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047568534 | claims | 1. Process for the conversion into a usable condition of actinide ions contained in the solid residue of a sulfate reprocessing process for organic, actinide-containing radioactive solid waste, which are present in the form of water soluble sulfate complexes, the solid residue being one which can contain insoluble constituents, comprising: (a) dissolving the solid residue with water or 1 to 2 molar nitric acid so that the residue goes into the solution or the largest amount of the residue goes into the solution, (b) in the case where the solid residue contains insoluble constituents, separating the resulting solution from the insoluble constituents of the residue, and heating the solution or the separated solution to a temperature in the range of 40.degree. C. to below the boiling point of the solution to form a hot solution, (c) adding to the hot solution an aqueous barium nitrate solution having an amount of barium ions which corresponds to a small excess of barium ions over the amount required stoichiometrically for complete precipitation of the sulfate ions, and holding the resulting reaction solution at a selected temperature in the same range as in step b) for a period in the range of 0.5 to 2 hours to precipitate barium sulfate, (d) subsequently cooling the reaction solution to room temperature and then separating the reaction solution from the barium sulfate precipitate to form a sulfate free actinide-nitrate aqueous solution, and (e) directly feeding without conducting further intermediate steps the sulfate free actinide-nitrate aqueous solution obtained after the separation to an aqueous nitric acid phase of an extractive reprocessing process of exposed nuclear fuel- and/or fertile materials. 2. Process according to claim 1, wherein several actinides are present in the solid residue and the sulfate free actinide-nitrate solution is fed into the aqueous phase before the uranium-plutonium-separation. 3. Process according to claim 1, wherein Pu is present in the solid residue and the sulfate free actinide-nitrate solution is fed into the aqueous phase before the first Pu-purification cycle. 4. The process according to claim 1, wherein U is present in the solid residue and the sulfate free actinide-nitrate solution is fed into the aqueous phase before the first U-purification cycle. |
summary | ||
048250880 | summary | BACKGROUND OF THE INVENTION This invention generally relates to casks for transporting radioactive materials, and is specifically concerned with an improved lightweight cask assembly having high strength titanium walls for transporting a maximum amount of radioactive material within a given weight limit. Casks for transporting radioactive materials such as the waste products produced by nuclear power plant facilities are known in the prior art. The purpose of such casks is to ship radioactive wastes in as safe a manner as possible. Such casks may be used, for example, to ship high-level vitrified waste cannisters to a permanent waste isolation site or spent fuel rods to a reprocessing facility. At the present time, relatively few of such transportation casks have been manufactured and used since most of the spent fuel and other wastes generated by nuclear power plants are being stored at the reactor facilities themselves. However, the availability of such on-site storage space is steadily diminishing as an increasing amount of fuel assemblies and other wastes are loaded into the spent-fuel pools of these facilities. Additionally, the U.S. Department of Energy (D.O.E.) has been obligated, by way of the National Waste Policy Act of 1983, to move the spent fuel assemblies from the on-site storage facilities of all nuclear power plants to a federally operated nuclear waste disposal facility starting in 1998. While the transportation casks of the prior art are generally capable of safely transporting wastes such as spent fuel to a final destination, the applicants have observed that there is considerable room for improvement, particularly with respect to vehicle-drawn, Type B casks. Specifically, the applicants have observed that the structural materials and design configuration used in these casks do not lend themselves to a maximum loading of radioactive wastes. The resulting less-than-maximum loading necessitates a larger number of trips by the shipper in order to complete the transportation of a given amount of radioactive waste, thus increasing both the time and the cost of transport. However, before the problems associated with maximizing the amount of waste carried by a particular cask may be fully appreciated, some understanding of the constraints imposed by U.S. government regulations is necessary. U.S. Department of Transportation (DOT) and state highway regulations limit the gross weight of the waste carrying road vehicle to about 80,000 pounds for shipments without special permits. Since the typical tractor and trailer weighs approximately 30,000 pounds, the weight of a cask and its contents must not exceed approximately 50,000 pounds. These same regulations specify that the surface radiation of such cask be no greater than 200 millirems at any given point, and that the radiation emitted by the cask be no greater than ten millirems at a distance of two meters from the vehicle. Other DOT regulations require that the cask be capable of sustaining impact stresses of up to ten Gs in the longitudinal direction, five Gs in the lateral direction, and two Gs in the vertical direction without yielding the wastes. The end result of these regulations is that much of the 50,000 pounds must be expended in providing a wall structure that is dense enough to provide adequate shielding and strong enough to withstand the designated impact stresses. The resulting thickness of the wall necessary to provide the required radiation shielding and impact stresses leaves only a relatively small amount of space in the center of the cask which can actually be used to contain and transport radioactive waste. To maximize the amount of carrying volume, the most effective shielding materials known are frequently integrated into the walls of the cask structure. Such materials include lead, depleted uranium, and tungsten. However, as these materials are of a very high density, the radius of the cask walls cannot be made too large, or the gross weight limitation of 50,000 pounds of the combination of cask and waste material will be exceeded. Moreover, as U.S. government regulations require the cask design engineer to assume that such shielding materials have no structural strength and cannot be relied upon at all for compliance with the impact stress requirement, they must be integrated within structural walls which are capable of withstanding the designated stresses. At the present time, stainless steel is the most commonly used structural wall material. The end result of the foregoing constraints of structural strength, shielding effectiveness, and the high density of the most effective known shielding materials results in a very large portion of the 50,000 pounds weight allocation for a loaded cask going to the cask structure itself, rather than the weight of the waste being transported. If the cost of transporting a particular amount of radioactive waste is to be minimized, then the weight of the cask structure relative to the weight of the waste being carried must be minimized. The applicants have further observed that this objective may be accomplished by the fulfillment of two criteria. First, the radial distance between the waste being carried and the shielding material integrated into the walls of the cask structure must be minimized. If this criteria is realized, an optimum shielding geometry results wherein a maximum amount of shielding is achieved with a minimum weight of shielding material. Second, the structural walls of the cask that overlie and support the shielding material should be fabricated from a material which affords maximum strength per unit weight of wall material. The applicants have further observed that, for many materials, these two criteria are incompatible with one another. Such incompatibility becomes evident when one considers that the interior surface of the shielding material must be lined with an inner structural wall in order to support the shielding material within the cask walls and to comply with the government impact stress regulations. If the distance between the waste and the shielding is to be minimized, then the material forming the inner wall must be as strong as possible per given thickness (or volume) of material. The thicker the material forming this wall is, the greater the distance between the waste and the shielding material, and the greater the radius (and hence weight) of the shielding material. Hence the use of a material such as a high-strength aluminum alloy would not necessarily result in any significant weight decrease of the cask as a whole. Even though such an alloy might be stronger than stainless steel on a pound-per-pound basis, and hence might reduce the weight of the outer structural wall, it would actually increase the weight needed for additional shielding material if the minimum thickness required for the inner wall was greater than the minimum thickness of the inner wall fabricated from stainless steel. The end result is that both of these weight reducing criteria are fulfilled only with a material that is substantially stronger than stainless steel both on a pound-per-pound and a volume-per-volume basis. Such a material would result in an outer structural wall of reduced weight, and would actually decrease the required amount of high density shielding material required to achieve the maximum surface radiation constraints. Clearly, what is needed is a cask capable of containing a maximum amount of radioactive waste in a structure having a minimum amount of weight. Such a cask must also be capable of conducting and dissipating the heat of decay of the radioactive materials contained therein at least as well as cask wall structures made of stainless steel to avoid the creation of dangerous internal pressures. Finally, such a cask should be relatively simple and inexpensive to fabricate. SUMMARY OF THE INVENTION The invention is an improved lightweight cask assembly that achieves the aforementioned objective of carrying a maximum amount of radioactive wastes in a cask structure which conforms to all U.S. government regulations concerning cask weight, surface radiation and impact strength limits. Generally, the improved cask assembly comprises inner and outer structural walls formed substantially from a titanium alloy with a radiation shielding wall disposed therebetween. In the preferred embodiment, the shielding wall may be made of a high-density gamma absorbing material such as depleted uranium, lead or tungsten. To optimize shielding geometry, the inner wall of titanium alloy is rendered thick enough to comply with the impact strength requirement defined by U.S. government regulations within a broad margin of safety, but yet thin enough to provide a minimum distance between the radioactive materials disposed within the interior of the container and the shielding wall. The structural walls may further include a reinforcing ring for connecting together the top edges of the inner and outer structural walls, as well as an end plate assembly for connecting together the bottom edges of these walls. In the preferred embodiment, both the inner and outer structural walls, the reinforcing ring and the end plate assembly are each formed from a titanium alloy designated as Ti-3-Al-2.5V for its tensile and impact strength, and its relatively easy weldability. In the preferred embodiment of the cask assembly two separate shielding walls are provided, one for shielding gamma radiation, and the other for shielding neutron radiation. The first of these shielding walls may be an inner wall formed from a gamma-absorbing material such as depleted uranium, while the second of these shielding walls may be an outer shielding wall formed from a neutron-absorbing material such as particles of boron suspended in a matrix of silicone. In such an embodiment, the structural walls of the cask assembly include an inner wall, an intermediate wall and an outer wall all formed from a titanium alloy. The inner shielding wall is disposed and supported between the inner and the intermediate walls, while the outer shielding wall is disposed between and supported by the intermediate and outer structural walls. The improved cask assembly of the invention not only reduces the weight of the cask structure on the order of fifty percent, but further has superior heat conducting properties which allows the cask structure to conduct and to dissipate the heat of decay of the radioactive materials contained inside in a more efficient manner. This in turn minimizes any internally-generated pressures within the cask assembly, and contributes to the overall safety characteristics of the cask. |
050540416 | summary | BACKGROUND OF THE INVENTION This invention relates to x-ray collimators for use in computed tomography systems and the like and specifically to a collimator for precisely controlling an x-ray fan beam. Computed tomography systems, as are known in the art, typically include an x-ray source collimated to form a fan beam directed through an object to be imaged and received by an x-ray detector array. The x-ray source, the fan beam and detector array are orientated to lie within the x-y plane of a Cartesian coordinate system, termed the "imaging plane". The x-ray source and detector array may be rotated together on a gantry within the imaging plane, around the imaged object, and hence around the z-axis of the Cartesian coordinate system. Rotation of the gantry changes the angel at which the fan beam intersects the imaged object, termed the "gantry" angle. The detector array is comprised of detector elements each of which measures the intensity of transmitted radiation along a ray path projected from the x-ray source to that particular detector element. At each gantry angle a projection is acquired comprised of intensity signals from each of the detector elements. The gantry is then rotated to a new gantry angle and the process is repeated to collect an number of projections along a number of gantry angles to form a tomographic projection set. Each acquired tomographic projection set may be stored in numerical form for later computer processing to reconstruct a cross sectional image according to algorithms known in the art. The reconstructed image may be displayed on a conventional CRT tube or may be converted to a film record by means of a computer controlled camera. The x-ray source is ordinarily an x-ray "tube" comprised of an evacuated glass x-ray envelope containing an anode and a cathode. X-rays are produced when electrons from the cathode are accelerated against a focal spot on the anode by means of a high voltage across the anode and cathode. The x-rays produced by the x-ray tube diverge from the focal spot in a generally conical pattern. A fan beam is formed by passing the x-rays through a slot flanked by x-ray opaque material. The process of restricting the x-ray beam to the desired fan beam is termed "collimation" and the slot assembly is termed a "collimator". A collimator is typically comprised of two opposing metallic blades that may be opened and closed to change the width of the slot and hence to produce a fan beam with varying "thickness", as measured along the z-axis. Alternatively, the blades may be moved in the same direction to displace the centerline of the slot and hence change the fan beam angle with respect to the z-axis. Such a collimator will be termed an "adjustable blade collimator". It is important that the fan beam have a uniform thickness. Variations in fan beam thickness will cause different detector elements in the detector array to receive different amounts of x-ray radiation despite possible constant attenuation of the imaged object. Generally, such variations in exposure of the detector elements, other than that those caused by the attenuation of the x-ray beam by the imaged object, will produce image artifacts and reduce the dynamic range of the reconstructed image. When the fan beam is very narrow, uniform thickness of the fan beam is increasingly critical. Small absolute variations in fan beam width create large percentage changes in the exposure between detector elements. Such variations in fan beam width may result from collimator blades that are not parallel. Motion of the focal spot of the x-ray, primarily the result of thermal expansion of the anode support structure as the x-ray source heats up, will affect the alignment of the fan beam with the imaging plane. The mathematics of image reconstruction assumes that each acquired projection is taken within a single plane. Lack of parallelism of the fan beam with the imaging plane will produces shading and streak image artifacts in the reconstructed image. Both "ionization" type detectors and "solid state"detectors, as are known in the art, also exhibit changes in their sensitivity to x-rays as a function of the position of the fan beam along their surface. Accordingly, movement of the fan beam as a result of thermal drift of the focal spot may change the strength of the signal from the detector array. Such changes in signal strength during the acquisition of a tomographic projection set produce ring-like image artifacts in the resultant reconstructed image. Copending application serial number U.S. Pat. No. 4,991,189 entitled: "Collimation Apparatus for X-ray Beam Correction"and assigned to the same assignee as the present invention, teaches the correction of the alignment of the fan beam with the detector array and the imaging plane by movement of the collimator slot along the z-axis direction. In such a system, it is desirable that the center of the collimator slot may be accurately translated along the z-axis to compensate for thermal drift of the focal spot. For the reasons described above, such z-axis translation should occur without changing the fan beam width or affecting the fan beam parallelism. As previously mentioned, the gantry is rotated about the imaged object and the collimator is fixed relative to the gantry. Accordingly, the collimator experiences a constantly changing force of gravitational acceleration as well as other forces incident to such rotation. It is important, therefore, that a collimator also be able to resist such forces without adverse change in the fan beam's position or parallelism. SUMMARY OF THE INVENTION According to the present invention, a collimator is comprised of an x-ray absorbing mandrel having at least one diametrically directed passage extending along the length of the mandrel to create an aperture. A bearing supports the mandrel so that it may be rotated about its axis within an x-ray beam. It is one object of the invention to provide an x-ray collimator to produce a fan beam of uniform thickness whose angle may be precisely controlled. The aperture in the mandrel is fixed in width and hence may be accurately machined to produce a highly uniform fan beam width. The rotating bearings and shape of the aperture allow limited translation of the center of the aperture along the z-axis, permitting accurate control of the fan beam angle without change in the fan beam width. In one embodiment of the invention, additional diametrically directed passages are circumferentially spaced around the mandrel so that rotation of the mandrel will bring successive such passages into alignment with the x-ray beam. Each passage creates an aperture of different width. It is thus another object of the invention to provide a collimation system that may produce fan beams of various widths, each such fan beam having a precisely repeatable width. Rotation of the mandrel about its axis by large amounts changes the aperture selected. Rotation of the mandrel by smaller amounts permits accurate control of the fan beam angle. It is another object of the invention to produce a collimator that may be rapidly adjusted without the need for complex mechanisms. The collimator width and the fan beam angle are both adjusted by rotation of the mandrel. This rotation may be accurately controlled by a position feedback loop. A simple bearing assembly accurately maintains the collimator alignment. A low backlash brake holds the mandrel against rotation when it is not being repositioned. The brake is comprised of a friction element providing a threshold frictional torque resisting rotation of the mandrel and a motor controller which reduces the motor restoring torque during braking. It is therefore a further object of the invention to produce a robust collimator mechanism resistant to the perturbing torques from accelerative forces acting on the collimator as the gantry rotates. The mandrel is compact, reducing it moment of inertia and hence the torquing actions of external forces. Motion other than rotation is prevented by the bearings which hold either end of the mandrel. The low backlash brake is activated when the mandrel is not being moved. Other objects and advantages besides those discussed above shall be apparent, to those experienced in the art, from the description of a preferred embodiment of the invention which follows. In the description, reference is made to the accompanying drawings, which form a part hereof, and which illustrate one example of the invention. Such example, however, is not exhaustive of the various alternative forms of the invention, and therefore reference is made to the claims which follow the description for determining the scope of the invention. |
abstract | A multi-beam x-ray system includes an x-ray source which emits x-rays and a housing with a first part and a second part. The second part is moveable relative to the first part and includes a plurality of optics of different performance characteristics. Each optic, through the movement of the second part relative to the first part, is positioned to a working position so that the optic receives the x-rays from the x-ray source and directs the x-rays with the desired performance attributes to a desired location. |
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abstract | An integrated X-ray source is provided. The integrated X-ray source includes a target for emitting X-rays upon being struck by one or more excitation beams, and one or more total internal reflection multilayer optic devices in physical contact with the target to transmit at least a portion of the X rays through total internal reflection to produce X-ray beams, wherein the optic device comprises an input face for receiving the X rays and an output face through which the X-ray beams exit the integrated X-ray source. |
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045267120 | abstract | A process for treating radioactive sludge waste wasted in a nuclear power plant comprises the steps of pulverizing the radioactive sludge waste into dry powder which is combustible, burning the powder into ashes, and pelletizing the ashes. The radioactive sludge waste including granular ion-exchange resins, powder resins, filter sludge, etc. is reduced in volume by subjecting to combustion. |
claims | 1. An apparatus for use with a reactor pressure vessel defining an internal volume filled with primary coolant, comprising:an isolation valve in fluid communication with the internal volume of the pressure vessel, including:a mounting flange configured to connect with a mating flange of the pressure vessel,a valve body defining a central bore having an axis orthogonal to a longitudinal axis of the pressure vessel;a valve seat formed in the central bore of the valve body, anda valve member movable between an open position permitting flow through the isolation valve and a closed position in which the valve member seals against the valve seat to block flow through the isolation valve,wherein the valve seat is aligned with the mounting flange along the bore axis and along a radius of the central bore with a vessel penetration flange assembly formed by the mounting flange and the mating flange when the mounting flange is connected with the mating flange of the pressure vessel. 2. The apparatus of claim 1, wherein the isolation valve further comprises:a biasing member operatively connected to the valve member that biases the valve member towards the open position. 3. The apparatus of claim 2, wherein the biasing member is configured to provide bias effective to keep the valve member in the open position except when a differential fluid pressure across the isolation valve and directed outward from the pressure vessel exceeds a threshold pressure. 4. The apparatus of claim 1, wherein the mounting flange of the isolation valve includes a portion adapted to be received in a bore in the associated reactor vessel. 5. The apparatus of claim 1,wherein the mounting flange of the isolation valve is connected with the mating flange of the pressure vessel. 6. The apparatus of claim 1, further comprising:a nuclear reactor comprising (i) the pressure vessel including the mating flange and (ii) a nuclear reactor core comprising fissile material disposed in the pressure vessel;wherein the mounting flange of the isolation valve is connected with the mating flange of the pressure vessel of the nuclear reactor. 7. The apparatus of claim 6, further comprising:a coolant makeup line connected with the mating flange of the pressure vessel;wherein the isolation valve is interposed between the coolant makeup line and the mating flange of the pressure vessel. 8. The apparatus of claim 6, further comprising:a coolant letdown line connected with the mating flange of the pressure vessel;wherein the isolation valve is interposed between the coolant letdown line and the mating flange of the pressure vessel. |
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description | Hereafter, an embodiment of the present invention will be described with reference to examples. In the following description, terms xe2x80x9cellipsoidal surfacexe2x80x9d, xe2x80x9cellipsoid of revolutionxe2x80x9d, xe2x80x9cparaboloidxe2x80x9d, and xe2x80x9cparaboloid of revolutionxe2x80x9d are used. A paraboloid is obtained by making one of two focal points of an ellipsoid infinity. Note that, in the description from the another view point, a quadratic surface of revolution having a form obtained by rotating, using an x-axis (optical axis) as a center, a quadratic curve represented by a quadratic equation for orthogonal coordinates (x, y) ax2+2hxy+by2+2gx+sfy+c=0 (where each of a, b, c, f, g, and h is constant) is defined as an xe2x80x9cellipsoidal surfacexe2x80x9d, xe2x80x9cellipsoid of revolutionxe2x80x9d, xe2x80x9cparaboloidxe2x80x9d, or xe2x80x9cparaboloid of revolutionxe2x80x9d. An ellipse is represented by h2xe2x88x92ab less than 0, and a parabola is represented by h2xe2x88x92ab=0. Using a RF magnetron sputtering apparatus provided with a plurality of raw material targets, multilayer films each comprising repeatedly layered Mo layers (correspond to 2 of FIG. 1) and Be layers (correspond to 3 of FIG. 1) were produced on a substrate (corresponds to 1 of FIG. 1) by evacuating a film formation chamber to 10xe2x88x928 torr level, introducing Ar gas into the resultant film formation chamber to keep the inside of the film formation chamber in Ar atmosphere of 3xc3x9710xe2x88x928 torr pressure, and then generating electric discharge. The number of the pairs of the Mo layers and Be layers was controlled to be 40 and the cycle length was controlled to be 6 nm. The ratio of the thickness dMo of Mo to the sum thickness (the cycle length D) of a single Mo layer and a single Be layer was changed in a range of 10 to 90%. The correlation of the reflectance of the multilayer films with the wavelength was measured using a reflectance meter employing photon radiation and the results of the measurement were showed in the table 1. In the case the thickness of a Mo layer was 50% to the cycle length, the reflectance reached the maximum, which was 62%. The reflectance was as high as 40% or higher in the case the thickness was in a range 20 to 70% to the cycle length. Multilayer films comprising repeatedly layered Moxe2x80x94N layers (correspond to 2 of FIG. 1) containing 5 atomic % (at. %) of N and Bexe2x80x94N layers (correspond to 3 of FIG. 1) containing 5 at. % of N were produced on a substrate (corresponds to 1 of FIG. 1) in the same manner as that for the example 1. It should be noted that the at. % is the percentage of an element included in an object based on the number of atoms. For example, in H2O (water), since the molecule has two hydrogen atoms and one oxygen atom, the percentage of the oxygen atoms is calculated by 1/(1+2)*100=33. Thus, water contains 33 at. % oxygen atoms. The multilayer films were produced while the number of the pairs of the Moxe2x80x94N layers and Bexe2x80x94N layers being controlled to be 40 and 80 and the cycle length being controlled to be 6 nm and 5.6 nm, respectively. The ratio of the thickness dMoxe2x80x94N of Mo to the sum thickness D of one Moxe2x80x94N layer and one Bexe2x80x94N layer was changed within a range of 10 to 90%. The correlation of the reflectance of the multilayer films with the wavelength was measured using a reflectance meter in the same manner as that for the example 1 and the multilayer film with cycle length 6 nm showed 69% reflectance of soft x-rays with 114 xc3x85 wavelength in the case the thickness of a Moxe2x80x94N layer was 50% to the cycle length and as same as that of the example 1, the reflectance was as high as 45% or higher in the case the thickness of a Moxe2x80x94N layer was in a range 20 to 70% to the cycle length. Further, the multilayer film with cycle length 6 nm showed 55% reflectance of soft x-rays with 108 xc3x85 wavelength in the case the thickness of a Moxe2x80x94N layer was 55% to the cycle length and as same as that of the example 1, the reflectance of the ray with 110 xc3x85 or shorter wavelength was as high as 45% or higher, which had not been achieved before, in the case the thickness of a Moxe2x80x94N layer was in a range from 45 to 70% to the cycle length. In the same manner as that for the example 1, using Rh for one type of layers (correspond to 2 of FIG. 1) and Be for the other type of layers (correspond to 3 of FIG. 1), multilayer films comprising repeatedly formed layers of these elements were produced on a substrate (corresponds to 1 of FIG. 1) by sputtering method. The number of the pairs of the Rh layers and Be layers was controlled to be 40 and the cycle length was controlled to be 6 nm. The ratio of the thickness dRh of Rh to the sum thickness (the cycle length D) of a single Rh layer and a single Be layer was changed within a range of 10 to 70%. The correlation of the reflectance of the multilayer films with the wavelength was measured using a reflectance meter employing photon radiation and the results of the measurement were showed in the table 2. In the case the thickness of a Rh layer was 30% to the cycle length, the reflectance reached the maximum, which was 65%. The reflectance was relatively high, not lower than 30%, in the case the thickness of a Rh layer was within a range 20 to 70% to the cycle length and was considerably high, not lower than 55%, in the case the thickness of a Rh layer was within a range 20 to 40%. In the same manner as that for the example 1, using Ru for one type of layers (correspond to 2 of FIG. 1) and Be for the other type of layers (correspond to 3 of FIG. 1), multilayer films comprising repeatedly formed layers of these elements were produced on a substrate (corresponds to 1 of FIG. 1) by sputtering method. The number of the pairs of the Rh layers and Be layers was controlled to be 40 and the cycle length was controlled to be 6 nm. The ratio of the thickness dRu of Ru to the sum thickness (the cycle length D) of a single Ru layer and a single Be layer was changed within a range of 10 to 90%. The correlation of the reflectance of the multilayer films with the wavelength was measured using a reflectance meter employing photon radiation and the results of the measurement were showed in the table 3. In the case the thickness of a Ru layer was 50% to the cycle length, the reflectance reached the maximum, which was 67%. The reflectance was as high as 50% or higher in the case the thickness of a Ru layer was within a range 30 to 70% to the cycle length and was considerably high, not lower than 55%, in the case the thickness of a Ru layer was within a range 30 to 60%. In the same manner as that for the example 1, using Moxe2x80x94Rh alloys for one type of layers and Be for the other type of layers, multilayer films comprising repeatedly formed layers of these substances were produced on a substrate by sputtering method. The number of the pairs of the Moxe2x80x94Rh layers and Be layers was controlled to be 40 and the cycle length was controlled to be 6 nm. The multilayer films were produced while the ratio of the thickness dMoxe2x80x94Rh of a Moxe2x80x94Rh layer to the cycle length being changed within a range of 10 to 90% and the composition ratio of Mo and Rh being changed within a range of 10 to 90%. The correlation of the reflectance of the multilayer films with the wavelength was measured in the same manner as that f or the example 1 and it was found that the multilayer films having the composition ratio of Rh in the Moxe2x80x94Rh alloys within a range 30 to 70% and dMoxe2x80x94Rh/D within a range of 30 to 70% showed a considerably high reflectance, which exceeds 60%, in the condition that the direct incident angle (the inclination angle from the normal of the multilayer films) was 3xc2x0 and peak wavelength was near 114 xc3x85. Especially, in the case that the composition ratio Rh in the Moxe2x80x94Rh alloys was 50% and dMoxe2x80x94Rh/D was 45%, the above defined reflectance was as high as 72%. In the same manner as that for the example 1, using Moxe2x80x94Ru alloys for one type of layers and Be for the other type of layers, multilayer films comprising repeatedly formed layers of these substances were produced by sputtering method. The number of the pairs of the Moxe2x80x94Ru layers and Be layers was controlled to be 40 and the cycle length was controlled to be 6 nm. The multilayer films were produced while the ratio of the thickness dMoxe2x80x94Ru of a Moxe2x80x94Ru layer to the cycle length being changed within a range of 10 to 90% and the composition ratio of Mo and Ru being changed within a range of 10 to 90%. The correlation of the reflectance of those multilayer films with the wavelength was measured in the same manner as that for the example 1 and it was found that the multilayer films having the composition ratio of Ru in the Moxe2x80x94Ru alloys within a range 30 to 70% and dMoxe2x80x94Ru/D within a range of 30 to 70% showed a considerably high reflectance, which exceeds 60%, in the condition that the direct incident angle (the inclination angle from the normal of the multilayer films) was 3xc2x0 and peak wavelength was in a wide range from near 112 xc3x85 to near 117 xc3x85. Especially, in the case that the composition ratio Ru in the Moxe2x80x94Ru alloys was 50% and dMoxe2x80x94Ru/D was 40%, the above defined reflectance was as high as 72%. In the same manner as that for the example 1, using Ruxe2x80x94Rh alloys for one type of layers and Be for the other type of layers, multilayer films comprising repeatedly formed layers of these substances were produced by sputtering method. The number of the pairs of the Ruxe2x80x94Rh layers and Be layers was controlled to be 40 and the cycle length was controlled to be 6 nm. The multilayer films were produced while the ratio of the thickness of a Ruxe2x80x94Rh layer to the cycle length being changed within a range of 10 to 90% and the composition ratio of Ru and Rh being changed within a range of 10 to 90%. The correlation of the reflectance of those multilayer films with the wavelength was measured in the same manner as that for the example 1 and it was found that the multilayer films having the composition ratio of Rh in the Ruxe2x80x94Rh alloys within a range 30 to 70% and dRuxe2x80x94Rh/D within a range of 10 to 60% showed a considerably high reflectance, which exceeds 60%, in the condition that the direct incident angle was 3xc2x0 and peak wavelength was near 113 xc3x85. Especially, in the case that the composition ratio Ru in the Ruxe2x80x94Rh alloys was 50% and dRuxe2x80x94Rh/D was 25%, the above defined reflectance was as remarkable high as 78%. In the same manner as that for the example 1, using Mo for one type of layers and Bxe2x80x94Be compounds for the other type of layers, multilayer films comprising repeatedly formed layers of these substances were produced. The number of the pairs of the Mo layers and Bxe2x80x94Be compound layers was controlled to be 60 and the cycle length was controlled to be 6 nm. The composition ratio of B and Be in the Bxe2x80x94Be compound layers was changed within a range of 20 to 90% and the ratio of the thickness dMo of a Mo layer to the cycle length D was changed within a range of 10 to 90%. The correlation of the reflectance of thus produced multilayer films with the wavelength was measured in the same manner as that for the example 1 and it was found that the multilayer films having dMo/D within a range 30 to 70% showed a relatively high reflectance, which exceeds 50%, at the direct incident angle of 3xc2x0 and peak wavelength near 115 xc3x85. Especially, in the case that B2Be and B6Be were used as the Be compounds, the maximum reflectance was over 60%. Further, in the case those multilayer films were heated at 400xc2x0 C. for 1 hour in vacuum of 10xe2x88x925 torr and then the reflectance measurement was carried out in the same manner as that before heating, the decrease of reflectance was 5 to 18% to show excellent heat resistance. Especially, in the case of using B2Be and B6Be, the decrease of reflectance was as low as 5 to 9% to show excellent heat resistance. Reference 1 After the same heating treatment as that for the example 8 was carried out for a Mo/Be multilayer film produced by the example 1, the same reflectance measurement was carried out as that before heating and the reflectance was found decreasing by 45% as compared with that before heating. In the same manner as that for the example 1, using Moxe2x80x94Rh alloys for one type of layers and Bxe2x80x94Be compounds for the other type of layers, multilayer films comprising repeatedly formed layers of these substances were produced. The number of the pairs of the Moxe2x80x94Rh layers and Bxe2x80x94Be compound layers was controlled to be 60 and the cycle length was controlled to be 6 nm. The composition ratio of Rh in the Moxe2x80x94Rh alloys was changed within a range of 30 to 70%, the composition ratio of B and Be in the Bxe2x80x94Be compound layers was changed within a range of 20 to 90% and the ratio of the thickness Moxe2x80x94Rh of a Moxe2x80x94Rh layer to the cycle length D was changed within a range of 30 to 70%. The correlation of the reflectance of thus produced multilayer films with the wavelength was measured in the same manner as that for the example 1 and it was found that the multilayer films having the composition ratio of Rh in the Moxe2x80x94Rh alloys within 30 to 70%, the thickness dMoxe2x80x94Rh/D within a range 40 to 60%, and the composition ratio of B in the Bxe2x80x94Be compounds within 30 to 90% showed a relatively high reflectance, which exceeds 50%, at the direct incident angle of 3xc2x0 and peak wavelength near 114 xc3x85. Further, in the case those multilayer films were heated at 400xc2x0 C. for 1 hour in vacuum of 10xe2x88x925 torr and then the reflectance measurement was carried out in the same manner as that before heating, the decrease of reflectance was 5 to 20% to show higher heat resistance than that of a Mo/Be multilayer film. In the same manner as that for the example 1, using Moxe2x80x94Ru alloys for one type of layers and Bxe2x80x94Be compounds for the other type of layers, multilayer films comprising repeatedly formed layers of these substances were produced. The number of the pairs of the Moxe2x80x94Ru layers and Bxe2x80x94Be compound layers was controlled to be 60 and the cycle length was controlled to be 6 nm. The composition ratio of Ru in the Moxe2x80x94Ru alloys was changed within a range of 30 to 70%, the composition ratio of B and Be in the Bxe2x80x94Be compound layers was changed within a range of 20 to 90% and the ratio of the thickness dMoxe2x80x94Ru of a Moxe2x80x94Ru layer to the cycle length D was changed within a range of 30 to 70%. The correlation of the reflectance of thus produced multilayer films with the wavelength was measured in the same manner as that for the example 1 and it was found that the multilayer films having the composition ratio of Ru in the Moxe2x80x94Ru alloys within 30 to 70%, dMoxe2x80x94Ru/D within a range 40 to 60%, and the composition ratio of B in the Bxe2x80x94Be compounds within 30 to 90% showed a relatively high reflectance, which exceeds 50%, at the direct incident angle of 3xc2x0 and peak wavelength near 114 xc3x85. Further, in the case those multilayer films were heated at 400xc2x0 C. for 1 hour in vacuum of 10xe2x88x925 torr and then the reflectance measurement was carried out in the same manner as that before heating, the decrease of reflectance was 5 to 22% to show higher heat resistance than that of a Mo/Be multilayer film. In the same manner as that for the example 1, using Rhxe2x80x94Ru alloys for one type of layers and Bxe2x80x94Be compounds for the other type of layers, multilayer films comprising repeatedly formed layers of these substances were produced. The number of the pairs of the Rhxe2x80x94Ru layers and Bxe2x80x94Be compound layers was controlled to be 60 and the cycle length was controlled to be 6 nm. The composition ratio of Ru in the Rhxe2x80x94Ru alloys was changed within a range of 30 to 70%, the composition ratio of B and Be in the Bxe2x80x94Be compound layers was changed within a range of 20 to 90% and the ratio of the thickness dRhxe2x80x94Ru of a Rhxe2x80x94Ru layer to the cycle length D was changed within a range of 10 to 60%. The correlation of the reflectance of thus produced multilayer films with the wavelength was measured in the same manner as that for the example 1 and it was found that the multilayer films having the composition ratio of Ru in the Rhxe2x80x94Ru alloys within 30 to 70%, dRhxe2x80x94Ru/D within a range 20 to 40%, and the composition ratio of B in the Bxe2x80x94Be compounds within 30 to 90% showed a relatively high reflectance, which exceeds 60%, at the direct incident angle of 3xc2x0 and peak wavelength near 114 xc3x85. Further, in the case those multilayer films were heated at 400xc2x0 C. for 1 hour in vacuum of 10xe2x88x925 torr and then the reflectance measurement was carried out in the same manner as that before heating, the decrease of reflectance was 5 to 24% to show higher heat resistance than that of a Mo/Be multilayer film. Using Rhxe2x80x94Ru alloys containing C for one type of layers and Be for the other type of layers, multilayer films comprising repeatedly formed layers of these substances were produced by a sputtering method in the same manner as that for the example 1. The number of the pairs of the C-containing Ruxe2x80x94Rh layers and Be layers was controlled to be 40 and the cycle length was controlled to be 6 nm, and also the number of pairs to be 80 and the cycle length to be 5.6 nm. The multilayer films were produced while the ratio of the thickness of a C-containing Ruxe2x80x94Rh layer to the cycle length D being controlled to be 25% and the composition of Ru and Rh to be 50%. The correlation of the reflectance of thus produced multilayer films with the wavelength was measured in the same manner as that for the example 1 and it was found that the multilayer films having the composition ratio of C in the C-containing Ruxe2x80x94Rh alloys within 2 to 20% and the cycle length of 6 nm showed a high reflectance, which exceeds 55%, at the direct incident angle of 3xc2x0 and peak wavelength near 113 xc3x85 and those having the cycle length of 5.6 nm showed a reflectance of 53% at 108 xc3x85 wavelength. Further, in the case those multilayer films were heated at 400xc2x0 C. for 1 hour in vacuum of 10xe2x88x925 torr and then the reflectance measurement was carried out in the same manner as that before heating, the decrease of reflectance was 4 to 14% to show excellent heat resistance. Using Rhxe2x80x94Ru alloys containing B for one type of layers and Be for the other type of layers, multilayer films comprising repeatedly formed layers of these substances were produced by a sputtering method in the same manner as that for the example 1. The number of the pairs of the B-containing Ruxe2x80x94Rh layers and Be layers was controlled to be 40 and the cycle length was controlled to be 6 nm. The multilayer films were produced while the ratio of the thickness of a B-containing Ruxe2x80x94Rh layer to the cycle length being controlled to be 25% and the composition of Ru and Rh to be 50%. The correlation of the reflectance of thus produced multilayer films with the wavelength was measured in the same manner as that for the example 1 and it was found that the multilayer films having the composition ratio of B in the B-containing Ruxe2x80x94Rh alloys within 1 to 20% showed a high reflectance, which exceeds 55%, at the direct incident angle of 3xc2x0 and peak wavelength near 113 xc3x85. Further, in the case those multilayer films were heated at 400xc2x0 C. f or 1 hour in vacuum of 10xe2x88x925 torr and then the reflectance measurement was carried out in the same manner as that before heating, the decrease of reflectance was 7 to 20% to show excellent heat resistance as compared with that of a Mo/Be multilayer film. Using Rhxe2x80x94Ru alloys containing O for one type of layers and Be for the other type of layers, multilayer films comprising repeatedly formed layers of these substances were produced by a sputtering method in the same manner as that for the example 1. The number of the pairs of the O-containing Ruxe2x80x94Rh layers and Be layers was controlled to be 40 and the cycle length was controlled to be 6 nm. The multilayer films were produced while the ratio of the thickness of an O-containing Ruxe2x80x94Rh layer to the cycle length being controlled to be 25% and the composition of Ru and Rh to be 50%. The correlation of the reflectance of thus produced multilayer films with the wavelength was measured in the same manner as that for the example 1 and it was found that the multilayer films having the composition ratio of O in the O-containing Ruxe2x80x94Rh alloys within 2 to 20% showed a high reflectance, which exceeds 55%, at the direct incident angle of 3xc2x0 and peak wavelength near 113 xc3x85. Further, in the case those multilayer films were heated at 40xc2x0 C. for 1 hour in vacuum of 10xe2x88x925 torr and then the reflectance measurement was carried out in the same manner as that before heating, the decrease of reflectance was 6 to 17% to show excellent heat resistance as compared with that of a Mo/Be multilayer film. Using Rhxe2x80x94Ru alloys containing N for one type of layers and Be for the other type of layers, multilayer films comprising repeatedly formed layers of these substances were produced by a sputtering method in the same manner as that for the example 1. The number of the pairs of the N-containing Ruxe2x80x94Rh layers and Be layers was controlled to be 40 and the cycle length was controlled to be 6 nm. The multilayer films were produced while the ratio of the thickness of a N-containing Ruxe2x80x94Rh layer to the cycle length being controlled to be 25% and the composition of Ru and Rh to be 50%. The correlation of the reflectance of thus produced multilayer films with the wavelength was measured in the same manner as that for the example 1 and it was found that the multilayer films having the composition ratio of N to Ruxe2x80x94Rh in the N-containing Ruxe2x80x94Rh alloys within 2 to 20% showed a high reflectance, which exceeds 55%, at the direct incident angle of 3xc2x0 and peak wavelength near 113 xc3x85. Further, in the case those multilayer films were heated at 400xc2x0 C. for 1 hour in vacuum of 10xe2x88x925 torr and then the reflectance measurement was carried out in the same manner as that before heating, the decrease of reflectance was 6 to 16% to show excellent heat resistance. Using Mo containing C for one type of layers and Be for the other type of layers, multilayer films comprising repeatedly formed layers of these substances were produced by a sputtering method in the same manner as that for the example 1. The number of the pairs of the C-containing Mo layers and Be layers was controlled to be 40 and the cycle length was controlled to be 6 nm. The multilayer films were produced while the ratio of the thickness of a C-containing Mo layer to the cycle length being controlled to be 40%. The correlation of the reflectance of thus produced multilayer films with the wavelength was measured in the same manner as that for the example 1 and it was found that the multilayer films having the composition ratio of C in the C-containing Mo within 2 to 20% showed a high reflectance, which exceeds 55%, at the direct incident angle of 3xc2x0 and peak wavelength near 113 xc3x85. Further, in the case those multilayer films were heated at 400xc2x0 C. for 1 hour in vacuum of 10xe2x88x925 torr and then the reflectance measurement was carried out in the same manner as that before heating, the decrease of reflectance was 1 to 9% to show excellent heat resistance. Using Rhxe2x80x94Ru alloys for one type of layers and Be to which Ca, Co, Fe, Mo, Nb, Ti, V and W were independently added for the other type of layers, multilayer films comprising repeatedly formed layers of these substances were produced by a sputtering method in the same manner as that for the example 1. The number of the pairs of the Ruxe2x80x94Rh alloy layers and Be layers was controlled to be 40 and the cycle length was controlled to be 6 nm. The multilayer films were produced while the ratio of the thickness of a Ruxe2x80x94Rh layer to the cycle length being controlled to be 25% and the composition of Ru and Rh to be 50%. The correlation of the reflectance of thus produced multilayer films with the wavelength was measured in the same manner as that for the example 1 and it was found that the multilayer films having the composition ratio of each additive in the Be layers containing independently one of Ca, Co, Fe, Mo, Nb, Ti, V and W within 1 to 33% showed a high reflectance, which exceeds 50%, at the direct incident angle of 3xc2x0 and peak wavelength near 113 xc3x85. Further, in the case those multilayer films were heated at 400xc2x0 C. for 1 hour in vacuum of 10xe2x88x925 torr and then the reflectance measurement was carried out in the same manner as that before heating, the decrease of reflectance was 7 to 18% to show excellent heat resistance. In the same manner as that for the example 1, using Ru for one type of layers and B6Be for the other type of layers, multilayer films comprising repeatedly formed layers in 40 pairs of Ru layers and B6Be layers and having the cycle length within 3.9 to 7 nm at every 2 xc3x85 were produced. The ratio of the thickness of layers was controlled to be 1:1. The correlation of the reflectance of thus produced multilayer films to the wavelength was measured in the same manner as that for the example 1 and it was found that a multilayer film type reflecting mirror comprising a multilayer film constituted of those layers in combination had a reflectance as high as 25% even to radiation about 78 xc3x85 peak wavelength corresponding to the cycle length at direct incident angle 3xc2x0, which was extremely high reflectance in such a wavelength region, further the reflectance was 35% to 100 xc3x85 wavelength, 57% to 114 xc3x85 wavelength, and at least 45% to radiation with wavelength in a range from 78 xc3x85, the wavelength longer than the foregoing value, to 140 xc3x85. In the same manner as that for the example 1, using Ru for one type of layers and B for the other type of layers, multilayer films having a repeated structure of these two layers were produced by the sputtering method. The multilayer films were produced while the number of the pairs of Ru layers and B layers being controlled to be 60 and the cycle length to be 5.1 nm or 5.5 nm. The ratio of the Ru thickness to the sum thickness of a single Ru layer and a single B layer was changed in a range of 10 to 90% and the correlation of the reflectance of the multilayer films with the wavelength was measured using a soft x-ray reflectance meter in the same manner as that for the example 1. In the case of 5.1 nm cycle length, the reflectance reached the maximum, which was 52%, to the soft x-ray wavelength of 100 xc3x85 when the thickness of a Ru layer was 45% to the cycle length. The reflectance was relatively high, 35% or higher, in the case the thickness of a Ru layer to the cycle length was in a range 30 to 60% to the cycle length and was 45% or higher, which was extremely high to the wavelength, in the case the thickness of a Ru layer to the cycle length was in a range 40 to 50%. On the other hand, in the case of 5.5 nm cycle length, the reflectance reached the maximum, which was 58%, to the soft x-ray wavelength of 108 xc3x85 when the thickness of a Ru layer was 45% to the cycle length. The reflectance was relatively high, 40% or higher, in the case the thickness of a Ru layer to the cycle length was in a range 30 to 60% to the cycle length and was 50% or higher, which was extremely high to the wavelength, in the case the thickness of a Ru layer to the cycle length was in a range 40 to 50%. In the same manner as that for the example 18, using Ru containing 5 at. % of N for one type of layers and B containing 5 at. % of N for the other type of layers, multilayer films having a repeated structure of these two layers were produced by the sputtering method. The multilayer films comprising 60 pairs of Ruxe2x80x94N layers and Bxe2x80x94N layers were produced while the cycle length being controlled to be 5.1 nm or 5.5 nm. The ratio of the Ruxe2x80x94N thickness to the sum thickness of a single Ruxe2x80x94N layer and a single Bxe2x80x94N layer was changed within a range of 10 to 90% and the correlation of the reflectance of the multilayer films with the wavelength was measured using a soft x-ray reflectance meter in the same manner as that for the example 1. In the case of 5.1 nm cycle length, the reflectance reached the maximum, which was 51%, to the soft x-ray wavelength of 100 xc3x85 when the thickness of a Ruxe2x80x94N layer was 45% to the cycle length just the same as that in the case of the example 18. The reflectance was relatively high, about 35% or higher, in the case the thickness of a Ruxe2x80x94N layer to the cycle length was in a range 30 to 60% to the cycle length and was about 45% or higher, which was extremely high to the wavelength, in the case the thickness of a Ruxe2x80x94N layer to the cycle length was in a range 40 to 50%. On the other hand, in the case of 5.5 nm cycle length, the reflectance reached the maximum, which was 56%, to the soft x-ray wavelength of 108 xc3x85 when the thickness of a Ruxe2x80x94N layer was 45% to the cycle length. The reflectance was relatively high, about 40% or higher, in the case the thickness of a Ruxe2x80x94N layer to the cycle length was in a range 30 to 60% to the cycle length and was about 50% or higher, which was extremely high to the wavelength, in the case the thickness of a Ruxe2x80x94N layer to the cycle length was in a range 40 to 50%. X-ray reflecting mirrors with an ellipsoid of revolution (in the present invention), which has multilayer films or Mo/Si multilayer films of the example 1 to the example 20 produced by the same manner as that of the example 1 were so arranged as to surround a cryotarget laser plasma x-ray point source (point-like x-ray generation part) 32, serving as a point-like x-ray generation part, at about several to several ten centimeter to the light source just as illustrated in FIGS. 3C and 3D to obtain high light concentration efficiency (about 3 steradian of solid angle) to the x-rays emitted out of the point source and simultaneously high reflectance (50% or higher). In this case, the cryotarget laser plasma x-ray point source used a rare gas element, as a target material generating the x-ray, in a liquid or solid state at a low temperature or in a low temperature gas state at vapor density near the liquid density. Since the x-ray generation efficiency of x-rays with reflected wavelength width of the foregoing multilayer film type reflecting mirrors by plasma was verified to have 1% per 1 steradian solid angle by using a pulsed laser with 500 pulses or more repeated at every several seconds, 0.5 J or higher pulse energy and about 10xe2x88x928 second pulse width, a laser plasma x-ray generation apparatus capable of taking out the x-rays with uniform spectra with 3.8 W or higher average intensity as a) a parallel beam and b) a converged beam could be constituted. FIGS. 3C, 3D, and 3E illustrate an example of the arrangement of an ellipsoid of revolution (in the example only the upper half portion is illustrated and the lower half portion is omitted) for condensing more x-rays which are emitted from the laser plasma x-ray point source by the foregoing x-ray optical system. Assuming that xcex8 is an angle from a normal (vertical line) to the laser target surface, the angular distribution of x-ray emission intensities is almost determined depending on the ratio of the concentrated light diameter of the pulse laser, i.e., the diameter of plasma to be generated, to the scale length of plasma expanding by heating. For example, when the concentrated light diameter is about 100 xcexcm, if the pulse duration of the laser is about 10 nsec, the angular distribution is isotropic; and if the pulse width is 1 nsec or shorter, the angular distribution is approximately proportional to cos xcex8. Therefore, the reflecting mirror has a shape to ensure a reflecting surface with respect to the normal, and the aperture is arranged in a part of the reflecting surface for only the incidence of a laser ray. FIGS. 3A and 3B are illustrated as the references to show the characteristic features of the present invention, in which FIG. 3A illustrates a ring-shaped paraboloid of revolution, and FIG. 3B illustrates a ring-shaped ellipsoid of revolution. In FIGS. 3A and 3B, 31 shows the incidence laser ray which is incident from an axial direction of the ring-shaped paraboloid of revolution or ring-shaped ellipsoid of revolution, 32 shows the target, 33 shows the emitted x-ray obtained by heating the target 32 by the incidence laser ray 31, and 34 is a reflecting mirror which generates, from x-rays emitted from near the surface of the target 32, parallel rays or converged rays obtained by converging the x-rays on or near a focal point. FIGS. 3C, 3D, and 3E illustrate a basic constitution of a laser plasma x-ray generation apparatus using a multilayer film type x-ray reflecting mirror according to the present invention. In FIGS. 3C, 3D, and 3E, the same reference numerals as in FIGS. 3A and 3B denote the same parts. In FIGS. 3C and 3D, the reflecting mirror 34 has the structure obtained by cutting an ellipsoid with two focal points along the major axis, and the surface of the target 32 placed on one of the two focal points is heated by an incidence laser ray to generate point-like laser plasma x-rays on that focal point. The incident laser ray 31 is incident from a direction outside a range of 30xc2x0 from the normal to the x-ray emitting surface of the target 32 which is placed almost parallel to the major axis of the ellipsoidal surface of the ellipsoid. The soft x-rays emitted from the x-ray emitting surface of the target 32 by the incidence laser ray 31 are bombarded against the multilayer film type reflecting mirror 34 positioned on the inner surface of the ellipsoid and are reflected by the multilayer film type reflecting mirror 34. The reflected x-rays 33 converge on or near the other focal point of the ellipsoidal surface. The light concentration efficiency defined as an amount obtained by dividing the light amount of the converged reflected x-rays 33 by the amount of all x-rays emitted from the target depends on the form of the angular distribution for emission of the x-rays from the x-ray emitting surface of the target, and can be adjusted by changing the angle of the x-ray emitting surface with respect to the major axis of the ellipsoid. Note that 34a is an aperture formed in the reflecting mirror 34 as shown in FIG. 3C, and through the aperture 34a, the incidence laser ray 31-1 is received from the outside. FIG. 3D illustrates a cross-sectional view taken along a surface which is perpendicular to the major axis (rotation symmetry axis) in FIG. 3C and includes the point-like x-ray source. 34b is an aperture formed in the reflecting mirror 34 as shown in FIG. 3D, and through the aperture 34b, the incidence laser ray 31-2 is received from the outside. The incidence laser 31-2 is shown as another example of 31-1, these incidence laser rays do not have the incidence direction of xcex8 less than 30xc2x0 to the normal of the target surface, and the soft x-rays emitted from the target are emitted to xcex8 less than 300 relatively intensively. Obviously, a ray source to which the present invention is applied is not limited to a soft x-ray and may be an x-ray. A laser ray is used in this example, but the present invention is not obviously limited to this as far as light is an energy beam. In the foregoing example, the structure obtained by cutting the ellipsoid along the major axis, i.e., an x-ray radiation part using the x-ray optical system which has 0.1 or more steradian condensing solid angle around an x-ray generation part with a target surface, and has a partial surface, as the x-ray reflecting mirror, of an ellipsoid of revolution (ellipsoidal surface) obtained by rotating an ellipse about its major axis as a rotation axis passing through the x-ray generation part by only a rotation angle of less than 180 degrees is used. However, the present invention may use a structure (e.g., the structure in FIG. 3F) in which a paraboloid of revolution serving as a source making infinity one focal point, of two focal points of an ellipse, at which the reflected x-rays converge, i.e., a source making the reflected x-rays parallel or almost parallel is defined as the x-ray reflecting mirror. This paraboloid of revolution with the foregoing structure has an x-ray optical system having a partial surface, as an x-ray reflecting mirror, of the paraboloid of revolution obtained by rotating the paraboloid of revolution about its major axis as a rotation axis by only a rotation angle of less than 180 degrees. Further, when a Mo/Si multilayer film is used, 2 to 20% of C are added to either of the layers, so that the reflecting mirror with excellent heat resistance can be obtained according to the finding of the present inventors. As is understood from the embodiment shown in FIGS. 3C to 3F, the portion of the reflecting mirror of the x-ray radiation part in the second focal direction is cut to have a shape so as to introduce the reflected x-rays to the outside. However, the x-ray radiation part may have any shape if reflected x-rays are guided outside, as in the case wherein the aperture for introducing the incidence ray to the inside is formed in the reflecting mirror. An aperture may be formed to guide the x-rays outside. As described above, the multilayer films of the present invention could improve the direct incidence reflectance by using materials with optical constants suitable for giving a high reflectance to wavelength within a range from 69.5 xc3x85 to 124 xc3x85, selecting the structure, and smoothing the interfaces. Further, the heat resistance of the multilayer film was improved by using compounds or mixtures having optical constants suitable for heightening the reflectance and giving excellent heat resistance. Consequently, as compared with a conventionally invented Mo/Be multilayer film type reflecting mirror, the multilayer film type mirrors of the present invention had heightened direct incidence reflectance or improved heat resistance or improved values of both. In the case a multilayer film with heightened reflectance is used (1) for various analysis methods using x-rays and soft x-rays, the sensitivity and the precision can be improved and in the case of use (2) for x-ray lithography, the throughput can be improved more than that of a multilayer film comprising Mo for one type of layers. Moreover, in the case a multilayer film type x-ray reflecting mirror with heightened reflectance is used (1) for various analysis methods using x-rays and soft x-rays, the sensitivity and the precision can be improved since the alteration of the reflectance during the use is suppressed as compared with that of a conventional multilayer film type reflecting mirror owing to the more improved heat resistance than that of the conventional reflecting mirror and in the case of use (2) for x-ray lithography, the proper exposure time can precisely be determined for the same reason as the reason of (1) and further the life of the multilayer film type reflecting mirror itself can be prolonged. In this description, materials and structures suitable for near 114 xc3x85 wavelength were exemplified, and no need to say, the reflection peak wavelength can be changed by changing the cycles according to the Bragg approximation. Also, that a high reflectance in a range from approximately the absorption edge (69.5 xc3x85) of B to approximately the absorption edge (123 to 125 xc3x85) of Si or to the longer wavelength could be obtained in the case of combination of a compound B and Be with a metal was exemplified by combining Mo with the compounds of B and Be such as B6Be and that was only one example, and it is also needless to say that the same effect can be obtained by using any one of Ru, Rh and Mo, or using their alloys, or using substances containing any one of these metals together with additives of other elements, or using alloys containing two or more of these metals together with additives of other elements, or further by using compounds or mixtures of B and Be such as BBe instead of B6Be. Especially, when the Mo/Si multilayer films or the Mo-/Si-based multilayer films with improved heat resistance are used as the materials of the multilayer films, the same effect can be obtained in the long wavelength region over the absorption edge (123 to 125 xc3x85) of Si or longer. By installing or combining x-ray optical system comprising an x-ray reflecting mirror or a plurality of x-ray reflecting mirrors having the foregoing multilayer films in the periphery of a cryotarget laser plasma x-ray point source, a constituted x-ray generation apparatus can be a compact and practical apparatus capable of generating the x-ray parallel beam, or converged beam, or condensed beam with uniform spectra and high average intensity. Owing to actualization of such an x-ray generating apparatus, applied appliances for x-ray reduction projection exposure and an x-ray beam processing apparatus can be made available for practical use. |
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summary | ||
claims | 1. A method, comprising:determining whether a specimen to be tested includes at least one positron emitter therein that will be activated in response to photon bombardment;selecting a positron emitter to be activated;determining a threshold photon energy required to activate the selected positron emitter;determining a half-life of the selected positron emitter; andwhen the half-life of the selected positron emitter is less than a selected half-life, then performing a rapid activation/analysis process, said rapid activation/analysis process comprising:activating for an activation time the selected positron emitter by bombarding the specimen with photons having energies at least as great as the threshold photon energy;detecting for a detection time gamma rays produced by annihilation of positrons with electrons in the specimen; andrepeating said steps of activating for an activation time and detecting for a detection time until detecting a sufficient number of gamma rays to determine at least one material characteristic of said specimen;when the half-life of the selected positron emitter is greater than or equal to the selected half-life, then performing a normal activation/analysis process, said normal activation/analysis process comprising:activating the selected positron emitter by bombarding the specimen with photons having energies at least as great as the threshold photon energy; anddetecting gamma rays produced by annihilation of positrons with electrons in the specimen. 2. The method of claim 1, further comprising determining a positron lifetime based on the detected gamma rays. 3. The method of claim 1, further comprising using a Doppler broadening algorithm to determine the at least one material characteristic. 4. The method of claim 1, further comprising using a three dimensional imaging algorithm to determine a position within the specimen of a positron/electron annihilation event. 5. A method, comprising:providing a specimen comprising at least one positron emitter;determining a threshold energy for activating the at least one positron emitter;comparing a half-life of the at least one positron emitter with a selected half-life;when the half-life of the at least one positron emitter is greater than or equal to the selected half-life:activating the at least one positron emitter by bombarding the specimen with photons having energies greater than the threshold energy; anddetecting gamma rays produced by annihilation of positrons with electrons within the specimen; or,when the half-life of the at least one positron emitter is less than the selected half-life:activating for an activation time the at least one positron emitter by bombarding the specimen with photons having energies greater than the threshold energy;detecting for a detection time gamma rays produced by annihilation of positrons with electrons within the specimen; andrepeating said steps of activating for an activation time and detecting for a detection time until detecting a sufficient number of gamma rays to determine at least one material characteristic of said specimen. 6. The method of claim 1, wherein the selected half-life is on the order of tens of seconds. 7. The method of claim 1, wherein selected half-life is about 17 seconds. 8. The method of claim 1, wherein the detection time is about equal to the half-life of the selected positron emitter. 9. The method of claim 1, wherein the rapid activation/analysis process further comprises alternately moving the specimen between an activation position and a detection position, the activation position being adjacent a photon source, the detection position being adjacent a detector. 10. The method of claim 1, wherein the rapid activation/analysis process further comprises alternately moving a photon source adjacent the specimen during the activation time and away from the specimen during the detection time and alternately moving a detector adjacent the specimen during the detection time and away from the specimen during the activation time. 11. The method of claim 1, wherein the rapid activation/analysis process further comprises activating a photon source to bombard the specimen with photons during the activation time and de-activating the photon source during the detection time. 12. The method of claim 5, further comprising determining a positron lifetime based on the detected gamma rays. 13. The method of claim 5, further comprising using a Doppler broadening algorithm to determine the at least one material characteristic. 14. The method of claim 5, further comprising using a three dimensional imaging algorithm to determine a position within the specimen of a positron/electron annihilation event. 15. The method of claim 5, wherein the selected half-life is on the order of tens of seconds. 16. The method of claim 5, wherein selected half-life is about 17 seconds. 17. The method of claim 5, wherein the detection time is about equal to the half-life of the at least one positron emitter. 18. The method of claim 5, further comprising alternately moving the specimen between an activation position and a detection position, the activation position being adjacent a photon source, the detection position being adjacent a detector. 19. The method of claim 5, further comprising alternately moving a photon source adjacent the specimen during the activation time and away from the specimen during the detection time. 20. The method of claim 19, further comprising alternately moving a detector adjacent the specimen during the detection time and away from the specimen during the activation time. 21. The method of claim 5, further comprising activating a photon source to bombard the specimen with photons during the activation time and de-activating the photon source during the detection time. 22. A method, comprising:providing a specimen comprising at least one positron emitter;determining a threshold energy for activating the at least one positron emitter;comparing a half-life of the at least one positron emitter with a selected half-life;when the half-life of the at least one positron emitter is less than the selected half-life:alternately activating the at least one positron emitter and detecting gamma rays produced by annihilation of positrons within the specimen until detecting a sufficient number of gamma rays to determine at least one material characteristic of said specimen. 23. The method of claim 22, wherein said activating the at least one positron emitter comprises activating for an activation time the at least one positron emitter by bombarding the specimen with photons having energies greater than the threshold energy. 24. The method of claim 23, further comprising determining a positron lifetime based on the detected gamma rays. 25. The method of claim 23, further comprising using a Doppler broadening algorithm to determine the at least one material characteristic. 26. The method of claim 23, further comprising using a three dimensional imaging algorithm to determine a position within the specimen of a positron/electron annihilation event. 27. The method of claim 23, wherein the selected half-life is on the order of tens of seconds. 28. The method of claim 23, wherein selected half-life is about 17 seconds. 29. The method of claim 23, wherein detecting gamma rays is performed for a time that is about equal to the half-life of the at least one positron emitter. 30. The method of claim 23, further comprising alternately moving the specimen between an activation position and a detection position, the activation position being adjacent a photon source, the detection position being adjacent a detector. 31. The method of claim 23, further comprising alternately moving a photon source adjacent the specimen during the activation time and away from the specimen during the step of detecting gamma rays. 32. The method of claim 31, further comprising alternately moving a detector adjacent the specimen during the step of detecting gamma rays and away from the specimen during the activation time. 33. The method of claim 23, further comprising activating a photon source to bombard the specimen with photons during the activation time and de-activating the photon source during the step of detecting gamma rays. |
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048896837 | claims | 1. In a liquid metal cooled nuclear reactor, a thermally responsive trigger device for releasing a neutron absorbing element suspended above the reactor core, wherein the improvement comprises, a. a closed bellows having a fixed end, and a free end which defines an axially extending push member, the bellows being oriented substantially vertically with the fixed end uppermost and located in the reactor so as to be responsive to the temperature of the reactor coolant; b. liquid metal filling the bellows so as to expand the bellows axially and move said push member axially in response to increasing temperatures; c. a rotatable plate means below the bellows and having at least one portion thereof for suspending a neutron absorber element therefrom, and d. cooperating interengaging cam means carried in part by the push member and in part by the plate means, the cam means being constructed and arranged such that downward movement of the push member as a result of axial expansion of the bellows in response to temperature rise of the coolant causes rotary movement of the plate means thereby to release the neutron absorber element. 2. The combination as claimed in claim 1, including a support means for the plate means, the support means defining an aperture through which the push member extends and inhibiting lateral displacement of the push member. 3. The combination as claimed in claim 1, wherein the liquid metal in the bellows is the same as the liquid metal reactor coolant. 4. The combination as claimed in claim 1, wherein the device is located in a demountable sub-assembly vehicle in the reactor. |
description | FIG. 1 shows diametrically an X-ray apparatus which includes a filter in accordance with the invention. The X-ray source 1 emits an X-ray beam 2 which irradiates an object 3, for example a patient to be examined. As a result of local differences in the absorption of X-rays in the object 3 and X-ray image is formed on the X-ray detector 4 which in this case an image intensifier 6 and is converted into a light image on the exit window 7; this light image is imaged on a video camera 9 by means of a lens system 8. The video camera 9 forms an electronic image signal from the light image. The electronic image signal is applied, for example for further processing, to an image processing unit 10 or to a monitor 11 on which the image information in the X-ray image is displayed. Between the X-ray source 1 and the object 3 there is arranged a filter 12 for local attenuation of the X-ray beam 2. The filter 12 includes various tubular filter elements 13 whose X-ray absorptivity can be adjusted by application of electric voltages to the wall of the filter elements by means of an adjusting circuit 14. The electric voltages are adjusted, for example on the basis of the setting of the X-ray source 1, by means of the power supply 15 of the X-ray source and/or on the basis of, for example brightness values of the X-ray image which can be derived from the signal present on the output terminal 16 of the video camera 9. The general construction of a filter 12 of this kind and the composition of the liquid filling thereof are described in greater detail in U.S. Pat. No. 5,625,665 (PHN 15.044). FIG. 2a is a diagrammatic sectional view of the tubular filter element 13 of a filter as shown in FIG. 1. The filter element 13 is filled, via the supply duct 20, with the liquid filling 22 which is formed by one electrically conductive and X-ray absorbing liquid. For each filter element the longitudinal direction z and the internal volume 21 are defined, the latter being bounded by the walls 28 of the filter element. Each filter element includes the first electrode 23 in the form of an electrically conductive layer which is electrically isolated from the liquid filling in the internal volume 21 by means of an isolator layer 34, an inert cover layer 24 which is provided on an inner side of the walls 28, and a second electrode 29 for applying an electric potential to the liquid filling. The electrically conductive layer 23 of the filter element 13 is coupled to a switching element which, in the present embodiment, is formed by a drain contact 30 of a field effect transistor 25 whose source contact 31 is coupled to a power supply circuit 26. The field effect transistor 25 is turned on, i.e. the switching element is closed, by means of a control voltage which is applied, via the control line 27, to a gate contact 32 of the field effect transistor 25. The electric voltage of the voltage line 26 is applied to the electrically conductive layer 23 by closing the switching element. When the voltage line is adjusted to the value of the xe2x80x9cfillingxe2x80x9d voltage, the contact angle xcex8 between the liquid filling 22 and the inert cover layer 24 decreases and the relevant filter element is filled with the liquid filling. FIG. 2b is a diagrammatic sectional view of the tubular filter element 113 of a filter as shown in FIG. 1 in case the filter element is filled with a liquid filling composed of an electrically conductive liquid component 122 and an X-ray absorbing liquid component 124 which is not miscible therewith. The liquid components are supplied via respective supply ducts 120 and 121. The other functional parts of the filter element 113 are substantially identical to those of the filter element 13, so that the control chart for the electrically conductive liquid component can be executed in a similar manner. This control chart determines the level of the electrically conductive liquid component 122 in the internal volume 21 of the filter element 113 which in its turn determines the level of the X-ray absorbing liquid component 124 in the filter element 113, because the respective components constitute one common liquid column with an interface 130. The degree of X-ray absorption is in this case determined by the degree of filling of the filter element 113 with the X-ray absorbing component 124. FIG. 3a is a diagrammatic cross-sectional view of a first embodiment of the tubular filter element 13. In this embodiment the filter element 13 has a circular cross-section whereas, generally speaking, the cross-section of the filter element may be a polygon. The filter element contains the liquid filling 22 which is in contact with the inert cover layer 24. The liquid filling is electrically isolated from the first electrode 23 by means of the isolator layer 34; this involves a capacitance per unit of surface area of the filter element. The electrode 23 is provided on a substrate 38. FIG. 3b is a 360xc2x0 view of the projection of the electrode 23 on the substrate 38. In order to enable local variation of the capacitance per unit of surface area in the longitudinal direction z of the filter element, the electrode 23 in this embodiment is subdivided into successive first electrode segments 37 and second electrode segments 39 of different surface area. The voltage line 27 enables application of the electric voltage to the electrode 23. FIG. 4 is a diagrammatic sectional view of a second embodiment of the filter element 13. The filter element in this embodiment is provided with an isolator layer which is composed of different isolator segments. The isolator layer 134 is subdivided into first isolator segments 136 and second isolator segments 138 which succeed one another in the longitudinal direction z of the filter element. The first isolator segment 136 has a dielectric constant which is higher than that of the second isolator segment 138, thus enabling a local variation of the capacitance per unit of surface area in the longitudinal direction of the filter element. This step enables the step-wise filling of the filter element 13 with the liquid filling 22. FIG. 5 is a diagrammatic sectional view of the third embodiment of the filter element 13 which is provided with an isolator layer composed of different isolator layer segments. The isolator layer 234 is subdivided into first isolator layer segments 236 and second isolator layer segments 238 which succeed one another in the longitudinal direction of the filter element. The thickness of the first isolator layer segment 236 is greater than that of the second isolator segment 238, thus enabling a local variation of the capacitance per unit of surface area in the longitudinal direction of the filter element. This step enables the step-wise filling of the filter element 13 with the liquid filling 22. In order to realize an optimum effect of this embodiment it is advantageous when the diameter of the tubular filter element 13 is reduced only slightly at the area of the first isolator layer segment 236. |
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043449140 | claims | 1. A retrievable and reinsertable nuclear reactor fuel pin having an end member for fastening said fuel pin to a transversely extending rail wherein said end member has a pair of blades having outer ends and facing surfaces defining a longitudinally extending slot therebetween for receiving said rail, said end member being formed at least in part of resilient material and having a configuration which requires wedging apart of said blades by said rail when said fuel pin is pulled away from said rail, the facing surfaces of said blades which define a first region of said slot are spaced apart a distance smaller than the spacing of the facing surfaces of said blades which define a second region of said slot, said first region of said slot being located closer to the outer ends of said blades than said second region of said slot, said facing surfaces of said blades defining a third region of said slot, said third region of said slot having a spacing of substantially constant distance between said facing surfaces and greater than the distance between said facing surfaces of said first region and being located closer to the outer ends of said blades than said first region. 2. A fuel pin as set forth in claim 1 wherein the facing surfaces of said blades additionally define an outer end region of said slot in which the facing surfaces are angled relative to each other to cause said outer end region of said slot to be of progressively greater width towards the ends of said blades. 3. A fuel pin as set forth in claim 2 wherein said ends of said blades are pointed. 4. A fuel pin as set forth in claim 1 wherein said end member has an end plug portion secured to said fuel pin and forming an end closure thereof and wherein said pair of blades extend from said end plug portion. 5. A fuel pin as set forth in claim 4 wherein said end member including said end plug portion and said pair of blades are a single integral element formed of said resilient material. 6. A fuel pin as set forth in claim 1 wherein said rail has a rounded surface of predetermined diameter which is received in said slot and wherein the facing surfaces of said blades which define said slot have a configuration and spacing which causes said first region of said slot to have a width smaller than said predetermined diameter and which causes said second region of said slot to have a wider curved profile substantially conforming to said rounded surface of said rail. 7. A fuel pin as set forth in claim 6 wherein said facing surfaces further define an inner region of said slot that is of less width than said predetermined diameter. 8. A fuel pin as set forth in claim 1 wherein said resilient material is formed to establish spring forces which prevent withdrawal of said fuel pin from said rail except by an axial force on said fuel pin which exceeds a pedetermined magnitude, said axial force of predetermined magnitude being greater than the maximum axial forces which may be exerted on said fuel pin during operation of said reactor. 9. A fuel pin as set forth in claim 1 wherein said second region of said slot defines a seat region in which said rail seats, and wherein said first region of said slot defines a land region of lesser width than said seat region, said blades being proportioned to cause release of spring tension from said resilient material when said rail seats in said seat region of said slot. 10. An end member for a nuclear reactor fuel pin which enables fastening of said fuel pin to a transverse attachment rail and withdrawal of said fuel pin from said rail by axial forces of greater than a predetermined magnitude, said end member having an end plug portion shaped to form an end closure for said fuel pin and further having a pair of spaced apart blade portions extending from said end plug portion and having facing surfaces forming a slot for receiving said rail, said facing surfaces in a land region thereof being spaced apart a distance less than the thickness of said rail, said facing surfaces in a subsequent rail receiving region which is closer to said end plug portion being spaced apart a greater distance than said land region, said facing surfaces in an outer end region which is further from said end plug portion than said land region being spaced apart over a non-tapering distance substantially equal to the spaced distance of the rail receiving region, at least said blades being formed of resilient material. 11. An end member for a nuclear reactor fuel pin as set forth in claim 10 wherein said end member including said end plug portion and said blades are formed as a single integral element of resilient metal. 12. An end member for a nuclear reactor fuel pin as set forth in claim 10 wherein said blade portions which are remote from said end plug portion include pointed tips and wherein said facing surfaces of said blade portions are divergent in the region of said tips. |
abstract | A method of characterizing surfaces comprises the steps of: directing a beam (2) of neutral atoms or molecules on a surface (3) for characterizing; and detecting in position-sensitive manner the neutral atoms or molecules of said beam that have been diffused forwards by said surface (3) for characterizing; |
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abstract | A drain sump of a reactor containment vessel having a containment vessel floor down below a reactor pressure vessel, and includes a heat-proof sump cover and two or more drain flow paths. The drain sump is arranged inside the containment vessel floor. The heat-proof sump cover has a thickness, and covers an upper part of the drain sump. The thickness allows a top surface of the sump cover to lie in the same surface as a top surface of the containment vessel floor. The drain flow paths pass through the sump cover in a thickness direction to flow water therethrough and solidify a molten corium therein. The molten corium is produced in the unlikely event of a severe accident. |
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043226221 | abstract | An achromatic magnetic deflection device for deflecting by an angle .phi. between .pi. and 2.pi. a beam of charged accelerated particles having different momentum. This device comprises an electromagnet provided with pole pieces delimiting three contiguous sectors, the whole of these sectors, having an axis of symmetry XX, presenting flat input E and output S faces and common faces F.sub.1 and F.sub.2 in an arc of a circle, the position, the radius of curvature of these faces F.sub.1, F.sub.2 as well as the value of the magnetic induction in the sectors being chosen so that the different paths are substantially orthogonal both to faces F.sub.1, F.sub.2 and to axis XX. |
claims | 1. A spent nuclear fuel rod canister, comprising:a submersible pressure vessel comprising a casing that defines an interior cavity, the casing comprising a corrosion resistant and heat conductive material;a rack enclosed within the interior cavity and configured to support one or more spent nuclear fuel rods;a riser that defines a fluid pathway between a top portion of the interior cavity and a bottom portion of the interior cavity;an annulus defined between the riser and the casing; anda heat exchanger attached to the casing of the pressure vessel,the heat exchanger comprising at least one conduit that is at least partially disposed exterior to the casing,the at least one conduit comprising an interior volume flowpath that is in fluid communication with the interior cavity of the pressure vessel,the at least one conduit comprisinga first conduit comprising an end of the interior volume flowpath that includes an opening located in the riser anda second conduit comprising an end of the interior volume flowpath that includes an opening located in the annulus. 2. The spent nuclear fuel rod canister of claim 1, further comprising:a first hemispherical enclosure coupled to the casing at a top end of the casing, the first hemispherical enclosure comprising a radiussed interior surface that defines a top portion of the interior cavity; anda second hemispherical enclosure coupled to the casing at a bottom end of the casing, the second hemispherical enclosure comprising a radiussed interior surface that defines a bottom portion of the interior cavity. 3. The spent nuclear fuel rod canister of claim 1, further comprising a fuel basket positioned in the interior cavity within the riser and near the bottom portion of the interior cavity. 4. The spent nuclear fuel rod canister of claim 3, wherein the fuel basket comprises:a perforated support plate adjacent a bottom surface of the rack, the fluid pathway fluidly coupled to the bottom portion of the interior cavity through the perforated support plate. 5. The spent nuclear fuel rod canister of claim 1, wherein the at least one conduit further comprises a third conduit comprising another end of the interior volume flowpath that includes an opening located in the annulus. 6. The spent nuclear fuel rod canister of claim 1, wherein the casing is configured to permit radiation from the one or more spent nuclear fuel rods therethrough. 7. The spent nuclear fuel rod canister of claim 2, wherein the end of the first conduit is positioned below a liquid level of a coolant that at least partially fills the interior cavity of the casing. 8. The spent nuclear fuel rod canister of claim 7, further comprising a fuel basket positioned in the interior cavity within the riser and near the bottom portion of the interior cavity. 9. The spent nuclear fuel rod canister of claim 8, wherein the fuel basket comprises:a perforated support plate adjacent a bottom surface of the rack, the fluid pathway fluidly coupled to the bottom portion of the interior cavity through the perforated support plate. 10. The spent nuclear fuel rod canister of claim 9, wherein the at least one conduit further comprises a third conduit comprising another end of the interior volume flowpath that includes an opening located in the annulus. 11. A method of dissipating decay heat generated by a spent nuclear fuel rod, the method comprising:loading at least one spent nuclear fuel rod into a rack positioned within an interior cavity of a spent nuclear fuel rod canister, the canister comprising:a submersible pressure vessel comprising a casing that defines an interior cavity that is at least partially filled with a fluid coolant,the casing comprising a corrosion resistant and heat conductive material,a rack enclosed within the interior cavity and configured to support one or more spent nuclear fuel rods, anda heat exchanger attached to the casing of the pressure vessel,the heat exchanger comprising at least one conduit that is at least partially disposed exterior to the casing,the at least one conduit comprising an interior volume flowpath that is in fluid communication with the interior cavity of the pressure vessel,the at least one conduit comprisinga first conduit comprising an end of the interior volume flowpath that includes an opening located in a riser that defines a fluid pathway between a top portion of the interior cavity and a bottom portion of the interior cavity anda second conduit comprising an end of the interior volume flowpath that includes an opening located in an annulus defined between the riser and the casing;submerging the spent nuclear fuel rod canister in a heat transfer fluid contained in a spent fuel pool;transferring decay heat from the spent nuclear fuel rod to the fluid coolant;circulating the heated fluid coolant through the riser and into the end of the first conduit;transferring the decay heat from the heated fluid coolant, through the casing, and to the heat transfer fluid in the spent fuel pool; andcirculating the fluid coolant from the end of the second conduit to and through the annulus. 12. The method of claim 11, wherein the fluid coolant is circulated through natural circulation. 13. The method of claim 11, further comprising exposing the casing of the spent fuel canister to ambient air. 14. The method of claim 13, further comprising:based on the exposure to ambient air, phase changing a portion of the fluid coolant from a liquid to a gas in the spent nuclear fuel rod canister; andphase changing the gas back to a liquid condensate on an interior surface of the casing based at least in part on heat transfer between the gas and the ambient air. 15. The method of claim 11, wherein transferring the decay heat from the heated fluid coolant, through the casing, and to the heat transfer fluid in the spent fuel pool comprises:convectively transferring the decay heat from the heated fluid coolant to the casing; andconvectively transferring the decay heat from the casing to the heat transfer fluid. 16. The method of claim 11, wherein a rate at which heat is transferred from the spent fuel rod is at least as great as a rate at which the spent nuclear fuel rod produces decay heat. 17. The method of claim 11, wherein the casing is configured to permit radiation from the at least one spent nuclear fuel rod therethrough. 18. The method of claim 11, wherein the at least one conduit further comprises a third conduit comprising another end of the interior volume flowpath that includes an opening located in the annulus. 19. The method of claim 18, further comprising circulating the fluid coolant from the end of the third conduit to and through the annulus. 20. The method of claim 19, wherein the fluid coolant is simultaneously circulated from the ends of the second and third conduits to the annulus. |
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description | This Application is a Continuation-in-Part of U.S. Ser. No. 09/990,532 filed Nov. 21, 2001. 1. Field of the Invention This invention relates to electronic commerce transactions. In particular, the invention relates to a system and method of secure electronic commerce transactions that provides for the tracking and recording of the distribution and usage of assets. 2. Description of Related Art Today, the term electronic commerce has come to be associated with the buying and selling of tangible assets (e.g. goods), services, and intangible digital assets over the Internet between a business and a connected computer user. Further, electronic commerce also typically involves some method of securing transactions, authorizing payments, and moving money between accounts. Electronic commerce also involves business-to-business transactions, expanding on the older and more traditional EDI (Electronic Data Interchange) techniques of exchanging purchase orders, invoices, and other documents in electronic form. EDI and other forms of business transactions have been taking place over public and private networks for some time. The financial system literally runs over the telecommunication network. For example, millions of stock market transactions take place everyday using electronic means. However, what is different with electronic commerce using the Internet, is that these transactions take place over public networks between buyers and sellers who may not have had any previous business relationship. The element of trust is missing and must be established in some way. Thus, electronic transactions need to be secure between the buyer and seller, which today, is not always the case. Nonetheless, the Internet today has become a gateway for connected users to purchase a wide variety of tangible assets, services, and intangible digital assets. Today, tangible assets such as books, CDs, home appliances, or any type of retail good, can now be purchased from a supplier over the Internet. Moreover, intangible digital assets such as music, videos, movies, multimedia, software, etc. can also increasingly be purchased over the Internet and downloaded to the connected user. With the Internet's 24-hr. availability, global reach, ability to interact and provide custom information and ordering, and multimedia interaction with customers, the use of the Internet is rapidly becoming a multi-billion dollar source of revenue for today's businesses that have a world-wide presence via the Internet. Desired security features for Internet based electronic commerce transactions include authenticating business transactors, controlling access to resources such as Web pages for registered users, encrypting communications, and, in general ensuring the privacy and effectiveness of transactions. Today, among the most widely used security technologies is the secure sockets layer (SSL), which is built into both of the leading Web browsers. SSL is a transport-level protocol developed by Netscape that provides channel security. With SSL, the client and server use a handshaking technique to agree on the level of security they want to use during a session. Authentication takes place over a secure channel, and all information transmitted during a session is encrypted. Unfortunately, even with the security features provided by SSL in conjunction with other security features commonly offered by Web-based businesses, proper security is still lacking. For example, often the ability to positively determine whether a transmission is from an authentic source or from someone or something masquerading as that source is often completely lacking in Internet based transactions. In most of today's Internet based transactions, a customer cannot be uniquely identified and authenticated by a Web-based businesses' server with a high degree of trust. Further, because of a lack of readily available techniques to uniquely identify a customer and to specifically encrypt digital assets (e.g. music, videos, movies, multimedia, software, etc.) for that uniquely identified customer, content owners have been hesitant to provide digital assets directly to potential customers over the Internet or to license digital assets to third party providers who can then provide them to customers over the Internet—due to the fear of unauthorized duplication of the digital asset. Moreover, techniques are not readily available to track and record the purchase, rental, and number of uses of digital assets by a customer, either directly by the content owner, or indirectly by a third party provider. Accordingly, it is difficult for a third party provider to accurately report transactions regarding licensed digital assets to the ultimate content owner for licensing fees (e.g. royalty tracking). This further limits the potential benefit of the Internet to be used to sell and provide digital assets to customers and to provide a secure revenue opportunity for content providers (especially the ultimate content owner (i.e. the copyright holder)). The present invention relates to electronic commerce transactions. In particular, the invention relates to a system and method for electronic commerce transactions that provides for tracking the usage of rented digital assets over a computer network. In one embodiment, the server includes an asset database. The asset database stores a digital asset, the title of the digital asset, and a server usage count for the digital asset. The server is coupled to a computing device through a computer network. The computing device stores a rented digital asset. The computing device further stores an asset usage count list that includes the title of the rented digital asset and a usage count that indicates the amount of usage of the rented digital asset by the computing device. The server uploads the asset usage count list from the computing device and matches the title of the rented digital asset from the asset usage count list of the computing device with the title of the same digital asset stored in the asset database. Further, the server adds the usage count of the rented digital asset from the asset usage count list of the computing device to the server usage count for the digital asset in the asset database. In this way, the server can determine the amount of usage of rented digital assets by computing devices. The system and method as previously described can be used either directly by a content owner to track the distribution and use of rented digital assets or by a third party provider to track the distribution and use of rented digital assets and further in order to keep an accounting of licensing fees (e.g. royalties) due to the content owner. In the following description, the various embodiments of the present invention will be described in detail. However, such details are included to facilitate understanding of the invention and to describe exemplary embodiments for implementing the invention. Such details should not be used to limit the invention to the particular embodiments described because other variations and embodiments are possible while staying within the scope of the invention. Furthermore, although numerous details are set forth in order to provide a thorough understanding of the present invention, it will be apparent to one skilled in the art that these specific details are not required in order to practice the present invention. In other instances details such as, well-known methods, types of data, protocols, procedures, components, networking equipment, processes, interfaces, electrical structures, circuits, etc. are not described in detail, or are shown in block diagram form, in order not to obscure the present invention. Furthermore, aspects of the invention will be described in particular embodiments but may be implemented in hardware, software, firmware, middleware, or a combination thereof. Referring now to FIG. 1, FIG. 1 shows a block diagram illustrating an exemplary system 100 to deliver a multimedia presentation of an audio file to a computing device 102, according to one embodiment of the present invention. One or more servers 104 are coupled to computing device 102 through a computer network (e.g. the Internet) 105. In one embodiment, in response to a user selecting a musical piece at a computing device 102, server 104 transmits a session file associated with the musical piece to the computing device 102 through the computer network (e.g. the Internet) 105. The session file includes a digital audio file and multimedia data. The computing device 102 processes the session file to present the multimedia presentation of the audio file to the user, as will be discussed. The server or server(s) 104 are also coupled through network connections to an asset database 107 that stores session files, and other assets, and a user information database 109 that stores information related to users, as will be discussed. An interface device 106, including a security device 110, is connected to the computing device 102 and the user's musical instrument 112 (e.g. a guitar). The interface device 106 couples the musical instrument 112 to the computing device 102 over an input/output (I/O) link 114 (e.g. a Universal Serial Bus link) such that the user can play the musical instrument 112 in conjunction with a multimedia presentation of the digital audio file being processed by the computing device 102. Furthermore, the interface device 106 can be connected an analog sound device, such as amplified speakers 120 or headphones 122, to play the audio file associated with selected musical piece along with sound from the user's musical instrument 112, as the user plays along with his or her musical instrument. More specifically, the interface device 106 performs analog to digital (A/D) conversion of the audio signal from the musical instrument 112 and transmits the digitized audio signal of the musical instrument 112 via I/O link 114 to the computing device 102 where the digitized audio signal of the musical instrument 112 may undergo digital signal processing (DSP) performed by a software module to create a processed digital audio signal of the musical instrument, for example, to tailor it to the audio file of the musical piece that was selected by the user. The computing device 102 creates a mixed digital signal of both the digital audio file and the processed digital signal of the musical instrument, which is transmitted back from the computing device 102 along I/O link 114 to the interface device 106, where the mixed digital signal is converted to analog form (D/A conversion) into a mixed analog audio signal that is outputted through an analog sound device, such as speakers 120 or headphones 122. Thus, a user can play along with the downloaded musical piece, which is presented in a multimedia presentation format on the computing device, to facilitate learning by the user. Moreover, as will be discussed, the user is provided with quick and easy access to a wide variety of musical pieces that they can download from the server 104. It should be appreciated by those having skill in the network-related arts that computing device 102 and the server(s) 104 may be coupled to the computer network 105 in a variety of ways including through direct or dial-up telephone or other network transmission lines, using a modem pool (not illustrated), or through an additional network and gateway (not illustrated). For example, the computing device 102 can communicate with a server 104 via a link utilizing one or more of the plain old telephone system (POTS), a cellular phone system, cable, Digital Subscriber Line, Integrated Services Digital Network, satellite connection, computer network (e.g. the Internet, a wide area network (WAN), or a local area network (LAN), etc.), or generally any sort of private or public telecommunication system, and combinations thereof. Examples of a transport medium for the links include, but are not limited or restricted to electrical wire, optical fiber, cable including twisted pair, or wireless channels (e.g. radio frequency (RF), terrestrial, satellite, or any other wireless signaling methodology). More particularly, the computer network 105 is typically a computer network (e.g. the Internet, a wide area network (WAN), or a local area network (LAN), etc.), which is a packetized, packet-switched, connection oriented, etc., network that can utilize Transmission Control Protocol/Internet Protocol (TCP/IP), Asynchronous Transfer Mode (ATM), Frame Relay (FR), Point-to Point Protocol (PPP), Systems Network Architecture (SNA), Voice over Internet Protocol (VoIP), or any other sort of protocol. The computer network 105 allows the communication of data traffic between the computing device 102 and the server(s) 104 using packets. Data traffic through the network computer 105 may be of any type including audio, text, graphics, video, e-mail, Fax, multimedia, documents, voice, and other generic forms of data. The computer network 105 is typically a data network that may contain switching or routing equipment designed to transfer digital data traffic. It should be appreciated that the FIG. 1 environment is only exemplary and that embodiments of the present invention can be used with any type of telecommunication system and/or computer network, protocols, and combinations thereof. Moreover, the network connections between the server(s) 104 and the asset database 107 and user information database 109 can also be coupled in ways exemplified by the previously described examples. Having briefly described an exemplary network environment in which embodiments of the present invention can be practiced, FIG. 2a illustrates a conventional data processing or computer system 200 useable with embodiments of the present invention. More particularly, FIG. 2a illustrates an example of a general data processing or computing system 200 for use as an exemplary computing device 102 (e.g. personal computer) or server computer system 104, in which various aspects of the present invention may be utilized. As illustrated, data processing or computer system 200 is comprised of a system unit 202, output devices such as display device 204 and printer 210, and input devices such as keyboard 208, and mouse 206. Data processing system 200 receives data for processing by the manipulation of input devices 208 and 206 or directly from fixed or removable media storage devices such as disk 212 and network connection interfaces (not illustrated). Data processing system 200 then processes data and presents resulting output data via output devices such as display device 204, printer 210, fixed or removable media storage devices like disk 212 or network connection interfaces. It should be appreciated that the computing device 102 can be any sort of computer system or computing device (e.g. personal computer (laptop/desktop), network computer, handheld computing device, server computer, or any other type of computer). Moreover, in the case of the computing device 102, the data processing system 200 includes a serial I/O port 113 (e.g. a USB port) to accommodate input and output data from the interface device 102 through I/O link 114 (e.g. a USB link). Referring now to FIG. 2b, there is depicted a high-level block diagram of the components of a data processing system 200 such as that illustrated by FIG. 2a. In a conventional computer system, system unit 202 includes a processing device such as processor 220 in communication with main memory 222 which may include various types of cache, random access memory (RAM), or other high-speed dynamic storage devices via a local or system bus 214 or other communication means for communicating data between such devices. The processor processes information in order to implement the functions of the embodiments of the present invention. As illustrative examples, the “processor” may include a central processing unit having any type of architecture such as complex instruction set computers (CISC), reduced instruction set computers (RISC), very long instruction word (VLIW), or hybrid architecture, or a digital signal processor, a microcontroller, a state machine, etc. Main memory 222 is capable of storing data as well as instructions to be executed by processor 220 and may be used to store temporary variables or other intermediate information during execution of instructions by processor 220. Computer system 200 also comprises a read only memory (ROM) and/or other static storage devices 224 coupled to local bus 214 for storing static information and instructions for processor 220. Examples of non-volatile memory 224 include a hard disk, flash memory, battery-backed random access memory, Read-only-Memory (ROM) and the like whereas volatile main memory 222 includes random access memory (RAM), dynamic random access memory (DRAM) or static random access memory (SRAM), and the like. System unit 202 of data processing system 200 also features an expansion bus 216 providing communication between various devices and devices attached to the system bus 214 via bus bridge 218. A data storage device 228, such as a magnetic disk 212 or optical disk such as a CD-ROM or DVD and its corresponding drive may be coupled to data processing system 200 for storing data and instructions via expansion bus 216. Computer system 200 can also be coupled via expansion bus 216 to a display device 204, such as a cathode ray tube (CRT) or a liquid crystal display (LCD), for displaying data to a computer user such as generated meeting package descriptions and associated images. Typically, an alphanumeric input device 208, including alphanumeric and other keys, is coupled to bus 216 for communicating information and/or command selections to processor 220. Another type of user input device is cursor control device 206, such as a conventional mouse, trackball, or cursor direction keys for communicating direction information and command selection to processor 220 and for controlling cursor movement on display 204. Moreover, in the case of the computing device 102, the data processing system 200 includes a serial I/O port 113 (e.g. a USB port) to accommodate input and output data from the interface device 106 through serial I/O link 114 (e.g. a USB link). A communication device 226 is also coupled to bus 216 for accessing remote computers or servers, such as server 104, or other servers via the Internet, for example. The communication device 226 may include a modem, a network interface card, or other well-known interface devices, such as those used for interfacing with Ethernet, Token-ring, or other types of networks. In any event, in this manner, the computer system 200 may be coupled to a number of servers 104 via a network infrastructure such as that illustrated in FIG. 1 and described above. In continuing with the example of the conventional data processing or computer system 200, both the computing device 102 and server 104 may operate under the control of an operating system that is booted into the memory of the device for execution when the device is powered-on or reset. In turn, the operating system controls the execution of one or more software modules or computer programs. These software modules typically include application programs that aid the user in utilizing the computing device 102 and the server 104, and the various functions associated with delivering a multimedia presentation of an audio file to a computing device 102 for display to user, and to allow the user to play a musical instrument in conjunction with the multimedia presentation, as well as, other functions related to security and commerce methods, as will be discussed. These functions can be implemented as one or more instructions (e.g. code segments), to perform the desired functions of the invention. When implemented in software (e.g. by a software module), the elements of the present invention are the instructions/code segments to perform the necessary tasks. The instructions which when read and executed by a machine or processor (e.g. processor 220), cause the machine or processor to perform the operations necessary to implement and/or use embodiments of the invention. The instructions or code segments can be stored in a machine readable medium (e.g. a processor readable medium or a computer program product), or transmitted by a computer data signal embodied in a carrier wave, or a signal modulated by a carrier, over a transmission medium or communication link. The machine-readable medium may include any medium that can store or transfer information in a form readable and executable by a machine (e.g. a processor, a computer, etc.). Examples of the machine readable medium include an electronic circuit, a semiconductor memory device, a ROM, a flash memory, an erasable programmable ROM (EPROM), a floppy diskette, a compact disk CD-ROM, an optical disk, a hard disk, a fiber optic medium, a radio frequency (RF) link, etc. The computer data signal may include any signal that can propagate over a transmission medium such as electronic network channels, optical fibers, air, electromagnetic, RF links, etc. The code segments may be downloaded via networks such as the Internet, Intranet, etc. Turning now to FIG. 3a, FIG. 3a illustrates a top view of an interface device 106, according to one embodiment of the present invention. The interface device 106 couples the musical instrument 112 to the computing device 102 over the input/output (I/O) link 114 such that the user can play a musical instrument 112 in conjunction with a multimedia presentation of the audio file being processed by the computing device 102. As shown in the top view of FIG. 3a, the interface device 106 includes a volume dial or knob 304 to adjust the volume of the musical instrument 112 and the audio file and an LED indicator 308 to indicate interface device operating status (i.e. whether power is on or off). The interface device 106 can include a metal, plastic, or metallized plastic housing to contain the internal electronic components. Turning briefly to FIG. 3b, which illustrates a front view of the interface device 106, according to one embodiment of the invention, the interface device includes an input port 310 to receive an input jack (or other input device) from a musical instrument 112 such that the musical instrument is electrically coupled to the interface device 106. Referring now to FIG. 3c, FIG. 3c illustrates a back view of the interface device 106, according to one embodiment of the present invention. The interface device 106 includes left and right speaker output ports 320 and 322 that can be used to accept speaker jacks for amplified speakers 120 so that the interface device 106 can be connected to amplified speakers. This allows a user playing his or her musical instrument 112 to hear both the musical instrument as well as an audio file associated with the musical piece being processed by the computing device 102. Furthermore, the interface device 106 includes an additional line in port 323. For example, the additional line in port 323 can be used to support input from a sound card of the computing device 102 such that sounds from games and other software programs from the computing device 102 can simply be routed through the interface device 106 to the speakers 120 or headphones 122. Also, interface device 106 includes a headphone output port 326 that can be used to accept a headphone jack for headphones 122 to allow the user to listen to his or her musical instrument 112, as well as the audio file, using headphones 122. The interface device 106 further includes a serial I/O port 330 (e.g. a USB port) to accept an I/O connector (e.g. a USB connector) such that the I/O link 114 (e.g. a USB link) can be formed between the interface device 106 and the computing device 102. It should be appreciated that the interface device 106 can also include any number of other input and outputs. Turning now to FIG. 3d, FIG. 3d is a schematic view of the internal components 334 of the interface device 106, according to one embodiment of the present invention. The interface device 106 includes a microprocessor 340 that controls components of the interface device 106 to perform functions related to A/D and D/A conversion of signals between the musical instrument 112 and the computing device 102, as well as security functions utilizing a security device 110, as will be discussed in more detail later. As shown in FIG. 3d, the interface device 106 includes an instrument in line from input port 310 that is connected to an amplifier 336. Thus, as an example, an analog audio signal from a musical instrument 112 coming in from input port 310 is amplified by amplifier 336. The amplifier 336 is connected to an analog to digital (A/D) converter 338 such that the amplified analog audio signal is processed by the A/D converter 338 and is converted into a digitized audio signal of the musical instrument. The microprocessor 340 of the interface device 106 is coupled to components of the security device 110, a buffer RAM 344, and a digital audio interface 346. The microprocessor 340 controls components 334 of the interface device 106 to perform functions related to A/D and D/A conversion of signals between the musical instrument 112 and the computing device 102. The digital audio interface 346 performs conventional functions related to formatting and timing the digitized audio signals. The digital audio interface 346 may include a number of timing clocks to perform these functions. Thus, continuing with the present example, the digitized audio signal of the musical instrument 112 is next formatted by the digital audio interface 346. Further, the digital audio interface 346 is coupled to a buffer RAM 344 that is used to store portions of the digitized audio signal for rate matching. Moreover, the buffer RAM 344 is connected to the microprocessor 340 and a serial I/O controller 348. The serial I/O controller 348 controls the flow of digital data to and from the computing device 102 along serial I/O link 114. In one example, the serial I/O controller 348 can be a USB controller and the serial I/O link 114 can be a USB link. The digital data controlled by the serial I/O controller 348 can include the digitized audio signal coming directly from the musical instrument 112 which is being sent to the computing device 102 for digital signal processing (DSP) and the mixed digital signal of both the processed digital audio signal of the musical instrument that has undergone DSP by the computing device 102 and the digital audio file associated with selected musical piece coming from the computing device 102. However, it should be appreciated that the digitized signal of the musical instrument does not have to be passed through the computing device 102 for DSP processing and can be passed straight through to the DAC 350 and onto the analog sound device such that the user can still play along with an audio file. The buffer RAM 344 is also used to store the digital audio signal of the musical instrument (pre-DSP processing), the digital audio file, and the mixed digital signal, for conventional purposes, such as rate matching. The digital audio interface 346 is further connected to a digital to analog converter (DAC) 350. The mixed digital signal of both the processed digital audio signal of the musical instrument and the digital audio file from the computing device 102 are processed by the DAC 350 to convert this mixed digital signal into analog form, i.e. a mixed analog audio signal, such that the mixed analog audio signal can be played back through an analog sound device, such as amplified speakers 120 or headphones 122. However, as previously discussed, it should be appreciated that the digitized signal of the musical instrument does not have to be passed through the computing device 102 for DSP processing and can be passed straight through to the DAC 350 and onto the analog sound device such that the user can still play along with an audio file. Connected to the outputs of the DAC 350 is a mixer 352. The mixer 352 receives analog audio signal inputs from other line in sources such as the line in port 323, which are amplified by amplifiers 358 and 360, respectively, such that they can also be played through the amplified speakers 120 or headphones 122. These additional analog audio signal inputs from line in port 323 can be mixed with the analog audio signal of the musical instrument and the audio file or can simply be routed through the interface device to the speakers 120 or headphones 122. For example, the additional line in inputs from line in port 323 can be from a sound card of the computing device 102 such that sounds from games and other software programs from the computing device 102 can simply be routed through the interface device 106 to the speakers 120 or headphones 122. In this way, other software programs can still be used with the interface device 106 hooked up to the computing device 102 (e.g. a personal computer), and the user does not have to reconfigure his or her personal computer system to switch between using the interface device and not using the interface device. The analog signals from the mixer 352 are then passed through line outs (e.g. left and right) 360 and 362 via speaker ports and 320 and 322 to the amplified speakers 120. Particularly, the analog signals can be amplified by amplifiers 364 and 366 under the control of a volume controller 368, which is in turn controlled by the volume dial 304. Similarly, the analog signals from the mixer 352 are also passed through the line outs 360 and 362 (e.g. left and right) via headphone port 326 to the headphones 122. Likewise, the analog signals can be amplified by amplifiers 374 and 376 under the control of the volume controller 368, which is in turn controlled by the volume dial 304. Thus, the interface device 106 couples a musical instrument 112 to a computing device 102 over an input/output (I/O) link 114 such that the user can play a musical instrument 112 in conjunction with a multimedia presentation of an audio file being processed by the computing device 102. More specifically, as previously described, the interface device 106 performs analog to digital (A/D) conversion of the audio signal from the musical instrument 112 and transmits the digitized audio signal of the musical instrument via I/O link 114 to the computing device 102 where the digitized audio signal of the musical instrument 112 may undergo digital signal processing (DSP) performed by a software module (e.g. to tailor it to the audio file of the musical piece that was selected by the user). A mixed digital signal of both the digital audio file and the processed digital signal of the musical instrument is transmitted back from the computing device 102 along I/O link 114 to the interface device 106 where the mixed digital signal is converted to analog form (D/A conversion), i.e. a mixed analog audio signal, which is outputted through the speakers 120 or headphones 122. Thus, a user can play along with the downloaded musical piece, which is presented in a multimedia presentation format on the computing device, as will be discussed later, to facilitate learning by the user. Interface device 106 also includes a security device 110. The security device 110 includes components that can be utilized to uniquely identify the interface device 106 to the server 104 such that access to the server 104 is only granted to a user operating with an authorized interface device. Moreover, the security device 110 in conjunction with the server 104, is used to ensure that audio files are properly encrypted and decrypted such that only a properly authorized interface device 106 can receive and utilize audio files. This protects against unauthorized duplication of licensed material and provides a secure revenue opportunity for content (e.g. audio file) providers. The security device includes a microprocessor 340, a secure memory 379 having security logic 380, program storage 382 to store security firmware 383, and nonvolatile memory (e.g. EEPROM) 384. Generally, the security firmware 383 when executed by the microprocessor 340 in conjunction with the secure memory 379 and the nonvolatile memory 384, provide for secure operations that allow the server 104 to uniquely identify the interface device 106 and allow the computing device 102 in conjunction with the interface device 106 to decrypt audio files specifically encrypted for use by the authorized interface device 106. The secure memory 379 includes both read-only memory (ROM) and writeable memory, which can be locked and unlocked for reading and writing using the hardware implemented security logic 380. A unique identifier, such as user key 387, associated with serial number 386 of the interface device 106 is used by the security logic 380 to authenticate the interface device 106 to the server 104. Also, a memory key 389 is used by the security logic 380 to initially unlock the secure memory 379. The serial number 386, user key 387, and memory key 389 are sealed in the secure memory 379 during manufacturing and thereafter can no longer be written over once the secure memory 379 is sealed. The serial number 386, user key 387, and memory key 389 are also stored at the server's user information database 109 so that the server 104 can initially generate a challenge and response to uniquely authenticate the interface device 106 and open and lock the secure memory 379 and the nonvolatile memory 384, as will be discussed in more detail later. The nonvolatile memory 384 is used as an extension to the secure memory 379. The firmware 383 prevents access to the nonvolatile memory 384 unless the secure memory 379 has also been unlocked. The nonvolatile memory 384 has hardware write protection, which is controlled by the firmware 383. The nonvolatile memory 384 stores keys 388 such as asset encryption keys (e.g. audio file keys) associated with particular purchased assets (e.g. audio files), the current date and subscription dates for certain assets 390, and asset information (e.g. information about assets) 392. It should be appreciated that the serial number 386, the user key 387, the memory key 389, keys 388, the dates 390, the asset information 392 and even the firmware 383 can instead be located or co-located at any of the security device memories: program storage 382, secure memory 379, or nonvolatile memory 384; this particular arrangement being only one embodiment. As will be discussed in more detail later, the security device 110 in conjunction with the computing device 102 and the server 104, allow the server 104 to uniquely identify the interface device 106 and allow the computing device 102 in conjunction with the interface device 106 to decrypt audio files specifically encrypted for use by the authorized interface device 106, along with many other functions. FIG. 4 is a block diagram illustrating a more detailed view of the exemplary system 100 to deliver a multimedia presentation of an audio file to a computing device 102, showing typical software modules utilized, according to one embodiment of the present invention. Briefly, as previously discussed, server(s) 104 are coupled to computing device 102 through a computer network (e.g. the Internet) 105. Further, an interface device 106 is coupled to the computing device 102 and a musical instrument 112 is coupled to the interface device. In one embodiment, in response to a user selecting the musical piece at a computing device 102, server 104 transmits a session file associated with a musical piece to the computing device 102 through the computer network (e.g. the Internet) 105. The session file includes an audio file and multimedia data. The computing device 102 processes the session file to present the multimedia presentation of the audio file to the user such that a user can play a musical instrument 112 in conjunction with a multimedia presentation of the audio file being processed by the computing device 102. More particularly, as shown in FIG. 4, the computing device 102 and server 104 each include a plurality of software modules that enable the functions of the embodiments of the present invention. These software modules typically include application programs that aid the user in utilizing the computing device 102 and the server 104, and the various functions associated with delivering a multimedia presentation of an audio file to a computing device 102 for display to user, and to allow the user to play a musical instrument in conjunction with the multimedia presentation, as well as, other functions related to security and commerce methods, as will be discussed. For example, the computing device 102 includes an application software module 402 that further includes an embedded browser 404, an audio playback software module 406, and a security software module 408. Further the computing device 102 includes a device driver software module 410 and an audio DSP software module 412. On the server side, the server 104 includes a server software module 415, an application software module 416, a database software module 418, a commerce software module 420, and a security software module 422. The application software module 402 of the computing device 102 interfaces and controls the implementation of the embedded browser 404 and all the other software modules (e.g. the audio DSP software module 412, the audio playback software module 406, the device driver software module 410 and the security software module 408) such that the embodiments of the invention related to displaying a multimedia presentation of an audio file to a user to allow the user to play a musical instrument in conjunction with a multimedia presentation, as well as other functions related to security and commerce functions, are properly implemented. In one embodiment, the application software module 402 in conjunction with the embedded browser 404 initially displays a Web page (e.g. a home page) to the user providing the user with a multitude of musical pieces from which to select. The embedded browser 404 is specifically tailored for the application software module 402 and its various functions and can be based on any type of conventionally known browsers such as Microsoft Explorer. The application software module 402 also causes the display of a control panel graphical interface for a musical instrument 112 that includes settings that define sound characteristics for the musical instrument. The control panel graphical interface also allows the user to set sound characteristics for the musical instrument 112. Further, in response to the multimedia data of the session file for a selected musical piece (e.g. selected by the user) sent to the computing device 102 by the server 104, the application software module 402 sets the settings of the control panel graphical interface to predefined values to model the sound characteristics of the musical instrument associated with the audio file for the musical piece selected by the user. Also, the application software module 402 can play a musical piece selected by the user (e.g. and sent from the server 104 to the computing device 102), that has a track associated with the user's musical instrument removed from the audio file, such that the user can play his or her musical instrument 112 in conjunction with a multimedia presentation of the audio file that does not include the user's musical instrument. Moreover, the application software module 402 processes the multimedia data of the session file to cause the display of music notation associated with the audio file of the musical piece to the user. The display of the multimedia presentation may occur on a display device 204 of the computing device 102 and sound can be routed through the amplified speakers 120 of the interface device 106. In order to accomplish these functions, the application software module 402 utilizes a conventional device driver software module 410, an audio DSP software module 412, and an audio playback software module 406. The audio DSP software module 412 processes the audio signal of the musical instrument 112 (e.g. utilizing DSP algorithms) such that the user can set the sound characteristics for the musical instrument. As previously described, the audio DSP software module 412 can be utilized by the application software module 402 to set the settings of the control panel graphical interface to predefined values to model the sound characteristics of the musical instrument such that it is properly associated with a musical piece selected by the user. Furthermore, the audio DSP software module 412 combines both the digital audio file and the processed digital audio signal of the musical instrument to create the mixed digital audio signal, previously discussed. Moreover, the application software module 402 controls an audio playback software module 406 to control the transmission of the mixed digital signal of the digital audio file and the digitally processed sound of the musical instrument 112 back to the interface device 106 where it is played back through amplified speakers 120 or headphones 122 to the user. However, the application software module 402 can also control the audio playback software module 406 to control the transmission of only the digital audio file, in the case where the musical instrument is only routed through the interface device 106 and not the computing device 102 for processing. It should be appreciated audio DSP software modules for a variety of different musical instruments are known in the art. For example, general types of DSP software modules that can alter MIDI files are well known (e.g. MIDI SHOP). Also, audio playback software modules that are used to playback audio files and audio signals from musical instruments are also well known. In one particular embodiment, that will hereinafter be used to describe aspects of the present invention, the application software module 402, the audio DSP software module 412, the Web page the user logs on to, and the control panel graphical interface are directed to support a guitar as the musical instrument 112. In particular, it should be appreciated that DSP algorithms for altering the audio signals from a guitar are known in the art and can be easily implemented in software on the computing device 102. For example, one example of DSP algorithms for altering the audio signals from a guitar to model various amplifiers and speaker cabinet configurations which may be used in the audio DSP software module 412 to implement aspects of the present invention are particularly described in U.S. Pat. No. 5,789,689 entitled “Tube Modeling Programmable Digital Guitar Amplification System”, which is hereby incorporated by reference. Moreover, a wide variety of software implemented control panel graphical interfaces for a multitude of different instruments are known, and there are some basic control panel graphical interfaces known for guitars, e.g. AMP FARM includes one type of software implemented control panel graphical interface for a guitar. However, none of them include many of the novel and non-obvious features of the guitar control panel graphical interface to be described in more detail later. Furthermore, the aspects of the security software module 408 of the computing device 102 will also be described in more detail later. In one embodiment of the present invention, the server 104 includes a server software module 415, an application software module 416, a database software module 418, a commerce software module 420, and a security software module 422. The application software module 416 interfaces and controls the implementation of the server software module 415 and all the other software modules (e.g. the database software module 418, the commerce software module 420, and the security software module 422), at the server 104 such that the embodiments of the invention related to displaying a multimedia presentation of an audio file to a user to allow the user to play a musical instrument in conjunction with the multimedia presentation, as well as other functions related to security and commerce functions, are properly implemented. At the server 104, the application software module 416 in conjunction with the server software module 415 provides the computing device 102 with the data necessary to implement the functions of the invention, as will be discussed. The server software module 415 can be conventional server software for transmitting and receiving data to and from computing devices 102. For example, using the Hypertext Transfer Protocol (HTTP) and Hypertext Markup Language (HTML) or Extensible Markup Language (XML), the server 104 can communicate with the computing device 102 across the computer network 105 to provide various functions and data to the user. At the computing device 102, utilizing the embedded browser 404, which is part of the application software module 402, or even other browsers such as Netscape™ Navigator™ published by Netscape™ Corporation of Mountain View, Calif., the Internet Explorer™ published by Microsoft™ Corporation of Redmond, Wash., the user interface of America Online™, or any other browser or HTML/XML translator from a well-known supplier, computing device 102 may supply data to, and access processed or unprocessed data from, the server 104. According to one embodiment of the present invention, as previously discussed, the server software module 415 under the control of the application software module 416 transmits a session file to the computing device 102 through the computer network 105, in response to user selecting a musical piece at the computing device 102. The session file includes an audio file and multimedia data such that the computing device 102 can process the session file to present a multimedia presentation to the user to allow the user to play his or her musical instrument 112 (e.g. a guitar) in conjunction with the multimedia presentation of the audio file. Moreover, as will be discussed, the server software module 415, under the control of the application software module 416, receives and transmits a variety of different types of data to and from the computing device 102 to implement the functions of the invention. The database software module 418 can be conventional database software, such as MySQL, to control the input and output of data from the asset database 107 and the user information database 109, under the control of the application software module 416, as will be discussed in more detail later. Furthermore, the aspects and functions of the commerce software module 420 and security software module 422 will be discussed in more detail later. The data communicated between the server 104 and the computing device 102 includes session files having multimedia data and audio files, user information, commerce information to track the purchases and licensing restriction of audio files and other items, security information including encrypted keys and encrypted asset and audio files, multimedia data for the presentation of a Web-site, along with a multitude of other data. Much of the information related to session files, multimedia data, audio files, commerce information, and other assets, as will be discussed, may be stored in the asset database 107. User information including the user's name, email address, home address, computer connection speed, credit card number, subscription information, type of computer, the type of musical preferences the user has, and security information including a user's serial number for his or security device 110, user key, memory key, and other user information, as will be discussed, may be stored in the user information database 109. It will be readily appreciated by those having ordinary skill in the relevant arts that the asset database 107 and user information database 109 may be stored in storage devices including various mass storage devices such as one or more DASD arrays, tape drives, optical drives, or the like, and that the aforementioned information may be stored in any one of a variety of formats or data structures. In one particular embodiment, that will hereinafter be used to describe some of the aspects of the present invention, the computing device 102, the server 104 and its associated asset and user information databases 107 and 109, and the interface device 106, along with the associate software modules, are used to support a guitar 112 as the musical instrument. However, it should be appreciated by those skilled in the art that the present invention may be used to support any type of musical instrument. Moreover, it should be appreciated that the present invention can also support the case where a microphone is used as the musical instrument and the input audio signal is a human voice such that embodiments of the invention could operate as a virtual karaoke machine. These aspects will be further appreciated after a further reading of the disclosure. With reference also to FIG. 5a, FIG. 5a is a flowchart illustrating a method 500 for delivering a multimedia presentation to a user, according to one embodiment of the present invention, utilizing the previously described exemplary system 100 of FIG. 4. At block 502, after a user has loaded the application software module 402 onto his or her computing device 102, the application software module 402 presents the user with a control panel graphical interface 600 as shown in FIG. 6a. For example, the control panel graphical interface 600 can be displayed on the display device 204 of the computing device 102. Next, the computing device 102 utilizing the application software module 402 permits the user to log onto the server 104 and to access the server. Thus, the application logs the user onto the server. According to one particular guitar embodiment, to be discussed hereinafter, the server presents the user a Web-site related to guitars, hereinafter termed the GUITARPORT Web-site. Thus, the user is first presented with a GUITARPORT homepage and other GUITARPORT Web pages thereafter. With reference also to FIG. 6a, logging on to the server 104 can be accomplished by the user selecting the GUITARPORT online button 606. For example, the computing device 102 can contact the server 104 through the computer network (e.g. the Internet) utilizing standard computer network protocols (e.g. TCP/IP). At block 506, the server 104 under the control of the application software module 416 and in conjunction with the security software module 422 identifies the user based on a unique identifier from the security device 110 (e.g. the Serial No. of the interface device 106) to determine whether access to the server 104 should be authorized. These security features will be discussed in more detail later. If the user is not authorized by the server 104, then the session is terminated at block 508. However, if the user is authorized to utilize the server 104, then the method 500 moves on to block 510. At block 510, the application software module 402 utilizing the embedded browser 404 displays the server the GUITARPORT homepage received from the server 104, as shown in FIG. 6b. The GUITARPORT homepage is initially displayed beneath the guitar control panel graphical interface 600. With reference also to FIG. 6b, the GUITARPORT homepage includes Features, News, Discussion, User Page, Guitar Tools, Musical Pieces (e.g. Newest Jamtracks), and Tones. The GUITARPORT homepage will be particularly discussed later. Moreover, based on user information for the user (e.g. particularly the musical preferences of the user) stored in the user information database 109 at the server 104, the server 104 can particularly tailor the GUITARPORT homepage to fit the musical preferences of the user. For example, if a user prefers rock-and-roll then the Newest Jamtracks (e.g. musical pieces) will be directed towards rock-and-roll musical pieces, as well as, particular rock-and-roll Tones. Further, the other components of the GUITARPORT homepage can also be geared to the user's preference, for example, News, Features, etc. At block 512, the user is allowed to select a Tone or a musical piece (e.g. a Jamtrack). If the user selects a tone then the method 500 proceeds to FIG. 5b at block 514. On the other hand, if the user selects a musical piece (e.g. a Jamtrack) the method 500 proceeds to FIG. 5c at block 516. A Jamtrack is one type of musical piece that can be downloaded from the server 104. To aid in the explanation of methods of the invention and associated control panel interfaces, some of the control panel graphical interfaces will now be discussed. Referring now to FIG. 6a, FIG. 6a is a screenshot particularly illustrating the control panel graphical interface for a guitar 600. As previously discussed, the application software module 402 generates the control panel graphical interface 600, and in conjunction with the audio DSP software module 412, allows the user to change the settings of the control panel graphical interface (or the settings can be set to predefined settings determined by a session file or a predefined patch) such that the audio DSP software module 412 processes the audio signal from the guitar 112 to match the desired settings. The settings of the control panel graphical interface 600 for a guitar will now be described. The control panel graphical interface 600 includes a plurality of standard control knobs 604 common to most guitar amplifiers including: a drive control knob 606, a bass control knob 608, a middle control knob 610, a treble control knob 612, a presence control knob 614, and a volume control knob 616. These control knobs are selectable by the user to change the sound of the guitar. The control panel graphical interface 600 further includes a boost switch 620 to increase the power of the audio signal from the guitar. A bypass button 622 when selected turns off the DSP processing such that the straight unprocessed audio signal from the guitar is used. A compare button 624 when selected allows two different control panel graphical interface configurations to be compared side by side. A collapse button 628 when selected reduces the size of the control panel graphical interface 600. A mute guitar button 630 when selected mutes the audio signal from the guitar. The Master Volume dial 632 controls both the volume of the audio signal of the guitar 112 and the volume of any other audio signals (e.g. from an audio file) currently being processed. Selection of the hum reducer button 634 allows the user to reduce the hum interaction between the guitar 112 and the display device 204. Once the hum reducer button 634 is selected and the learn button 636 is depressed, the computing device 102 measures the hum interaction between the guitar 112 and the display device 204 (e.g. the user can move his or her guitar next to the display device) and DSP processing will compensate for the hum interaction and remove it. The noise gate button 638 when selected attenuates the input audio signal from the guitar, if it is below a threshold level, but does not attenuate the audio signal from the guitar if it is above the threshold level. Thus, the noise gate button 638 may be used to get rid of such things as guitar handling noise. A guitar pan slide 640 may be used to pan the sound of the guitar between the left and right speakers. Further, as previously discussed, the user may select a tone or a tone may be automatically selected for the user to go along with the musical piece selected by the user. The type of tone selected is showing in the tone field 642. Any number of tones representing amplifier models based on most any type of guitar amplifier (e.g. MARSHALL, FENDER, VOX, ROLAND, etc.), most any type of speaker cabinet, and most any type of effect can be reproduced. For example, tones for the Hells Bells rhythm section by AC/DC, a heavy funk rock lead, a '64 Fender Deluxe, or any other tone may be selected (e.g. see Top 10 Tones 685 (FIG. 6b)) or created by the user. In particular, it should be appreciated that DSP algorithms for altering the audio signals from a guitar 112 are known in the art and can be easily implemented in software on a computing device 102. For example, one example of DSP algorithms for altering the audio signals from a guitar to model various amplifiers and speaker cabinet configurations which may be used in the audio DSP software module 412 to implement aspects of the present invention is particularly described in U.S. Pat. No. 5,789,689 entitled “Tube Modeling Programmable Digital Guitar Amplification System”, which is hereby incorporated by reference. Typically, a tone can be defined by the guitar amplifier, the speaker cabinet, and a number of different effects, as well as other settings. Again the tone can be selected by the user, created by the user, or can be preset to go along with the selected musical piece. The type of guitar amplifier tone being modeled is shown in the amplifier model field 644 (e.g. '90 Marshall JCM-800). The speaker cabinet configuration tone being modeled is shown in the speaker cabinet model field 646 (e.g. 4×12 '78 Marshall with Stock 70s). The speaker cabinet configuration 646 emulates the effects of a speaker cabinet on the amplified guitar sound. Further, a number of a digitally reproduced well known effect boxes are provided by the control panel graphical interface 600 to create tones. Particularly, a compression effect box 650, a delay effect box 652, a modulation effect box 654 (e.g. including chorus, flanger, rotary, tremolo, etc.), and a reverb effect box 656 are provided. Effect boxes are typically found in additional digital audio instrument processors that are coupled to a guitar and a standard amplifier. Also, this particular control panel graphical interface 600 shows that the delay effect box 652 is currently selected and shows specific attributes of the delay effect such as delay time 660, feedback percentage 662, and level percentage 664. Moreover, as previously discussed, a user can log on to the GUITARPORT Web-site by selecting the GUITARPORT online button 606. Turning now to FIG. 6b, FIG. 6b is a screenshot of the display illustrated to the user when they successfully log on to the server 104, according to one embodiment of the present invention. Particularly, the application software module 402 and the embedded browser 404 display the GUITARPORT homepage 670 received from the server 104, which is located below the control panel graphical interface 600, and in conjunction with the data received from the server 104, perform many of the functions requested by the user. It should be noted that control panel graphical interface 600 is the same as that shown in FIG. 6a, except that in this instance, the compression effects box has been selected and a compression effects window (e.g. allowing for the selection of different compression ratios) is shown. As shown in FIG. 6b, the GUITARPORT homepage 670 includes a Home button 671, a Features button 672, a News button 673, a Discussion button 674, a Users button 675, and a Guitar Tools button 676. When the home button 671 is selected by a user, the user is returned to the GUITARPORT homepage. Depression of the Features button 672 brings the user to a Features page, which includes such things as interviews with artists, studio notes, and other articles related to the field of music that the user may find useful. Selection of the News button 673 brings the user to a News page that provides news articles related to the field of music and guitars in particular. When the user picks the Discussion button 674, the user is brought to a bulletin board that allows users to post messages (e.g. questions, answers, news, articles, etc.) in any subject but is usually related to music and guitars in particular. Selection of the Users button 675 provides the user with a user page that allows the user to update their user profile (e.g. name, address, type of subscription, musical preferences, etc.). Depression of the Guitar Tools button 676 brings the user to a utility page that provides the user with information related to guitar playing, for example: what is the figuring for a C chord, how do I set up my amplifier, etc. This can be accomplished by frequently asked questions (FAQ) listings, a searchable database, email questions to a guitar technician, etc. The GUITARPORT homepage can also be populated with selectable icons representing links to new articles, interviews, news, chords, guitar licks, Newest Jamtracks (e.g. musical pieces), and the most popular Tones. For example, FIG. 6b shows selectable Studio Notes icon links 678 and 679, a selectable Interview icon link 680, a selectable Today's News icon link 681, a Chord of the Week icon link 682, and a Lick of the Week icon link 683, as well as, Newest Jamtracks (e.g. musical pieces) links 684, and Tone links 685. Moreover, as previously discussed, the GUITARPORT Web-site can be particularly tailored to a user based on user information (e.g. particularly the musical preferences of the user) stored in the user information database 109 at the server 104. With this information, the server 104 can particularly tailor the GUITARPORT Web-site to fit the musical preferences of the user. For example, if a user prefers rock-and-roll, then the Newest Jamtracks 684 (e.g. musical pieces) will be directed towards rock-and-roll musical pieces as well as particular Tones 685. Further, the other components of the GUITARPORT Web-site can also be geared to the user's preference, for example, Studio Notes, Interviews, News, Chord of the Week, Lick of the Week, etc. Further, the control panel graphical interface 600 has some selectable buttons that interact with the GUITARPORT Web-site. As shown in FIG. 6b, the GUITARPORT online button 606 to connect to the GUITARPORT Web-site is already depressed. An Artist and Gear button 687 is provided, and when selected, provides a user a list of artists from which they can choose, such that the user can find articles written about the artist providing artist biographies and the type of musical gear that they use. The tracks button 688 when selected, provides the user a list of musical pieces (e.g. Jamtracks) that the user can select. In response to a user selecting a musical piece (e.g. Jamtrack), the server 104 transmits a session file associated with the selected musical piece to the computing device 102 through the computer network (e.g. the Internet) 105. The session file includes an audio file and multimedia data. The computing device 102 processes the session file to present a multimedia presentation of the audio file to the user, as will be discussed. The Tone button 689 when selected, provides the user a list of tones that the user can select. In response to a user selecting a tone, the server 104 transmits patch information (e.g. type of amplifier, speaker cabinet, effect settings, etc.) such that the control panel graphical interface 600 is properly configured and the DSP software module 412 properly processes the guitar signal to emulate the proper tone. However, it should be appreciated that with or without a connection to the GUITARPORT Web-site, the user can utilize previously stored tones and musical pieces (e.g. Jamtracks). Also, the control panel graphical interface 600 has a tuner button 690 that when selected, allows the computing device to act as a chromatic tuner such that user can tune his guitar. The control panel graphical interface 600 also has a Help button 691 that when selected provides standard Help features to the user. Further, the control panel graphical interface 600 has standard Back and Forward arrows 692 and 693 that allow the user to toggle back and forth through previously visited web pages of the GUITARPORT Web-site. As previously discussed, if the user selects a Tone then the method 500 proceeds to FIG. 5b (block 514). For example, the user can select one of the Tones provided by selecting the Tones button 689 or one of the Top Tones 685 (e.g. Heavy Funk Rock Lead (FIG. 6b)). Turning to FIG. 5b, FIG. 5b is a flowchart illustrating a method 501 of providing a tone to a user, according to one embodiment of the present invention. In response to a user selecting a tone, the server 104 transmits patch information (e.g. type of amplifier, speaker cabinet, effect settings, etc.) to the computing device 102 (block 518). The application software module 402 sets the control panel graphical interface 600 to the proper configuration to model the sound characteristics of the tone for the musical instrument (e.g. the guitar) (block 520). Further, the DSP software module 412 properly processes the guitar audio signal to emulate the proper tone. Thus, the user can play his or her guitar 112 connected through the interface device 106 to the computing device 102 in the proper tone. For example, patches can represent guitar tones for various recording artists (e.g. Jimi Hendrix, Eric Clapton, Jerry Garcia, Chet Atkins, Robert Cray, etc.) or can be particularly created for the GUITARPORT Web-site to represent various guitar styles—rock, country, jazz, etc. As previously discussed, if the user selects a musical piece then the method 500 proceeds to FIG. 5c (block 516). For example, the user can select one of the musical pieces (e.g. Jamtracks) provided by selecting the Tracks button 688 or one of the Newest Jamtracks 684 (e.g. Welcome to the Jungle (FIG. 6b)). Turning to FIG. 5c, FIG. 5c is a flowchart illustrating a method 503 of providing a musical piece to a user according to one embodiment of the present invention. Particularly, in response to a user selecting a musical piece (e.g. Jamtrack), the server 104 transmits a session file associated with the selected musical piece (e.g. Jamtrack) to the computing device 102 through the computer network (e.g. the Internet) 105 (block 524). The session file includes an audio file and multimedia data. Turning briefly to FIG. 5d, FIG. 5d illustrates the contents of a session file 539, according to one embodiment of the present invention. The session file 539 includes an audio file 540 associated with the musical piece (e.g. Jamtrack). The audio file 540 of the musical piece is typically a song that the user wants to play along with. The audio file 540 can be the full song (i.e. with all the instrument tracks and vocal tracks). Alternatively, the audio file 540 can have one or more tracks removed, for example: one or more guitar tracks can be removed, one or more vocal tracks can be removed, one or more bass tracks can be removed, one or more drum tracks can be removed, etc. For example, as will be discussed, the user can select a musical piece (e.g. Jamtrack) with the guitar track removed such that the audio file 540 is played by the computing device 102 and the interface device 106 (e.g. through the amplified speakers 120), with the guitar track removed, so that the user can play along with the song with the guitar track removed. Further, the session file 539 has a multimedia block 542, which includes HTML data embedded with JavaScript to represent and display multimedia information to the user. Particularly, with brief reference to FIG. 6c, which will be discussed in more detail later, the multimedia data can be processed by the application software module 402 and the embedded browser 404 of the computing device 102 (along with other software modules of the computing device 102) to represent the name of the song or musical piece 601, and the music notation 603 associated with the lead sheet 605, such that the user can play along with the audio file 540 being played. The multimedia data block 542 also includes all the other necessary data to achieve these functions. The session file 539 also includes a patch block 544 that includes patch information such that the guitar 112 has the proper tone or sound to go along with the associated selected musical piece/audio file 540. The patch information includes the type of amplifier, speaker cabinet, effect settings, etc., such that the guitar settings of the control panel interface 600 are set to go along with the selected musical piece/audio file. The application software module 402 sets the control panel graphical interface 600 to the proper configuration to model the sound characteristics of the tone for the guitar for the particular musical piece/audio file 540. Further, the DSP software module 412 properly processes the guitar signal to emulate the proper tone such that the guitar sound goes along with the musical piece/audio file 540. Moreover, the session file 539 includes a MIDI file 546 that represents the tempo changes, program changes, key signature changes, position markers, etc., for the selected musical piece/audio file 540. MIDI files are well known in the art. The computing device 102 (e.g. utilizing the application software module 402) interprets the tempo map from the MIDI file during playback to convert the current audio playback position to the corresponding audio file position in the MIDI file for the purpose of determining what events in the MIDI file should occur. Program changes from the MIDI file are used to select patch information 544 to select amplifier, speaker cabinet, and effects settings, etc., for the amplifier controls of the control panel graphical interface 600 that are needed for the particular position in the audio file (e.g. the particular tone for the guitar being emulated using the DSP software module 412). Key signature changes from the MIDI file 546 are used for displaying the current key signature to the user. Markers of the MIDI file 546 are used to cause display events at various points in the musical piece. Each marker in the MIDI file 546 is assigned a text label. The label corresponds to a JavaScript function to be executed when the label is reached. For example, turning briefly to FIG. 6c, the musical piece (e.g. Jamtrack) LA Smooth Jazz in C 601, and it's associated lead sheet 605 with musical notation 603 has been selected by user and is shown. Associated with the LA Smooth Jazz musical piece are MIDI markers. The text labels 609 for the MIDI markers 607 are displayed above the musical notation 603 and come from the MIDI file 546 of the session file 539. In this example, the text labels 609 of the MIDI markers 607 represent different portions of the musical piece/audio file 540, as shown: Intro, Verse, Bridge, Chorus, Solo 1, etc. For example, a MIDI marker 607 may have the text label 609 “Chorus”. The MIDI marker 607 for the text label 609 “Chorus” causes the music notation 603 (e.g. chords, notes, guitar tablature, and lyrics, etc.) to be displayed whenever the chorus of the song begins. As another example, as shown in FIG. 6c, the music notation 603 for the Intro (e.g. chords) is shown. Thus, when the computing device 102 receives a MIDI marker 607 from associated session file 539, it processes the MIDI marker utilizing JavaScript, which looks up the corresponding function and executes the script for it. The JavaScript typically loads a picture or draws something on the display device. In this example, the JavaScript displays the musical notation 603 (e.g. chords) for the Intro of the selected musical piece, LA Smooth Jazz in C when it receives the MIDI marker 607 for the “Intro”. Returning to FIG. 5c, illustrating method 503, at block 528, the session file 539 (e.g. the audio file 540 and the rest of the multimedia data) is processed to present a multimedia presentation of an audio file 540 to the user (e.g. including musical notation 603). This allows the user to play a guitar 112 in conjunction with the multimedia presentation of the audio file 540 (block 530). Referring also to FIG. 6c, the computing device 102 can display pictures, text, and graphics during playback (e.g. on the display device 204). For example, the computing device can display musical notation 603 such that while the musical piece/Jamtrack (e.g. including audio file 540) plays, the current position within the musical pieces is displayed, typically along with other information: such as the lyrics, the key signature, and guitar tablature (e.g. chords, notes, figuring diagrams, etc.), and a user is allowed to play his or her guitar 112 in conjunction with the multimedia presentation of the audio file 540. For example, in the present example of FIG. 6c, the musical piece (e.g. Jamtrack) LA Smooth Jazz in C 601, and it's associated lead sheet 605 with musical notation 603, has been selected by user and is display on the GUITARPORT Display 671. In this example, the text labels 609 of the MIDI markers 607 are displayed and represent different portions of the musical piece/audio file 540, as shown: Intro, Verse, Bridge, Chorus, Solo 1, etc. As shown in FIG. 6c, the music notation 603 for the Intro (e.g. chords) is shown. In this example, the JavaScript displays the musical notation 603 (e.g. chords) for the Intro of the selected musical piece, LA Smooth Jazz in C when it receives the MIDI marker 607 for the “Intro”. Accordingly, the user can play his or her guitar 112 in conjunction with the musical notation 603 and the audio file 540. As the audio file 540 progresses, the musical notation 603 can be automatically updated (e.g. to next portion of the musical piece—Bridge, Chorus, solo, etc.) such that the user can read the musical notation and play along. Moreover, the user can choose versions of the musical piece/audio file 540 with and without a guitar track to enable learning and jamming. Further, as previously discussed, musical pieces/audio files can be chosen that have the vocals, drums, bass, etc., removed. Further, a patch block 544 that includes patch information such that the guitar 112 has the proper tone or sound to go along with the associated musical piece/audio file 540. The patch information includes the type of amplifier, speaker cabinet, effect settings, etc., such that the guitar settings of the control panel interface 600 are set to go along with the selected musical piece/audio file and can even accommodate changes within the musical piece itself. This can be triggered by the MIDI markers, as previously discussed. The application software module 402 sets the control panel graphical interface 600 to the proper configuration to model the sound characteristics of the tone for the guitar for the particular musical piece or portion of the musical piece and the DSP software module 412 properly processes the guitar signal to emulate the proper tone such that the guitar sound goes along with the musical piece/audio file 540. As previously discussed, the user's guitar is electrically routed through the computing device 102, allowing the computing device 102 to control the sound of a guitar during playback so that the amplifier model, its settings and any effects can change dynamically as required throughout the musical piece/audio file 540. As shown in FIG. 6c, an amplifier model based on a '90 Marshall JCM-800 amplifier with a Delay setting is used to emulate a jazz sound to go along with the Intro. for the selected LA Smooth Jazz in C musical piece. Thus, matching patches for each portion of a musical piece/Jamtrack are automatically provided, for example to go from one tone during the Chorus and to another tone during the Solo. Looking at FIG. 6c, particular aspects of the GUITARPORT Display 671 will be discussed to point out other particular features of the invention. As shown, the Tracks button 688 has been selected, and the musical piece LA Smooth Jazz in C 601 has been particularly selected by the user. Accordingly, the LA Smooth Jazz in C's 601 associated lead sheet 605 with musical notation 603 is further displayed on the GUITARPORT Display 671. Below the selected musical piece (e.g. Jamtrack) LA Smooth Jazz in C 601 are buttons that control the way musical pieces can be selected. The Web Load button 611 allows a user to select a musical piece from the GUITARPORT Web-site and load it onto the user's computing device 102 (e.g. store it in local memory). The Hard Disk button 613 allows a user to select a musical piece already stored locally at the computing device 102 (e.g. on the user's hard disk). The CD button 615 allows a user to select a musical piece from a CD in the CD drive of the user's computing device 102. When a song is selected on the CD, the GUITARPORT server 104 determines if it has an associated session file 539 for the song, and if so, if a user so chooses, provides the multimedia presentation of the song (e.g. patch file, musical notation, etc.) to the user. The Jam button 617, when selected by the user, begins the multimedia presentation of a musical piece (e.g. Jamtrack), previously discussed, such that the user can jam along. The Mixer Slide 619 controls the volume of the musical piece. The Autoselect On/Off button 621 can be used to toggle between using the pre-defined patch settings for the control panel graphical interface 600 (i.e. the amplifier settings) automatically selected for the currently playing multimedia presentation (e.g. Autoselect On), as opposed to, the user setting the control panel graphical interface 600 settings (i.e. the amplifier settings) themselves to their own liking (e.g. Autoselect Off). A typical timer display 623 for musical pieces (e.g. Jamtracks) and loops is provided along with conventional digital multimedia control features 625 (e.g. play, record, stop, rewind, fast forward, etc.). A Lick Learner button 627, when selected, slows down the tempo of the currently playing musical piece (e.g. Jamtrack), without altering the pitch, to facilitate learning. Also, a Loop button 629 is provided, that when selected, loops (i.e. plays repeatedly), a current portion of a musical piece/Jamtrack (e.g. Intro, Chorus, etc.) to facilitate learning that portion of the musical piece. Moreover, track details 631 can be selected which provides information about the musical piece. For example, when it was recorded, information about the artists, what type of guitars, amplifiers, and effects that were used. Also, credits 633 can be selected which provides information about where the musical piece came from, e.g. Sony, Arista, etc., or whether the musical piece was specifically created (and by who) for the GUITARPORT Web-site. For example, musical pieces (e.g. Jamtracks) can be custom-created to facilitate the learning of particular types of music—e.g. rock, blues, jazz, country, etc.—exclusively for the GUITARPORT Web-site. Accordingly, the present invention allows a user to couple his or her guitar 112 into the computing device 102, via the interface device 106, such that he or she can download tones and musical pieces from the GUITARPORT Web-site. The interface device 106 along with a subscription is required to obtain the online subscription services (e.g. downloading the musical pieces and tones). The interface device 106 uniquely identifies the user and, in conjunction with the rest of system 100, is used to authorize the user, encrypt and decrypt audio files, and to track the purchases of assets, as will be discussed in more detail later. Moreover, in response to a user selecting a musical piece (e.g. Jamtrack), the server 104 transmits a session file 539 associated with the musical piece to the computing device 102 through the computer network 105. The session file 539 includes an audio file and multimedia data such that the computing device can process the session file to present the multimedia presentation of the audio file to the user. The computing device 102 processes the session file 539 to present the multimedia presentation of the audio file to the user (e.g. including scrolling music notation 603) such that a user can play his or her guitar 112 in conjunction with the multimedia presentation of the audio file. Furthermore, an intuitive control panel graphical interface 600 for the guitar resembling familiar guitar equipment is provided. The control panel graphical interface 600 includes an amplifier panel with standard controls, allowing the user to select from several different types of amplifiers to achieve different tones. Also, a set of effect boxes is also provided. As previously described, users can listen to musical pieces while viewing musical notation 603 (e.g. chords, notes, tablature (fingering diagrams), lyrics, etc.). These musical pieces can include both commercial musical pieces and musical pieces created exclusively for use by the GUITARPORT Web-site to facilitate the learning of the guitar. Users can jam along with versions of a musical piece with and without the original guitar track to facilitate practice. Thus, users are provided quick and easy access to a wide variety of musical pieces (e.g. Jamtracks) that they can download from a server 104, and the user can then play along with the downloaded musical piece, which is presented in a multimedia presentation format to facilitate learning. Users can be provided with access to hundreds or thousands of musical pieces (e.g. Jamtracks) in a range of different styles. Musical pieces may include the following: pre-existing sound recordings; remixes of pre-existing sound recordings (example without the guitar track or vocal tracks); re-recorded versions of previously published copyrighted songs; original songs produced for the GUITARPORT Web-site (e.g. songs created to facilitate the learning of guitar); drum loops; grooves, etc. Furthermore, grooves (e.g. rhythm sections, drumbeats, etc.) can be provided to facilitate jamming and practice. Moreover, the GUITARPORT Web-site can also provide for the sale of many other music related assets, besides musical pieces (e.g. Jamtracks), such as: CDs by a multitude of recording artists, printed sheet music, tablature, guitar notation, chord charts, lyrics, digital sheet music, T-shirts, music memorabilia etc. Additionally, as will be discussed in detail later, each unique musical piece or tone downloaded, or any type of purchase, is tracked and recorded for accurate reporting to content licensing partners (e.g. the copyright owner). Embodiments of the present invention further provide a security device 110 to uniquely identify a user and to decrypt encrypted assets for use by the computing device 102. Thus, the security device protects against unauthorized duplication of licensed material and provides a secure revenue opportunity for content providers. Typically assets relate to musical pieces (e.g. Jamtracks) including audio files (e.g. copyrighted sound recordings), however, it should be appreciated that assets can be any sort of data (e.g. multimedia, video, movies, voice, software, generic data forms, etc.) transmitted over a computer network. As will be discussed in more detail later, the security device 110 in conjunction with the computing device 102 and the server 104, allow the server 104 to uniquely identify the security device 110 and allow a computing device 102 coupled to the authorized security device 110 to decrypt assets specifically encrypted for use by the authorized security device 110, along with many other functions. As will be discussed, the security device 110 includes an embedded electronic Serial No. and user key that is combined with hardware encryption and key storage circuitry, to uniquely identify each security device 110 to the server 104, and to ensure that assets will only operate with a computing device 102 coupled to an authorized security device thereby providing a secure revenue opportunity for content providers. Referring now to FIG. 7a, FIG. 7a illustrates a security system 700, according to one embodiment of the present invention. As previously discussed, the server 104 is coupled through the computer network 105 (e.g. the Internet) to the computing device 102, and the computing device 102 is in turn connected through an I/O link 114 (e.g. a USB link) to a security device 110. Shown to highlight the security aspects of the security system 700, the server 104 includes the security software module 422, the application software module 416, the server software module 415, the database software module 418 and, not shown here, the commerce software module 420. Moreover, coupled to the server 104 through computer network connections are the asset database 107 and the user information database 109. Further shown to highlight the security aspects of the security system 700, the computing device 102 includes the application software module 402 including the security software module 408 and security hardware interface software 704. The security device 110 includes security services 706 and security components 710 to implement the security services 706. Moreover, local asset storage 712, for example local memory such as a hard drive is coupled through I/O link 714 to the computing device 102 or is part of the computing device 102. Local asset storage 712 can be used to store assets (e.g. audio files) previously downloaded by the user. The security device 110 includes security components 710 that can be utilized to implement security services 706. Such security services 706 include uniquely identifying the security device 110 to the server 104 such that access to the server 104 is only granted to a user operating with an authorized security device 110. Another security service 706, performed by the security device 110 in conjunction with the server 104, is to ensure that assets (e.g. audio files) are properly encrypted and decrypted such that only a computing device 102 coupled to properly authorized security device 110 can receive and utilize assets. Looking particularly at the server 104, the server 104 includes the security software module 422 that contains security programs and algorithms for performing security functions, as will be discussed. The security software module 422 coordinates information from a clock/calendar of the server 104 and the various databases—i.e., the user information database 109 and the asset database 107, to authenticate users and deliver encrypted assets to authenticated users. The clock/calendar is a typical part of a server computer 104 that allows it to accurately determine the date and time. Further, the server 104 operates in secure operating environment (e.g. utilizing secure sockets layer (SSL), S-HTTP, etc). The user information database 109 includes subscription and registration information for each user who is registered to access the server 104 (e.g. in one embodiment, a GUITARPORT Web-site subscriber) and who also has an authorized security device 110. The subscription information for each user includes the expiration date for the user's subscription and the user's unique serial number for his or her security device 110, user key, and memory key, which are needed for determining the authenticity of each security device 110 and for encrypting and decrypting assets, as will be discussed. It should be noted that the unique user serial numbers stored at both the server and the security devices, respectively, may consist of digits, letters, printable characters, binary codes, alphanumeric codes, or basically any sort of designator for unique identification. The asset database 107 contains assets (e.g. multimedia presentations associated with musical pieces and audio files, and as previously discussed Jamtracks including full songs and songs with various instrumental tracks removed), as well as any other sort of digital data asset. Moreover the asset database 107 includes unique asset encryption keys for each asset (e.g. each audio file). Further, it should be appreciated that the asset database 107 can include any other assets that can be purchased or rented and downloaded to a computing device 102 over a computer network 105. Looking particularly at the computing device 102, the computing device 102 particularly includes the application software module 402 and the security software module 408. The security software module 408 includes standard encryption and decryption routines to encrypt and decrypt assets, as will be discussed. Any suitable block mode cipher that utilizes pseudo-random generators to XOR pseudo-random numbers with data can be used. Some examples include Data Encryption Standard (DES), International Date Encryption Algorithm (IDEA), etc. Further, the security software module 408, as will be discussed later, allows the computing device 102 to be used as a conduit for interaction between the server 104 and the security device 110 and to particularly authenticate the service device 110. However, the application software module 402 and the security software module 408 are not assumed to execute in a secure operating environment. The security hardware interface software 704 provides a standard input/output interface (e.g. a USB interface) between the computing device 102 and the security device 110. Furthermore, the computing device uses a standard clock/calendar (i.e. common to most all computing devices) that allows the application software module 402 to accurately determine the date and time for interactions between the computing device 102 and the security device 110. Looking particularly at the security device 110 and referring now to FIG. 7b, FIG. 7b illustrates the pertinent security components 710 of the security device 110 according to one embodiment of the present invention. As shown in FIG. 7b, the security device 110 includes a microprocessor 340, a secure memory 379 having security logic 380, program storage 382 to store security firmware 383, and nonvolatile memory 384 (e.g. EEPROM). Also, an I/O controller 716 controls the flow of digital data to and from the computing device 102 along serial I/O link 114. In one example, the serial I/O controller 716 can be a USB controller and the serial I/O link 114 can be a USB link. The digital data controlled by the serial I/O controller 716 can include keys, asset information and other data, as will be discussed. Generally, the security firmware 383 when executed by the microprocessor 340 in conjunction with the secure memory 379 and the nonvolatile memory 384, provide for secure operations that allow the server 104 to uniquely identify the security device 110 and allow the computing device 102 in conjunction with the security device 110 to decrypt assets specifically encrypted for use by a computing device 102 coupled to the authorized computing device 102. The secure memory 379 includes both read-only memory (ROM) and writeable memory, which can be locked and unlocked for reading and writing using the hardware implemented security logic 380. As previously discussed, a unique identifier, such as user key 387, associated with serial number 386 of the security device 110 is used by the security logic 380 to authenticate the security device 110 to the server 104. Also, a memory key 389 is used by the security logic 380 to initially unlock the secure memory 379. The serial number 386, user key 387, and memory key 389 are sealed in the secure memory 379 during manufacturing and thereafter can no longer be written over once the secure memory 379 is sealed. The serial number 386, user key 387, and memory key 389 are also stored at the server's user information database 109 so that the server 104 can initially generate a challenge and response to uniquely authenticate the security device 110 and open and lock the secure memory 379 and the nonvolatile memory 384, as will be discussed in more detail later. The nonvolatile memory 384 is used as an extension to the secure memory 379. The firmware 383 prevents access to the nonvolatile memory 384 unless the secure memory 379 has also been unlocked. The nonvolatile memory 384 has hardware write protection, which is controlled by the firmware 383. The nonvolatile memory 384 stores keys 388 such as asset encryption keys (e.g. audio file keys) associated with particular purchased assets (e.g. audio files), the current date and subscription dates for certain assets 390, and asset information (e.g. information about assets) 392. It should be appreciated that the serial number 386, the user key 387, the memory key 389, keys 388, the dates 390, the asset information 392 and even the firmware 383 can instead be located or co-located at any of the security device memories: program storage 382, secure memory 379, or nonvolatile memory 384; this particular arrangement being only one embodiment. Moreover, as will be discussed, the security software of the server 104, computing device 102, and the firmware of the security device 110, include standard encryption and decryption routines to encrypt and decrypt assets, keys, dates and other data sent between these devices. Any suitable block mode cipher that utilizes pseudo-random generators to XOR pseudo-random numbers with data can be used. Some examples include Data Encryption Standard (DES), International Date Encryption Algorithm (IDEA), etc. Various security functions implemented by the combination of the server 104, computing device 102, and security device 110, will now be discussed with reference to the flowcharts of FIGS. 8a–8i. One of the security functions to be performed is that the server 104 uniquely identifies a security device 110 to ensure that the computing device 102 coupled to security device 110 is authorized to access the server 104 and its many functions (e.g. in one embodiment, the GUITARPORT Web-site). Further, the server 104 determines the authenticity of the security device 110 to prevent unauthorized access to the server 104 and its assets (e.g. audio files). This is done when a user initially tries to log on to the server 104 and can be performed periodically thereafter. This authentication process includes the server 104 issuing a coded challenge to the security device via a scripting language performed by the security software module 422 of the server 104. The firmware 383 of the security device 110 executes a program to generate a response. An authorized security device 110 will return a unique response, which the server 104 utilizing the security software module 422 will validate. If the response is valid for the specific security device 110, the session is continued. If the response is not valid, the session is terminated. Turning to FIG. 8a, FIG. 8a is a flow diagram illustrating a process 800 for the server 104 to authenticate the security device 110, according to one embodiment of the present invention. These process steps 800 are generally implemented by the security software module 422 of the server 104 in conjunction with the other software modules at the server. First, the server 104 requests a unique identifier, such as the Serial No. 386, stored in the secure memory 379 of the security device 110 from the security device 110 (block 802). In response to the received Serial No., at block 803, the server determines whether the Serial No. is in the user information database 109. If not, the session is terminated (block 805). However, if the Serial No. is in the user information database 109, then the server 104 obtains the user key for the Serial No. from the user information database 109 (block 806) . As previously discussed, the user information database 109 stores a unique user key for each Serial No. associated with each security device 110. The server 104 also obtains a time and date from the clock/calendar of the server 104, which will be used later to see if the subscription is expired (block 808). Next, the server 104 computes a challenge (block 810) and the expected response from the security device 110 (block 812). The challenge/response sequence is basically a request for the security device 110 to accurately identify itself to the server by sending an appropriate response. In one embodiment, the challenge is a random or pseudo-random number generated by the server 104 and can be based on the current time and date (e.g. as a seed value). The expected response is created at the server 104 by performing a mathematical transformation on the user key 387 associated with the security device 110 and the challenge. Both the server 104 and the security device 110 utilize the same mathematical transformation and have the same user key 387 such that the response generated at the security device 110 should be the same as the expected response created at the server 104 (assuming it actually is the security device associated with the serial number for the user). In one embodiment, the common mathematical transformation of the server 104 and security device 110 can be any suitable one-way hashing function. The challenge is then sent from the server 104 to the security device 110 (block 814). The server 104 then waits for the response from the security device 110 (block 816). If a predefined period of time passes, the process 800 is timed out, and the session is terminated (block 817). However, if a response is received within the predefined period of time, the server 104 determines whether the response from the security device 110 matches the expected response (block 818). If not, the session is terminated (block 819). If so, the user is allowed to log on to the server 104 and the process 800 is complete (block 821). For example, the use can access the GUITARPORT Web-site, previously discussed. Referring now to FIG. 8b, FIG. 8b is a flow diagram illustrating a process 822 for the security device 110 to respond to the authentication challenge from the server 104, according to one embodiment of the present invention. These process steps 822 are generally implemented under the control of the firmware 383 of the security device 110. First, the user key 389 is obtained from the secure memory 379 (block 824). Next, at block 826, the response to the challenge is computed. As previously described, the response is typically a mathematical transformation (e.g. a one-way hashing function), common to both the server 104 and security device 110, of the user key 389 (again, common to both the server 104 and security device 110) and the challenge. The response to the challenge is then sent to the server 104 (block 828). The process 822 is then complete (block 830). Other security functions implemented by the combination of the server 104, computing device 102, and security device 110, relate to updating the current date and the subscription expiration date stored at the security device 110. The current date and the subscription expiration date 390 are stored in nonvolatile memory 384 of the security device 110. The server 104 updates both the subscription expiration date and the current date 390 in the security device 110. However, the application software module 402 of the computing device 102 also updates the current date 390 when the server 104 is not connected. Because the application software module 402 is not considered secure, the server 104 updates the subscription expiration date and the current date 390, when it is connected, to maintain security. Turning to FIG. 8c, FIG. 8c is a flow diagram illustrating a process 832 for the server 104 to update the security device 110 with the current date and the subscription expiration date, according to one embodiment of the present invention. These process steps 832 are generally implemented by the security software module 422 of the server 104 in conjunction with the other software modules at the server 104. First, the subscription expiration date from the user information database 109 is obtained for the user (block 834). Next, the current date from the clock/calendar of the server 104 is obtained (block 836). The subscription expiration date and the current date are then encrypted (block 838). Further, the server 104 sends a command to the security device 110 to unlock the security device memory 721 including the nonvolatile memory 384 (block 840). FIG. 8d, as will be discussed, describes the process of unlocking the security device memory 721. Based on a response from the security device 110 as to whether the security device memory 721 has been successfully unlocked, the server 104 determines whether the unlock operation was successful or not (block 842). If the security device memory 721 was not successfully unlocked, the process 832 fails (block 844). However, if the security device memory 721 was successfully unlocked, then the server 104 sends the encrypted subscription expiration date and the current date to the security device 110 where the security device 110 updates the dates (block 846). FIG. 8e, as will be discussed, describes the process of the security device 110 updating the dates. The server then sends a command to the security device to lock the security device memory 721 (block 848). FIGS. 8f and 8g, as will be discussed, describe the process of locking the security device memory 721. The process 832 is then complete (block 850). Referring to FIG. 8d, FIG. 8d is a flow diagram illustrating a process 852 for the server 104 to unlock the security device memory 721 of the security device 110, according to one embodiment of the present invention. At block 854 the server 104 obtains the Serial No. 386 from the security device 110. Next, at block 856 the server obtains the memory key 389 associated with the Serial No. for the user from the user information database 109. The server 104 then obtains the current time and date from the clock/calendar of the server 104 (block 858). The server then obtains the current cryptogram from the security device 110 (block 860). The current cryptogram is a random number generated by the security device 110 each time the security device 110 is authenticated by the server 104. The server 104 next computes an unlock message to unlock the security device memory 721 and an appropriate expected response value from the security device 110 (block 862). Then, the server 104 sends the memory unlock message to the security device 110 (block 864). If the unlock message is valid, i.e. decipherable by the security device 110 to properly command the security device 110 to unlock its security device memory 371 (such that both the security device and the server must be authorized participants), the security device 110 will send the expected response back to the server 104. The server 104 requires an appropriate expected response back from the security device 110 to verify that it is the authorized security device 110 and that the security device memory 371 has therefore been unlocked. Conversely, the security device 110, based on the unlock message, can verify that the server 104 is authorized to command the security device to unlock its security device memory 371. The symmetrical expected response generated at the server 104 and the response generated at the security device 110, utilizing the memory key 389 and the cryptogram, in one embodiment, can be based upon a proprietary anti-wire tapping algorithm created and licensed by the ELVA Corporation. However, any suitable zero-knowledge proof algorithm for accurately authenticating two parties can be used. Furthermore, in one embodiment, the security logic 380 that implements the ELVA anti-wire tapping algorithm may be a cryptography device produced by the ATMEL Corporation. Continuing with the present example, the server 104 waits for an appropriate response from the security device 110 for a predefined period of time (block 866). If the security device 110 does not respond with a predefined period of time then the process 852 fails (block 868). If the server 104 receives a response from the security device 110 in time, then at block 870, the server 104 determines whether it has received the expected response from the security device 110. If not, the process 852 fails (block 872). If the server 104 receives the expected response from the security device 110, then the server 104 knows that the security device memory 721 of the security device 110 has been unlocked. Accordingly, as will be discussed with reference to FIG. 8e, the memory is unlocked such that the security device can update the current and subscription expiration dates received from the server 104. The process 852 is then complete (block 873). Moreover, it should be appreciated that the security device memory 721 can be unlocked to perform many other functions, for example, to store asset information 392, asset keys 391, etc., as will be discussed. Referring to FIG. 8e, FIG. 8e is a flow diagram illustrating a process 874 for the security device 110 to update the current and subscription expiration dates received from the server 104, according to one embodiment of the present invention. Again, the security device operates under the control of the firmware 383 to implement its functions. At block 876 the security device 110 decrypts the current date and the subscription expiration date received from the server 104. Next, at block 878, the security device 110 stores the current date and the subscription expiration date 390 in nonvolatile memory 384. The process 874 is then complete (block 880). Referring to FIG. 8f, FIG. 8f is a flow diagram illustrating a process 882 for the server 104 to lock the nonvolatile memory 384 of the security device memory 721 of the security device 110, according to one embodiment of the present invention. In order to accomplish this, the server 104 merely sends a memory lock command to the security device 110 (block 884). The process 882 is then complete (block 886). After the server 104 sends a memory lock command to lock the nonvolatile memory 384, the security device 110 can lock the secure memory 379. Turning now to FIG. 8g, FIG. 8g is a flow diagram illustrating a process 888 for the security device 110 to lock the secure memory 379, according to one embodiment of the present invention. At block 890, the security device 110 determines whether the secure memory 379 is unlocked. If not, indicating that the secure memory 379 is already locked, the process 888 is complete (block 899). If the secure memory 379 is unlocked, the security device 110 checks to see whether the lock memory command has already been received (block 892). If so, the security device 110 locks the secure memory 379 and the security logic 380 (block 894) and disables access to the nonvolatile memory 384 (block 898). The process 888 is then complete (block 899). However, if the lock memory command has not been received at block 892 then the security device 110 checks to see whether the memory unlock time has been exceeded. If not, the process 888 is complete and the security device 110 can lock the security device memory 721 later (block 899). On the other hand, if the memory unlock time has been exceeded, then the security device 110 locks the secure memory 379 and the security logic 380 (block 894) and disables access to the nonvolatile memory 384 (block 898) such that the process 888 is then complete (block 899). Accordingly, once the secure memory 379 is locked, as well as, the nonvolatile memory 384, the whole security device memory 721 is locked. Thus, after the security device memory 721 has been unlocked to update the current and subscription expiration dates, to store asset information 392, asset keys 391, etc., it can be locked again. As previously discussed, the application software module 402 and the security software module 408 of the computing device 102 can be used to update the current date and time in the security device 110. However, this is not secure, and these dates and times are always scrutinized against the dates and times received from the server 104 as previously discussed. Referring now to FIG. 8h, FIG. 8 is a flow diagram illustrating a process 801 for the application software module 402 of the computing device 102, in conjunction with the other software modules, to update the current date at the security device 110, according to one embodiment of the present invention. At block 805 the computing device 102 determines whether the security device 110 is requesting the date and time. If not, the process 801 is complete (block 807). However, if the security device 110 is requesting the date and time, then the computing device 102 obtains the date and time from the clock/calendar of the computing device 102 (block 809). The computing device 102 then sends the date and time to the security device 110 (block 811). The process 801 is then complete (block 813). Turning now to FIG. 8i, FIG. 8i is a flow diagram illustrating a process 815 for the security device 110 to update the current date and time received from the computing device 102, according to one embodiment of the present invention. At block 823, the security device 110 determines whether the current date received is beyond the subscription expiration date. If so, the security device 110 records the expiration of the subscription (e.g. in nonvolatile memory 384) (block 825). The process 815 is then complete (block 827). The security device 110 may then instruct the computing device 102 to display to the user that his or subscription has expired and the server 104 will direct the user to update the subscription upon the next connection. On the other hand, if the current date is not beyond the subscription expiration date, the security device 110 will check to see that the date received from the application software module 402 of the computing device 102 is valid as compared to the trusted date and time received from the server 104 from the last update (block 829). If not, the security device 110 will then assume there has been a breach of security and will record the expiration of the subscription (block 825). The process 815 is then complete (block 827). Again, the security device 110 may then instruct the computing device 102 to display to the user that his or subscription has expired and the server 104 will direct the user to update the subscription upon the next connection. However, if the date from the application software module 402 of the computing device 102 is determined to be valid by the security device 110 then the security device will then store the date and time 390 in the nonvolatile memory 384 (block 831). The process 815 is then complete (block 833). Another security service 706, performed by the security device 110 in conjunction with the server 104, is to ensure that digital assets (e.g. audio files) are properly encrypted and decrypted such that only a computing device 102 coupled to properly authorized security device 110 can receive and utilize the assets. As previously discussed, the asset database 107 contains assets (e.g. multimedia presentations associated with musical pieces, audio files (e.g., as previously discussed Jamtracks including full songs and songs with various instrumental tracks removed), as well as other digital data assets). Moreover the asset database 107 includes unique asset encryption keys for each asset (e.g. for each audio file). Further, it should be appreciated that the asset database 107 can include any other type of digital data asset (e.g. multimedia data, video data, voice data, software, other generic forms of data, etc.) that can be purchased or rented and downloaded to a computing device 102 coupled to an authorized security device 110 over a computer network 105. Thus, the term “asset” as it will be used hereinafter specifically includes audio files (e.g. such as the Jamtracks previously discussed with reference to the GUITARPORT Web-site) but further includes any other sort of digital asset. Embodiment of the present invention further provides a secure asset delivery system. Assets are encrypted by the security system 700 (referring also to FIG. 7a again) to protect against unauthorized duplication of licensed material. Each asset is stored in the asset database 107 of the server 104 and is encrypted with a different, unique asset key particularly for that asset. Each asset is uniquely encrypted utilizing the security software module 422 of the server 104, in conjunction with the other software modules. As each encrypted asset is streamed to the requesting computing device 102, the encrypted asset is stored in the asset storage 712 of the computing device 102. Further, the asset key for the asset is encrypted using the user key of the associated security device 100 of the requesting computing device 102, and the encrypted asset key is also streamed to the requesting computing device 102, where it is stored in the asset storage 712 of the computing device 102. As previously discussed each user key 389 is unique to each user's security device 110 and each user key 389 is stored at both the security device 110 and at the user information database 109 at the server 104. When it is time to access the asset at the computing device 102, for example, the user wants to play a downloaded audio file asset (e.g. as part of a multimedia presentation for a Jamtrack to facilitate learning of the guitar), the security software module 408 in conjunction with the application software module 402 and the other software modules of the computing device 102, sends the encrypted asset key to the security device 110 to be decrypted. The decrypted asset key is then sent back from the security device 110 to the computing device 110 where it is used by the computing device 102, operating again with the security software module 408 in conjunction with the application software module 402 and the other software modules, to decrypt the asset (e.g. an audio file) into memory. The decrypted asset can then be utilized. For example, a decrypted audio file can be decompressed for playback. Referring now to FIG. 9, FIG. 9 illustrates an example of a secure asset delivery system 900, as previously described, according to one embodiment of the present invention. At block 902, an asset (A) 904 is encrypted with an asset key (AK) 906. The encrypted asset 905 (e.g. (EAK(A))) is then sent to the computing device 102 where it is stored in memory (e.g. asset storage 712) (block 910). Also, at block 920 the asset key (AK) 906 is encrypted with the user's user key (UK) 389. The encrypted asset key 909 (e.g. (EUK(AK))) is then sent to the computing device 102 where it is stored in memory (block 924). At block 930, the security device 110 decrypts the encrypted asset key 909 with the user's unique user key (UK) 389 (e.g. DUK[EUK(AK)]) to yield the asset key 906 (AK), which is then forwarded onto the computing device 102. Then, at block 932, the computing device 102 can decrypt the encrypted asset 905 with the asset key (AK) 906 (e.g. DAK[EAK(A)]) to yield the asset (A). The asset can then be utilized by the application software module 402 of the computing device 102. For example, if the asset is an audio file, the audio file can be decompressed for playback as part of a multimedia presentation of a Jamtrack to facilitate learning of guitar. It should be appreciated that encryption and decryption algorithms are well known in the art, and that various types of encryption and decryption algorithms can be used by the server 104, the computing device 102, and the security device 110. The security software of the server 104, computing device 102, and the firmware of the security device 110, include standard encryption and decryption routines to encrypt and decrypt assets, keys, dates and other data sent between these devices. Any suitable block mode cipher that utilizes pseudo-random generators to XOR pseudo-random numbers with data can be used. Some examples include Data Encryption Standard (DES), International Date Encryption Algorithm (IDEA), etc. A more detailed embodiment of the secure asset delivery system 900, according to one embodiment of the present invention, will now be discussed. As previously discussed, the server 104 encrypts each asset sent to a user with a unique asset key. Moreover, the server 104 also sends an indication as to whether the asset is to be rented or owned by the user. Assets that are rented expire when the user's subscription expires and cannot be used after the subscription. Assets that are owned by the user do not expire when the user's subscription expires. The server 104 further sends the unique asset key required to decrypt the asset to the user in an encrypted form—wherein the asset key is encrypted with the user key 389 of the security device 110 for the user such that the security device 110 can decrypt the encrypted asset key and the computing device 102 can then decrypt the asset with the decrypted asset key to provide the user access to the asset. Thus, an asset can be delivered securely to a specific user having a particular security device. The computing device 102, operating with the application software module 402, the security software module 408 and in conjunction with the other software modules, performs many functions related to decrypting and accessing the asset, as has been previously discussed. The computing device 102 receives and stores the encrypted asset and the encrypted asset key in local memory (e.g. asset storage 712). The computing device 102 sends the encrypted asset key (and an indication of whether the asset is rented our owned) to the security device 110. The security device 110, under control of the firmware 383, decrypts the asset key and determines whether the asset has expired due to a lapsed subscription. If the asset has not expired, the security device 110 sends the decrypted asset key to the computing device 102 so that the asset can be decrypted by the computing device and can then be utilized. As previously discussed, the computing device 102 decrypts the asset with the asset key to yield the asset. On the other hand, if the subscription has expired, the security device 110 notifies the computing device 102, and the computing device 102 notifies the user that the subscription has expired. Specific process steps will now be discussed to implement this functionality. Referring to FIG. 10a, FIG. 10a is a flow diagram illustrating a process 1000 for the server 104 to encrypt assets, according to one embodiment of the present invention. The server 104 operates under the control of the application software module 416, the security software module 422 and in conjunction with the other software modules, to implement the functions of the processes, as will be discussed. At block 1002, the server 104 obtains the time and date from the clock/calendar of the server 104. Next, the server 104 generates an encryption key (block 1004). The server 104 then encrypts the asset with a unique asset key (block 1006). The server 104 then stores the encrypted asset and the asset key in the asset database 107 (block 1008). The process 1000 is then complete (block 1010). Referring now to FIG. 10b, FIG. 10b is a flow diagram illustrating a process 1012 for the server 104 to deliver the asset, according to one embodiment of the present invention. At block 1014, the server 104 obtains the asset, the asset key, and a status indication of whether the asset is owned or rented from the asset database 107. The status indication may be implemented as a rental flag—e.g. a rental flag that is set corresponds to the asset being rented by the user and a rental flag that is not set corresponds to the asset being owned or purchased by the user. Further, the server 104 obtains the user key 389 for the user (corresponding to the user's security device 110) from the user information database 109 (block 1016). Next, the server 104 encrypts the asset key and the rental flag utilizing the user's user key 389 (block 1018). The server 104 then sends the encrypted asset key and rental flag to the computing device 102 (block 1020). Further, the server 104 sends the encrypted asset to the computing device 102 (block 1022). The process 1012 is then complete (block 1024). Turning now to FIG. 10c, FIG. 10c is a flow diagram illustrating a process 1026 by which the computing device 102 performs the functions of extracting the asset key from the security device 110, according to one embodiment of the present invention. The computing device 102 operates under the control of the application software module 402, the security software module 408 and in conjunction with the other software modules, to implement the functions of the processes, as will be discussed. At block 1028, the computing device 102 sends the encrypted asset key and rental flag received from the server 104 to the security device 110. Next, the computing device 102 obtains a response from the secure device 110 (block 1030). The response includes a notification as to whether the asset has expired, and if the asset has not expired, the decrypted asset key. The generation of the response at the security device 110 will be discussed later with reference to FIG. 10e. At block 1032, the computing device 102 determines, based on the response from the security device 110, whether access to the asset has expired (block 1032). For example, if the asset is rented and the subscription has expired (i.e. the current date is passed the subscription expiration date for the asset), then access to the asset has expired. Thus, if access to the asset has expired, then at block 1034, the computing device 102 notifies the user that access to the asset has expired. If access to the asset has not expired (i.e. the asset is owned or the subscription expiration date has not passed), then the computing device extracts the asset key from the security device response (block 1036). The process 1026 is then complete (block 1038). Referring now to FIG. 10d, FIG. 10d is a flow diagram illustrating a process 1040 by which the computing device 102 performs the functions of decrypting the asset, according to one embodiment of the present invention. At block 1042, the computing device 102 initializes a decryption algorithm with the asset key received from the security device 110. Next, the computing device 102 loads the encrypted asset into memory (block 1044). The computing device 102 then decrypts the memory copy of the encrypted asset utilizing the asset key received from the security device 110 to decrypt the encrypted asset (i.e. the encrypted asset being encrypted with the asset key) (block 1046). Thus, the asset is yielded to the computing device 102, for use by the computing device 102. The asset can then be utilized by applications of the computing device 102. For example, if the asset is an audio file, the audio file can be decompressed for playback as part of a multimedia presentation of a Jamtrack to facilitate the learning of guitar, as previously discussed. Turning now to FIG. 10e, FIG. 10e is a flow diagram illustrating a process 1050 by which the security device 110 extracts the asset key, according to one embodiment of the present invention. As previously discussed, the security device 110 operates under the control of the firmware 383. At block 1052, the security device 110 receives the encrypted asset key and the rental flag from the computing device 102. The encrypted asset key and rental flag being encrypted with the user key. The security device 110 then obtains the user key 389 from nonvolatile memory 384 (block 1054). Next, the security device 110 decrypts the asset key and rental flag with the user key 389 (block 1056). The security device then determines whether the asset is rented (block 1058). If not (i.e. it is owned), the security device 110 returns the decrypted asset key to the computing device 102 (block 1060) and process 1050 is complete (block 1068). However, if the asset is rented, the security device 110 next determines whether the subscription has expired (i.e. whether the current date is passed the subscription expiration date for the asset) (block 1062). If not, the security device 110 returns the decrypted asset key to the computing device 102 (block 1060) and the process 1050 is complete (block 1068). However, if the subscription has expired, then the security device 110 returns a response with an indication to the computing device 102 that the subscription has expired (block 1064). The process 1050 is then complete (block 1068). It should be appreciated that the security software of the server 104, computing device 102, and the firmware of the security device 110, utilize standard encryption and decryption routines to encrypt and decrypt assets, keys, dates and other data sent between these devices, as has been discussed. Any suitable block mode cipher that utilizes pseudo-random generators to XOR pseudo-random numbers with data can be used. Some examples include Data Encryption Standard (DES), International Date Encryption Algorithm (IDEA), etc. Accordingly, as previously described, the secure asset delivery system ensures that digital assets are encrypted and decrypted such that only a computing device coupled to properly authorized security device, that is associated with a particular user/subscriber, can receive and utilize the assets. Embodiments of the present invention provide a secure asset delivery system wherein digital assets are properly encrypted by the secure server 104 and can only be decrypted by a computing device 102 that is coupled to a properly authorized security device 110 such that only that properly authorized computing devices 102 can receive and utilize the assets—thereby protecting against unauthorized duplication of licensed material. As previously discussed, in one embodiment, the asset database 107 contains assets (e.g. multimedia presentations associated with musical pieces, audio files—such as Jamtracks including full songs and songs with various instrumental tracks removed)), as well as other digital assets. For example, in one embodiment, if the asset is an audio file, the audio file can be decompressed for playback as part of a multimedia presentation of a Jamtrack to facilitate the learning of guitar, as previously discussed. Further, it should be appreciated that the asset database 107 can include any other digital assets (e.g. multimedia, videos, movies, voice, sound recordings, software, other generic forms of data etc.) that can be purchased or rented and downloaded to a computing device 102 over a computer network 105. Turning now to FIG. 11, embodiments of the present invention further provide a secure electronic commerce system 1100 to track and record the distribution and use of assets. As previously discussed, embodiments of the invention include a security device 110 coupled to a computing device 102 that is uniquely identified and authenticated by a server 104 to establish a high degree of trust between a user utilizing the computing device 102 and the server 104 thereby enabling secure electronic commerce transactions between the computing device 102 and the server 104. This involves the use of a unique identifier, such as a serial number, an associated user key, and a plurality of non-obvious methods and procedures to uniquely identify and authenticate the security device. Also, as has been discussed, the security device 110 allows for the decryption of digital assets specifically encrypted for use by the authorized security device 110, along with many other functions. Accordingly, encrypted digital assets only operate with a computing device 102 coupled to an authorized security device 110 to protect against unauthorized duplication of licensed material and to provide a secure revenue opportunity for content providers. Moreover, as will be described, the secure electronic commerce system 1100 tracks and records the distribution and use of assets. Particularly, the secure electronic commerce system 1100 tracks the purchase, rental, and number of uses of assets by a user. The secure electronic commerce system 1100 can be used either directly by the content owner to track the distribution and use of assets or by a third party provider to track the distribution and use of assets and further in order to keep an accounting of licensing fees (e.g. royalties) due to the content owner (e.g. the copyright holder). In this way, the secure electronic commerce system 1100 makes it easy for a third party provider to accurately report transactions regarding licensed assets to the ultimate content owner for licensing fees (e.g. royalty tracking). Accordingly, the secure electronic commerce system 1100 promotes the distribution of assets to customers in a secure manner and provides a secure revenue opportunity for content providers (especially the ultimate content owner (i.e. the copyright holder)). With particular reference to FIG. 11, the secure electronic commerce system 1100 includes the security device 110, the computing device 102, the servers 104, a customer service system 1120, a trusted authority 1130, and banks 1140. Particularly, the servers 104, include a customer server 104a, a database server system 104b, and a customer service server 104c. It should be noted that the servers 104a, 104b, and 104c, can be physically separate servers or can be logical divisions of one server computer. The security device 110 includes security components 710, security services 706, a serial number 386, a user key 387, asset information 392, etc., as has been previously discussed in detail. Turning to the computing device 102, the computing device 102 includes software modules for interacting with the servers 104 via the computer network 105 (e.g. the Internet). The computing device 102 includes the application software module 402, as previously discussed. In addition to the previously discussed functions of the application software module 402, the application software module 402 in the secure electronic commerce system 1100 further provides forms (received from the server) to the user for entering registration and subscription information (e.g. to initially register and for registration updates) and allows the user to make online purchases. For example, the user can purchase or rent digital assets from the server 104, which are then specifically encrypted for decryption by the user's security device 110, and are then transmitted to the computing device 102 for use by the user. The digital asset can be any sort of digital asset, e.g. audio files (songs, music, etc.), multimedia, videos, movies, voice, sound recordings (songs, music, etc.), software, other generic forms of data etc., or can be, in the GUITARPORT embodiment, an audio file associated with a Jamtrack (i.e. a multimedia presentation associated with an audio file for learning guitar). However, it should be appreciated that tangible assets such as CDs, books, shirts, are any sort of tangible product, can be purchased using the secure electronic commerce system 1100. In addition, the application software module 402 keeps track of the number of uses of rented digital assets for royalty tracking purposes. For example, in one embodiment, the computing device 102 stores an asset usage count list 1102 of rented assets in a storage device (e.g. a hard drive), which includes the title of the rented asset, the dates on which the asset has been accessed or used, and the total number of days on which the asset has been accessed or used. Of course, other asset usage count schemes could be utilized. Also, the computing device 102 can also store a list of digital assets that have been purchased by the user. As previously discussed, digital assets that are rented expire when the user's subscription expires and cannot be used after the subscription expires, whereas digital assets that are owned by the user do not expire when the user's subscription expires. The computing device 102 also includes a security software module 408, as previously discussed, in conjunction with secure sockets layer (SSL) software 409, to allow the computing device 102 to interact securely with the servers 104 via the computer network 105 (e.g. the Internet). Secure sockets layer (SSL) is a widely used security protocol, which is built into both of the leading Web browsers. SSL is a transport-level protocol developed by Netscape that provides channel security. With SSL, the client and server use a handshaking technique to agree on the level of security they want to use during a session. Authentication takes place over a secure channel, and all information transmitted during a session is encrypted. Turning now to the customer server 104a, in one embodiment of the present invention, the customer server 104a includes a server software module 415, a commerce software module 420, a database software module 418, a security software module 422, and Secure Socket Layer (SSL) software 1103. The server software module 415 can be conventional server software for transmitting and receiving data to and from computing devices 102. For example, using the Hypertext Transfer Protocol (HTTP) and Hypertext Markup Language (HTML) or Extensible Markup Language (XML), the server 104 can communicate with the computing device 102 across the computer network 105 to provide various functions and data to the user. At the computing device 102, utilizing the embedded browser 404, which is part of the application software module 402, or even other browsers such as Netscape™ Navigator™ published by Netscape™ Corporation of Mountain View, Calif., the Internet Explorer™ published by Microsoft™ Corporation of Redmond, Wash., the user interface of America Online™, or any other browser or HTML/XML translator from a well-known supplier, computing device 102 may supply data to, and access processed or unprocessed data from, the server 104. According to one embodiment of the present invention, the commerce software module 420 controls the delivery of digital assets to the computing device 102 when they are purchased or rented. Further, the commerce software module 420, in conjunction with the database software module 418, tracks the purchase, rental, and number of uses of digital assets by a user, as well as account balances for users. Additionally, the commerce software module 420, in conjunction with the database software module 418, performs functions related to initially registering users, registration updates, billing, and royalty tracking. The particular functions of the commerce software module 420 will be discussed in more detail later. The database software module 418 can be conventional database software, such as MySQL, to control the input and output of data from the asset database 107 and the user information database 109, under the control of the commerce software module 420. The security software module 422, as previously discussed, in conjunction with the Secure Socket Layer (SSL) software 1103, implements a secure protocol for the transferring of data between the computing device 102 and the customer server 104a. Further, as previously discussed, the computer network connection 105 (e.g. an Internet connection) provides network access between the customer server 104a and the computing device 102 of the user. Moreover, a secure SSL computer network connection 1150 (e.g. a private connection or public Internet connection) can also be made to a trusted authority (e.g. an online banking transaction mediator) to provide a path and protocol to a bank for banking transactions, as will be discussed. Additionally, another network connection 1152 is made between the customer server 104a, the database server 104b, and customer service server 104c. The network connection 1152 may be through a private network (e.g. a LAN) or through a public network (e.g. the Internet). The network connection 1152 is a secure connection. The servers 104a, 104b, and 104c operate in a secure environment. Looking now at the database server system 104b, the database server system 104b includes a database server software module 1104, a transaction log 1105, the asset database 107, and the user information database 109. The database server software module 1104 includes programs for providing access to the user information database 109 and the asset database 107. For example, the database server software module 1104 can be conventional database software, such as MySQL, to control the input and output of data from the asset database 107 and the user information database 109. The database server system 104b, in conjunction with the customer server 104a and the customer service server 104c, operate in a secure environment. Access to the database server system 104b is “transaction-safe”, which means any transaction that fails to complete does not alter the consistency or state of the database server system 104b. The network connection 1152 to the customer server 104a and customer service server 104c provides a path for sharing data from the database server system 104b (e.g. data from the user information database 109 and the asset database 107) with the customer server 104a and the customer service server 104c. The user information database 109 includes subscription and registration information 1106 for each registered user. The subscription and registration information 1106 include data such as the user's name, email address, home address, computer connection speed, credit card number, credit card expiration date, subscription information, type of computer, and security information including a user's serial number for his or security device 110, user key, memory key, and other user information. Moreover, the user information database 109 may include the user's preferences such as musical preferences, movie preferences, book preferences, or any other type of preferences that would be suitable to tailor the presentation of preferred assets to the user. In the GUITARPORT embodiment, the user information may also include the type of musical preferences of the user to tailor preferred Jamtracks offerings to the user (as previously discussed). The asset database 107 can include any type of digital asset (e.g. music, sound recordings, voice, multimedia, videos, movies, software, or any other type of digital data, etc.) that can be purchased or rented by a user and downloaded to a computing device 102 over a computer network 105. Moreover, the asset database 107 stores unique asset encryption keys 1112 for each digital asset such that a digital asset can be uniquely encrypted for a particular authorized security device 110 (in conjunction with the unique user key for the particular security device) and sent to a user operating a computing device 102 with that authorized security device 110—so that only that authorized security device 110 can decrypt the uniquely encrypted asset, as previously discussed. In the GUITARPORT embodiment, as previously discussed, the asset database 107 contains assets 1111 such as session files, multimedia data for multimedia presentations associated with musical pieces, audio files, and audio files associated with Jamtracks including full songs and songs with various instrumental tracks removed, sound recordings, etc., as previously discussed. It will be readily appreciated by those having ordinary skill in the relevant arts that the asset database 107 and user information database 109 may be stored in storage devices including various mass storage devices such as one or more DASD arrays, tape drives, optical drives, or the like, and that the aforementioned information may be stored in any one of a variety of formats or data structures. The database server system 104c also includes a transaction log 1105 that contains an audit trail for all operations that alter the user information database 109 and the asset database 107. The transaction log 1105 further includes a timestamp for each entry and sufficient information to retrace steps performed by the servers and by customer support personnel. It should be appreciated that transaction logs for such purposes are well known in the art. Turning now to the customer service server 104c, the customer service server 104c includes a customer service server software module 1115 that includes programs for updating registration information, handling transfers of ownership, making account adjustments, and canceling accounts. Customer service software modules to fulfill these functions are well known in the art. The Secure Socket Layer (SSL) software 1116, implements a secure protocol for the transferring of data between the customer service server 104c and the customer service system 1120 and the trusted authority 1130. A secure SSL computer network connection 1160 (e.g. a private connection or public Internet connection) can be made to a trusted authority (e.g. an online banking transaction mediator) to provide a path and protocol to a bank for banking transactions, as will be discussed. Another secure SSL computer network connection 1162 (e.g. a private connection or public Internet connection) can also be made to the customer service system 1120. Additionally, another network connection 1152 is made between the customer server 104a, the database server 104b, and customer service server 104c. The network connection 1152 may be through a private network (e.g. a LAN) or through a public network (e.g. the Internet). The network connection 1152 is a secure connection. The servers 104a, 104b, and 104c operate in a secure environment. Referring now to the customer service system 1120, the customer service system 1120 includes at least one personal computer that stores a customer service application software module 1122 that provides functionality for interacting with the customer service server 104c. The customer service application software module 1122 provides forms that can be utilized by operators for updating registration information, handling transfers of ownership, making account adjustments, and canceling accounts. The personal computers at the customer service system 1120 can be utilized by operators to make changes regarding registration updates, ownership issues, account adjustments, the cancellation of accounts, etc., directly to the customer service server 104c, via computer network connection 1162, for users who call into the customer service system 1120 or otherwise communicate with the customer service system 1120. This information can then be accurately updated and reflected in the database server system 104b. Customer service application software to fulfill these functions is well known in the art. Thus, as one example, a user can talk with an operator at the customer service system 1120 to make changes with a Web-based business server 104. Accordingly, users can contact operators at the customer service system 1120 to update their accounts and correct problems with their accounts. Alternatively, as previously discussed, a user can make changes to their accounts using their own computing device 102 with forms presented by the application software module 402. Secure Socket Layer (SSL) software 1124, implements a secure protocol for the transferring of data between the customer service system 1120 and the customer service server 104c. A secure SSL computer network connection 1162 (e.g. a private connection or public Internet connection) can be made to the customer service system 1120 to transfer data. Furthermore, although the customer service system 1120 is shown as being separate from the location of the servers 104, it should be appreciated that the customer service system 1120 can be co-located with the servers 104. The trusted authority/online banking transaction mediator 1130 is a service bureau provided by a third party for verifying credit cards and performing online banking transactions (with banks 1140) including managing the transfer of funds between bank accounts. Typically, the trusted authority 1130 provides a password-protected login account and requires the use of an underlying security protocol. For example, Verisign is a well known trusted authority that can be utilized. With reference now to FIG. 12a, FIG. 12a illustrates a process 1200 for processing a client form at the client device in order for a user to register and subscribe to a server 104, according to one embodiment of the present invention. As previously discussed, the computing device 102 includes software modules for interacting with the servers 104 via the computer network 105 (e.g. the Internet) of the secure electronic commerce system 1100. Particularly, the computing device 102 includes the application software module 402, as previously discussed, which provides forms (received from the server) to the user for entering registration and subscription information to implement process 1200 (e.g. to initially register and subscribe the user). Particularly, each user must register before using the secure electronic commerce system 1110. Basically, registration consists of filling out a form to provide personal information and to designate a credit card for billing purposes. Moreover, a user's security device serial number identification is automatically retrieved at the time of registration to uniquely identify and authenticate the security device. As shown in FIG. 12a, at block 1205 the serial number 386 is obtained from the security device 110. Once the serial number 386 is obtained, the challenge/response process to authenticate the security device 110 is performed, as previously described with reference to FIGS. 8a and 8b. At block 1210, a secure sockets layer (SSL) session is begun between the computing device 102 and the customer server 104a. Next forms are displayed having entry bocks for the entry of user registration and subscription input data (block 1215). This can be implemented as a single form or as two separate forms—e.g. a first registration form and a second registration form. For example, a first registration form is displayed. The type of registration input data requested by the first form may include the user's name, home address, country, email address, type of computer, computer connection speed, etc. Further, the first form may include a user agreement having accept and decline selection buttons that the user must accept (by selecting the accept button) before the forms can be processed. Next, a second subscription information form is displayed requesting billing information such as the user name, billing address, credit card number, and credit card expiration date, etc. This second form further includes a selectable submit button. Such forms are standard and are known in the art. At block 1220, the computing device 102 processes the users inputs from the forms. The process 1200 further monitors for whether the operation has been canceled (block 1225). If so, the process 1200 stops the SSL session with the customer server 104a (block 1250) and process 1200 is complete (block 1251). If not, the process 1200 determines whether the submit button of the second form has been selected by the user (e.g. pressed) such that the user wishes to submit his or her user information to the customer server 104a to register with the Web based business server (block 1230). For example, in one embodiment, the Web based business can be the GUITARPORT business model previously discussed. If the submit button has not been selected, the process 1200 returns to block 1220 to continue processing user inputs. On the other hand, if the submit button is not selected (e.g. the user selects a return to form entry button or the like), then the computing device 102 submits the user forms to the customer server 104a via the computer network 105 (block 1235). At block 1240, the process 1200 determines whether the customer server 104a accepted the user's subscription and registration information submitted in the forms (this process will be discussed with reference to FIG. 12b). If the customer server 104a does not accept the user information submitted in the forms (e.g. due to erroneous or incomplete information), then the computing device 102 displays a notification from the server to the user that the user subscription and registration information has not been accepted and the process 1200 returns to block 1220 to further process the user subscription and registration input data. For example, the user may be allowed to correct erroneous subscription and registration information or to enter subscription and registration information left that was out. If the customer server 104a accepts the user subscription and registration information submitted in the forms then at block 1250 the user is registered with the server (e.g. a Web-based business) and the SSL session is stopped. The process 1200 is then complete (block 1251). With reference now to FIG. 12b, FIG. 12b illustrates a process 1252 for processing client forms received from the client device 102 at the server 104 in order for a client to register and subscribe to the server 104, according to one embodiment of the present invention. As previously discussed, customer server 104a includes the commerce software module 420, in conjunction with the database software module 418, to perform functions related to registering users (and further to perform registration updates) to implement process 1252. As shown in FIG. 12b, at block 1255 a secure sockets layer (SSL) session is initiated between the customer server 104a and the computing device 102. At block 1260 blank registration and subscription forms (e.g. the first and second registration and subscription forms previously discussed) are sent to the computing device 102. The process 1252 then awaits submission of the forms from the computing device 102 (block 1262). Further, the process 1252 monitors for whether the user at the computing device 102 has canceled the registration and subscription operation (block 1264). If the user cancels the registration and subscription operation, then the process 1252 is complete (block 1280). However, if the user does not cancel the registration and subscription operation then the process 1252 next verifies whether the form contents are valid or not (block 1266). If the form contents are not valid and the customer server 104a does not accept the user information submitted in the forms (e.g. due to erroneous or incomplete information), then the process 1252 returns to block 1262 to further await submission of forms from the computing device 102 that include the correct or required information. Moreover, as previously discussed, the customer server 104a sends a command to the computing device 102 to display a notification to the user that the user subscription and registration information has not been accepted and is either incomplete or erroneous (block 1268). The process 1252 then returns to block 1262 to await submission of forms with valid information from the computing device 102. In this way, the user can correct erroneous subscription and registration information or enter subscription and registration information that was previously left out. On the other hand, if the form contents are valid, the process 1252 issues a charge request to the trusted authority 1130 to verify that the user's credit card is valid (block 1270). Next, at block 1272, the process 1252 determines whether or not the charge request was accepted or denied by the trusted authority 1130. If the trusted authority 1130 denies the charge request, then the customer server 104a notifies the user at the computing device 102 that his or her charge request was denied (e.g. the user's credit card was denied) (block 1274). The process 1252 then returns to block 1262 to again wait for the submission of forms that include a valid credit card number. However, if the trusted authority 1130 accepts the charge request (e.g. the credit card is valid), then the customer server 104a saves the registration and subscription information for the user in the user information database 109 (e.g. subscription and registration information 1106) (block 1276). The process 1252 then stops the SSL session between the customer server 104a and the computing device 102 (block 1278). The process is then complete (block 1280). Thus, the user has successfully been registered and subscribed with the Web based business server 104. For example, in one embodiment, the Web based business server can be the GUITARPORT embodiment, previously discussed. However, it should be appreciated that the previously described processes can be used to register and subscribe users to any type a Web based business server. With reference now to FIG. 13a, FIG. 13a illustrates a process 1300 for allowing a user to purchase or rent an asset at the client device 102 using the secure electronic commerce system 1100, according to one embodiment of the present invention. As previously discussed, the computing device 102 includes the application software module 402, which allows the user to make online purchases and rentals and aids in implementing the process 1300. For example, the user can purchase or rent digital assets from the server 104, which are then specifically encrypted for decryption by the user's security device 110, and are then transmitted to the computing device 102 for use by the user. The digital asset can be any sort of digital asset, e.g. audio files (songs, music, etc.), multimedia, videos, movies, voice, sound recordings (songs, music, etc.), software, other generic forms of data etc., or can be, in the GUITARPORT embodiment, an audio file associated with a Jamtrack (i.e. a multimedia presentation associated with an audio file for learning guitar). However, it should be appreciated that tangible assets such as CDs, books, shirts, are any sort of tangible product, can be purchased using the secure electronic commerce system 1100. Generally, a user may make an online purchase and the transactions for the purchase or rental are coordinated by the customer server 104a. The secure electronic commerce system 1100 supports instant purchases or rentals, which are automatically charged to a registered credit card of the user. Further the secure electronic commerce system 1100 also supports purchases or rentals that are added to the monthly amount due by the user and are automatically billed at the end of the billing cycle. In order to implement process 1300, it is assumed that the computing device 102 has already successfully logged on to the customer server 104a by satisfying the challenge/response process to authenticate the security device 110, as previously described with reference to FIGS. 8a and 8b. As shown in FIG. 13a, at block 1302 the process 1300 obtains the serial number 386 from the security device 110. Next, the process 1300 starts a secure sockets layer (SSL) session between the computing device 102 and the customer server 104a (block 1304). The process 1300 then displays a purchase selection form at the computing device 102 to allow the user to select an asset for purchase (block 1306). Typically, the purchase selection form will be displayed after a user selects an asset for purchase, for example, by double clicking on an asset. For example, the purchase selection form may be a simple dialog box asking if the user is sure they want to purchase or rent this asset with a selectable yes or no button. For example, in the GUITARPORT embodiment, a user may select a Jamtrack asset for purchase or rental. The purchase selection form would then be presented allowing the user to purchase or rent the Jamtrack by selecting the yes button. However, any type of digital asset can be simply purchased in this way. For example, a user could double click on a song they want to purchase on a music related Web-site, select the yes button of the purchase selection form, and they will have instantly purchased the song without the need to enter a great deal of information as with current electronic commerce systems. The process 1300 then processes user inputs related to the purchasing of an asset (block 1308). Furthermore, the process 1300 monitors the purchase operation to verify that the user does not cancel the purchase operation (block 1310). If the user cancels the purchase operation, then the SSL session between the computing device 102 and the customer server 104a is stopped (block 1312). The process 1300 is then complete (block 1314). If the purchase operation is not canceled by the user, then the process 1300 determines whether or not a purchase or rental of an asset was requested (block 1316). At block 1316, if the process 1300 determines that a purchase or rental has not been requested, the process returns to block 1308 to continue processing user inputs related to the purchasing or renting of assets. On the other hand, if the purchase or rental of an asset has been requested then the process 1300, at block 1318, submits the purchase or rental request for the asset to the customer server 104a. At block 1320, the process 1300 determines whether or not the purchase or rental request will be accepted by the customer server 104a (as will be discussed with reference to FIG. 13b). If the purchase or rental request for the asset is denied by the customer server 104a then the process 1300 displays a notification from the customer server 104a on computing device 102 that the purchase or rental request for the asset has been denied. The process 1300 then returns to block 1308 to continue processing user inputs related to the purchasing or renting of assets. On the other hand, if the customer server 104a accepts the purchase or rental request for the asset, then a record of the purchase or rental is recorded in the security device 110 (block 1324). In order to accomplish this, the customer server 104 unlocks the security device memory 721 of the security device 110, as previously described with reference to FIG. 8d, in order to record the purchase or rental. At block 1326, the process 1300 determines whether a download is required. If a download is required, then the asset is downloaded from the customer server 104a to the computing device 102 (block 1328). The process of downloading intangible digital assets (e.g. audio files, sound recordings, video, multimedia, etc.) from the customer server 104a to the computing device 102 and the security device 110, has been previously described in detail (including the novel and non-obvious encryption/decryption security techniques for downloading digital assets) with reference to FIGS. 9, 10a, and 10b. However, in the case of a tangible asset such as a retail product (e.g. CD or book) where a download is not required, the retail product can be sent to the user by conventional means (e.g. through the mail system). Next, at block 1330, the user of the computing device 102 is notified that the purchase or rental is complete. Further, after this step the security device memory 721 of the security device 110 is locked as described in detail previously with reference to FIGS. 8f and 8g. Moreover, the purchased or rented is uniquely encrypted digital asset can then only be accessed and utilized by the computing device 102, in conjunction with the authenticated security device 110, as previously described in detail with reference to FIGS. 10c–10e. As previously discussed, the digital asset can be stored in encrypted from on the hard drive of the computing device 102 and the asset key to decrypt the asset is stored in the security device 110. The SSL session between the computing device 102 and customer server 104a is then stopped (block 1332) and the process 1300 is complete (block 1334). With reference now to FIG. 13b, FIG. 13b illustrates a process 1336 implemented by the customer server 104a for allowing a user to purchase or rent an asset at the client device 102 using the secure electronic commerce system 1100, according to one embodiment of the present invention. As previously discussed, the customer server 104a includes commerce software module 420 that controls the purchase and rental of digital assets by the user of a computing device 102. Further, the commerce software module 420, in conjunction with the database software module 418, tracks the purchase, rental, and number of uses of digital assets by a user, as well as account balances for users. As shown in FIG. 13b, at block 1340 the process 1336 starts a secure sockets layer (SSL) session between the customer server 104a and the computing device 102. At block 1342, in response to a user selecting an asset, the customer server 104a sends a purchase selection form to the computing device 102. The customer server 104a then waits for a purchase request from the client device 102 (e.g. a user verifying that they wish to purchase or rent an asset by selecting the yes button on the purchase selection form) (block 1344). The process 1336 monitors for whether the purchase request has been canceled (block 1346). If the user cancels the request, then the process 1336 stops the SSL session between the customer server 104a and the computing device 102 (block 1348) and the process 1336 is complete (block 1350). On the other hand, if the user does not cancel their purchase request then the process 1336 next determines, at block 1350, whether or not this is an instant purchase. An instant purchase is a purchase or rental that is automatically and instantly charged to the user's credit card whereas a non-instant purchase is a purchase or rental that is simply added to the user's account balance which is then billed to the user at the user's next billing cycle (e.g. monthly). Thus, if the purchase or rental is a non-instant purchase the purchase amount is simply added to the user's account balance (block 1351). However, if the purchase or rental is an instant purchase, then at block 1352, a charge request is issued to a trusted authority 1130. The process 1336 next determines whether the charge request was accepted by the trusted authority (block 1354). If not, the process 1336 stops the SSL session with the computing device 102 (block 1348) and the process 1336 is complete (block 1350). On the other hand, if the charge request was accepted by the trusted authority 1130, then the purchase or rental is logged to the user in the user information database 109. The user information database 109 stores records for each user identifying the assets they have purchased or rented and the number of times they have used or accessed each rented asset. Next, at block 1358, the process 1336 determines whether or not a download is required. As previously discussed, intangible digital assets are downloaded from the customer server 104 a to the computing device 102 in encrypted form whereas the purchase of tangible assets (e.g. products-CDs, shirts, etc.) do not require a download and can simply be delivered through the conventional mail system. If a download is not required, then the process 1336 simply stops the SSL session with the computing device 102 (block 1362) and the process 1336 is complete (block 1364). Conversely, if a download is required, then the customer server 104a downloads the digital asset to the computing device (block 1360), as previously described in detail. Afterwards, the process 1336 stops the SSL session with the computing device 102 (block 1362) and the process 1336 is complete (block 1364). Thus, the secure electronic commerce system 1100 tracks and records the distribution (e.g. purchases and rentals) and use of assets. Particularly, the secure electronic commerce system 1100 tracks the purchase, rental, and number of uses of assets by a user. Therefore, the secure electronic commerce system 1100 can be used either directly by the content owner to track the distribution and use of assets or by a third party provider to track the distribution and use of assets and further in order to keep an accounting of licensing fees (e.g. royalties) due to the content owner (e.g. the copyright holder). In this way, the secure electronic commerce system 1100 makes it easy for a third party provider to accurately report transactions regarding licensed assets to the ultimate content owner for licensing fees (e.g. royalty tracking). Accordingly, the secure electronic commerce system 1100 promotes the distribution of assets to customers in a secure manner and provides a secure revenue opportunity for content providers (especially the ultimate content owner (i.e. the copyright holder)). In order to track the number of uses of assets by a user, the customer server 104a periodically queries the computing device 102 to determine the amount of usage of rented assets in order to report the usage to licensors and to use in determining the amount of royalties owed to the licensor (e.g. for royalty tracking). As previously discussed, the computing device 102 includes application software module 402 that keeps track of the number of uses of rented digital assets for royalty tracking purposes. For example, in one embodiment, the computing device 102 stores an asset usage count list 1102 for rented assets in a storage device (e.g. a hard drive), which for each rented asset includes the title of the rented asset, the dates on which the rented asset has been accessed or used, and the total number of days on which the asset has been accessed or used (termed the usage count). Also, the computing device 102 can also store a list of digital assets that have been purchased by the user. As previously discussed, digital assets that are rented expire when the user's subscription expires and cannot be used after the subscription expires, whereas digital assets that are owned by the user do not expire when the user's subscription expires. With reference now to FIG. 14a, FIG. 14a illustrates a process 1400 implemented by the computing device 102 for tracking the number of uses of rented digital assets using the secure electronic commerce system 1100, according to one embodiment of the present invention. As previously discussed, the computing device 102 includes application software module 402 that keeps track of the number of uses of licensed or rented digital assets for royalty tracking purposes and that may be used to implement the process 1400. As shown in FIG. 14a, the process 1400 first determines whether a licensed or rented asset is being used (block 1402). If not, the process is complete (block 1414). Conversely, if a licensed or rented asset is being used, the process 1400 next determines whether this is the first time the asset has been used on the current day. If not, the process is complete (block 1414). However, if this is the first time the asset has been played on the current day, the process 1400 next determines whether the licensed or rented asset is in the list of rented assets in the asset usage count list 1102, which for each rented asset includes the title of the rented asset 1403, the dates on which the asset has been accessed or used 1405, and the total number of days 1407 on which the asset has been accessed or used (termed usage count). If the rented asset is not in the list, then at block 1408 the asset is added to the list with a usage count of zero (e.g. the total number of days or usage count 1407 is set to zero). However, at block 1410, a numeric one is added to the usage count such that the usage count 1407 is set to one. On the other hand, if this is the first time the asset has been played on the current day and the asset is already in the asset usage count list 1102, a numeric one is added to the usage count 1407 for the asset (block 1410). Furthermore, the current date on which the asset has been accessed or used is also recorded in the asset usage count list 1102 (e.g. in the dates asset used field 1405) (block 1412). The process 1400 is then complete (block 1414). With reference now to FIG. 14b, FIG. 14b illustrates a process 1420 implemented by the commerce server for tracking the number of uses of rented digital assets by computing devices using the secure electronic commerce system 1100, according to one embodiment of the present invention. As previously discussed, the commerce server 104a utilizing commerce software module 420, in conjunction with the database software module 418, tracks the purchase, rental, and number of uses of digital assets by a user and may be used to implement the process 1420. More particularly, the customer server 104a periodically queries the computing device 102 to determine the amount of usage of licensed or rented assets in order to report the usage to licensors and to use in determining the amount of royalties owed to the licensor (e.g. for royalty tracking). For example, when the user logs on to the customer server 104a, the customer server 104a can poll the computing device 102 to determine the number of uses of rented digital assets, or, whenever the user goes on-line (e.g. accesses the Internet) the computing device 102 can notify the customer server 104a that the user is on-line and the customer server 104a can poll the computing device 102 to determine the number of uses of rented digital assets, as will be discussed. As shown in FIG. 14b, the process 1420 implemented at the customer server 104a requests the asset usage count lists 1102 from the computing devices 102 in the secure electronic commerce system 1100 on a periodic basis. In other words, the customer server 104a polls the plurality of computing devices for their asset usage count lists 1102. Particularly, examining the process 1420 as to the customer server 104a polling a single computing device 102, the process 1420 determines whether an asset usage count list 1102 has been received from the computing device 102 (block 1422). If not, the process 1420 is complete (block 1434). If an asset usage count list 1102 from a computing device 102 is received, the process 1420 obtains the first entry from the asset usage count list 1102 (e.g. Title1, Dates11-1N, Total1). Next, the customer server 104a implementing process 1420 looks up the title of the asset in the asset database 107 (block 1426). The process 1420 adds the total usage count from the polled computing device 102 to the total aggregated usage count 1110 for that particular asset contained in the asset database 107 (block 1428). Thus, the asset database 107 includes a total aggregated usage count 1110 for each asset that is an aggregation of the total usage counts of all the computing devices 102 polled. The process 1420 implemented by the customer server 104a then determines if there are any more entries in the asset usage count list of the current polled computing device 102 (block 1430). If not, the process 1420 is complete (block 1434). However, if there are more entries, the process 1420 proceeds to block 1432 to get the next entry from the asset usage count list (e.g. Title2, Dates21-2N, Total2). The process 1420 then returns to block 1426 to look up the title of the asset in the asset database 107 and adds the total usage count from polled computing device 102 to the total aggregated usage count 1110 for that particular asset. The process 1420 iteratively goes through this procedure for every asset in the asset usage count list 1102 of the polled computing device until the last asset is reached (e.g. TitleN, DatesN1-NN, TotalN). Moreover, the customer server 104a implementing the process 1420 does this for every computing device 102 in the secure electronic commerce system network 1120. In this way, every asset 1111 in the asset database has a usage count 1110 that represents the aggregated total number of uses by every computing device 102 in the network (for a given period of time). Accordingly, the total amount of usage of licensed or rented assets can be determined in order to report the usage to licensors and to be used in determining the amount of royalties owed to the licensors (e.g. for royalty tracking). With reference now to FIG. 14c, FIG. 14c illustrates a process 1440 implemented by a computing device 102 to transfer the asset usage count list 1102 of the computing device 102 to the customer server 104a, according to one embodiment of the present invention. Briefly, the computing device 102, in response to the request for the asset usage count list 1102 by the customer server 104a, simply sends the asset usage count list 1102 to the customer server 104a and then the erases the list from the local memory (e.g. the hard disk) of the computing device 102. As shown in FIG. 14c, the process 1440 implemented by the computing device 102 first determines whether an asset usage count list 1102 is present (block 1442). If not process 1440 is complete (block 1448). If on the other hand, an asset usage count list 1102 is present then the computing device 102 simply sends the asset usage count list 1102 to the customer server 104a (block 1444). Then, the computing device 102 erases the asset usage count list 1102 (block 1446). The process 1440 is then complete (block 1448). Thus, the processes for retrieving rented material usage counts happens behind the scenes and does not involve any interaction with the end-user. Accordingly, the secure electronic commerce system 1100 tracks and records the distribution and use of assets. Particularly, the secure electronic commerce system 1100 tracks the rental and number of uses of assets by users. The secure electronic commerce system 1100 as previously described can be used either directly by the content owner to track the distribution and use of assets or by a third party provider to track the distribution and use of assets and further in order to keep an accounting of licensing fees (e.g. royalties) due to the content owner (e.g. the copyright holder). Furthermore, the secure electronic commerce system 1100 makes it easy for a third party provider to accurately report transactions regarding licensed assets to the ultimate content owner for licensing fees (e.g. royalty tracking). Therefore, the secure electronic commerce system 1100 promotes the distribution of assets to customers in a secure manner and provides a secure revenue opportunity for content providers (especially the ultimate content owner (i.e. the copyright holder)). Turning now to FIG. 15, FIG. 15 illustrates a process 1500 performed by the customer server 104a to implement the cycled billing of users, according to one embodiment of the present invention. The process 1500 may be implemented by the commerce software module 420, in conjunction with the database software module 418, of the customer server 104a. Generally, the customer server 104a automatically charges any outstanding balance for a user at the end of a billing cycle directly to the registered credit card for that user. The billing cycle can, for example, be monthly and occur on the monthly anniversary of the registration date of the user. As shown in FIG. 15, the process 1500 first obtains a first subscriber account from the user information database 109 (block 1502). Next, the process 1500 determines whether or not the account is due (block 1504). If the account is a not due, the process 1500 moves to block 1520 and the process 1500 determines whether or not there are more user accounts to check. If not the process 1500 is complete (block 1524). However, if there are still more accounts to check then the process 1500 returns to block 1504 to determine whether the next account is due and the process 1500 begins again. If an account at block 1504 is due, then the process 1500 determines whether the amount of money due is greater than zero (block 1506). If the account balance due is a not greater than zero (i.e. it is zero or has a credit), the process 1500 moves to block 1516 where a next due date for the user's account is set for cycled billing. Then, the user's account is updated in the user information database 109 (block 1518). Next, at block 1520, the process 1500 determines whether or not there are more user accounts to check. If not the process 1500 is complete (block 1524). However, if there are still more accounts to check then the process 1500 returns to block 1504 to determine whether the next account is due and the process 1500 begins again. On the other hand, if the account balance due is greater than zero, then the process 1500 issues a charge request to a trusted authority 1130 (block 1508). The process 1500 then determines whether the charge request was successful (block 1510). If the charge request was not successful (i.e. the credit card was not successfully charged), then the subscriber's account is canceled (block 1512), the user information database 109 is updated (block 1518), and the user is notified of the cancellation and of his or her credit card not being able to be charged on the billing statement sent to the user and/or by a notification the next time the user attempts to log on to the customer server 104a. The process 1500 then moves to block 1520 and the process 1500 determines whether or not there are more user accounts to check. If not, the process 1500 is complete (block 1524). However, if there are more accounts to check then the process 1500 returns to block 1504 to determine whether the next account is due and process 1500 begins again. Conversely, if the charge request is successful (i.e. the credit card is successfully charged), then the user's account balance is set to zero (block 1514). Then, a next due date for the user's account is set for cycled billing (block 1516). Next, the user's account is updated in the user information database 109 (block 1518). The process 1500 then moves to block 1520 and the process 1500 determines whether or not there are more user accounts to check. If not, the process 1500 is complete (block 1524). However, if there are more accounts to check then process 1500 returns to block 1504 to determine whether the next account is due and process 1500 begins again. Turning now to FIG. 16, FIG. 16 illustrates a process 1600 to update a user's registration and subscription information at the server 104, according to one embodiment of the present invention. A user's registration and subscription information may be updated by the user himself at the user's computing device 102. For example, this can be accomplished by the user inputting different subscription and registration information into the forms already discussed. In this instance, the customer server 104a updates the user's subscription and registration information 1106 in the user information database 109. Alternatively, a customer service operator utilizing the customer service system 1120, previously discussed, may also change the registration and subscription information in the registration and subscription forms on behalf of the user. In this instance, the customer service server 104c will update the user's subscription and registration information 1106 in the user information database 109. Thus, either the customer server 104a or the customer service server 104c may implement the process 1600 with the information received from the user at the computing device 102 or the customer service operator at the customer service system 1120, respectively. As shown in FIG. 16, the process 1600 implemented by the server 104 (either the customer server 104a or the customer service server 104c) first starts a secure sockets layer (SSL) session with either the computing device 102 or the customer service system 1120, respectively (block 1602). Next, the registration and subscription information for the user is retrieved from the user information database 109 (block 1604). Registration and subscription update forms are then sent to the client (e.g. the user at the client device 102 or the customer service operator at the customer service system 1120) (block 1606). The server 104 (e.g. the customer server 104a or the customer service server 104c) then waits for the forms to be submitted (block 1608). At block 1610, the process 1600 performs monitoring to see if the forms have been canceled. If the forms are canceled, then the process 1600 is complete (block 1620). If the forms are not canceled, then the process 1600 next determines whether the contents in the forms are valid (block 1612). If the former contents are not valid, the client (e.g. the user or the customer service operator) is notified of the incorrect contents and the process 1600 returns to block 1608 to await the submission of revised forms. On the other hand, if the form contents are valid, then the new registration and subscription information data is stored in the subscription and registration information 1106 for the user in the user information database 109. The SSL session is then stopped (block 1618) and the process 1600 is complete (block 1620). Turning now to FIG. 17, FIG. 17 illustrates a process 1700 to cancel a user's subscription at the server 104, according to one embodiment of the present invention. A user's subscription may be canceled by the user himself at the user's computing device 102. In this instance, the customer server 104a deactivates the account for the user in the user information database 109. Alternatively, a customer service operator utilizing the customer service system 1120, previously discussed, may also cancel a user's subscription on behalf of the user. In this instance, the customer service server 104c deactivates the account for the user in the user information database 109. Thus, either the customer server 104a or the customer service server 104c may implement the process 1700 to deactivate a user's account. As shown in FIG. 17, the process 1700 implemented by the server 104 (e.g. either the customer server 104a or the customer service server 104c) first starts a secure sockets layer (SSL) session with either the computing device 102 or the customer service system 1120, respectively (block 1702). Next, an account cancellation form is sent to the client (e.g. the user at the client device 102 or the customer service operator at the customer service system 1120) from the server 104 (e.g. the customer server 104a or the customer service server 104c) (block 1704). The server 104 then waits for the cancellation form to be submitted (block 1706). At block 1708, the process 1700 performs monitoring to see if the cancellation operation has been canceled. If the cancellation operation is canceled, then the SSL session is stopped (block 1720) and the process 1700 is complete (block 1722). On the other hand, if the cancellation operation is not canceled, the process 1700 determines whether or not an outstanding balance is due by the user (block 1710). If there is no outstanding balance, then the user's account is deactivated in the user information database 109 (block 1718). The SSL session is stopped (block 1720) and the process 1700 is complete (block 1722). However, if there is an outstanding balance due, a charge request is issued to a trusted authority (block 1712). If the charge request is not successful (i.e. the credit card is not successfully charged), then the client (e.g. the user at the client device 102 or the customer operator at the customer service system 1120) is sent a rejection notification (block 1716) and the process 1700 returns to block 1706 to again await for the submission of cancellation forms. On the other hand, if the charge request is successful (i.e. the credit card successfully charged), then the user's account is deactivated in the user information database 109 (block 1718), the SSL session is stopped (block 1720), and the process 1700 is complete (block 1722). Turning now to FIG. 18, FIG. 18 illustrates a process 1800 to transfer the ownership of a security device from one user to another, according to one embodiment of the present invention. The customer service operators that work at the customer service system 1120 are provided forms for transferring the ownership of a security device from one user to another user. For example, this can occur when a first user sells a security device to a second user, and the second user wants to update the registration and subscription information for billing purposes. Continuing with this example, the second user would then call a customer service operator to update his or her registration and subscription information (or would communicate with the customer service operator by other means—such as e-mail or fax). As previously discussed, a customer service operator at the customer service system 1120 interacts with the customer service server 104c of the server 104 to implement changes, such as the transfer of ownership of a security device. Thus, the customer service server 104c may implement the process 1800 to transfer the ownership of a security device. As shown in FIG. 18, the process 1800 implemented by the customer service server 104c first starts a secure sockets layer (SSL) session with the customer service system 1120 (block 1802). Next, at block 1804, the customer service server 104c sends a transfer of ownership form to a customer service operator at the customer service system 1120. The customer service server 104c waits for the transfer of ownership form to be submitted back from the customer service system 1120 (block 1806). At block 1810, the process 1800 performs monitoring to see if the transfer of ownership operation has been canceled. If the transfer of ownership operation has been canceled, then the SSL session is stopped (block 1814) and the process 1800 is complete (block 1816). On the other hand, if the transfer of ownership operation is not canceled, then the subscription and registration information 1106 in the user information database 109 is updated to reflect the change of ownership as present in the from the customer service operator (block 1812). Next, the SSL session is stopped (block 1814) and the process 1800 is complete (block 1816). Referring now to FIG. 19, FIG. 19 illustrates a process 1900 to provide account adjustments for users, according to one embodiment of the present invention. The customer service operators that work at the customer service system 1120 are provided with the authority to make account adjustments for users. Particularly, customer service operators are provided with forms to adjust account balances for users including crediting accounts and issuing refunds. For example, a user may call a customer service operator to request a credit for an asset that was not received (or would communicate with the customer service operator by other means—such as e-mail or fax). As previously discussed, a customer service operator at the customer service system 1120 interacts with the customer service server 104c of the server 104 to implement changes, such as making account adjustments for users. Thus, the customer service server 104c may implement the process 1900 to make account adjustments for users. As shown in FIG. 19, the process 1900 implemented by the customer service server 104c first starts a secure sockets layer (SSL) session with the customer service system 1120 (block 1902). Next, at block 1904, customer service server 104c sends an account adjustment form to a customer service operator at the customer service system 1120. The customer service server 104c then waits for the account adjustment form to be submitted back from the customer service system 1120 (block 1904). At block 1906, the process 1900 performs monitoring to see if the account adjustment operation has been canceled. If the account adjustment operation has been canceled, then the SSL session is stopped (block 1920) and the process 1900 is complete (block 1922). On the other hand, if the account adjustment operation is not canceled, then either a credit or charge request is issued to a trusted authority 1130 (block 1908). Next, the process 1900 determines if the charge request or credit is successful or not (block 1910). If the charge request or credit is not successful, then a notification of the rejection of the account adjustment—e.g., the charge request or credit—is sent to the customer service operator at the customer service system 1120 (block 1912). The process 1900 then proceeds back to block 1904 in which the customer service server 104c waits for account adjustment forms to be submitted. However, if the charge request or credit is successful, then the account balance for the user at the server 104 (e.g. in the user information database 109) is updated (block 1914). Further, a notification is sent to the customer service operator and the user that the submission for the account balance adjustment (e.g. the charge request or credit) has been accepted. The SSL session is then stopped (block 1920) and the process 1900 is complete (block 1922). As previously discussed, the secure electronic commerce system 1100 tracks and records the distribution and use of assets. Particularly, the secure electronic commerce system 1100 tracks the purchase, rental, and number of uses of assets by a user. The secure electronic commerce system 1100 can be used either directly by the content owner to track the distribution and use of assets or by a third party provider to track the distribution and use of assets and further in order to keep an accounting of licensing fees (e.g. royalties) due to the content owner (e.g. the copyright holder). In this way, the secure electronic commerce system 1100 makes it easy for a third party provider to accurately report transactions regarding licensed assets to the ultimate content owner for licensing fees (e.g. royalty tracking). Accordingly, the secure electronic commerce system 1100 promotes the distribution of assets to customers in a secure manner and provides a secure revenue opportunity for content providers (especially the ultimate content owner (i.e. the copyright holder)). Moreover, the secure electronic commerce system 1100, as previously described, further provides other functions related to uniquely identifying and authorizing a security device 1100 attached to a computing device 102 and then allowing the user with the authorized security device to register and subscribe to a Web-based business server. Further, the secure electronic commerce system 1100 provides for cycled billing utilizing a trusted authority, registration and subscription updates, cancellation, the transfer of ownership of authorized security devices, and account adjustments. The various aspects of the previously described inventions can be implemented as one or more instructions (e.g. software modules, programs, code segments, etc.) to perform the previously described functions. The instructions which when read and executed by a processor, cause the processor to perform the operations necessary to implement and/or use embodiments of the invention. Generally, the instructions are tangibly embodied in and/or readable from a machine-readable medium, device, or carrier, such as memory, data storage devices, and/or remote devices. The instructions may be loaded from memory, data storage devices, and/or remote devices into the memory of the computing device 102, server 104, and interface device 106 or security device 110 for use during operations. The instructions can be used to cause a general purpose or special purpose processor, which is programmed with the instructions to perform the steps of the present invention. Alternatively, the features or steps of the present invention may be performed by specific hardware components that contain hard-wired logic for performing the steps, or by any combination of programmed computer components and custom hardware components. While, embodiments of the present invention have been described with reference to the World-Wide Web, the methods, systems, and apparatuses described herein are equally applicable to other network infrastructures or other data communications systems. While the present invention and its various functional components have been described in particular embodiments, it should be appreciated the embodiments of the present invention can be implemented in hardware, software, firmware, middleware or a combination thereof and utilized in systems, subsystems, components, or sub-components thereof. When implemented in software (e.g. as a software module), the elements of the present invention are the instructions/code segments to perform the necessary tasks. The program or code segments can be stored in a machine readable medium, such as a processor readable medium or a computer program product, or transmitted by a computer data signal embodied in a carrier wave, or a signal modulated by a carrier, over a transmission medium or communication link. The machine-readable medium or processor-readable medium may include any medium that can store or transfer information in a form readable and executable by a machine (e.g. a processor, a computer, etc.). Examples of the machine/processor-readable medium include an electronic circuit, a semiconductor memory device, a ROM, a flash memory, an erasable programmable ROM (EPROM), a floppy diskette, a compact disk CD-ROM, an optical disk, a hard disk, a fiber optic medium, a radio frequency (RF) link, etc. The computer data signal may include any signal that can propagate over a transmission medium such as electronic network channels, optical fibers, air, electromagnetic, RF links, etc. The code segments may be downloaded via computer networks such as the Internet, Intranet, etc. While this invention has been described with reference to illustrative embodiments, this description is not intended to be construed in a limiting sense. Various modifications of the illustrative embodiments, as well as other embodiments of the invention, which are apparent to persons skilled in the art to which the invention pertains are deemed to lie within the spirit and scope of the invention. |
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055330746 | abstract | A system for determining the level of coolant in a depressurized nuclear reactor comprises a first set of pressure transducers located in the coolant piping and a second set of pressure tranducers located at the top or near the top of the pressurizer. Electrical signals from these independent transducers are fed by cable to a controller with a microprocessor in the reactor control room where the coolant level is calculated and displayed. Compensations for signal error, coolant temperature and coolant chemistry are provided. |
summary | ||
claims | 1. A CT scanner, comprising:a means for rotating a radiation source around an examination region;a means for generating an analog data signal that varies with an intensity of radiation traversing the examination region;a means for converting the analog data signal to a digital data signal including aperiodic pulses varying in frequency with the intensity of the radiation traversing the examination region as the radiation source rotates about the examination region and adding a minimized offset signal to the analog data signal prior to the converting so that the intensity of the analog data signal is such that at least one aperiodic pulse occurs on the digital data signal ever 2-½ data intervals;a means for producing a time signal indicative of data intervals;a means for determining average radiation intensity in each data interval by counting the pulses of the digital data signal starting with a digital data signal pulse occurring in a preceding data interval and continuing to a digital data signal pulse occurring in a succeeding data interval. 2. The CT scanner as set forth in claim 1, the time signal producing means further including:a means for detecting a start of a first measured data interval and a start of a next data interval. 3. The CT scanner as set forth in claim 2, the determining means further including:a means for storing a first digital data signal pulse count in a first start data location and storing a first time signal value associated with the first digital data signal pulse count in a first start time location each time a pulse occurs on the digital data signal until the first measured data interval starts and for storing a second digital data signal pulse count in an end data location and storing a second time signal value associated with the second digital data signal pulse count in an end time location when the next pulse occurs on the digital data signal after the start of the next data interval is detected;wherein the determining means determines the average intensity of the detected radiation for the first measured data interval by dividing a difference between the pulse count stored in the end data location and the pulse count stored in the first start data location by a difference between the value stored in the end time location and the value stored in the first start time location. 4. The CT scanner as set forth in claim 3 the converting means further including:a means for adding a minimized offset signal to the analog data signal so that the intensity of the analog data signal is such that at least one aperiodic pulse occurs on the digital data signal during each data interval;wherein the determining means considers the minimized offset signal when determining the average intensity. 5. The CT scanner as set forth in claim 1, the converting means further including:a means for adding a minimized offset signal to the analog data signal prior to the converting so that the intensity of the analog data signal is such that at least one aperiodic pulse occurs on the digital data signal every 2½ data intervals. 6. A method of measuring an intensity of detected radiation in a CT scanner, the method comprising:a) rotating a radiation source around an examination region;b) generating an analog data signal that varies with an intensity of radiation traversing the examination region;c) converting the analog data signal to a digital data signal including aperiodic pulses varying in frequency with the intensity of the radiation traversing the examination region as the radiation source rotates about the examination region and adding a minimized offset signal to the analog data signal prior to the converting so that the intensity of the analog data signal is such that at least one aperiodic pulse occurs on the digital data signal every 2½ data intervals;d) producing a time signal indicative of data intervals;e) determining average radiation intensity in each data interval by counting the pulses of the digital data signal starting with a digital data signal pulse occurring in a preceding data interval and continuing to a digital data signal pulse occurring in a succeeding data interval, and storing the average radiation intensity. 7. The method as set forth in claim 6 wherein step e) further includes:f) storing a first digital data signal pulse count in a first start data location and storing a first time signal value in a first start time location each time a pulse occurs on the digital data signal until a first measured data interval starts;g) detecting a start of the first measured data interval and detecting a start of a next data interval;h) after the start of the next data interval is detected, storing a second digital data signal pulse count in an end data location and storing a second time signal value in an end time location when the next pulse occurs on the digital data signal; andi) determining an average intensity of the detected radiation for the first measured data interval by dividing a difference between the pulse count stored in the end data location and the pulse count stored in the first start data location by a difference between the value stored in the end time location and the value stored in the first start time location. 8. The method as set forth in claim 7, further including:in step c), adding a minimized offset signal to the analog data signal prior to the converting so that the intensity of the analog data signal is such that at least one aperiodic pulse occurs on the digital data signal during each data interval; andin step i), considering the minimized offset signal when determining the average intensity. 9. The method as set forth in claim 7, further including:in step a), adding a minimized offset signal to the analog data signal prior to the converting so that the intensity of the analog data signal is such that at least one aperiodic pulse occurs on the digital data signal every 2½ data intervals;in step f), continuing to store the digital data signal pulse count in the same manner until the start of a second data interval;in step g), detecting a start of the second measured data interval between the start of the first measured data interval and the start of the next data interval; andin step i), determining the average intensity for the second measured data interval rather than the first measured data interval and considering the minimized offset signal when determining the average intensity. 10. The method as set forth in claim 1 wherein step e) further includes:f) storing a first digital data signal pulse count in a first star data location and storing a first time signal value in a first start time location each time a pulse occurs on the digital data signal during first and second preceding data intervals until a first measured data interval starts wherein the first preceding data interval is adjacent to the first measured data interval and the second preceding data interval is adjacent to the first preceding data interval. 11. The method as set forth in claim 10 wherein step e) further includes:g) detecting a start of the first measured data interval and detecting a start of a first succeeding data interval adjacent to the first measured data interval;h) after the start of the first succeeding data interval is detected, storing a second digital data signal pulse count in a first end data location and storing a second time signal value in a first end time location when the next pulse occurs on the digital data signal during the first succeeding data interval; andi) determining an average intensity of the detected radiation for the first measured data interval by dividing a difference between the pulse count stored in the first end data location and the pulse count stored in the first start data location by a difference between the value stored in the first end time location and the value stored in the first start time location. 12. The method as set forth in claim 10 wherein step e) further includes:g) detecting a start of the first measured data interval, detecting a start of a first succeeding data interval adjacent to the first measured data interval, and detecting a start of a second succeeding data interval adjacent to the first succeeding data interval;h) after the start of the second succeeding data interval is detected, storing a second digital data signal pulse count in a first end data location and storing a second time signal value in a first end time location when the next pulse occurs on the digital data signal during the second succeeding data interval; andi) determining an average intensity of the detected radiation for the first measured data interval by dividing a difference between the pulse count stored in the first end data location and the pulse count stored in the first start data location by a difference between the value stored in the first end time location and the value stored in the first start time location. 13. The method as set forth in claim 10 wherein step e) further includes:g) detecting a start of the first measured data interval and detecting a start of a first succeeding data interval adjacent to the first measured data interval;h) when the start of the first succeeding data interval is detected, storing a second digital data signal pulse count in a first end data location and storing a second time signal value in a first end time location; andi) determining an average intensity of the detected radiation for the first measured data interval by dividing a difference between the pulse count stored in the first end data location and the pulse count stored in the first start data location by a difference between the value stored in the first end time location and the value stored in the first start time location. 14. The method as set forth in claim 13 wherein:the first succeeding data interval is a second measured data interval; andstep e) further including:j) storing a third digital data signal pulse count in a second start data location and storing a third time signal value in a second start time location each time a pulse occurs on the digital data signal during first and second preceding data intervals with respect to the second measured data interval until the second measured data interval starts, wherein the first preceding data interval is adjacent to the second measured data interval and the second preceding data interval is adjacent to the first preceding data interval;wherein step e) further includes:k) detecting a start of the second measured data interval and detecting a start of first and second succeeding data intervals with respect to the second measured data interval, wherein the first succeeding data interval is adjacent to the first measured data interval, wherein the second succeeding data interval is adjacent to the first succeeding data interval;l) after the start of the second succeeding data interval is detected, storing a fourth digital data signal pulse count in a second end data location and storing a fourth time signal value in a second end time location when the next pulse occurs on the digital data signal during the second succeeding data interval; andm) determining an average intensity of the detected radiation for the second measured data interval by dividing a difference between the pulse count stored in the second end data location and the pulse count stored in the second start data location by a difference between the value stored in the second end time location and the value stored in the second start time location. 15. The method as set forth in claim 1 wherein step e) further includes:f) detecting a start of the first measured data interval;g) when the start of the first measured data interval is detected, storing a first digital data signal pulse count in a first start data location and storing a first time signal value in a first start time location. 16. The method as set forth in claim 15 wherein step e) further includes:h) detecting a start of a first succeeding data interval adjacent to the first measured data interval;i) after the start of the first succeeding data interval is detected, storing a second digital data signal pulse count in a first end data location and storing a second time signal value in a first end time location when the next pulse occurs on the digital data signal during the first succeeding data interval; andj) determining an average intensity of the detected radiation for the first measured data interval by dividing a difference between the pulse count stored in the first end data location and the pulse count stored in the first start data location by a difference between the value stored in the first end time location and the value stored in the first start time location. 17. The method as set forth in claim 16 wherein:the first succeeding data interval is a second measured data interval; andstep e) further including:k) storing a third digital data signal pulse count in a second start data location and storing a third time signal value in a second start time location each time a pulse occurs on the digital data signal during first and second preceding data intervals with respect to the second measured data interval until the second measured data interval starts, wherein the first preceding data interval is adjacent to the second measured data interval and the second preceding data interval is adjacent to the first preceding data interval;wherein step e) further includes:l) detecting a start of the second measured data interval and detecting a start of a first succeeding data interval with respect to the second measured data interval, wherein the first succeeding data interval is adjacent to the second measured data interval;m) when the start of the first succeeding data interval is detected, storing a fourth digital data signal pulse count in a second end data location and storing a fourth time signal value in a second end time location; andn) determining an average intensity of the detected radiation for the second measured data interval by dividing a difference between the pulse count stored in the second end data location and the pulse count stored in the second start data location by a difference between the value stored in the second end time location and the value stored in the second start time location. 18. The method as set forth in claim 15 wherein step e) further includes:h) detecting a start of the first measured data interval, detecting a start of a first succeeding data interval adjacent to the first measured data interval, and detecting a start of a second succeeding data interval adjacent to the first succeeding data interval;i) after the start of the second data interval is detected, storing a second digital data signal pulse count in a first end data location and storing a second time signal value in a first end time location when the next pulse occurs on the digital data signal during the second succeeding data interval; andj) determining an average intensity of the detected radiation for the first measured data interval by dividing a difference between the pulse count stored in the first end data location and the pulse count stored in the first start data location by a difference between the value stored in the first end time location and the value stored in the first start time location. 19. The method as set forth in claim 18 wherein:the first succeeding data interval is a second measured data interval; andstep e) further including:k) storing a third digital data signal pulse count in a second start data location and storing a third time signal value in a second start time location each time a pulse occurs on the digital data signal during first and second preceding data intervals with respect to the second measured data interval until the second measured data interval starts, wherein the first preceding data interval is adjacent to the second measured data interval and the second preceding data interval is adjacent to the first preceding data interval;wherein step e) further includes:l) detecting a start of the second measured data interval and detecting a start of a first succeeding data interval with respect to the second measured data interval, wherein the first succeeding data interval is adjacent to the second measured data interval;m) after the start of the first succeeding data interval is detected, storing a fourth digital data signal pulse count in a second end data location and storing a fourth time signal value in a second end time location when the next pulse occurs on the digital data signal during the first succeeding data interval; andn) determining an average intensity of the detected radiation for the second measured data interval by dividing a difference between the pulse count stored in the second end data location and the pulse count stored in the second start data location by a difference between the value stored in the second end time location and the value stored in the second start time location. 20. A method of measuring an intensity of detected radiation in a CT scanner, the method comprising:rotating a radiation source around an examination region;generating an analog data signal that varies with an intensity of radiation traversing the examination region;converting the analog data signal to a digital data signal including aperiodic pulses varying in frequency with the intensity of the radiation traversing the examination region as the radiation source rotates about the examination region;producing a time signal indicative of data intervals; anddetermining average radiation intensity in each data interval by counting the pulses of the digital data signal starting with a digital data signal pulse occurring in a preceding data interval and continuing to a digital data signal pulse occurring in a succeeding data interval, and storing the average radiation intensity, wherein determining includes:storing a first digital data signal pulse count in a first start data location and storing a first time signal value in a first start time location each time a pulse occurs on the digital data signal until a first measured data interval starts;detecting a start of the first measured data interval and detecting a start of a next data interval;after the start of the next data interval is detected, storing a second digital data signal pulse count in an end data location and storing a second time signal value in an end time location when the next pulse occurs on the digital data signal; anddetermining an average intensity of the detected radiation for the first measured data interval by dividing a difference between the pulse count stored in the end data location and the pulse count stored in the first start data location by a difference between the value stored in the end time location and the value stored in the first start time location. |
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description | The subject application is a continuation of PCT Patent Application No. PCT/US15/61356, filed Nov. 18, 2015, which claims priority to Russian Patent Application No. 2014146574, filed on Nov. 19, 2014, both of which are incorporated by reference herein in their entirety for all purposes. The subject matter described herein relates generally to neutral beam injectors and, more particularly, to a photon neutralizer for a neutral beam injector based on negative ions. A traditional approach to produce a neutral beam from a negative ion H−, D− beam for plasma heating or neutral beam assisted diagnostics, is to neutralize the negative ion beam in a gas or plasma target for detachment of the excess electrons. However, this approach has a significant limitation on efficiency. At present, for example, for designed heating injectors with a 1 MeV beam [R. Hemsworth et al., 2009, Nucl. Fusion 49 045006], the neutralization efficiency in the gas and plasma targets will be about 60% and 85%, respectively [G. I. Dimov et al., 1975, Nucl. Fusion 15, 551], which considerably affects the overall efficiency of the injectors. In addition, the application of such neutralizers is associated with complications, including the deterioration of vacuum conditions due to gas puffing and the appearance of positive ions in the atomic beam, which can be significant in some applications. Photodetachment of an electron from high-energy negative ions is an attractive method of beam neutralization. Such method does not require a gas or plasma puffing into the neutralizer vessel, it does not produce positive ions, and it assists with beam cleaning of fractions of impurities due to negative ions. The photodetachment of an electron corresponds to the following process: H−+hω=H0+e. Similar to most negative ions, the H− ion has a single stable state. Nevertheless, photodetachment is possible from an excited state. The photodetachment cross section is well known [see, e.g., L. M.Branscomb et al., Phys. Rev. Lett. 98, 1028 (1955)]. The photodetachment cross section is large enough in a broad photon energy range which practically overlaps all visible and near IR spectrums. Such photons cannot knock out an electron from H0 or all electrons from H− and produce positive ions. This approach was proposed in 1975 by J. H. Fink and A. M. Frank [J. H. Fink et al., Photodetachment of electrons from negative ions in a 200 keV deuterium beam source, Lawrence Livermore Natl. Lab. (1975), UCRL-16844]. Since that time a number of projects for photon neutralizers have been proposed. As a rule, the photon neutralizer projects have been based on an optic resonator similar to Fabri-Perot cells. Such an optic resonator needs mirrors with very high reflectance and a powerful light source with a thin line, and all of the optic elements need to be tuned very precisely. For example, in a scheme considered by Kovari [M. Kovari et al., Fusion Engineering and Design 85 (2010) 745-751], the reflectance of the mirrors is required to be not less than 99.96%, the total laser output power is required to be about 800 kW with output intensity of about 300 W/cm2, and the laser bandwidth is required to be less than 100 Hz. It is unlikely that such parameters could be realized together. Therefore, it is desirable to provide a non-resonance photo-neutralizer. Embodiments provided herein are directed to systems and methods for a non-resonance photo-neutralizer for negative ion-based neutral beam injectors. The non-resonance photo-neutralizer described herein is based on the principle of nonresonant photon accumulation, wherein the path of the photon becomes tangled and trapped in a certain space region, i.e., the photon trap. The trap is preferably formed as two smooth mirror surfaces facing each other with at least one surface being concave. In the simplest form, the trap is preferably elliptical in shape. A confinement region of the trap is a region near a family of normals that are common to both mirror surfaces of the trap. The photons with a sufficiently small angle of deviation from the nearest common normal are confined. Depending on specific conditions, the shape of the trap may be one of spherical, elliptical, cylindrical, toroidal, or a combination thereof. In operation, photon beams with a given angular spread along and across the trap are injected through one or more small holes in one or more of the mirrors. The photon beams can be from standard industrial power fiber lasers. The photo neutralizer does not require high quality laser radiation sources pumping a photon target, nor does it require very high precision adjustment and alignment of the optic elements Other systems, methods, features and advantages of the example embodiments will be or will become apparent to one with skill in the art upon examination of the following figures and detailed description. It should be noted that elements of similar structures or functions are generally represented by like reference numerals for illustrative purpose throughout the figures. It should also be noted that the figures are only intended to facilitate the description of the preferred embodiments. Each of the additional features and teachings disclosed below can be utilized separately or in conjunction with other features and teachings to provide a non-resonance photo-neutralizer for negative ion-based neutral beam injectors. Representative examples of the embodiments described herein, which examples utilize many of these additional features and teachings both separately and in combination, will now be described in further detail with reference to the attached drawings. This detailed description is merely intended to teach a person of skill in the art further details for practicing preferred aspects of the present teachings and is not intended to limit the scope of the invention. Therefore, combinations of features and steps disclosed in the following detail description may not be necessary to practice the invention in the broadest sense, and are instead taught merely to particularly describe representative examples of the present teachings. Moreover, the various features of the representative examples and the dependent claims may be combined in ways that are not specifically and explicitly enumerated in order to provide additional useful embodiments of the present teachings. In addition, it is expressly noted that all features disclosed in the description and/or the claims are intended to be disclosed separately and independently from each other for the purpose of original disclosure, as well as for the purpose of restricting the claimed subject matter independent of the compositions of the features in the embodiments and/or the claims. It is also expressly noted that all value ranges or indications of groups of entities disclose every possible intermediate value or intermediate entity for the purpose of original disclosure, as well as for the purpose of restricting the claimed subject matter. Embodiments provided herein are directed to a new non-resonance photo-neutralizer for negative ion-based neutral beam injectors. A detailed discussion of a negative ion-based neutral beam injector is provided in Russian Patent Application No. 2012137795 and PCT Application No. PCT/US2013/058093, which are incorporated herein by reference. The non-resonance photo-neutralizer described herein is based on the principle of nonresonant photon accumulation, wherein the path of the photon becomes tangled and trapped in a certain space region, i.e., the photon trap. The trap is preferably formed as two smooth mirror surfaces facing each other with at least one surface being concave. In the simplest form, the trap is preferably elliptical in shape. A confinement region of the trap is a region near a family of normals that are common to both mirror surfaces of the trap. The photons with a sufficiently small angle of deviation from the nearest common normal are confined. Depending on specific conditions, the shape of the trap may be one of spherical, elliptical, cylindrical, toroidal, or a combination thereof. In operation, photon beams with a given angular spread along and across the trap are injected through one or more small holes in one or more of the mirrors. The photon beams can be from standard industrial power fiber lasers. The photo neutralizer does not require high quality laser radiation sources pumping a photon target, nor does it require very high precision adjustment and alignment of the optic elements. Turning to the figures, an embodiment of a non-resonance photon trap 10 is shown in FIG. 1. As depicted in a two-dimensional case, the trap 10 comprises a bottom flat mirror 20 and a top concave mirror 30. A photon γ with a small angle to vertical axes within the trap 10, will develop with each reflection from the upper mirror 30 some horizontal momentum difference to central axes of trap 10. The position of the photon γ after an n-th reflection is defined by the abscissa of a reflection point, xn, with a height, F(xn), an angle φ from a vertical and a photon speed, βn. The horizontal motion is described by the following system of equations: x n + 1 - x n = ( F ( x n + 1 ) + F ( x n ) ) tg β n ( 1 ) β n + 1 - β n = 2 dF ( x n + 1 ) dx ( 2 ) For stability investigation, linearize versions of equations (1)and (2) are combined and the following equations are obtained: x n + 1 - x n = 2 F ( 0 ) β n ( 3 ) β n + 1 - β n = 2 d 2 F ( 0 ) dx 2 x n + 1 ( 4 ) By combining equations (3) and (4), the following linear recurrence relation is obtained: x n + 2 - 2 x n + 1 + x n = 4 F ( 0 ) d 2 F ( 0 ) dx 2 x n + 1 = - 4 ( 0 ) x n + 1 R , ( 5 ) where R is the curvature radius of top mirror 30. Equation (5) is a type of finite-difference scheme for an oscillation system with unit time step and with Eigen frequency ω 0 = 2 F ( 0 ) R . The solution is representable in the form xn=A·qn, where q is a complex number. Then for q defined as: q 1 , 2 = 1 - 2 F ( 0 ) R ± ( 1 - 2 F ( 0 ) R ) 2 - 1 , ( 6 ) The stability condition is |q|≤1, from which photons confinement in a geometric optic, when taking into account non-negativity of value F ( 0 ) R ,is determined asF(0)<R, ω02<4 (7)The curvature radius of the upper mirror 30 impacts photon confinement. Recurrent systems (1) and (2) allow the production of the integral of motion: ∑ n tg β n ( β n + 1 - β n ) = ∑ n 2 ( x n + 1 - x n ) F ( x n + 1 ) + F ( x n ) dF ( x n + 1 ) dx , ( 8 ) In the case of a sufficiently small curvature of the upper mirror 30 and small steps, such as Δ F ⪡ F , dF dx ⪡ 1 , Δβ ⪡ 1 , ( 9 ) the integral sums (8) is approximately transformed into ln cos β 0 cos β = ln F ( x ) F ( x 0 ) or into standard adiabatic invariantF(x)cos(β)=const (10)Relation (10) determines the region filled by photons. These estimations enable the design of an effective photon neutralizer for negative ion beams. Turning to FIGS. 2 and 3, a reasonable three-dimensional geometry of the trap 10 is a long arch assembly of four components. As depicted in FIG. 2, the trap 10 preferably comprises a bottom or lower mirror 20 at the bottom of the trap 10 that is planar or flat in shape, and an upper mirror assembly 30 comprising a central mirror 32 that is cylindrical in shape, and a pair of outer mirrors 34 that are conical in shape and coupled to the ends of the central mirror 32. As shown, an ion beam H− is passed along the photon trap. The sizes are taken from the characteristic scales of a single neutralizer channel of a beam injector for the International Thermonuclear Experimental Reactor (ITER). The following provides results of a numerical simulation of a photon neutralizer for ITER NBI. This simulation has been carried out by using ZEMAX code. FIG. 4 shows a one ray trace in the trap system 10 given in FIG. 2 with a random angle from −3° to 3° in the XY plane, and −5° to 5° along the trap 10. The trajectory presented in FIG. 4 contains 4000 reflections, after which the ray remained in the trap system. In a resonance device [M Kovari, B. Crowley. Fusion Eng. Des. 2010, v. 85 p. 745-751], the storage efficiency under a mirror reflectance r2=0.9996 is about P/Pin≈500. In the case noted herein, with a lower mirror reflectance of r2=0.999, the determined storage efficiency is P P in ≈ 1 1 - r 2 ≈ 1000 ( 11 ) Losses will tend to be associated chiefly with a large number of surfaces inside the cavity and diffraction. [J. H. Fink, Production and Neutralization of Negative Ions and Beams: 3rd Int. Symposium, Brookhaven 1983, AIP, New York, 1984, pp. 547-560] The distribution of the radiant energy flux through a horizontal plane inside the trap 10 is shown in FIG. 5, where the reflection coefficient of all surfaces is equal to 0.999 and the input radiant power is equal to 1 W. The calculated accumulated power in the cavity of the trap 10 is equal to 722 watts. Taking into account calculation losses (Zemax code monitors and evaluates such losses) the accumulated power value should be increased by 248 watts. Therefore, the storing efficiency reaches almost a maximum possible value (11). Thus, quasi-planar systems allow within the geometrical optics the creation of a confinement region with a given size. Note, that the end cone mirrors 34 and main cylindrical mirrors 32 and 20 form broken surface as shown in FIGS. 2 and 3. The broken surfaces tend to have a negative effect on the longitudinal confinement of photons because this forms an instability region (see (7)). However, the number of crossings of these borders by a ray during the photon lifetime is not large in comparison with the total number of reflections, and, thus, the photon does not have time to significantly increase longitudinal angle and leave the trap through the ends of the trap 10. Radiation Injection into Trap and Sources To pump the optic cell, photons beams with a given angular spread along and across the trap 10 can be injected through one or more small holes in one or more mirrors. For example, it is possible by using a ytterbium fiber laser (γ=1070 nm, total power above 50 kW) [http://www.ipgphotonics.com/Collateral/Documents/English-US/HP_Brochure.pdf]. These serial lasers have sufficient power and their emission line is near optimal. The radiation beam with necessary angular spread can be prepared from fiber laser radiation by special adiabatic conical or parabolic shapers. For example, radiation with a spread of 15° from fiber and Ø300μ may be transformed to 5° and Ø1 mm, which is sufficient for the neutralizer trap 10 described herein. Efficiency of Photon Neutralization The degree of neutralization is representable as K ( P ) = 1 - exp ( σ P E 0 dV ) ( 12 ) where d is the width of the neutralization region, E0 is the photon energy, V is the velocity of the ions. P is the total accumulated power defined as P = P 0 1 - r 2 ,where P0 is the optic pumping power. The neutralization efficiency of D− flux by the laser with overall efficiency ηl may be determined as η ( P 0 ) = K ( P ) P - P - + P 0 η l ( 13 ) where P_ is the negative ion beam power. The efficiency increases with growth of D− beam power. The efficiency (13) and degree of neutralization (12) are shown in FIG. 6. This curve has been calculated for a single channel gas neutralizer in ITER injectors, in which 10 MW part is passed. Thus, in such an approach nearly 100% neutralization can be achieved with very high energetic efficiency of about 90%. For comparison, ITER neutral beam injector has a 58% neutralization [R. Hemsworth et al.// Nucl. Fusion. 2009, v. 49, 045006] and correspondently the same efficiency. The overall injector efficiency while taking into account accelerator supply and transport losses has been estimated by Krylov [A. Krylov, R. S. Hemsworth. Fusion Eng. Des. 2006, v.81, p. 2239-2248]. A preferred arrangement of an example embodiment of a negative ion-based neutral beam injector 100 is illustrated in FIGS. 7 and 8. As depicted, the injector 100 includes an ion source 110, a gate valve 120, deflecting magnets 130 for deflecting a low energy beam line, an insulator-support 140, a high energy accelerator 150, a gate valve 160, a neutralizer tube (shown schematically) 170, a separating magnet (shown schematically) 180, a gate valve 190, pumping panels 200 and 202, a vacuum tank 210 (which is part of a vacuum vessel 250 discussed below), cryosorption pumps 220, and a triplet of quadrupole lenses 230. The injector 100, as noted, comprises an ion source 110, an accelerator 150 and a neutralizer 170 to produce about a 5 MW neutral beam with energy of about 0.50 to 1.0 MeV. The ion source 110 is located inside the vacuum tank 210 and produces a 9 A negative ion beam. The vacuum tank 210 is biased to −880 kV which is relative to ground and installed on insulating supports 140 inside a larger diameter tank 240 filled with SF6 gas. The ions produced by the ion source are pre-accelerated to 120 keV before injection into the high-energy accelerator 150 by an electrostatic multi aperture grid pre-accelerator 111 in the ion source 110, which is used to extract ion beams from the plasma and accelerate to some fraction of the required beam energy. The 120 keV beam from the ion source 110 passes through a pair of deflecting magnets 130, which enable the beam to shift off axis before entering the high energy accelerator 150. The pumping panels 202 shown between the deflecting magnets 130 include a partition and cesium trap. A more detailed discussion of the negative ion-based neutral beam injector is provided in Russian Patent Application No. 2012137795 and PCT application No. PCT/US2013/058093, which are incorporated herein by reference. The example embodiments provided herein, however, are merely intended as illustrative examples and not to be limiting in any way. In the foregoing specification, the invention has been described with reference to specific embodiments thereof. It will, however, be evident that various modifications and changes may be made thereto without departing from the broader spirit and scope of the invention. For example, the reader is to understand that the specific ordering and combination of process actions shown in the process flow diagrams described herein is merely illustrative, unless otherwise stated, and the invention can be performed using different or additional process actions, or a different combination or ordering of process actions. As another example, each feature of one embodiment can be mixed and matched with other features shown in other embodiments. Features and processes known to those of ordinary skill may similarly be incorporated as desired. Additionally and obviously, features may be added or subtracted as desired. Accordingly, the invention is not to be restricted except in light of the attached claims and their equivalents. |
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048715093 | summary | BACKGROUND OF THE INVENTION This invention relates to fuel rods. More particularly, a spring clamp for maintaining fuel pellets compressed within a fuel rod during both manufacture and shipment is disclosed. SUMMARY OF THE PRIOR ART Fuel rods having fuel pellets contained therein are basic elements in a nuclear reactor. Typically, the so-called "fuel rod" includes a Zircaloy cylinder loaded with cylindrical uranium or plutonium fuel pellets. The cylindrical fuel pellets have an outside cylindrical diameter less than the inside diameter of the cylindrical and hollow Zircaloy rod into which they are placed. A fuel rod is typically on the order of 165-inches long and, dependent upon the designed fuel load, has between 140 and 150-inches of its total length occupied by the fuel pellets. The fuel rod is typically plugged and sealed at both ends. Usually, one end of the rod is plugged first. Thereafter, the fuel pellets are installed. A retainer spring is then inserted to bias the fuel pellets to the plugged end of the fuel rod. A cylindrical canister filled with Zirconium alloy chips and having holes in its ends is also installed. The Zirconium alloy chips absorb any hydrogen which may be present in the fuel rod. If free hydrogen were present it would be absorbed by the fuel rod tubing and would embrittle the tubing. The canister and the Zirconium alloy chips are referred to as a "getter". Next, the second plug is held in place and welded to the fuel rod tube. This second plug compresses the spring, so that an axial force is required to hold it in place during the welding operation. Next the gases present in the fuel rod are pumped out through a small hole and the fuel rod is back filled with helium. Helium pressure is typically between one and ten atmospheres (14.7 to 147 pounds per square inch). The fuel rod is then sealed. The sealed fuel rod contains the fuel pellet column, the retainer spring, and the getter. The remaining volume is initially occupied by the helium fill gas. During reactor operation, inert gases xenon and krykton are produced as a byproduct of the nuclear fission process. These gases must also be contained in the volume initially occupied by the helium fill gas. As the inert gases accumulate, the pressure rises. Typically, end of life pressures are in the range of 1,000 to 3,000 pound per square inch. To minimize this pressure, it is desirable to minimize the volume occupied by the retainer spring. In anticipation of the pressure ultimately to be encountered, the fuel rods are dimensioned and plugged at both ends. The rods are given a cylindrical side wall dimension that will not burst or crack under pressure of the accumulated gas. Moreover, Zircaloy plugs are welded at each end of the rods. These plugs are welded in gas tight relationship to prevent gas escape. In short, a fuel rod nearing the end of its life in a nuclear reactor is, among other things, a pressure vessel constructed to contain gases under high pressure and temperature. When the fuel rods are initially fabricated they are loaded with their pellets while horizontally disposed. Further, when the loaded rods are moved, they are also horizontally disposed. The rods on their side are moved from place to place while the steps required for the ultimate fabrication are completed. During such horizontally disposed movement, there is always a danger that the relatively heavy pellets will move from a compacted position (to and towards the bottom of the fuel rod) into a non-compacted position occupying the gas space at the top of the rod. During shipment from the site of fabrication to the nuclear reactor where the rods are ultimately placed in a fuel bundle and utilized, the rods are typically placed on their side. If the fuel pellets are not restrained, movement of the pellets from a compacted disposition into the gas space can take place. When the rods are installed within a reactor, they are disposed vertically. If the fuel column has gaps, these gaps will not close, because of pellet wedging and friction. The presence of axial gaps would lead to undesirable consequences. Specifically, reactors operate under pressure in the range of 1,000 psi. It will be remembered that initially the pressure on the inside of the rods was in the order of 200 psi. If a pellet or pellets are out of their required stacked and end to end relationship when a fuel rod is installed, the rod in the area of pellet separation can neck down under the pressure of the reactor and hold the pellet out of place. Such a phenomenon can occur where one pellet when moved out of place becomes canted at an angle. The pellet can then wedge itself to the inside diameter of the rod and remain spatially separated from its adjacent pellets. In such a case, the unoccupied volume on the inside of the fuel rod can neck down initially under the pressure of the reactor. Two consequences follow from a rod with fuel pellets out of place. First, the axial power distribution is altered to give high local powers near the axial gap in the fuel column. The high local power cause local overheating of the fuel rod. Second, overstressing or cracking of the fuel rod can occur. In view of these difficulties, the prior art has included a spring in the fuel assemblies. The spring bears against the welded end plug at one end of the rod. The spring also bears against the adjacent fuel pellet at the end of the fuel rod. Typically, the spring is configured to either contain or bear against the getter. In any event, the spring exerts a force tending to keep the fuel pellets compacted towards one end of the fuel rod after the ends of the rod are sealed. Statement of the Problem This type of spring assembly--after having been closely analyzed in an effort to achieve this improved design--has been noted to include at least five problems. First, the spring extends from the last fuel pellet to the end plug of the fuel rod. This occupancy of the full length--in the order of 12-inches--adds to the volume of the spring and reduces the volume available for the fuel column and for the gases produced by nuclear fission events in the fuel pellets. Second, the spring is a neutron absorber. Neutrons--which might otherwise be used in the desired chain reaction--are absorbed and lost when they come into contact with the excess mass of material of the spring. Third, the full volume between the end plug and the fuel pellets varies in length. Consequently, the length configuration of the springs used for various lengths of pellet loading must vary. In short, different fuel designs require different springs--a complicating factor in the production of fuel rods. Fourth, the spring installation is one of the last steps in the fuel rod fabrication. During earlier fabrication steps, the spring is not present, and there is a possibility of opening gaps between pellets in the fuel column. Finally, the end of the spring adjacent the end plug bears against the end plug while welding occurs. An axial force is required to hold the end plug in position. Further, this portion of the spring is in the area highly heated by the weld. The heat of the weld can change the spring characteristics. It will be understood that recognition of a problem can constitute invention. Insofar as this recognition constitutes invention invention is claimed. SUMMARY OF THE INVENTION A spring retainer is disclosed for use in retaining fuel pellets in a fuel rod both during fabrication and shipment to prevent the fuel pellets from being moved from their design location before installation within a reactor. The cylindrical and solid nuclear pellets containing the reactor fuel are placed within the fuel rods and have an outside diameter sightly less than the inside diameter of the fuel rod. Once the pellets are in place, a two-part spring holder is inserted into the end of the fuel rod. A first compression spring part of the coil spring holder is a conventional coil spring which, acting in compression, bears against the fuel pellets with a preselected force typically forcing the pellets when in the horizontal position into a compacted disposition when the fuel rod is horizontal. This conventional coil spring has a diameter which is less than the inside diameter of the fuel rod. A second locking spring part of the coil spring holder is a coil spring having a diameter which exceeds the inside diameter of the fuel rod. This helical locking spring is spirally wound down to an outside diameter less than that of the inside diameter of the fuel rod for insertion into the rod, and then released to key to the inside diameter of the rod. Winding occurs through a special tool. By winding one end of the locking coil spring relative to the other end of the locking coil spring, spiral winding of the helical spring to a diameter less than the inside diameter of the rod occurs. Installation includes winding the locking spring, inserting the wound locking spring, compressing the installed fuel pellets with the compression spring, and releasing the spirally wound helical locking spring to unwind the locking spring so that it keys to the inside walls of the fuel rods. The disclosed design accommodates conventional fuel getters and is shown with a preferred one piece construction where the compression and locking spring sections are fabricated from the same single piece of wire. Other Objects, Features and Advantages An object of this invention is to disclose a simplified two-part spring clamp for retaining fuel pellets under compression within a fuel rod. A spring having two sets of helical coils is disclosed. The first set of coils is a compression spring bearing against the fuel pellets. The second set of coils is a locking spring having a diameter which exceeds the inside diameter of the fuel rod. This helical locking spring is spirally wound down to an outside diameter less than the inside diameter of the fuel rod. As wound, it is inserted with compression spring disposed to and toward the fuel pellets. The fuel pellets are compressed by the compression spring. When the fuel pellets come under the desired compression, the locking spring is released, and keys to the inside rod walls with securing of the fuel pellets in place under compression occurring. An advantage of the disclosed two-part spring clamp is that it occupies the minimal volume within the fuel rod. No longer need the spring extend between the last pellet and the end plug. Instead the spring can occupy a relatively short distance on the order of 2 to 4 inches. Second, the new spring introduces a minimum amount of metal into the fuel rod. Not only is the spring clamp less expensive than those contacting the end plug but additionally a smaller volume of metal is present for the undesired adsorption of neutrons. Third, the new spring accommodates variation in the total length of pellets used within the fuel rod. One spring design can be used for all loads of fuel pellets--short or long. Fourth, the new spring is inserted immediately after insertion of the fuel pellets. Then the pellets are restrained during subsequent fabrication steps. Finally, the clamp keying to the side walls of the fuel cladding or rod, no longer bears against the end plug. As no force is now exerted against the end plug, it is no longer necessary to overcome a force during welding to permit sealing of the end plug. Further, the clamp keys to the side walls of the fuel rod remote from the site of the welding. This being the case, the heat of the weld does not adversely affect the metallic properties of the clamp. A further object to this invention is to disclose a process and apparatus for the installation of the clamp. According to this aspect of the invention, at least the second part of the coil spring which has a diameter which exceeds the inside diameter of the fuel rod, is wound to a smaller diameter while the spring is inserted into the fuel rod. This helical spring is spirally wound down to an outside diameter less than the inside diameter of the fuel rod by a tool exerting a spirally winding torsional force. Thereafter, the wound spring and its depending conventional compression coil spring member are inserted into the rod. Forced insertion is continued to achieve the designed compressive force on the fuel pellets--a force in the order of 7 pounds. Once this force is achieved, the wound spring is released. The released spring keys to the inside diameter of the cylindrical cladding walls. Securing of the pellets occurs. An advantage of the disclosed process is that it is simple and remote. It is easily done by those having minimum skill. A further advantage of the process is that the force of spring compression on the pellets is readily measured. Thus, precise precompression of the pellets can occur when the clamp keys to the inside diameter of the fuel rod before the rod is sealed. Yet another advantage of the process is that the spring, once in place, secures the pellets. This securing occurs long before the ends of the rod are sealed. Not only is there an absence of a force tending to push on the end plug as it is welded, but from the moment of time that the spring clamp is placed, the pellets are under the desired compressive load. |
summary | ||
description | This application claims priority under 35 U.S.C. § 119 to U.S. Provisional Application 62/946,901, filed Dec. 11, 2019 and incorporated by reference herein in its entirety. FIG. 1A is a cross-section of a related art transfer cask 10 used for storing heat-generating waste, including radioactive materials like spent nuclear fuel and irradiated waste. As shown in FIG. 1, cask 10 includes inner shielding 11 and outer shielding 12 that define a central open space into which fuel assembly 1 and handling basket 2 may be inserted and stored. Inner shielding 11 may be depleted uranium that maintains structural containment and blocks radiation emitted by contents of cask 10. Outer shielding 12 may be a thicker boron carbide jacket that provides further impact shielding and particularly neutron radiation shielding. Retaining sleeve 14 at a top of the cavity within this shielding may align and keep positioned fuel assembly 1 during insertion and storage, as well as allow for indexing and removal of the same. The cavity inside inner shielding 11 may be backfilled with helium to keep the heat-generating contents chemically static while avoiding large pressure differentials across cask 10. Drip pan 16 may catch liquid or solid debris that falls from stored contents. FIG. 1C is a cross-section of related-art cask 10 at elevation line h1, showing inner shielding 11 as a ring jacketed by outer shielding 12. Several reinforcing dividers 15A, 15B, and 15C, which may be high-strength stainless steel, divide and reinforce the shielding and form an outer surface of cask 10. Void 13 at a top of cask 10 may connect up to bi-stem assembly 20 at the top end of cask 10. Active pumps and fluid recirculators may connects through bi-stem assembly 20 into void 13 to actively cool and move heat away from contents of cask 10. As seen in FIG. 1B, taken as a cross-section at elevation line h2, bi-stem assembly 20 may allow for handling of cask 10, such as through a crane or other connection to assembly 20. With proper ambient conditions and active cooling provided to cask 10, high-energy contents that generate large amounts of heat through radiation may be stored and transported for long periods of time without damaging cask 10 or irradiating the environment. US Patent Publication 2014/0177775 published Jun. 26, 2014 Loewen et al. describes another related art cask for spent nuclear fuel with active cooling devices to also dissipate cask heat and is incorporated by reference herein in its entirety. Example embodiments include casks that passively rid themselves of heat that may be generated by their contents, with shielding around the contents to stop alpha, beta, gamma, or neutron radiation from leaking to the surrounding environment and one or more heat transport paths that allow the heat to easily move from inside the cask and shielding to outside the cask and ultimately into the environment or an external heat sink. The transport path may be any structure with high heat convection, conduction, and/or radiation, sufficient to prevent internal temperatures from reaching damaging temperatures, including heat pipes and conductive rods. The heat transport path may be bent or otherwise provide no straight line from inside to outside the cask, so that radiation travelling along such a line always hits shielding. An openable and closeable damper may surround an end of the heat transport path to control fluid convection about the heat transport path and ultimately heat loss from the cask. A jacket of fluid or meltable material that conducts heat by convection may surround the stored materials ensure an even temperature within the cask. The heat transport path and/or a heating element may be in communication with the jacket to cool and/or heat the jacket as desired. Example embodiment casks are useable to store, transport, and dispose of any sensitive or heat-generating material without damaging buildup of heat or irradiation. This may include radioactive waste, irradiated components, spent or fresh nuclear fuel, etc. Casks may be opened or closed to simultaneously load and offload materials at a consistent operating temperature provided by heaters in the cask. Several fuel assemblies and other highly radioactive structures can be placed and stored in casks without risk of melting or loss of containment due to the passive heat removal from the cask. Because this is a patent document, general broad rules of construction should be applied when reading it. Everything described and shown in this document is an example of subject matter falling within the scope of the claims, appended below. Any specific structural and functional details disclosed herein are merely for purposes of describing how to make and use examples. Several different embodiments and methods not specifically disclosed herein may fall within the claim scope; as such, the claims may be embodied in many alternate forms and should not be construed as limited to only examples set forth herein. Modifiers “first,” “second,” “another,” etc. may be used herein to describe various items, but they do not confine modified items to any order or relationship. These terms are used only to distinguish one element from another; where there are “second” or higher ordinals, there merely must be that many number of elements, without necessarily any difference or other relationship between elements. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element, unless an order or difference is separately stated. In listing items, the conjunction “and/or” includes all combinations of one or more of the associated listed items. The use of “etc.” is defined as “et cetera” and indicates the inclusion of all other elements belonging to the same group of the preceding items, in any “and/or” combination(s). When an element is related, such as by being “connected,” “coupled,” “mated,” “attached,” “fixed,” etc., to another element, it can be directly connected to the other element, or intervening elements may be present. In contrast, when an element is referred to as being “directly connected,” “directly coupled,” etc. to another element, there are no intervening elements present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., “between” versus “directly between,” “adjacent” versus “directly adjacent,” etc.). Similarly, a term such as “communicatively connected” includes all variations of information exchange and routing between two devices, including intermediary devices, networks, etc., connected wirelessly or not. As used herein, singular forms like “a,” “an,” and “the” are intended to include both the singular and plural forms, unless the language explicitly indicates otherwise. Indefinite articles like “a” and “an” introduce or refer to any modified term, both previously-introduced and not, while definite articles like “the” refer to the same previously-introduced term. Possessive terms like “comprises,” “includes,” “has,” or “with” when used herein, specify the presence of stated features, characteristics, steps, operations, elements, and/or components, but do not themselves preclude the presence or addition of one or more other features, characteristics, steps, operations, elements, components, and/or groups thereof. Rather, exclusive modifiers like “only” or “singular” may preclude the presence or addition of multiple or other subject matter in modified terms. As used here, a “heat transport path” is a solid structure transferring heat at a high rate, higher than surrounding materials, without outside power or driven solid components, including conductive rods and heat pipes. The structures and operations discussed below may occur out of the order described and/or noted in the figures. For example, two operations and/or figures shown in succession may in fact be executed concurrently or may sometimes be executed in the reverse order, depending upon the functionality/acts involved. Similarly, individual operations within example methods described below may be executed repetitively, individually or sequentially, so as to provide looping or other series of operations aside from single operations described below. It should be presumed that any embodiment or method having features and functionality described below, in any workable combination, falls within the scope of example embodiments. The inventors have recognized that. The inventors have developed example embodiments and methods described below to address these and other problems recognized by the Inventors with unique solutions enabled by example embodiments. The present invention is. In contrast to the present invention, the few example embodiments and example methods discussed below illustrate just a subset of the variety of different configurations that can be used as and/or in connection with the present invention. FIG. 2A is a profile cross-section of an example embodiment heat transfer cask 100 using a heat transport path that passively removes heat from the contents of the cask. Cask 100 may have some similar configurations to related art casks discussed above or shown in FIGS. 1A-C, with heat transport elements added as described below and structural and shielding elements made of strong, non-reactive materials. Example embodiment heat transfer cask 100 is robust and seals with the integrity of containment, and, as such is useable to store, transport, and dispose of dangerous or sensitive material, including radioactive components and nuclear material, without risk of leakage, reaction, or damage when exposed to force or harsh environments. As shown in FIG. 2A, in example embodiment heat transfer cask 100, heat transport path 150 directly connects an inner portion of cask 100 to an exterior or near exterior, to carry heat directly away from cask 100 without any solid moving part. For example, a first end of heat transport path 150 may extend deep into shielding, including inner shielding 11 and even a cavity holding heat-generating stored objects, such as spent nuclear fuel 1. An opposite end of heat transport path 150 may pass to an outer portion, such as outer damper 160 or even to an exterior of cask 10, to be in direct communication with the environment. FIG. 2B is a detail of heat transport path 150 from FIG. 1A, showing a directional change in path 150 to avoid a direct, linear path from inside example embodiment heat transfer cask 100 to the surrounding environment. Because path 150 may be fully shielding, differently shielding, or not necessarily shielding at all, a straight line from a radiation producing stored element, such as spent fuel 1, to outside cask 100 may provide an exposure path through which dangerous or unwanted radiation may escape. To prevent or reduce such irradiation outside cask 10, path 150 may change direction, such as via lateral jog in FIG. 2B through surrounding outer shielding 12, to remove any straight path through radiation shielding of cask 100. Flow path 150 may curve, angle, bend, etc. in any number of different directions to prevent any escape line from inside cask 100 to outside the same. Additionally or alternatively, flow path 150 may incorporate shielding materials or be shielded at ends to further prevent radiation escape. Heat transport path 150 readily transmits heat between its portions near an inside of cask 100 and outside cask 100. For example, as shown in FIG. 2C, heat transport path 150 may be a solid, heat conductive rod such as copper, iron, tungsten, aluminum, and/or conductive alloys such as aluminum nitride or silicon carbide. As shown in FIG. 2A, heat transport path 150 may be a heat pipe with an internal transport path conducting heat via convection and conduction through an evaporating and condensing coolant. Any number of heat transport paths 150 may be used in example embodiments, necessary only to remove expected heat loads. For example, sufficiently sized and numbered heat transport paths 150, such as 20 1 kW heat pipes, may be used to ensure temperatures do not exceed or even approach 650° C. based on the radioactivity of objects placed into cask 100. Heat transport path 150, like other structural elements of cask 100, is fabricated of materials that are sufficiently strong to preserve the structural integrity of cask 100 while not undergoing substantial strength or material changes or degradation when exposed to radiation, including stainless steels, aluminum alloys, nickel alloys, zirconium alloys, carbides, etc. In this way, heat transport path 150 may readily allow heat to passively escape cask 100 while ensuring cask 100 is robust and maintains containment to radioactive elements inside, without external power or moving structures. Example embodiment heat transfer cask 100 may include dampers 160 at a cooling or ambient portion of heat transport path 150. For example, dampers may form a skirt or ring about a perimeter of an end of cask 100, or be placed anywhere else about heat transfer path 150. Dampers 160 may be manually or automatically opened to allow air flow and convection over heat transfer path 150, maximizing heat transfer out of cask 100, or partially opened or closed to allow heating of cask 100. Example embodiment heat transfer cask 100 may include a convective jacket or ring 110 that acts as a conductive heat reservoir. For example, ring 110 may be a 2-inch sodium ring that will melt and be convective liquid at typical inner temperatures of cask 100. Ring 110 may be in direct or nearby connection with a heated or innermost portion of heat transport path 150 to transfer heat to path 150, which is then transferred through path 150 to an outer portion, such as near dampers 160. Ring 110 may be between inner shielding 11 and outer shielding 12, which may be thinner than in related art casks to achieve a same outer diameter, or same or larger sizes with a different outer diameter. Inner cavity 160 defined by shielding and internal structural dividers of example embodiment cask 100 may be sized to house any number of heat-generating materials, including as such as six fuel assemblies 1 for liquid metal reactors, light or heavy water reactors, graphite-moderated reactors, etc. Inner cavity need not be filled with helium but can use any inert filler, including argon or nitrogen, given the heat transfer abilities of cask 100. Central rod 105 may be used to pack cavity 160, absorb radiation, and/or extend from a top of cask 100 to allow handling. For example, central rod 105 may be strong boron carbide that is both a neutron absorber and is structural with the remainder of cask 100 and allows handling the same where it passes up through an end. This may limit fission possibilities in cavity 160 even when filled with several nuclear fuel assemblies 1. As shown in FIG. 2C, cavity 160 may be surrounded by a perimeter of several heat transport paths 150 as well as shielding 11/12 and ring 110, in any ordering or thickness with structural separators. In this way, cavity 160 may be evenly and fully cooled/heated by transport paths 150 and ring 110. Example embodiment heat transfer cask 100 may include immersion heating rod 120 to heat ring 110 and contents of cavity 160 to a desired temperature. Immersion heating rods 120 may be similarly positioned to heat transport paths 150 and work in a largely opposite manner, delivering heat into, or generating heat in, cask 100. For example, immersion heating rods 120 may be electric resistant heaters with power connections 121 near a top end of casks 100 to heat rods 120 and conduct the heat down into ring 110 and/or cavity 160. Rods 120 may be staggered about a perimeter into ring 110 with heat transport paths 120, as shown in FIG. 2C, for even heating and cooling. For example, if cask 100 is used to store and transport new fuel assemblies 1 for insertion into a liquid metal reactor, it may be desirable to bring the stored components near operating temperatures over 200° C. by activating immersion heating rod 120. During such operation, damper 160 may be closed to prevent or reduce convection to a cold end of heat transport path 150, so heat is not lost from cask 100. Example embodiment heat transfer cask 100 may include a lid or seam at an end allowing insertion or removal of contents of cavity 160 during this time, and cask 100 may be kept open and at an operating temperature during all loading and unloading because it is kept at an operating temperature by immersion heating rod 120. Some example embodiments and methods thus being described, it will be appreciated by one skilled in the art that examples may be varied through routine experimentation and without further inventive activity. For example, although casks with several annular shields are used in some example systems, it is understood that other cask configurations are useable with examples. Variations are not to be regarded as departure from the spirit and scope of the example embodiments, 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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040574636 | description | DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 shows a schematic representation of a typical pressurized water reactor which can employ the method of this invention to avoid the operating difficulties experienced by the prior art. The reactor of FIG. 1 includes a vessel 10 which forms a pressurized container when sealed by its head assembly 12. The vessel has coolant flow inlet means 16 and coolant flow outlet means 14 formed integral with and through its cylindrical walls. As is known in the art, the vessel 10 contains a nuclear core 18 of the type previously described and more specifically illustrated in FIG. 2, consisting mainly of a plurality of clad nuclear fuel elements 20 which generate substantial amounts of heat depending primarily upon the position of the part length 22 and full length 24 control rods previously described. The heat generated by the reactor core 18 is conveyed from the core by coolant flow entering through inlet means 16 and exiting through outlet means 14. Generally the flow exiting through outlet means 14 is conveyed through an outlet conduit 26 to a heat exchange steam generator system 28, wherein the heated coolant flow is conveyed through tubes which are in heat exchange relationship with water which is utilized to produce steam. The steam produced by the generator is commonly utilized to drive a turbine for the production of electricity. The flow of the coolant is conveyed from the steam generator 28 through a cool leg conduit 30 to inlet means 16. Thus a closed recycling primary of steam generating loop is provided with the coolant piping coupling the vessel 10 and the steam generator 28. The vessel illustrated in FIG. 1 is adaptable for three such closed fluid flow systems or loops, though, it should be understood that the number of such loops vary from plant to plant and commonly 2, 3, or 4 are employed. In the production of thermal power within the core important parameters effecting the axial power distribution, as previously explained, are the level of control rod insertion of both the full length or part length rods, the burn-up history of the core, the power level of the reactor and the xenon distribution. FIGS. 3A, 3B, 3C, 3D and 3E show the sensitivity of the power distribution to each of these parameters. The xenon distribution at any time is a result of the operating history for at least the previous twenty hours. Therefore, in order to obtain the xenon distribution, a precise trace of the power history is necessary. An example of the xenon concentration change during an exemplary power change is illustrated in FIGS. 4A and 4B. From the graphical representation it is apparent that xenon concentration changes exponentially in a direction inverse to that of the corresponding power change. Thus it can be appreciated that due to the exponential decay of the xenon concentration the resultant neutron absorption effect will be cumulatively dependent upon the overall operating history of the reactor. FIG. 5 illustrates an exemplary axial power distribution and corresponding xenon distribution for the indicated control rod insertion and a given core power history. Xenon and control rod insertion are plotted proportional to their neutron absorptions. From the graphical representation provided in FIG. 5 it is apparent that the neutron absorption capability of the control rod group is about a quarter of the neutron absorption capability of the xenon present in the core. This means that once the xenon distribution is destroyed, i.e., skewed as shown in the upper core section illustrated in FIG. 5, which normally occurs as a result of a past skewed power distribution, the part length rods are not necessarily strong enough to obtain the desired power distribution. Therefore, in order to assure the lowest power peaking factor, which is the lowest power linear density, so as to avoid power penalties, it is desirable to maintain the power distribution as symmetric as possible during plant operation, including changes in load. As previously mentioned the axial offset is a useful parameter for monitoring the axial power distribution within the core. In accordance with the invention, if the core is operated so as to maintain the axial offset at a constant value, the power generation will always be balanced between the top and bottom parts of the core, resulting in a symmetric axial xenon distribution. This eliminates the creation of a skewed xenon distribution having a second harmonic component, which causes skewness of the power distribution and is relatively slow to decay. Reactors of the type illustrated in FIG. 1 generally include two section excore detectors 32 positioned around the periphery of the reactor vessel 10 coextensive with the axial length of the core 18, which provide complete information on the axial offset. The detectors give the flux difference, Delta I, which is defined as: EQU Delta I = P.sub.T -P.sub.B the correspondence between the axial offset and the flux difference can be expressed as: EQU Axial Offset = Delta I/P where P denotes the relative power of the reactor. The method of this invention requires that the axial offset be maintained at a constant predetermined target value, or alternatively, within a narrow band around this target value. Preferably, the target axial offset is measured at full power, equilibrium xenon, with all control rods out of the fuel region of the core. This is the most stable axial distribution and most flux oscillations if there are any move around this distribution. The target axial offset will vary slowly as a function of fuel depletion, commonly referred to as fuel burnup. FIG. 6 shows variations in the axial offset for various fuel cycles. Therefore, it is desirable to remeasure the axial offset target value periodically to compensate for fuel depletion. Desirably this is accomplished by updating the target axial offset value every equivalent full power month by measuring the axial offset at full power with equilibrium xenon with all control rods out of the reactive region of the core. This updating procedure by measurement assures that the axial power distribution is maintained in the most stable condition during load follow operations. Again this procedure is implemented by employing the outputs of the excore detectors to calculate the axial offset value. In accordance with one mode of operation of this invention, constant axial offset operation is obtained without the use of part length rods. A power reduction always tends to move axial offset in a positive direction because of the negative moderator temperature coefficient, which results in greater reactivity at the top of the core. Therefore, the proper amount of full length rod insertion helps move the axial offset back to the original target value. In this mode, the full length rods are used for two purposes, to absorb the reactivity associated with a power reduction and to maintain the axial offset at its original value. The prime factor in determining the full length rod insertion is axial offset control, not reactivity control. Therefore, full length rod insertion is usually not enough to control the reactivity change associated with a power reduction. The balance of the reactivity has to be controlled through changes in the neutron absorbing element within the moderator or coolant medium. Generally, in pressurized water reactors, where water is circulated as the coolant medium, a solution of boron within the water is employed as the neutron absorbing element. In this mode of operation it should be remembered that the part length rods are fully withdrawn from the core at all times. By proper deployment of the full length rods it is possible to preserve the power distribution throughout a load change operation with the excess overall reactivity control associated with the power change being taken up by the boron system. The success of this type of operation can better be appreciated by reference to FIGS. 7A and 7B which compare exemplary power distributions at full power and at 50% power for both beginning of life (FIG. 7A) and end of life (FIG. 7B) operation. This mode of operation has many advantages for fuel integrity as will be appreciated from following discussions. A minor drawback to this mode of operation is that there is some difficulty experienced in changing the reactor power at a relatively fast rate, because the reactivity change depends on the boron system to some extent. This is especially noticeable when quick return to full power operation is required. The full length rod insertion during part power operation is not enough to give the required reactivity to return to full power and boron dilution is necessary. Though, if a fast boron dilution system is employed this difficulty can be overcome. Another alternative for faster response to load follow is provided by the following alternative mode of operation which employs part length rods. A second mode of operation contemplated by this invention employs part length rods for axial power distribution control. In order to assure the spinning reserve capacity, which is the difference between the full power rating an the current rating that can be counted upon in the event of a sudden large demand in power, the full length rods in this mode of operation should be inserted much deeper than required in the operation without part length rods. This deep insertion of full length rods makes the axial offset strongly negative and results in a skewed xenon distribution. A balanced power distribution is obtained by putting the part length rods in the bottom of the core, as shown in FIG. 8A. In the case of a return to full power, the full length rods are removed from the core to provide a reactivity increase, then the part length rods are moved to the center of the core to preserve the axial offset at its original value as will be appreciated by referring to the full power and 50% power graphical representations provided in FIGS. 8B and 8A respectively. These two power distributions have the same axial offset. The main difference between the two distributions is the third harmonic of the xenon distribution, which decays quickly without harmful effects. Thus, in this mode of operation, the full length rods are used for the reactivity control associated with the power change, and the part length rods are employed for axial offset control. The reactivity change due to xenon buildup or depletion is controlled by the boron system. In operation with part length rods the full length rod insertion is searched to give enough reactivity to return to full power when withdrawn from the core region with the part length rods moved to the center of the core. It should be appreciated that full length rod insertion varies almost linearly as a function of power and will remain at a given insertion level when the desired power level is achieved. This is mainly because the xenon distribution and integral rod worth are perceived well during part power operation. Constant axial offset operation with part length rods provides low peaking and stable power distribution throughout load follow operation with the capability of responding to any sudden power damand upon request. During constant axial offset operation at full power the part length rods are normally maintained around the center of the core while at part power the part length rods are generally positioned around the bottom of the core. Deeper part length rod insertion will correspond to lower reactor power levels. In this respect the part length rods are a very flexible tool for axial power distribution control. However, some caution is necessary in their use. The main drawback of the part length rods is that full length rod insertion coincident with the part length rods at the bottom of the core sometimes "pinches" the axial power distribution. This distribution has a small axial offset, but a high power peak around the center core location as illustrated in FIG. 9. The current two section excore detectors are not capable of distinguishing between a normal power distribution and a pinched distribution. A pinched power distribution is usually acceptable during part power operation, since the power peak is generally below acceptable power limits, but not during full power operation due to the magnitude of the power peak, which if not reduced will result in a power penalty. According to the modes of operation of this invention, deep insertion of the part length rods is only required during part power operation. Therefore, it is advisable to prohibit deep part length insertion during full power operation in order to avoid the possibility of a pinched power distribution. FIG. 10 shows that part length rod insertion should be limited to approximately 70% insertion at full power and linearly increased to approximately 90% insertion at 50% power. Any part length rod insertion beyond 90% decreases the effect of the part length rods because of the small amount of power in the extreme lower region of the core. Full length rod insertion during operation with part length rods is defined to give a reactor a spinning reserve capability, assuming simultaneous movement of the part length rods for constant axial offset control. The required full length insertion is a function of the reactor power providing axial offset control is achieved. FIG. 11 shows a typical full length rod insertion line to maintain a spinning reserve capability. This insertion line is normally referred to as the full length rod target insertion line, and is a function of the plant power defect, which is the reactivity difference associated with a power change. In practicing the modes of operation of this invention reactor operators are required to keep full length rod insertion along this line as much as possible. Deviations from the target insertion results in diminishing the plants performance. For example, if the full length rods are kept above the target line the spinning reserved capability will be limited. Because of inadequate full length rod insertion, the reactivity associated with full length rod withdrawal will not be enough to bring the reactor to full power. Additional dilution will be required within the boron system to obtain the desired power limit. However, this limitation is not safety related. As another example, if the full length rods are maintained below the target line in the case of a return to full power the reactor will become critical with a relatively deep rod insertion. This requires the part length rods to be moved to the bottom of the core for constant axial offset control. As discussed previously part length rod insertion during full power is limited to 70% to avoid a pinched power distribution. Consequently, the power distribution tends to shift to the bottom of the core and could result in a high peaking factor. This will be detected by the excore axial offset measurement and will necessitate a power reduction. The best constant axial offset load follow operation is achieved only when: i. the part length rod worth, when calculated on a full length rod basis, is equal or slightly greater than the full length rod worth; and ii. the boron system has enough capability to compensate for the reactivity change associated with xenon buildup or depletion. Full length rod withdrawal above the target line is a remedy for this condition at the expense of the spinning reserve capability. When the part length rod worth calculated on the basis of full length rod length, is smaller than the full length rod worth, the axial offset will become heavily negative during part power operation with full length rod insertion maintained just enough to keep the spinning reserve capability. Under these conditions the axial offset will shift as negative as minus 30% during part power operation. Thus a skewed power distribution is formed which destroys the desired xenon distribution. When the reactor returns to full power, high peaking is created in the bottom of the core. This problem is solved by allowing the full length rods to withdraw to maintain the axial offset at a constant value. However, this operation sacrifices the spinning reserve capability. The full length rod insertions are 60% for the spinning reserve capability and 40% for constant axially offset control. The difference in full length rod insertion is related to the penalty in the spinning reserve capability. The boron system has to be designed to have the dilution capability to offset changes in reactivity associated with xenon buildup or depletion. The dilution capability of the boron system depends on the boron concentration within the core. The higher boron concentration, the greater the dilution capability. As the core approaches the end of cycle life, boron concentration becomes less and the dilution process becomes more difficult. Full length rod insertion is determined for the spinning reserve capability from the scheduled power. However, because of this lack of dilution capability, which is required after power reduction to compensate for xenon buildup, the reactor power cannot be maintained at the scheduled level but is subject to further reduction. Full length rod withdrawal from the target line removes this problem, once again at the expense of the spinning reserve capability. It should be noted that the full length rod withdrawal above the target line is always favorable from the viewpoint of axial offset control, thus assuring low peaking factor operation. Of course, proper design of the boron system in anticipation of implementing the concepts of this invention will avoid such difficulties. In order to keep the axial offset at a constant value at all times, continuous operator attention and corrective action, such as part length rod and boron system maneuvering is necessary. However, experimental results show that some flexibility is possible without destroying the symmetry of the axial xenon distribution. Analytical results show that one hour idle operation generally gives quite stable behavior during load follow. However, care should be taken not to be idle just after a return to full power. Accordingly, with the precaution noted for after a return to full power, a one hour violation of axial offset control will still be acceptable. The target axial offset as previously defined for constant axial offset control is the axial offset at full power, equilibrium xenon, with all control rods out of the fuel region of the core. In actual operation, some allowance is necessary for control flexibility. Experimental studies have been made to determine what deviations from the target axial offset are allowable without losing the merits of constant axial offset control. Based on previous reactor operating experience, at lower power levels a larger axial offset deviation is permitted than at higher power levels from the viewpoint of minimizing F.sub.z (axial peaking factor) at full power. By taking advantage of the measured flux difference, an allowable axial offset band can be defined as a constant delta I band. Accordingly, the allowable axial offset deviation is inversely proportional to the power level. FIG. 12A shows the axial offset band as the function of burnup corresponding to a constant delta I band illustrated in FIG. 12B (plus or minus 5% around a value corresponding to the target axial offset). The target axial offset is assumed to be minus 10% at the beginning of life and 0% at the end of life for explanatory purposes. Experimental calculations were performed and the results concluded that constant axial offset control is quite acceptable even if the core is operated at the extremes of the delta I band, and thus, guarantees a favorable power distribution when the reactor returns to full power. In actual operation, it is quite unlikely that the reactor will be operated at this extreme axial offset for six hours which was one of the controlling criteria of the calculations. The delta I band is used such that whenever delta I goes outside the band, the operator is required to take corrective action to put the axial offset at the target value. Thus, even though the reactor is operated at its extreme axial offset deviation for as long as six hours the reactor power capability is still preserved. The operation with part length control rods has certain advantages over operation without part length control rods such as the ability to provide quick changes in power level and easiness of axial offset control. A disadvantage of this operation is the burnup shadowing caused by the part length rods, which are positioned near the middle of the core during full power operation. Because part length rods act as neutron absorbers the fuel screened by the part length rods depletes at a much lesser rate than the remaining core. This could result in high peaking near the center of the core when the part length rods are withdrawn if extended load operation is performed. Uncovering of this less burnt fuel when the part length rods are withdrawn is known as "burnup shadowing". It has been observed from experimental calculations that from 50 to 60% part length depletion does not create a large penalty in the radial flux peaking factor. Therefore, in accordance with the operating procedures of this invention it is recommended that the use of part length control rods be limited to 60% during every thirty full power days. Based on the basic physics studies mentioned above, plant operating instructions are presented below. Instructions for operation with or without part length control rods and procedures for transition between operation with part length rods and operation without part length rods are specifically set forth. Each of the individual steps has as its underlying basis the inventive concepts presented above and will be understood if considered with the foregoing explanations. Accordingly, the two modes of operation previously identified are set forth in the following paragraphs which provide full control through load follow maneuvers. The first embodiment which provides substantially constant axial offset control without the use of the part length control rods will be described as mode A operation while the remaining embodiment described as exemplary of this invention which employs the part length control rods will be referred to as mode B operation. The resulting difference between the two modes as previously explained is the rate at which the core can be brought to full power. These procedures are designed to maintain peaking factors in the core as low as practical so as to minimize power penalties. RESTRICTIONS COMMON TO BOTH MODE A AND MODE B OPERATIONS 1. The power dependent rod insertion limits on the part length and the full length control rods must be observed at all times. 2. The flux difference extreme limits, which are given as part of the reactor's technical specifications, if any, must be observed at all times. 3. Axial power distribution monitoring system limits, if any exist according to the technical specifications of the reactor, must be observed at all times. 4. Above 90% licensed power flux difference must be maintained approximately within plus or minus 5% of the flux difference corresponding to the target value for the axial offset. Below 90% of license power flux difference should be maintained approximately within the band plus or minus 5% of the flux difference corresponding to the target value axial offset. ADDITIONAL RESTRICTION FOR MODE A OPERATION 5. The part length control rods must remain withdrawn from the core. ADDITIONAL RESTRICTION FOR MODE B OPERATION 6. The full length control rods should preferably remain within the prescribed band. 7. Operation in mode B should be limited in accumulated usage to not more than 60% of each one-thousand MWD/MTU (megawatt day metric ton of uranium) of core average burnup. MODE A PROCEDURE Initial Conditions: 1. The secondary plant is ready to accept load changes. 2. The full length control rods may be in the automatic or manual mode of operation. 3. The part length control rods are fully withdrawn from the core. 4. The flux difference is in the permitted range (the flux difference being equal to the axial offset multiplied by the fractional power. INSTRUCTIONS Upon a plant load reduction, the power of the reactor is reduced and control rod insertion occurs in accordance with the load dependent program for the reactor coolant temperature, where an average coolant temperature control system is used for normal reactor control. Such an average temperature system is described in the patent to C. F. Currey, U.S. Pat. No. 3,423,285, issued Jan. 21, 1969. Flux difference limits should be maintained by boration. In the event that boration cannot be performed rapidly enough to maintain the flux difference within plus or minus five percent of the flux difference target value the period of violation should be kept as short as possible. Deviations lasting less than 1 hour should not have any adverse effect on the ability to meet limits on a subsequent return to high power. When the plant load reduction is completed the control rods will start moving upwards from the position which maintains the correct flux difference, as a result of the xenon buildup. Start diluting the boron concentration of the reactor coolant to maintain the correct flux difference. The rate of dilution will vary with time according to flux difference requirements. Upon demand for a plant load increase the control rods will move out to a new position. Further dilution will be required to keep flux difference within limits and to reach the desired power level. At the higher power level xenon will be decreased and the control rods will insert into the core. The flux difference limits and rod insertion limits must be maintained by boration of the reactor coolant. After several hours at the high power level the xenon concentration will again begin to increase due to the 6 or 7 hour delay period that it takes radioactive iodine to decay. Slow dilution of the boron concentration will be required to offset the increase in xenon. The previous steps set forth above are repeated for cyclic load follow. Other forms of load changing may require application of parts of this procedure. MODE B PROCEDURE Initial Conditions: 1. The secondary plant is ready to accept load changes. 2. The full length control rods are positioned in the prescribed band. It is recommended that they be placed in automatic operation. 3. The part length control rods are inserted. 4. The flux difference is in the permitted range. INSTRUCTIONS: Upon a plant load reduction, the power of the reactor is reduced and control rod insertion occurs in accordance with the load dependent program for reactor coolant temperature. Flux difference limits should be maintained by manual operation of the part length rods without violation of the part length rod insertion limits. The full length rods should remain automatically within the prescribed band of operation, however; small boron concentration adjustments (dilution or boration) may be required to insure compliance. When the plant load reduction is completed, or sooner if the load reduction was performed slowly, the full length control rods will start moving upwards from the required position as a result of xenon buildup. Adjust the boron concentration to maintain compliance with the insertion band of the full length rods. Maintain flux difference within the desired range by the movement of the part length control rods. If the part length rods reach their insertion limits and flux difference cannot be kept within the limits prescribed, the period of the violation should be kept as short as possible and the amount of violation as small as possible. If the period of violation continues for an extended period the full length rods should be adjusted to correct the flux differences. Upon demand for plant load increase the full length control rods will move out to a new position. Flux difference is maintained by manual operation of the part length control rods. At the higher power level xenon will decrease and the full length control rods will move into the core. The full length control rods are maintained within the specified band of operation by suitable boration. After several hours at the high power levels xenon will again begin to increase and slow dilution of the moderator will be required. The previous steps should be repeated for cyclic load follow. Other forms of load changes may require application of parts of this procedure. PROCEDURE FOR TRANSITION FROM MODE A TO MODE B Initial Conditions: SAME AS MODE A ABOVE INSTRUCTIONS: If a plant power reduction below approximately 80% of full power is planned the part length control rod insertion can be initiated when the power level is below approximately 80% and the part length rod insertion will cause the full length control rods to adjust reactivity. During this maneuver it is expected that the flux difference restriction of being within plus or minus 5% of the target value will be violated, so the insertion to the appropriate position for compliance with mode B restrictions should be accomplished as rapidly as possible. If the desired plant power level is above 50%, dilution may be required to stabilize the core in the mode B condition. If no plant power reduction is planned then the transition can only be accomplished by a forced reduction in power. At high power levels dilution will be required to bring the part length control rods in and to return to full power. Again, flux difference restrictions of being within plus or minus 5% of the value corresponding to the target axial offset should be violated for as short a period as possible, preferably less than one hour. PROCEDURE FOR TRANSITION FROM MODE B TO MODE A Initial Conditions: THE SAME AS FOR MODE B OPERATION. INSTRUCTIONS: When the core is operating at less than 80% power then withdrawal of the part length control rods can be accomplished by dilution if necessary while moving the part length rods from a position low in the core to the center of the core, followed by boration as the part length rods are fully withdrawn. In this maneuver, since the motion of the part length control rods will alter the flux difference, extreme flux limits must be met either by operating at sufficiently low power or by adjusting the full length control rod position through changes in boration concentration. This latter option requires dilution and boration through the maneuver. Accordingly, this invention provides an improved procedure for operating a nuclear reactor that provides substantially symmetric axial xenon distribution during reactor operation including load follow. The desired xenon distribution is accomplished by maintaining a relatively uniform axial power distribution during load follow maneuvers, which in essence minimizes total peaking factors and thus avoids power penalties. Furthermore, operating within the specified limits prescribed by the steps of this invention simplifies nuclear analysis procedures, minimizes pellet clad interaction effects and reduces the probability of hitting plant alarm limits which can interrupt plant operation. Thus, implementing the procedures set forth above will enable more efficient use of reactor facilities. |
abstract | An apparatus is disclosed that forms a basic integrated radiation shield for a PET isotope production system to create a safe environment. The apparatus and the system combine several subsystems to provide a high degree of integration and a nice aesthetic impression. The apparatus contains a cyclotron system and contains integrated target media handling for gas targets and water dispensing systems for water targets. A compartment including first and second additional radiation shields, respectively, that contains additional processing systems. The apparatus forms a closed radiation-proof system by means of a casing formed of four molded sections. A first and second section constitute a main body containing;the cyclotron system and a third and a fourth section constituting a pair of tight doors for encompassing the cyclotron into a sealed radiation shield. The first section additionally contains a Waste Gas Delay Line embedded in its shielding material. |
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044184220 | summary | TECHNICAL FIELD The invention refers to a distal aiming device for the nail setting of bones. BACKGROUND ART In a common orthopedic technique for repairing broken or shattered bones, an elongated metal pin or nail is inserted along the central portion of the bone. The nail strengthens the bone and holds the parts of the bone together. Such a technique is often used in repairing the femur, the bone that connects the pelvis with the knee, or the tibia, one of the bones that connects the knee with the ankle. To insure that the parts of the bones are maintained together and in the correct position, transverse fasteners extend through the bone and the pin at each end. The pin contains holes at each end for this purpose. In the surgical procedure, the bone is reamed out and the pin inserted along the central portion. However, once the pin is lodged in the bone, a problem arises. How does the surgeon know where to drill the fastener holes in the bone so that they will line up with the preestablished holes in the pin, thus permitting insertion of the fasteners? For the proximal end of the pin, that is, the end nearest the point of insertion, a jig may be fastened to the exposed end of the pin. The jig extends along the bone and positions aiming sleeves that provide the necessary guide to the drill. However, the problem is more difficult for the distal end of the pin, that is, the end buried in the bone. Jigs connected with the pin have been used to aim at the distal perforations or bores in the locking pin. However, due to the curved shape of bones, such as the femur, and the danger that the pin might twist during setting of the pin, the known device is not well suited. DISCLOSURE OF THE INVENTION The fundamental object of the invention is thus to provide an aiming device for pin or nail setting at the distal end of the pin wherein the aiming procedure can be made in a rapid manner, surely, and without complications. This problem is solved such that socket means for the aiming sleeve is attached to a housing for an X-ray source and positioned at a distance from the exit window of the ray source and substantially coaxial to the main beam path of the ray source. The aiming procedure using the invention starts with placing the X-ray source, i.e. its beam path, perpendicularly to the longitudinal axis of the pin or nail and centering it with respect to a distal hole or bore of the pin or nail. The X-ray image occuring in receiver means is for example transmitted from the receiver means to a monitor through a multiplier, whereupon the hole of the pin or nail inclusive other parts can be seen on the monitor screen. By changing the position of the aiming device and/or the position of the patient, the image of the hole can be brought into an overlapping position with the socket of the aiming sleeve, so that the axis of the aiming sleeve is coaxial with the axis of the hole. After making an incision, the aiming sleeve for the femur or the tibia, is inserted in the socket and moved up to the corticalis and fixed in this position. All the other steps, such as incision, making bores, tightening of the screws and so on can be made by means of the aiming sleeve. It is, in addition, possible to make a check after each operative phase and if necessary to again adjust the aiming device. For mechanical reasons and in order to achieve a simple and suitable adjustment, it is preferred to use a receiving bushing or socket in which the aiming sleeve is slidably received and which can be fixed in selected positions. The socket for the aiming sleeve is fixed to the housing of the X-ray source through an appropriate retaining means, so that it may be placed at a distance from the exit window of the source within the main beam path. A particular embodiment of the invention provides for this reason that the socket for the aiming sleeve is slidably mounted with respect to the housing. The sliding support of the sleeve enables the operator to adjust the desired distance with respect to the leg of the patient. The retaining means for the socket of the aiming sleeve can be designed in any suitable way. An additional embodiment of the invention provides in this respect fo the aiming sleeve socket to be mounted on bifurcated support means and two bushes fixed to the housing to accommodate the fork ends of prongs. By means of the bifurcated support the aiming sleeve socket can be continuously adjusted. In order to maintain the adjusted position of the socket, another embodiment of the invention provides that the housing of the X-ray source arranged thereat has at least one arresting adjusting element that fixes the fork in a selected position. In order to fix the fork on the housing another embodiment of the invention provides on the housing of the X-ray source a bracket carrying the bushes for the fork prongs. In order to have as little obstruction as possible, the fork is fixed on the bottom side of the housing. To facilitate the insertion of the fork, which is preferably made of sterilizeable material, an additional embodiment of the invention provides that the bracket be composed of a base plate connected rigidly to the housing and a bracket plate retaining the bushes and pivotally supported at the base plate. For the insertion of the fork the pivotable bracket plate is pivoted downwards and thereafter pivoted back again to its starting position. So that the plate remains in its working position, another embodiment of the invention provides that on the base plate there is a hand operated locking mechanism and the pivotable bracket plate includes a locking portion that can be brought into interlocking engagement with the locking device. The locking means is suitably designed such that the interlocking portion becomes automatically arrested when the plate is pivoted back into its working position. Other advantageous embodiments of the invention are described below. |
abstract | An apparatus for manufacturing a radioisotope comprises a container. The container comprising a portable neutron source and a solution that comprises a particular isotope. The portable neutron source is surrounded by the solution. The solution comprises at least one of copper phthalocyanine or copper salicylaldehyde o-phenylene diamine. The portable neutron source emits neutrons that react with the particular isotope resulting in the transformation of the particular isotope into the radioisotope. |
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abstract | Disclosed is a water-soluble coating composition, which is applied on the surface of fuel rods to prevent scratching of the surface of the fuel rods upon manufacturing a nuclear fuel assembly for light water reactors. This water-soluble coating composition facilitates the formation and removal of a coating film and the resulting coating film can exhibit strength and durability equivalent to those of an existing lacquer (nitrocellulose) coating film, and can thus be used as an alternative to lacquer, thereby easily removing the coating film and improving workplace safety, ultimately achieving improvements in the working environment and high workplace safety. |
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abstract | A modular submersible repairing system includes a working unit having a tool module capable of repairing structures in a reactor. A scanning/pitching module is capable of being selectively connected to or disconnected from the tool module, and is provided with a scanning/pitching shaft for scanning or pitching the tool module. A submersible fan module is capable of being selectively connected to or disconnected from the scanning/pitching module. A first buoyant module keeps an orientation of the tool module. A base unit includes a manipulator module internally provided with an actuator driving mechanism. An adsorbing module is capable of being detachably mounted on the manipulator module and a wall. A second buoyant module keeps the orientation of the manipulator module. The scanning/pitching module and the manipulator module are provided with a submersible connecting device capable of being operated in water for engagement and disengagement. |
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051907208 | summary | This application is related to pending applications for patent Ser. No. 07/350,187, filed May 11, 1989, and Ser. No. 07/541,647, filed June 21, 1990. FIELD OF THE INVENTION This invention relates to an improvement in liquid metal cooled nuclear reactors plants having a pool of liquid metal coolant with the heat generating fissionable fuel core substantially immersed in the liquid metal pool, such as the type disclosed in U.S. Letters Pat. No. 4,508,677, issued Apr. 2, 1985. BACKGROUND OF THE INVENTION In the operation of liquid sodium or sodium-potassium metal cooled nuclear reactors for power generation, it may be necessary to shut down the fission reaction of the fuel to deal with emergencies or carry out routine maintenance services. Reactor shut down is attained by inserting neutron absorbing control rods into the core of fissionable fuel to deprive the fuel of the needed fission producing neutrons. However decay of the fuel in the shut down reactor continues to produce heat in significant amounts which must be dissipated from the reactor unit. The heat capacity of the liquid metal coolant and adjacent structure aid in dissipating the residual heat. However, the structural materials of the nuclear reactor may not be capable of safely withstanding prolonged high temperatures. For example the concrete of the walls of the typical housing silo may splay and crack when subjected to high temperatures. Accordingly, auxiliary cooling systems are commonly utilized to safely remove heat from the nuclear reactor structure during shut down. Conventional nuclear reactors have utilized a variety of elaborate energy driven cooling systems to dissipate heat from the reactor. In many of the situations warranting a shutdown, the energy supply to the cooling systems make the cooling systems themselves subject to failure. For example, pumps and ventilation systems to cool the core may fail. Furthermore, if operator intervention is necessary, there are foreseeable scenarios in which the operator would be unable to provide the appropriate action. The most reliable and desirable cooling system would be a completely passive system which could continuously remove the residual heat generated after shutdown regardless of conditions. Liquid metal cooled reactors such as the modular type disclosed in U.S. Pat. No. 4,508,677, utilizing sodium or sodium-potassium as the coolant provides numerous advantages. Water cooled reactors operate at or near the boiling point of water. Any significant rise in temperature results in the generation of steam and increased pressure. By contrast, sodium or sodium-potassium has an extremely high boiling point, in the range of 1800 degrees Fahrenheit at one atmosphere pressure. The normal operating temperature of the reactor is in the range of about 900 degrees Fahrenheit. Because of the high boiling point of the liquid metal, the pressure problems associated with water cooled reactors and the steam generated thereby are eliminated. The heat capacity of the liquid metal permits the sodium or sodium-potassium to be heated several hundred degrees Fahrenheit without danger of materials failure in the reactor. The reactor vessels for pool-type liquid-metal cooled reactors are essentially open top cylindrical tanks without any perforations to interrupt the integrity of the vessel walls. Sealing of side and bottom walls is essential to prevent the leakage of liquid metal from the primary vessel. The vessel surfaces must also be accessible for the rigorous inspections required by safety considerations. In the typical sodium cooled reactor, two levels of heat conveying sodium loops or cooling circuits are used. Usually, a single primary loop and two or more secondary loops are used. The primary heat transferring loop contains very radioactive sodium which is heated by the fuel rods. The primary loop passes through heat exchangers to exchange the heat with one of the non-radioactive secondary sodium loops. In general, sodium cooled reactors ar designed to incorporate redundant secondary heat transferring loops in the event of failure of one loop. Upon shutdown of the reactor by fully inserting the control rods, residual heat continues to be produced and dissipated according to the heat capacity of the plant. Assuming that the reactor has been at full power for a long period of time, during the first hour following shutdown, an average of about 2% of full power continues to be generated. The residual heat produced continues to decay with time. Exaggerated conservative safety concerns for dealing with postulated worst possible scenario accident conditions have raised questions as to means for coping with events such as the coincidental failure of both the reactor vessel and the containment or guard vessel, whereupon liquid coolant loss due to the resulting leakage could significantly lower the coolant level within the reactor vessel. Reduced reactor coolant levels can significantly impede or interrupt the normal coolant circulation flow through a coolant loop or circuit, whereby heat is transported away from the fuel core during routine operation. This impediment or termination due to reduced coolant level also applies to designed passive cooling systems employing inherent processes comprising the natural convection of fluids, conduction, radiation and convection, as a means of removing heat through its transfer by such means. Other such improbable extreme events possible affecting coolant levels include a hypothetical core disassembly accident that damages the fuel core and results in expulsion of coolant such as sodium up into the head access area of the reactor structure, or a maintenance accident involving a break in the reactor closure head. This invention comprises improvements in safety systems for coping with shutdown decay heat from a liquid metal cooled nuclear reactor such as the unit disclosed and claimed in U.S. Letters Pat. No. 4,678,626, issued Dec. 2, 1985. The disclosed contents of the above noted U.S. Letters Pat. Nos. 4,508,677 and 4,678,626, comprising related background art, are incorporated herein by reference. SUMMARY OF THE INVENTION This invention comprises improvements in liquid metal cooled nuclear reactor plant systems comprising passive heat removal safety arrangements which transfers reactor shut down decay and sensible heat from the fuel core and liquid metal coolant by means of the inherent thermal energy transfer mechanisms of conduction, radiation, convection and natural convection of fluids out to the ambient atmosphere. The improvements of this invention include measures which preclude release of radiation contaminants due to the liquid metal coolant attacking and destroying the containment housing, silo vessel and other retaining structures of the nuclear reactor and/or escaping through breaches in the structure. The improved measures of the invention provide added auxiliary passive cooling means in combination with effective means for retaining the liquid metal coolant while precluding its destructive action upon reactor containing structures. OBJECTS OF THE INVENTION It is a primary object of this invention to provide improvements in passive cooling safety systems for liquid metal cooled nuclear reactors for the removal of decay and sensible heat under conditions of accidental malfunctions. It is also an object of this invention to provide measures for enhancing the protection afforded by indirect cooling safety means for the passive cooling of liquid metal cooled nuclear reactors comprising a core of fissionable fuel substantially immersed within a pool of liquid metal coolant. It is another object of this invention to provide added protective measures for passive cooling safety systems in liquid metal cooled nuclear reactors comprising an auxiliary cooling circuit for removing heat from a reduced level of reactor coolant. It is a further object of this invention to provide means for improving the operating safety of heat removing systems for liquid metal cooled nuclear reactors which are entirely passive and operate by the inherent phenomenon of natural convection in fluids, conduction, convection and thermal radiation. It is a still further object of this invention to provide passive safety systems for removing decay and sensible heat produced during shut down or an accidental interruption in a liquid metal cooled nuclear reactors which affords effective protection against the destructive effects of escaping liquid metal coolant and inhibits its escape from the plant components. |
claims | 1. A method for reducing in-core instrumentation within an in-core instrumentation pattern in a reactor core of a pressurized water reactor, said pattern having a plurality of in-core instruments contained therein, the method comprising: removing at least one of said plurality of in-core instruments from within said pattern while retaining (i) each of said plurality of in-core instruments that belong to at least one tilt group, (ii) each of said plurality of in-core instruments that provide information about power distributions in those assemblies that contribute most neutron flux to ex-core detectors, (iii) a uniform distribution of instrumented fuel assemblies from the periphery of said reactor core to the center and in each quadrant of said reactor core, (iv) said plurality of in-core instruments such that misloading of a fuel assembly in any location is detected by at least one of said plurality of in-core instruments, and (v) said plurality of in-core instruments such that at least one in-core instrument is sufficiently close to a control rod location to enable detection of a perturbation in the power distribution associated with movement of a lead control rod bank, thereby forming a reduced pattern; and evaluating the performance of said reduced pattern against at least one predetermined performance criterion. 2. The method of claim 1 , wherein said at least one predetermined performance criterion includes ensuring that differences between predicted core power distributions and core power distributions synthesized from said reduced number of said plurality of in-core instruments fall within licensed limits of the pressurized water reactor. claim 1 3. The method of claim 2 , wherein said at least one predetermined performance criterion is achieved when a basic measurement uncertainty and a synthesis uncertainty fall within licensed limits of the pressurized water reactor, said pressurized water reactor containing said reactor core. claim 2 4. The method of claim 1 , wherein a second said at least one predetermined performance criterion includes ensuring that said reduced pattern provides the ability to detect fuel misloadings. claim 1 5. The method of claim 4 , wherein said at least one predetermined performance criterion is achieved when power distribution differences obtained from detector signals from said plurality of in-core instruments for a properly loaded core are discernable from power distribution differences from a simulated misloaded core. claim 4 6. The method of claim 1 , wherein the step of removing further comprises: reducing the number of operable said at least one of said plurality of in-core instruments by about 25%. claim 1 7. The method of claim 1 , wherein said evaluating step further comprises: claim 1 (i) evaluating said candidate pattern to minimize power distribution measurement uncertainties; (ii) ensuring that said reduced pattern provides the ability to detect fuel misloadings; and (iii) insuring operability of said candidate pattern with 25% of the reduced pattern inoperable. |
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042631637 | summary | THE GENERAL BACKGROUND OF THE INVENTION For, approximately, twenty-five years, certain materials, such as zeolite, vermiculite, perlite, and the like have been expanded into light-weight aggregates. Since 1946, there has been developed apparatus and methods for expanding these certain materials. These materials are given a heat treatment in the range of about 700.degree. F. to about 3000.degree. F. to process them into expanded solid particles. A material which may be used for illustrative purposes is perlite. Perlite is an aluminal-silicate mineral that is non-crystaline and glasslike in its nature. When perlite ore is ground to the approximate particle size of sand, it has a density of about 75 lbs. per cubic foot, although this density can vary somewhat. Perlite contains a small amount of sodium oxide and potassium oxide which acts as a flux and reduces the melting point of the mixture of the perlite and the oxide. Also, there is a small percentage of chemically combined water in the perlite. When high temperature is applied to a perlite particle, the surface softens and the water turns to steam causing the perlite particle to expand. The average density of the expanded perlite particle is 8 lbs. per cubic foot, although it is possible to get the density as low as 3 or 4 lbs. per cubic foot. The particle size of the expanded product is controlled, to a degree, by the particle size of the ore. The various markets for expanded perlite particles are, essentially, controlled by the particle size of the expanded product. The perlite ore is mined by open pit methods, either drill and blast, or in some cases, dug, directly, with large bulldozers and rippers. The ore is then transported to a mill where the rock is crushed, ground, dried, and screened to various particle size ranges to meet specifications for various markets. The finished ore is then shipped by covered hopper cars all over the country to expanding plants where it is heated and expanded into its final form and distributed from these plants. The ore presently used comes from five states: New Mexico, Colorado, Arizona, California, and Idaho. Probably, 85% of the ore is mined at No Agua, New Mexico, and shipped from Antonito, Colorado, the closest rail head. At the present time, the largest particle size of perlite ore used for expansion purposes is about 1/8" in diameter. The largest expanded perlite particle does not exceed about 3/8" in diameter. The perlite industry received its start toward the end of World War II. In the formative years of the perlite industry, three types of furnaces were developed for expanding the perlite ore to form expanded perlite particles. These three types of furnaces were the stationary horizontal furnace, rotary furnace, and vertical furnace. The vertical furnace is by far the most popular design. The rotary furnace is next in popularity with the stationary horizontal furnace being third in popularity. The vertical furnace is capable of heating and expanding all gradations of ore. The rotary furnace works best on coarse ore. The horizontal stationary furnace is used on fine ores. The vertical furnace comprises a vertical tube. A burner is placed at the bottom of the tube looking upwardly and a draft is provided by a fan downstream from the vertical tube. The ore is dropped directly into the flame about midway of the tube. The particles fall down, downwardly, and due to the heat in the vertical tube, the particles are heated and start to expand. With expansion, the density of the particles decreases, and the rate of fall in the vertical furnace slows. Then, when the particles have expanded, sufficiently, the density of the particles decreases and the force of gravity on the particles is overcome by the upward draft in the furnace and the particles reverse their direction and exit out the top of the vertical furnace or vertical tube. These expanded particles are carried, pneumatically, to a collector, such as a cyclone or bag house and collected. The rotary furnace is, essentially, a set of concentric cylinders that are set, horizontally, and rotate in the same manner as the rotary kiln. There are three cylinders, one inside the other. The ore is fed into the annular space between the inside cylinder and the center cylinder. The ore is preheated in this space. The preheated ore is then fed into the inside cylinder. This inside cylinder has a burner mounted in it that provides the heat. As the ore expands, the lighter expanded particles enter into the airstream passing through the furnace and are carried out of the furnace. The heavier particles are expanded into the expanded particles and put into the airstream at the end of the furnace. The expanded particles are collected in a fashion similar to that with a vertical furnace in that these particles can be collected in a cyclone or bag house. The horizontal stationary furnace comprises a cylinder and has a burner to supply heat. The fine solid particles are introduced into this cylinder and heated to expand the fine particles. An airstream passes through the horizontal cylinder and the expanded particles, which have a low density, are carried out of the furnace in the airstream and collected in a bag house or a cyclone. The source of heat or the source of heat energy is a gas, such as natural gas. This gas is burned to supply the heat energy which is used to expand the solid particles. There is also used liquified petroleum gas or a mixture of propane-butane. The quantity of heat energy required to heat a ton of solid perlite particles to form an expanded perlite particle is in the range of about 3 million to 4.5 million BTU's per ton. It is my understanding that with these three furnaces, viz., the rotary furnace, the horizontal stationary furnace, and the vertical furnace, that the products which can be heat treated are zeolite, vermiculite, and perlite, and products of that class. It is not possible to heat treat diatomaceous earth, clay, cement, fly ash, and titanium dioxide, for example, in the vertical furnace or the stationary horizontal furnace or the rotary furnace. In these furnaces, it may be considered that two types of air are introduced. One type of air is for combustion purposes so that the fuel, such as a hydrocarbon gas, can be burned to give off heat energy. The second type of air can be considered to be an expansion air. The expansion air, along with the particles to be expanded, is heated to be able to carry away the expanded solid particles or the expanded perlite. Because of the necessity of heating the expansion air, a considerable amount of heat energy is used. The expansion air, at ambient temperature, enters into the furnace, is heated and the temperature elevated to that temperature in the furnace, and this heated expansion air used to carry away the expanded solid products and then the heated expansion air is exhausted to the atmosphere. In one manner of thinking, the heating of the expansion air is a waste of heat energy. As a result of my having worked with these furnaces and having worked in the industry for expanding zeolite, vermiculite, perlite, and the like, I have become familiar with the industry and consider that if a furnace could be devised to eliminate the expansion air, then the heat energy required to make the expanded solid particle would be reduced and there would be a saving in energy. Therefore, I have devised a furnace which can be used for expanding zeolite, vermiculite, perlite, and can process diatomaceous earth, clay, cement, fly ash, titanium dioxide, pumice, and the like, and which furnace uses, essentially, only air for burning the combustible fuel and does not require expansion air for carrying away the expanded solid particles. THE GENERAL DESCRIPTION OF THE INVENTION This invention comprises a furnace having two opposed sets of refractories. The refractory may be furnace brick. These refractories are arranged in two circular paths. There is a lower refractory in a circular path and an upper refractory in a circular path with the upper refractory being positioned above the lower refractory. There is a means for rotating one of these refractories. Generally, the lower refractory is rotated. Also, there is means for introducing solid particles onto the lower refractory so the solid particles can be heat treated and, in certain instances, expanded. Also, there is a means to remove the expanded solid particles from the lower refractory and from the furnace. The refractory can be porous so that a gaseous fuel can pass through the refractory and burn near the surface of the refractory. The furnace requires, essentially, only combustible air for burning the combustible fuel. The furnace does not need expansion air as the expanded solid particle or the heat treated particle is not removed from the furnace by means of expansion air. The expanded solid particle or the heat treated particle is removed from the furnace, mainly, by force of gravity. In certain instances, it is possible to use a solid fuel, such as coal, or to use a liquid fuel, such as fuel oil and to vaporize the liquid fuel prior to introducing it into the furnace. With the furnace requiring, essentially, only combustible air for burning the combustible fuel, there is a saving in heat energy and fuel as it is not necessary to heat expansion air and fuel is not wasted in heating the expansion air. THE OBJECTS AND ADVANTAGES One of the objects and advantages of this invention is the provision of a furnace which is, relatively, small and compact for the quantity of product produced by the furnace; another important advantage is the provision of a furnace which, for a unit of product, uses less fuel than is used with the present, commerically, available furnaces for heat treating and expanding particles; another object is to provide a furnace which, as compared with commerically available furnaces, has a lower initial cost; an additional object is to provide a furnace which has a high output of product for a unit volume of the furnace; another object is to provide a furnace having refractories which are arranged in a circular pattern for ease of introducing raw material into the furnace and for ease of removal of the heat treated product from the furnace; a further object is to provide for a, relatively, short residence time in the furnace; to provide a furnace requiring a, relatively, small number of accessories; to provide a furnace which is capable of realizing a higher temperature than with a present commerically available furnace; to provide a furnace having opposed heating surfaces so that there is a beneficial effect from radiation; to provide a furnace with two sets of refractories and which refractories are opposed to each other and facing each other; to provide a furnace having a first refractory which is porous and permits fuel to flow through the refractory and burn in close proximity to said refractory; to provide a furnace having a second refractory which is heated by radiation from the fuel burning near said first refractory; to provide a furnace for utilizing incoming air for combustion purposes and to minimize incoming air needed for expansion purposes of expanded solid particles; to provide a furnace wherein the material in the furnace can be elevated from ambient temperature to about 2000.degree. F. in, approximately, 5 minutes; to provide a furnace wherein the refractory rotates in a circle; to provide a furnace wherein the rotational speed of the refractory can be varied for accommodating raw material of different characteristics; to provide a furnace wherein the temperature in the furnace of, approximately, 2600.degree. F., can be realized; to provide a furnace wherein raw material can be fed, continuously, to the furnace and also the product discharged, continuously, from the furnace; to provide a furnace wherein refractory brick of substantially the same characteristics are used; to provide a furnace wherein the ends and sides of the refractory brick are sealed to direct the flow of the gaseous fuel through the main part of the refractory brick; to provide a furnace wherein refractory brick is placed in a side-by-side relation and the space between adjacent refractory brick is sealed; to provide a furnace wherein the exposed surface of the refractory brick is coated with porous aluminum oxide; to provide a furnace wherein raw material can be expanded to make an aggregate for light-weight concrete; to provide a furnace requiring lower capital investment as less pollution controls are required; to provide a furnace which can accommodate various fuels such as a solid fuel, a liquid fuel, and a gaseous fuel; to provide a process where less air is used and less fuel used as compared with the commercially available processes for heat treating particles and for expanding particles; to provide a process for producing expanded particles of, comparatively, very large size; to produce a stronger expanded product than can be produced with, presently, commerically, available processes in that the expanded product can be annealed; to provide a process for making a shielded encapsulated radioactive material; to expand larger particles to make strong expanded particles which were not, previously, commerically possible as large expanded particles were soft; to expand large particles without suspending the large particles in air; to expand small particles and to collect the expanded particles in a gaseous stream; to expand particles without the necessity of drying the particles to a moisture content of less than about 1% moisture; to expand particles of the moisture content up to about 10% moisture; to provide a process wherein there is a variable residence time to heat treat solid particles and to accommodate solid particles with different characteristics; to process a radioactive material and particles and to encapsulate said radioactive material in a particle to store in a safe manner; to process radioactive salt cake with particles to encapsulate said radioactive salt cake and particles; to process said encapsulated radioactive salt cake so as to retrieve the radioactive material; to process radioactive salt cake with particles to encapsulate the radioactive salt cake and to shield the radioactive material; to process the shielded radioactive salt cake so as to retrieve the radioactive material; to process solid particles to make an expanded solid particle to be used as a light-weight aggregate in concrete; to heat treat solid particles which, prior to my invention, could not be heat treated; to process radioactive material so as to make the material into a form which is not leachable and which form is easier to store; to agglomerate small particles into larger particles so as to achieve a more precise control of bed thickness in a furnace and to realize a faster and more efficient heat transfer to the agglomerated larger particles; to process waste material to make useful products; to agglomerate fines and to process said agglomerated fines to make useful products; and, to heat treat and also to expand particles with various fuels such as a solid fuel, a liquid fuel, and a gaseous fuel. These and other important objects and advantages of the invention will be more particularly brought forth upon reference to the detailed description of the invention, the appended claims and the accompanying drawings. |
claims | 1. A method of generating a metallic ion source, comprising:heating an inert carrier gas;vaporizing a metallic element or metallic element salt in the presence of the heated inert carrier gas;transporting the vaporized metallic element or salt in the heated inert carrier gas to a temperature-controlled ionization chamber; andionizing the vaporized metallic element or salt in the ionization chamber in the presence of the heated inert carrier gas to generate ions of the metal. 2. The method of claim 1, further comprising extracting an ion beam from the chamber. 3. The method of claim 1, wherein the carrier gas is heated to a temperature at which the vapor pressure of the metallic element or salt of at least 0.01 mTorr. 4. The method of claim 1, wherein the carrier gas is heated to a temperature at which the vapor pressure of the metallic element or salt of at least 5 mTorr. 5. The method of claim 3, wherein the carrier gas is heated to a temperature between about 100 and 1000° C. 6. The method of claim 3, wherein the ionization chamber is heated to about the same temperature as the carrier gas. 7. The method of claim 1, wherein the ionization chamber is heated at least in part by resistive heating elements in or on the chamber walls. 8. The method of claim 1, wherein the inert carrier gas is Ne. 9. The method of claim 7, wherein the metallic element or salt is selected from the group consisting of alkaline earth metals and transition metals with vapor pressures greater than 0.01 mTorr at temperatures below 1000° C., and salts thereof. 10. The method of claim 1, wherein the ionization is a photo-ionization. 11. The method of claim 10, wherein the photo-ionization is conducted with light having a wavelength of about 600 to 2100 Å. 12. The method of claim 11, wherein the carrier gas is not ionized. 13. The method of claim 2, further comprising conducted ion implantation of a substrate with the ion beam. 14. The method of claim 13, wherein the ion beam comprises ions of a metallic element is selected from the group consisting of Ca, Sr, Ba, Cd, Zn and Mn. 15. The method of claim 14, wherein the substrate is a material selected from the group consisting of silicon, SiO2, ZnO2 and HfO2. 16. The method of claim 15, wherein the metallic element is Ca and the substrate is SiO2. 17. An apparatus for vaporizing and ionizing a metallic element or metallic element salt, comprising:a carrier gas heating chamber configured to heat an inert carrier gas to a temperature in the range of 100 to 1000° C.;a vaporizer chamber, connected with the carrier gas heating chamber, and configured to vaporize a metallic element in the presence of the inert carrier gas heated in the carrier gas heating chamber; andan ionization chamber connected with the vaporizer chamber, the ionization chamber having surfaces heated to prevent deposition of the vaporized metallic element or salt thereon, and configured to ionize the vaporized metallic element in the presence of the inert carrier gas heated in the carrier gas. 18. The apparatus of claim 17, wherein the ionization chamber surfaces contain or contact resistive heating elements. 19. The apparatus of claim 18, further comprising a photo-ionization source appended to the ionization chamber. 20. The apparatus of claim 19, wherein interior surfaces of the ionization chamber have a mirror finish. 21. The apparatus of claim 20, wherein a sheet of glass separates the light source from the ionization chamber. 22. The apparatus of claim 21, wherein the sheet of glass comprises embedded resistive heating elements. 23. The apparatus of claim 22, wherein the sheet of glass has a one way mirrored surface facing the ionization chamber interior. |
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abstract | According to an embodiment, a nuclear reactor monitoring device comprises: an ultrasonic wave transmission means which is installed on the outside surface of a reactor pressure vessel and transmits ultrasonic pulses to the interior of the reactor pressure vessel; an ultrasonic wave receiving means which is installed on the outside surface of the reactor pressure vessels and receives reflected pulses including ultrasonic waves from the ultrasonic pulses reflected by an inspection object in the reactor pressure vessel; a preprocessing means which specifies and removes the reflected ultrasonic pulses generated in the wall of the reactor pressure vessel from the reflected pulse signal received by the ultrasonic wave receiving means or selectively extracts the reflected pulse signal; and a calculation means which determines the vibration of the inspection object from the reflection pulse signal processed by the preprocessing means in accordance with the observation time of the inspection object. |
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claims | 1. A method for treating a waste material which includes at least one type of radioactive isotope to be alloyed with a reactant metal alloy, the method comprising the steps of: (a) identifying each radioactive isotope which is present in the waste material at a detectable level and determining the concentration of each said radioactive isotope in the waste material; (b) producing the reactant metal alloy for a selected volume of the waste material, the reactant metal alloy being held in a molten state and including at least one chemically active metal and, for each type of expected radioactive emission associated with the selected volume of the waste material, at least one corresponding radiation absorbing metal, each corresponding radiation absorbing metal being capable of absorbing the respective type of expected radioactive emission; and (c) adding the selected volume of the waste material to the molten reactant metal alloy. 2. The method of claim 1 wherein the molten reactant metal alloy includes a sufficient quantity of each corresponding radiation absorbing metal so that, once the selected volume of waste material has been added to the molten reactant metal alloy, the molten reactant metal alloy includes a minimum ratio of atoms of each corresponding radiation absorbing metal to each expected radioactive emission within the volume of the molten reactant metal alloy, the minimum ratio being no less than seven hundred and twenty-seven (727) corresponding radiation absorbing atoms for each respective expected radioactive emission. claim 1 3. The method of claim 1 further comprising the step of: claim 1 (a) maintaining the amount of the chemically active metal in the molten reactant metal alloy at no less than forty percent of the total molten reactant metal alloy by weight. 4. The method of claim 1 further comprising the step of: claim 1 (a) maintaining the molten reactant metal alloy at an operating temperature of no less than 770 degrees Celsius as the waste material is added to the molten reactant metal alloy. 5. The method of claim 1 wherein each chemically active metal is selected from the group consisting of magnesium, aluminum, lithium, zinc, calcium, and copper. claim 1 6. The method of claim 1 further comprising the step of: claim 1 (a) monitoring radioactive emissions from a stream of the selected volume of waste material being directed to the molten reactant metal alloy to be added thereto, the monitoring providing an indication of the level of radioactive emissions from the stream of waste material; and (b) halting the stream of waste material in response to an anomalous radioactive emission level detected from the stream of waste material. 7. A method for treating a waste material which includes at least one type of radioactive isotope to be alloyed with a reactant metal alloy, the method comprising the steps of: (a) identifying each radioactive isotope which is present in the waste material at a detectable level and determining the amount of each said radioactive isotope in the waste material; (b) producing the reactant metal alloy for a selected volume of the waste material, the reactant metal alloy being held in a molten state and including at least one chemically active metal and, for each type of expected radioactive emission associated with the selected volume of the waste material, at least one corresponding radiation absorbing metal, each corresponding radiation absorbing metal being capable of absorbing the respective type of expected radioactive emission; and (c) adding the selected volume of the waste material to the molten reactant metal alloy. 8. The method of claim 7 wherein the molten reactant metal alloy includes a sufficient quantity of each corresponding radiation absorbing metal so that, once the selected volume of waste material has been added to the molten reactant metal alloy, the molten reactant metal alloy includes a minimum ratio of atoms of each corresponding radiation absorbing metal to each expected radioactive emission within the volume of the molten reactant metal alloy, the minimum ratio being no less than seven hundred and twenty-seven (727) corresponding radiation absorbing atoms for each respective expected radioactive emission. claim 7 9. The method of claim 7 further comprising the step of: claim 7 (a) maintaining the amount of the chemically active metal in the molten reactant metal alloy at no less than forty percent of the total molten reactant metal alloy by weight. 10. The method of claim 7 further comprising the step of: claim 7 (a) maintaining the molten reactant metal alloy at an operating temperature of no less than 770 degrees Celsius as the waste material is added to the molten reactant metal alloy. 11. The method of claim 7 wherein each chemically active metal is selected from the group consisting of magnesium, aluminum, lithium, zinc, calcium, and copper. claim 7 12. The method of claim 7 further comprising the step of: claim 7 (a) monitoring radioactive emissions from a stream of the selected volume of waste material being directed to the molten reactant metal alloy to be added thereto, the monitoring providing an indication of the level of radioactive emissions from the stream of waste material; and (b) halting the stream of waste material in response to an anomalous radioactive emission level detected from the stream of waste material. |
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summary | ||
047524405 | summary | BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a control rod for nuclear reactors which comprises a number of elongated absorber plates which are each provided with a plurality of channels, these channels extending substantially perpendicularly to the longitudinal direction of the absorber plate, and containing powdered boron carbide or other powdered absorber material which gives off gas and swells upon irradiation, these channels being hermetically separated from the surroundings of the control rod by an edge portion which is arranged at an edge running in the longitudinal direction of the absorber plate and which comprises a gas-tight edge, a longitudinally-extending space being provided inside the edge and in open connection with and permitting a gas flow between the different channels in the absorber plate. The Prior Art A control rod of this kind is known from U.S. Pat. No. 3,448,008. According to this U.S. patent, the edge portion comprises an outwardly sealed, longitudinally extending slot in the absorber plate in which a longitudinal bar is arranged to cover in part the orifices of the channels at the bottom of the slot. When boron carbide is subjected to irradiation, helium gas is formed. Since absorber plates in a control rod are not subjected to uniform irradiation, the amount of gas developed will be different in different channels with absorber material. In the known control rod described above, an equalization of the gas pressure arising is achieved in the different channels by the fact that, as mentioned above, the channels are sealed with an edge portion which permits a gas flow between the different channels. Another property of boron carbide is that it swells upon irradiation. The present invention is based on the realization that the life of a control rod can be considerably extended if measures are taken to counteract the consequences of the swelling. An extension of the life is of the utmost importance. It involves not only reduced costs of new control rods but also reduced costs for taking care of and disposal of spent control rods. SUMMARY OF THE INVENTION The swelling of the abosrber material in a channel may cause stress corrosion in the construction material in the channel surrounding the absorber material, that is, in the material of which the control rod is manufactured. The risk of cracks in the construction material caused by stress corrosion increases with increasing irradiation and swelling of the absorber material. If a crack occurs at a channel, a transportation of boron carbide from the channel takes place so that the channel is depleted of boron carbide. In addition, a transportation of absorber material from other nearby, undamaged channels occurs, especially in the region located nearest the edge portion, because the edge portion does not efficiently prevent the transportation of liquid from the defective channel to an undamaged channel and the transportation of liquid together with absorber material from an undamaged channel to the defective channel and from there to the surroundings. According to the present invention, the above-mentioned transportation of powdered absorber material is prevented or radically counteracted by arranging, between the powdered absorber material and the edge portion in a plurality of channels, a body consisting of hafnium or other metallic absorber material, this body forming between it and the inner wall of the channel a gap which permits a gas flow but which is smaller than at least the main part of the grains in the powdered absorber material. The channels and this body preferably have a circular cross-section and the body preferably a circular-cylindrical shape. A transportation of absorber material can be very efficiently counteracted according to the present invention by the fact that a gap with an accurately predetermined width can be achieved without difficulty between the channel and the body of metallic absorber material. This result can be achieved without the outer dimensions of the control rod having to be changed or its neutron-absorbing capacity having to be significantly reduced. Preventing such transportation only by the use of the edge portion would require additional, very time-consuming operations in connection with the pressing and welding operations which are part of its manufacture, and would furthermore yield an unreliable result owing to the nature of these work operations. In the powdered absorber material, preferably at least 50% of the grains have a size exceeding 0.13 mm. The gap between the inner wall of the channel and the body of metallic absorber material (the distance between the inner wall of the channel and the surface of the body in a direction perpendicularly to the longitudinal direction of the channel) preferably amounts to 0.01-0.13 mm. If the channel and the body have circular cross-section, the body has a diameter which is preferably 0.01-0.13 mm smaller than the diameter of the channel. The length of the body preferably amounts to 5-25 mm. |
abstract | A means for installing material, through a fuel assembly instrument thimble insert, into the existing instrument thimbles in nuclear fuel assemblies for the purpose of allowing the material to be converted to commercially valuable quantities of desired radioisotopes during reactor power operations during a remainder of a fuel cycle and removing the radioisotopes from the core through the reactor flange opening once the fuel assemblies have been removed for refueling. The invention also describes methods that can be used to harvest the irradiated material so it can be packaged for transportation from the reactor to a location where the desired radioisotope(s) can be extracted from the fuel assembly instrument thimble insert. |
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description | This application is a divisional of U.S. patent application Ser. No. 10/068,093, filed Feb. 5, 2002 now U.S. Pat. No. 6,793,450, which is hereby incorporated by reference in its entirety. This invention relates to the field of storing and transferring spent nuclear fuel and specifically to a method and system for transferring spent nuclear fuel from a transfer cask to a receiving cask. In the operation of nuclear reactors, it is customary to remove fuel assemblies after their energy has been depleted down to a predetermined level. Upon removal, this spent nuclear fuel is still highly radioactive and produces considerable heat, requiring that great care be taken in its packaging, transporting, and storing. In order to protect the environment from radiation exposure, spent nuclear fuel is first placed in a canister. The loaded canister is then transported and stored in large cylindrical containers called casks. A transfer cask is used to transport spent nuclear fuel from location to location while a storage cask is used to store spent nuclear fuel for a determined period of time. In a typical nuclear power plant, spent nuclear fuel is loaded into a canister while submerged in a pool of water. The canister is sealed and loaded into a transfer cask while still submerged in the pool. Once loaded with the canister, the transfer cask is used to transport the canister to a receiving cask (i.e., a storage cask or a transport cask). The loaded canister is then transferred from the transfer cask to the receiving cask for either storage or further transport. During transfer from the transfer cask to the receiving cask, it is imperative that the loaded canister is not exposed to the environment. As a result of this need, the prior method for transferring a loaded canister from a transfer cask to a receiving cask is to raise the transfer cask above the receiving cask and secure the transfer cask atop the receiving cask so that the casks are in a vertically stacked orientation. The transfer cask is adapted so that its bottom can be opened while it remains stacked upon an open receiving cask. Once the bottom of the transfer cask is opened, the loaded canister is lowered from the transfer cask into the receiving cask with a negligible amount of radiation exposure to operations personnel. Most casks are very large structures and can weigh up to 250,000 lbs. and have a height of 16 ft. or more. As such, stacking a transfer cask atop a receiving cask requires a lot of space a large overhead crane and possibly a restraint system for stabilization. Typically, the transfer of a loaded canister using this stacking method is done inside a 10 C.F.R. 50 structure of a nuclear power plant, which is fully equipped with an overhead crane and radiation containment devices to protect the health and safety of the surrounding communities in the event of a loading mishap. However, numerous nuclear power plants do not possess a 10 C.F.R. 50 qualified staging area that is either large enough to accommodate the stacking of the transfer cask and receiving cask, qualified to support the load of the stacked casks, and/or possesses qualified load handling equipment to make the canister transfer indoors. For such sites, the canister transfer must be completed outdoors using systems and devices that provide the same or greater level of operational safeguards that are available inside a nuclear power plant structure that is fully certifiable for indoor transfer. It is an object of the present invention to provide a method and system for transferring a loaded canister of spent nuclear fuel from a transfer cask to a receiving cask that requires less vertical space. Another object of the present invention is to provide a method and system for outdoor transfer of a loaded canister of spent nuclear fuel from a transfer cask to a receiving cask outdoors that provides the same or greater level of operational safeguards that are available inside a fully certified nuclear power plant structure. Yet another object of the present invention is to provide a method and system for ergonomically completing cask operations necessary for transferring a loaded canister of spent nuclear fuel from a transfer cask to a receiving cask. Still another object of the present invention is to provide a method and system that greatly enhances the radiation shielding during the transfer of a spent nuclear fuel from a transfer cask to a receiving cask. Another object of the present invention is to provide a method and system that eliminates personnel lifts and scaffolding that is needed to complete transfer of spent nuclear fuel from a transfer cask stacked atop a receiving cask to the receiving cask. These objects and others are met by the present invention which in one aspect is a system for transferring spent nuclear fuel to a cask comprising a below grade opening adapted for receiving a cask; a cask support means positioned within the opening, the cask support means capable of vertical movement; and means for vertically moving the cask support means; wherein the cask support means is capable of lowering the cask within the opening. Preferably, the system further comprises a shell having a cross section, the shell forming walls of the opening wherein the cross section of the shell is slightly larger than the cross section of the cask. The shell and the cask are usually cylindrical. Also preferably, the means for vertically moving the cask support means is at least two lifting jacks. Moreover, the at least two jacks can be coupled so as to keep the cask support means approximately level during vertical movement. In the preferred embodiment of the system, the number of lifting jacks is three and are located outside the opening and accessible from grade level. The cask support means has a fully lowered position and a fully raised position. Preferably, when the cask support means is in the fully raised position, the cask support means is below grade. Also preferably, when the cask support means is in the fully lowered position and supporting a cask having a height, at least a major portion of the cask's height is below grade, with approximately 30 inches of the cask above grade when the cask support means is in the fully lowered position and supporting a cask. The opening can have a bottom, and the system can further comprise a setdown structure positioned at the bottom of the opening and below the cask support means. In such an embodiment, when the cask support means is in a fully lowered position, the cask support means contacts the setdown structure and the cask support means, and any load being borne by the cask support means is supported by the setdown structure. Preferably, the cask support means is a platform having a center and a top surface wherein the cask support means has a hole near the center and a plurality of cask positioning plates on the top surface. The system can further include vertical guide rods on which the cask support means can move. Preferably, the vertical guide rods have a top and a bottom, the vertical guide rods being secured at the top so that upon loading the cask support means, the vertical guide rods are in tension. In another aspect, the invention is a method of transferring a canister of spent nuclear fuel to a cask comprising the steps of: lowering a receiving cask having a height into a below grade opening so that a portion of the receiving cask's height is below grade level; and transferring the canister to the receiving cask. The preferred method further comprises placing the receiving cask on a cask support means located within the opening, the cask support means capable of vertical movement; lowering the receiving cask into the opening by lowering the cask support means; aligning the canister above the receiving cask; and lowering the canister into the receiving cask. Preferably, jacks are used to lower the cask support means wherein the lifting jacks can be coupled so as to keep the cask support means approximately level during vertical movement. The preferred number of lifting jacks is three and the jacks are preferably outside the opening and are accessible from grade level. Also preferably, a shell having a cross section can be used to form walls of the opening. The shell and the receiving cask can be cylindrical. The cross section of the shell is preferably slightly larger than the cross section of the cask. Also preferably one or more lateral restraints are inserted between the shell and receiving cask. Preferably, the cask support means has a fully lowered position and a fully raised position, wherein when the cask support means is in the fully raised position the cask support means is below grade level. Also preferably, when the cask support means is in the fully lowered position, at least a major portion of the cask's height is below grade level. When the cask support means is in the fully lowered position, it is preferable that about 30 inches of the cask be above grade level. The opening preferably has a bottom with a setdown structure positioned at the bottom of the opening and below the cask support means. It is preferable that when the cask support means is in a fully lowered position, the cask support means contacts the setdown structure, the cask support means and any load being borne by the cask support means being supported by the setdown structure. Preferably, the cask support means is a platform having a center and a top surface wherein the cask support means has a hole near the center and a plurality of cask positioning plates positioned on the top surface. Also preferably, the cask support means moves along a plurality of vertical guide rods. It is preferred that the vertical guide rods have a top and a bottom, the vertical guide being secured at the top so that any loading from the cask support means results in the vertical guide rods being in tension. FIG. 1 illustrates an embodiment of the system of the present invention, a below grade cask transfer facility (“CTF”) 2. As used herein, the term “below grade” means elevationally below ground surface level 6. Generally, CTF 2 comprises below grade opening 3, circular platform, and at least two jacks 5. In the illustrated embodiment, there are three high-capacity jacks 5 (only two are visible in the illustration). While jacks 5 are used to vertically move circular platform 4, circular platform 4 can be vertically moved by any type of pneumatic or mechanical lifting device capable of lifting the applied load. Referring to FIG. 2, CTF 2 is constructed so that receiving cask 9 having lid 22, top surface 12 (FIG. 5) and base 13 can be placed on and supported by platform 4. Receiving cask 9 can be a storage cask or a transport cask. Receiving cask 9 is placed on platform 4 when platform 4 is in a fully raised position. When platform 4 is in the fully raised position, top surface 8 (FIG. 1) of platform 4 is below grade. When receiving cask 9 is placed thereon, base 13 of receiving cask 9 is also below grade, preferably about 40 inches. Platform 4 is capable of vertical movement, including lowering receiving cask 9 into opening 3. Referring to FIGS. 3 and 4, platform 4 can be lowered to a fully lowered position while supporting receiving cask 9. CTF 2 is designed so that when platform 4 is supporting receiving cask 9 and in the fully lowered position, receiving cask 9 is in a position wherein a majority of its height is below grade. Preferably, all of receiving cask 9 will be below grade except about 30 inches. When all but about 30 inches of receiving cask 9 is below grade, top surface 12 (FIG. 5) of receiving cask 9 is at an ergonomic height to facilitate cask operations. Referring to FIGS. 1 and 2, in the illustrated embodiment, CTF 2 further comprises a shell 15 that forms the walls of opening 3. In constructing CTF 2, shell 15 is placed in an oversized hole in the ground 6 and leveled approximately flush with the ground surface 6. The area surrounding shell 15 can be backfilled with soil and/or concrete to secure shell 15 in the ground 6 and to provide extra radiation shielding. As such, shell 15 establishes the inner form for a concrete pour. The bottom of shell 15 may be open-bottomed to allow the inside bottom to be filled with concrete and leveled or equipped with setdown structure 16. In the illustrated embodiment, shell 15, opening 3, and receiving cask 9 are cylindrical. However, shell 15, opening 3, and receiving cask 9 can be made to be any shape or size. Preferably, shell 15 has a cross-section that is shaped and sized so that there is a tight clearance between shell 15 and receiving cask 9 when receiving cask 9 is resting on platform 4. Having a tight clearance between shell 15 and receiving cask 9 provides a safeguard against receiving cask 9 tipping over during a seismic event. When there is a tight clearance between shell 15 and receiving cask 9, receiving cask 9 can not tip over during a seismic event when receiving cask 9 is resting on platform 4 in the fully lowered position. When receiving cask 9 is resting on platform 4 in the fully raised position, base 13 of receiving cask 9 is below grade. Thus, a portion of receiving cask 9 forms a tight clearance with shell 15, providing seismic stabilization and decreasing the chance that receiving cask 9 will tip over during a seismic event. Additionally, shell 15 is designed to have a plurality of extension spaces 17 for mounting jacks 5. Extension spaces 17 provide space outside the main circumference of shell 15 so that jacks 5 do not contact or interfere with receiving cask 9 when it is lowered. Because jacks 5 are mounted to shell 15, shell 15 provides the support for jacks 5 during lifting and lowering of platform 4 (and any applied load). Shell 15 also provides lateral support of platform 4 during operations. While in the illustrated embodiment, shell 15 is used to form the walls of opening 3, CTF 2 can be constructed without employing shell 15. In such a situation, opening 3 is formed by digging a hole in ground 6 that approximates the desired size of opening 3. In FIG. 1, platform 4 is a circular platform having hole 7. Hole 7 provides personnel access to the underside of the circular platform. Alternatively, platform 4 can be a frame or other structure capable of supporting receiving cask 9 containing loaded canister 11. As illustrated, platform 4 has top surface 8 with cask positioning plates 14 located thereon. Cask positioning plates 14 act as key ways to help center receiving cask 9 on platform 4 and within opening 3. Platform 4 is designed to approximate the shape and size of receiving cask 9, with projections 16. Platform 4 is a rugged steel weldment that provides support for receiving cask 9 and transmits lateral loads to shell 15 during seismic events. Platform 4 also transmits the lifting and controlled lowering forces supplied by jacks 5 to receiving cask 9. This is accomplished by projections 16 that form lifting locations for jacks 5. Projections 16 ride inside extension spaces 17. Jacks 5 are located just outside the main diameter of the shell 15 in extension spaces 17. Jacks 5 are supported at their top end in extension spaces 17. Jacks 5 comprise guide rods 25 that guide the movement of platform 4. Because jacks 5 are connected to shell 15 only at their top, vertical guide rods 25 are in constant tension under loading conditions, which eliminates the danger of “buckling.” When jacks 5 lower platform 4 and any load supported thereby to the fully lowered position, platform 4 contacts and rests on setdown structure 16. At this position, setdown structure 16 bears the entire load of platform 4 (and any load supported thereby), freeing jacks 5 and vertical guide rods 25 from supporting the applied load (FIG. 3). Jacks 5 are coupled mechanically or electronically to keep platform 4 level during lifting operations. Jacks 5 provide sufficient lift force to raise the platform 4 when loaded with receiving cask 9 and are overrated to provide an extra safety margin. Jacks 5 contact the underside of projections 16 of platform 4 in extension spaces 17. All parts of jacks 5 and their drives 18 are located below grade to prevent interference with delivery of transfer cask. Jacks 5 and their drives 18 are situated in shallow steel or concrete-lined trenches and covered with removable, recessed covers 19. Drives 18 and their control system provide the power and control for jacks 5. An electronic feedback system monitors the position of each jack 5 to maintain synchronous movement of platform 4. Redundant position switches (not illustrated) limit the travel beyond established points (independent of the drive and control system). Level monitoring switches independently monitor the platform level and shut off jack drives 18 if an out-of-level condition is detected. The control station is located near CTF 2 but is sufficiently far away for the operator to oversee the movement operations. Power and control wires going from the control station to drives 18 are located underground to prevent interference and damage during cask operations. CTF 2 is used to facilitate the transfer of a canister of spent nuclear fuel from a transfer cask to a receiving cask in a more safe, efficient, and cost effective manner. Referring to FIGS. 1 and 2, in utilizing CTF 2 for the transfer, empty receiving cask 9 is placed on platform 4 when platform 4 is in the fully raised position. As receiving cask 9 is placed on platform 4, cask positioning plates 14, located on the top surface 8 of platform 4, act as key ways to help center receiving cask 9 in CTF 2. Referring to FIGS. 3 and 4, platform 4 (with receiving cask 9 positioned thereon) is then lowered to a fully lowered position, leaving top surface 12 (FIG. 5) of receiving cask 9 approximately 30 inches above ground surface level 6. A set of lateral restraints 20 can then be installed between receiving cask 9 and shell 15 for sites that are prone to severe earthquakes. Lateral restraints 20 act like hard bumpers to limit the radial movement of receiving cask 9 during a seismic event. Referring to FIGS. 5 and 6, lid 22 (FIG. 4) of receiving cask 9 is then removed. In the illustrated embodiment, mating device 21 is then attached to top surface 12 of receiving cask 9. Mating device 21 provides the connection between transfer cask 10 and receiving cask 9. While in the illustrated embodiment, mating device 21 is used to provide a connection between transfer cask 10 and receiving cask 9 (FIG. 7), it is possible to connect transfer cask 10 directly to receiving cask 9. The method of connection is dictated by the specific designs of the transfer cask and receiving cask used and does not affect the scope of the present invention. Referring to FIG. 7, in the illustrated embodiment, transfer cask 10, containing a loaded and sealed canister 11, is then raised, placed into, and rigidly secured to mating device 21. Base 23 (shown partially in section) of transfer cask 10 is removed using mating device 21, leaving an unobstructed pathway for canister 11 to be lowered into receiving cask 9. Referring to FIG. 8, canister 11, using slings 24 attached to top surface 27 of canister 11, is then fully lowered into receiving cask 9 until canister 11 contacts bottom 26 of receiving cask 9. Slings 24 are disconnected and empty transfer cask 10 and mating device 21 are removed (not illustrated). Lid 22 is then placed back on and secured to receiving cask 9. Receiving cask 9 is then raised by platform 4 of CTF 2 to the fully raised position. Receiving cask 9 is then lifted and removed from CTF 2 by cask transporter 28 (FIG. 9) or some other lifting device such as a crane. The loading operations for transferring a loaded canister from a transfer cask to a receiving cask summarized above aid in understanding the operations of CTF 2. Actual operations and cask-specific equipment at a particular nuclear site may vary from those described herein. The foregoing discussion discloses and describes merely exemplary embodiments of the present invention. As will be understood by those skilled in this art, the invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. Accordingly, the disclosure of the present invention is intended to be illustrative, but not limiting, of the scope of the invention, which is set forth in the following claims. |
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048045152 | claims | 1. Apparatus for processing a plurality of signals produced by sensors monitoring selected parameters in a complex process for use by a process protection system, said apparatus comprising a plurality of independent, digital signal processors smaller in number than said plurality of sensor signals for generating digital protection system actuation signals for said protection system in response to predetermined combinations of values of said sensor signals indicative of predetermined conditions within said complex process, with at least some of said signal processors generating at least two such actuation signals and wherein for at least a given one of said predetermined conditions, a first of said independent signal processors generates a primary actuation signal for said given condition from a first combination of values of a first set of sensor signals and a second of said independent signal processors generates a secondary actuation signal for the given condition from a second combination of values of a second set of sensor signals, whereby although at least two protection system actuation signals are generated by at least some of said independent signal processors, the primary and secondary actuation signals indicative of a given predetermined process condition are generated in separate independent signal processors. 2. The apparatus of claim 1 wherein each of said independent digital, signal processors has a separate digital output line for transmitting each protection system actuation signal generated thereby to the process protection system, and wherein said apparatus includes electrical isolation means in each said digital output line to electrically isolate each digital signal processor from the process protection system. 3. The apparatus of claim 2 wherein each of said independent digital signal processors includes means for generating from the sensor signals applied thereto processed parameter signals representative of the analog value of selected parameters associated with said complex process, and wherein said apparatus includes, a common parameter signal output device, a common electrical isolation means, data link means connecting each of said independent digital signal processors with said common parameter output device through said common electrical isolation means, and a communications processor for controlling said data link means to sequentially transmit the parameter signals from each of said independent digital, signal processors to said common parameter signal output device through said common electrical isolation means. 4. The apparatus of claim 3 including a second parameter signal output device and a second common electrical isolation means and wherein said data link means transmits said processed parameter signals to said second parameter signal output device through said second common electrical isolation means under the control of said communications processor. 5. The apparatus of claim 3 including a second data link means, a second common electrical isolation means and a second communications processor and wherein said plurality of independent, digital, signal processors are divided into two groups with those in the first group connected to said common parameter signal output device by the first mentioned data link means through the first mentioned common electrical isolation means controlled by the first mentioned communications processor and those independent, digital signal processors in the second group are connected to said common parameter signal output device by said second data link means through said second common electrical isolation means under the control of said second communications processor. 6. The apparatus of claim 2 for use in processing redundant sets of signals produced by multiple sensors monitoring the selected parameters in the complex process and wherein said plurality of independent, digital, signal processors constitutes a channel set which processes one set of said redundant sensor signals and wherein said apparatus includes redundant channel sets each comprising a plurality of independent, digital, signal processors which process a set of said redundant sensor signals. 7. The apparatus of claim 6 wherein each of said independent, digital, signal processors includes input/output means for receiving said sensor signals required for said signal processor to generate said protection system actuation signals and for generating an active signal on each output line which goes inactive in response to the associated actuation signal, and wherein each channel set includes a common tester/bypass means which includes means for individually and sequentially as to each actuation signal replacing with selected actuating generating test signals at the input/output means only the required sensor signals for that actuation signal and for disconnecting only the actuation signal generated by the test signal from the associated output line and applying it instead to said test/bypass means, and means for sensing and recording the actuation signal generated by said test signal, whereby each actuation signal is individually bypassed by the generation of a continuous active signal on the associated output line when it is under test. 8. Apparatus for processing for use in a process protection system and a process control or monitoring system signals generated by a plurality of redundant sets of sensors monitoring selected parameters in a complex process comprising: multiple channel sets for separately processing each set of redundant sensor signals and each including; a plurality of independent, digital, signal processors for generating from selected sensor signals of the channel set protection system actuation signals indicative of predetermined conditions within said complex process with at least some of said signal processors generating more than one actuation signal but with related actuation signals indicative of the same condition generated in different signal processors, and for generating from said sensor signals processed parameter signals representative of the analog value of selected parameters within the complex process; input/output means for said digital signal processors including means for receiving the sensor signals required by the signal processor to generate the assigned actuation signals and processed parameter signals and means for connecting each of the actuation signals to a separate electrically isolated output line; common tester/bypass means for sequentially one at a time as to each actuation signal, replacing the required sensor signals with test signals which generate an actuation signal and for disconnecting the actuation signal from the output line and applying it to the tester/bypass means instead for sensing and recording of the actuation signal/common parameter signal output means; a common electrical isolation means; common data link means connecting each of said independent digital, signal processors with said common parameter signal output means through said common electrical isolation means and a common communications processor for sequentially controlling the transmission of said parameter signals by said data link means from said independent, digital signal processors to said common parameter signal output means through said common electrical isolation means. 9. The apparatus of claim 8 wherein said data link means are also connected to said tester/bypass means and wherein said communications processor also controls the sequential transmission of said parameter signals by said data link means from said independent, digital signal processors to said tester/bypass means, and the tester/bypass means includes means for storing and outputing said parameter signals through a common additional isolation means. 10. The apparatus of claim 8 wherein said independent, digital, signal processors in each channel set are divided into two groups, with those in each group transmitting their processed parameter signals by a data link means common to the group to one processed parameter output device common to the channel set through an electrical isolation means common to the group under the control of a communications processor also common to the group. 11. A method of processing signals generated by sensor monitoring selected parameters of a complex process using a plurality of independent, digital, signal procesors, said method comprising the steps of: applying to each independent, digital signal processor, the sensor signals required for the generation of selected protection system actuation signals, some of which are a primary indication of the occurrence of a given event in the process requiring emergency action and others of which are a secondary indication of the occurrence of the given events, with sensor signals required for the generation of more than one of said selected actuation signals applied to at least some of said independent, digital, signal processors, but with the sensor signals required for the generation of the primary actuation signal and the secondary actuation signal for a given event applied to different independent, digital, signal processors; operating the independent, digital signal processors to generate the selected actuation signals in response to the predetermined values of the applied sensor signals; and applying each of said actuation signals to a separate output line separately electrically isolated from the signal processor in which it is generated. applying the sensor signals in each redundant set of sensor signals to a separate group of said independent, digital, signal processors to form redundant channel sets, and within each channel set applying to individual independent, digital, signal processors the sensor signals required to generate within said signal processors selected partial protection system actuation signals, some of which are a primary indication of a given event in the plant requiring emergency action and others of which are a secondary indication of the given event, with sensor signals required to generate the primary actuation signal and the secondary actuation signal for a given event applied to separate independent, digital, signal processors within the channel set; operating the independent, digital, signal processors in each channel set to cyclically generate the selected partial actuation signals in response to predetermined values of the applied sensor signals; and applying each of said partial actuation signals to a separate output line separately electrically isolated from the signal processor in which it is generated. 12. The method of claim 11 including the steps of sequentially, one at a time, as to each protection system actuation signal, disconnecting the actuation signal from its separate output line, removing the sensor signals required for the generation of the actuation signal from the associated independent, digital signal processor to which they are applied and substituting therefore test signals selected to generate the actuation signal, and generating a test fail signal if an actuation signal is not generated by the independent, digital signal processor in response to the test signals, whereby each actuation signal is tested individually while the remaining actuation signals, including any generated by the same independent, digital signal processor as the actuation signal under test, remain on line. 13. The method of claim 11 wherein the step of operating said independent, digital, signal processors includes generating from the applied sensor signals and storing processed parameter signals indicative of the analog value of selected process parameters, and sequentially one at a time transmitting each of said stored processed parameter signals over a data link to a common processed parameter signal output device through a common electrical isolation means. 14. A method of processing signals generated by redundant sets of sensors monitoring selected parameters in a nuclear fueled electric power generating plant using a plurality of independent, digital, signal processors, said method including the steps of: 15. The method of claim 14 including the steps of repetitively for each channel set generating a ramp signal, continuously applying said ramp signal to each of said independent, digital, signal processors in the channel set, operating each of said signal processors to cyclically generate, along with the generation of said partial protection system actuation signals, a test actuation signal when said applied ramp signal reaches a preset value, the time interval required for said repetitive ramp signals to reach said preset value being longer than the interval required for the signal processors to generate all of its assigned partial actuation signals and the test actuation signal, monitoring each signal processor for the generation of the test actuation signal and generating an alarm signal if said test actuation signal is not generated by a signal processor when the ramp signal reaches the preset value. 16. The method of claim 15 wherein the step of applying each partial protection system actuation signal to a separate output line includes generating a signal having a first level on the output line in the absence of the associated actuation signal and generating signal having a second level on the output line in the presence of the actuation signal; and including the steps of sequentially, one at a time as to each actuation signal in only one channel set, removing the sensor signals required to generate that actuation signal from the associated independent, digital, signal processor and replacing them with test signals having values selected to generate said actuation signal, disconnecting the actuation signal from the associated output line so that the signal having the first level remains on that output line, applying the actuation signal instead to a tester/bypass device which generates a test fail signal if the actuation signal is not generated in response to the test signals, removing the test signal from the signal processor and reapplying said sensor signals to the signal processor and said actuation signal to the output line, whereby only one actuation signal in one channel set at a time is tested and during the sequential testing the actuation signal is effectively bypassed by the generation of the signal having said first level on the associated output line. 17. The method of claim 16 including after removal of each test signal from a signal processor, the steps of, maintaining the magnitude of the test signal at a value above that which would cause the signal processor to generate a partial protection system actuation signal, monitoring the signal on the associated output line, and generating an alarm signal if an actuation signal appears on said output line whereby a check is made to assure that the tester is disconnected from the signal processor following each test. 18. The method of claim 16 including the steps of operating said independent, digital, signal processors to generate from the applied sensor signals, parameter signals representative of the analog value of selected process parameters, storing said parameter signals in the associated signal processor, and as to each channel set; sequentially transmitting the stored parameter signals by common data link means, through a common electrical isolation means to a common parameter signal output device. |
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claims | 1. A collimator module for collimating X-rays comprising:a plurality of collimator single plates each having a rectangular shape including a pair of long sides having a first length and a pair of short sides having a second length shorter than the first length of the pair of long sides;a pair of blocks comprising a plurality of first grooves extending along an irradiation direction of the X-rays, the short sides of the collimator single plates inserted into the plurality of first grooves of the pair of blocks to support the plurality of collimator single plates in a vertical orientation along the irradiation direction of X-rays; anda supporting member configured to cover the long sides of the plurality of the collimator single plates from an incident side and an emission side of the X-rays, the supporting member having an X-ray transmission property and comprising an incident side fixing sheet and an emission side fixing sheet that each include a plurality of second grooves, the long sides of the collimator single plates inserted into the plurality of second grooves to support the plurality of collimator single plates,wherein the incident side fixing sheet and the emission side fixing sheet cover the plurality of first grooves and at least a portion of each of the long sides of the plurality of collimator single plates adjacent to the first grooves from the incident side and the emission side of the X-rays, andwherein the collimator module is configured to form a collimator when a plurality of collimator modules are arranged in a channel direction. 2. The collimator module according to claim 1, wherein the incident side fixing sheet and the emission side fixing sheet comprise a first incident side fixing sheet and a first emission side fixing sheet that cover the portion of each of the long sides adjacent to the plurality of first grooves from the incident side and the emission side of the X-rays, andwherein the supporting member further comprises a second incident side fixing sheet and a second emission side fixing sheet that each include the plurality of second grooves to which the long sides of the collimator single plates are inserted, the second incident side fixing sheet and the second emission side fixing sheet covering the long sides of the collimator single plates, wherein gaps are defined between the first incident side fixing sheet and the first emission side fixing sheet and between the second incident side fixing sheet and the second emission side fixing sheet. 3. The collimator module according to claim 2, wherein the supporting member comprises a plurality of second incident side fixing sheets spaced apart from one another and a plurality of second emission side fixing sheets spaced apart from one another. 4. The collimator module according to claim 2, wherein the supporting member further comprises a third incident side fixing sheet and a third emission side fixing sheet that each include a plurality of third grooves to which the long sides of the collimator single plates are inserted, the third incident side fixing sheet and the third emission side fixing sheet covering the long sides of the collimator single plates and positioned within the gaps defined between the first incident side fixing sheet and the first emission side fixing sheet and between the second incident side fixing sheet and the second emission side fixing sheet. 5. The collimator module according to claim 2, wherein the supporting member comprises a pair of supporting sheets extended between the pair of blocks and layered on the first incident side fixing sheet and the first emission side fixing sheet, and wherein the pair of supporting sheets are coupled to the plurality of collimator single plates. 6. The collimator module according to claim 1, wherein each fixing sheet comprises a carbon fiber reinforced plastic that is fixed to the collimator single plates and the pair of blocks by an adhesive. 7. An X-ray detector comprising:a base member extending in a channel direction;a plurality of collimator modules arranged in the channel direction on the base member, each of the plurality of collimator modules comprising:a plurality of collimator single plates each having a rectangular shape including a pair of long sides having a first length and a pair of short sides having a second length shorter than the first length of the pair of long sides;a pair of blocks comprising a plurality of first grooves extending along an irradiation direction of X-rays, the short sides of the collimator single plates inserted into the plurality of first grooves to support the plurality of collimator single plates in a vertical orientation along the irradiation direction of X-rays; anda supporting member configured to cover the long sides of the plurality of the collimator single plates from an incident side and an emission side of the X-rays, the supporting member having an X-ray transmission property and comprising an incident side fixing sheet and an emission side fixing sheet that each comprise a plurality of second groves, the long sides of the collimator single plates inserted into the plurality of second grooves to support the plurality of collimator single plates, the incident side fixing sheet and the emission side fixing sheet covering the plurality of first grooves of the pair of blocks and at least a portion of each of the long sides of the plurality of collimator single plates adjacent to the first grooves from the incident side and the emission side of the X-rays; anda plurality of X-ray detector elements set on an emission side of the plurality of collimator modules. 8. The X-ray detector according to claim 7, wherein the incident side fixing sheet and the emission side fixing sheet comprise a first incident side fixing sheet and a first emission side fixing sheet that cover the portion of each of the long sides adjacent to the plurality of first grooves from the incident side and the emission side of the X-rays, andwherein the supporting member further comprises a second incident side fixing sheet and a second emission side fixing sheet that each comprise the plurality of second grooves to which the long sides of the collimator single plates are inserted, the second incident side fixing sheet and the second emission side fixing sheet covering the long sides of the collimator single plates, wherein gaps are defined between the first incident side fixing sheet and the first emission side fixing sheet and between the second incident side fixing sheet and the second emission side fixing sheet. 9. The X-ray detector according to claim 8, wherein the supporting member comprises a plurality of second incident side fixing sheets spaced apart from one another and a plurality of second emission side fixing sheets spaced apart from one another. 10. The X-ray detector according to claim 8, wherein the supporting member further comprises a third incident side fixing sheet and a third emission side fixing sheet that each include a plurality of third grooves to which the long sides of the collimator single plates are inserted, the third incident side fixing sheet and the third emission side fixing sheet covering the long sides of the collimator single plates and positioned within the gaps defined between the first incident side fixing sheet and the first emission side fixing sheet and between the second incident side fixing sheet and the second emission side fixing sheet. 11. An X-ray computed tomography (CT) device for reconstructing a CT image, the X-ray CT device comprising:an X-ray detector including a base member extending in a channel direction;a plurality of collimator modules arranged in the channel direction on the base member, each of the plurality of collimator modules comprising:a plurality of collimator single plates each having a rectangular shape including a pair of long sides having a first length and a pair of short sides having a second length shorter than the first length of the pair of long sides;a pair of blocks comprising a plurality of first grooves extending along an irradiation direction of the X-rays, the short sides of the collimator single plates inserted into the plurality of first grooves of the pair of blocks to support the plurality of collimator single plates in a vertical orientation along the irradiation direction of X-rays; anda supporting member configured to cover the long sides of the plurality of the collimator single plates from an incident side and an emission side of the X-rays, the supporting member having an X-ray transmission property and comprising an incident side fixing sheet and an emission side fixing sheet that each include a plurality of second grooves, the long sides of the collimator single plates inserted into the plurality of second grooves to support the plurality of collimator single plates, wherein the incident side fixing sheet and the emission side fixing sheet cover the plurality of first grooves and at least a portion of each of the long sides of the plurality of collimator single plates adjacent to the first grooves from the incident side and the emission side of the X-rays; anda plurality of X-ray detector elements set on an emission side of the plurality of collimator modules. 12. The X-ray CT device according to claim 11, wherein the incident side fixing sheet and the emission side fixing sheet comprise a first incident side fixing sheet and a first emission side fixing sheet that cover the portion of each of the long sides adjacent to the plurality of first grooves from the incident side and the emission side of the X-rays, andwherein the supporting member further comprises a second incident side fixing sheet and a second emission side fixing sheet that each include the plurality of second grooves to which the long sides of the collimator single plates are inserted, the second incident side fixing sheet and the second emission side fixing sheet covering the long sides of the collimator single plates, wherein gaps are defined between the first incident side fixing sheet and the first emission side fixing sheet and between the second incident side fixing sheet and the second emission side fixing sheet. 13. The X-ray CT device according to claim 12, wherein the supporting member comprises a plurality of second incident side fixing sheets spaced apart from one another and a plurality of second emission side fixing sheets spaced apart from one another. 14. The X-ray CT device according to claim 13, wherein the supporting member further comprises a third incident side fixing sheet and a third emission side fixing sheet that each include a plurality of third grooves to which the long sides of the collimator single plates are inserted, the third incident side fixing sheet and the third emission side fixing sheet covering the long sides of the collimator single plates and positioned within at least one of the gaps defined between the first incident side fixing sheet and the first emission side fixing sheet and between the second incident side fixing sheet and the second emission side fixing sheet, and gaps defined between adjacent second incident side fixing sheets and between adjacent second emission side fixing sheets. 15. A method for assembling a collimator module comprising:a plurality of collimator single plates each having a rectangular shape including a pair of long sides having a first length and a pair of short sides having a second length shorter than the first length of the pair of long sides;a pair of blocks comprising a plurality of first grooves extending along an irradiation direction of X-rays; anda supporting member configured to cover the long sides of the plurality of the collimator single plates from an incident side and an emission side of the X-rays and having an X-ray transmission property, wherein the supporting member comprises:a first incident side fixing sheet and a first emission side fixing sheet each having a plurality of second grooves and configured to cover the plurality of first grooves of the pair of blocks and at least a portion of each of the long sides of the plurality of collimator single plates adjacent to the first grooves from the incident side and the emission side of the X-rays; anda second incident side fixing sheet and a second emission side fixing sheet that each include the plurality of second grooves, wherein gaps are defined between the first incident side fixing sheet and the first emission side fixing sheet and between the second incident side fixing sheet and the second emission side fixing sheet,the method comprising:inserting the short sides of the collimator single plates into the plurality of first grooves of the pair of blocks;arraying the collimator single plates by positioning the collimator single plates against one sidewall surface of each of the first grooves in the channel direction using a pressing component positioned to sandwich the long sides of each of the plurality of collimator single plates;fixing the long sides of the collimator single plates to the second grooves of the first incident side fixing sheet, the first emission side fixing sheet, the second incident side fixing sheet, and the second emission side fixing sheet, wherein the pressing component is positioned in the gaps defined between the first incident side fixing sheet and the first emission side fixing sheet and between the second incident side fixing sheet and the second emission side fixing sheet; andremoving the pressing component from the collimator single plates, wherein the collimator module is configured to form a collimator when a plurality of collimator modules are arranged in a channel direction. 16. The method for assembling a collimator module according to claim 15, wherein the supporting member comprises a plurality of second incident side fixing sheets spaced apart from one another and a plurality of second emission side fixing sheets spaced apart from one another, and whereinfixing the long sides to the second grooves further comprises fixing the long sides of the collimator single plates to the plurality of second incident side fixing sheets and to the plurality of second emission side fixing sheets, wherein the pressing component is positioned in gaps defined between adjacent second incident side fixing sheets and between adjacent second emission side fixing sheets. 17. The method for assembling a collimator module according to claim 15, further comprising inspecting an arrayed state of the plurality of collimator single plates from the gaps after the pressing component is removed from the gaps. 18. The method for assembling a collimator module according to claim 15, wherein the pressing component includes a reference board configured to contact the long sides of the collimator single plates, a comb-shaped portion configured to receive the long sides of the collimator single plates, and a spring board configured to move the long sides of the collimator single plate, andarraying the collimator single plates comprises pushing the collimator single plates against one sidewall surface of each of the first grooves in the channel direction by touching the long sides of the collimator single plates to the reference board and moving the spring board toward the comb-shaped portion. 19. The method for assembling a collimator module according to claim 15, wherein arraying the collimator single plates further comprises pushing a pair of long sides of the collimator single plates using a plurality of pressing components to array the collimator single plates. 20. The collimator module according to claim 3, wherein the supporting member further comprises a third incident side fixing sheet and a third emission side fixing sheet that each include a plurality of third grooves to which the long sides of the collimator single plates are inserted, the third incident side fixing sheet and the third emission side fixing sheet covering the long sides of the collimator single plates and positioned within the gaps defined between adjacent second incident side fixing sheets and between adjacent second emission side fixing sheets. |
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054694817 | abstract | A method is provided for forming a three-layer cladding tube having an outer substrate, a zirconium barrier layer, and an inner liner having alloying elements, in which the zirconium barrier layer (located between an outer substrate and inner liner) is at least partially alloyed with alloying elements that impart resistance to corrosion. The barrier layer has a diffusion layer extending from its inner surface (facing the fuel) to the barrier layer's interior (the interior being defined between the barrier layer's inner and outer surfaces). At the interior edge of the diffusion layer, there will be substantially no alloying elements beyond those normally present in zirconium. The methods of forming such structure include a diffusion anneal of a three-layer cladding in the range of 650.degree.-1000.degree. C. for times between about 1 minute and 20 hours. This anneal drives some of the alloying elements from the inner liner into the zirconium barrier layer to form the diffusion layer. The exact time and temperature depends upon the fabrication stage at which the heat treatment occurs. |
description | This application claims priority to U.S. Provisional Patent Application Ser. No. 62/141,790, filed Apr. 1, 2015, which is herein incorporated by reference. This invention was made with government support under Contract No. DE-AC02-05CH11231 awarded by the U.S. Department of Energy. The government has certain rights in this invention. Many experimental techniques (e.g., small-angle x-ray scattering) utilize highly concentrated beams of electromagnetic radiation (e.g., x-rays) directed at a sample. When x-rays interact with the sample, a portion of the x-rays are scattered or diffracted by the sample (e.g., x-rays are diffracted in protein crystallography). These scattered or diffracted x-rays travel to a detector (e.g., a Pilatus detector or a silicon pixel detector). Experimenters use the pattern of scattered or diffracted x-rays captured by the detector to obtain information about the sample. Much of the x-ray beam, however, passes through the sample without interacting with the sample. This portion of the x-ray beam also travels toward the detector. If this unscattered portion of the beam is allowed to interact with the detector, it may overwhelm and/or slowly damage the detector and the scattered x-rays may not be observable. In order to prevent this, a beam stop can be placed between the sample and the detector to prevent the unscattered x-rays from hitting the detector. In order to be fully effective and useful, a beam stop should be as small as possible to prevent obstruction of the scattered x-rays and dense enough to absorb the unscattered x-rays. FIG. 1 shows an example of a schematic illustration of a setup at a beamline (e.g., at a synchrotron light source), including a sample, a detector, and a beam stop. The unscattered portion of the x-ray beam, however, does carry information about the intensity, size, and position of the x-ray beam. If the unscattered x-rays could be characterized, in real time, during an experiment, such information potentially would be useful to experimenters. One innovative aspect of the subject matter described in this disclosure can be implemented in a device that includes a luminescent material (e.g., cerium-doped yttrium aluminum garnet (YAG)) and an optical fiber bonded to the luminescent material. The luminescent material emits light (e.g., scintillates) when the x-ray beam impinges on it and can provide information about the x-ray beam. The light can travel to the other end of the optical fiber to a light measuring device (e.g., a photodiode) which is in contact with the optical fiber. In some implementations, the device is highly responsive (e.g., nearly instantaneous response to changes in beam intensity), and real-time information about the x-ray beam can be obtained with no disruption to an experiment. Details of one or more embodiments of the subject matter described in this specification are set forth in the accompanying drawings and the description below. Other features, aspects, and advantages will become apparent from the description, the drawings, and the claims. Note that the relative dimensions of the following figures may not be drawn to scale. Reference will now be made in detail to some specific examples of the invention including the best modes contemplated by the inventors for carrying out the invention. Examples of these specific embodiments are illustrated in the accompanying drawings. While the invention is described in conjunction with these specific embodiments, it will be understood that it is not intended to limit the invention to the described embodiments. On the contrary, it is intended to cover alternatives, modifications, and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. Particular example embodiments of the present invention may be implemented without some or all of these specific details. In other instances, well known process operations have not been described in detail in order not to unnecessarily obscure the present invention. Various techniques and mechanisms of the present invention will sometimes be described in singular form for clarity. However, it should be noted that some embodiments include multiple iterations of a technique or multiple instantiations of a mechanism unless noted otherwise. Some embodiments described herein refer to beam stops for x-rays and small angle x-ray scattering. The device and methods described herein also may be used in other experiments utilizing the scattering of or the diffraction of electromagnetic radiation. FIG. 2A and 2B show examples of illustrations of a luminescent beam stop. FIG. 2A shows an example of an isometric illustration of a luminescent beam stop. FIG. 2B shows an example of an illustration of a luminescent beam stop from a vantage point of an x-ray beam (e.g., generated at a synchrotron light source or generated by an x-ray generating device) that would impinge on a luminescent material. As shown in FIGS. 2A and 2B, a luminescent beam stop 200 includes a luminescent material 210, a beam stop plate 220, and an optical fiber (i.e., a fiber optic) 230. In some embodiments, the luminescent beam stop 200 further includes a light sensing device 240 and a hollow sleeve 250. The beam stop plate 220 is attached to or bonded to a side of the luminescent material 210. A first end 235 of the optical fiber 230 is attached to or bonded to a different side of the luminescent material 210. The side of the luminescent material 210 having the beam stop plate 220 attached thereto and the side of the luminescent material 210 having the optical fiber 230 attached thereto are perpendicular or substantially perpendicular (e.g., within a few degrees of being perpendicular) to one another. A second end 237 of the optical fiber 230 is attached to the light sensing device 240. Larger illustrations of the luminescent material 210, the beam stop plate 220, and the hollow sleeve 250 are shown in FIGS. 3, 4A, 4B, 4C, and 5. The luminescent material 210 and beam stop plate 220 of the luminescent beam stop 200 can be positioned between a sample and a detector in a beamline experiment, with the beam of electromagnetic radiation that passes through a sample with no scattering impinging on the luminescent material 210 and then the beam stop plate 220. This portion of the radiation (i.e., the unscattered electromagnetic radiation) causes the luminescent material 210 to generate light (e.g., by scintillation or fluorescence). The light generated by the luminescent material 210 is transmitted to the light sensing device 240 though the optical fiber 230. In some embodiments, the luminescent material 210 and beam stop plate 220 are positioned about 1 centimeter (cm) to 6 cm, or about 2 cm to 3 cm, from the sample. In some embodiments, the luminescent material 210 and beam stop plate 220 are positioned about 1 cm to 15 meters, about 10 meters to 15 meters, or greater than about 10 meters, from the sample. The luminescent material 210 will generally generate more light the more intense the beam of electromagnetic radiation is. Thus, the luminescent beam stop 200 allows for the determination of the intensity of the electromagnetic radiation or the alignment of the luminescent material 210 and beam stop plate 220 with the beam of electromagnetic radiation. Generally, the dimensions of the luminescent material 210 are specified so that the entire beam of electromagnetic radiation impinges on the luminescent material. If the beam is 100 microns by 100 microns, the dimensions of the side of the luminescent material on which beam impinges may be about 500 microns by 500 microns, for example. Having the dimensions of the luminescent material larger than the cross-sectional dimensions of the beam aid in ensuring that the entire beam impinges on the luminescent material. The beam of electromagnetic radiation that impinges on the sample and passes through a sample with no scattering may have a square cross section with dimensions of about 50 microns to 500 microns by about 50 microns to 500 microns. For example, at some beamlines, the beam has a square cross section having dimensions of about 100 microns by about 100 microns. The beam of electromagnetic radiation can also be collimated to have different shapes and dimensions. For example, at some beamlines, the beam may have an elliptical or a circular cross section, with a dimension (e.g., a radius of a circle or a major axis of an ellipse) of the beam being about 2 microns to 200 microns. FIG. 3 shows an example of an illustration of a luminescent material. A luminescent material is a material that emits light not resulting from heat or the temperature of the material. Scintillation is a type of luminescence in which a material (e.g., a transparent material) emits a flash of light due to the passage of a particle (e.g., an electron, an alpha particle, an ion, or a high-energy photon) in the material. Photoluminescence is another type of luminescence and is the result of absorption of photons. Fluorescence and phosphorescence are types of photoluminescence. In some embodiments, the luminescent material 210 shown in FIG. 3 has a shape of a parallelepiped having a first side 310 and a second side (not shown) that are squares and having a third side 320 that is a rectangle. A parallelepiped is a three-dimensional object formed by six parallelograms. The fourth side 330, the fifth side (not shown), and the sixth side (not shown) are also rectangles. The first side 310 and the second side are perpendicular to the third side 320. Stated in a different manner, the luminescent material may have a square shaped cross-section including a first square side and a second square side. The third side is rectangular and is perpendicular to the first square side and the second square side. The luminescent material may also have a different shape. For example, in some embodiments, the luminescent material may be a cube. Is some embodiments, the luminescent material may be a rectangular parallelepiped. A rectangular parallelepiped is a parallelepiped of which all faces are rectangular. In some embodiments, the luminescent material comprises a scintillating material or a fluorescing material. In some embodiments, the luminescent material comprises a material selected from a group consisting of yttrium aluminum garnet (Y3Al5O12, YAG), cerium-doped YAG, lead tungstate (PbWO4), cadmium tungstate (CdWO4), and diamond (i.e., the allotrope of carbon). The luminescent material used depends on the energies of the electromagnetic radiation at the beam line. For example, cerium-doped YAG emits light in response to electromagnetic radiation when the electromagnetic radiation has an energy of about 6000 eV to 16,000 eV. In some embodiments, the first side and the second side of the luminescent material are about 250 microns to 1 millimeter (mm) by about 250 microns to 1 mm, and the third side of the luminescent material is about 250 microns to 1 mm by about 250 microns to 1 mm. That is, the dimensions of the luminescent material may be about 250 microns to 1 mm by about 250 microns to 1 mm by about 250 microns to 1 mm. In some embodiments, the first side of the luminescent material 210 is about 500 microns by about 500 microns, and the third side of the luminescent material 210 is about 500 microns by 600 microns. That is, the dimensions of the luminescent material may be about 500 microns by about 500 microns by about 600 microns. In some embodiments, the dimensions of the luminescent material are about 500 microns by about 500 microns by about 500 microns. In some embodiments, the dimensions of the luminescent material are about 600 microns by about 600 microns by about 1 mm. In some embodiments, some surfaces of the luminescent material 210 are coated with a reflective material. For example, the sides of the luminescent material 210 parallel to the direction of the electromagnetic beam propagation when the luminescent beam stop is being used may be coated with a reflective material. The area where the optical fiber 230 is attached to the side of the luminescent material 210 would not be coated with a reflective material. In some embodiments, the side of the luminescent material 210 on which the beam of electromagnetic radiation impinges is not coated with a reflective material. For example, the reflective material may be a white paint, a silver paint (e.g., a paint containing silver particles), or a gold paint (e.g., a paint containing gold particles). The reflective material may further increase the intensity of the light transmitted to the optical fiber. In some embodiments, the side of the luminescent material 210 on which the beam of electromagnetic radiation impinges is coated with a reflective material. For example, the reflective material may comprise aluminum or an aluminum paint (e.g., a paint containing aluminum particles). Such a coating would aid in preventing external light (e.g., light not generated by the luminescent material) from being transmitted to the optical fiber. Such a coating may also increase the intensity of light transmitted to the optical fiber. FIGS. 4A and 4B show examples of illustrations of a beam stop plate. The beam stop plate 220 shown in FIGS. 4A and 4B is attached to the first side of the luminescent material 210. In some embodiments, the beam stop plate is attached to the luminescent material with an adhesive. For example, the adhesive may be a cyanoacrylate adhesive, such as Permabond 910 (Permabond LLC, Pottstown, Pa.). In some embodiments, the beam stop plate 220 comprises a material that is thick enough and dense enough to block the electromagnetic radiation transmitted through a sample and the luminescent material 210 with no scattering from impinging on the detector. In some embodiments, the beam stop plate comprises a metal selected from a group consisting of silver, gold, tantalum, tungsten, lead, platinum, and molybdenum. In some embodiments, the beam stop plate is about 100 microns to 1 mm thick, or about 200 microns thick. In some embodiments, the beam stop plate has circular shape and a diameter of about 250 microns to 2 mm, about 1.25 mm, or about 1 mm. In some embodiments, the beam stop plate 220 includes a depression 410 defined in one surface of the beam stop plate 220. In some embodiments, the depression 410 includes a center depression or well defined at or near a center of the beam stop plate 220 and a channel depression or trench that extends to an edge of the beam stop plate 220. In some embodiments, the center depression and the channel depression are connected. In some embodiments, the side of the beam stop plate 220 including the depression 410 is attached to the side of the luminescent material 210. In some embodiments, the depression 410 aids in wicking an adhesive used to attach the beam stop plate 220 to the luminescent material 210 away from the sides of the luminescent material 210 not in contact with the beam stop plate 220. In some embodiments, the beam stop plate 220 includes lines 420 and 425. For example, the lines 420 and 425 may be scored or otherwise marked on the surface of the beam stop plate 220. The lines 420 and 425 may aid in aligning the luminescent material 210 on the beam stop plate 220. For example, the luminescent material 210 may be positioned on the beam stop plate 220 so that two sides of the luminescent material 210 are parallel with the lines 420 and 425 before attaching the luminescent material 210 to the beam stop plate 220 In some embodiments, the beam stop plate has an oval shape or elliptical shape with an about 250 micron to 2 mm short axis and an about 300 micron to 3 mm long axis, as shown in FIG. 4C. In some embodiments, the beam stop plate has an oval shape with an about 1.25 mm short axis and an about 2.5 mm long axis. In some embodiments, the beam stop plate 220 has dimensions such that it covers the entire area of the side of the luminescent material to which is it attached. In some embodiments, the optical fiber 230 comprises a single optical fiber or comprises only one optical fiber. In some embodiments, the optical fiber 230 consists of a single optical fiber or consists of only one optical fiber. In some embodiments, the optical fiber 230 has a circular cross section and has a diameter of about 200 microns to 600 microns, about 350 microns to 450 microns, or about 400 microns. In some embodiments, the dimensions of the end 235 of the optical fiber 230 are specified so that the entire area of the end 235 of the optical fiber 230 is attached to the luminescent material 210. For example, if the luminescent material 210 has dimensions of about 500 microns by 500 microns by 500 microns, the diameter of the optical fiber would be about 500 microns or less than about 500 microns. In some embodiments, the optical fiber comprises a multi-mode optical fiber. A multi-mode optical fiber has a larger core diameter than a single-mode optical fiber. Multi-mode optical fibers also generally have higher light-gathering capacities than single-mode fibers. In some embodiments, optical fiber can transmit light having wavelengths of about 400 nanometers to 700 nanometers. In some embodiments, the optical fiber is attached to the luminescent material with an optical adhesive. An optical adhesive can join two optical components and allow for light transmission between the two components with minimal light loss. Optical adhesives include clear, colorless, liquid photopolymers that cure when exposed to ultraviolet light. Two examples of optical adhesives are Norland Optical Adhesive 61 and Norland Optical Adhesive 63 (Norland Products, Cranbury, N.J.). In some embodiments, the optical fiber 230 has a length of about 10 cm to 2 meters, about 0.5 meters to 2 meters, or about 1 meter to 2 meters. At some beamlines, the optical fiber may be positioned in a horizontal plane. A plane is said to be horizontal at a given point if it is perpendicular to the gradient of the gravity field at that point. In some embodiments, the optical fiber 230 may be supported at a distance of about 5 cm to 25 cm, or about 10 cm to 13 cm, from the luminescent material 210 and beam stop plate 220. In this configuration, the stiffness of the optical fiber 230 supports the luminescent material 210 and beam stop plate 220 as a cantilever support. With the optical fiber 230 supported at such a distance from the luminescent material 210 and beam stop plate 220, scattered electromagnetic radiation may interact with the optical fiber 230 before being recorded by a detector. The small diameter of the optical fiber 230 would not block very much of the scattered x-rays from reaching the detector. Further, because optical fiber 230 is amorphous, the optical fiber may not substantially further scatter x-rays. In some embodiments, the luminescent beam stop 200 includes a hollow sleeve 250. FIG. 5 shows an example of an illustration of a hollow sleeve. An end 505 of the hollow sleeve 250 is attached to the beam stop plate 220, the same side of the beam stop plate attached to the luminescent material 210. The hollow sleeve 250 surrounds the luminescent material 210. The hollow sleeve 250 includes a cutout 510 to allow the optical fiber 230 to contact the luminescent material 210. In some embodiments, the hollow sleeve 250 comprises a material that is thick enough and dense enough to block electromagnetic radiation scattered by the luminescent material. In some embodiments, the hollow sleeve 250 comprises a metal selected from a group consisting of silver, gold, tungsten, and tantalum. In some embodiments, the hollow sleeve 250 and the beam stop plate 220 comprise the same metal. In some embodiments, the hollow sleeve 250 and the beam stop plate 220 comprise different metals. In some embodiments, the end 505 of the hollow sleeve 250 is attached to the beam stop plate 220 with an adhesive. For example, the adhesive may be a cyanoacrylate adhesive. In some embodiments, a wall of the hollow sleeve is about 100 microns to 300 microns thick, or about 200 microns thick. In some embodiments, the hollow sleeve is a hollow cylinder. In some embodiments, when the hollow sleeve is a hollow cylinder, an outer diameter of the hollow sleeve is about 250 microns to 2 mm, about 1.25 mm, or about 1 mm. In some embodiments, the beam stop plate has a circular shape, the hollow sleeve is a hollow cylinder, and an outer diameter of the hollow cylinder is the same as the diameter of the beam stop plate. In some embodiments, a height of the hollow sleeve is about 250 microns to 1 mm. In some embodiments, a height of the hollow sleeve is the same as or greater than the length of the side of the luminescent material to which the fiber optic is attached. That is, the hollow sleeve may surround the luminescent material so that only a single face of the luminescent material is visible. The hollow sleeve may aid in preventing electromagnetic radiation (e.g., x-rays) scattered by the luminescent material from impinging on the detector. Further, the hollow sleeve may increase the intensity of the light that is transmitted to the optical fiber. For example, the interior surface of the hollow sleeve may be reflective. More light generated by the luminescent material would be transmitted to the optical fiber by the light being reflected by the interior surfaces of the hollow sleeve to the optical fiber. When the hollow sleeve is a hollow cylinder and when the luminescent material is shaped as a parallelepiped, an open volume exists between the hollow sleeve and the luminescent material. In some embodiments, the surfaces of the hollow sleeve and/or the luminescent material defining the open volume between the hollow sleeve and the luminescent material are coated with a reflective material. For example, the reflective material may be a white paint, a silver paint, or a gold paint. The reflective material may further increase the intensity of the light transmitted to the optical fiber. In some embodiments, as shown in FIG. 2B, the light sensing device 240 is attached to or connected to the second end 237 of the optical fiber 230. The light sensing device 240 may be able to convert the light signal of the luminescent material 210 to an electrical signal that can be recorded. In some embodiments, the light sensing device 240 includes a photodiode or a photodarlington device. A photodiode is a semiconductor device that converts light into current, and generates the current when photons are absorbed in the photodiode. The current generated by the photodiode can be recorded with an instrument, such as an ammeter or a picoammeter, for example. In some embodiments, the optical fiber attached to a side of the luminescent material is one of a plurality of optical fibers, one of three optical fibers, or one of four optical fibers comprising a bundle of optical fibers. Alternatively, in some embodiments, the optical fiber 230 shown in FIGS. 2A and 2B is replaced with a bundle of optical fibers including a plurality of optical fibers, three optical fibers, or four optical fibers. FIG. 6 shows an example of an illustration of a bundle of optical fibers. The bundle of optical fibers 600 shown in FIG. 6 includes a first optical fiber 605, a second optical fiber 610, and a third optical fiber 615. In some embodiments, each optical fiber in the bundle of optical fibers has a circular cross section having a diameter of about 100 microns to 300 microns, about 220 microns, or about 200 microns. In some embodiments, the bundle of optical fibers has a length of about 10 centimeters to 2 meters, about 0.5 meters to 2 meters, or about 1 meter to 2 meters. In some embodiments, the optical fibers in the bundle of optical fibers are bonded to each other with an adhesive. For example, the adhesive may be a cyanoacrylate adhesive. In some embodiments, the bundle of optical fibers has a higher stiffness than a single optical fiber and is better able to support the luminescent material 210 and beam stop plate 220 when the bundle of optical fibers is positioned in a horizontal plane. FIG. 7 shows an example of an illustration of a luminescent beam stop. The luminescent beam stop 700 shown in FIG. 7 includes a bundle of optical fibers 730. Also shown in FIG. 7 are a luminescent material 710, a beam stop plate 720, and a hollow sleeve 750. The luminescent material 710, the beam stop plate 720, and the hollow sleeve 750 may be similar to the components described above with respect to FIGS. 2A, 2B, 3, 4A-4C, and 5. In some embodiments, the luminescent material comprises two to five individual blocks of material, or three blocks of material. For example, when a luminescent material of specified dimensions is not available, the luminescent material may be assembled from individual blocks of material. In some embodiments, each block of material has dimensions of about 250 microns to 1 mm by about 250 microns to 1 mm by about 80 microns to 350 microns. For example, each block of material may have dimensions of about 500 microns by about 500 microns by about 200 microns. In some embodiments, the blocks of material are joined to each other with an adhesive. For example, the adhesive may be a cyanoacrylate adhesive. FIGS. 8A and 8B show examples of illustrations of a frame with blocks of a luminescent material disposed therein. The frame 810 shown in FIGS. 8A and 8B can be used to assemble the luminescent material from individual blocks 820, 830, and 840 of material. The frame 810 may be fabricated from a metal, such as gold, tantalum, or tungsten, for example. In some embodiments, the frame has a thickness of about 50 microns to 150 microns, or about 100 microns. When a frame is used in a luminescent beam stop, the frame itself may absorb some of the electromagnetic radiation (e.g., x-rays). For example, the side 850 of the frame 810 can serve as the beam stop plate. In some embodiments, if the side 850 is not thick enough absorb the electromagnetic radiation, a beam stop plate is attached to the side 850 of the frame 810. FIG. 9 shows an example of an illustration of a luminescent beam stop. The luminescent beam stop 900 shown in FIG. 9 includes the frame 810, a luminescent material 910, a beam stop plate 920, and a bundle of optical fibers 930. The luminescent material 910 includes three blocks of material. The bundle of optical fibers 930 includes three optical fibers. The luminescent beam stop 900 further includes a plate 940. The plate 940 defines an open region, and the bundle of optical fibers 930 passes through the open region in the plate 940 before contacting the luminescent material 910. In some embodiments, the plate 940 contacts the sides of the optical fibers in the bundle of optical fibers 930. In some embodiments the plate 940 contacts the frame 810. In some embodiments, the plate 940 contacts the luminescent material 910. The plate 940 may be fabricated from the same metal as the frame 810. For example, the plate 940 may be gold, tantalum, or tungsten. In some embodiments, the plate has a thickness of about 50 microns to 150 microns, or about 100 microns. In some embodiments, the plate 940 increases the intensity of the light transmitted to the optical fiber. While the frame 810 serves to aid in the assembly of the blocks of the luminescent material, it also may serve a similar function as the hollow sleeve 250 shown in FIGS. 2A, 2B, and 5. That is, the frame 810 may prevent electromagnetic radiation (e.g., x-rays) scattered by the luminescent material from impinging on the detector. The frame 810 may also increase the intensity of the light that is transmitted to the optical fiber. As shown in FIGS. 8A and 8B, two sides of the blocks of luminescent material 820, 830, and 840 are in contact with the frame 810, and two sides of the blocks of material 820, 830, and 840 are not in contact with the frame 810. The block of material 820 contacts the frame 810 with three sides. Contact between the blocks of material 820, 830, and 840 and the frame 810 may increase or maximize the light that is transmitted to the optical fiber. In some embodiments, the frame 810 is fabricated so that three sides of the blocks of material 820, 830, and 840 are in contact with the frame 810. This may further increase the intensity of the light that is transmitted to the optical fiber. In some embodiments, the frame 810 is fabricated so that the plate 940 also is in contact with the blocks of material 820, 830, and 840. In some embodiments, surfaces of the frame 810 defining gaps between the frame 810 and the blocks of luminescent material 820, 830, and 840 are coated with a reflective material. For example, the reflective material may be a white paint, a silver paint, or a gold paint. The reflective material may further increase the intensity of the light transmitted to the optical fiber. FIG. 10 shows an example of a flow diagram illustrating a manufacturing process for a luminescent beam stop. The process shown in FIG. 10 can be used to manufacture the embodiments of a luminescent beam stop described above. Starting at block 1010 of the method 1000, a luminescent material is provided. In some embodiments, the luminescent material is a parallelepiped having a first side and a second side that are squares and having a third side that is a rectangle or a square. The first side and the second side are perpendicular to the third side. At block 1020, a first side of a beam stop plate is attached to the first side of the luminescent material. In some embodiments, the beam stop plate is attached to the first side of the luminescent material with an adhesive. In some embodiments, the adhesive comprises a cyanoacrylate adhesive. At block 1030, a first end of an optical fiber is attached to the third side of the luminescent material. In some embodiments, the first end of the optical fiber is attached to the third side of the luminescent material with an optical adhesive. At block 1040, a hollow sleeve is attached to the first side of the beam stop plate. In some embodiments, the hollow sleeve is attached to the first side of the beam stop plate with an adhesive. In some embodiments, the adhesive comprises a cyanoacrylate adhesive. In some embodiments, an interior surface of the hollow sleeve is coated with a reflective material before the hollow sleeve is attached to the first side of the beam stop plate. For example, the reflective material may be a white paint, a silver paint, or a gold paint. In some embodiments, after block 1030, sides of the luminescent material are coated with a reflective material. In some embodiments, after block 1030, sides of the luminescent material, except the side of the luminescent material on which the electromagnetic radiation will impinge, are coated with a reflective material. For example, the reflective material may be a white paint, a silver paint, or a gold paint. In some embodiments, a bundle of optical fibers is used instead of an optical fiber or a single optical fiber. In some embodiments, a bundle of fiber optics is assembled. Assembling the bundle of optical fibers may include, for example, stripping a plastic coating off of the optical fibers, cleaving ends of the optical fibers, and bonding a plurality of optical fibers, three optical fibers, or four optical fibers together using an adhesive. In some embodiments, the adhesive comprises a cyanoacrylate adhesive. In some embodiments, a luminescent is assembled from blocks of a material, as described with respect to FIGS. 8A and 8B. In some embodiments, a frame is fabricated by cutting and then bending a layer or sheet of gold (e.g., work-hardened gold). A laser mill may be used to score the gold so that the gold can be folded to form the frame. The individual blocks of the material may be cut to a specified size or sizes. For example, a laser mill may be used to cut the individual blocks of the material. After the frame is fabricated and the individual blocks of material are cut, the individual blocks of material can be positioned in the frame. An adhesive can be used to bond the individual blocks of material to the frame and to each other. In some embodiments, the adhesive comprises a cyanoacrylate adhesive. Potential uses of the luminescent beam stop described herein include measuring the radiation dose to a sample during data collection at a beamline and monitoring the x-ray beam intensity during data collection at a beamline. The radiation dose to a sample can be used to determine a length of exposure time to the x-ray beam to generate an image and the total dose of x-rays received by a sample per image generated. The luminescent beam stop can be used to determine if an x-ray beam is present during an experiment. The luminescent beam stop also can be used to determine the x-ray beam position during an experiment. FIG. 11 shows an example of the results generated by a luminescent beam stop. In FIG. 11, the output (e.g., nanoamps) from a light sensing device attached to the end of the optical fiber of a luminescent beam stop versus the collimated beam intensity (microamps, as measured with a reference device separate from the luminescent beam stop) is plotted. As the collimated beam intensity increases, the response of the light sensing device increases linearly. The straight line indicates that the signal from the luminescent beam stop accurately reflects the intensity variations of the beam; i.e., as the beam flux increases, the signal from the luminescent beam stop increases proportionately to the intensity reading on the reference device. If the collimated beam intensity (i.e., the portion of the raw beam that hits a sample) changed by 10%, but the luminescent beam stop signal changed by significantly more or less than 10%, for example, it would mean the luminescent beam stop could not be used to accurately determine how much beam was actually being delivered to the sample. In some embodiments, the luminescent beam stop does not completely block the unscattered electromagnetic radiation. For example, the luminescent beam stop may attenuate the unscattered electromagnetic radiation to a level that is safe for the detector. To accomplish this, in some embodiments, the luminescent beam stop does not include a beam stop plate. In some embodiments, the luminescent beam stop includes a beam stop plate comprising a material of a thickness that allows a portion of the unscattered electromagnetic radiation to pass through the beam stop plate. In some embodiments, the luminescent material comprises a material that minimally attenuates the electromagnetic radiation (e.g., diamond). In some embodiments, a thickness of the luminescent material is small so that the luminescent material minimally attenuates the electromagnetic radiation. In some embodiments, the luminescent beam stop is used to measure the intensity of the electromagnetic radiation at an intermediate point of the beamline. For example, the luminescent beam stop could be used to measure the intensity of the electromagnetic radiation before the electromagnetic radiation interacts with the sample. To accomplish this, in some embodiments, the luminescent beam stop does not include a beam stop plate. In some embodiments, the luminescent material comprises a material that minimally attenuates the electromagnetic radiation (e.g., diamond). In some embodiments, a thickness of the luminescent material is small so that the luminescent material minimally attenuates the electromagnetic radiation. In the foregoing specification, the invention has been described with reference to specific embodiments. However, one of ordinary skill in the art appreciates that various modifications and changes can be made without departing from the scope of the invention as set forth in the claims below. Accordingly, the specification and figures are to be regarded in an illustrative rather than a restrictive sense, and all such modifications are intended to be included within the scope of invention. |
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048511862 | claims | 1. A core of a nuclear reactor comprising detachable vertical assemblies having a lower part, a bolster including hollow pillars each having a vertical axis and receiving said lower part of said assemblies, first openings in said pillars for the passage of a coolant fluid for the reactor, second openings in said lower parts of said assemblies in alignment with said first openings in said pillars, each pillar including at least one means for orienting the respective assembly about said axis of said pillar and each assembly comprising (a) a vertical body having an upper part in the form of an open tubular case having a lateral wall and openings extending through said lateral wall of said tubular case and so located that the body of the assembly is placed in a predetermined position as concerns its orientation about its vertical axis below a handling device having claws engaged in said openings; and (b) a lower part having at least one orientation means adapted to cooperate with the corresponding orientation means of said pillar, when introducing said lower part of the assembly in the said pillar in a predetermined orientation by means of said handling device. 2. A core of a nuclear reactor according to claim 1, wherein the orientation means of said pillar comprises a prismatic cavity provided inside said pillar and the corresponding orientation means of said lower part of said assembly comprises a male prismatic surface of corresponding shape provided on said lower part of said assembly and being coaxial with said assembly. 3. A core of a nuclear reactor according to claim 2, wherein said prismatic surfaces have a hexagonal cross-sectional shape. 4. A core of a nuclear reactor according to claim 3, wherein the assemblies of the core comprise an annular member having an inner part connected to said tubular case of said body of said assembly located below said seizing means, and bars of a material absorbing neutrons constituting an upper neutronic protection carried by said annular member of the assembly. 5. A core of a nuclear reactor according to claim 1, wherein said assemblies of the core comprise a body of prismatic shape whose cross section is hexagonal. |
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claims | 1. A computer, comprising:a processor configured to be coupled to a medical device, wherein the processor is configured to execute routines for:receiving an input representative of a medical device measurement data;generating simulated medical information from the input;comparing the simulated medical information to an expected result; anddetermining a certification of the computer to generate medical information from the medical device based on the comparison. 2. The computer of claim 1, comprising stopping or exiting routines for processing a signal from the medical device if the simulated medical information deviates from the expected result. 3. The computer of claim 1, comprising displaying an indication related to the certification on a display. 4. The computer of claim 1, comprising accessing the input representative of the medical device from a memory associated with a medical sensor. 5. The computer of claim 1, comprising accessing the input representative of the medical device from a portable mass storage device. 6. The computer of claim 1, comprising accessing the input representative of the medical device from a memory of the computer. 7. The computer of claim 1, comprising providing information related to the certification to a regulatory agency. 8. The computer of claim 1, wherein the medical device comprises a pulse oximetry sensor. 9. The computer of claim 8, wherein the simulated medical device information comprises a plethysmographic waveform, a heart rate, or an oxygen saturation value. 10. A method, comprising:using a computer to:access a memory element associated with a medical device, wherein the memory element comprises stored information representative of a measurement data output of the medical device;generate simulated medical information from the stored information;compare the simulated medical information to an expected result; anddetermine a certification of the computer to generate medical information from the medical device based on the comparison. 11. The method of claim 10, wherein the memory element further comprises stored specification requirements. 12. The method of claim 11, further comprising using the computer to compare the specification requirements to specifications of the computer. 13. The method of claim 12, comprising using the computer to generate an output that the computer is not compatible with the medical device if the specification requirements do not match the specifications of the computer. 14. The method of claim 10, comprising using the computer to generate an output that the computer is not compatible with the medical device if the simulated medical information deviates from the expected result. 15. The method of claim 10, comprising using the computer to prevent generating medical information from the medical device if the simulated medical information deviates from the expected result. |
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abstract | A system for encapsulating and storing disused radiological sources in sealed capsules is provided, the system having a basket to removably position capsules relative to each other, the capsules containing the radiological sources; a containment vessel for receiving the basket; and a cask reversibly encapsulating or otherwise housing the containment vessel. Also provided is a method for packaging, transporting and storing disused radiological sources, the method having the steps of transporting sealed capsules containing radiological sources from water pools to baskets; placing the basket in a containment vessel and sealing the vessel with helium backfill; placing the vessel in a cask and reversibly capping the cask; surrounding the cask with personnel a shield and crumple zones to create a construct; and transporting and storing the construct until its final disposal at a geological repository or a deep borehole, all without repackaging of the disused radiological sealed capsules. |
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051981823 | summary | BACKGROUND OF THE INVENTION This invention relates to neutron-absorbing or neutron-shielding material, and in particular to a novel process of forming such material into a tube, and the resulting tube. In U.S. Pat. No. 4,027,377, which is assigned to the assignee of the present application and the disclosure of which is incorporated herein by reference, disclosed is the production of neutron-absorbing or shielding material comprised of a thin, rigid sheet having a neutron-absorbing material, preferably boron carbide, surrounded by aluminum plate. In forming the sheet, an ingot is first formed with a hollow interior, and a mixture of neutron-absorbing material, such as boron carbide powder, and a finely divided metal powder, such as atomized aluminum, is installed in the hollow interior of the ingot. Thereafter, the ingot is sealed, heated to a temperature below the melting point of the metal powder, and is then hot rolled to reduce its thickness a desired amount. The hot rolling causes the particles of metal powder and boron carbide to become metallurgically bonded together so that in subsequent use the material retains its neutron-absorbing properties. A problem with the material of U.S. Pat. No. 4,027,377 is its inability to be bent and retain its neutron-absorbing capacity at the area of the bend. Consequently, the process of U.S. Pat. No. 4,751,021 was developed to provide a sheet that can be bent. However, the bend cannot be abrupt, and therefore a relatively gentle bend is the result, with the neutron-absorbing boron carbide core being offset to one side of the sheet. That patent requires precision in manufacture, and although a quite satisfactory neutron-absorbing sheet is produced, the process is expensive. SUMMARY OF THE INVENTION The present invention relates to a method of making sections of a neutron-absorbing tube, or a tube itself, through a series of steps. First, an elongate, generally rectangular metal ingot is formed having a hollow interior. At least one elongate metal divider is installed in the hollow interior to form at least two chambers in the interior of the ingot. The chambers are then filled with a substantially uniformly dispersed mixture of a finely divided neutron-absorbing boron compound and a finely divided metal powder. Thereafter, the ingot is soaked to bring it to an elevated temperature below the melting temperature of the metal powder. With the temperature of the ingot thus-elevated, the ingot is hot rolled to reduce its thickness to form a thin, rigid neutron-absorbing sheet having opposite metal edge portions and an elongated metal spacer portion at the location of each metal divider. Finally, the sheet is longitudinally bent at each spacer portion. In accordance with the preferred form of the invention, only one metal divider is installed in the ingot, and the bending step includes longitudinally bending the sheet to an L-shaped cross section. A tube is formed by making a second, substantially identical section and joining the two sections at their metal edge portions to form the tube. Preferably, one of the metal edge portions of each of the sheets is also bent to an L-shaped cross section before the sheets are joined and welded along their side edges to form a tube. In accordance with the preferred form of the invention, when the sheet is formed and before bending of the sheet, one of the metal edge portions of the sheet is formed with a greater width than the other edge portion. That greater-width edge portion is the edge portion which is then bent to an L-shaped cross section. In accordance with a second form of the invention, a neutron-absorbing tube is formed by forming an elongate, generally rectangular metal ingot having a hollow interior, and a series of elongate metal dividers are installed in the interior of the ingot to form at least four chambers in the interior. Those chambers are then filled with the uniformly dispersed mixture of the finely divided neutron-absorbing boron compound and metal powder, the ingot is soaked to bring it to an elevated temperature, and the ingot is then hot rolled to reduce its thickness to form a thin, rigid neutron-absorbing sheet having opposite metal edge portions and an elongated metal spacer portion at the location of each of the metal dividers. The sheet is then longitudinally bent at each of the spacer portions, and the metal edge portions are joined to form a tube. In this form of the invention, also, it is preferred that the formation of the metal edge portions of the sheet is such that one of the metal edge portions has a greater width than the other edge portion so that the one metal edge portion can be bent to an L-shaped cross section before the two edge portions are joined. |
claims | The ornamental design for a radiation shielding device, as shown and described. |
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060977787 | claims | 1. A gravity driven suction pump system for a nuclear reactor including a gas chamber, said system comprising: a condenser configured to be submerged in a condenser pool of water; at least one condensate drain line comprising a venturi section in fluid communication with said condenser and configured to deliver condensate-and noncondensible gases from said condenser to the gas chamber; and at least one suction line extending from said condenser into said venturi section of said drain line. an intake line in fluid communication with the gas chamber and a heat exchanger; and said heat exchanger configured to utilize a condensate to deliver said noncondensible gases from said heat exchanger to the gas chamber. a first header in fluid communication with said intake line wherein said intake line directs condensible and noncondensible gases to said first header; a condensing section in fluid communication with said first header; and a second header in fluid communication with said condensing section. a condenser; at least one condenser drain line comprising a venturi section and a loop seal; at least one suction line extending from said condenser into said venturi section of said drain line. a heat exchanger; and an intake line in fluid communication with the gas chamber and said heat exchanger. a first header in fluid communication with said intake line; a condensing section in fluid communication with said first header; and a second header in fluid communication with said condensing section. 2. A gravity driven suction pump system in accordance with claim 1 wherein said condenser comprises : 3. A gravity driven suction pump system in accordance with claim 2 wherein said heat exchanger comprises: 4. A gravity driven suction pump system in accordance with claim 3 wherein said condensing section comprises at least one condenser tube. 5. A gravity driven suction pump system in accordance with claim 3 wherein said condensing section comprises at least one condenser plate. 6. A gravity driven suction pump system in accordance with claim 3 wherein said at least one drain line is in fluid communication with the gas chamber and further comprises a loop seal between a first end and a second end of said drain line. 7. A gravity driven suction pump system in accordance with claim 6 further comprising N drain lines, in fluid communication with said second header of said condenser, a first said drain line directly coupled to said second header, said N drain lines positioned sequentially with respect to said first drain line, said first drain line through said N-1 drain line comprising a venturi section, and wherein N is an integer greater than or equal to 2. 8. A gravity driven suction pump system in accordance with claim 7 further comprising N-1 spill-over connection lines, each said spill-over line extending between and coupled at opposing ends to a first section of adjacent drain lines. 9. A gravity driven suction pump system in accordance with claim 8 further comprising a plurality of N-1 suction lines, wherein each said suction line extends from said second header into a corresponding drain line, each said suction line having a first end and a second end, said first end located in said second header, and said second end located in said venturi section of said drain line. 10. A gravity driven suction pump system in accordance with claim 9 wherein N is equal to 4. 11. A gravity driven suction pump system for a nuclear reactor system, the nuclear reactor system including a gas chamber, said gravity driven suction pump system comprising: 12. A gravity driven suction pump system in accordance with claim 11 wherein said condenser comprises: 13. A gravity driven suction pump system in accordance with claim 12 wherein said heat exchanger comprises: 14. A gravity driven suction pump system in accordance with claim 13 wherein said condensing section comprises at least one condenser tube. 15. A gravity driven suction pump system in accordance with claim 13 wherein said condensing section comprises at least one condenser plate. 16. A gravity driven suction pump system in accordance with claim 13 further comprising N drain lines, in fluid communication with said second header of said condenser, a first said drain line directly coupled to said second header, said N drain lines positioned sequentially with respect to said first drain line, said first drain line through said N-1 drain line comprising a venturi section, and wherein N is an integer greater than or equal to 2. 17. A gravity driven suction pump system in accordance with claim 16 further comprising N-1 spill-over connection lines, each said spill-over connection line extending between and coupled at opposing ends to a first section of adjacent drain lines. 18. A gravity driven suction pump system in accordance with claim 17 further comprising N-1 suction lines, wherein said suction line extends from said second header into corresponding drain line, each of said suction line having a first end and a second end, said first end located in said second header, and said second end located in said venturi section of said drain line. |
047160071 | description | DESCRIPTION OF THE PREFERRED EMBODIMENT In the operation of a commercial pressurized water reactor it is desirable to be able to prolong the life of the reactor core to better utilize the uranium fuel and to be able to effectively change the reactor core power output in response to load follow requirements. The invention described herein provides a means to control a spectral shift reactor during load follow. Referring to FIG. 1, the nuclear reactor is referred to generally as 20 and comprises a reactor vessel 22 with a removable closure head 24 attached to the top end thereof. An inlet nozzle 26 and an outlet nozzle 28 are connected to reactor vessel 22 to allow a coolant such as water to circulate through reactor vessel 22. A core plate 30 is disposed in the lower portion of reactor vessel 22 and serves to support fuel assemblies 32. Fuel assemblies 32 are arranged in reactor vessel 22 and comprise reactor core 34. As is well understood in the art, fuel assemblies 32 generate heat by nuclear fissioning of the uranium therein. The reactor coolant flowing through reactor vessel 22 in heat transfer relationship with fuel assemblies 32 transfers the heat from fuel assemblies 32 to electrical generating equipment located remote from nuclear reactor 20. A plurality of control rod drive mechanisms 36 which may be chosen from those well known in the art are disposed on closure head 24 for inserting or withdrawing control rods (not shown) from fuel assemblies 32. In addition, a plurality of displacer rod drive mechanisms 38 are also disposed on closure head 24 for inserting or withdrawing displacer rods 40 from fuel assemblies 32. Displacer rod drive mechanism 38 may be similar to the one described in copending United States patent application Ser. No. 217,055, filed Dec. 16, 1980 in the name of L. Veronesi et al. entitled "Hydraulic Drive Mechanism" and assigned to the Westinghouse Electric Corporation. For purposes of clarity, only a selected number of displacer rods 40 are shown in FIG. 1. However, it should be understood, that the number of displacer rods 40 are chosen to correspond to the number of displacer rod guide tubes in fuel assemblies 32. A plurality of displacer rod guide structures 42 are located in the upper section of reactor vessel 22 with each being in alignment with a displacer rod drive mechanism 38 for guiding the movement of displacer rods 40 through the upper section of reactor vessel 22. A calandria 44 may be arranged between fuel assemblies 34 and displacer rod guide structures 42 and comprises a multiplicity of hollow stainless steel tubes arranged in colinear alignment with each displacer rod and control rod for providing guidance of the displacer rods and control rods through the calandria area and for minimizing flow induced vibrations in the displacer rods and control rods. Referring now to FIGS. 2-4, fuel assemblies 32 comprise fuel elements 48, grids 50, bottom nozzle 52, top nozzle 54, and guide tubes 56. Fuel elements 48 may be elongated cylindrical metallic tubes containing nuclear fuel pellets and having both ends sealed by end plugs. Fuel elements 48 may be arranged in a substantially 20.times.20 rectangular array and are held in place by grids 50. Guide tubes 56 which may number 25 are arranged in a generally 5.times.5 array within each fuel assembly 32. Each guide tube 56 occupies the space of about four fuel elements 48 and extend from bottom nozzle 52 to top nozzle 54 and provide a means to support grids 50, top nozzle 54 and bottom nozzle 52. Guide tubes 56 may be hollow cylindrical metallic tubes manufactured from Zircaloy and capable of accommodating rods such as displacer rods 40 or control rods. Displacer rods 40 and control rods are manufactured to be approximately the same size so that each guide tube 56 can equally accommodate either a displacer rod or a control rod. When not occupied by a rod, guide tubes 56 are filled with reactor coolant; however, when displacer rods 40 are inserted in guide tubes 56 displacer rods 40 displace the coolant therein. Grids 50 are positioned at various locations along the length of fuel assembly 32 and serve to space fuel elements 48 and guide tubes 56 at appropriate distances from each other and to allow the reactor coolant to circulate in heat transfer relationship with fuel elements 48. A more detailed description of a similar grid may be found in U.S. Pat. Nos. 3,379,617 and 3,379,619, both issued in the name of H. H. Andrews et al. As can be seen in FIG. 4, displacer rods 40 are elongated cylindrical substantially hollow rods which can be manufactured out of Zircaloy and may be of the type described in copending United States patent application Ser. No. 217,052 entitled "Displacer Rod For Use In A Mechanical Spectral Shift Reactor" filed Dec. 16, 1980 in the name of R. K. Gjertsen et al. and assigned to the Westinghous Electric Corportion now U.S. Pat. No. 4,432,934 dated Feb. 21, 1984. Displacer rods 40 may also contain ZrO.sub.2 or Al.sub.2 O.sub.3 pellets for weighting the rod and enhancing its lowerability. As described in U.S. Pat. No. 4,432,934 the Zircaloy members 40 are thin-walled and can contain a filling of solid or annular zirconium oxide pellets or aluminum oxide pellets to provide structural support as well as mass. The construction of displacer rod 40 is such that it provides a low neutron absorbing rod that is capable of displacing reactor coolant-moderator when inserted into a fuel assembly. Displacer rods 40 are arranged so as to be in colinear alignment with guide tube 56 so that displacer rods 40 may be inserted in guide tubes 56 when it is desired. Displacer rods 40 are supported from a common attachment known as a spider 58. Spider 58 comprises a body 60 with struts 62 radially extending from body 60. Displacer rods 40 are individually attached to each strut 62 to form an array corresponding to the array of guide tubes 56 into which displacer rods may be inserted. Spider 58 is attached to drive shaft 64 which is connected to displacer rod drive mechanism 38. Activation of displacer rod drive mechanism 38 causes drive shaft 64 to be either lowered or raised thereby inserting or withdrawing displacer rods 40 from fuel assemblies 32 of core 34. It is important to note that each spider 58 is arranged to be able to insert displacer rods 40 into more than one fuel assembly 32. For example, as shown in FIG. 4, spider 58 is capable of inserting 25 displacer rods in center fuel assembly 32 and 4 displacer rods in each of the adjacent 4 fuel assemblies. In this manner displacer rods 40 can be moved in and out of fuel assemblies 32 without increasing the number of spiders and drive mechanisms. Referring now to FIGS. 5 and 6, displacer rod guide structure 42 comprise a plurality of split tube guides 70 which are designed to allow rods such as displacer rods or control rods to pass therethrough. Displacer rod guide structures 42 are located between calandria 44 and closure head 24 as shown in FIG. 1 and are arranged to correspond to each displacer rod drive mechanism 38. A number of spacers 72 are located at various locations along split tube guides 70 and together with split tube guides 70 serve to guide displacer rods 40 through the upper section of reactor vessel 22. As can be seen in FIG. 6, 8 split tube guides 70 may be provided for guiding displacer rods 40. The "split" in split tube guides 70 along with slots 74 in spacers 72 allow spider 58 to pass therethrough while maintaining alignment of the rods with guide tubes 56 in fuel assemblies 32. A center slot 76 is also provided for accommodating drive shaft 64 so that spider 58 may be moved therethrough. Referring again to FIG. 1, calandria 44 which comprises a multiplicity of tubes provides guidance for the rods such as displacer rods 40 through the calandria area. In general, the tubes in calandria 44 are not split tubes, as are split tube guides 70, so that spider 58 stops its descent when spider 58 nears the top of the tubes in calandria 44. When stopped at the top of the calandria 44 all rods extend through the calandria tubes and are fully inserted in fuel assembly 32. While inserted in the calandria tubes, the rods are protected from the flow of reactor coolant thereby minimizing vibrations that would otherwise be induced by the high velocity of the reactor coolant in that area. In the invention as described herein, at least three different types of rods are capable of being inserted into guide tubes 56. For example, displacer rods, control rods, and gray rods may be arranged to be inserted in guide tubes 56. All of the rods are approximately the same size and configuration, but because of the materials with which they are made serve different purposes. Displacer rods 40 which may be either a hollow thick walled tube or may contain a low neutron absorbing material such as ZrO.sub.2 or Al.sub.2 O.sub.3 pellets are used to displace reactor coolant and thereby control reactor moderation. Control rods contain neutron absorbing material as is well understood in the art and serve to control core reactivity in a commonly understood fashion. Gray rods are similar to displacer rods 40 but are made of an intermediate neutron absorbing material such as stainless steel so that their reactivity worth per rod is greater than that of displacer rods 40. Referring not to FIGS. 7-11, the quarter core arrangement of fuel elements 48, displacer rods 40, control rods 80, gray rods 82, and unrodded locations 84 are shown. It is to be understood that the full reactor core configuration can be established by extrapolating the quarter core shown in FIG. 7. Actually, the quarter core shown in FIG. 7 is a mirror image of the eighth core taken along line A--A of FIG. 7. However, the quarter core of FIG. 7 is being shown for clarity. As can be seen in FIG. 10, each fuel assembly 32 comprises an array of fuel elements 48 and an array of guide tubes 56. Generally, control rods 38 and gray rods 82 are used only in the diagonally arranged guide tubes 56 while displacer rods 40 are generally used in all guide tubes 56 of a given fuel assembly. In addition, an instrument tube 88 is provided near the center of each fuel assembly 32 for accommodating date instrumentation. While each fuel assembly 32 is essentially identical to the one shown in FIG. 10, each fuel assembly 32 can produce a different function depending on whether guide tubes 56 are occupied by reactor coolant, displacer rods 40, control rods 80, or gray rods 82. Displacer rods 40 and gray rods 82 are generally chosen to be approximately the same size so as to displace approximately the same volume of water. However, gray rods 82 can be thick walled stainless steel cylindrical rods which gives each individual gray rod a higher reactivity worth than a single displacer rod. The wall thickness of the gray rods may be approximately 0.065 inches. But since the gray rods are usually arranged in clusters of 9 as opposed to clusters of 41 displacer rods, each gray rod cluster has a smaller reactivity worth than a displacer rod clusters. Thus, by proper selection of materials and by proper selection of the number of rods, a balanced reactivity worth can be attained for the gray rods and displacer rods. In addition, since the reactivity worth of a gray rod cluster may be approximately 25% of a displacer rod cluster, various combinations of movements of gray rods clusters and displacer rod clusters can yield numerous reactivity worths throughout the core. Referring now to FIG. 11, a fuel assembly 32 in which no control rods 80 or gray rods 82 are used and in which only displacer rods 40 are used in guide tubes 56 is referred to generally as displacer assembly 90. A fuel assembly 32 in which both displacer rods 40 and control rods 80 are employed (but no gray rods) is referred to as control assembly 92. Similarly, a fuel assembly 32 in which both displacer rods 40 and gray rods 82 are used is called a gray assembly 94. It should be noted that in FIG. 11 fuel elements 48 have been omitted for clarity and that those fuel assemblies are similar to those shown in FIG. 10. Still referring to FIG. 11, each of the control rods 80 and gray rods 82 are attached to a spider (not shown) similar to spider 58 except that the spider for the control rods 80 or gray rods 82 generally only effects one fuel assembly. In this manner, all control rods 80 or gray rods 82 in a given fuel assembly can be raised or lowered by a single drive mechanism. Furthermore, since each displacer rod spider 58 can extend into the adjacent fuel assemblies (as illustrated in the center portion of FIG. 11 and in FIG. 4), the displacer rod spider's 58 movement effects the control on five fuel assemblies and reduces the number of displacer rod drive mechanisms needed. Of course, on the periphery of the quarter core (as shown in FIG. 7) the particular spiders may move less than the usual number of rods because there are no adjacent fuel assemblies or there are unrodded locations 84. Referring again to FIGS. 8 and 9 which comprise FIG. 7, a quarter core arrangement. Each row or partial row is numbered 100-114 and each column or partial column is numbered 116-130 and comprises: ______________________________________ Fuel Assembly ______________________________________ (100,116) quarter displacer assembly (100,118) half control assembly (100,120) half displacer assembly (100,122) half control assembly (100,124) half displacer assembly (100,126) half control assembly (100,128) half displacer assembly (100,130) half gray assembly (102,116) half control assembly (102,118) full displacer assembly (102,120) full gray assembly (102,122) full displacer assembly (102,124) full gray assembly (102,126) full displacer assembly (102,128) full control assembly (102,130) full displacer assembly (104,116) half displacer assembly (104,118) full gray assembly (104,120) full displacer assembly (104,122) full control assembly (104,124) full displacer assembly (104,126) full control assembly (104,128) full displacer assembly (104,130) partial control-unrodded assembly (106,116) half control assembly (106,118) full displacer assembly (106,120) full control assembly (106,122) full displacer assembly (106,124) full control assembly (106,126) full displacer assembly (106,128) full control assembly (106,130) full displacer assembly (108,116) half displacer assembly (108,118) full gray assembly (108,120) full displacer assembly (108,122) full control assembly (108,124) full displacer assembly (108,126) full control assembly (108,128) full displacer assembly (110,116) half control assembly (110,118) full displacer assembly (110,120) full control assembly (110,122) full displacer assembly (110,124) full control assembly (110,126) full displacer assembly (110,128) partial displacer unrodded assembly (112,116) half displacer assembly (112,118) full control assembly (112,120) full displacer assembly (112,122) full control assembly (112,124) full displacer assembly (112,126) partial displacer unrodded assembly (114,116) half gray assembly (114,118) full displacer assembly (114,120) partial control unrodded assembly (114,122) full displacer assembly ______________________________________ As can be seen from the above description of the quarter core, the core configuration based on this concept can be illustrated generally as shown in FIG. 11. Basically, the fuel assembly in the center of the full core as represented by fuel assembly (100,116) in FIG. 7 can be chosen to be either a control assembly 92 or preferably a displacer assembly 90. Once this is chosen, the four fuel assemblies immediately adjacent to the flat sides of the center fuel assembly are chosen to be the other type and the fuel assemblies on the diagonal are chosen to be the same type as the center assembly. This pattern is then continued in an alternating fashion. For example, the center fuel assembly (100,116) in FIG. 7 was chosen to be a displacer assembly 90 so that the fuel assemblies on its adjacent flat sides are chosen to be either control assemblies 92 or gray assemblies 94 while those on the diagonal are chosen to be displacer assemblies 90. This pattern is repeated in alternating fashion until the periphery of the core is reached where the end fuel assemblies may be chosen to be hybrid assemblies based on the nuclear physics of the particular core. Whether a particular assembly is chosen to be a control assembly 92 or a gray assembly 94 is determined by first selecting the number and location of control assemblies needed based on conventional core design. The remainder of the assemblies not chosen to be control assemblies 92 are then used as gray assemblies 94. Thus, substantially the entire core can be arranged on an alternating pattern of displacer assemblies and control or gray assemblies with practically all the fuel assembies being served by at least one displacer rod spider 58 and with each displacer rod spider 58 serving generally 5 fuel assemblies. Moreover, each fuel assembly is served by at least one drive mechanism for either displacer rods, control rods or gray rods. The illustrated core arrangement provides a means by which the neutron spectrum can be controlled in a "spectral shift" fashion by controlling the moderator volume in the core. This can be accomplished by displacing and replacing the water coolant in the core at appropriate times thereby changing the moderation of the core. In the present invention, displacer rods 40 and gray rods 82 can be used to effect this moderation change. In operation, all displacer rods 40 and gray rods 82 are inserted in core 34 at the beginning of the core life. However, none of the control rods 80 need be inserted at that time. The insertion of displacer rods 40 and gray rod 82 is done by activating the appropriate drive mechanism such as displacer rod drive mechanism 38. When the drive mechanism is activated, displacer rods 40 and gray rods 82 fall into the appropriate guide tubes 56 in fuel assemblies 32. The displacer rods and gray rods will displace their volume of coolant (water) thus reducing the volume of moderator in core 34. The reduction of moderator hardens the neutron spectrum of the core and increases plutonium production. This hardening of the neutron spectrum is generally referred to as "spectral shift". The harder neutron spectrum reduces boron chemical shim requirements, results in a more negative moderator temperature coefficient, and reduces or eliminates burnable poison requirements. As the uranium fuel in the core is depleted over the life of the core, a certain number of displacer rods 40 and/or gray rods 82 may be withdrawn from the core by activating their respective drive mechanisms. The withdrawal of the rods allows more water-moderator into the core region and increases moderation of the core. This, in effect, introduces reactivity worth at a time when fuel depletion is causing a reactivity worth depletion. Thus, the reactivity of the core can be maintained at appropriate levels for a longer time. The withdrawal of the rods can continue at a selective rate (depending on core conditions) until, near the end of core life, all displacer rods 40 have been withdrawn from the core. In addition to the use of displacer rods 40 and gray rods 82 for the purpose of "spectral shift", these rods can also be used for load follow purposes. For example, when the concentration of boron in the reactor coolant fails below approximately 100 ppm the capability of a boron bleed-and-feed operation to compensate for the xenone transient during load follow may not be practical. However, by withdrawing or inserting selected displacer rods 40 or gray rods 82, a proper reactivity change can be made to compensate for the xenon transient. Moreover, such a maneuver can be performed to adjust overall power requirements or to adjust radial power distributions. Since gray rods 82 have a different reactivity worth than displacer rods 40 and since gray rods 82 and displacer rods 40 are located in different core locations, proper selection and movement of the rods can accomplish delicate reactor control. Calculations of the reactivity worth of a 41-rod displacer rod cluster indicates that such a cluster may have a reactivity worth of approximately 75 pcm. That is, core reactivity is expected to increase by about 75 pcm when a single 41-rod displacer rod cluster is moved from fully inserted to fully withdrawn when fuel burnup is about 11,000 MWD/MTU. At the same time, the moderator temperature coefficient of reactivity is predicted to be about -35 pcm/.degree.F. Hence, withdrawal of a single 41-rod displacer rod cluster, with no associated change in control rod position or power level, will result in a reactor coolant average temperature increase of about 2.degree. F. with the temperature change lagging behind displacer rod movement by about 10-20 seconds (one loop transit time). Since the coolant average temperature changes in response to displacer movement are small and occur slowly, coolant temperature change can be used to "cushion" the effect of displacer movement on overall core reactivity. That is, due to the negative moderator temperature coefficient, the reactor coolant temperature change will tend to offset a portion of the reactivity change caused by the displacer rod movement thus providing a smooth transition in core reactivity when a displacer rod cluster is moved. Since displacer rod cluster reactivity worth and the absolute value of the moderator temperature coefficient change in the same direction and at comparable fractional rates with changing boron concentration and hydrogen-to-uranium ratio in the core, the temperature change per unit displacer rod cluster movement is generally independent of core conditions throughout the latter part of the core life. Referring to FIG. 12, utilizing these concepts for reactor control two reactor coolant temperature bands can be selected for reactor operating purposes. These bands may be different from and wider than the conventional operating bands. One band, band A, is the wide band and is selected to be approximately 4.degree. F. wide 2.degree. F. on either side of the reactor coolant average temperature set point, T.sub.s. T.sub.s is chosen to be the reactor coolant average temperature at which it is desired to operate the reactor. As an alternative, the average cold leg temperature may be used. An administrative guidance limit or narrow band, band B, may be chosen to be approximately 3.degree. F. wide, 1.5.degree. F. on either side of set point temperature T.sub.s. Band A is chosen so that if the reactor coolant temperature reaches this limit automatic systems are initiated to reverse the temperature drift. Band B is chosen as a working guide limit so that as the reactor coolant temperature approaches this limit either operator or automatic selection and initiation of displacer rod movement may begin to avoid reaching the band A limit. In this manner, as the reactor coolant temperature drifts downwardly such as during xenon accumulation as illustrated between t.sub.0 and t.sub.1, withdrawal of a particular displacer or gray rod cluster is initiated. Between t.sub.1 and t.sub.2 the rod cluster is withdrawn which takes approximately 15 minutes to achieve complete withdrawal. The withdrawal of a rod cluster allows additional water-moderator to enter the core which increases core reactivity and results in the reactor coolant temperature drifting upwardly. As the xenon continues to accumulate the coolant temperature begins to drop again as illustrated between t.sub.2 and t.sub.3. As t.sub.3 is approached, it again becomes necessary to select and withdraw the next rod cluster, either a 41 rod displacer cluster or a 9 rod gray cluster depending on the reactivity addition needed. The time frame between t.sub.4 and t.sub.5 indicates the time frame in which the next rod cluster should begin to be withdrawn to avoid reaching band A's limit. In this manner reactor coolant temperature variations such as those due to xenon transients can be compensated for without adjusting the boron concentration in the coolant and while prolonging the core life. In addition to determining when a particular cluster should be moved, it is also necessary to determine which cluster or group of clusters should be moved and whether they should be moved in or out of the core. In this regard it can be appreciated that since a displacer rod cluster effects a larger core area than does a gray rod cluster and since individual gray rods have a different reactivity worth than do individual displacer rods, a proper selection and movement of various clusters can effect core reactivity levels and radial power disbribution. Referring now to FIG. 13, a power sharing fraction calculator 100 determines the fraction of the total core power that is attributed to each fuel assembly. This can be ascertained in conventional manner by having a sufficient number of in-core radiation detectors to determine local neutron flux or nuclear power level magnitudes. For example, about 60 fuel assemblies may be equipped with about 5 radiation detectors such as gamma detectors. The 5 radiation detectors can be axially spaced along the fuel assembly so that, in all, about 300 in core detectors can provide instantaneous reactivity levels for 60 core zones. These readings, together with calibration and weighting factors, can be fed to power sharing fraction calculator 100 for determining the power sharing fraction borne by each core zone. At the same time, current condition compiler 102 complies other core conditions such as boron concentration, hydrogen-to-uranium fraction, and present cluster positions. This information together with the information from power sharing fraction calculator 100 is transmitted to displacer movement effect predictor 104 which determines the reactivity change and power sharing fraction change that would occur by moving each cluster. It has been found that the reactivity change associated with a particular fuel assembly by moving the corresponding cluster is related to the present fuel assembly power density. The correlation can be expressed as follows: EQU .DELTA.R=m.times.APD where .DELTA.R=reactivity change of the fuel assembly by inserting or withdrawing the corresponding cluster (displacer rods or gray rods); PA1 APD=fuel assembly power density before moving the cluster; and PA1 m=straight line slope PA1 NPD=new fuel assembly power density PA1 OPD=old fuel assembly power density PA1 BU=burnup in MWD/MTU It has also been determined that the slope, m, can be related to burnup as illustrated by the following data: ______________________________________ Burnup Slope, m (MWD/MTU) (pcm per cluster/unit power density) ______________________________________ 1,000 5.4 6,000 32.8 11,000 60.0 ______________________________________ yielding a relation of slope to burnup of: EQU m=0.0054.times.BU where BU.times.burnup in MWD/MTU. Therefore, EQU .DELTA.R=0.0054.times.BU.times.APD By using this relationship, movement effect predictor 104 can predict the reactivity change to be expected from moving the cluster corresponding to that fuel assembly. This information is then transmitted to cluster selector 106. It has also been found that the post-withdrawal power density of a particular fuel assembly can be related as follows: EQU NPD=(1.17+0.000033.times.BU).times.OPD where Thus the power density change in a particular fuel assembly can be found based on its power density prior to cluster movement. This information is then transmitted to cluster selector 106. A requirements predictor 108 which may be chosen from those well known in the art is arranged to determine and transmit to cluster selector 106 the amount of reactivity increase or decrease that is anticipated to be needed. This can be based on data such as coolant average temperature, power level, band limits, and set point considerations. Power sharing fraction calculator also feeds the power sharing fraction for each fuel assembly to cluster selector 106. Cluster selector 106 accepts the power sharing fraction for each fuel assembly prior to a cluster movement, the reactivity change to be expected if a cluster were moved, the present fuel assembly power density (OPD) for each fuel assembly, the predicted fuel assembly power density (NPD) for each fuel assembly, and the reactivity change required. From this, a new power sharing fraction for each fuel assembly can be determined. Based on this information and the current position of each cluster, cluster selector 106 can select the one or more groupings of cluster movements that will achieve the desired reactivity change without distorting the overall power sharing profile. In general, this search may include predicting the next reactivity change and the movement required thereby so as to prevent making a cluster movement that could hinder latter cluster movements. The selected cluster groupings can be transmitted directly to power distribution verifier 110, operator readout 112, and automatic system control 114. Power distribution verifier can check the predicted power sharing fractions to the old power sharing fractions and can trip alarm 116 if the predicted change is outside set limits. The operator can view operator readout 112 and select which of the selected cluster groupings to use or the selection can be made automatically by cluster selector 106 and transmitted to automatic system control 114 for implementation of the cluster movement. Thus, based on these criteria, various movements (insertions or withdrawals) of numerous combinations of available displacer rod or gray rod clusters can be evaluated and implemented for controlling a pressurized water reactor such as during load follow. Therefore, the invention provides apparatus for operating a pressurized water nuclear reactor in which the reactor power level can be changed without making control rod or chemical shim changes. |
summary | ||
047939656 | abstract | A support for the top ends of plural rod guides of at least first and second types which are generally vertically disposed within a pressurized water reactor vessel in corresponding, first and second interleaved matrices. Lower ends of the rod guides are affixed to a lower support structure and the upper ends thereof are disposed adjacent to and spaced vertically below an upper support structure of the vessel. Corresponding, first and second types of top support plates are disposed on and connected to respective top ends of the first and second types of rod guides. The first and second types of top support plates have mating exterior peripheral surfaces which are assembled in sliding, telescoping relationship, a transverse extension from one peripheral surface being received in a vertically extending, recessed channel in a mating peripheral surface of the contiguous support plates. A linkage is secured to a top support plate of one type and to each of the mating top support plates of the other type contiguously surrounding it, providing rigid lateral interconnection and resilient vertical interconnection of the top plates and maintaining same in a concatenated relationship. Aligned keyway segments of the assembled and contiguous first and second plates receive keys which are bolted in place and provide limit stops to relative displacement of the contiguous, interconnected plates. |
claims | 1. A method of fabricating nuclear fuel elements, the method comprising:determining at least one technological uncertainty factor for nuclear fuel elements, using, for at least one fabrication parameter:a collective variation in the at least one fabrication parameter about a nominal value within a batch of fabricated elements, and in addition to the collective variation,an individual variation in the at least one fabrication parameter about a nominal value for an individual element; andfabricating the nuclear fuel elements based on the at least one technological uncertainty factor,wherein the technological uncertainty factor is determined for linear power density at a hot point FQE. 2. The method as recited in claim 1 wherein the collective variation is multiplied by a macroscopic sensitivity coefficient. 3. The method as recited in claim 2 wherein the individual variation is multiplied by a microscopic sensitivity coefficient. 4. The method as recited in claim 3 wherein the determining at least one technological uncertainty factor for nuclear fuel elements includes determining the technological uncertainty factor for linear power density at the hot point FQE according to a formula of: F Q E = 1 + 1.645 1.96 ∑ i ( α i 2 T i 2 μ i 2 + θ i 2 TL i 2 μ i 2 ) where Ti and TLi respectively designate individual and collective variations in a fabrication parameter Fi, and αi and θi respectively designate the microscopic and the macroscopic sensitivity coefficients for the fabrication parameter, and where μi designates a mean for the fabrication parameter Fi. 5. The method as recited in claim 1 wherein the collective variation is a collective tolerance, a deviation between a mean of real values for the fabrication parameter within a batch of elements and nominal value being required to comply with the collective tolerance. 6. The method as recited in claim 5 wherein the individual variation is an individual tolerance, a deviation between a real value of the fabrication parameter for an individual element and a nominal value needing to comply with the individual tolerance. 7. A method of fabricating nuclear fuel elements, the method comprising:determining at least one technological uncertainty factor for nuclear fuel elements, using, for at least one fabrication parameter:a collective variation in the at least one fabrication parameter about a nominal value within a batch of fabricated elements, and in addition to the collective variation,an individual variation in the at least one fabrication parameter about a nominal value for an individual element; andfabricating the nuclear fuel elements based on the at least one technological uncertainty factor,wherein the technological uncertainty factor is determined for a hot channel FΔHE1. 8. The method as recited in claim 7 wherein the collective variation is multiplied by a macroscopic sensitivity coefficient. 9. The method as recited in claim 8 wherein the individual variation is multiplied by a microscopic sensitivity coefficient. 10. The method as recited in claim 9 wherein the determining at least one technological uncertainty factor for nuclear fuel elements includes determining the technological uncertainty factor for the hot channel FΔHE1 according to a formula of: F Δ H E 1 = 1 + 1.645 1.96 ∑ i ( α i 2 TL i 2 μ i 2 + θ i 2 TL i 2 μ i 2 ) where TLi designates the collective variation in a fabrication parameter Fi, where αi and θi designate respectively the microscopic and the macroscopic sensitivity coefficients in the fabrication parameter, and where μi designates a mean for the fabrication parameter Fi. 11. The method as recited in claim 7 wherein the collective variation is a collective tolerance, a deviation between a mean of real values for the fabrication parameter within a batch of elements and nominal value being required to comply with the collective tolerance. 12. The method as recited in claim 11 wherein the individual variation is an individual tolerance, a deviation between a real value of the fabrication parameter for an individual element and a nominal value needing to comply with the individual tolerance. |
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description | The present invention provides a wafer holder assembly that is well-suited for SIMOX wafer processing, which includes the use of relatively high ion beam energies and temperatures. In general, the wafer holder assembly has a structure that maintains its integrity and reduces the likelihood of wafer contamination during extreme conditions associated with SIMOX wafer processing. The wafer holder assembly can be formed from electrically conductive materials to provide an electrical path from the wafer to ground for preventing electrical charging of the wafer, and possible arcing, during the ion implantation process. FIGS. 1-2 show a wafer holder assembly 100 in accordance with the present invention. The assembly includes first and second main structural rail members 102,104 that are substantially parallel to each other and spaced apart at a predetermined distance. In the exemplary embodiment shown, the main structural members 102,104 are generally C-shaped. A first wafer-holding arm 106 is rotatably secured to a distal end 108 of the holder assembly and a second wafer-holding arm 110 is pivotably secured to the assembly at a generally proximal region 112 of the assembly. The first arm 106 includes a transverse member 114 having first and second portions 116,118 each of which terminates in a respective distal end 120,122. Wafer-contacting pins 124,126 are secured to the distal ends 120,122 of the first and second arm portions. The first arm 106 is rotatable about a first axis 128 that is generally parallel to the first and second main structural members 102,104. By allowing the first arm 106 to rotate about the first axis 128, the first and second arm portions apply substantially equal pressure to the wafer edge via the spaced apart wafer-contacting pins 124,126. The second arm 110 is pivotable about a second axis 130 that is generally perpendicular to the main structural members 102,104 to facilitate loading and unloading of the wafers. A wafer-contacting pin 132 is affixed to the distal end 134 of the second arm to provide, in combination with the pins 124,126 coupled to the first arm, three spaced apart contact points to securely hold the wafer in place. Typically, placement of the pins about the circumference of the wafer is limited by a notch or xe2x80x9csignificant flatxe2x80x9d in the wafer that is used for orientating the wafer on the holder assembly. Some processing techniques include rotating the wafer a quarter turn, for example, one or more times during the implantation process to ensure uniform doping levels. The wafer holder assembly can further include a series of retaining members for securing the components of the assembly together without the need for conventional fasteners and/or adhesives. It is understood that adhesives can vaporize or outgas during the ion implantation process and contaminate the wafer. Similarly, conventional fasteners, such as exposed metal screws, nuts, bolts, and rivets can also contaminate the wafer. In addition, such devices may have incompatible thermal coefficients of expansion making the assembly prone to catastrophic failure. In one embodiment, the assembly includes a distal retaining member 136 coupling the first arm 106 to the assembly and an intermediate retaining member 138 affixed to a bottom of the assembly to maintain the spacing of the first and second main structural members 102,104 in a middle region 140 of the assembly. The assembly can further include a proximal retaining member 142 securing the structural members in position at the proximal region 112 of the assembly. FIGS. 3-7 (shown without the wafer-contacting pins), in combination with FIGS. 1 and 2, show further details of the wafer holder assembly structure. The first arm 106 includes a support member 144 extending perpendicularly from the transverse member 114 (FIGS. 3-4). The support member 144 includes an intermediate region 146 and an arcuate coupling member 148. A bearing member 150 extends through a longitudinal bore 152 in the intermediate region 146 of the support member 144 (FIGS. 3-4). A first cross member 154 is matable with the distal ends 156,158 of the main structural members 102,104 and a second cross member 160 is matable to the main structural members at a predetermined distance from the first cross member 154 (FIGS. 5-6). The first and second cross members 154,160 are adapted for mating with opposite edges of the main structural members 102,104. It is understood that notches can be formed in the various components to receive mating components. Each of the first and second cross members 154,160 includes a respective bore 162,164 for receiving an end of the bearing member 150. (FIG. 7). In one embodiment, the bearing member is a rod having each end seated within respective sleeve members 166,168 disposed within an aperture in the cross members 154,160. The sleeve members 166,168 allow the first arm 106 to freely rotate while minimizing particle generation due to graphite on graphite contact during rotation of the first arm. In one embodiment, the sleeves are formed from a hard, insulative material, such as aluminum oxide (sapphire). FIG. 8, in combination with FIGS. 1 and 2, show further details of the distal retaining member 136 having a first end 170 with a first notch 172 for coupling to one of the main structural members 102 and a second notch 174 for engaging the coupling member 148 (FIG. 3) of the first arm. A second end 176 of the distal retaining member 136 is matable to the intermediate region 140 of the assembly. Indents 178 can be formed in the main structural members 102,104 to facilitate engagement of the second end 176 to the assembly (FIG. 1). FIGS. 9-10 show alternative embodiments of the distal retaining member in the form of a helical spring 136xe2x80x2 and a bellows 136xe2x80x3, respectively. It is understood that one of ordinary skill in the art can readily modify the geometry of the retaining members. In one embodiment, the distal retaining member 136 is under tension so as to apply a force having a direction indicated by arrow 180 (FIG. 5) on the coupling member 148 of the support member. The force applied by the distal retaining member 136 pressures a neck 182 (FIG. 3) of the support member against the second cross member 160. The applied force also pressures the first cross member 154, via the bearing member 150, against the main structural members 102,104 as the second cross member 160 functions as a fulcrum for the support member 144. However, the transverse portion 114, as well as the support member 144 of the first arm, freely rotate about the first axis 128, i.e., the bearing member 150, such that the pins 124,126 at the distal ends of the first arm portions 116,118 provide substantially equal pressure on the wafer. FIGS. 11 and 12 (bottom view), in combination with FIGS. 1 and 2, show further details of the second proximal region 112 of the wafer holder assembly 100. FIG. 11 is shown without the second main structural member 104 for clarity. First and second stop members 184 (FIG. 1), 186 extend from the main structural members 102,104. In an exemplary embodiment, the second arm 110 includes wing regions 188 (FIG. 1) that are biased against the ends of the stop members 184,186 by a bias member 190. In one embodiment, the bias member 190 is under compression so as to pressure the second arm 110 against the stop members 184,186, e.g., the wafer-hold position. The bias member 190 includes a U-shaped outer portion 192 having a first end 194 mated to the first structural member 102 and a second end 196 coupled to the second structural member 104 (FIG. 12). A spring portion 198 of the second bias member includes one end abutting the second arm member 110 and the other end extending from a bottom of the U-shaped outer member 192. The second arm 110 pivots at its bottom end about a second bearing member 200 disposed on the second axis 130, which is generally perpendicular to the main structural members 102,104. The second bearing member 200 extends through a bore in the second arm with each end of the bearing member being seated in a sleeve inserted within a respective main structural member 102,104. Rotation of the second arm 110 is limited by respective brace members 202,204 extending from the main structural members 102,104. FIG. 13 (bottom view), in combination with FIGS. 1 and 2, shows further details of the intermediate retaining member 138, which is mated to the main structural members 102,104 in the intermediate region 140 of the assembly. The intermediate retaining member 138 includes first and second opposing U-shaped outer members 206,208 with a spring member 210 extending therebetween. The first outer member 206 has first and second arms 212,214 for mating engagement with corresponding notched protrusions 216,218 formed on the bottom of the main structural members 102,104. Similarly, the second outer member 208 includes arms that are matable with notched protrusions 220,222. In one embodiment, the U-shaped outer members 206,208 are forced apart to facilitate mating to the protrusions. Upon proper positioning, the outer members 206,208 are released such that spring member 210 biases the outer members against the protrusions. The intermediate retaining member 138 is effective to maintain the spacing between the first and second main structural members 102,104 and enhance the overall mechanical strength of the assembly. FIG. 14 shows the proximal retaining member 142, which provides structural rigidity in the proximal region 112 of the wafer holder assembly. In one embodiment, the proximal retaining member 142 includes upper and lower members 224,226 coupled by a spring member 228. The spring member 228 can be engaged to the main structural members such that the spring member is under tension. The proximal retaining member 142 can include a protruding member 230 having a slot 232 formed therein. As shown in FIG. 15, the assembly 100 is matable with a rotatable hub assembly 250 to which a series of wafer holder assemblies can be secured. A shield 252 can be secured to the proximal region 112 of the assembly to protect exposed regions of the assembly from beam strike. The shield 252 prevents sputtering from the assembly components, as well as any metal devices used to affix the assembly to the hub 250, during the ion implantation process. In addition, the assembly components are not heated by direct exposure to the ion beam. In one embodiment, an edge of the shield 252 is captured in the slot 232 (FIG. 14) located in the proximal retaining member 142. It is understood that the shield 252 can have a variety of geometries that are effective to shield the assembly components from beam strike. In one embodiment, the shield 252 is substantially flat with an arcuate edge 254 proximate the second wafer-holding arm 110 to increase the shielded region of the assembly. It is further understood that the shield can be formed from various materials that are suitably rigid and are opaque to the ion beam. One exemplary material is silicon having properties that are similar to a silicon wafer. The wafer-contacting pins 124,126,132 coupled to ends of the wafer-holding arms are adapted for contacting and securing the wafer in the wafer holder assembly 100. In general, the pins should apply sufficient pressure to maintain the wafers in the holder assembly during the load and unload process in which the wafers are manipulated through a range of motion that can include a vertical orientation. However, undue pressure on the wafers should be avoided since damage to the wafer surface and/or edge can result in the formation of a slip line during the subsequent high temperature annealing process. In addition, the wafer-contacting pins should not electrically insulate the wafer from the assembly. Further, the pins should be formed from a material that minimizes contamination of the wafer. FIGS. 16A-B show a wafer-contacting pin 300 adapted for use with a wafer holder assembly in accordance with the present invention. The pin has a distal portion 302 having a geometry adapted for holding the edge of a wafer and a proximal portion 304 having a contour complementing a corresponding channel formed in the ends of the wafer arms 106,110 (FIG. 1). It is understood that a variety of shapes and surface features can be used to securely and releasably mate the pin 300 to the wafer-holding arms. The distal portion 302 of the pin includes a ridge 306 extending from an arcuate wafer-receiving groove 308 in the pin. A tapered surface 310 extends proximally from the groove 308. As shown in FIG. 17, the pin should contact the top 352 and bottom 354 of the wafer 350 to prevent movement and/or vibration of the wafer as the holder assembly is rotated during the implantation process. In addition, the tapered surface 310 provides a ramp on which the wafer edge may first contact and slide upon during the wafer load process until meeting the ridge 306. FIGS. 18-23 show a wafer-contacting pin 400 in accordance with the present invention having a more limited profile. The pin 400 includes a distal portion 402 for holding a wafer and a proximal portion 404 for coupling to the arm ends. The distal portion 402 of the pin is rounded to minimize the amount of pin material proximate the wafer edge for reducing the likelihood of electrical discharge from the wafer to the pin. In addition, the pin geometry is optimized to maximize the distance between the wafer edge and the pin except at the wafer/pin contact interface. Further, the wafer-contacting region of the pin 400 should be smooth to minimize the electric field generated by a potential difference between the wafer and the pin. The pin should also minimize the wafer/pin contact area. The distal portion 402 of the pin includes a wafer-receiving groove or neck 406 disposed between a wedge-shaped upper region 408 and a tapered surface 410. The neck 406 can be arcuate to minimize the contact area between the wafer edge and the pin. The upper region 408, including the neck 406, can taper to a point or edge 412 for reducing the amount of pin material near the wafer edge to inhibit electrical arcing between the wafer and the pin. It is understood that the term wedge-shaped should be construed broadly to include a variety of geometries for the pin upper region. In general, the wedge-shaped upper region broadens from a point nearest a center of a wafer held in the assembly. Exemplary geometries include triangular, arcuate, and polygonal. In a further aspect of the invention, a wafer-contacting pin, such as one of the pins 122,300,400 shown in FIGS. 1, 15, 18, is coated with a relatively hard, electrically conductive film, such as titanium nitride (TiN) or titanium aluminum nitride (TiAlN). The coating provides a relatively hard, abrasion resistant material that enhances the ruggedness of the pin. In the case where the pin is formed from silicon, the TiN coating, for example, is more conductive than the silicon pin such that the likelihood of electrical arcing is reduced in comparison with an uncoated pin. In addition, the coating inhibits so-called wafer bonding in which two silicon surfaces tend to stick together during extreme processing conditions, e.g., relatively high temperatures. It is understood that potentially contaminating particles can be generated when a wafer bond between a wafer and a wafer-contacting pin is broken. The coating can be applied to the pin using a variety of techniques including chemical vapor deposition and reactive sputtering. For chemical vapor deposition to provide a TiN coating, an exemplary precursor gas is titanium chloride. For reactive sputtering a titanium target can be used and nitrogen gas can be added to an argon gas environment. It is understood that the TiN or TiAlN coating can be applied to cover the entire pin, as well as only targeted portions corresponding to the pin/wafer interface. It is further understood that the TiN coating can be applied in discrete portions or as a continuous coating. The thickness of the coating can vary from about 0.1 micrometers to about 10.0 micrometers, and more preferably from about 2 micrometers to about 5 micrometers. A preferred coating thickness is about 5 micrometers. In a further aspect of the invention, the materials for the various components are selected to provide desired features of the assembly, e.g., mechanical durability; electrical conductivity; and minimal particulation. Exemplary materials for the wafer-contacting pin include silicon and graphite. It is understood that silicon is conductive in its intrinsic state at elevated temperatures. Exemplary materials for the main structural members, the retainer members, and the bias member include silicon carbide, graphite and vitreous or vacuum impregnated graphite, which can be coated with titanium carbide. The graphite retainer and bias members can be fabricated from graphite sheets using wire electron discharge machine (xe2x80x9cwire EDMxe2x80x9d), laser machining and conventional cutting techniques. The graphite bias and retaining members maintain a steady, i.e., invariant, spring constant over a wide range of temperatures. This allows the wafer holder assembly to be adjusted at room temperature for operation at temperatures of 600xc2x0 C. and higher, which can occur during the ion implantation process. The graphite components also provide a conductive pathway for grounding the wafer, even where insulative sleeves for the bearing members are used. The wafer holder assembly of the present invention provides a structure that withstands the relatively high temperatures and ion beam energies associated with SIMOX wafer processing. In addition, the likelihood of wafer contamination is reduced since the ion beam strikes only silicon thereby minimizing carbon contamination and particle production. Furthermore, the likelihood of the electrical discharge from the wafer is minimized due to the selection of conductive materials/coatings for the assembly components and/or the geometry of the wafer-contacting pins. One skilled in the art will appreciate further features and advantages of the invention based on the above-described embodiments. Accordingly, the invention is not to be limited by what has been particularly shown and described, except as indicated by the appended claims. All publications and references cited herein are expressly incorporated herein by reference in their entirety. |
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040509842 | summary | BACKGROUND OF THE INVENTION The present invention is directed to a closed cycle gas-cooled nuclear power plant including a high-temperature nuclear reactor, a gas turboset, heat exchange apparatus consisting of recuperators, pre-coolers and intermediate coolers, and a conduit system for conducting the gas coolant through the individual components of the plant and, more particularly, it is directed to the arrangement of the plant within a prestressed concrete pressure tank (cycle-tank construction). Closed cycle plants have an obvious advantage over nuclear power plants of the type where the energy is given off in a secondary cycle, since they combine the simplicity and good output of single circuit plants with the advantages of gas turbines. By arranging the nuclear reactor, the gas turboset and the other cycle components in a common pressure tank (integrated construction), special connecting elements are avoided between individual parts of the plant through which the gas coolant flows and, as a result, a very favorable effect is obtained in the construction and operation of high-temperature reactors. Therefore, an integrated construction is preferred in a number of special nuclear power plant types. In DAS 1, 156, 903 a power engine unit of the above type is disclosed which is used for vehicles and has a very compact design. In the turboset, the turbine and compressor are located on opposite sides of the reactor core and the common shaft is hollow and extends through the reactor core and the intermediate coolers are located in the annular space between the reactor core and the pressure tank wall. This compact design is based on the consideration that the turbine does not require attendance and, as a result, the turbine and the other cycle components cannot be disassembled. A similar design of the nuclear reactor is contained in DOS 2,005,208, however, in that arrangement a pressure blanket is provided inside the pressure tank which is open at its end faces and is spaced from the inner wall of the tank in such a way that the heat exchanger is accommodated in the space formed. In DOS 2,028,736 a closed cycle gas-cooled nuclear power plant is described. The power plant is of the two-tank type with the gas turbine and other components of the gas cycle positioned in a machine block formed of prestressed concrete and separated from the concrete pressure tank to afford a simpler construction of the charging and regulating unit. A similar design of the concrete pressure tank is illustrated in DAS 1,614,610 in which two closed pressure-proof chambers are provided, with one of the chambers containing the reactor and the other serving as a containment for the remaining power plant equipment. The working medium is carried in lines which penetrate through a partition between the two pressure-proof chambers passing from the reactor to the turbine to the compressor and then back into the annular space below the reactor core. This so-called igloo-construction is technically difficult to realize and the nuclear power plant is very uneconomical, because of the manner in which it is arranged. In DOS 2,062,934 another gas-cooled nuclear reactor is shown in an integrated construction with the gas turbine arranged in a cavity in the wall of the pressure tank surrounding the reactor core. By means of a bypass, a portion of the cold gas coolant for the reactor core can be bypassed about the core and mixed directly with the hot gas coolant issuing from the core. In still another nuclear power plant of the above-described type as set forth in DOS 1,764,248 the nuclear reactor and all of the coolant cycle components are arranged in closely spaced parallel vertical bores within the concrete pressure tank and the components are accessible from the exterior and passageways are provided for the cooling medium in the wall of the pressure tank and between the individual vertical bores. However, in this arrangement the cooling medium must traverse very long flow paths and the plant requires a relatively large pressure tank. SUMMARY OF THE INVENTION Therefore, based on the above state of the art, it is the primary object of the present invention to overcome the disadvantages of the known nuclear power plants by a special arrangement of all the plant components and the conduit system interconnecting the components which permits a compact construction of the nuclear power plant. In accordance with the present invention, a prestressed concrete pressure tank encloses the nuclear reactor and a number of vertical shafts (pods) are formed in the tank, the vertical shafts are disposed in an annular arrangement about the vertical axis of the tank and are located radially outwardly from the reactor and inwardly from the radially outer surface of the tank. The gas turboset is arranged within the pressure tank in a horizontal position spaced below the reactor and the various heat exchange components are located in the vertical shafts. The heat exchange components include recuperators, precoolers and intermediate coolers, with the recuperators positioned in the shaft either above or below the coolers. The conduit system for the entire coolant cycle downstream from the gas turboset is divided into partial flow paths which include lines connecting the turboset to separate ring segment conduits each of which conduits is connected to a group of the recuperators and another ring segment conduit collects the gas coolant from each group after it has passed through the coolant and returns the gas into a vertical collecting main. In accordance with the invention, the entire gas cycle is divided into several separate groups each of which has short tie lines interconnecting the gas turboset and the heat exchange components in each group. Further, ring segment conduits are associated with the inlet and outlet to each of the groups for providing a compact arrangement for supplying and collecting the gas flowing through the group. In this way an optimum distribution of the gas coolant conduit system is obtained within the pressure tank and it limits the number and the length of the individual conduits required. The hot low-pressure gas issuing from the turbine flows through the recuperators arranged in parallel within each of the groups which laterally enclose the reactor core in a blanket-like arrangement with the gas flowing upwardly and the same direction of flow is maintained in the pre-coolers located within the shafts above the recuperators, the pre-coolers cool the gas to the inlet temperature of the compressor. The arrangement of the individual components is selected so that the plant can be arranged for any desired power increase, that is, the extrapolation to a larger or smaller power unit is readily possible, and such a feature is of great importance in the development of new nulear reactors. Preferably, the gas turboset is located in a horizontally extending tunnel spaced a sufficient distance below the nuclear reactor so that adequate shielding of the turboset from radiation is ensured. For its assembly and disassembly, the turboset is arranged in a so-called plug-in design. The turboset has one shaft, since a single-shaft plant has decisive advantages over a multiple-shaft plant, that is, its operating and regulating behavior are easy to control, only one shaft packing is required in the prestressed concrete tank, and the costs of a single-shaft plant are lower. In this arrangement, the turbine is rigidly coupled with the generator. High temperature gas issuing from the nuclear reactor flows first to a collecting chamber and then over vertically arranged lines directly into the turbine inlet. To increase the efficiency of the nuclear power plant, an intermediate cooling system is provided in the main cycle and preferably is arranged in the vertical shafts of the pressure tank. In a preferred arrangement, the intermediate coolers of the intermediate cooling system are positioned in the spaces below the recuperators in the shafts. Like the recuperators and pre-coolers, the intermediate coolers are combined in groups and each group is connected by a ring segment conduit, which, in turn, is connected to the compressor by a short tie line. Gas flowing from the intermediate coolers in each group is received in a separate ring segment conduit and a tie line carries the gas from the ring segment conduit to the high-pressure stage of the compressor. Downstream from the compressor, the gas flow is again divided over tie lines and directed to separate ring segment conduits. Each of these ring segment conduits is connected to the nests of tubes in one group of the recuperators for proportioning the flow of high-pressure gas and such gas is preheated by the low-pressure gas flowing through the recuperators about the nest of tubes. From the recuperators, radially arranged lines conduct the gas coolant back into the cold gas collecting chamber of the reactor. In this arrangement, the same number of recuperators and pre-coolers are always combined in a group. In a plant rated at about 1,000 MW, two separate groups of recuperators and pre-coolers are provided with each group containing three recuperators and three pre-coolers interconnected by ring segment conduits. This particular arrangement represents the optimum solution, as far as the required conduit system for the plant is concerned. The two groups are symmetrically disclosed in an annular arrangement. If a nuclear power plant of this rating is equipped with intermediate coolers, four such coolers are sufficient with two being arranged in each group and they are connected to the gas flow conduit system by a gas inlet and a gas outlet ring segment conduit. As indicated above, the intermediate coolers improve the efficiency of the plant. However, it is possible to provide a nuclear power plant in which a reduction in efficiency is intentionally accepted by omitting the intermediate coolers for obtaining a number of other advantages. Briefly, the more important of these advantages are as follows: a considerable reduction in the size of the prestressed concrete plant, the elimination of expensive parts (that is, in addition to the intermediate coolers, armored pipes, gas coolant supply means and means for facilitating disassembly), a reduction in the cooling system, and a reduction in cycle pressure losses. In such a nuclear power plant, the gas flow from the compressor is directed into the recuperators. Preferably, a shut-down heat elimination system is provided within the prestressed concrete pressure tank which includes, in a known manner, a blower with or without a recuperator and a cooler. This emergency cooling system, which is independent of the main coolant cycle, ensures the elimination of reactor heat if the turboset fails in a single-shaft gas turbine plant either during down time or in the event of a problem within the reactor plant. The shut-down heat elimination system can be arranged in one of the vertical shafts. For the regulation of the single-shaft gas turboset, in addition to regulation of a bypass and the filling capacity, a frequency regulating system is provided which serves to control the frequency of the gas turboset due to the fluctuation of flow within the mains. The frequency regulating system consists of several gas storage tanks which are preferably housed in the vertical shafts. This arrangement affords particularly short flow paths for the gas as it flows back and forth between the storage tanks and the main cycle as required. Other advantages of this arrangement are the ready availability of the gas and its great safety and compactness. Further, it is preferable if all of the main cycle fittings are arranged within the prestressed concrete pressure tank so that the safety and compactness of the plant is enhanced. The fittings within the tank are arranged so that they are accessible from the exterior of the tank. All of the parts of the nuclear power plant carrying the gas coolant are preferably arranged within a safety tank (containment) into which access can be gained during the operation of the power plant. Further, the safety tank contains the necessary openings for the disassembly of the plant components which require maintenance and repair. The prestressed concrete tank is centered within and spaced inwardly from the safety tank and a revolving crane is located in the upper part of the safety tank for use in the disassembly of the plant components. In a nuclear power plant rated at about 1,000 MW, it is preferably if the safety tank is provided with a cylindrical recess which can be closed in a pressure-and gas-tight manner as an enclosure for the generator rigidly coupled within the gas turboset. If necessary, the generator can be inserted into the cylindrical recess along with its foundation so that it can be disassembled. The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its use, reference should be had to the accompanying drawings and descriptive matter in which there is illustrated and described a preferred embodiment of the invention. |
039880753 | abstract | A method of protecting the cladding of a nuclear fuel element from internal attack and a nuclear fuel element for use in the core of a nuclear reactor are disclosed. The nuclear fuel element has disposed therein an additive of a barium-containing material and the barium-containing material collects reactive gases through chemical reaction or adsorption at temperatures ranging from room temperature up to fuel element plenum temperatures. The additive is located in the plenum of the fuel element and preferably in the form of particles in a hollow container having a multiplicity of gas permeable openings in one portion of the container with the openings being of a size smaller than the size of the particles. The openings permit gases and liquids entering the plenum to contact the particles. The additive is comprised of elemental barium or a barium alloy containing one or more metals in addition to barium such as aluminum, zirconium, nickel, titanium and combinations thereof. |
056087683 | summary | TECHNICAL FIELD This invention relates generally to nuclear reactors, and particularly to the manner in which certain fuel rods in a fuel bundle are secured to a lower tie plate assembly. BACKGROUND Typical fuel bundle assemblies in boiling water nuclear reactors include a plurality of elongated fuel rods supported between upper and lower tie plates. The fuel rods pass through a plurality of fuel rod spacers which provide intermediate support to retain the elongated rods in spaced relation and to restrain the rods from lateral vibration. Each of the fuel rods comprises an elongated tube containing the fissile fuel (such as uranium or plutonium dioxide) in the form of pellets, particles, powder or the like, sealed in the tube by upper and lower end plugs. Most of the lower end plugs are formed with a taper for registration and support within cavities formed in the lower tie plate, while corresponding upper end plugs are formed with extensions which register with support cavities formed in the upper tie plate. These full length rods are spring biased towards the lower tie plate so as to prevent undesirable axial movement of the rods. It would be desirable to eliminate or reduce the number of parts associated with the upper tie plate while at the same time eliminating concerns about coolant flow impact on the conventional protruding lower tie plate end plugs. Each fuel bundle assembly in current designs also contains several fuel rods which have threaded lower end plugs. These would typically include eight tie rods and as many as fourteen partial length fuel rods (PLR's) which terminate short of the upper tie plate. Fuel bundles with PLR's are disclosed, for example, in commonly owned U.S. Pat. Nos. 5,112,570 and 5,017,332. Fuel bundles including fuel rods serving as tie rods with threaded upper and lower end plugs are disclosed, for example, in commonly owned U.S. Pat. Nos. 4,357,298 and 4,420,458. After irradiation, it has been found that many of the threaded rods are not removable without extreme measures which are time consuming and which can damage the rods beyond repair. The apparent cause of the problem is that the lower end plugs of the rods stick in the lower tie plate as the result of corrosion which occurs on the male threads of the Zircaloy end plugs. It will be appreciated that increasing the number of fuel rods which are threadably connected to the lower tie plate will increase the chances of experiencing fuel rod sticking. Thus, there is a need for a simple and cost effective means for minimizing or eliminating the problem. DISCLOSURE OF THE INVENTION It is one object of this invention to eliminate the biasing springs in the upper tie plate normally used to bias non-threaded full length fuel rods toward the lower tie plate. This objective is achieved by utilizing a threaded end plug with all of the full length fuel rods. This invention has for another object the solution of the fuel rod sticking problem described hereinabove. In the exemplary embodiment, the invention comprises replacing the integral threaded Zircaloy end plug shank with a stainless steel connecting shank which is threaded at opposite ends thereof. The stainless steel shank can thus be threaded into a tapped hole in the Zircaloy end plug body at one end, while the other end is threaded into a hole in the lower tie plate. It is an additional feature of this invention that the opposite ends of the connecting shank can be threaded in opposite directions, i.e., one end is formed with a right-hand thread while the other is formed with a left-hand thread. With this arrangement, when torque is applied which loosens the connecting shank in the tie plate, the shank attachment to the end plug body is tightened. Conversely, when torque is applied which tightens the connecting shank in the tie plate, the shank attachment to the end plug body is loosened. Thus, when removing the fuel rod, the stainless steel connecting shank can either remain in the lower tie plate, or remain in the Zircaloy end plug body and thus be removed with the fuel rod. This capability provides a further option in the event threads are frozen in one of the two threading directions. Thus, in its broader aspects, the present invention relates to an end plug for a fuel rod of a nuclear reactor fuel bundle assembly including upper and lower tie plates, the end plug comprising an upper portion constructed of a first alloy material and including an exterior fuel rod receiving surface and a tapped hole in a lower end thereof; and a removable lower portion constructed of a second alloy material and including upper and lower threaded sections, the upper threaded section receivable within the tapped hole and the lower threaded section receivable within a correspondingly threaded hole in the lower tie plate. In another aspect, the invention relates to a fuel bundle assembly for a nuclear reactor having a plurality of fuel rods including a plurality of full length fuel rods extending between upper and lower tie plates and at least one partial length fuel rod extending between the lower tie plate and a spacer located between the upper and lower tie plates, the improvement comprising an end plug for at least the partial length fuel rod, the end plug secured between the partial length fuel rod and the lower tie plate, the end plug comprising an upper portion constructed of a first alloy material and including an exterior partial length fuel rod receiving surface and a tapped hole in a lower end thereof; and a lower portion constructed of a second alloy material and including upper and lower threaded sections, the upper threaded section receivable within the tapped hole and the lower threaded section receivable within a tapped hole in the lower tie plate. In still another aspect, the invention relates to a method of removing a fuel rod from a fuel rod bundle assembly in a nuclear reactor, wherein the fuel rod bundle assembly includes a plurality of fuel rods extending between upper and lower tie plates, the method comprising the steps of: a) providing an end plug for a lower end of at least one of the fuel rods comprising an upper portion constructed of a first alloy material and including an exterior fuel rod receiving surface and a tapped hole in a lower end thereof; and a lower portion constructed of a second alloy material and including upper and lower threaded sections, the upper threaded section receivable within the tapped hole and the lower threaded section receivable within a correspondingly threaded hole in the lower tie plate; and b) rotating the fuel rod in a first direction to separate the fuel rod and the fuel rod end plug from the tie plate. An optional method step is available if the upper and lower sections of the end plug lower portion are threaded in opposite directions. This construction permits rotating the first rod in a second opposite direction to separate the fuel rod and the upper end plug portion from the lower end plug portion, leaving the latter in the lower tie plate. Other objects and advantages of the present invention will become apparent from the detailed description which follows. |
062298771 | summary | BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a radiation image recording and read-out method and apparatus. This invention particularly relates to prevention of deterioration in image quality due to scattered radiation. 2. Description of the Prior Art Operations for recording radiation images are carried out in various fields. For example, radiation images to be used for medical purposes are recorded as in X-ray image recording for medical diagnoses. Also, radiation images to be used for industrial purposes are recorded as in radiation image recording for non-destructive inspection of substances. In order to carry out such operations for recording radiation images, there has heretofore been utilized the so-called "radiography" in which radiation films and intensifying screens are combined with each other. With the radiography, when radiation, such as X-rays, carrying image information of an object impinges upon the intensifying screen, a fluorescent material contained in the intensifying screen absorbs energy from the radiation and produces fluorescence (i.e. instantaneously emitted light). Therefore, the radiation film, which is superposed upon the intensifying screen in close contact therewith, is exposed to the fluorescence produced by the fluorescent material, and a radiation image is thereby formed on the radiation film. In this manner, the radiation image can be directly obtained as a visible image on the radiation film. The applicant proposed radiation image read-out apparatuses, which are referred to as the computed radiography (CR) apparatuses. With the proposed CR apparatuses, a stimulable phosphor sheet, on which a radiation image has been stored, is exposed to stimulating rays, such as a laser beam, which cause it to emit light in proportion to the amount of energy stored thereon during its exposure to radiation. The light emitted by the stimulable phosphor sheet, upon stimulation thereof, is photoelectrically detected and converted into an electric image signal. The image signal having been obtained from the CR apparatuses is utilized for reproducing and displaying a visible image on a cathode ray tube (CRT) display device or for reproducing a visible image on film by a laser printer (LP), or the like. The reproduced image is utilized for making a diagnosis, e.g. for investigating the presence or absence of a diseased part or an injury or for ascertaining the characteristics of the diseased part or the injury. However, in order for a radiation image to be obtained by utilizing radiation film, when the radiation image is to be visualized directly, it is necessary for sensitivity regions of the radiation film and the intensifying screen to be set so as to coincide with each other during the image recording operation. Also, it is necessary for a developing process to be carried out on the radiation film. Therefore, the problems occur in that considerable time and labor are required to obtain the radiation image by utilizing the radiation film. Further, with the apparatuses for photoelectrically reading out a radiation image from radiation film or a stimulable phosphor sheet, the radiation image must be converted into an electric image signal, and image processing must be performed on the image signal such that a visible image having desired image density and contrast may be obtained. For such purposes, it is necessary for the scanning for reading out the radiation image to be performed by utilizing image read-out means. Therefore, operations for obtaining a visible radiation image cannot be kept simple, and considerable time is required to obtain the visible radiation image. Such that the problems encountered with the conventional techniques may be solved, apparatuses utilizing semiconductor devices (referred to as the solid-state radiation detectors), which detect radiation and convert it into an electric signal, have been proposed. As the solid-state radiation detectors, various types of radiation detectors have been proposed. One of typical solid-state radiation detectors comprises two-dimensional image read-out means and a fluorescent material layer (i.e., a scintillator) overlaid upon the two-dimensional image read-out means. The two-dimensional image read-out means comprises an insulating substrate and a plurality of photoelectric conversion devices, which are formed in a two-dimensional pattern on the insulating substrate and each of which corresponds to one pixel. When the scintillator is exposed to radiation carrying image information, it converts the radiation into visible light carrying the image information. (The solid-state radiation detector having such a constitution will hereinbelow be referred to as the "photo conversion type of solid-state radiation detector.") Another typical solid-state radiation detector comprises two-dimensional image read-out means and a radio-conductive material overlaid upon the two-dimensional image read-out means. The two-dimensional image read-out means comprises an insulating substrate and a plurality of charge collecting electrodes, which are formed in a two-dimensional pattern on the insulating substrate and each of which corresponds to one pixel. When the radio-conductive material is exposed to radiation carrying image information, it generates electric charges carrying the image information. (The solid-state radiation detector having such a constitution will hereinbelow be referred to as the "direct conversion type of solid-state radiation detector.") The photo conversion types of solid-state radiation detectors are described in, for example, Japanese Unexamined Patent Publication Nos. 59(1984)-211263 and 2(1990)-164067, PCT International Publication No. WO92/06501, and "Signal, Noise, and Read Out Considerations in the Development of Amorphous Silicon Photodiode Arrays for Radiotherapy and Diagnostic X-ray Imaging," L. E. Antonuk et al., University of Michigan, R. A. Street Xerox, PARC, SPIE Vol. 1443, Medical Imaging V; Image Physics (1991), pp. 108-119. Examples of the direct conversion types of solid-state radiation detectors include the following: (i) A solid-state radiation detector having a thickness approximately 10 times as large as the ordinary thickness, the thickness being taken in the direction along which radiation is transmitted. The solid-state radiation detector is described in, for example, "Material Parameters in Thick Hydrogenated Amorphous Silicon Radiation Detectors," Lawrence Berkeley Laboratory, University of California, Berkeley, Calif. 94720 Xerox Parc. Palo Alto. Calif. 94304. PA1 (ii) A solid-state radiation detector comprising two or more layers overlaid via a metal plate with respect to the direction along which radiation is transmitted. The solid-state radiation detector is described in, for example, "Metal/Amorphous Silicon Multilayer Radiation Detectors, IEE TRANSACTIONS ON NUCLEAR SCIENCE, Vol. 36, No. 2, April 1989. PA1 (iii) A solid-state radiation detector utilizing CdTe, or the like. The solid-state radiation detector is proposed in, for example, Japanese Unexamined Patent Publication No. 1(1989)-216290. PA1 i) a first electrical conductor layer having permeability to recording radiation, PA1 ii) a recording photo-conductive layer, which exhibits photo-conductivity when it is exposed to the recording radiation having passed through the first electrical conductor layer, PA1 iii) a charge transporting layer, which acts approximately as an insulator with respect to electric charges having a polarity identical with the polarity of electric charges occurring in the first electrical conductor layer, and which acts approximately as a conductor with respect to electric charges having a polarity opposite to the polarity of the electric charges occurring in the first electrical conductor layer, PA1 iv) a reading photo-conductive layer, which exhibits photo-conductivity when it is exposed to a reading electromagnetic wave, and PA1 v) a second electrical conductor layer having permeability to the reading electromagnetic wave, PA1 the layers being overlaid in this order. PA1 i) locating a radiation source, which produces radiation, on one side of an object, PA1 ii) locating two-dimensional image read-out means on the other side of the object, the two-dimensional image read-out means comprising stripe-shaped electrodes for reading latent image charges, which carry image information, and PA1 iii) performing an operation for recording and reading out a radiation image of the object, PA1 wherein a grid plate is located between the object and the two-dimensional image read-out means, the grid plate guiding only the radiation, which comes from a specific direction, to the two-dimensional image read-out means, and PA1 the operation for recording and reading out the radiation image of the object is performed in this state. PA1 i) a radiation source, which produces radiation, PA1 ii) two-dimensional image read-out means comprising stripe-shaped electrodes for reading latent image charges, which carry image information, and PA1 iii) a grid plate, which is located between the radiation source and the two-dimensional image read-out means, the grid plate guiding only the radiation, which comes from a specific direction, to the two-dimensional image read-out means. PA1 the grid plate is constituted of radiation absorbing substance regions and radiation-permeable substance regions, which are arrayed alternately at a predetermined grid pitch so as to stand side by side in the direction approximately normal to the longitudinal direction of each stripe-shaped electrode, (i.e., the stripe-shaped electrodes and the radiation absorbing substance regions of the grid plate are arrayed in parallel with each other) and PA1 a spatial frequency fC of the pitch of the stripe-shaped electrodes is at least two times as high as a spatial frequency fG of the grid pitch. PA1 the grid plate is constituted of radiation absorbing substance regions and radiation-permeable substance regions, which are arrayed alternately at a predetermined grid pitch so as to stand side by side in the longitudinal direction of each stripe-shaped electrode, (i.e., the stripe-shaped electrodes and the radiation absorbing substance regions of the grid plate are arrayed so as to intersect perpendicularly to each other) and PA1 a spatial frequency fS of a sampling pitch, at which the latent image charges are read with scanning in the longitudinal direction of each stripe-shaped electrode, is at least two times as high as a spatial frequency fG of the grid pitch. PA1 the grid plate is constituted of radiation absorbing substance regions and radiation-permeable substance regions, which are arrayed alternately at a predetermined grid pitch so as to stand side by side in the direction approximately normal to the longitudinal direction of each stripe-shaped electrode, (i.e., the stripe-shaped electrodes and the radiation absorbing substance regions of the grid plate are arrayed in parallel with each other) and PA1 a difference between a spatial frequency fC of the pitch of the stripe-shaped electrodes and a spatial frequency fG of the grid pitch is at least 1 cycle/mm. PA1 the grid plate is constituted of radiation absorbing substance regions and radiation-permeable substance regions, which are arrayed alternately at a predetermined grid pitch so as to stand side by side in the longitudinal direction of each stripe-shaped electrode, (i.e., the stripe-shaped electrodes and the radiation absorbing substance regions of the grid plate are arrayed so as to intersect perpendicularly to each other) and PA1 a difference between a spatial frequency fS of a sampling pitch, at which the latent image charges are read with scanning in the longitudinal direction of each stripe-shaped electrode, and a spatial frequency fG of the grid pitch is at least 1 cycle/mm. PA1 i) locating a radiation source, which produces radiation, on one side of an object, PA1 ii) locating two-dimensional image read-out means and a radio-conductive material, which is formed on the two-dimensional image read-out means, on the other side of the object, the two-dimensional image read-out means comprising an insulating substrate and a plurality of charge collecting electrodes, which are formed in a two-dimensional pattern on the insulating substrate and each of which corresponds to a single pixel, the radio-conductive material generating electric charges carrying image information when it is exposed to radiation carrying the image information, and PA1 iii) performing an operation for recording and reading out a radiation image of the object, PA1 wherein a grid plate is located between the object and the radio-conductive material, the grid plate guiding only the radiation, which comes from a specific direction, to the radio-conductive material, and PA1 the operation for recording and reading out the radiation image of the object is performed in this state. PA1 i) a radiation source, which produces radiation, PA1 ii) two-dimensional image read-out means comprising an insulating substrate and a plurality of charge collecting electrodes, which are formed in a two-dimensional pattern on the insulating substrate and each of which corresponds to a single pixel, PA1 iii) a radio-conductive material, which is formed on the two-dimensional image read-out means, the radio-conductive material generating electric charges carrying image information when it is exposed to radiation carrying the image information, and PA1 iv) a grid plate, which is located between the radiation source and the radio-conductive material, the grid plate guiding only the radiation, which comes from a specific direction, to the radio-conductive material. PA1 the grid plate is constituted of radiation absorbing substance regions and radiation-permeable substance regions, which are arrayed alternately at a predetermined grid pitch so as to stand side by side in at least either one of the X direction and the Y direction, and PA1 a spatial frequency fD of the charge collecting electrodes in the grid array direction is at least two times as high as a spatial frequency fG of the grid pitch. PA1 the grid plate is constituted of radiation absorbing substance regions and radiation-permeable substance regions, which are arrayed alternately at a predetermined grid pitch so as to stand side by side in at least either one of the X direction and the Y direction, and PA1 a difference between a spatial frequency fD of the charge collecting electrodes in the grid array direction and a spatial frequency fG of the grid pitch is at least 1 cycle/mm. PA1 i) a radiation source, which produces radiation, PA1 ii) two-dimensional image read-out means comprising an insulating substrate and a plurality of photoelectric conversion devices, which are formed in a two-dimensional pattern on the insulating substrate and each of which corresponds to a single pixel, PA1 iii) a fluorescent material, which is formed on the two-dimensional image read-out means, the fluorescent material converting radiation carrying image information into visible light carrying the image information when it is exposed to the radiation carrying the image information, and PA1 iv) a grid plate, which is located between the radiation source and the fluorescent material, the grid plate guiding only the radiation, which comes from a specific direction, to the fluorescent material, PA1 wherein the photoelectric conversion devices of the two-dimensional image read-out means are arrayed at a predetermined pitch in an X direction and at a predetermined pitch in a Y direction, PA1 the grid plate is constituted of radiation absorbing substance regions and radiation-permeable substance regions, which are arrayed alternately at a predetermined grid pitch so as to stand side by side in at least either one of the X direction and the Y direction, and PA1 a spatial frequency fP of the photoelectric conversion devices in the grid array direction is at least two times as high as a spatial frequency fG of the grid pitch. PA1 i) a radiation source, which produces radiation, PA1 ii) two-dimensional image read-out means comprising an insulating substrate and a plurality of photoelectric conversion devices, which are formed in a two-dimensional pattern on the insulating substrate and each of which corresponds to a single pixel, PA1 iii) a fluorescent material, which is formed on the two-dimensional image read-out means, the fluorescent material converting radiation carrying image information into visible light carrying the image information when it is exposed to the radiation carrying the image information, and PA1 iv) a grid plate, which is located between the radiation source and the fluorescent material, the grid plate guiding only the radiation, which comes from a specific direction, to the fluorescent material, PA1 wherein the photoelectric conversion devices of the two-dimensional image read-out means are arrayed at a predetermined pitch in an X direction and at a predetermined pitch in a Y direction, PA1 the grid plate is constituted of radiation absorbing substance regions and radiation-permeable substance regions, which are arrayed alternately at a predetermined grid pitch so as to stand side by side in at least either one of the X direction and the Y direction, and PA1 a difference between a spatial frequency fP of the photoelectric conversion devices in the grid array direction and a spatial frequency fG of the grid pitch is at least 1 cycle/mm. PA1 a) a first thin metal film layer, which acts as a lower electrode, PA1 b) an amorphous silicon nitride insulation layer (a-SiN.sub.x), which blocks passage of electrons and holes, PA1 c) a hydrogenated amorphous silicon photoelectric conversion layer (a-Si:H), PA1 d) an injection blocking layer selected from the group consisting of an n-type injection blocking layer, which blocks injection of hole carriers, and a p-type injection blocking layer, which blocks injection of electron carriers, and PA1 e) a layer selected from the group consisting of a transparent electrode layer, which acts as an upper electrode, and a second thin metal film layer, which is formed on a portion of the injection blocking layer, PA1 the layers being overlaid in this order on the insulating substrate. PA1 the first image processing means performs processing for suppressing the signal components SG, which carry the spatial frequency fG of the grid pitch, on the digital image signal, or the second image processing means performs processing for suppressing the signal components SM, which carry the moire frequency occurring due to the grid, on the digital image signal. PA1 a) the first thin metal film layer, which acts as the lower electrode, PA1 b) the amorphous silicon nitride insulation layer (a-SiN.sub.x), which blocks passage of electrons and holes, PA1 c) the hydrogenated amorphous silicon photoelectric conversion layer (a-Si:H), PA1 d) the injection blocking layer selected from the group consisting of the n-type injection blocking layer, which blocks injection of hole carriers, and the p-type injection blocking layer, which blocks injection of electron carriers, and PA1 e) the layer selected from the group consisting of the transparent electrode layer, which acts as the upper electrode, and the second thin metal film layer, which is formed on a portion of the injection blocking layer, PA1 the layers being overlaid in this order on the insulating substrate. Also, in Japanese Patent Application No. 9(1997)-222114, the applicant proposed a solid-state radiation detector improved over the direct conversion type of solid-state radiation detector. (The proposed solid-state radiation detector will hereinbelow be referred to as the "improved direct conversion type of solid-state radiation detector.") The improved direct conversion type of solid-state radiation detector comprises: In the improved direct conversion type of solid-state radiation detector, latent image charges carrying image information are accumulated at an interface between the recording photo-conductive layer and the charge transporting layer. In the improved direct conversion type of solid-state radiation detector, the latent image charges may be read with a technique, wherein the second electrical conductor layer (i.e., a reading electrode) is constituted of a flat plate-shaped electrode, and the reading electrode is scanned with spot-like reading light, such as a laser beam, the latent image charges being thereby detected. Alternatively, the latent image charges may be read with a technique, wherein the reading electrode is constituted of comb tooth-shaped electrodes (i.e., stripe-shaped electrodes), and the stripe-shaped electrodes are scanned with light, which is produced by a line light source extending along a direction approximately normal to the longitudinal direction of each stripe-shaped electrode, and in the longitudinal direction of each stripe-shaped electrode, the latent image charges being thereby detected. An image signal, which has been obtained from one of various types of solid-state radiation detectors described above, is amplified by an amplifier of the solid-state radiation detector. The amplified image signal is then subjected to predetermined image processing and used for reproducing a visible image on image reproducing means, such as a cathode ray tube (CRT) display device. With such solid-state radiation detectors, a visible radiation image of an object can be reproduced immediately in a real time mode and without complicated operations being required. Therefore, the problems encountered with the aforesaid apparatuses utilizing radiation film, or the like, can be eliminated. With each of the radiation image recording and read-out apparatuses utilizing various types of solid-state radiation detectors described above, in cases where a radiation image of an object is to be read out with the solid-state radiation detector, radiation having been produced by a radiation source is irradiated to the object, and the radiation carrying image information of the object is detected by the solid-state radiation detector. However, the radiation is scattered to various directions in the object, and signal components caused to occur by the scattered radiation mix in the image signal, which carries the image information of the object. Therefore, the problems occur in that a sufficiently high signal-to-noise ratio cannot be obtained, or high resolution cannot be obtained. As a result, a visible image having good image quality cannot be obtained. SUMMARY OF THE INVENTION The primary object of the present invention is to provide a radiation image recording and read-out method utilizing a solid-state radiation detector, wherein deterioration in image quality due to scattered radiation is prevented. Another object of the present invention is to provide an apparatus for carrying out the radiation image recording and read-out method. The present invention provides a first radiation image recording and read-out method, comprising the steps of: The present invention also provides a first radiation image recording and read-out apparatus for carrying out the first radiation image recording and read-out method in accordance with the present invention. The first radiation image recording and read-out apparatus in accordance with the present invention is provided with the improved direct conversion type of solid-state radiation detector described above and will hereinbelow be referred to as the "improved direct conversion type of radiation image recording and read-out apparatus." Specifically, the present invention also provides a first radiation image recording and read-out apparatus, comprising: The first radiation image recording and read-out apparatus in accordance with the present invention should preferably be constituted such that the stripe-shaped electrodes of the two-dimensional image read-out means are arrayed at a predetermined pitch so as to stand side by side in a direction, which is approximately normal to a longitudinal direction of each stripe-shaped electrode, The term "spatial frequency fC of a pitch of stripe-shaped electrodes" as used herein means the frequency represented by the formula of fC=1/PC, in which PC represents the pitch of the stripe-shaped electrodes. Also, the term "spatial frequency fG of a grid pitch" as used herein means the frequency represented by the formula of fG=1/PG, in which PG represents the grid pitch. (This also applies to radiation image recording and read-out apparatuses in accordance with the present invention provided with two-dimensional image read-out means constituting other conversion types of solid-state radiation detectors, which will be described later.) Also, the first radiation image recording and read-out apparatus in accordance with the present invention should preferably be constituted such that the stripe-shaped electrodes of the two-dimensional image read-out means are arrayed at a predetermined pitch so as to stand side by side in a direction, which is approximately normal to a longitudinal direction of each stripe-shaped electrode, The term "spatial frequency fS of a sampling pitch" as used herein means the frequency represented by the formula of fS=1/PS, in which PS represents the sampling pitch. Further, the first radiation image recording and read-out apparatus in accordance with the present invention may be constituted such that the stripe-shaped electrodes of the two-dimensional image read-out means are arrayed at a predetermined pitch so as to stand side by side in a direction, which is approximately normal to a longitudinal direction of each stripe-shaped electrode, Furthermore, the first radiation image recording and read-out apparatus in accordance with the present invention should preferably be constituted such that the stripe-shaped electrodes of the two-dimensional image read-out means are arrayed at a predetermined pitch so as to stand side by side in a direction, which is approximately normal to a longitudinal direction of each stripe-shaped electrode, The present invention further provides a second radiation image recording and read-out method, comprising the steps of: The present invention still further provides a second radiation image recording and read-out apparatus for carrying out the second radiation image recording and read-out method in accordance with the present invention. The second radiation image recording and read-out apparatus in accordance with the present invention is provided with the direct conversion type of solid-state radiation detector described above and will hereinbelow be referred to as the "direct conversion type of radiation image recording and read-out apparatus." Specifically, the present invention still further provides a second radiation image recording and read-out apparatus, comprising: The second radiation image recording and read-out apparatus in accordance with the present invention should preferably be constituted such that the charge collecting electrodes of the two-dimensional image read-out means are arrayed at a predetermined pitch in an X direction and at a predetermined pitch in a Y direction, The term "grid array direction" as used herein means the direction in which the radiation absorbing substance regions and the radiation-permeable substance regions are arrayed alternately. Also, the term "spatial frequency fD of charge collecting electrodes in a grid array direction" as used herein means the frequency represented by the formula of fD=1/PD, in which PD represents the pitch of the charge collecting electrodes in the grid pitch direction. Also, the second radiation image recording and read-out apparatus in accordance with the present invention may be constituted such that the charge collecting electrodes of the two-dimensional image read-out means are arrayed at a predetermined pitch in an X direction and at a predetermined pitch in a Y direction, The present invention also provides a third radiation image recording and read-out apparatus, which is provided with the photo conversion type of solid-state radiation detector described above and will hereinbelow be referred to as the "photo conversion type of radiation image recording and read-out apparatus." Specifically, the present invention also provides a third radiation image recording and read-out apparatus, comprising: The term "spatial frequency fP of photoelectric conversion devices in a grid array direction" as used herein means the frequency represented by the formula of fP=1/PP, in which PP represents the pitch of the photoelectric conversion devices in the grid pitch direction. The present invention further provides a fourth radiation image recording and read-out apparatus, comprising: In the third and fourth radiation image recording and read-out apparatuses in accordance with the present invention, each of the photoelectric conversion devices should preferably comprise: The first, second, third, and fourth radiation image recording and read-out apparatuses in accordance with the present invention should preferably be provided with first image processing means for suppressing signal components SG, which are contained in an image signal having been detected by the two-dimensional image read-out means and which carry a spatial frequency fG of a grid pitch. Also, in cases where the first, second, third, and fourth radiation image recording and read-out apparatuses in accordance with the present invention are not constituted such that a spatial frequency f0 of a sensor is at least two times as high as the spatial frequency fG of the grid pitch, they should preferably be provided with second image processing means for suppressing signal components SM, which are contained in an image signal having been detected by the two-dimensional image read-out means and which carry a moire frequency occurring due to the grid. In the cases of the improved direct conversion type of solid-state radiation detector, the term "spatial frequency f0 of a sensor" as used herein means the spatial frequency fC of the pitch of the stripe-shaped electrodes or the spatial frequency fS of the sampling pitch. In the cases of the direct conversion type of solid-state radiation detector, the term ,spatial frequency f0 of a sensor" as used herein means the spatial frequency fD of the charge collecting electrodes in the grid array direction. In the cases of the photo conversion type of solid-state radiation detector, the term "spatial frequency f0 of a sensor" as used herein means the spatial frequency fP of the photoelectric conversion devices in the grid array direction. In cases where the grid pitch PG and a sensor pitch P0 are different from each other, even if uniform radiation is irradiated, a periodical striped pattern, i.e. a moire, occurs in the image due to a spatial phase difference. The term "moire frequency occurring due to a grid" as used herein means the repetition frequency of the striped pattern in the moire phenomenon. Specifically, in the cases of the improved direct conversion type of radiation image recording and read-out apparatus, the term "moire frequency occurring due to a grid" as used herein means the difference between the spatial frequency fC of the pitch of the stripe-shaped electrodes and the spatial frequency fG of the grid pitch, or the difference between the spatial frequency fS of the sampling pitch, at which the latent image charges are read with scanning in the longitudinal direction of each stripe-shaped electrode, and the spatial frequency fG of the grid pitch. In the cases of the direct conversion type of radiation image recording and read-out apparatus, the term "moire frequency occurring due to a grid" as used herein means the difference between the spatial frequency fD of the charge collecting electrodes in the grid array direction and the spatial frequency fG of the grid pitch. In the cases of the photo conversion type of radiation image recording and read-out apparatus, the term "moire frequency occurring due to a grid" as used herein means the difference between the spatial frequency fP of the photoelectric conversion devices in the grid array direction and the spatial frequency fG of the grid pitch. In the cases of the improved direct conversion type of solid-state radiation detector, the term "sensor pitch P0" as used herein means the pitch PC of the stripe-shaped electrodes or the sampling pitch PS. In the cases of the direct conversion type of solid-state radiation detector, the term "sensor pitch P0" as used herein means the pitch PD of the charge collecting electrodes in the grid pitch direction. In the cases of the photo conversion type of solid-state radiation detector, the term "sensor pitch P0" as used herein means the pitch PP of the photoelectric conversion devices in the grid pitch direction. Further, the radiation image recording and read-out apparatuses in accordance with the present invention should preferably be constituted such that the apparatuses further comprise an analog-to-digital converter for converting the image signal, which has been detected by the two-dimensional image read-out means, into a digital image signal, and With the first radiation image recording and read-out method and the first radiation image recording and read-out apparatus in accordance with the present invention, which are of the improved direct conversion type, the grid plate is located between the radiation source and the two-dimensional image read-out means, the grid plate guiding only the radiation, which comes from a specific direction, to the two-dimensional image read-out means. Therefore, the radiation scattered in the object is absorbed by the radiation absorbing substance regions of the grid plate. As a result, the problems can be prevented from occurring in that the image quality becomes bad due to the scattered radiation. With the second radiation image recording and read-out method and the second radiation image recording and read-out apparatus in accordance with the present invention, which are of the direct conversion type, the grid plate is located between the radiation source and the radio-conductive material, the grid plate guiding only the radiation, which comes from a specific direction, to the radio-conductive material. Therefore, as in the first radiation image recording and read-out method and the first radiation image recording and read-out apparatus in accordance with the present invention, the problems can be prevented from occurring in that the image quality becomes bad due to the scattered radiation. With all of the radiation image recording and read-out apparatuses in accordance with the present invention, in cases where the spatial frequency f0 of the sensor is at least two times as high as the spatial frequency fG of the grid pitch, the striped pattern occurring in the image due to the moire phenomenon can be rendered imperceptible in accordance with the so-called "sampling theorem." Also, in cases where the signal components SG, which are contained in the image signal having been detected by the two-dimensional image read-out means and which carry the spatial frequency fG of the grid pitch, are suppressed, the grid pattern occurring in the image can be rendered visually imperceptible. Also, with all of the radiation image recording and read-out apparatuses in accordance with the present invention, in cases where they are not constituted such that the spatial frequency f0 of the sensor is at least two times as high as the spatial frequency fG of the grid pitch, the moire frequency may be rendered to be at least 1 cycle/mm, and the number of stripes periodically occurring in the image due to the moire phenomenon may thereby be decreased. In this manner, the striped pattern can be rendered visually imperceptible. In cases where the first, second, third, and fourth radiation image recording and read-out apparatuses in accordance with the present invention are not constituted such that the spatial frequency f0 of the sensor is at least two times as high as the spatial frequency fG of the grid pitch, the signal components SM, which are contained in the image signal having been detected by the two-dimensional image read-out means and which carry the moire frequency occurring due to the grid, may be suppressed. In this manner, the moire occurring in the image can be rendered visually imperceptible. In such cases, there is no risk that the important components of at most 1 cycle/mm, which are contained in the image information, are lost. With the third and fourth radiation image recording and read-out apparatuses in accordance with the present invention, which are of the photo conversion type, each of the photoelectric conversion devices may comprise: In such cases, the two-dimensional image read-out means having a large area and high performance can be produced with an ordinary thin film forming apparatus, such as a chemical vapor deposition (CVD) apparatus or a sputtering apparatus. Also, the two-dimensional-image read-out means can be produced with a small number of simple processes, at a high yield, and at a low cost. |
abstract | A laser atom probe (100) situates a counter electrode between a specimen mount and a detector (106), and provides a laser (116) having its beam (122) aligned to illuminate the specimen (104) through the aperture (110) of the counter electrode (108). The detector, specimen mount (102), and then be pulsed to bring the specimen to ionization. The timing of the laser pulses may be used to determine ion departure and arrival times allowing determination of the mass-to-charge ratios of the ions, thus their identities. Automated alignment methods are described wherein the laser is automatically directed to areas of interest. |
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053655672 | abstract | A K-edge filter whose main portion functions as a filter member and is made of a material containing at least two kinds of elements, and an X-ray apparatus is fabricated so as to include such a K-edge filter. |
053217306 | abstract | A process for oxidation of hydrogen in a containment of a nuclear reactor plant with the aid of finely distributed catalyst particles, includes spraying catalyst particles in the form of a solution or suspension inside or outside the containment. The sprayed solution or suspension is subsequently dried by heating inside or outside the containment to produce aerosols. The aerosols produced outside are introduced into the containment. A device for oxidation of hydrogen in a containment of a nuclear reactor plant with the aid of finely distributed catalyst particles includes a container for receiving catalyst particles in the form of a solution or suspension. A distributor configuration is connected to the container for spraying the solution or suspension inside or outside the containment. A heater dries the sprayed solution or suspension before the solution or suspension is released into the containment. |
description | This application claims priority from Japanese Patent Application No. 2014-009679, filed on Jan. 22, 2014, the entire subject matter of which is incorporated herein by reference. 1. Technical Field The present invention relates to a charged particle beam apparatus and a processing method. 2. Description of the Related Art Hitherto, a processing apparatus that performs processing by beam irradiation has been known (for example, see JP-B2-1993-004660). It is also known that processing accuracy is improved by increasing a field-of-view magnification and reducing a beam diameter. However, when a field-of-view magnification is increased in order to perform processing with a high level of accuracy, a processing region may not fall within one field of view (FOV). FIGS. 12A and 12B are a schematic diagram showing an example of a screen displayed on a display unit of a processing apparatus which is known in the related art. FIG. 12A is a schematic diagram showing an example of a screen on which a processing region is displayed at a low magnification. In the example shown in the drawing, the entirety of a processing region 901 is displayed. FIG. 12B is a schematic diagram showing an example of a screen on which a processing region is displayed at a high magnification. In the example shown in the drawing, only a region 902 which is a portion of the processing region 901 is displayed. In this manner, when a field-of-view magnification is increased, the entire processing region may not be displayed within one screen. In addition, the upper limit of the number of beams with which a range capable of being displayed on one screen can be irradiated is determined. Accordingly, when a beam is narrowed in order to increase processing accuracy and processing is performed at a magnification for making a processing region fall within one screen in a state where a beam diameter is smaller than a pixel pitch, a portion which is not irradiated with the beam is generated within a processing range. FIG. 13 is a schematic diagram showing a processing example in a case where processing is performed at a magnification for making a processing region fall within one screen in a state where a beam diameter is smaller than a pixel pitch, using a processing apparatus which is known in the related art. In the example shown in the drawing, a portion which is not irradiated with a beam remains, and thus a processing result became spotted. The present invention has been made in view of the above-described circumstances, and one of objects of the present invention is to provide a charged particle beam apparatus and a processing method which are capable of displaying the entirety of a processing region within one screen and performing processing with a higher level of accuracy. According to an exemplary embodiment of the present invention, there is provided a charged particle beam apparatus including: a charged particle beam column configured to irradiate a charged particle beam; and a controller configured to control the charged particle beam column to irradiate the charged particle beam at a first pixel interval for a first region and to irradiate the charged particle beam at a second pixel interval different from the first pixel interval for a second region included in the first region. According to another exemplary embodiment of the present invention, there is provided a processing method including: controlling a charged particle beam column to irradiate the charged particle beam at a first pixel interval for a first region; and controlling the charged particle beam column to irradiate the charged particle beam at a second pixel interval different from the first pixel interval for a second region included in the first region. Hereinafter, embodiments of the present invention will be described with reference to the drawings. (First Embodiment) Hereinafter, a first embodiment according to the present invention will be described with reference to the accompanying drawings. FIG. 1 is a schematic diagram showing the configuration of a processing apparatus (charged particle beam apparatus) according to this embodiment. In the example shown in the drawing, a processing apparatus 1 includes an ion beam column 11 (charged particle beam column), a sample chamber 12, an ion beam control unit 13, a secondary electron detector 14, an image forming unit 15, a control unit 16, an input unit 17, and a display unit 18. The ion beam column 11 performs irradiation with an ion beam 111. The sample chamber 12 accommodates a sample stage 121. The sample stage 121, which is a stage for mounting a sample 1211, can move, be inclined, and rotate at least in a two-dimensional direction. The ion beam column 11 is disposed so as to be able to irradiate the sample 1211 mounted on the sample stage 121 with the ion beam 111. The sample 1211 is an object to be processed. When the sample 1211 is irradiated with the ion beam 111 by the ion beam column 11, the sample generates secondary electrons. The ion beam control unit 13 outputs an irradiation signal to the ion beam column 11 and causes the ion beam column 11 to perform irradiation with the ion beam 111. In addition, the ion beam control unit 13 controls an input of the ion beam column 11 to a lens electrode and a scanning electrode to thereby control an irradiation position, a beam diameter, and the amount of beam irradiation of the ion beam 111 with which the ion beam column 11 performs irradiation. The secondary electron detector 14 detects the secondary electrons generated by the sample 1211. The image forming unit 15 forms an SIM image using a signal for performing scanning with the ion beam 111 and a signal of the secondary electrons detected by the secondary electron detector 14. The control unit 16 controls units included in the processing apparatus 1. The input unit 17 includes, for example, a keyboard and the like and receives various types of input from an operator or the like. The display unit 18 is, for example, a liquid crystal display and displays an SEM image formed by the image forming unit 15, and the like. Next, the control unit 16 will be described. FIG. 2 is a block diagram showing the configuration of the control unit 16 according to this embodiment. In the example shown in the drawing, the control unit 16 includes at least a beam position control unit 161 and a bitmap storage unit 162. The beam position control unit 161 controls the ion beam control unit 13 and controls an irradiation position, a beam diameter, and the amount of beam irradiation of the ion beam 111 with which the ion beam column 11 performs irradiation. The bitmap storage unit 162 stores a bitmap showing a position to be irradiated with the ion beam 111. Meanwhile, for example, the beam position control unit 161 and the ion beam control unit 13 are equivalent to a controller recited in claims. Next, a processing method of the processing apparatus 1 will be described. One irradiation unit performing irradiation with the ion beam 111 will be referred to as “one pixel”, and one irradiation region which is a set of irradiation units will be referred to as “one frame”. In this embodiment, scanning is performed multiple times by shifting a position irradiated with the ion beam 111, and the inside of one pixel is irradiated with the ion beam 111 multiple times. FIGS. 3A to 3D are schematic diagrams showing positions irradiated with the ion beam 111 by the processing apparatus 1 in this embodiment. FIG. 3A is a schematic diagram showing a position irradiated with the ion beam 111 by the ion beam column 11 during a first scanning. In the example shown in the drawing, the position irradiated with the ion beam 111 by the ion beam column 11 during the first scanning is an upper left position of each pixel. FIG. 3B is a schematic diagram showing a position irradiated with the ion beam 111 by the ion beam column 11 during a second scanning. In the example shown in the drawing, the position irradiated with the ion beam 111 by the ion beam column 11 during the first scanning is an upper right position of each pixel. FIG. 3C is a schematic diagram showing the position irradiated with the ion beam 111 by the ion beam column 11 during a third scanning. In the example shown in the drawing, the position irradiated with the ion beam 111 by the ion beam column 11 during the third scanning is a lower left position of each pixel. FIG. 3D is a schematic diagram showing the position irradiated with the ion beam 111 by the ion beam column 11 during a fourth scanning. In the example shown in the drawing, the position irradiated with the ion beam 111 by the ion beam column 11 during the fourth scanning is a lower right position of each pixel. In this manner, an irradiation process (scanning) of performing irradiation with the ion beam 111 once for each pixel region designated in a bitmap is performed multiple times while moving an irradiation position so that the irradiation position is different within each pixel region. That is, irradiation with the ion beam 111 is performed in units of sub-pixels within each pixel region. In the examples shown in FIG. 3, four sub-pixels are included in each pixel region. Thereby, it is possible to reduce portions which are not irradiated with the ion beam 111. Meanwhile, the number of times of scanning (the number of irradiation processes) is four in the examples shown in FIG. 3, but is not limited thereto. For example, an FOV including the entire processing region is set to FOV_A. In addition, an FOV equivalent to a target level of accuracy is set to FOV_B. In this case, an amount by which a position irradiated with the ion beam 111 is shifted for one scanning (the amount of shifting, the amount of sub-pixels) is a pixel size of FOV_B. In addition, the total number of times of scanning is ((FOV_A)/(FOV_B)) by ((FOV_A)/(FOV_B)). For example, when the irradiation position of the ion beam 111 can be moved in units of one-sixteenth of one pixel, scanning is performed 256 times while shifting the irradiation position of the ion beam 111 in units of one-sixteenth of one pixel both crosswise and lengthwise, and thus it is possible to perform processing with a higher level of accuracy. In addition, since the same scan data is used during each scanning, it is possible to perform processing without increasing the amount of data. For example, when scan data is created so that the inside of one pixel is irradiated with the ion beam 111 multiple times through one scanning, the amount of data is increased further than scan data for irradiating the inside of one pixel with the ion beam 111 once through one scanning. However, in this embodiment, since scanning is performed multiple times by shifting a position irradiated with the ion beam 111 using scan data for irradiating the inside of one pixel with the ion beam 111 once through one scanning, it is possible to prevent an increase in the amount of scan data. In this embodiment, the irradiation position of the ion beam 111 is accurately aligned by performing drift correction. During the drift correction, the irradiation position of the ion beam 111 is adjusted based on a correction mark (point hole) which is determined in the sample 1211 in advance and is corrected so that a processing position is not shifted. In this manner, the correction is performed based on the correction mark during the drift correction. For this reason, if the position of the correction mark is not captured with a high level of accuracy, the accuracy of the drift correction deteriorates. The region including a position at which the correction mark is provided is set as a correction mark detection region. Consequently, in this embodiment, when an image in the vicinity of the correction mark is acquired, scanning is performed by reducing a pixel interval during the scanning, and thus the position of the correction mark is captured with a high level of accuracy. FIGS. 4A and 4B are schematic diagrams showing a relationship between a correction mark and a pixel interval during scanning. FIG. 4A is a schematic diagram showing a relationship between a correction mark and a pixel interval in a case where the pixel interval during scanning is large. In the example shown in the drawing, there is only one pixel 402 among pixels including more than half of a correction mark 401 within a pixel, and the pixel deviates from the centroid of the correction mark 401. FIG. 4B is a schematic diagram showing a relationship between a correction mark and a pixel interval in a case where the pixel interval during scanning is smaller. In the example shown in the drawing, there are nine pixels 403 to 411 among pixels including more than half of a correction mark 401 within a pixel, and the pixels deviate a little from the centroid of the correction mark 401. In this manner, scanning is performed by reducing the pixel interval when acquiring an image in the vicinity of the correction mark 401, and thus it is possible to capture the position of the correction mark 401 with a high level of accuracy. FIG. 5 is a schematic diagram showing a relationship between a field-of-view region with a low magnification A and a field-of-view region with a high magnification C in this embodiment. In the example shown in the drawing, a field-of-view region 500 with a magnification A for making the entirety of a processing region 501 fall within one screen is shown. The processing region 501 and a drift correction region 502 are included in the field-of-view region 500. In addition, a magnification for making the entire drift correction region 502 fall within one screen is set to a magnification C. That is, a field-of-view region 503 having the magnification C is the same region as the drift correction region 502. The correction mark 401 is included within the drift correction region 502. FIG. 6 is a schematic diagram showing a relationship with an image which is acquired by the processing apparatus 1 in this embodiment. In the example shown in the drawing, an image within the drift correction region 502 is enlarged and displayed, as compared with the drawing shown in FIG. 5. This is because a pixel interval during the scanning of the inside of the drift correction region 502 is narrowed further than during processing. Meanwhile, parts other than the image within the drift correction region 502 are the same as those in the drawing shown in FIG. 5. For example, an FOV of the field-of-view region 500 including the entire processing region 501 is set to FOV_A. In addition, an FOV of the drift correction region 502 (field-of-view region 503) is set to FOV_C. In this case, the size of a scanned image of the drift correction region 502 is set to (FOV_A)/(FOV_C) times both crosswise and lengthwise. Accordingly, the number of pixels of the scanned image of the drift correction region 502 is set to ((FOV_A)/(FOV_C)) times. Meanwhile, a bitmap becomes larger in accordance with the size of the processing region 501 in the scanning during processing. However, only the scanning of the drift correction region 502 is performed in the scanning during drift correction. For this reason, the bitmap falls within a creatable size even with a high-definition pixel interval. For example, when a scanning region during the correction of the drift correction region 502 is set to 100 by 100 pixels and a pixel interval during correction scanning is set to one-eighth of the pixel during the processing, the size of the bitmap is set to 800 by 800 pixels. This size is smaller than the size of a screen displayed on the display unit 18 and is a size for which scanning is capable of being performed. Next, a processing procedure of the processing apparatus 1 will be described. FIG. 7 is a flow chart showing a processing procedure of the processing apparatus 1 according to this embodiment. Meanwhile, in this embodiment, when processing is performed, the field-of-view region 500 including the entire processing region 501 is set. Step S101: The beam position control unit 161 reads out a bitmap stored in the bitmap storage unit 162 and creates a scanning bitmap. Thereafter, the process proceeds to the process of step S102. Step S102: The beam position control unit 161 performs drift correction. Thereafter, the process proceeds to the process of step S103. A detailed process procedure of the drift correction will be described later. Step S103: The beam position control unit 161 controls the ion beam column 11 through the ion beam control unit 13, performs the scanning of a region which is designated in the scanning bitmap created in the process of step S101, and processes the sample 1211. Thereafter, the process proceeds to the process of step S104. Step S104: The beam position control unit 161 shifts the scanning bitmap by the amount of sub-pixels (an amount by which a position irradiated with the ion beam 111 is shifted for each scanning, the amount of shifting). Thereafter, the process proceeds to the process of step S105. Step S105: The beam position control unit 161 determines whether or not the inside of each pixel to be processed has been completely covered by the irradiation with the ion beam 111. That is, it is determined whether or not the inside of each pixel to be processed has been completely covered by the irradiation with the ion beam 111 for one pixel. When it is determined that the inside of each pixel to be processed has been completely covered by the irradiation with the ion beam 111 for one pixel, the process proceeds to the process of step S106. Otherwise, the process returns to the process of step S103. Step S106: The beam position control unit 161 determines whether or not a target number of times of scanning has been performed. When the beam position control unit 161 determines that the target number of times of scanning has been performed, the process is terminated. Otherwise, the process returns to the process of step S102. Meanwhile, in the example shown in FIG. 7, the drift correction process (process of step S102) is performed whenever one pixel is completely covered by the irradiation with the ion beam 111, but the invention is not limited thereto. For example, the number and intervals of drift correction processes vary depending on a processing material and a target processing accuracy. Accordingly, when the number of drift correction processes is increased, the drift correction process may be performed before one pixel is completely covered by the irradiation with the ion beam 111. In addition, when the number of drift correction processes is reduced, the drift correction process may be performed after a plurality of frames are scanned. Next, a process procedure of the drift correction of the processing apparatus 1 will be described. FIG. 8 is a flow chart showing a drift correction process procedure of the processing apparatus 1 according to this embodiment. Step S201: the beam position control unit 161 changes a pixel pitch to 1/n and controls the ion beam column 11 through the ion beam control unit 13 to perform the scanning of the drift correction region 502. Thereafter, the process proceeds to the process of step S202. Step S202: The beam position control unit 161 calculates the amount of drift correction. Thereafter, the process proceeds to the process of step S203. Meanwhile, for example, a method known in the related art is used as a method of calculating the amount of drift correction. In addition, the amount of drift correction at this point in time is the amount of drift correction when a pixel pitch is set to 1/n times. Step S203: The beam position control unit 161 sets the amount of drift correction calculated in the process of step S202 to 1/n and converts the amount of drift correction into the amount of drift correction in the field-of-view region 500 including the entire processing region 501. Thereafter, the process proceeds to the process of step S204. Step S204: The beam position control unit 161 shifts the scanning bitmap by the amount of drift correction which is converted in the process of step S203. Thereafter, the drift correction process is terminated. As described above, according to this embodiment, the beam position control unit 161 controls the ion beam column 11 through the ion beam control unit 13 to perform a plurality of irradiation processes (scanning) of performing irradiation with the ion beam 111 once for each pixel region designated in the bitmap while moving an irradiation position so that the irradiation position is different within each pixel region. Thereby, it is possible to reduce portions which are not irradiated with the ion beam 111. In this embodiment, when an image in the vicinity (drift correction region 502) of the correction mark 401 is acquired during the drift correction, the pixel interval during scanning is reduced. Thereby, it is possible to capture the position of the correction mark 401 with a high level of accuracy. Therefore, it is possible to perform the drift correction with a higher level of accuracy. (Second Embodiment) Next, a second embodiment will be described. For example, the size of a screen is 800 by 800 pixels, and the above-mentioned ratio of a magnification A which is a low magnification to a magnification C which is a high magnification is set to eight times. In this case, in order to make an image of an enlarged drift correction region 502 fall within one screen, the drift correction region 502 can be secured up to a maximum of 100×100 pixels. Accordingly, when there is a desire to secure the length along an edge as in edge drift correction, it is assumed that the size of the drift correction region 502 is not sufficient. Consequently, in this embodiment, also when the scanning of the drift correction region 502 is performed, an image with a high magnification is acquired by performing the scanning while performing a shift by a pixel pitch with a magnification C which is a high magnification and by synthesizing acquired images, similarly to the case of the processing of a processing region 501. Meanwhile, the configuration of a processing apparatus 1 according to this embodiment is the same as the configuration of the processing apparatus 1 according to the first embodiment. In addition, a processing procedure of the processing apparatus 1 according to this embodiment is the same as that in the first embodiment, except for a drift correction process. Next, a process procedure of the drift correction of the processing apparatus 1 according to this embodiment will be described. FIG. 9 is a flow chart showing a drift correction process procedure of the processing apparatus 1 according to this embodiment. Step S301: A beam position control unit 161 controls an ion beam column 11 through an ion beam control unit 13 and performs the scanning of the drift correction region 502. Thereafter, the process proceeds to the process of step S302. Step S302: The beam position control unit 161 shifts a bitmap of the drift correction region 502 by an amount of sub-pixels (an amount by which a position irradiated with an ion beam 111 is shifted for each scanning, the amount of shifting). Thereafter, the process proceeds to the process of step S303. Step S303: The beam position control unit 161 determines whether or not the scanning for one pixel (m wide by m long) has been performed. When it is determined that the scanning for one pixel has been performed, the process proceeds to the process of step S304. Otherwise, the process returns to the process of step S301. Step S304: An image forming unit 15 generates m by m images of the drift correction region 502 based on the result of the scanning performed m wide by m long. In addition, the image forming unit 15 synthesizes the generated m by m images of the drift correction region 502 to thereby generate an image having a size of m by m of the drift correction region 502. Thereafter, the process proceeds to the process of step S305. Step S305: The beam position control unit 161 calculates the amount of drift correction based on the image having a size of m by m of the drift correction region 502 which is generated in the process of step S304. Thereafter, the process proceeds to the process of step S306. Meanwhile, for example, a method known in the related art is used as a method of calculating the amount of drift correction. In addition, the amount of drift correction at this point in time is the amount of drift correction when a pixel pitch is set to 1/m times. Step S306: The beam position control unit 161 sets the amount of drift correction calculated in the process of step S305 to 1/m, and converts the amount of drift correction into the amount of drift correction in a field-of-view region 500 including the entire processing region 501. Thereafter, the process proceeds to the process of step S307. Step S307: The beam position control unit 161 shifts a scanning bitmap by the amount of drift correction which is converted in the process of step S306. Then, the drift correction process is terminated. As described above, according to this embodiment, also when the scanning of the drift correction region 502 is performed, an image with a high magnification is acquired by performing the scanning while performing a shift by a pixel pitch with a magnification C which is a high magnification and by synthesizing acquired images, similarly to the case of the processing of a processing region 501. Thereby, in a method of scanning only the drift correction region 502 at a high magnification, it is possible to acquire an image with a high magnification of the drift correction region 502 also in a case where the size of the drift correction region 502 is not sufficient. Therefore, it is possible to perform drift correction with a higher level of accuracy. (Third Embodiment) Next, a third embodiment will be described. Even when a processing region 501 completely falls within a field-of-view region 500 with a low magnification (magnification A), a drift correction region 502 may not be provided in the vicinity of the processing region 501. Even in this case, if the drift correction region 502 is determined in the wide field-of-view region 500 with a low magnification (magnification A), it is possible to perform accurate processing with a high magnification (magnification C). However, in this case, since the drift correction region 502 becomes distant from the processing region 501, a deviation occurs in the shape of a beam, which results in a concern of accuracy not being improved. Meanwhile, also in case where the drift correction region 502 and the processing region 501 are separated from each other, the positioning of the drift correction region 502 in a horizontal or vertical direction with respect to the processing region 501 results in only longitudinal and transverse deviations of an ion beam 111. Consequently, in this embodiment, the amounts of drift correction in longitudinal and transverse directions are independently measured, and thus the amount of drift is calculated with a high level of accuracy. Meanwhile, the configuration of a processing apparatus 1 according to this embodiment is the same as the configuration of the processing apparatus 1 according to the first embodiment. In addition, a processing procedure of the processing apparatus 1 according to this embodiment is the same as that in the first embodiment, except that the amounts of drift correction in longitudinal and transverse directions are independently measured. FIG. 10 is a schematic diagram showing a relationship between a processing region 501, a longitudinal drift correction region 502-1, and a transverse drift correction region 502-2 in this embodiment. In the example shown in the drawing, a field-of-view region 500 with a magnification A for making all of the processing region 501, the longitudinal drift correction region 502-1, and the transverse drift correction region 502-2 fall within one screen is shown. The processing region 501, the longitudinal drift correction region 502-1, and the transverse drift correction region 502-2 are included in the field-of-view region 500. In addition, a magnification for making the entire longitudinal drift correction region 502-1 fall within one screen is set to a magnification C. In addition, a magnification for making the entire transverse drift correction region 502-2 fall within one screen is set to a magnification C. That is, a field-of-view region 503-1 with a magnification C is the same region as the longitudinal drift correction region 502-1. In addition, a field-of-view region 503-2 with a magnification C is the same region as the transverse drift correction region 502-2. A correction mark 401-1 is included in the longitudinal drift correction region 502-1. A correction mark 401-2 is included in the transverse drift correction region 502-2. In this manner, the longitudinal drift correction region 502-1 and the transverse drift correction region 502-2 are provided, and the amounts of drift correction in longitudinal and transverse directions are independently measured, and thus it is possible to calculate the amount of drift with a high level of accuracy. (Fourth Embodiment) Next, a fourth embodiment will be described. In the first embodiment, a case where a beam diameter is smaller than a pixel size has been described, but the invention is not limited thereto. For example, even when the beam diameter is larger than the pixel size, it is confirmed that the reliability of an image obtained by narrowing a beam interval is increased. From this, even when both the processing region 501 and the drift correction region 502 fall within a field of view with a high magnification (magnification C), an image of the drift correction region 502 becomes finer by using the drift correction described in the first embodiment, and thus it is possible to expect to increase the accuracy of drift correction. FIG. 11 is a schematic diagram showing a relationship between the processing region 501 and the drift correction region 502 in this embodiment. In the example shown in the drawing, a field-of-view region 500 with a low magnification (magnification A) is shown. A drift correction region 502 is included in the field-of-view region 500. A processing region 501 is included in the drift correction region 502. That is, both the processing region 501 and the drift correction region 502 fall within a field of view 503 with a high magnification (magnification C). In this manner, even when both the processing region 501 and the drift correction region 502 fall within a field of view with a high magnification (magnification C), an image of the drift correction region 502 becomes finer by using the drift correction described in the first embodiment, and thus it is possible to expect to increase the accuracy of drift correction. Meanwhile, all or some of the functions of the units included in the processing apparatus 1 according to the above-described first to fourth embodiments may be realized by recording a program for realizing the functions in a computer-readable recording medium, by causing a computer system to read the program recorded in the recording medium, and by executing the program. Meanwhile, the term “computer system” used herein includes hardware such as an OS and a peripheral device. In addition, the “computer-readable recording medium” refers to a portable medium such as a flexible disk, a magneto-optical disc, a ROM, and a CD-ROM and a storage unit such as a hard disk which is built into a computer system. Further, the “computer-readable recording medium” may include one that dynamically holds a program for a short period of time such as a communication line for transmitting a program through a network such as the Internet or a communication line such as a telephone line, and may include one that holds the program for a certain period of time, such as a volatile memory within a computer system serving as a server or a client. In addition, the above-mentioned program may be one for realizing a portion of the above-mentioned functions, or may realize the above-mentioned functions in combination with a program that has been already stored in the computer system. The first to fourth embodiments according to the present invention have been described so far in detail with reference to the accompanying drawings. However, a specific configuration is not limited to the embodiments, and a design and the like are included without departing from the scope of the invention. For example, in the above-described embodiments, an ion beam has been used and described as an example of a charged particle beam, but the invention is not limited thereto: For example, an electron beam may be used as the charged particle beam. |
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047626690 | claims | 1. In a nuclear reactor fuel assembly including a top nozzle, a bottom nozzle, a plurality of guide thimbles extending longitudinally between and connected at their opposite ends to said top and bottom nozzles, a multiplicity of elongated fuel rods, a plurality of support grids axially spaced along and supported by said guide thimbles, each of said support grids defining a multiplicity of cells at least equal in number to said multiplicity of fuel rods for receiving respective ones of said fuel rods therethrough and supporting said fuel rods in a side-by-side array with respect to one another and to said guide thimbles, the improvement which comprises: (a) a plurality of annular anti-vibration grids axially spaced along, and connected to at least some of, said guide thimbles between at least some of said support grids; (b) said annular grids being separate from and unconnected to said support grids; (c) each of said annular grids defining a plurality of cells being less in number than said multiplicity of fuel rods but at least equal in number to a plurality of said fuel rods positioned about the periphery of said multiplicity of fuel rods, said annular grid cells for receiving therethrough respective ones of said fuel rods in said plurality thereof and engaging said fuel rods so as to dampen any coolant fluid cross flow vibration induced therein. (a) a plurality of annular anti-vibration grids axially spaced along, and connected to at least some of, said guide thimbles between at least some of said support grids; (b) said annular grids being separate from and unconnected to said support grids; (c) each of said annular grids defining a plurality of cells being less in number than said multiplicity of fuel rods but at least equal in number to a plurality of said fuel rods positioned about the periphery of said multiplicity of fuel rods, said annular grid cells for receiving therethrough respective ones of said fuel rods in said plurality thereof and engaging said fuel rods so as to dampen any coolant fluid cross flow vibration induced therein; (d) each of said annular grids being composed of a plurality of interleaved members arranged in an egg-crate configuration to define said plurality of cells and a central void region of a size to receive therethrough the rest of said fuel rods in said multiplicity thereof; (e) each of said annular grids including (a) a reactor core composed of a plurality of fuel assemblies disposed in side-by-side spaced relationships, a first group of said fuel assemblies defining the periphery of said core and a second group of said fuel assemblies positioned inwardly of and encompassed by said first group thereof; (b) each of said fuel assemblies having a plurality of elongated guide thimbles, a multiplicity of elongated fuel rods, a plurality of support grids axially spaced along and supported by said guide thimbles, each of said support grids defining a multiplicity of cells at least equal in number to said multiplicity of fuel rods for receiving respective ones of said fuel rods therethrough and supporting said fuel rods in a side-by-side array with respect to one another and to said guide thimbles; (c) a baffle structure extending about said reactor core adjacent said fuel assemblies in said first group thereof, said baffle structure having components being subject to unpredictable loosening with respect to one another so as to permit jetting of coolant fluid from the exterior to the interior of said baffle structure and impingement upon fuel rods in said fuel assemblies of said first group thereof so as to cause vibration of said fuel rods; and (d) a plurality of annular anti-vibration grids axially spaced along, and connected to at least some of, said guide thimbles of said fuel assemblies in said first group thereof between at least some of said support grids of said fuel assemblies in said first group thereof, said annular grids being separate from and unconnected to said support grids, each of said annular grids defining a plurality of cells being less in number than said multiplicity of fuel rods of each of said fuel assemblies in said first group thereof but at least equal in number to the plurality of said fuel rods positioned about the periphery of said each fuel assembly in said first group thereof for receiving respective ones of said fuel rods therethrough and engaging said fuel rods so as to dampen vibration thereof due to impingement by coolant fluid jetting from said baffle structure. (a) a reactor core composed of a plurality of fuel assemblies disposed in side-by-side spaced relationships, an outer group of said fuel assemblies defining the periphery of said core and an inner group of said fuel assemblies positioned inwardly of and encompassed by said outer group thereof; (b) each of said fuel assemblies having a plurality of elongated guide thimbles, a multiplicity of elongated fuel rods, a plurality of support grids axially spaced along and supported by said guide thimbles, each of said support grids defining a multiplicity of cells at least equal in number to said multiplicity of fuel rods for receiving respective ones of said fuel rods therethrough and supporting said fuel rods in a side-by-side array with respect to one another and to said guide thimbles; (c) a baffle structure extending about said reactor core adjacent said fuel assemblies in said outer group thereof, said baffle structure having components being subject to unpredictable loosening with respect to one another so as to permit jetting of a coolant fluid from the exterior to the interior of said baffle structure and impingement upon fuel rods in said fuel assemblies of said outer group thereof so as to cause vibration of said fuel rods; and (d) a plurality of annular anti-vibration grids axially spaced along, and connected to at least some of, said guide thimbles of said fuel assemblies in said outer group thereof between at least some of said support grids of said fuel assemblies in said outer group thereof, said annular grids being separate from and unconnected to said support grids, each of said annular grids defining a plurality of cells being less in number than said multiplicity of fuel rods of each of said fuel assemblies in said outer group thereof but at least equal in number to the plurality of said fuel rods positioned about the periphery of said each fuel assembly in said outer group thereof for receiving respective ones of said fuel rods therethrough and engaging said fuel rods so as to dampen vibration thereof due to impingement by coolant fluid jetting from said baffle structure; (e) each of said annular grids being composed of a plurality of interleaved members arranged in an egg-crate configuration to define said plurality of cells and a central void region of a size to receive therethrough the rest of said fuel rods in said multiplicity thereof, each of said annular grids including 2. The fuel assembly as recited in claim 1, wherein each of said annular grids is composed of a plurality of interleaved members arranged in an egg-crate configuration to define said plurality of cells and a central void region of a size to receive therethrough the rest of said fuel rods in said multiplicity thereof. 3. The fuel assembly as recited in claim 1, wherein each of said annular grids includes a plurality of interleaved members defining said plurality of cells and means defined on said members and projecting within said cells for engaging said fuel rods in said plurality thereof. 4. The fuel assembly as recited in claim 3, wherein said fuel rod engaging means includes a plurality of protrusions formed on said members and projecting into each of said cells in said plurality thereof through a sufficient distance to contact opposing sides of said fuel rod received through said each cell. 5. The fuel assembly as recited in claim 1, wherein each of said annular grids includes a plurality of interleaved members defining said plurality of cells and coolant flow deflecting means defined on said members and projecting upwardly and inwardly toward a longitudinal axis of said each cell. 6. The fuel assembly as recited in claim 1, wherein said each of said annular grids includes a number of sleeves adapted to receive a like number of said guide thimbles therethrough, said number of said guide thimbles being less than said plurality thereof, said sleeves being attached to said guide thimbles and unconnected with, and shorter in length than the distance between, the ones of said support grids disposed adjacent to said each annular grid. 7. The fuel assembly as recited in claim 1, wherein said plurality of annular grids are positioned between said support grids located nearer to said bottom nozzle than to said top nozzle. 8. In a nuclear reactor fuel assembly including a top nozzle, a bottom nozzle, a plurality of guide thimbles extending longitudinally between and connected at their opposite ends to said top and bottom nozzles, a multiplicity of elongated fuel rods, a plurality of support grids axially spaced along and supported by said guide thimbles, each of said support grids defining a multiplicity of cells at least equal in number to said multiplicity of fuel rods for receiving respective ones of said fuel rods therethrough and supporting said fuel rods in a side-by-side array with respect to one another and to said guide thimbles, the improvement which comprises: 9. In a nuclear reactor, the combination comprising: 10. The nuclear reactor as recited in claim 9, wherein each of said annular grids is composed of a plurality of interleaved members arranged in an egg-crate configuration to define said plurality of cells and a central void region of a size to receive therethrough the rest of said fuel rods in said multiplicity thereof. 11. The nuclear reactor as recited in claim 9, wherein each of said annular grids includes a plurality of interleaved members defining said plurality of cells and means defined on said members and projecting within said cells for engaging said fuel rods in said plurality thereof. 12. The nuclear reactor as recited in claim 11, wherein said fuel rod engaging means includes a plurality of protrusions formed on said members and projecting into each of said cells in said plurality thereof through a sufficient distance to contact opposing sides of said fuel rod received through said each cell. 13. The nuclear reactor as recited in claim 9, wherein each of said annular grids includes a plurality of interleaved members defining said plurality of cells and coolant flow deflecting means defined on said members and projecting upwardly and inwardly toward a longitudinal axis of said each cell. 14. The nuclear reactor as recited in claim 9, wherein said each of said annular grids includes a number of sleeves adapted to receive a like number of said guide thimbles therethrough, said number of said guide thimbles being less than said plurality thereof, said sleeves being attached to said guide thimbles and unconnected with, and shorter in length than the distance between, the ones of said support grids disposed adjacent to said each annular grid. 15. The nuclear reactor as recited in claim 9, wherein said plurality of annular grids are positioned between said support grids located nearer to the bottom than to the top of said fuel assemblies. 16. In a nuclear reactor, the combination comprising: |
description | This application is related to the subject matter of U.S. Patent Application entitled PRECISE X-RAY INSPECTION SYSTEM UTILIZING MULTIPLE LINEAR SENSORS, Ser. No. 10/394,632 filed 21 Mar. 2003 by Gerald L. Meyer and assigned to Agilent Technologies, Inc. For brevity and the sake of completeness, PRECISE X-RAY INSPECTION SYSTEM UTILIZING MULTIPLE LINEAR SENSORS is hereby incorporated herein by reference. The electronic assemblies of today, whether they be a large IC (Integrated Circuit) of a PCA (Printed Circuit Assembly) can posses an extraordinary degree of functionality. This has created issues related to initial testing and performance verification upon manufacture, as well as to periodic testing and performance verification during routine maintenance or trouble shooting and repair. In many cases, the old technique of having a test procedure followed by a trained technician that understands how the thing works is simply out of the question: the overwhelming complexity and issues of time and cost force us to seek other approaches. In manufacturing large complex electronic assemblies the philosophy has tended toward one of ensuring that the design is sound, and then using good parts to correctly form the assembly. The expectation is that the completed assembly should work as desired. Associated with this is the notion that the sooner a defect can be discovered in the manufacturing process, the less it costs to discover and fix it. Some defects can only be discovered through performance testing, while others, especially those related to mechanical properties, can be discovered by inspection. Both performance testing and inspection can be automated to a significant degree. And since the effect on performance of a mechanical defect, such as a solder bridge between two traces on the PCA, or a break in a trace, might be pronounced (“It's dead and oozing stinky smoke . . . ”) or subtle (“Every so often it does something goofy . . . ”), and since finding a mechanically based electrical fault by analysis of electrical operation is like looking through the wrong end of a telescope, it is generally agreed that a through mechanical inspection should precede an attempt to operate the assembly. Automated mechanical inspection of assembled PCAs turns out to be something that can be effectively accomplished. What one might call an “x-ray vision system” is proving to be an agreeable and cost effective way of reliably finding breaks in traces, bridges between traces, and voids in solder joints. Since x-rays are involved, these defects need not be upon an exposed surface to be discovered. The determination that a defect is present can be made by analysis of a suite of work images (say, for a solder joint) or by comparison of a work image with a stored exemplar (say, for trace integrity). Such automated x-ray inspection systems have found acceptance in the marketplace, and new and refined techniques are appearing that both lower the cost and increase the capability of new automated inspection systems. One of the ways to lower the cost of an x-ray imaging system is to reduce its mechanical complexity. One form for an early system used a circularly deflects x-ray beam and a rotating sensor. These items might be twelve to twenty inches away from each other, with the PCA disposed between them, but all must be in precision alignment if features (and defects) on the order of a few thousandths of an inch are to be resolved during testing. Such requirements add significantly to the mechanical complexity and cost of the imaging system. An attractive alternative to such a design is one using a stationary line scan camera (1), such as is set out in the incorporated “PRECISE X-RAY INSPECTION SYSTEM . . . ”, which we now summarize with the help of FIG. 1. As shown in FIG. 1, a plurality of multi-element imaging sensors (2) is disposed beneath a divergent x-ray ‘point source’ (3). The image sensors 2 may each be just one pixel wide, or may be several pixels wide for use with a TDI (Time Domain Integration) style line scan camera, and each has perhaps 2048 pixels uniformly distributed along a length of say, six to eight and one half inches. (The rationale for equating an imaging sensor one pixel wide and a TDI sensor several pixels wide arises from the fact that in either case, just one pixel value per clock cycle is produced for the TDI case, as if it were only one pixel wide—which it is not, so the pixel values produced are different, but still are just one value per clock cycle.) The image sensors may be similar to contact image sensors used in the visual scanning of documents, save that they include a thin covering of material that fluoresces (or scintillates) with visible light when excited by x-rays. The long axes of the image sensors are all parallel to one another, and we shall call this direction the x axis. The arrangement in x and y of the individual image sensors their plurality is not a particular issue here, and we show them as spread out over an area, there better to mimic the spatial aspects of an ‘area’ image sensor. And while not essential, it is convenient if they cover a contiguous portion of the x axis with no embedded gaps corresponding to where one sensor stops and another starts. Before proceeding we should address an issue relating to terminology and the use of the term ‘camera’ in this setting. We are aware that some practitioners use the term ‘camera’ to refer to an individual multi-element imaging sensor, even if it is but one pixel in width (or more, for TDI applications), and that they would be inclined to refer to the overall line scan apparatus as the ‘line scan system.’ We find this somewhat cumbersome, as the term multi-element image sensor is perfectly descriptive, as is the notion of a camera whose output is an image representing a slice of the entire three dimensional object, and which happens to use a line scan technique upon multi-element imaging sensors that are one pixel wide, and which we shall be content to call a ‘line scan camera.’ We shall arrange that the location from which the x-rays (4) emanate is above a central location within the arrangement of imaging sensors, and that the x-rays diverge uniformly in a generally conical manner toward the imaging sensors. The imaging sensors are all mounted with uniform height at known locations within a plane (5) that is perpendicular to the axis of the conical dispersion of the x-rays. We may assume, in the absence of any intervening material that absorbs or block x-rays, that each pixel location in the generally circular array of image sensors receives roughly the same level of x-ray illumination, and that each produces about the same level of electrical signal. (We also expect that any signal variations occurring under such ‘neutral’ conditions have been noted, and can if desired, be removed from measured data as effects of offsets and scaling, to leave in place indications related only to conditions within a PCA being tested.) A PCA (6) to be tested is interposed between the x-ray source and the imaging sensors, and is generally parallel to the plane 5 of the imaging sensors. The size of the PCA may exceed that of the planar array of imaging sensors by many times over, and to accommodate that are well as allow each image sensor to ‘see’ every feature of interest on the PCA, the PCA is translated at a generally uniform velocity (Vscan) along a serpentine path 9 that is known in advance and under the control of a transport control mechanism (8), which may be a computer programmed and connected to operate in this manner. This is primarily smooth continuous motion back and forth along the y direction, with intervening discrete steps in the x direction at the extremes of y motion. During portions of the serpentine path when x-ray shadows of interest fall on the imaging sensors, the data signals from the imaging sensors (denoted by the lower case Greek α) are read out at a regular clock rate and stored in a (rather large!) memory (7). Thus, at the end of a serpentine scan we have a whole big bundle of data that can be algorithmically manipulated (8) with software executed by a computer to produce (8) images of interest, and which may then be analyzed in isolation or compared to one or more exemplars, and in any case evaluated (10) using selected criteria. These techniques for analysis and comparison are conventional, and are not of further interest here. Our interest lies more in an aspect of the manner in which an image is obtained in the first instance. To assist us in this, we may reduce the scope of the above described activity to obtaining a partial image along just one portion of one y-direction leg of the serpentine with data from just one imaging sensor. [This is done with the understanding, of course, that what we do for one imaging sensor we also do for the others, and that there are known ways for the processed data for the various sensors to be combined to produce a ‘recontructed’ (think: ‘complete’) image of interest.] To continue, we note that a notion of ‘in focus’ can be developed. Consider some pixel position along some imaging sensor. It basically represents all or a portion of an x-ray shadow of some target feature on the PCA that lies along the line (ray trace) from that pixel position to the origin of the x-rays (assumed to be a bright point-like spot). As the PCA moves, several values for our pixel location are clocked out and captured. These values are for different locations in y but at the same location (i) in x. Let's call such a thing a ‘Y alpha sequence at (some) X,’ or Yα@Xi. At the same time this is also happening for other pixel locations on the same imaging sensor (at another value of i for Xi), and at the corresponding pixel location (if there is one at the x) on all the other imaging sensors. The arrangement of imaging sensors is such that at least one other imaging sensor will eventually produce a sequence of signals (various α values) for that same target feature. (‘Eventually’ might mean at a different location on the same leg of the serpentine, or on a different leg). Now, for all the other imaging sensors that produced a sequence of signals for the target feature (which might well be all of them), place the elements of these various Yα@Xi into correspondence: this element of the sequence from this sensor corresponds to that element of the sequence from another sensor, and so on. We note that these elements (various α values) were probably not obtained at the same time, as the feature might have been imaged at a different place along the serpentine path. The important thing is to agree that such a correspondence between ‘the same location in x’ on different imaging sensors exists, and the effects of sensor separation can be represented as shifts or offsets of element positions between the sequences: a shift (or offset) of so many elements between a Yα@X1 and a Yα@X2, and of a different number of elements between Yα@X1 and a Yα@X3, and so on. A similar correspondence can be formed with shifts between different pixel locations in x that ‘have the same y,’ whether they are on the same imaging sensor or on two that each lie on the other's axial extension (along the x axis or along a line parallel to it). That is, the data also contains various instances of an ‘X alpha sequence at (some) Y,’ or, Xα@Yj. (A note about notation is in order here. We will write Yα@Xi and Xα@Yj instead of Yα@Xi and Xα@Yi, lest it appear that when considering these two at the same time the subscript i is a common value for each. When we write Yα@Xi and Xα@Yj, each of i and j are allowed to range independently, and might be the same or might be different, as the case requires. What we mean is no more or no less than just ‘some X’ and ‘some Y.’) A moment's thought will confirm the assertion that the height of the target feature above the imaging sensors also has an effect (discussed below in connection with magnification, M) in that it determines how far apart in the imaging plane two shadows along different diverging rays fall upon the imaging plane. Now, if we pick from some Yα@Xi and Xα@Yj that contain a common element that belongs to (is contained) in the target feature, and with knowledge of sensor separation and a desired height in z, we ‘properly’ shift their respective other Yα@Xi and Xα@Yj into correspondence with them and then combine (say, by averaging) all instances of that element (for the target feature) for all the sequences, we can favor the desired location along the z axis in that: For all the ray traces passing through the target feature at that z and reaching an image sensor, each has a signal value α related to the target feature, and we may take their average as representative thereof, while for other rays that might reach a sensor after passing through a different z location the associated signal values tend to cancel each other (average out). Note that: which pixel position along the length of a sensor has determined an x coordinate (as further understood by which leg in the serpentine the PCA was happening when that pixel value was taken); the location within the sequence of clocked out sensor values (which αj) within a leg determines the y coordinate; and, the desired z coordinate further affects the pattern of shifts or offsets between the Yα@Xi and Xα@Yj from for the imaging sensors. The averaged value obtained here is the value of the pixel at (x, y, z), i.e., its intensity, which we might call A (the Greek upper case alpha). We have just found (x, y, z, A), or a pixel description for a location in space, which might belong to a solder ball affixing a huge IC to a ball grid array. We do this for not just one pixel location, but for all pixel locations that may be of interest (there might be parts of a PCA that we do not bother to inspect). That is, we can pick an (x, y) location and then shift in x as y remains fixed, and then shift in y as x remains fixed. Then we pick another (x, y) location, and so on. What emerges is an (x, y) image in A at some height in z. We probably want the same (x, y) regions at other values for z, as well, and it will be appreciated that in this general manner a desired complete two or three dimensional image can be constructed. The serpentine path serves to cover the entire PCA, while an increased plurality of imaging sensors provides improved cancellation of the ‘out of focus’ planes in z. Before leaving this somewhat simplified description of how a line scan camera operates, we should point out a few other details that will be of interest in what follows. The topic is: “How do we know how much to shift (or offset) the elements of the various sequences from the associated imaging sensors?” Hmm. Well, on the one hand we know the relative position of each imaging sensor with respect to all the others (or at least we believe so . . . ). It turns out that, given the measurement precision that the x-ray line scan camera is otherwise capable of, we are well advised if we become suspicious of the effects of temperature change. Furthermore, as the next few paragraphs show, there is a particular magnification parameter called Mref that is also rooted in the mechanical aspects of the whole line scan camera. With reference now to FIG. 2, it will be appreciated that as the divergent x-rays 4 spread out on their journey from the x-ray spot on the source 3, a given sized target object (12) in the PCA will create a larger shadow 13 (in spatial terms measured in pixel-to-pixel spacings at the imaging sensor) if the target object is closer (11) to the x-ray spot on the source, than it does (14) when further away (15). The ratio between the actual size of the target object and its apparent size according to the corresponding shadow on the sensor (and, of course, taking the spacing of the sensor elements into account) is called the magnification, or M. We are most interested in knowing an accurate value of M for out instances of testing, as it figures in how much to shift the sequence of measured α values from each sensor to correspond to those of another sensor, or to shift a sequence of α values from a given sensor element for combination with the un-shifted sequence for the same sensor element, and thus ‘focus’ at a desired value of z. Now, when we shift one collection of α values to combine with another, one collection moves relative to the other: it won't do if they both move the same amount, as the net effect would be no shift at all. So, if there are several collections to be shifted by different amounts and then combined, we can appreciate that all of these can be thought of as being shifted by the requisite amount relative to something that does not shift. That ‘something’ is the image, or slice, (which is some collection of α values) at some z height of convenience, say, zk. We shall refer to this height zk in z as the reference plane. When consider what magnification M is afoot for the focusing of reconstructed images, the necessary shifting will be performed relative to zk, and the value of M that arises from using that particular value for z will be called Mref. Now, it is not so much that we don't have a general idea of what Mref is, or that Mref changes abruptly from day to day as the system is in use. A given x-ray line scan camera has a certain Mref. It is more that it would be rash to operate the system for weeks or months at a time and expect Mref to remain absolutely constant. Or to expect that mechanical wear, adjustment and other maintenance do not affect Mref. It has been found that an x-ray line scan camera of the sort described here has sufficient resolution and accuracy that modest changes in temperature can produce detectable changes in the effective value of Mref. But our ability to know where in z an image is located (and this is the stock in trade of an ‘x-ray vision’ PCA inspection system) depends on knowing Mref! Indeed, if Mref is too far off, images will not appear to be in focus at all, owing to significant subversion of the shift and average technique used to cancel out that which is ‘out of focus’ and leave just that which is ‘in focus.’ We believe that it is prudent to find Mref whenever the system is powdered up, after maintenance, perhaps at least once or twice a day whether it needs it or not, and at any other time when it seems like a good idea. There are prior art solutions to discovering an actual value of Mref for a particular line scan camera system. For example, the measured distance between two index lines or marks can be compared to what is thought to be their true distance. Unfortunately, the limits imposed on measurement precision by the pixelation of the image sensors, and the uncertainty of other system variables conspire to limit the accuracy with which the true value of Mref can be discovered by this method. What we need is a better way to easily discover the true value of Mref whenever it seems useful to do so. How to do it? The magnification Mref for a line scan camera can be found by exploiting a difference in the way Mref affects the notion for ‘focus’ in the x and y directions. It turns out that Mref enters into the calculations for selecting z while focusing in the y direction, but not in x. A calibration target is provided at a convenient height in z, and which may or may not be that particular height zk we call the reference plane. It is preferred that physically, the calibration target be part and parcel of the transport mechanism that carries the PCAs as they are interposed for serpentine movement between a stationary point source of divergent x-rays and a stationary plane of imaging sensors, and that the calibration target is permanently affixed thereto and not part be of any PCA. The calibration target is thin and opaque to x-rays (e.g., of tungsten), and has a straight edge aligned parallel to the x direction and a straight edge aligned parallel to the y direction. These may be two sides of an isosceles right triangle shape removed from a square of tungsten. The tungsten square is planar and is parallel to the imaging plane. To find Mref the line scan camera forms image of the calibration target over a range of z values known to include the height of the calibration target. An arbitrary (and possibly either correct or incorrect) or perhaps a known incorrect trial value Mi of Mref is then assumed and many slices of the calibration target are calculated. Within these slices the edge parallel to the x direction will be sharply defined for some zx, while at some other zy the edge parallel to the y direction will be sharply defined. Make a note of ei=zx−zy. Repeat these steps for some number (e.g., thirty or fifty) different trial Mi that cover the plausible range of Mref. Now fit a curve (e.g., a quadratic) to the data set {(ei, Mi)}, and find the y-intercept (where e=0). The associated value of M is the magnification in the reference plane containing the calibration target, and we found it without knowing the actual length of any part of the calibration target. We turn now to a topic that provides the basis for a technique of discovering the magnification Mref in a line scan camera, and which does not rely upon advance knowledge of the particular dimensions of a calibration target that is imaged as part of the discovery process. That ‘topic’ is the observation that the ‘shift and add/average’ operation used to ‘focus’ a slice at a particular z value is a function of Mref for such operations on an Yα@Xi, but not for those operations on an Xα@Yj. Said another way, this means that we need to use an Mref (i.e., “know it”) to get ‘focusing’ to happen for the Yα@Xi, but that no such Mref is needed for the Xα@Yj. Leaving a demonstration of that assertion aside for just a moment, if we accept it as true we can exploit that idea by imaging a calibration target that has co-planar straight-line edges that are parallel to the x and y axes and in a plane parallel to the imaging plane, and noting when the edges appear to be ‘sharp,’ or well defined, as Mref is varied during a suite of trial imaging operations. The value of Mref that causes the ‘best edge’ simultaneously in both x and y is the sought after actual value of Mref for the imaging system. We now undertake a demonstration of why focusing for Yα@Xi is a function of Mref, while focusing in Xα@Yj is not. The short answer is this: Projected image size (in pixels) in the x direction is function of Mref for reasons illustrated in FIG. 2, because when data is clocked out from the imaging sensors the entire projection of a feature falls on the sensors (or at least would if it is not too big . . . ). The divergence of the x-rays, over the distance traveled, produces an expansion Mref of the imaged feature; and we note that the the greater the expansion, the more x direction pixel positions are involved in representing the size of the feature, and that any single clocking of the sensor reveals them all to at once. In contrast, the projected image size in pixel locations along the y direction is only a function of how often the data is clocked out of the imaging sensors for any given velocity of the feature being imaged. FIG. 2 serves to support the notion that Mref is involved in the focusing operations of ‘shift and add’ for the Yα@Xi; Mref affects the number of pixels needed to represent the projection of a feature, and experience suggests that appreciation of that idea is not difficult. On the other hand, experience also suggests that the notion that Mref does not figure in the ‘same’ focus operations for the Xα@Yj is not intuitive, and we turn now to FIG. 3 to show why such independence from Mref is indeed the case. With reference now to FIG. 3, let us suppose that we image the same feature (16) at two different z heights, z1 and z2. In a setting such as FIG. 2 we would expect to get, and indeed would get, different numbers of pixel locations (along the y axis) on the image sensor at the two different projections of the feature onto the sensor. That happens because the sensing element are really ‘all there,’ under the projection of the diverging x-rays. But, as is shown in FIG. 3, along the x axis direction there is a width of just one sensing element, and the only thing that causes change in what that sensing element reports to the outside world about x axis activity is how often it is clocked and the velocity of the feature. Here in detail, is how to appreciate FIG. 3. On the left side of FIG. 3 is a ‘BEFORE’ scenario, and on the right is an ‘AFTER’ scenario. In each case we are imaging the same feature 16 on the same PCA. BEFORE shows doing the imaging at height z1 and again also at z2, and in each case the location of the x-ray beam has progressed to about half-way between the opposite ends of the feature 16. We are not suggesting that both heights could be imaged at once; instead, they are shown together because even if they are done at different times the operation is, in a schematic sense, identical except for the difference in z. The same remarks apply to the AFTER half of the figure, which depicts the situation after clocking out three additional values of αi subsequent to the situation of the BEFORE scenario. The PCA is moving with some generally constant velocity Vscan in the y direction. Let us say for the sake of a definite example that the feature 16 is ten samples long in the y direction. Thus, there will be ten Δys, and every amount of movement by Δy is accompanied by a new value of αj from the sensor's element for xi. We thus expect a sequence of Yα@Xi that has ten values, or: {α0 . . . α9}. We can learn what we need to about Mref from examining what αi emerge for xi, and need not investigate the other α sequences for the other xi+1, as we would just learn the same thing, and the increased complexity for the necessary notation is simply not worth the effort. With regard to the ‘generally constant’ velocity mentioned in the preceding paragraph, there are at least two possibilities. One would be that the actual velocity of the PCA (Vscan) is really constant, and we create Δy by observing transitions in a clock signal of constant frequency. Another, and perhaps preferable, arrangement is to allow Vscan to be ‘unregulated’ and detect amounts of PCA motion that are Δy in size, and clock the imaging sensor 2 upon such detection. The next step in considering FIG. 3 is to note the sequence 17 Yα@Xi for the imaged feature 16 at height z1. If the feature 16 is divided by sampling into j=10 regions, and ordered as from j=0 to j=9, then the sequence 17 is some series of j-many αi each dependent upon the opacity to x-rays for those respective samples: {αj9, αj8, αj7, . . . , αj2, αj1, αj0}. Other than noting what this sequence is, there is nothing else remarkable about it (except perhaps to notice that since the portion of feature 16 at j=0 was imaged and its corresponding αj0 clocked out first, we put αj0 on the far right of a customary time axis running from left to right . . . ). Now consider the same feature 16 at height z2. Although the sequence {αj9, αj8, αj7, . . . , αj2, αj1, αj0} for z2 is produced at different clock cycles relative to the mechanical motion of the PCA past some fixed point of reference when compared to z1, it is still identical sequence 17 as was obtained for operation at height z1. Therefore, the height in z, and hence Mref, does not affect focusing in the y direction, as we have the same sequence of αi data to work with in each case. Refer now to FIG. 4, which is a simplified flowchart 18 of a procedure that discovers during a calibration activity a value of M (Mref) that may be used for general line scan camera use during the actual line imaging and testing of production PCAs. The method of doing this discovery according to the flowchart 18 does not depend upon the measurement of known lengths in either of the x or y directions, and experience has shown that it is actually more accurate in discovering Mref than is an attempt to measure a known length. The first step 19 in flowchart 18 is to scan a calibration target, such as the one 20 illustrated in the inset next to step 19. Although other calibration targets are possible, the one shown in an actual one used with good success, and is a right isosceles triangle void or cutout 21 whose equal edges are each fifty mils long and respectively parallel to the x and y axes, the triangular void or cutout located within the central portion of a square (or other shape containing the cutout) of tungsten, say, 2 mils thick. It is the edges of the cutout 21 in the x and y directions that we will be interested in, and with that in mind it will be appreciated that there are other shapes that may be used in the same manner as set out below. In any event, the scanning of step 19 is the creation of an entire collection of Xα@Yi and Yα@Xi in the vicinity known to contain the calibration target 20. Once we have such a collection of Xα@Yj and Yα@Xi we can variously ‘put them in focus’ at a collection some {zi} without any further scanning steps. Now, the operation of ‘putting them into focus at some instance of zi’ requires some value of Mref. That, of course, is what we don't know in particular, although (absent some pernicious malfunction) we can almost certainly say that Mref we seek is between some Mmin and an Mmax. And, as a reminder, according to the discussions of FIGS. 2 and 3, if we have picked some zi and discover that some trial Mi (or vice versa) provides ‘in focus’ images in both the x and y directions, then we have found a value of Mi that we are justified as taking as Mref. To make just such a discovery is the purpose of flowchart 18 of FIG. 4. The next step 22 is to set or select an arbitrary trial value for Mi. The selected value might accidently be the ‘right’ value (chances of that are slim) or it might (much more likely) be a ‘wrong’ value. Either way, it won't matter, as we are going to try a whole bunch of them, anyway. We might even pick an Mi that is a known wrong value, say, either Mmax or Mmin. Now at step 23 we cycle through all the various values of zi from a zmin to a zmax (reasonable conservative values for which are known ahead of time because of where the calibration target 20 has been placed—it is a permanent part of the imaging system's transport mechanism and not part of a PCA that might have some defect). Now, for the set of values {zi} there will be a zx that appears to created the ‘in focus’ condition along the x direction for the trial Mi at hand, and there will be a zy that appears to create the ‘in focus’ condition along the y direction for that same trial Mi. But unless that Mi is also Mref, Zy≠zx, and conversely, if zy=zx, then Mi is Mref. There are various known ways that the condition of ‘a sharp edge’ for an image expressed in pixels can be determined. The technique preferred here, and that has been found to be entirely satisfactory, is one based on the notion of taking the variance of the image with the edge after convolution of the image with a Sobel edge detection procedure. This involves pairs of alternate row and alternate columns in the pixel level description, and looking for pronounced differences. This is a known technique, and those wishing further information about how it works and how to do it may refer to one of the standard text on the matter: e.g., Machine Vision by Ramesh Jain, Rangachar Katsuri and Brian g. Schunck, published in 1995 in McGraw-Hill. The explanation of the Sobel technique in this edition of that work will be found at pages 147-148. It will be appreciated that this is but one of several techniques that may be used in support of performing step 24. Step 24 is the enquiry about equality for the above described zx and zy, for all of the slices created a step 23 for the various zi. At step 25 we find and save the difference (an error ei in the trial Mi) between the zx and zy associated with each zi. We write ei=zx−zy, although we could have just as easily written either of:ei=zy−zx or ei=|zy−zy|, etc. Now, at step 26 we enquire if we have done steps 23, 24 and 25 for the last Mi in the collection thereof. If not, then the NO branch of the qualifier leads to step 27, where the next value of Mi (in some convenient ordering thereof) is instituted, and steps 23, 24 and 25 are repeated until the last Mi has been used in those steps. At that point the YES branch from qualifier 26 leads to step 28. At step 28 a convenient form of function is fitted to the mapping described by the set of points {(ei), (Mi)}. For example, a quadratic function for f has been found to be satisfactory. Now at step 29 we find the y intercept for e=f (M) (i.e., where e=0), and we have accordingly discovered the value of Mi that equal Mref. Subsequent to that discovery, the line scan cameras can be put to use in a production sense with confidence that with Mref used as the value for magnification, all slices at various zi for PCAs under test will be in focus for both the x and y directions. Finally, it will be appreciated that a line scan camera uses actinic radiation to produce the Yαi@Xi and Xαi@Yj that are responsive to the amount of actinic radiation reaching the individual imaging sensor elements and that these Yαi@Xi and Xαi@Yj are focused at desired slices represented by a value for zi by shift and accumulate techniques. In the case where a workpiece to be imaged is a PCA the actinic radiation may be x-rays, as previously described. It will be further appreciated that if the workpiece is transparent to some wavelengths of visible light, or perhaps ultra violet or infrared light, then the actinic radiation could be of such a wavelength. All that we should further attend to is that the calibration target has the requisite properties of opacity for the actinic radiation in use, as well as the edges herein bordering transparent regions which are parallel to the x and y aces. It will be further appreciated with respect to the foregoing, that the discovery of Mref can be performed with just one imaging sensor, provided that it is either long enough so that a single scan will cover the entire object to be imaged, or if not, a suitable serpentine or other scan pattern is employed. Furthermore, the placement of the imaging sensors (2) within the imaging plane (5) may be arbitrary (i.e., random, or at least irregular), or regular. ‘Regular’ means in accordance with some regular or symmetrical geometrical figures, such as equally spaced locations around the perimeter or circumference of a circular or elliptical shape, or at the vertices of a regular polygon. |
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048448575 | abstract | Pressurized water reactor with a primary circuit including therein a reactor pressure vessel, a steam generator and a main coolant pump, and with an auxiliary system having high pressure pumps for feeding water into the primary circuit, including a line extending from an upper side of the pressure vessel and having at least one shut-off valve therein, the line connecting the reactor pressure vessel and a part of the auxiliary system wherein a lower pressure prevails than in the reactor pressure vessel. |
047175338 | claims | 1. A spacing grid for a longitudinal nuclear fuel assembly having a bundle of parallel fuel elements arranged in a regular triangular array, said grid having a peripheral frame of regular hexagonal shape consisting of six side plates and at least two beds of wires spaced in a longitudinal direction, each of said beds having only two separate series of mutually parallel wires, said wires having ends secured to said frame, the wires of a same one of said series being parallel to two opposed sides of said frame, all said wires defining passages for supporting said fuel elements and said beds including at least one respective series of wires parallel to each side of said frame. 2. A spacing grid according to claim 1, wherein said wires in each bed provide two support points for each fuel rod and the wires of two different beds in the grid provide two diametrically opposite support points to a same one of said fuel rods. 3. A spacing grid according to claim 1, wherein the wires in each of said beds provide four supporting points for each fuel rod. 4. A spacing grid according to claim 1, wherein said wires of the two series in each of said beds bind at the crossing points thereof. 5. A spacing grid according to claim 1, wherein end portions of said wires are passed in openings of said peripheral frame and are thermally deformed against the outer surface of said frame, whereby projecting bosses for contact between adjacent fuel assemblies are formed. 6. A spacing grid according to claim 1, wherein end portions of said wires are engaged into openings of said peripheral frame and brazed. 7. A spacing grid according to claim 1, wherein said side plates are corrugated at the same pitch as said array. 8. A spacing grid according to claim 1, wherein successive ones of said beds are at different angles with a longitudinal axis of said grid. 9. A nuclear fuel assembly having: a framework including end nozzles and elongated members connecting said end nozzles, a bundle of parallel fuel elements arranged in a regular triangular array between said end nozzles, and a plurality of separate spacing and retaining grids distributed along said bundle and connected to at least some ones of said elongated elements, wherein each of said grids has a peripheral frame of regular hexagonal shape and at least two beds of wires spaced in a longitudinal direction along said frame, each of said beds having only two separate series of mutually parallel wires whose end portions are secured to said frame, the wires of a same one of said series being parallel to two opposed sides of said frame and all said wires defining passages for supporting said fuel elements, said beds including at least one respective series of wires parallel to each side of said frame. a framework including end nozzles, and elongated members connecting said end nozzles, a bundle of parallel fuel elements arranged in a regular triangular array between said end nozzles, said elongated members being substituted for some of said fuel elements in said array, and a plurality of separate spacing and retaining grids distributed along said bundle and connected to at least some ones of said elongated elements, wherein each of said grids has a peripheral frame of regular hexagonal shape and at least three beds of wires spaced in a longitudinal direction, each of said beds having only two separate series of mutually parallel wires whose end portions are secured to said frame, the wires of a same one of said series being parallel to two opposed sides of said frame, with the six total series having a respective two series parallel to each of the three opposed sides, and all said wires defining passages for said fuel elements, the wires in each of said beds defining openings each traversed by a set of four fuel elements each having two contact points with the wires of the respective bed and each fuel element having six contact points distributed at equal intervals with the wires in a grid. 10. A fuel assembly according to claim 9, wherein each of said fuel elements and said wires define a coolant flow passage in each of said beds and wherein said flow passages associated with a same one of said fuel elements are helically disposed along the fuel element. 11. A nuclear fuel assembly having: |
039376494 | abstract | A process and system for removing tritium, particularly from high temperature gas cooled atomic reactors (HTGR), is disclosed. Portions of the reactor coolant, which is permeated with the pervasive tritium atom, are processed to remove the tritium. Under conditions of elevated temperature and pressure, the reactor coolant is combined with gaseous oxygen, resulting in the formation of tritiated water vapor from the tritium in the reactor coolant and the gaseous oxygen. The tritiated water vapor and the remaining gaseous oxygen are then successively removed by fractional liquefaction steps. The reactor coolant is then re-circulated to the reactor. |
060524308 | summary | BACKGROUND OF THE INVENTION The present invention relates to radiation therapy machines, and more particularly, to a system and method for improving dose volume histograms by introducing intensity modulation in a subspace around the edges of a multi-leaf collimator defined static radiation field. DESCRIPTION OF THE RELATED ART Radiation emitting devices are generally known and used, for instance, as radiation therapy devices for the treatment of tumors. A radiation therapy device generally includes a gantry which can be swiveled around a horizontal axis of rotation in the course of a therapeutic treatment. A linear accelerator is located in the gantry for generating a high energy radiation beam for therapy. This high energy radiation beam can be an electron beam or photon (X-ray) beam. During treatment, this radiation beam is directed at the tumor in a patient. It is known that the cure rates for tumors are a function of the dose delivered to the tumor. In order to control the radiation emitted toward the tumor, a beam shielding device, such as a plate arrangement or a collimator, is typically provided in the trajectory of the radiation beam between the radiation source and the tumor. The beam shielding device defines a field on the object to which a prescribed amount of radiation is to be delivered. The usual treatment field shape results in a three-dimensional treatment volume which includes segments of normal tissue, thereby limiting the dose that can be given to the tumor. The radiation dose that can be delivered to a portion of an organ of normal tissue without serious damage can be increased if the size of that portion of the organ receiving such radiation can be reduced. Avoidance of damage to the organs surrounding and overlying the tumor determines the dosage that can be delivered to the tumor. Treatment techniques provide several fields directed from different gantry angles and shaped to conform to the tumor using a multi-leaf collimator. A multi-leaf collimator employs a plurality of relatively thin plates or rods, typically opposing leaf pairs. The plates themselves are formed of a relatively dense and radiation impervious material. Multi-leaf collimators are known to be used for both static field and dynamic field applications. For a static field dose, the collimator leaves are fixed in space for a predetermined period for each selected gantry angle to deliver static fields. This technique has the advantage that applied dosages are readily determined, however, such static field dosages do not necessarily provide a particularly accurate match to the tumor volume and therefore has a less than desirable therapeutic benefit. In particular, a clinician may identify a planning target volume, which includes the tumor, may also include adjacent tissues that may contain tumor cells, and sometimes regional lymph nodes. As such, the actual treated volume, however, is designed to treat the target volume plus a surrounding region, or margin. The margin accounts for uncertainties in defining the planning tumor volume, such as dose fall-off or penumbra at the beam edge, as well as inaccuracies in defining the target volume. The larger the margin, the more healthy tissue that may be irradiated. One method of avoiding irradiating healthy tissue is through use of a dynamic multi-leaf collimator technique to delimit the applied radiation beam path. With this technique, the leaf pairs move continuously or quasi-continuously throughout the whole field. To match tumor volume, the leaves typically move throughout the entire treatment period with a variable velocity. As can be readily appreciated, a plurality of leaf pairs moving at a variety of leaf velocities requires an relatively large amount of hardware and software overhead to control, and is also very difficult to verify while in progress. Further, changing the velocity of the collimator leaves can result in undesirable forces acting on the treatment head, causing it to destabilize or go out of alignment. This causes the system to shut down or lock-out. Since the leaves are relatively heavy, and the radiation beam must be delivered at an accuracy on the order of millimeters, rapidly moving leaves combined with frequent direction changes can result in frequent lock-outs. A prior method of verification of a treatment field is through the use of port films. A port film is a radiograph taken when the treatment beam, the patient and variables, such as gantry angle, are set treatment. Typically, such films are taken only prior to the start of treatment and, due to delays necessary to take, develop and analyze the port films, cannot provide real-time verification of treatment for the dynamic techniques. In fact, evaluation of port films typically occurs only on a weekly basis. Continuous feedback control is thus necessary to verify the accuracy of radiation delivery in the treatment field. Electronic portal imaging devices have been developed which provide an image on a video monitor. While these could be used to provide such continuous feedback, the computations are known to be relatively intensive. As such, a time lag exists between analysis of actual and planned delivery. In addition, evaluation of the image is typically difficult, since the field of view is restricted to the collimator settings and a view of the surrounding anatomy cannot be made. Finally, record-and-verify systems are known in which treatment parameters are recorded, and treatment is begun only when the user-defined parameters are verified during set-up. However, the set of parameters required to define dynamic fields is generally very large, cumbersome and time-consuming. Moreover, dynamic treatments are difficult to resume if there is a power failure in the middle of treatment. Additionally, the requirement of continuously-moving leaf pairs at variable leaf velocities causes relatively more mechanical cycling of the leaves, thereby decreasing the lifetime and the reliability of the dynamic multi-leaf collimator. Accordingly, there is a need for an improved system and method for shaping treatment volumes more closely to tumor volumes in a known manner. SUMMARY OF THE INVENTION These problems in the prior art are overcome in large part by a system and method for dynamic subspace intensity modulation according to the present invention. More particularly, the margin regions at the edges of a multi-leaf collimator-defined static radiation field are intensity modulated during part or all of the delivery of each static radiation field. This is accomplished through moving the collimator leaves at a constant velocity over the subspace margin. By keeping the major portion of the field static and by only moving the leaves at one fixed velocity over a small subspace of the intensity profile, the dose volume histogram is relatively easier to determine. As such, the dose volume histogram can be calculated more accurately. Moreover, the treatment can be more readily resumed after a power failure. A method according to one embodiment of the present invention includes obtaining an intensity profile defining a histogram of radiation intensity levels to be applied over a given tumor volume. The method further includes digitizing the profile and determining the optimal way to deliver the digitized portions of the intensity map. Optimizing delivery of the digitized intensity map includes accounting for all leaf pairs and any associated constraints. The set of multiple static fields to be applied is then determined. The original intensity profile is compared with the digitized profile in order to determine whether excess slopes can be piggy-backed onto the edges of any of the static fields previously determined. The slopes of the profiles can be matched either over the distance over which the slope occurs or over the number of monitor units delivered for the given slope. For each leaf that has to deliver a slope, the number of monitor units after which the leaf should start moving is determined. If the match is by monitor units, the leaf is moved throughout the entire treatment. If the match is by distance, the number of monitor units after which the leaf should start moving is equal to the total number of monitor units in the static field minus the distance over which the leaf should move times the absolute value of the slope that a leaf can deliver. The leaves may be moved either inward or outward. |
052020827 | description | DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 illustrates a typical pressurizer 10 used in a nuclear reactor coolant system. Pressurizer 10 is a vertical, cylindrical vessel with replaceable electric heaters 12 in its lower section. Heaters 12 extend through heater sleeves 14 in the vessel wall 16 into the lower portion of pressurizer 10. Heater sleeves 14 extend through the vessel wall 16 which is approximately six inches thick and made of carbon steel or low alloy steel. A plurality of nozzles such as that indicated by the numeral 15 may also extend through a bore in the vessel wall at a variety of locations on the pressurizer. Only one is shown for ease of illustration. As seen in FIG. 2, a cladding 18 normally made from stainless steel is used on the interior surface of the wall 16 for corrosion protection. For ease of illustration, heater 12 is not shown in FIG. 2. For purposes of simplicity, the followng description is directed to the replacement of a heater sleeve. As seen in FIG. 2, the invention is generally indicated by the numeral 20. Replacement heater sleeve 20 is generally comprised of first seal ring 22, sleeve 24, flange 26 on sleeve 24, and means 28 for providing a seal between flange 26 and the exterior surface of pressurizer 10. The following work must be performed before replacement heater sleeve 20 can be installed. The original electric heater 12 and original heater sleeve 14 exterior of pressurizer 10 are removed. A portion of original heater sleeve 14 in heater sleeve bore 30 is removed and heater sleeve bore 30 is partially tapped adjacent the exterior surface of vessel wall 16 to provide threaded area 32. First seal ring 22 is positioned against original heater sleeve 14 inside heater sleeve bore 30. Sleeve 24 is threaded into bore 30 such that the upper end of sleeve 24 presses against first seal ring 22 to create a seal between original heater sleeve 14 and sleeve 24. Sleeve 24 is provided with threads 33 that threadably engage threads 32. It should be understood that reference to upper or lower ends of parts are merely for ease of reference and should not be considered as limiting to the elements of the invention. Sleeve 24 has flange 26 adjacent its lower end and positioned thereon such that flange 26 is located very near the external surface of pressurizer vessel wall 16 when sleeve 24 is in the installed position described above. Means 28 for providing a seal between flange 26 and the exterior of pressurizer 10 is incorporated into flange 26 and is generally comprised of second seal ring 36, disk 38, and jack bolts 40. Disk 38 is slidably received in a groove that extends around the upper end of flange 26. Second seal ring 36 is received in the groove on disk 38. A plurality of jack bolts 40 are threadably received in bores 42 spaced circumferentially around flange 26 (illustrated in FIG. 3). As seen in FIG. 2, each jack bolt 40 extends through bore 42 to bear against disk 38. In this manner, jack bolts 40 may be tightened or threaded into bores 40 a sufficient distance to cause disk 38 to in turn apply pressure to second seal ring 36. This forms a seal between flange 26 and the exterior of pressurizer 10. The provision of two seals, one at first seal ring 22 and one at second seal ring 36, serves to insure that pressurized coolant inside pressurizer 10 will not leak out of pressurizer 10 between replacement heater sleeve 20 and heater sleeve bore 30. To replace a defective heater sleeve, the original heater 12 is removed. The original heater sleeve 14 exterior of pressurizer 10 and a portion of original heater sleeve 14 in heater sleeve bore 30 are removed. Heater sleeve bore 30 is partially tapped to provide threaded area 32 at its lower end. First seal ring 22 is positioned in heater sleeve bore 30 against original heater sleeve 14. Sleeve 24 is installed in heater sleeve bore 30 by threading sleeve 24 thereinto such that the upper end of sleeve 24 presses against first seal ring 22. This creates a seal between original heater sleeve 14 and sleeve 24. It should be understood that sleeve 24 and first seal ring 22 may be simultaneously installed in heater sleeve bore 30. Jack bolts 40 are then used to cause disk 38 to bear against second seal ring 36. This provides a seal between flange 26 and the exterior of pressurizer 10 A replacement heater is then installed through replacement heater sleeve 20. The replacement heater is welded in place utilizing weld prep 44 provided at the lower end of sleeve 24. Flange 26 and disk 38 have their surfaces that face or may contact the exterior of pressurizer 10 shaped to closely match the contour of that portion of pressurizer 10 where the work is being performed. The use of a replacement heater sleeve that has the same diameter as and is installed immediately adjacent the original heater sleeve maintains the original heater alignment and precludes the need for special alignment procedures. It should be understood that the method and apparatus described and illustrated are applicable to the replacement of a heater sleeve or a nozzle. The terms heater sleeve and nozzle should be considered as interchangeable for the purposes of this description since it is common in the industry to refer to a heater sleeve as a heater nozzle. Therefore, reference to the replacement of a nozzle in the claims should be understood as being applicable to a nozzle or a heater sleeve. Because many varying and differing embodiments may be made within the scope of the inventive concept herein taught and because many modifications may be made in the embodiment herein detailed in accordance with the descriptive requirement of the law, it is to be understood that the details herein are to be interpreted as illustrative and not in a limiting sense. |
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claims | 1. A mobile radiation oncology coach system comprising:a trailer configured to include a control console area and a treatment area, the treatment area being equipped with a medical treatment facility that can emit radiation;internal shielding disposed between the control console area and the treatment area; andexternal shielding provided at a predetermined location outside of the trailer. 2. The mobile radiation oncology coach system of claim 1, wherein said internal shielding comprises interlocked lead bricks. 3. The mobile radiation oncology coach system of claim 2, wherein the interlocked lead bricks comprises a predetermined thickness to provide substantially effective shielding between the control console area and the treatment area. 4. The mobile radiation oncology coach system of claim 2, wherein the plurality of barriers are made of concrete. 5. The mobile radiation oncology coach system of claim 1 further comprising:a vestibule area located between the control console area and the treatment room; anda second internal shielding provided between the vestibule area and the control console area. 6. The mobile radiation oncology coach system of claim 5, wherein the second internal shielding comprises additional interlocked lead bricks comprising a second thickness to provide substantially effective shielding between the control console area and the vestibule area. 7. The mobile radiation oncology coach system of claim 5 further comprising:a first door configured and providing access between the treatment area and the vestibule area, the first door including first shielding; anda second door configured and providing access between the vestibule area and the control console area, the second door is further configured to be constructed near an opposite side of said trailer, preventing a direct line of sight between the treatment area and the control console area. 8. The mobile radiation oncology coach system of claim 1 further comprising:an alternating door between the treatment room and the control console area, wherein the alternating door contains interlocked lead bricks to shield direct line of sight of the medical treatment facility and people located in the control console area. 9. The mobile radiation oncology coach system of claim 1 further comprising:a first door configured and providing access between the treatment area and the control console area, the first door including first supplemental shielding. 10. The mobile radiation oncology coach system of claim 9, wherein the first door is further configured to be constructed and positioned to prevent a direct line of sight between the treatment area and the control console area. 11. The mobile radiation oncology coach system of claim 9, further comprising:a swing door including a second supplemental shielding, and constructed and positioned to shield radiation that may be emitted in an area associated with the first door between the treatment area and the control console area. 12. The mobile radiation oncology coach system of claim 1, wherein the medical treatment facility includes medical linear particle accelerator (LINAC). 13. The mobile radiation oncology coach system of claim 1, wherein the external shielding comprising a plurality of barriers. 14. The mobile radiation oncology coach system of claim 1 further comprising a support pad dimensioned to support the trailer, and wherein the support pad comprises concrete. 15. The mobile radiation oncology coach system of claim 1 further comprising a tractor, and wherein said tractor and said trailer are arranged in tandem. 16. The mobile radiation oncology coach system of claim 1, wherein said external shielding is configured to be a predetermined distance and separate from said internal shielding. 17. The mobile radiation oncology coach system of claim 1, wherein an amount required for said external shielding is dependent on one or more of the following factors: workload, distance to surrounding areas, occupancy of surrounding areas, height of surrounding buildings, density of said external shielding, or location of said external shielding. 18. The mobile radiation oncology coach system of claim 1, wherein a height of said external shielding is configured to block a direct line of sight of the leakage coming from any gantry position. 19. The mobile radiation oncology coach system of claim 1, wherein said external shielding blocks any ground scatter from the rear of the trailer. 20. The mobile radiation oncology coach system of claim 1, wherein said external shielding is removable from the site after use. 21. The mobile radiation oncology coach system of claim 1, wherein said external shielding is provided at a predetermined location outside and around a predetermined area of the trailer. 22. A method for providing a mobile radiation oncology services, the method comprising:moving a trailer to a designated site, the trailer having a control console area and a treatment area being equipped with a medical treatment facility that can emit radiation;providing an internal shielding disposed between the control console area and the treatment area; andproviding an external shielding at a predetermined location outside of the trailer. 23. The method of claim 22, wherein the internal shielding comprising interlocked lead bricks. 24. The method of claim 22 further comprising:providing an alternating door positioned between the treatment area and the control console area, wherein the alternating door contains interlocked lead bricks to take away direct line of sight of the medical treatment facility and people located in the control console area. 25. The method of claim 22, wherein the medical treatment facility is a LINAC. 26. The method of claim 22, wherein the external shielding comprising a plurality of barriers. 27. The method of claim 26, wherein the plurality of barriers is made of concrete. 28. The method of claim 22 further comprising:providing a support pad dimensioned to support the trailer, wherein the support pad is made of concrete. 29. The method of claim 22 further comprising:providing a tractor, wherein the tractor and the trailer are arranged in tandem. 30. The method of claim 22 further comprising:securing the trailer after the trailer is moved to the designated site. 31. The method of claim 22 further comprising:removing the external shielding after the services is complete. 32. The method of claim 22, said external shielding are not moving with the trailer. |
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039727726 | summary | The invention of the instant application relates to a steam power plant for nuclear power stations having pressurized water reactors wherein quantities of blowdown water, which are produced due to an accumulation of existing and continually developing impurities in the water circulation system, are to be removed. Generally the quantities of blowdown water used to be brought initially to a relatively low pressure in an expansion or blowdown tank, thereafter the blowdown was cooled to temperatures of 40.degree.C, for example, through a brine cooler, and the blowdown would then be discarded. Considerable water losses can be produced thereby. Another disadvantage is that when there are leakages between the primary and the secondary circulatory systems, the blowdown water must be further treated in the purification or preparation plant for radioactive waste waters. If the capacity of the preparation plant is thereby exceeded, the power station must be shut-down. It is accordingly an object of the invention to provide steam power plant for nuclear power stations having pressurized water reactors which avoids the foregoing disadvantages of the heretofore known plants of this general type. With the foregoing and other objects in view, there is provided, in accordance with the invention, in steam power plant for nuclear power stations having pressurized water reactors and including a water circulation system from which quantities of blowdown water produced due to an accumulation of existing and continually developing impurities therein are removable through a blowdown line, a purifying device connected in the blowdown line and comprising an electromagnetic filter, a mixed bed filter connected thereto, and means for returning to the water circulation system at least part of the water contained in the quantities of blowdown water. If the blowdown water is now cleaned by the electro-magnetic filters or by filters, operating in a similar manner as well as by mixed bed or powdered resin filters, to such an extent that it is returnable to the circulatory system, the need for additional water will be considerably reduced. When leakages occur between the primary and the secondary cycle, the non-dissolved and dissolved activity carriers entrained thereby, can be removed from the water so that the operation of the plant can be maintained. Only the much smaller amounts of rinsing and regenerating waters that accumulate must be further treated in the preparation plant for radio-active waste waters. Although the invention is illustrated and described herein as embodied in steam power plant for nuclear power stations having pressurized water reactors, 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 single FIGURE of the drawing which is a schematic view of the blowdown water purifying device for the circulatory system of a steam power plant for a nuclear power station having a pressurized water reactor, in accordance with the invention. |
abstract | The present invention provides a system and method for reclaiming energy from the heat emanating from spent nuclear fuel contained within a canister-based dry storage system. The inventive system and method provides continuous passive cooling of the loaded canisters by utilizing the chimney-effect and reclaims the energy from the air that is heated by the canisters. The inventive system and method, in one embodiment, is particularly suited to store the canisters below-grade, thereby utilizing the natural radiation shielding properties of the sub-grade while still facilitating passive air cooling of the canisters. In another embodiment, the invention focuses on a special arrangement of the spent nuclear fuel within the canisters so that spent nuclear fuel that is hotter than that which is typically allowed to be withdrawn from the spent fuel pools can be used in a dry-storage environment, thereby increasing the amount energy that can be reclaimed. |
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039740277 | description | DETAILED DESCRIPTION OF THE INVENTION As illustrated, the pressure vessel 1 has a major portion 2 of its side wall in the form of a cylinder of uniform diameter, the radiating coolant pipe connections or nozzles 3 extending, however, from the upper side wall portion 4 of thicker wall diameter and, therefore, having the larger outside diameter than the portion 2. The spherical bottom 5 of the vessel has a peripheral portion resting on a support 6. The pressure vessel has a head 8 held down on top of the pressure vessel flange 9 by a mounting ring 10, the head having a spherical top 12, closing the top of the pressure vessel. The ring 10 is secured by hinge hooks 14 which engage the ring via a declining surface 15 in a self-locking manner. The hook hinge pins 16 are anchored to the upper part 17 of the concrete biological shield 18 which forms the concrete wall surrounding the pressure vessel side wall. It is this biological shield that forms the concrete pit in which the pressure vessel 1 is supported via its support 6. The encasement of this invention is generally indicated at 19. This encasement is built in the form of a shell comprising an inner layer 20 of the segmental cylindrical segments of pressure-resistant, heat-insulating material, and an outerlayer 21 made of similar segments. These segments or blocks are shaped so that the inner layer 20 engages the pressure vessel's side wall, including its portion 2 and 4, throughout the height of this side wall. The stack of segments forming the layer 20 below the side wall portion 4 are thicker than the segments contacting the portion 4, so that the outer surface of the layer 20 forms a cylinder of uniform diameter throughout, and on this layer is stacked the segments of the layer 21. As to both layers, there are a plurality of the segments both circumferentially and vertically and the segments are separable from each other. The inner surface of the layer 21 is shaped to conform exactly to the contour of the outside of the pressure vessel's side wall. By appropriately shaped segments, this includes the side of the bottom 5 which is of smaller diameter than the portion 2. The above segments or blocks may be made from a gas-containing concrete which has a specific gravity of 1.75 g/cm.sup.3 or, in other words, of so-called Leca concrete. The total thickness of both of the layers 20 and 21 may be in the neighborhood of 400 to 500 mm. The inner and outer surfaces of the layer 21 are, of course, both cylindrical and of uniform diameters throughout their lengths. The high-tensile strength steel cylinders are shown at 23, 24 and 25 and each extend over about 1/3 of the axial height of the pressure vessel side wall. However, a finer subdivision of the cylinders may be used if considered desirable from the fabrication and handling viewpoints. These rings are stacked end to end to form a substantially complete cylindrical wall. The top one of the rings 25 is formed with cutouts 26 to provide clearance for the coolant pipes 27 and, although only one of these pipes is shown, it is to be understood that a plurality of these pipes radiate from the vessel's portion 4. This permits the ring 25 to be lifted when the pressure vessel's cover has been removed and the hooks 14 swing out of the way. After this ring 25 is removed, the segments may be removed piece by piece, using simple manipulation worked from above the vessel's pit. The segments surrounding the coolant pipes 27 and the connections or nozzles 3 must also have cutouts to provide the necessary clearance. However, after removal of the segments above the pipes, and their connections or nozzles, removal of the segments on either side of the pipes and connections provide clearance for removal of the segments below these obstructions. Removal of the segments of the layer 21 upwardly from the annular space, then permits the segments of the layer 20 to be moved radially outwardly as required to clear the portion 4 of enlarged diameter, including any other shouldered parts such as at the junction between the lower vessel portion 5 and the balance of the vessel, and be then also removed upwardly. As previously indicated, the proportions of the segments and the steel cylinders are such that they are all loose relative to each other and the pressure vessel side wall when the pressure vessel is at or close to room temperatures, such as in the area of 20.degree. to 40.degree.C. When the encasement is installed and the pressure vessel expands while the steel cylinders 23, 24 and 25 remain somewhat colder, the thermal expansion of the vessel presses its side wall against the layers of segments which are then placed in compression by the reaction of the steel cylinders, thus applying the desired compressive restraint to the pressure vessel's side wall, for rupture protection. With the encasement of the present invention, the concrete wall 18 is no longer required as a mechanical containment for the vessel and it need only be designed for biological shielding purposes. Consequently, the concrete side wall need not be provided with steel reinforcements such as have heretofore been required although it may include tension rods or cables to carry the stress from the hooks 14 to the bottom of the concrete construction. In FIG. 2 the steel rings 30 are shown surrounding the main coolant lines 27 of which two are shown in this instance. These steel rings are mounted directly on the pipes 27 and are shown as having square cross sections and interspaced from each other a distance about equal to their thickness. The thickness of the square cross section rings should be at least equal to the wall thickness of the pipes 27. These steel rings are sufficient to prevent large pieces of the pipes 27 from becoming missles in the event of a rupture of the main coolant lines 27. At the same time the holes 31 in the concrete wall through which the pipes 27 pass, need not be made with undesirably large diameters. FIG. 2 shows the joints 33 which extend in the vertical direction and which in conjunction with the joints 34 which extend in the horizontal direction, permit the removal of the segments as described. In other words, the two layers are subdivided both radially and axially with respect to the pressure vessel. The segments of the two layers should be of such size as to permit them to be transported and handled in a practical manner. |
claims | 1. A fuel assembly mechanical flow restriction apparatus for detecting failure of a nuclear fuel rod in a nuclear fuel assembly situated in a reactor core of a boiling water reactor, the reactor core comprising a plurality of nuclear fuel assemblies comprising parallel fuel rods supported at an upper end by an upper tie plate and an outer channel surrounding the fuel rods for the passage of reactor coolant from a lower end to the upper end of the fuel assembly, the outer channel having upper edges, the upper end of the fuel assembly passing through and being supported by a reactor core top guide structure, the fuel assembly mechanical flow restriction apparatus comprising: a testing hood comprising a top plate and side plates to form a structure with an open bottom forming an internal volume for positioning over the tops of at least one of the nuclear fuel assemblies and for receiving gases escaping from a failed fuel rod within the fuel assembly, the side plates for resting on the reactor core top guide structure; a flow restrictor positioned within the testing hood and over at least one of the nuclear fuel assemblies, the flow restrictor comprising a sealing plate for positioning on the upper edges of the outer channel of the fuel assembly for mechanically blocking fuel assembly coolant flow exiting the upper end of the fuel assembly; a probe assembly having at least one probe head with at least one thermocouple for sampling the coolant water within the fuel assembly for detecting failure of a nuclear fuel rod in the nuclear fuel assembly; means for causing the sealing plate of the flow restrictor to be positioned on the upper edges of the outer channel of the fuel assembly for mechanically blocking fuel assembly coolant flow from exiting the upper end of the fuel assembly and for causing the probe head to be immersed in the fuel assembly reactor coolant water within the outer channel wherein the means for causing the sealing plate to be positioned on the outer channel of the fuel assembly is hydraulic. 2. A fuel assembly mechanical flow restriction apparatus for detecting failure of a nuclear fuel rod in a nuclear fuel assembly situated in a reactor core of a boiling water reactor, the reactor core comprising a plurality of nuclear fuel assemblies comprising parallel fuel rods supported at an upper end by an upper tie plate and an outer channel surrounding the fuel rods for the passage of reactor coolant from a lower end to the upper end of the fuel assembly, the outer channel having upper edges, the upper end of the fuel assembly passing through and being supported by a reactor core top guide structure, the fuel assembly mechanical flow restriction apparatus comprising: a testing hood comprising a top plate and side plates to form a structure with an open bottom forming an internal volume for positioning over the tops of at least one of the nuclear fuel assemblies and for receiving gases escaping from a failed fuel rod within the fuel assembly, the side plates for resting on the reactor core top guide structure; a flow restrictor positioned within the testing hood and over at least one of the nuclear fuel assemblies, the flow restrictor comprising a sealing plate for positioning on the upper edges of the outer channel of the fuel assembly for mechanically blocking fuel assembly coolant flow exiting the upper end of the fuel assembly; a probe assembly having at least one probe head with at least one thermocouple for sampling the coolant water within the fuel assembly for detecting failure of a nuclear fuel rod in the nuclear fuel assembly; means for causing the sealing plate of the flow restrictor to be positioned on the upper edges of the outer channel of the fuel assembly for mechanically blocking fuel assembly coolant flow from exiting the upper end of the fuel assembly; and means for causing the probe head to be immersed in the fuel assembly reactor coolant water within the outer channel wherein the means for causing the sealing plate to be positioned on the outer channel of the fuel assembly and for causing the probe head to be immersed in the fuel assembly reactor coolant water within the outer channel is hydraulic. 3. A fuel assembly mechanical flow restriction apparatus for detecting failure of a nuclear fuel rod in a nuclear fuel assembly situated in a reactor core of a boiling water reactor, the reactor core comprising a plurality of nuclear fuel assemblies comprising parallel fuel rods supported at an upper end by an upper tie plate and an outer channel surrounding the fuel rods for the passage of reactor coolant from a lower end to the upper end of the fuel assembly, the outer channel having upper edges, the upper end of the fuel assembly passing through and being supported by a reactor core top guide structure, the fuel assembly mechanical flow restriction apparatus comprising: a testing hood comprising a top plate and side plates to form a structure with an open bottom forming an internal volume for positioning over the tops of at least one of the nuclear fuel assemblies and for receiving gases escaping from a failed fuel rod within the fuel assembly, the side plates for resting on the reactor core top guide structure; a flow restrictor positioned within the testing hood and over at least one of the nuclear fuel assemblies, the flow restrictor comprising a sealing plate for positioning on the upper edges of the outer channel of the fuel assembly for mechanically blocking fuel assembly coolant flow exiting the upper end of the fuel assembly; a probe assembly having at least one probe head with at least one thermocouple for sampling the coolant water within the fuel assembly for detecting failure of a nuclear fuel rod in the nuclear fuel assembly; means above the top plate of the testing hood for causing the sealing plate of the flow restrictor to be positioned on the upper edges of the outer channel of the fuel assembly for mechanically blocking fuel assembly coolant flow from exiting the upper end of the fuel assembly and for causing the probe head to be immersed in the fuel assembly reactor coolant water within the outer channel wherein the means above the top plate of the testing hood for causing the sealing plate to be positioned on the outer channel of the fuel assembly is hydraulic. 4. A fuel assembly mechanical flow restriction apparatus for detecting failure of a nuclear fuel rod in a nuclear fuel assembly situated in a reactor core of a boiling water reactor, the reactor core comprising a plurality of nuclear fuel assemblies comprising parallel fuel rods supported at an upper end by an upper tie plate and an outer channel surrounding the fuel rods for the passage of reactor coolant from a lower end to the upper end of the fuel assembly, the outer channel having upper edges, the upper end of the fuel assembly passing through and being supported by a reactor core top guide structure, the fuel assembly mechanical flow restriction apparatus comprising: a testing hood comprising a top plate and side plates to form a structure with an open bottom forming an internal volume for positioning over the tops of at least one of the nuclear fuel assemblies and for receiving gases escaping from a failed fuel rod within the fuel assembly, the side plates for resting on the reactor core top guide structure; a flow restrictor positioned within the testing hood and over at least one of the nuclear fuel assemblies, the flow restrictor comprising a sealing plate for positioning on the upper edges of the outer channel of the fuel assembly for mechanically blocking fuel assembly coolant flow exiting the upper end of the fuel assembly; a probe assembly having at least one probe head with at least one thermocouple for sampling the coolant water within the fuel assembly for detecting failure of a nuclear fuel rod in the nuclear fuel assembly; means above the top plate of the testing hood for causing the sealing plate of the flow restrictor to be positioned on the upper edges of the outer channel of the fuel assembly for mechanically blocking fuel assembly coolant flow from exiting the upper end of the fuel assembly; and means above the top plate of the testing hood for causing the probe head to be immersed in the fuel assembly reactor coolant water within the outer channel wherein the means above the top plate of the testing hood for causing the sealing plate to be positioned on the outer channel of the fuel assembly and for causing the probe head to be immersed in the fuel assembly reactor coolant water within the outer channel is hydraulic. 5. A fuel assembly mechanical flow restriction apparatus for detecting failure of a nuclear fuel rod in a nuclear fuel assembly situated in a reactor core of a boiling water reactor, the reactor core comprising a plurality of nuclear fuel assemblies comprising parallel fuel rods supported at an upper end by an upper tie plate and an outer channel surrounding the fuel rods for the passage of reactor coolant from a lower end to the upper end of the fuel assembly, the outer channel having upper edges, the upper end of the fuel assembly passing through and being supported by a reactor core top guide structure, the fuel assembly mechanical flow restriction apparatus comprising: a testing hood comprising a top plate and side plates to form a structure with an open bottom forming an internal volume for positioning over the tops of at least one of the nuclear fuel assemblies and for receiving gases escaping from a failed fuel rod within the fuel assembly, the side plates for resting on the reactor core top guide structure; a flow restrictor positioned within the testing hood and over at least one of the nuclear fuel assemblies, the flow restrictor comprising a sealing plate for positioning on the upper edges of the outer channel of the fuel assembly for mechanically blocking fuel assembly coolant flow exiting the upper end of the fuel assembly; a probe assembly having at least one probe head with at least one thermocouple for sampling the coolant water within the fuel assembly for detecting failure of a nuclear fuel rod in the nuclear fuel assembly; raising and lowering means for causing the sealing plate of the flow restrictor to be positioned on the upper edges of the outer channel of the fuel assembly for mechanically blocking fuel assembly coolant flow from exiting the upper end of the fuel assembly and for causing the probe head to be immersed in the fuel assembly reactor coolant water within the outer channel wherein the raising and lowering means for causing the sealing plate to be positioned on the outer channel of the fuel assembly is hydraulic. 6. A fuel assembly mechanical flow restriction apparatus for detecting failure of a nuclear fuel rod in a nuclear fuel assembly situated in a reactor core of a boiling water reactor, the reactor core comprising a plurality of nuclear fuel assemblies comprising parallel fuel rods supported at an upper end by an upper tie plate and an outer channel surrounding the fuel rods for the passage of reactor coolant from a lower end to the upper end of the fuel assembly, the outer channel having upper edges, the upper end of the fuel assembly passing through and being supported by a reactor core top guide structure, the fuel assembly mechanical flow restriction apparatus comprising: a testing hood comprising a top plate and side plates to form a structure with an open bottom forming an internal volume for positioning over the tops of at least one of the nuclear fuel assemblies and for receiving gases escaping from a failed fuel rod within the fuel assembly, the side plates for resting on the reactor core top guide structure; a flow restrictor positioned within the testing hood and over at least one of the nuclear fuel assemblies, the flow restrictor comprising a sealing plate for positioning on the upper edges of the outer channel of the fuel assembly for mechanically blocking fuel assembly coolant flow exiting the upper end of the fuel assembly; a probe assembly having at least one probe head with at least one thermocouple for sampling the coolant water within the fuel assembly for detecting failure of a nuclear fuel rod in the nuclear fuel assembly; raising and lowering means for causing the sealing plate of the flow restrictor to be positioned on the upper edges of the outer channel of the fuel assembly for mechanically blocking fuel assembly coolant flow from exiting the upper end of the fuel assembly; and raising and lowering means for causing the probe head to be immersed in the fuel assembly reactor coolant water within the outer channel wherein the raising and lowering means for causing the sealing plate to be positioned on the outer channel of the fuel assembly and for causing the probe head to be immersed in the fuel assembly reactor coolant water within the outer channel is hydraulic. |
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052079767 | summary | BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates generally to nuclear fuel pellet inspection and, more particularly, is concerned with an apparatus for inspecting fuel pellets for surface defects that employs a pellet slide and inspection assembly providing improved inspecting and handling of fuel pellets. 2. Description of the Prior Art Nuclear reactors include fuel assemblies which contain pellets of fissionable material as their basic fuel element. In one exemplary embodiment, a pellet ideally takes the form of a right cylinder with slightly concave or dished opposite ends. For incorporation into fuel assemblies, a number of pellets are stacked end to end in a fuel rod cladding tube which, like the pellets, is usually of circular cross-section. Then, a given number of fuel rods are grouped together in a fuel assembly. It is essential that all pellets used in the fuel assembly be free of circumferential defects, such as cracks and chips, in order to achieve desired stacking of the pellets within the fuel rod tube as well as uniform heat transfer between the stacked pellets and cladding tube and uniform consumption of the pellets during operation of the reactor core. Consequently, an important step in the manufacture of the nuclear fuel pellet is the inspection of its surface to ascertain whether there are any deflects present. Exemplary prior art systems for inspecting and classifying nuclear fuel pellets are disclosed in U.S. Patent Nos. to Jones (U.S. Pat. Nos. 3,221,152; 3,272,332; and 3,282,116), Ryden, Jr. (U.S. Pat. No. 4,037,103), Marmo (U.S. Pat. No. 4,193,502), and Wilks et al (U.S. Pat. No. 4,349,112). While the inspection systems of these prior art patents appear to achieve their objectives under the range of operating conditions for which they were designed, none of these systems appear to be adapted to perform inspection of a pellet for circumferential or surface defects. One commercial inspection apparatus, sold under the registered trademark, Inspector General, by Cochlea Corporation of San Jose, Calif., for inspecting and sorting small parts uses non-contact, three-dimensional ultrasonic vision to verify the identity, shape, defects, orientation, and sequence of parts. Its overall objective is to acoustically detect and cull out parts with shape defects. For a detailed understanding of this Cochlea Corporation inspection apparatus, attention is directed to a publication entitled "Inspector General User's Guide" dated Aug. 1987 and to U.S. Patent Nos. to Buckley et al (U.S. Pat. Nos. 4,557,386; 4,576,286; and 4,690,284) and Pinyan et al (U.S. Pat. No. 4,677,852) assigned to Cochlea Corporation. Basically, inspection by this apparatus is accomplished while the parts are in transit. The parts to be inspected are fed down a chute from a vibratory bowl feeder by a singulation device. As each part is in transmit, it is exposed to 40 kHz sound waves emanating from suitable positioned emitters. The waves bounce off the part, and the reflections are then picked up by an array of transducers or sensors. Analysis of reflected sound waves gives each part an unique "acoustic signature", which is compared to a previously "learned" good part signature. Acceptance or rejection is based on the comparison. This acoustically-based system is said to outperform and be more versatile than more traditional vision, laser, tactile and proximity-sensing techniques. However, in its approach to parts handling and positioning, this "off-the-shelf" inspection apparatus is designed for general purpose parts inspection and sorting and thus cannot be used directly without modification, to inspect nuclear fuel pellets. Certain improvements were made to this "off-the-shelf" inspection apparatus in U.S. Pat. No. 4,894,201 to Ahmed, which is assigned to the same assignee as the subject invention. These improvements adapt the apparatus for inspection of fuel pellets for surface defects, such as chips and cracks, by substituting a single pellet feeder, a pellet guide chute assembly, and a pellet discharge conveyor. The pellet guide chute assembly is inclined and extends through the inspection chamber. In sliding down the guide chute assembly, the pellets move along an inclined straight, or linear, path one at a time through the inspection chamber. Slots are provided in the chute assembly at the inspection chamber for receiving an ultrasonic inspection head. The inspection head mounts acoustical energy transmitting and receiving transducers which transmit acoustical energy into and received it from the inspection chamber for propagating such energy to and from the pellet as the pellet slid under the influence of gravity down the inclined chute assembly. The pellet position along the inclined chute assembly is sensed by light transmitting and receiving devices. Light is transmitted across the inspection chamber through openings in the chute assembly and thus across the path of movement of the pellets. A drawback of the improved apparatus of the cited Ahmed patent is that, other than the particular inclination chosen for the chute assembly itself, there is no means of controlling the speed of the pellets as they slid down the inclined straight path defined by the chute assembly. The rapid rate at which pellets are allowed to slide uncontrolled down the straight inclined chute assembly often result in high impacts at the bottom with the pellet discharge conveyor, leading to cracking or chipping of the inspected pellets. Consequently, a need still exists for additional improvements to better adapt this "off-the-shelf" ultrasonic inspection apparatus for use in inspection of nuclear fuel pellets. SUMMARY OF THE INVENTION The present invention provides an nuclear fuel pellet surface defect inspection apparatus designed to satisfy the aforementioned needs. In accordance with the present invention, the apparatus incorporates a pellet slide and inspection assembly which more accurately inspects one pellet at a time for surface defects while handling each pellet more gently. The pellet slide and inspection assembly includes a pellet slide defining an inclined track and a pair of lower and upper sound reflectors disposed at an inspection station along the slide. The lower and upper reflectors are configurated to define an annular inspection chamber through which a pellet moves as it slides down the inclined track. The annular inspection chamber completely encloses the circumference of the pellet at the moment when a reading is taken, thereby enhancing the accuracy of the reading by making the sound signal emitted to and reflected from the pellet completely surround the pellet being inspected. The pellet slide has upper and lower portions on opposite sides of the inspection chamber, the lower portion having a shallower, or more gradual, slope than the upper portion. After a pellet moves through the inspection chamber, it is decelerated by the change in the slope of the lower portion of the pellet slide track. This reduces the exit velocity of the inspected pellet, which greatly reduces the possibility of the pellet chipping due to contact with the discharge conveyor at the exit end of the pellet slide. Thus, more accurate ultrasonic inspection of each pellet is achieved while each pellet is handled in a manner that will prevent cracking or chipping. These and other features and advantages 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. |
061480541 | claims | 1. A fuel bundle for a nuclear reactor comprising: a plurality of fuel rods spaced laterally from one another in a matrix thereof enabling flow of liquid about the rods from a lower end of the fuel bundle toward an upper end thereof; a plurality of spacers spaced one from the other along the fuel bundle, each said spacer having openings for receiving the fuel rods and maintaining the rods spaced from one another in the matrix thereof; at least one of said rods being a part-length fuel rod terminating in an upper end below upper ends of surrounding fuel rods and below at least one of said plurality of spacers, said part-length rod defining with respect to said surrounding rods a vent volume overlying said part-length rod and having a connecting structure adjacent an upper end thereof; a support structure extending through an opening in said one spacer in registration with said part-length rod and having a connecting structure adjacent a lower end thereof, said support structure carrying a separation device disposed in the vent volume when said upper and lower connecting structures are connected to one another for flowing liquid laterally outwardly onto surfaces and into interstices of said surrounding fuel rods; said separation device including a swirler projecting laterally outwardly of said support structure; said separation device and the opening of said one spacer being sized relative to one another to enable withdrawal of said support structure and said separation device through the opening of said one spacer; said spacers having a plurality of ferrules arranged in a regular rectilinear matrix thereof, an opening in said one spacer aligned vertically above said part-length rod being void of a ferrule, the swirler comprising a plurality of blades disposed above said opening void of the ferrule such that blade tips project laterally to overlie substantially the entirety of said opening void of the ferrule. 2. A fuel bundle according to claim 1 wherein said swirler blades have a plan area in part overlying portions of underlying ferrules adjacent said opening void of the ferrule, said swirler and said underlying ferrule portions being sized and configured to enable said blades to pass through said opening void of the ferrule in response to relative rotation of said support structure and said one spacer and axial movement of said structure relative to said one spacer. 3. A fuel bundle according to claim 1 wherein said opening void of a ferrule is substantially square and defined in part by apices at corners thereof adjacent diagonally located ferrules and middle ferrules between said diagonally adjacent ferrules, said blades projecting laterally such that when projected onto the spacer opening, blade tips extend closely adjacent said diagonal ferrules and between said middle ferrules. |
062531638 | description | DESCRIPTION OF THE PREFERRED EMBODIMENTS One way to implement the invention is comprised, in a first variant, of using a microprocessor card operating by means of an operating system stored in the card and constituting a so-called "smart card" that is pre-initialized with the self-diagnostic data, and of having this data taken into account by the terminal when testing the application software. An application software in a terminal can be broken down into elementary tasks which occur at predetermined moments. For example, for a banking application, a transaction can be broken down into the following elementary tasks (Ti): Verification (T1, FIG. 1) of whether the card inserted is authorized, Authentication (T2) of the bearer, Acquisition (T3) of the data of the transaction in the terminal, Writing of this data into the microcircuit of the card, and Validation (T4) of the transaction in the terminal and the card. In addition, and always during a transaction, the application software manipulates data. This data can be used temporarily, like the Code created by the bearer (Cp), which is stored in the memory of the terminal, or the identity of the bearer (Ip), which is stored in the card, or like the Amount of the transaction (Mt) or the Date of the transaction (Dt), which are stored in the terminal and the card. During the execution of each elementary task, each of these data may be initialized, modified or unchanged. The self-diagnostic utility function of the application software is comprised of verifying the data of the transaction at the time of certain tasks, under normal usage conditions. This function can be performed either by the basic software or by the application software. To do this, the operator responsible for the test develops a grid composed, on one side, of the identifiable elementary tasks, designated Ti, and on the other side of data Dj constituted by information such as: Cp, Ip, Mt and Dt. FIG. 1 shows an example of such a grid. In order to test the correct execution of a transaction, the operator chooses to verify the value of certain data during the execution of specific tasks. This involves associating a datum Dj with a task Ti; these associations are symbolized by crosses in the grid of FIG. 1. A third piece of information Sk is added. The value of this code indicates the type of output used to which the datum to be verified is to be sent. For example, the data is sent to the network when Sk is at a first value, for example 11111 (Sk=1), to the printer when Sk is at a second value, for example 11211 (Sk=2), or to the screen when Sk is at a third value, for example 11311 (Sk=3). The operator enters the triplets of information (Ti, Dj, Sk) into a special so-called diagnostic central processor, which central processor is equipped with a card reader. The diagnostic software is configured in accordance with the application to be tested so that the triplets (Ti, Dj, Sk), when captured, are identified on the screen by the precise indication of the elementary tasks and the data to be verified, and not the numeric labels Ti, Dj, Sk. The card containing the self-diagnostic data is either a special card or a general-purpose card normally used for an application. A detailed description of an embodiment is given for each case. The first case described is that in which a special card called a "test card" (20, FIG. 2) is used to contain the self-diagnostic data. A security procedure is implemented to prevent a defrauder from being able to use a card of this type in an unauthorized manner. The test card contains in a secret memory area, not shown, a secret so-called diagnostic code "KD." This secret code must first be presented to the card, which verifies it and, if it is equal to a reference code, authorizes the writing of the self-diagnostic data into the programmable memory of the card. While providing for the storage of the self-diagnostic data, the non-volatile programmable memory of the test card also has, in addition to the system area ZS which contains the operating system of the card and the other usable area (AZU) which allows other types of storage, an area (22) called "ZD." It is in this area that the triplets (Ti, Dj, Sk) are stored in-succession. Thus, a first area (220) of a memory allows the storage of the first triplet T1, D2, 1; a second area (221) allows the storage of the second triplet T2, D1, 2; a third area (222) allows the storage of the third triplet T3, D1, 1; a fourth area (223) allows the storage of the fourth triplet D4, D3, 3; a fifth area (224) allows the storage of the triplet T4, D4, 1; T1, T2, T3, T4, D1, D2, D3, D4 respectively representing the information in FIG. 1. It is obvious that the portable object can comprise more or fewer triplets depending on the type of supervision or self-diagnosis that it is desirable to perform on the tasks executed by the application program. The area ZD is labelled by its start address "ADD-ZD" and its end address "ADF-ZD"; the two address values are stored in the part (230, 231) of the programmable memory allocated to the operating system. The non-volatile programmable memory is of the EPROM, EEPROM, FeRAM, SRAM or FLASH type. FIG. 2 describes the organization of this memory using the information cited in FIG. 1. Advantageously, the datum Dj is the physical address of the datum to be verified in the working memory of the terminal. Once programmed, the test card is inserted into the terminal in which the self-diagnostic function must be run. FIG. 3 is a flow chart illustrating the chronology of the events of the program, constituted by a wait and test sequence (1, 2, 3), the test triggering, as a function of the result, either a sequence for loading the terminal with the self-diagnostic data (4 through 7, FIG. 3), or a sequence for executing the self-diagnostic program (8 through 16, FIG. 3), which is incorporated either into the basic software of the terminal or into the-application software. Step 1 is the initialization of the terminal after it is powered up, and step 2 is the phase for waiting for an order or an insertion of a card. In step 3, the terminal tests whether the card inserted into the reader is a general-purpose card, and in step 4 whether the card is a test card. In the latter case, the terminal executes in step 5 a procedure for authenticating the card by means of a reference code or by means of a standard challenge-response authentication schema using an algorithm and a secret key (KD). Once the test card has been identified and authenticated, the program of the terminal reads in step 6 the information contained in the area ZD. The selection and the location of the triplets are performed with the aid of the two pointers ADD-ZD and ADF-ZD. The triplets (Ti, Dj, Sk) read successively in the area ZD are stored in the same order in an area of the memory of the terminal called ZTD. Once the last triplet has been stored in the area ZTD, the terminal program, in step 7, sets a self-diagnostic indicator "Ind-DT" in the memory of the terminal to the active state. Then the terminal program loops back to wait for a command or another insertion of a card in step 2. A new card is inserted and if it is a general-purpose card compatible with the application run by the terminal. As stated above, the application software in the terminal is broken down into elementary tasks Ti which can be executed individually (step 8). At the end of the execution of each task, which can be labelled by the code Ti, the application program, in step 9, tests the indicator Ind-DT of the terminal. If it is inactive, the self-diagnostic function is not operational, and the program continues to execute the other tasks. If the indicator Ind-DT is active, the program of the terminal, in step 10, searches the area ZTD of the memory of the terminal for the first triplet (Ti, Dj, Sk) for which Tt=Ti, that is, to see if there is a datum to be tested as a result of the task that has just been executed. if yes, in step 11, the value "Val" of this datum (Dj) is temporarily stored in the memory of the terminal, and as a function of the value of Sk, it is processed in the following way: If Sk is equal to "1" (step 12), the datum Dj must be sent to the network. In this case, a block of three data is constituted by the value of the field Tt, the label Dj of the datum to be analyzed and the value "Val" of this datum extracted from the memory of the terminal. These blocks are stored one after another in an area of the memory of the terminal called "ZDR." The content of this area is sent to the network at the end of the transaction or when there is a request by the network for self-diagnostic data. Once all the data have been transmitted, the area ZDR is cleared so that it can be reused when a there is new insertion of a card. If Sk is equal to "2" (step 13), the datum Dj must be sent to the printer of the terminal for printing. In this case, a message is created in the software buffer of the printer; it is composed of a text (ASCII code) indicating the nature of the datum, for example "AMOUNT," followed by the decimal or hexadecimal value of the datum Dj; the message ends with a separator and a "CARRIAGE RETURN--SKIP LINE." It is possible to gather all of the self-diagnostic messages and print them at the end of the transaction. If Sk is equal to "3" (step 14), the datum must be sent to the display unit of the terminal for display in this case, a message is created in the buffer of the display unit, composed of a text (ASCII code) indicating the nature of the datum, for example "AMOUNT," followed by the decimal or hexadecimal value of the datum Dj. The messages corresponding to each element (Tt, Dj, "3") are successively displayed for a certain time set by the program. It is possible to gather all of the messages and display them at the end of the transaction; the scrolling of the messages can be controlled by pressing a key on the keyboard of the terminal. Once the datum Dj has been processed, the program verifies in step 15, whether there are other triplets in ZTD for which Ti=Tt. If yes, the program loops back to step 11 and processes a new triplet. For each elementary task, the search for triplets is performed by scanning the entire area ZTD. If there are no more triplets (Ti=Tt, Dj, Sk) to be processed, the program, in step 16, continues in sequence and may, in a variant, proceed to another task without executing the steps 17 and 18 described below. If there are no other tasks to be executed, the program loops back to step 3, to wait for a command or for a new insertion of a card. It is possible to associate a counter initialized with a certain number with the indicator Ind-DT in the terminal so that the self-diagnostic function is only activated for this number of general-purpose card insertions. In order to do this, the operator has pre-entered this number into a specific location (21, FIG. 2) of the programmable memory of the test card, for example, next to the locations (230, 231) of ADD-ZD and ADF-ZD. In this case, this number is stored in the memory of the terminal after the insertion of the test card in step 6. Then this number is decremented (step 17) at the end of each execution of a self-diagnostic function (a YES output from step 16). When it reaches 110,11 the indicator Ind-DT is set to the inactive position (step 18) and the content of the area ZTD is possibly erased. If the counter is not installed, steps 17 and 18 do not exist and the self-diagnostic function is executed only once or indefinitely until a new insertion of the test card switches the indicator Ind-DT to the inactive position. It is possible to avoid the utilization of a test card and to use only general-purpose cards, on condition that they support the special self-diagnostic functions. For this reason, the programmable memory of the general-purpose card contains, in addition to the system area ZS and the user area ZU, an area ZD which is labelled by its start address "ADD-ZD" and its end address "ADF-ZD" (see FIG. 4). The programmable memory of the general-purpose card also contains in its system area, in a location (232), an indicator "Ind-D" which indicates whether or not the self-diagnostic function is active. All of these data ADD-ZD, ADF-ZD, Ind-D are stored in locations (230, 231, 232) of the part ZS of the programmable memory allocated to the operating system. The two address values are determined and written into the area ZD during the customization of the card; this method is simple to implement but has the drawback of requiring the reservation of a sizeable location in all cards that can be used for the self-diagnosis. Advantageously, the location in the area ZD can be allocated dynamically by the operating system of the card after the correct entry of the code KD. The operator indicates to the card the number of triplets (Ti, Dj, Sk) or the number of octets to be reserved for ZD. The operating system of the card then searches in the programmable memory for a blank location of sufficient size. If the memory does not contain any such blank location, the operating system returns an error message and interrupts the procedure for entering the self-diagnostic data. In the opposite case where there is sufficient space, the operating system stores the start address "ADD-ZD" and the end address "ADF-ZD." It will be seen below how, after the execution of the self-diagnostic function, it is possible to erase the presence of the area ZD, thus releasing this memory space. The same is true for the test card. A security procedure is provided in order to prevent a defrauder from being able to use a general-purpose card to enter self-diagnostic data. A mechanism of the challenge-response type with an algorithm and a secret code makes it possible to authenticate the operator and authorize the writing and reading (it will be seen why below) of the triplets in ZD. In the case where a general-purpose card is used to transmit the self-diagnostic data, the code Sk can assume a fourth value 4; this value indicates that the value of the datum Dj to be verified has been written into the card. In this case, a fourth field located at an address "Adr-VII" is allocated at the end of the triplet (Ti, Dj, Sk=4), and thus quadruplets are stored. The size of this field corresponds to that of the data to be written; the operator must therefore specify the number of octets "Nb-V" in this fourth field, and its content is initially constituted by the write address (Adr-V), then after the output by the value "Val," as seen below. The fifth triplet (225) of FIG. 4 has this structure. When all of the triplets (Ti, Dj, Sk) (220 through 225) have been entered into the area ZD, the indicator "Ind D" is set to the active position, thus indicating that the self- diagnostic function is active in this card. FIG. 5 shows the sequence of operations when the card described above is inserted into a terminal. Step 1 is the initialization of the terminal after it is powered up and step 2 is the phase for waiting for the insertion of a card; the program continues when the card is recognized as being compatible with the application through the terminal's recognition of the presence of the necessary information. In this step 2, the program performs the selection of the entity corresponding to the application. Unlike the test card, when the general-purpose card is inserted by the bearer, the latter can be completely unaware that the self-diagnostic function is active. In step 3, the terminal tests whether the indicator Ind-D in the card is set to the active position and thus whether the self-diagnostic function is operational. The indicator can be sent either by a particular value in the octets transmitted by the card during the power-up phase, or by a particular value transmitted during the selection of the entity corresponding to the application used in the card. If Ind-D is active, the program proceeds to step 4. During this step 4, the area ZD is read with the aid of the two address values ADD-ZD and ADF-ZD and all of the triplets read in the card are stored in the memory ZTD of the terminal. If the triplet comprises a datum Sk whose value is "4," the operating system of the card returns, in addition to the three values Ti, Dj and Sk, the address "Adr-v" of the fourth field reserved for writing the datum into ZD and the number of octets "Nb-v" in this field. For security reasons, read access to the area ZD of the card is only granted by the operating system of the card if the indicator Ind-D of the card is active. Once all of the information contained in the area ZD has been stored in the memory area ZTD of the terminal, the terminal sets its self-diagnostic indicator Ind-D to the active position (step 5). Steps 3, 4 and 5 are parts of the sequence for initializing the dialogue between the general-purpose card and the terminal and are executed before the execution of the application program. As stated above, the application software is broken down into elementary tasks which can be tested individually. At the end of the execution of each task, which can be labelled by a number Tt (step 6) for example the basic software resumes control and tests whether the diagnostic indicator inside the terminal is active (step 7). If it is active, in step 8 the program searches to see if there is an element (Ti, Dj, Sk) stored in the area ZTD that has a field value Ti equal to that of Tt. If yes, there is a datum (labelled Dj) to be verified as a result of the task that has just been executed; the value of this datum is then temporarily stored in the memory of the terminal. As a function of the value of Sk, it is processed in the following way (step 9): If Sk is equal to "1" (step 10), the datum Dj must be sent by the terminal to the network. A block of three data is then constituted by the value of the field Tt, the label Dj of the datum to be analyzed and the value "Val" of this datum extracted from the memory of the terminal. These blocks are stored one after another in an area of the memory of the terminal called "ZDR." The content of this area is sent to the network at the end of the transaction or when there is a request from the network for the self-diagnostic data. Once all of the data has been transmitted, the area ZDR is cleared so that it can be reused when a there is a new insertion of a card. If Sk is equal to "2," the datum must be sent to the printer of the terminal, and the program continues with step 11. During this step 11 a message is created in the buffer of the printer, composed of a text (ASCII code) indicating the nature of the datum, for example "AMOUNT," followed by the decimal or hexadecimal value of the datum Dj, and the message ends with a separator and a "CARRIAGE RETURN--SKIP LINE." Advantageously, it is possible to gather all of the messages and print them at the end of the transaction. If Sk is equal to "3," the datum must be sent to the display unit of the terminal, and the program continues with step 12. During this step 12, a message is created in the buffer of the display unit, composed of a text (ASCII code) indicating the nature of the datum, for example "AMOUNT," followed by the decimal or hexadecimal value of the datum Dj. The messages corresponding to each element (Tt, Dj, "3") are successively displayed for a certain time set by the self-diagnostic software. Advantageously, it is possible to gather all of the messages and display them at the end of the transaction; the scrolling of the messages can be controlled by pressing a key on the keyboard of the terminal. If Sk is equal to "4," the datum must be stored in the card, and the program continues with step 13. During this step 13, a fourth field is reserved for this purpose in ZD, the address "Adr-v" of this fourth field and the number of octets "Nb-v" in this field having been stored in the area ZTD during the loading of the self-diagnostic data into the terminal. The terminal then sends the card a write command with the following parameters: Write address: Adr-v Number of octets to be written: Nb-v Value to be written: "Val" of the datum Dj. The write operation in the area ZD is only authorized by the operating system of the card when the fourth field of a triplet of the Sk=4 type corresponds to the Ti. In the case where the triplet Ti of the card is not of the Sk=4 type, the write operation is denied. An execution report is systematically returned to the terminal after each write command; if the latter has not been successful, the terminal warns the user with a message. The utilization of the stored data is explained below. A variant is comprised of temporarily storing all the values of the data Dj of the Sk=4 type and of executing the commands for writing the values at the end of the transaction. Once the datum Dj has been processed, in step 14, the program verifies whether there are other triplets in the area ZTD for which Tt=Ti. If yes, the program loops back to step 9 and processes a new triplet. For each elementary task, the search for triplets is performed by scanning the entire area ZTD. If there are no more triplets (Ti=Tt, Dj, Sk) to be processed, the program proceeds to step 15, searching for another task to be executed. If there are no other tasks to be executed, the program loops back to step 2 to wait for a new insertion of a card. In the case where a general-purpose card is used to transmit the self-diagnostic data, the self-diagnostic function should be able to be executed only once. In effect, the operator may intend to perform only one test of the card reader terminal, after which the data must not leave the terminal. Moreover, if the datum to be verified has a field Sk of the 4 type only, a single storage is possible. In order to start the function another time, the card must be reprogrammed by the operator. To prevent it from being used several times with the self-diagnostic function, just after the reading of the area ZD by the terminal, the operating system of the card will set the indicator Ind-D to the inactive state. For security reasons, it can also erase all the triplets of the Sk=1, 2 and 3 types. The indicator Ind-D is inactive, and the reading of the area ZD is no longer possible. The data corresponding to the type SK=4 are processed when the general-purpose card enters a terminal authorized to read it, that is, a terminal that is authenticated in the same way as when the self-diagnostic data are written. Once all the triplets have been read, the total erasure of the area ZD an be carried out. This erasure can be triggered by a special command or during the first write operation in the area ZD. The erasure, which is justified for security reasons, makes it possible to release the space occupied by the area ZD. This location can be used by the application. This "one-shot" style of operation of the self-diagnostic function can be advantageous when a person reports his credit card to a bank branch declaring that his card "does not work" in a certain type of payment terminal. The branch will store the self-diagnostic data in this card, specifying that the data of the transaction (amount, date, certificate value) are to be written into the card by setting the third field Sk, in each triplet corresponding to a task to be recorded, at the value "4" (Sk=4). The person returns to the merchant where the terminal to be tested is located, executes a transaction and returns to his branch, which analyzes the information stored in ZD, or has it analyzed remotely. One-shot operation is also advantageous for verifying the operation of a terminal suspected of fraud. A banking institution discovers that transactions in a terminal have been credited without there having been any request to debit client accounts. The banking institution sends inspectors provided with general-purpose cards with the self-diagnostic function. Upon their return, the data loaded into the card are analyzed. Another example: a banking institution may find it advantageous to quickly learn the time and the place where the card is used for the first time. For this reason, before the card is delivered to its bearer, it contains two triplets of the Sk=1 type, in which each third field Sk is at the value "1." In the area ZD, with the datum Dj corresponding to the date of the transaction and the datum Dj corresponding to the identity of the terminal, during the first transaction, the two blocks (Ti, Dj, "date") and (Ti, Dj', "terminal ID") will be sent to the network immediately. GENERAL SUMMARY While the preferred forms and embodiments of the invention have been illustrated and described, it will be apparent to those of ordinary skill in the art that various changes and modifications may be made without deviating from the inventive concept and spirit of the invention as set forth above, and it is intended by the appended claims to define all such concepts which come within the full scope and true spirit of the invention. |
059237201 | description | DETAILED DESCRIPTION OF THE INVENTION The present invention is designed to perform angle dispersive x-ray diffraction and is composed of several components shown in FIG. 1. X-rays emanating from an x-ray source 10 are focused by a curved crystal monochromator 12, with the unique design that will be described presently below. The x-rays are focused onto a sample specimen 14 which has a well-defined periodicity along the z-axis. Diffracted intensities from the sample within an angular range defined by the focus convergence are detected simultaneously at different diffraction angles on a position-sensitive x-ray detector 16. The x-ray sources hereinafter referred to as the "source" may be sources well-known in the art such as sealed x-ray tubes or rotating anodes. In x-ray laboratory sources, a common source is CuK.sub..alpha. radiation, but the source could equally be generated from molybdenum, silver, chromium, rhodium, iron and other target materials. The convergence of the monochromator focus and the focal size are dependent upon x-ray energy and also the orientation of the reflecting atomic planes to the monochromator surface. These features are taken into consideration in the analysis which follows. Position sensitive detectors which are known in the art are suitable for use in the x-ray spectrometer of the invention. Suitable position sensitive detectors include linear position-sensitive proportional detectors, linear photodiode arrays, linear charge coupled devices, two-dimensional proportional x-ray detectors, two-dimensional charge coupled devices. The x-ray spectrometer of the invention is useful in analyzing any material which exhibits a well-defined periodicity along at least one dimension. By way of example only, the sample includes natural or synthetic lipids, epitaxially grown layers, evaporated layers, and epitaxially grown multilayers or superlattices. The sample surface may be a solid or a liquid; in the latter case, the sample is horizontal within the spectrometer. The monochromator crystal desirably is a perfect single crystal, the exact composition of which may be chosen according to the needs of the particular application. Single crystal germanium, silicon and lithium fluoride are preferred single crystals for use in the present invention. The crystal is oriented along a selected diffraction plane; however, the particular diffraction plane is not of great significance to the invention. Orientation of the crystal monochromator will have an effect on the diffracting angle of the crystal, which may be taken into consideration in the curvature of the crystal as discussed below. In addition, it is recognized that certain synthetic multilayers may be used in place of the perfect crystal. These multilayers may consist of alternating thin films of two or more materials, e.g., Si/W deposited on a thin bendable substrate. The monochromator with dimensions as shown in FIG. 3 is bent by a four point bender (shown schematically in FIG. 2) to assume the shape which substantially approximates that of a logarithmic spiral which provides perfect focusing from an extended source. This is in contrast to the Johansson-type monochromator (described by Luken et al.) which requires a point source to achieve perfect focusing. Since real laboratory x-ray sources have a finite size, the logarithmic spiral form is better suited for laboratory experiments. Prior to subjecting the monochromator crystal to a four-point bending process in order to approximate a logarithmic spiral curvature, the sides of the monochromator crystal which define the width are ground in order to bend the real monochromator to a shape which significantly improves the mechanical approximation to the ideal logarithmic spiral. The shaping introduces a taper and preferably a linear taper along the length of the crystal. The taper is selected commensurate with the application of the apparatus, the composition of the crystal, the wavelength of the x-ray and the geometry of the spectrometer; however, tapers of less than 0.10 radians and preferably less than 0.02 radians are typical. A crystal exhibiting an exemplary taper of the invention is shown in FIG. 3. Referring to FIG. 3, in which the unbent, flat crystal is shown in plain view, L is defined as the length of the monochromator crystal, W.sub.0 is the width of the crystal at the center line (CL) of the crystal, W.sub.1 is the width of the crystal at its larger end and W.sub.2 is the width of the crystal at its smaller end. For the unbent crystal shown in FIG. 3, the width dimension of the coincident along the y-axis, the length L is coincident along the x-axis and the thickness is coincident with z-axis. A linear taper is defined by and angle .tau.=arctan {(W.sub.1 -W.sub.2)/L}. These dimensions are indicated in FIG. 3. This new design produces a beam focus which is at least an order of magnitude smaller than that described in the prior art (de Wolff), without a restriction in the source size; furthermore, the focus quality of the present invention makes it possible to perform x-ray diffraction and x-ray reflection in a high resolution scanning mode. The taper may be introduced into the crystal using standard crystal handling techniques. For example, the crystal may be securely mounted in a clamping device in a surface grinding apparatus. The edge of the crystal is indicated with a dial indicator which is a sensitive spring-loaded mechanical measuring tool. Such instruments can determine the relative displacement of a surface to 0.0005" (0.5 mil) or less. The crystal may then be tilted until the edge has the desired relative displacement from one end to the other corresponding to the desired taper. The taper is introduced by applying a grinding surface such as a diamond grinding wheel across the crystal edge. The process is then repeated on the other side of the crystal. A camera-equipped apparatus, such as an optical comparitor, may be used for such an operation. For sample specimens in which diffuse scattering distorts or prohibitively increases the background intensity relative to the specular intensity, a single or "ladder" slit 20 can be used to determine the integrated specular scattering above the background, as is shown in FIG. 4. The slit 20 serves to define a beam with an angular convergence much smaller than that defined over the entire monochromator. The purpose is to create a highly collimated beam which is incident on the sample at a specific angle. One would observe on the PSD a single well-defined peak corresponding to the specularly reflected beam. One or more slits may be employed in the spectrometer, as needed. The method and apparatus may be adapted for use with a solid or a liquid sample. In addition, the spectrometer may include a second focusing device. The second focusing device typically is positioned within the spectrometer so as to focus in the plane substantially perpendicular to the curved crystal monochromator. This provides focus along a second axis resulting in a reduced spot size of the x-ray beam. The reduced spot size makes the spectrometer well suited for used as a diffraction microprobe. The second focusing device may be any conventional focusing crystal or mirror. In a preferred embodiment, it may also be a curved crystal monochromator of the type described herein. The log spiral (LS). The specific curvature for the LS monochromator is determined by 1) the desired x-ray wavelength, and 2) the orientation of the crystallographic diffraction planes with respect to the monochromator surface and 3) the monochromator/source and monochromator/focus distances. The important feature of the logarithmic spiral is that the angle, .phi., formed between a vector from the origin and the tangent to any point on the spiral curve is constant. In FIG. 5, this geometry is realized for the present spectrophotometer by providing a crystal monochromator having an ideal logarithmic spiral with the origin representing a focus on a sample surface, F.sub.0. For the general case where the diffracting crystallographic planes of the monochromator are oriented at an angle .sigma. with respect to the monochromator surface, the constant grazing angle of incidence is given as: EQU .phi.=.theta..sub.BRAGG -.sigma., (1) where .theta..sub.BRAGG is the Bragg angle of diffraction for the monochromator and .sigma. is the orientation angle of diffracting crystallographic planes with respect to the monochromator surface, and where the Bragg angle of the monochromator for a given wavelength and diffraction plane is: ##EQU1## where .lambda. is the x-ray wavelength and d is the characteristic atomic spacing between the monochromator's diffraction plane. For the purposes of this disclosure, a quantitative description of the LS is presented in order to demonstrate the ability of this invention to achieve micron scale focal dimensions. The mathematical representation of the LS has the following form in polar coordinates (r,.theta.) where r is the polar distance from origin to a point on the logarithmic spiral; .theta. is the polar angle of the logarithmic spiral; and .alpha., .beta. are constants: EQU r =.alpha.e.sup..beta..theta., (3) which can be written parametrically in Cartesian coordinates, (x,y), as a function of .theta.: ##EQU2## assuming the geometry shown in FIG. 5, with the focus placed at the origin and the center of the crystal positioned at x=.alpha.=F.sub.0 M.sub.0 and y=0. F.sub.0 M.sub.0 represents the distance from the center of the monochromator crystal (M.sub.0) to the sample surface (F.sub.0). F.sub.0 also coincides with the origin corresponding to the ideal logarithmic spiral. The constant .beta. is a function of the constant .phi. and determined from the scalar product between the unit ray along F.sub.0 M: EQU u=cos.theta.i+sin.theta.j, (5) and the unit tangent at M where M represents an arbitrary point on surface of the monochromator: ##EQU3## where i and jare unit vectors in the x and y directions, respectively. Thus, ##EQU4## By the present convention in which a clockwise rotation of .theta. is negative, the positive value for .beta. is chosen. Of additional relevance to this disclosure are the arclength, s, along the logarithmic spiral axis: ##EQU5## and the radius of curvature, R.sub.LS (.theta.): EQU R.sub.LS (.theta.)=.alpha.e.sup..beta..theta. .sqroot..beta..sup.2 +1=s.beta.+.alpha..sqroot..beta..sup.2 +1, (10) where R.sub.LS (.theta.)is the radius of curvature at the point on the spiral defined by .theta.. For our exemplary case of the diffractometer design, we choose a copper x-ray source with a germanium single crystal monochromator selecting the Cu K.sub..alpha.1 radiation (1.5407 .ANG.), reflecting from the Ge(111) crystallographic planes. A symmetric reflection geometry for the LS will be adopted, where .phi.=.theta..sub.BRAGG =13.63.degree. (0.2379 radians). The distances F.sub.0 M.sub.0 =M.sub.0 S.sub.0 as represented in FIG. 5 may be typically 165 mm. One of the advantages of the LS monochromator is that it views an extended x-ray source, shown in FIG. 6 as the line at S.sub.0 S.sub.1. The x-ray source size in a conventional laboratory system is defined by the rectangular portion of a target on which is focused an accelerated electron beam. In a typical configuration of this invention, a Cu x-ray tube with target dimensions 2 mm.times.12 mm may be employed. The tube may be tilted so that the monochromator views the 2 mm dimension from a takeoff angle of 10.degree. (0.174 radians), making the effective source size seen by the monochromator equal to (2 mm)Sin(0.174)=0.35 mm. Based on this value, a typical 30 mm length of the crystal will collect and reflect a fan of radiation with a convergence angle, .omega., equal to 0.045 radians (de Wolff). The radius of curvature of the monochromator at M.sub.0 is 700 mm. A 0.5 mm thick crystal may be used. The x-ray focus characteristics are determined by the quality of the match between the bent crystal and the ideal logarithmic spiral. By using a four-point bending apparatus, de Wolff approximated the ideal logarithmic shape to second order in s (de Wolff) . In this invention disclosure, we describe a method by which the logarithmic shape can be bent to a vanishingly small third order term for the best case; and even if the best case situation can not be met exactly, a finite but small second order term remains, but this term is at least one order of magnitude less than the remainder term in the prior art. It is precisely this focusing geometry that makes micron resolution scanning possible with our invention. Below we demonstrate that the focus in our new monochromator design is superior to that described in the prior art. We first describe the radius of curvature for the longarithmic spiral monochromator crystal (equation 10) in the form: EQU R.sub.LS =R.sub.0,LS (1+A.sub.LS s) (11) where ##EQU6## and R.sub.0,LS is the radius of curvature at s =0, at the center of the crystal and A.sub.LS is the coefficient of s in equation (11) for the radius of curvature for the logarithmic spiral. This curvature radius is compared to that for a four-point bender in which two adjustable loads are applied evenly across the crystal width and symmetric about the center line of the crystal, with two symmetric supports across the width, but closer to the center than where the adjustable loads are applied (see FIG. 2). The prior art (de Wolff, Luken et al.) employ a rectangular shaped crystal monochromator. Our invention employs a linearly tapered crystal such that the moment of inertia I along the bending axis, x, is: ##EQU7## where w is the width of the crystal, t is the thickness and A.sub.cryst is the slope of the taper. It is apparent that, for the prior art crystal where the taper A.sub.cryst =0, the moment of inertia is the same along the length of the crystal, whereas for the crystal monochromator of the invention, the moment of inertia varies along the axis of bending. From elementary beam theory, the curvature of the linear taper crystal at point x, along the bending axis bent in the described four-point bender is: ##EQU8## where L.sub.0 is the bending moment (the change in bending moment of inertia along the taper) at the crystal center, E is the Young's modulus of the monochromator, I.sub.0 is the bending moment of inertia at the crystal center, and B.sub.cryst is the slope of the bending moment from point 2 to point 3 in FIG. 2 introduced by unequal loading at points 1 and 4 in FIG. 2. We recognize that the curvature for the ideal LS form (equation 11) is cast as a function of s, while the dimension, x, described in equation 14 is measured along the axis perpendicular to the reaction forces. The two lengths differ in third order: ##EQU9## The best match between the logarithmic spiral and the real crystal will be given when ##EQU10## A.sub.LS, and R.sub.0,LS are defined by .phi. and F.sub.0 M.sub.0 in equation 12. Recognizing that the aberration error at the focus is due to the difference in direction between rays reflected from neighboring points on the LS and the corresponding real crystal (see FIG. 7), one can write the integrated error for half of the monochromator .PHI. as: ##EQU11## where it is understood that M.sub.1 is measured along the s axis, M.sub.1 is the effective endpoint closest to the focus on the surface of the monochromator crystal, R.sub.0 is the monochromator crystal radius of curvature at the center of the bending axis, and the following expansions have been used: ##EQU12## we arrive at the significant result that ##EQU13## Using .phi.=0.238 radians and F.sub.0 M.sub.0 =165 mm, equation 12 gives A.sub.LS =5.89E-3. With .omega.=0.045 radians, the best match between our mechanical approximation and the ideal logarithmic spiral curve the size of the focus is only 5E-3 microns (equation 12). Without a linear taper in the crystal monochromator width, the focal size using the same exemplary geometry would be 20 microns for a crystal of the same dimensions. We recognize that, due to uncertainties in the shaping of the monochromator taper, this ideal condition may not be met. The uniqueness of this instrument is that the four-point bender is used to correct for these shape errors. We shall assume that the error can be corrected to first order by setting the unequal loads such that A.sub.cryst -B.sub.cryst =A.sub.LS in equation 17. For this case where the taper in the crystal deviates slightly from the ideal case, the best focus that can be achieved is given by: ##EQU14## In practice, the major factor in deforming the quality of the focus is due to the finite error associated with grinding the sides of the monochromator crystal. Recognizing that A.sub.cryst is the tangent of the convergence angle for the width of the monochromator, a conservative estimate for the grinding precision is on the order of 0.001 radians. Setting A.sub.cryst -A.sub.LS =0.001, A.sub.LS =5.89E-3radians, M.sub.1 =15 mm and adjusting the bending loads such that A.sub.cryst -B.sub.cryst =0, equation 20 and 21 defines the focus size of 3.1 microns. Application to Lipid Membrane Structure. The invention can be used to determine the electron density profile in lipid bilayers with applications in the field of drug testing. Compared to the standard methods of x-ray diffraction from bilayer stacks, the use of angle dispersive x-ray diffraction as described herein is cost-effective, enables faster data collection times, permits straightforward sample preparation and may be easily adapted for batch sampling processing for screening of a large number of samples. Two methods are currently employed in the prior art to collect the x-ray intensity generated by diffraction of the lipid bilayer as a function of the scattering angle for the lamellar systems. In the simplest case, the multilayer stacks of the lipid bilayers are centrifuged from vesicles in an aqueous medium and spun down onto a flat substrate; they are found to spontaneously align with the stacking axis normal to the substrate surface. The substrate is then mounted on a goniometer which rotates the sample to an angle .theta. with respect a fixed x-ray beam while the reflected intensity is collected on either a scintillation detector rotated to angle 2.theta. with respect to the incident beam or linear position-sensitive x-ray detector. This method has the advantage that with monochromatization and collimation of the x-rays, high resolution with low background allows a high quality electron density profile to be extracted. The drawback is that the intensity must be collected at each scattering angle individually, leading to long collection times on the order of hours. In the second prior art method, the sample is prepared in the same fashion as described above; however, the substrate is made from a bendable aluminum foil which is then mounted on a curved surface with a radius of curvature of about 20 mm. The incident beam is then focused with a curved grazing incidence mirror to illuminate the curved surface with an intense beam of low angular divergence. Different parts of the incident beam intersect the curve surface at different angles of incidence, and the scattering from the entire beam is measured on a position-sensitive x-ray detector. The advantage to this arrangement is the speed and simplicity of data collection. The entire scattering curve is collected over the desired range of angles simultaneously without the need for goniometer motion control. The disadvantage to this approach is that the beam is not truly monochromatic, but composed mainly of the K.sub..alpha.1 and K.sub..alpha.2 doublet over a background of primarily lower energy x-rays. Scattering from the low energy x-ray tail distribution as well as off-specular diffuse scattering increases the background noise and can obscure weaker diffraction lines. Furthermore, the mounting of samples is time-consuming and subject to errors associated with buckling of the substrate during mounting. While the position sensitive detection increases the speed of data collection, one must also account for x-ray intensity distributions across the beam reflected from the focusing mirror. The present invention provides a means of measuring electron density in lipid bilayers that represents an improvement over the current prior art methods. The apparatus is shown generally in FIG. 1. The instrument may be set up to illuminate a stack of lipid bilayers centrifuged down to a flat smooth substrate (for example, a glass slide or polished Si wafer). The lipids align with their lamellar stacks oriented along the surface normal, creating a system with one-dimensional ordering along the normal to the flat substrate. Rather than using aluminum substrates which are subsequently glued to curved cylindrical surface as described in the prior art, the lipids may be centrifuged down onto inexpensive glass substrates no more than 10 mm on a side or in diameter. The entire diffraction apparatus may then be sealed and flushed with dry helium to reduce air scattering and attenuation of the x-ray beam. The sample may be housed in a separate chamber which will be temperature controlled by water circulation and through which dry He and water-saturated He can be flowed in variable proportions to adjust the relative humidity in the lipid matrix. X-rays from a conventional copper x-ray tube may be simultaneously monochromatized and focused onto a flat substrate onto which the lipids have been deposited. The monochromator is bent to approximate a logarithmic spiral along the bending axis according to the methodology described hereinabove. This shape ensures that the focus is of high quality and that the beam incident on the sample will be only the K.sub..alpha.1 component from the Cu x-ray tube source. The invention can measure the diffraction intensity over a range of angles, .theta..sub.diff, simultaneously. From previous studies of these systems, the scans need to be extended to the range of at least 6.degree.. In certain cases, the range must be extended by tilting the sample, while the diffraction intensities are indexed in a storage file as a function of the vector k, defined by: ##EQU15## The data may be indexed in the storage file as a function of the scattering vector. As opposed to longer date accumulation times at two or three sample angles as is conducted in the prior art, the scanning mode ensures that each resolution element within the fan of radiation is used to accumulate the scattering intensity at a given angle. The data collection scheme precludes the need to measure the intensity profile across the radiation fan. Once the raw diffraction data are collected, the data analysis may be fully automated. The diffraction intensities of the swollen films may be used to calculate the phase of the scattering amplitude for a given diffraction peak by least squares analysis. Once the phases are known, the relative electron densities can be calculated for the lipid bilayer by a discrete Fourier transform. The density can be normalized to the maximum density in the layer for purposes of comparison with other bilayer systems. In one embodiment, the lipid vesicles are incubated with a candidate drug before centrifugation into the lamellar stack in order to determine the hospitality of the lipid matrix for that candidate. After centrifugation and angular dispersive x-ray diffraction analysis, the bilayer system treated with a drug candidate may be compared with the control standard; any statistical difference in the electron density profile is an indication that the drug is incorporated in the membrane. Further analysis can be used to determine the localization. The interested reader is directed to Mason and Trumbore, which is hereby incorporated by reference, for further detail on the analysis of drug localization. Additional applications related to lipid research is the possibility of using the angular dispersive x-ray as a method for determination of drug/lipid compatibility in a combinatorial process. The small sample spot size of the beam makes the angular dispersive x-ray amenable to small area illumination, for example on a sample tray containing a large number of samples. Application to Epitaxial Film Structure Determination and Growth. In another aspect of the invention, the angular dispersive x-ray apparatus of the invention may be adapted for use in the rapid elucidation of structure and lattice mismatch in epitaxial films. With the growing variety of epitaxial methods to prepare epitaxial and superlattice structures of metals, semiconductors and insulators comes the increasing need to find efficient and rapid in situ methods of monitoring and controlling the growth process. The deficiencies of the prior art which have been discussed in the Background of the Invention include imprecision due to wide detector slits and complicated and time-consuming data collection methods. The apparatus and method of the present invention combine the advantages of partial reciprocal space mapping with speed of data collection. The present invention will permit data collection concerning the lattice mismatch and superlattice period of a growing epitaxial layer in times on the order of 1 second. The invention may be configured in accordance with FIG. 1 to illuminate a substrate with an epitaxial grown film at high angles corresponding to diffraction which probes interatomic spacings. The angular interval covered by the focusing optics is sufficient to encompass diffraction from both the substrate, used for reference purposes, and the epitaxial layer. X-rays from a conventional copper x-ray tube may be simultaneously monochromatized and focused onto the growing epitaxial layer. The monochromator is bent to approximate a logarithmic spiral along the bending axis according to the methodology described hereinabove. The monochromatic beam is convergent on the sample within an envelop of .DELTA.(.OMEGA.) and is simultaneously diffracted within an envelop of .DELTA.(2.OMEGA.) onto a position sensitive detector. Typical values of the .DELTA.(.OMEGA.) envelop may be about 2.degree., and the incident angle of .OMEGA. about which the source is centered depends on the reflection of interest and the constraints imposed by the surrounding epitaxial equipment. The .OMEGA. may vary over a wide range and may typically range from about 15.degree. to over 50.degree.. The only moving part is a slit positioned between the x-ray source and the curved monochromator crystal. The slit may be left open for dispersive, real time mode or narrowed for reciprocal space mapping. The apparatus may optionally include in-situ reciprocal space mapping capability. The system further may be integrated into a conventional film deposition system, such a metalorganic chemical vapor deposition (MOCVD) system or physical vapor depositions systems, such as molecular beam epitaxy, laser ablation, ion beam sputtering, reactive evaporation, e-beam evaporation and the like. This method is superior to conventional rocking curve approaches since the diffraction intensities are measured simultaneously and registered on a position-sensitive detector. Furthermore, due to the rapid data collection, the diffractometer may be used to accumulate diffraction intensities during deposition. The rapid intensity determination may then be used to control the deposition characteristics in order to control the film structure. Surface Mapping. Because of the fine focusing characteristics of this invention, x-ray diffraction may be performed on a lateral scale on the order of microns, which is not currently feasible with current laboratory x-ray sources. For further lateral resolution perpendicular to the focusing plane, the invention may be equipped with a focusing device perpendicular to the monochromator. Because the diffraction is measured in the plane of incidence corresponding to that of the monochromator, the alternate focusing may be performed by a curved mirror, or another curved monochromator (either synthetic multilayer or single crystal type). Film Thickness Measurement. The invention may be used to measure the thickness and density of thin films (up to about 200 nm in thickness) by using the convergent x-ray beam from the monochromator to illuminate a thin film covered substrate at grazing incident angles (0-0.3.degree.) and measuring the x-ray reflectivity on the position sensitive detector. One observes interference maxima and minima as a function of angle and these can be related directly to the film thickness and density by the modified Bragg equation: ##EQU16## where .theta. is the angle at which a maximum or minimum in the reflectivity occurs, .lambda. is the x-ray wavelength, d is the film thickness and .delta. is the real correction to the x-ray index of refraction; this term is on the order of 10.sup.-6 and in a direction proportional to the film density. N is used to index the maxima and minima in the reflectivity, and will have the values 1, 2, 3 . . . for .theta..sub.max. and 0.5, 1.5, 2.5, . . . for .theta..sub.min.. Because the x-ray reflectivity is measured simultaneously over a range of angles, the data collection is orders of magnitude faster than the conventional x-ray reflectivity scan, in which the reflection intensity is measured one angle at a time. This makes it possible to use the thickness derived from our invention to perform real-time in situ control of film thickness as a part of a larger deposition system. Film deposition systems which are known in the art may be adapted to accommodate the thickness measuring apparatus and method of the invention. The system may be integrated into a conventional film depostition system, such a metalorganic chemical vapor deposition (MOCVD) system or physical vapor depositions systems, such as molecular beam epitaxy, laser ablation, ion beam sputtering, reactive evaporation, e-beam evaporation and the like. The interested reader is referred to Luken et al for further information on the in situ growth monitoring of crystallographic layers, which is hereby incorporated by reference. |
052395642 | description | DESCRIPTION OF PREFERRED EMBODIMENT FIG. 1 shows the vessel 1 of a pressurized-water nuclear reactor, mounted inside a vessel well 2 made within a concrete structure 3 constituting part of the reactor building of the nuclear power station. The vessel 1, which is of generally cylindrical shape, is arranged in the vessel well 2 with its axis vertical, and has its lower part closed by a domed bottom and its upper part by a cover 1a, likewise of domed shape. Above the cover 1a of the vessel is arranged the set 4 of mechanisms for controlling the bars adjusting the reactivity of the core of the reactor, which consists of juxtaposed fuel assemblies placed inside the vessel 1. The vessel 1 is connected by means of connection pieces 5 to the pipelines 6 of the various loops of the primary circuit of the reactor, in which circulates the pressurized water coming into contact with the core assemblies within the vessel 1 and ensuring the heating and evaporation of feed water inside the steam generators of the power station. The concrete structure 3 forms, above the vessel well 2, a pool 8 which can be filled with water up to the vicinity of its upper level 8a, to make it possible to execute handling and maintenance operations on the inside of the vessel of the nuclear reactor during the reactor shutdowns and after removal of the control set 4 and of the cover 1a of the vessel. The pool 8 comprises a part 9 which is placed laterally of the actual reactor pool located vertically in line with the vessel and in which the internal equipment of the reactor vessel can be arranged in order to carry out underwater maintenance or repair operations. The bottom of the vessel 1 has passing through it instrumentation conduits 10 which are connected to an instrumentation room located laterally of the vessel well 2. FIG. 2 illustrates the vessel 1 of a pressurized-water nuclear reactor during a dismantling operation executed by the use of the process according to the invention. The process according to the invention is put into practice after a permanent shutdown of the nuclear reactor and after unloading of the core assemblies and of the internal equipment of the nuclear reactor. After the shutdown and cooling of the nuclear reactor, the pool 8 is filled with water and the vessel cover is removed. The unloading of the core assemblies and the dismounting and disposal of the internal equipment of the vessel are then carried out under water. The fuel assemblies can be placed in containers to ensure their transport and disposal towards a reprocessing factory. The generally highly-irradiated internal equipment can be stored temporarily, before being dismantled under water and disposed of in transport containers. It is also possible at least partially to carry out the underwater dismantling of the internal equipment of the vessel on the inside of the latter. After the unloading of the vessel, the disposal of the internal equipment and the emptying of the pool, there is installed above the upper level 8a of the reactor pool a supporting structure 11 which consists of beams and on which rests the upper part of a lifting device 12, comprising particularly a mast of great length 13 which is arranged vertically along the axis of the vessel 1 and whose lower part is connected to the bottom of the vessel 1. The mast 13 is arranged within a tubular structure 14 placed vertically along the axis of the vessel 1 and having its upper part connected to the supporting structure 11. Arms 15 for centering and retaining the device 12 on the inside of the vessel, each having a jack 16 at its end, are fastened to the lower part of the tubular structure 14 and are arranged in the form of a star around this tubular structure. The jacks 16, which come to bear with their end part on the inner surface of the vessel 1, make it possible to carry out the centering and retention of the vessel 1 in relation to the tubular structure 14 and to the mast 13. The mast 13 comprises a toothing 13a over a substantial part of its length, the toothing 13a interacting with pawls 18 of a vessel-lifting mechanism 20 resting on the supporting structure 11 by means of a rotary thrust bearing 19. The rotating part of the bearing 19 can be driven in rotation about the vertical axis common to the vessel well 2 and to the vessel 1 by means of a motor 21. The lower part of supporting structure 11 carries a circular rail 22 on which are mounted movably in terms of rotation about the axis of the vessel well, by means of carriages, two monorails 23 and 23', shown in FIG. 5, allowing the displacement of hoists 24 in the entire zone located above the upper edge of the vessel 1 and in the storage pool 9 for the internal equipment as a result of the presence of fixed rails 25 and 25', in the extension of which the rotationally movable rails 23 and 23' can be placed. As will be explained later, the cutting of blocks 26 of irradiated material from the wall of the vessel is carried out substantially level with the bottom 9a of the pool 9 for the internal equipment, i.e., at the upper level of the vessel well. When a block 26 has been cut from the wall of the vessel 1, a hoist 24 can ensure that this block is picked up in any position and the block 26 transported into the pool 9 for the internal equipment, in which is arranged a container 27 for the storage and transport of the blocks 26 of irradiated material. The hoist 24 makes it possible to transport the blocks 26 between their cutting zone and their storage zone within the container 27. Zone containment walls 28 are placed at the upper level of the pool, below the supporting structure 11, in order to isolate the zone in which the cutting of the blocks 26 is carried out during the dismantling of the vessel 1, from the zone located above the pool, from which the control of the various operations put into effect for the dismantling is executed. Likewise, walls 29 make it possible to separate the pool for storing the internal equipment of the reactor from the zone 8 located vertically in line with the vessel, although passages are provided for the hoists 24 for transporting the blocks 26. Finally, the inner volume of the vessel 1 is isolated from the reactor pool 8 by means of walls 30, in order to limit the radiation in the zone located above the vessel well 2. FIGS. 3 and 4 illustrate the lower part of the mast 13 of the lifting device 12 for the vessel 1. This lower part consists of a platen 32 which can be fastened to the lower part of the mast 13 in its axial direction by means of a threaded part 32a engaged in an internally-threaded hole at the end of the mast 13. The platen 32 comprises four orifices 33 and a centering stud 34 intended for ensuring the fastening and positioning of the end of the mast 13 on the bottom of the vessel 1. After unloading of the vessel, the connection pieces joining this vessel to the primary circuit and all the auxiliary pipework as well as the instrumentation tubes 10 of the vessel bottom are severed and then closed off. Four passage holes through the vessel bottom are machined or remachined in arrangements corresponding to the arrangements of the passage holes 33 of the platen 32 of the mast 13. It is also possible to fasten the vessel to the mast 13 by the use of a number of passage holes through the vessel bottom and a number larger than four of ties fastened in these holes, so as to employ ties and to machine holes of smaller diameter. The mast 13 can be installed by introducing the centering stud 34 into an instrumentation passage hole and by bringing the holes 33 into coincidence with the orifices of the vessel bottom which have been machined or remachined. All the passage orifices of the instrumentation tubes, with the exception of the orifices which have been remachined as appropriate, are closed off, and the fastening of the mast 13 is ensured by means of threaded rods 37 fastened to the platen 32 by nuts 35. A fastening plate 36 (see FIG. 2) having orifices in positions corresponding to the orifices 33 of the platen 32 is placed under the vessel bottom in such a way that the threaded rods 37 engage into the orifices of this fastening plate 36. The fastening of the mast 13 is completed by nuts engaged on the rods 37 and coming to bear with a clamping effect against the lower face of the plate 36. The vessel 1 is thus firmly fixed at the end of the mast 13 which is mounted movably in the vertical direction along the axis of the tubular structure 14 and on the inside of this structure. Devices for wedging in the radial directions are also interposed between the tubular structure 14 and the mast 13, so as to ensure the guidance and retention of the mast 13 during its displacements in the vertical direction. Inflatable gaskets are likewise interposed between the mast 13 and the structure 14, so as to ensure the isolation or containment of the inner volume of the vessel 1 during the dismantling operations. Finally, as mentioned above, the vessel is retained by the arms 15 and jacks 16 in a position such that its axis is aligned with the axis of the mast 13 and of the tubular structure 14. As can be seen in FIG. 5, the supporting structure 11 comprises two parallel main beams 11a and 11b and four lateral beams 11c, 11d, 11e and 11f arranged in the form of a star around the axis of the vessel well of the reactor. The ends of the beams 11a to 11f rest on the concrete structure of the reactor, for example on the bearing surfaces of the anti-missile slab arranged vertically in line with the vessel well and at the upper level 8a of the reactor pool. FIG. 6 illustrates the entire apparatus for dismantling the vessel during an operation for cutting the wall of the vessel. The corresponding elements in FIGS. 2 and 6 bear the same references, the apparatus, as illustrated in FIG. 6, comprising, in addition to the means for lifting the vessel and for handling the cut blocks 26, a horizontal cutting unit 40 and a vertical cutting unit 70 which are mounted on the tubular structure 14. The horizontal cutting unit 40 consists of a band saw 41 mounted on a support 42 fastened to the tubular structure 14 by means of a pivot bearing 43. The saw support 42 can be displaced, for the purpose of executing the cutting of the wall of the vessel, in the way which will be described in detail hereinbelow. The vertical cutting unit 70 consisting of a second band saw 71 makes it possible to separate the segment of the vessel wall cut by the saw of substantially horizontal displacement into blocks of irradiated materials 26, which are transported by the hoists 24 into the storage pool 9 for the internal equipment and deposited in a storage and disposal container 27. The cutting of the wall of the vessel over a particular height is carried out after the vessel 1 has been raised some distance in the vertical direction by means of the mast 13 and the lifting unit 20. The lifting unit 20 consists of a pawl device which will be described below. An appliance 46 for the suction and filtration of the gases in the storage pool 9 for the internal equipment is arranged in an isolated zone of this pool, in order to clear away the gases contaminated by radioactive materials present in the dismantling zone and in the storage zone for the irradiated material. An access orifice making it possible to dispose of the container 27 containing the blocks of irradiated material is provided in the biological containment wall 28, this orifice being closed during the dismantling operations by a slab 48 of radiation-absorbing material. As can be seen in FIG. 7, the pawl-type lifting device 20 comprises a support 50 resting on the supporting structure 11 by means of the pivoting bearing 19, the axis of which is the axis of the mast 13 coinciding with the axis of the vessel well 2 and the axis of the vessel 1. The bearing 19 is a roller bearing, the rollers 51 of which are inclined inwards and downwards so as to ensure perfect alignment of the axis of the mast 13 with the axis of the vessel well. The support 50 of the lifting device 20 has an annular shape and carries four fixed pawls, such as the pawl 18a, arranged at 90.degree. relative to one another about the axis of the mast 13, and mounted pivotably on the support 50 about horizontal axes, such as the axis 52a. The upper part of the support 50 constitutes a jack body 54 which is level with each of the fixed pawls 18a and in which is mounted a jack rod 55 of large cross-section, carrying at its upper end a support 56 in which a movable pawl 18b is mounted pivotably about a horizontal axis 52b. The pawls 18a and 18b comprise a profiled end part, the shape of which corresponds to the shape of the space delimited between two successive teeth of the toothing 13a of the mast 13. The pawls 18a and 18b are capable of pivoting through a particular angle of low amplitude between their position shown in solid lines in FIG. 7 and their position shown in broken lines. In the position shown in solid lines, the pawls are in engagement with the toothing 13a of the mast 13, and in their position is shown in broken lines, they are in a position disengaged from the toothing 13a. FIGS. 8A to 8F show schematically the pawls 18a and 18b, the mast 13 and the actuating jack 54 of the movable pawls 18b in successive positions during a displacement phase in the vertical direction and towards the top of the mast 13, to the lower part of which the vessel 1 is fastened. In FIG. 8A, the mast 13 bears on the fixed pawl 18a in its engagement position within the toothing 13a. The jack rod 55 is in the low position. To execute the lifting of the mast 13 and of the vessel 1, the chamber of the jack 54 is fed in such a way as to displace the piston 55 and the support 56 upwards, as shown in FIG. 8B. The bearing pawl 18a, which has a ramp corresponding to the slope of the toothing 13a, comes into the disengaged position as a result of the sliding of its ramp on the toothing. The mast 13 rests on the movable pawl 18b which ensures that it is lifted by means of the jack 54. During the lifting of the mast 13, as shown in FIGS. 8C and 8D, the fixed pawl 18a disengages completely from the toothing as a result of an upward pivoting, and then escapes at the tip of the tooth with which it was in contact, when the tip of the tooth comes level with the end of the pawl 18a. The pawl 18a is then released and falls by pivoting back into the space located below the tip of the tooth, its inclined surface coming into contact with the slope of the toothing 13a. As illustrated in FIG. 8E, the double-action jack 54 is fed in such a way as to cause the descent of the rod 55 and of the movable pawl 18b which disengages from the toothing 13a, the mast 13 coming to rest on the fixed pawl 18a. As can be seen in FIG. 8F, the pawl 18b comes into position again in a space between two teeth located below the space in which this pawl 18b was engaged before the displacement of the mast 13, as shown in FIG. 8A. The pawls 18a and 18b are in identical positions in FIGS. 8A and 8F, the mast 13 having been displaced by one pitch of the rack 13a. The displacement of the jack 55 is equal to the pitch of the rack plus some play necessary for bringing about the engagement and disengagement of the pawls 18a and 18b. To carry out the lifting of a vessel of a pressurized-water nuclear reactor, four sets of pawls 18a and 18b and four jacks arranged at 90.degree. relative to one another about the axis of the mast 13 have been used. Each of the jacks has a lifting force of 100 tons, so that the total lifting capacity is 400 tons. The jacks have a stroke of 60 mm and the pitch of the toothing 13a of the mast 13 is 50 mm. The progressive raising of the mast 13 and of the vessel 1 is carried out in complete safety by means of the pawls, with which are associated devices for monitoring the correct engagement of the pawls in the toothing 13a. The lifting of the vessel is executed over a vertical distance corresponding to a particular number of displacement pitches of the rack, so as to provide above the level of the bottom of the pool for the internal equipment some wall height of the vessel 1, on which the cutting of blocks of material is carried out in a manner to be described below. FIGS. 9 and 10 illustrate in more detail the cutting machine 40 which consists of a band saw shown in FIG. 6. The band 41 of the saw is mounted on pulleys 44a and 44b driven in rotation by a motor means. The cutting of the wall of the vessel 1 is performed at a level located just above the level of the bottom 9a of the pool for the internal equipment. A guiding and centering device 60 is placed on the upper rim of the vessel well 2, level with the bottom 9a of the storage pool 9 for the internal equipment. The device 60 comprises bearing abutments 61 making it possible to carry out the centering of the vessel 1 and the alignment of its axis with the axis common to the well 2 and to the tubular structure 14, to which the cutting device 40 is fastened by means of the 43. The guiding device 60 comprises a helical groove 62 the axis of which corresponds to the axis of the vessel well 2. The cutting machine 40 has a guide roller 64 which moves along within the groove 62 during the cutting of the vessel. The groove 62 has an angular amplitude determining the rotational displacement of the saw blade 41 about the axis of the vessel, of the order of 30.degree.. The support 42 of the cutting machine, which is mounted rotatably on the tubular structure 14 by means of the pivot bearing 43, is displaced in rotation about the axis of the tubular structure 14 coinciding with the axis of the vessel, so as to describe an angle of 30.degree. about this axis, at the same time making a cut in part of the wall of the vessel 1 along a helix, the shape of which is homothetic with the helix formed by the guide groove 62. During this displacement, the support 42 of the cutting machine is also capable of pivoting in a vertical direction as a result of the construction of the bearing 43 in the form of a ball joint. The saw blade 41 taking the form of a band is driven in rotation by a drive motor. After the wall of the vessel 1 has been cut along a cylindrical sector of an amplitude of 30.degree. and along a helix the axis of which is the axis of the vessel, the cutting machine 40 is returned to its initial position, and the vessel is rotated oppositely to the cutting direction by means of the device, 21 for setting the mast 13 in rotation, while at the same time it is raised over a height corresponding to one displacement pitch of the mast 13, so as to return the cutting blade 41 to the end of the helical incision previously made. A new cut of an amplitude of 30.degree. and of helical shape is made in the wall of the vessel as a result of the rotational displacement of the cutting machine 40 about the axis of the vessel. A cut of helical shape can thus be made over all or part of the periphery of the vessel by means of successive rotational displacements of the cutting machine 40 and translational and rotational displacements of the vessel 1. The total height H of the segment of the wall cut in the course of a complete revolution of the cutting machine is equal to the displacement pitch P of the mast 13 multiplied by the number of rotational displacements of the machine in the direction in which cutting is being carried out. For a rotational displacement of the machine of 30.degree., the number of displacements in the course of one revolution is 12, hence H=12P where the pitch P is 50 mm and the height H cut during each revolution is 600 mm. FIG. 13 shows a developed view of the helical cuts 65a, 65b, 65c, slightly inclined relative to the horizontal plane, which are made in the wall of the vessel 1 by the cutting machine illustrated in FIGS. 9 and 10. FIGS. 11 and 12 show the cutting machine 70 allowing straight cuts to be made in a direction forming a small angle relative to the vertical, so as to execute a sectioning of the vessel wall, in which one or more cuts, such as the cuts 65a, 65b, 65c shown in FIG. 13, have been made in a substantially horizontal direction. The cutting machine 70 illustrated in FIGS. 11 and 12 allows successive cuts 66 (FIG. 13) to be made in the wall of the vessel 1, in order to form blocks 26 of irradiated material which are delimited by the horizontal and vertical cuts. As explained above, the blocks 26 are picked up by a hoist 24 which makes it possible to transport these blocks into a storage container 27 arranged in the pool for the internal equipment. The machine 70 for cutting in the vertical direction comprises a support 72 mounted pivotably about a horizontal axis 73 on a second support 74 itself fixed to the rotating part 75 of a bearing mounted rotatably about the tubular structure 14. An actuating jack 76, of which the body is fixed to the tubular structure 14 and the rod is connected to the support 72 of the cutting machine 70, makes it possible to pivot the support 72 about the axis 73. FIG. 11 illustrates a first position, shown in solid lines, of the support 72 and two positions 72' and 72", shown in solid lines, which are obtained during the upward pivoting of the support 72 from its low position shown in solid lines. The actual cutting tool consists of a band saw mounted on the lower part of the support 72. The tensioning and driving of the band 71 of the saw are ensured by two pulleys 77a and 77b mounted loosely on the support 72, and by a driving pulley 78. The pivoting axis 73 of the support 72 in relation to the support 74 can be inclined slightly relative to the horizontal plane, so that the pivoting of the support 72 and of the saw band 71 under the effect of the jack 76 takes place in a plane slightly inclined relative to the vertical. This provides cuts, such as the cuts 66, inclined slightly in relation to the vertical direction. By rotating the support 72 about the axis of the vessel by means of the bearing 75, the cutting tool 70 can be placed in such successive positions that the band 71 executes the cutting of blocks 26 in the wall of the vessel 1, after horizontal cuts, such as the cuts 65a, 65b, 65c shown in FIG. 13, have been made. The centering of the vessel 1 and the alignment of its axis with the axis of the tubular structure 14 are ensured by the centering arms 15 and the jacks 16 and by the external centering devices 61. As can be seen in FIG. 13, the first cut 65a in the circumferential direction of the vessel, inclined slightly in relation to the horizontal plane, allows the horizontal cutting saw to penetrate into the metal of the vessel wall at a small angle and permits a progressive advance in the axial direction of the vessel. The first ring of metal delimited by a helical cut is sectioned by the vertical cutting saw according to the cuts 66, in order to form a first series of blocks 26 which can be disposed of and stored in a container placed in the pool for the internal equipment. The succeeding rings delimited by helical cuts and of substantially constant height are likewise sectioned by the vertical cutting saw, to form blocks 26 of substantially rectangular or square shape which are disposed of in sequence. The dismantling of the vessel is effected by a successive execution of substantially horizontal cuts and of substantially vertical cuts delimiting blocks 26 which are disposed of in sequence. During the cutting of the blocks for the purpose of dismantling of the vessel, the vessel can be filled with water up to a level below the part which is being cut or, if appropriate, can be empty of water. The water level in the vessel can be lowered during the progress of the cutting in the direction of the vessel bottom, before each operation of lifting the vessel between two successive series of cutting operations. The cutting operations are conducted at a substantially constant level located slightly above the upper level of the vessel well. This avoids the need to carry out the cutting on the inside of the vessel well and from the inner surface of the vessel, thus limiting the pollution of the concrete structures delimiting the vessel well by radioactive products. Moreover, the tools used for cutting are more easily accessible and it likewise becomes easier to control and guide them. FIGS. 14 and 15 and FIGS. 16 and 17 illustrate alternative embodiments of the horizontal cutting device and of the vertical cutting device making it possible to dismantle the vessel 1 by cutting blocks from the wall. The horizontal cutting device 80 illustrated in FIGS. 14 and 15 and the vertical cutting device 90 illustrated in FIGS. 16 and 17 consist of a respective circular saw 81 and 91 mounted movably in a radial direction in relation to the vessel 1, on a respective gantry 82 and 92 placed in a transverse direction above the vessel well. Where the device 80 for cutting in a horizontal direction is concerned, the disk 83 of the circular saw 81 is placed in a horizontal plane and mounted rotatably about a vertical axis. The advancing movement of the circular saw 81 in the direction of the arrow 84 allows a horizontal cut to be made in the wall of the vessel 1 and over its entire thickness, slightly above the vessel well and the bottom 9a of the pool for the internal equipment. If a cutting device comprising a circular saw is used, it is possible to make a perfectly horizontal cut, the penetration into the metal of the vessel wall being effected from inside the vessel and in a cross-sectional plane thereof. The circular saw for vertical cutting 91 comprises a saw disk 93 arranged in a vertical plane and mounted rotatably about a horizontal axis. The penetration into the metal of the vessel wall is effected from inside the vessel and in an axial plane. The cuts can be perfectly vertical and perpendicular to the horizontal cuts made previously. This provides blocks 26 of irradiated material of rectangular or square shape, delimited by the horizontal cuts and the vertical cuts. The cutting of the vessel wall is executed by rotating the vessel through a particular angle between two cutting operations involving successively the device 80 for cutting in the horizontal direction and the device 90 for cutting in the vertical direction. The cutting tools are controlled remotely, and the cutting operations are in all cases carried out in a zone making it possible to avoid major contamination of the reactor structures by radioactive products. FIG. 18 shows a vessel 101 of a water-cooled nuclear reactor during a preparatory phase prior to its dismantling. The vessel 101 is arranged inside a vessel well 102 within the concrete structure 103 of the nuclear reactor. The vessel well 102 opens out in its upper part into the pool 104 of the reactor. To dismantle the components of the reactor and particularly the vessel 101, the reactor is cooled after its permanent shutdown and the pool 104 is filled with water. The cover of the vessel is then dismounted and the core assemblies and of the internal equipment arranged in the vessel are unloaded underwater. The pool of the reactor is subsequently emptied and the vessel decontaminated, for example by the circulation of a chemical reagent in contact with its inner surface. The vessel is emptied and a device for the containment of the vessel well is installed. A scaffolding 107 is erected in the extension of the vessel well, underneath the hemispherical vessel bottom 101a. Cutting tool equipment is introduced into the vessel well so as to carry out the cutting of the pipework connecting the vessel to the reactor circuit, in the region of the connection pieces 105, 105' and 106, 106'. The cutting of the guide tubes or instrumentation tubes 108 passing through the bottom 101a of the vessel is also executed. This operation is conducted from the upper part of the scaffolding 107. A support 110, which can be seen particularly in FIG. 19, is put in place under the bottom 1a of the vessel. The support 110 comprises a bearing plate 10a which is fastened under the vessel bottom by means of rods 111 engaged in guide tubes or instrumentation tubes passing through the vessel bottom 101a, depending on the type of nuclear-reactor vessel for which the dismantling process according to the invention is used. The rods 111 have a threaded end which is engaged into an orifice passing through the plate 110a and onto which a nut is screwed. The nuts screwed onto the threaded end parts of the rods 111 make it possible to ensure the fastening of the plate 110a which carries abutments 112 coming to bear on the vessel bottom 101a during the tightening of the nuts. Before the displacement of the vessel 101 in successive steps in the vertical direction is executed to allow it to be cut in a zone located in the vicinity of the upper part of the vessel well 102, on the inside of the reactor pool 104, there are installed around the upper part of the vessel 101 an inflatable gasket 113 for closing the upper part of the vessel well 102 and guide jacks 114 for centering and guidance of the vessel 101 during its displacements in the vertical direction. Likewise installed in the pool 104 and in a room 104' arranged laterally of pool 4 are cutting and handling means which can be similar to the means described above and which enable cutting of blocks from the wall of the vessel 101 and the disposal of the cut blocks in storage containers. The reactor vessel 101, for which the dismantling process according to the invention is used, rests by means of supporting feet 116 on a supporting ring 115 fastened to the concrete structure 103 of the reactor at the upper level of the vessel well 102. In FIG. 21, the supporting ring 115 has been shown in a plan view, the upper surface of the ring 115 comprising eighteen successive zones 117 in the circumferential direction, the angular amplitude of each of these zones being 20.degree.. Fifteen zones 117 are intended for receiving bearing surface of a supporting foot 116 of the vessel 101. The three remaining zones 117a, 117b and 117c, which are arranged vertically in line with the connection pieces joining the vessel to the reactor circuit, such as the connection pieces 105 and 105', do not receive supporting feet of the vessel 101 coming to bear on the ring 115. As can be seen in FIGS. 19 and 20, an initial lifting of the vessel can be carried out by means of jacks 120 which are interposed between the supporting ring 115 and some of the supporting feet 116. The jacks 120 are arranged within cutouts 121 of the supporting ring 115 and are brought to bear on wedging pieces 122. The height of the cutouts 121 is sufficient to ensure that a jack 120 bearing on the wedges 122 can be placed underneath a supporting foot 116 at the initial moment of prior lifting of the vessel 101. As can be seen in FIG. 21, the cutouts 121 are made in three zones distributed at 120.degree. around the ring 115 and corresponding to two successive zones 117 allowing the bearing of a supporting foot 116. Three sets of two jacks 120 are placed in the cutouts 121, each made in two successive zones 117 of the ring 115. The vessel is lifted in passes by the simultaneous action of three jacks 120, each arranged in one of the three cutouts 121 distributed over the periphery of the vessel. After the vessel has been lifted over the height of a pass by the use of three jacks each located in a cutout 121, a wedging piece of a height corresponding to the height of the pass is placed underneath each of the jacks which have not been used for the lifting and which are arranged in the vicinity of the jacks which have executed the lifting, in the same cutout 121 of the ring 115. The next lifting pass is executed by using the jacks, the wedging of which has just been carried out, thus making it possible to raise the vessel an additional step. The wedging of the first set of three jacks which executed the lifting of the vessel is then carried out. This ensures the lifting of the vessel in successive passes by the placing of the wedging elements 23 (see FIG. 20) under each of the jacks 120. During the successive steps of the lifting of the vessel, wedging pieces are placed under all or some of the supporting feet 116 of the vessel which are not being used for lifting of the vessel as a result of interaction with a jack 120. At the end of the operation for the initial lifting of the vessel, there are placed underneath the supporting feet, in two zones 125 and 125', wedging pieces of sufficient height to maintain the vessel in the high position reached at the end of the initial lifting. The supporting ring 115 of the vessel is then cut in four zones aligned two by two to allow the passage of two parallel sections or girders 127, 127' intended for constituting part of the stationary support of the vessel during its subsequent displacement in successive steps in the vertical direction. The sections 127, 127' have the same height as the ring 115 and come to rest on the concrete structure 103 of the reactor in a lateral orifice 131, as can be seen in FIG. 19. The wedging pieces 128 make it possible to ensure good stability of the sections 127 and 127' which, together with the ring 115, constitute a stationary support on which the vessel rests during its lifting in successive steps and its cutting. As can be seen in FIGS. 22 and 23, at the end of the operation for the initial lifting of the vessel by the use of the jacks 120 and the wedging pieces 123, the vessel bottom 101a and the support 110 are at a particular height above the upper surface of the stationary support consisting of the ring 115 and of the sections 127. The vertical spacing present between the upper surface of the sections 127 and the lower bearing surface of the support 110 makes it possible to introduce between these elements a lifting module 130 which will be described below. The lifting module 130 is introduced through the lateral orifice 131 made in the concrete structure of the reactor, at a level located in the vicinity of the vessel bottom 101a. The rails 127 and 127' are arranged over the length of the orifice 131 and form a transfer track for the modular lifting element 130 when it is being put in place underneath the support 110 fixed bottom 101a. The lifting element 130, which will now be described with reference to FIGS. 22, 23 and 24, comprises a raising device 132 and a modular supporting element 133 which are assembled together by means of keys 134. The raising device 132 takes the form of a frame comprising two parallel uprights 135a and 135b assembled together by means of spacers 136. The uprights and the spacers consist of metal plates assembled by welding. Fastened to the ends of the uprights 135a and 135b are jack boxes, such as 137a and 137b, inside each of which is placed a hydraulic jack, the body of which bears on the bottom of the corresponding jack box. As can be seen in FIG. 24, when the lifting element 130 is in vertical alignment with the vessel bottom 101a, as shown in FIGS. 22 and 23, the jack boxes 137a and 137b the raising device 132 are vertical alignment with the supporting ring 115. The rods of jacks 138a and 138b (FIG. 23) arranged inside the jack boxes 137a and 137b come to bear on the upper surface of the supporting ring 115. By feeding the jacks, such as 138a and 138b, of the raising device 132 in the direction bringing about the extension of the jack rods, the frame of the device 132 is raised in a direction perpendicular to the frame by means of the jack body coming to bear on the bottom walls of the corresponding jack boxes. By means of the frame of the raising device 132, the modular supporting element 133 fastened to the frame of the raising device 132 by means of the keys 134 is raised. The modular supporting element 133 takes the form of a frame of square cross-section, the faces 139 of which are connected at each of their ends to columns 140 in the region of the corners of the frame. The columns 140 are diametrically penetrated by orifices allowing the passage of the assembly keys 134 and having male or female frustoconical ends allowing a stable stacking of identical modular elements. The dimensions of the modular supporting element 133 are such that this modular element can come into place within the frame of the raising device 132 delimited by the uprights 135a and 135b and the spacers 136. In FIG. 24, the raising device 132 and the modular supporting element 133 are shown in their assembly position, the uprights 135a and 135b having through-orifices in alignment with the orifices of the columns 140 of the modular supporting element 133. In this position, the keys 134 can be introduced into the aligned orifices of the uprights 135a and 135b and of the columns 140. The columns 140 of the modular element 133 are arranged vertically in line with the supporting sections 127 and 127' when the lifting module 130 is in its operating position beneath the vessel bottom 101a. Feeding the jacks, such as 138a and 138b of the raising device 132 causes, by the extraction of the jack rods, the frame of the 132 and of the modular supporting element 133 which is fastened thereto to to be raised. The upper part of the modular supporting element 133 taking the form of a turntable 141 (see FIG. 22) comes into contact with the lower surface of the plate 110a of the support 110 fixed to the vessel bottom 101a. The vessel 1 resting by means of the support 110 on the modular supporting element 133 can thereby be raised over a particular height corresponding to the amount of vertical displacement of the raising device 132. As can be seen in FIG. 25, when the lifting element 130 is in the high position, obtained as a result of the extension of the jacks, such as 138a and 138b, a second modular supporting element 133' identical to the element 133 can be introduced underneath the element 133 raised by the device 132. The element 133 is displaced by transfer along the track consisting of the sections 127 and 127'. The amount of raising of the device 132 corresponds to the height of a modular lifting element, such as 133 or 133', plus a clearance allowing the passage of the element 133' underneath the frame of the device 132 and the modular supporting element 133 fastened within the frame of the device 132. The device 133' is arranged so as to be in exact vertical alignment with the modular element 133. The jacks, such as 138a and 138b of the raising device 132, are fed oppositely to the raising direction, in such a way that the element 133 comes to rest on the element 133', itself bearing on the sections 127 and 127', by means of frustoconical bearing surfaces of the columns 140. The assembly keys 134 making the connection between the frame of the raising device 132 and the modular supporting element 133 are then removed. The descending movement of the device 132 is then continued by feeding the jacks in the desired direction, up to the moment when the frame of the device 132 has returned to its initial position. The modular supporting element 133' is then in the position of the modular element 133 shown in FIG. 24. The modular supporting element 133' and the raising device 132 can be assembled by introducing keys 134 into the aligned orifices of the uprights of the device 132 and of the columns of the modular supporting element 133'. A lifting element identical to the lifting element 130 and consisting of the raising device 132 to which the modular supporting element 133' is fastened is then placed underneath the modular supporting element 133 on which the vessel rests by means of the support 110. The vessel 101 is raised inside the well 102, in such a way that its upper part, consisting particularly of the vessel flange 101b, can be cut on the inside of the reactor pool 104 and in the vicinity of the upper part of the vessel well 102. It should be noted that, during the cutting at the end of the vertical displacement of the vessel by the agency of the raising device 132, the vessel 101, while it is being raised, rests by means of its bottom 101a, the support 110 and the modular supporting elements 133 and 133' on the rails 127 and 127' constituting elements of the stationary support of the vessel 101. The vessel 101 is therefore not suspended inside the vessel well 102 but rests, during the cutting operations, by means of its bottom on supporting elements bearing on the fixed structure of the reactor. The operations of cutting and handling the blocks cut from the wall of the vessel 101 can be conducted in the way described above. At the end of the cutting operation conducted on the part of the vessel located above the upper level of the vessel well after the vertical displacement of the vessel by means of the displacement device 132, the latter can execute a new vertical displacement of the vessel 101 which rests on the element 133', assembled together with the frame of the raising device 132, by means of the support 110 and the modular element 133. The vessel is raised by an amount slightly greater than the height of a modular supporting element, such as 133 and 133'. A third modular supporting element 133" identical to the modular supporting elements 133 and 133' is displaced by shifting on the sections 127 and 127' and is vertically aligned with the element 133' fixed to the frame of the raising device 132 and placed in the high position by this raising device. The jacks of the raising device 132 are subsequently fed oppositely to the raising direction, in such a way as to bring the element 133', on which the vessel rests by means of the element 133 and the support 110, to rest on the modular supporting element 133". The vessel 101 is now in a new lifting position in the vertical direction which allows a new segment of the vessel wall to be cut on the inside of the pool 104 above the upper level of the vessel well 102. The cutting of the vessel wall is thus executed in successive segments after each of the unit lifts of the vessel making it possible to place a new modular supporting element underneath the element, which is raised of the device 132, and to bring the vessel to rest, by means of the stacked modular elements, on this new element resting on the stationary support of the vessel formed by the rails 127. As can be seen in FIG. 26, the raising of the vessel in successive steps makes it possible to execute its cutting as far as the level of the domed bottom 101a. Successive supporting elements 133, 133', 133", . . . 133n have been interposed between the support 110 fixed to the vessel bottom and the stationary support of the vessel formed by the rails 127 and 127'. It is thus also possible to cut of the vessel bottom 101a in the vicinity of the upper level of the vessel well 102 by the use of a specially adapted cutting tool outfit. It has been possible to execute the cutting of the vessel in the course of successive operations, during each of which the vessel rests, by means of a stack of modular supporting elements, on a stationary structure, itself bearing on the vessel bottom. The successive lifts of the vessel are of identical amount and are obtained from the same raising device which interacts successively with each of the modular supporting elements bearing on the stationary support. The process and apparatus according to the embodiment just described make it possible to obtain a vertical displacement of the vessel in successive steps, simply and in such a way that the vessel has a stable bearing during each of the cutting operations following a displacement in the vertical direction. The lifting of the vessel can be executed by a pull or a push on the vessel bottom by the use of means different from those described. Where the vessel is lifted by a push on the bottom the initial displacement of the vessel in the vertical direction, making it possible to install the lifting element underneath the vessel bottom, can be effected by any means allowing the vessel to be raised by a push on its lower part. The raising device and the modular supporting element of the lifting unit employed for executing a unit lift of the vessel can have forms and structures different from those described. The push on the lower bottom of the vessel or, more generally, of the component being dismantled can be exerted by means of an intermediate support, as described, or directly on one or more push surfaces formed on the lower part of the component. The tools for cutting sections of irradiated material from the wall of the vessel can be different from a band saw or a circular saw. These cutting means can be non-mechanical, for example, an oxygen cutting torch, although thermal cutting processes give rise to the formation of vapor and of fine particles containing radioactive products, the trapping and filtration of which can be difficult to carry out. The cutting tools can comprise means for displacement and guidance over a complete revolution about the axis of the vessel. In this case, the dismantling of the vessel can be executed without the need to rotate the vessel about its axis. The disposal and storage of the sections of irradiated material can be carried out by means different from those described. The sections disposed of can be processed on the site of the reactor before their storage at a deactivation site or, on the contrary, transported to a processing factory and conditioned there for long-term storage. The cutting of the domed bottom of the vessel can be carried out by using the tools for cutting the cylindrical wall of the vessel as a result of accessory means for handling the domed bottom or, on the contrary, by using special tool outfits. Finally, the process according to the invention can be used for dismantling the vessel of any water-cooled nuclear reactor of the PWR or BWR type or for dismantling the internal equipment of such vessels. More generally, the process according to the invention can be used for carrying out the dismantling of any irradiated component of a nuclear reactor comprising at least one part of tubular shape arranged with its axis vertical. |
050826212 | description | DETAILED DESCRIPTION OF THE INVENTION The instant invention is an improved neutron reflecting supermirror which comprises a plurality of stacked sets of bilayers of high and low neutron scattering powered materials. The high and low neutron scattering power materials are deposited on a substrate, which substrate is typically selected from the group consisting of pyrex glass, boron containing glasses, float glass and silicon. One layer of each of said sets of bilayers consists of titanium and second layer of each set of said bilayers consists of an alloy including nickel and a microstructure enhancing element. In a first preferred embodiment the microstructure enhancing element has a high neutron scattering potential and is present interstitially in the nickel layer so as to reduce the nickel grain size. In a further preferred embodiment the microstructure enhancing element is carbon and is present in the nickel layer in concentrations between five and fifty percent and particularly in concentrations between twelve and thirty percent. The nickel alloy layer of each of said sets of bilayers typically has the nominal composition of Ni.sub.86 C.sub.14 or Ni.sub.72 C.sub.28. As referred to hereinabove, the improved neutron reflecting supermirror comprises a number of stacked sets of bilayers, which sets of bilayers is typically numbered between two and one thousand and most preferably between twenty and five hundred. The thickness of each of said sets of bilayers is typically between five and two hundred nm. The improved neutron reflecting supermirror may further include a buffer layer disposed either between said substrate and the first of said sets of bilayers, or atop the uppermost layer of the top set of bilayers. The buffer layer is typically between 10 and 1500 nm thick and most preferably approximately one hundred nm. The buffer layer is typically a layer of nickel or nickel carbon alloy disposed to a thickness of approximately one hundred nm. The improved neutron reflecting supermirror may further include an intermediate layer disposed between between each of said alternating layers of titanium and nickel carbon alloy. In a preferred embodiment the intermediate layer is a layer of carbon deposited to a thickness of between two and five hundred nms. Referring now to FIG. 1, there is illustrated therein the improved neutron reflecting supermirror structure of the present invention. The supermirror structure 18 is constructed as a plurality of stacked sets of bilayers 20, only two of which are illustrated, but which typically would be between two and one thousand sets. Each of the layer sets 20 is formed from at least two units U.sub.1 and U.sub.2. Each of the layer sets have respective d spacings of d.sub.1 and d.sub.2, which may or may not be equal to one another. One of the units U.sub.1 and U.sub.2 includes at least one layer of material which has a relatively high neutron scattering power or potential and the other of said units of U.sub.1 and U.sub.2 includes at least a layer of material with relatively low neutron scattering potential material. In a preferred embodiment, U.sub.1 is a relatively low neutron reflecting material such as titanium disposed atop a layer of relatively high neutron scattering potential material such as a layer nickel. It is the essence of the invention that the relatively high neutron scattering power layer include a microstructure enhancing element also having a high neutron scattering potential. In the preferred embodiment the microstructure enhancing element is carbon and is present interstitially in the nickel crystal grain in concentrations between five and fifty percent. In one embodiment, the nominal composition of the high neutron scattering potential layer, U.sub.2 is Ni.sub.72 C.sub.28. In a second embodiment of the instant invention the nominal composition of the layer U.sub.2 is Ni.sub.86 C.sub.14. It is however to be understood that the instant invention contemplates high neutron scattering potential layers having carbon present in concentrations from 5% to 50%. i.e., Ni.sub.95 C.sub.5 through Ni.sub.50 C.sub.50. While not wishing to be bound by theory, the instant inventors have hypothesized that layers of pure Ni alone a insufficiently dense: i.e., too many voids exist in the Ni crystalline lattice. The result is the buckling, cusping, and layer distortion reported by earlier researchers. Conversely, it is believed that the microstructure enhancing material, carbon, may be serving as a catalyst to prevent the buckling and cusping by occupying otherwise vacant parts of the Ni lattice. The result is a smoother, flatter Nickel alloy layer free from the cusping and layer distortions found in previous Ni-Ti supermirrors, and hence better able to reflect neutrons incident thereupon. The neutron reflecting supermirror structure of the instant invention is disposed atop the substrate 19 and may further include a buffer layer 21a. The buffer layer 21a may be disposed either upon said substrate 19 and below the first set of bilayers 20, or as is illustrated in FIG. 1, the buffer layer 21 may be disposed upon the top or uppermost of said sets of bilayers 20. Alternatively the neutron reflecting supermirror may include said buffer layer disposed as both the uppermost and lowermost layers. The buffer layer 21 and 21a is typically between one and one thousand nm thick and preferably approximately one hundred nm thick. The buffer layer 21 and 21a is typically formed as a layer of nickel, a nickel carbon alloy or carbon deposited upon said substrate and providing a base upon which to subsequently deposit said plurality of sets of bilayers, or upon the uppermost set of bilayers. The neutron reflecting supermirror of FIG. 1 further possess a neutron dispersion pattern which can be altered to reflect incident neutrons from desired angles. Specifically, an incident beam of cold neutrons is made up of neutrons of a single wavelength (lambda) of 4 angstroms. The reflected beam is hence made up of a single wavelength of 4 angstroms reflected at an angle theta approximately according to Bragg's Law: EQU n lambda=2d sine theta wherein n=1 (for consideration of 1st order reflections); lambda=4 angstroms, the wavelength of cold neutrons; and 2d=the period or thickness of a given set of bilayers Since the value of n lambda remains constant it is thus possible to alter the reflected angle theta by varying the value for 2d. Algorithms for fabricating basic layered supermirror structures are disclosed in, for example, Majkrzck, et al, MRS Proc., "Fe-W Supermirrors for Polarizing Neutrons", 103, 115-120 (1988); and Hayter and Mook, J. Appl. Cryst., "Discrete Thin-Film Multilayer Design for X-Ray and Neutron Supermirrors", 22, 35-41 (1989) the disclosure of which is incorporated herein by reference. The result of employing a known algorithm is a distribution of bilayer (2d) thicknesses that cause overlapping Bragg diffraction peaks to occur from the region just above the Nickel cutoff angle to some increased angle of acceptance. It is of course critical that reflectivity remain near 100% as the reflection angle is extended, since otherwise the cumulative reduction from each reflection along the guidetube would result in an unacceptable loss of neutron flux. It is this point which the inventive neutron reflecting supermirror addresses. More specifically and referring now to FIG. 2, there is illustrated therein a plot of reflectivity versus angle for a standard Nickel coating and the improved neutron reflecting supermirror. A perusal of FIG. 2 illustrates that the reflectivity of the best standard nickel coating, illustrated by Curve 30, is extremely good, i.e., approximately 100% up to the critical angle of nickel, approximately 0.4 degrees theta. However, as the critical angle increases, the reflectivity of the nickel coating falls off drastically; down to 0% reflectivity before 2.times. the critical angle of nickel, (approx. 0.8 degrees theta) and certainly to less than 10% by 0.5 degrees theta. Conversely, Ti:Ni-C alloy supermirrors as illustrated in FIG. 1 demonstrate excellent neutron reflectivity, i.e. greater than 95% at critical angles of up to 3.times. the critical angle of nickel alone. More specifically, Curves 32 and 34 illustrate a Ti:Ni.sub.72 -C.sub.28 alloy in two different layering algorithm structures. The structure illustrated in Curve 32 demonstrates reflection of approximately 95% out to two times the critical angle of the best standard Ni coating. The structure of Curve 34 demonstrates even better performance, having reflection of approximately 97% out to three times the critical angle of the best standard Ni coating. In order to better understand the structure of the neutron reflecting supermirror structures of the instant invention, the following examples are presented as illustrative of the method of fabricating the same. EXAMPLE The inventive neutron reflecting supermirror structure of the instant invention was fabricated with a Ti/Ni.sub.72 C.sub.28 coating deposited on 5 cm.times.10 cm float glass. The glass substrate was cut to size from a 4 in .times.4 in piece of float glass. Prior to deposition of the neutron reflecting supermirror structure upon the float glass, said substrate was cleaned by first hand washing said substrate in a CDC degreaser, which is thereafter thoroughly rinsed off in de-ionized water. Thereafter the substrate was immersed in a de-ionized water ultrasonic bath for one half hour and was then rinsed with methanol and blown dry with nitrogen. The substrate is then loaded into an ion beam chamber and mounted on the substrate spinning rotation stage. The chamber was a horizontal cylinder with two 5" round by a 1/4" thick target materials screwed onto opposite sides of a water cooled stainless steel block. The target block centered in the chamber and fixed to a horizontal shaft pointing inwards radially to the cylinder. The targets were positioned at a 45% angle to the horizontal and rotate 180.degree. at specified intervals. The ion beam source was a 5 cm Hollow Cathode Source fixed to the end of the cylinder. An ion beam of Ar+ ions from the source was propelled towards the target block along the axis of the cylindrical chamber. Between the source and the target block was a Hollow Cathode Neutralizer which is aimed at a perpendicular to the beam of ions, intersecting with the beam roughly 3" from the source. The Hollow Cathode Neutralizer neutralizes the argon ions, which keeps the beam from spreading out from charge repulsion. Atoms strike the target materials, causing atoms of the target materials to be ejected. The sputtered atoms leave the target in all directions, with the highest percentage leaving at a perpendicular to the target. The substrates to be coated were approximately seven inches from the target. Also at a 45.degree. angle, the substrate was parallel to the target and rotated slowly in order to insure the uniformity of the coating. The substrate assembly attached to the end of the chamber, just above the 5 cm source. The 5 cm source parameters are: 1500 V beam, 180 V Accelerator, and 50 mA beam current. The system was pumped down to 1.OE-6 torr with a cryogenic pump. Argon gas was introduced into the chamber through a hollow cathode at a rate of 4.0 sccms/sec, bringing the chamber pressure to 2.OE-4 torr. A Ni-alloy target was constructed by covering 30% of a carbon target with four inward pointing triangles of nickel foil. The foil was tied to the target with nickel wire. The other target sputtered was simply solid titanium. After the beam sputters a target for a set length of time, the beam shuts off, the target block rotates 180.degree. and exposes the other target, then the beam starts back up again. The timers were connected to magnetic proximity switches, which stopped the target every 180.degree. and told the stepper motor when to turn the target block. This process is repeated over and over, resulting in a stack of layers of alternating materials on the substrate. One layer of material 1 (e.g. NiC), together with one layer of material 2 (Ti), constitutes a d-spacing. Calibration runs were performed in order to relate the time a target si sputtered to resultant thicknesses of that material on the substrate. The sputtering times for the various d-spacings required for a supermirror were interpolated from a graph of sputter time vs layer thickness for the two materials with a straight line connecting the two data points. Following all depositions, the substrates and system are allowed to cool in a vacuum with a background pressure of argon gas. As the layer structure of the supermirror is multiple graded, i.e., the d-spacing of each of said sets of bilayers is different, the deposition time of the titanium and nickel carbon alloy for each bilayer set will vary. The grading herein and the pattern for setting down the graded layers is established by a layer algorithm of the type disclosed hereinabove in, for example, the Hayter and Mook reference. While the invention has been described in connection with preferred embodiments and procedures be understood that it is not intended to limit the invention to the described embodiments and procedures. On the contrary it is intended to cover all alternatives, modifications and equivalents which may be included within the sphere and scope of the invention as defined by the claims appended herein after. |
description | The present application claims priority to U.S. Provisional Patent Application Ser. No. 61/590,368 of Thomas Vogt titled “Na3WO4F and Derivatives Thereof as a Scintillation Material and Their Methods of Making” filed on Jan. 25, 2012, the disclosure of which is incorporated herein by reference. Scintillator materials are used to detect γ-rays, x-rays, neutrons and electrons in research and medical imaging devices. Furthermore, high-energy and nuclear physics relies on scintillation to detect weakly interacting particles and energies such as dark matter and dark energy. Some of the basic requirements for scintillator materials are: (1) a fast response time in the range of 10-100 ns for time-resolution, (2) a high light yield in excess of tens of thousands of photons per absorbed radiation particle, (3) a high density p and atomic number for efficient y-ray detection, since the latter is proportional to ρZ3-4, (4) good match of the scintillation output with the sensitivity of light sensor (i.e. photomultiplier tube), and (5) availability of large single crystals. Early scintillation materials to detect radiation were K2Pt(CN)4 and CaWO4 introduced in 1895 by Roentgen and in 1896 by Becquerel. CaWO4 converts x-rays into blue light and was used early on for x-ray photography and medical imaging. The light yield (Yhy) of scintillators given in photons/MeV can be approximated by a simple formula: Yhv=[106/βEg] S QE, with β being a materials dependent constant (2.5 for halides), Eg the band gap of the host lattice, S the energy transfer efficiency from the host lattice to the activator and QE the quantum efficiency of the activator. The product of βEg is the energy required to produce one exciton. To maximize light yield S and QE must be close to 100% and Eg small. The two main techniques used in medical imaging are X-ray tomography and positron emission tomography (PET). In X-ray tomography, radioisotopes are injected into the body by administering compounds containing radioactive isotope such as 99Tc. The emitted radiation in the 120-150 keV energy range is then detected using a scintillator material. By appropriate camera rotations around the patient and the use of multiple detectors mathematical algorithms are used to reconstruct a three-dimensional image of the biological entity investigated. Modern computer tomography (CT) scanners use thousands of individual X-ray detectors spaced about 1 mm apart. Scintillators used for CT are (Y,Gd)2O3:Eu3+, Gd2O2S:Pr3+and CdWO4. The emissions are at 612 nm due to a 5D0→7F2 transition in (Y,Gd)2O3:Eu3+and 510 nm due to a 3P0→3H2, 3F3 transition in Gd2O2S:Pr3+. The 480 nm emission in CdWO4 is a charge transfer transition. The various tungstates AWO4 (A=Ca, Ba, Cd, Zn) adopting the scheelite structure are also widely used scintillator materials. Again a strongly distorted excited state that differs significantly from the ground state leads to the emission of a broad-band with a large Stokes shift. The Cd2+4d electronic states are located near the bottom of the valence band which is formed by the oxygen 2p orbitals. The conduction band has mainly W 5d character. The scintillator properties of this material are based on the WO42− entities and can be rationalized as resulting from the charge transfer out of the O2−2p states into W6+5d0 states with contributions from Cd2+4d states. In these tungstates thermal quenching at room temperature is usually very small and quantum efficiencies of up to 70% can be achieved. Using a simple approximation for the energy efficiency of scintillator materials developed above a theoretical conversion efficiency of 6% can be calculated. Experimental values of 3.5% have been found. The light yields of all these scintillators are moderate and produce about 10,000 photons/MeV. In PET, the annihilation of positrons is exploited for imaging purposes. The predominantly used positron emitters are the isotopes of 11C (t1/2˜20 min), 13N (t1/2˜10 min, 15O (t1/2˜2 min) and 18F (t1/2˜110 min). Due to their positive charge and strong interaction with matter, the emitted positrons are stopped in biological tissue after traveling just a few millimeters. When slowing down, positrons will annihilate with electrons in condensed matter and emit in most cases two γ-rays in opposite directions which both have energies of 511 keV. PET makes use of this collinear emission of two γ-rays by measuring the temporal coincidence data along straight lines. This also permits the reconstruction of 3-dimensional biological objects using appropriate algorithms. Bi4Ge3O12(BGO) crystals are used in PET scanners as scintillator materials. The structure of Bi4Ge3O12 consists of isolated GeO4 tetrahedrons and Bi3+ ions which have an asymmetric coordination with three short (2.16 Å) and three long (2.60 Å) Bi-oxygen distances as a consequence of the 6s2 lone pair electronic configuration. In the excited state, this coordination is more symmetric. However, this material has high thermal quenching and at room temperature about ⅔ of the light efficiency of BGO is quenched. The experimental value of the energy efficiency of BGO is about 2%. The density of BGO is 7.1 g/cm3 and its effective Z with 75 is very high. The Stokes shift is quite large with 14,000 cm−1 which minimizes self-absorption and allows thin slabs to be used as detectors since the crystal is transparent to its emission light at 480 nm. Nal:Tl+ is another commonly scintillator material used in PET and as an x-ray phosphor. Its density is about half of that of Bi4Ge3O12(3.86 g/cm3) and its Zeff is 51. With a light yield of about 40,000 photons/MeV , a decay time of 230 ns, non-proportionality of the light yield in the 60-1275 keV range and hygroscopic behavior requiring the crystals to be sealed one would not give this material a big chance for market penetration. However, easy and low cost manufacturing have provided economic opportunities despite rather mediocre technical specifications. As such, a need exists for improved scintillator materials. Objects and advantages of the invention will be set forth in part in the following description, or may be obvious from the description, or may be learned through practice of the invention. Direct synthesis methods are generally provided that include reacting Na2(WO4)·2H2O (and/or Na2(GeO4)·2H2O) with NaF in an inert atmosphere at a reaction temperature of about 950° C. to about 1400° C., along with the resulting structures and compositions. In one embodiment, Na2(WO4)·2H2O can be reacted with NaF according to the reaction:(1−x)Na2[WO4]·2H2O+xNa2[MO4]·H2O+NaF→Na3W1−xMxO4Fwhere 0≦x≦0.2 (e.g., 0<x≦0.2) and M is B, Al, Si, P, S, Cr, V, Nb, Ta, Zr, Hf, Sc, Y, La, Ga, Ge, In, Mo, or combinations thereof. For instance, x can be 0 such that Na3(WO4)F is formed according to one particular embodiment. According to this method, Na3WO4F can be formed into single crystals having an impurity concentration present at a concentration of less than about 500 ppb (e.g., less than about 100 ppb). In another embodiment, 0<x≦0.2 and M is Mo such that Na3W1−xMoxO4F is formed. A crystal structure comprising Na3(WO4)F with impurities present in a concentration of less than about 500 ppb (e.g., less than about 100 ppb) is also provided. A composition of matter is also generally provided that has the formula:Na+3−a−2b−3cA+aB2+bC3+cW1−xMxO4Fwhere 0≦a≦2; A+ is an alkali metal ion; 0≦b≦1; B2+ is an alkaline earth metal ion selected from Be2+, Mg2+, Ca2+, Sr2+, and/or Ba2+, a rare earth divalent cation from the atomic numbers 57-71, an activator cation of Cr, Mn, Re, Cu, Ag, Au, Zn, Cd, Hg, Sn, or any combinations thereof; 0≦c≦1; C3+ is an, a rare earth cation from the atomic numbers 57-71, an activator cation of Ac, U, Cr, Mn, As, Sb, Bi, In, Tl, or any combinations thereof; 0≦x≦0.2; and M is B, Al, Si, P, S, Cr, V, Nb, Ta, Zr, Hf, Sc, Y, La, Ga, Ge, In, Mo, or combinations thereof. This material can have an impurity concentration present at a concentration of less than about 500 ppb. For example, in one embodiment, a=b=c=0 such that the composition of matter has the formula:Na3(W1−xMxO4)F,where 0≦x≦0.2, and M is B, Al, Si, P, S, Cr, V, Nb, Ta, Zr, Hf, Sc, Y, La, Ga, Ge, In, Mo, or combinations thereof. X can be 0, or 0≦x≦0.2. In another embodiment, a is 0; b is 0; 0≦c≦0.1; C is Ce, Eu, or a combination thereof; and 0≦x≦0.2. A crystal structure is also provided that comprises Na3(GeO4)F with impurities present in a concentration of less than about 500 ppb. Scintillator material and phosphor materials comprising the composition and/or crystal structure of any of these materials are also generally provided. Other features and aspects of the present invention are discussed in greater detail below. Reference now will be made to the embodiments of the invention, one or more examples of which are set forth below. Each example is provided by way of an explanation of the invention, not as a limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the invention without departing from the scope or spirit of the invention. For instance, features illustrated or described as one embodiment can be used on another embodiment to yield still a further embodiment. Thus, it is intended that the present invention cover such modifications and variations as come within the scope of the appended claims and their equivalents. It is to be understood by one of ordinary skill in the art that the present discussion is a description of exemplary embodiments only, and is not intended as limiting the broader aspects of the present invention, which broader aspects are embodied exemplary constructions. Chemical elements are discussed in the present disclosure using their common chemical abbreviation, such as commonly found on a periodic table of elements. For example, hydrogen is represented by its common chemical abbreviation H, helium is represented by its common chemical abbreviation He; and so forth. Na3WO4F and its derivatives are generally provided as new scintillation materials for use in medical imaging and the detection of particles and energies including, y-rays, x-rays, neutrons, neutrinos and weakly interaction massive particles (WIMPS). For example, derivatives of Na3WO4F can include a substituted material(s) in a portion of the tungsten (W) locales (e.g., Na3(W1−xMxO4)F, where 0≦x≦0.2 and M is B, Al, Si, P, S, Cr, V, Nb, Ta, Zr, Hf, Sc, Y, La, Ga, Ge, In, Mo, or combinations thereof). As shown in FIG. 1A and 1B, the structure of Na3WO4F is best described as an anti-perovskite structure 10 (WO4)FNa3, where the F ions 20 are in the center of an FNa6 octahedron 24 formed with the Na cations 12, 14 and face-sharing FNa6 octahedra columns are stacked in a hexagonal closest packing parallel to the a-axis. The isolated WO42− tetrahedra 22 are formed by the W ions 16 and the O ions 18, and occupy the pores between the FNa6 octahedron 24. As such, there are two distinct Na cation sites 12 and 14. These WO4 tetrahedra are, as outlines above, important structural units and necessary for scintillation and photoluminescence. As explained in greater detail below, the tungsten in these MO4n− units can be partially substituted with B, Al, Si, P, S, Cr, V, Nb, Ta, Zr, Hf, Sc, Y, La, Ga, Ge, In, Mo, or combinations thereof. In certain embodiments, for example, the tungsten in these MO4n− units can be partially substituted with Mo, In, Cr, Ge, Ga, and/or Al. In these MO4n− subunits of members of the family of ordered oxyfluorides (MO4)FAnBm, where M is B, Al, Si, P, S, Cr, V, Nb, Ta, Zr, Hf, Sc, Y, La, Ga, Ge, W, In, Mo, or combinations thereof and A and B are independently alkali and/or alkaline earth metals, ligand-to-metal charge transfers are facilitated where an electron is transferred from an oxygen based molecular orbital (MO) to the metal-based one. Increasing the oxidation state of M effectively increases its electronegativity and thus lowers the energy of this HOMO-LUMO gap. As one reduces the charge on Mn+ one increases the Lewis base character of the tetrahedral unit. As one moves down a d-transition metal group CrO42−→MoO42−→WO42− one increases the gap energy (3.3, 5.3 and 6.2 eV respectively) since the relative sizes of the d-orbitals increase. Another way of describing this is that the Lewis base character increases. A strong Lewis base will impact the electronic environment of activators such as Eu3+ in its vicinity. With the chemical diversity of available MO4n− tetrahedrons that can be accommodated in these materials an exquisite control of PL properties is within reach. (See also, U.S. Publication No. 2009/0302236 of Vogt, et al. and U.S. Publication No. 2009/0174310 of Vogt, et al.; both of which are incorporated by reference herein). Defects in the cation sublattice can be introduced into Na3WO4F by substitution of two sodium ions (Na+) with an alkali, an alkaline earth metal, a rare earth metal, and/or lanthanide activators such as Eu2+. Additionally, a partial substitution of W4+ by Ga3+ and In3+ subsequently allows the substitution of A2+ and A3+ ions on the A-site of this AnFMO4 family of materials within this host lattice. In one embodiment, for example, the composition can be represented according to the formula:Na+3−a−2b−3cA+aB2+bC3+cW1−xMxO4F,where A+ is an alkali metal ion (e.g., Li+, K+, and/or Rb+), 0≦a≦2; B2+ is cation having a +2 charge, such as an alkaline earth metal ion selected from Be2+, Mg2+, Ca2+, Sr2+, and/or Ba2+, a rare earth divalent cation from the atomic numbers 57-71 (i.e., the lanthanoid series including the fifteen elements with atomic numbers 57 through 71: La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu), an activator divalent cation of Cr, Mn, Re, Cu, Ag, Au, Zn, Cd, Hg, Sn, and/or any combinations thereof; 0≦b≦1; C is a is cation having a +3 charge, such as a rare earth trivalent cation from the atomic numbers 57-71 (i.e., the lanthanoid series including the fifteen elements with atomic numbers 57 through 71: La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu), an activator trivalent cation of Ac, U, Cr, Mn, As, Sb, Bi, In, Tl, and/or any combinations thereof; 0≦c≦1; M is B, Al, Si, P, S, Cr, V, Nb, Ta, Zr, Hf, Sc, Y, La, Ga, Ge, In, Mo, or combinations thereof; and 0≦x≦0.2. For example, the compound can be rare earth doped such as having the formula Na3−3cCecW1−xMoxO4F, where 0<c≦0.1 and 0≦x<0.2 (e.g., Na2.85Ce0.05WO4F) or Na3−3cEucW1−xMoxO4F, where 0<c≦0.1 and 0≦x<0.2 (e.g., Na2.85Eu0.05WO4F). As stated, dopants can also be included into the Na3WO4F. For example, in one embodiment, the tungsten atoms can be replaced by other metals in the structure, such as represented by the formula: Na3(W1−xMxO4)F, where 0<x≦0.2 and M is B, Al, Si, P, S, Cr, V, Nb, Ta, Zr, Hf, Sc, Y, La, Ga, Ge, In, Mo, or combinations thereof. For example, the parent compound FAnBm(MO4) with A=B=Na, n is 1, m is 2, and M is W (i.e., FNa3(WO4)) can be modified by aliovalent substitution with A being Li, K, Rb, Cs or combinations thereof and/or with MO42− entities such as M being Mo, W or combinations thereof. In addition or in the alternative, high-Z MO43− (where M is Nb, Ta or combinations thereof) can be substituted where A is Li, Na, K, Rb, Cs or combinations thereof, n=2, B is Ca, Sr, Ba or combinations thereof, and m=1. If MO44− entities are used (where M is Zr, Hf or combinations thereof), then A is Li, Na, K, Rb, Cs or combinations thereof, n=1, B is Ca, Sr, Ba, or combinations thereof, and m=2. If MO45− units with M being Y, La or combinations thereof are used, then n=0, B is Ca, Sr, Ba or combinations thereof, and m is 3. As stated, this material is part of an even larger family of ordered oxyfluorides (MO4)FAnBm , where M is B, Al, Si, P, S, Cr, V, Nb, Ta, Zr, Hf, Sc, Y, La, Ga, Ge, W, In, Mo, or combinations thereof and A and B are independently alkali and/or alkaline earth metals, that are best described as anti-perovskites such as Sr3AlO4F and others, which have found applications in lighting and as optical host lattices. For example, U.S. Publication Nos. 2009/0302236 and 2009/0174310 of Vogt, et al. describe such structures and are incorporated by reference herein. FIGS. 5A and 5B show, respectively, the ac-plane and the ab plane projections of Na3(GeO4)F, which is essentially the same structure as in FIGS. 1A and 1B except for containing GeO4 tetrahedra instead of WO4 tetrahedra. Such a structure, along with its derivatives, can be prepared according to any discussion herein by substituting Ge for W. A direct synthesis method can be utilized to form the materials (e.g., Na3(W1−xMxO4)F, where 0≦x≦0.2 and M is B, Al, Si, P, S, Cr, V, Nb, Ta, Zr, Hf, Sc, Y, La, Ga, Ge, In, Mo, or combinations thereof. In one embodiment, the method can involve the following reaction in an inert atmosphere (e.g., argon) and at elevated temperatures (e.g., about 950° C. to about 1400° C.):(1−x)Na2[WO4]·2H2O+xNa2[MO4]·H2O+NaF→Na3W1−xMxO4Fwhere 0>x≦0.2 and M is B, Al, Si, P, S, Cr, V, Nb, Ta, Zr, Hf, Sc, Y, La, Ga, Ge, In, Mo, or combinations thereof. In one particular embodiment, x is greater than 0 but less than or equal to 0.2 (i.e., 0<x≦0.2). One particularly suitable compounds that can be formed from this method is Na3W1−xMoxO4F, where 0<x≦0.2 (i.e., where M is Mo). For example, direct synthesis methods of Na3(WO4)F (i.e., where x is 0 in the formula shown above) can be achieved by reacting Na2(WO4)·2H2O with NaF in an inert atmosphere (e.g., argon) and at elevated temperatures (e.g., about 950° C. to about 1400° C.). In one particular embodiment, the components of the material are added in stoichiometric amounts. Due to this direct synthesis method, the Na3WO4F material can be formed into single crystals having controllable purity, with impurity concentrations in the parts-per-billion (ppb) scale (e.g., impurities are present at a concentration of less than about 500 ppb, such as less than about 100 ppb). Compounds were prepared via the direct synthesis method described above to have the formulas: Na3W1−xMoxO4F, where x is 0, 0.25, 0.5, 0.75, and 1. FIG. 2 shows the excitation and emission spectra for these compounds. Two compounds were prepared via the direct synthesis method described above to have the formulas: (1) Na2.85Eu0.05WO4F and (2) Na2.85Eu0.05MoO4F. FIG. 3 shows the excitation and emission spectra for these compounds. Two compounds were prepared via the direct synthesis method described above to have the formulas: (1) Na2.85Eu0 05WO4F and (2) Na2.85Eu0.05MoO4F. FIG. 4 shows the excitation and emission spectra for these compounds. These and other modifications and variations to the present invention may be practiced by those of ordinary skill in the art, without departing from the spirit and scope of the present invention, which is more particularly set forth in the appended claims. In addition, it should be understood the aspects of the various embodiments may be interchanged both in whole or in part. Furthermore, those of ordinary skill in the art will appreciate that the foregoing description is by way of example only, and is not intended to limit the invention so further described in the appended claims. |
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description | The present invention is related to a dosimetry device and method allowing accelerator factory testing, commissioning, acceptance and quality assurance (QA) for verification of the quality of the radiation delivery in standard and conformal radiotherapy, as well as partial QA in IMRT (intensity modulated radio therapy) applications and tomotherapy applications. In treating patients with radiation, the radiation oncologist prescribes a treatment regimen whose goal is to cure or control the disease by precisely delivering an optimal radiation dose to the tumor and reducing the side effects on healthy surrounding tissues. In general, published clinical and experimental results demonstrate that the response of tumours and normal tissues to radiation is highly variable. Moreover, for some tumours and normal tissues, the dose response curves may be very steep in the therapeutic dose range, i.e., a small change in dose can result in a large change in clinical response. In addition, the prescribed radiation dose to the tumour is usually, by necessity, constrained by the tolerance dose of the surrounding normal tissues. Consequently, since the “window” for optimal treatment can be quite narrow, the radiation dose must be delivered accurately and consistently. Delivery of treatment in an accurate and consistent manner is by no means easy to achieve, since the radiation therapy process is a complex interweaving of a number of related tasks for designing and delivering radiation treatments. Therefore, general prescriptions including particular dosimetry tests have been established in order to have a control and an (on-line) verification of said delivery of treatment. Usually, these tests are performed at first at the release of a new radiotherapy device from production and then at its installation in a clinical institution in order to control that the expected dose is really delivered as required. These tests are performed by the accelerator manufacturers for the release from production and after any important maintenance intervention and by the medical physicist of the clinical institution for the device acceptance and commissioning in order to prove the compliance of the equipment to the norms set by regulation authorities. Furthermore, regular tests based on a routine schedule have also to be performed by the users in order to check the behaviour of the radiotherapy device. Again, dosimetry tests are therefore performed. They are defined as quality assurance. Among others, recommendations for performing such tests for quality assurance are described in details in AAPM REPORT NO. 46 “Comprehensive QA for Radiation Oncology”, published for the American Association of Physicists in Medicine by the American Institute of Physics, reprinted from MEDICAL PHYSICS, Volume 21, Issue 4, 1994. A device able to measure field profiles, hereafter called beam profiler, is needed in order to perform some of the required dosimetry tests. Especially in an IMRT application, using a multi-leaf collimator (MLC), it is important to be able to determine the positions and penumbrae of the leaves of the MLC. One of the most known instruments used in order to measure field profiles is the “water phantom” instrument. This dosimetry instrument is in the form of a water tank which uses a single detector that moves immersed in the water inside the tank, recording the dose profiles in the three dimensions. Although this device represents the golden standard in accelerator commissioning, acceptance and routine QA, thanks to its flexibility in recording the dose profiles, performing the needed measurements with it is a cumbersome and long lasting task: the water tank is a heavy and bulky device and takes long to set it up; the scans take time to be performed as normally only one detector is present, etc. Other possible dosimetry equipments include devices comprising several radiation detectors performing such measurement, possibly in the form of matrixes or arrays. Two main families of such devices can be described: the one using diodes and the one using ionisation chambers. An example of such devices using diodes is described in U.S. Pat. No. 6,125,335 wherein a beam profiler is in the form of an array of 46 sensor diodes, S1-S46 and 4 off-axis horizontal sensor diodes, S48-S51. An example of a typical beam profiler is the off-the-shelf multi-sensor radiation detector array entitled: Profiler Model 1170, manufactured by the assignee of the subject invention, Sun Nuclear Corporation of Melbourne, Fla. The Sun Nuclear Profiler generates a real time graphic image which is a trace of individual data points spaced approximately 5 mm apart and updated each second. The 46 diodes, S1-S46 and off-axis detectors S48-S51 provide a real time profile of the emitted radiation beams and off axis analysis. However, the main problem of these devices is the fact that they use diodes which have a non-linear response to dose, requiring accordingly complex calibration methods such as the one described in document U.S. Pat. No. 6,125,335. Furthermore, compared to dosimetry equipments based on ionisation chambers, a device using diodes has a cost price per unit (pixel) higher than a device using ionisation chambers. Another family consists in dosimetry instruments which implement arrays of ionisation chambers instead of diodes. Recently, very efficient ionisation chamber arrays have been developed by Bonin et al. in “A pixel chamber to monitor the beam performances in hadron therapy” Nuclear Instruments and Methods in Physics Research A 519 (2004)-674-686. This document describes a device made up of a 2-D array of 1024 successive ionisation chambers arranged in a regular matrix of 32×32 pixels. The general principle of an ionisation chamber is as follows: a high voltage is applied between two electrodes. A gas (here air or nitrogen) present between the electrodes is ionised by the radiation traversing it. As a result of the electric field, the ions are collected on the electrodes, and the charge can be measured. As the creation of one electron-ion pair requires a known average energy, depending on the gas and on the irradiation type, the collected charge is directly proportional to the energy deposited in the gas. A recycling integrator circuit provides a 16-bit counter proportional to the detected charge. The recycling integrator was developed as a 0.8 μm CMOS technology chip (TERA06) by INFN (Istituto Nazionale di Fisica Nucleare, Torino). Each of these chips provides 64 channels. The minimum detectable charge is adjustable between 50 fC and 800 fC, and the read rate in the linear region can be as high as 5 MHz. As described above, the monitor comprises 32×32 air vented ionisation chamber pixels arranged in a matrix with a pitch of 7.5 mm. Although this device is considered to be very efficient, its geometry, a matrix of 32×32 ionisation chamber pixels, is best adapted to the complexity of the dose distributions delivered in IMRT but well too complex and expensive for standard and conformal RT, where normally only the profiles on the main axis and diagonals are needed. Furthermore, the complexity of arranging such a high number of detectors and their read-outs in a matrix had an impact on the dimensions of such a device, which is not large enough to cover all the field dimensions which need to be checked both in routine QA and in accelerator commissioning/acceptance. Another dosimetry device, using any type of radiation detectors, e.g. ionisation chambers or semiconductor detectors, is known from U.S. Pat. No. 4,988,866. This device comprises only a limited number of sensors, located at specific positions, for performing specific measurements. Therefore, it cannot verify the quality of a radiation field of any size, according to any recommended QA protocol. Moreover, with a single absorber, only a single radiation energy (or a very narrow energy range) can be measured. Still another dosimetry device, using any type of radiation detectors, is known from DE-101 43 609. This device aims at improving the spatial resolution of measurement, without increasing the number of individual sensors (17). This result is obtained by installing a set of sensors (17, 17′, and 17″) on lines (19) on a support (7). The support (7) is rotatable around a bearing (18). The sensors on one line (17′) are located at a different radius from sensors (17″) located on another line. The support is successively rotated along an angle of 1° or 2°. From the successive measurements of e.g. 88 sensors on 100 angular steps, a set of 8 800 measurements points can be obtained, giving a much higher spatial resolution. However, this device requires a mechanical drive for the sensor, and the measurement is more time-consuming. In addition, because one takes a set of measurements at successive times, one relies on the stability and constancy of the radiation source. No means are provided for measuring radiation beam energy. Although some of the devices of the state of the art are providing energy measurements e.g. by means of build-up plates of different thicknesses, they always need the user to enter several times into the treatment room to perform the measurement with the required build-up plate for different energies. A method for determining the position of a leaf of a MLC has been described by Yang Y and Xing L in “Using the volumetric effect of a finite-sized detector for routine quality assurance of multi leaf collimator leaf positioning” Med. Phys. 30 433-441. According to this method, a finite-sized detector, such as an ion chamber, is located at the location of a leaf as projected in the isocenter plane. A leaf position error increase or decreases the irradiated volume of the detector. Therefore, a measurement of the dose can be related to the position error. However, no means are provided for measuring other parameters such as the radiation energy. Accordingly, no practical solution is proposed to perform an easy and fast beam profile and energy measurement with a known device. The present invention aims to provide a dosimetry device that does not present the drawbacks of the state of the art. In particular, the present invention aims to provide a dosimetry device and a method which requires a limited number of individual radiation detectors while still providing the required accuracy, ease of use and fast operation. Furthermore, the present invention aims to provide a device and a method which will not need the user to enter several times in the treatment room to perform the measurements. A further aim of the present invention is to provide a device which also allows the fast and efficient measurement of the beam energy of electrons and photons. The present invention also aims to provide a device which can be used for accelerator factory testing, commissioning, acceptance and quality assurance (QA). A further aim of this invention is to provide a limited set of tests to be used in IMRT QA. Finally, the present invention aims to provide a device having a reasonable price. According with a first aspect, the present invention relates to a dosimetry device for verification of the quality of a radiation beam in standard and conformal radiation therapy, and in particular for IMRT (Intensity Modulated Radiation Therapy) applications, comprising an active area including a limited number of lines of individual radiation detectors dedicated to the measurement of the beam profile. Said active area further comprises extra radiation detectors dedicated to the energy measurement of electrons or photons, and a build-up plate, with energy degraders. Said energy degraders are located upstream said extra radiation detectors in the path of the radiation beam. Preferably, said extra radiation detectors are not located on the above-mentioned lines. By limited number of lines, it should be understood at least two lines. By line, it should be understood a linear arrangement of individual pixel. In an advantageous embodiment of the invention, according to the first aspect, said radiation detectors are ionisation chambers. In another advantageous embodiment of the invention, according to the first aspect, said radiation detectors are diodes. In a typical embodiment of the invention, according with the first aspect, the limited number of lines is one set of two lines radiation detectors, said two lines being essentially orthogonal to each other. Advantageously, this limited number of lines is one set of four lines of radiation detectors, said four lines being essentially oriented at an angle of 45° to each other. In a specific embodiment of the invention, according with the first aspect, said energy degraders are either in the form of bumps of different thicknesses in said build-up plate and/or in the form of bumps or recesses with inserts of a different radiation absorbing materials. Advantageously, said energy degraders are positioned in the quadrants or octants defined by said sets of lines dividing the active area, in the vicinity of the intersection of said lines. In a specific embodiment of the invention, according with the first aspect, the invention is adapted for determining positions of leaves of a MLC in an IMRT radiation therapy apparatus. In this embodiment said limited number of lines of radiation detectors comprises further extra line(s) of radiation detectors dedicated to the measurement and determination of the projection of said leaves position at the isocenter of said IMRT radiation therapy apparatus, said one or more extra lines of radiation detectors being located at or near the positions where the leaves are expected to project. Advantageously, according with the first aspect, said extra lines of radiation detectors comprises at least three parallel extra lines of radiation detectors on two opposite sides of said dosimetry device. A second aspect of the invention relates to a method for verifying quantities of interest of a radiation beam in radiation therapy apparatus comprising an MLC provided with leaves, or jaws. This method comprises the steps of: providing a dosimetry device comprising one or more line of radiation detectors; positioning the leaves of the MLC or the single jaw in a predetermined position; delivering a radiation dose to said dosimetry device through said MLC or through said single jaw; measuring the dose absorbed by a plurality of radiation detectors of a line of radiation detectors located in the penumbra region of said leaf; determining all the quantities of interest in the penumbra region created by said leaf by fitting said measured doses with a function which recalls the shape of the field penumbra. Said quantities of interest may comprise the position of one of said leaves or jaws, the position and/or width of penumbra region, the positions where a beam profile reaches a given percent (e.g. 20% and 80%) of the value of the beam in the centre of the beam, the skewness of the beam, the flatness of the beam and the position of the centre of the radiation beam. By using this method, one can improve the spatial resolution of the measured profiles in the penumbra region and therefore precisely determine quantities of interest like the positions where the profile reaches a given percent of the value in the field central axis. In a preferred embodiment of the method according to the second aspect of the invention, said function is a Fermi function and one determines the position of said leaf as the position corresponding to the 50% value of said Fermi function. Advantageously, according to the second aspect of the invention, one determines the penumbra p according to the expression p=B/a, where B is a parameter selected between 2 and 3. If one defines the penumbra as the region where the dose goes from 80% to 20%, the correct value of B is 2.77 In another preferred embodiment of the method according to the second aspect of the invention, said step of providing a dosimetry device comprising three or more lines of radiation detectors, said lines being parallel to each other, and perpendicular to the leaf travel direction, radiation detectors on said lines being located under the projection of leaves of said MLC, thereby allowing the simultaneous determination of the positions and/or penumbrae of a plurality of leaves. In accordance with a third aspect of the invention, there is provided a use of the device of the invention for performing method according to the invention. In relation to the appended drawings, the present invention is described in details for an embodiment using ionisation chamber technology. It is apparent however that a person skilled in the art can imagine several other equivalent embodiments or other ways of executing the present invention, such as suggesting diodes instead of ionisation chambers for the radiation detectors, the spirit and the scope of the present invention being limited only by the terms of the claims. FIG. 1 represents an exploded view of a device according to a preferred embodiment of the present invention, which is using ionisation chambers in order to perform dosimetry tests. This dosimetry device 10 essentially consists in a stack of three main planar components: 1) a top layer 20, constituting the electrode top layer; 2) a mid layer 30 wherein drilled holes 31 delimit the gas volumes of the ionisation chambers; 3) a bottom layer 40 being the segmented electrode and carrying also the electronic chips 41 and the tracks bringing the signals from the ionisation chambers to the electronic chips 41; 4) either a removable build-up plate 50 for electron beams with energy degraders 51, or a removable build-up plate 60 for photon beams, with energy degraders 61. According to an important aspect of the present invention, as shown in FIG. 2, extra radiation detectors 52 are dedicated to the measurement of the energy of the electrons. Therefore, on the build-up plate 50 covering the top layer 20 of the dosimetry device 10, and dedicated to the electron beam measurements, a set of degraders 53 of different materials or different thicknesses having a different water-equivalent thickness from one degrader to the other are embedded in the build-up plate 50. Preferably, the combination of materials and thicknesses of said degraders gives an increasing water-equivalent thickness within a range comprised between 5 to 100 mm, while the build-up plate has a thickness which allows measuring the field profiles of all the electron energies (10 mm water-equivalent in the preferred embodiment of FIG. 1). Of course, said degraders 53 are placed on top of radiation detectors so that the electrons detected by such radiation detectors have been crossing the degraders before entering the active volumes of them. The general principle of an ionisation chambers is again explained hereunder. The radiation traversing the chambers ionises the gas present in between the top layer and the bottom layer. When a high voltage is applied between the two electrodes, an electric field is created and the ions are collected on the electrodes thereby creating a signal which can be measured. The technology used for manufacturing these ionisation chambers can be any one described in the state of the art and can be for example the one described by BONIN et al. using the so-called TERA electronics. Further, FIG. 3 includes a schematic representation of a collimator 65, shown in dashed lines, having a plurality of collimator leaves 66 and an isocenter at reference number 68. FIG. 4 includes a schematic representation of the collimator 65 having jaws 67 and an isocenter at reference number 68. FIG. 4B is a schematic representation of a collimator 65 having jaws 67, as shown in dashed lines. According to a preferred embodiment, the dosimetry device can comprise, in particular, the following layers: the top layer constituting the top electrode: a 50 μm thick printed Polyimide (Pyralux AP 8525R) layer covered with 25 μm carbon layers on both sides. The inner layer is structured according to the holes of the mid layer with a round shape of e.g. 0.1 mm smaller than the holes diameter (diam. 2.8 mm). The top carbon layer acts as an EMC shield; the mid layer: a layer which consists in an approximately 5 mm thick pure polycarbonate plate with drilled holes of e.g. 3 mm diameter and spaced from each other over a length of 5 mm; ventilation can also be provided; therefore the mid layer is laminated to the top and to the segmented electrode on the bottom layer by means of adhesive dots that act as standoffs; the bottom layer: a layer manufactured according to printed circuit board (PCB) techniques. An example of such a bottom layer using PCB techniques is described in the US provisional application filed in the name of the inventors of the present patent application on May 27, 2005, this document being incorporated by reference in the present application. FIG. 3 represents a preferred configuration of an active area for one preferred embodiment of the present invention, wherein the active area is constituted by individual radiation detectors being ionisation chambers radiation detectors. However, exactly the same configuration can apply to diode radiation detectors. According to the present invention, said configuration consists in at least one set of two essentially orthogonal lines of radiation detectors. Said lines are preferably passing through the centre of the active area and comprise preferably the majority of the radiation detectors present in said active area. In such case, one should assume that the two lines comprise m and n radiation detectors respectively, n and m being integers and higher than 1. More preferably, said preferred configuration consists in at least two sets of essentially orthogonal lines of radiation detectors, said lines passing preferably through the centre of the active area and comprising preferably the majority of the radiation detectors present in said active area. One can say that the configuration of the active area consists in a limited number of lines of radiation detectors. By “limited” number of lines, it should be understood at least 2 and strictly less than the number of radiation detectors of any line. In order to have a line, the number of radiation detectors should be an integer of at least 3 but preferably of at least 10, and more preferably of at least 20. Furthermore, “limited” number of lines means equal to or less than 8, more preferably equal to or less than 4, more preferably equal to 2. However, said configuration of radiation detectors does not cover all the surface of the mid layer. Said configuration cannot be considered as a matrix defined as an n×m radiation detectors matrix which corresponds to an embodiment of the state of the art, n and m being the number of radiation detectors of any two orthogonal lines. Accordingly, the total number of radiation detectors of the present invention is a linear function f(n+m), or f(n) if n=m, while the number of radiation detectors for an embodiment of the state of the art (matrix configuration) is a function f(n×m), or f(n2) if n=m. Another way to understand the present invention can be as follows: only very few radiation detectors are present in the area divided by the lines, namely in the quarters, if the division of the active area is performed by one set of two lines, or in the octants, if the active area is divided by four lines. If we compare the number of radiation detectors used in a device built according to the state of the art and in a device according to the present invention, it is obvious that the present invention implies a device with a lower number of radiation detectors and, accordingly, with a lower price. But if we build a device having a larger number of radiation detectors or even the same number of radiation detectors as, for instance, the device as described by Bonin et al., namely a dosimetry device having 32×32 radiation detectors (1024 radiation detectors), a device according to the preferred embodiment of the invention having two sets of two lines of 256 radiation detectors each will show either a surface for the active area (up to 8×, which is actually unrealistic) higher than the device suggested by Bonin et al. with comparable results relating to the measurements of the beam profiles or with a configuration with a (down to 8×, which is actually unrealistic) smaller pitch than the device suggested by Bonin et al. and then able to give a more precise result for the measurement. Of course, in practice, a compromise of these several requirements is sought: reduction of the total number of radiation detectors, while increasing the surface of the active area, while decreasing the pitch between two consecutive radiation detectors. As represented on FIG. 3, the two rows (70 and 71) of the first set essentially consist in the median lines (longitudinal and transversal axes) of the active area, while the two rows (80 and 81) of the second set essentially consist in the diagonals of said active area, all of them passing through the centre O, the shape of the active area of said active area being essentially a square of e.g. between 200×200 mm2 to 400×400 mm2. Preferably, each row or line (70, 71, 80 or 81) comprises at least 50 radiation detectors with a pitch less than 7 mm and preferably less than 5 mm and even preferably less than 4 mm. According to a particular embodiment, the pitch on the median lines and the diagonal lines can be the same. According to another preferred embodiment, the pitches are different on the median lines and on the diagonal lines. For instance, the pitch on the diagonal lines corresponds to √{square root over (2)} times the pitch on the median lines. By “line”, “row” or “column” of radiation detectors, one should understand either individual radiation detectors placed on a line or in staggered rows, within a certain width (as small as possible) along a line, said “line”, “row” or “column” comprising at least 3 radiation detectors, preferably at least 10 radiation detectors and more preferably at least 20 radiation detectors. The spatial resolution of the measurements at the field penumbras and field gradients can be, according to a preferred embodiment, improved in respect to the spacing of the radiation detectors by applying a data interpolation based on the well known Fermi function: F ( x ) = 1 1 + ⅇ a ( x 0 - x ) wherein the dose in the homogeneous part of the field is normalized to 1, as shown in FIG. 6; x0 represents the 50% position of the normalized dose; and the 20% to 80% distance (generally indicated as penumbra) is estimated by the relation a=2.4/p. By applying such an interpolation, the precision in identifying the field penumbra, the field width and all the field related quantities determined in the penumbra region is improved to a fraction of 1 mm for a pitch of 5 mm. The fact that the individual radiation detectors are placed in lines allows the acquisition of the field profiles in a one-step measurement, thereby avoiding any moving or manipulation of the dosimetry device. Said measurement can be considered as instantaneous. Thanks to its fast electronics, the device can also be used as a “real time” measurement device, allowing the steering of some accelerator parameters while observing the modifications induced on the measured profiles. Furthermore, the fact that the radiation detectors organised in lines are not covering the whole surface of the active area will obviously reduce the price of the electronics attached to said dosimetry device and accordingly the final price of the dosimetry device. According to another aspect of the present invention, in order to be able to cover field sizes bigger than the detector active area, the device can be coupled with a frame holding it at a source-axis distance (SAD) less than 100 cm. Optionally, to provide a measurement dedicated to IMRT QA and more specifically to Multi Leaf (ML) Collimator QA as represented in FIGS. 1, 2, 4, 5, one or several lateral (vertical) bands 90 of radiation detectors are provided at different positions. Each band is composed of a few (typically 3 to 5) columns or rows of radiation detectors with a spacing of 0.5 or 1 cm corresponding to the leaf width if the plane of measurement is at isocenter in the longitudinal (i.e. vertical on FIGS. 1, 2, 4, 5, or perpendicular to leaf travel direction) direction, with a pitch of 2 to 8 mm in the transversal (i.e. horizontal on FIGS. 1, 2, 4, 5, or parallel to leaf travel direction) direction. When there are two bands centered at +/−10 cm, the detector is placed at isocenter and the several leaves are positioned as to give a 20×20 cm2 field on the detector, each transversal row of a few radiation detectors is then providing the measurement of the position of a single leaf, again by using a Fermi fit on the measured penumbra, with a spatial precision of a fraction of 1 mm. Another embodiment can provide only one row (FIGS. 1, 3, 5) of radiation detectors which are dedicated to the leaf measurement, in place of the bands of rows. In this case, a comparison of the relative signal of each radiation detector provides a relative position of the leaves. This design allows the verification of the position on the leaves of a MLC for a limited, predetermined set of leaf positions, where said leaf positions project on the isocenter plane. According to the preferred embodiment described in FIG. 2, eight degraders 53 and corresponding radiation detectors 52 are placed on the periphery of a circle included in a 20×20 cm2 field. Of course, the energy degraders 53 are placed not too close to the radiation detectors 52 present in the several rows intended to measure the field profiles, in order not to disturb the simultaneous acquisition of the field profiles. According to another important feature of the present invention, extra radiation detectors 62 can be dedicated to the measurement of the energy of the photons. Therefore, on a build-up plate 60 covering the top layer 20 of the dosimetry device 10 and dedicated to the photon measurements, several extra energy degraders 63 are provided within a given field at isocenter (10×10 cm2 in the preferred embodiment of FIG. 1). Said degraders have different water equivalent thicknesses within a range comprised between 5 to 200 mm (in the preferred embodiment of FIG. 1, two degraders corresponding to 10 and 20 cm water-equivalent respectively), while the build-up plate 60 has a thickness equal or higher to Dmax of the maximum photon energy measured (50 mm water-equivalent in the preferred embodiment of FIG. 1). Again, said degraders are placed on top of radiation detectors 62 so that the electrons detected by them have been crossing the degraders 63 before entering the active volumes of them. The detectors dedicated to the measurement of energy may have different dimensions than the detectors present on the rows, (70, 71, 80 and 81). Three possibilities are provided in order to realise the variation of the water-equivalent thickness of the degraders and accordingly the variation of the energy absorption: either having bumps on the build-up plate with different thicknesses, or having bumps on the build-up plate made of different materials and thicknesses or recesses with inserts in the thickness of the build-up plate, again made of different materials and thicknesses, or combinations of the above possibilities. Once again, the fact that several energy degraders are present on each build-up plate will allow an energy measurement which can be performed in one step together with the relative field profiles, without any moving or any manipulation of said dosimetry device and build-up plates. Therefore, there is no need for an operator to enter the treatment room for changing a build-up plate. The results of the energy measurement performed with eight energy degraders will allow to uniquely identify each beam energy, from two or more measurement points on the slope of each electron energy measurement as described in relation to FIG. 7. FIG. 7 is representing a particular example of a set of electron PDDs (Percent Depth Dose) corresponding to energies of 4, 6, 8, 9, 10, 12, 15, 18, 20, 22 MeV, with corresponding set of 8 values of water-equivalent depths corresponding to a set of 8 degraders. In a an similar way, the results of the energy measurement performed with the photon energy degraders will allow to uniquely identify each beam energy, from two or more measurement points on the slope of each photon energy measurement as described in FIG. 8. FIG. 8 represents the relative dose in % measured in function of the depth in water (Z [mm]) for various photon beam energies. It represents a particular example of a set of photon PDDs corresponding to energies of 4, 6, 8, 9, 10, 12, 15, 18, 20, 25 MeV, with corresponding 2 values of water-equivalent depths corresponding to a set of 2 degraders (100 mm and 150 mm, represented by two vertical dashed lines). The above description should be considered as illustrative examples not limiting the scope of the invention. For example, the method for verifying the positions of a leaf of a MLC should also be considered as covering a MLC comprising a single leaf on each side, i.e. jaws. |
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abstract | The present invention relates to a method for the determination of the coefficient of performance of a refrigeration machine, in particular of a heat pump, which includes a closed circuit which has a refrigerant and in which an evaporator, a compressor, a condenser and an expansion valve are arranged. In the method, at least three temperatures of the refrigerant are determined using temperature sensors arranged in the circuit. Alternatively, at least two temperatures and at least one pressure of the refrigerant is determined using sensors arranged in the circuit. Enthalpies of the circuit are calculated from the determined refrigerant temperatures and refrigerant pressures and the heat output and the taken up electrical power of the refrigeration machine are calculated therefrom to determine the coefficient of performance of the refrigeration machine from the quotient of the calculated heat output and the calculated taken up electrical power. The invention also relates to a refrigeration machine for the carrying out of such a method. |
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048312703 | summary | TECHNICAL FIELD This invention relates generally to the field of ion implantation, and more particularly relates to an improved high current, high throughput ion implantation apparatus. BACKGROUND Ion implantation involves the introduction of impurities into a solid workpiece by directing an energetic beam of particles at the workpiece surface. When sufficiently energetic ions are used, the ions penetrate the workpiece surface and impregnate the near-surface region of the solid. Generally, the advantages of "doping" solids using ion implantation, over prior art methods such as high temperature diffusion or impregnation during crystalline growth, are (1) precise control over the type and amount (or "dosage") of impurity introduced and (2) precise control over the depth and uniformity of the impurity distribution. While a number of scientific and engineering applications of ion implantation are known, a fairly recent and major application relates to the area of semiconductor device manufacture, where ion implantation has become a relatively standard doping technique in the fabrication of diodes, MOS transistors, resistors and the like. Typically, silicon is doped with boron, phosphorus or arsenic dopant ions having an energy of between about 3 and about 500 keV, yielding an implantation depth of about 100 to 10,000 Angstroms. Such a process thus places the implanted ions well below the surface, the depth of implantation being roughly proportional to the ionic energy. Upon annealing (heating to temperatures on the order of about 600 to 1000 degrees Centigrade), dopant concentrations of about 10.sup.14 to 10.sup.21 atoms per cubic centimeter are obtained. A typical ion implantation apparatus includes at one end a gaseous source of appropriate material such as BF.sub.3 or AsH.sub.3, a means for controlling the flow of gas to an ion source, e.g. an adjustable valve, and a high voltage power supply which energizes the ion source so as to create a plasma therein, at pressures generally of about 10.sup.-3 torr. As the plasma is formed, the ions contained in the plasma are continuously extracted and accelerated through a voltage of about 10,000 to about 50,000 V. An analyzer magnet selects the ionic species of interest, which as a beam is then passed through a vacuum to the target. Examples of ion implantation devices known in the art include those disclosed in U.S. Pat. Nos. 4,008,683 to Rose; 4,346,301 to Robinson et al.; 4,498,833 to Hertel; and 4,628,209 to Wittkower. U.S. Pat. No. 4,628,209 to Wittkower, for example, describes an ion implantation apparatus for doping a plurality of semiconductor wafers, wherein the wafers are supported on a rapidly rotating wheel and implanted by an ion beam which scans repeatedly over the wafer surfaces. The Wittkower invention includes an on-line method of monitoring the beam profile and thus improves one's control over the uniformity and dose of implantation. The ion implantation devices of the prior art, though, still present several problems. First, metal oxides--e.g., gate oxides--on the semiconductor surface may be undesirably degraded by charge build-up during implantation. Second, as ion implantation technology has advanced, there has been an increasing and as yet unsatisfied demand for lower charge and particle build up, as well as for more precise control over uniformity and dose of implant as well as for improved surface smoothness. A further problem with conventional implantation systems is the limited throughput which is achievable with them. That is, large volumes are not generally attainable. Most systems use some form of wheel on which to mount the semiconductor wafers. Normally these wheels are positioned in a horizontal plane for loading and then raised to a vertical position for implantation. The size of these wheels and the associated equipment is therefore necessarily limited by the amount of typical floor-to-ceiling space commercially available, which is usually eight to ten feet. Known exceptions to this are a system which mounts the wafers on the side of a rotating cylinder, as described in U.S. Pat. No. 4,346,301; and a system which uses a horizontal wheel and impinges the wafers from below, as described in "Computer Automation of High Current Ion Implanters", by Woodard et al., Nuclear Instruments and Methods in Physices Research, B6 (1985), pp. 146-153. These systems all require, during at least some stage of the wafer implantation process, that the wafers be mechanically clipped or otherwise held on a wafer support plate. Such contact with the wafer produces atmospheric pollutants, some of which inevitably end up on the wafers as unwanted particles. Particle build up also results from handling and manipulating the wafers prior to loading onto and unloading off of a wafer-support wheel in nonvacuum conditions. Typically, wafers are provided to a transfer station in a carrier cassette in a clean-room environment in which people and other equipment are located. There is thus substantial opportunity for surface particle transfer and contamination of the wafers. SUMMARY OF THE INVENTION The present invention provides an ion implantation system which overcomes many of these disadvantages of the prior art. More particularly, it provides a system which permits the treatment of a large number of wafers at a time. It does so in a way which increases the rate of wafer throughput without encountering damaging charge buildup problems. This is preferably provided by presenting the wafers generally horizontally to an ion beam which is directed at them from above. Further, in one aspect of the invention means are provided for varying the beam across an impingement region which is controlled from externally of an evacuated enclosure surrounding the beam transmission path. The present invention also provides a system wherein the wafers are handled during transit to the implantation enclosure, as well as during loading, unloading, and implantation in a near vacuum environment which minimizes the number of free particles to which the wafers are subject. The present invention also preferably provides an ion implantation system generally having means for generating an implantation ion beam directed along a beam transmission path along an initial beam axis; target support means for supporting a target element or wafer spaced from the initial beam axis during ion implantation; beam diversion means disposed relative to the beam transmission path for diverting a beam generated by the generating means from the initial beam axis toward a beam impingement region of the target support means, the diversion means being mounted relative to the generating means for movement along the initial beam axis; and means for moving the diverted beam across the target support means both laterally of and in line with the first impingement line, whereby a target material supported on the target support means is scanned within the beam impingement region. The target support means is preferably in the form of a generally horizontally disposed wheel on which the target elements are supported. The initial beam axis is generally horizontal so that the beam is diverted or deflected in a downward direction into the impingement region. Further, the diverted beam is preferably shaped to be elongate in line with the initial beam axis and that the beam is moved relative to the impingement region in line with the initial beam axis by physically moving the diversion means along the initial beam axis. This latter feature is provided by magnetically coupling a driven carrier external of an enclosure containing the diversion means to the diversion means disposed in the enclosure. Another preferred feature of the present invention is a housing which includes an evacuatable chamber for transporting the target elements to and from the evacuated enclosure. It includes a transfer port sealingly engageable with an entry port on the implantation enclosure for loading and unloading the target elements from the target stations. It can be seen that such a system provides the advantages described above. Most importantly, it provides a system which can be sized to have increased throughput which results in fewer surface particles and less wafer contamination than other known systems. These and other features and advantages of the invention will become apparent from a consideration of the drawings and the following detailed description of the preferred embodiments. |
039376524 | summary | This invention relates to nuclear power installations, and more particularly such installations including a nuclear reactor in which the reactor core is cooled by a fluid such as carbon dioxide or helium which is circulated by one or more coolant fluid circulators. In such an installation, it may be advantageous to drive the coolant circulators by means of steam turbines; and, in cases where the heat removed from the reactor core by the coolant is used to generate high-pressure steam in one or more main boilers which supply the steam to one or more main turbo-generators, it has been proposed to drive the coolant circulators by steam turbines supplied with steam from this main system, preferably from the cold reheat line thereof (i.e. at an intermediate stage in the main turbine expansion process) since this minimises the loss in thermodynamic efficiency. In cases of this kind, and in which steam reheat in the main steam system is effected within the reactor vessel by heat exchange with the hot coolant, the connection of the circulator turbines in the steam reheat line is quite convenient since this latter is returned to the reactor vessel (where the circulators are located) in any event. However, in a case where a steam-to-steam reheat cycle is used (i.e. in which either live or bled steam is used for reheat purposes), it would be expensive to return steam to the reactor merely for driving the coolant circulators. According to the present invention, there is provided a nuclear power installation comprising a nuclear reactor which includes a reactor core, at least one main boiler, at least one main coolant circulator arranged to circulate coolant fluid through the core and through the main boiler, and a circulator-driving steam turbine arranged to drive said main coolant circulator, wherein the installation further comprises at least one auxiliary boiler which is arranged to be heated by the coolant fluid and to generate steam and which is connected to supply said steam to said circulator-driving steam turbine. The invention may be incorporated in reactor systems such as are described and claimed in U.S. Ser. No. 178525 filed on Aug. 30, 1971 and now abandoned comprising a main boiler system and an auxiliary boiler system both heated by heat transferred to them from the reactor core by fluid coolant circulated by coolant circulators, the auxiliaary boilers providing steam for essential electrical power and having a capacity, typically, of some 20% of the maximum station output. |
claims | 1. An imaging apparatus which has a movable element related to imaging and an image sensing element, and has a function of sensing an image of an object with the image sensing element and reading as an image signal a signal generated by the image sensing element, comprising:a radiation generation device adapted to emit radiation;an image sensing element which converts the radiation to an electrical signal;a control unit arranged to stop movement of the element related to imaging, and, after stopping the movement a vibration of the element has become smaller than a predetermined level after stopping movement control for the element, starting to start reading of a signal generated by the image sensing element, andan imaging control device adapted to control said image sensing element to be in at least one of a state of sweeping out an electrical charge and a state of accumulating an electrical charge,wherein said imaging control device controls said image sensing element to bring said image sensing element into a second state in which the sweeping out operation is repeated with a second time interval after said image sensing element has been brought into a first state in which the sweeping out operation is repeated with a first time interval. 2. The apparatus according to claim 1, wherein the element related to imaging is a grid arranged between the object and the image sensing element. 3. The apparatus according to claim 1, wherein said apparatus further comprises an irradiation detection unit arranged to detect irradiation for the object, and said control unit controls the stopping of movement of the elementrelated to imaging on the basis of a detection result from said irradiation detection unit. 4. The apparatus according to claim 1, wherein after stopping movement of a grid, said control unit starts reading the signal from the image sensing element after an elapse of a predetermined time. 5. The apparatus according to claim 4 1, wherein said control unit determines in advance the predetermined time on the basis of at least one of an irradiation time for the object and a moving speed of the element related to imaging. 6. The apparatus according to claim 1, wherein said apparatus further comprises a vibration detection unit arranged to detect a vibration state of the image sensing element due to movement of the element related to imaging, and said control unit controls a start of reading an accumulated signal from the image sensing element on the basis of a detection result from said vibration detection unit. 7. The apparatus according to claim 1, wherein irradiation for the object includes radiation irradiation. 8. An imaging apparatus which has a movable element related to imaging and an image sensing element, and has a function of sensing an image of an object with the image sensing element and reading as an image signal a signal generated by the image sensing element, comprising:drive unit arranged to move the element related to imaging by the image sensing element; andcontrol unit arranged to control said drive unit to operate the element related to imaging at a predetermined speed without any acceleration during an operation period related to reading a signal from the image sensing element. 9. The apparatus according to claim 8, wherein the element related to imaging is a grid inserted between the object and the image sensing element. 10. The apparatus according to claim 8, wherein irradiation for the object includes radiation irradiation. 11. The apparatus according to claim 10, wherein the radiation comprises X-rays. 12. An imaging apparatus which has a movable element related to imaging and an image sensing element, and has a function of sensing an image of an object with the image sensing element and reading as an image signal a signal generated by the image sensing element, comprising:drive unit arranged to move the element related to imaging; andcontrol unit arranged to control said drive unit to operate the element related to imaging at a uniform acceleration during an operation period related to reading a signal from the image sensing element. 13. The apparatus according to claim 12, wherein the element related to imaging is a grid inserted between the object and the image sensing element. 14. The apparatus according to claim 12, wherein irradiation for the object includes radiation irradiation. 15. The apparatus according to claim 14, wherein the radiation comprises X-rays. 16. An imaging apparatus which has a movable element related to imaging and an image sensing element, and has a function of sensing an image of an object with the image sensing element and reading as an image signal a signal generated by the image sensing element, comprising:drive unit arranged to move the element related to imaging; andcontrol unit arranged to control execution of a drive operation related to image acquisition upon determining that a value of a vibration is not more than a predetermined value during an operation period related to an image read froth the image sensing element. 17. The apparatus according to claim 16, wherein the element related to imaging is a grid inserted between the object and the image sensing element. 18. The apparatus according to claim 16, wherein irradiation for the object includes radiation irradiation. 19. The apparatus according to claim 18, wherein the radiation comprises X-rays. 20. An imaging apparatus having a function of sensing an image of an object with an image sensing element and reading as an image signal a signal generated by the image sensing element, comprising:drive unit arranged to move the image sensing element; andcontrol unit arranged to stop movement of the image sensing element by said drive unit, and after stopping the movement, starting reading of an accumulated signal from the image sensing element. 21. The apparatus according to claim 20, wherein after stopping movement of the image sensing element, said control unit starts reading the signal from the image sensing element after an elapse of a predetermined time. 22. The apparatus according to claim 20, wherein said apparatus further comprises vibration detection unit arranged to detect a vibration state of the image sensing element, andsaid control unit controls a start of reading of the signal from the image sensing element on the basis of a detection result from said vibration detection unit. 23. The apparatus according to claim 20, wherein irradiation for the object includes radiation irradiation. 24. An imaging apparatus having a function of sensing an image of an object with an image sensing element and reading as an image signal a signal generated by the image sensing element, comprising:drive unit arranged to move the image sensing element; andcontrol unit arranged to control said drive unit to operate the image sensing element at a predetermined speed without any acceleration during an operation period related to reading a signal from the image sensing element. 25. The apparatus according to claim 24, wherein irradiation for the object includes radiation irradiation. 26. The apparatus according to claim 25, wherein the radiation comprises X-rays. 27. An imaging apparatus having a function of sensing an image of an object with an image sensing element and reading as an image signal a signal generated by the image sensing element, comprising:drive unit arranged to move the image sensing element; andcontrol unit arranged to control said drive unit to operate the image sensing element at a uniform acceleration during an operation period related to reading a signal from the image sensing element. 28. The apparatus according to claim 27, wherein irradiation for the object includes radiation irradiation. 29. The apparatus according to claim 28, wherein the radiation comprises X-rays. 30. An imaging apparatus having a function of sensing an image of an object with an image sensing element and reading as an image signal a signal generated by the image sensing element, comprising:drive unit arranged to move the image sensing element; andcontrol unit arranged to control execution of a drive operation related to image acquisition upon determining that a value of a vibration is not more than a predetermined value during an operation period related to an image read from the image sensing element. 31. The apparatus according to claim 30, wherein irradiation for the object includes radiation irradiation. 32. The apparatus according to claim 31, wherein the radiation comprises X-rays. 33. An imaging method of sensing an image of an object with an image sensing element and reading a signal generated by the image sensing element while moving a movable element related to imaging, comprising:irradiating the image sensing element with radiation emitted from a radiation generation device;converting the radiation to an electrical signal;stopping movement of the element related to imaging, and, after stopping the movement a vibration of the element has become smaller than a predetermined level after stopping movement control for the element, starting reading of a signal from the image sensing element, andcontrolling said image sensing element to be in at least one of a state of sweeping out an electrical charge and a state of accumulating an electrical charge,wherein said image sensing element is brought into a second state in which the sweeping out operation is repeated with a second time interval after said image sensing element has been brought into a first state in which the sweeping out operation is repeated with a first time interval. 34. An imaging method of sensing an image of an object with an image sensing element and reading a signal generated by the image sensing element while moving a movable element related to imaging, comprising:in moving the element related to imaging at the time of image sensing by the image sensing element, controlling operation of the element related to imaging at a predetermined speed without any acceleration during an operation period related to reading of a signal from the image sensing element. 35. An imaging method of sensing an image of an object with an image sensing element and reading a signal generated by the image sensing element while moving a movable element related to imaging, comprising:in moving the element related to imaging at the time of image sensing by the image sensing element, controlling operation of the element related to imaging at a uniform acceleration during an operation period related to reading a signal from the image sensing element. 36. An imaging method of sensing an image of an object with an image sensing element and reading a signal generated by the image sensing element while moving a movable element related to imaging, comprising:in moving the element related to imaging at the time of image sensing by the image sensing element, controlling execution of a drive related to image acquisition upon determining that a value of a vibration of the image sensing element is not more than a predetermined value during an operation period related to an image read from the image sensing element. 37. An imaging method of sensing an image of an object with a movable image sensing element and reading a signal generated by the image sensing element, comprising:stopping movement of the image sensing element, and after stopping the movement, starting reading of a signal from the image sensing element. 38. An imaging method of sensing an image of an object with a movable image sensing element and reading a signal generated by the image sensing element, comprising:controlling operation of the image sensing element at a predetermined speed without any acceleration during an operation period related to reading a signal from the image sensing element. 39. An imaging method of sensing an image of an object with a movable image sensing element and reading a signal generated by the image sensing element, comprising:controlling operation of the image sensing element at a uniform acceleration during an operation period related to reading a signal from the image sensing element. 40. An imaging method of sensing an image of an object with a movable image sensing element and reading a signal generated by the image sensing element, comprising:controlling execution of a drive operation related to image acquisition upon determining that a value of a vibration of the image sensing element is not more than a predetermined value during an operation period related to an image read from the image sensing element. 41. A computer-readable storage medium wherein said storage medium stores a processing program for executing said imaging method of claim 33. 42. A computer-readable storage medium wherein said storage medium stores a processing program for executing said imaging method of claim 34. 43. A computer-readable storage medium wherein said storage medium stores a processing program for executing said imaging method of claim 35. 44. A computer-readable storage medium wherein said storage medium stores a processing program for executing said imaging method of claim 36. 45. A computer-readable storage medium wherein said storage medium stores a processing program for executing said imaging method of claim 37. 46. A computer-readable storage medium wherein said storage medium stores a processing program for executing said imaging method of claim 38. 47. A computer-readable storage medium wherein said storage medium stores a processing program for executing said imaging method of claim 39. 48. A computer-readable storage medium wherein said storage medium stores a processing program for executing said imaging method of claim 40. |
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