Formula 2](x1,y1)=(x0−1,y0+2) (2)[Formula 3](x2,y2)=(x0+1,y0−2) (3) Set the weight coefficient W to be ½ for two previous points and ignore deviation tendencies of points previous to the two points to get the equation (4): [ Formula 4 ] W i = { 1 ( i = 1 ) 1 / 2 ( i ≥ 2 and i = n , n - 1 ) 0 ( i ≥ 3 and i ≤ n - 2 ) ( 4 ) The evaluation value E of a correction table is calculated using the following equation (5) based on the equations (1) and (4): [ Formula 5 ] E i = { 1 D i ( i = 1 ) 2 D i + D i - 1 ( i ≥ 2 ) ( 5 ) where D0=0. FIG. 5B shows coordinates checked by the checking apparatus and the review apparatus, corrected coordinates calculated using the equations (2) and (3), and specific numerical value examples of evaluation values calculated using the equation (5). Setting a table 1 (equation (2)) as an initial correction table, the review is executed using the correction table 1 from the first point through the fifth point inclusive, and a correction table 2 will be used after the fifth point where an evaluation value of the table 2 exceeds that of the table 1. Referring to FIG. 6, the switching to a table will be described more conceptually. FIG. 6 is an exemplary graph representing a correction result using coordinate correction tables A (604), B (605) and C (606) with a review order (601) on the abscissa axis and deviation amounts (602) on the ordinate axis. Inverse numbers of evaluation values (603) instead of the deviation amounts (602) on the ordinate axis can also yield the same graph tendency. If the coordinate correction table A (604) is selected as an initial table, the coordinate correction table C (606) is used after the second point according to an evaluation result at the first point. Further, the coordinate correction table B (605) is selected after a crossing point (607) according to an evaluation result at the crossing point (607). Similarly, If the coordinate correction table C (606) is selected as the initial table, the coordinate correction table C (606) continues to be used till the crossing point (607); the coordinate correction table B (605) is used after the crossing point (607) according to an evaluation result at the crossing point (607). Further, if the coordinate correction table C (606) is selected as the initial table, the coordinate correction table C (606) continues to be used after the second point according to an evaluation result at the first point, and the coordinate correction table B (605) is used after the next point to the crossing point (607) according to an evaluation result at the crossing point (607). In this way, an optimal correction table is used during the review to allow search for a defect with the minimum deviation amount. In addition, the computational complexity of the comparison and evaluation processing on the coordinate correction tables is so small that the processing can be executed without reducing ADR throughput. FIG. 7 is a flowchart illustrating a function of automatically updating the correction tables. This function is operated by the central control unit 113 unless otherwise noted. In FIG. 7, at the end of the ADR (701), if an automatic update function for the coordinate correction tables is enabled (702), evaluation values of the coordinate correction tables to be compared are calculated (703). Next, a coordinate correction table with the maximum evaluation value among the coordinate correction tables are calculated (704), and then the table is set as an initial coordinate correction table for ADR (705). The coordinate correction tables for the comparison can be newly created coordinate correction tables to be added based on a tendency of deviation measured in previous ADR, or coordinate correction tables to be added that are updated by adding measurement data to the existing coordinate correction tables. The coordinate correction and the creation of the coordinate correction tables can be performed as described in JP Patent Publication (Kokai) No. 2001-338601 (2001), or otherwise. The equation 6 is an exemplary calculating formula of an evaluation value to automatically update the coordinate correction tables. As opposed to the equation 1, the weight coefficient W reflecting a sample position is fixed (W=1). [ Formula 6 ] E n = 1 ∑ i = 1 n D i ( 6 ) FIG. 8 is an exemplary display screen for an evaluation result of coordinate correction tables. A name or ID of a checking apparatus to be evaluated is displayed in a box 801 and a check condition is displayed in a box 802. Coordinate correction tables to be evaluated can be selected in boxes 803, while deviation tendencies are displayed as vectors in circles 804 on a wafer map. Average values of deviation amounts are displayed in boxes 805, while values 3σ (triple of variance) (statistically, most information is included within a range of 3σ) are displayed in boxes 806. Values FOV (Field of View) representing sizes of recommended fields of view obtained from the values 3σ are displayed in boxes 807. Further, recommended magnifications corresponding to the recommended FOV are displayed in boxes 808. To notify a checking apparatus of the information as described above, one of send buttons 809 is pushed. A sending function is preferably automatic sending, but a user can push the send button 809 to notify the checking apparatus when the user desires to notify. In the automatic sending, the sending is performed only if a condition is satisfied, for example, a deviation is over a certain value or difference from a previous deviation is more than a certain value. Such automatic sending can be used to determine whether or not the checking apparatus needs maintenance. Although direct notification to a checking apparatus calculating coordinates is described herein as an example, notification to a system managing the checking apparatus has similar effect. As described hereinabove, in the review apparatus according to the second embodiment, the coordinate correction table switching is dynamic in correspondence to the change, thereby obtaining a good correction result even if a desired correction result cannot be obtained using a coordinate correction table initially selected depending on, for example, temporal changes in a checking apparatus or a review apparatus. Further, a coordinate correction table is automatically updated in the second embodiment, thereby allowing to use an optimal correction table and obtain a good correction result after the start of the coordinates correction processing. Furthermore, in the second embodiment, the amount of a deviation of a defect detected positions between a checking apparatus and a review apparatus is notified to the checking apparatus. If the deviation amount is too large, an administrator can maintain the checking apparatus. Meanwhile, the present invention can also be embodied in a software program code for realizing the functions of the embodiments. In that case, a system or an apparatus is provided with storage media recording the program code, and the program code is read out that stores a computer (or CPU, MPU) for the system or the apparatus in the storage media. The program code read out from the storage media realizes the functions of the previously mentioned embodiments, and the present invention is embodied in the program code and the storage media storing the code. The storage media for supplying the program code includes, for example, a floppy (R) disc, a CD-ROM, a DVD-ROM, a hard disk, an optical disc, an optical magnetic disc, a CD-R, a magnetic tape, a non-volatile memory card, a ROM and the like. An OS (operating system), for example, running on the computer can perform part or whole of actual processing based on indications by the program code, such that the previously mentioned functions of the embodiments can be realized by the processing. The CPU in the computer can also perform part or whole of actual processing based on indication by the program code after the program code read out from the storage media is written into a memory on the computer, such that the previously mentioned functions of the embodiments can be realized by the processing. The functions can be also achieved such that the software program code for realizing the functions of the embodiments is distributed via a network, stored in storage means such as the hard disk or the memory in the system or the apparatus or storage media such as a CD-RW or a CD-R, and executed after the program code is read out that is stored in the relevant storage means or the relevant storage media by the computer (or CPU, MPU) for the system or the apparatus. |
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047449411 | claims | 1. An antiseismic support structure for a pile block in a building well having a top and a bottom, said pile block containing a reactor vessel of a nuclear reactor and having a top and a bottom, said support structure comprising: a first floor supporting said building well; a second floor below said first floor; elastic support means separating said first and second floor for permitting a horizontal oscillatory displacement of one floor relative to the other to filter horizontal components of an earthquake with respect to the pile block; a series of elastic, absorbing supports between the bottom of said pile block and said first floor, for filtering vertical components of seismic waves; and a plurality of vertical guiding means between said building well and said pile block and arranged between the top and bottom of the building well, said vertical guiding means being horizontally rigid for preventing horizontal displacement and rocking of said pile block relative to said building well under the action of horizontal components of seismic waves, said vertical guiding means being vertically flexible for permitting and guiding a relative vertical movement between the pile block and the building well during a seismic occurrence. 2. A support structure according to claim 1, wherein the elastic absorbing supports comprise viscous absorbing means. 3. An antiseismic support structure for a pile block in a building well having a top and a bottom, said pile block containing a reactor vessel of a nuclear reactor and having a top and a bottom, said support structure comprising: a first floor supporting said building; a second floor below said first floor; elastic support means separating said first and second floor for permitting a horizontal oscillatory displacemnt of one floor relative to the other to filter horizontal components of an earthquake with respect to the pile block; a series of elastic, absorbing supports between the top of said pile block and the top of said building well, for filtering vertical components of seismic waves; and a plurality of vertical guiding means between said building well and said pile block and arranged between the top and bottom of the building well, said vertical guiding means being horizontally rigid for preventing horizontal displacement and rocking of said pile block relative to said building well under the action of horizontal components of seismic waves, said vertical guiding means being vertically flexible for permitting and guiding a relative vertical movement between the pile block and the building well during a seismic occurrence. 4. A support structure according to claim 3, wherein the elastic absorbing supports comprise viscous absorbing means. |
description | This is a national stage application of International Application No. PCT/CA2016/051342 filed on Nov. 17, 2016, which claims priority to U.S. Provisional Application No. 62/256,376 filed on Nov. 17, 2015, the entire contents of which are hereby incorporated herein by reference. The present disclosure relates to materials science and nuclear technology. The following paragraphs are intended to introduce the reader to the detailed description that follows and not to define or limit the claimed subject matter. Furthermore, the following paragraphs are not an admission that anything discussed in them is prior art or part of the knowledge of persons skilled in the art. Magnetite is an iron oxide corrosion product that may be found in feedwater systems in nuclear power plants. The deposition of magnetite on heat transfer surfaces, e.g., steam generator (SG) tubes, may result in increased thermal resistance to heat transfer, and in extreme cases flow oscillations and loss of SG level control. Magnetite particles may be employed in fouling experiments which attempt to simulate accumulation of deposit on a heat transfer surface. Furthermore, radiotracing techniques may be used to investigate kinetics of fouling processes under various thermal hydraulic and chemistry conditions (e.g., at various steam qualities). Radiotracing techniques may provide a direct measure of the deposit mass per unit area on a test section without requiring additional assumptions regarding the physical properties of the deposit, such as density and thermal conductivity. A reliable and reproducible method to produce high quality iron oxide products, for use in fouling experiments, is desirable. The quality of the synthesized magnetite products may be determined by the composition (i.e. purity) and morphology (i.e. correct phase, uniform size, and shape) of the particles. Radiotraced magnetite has been prepared by neutron activation of magnetite particles. Alternatively, it is possible to use wet chemical methods to produce radiotraced magnetite from a radioactive solution containing the desired iron isotope. However, the counter ion in a commercially available radioactive solution is the sulphate ion (SO42−), which may be strongly adsorbed to the magnetite surface and could interfere with the synthesized particle. The inventors of the present disclosure have developed a process to convert FeSO4 into FeCl2 using an ion-exchange resin as a starting solution for the synthesis of colloidal magnetite. The process may be repeated using radiotraced 59FeSO4 solution to produce 59FeCl2. The inventors used the ion-exchange resin (e.g., PUROLITE® NRW 400™ resin) to substitute anions (e.g., sulphate is replaced with chloride ion) followed by the production of colloidal magnetite. Results from particle characterization confirm the high quality (i.e. high purity with magnetite phase structure) of the synthesized corrosion product. The particle morphology was examined using the X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). Semi-quantitative analyses of the oxide composition were performed using Energy Dispersive X-Ray Spectroscopy (EDX). Other aspects and features of the teachings disclosed herein will become apparent, to those ordinarily skilled in the art, upon review of the following description of the specific examples of the present disclosure. Various apparatuses or methods will be described below to provide an example of an embodiment of each claimed invention. No embodiment described below limits any claimed invention and any claimed invention may cover apparatuses and methods that differ from those described below. The claimed inventions are not limited to apparatuses and methods having all of the features of any one apparatus or method described below, or to features common to multiple or all of the apparatuses or methods described below. It is possible that an apparatus or method described below is not an embodiment of any claimed invention. Any invention disclosed in an apparatus or method described below that is not claimed in this document may be the subject matter of another protective instrument, for example, a continuing patent application, and the applicant(s), inventor(s) and/or owner(s) do not intend to abandon, disclaim or dedicate to the public any such invention by its disclosure in this document. The present disclosure is directed to methods that can produce low impurity magnetite particles. Generally, the methods may involve: providing a first solution of substantially ferrous sulphate; converting the first solution by replacing sulphate ions with chloride ions to produce a second solution of substantially ferrous chloride; and oxidizing the second solution to produce a third solution of substantially iron oxide. The preparation of magnetite by direct oxidation of a solution containing Fe(II) under alkaline conditions and at low temperature can provide magnetite of high quality (i.e. high purity iron oxide, correct phase and uniform size and shape). Colloidal magnetite may be employed effectively as a radiotracer, which is a key component for in situ measurement of fouling using gamma spectrometry. Sulphate in a ferrous solution can be replaced by chloride resulting in a FeCl2 solution eluted from an ion-exchange process. As demonstrated herein, magnetite particles produced from this method exhibited a typically spherical shape with diameter between 0.1 to 1.0 micrometers and approximately 99% purity. In accordance with the teachings of the present disclosure, the sulphate in commercially available 59FeSO4 solution may also be converted into 59FeCl2. Preparation of FeCl2 Solution from FeSO4 The ion-exchange resin, PUROLITE® NRW 400™ resin, was used to replace sulphate ions from the FeSO4 solution with chloride ions. PUROLITE® NRW 400™ resin is a strongly basic ion-exchange resin with (OH−) functional group. It has an “as received” form of a clear spherical bead. The resin was pretreated with deionized water to remove dirt before use. Fresh resins showed uniform structure and smooth surface with the particle sizes ranging between about 0.3 and 0.6 mm. Laboratory grade chemicals were used, and are listed in Table 1. TABLE 1Chemicals used in magnetite synthesis from FeSO4 solutionApproximateChemicalConcentrationSupplierFor AnionNRW 400 ™ resin1.0eq/LPuroliteConversion(solid)HCl (aqueous)0.1 and 0.5 mol/LAnachemiaFeSO4 (aqueous)0.1mol/LFisher Scientific The nature of the ion-exchange resin may be greatly influenced by the network structure of its polymer matrix. The polymer matrix of most ion-exchange resins is mainly a copolymer of styrene and divinylbenzene (DVB). The functional group of the strong anion resin used by the inventors is originally in OH− form. The equilibrium can be written as shown in Equation 1.R—N(CH3)3—OH↔R—N+(CH3)3+OH− (Eq. 1) A solution of target anion, i.e. Cl− as HCl, is introduced to establish the chloride form of the resin; the equilibrium can be written as shown in Equation 2. An excess amount of Cl favors the production of chloride saturated resin.R—N+(CH3)3+OH−+HCL↔R—N(CH3)3Cl+H2O (Eq. 2) In the final step, the original solution containing sulphate is introduced to the resin column to form a final product that contains chloride ion. At this stage, the equilibrium equation is shown by Equation 3.2R—N(CH3)3—Cl+FeSO4↔[R—N(CH3)3]2SO4+FeCl2 (Eq. 3) The anion to be replaced, i.e. sulphate in this case, must have a higher ion selectivity for the ion-exchange resin than the ion which is on the resin, i.e. the chloride ion. The relative selectivity for strong acid forming anions in a dilute solution is as follows: SO42>I−>NO3−>CrO42−>Br−>Cl−. According to this series, therefore, a sulphate anion will readily displace a chloride anion on the resin. It is noted that the ion-exchange capacity of PUROLITE® NRW 400™ resin is 1.0 eq/L of resin. To convert 1 L of 0.1 mol/L FeSO4 solution, which gives 0.2 equivalents of sulphate, the required volume of resin is 200 mL. In addition, at least 2 L of 0.1 mol/L of HCl solution is required to saturate 200 mL of resin. Fourteen tests were carried out to study the variation in the addition rate and the amount of resin used. An exemplary ion-exchange apparatus is shown in FIG. 1. Referring to FIG. 1, the ion-exchange apparatus is illustrated generally at reference numeral 100. In the example illustrated, the apparatus 100 includes a solution tank 102 and a pump 104. The pump 104 drives solution from the tank 102 to first and second ion-exchange columns 106, 108, which are shown arranged and connected in parallel. An online pH measurement device 110 is positioned to read the pH of the solution flowing from the ion-exchange columns 106, 108 to a product collection reservoir 112. The aim was to produce approximately 1 L of FeCl2 solution for the magnetite synthesis. The first six experiments were carried out by manually adding solutions (once through) from the top of the resin column. Based on the sulphate removal ratio obtained from manual addition experiments, the procedure for the preparation of FeCl2 from FeSO4 using PUROLITE® NRW 400™ resin utilized a continuous feed system using the pump 104 (e.g., a peristaltic pump) to provide a constant feeding rate. The arrangement aimed to improve the flow control for the remaining experiments. At the end of each test, the final solution was analyzed for Cl− and SO42− using Ion Chromatography (IC). Results were reported as sulphate removal ratio calculated from the amount of removed sulphate divided by amount of sulphate in the FeSO4 feed solution. A summary of the ion-exchange experiments is listed in Table 2. Experimental reproducibility was verified by duplicate experiments in runs 13 and 14. TABLE 2Summary of ion-exchange experimentsVolumeEquivalentVolumeofVolumeRatio ofof 0.1MConcentrationConcentrationSulphateResinof HClHCl toFeSO4of Chloride inof Sulphate inRemovalRun(mL)(mL)Resin Site(mL)Effluent (mg/L)Effluent (mg/L)Ratio1506001.2300267158510.442506001.2300405237590.6431006000.6300N/AN/AN/A410012001.2300515218210.83515018001.230060639740.91615020001.330067326940.93750080001.62000234265720.37825040001.62000601110660.90925040001.62000609210780.901030050001.61000501824700.761135020002.91400669614100.861235015002.1140066267560.931340015001.9110074352560.981440015001.9110074565480.95 Fresh PUROLITE® NRW 400™ resin was pretreated by generously flushing resin beads with deionized water (approximately 10 times of the resin volume) to ensure no channels that would allow solution by pass the resin when solution flowed through the column. Visual observation was made for water channels and/or bubbles between the resin beads. HCl solution was introduced to convert the resin to the Cl− form as established in Equation 2. The ratio of HCl to resin site can be calculated as shown Equation 4. Concentration HCl ( mol / L ) × Volume HCl ( mL ) Volume resin ( mL ) × Exchange capacity resin ( 1.0 eq / L ) ( Eq . 4 ) An excess of Cl− as given by the ratio of HCl to resin site (in Table 2) was used. The molar equivalent ratio of HCl to resin was varied from 0.6 to 2.9 for various resin volumes. When the ratio of HCl to resin site was below 1.0, as shown in run 3, there was incomplete conversion of OH− into Cl− resulting in the formation of a dark green precipitate, likely ferrous hydroxide. Run 3 was stopped and aborted due to the plugged column. After the manual addition experiments, continuous flow was used for the remaining runs 7 to 14. The resin volume was increased to 500 mL in run 7, the first continuous flow experiment. The service flow rate was chosen at 3 to 4 bed volumes per hour, with bed volume referring to the volume of resin used in the experiment. The chosen flow rate reflected the high ion-exchanger capacity and the capability to maintain a steady flow in the system set up in FIG. 2. At relatively large resin volume and the top to bottom flow direction in run 7, it was observed that the volume of the resin was reduced after the acid flow indicating that resin beads have shrunk during the acid flow resulting in bubbles and air channels inside a column. Air bubbles affected directly the ion-exchange capacity (between Cl− and SO42−). The sulphate removal ratio dropped to 0.37 in run 7. The downside of dealing with a large resin volume (at 500 mL resin compared to 50, 100, and 150 mL in previous runs) was that several hours were consumed when large amounts of HCl solution are required to saturate the resin. As a consequence, the concentration of HCl was raised to 0.5 mol/L (in run 11) in order to produce target amount of final product (e.g., 1 L of 0.1 mol/L FeCl2 solution). The ratio of HCl to resin site increased by 80% in run 11 compared to run 10, however, the capability to remove sulphate ions only increased by 13%. It is noted that a 0.1 mol/L HCL solution was fed into the resin column for runs 1 to 10, a 0.5 mol/L HCL solution was fed into the resin column for runs 11 to 14, and the direction of flow in runs 11 to 14 was reversed (i.e. from bottom to top of the resin column) to ensure no air bubble formed during the operation. In runs 12 to 14, the volume of acid solution was lowered to 1500 mL for shorter flow duration. Based on the sulphate removal ratios in Table 2, the optimum parameters were suggested to be as follows: The ratio of HCl to resin site must be at least approximately 2.0 to achieve more than 93% replacement of sulphate with chloride. The recommended flow control for the small scale batch production is the reverse flow direction with the operating flow rate between 3 to 4 bed volumes per hour to maximize the ion-exchange capacity. The higher concentration of HCl may be chosen to reduce the time the solution takes to flow through the resin column. However, care must be taken when handling with strong acid solution. For example, an HCl solution higher than 6.0 mol/L may require use of a certified fume hood. The maximum sulphate removal is reported at 98% in run 13. The final solution from runs 13 and 14 were then used as a starting material for the synthesis of magnetite discussed below. Preparation of Colloidal Magnetite Magnetite was prepared by direct oxidation of a solution of FeSO4 containing Fe(II) at low temperature. Operational experience suggested that the removal of sulphate from the final product was difficult because of the tendency of sulphate to adsorb onto the surface of the particles. In other words, a residual amount of sulphate ion may be hard to remove from the particle surface and also may induce particle agglomeration in the suspension. 1 L of 0.1 mol/L of FeSO4 was replaced by 1 L of 0.1 mol/L FeCl2 eluted from an ion-exchange process. The solution was purged with argon gas for one hour prior to a drop wise addition of 1 mol/L NaOH solution (approximately 200 to 300 mL) to raise the pH of the solution to about 11.0. Greenish particles were formed confirming the presence of ferrous oxide. The suspension was heated to 90° C. for one hour and sparged with air to produce oxidizing conditions. In this stage, the suspension color turned black consistent with the formation of magnetite particle. The synthesised particles were purified by recirculating the suspension through a double column dialysis membrane system. An exemplary purification system is shown in FIG. 2. Referring to FIG. 2, the purification system is illustrated generally at reference numeral 200. In the example illustrated, the system 200 includes a solution reservoir 202 having a stirring device 204 arranged to stir iron oxide solution in the reservoir 202. A pump 206 draws a first stream of the solution from the reservoir 202 and delivers it to an inlet 208 of a first membrane unit 210. In the example illustrated, an outlet 212 of the first membrane unit 210 is connected to an inlet 214 of a second membrane unit 216 to deliver a second stream of the solution to the second membrane unit 216. The first and second membrane units 210, 216 are shown arranged and connected in parallel. An outlet 218 of the second membrane unit 216 returns a third, purified stream of the solution back to the reservoir 202 after completing one cleaning cycle. The membrane units 210, 216 may each take the form of a double-column dialysis membrane device (e.g., supplied by Spectrum Labs, Rancho Dominguez, Calif.). As illustrated, the membrane units 210, 216 may be connected to a deionized water source 220, and a pump 222 may circulate water between the source 220 and the membrane units 210, 216. A measurement tool 224 may be used to monitor conductivity of water in the source 220. Excess ions were removed from the particles by osmosis through the membrane units 210, 216. The suspension of iron oxide and the deionized water flow on the inside and outside of the membrane, respectively. Deionized water from the source 220 was replaced regularly in the membrane units 210, 216 until the conductivity of the dialysate was below 5 μs/cm. At this point, the suspension may be transferred to a particle carboy, and may be stored until eventual use in a fouling experiment. For the purpose of particle characterization, an aliquot of suspension was filtered using 0.45 μm filter paper and left to dry under room temperature. The magnetite powder was submitted for analyses. Results from Characterization of Magnetite Two magnetite batches were obtained from the syntheses using FeCl2 eluted from runs 13 and 14. They are labelled as batches MM1 and MM2, respectively. XRD analysis was conducted to distinguish different iron oxides such as magnetite, hematite, maghemite and other corrosion products containing only Fe and O. Similar XRD patterns are shown in FIGS. 3 and 4 for magnetite particles synthesised from FeCl2 eluted from ion-exchange process. Sharp peaks show high degree of crystallinity of the synthesised particles. The results from XRD analysis shows that all diffraction peaks of each sample matched the diffraction peaks for pure magnetite (Fe3O4) from the International Centre for Diffraction Data database (ICDD). Observed peaks from XRD were only for magnetite. The XRD results also confirmed the purity of the products via the absence (or the amount of others are below the detection limit of approximately 1 weight % of the instrument) of other phases of iron oxide (i.e. maghemite or hematite) in the samples. Micrographs are shown in FIGS. 5 and 6. It is assumed that a single crystal in SEM micrograph is the particle which has a grain boundary that could clearly be distinguished from others. The resulting magnetite particles were colloidal with diameters of few hundred nanometers. The particles are typically in spherical shape. The results from SEM micrographs showing spherical particles with the particle diameter between 0.2 to 1.0 micrometers. The EDX analysis was performed on the representative areas of the magnetite powder prepared from the final solution FeCl2 from runs 13 and 14. As expected, the powder samples (MM1 and MM2) were rich in Fe with trace amounts of Si and Al (each less than 0.6 wt %) in batch MM1 (from run 13; FIG. 7) and only Si was reported at concentration less than 0.6 wt % in batch MM2 (from run 14; FIG. 8). Dotted lines in FIGS. 7 and 8 represent the amount of iron in Fe3O4 molecule from theoretical calculation. The methods disclosed herein may be used to produce radioactive colloidal iron oxides, which may be employed as a radiotracer. Accordingly, the radiotracer may be manufactured in a laboratory environment, the time an operator is being exposed to the radioisotope may be minimal, and the production time may be manageable. The radiotracer can be used to measure a real-time deposition rate under elevated pressure/temperature. This radiotracing technique may be used to investigate the deposit accumulation in SG tubes, for example. Although the present disclosure relates particularly to the preparation of magnetite particles for use in fouling experiments for SG tube coatings and adsorption studies, it should be appreciated that the synthesized magnetite may be used as a model particle in other works requiring low impurities in the system. Other applications of the teachings herein are contemplated. While the above description provides examples of one or more apparatuses or methods, it will be appreciated that other apparatuses or methods may be within the scope of the accompanying claims. |
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description | 1. Field This invention pertains generally to spent fuel pools in nuclear power plants and, more particularly, to systems and methods for measuring and monitoring axial flux to evaluate subcriticality in a spent fuel pool. 2. Description of Related Art The generation of electric power in a nuclear power plant is accomplished by the nuclear fission of radioactive materials. Due to the volatility of the nuclear reaction, nuclear power plants are required by practice to be designed in such a manner that the health and safety of the public is assured. In conventional nuclear power plants used for generating electric power, the nuclear fuel becomes spent and is removed at periodic intervals from the nuclear reactor and replaced with fresh fuel. The spent fuel generates decay heat and remains radioactive after it has been removed from the nuclear reactor. Thus, a safe storage facility is provided to receive the spent fuel. In nuclear reactors, such as pressurized water reactors, a pool is provided as a storage pool for the spent fuel. The spent fuel pool is designed to contain a level of water such that the spent fuel is stored underwater. The spent fuel pool is typically constructed of concrete and is at least 40 feet deep. In addition to the level of the water being controlled and monitored, the quality of the water is also controlled and monitored to prevent fuel degradation when it is in the spent fuel pool. Further, the water in the spent fuel pool is continuously cooled to remove the heat which is produced by the spent fuel. A spent fuel pool in a nuclear power plant typically consists of more than several hundred fuel assembly storage racks filled with either depleted or fresh fuel assemblies. Reactivity of the pool is expressed by a neutron effective multiplication factor, k-effective. The value of k-effective is typically determined by analytical means, such as by the use of Monte Carlo simulations. Known storage configurations in the spent fuel pool can include close-packed, checker-boarding with empty water cells, and with or without neutron absorbers. The selected storage configuration depends on the reactivity of the depleted assemblies. The storage configuration is selected to ensure that the overall reactivity of the pool remains below regulatory limits. Monitoring and controlling the margin of subcriticality in the spent fuel pool can assure safe operation of the pool. It is known to obtain this information by means of analytical methods which are based on conservative input assumptions to encompass a wide range of core operating parameters for depleted fuel assemblies. As a result, a considerable amount of subcritical margin may exist in the spent fuel pool based on the analytical results. Due to a lack of reprocessing and a shortage of permanent disposal sites, commercial nuclear utilities are interested in systems and methods to increase storage capability as some nuclear power plants operate near full capacity in the spent fuel pool. Higher initial enrichments in close-packed storage configurations and degradation problems with reactivity control materials are a couple of the factors which compound the uncertainty associated with pool reactivity and therefore, creates regulatory concerns over the safe operation of spent fuel pools. Thus, there is a desire in the nuclear power industry to develop a system and method for measuring k-effective with increased certainty and decreased margin so as to achieve at least one of the following benefits: (1) an increase in the amount of soluble boron that can be credited and thereby effectively increasing the storage capacity, reducing the number of different and complex storage configurations, and simplifying the technical specification compliance, and (2) eliminate the regulatory concerns on the uncertainties as to whether there is enough margin to criticality or whether the regulatory limits are satisfied. This invention addresses the issues above-described by providing systems and methods for measuring and monitoring the margin of subcriticality in the spent fuel pool which is based on measuring axial flux in the spent fuel pool, generating an axial flux curve, and correlating the curve with analytical data to determine the k-effective and monitor any reactivity changes, e.g., inadvertent and anticipated, in the spent fuel pool. In one aspect, this invention provides a system for measuring and monitoring axial flux to determine subcriticality in a spent fuel pool of a nuclear power plant. The system includes one or more neutron detectors which are operable to generate signals resulting from neutron interactions in the spent fuel pool, a counting device for counting said signals generated by the one or more neutron detectors, a connecting means to electrically connect the one or more neutron detectors to the counting device, a signal analyzer to determine reactivity of the fuel assemblies in the spent fuel pool based on counted signals, a power supply for the neutron detectors, the counting device and the signal analyzer, and a software code to correlate the counted signals to a predetermined axial flux curve index to determine the subcriticality of the spent fuel pool. In another aspect, this invention provides a method for measuring and monitoring axial flux to evaluate subcriticality in a spent fuel pool of a nuclear power plant. The method includes determining a plurality of highly reactive regions in the spent fuel pool, measuring axial flux at the plurality of regions for a plurality of soluble boron concentrations, generating measured axial flux data, plotting measured axial flux data to generate a measured axial flux curve for each of the plurality of soluble boron concentrations, determining a slope for the measured axial flux curve, correlating the slope of the measured axial flux curve with a slope of an axial flux curve index generated from predetermined analytical data, and determining k-effective for the measured axial flux curve. This invention relates to systems and methods for measuring and monitoring axial flux in a spent fuel pool of a nuclear power plant to evaluate the degree of subcriticality in the spent fuel pool. Generally, the systems and methods of this invention evaluate the degree of subcriticality using the shape of the axial flux distribution in the presence of a neutron source. The measurement system includes neutron detectors, a signal analysis system and neutron source in the spent fool pool. The signal analysis system contains a correlation curve for the axial shape index to the degree of subcriticality. In certain embodiments, the nuclear power plant is a pressurized water reactor. A typical spent fuel pool in a nuclear power plant, such as a pressurized water reactor, consists of more than several hundred fuel assembly storage racks filled with either depleted or fresh fuel assemblies. Reactivity of the spent fuel pool is expressed by the neutron effective multiplication factor, k-effective, and is controlled by various means, such as, for example, high concentration of soluble boron in the spent fuel pool water and other fixed or movable neutron absorbing devices which act as neutron absorbers for reactivity hold-down. Neutron absorbing devices can include borated stainless steel racks, Boral panels and Metamic inserts. The fuel assemblies can be stored in the spent fuel pool in various configurations, such as, close-packed and checker-boarding with empty water cells, with or without neutron absorbers. The particular configuration employed depends on the reactivity of the depleted assemblies. The reactivity of the depleted assemblies can depend on the initial enrichment, burn-up, depletion history and cooling period (e.g., the time after discharge from the reactor core). The storage configuration is selected with the objective of ensuring that the overall reactivity of the spent fuel pool remains below regulatory limits. In the United States, the Nuclear Regulatory Commission (NRC) establishes requirements for the safe operation of nuclear power plants. Currently, the NRC requirements are that k-effective of the spent fuel pool shall not exceed 0.95 in normal conditions and k-effective is to remain less than 1.0 with no soluble boron present, if credit is taken for the presence of soluble boron in normal operations. In general, the amount or degree that the spent fuel pool is subcritical is useful in assessing whether the spent fuel pool is being operated and maintained in a safe condition. Typically, this information is obtained by analytical methods which are based on very conservative input assumptions to encompass a wide range of core operating parameters with which the fuel assemblies can be depleted. As a result, a considerable amount of subcritical margin may exist in the spent fuel pool. Particularly, in the presence of high concentrations of soluble boron. Without being bound by any particular theory, it is believed that determining and evaluating the amount or degree that the spent fuel pool is subcritical by employing systems and methods that use measured values (e.g., axial flux measurements) directed to actual operating parameters will provide advantages over the known conservative systems and methods. For example, at least one of the following benefits may be realized in generating a measured k-effective value: (1) increasing the amount of soluble boron that can be credited thereby effectively increasing the storage capacity, reducing the number of different and complex storage configurations, and simplifying the technical specification compliance, and (2) eliminating regulatory concerns on the uncertainties as to whether there is sufficient margin to criticality or if the regulatory limits are satisfied. In this invention, measuring and monitoring systems and methods that are based on the sensitivity of flux shape versus the degree of subcriticality are used to determine the k-effective and evaluate any reactivity changes (e.g., inadvertent and anticipated) in the spent fuel pool. In general, axial flux in the spent fuel pool environment is measured such that a degree of subcriticality can be determined or inferred therefrom. Various methods and devices for measuring axial flux in a spent fuel pool are known in the art. These known and conventional methods and devices are suitable for use in this invention. In this invention, the axial flux is measured in the most reactive regions of the spent fuel pool because, without intending to be bound by any particular theory, it is believed that the k-effective of the spent fuel pool is driven by the most reactive region of the spent fuel pool and therefore, the degree of subcriticality can be inferred based on the axial flux measurement in the most reactive fuel assembly. In certain embodiments, for example, in a pressurized water reactor, the top portion of a depleted fuel assembly is significantly under-burned relative to the middle portion due to axial power and moderator density profiles during depletion. When the depleted assembly is placed in the spent fuel pool, a majority of the reactivity contribution will be as a result of the top portion of the assembly. The most reactive regions can be determined using various methods and devices known in the art. In certain embodiments, the most reactive regions are determined by simulations, such as by using Monte Carlo analysis. The existence of neutron flux in a subcritical spent fuel pool is maintained by extraneous neutron sources in the pool. Without intending to be bound by any particular theory, it is believed that when there exists a significant margin of subcriticality in the spent fuel pool, e.g., the pool is not close to criticality, the axial flux will depend on the extraneous source (in addition to the small amount of spontaneous fission source). When there is a small margin of subcriticality in spent fuel pool, e.g., the pool is close to approaching criticality, the axial flux will change as the number of neutrons from induced chain reaction fissions increases and starts to drive axial flux. This behavior is demonstrated in FIG. 1 which shows results of Monte Carlo simulations for an array of depleted fuel assemblies stored in the spent fuel pool. In this assembly configuration, a fixed neutron source provides a constant stream of neutrons around the midplane of the fuel assembly. The subcriticality of the spent fuel pool is varied either by changing the soluble boron concentration or the configuration of the spent fuel pool. For illustration purposes, axial flux measurements were taken in the spent fuel pool at varying soluble boron concentrations, particularly, 1500 ppm, 1600 ppm, 1700 ppm, 1800 ppm and 2400 ppm. These measurements were plotted to generate a curve or shape of axial flux for each of the soluble boron concentrations. As seen from FIG. 1, the axial flux shape is mid-peaked due to the fixed neutron source in a highly subcritical pool (e.g., high boron concentration of 2400 ppm). As the spent fuel pool approaches criticality, the induced fission reactions in the top portions of the assembly start generating more neutrons relative to the fixed source, thereby skewing the axial flux shape. The top portions of the assembly are significantly under-burned and therefore, more reactive. In certain embodiments, axial flux measurements are taken in the spent fuel pool at various soluble boron concentrations. The measurements are plotted for each of the soluble boron concentrations and curves or shapes are generated such that each boron concentration has an axial flux curve or shape associated therewith. The plotting of the data to obtain a curve or shape can be conducted manually or by use of an electronic device. The slope of these curves or shapes can be determined using conventional methods and devices known in the art. Further, axial flux curves or shapes for a spent fuel pool can be analytically obtained for selected soluble boron concentrations using analytical tools such as Monte Carlo analysis (e.g., simulation). As a result, an axial shape curve index can be generated. The slope of the analytical curves or shapes can be determined using the analytical tools. The slope value can be used to obtain a k-effective value. The curves or shapes derived from measured axial flux data can be correlated with the axial flux curves or shapes index derived from analytical data. For example, the slope of the curve or shape derived from measured axial flux can be correlated with the slope of the axial flux curves or shapes index. As a result of this correlation, a k-effective value for each of the measured axial flux curves or shapes is obtained. In accordance with certain embodiments of the invention, the following simplified analysis demonstrates analytically the flux behavior in a subcritical system in the presence of an extraneous source. The following cases are considered: (I) one-group and one-dimensional homogeneous medium without chain reaction fission and (II) one-group and one-dimensional homogeneous medium with chain reaction fission. I. Analysis without Chain Reaction Fission Term The diffusion equation for this analysis with a point source located at x=0 is,−D(d2φ/dx2)+Σαφ=Sδ(x) (1). The flux shape is given by the solution of the equation away from the source location,−D(d2φ/dx2)+Σαφ=0 (2). In terms of the diffusion length, L, Equation 2 can be rewritten as,−L2(d2φ/dx2)+φ=0 (3)wherein,L=√{square root over ((D/Σα))} (4). The solution to Equation 3 is the simple exponential function in Equation 5, with its magnitude set by the source strength in Equation 1,ω(x)=SL/2Dexp(−x/L) (5). II. Analysis with Chain Reaction Fission Term The above Analysis I is modified by adding to it the chain reaction fission term as follows,−D(d2ω/dx2)+Σαφ=Σjφ+Sδ(x) (6). Equation 6 can be written as,−D(d2φ/dx2)+Σα(1−Σf/Σα)φ=Sδ(x) (7). In terms of the multiplication factor, k, or the subcriticality (1−k), Equation 7 can be rewritten as,−D(d2φ/dx2)+Σα(1−k)φ=Sδ(x) (8)wherein,k=Σf/Σα (9)andL=√{square root over ((D/Σα))} (4). The comparison of Equation 8 with Equation 1, shows that the absorption cross-section is multiplied with the subcriticality factor (1-k) and therefore the flux distribution in Equation 5 is changed correspondingly to the following general form,φ(x)=(SL/2D√{square root over ((1−k))})exp(−x√{square root over ((1−k))}/L)) (10). The above equation demonstrates how the exponent varies with the subcriticality. The further the spent fuel pool is to being critical, the steeper is the exponential slope. As the spent fuel pool approaches criticality, the flux distribution approaches a flat constant which is the fundamental mode for a homogeneous medium. In certain embodiments, the methods and systems of this invention includes a neutron detectors system installed in the spent fuel pool. The neutron detector system can be selected from those which are known in the art and commercially available. Suitable neutron detector systems for use in this invention include those systems which are capable of operating in the spent fuel pool environment. The neutron detector system includes one or more neutron detectors which are operable to and capable of generating signals as a result of detecting neutron interaction in the spent fuel pool. It is preferable for the neutron detector to be relatively small in size such that it can fit amongst and around the fuel storage racks. In particular, a plurality of neutron detectors is installed in the most reactive regions in the spent fuel pool. In certain embodiments, each of the neutron detectors includes at least one silicon carbide (SiC) semiconductor diode and the associated electronics. A SiC detector is typically compact. For example, the detector diameter can be about 1 inch. Further, the SiC detector is capable of operating at elevated temperatures (in excess of about 500° C.) and in high radiation fields (about 50,000 R/hr). Furthermore, one of the key characteristics of the SiC detector is its ability to operate in neutron pulse mode when exposed to high gamma-ray fields. A counting device or counting electronics is provided which is operable to and capable of counting the signals which are generated by the one or more neutron detectors. The neutron detector and counting device or counting electronics are electrically connected or coupled by a connecting means or mechanism such as, but not limited to a cable, which transfer the signals counted by the counting device or counting electronics. The counted signals are received as input in a signal analyzer. The signal analyzer is operable to and capable of determining the reactivity of the fuel assemblies in the spent fuel pool based on the counted signals. These components are connected or coupled to a computer system which has a software program, such as a computer code, which contains an axial flux curve or shape index. This index is based on analytical or predetermined data. The software program is operable to and capable of correlating the counted signals with the axial flux curve or shape index to evaluate the subcriticality of the spent fuel pool. Additional equipment includes a high voltage supply to power the neutron detector system and a power supply for the counting device or counting electronics. In certain embodiments, in a spent fuel pool of a nuclear power plant, one or more SiC diodes are mounted within a watertight housing. Within the housing, the SiC diode is electrically connected to a watertight cable that transfers signals resulting from neutron interactions in the spent fuel pool to one or more counting electronics. Signal pulses will be counted and the count rate will be determined by a computer, which will then determine and display the reactivity of the fuel assemblies in the spent fuel pool. FIG. 2 is a schematic of a spent fuel pool subcriticality measuring and monitoring system in accordance with certain embodiments of this invention. As shown in FIG. 2, a detector device measures the neutron reactions in the spent fuel pool and generates electrical signals therefrom. A counting device receives and counts the electrical signals generated by the detector device. A signal analyzer receives the counted signals, produces purified signals and determines the measured reactivity of the fuel assemblies in the spent fuel pool. The signal analyzer includes a voltage bias/separation circuit box, an amplifier, a discriminator and a computer. The voltage bias/separation circuit box, amplifier and discriminator are operable to purify the counted signals. The purified signals are then received by the computer as input. The computer also receives analytical data input by the user, such as, for example, pool-specific operating parameters. The computer employs a software program containing an axial flux curve or shape index. The purified signals are correlated with the axial flux curve or shape index. As a result of this correlation, the measured reactivity of the spent fuel pool is obtained for use in evaluating the subcriticality of the pool. Further, the spent fuel pool subcriticality measuring and monitoring system shown in FIG. 2 includes a power supply. While specific embodiments of the invention have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular embodiments disclosed are meant to be illustrative only and not limiting as to the scope of the invention which is to be given the full breadth of the appended claims and any and all equivalents thereof. |
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abstract | A nuclear reactor includes a plurality of mechanisms (11) that drive the contact members (9) that control the reactivity, of the core. Each mechanism includes a driving member (21) including a driving part (23) forming one out of a screw or a nut, a member (27) for applying a rotary torque of the rotor (19) to the driving member (21), a driven member (29) translationally connected to one of the control members (9) and including the other out of screw and a nut; and a member (33) that is selectively mobile between a position of blocking the driving member (21) and a position of releasing the driving member (21). In each drive mechanism (11), the motor (15) is fully immersed in the primary coolant inside the vessel (3); the rotor (19) has a central passage (35), the member for applying the rotary torque (27) being situated in or near the central passage (35); the driving member (21) includes a connecting part (37) engaged in the central passage (35) and collaborating with the member for applying the rotary torque (27), the connecting part (37) being free to effect a translational movement inside the central passage (35) with respect to the rotor (19) when the or each blocking member (33) is in the releasing position. |
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description | The present invention relates to a method for manufacturing a medical wire and a colored medical device. In the past, techniques have been proposed such as coating a fluororesin onto a superelastic alloy wire of Ni—Ti or the like to improve the sliding characteristics of a medical wire, or using a pigment-containing fluororesin as the outermost layer of a medical wire so that physicians and the like in a treatment facility are able to identify the appropriate medical wire using only the external appearance (for example, see Japanese Published Unexamined Patent Application No. 2003-250905). Usually in such cases, a fluororesin will exhibit superior properties only after it is baked at a temperature at or above its melting point (usually 350-400° C.). For this reason, medical guide wires coated with a fluororesin (referred to below as fluororesin-coated medical guide wires) are subjected to a final baking treatment for a period of about 1 minute in an air-circulating oven or the like where the temperature is increased to be at or above the melting point of the fluororesin (for example, see Japanese Published Unexamined Patent Application No. 2004-130123). However, such a method has a problem in that the elastic modulus of the superelastic alloy wire is somewhat impaired when the fluororesin-coated medical guide wire is baked (however, this is not a problem in practice). Moreover, when the fluororesin-coated medical guide wire is baked, if the fluororesin contains a coloring substance such as a pigment, there will be a problem if the color of the pigment contained in the fluororesin ends up fading and cannot produce the desired color. The subject of the present invention is to offer a method for the manufacture of a medical wire that can elicit the superior qualities of a fluororesin while sustaining the elastic modulus of the superelastic alloy wire. In addition, another object of the present invention is to offer a method for the manufacture of a colored medical device that can elicit the superior qualities of a fluororesin while maintaining the color of the pigment contained in the fluororesin. The method for manufacturing the medical wire that relates to the present invention is provided with a process for manufacturing a fluororesin-coated wire and a process for irradiating with infrared radiation. In the process for manufacturing the fluororesin-coated wire, the fluororesin-coated wire is manufactured with a fluororesin-containing liquid or a fluororesin powder body being applied to the outer circumference of a superelastic alloy wire or synthetic resin-coated superelastic alloy wire. Furthermore, synthetic resin-coated superelastic alloy wire as used here is a superelastic alloy wire that is coated with a synthetic resin. In addition, synthetic resin as used here is a resin other than a resin containing fluororesin only (that would correspond to a synthetic resin that has a partial fluororesin). Moreover, fluororesin-containing liquid as used here is a liquid that contains fluororesin. In the process for irradiating with infrared radiation, the fluororesin-coated wire is irradiated with a defined wavelength of infrared radiation for a defined period of time. Furthermore, defined wavelength as used here is preferably a wavelength of 0.9-5.6 μm (micrometer). Additionally, defined period of time as used here is preferably 3-20 seconds. Further preferred is 5-10 seconds. The reasons why the abovementioned manufacturing method maintains the elastic modulus of a superelastic alloy wire are considered below. With a circulating hot air oven (thermostatic oven) being used for baking the fluororesin, the fluororesin coated onto the outer circumference of a superelastic alloy wire is provided with heat energy through contact of the surface with hot air, and when it is heated to the melting temperature or above, it will melt, which is considered to constitute the baking process. For this reason, since it takes a relatively long period of time for the fluororesin surface to reach the fluororesin melting point or higher, the heat energy is thought to be transmitted to the interior during this period. Consequently, when the fluororesin is baked in a circulating hot air oven, it becomes more difficult to protect the superelastic alloy wire in the interior from the heat energy. At the same time, with heating that is due to light energy or electromagnetic wave energy, an energy transfer medium such as air is unnecessary, and a substance can be heated directly by light or electromagnetic radiation. For example, when using near infrared radiation, it is possible to heat the fluororesin in the vicinity of the surface up to the temperature of 400° C. for only 1-3 seconds. In addition, a quartz heater that is a typical infrared radiative heater that can irradiate infrared radiation of the middle infrared radiation region can heat itself, and can also increase the level of the ambient temperature of the surroundings. In other words, if a quartz heater is used, when the ambient temperature can be regulated in the vicinity of from 200° C. to 300° C. that is at or below the allowable temperature limit for the superelastic alloy wire, the object will be irradiated with middle infrared radiation in the vicinity of 1.5-2.0 μm at the ambient temperature. For this reason, if a quartz heater is used, it will exert practically no effect on the superelasticity of the superelastic alloy wire, and the fluororesin in the vicinity of the surface is considered to be able to reach the fluororesin melting point for a short period of time. Moreover, the method for the manufacture of a colored medical device that relates to the present invention is provided with a process for manufacturing a colored medical device substrate and a process for irradiating with infrared radiation. Furthermore, medical device as used here is a guide wire or catheter or the like. In the process for manufacturing a colored medical device substrate, the colored medical device substrate is manufactured by a colored fluororesin-containing liquid or fluororesin powder body that contains a coloring substance being applied to the external surface of a medical device substrate. Furthermore, colored fluororesin-containing liquid as used here is a liquid that contains a fluororesin and a coloring substance. In addition, coloring substance as used here is a pigment or dye or the like. In the process for irradiating with infrared radiation, a colored medical device substrate is irradiated with a defined wavelength of infrared radiation for a defined amount of time. Furthermore, defined wavelength as used here is preferably a wavelength of 0.9-5.6 μm (micrometer). Additionally, defined period of time as used here is preferably 3-20 seconds. Further preferred is 5-10 seconds. Moreover, the method for the manufacture of a fluororesin-coated colored medical device relating to the present invention is provided with a process for manufacturing a colored medical device substrate, a process for manufacturing a fluororesin-coated colored medical device substrate, and a process for irradiating with infrared radiation. In the process for manufacturing a colored medical device substrate, the colored medical device substrate is manufactured by a colored fluororesin-containing primer liquid being applied to the outer surface of the medical device substrate. Furthermore, colored fluororesin-containing primer liquid as used here is a primer liquid that contains fluororesin and a coloring substance. In the process for manufacturing a fluororesin-coated colored medical device substrate, a fluororesin-coated colored medical device substrate is manufactured by a fluororesin-containing liquid or fluororesin powder body that does not contain a coloring substance being applied to the external surface of a colored medical device substrate. Furthermore, fluororesin-containing liquid as used here is a liquid that contains fluororesin and does not contain a coloring substance. In the process for irradiating with infrared radiation, a fluororesin-coated colored medical device substrate is irradiated with a defined wavelength of infrared radiation for a defined period of time. If the method for manufacturing a fluororesin-coated colored medical device relating to the present invention is used, the color of the coloring substance can be maintained while the fluororesin is baked sufficiently, and the sliding characteristics of the colored medical device can be maintained at a high level. In addition, the method for manufacturing a colored medical device relating to the present invention is provided with a process for manufacturing a first colored medical device substrate, a process for manufacturing a second colored medical device substrate, and a process for irradiating with infrared radiation. In the process for manufacturing a first colored medical device substrate, the first colored medical device substrate is manufactured by a colored fluororesin-containing primer liquid being applied to the outer surface of the medical device substrate. Furthermore, colored fluororesin-containing primer liquid as used here is a primer liquid that contains fluororesin and coloring substance. In the process for manufacturing a second colored medical device substrate, the second colored medical device substrate is manufactured by a colored fluororesin-containing liquid or fluororesin powder body that contains a coloring substance being applied to the external surface of the first colored medical device substrate. Furthermore, colored fluororesin-containing liquid as used here is a liquid that contains a fluororesin and a coloring substance. In the process for irradiating with infrared radiation, a second colored medical device substrate is irradiated with a defined wavelength of infrared radiation for a defined period of time. If the method for manufacturing a colored medical device relating to the present invention is used, the color of the coloring substance can be maintained while the fluororesin is baked sufficiently, and the color of interest can be more easily brought out. The reasons why the abovementioned manufacturing method maintains the freshness of the color of the coloring substance are considered below. With a circulating hot air oven (thermostatic oven) being used for baking the fluororesin, the fluororesin that is coated onto the outer surface of a medical device substrate is provided with heat energy through contact of the surface with hot air, and when it is heated to the melting temperature or above it melts, which is considered to constitute the baking process. For this reason, since it takes a relatively long period of time for the fluororesin surface to reach the melting point or higher, it is thought that the heat energy will be substantially transmitted to the coloring substance over this period. Consequently, when the fluororesin is baked in a circulating hot air oven, it becomes more difficult to protect the coloring substance that is contained in the fluororesin from the heat energy. At the same time, in heating due to light energy or electromagnetic wave energy, an energy transfer medium such as air is unnecessary, and a substance can be heated directly by light or electromagnetic radiation. For example, when using near infrared radiation, it is possible to heat the fluororesin in the vicinity of the surface up to the temperature of 400° C. for only 1-3 seconds. In addition, a quartz heater that is a typical infrared radiative heater that can irradiate infrared radiation of the middle infrared radiation region can heat itself, and can also increase the level of the ambient temperature of the surroundings. In other words, if a quartz heater is used, when the ambient temperature can be regulated in the vicinity of from 200° C. to 300° C. that is at or below the allowable temperature limit for the coloring substance, the object will be irradiated with middle infrared radiation in the vicinity of 1.5-2.0 μm at the ambient temperature. For this reason, if a quartz heater is used, the fluororesin in the vicinity of the surface can reach the fluororesin melting point for a short period of time, and the baking treatment can be completed within a short period of time. Consequently, it is thought that the fluororesin can be baked while practically no effect will be exerted on the color of the coloring substance. Furthermore, if the colored medical device substrate is a superelastic alloy wire or a superelastic alloy wire coated with a synthetic resin (excluding a synthetic resin containing fluororesin only), use of the manufacturing method relating to the present invention can maintain the elastic modulus of the superelastic alloy wire. The reasons why the abovementioned manufacturing method maintains the elastic modulus of a superelastic alloy wire are considered below. With a circulating hot air oven (thermostatic oven) being used for baking the fluororesin, the fluororesin that is coated onto the outer circumference of a superelastic alloy wire is provided with heat energy through contact of the surface with hot air, and when it is heated to the melting temperature or above it melts, which is considered to constitute the baking process. For this reason, since it takes a relatively long period of time for the fluororesin surface to reach the melting point or higher, the heat energy is thought to be transmitted to the interior over this period. Consequently, when the fluororesin is baked in a circulating hot air oven, it becomes more difficult to protect the superelastic alloy wire in the interior from the heat energy. At the same time, with heating due to light energy or electromagnetic wave energy, an energy transfer medium such as air is unnecessary, and a substance can be heated directly by the light or electromagnetic radiation. For example, when using near infrared radiation, it is possible to heat the fluororesin in the vicinity of the surface up to the temperature of 400° C. for only 1-3 seconds. In addition, a quartz heater that is a typical infrared radiative heater that can irradiate infrared radiation of the middle infrared radiation region can heat itself, and can also increase the level of the ambient temperature of the surroundings. In other words, if a quartz heater is used, when the ambient temperature can be regulated in the vicinity of from 200° C. to 300° C. which is at or below the allowable temperature limit for the superelastic alloy wire, [the object] is irradiated with middle infrared radiation in the vicinity of 1.5-2.0 μm at ambient temperature. For this reason, if a quartz heater is used, it will exert practically no effect on the superelasticity of the superelastic alloy wire, and the fluororesin in the vicinity of the surface is thought to be able to reach the fluororesin melting point for a short period of time. The inventors of the present application, from the results of carefully repeated experiments and examination, discovered that by irradiating a fluororesin-coated wire with infrared radiation of 0.9-5.6 μm for 3-20 seconds, the fluororesin is baked sufficiently without any impairment of the elastic modulus of the superelastic alloy wire and the fluororesin could be baked sufficiently while maintaining the color of the coloring substance. Consequently, according to the method for the manufacture a medical wire relating to the present invention, the superior properties of the fluororesin can be elicited without any impairment of the elastic modulus of the superelastic alloy wire. Additionally, according to the method for the manufacture of a medical wire relating to the present invention, the superior properties of the fluororesin can be elicited without any fading of the color of the coloring substance. Furthermore, in the method for the manufacture of a medical wire and the method for the manufacture of a colored medical device of the present invention, the time period for baking the fluororesin is substantially shortened when compared to conventional methods. Consequently, according to the method for the manufacture a medical wire and the method for the manufacture of a colored medical device relating to the present invention, the costs for manufacturing a medical wire that is coated with fluororesin and for a colored medical device will be substantially reduced. A method for manufacturing a wire that relates to an embodiment of the present invention is chiefly constituted from a primer application process, a colored fluororesin coating process and a colored fluororesin baking process. Moreover, the raw materials that are necessary in this method for manufacturing a wire are chiefly a superelastic alloy wire, primer, fluororesin and a coloring substance. Below, after the necessary raw materials for implementing the present manufacturing method are mentioned, each process in the present manufacturing method will be described in detail. Raw Materials (1) Superelastic Alloy Wire For the superelastic alloy wire that is utilized in an embodiment of the present invention, either a straight shape or a fine-pointed taper shape is preferred. Examples of the superelastic alloy that can be named include Ni—Ti (Ni: 49-51 atom %, including a third element added to Ni—Ti), Cu—Al—Zn (Al: 3-8 atom %; Zn: 15-28 atom %), Fe—Mn—Si (Mn: 30 atom %, Si: 5 atom %), Cu—Al—Ni (Ni: 3-5 atom %, Al: 28-29 atom %), Ni—Al (Al: 36-38 atom %), Mn—Cu (Cu: 5-35 atom %), Au—Cd (Cd: 46-50 atom %) and the like. Furthermore, this superelastic alloy is also known as a shape-memory alloy. In the present invention, the Ni—Ti alloy is preferred. It is preferable for the size of the superelastic alloy wire to be selected by considering the inner diameter of the catheter with which it is to be used and a flexibility that is suitable for this use. In concrete terms, it is desirable to use a superelastic alloy wire with a diameter on the order of approx. 0.3-1 mm. Furthermore, as the superelastic alloy wire in the present embodiment, it is also desirable to use a superelastic alloy wire that is coated with a synthetic resin (referred to below as a synthetic resin-coated superelastic alloy wire). Further, examples of the synthetic resin that can be named include common synthetic resins such as polyamide resin such as nylon, poly(vinyl chloride) resin, polypropylene resin, epoxy resin, poly(phenylene sulfide) resin, polyether sulfone resin, polyether ketone resin, polysulfone resin, polyamideimide resin, polyether amide resin, polyimide resin, silicone rubber, polyurethane resin and blends of the foregoing. (2) Primer The primer in the present embodiment is the solution of a resin with superior adhesive properties with respect to the superelastic alloy wire or a precursor of such a resin containing a fluororesin. Examples of resins that have superior adhesive properties with respect to the superelastic alloy wire include acrylic resin, epoxy resin as well as blends of the foregoing. Examples of the fluororesin that can be named include poly(tetrafluoroethylene) (PTFE), tetrafluoroethylene-perfluoroalkylvinyl ether copolymer (PFA), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), poly(chlorotrifluoroethylene) (PCTFE), poly(vinylidene fluoride) (PVDF), poly(vinyl fluoride) (PVF) as well as tetrafluoroethylene-ethylene copolymer (PETFE) or blends of the foregoing. (3) Fluororesin The fluororesin is preferably at least one fluororesin selected from the group consisting of poly(tetrafluoroethylene) (PTFE), tetrafluoroethylene-perfluoroalkylvinyl ether copolymer (PFA), poly(chlorotrifluoroethylene) (PCTFE), poly(vinylidene fluoride) (PVDF), poly(vinyl fluoride) (PVF), tetrafluoroethylene-hexafluoropropylene copolymer (FEP) or tetrafluoroethylene-ethylene copolymer (PETFE). Fluororesin is stable and inert, since it must be safe even when it comes into contact with blood when introduced into the body. Furthermore, in the method for manufacturing the medical wire of the present embodiment, a dispersion or powder body form of the fluororesin can also be used. (4) Pigment For the pigment, it is preferable to select at least one pigment selected from the group consisting of inorganic white pigments such as zinc oxide (zinc white), lead white (silver white), lithopone (pigment mixture of zinc oxide and zinc sulfide), titanium dioxide (titanium white), ceramic white and the like, inorganic extender pigments such as precipitated barium sulfate and barite powder, inorganic red pigments such as red lead, Bengal red (red iron oxide), cadmium red, vermillion and the like, inorganic orange pigments such as cadmium orange, chrome vermillion and the like, inorganic yellow pigments such as yellow lead (chrome yellow), yellow zinc (zinc chromate, zinc yellow), cadmium yellow, yellow ochre, nickel titanium yellow, bismuth vanadium yellow and the like, inorganic brown pigments such as sienna earth, amber earth, Vandyke brown and the like, inorganic blue pigments such as ultramarine blue, iron blue (Prussian blue), cobalt blue, cerulean blue, manganese blue and the like, inorganic green pigments such as viridian, chrome oxide green, cobalt green and the like, inorganic purple pigments such as cobalt violet, manganese violet and the like, inorganic black pigments such as ivory black, peach black, lamp black, Mars black, compound oxide black, carbon black and the like, organic red pigments such as alizarin red, quinacridone red, naphthol red, monoazo red, polyazo red and the like, organic orange pigments such as benzimidazolone orange and the like, organic yellow pigments such as monoazo yellow, disazo yellow, polyazo yellow, benzimidazolone yellow, isoindolinone yellow and the like, organic brown pigments such as benzimidazolone brown, sepia and the like, organic blue pigments such as phthalocyanine blue and the like, organic green pigments such as phthalocyanine green and the like, organic purple pigments such as dioxazine violet, quinacridone violet and the like, and organic black pigments such as aniline black. Respective Manufacturing Processes (1) Primer Application Process In the primer application process, primer is applied to the outer circumference of the superelastic alloy wire or the synthetic resin coated superelastic alloy wire (this wire is referred to below as a primer-coated wire). Furthermore, when primer is applied to the superelastic alloy wire or the synthetic resin coated superelastic alloy wire, by regulating the viscosity of the primer liquid, it is possible to control the primer thickness when the superelastic alloy wire is withdrawn from the primer liquid at a constant rate of speed after the superelastic alloy wire is immersed. Further, the thickness of primer in this case is preferably in the range of 1-10 μm. More preferable is for the thickness to be in the range of 2-5 μm. Moreover, it is acceptable for inorganic powders such as metal, ceramic or the like or fluororesin powder to be added to the primer liquid. If this is done, it is possible as mentioned below to form microscopic protuberances in the surface of the fluororesin layer of the fluororesin-coated wire, and to further reduce the frictional resistance with the inner wall of the catheter. Furthermore, it is acceptable to use a pigment-containing primer that is a primer liquid that contains a pigment. With pigment being contained in the primer liquid, it will not be necessary for the fluororesin mentioned below to contain a pigment. In addition, if a pigment-containing primer and a pigment-containing fluororesin are used in the primer liquid application process and the fluororesin application process, the thickness of the pigment-containing layer can become thicker, and it can conceal the backing with a vivid color being easily brought out. (2) Colored Fluororesin Application Method In the colored fluororesin application method, a pigment-containing fluororesin dispersion, a fluororesin enamel liquid that contains a pigment, a pigment-containing fluororesin powder body or the like is applied to a primer-coated wire. Furthermore, if a pigment-containing fluororesin dispersion or a fluororesin enamel liquid that contains a pigment is applied to the primer-coated wire, by regulating the viscosity of the pigment-containing fluororesin dispersion or a fluororesin enamel liquid that contains a pigment, it is possible to control the thickness of the pigment-containing fluororesin if the primer-coated wire is withdrawn from the pigment-containing fluororesin dispersion or a fluororesin enamel liquid that contains a pigment at a constant rate of speed after the primer-coated wire has been immersed. Thereafter, the pigment-containing fluororesin dispersion or a fluororesin enamel liquid that contains a pigment on the primer-coated wire is dried, and a pigment-containing fluororesin layer is formed on the primer-coated wire (this wire is referred to below as a pigment-containing fluororesin-coated wire). Additionally, when a pigment-containing primer has been used in the aforementioned primer application process, it is not necessary for the fluororesin to contain a pigment. In addition, if a pigment-containing primer and a pigment-containing fluororesin are used in the primer liquid application process and the fluororesin application process, the thickness of the pigment-containing layer can become thicker, and it can conceal the backing with a vivid color being easily brought out. In addition, if a pigment-containing powder body is applied to the primer-coated wire, the thickness of the fluororesin can be controlled if a suitable particle size is selected for the fluororesin powder body. Furthermore, this thickness of the pigment-containing fluororesin is preferably in the range 1-50 μm, and is preferably thinner than the thickness of the synthetic resin layer. If the thickness of the pigment-containing fluororesin layer exceeds 50 μm, the rigidity of the fluororesin will exert an effect on the flexibility of the wire, and moreover if the thickness is ≦1 μm, sufficient sliding characteristics and durability will not be obtained. Additionally, the layer with a thickness of 5-30 μm is more preferred. In addition, the layer with a thickness of 5-20 μm is further preferred. Moreover, it is acceptable for inorganic powders such as metal, ceramic or the like or fluororesin powder to be added to the pigment-containing fluororesin dispersion or fluororesin enamel liquid that contains a pigment. If this is done, it is possible to form microscopic protuberances in the surface of the fluororesin layer, and to further reduce the frictional resistance with the inner wall of the catheter. Additionally, in the present invention, it is also possible to use dyes without exceeding the scope of the present invention. (3) Colored Fluororesin Baking Process In the colored fluororesin baking process, the pigment-containing fluororesin-coated wire is passed into a tunnel furnace that comprises a quartz heater, and the pigment-containing fluororesin that constitutes the outermost layer of the pigment-containing fluororesin-coated wired is heated and baked. Furthermore, in this case, it is preferred to use the quartz heater that can irradiate infrared radiation with a peak wavelength of 1.5-5.6 μm (middle infrared region). In addition, the use of the quartz heater that can irradiate infrared radiation with a peak wavelength of 0.9-1.6 μm (near infrared region) is further preferred. Furthermore, while it is preferable for the abovementioned primer application process, colored fluororesin application process and colored fluororesin baking process to be carried out continuously, it is acceptable for them to be carried out in batch mode. Further, while a guide wire was manufactured using the abovementioned method for manufacturing that relates to the present invention, this manufacturing method that relates to the present invention can also be used for manufacturing a catheter or other medical devices. If this is done, it is possible to obtain the same effect. The present invention is further explained below in concrete terms using various Examples. After a Ni—Ti (Ni: 49-51 atom %) superelastic alloy wire with a diameter of 0.35 mm was immersed in a fluororesin primer liquid (solid fraction concentration: 35 wt %) (DuPont Co. tradename: 855-300) at 23° C. with the viscosity regulated at 110 cP (centipoise), it was withdrawn at a constant rate of speed and then dried at 150° C. This resulted in a fluororesin layer with a thickness of approx. 1 μm being formed on the Ni—Ti superelastic alloy wire (this wire is referred to below as a primer-coated wire). Next, after the primer-coated wire was immersed in a PTFE dispersion (DuPont Co. tradename: 855-510) that contains zinc yellow pigment (solid fraction concentration: 50 wt %), it was withdrawn at a constant rate of speed and was then allowed to dry naturally. This resulted in a yellow-colored PTFE resin layer with a thickness of approx. 5 μm being formed on the primer-coated wire (this wire is referred to below as a yellow-colored PTFE resin-coated wire). To continue, the yellow-colored PTFE resin-coated wire was passed into a tunnel furnace that comprises a quartz heater (peak wavelength 3 μm) at a temperature of 350° C. as measured by thermocouple for a period of 10 seconds to bake the yellow-colored PTFE resin (this wire is referred to below as a baked yellow-colored PTFE resin-coated wire). When the color of the baked yellow-colored PTFE resin-coated wire obtained thereby was checked, no discoloration was observed. Moreover, when the yellow-colored PTFE resin layer and the fluororesin primer layer were removed from the thus obtained baked yellow-colored PTFE resin-coated wire and the outer surface of the Ni—Ti superelastic alloy wire was observed, no discoloration of the Ni—Ti superelastic alloy wire was observed. In addition, after the baked yellow-colored PTFE resin-coated wire was wrapped around a pipe of diameter 10 mm and then released, it returned to its original shape without taking on a bending habit. From this fact it was concluded that the superelasticity of the Ni—Ti superelastic alloy wire was maintained. A baked yellow-colored PFA resin-coated wire was manufactured under the same conditions as were used for the first example, except that the PTFE dispersion of the first example was replaced with a PFA dispersion. When the color of the baked yellow-colored PFA resin-coated wire obtained thereby was checked, no discoloration was observed. Additionally, when the yellow-colored PFA resin layer and the fluororesin primer layer were removed from the thus obtained baked yellow-colored PFA resin-coated wire and the outer surface of the Ni—Ti superelastic alloy wire was observed, no discoloration of the Ni—Ti superelastic alloy wire was observed. Moreover, after baked PFA resin-coated wire was wrapped around a pipe of diameter 10 mm and then released, it returned to its original shape without taking on a bending habit. From this fact it was concluded that the superelasticity of the Ni—Ti superelastic alloy wire was maintained. A Ni—Ti (Ni: 49-51 atom %) superelastic alloy wire with a diameter of 0.35 mm, after being immersed in a fluororesin primer liquid (solid fraction concentration: 35 wt %) (DuPont Co. tradename: 855-300) at 23° C. with the viscosity regulated at 110 cP (centipoise), was withdrawn at a constant rate of speed (this wire is referred to below as a primer-coated wire), and then without the fluororesin primer liquid on the primer-coated wire being completely dried, a powder body of zinc yellow pigment-containing PTFE powder (Asahi Glass Co. tradename: L150J (mean particle size: approx. 9 μm)) was applied the primer-coated wire, which was then allowed to dry naturally (this wire is referred to below as a yellow-colored PTFE resin-coated wire). To continue, the yellow-colored PTFE resin-coated wire was passed into a tunnel furnace that comprises a quartz heater (peak wavelength 1 μm) at a temperature of 350° C. as measured by thermocouple for a period of 10 seconds to bake the yellow-colored PTFE resin (this wire is referred to below as a baked yellow-colored PTFE resin-coated wire). When the color of the baked yellow-colored PTFE resin-coated wire obtained thereby was checked, no discoloration was observed. Moreover, when the yellow-colored PTFE resin layer and the fluororesin primer layer were removed from the thus obtained baked yellow-colored PTFE resin-covered wire and the outer surface of the Ni—Ti superelastic alloy wire was observed, no discoloration of the Ni—Ti superelastic alloy wire was observed. In addition, after the baked yellow-colored PTFE resin-coated wire was wrapped around a pipe of diameter 10 mm and then released, it returned to its original shape without taking on a bending habit. From this fact it was concluded that the superelasticity of the Ni—Ti superelastic alloy wire was maintained. A pigment-containing primer liquid was prepared by adding polyamidoimide varnish (Hitachi Chemical Co., Ltd., tradename: HPC-1000) and zinc yellow pigment to a PTFE dispersion (Asahi Glass Co. tradename: AD912) so that the polyamidoimide varnish can be 20 wt % and the zinc yellow pigment can be 30 wt of to the total weight. Then, a primer-coated wire was manufactured in the same manner of conditions as in the first example, except that the primer liquid used in the first example was replaced with the pigment-containing primer liquid. Next, except for the zinc yellow pigment-containing PTFE dispersion in the first example being replaced by a PTFE dispersion (Asahi Glass Co. tradename: AD912), the coating and baking of the PTFE resin was carried out under the same conditions used in the first example. When the color of the baked yellow-colored PTFE resin-coated wire obtained thereby was checked, no discoloration was observed. Moreover, when the PTFE resin layer and the yellow-colored fluororesin primer layer were removed from the thus obtained baked yellow-colored PTFE resin-coated wire and the outer surface of the Ni—Ti superelastic alloy wire was observed, no discoloration of the Ni—Ti superelastic alloy wire was observed. Additionally, after the baked yellow-colored PTFE resin-coated wire was wrapped around a pipe of diameter 10 mm and then released, it returned to its original shape without taking on a bending habit. From this fact it was concluded that the superelasticity of the Ni—Ti superelastic alloy wire was maintained. With the exception of the PTFE dispersion in fourth example being replaced by a zinc yellow pigment-containing PTFE dispersion, the PTFE resin was coated and baked under the same manner of conditions as for the fourth example. When the color of the baked yellow-colored PTFE resin-coated wire obtained thereby was checked, no discoloration was observed. Moreover, when the yellow-colored PTFE resin layer and the yellow-colored fluororesin primer layer were removed from the thus obtained baked yellow-colored PTFE resin-coated wire and the outer surface of the Ni—Ti superelastic alloy wire was observed, no discoloration of the Ni—Ti superelastic alloy wire was observed. In addition, after the baked yellow-colored PTFE resin-coated wire was wrapped around a pipe of diameter 10 mm and then released, it returned to its original shape without taking on a bending habit. From this fact it was concluded that the superelasticity of the Ni—Ti superelastic alloy wire was maintained. The tunnel furnace in the first example was replaced with a circulating hot air oven with an ambient air temperature of 390° C., and the yellow-colored PTFE resin-coated wire was baked for 30 minutes. When the color of the baked yellow-colored PTFE resin-coated wire obtained thereby was checked, a slight discoloration was observed. Moreover, when the yellow-colored PTFE resin layer and the fluororesin primer layer were removed from the thus obtained baked yellow-colored PTFE resin-coated wire and the outer surface of the Ni—Ti superelastic alloy wire was observed, the Ni—Ti superelastic alloy wire was observed to have undergone a color change to a gold color, which was interpreted as due to oxidation. In addition, after the baked yellow-colored PTFE resin-coated wire was wrapped around a pipe of diameter 10 mm and then released, it did not return to its original shape and had taken on a bending habit. From this fact it was concluded that the superelasticity of the Ni—Ti superelastic alloy wire was impaired. The PTFE dispersion in the first example was replaced with an FEP dispersion, and further the tunnel furnace in the first example was replaced with a circulating hot air oven with an ambient air temperature of 350° C., and the yellow-colored FEP resin-coated wire was baked for 30 minutes. When the color of the baked yellow-colored FEP resin-coated wire obtained thereby was checked, a slight discoloration was observed. Additionally, when the yellow-colored FEP resin layer and the fluororesin primer layer were removed from the thus obtained baked yellow-colored FEP resin-coated wire and the outer surface of the Ni—Ti superelastic alloy wire was observed, the Ni—Ti superelastic alloy wire was observed to have undergone a color change to a gold color, which was interpreted as due to oxidation. Moreover, after the baked yellow-colored PTFE resin-coated wire was wrapped around a pipe of diameter 10 mm and then released, it had taken on a bending habit and did not return to its original shape. From this fact it was concluded that the superelasticity of the Ni—Ti superelastic alloy wire was impaired. A Ni—Ti (Ni: 49-51 atom %) superelastic alloy wire with a diameter of 0.35 mm was passed into a tunnel furnace that comprises a quartz heater (peak wavelength 3 μm) at a temperature of 350° C. as measured by thermocouple for a period of 10 seconds. When the outer surface of the Ni—Ti superelastic alloy wire was observed after passing through the tunnel furnace, no discoloration was observed. A Ni—Ti (Ni: 49-51 atom %) superelastic alloy wire with a diameter of 0.35 mm was allowed to stand in a circulating hot air oven with an ambient air temperature of 350° C. for a period of 30 minutes. When withdrawn from the oven, the Ni—Ti superelastic alloy wire was observed to have undergone a color change to a gold color, which was interpreted as due to oxidation. The method for manufacturing a medical device that relates to the present invention has exceptional utility in that the elastic modulus of a superelastic alloy wire is maintained when the superelastic alloy wire is coated with a fluororesin. Moreover, the method for the manufacture a medical wire relating to the present invention possesses the characteristics that the superior properties of the fluororesin can be elicited without any fading of the color of the colored substance, and the use of fluororesin as the material for the outermost layer constitutes an extremely effective way to color a medical device. |
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claims | 1. A method for inspecting an object that comprises multiple regions of interest, the method comprising:determining a first spatial relationship between at least two regions of interest positioned along a first axis; andpositioning the object under multiple beams of a beam array having a beam array axis, such that at least two beams of the beam array irradiate substantially simultaneously the at least two regions of interest, wherein said positioning step comprises orienting the first axis in an angular relation to the beam array axis, the angular relation selected at least in response to the first spatial relationship wherein the beams are charged particle beams. 2. The method of claim 1 wherein the stage of positioning comprises rotating the object in relation to the array of beams. 3. The method of claim 1 wherein the stage of positioning comprises rotating the array of beams in relation to the object. 4. The method of claim 1 wherein an orientation angle between the first axis and the beam array axis is responsive to a ratio of beam array spacing and between a region of interest spacing. 5. The method of claim 1 wherein the stage of determining comprises image processing. 6. The method of claim 1 wherein the aggregate area of the multiple regions of interest is relatively small in relation to the size of a surface of the object. 7. The method of claim 1 wherein the object is a wafer or a reticle. 8. The method of claim 1 wherein the array of beams comprises a grid of beams. 9. The method of claim 1 wherein the stage of positioning comprises orienting the object in relation to the beam array axis prior to inserting the object into an inspection system that comprises an array of beams generator. 10. An inspection system, comprising:a beam array generator adapted to generate an array of beams having a beam array axis; anda processor adapted to determine a first spatial relationship between at least two regions of interest positioned along a first axis of an object; andat least one mechanism adapted to position the object under the array of beams and to orient the first axis in angular relation to the beam array axis such that at least two beams in the array of beams irradiate substantially simultaneously at least two regions of interest of the object wherein the beams are charged particle beams. 11. The system of claim 10 wherein the at least one mechanism is adapted to rotate the object in relation to the array of beams. 12. The system of claim 10 wherein the at least one mechanism is adapted to rotate the array of beams in relation to the object. 13. The system of claim 10 wherein an orientation angle between the first axis and the beam array axis is responsive to a ratio of beam array spacing and between a region of interest spacing. 14. The system of claim 10 adapted to determine by image processing the first spatial relationship between the at least two regions of interest positioned along the first axis. 15. The system of claim 10 wherein the aggregate area of the multiple regions of interest is relatively small in relation to the size of a surface of the object. 16. The system of claim 10 wherein the object is a wafer or a reticle. 17. The system of claim 10 wherein the array of beams comprises a grid of beams. 18. The system of claim 10 wherein the at least one mechanism is adapted to orient the object in relation to the beam array axis prior to inserting the object into the inspection system. |
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description | The invention relates to a cluster for adjusting the reactivity of a pressurized-light-water-cooled nuclear reactor core and an absorber rod in such an adjusting cluster. Nuclear reactors such as pressurized water reactors comprise a core consisting of fuel assemblies placed adjacent to each other within the reactor vessel. A fuel assembly comprises a bundle of fuel rods held in a supporting structure called a skeleton assembly which comprises the frame for the assembly. This skeleton assembly in particular includes guide tubes located in the axial direction of the fuel assembly connecting the top and bottom ends and supporting the spacer grids for the fuel rods. The purpose of these guide tubes is to ensure that the framework has satisfactory rigidity and to allow the assembly of neutron-absorbing rods used to control the reactivity of the nuclear reactor core to be inserted. The absorber rods are connected together at their top ends by a support which is generally called a “spider”, to form a bundle called a control cluster. The set of absorber rods can move within the guide tubes of the fuel assembly. In order to regulate the reactivity of the nuclear reactor core while the reactor is in operation the vertical positions of the control clusters within particular assemblies of the core are changed, either so that they are inserted, the control cluster being then moved downwards, or extracted, the control cluster being then moved upwards, so that a variable length of absorber rod is inserted into the core assemblies. Control clusters of different types are generally used in different parts of the nuclear reactor core to control the core's reactivity and the power distribution within the reactor core while the nuclear reactor is in operation. Highly absorbent clusters, black clusters, and less absorbent clusters, grey clusters, are used in particular. In general the absorber rods comprise a tube closed at its upper end by a first end plug called a top end plug and at its bottom end by a second plug called a bottom end plug for the rod. The absorber rods are secured to the holding spider through their top end plugs. Generally, in the case of black clusters the rod assembly comprises rods having a high neutron absorption capacity. These absorber rods may comprise a cladding tube enclosing pellets of an absorbent material such as boron carbide B4C, tubes of a neutron-absorbing material which do not enclose absorbent pellets, or again tubes of absorbent material enclosing pellets of boron carbide B4C. In particular it has been suggested that hafnium tubes should be used as tubes of absorbent material for the rods in control clusters. Clusters adjusting the reactivity of nuclear reactors may therefore consist wholly or in part of absorber rods comprising a hafnium tube which may include pellets of an absorbent material such as B4C. In some circumstances it has been suggested that only a part of the absorber rods, for example the bottom part, should be made of hafnium. Grey clusters include both absorber rods and inert rods consisting of a simple tube of a material which is not absorbent or has little absorbency, closed by end plugs at its extremities. Absorber rods may comprise tubes of absorbent material such as hafnium. Hafnium has the advantage over other absorbent materials that it has excellent compatibility with the primary fluid, shows little swelling under irradiation and has good creep resistance at the operating temperature of a pressurized water nuclear reactor. It can therefore be used without any sheathing. However, hafnium can only be welded to alloys of the same family (titanium, zirconium, hafnium) or alloys forming continuous solid solutions with hafnium. If hafnium is used for the top end plug, the mechanical strength of the control cluster is not optimal because hafnium does not have sufficiently good mechanical properties for the stresses experienced by the cluster when in operation. Furthermore, the use of a hafnium plug in the top part of an absorber rod is not really justified on the grounds of neutron absorption, given that the top plug is only exposed to a very low neutron flux because it remains above the top of the core. Finally, the use of hafnium for the top end plug is accompanied by an increase in the mass of the cluster, and this may constitute a strong operational constraint. The use of zirconium alloy for the top end plug would be compatible with the mass requirements without any deterioration in absorbency. However, the mechanical properties of these alloys are also inadequate. Conversely, the properties of titanium alloys are perfectly compatible with the performance required. As far as the bottom end plug is concerned, the use of hafnium is not ruled out for mechanical strength reasons because the properties of this material are compatible with the mechanical stresses applied to that component. In this area where there is a high neutron flux it is useful to have neutron absorption capacity. Finally as the volume of the bottom end plug is small, the resulting increase in mass is small and compatible with the requirements for the mass of control clusters. The bottom end plug may therefore be made of hafnium, or a zirconium alloy, while remaining compatible with functional requirements. The objective of the invention is therefore to provide a control cluster for a pressurized water nuclear reactor comprising a bundle of neutron-absorbing rods each of which comprises a metal tube called cladding which is sealed off by a top end plug at its top end and by a bottom end plug at its bottom end and has a support, or spider, of radiating shape to which the absorber rods are attached through their upper end plugs, characterised in that the cladding of at least some of the absorber rods is weld-free hafnium tubes, the top end plugs of the absorber rods having hafnium cladding being of titanium-based alloy and being welded to the top end part of the hafnium cladding of the absorber rod, the bottom end plugs being of massive hafnium and being welded to the bottom end of the hafnium cladding of the absorber rod. In an example embodiment, the top end plugs of absorber rods having hafnium cladding are made of TA6V or TA3V2.5 titanium alloy, protection against wear of the rods is provided by a flow of oxidising atmosphere in a travelling arrangement to the cladding welded to the bottom end plug, protection against wear of the top end plugs made of titanium alloy is obtained by static furnace treatment in an oxidising atmosphere under conditions ensuring that the properties of the alloy are maintained, the welds for at least one of the top and bottom end plugs are made using one of the following procedures: friction welding, resistance welding, TIG welding, and the hafnium used for manufacture of the cladding and the bottom end plugs contains more than 300 ppm of oxygen. The invention also relates to an absorber rod of a cluster adjusting a pressurized water nuclear reactor characterised in that it comprises a hafnium tube, a titanium alloy top end plug welded to the top extremity of the hafnium tube and a bottom end plug of massive hafnium welded to the bottom extremity of the hafnium tube. Finally, the invention also relates to a cluster for adjusting a pressurized water nuclear reactor comprising a bundle of rods and a support of radiating shape, called a spider, to which the absorber rods are attached through their top end plugs, characterised in that the spider is made of titanium-based alloy. In an example embodiment, at least some of the absorber rods in the cluster comprises a hafnium tube and a top end plug of titanium alloy welded to the top extremity of the hafnium tube. Hafnium tubes or hollow bars are prepared in accordance with a process by drawing pierced billets on a needle, and then hot drawing on a deformable mandrel, the mandrel being removed in the final operation by cold drawing up to failure. The advantage of this hot shaping process is that it makes it possible to use metal with a very much higher oxygen content than it should have for cold forming operations. It is generally felt that above 300 ppm of oxygen hafnium can no longer be cold rolled. This process makes it possible to use billets containing more than 300 ppm and even more than 700 ppm of oxygen, as obtained after first fusion by electron bombardment in the conventional method of preparation. The oxygen concentration makes it possible to increase the mechanical properties of the metal, which considerably reduces sensitivity to surface and manufacturing defects (marks, out-of-alignment, etc.). Zirconium or hafnium end plugs are obtained by the machining of solid bars of suitable diameter. This design makes it possible to satisfy the neutron, mechanical and weight requirements. However, longitudinal and orbital movements of the cluster are likely to give rise to wear in the cluster guides (continuous guides and guide cards) and the fuel assembly (wear on the tip). It is known that these materials (titanium, zirconium and hafnium) do not withstand wear well. One known way of protecting these materials against wear is to provide high temperature oxidation treatment in an oxidising atmosphere. Such treatment produces an oxygen diffusion layer which provides protection against wear and a layer of oxide whose formation is hard to prevent because of the very low equilibrium pressure of the oxide in an oxidising atmosphere. The depth of oxygen diffusion required to ensure wear resistance is some 20 micrometres. The minimum target depth for this operation is therefore 35 to 50 μm. Implementation of a process for furnace oxidising 3.5 to 4.6 m bars would require a furnace of sufficient size capable of working in an oxidising atmosphere at 800-1000° C. The invention therefore also relates to the use of oxidising treatment in a travelling arrangement at a higher temperature which ensures oxygen diffusion to a sufficient depth to provide wear resistance, maintaining a constant temperature—a measure of the uniformity of the oxidised bar—without introducing straightness or mechanical inhomogeneities. Diffusion of oxygen over ˜50 μm may be obtained by induction heating at 1300-1700° C. in an oxidising atmosphere consisting of argon and oxygen, at a rate of travel of 50-250 mm/min. Heating to a higher temperature is likely to cause phase changes in the metal (1725-1775° C.) or in the oxide (˜1700° C.). Travelling oxidation is carried out on absorber rods which have been welded to their bottom end plugs. Furthermore, the bottom end plugs of welded tubes are treated to ensure continuity of protection against wear within the area of the bottom end plug of ogival shape. However, the processing of completed rods (with welded top end plugs) is undesirable. In fact in some rods the presence of packing pieces, a column of B4C pellets and a supporting arrangement disturbs heating, restricts the choice of packing pieces and supporting devices (materials which are likely to give rise to molten eutectics at the processing temperature must be ruled out). In addition to this, the change in heating conditions at the hafnium-titanium junction is difficult to control without risking excessive heating of the titanium, heating which would prejudice persistence of its mechanical properties. Treatment in a travelling arrangement also makes it possible to avoid oxidising the part which will be welded to the top end plug, thus avoiding contaminating the weld. The top end plugs of rods are protected against wear by treatment in a static furnace in an oxidising atmosphere under conditions which ensure that the alloy's properties are acquired. Treatment in a static furnace is generally carried out at a temperature of between 550° C. and 850° C., for a period of 2 to 12 hours. For example treatment may be carried out for 4 hours at 730° C. Finally the invention also relates to a control cluster whose spider is made of titanium-based alloy. This arrangement makes it possible to benefit from the better mechanical properties of these alloys and their lesser density. Thus design of the cluster becomes easier because part of the mass of the spider can be allocated to the absorber rods. The spider supporting the absorber rods in the cluster may be constructed to be of a shape and dimensions identical to those of the supporting spiders for the absorber rods of control clusters according to the prior art. However, in some circumstances, depending upon the shape and size of the titanium alloy top end plug, the shape and dimensions of the parts of the spider to which the absorber rods are attached can be altered. Instead of a steel supporting spider for the absorber rods, use of a spider made of titanium-based alloy makes it possible to benefit from mechanical properties of a higher grade than those of steel. The reliability and service life of the spider can therefore be increased as a result of these improved mechanical properties. It is also possible to effect a slight reduction in the transverse dimensions of the spider supporting the control clusters when the spider is made of titanium-based alloy having superior mechanical properties. The loss of head when the control cluster is lowered into the nuclear reactor core and thus reduced, and the lowering time is also reduced. The spider may be constructed by cutting it out from a piece of titanium alloy whose metallurgical soundness has been checked. The risk of defects is thus reduced and the number of welded or brazed joints between the constituent components of the spider is reduced. Cutting out may be effected by mechanical, chemical or electrical machining, or by water jet cutting. Titanium alloys as envisaged above are not affected by corrosion within the nuclear reactor vessel. Fewer activatable products are therefore delivered to the primary circuit. Finally the metallurgical soundness of the material and the simplicity of manufacturing a spider from titanium-based alloy makes it possible to reduce manufacturing costs and operational abnormalities and increase productivity in the manufacture of control clusters. A spider of titanium-based alloy can be used for any control cluster whether or not it includes rods with hafnium tubes. Tests have been performed on the mechanical strength of control clusters according to the invention under conditions reproducing the conditions in a functioning nuclear reactor. Wear tests have also been carried out on the different parts of absorber rods to validate anti-wear treatments using oxidation. The tests performed were designed to check the wear resistance of the absorber rod end plugs and in particular the top end plugs, the hafnium tubes of the absorber rods and the parts linking the top end plugs with the control cluster spider. Endurance tests were carried out and showed that control clusters according to the invention can operate within a nuclear reactor without premature destruction for the envisaged service lives of nuclear reactors according to the current art. In order that the invention may be understood a control cluster and an absorber rod according to the invention will be described by way of example with reference to the appended figures. In FIG. 1 a control cluster for a pressurised water nuclear reactor is indicated in general by the reference number 1. Control cluster 1 comprises a bundle of absorber rods 2 and a spider 3 supporting and holding rods 2 in the form of a bundle in which the rods are parallel with each other and laterally positioned in the same arrangement as the fuel assembly guide tubes. Spider 3 comprises a cylindrical hub 3a with internal grooves so that the control cluster can be connected to an absorber rod in order to move it in a vertical direction within the core and arms 3b which are of one piece with hub 3a, to each of which absorber rods 2 are attached by their top end plugs. Some at least of rods 2 in control cluster 1 comprise a tubular body comprising a hafnium tube. In the case where cluster 1 is a black cluster, the tubes of all absorber rods 2 in the cluster may be of hafnium. In the case of a grey cluster, only some of rods 2 comprise a hafnium tube, the tubes of the other rods being of steel or any other non-absorbent material which satisfies operational requirements within a nuclear reactor. FIG. 2 shows an absorber rod according to the invention in a black cluster which can be used for example in a pressurized-water-cooled nuclear reactor operating at a power of 1300 MWe. Rod 2 illustrated in FIG. 2 comprises a hafnium tube 4 enclosing a stack of highly absorbent boron carbide B4C pellets 5 which is sealed off at its upper extremity by a titanium alloy plug 6 and at its lower extremity by a hafnium or zirconium alloy plug 7 of ogival shape. Oxygen diffusion 11 has been carried out on the tube welded to the bottom end plug and provides protection against wear. The top end plug may or may not be protected by oxygen diffusion 12. The hafnium used may contain more than 300 ppm of oxygen. The stack of boron carbide B4C pellets 5 is held within hafnium tube 4 by a spring or any other immobilising device 8, the bottom end of the column of pellets bearing against bottom end plug 7 through a strut 7a. Bottom end plug 7 of hafnium rod 2 is made of one piece with the bottom end of hafnium tube 4 through a weld bead 7b, welding being carried out for example using a laser beam, a beam of electrons, TIG, friction or resistance welding. The weld obtained is sound and strong. In accordance with the invention, top end plug 6 of rod 2 is made of titanium or titanium alloy, for example Ti-6Al-4V (TA6V) alloy or TA3V2.5 alloy, and it is rigidly and leaktightly secured to the top end of tube 4 through a weld 9. Tests have demonstrated that the weld between titanium alloy plug 6 and hafnium tube 4 can be made using for example a laser beam, an electron beam, TIG, friction or resistance welding. The weld obtained is perfectly sound and perfectly strong. In the case of TIG or friction welds, the failure zone of a hafnium/titanium or hafnium/Zircalloy test piece lies outside the welded zone. Failure occurs under a load corresponding to the ultimate strength of the solid material. As illustrated in FIG. 3, top end plug 6 of titanium alloy which secures absorber rod 2 to an arm 3b of spider 3 of the control cluster may be of a shape and dimensions which are identical to those of a top end plug of an absorber rod according to the prior art. The top end plug 6 which has a thread for securing the absorber rod to arm 3b of spider 3 may be either screwed into the spider arm or placed in a transverse position and held by means of a top nut 10 which also guides the cluster when it is being raised. As illustrated in FIG. 3, the top end plug of absorber rod 6 has a part of small cross-section 3c which provides the rod with the required flexibility. Furthermore, it has been established that weld 9 between titanium alloy plug 6 and the top end of hafnium tube 4 (FIG. 2) withstands mechanical, thermal and chemical stresses within a nuclear reactor environment without any additional corrosion being observed at the connecting weld 9 of top end plug 6. Furthermore, when the control cluster is used in the core of a nuclear reactor, plug 6 lies above the top surface of the core, in a zone which is not subjected to the intense neutron flux obtaining within the nuclear reactor core. The titanium alloy top end plug is therefore not subjected to conditions giving rise to swelling under irradiation or loss of mechanical properties. The top end plug having high grade mechanical properties thus retains its characteristics over long periods of service within the core of a nuclear reactor. Furthermore, the top end plug of hafnium absorber rods in the control cluster according to the invention which is made of titanium alloy having high grade mechanical properties may be constructed in such a way as to have the greatest possible length compatible with use of the control cluster. The length of the hafnium tube can thus be reduced, making it possible to reduce the cost and adjust the mass of the absorber rods. The invention applies to any control cluster for a light water cooled nuclear reactor comprising absorber rods comprising a hafnium tube. |
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description | This application claims the benefit under 35 U.S.C. Section 119(e) of U.S. Provisional Patent Application Ser. No. 61/644,660 filed May 9, 2012, and U.S. Provisional Patent Application Ser. No. 61/761,350 filed Feb. 6, 2013 both entitled “A POSITRON EMISSION TOMOGRAPHY PROBE TO MONITOR SELECTED SUGAR METABOLISM IN VIVO” the contents of each which are incorporated herein by reference. This invention was made with Government support under Grant Number DE-SC0001249, awarded by the U.S. Department of Energy and under Grant Number CA098010, awarded by the National Institutes of Health. The Government has certain rights in the invention. The present disclosure relates to tomography probes useful as selective imaging agents. Positron emission tomography (PET) is a medical imaging technique that is commonly used to produce three-dimensional images in vivo. This technique detects gamma rays emitted by a positron-emitting radionuclide tracer that has been administered to a subject. Three-dimensional images of tracer concentrations within the subject's body can then be constructed by computer analysis. In this way, PET can be used, for example, to observe a variety of organs and/or physiological processes such as cellular metabolism and protein synthesis, as well as well as pathological conditions such as cancer and heart disease. 18F-Fluoro-2-Deoxy-D-glucose (18F-FDG) is a common clinical PET probe that is used, for example, to diagnose certain pathological conditions including cancer as well as to evaluate the effects of certain therapeutic regimens. 18F-FDG however, has high absorption ratios in certain tissues such as the brain, heart, kidney and bladder. For this reason, background signals can be a problem when using this molecule at a probe. In addition, some tissues of primary liver cancer and clear cell renal cell carcinoma (CCRCC) do not selectively absorb 18F-FDG, a phenomena that can lead to false negatives. 18F-FDG also has high absorption ratios in inflamed areas, another characteristic which can contribute to erroneous diagnoses. These characteristics of 18F-FDG's limit its applications in vivo. Compounds useful as probes in positron emission tomography can contain [18F]-2-fluoro-2-deoxyarabinose ([18F]-FDA) as part of the molecule, such as 1-(2′-deoxy-2′-[18F]fluoro-β-D-arabinofuranosyl)cytosine (see, e.g. Radu et al. Nat Med. 2008 July; 14(7):783-8), 1-(2′-deoxy-2′-[18F]fluoro-β-D-arabinofuranosyl)-5-methylcytosine (see, e.g. Shu C J, et. al. J Nucl Med. 2010 July; 51(7):1092-8), and 2′-deoxy-2′-[18F]fluoro-9-β-D-arabinofuranosylguanine (see, e.g. Namavari M, et al. Mol Imaging Biol. 2011 October; 13(5):812-8). However, it has not been determined if any discrete [18F]-FDA compound alone possesses a pharmacokinetic profile that allows it to be used as a PET probe in vivo, much less if a [18F]-FDA compound may be useful to monitor specific physiological processes in vivo. The invention disclosed herein provides compounds that are useful as probes in processes such as positron emission tomography, as well as methods for making and using them. Embodiments of the invention include methods for using the PET probes to observe specific organs and tumor subtypes, as well certain metabolic disorders in mammals. The working embodiments of the invention that are disclosed herein demonstrate how these probes can be used to monitor liver function in vivo, in order to, for example, identify areas of abnormal activity in the liver (including the presence of primary and secondary neoplastic lesions), and/or to observe liver dysfunction, and/or to observe liver regeneration. The invention disclosed herein has a number of embodiments. One embodiment of the invention is a composition of matter comprising a positron emission tomography probe selected from the group consisting of 18F labelled: 2-fluoro-2-deoxyarabinose; 3-fluoro-3-deoxyarabinose; 2-fluoro-2-deoxyribose; 3-fluoro-3-deoxyribose; 1-fluoro-1-deoxy-alpha-ribose; and 1-fluoro-1-deoxy-beta-ribose. As discussed in detail below, it has been discovered that when these PET probes are administered to a subject, they selectively accumulate in certain tissues, a phenomena that can be observed via a process such as positron emission tomography. In illustrative embodiments of the invention that are disclosed herein, a 18F labelled 2-fluoro-2-deoxyarabinose PET probe is shown to selectively accumulate in murine liver, kidney and intestinal tissues. Embodiments of the invention include methods of observing cellular metabolism in vivo in a mammal using the PET probes disclosed herein. These methods typically comprise the steps of administering a composition to the mammal comprising a positron emission tomography probe selected from the group consisting of 18F labelled 2-fluoro-2-deoxyarabinose, 3-fluoro-3-deoxyarabinose, 2-fluoro-2-deoxyribose, 3-fluoro-3-deoxyribose, 1-fluoro-1-deoxy-alpha-ribose or 1-fluoro-1-deoxy-beta-ribose and then allowing the probe to accumulate in cells/tissues of the mammal The cells/tissues having this accumulated probe can then be observed using a positron emission tomography and/or computed tomography (CT) process. Embodiments of the invention use the disclosed PET probes to observe metabolic phenomena that are characteristic of certain biological processes. For example, in some embodiments of the invention a PET probe is used to examine cells for metabolic phenomena that are observed in disease syndromes such as cancer or diabetes. In other embodiments of the invention a PET probe is used to examine cells for metabolic phenomena that are observed in cells responding to a therapeutic agent such an anti-cancer agent or anti-diabetic agent administered to the mammal In illustrative embodiments of the invention, a PET probe is used to examine cells for metabolic phenomena that are observed in cells responding to an oxythiamine, insulin, metformin, leflunomide or a methotrexate composition. In one specific illustrative embodiment of the invention, the mammal is a human, the PET probe consists of 2-fluoro-2-deoxyarabinose: and cellular metabolism in liver, kidney, and/or intestinal tissues is selectively observed using a positron emission tomography process. Related embodiments of the invention include methods of selectively observing an in vivo tissue or organ in a mammal such as liver, kidney, and/or intestinal tissues. Such methods comprise the steps of administering a composition to the mammal that includes a positron emission tomography probe selected from the group consisting of 18F labelled 2-fluoro-2-deoxyarabinose, 3-fluoro-3-deoxyarabinose, 2-fluoro-2-deoxyribose, 3-fluoro-3-deoxyribose, 1-fluoro-1-deoxy-alpha-ribose, and 1-fluoro-1-deoxy-beta-ribose. Typically in these methods, the positron emission tomography probe is administered to the mammal in combination with a pharmaceutically acceptable compound comprising a diluent, a carrier, or a binding agent. Following this administration, the probe is then allowed to selectively accumulate in a tissue or organ such as liver, kidney, and/or intestinal tissues. The probe in the mammal can then be used to observe an in vivo tissue or organ where it has accumulated, typically by using a positron emission tomography and/or a computed tomography process. In this way, a mammalian tissue or organ such as liver, kidney, and/or intestinal tissues can selectively observed in vivo. Embodiments of the invention use the disclosed PET probes to observe metabolic phenomena that are characteristic of certain biological processes such as the cellular metabolism of liver, kidney, and/or intestinal tissue. For example, some embodiments of observed cellular metabolism in such a tissue to detect the presence or absence of metabolic phenomena that are characteristic of a metabolic disorder, tumor growth, gluconeogenesis, a neurodegenerative syndrome, a syndrome characterized by ischemia, a syndrome characterized by chronic inflammation, congestive heart failure, stroke or the like. Similar embodiments of the invention include methods for observing a physiological activity in the liver that is observed in liver dysfunction, liver cancer or liver regeneration. Other embodiments of the invention include methods of synthesizing PET probes such as [18F]-2-fluoro-2-deoxy-arabinose. As discussed in detail below, in one embodiment of the invention, this method comprises synthesizing [18F]-2-fluoro-2-deoxy-arabinose by producing [18F]-fluoride ion by bombarding enriched [18O] water, treating the [18F]-fluoride ion with K2CO3 and 4,7,13,16,21,24-Hexaoxa-1,10-diazabicyclo[8.8.8]-hexacosane so as to form a first mixture, performing azeotropic distillation on the first mixture, adding 2-O-(trifluoromethylsulfonyl)-1,3,5-tri-O-benzoyl-alpha-D-ribofuranose to the first mixture, loading the first mixture onto a silica matrix, eluting [18F]-2-fluoro-2-deoxy-1,3,5-tri-O-benzoyl-alpha-ribofuranose from the matrix with ethyl acetate; and then adding sodium methoxide to the [18F]-2-fluoro-2-deoxy-1,3,5-tri-O-benzoyl-alpha-ribofuranose to form a second mixture, wherein the second mixture forms [18F]-2-fluoro-2-deoxy-arabinose. Typically these methods comprise loading the second mixture onto a chromatographic column system; and then eluting the [18F]-FDA with water. Other embodiments of the invention include kits, for example, those including a plurality of containers that hold one or more reagents useful in a PET process. In one illustrative embodiment, the kit includes one or more compounds selected from the group consisting of 2-fluoro-2-deoxyarabinose, 3-fluoro-3-deoxyarabinose, 2-fluoro-2-deoxyribose, 3-fluoro-3-deoxyribose, 1-fluoro-1-deoxy-alpha-ribose or 1-fluoro-1-deoxy-beta-ribose as well as articles or materials useful to label the compound with 18F (e.g. an article or material disclosed in Example 1 below). In some embodiments of the invention, the kit includes articles useful to administer the probe, for example a capsule that can surround the probe (e.g. for use when the probe is administered orally) or a needle and syringe (e.g. for use when the probe is administered parenterally). Other objects, features and advantages of the present invention will become apparent to those skilled in the art from the following detailed description. It is to be understood, however, that the detailed description and specific examples, while indicating some embodiments of the present invention are given by way of illustration and not limitation. Many changes and modifications within the scope of the present invention may be made without departing from the spirit thereof, and the invention includes all such modifications. Unless otherwise defined, all terms of art, notations and other scientific terms or terminology used herein are intended to have the meanings commonly understood by those of skill in the art to which this invention pertains. Many of the techniques and procedures described or referenced herein are well understood and commonly employed using conventional methodology by those skilled in the art. All publications mentioned herein are incorporated herein by reference to disclose and describe the methods and/or materials in connection with which the publications are cited. Publications cited herein are cited for their disclosure prior to the filing date of the present application. Nothing here is to be construed as an admission that the inventors are not entitled to antedate the publications by virtue of an earlier priority date or prior date of invention. Further the actual publication dates may be different from those shown and require independent verification. In the description of the preferred embodiment, reference is made to the accompanying drawings which form a part hereof, and which is shown by way of illustration a specific embodiment in which the invention may be practiced. It is to be understood that other embodiments may be utilized and structural changes may be made without departing from the scope of the present invention. The invention disclosed herein provides ribose compounds having properties that make them useful as PET probes, for example, to monitor ribose metabolism in vivo. The data presented herein demonstrates that compounds including [18F]-2-fluoro-2-deoxyarabinose very specifically localize to certain tissues that express ribokinase, such as the liver. The data presented herein further illustrates the usefulness of these PET probes by demonstrating that [18F]-FDA uptake in the liver is dependent on the metabolic status of the mouse, with leptin knockout mice (a mouse model of type 2 diabetes) showing a severe deficit in uptake of the probe compared with wild-type mice (FIG. 2). Ribose is an intermediate in the pentose phosphate pathway, where it can be metabolized through gluconeogenic pathways to glucose. Hence, this information, in combination with the discoveries and data presented herein, provides evidence that [18F]-FDA can be used to probe specific aspects of gluconeogenesis and/or pathological conditions associated with aberrant gluconeogenesis. Embodiments of the invention include compositions of matter comprising a positron emission tomography probe selected from the group of isomers consisting of: 18F labelled 2-fluoro-2-deoxyarabinose; 3-fluoro-3-deoxyarabinose; 2-fluoro-2-deoxyribose; 3-fluoro-3-deoxyribose; 1-fluoro-1-deoxy-alpha-ribose; and 1-fluoro-1-deoxy-beta-ribose (see, e.g. FIGS. 4 and 5). As shown in FIGS. 4 and 5, the ribose molecules of the invention are discrete compounds and not covalently coupled to other atom(s). The compositions of the invention can include a pharmaceutically acceptable carrier such as a diluent, a binding agent, or an agent selected for its ability to inhibit microbial growth. As discussed in detail below, it has been discovered that when these PET probes are administered to a subject, they selectively accumulate in certain tissues, a phenomena that can be observed via processes such as positron emission tomography. In working embodiments of the invention that are disclosed herein, positron emission tomography is used to show the selective accumulation of 18F labelled 2-fluoro-2-deoxyarabinose in murine liver, kidney and intestinal tissues. Other embodiments of the invention include using the PET probes in methods of observing physiological characteristics in vivo, for example one or more physiological phenomena associated with cellular metabolism. Such methods comprise the steps of administering a composition to the mammal comprising a positron emission tomography probe selected from the group consisting of 18F labelled 2-fluoro-2-deoxyarabinose, 3-fluoro-3-deoxyarabinose, 2-fluoro-2-deoxyribose, 3-fluoro-3-deoxyribose, 1-fluoro-1-deoxy-alpha-ribose or 1-fluoro-1-deoxy-beta-ribose and then allowing the probe to accumulate in cells/tissues of the mammal The cells/tissues having this accumulated probe can then be observed using a positron emission tomography and/or computed tomography process (see. e.g. FIG. 2). The PET probes disclosed herein have a number of desirable characteristics including an ability to specifically accumulate in distinct cell types, tissues or organs. Without being bound by a specific scientific theory or mechanism of action, it is believed that a cellular mechanism that leads to the observed accumulation of 18F in tissues such as the liver is the phosphorylation of the ribose probes by the protein ribokinase (see Park et al., FEBS Letters 581 (2007) 3211-3216 for a description of this ribokinase enzyme). This phosphorylation of the PET probes (at the 5′-position) by ribokinase is believed to alter the mobility of these molecules so that they accumulate in cells. FIG. 4 provides information on cellular mechanisms associated with the accumulation of the disclosed PET probes in cells and the phosphorylation of the hydroxyl group at the 5-position of these ribose molecules. FIG. 4 further illustrates chemical structures of various ribose compounds and the phosphorylated products that they form in the presence of ribokinase (high levels of which are found in the liver, kidney, and intestines). Because the hydroxyl group at the 5-position of the disclosed PET probes appears to require phosphorylation for 18F (the radionuclide of fluorine imaged in processes such as positron emission tomography) accumulation to occur in cells, the disclosed compounds will exhibit different in vivo accumulation profile as compared to compounds that are not amenable to phosphorylation by ribokinase (see, e.g. the compound disclosed in Onega et al., Chem. Commun., 2010, 46, 139-141). In this context, FIG. 10 provides data showing that Ribokinase is predominantly expressed in the liver, kidneys, and intestines, and that 2-fluoro-2-deoxyarabinose accumulates in these organs having high levels of ribokinase. Embodiments of the invention use the disclosed PET probes to observe metabolic phenomena that are characteristic of certain biological processes. For example, in some embodiments of the invention a PET probe is used to examine cells for metabolic phenomena that are observed in disease syndromes such as cancer or diabetes. In other embodiments of the invention a PET probe is used to examine cells for metabolic phenomena that are observed in cells responding to a therapeutic agent such an anti-cancer agent or anti-diabetic agent administered to the mammal In illustrative embodiments of the invention a PET probe is used to examine cells for metabolic phenomena that are observed in cells responding to a therapeutic agent such as an oxythiamine, an insulin, an metformin, a leflunomide or a methotrexate composition. In a specific illustrative embodiment of the invention, the mammal is a human the PET probe consists of: and cellular metabolism in liver, kidney, and/or intestinal tissues is selectively observed using a positron emission tomography process. Embodiments of the invention can be adapted to monitor a number of physiological conditions including pathological syndromes. For example, embodiments of the invention can be used to monitor diseases in which the pentose phosphate or the de novo nucleotide synthesis pathways are dysregulated. Such diseases include, for example, neurodegenerative syndromes, syndromes characterized by ischemia, syndromes characterized by chronic inflammation, congestive heart failure, stroke and the like. In addition, embodiments of the invention can be used to monitor physiological responses to therapies that alter the activity of the pentose phosphate and de novo nucleotide synthesis pathways, including, for example, treatment with oxythiamine, insulin, metformin, leflunomide, and methotrexate. Embodiments of the invention can also be used to monitor a physiological activity of organs or tissues having ribose metabolism in vivo including the spleen, muscle, heart, thyroid, intestines, blood, kidney and liver. The data shown, for example, in FIGS. 6 and 7 includes metabolite studies that show that enzymes in the pentose phosphate pathway metabolize 18F labelled 2-fluoro-2-deoxyarabinose so of a probe in vitro and in vivo (FIGS. 6 and 7). This provides evidence that such working embodiments can be used to monitor changes in the pentose phosphate pathway, caused either by disease or therapeutic agents. Other derivatives of this working embodiment may be metabolized by the de novo nucleotide synthesis pathway and used in the same way. The data shown, for example, in FIGS. 6 and 7 includes metabolite studies that show that 18F labelled 2-fluoro-2-deoxyarabinose is metabolized by tissues in addition to the liver, including the spleen, muscles, heart, blood, thyroid, and kidneys (FIG. 7). This was unexpected, and although this probe predominantly accumulates in the liver during physiological conditions, the fact that other tissues metabolize the probe provides evidence that under pathological conditions, these tissues accumulate significant levels of the probe as well. This data provides evidence that the probe may access a variety of tissues in addition to the liver, including the spleen, muscles, heart, blood, thyroid, and kidneys. Embodiments of the invention include methods of selectively observing an in vivo tissue or organ in a mammal such as liver, kidney, and/or intestinal tissues using a PET probe ribose isomer in a positron emission tomography and computed tomography process. In illustrative embodiments of the invention, liver, kidney, salivary gland and/or intestinal tissue is imaged. Moreover, mass spectrometry data provides evidence that the heart, blood, and spleen tissues accumulate the PET probes disclosed herein. In addition, in certain diseases and/or dysfunction, tissues may become more visible when exposed to a PET probe. For example, the literature teaches that, following ischemic insult, heart tissues accumulate high levels of ribose, a phenomenon that can be imaged using embodiments of the invention. Methods of selectively observing an in vivo tissue or organ in a mammal typically comprise the steps of administering a composition to the mammal that includes a positron emission tomography probe selected from the group consisting of 2-fluoro-2-deoxyarabinose, 3-fluoro-3-deoxyarabinose, 2-fluoro-2-deoxyribose, 3-fluoro-3-deoxyribose, 1-fluoro-1-deoxy-alpha-ribose, and 1-fluoro-1-deoxy-beta-ribose. Typically in these methods, the positron emission tomography probe is administered to the mammal in combination with a pharmaceutically acceptable compound comprising a diluent, a carrier, or a binding agent. Following this administration, the probe then selectively accumulates in tissues or organs having cells that express ribokinase such as liver, kidney, and/or intestinal tissues. The probe can be used to observe an in vivo tissue or organ where it has accumulated, typically by using a positron emission tomography and/or a computed tomography process. In this way, a mammalian tissue or organ such as liver, kidney, and/or intestinal tissues can be selectively observed in vivo. Embodiments of the invention can use the disclosed PET probes to observe metabolic phenomena that are characteristic of certain biological processes such as the cellular metabolism in liver, kidney, and/or intestinal tissues. For example, some embodiments of observed cellular metabolism in such a tissue to detect the presence or absence of metabolic phenomena that are characteristic of a metabolic disorder, tumor growth, gluconeogenesis, a neurodegenerative syndrome, a syndrome characterized by ischemia, a syndrome characterized by chronic inflammation, congestive heart failure, stroke or the like. Similar embodiments of the invention include methods for observing a physiological activity in the liver that is observed in liver dysfunction, liver cancer or liver regeneration. Embodiments of the invention include methods to synthesize the compounds disclosed herein (see Example 1 below and FIG. 11). Briefly, in one exemplary implementation, the synthesis of the [18F]-FDA and its purification is carried out as follows: Using a RDS-111 cyclotron, non-carrier-added [18F]-fluoride ion is produced by 11 MeV proton bombardment of 98% enriched [18O] water in a silver target. 100 microL of aqueous [18F]-fluoride ion is treated with a solution of K2CO3 (1.5 mg) dissolved in 14 microL water and Kryptofix K222 (10 mg) dissolved in 950 microL of anhydrous acetonitrile and then mixed. The mixture is heated at 105 degrees Celsius and evaporated under nitrogen flow and vacuum for 7 min with two 1 mL anhydrous acetonitrile additions to complete the azeotropic distillation. 2-O-(Trifluoromethylsulfonyl)-1,3,5-tri-O-benzoyl-alpha-D-ribofuranose is added to the dry complex and the reaction mixture is heated at 155 degrees Celsius for 15 min under sealing conditions. After the fluorination, the solution is cooled to 40 degrees Celsius and loaded into a silica cartridge. [18F]-2-fluoro-2-deoxy-1,3,5-tri-O-benzoyl-alpha-ribofuranose is eluted from the cartridge with 2 mL of anhydrous ethyl acetate into a second vessel. The anhydrous ethyl acetate is evaporated at 60 degrees Celsius under nitrogen flow and vacuum for 3 min. To the dry product, 500 microL of sodium methoxide (0.5 M in methanol) is added and the mixture is heated at 100 degrees Celsius for 5 min under sealed conditions. The mixture is purified on a SPK column system consisting of a SCX maxi clean cartridge (preconditioned with 10 mL water) followed by an alumina cartridge (preconditioned with 10 mL water) and a C18 cartridge (preconditioned with 6 mL anhydrous ethanol followed by 10 mL water). The [18F]-fluororibose is finally eluted from the column system with sterile water and sterilized by passing it through a 0.22 micrometer filter. The radiochemical purity is determined by radio TLC and is ˜99% pure. Overall purity is determined using a radio analytical HPLC consisting of a Phenomenex luna column (25 cm×0.46 cm, 5 u particle size) eluted with mobil phase (1-9% Ethanol-water v/v) and monitored with a gamma radio detector (Bioscan), and UV detector (200 nm). Another embodiment of the invention is a method of forming [18F]-2-fluoro-2-deoxyribose. As discussed in Example 1 below, this method combines isopropyl 2-O-(trifluoromethylsulfonyl)-3,5-di-O-(4-nitrobenzyl)-beta-D-arabinofuranoside with [18F]-fluoride ion and CH3CN so as to form a first mixture. In this embodiment, this mixture is then loaded on to and then eluted from silica matrix. Isopropyl 2-O-(trifluoromethyl-sulfonyl)-3,5-di-O-(4-nitrobenzyl)-β-D-arabinofuranoside is then eluted from the silica matrix. Raney Nickel is then added to the Isopropyl 2-O-(trifluoromethyl-sulfonyl)-3,5-di-O-(4-nitrobenzyl)-β-D-arabinofuranoside to form a second mixture comprising [18F]-2-fluoro-2-deoxyribose. Detailed methods and materials associated with such methods are discussed in Example 1 below and shown in FIG. 11 (e.g. purification steps using a cartridge comprising alumina and the like). Another embodiment of the invention is a method of forming [18F]-3-fluoro-3-deoxyarabinose. As discussed in Example 1 below, this method comprises the steps of combining 1,2-O-isopropilydene-3-O-(trifluoromethylsulfonyl)-5-O-triphenylmethyl-lyxofuranoside with [18F]-fluoride ion and CH3CN so as to form a first mixture comprising 3a as shown in FIG. 11. 3a is then combined with trifluoroacetic acid and water to form a second mixture, wherein the second mixture forms [18F]-3-fluoro-3-deoxyarabinose. Another embodiment of the invention is a method of forming 3-fluoro-3-deoxyribose. As discussed in Example 1 below, this method comprises the steps of combining 1,2-O-benzylidene-3-O-(trifluoromethylsulfonyl)-5-O-triphenylmethyl-xylofuranoside with [18F]-fluoride ion and CH3CN so as to form a first mixture comprising 4a as shown in FIG. 11. 4a is then combined with trifluoroacetic acid and water to form a second mixture, wherein the second mixture forms [18F]-3-fluoro-3-deoxyribose. Detailed methods and materials associated with such methods are discussed in Example 1 below and shown in FIG. 11 (e.g. purification steps using a cartridge comprising alumina and the like). In typical embodiments of the present invention, a PET probe compound(s) such as one or more of those described above is synthesized and purified and then injected into a mouse. After approximately 1 hour, the mouse can be imaged by a process such as PET/CT. In an exemplary implementation, 40-200 microCi of probe is injected intravenous into a mouse. Following one hour of uptake, the mouse is imaged on a microPET imaging system. In this way, the PET probes disclosed herein can be used as diagnostic tools, radio tracers, monitoring agents and the like in various diagnostic methods, for example in in vivo imaging (e.g. selective imaging of the liver). In this context, artisans can utilize and/or adapt existing PET methods and materials to practice embodiments of the invention disclosed herein. See, for example, Radu, C. G. et al., Nat Med. 2008 July; 14(7):783-8 (2012), Positron emission tomography probes for imaging immune activation and selected cancers; U.S. Pat. No. 8,101,740; as well as Positron Emission Tomography by Anatoliy Granov, Leonid Tiutin and Thomas Schwarz (2013); Basics of PET Imaging: Physics, Chemistry, and Regulations by Gopal B. Saha (2010); and Positron Emission Tomography (Methods in Molecular Biology) by Malik E. Juweid and Otto S. Hoekstra (2011), the contents of which are incorporated by reference). See also Haradahira et al., Nucl. Med. Biol. Vol. 22. No. 6. 719-725 (1995) and U.S. Pat. No. 8,241,607, the contents of which are incorporated by reference. In embodiments of the invention, methods for detecting the labelled isomer of the present invention may include Position Emission Tomography (PET), Single Photon Imaging Computed Tomography (SPECT), Magnetic Resonance Spectroscopy (MRS), Magnetic Resonance Imaging (MRI), and Computed Axial X-ray Tomography (CAT), or combinations thereof. In typical embodiments of the invention, the PET probes are used imaging tracers that detect and quantify cancer/tumor cell densities within live tissues. For live tissue imaging, preferably the radiotracers of the invention can be administered to subjects in an amount suitable for in vivo imaging thereof, and to locate, diagnose, identify, evaluate, detect and/or quantify cancer cells. Generally, a unit dosage comprising a PET probe radiotracer of the invention may vary depending on subject or patient considerations. Such considerations include for example, age, condition, sex, extent of disease, contraindications, or concomitant therapies. The PET probe imaging compounds of the present invention can be formulated as pharmaceutical compositions and administered to a mammalian host, such as a human patient in a variety of forms adapted to the chosen route of administration, i.e., orally or parenterally, by intravenous, intramuscular, topical or subcutaneous routes. Thus, the present compounds may be systemically administered, e.g., orally, in combination with a pharmaceutically acceptable vehicle such as an inert diluent or an edible carrier. They may be enclosed in hard or soft shell gelatin capsules, may be compressed into tablets, or may be incorporated directly with the food of the patient's diet. For oral administration, the PET probes disclosed herein may be combined with one or more excipients and used in the form of ingestible tablets, buccal tablets, troches, capsules, elixirs, suspensions, syrups, wafers, and the like. Tablets, troches, pills, capsules, and the like may also contain the following: binders such as gum tragacanth, acacia, corn starch or gelatin; excipients such as dicalcium phosphate; a disintegrating agent such as corn starch, potato starch, alginic acid and the like; a lubricant such as magnesium stearate; and a sweetening agent such as sucrose, fructose, lactose or aspartame or a flavoring agent such as peppermint, oil of wintergreen, or cherry flavoring may be added. When the unit dosage form is a capsule, it may contain, in addition to materials of the above type, a liquid carrier, such as a vegetable oil or a polyethylene glycol. Various other materials may be present as coatings or to otherwise modify the physical form of the solid unit dosage form. For instance, tablets, pills, or capsules may be coated with gelatin, wax, shellac or sugar and the like. A syrup or elixir may contain the probe, sucrose or fructose as a sweetening agent, methyl and propyl parabens as preservatives, a dye and flavoring such as cherry or orange flavor. Any material used in preparing any unit dosage form should be pharmaceutically acceptable and substantially non-toxic in the amounts employed. In addition, the probe may be incorporated into sustained-release preparations and devices. The probe may also be administered, for example, intravenously or intraperitoneally by infusion or injection. Solutions of the probe or its salts can be prepared in water, optionally mixed with a nontoxic surfactant. Dispersions can also be prepared in glycerol, liquid polyethylene glycols, triacetin, and mixtures thereof and in oils. Under ordinary conditions of storage and use, these preparations contain a preservative to prevent the growth of microorganisms. The pharmaceutical dosage forms suitable for injection or infusion can include sterile aqueous solutions or dispersions or sterile powders comprising the active ingredient which are adapted for the extemporaneous preparation of sterile injectable or infusible solutions or dispersions, optionally encapsulated in liposomes. In all cases, the ultimate dosage form should be sterile, fluid and stable under the conditions of manufacture and storage. The liquid carrier or vehicle can be a solvent or liquid dispersion medium comprising, for example, water, ethanol, a polyol (for example, glycerol, propylene glycol, liquid polyethylene glycols, and the like), vegetable oils, nontoxic glyceryl esters, and suitable mixtures thereof. The proper fluidity can be maintained, for example, by the formation of liposomes, by the maintenance of the required particle size in the case of dispersions or by the use of surfactants. The prevention of the action of microorganisms can be brought about by various antibacterial and antifungal agents, for example, parabens, chlorobutanol, phenol, sorbic acid, thimerosal, and the like. In many cases, it will be preferable to include isotonic agents, for example, sugars, buffers or sodium chloride. Prolonged absorption of the injectable compositions can be brought about by the use in the compositions of agents delaying absorption, for example, aluminum monostearate and gelatin. Sterile injectable solutions are prepared by incorporating the probe in the required amount in the appropriate solvent with various other ingredients enumerated above, as required, followed by filter sterilization. In the case of sterile powders for the preparation of sterile injectable solutions, the preferred methods of preparation are vacuum drying and the freeze drying techniques, which yield a powder of the active ingredient plus any additional desired ingredient present in the previously sterile-filtered solutions. Useful solid carriers include finely divided solids such as talc, clay, microcrystalline cellulose, silica, alumina and the like. Useful liquid carriers include water, alcohols or glycols or water-alcohol/glycol blends, in which the present compounds can be dissolved or dispersed at effective levels, optionally with the aid of non-toxic surfactants. Agents such as flavorings and additional antimicrobial agents can be added to optimize the properties for a given use. As noted above, the PET probe compounds of the invention can be administered to a subject or patient with other therapeutic agents that may be useful in the treatment of a pathological condition such as diabetes or cancer. One such embodiment of the invention is a method for administering an effective amount of one or more compounds of the invention to a subject suffering from or believed to be at risk of suffering from a pathological condition such as diabetes or cancer. The method also comprises administering either sequentially or in combination with one or more compounds of the invention, a conventional therapeutic measure protocol, or agent that can potentially be effective for the treatment or prophylaxis of a pathological condition such as diabetes or cancer. Administration of a PET probe compositions of the invention to a subject may be local or systemic and accomplished orally, intradermally, intramuscularly, subcutaneously, intravenously, intra-aterially or intrathecally (by spinal fluid); or via powders, ointments, drops or as a buccal or nasal spray. A typical composition for administration can comprise a pharmaceutically acceptable carrier for the compound or radiotracer of the invention. Pharmaceutically acceptable carrier include, without limitation, aqueous solutions, non-toxic excipients comprising salts, preservative or buffers, amongst others known within the art. The following examples provide illustrative methods and materials that can be used with embodiments of the invention. Materials and Methods [18F]-FDA Synthesis (1). The synthesis of the [18F]-FDA and its purification was carried out as follows: Using a RDS-111 cyclotron, non-carrier-added [18F]-fluoride ion was produced by 11 MeV proton bombardment of 98% enriched [18O] water in a silver target. 100 μL of aqueous [18F]-fluoride ion was treated with a solution of K2CO3 (1.5 mg) dissolved in 14 μL water and Kryptofix K222 (10 mg) dissolved in 950 μL of anhydrous acetonitrile and then mixed. The mixture was heated at 105° C. and evaporated under nitrogen flow and vacuum for 7 min with two 1 mL anhydrous acetonitrile additions to complete the azeotropic distillation. 2-O-(Trifluoromethylsulfonyl)-1,3,5-tri-O-benzoyl-alpha-D-ribofuranose (Advanced Biochemical Compounds) was added to the dry complex and the reaction mixture was heated at 155° C. for 15 min under sealing conditions. After the fluorination, the solution was cooled to 40° C. and loaded into a silica cartridge. [18F]-2-Fluoro-2-deoxy-1,3,5-tri-O-benzoyl-alpha-ribofuranose was eluted from the cartridge with 2 mL of anhydrous ethyl acetate into a second vessel. The anhydrous ethyl acetate was evaporated at 60° C. under nitrogen flow and vacuum for 3 min. To the dry product, 500 μL of sodium methoxide (0.5 M in methanol) was added and the mixture was heated at 100° C. for 5 min under sealed conditions. The mixture was purified on a SPK column system consisting of a SCX maxi clean cartridge (preconditioned with 10 mL water) followed by an alumina cartridge (preconditioned with 10 mL water) and a C18 cartridge (preconditioned with 6 mL anhydrous ethanol followed by 10 mL water). The [18F]-fluororibose was finally eluted from the column system with sterile water and sterilized by passing it through a 0.22 micrometer filter. The radiochemical purity was determined by radio TLC and was ˜99% pure. Overall purity was determined using a radio analytical HPLC consisting of a Phenomenex luna column (25 cm×0.46 cm, 5 u particle size) eluted with mobil phase (1-9% Ethanol-H2O v/v) and monitored with a gamma radio detector (Bioscan), and UV detector (200 nm). [18F]-2-Fluoro-2-deoxyribose Synthesis (2). Isopropyl 2-O-(trifluoromethyl-sulfonyl)-3,5-di-O-(4-nitrobenzyl)-β-D-arabinofuranoside (2a) was prepared in ten steps according to Scheme 1 as shown in FIG. 11A. To a solution of 3.05 g (9.6 mmol) 1,2,3,5-tetra-O-acetyl-β-ribofuranose (2e) in 30 mL of dry (4 A molecular sieves for 4 hours) acetone was added 0.6 g (2.4 mmol) of elemental iodine and the reaction was stirred under argon at room temperature for 3.5 hours. Methylene chloride (100 mL) were added and the reaction was washed with NaHCO3 (20 mL saturated aqueous solution) followed by Na2S2O3 (20 mL of 10% aqueous solution). The aqueous fractions were extracted with 2×30 mL of CH2Cl2 and the combined organic fractions were washed with 50 mL of brine, dried with Na2SO4 and the solvent was removed via rotary evaporation. The crude material was dissolved in 30 mL of dry MeOH and 0.2 g of NaOMe was added to the solution. The reaction was stirred for 30 min at 50° C. Once TLC (4% MeOH in CH2Cl2) showed a single spot with Rf=0.34, Amberlyst-15 resin was added to neutralize the reaction. The resin beads were removed by filtration and mother liquor was removed via rotary evaporation. The crude material was co-evaporated with 10 mL of toluene and mixed with 10 g (43 mmol) of Ag2O and 10 g of activated (150° C. for 3 days) 4Å molecular sieves. The solids were suspended in 80 mL of dry CH2Cl2 and stirred for 1 hour, then 6.5 g (28 mmol) of 4-nitrobenzyl bromide was introduced and the reaction was stirred at 40° C. under argon for 16 hours. The reaction was filtered through Celite washed with 3×15 mL of CH2Cl2 and dried under vacuum. The crude material was dissolved in AcOH (50 mL of 30% aqueous solution) and refluxed for 3 hours. The solvent was then removed under high vacuum and the crude material was sonicated with 50 ml of a 1/9 EtOAc/hexanes mixture, which was decanted upon cooling in an ice water bath. The remaining solid was dried under high vacuum and dissolved in 10 mL of acetic anhydride along with 0.015 g of I2. The reaction was stirred overnight at 17° C. TLC (1/2 EtOAc/hexanes) indicated a single spot with Rf=0.3. The reaction mixture was dried under vacuum and the crude material was extracted from NaHCO3 (10 ml of saturated solution) with 3×50 mL of CH2Cl2. The organic phases were combined and dried over Na2SO4 and the solvent was removed via rotary evaporation. The crude material was dissolved in 15 mL of dry THF. To that solution were added iodine (0.35 g, 1.39 mmol) and dry (4 A mol. sieves overnight) isopropanol (2 mL, 27 mmol) and the reaction was refluxed under argon for 8 hours. The solvent was rotary evaporated and dissolved in 100 mL of CH2Cl2. The solution was washed with NaHCO3 (20 mL saturated aqueous solution) followed by Na2S2O3 (20 mL of 10% aqueous solution), dried over Na2SO4 and evaporated under vacuum. The crude material was dissolved in 30 mL of dry MeOH and 0.2 g of NaOMe was added to the solution. The reaction was stirred for 30 min at 50° C. TLC (EtOAc/hexanes=1/2) showed one major spot with Rf=0.18. Amberlyst-15 resin was added to neutralize the reaction. The resin beads were removed by filtration and the solvent was completely removed using rotary evaporation. The crude material was chromatographed on silica gel eluting with a gradient of 20% to 40% of EtOAc in hexanes to afford 1.98 g of 2d: 1H NMR (300 MHz, CDCl3) δ 8.18 (dd, J=8.9, 2.0 Hz, 2H), 8.14 (dd, J=8.9, 2.0 Hz, 2H), 7.48 (dd, J=8.8, 2.2 Hz, 2H), 7.46 (dd, J=8.9, 2.0 Hz, 2H), 5.09 (s, 1H), 4.72 (d, J=12.9 Hz, 1H), 4.69 (d, J=12.9 Hz, 1H), 4.67 (s, 2H), 4.27 (ddd, J=5.7, 5.7, 5.0 Hz, 1H), 4.13 (dd, J=4.8, 4.8 Hz, 1H), 4.12 (m, 1H), 3.89 (septet, J=6.1 Hz, 1H), 3.67 (dd, J=10.2, 5.0 Hz, 1H), 3.65 (dd, J=10.2, 5.7 Hz, 1H), 2.54 (d, J=3.4 Hz, 1H), 1.13 (d, J=6.3 Hz, 3H), 1.09 (d, J=6.3 Hz, 3H). The ribofuranoside (2d) was dissolved in 16 mL of a mixture of 4/1 DMSO/Ac2O and stirred at room temperature for 18 hours. TLC (50% EtOAc in hexanes) indicated a single, slightly higher spot. The reaction was dissolved in CH2Cl2 (100 mL) and washed with water 2×100 mL and the organic layer was dried with Na2SO4 and the solvent was removed via rotary evaporation. The crude material was dissolved in 10 mL of a 7:1:2 EtOH:H2O:CH2Cl2 mixture and NaBH4 (0.8 g) was added with stirring at 0° C. for 30 min. The reaction was then warmed to ambient temperature and quenched with 10% AcOH (30 mL). The mixture was extracted from NaHCO3 (sat. 100 mL) with 2×100 mL of EtOAc, the combined organic layer was washed with 2×100 mL of water and then dried over Na2SO4. The solvent was removed under vacuum. Column chromatography of the residue on silica gel (30% to 50% of EtOAc in hexanes) afforded 2c: 1H NMR (300 MHz, CDCl3) δ 8.20 (dd, J=8.9, 2.0 Hz, 2H), 8.16 (dd, J=8.9, 2.0 Hz, 2H), 7.50 (dd, J=8.9 Hz, 2H), 7.47 (d, J=8.9 Hz, 2H), 5.11 (d, J=4.5 Hz, 1H), 4.92 (d, J=13.3 Hz, 1H), 4.76 (d, J=13.3 Hz, 1H), 4.67 (s, 2H), 4.27 (ddd, J=9.4, 6.1, 4.9 Hz, 1H), 4.13 (ddd, J=5.8, 5.8, 5.7 Hz, 1H), 3.96 (septet, J=6.1 Hz, 1H), 3.85 (dd, J=5.9, 5.9 Hz, 1H), 3.65 (d, J=5.8 Hz, 2H), 2.64 (d, J=9.4 Hz, 1H), 1.19 (d, J=6.2 Hz, 3H), 1.15 (d, J=6.2 Hz, 3H). To a solution of 0.025 g (0.054 mmol) of the ribofuranoside (2c) and 0.066 mL (0.81 mmol) of pyridine in 1 mL of dry CH2Cl2 was added Tf2O (0.11 mL of 1 M solution in CH2Cl2) at 0° C. The reaction was stirred under argon in an ice-bath for 30 min, then quenched with 5 mL of a 1:1 mixture of ice and saturated NaHCO3 solution. The mixture was extracted with 2×10 mL of CH2Cl2, the combined organic layer was dried over Na2SO4, and dried under high vacuum at 17° C. To this was added 5 ml of n-heptane and the resulted suspension was dried under high vacuum at 17° C. The crude triflate obtained (31 mg, 97%) 2b was 99% pure. 2b: 1H NMR (300 MHz, CDCl3) δ 8.22 (dd, J=8.9, 2.0 Hz, 2H), 8.16 (dd, J=8.9, 2.0 Hz, 2H), 7.50 (d, J=8.9 Hz, 2H), 7.42 (d, J=8.9 Hz, 2H), 5.25 (d, J=4.5 Hz, 1H), 5.09 (dd, J=6.3, 4.9 Hz, 1H), 4.73 (s, 2H), 4.67 (s, 2H), 4.34 (dd, J=6.6, 5.1 Hz, 1H), 4.17 (ddd, J=6.7, 5.8, 5.7 Hz, 1H), 3.92 (septet, J=6.1 Hz, 1H), 3.69 (dd, J=9.9, 5.7 Hz, 1H), 3.66 (dd, J=9.9, 6.4 Hz, 1H), 1.19 (d, J=6.2 Hz, 3H), 1.18 (d, J=6.2 Hz, 3H). Scheme 2 as shown in FIG. 11B illustrates the synthesis of 2-fluoro-2-deoxyribose (2). 13 mg (34.58 μmol) of Kryptofix 222 (K222), 18 μl of 1 M of aqueous K2CO3 solution, and 0.9 ml of anhydrous MeCN was placed into the reaction vessel inside the cavity of the microwave (MW). [18F]fluoride solution in [18O]H2O from the cyclotron was added and mixed with a magnetic stir bar. The vacuum was applied to the mixed solution under nitrogen flow (5 psi) and it was exposed 5 times to 20 W power for 2 min with two additions of acetonitrile, to complete the drying and remove the water by azeotropic evaporation and form the K222/[18F]F complex. To the K222/[18F]F complex was added the 5 mg of the fully protected precursor dissolved in 500 μl of acetonitrile and heated in the microwave cavity at 115° C. at 40 watts potency for 20 min. The reaction mixture is then loaded in a silica Sep-pak cartridge preconditioned with hexane and eluted with 2 mL of ethyl acetate. The solvent is evaporated at 82° C. in oil bath and under nitrogen until dryness. 100 mg of Ni-Raney was added with 200 μl of formic acid and the reaction mixture was heated at 76° C. for 15 min, filtered with a polypropilene filter 0.45 nm. 10% EtOH/water was added to rinse the filter. The mixture was loaded onto an ion and anion exchange column followed by tC18 cartridge and alumina cartridge and passed through a millipore filter (0.22 um). The eluted product is 2-fluoro-2-deoxy-ribose. The radiochemical purity was determined by radio TLC and is ˜99% pure. [18F]-3-Fluoro-3-deoxyarabinose Synthesis (3). 1,2-O-Isopropylidene-3-O-(trifluoromethanesulfonyl)-5-O-triphenylmethyl-lyxofuranoside (3b) was prepared according to Scheme 3. Scheme 3 as shown in FIG. 11C illustrates the synthesis of 1,2-O-isopropylidene-3-O-(trifluoromethanesulfonyl)-5-O-(triphenylmethyl)lyxofuranoside (3b). Fluorination, deprotection, and purification were performed as described above for [18F]-FDA with modifications according to Scheme 4 as shown in FIG. 11D. Scheme 4 as shown in FIG. 11B illustrates the synthesis of 3-fluoro-3-deoxyarabinose Synthesis (3). [18F]-3-Fluoro-3-deoxyribose Synthesis (4). 1,2-O-benzylidene-3-O-(trifluoro-methanesulfonyl)-5-O-(triphenylmethyl)xylofuranoside (4b) was prepared following the Scheme 5. Scheme 5 as shown in FIG. 11E illustrates the synthesis of 1,2-O-benzylidene-3-O-(trifluoromethanesulfonyl)-5-O-(triphenylmethyl)xylofuranoside (4b). Fluorination, deprotection, and purification were performed as described above for [18F]-3-FDA (Scheme 6). Scheme 6 as shown in FIG. 11F illustrates the synthesis of 3-fluoro-3-deoxyribose (4). [18F]-1-Fluoro-1-deoxy-p-ribose Synthesis (5). Chloro 2,3,5-tri-O-p-chloro-benzoyl-α-D-ribofuranoside (Toronto Research Chemicals Inc) was fluorinated, deprotected, and purified as described above for [18F]-FDA. [18F]-1-Fluoro-1-deoxy-α-ribose Synthesis (6). Chloro 2,3,5-tri-O-p-chloro-benzoyl-β-D-ribofuranoside (Toronto Research Chemicals Inc) was fluorinated, deprotected, and purified as described above for [18F]-FDA. Ribokinase Assay. Human ribokinase plasmid was purchased from OriGene (NM_022128.1). A FLAG sequence was appended 5′ to the ribokinase sequence and the FLAG-tagged ribokinase was subcloned into the retroviral vector pMSCV-IRES-YFP (pRBKS). 293T cells were transfected with the pRBKS vector and Lipofectamine 2000 (Invitrogen) according to manufacturer's protocol. Cells were lysed in RIPA buffer (1% NP-40, 1% Sodium deoxycholate, 0.3% Sodium dodecyl sulfate, 0.15 mM NaCl, 1 mM EDTA, 50 mM Tris-HCl pH 6.8). Protein concentration was determined by the BCA Protein Assay Kit (Pierce), and FLAG-tagged ribokinase was captured from 1 mg of lysate with anti-FLAG M2 Magnetic Beads (Sigma) and eluted with 100 μL of FLAG peptide (Sigma), as per the manufacturer's protocol. Cells not transfected with RBKS were lysed as a control. 1 μL of FLAG-tagged ribokinase or control eluent was added to 50 mM Tris-HCl, pH 7.8, 3 mM ATP, 100 mM KCl, 10 mM MgCl2, 1× protease inhibitor cocktail (Roche), and 1 μCi [3H]-Ribose (Moravek) or [18F]-FDA in a 10 μL volume. The reactions were incubated for 20 minutes at 37° C., after which 40 μL of ice-cold H2O was added, and the samples were heated to 95° C. for 2 minutes. 40 μL of this solution was added to DE-81 DEAE Whatman cellulose paper (Sigma) and allowed to dry at room temperature for 5 minutes. The cellulose paper was subsequently washed 3×5 minutes with 4 mL of 400 mM ammonium formate and 2×5 minutes with 4 mL of 95% EtOH. In the case of [3H]-ribose, the samples were dried, placed into scintillation vials, 3 mL of Bio-Safe NA (RPI Corp) was added to each vial, and the samples were measured on a scintillation counter. In the case of [18F]-FDA, the samples were placed into scintillation vials and counted on a gamma counter. Separately, 3 μL of the water-diluted kinase reactions was added to DE-81 DEAE Whatman cellulose paper, allowed to dry, and then counted on a scintillation or gamma counter. These values were used to determine the total activity of the sample. Western Blot. 30 μg of 293T cells transfected with or without pRBKS, and 10 μL of isolated FLAG-tagged ribokinase or control eluent were resolved on a 4-20% Precise Tris-HEPES SDS-PAGE gel (Pierce) and transferred to nitrocellulose membrane. The membrane was probed with an anti-FLAG antibody (1:1000, Cell Signaling #2368) and visualized with ECL. Mass Spectrometry Analysis of 2-fluoro-2-deoxyarabinose Metabolites. Mice (8-12 weeks old) were treated with 25 μL of 500 mM 2-fluoro-2-deoxyarabinose. 1 hour later, the mice were sacrificed and the metabolites from distinct organs were extracted with 3× with 80% MeOH. Extracted metabolites were dried and analyzed by multiple reaction monitoring liquid chromatography-mass spectrometry (MRM LC-MS). Positron Emission Tomography, Computed Tomography Imaging. 6-12-week old C57BL/6J female mice and 12-week old female B6.V-Lepob/J (Ob/Ob) mice were purchased from the Jackson Laboratory. Animals were anesthetized with 2% isofluorane and injected intravenous in the tail vein with 75-150 μCi of [18F]-FDA. One hour post-injection, the mice were imaged for 10 minutes on a Siemens Inveon PET scanner and 10 minutes on a MicroCAT II CT system. The PET and CT images were coregistered (see, e.g. Chow, P. L., Stout, D. B., Komisopoulou, E., and Chatziioannou, A. F., A method of image registration for small animal, multi-modality imaging. Physics in Medicine and Biology 51 (2), 379 (2006)), the images were initially processed with AMIDE software (v1.0.1) (see, e.g. Loening, A. M. and Gambhir, S. S., AMIDE: A completely free system for medical imaging data analysis. Journal of Nuclear Medicine 42 (5), 192P (2001)), and the images are displayed using the OsiriX DICOM viewer (v3.9.3) (see, e.g. Rosset, A., Spadola, L., and Ratib, O., OsiriX: An open-source software for navigating in multidimensional DICOM images. Journal of Digital Imaging 17 (3), 205 (2004)). Biodistribution studies. For biodistribution studies, animals were imaged as described above, sacrificed, and the organs were removed, weighed, and the radioactivity counted on a gamma counter. The foregoing description of one or more embodiments of the invention has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Many modifications and variations are possible in light of the above teaching. All publications, patents, and patent applications cited herein are hereby incorporated by reference in their entirety for all purposes. |
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055815871 | summary | BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for driving a control rod for adjusting power from a reactor, preferably adapted for a boiling water reactor. 2. Description of the Related Art In general, the basic operation for controlling power from a nuclear reactor is an adjustment of a reactivity thereof. By adequately controlling the quantity of the reactivity, the reactor plant can totally be controlled. In many reactors, control of the reactivity is performed by inserting or withdrawing a control rod, in which a neutron absorber is enclosed, to and from a reactor core. In a boiling water reactor (BWR), four fuel assemblies are disposed around a cross-shaped control rod to form one unit, and a plurality of the thus-arranged units are disposed so as to constitute the reactor core. The reactivity of the BWR is controlled by withdrawing or inserting the control rod from or into the reactor core. The control rod is inserted/withdrawn by a control rod driving apparatus connected to the control rod. FIG. 10 is a view which illustrates an example of the structure of a conventional control-rod drive apparatus. The control rod driving apparatus 1 is inserted into a housing 3 which is formed integrally with a reactor pressure vessel 2 by welding. The control rod driving apparatus 1 has an electric motor 4 at the lower end thereof. A ball spindle 5, the rotations of which are controlled by the electric motor 4, is supported by a bearing 6 and a roller 7 through a rotational shaft 21. A ball nut 9, the rotations of which are inhibited by a groove, not shown, vertically formed in the inner surface of a guide tube 8, is attached to the ball spindle 5 by means of a thread. A connection pipe 10 having the lower end supported by the ball nut 9 establishes the connection with a control rod 11 to be inserted/withdrawn from a reactor core, not shown, of the reactor. The connection pipe 10 has a structure that its rotation is inhibited similarly to the ball nut 9. Furthermore, a lower guide roller 12 is disposed adjacent to the lower portion of the connection pipe 10 so that movement of the connection pipe 10 in the circumferential direction is restricted and its axial directional movement is smoothened. The lower end of the guide tube 8 is placed on a cylinder member 51 connected to the housing 3 through a spool piece 20, the guide tube 8 having the top end to which a damper 13 is attached. The damper 13 is supported by an upper guide 15 through a disc spring 14 so as to be capable of moving upwards a small distance. The upper guide 15 is attached to the reactor pressure vessel 2 through a damper sleeve 16. In addition, outward leakage of reactor water is prevented by a shaft sealing packing 17 disposed between the ball spindle 5 and a cylinder member 51 so that a water-tight seal is realized. In the thus-constituted control rod driving apparatus 1, when the ball spindle 5 is rotated due to rotations of the electric motor 4, the ball nut 9 allowed to engage with the ball spindle 5 is permitted to be moved only in the axial direction. Therefore, the connection pipe 10 mounted on the ball nut 9 follows the movement of the ball nut 9, causing the control rod 11 connected to the connection pipe 10 to be moved vertically. If the control rod 11 is rapidly inserted (hereinafter called "scram") during an emergency for the reactor, water accumulated in an accumulator, not shown, is passed through a scram-water injection pipe 18 so as to be introduced into the guide tube 8. As a result, the connection pipe 10 is rapidly pushed in the upper direction so that the scram is performed. Thus, the control rod driving apparatus 1 is, as described above, driven by the electric motor operated in a usual operation and by the hydraulic pressure used in the case where the scram is performed. The positions of the connection pipe 10 and the control rod 11 are maintained by the maintaining torque of the electric motor 4 and the friction of the shaft sealing packing 17. In the case where the scram-water injection pipe 18 is broken, for example, it may be considered that hydraulic pressure for pushing the connection pipe 10 in the downward direction acts. Accordingly, an electro-magnetic brake 19 is attached below the electric motor 4. Since the body of the control rod driving apparatus has no sliding and contact elements such as the piston seal, it has been considered that it has no element which must be periodically changed in a period of forty years which is the life of the reactor. That is, a substantially maintenance-free state has been achieved for the body of the control rod driving apparatus. Since the shaft sealing packing 17 is gradually degraded due to sliding and high temperature environment in the shaft sealing portion, periodical change is required. The shaft sealing packing 17 is periodically changed in a procedure such that initially the electric motor 4 is removed, and the spool piece 20 accommodating the shaft sealing portion is removed. Then, the spool piece 20 is decomposed, and the shaft sealing packing 17 is changed. Assembly is performed by the inverse of the foregoing procedure. FIG. 11 is a view which illustrates another example of the structure of a conventional control rod driving apparatus. In this example, a connection pipe 30 is connected to a control rod 11 through a joining member 31. A drive piston 32 is disposed at the lower end of the connection pipe 30. The drive piston 32 constitutes a piston cylinder structure in association with a piston tube 33 and a cylinder tube 34. When hydraulic pressure is applied to an insertion port 35, drive water is allowed to pass through a passage designated by an arrow 36 so as to act on the lower surface of the drive piston 32. Thus, the drive piston 32 is pushed upwards. Therefore, the connection pipe 30 is moved upwards so that the control rod 11 is inserted into a reactor core. The position of the inserted control rod 11 is fixed because a control-rod position fixing finger 38 is received in a Groove 37 formed in the surface of the connection pipe 30. Therefore, the control rod 11 is fixed at step positions, the intervals of which correspond to the positions at which the grooves 37 are formed. When the control rod 11 is withdrawn from the reactor core, hydraulic pressure is applied to a withdrawal port 39. Driving water is allowed to pass through a passage designated by an arrow 40 to pass through a hole 41 formed in the upper portion of the piston tube 33 and pass through a space between the piston tube 33 and the connection pipe 30 so as to act on the top surface of the drive piston 35. As a result, the drive piston is pushed downwards. On the other hand, a portion of the driving water is allowed to pass through a passage designated by an arrow 42 so as to act on the lower surface of the piston 43 and push the piston 43 upwards. Further, the control-rod position fixing finger 38 formed integrally with the piston 43 is moved upwards and widened by a guide member 44 so as to be separated from the groove. If the control rod 11 is rapidly inserted into the reactor core during an emergency for the reactor, high-pressure water accumulated in an accumulator, not shown, is supplied to the insertion port 35 so as to rapidly push up the drive piston 32 and the connection pipe 30. Thus, the control rod 11 is inserted into the reactor core to cope with the emergency. In a conventional BWR, either of the control-rod drive apparatuses respectively shown in FIGS. 10 and 11 is employed for all units constituting the reactor core without using the two types of the apparatus in a combined manner. The reason for this is that the combination necessitates the power source and the hydraulic pressure source as a drive source. Further, two types of control rod driving apparatus must be used because of differences in the control methods, thus causing the system's structure to be complicated. Therefore, an economical disadvantage arises. A hydraulic pressure supply system in a conventional BWR arranged in a case where a hydraulic piston drive method as shown in FIG. 11 is employed will now be described. FIG. 12 illustrates the schematic structure of a hydraulic pressure supply system in a conventional example. The piping structure is arranged in such a manner that a hydraulic-pressure supply portion 100 comprises a pump 101, a flow meter 102, a flow-rate adjustment valve 103, a pressure-adjustment valve 104 and a stabilizing circuit 105. The stabilizing circuit 105 comprises two systems of electromagnetic valves 106 and 107. One hydraulic-pressure supply portion 100 is provided for one atomic reactor plant. Pipes represented by pipes 109, 110, 111 and 112 are connected from the hydraulic-pressure supply portion 100 to a hydraulic-pressure control unit 108 which has pipes corresponding to those in the control rod driving apparatus 1. Water flows in the hydraulic-pressure supply portion 100 and in each pipe are designated by arrows. The pipe 109 is a charging pipe for an accumulator 113 which acts when the control rod is inserted to cope with an emergency so that the accumulator 113 is charged with high-pressure water. The accumulator 113 includes a piston 114. The lower portion of the piston 114 is connected to a nitrogen container 116 through a pipe 115. High-pressure nitrogen gas is enclosed in the nitrogen container 116. Reference numerals 117 and 118 respectively represent a scram inlet valve and a scram outlet valve which are closed in a usual state so that the accumulator 113 is maintained at a high pressure state. In response to a control rod emergency insertion signal, the valves 117 and 118 are opened so that the high-pressure water in the accumulator 113 flows through an insertion pipe 119 connected to the lower surface of a drive piston of the control rod driving apparatus 1 so as to flow in the control rod driving apparatus 1. On the other hand, waste water discharged through the top surface of the drive piston flows to a withdrawing pipe 120 to flow through the scram outlet valve 118 so as to flow to a discharge container 121. As a result, a control rod is inserted into the reactor core to cope with the emergency. The pipe 110 is a pipe for supplying water for driving the control rod when the output from a reactor is adjusted, the pipe 110 being connected to a direction-control circuit 126 composed of four electromagnetic valves 122, 123, 124 and 125 disposed in the hydraulic-pressure control unit 108. The direction-control circuit 126 acts to change over the hydraulic-pressure supply line in accordance with insertion/withdrawal of the control rod when a pair of two electromagnetic valves is opened. The driving water flows through the electromagnetic valve 122 and an insertion pipe 119 to be supplied to the lower surface of the drive piston of the control rod driving apparatus 1. On the other hand, discharged water from the top surface of the drive piston flows through the withdrawal pipe 120 and the electromagnetic valve 124 so as to be discharged from the hydraulic-pressure control unit 108 through a water-discharge pipe 112, the discharged water then being joined together the pipe 111. When the control rod is withdrawn, the electromagnetic valves 123 and 125 are opened. The driving water flows through the electromagnetic valve 125 and the withdrawing pipe 120 so as to be supplied to the top surface of the drive piston. On the other hand, discharged water from the lower surface of the drive piston flows through the insertion pipe 119 and the electromagnetic valve 123 and is discharged from the hydraulic-pressure control unit 108 through the water-discharge pipe 112, the discharged water being then joined together the pipe 111. The pipe 111 is a pipe for water for cooling the control rod driving apparatus 1 so that cooling water, the pressure of which is adjusted, always flows through the insertion pipe 119 to flow in the control rod driving apparatus 1. The electromagnetic valves 106 and 107 of the stabilizing circuit 105 are opened in a usual state so that water of a quantity required for the insertion of the control rod flows through the electromagnetic valve 106 and water of a quantity required for the withdrawal of the same flows through the electromagnetic valve 107. As a result, water flows in a cooling-water header 127 as a portion of cooling water. In the stabilizing circuit 105, the electromagnetic valve 106 is closed when the control rod is inserted in a usual state so that water of a quantity, which is the same as the quantity of water flowing through the electromagnetic valve 106, flows to the control rod driving apparatus 1. When the control rod is withdrawn, the electromagnetic valve 107 is closed so that water of a quantity, which is the same as the quantity of water flowing through the electromagnetic valve 107, flows to the control rod driving apparatus 1. As a result, the stabilizing circuit 105 stabilizes the pressure of drive water. The conventional control rod driving apparatus of the structure described above is required to remove its electric motor and spool piece and decompose the spool piece by a predetermined number in one year in order to periodically change the shaft sealing packing. The operations for removing the electric motor and the spool piece are performed in a lower portion of the reactor pressure vessel, thus causing a possibility of radiation exposure for operators due to reactor water having a high radiation dose. A great number of people and a large amount of manufacturing labor are required to complete a series of the operations, and therefore, periodical inspection period cannot be completed in a short time. What is worse, the shaft sealing packing undesirably enlarges the start torque due to coagulation between the shaft sealing packing and the rotational shaft if the ball spindle is left for a long time without being rotated. In this case, there is a possibility that operation of the electric motor cannot be performed smoothly. All electric motors must therefore be inspected at each periodical inspection of the reactor in order to inspect the operations of the electric motors. Also the foregoing fact inhibits the periodical inspection being completed in a short period of time. It should be noted that the reactor core is designed in such a manner that power-adjustment units are previously determined, only their control rods are moved in the reactor core and the control rods for the residual units are completely removed from the core when the reactor is operated for the purpose of lightening the labor for operators and of reducing the fuel consumption cost. It is preferable that the control rods for the power-adjustment units are of a type capable of fine motion in the core and of precisely controlling the power from the reactor. On the other hand, the control rods for the units except the power-adjustment units must have a function with which they can be rapidly inserted into the core to shutdown the reactor in an emergency without a necessity of having a capability of the precise movement. In order to improve the operational facility and to reduce the cost of the fuel, it is advantageous for a reactor of a type having the foregoing core structure to dispose a driving apparatus suitable for the functions required for the control rods. However, the same drive method is, at present, employed in the control rod driving apparatus for all units, and it can be said that the optimum arrangement has not yet been made available. For example, the conventional control rod driving apparatus shown in FIG. 10 is able to precisely adjust and move the control rod by controlling the rotational angle of the spindle thereof. Therefore, the apparatus has a structure suitable to serve as the control rod driving apparatus for the power-adjustment unit. On the other hand, the control rod driving apparatus shown in FIG. 11 basically employs the step drive. Therefore, it is not an optimum structure to meet a desire of precisely driving the power-adjustment units, but it is preferable that the same is used in units except the power-adjustment units. Hence, it is most preferred to use the two types of the control rod driving apparatuses in a combined manner in the core to meet the corresponding objects. However, the combined use requires using both the electric power source and the hydraulic pressure source because different drive methods are employed. Since also the control methods are different between these two types, two types of control apparatuses are required, thus resulting in the system structure becoming too complicated. What is worse, the cost reduction capability is inferior to the case where the single-method control rod driving apparatuses are used. Thus, the combined use has not been employed at present. SUMMARY OF THE INVENTION An object of the present invention is to substantially eliminate the defects or drawbacks encountered in the prior art and to provide a control rod driving apparatus having a structure realizing excellent maintenance facility and reliability and being capable of simplifying the structure of an overall control rod driving system for driving the control rod driving apparatus. This and other objects can be achieved according to the present invention by providing a control rod driving apparatus adapted to drive a control rod assembly for a nuclear reactor and disposed in a housing mounted to a reactor pressure vessel of the nuclear reactor, comprising: a guide tube disposed in the housing; PA1 a connection pipe disposed inside the guide tube coaxially therewith and having one end to which a control rod assembly is connected; PA1 a ball spindle disposed inside the connection pipe and supported thereby so as to be rotatable; PA1 a ball nut assembly to be engaged with the ball spindle so as to be axially movable along the ball spindle, the ball nut assembly supporting another end of the connection pipe; PA1 a hydraulic drive means operatively connected to the ball spindle to rotate the ball spindle; and PA1 a transmission means operatively connected to the drive means for transmitting power of the drive means to the ball spindle, PA1 wherein when the hydraulic drive means is driven, the ball spindle is rotated, the ball nut assembly engaged with the ball spindle is axially rotated, and the connection pipe supported by the ball nut assembly is then driven vertically to thereby drive the control rod assembly for inserting or withdrawing the same into or from a reactor core. In preferred embodiments, the hydraulic drive means is a turbine-type hydraulic motor unit. The turbine-type hydraulic motor unit comprises a motor case, a first hydraulic motor for inserting the control rod assembly into the reactor core and a second hydraulic motor for withdrawing the control rod assembly from the reactor core. The transmission means comprises first bevel gear means operatively connected to either one of the hydraulic motors for insertion and withdrawal of the control rod assembly and worm gear means operatively connected to the ball spindle. The hydraulic motor unit is driven by a pressure of driving water, and discharge water of the driving water after driving is discharged to a portion, having a pressure lower than an inner pressure inside the reactor pressure vessel, outside the reactor pressure vessel, through a discharge pipe connected to the hydraulic motor unit. The driving water is introduced into the hydraulic motor unit by means of a hydraulic pressure supply pipe through which the pressure in the reactor pressure vessel is applied thereto. A change-over valve is disposed at an intermediate portion of the hydraulic pressure supply pipe, the change-over valve having a structure capable of changing over flow of the driving water while enabling at least two operations of the control rod insertion operation, the control rod withdrawal operation and an emergency control rod insertion operation. The change-over valve comprises an introduction port for introducing the driving water, a plurality of ports branched from the introduction port, spring means disposed inside the respective ports and a valve body opened and closed due to a balance between a force of the spring means and a hydraulic pressure transmitted through the introduction port. The change-over valve is disposed inside or outside the motor case of the hydraulic motor unit. The turbine-type hydraulic motor unit comprises a single hydraulic motor of a structure capable of being reversibly operated for inserting the control rod assembly into the reactor core and for withdrawing the control rod assembly from the reactor core and wherein the transmission means comprises a bevel gear means operatively connected to the single hydraulic motor and a worm gear means operatively connected to the ball spindle. In the above embodiments, the nuclear reactor is a boiling water reactor in which four fuel assemblies are disposed in respective sections formed as a unit fuel assembly structure by a cross-shaped control rod and a plurality of such unit fuel assembly structures are arranged in a core of the boiling water reactor, the control rods being driven by a control rod driving system including control rod driving apparatus for driving control rods including a control rod for power-adjustment unit, the control rod driving apparatus having a screw-drive structure comprising a spindle in which a nut is allowed to engage with a mechanism for vertically moving the connection pipe for establishing connection with the control rods and another control rod driving apparatus for driving control rods for units except the power-adjustment unit which is formed into a hydraulic pressure piston drive structure comprising a mechanism for vertically moving a connection pipe for establishing connection with the control rod, a piston and a cylinder. The screw drive structure is driven by a hydraulic motor. A source for supplying driving water for driving the hydraulic pressure piston drive structure and a source for supplying driving water for driving the screw drive structure are made to be a common hydraulic pressure supply apparatus. The control rod for the power-adjustment unit has a drive structure which simultaneously drives a plurality of the control rods. According to the control rod driving apparatus of the structures and features described above, a power, which is generated by the hydraulic motor unit when the operation for inserting or withdrawing the control rod is performed, is transmitted to the ball spindle by the transmission mechanism. The ball spindle is rotated by the driving power of the hydraulic motor unit, and the rotations of the ball spindle vertically move the ball nut which is allowed to engage with the ball spindle. Thus, the control rod mounted on the ball nut can be inserted or withdrawn through the connection pipe. The use of the hydraulic motor unit enables the shaft sealing portion to be omitted. Therefore, sliding portions are eliminated from the structure, thus simplifying the overall structure of the control rod driving system. The water discharged from the motor, which is rotated by the hydraulic pressure, is passed through a discharge pipe connected to the outside of the reactor pressure vessel for the reactor. The pressure in the reactor pressure vessel is used to drive the motor, which is rotated by the hydraulic pressure, thereby eliminating an external driving water source. The change-over valve disposed at an intermediate position of the hydraulic-pressure supply pipe for supplying the hydraulic pressure to the hydraulic motor is used to select the water passage downstream from the change-over valve. As a result, the two or more operations such as of a control rod insertion operation, control rod withdrawal operation and control rod emergency insertion operation can be performed. When the control rod driving system including the above control rod driving apparatus is accommodated in the boiling water reactor, the control rod driving apparatus for the power-adjustment unit is formed into the screw-drive structure suitable for the precise movement and the control rod driving apparatus for units except the power-adjustment units is formed into the hydraulic pressure piston drive structure. Therefore, the control rods can be operated so as to be adaptable to the functions of the core. As a result, the controllability of the reactor can be improved. In such structure, in modification, all control rod driving apparatuses employ the hydraulic pressure driving structure. All driving water supply sources are connected to the common hydraulic pressure supply apparatus, thereby simplifying the structure of the driving source. The boiling water reactor employs simultaneous driving of the plurality of control rods for the power-adjustment units. Therefore, the operation mechanism provided for the drive source can be simplified and the operation can be facilitated. Other and further objects, features and advantages of the present invention will be made more clear through the following descriptions made with reference to the accompanying drawings. |
claims | 1. An aperture position adjusting mechanism in an X-ray CT system capable of adjusting the position of an aperture, comprising: a pair of rails disposed along a direction in which said aperture is to be adjusted, for slidably mounting said aperture, said aperture having an aperture opening for limiting an X-ray irradiation range; a first shaft that is hollow and is provided with a bore passing in parallel with a center axis of said first shaft at a position offset from said center axis, said first shaft being rotatably supported by a base portion of said aperture orthogonally to said pair of rails; a second shaft that is received and is rotatably supported within said bore of said first shaft; and a driving device for rotating said second shaft in reciprocal directions around an eccentric axis offset from a center axis of said second shaft, said mechanism characterized in that: said aperture is moved along said rails as said second shaft is eccentrically rotated by said driving device and, following said eccentric rotation and in a direction opposite to that of said rotation, said first shaft is eccentrically rotated around the center axis of said bore. 2. A gantry apparatus in an X-ray CT system, comprising the aperture position adjusting mechanism as defined by claim 1 . claim 1 3. The gantry apparatus as defined by claim 2 , comprising an X-ray detecting device in which a plurality of detector rows are arranged in a carrying direction of a table for carrying a subject, each of said detector rows having a group of detector elements arranged in a direction orthogonal to said carrying direction. claim 2 4. The gantry apparatus as defined by claim 3 , wherein the direction in which said aperture is to be adjusted coincides with said carrying direction. claim 3 5. The gantry apparatus as defined by claim 4 , further comprising a control device for feedback-controlling said driving device so that outputs from detector elements at a predefined position in said detector rows are equalized when the focal position of an X-ray source shifts. claim 4 6. A method of controlling a gantry apparatus in an X-ray CT system comprising: a gantry rotating device for integrally rotating an X-ray detecting device and an X-ray source, said X-ray detecting device comprising a plurality of detector rows arranged in a carrying direction of a table for carrying a subject, each of said detector rows having a group of detector elements arranged in a direction orthogonal to said carrying direction, said X-ray source disposed at a position opposite to said X-ray detecting device across a cavity portion for inserting said table; an aperture having an aperture opening for limiting an irradiation range of X-rays from said X-ray source; and adjusting device for adjusting the position of said aperture in said carrying direction, said adjusting device comprising: a pair of rails disposed along a direction in which said aperture is to be adjusted, for slidably mounting said aperture; a first shaft that is hollow and is provided with a bore passing in parallel with a center axis of said first shaft at a position offset from said center axis, said first shaft being rotatably supported by a base portion of said aperture orthogonally to said pair of rails; a second shaft that is received and is rotatably supported within said bore of said first shaft; and a driving device for rotating said second shaft in reciprocal directions around an eccentric axis offset from a center axis of said second shaft, said method comprising the steps of: performing a scan for collecting X-ray projection data of the subject during a rotation of said gantry rotating device; and feedback-controlling said driving device so that outputs from detector elements at a predefined position in said detector rows are equalized when the focal position of the X-ray source shifts during the rotation of said gantry rotating device. |
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description | The present patent document is a §371 nationalization of PCT Application Serial Number PCT/EP2010/054637, filed Apr. 8, 2010, designating the United States, which is hereby incorporated by reference. This patent document also claims the benefit of DE 10 2009 017 344.7, filed Apr. 14, 2009, which is also hereby incorporated by reference. The present embodiments relate to a beam head. Electrons emitted from a beam head serve, for example, for the physical sterilization of packaging materials and containers (e.g., bottles). The electrons are generated in an electron source and are accelerated by application of a high voltage to a defined kinetic energy. Following acceleration, the electrons drift through a beam finger and, after passing through the outlet window, impinge upon a region to be sterilized. The high voltage required for electron production and for electron acceleration is generated in a separate transformer (e.g., a high voltage generator) for each beam head and is fed using a high voltage cable and a suitable high voltage plug-and-socket connection to the relevant beam head. Due to the separate transformer and dedicated transformer housing and a dedicated high voltage cable, the conventional beam head uses, in each case, a correspondingly large structural volume. For use in a beverage filling machine, a design of this type is to be repeated multiple times, so that the resulting relatively large structural size of the beam head is disadvantageous. With this design, the high voltage plug-and-socket connection also represents a weak point with regard to reliability. The present embodiments may obviate one or more of the drawbacks or limitations in the related art. For example, a beam head that is designed to be compact and has a high degree of operational reliability is provided. A beam head includes a vacuum housing, in which an electron source is arranged, and a beam finger that is connected to the vacuum housing and has an outlet window at a distal end. The beam head also includes a transformer housing, in which a transformer connected to the electron source is arranged. According to the present embodiments, the transformer housing is arranged directly at the vacuum housing. With the beam head according to the present embodiments, the vacuum housing and the transformer housing form a common beam head housing. The beam head according to the present embodiments is therefore configured with a single housing. The beam head according to one embodiment is designed significantly more compactly than a beam head according to the prior art. For a connection between the transformer and the electron source, no high voltage plug-and-socket connection situated outside the beam head housing is required, so that the operational reliability of the beam head according to the present embodiments is increased. When the beam head with the single-housing configuration is used in a beverage filling machine, the design of the present embodiments enables a plurality of high-voltage cables and high-voltage plug-and-socket connections to be dispensed with. A central control system and a central power supply are provided for all the beam heads of a beverage filling machine. In one embodiment, the transformer housing is arranged on a side of the vacuum housing remote from the beam finger. This therefore increases the height and not the width of the beam head. An embodiment of the beam head of this type may be for use in a filling plant. The transformer housing may be evacuated. Filling of the transformer housing with oil is also possible. As an alternative to electrical insulation using vacuum or oil, the transformer may be filled with a casting compound by filling the transformer housing therewith. In one embodiment of the beam head, the beam finger has a cross-section that is smaller than the cross-section of the vacuum housing. The cross-section may be matched to an opening of the containers to be sterilized. A beam head of this type may be passed, with the beam finger of the beam head, through the opening of the container, and the majority of the unfocused emergent electrons fall upon an inner wall of the container. According to an advantageous exemplary embodiment, the vacuum housing and the beam finger are made from stainless steel. In the beam head according to the present embodiments, the electrons may be generated either by field emission or by thermal emission (e.g., by application of an electric voltage or by laser-induced electron emission). The electron source may be configured as a flat emitter or as an incandescent filament. In an embodiment of the beam head, the outlet window has a layer thickness of between 10 μm and 20 μm. The electrons emerging from the beam finger consequently suffer only slight losses due to attenuation of the intensity and by scattering. According to an embodiment, the outlet window is made from titanium (Ti). Titanium has high strength and a relatively low density and in air, forms an extremely resistant oxidic protective layer, making titanium corrosion-resistant in many media. An exemplary embodiment is described below in greater detail making reference to FIG. 1, but without limiting the invention to the exemplary embodiment. A beam head, which is shown in FIG. 1, includes a vacuum housing 1, in which an electron source 2 and a beam finger 3 that is connected to the vacuum housing 1 are arranged. The beam finger 3 has an outlet window 5 at a distal end 4 (e.g., an outlet aperture). In the embodiment of the beam head shown, the vacuum housing 1 forms, together with the beam finger 3, a permanently hard vacuum-tight vacuum shell 6 that is made, for example, from stainless steel. In the exemplary embodiment shown, the vacuum shell 6, which is formed from the vacuum housing 1 and the beam finger 2, is, for example, at earth potential, where the electron source 2 arranged in the vacuum housing 1 is at a potential of, for example, between −50 keV and −200 keV. On application of a correspondingly high voltage, electrons 7 emitted by the electron source 2 (e.g., shown in the drawing as a dashed line) are therefore accelerated in a direction of the outlet window 5, which is also at earth potential. After emergence of the electrons 7 from the beam finger 3 (via the outlet window 5), the electrons impinge in unfocused manner on a surface of packaging material or on a surface of a container (not shown in the drawing). The surfaces that are irradiated with the electrons 7 emerging from the outlet window 5 are thereby sterilized. In the beam head according to the present embodiments, the electrons 7 may be generated either by field emission or by thermal emission (e.g., by application of an electric voltage or by laser-induced electron emission). In the exemplary embodiment shown, the electron source 2 is configured as a cathode (e.g., a flat emitter, an incandescent filament). The cathode 2 is connected via a high voltage connection 8 and a high voltage cable 13 to a transformer 15 (e.g., a high voltage source, a high voltage generator). The transformer 15 includes a primary winding 18, a secondary winding 19, and a current supply cable 20. Further details of the transformer 15 are not shown for reasons of clarity. The transformer 15 is arranged in a transformer housing 16 that is arranged directly at the vacuum housing 1. In the beam head according to the present embodiments, the vacuum housing 1 and the transformer housing 16 form a common beam head housing. The beam head according to the present embodiments is therefore configured with a single housing. The beam head according to the present embodiments is constructed substantially more compactly compared with a beam head according to the prior art. In addition, no high voltage plug-and-socket connector situated outside the beam head housing is necessary for a connection between the transformer 15 and the electron source 2 (cathode), so that operational reliability is increased with the beam head according to the present embodiments. When the beam head with a single housing design is used in a beverage filling machine, a plurality of high voltage cables and high voltage plug-and-socket connections may be dispensed with due to the design of the present embodiments. For all the beam heads of a beverage filling machine, central control and a central power supply are provided. According to the embodiment shown, the transformer housing 16 is arranged directly on a side 17 of the vacuum housing 1 remote from the beam finger 3. The result is that the beam head housing is extended in the height and not the width. Such an embodiment of the beam head may be for use in a filling plant. The cathode 2 is also cylindrically surrounded by a Wehnelt cylinder 9 (e.g., a control electrode with negative voltage applied) that focuses the electrons 7 emerging from the cathode 2 into an electron beam. The cathode 2, the high voltage connection 8 and the Wehnelt cylinder 9 are mechanically fastened in the vacuum housing 1 via an insulator 10 at the side 17 remote from the beam finger 3. The transition from the vacuum housing 1 to the beam finger 3 (e.g., a region, at which the electron beam 7 emerges from the vacuum housing 1 and enters the beam finger 3) is protected against discharge effects, arcing, and consequent deterioration of the quality of the electron beam 7 by a corona ring 11. The constriction of the electric field prevents field peaking, so that the high voltage strength and thus the high voltage protection are provided. The arrangement of the corona ring 11 significantly increases a radius of curvature in the region of transition from the vacuum housing 1 to the beam finger 3 and therefore reliably prevents a sharp-edged transition that would lead to field peaking. The corona ring 11 also, as far as possible, prevents any fanning out of the electron beam 7 on a route to the outlet window 5 before entry of the electrons 7 into the beam finger 3. The corona ring 11 therefore also acts as a focusing ring. Electrons 7 that are possibly not focused are collected on an anode plate 12 arranged on the inside of the vacuum housing 1 adjacent to the beam finger 3. In the beam head shown in FIG. 1, the beam finger 3 has a cross-section that is smaller than the cross-section of the vacuum housing 1. The cross-section may be matched to an opening of a container to be sterilized. A beam head of this type may be fed through the opening of the container, and the emerging electrons 7 may impinge on an inner wall of the container. In the embodiment of the beam head shown in FIG. 1, the outlet window 5 is made from titanium (Ti) and has a layer thickness of between 10 μm and 20 μm. As a result, electrons emerging from the beam finger 3 suffer only slight losses through attenuation of the intensity and through scattering. While the present invention has been described above by reference to various embodiments, it should be understood that many changes and modifications can be made to the described embodiments. It is therefore intended that the foregoing description be regarded as illustrative rather than limiting, and that it be understood that all equivalents and/or combinations of embodiments are intended to be included in this description. |
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claims | 1. A light water reactor core comprising fuel which is enriched by adding plutonium or plutonium and an actinide to a uranium containing at least one of a depleted uranium, natural uranium, a degraded uranium and a low enriched uranium, which further comprises: fuel assemblies having fuel rods arranged in a triangular lattice configuration; and large-diameter control rods to be inserted into said fuel assemblies, said large-diameter control rod comprising at least one absorption rod and guide tubes in which said large diameter control rods are inserted, each said guide tube being disposed in a region having an area equivalent to at least 7 fuel rod unit lattice cells, wherein a breeding ratio of the reactor core is near 1.0 or larger than 1.0, and a void coefficient of the reactor core is negative. 2. A light water reactor core comprising fuel which is enriched by adding plutonium or plutonium and an actinide to a uranium containing at least one of a depleted uranium, natural uranium, a degraded uranium and a low enriched uranium, which further comprises; fuel assemblies having fuel rods arranged in a triangular lattice configuration; and large-diameter control rods to be inserted into said fuel assemblies, said large-diameter control rod comprising at least one absorption rod and guide tubes in which said large diameter control rods are inserted, each said guide tube being disposed in a region having an area equivalent to at least 7 fuel rod unit lattice cells, wherein a breeding ratio of the reactor core is near 1.0 or larger than 1.0, and a power coefficient of the reactor core is negative, and a void coefficient of the reactor core is positive or zero. 3. A light water reactor core according to claim 1 , wherein said breeding ratio is within the range of 1.0 to 1.15. claim 1 4. A fuel assembly comprising fuel which is enriched by adding plutonium or plutonium and an actinide to a uranium containing at least one of a depleted uranium, natural uranium, a degraded uranium and a low enriched uranium, which further comprises: fuel assemblies having fuel rods arranged in a triangular lattice configuration; and at least one guide tube to insert a large-diameter control rod thereinto, said guide tube disposed in a region having an area equivalent to at least 7 fuel rod unit lattice cells, wherein a breeding ratio of the fuel assembly is near 1.0 or larger than 1.0. 5. A fuel assembly according to claim 4 , which comprises a water-excluding region on a surface of said guide tube, said water-excluding region being formed of a substance having a slowing down power smaller than a slowing down power of light water. claim 4 6. A fuel assembly according to claim 4 , which comprises fuel rods closely arranged in a triangular lattice configuration, and a gap between said rods is within the range of 0.7 to 2.0 mm. claim 4 7. A light water reactor core, which is composed of the fuel assemblies according to claim 6 . claim 6 8. A fuel assembly according to claim 4 , which comprises fuel rods closely arranged in a triangular lattice configuration, and an effective water-to-fuel volume ratio of the fuel assembly is within the range of 0.1 to 0.6. claim 4 9. A light water reactor core, which comprises the fuel assemblies according to claim 8 . claim 8 10. A light water reactor core according to claim 1 , wherein an average fissionable plutonium enrichment in the reactor core except for an outer peripheral portion and blanket portions of a top and a bottom end portions is within the range of 6 to 20 wt %. claim 1 11. A fuel assembly according to claim 4 , wherein an average fissionable plutonium enrichment in a fuel region except for blanket portions of a top and a bottom end portions is within the range of 6 to 20 wt %. claim 4 12. A light water reactor core according to claim 1 , wherein a core-average void fraction under operation of an output power higher than 50% of a rated output power is within the range of 45 to 70%. claim 1 13. A light water reactor core according to claim 1 , wherein all the large-diameter control rods connected to one control drive mechanism are inserted into one fuel assembly, and said large-diameter control rods are inserted into all of the fuel assemblies loaded in a region except for an outermost peripheral of the reactor core. claim 1 14. A light water reactor core according to claim 13 , wherein a shape of a transverse plane of said fuel assembly is hexagonal or square. claim 13 15. A light water reactor core according to claim 1 , wherein the plurality of large-diameter control rods connected to one control drive mechanism are inserted into three hexagonal fuel assemblies, and said large-diameter control rods are inserted into all of the fuel assemblies loaded in a region except for an outermost peripheral of the reactor core. claim 1 16. A light water reactor core according to claim 1 , wherein the plurality of lare-diameter control rods connected to one control drive mechanism are inserted into four square fuel assemblies, and said large-diameter control rods are inserted into all of the fuel assemblies loaded in a region except for an outermost peripheral of the reactor core. claim 1 17. A light water reactor core according to claim 1 , wherein said large-diameter control rod comprises a follower portion in a top end portion, said follower portion being made of a substance having a slowing down power smaller than a slowing down power of light water. claim 1 18. A fuel assembly according to claim 4 , wherein an average value of fissionable plutonium enrichments of a fuel rod arranged in a region adjacent to said guide tube and a fuel rod arranged in a region most distant from a center of said fuel assembly is smaller than an average value of fissionable plutonium enrichments of fuel rods arranged in the other positions. claim 4 19. A light water reactor core according to claim 1 , wherein an average output power density of in a reactor core region except for an outer peripheral portion and blanket portions of a top and a bottom end portions is within the range of 100 to 300 kW/l. claim 1 20. A light water reactor core according to claim 1 , wherein in regard to a height direction of the core except for blanket portions of a top and a bottom end portions, a length having an average fissionable plutonium enrichment with respect to a horizontal cross section of the fuel assembly higher than 6 wt % is within the range of 40 cm to 140 cm. claim 1 21. A fuel assembly according to claim 4 , wherein in regard to a height direction of the reactor core except for blanket portions of a top and a bottom end portions, a length having an average fissionable plutonium enrichment with respect to a horizontal cross section of the fuel assembly higher than 6 wt % is within the range of 40 cm to 140 cm. claim 4 22. A fuel assembly according to claim 4 , wherein an average value of fissionable plutonium enrichment in an upper half of the fuel assembly except for blanket portions of a top and a bottom end portions is lower than an average value of fissionable plutonium enrichment in an lower half. claim 4 23. A fuel assembly according to claim 4 , wherein in regard to a height direction of the fuel assembly except for blanket portions of a top and a bottom end portions, the fuel assembly comprises regions having an average fissionable plutonium enrichment higher than 6 wt % in an upper and a lower parts of the fuel assembly; and a region having an average fissionable plutonium enrichment lower than 6 wt % in a region near a middle portion between the upper and the lower regions. claim 4 24. A fuel assembly according to claim 23 , wherein in regard to a height direction of the fuel assembly except for blanket portions of the top and the bottom end portions, the average fissionable plutonium enrichments in the upper and the lower regions sandwiching the portion having the average fissionable plutonium enrichment lower than 6 wt % in the region near the middle portion between the upper and the lower regions are different from each other. claim 23 25. A light water reactor core according to claim 1 , wherein a steam weight ratio at an exit of the reactor core under operation of an output power higher than 50% of a rated output power is within the range of 20 wt % to 40 wt %. claim 1 26. A light water reactor core according to claim 1 , wherein the reactor core except for an outermost periphery of the reactor core is radially divided into two equal-area regions, and fuel assemblies are loaded so that an average value of number of cycles staying in the reactor core of the fuel assemblies loaded in the outer reactor core region is smaller than an average value of number of cycles staying in the reactor core of the fuel assemblies loaded in the inner reactor core region. claim 1 27. A light water reactor core according to claim 1 , wherein an average value of orifice pressure drop coefficient of fuel assemblies in an outermost periphery of the reactor core and adjacent to the outermost periphery is larger than an average value of orifice pressure drop coefficient of fuel assemblies in the other regions. claim 1 28. A fuel assembly according to claim 4 , wherein plutonium and uranium extracted from used fuel as loaded into the fuel assembly to be recycled together. claim 4 29. A light water reactor core composed of the fuel assemblies according to claim 28 . claim 28 30. A fuel assembly according to claim 4 , wherein plutonium, uranium and actinides extracted from used fuel are loaded at a time to be recycled together. claim 4 31. A light water reactor core composed of the fuel assemblies according to claim 30 . claim 30 32. A light water rector core comprising fuel which is enriched by adding plutonium or plutonium and an actinide to a uranium containing at least one of a depleted uranium, natural uranium, a degraded uranium and a low enriched uranium, which further comprises: fuel assemblies having fuel rods arranged in a triangular lattice configuration; and large-diameter control rods to be inserted into said fuel assemblies, said large-diameter control rods each comprising at least one absorption rod having a transverse cross-sectional area larger than a cross-sectional area of a unit lattice cell of the fuel rod; and guide tubes in which said large-diameter control rods are inserted, said guide tubes each having water excluding rods outside for excluding light water between said guide tube and fuel rods adjacent to said guide tube and disposed in a region having an area equivalent to at least 7 fuel rod unit lattice cells, wherein a breeding ratio of the reactor core is near 1.0 or larger than 1.0, and a void coefficient of the reactor core is negative. |
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abstract | In conjunction with a pressurized water reactor (PWR) and a pressurizer configured to control pressure in the reactor pressure vessel, a decay heat removal system comprises a pressurized passive condenser, a turbine-driven pump connected to suction water from at least one water source into the reactor pressure vessel; and steam piping configured to deliver steam from the pressurizer to the turbine to operate the pump and to discharge the delivered steam into the pressurized passive condenser. The pump and turbine may be mounted on a common shaft via which the turbine drives the pump. The at least one water source may include a refueling water storage tank (RWST) and/or the pressurized passive condenser. A pressurizer power operated relief valve may control discharge of a portion of the delivered steam bypassing the turbine into the pressurized passive condenser to control pressure in the pressurizer. |
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051577020 | abstract | A double-crystal X-ray monochromator includes entrance and exit crystal assemblies mounted on a support structure to provide full parallelism of the crystals while one crystal is rotated and the other rotated and translated with respect to the first, allowing selection of the wavelength of X-rays to be passed through the monochromator. The monochromator is mounted in an ultra-high vacuum chamber by supports which pass through the vacuum chamber to support the monochromator independently of the vacuum chamber. Bearings supporting the monochromator provide very low friction to linear movement and rotation to allow high precision to be obtained. To compensate for the heating of the entrance crystal due to impingement of high energy X-rays on the crystal, the entrance crystal is cooled using a radiation heat transfer system which provides no physical contact between the radiator connected to the entrance crystal assembly and the heat transfer structure on the vacuum chamber. The exit crystal may be heated so that its temperature can be matched to that of the entrance crystal to allow the precision alignment of the crystals to be maintained. |
abstract | A fuel assembly, particularly, a fuel assembly including short-length fuel rods and fuel spacers, is used for a boiling water reactor, which is capable of sufficiently reducing the pressure loss of at least one of the fuel spacers positioned above the upper ends of the short-length fuel rods, irrespective of the arrangement of the short-length fuel rods, and also ensuring the structural strength of the fuel spacer. The fuel assembly includes fuel rods located in a square lattice array, two water rods arranged in a region in which seven of the fuel rods are arrangeable, two fuel spacers for holding the fuel rods and the water rods with mutual intervals kept immovable. Each of the fuel spacers includes cells which are connected to each other and in which the fuel rods are to be inserted, respectively, and a band for surrounding the outermost peripheries of the cells. The short-length fuel rods include four first short-length fuel rods arranged in the outermost peripheral region of the square lattice array. One of the fuel spacers, positioned upward from the upper ends of the short-length fuel rods, is configured such that the cells located at lattice positions associated with the first short-length fuel rods are removed and instead supporting members, each being adapted to connect two of the cells adjacently located on both sides of each of the lattice positions in the outermost peripheral region to the band, are provided at the lattice positions. |
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054003733 | claims | 1. Apparatus for the assembly of a grid structure used to support elongated fuel rods for a nuclear reactor comprising (a) a rectangular grid assembly plate (1) supported above a work surface (3) and having a flange (5) on each side of the plate, (b) a clamp support plate (8) mounted to and projecting away from each flange (5) of the plate, (c) a toggle action clamp assembly (9) attached to each clamp support plate (8) adapted to move and hold a clamping pad (12) against a side of the plate (1) over the side flange (5). (a) placing a plurality of grid straps (7) around the sides of a rectangular grid assembly plate (1), (b) temporarily holding the grid straps (7) against the sides of the rectangular grid assembly plate (1) using a toggle clamp assembly (9) attached to each side of the plate (1), (c) placing a strap retention assembly (13) around the grid straps (7) to hold the grid straps (7) tightly against the sides of the plate (1), (d) releasing the toggle clamp assemblies (9) from contact with the grid straps (7), (e) welding the grid straps (7) together, (f) removing the strap retention assembly (13) from around the welded grid straps (7). 2. The apparatus of claim 1 in which the grid assembly plate (1) is surrounded with a strap retention assembly (13). 3. The apparatus of claim 1 in which the grid assembly plate (1) is adjustable relative to the work surface (3). 4. The apparatus of claim 1 in which the toggle action clamp assemblies (9) are actuated manually. 5. The apparatus of claim 1 in which the toggle action clamp assemblies (9) are actuated pneumatically. 6. The apparatus of claim 1 in which the clamping pad (12) is substantially the length of the side flange (5). 7. A method for assembling a grid used to support elongated fuel rods in a nuclear reactor comprising; |
044949871 | abstract | Precipitation hardening, austenitic type superalloys are described. These alloys contain 0.5 to 1.5 weight percent silicon in combination with about 0.05 to 0.5 weight percent of a post irradiation ductility enhancing agent selected from the group of hafnium, yttrium, lanthanum and scandium, alone or in combination with each other. In addition, when hafnium or yttrium are selected, reductions in irradiation induced swelling have been noted. |
summary |
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