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047117567 | description | DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is an elevational view of a typical rod and spider assembly which can be constructed according to the present invention. This assembly includes a spider 2 which supports a plurality of rods 4 for vertical movement as needed to achieve the required reactor control. Each rod is supported on spider 2 via a respective support unit 6, one embodiment of which is shown in FIG. 2. The support unit 6 is composed of a housing 8 and a housing cap 10 which together delimit a cylindrical chamber 12. Each control rod 4 is connected to an extension piece 16 into which is threaded a support rod 20 that extends vertically through unit 6 and its chamber 12 and is movable axially relative to unit 6. A ring 22 is fixed to rod 20 and a compression spring 24 is interposed between ring 22 and the bottom wall of chamber 12. Thus, rod 20 is supported by unit 6 via spring 24. Reverting to FIG. 1, when the assembly composed of spider 2 and rods 4 is raised into the upper internals of the reactor vessel in order to withdraw rods 4 from the active core region of the reactor, each rod 4 is guided by guide sections or cards 30 (note: this reference numeral must be added to FIG. 1), which are spaced apart around the associated rod 4. Contact between each rod 4 and its associated guide sections or cards 30 produces drag forces whenever rods 4 are raised or lowered. These drag forces, of course, produce a certain amount of wear on the outer surface of the rod 4. As the assembly 2, 4 arrives at its uppermost position, the upper end of each support rod 20 comes to abut against a stop 34 installed in the guide tube and positioned so that when assembly 2, 4 is in its uppermost position, each ring 22 will have been pushed downwardly in chamber 12 from the position illustrated in FIG. 2 and spring 24 will be essentially fully compressed. According to the present invention, this downward movement of ring 22, together with support rod 20, extension piece 16 and the associated rod 4 will be accompanied by a rotation relative to housing 8. This rotation will change the locations of each rod 4 which are in contact with its associated guide sections or cards. One suitable mechanism for effecting the desired rotation is illustrated in developed form in FIG. 3. This mechanism includes a boss 36 on the outer surface of support rod 20, as well as a group of upper bosses 38, 40, 42 . . . and a group of lower bosses 44, 46 . . . provided on the wall of chamber 12 and extending around the periphery thereof. Boss 36 is provided with a lower camming surface 50 arranged to cooperate with guide surfaces 52, 54 on lower bosses 44, 46, respectively. In addition, boss 36 is provided with an upper camming surface 58 arranged to cooperate with guide surfaces such as 60, 62 on upper bosses 40, 42, respectively. Rotation of support rod 20, together with extension piece 16 and the associated control rod is effected each time the assembly 2, 4 is raised into the parked position and then lowered again into the reactor core. When the assembly reaches its uppermost position, the upperend of each support rod 20 is halted by its associated stop member 34. Spider 2 and housings 8 then continue to move upwardly over a short distance relative to support rods 20 so that camming surface 50 of cam 36 slides along guide surface 52, thereby effecting an incremental rotation of support rod 20. Thus, cam 36 comes into alignment with the gap between lower bosses 44 and 46. Then, when spider 2 is again lowered, each support rod 20 initially remains in contact with its associated stop 34 so that each housing 8 moves downwardly relative to its associated rod 20 as spring 24 expands. During this time, camming surface 58 will slide upwardly along guide surface 60 of upper boss 40, thereby effecting a further incremental rotation of support rod 20 and bringing boss 36 into alignment with the gap between upper bosses 40 and 42. According to one embodiment of the invention, the total rotation imparted to rod 20 by the sliding movement along surfaces 52 and 60 will be of the order of 45 degrees. Then, when the assembly is lowered into the reactor core, each control rod 4 will have an angular position which is offset by 45 degrees from the previous position. As a result, each guide section, or card will contact a new surface area of its associated rod 4, at a location which is angularly offset from the surface area which it previously contacted. FIG. 4 illustrates an alternative rod support unit 64 which includes a top end plug 66 fastened to spider 2 and having an axial passage for support rod 20. A housing 68 is screwed onto the bottom of plug 66 and is then secured thereto by a locking pin. This embodiment allows for a larger space within housing 68 to accommodate a larger spring 24 and facilitate formation of bosses, such as 38, 40, etc of FIG. 3, on the inner wall of housing 68. FIG. 5 illustrates a second embodiment of a mechanism for rotating each rod in accordance with the present invention. This embodiment includes a housing 68 having the same form as that shown in FIG. 4. However, one advantage of the structure illustrated in FIG. 5 is that the interior of housing 68 need not be provided with bosses, such as 38, . . . In this embodiment, the control or water displacer rod is supported by means of a support rod 70 which, in turn, is supported in housing 68 by means of compression spring 24. Extending downwardly into housing 68 is a drive rod 72 which extends upwardly through the top end plug connected to rod 68, the top end plug being as shown in FIG. 4 and not being illustrated in FIG. 5. The upper end of drive rod 72 is disposed to engage the stop 34 shown in FIG. 1. The lower end of drive rod 72 carries a rotation producing member 74 provided with two individual, angularly offset external threads 75 which engage in helical recesses 76 in the inner wall of housing 68. The lower end of member 74 has an annular sawtooth structure composed of vertical surfaces alternating with gradually sloping surfaces. Fixed to the upper end of support 70 is a disk 78 having, at its top, a sawtooth structure constructed to mate with the sawtooth structure at the lower end of member 74. The lower end of disc 78 is equally provided with an annular sawtooth structure composed of vertical surfaces alternating with inclined surfaces, with these inclined surfaces being inclined in the opposite direction to the gradually sloping surfaces at the upper end of disk 78. In the normal operating state, when spider 2 is spaced from the retracted position, spring 24 is in its elongated state and presses disk 78 against member 74, so that member 74 and drive rod 72 are equally supported by spring 24. The spider is lifted into its retracted position, and the upper end of drive rod 72 comes to abut against stoop 34, continued upward movement of housing 68 together with spider 2 causes the external threads 75 to be guided in helical recesses 76, thereby imposing a rotational movement on member 74, so that member 74 is thereby driven downwardly relative to housing 68. As a result of cooperation of the sawtooth structure at the lower end of member 74 and the upper end of disk 78, this equally causes disk 78, rod 70 and the control rod supported thereby to rotate and to move downwardly relative to housing 68. This rotational movement is not impeded by spring 24 since, as is apparent from FIG. 5, the upper end of spring 24 will slide along the inclined surfaces at the lower end of disk 78. The lower end of spring 24 is seated in a bore formed at the bottom of the chamber defined by housing 68, so that spring 24 is itself prevented from rotating. However, spring 24 will be axially depressed by the downward movement of disk 78 relative to housing 68. According to one exemplary embodiment of the invention, drive rod 72, threads 75 and receses 76 are dimensioned to cause the rod rotation system to undergo a rotation of between 90 and 180 degrees as the spider moves to its fully retracted position. Then, as the spider is subsequently moved downwardly away from the retracted position, spring 24 becomes active to urge disk 78 upwardly relative to housing 68. This produces an upward force on member 74 which causes member 74 to move upwardly relative to housing 68 while threads 75 travel along recesses 76 in order to also rotate member 74. However, during this movement, the upper end of spring 24 will come to abut against one of the vertical surfaces of the sawtooth structure at the lower end of disk 78, whereupon further rotation of disk 78 and support rod 70 will be prevented and the sloping surfaces of the sawtooth structure at the lower end of member 74 will be forced to slide along the sloping surfaces at the upper end of disk 78. At the end of this return movement, member 74 and disk 78 will again be in the positions shown in FIG. 5, but disk 78, support rod 70 and the control rod supported thereby will have undergone a net rotation of 90.degree.. While FIG. 5 illustrates sawtooth structures, each composed of 4 teeth, it will be appreciated that a different number of teeth can be provided, if desired, and the inclination of threads 75 and helical recesses 76 can be varied in order to produce a different amount of rotation during each retraction movement of the spider. It will be noted that in the normal operating position shown in FIG. 5, when the spider assembly is spaced from its retracted position, each vertical surface of the sawtooth at the bottom of member 74 is spaced circumferentially from the associated vertical surface of the sawtooth structure at the top of disk 78. This spacing is provided to assure that, when member 74 is being urged upwardly relative to housing 68 by the action of spring 24, member 74 will come to rest at a position where the vertical surfaces of its associated sawtooth structure will be properly positioned relative to the vertical surfaces of the sawtooth structure at the top of disk 78 to produce the next 90.degree. rotation of disk 78 and the components secured thereto. A significant advantage of this structure is that very little machining must be carried at the interior of housing 68. In effect, the only machining required is the formation of a small diameter bore at the bottom of the chamber enclosed by housing 68 and the machining of helical grooves 76 near the open top of housing 68. The machining of such grooves at that location is a relatively simple matter. FIGS. 6 and 7 are detail plan views illustrating portions of two types of guide arrangements which can be employed for guiding rods 4 primarily during movement in the upper internals of the reactor pressure vessel. Such guide arrangements are fixed in the pressure vessel so that the rods move vertically therepast. FIG. 6 illustrates a portion of one guide card which can be employed for guiding the rods of a rod cluster control. A complete card can be in the form of a cruciform structure, one arm of which is illustrated. This card is compared simply of a plate 82 having a central slot 84 for passage of an arm of spider 2, and accurate openings 86. Each opening 86 guides a respective rod, so that the total number of openings 86 is a card 82 will equal the number of rods carried by spider 2 of FIG. 1. Plate 82 is of a suitable metal and of a suitable thickness, for example 3.7 cm. The openings 86 are slightly larger in diameter than the rods 4 which they guide so that, as a general rule, each rod 4 bears against a particular part of the periphery of its associated opening 86, at which location the rod 4 will be subject to wear. When rod 4 is rotated, the portion of its surface which bears against the particular part of opening 86 changes. Typically, a number of, e.g. five, cards or plates, 82 is provided, the cards being spaced apart vertically along the upper portion of the pressure vessel interior. FIG. 7 illustrates a similar portion of a guide arrangement suitable for guiding the rods of a water displacer rod assembly. Here, the guide region is delineated by upper and lower end plates 88 having slots 90 and between which extend, vertically, a plurality of C-tubes, such as 92, and a plurality of half-tube assemblies, such as 94. Each tube 92 and assembly 94 guides a respective water displacer rod. As shown, each assembly 94 is composed of two tube sections each coextensive with less than half the diameter of an associated rod. Here, again, the internal diameter of tubes 92 and assemblies 94 are slightly less than the diameters of rods 4 so that each rod will tend to bear against a particular part of its associated tube or half-tube assembly. In the case of water displacement rods, the above-described rotation will have the effect of renewing the locations at which the guide sections or cards bear against the rod surfaces, so that the locations where wear occurs will be varied. The new contact surfaces on each rod 20 will previously have become oxidized to form a hard zirconium layer which serves to retard wear. The magnitude of each rotation step, for example 45 degrees, can be selected to take advantage of the longitudinal growth of zircalloy due to fast fluence effects while the rods are in the reactor core. As a result, even after the rods have undergone a rotation of 360 degrees, the new wear locations will not coincide with the locations which existed prior to the full 360 degrees of rotation. Moreover, the resulting helical wear paths will have a less significant effect on the longitudinal strength of the control rods. In the case of rod cluster control, the magnitude of each rotation step can be selected to renew the contact surfaces, and also to keep the wear lines symetrically located. This will reduce any effect which the wear lines may have upon bowing of the control rods. It will be understood that the above description of the present invention is susceptible to various modifications, changes and adaptations, and the same are intended to be comprehended within the meaning and range of equivalents of the appended claims. |
048184730 | claims | 1. A fuel bundle for a nuclear reactor including a top plate, a bottom plate, a plurality of nuclear fuel elements extending between said top and bottom plates, said fuel bundle also including at least one tie rod extending between said plates, a key extending from the bottom of said tie rod, a receptacle for said key in said bottom plate enabling said key to penetrate through said bottom plate and to be turned by turning said tie rod, said key and receptacle being formed so that by said turning of said tie rod in said receptacle, said key positively blocks the removal of said bottom plate by engagement with the under surface of said bottom plate, said tie rod having an end plug at the top extending through said top plate and said fuel bundle including means for engaging said plug to lock said tie rod positively with said key turned to said blocking position and also including a locking cup interconnected with both said engaging means and said plug, said plug and locking cup cooperating to suppress rotation of said tie rod to prevent said tie rod from becoming undesirably disengaged. 2. The fuel bundle of claim 1 wherein the tie rod is a nuclear fuel element. 3. The fuel bundle of claim 1 wherein the key is a generally flat plate extending from the bottom of the tie rod and the receptacle includes a slot in the bottom plate shaped to pass said flat plate to a position below the slot, whereby by turning the tie rod, the key is turned so that removal of the tie rod is blocked by the under surface of the bottom plate. 4. The fuel bundle of claim 1 wherein the tie rod at its upper end is provided with a threaded end plug having flattened axially extending surfaces, and the top plate has a generally rectangular slot through which said end plug passes, the thread on said end plug being engaged by a nut, to secure said tie rod to said top plate. 5. The fuel bundle of claim 4 wherein the nut has a crimping lip which is crimped to the flattened surfaces of the end plug. 6. The fuel bundle of claim 1 having spacer-grids along its length, wherein the at-least one tie rod includes tabs along its length to prevent displacement axially of the grids. 7. A fuel bundle for a nuclear reactor including a top plate, a bottom plate, a plurality of nuclear fuel elements extending between said top and bottom plates, said bundle also including at least one tie rod extending between said top and bottom plates, a key extending from the bottom of said tie rod, a slot in said bottom plate shaped with respect to the contour of said key so as to be penetrated by said key to the underside of said bottom plate, said key, on penetrating said slot, being rotatable by rotating said tie rod to a position in the underside of said bottom plate in which said key is at an angle to said slot, said tie rod having an end plug at the top, said end plug having a non-circular transverse cross-section and said top plate having a non-circular opening engaged by said end plug, said opening having an inner peripheral shape matching the non-circular outer-surface of said end plug and said end plug being a slip fit in said opening, and means, connected to the top of said tie rod, for securing said tie rod to said top plate with said key at an angle to said opening whereby said tie rod is simultaneously locked positively to said bottom plate by the engagement of said key with the underside of said bottom plate by said securing of said rod to said top plate. 8. A fuel bundle for a nuclear reactor including a top plate, a bottom plate, a plurality of nuclear fuel elements extending between said top and bottom plates, said fuel bundle also including at least one tie rod extending between, and penetrating, said top and bottom plates, a key extending from the bottom of said tie rod, a receptacle for said key in said bottom plate enabling said key to penetrate through said bottom plate on penetration of said bottom plate by said tie rod and to be turned by turning said tie rod, said key and receptacle being formed so that by said turning of said tie rod in said receptacle, said key positively blocks the removal of said bottom plate by engagement with the under surface of said bottom plate, said tie rod having an end plug at the top extending through said top plate on penetration of said top plate by said tie rod and said fuel bundle including means for engaging said plug to lock said tie rod positively with said key turned to said blocking position and also including a locking cup extending from said engaging means and engaging said plug, said plug and locking cup cooperating to suppress rotation of said tie rod to prevent said tie rod from becoming undesirably disengaged. 9. A fuel bundle for a nuclear reactor including a top plate, a bottom plate, a plurality of nuclear fuel elements extending between said top and bottom plates, said fuel bundle also including at last one tie rod extending above the top of said top plate and below the bottom of said bottom plate, said tie rod including a key extending from the bottom of said tie rod and said bottom plate including a receptacle for said key enabling said key to penetrate said bottom plate and to be conditioned by turning said tie rod, to be locked positively to the underside of said bottom plate, said tie rod having an end plug at the top, said end plug having a non-circular transverse cross-section and said top plate having a non-circular opening engaged by said end plug, said opening having an inner peripheral shape matching the non-circular outer-surface of said end plug and said end plug being a slip fit in said opening, and means, cooperative with said key and tie rod, with said end plug of said tie rod near its top above said top plate, for, both, locking said tie rod to said top plate and positively locking said key to said underside of said bottom plate. 10. The method of forming a fuel bundle of a nuclear reactor, said fuel bundle being formed of a top plate, a bottom plate, a plurality of fuel rods, and at last one tie rod, said tie rod having a key near its lower end and at its upper end being of non-circular transverse cross-section, said top plate having a non-circular opening to engage said upper end, said opening in said top plate having an inner peripheral surface which matches the outer surface of said upper end, said upper end being a slip fit in said opening in said top plate, and said upper end having a length so that it is capable of penetrating said opening and extending at least in part above said top plate, and said bottom plate having a receptacle for said key; the said method including: positioning said fuel rods in said bottom plate, positioning said tie rod in said bottom plate with said key passed through said receptacle to the underside of said bottom plate, after said tie rod is so positioned turning said tie rod so that the key is in engagement with the underside of said bottom plate, thereafter mounting said top plate in engagement with said fuel rods with the upper end of said tie rod extending through said opening in said top plate and extending above said top plate, and next securing said tie rod to the upper side of said top plate thus simultaneously securing said key to the underside of said bottom plate. 11. The fuel bundle of claim 9 wherein the tie rod has a plug having an end that has a flattened contour in transverse cross section, said end extending above the top of the top plate, said top plate having a hole of flattened contour corresponding to the contour of said flattened end for receiving said flattened end, whereby any tendency to said tie rod to turn in said hole on the engagement of the locking means with the top plate is suppressed. |
description | The present application is related to and claims the benefit of the earliest available effective filing date(s) from the following listed application(s) (the “Related Applications”) (e.g., claims earliest available priority dates for other than provisional patent applications or claims benefits under 35 USC §119(e) for provisional patent applications, for any and all parent, grandparent, great-grandparent, etc. applications of the Related Application(s)). All subject matter of the Related Applications and of any and all parent, grandparent, great-grandparent, etc. applications of the Related Applications is incorporated herein by reference to the extent such subject matter is not inconsistent herewith. For purposes of the USPTO extra-statutory requirements, the present application constitutes a continuation-in-part of United States Patent Application No. 12/800,400, entitled LIQUID FUEL NUCLEAR FISSION REACTOR, naming Roderick A. Hyde and Jon D. McWhirter as inventors, filed May 25, 2010 now U.S. Pat. No. 9,183,953, which is currently co-pending, or is an application of which a currently co-pending application is entitled to the benefit of the filing date. The United States Patent Office (USPTO) has published a notice to the effect that the USPTO's computer programs require that patent applicants reference both a serial number and indicate whether an application is a continuation or continuation-in-part. Stephen G. Kunin, Benefit of Prior-Filed Application, USPTO Official Gazette Mar. 18, 2003, available at http://www.uspto.gov/web/offices/com/sol/og/2003/week11/patbene.htm. The present Applicant Entity (hereinafter “Applicant”) has provided above a specific reference to the application(s) from which priority is being claimed as recited by statute. Applicant understands that the statute is unambiguous in its specific reference language and does not require either a serial number or any characterization, such as “continuation” or “continuation-in-part,” for claiming priority to U.S. patent applications. Notwithstanding the foregoing, Applicant understands that the USPTO's computer programs have certain data entry requirements, and hence Applicant is designating the present application as a continuation-in-part of its parent applications as set forth above, but expressly points out that such designations are not to be construed in any way as any type of commentary and/or admission as to whether or not the present application contains any new matter in addition to the matter of its parent application(s). This patent application relates to nuclear fission reactors. Disclosed embodiments include nuclear fission reactors, nuclear fission fuel pins, methods of operating a nuclear fission reactor, methods of fueling a nuclear fission reactor, and methods of fabricating a nuclear fission fuel pin. The foregoing is a summary and thus may contain simplifications, generalizations, inclusions, and/or omissions of detail; consequently, those skilled in the art will appreciate that the summary is illustrative only and is NOT intended to be in any way limiting. Other aspects, features, and advantages of the devices and/or processes and/or other subject matter described herein will become apparent in the teachings set forth herein. In the following detailed description, reference is made to the accompanying drawings, which form a part hereof. In the drawings, similar symbols typically identify similar components, unless context dictates otherwise. The illustrative embodiments described in the detailed description, drawings, and claims are not meant to be limiting. Other embodiments may be utilized, and other changes may be made, without departing from the spirit or scope of the subject matter presented here. The present application uses formal outline headings for clarity of presentation. However, it is to be understood that the outline headings are for presentation purposes, and that different types of subject matter may be discussed throughout the application (e.g., devices/structures may be described under processes/operations headings and/or processes/operations may be discussed under structures/processes headings; and/or descriptions of single topics may span two or more topic headings). Hence, the use of the formal outline headings is not intended to be in any way limiting. Illustrative Nuclear Fission Reactors Given by way of overview and referring to FIG. 1A, in a non-limiting embodiment an illustrative nuclear fission reactor 10 includes a reactor vessel 12. A solution 14 of fissile nuclear fission fuel material dissolved in neutronically translucent liquid carrier material is received in the reactor vessel 12. Undissolved fertile nuclear fission fuel material 16 is disposed in contact with the solution 14. The fertile nuclear fission fuel material 16 is transmutable into the fissile nuclear fission fuel material. Still by way of overview, in operation a portion of the undissolved fertile nuclear fission fuel material 16 is transmuted into the fissile nuclear fission fuel material. The transmuted fissile nuclear fission fuel material is diffused to the solution 14. Thus, in some embodiments diffusion of transmuted fissile nuclear fission fuel material to the solution 14 could help replenish a portion of the fissile nuclear fission fuel material that is consumed during fissioning of the fissile nuclear fission fuel material. Non-limiting, illustrative details will be set forth below by way of example and not of limitation. Still referring to FIG. 1A, solubility of the fissile nuclear fission fuel material in the neutronically translucent liquid carrier material is greater than solubility of the fertile nuclear fission fuel material 16 in the neutronically translucent liquid carrier material. In some embodiments and as mentioned above, the fissile nuclear fission fuel material is solvable in the neutronically translucent liquid carrier material, thereby making the solution 14. In some embodiments, the fertile nuclear fission fuel material 16 is substantially insoluble in the neutronically translucent liquid carrier material. The liquid carrier material, the fissile nuclear fission fuel material, and the fertile nuclear fission fuel material 16 may be selected among as desired according to the above solubility and neutronic translucency relationships. For example, in various embodiments the neutronically translucent liquid carrier material may include liquid materials such as Mg, Ag, Ca, Ni, and the like. In some embodiments the fissile nuclear fission fuel material may include 239Pu. Also, in some embodiments the fertile nuclear fission fuel material 16 may include 238U. An example will be explained by way of illustration and not of limitation. In one illustrative embodiment, the liquid carrier material may include liquid Mg, the fissile nuclear fission fuel material may include 239Pu, and the fertile nuclear fission fuel material 16 may include 238U. In such an illustrative case, Mg has a melting point around 650° C. The liquid Mg carrier material is a solvent for the 239Pu fissile nuclear fission fuel material, and the plutonium lowers the melting point of the magnesium. Given by way of non-limiting example, at around 5 atom percent Pu, a eutectic composition is formed with a melting temperature of around 600° C. The liquid Mg carrier material is not a solvent for the 238U fertile nuclear fission fuel material 16 (and is substantially immiscible in solid and liquid form). Also, Mg has a neutron absorption cross section in the fast spectrum on the order of around 1 mb. Such a low neutron cross section in the fast spectrum thus makes the liquid Mg carrier material neutronically translucent to the 239Pu fissile nuclear fission fuel material. It will be appreciated that mass transfer diffusion coefficients affect diffusion of the transmuted fissile nuclear fission fuel material. For the non-limiting combination of materials discussed above, the mass transfer diffusion coefficient for Pu through liquid Mg is approximately 1 E-05 cm2/s. As will be discussed further below, the transmuted fissile nuclear fission fuel material first diffuses through the fertile nuclear fission fuel material 16 to get to the solution 14. With that in mind, the mass transfer diffusion coefficient for Pu through U is approximately 1E-12 cm2/s. As mentioned above, the undissolved fertile nuclear fission fuel material 16 is disposed in contact with the solution 14. In some embodiments, the fertile nuclear fission fuel material 16 may be in direct physical contact with the neutronically translucent liquid carrier material. Moreover, in some embodiments the fertile nuclear fission fuel material 16 may be suspended in the neutronically translucent liquid carrier material. To that end, in some embodiments the fertile nuclear fission fuel material 16 may be provided in solid form. In various embodiments, the fertile nuclear fission fuel material may be provided in various forms such as granular form, wire form, plate form, foam form, and the like. Regardless of form in which the fertile nuclear fission fuel material is provided and as mentioned above, the transmuted fissile nuclear fission fuel material first diffuses through the fertile nuclear fission fuel material 16 to get to the solution 14. It will be appreciated that the larger the specific surface area provided by the form of the fertile nuclear fission fuel material, the greater the rate of diffusion of transmuted fissile nuclear fission fuel material through the fertile nuclear fission fuel material to the liquid carrier material. It will also be appreciated that, when the fertile nuclear fission fuel material is provided in granular form, a small particle size can help introduce a large concentration gradient (of transmuted fissile nuclear fission fuel material) without large differences in concentration (between transmuted fissile nuclear fission fuel material distributed in the fertile nuclear fission fuel material and fissile nuclear fission fuel material dissolved in the neutronically translucent liquid carrier material). Thus, a concentration of the fissile nuclear fission fuel material in the fertile nuclear fission fuel material 16 is established that is greater than a concentration of the fissile nuclear fission fuel material in the neutronically translucent liquid carrier material. It is this concentration gradient that causes the transmuted fissile nuclear fission fuel material to diffuse through the fertile nuclear fission fuel material 16 to the solution 14. Still referring to FIG. 1A, the solution 14 and the fertile nuclear fission fuel material 16 may be distributed in the reactor vessel 12 in any manner as desired. To that end, no limitation is implied, and is not to be inferred, from the illustration shown in FIG. 1A. Referring now to FIG. 1B, in some embodiments the solution 14 and the fertile nuclear fission fuel material 16 may be distributed homogeneously in the reactor vessel 12. For example, the fertile nuclear fission fuel material 16 may be provided in any format that may lend itself to homogeneous distribution within the solution 14, such as without limitation any one or more format like pellets, rods, particle suspension, foam, and the like. Given by way of nonlimiting example of a homogeneous distribution, for depleted U in the 60 v/o range, 8-9 v/o of Pu in Mg is entailed in order to attain a potentially critical configuration (that is, k∞>1). Too much depleted U by volume results in k∞<1, which is not useable as a fuel (that is, it does not become self-sustaining). At about 9 v/o Pu in Mg (around 50 w/o Pu), liquid Pu comes out of solution from the Mg and forms a two liquid system, so this is another constraint on the level of Pu from the high end. The effect of the depleted U on k∞ can be reduced in any one or more of several ways, such as by: (i) suspending the U at a reduced concentration in the Pu—Mg solution, thereby resulting in a higher k∞; or (ii) diluting the U with a solid, insoluble, neutronically translucent material such as MgO; or (iii) providing the U in a foam form with much higher porosity and hence lower concentration, thereby resulting in a higher k∞. In any of these cases, if the U content is reduced to below about 50 v/o, then a lower Pu concentration, such as on the order of around 3-5 v/o, can result in k∞>1. In some other embodiments and referring to FIG. 1C and 1D, the solution 14 and the fertile nuclear fission fuel material 16 may be distributed heterogeneously in the reactor vessel 12. The heterogeneous distribution may be any heterogeneous distribution as desired and is not intended to be limited to heterogeneous distributions shown in the drawings. Given by way of non-limiting example and as shown in FIG. 1C, in some embodiments a portion 18 of the solution 14 may be received in a fission region 20 of the reactor vessel 12. The fertile nuclear fission fuel material 16 and a portion 22 of the solution 14 may be received in a fertile blanket region 24 of the reactor vessel 12. In such embodiments, the fertile blanket region 24 is in hydraulic communication with the fission region 20 (because the liquid carrier material occupies the fission region 20 and the fertile blanket region 24) and neutronic communication with the fission region 20 (because the solution 14 of the fissile nuclear fission fuel material dissolved in the neutronically translucent liquid carrier material occupies the fission region 20 and the fertile blanket region 24). In other embodiments and referring now to FIG. 1E, nuclear fission fuel pins 26 may be received in the reactor vessel 12. Each nuclear fission fuel pin 26 has an axial end 28 and an axial end 30. Referring additionally to FIG. 1F, in some embodiments a portion 32 of at least one of the nuclear fission fuel pins 26 may be disposed in the fission region 20 and at least a portion 34 of the at least one nuclear fission fuel pin 26 may be disposed in a fertile blanket region 24. Referring additionally to FIG. 1G, in some embodiments the solution 14 is distributed throughout each of the plurality of nuclear fission fuel pins 26 and the fertile nuclear fission fuel material 16 may be received in fertile blanket zones 36 and 38 disposed toward the axial ends 28 and 30. Thus, it will be appreciated that in some embodiments a fertile blanket region 24 (FIG. 1F) could be located toward the axial ends 28 of the nuclear fission fuel pins 26 and another fertile blanket region 24 (FIG. 1F) could be located toward the axial ends 30 of the nuclear fission fuel pins 26. Referring now to FIGS. 1H and 1J, in some embodiments fertile blanket modules 40 may be disposed in the fertile blanket region 20. In such embodiments the fertile nuclear fission fuel material 16 is received in the fertile blanket modules 40. Referring now to FIGS. 1I and 1J, in some embodiments at least one heat exchanger element 42 may be disposed in thermal communication with the solution 14. FIG. 1I represents a general depiction of an embodiment in partial schematic form while FIG. 1J represents a more detailed view of an embodiment that includes the fertile blanket modules 40. In some cases, the heat exchanger element 42 may be immersed in the solution 14. Also, in some cases an annulus 44 may be disposed in the reactor vessel 12 adjacent the heat exchanger element 42 such that natural circulation of the solution may be established through the heat exchanger element 42 and around the annulus 44. To that end, the reactor vessel 12 is filled with the solution 14 up to a level 45 that is above the heat exchanger element 42 and the annulus 44. In such an arrangement, heat from fission in the fission region 20 causes the fissile solution 14 to rise, as indicated by arrow 46. The rising solution 14 flows around the annulus 44 into the heat exchanger element 42, as indicated by arrows 47. The heat exchanger element 42 cools the solution 14 that flows therethrough. The solution 14 that has been cooled by the heat exchanger element 42 moves downwardly as indicated by arrows 48. The downwardly-flowing solution 14 flows around the annulus 44 and into the fission region 20, as indicated by arrows 49, thereby establishing a natural circulation loop. It will be appreciated that reactivity may be controlled in any manner as desired. For example, given by way of illustration and not of limitation, reactivity may be controlled by way of any one or more illustrative reactivity control methodologies, such as without limitation: dissolving neutron absorbing poisons in the liquid carrier material; inserting and extracting control rods (not shown) of neutron absorbing material into and out of the solution 14; redistributing the fertile nuclear fission fuel material 16 and the fissile nuclear fission fuel material as desired; adding neutronically translucent liquid carrier material to reduce concentration of fissile nuclear fission fuel material in the neutronically translucent liquid carrier material; inserting neutronically translucent material to displace the solution 14 (that contains fissile nuclear fission fuel material); and/or the like. Reactivity may be controlled in similar manners in all embodiments disclosed herein. As such, for the sake of brevity, details of reactivity control need not be repeated in all embodiments for an understanding of the disclosed embodiments. Now that an overview of embodiments and aspects has been set forth, additional embodiments, aspects, and illustrative details will be described. In the interest of brevity, details for components that are common to previously-described embodiments need not and will not be repeated, and the same reference numbers will be re-used. Referring now to FIGS. 2A and 2B, a nuclear fission reactor 200 includes a reactor vessel 12 having a solution 14 of fissile nuclear fission material dissolved in neutronically translucent liquid carrier material. The reactor vessel 12 defines a fission region 20 toward a centralized region 221 of the reactor vessel 12 and a fertile blanket region 24 toward a peripheral region 225 of the reactor vessel 12. Undissolved fertile nuclear fission fuel material 16 is disposed in the fertile blanket region 24 in contact with the solution. The fertile nuclear fission fuel material 16 is transmutable into the fissile nuclear fission material. In some embodiments the reactor vessel 12 may be cylindrical. In such cases and as shown in FIG. 2A, the peripheral region 225 may include a radially peripheral region. However, the reactor vessel 12 need not be cylindrical, and may have any shape as desired. Regardless of shape of the reactor vessel 12 and as shown in FIG. 2B, in some embodiments the peripheral region 225 may include an axially peripheral region. As also shown in FIG. 2B, it will be appreciated that fertile blanket regions 24 may be established at both axially peripheral regions 225. However, it will also be appreciated that fertile blanket regions 24 need not be established at both axially peripheral regions 225. To that end and in some embodiments, a fertile blanket region 24 may be established at either one but not both of the axially peripheral regions 225. Some aspects that previously have been explained in detail will be mentioned briefly below. As discussed above, solubility of the fissile nuclear fission fuel material in the neutronically translucent liquid carrier material is greater than solubility of the fertile nuclear fission fuel material 16 in the neutronically translucent liquid carrier material. In some embodiments and as mentioned above, the fissile nuclear fission fuel material is solvable in the neutronically translucent liquid carrier material, thereby making the solution 14. In some embodiments, the fertile nuclear fission fuel material 16 is substantially insoluble in the neutronically translucent liquid carrier material. In various embodiments, the neutronically translucent liquid carrier material may include liquid materials such as Mg, Ag, Ca, Ni, and the like. In some embodiments the fissile nuclear fission fuel material may include 239Pu. Also, in some embodiments the fertile nuclear fission fuel material 16 may include 238U. As mentioned above, the undissolved fertile nuclear fission fuel material 16 is disposed in contact with the solution 14. In some embodiments, the fertile nuclear fission fuel material 16 may be in direct physical contact with the neutronically translucent liquid carrier material. Moreover, in some embodiments the fertile nuclear fission fuel material 16 may be suspended in the neutronically translucent liquid carrier material. In some embodiments the fertile nuclear fission fuel material 16 may be provided in solid form. In various embodiments, the fertile nuclear fission fuel material may be provided various forms such as granular form, wire form, plate form, foam form, and the like. Referring now to FIGS. 2C and 2E, in some embodiments fertile blanket modules 40 may be disposed in the fertile blanket region 20 toward the peripheral region 225. In such embodiments the fertile nuclear fission fuel material 16 is received in the fertile blanket modules 40. Referring now to FIGS. 2D and 2E, in some embodiments at least one heat exchanger element 42 may be disposed in thermal communication with the solution 14. FIG. 2D represents a general depiction of an embodiment in partial schematic form while FIG. 2E represents a more detailed view of an embodiment that includes the fertile blanket modules 40 disposed toward the peripheral region 225. In some cases, the heat exchanger element 42 may be immersed in the solution 14. Also, in some cases an annulus 44 may be disposed in the reactor vessel 12 adjacent the heat exchanger element 42 such that natural circulation of the solution may be established through the heat exchanger element 42 and around the annulus 44. Details are similar to those described above with reference to FIGS. 1H-1J and need not be repeated. Referring now to FIG. 3A, in another illustrative embodiment a nuclear fission reactor 300 includes a reactor vessel 12 and nuclear fission fuel pins 26 received in the reactor vessel 12. Each nuclear fission fuel pin has an axial end 28 and an axial end 30. A solution 14 of fissile nuclear fission material is dissolved in neutronically translucent liquid carrier material, and the solution 14 is distributed throughout each nuclear fission fuel pin 26. A centralized axial region 321 of the nuclear fission fuel pins 26 defines a fission region 20 of the reactor vessel 12. Undissolved fertile nuclear fission fuel material 16 is disposed in contact with the solution in fertile blanket zones 36 and 38 disposed toward the axial ends 28 and 30, respectively, of each nuclear fission fuel pin 26. The fertile nuclear fission fuel material 16 is transmutable into the fissile nuclear fission material. The fertile blanket zones 36 and 38 of the nuclear fission fuel pins 26 define the fertile blanket regions 24. An illustrative nuclear fission fuel pin 26 has been discussed above with reference to FIG. 1G, and its details need not be repeated. Some aspects that previously have been explained in detail will be mentioned briefly below. As discussed above, solubility of the fissile nuclear fission fuel material in the neutronically translucent liquid carrier material is greater than solubility of the fertile nuclear fission fuel material 16 in the neutronically translucent liquid carrier material. In some embodiments and as mentioned above, the fissile nuclear fission fuel material is solvable in the neutronically translucent liquid carrier material, thereby making the solution 14. In some embodiments, the fertile nuclear fission fuel material 16 is substantially insoluble in the neutronically translucent liquid carrier material. In various embodiments, the neutronically translucent liquid carrier material may include liquid materials such as Mg, Ag, Ca, Ni, and the like. In some embodiments the fissile nuclear fission fuel material may include 239Pu. Also, in some embodiments the fertile nuclear fission fuel material 16 may include 238U. As mentioned above, the undissolved fertile nuclear fission fuel material 16 is disposed in contact with the solution 14. In some embodiments, the fertile nuclear fission fuel material 16 may be in direct physical contact with the neutronically translucent liquid carrier material. Moreover, in some embodiments the fertile nuclear fission fuel material 16 may be suspended in the neutronically translucent liquid carrier material. In some embodiments the fertile nuclear fission fuel material 16 may be provided in solid form. In various embodiments, the fertile nuclear fission fuel material may be provided various forms such as granular form, wire form, plate form, foam form, and the like. Illustrative Nuclear Fission Fuel Pins Referring now to FIG. 4A, in another illustrative embodiment a nuclear fission fuel pin 426 includes cladding 450 that defines an elongated enclosure 452. A solution 14 of fissile nuclear fission fuel material is dissolved in neutronically translucent liquid carrier material. The solution 14 is distributed throughout the elongated enclosure 452. Undissolved fertile nuclear fission fuel material 16 is disposed in contact with the solution 14 in the elongated enclosure 452. The fertile nuclear fission fuel material 16 is transmutable into the fissile nuclear fission fuel material. In some embodiments the elongated enclosure 452 has axial ends 28 and 30 and a centralized axial region 29 between the axial ends 28 and 30. Still referring to FIG. 4A, the solution 14 and the fertile nuclear fission fuel material 16 may be distributed in the elongated enclosure 452 in any manner as desired. To that end, no limitation is implied, and is not to be inferred, from the illustration shown in FIG. 4A. In some embodiments the solution 14 and the fertile nuclear fission fuel material 16 may be distributed homogeneously in the elongated enclosure 452. Referring now to FIG. 4B, in some other embodiments the solution 14 and the fertile nuclear fission fuel material 16 may be distributed heterogeneously in the elongated enclosure 452. The heterogeneous distribution may be any heterogeneous distribution as desired and is not intended to be limited to heterogeneous distributions shown in the drawings. Still referring to FIG. 4B, in some embodiments the centralized axial region 29 defines a fission region 20 of the nuclear fission fuel pin 426. In some embodiments the fertile nuclear fission fuel material 16 may be disposed toward the axial ends 28 and 30. In such cases, the axial ends 28 and 30 may define fertile blanket zones 36 and 38, respectively, of the nuclear fission fuel pin 426. Some aspects that previously have been explained in detail will be mentioned briefly below. Referring now to FIGS. 4A and 4B and as discussed above, solubility of the fissile nuclear fission fuel material in the neutronically translucent liquid carrier material is greater than solubility of the fertile nuclear fission fuel material 16 in the neutronically translucent liquid carrier material. In some embodiments and as mentioned above, the fissile nuclear fission fuel material is solvable in the neutronically translucent liquid carrier material, thereby making the solution 14. In some embodiments, the fertile nuclear fission fuel material 16 is substantially insoluble in the neutronically translucent liquid carrier material. In various embodiments, the neutronically translucent liquid carrier material may include liquid materials such as Mg, Ag, Ca, Ni, and the like. In some embodiments the fissile nuclear fission fuel material may include 239Pu. Also, in some embodiments the fertile nuclear fission fuel material 16 may include 238U. As mentioned above, the undissolved fertile nuclear fission fuel material 16 is disposed in contact with the solution 14. In some embodiments, the fertile nuclear fission fuel material 16 may be in direct physical contact with the neutronically translucent liquid carrier material. Moreover, in some embodiments the fertile nuclear fission fuel material 16 may be suspended in the neutronically translucent liquid carrier material. In some embodiments the fertile nuclear fission fuel material 16 may be provided in solid form. In various embodiments, the fertile nuclear fission fuel material may be provided various forms such as granular form, wire form, plate form, foam form, and the like. Referring now to FIG. 4C, in some embodiments the fertile nuclear fission fuel material 16 may disposed in contact with a wall of the elongated enclosure 452. Given by way of non-limiting example, the fertile nuclear fission fuel material 16 may be disposed in contact with an inner surface 456 of the wall 454. Now that various embodiments including nuclear fission reactors and nuclear fission fuel pins have been discussed, other embodiments including various methods will be discussed below. Further illustrative details regarding neutronics and mass transfer will be set forth by way of non-limiting examples. Illustrative Methods Following are a series of flowcharts depicting implementations. For ease of understanding, the flowcharts are organized such that the initial flowcharts present implementations via an example implementation and thereafter the following flowcharts present alternate implementations and/or expansions of the initial flowchart as either sub-component operations or additional component operations building on one or more earlier-presented flowcharts. Those having skill in the art will appreciate that the style of presentation utilized herein (e.g., beginning with a presentation of a flowchart presenting an example implementation and thereafter providing additions to and/or further details in subsequent flowcharts) generally allows for a rapid and easy understanding of the various process implementations. In addition, those skilled in the art will further appreciate that the style of presentation used herein also lends itself well to modular and/or object-oriented program design paradigms. Illustrative details regarding the fissile nuclear fission fuel material, the neutronically translucent carrier material, the solution of the fissile nuclear fission fuel material dissolved in the neutronically translucent carrier material, and the fertile nuclear fission fuel material have been discussed above and need not be repeated in the context of the following illustrative, non-limiting methods. Referring now to FIG. 5A, in an embodiment an illustrative method 500 is provided for operating a nuclear fission reactor. The method 500 starts at a block 502. At a block 504 a portion of undissolved fertile nuclear fission fuel material is transmuted into fissile nuclear fission fuel material, with the undissolved fertile nuclear fission fuel material being disposed in contact with a solution of the fissile nuclear fission fuel material dissolved in neutronically translucent liquid carrier material. Given by way of example and not of limitation, when 238U is exposed to a neutron flux, the 238U will be transmuted to 239Pu. More particularly, when an atom of 238U is exposed to a neutron flux, its nucleus will capture a neutron, thereby changing it to 239U. The 239U then rapidly undergoes two beta decays. After the 238U absorbs a neutron to become 239U it then emits an electron and an anti-neutrino (νe) by β− decay to become 239Np and then emits another electron and anti-neutrino by a second β− decay to become 239Pu. At a block 506 the transmuted fissile nuclear fission fuel material is diffused to the solution. The method 500 stops at a block 508. Referring additionally to FIG. 5B, in some embodiments at a block 510 intermediate transmuted material may be diffused to the solution. Given by way of non-limiting examples, as discussed above the intermediate transmuted material may include without limitation 239U and 239Np. Referring additionally to FIG. 5C, in some embodiments at a block 512 a portion of the fissile nuclear fission fuel material fissions. In such cases, fissioning of the fissile nuclear fission fuel material can provide the neutron flux to which the fertile nuclear fission fuel material is exposed, thereby causing transmuting of a portion of undissolved fertile nuclear fission fuel material at the block 504 (FIG. 5A). Referring additionally to FIG. 5D, in some embodiments diffusing the transmuted fissile nuclear fission fuel material to the solution at the block 506 may include diffusing the transmuted fissile nuclear fission fuel material through the undissolved fertile nuclear fission fuel material at a block 514. For example and as discussed above, regardless of form in which the fertile nuclear fission fuel material is provided, the larger the specific surface area provided by the form of the fertile nuclear fission fuel material, the greater the rate of diffusion of transmuted fissile nuclear fission fuel material through the fertile nuclear fission fuel material to the liquid carrier material. It will also be appreciated that, when the fertile nuclear fission fuel material is provided in granular form, a small particle size can help introduce a large concentration gradient (of dissolved fissile nuclear fission fuel material) without large differences in concentration (between transmuted fissile nuclear fission fuel material dissolved in the fertile nuclear fission fuel material and fissile nuclear fission fuel material dissolved in the neutronically translucent liquid carrier material). Thus a concentration of the fissile nuclear fission fuel material in the fertile nuclear fission fuel material is established that is greater than a concentration of the fissile nuclear fission fuel material in the neutronically translucent liquid carrier material. It is this concentration gradient that causes the transmuted fissile nuclear fission fuel material to diffuse through the fertile nuclear fission fuel material to the solution. Referring now to FIG. 6A, in another illustrative embodiment a method 600 is provided for operating a nuclear fission reactor. The method 600 starts at a block 602. At a block 604 a first concentration is established of fissile nuclear fission fuel material in a solution of the fissile nuclear fission fuel material dissolved in neutronically translucent liquid carrier material. At a block 606 a second concentration is established of the fissile nuclear fission fuel material in undissolved fertile nuclear fission fuel material disposed in contact with the solution, with the second concentration being greater than the first concentration. At a block 608 fissile nuclear fission fuel material is diffused through the undissolved fertile nuclear fission fuel material toward the solution. The method 600 stops at a block 610. Referring additionally to FIG. 6B, in some embodiments establishing a first concentration of fissile nuclear fission fuel material in a solution of the fissile nuclear fission fuel material dissolved in neutronically translucent liquid carrier material at the block 604 may include consuming a portion of the fissile nuclear fission fuel material in the solution of the fissile nuclear fission fuel material dissolved in neutronically translucent liquid carrier material at a block 612. Referring additionally to FIG. 6C and given by way of non-limiting example, consuming a portion of the fissile nuclear fission fuel material in the solution of the fissile nuclear fission fuel material dissolved in neutronically translucent liquid carrier material at the block 612 may include fissioning a portion of the fissile nuclear fission fuel material in the solution of the fissile nuclear fission fuel material dissolved in neutronically translucent liquid carrier material at a block 614. Referring additionally to FIG. 6D, in some embodiments establishing a second concentration of the fissile nuclear fission fuel material in undissolved fertile nuclear fission fuel material disposed in the solution, the second concentration being greater than the first concentration, at the block 606 may include transmuting a portion of the fertile nuclear fission fuel material into the fissile nuclear fission fuel material at a block 616. Given by way of example and not of limitation, in some embodiments as discussed above when 238U is exposed to a neutron flux, the 238U will be transmuted to 239Pu. More particularly, when an atom of 238U is exposed to a neutron flux, its nucleus will capture a neutron, thereby changing it to 239U. The 239U then rapidly undergoes two beta decays. After the 238U absorbs a neutron to become 239U it then emits an electron and an anti-neutrino (νe) by β− decay to become 239Np and then emits another electron and anti-neutrino by a second β− decay to become 239Pu. Referring additionally to FIG. 6E, in some embodiments at a block 618 intermediate transmuted material may be diffused to the solution. Given by way of non-limiting examples, as discussed above the intermediate transmuted material may include without limitation 239U and 239Np. Referring now to FIG. 1A, in another embodiment a method 700 is provided for operating a nuclear fission reactor. The method 700 starts at a block 702. At a block 704, in a fission region of a reactor core of a nuclear fission reactor, a portion of fissile nuclear fission fuel material, in a solution of the fissile nuclear fission fuel material dissolved in neutronically translucent liquid carrier material, is fissioned. At a block 706, in a fertile blanket region of the reactor core, material a portion of undissolved fertile nuclear fission fuel material disposed in contact with the solution is transmuted into the fissile nuclear fission fuel. Given by way of example and not of limitation, in some embodiments as discussed above when 238U is exposed to a neutron flux (such as may be caused by leakage from the fission region of neutrons from fissioning of the fissile nuclear fission fuel material at the block 704), the 238U will be transmuted to 239Pu. More particularly and as discussed above, when an atom of 238U is exposed to a neutron flux, its nucleus will capture a neutron, thereby changing it to 239U. The 239U then rapidly undergoes two beta decays. After the 238U absorbs a neutron to become 239U it then emits an electron and an anti-neutrino (νe) by β− decay to become 239Np and then emits another electron and anti-neutrino by a second β− decay to become 239Pu. At a block 708 the transmuted fissile nuclear fission fuel is diffused. The method 700 stops at a block 710. Referring additionally to FIG. 7B, diffusing the transmuted fissile nuclear fission fuel material at the block 708 may include diffusing the transmuted fissile nuclear fission fuel material through the fertile nuclear fission fuel material at a block 712. For example and referring additionally to FIG. 7C, diffusing the transmuted fissile nuclear fission fuel material through the fertile nuclear fission fuel material at the block 714 may include diffusing the transmuted fissile nuclear fission fuel material through the fertile nuclear fission fuel material to the solution at a block 714. Referring now to FIGS. 7A and 7D, in some embodiments, in a fission region of a reactor core of a nuclear fission reactor, fissioning a portion of fissile nuclear fission fuel material in a solution of the fissile nuclear fission fuel material dissolved in neutronically translucent liquid carrier material at the block 704 may include, in a fission region of a reactor core of a nuclear fission reactor, consuming a portion of fissile nuclear fission fuel material in the solution of the fissile nuclear fission fuel material dissolved in neutronically translucent liquid carrier material at a block 716. Referring additionally to FIG. 7E, it will be appreciated that, in a fission region of a reactor core of a nuclear fission reactor, consuming a portion of fissile nuclear fission fuel material in the solution of the fissile nuclear fission fuel material dissolved in neutronically translucent liquid carrier material at the block 716 may include establishing in the fissile region a first concentration of the fissile nuclear fission fuel material in the solution at a block 718. Referring additionally to FIG. 7F, it will also be appreciated that, in a fertile blanket region of the reactor core, transmuting into the fissile nuclear fission fuel material a portion of undissolved fertile nuclear fission fuel material disposed in the solution at the block 706 may include establishing, in the fertile blanket region, a second concentration of the fissile nuclear fission fuel material in the fertile nuclear fission fuel material, the second concentration being greater than the first concentration at a block 720. Referring additionally to FIG. 7G, in some embodiments at a block 722 intermediate transmuted material may be diffused to the solution. Given by way of non-limiting examples, as discussed above the intermediate transmuted material may include without limitation 239U and 239Np. It will be appreciated that blocks of the methods 500 (FIGS. 5A-5D), 600 (FIGS. 6A-6E), and 700 (FIGS. 7A-7G) may occur in any suitable host environment. Given by way of non-limiting examples, the blocks may occur in any suitable reactor vessel, such as without limitation reactor vessels described above. In some embodiments, the blocks may occur in suitable nuclear fission fuel pins, such as without limitation nuclear fission fuel pins described above. Referring now to FIG. 8A, in an embodiment an illustrative method 800 is provided for fueling a nuclear fission reactor. The method 800 starts at a block 802. At a block 804 liquid carrier material is received in a reactor core of a nuclear fission reactor. At a block 806 insoluble fertile nuclear fission fuel material and soluble fissile nuclear fission fuel material are disposed in the liquid carrier material. The liquid carrier material is neutronically translucent to the soluble fissile nuclear fission fuel material, and the fertile nuclear fission fuel material is transmutable into the fissile nuclear fission fuel material. The method 800 stops at a block 808. Referring additionally to FIG. 8B, in some embodiments the fissile nuclear fission fuel material may be dissolved in the neutronically translucent liquid carrier material at a block 810. Referring additionally to FIG. 8C, at a block 812 the fertile nuclear fission fuel material may be disposed in contact with a solution of the fissile nuclear fission fuel material dissolved in the neutronically translucent liquid carrier material, the fertile nuclear fission fuel material remaining undissolved in the solution. Referring additionally to FIG. 8D, in some embodiments disposing the fertile nuclear fission fuel material in contact with a solution of the fissile nuclear fission fuel material dissolved in the neutronically translucent liquid carrier material, the fertile nuclear fission fuel material remaining undissolved in the solution, at the block 812 may include disposing undissolved fertile nuclear fission fuel material in direct physical contact with the solution at a block 814. For example and referring additionally to FIG. 8E, in some embodiments disposing the fertile nuclear fission fuel material in direct physical contact with a solution of the fissile nuclear fission fuel material dissolved in the neutronically translucent liquid carrier material, the fertile nuclear fission fuel material remaining undissolved in the solution, at the block 814 may include suspending fertile nuclear fission fuel material in the solution at a block 816. Referring additionally to FIG. 8F, in some embodiments disposing the fertile nuclear fission fuel material in contact with a solution of the fissile nuclear fission fuel material dissolved in the neutronically translucent liquid carrier material, the fertile nuclear fission fuel material remaining undissolved in the solution, at the block 812 may include disposing, homogeneously in the reactor core, fertile nuclear fission fuel material in contact with a solution of the fissile nuclear fission fuel material dissolved in the neutronically translucent liquid carrier material, the fertile nuclear fission fuel material remaining undissolved in the solution, at a block 818. In some other embodiments and referring additionally to FIG. 8G, disposing the fertile nuclear fission fuel material in contact with a solution of the fissile nuclear fission fuel material dissolved in the neutronically translucent liquid carrier material, the fertile nuclear fission fuel material remaining undissolved in the solution, at the block 812 may include disposing, heterogeneously in the reactor core, the fertile nuclear fission fuel material in contact with a solution of the fissile nuclear fission fuel material dissolved in the neutronically translucent liquid carrier material, the fertile nuclear fission fuel material remaining undissolved in the solution, at a block 820. Given by way of non-limiting example and referring additionally to FIG. 8H, in some embodiments disposing, heterogeneously in the reactor core, the fertile nuclear fission fuel material in contact with a solution of the fissile nuclear fission fuel material dissolved in the neutronically translucent liquid carrier material, the fertile nuclear fission fuel material remaining undissolved in the solution, at the block 820 may include disposing undissolved fertile nuclear fission fuel material in contact with a solution of the fissile nuclear fission fuel material dissolved in the neutronically translucent liquid carrier material in a fertile blanket region of the reactor core at a block 822. In another embodiment and referring now to FIG. 9A, an illustrative method 900 is provided for fabricating a nuclear fission fuel pin. The method 900 starts at a block 902. At a block 904 liquid carrier material is received in an elongated enclosure of cladding. At a block 906 insoluble fertile nuclear fission fuel material and soluble fissile nuclear fission fuel material are disposed in the liquid carrier material. The liquid carrier material is neutronically translucent to the soluble fissile nuclear fission fuel material, and the fertile nuclear fission fuel material is transmutable into the fissile nuclear fission fuel material. The method 900 stops at a block 908. Referring additionally to FIG. 9B, in some embodiments at a block 910 the fissile nuclear fission fuel material may be dissolved in the neutronically translucent liquid carrier material. Referring additionally to FIG. 9C, in some embodiments at, a block 912 the fertile nuclear fission fuel material may be disposed in contact with a solution of the fissile nuclear fission fuel material dissolved in the neutronically translucent liquid carrier material, the fertile nuclear fission fuel material remaining undissolved in the solution. Referring additionally to FIG. 9D, in some embodiments the fertile nuclear fission fuel material may be disposed in contact with a wall of the elongated enclosure of cladding at a block 914. Referring, now to FIGS. 9A-9C and 9E, in some embodiments at a block 916 an elongated enclosure of cladding may be defined, the elongated enclosure having a first axial end, a second axial end, and a centralized axial region between the first and second axial ends. Referring additionally to FIG. 9F, in some embodiments disposing in the elongated enclosure undissolved fertile nuclear fission fuel material in contact with the solution, the fertile nuclear fission fuel material being transmutable into the fissile nuclear fission fuel material, at the block 912 may includes disposing homogeneously in the elongated enclosure undissolved fertile nuclear fission fuel material in contact with the solution, the fertile nuclear fission fuel material being transmutable into the fissile nuclear fission fuel material, at a block 918. In some other embodiments and referring now to FIGS. 9A-9C, 9E, and 9G, disposing in the elongated enclosure undissolved fertile nuclear fission fuel material in contact with the solution, the fertile nuclear fission fuel material being transmutable into the fissile nuclear fission fuel material, at the block 912 may include disposing heterogeneously in the elongated enclosure undissolved fertile nuclear fission fuel material in contact with the solution, the fertile nuclear fission fuel material being transmutable into the fissile nuclear fission fuel material, at a block 920. For example and referring additionally to FIG. 9H, in some embodiments disposing heterogeneously in the elongated enclosure undissolved fertile nuclear fission fuel material in contact the solution, the fertile nuclear fission fuel material being transmutable into the fissile nuclear fission fuel material, at the block 920 may include, at a block 922, disposing toward first and second axial ends of the elongated enclosure undissolved fertile nuclear fission fuel material in contact with the solution, the fertile nuclear fission fuel material being transmutable into the fissile nuclear fission fuel material. Referring additionally to FIG. 9I, in some embodiments disposing in the elongated enclosure undissolved fertile nuclear fission fuel material in contact with the solution, the fertile nuclear fission fuel material being transmutable into the fissile nuclear fission fuel material, at the block 912 may include disposing in the elongated enclosure undissolved fertile nuclear fission fuel material in direct physical contact with the solution, the fertile nuclear fission fuel material being, transmutable into the fissile nuclear fission fuel material, at a block 924. Given by way of non-limiting example and referring additionally to FIG. 9J, in some embodiments disposing in the elongated enclosure undissolved fertile nuclear fission fuel material in direct physical contact with the solution, the fertile nuclear fission fuel material being transmutable into the fissile nuclear fission fuel material, at the block 924 may include suspending fertile nuclear fission fuel material in the solution, the fertile nuclear fission fuel material being transmutable into the fissile nuclear fission fuel material, at a block 926. Referring now to FIG. 10A, in another embodiment an illustrative method 1000 is provided for fabricating a nuclear fission fuel pin. The method 1000 starts at a block 1002. At a block 1004 liquid carrier material that is a solvent for fissile nuclear fission fuel material and that is neutronically translucent to the fissile nuclear fission fuel material is disposed in an elongated enclosure of cladding. At a block 1006 undissolved fertile nuclear fission fuel material is disposed in contact with the neutronically translucent liquid carrier material, the fertile nuclear fission fuel material being transmutable into the fissile nuclear fission fuel material. The method 1000 stops at a block 1008. Referring additionally to FIG. 10B, in some embodiments fissile nuclear fission fuel material may be dissolved in the neutronically translucent liquid carrier material at a block 1010. Referring additionally to FIG. 10C, in some embodiments disposing undissolved fertile nuclear fission fuel material in contact with the neutronically translucent liquid carrier material, the fertile nuclear fission fuel material being transmutable into the fissile nuclear fission fuel material, at the block 1006 may include disposing, homogeneously in the elongated enclosure, undissolved fertile nuclear fission fuel material in contact with the neutronically translucent liquid carrier material, the fertile nuclear fission fuel material being transmutable into the fissile nuclear fission fuel material, at a block 1012. In some other embodiments and referring to FIGS. 10A, 10B and 10D, disposing undissolved fertile nuclear fission fuel material in contact with the neutronically translucent liquid carrier material, the fertile nuclear fission fuel material being transmutable into the fissile nuclear fission fuel material, at the block 1006 may include disposing, heterogeneously in the elongated enclosure, undissolved fertile nuclear fission fuel material in contact with the neutronically translucent liquid carrier material, the fertile nuclear fission fuel material being transmutable into the fissile nuclear fission fuel material, at a block 1014. Given by way of non-limiting example and referring additionally to FIG. 10E, in some embodiments disposing, heterogeneously in the elongated enclosure, undissolved fertile nuclear fission fuel material in contact with the neutronically translucent liquid carrier material, the fertile nuclear fission fuel material being transmutable into the fissile nuclear fission fuel material, at the block 1014 may include disposing toward first and second axial ends of the elongated enclosure undissolved fertile nuclear fission fuel material in contact with the neutronically translucent liquid carrier material, the fertile nuclear fission fuel material being transmutable into the fissile nuclear fission fuel material, at a block 1016. Referring additionally to FIG. 10F, in some embodiments at a block 1018 an elongated enclosure of cladding may be defined, the elongated enclosure having a first axial end, a second axial end, and a centralized axial region between the first and second axial ends. Referring additionally to FIG. 10G, in some embodiments disposing undissolved fertile nuclear fission fuel material in contact with the neutronically translucent liquid carrier material, the fertile nuclear fission fuel material being transmutable into the fissile nuclear fission fuel material, at the block 1006 may include disposing in the elongated enclosure undissolved fertile nuclear fission fuel material in direct physical contact with the neutronically translucent liquid carrier material, the fertile nuclear fission fuel material being transmutable into the fissile nuclear fission fuel material at a block 1020. For example and referring additionally to FIG. 10H, in some embodiments disposing undissolved fertile nuclear fission fuel material in direct physical contact with the neutronically translucent liquid carrier material, the fertile nuclear fission fuel material being transmutable into the fissile nuclear fission fuel material, at the block 1020 may includes suspending fertile nuclear fission fuel material in the neutronically translucent liquid carrier material, the fertile nuclear fission fuel material being transmutable into the fissile nuclear fission fuel material, at a block 1022. Referring now to FIGS. 10A and 10I, in some embodiments the fertile nuclear fission fuel material may be disposed in contact with a wall of the elongated enclosure of cladding at a block 1024. Those skilled in the art will appreciate that the foregoing specific illustrative processes and/or devices and/or technologies are representative of more general processes and/or devices and/or technologies taught elsewhere herein, such as in the claims filed herewith and/or elsewhere in the present application. Those skilled in the art will recognize that it is common within the art to implement devices and/or processes and/or systems, and thereafter use engineering and/or other practices to integrate such implemented devices and/or processes and/or systems into more comprehensive devices and/or processes and/or systems. That is, at least a portion of the devices and/or processes and/or systems described herein can be integrated into other devices and/or processes and/or systems via a reasonable amount of experimentation. Those having skill in the art will recognize that examples of such other devices and/or processes and/or systems might include—as appropriate to context and application—all or part of devices and/or processes and/or systems of (a) an air conveyance (e.g., an airplane, rocket, helicopter, etc.), (b) a ground conveyance (e.g., a car, truck, locomotive, tank, armored personnel carrier, etc.), (c) a building (e.g., a home, warehouse, office, etc.), (d) an appliance (e.g., a refrigerator, a washing machine, a dryer, etc.), (e) a communications system (e.g., a networked system, a telephone system, a Voice over IP system, etc.), (f) a business entity (e.g., an Internet Service Provider (ISP) entity such as Comcast Cable, Qwest, Southwestern Bell, etc.), or (g) a wired/wireless services entity (e.g., Sprint, Cingular, Nextel, etc.), etc. In certain cases, use of a system or method may occur in a territory even if components are located outside the territory. For example, in a distributed computing context, use of a distributed computing system may occur in a territory even though parts of the system may be located outside of the territory (e.g., relay, server, processor, signal-bearing medium, transmitting computer, receiving computer, etc. located outside the territory). A sale of a system or method may likewise occur in a territory even if components of the system or method are located and/or used outside the territory. Further, implementation of at least part of a system for performing a method in one territory does not preclude use of the system in another territory. With respect to the use of substantially any plural and/or singular terms herein, those having skill in the art can translate from the plural to the singular and/or from the singular to the plural as is appropriate to the context and/or application. The various singular/plural permutations are not expressly set forth herein for sake of clarity. The herein described subject matter sometimes illustrates different components contained within, or connected with, different other components. It is to be understood that such depicted architectures are merely exemplary, and that in fact many other architectures may be implemented which achieve the same functionality. In a conceptual sense, any arrangement of components to achieve the same functionality is effectively “associated” such that the desired functionality is achieved. Hence, any two components herein combined to achieve a particular functionality can be seen as “associated with” each other such that the desired functionality is achieved, irrespective of architectures or intermedial components. Likewise, any two components so associated can also be viewed as being “operably connected”, or “operably coupled,” to each other to achieve the desired functionality, and any two components capable of being so associated can also be viewed as being “operably couplable,” to each other to achieve the desired functionality. Specific examples of operably couplable include but are not limited to physically mateable and/or physically interacting components, and/or wirelessly interactable, and/or wirelessly interacting components, and/or logically interacting and/or logically interactable components. One skilled in the art will recognize that the herein described components (e.g., operations), devices, objects, and the discussion accompanying them are used as examples for the sake of conceptual clarity and that various configuration modifications are contemplated. Consequently, as used herein, the specific exemplars set forth and the accompanying discussion are intended to be representative of their more general classes. In general, use of any specific exemplar is intended to be representative of its class, and the non-inclusion of specific components (e.g., operations), devices, and objects should not be taken limiting. While particular aspects of the present subject matter described herein have been shown and described, it will be apparent to those skilled in the art that, based upon the teachings herein, changes and modifications may be made without departing from the subject matter described herein and its broader aspects and, therefore, the appended claims are to encompass within their scope all such changes and modifications as are within the true spirit and scope of the subject matter described herein. It will be understood by those within the art that, in general, terms used herein, and especially in the appended claims (e.g., bodies of the appended claims) are generally intended as “open” terms (e.g., the term “including” should be interpreted as “including but not limited to,” the term “having” should be interpreted as “having at least,” the term “includes” should be interpreted as “includes but is not limited to,” etc.). It will be further understood by those within the art that if a specific number of an introduced claim recitation is intended, such an intent will be explicitly recited in the claim, and in the absence of such recitation no such intent is present. For example, as an aid to understanding, the following appended claims may contain usage of the introductory phrases “at least one” and “one or more” to introduce claim recitations. However, the use of such phrases should not be construed to imply that the introduction of a claim recitation by the indefinite articles “a” or “an” limits any particular claim containing such introduced claim recitation to claims containing only one such recitation, even when the same claim includes the introductory phrases “one or more” or “at least one” and indefinite articles such as “a” or “an” (e.g., “a” and/or “an” should typically be interpreted to mean “at least one” or “one or more”); the same holds true for the use of definite articles used to introduce claim recitations. In addition, even if a specific number of an introduced claim recitation is explicitly recited, those skilled in the art will recognize that such recitation should typically be interpreted to mean at least the recited number the bare recitation of “two recitations,” without other modifiers, typically means at least two recitations, or two or more recitations). Furthermore, in those instances where a convention analogous to “at least one of A, B, and C, etc.” is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., “a system having at least one of A, B, and C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). In those instances where a convention analogous to “at least one of A, B, or C, etc.” is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., “a system having at least one of A, B, or C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). It will be further understood by those within the art that typically a disjunctive word and/or phrase presenting two or more alternative terms, whether in the description, claims, or drawings, should be understood to contemplate the possibilities of including one of the terms, either of the terms, or both terms unless context dictates otherwise. For example, the phrase “A or B” will be typically understood to include the possibilities of “A” or “B” or “A and B”. With respect to the appended claims, those skilled in the art will appreciate that recited operations therein may generally be performed in any order. Also, although various operational flows are presented in a sequence(s), it should be understood that the various operations may be performed in other orders than those which are illustrated, or may be performed concurrently. Examples of such alternate orderings may include overlapping, interleaved, interrupted, reordered, incremental, preparatory, supplemental, simultaneous, reverse, or other variant orderings, unless context dictates otherwise. Furthermore, terms like “responsive to,” “related to,” or other past-tense adjectives are generally not intended to exclude such variants, unless context dictates otherwise. While various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated by the following claims. |
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051596210 | abstract | An X-ray transmitting window for use in X-ray lithography, for allowing transmission therethrough of X-rays from a vacuum ambience to a different ambience, includes an X-ray transmitting film, and a gasket material gas-tightly provided on at least one of opposite surfaces in a peripheral portion of the X-ray transmitting film. The gasket material has a Brinell hardness smaller than that of the X-ray transmitting film. The formed X-ray transmitting window is able to be sandwiched and fastened between a pair of flanges in a gas-tight manner. |
claims | 1. A particle beam therapy system comprising:an irradiation nozzle that scans and irradiates a particle beam supplied from an accelerator, by use of two electromagnets whose scanning directions are different from each other, said two electromagnets including an upstream electromagnet and a downstream electromagnet; anda multileaf collimator that is disposed on a beam orbit of a particle beam irradiated from the irradiation nozzle and that limits or forms an irradiation field of the charged particle beam in such a way that the irradiation field conforms to the shape of an irradiation subject, the multileaf collimator comprising:a leaf row in which a plurality of leaf plates are arranged in a thickness direction thereof in such a way that respective inner end faces of the leaf plates are trued up; anda leaf plate drive mechanism configured to (i) drive each of the plurality of leaf plates in such a way that an inner end face approaches or departs from a beam axis of the charged particle beam and (ii) drive the plurality of leaf plates along a circumferential orbit around a scanning axis of the downstream electromagnet and at a preset distance from the scanning axis of the downstream electromagnet, wherein the particle beam is irradiated through a scanning method. 2. The particle beam therapy system according to claim 1,wherein in each of the plurality of leaf plates, a facing side facing a leaf plate that is adjacent to that leaf plate in the thickness direction is formed of a plane including a scanning axis of the upstream electromagnet, which is perpendicular to the beam axis and is set at a first position on the beam axis, andwherein the circumferential orbit along the scanning axis of the downstream electromagnet, around which the plurality of leaf plates are driven, is perpendicular to the beam axis and the scanning axis of the upstream electromagnet and is set at a second position that is on the beam axis and separates from the first position by a predetermined distance. 3. The particle beam therapy system according to claim 2, wherein the respective inner end faces of the plurality of leaf plates are on a plane including the scanning axis of the downstream electromagnet. 4. The particle beam therapy system according to claim 2, wherein the respective inner end faces of the plurality of leaf plates are driven by the leaf plate drive mechanism in such a way as to be on a plane including the scanning axis of the downstream electromagnet. 5. The particle beam therapy system according to claim 1, wherein each of the leaf plates of the plurality of leaf plates has four end faces, and wherein an incident-side end face and an emitting-side end face, among the four end faces, which are adjacent to the inner end face, are formed in the shape of an arc whose center is the scanning axis of the downstream electromagnet. |
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abstract | An X-ray diffraction system includes an X-ray detector that is configured to detect diffracted X-rays diffracted from a sample when a surface of the sample is irradiated with X-rays. The apparatus may include a counter arm which rotates around a rotation center axis set within the surface of the sample while the X-ray detector is installed on the counter arm and a plate-like X-ray shielding member that is installed on the counter arm and rotated together with the X-ray detector. |
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claims | 1. A nuclear power plant comprising:a reactor;a reactor coolant system;a generator powered by the reactor coolant system;an emergency core cooling system, the emergency core cooling system including a water source, a pump having a pump inlet receiving water from the water source and a pump outlet providing the water to the reactor coolant system, and a nanoparticle supply containing nanoparticles, the nanoparticle supply having a supply outlet between the pump and the water source, the nanoparticles entering the emergency core cooling system at the supply outlet when released from the nanoparticle supply. 2. The nuclear power plant as recited in claim 1 wherein the supply outlet is at the pump inlet. 3. The nuclear power plant as recited in claim 1 wherein the pump is a high-pressure pump. 4. The nuclear power reactor as recited in claim 3 wherein the pump outlet connects to the reactor coolant system downstream of the generator and upstream of the reactor. 5. The nuclear power plant as recited in claim 1 wherein the nanoparticle supply includes a nanofluid. 6. The nuclear power plant as recited in claim 1 wherein the pump is a low-pressure pump. 7. The nuclear power plant as recited in claim 1 wherein the emergency core cooling system includes a heat exchanger, the pump outlet being connected to the heat exchanger. 8. The nuclear power plant as recited in claim 1 wherein the emergency core cooling system includes a second pump, and further comprising a second nanoparticle supply having a second supply outlet between the second pump and the water source. 9. The nuclear power plant as recited in claim 1 wherein the water source is a water storage tank. 10. The nuclear power plant as recited in claim 1 wherein the water source is a containment sump. 11. The nuclear power plant as recited in claim 1 wherein the water source is a containment sump and a water storage tank. 12. The nuclear power plant as recited in claim 1 wherein the nanoparticle supply is ZrO2. 13. The nuclear power plant as recited in claim 1 wherein the nanoparticle supply is C. 14. The nuclear power plant as recited in claim 1 wherein the nanoparticle supply is Al2O3. 15. The nuclear power plant as recited in claim 1 wherein the nanoparticle supply is SiO2. 16. The nuclear power plant as recited in claim 1 wherein the nanoparticle supply is Fe3O4. 17. The nuclear power plant as recited in claim 1 wherein the nanoparticle supply is Cu. 18. The nuclear power plant as recited in claim 1 wherein the nanoparticle supply is CuO. 19. The nuclear power plant as recited in claim 1 wherein the nanoparticle supply is one of ZrO2, C, Al2O3, SiO2, Fe3O4, Cu and CuO. 20. A nuclear power plant comprising:a reactor;a reactor coolant system;a generator powered by the reactor coolant system; andan emergency core cooling system having:an accumulator having an accumulator outlet exiting in the reactor coolant system and a first nanoparticle supply having a supply outlet exiting into the accumulator;a high pressure source of water including a first water source, a high pressure pump coupled to the first water source, and a second nanoparticle supply having a supply outlet between the high pressure pump and the first water source; anda low pressure source of water including a second water source, a low pressure pump coupled to the second water source, and a third nanoparticle supply having a supply outlet between the low pressure pump and the second water source. 21. The nuclear power plant as recited in claim 20 wherein the first, second and third nanoparticle supplies provide a nanofluid. 22. The nuclear power plant as recited in claim 21 wherein the first, second and third nanoparticle supplies provide a pressurized gas containing nanoparticles. 23. The nuclear power plant as recited in claim 20 wherein the nanoparticle supply is ZrO2. 24. The nuclear power plant as recited in claim 20 wherein the nanoparticle supply is C. 25. The nuclear power plant as recited in claim 20 wherein the nanoparticle supply is Al2O3. 26. The nuclear power plant as recited in claim 20 wherein the nanoparticle supply is SiO2. 27. The nuclear power plant as recited in claim 20 wherein the nanoparticle supply is Fe3O4. 28. The nuclear power plant as recited in claim 20 wherein the nanoparticle supply is Cu. 29. The nuclear power plant as recited in claim 20 wherein the nanoparticle supply is CuO. 30. The nuclear power plant as recited in claim 20 wherein the nanoparticle supply is one of ZrO2, C, Al2O3, SiO2, Fe3O4, Cu and CuO. |
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description | In the various figures, the same reference notations denote identical or similar components. The process of the invention, for the use of non-free-flowing UO2 powder, comprises basically a process for the manufacture of (U,Pu)O2 mixed oxide fuel pellets, that is to say overall (FIG. 2). dosing and first blending (step 1) of PuO2 powders and/or UO2 powders and/or fuel manufacturing scrap; micronization (step 2) of this first blend, particularly by milling, and forced sieving (step 3) of its product, for example through a 250 xcexcm screen mesh; additional dosing and second blending (step 4) of the first blend thus treated, UO2 and, where appropriate, fuel manufacturing scrap; addition, and blending with the resulting second blend of one or more lubricants and/or poreformers (step 5), the latter step possibly being completely or partly combined with step 4; compression (step 6) of the second blend into pellets using pelletizing presses; and sintering (step 7) of the pellets thus formed, preferably in an atmosphere of moistened argon (or nitrogen) and hydrogen. This mixed oxide fuel pellet manufacturing process may also usually include, for the pellets thus obtained, steps of: dry grinding (step 8); visual inspection (step 9); stacking up to length (step 10); loading the pellets into a cladding and welding the latter so as to form a fuel rod (step 11, FIG. 1); pressurizing the rods; nondestructive testing/examination of the rods (step 12); and assembling of the rods (step 13). Said process of the invention furthermore includes (FIG. 2) a prior mechanical granulation treatment of all or part of the nonflowing UO2 (step 29). This treatment may comprise, for example: either (FIG. 3) steps of compressing the non-free-flowing UO2 into tablets (step 30) and of crushing these tablets (step 31) and, where appropriate, of sieving the crushed material (step 32) in order to form free-flowing granules having properties suitable for being incorporated as the basic constituent in the second blending operation (step 4) or, in a variant, in both blending operations (steps 1 and 4), while maintaining the original chemical composition and original particle size of the original UO2; or an agglomeration/precompaction/granulation step by forcing the non-free-flowing UO2 powder through a screen or sieve (step 29), the amount of additive (s), the mesh size of the screen or sieve and the pressure exerted on the powder being adjusted in order to form granules having the suitable properties described above. A few nonlimiting parameters of the pellet manufacturing process are given below by way of example: batch/campaign operation rather than continuous operation; plutonium content of the first blend: 20 to 40% (step 1); milling (step 4) in 60 kg batches for a minimum effective time of 5 hours; use of non-free-flowing UO2 powders coming from a wet conversion (for example, ex-ADU or ammonium diuranate powder) or from a dry conversion (said conversions being known to those skilled in the art); addition of 0.2 to 0.5% of zinc stearate and 0 to 1% of an AZB pore former (known to those skilled in the art); pelletizing compression (step 6) at a pressure between 400 and 700 MPa; sintering (step 7) for at least 4 hours at a temperature between 1600 and 1760xc2x0 C. in an argon atmosphere containing 5% hydrogen, with an H2/H2O ratio of 10 to 30; and dry centerless grinding (step 8). By way of nonlimiting example, the compression step (step 30) may be carried out at a pressure of between 50 and 200 MPa, this being tailored according to the characteristics of the non-free-flowing powder. These pressures are therefore higher than the granulation pressures (4 to 10 MPa) generally used in UO2 nuclear fuel manufacturing plants. Some binder and/or lubricant, both well known to those skilled in the art, may be incorporated into the non-free-flowing UO2 powder before compression: by way of nonlimiting example, the compression may thus be carried out at a pressure of between 40 and 100 MPa. Also by way of nonlimiting example, the aforementioned tablets may be crushed in one or more jaw crushes or roll mills of 200-250 xcexcm aperture. This crushing may be followed by sieving it the crusher lets through, or runs the risk of letting through, granules having a size greater than 250 xcexcm. The fines possibly resulting from the crushing may usefully be incorporated as raw material into the first blending operation (step 1). By way of yet another nonlimiting example, the operation of forcing the powder through a sieve (step 29) may be carried out in a machine of the kind used in MIMAS-type processes (step 3) to fill the first blend (after the micronization of step 2) before the second blending (step 4). Such machines, which combine agglomeration/precompaction upstream of the sieve and control of the maximum granule size by passing the powder through this same sieve, may produce granules of the desired characteristics directly. Experience has shown the Applicant that a non-free-flowing powder treated according to the processs forming the subject matter of the invention can be used in existing MOX manufacturing plants, by passing the parameters of this second blending operation (step 4), the pelletizing (step 6) and the sintering (step 7), within the adjustment limits routinely used to optimize the manufacturing process according to the characteristics of the various free-flowing UO2 powders used for MOX fuel manufacture. The process of the invention therefore makes it possible to extend the range of UO2 powders which can be used to manufacture MOX fuel, without loosing the benefit of the similarity between the MOX fuel produced according to the invention and the UO2 fuel manufactured on an industrial scale by the processes known hitherto, starting from the same non-free-flowing UO2 powder. It should be understood that the present invention is in no way limited to the methods of implementation described above and that many modifications may be made thereto without departing from the scope of the claims given hereafter. The non-free-flowing UO2 conditioning process may especially be applied to UO2 coming from a conversion other than the conversion of uranium hexafluoride into UO2. |
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description | This application claims priority from U.S. Provisional Patent Application 61/479,149, filed Apr. 26, 2011, which is hereby incorporated by reference. The invention relates to a method for determining a reconstructed image using a particle-optical apparatus. In a TEM an object, also referred to as a sample, is irradiated with a beam of electrons, the electrons having an energy of e.g. between 50 keV and 400 keV. Some of the electrons are transmitted through the sample, and these electrons are focused on the image plane to form an enlarged image of the sample. The imaging of the sample on the image plane is realized with a projection system, that can be set to a configurable magnification of e.g. between 103 and 106 times. Typically a detector, such as a CCD camera or CMOS camera, is placed in the image plane, whereby the image is detected. Such detector may e.g. have a semiconductor sensor having 4 k×4 k pixels arranged in a two-dimensional array. With such detector, the electrons impinge on the semiconductor chip of the CCD or CMOS sensor and generate electron hole pairs, thereby forming the charge to be detected by the CCD or CMOS chip. For some applications, a very low dose of electrons is required. For example, biological materials may already degrade at doses of 10-30 electrons per 0.1 nm×0.1 nm within a frame time of 8-10 seconds. This may result in an average dose of 0.001-0.1 electrons per pixel or even less at the detector. Although CCD and CMOS cameras are constantly improving, Signal to Noise Ratio (SNR) and Modulation Transfer Function (MTF) may still be limiting the performance of the detector. For an exemplary direct electron detection CMOS camera in a TEM, one incident electron may generate thousands of electron hole pairs which diffuse over an area of e.g. 5×5 pixels and finally generate about a total of 240 output signal counts in the 5×5 pixels. As a result, the Point Spread Function (PSF) may be significant larger than the spatial sampling dimensions (one pixel). In the following, any reference to the length of the PSF may refer to the width of the PSF in terms of number of pixels: the length is five when the electron hole pairs diffuse over an area of 5×5 pixels. At halve-Nyquist frequency of the sensor, an MTF less than 0.5 is achieved. The MTF at Nyquist is approaching to zero. This results in a loss of MTF and thus resolution. Secondly, the peak count at the center pixel may be roughly 30 counts, while the dark current noise of the semiconductor sensor may typically vary between 0 and 30 counts. This results in an SNR around 1. At these low doses, both SNR and MTF determine the image quality. Due to the relatively high noise level, known image improvement technologies like image deconvolution are not very successful to recover from this noise and point spread function. Besides the dark current noise, also the number of electron hole pairs that are being generated in the semiconductor sensor for a single incident electron, and thus of the deposited energy per electron, may vary wildly and affect the SNR. One incident electron of 300 keV may e.g. result in any number of electron hole pairs between 0 and 80.000 and a corresponding spread in detected charge. In the following, the charge detected by a pixel of the semiconductor chip will be represented by a corresponding pixel signal with a signal strength representing a certain number of signal counts. It is known to determine whether an electron is present on a pixel by comparing the pixel signal to a predetermined reference level in so-called threshold detection. However, such threshold detection may result in many misdetections when the dose is low and when the SNR around 1. To overcome the effects of the Point Spread Function, it has been proposed to use Partial Response (PR) detection, using a Partial Response function resembling the Point Spread Function. For binary images, a Partial Response Maximum Likelihood (PRML) detection and Viterbi Detection have been proposed with success. However, the inventor has found that such known methods do not give a satisfactory results when applied to an image obtained in a TEM, especially not in the presence of SNR is around 1 and/or when the spread in signal counts for a single incident electron is large. A disadvantage of the aforementioned methods is that the achievable resolution may be compromised. Especially when the dose is low, it may not be possible to determine the number of incident electrons on each pixel with a sufficient reliability. Accordingly, there is a need to provide a method wherein the quality of an image acquired by a detector in a particle-optical apparatus, such as a TEM, is improved, especially at low dose and where the signal of a single incident particle, such as an electron, is spread over a plurality of pixels, e.g. due to diffusion in the semiconductor sensor. An object of the invention is to improve the quality of an image acquired by a detector in a particle-optical apparatus, such as a TEM. The invention relates to a method for determining a reconstructed image using a particle-optical apparatus. The particle-optical apparatus comprises a particle source for producing a beam of particles, an object plane on which an object to be imaged may be placed, a condenser system for illuminating the object plane with the beam of particles, a projection system for forming an image of the object plane by imaging particles transmitted through the object on an image plane, and a detector for detecting the image, wherein the detector comprising a semiconductor sensor having an array of pixels for providing a plurality of pixel signals from respective pixels of the array in response to particles incident on the detector. The invention further relates to a particle-optical apparatus arranged to execute such method for determining a reconstructed image. The invention further relates to a computer program product comprising instructions for causing a processor system to perform such method. The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter. It should be appreciated by those skilled in the art that the conception and specific embodiments disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims. The accompanying drawings are not intended to be drawn to scale. In the drawings, each identical or nearly identical component that is illustrated in various figures is represented by a like numeral. For purposes of clarity, not every component may be labeled in every drawing. Embodiments of the invention provides a method wherein the quality of an image acquired by a detector in a particle-optical apparatus, such as a TEM, is improved, especially at low dose and where the signal of a single incident particle, such as an electron, is spread over a plurality of pixels, e.g. due to diffusion in the semiconductor sensor. A method according to one embodiment of the invention comprises: receiving the plurality of pixel signals, and determining a reconstructed image from using Viterbi Detection on the plurality of pixel signals, the Viterbi Detection using a plurality of different states corresponding to a plurality of configurations of particles incident on the detector, and at least two states of the plurality of different states corresponding to a same, non-zero multiplicity of incident particles on a single pixel of the plurality of pixel signals. The non-zero multiplicity of incident particles on the single pixel may in particular be one, whereby the at least two states of the plurality of different states correspond to a single electron being incident on the single pixel. In this embodiment, the Viterbi Detection may use a first state of the plurality of different states wherein a single electron is incident on a pixel and generates a first pixel signal, i.e. a first number of pixel counts, and a second state of the plurality of different states wherein again a single electron is incident on the pixel, but wherein the single electron generates a different, second pixel signal, i.e. a second number of pixel counts different from the first number. The first and second state may thus both relate to configurations wherein a single electron is incident on the pixel, but with different signal count. The Viterbi Detection may thus successfully account for the large spread in generated number of electron hole pairs from a single incident electron and the corresponding spread in detected charge, in contrast to known Viterbi Detection schemes wherein no such plurality comprising at least such first state and such second state is used. In an embodiment of the method according to the invention, the different states are modelled using a different multiplicity of particles. In this embodiment, the states may e.g. be modeled as if all electrons generate substantially the same number of electron hole pairs and therefore substantially the same pixel signal, i.e. a predetermined signal count. The first state may then be modeled as one electron with the corresponding predetermined pixel count, whereas the second state may be modeled as two electrons, each generating the corresponding predetermined pixel count, i.e., with twice the pixel count of a single electron. When the Viterbi Detection decides that the second state is the most likely state, the Viterbi Detection will however output that a single electron was present. Especially when the dose is relatively low and when the predetermined signal count is suitably selected, this may improve the reconstructed image, as the likelihood of having two electrons on a single pixel may then be significantly smaller than the likelihood that a single electron has resulted in a larger signal count. In an embodiment of the method according to the invention, the different states are modelled using different deposited energies of the particle(s). In this embodiment, the states of the Viterbi Detection explicitly take into account that a single electron may result in different pixel counts. The first state may e.g. relate to a single electron of a first predetermined signal count and the second state may e.g. relate to a single electron of a second, different predetermined signal count, the second predetermined signal count being e.g. twice the first predetermined signal count. The Viterbi Detection will thus not only result in the determination whether an electron was incident on a pixel, but, when it was present, also provide the likely signal count of the electron. In an embodiment of the method according to the invention, the different states are modelled using different point spread functions in modelling deposited energies of the particle(s). In this embodiment, the first state may e.g. relate to a single electron generating pixel counts in a plurality of neighboring pixels according to a first point spread function, and the second state may e.g. relate to a single electron generating pixel counts in a plurality of neighboring pixels according to a second point spread function, the second point spread function being different from the first point spread function. The Viterbi Detection may thus account for possible different signal count distributions in response to a single electron being incident on a pixel. The different point spread functions may e.g. corresponds to a different relative amplitude and/or a different shape and/or a different length. In an embodiment of the method according to the invention, the different states are used in different iterations of the Viterbi Detection. In this embodiment, the Viterbi Detection uses in e.g. a first iteration a first state corresponding to an incident electron resulting in a first, large pixel count, and a second iteration wherein a second state is used corresponding to an incident electron resulting in a second, smaller pixel count. After the first iteration, contributions from all detected electrons may be modeled and removed from the pixel signals. Hereby, the first iteration detects electrons with a high pixel count and the second iteration detects electrons with a low pixel count. Preferably, the states used in successive iterations correspond to decreasing signal level of a single electron. In an embodiment of the method according to the invention, wherein the array of pixels is a one-dimensional array. The semiconductor sensor thus forms a line sensor, which may e.g. be scanned along the image plane. Using such line sensor may be advantageous because of reduced computational complexity and memory requirements, as the Viterbi Detection only has to accommodate for contributions from neighboring pixels in one dimension. The Viterbi Detection may thus use a smaller number of states compared to the situation wherein a two-dimensional array is used, and states have to be considered wherein an electron is incident in a two-dimensional environment of the pixel. In an embodiment of the method according to the invention, the array of pixels is a two-dimensional array and the Viterbi Detection is applied to sequences of pixel signals per row of pixels of the two-dimensional array. In this embodiment, the Viterbi Detection substantially operates row-by-row. Hereby, the number of states—and hence computational complexity and memory requirements—that are being considered in the Viterbi Detection is reduced compared to a full two-dimensional Viterbi Detection, whereas the benefits of using Viterbi Detection largely remain. The Viterbi Detection preferably uses a two-dimensional PSF and considers the contributions of pixels in a two-dimensional area around the pixels on the row for each state, in order to optimally model the pixel signal. In an embodiment of the method according to the invention, the array of pixels is a two-dimensional array and the Viterbi Detection is applied to sequences of pixel signals per column of pixels of the two-dimensional array. In this embodiment, the Viterbi Detection substantially operates column-by-column, with similar advantages and effects as when operating row-by-row. In a further embodiment, the Viterbi Detection uses a first iteration with a row-by-row operation and a second iteration with a column-by-column operation, after which the results of the first and second iteration are combined to obtain the output of the Viterbi Detection. The combining may e.g. comprises an averaging, or a selection based on determined path metrics obtained from first and second iterations. In further embodiments, the states of the Viterbi Detection correspond to predetermined two-dimensional configurations of particles incident on the detector. The Viterbi Detection may thus e.g. determine contributions from particles incident on the respective pixel on the row or column, as well as from particles incident on pixels of neighboring rows or columns, which may also contribute to the pixel signal. This embodiment may be referred to as strip-wise Viterbi Detection. In an embodiment of the method according to the invention, the method further comprises, after having detected one or more incident particles on a pixel, removing a contribution from the detected one or more incident particles from the plurality of pixel signals. In this embodiment, the plurality of pixel signals that is being considered is substantially free from the contributions from electrons that have already been detected. Computational complexity and/or robustness may thus be improved. In an embodiment of the method according to the invention, the Viterbi Detection uses a PR (13531) or PR (13531)2 response. Such PR responses have been found to result in a good balance between computational complexity and memory requirements and performance of the Viterbi Detection. The plurality of pixels of semiconductor sensor may be dimensioned and arranged such that the diffusion pattern substantially corresponds to a point spread function corresponding to such PR responses. An alternative PR response may be used, and e.g. selected in accordance with an energy deposition pattern of a particle incident on the semiconductor sensor. In embodiments of the method according to the invention, the Viterbi Detection uses a path memory length in a range of 2-5, preferably 2-4, even more preferably 3-4, times the length of a Point Spread Function used in the Viterbi Detection, the Point Spread Function corresponding to a PR-response used in the Viterbi Detection. The inventors have found that, with the length of the path memory is chosen in the indicated ranges, a good balance between computational complexity and memory requirements and performance of the Viterbi Detection is obtained. In an embodiment of the method according to the invention, the image detected by the detector comprises a dose in a range of 0.0001-0.5, preferably 0.001-0.3, even more preferably 0.01-0.1 particle per pixel. The inventors have found that the Viterbi Detection according to the invention when the dose is in the ranges indicated. These ranges are particularly suitable for allowing a reasonably low number of states, and thus reasonable computational complexity, while maintaining a good performance. In an embodiment of the method according to the invention, the method comprises: receiving a first plurality of pixel signals from respective pixels of the array in response to particles incident on the detector upon detecting a first image of the object, determining a first reconstructed image from using the Viterbi Detection on the first plurality of pixel signals, receiving a second plurality of pixel signals from the respective pixels of the array in response to particles incident on the detector upon detecting a second image of the object, determining a second reconstructed image from using the Viterbi Detection on the second plurality of pixel signals, and combining the first reconstructed image and the second reconstructed image to form the reconstructed image. The method may further comprise receiving at least one further plurality of pixel signals from the respective pixels of the array in response to particles incident on the detector upon detecting at least one respective further image of the object, determining at least one further reconstructed image from using the Viterbi Detection on the respective further plurality of pixel signals, and combining the first reconstructed image, the second reconstructed image and the at least one further reconstructed images to form the reconstructed image. Thus, the method acquires and processes two or more reconstructed images of the same object, and combines the corresponding reconstructed images to form the reconstructed image. The two or more reconstructed images may e.g. have been acquired at a low dose, e.g. selected to prevent damage to the object, while the reconstructed image as obtained from combining the two or more reconstructed images may effectively correspond to a higher dose. Hereby, the quality of the reconstructed image may be improved. Combining the first and second (and, if applicable, the further) reconstructed images may e.g. comprise an addition or an averaging of the first and second (and, if applicable, the further) reconstructed images, but may, in further embodiments, comprise correcting for a shift and/or distortion between the first and second (and, if applicable, the further) reconstructed images. The shift and/or distortion may e.g. be determined from the first and second (and, if applicable, the further) reconstructed images that are being combined. The shift and/or distortion may alternatively be predetermined or be provided by other parts of the particle-optical apparatus, e.g. from the projection system. In some embodiments of the method according to the invention, the method comprises: producing a beam of particles, placing an object to be imaged on an object plane, illuminating the object plane with the beam of particles, forming an image of the object plane by imaging particles transmitted through the object on an image plane, and detecting the image with the detector comprising the semiconductor sensor and providing a plurality of pixel signals from the respective pixels of the array in response to the particles incident on the detector. A further aspect of the invention provides a particle-optical apparatus comprising: a particle source for producing a beam of particles, an object plane on which an object to be imaged may be placed, a condenser system for illuminating the object plane with the beam of particles, a projection system for forming an image of the object plane by imaging particles transmitted through the object on an image plane, a detector for detecting the image, the detector comprising a semiconductor sensor having an array of pixels for providing a plurality of pixel signals from respective pixels of the array in response to particles incident on the detector, and a signal processor arranged to: receive the plurality of pixel signals, and determine a reconstructed image from using Viterbi Detection on the plurality of pixel signals, the Viterbi Detection using a plurality of different states corresponding to a plurality of configurations of particles incident on the detector, and at least two states of the plurality of different states corresponding to a same, non-zero multiplicity of incident particles on a single pixel of the plurality of pixel signals. The signal processor may be part of the detector, or be arranged as a separate unit in communication with the detector. In a further aspect of the invention, a computer program product is provided comprising instructions for causing a processor system to perform the method set forth. It will be appreciated by those skilled in the art that two or more of the above-mentioned embodiments, implementations, and/or aspects of the invention may be combined in any way deemed useful. Modifications and variations of the particle-optical apparatus and/or the computer program product, which correspond to the described modifications and variations of the method, can be carried out by a person skilled in the art on the basis of the present description. FIG. 1 schematically shows an apparatus according to the invention. It shows a TEM, comprising a vacuum housing 120 evacuated via tube 121 by a vacuum pump 122. A particle source in the form of an electron source 101 produces a beam of electrons along a particle-optical axis 100. The particle source may be any type of electron source, such as e.g. a field emitter gun, a Schottky emitter, or a thermionic electron emitter. The electron source can be e.g. a field emitter gun, a Schottky emitter, or a thermionic electron emitter. The electrons are then accelerated to an adjustable energy of typically between 80-300 keV, although TEM's using electrons with an adjustable energy of e.g. 50-500 keV are known. Deflectors 102 centre the beam of particles on beam limiting aperture 103. The beam then passes through a condenser system comprising two lenses 104. A sample 111 is held by a manipulator 112, positioning the sample in the object plane of the objective lens 105. The sample is imaged by a projection system comprising lenses 106 onto fluorescent screen 107, and can be viewed through a window 108. The fluorescent screen 107 is connected to a hinge 109 and can be retracted/folded away, so that the image made by the projection system is imaged on detector 150. It is noted that the projection system may need to be re-focused so as to form the image on the detector 150 instead of on the fluorescent screen. The image formed on the screen or on the detector typically has a magnification of between 103 to 106 times and may show details as small as 0.1 nm or smaller. It is further noted that the projection system may form intermediate images. The detector 150 comprises a semiconductor sensor 151, such as a charge coupled device (CCD) or a CMOS device, for detecting impinging electrons. The semiconductor sensor 151 has a plurality of pixels (not shown in FIG. 1) arranged in a two-dimensional array. One incident electron may generate thousands of electron hole pairs which diffuse over an area of e.g. 5×5 pixels of the array, where the charge is collected to generate pixel signals. The pixel signals may be referred to as ‘raw pixel data’ or ‘data samples’. The plurality of pixel signals may be referred to as ‘raw image’. The detector 150 further comprises a signal processor 152, for processing the pixel signals and determining an improved image, representing a reconstruction of the configuration of electrons incident on the detector 150. The improved image may further be referred to as ‘output image’. It is noted that in alternative embodiments, the plurality of pixels may also be arranged in other configurations, such as in a one-dimensional array, forming a line sensor. The line sensor may be movable relative to the projected image to obtain a sequence of one-dimensional images which together form a two-dimensional image. It is noted that FIG. 1 shows a schematic description of a typical TEM only, and that in reality a TEM comprises many more deflectors, apertures etc. Also TEM's with correctors for correcting the aberration of the objective lens 105 are known, said correctors employing multipoles and round lenses. Also other detectors may be used, such as secondary electron detectors, X-ray detectors, etc. These detectors may be positioned at the side of the sample facing the gun or the side of the sample facing detector 150. FIG. 1 further shows an interface device 160 which connects the TEM to a user interface system, herein shown as a computer, having input means 170, such as a keyboard and a mouse, and visualization means 175, such as a display screen. The user interface system may also have a storage device, such as a hard disk drive and an optical disk drive, as well as interfacing devices for connecting with removable solid state storage, such as a USB-stick, and/or for connecting to a network, such as the internet or a local network. The interface device 160 is further connected to the detector 150 for obtaining the output image from the detector 150 and to provide the output image the user interface system. Further, the interface device 160 is connected to the signal processor 152 allowing a user to adapt setting of the signal processor 152. Further, the interface device 160 is connected to the TEM for operating the TEM from the user interface device, e.g. allowing the user to input commands using the input means to operate parts of the TEM, such as e.g. to operate the vacuum pump 122, the electron source 101, the manipulator 112 and the hinged screen 107. The signal processor 152 is arranged to process the raw pixel signals and to determine an output image, representing a reconstruction of the configuration of electrons incident on the detector 150. It is known to process the raw pixel signals using a threshold detector, which compares each raw pixel signal to a predetermined threshold value, and determines that an incident electron was present when the raw pixel signal is larger than the predetermined threshold value, whereas it is determined that no incident electron was present when the raw pixel signal is smaller than the predetermined threshold value. Such threshold detection however only shows a sufficient performance when the signal to noise ratio is sufficiently large to discriminate between noise (resulting in a raw pixel signal below the predetermined threshold) and the presence of an electron (resulting in a raw pixel signal above the predetermined threshold). However, when the dose is low, such threshold detection will not result in a satisfactory performance. Moreover, one incident electron will generate signals in a plurality of adjacent pixels in a semiconductor sensor, which may be characterized by a point spread function and which may be referred to as inter-symbol-interference (ISI). It is known to use deconvolution techniques to accommodate for such ISI, but known deconvolution techniques do not result in a satisfactory performance when the signal to noise ratio is very poor. For one-dimensional signals corresponding to binary data as well as for two-dimensional signals corresponding to binary data, it is known to use a signal processing techniques known as Viterbi Detection. A Viterbi Detector performs maximum-likelihood detection in an efficient manner using a technique known as dynamic programming Hereto, the Viterbi Detector operates on a sequence of data samples. In data storage, this sequence corresponds to a sequence of data samples in the time domain, but in embodiments of the image reconstruction, the sequence corresponds to a sequence of adjacent pixels. Central to Viterbi Detection is the notion of states: a state corresponds to a possible configuration of the original data. An example will be given below. When considering the next data sample of the sequence, transitions are considered between the possible state(s) of the current data sample and the possible state(s) of the next data sample. A weight may be accorded to each transition to indicate the likelihood of such transition. The weight may be determined from evaluating the difference between the actual state of a pixel and a model of the state of the pixel. The model of the state of the pixel may e.g. be represented by a calculation of the pixel signal that would be obtained for the state using a model that models the contribution of the configuration of the original data corresponding to the state while ignoring noise, hereby obtaining a modelled pixel signal. The weight may then be determined as e.g. the absolute value of difference of the actual pixel signal and the modelled pixel signal. Such weight may be calculated between the actual pixel signal and a plurality of modelled signals, one for each state. For the state representing the actual configuration, the weight will substantially only be noise. For other states, the value will deviate more. In order to improve the performance, a Viterbi Detector does not decide on the basis comparing a single pixel with all possible states, but uses sequences of states instead. The number of successive states of a sequence is referred to as the path memory length. The path memory length is preferably between 2 and 5 times the length of the PSF, preferably between 3 and 4 times. A sequence of states comprises transitions between successive states, each with their respective weight. In such sequence, a weight relating one transition (from one data sample to the next) is referred to as ‘branch metric’. The sum of all weights of a sequence of states is referred to as ‘path metric’. The sequences of states and the transitions between successive states are referred to as a trellis diagram. Viterbi Detection relates to finding the path with the lowest path metric through the trellis diagram. A complete maximum likelihood detector would evaluate and keep track of all possible paths through the trellis diagram. The complexity of a Viterbi Detector is reduced by only keeping track of those paths that may result in the path with the lowest metric. Hereto, the Viterbi Detector determines for each state along the trellis which path(s) have the smallest path metric leading to that state along the trellis, and maintains those as ‘survivor path(s)’, while the other path(s) are discarded from further use. Viterbi Detection has been developed for data storage and mobile communication. Hereby, Viterbi Detection can accommodate for inter-symbol-interference and noise, provided the characteristics of the system can be well modelled. Now, an example of Viterbi Detection of a known type is described. The example relates to an exemplary system with a binary input signal, i.e., with data values ‘0’ or ‘1’, and a point spread function PSF=(121) defining that each data value ‘1’ results in relative signal contributions 1:2:1 in adjacent data samples, whereas data value ‘0’ does not result a signal contribution. The system has white noise. Further, the system is characterized by a run-length constraint that there should be at least two ‘0’s between two ‘1’s. FIG. 2 shows an example of states and transitions of such exemplary Viterbi Detector. As shown in FIG. 2, the Viterbi Detector has a plurality 200 of states, consisting of one states, labelled s0, with three successive data values of ‘0’, and three different states, labelled s1, s2 and s3, with one data value ‘1’ and two data values ‘0’. The states s0, s1, s2 and s3 may also be referred to as ‘000’, ‘001’, ‘010’ and ‘100’. FIG. 2 shows that the run-length constraint defines a plurality 204 of transitions from the plurality 200 of states to the next plurality of states 202: state s0 can only be followed by state s0 or s1 as shown by transitions t00 and t01, state s1 can only be followed by state s2 as shown by transition t12, state s2 can only be followed by state s3 as shown by transition t23, state s3 can only be followed by states s0 and s1 as shown by transitions t30 and t31. FIG. 3 and FIG. 4 illustrate the operation of the Viterbi Detector. FIG. 3 shows a plurality of k=0, . . . , 9 successive input data values ak 222 of values ‘0’ or ‘1’ indicated in boxes. For k<0, all input data values are considered to be 0. FIG. 3 also shows the corresponding data samples rk 224. Dashed box 230 indicates the range of data samples that are being considered over a path memory length L for a first detection of the Viterbi Detector. Modelled, noiseless detector values xi may be obtained from convoluting the PSF=(121) with the input data values: for the center pixel of each state, states s0, s1, s2 and s3 thus correspond to modelled, noiseless detector values x0=0, x1=1, x2=2 and x3=1. FIG. 3 also shows a trellis 210. The trellis 210 indicates all possible transitions between successive states. The trellis also indicates the survivor paths 216, i.e. the paths that have the lowest summed branch metrics for the successor state up along the trellis. As branch metric BM, the absolute difference between the modelled, noiseless detector value xi and the data sample rk is used, i.e.BM=|xi−rk|. The skilled person will appreciate that alternative branch metrics BM′ may be used, such as e.g.:BM′=(xi−rk)2. As an example, at k=0, the input data value is a0=1, noiseless detector values are x0=0, x1=1, x2=2 and x3=1, r0=2, so the branch metrics BM=|xi−rk| are: BM(s0)=2, BM(s1)=1, BM(S2)=0, BM(s3)=1. Thus, the survivor path leading to s0 as successor state is selected as the minimum from transition t00 and t30 with corresponding branch metrics 2 and 1: to reach s0 at k=1, only the path consisting of transition t30 from s3 is kept as candidate path, whereas the path from s0 is discarded. The other survivor paths leading to s1, s2 and d3 at k=1 are respectively t31 (the lowest BM of transitions t21 and t31), t12 (the only possible transition to s2) and t23 (the only possible transition to s3). Likewise are the survivor paths to states at k=2, . . . , 9 indicated in the trellis with full errors 216 and all discarded paths are discarded with dashed arrows 214. The Viterbi Detector determines at k=8 which of all survivor paths along the path memory length has the lowest path metric. For the example shown, the path metrics at k=8 are 3, 3, 2 and 0 to states s0, s1, s2 and s3 respectively. Thus, the path leading to s3 is selected as the path with the maximum likelihood of representing the actual sequence of states. The Viterbi Detector traces back this path to its originating state at k=0, and finds state s2, i.e. ‘010’ at k=0. The left-most value of this state, i.e. ‘0’, is outputted as the output value for the previous position: the reconstructed output value for k=−1 thus equals ‘0’. Then, the Viterbi Detector shifts to the next data sample to obtain the situation as shown in FIG. 4. Dashed box 231 indicates the range of data samples that are now being considered a second detection of the Viterbi Detector. Trellis 211 of FIG. 4 corresponds to the trellis of 210, wherein the transitions from k=0 to k=1 are discarded and new branch metrics from k=8 to k=9 have been calculated and the trellis 211 is extended with the corresponding survivor paths. It may be observed that s0 and s1 both have a path metric of 0 at k=9. Both originate from s3 at k=1. So the Viterbi Detector finds states s3, i.e. ‘100’ at k=1, and outputs a reconstructed output value for k=0 as ‘1’. The Viterbi Detector may this continue until all output values have been determined When the right-most value of the range of data samples that are being considered is the last value of the sequence, the Viterbi Detector may output the complete path as outputs for the last 9 states. Alternatively, the Viterbi Detector may use ak=0 for subsequent data samples. The above described Viterbi Detector may be very effective for systems wherein the model of the system is sufficiently accurate to model the noiseless detector value xi for each possible configuration of input data values ak, wherein at the same time a sufficient discrimination between a true input signal and noise can be obtained. Such and similar Viterbi Detectors may successfully be used to recover from the ISI for one-dimensional binary data with a significant amount of ISI, i.e. a point spread function of several data samples. Also, such and similar Viterbi Detectors may successfully be used to reconstruct two-dimensional binary data, such as Smart Codes used to for identification. For two-dimensional data, a Viterbi Detector may e.g. be used strip-wise, wherein Viterbi Detection is used along rows, and hard decisions are made from row to row or from strip to strip. However, the Viterbi Detector as described above does not work well with TEM images. FIG. 5 illustrates the performance of the above described Viterbi Detector for an exemplary one-dimensional TEM image. The Viterbi Detector uses the same states and same transitions as the Viterbi Detector described with reference to FIGS. 3 and 4. In these states and their branch metrics, the modelled signal level is defined as the peak signal level Epeak of the distribution of signal levels resulting from a single incident electron. The model hereby uses the knowledge that an incident electron of 300 keV may result in any number of electron hole pairs between 0 and 80.000 and a corresponding distribution of detected charge, with a distribution that is similar to a Landau-function, i.e., strongly peaked at the signal level Epeak. The k=0, . . . , 9 successive input data values ak 222 of values ‘0’ or ‘1’ indicate the absence or presence of an electron on the corresponding pixel and is indicated in the boxes. FIG. 5 also shows the corresponding data samples rk 224a, which are equal to the values from FIG. 3, except for r0 and r1 relating to positions k=0 and k=1. The inventor believes that the different values for r0 and r1 originate from an electron having resulted in a significantly larger amount of charge in the sensor than the amount of charge corresponding to Epeak. For this exemplary situation, the trellis and the paths with minimum path metric are indicated FIG. 5. It is observed that two paths with the same minimum path metric are obtained: one originating from s2 and the other from s3. For the Viterbi Detector, both paths have an equal likelihood. The Viterbi Detector may thus output either a ‘0’ according to state s2, or a ‘1’ according to state. However, the correct output is ‘1’ as there is a single electron at k=0. The Viterbi Detector may thus erroneously output ‘0’. FIG. 6 shows an example of states and transitions for use with a Viterbi Detector in an embodiment of the invention. As shown in FIG. 6, the Viterbi Detector has a plurality 300 of states, consisting of one states, labelled s0, with three successive data values of ‘0’, three different states, labelled s1, s2 and s3, each having one data value ‘1’ and two data values ‘0’ and three different states, labelled s4, s5 and s6, each having one data value ‘2’ and two data values ‘0’. FIG. 6 also shows all allowable transitions 304, allowing to define the full trellis diagram. In a first embodiment, the numerical value indicated in the boxes in FIG. 6 indicates the number of electrons incident on a single pixel. Compared to FIG. 2, it may thus be seen that the states are extended with states wherein more than one electron is incident on the same pixel, i.e. states s4, s5 and s6. According to this embodiment, a new trellis is constructed and a corresponding Viterbi Detector will obtain state s6=‘200’ at k=1 as resulting in the minimum path metric: the trellis is shown in FIG. 7. The Viterbi Detector will thus output ‘2’ as a result, indicative of the presence of two electrons on the corresponding pixel. After having obtained the output from the Viterbi Detector, the method according to the first embodiment analyses the output from the Viterbi Detector and adjusts all non-zero output values to ‘1’. Hereby, assuming a low coincidence rate of two electrons on a single pixel, the most likely multiplicity of electrons per pixel, i.e. just one instead of two, may be used as the output of the method. Thus, in this first embodiment, a plurality of different states of the Viterbi Decoder relates to the same multiplicity (in this case, one) of incident electrons as output of the method, the different states being modelled using a different multiplicity of electrons. It will be appreciated that, for a low dose, e.g. of 0.01 electron per pixel, and with the reference level suitable selected, the frequency of occurrence of two electrons on a single pixel may significantly smaller, e.g. an order of magnitude smaller, than the frequency of occurrence of a single electron with a double deposited energy. In a second embodiment, the numerical value indicated in the boxes in FIG. 6 indicates an energy bin accorded to a single electron incident on a single pixel. Compared to FIG. 2, it may thus be seen that the states are extended with states wherein a single electron is incident on the same pixel, but of a different typical energy, i.e. states s4, s5 and s6. According to this embodiment, a new trellis is constructed and a corresponding Viterbi Detector will obtain state s6=‘200’ at k=1 as resulting in the minimum path metric: the trellis is shown in FIG. 7. The Viterbi Detector will thus output ‘2’ as a result, indicative of the presence of a single electron of energy bin ‘2’ on the corresponding pixel. Thus, in this second embodiment, a plurality of different states of the Viterbi Decoder relates to the same multiplicity of incident electrons (in this case, one) as output of the method, the different states being modelled using different deposited energies of the electron(s). In another embodiment, the different states are modelled using different point spread functions in modelling deposited energies of the particle(s). The different point spread functions may e.g. have different amplitudes, thereby modelling different deposited energies of the electron(s). FIG. 8 illustrates a third embodiment using the same states as shown in FIG. 6. In the third embodiment, the Viterbi Decoder operates in a plurality of iterations. In each iteration, state s0 is used together with a plurality of different states, each of the plurality of different states having one data value of a specific data value (with the same specific data value for all three states) and two data values ‘0’, where the data values of the specific data value are located at different positions for each of the different state. The third embodiment is illustrated using an example shown in FIG. 8. The example shows a configuration of electrons labelled with their deposited energy bin ‘0’, ‘1’ or ‘2’ in row 350, and with corresponding data samples 352. In the example shown, the Viterbi Decoder operates in a first iteration with a first plurality 360 of states s0, s4, s5 and s6. States s4, s5 and s6 may be defined similarly to those in the first embodiment, or, alternatively, to those in the second embodiment. In the first iteration, the Viterbi Decoder will thus effectively only reconstruct electrons with an energy corresponding to that of states s4, s5 and s6, but not to that of states s1, s2 and s3. The number of states is thus reduced to 4 and the number of transitions to 6, whereby trellis is significantly simplified compared to the trellis associated with the first and second embodiments. The Viterbi decoder outputs from this first iteration, for the example shown, two electrons indicated with E2 on 370, which correspond to data values as shown in 372. The data values 372 corresponding to the found electrons are then subtracted from the corresponding original data values 352, to result in residue data values 376. The residue data values 376 are then used as input to a second iteration of the Viterbi Decoder with a second plurality 380 of states s0, s1, s2 and s3. The Viterbi decoder outputs from this second iteration, for the example shown, two electrons indicated with E1 on 390. The outputs of the first and second iteration are then added to result in the complete output shown as 390: all 4 electrons, two of a deposited energy around E2 and one of a deposited energy around E1, have been reconstructed. Thus, in this third embodiment, a plurality of different states of the Viterbi Decoder relates to the same multiplicity of incident electrons (in this case, one) as output of the method, the different states being used in different iterations of the Viterbi Decoder. FIG. 9 shows the states of a fourth embodiment. The fourth embodiment comprises the same states as the first embodiment, as well as three additional different states s7, s8 and s9, each having two data values ‘2’ and one data values ‘0’. States s0-s9 thus define 10 different states having 0, 1 or 2 electrons. As in the first embodiment, after having obtained the output from the Viterbi Detector, the method according to the fourth embodiment analyses the output from the Viterbi Detector and adjusts all non-zero output values to ‘1’. Hereby, assuming a low coincidence rate of two electrons on a single pixel, the most likely multiplicity of electrons per pixel, i.e. just one instead of two, may be used as the output of the method. Thus, in this fourth embodiment, a plurality of different states of the Viterbi Decoder relates to the same multiplicity (in this case, one) of incident electrons as output of the method, the different states being modelled using a different multiplicity of electrons on a single pixel. An advantage of the fourth embodiment may be that a larger dose can be accommodated, at the cost of more states, resulting in a larger memory requirement and a larger computational load. It will be appreciated that the invention is not limited to the exemplary embodiments described above, but also includes e.g. other PSFs and other multiplicities of electrons than two or a larger number of energy bins than two. The embodiments described above used one-dimensional data sequences. The embodiments may be extended to two-dimensional data sequences, such obtained from a two-dimensional array of pixels e.g. as described in the following. FIG. 10 schematically shows a two-dimensional semiconductor sensor of a plurality of pixels arranged in a matrix 500, organized in a plurality of columns (of which 15 are shown; not numbered) and a plurality of rows of which rows numbered R0-R12 are shown. Four electrons are incident on the sensor, resulting in four regions on 3×3 pixels, denoted by 501, 502, 503 and 504. The electron hole pairs generated by each of the electrons diffuses to generate charge with a distribution according to a two-dimensional Point Spread Function PSF2=(121)2. The numbers 1 and 2 in areas 501-504 thus indicate the relative contribution of an electron incident on the center pixel of the respective area to all surrounding pixels. FIG. 10-FIG. 12 schematically illustrate the operation of a two-dimensional method using Viterbi Detection according to a further embodiment of the invention. Along a row, the Viterbi Detector operates analogously to that described above for a one-dimensional sequence of data samples: the adjacent pixels on a row for the one-dimensional sequence of data samples which are processed sequentially, in a direction indicated with arrow 520. Hashed area 510 in FIG. 11 and FIG. 12 indicated the area where detection has been completed. A first electron 511 corresponding to 3×3 region 501, a second electron 512 corresponding to 3×3 region 502 and a third electron 513 corresponding to 3×3 region 503 have been detected. Preferably, the (modelled) contributions to the pixel signals in the corresponding 3×3 regions has been subtracted from the data samples in the 3×3 regions. Hereby, their contribution to the data samples used for further detection has been deleted. No further electrons are detected in the rest of area 510. The method has proceeded to decide on the value of pixel 531. Hereto, the Viterbi Detector analyses the trellis, its branch metrics and states for the sequence of pixels in area 530, extending over a path memory length L from the pixel indicated with 530-0 to the pixel indicated with 530-8. In an embodiment, the Viterbi Detector calculates the branch metric for a state using a predetermined area around a respective pixel of pixels 530-0 to 530-8. The size of the predetermined are corresponds preferably substantially to the PSF. Hereby, all contributions of electrons at positions in the predetermined area to the respective pixel are summed and model the total pixel signal according to the state. The Viterbi Detector may e.g. use the plurality of states shown in FIG. 14 or FIG. 15. In the embodiment described with reference to FIG. 12, the Viterbi Detector operates row-wise, i.e. the Viterbi Detection is applied to sequences of pixel signals per row of pixels of the two-dimensional array. In another embodiment, the Viterbi Detector operates column-wise, i.e., the Viterbi Detection is applied to sequences of pixel signals per column of pixels of the two-dimensional array. FIG. 14 schematically shows a plurality 560 of states used in a first further embodiment using a PSF=(121)2, indicating the configuration of electrons incident on a 3×3 area of the sensor. FIG. 15 schematically shows another plurality 580 of states used in a second further embodiment. It is noted that the hashed area, corresponding to the pixels for which the Viterbi Detector has already taken a decision, may comprise an electron, but as its contribution has already been subtracted in the hashed as well as the non-hashed area (see above), such presence can be disregarded without any loss of generality. It will be understood that, when such contributions have not been subtracted while an electron has been detected, its contribution to the center pixel of the state will also have to be considered. However, as the decision on its presence has already been taken, it is not necessary to also consider the hashed positions as variable in the state definition. FIG. 14 relates to a first further embodiment wherein a PSF is used on a 3×3 area. The PSF is shown in dashed form with reference number 569. The plurality of states 560 of FIG. 14 comprises one state 561 without any electrons; six different states 562 with one electron, on six different positions; six states 563 with two electrons on a single position within a state (or one double energy electron, cf. the first and second embodiment of the one-dimensional examples given above) but different between states; and, optionally, fifteen different states 564 with two electrons at different positions. FIG. 15 relates to a second further embodiment wherein the same PSF=(121)2 is used, but the states are defined based on a cross-shaped area of 1+3+1 pixels. The PSF is shown in dashed form with reference number 579. The plurality of states 580 of FIG. 15 comprises one state 571 without any electrons; four different states 582 with one electron, on four different positions; four states 584 with two electrons on a single position within a state (or one double energy electron, cf. the first and second embodiment of the one-dimensional examples given above) but different between states; and, optionally, six different states 574 with two electrons at different positions. A Viterbi Decoder may use the states of FIG. 14 or FIG. 15 depending on the dose, allowed or required computational complexity and memory requirements etc. It will be appreciated that, similarly to the third embodiment described with reference to FIG. 9, the Viterbi Decoder may also for the two-dimensional PSF, employ a plurality of iterations using a different multiplicity of electrons, or a different energy bin, per iteration. FIG. 16-FIG. 17 schematically illustrate the operation of a two-dimensional method using Viterbi Detection according to again a further embodiment of the invention, similarly to the embodiments of FIG. 10-FIG. 15, but with a wider Point Spread Function. FIG. 16 schematically shows a two-dimensional semiconductor sensor of a plurality of pixels arranged in a matrix 600, organized in a plurality of columns (of which 15 are shown; not numbered) and a plurality of rows of which rows numbered R0-R12 are shown. Four electrons are incident on the sensor, resulting in four regions on 5×5 pixels, denoted by 601, 602, 603 and 604. The electron hole pairs generated by each of the electrons diffuses to generate charge with a distribution according to a two-dimensional Point Spread Function PSF3=(13531)2. This PSF closely resembles the actual diffusion in an exemplary CMOS sensor having 4 k×4 k pixels of approximately 15 μm×15 μm size and a thickness of its active layer of 15 μm. Hashed area 610 indicates the area where detection has been completed. Three electrons 611, 612, 613 have already been detected. The method has proceeded to decide on the value of pixel 631. Hereto, the Viterbi Detector analyses the trellis, its branch metrics and states for the sequence of pixels in area 630, extending over a path memory length L from the pixel indicated with 630-0 to the pixel indicated with 630-8. In an embodiment, the Viterbi Detector calculates the branch metric for a state using a predetermined area around a respective pixel of pixels 630-0 to 630-8. The size of the predetermined are corresponds preferably substantially to the PSF. Hereby, all contributions of electrons at positions in the predetermined area to the respective pixel are summed and model the total pixel signal according to the state. The Viterbi Detector may e.g. use one of the embodiments of the plurality of states shown in FIG. 17. The numbers 1, 3 and 5 in area 604 indicate the relative contribution of an electron incident on the center pixel of area 604 to all surrounding pixels. FIG. 17 schematically three different embodiments defining the states of the Viterbi Detector, wherein question marks indicate the positions within an area around a pixel of the sequence of pixels used to determine the branch metrics upon which an electron may be incident. As in FIG. 14, the hashed area corresponds to the pixels for which the Viterbi Detector has already taken a decision (when scanning a previous row or earlier on the same row). The number of states increases with the total number of allowable electrons and with the number of allowable positions for an electron. A larger number of allowable electrons and/or a larger number of positions may however be preferred with increasing dose. Embodiment 661 schematically indicates states having one, or in further embodiments more than one, of fifteen different positions which may have zero, one or a plurality of electrons. Embodiment 662 schematically indicates states having one, or in further embodiments more than one, of thirteen different positions which may have zero, one or a plurality of electrons. Embodiment 663 schematically indicates states having one, or in further embodiments more than one, of nine different positions which may have zero, one or a plurality of electrons. FIG. 18A and FIG. 18B schematically illustrates frequency of occurrence of a signal level from a pixel when one electron is incident on the pixel of a typical semiconductor sensor. Signal level is increasing along the horizontal axis, relative frequency of occurrence is increasing along the vertical axis. Curve 702 indicates the frequency of occurrence of the signal level. Curve 702 is approximately a Landau-distribution. Curve 702 shows a clear peak at a signal level indicated with Epeak. Arrow 704 indicates the dark current noise of the semiconductor sensor. FIG. 18A and FIG. 18B also shows examples of reference levels used to define an energy bin or a multiplicity of electrons as used in the internal states. Below, we will refer to reference levels defining the ‘number of electrons’ on a single pixel in a state (cf. the first embodiment), but the reader shall understand that this may also be interpreted as ‘energy bin’ of an electron in a state (cf. the second embodiment). In FIG. 18A, the reference level E1, associated with the number of electrons in a single pixel of a state being one, is chosen to correspond to the peak Epeak of the curve 702. It may however also be observed that the noise level extends well beyond halve the peak value. Using such choice for the reference level may thus have a risk of a relatively high ‘false positives’ where an electron is detected without actual an electron being incident on the detector. However, such choice may advantageously have relatively few little ‘false negatives’ where no electron is detected despite it being present. Reference levels E2, E3, E4 and E5, associated respectively with two, three, four and five electrons on one pixel, are selected and used to define states accordingly, in order to also detect electrons with a higher pixel signal, i.e. a larger energy deposit, with a sufficient reliability. Thus, in the embodiment of FIG. 18A,En=n*Epeak,n=1, . . . , N, with N preferably being 4, 5 or larger. In FIG. 18B, the reference level E1, associated with the number of electrons in a single pixel of a state being one, is chosen to correspond to twice the value of the peak Epeak of the curve 702, Further reference levels are chosen as multiples of E1, orEn=n*2*Epeak,n=1, . . . , N, with N preferably being 2 or 3. Using such choice for the reference levels may reduce the number of states significantly, but may have the risk that several electrons with only a low deposited energy are not detected as electrons, but being overseen as noise. It will be understood that other choices of reference levels may be used. The choice of reference levels and their number may e.g. be selected based on available resources for the Viterbi Detection, such as computational power, available memory size and available computation time per image, or e.g. on required image quality of the reconstructed image FIG. 19 shows a result of a simulation of a method according to the invention. The method used in the simulation uses a dose of 0.01, i.e. with an average number of 1 electron on 100 pixels, a PSF=(13531)2, 15 positions per state (cf. 661 in FIG. 17), maximum 2 electrons per state, with the reference level for a single electron being selected as twice the peak value of curve 702. The simulation uses a CMOS semiconductor sensor used in a TEM and electrons of typical energy when analysing a biological sample at such low dose. FIG. 19 shows the Modulation Transfer Function, which is a measure of the resolution obtained. The horizontal axis corresponds to a frequency of a repeating pattern, and extends from zero to the Nyquist frequency. The vertical axis is the relative output level from such repeating patterns. It is observed that the MTF 900 of the detector itself, i.e. of the raw data signals, is already smaller than 0.5 at half the Nyquist frequency. The output 902 of the Viterbi Detector however remains above 0.8 until the Nyquist frequency. The Viterbi Detector thus allows to substantially recover the full pixel resolution of the sensor, which is indicated by line 904. FIG. 20 schematically shows an overview of a method according to an embodiment. The method 1 shown in FIG. 20 comprises: producing 10 a beam of particles, placing 20 an object 111 to be imaged on an object plane, illuminating 30 the object plane with the beam of particles, forming 40 an image of the object plane by imaging particles transmitted through the object on an image plane, and detecting 50 the image with the detector comprising the semiconductor sensor and providing a plurality of pixel signals from the respective pixels of the array in response to the particles incident on the detector, receiving 60 the plurality of pixel signals by a Viterbi Detector, and determining 70 a reconstructed image from using Viterbi Detection on the plurality of pixel signals by the Viterbi Detector, the Viterbi Detection using a plurality of different states corresponding to a plurality of configurations of particles incident on the detector, and at least two states of the plurality of different states corresponding to a same, non-zero multiplicity of incident particles on a single pixel of the plurality of pixel signals. The determining 70 may be performed according to any one of the embodiments described above, to any useful combination of two or more of the embodiments described above or to a modification of any one of the embodiments or their combination. FIG. 21 schematically illustrates a further embodiment. In the embodiment of FIG. 21, the method comprises receiving 61a first plurality of pixel signals from respective pixels of the array in response to particles incident on the detector upon detecting a first image of the object and determining 71a first reconstructed image from using the Viterbi Detection on the first plurality of pixel signals. The Viterbi Detection may be performed according to any of the embodiments described above, The method further comprises receiving 62 a second plurality of pixel signals from the respective pixels of the array in response to particles incident on the detector upon detecting a second image of the object and determining 72 a second reconstructed image from using the Viterbi Detection on the second plurality of pixel signals. As indicated with dashed lines, the method may further comprise receiving 63 at least one further plurality of pixel signals from the respective pixels of the array in response to particles incident on the detector upon detecting at least one respective further image of the object and determining 73 at least one further reconstructed image from using the Viterbi Detection on the respective further plurality of pixel signals. The method then combines 80 the first reconstructed image, the second reconstructed image and, if appropriate, the at least one further reconstructed images to form the reconstructed image. FIG. 22 shows a computer readable medium 500 comprising a computer program 1020, the computer program 1020 comprising instructions for causing a processor system to perform a method according to an embodiment. The computer program 1020 may be embodied on the computer readable medium 1000 as physical marks or by means of magnetization of the computer readable medium 1000. However, any other suitable embodiment is conceivable as well. Furthermore, it will be appreciated that, although the computer readable medium 1000 is shown in FIG. 22 as an optical disc, the computer readable medium 1000 may be any suitable computer readable medium, such as a hard disk, solid state memory, flash memory, etc., and may be non-recordable or recordable. It will be appreciated that the invention also applies to computer programs, particularly computer programs on or in a carrier, adapted to put the invention into practice. The program may be in the form of a source code, an object code, a code intermediate source and an object code such as in a partially compiled form, or in any other form suitable for use in the implementation of the method according to the invention. It will also be appreciated that such a program may have many different architectural designs. For example, a program code implementing the functionality of the method or system according to the invention may be sub-divided into one or more sub-routines. Many different ways of distributing the functionality among these sub-routines will be apparent to the skilled person. The sub-routines may be stored together in one executable file to form a self-contained program. Such an executable file may comprise computer-executable instructions, for example, processor instructions and/or interpreter instructions (e.g. Java interpreter instructions). Alternatively, one or more or all of the sub-routines may be stored in at least one external library file and linked with a main program either statically or dynamically, e.g. at run-time. The main program contains at least one call to at least one of the sub-routines. The sub-routines may also comprise function calls to each other. An embodiment relating to a computer program product comprises computer-executable instructions corresponding to each processing step of at least one of the methods set forth herein. These instructions may be sub-divided into sub-routines and/or stored in one or more files that may be linked statically or dynamically. Another embodiment relating to a computer program product comprises computer-executable instructions corresponding to each means of at least one of the systems and/or products set forth herein. These instructions may be sub-divided into sub-routines and/or stored in one or more files that may be linked statically or dynamically. The carrier of a computer program may be any entity or device capable of carrying the program. For example, the carrier may include a storage medium, such as a ROM, for example, a CD ROM or a semiconductor ROM, or a magnetic recording medium, for example, a hard disk. Furthermore, the carrier may be a transmissible carrier such as an electric or optical signal, which may be conveyed via electric or optical cable or by radio or other means. When the program is embodied in such a signal, the carrier may be constituted by such a cable or other device or means. Alternatively, the carrier may be an integrated circuit in which the program is embedded, the integrated circuit being adapted to perform, or used in the performance of, the relevant method. In this document, the term “particles” does not include photons, but refers to particles with a rest energy different from zero. The term “particles” may in particular relate to electrons. The particle-optical apparatus may e.g. comprise a TEM. It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. Use of the verb “comprise” and its conjugations does not exclude the presence of elements or steps other than those stated in a claim. The article “a” or “an” preceding an element does not exclude the presence of a plurality of such elements. The invention may be implemented by means of hardware comprising several distinct elements, and by means of a suitably programmed computer. In the device claim enumerating several means, several of these means may be embodied by one and the same item of hardware. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions, and alterations can be made to the embodiments described herein without departing from the spirit and scope of the invention as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure of the present invention, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present invention. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps. |
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claims | 1. A package including components from a decommissioned and dismantled nuclear reactor, the package comprising:a vessel encapsulated in a container; anda plurality of components encapsulated in the vessel, wherein the components are configured to define one or more cutting zones in the vessel for cutting the package into a plurality of sections. 2. The package of claim 1, wherein each of the one or more cutting zones is defined between at least first and second predefined sections in the vessel. 3. The package of claim 1, wherein the components are entirely contained within at least one of the first and second predefined sections. 4. The package of claim 1, wherein at least some of the components are repackaged internal components from the decommissioned and dismantled nuclear reactor. 5. The package of claim 4, wherein the repackaged internal components are repositioned the decommissioned and dismantled nuclear reactor from their original positioning to define a cutting zone in the vessel. 6. The package of claim 1, wherein the components include other irradiated components from the nuclear reactor. 7. The package of claim 1, wherein at least some of the components are internal components from the decommissioned and dismantled nuclear reactor in their original positioning. 8. The package of claim 1, wherein each of the one or more cutting zones includes first and second dividers spaced a predetermined distance from one another to define a space therebetween. 9. The package of claim 8, further comprising a cutting material disposed between the first and second dividers. 10. The package of claim 8, wherein each of the one or more cutting zones includes a prefabricated divider assembly including first and second dividers. 11. The package of claim 10, wherein the first and second dividers are made from a structural material. 12. The package of claim 10, wherein the first and second dividers are attached to the interior surface of the vessel. 13. The package of claim 10, wherein the first and second dividers include one or more pathways for encapsulation material passage. 14. The package of claim 1, wherein each of the one or more cutting zones is a single divider. 15. The package of claim 1, wherein the container includes exterior circumferential grooves to align with the one or more cutting zones in the vessel. 16. The package of claim 1, wherein at least a portion of the cladding of the vessel interior is removed prior to repackaging near or at the one or more cutting zones. 17. The package of claim 1, wherein the vessel is encapsulated in a first material. 18. The package of claim 17, wherein the plurality of components are encapsulated in a second material, wherein the second material is the same or different from the first material. 19. The package of claim 1, wherein each of the one or more cutting zones is defined between at least first, second, and third predefined sections of the vessel. 20. A plurality of sub-packages including components from a decommissioned and dismantled nuclear reactor, the sub-package comprising:at least a portion of a vessel encapsulated in a container; andat least a portion of a plurality of components encapsulated in the vessel; andend caps affixed at the ends of each of the sub-packages. 21. The plurality of sub-packages of claim 20, wherein the end caps have a skirt. |
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050733346 | abstract | A self-actuated nuclear reactor shutdown system includes a control rod, a temperature sensitive electromagnet disposed above the control rod for causing the control rod to latch thereto and unlatch therefrom, and a control rod insertion portion around which a plurality of wrapper tubes each accommodating a fuel assembly are arranged. The present invention is characterized in that the upper part of the wrapper tube or an extension tube connected to the upper end of the wrapper tube is made of a temperature-sensitive magnetic material having a characteristic by which the saturation flux density thereof will be reduced at the time of an extraordinary rise in the temperature of a coolant flowing through the fuel assembly. The temperature sensitive magnetic material constitutes a part of a magnetic circuit of the electromagnet. When the coolant at a high temperature raises the temperature of the temperature-sensitive magnetic material, the magnetic circuit of the electromagnet is broken, and the control rod is released from the electromagnet and drops into the reactor core to shut down the reactor. |
abstract | An apparatus for radiation image recording includes a radiation receiver to which radiation can be applied and which converts the incident radiation to an electrical charge which represents a measure of the incident radiation and which can be read line-by-line via a reading device. It further includes a scattered beam grid, which is associated with the radiation receiver and which includes absorption elements which run in straight lines. The absorption elements are arranged at an angle to the line-by-line reading direction. |
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045267456 | abstract | A fuel assembly for a boiling water reactor is provided with at least one vertical water channel (4, 5) for a by-pass flow through the fuel assembly. At its lower end the channel is connected to a radial tube (10) which opens out at the outer side surface of the fuel assembly. Below the radial tube, the wall of the assembly base (2) is provided with a through-hole (12). |
claims | 1. A pre-subject filter assembly for a CT imaging system having a detector assembly and a high frequency electromagnetic energy projection source configured to rotate about a subject during an imaging session, the filter assembly comprising:a beam shaping filter having a body defining multiple filtering profiles, the filter rotatable about an axis of rotation that extends through the body;wherein the beam shaping filter includes a first end and a second end, wherein the body extends between the first end and the second end and comprises a plurality of depressions to define a plurality of body diameters defining the multiple filtering profiles; anda controller to cause rotation of the beam shaping filter about the axis of rotation during an imaging session to dynamically filter high frequency electromagnetic energy projected toward the subject as a function of view angle and independent of voltage applied to the high frequency electromagnetic energy projection source. 2. The pre-subject filter assembly of claim 1 wherein the beam shaping filter has at least two filtering profiles defined orthogonally from one another, wherein the plurality of depressions comprise at least two depressions, wherein the at least two depressions define at least two body diameters defining the at least two filtering profiles defined orthogonally from one another, wherein the at least two depressions are positioned orthogonally from one another. 3. The pre-subject filter assembly of claim 2 wherein a first filtering profile of the at least two filtering profiles defines a maximum filtering profile and a second filtering profile of the at least two filtering profiles defines a minimum filtering profile, and wherein each filtering profile is defined by at least one of a geometry or a composition of the beam shaping filter. 4. The pre-subject filter assembly of claim 3 wherein the beam shaping filter includes a varying filter profile continuum connecting the first filtering profile to the second filtering profile. 5. The pre-subject filter assembly of claim 1 further comprising a pair of end caps, each of which is connected to a respective one of the first and second ends of the beam shaping filter, one end cap having a drive shaft connectable to a motor and the other end cap having a drive shaft connectable to a bearing assembly. 6. The pre-subject filter assembly of claim 1 wherein the beam shaping filter includes a bowtie filter. 7. The pre-subject filter assembly of claim 1 wherein the beam shaping filter includes a first filtering profile that has a maximum point and a minimum point and a second filtering profile has a maximum point and a minimum point, wherein a slope between the maximum point and the minimum point of the first filtering profile is larger than a slope between the maximum point and the minimum point of the second filtering profile, and wherein the controller is further configured to present the first filtering profile in a path of high frequency electromagnetic energy when the subject has a first cross-section and to present the second filtering profile in a path of high frequency electromagnetic energy when the subject has a second cross-section, the first cross-section being narrower and thicker than the second cross-section. 8. The pre-subject filter assembly of claim 1 wherein the plurality of depressions comprises a first depression and a second depression that are formed in the body so as to be acutely or obtusely defined with respect to one another and to define first and second body diameters, of the plurality of body diameters, defining first and second filtering profiles, of the multiple filtering profiles. 9. A CT system comprising:a rotatable gantry having an opening to receive a subject to be scanned;a movable high frequency electromagnetic energy projection source configured to project a high frequency electromagnetic energy beam toward the subject at least two view angles;a movable pre-subject filter having a beam shaping filter that is rotatable about itself relative to an axis of rotation extending through the beam shaping filter during an imaging session, the beam shaping filter having a first end and a second end, the first end having a motor assembly connected thereto and the second end having a bearing assembly connected thereto, such that the motor assembly and bearing assembly, when commanded, cause the beam shaping filter, which has multiple filtering profiles, to rotate about the axis of rotation that is defined by a length of the beam shaping filter that is generally perpendicular to the energy beam that is projected toward the subject;wherein the beam shaping filter includes a body that extends between the first end and the second end and comprises a plurality of depressions to define a plurality of body diameters defining the multiple filtering profiles;a scintillator array having a plurality of scintillator cells wherein each cell is configured to detect high frequency electromagnetic energy passing through the subject;a photodiode array optically coupled to the scintillator array and comprising a plurality of photodiodes configured to detect light output from a corresponding scintillator cell;a data acquisition system (DAS) connected to the photodiode array and configured to receive the photodiode outputs;an image reconstructor connected to the DAS and configured to reconstruct an image of the subject from the photodiode outputs received by the DAS; anda computer programmed to rotate the beam shaping filter about the axis of rotation such that at a first view angle a first filtering profile filters the high frequency electromagnetic energy beam and at a second view angle a second filtering profile filters the high frequency electromagnetic energy beam. 10. The CT system of claim 9 wherein the beam shaping filter includes a bowtie filter designed to reduce high frequency electromagnetic energy dosage to the subject as a function of projection source view angle. 11. The CT system of claim 9 wherein the first filtering profile has a maximum point and a minimum point and the second filtering profile has a maximum point and a minimum point, and wherein a slope between the maximum point and the minimum point of the first filtering profile is larger than that between the maximum point and the minimum point of the second filtering profile. 12. The CT system of claim 11 wherein the computer is further programmed to present the first filtering profile when the high frequency electromagnetic energy source is projecting high frequency electromagnetic energy toward a thickest cross-section of the subject. 13. The CT system of claim 12 wherein the computer is further programmed to present the second filtering profile when the high frequency electromagnetic energy source is projecting high frequency electromagnetic energy toward a thinnest cross-section of the subject. 14. The CT system of claim 9 wherein the first view angle is orthogonal of the second view angle, wherein the plurality of depressions comprise first and second depressions, wherein the first and second depressions define first and second body diameters defining the first and second filtering profiles, wherein the first and second body diameters define the first and second filtering profiles orthogonally from one another, wherein the first and second depressions are positioned orthogonally from one another. 15. The CT system of claim 9 incorporated into at least one of a medical imaging system and a parcel inspection apparatus. 16. A method of reducing x-ray exposure during CT data acquisition comprising the steps of:positioning a subject to be scanned in a scanning bay;positioning a first profile of a multi-profile, beam shaping filter between an x-ray source and the subject when the x-ray source is projecting x-rays at a first view angle, wherein the multi-profile, beam shaping filter includes a first end, a second end, and a body that extends between the first end and the second end and comprises a plurality of depressions to define a plurality of body diameters defining multiple filtering profiles that comprise the first profile and a second profile;projecting x-rays in an x-ray beam toward the subject from the x-ray source at the first view angle;rotating the x-ray source to a second view angle;positioning and rotating the multi-profile, beam shaping filter about an axis of rotation that extends through a length of the multi-profile, beam shaping filter and perpendicular to the x-ray beam such that the second profile of the multi-profile, beam shaping filter is positioned between the x-ray source and the subject when the x-ray source is projecting x-rays at the second view angle; andprojecting x-rays in an x-ray beam toward the subject from the x-ray source at the second view angle. 17. The method of claim 16 wherein the first profile is orthogonal to the second profile, wherein the plurality of depressions comprise first and second depressions, wherein the first and second depressions define first and second body diameters defining the first and second profiles, wherein the first and second body diameters define the first and second profiles orthogonally from one another, wherein the first and second depressions are positioned orthogonally from one another. 18. The method of claim 16 wherein the second profile has a rate change between a maximum filtering point and a minimum filtering point that is less than that between a maximum filtering point and a minimum filtering point of the first profile. 19. The method of claim 18 wherein the first view angle corresponds to a position generally adjacent a side of the subject and the second view angle corresponds to a position generally above the subject. 20. The method of claim 16 further comprising the step of rotating the multi-profile, beam shaping filter about the axis of rotation synchronously with rotation of the x-ray source around the subject. |
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description | This application claims priority under 35 U.S.C. §119(e) to U.S. provisional patent application 60/840,899 filed on Aug. 28, 2006, which application is hereby incorporated by reference in its entirety. 1. Field of the Invention The present invention generally relates to lithography, more specifically lithography for semiconductor processing. More specifically, this invention relates to a method for measuring contamination of a lithographical element. This invention also relates to a system for measuring contamination of a lithographical element. 2. Description of the Related Technology Optical lithography nowadays uses wavelengths of 248 nm or 193 nm. With 193 nm immersion lithography integrated circuit (IC) manufacturing is possible down to 45 nm or even down to 32 nm node. However for printing in sub-32 nm half pitch node, this wavelength is probably not satisfactory due to theoretical limitations, unless double patterning is used. Instead of using wavelengths of 193 nm, a more advanced technology has been introduced, also referred to as extreme ultraviolet lithography (EUV lithography), which uses wavelengths of 10 nm to 14 nm, with a typical value of 13.5 nm. This technique was previously also known as soft X-ray lithography more specifically using wavelengths in the range of about 2 nm to 50 nm. In optical lithography at some wavelengths in the deep ultra violet (DUV) range, the electromagnetic radiation is transmitted by most materials, including glass used for conventional lenses and masks. At short wavelengths however, e.g. for extreme ultraviolet lithography and soft X-ray lithography, the electromagnetic radiation is absorbed by most materials, including glass used for conventional lenses and masks. Therefore a completely different tool is necessary for performing EUV lithography compared to conventional optical lithography. Instead of using lenses, such an imaging system presently relies on all-reflective optics and therefore is composed of reflective optical elements, also referred to as catoptric elements, for example mirrors. These reflective optical elements, e.g. mirrors preferably are coated with multilayer structures designed to have a high reflectivity (up to 70%) at the 13.5 nm wavelength. Furthermore, since air will also absorb EUV light, a vacuum environment is necessary. Although EUV lithography is considered applicable using wavelengths less than 32 nm, still a lot of problems need to be overcome to reach a mature technology. As presented in a publication of K. R. Dean et al in Proc. of SPIE 6153E, p. 1-9 (2006), one of these problems is contamination of the optics by chemical components, also referred to as “contamination”, which components are usually gaseous components originating from outgassing of the resist. This resist outgassing occurs due to the EUV irradiation of the EUV resist. It was noticed that at the regions where radiation falls on the EUV optics, the components contamination that outgases during the exposure may contaminate the EUV optics and as a consequence diminishes both the reflectivity of the reticle as well as the reflectivity of the imaging optics. As a consequence the lifetime of the EUV optics is reduced seriously due to contamination. Following the International Technology Roadmap for Semiconductors (ITRS) the organic material outgassing rate for 2 minutes under the lens should be lower than 5e13 molecules/cm2-sec. In order to reduce the resist outgassing rate, metrology tools are necessary which are able to measure the amount of resist outgassing for certain resists. One possibility for screening resist outgassing is also described in a publication of K. R. Dean et al in Proc. of SPIE 6153E, p. 1-9 (2006). An outgassing chamber is built on a synchrotron beam line. Together with the wafers, a Si3N4 witness plate is put in the chamber and exposed to EUV irradiation. This witness plate is then analyzed with electron spectroscopy for chemical analysis (ESCA) to find evidence of the contamination build up. The contaminants are collected in thermal desorption (TD) tubes. The contaminants in these TD tubes are analyzed by gas chromatography/mass spectroscopy (GC/MS) for chemical analysis. US 2003/0011763 describes a projection exposure apparatus useful for projection exposure of a pattern defined on a mask onto a substrate in the manufacture of a semiconductor device. The apparatus comprises a cleaning device for cleaning an optical member. Contamination of a substrate-opposed surface of an optical member at the time of pattern transfer can be reduced by, prior to pattern transfer, removing the contaminants caused by the previous pattern transfer by a cleaning operation. In embodiments of US 2003/0011763, the cleaning operation may be performed only when a numerical value for a contamination level which is determined based on a difference between a predetermined reflectance and an actually determined reflectance of the optical member is out of a certain permissible range. The predetermined reflectance is determined immediately after the apparatus is manufactured. US 2005/0083515 describes a method for evaluating reflection uniformity of an optical component having EUV reflective surface for use in EUV lithography. The method may be used to determine coating and substrate induced reflectivity losses of a substrate. According to embodiments of US 2005/0083515 a reflectivity map of a test piece is compared to a reference piece of identical design that has been independently characterized. Other techniques and systems still are required to analyze resist outgassing, with a special interest for in-situ measurement of the contamination. Certain inventive aspects provide good methods and systems for characterizing contamination of a lithographical element. It is an advantage of embodiments of the present invention to provide methods and systems for directly measuring a parameter of a contaminated lithographical element, such as a contaminated lithographical optical element, e.g. measuring reflectivity or transmissivity of the contaminated lithographical element which may be a reflective optical element, e.g. a mirror, or such as a contaminated reticle. According to some embodiments of the present invention, a method for measuring the contamination of a lithographical element compares a parameter of a contaminated lithographical element with a reference parameter relevant for this lithographical element in uncontaminated condition. Directly measuring thereby may be measuring a parameter on the lithographical element itself. According to some embodiments of the present invention, the parameter, e.g. reflectivity, is measured in the process chamber, which means that ex-situ reflectance measurements are generally unnecessary. It is an advantage of such embodiments that parameters of the process chamber, such as e.g. the irradiation source used, can be directly taking into account. According to some embodiments of the present invention, the parameter, e.g. reflectivity, is measured in the process chamber of a metrology system. According to some embodiments of the present invention, the parameter, e.g. reflectivity, is measured in the process chamber of a lithographic process system. The method avoids to a large extent manipulation of the lithographical elements, hence reduces the risk on variation of the measured value due to manipulation of the contaminated lithographical elements. The method avoids the use of vulnerable reference optical elements such as reference mirrors. The method allows an in-situ measurement of relevant optical parameters of the contaminated element, and reduces the necessity of expensive and time consuming test setups and recalibration procedures. It is an advantage of embodiments of the present invention to provide a system for performing the method according to certain embodiments. According to some embodiments of the present invention, the system may be a metrology system or a lithographic process system. According to a first aspect of the present invention, a method is provided for measuring contamination of a lithographical element, the method comprising: providing a first lithographical element in a process chamber, providing a second lithographical element in the process chamber, covering part of the first lithographical element, providing a reference region on the first lithographical element being the covered part of the first lithographical element and a test region on the first lithographical element being the uncovered part of the first lithographical element; providing a contaminant in the process chamber, directing an exposure beam on the test region of the first lithographical element and the second lithographical element whereby at least one of the lithographical elements gets contaminated by the contaminant, measuring the level of contamination of the at least one contaminated lithographical element in the process chamber. The method preferably comprises uncovering the covered part of the first lithographical element, providing an uncovered reference region. The measuring the level of contamination preferably comprises optically measuring the level of contamination. It is an advantage of certain embodiments that optical measurements are used on the same object, as this allows to work with the same parameters/conditions of that object, therefore providing more accurate parameters and therefore more accurate determination of the contamination level. By using a test region and a reference region on the same object, a more precise correlation can be made. It is an advantage of embodiments of the present invention that contamination can be measured in the process system. It is an advantage of embodiments of the present invention that contamination can be measured using the same light beam as exposure beam as well as optical measurement beam. It is an advantage of embodiments of the present invention that contamination is measured by determining optical properties of the contaminated component alone, it is that no separate element is required. According to some embodiments of the present invention, the process of covering part of the first lithographical element may comprise the provision of a shield to cover part of the first lithographical element and providing a hard contact, i.e. direct contact, between the shield and at least part of the first lithographical element. According to other embodiments of the present invention, the process of covering part of the first lithographical element may comprise the provision of a shield to cover part of the first lithographical element and providing a soft contact between the shield and at least part of the first lithographical element. Optically measuring the contamination level may comprise measuring an optical parameter on a test region and a reference region. According to some embodiments of the present invention, the process of covering part of the first lithographical element may comprise the provision of a shield for shadowing at least part of the first lithographical element. According to some embodiments of the present invention, resist may be provided in the process chamber, and the contaminant may be provided in the process chamber by outgassing of the resist. The first lithographical element may be a lithographical optical element. According to some embodiments of the present invention, the first lithographical element may be a mirror or a lens. According to some embodiments of the present invention, the method further may comprise removing the contaminant from the process chamber before measuring the level of contamination of the at least one contaminated lithographical element in the process chamber. Removing the contaminant may comprise removing the contamination source. Removing the contaminant furthermore may comprise reducing the remaining contamination present in gaseous form in the chamber. Removing the contaminant may comprise removing a lithographic element comprising a resist layer on top and/or removing the outgassing gas outgassed by the resist layer from the process chamber. Removing the contaminant also may be removing contamination gasses previously introduced in the chamber. Such a removal may e.g. be performed by purging the chamber with a purge gas or by pumping down the chamber to a predetermined level. Optically measuring the contamination level may comprise measuring an optical parameter on a test region and the uncovered reference region. According to some embodiments of the present invention, the method further may comprise cleaning the process chamber before measuring the level of contamination of the at least one contaminated lithographical element in the process chamber. According to some embodiments of the present invention, the at least one of the contaminated lithographical element is the first lithographic element. According to some embodiments of the present invention, the process of measuring the level of contamination of the at least one lithographical element in the process chamber may comprise measuring the level of contamination of the first lithographical element. According to some embodiments of the present invention, the process of measuring the level of contamination of the first lithographical element in the process chamber may comprise: measuring a value for a parameter at the uncovered reference region of the first lithographical element, being the reference value of the parameter, measuring a value for the parameter at the test region of the first lithographical element, being the test value of the parameter, determining, e.g. by calculation, the difference between the reference value and the test value. According to some embodiments of the present invention, the process of measuring the reference value of the parameter may comprise: redirecting the exposure beam via the reference region of the first lithographical element towards a sensor. Alternatively, different beams could be used for exposing the lithographic elements and for optically measuring. According to some embodiments of the present invention, the process of measuring the test value of the parameter may comprise: redirecting an exposure beam via the test region of the first lithographical element towards a sensor. According to some embodiments of the present invention, the second lithographical element may comprise the contaminant. According to some embodiments of the present invention, the second lithographical element may comprise resist, the resist comprising the contaminant. According to some embodiments of the present invention, the second lithographical element may be a lithographical optical element. Possibly the second lithographical element is a mask. According to some embodiments of the present invention, the providing of a contaminant in the process chamber may comprise providing gaseous compound in the chamber. According to some embodiments of the present invention, at least the second lithographical element may be contaminated by the contaminant in the process of redirecting an exposure beam via the test region of the first lithographic element towards the second lithographical element. According to some embodiments of the present invention, the process of measuring the level of contamination of the at least one lithographic element in the process chamber may comprise measuring the level of contamination of the at least second lithographical element in the process chamber. According to some embodiments of the present invention, the process of measuring the level of contamination of the at least second lithographical element may comprise: measuring a second element test value for the parameter at the test region of the second lithographical element by redirecting the exposure beam via the reference region of the first lithographical element towards the second lithographical element and further towards a sensor. According to some embodiments of the present invention, the process of measuring the second element test value further comprises: redirecting the exposure beam via the test region of the first lithographical element towards the second lithographical element towards a sensor. According to some embodiments of the present invention, the first lithographic element may be a mirror. According to some embodiments of the present invention, the parameter measured may be the reflectivity of the first lithographic element. The sensor may be a reflectivity sensor. According to some embodiments of the present invention, the first lithographic element may be a lens. According to some embodiments of the present invention, the parameter measured may be the transmissivity of the first lithographic element. The sensor may be a transmissivity sensor. According to some embodiments of the present invention, the sensor may comprise a diode. According to some embodiments of the present invention, the test region may comprise a plurality of test zones. The reference region may comprise a plurality of reference zones. According to a second aspect of the present invention, a system for measuring contamination of a lithographic element is provided, which system comprises: a process chamber, an inlet for introducing a contaminant. a first energy source for providing a first energy beam in the process chamber, the energy beam at least adapted to cause contamination of at least one of the lithographic elements by directly or indirectly exposing the at least one of the lithographic elements in the presence of the contaminant; an element for covering at least part of the first lithographic element for providing a reference region on the first lithographic element, whereby the element for covering is adapted such that the reference region is not contaminated when the first lithographic element is exposed by the first energy beam, and a sensor for measuring contamination. The system may comprise an element for introducing a first lithographic element into the process chamber and an element for introducing a second lithographic element into the process chamber. According to embodiments of the present invention, the first energy beam may be adapted for measuring a parameter of the at least one of the lithographic elements. According to embodiments of the present invention, the system further may comprise a second energy source for providing a second energy beam in the process chamber, the second energy beam is adapted for measuring a parameter of the at least one of the lithographic elements. According to embodiments of the present invention, the process chamber may be a vacuum process chamber. According to embodiments of the present invention, the first energy source may emit electromagnetic radiation in the extreme ultra-violet range. According to embodiments of the present invention, the sensor may be a reflectivity sensor or a transmissivity sensor. The sensor may be an optical sensor. According to embodiments of the present invention, the sensor may comprise a diode. Another inventive aspect also relates to a method for measuring in a process chamber contamination of a lithographical element from a lithographical system, the process chamber comprising at least a first lithographical element and a second lithographical element, the method comprising: providing a contaminant in the process chamber exposing a test region of the first lithographical element and the second lithographical element whereby at least one of the lithographical elements gets contaminated by the contaminant, leaving part of the at least one of the lithographical elements unexposed resulting in a reference region of the at least one contaminated lithographical element, and optically measuring the level of contamination of the at least one contaminated lithographical element in the process chamber by measuring an optical parameter on the test region and the reference region of the at least one contaminated lithographical element. Other features and characteristics of the method and corresponding system may be as set out in the other methods and systems described herein. In another inventive aspect, a system for measuring contamination of a lithographical element is disclosed. The system comprises means for accommodating a first lithographical element, a second lithographical element, and a contaminant. The system further comprises means for covering part of the first lithographical element, thus providing a reference region on the first lithographical element being the covered part of the first lithographical element and a test region on the first lithographical element being the uncovered part of the first lithographical element. The system further comprises means for directing an exposure beam via the test region of the first lithographical element towards the second lithographical element such that at least one of the lithographical elements gets contaminated by the contaminant. The system further comprises means for uncovering the covered part of the first lithographical element, thus providing an uncovered reference region. The system further comprises means for optically measuring the level of contamination of the at least one contaminated lithographical element in the process chamber. Different advantages of the proposed embodiments with respect to prior art may be obtained. In the prior art contamination measurements of a lithographical element, more specifically lithographic optics are done by collecting various contaminating chemical components and by analyzing these chemical components with a mass spectrometer or a similar analysis technique such as mentioned in a publication of K. R. Dean et al in Proc. of SPIE 6153E, p. 1-9 (2006). The contaminants are collected in thermal desorption (TD) tubes. The contaminants in these TD tubes are analyzed by gas chromatography/mass spectroscopy (GC/MS) for chemical analysis. This technique of collecting the contaminating chemical components is not repeatable, as the samples are destructed. The results hence suffer from relatively large statistical variation. The understanding of the impact of these contaminating components on the optical lithographical elements further requires complex calculations and simulations, thus introducing additional uncertainty and variation. With various embodiments of the present invention this disadvantage of chemical analysis techniques is at least partially overcome by directly measuring a parameter of the contaminated lithographical optical element itself, e.g. measuring reflectivity or transmissivity of the contaminated mirror, or e.g. measuring reflectivity or transmissivity of the contaminated reticle. The parameter, e.g. reflectivity, is measured in the process chamber, which means that ex-situ reflectance measurements are generally unnecessary. Generally a reflectance measurement, e.g. with a standard reflectometer, is conducted by monitoring source and sample simultaneously to obtain a value representing the reflection of the sample with regard to a reference. This approach requires a reference mirror to split the incident beam and may require the provision of an additional second detector. For measuring contamination of a lithographical element, the requirements are very stringent. A long term reflectivity change of about 1% is expected, which means that a repeatability of 0.1% or better is aimed for. The stability of the reference mirror, as used in general reflectance measurements, may be a serious problem, because it will become contaminated as well over time, although at a much slower rate, thus creating artifacts. Similarly, the fact that two detectors may be necessary, may create a problem. To avoid artifacts, complex recalibration procedures are needed, together with golden standards in terms of mirrors and detectors. With the embodiments of the present invention some or even all these problems and disadvantages of standard reflectometry measurements may be overcome. Only one detector may be used and the reference mirror is integrated on the sample, e.g. mirror or reticle, itself as the reference region. Further, in standard reflectometry, the use of a reference mirror is further complicated by the fact that mirrors with different composition and stack need to be tested. This means that different samples will require different reference mirrors, as well as different recalibration procedures. These disadvantages can be overcome by the embodiments of the present invention where different reference regions and different test regions on one sample (e.g. mirror) may be provided. Particular and preferred aspects of the invention are set out in the accompanying independent and dependent claims. Features from the dependent claims may be combined with features of the independent claims and with features of other dependent claims as appropriate and not merely as explicitly set out in the claims. Although there has been constant improvement, change and evolution of devices in this field, the present concepts are believed to represent substantial new and novel improvements, including departures from prior practices, resulting in the provision of more efficient, stable and reliable devices of this nature. The above and other characteristics, features and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention. This description is given for the sake of example only, without limiting the scope of the invention. The reference figures quoted below refer to the attached drawings. In the different figures, the same reference signs refer to the same or analogous elements. The present invention will be described with respect to particular embodiments and with reference to certain drawings but the invention is not limited thereto but only by the claims. The drawings described are only schematic and are non-limiting. In the drawings, the size of some of the elements may be exaggerated and not drawn on scale for illustrative purposes. The dimensions and the relative dimensions do not correspond to actual reductions to practice of the invention. Furthermore, the terms first, second, third and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequence, either temporally, spatially, in ranking or in any other manner. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other sequences than described or illustrated herein. Moreover, the terms top, over and the like in the description and the claims are used for descriptive purposes and not necessarily for describing relative positions. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other orientations than described or illustrated herein. It is to be noticed that the term “comprising”, used in the claims, should not be interpreted as being restricted to the means listed thereafter; it does not exclude other elements or steps. It is thus to be interpreted as specifying the presence of the stated features, integers, steps or components as referred to, but does not preclude the presence or addition of one or more other features, integers, steps or components, or groups thereof. Thus, the scope of the expression “a device comprising means A and B” should not be limited to devices consisting only of components A and B. It means that with respect to the present invention, the only relevant components of the device are A and B. Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment, but may. Furthermore, the particular features, structures or characteristics may be combined in any suitable manner, as would be apparent to one of ordinary skill in the art from this disclosure, in one or more embodiments. Similarly it should be appreciated that in the description of exemplary embodiments of the invention, various features of the invention are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the disclosure and aiding in the understanding of one or more of the various inventive aspects. This method of disclosure, however, is not to be interpreted as reflecting an intention that the claimed invention requires more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive aspects lie in less than all features of a single foregoing disclosed embodiment. Thus, the claims following the detailed description are hereby expressly incorporated into this detailed description, with each claim standing on its own as a separate embodiment of this invention. Furthermore, while some embodiments described herein include some but not other features included in other embodiments, combinations of features of different embodiments are meant to be within the scope of the invention, and form different embodiments, as would be understood by those in the art. For example, in the following claims, any of the claimed embodiments can be used in any combination. Furthermore, some of the embodiments are described herein as a method or combination of elements of a method that can be implemented by a processor of a computer system or by other means of carrying out the function. Thus, a processor with the necessary instructions for carrying out such a method or element of a method forms a means for carrying out the method or element of a method. Furthermore, an element described herein of an apparatus embodiment is an example of a means for carrying out the function performed by the element for the purpose of carrying out the invention. In the description provided herein, numerous specific details are set forth. However, it is understood that embodiments of the invention may be practiced without these specific details. In other instances, well-known methods, structures and techniques have not been shown in detail in order not to obscure an understanding of this description. The following terms are provided solely to aid in the understanding of the description. The term “outgassing” is to be understood as the release of gaseous contamination by facilities, equipment, or tools or components thereof in a clean room and/or in process chambers; the term also may be referred to as offgassing. With resist outgassing is meant that gases or vapors are released by the resist in a lithographic process over a period of time. With “shielding” is meant that a region of a lithographic element is prevented of being irradiated with a radiation, such that it will not be contaminated when being subjected to a contaminant and irradiation. A number of ways for shielding may be provided. Hard contact is to be understood as providing a contact between a shield or cover and a lithographic element substantially “no spacing” is in between the shield or cover and the lithographical element, i.e. the shield or cover and the lithographic element are in direct contact with each other. The contact may be air-tight, so that no gaseous contamination can reach the contacted area of the lithographic element, although the embodiments of the present invention are not limited thereto. Soft contact is to be understood as providing shielding by a shield on a lithographic element. Such shielding preferably is such that substantially no irradiation can reach the shielded area of the lithographic element or that the irradiation that can reach the shielded area is substantially reduced compared to when direct irradiation would be possible. For this purpose, the shield may be provided in proximity to the lithographic element. The latter may e.g. be at a distance less than about 1 mm. Such a reduction may be, e.g., a reduction with about 60%, more preferably with 80%, even more preferably with 95%, still more preferably with 99%. The shielding thus may be shadowing whereby the shield is positioned separately from the lithographic element but such that incident radiation is not passed through the shield, which shield throws a shadow on a region of the lithographic element which is thus prevented on being directly irradiated. The term “Extreme ultraviolet radiation” includes electromagnetic radiation in the wavelength range of about 31 nm to 1 nm. The term “X-ray radiation” typically includes electromagnetic radiation in the wavelength range of about 10 nm to 0.01 nm. The term “deep ultraviolet radiation” is typically electromagnetic radiation in the wavelength range of about 300 nm to 7 nm. The invention will now be described by a detailed description of several embodiments of the invention. It is clear that other embodiments of the invention can be configured according to the knowledge of persons skilled in the art without departing from the true spirit or technical teaching of the invention, the invention being limited only by the terms of the appended claims. The embodiments of the present invention are suitable for lithographic systems and methods using electromagnetic radiation with wavelengths having the same order of magnitude or being smaller than the reticle feature thickness. The latter typically includes extreme ultraviolet (EUV) radiation, deep ultraviolet and X-ray radiation. It is to be noticed that the invention is not limited thereto and that slight variations in wavelength range may occur. The embodiments of the present invention typically may be related to a lithographic metrology system. A lithographic metrology system is used typically for characterization and/or optimization of parameters in a lithographic process or in a lithographic process system. A lithographic process is typically performed in a lithographic process system, also often referred to as lithographic exposure tool. The embodiments of the present invention may also be related to a lithographic process system. The term “contaminant” as referred to in this application is used to define an object, a material or a substance which induces contamination. Contaminant may be for example—but not limited thereto—formed by or related to a solid or gaseous contaminant, e.g. originating from a photoresist. Contaminants also may be present in gaseous form in any other suitable way. Contamination may be introduced by the presence of foreign species, such as e.g. water vapor or hydrocarbons in the vacuum and/or e.g. either by resist outgassing, e.g. yet only hydrocarbons, or intentionally introduced components through the leak valve. Contamination also may refer to a reduction of reflectivity by adsorbed species, also referred to as reflectivity loss or absorbed contamination. When photoresist is exposed, resist outgassing occurs. Resist outgassing is caused by photo-products which outgas from the resist, when exposed. These outgassed components will condense on the exposure tool's optical elements degrading the optics of the lithographic system. Contamination of components may occur on the optical components and on other parts of the chamber, during exposure or at periods without exposure. Nevertheless, when exposure is performed, contamination on irradiated surfaces is significantly higher and in some embodiments of the present invention the main focus is on contamination of irradiated surfaces. Typically for advanced photolithography chemically amplified photoresists are used. These resists contain photoacid generators (PAGs) which outgas under EUV radiation under vacuum. In general a resist consists of a polymer backbone, a solvent, protection groups, quenchers and proprietary additives. The most common outgassing products are from the protective groups and decomposition products from the PAG. In EUV lithography, also contamination occurs due to the hydrocarbons from the outgassing components from the resist polymer itself during the EUV radiation in the vacuum environment. Possible resist outgassing components may be for example—but not limited thereto—isobutane, isobutene, acetone, tert-butyl-benzene, methylstyrene, hydronaphthalene, benzene and alike depending on the resist which is used. Another contaminant may also be any (inorganic or organic) compound which is added into the lithographic system, for example via a gas inlet, and which may induce contamination on the lithographic optics, e.g. from cleanroom air, e.g. filtered particles, usually not molecular contaminants; from cleanroom materials, e.g. floor covering, filters, sealing materials, tubing, wafer boxes, wafer carriers, adhesives and tapes used in mounting pellicles, as well as monomers and oligomers, e.g. caprolactam from Nylon vessels, silicones, siloxanes from sealing materials, additives like process enablers and stabilizers, plasticizers e.g. dioctyl phthalate, dibutul phthalate, cross-linking agents, diacetyl benzene, anti-oxidants like benzoquionones, fire retardants like organophosphates, tributylphosphate. A lithographic system (e.g. EUV tool, immersion tool, . . . ) is typically installed in a cleanroom environment and by introducing e.g. a wafer from this cleanroom environment into the lithographic system, the organic compounds present in this cleanroom environment may enter the lithographic system and form a source of contamination. The term “lithographic optical element” as referred to in this application is used to define an optical element, which is typically used in a lithographic process system. Depending on the wavelengths of the electromagnetic radiation used in the lithographic process, different optical elements are used. For example, in an EUV lithographic system, the optical elements presently need to be reflective since a wavelength of 13.5 nm is used in vacuum. At least four optical components are required for EUV lithographic exposure: a collector which captures as much radiation from the illumination source as possible, an illumination system which homogeneously illuminates the used field on the mask, the mask itself containing the pattern to be transferred to the wafer substrate, and imaging optics which demagnify the structures from the mask to the wafer. For EUV lithography, all these optics presently consist of reflective elements such as mirrors. Also the mask, also often referred to as reticle, is an optical element, more specifically being a reflective mirror. A reticle is typically a kind of mask used for a stepper or scanner, typically using reduction optics, such that the image on the reticle is magnified. A mask/reticle is a plate with a pattern of transparent and opaque areas used to create patterns on wafers. For EUV lithography, the mask/reticle starts out as a perfect EUV mirror, and the pattern is applied on the top surface, either as an absorbing layer, or through etching into the mirror to make some parts non-reflective. An EUV mirror (e.g. used in the illumination system) starts out as a curved but atomically flat surface, to which a special multilayered coating is applied. The coating is tuned to give peak reflectivity for just one wavelength of EUV light (e.g. at about 13.5 nm). Alternatively the lithographic optical element may be a lens as used in for example deep ultraviolet (DUV) lithography. DUV lithography uses longer wavelengths (e.g. about 248 nm, 193 nm, 157 nm, . . . ) compared to EUV lithography (e.g. about 13.5 nm). At these longer wavelengths light may be transmitted by conventional lenses. A first embodiment relates to a method for measuring contamination of a lithographic element. Typical processes performed in the method according to the embodiments of the present invention are shown in a flow diagram of an embodiment of a method for measuring contamination (100) in FIG. 1. The method for measuring contamination of a lithographic element comprises providing a first lithographical element in a process chamber (101), providing a second lithographical element in the process chamber (102), covering part of the first lithographical element (103) for providing a reference region on the first lithographic element being the covered part of the element and providing a test region being the uncovered part of the first lithographic element, providing a contaminant in the process chamber (104), directing an exposure beam via the test region of the first lithographical element towards the second lithographical element whereby at least one of the lithographical elements gets contaminated by the contaminant (105), measuring the level of contamination of the at least one contaminated lithographical element in the process chamber (106). The exposure beam also first may be directed on the second lithographical element and thereafter on the first lithographical element, in other words, the sequence in which the lithographical elements are illuminated may differ. The latter is especially the case when contamination is measured in a metrology tool, although it also may be applied in an actual lithographic processing tool. Referring to FIG. 2a, FIG. 2b and FIG. 2c each of these processes will now be described in more detail. In a first process of the method for measuring contamination in a lithographic system a first lithographical element is introduced into a process chamber (101). The process chamber may part of a lithographic metrology system or of a lithographic process system. The providing process also may refer to a situation wherein no active providing is required anymore, e.g. in a system wherein the first lithographical element is already present, such as for example a lithographic system wherein measurement facilities for performing the present method are provided but that is also used for effective lithographic processing. The provision of the first lithographical element therefore may be performed during set-up of the system or in prior actions. In other words, an active providing process may be optional. The first lithographical element (201) may be directly introduced from an atmospheric environment in the lithographic system (not shown in FIG. 2a). However in case of a lithographic system under vacuum, such as for example an EUV lithographic system, the lithographic system needs to be pumped down again to vacuum level after the introduction of the first lithographical element (201). Therefore, for introducing the first lithographical element (201), preferably a load-lock chamber (202) may be used. A load-lock chamber is an atmosphere (202a)-to-vacuum (202b) entry system for facilitating the transfer of objects in and out vacuum systems. For example, in an EUV lithographic system, the environment inside the EUV tool is under vacuum (202b). By using a load-lock chamber (202) the lithographic system can be kept under vacuum when introducing a first lithographical element from an atmospheric environment (202a) into the EUV tool. First the first lithographical element (201) is transferred from the atmospheric environment (202a) in the load-lock chamber (202). Next the load-lock chamber is pumped down to a pressure which is comparable to the pressure in the lithographic system, e.g. about 10−7 mbar. Next the first lithographical element (201) is transferred from the load-lock chamber (202) into the lithographic system, which is under the same or at least comparable pressure as the load lock (202b). In the lithographic system (202b) the first lithographical element may be positioned on a movable stage such that the first lithographical element is movable into the lithographic system. The first lithographical element may be movable as may be required for the process of comparing the level of contamination as will be explained further. This first lithographical element may be a lithographical optical element. The first lithographical element may be, e.g., mirror or a lens. In EUV lithography, a reflective mirror is typically used. The reflective mirror may be made with coatings of alternating films of molybdenum (Mo) and silicon (Si). By increasing the number of alternating layers the reflectivity of the mirror can be increased. In DUV lithography, conventional lenses are used. A lens will transmit the electromagnetic radiation, whereas a mirror will reflect the electromagnetic radiation. When using mirror, reflectivity of electromagnetic radiation may be typically measured to characterize the mirror. When using a lens, transmissivity of electromagnetic radiation may be typically measured to characterize the lens. Also contamination of the mirrors or lenses can be measured by measuring their reflectivity or transmissivity respectively. In a next process of the method for measuring contamination of a lithographic element, a second lithographical element (203) is introduced into the process chamber (102). Again active introduction may be optional as the second lithographic element already may be present in the process chamber, e.g. introduced during installation or during previous actions. For introducing the second lithographical element (203), a load-lock chamber may be used (not shown in FIG. 2a). Alternatively the second lithographical element (203) may also be directly introduced from an atmospheric environment in the lithographic system (as in FIG. 2a). In case of a lithographic system under vacuum, such as for example an EUV lithographic system, the lithographic system needs to be pumped down again to vacuum level after the introduction of the second lithographical element (203). In another process of the method for measuring contamination of a lithographic element, a part of the first lithographic element is covered (103), providing the reference region (201b). Such covering may be done prior to or after introduction of the contaminant, preferably prior to introduction of the contaminant. The covering certainly needs to be performed prior to exposure of the lithographic elements. With covering part of the first lithographic element (201) is meant that at least a part or reference region (201b) of the first lithographical element (201) is covered and will remain unchanged and can thus serve as a reference when comparing different regions of the first lithographical element. The covered part, referred to as reference region (201b), remains the same before and/or after exposure to the electromagnetic radiation of the exposure beam and/or the contaminant. Neither the contaminant nor the exposure radiation will interact with the covered part or reference region 201b. The uncovered part, referred to as test region (201a), from the first lithographical element will be exposed to the electromagnetic radiation and/or the contaminant. As a consequence the contaminant or exposure radiation will interact with the uncovered part or test region 201a. The process of covering part of the first lithographical element may comprise shielding the first lithographical element from the contaminant by a shield. Shielding the first lithographical element from the contaminant may comprise providing a hard contact between the shield and the part of the first lithographical element. Alternatively, shielding the first lithographical element from the contaminant may comprise providing a soft contact between the shield and the part of the first lithographical element. Alternatively the shield may be positioned in such a way that the shield avoids radiation to fall onto the reference region, i.e. shadows the reference part of the first lithographical element. FIG. 2b shows the process of shielding at least part (201b) of the first lithographic element in order to prevent the reference region (201b) to be contaminated. This shielding (204) may be done for example by mechanically using a shutter which moves in front of the reference region (201b) and making a hard contact or soft contact between the shield and the first lithographical element, or which shutter or shield throws a shadow on a region of the first lithographic element, i.e. prevents the radiation incident on the shielded region of the first lithographic element. Dependent on the contaminant the spacing may be different. The spacing preferably is such that no contaminant can reach or interact with the shielded part of the lithographical element. The shield may be positioned in such a way that the contaminant cannot interact with the shadowed part of the lithographical element. The shield may be any material that has the properties to prevent the contaminant from interacting with the underlying part of the lithographical element. Preferably one reference region is defined on the first lithographical element. Alternatively the reference region may comprise a number of reference zones, e.g. two or three reference zones. Preferably one uncovered part, forming a test region, is defined on the first lithographical element. Alternatively, in another embodiment of the present invention, the uncovered part comprises a plurality of uncovered parts forming a plurality of test zones. More test regions can thus be defined, e.g. two reference zones can be defined, three reference zones can be defined. By defining more test zones on the first lithographical element, different properties of the first lithographical element may be analyzed during one measurement. For example—but not limited thereto—if the first lithographical element is a mirror, two reference zones and two test zones can be defined on the mirror (FIG. 4). A mirror can, for example, be fabricated which has a first part (401) containing 40 Mo/Si layers with a specific capping layer on top and a second part (401*) containing 40 Mo/Si layers with no capping layer on top. In the first part (401) one first zone (401b) of the reference region may be covered and a second part (test zone 401a) may remain uncovered. In the second part (401*) of the mirror one first zone (being a second reference zone 401b*) may be covered and a second part (being a second test zone 401a*) may remain uncovered. The reference zones (401b and 401b*) may be covered simultaneously by a shield 404. Alternatively separate shields may be used to cover the reference zones. In a next process of the method for measuring contamination of a lithographic element, a contaminant is provided into process chamber of the lithographic system (104). The contaminant may be any component which enables contamination of the first and/or second lithographical element. The contaminant may be, for example—but not limited thereto—organic compounds or any gaseous compound. The organic compounds can be directly introduced into the process chamber or can be indirectly introduced into the process chamber. By directly introducing the contaminant is meant introducing the contaminant via an inlet (310)(FIG. 3a) into the lithographic system. These are for example gases, such as a carrier gas contaminated with organic compounds mentioned above. By indirectly introducing the contaminant is meant introducing the contaminant by the second lithographical element. In a particular embodiment of the present invention, the second lithographical element comprises the contaminant. The second lithographical element may comprise resist. For example, if the second lithographical element (203) is a wafer, this wafer may be covered with a resist (203′) comprising the contaminant, which resist is typically used in lithography to define the mask pattern on a wafer. It is known from the prior art that the resist comprises contaminant, since resist outgassing occurs as soon as the wafer (with resist on top) is subjected to vacuum and/or exposed to electromagnetic radiation. In a next process of the method for measuring contamination of a lithographic element, an exposure beam is directed via the test region of the first lithographical element towards the second lithographical element whereby at least one of the lithographical elements gets contaminated by the contaminant (105). In an embodiment of the present invention, the first lithographic element gets contaminated by the contaminant in the process of redirecting an exposure beam (205) via the test region of the first lithographical element towards the second lithographical element whereby at least one of the lithographical elements gets contaminated by the contaminant. In this process the first lithographical element is exposed for example by electromagnetic radiation (205) from an EUV source (207) or using any other wavelength which can be used in a lithographic set-up (FIG. 2b). Due to the exposure to the beam and the interaction with the contaminant, the non-shielded regions (including the at least one test region (201a)) of the first lithographical element (201) will be contaminated. The shielded region or the at least one reference region (201b) of the first lithographical element will remain uncontaminated. The first lithographical element may be a mirror (201) and the second lithographical element is a wafer (203) with resist (203′) (as contaminant) on top. An EUV source (207) emits EUV electromagnetic radiation (205) onto the mirror (201). Due to the mirror, which is positioned under an angle α, the EUV light (205′) is reflected from this mirror (201) to the wafer (203) with resist (203′). As soon as the wafer with resist on top is exposed to the EUV light, resist outgassing will occur (206). The component provided by resist outgassing may contaminate the at least one test region (201a) of the mirror, but will not contaminate the at least one reference region (201b) of the mirror, due to the shielding from the resist outgassing which is positioned on top of the at least one reference region. Alternatively, DUV light may be used to expose the first lithographical element. In this case the light will not be reflected (as with EUV light), but will be transmitted. The mirror is positioned under an angle α, such that the beam from the beam source is reflected under this angle α from the first lithographical element towards the second lithographical element. This angle α is preferably 45 degrees, but may in principle range from almost zero to almost 90 degrees. The second lithographic element, e.g. wafer, may be scanned during the process of contamination in order to induce enough resist outgassing. In a subsequent process of the method for measuring contamination of a lithographic element, the contaminant, more particularly the contamination source, may be removed from the process chamber and the process chamber is cleaned. If the contamination rate is sufficiently low compared to the contamination measurement time and/or depending on the accuracy of the measurement required, this process may be not performed. Such a process therefore is optional. With removing the contaminant is meant taking away the contamination source such that further contamination does not further occur. If for example the contaminant is a component of the outgassing of a resist on top of wafer, the wafer with resist on top can be removed, such that it will not be exposed anymore to electromagnetic radiation (FIG. 2c) or even removed from the chamber to avoid outgassing under vacuum. If the resist is not exposed anymore to electromagnetic radiation, no resist outgassing will occur. Cleaning of the process chamber may be done, e.g. by outbaking, to eliminate these gases or other contaminants present in the process chamber. Outbaking is the heating of vacuum equipment, particularly workpieces to be included in a vacuum chamber during operation, while maintaining the lowest possible operating pressure, in order to remove adsorbed gas from surfaces and cavities in the vacuum chamber. Also other cleaning methods may be used as known for a person skilled in the art. It will be clear that for obtaining information of the contamination of a lithographic element, such elements will not be cleaned prior to determination of the contamination occurring. In a next process of the method for measuring contamination of a lithographic element, the level of contamination of the at least one contaminated lithographical element in the process chamber is measured. For this process different preferred embodiments are described. The process preferably comprises uncovering, i.e. remove the cover of the reference region of the first lithographical element. The shielding of the at least one reference region (covered part or reference region) of the first lithographical element is thus removed. With removing the shielding is meant that whatever was protecting, covering or shadowing the at least one reference region is removed (FIG. 2c). This “unshielding” may be done for example mechanically using a shutter which moves away (204′) from of the at least one reference region (201b). After this process, which is done after exposure, the first lithographical element contains at least one part (201b) which is unchanged compared to the part before exposure (201b) and at least one part (at least one test region) (201a′) which is contaminated compared to the part before exposure (201a). In a particular embodiment of the present invention the process of measuring the level of contamination of the at least one lithographical element in the process chamber further is measuring the level of contamination of the first lithographical element (106). The process of measuring the level of contamination of the first lithographical element in the process chamber further comprises measuring a value for a parameter of the reference region of the first lithographical element, i.e. obtaining a reference value for the parameter, measuring a value for the parameter of the test region of the first lithographical element, i.e. obtaining a test value for the parameter, and determining, e.g. by calculating, the difference between the reference value and the test value. By comparing the level of contamination (which is related to the test value) on the at least on test region with the level of contamination (which is related to the reference value) on the reference region, the difference, e.g. the relative loss of the value of parameter of the first lithographical element due to the contamination by the contaminant may be determined, e.g. calculated. In case the first lithographic element is a reflective element, e.g. a mirror, depending on the amount of contamination by the contaminant, the reflectivity of the first lithographical element may change. For an EUV lithographic measurement the reflectivity of the mirrors, for example, is preferably around about 70%. Due to contamination, for example due to presence of components resulting from resist outgassing, the reflectivity of the mirrors can deteriorate by a few percentages (typically about 1-2%) depending on the amount of contaminant and exposure dose. As a consequence the lifetime of the optical elements (such as mirror, mask, . . . ) is reduced, which is a major concern in lithography since these optical elements are very expensive. Taking into account that multiple mirrors are used in a EUV lithographic exposure tool, the total loss of reflectivity is increased. It is thus important to keep the change in reflectivity due to contamination as low as possible, preferably smaller than 0.1% or a few 0.1%. To measure the (relative) change of reflectivity of an object due to contamination, the reflectivity from at least one test region of the object is compared with the reflectivity from at least one reference region of the object. Whereas the parameter used for detecting contamination is indicated as being reflectivity, the latter may be adapted to the system and/or lithographic system under test and may for example diffusivity of the surface, specular reflection, total reflection, transmissivity for example in case a lens is used. FIG. 2d shows one embodiment of the present invention to measure the contamination of a lithographic optical element in-situ, i.e. in the process chamber. The measurement performed for detecting contamination may be an optical measurement. After removing the shielding from the at least one reference region (201b) of the first lithographical element, the at least one (contaminated) test region (201a′) of the first lithographical element is exposed (205) to an exposure beam, e.g. electromagnetic radiation from a radiation source (207). The radiation source thereby may be the same radiation source as used for lithographic processing or for introducing contamination or it may be a separate radiation source used for performing optical measurement of the contamination e.g. by deriving an optical parameter from the contaminated lithographical element. Such a radiation source may provide electromagnetic radiation, e.g. extreme ultraviolet radiation, deep ultraviolet radiation, ultraviolet radiation, visible light, etc. The exposure radiation beam, e.g. light beam will be reflected from the first lithographical element, such that the reflected radiation beam (205″) will impinge on a sensor (208) for measuring the reflected radiation intensity of the at least one test region (201a′) of the first lithographical element. The contaminant will thus not influence the reflectivity of the first lithographical element; since the contaminant is not exposed anymore (the contaminant was removed). In a following process the movable first lithographical element is moved (209) such that the exposure radiation beam from the source exposes the at least one reference region (201b) of the first lithographical element. Again the radiation is reflected from the at least one reference region towards a sensor which measures the reflected radiation intensity of the at least one reference region of the first lithographical element. FIG. 2d shows a typical reflectivity curve which may be extracted. The difference, Δ, is the difference in reflected radiation intensity between the at least one test region (201a′) of the first lithographical element and the at least one reference region (201b) of the first lithographical element. If the at least one test region (201a′) is contaminated a decrease will be measured in reflectivity. It should be noted that with this in-situ measurement only relative numbers on the reflectivity can be obtained. For obtaining absolute values on the reflectivity for the at least one test region and the at least one reference region additional reflectivity measurements may be performed ex-situ, i.e. outside the process chamber. These ex-situ reflectivity measurements can be done by any technique well-known for a person skilled in the art such as for example reflectometry. The irradiation source used during the process of contaminating is preferably the same as the irradiation source used for analyzing the lithographical element. Alternatively different irradiation sources may be used. Alternatively in case DUV radiation is used (instead of EUV radiation), the difference in transmissivity can be measured between the at least one test region and the at least one reference region. After removing the shielding from the at least one reference region of the first lithographical element, the at least one (contaminated) test region of the first lithographical element is analyzed using the radiation of the irradiation source. The irradiation source is preferably the same as the irradiation source used for exposing the first lithographical element, although the invention is not limited thereto. In case DUV radiation is used, the radiation will be transmitted through the first lithographical element, such that the transmitted light beam will impinge on a sensor for measuring the transmissivity of the at least one test region of the first lithographical element. The contaminant will thus not influence the transmissivity of the first lithographical element; since the contaminant is not exposed anymore (the contaminant was removed). In a following process the movable first lithographical element is moved such that the light from the light source exposes the at least one reference region of the first lithographical element. Again the light is transmitted from the at least one reference region towards a sensor which measures the transmissivity of the at least one reference region of the first lithographical element. If an optical parameter of the at least one contaminated lithographic element is to be determined, the latter may be performed using any suitable optical detector, suitable for detecting radiation from the irradiation source used in the contamination measurement. Reflectivity may be measured with a reflectivity sensor, which sensor may be a diode. Alternatively, transmissivity is measured with a transmissivity sensor. This sensor may be a diode. The sensor for measuring the reflectivity may be an EUV sensitive diode, or any other kind of EUV detector, of any complexity. Alternatively, if a electromagnetic radiation source with a wavelength in the DUV region is used, an DUV sensitive diode or any other DUV detector may be used. In another embodiment of the present invention describing a method for measuring contamination of a lithographic optical element, the second lithographical element is a reticle or a mask. For example, several exposure dose levels can be provided on the reticle (e.g. at different locations) and only one test location is used, e.g. on a mirror (being the first lithographical element). Using FIG. 3a to FIG. 3c each of the processes will now be described in more detail for measuring contamination of a lithographic element wherein the second lithographical element is a mask or a reticle. In a first process of the method for measuring contamination of the second lithographic element, with the second lithographical element being a mask or a reticle, a first movable lithographic element (301) is introduced in the lithographic system. The first lithographic element (301) may be directly introduced from an atmospheric environment in the lithographic system (not shown in FIG. 3a). However in case of a lithographic system under vacuum, such as for example an EUV lithographic system, the lithographic system needs to be pumped again to vacuum level after the introduction of the first lithographical element (301). Therefore, for introducing the first lithographical element (301), preferably a load-lock chamber (302) may be used. The first lithographical element may be positioned on a movable stage such that the first lithographical element is movable in the lithographic system. Similar as above, the first lithographical element may already be positioned in the system, e.g. during installation of the system or during previous actions. In a next process of the method for measuring contamination of the second lithographic element, a second lithographical element (303), being a reticle or a mask, is introduced into the process chamber. For introducing the second lithographical element (303), a load-lock chamber may be used (not shown in FIG. 3a). Alternatively the second lithographical element (303) may also be directly introduced from an atmospheric environment in the lithographic system (as in FIG. 3a). Similar as above, the first lithographical element may already be positioned in the system, e.g. during installation of the system or during previous actions. In a next process of the method for measuring contamination of the second lithographic element, a contaminant is generated in or inserted into the lithographic system. The contaminant (306) may be any component which cause contamination of the first and/or second lithographical element (shown with asterisk in FIG. 3b). The contaminant may be, for example but not limited thereto—organic compounds. The organic compounds are directly introduced into the lithographic system. By directly introducing the contaminant (intentional contamination) is meant introducing the contaminant via an inlet (310) (FIG. 3a) into the lithographic system. This may be for example gases, such as a carrier gas contaminated with organic compounds as mentioned above. In another process of the method for measuring contamination of the second lithographic element, with the second lithographical element being a mask or a reticle, at least one reference region is defined by shielding on the first lithographical element and at least one test region is defined on the first lithographical element. With reference region (301b) is meant a part or region of the first lithographical element which will remain unchanged during the process and can serve as a reference when measuring the contamination level of the second lithographical element. The reference region (301b) thus remains unchanged during exposure to the electromagnetic radiation and/or the contaminant. Shielding or covering should preferably be done before adding the contaminant. The latter allows to substantially reduce or even exclude contamination on the shielded areas, even when the exposure is off. Nevertheless, as the major contamination problems are caused when contamination of the surfaces occurs during exposure of these walls, shielding or covering also could be performed in between introduction of the contaminants and exposing of the optical elements. Thus once the mirror/mask is irradiated, the shielding or covering preferably is present. Neither the contaminant nor the exposed light will interact with the reference region. With test region (301a) is meant a part or region from the first lithographical element which will be exposed to the light and/or the contaminant. The contaminant or exposed light will interact with the test region. Preferably one reference region is defined on the first lithographical element. Alternatively the reference region may comprise more than one reference zone, e.g. two or three reference zones. Preferably one test region is defined on the first lithographical element. Alternatively the test region may comprise more than one test zone, e.g. two or three reference zones. The at least one reference region of the first lithographical element is shielded (FIG. 3b), in order to prevent the at least one reference region (301b) to be contaminated. With shielded is meant that the reference region (301b) is covered (304) such that it will not be contaminated when being subject to the contaminant, or at least is covered such that it will not be subject to the contaminant and exposure at the same time. This shielding (304) may be done for example mechanically using a shutter which moves in front of the reference region (301b) thereby shadowing the reference region on the first lithographic element. Another possibility to shield the at least one reference region of the first lithographical element may be any method that causes a soft contact or hard contact in between the shield and the at least one reference region of the first lithographical element. Any shielding may be used, e.g. one causing a shadow or a method providing soft contact or hard contact between a shield and the first lithographic element, e.g. a mirror. In a next process of the method for measuring contamination of the second lithographic element, with the second lithographical element being a reticle or a mask, an exposure beam (305, 305′) is directed via the test region of the first lithographical element towards the mask or reticle whereby at least one of the lithographical elements gets contaminated by the contaminant. Due to the inserted contaminants (306) the second lithographic element, being a mask or a reticle, will be contaminated (303′). Possibly also the test region of the first lithographic element, e.g. a mirror (301a′), may be contaminated. Due to the exposure to radiation (305, 305′) and the interaction with the contaminant, e.g. from other parts of the tool, the non-shielded zones (the at least one test region (301a)) of the first lithographical element (301) and the second lithographic element (303′) will be contaminated. The shielded region or the at least one reference region (301b) of the first lithographical element will remain substantially uncontaminated. For example, the first lithographical element is a mirror (301) and the second lithographical element is a mask or reticle (303). An EUV source (307) emits EUV light (305) onto the mirror (301). Due to the mirror which is positioned under an angle α, such as 45° plus or minus 6°, the EUV light (305′) is reflected from this mirror (301) to the mask or reticle (303). The contaminant (306) present in the vacuum chamber may contaminate the at least one test region (301a) of the mirror, but will not contaminate the at least one reference region (301b) of the mirror, due to the shielding which is positioned on top of the at least one reference region. Also the reticle or mask will be contaminated by the contaminant (306), since a mask in EUV comprises a mirror. The second lithographic element, e.g. the mask or reticle, will be typically scanned during the process of contamination. Different test zones may be defined on the second lithographic element to compare the level of contamination between the test regions of the second lithographic element. In a next process of the method for measuring contamination of the second lithographic element, with the second lithographical element being a reticle or a mask, the contaminant is removed from the chamber. If the contamination rate is sufficiently low compared to the contamination measurement time and/or depending on the accuracy of the measurement required, this process may be not performed. Such a process therefore is optional. With removing the contaminant is meant taking away the contaminant such that it cannot further contaminate. If for example the contaminant (306) is a gas which is present in the vacuum chamber, the method furthermore may comprise removing the contamination present on the system walls e.g. by a cleaning process of the vacuum chamber, e.g. outbaking, can be performed to eliminate these gases. In other words, the method may comprise an additional process of cleaning the chamber. In a next process of the method for measuring contamination of the second lithographic element, the second lithographical element being a reticle or a mask, the shielding of the at least one reference region of the first lithographical element is removed. With removing the shielding is meant that whatever was covering the at least one reference region is removed (FIG. 3c). This “unshielding” may be done for example mechanically using a shutter which moves away (304′) from of the at least one reference region (301b). After this process, which is done after exposure, the first lithographical element contains at least one reference region (301b) which is remained unchanged and at least one test region (301a′) which is contaminated. The second lithographical element, being a mask or reticle (303′), is also contaminated. In a next process of the method for measuring contamination of the second lithographic element, the second lithographical element being a reticle or a mask, the contamination level of the second lithographical element is measured in-situ, i.e. in the process chamber. This measurement is done by redirecting the exposure beam (305) via the reference region of the first lithographical element towards the second lithographical element, and further towards a sensor (308). The reference part is now no longer shielded or covered. During this process a test value for a parameter is measured, which is preferably the reflectivity of the contaminated reticle. For wavelengths where transmissive masks are used, transmissivity of the contaminated reticle or mask may be measured in a similar way. In this case lenses are used instead of mirrors for transmitting the electromagnetic radiation from the beam source via the first lithographical element towards the second lithographical element towards the sensor. In one embodiment, the contamination of the second lithographical element is measured or determined by measuring an optical parameter such as transmissivity or reflectivity on a reference zone on the second lithographical element and a test zone on that second lithographical element. The reference zone on the second lithographical element may be obtained by shielding the second lithographical element, similar as described above, or may be obtained from a zone on the second lithographical element not being exposed with an exposure beam. In the latter case, a small amount of contamination may be present in the reference zone, although large contamination only takes place in exposed regions. Alternatively the first lithographical element may be moved (309) during the process of directing the exposure beam (305) via the uncovered reference region, i.e. previously covered part, of the first lithographical element towards the second lithographical element towards a sensor (308). Additionally to the reflectivity or transmissivity of the reticle (mask), also the reflectivity or transmissivity of the contaminated part of the first lithographical element, e.g. mirror, can be taken into account. It is known that the capping layer of a reticle may be different from the capping layer of mirror. This means a reticle may be contaminated in another way or to another degree than a mirror when being exposed to a contaminant, due to the different material properties of the reticle and the mirror. By combining the measurement of the contamination of the reticle, e.g. reflectivity of the reticle, with the measurement of the contamination of the mirror, e.g. reflectivity of the mirror, a comparison and characterization can be made on the contamination behavior on reticle and/or on mirror. It is an advantage of one embodiment that such a characterization can be done in-situ and simultaneously by one measurement. For example, in a EUV lithographic measurement the reflectivity of the mirrors, for example, is preferably around 70%. Due to the intentional contamination, the reflectivity of the mirrors can deteriorate by a few percents typically 1-2%, or maybe even more. As a consequence the lifetime of the optical elements (such as mirror, mask, . . . ) is reduced, which is a major concern in lithography since these optical elements are very expensive. It is thus important to keep the change in reflectivity due to contamination as low as possible. As a plurality of mirrors is present in an EUV lithographic system, additionally the contamination of the mirrors can be taken into account, when measuring the contamination of the reticle. If only the reticle would contaminate and not the mirrors the impact on throughput would be negligible (about 1-2%). To measure the (relative) change of reflectivity of the first and the second lithographic element due to contamination, the reflectivity from at least one test region of the first lithographic element is compared with the reflectivity from at least one reference region of the lithographic element. Furthermore these reflectivities are compared with the reflectivity of the second lithographical element, begin a mask or a reticle. After removing the shielding from the at least one reference region (301b) of the first lithographical element, the at least one (contaminated) test region (301a′) of the first lithographical element is exposed again by the exposure beam (305). The beam will be reflected from the first lithographical element, such that the reflected radiation beam will impinge on the second lithographical element (303′). The reflected light beam will be reflected from the second lithographical element towards a sensor for measuring the test reflectivity being a combination of the reflectivity of the at least one test region (301a′) of the first lithographical element and the reflectivity of the second lithographical element (303′) (FIG. 3c). The contaminant will thus not influence the reflectivity of the first lithographical element or the second lithographical element, since the contaminant is not exposed anymore (the contaminant was removed). In a following process the movable first lithographical element is moved (309) such that the light from the light source exposes the at least one reference region (301b) of the first lithographical element. Again the light is reflected from the at least one reference region towards the second lithographical element, reflecting the light beam further towards a sensor which measures the reference reflectivity, being a combination of the reflectivity of the at least one reference region of the first lithographical element and the reflectivity of the second lithographical element. The difference, Δ, is the difference between the test reflectivity and the reference reflectivity. If the at least one test region (301a′) is contaminated a decrease will be measured in reflectivity. If the second lithographical element is contaminated a decrease will be measured in reflectivity. It should be noted that with this in-situ measurement only relative numbers on the reflectivity can be obtained. For obtaining absolute values on the reflectivity for the at least one test region and the at least one reference region additional reflectivity measurements may be performed ex-situ. Alternatively in case DUV light is used (instead of EUV light), the difference in transmissivity can be measured in between the at least one test region and the at least one reference region. According to one embodiment, a system for measuring contamination of a lithographic element is provided. The system comprises a process chamber (501) (see FIG. 5). It may comprise an element (502) for introducing a first lithographic element into the process chamber and an element for introducing a second lithographic element (503) into the process chamber. The system also comprises an energy source in the process chamber for irradiating a first and second lithographic element introduced in the system. The latter furthermore may induce contaminating at least one of the lithographic elements by directly or indirectly exposing the at least one of the lithographic elements to radiation from this energy source (505). Alternatively, the process chamber may furthermore comprise an inlet for providing contamination to the process chamber. The system further comprises an element for covering at least part of the first lithographic element such that the covered part of the first lithographic element is not contaminated when exposed by the first energy source (505), thereby providing a reference region on the first lithographic element. The system further comprises a sensor (506) for measuring contamination and an inlet for introducing a contaminant (507). In this way, the system is adapted for measuring a parameter of the at least one of the lithographic elements. Preferably the process chamber is under vacuum e.g. when using an EUV energy source (505). Additionally the system may comprise a second energy source (505′). In this case a first energy source (505), e.g. a high power energy source, e.g. EUV source, may be used for directly or indirectly exposing the at least one of the lithographic elements so that contamination of at least one of the lithographic elements occurs. A second energy source (505′), e.g. a low power energy source, may be used for measuring a parameter of the at least one of the lithographic elements, e.g. reflectivity. In preferred embodiments, contamination is studied on areas of the lithographic element that are exposed, as contamination typically will be strong in such areas. The sensor may be a reflectivity sensor or a transmissivity sensor depending on the energy source used. The sensor may comprise a diode. The system for measuring contamination of lithographical element may possibly also be integrated into a lithograph process tool, i.e. a lithographic exposure tool. It is to be understood that although preferred embodiments, specific constructions and configurations, as well as materials, have been discussed herein for devices according to the present invention, various changes or modifications in form and detail may be made without departing from the scope and spirit of this invention. For example, any formulas given above are merely representative of procedures that may be used. Functionality may be added or deleted from the block diagrams and operations may be interchanged among functional blocks. Steps may be added or deleted to methods described within the scope of the present invention. The foregoing description details certain embodiments of the invention. It will be appreciated, however, that no matter how detailed the foregoing appears in text, the invention may be practiced in many ways. It should be noted that the use of particular terminology when describing certain features or aspects of the invention should not be taken to imply that the terminology is being re-defined herein to be restricted to including any specific characteristics of the features or aspects of the invention with which that terminology is associated. While the above detailed description has shown, described, and pointed out novel features of the invention as applied to various embodiments, it will be understood that various omissions, substitutions, and changes in the form and details of the device or process illustrated may be made by those skilled in the technology without departing from the spirit of the invention. The scope of the invention is indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope. |
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summary | ||
abstract | The present invention extends to methods, systems, and computer program products for remote collection and management of diagnostic information. Embodiments of the invention facilitate remote configuration, management, and collection of diagnostic results. A remote diagnostic system connects to the local diagnostics of a service or computer system in a non-invasive way to collect diagnostic information. Filter and subscription requests are used to guide the collection and retention of diagnostic information. A diagnostic user connects to the remote diagnostic system to dynamically change the filter and subscription requests as part of a diagnostic process. The collected diagnostic information can then be transmitted to interested system operators using either syndication subscriptions or push subscriptions. |
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042696585 | abstract | Apparatus for producing a pinched plasma at high kinetic energy levels which includes an elongated containment means having a generally cylindrically shaped bore defining a reservoir, an electrically conductive liquid within the bore and means for rotating the liquid to create centrifugal force sufficient to create a cylindrical space generally along the axis of the bore, means for creating a plasma within the cylindrical space, means for applying a magnetic field the length of the bore and means for mechanically reducing the diameter of the bore and cylindrical space to compress the magnetic field to provide a pinch effect on the plasma. |
046366458 | description | DESCRIPTION OF THE PREFERRED EMBODIMENT With reference first to FIG. 3, cask base element 38 has a cylindrical cavity 40 which extends from floor 42 to stepped mouth region 44. During use, cavity 40 typically contains a basket arrangement (not illustrated) which mechanically supports the spent fuel in storage slots and which transfers the heat generated thereby to wall 46 of element 38. The storage slots of the basket arrangement have axes that are parallel to the axis of element 38 and are open, in the vincinity of mouth region 44, to receive fuel assemblies 26 and/or fuel in consolidation canisters. With continuing reference to FIG. 3, cask base element 38 includes a carbon steel portion 48 which is approximately 25 cm thick and which serves to protect the environment from gamma rays. A stainless steel cladding layer 50 is applied to the interior of portion 48, for example, by placing portion 48 on a turntable and rotating it while welding a continuous spiral path around the interior using stainless steel welding rods, so that a stainless steel surface covers the interior of portion 48 entirely in order to protect it from chemical attack. Portion 48 is surrounded by a layer about 7.0 cm thick of neutron absorbing material 52, which may be a resin. A suitable neutron absorbing material is commercially available from Bisco Products, Inc., 1420 Renaissance Drive, Park Ridge, Ill. 60068, under Stock No. NS-3. Surrounding material 52 is an outer layer 54 of stainless steel to protect the cask from the environment. Carbon steel cooling finds 56 are welded to portion 48 and extend through material 52 and layer 54. Element 38 is typically about 4.8 meters high and has an outside diameter of about 2.5 meters, excluding fins 56. It has a mass of over a hundred thousand kilograms when loaded with spent fuel. Trunions (not illustrated) may be provided on element 38 to facilitate handling. Turning next to FIG. 4, stepped mouth region 44 includes a first annular step region 58 that is horizontally disposed when element 38 is positioned on cask pad 36 (FIG. 2), an annular projection 60 providing a second annular step region 62 which is also horizontally disposed when element 38 is on pad 36, and an annular groove 64 between step regions 58 and 62. Threaded bores 66 are provided around projection 60. Stainless steel layer 50 extends upward to groove 64, where it terminates in a region 68 of increased thickness. This can be accomplished by providing a recess (not numbered) in portion 48 and filling the recess with excess stainless steel when the aforesaid spiral welding with stainless steel rods is performed. Regions 58 and 62 are machined to provide smooth, flat surfaces. With continuing reference to FIG. 4, closure system 70 cooperates with stepped mouth region 44 to seal base element 38, either temporarily or permanently in order to provide a completed cask. Closure system 70 includes a generally disk-shaped primary cover 72 of stainless steel, about 10 cm thick. The bottom side of primary cover 72 has an annular groove 74 while the top side is provided with an annular recess 76. A first mechanical seal is provided by O-ring 78, which is housed in groove 74 and compressed against first region 58 by the weight of cover 72. it will be apparent that the first mechanical seal could alternately be provided by a O-ring which is housed in a groove that is cut into region 58, or by shallow grooves adjacent each other in both region 58 and cover 72, or by no grooves at all. However it is convenient to permanently install O-ring 78 in groove 74 so that primary cover 72 can be shipped and installed as a single unit. Referring next to both FIGS. 4 and 5, primary cover 72 includes an annular canopy element 80 of stainless steel. Element 80 can be fabricated, for example, by sawing away the outer portion of a hoop of stainless steel tubing. Bottom edge 82 of canopy element 80 is welded to primary cover 72 at region 84 thereof in such a manner that the weld extends around the periphery of element 72, and intermediate portion 86 of element 80 extends into recess 76. Thus canopy element 80 need not be shipped or installed independently of cover 72. Primary cover 72 is installed under water, after cask base element 38 has been lowered to cask pad 36 (FIG. 2) and loaded with spent fuel. After the loading operation primary cover 72 is lowered by remote control into mouth region 44 until its periphery rests on region 58 of element 38. The weight exerted on O-ring 78 provides a mechanical seal, but shear keys 88 and 90 (FIGS. 6A and 6B) are inserted into groove 64 by remote control, before cask base element 38 is moved, in order to prevent primary cover 72 from becoming displaced during a drop accident or other mishap. After keys 88 and 90 have been installed the water within cask base elements 78 is removed via a drain (not illustrated) and gas is injected. The gas is preferably inert, such as helium, although other gases or even air can be used instead. After primary cover 78 is applied and the water in cask base element 38 is replaced by gas, element 38 is lifted from pool 30 (FIG. 2). Primary cover 72 attenuates the radiation enough to make it safe for workers to be exposed to mouth region 44 for limited periods of time. With reference next to FIGS. 6A and 6B, shear keys 88 include insertion portions 92 and riser portions 94, which are bounded by parallel sides 96 and 98. Shear keys 90 include insertion portions 100 and riser portions 102, which are bounded by angularly disposed sides 104 and 106. Shear keys 88 and 90 can be fabricated by machining stainless steel to provide a disk which is as thick as riser portions 94 and 102, reducing the thickness at the periphery of the disk to provide insertion portions 92 and 100, and then cutting away a circular region at the center of the disk to provide an annular structure somewhat resembling in a large washer. The annular structure is thereafter cut into segments to provide individual shear keys 88 and 90. FIG. 7 illustrates base element 38 after primary cover 72 has been installed and secured by shear keys 88 and 90. It will be noted that keys 88 and 90 alternate around the periphery of cover 72. The reason why the sides of keys 88 and 90 are configured differently is to permit the keys to be inserted into and removed from groove 64; if the shear keys were fabricated by radially cutting the aforesaid annular element, so that all of the keys were identical, it will be apparent that keys could not be inserted into groove 64 in a full, 360.degree. ring. However since the sides 96 and 98 of shear keys 88 are parallel they can be readily slid into position or removed from groove 64, thereby allowing access to the adjacent shear keys 90. However it is not necessary that sides 96 be parallel to sides 98; keys 88 would still be removeable if sides 96 and 98 sloped toward an apex which is nearer to end 108 than it is to riser portion 94. In contrast, sides 104 and 106 of shear key 90 slope toward an apex that is closer to riser portion 102 than it is to end 110. Returning to FIGS. 4 and 5, primary cover 72 is installed without welding upper edge 112 of canopy element 80 to region 68 if cask base element 38 is to be temporarily sealed. That is to say, for a temporary seal edge 112 is not welded to base element 38 in the manner shown in FIG. 4, but instead is simply positioned in the upper portion of recess 76 without being permanently connected. If the ask seal is to be permanent, however, shear keys 88 and 89 are removed sequentially to expose segments of canopy element 80, and the portion of edge 112 thereby rendered accessible is welded at region 68. After a segment has been welded the shear keys are re-inserted, whereupon the shear keys are removed from the next segment and welding resumes. This process continues until edge 112 is continuously welded to cask base element 38. It will be apparent that the welding of edge 112 in this manner creates a permanent seal, since edge 82 of element 80 is welded to primary cover 72. Moreover, since there is a degree of flexibility between edges 82 and 112 of element 80, it will be aparent that primary cover 72 can expand differentially with respect to cask base element 38 in response to temperature changes. That is to say, element 80 accommodates minor movement of cover 72 with respect to mouth region 44 without unduly straining the welded seal. With continuing reference to FIG. 4, closure system 70 also includes a generally disk-shape secondary cover 114 of carbon steel about 15 cm thick. Cover 114 includes bores 115 spaced about its periphery, annular grooves 116 and 118, and central projection 120. Secondary cover 112 is affixed to base element 38, either with edge 112 of canopy element 80 being welded for a permanent seal or not, by bolts 122. Projection 120 is separated by a narrow gap 124 from primary cover 72, thereby accommodating differential expansion while nevertheless providing additional mechanical support in the event that primary cover 72 is jolted during a drop accident. Projection 120 also serves to ensure that shear keys 88 and 90 do not become dislodged. A second mechanical seal is provided by O-ring 126, which is disposed in groove 118. In the event that the cask is to be permanently sealed a canopy element 128 having lower edge 130 and upper edge 132 is disposed in groove 116 before bolts 122 are inserted, and edges 130 and 132 welded to base element 38 and secondary cover 114, respectively. As was the case with canopy element 80, the welds on canopy element 128 extend all the way around. Canopy element 128 not only permits differential expansion due to temperature changes, it also allows the position of secondary cover 114 to be adjusted slightly during installation of bolts 122 in order to align bores 115 with threaded bores 66. Cap 134 having a core 136 of neutron absorbing material enclosed by a layer 138 of stainless steel is affixed to base element 38 after the closure system is applied, either temporarily or permanently. From the foregoing discussion it will be apprent that the closure system of the present invention provides redundant covers each having a mechanical seal for a short-term use if the cask is to be reopened. Since the long-term effectiveness of mechanical seals has not been established, particularly if the cask is flooded with helium, each mechanical seal has a welded back-up seal for use during long-term storage. The welded seals employ canopy elements which permit the covers to move slightly. The primary cover is installed and secured under water, and may be weld-sealed after the cask base element is raised and before the secondary shield is installed. The mechanical seals of the closure system are sufficient during development, testing, and refinement of the cask, and the welded seals can be installed to adapt the cask to long-term storage without re-engineering either the closure system or the mouth region of the cask base element. It will be understood that the above description of the invention is susceptible to various modifications, changes, and adaptations, and the same are intended to be comprehended within the meaning and range of equivalents of the appended claims. |
055369456 | claims | 1. A transportation container for a syringe containing radioactive material comprising, a radiopharmaceutical pig having an upper portion removably securable to a lower portion, each portion of the radiopharmaceutical pig having an inner surface defining an internal cavity oriented to define a chamber when the upper and lower portions of the radiopharmaceutical pig are secured together, the radiopharmaceutical pig including radiation-resistant material surrounding the chamber such that radioactive material may be safely stored within the chamber; and a tubular sharps container having a cap and a housing configured to fit the chamber of the radiopharmaceutical pig, the the cap having a closed end and an open mating end with at least one resilient snap; the housing having a closed end and an open mating end with at least one ledge for the engagement of the resilient snap when the mating end cap contacts the mating end of the housing, the engagement of the resilient snap with the ledge fastening the cap to the housing, the fastened cap and housing configured to hold the syringe therein and to fit within the chamber of the radiopharmaceutical pig. the housing has a window through which at least part of the syringe is visible when it is inside the fastened container. the housing is constructed from a transparent material. the cap has at least two resilient snaps; and the housing has at least two ledges, each of which is aligned with an associated resilient snap. the mating end of the cap includes at least two radially spaced, cylindrical ridges extending longitudinally toward the mating end of the closure; the mating end of the housing further including a cylindrical sealing wall extending longitudinally to fit between the ridges on the cap when the housing is attached to the cap, thereby creating a leak resistant seal. a tubular cap having an open mating end, a closed end, and a wall having an inner surface defining an internal cavity between the open mating end and the closed end, the mating end of the cap having at least one resilient snap; a tubular housing having an open mating end, a closed end, and a wall having an inner surface defining an internal cavity between the open mating end and the closed end; the mating end of the housing including at least one ledge, each ledge sized and positioned to engage an associated snap on the cap, thereby fastening the cap to the housing; the housing further includes an internal sealing wall extending from the inner surface of the housing toward the mating end of the housing, the sealing wall abutting the inner surface of the wall of the cap when the cap is fastened to the housing; the cavity of the cap and the cavity of the housing cooperatively defining an inner chamber for holding the syringe when the snap of the cap engages the ledge of the housing and the mating end of the cap abuts the mating end of the housing inside the sharps container; and the housing further includes a window through which the syringe is visible when it is in the inner chamber formed when the cap and the housing is fastened together. the cap has at least two opposed snaps and the housing has at least two opposed notches for guiding the snaps until they engage the ledges in the housing. a radiopharmaceutical pig having an upper portion removably securable to a lower portion, the upper portion and the lower portion configured to cooperatively define an internal chamber when the upper portion is secured to the lower portion, the chamber being surrounded by a radiation-resistant material; a sharps container having a cap and a housing, the housing is made of transparent material. a radiopharmaceutical pig having an upper portion removably securable to a lower portion, the upper portion and the lower portion configured to cooperatively define an internal chamber when the upper portion is secured to the lower portion, the chamber surrounded by a radiation-resistant material; a sharps container having a cap and a housing, a hollow shield of radiation resistant material having an upper portion with an inner cavity and a lower portion with an inner cavity, the upper and lower portions positionable such that their cavities cooperatively define a space to enclose the housing and the cap; and a hollow outer container having an upper shell with an inner cavity and a lower shell with an inner cavity, the upper shell and the lower shell removably secured together such that the cavities of both shells cooperatively define a space for the housing, the closure, and the radiation shield to nest therein. the cap further having two internal sealing ridges extending from the shoulder of the cap toward the mating end of the cap and radially spaced apart to accept the sealing wall of the housing between them to form a seal. 2. The transport container as defined in claim 1, wherein 3. The transport container as defined in claim 1, wherein 4. The transport container as defined in claim 1, wherein 5. The transportation container as described in claim 1, wherein 6. A sharps container for a syringe containing radioactive material, the container comprising: 7. The sharps container as defined in claim 6, wherein the housing is constructed from a transparent material. 8. The sharps container as defined in claim 7, wherein 9. A transportation container for a syringe containing radioactive material, the container comprising: 10. The transportation container as defined in claim 9, wherein 11. The transportation container as defined in claim 10, wherein the housing has an inner cylindrical sealing wall extending longitudinally from its shoulder, the sealing wall abutting the shoulder of the cap when the snaps on the mating end of the cap are engaged with the ledges on the mating end of the housing. 12. A sharps container for a syringe, the sharps container comprising: 13. The sharps container as defined in claim 12, further having a sealing wall extending longitudinally from the internal shoulder of the housing toward the mating end thereof, |
claims | 1. A method for transferring spent fuel from wet storage to dry storage, the method comprising:loading a container of spent fuel into a cavity of a transfer cask submerged in a spent fuel pool;placing a shielding sleeve around the transfer cask, the shielding sleeve being attached to a lifting system;attaching the lifting system to the transfer cask, the shielding sleeve remaining attached to the lifting system;simultaneously lifting the transfer cask and shielding sleeve from the spent fuel pool;positioning the transfer cask and the shielding sleeve over a storage cask; andtransferring the container of spent fuel from the transfer cask to the storage cask. 2. The method of claim 1, further comprising lowering the transfer cask into the spent fuel pool comprising the container of spent fuel. 3. The method of claim 1, wherein the container of spent fuel is loaded into the cavity of the transfer cask in a first area of the spent fuel pool, and further comprising moving the transfer cask from the first area of the spent fuel pool to a second area of the spent fuel pool. 4. The method of claim 3, wherein the shielding sleeve is placed around the transfer cask in the second area. 5. The method of claim 4, wherein a width of the first area is greater than a diameter of the transfer cask and the width of the first area is less than a diameter of the shielding sleeve. 6. The method of claim 1, wherein the shielding sleeve and transfer cask are configured to be modified to meet at least one of a weight limitation or a dimension limitation of the spent fuel pool. 7. The method of claim 1, wherein a combined weight of the transfer cask and shielding sleeve exceeds a weight capacity of a floor of the spent fuel pool containing the spent fuel. 8. The method of claim 1, further comprising:transferring the transfer cask surrounded by the shielding sleeve to a platform outside of the spent fuel pool. 9. The method of claim 1, wherein the shielding sleeve comprises a radiation shield designed to shield radiation emitted from the container of spent fuel. 10. The method of claim 1, wherein a weight of the shielding sleeve is supported by the lifting system while the shielding sleeve is positioned around the transfer cask and prior to removal from the spent fuel pool. 11. The method of claim 1, wherein the container of spent fuel is loaded into the cavity of the transfer cask in the fuel pool, and further comprising moving the transfer cask from the spent fuel pool to an area outside the spent fuel pool. 12. The method of claim 1, further comprising opening a door at a bottom portion of the transfer cask, the container of spent fuel being transferred from the transfer cask to the storage cask via the opening at the bottom portion of the transfer cask. 13. A method, comprising:loading a container of spent fuel into a cavity of a transfer cask that is submerged into a spent fuel pool;lowering a shielding sleeve into the spent fuel pool, the shielding sleeve being engaged with a lifting system via a first set of lifting components;positioning the shielding sleeve around the transfer cask, the shielding sleeve remaining engaged with the lifting system;attaching the transfer cask to the lifting system via a second set of lifting components; andsimultaneously lifting the transfer cask and the shielding sleeve from the spent fuel pool via the lifting system. 14. The method of claim 13, wherein a total weight of the shielding sleeve and the transfer cask exceeds a weight limitation of a floor of the spent fuel pool, the shielding sleeve remaining engaged with the lifting system such that a weight of the shielding sleeve is not transferred to the floor of the spent fuel pool. 15. The method of claim 13, wherein the container of spent fuel is loaded into the transfer cask in a first area of the spent fuel pool, and further comprising moving the transfer cask to a second area of the spent fuel pool prior to lowering the shielding sleeve around the transfer cask. 16. The method of claim 15, wherein the transfer cask is moved to the second area of the spent fuel pool based at least in part on a dimension of the shielding sleeve exceeding a dimension limitation of the first area of the spent fuel pool. 17. The method of claim 15, further comprising:placing, via the lifting system, the transfer cask surrounded by the shielding sleeve in an area outside of the spent fuel pool for transfer cask operations to prepare for dry storage. 18. The method of claim 17, further comprising:simultaneously lifting the transfer cask and shielding sleeve from the area outside the spent fuel pool;positioning the transfer cask and shielding sleeve over a storage cask; andtransferring the container of spent fuel from the transfer cask to the storage cask. 19. The method of claim 13, wherein the shielding sleeve comprises a radiation shield designed to shield radiation emitted from the container of spent fuel. |
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abstract | A cleaning device of a porous plate for nuclear power including: cleaning tanks (72, 73) that is capable of storing a cleaning liquid therein and is capable of housing the porous plate (43) in an upright state; a rotation device (84) that is capable of rotating the porous plate (43) within the respective cleaning tanks (72, 73); and an ultrasonic wave oscillation device (111) that irradiates the porous plate (43) within the cleaning tanks (72, 73) with ultrasonic wave. Thus, it is possible to efficiently remove the adhered foreign substances. |
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041522079 | description | DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. 1 there are shown portions of a reactor of the liquid metal fast breeder type. The reactor includes a vessel 10 housing a nuclear core 12. The core 12 includes a plurality of substantially vertical and coextending fuel elements 14. The fuel elements 14 shown are of the ducted type, having a duct 16 and a plurality of internally contained fuel rods (not shown) which can include both fertile and fissile fuels as well known in the art. The core elements are supported upon a perforated lower core plate 18 either directly or through a plurality of modules 20, and are typically arranged to approach the configuration of a right circular cylinder. The main flow of a reactor coolant fluid such as liquid sodium or water enters the vessel through inlet nozzles 22, flows upwardly through the plate 18 and within the duct 16, and is discharged through outlet nozzles 24. The heat energy imparted to the coolant passing through the core is typically transferred in apparatus, not shown, ultimately for the purpose of electrical power generation. Each fuel element duct includes lateral load pads 26 at given elevations which abut against the load pads 26 of adjacent assemblies. Lateral core support has typically been provided by restraints 28 about the core radial periphery. The restraints are supported by a radial core structure 30. This invention addresses, among other items, improved restraints. The invention, applicable to the examplary reactor shown or other reactors and core types, can best be understood by reference to FIG. 2. Shown in the figure are a core 12 having aligned load pads 16, and a lateral restraint and control system 32. The system includes an electromagnet 34, an armature 36, and a movable restraint 38 connected to the armature. The electromagnet 34 is powered through leads 40 from a source preferably external to the reactor vessel. The electromagnet 34 is desirably made of a material having a predetermined curie temperature so that a selected amount of its magnetic capacity is reduced at a specified temperature rise above the normal operating temperature. The electromagnet 34 is also positioned so that the flow of reactor coolant exiting the core is in thermal contact with the electromagnet or other selected components included in a magnetic circuit. It is well known that the criticality of a core is dependent upon the density or geometric configuration of the nuclear fuel. The apparatus shown in FIG. 2 provides means for inherently altering the core geometry in response to an undesirable coolant temperature rise. During normal operation the electromagnet 34 is energized and provides sufficient force to position the armature 36 and affixed restraint 38 so as to radially compress the core 12 as shown by the solid core outline 12a. One or more restraint systems 32 can be utilized. Upon an abnormal rise in coolant temperature to a preselected temperature range, the temperature of the armature 36 is raised to the predetermined temperature range at which a selected amount of the compressing force is relaxed. Accordingly, the restraint 38 freely moves about a pivot 42, allowing the core 12 to radially expand as shown by the dotted outline 12b. The expansion in core geometry will serve to shutdown the nuclear reaction. The expansion can be allowed to propagate throughout the entire core, or merely along selected radii or segments. Also, restraints can be utilized at various elevations, allowing broad expansion along the entire core height. Arrangements of many types can be utilized to allow or assist expansion upon relieving of the compressing force. For example, FIG. 3 shows a cross section of an hexagonal fuel element duct 16 having load pads 26 at various elevations. The pads 26a are provided with compressible means, such as Belleville or other type springs 44, which are compressed or relaxed as the case may be between adjacent fuel elements 14. Alternatively, axial support of the elements 14 can be arranged to accommodate the expansion. For example, the elements can be pinned into the lower core plate 18 at a spacing which accommodates sufficient radial expansion at the upper portions of the core. Dependent upon the height and type of elements, and the core configuration, approximately a one inch radial expansion across the active core can provide a sufficient change in reactivity for control purposes. The bending required in each individual assembly under such conditions can be reconciled without unduly stressing the assemblies and contained fuel rods, as well as allowing insertion of control rods 46 (FIG. 1). Also, the control rods can be located to enter elements 14 in the core at positions not directly affected by the expansion by using elongated guide ducts for the control rods, and the electromagnet can also be associated with other reactor monitoring and control equipment so that electric power to the magnet can be terminated in response to any abnormal condition, allowing the core to expand. Another embodiment is illustrated in FIG. 4. Here, selected load pads 26 and portions 48 of the elements 14 are comprised of ferromagnetic material, as is a magnetic circuit conducting beam 50. The beam 50, exposed to the coolant fluid exiting the core, can be an alloy having a predetermined curie temperature, such as those including compositions of iron and nickel or iron and chromium. It should be noted that components within a typical reactor vessel are composed of 316 stainless steel, Inconel, or other high strength and high temperature materials, which are non-magnetic. In conjunction with the ducts, pads and beam, a magnetic circuit is formed through a magnetic core 52 by coils 54. Although differing compositions may be used, the magnetic core 52 is preferably comprised of iron, shielded from direct contact with the coolant, and the coils of nickel-plated silver encased in a high temperature insulation such as Al.sub.2 O.sub.3. The beam 50 can take many geometric configurations ranging from a perforated plate above the core to a plurality of webs or plates along selected core radii. The beam must form part of a magnetic circuit, as indicated by the broken line 56, and preferably contacts a peripheral element 14a through a bending component 50a or a sliding motion. For sliding motion, an upwardly extended outer pad 26a can be utilized which slidingly contacts the beam 50. The embodiment can be utilized with elements 14 of the type shown in FIG. 3, where only selected load pads (26a) and portions 48 of the duct are composed of a ferromagnetic material, and other load pads are non-magnetic. The coils 54 producing the magnetic flux can be controlled by other reactor safety mechanisms, as discussed hereinabove, and the magnetic force advantageously can similarly be decreased by a rise in coolant temperature. It is estimated that the ferromagnetic curie temperature alloys utilize for the beam, and/or for the pads or portions of the ducts, can be selected such that the attractive compressing magnetic force falls approximately thirty to fifty percent upon a one-hundred to two-hundred Fahrenheit degree rise in the normal coolant outlet temperature. The resulting core expansion can provide sufficient negative reactivity to shutdown the reactor. A similar embodiment is shown in FIG. 5. Here a plurality of electromagnets 51 each form a magnetic flux path 53 through temperature sensitive struts 55, an upper internals shroud 57, the fuel elements 14, and a flexible structure 59. The magnetic material, or portions thereof, can be removed during refueling operations. Many other arrangements may be utilized incorporating the inventive teachings. For example, FIG. 6 shows a restraint and control system in which an electromagnet 58 is positioned external to the reactor vessel 10. A tapered ring 60 of ferromagnetic material is supported between a fixed pad 62 and the lateral load pads 26 on the peripheral fuel elements 14. The fixed pads 62 can be affixed to the vessel wall, the radial core structure 30, or other support structures within the vessle 10. The ring 60 can be comprised of a material having a predetermined curie temperature. The ring, as shown, can be located below the top of the fuel elements 14, but is positioned in heat transfer relation with the flowing coolant. Upon energizing the electromagnet 58, an upward magnetic force is produced upon the ring, which radially compacts the core as a result of its tapered configuration. Yet, another exemplary restraint and control system 32 is shown in FIG. 7, also incorporating an electromagnet 64 located external to the vessel 10. In this arrangement compaction forces for core lateral restraint are provided by a number of pivoted arms 66 spaced at selected intervals about the core periphery. Each arm is connected to a selected curie temperature armature 68 which is laterally moved by the magnetic force provided by the electromagnet. Radially outward motion of the armature is translated into a radially inward force on the core through the motion of the arm 66 about a pivot 70. The pivot 70 is supported by the vessel or other reactor internals structures. To provide inherent operation in response to a coolant temperature rise, coolant flow patterns must be sufficient to bathe the armature 68 in coolant exiting the core, and additional flow control structures can be provided for this purpose. Selection of the materials and associated curie temperatures will vary dependent upon the reactor type and its operating parameters. In all cases, however, the curie temperature chosen is preferably higher by a suitable margin than the normal core outlet coolant temperature in order to preclude inadvertent deactivation of the compressing force upon the core. Some candidate ferromagnetic materials are listed in Table I which are applicable to the operating temperature range of many existing reactor types. TABLE I ______________________________________ Curie Temperature Material .degree. C. .degree. F. ______________________________________ Iron 770.degree. 1480.degree. Silicon-Iron 690.degree. 1274.degree. Grain-Oriented Si-Fe 740.degree. 1364.degree. ______________________________________ For liquid metal cooled fast breeder reactors with a mixed core outlet temperature in the range of 900.degree. to 1200.degree. F., (482.degree. to 649.degree. C.) promising candidate materials also include iron-nickel and iron-chromium alloys. There has therefore been described a nuclear core restraint and control system inherently operable for control purposes upon a preselected rise in reactor coolant fluid temperature. Although described primarily in relation to a liquid metal cooled fast breeder reactor having ducted assemblies, it is to be understood that the various embodiments and teachings of the invention are applicable to other reactor and core designs, including those with open lattice or grid-type elements. If desirable to have such elements included as part of the magnetic circuit, such as described in reference to FIG. 4, adjacent grids or supplementary structures can easily be so adapted. It will be apparent that many additional modifications are possible in view of the above teachings. It therefore is to be understood that within the scope of the appended claims the invention may be practiced other than as specifically described. |
summary | ||
abstract | Provided is a laser welding apparatus for spacer grid of nuclear fuel assembly comprising a base frame in which a chamber installment hole is formed horizontally to the center in a way that the hole penetrates the chamber and a guide rail is installed along the chamber installment hole; a welding chamber unit assembled with the base frame in guidance by the guide rail and equipped with an operable door in front and a glass window at the top to be airtight; a laser welding unit mounted on the base frame for radiating laser through the glass window to weld spacer grid in the welding chamber; and a locking member for fixing the welding chamber on the base frame. |
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summary | ||
description | Referring now to FIG. 1, there is illustrated a control rod constructed in accordance with the present invention and including an upper cruciform absorber section or body 12 and a lower velocity limiter section 14. The blades or wings 16 of the upper section 12 typically include tubes filled with a neutron poison such as boron carbide, the tubes conventionally extending vertically within each of the blades 16. The lower velocity limiter is typically mounted in a control rod guide tube, not shown, for movement in a vertical direction between the correspondingly-shaped cruciform portions in the interstices of the core among the fuel bundle assemblies. The control rod is typically under hydraulic fluid control for movement vertically to allow axial positioning of the absorber section adjacent to the fuel bundle assemblies in the event of a SCRAM or for reactivity regulation. Referring to FIGS. 2 and 3, the component parts of the velocity limiter 14 include a set of fins 18 aligned vertically with the blade 16 of the upper section of the control rod and transition piece 20 and a vane 22, the transition piece mounting a socket 24 at its lower end. The socket 24 is adapted for connection to a control rod drive, not shown, whereby the control rod can be vertically positioned relative to the fuel bundle assemblies. The vane 22 is illustrated in FIG. 4 and includes a generally frustoconical section having a hollow interior 26 open at its bottom for receiving the coolant/moderator. An annular turning vane 28 is disposed in the vane 22 and defines an annular flow channel 30 between the vane 28 and the upper portion of vane 22. The vane 28 mounts a plurality of lugs 32 which mount rollers, not shown, for engaging along the interior surfaces of the control rod guide tube whereby the control rod can be displaced vertically. Referring to FIGS. 5A and 5B, two separate transition pieces 20a and 20b are provided, only one of which is employed in the formation of the velocity limiter for a particular control rod. In FIG. 5A, the transition piece 20a is generally in the form of a hollow cylinder having a sleeve 34 projecting from its upper end. The cylinder of the transition piece is of a relatively thin wall. The lower end of the transition piece 20a is secured, for example, by welding to the upper end of the socket 24. In FIG. 5B, there is illustrated a similar transition piece 20b which is heavier than the transition piece 20a of FIG. 5A. Particularly, transition piece 20b is similar in external configuration to the transition piece 20a. However, transition piece 20b is formed of a substantially solid interior with a small axial passageway 36. An imaginary outline 38 of the interior wall of the lighter transition piece 20a is illustrated in the heavier transition piece 20b to indicate the extent of the increase in material and, hence, weight of the heavier transition piece 20b as compared with the lighter transition piece 20a. Transition pieces are preferably formed of a stainless steel material. Referring to FIGS. 7A, 7B, 8A and 8B, there are illustrated two sets of fins 18. The first set of fins 18a comprise four fin halves which have short, vertically extending side edges 39 followed by long, downwardly inclined outer edges 40 terminating at their lower ends in contoured edges 42 for connection to the transition piece 20. In FIGS. 8A and 8B, the fins 18b are similarly formed except that the outside vertical edge 41 of each fin extends vertically downwardly to a greater extent than the outside vertical edge 39 of each of fins 18a of FIGS. 7A and 7B. Also, the inclined edge 44, which transitions between the vertical edge and the contoured edge 42 for seating on the transition piece is at a greater downwardly inclined angle to the vertical. Furthermore, the thickness of the fins shown in FIGS. 8A and 8B is substantially greater than the thickness of the set of fins shown in FIGS. 7A and 7B. It will be appreciated that upon comparing the configurations of the fin sets of FIGS. 7A and 7B with those of FIGS. 8A and 8B, the second sets of fins 18b are heavier than the first set of fins 18a. The increase in weight is due solely to the increase in material forming the fins. While there is an increased surface area for the heavier fins 18b as compared with the lighter fins 18a, the external geometry is not altered sufficiently to have significant extent on the fluid mechanical properties of the velocity limiter. It will also be appreciated that four fin halves of the selected set are used at right angles to one another for each control rod. To provide a control rod of selectively adjustable weight corresponding to a target or licensed weight, the weight of the velocity limiter is determined by the weight of the neutron absorber section, i.e., upper section 12. The total weight of the control rod will be the combined weight of the upper section 12 and the velocity limiter 14. Given the weight of the upper section which can vary substantially with respect to the design of the upper control rod section, the total control rod weight can be adjusted to meet the target or licensing weight by adjusting the weight of the velocity limiter. To accomplish this for a given known weight of the control rod absorber section, a combination of the selected transition pieces and fins will be made to approximate the desired weight. For example, if the upper section of the control rod is heavy, the lightest of the transition pieces, i.e., transition piece 20a, and the lightest of the fin sets 18, i.e., fin set 18a, may be selected for combination with the vane 22 and socket 24. This affords the lightest control rod for the given heavy weight of absorber section. Conversely, for a control rod design having an extremely light absorber section, the heavier velocity limiter 20b may be selected and combined with the heavier set of fins 18b. This affords the heaviest control rod for the given light weight of absorber section. By forming two sets each of heavier and lighter transition pieces and fins interchangeable for use with the vane and socket, it will be appreciated that the weight of the velocity limiter can be varied between a maximum and minimum range and with a mix of the light and heavier fin sets and transition pieces. That is, to meet weights in-between the maximum and minimum weights of the velocity limiter, a different combination of fin sets and transition pieces can be utilized, i.e., a heavy transition piece with a set of light fins or a light transition piece with a set of heavy fins. Additionally, once a fin set and the heavier transition piece are selected from the light and heavier fin sets and transition pieces, respectively, the weight of the heaviest transition piece can be adjusted, i.e., lowered. Thus, if the heavier transition piece is selected, a weight between it and the weight of the lighter transition piece can be provided by removing material from within the bore of the transition piece 20b. From a review of FIG. 5B, it will be appreciated that more or less of the material within the bore 36 of the heaviest transition piece 20b can be removed, down to the weight of the lightest transition piece 20a. The extent of passable removal of the material is illustrated in FIG. 5B by the material volume between bore 36 and the dashed lines 38. Consequently, greater control over the total control rod weight is achieved by using selected transition pieces and sets of fins and further adjustment of the weight of the transition piece should the heavier transition piece be selected. It will also be appreciated that additional material can be provided the lighter transition piece 20a to render it heavier. For example, weld material could be suitably secured along the interior wall of the transition piece 20a to increase its weight. Accordingly, there has been provided a system for adjusting the weight of a control rod within predetermined maximum and minimum limits to arrive at a target weight. While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. |
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05999584& | description | DESCRIPTION OF THE PREFERRED EMBODIMENTS In the following description, like reference characters designate like or corresponding parts throughout the several views. Also in the following description, it is to be understood that such terms as "forward", "rearward", "left", "right", "upwardly", "downwardly", and the like are words of convenience and are not to be construed as limiting terms. Referring now to the drawings in general and FIG. 1 in particular, it will be understood that the illustrations are for the purpose of describing a preferred embodiment of the invention and are not intended to limit the invention thereto. As best seen in FIG. 1, there is illustrated a prior art system for lifting a reactor pressure vessel head. The lifting operation is conducted using a cable (not shown) connected to lifting eye 300 of tripod handling fixture 100 ("tripod"). Each leg of tripod 100 carries a rigging component used to lift reactor pressure vessel head 105. In the prior art system, turnbuckle pendants 102 extend downwardly from each tripod mounting point. A clevis 104 is provided at the lower end of each turnbuckle pendant 102 for attaching additional components. Typically, a solid rod lifting pendant 113 as shown in the exploded view of FIG. 2 is connected between the lower end of turnbuckle pendant 102 and pressure vessel head lifting eye 107. Alternatively, a bridge strand pendant (not shown) may be used in place of the turnbuckle pendant. In this example, three of each of the items discussed above are provided at equidistant points around the circumference of reactor closure head 105. Secured to the top of head 105 is a service structure 117. Atop the service structure is positioned a work platform 116 which serves as a staging area for personnel and equipment. Solid rod lifting pendants 113 extend through openings 118 and work platform 116 to make up the necessary connections. Alternatively, bridge strands (not shown) may be substituted for the solid rod lifting pendants 113. The prior art rigging system described above requires four rigging changes during an outage because the components that are suitable for mating up to the pressure vessel head 105 are not suitable for mating up to the reactor internals. Although the type of connections that must be made up are relatively simple, the large weight of the components makes their handling difficult, time consuming, and necessitates prolonged exposure to high radiation components. For example, the turnbuckle pendants 102 and the bridge strands each weigh several hundred pounds each. The connecting pins 107 for these components may weigh one hundred pounds or more and must be positioned and driven into place by hand. The workers carrying out these tasks must often work at awkward angles thus increasing the possibility of personal injury as the number of required rigging changes increases. A rigging system constructed according to the present invention is illustrated in FIGS. 3 and 4. Tripod 100 carries three latchbox pendants 211 each of which include a leveling turnbuckle 212 and a latchbox 219. The construction and operation of latchbox 219 is well known in the art and will not be described in detail here. According to the present invention, each of the latchbox pendants 211 is secured to a novel solid rod lifting pendant 213. As shown in FIG. 4, each solid rod lifting pendant 213 includes a T-shaped lifting lug 250 at a first end, a clevis 215 at the opposite end and an adjustable turnbuckle 216 adjacent to the T-shaped lifting lug 250 which allows the reactor head 105 or other item being lifted to be leveled without changing the reactor internals lift settings on the latchbox pendants 211 after they have been initially set. In operation, as the tripod 100 and the downwardly extending latchbox pendants 211 are lowered through access openings 118 in the work platform 116, each lifting lug 250 engages a corresponding latchbox 219 without the need for manhandling a connector or cable. Although a T-shaped lug 250 is illustrated in FIG. 4, other lugs types will work as well, depending on the internal design of the particular latchbox 219. The advantages of the present invention stems from the fact that the latchbox pendants 211 may be rigged once to tripod 100 and left in place throughout the entire rigging sequence. There is no need to rig latchbox pendants 211 to tripod 100 for reactor internals handling (see FIG. 5) and then change to turnbuckle pendants 102 for reactor closure head handling. For reactors that have solid lifting rods already installed in place of cables, the practice of the present invention requires only that adjustable turnbuckles 216 and lifting lugs 250 be installed thereon. Note that the present invention does not affect the interface between the shielded work platform (not shown) and the service structure work platform 116 and, therefore, does not require expensive modifications to the structure. Certain modifications and improvements will occur to those skilled in the art upon a reading of the foregoing description. By way of example, while the preferred embodiment of the invention teaches adding the lifting lug and turnbuckle to a solid lifting rod, the present invention can still be used on cable-type systems by manually inserting the lifting lug into the latch box pendant. It should be understood that all such modifications and improvements have been deleted herein for the sake of conciseness and readability but are properly within the scope of the following claims. |
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description | This is a non-provisional application calming the benefit of U.S. Provisional Application No. 61/135,620, filed Jul. 22, 2008, and International Application No. PCT/EP2009/059428, filed Jul. 22, 2009. The invention relates to a method for reducing or minimizing interference and/or crosstalk that may appear in an apparatus comprising a double optical tweezers using a single laser source. Optical tweezers have been used over the two past decades to probe biological objects of various sizes, from whole cells down to individual proteins. Force measurement devices based on double optical tweezers have initially been used to manipulate non spherical particles such as bacteria, and increasingly became an important tool for single molecule studies of nucleic acids, and their interactions with proteins. An important feature of double optical tweezers derived from a single laser source is that, although the absolute position of each trap is sensitive to external mechanical perturbations, their relative position can be precisely imposed. Beam steering may be achieved with galvanometer, piezoelectric tilt mount or acousto-optic deflectors. The force acting on one bead is often measured with the back focal plane method, which allows decoupling the force signal from trap displacement, and hence external vibrations. The two traps usually exhibit perpendicular polarization in order to reduce interference as well as to easily discriminate between them for detection. A laser of different wavelength can be used for detection, but a parasitic signal may then arise from the relative drift between the trapping and detection lasers. When one of the two trapping beams is used for force measurement, it has to be distinguishable from the second beam of the double trap. Orthogonal polarizations can be used for this purpose. However, when linearly polarized light goes through a system of microscope objectives, such as in an optical tweezers apparatus, it suffers form the rotation of polarization, resulting in a non homogeneous polarization when it exits the microscope. Consequently, important crosstalk may occur when force is measured in this configuration. This crosstalk limits the force resolution of the force measurements. It is an objective of the invention to provide a method that reduces the occurring crosstalk in force measurements using double optical tweezers with a single laser source. In one embodiment, this objective is achieved by a method according to the invention that rectifies the polarization by going through the microscope lens and the condenser twice and compensating rotation of the polarization by a quarter-wave plate. In another embodiment, the objective is also achieved by a method according to the invention that shifts the frequency of one of the two beams issued from the single laser source with an acousto-optic frequency shifter. The invention concerns also a double optical tweezers apparatus implementing at least one of the preceding methods. In a first part, we are going to discuss the rotation of polarization in a microscope. Conventional polarizing microscopy suffers from the rotation of polarization on lens surfaces or slides, which results in a loss of contrast when imaging a sample. A simple explanation of the rotation of polarization can be given as follows. For a linearly polarized beam refracting on the surface of a lens, the electric field exhibits different parallel and perpendicular components relative to the plane of incidence, depending on the position on the lens. Since, according to the Fresnel equations, the two components are refracted differently, the polarization of the total electric field is rotated. As described in more detail in the following description, this effect induces difficulties when detecting force with double optical tweezers. For sake of simplicity, the propagation of light is described in a simple model, to give a qualitative understanding of the effects coming from the rotation of polarization in optical tweezers. These effects are of general validity for centered systems, and the main results regarding field symmetry are the same for complex objectives. As shown in FIG. 1, the trapping objective and the condenser collecting light from a trapped particle are modeled by two plano-convex lenses (La and Lb), faced front to front. We assume a radius rL, of the two plano-convex lenses and a glass refractive index iGR. The two lenses are identical, centered on the same axis and the back focal plane of the first lens coincides with the front focal plane of the second lens. The Gaussian beam entering this two lens system is supposed to be parallel, linearly polarized (as shown in FIG. 2a, incident electric field) and refracting according to the Fresnel equations. Propagation of light is described in the limit of ray optics and spherical aberration is neglected. The electric field occurring in the back focal plane of the second lens Lb is presented in FIG. 2b. Polarization is rotated, except for the x and y axes, which are perpendicular to the optical axis and respectively perpendicular and collinear to the incident polarization. In FIG. 2b, the lines of the contour plot correspond to rotation of polarization of −8°, −6°, 4°, −2°, 2°, 4°, 6° and 8°, and gray scales are used to facilitate visualization. The x1 and y1 axes are the first and the second bisecting lines. For a given direction in the back focal plane starting from the center, the magnitude of the rotation of polarization increases with numerical aperture (as shown in FIG. 2c, illustrating the rotation of polarization of the electric field exiting from the two lens system on the y1 axis for y1>0). For a given radius, the rotation is stronger when the electric field exhibits similar parallel and orthogonal components according to the incidence plane on the lenses. Maximum values are reached close to the x1 and y1 axes, but not exactly on these axes, depending on numerical aperture (see FIG. 2d showing the rotation of polarization of the electric field exiting from the two lens system on the perimeter of N.A.=0.20 (solid), N.A.=0.30 (dotted), N.A.=0.45 (dashed) and N.A.=0.49 (dash-dotted).). In reference to FIGS. 3 and 4, we are going to describe a double optical tweezers apparatus according to the invention. The apparatus of FIG. 3 is based on a custom-designed inverted microscope. For optical trapping and force detection, the apparatus comprises, here, a CW linearly polarized diode pumped Nd:YVO4 laser (1.064 μm, 10 W). The laser beam is first expanded through a beam expander comprising two lenses (L1 and L2). Then, in order to create two independent traps, the laser beam is split by polarization by the combination of a half-wave plate (λ/2) and a first polarizing cube beamsplitter (C1). The direction of one of the two beams is varied by a piezoelectric mirror mount with integrated position sensor operating in feedback loop (piezo stage on FIG. 3). After recombination with a second polarizing cube beamsplitter (C2), the two beams exhibit perpendicular polarization and their directions are slightly tilted to obtain two separate traps. Lenses (L3) and (L4) form a beam steering and image the center of the mirror mounted on the piezoelectric stage on a back focal plane of a trapping objective (microscope objective on FIG. 3). The beams are then collimated by a second objective (condenser on FIG. 3). Finally, a Glan-laser polarizer reflects one of the two beams, and a lens (L5) images the back focal plane of the second objective on a position sensitive detector (PSD). As it can be seen on FIG. 3, a part of the optical path of the apparatus according to the invention is also used to image the sample on a CCD camera. In order to avoid fluctuations from air currents, the optical path is fully enclosed. Most mechanical parts are designed to reduce drift and vibration. In variant, any other suitable polarizer can be used in place of the Glan-laser polarizer. Force measurements in optical tweezers generally use either laser light going through the particle or bead, trapped by the first objective, for interferometric position detection or white light illumination for video based detection. The apparatus according to the invention uses back focal plane interferometry to measure the force. The method implemented consists in evaluating the pattern of laser light diffracted by one of the trapped beads in the back focal plane of the condenser (or second objective) by imaging the pattern on a four-quadrant photodiode or any other suitable position sensitive detector (PSD). As the two beams entering the trapping objective are of perpendicular polarization, if one wants to separately detect the position of one of the beads in its trap, one has to split by polarization the beams used to trap. Since a linearly polarized beam suffers from a non homogeneous rotation of polarization when going through the optical components of a microscope, the discrimination of the two beams according to polarization cannot be perfectly achieved. If the polarization of one beam is checked after the back focal plane of the second objective with the polarizer, it can be observed that the transmitted light pattern exhibiting a polarization perpendicular to the incident beam is cross-shaped, in agreement with the calculation presented in FIG. 2b. Consequently, the rotation of polarization allows for interference between the two beams, and the crosstalk that occurs is not simply the sum of the signals coming from the two beams separately. To understand the interference pattern appearing in the back focal plane of the second objective, we use the model of FIG. 1. For the sake of simplicity, we restrict the theoretical study to the case where no bead is trapped. To describe the interference pattern, we need to know the amplitudes and phases of the two beams in the detector plane. For this purpose, we now closely consider the microscope and detection part of the apparatus (see FIG. 4) and in particular image planes (A1), (A2), (B), (C) and (D). The back focal plane (C) of the second objective is conjugated with the detector plane (D). The back focal planes, (B) and (C), of the two objectives are also conjugated, and finally the lenses (L3) and (L4) conjugate the back focal plane (B) of the trapping objective with plane (A1) centered on the mirror mounted on the piezoelectric stage for the first beam (directed by x′ and y′ axes) and with the equally distant plane (A2) on the other path for the second beam. Planes (A1) and (A2) are consequently conjugated with the detector plane (D). When the traps overlap, the beams enter the microscope with exactly the same angle. The phase shift ΔφA between the phases of planes (A1) and (A2), respectively ΔφA1 and ΔφA2, is constant on the plane (A1), so that ΔφA=ΔφA1−ΔφA2=φ0. This phase shift depends on the relative length of the optical paths of the two beams and is difficult to avoid because it corresponds to subwavelength (i.e. submicrometer) displacements of the optical components and is therefore particularly sensitive to thermal drift. To separate the two traps, one has to tilt the mirror mounted on the piezoelectric stage by an angle θ around the y′ axis. If the rotation axis is centered on the optical path, and if θ<<1, and as the beam is parallel, its phase is constant on any plane perpendicular to its direction of propagation, and in particular its phase is constant on segment [OH] (See FIG. 5). As O is on the rotation axis of the mirror, the phase of ray 1 reflecting on O is constant on the plane (A1) with the deflection of the beam. In comparison to ray 1, the ray 2 passing on point J, of abscissa x′, has the additional path [HJ]=2θ x′ before hitting plane (A1), so that its phase is φA1(x′,θ)=φA1(0,θ)+2θx′2π/λ. Finally, as the phase on plane (A2) is still constant, the phase shift between the planes (A1) and (A2) is the corresponding phase shift takes the simple form Δ ϕ A ( x ′ , θ ) = ϕ 0 + 4 π λ θ x ′ where λ is the light wavelength. Assuming that the magnification between planes (A1 and A2) and the detector plane (D) is α, the phase shift between the two beams in the plane (D) is given by Δ ϕ D ( x , θ ) = ϕ 0 + 4 π λα θ x The amplitude and phase of light going through two real microscope objectives may be difficult to calculate and requires knowledge of curvature, material and coating of each element. The field symmetry should nevertheless be identical to the simpler case illustrated by FIG. 1. Thus we use the model of FIG. 1 to describe the field amplitudes of the two beams on plane (D) and to evaluate the components that are transmitted by the polarizer. As the phase shift between the two beams and their respective field amplitudes are given, we can describe the interference pattern occurring on the detector plane (D). We consider the specific and most useful case in which the polarizer after the second objective is rotated to reject the maximum of light coming from the moving trap. The vectors {right arrow over (ε)}1={right arrow over (E)}1eiωt and {right arrow over (ε)}2={right arrow over (E)}2eiωt denote the electric fields in the detector plane of the light coming from the fixed and mobile trap respectively. The light intensity I=ε0c|{right arrow over (ε)}1+{right arrow over (ε)}2|2 on the detector is given byI(x,y,θ)=ε0c|{right arrow over (E)}1(x,y,θ)|2+|{right arrow over (E)}2(x,y,θ)|2+2{right arrow over (E)}1(x,y,θ).{right arrow over (E)}2(x,y,θ). cos(ΔφD(xθ)) (1) The sum of the first two terms of equation (1) describes roughly the amplitude of a Gaussian beam, and we rewrite it asε0c|{right arrow over (E)}1(x,y,θ)|2+|{right arrow over (E)}2(x,y,θ)|2=A(x,y,θ) If the optical components are perfectly centered and the two Gaussian beams impinge on the center of the back focal plane of the trapping objective, the symmetry of the system implies that A (x,y,θ)=A(x,−y,θ). However, when θ≠0, the rotation of polarization on the mobile trap is no more symmetrical regarding the x>0 and x<0 halves. As shown in FIG. 1, when the beam is refracted from air to the spherical interface of (La) the upper ray is refracted by a wider angle than the lower one. When the beam is refracted from the spherical interface of (Lb) to air, what used to be the upper ray of the beam is now refracted by a smaller angle than what used to be the lower one. Because Fresnel coefficients differ when light is refracted from air to glass and glass to air, even if the paths of the two rays are symmetrical, the rotation of polarization that the two rays endure is not identical after passing through the two lenses. As a result, except for a few points, A(x,y,θ)≠A (x,y,θ). The last term of equation (1) creates interference, and we rewrite it asε0c2{right arrow over (E)}1(x,y,θ).{right arrow over (E)}2(x,y,θ). cos(ΔφD(x,θ))=B(x,y,θ) Once more, if alignment is perfect, the symmetry of the system implies that B(x,y,θ)=−B(x,−y,θ). On the other hand, because the refraction is asymmetrical as described above, except for a few special points, B(x,y,θ)≠B(−x,y,θ). The illumination calculated assuming perfect alignment is shown in FIG. 6 (this figure is obtained for an angular difference between the two beams of 1 mrad and a numerical aperture of 0.47). The fringes are parallel to the y axis, and in each quarter, the distance between neighboring maxima equals αλ/2θ. The contrast of the fringes increases with the absolute rotation of polarization and contrast inversion appears when going from left to right and from top to bottom due to the relative direction of the electric fields. To calculate the expected normalized output signal of the position sensitive detector, we subtract the illumination on the x>0 half by the one on the x<0 half and divide this difference by the total illumination. When we increase the angle between the two beams, the system symmetry implies that the fringes have no effect on the detector signal, only the asymmetric refraction leads to a linear dependence of the signal on the angular position (for 2.5 mrad, the normalized difference reaches −5×10−6). In practice, the beams can be aligned to a precision of a few micrometers. To illustrate the consequence of this limitation, we now consider the case where one of the two beams is slightly translated from its centered position. As a typical example, if the beam creating the fixed trap is translated by 5 μm along the y axis in the back focal plane (B) of the trapping objective, the image on the detector plane still looks close to the perfectly aligned case. The signal coming out of the detector is however very different as shown in FIG. 7. In this FIG. 7, it is shown the theoretically expected normalized output signal of a position sensitive detector in the presence of the two beams when the mobile beam is deflected and N.A.=0.47. The fixed trap is translated by +5 μm along the y axis in the detector plane (D). The phase difference φ0 between the two beams is 0 (dashed), π/3 (dotted), π/2 (solid) and π (dash-dotted). The magnitude of the parasitic signal is higher, increases with the translation of the beam (data not shown) and shows a dependence on the phase shift φ0 The variation of the signal when the traps move apart is closely linked to the appearance of new fringes on the detector plane. As a result, the parasitic signal takes a complicated form, depending on misalignments and numerical apertures. In order to evaluate the crosstalk occurring during a force measurement, we assume that we trap two beads in the two optical tweezers, one bead is fixed and the other one is moved apart such as in a single molecule experiment. The force is measured on the bead in the fixed trap. Force is calibrated by measuring the power spectrum of the Brownian motion of a trapped bead with a spectrum analyzer. Exciting separately the mobile or the fixed trap and selecting the corresponding polarization in the detection path, we measured the stiffness of each trap of the double tweezers. The difference between these two stiffness is below 5%, an uncertainty comparable to the one caused by common bead to bead variation. When the two beads are separated by a few micrometers in the sample, the observed light interference pattern exhibits the characteristics previously described theoretically. Force measurements resulting from the evaluation of the light pattern on a position sensitive detector (PSD) are done at different laser powers; we measure a few curves for each power to illustrate the effect of drift on the signal (see FIGS. 8 a, b and c). In FIG. 8, dependence of the parasitic signal on the stiffness and the separation between the two traps are illustrated. In these examples, the force is measured on the fixed trap using two unlinked beads. The stiffness kf of the fixed trap and the total laser power in the back focal plane of the trapping objective P are (a) kf=192 pN/μm, P=800 mW (b) kf=339 pN/μm, P=1.40 W (c) kf=593 pN/μm, P=2.05 W. The displacement velocity between the two traps is 1 μm/s and sampling is done at 800 Hz with an anti-alias filter of 352 Hz. Individual curves are vertically shifted for clarity (1.5 pN between subsequent curves in (a), 2 pN in (b), 4 pN in (c)). Notice the change in vertical axis scaling between (a), (b) and (c). The interference pattern creates a parasitic signal which magnitude decreases when the distance between the beads increases, and is approximately proportional to laser power. Actually, when the back focal plane method is used to measure force, one easily finds that force is proportional to the difference of illumination on the two detector halves. Consequently, the output voltage of the detector is commonly proportional to the force regardless of laser power, while a given interference pattern generates a signal proportional to the laser power. The pattern of the signal is difficult to reproduce because it depends on alignments and is subject to drift. Apparatus alignments are an important issue that should be considered carefully. First, to ensure that the number of fringes is equal for x>0 and x<0, the phase shift between the two beams must be adjusted. One way to adjust the phase is to add a parallel glass slide in the path of one of the beams before they are combined. A rotation of the glass slide will add a phase for this beam until the number of fringes is exactly the same for both detector halves. This rotation also adds a small translation of the beam, but it is possible to keep the translation small enough to not increase significantly the parasitic signal. Second, the image of the center of rotation of the mirror mounted on the piezoelectric stage has to be exactly in the center of the detector to assure the symmetry of the pattern when rotating the mirror. Finally, as it has already been pointed out in the previous paragraph, the beams should be centered on the back focal planes (B, C) of both objectives, and the back focal plane (C) of the second objective should be centered on the detector plane (D). According to one embodiment of the invention, as the interference originates from the rotation of polarization in the microscope, the method for reducing crosstalk comprise a step of reducing the rotation. This step consists in going through the microscope twice, particular through the trapping objective and second objective, and compensating rotation of polarization by a quarter-wave plate. A schematic layout is given in FIG. 9. Let us consider a linearly polarized Gaussian beam entering the system (α). When it passes the two objectives the first time, the electric field endures a first transformation due to rotation of polarization (β). The beam is reflected in the upper part of the rectifier and passes twice through the quarter-wave plate. This adds twice the opposite initial rotation (γ). Finally, when the beam goes through the microscope the second time, it again endures the initial transformation (δ). As the electric field is rotated twice by the same angle and once by the double opposite angle, the electric field going out of the polarization rectifier is theoretically perfectly linearly polarized. It remains to detect the bead position by back focal plane interferometry, requiring imaging the light pattern of the back focal plane of the second objective (β) with a corrected polarization. The rectifier comprises a combination of the lenses (L8), (L9) and the mirror (M) that enables us to image the plane (C) on itself, and as planes (C) and (D) are conjugated, the light pattern used for detection (β) is finally seen on plane (D). As the polarization is corrected with the rectifier, the light pattern on plane (D) is appropriate for back focal plane interferometry. However, some critical points have to be mentioned concerning this embodiment. First, by going back in the microscope, the beams create replicated tweezers that should not perturb the trapping ones. In our configuration it is possible to align the beams going first in the microscope on the optical axis, and then to tilt as less as possible the mirror (M) so that replicated tweezers are far enough to not disturb the trapping tweezers. Second, when the beams are entering the microscope the first time, a significant part of the light is reflected on surfaces, and especially by the glass water interfaces. This generates reflected beams that may be difficult to separate from the ones we want to detect. Third, as the beams are trapping beads only when they first go through the microscope, but not when they go back, paths are different in the two directions. Finally, because Fresnel coefficients are different when light is refracted from glass to air and air to glass interfaces, the rotation of polarization is different when a beam passes through an objective with opposite directions on the same path. As a result, the rotation of polarization may be the same when going through the microscope with opposite direction only if the trapping objective and the condenser are identical. If it is not the case, the transformation may not be perfectly achieved. During experimentation, using the trapping objective described above and a high N.A. oil immersed objective as a collimation objective (100×/1.3 oil, EC Plan-NeoFluar; Carl Zeiss, Thornwood, N.Y.), this method permits us to decrease crosstalk by a factor of four. The power ratio of the two perpendicularly polarized beams measured with the Glan-laser polarizer is 4×10−3 without the rectifier and 1×10−3 when it is used at N.A.=1.3. The method appears to be better suited when high N.A. is used. An improvement of below two is found at N.A. lower than 0.9. According to another embodiment of the invention, a second method to reduce the crosstalk coming from interference comprises a step of shifting the frequency of one of the two beams. This step of frequency shifting can be realized by different means, for instance by acousto-optic or electro-optical devices. In our apparatus, the beam of the mobile trap goes through an acousto-optic frequency shifter before being deflected by the piezoelectric tilt stage. In this way, as one retrieves the first order of the acousto-optic device, the beam coming from the mobile trap is shifted by the acoustic frequency f0 of the shifter. The intensity on the detector plane is nowI(x,y,θ)=ε0c(|{right arrow over (E)}1(x,y,θ)|2+|{right arrow over (E)}2(x,y,θ)|2+2{right arrow over (E)}1(x,y,θ).{right arrow over (E)}2(x,y,θ). cos(2πf0t+ΔφD(x,θ)) The electronics of the position sensitive detector has a bandwidth much smaller than the acoustic frequency f0 of the shifter. The signal coming from the rapidly moving fringes is therefore rejected by the electronics and crosstalk coming from the interference pattern is no more measurable. In our experimentations, f0 was about 80 MHz and the bandwidth of the position sensitive detector was about 100 kHz. FIG. 10 provides an example of force measurements done with and without the frequency shifter. The signal measured with the frequency shifter shows no dependence on the bead separation, except for the first 600 nm where the proximity of the beads affects detection. In these examples, the force measurements were done with two 0.97 μm silica beads trapped with the frequency shifter on (bottom; kf=213 pN/μm, P=910 mW) and off (top; kf=192 pN/μm, P=800 mW). The displacement velocity between the two beads is 1 μm/s, and sampling is done at 800 Hz with an anti-alias filter of 352 Hz. The signal measured without the frequency shifter on is shifted vertically for better visualization. While frequency shifting indeed enables us to average out interference effects, one should remember that rotation of polarization still occurs and two beams are seen on the detector plane. We did the following experiment to estimate the influence of the mobile trap on the detection of force in the fixed trap. The conversion coefficient which relates force to the output voltage of the detector was determined by measuring the power spectrum of the Brownian motion of one 0.97 μm silica bead in its trap. This measurement was done separately for the two traps (the other trap was switched off during the measurement). The laser light from the mobile trap was reflected with the polarizer. From these measurements we estimated that the conversion coefficient for the fixed trap was 0.26 V/pN and 5.4×10−3 V/pN for the mobile trap, meaning that about 2% of the force applied on the bead in the moving trap is detected on the fixed trap. This effect should be considered when an accurate measurement of the absolute value of the force measurement is needed. In contrast to the interference effect, this direct crosstalk does not depend on laser power. In conclusion, the rotation of polarization in double optical tweezers creates parasitic signals that should be taken care of, especially for applications that require high trap stiffness or high laser power. Indeed, whereas the output voltage of the detector is commonly proportional to the force regardless of laser power, a given interference pattern generates a signal proportional to the laser power. Consequently, an important feature of this phenomena is that it is usually seen when laser power is high (i.e. 0.5 W or higher). For a low power trapping laser, parasitic signal still exists but may be hidden by noise. The rectification of polarization enables us to decrease the crosstalk between the two traps, but not to annihilate it. We found that an even simpler and most effective method is to shift the frequency of one of the two beams. Even if crosstalk between the two traps is still occurring, it is small enough for most applications. In reference to FIGS. 11 and 12, we are going to briefly describe two applications of the method and device according to the invention. For this, we have performed single molecule force measurements on DNA (3) and RNA (4) molecules in aqueous solution. In the former case as illustrated in FIG. 11, a DNA molecule (3) is extended and its mechanical response is measured. The DNA molecule (3) is, here, a 10000 basepair long DNA molecule attached between two beads (1, 2), as illustrated in the inset of FIG. 11. The two beads (1, 2) are hold in the double optical trap according to the invention. One trap (2) is displaced with respect to the other (1), thus extending the molecule, and force is determined from the displacement of the bead (1) in the immobile trap. The curve of the FIG. 11 shows the measurement of the obtained mechanical response. In the latter case as illustrated in FIG. 12, the mechanical constraint is applied to a construction containing a folded RNA structure (4), as shown in the inset of FIG. 12. The folded RNA structure (4) comprises, here, a 173 nucleotide RNA fragment. The force versus displacement curve of FIG. 12, showing the force induced unfolding of this 173 nucleotide RNA fragment, here involves three major steps (S1, S2, S3), corresponding to the sudden force drops from about 8 to 7.5 pN (step S1), 7.5 to 6.7 pN (step S2) and 7 to 6.3 pN (step S3), respectively. Such features in force versus displacement curves reveal valuable informations on the DNA and RNA base sequences, including the stability and dynamics of local structures induced by base pairing. Reviews of the corresponding fields of applications can be found in the literature (see e.g. U. Bockelmann, Cur. Opin. Struct. Biol. 14, 368 (2004) and references therein). These two examples illustrate the technical performance and two possible applications of the invention, without restricting its general use. |
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062401548 | summary | FIELD OF THE INVENTION The present invention relates to the field of nuclear power plants. More particularly, the present invention relates to a self-actuating louver system that vents the CEDM cooling system of a nuclear reactor with ambient air when a forced stream of cooled air in the cooling system is discontinued. BACKGROUND OF THE INVENTION FIG. 1 illustrates a portion of nuclear reactor used in a nuclear power plant. The reactor head (100) communicates with the reactor vessel (not shown) in which the nuclear reaction takes place. A head lift rig (106) is mounted over the reactor head (100) and contains the control element drive mechanism (CEDM) (105). The CEDM (105) is used to extend control rods (not shown) into the fissionable material in the reactor core in which the sustained nuclear reaction is occurring. The number of control rods used and the extent to which the control rods are extended into the reaction area controls the rate at which the nuclear reaction progresses. In the event of an emergency, an additional set of control rods can be rapidly extended into the core to halt the nuclear reaction entirely. To shield the CEDM (105) from the heat of the reactor vessel, a heat shield of insulation (101) is provided as shown in FIG. 1. However, this insulation (101) alone is insufficient to keep the optimal temperature in the head lift rig (106). Consequently, a cooling system is also provided to control the temperature in the head lift rig (106). The cooling system includes, for example, a pair of pipes (107) through which cooled air is forced into the head lift rig (106). The cooled air flows through the head lift rig (106), around the CEDM (105) and into a chamber (103) between the insulation (101) and the main body of the head lift rig (106). Exhaust holes (102) are provided in this chamber (103) to allow the cooled air to complete its circulation. While this cooling system is adequate to control the temperature in the head lift rig (106), obvious problems will arise if the cooling system malfunctions or must be turned off for any reason. Without the flow of air illustrated in FIG. 1, the temperature inside the head lift rig (106) will quickly rise if a nuclear reaction is ongoing, or will stay high even if no reaction is being sustained. Consequently, there is a need in the art for a device and method of supplementing the cooling system for a CEDM in the head lift rig of a nuclear reactor. SUMMARY OF THE INVENTION It is an object of the present invention to meet the above-described needs and others. Specifically, it is an object of the present invention to provide a self-actuating system that assists in venting heat from the head lift rig any time the flow of cooled air through the cooling system is discontinued. Additional objects, advantages and novel features of the invention will be set forth in the description which follows or may be learned by those skilled in the art through reading these materials or practicing the invention. The objects and advantages of the invention may be achieved through the means recited in the attached claims. To achieve these stated and other objects, the present invention may be embodied and described as a cooling system for a head lift rig of a nuclear reactor. The system includes at least one pipe through which cooled air is forced into the head lift rig; and a self-actuating louver over a vent opening in either of the at least one pipe or the head lift rig. When the cooled air is circulating, the louver is held closed by pressure created by the circulating air. But, when the cooled air is not circulated, the louver automatically falls open to allow hot air from the head lift rig to exhaust and cooler ambient air to enter the head lift rig. According to the present invention, there may be two self-actuating louvers, one of which is disposed over a vent opening in the at least one pipe and one of which is disposed over a vent opening in the head lift rig. Alternatively, the cooling system of the present invention may include a flap valve louver regulating a vent opening in each pipe that provides cooled air to the head lift rig. Similar to the system described above, when the cooled air is circulating, the flap valve louver is held closed by pressure created by the circulating air, but when the cooled air is not circulated, the flap valve louver automatically falls open to allow hot air from the head lift rig to exhaust and cooler ambient air to enter the head lift rig. This system may also include a louver over a vent opening in the head lift rig which operates like the flap valve louver, namely, when the cooled air is circulating, the louver is held closed by pressure created by the circulating air, but when the cooled air is not circulated, the louver automatically falls open to allow hot air from the head lift rig to exhaust and cooler ambient air to enter the head lift rig. The present invention also encompasses the methods of cooling a CEDM corresponding to the systems described above. Such a method may include the steps of (1) forcing cooled air through at least one pipe into the head lift rig; and (2) regulating a vent opening in either or both of the at least one pipe or the head lift rig with a self-actuating louver such that, when the cooled air is circulating, the louver is held closed by pressure created by the circulating air, but when the cooled air is not circulated, the louver automatically falls open to allow hot air from the head lift rig to exhaust and cooler ambient air to enter the head lift rig. Alternatively, the method of the present invention may include the steps of: (1) forcing cooled air through at least one pipe into the head lift rig; and (2) regulating a vent opening in each pipe with a flap valve louver such that, when the cooled air is circulating, the flap valve louver is held closed by pressure created by the circulating air, but when the cooled air is not circulated, the flap valve louver automatically falls open to allow hot air from the head lift rig to exhaust and cooler ambient air to enter the head lift rig. This method may also include the additional step of regulating a vent opening in the head lift rig with a self-actuating louver, such that, when the cooled air is circulating, the louver is held closed by pressure created by the circulating air, but when the cooled air is not circulated, the louver automatically falls open to allow hot air from the head lift rig to exhaust and cooler ambient air to enter the head lift rig. |
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claims | 1. A method for monitoring operation of a control loop in a process plant, comprising:collecting, at one or more of a plurality of computing devices, process gain data associated with a first operating region of a control loop in a process plant, the control loop associated with a unit operation in the process plant, wherein a load variable varies in the first operating region;determining, at one of the plurality of computing devices, an expected process gain behavior in the first operating region based on the collected process gain data, wherein an expected value of the process gain varies as the load variable varies;wherein determining the expected process gain behavior in the first operating region comprises fitting a curve to the collected process gain data, and wherein the curve corresponds to the expected process gain behavior in the first operating region;monitoring, at one of the plurality of computing devices, the process gain during operation of the control loop in the first operating region;determining, at one of the plurality of computing devices, when the monitored process gain substantially deviates from the curve corresponding to the expected process gain behavior in the first operating region;determining, at one of the plurality of computing devices, an abnormal situation associated with at least one of the control loop or the unit operation based at least on a substantial deviation from the curve corresponding to the expected process gain behavior in the first operating region; andgenerating, at one of the plurality of computing devices, an abnormal situation indicator when an abnormal situation is determined. 2. A method according to claim 1, wherein collecting process gain data associated with the first operating region of the control loop comprises at least one of:collecting data regarding a process variable versus the load variable;collecting data regarding the load variable versus the process variable;collecting data regarding a process gain versus the load variable;collecting data regarding the load variable versus a process gain; orcollecting data regarding the process variable versus one or more other process variables. 3. A method according to claim 2, wherein the load variable comprises at least one of a control output or another process variable. 4. A method according to claim 1, wherein determining the expected process gain behavior in the first operating region comprises at least one of:determining expected values of a variable; ordetermining expected rates of change of the variable. 5. A method according to claim 1, wherein determining the abnormal situation comprises determining an abnormal situation associated with the unit operation based at least on a substantial deviation from the curve corresponding to the expected process gain behavior in the first operating region of the control loop and a substantial deviation from an expected process gain behavior of a different control loop associated with the unit operation. 6. A method according to claim 1, further comprising:collecting, at one of the plurality of computing devices, process gain data associated with at least a second operating region of the control loop in the process plant;determining, at one of the plurality of computing devices, an expected process gain behavior in the at least the second operating region based on the collected process gain data;wherein determining the expected process gain behavior in the at least the second operating region comprises fitting another curve to the collected process gain data associated with the at least a second operating region, and wherein the other curve corresponds to the expected process gain behavior in the at least the second operating region;monitoring, at one of the plurality of computing devices, the process gain during operation of the control loop in the at least the second operating region;determining, at one of the plurality of computing devices, when the monitored process gain substantially deviates from the curve corresponding to the expected process gain behavior in the at least the second operating region; andwherein determining the abnormal situation comprises determining the abnormal situation based at least on a substantial deviation from the curve corresponding to the expected process gain behavior in the first operating region or a substantial deviation from the curve corresponding to the expected process gain behavior in the second operating region. 7. A method according to claim 1, wherein collecting process gain data associated with the first operating region of the control loop comprises collecting process gain data regarding a plurality of process gains associated with the control loop, the plurality of process gains including at least a first process gain and a second process gain;wherein determining the expected process gain behavior in the first operating region comprises determining an expected behavior of the first process gain with respect to at least the second process gain;wherein the curve corresponding to the expected process gain behavior in the first operating region corresponds to the expected behavior of the first process gain with respect to at least the second process gain;wherein monitoring the process gain during operation of the control loop in the first operating region comprises monitoring the first process gain and monitoring the second process gain;wherein determining when the monitored process gain substantially deviates from the curve corresponding to the expected process gain behavior in the first operating region comprises determining when the monitored first process gain substantially deviates from the expected behavior of the first process gain with respect to at least the second process gain. 8. A method according to claim 1, wherein determining when the monitored process gain substantially deviates from the curve corresponding to the expected process gain behavior in the first operating region comprises at least one of:determining when the monitored process gain is below the curve corresponding to the expected process gain behavior in the first operating region for a specified period of time; ordetermining when the monitored process gain is above the curve corresponding to the expected process gain behavior in the first operating region for the specified period of time. 9. A method according to claim 1, wherein determining the expected process gain behavior in the first operating region comprises determining a confidence interval for the first operating region;wherein determining when the monitored process gain substantially deviates from the expected process gain behavior in the first operating region comprises determining at least when the monitored process gain is outside of the confidence interval in the first operating region. 10. A method according to claim 9, wherein determining when the monitored process gain substantially deviates from the expected process gain behavior in the first operating region comprises determining when the monitored process gain is outside of the confidence interval in the first operating region for a specified period of time. 11. A method according to claim 1, if an abnormal situation is determined, further comprising at least one of:adjusting, at one of the plurality of computing devices, a control parameter associated with the control loop;initiating, at one of the plurality of computing devices, a diagnostic procedure; orshutting down, via one or more computing devices, equipment associated with the control loop. 12. A method according to claim 1, wherein generating an abnormal situation indicator comprises generating an alert. 13. A method according to claim 1, wherein determining the abnormal situation comprises determining at least one of:if the abnormal situation has occurred, orif the abnormal situation will likely occur in the future. 14. A method according to claim 1, further comprising:determining, at one of the plurality of computing devices, when the control loop is operating in a second operating region for which process gain data has not yet been collected; andcollecting, at one of the plurality of computing devices, process gain data associated with the second operating region of the control loop in the process plant after determining that the control loop is operating in the second operating region of the control loop;monitoring, at one of the plurality of computing devices, the process gain during operation of the control loop in the second operating region; anddetermining, at one of the plurality of computing devices, when the monitored process gain substantially deviates from the expected process gain behavior in the second operating region. 15. A method according to claim 14, further comprising;prompting, at one of the plurality of computing devices, an operator whether to collect process gain data associated with the second operating region of the control loop in the process plant after determining that the control loop is operating the second operating region of the control loop;wherein collecting process gain data associated with the second operating region of the control loop comprises process gain data associated with the second operating region if the operator indicates that process gain data associated with the second operating region of the control loop should be collected. 16. A method according to claim 14, wherein a unit of the process plant comprises the control loop;wherein determining when the control loop is operating in the second operating region comprises determining when the unit of the process plant is operating in an operating region for which process gain data associated with the unit has not yet been collected. 17. A tangible medium having stored thereon machine executable instructions, the machine executable instructions capable of causing one or more machines to:collect process gain data associated with a first operating region of a control loop in a process plant, wherein a load variable varies in the first operating region;determine an expected process gain behavior in the first operating region based on the collected process gain data, wherein an expected value of the process gain varies as the load variable varies;wherein determining the expected process gain behavior in the first operating region comprises fitting a curve to the collected process gain data, and wherein the curve corresponds to the expected process gain behavior in the first operating region;monitor the process gain during operation of the control loop in the first operating region;determine when the monitored process gain substantially deviates from the curve corresponding to the expected process gain behavior in the first operating region;determine an abnormal situation associated with at least one of the control loop or the unit operation based at least on a substantial deviation from the curve corresponding to the expected process gain behavior in the first operating region; andgenerate an abnormal situation indicator if the abnormal situation is determined. 18. A method for monitoring operation of a control loop in a process plant, comprising:collecting process gain data associated with a first operating region of a control loop in a process plant, wherein a load variable varies in the first operating region;determining an expected process gain behavior in the first operating region based on the collected process gain data associated with the first operating region, wherein an expected value of the process gain varies as the load variable varies;wherein determining the expected process gain behavior in the first operating region comprises fitting a curve to the collected process gain data, and wherein the curve corresponds to the expected process gain behavior in the first operating region;providing data indicative of the curve corresponding to the expected process gain behavior in the first operating region to an expert engine;providing process gain data associated with the control loop during operation of the control loop to the expert engine;utilizing the expert engine to detect an abnormal situation associated with the control loop based on the data indicative of the curve corresponding to the expected process gain behavior in the first operating region and the process gain data associated with the control loop during operation of the control loop; andgenerating an abnormal situation indicator if the abnormal situation is determined. 19. A method according to claim 18, wherein utilizing the expert engine to detect the abnormal situation associated with the control loop comprises determining whether the process gain in the first operating region substantially deviates from the curve corresponding to the expected process gain behavior in the first operating region. 20. A method according to claim 18, further comprising:providing process variable statistical data associated with the control loop during operation of the control loop to the expert engine; andwherein utilizing the expert engine to detect the abnormal situation associated with the control loop comprises utilizing the expert engine to detect the abnormal situation associated with the control loop further based on the process variable statistical data associated with the control loop. 21. A method according to claim 20, wherein the process variable statistical data associated with the control loop comprises statistical data generated by field devices associated with the control loop. 22. A system for monitoring operation of a control loop in a process plant, the system comprising:a process gain signature generator configured to generate a signature of expected process gain behavior associated with a control loop in a process plant, wherein the signature is indicative of a gain of a process variable of the control loop versus a load variable of the control loop, and wherein the gain of the process variable versus the load variable is expected to vary as the load variable varies;wherein the process gain signature generator is configured to fit a curve to collected process gain data, and wherein the signature of expected process gain behavior comprises the curve;a process gain evaluator configured to determine if an actual process gain substantially deviates from the curve; andan abnormal situation detector configured to detect an abnormal situation associated with a process unit associated with the control loop based at least in part on whether the actual process gain substantially deviates from the curve and to generate an abnormal situation indicator if the abnormal situation is detected. 23. A system according to claim 22, further comprising:an interval generator configured to generate an interval associated with the signature of expected process gain behavior;wherein the process gain evaluator is configured to determine if the actual process gain substantially deviates from the curve based on the interval associated with the signature of expected process gain behavior. 24. A system according to claim 22, further comprising an expert system, wherein the expert system comprises at least one of the process gain evaluator or the abnormal situation detector. 25. A system according to claim 24, wherein the expert system is configured to detect an abnormal situation associated with a process unit associated with the control loop based at least in part on whether the actual process gain substantially deviates from the curve. 26. A system according to claim 22, further comprising a process gain data collector configured to collect data to be used by the process gain signature generator to generate the signature of expected process gain behavior associated with the control loop. 27. A system according to claim 22, wherein the abnormal situation detector is configured to detect at least one of:if the abnormal situation has occurred, orif the abnormal situation will likely occur in the future. 28. A method for facilitating monitoring operation of at least a portion of a process plant, comprising:collecting, at one of a plurality of computing devices, process gain data indicative of respective process gains associated with respective unit operations in a process plant, wherein the respective process gains are associated with an operating region, wherein respective load variables vary in the operating region;determining, at one of the plurality of computing devices, expected process gains associated with respective unit operations based on the collected process gain data, wherein expected values of the respective process gains vary as the respective load variables vary;wherein determining the expected process gains associated with respective unit operations comprises fitting respective curves to the collected process gain data, and wherein the respective curves correspond to respective unit operations;providing, at one of the plurality of computing devices, a common set of criteria for determining for each unit operation an abnormal situation associated with the unit operation based at least on whether the process gain associated with the unit operation substantially deviates from the curve associated with the unit operation;permitting, at one of the plurality of computing devices, a user to modify the common set of criteria for a particular unit operation to generate a modified set of criteria;utilizing, at one of the plurality of computing devices, the modified set of criteria to determine for the particular unit operation an abnormal situation associated with the particular unit operation;utilizing, at one of the plurality of computing devices, the common set of criteria to determine for each of at least one other unit operation an abnormal situation associated with the other unit operation; andgenerating, at one of the plurality of computing devices, an abnormal situation indicator when an abnormal situation for a unit operation is determined. 29. A method according to claim 28, wherein the common set of criteria comprises expert rules to be applied by an expert engine. 30. A method for monitoring operation of a control loop in a process plant, comprising:collecting, at one of the plurality of computing devices, process gain data associated with an operating region of a control loop in a process plant, the control loop associated with a unit operation in the process plant, wherein the process gain data is indicative of a gain of a process variable of the control loop versus a load variable of the control loop, and wherein the gain of the process variable versus the load variable varies as the load variable varies;determining, at one of the plurality of computing devices, an expected process gain behavior in the operating region based on the collected process gain data, wherein the process gain is expected to vary as the load variable varies;wherein determining the expected process gain behavior in the operating region comprises fitting a curve to the collected process gain data, and wherein the curve corresponds to the expected process gain behavior in the operating region;monitoring, at one of the plurality of computing devices, the process gain during operation of the control loop in the operating region;determining, at one of the plurality of computing devices, when the monitored process gain substantially deviates from the curve;determining, at one of the plurality of computing devices, an abnormal situation associated with at least one of the control loop or the unit operation based at least on a substantial deviation from the curve; andgenerating, at one of the plurality of computing devices, an abnormal situation indicator when an abnormal situation is determined. 31. A method for facilitating monitoring operation of at least a portion of a process plant, comprising:collecting, at one of a plurality of computing devices, process gain data indicative of process gains associated with respective unit operations in a process plant, wherein each of the process gains is a gain of a process variable of the respective unit versus a load variable of the respective unit, and wherein each of the process gains varies as the respective load variable varies;determining, at one of the plurality of computing devices, expected process gains associated with respective unit operations based on the collected process gain data, wherein each of the expected process gains varies as the respective load variable varies; andwherein determining the expected process gains associated with respective unit operations comprises fitting respective curves to the collected process gain data, and wherein the respective curves correspond to respective unit operations;providing, at one of the plurality of computing devices, a common set of criteria for determining for each unit operation an abnormal situation associated with the unit operation based at least on whether the process gain associated with the unit operation substantially deviates from the curve associated with the unit operation. |
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051868873 | description | DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION FIGS. 1 to 3 depict an embodiment of the inspection apparatus for peripheral surfaces of nuclear fuel pellets in accordance with the present invention. The inspection apparatus comprises a handling unit 2 for holding a prescribed plural number of nuclear fuel pellets 1 in a line and rotating the same on their own axes, an image pick-up device 3 for picking up image data as to the peripheral surfaces 1a of the pellets 1, a judging device 4 for analyzing the image data outputted from the image pick-up device 3 to judge whether the pellets are acceptable or not, and a sorting unit 5 for separating defective pellets and non-defective pellets based on judging signals outputted from the judging device 4. The handling unit 2 includes a loading device 6, a smaller-diameter roller 7 and a larger-diameter roller 8. The loading device 6 includes a cylinder composed of a cylinder body 6a and a piston rod 6b, and a guide member 6c of a generally channel shaped cross-section mounted at the distal end of the piston rod 6b. This loading device 6 is disposed at the end of a belt conveyor 30, by which nuclear fuel pellets are conveyed in a line such that they are aligned with one another. The smaller-diameter roller 7 is disposed adjacent to the loading device 6 and is rotatably secured to a shaft 7a, which is parallel to the axes of the pellets 1. As shown in FIG. 1, a belt support 30a of the belt conveyor 30 includes a protruding portion disposed at its end position so as to extend laterally, and the smaller-diameter roller 7 is disposed immediately beneath the protruding portion. The larger-diameter roller 8 is disposed adjacent to the smaller-diameter roller 7, and is mounted on a shaft 8a for rotation therewith. The shaft 8a , which extends parallel to the shaft 7a, is connected to a drive means 8b such as an electric motor, so that the larger-diameter roller 8 can be rotated about the shaft 8a at a constant peripheral velocity. Thus, the smaller-diameter roller 7 and the larger-diameter roller 8 cooperate with each other to define an inspecting position therebetween, and the nuclear fuel pellets arranged in line are moved by the loading device 6 to the inspecting position. A pair of diagonally opposite ejecting grooves 10 are formed in the outer peripheral surface of the larger-diameter roller 8 so as to extend longitudinally thereof. Each ejecting groove 10 is dimensioned such that all of the pellets 1 located at the inspecting position 9 are received therein together. A guide frame 11 for preventing the pellets from falling out from the grooves 10 is provided so as to cover about half the peripheral surface of the larger-diameter roller 8. The sorting unit 5, which is disposed immediately beneath the larger-diameter roller 8, involves a discharging belt conveyor 12, a recovery box 13, a plurality of sorting members or plates 14 mounted so as to be pivotable about an axis 14a, and actuators 15 such as cylinders (operating means) operably connected to the judging device 4. The sorting plates 14 are arranged between the discharging belt conveyor 12 and the recovery box 13 in longitudinally spaced relation along the shaft 8a of the larger-diameter roller 8 such that their number corresponds to that of the pellets 1 in line. Each actuator 15 is operably connected to a respective one of the sorting plates 14 to pivot the plate such that the non-defective pellets 1b are conveyed to the discharging belt conveyer 12 while the defective pellets 1c are collected into the recovery box 13. The discharging belt conveyor 12 conveys the pellets 1 to a prescribed position at the next station. The image pick-up device 3, which is arranged right above the inspecting position 9 at the handling unit 5, includes a light source 16 and a sensor means such as a line sensor 17. The light source 16 radiates illuminating light 16a to the prescribed number of the pellets 1 held at the inspecting position 9, and the light 16b reflected from the peripheral surfaces of the pellets 1 is received by the line sensor 17 to produce video signals, which are outputted to the judging device 4. The judging device 4, which is operably connected to the image pick-up device 3, processes the video signals outputted from the image pick-up device 3 to detect the boundaries between the adjacent pellets 1 in line and to detect defects on the peripheral surface of each pellet 1, and outputs the judging signals regarding the defects. More specifically, as shown in FIG. 3, the video signals outputted from the line sensor 17 are converted by a binary conversion means 18 into binary signals based on the preset binary levels which are preset in accordance with the desired image of the pellets. Then, in a projection data obtaining means 19, which is operably connected to the binary conversion means 18, the number of picture elements which are located in a row corresponding to the circumferential direction and have one of the binary values is summed up through whole lines and is stored as projection data in memory. Subsequently, the effective image of the peripheral surface and the boundaries 25 of the pellets 1 arranged in line are detected based on the projection data, and a window based on the image of the peripheral surface and the boundaries of the pellets is determined by a window determining means 20, which is connected to the projection data obtaining means 19. The video signals outputted from the line sensor 17 are further inputted to a two-dimensional image conversion means 21, and are converted into two dimensional digital images therein. The window determined by the window determining means 20 is overlaid on these digital images by means of a gate means 22, and data 23 as to the developed peripheral surfaces, which are obtained based on the level of luminance of the video signals, are outputted to a judging means 24. Thereafter, in the judging means 24, the developed peripheral surface data 23 are evaluated, and data 26 regarding the defective pellets and data 26 regarding the non-defective pellets are selectively obtained. The inspection method using the above inspection apparatus will be hereinafter described. In the explanation, the picture images of the line sensor 17 includes 1024 lines and 1024 picture elements per line. First, the larger-diameter roller 8 is rotated at a constant peripheral velocity in a direction of the arrow indicated in FIG. 1. Then, the piston rod 6b of the loading device 6 is caused to extend, and the pellets 1 are conveyed by the guide member 6c to the inspecting position 9 when one of the ejection grooves 10 of the larger diameter roller 8 has passed the inspecting position 9. The pellets 1 thus moved to the inspecting position 9 begin to rotate on their own axes. When the rotation of the pellets 1 reaches the steady state, the line sensor 17 picks up light 16b reflected from the pellets 1 while illuminating light 16a is being radiated from the light source 16 to the pellets 1, and outputs video signals on the peripheral surfaces of the pellets 1 to the judging device 4. In the foregoing, the pellets 1 make at least one rotation. Subsequently, the video signals are converted by the binary conversion means 18 into binary signals based on the preset binary levels, and in the projection data obtaining means 19, the number of picture elements which are located in a row corresponding to the circumferential direction of the pellets and have one of the binary values is summed up through whole lines and is stored as projection data in memory. Then, the boundaries 25 of the pellets 1 arranged in line are detected based on the projection data, and a window is determined by the window determining means 20. In addition, the video signals are further outputted to the two-dimensional image conversion means 21, and are converted into two dimensional digital images therein. The window determined by the window determining means 20 is overlaid on these digital images by means of the gate means 22, and thus data 23 as to the developed peripheral surfaces, which are obtained based on the level of luminance of the video signals, are outputted to the judging means 24. Thereafter, in the judging means 24, the developed peripheral surface data 23 are evaluated, and the presence of defects on the pellets are detected. Then, those actuators 15 which correspond to the non-defective pellets 1b are driven based on the judging signals outputted from the judging means 24, and the sorting plates 14 corresponding to the non-defective pellets 1b pivot on their shafts 14a to the position as indicated by the solid line in FIG. 1, while those plates corresponding to the defective pellets 1c pivot on the shafts to the position as indicated by the two-dot chain line. When the larger-diameter roller 8 makes a half turn and the ejecting groove 10 is located immediately under the pellets 1, all of the pellets 1 are received together in the groove 10. As the larger-diameter roller 8 further rotates, the pellets 1 are carried by it and fall on the corresponding sorting plates 14, respectively. Thus, the non-defective pellets 1b are guided by the sorting plates 14 as indicated by the solid line in FIG. 1, into the discharging belt conveyor 12, while the defective pellets 1c are guided by the sorting plates 14 as indicated by two-dot chain line, into the recovery box 13. Then, the above procedures are repeated, and the pellets 1 are inspected as to their peripheral surfaces for every prescribed number of pellets. In the foregoing, as best shown in FIGS. 4a to 4d, while the pellets 1 located at the inspecting position 9 are being inspected, the next pellets 1 to be inspected are conveyed inside the guide member 6c of the loading device 6. As the belt conveyor 30 is stopped, the inspected pellets 1 are received by the ejecting groove 10 of the larger-diameter roller 8, and simultaneously the piston rod 6b of the loading device 6 is extended, so that the pellets 1 on the belt conveyor 30 are guided by the guide member 6c to the inspecting position 9. When the pellets 1 are loaded on the rollers 7 and 8, the piston rod 6b is retracted and the belt conveyor 30 begins to move, and the above procedures are repeated. As described above, the images of the peripheral surfaces of the pellets 1 conveyed in a line are picked up by the image pick-up device 3 while rotating the pellets 1, and the video signals outputted from the image pick-up device 3 are inputted to the judging device 4, in which the defects of the pellets 1 are judged. The actuators 15 are driven based on the output signals from the judging device 4 to pivot the sorting plates 14, and the non-defective pellets are guided by the sorting plates to the discharging belt conveyor 12 while the defective pellets are guided to the recovery box 13. Accordingly, the inspection of the peripheral surfaces of the nuclear fuel pellets and the sorting operation of the inspected pellets can be quickly carried out in a short operating time, so that the efficiency of the inspection operation can be substantially enhanced. Furthermore, with the above judging device 4, the boundaries of the prescribed number of pellets 1 conveyed in a line can be quickly detected, and the acceptance or rejection of the nuclear fuel pellets 1 can be quickly determined correctly. Moreover, inasmuch as the handling unit 2 includes the smaller-diameter roller 7 disposed adjacent to the loading device 6, the pellets 1 caused to move from the loading device 6 pass through the smaller-diameter roller 7 and are smoothly located at the inspecting position 9 with no shock given to the pellets 1. Obviously many modifications and variations of the present invention are possible in the light of the above teachings. For example, in the previous embodiment, the number of the ejecting grooves 10 is two. However, as shown in FIG. 5, the larger-diameter roller 8 may be modified so as to have three or more ejecting grooves 10a disposed in circumferentially equally spaced relation to one another. Furthermore, not only the larger-diameter roller 8 but also the smaller-diameter roller 7 may be driven by a suitable drive mechanism in the same direction at an identical peripheral velocity. FIG. 6 depicts gear arrangements for such a drive mechanism 31. The mechanism 31 comprises a larger-diameter gear 32 fixedly mounted on the shaft 8a for the larger-diameter roller 8, a smaller-diameter gear 33 fixedly mounted on the shaft 7a for the smaller-diameter roller 7, a drive gear 34 meshed with the gears 32 and 33 and mounted on a drive shaft 35, and a drive means such as a motor for rotating the drive shaft 35. |
042082498 | description | DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS For a more complete appreciation of the invention, attention is invited to FIG. 1 which shows a fuel assembly 10. Comprising the fuel assembly 10 is a group of long, slender fuel rods 11, the lengthwise axes of which are arranged in a generally parallel array. One end of the fuel rods is received in an end fitting 12. As illustrated, the end fitting 12 has a cellular grill 13 that is disposed in a direction which is transverse to the lengthwise axes of the fuel rods 11 in order to engage the ends of these rods, thereby to bear the movement of the fuel rods in a lengthwise direction. The end fitting 12 further includes a monolithic end casting 14 that supports the cellular grill 13. As shown, the end casting 14 is generally in the shape of a hollow cube, open at its transverse ends and provided in each of the respective cube faces with lengthwise slots 15, 16, 17 and 20. The slots 15, 16, 17 and 20 are parallel with the lengthwise axes of the fuel rods 11. These slots, moreover, penetrate each of the cube faces for about two thirds of the lengthwise depth of the middle portion of these faces, as measured from the transverse end of the casting 14 that is spaced in the lengthwise direction from the grill 13. Stops 21, 22, 23 and 24 that have the general appearance of rivets are secured in the slots 15, 16, 17 and 20, respectively, at about one quarter of the slot depth, again measured from the transverse end of the casting 14 that is spaced in a lengthwise direction from the grill 13. Spring pads 25, 26, 27 and 30, which will be described subsequently in more complete detail, protrude from the hollow interior of the end casting 14, through the respective slots 15, 16, 17 and 20 in order to enjoy a degree of travel in the lengthwise direction of the fuel rods 11 that is limited by the respective stops 21, 22, 23 and 24 and those portions of the end casting 14 that are adjacent to the cellular grill 13 and immediately below the slots. The entire fuel assembly 10 is aligned within the reactor core (not shown in the drawing) and braced to attenuate movement in the lengthwise direction of the fuel rods 11 by means of four internal pads, of which only pads 31, 32 are shown in FIG. 1. The pads 31, 32 are secured to and depend from a transversely disposed grid (also not shown in the drawing) that spans the area above the entire reactor core. The internal pads are generally rectangularly arranged in sets of four. Each of these sets are specific to a particular one of the fuel assemblies. The internal pads, of which the pads 31, 32 are illustrative, bear against those portions of the spring pads 25, 26, 27 and 30 that protrude through the respective slots 15, 16, 17 and 20 in the faces of the end casting 14. Turning now to FIG. 2, the end casting 14 is provided with a transverse shoulder 33 that catches an edge of a portion of the cellular grill 13. As shown, the slot 15 is blocked by means of the stop 21. The portion of the spring pad 25 that protrudes through the slot 15 bears against internal pad 34 which is fixed to the grid (not shown in the drawing). In accordance with a feature of the invention, the spring pad 25 is provided with an aperture 35. A hollow guide post 36 is received in the aperture 35 for relative movement in a lengthwise direction. A pin 37 also secures a cylindrical plunger 40 to the spring pad 25. The pin 37, moreover, secures the plunger 40 in the end of the guide post 36 in order to block the otherwise open end of the post 36. The fit between the cylindrical wall of the plunger 40 and the inner wall of the guide post 36 is sufficiently loose to permit the plunger to move freely in a lengthwise direction relative to the post but nevertheless provide a reasonably fluid-tight fit between the plunger and the wall. As illustrated, the guide post 36 is oriented with its longitudinal axis parallel with the lengthwise axes of the fuel rods 11. Guide post slots 41, 42 also are formed in the walls of the post in a longitudinal direction. The widths of these guide post slots 41, 42 are adequate to enable the pin 37 to move in a longitudinal direction relative to the guide post 36 during lengthwise movement of the post relative to the plunger 40 as described subsequent in more complete detail. The depths of these guide post slots 41, 42 moreover, are equal to about half the length of the guide post 36, the ends of the guide post slots occurring above the transverse surface of the cellular grill 13. Illustratively, the guide post 36 protrudes into and is secured to the cellular structure of the grill 13. As shown, portions 43 of the grill 13 are cut away to form recesses that accommodate the depth of the guide post 36 penetration into the grill 13. A disk-shaped plate 44 is secured within the guide post 36 to the transverse surface of the cellular grill 13. The diameter of the plate 44 is gauged to plug the end of the guide post 36 in which it is lodged. An orifice 45 is formed within the plate 44 to provide a means for fluid communication between guide post volume 46 that is formed between the plunger 40 and the plate 44 and the balance of the reactor core volume. In operation, and, as shown in FIG. 3 by means of a companion structure within the end fitting 12 to that which was described in connection with FIG. 2, as the reactor core sustains a major seismic or other shock, a lengthwise component of this force compels the fuel assembly 10 to move toward the internal pad 32. The pad 32 bears against the portion of the spring pad 30 that protrudes from the end casting 14 through the slot 20. Not only is this movement of the fuel assembly 10 retarded through the resilient properties of coil spring 47, but also through the hydraulic forces that are generated within a guide post 50. Thus, the pressurized water coolant in the reactor core that fills guide post volume 51 acts as a shock absorber, the water dissipating the imposed force as it flows out of the volume 51 by way of an orifice 52 in plate 53. One of the salient features of the invention, however, is the progressively decreasing discharge area that is provided by means of the relative lengthwise travel of a plunger 54 past the guide post slots, only guide post slot 55 being shown in FIG. 3. Thus, as the shock is applied initially to the reactor core, flow of water from the volume 51 is relatively unrestricted and the lengthwise motion retarding effect of the plunger and guide post combination is relatively slight. This initially slight retardation protects reactor core components from damage that otherwise would result from the abrupt application of major force to a rigid system. As the fuel assembly 10 moves in a lengthwise direction toward the internal pad 32, the plunger 54 progressively blocks the orifice provided by the guide post slot 55 and its companion slot in the guide post 50 that is out of the plane of FIG. 3. This progressive decrease in orifice area has the effect of increasing the impedance of flow from the volume 51 into the balance of the reactor core, thereby providing for a progressive attenuation of the applied force in a manner that gradually--rather than abruptly--absorbs this force. The progressive attenuation of the force in question that characterizes the invention protects the reactor core structure from possible damage that otherwise might be expected to occur if the force is applied to a rigid system. Further with respect to the operation of the invention, after the plunger 54 has completely blocked the guide post slots, controlled fluid discharge from the chamber 51 continues through the orifice 52 in the plate 53 until the applied force is fully absorbed. In this force absorption the coil spring 47 also participates to attenuate a share of the applied shock. Clearly, the combination of the coil spring 47, the orifice 52 and the progressively changing orifice area that is provided through the cooperative effect of the plunger 54 and the associated guide post slots produce a substantially better means for coping with these forces than any one or two of these components alone, even if the capacity of the individual components is increased to absorb the entire anticipated loading, in a way, moreover that actually removes parasitical neutron absorbing material from the reactor core. Thus, the hollow guide posts that characterize this invention eliminate inefficient neutron-absorbing matter from the reactor core in a way that nevertheless enhances the structural integrity of the core. Naturally, after the applied shock has been dissipated in the foregoing manner, the energy stored in the compressed coil spring 47 presses the fuel assembly 10 in a lengthwise direction away from the internal pad 32 unitl this motion is stopped through the action of the spring pad 30 and the stop 24. In most practical situations envisioned, it is expected that all of the shock attenuating guide posts in a reactor core structure will be involved in coping with major forces that might need to be withstood. |
055132286 | description | DETAILED DESCRIPTION FIG. 1 shows a penetration adapter 1 of the head 2 of the vessel of a pressurized water nuclear reactor, onto which is screwed and welded the lower part 3 of a tubular support of a thermocouple column 5 passing through the head of the vessel 2, inside the adapter 1. The support of the thermocouple column 5 includes an upper part 4 which is connected end-to-end with the lower part 3 fixed onto the adapter 1, with the interposition of a seal 6, by means of a clamp 7. The thermocouple column 5 is fixed in a leaktight manner inside the upper part 4 of the support, by a lifting and clamping assembly 8 allowing a pressure to be exerted on a seal interposed between a shoulder of the thermocouple column and a shoulder arranged opposite in the bore of the tubular support. The clamp 7 consists of two parts in the form of ring portions, including lugs traversed by assembly openings such as 7a and 7b. The lower part 3 and the upper part 4 of the tubular support include, in their end parts which are connected end-to-end, frustoconical shoulders, 3a and 4a respectively, and the clamp 7 includes annular internal surface portions of frustoconical shape intended to bear on the frustoconical surfaces 3a and 4a of the ends of the parts of the support. In order to assemble the two parts of the support, these are brought together, the seals 6 being interposed between their ends, which are connected end-to-end. The elements in the form of ring portions constituting the clamp 7 are fitted in the junction region of the two parts of the support, so that their internal surfaces come into contact with the frustoconical surfaces 3a and 4a of the two parts of the support. The assembly lugs of the ring portions are made to coincide and screws engaged in the openings such as 7a and 7b make it possible to assemble and tighten the clamp 7. The clamping of the ring portions which constitute two half-collars of the clamp is effected using threaded rods engaged in the openings such as 7a and 7b and tightened by nuts which bear on the assembly lugs. Such assembly takes a fairly long time to carry out, and the presence of at least two operators near the upper surface of the vessel head, i.e., near a component which emits radioactive radiation. Because of their mode of production and assembly, the two half-collars constituting the clamp are relatively heavy and their assembly requires the two half-collars to be held in their assembly position before insertion of the rods and screwing of the assembly nuts. The presence of two operators near the vessel head for an intervention time which may be long and lead to high radiation dose levels for the two operators. The use of articulated clamps which are more lightweight than clamps assembled by rods and nuts, and which are much faster to fit, allows the clamps to be fitted by a single operator in a shorter time, so that radiation doses received are themselves reduced. However, as explained above, these clamps whose clamping element consists of a transverse screw do not allow perfect control of leakage of pressurized cooling fluid of the reactor in the event of breakage of the screw. FIGS. 2 to 6 represent a clamp according to the invention, made in articulated form and including a blocking device making it possible to limit and control the rate of leakage of the cooling fluid of the reactor, in the event of breakage of the clamping screw. As can be seen in FIG. 2, the clamp 10 according to the invention includes three arms 11a, 11b and 11c which are joined together in articulated fashion by means of two bars 12a and 12b and pins 13 which are all parallel to each other and perpendicular to the plane side faces of the arms 11a, 11b and 11c. The arms 11a, 11b and 11c are machined on their inner faces to constitute three surfaces, 14a, 14b and 14c respectively, in the form of ring portions which all have, in the closed position of the clamp represented in FIG. 2, the same axis 15, which constitutes the axis of the clamp. The articulation pins 13 are also parallel to the axis 15. As can be seen in FIG. 3, the inner surfaces in the form of ring portions, such as the surface 14b of the arm 11b, include two side surfaces 16 and 16' inclined with respect to the mid-plane of the surface 14b, and of annular shape, intended to come into contact with the frustoconical annular surfaces such as 3a and 4a (FIG. 1) of two parts, which can be connected end-to-end, of a thermocouple column support. During closure and locking of the clamp 10, axial clamping of the two support components is produced, with respect to each other, with interposition of a seal, by the interaction of the surfaces 16 and 16' and of surfaces such as 3a and 4a of end parts of the components to be connected. The clamping and locking of the clamp 10 is effected by a device 18 including two bearing blocks 19 and 19' which come into contact when clamping and locking the clamp 10, with two recesses 17 and 17' in the form of cylinder portions with circular section machined in the parts of the arms 11a and 11c which point outwards. A description will now be given, with reference to FIGS. 2, 4, 5 and 6, of the device 18 for clamping and locking the clamp 10 according to the invention. The bearing blocks 19 and 19' each have a central part delimited by a cylindrical surface whose radius is equal to the radius of the recess 17 or 17' of the arm 11a or 11c on which the block 19 or 19' bears, and a plane surface parallel to the axis of the cylindrical surface made by milling to constitute a plane bearing surface for a nut. As can be seen in FIGS. 4, 5 and 6, the central part of the block 19 is delimited by the cylindrical surface 19a and the plane surface 19b; the block 19 includes, on either side of the central part, two journals 20a and 20b having a common axis 21 parallel to the axis of the central part. The block 19' has a shape similar to the shape of the block 19 and is situated in a symmetrical position, so that the cylindrical surfaces of the blocks 19 and 19' bear on the surfaces 17 and 17' of the arms 11a and 11c, which are situated opposite each other. The central part of each of the components 19 and 19' is traversed by an opening such as 23 (component 19) having a direction perpendicular to the axis 21 of the journals 20a and 20b and to the axis of the central part of the bearing block 19. A screw 22 is engaged by its threaded end parts 24 and 24' inside openings such as 23, which pass through the blocks 19 and 19', which have a diameter greater than the external diameter of the screw, in order to obtain a slide mounting of the bearing blocks by means of the end parts 24 and 24'. These parts 24 and 24' partially project with respect to each of the blocks 19 and 19', on either side of these blocks. Nuts 25 and 25', screwed onto the projecting end parts of the screw 22 on either side of the blocks 19 and 19', are placed in contact with the plane surfaces such as 19b of the blocks 19 and 19' to ensure that the cylindrical surfaces such as 19a bear against the recesses 17 and 17' of the arms 11a and 11c of the clamp, and to clamp and lock the clamp 10. The clamping and locking device 18 includes two bars 26a and 26b, each comprising a circular opening 27a or 27b and an oblong opening 28a or 28b in which the journals of the bearing blocks 19 and 19' are engaged. The journals of the bearing block 19' are engaged in the circular openings 27a and 27b of the bars 26a and 26b which are placed opposite each other, and the journals 20a and 20b of the block 19 are introduced into the oblong openings, 28a and 28b respectively, which are also situated opposite each other, since the bars 26a and 26b are identical. The bars 26a and 26b are placed parallel to each other, on either side of the screw 22 and in its axial direction. The journals such as 20a and 20b and the blocks 19 and 19' are held in the corresponding openings of the bars 26a and 26b by washer assemblies such as 29 and retaining pins such as 30, associated with parts of the journals which project with respect to the external face of the corresponding bars 26a and 26b. The journals 20a and 20b, whose diameter is less than the diameter of the oblong openings 28a and 28b, are mounted so as to slide in the oblong openings, so that the block 19 can be moved in the longitudinal direction of the oblong openings and of the bars, to make it possible to fit and clamp the clamp by means of the nut 25 bearing against the surface 19b of the bearing block 19. The clamping of the clamp is produced using the bearing block in contact with the recesses 17 and 17' of the articulated arms 11a and 11c of the clamp. According to the invention, the clamp 10 includes a blocking device 31 which is fitted after the clamp is clamped by means of the nut 25 which is screwed onto the threaded end 24 of the screw 22, so that the screw has an end part 32 which projects outwards with respect to the nut 25 and consists of the end of the threaded part 24. The blocking device 31 includes a support 33 consisting of a strut 34 whose length is substantially equal to the length of the central part of the bearing block 19 and of two profiled plates 35a and 35b which are fixed to the ends of the strut 34 and include raised edges whose separation is substantially equal to the width of the bars 26a and 26b. The strut 34 is traversed by a smooth opening 36 in which a lock nut 37 is mounted for rotational and sliding movement. The lock nut 37 includes a tapped internal bore 37a allowing it to be engaged by screwing onto the threaded projecting end 32 of the screw 22. The tapped bore 37a is open at one of the ends of the lock nut 37, following which the lock nut 37 has a bearing flange 38 on the outside. At its end opposite the bearing flange 38, the nut 37 includes a profiled opening 39, for example with hexagonal cross-section, making it possible to turn the lock nut 37 inside the smooth opening 36 which is screwed onto the end 32 of the screw 22, using a suitable tool. A blocking component 40, intended to block and trap the lock nut 37, includes a square base having inclined edges which are engaged against the inclined edges of an opening in the strut 34, so as to provide a dovetail assembly between the square base of the blocking component 40 and the strut 34. On the base of the blocking component 40, a thin deformable ferrule 41 is fixed, the internal diameter of which is slightly greater than the external diameter of the lock nut 37. The lock nut 37 includes recesses 42 in which the deformable ferrule 41 can be engaged and crimped after the lock nut is screwed onto the end 32 of the screw 22, inside the blocking component 40 which includes an opening allowing passage for the lock nut 37, in the extension of the ferrule 41. The strut 34 has, at its ends fixed onto the plates 35a and 35b, two slots 43a and 43b, in each of which an end part of a blocking finger 44a or 44b is engaged, which finger is mounted so as to pivot on the strut 34 by means of a pin 45a or 45b perpendicular to the axis of the screw 22 which constitutes the axis of the clamp. The slots 43a and 43b and the end part of the blocking fingers 44a and 44b are produced so as to allow the fingers 44a and 44b to pivot between a blocking position represented in FIG. 5, and an open position, represented in FIG. 6. Each of the fingers 44a and 44b includes a blocking stud 46 and a push button 47 on one of its substantially plane faces. The opposite face of the blocking finger includes an inclined surface 48 intended to come into contact with the end of the flange 38 of the lock nut 37, which holds the finger in the blocking position when the lock nut 37 is screwed onto the end 32 of the screw in order to block it, as represented in FIG. 5. When the lock nut 37 is not engaged with the end part 32 of the screw, the flange 38 bears against the inner surface of the strut 34 and frees the blocking fingers which can be tilted inwards by pushing on the buttons 47, as shown in FIG. 6. The plates 35a and 35b are traversed by openings allowing passage for the buttons 47 and the blocking studs 46. After the clamp is fitted and clamped by torquing the nut 25 onto the end of the screw 22, in order to produce the leaktight connection of two tubular components such as two parts of a thermocouple column support, the plates 35a and 35b of the device 31, whose blocking fingers 44a and 44b are placed in the open position by pressing on the buttons 47, the lock nut 37 being in its position bearing against the strut 34 by its flange 38, are engaged on the end parts of the bars 26a and 26b on the oblong openings 28a and 28b side. The blocking means 40 placed in the opening of the strut 34 is engaged on the projecting external surface of the lock nut. The blocking device 31, whose plates 35a and 35b are engaged on the end parts of the bars 26a and 26b, is held in place, and the lock nut 37 is screwed onto the end 32 of the screw 22 which projects out of the nut 25, by using a profiled key introduced into the opening 39. The lock nut 37 is screwed until the flange 38 bears against the nut 25. During the screwing of the lock nut, the external edge of the flange 38 interacts with the actuation surface 48 of each of the blocking fingers, in order to pivot the fingers outwards so that the blocking stud 46 is introduced into the corresponding oblong opening 28a or 28b, at the end of screwing, when the flange 38 abuts against the nut 25. The blocking studs 46 abut against the outer end of the corresponding oblong opening 28a or 28b, between this end and the journal 20a or 20b. In fact, the oblong openings 28a and 28b are designed so that, in the clamping and locking position of the clamp, a space of length greater than the diameter of the blocking stud 46 remains between the journals 20a and 20b and the outer end of the oblong openings 28a and 28b. The lock nut 37 is made irremovable and captive by the crimping of the parts of the deformable ferrule 41 into the recesses 42 of the lock nut 37. After a repair or maintenance operation on the nuclear reactor, requiring dismounting of the support of one or more thermocouple columns, the support or supports are assembled and clamped in a leaktight manner by using one or more clamps according to the invention. After restarting of the nuclear reactor, the clamps undergo stresses under the effect of the high-pressure cooling fluid of the reactor. The locking nuts 25 of the clamps are made irremovable by the fact that the lock nut 37 bears via a flange 38 on the locking nut 25 and constitutes a nut retention device. In the event of breakage of a screw 22 of a clamp according to the invention including a blocking device 31, the forces tending to open the clamp and separate the branches 11a and 11c and the bearing components 19 and 19' are taken up by the nut 25, the lock nut 37 bearing on the nut, the strut 34, the blocking fingers 44a and 44b and the bars 26a and 26b. The forces are looped round by means of the bearing block 19' engaged by its end journals in the circular openings of the bars 26a and 26b. Only very slight movement of the branches of the clamp can thus occur, so that the loss in leaktightness of the junction between the tubular elements is itself very small. The leakage of reactor cooling fluid under very high pressure is therefore greatly limited, which makes it possible to carry out the emergency shutdown of the nuclear reactor in complete safety, without substantial escape of radioactive material. After shutdown and cooling of the nuclear reactor, it is possible both to remove the defective clamp and to fit a new clamp for the tubular components very quickly. In order to carry out scheduled or unscheduled repair or maintenance operations, it is possible to remove the clamps easily and quickly, after removal of the blocking device. In order to remove the blocking device, the fastening ferrule 41 is first cut and separated from the lock nut 37, then the lock nut is unscrewed so as to separate it from the end part 32 of the screw. The blocking device 31 can then be separated in its entirety from the clamp by exerting pressure on the buttons 47, as represented in FIG. 6. The blocking studs 46 are thus released from the oblong openings 28a and 28b, and the blocking device 31 can be separated from the clamp by a simple pulling action. The device according to the invention therefore makes it possible to ensure complete safety of the clamps of tubular components subjected to very high stresses. Furthermore, this blocking device can be fitted or removed easily; it can be easily fitted to existing clamps. The support of the blocking device, the lock nut and the fingers may be produced in a form or manner different from those which have been described. It is possible to make the lock nut irremovable and captive in a manner different from that which has been described. Similarly, the actuation of the blocking fingers may be produced by means different from those which have been described. The invention applies not only to the case of leaktight joining of tubular supports of thermocouple columns, but also to the case of leaktight end-to-end joining of any tubular components which undergo high stresses in use. |
040381366 | claims | 1. A support structure for the lateral neutron shield system of a fast reactor core, said core being a vertical axis of symmetry and including a core support structure and a lateral neutron shield wherein said structure is a horizontal ring having an internal contour coinciding exactly with an external contour of the reactor core, a bottom face of said ring being supported by a periphery of said core support structure, said ring comprising a plurality of horizontal layers of metallic plates, clamping members maintaining said layers in relative positional relation, said metallic plates of one layer being angularly displaced around said axis of symmetry and overlappedly engaging said plates of adjacent layers, vertical through-holes in said ring receiving bottom end-connectors of elements of said neutron shield. 2. A structure according to claim 1, wherein the layers of metallic plates are contiguous. 3. A structure according to claim 1, including thin washers separating two successive layers of metallic plates. 4. A structure according to claim 1, wherein said clamping members are tie-bolts. 5. A structure according to claim 4, including thin washers separating said layers and traversed by said tie-bolts. |
043495052 | description | DETAILED DESCRIPTION Referring now to FIG. 1, there is shown schematically a prior art neutral beamline with direct energy recovery of positive ion energy. One typical neutral beamline of this type is described in U.S. Pat. No. 3,713,967, issued Jan. 30, 1973, to Gordon W. Hamilton et al for "Energetic Neutral Particle System for Controlled Fusion Reactor." A light isotopic species positive ion source 11 is operated at a high positive potential, typically +40 kv for a source of hydrogen (H) or deuterium ions, for example. The ion source may be mounted to a vacuum enclosure 13 for the beamline system by means of an electrical insulator and seal assembly 15. The ion beam from the source 11, is accelerated by means of a +40 kv power source 19 connected between ground and the plasma grid 17 of the source 11. A slight decel voltage typically 1 kv negative is applied by means of a -1 kv power source 21 between ground and the extraction grid 23 of the ion source. The exit grid 25 of the source is tied to ground potential. The negative decel voltage applied between the extraction grid 23 and the exit grid 25 prevents electrons generated in the neutralizer cell 27 from drifting back into the ion source 11. The beam of positive ions extracted from the ion source 11 is thus accelerated to ground potential and remain at ground potential through the gas cell neutralizer 27 by connecting the neutralizer cell to ground potential. In the gas cell, some of the positive ions entering the cell are converted to neutral particles with high kinetic energy and travel along the accelerated beam path and into an evacuated drift tube 29 coupled to a neutral beam utilization device, such as a fusion reactor 31 to heat a magnetically confined reactor plasma. Magnet poles 33, located along the beamline a short distance from the exit end of the neutralizer cell 27 are arranged to deflect the positive ions from the neutral beamline into converter cells 35. In the converter cells 35, the electrons contained in the beam for space charge neutralization are blocked by means of electrostatic fields and strong positive fields are used to decelerate and collect the ions. The current produced from the collection may flow through an electrical load 37 or be fed back to reduce the acceleration source 19 power requirements. An alternate scheme has been proposed for energy recovery based on magnetic suppression of electrons, as discussed above which employs a funnel-shaped ion collector encircling the beam downstream of the electrostatic suppressor electrode. This collector is also operated at a high positive decelerating potential and the recovered energy in the form of recovered ion current may be fed back to supplement the ion source current. These prior art systems have inherent disadvantages as pointed out above. According to the present invention, a neutral beam generator with direct positive ion energy recovery based on transverse magnetic field suppression of electrons at the neutralizer tube output will now be described with reference to FIG. 2. It will be understood that the beam must be manipulated within a vacuum containment, such as the vacuum casing 13 shown in FIG. 1. However, in order to simplify the drawing, the vacuum casing is not shown in FIG. 2. Further, it will be obvious that it is necessary to remove the background gases and the deenergized species from which the charge has been collected. This is done as in any conventional beamline by cryocondensing vacuum pumping panels or other suitable vacuum pumping means (not shown). Referring now to FIG. 2, a positive ion source 41, has its plasma grid 43 connected to a positive voltage source 45 of typically +4 kv for providing an acceleration boost voltage (V.sub.boost). The primary ion acceleration voltage (V.sub.accel) is provided by supply 47 which is connected between ground and the neutralizer gas cell 49, which is also connected to the exit grid 51 of the ion source. The acceleration voltage will depend upon the beam energy requirements and the ion source capacity. For the illustration here V.sub.accel is -40 kv for a 60 amp ion current. This is typical for heating plasmas in the Princeton Large Torus (PLT) research fusion reactor. A deceleration voltage (V.sub.decel) supply 53 is connected between the neutralizer tube 49 and the extraction grid 55 of ion source to provide a slightly negative (typically -1 kv) extraction grid voltage relative to the neutralizer tube 49 voltage to prevent the drift of electrons from the neutralizer back into the ion source. This biasing arrangement provides the potential distribution along the beamline as shown in FIG. 3. As will be seen from FIGS. 2 and 3, the ion beam 57 diverted from the neutral beamline 59 is decelerated to ground potential and the ion charge is collected on a grounded collector 61. It will be appreciated that the entire grounded enclosure may be used as an ion collector since the ions are decelerated to ground potential immediately at the neutralizer exit and thus may eliminate the need for the specific collector surface 61 to obtain energy recovery. In order to obtain the energy recovery at ground potential, the electrons must be blocked at the neutralizer exit. If the electrons are allowed to go to one of the grounded surface potentials, they would be accelerated across the dotted path (the ion deceleration potential) in FIG. 3 and would collectively give up more energy than could be recovered from the positive ions. In fact, they would overcurrent the high voltage supply 47 and turn off the ion source. To accomplish electron blocking, a magnetic field is provided transverse to the beam in the exit end of the neutralizer tube 49. Referring to FIGS. 2, 4, and 5, it will be seen that the field is provided by means of electromagnetic pole pieces 63a and 63b or equivalent magnetic field-producing means are disposed in juxtaposition across the beam path in the exit end of the neutralizer tube 49. The magnetic field may be varied to obtain the proper field strength to block the exit of the electrons. Also, the magnet pole pieces 63 may be tilted at a 45.degree. angle, as shown, or placed at any convenient angle so long as the neutralizer tube 49 is tapered to conform to the magnets. As shown in FIGS. 2, 4 and 5, the end of the neutralizer tube 49 is tapered to conform to the 45.degree. tilt of the magnet poles orientation and extended into the center of the axial extent of the magnetic field along the beamline provided by the pole pieces to closely couple the magnetic field with the neutralizer end geometry. This ensures a maximum magnetic field for blocking the neutralizer generated electrons. It will be appreciated that other configurations for producing the field transverse to the beam may be employed, especially since the ion beam charge is collected at ground potential. To remove the small portion of electrons, which are not forced back into the neutralizer by the blocking magnetic field, an electron collector ring 65 is mounted around the end opening of the neutralizer tube by means of electrical insulators 67. The collector ring is made of a nonmagnetic electrically conductive material, such as copper, in the form of a collar with the same end geometry as the neutralizer tube 49 end, i.e., tapered at a 45.degree. angle at the tube exit end, and extends about 1.5 centimeters past the neutralizer tube end. A positive voltage supply 69 is connected between the neutralizer 49 and the electron collector collar 65 to apply a slightly positive (approx. 300 V) bias voltage (V.sub.collector, FIG. 3) relative to the neutralizer 49 which is biased highly negative. The operation of the system may best be explained with specific reference to FIGS. 4 and 5. The electrons streaming toward the exit of the neutralizer 49 together with the ions and neutrals generated in the neutralizer gas cell first experience an increasing magnetic field (B) perpendicular to the general direction of electron travel with the beam as well as an accelerating primary electric field (E) generated by the negatively biased neutralizer 49 and the rest of apparatus at ground potential exterior to the neutralizer as they approach the end of the neutralizer tube 49. The electrons are then carried out toward the neutralizer end edge by an E x B drift while gyrating as indicated by the e path illustrated in FIG. 5. Once the electrons pass the edge of the neutralizer tube they are accelerated into the electron collector ring. The ring is preferably coaxially disposed about and spaced from the neutralizer tube exit end and functions as an interposed surface, biased a few hundred volts positive with respect to the neutralizer, that terminates the electrons. The energy loss is only a few hundred electron volts of energy instead of the typically 40 keV (depends on the value of V.sub.accel) they would give up in traveling to one of the grounded surfaces. It should be pointed out here that all the vacuum enclosed surfaces beyond the neutralizer cell 49 are at ground potential including the magnet pole pieces 63. Therefore, the ions coming out of the neutralizer 49 experience both retardation due to the primary electric field and transverse deflection due to the magnetic field. Initially, the ion gyroradius is typically several times greater than the gas cell diameter, but it is reduced as the ions are decelerated within the pole region to a speed corresponding to the accelerator boost potential. When they finally reach the surroundings (the ion collector, 61, vacuum chamber walls or pole faces), they impart only the energy corresponding to the accelerator boost potential. The boost potential 45 is kept as low as possible and lies between 2% and 10% of the V.sub.accel potential 47 depending upon various beamline parameters. The role of the V.sub.boost potential is to ensure the ions have enough energy to strike a grounded surface (energy recovery) rather than deflect back into the neutralizer cell 49 (total energy loss). The exact motion of the ions, however, depends on the electric and magnetic field configuration in the magnetic pole region. Free electrons outside the gas cell, in the magnet region and the surroundings, will not hinder the ion current recovery since they are approximately in the field free-region at ground potential. The deceleration of the full-energy ions to an impact velocity at an energy level equal to the V.sub.boost potential returns most of their kinetic energy (corresponding to the V.sub.accel potential) to the electrical power supply system used to accelerate them. Thus, their main energy content is recovered, and the ions convert back to low energy neutral gas to be pumped out of the vacuum chamber as by cryopumping. In the neutralizer, three different energy groups of ions of the source species are present: full energy (corresponding to the initial kinetic energy provided by V.sub.accel +V.sub.boost), one-half energy, and one-third energy. The three energy groups originate in the atomic, diatomic and triatomic states of the source species. As pointed out above various light isotopic species may be used depending upon the particular reactor application requirements. The full energy ions are of primary interest for the purpose of energy recovery since they represent the primary energy component of the beam (85-90%). However, if the one-half and one-third energy ions exit the neutralizer with the full energy ions they do not have sufficient energy to reach the ground potential surfaces since the potential drop between the gas cell and the surroundings is almost the full-energy potential. These ions tend to bend in smaller orbits due to the magnetic field and are forced to strike either the neutralizer tube or electron collector at which point their energy is lost. If they strike an exterior wall of the neutralizer tube or electron collector, additional energy may be lost due to secondary electrons emitted at impact some of which may travel to a grounded surface. The secondary electrons which are accelerated directly to ground potential detract from the energy recovery efficiency of the full energy ions. This loss can be controlled substantially by proper selection of the magnetic field strength to block the fractional energy ions from exiting the neutralizer. Thus, the fractional energy ions are dumped back into the neutralizer without generating parasitic secondary electrons. EXAMPLE A modified duo PIGatron ion source capable of 40 kv/60 A operation (developed for heating plasmas in the PLT and impurity study experiment) was used to test an experimental configuration as illustrated in FIG. 2. This source is particularly well suited for every recovery investigation due to the high-percentage (approx. 85%) full-energy ion component with a hydrogen beam. An available ion current (I.sub.A) of 18 amps at 40 keV was used. The proof of principle experiment was limited to approximately 20 kV due to electronic problems. The following supply voltages were used: V.sub.boost =800 v PA1 V.sub.accel =20 kV PA1 V.sub.decel =1 kV PA1 V.sub.collector =300 v A conventional neutral beam target was used to measure the neutral beam energy. The recovered ion current I.sub.R was typically 1 amp. The electron leakage current, from full energy electrons impinging upon the grounded ion collector, was typically less than 1 amp. The leakage current (I.sub.e) was determined by calorimetrically measuring the power drain to water cooled, ground potential plates covering the magnet poles and dividing this power by the V.sub.accel potential. The efficiency (n), which may be defined as follows ##EQU1## varied between 20% and 80%. The large error was due to subtracting two large numbers to obtain a small difference. The magnetic field strength was typically 1000 Gauss. In one test run, the magnetic field was turned off, the electron collector current immediately destroyed the 400 amp rated blocking diodes in the collector voltage supply. This illustrates the electron blocking function of the strong magnetic field at the neutralizer exit. Since electron blocking is achieved by a magnetic field, the size and density of the beam are not critical as in electrostatic blocking schemes. Thus, it will be seen that a charged particle recovery system for a neutral ion beam generator based on magnetic blocking of electrons is provided. The blocking magnet in combination with the ion retarding electric field at the beam neutralizer exit end separates the charged ionic particles from the neutral beam and electrons to provide energy recovery of the full energy ion component of the beam. The foregoing description of a preferred embodiment of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed, and obviously many modifications and variations are possible in light of the above teaching. The embodiment was chosen and described in order to best explain the principles of the invention and its practical application to thereby enable others skilled in the art to best utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto. |
claims | 1. A system for cooling multiple single-type window foils of an electron beam accelerator comprising:a primary single-type window foil communicating with a vacuum side of a scanning horn of the electron beam accelerator;a secondary single-type window foil positioned on an atmospheric side of the scanning horn, wherein the distance of the secondary window to a biomass material under irradiation is more than 0.1 cm and less than 10 cm;a first flow path for providing a first cooling gas across the primary single-type window foil and second flow path for providing a second cooling gas across the secondary single-type window foil, the secondary single-type window foil being exposed to atmospheric pressure;a pivoting beam stop configured to pivot between the primary single-type window and the secondary single-type window to block an electron beam of the accelerator;a conveyor that is configured to move the biomass material through an irradiation zone under the secondary single-type window foil;wherein the primary and secondary single-type window foils are positioned with a gap of less than about 9 cm between them. 2. The system of claim 1, wherein the window foils are metallic. 3. The system of claim 2, wherein both the primary single-type window foil and the secondary single-type window foil are part of the scanning horn of the electron beam accelerator, whereat least one inlet is provided and which allows a cooling gas to enter the gap defined between the primary and the secondary single-type window foils andat least one outlet is provided to extract cooling gases from the gap defined between the primary and secondary single-type window foils. 4. The system of claim 3, further including a cooling chamber, the cooling chamber including four walls and the interior volume is approximately rectangular prism in shape. 5. The system of claim 2, further including a treatment enclosure with a cover surface, where the enclosure is positioned on a side of the secondary single-type window foil opposite the electron beam accelerator and the conveyor is within the treatment enclosure. 6. The system of claim 5, wherein the secondary single-type window foil is mounted on the cover surface and is integral to the treatment enclosure. 7. The system of claim 6, wherein the cover surface is perpendicular to the electron beam accelerator. 8. The system of claim 7, wherein the treatment enclosure has a first opening. 9. The system of claim 8, wherein the conveyor is configured to move the biomass material through the first opening prior to moving the biomass material under the secondary single-type window. 10. The system of claim 9, wherein the treatment enclosure includes a second opening. 11. The system of claim 10, wherein the conveyor further provides for moving the treated biomass material out of the treatment enclosure through the second opening. 12. The system of claim 11, further providing for purging the treatment enclosure with an inert gas. 13. The system of claim 1, wherein the primary single-type window foil is made from an element selected from the group consisting of: titanium, scandium, vanadium, chromium, nickel, zirconium, niobium, molybdenum, ruthenium, rhodium, palladium, hafnium, tantalum, tungsten, rhenium, platinum, iridium, and alloys or mixtures of any of these. 14. The system of claim 1, wherein the secondary single-type window foil is made from an element selected from the group consisting of: titanium, scandium, vanadium, chromium, nickel, zirconium, niobium, molybdenum, ruthenium, rhodium, palladium, hafnium, tantalum, tungsten, rhenium, platinum, iridium, beryllium, aluminum, silicon, and alloys or mixtures of any of these. 15. The system of claim 1, wherein the primary single-type window foil is from 10 to 50 microns thick. 16. The system of claim 15, wherein the primary single-type window foil is from 15 to 40 microns thick. 17. The system of claim 15, wherein the primary single-type window foil is from 20 to 30 microns thick. 18. The system of claim 15, wherein the secondary single-type window foil is from 5 to 30 microns thick. 19. The system of claim 15, wherein the secondary single-type window foil is from 8 to 25 microns thick. 20. The system of claim 15, wherein the secondary single-type window foil is from 10 to 20 microns thick. 21. The system of claim 9, wherein the biomass material is selected from the group consisting of: cellulosic material, lignocellulosic material, and starchy material. 22. The system of claim 9, wherein the biomass material is selected from the group consisting of paper, paper products, paper waste, wood, particle board, sawdust, agricultural waste, sewage, silage, grasses, wheat straw, rice hulls, bagasse, cotton, jute, hemp, flax, bamboo, sisal, abaca, straw, corn cobs, corn stover, alfalfa, hay, coconut hair, seaweed, algae, and mixtures thereof. 23. The system of claim 9, wherein the biomass material is treated with between 10 and 200 Mrad of radiation. 24. The system of claim 9, wherein the biomass material is treated with between 10 and 75 Mrad of radiation. 25. The system of claim 9, wherein the biomass material is treated with between 15 and 50 Mrad of radiation. 26. The system of claim 9, wherein the biomass material is treated with between 20 and 35 Mrad of radiation. 27. The system of claim 2, wherein the electron beam accelerator includes electrons having an energy of about 0.5-10 MeV. 28. The system of claim 2, wherein the electron beam accelerator includes electrons having an energy of about 0.8-5 MeV. 29. The system of claim 2, wherein the electron beam accelerator includes electrons having an energy of about 0.8-3 MeV. 30. The system of claim 2, wherein the electron beam accelerator includes electrons having an energy of about 1-3 MeV. 31. The system of claim 2, wherein the electron beam accelerator includes electrons having an energy of about 1 MeV. 32. The system of claim 2, wherein the electron beam accelerator includes a beam current of at least about 50 mA. 33. The system of claim 2, wherein the electron beam accelerator includes a beam current of at least about 60 mA. 34. The system of claim 2, wherein the electron beam accelerator includes a beam current of at least about 70 mA. 35. The system of claim 2, wherein the electron beam accelerator includes a beam current of at least about 80 mA. 36. The system of claim 2, wherein the electron beam accelerator includes a beam current of at least about 90 mA. 37. The system of claim 2, wherein the electron beam accelerator includes a beam current of at least about 100 mA. 38. The system of claim 2, wherein the electron beam accelerator includes a beam current of at least about 125 mA. 39. The system of claim 2, wherein the electron beam accelerator includes a beam current of at least about 150 mA. 40. The system of claim 1, wherein the beam stop is moveable to absorb different amounts of the electron beam. 41. The system of claim 1, wherein the beam stop absorbs at least 20% of incident electrons. 42. The system of claim 1, wherein the beam stop absorbs at least 40% of incident electrons. 43. The system of claim 1, wherein the beam stop absorbs at least 60% of incident electrons. 44. The system of claim 1, wherein the beam stop absorbs at least 80% of incident electrons. 45. The system of claim 1, wherein the conveyor is configured to move the biomass material through the irradiation zone which is at atmospheric pressure. |
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description | 1. Field of the Invention The present invention relates to a method and apparatus for automatically correcting aberrations in a charged-particle beam and also to a method of controlling an aberration corrector for a charged-particle beam. 2. Description of Related Art A scanning electron microscope (SEM) is an example of a surface imaging apparatus using charged particles. A surface imaging apparatus is described, taking a scanning electron microscope as an example. FIG. 7 is a diagram showing the structure of a prior art scanning electron microscope equipped with an aberration corrector. The microscope has an emitter 1 emitting an electron beam 2. The trajectory of the beam 2 incident on the aberration corrector 6 is controlled by a lens 3 acting on the beam 2. The beam 2 transmitted through the corrector 6 is focused onto the surface of a sample 5 by an objective lens 4. At this time, the aberration corrector 6 corrects the aberration of the total lens system. The sample surface is scanned with the electron beam 2. Secondary electrons 7 are emitted from the sample surface in synchronism with the scanning and are detected by a secondary electron detector 8. Information about the sample surface based on the detected secondary electrons 7 is displayed as a visible image on a CRT 12 in synchronism with the scan signal. Normally, the efficiency of the secondary electron detector 8 which detects secondary electrons 7 is low. Therefore, noise is removed by an image accumulator 9. The image from which the noise has been removed in this way is displayed on the CRT 12. An aberration corrector equipped with multipole elements is known as an example of such aberration corrector 6 (see, for example, Zach et al. “Aberration correction in a low voltage SEM by a multipole corrector” (Nuclear Instruments and Methods in Physics Research, A 363 (1995), 316-325). The technique disclosed in the cited reference is described below as an example. FIG. 8 is a diagram showing the configuration of an aberration corrector and the trajectory of an electron beam passing through the corrector. The aberration corrector, indicated by numeral 6, has four stages of multipole elements, which are shown, respectively, as first stage of multipole elements 6a, second stage of multipole elements 6b, third stage of multipole elements 6c, and fourth stage of multipole elements 6d. Normally, each stage of multipole elements has eight or more pole elements. The electron beam 2 incident on the aberration corrector 6 undergoes a focusing action and a diverging action simultaneously by the lens action of the first stage of multipole elements 6a. As shown, it is assumed that the electron beam 2 undergoes the diverging action in an X trajectory 6e and that the beam 2 undergoes the focusing action in a Y trajectory 6f. The lens strength of the first stage of multipole elements 6a is so adjusted that the Y trajectory 6f passes through the center of a lens field produced by the second stage of multipole elements 6b and is focused in the Y-direction. The lens strength of the second stage of multipole elements 6b is so adjusted that the X trajectory 6e passes through the center of a lens field produced by the third stage of multipole elements 6c and is focused in the X-direction. At this time, in the second stage of multipole elements 6b, the Y trajectory 6f passes through the center of the lens field produced by the second stage of multipole elements 6b and is focused in the Y-direction and so only the X trajectory 6e undergoes the lens action of the second stage of multipole elements 6b. Similarly, in the third stage of multipole elements 6c, the trajectory 6e passes through the center of the lens field produced by the third stage of multipole elements 6c and is focused in the X-direction. Therefore, only the Y trajectory 6f undergoes the lens action of the third stage of multipole elements 6c. In this way, the requirement is that the Y trajectory 6f of the electron beam 2 is focused on and passes through the center of the lens field produced by the second stage of multipole elements 6b and the X trajectory 6e of the beam 2 is focused on and passes through the center of the lens field produced by the third stage of multipole elements 6c. In the prior art, these corrections (alignments) of the trajectories of the electron beam have been made by adjusting the lens strengths of the plural stages of multipole elements 6a-6d while viewing the amount of movement of the image produced when the lens strengths of the stages of multipole elements 6a-6d are wobbled. In particular, there are mechanical deviations among the center axes of the various stages of multipole elements 6a-6d. It is difficult to correct these mechanical deviations of the center axes among the stages of multipole elements 6a-6d by adjusting the mechanical positions of the stages of multipole elements 6a-6d. Accordingly, the conventional method is to adjust the lens field strength electrically produced by the stages of multipole elements 6a-6d to the appropriate electron beam pass. Consequently, substantial hindrance is prevented even if there are mechanical positional deviations among the stages of multipole elements 6a-6d. The lens fields produced by the stages of multipole elements 6a-6d contain dipole and quadrupole fields. When the dipole field produced by the multipole elements to be adjusted is adjusted, the quadrupole field produced by the multipole elements located behind the multipole elements to be adjusted is made to wobble. The dipole field produced by the multipole elements to be adjusted is adjusted such that the image taken during the wobbling does not move. In this way, the trajectory of the electron beam is aligned. As described previously, it is necessary that the Y trajectory 6f of the beam 2 is focused on and passes through the center of the lens field produced by the second stage of multipole elements 6b and the X trajectory 6e of the beam 2 is focused on and passes through the center of the lens field produced by the third stage of multipole elements 6c. To achieve this requirement, the quadrupole fields produced by the stages of multipole elements 6a-6d need to be adjusted. During this adjustment, the dipole field produced by the multipole elements located next to the multipole elements to be adjusted is made to wobble. The quadrupole field produced by the multipole elements to be adjusted is adjusted such that the image obtained during the wobbling of the dipole field does not shift. In this way, the trajectory of the electron beam pass is aligned. The procedure of adjustment of the dipole field produced by the aforementioned multipole elements is linked to the procedure for adjustment of the quadrupole fields produced by the other multipole elements such that the electron beam trajectory adjusted by one of these two kinds of fields is affected by adjustment of the other kind of field. Therefore, the operator has spent a long time in adjusting the lens field (multipole field) of each multipole element while checking the motion and quality of the image during wobbling, relying on his experience and intuition. As described previously, in the aberration corrector composed of multiple stages of multipole elements, there are deviations among the mechanical center axes of the stages of multipole elements. By adjusting the multipole fields (dipole and quadrupole fields) produced by the stages of multipole elements by the aforementioned method (i.e., given multipole field produced by the multipole elements located behind the multipole elements to be adjusted is made to wobble), the operator empirically aligns the trajectory of the electron beam such that the beam is focused and passes through the center of the corresponding stages of multipole elements within the aberration corrector. To achieve this, the operator manually adjusts and corrects the lens strengths of the stages of multipole elements. These procedural operations are complexly linked. There is the problem that the operator spends a lot of time in making the manual adjustment according to the movement and quality of the image while relying on his experience and intuition. It is an object of the present invention to provide a method and apparatus for automatically correcting the trajectory of a charged-particle beam without a normal operator manually adjusting an aberration corrector. It is another object to provide a method of controlling an aberration corrector for a charged-particle beam. A method of automatically correcting a charged-particle beam in accordance with the invention comprises the steps of: irradiating a sample with the charged-particle beam via an aberration corrector and an objective lens, the aberration corrector having stages of multipole elements; obtaining information about a cross section of the charged-particle beam based on plural images of a surface of the irradiated sample; calculating an amount of axial deviation of the optical axis of the charged-particle beam relative to the center of a multipole field in the aberration corrector based on the obtained information about the cross section of the beam; automatically applying feedback to the aberration corrector or to the objective lens according to the calculated amount of axial deviation. An apparatus for automatically correcting a charged-particle beam in accordance with the present invention comprises: a cross-sectional information-obtaining device for obtaining information about a cross section of the charged-particle beam based on plural images of a surface of a sample irradiated with the beam via an aberration corrector and via an objective lens, the corrector being equipped with multipole elements; a calculator for calculating an amount of axial deviation of the optical axis of the beam relative to the center of a multipole field in the aberration corrector based on the obtained information about the cross section of the beam; and a feedback circuit for automatically applying feedback to the aberration corrector or to the objective lens according to the calculated amount of axial deviation. Another apparatus for automatically correcting a charged-particle beam in accordance with the present invention comprises: an aberration corrector for correcting aberration in the beam, the corrector being equipped with stages of multipole elements; an aberration correction controller for controlling the strength of a multipole field produced by the aberration corrector; an objective lens; a control unit for supplying a control signal to the aberration correction controller or to the objective lens; a cross-sectional information-obtaining device for obtaining a SEM image in synchronism with operation of the control unit to obtain information about a cross section of the beam; an axial deviation quantification device for obtaining a quantified amount of the axial deviation of the optical axis of the beam from the obtained information about the cross section of the beam; a decision unit for making a decision from the quantified amount of axial deviation as to whether an automated correction is completed or not; and a feedback circuit for producing an amount of feedback to the aberration correction controller or to the objective lens from the quantified amount of axial deviation. In the method of controlling the aberration corrector for the charged-particle beam, the corrector is made up of plural stages of multipole elements. The control unit controls the whole aberration corrector as a single lens. During the control operation, the ratio of the strengths of the lenses of the stages of multipole elements is kept constant. Furthermore, the present invention provides another method of controlling an aberration corrector for a charged-particle beam, the corrector being made up of plural stages of multipole elements. In this method, a control unit controls the whole aberration corrector as a single lens. During the control operation, the ratio of the strengths of the lenses of the stages of multipole elements and the objective lens is kept constant. The method of automatically correcting a charged-particle beam in accordance with the present invention makes it possible for the operator to automatically correct the beam without relying on manual operations. The apparatus for automatically correcting a charged-particle beam in accordance with the present invention similarly permits automated correction of the beam without relying on operator's manual operations. According to the method of controlling an aberration corrector for a charged-particle beam in accordance with the present invention, the whole aberration corrector can be controlled as a single lens with one control signal by maintaining the ratio of the strengths of the lenses formed by the stages of multipole elements constant. Axial deviation can be corrected well by simplifying the control system. In addition, according to the other method of controlling an aberration corrector for a charged-particle beam in accordance with the present invention, the whole aberration corrector can be controlled as a single lens with one control signal by maintaining the ratio of the strengths of the stages of multipole lenses and objective lens constant. Axial deviation can be corrected well by simplifying the control system. Other objects and features of the invention will appear in the course of the description thereof, which follows. The preferred embodiments of the present invention are hereinafter described in detail with reference to the accompanying drawings. FIG. 1 shows the configuration of an apparatus according to the present invention. Like components are indicated by like reference numerals in both FIGS. 1 and 7. In FIG. 1, an emitter 1 emits an electron beam (or a charged-particle beam) 2. A lens 3 acts on the beam 2. An aberration corrector 6 performs various corrections on the electron beam 2 undergoing a lens action from the lens 3. An objective lens 4 focuses the beam 2 onto a sample 5. Secondary electrons 7 are released from the sample 5. A secondary electron detector 8 detects the secondary electrons 7. An image accumulator 9 accumulates images to obtain a secondary electron image in which noise has been reduced. An aberration correction controller 10 supplies control signals to the aberration corrector 6 to correct aberrations. An automated aligner 11 supplies an automated alignment control signal to the aberration correction controller 10 or to the objective lens 4. As an example, a computer is used as the automated aligner 11. A CRT (display device) 12 is connected with the image accumulator 9 to display various information. In the present invention, a particle having a circular cross-sectional contour, such as a spherical particle, can be used as the sample 5. In particular, the controllability of the automated aligner 11 is improved if a spherical particle of gold or resin is used. The operation of the apparatus constructed in this way is described below. The electron beam 2 is emitted from the emitter 1. The lens 3 controls the electron beam 2 incident on the aberration corrector 6. The beam 2 transmitted through the corrector 6 is focused onto the surface of the sample 5 by the lens action of the objective lens 4. The beam 2 is scanned across the surface of the sample. Secondary electrons 7 emitted from the surface of the sample 5 in synchronism with the scanning are detected by the secondary electron detector 8. Thus, the secondary electrons are displayed as a SEM image on the CRT 12 in synchronism with the scan signal. Since the effective signals of the secondary electrons detected by the secondary electron detector 8 are normally low, noise in the signals is removed by the image accumulator 9. The aberration correction controller 10 controls the lens strength (focusing strength) of the aberration corrector 6. The automated aligner 11 obtains a SEM image from the image accumulator 9 and calculates a lens strength for correcting axial deviation of the aberration corrector 6. The aligner also calculates a lens strength for the multipole stages of the aberration corrector 6 for correcting the trajectory of the beam 2 in the aberration corrector 6 into a desired trajectory by means of the aberration corrector 6. After the calculations, the aligner 11 gives instructions to the aberration correction controller 10. The structure and operation of the aberration corrector 6 are described in detail in the above-cited reference which is incorporated herein by reference. The structure and operation of the automated aligner 11 according to the present invention are hereinafter described in detail by referring to FIG. 2. FIG. 2 shows an example of configuration of the automated aligner 11. This aligner 11 has an alignment controller 11a producing a control signal ΔVn for alignment control. A beam profile extractor 11b that is a device for obtaining information about a cross section of the beam receives the output from the alignment controller 11, receives the SEM image 20, and obtains information about the cross section of the beam. The beam profile extractor 11b outputs information about the beam profile 13 that is one kind of information about the beam cross section. An axial deviation quantification device 11c receives the beam profile 13 and quantifies the axial deviation of the optical axis of the electron beam 2 relative to the center of the multipole field in the aberration corrector 6. A decision unit 11e receives the output value from the axial deviation quantification device 11c and makes a decision as to whether feedback control is provided. A feedback unit 11d receives the output from the decision unit 11e and outputs a feedback control signal Vn. The operation of the apparatus constructed in this way in accordance with the present invention is next described. The automated aligner 11 gives instructions to the aberration correction controller 10 to vary the strengths of plural dipole fields produced by multipole elements constituting the aberration corrector 6 to check the amount of axial deviation of the aberration corrector 6. Furthermore, the aligner 11 gives instructions to the aberration correction controller 10 to vary the strengths of lenses produced by plural multipole elements constituting the aberration corrector 6 for checking whether the electron beam 2 is in a given trajectory inside the corrector 6. The beam profile extractor 11b gains a SEM image when there is no change in the lens strengths and a SEM image when there is any change in the lens strengths in synchronism with the control signal ΔVn from the alignment controller 11a for giving an instruction to vary the lens strengths, and calculates the beam profile (cross-sectional shape of the beam). A method of extracting the beam profile from the two SEM images is described in detail in U.S. Pat. No. 6,858,844. The method is described briefly herein. Let g1 be a SEM image produced when the strength of a lens is varied. Let g0 be a SEM image produced when the strength of the lens is not varied. Let s be the transfer function of the sample surface. Let p1 be the beam profile when the lens strength is varied. Let p0 be the beam profile when the lens strength is not varied. The SEM images g1 and g0 are expressed respectively byg1=s*p1 (1)g0=s*p0 (2) where * indicates a convolution. Eqs. (3) and (4), shown below, are obtained by Fourier-transforming of Eqs. (1) and (2).G1=S·P1 (3)G0=S·P0 (4) where · indicates a product in a Fourier space. Capital letters indicate results of Fourier transforms. Eq. (5), shown below, is obtained by eliminating S from Eqs. (3) and (4).G1=(P1·G0/P0)=P10·G0 (5) Here, we set P1/P0=P10. Inversely Fourier transforming Eq. (5) into a real space results in:g1=F−1[P10·G0] (6) where F−1 [ ] indicates an inverse Fourier transform. Since P10 is a known function, the beam profile g1 can be calculated using Eq. (6) if G0 is known. As an example, it is assumed that the beam profile g0 produced when there is no change in the beam strength is a function showing a Gaussian distribution. Since G0 is also a Gaussian distribution function, beam profile 13 (g1) can be calculated. As shown in FIG. 2, the axial deviation quantification device 11c quantifies the present amount of the axial deviation from the obtained beam profile 13 (g1). A method of the quantification is illustrated in FIG. 3. The center of the field of view (FOV) is taken at the origin O. Let G be the center of gravity of the beam profile 13 which shows the distribution of electron densities (distribution of particle densities) in the beam cross section. A vector OG is projected onto the X- and Y-axes. Let Gx[mode] be the deviation in the X-direction. Let Gy[mode] be the deviation in the Y-direction. Instead of the center of gravity, the geometric center of the outer periphery (contour) of the profile 13 can be used. It is now assumed that Gx[mode] and Gy[mode] be functions of mode, which means discrimination of instructions from the alignment controller 11a. For example, “mode=1” means that the quadrupole field produced by the first stage of multipole elements of the aberration corrector 6 has been varied. The feedback unit 11d calculates the amount of feedback Vn[mode] from the quantified amount of axial deviation Gx[mode] and Gy[mode] using the Eqs. (7-1) and (7-2). The aberration correction controller 10 or objective lens 4 is informed of this amount of feedback Vn[mode]. Similarly, amount of feedback Vn indicates that it is a function of mode. Normally, the amount of feedback Vn has directionality. Let Vnx and Vny be the amounts of feedback in the X- and Y-directions, respectively.Vnx[mode]=α[mode]×Gx[mode] (7-1)Vny[mode]=β[mode]×Gy[mode] (7-2) where α[mode] and β[mode] are similarly functions of mode. In this way, according to the present invention, automated alignment can be made using an aberration corrector by using the center of gravity or geometric center as the position of the beam profile of the electron beam (charged-particle beam). The decision unit 11e compares the amounts of axial deviations Gx[mode] and Gy[mode] discriminated using mode with their respective given threshold values. If the decision is that Gx and Gy are smaller than their threshold values, i.e., if the decision is that the axial deviation has been corrected, the correction is ended. If the decision is that the axial deviation has not been corrected sufficiently, the decision unit 11e instructs the alignment controller 11a to repeat these operations. As one method of control, if the following relations are satisfied by a threshold value γ[mode] set for each mode, the control is judged to be ended.|Gx[mode]|<γ[mode] and |Gy[mode]|<γ[mode] (8) According to the present invention, axial deviation can be corrected well by making axial deviation corrections on Gx and Gy independently. Furthermore, according to the present invention, automated alignment is repeated until the quantified amount of axial deviation falls below a given threshold value. Consequently, the amount of axial deviation can be reduced sufficiently. In this case, it is possible to make an automatic decision as to whether the trajectory of the electron beam has been corrected well by comparing the quantified amount of axial deviation with a given threshold value. A diagram of the aberration corrector 6 composed of four stages of multipole elements and the trajectory of the electron beam 2 passing through the corrector 6 are shown in FIG. 8. The four stages of multipole elements are shown to comprise first stage of multipole elements 6a, second stage of multipole elements 6b, third stage of multipole elements 6c, and fourth stage of multipole elements 6d. Normally, each stage of multipole elements has 8 or more multipole elements. In the present embodiment, each stage of multipole elements consists of 12 multipole elements. According to the above-cited Zach et al. reference, the beam 2 undergoes a focusing action and a dispersing action simultaneously from the first stage of multipole elements. Referring to FIG. 8, it is assumed that the electron beam 2 that has undergone the dispersing action is in X trajectory. 6e and that the electron beam 2 that has undergone the focusing action is in Y trajectory 6f. The lens strength of the first stage of multipole elements 6a is so adjusted that the Y trajectory 6f passes through the center of the multipole field (lens field) produced by the second stage of multipole elements 6b and becomes focused. The lens strength of the multipole elements 6b is so adjusted that the X trajectory 6e passes through the center of the multipole field (lens field) produced by the third stage of multipole elements 6c and becomes focused. At this time, in the second stage of multipole elements, the Y trajectory 6f passes through the center of the multipole field produced by the second stage of multipole elements 6b and thus is not affected by the multipole field produced by the second stage of multipole elements 6b. Only the X trajectory 6e undergoes the lens action. Similarly, in the third stage of multipole elements, the X trajectory 6e passes through the center of the multipole field (lens field) produced by the multipole element 6c and becomes focused. Therefore, the X-trajectory is not affected. Only the Y trajectory 6f undergoes the lens action. In this way, the Y trajectory 6f of the electron beam 2 must pass through the center of the multipole field produced by the second stage of multipole elements 6b and becomes focused. The X trajectory 6e must pass through the center of the multipole field produced by the third stage of multipole elements 6c and be focused. FIG. 4 illustrates a case where the electron beam has been shifted out of its trajectory by varying the lens strength of the first stage of multipole elements. The electron beam 2 passes through the center of the multipole field produced by the second stage of multipole elements 6b and passes through the center of the multipole field produced by the third stage of multipole elements 6c. However, the X trajectory 6e is not focused into the center of the multipole field produced by the third stage of multipole elements 6c. The Y trajectory 6f is not focused into the center of the multipole field produced by the second stage of multipole fields 6b. In this case, the tilt and position of the electron beam 2 passed through the aberration corrector 6 vary. It follows that the obtained image blurs. Furthermore, the obtained image moves when the lens strength of each stage of multipole elements is varied unless the beam 2 passes through the centers of the multipole fields produced by the stages of multipole fields. In the technique disclosed in the above-cited Zach et al. reference, the beam 2 is controlled by the quadrupole field contained in the multipole fields produced by the stages of multipole fields. When the beam 2 does not pass through the center of the quadrupole field produced by the multipole elements, the center of the quadrupole field in the multipole fields produced by the first stage of multipole elements 6a can be found by (A) wobbling the quadrupole field contained in the multipole fields produced by the first stage of multipole elements 6a, (B) controlling the beam 2 with a deflector (not shown) on the side of the electron source of the aberration corrector 6, and (C) searching for a point at which the image does not move. The center of the quadrupole field produced by the second stage of multipole elements 6b can be found by (A) wobbling the quadrupole field produced by the second stage of multipole elements 6b, (B) controlling the electron beam 2 by the dipole field (equivalent to deflection by a deflector) produced by the first stage of multipole elements 6a, and (C) searching for a point at which the image does not move. Similarly, the center of the quadrupole field produced by the third stage of multipole elements 6c and the center of the quadrupole field produced by the fourth stage of multipole elements 6d can be searched for. In addition, in order that the electron beam 2 passed through the aberration corrector 6 passes through the center of the lens field produced by the objective lens 4, the center of the lens field produced by the objective lens 4 can be searched for by wobbling the strength of the objective lens 4 and using the dipole field produced by the fourth stage of multipole elements 6d. In the present invention, these operations are performed by the automated aligner 11. For example, where the beam is passed through the center of the quadrupole field produced by the second stage of multipole elements 6b, an instruction is given to the aberration correction controller 10 such that the alignment controller I la varies the strength of the quadrupole field produced by the second stage of multipole elements 6b in a corresponding manner to ΔVn in the automated aligner 11 shown in FIG. 2. The aberration correction controller 10 controls the aberration corrector 6 to achieve the contents of the instruction. The corrector 6 varies the multipole field produced by the second stage of multipole elements 6b in a corresponding manner to ΔVn. As a result, the SEM image shifts. The beam profile extractor 11b receives the shifted SEM image, as well as the SEM image produced when the lens strength was not varied. The extractor 11b calculates the beam profile 13. The axial deviation quantification device 11c quantifies the amount of axial deviation. The feedback unit 11d calculates the amount of feedback provided by the first stage of multipole elements 6a to the dipole field and gives an instruction to the aberration corrector 6 or to the objective lens 4. The decision unit 11e gives an instruction to the alignment controller 11a to repeat the correction operations until the quantified amount of axial deviation satisfies Eq. (8). Additionally, the X trajectory must be focused into the center of the multipole field produced by the third stage of multipole elements 6c. Also, the Y trajectory must be focused into the center of the multipole field produced by the second stage of multipole elements 6b. The trajectory of the electron beam is shown in the X-Z plane and the Y-Z plane in FIGS. 9A and 9B. The X trajectory is shown in FIG. 9A. The Y trajectory is shown in FIG. 9B. decision is made as to whether the Y trajectory 6f is focused into the center of the multipole field produced by the second stage of multipole elements 6b depending on whether the electron beam 2 is focused into the center of the dipole field in the Y-direction in the multipole field produced by the multipole elements 6b. That is, when the strength of the dipole field in the Y-direction produced by the second stage of multipole elements 6b is varied in a corresponding manner to ΔVn, if the Y trajectory 6f is focused into the center of the dipole field produced by the second stage of multipole elements 6b as shown in FIG. 5, the electron beam 2 passed through the aberration corrector 6 is brought to a focus at one point on the surface of the sample 5 by the objective lens 4 provided that the dipole field varies in strength. Consequently, the obtained SEM image does not move. However, if the Y trajectory 6f is not focused into the center of the dipole field produced by the second stage of multipole elements 6b, an object point 18 shown in FIG. 5 will move when the strength of the multipole field produced by the second stage of multipole elements 6b is varied in a corresponding manner to ΔVn. As a result, the SEM image will shift. That is, the Y trajectory 6f is kept focused into the center of the multipole field produced by the second stage of multipole elements 6b by adjusting the strengths of the lens fields produced by the stages of multipole fields or lens field produced by the objective lens such that the SEM image does not move even if the strength of the dipole field produced by the second stage of multipole elements 6b is varied in a corresponding manner to ΔVn. The SEM image can be fixed by adjusting the quadrupole field produced by the first stage of multipole elements 6a in this way. However, as shown in FIG. 4, a multipole field produced by multipole elements exerts a focusing action and a diverging action on the electron beam 2 simultaneously, affecting the X and Y axes. Therefore, the multipole fields produced by all the stages of multipole elements or the lens field produced by the objective lens must be adjusted finally. The same theory applies to the case where the X trajectory 6e is focused into the center of the multipole field produced by the third stage of multipole elements 6c. That is, the strengths of the multipole fields produced by the stages of multipole elements or the strength of the lens field produced by the objective lens is adjusted such that the SEM image does not shift if the dipole field produced by the third stage of multipole elements 6c is varied. In the present invention, these operations are performed by the automated aligner 11. As an example, when the Y trajectory 6f is not focused on the center of the multipole field produced by the second stage of multipole elements 6b, an instruction is given to the aberration correction controller 10 such that the alignment controller 11a varies the strength of the dipole field in the Y-direction produced by the second stage of multipole elements 6b in a corresponding manner to ΔVn in the automated aligner 11 shown in FIG. 2. The aberration correction controller 10 controls the aberration corrector 6 to achieve the contents of the instruction. The aberration corrector 6 varies the strength of the dipole field in the Y-direction produced by the second stage of multipole elements 6b in a corresponding manner to ΔVn. As a result, the SEM image is shifted. The beam profile extractor 11b receives the shifted SEM image, as well as a SEM image produced when the strength was not varied. The extractor 11b extracts the beam profile 13. The axial deviation quantification device 11c quantifies the amount of axial deviation. The feedback unit 11d calculates the amount of feedback to the multipole fields produced by the stages of multipole elements or to the lens field produced by the objective lens. The feedback unit then gives an instruction to the aberration correction controller 10 or to the objective lens. The decision unit 11e gives an instruction to the alignment controller 11a such that it repeats the correction operations until the quantified amount of axial deviation satisfies Eq. (8). According to the present invention, an image of a surface of a sample can be obtained under the condition where a lens strength has been varied. Furthermore, the amount of axial deviation of the apparatus can be found by using one or two extracted beam profiles (i.e., information about the beam cross section) of a charged-particle beam and multiplying the difference between the position of the center of gravity and the origin by a certain constant. Moreover, the amount of axial deviation of the apparatus can be found by using one or two extracted beam profiles of the charged-particle beam and multiplying the difference between the position of the center and the origin by a certain constant. Further, according to the present invention, automated alignment can be performed using an aberration corrector by obtaining an amount of axial deviation, multiplying the amount of axial deviation by a certain constant, and applying feedback to the aberration corrector or objective lens according to the calculated product. In this way, the automated aligner 11 according to the present invention performs plural alignments, which are discriminated using the value of mode, for example, as described below. mode=1: The electron beam is passed through the center of a multipole field produced by the first stage of multipole elements. mode=2: The electron beam is passed through the center of a multipole field produced by the second stage of multipole elements. mode=3: The electron beam is passed through the center of a multipole field produced by the third stage of multipole elements. mode=4: The electron beam is passed through the center of a multipole field produced by the fourth stage of multipole elements. mode=5: The electron beam is passed through the center of a lens field produced by the objective lens. mode=6: The Y trajectory is focused into the center of a multipole field produced by the second stage of multipole elements. mode=7: The X trajectory is focused into the center of a multipole field produced by the third stage of multipole elements. The alignment controller 11a is monitoring the alignment conditions made with mode=1 to 7. The sequence of operations is repeated until all the conditions are satisfied. Alignment operations may be performed in numerical order of the value of mode, although this is not essential. The electron beam is passed through the center of each multipole field produced by the multipole elements. It is now assumed that mode assumes values from 1 to 5. Where mode=1, amounts of feedback Vnx[mode=1] and Vny[mode=1] calculated using Eqs. (7-1) and (7-2) are applied, respectively, to X and Y deflectors (not shown) located at the side of the emitter 1 on the aberration corrector 6. Where mode=2, amounts of feedback Vnx[mode=2] and Vny[mode=2] calculated using Eqs. (7-1) and (7-2) are applied, respectively, to X- and Y-direction dipole fields produced by the first stage of multipole elements 6a in the aberration corrector 6. Where mode=3, amounts of feedback Vnx[mode=3] and Vny[mode=3] calculated using Eqs. (7-1) and (7-2) are applied, respectively, to X- and Y-direction dipole fields produced by the second stage of multipole elements 6b in the aberration corrector 6. Where mode=4, amounts of feedback Vnx[mode=4] and Vny[mode=4] calculated using Eqs. (7-1) and (7-2) are applied, respectively, to X- and Y-direction dipole fields produced by the third stage of multipole elements 6c in the aberration corrector 6. Where mode=5, amounts of feedback Vnx[mode=5] and Vny[mode=5] calculated using Eqs. (7-1) and (7-2) are applied, respectively, to X- and Y-direction dipole fields produced by the fourth stage of multipole elements 6d in the aberration corrector 6. The focal point of the Y trajectory can be moved near the center of the multipole field produced by the second stage of multipole elements 6b while the X trajectory is kept focused in the center of the multipole field produced by the third stage of multipole elements 6c, by fixing the ratio of the applied lens strengths of the quadrupole fields produced by the first, second, and third stages of multipole fields at Ay:By:Cy. In order to fulfill the condition that the Y trajectory is focused into the center of a multipole field produced by the second stage of multipole elements 6b, the amount of feedback Vny[mode=6] calculated using Eq. (7-2) is applied to the quadrupole fields produced by the first, second, and third stages of multipole elements according to the applied lens strength ratio Ay:By:Cy. In particular, Ay·Vny is applied to the quadrupole field produced by the first stage of multipole elements 6a. By·Vny is applied to the quadrupole field produced by the second stage of multipole elements 6b. Cy·Vny is applied to the quadrupole field produced by the third stage of multipole elements 6c. The lens strength ratio is 4:−1:−1, for example. However, the invention is not limited to this ratio. When the lens strength ratio of the quadrupole field produced by the first stage of multipole elements 6a is experimentally set to Ay, the lens strengths of the quadrupole field produced by the second stage of multipole elements 6b and the quadrupole field produced by the third stage of multipole elements 6c may be set to By and Cy, respectively, such that the image is again focused. Similarly, the focal point of the X trajectory can be moved near the center of the multipole field produced by the third stage of multipole elements 6c while maintaining the Y trajectory in focus at the center of the multipole field produced by the second stage of multipole elements 6b, by fixing the applied lens strength ratio of the quadrupole fields produced by the second, third, and fourth stages of multipole elements to Bx:Cx:Dx. In order to fulfill the X trajectory is focused into the center of the multipole field produced by the third stage of multipole elements 6c, the amount of feedback Vnx[mode=7] calculated using Eq. (7-1) is applied to the quadrupole fields produced by the second, third, and fourth stages of multipole elements according to the applied lens strength ratio Bx:Cx:Dx. That is, Bx·Vnx, Cx·Vnx, and Dx·Vnx are applied, respectively, to the quadrupole fields produced by the second, third, and fourth stages of multipole elements 6b, 6c, and 6d, respectively. The lens strength ratio is −1:−1:4, for example, although the invention is not limited to this. When the lens strength ratio of the quadrupole field produced by the fourth stage of multipole elements 6d is experimentally set to Dx, the lens strengths of the quadrupole field produced by the second stage of multipole elements 6b and the quadrupole field produced by the third stage of multipole elements 6c may be set to Bx and Cx, respectively, such that the image is again focused. Another method of focusing the X trajectory into the center of a multipole field produced by the third stage of multipole elements 6c is as follows. The focal point of the X trajectory can be moved near the center of the multipole field produced by the third stage of multipole elements 6d while maintaining the Y trajectory in focus in the center of the multipole field produced by the second stage of multipole elements 6b by fixing the lens strength ratios of the quadrupole fields produced by the second and third stages of multipole elements at Bx:Cx. The amount of feedback Vnx[mode=7] calculated using Eq. (7-1) is applied to the quadrupole fields produced by the second and third stages of multipole elements according to the applied lens strength ratio Bx:Cx. At this time, the image is out of focus at the sample position. However, a correction can be made by adjusting the strength of the lens field produced by the objective lens 4 in order to make the image come into focus again. Accordingly, as an overall operation, the strength of the quadrupole field produced by the second stage of multipole elements 6b, the strength of the quadrupole field produced by the third stage of quadrupole field, and the strength of the applied lens field produced by the objective lens are fixed at Bx:Cx:Ox and feedback is provided to them. That is, Bx·Vnx, Cx·Vnx, and Ox·Vnx are applied, respectively, to the quadrupole field produced by the second stage of quadrupole multipole elements 6b, the quadrupole field produced by the third stage of multipole elements 6c, and the lens field produced by the objective lens. The lens strength ratio is −1:1:Ox, for example, though the invention is not limited to this ratio. When the lens strength ratio of the lens field produced by the objective lens is experimentally set to Ox, the lens strengths of the quadrupole field produced by the second stage of multipole elements 6b and the quadrupole field produced by the third stage of multipole elements 6c may be set to Bx and Cx, respectively, such that the image is again focused. According to the present invention, automated alignment can be performed using an aberration corrector by using two, three, or five sample surface images. Furthermore, automated alignment can be performed with an aberration corrector using an image obtained under the condition where the lens strength of the aberration corrector is shifted by a given amount as well as an image obtained under the present value. Furthermore, automated alignment can be performed with an aberration corrector using an image obtained under the condition where a lens strength of the aberration corrector has been shifted in the X- and Y-directions by given amounts as well as an image obtained under the present value. In addition, automated alignment can be performed with an aberration corrector consisting of four stages of multipole elements. Further, automated alignment can be performed with an aberration corrector consisting of four stages of multipole elements each of which has four or more poles. Especially, in the above-described embodiments, each of the multipole elements constituting the aberration corrector has twelve poles. Automated alignment can also be performed with an aberration corrector consisting of four stages of multipole elements each of which is a dipole element, quadrupole element, hexa-pole element, or octu-pole element. As described so far, according to the present invention, a normal operator can perform automated corrections of alignment of an aberration corrector unconsciously of the corrector. Furthermore, according to the present invention, the present amount of axial deviation is quantified and so the apparatus can assist the operator by displaying the state of operation of the automated aligner 11 (e.g., the histories of the beam profile 13 and the amount of axial deviation of the apparatus on the graphical user interface (GUI) 15 on the CRT 12 as shown in FIG. 6). The FOV of the beam profile is indicated by 14. Gx in the figure shows that the amount of axial deviation decreases gradually with increasing the number of trials. Gy indicates that the amount of axial deviation increases after a lapse of a certain time and then decreases. As described so far, the method of automatically correcting a charged-particle beam in accordance with the present invention comprises the steps of: irradiating a sample with the charged-particle beam via an aberration corrector and an objective lens, the aberration corrector having multipole elements; obtaining information about a cross section of the charged-particle beam based on plural images of a surface of the irradiated sample; calculating an amount of axial deviation of the optical axis of the beam relative to the center of a multipole field in the aberration corrector based on the obtained information about the cross section of the beam; and automatically applying feedback to the aberration corrector or to the objective lens according to the calculated amount of axial deviation. The apparatus for automatically correcting a charged-particle beam in accordance with the present invention comprises: an aberration corrector having multipole elements; means for obtaining information about a cross section of the charged-particle beam based on plural images of a surface of a sample irradiated with the beam via the aberration corrector and an objective lens; means for calculating an amount of axial deviation of the optical axis of the beam relative to the center of a multipole field in the aberration corrector based on the obtained information about the cross section of the beam; and feedback means for automatically applying feedback to the aberration corrector or to the objective lens according to the calculated amount of axial deviation. The number of used images of a surface of a sample may be any one of two, three, and five. Where the number of images of the surface of the sample is two, a first one of the images can be obtained when the lens strength of the aberration corrector is set to a first value, and a second one of the images can be obtained when the lens strength is set to a second value shifted from the first value by a given amount. Where the number of images of the surface of the sample is three, a first one of the images can be obtained when the lens strength of an aberration corrector is set to a first value, a second one of the images can be obtained when the lens strength is set to a second value shifted from the first value by a first given amount in an X-direction, and a third one of the images can be obtained when the lens strength is set to a third value shifted from the first value by a second given amount in a Y-direction. Where the number of images of the surface of the sample is five, a first one of the images can be obtained when the lens strength of the aberration corrector is set to a first value, a second one of the images can be obtained when the lens strength is set to a second value shifted from the first value by a first positive given amount in an X-direction, a third one of the images can be obtained when the lens strength is set to a third value shifted from the first value by a second negative given amount in the X-direction, a fourth one of the images can be obtained when the lens strength is set to a fourth value shifted from the first value by a third positive given amount in a Y-direction, and a fifth one of the images can be obtained when the lens strength is set to a fifth value shifted from the first value by a fourth negative given amount in the Y-direction. The aberration corrector can be equipped with four stages of multipole elements. At this time, each stage of the four stages of multipole elements constituting the aberration corrector can be equipped with four or more multipole elements. Furthermore, the aberration corrector can be equipped with four stages of multipole elements. Any one of dipole field produced by the stages of multipole elements in the aberration corrector, quadrupole field produced by the stages of multipole elements, hexa-pole field produced by the stages of multipole elements, octupole field produced by the stages of multipole elements, and lens field produced by the objective lens can be shifted in strengths. An image of the surface of the sample can also be obtained simultaneously with variation of the strength of any one of the fields. Furthermore, information about one or two cross sections of a charged-particle beam can be obtained. The amount of axial deviation can be calculated by multiplying the difference between the center of gravity of the distribution of particle densities contained in the obtained information about one or two cross sections and the position of the origin contained in the information about the cross sections by a constant value. Additionally, information about one or two cross sections of a charged-particle beam can be obtained. The amount of axial deviation can be calculated by multiplying the difference between the center position of the cross-sectional contour of the beam contained in the obtained information about one or two cross sections and the position of the origin contained in the information about the cross sections by a constant value. At this time, feedback may be applied to the aberration corrector or to the objective lens in proportion to the obtained amount of axial deviation. Further, the aberration corrector can be equipped with four stages of multipole elements. Feedback can be applied to any one of dipole field produced by the stages of multipole elements in the aberration corrector, quadrupole field produced by the stages of multipole elements, and lens field produced by the objective lens. Yet further, a decision as to whether the optical axis of the charged-particle beam has been corrected so as to enter a given range can be automatically made by comparing the amount of axial deviation with a threshold value. At this time, the processing for automated correction can be repeated until the amount of axial deviation falls below the threshold value. Yet additionally, the sample can be a reference sample. The sample can be made movable between a first position in a sample chamber where the sample is irradiated with the beam and a second position where the sample is on standby for transfer to the first position. The sample can be a particle having a circular cross-sectional contour. The sample can be a spherical particle made of gold or resin. The axial deviation can be corrected in X- and Y-directions independently. The obtained information about the cross section of the charged-particle beam and the calculated amount of axial deviation can be displayed. Another apparatus for automatically correcting a charged-particle beam in accordance with the present invention comprises: an aberration corrector equipped with multipole elements and acting to correct aberration in the charged-particle beam; an aberration correction controller for controlling the strength of a multipole field produced by the aberration corrector; an objective lens; a control unit for supplying a control signal to the aberration correction controller or to the objective lens; cross-sectional information-obtaining device for obtaining a SEM image in synchronism with operation of the control unit and obtaining information about a cross section of the charged-particle beam; an axial deviation quantification device for quantifying the amount of the axial deviation of the optical axis of the beam from the obtained information about the cross section of the beam; a decision unit for making a decision from the quantified amount of axial deviation as to whether automated correction is made; and a feedback device for outputting an amount of feedback to the aberration correction controller or to the objective lens from the quantified amount of axial deviation. In a method of controlling an aberration corrector for a charged-particle beam in accordance with the present invention, the aberration corrector is made up of plural stages of multipole elements. A control unit controls the whole aberration corrector as a single lens. During this control, the lens strength ratio of the stages of multipole lenses is kept constant. In another method of controlling an aberration corrector for a charged-particle beam in accordance with the present invention, the aberration corrector is made up of plural stages of multipole elements. A control unit controls the whole aberration corrector as a single lens. During this control, the lens strength ratio of the stages of multipole lenses and objective lens is kept constant. Feedback may be applied by the control unit either to a lens formed in such a way that the lens strength ratio of the stages of multipole elements in the aberration corrector is kept constant or to a lens formed in such a way that the lens strength ratio of the stages of multipole elements and objective lens is kept constant. Having thus described our invention with the detail and particularity required by the Patent Laws, what is desired protected by Letters Patent is set forth in the following claims. |
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052356248 | description | DESCRIPTION OF PREFERRED EMBODIMENTS FIGS. 1A, 1B, 2A and 2B, show a leak detection cell or sipping test container 1 for an individual fuel rod. The cell 1 comprises a dual-casing elongate tubular body 2 formed by an upper section 2a and a lower section 2b connected by a connecting device 3. The upper section 2a is fixed at its upper end to a head 4 on which rests a cap 5 for closing the cell 1. The lower portion of lower section 2b is integral with a foot portion 6. The upper section 2a comprises a tubular external casing 8a and an internal casing 9a likewise tubular and coaxial with the casing 8a. Likewise, the lower section 2b comprises an external tubular casing 8b and an internal casing 9b coaxial with the external casing 8b. The connecting device 3 comprises an upper flange 3a integral with the section 2a, a lower flange 3b integral with the section 2b and three bolts such as 3c mounted pivotally about a horizontal axis, on support feet fixed at 120.degree. to each other around the lower section 2b. The flanges 3a and 3b comprise peripheral cutouts in which the bolts 3c may be engaged. The flanges 3a and 3b are assembled and clamped by the nuts engaged onto the bolts 3c. The flanges 3a and 3b comprise a projecting cylindrical central portion whose diameter is substantially equal to the internal diameter of the casings 8a and 8b which are engaged onto the central portion of the flange 3a and onto the central portion of the flange 3b, respectively. The external casings 8a and 8b are fixed by welding onto the flanges 3a and 3b respectively, on the periphery of their central portion. In addition, the flanges 3a and 3b comprise a central bore whose diameter is substantially equal to the diameter of the internal casings 9a and 9b. The end portions of the casings 9a and 9b are engaged into the bores of the flanges 3a and 3b, respectively. When sections 2a and 2b are in their assembled position, as shown in FIG. 2, the internal casings 9a and 9b of the sections 2a and 2b, respectively, are in the extension of the one with the other and form a continuous internal casing delimiting a housing 10 for a fuel element 7 inside the cell 1. An external gasket 11 and an internal gasket 12 are sandwiched between the flanges 3a and 3b and placed in coaxial positions. The internal seal 12 provides the sealed closing of the housing 10, at the end junction of the casings 9a and 9b. The dual casing 8a, 8b; 9a, 9b makes it possible to produce thermal insulation of the housing 10 and contributes to the mechanical strength of the cell 1. The head 4 of the cell is traversed, in the axial extension of the casing 9a, by a channel 14 emerging in an opening 15 of the cap 5 at its upper end. The channel 14 and the opening 15 form the upper portion of the housing 10 of the cell 1 intended to receive a fuel rod 7. The foot portion 6 of the cell is traversed by an opening 16, in the axial extension of the casing 9b. The opening 16 comprises a tapped portion 16a in which a bolt 17 for closing the lower portion of the housing 10 is engaged. An adjustment rod 18 whose diameter is slightly less than the internal diameter of the housing 10 has a lower portion which bears, on the internal end of the bolt 17. The bolt 17 provides the sealed closing of the housing 10 at its lower portion. A cell such as the cell 1 is designed in order to permit the detection of a leak from fuel rods of different types having various lengths between a minimum value and a maximum value. In their configuration shown in FIGS. 2A and 2B, the cell 1 and the housing 10 have a minimum length making it possible to perform within the cell a detection on a fuel rod of the type having the shortest length. The detection of a leak from fuel rods of different types having greater lengths may be carried out within the cell by sandwiching additional sections, substantially similar to the upper section 2a and to the lower section 2b, between these two sections. Successive sections of the body 2 of the cell may be assembled by using connecting devices with flanges and pivoting bolts such as the device 3. In addition, the fuel rods of the same type may have certain dimensional variations and in particular certain differences in length, for example under the effect of the expansions undergone in the reactor environment. Insofar as the upper portion of the fuel rod 7 inserted into the housing 10 should be accurately located, use will be made of adjustment rods similar to the rod 18 in order to compensate for the variations in length of the various fuel rods inserted into the housing 10. The rods 18 are inserted through the end of the opening 16 of the foot 6 of the cell and these rods are clamped by the bolt 17 for closing the lower portion of the housing 10. The position of the fuel rod inside the housing 10 is generally adjusted in such a manner that the upper portion of the rod projects over a length of approximately 10 mm in relation to the upper surface of the head 4 of the cell on which the cap 5 rests. The external upper casing 8a of the body 2 carries a support foot 20 on which is fixed a pneumatic actuator 21 for opening and closing the cap 5. The rod 22 of the actuator 21 is integral with a drive shaft 23 mounted for sliding axial movement inside the head 4 of the cell, by use of sliding bearings. The drive shaft 23 comprises an upper end of reduced diameter engaging in the cap 5, inside an opening 24. The upper end of the drive shaft 23 comprises a diametral opening in which a pin 25 is engaged. The ends of the pin 25 traversing the upper portion of the shaft 23 are engaged in grooves machined in the cap 5. The opening 24 traversing the cap 5 emerges via a tapped end portion 24a at the upper surface of the cap. The upper portion of the drive shaft 23 is tubular and has over its internal surface a tapped portion 27 whose diameter and pitch are identical to the diameter and pitch of the tapped portion 24a of the opening 24. Above the tapped portion 27 the inner bore of the end of the shaft 23 is diametrally enlarged. A bolt 28 comprising a threaded portion 28a may be engaged in the tapped opening 24a and then in the tapped opening 27 of the end of the shaft 23, in order to provide a connection between the cap 5 and the shaft 23. The cap 5 connected at the end of the shaft 23 by the bolt 28 may be actuated by the pneumatic actuator 21 in the direction of the opening or of the closing of the cap 5. The double-action pneumatic actuator 21 is supplied by means of pipes connected to two connections 29a and 29b integral with the body of the actuator 21. The body of the actuator 21 is fixed in an articulated manner by means of a horizontal spindle 31 on the support foot 20. The drive shaft 23 carries a roller 34 rotatably mounted on a spindle transversly of the shaft 23. The roller 34 is engaged inside a groove 35 machined in the head 4 of the cell 1. The groove 35 comprises a rectilinear lower portion and a helically shaped upper portion having as axis the displacement axis of the shaft 23 integral with the rod 22 of the actuator. In order to open the cap 5, from its closed position shown in FIGS. 1 and 2, the pneumatic actuator 21 is actuated in the direction causing the upward displacement of the rod 22. The drive shaft 23 integral with the rod 22 of the actuator is also displaced upwards and effects lifting of the cap above the upper surface of the head 4, the cap 5 being integral with the drive shaft 23 by virtue of the bolt 28. When the roller 34 reaches the upper portion of the helically shaped groove 35, the co-operation of the roller 34 with the groove 35 causes the drive shaft 23 and the cap 5 to rotate about the axis of vertical displacement of the shaft 23. The cap 5 is placed, by pivoting about the axis of the rod 23, into the open position of the upper end of the housing 10 shown in FIG. 3. The closing of the cap 5 is provided by downward displacement of the rod 22 of the actuator and of the drive shaft 23, the cap first carrying out a rotation replacing it vertically above the opening of the housing 10 and subsequently a vertical displacement, these displacements being obtained by displacement of the roller 34 in contact respectively with the helical portion and with the reactilinear portion of the groove 35. In the event of a failure of the actuator 21, the opening or the closing of the cap 5 may be performed manually. Remote unbolting of the bolt 28 is performed by virtue of a pole at the end of which is placed a tool coming into engagement with the bolt head, the cell 1 being placed beneath a certain depth of water. The unbolting of the bolt 28 makes it possible to disconnect the cap 5 from the drive shaft 23. The cap 5 may be placed in the open position by virtue of a traction tool which is put into engagement with the handling lug 37 integral with the cap. The cap of the cell 1 which is used at a water depth of the order of 10 meters, may therefore be remotely actuated in all cases, either automatically by using the pneumatic actuator 21 or, in the event of failure of the actuator, manually. After opening the cap 5, a fuel element such as a rod 7 extracted from a defective assembly may be inserted inside the housing 10 of the cell 1, by way of an upwardly flared opening of the channel 14 of the head 4 of the cell. The position in the vertical direction of the rod 7 may be adjusted, as indicated hereinabove, by choosing an adjustment rod 18 of desired length. The housing 10 of the cell is filled with water from the pool into which the fuel element is immersed. The cap 5 is put back into the closed position. An O-ring 38 makes it possible to provide a sealed closing of the cap 5 which rests on the upper portion of the head 4 of the cell with a certain pressure which may be exerted by virtue of the actuator 21, by means of the drive shaft 23 and the bolt 28. The actuator 21 is supplied with compressed air by means of pipes 39a and 39b connected respectively to the nozzles 29a and 29b. The head 4 of the cell is pierced with channels for distributing fluid, to which are connected nozzles 40, 41 and 42 permitting the connection of fluid inlet pipes. The nozzle 40 communicates with a channel emerging in the upper portion of the channel 14, i.e., at the upper portion of the housing 10 of the cell. The nozzle 41 communicates with a channel connected by means of a pipe 43 to a three-way valve 45 fixed on the foot 6 of the cell. The nozzle 42 communicates with a channel connected by means of a flexible pipe 46 to one of the ways of the three-way valve 45. The nozzles 40, 41 and 42 make it possible to connect the cell to the supply pipes of a fluid circuit which is shown in FIG. 4 and which will be described hereinbelow. The nozzles 40 and 42 are connected to pipes of the fluid circuit in which demineralized water or compressed air may flow. The nozzle 40 enables the upper portion of the housing 10 of the cell to communicate with the fluid circuit while the nozzle 42 enables the lower portion of the housing 10 to communicate with the fluid circuit, by means of the three-way valve 45. The nozzle 41 which is connected to a compressed-air pipe of the fluid circuit makes it possible to control the three-way valve 45. The three-way valve 45 comprises a first way communicating with the pipe 46, a second way communicating with a channel 48 emerging at the lower portion of the housing 10 (FIG. 2B) and a third way (not shown) emerging inside the pool. FIG. 4 will now be referred to, in order to describe the fluid circuit connected to the cell 1 and permitting the various successive phases of the detection method according to the invention to be carried out. The cell 1 has been shown, in which the cap 5 may be actuated for opening or its closing by means of the double-action pneumatic actuator 21 whose chambers are supplied with compressed air by means of the pipes 39a and 39b. The housing 10 of the cell, as described hereinabove, is connected at its lower portion to the fluid circuit, via the channel 48, the three-way valve 45 and a pipe 46' comprising an end portion formed by the pipe 46 shown in FIGS. 1 and 2. The fluid circuit comprises a source 50 of pressurized demineralized water and a compressed-air source 51 which are both connected, via connecting pipes, to the pipe 46' connected to the three-way valve 45 at the lower portion of the cell 1 and to a pipe 53 connected at the upper portion of the cell via the nozzle 40. Solenoid valves such as 54a, 54b and 54c enable the pipes 46' and 53 to be connected with the source of demineralized water or with the source of compressed air whose pressure is of the order of 10 bars. The compressed-air source 51 is also connected to the pipes 39a and 39b for supplying the pneumatic actuator 21, via a pipe 55 and three-way valves 56a and 56b. The control of the three-way valves 56a and 56b enables one of the chambers of the actuator to be supplied with compressed air and the other chamber to be at atmospheric pressure, in order to control the displacement of the actuator in either direction, i.e., in the direction of opening or closing cap 5. Pressure gauges such as 57a, 57b, 57c and 57d make it possible to measure the pressure of the demineralized water or the compressed air coming from the sources 50 and 51. A three-way valve 58 is interposed on the pipe 53 connected at the upper portion of the housing of the chamber 1, between the nozzle 40 and the connection point of the pipe 53 with the demineralized water or compressed air inlet pipe 60 in which the solenoid valve 54c is placed. One of the ways of the valve 58 is connected to the nozzle 40 by means of the pipe 53, a second way is connected to the pipe 60 by means of a pipe 53', and the third way is connected by means of a pipe 61 to a water sampling device 62. The pipe 53' is extended beyond its branching with the pipe 60 in such a manner as to be connected to radioactive counter device 63 comprising a .gamma. or .beta. detector disposed inside a lead shield 64. The counter device 63 is itself connected, via a three-way valve, to a pumping circuit comprising a vacuum pump 66. The counting device 63 comprises a counting unit 65 formed by the .gamma. or .beta. detector and connected to an electronic module 67 enabling the results supplied by the counting unit 65 to be used, and to be displayed, in terms of output, on a recorder 67'. The sampling device 62 comprises a receptacle 68 having a capacity of approximately 1 liter, a sampling valve 69 and a flask 70 of 100 cm.sup.3 capacity. The sampling device 62 comprises an outlet pipe connected to a removal pipe 71 enabling the water sampled by the receptacle 68 to be returned into the pool 75 within which the cell 1 is immersed. A draining device 72 connected to the pipe 71 is also placed beneath the sampling flask 70. The three-way valve 45 fixed at the lower portion of the cell comprises a first way 45a connected via the channel 48 to the lower portion of the housing 10 of the cell, a second way 45b connected to the pipe 46' of the fluid circuit and a third way 45c connected to a pipe for removal of water emerging in the pool. The compressed-air inlet pipe 55 of the actuator 21 is also connected to the pipe 43, with interposition of a solenoid valve 73. The three-way valve 45 may thus be controlled by opening or closing the solenoid valve 73. As indicated hereinabove, in order to carry out a detection on a fuel rod 7, the rod 7 is inserted into the housing 10 of the cell whose cap is left open. First, the water contained in the pipes 46 and 46' is forced back, by means of compressed air, into the pool through the cell 1. To this end, the valve 54b is opened and the ways 45b and 45a of the valve 45 are put into communication. The cap 5 of the cell 1 is then closed in a sealed manner. Compressed air coming from the source 51 is injected into the upper portion of the housing 10 of the cell 1 via the pipes 60 and 53, the valve 54c being opened and the three-way valve 58 being placed into a position bringing the pipes 53' and 53 into communication. The three-way valve 45 is controlled in such a way that its ways 45a and 45c are brought into communication, in order to bring the channel 48 emerging at the lower portion of the housing 10 into communication with the pipe for removal of water, inside the pool 75. The compressed air penetrating into the upper portion of housing 10 enables the water contained in the housing 10 to be removed, inside the pool 75, via the channel 48 and the three-way valve 45. The three-way valve 45 is then placed in a position providing the connection between the ways 45b and 45a. Thus the entire circuit in which the solenoid valves 54b and 54c are disposed is filled with air. The closing of the solenoid valve 54c is controlled and the vacuum pump 66 is put into operation, in such a manner as to remove the air contained in the housing 10 of the cell 1 and to establish a pressure substantially less than atmospheric pressure in the housing. The outer surface of the fuel rod contained in the housing 10 is then subjected, to a reduced pressure, so that, in case the fuel rod has one or more leak-generating cracks, fission gases are sucked into the housing 10. The opening of the solenoid valve 54d is then controlled. Air is then introduced into the housing 10 of the cell 1 by its lower portion and scavenges the housing 10, causing entrainment of the fission gases previously released. The fission gases are entrained by the scavenging air into the counting device 63 whose volume is substantially greater than the volume of the housing 10. All or a substantial portion of the fission gases possibly released by the fuel rod are thus collected into the counting device 63. Radioactive counting carried out by the unit 65 in the device 63 makes it possible to display the results of the counting carried out, after processing by the electronic module 66, on the recorder 67. The presence of fission gases is then detected by comparing these results with the results of counting carried out on a sound rod, and from this it may be deduced that the fuel rod being examined is defective. If fission gases are not detected in significant quantity, it may be deduced that the rod being monitored does not exhibit a leak prohibiting its re-use. The recorder 67' may be so designed as to display clearly the diagnostic (defective or not defective) pertinent to the fuel rod. However, in all cases, the diagnostic carried out by counting on the scavenging gases from the housing 10, after the latter has been placed under reduced pressure, is checked by a second detection operation in the context of implementing the method according to the invention. To this end, the housing 10 is filled with demineralized water, by means of the solenoid valve 54a, the scavenging air previously introduced into the housing being removed by the counting circuit. The three-way valve 58 is placed into its position bringing the pipe 53 into communication with the sampling pipe 61. The demineralized water which has come into contact with the rod inside the housing 10 reaches the sampling receptacle 68. The sampling flask 70 is filled by opening the valve 69 and counting is carried out in the laboratory on the sample contained in the flask 70 in order to determine, by comparing with counting carried out on a sample of the pool water, the possible presence of fission products in the sample. When a certain result has been obtained, the rod is extracted from the cell after opening the cap 5, and the rod is deposited in a storage zone, before its removal to a reprocessing plant, inside a container, or its re-use inside a fuel assembly, depending on the result of the monitoring carried out. After having extracted the rod from the housing of the cell, following a detection operation, the cap of the cell is reclosed and the internal volume of the cell is decontaminated and washed by a flow of air and then by a flow of water. It is then checked that the cell has returned to its initial state and no longer contains fission product, by direct counting on the scavenging gas traversing the empty cell and by water sampling, the counting of which is carried out in the laboratory. The counting device 63 which is used for the detection of fission products in the gases flowing inside the cell comprises a .beta. detector combined with the counting channel 65, the electronic module 67 and the recorder 67'. After detection of a non-sealed rod, a complete cycle, analogous to the cycle implemented for the detection, is carried out on the cell not containing a fuel rod in its housing. After washing and decontamination, the cell is again ready to provide the detection on a fuel rod. The extraction and installation of the rods in the detection cell are carried out by means of a handling gripper which engages with the end of the rod which remains projecting in relation to the upper surface of the head 4 of the cell, after removing the cap 5. The length of this end portion, which enters the housing 15 of the cap in the closed position, is of the order of 10 mm; this length may be adjusted, as indicated hereinabove, by choosing an adjustment rod of desired length. The method and the device according to the invention make it possible to detect a leak from individual fuel elements, such as rods for fuel assemblies, very reliably, rapidly and by operations performed largely automatically. The counting, carried out on a sample of water taken from the housing of the cell and performed in the laboratory, makes it possible to check, under the best possible conditions, the results of the counting carried out on a gas which has flowed within the housing of the cell. The method and the device according to the invention make it possible to check the results obtained by a method for detecting defective fuel rods in an assembly using, for example, ultrasonic transducers or eddy current probes. It therefore becomes possible to monitor individually and to check the state of the rods of a fuel assembly, in such a manner as to refurbish the of this assembly very reliably. The detection cell may have a structure other than that which has been described. The body of the cell may be constructed as a single piece. However, the construction in the form of separate sections permits adjustment as a function of the length of the fuel elements on which the detection is carried out. The cap of the cell may comprise opening and closing means different from those which have been described. The fluid circuit may also be constructed in a different manner by using any hydraulic or pneumatic component, such as solenoid valves or direction control valves. The invention is applicable to the detection of a leak from any individual fuel element of an assembly for a water cooled nuclear reactor. |
description | Embodiments of the present invention are described in detail hereinafter with reference to the accompanying drawings. (Embodiment 1) A fuel assembly according to the first embodiment of the present invention is described with reference to FIGS. 1 and 2. The fuel assembly of this embodiment is loaded into a reactor core wherein a water gap width on a control rod side (control rod-side water gap width) and that on a side opposite to the control rod side (opposite-side water gap width) are almost equal to each other. FIG. 1 is a cross sectional view of the fuel assembly and FIG. 2 is a schematic longitudinal sectional view thereof. As shown in FIG. 2, the fuel assembly has a fuel bundle (without a symbol), an upper tie plate 14, a lower tie plate 15 and a channel box 13. The fuel bundle has a plurality of fuel rods 10, one water rod 21 (not shown in FIG. 1) and a plurality of spacers 16. The channel box 13 has a square pipe shape and covers the fuel bundle from the outside. The upper tie plate 14 and the lower tie plate 15 hold upper end portions and lower end portions of the fuel rods 10, respectively. The spacers 16 are disposed axially at predetermined certain intervals for holding spaces between the fuel rods 10. As shown in FIG. 1, ninety-one fuel rods 10 are arranged in a square lattice of 10 rows by 10 columns (10xc3x9710) and one water rod 21 of a square pipe shape is disposed in a central region of 3 rows by 3 columns (3xc3x973). Nine fuel rods 10 can be disposed in this central region. Each fuel rod 10 has a zircalloy clad tube packed with nuclear fuel pellets formed by a dioxide of enriched uranium. As shown in FIG. 1, if the fuel assembly is divided into a control rod side and a side (anti-control rod side) opposite to the control rod side by a diagonal line 13a, the water rod 21 is shifted toward the control rod side. In other words, a center of the water rod 21 is shifted toward the one where the control rod 24 is inserted, away from a cross sectional center of the fuel assembly. As shown in FIG. 2, the channel box 13 is fixed to the fuel bundle by fixing a channel fastener 17 to a corner post 18 that is attached to the upper tie plate 14 at the one corner where the control rod 24 is inserted. Thus, the aforementioned control rod side corresponds to the channel fastener side or the corner post side. In this embodiment, since the water rod 21 is shifted toward the control rod side (channel fastener side, corner post side), thermal neutron flux near the control rod 24 increases and hence it is possible to enhance the control rod worth. Therefore, in comparison with a case where the water rod is disposed at the center of the fuel assembly or shifted toward a side opposite the control rod side, the reactor shutdown margin can be increased while attaining higher burnup of the fuel assembly. As a result, it is possible to improve the fuel economy and decrease the amount of spent fuel. (Embodiment 2) A fuel assembly according to the second embodiment of the present invention is described with reference to FIG. 3. FIG. 3 is a cross sectional view of the fuel assembly. This second embodiment is different from the first embodiment in that two types of fuel rods are used that have different active fuel lengths. The active fuel length is the length of the portion of the fuel rod packed with nuclear fuel pellets. More specifically, one type of fuel rod is a long-length (full-length) fuel rod 11 having a relatively large active fuel length and the other type of fuel rod is a short-length (part-length) fuel rod 12 having an active fuel length about {fraction (15/24)} that of the long-length fuel rod 11. As shown in FIG. 3, eight short-length fuel rods 12 are disposed in the second layer from the outside of the fuel assembly. One of them is disposed on the control rod side and five are disposed on the side opposite to the anti-control rod side. In this embodiment, it is possible to increase the reactor shut-down margin as in the first embodiment. In addition, this embodiment attains the following effect. The short-length fuel rods generally contribute to a flattening of the moderator (water) distribution in an axial direction of the fuel assembly. In this embodiment, since the short-length fuel rods 12 are disposed in a larger number on the side opposite to the control rod side than on the control rod side, it is also possible to flatten the moderator distribution in a cross section of the fuel assembly. These effects contribute to flattening of the local power distribution and to a decrease in the rise of reactivity when the reactor is in a cold shut-down condition. As a result, the thermal margin can be increased. (Embodiment 3) A fuel assembly according to the third embodiment of the present invention is described with reference to FIG. 4. FIG. 4 is a cross sectional view of the fuel assembly. In this embodiment, short-length fuel rods 12, arranged separately in the second embodiment, are concentrated around a water rod 21 of a square pipe shape. More specifically, seven short-length fuel rods 12 are disposed at positions adjacent to the water rod 21 on the side opposite to the control rod side. Five of the short-length fuel rods 12 are disposed in a half area on the side opposite to the control rod side with respect to the diagonal line 13a. In this embodiment, an increase in the reactor shut-down margin and an increase in the thermal margin by flattening the local power distribution can also be attained as in the second embodiment. In addition, in this embodiment, a satisfactory moderation of neutrons is attained independently of the void fraction of the water (moderator) in the channel box 13 like a case that a cross sectional area of the water rod 21 increases effectively. Therefore, it is also possible to decrease an absolute value of the void coefficient. (Embodiment 4) A fuel assembly according to the fourth embodiment of the present invention is described with reference to FIG. 5. FIG. 5 is a cross sectional view of the fuel assembly. In this embodiment, which is a modification of the second embodiment, a certain improvement is made with respect to distribution of an average uranium enrichment (hereinafter referred to simply as xe2x80x9cenrichmentxe2x80x9d) of the fuel rods. More specifically, four types of long-length fuel rods with different enrichment are used, which include a fuel rod 1 of about 5 wt % (highest) enrichment, a fuel rod 2 of about 4 wt% enrichment, a fuel rod 3 of about 3 wt % enrichment, and a fuel rod 4 of about 2 wt % (lowest) enrichment. A fuel rod 1a can be the same short-length fuel rod as in the second embodiment and its enrichment is about 5 wt % (highest). Other constructional points are the same as in the second embodiment and therefore explanations thereof are omitted here. As shown in FIG. 5, the fuel rods 4 of the lowest enrichment are disposed at four corners of the outermost layer and the fuel rods 3 of the second lowest enrichment are disposed at positions close to the corners in the outermost layer. Fuel rods 2 of the second highest enrichment are disposed at positions adjacent to the water rod 21 in the row or column direction (vertical or transverse direction in FIG. 5). Further, fuel rods 1 of the highest enrichment are disposed at positions adjacent obliquely to the water rod 21. In a cross section perpendicular to an axis of the fuel assembly, the average enrichment of the fuel rods in one half area (hereinafter referred to as xe2x80x9copposite the control rod side areaxe2x80x9d) on the opposite the control rod side that is divided by the diagonal line 13a is higher than that of the fuel rods in the other half area (hereinafter referred to as the xe2x80x9ccontrol rod side areaxe2x80x9d) on the control rod side. In this embodiment, the same effect as in the second embodiment can be obtained. In addition, in this embodiment, since the average enrichment in the opposite to the control rod side area, where thermal neutron flux is relatively low, is set higher than that in said the control rod side area, the local power distribution can be flattened more effectively. (Embodiment 5) A fuel assembly according to the fifth embodiment of the present invention is described with reference to FIG. 6. FIG. 6 is a cross sectional view of the fuel assembly. In this embodiment, which is a modification of the fourth embodiment, a certain improvement is made with respect to an arrangement of gadolinia-filled fuel rods (hereinafter called xe2x80x9cGd fuel rodsxe2x80x9d). Gadolinia is one of burnable absorber. The Gd fuel rod 9 has an average uranium enrichment of about 4 wt % and an average gadolinia concentration of about 5 wt %. Sixteen Gd fuel rods 9 are arranged in the fuel assembly. Ten of them are disposed in the anti-control rod side area and six are disposed in the control rod side area. In the second layer from the outside of the fuel assembly, the Gd fuel rods 9 are disposed at eight positions adjacent to the fuel rods 1a (the short-length fuel rods of the highest enrichment) located at corner positions. Other constructional points are the same as in the second embodiment and therefore explanations thereof are omitted here. This embodiment also brings about the same effect as in the fourth embodiment. In addition, in this embodiment, since the Gd fuel rods are disposed in a larger number in the opposite the control rod side area, a larger number of neutrons are absorbed in the opposite the control rod side area than in the control rod side area. As a result, the thermal neutron flux in the control rod side area can be increased relatively and hence it is possible to enhance the control rod worth and increase the reactor shut-down margin in comparison with the fourth embodiment. (Embodiment 6) A fuel assembly according to the sixth embodiment of the present invention is described with reference to FIG. 7. FIG. 7 is a cross sectional view of the fuel assembly. In this embodiment, one cylindrical water rod 22 is disposed in the 33 central region instead of the water rod 21 in the third embodiment shown in FIG. 4. A cross sectional area of the water rod 22 is smaller than that of the water rod 21. Other constructional points are the same as in the third embodiment and therefore explanations thereof are omitted here. This embodiment also brings about the same effect as in the third embodiment. In addition, in this embodiment, since the cross sectional area of the water rod is set smaller than that in the third embodiment, wasteful absorption of neutrons by the water rod when the reactor is in a hot operating condition can be reduced. Therefore, it is possible to improve the neutron economy more than in the third embodiment. (Embodiment 7) A fuel assembly according to the seventh embodiment of the present invention is described with reference to FIG. 8. FIG. 8 is a cross sectional view of the fuel assembly. In this embodiment, which is a modification of the first embodiment shown in FIG. 1, the number of fuel rods is increased for the purpose of attaining higher burnup than in the first embodiment. That is, one hundred and five fuel rods 11 are arranged in a square lattice of 11 rows by 11 columns (11xc3x9711) and one water rod 23 of a square pipe shape is disposed in a central region of 4 rows by 4 columns (4xc3x974). Sixteen fuel rods can be disposed in this central region. As shown in FIG. 8, if the fuel assembly is divided into the control rod side and the opposite the control rod, the water rod 23 is shifted toward the control rod side. Therefore, this embodiment also brings about the same effect as in the first embodiment. Although one water rod is used in the above embodiments, there also may be used a plurality of water rods. In this case, if the water rods are shifted toward one corner where a control rod is inserted from a cross sectional center of the fuel assembly, the same effects as in the above embodiments can be obtained. Further, although enriched uranium is used as the nuclear fuel in the above embodiments, there also may be used a nuclear fuel obtained by replacing a portion or the whole of enriched uranium with plutonium-enriched uranium. In this case, the same effects as in the above embodiments can be obtained. |
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06222896& | claims | 1. A solid target suitable for use in producing .sup.186 Re via a (n,.gamma.) Szilard-Chalmers reaction, the target comprising a target layer formed on a surface of a substrate, the target layer comprising an inorganic rhenium compound and having a projected thickness of not more than about 150 nm, the compound including a .sup.t Re target nuclide in an oxidation state of not more than +6, where t is 185 for producing .sup.186 Re. a rhenium oxide which includes a .sup.t Re target nuclide in an oxidation state of not more than +6, where t is 185 for producing .sup.186 Re, and a M-hydroxide where M is a metal other than rhenium. a rhenium oxide which includes a .sup.t Re target nuclide in an oxidation state of not more than +6, where t is 185 for producing .sup.186 Re, and a tin oxide or a tin hydroxide. a rhenium oxide which includes a .sup.t Re target nuclide in an oxidation state of not more than +6, where t is 185 for producing .sup.186 Re, and a M-oxide or M-hydroxide wherein M is a metal other than rhenium, and wherein the amount of atomic oxygen present in the M-oxide or the M-hydroxide ranges from a stoichiometric amount to about four times the stoichiometric amount required for the target nuclide to react with the atomic oxygen to form the oxidized product nuclide. 2. The target of claim 1 wherein the target comprises a rhenium oxide which includes the .sup.185 Re target nuclide and an M-oxide or a M-hydroxide, where M is a metal other than rhenium. 3. The target of claim 2 wherein the metal, M, is present as an M-oxide. 4. The target of claim 2 wherein the metal, M, is present as an M-hydroxide. 5. The target of claim 2 wherein M is magnesium. 6. The target of claim 2 wherein M is tin. 7. The target of claim 2 wherein M is titanium. 8. A solid target material suitable for use in producing .sup.186 Re via a (n,.gamma.) Szilard-Chalmers reaction, the target material comprising granules of an inorganic rhenium compound, the compound including a .sup.t Re target nuclide in an oxidation state of not more than +6, the granules having an average radius of less than about 150 nm (1500 .ANG.), where t is 185 for producing .sup.186 Re. 9. The target of claim 8 wherein the target comprises a rhenium oxide which includes the .sup.185 Re target nuclide and an M-oxide or an M-hydroxide, where M is a metal other than rhenium. 10. The target of claim 9 wherein the metal, M, is present as an M-oxide. 11. The target of claim 9 wherein the metal, M, is present as an M-hydroxide. 12. The target of claim 9 wherein M is magnesium. 13. The target of claim 9 wherein M is tin. 14. The target of claim 9 wherein M is titanium. 15. A solid target suitable for use in producing .sup.186 Re via a (n,.gamma.) Szilard-Chalmers reaction, the target comprising 16. The target of claim 15 wherein M is magnesium. 17. The target of claim 15 wherein M is tin. 18. The target of claim 15 wherein M is titanium. 19. A solid target suitable for use in producing .sup.186 Re via a (n,.gamma.) Szilard-Chalmers reaction, the target comprising 20. The target of claim 19 wherein the tin is present in the target as a tin oxide. 21. A solid target suitable for use in producing .sup.186 Re via a (n,.gamma.) Szilard-Chalmers reaction, the target comprising 22. The target of claim 21 wherein the metal, M, is present as an M-oxide. 23. The target of claim 21 wherein the metal, M, is present as an M-hydroxide. 24. The target of claim 21 wherein M is magnesium. 25. The target of claim 21 wherein M is tin. 26. The target of claim 21 wherein M is titanium. |
abstract | An apparatus includes a yoke having a first end and a second end. The yoke is configured to hold a device that includes an aperture and a range compensation structure. A catch arm is pivotally secured to the first end of the yoke. The catch arm includes a locking feature. The locking feature and the second end of the yoke interface, respectively, to a first retention feature and a second retention feature defined by the aperture and the range compensation structure. The locking feature is configured to interface to the first retention feature and the second end of the yoke is configured to interface to the second retention feature. |
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abstract | A method of manufacturing a collimator mandrel having variable attenuation characteristics is presented. The manufacturing process includes the placement of a layer of attenuating material on a core of base material. The layer of attenuating material is relatively thin and varies in thickness circumferentially around the core. The collimator mandrel may be manufactured by placing a cast about a core of non-attenuating material, filling a void between the cast and the core with an attenuating material, allowing the material to cure, and removing the cast from the assembly. |
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claims | 1. A shield for absorbing high level radiation emitted during generation of a radioisotope, comprising:an inner portion fabricated from a first type of shielding material for shielding against a first type of high level radiation; andan outer portion fabricated from a second type of shielding material for shielding against a second type of high level radiation wherein the inner and outer portions are part of a shield arrangement adapted to shield against high level radiation and wherein the outer portion serves as a mold for forming the inner portion. 2. The shield according to claim 1 wherein the inner portion is fabricated from concrete. 3. The shield according to claim 1 wherein the outer portion is fabricated from high density polyethylene. 4. The shield according to claim 1 wherein additional shielding elements different from the first type of shielding material are embedded in the inner portion and wherein the shielding elements also reinforce the inner portion and do not become radioactive due to generation of the radioisotope. 5. The shield according to claim 4 wherein the shielding elements are fabricated from fiberglass. 6. The shield according to claim 1 further including additional shielding materials located adjacent to the inner portion. 7. The shield according to claim 1 wherein outer portion is formed by using a rotomolding process. 8. The shield according to claim 1 wherein the outer portion is formed by using a blow molding or an injection molding process. 9. The shield according to claim 1 further including ribs for supporting the outer portion. 10. The shield according to claim 1 wherein the radiation is generated by accelerating a particle beam and bombarding a target material with the particle beam. 11. The shield according to claim 1 wherein the inner portion shields against gamma rays. 12. The shield according to claim 1 wherein the outer portion moderates neutrons. 13. A particle accelerator system, comprising:a particle accelerator for generating a particle beam that bombards a target to generate a radioactive isotope wherein high level radiation is produced during generation of the radioisotope; anda shield used as part of a shield arrangement for absorbing high level radiation emitted during generation of the radioisotope wherein the shield includes an inner portion fabricated from a material which is adapted to shield against gamma rays and an outer portion fabricated from a material which is adapted to moderate neutrons wherein the outer portion serves as a mold for forming the inner portion. 14. The shield according to claim 13 wherein the inner portion is fabricated from concrete. 15. The shield according to claim 13 wherein the outer portion is fabricated from high density polyethylene. 16. The shield according to claim 13 wherein additional shielding elements having shielding properties different from that of the inner portion are embedded in the inner portion and wherein the shielding elements also reinforce the inner portion and do not become radioactive due to generation of the radioisotope. 17. The shield according to claim 16 wherein the shielding elements are fabricated from fiberglass. 18. The shield according to claim 13 further including additional shielding materials located adjacent to the inner portion. 19. The shield according to claim 13 wherein outer portion is formed by using a rotomolding process. 20. The shield according to claim 13 wherein the outer portion is formed by using a blow molding or an injection molding process. 21. The shield according to claim 13 further including ribs for supporting the outer portion. 22. A method for forming a shield for absorbing high level radiation emitted during generation of a radioisotope, comprising the steps of:providing an outer portion of the shield, wherein the outer portion is fabricated from a first type of shielding material for shielding against a first type of high level radiation, and;using the outer portion to form an inner portion of the shield, wherein the inner portion is fabricated from a second type of shielding material for shielding against a second type of high level radiation wherein the inner and outer portions are part of a shield arrangement adapted to shield against high level radiation. |
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summary | ||
060884185 | summary | BACKGROUND OF THE INVENTION 1. Field of Invention The present invention relates generally to an apparatus and method for controlled de-pressurization of a nuclear reactor, and more particularly, to an improved gas sparging system for reducing loads acting on structures submerged in a suppression pool. 2. Discussion In the event of over-pressurization of a nuclear reactor, relief valves may vent steam or reactor coolant into a suppression pool--a tank filled with liquid coolant--to dissipate the energy of the vented steam. The relief valve's abrupt opening, and subsequent delivery of high-pressure steam to the suppression pool, results in dynamic loads on suppression pool walls and structures. These dynamic loads, if large enough and if not properly accounted for during plant design, can damage structures submerged in the suppression pool. Dynamic loads within the suppression tank are thought to occur through at least two different mechanisms. In a typical pressure relief system, a relief valve exhausts high pressure steam into a discharge line, which is connected to a group of gas spargers. The spargers generally consist of vertical pipes whose ends are submerged in the suppression pool. When the pressure relief valve vents high pressure steam into the exhaust line, the steam must first displace noncondensable gas and liquid coolant present in the sparger pipe. During this sparger line clearing process, the high pressure steam compresses the noncondensable gas because of the relatively large inertia and high flow resistance of the liquid coolant. As the compressed noncondensable gas emerges from the sparger nozzles, it expands rapidly and then contracts due to over expansion. The expansion and contraction of the noncondensable gas repeats during the line clearing process, resulting in oscillatory pressure waves that impact submerged structures within the suppression pool. At some point after the liquid coolant has cleared the sparger pipe, the sparger injects high pressure steam into the suppression pool, creating a vapor-phase injection zone adjacent to the sparger nozzles (in practice there appears to be no clear transition between non-condensable gas venting and steam venting). Because of time-dependent imbalances between the steam mass flux and condensation rate, the high pressure steam injection process results in pressure oscillations. Like the line clearing process, oscillatory pressure waves during steam injection give rise to dynamic pressure loads on submerged structures within the suppression pool. In many conventional pressure relief systems, the gas spargers simultaneously exhaust steam into the liquid coolant at different locations, which distributes pressure forces acting on submerged structures within the suppression pool. But, dynamic loads on submerged structures can still be large because pressure disturbances from different spargers can combine. For example, if pressure disturbances from two adjacent spargers have the same frequency and phase relationship, the amplitude of the two pressure disturbances will add, resulting in a combined pressure disturbance that is greater than the individual pressure disturbances. Thus, pressure relief systems that take into account the interaction of pressure disturbances from individual spargers in order to minimize dynamic loads on structures within the suppression pool would be desirable. SUMMARY OF THE INVENTION In accordance with one aspect of the present invention, there is provided a method of mitigating pressure disturbances resulting from venting gas through a series of spargers into a suppression pool. The method comprises the steps of obtaining fundamental frequencies of the pressure disturbances arising at each of the spargers, and adjusting the time delay between the start of gas venting of any two successive spargers in order to optimize at substantially the following relation: ##EQU1## where .tau. represents the time delay and f represents the fundamental frequency of the disturbance at the later venting sparger. In accordance with another aspect of the present invention, there is provided a second method of mitigating pressure disturbances resulting from venting gas through a series of N spargers submerged in a suppression pool. The method comprises the steps of obtaining fundamental frequencies of the pressure disturbances arising at each of the spargers, and adjusting phase angles of the disturbances at two successive spargers so that they optimize at substantially the relation ##EQU2## where .phi..sub.i and .phi..sub.i-1 represent the phase angles of the disturbances at two successive spargers, i is an integer greater than one and less than or equal to N and denotes the serial position of the sparger, and m is a positive integer greater than or equal to zero. The step of adjusting the phase angles to satisfy the phase angle relationship is repeated for every pair of successive spargers. In accordance with a further aspect of the present invention, there is provided an apparatus for mitigating pressure disturbances resulting from venting steam from a nuclear reactor into a suppression pool. The apparatus comprises a series of N spargers submerged in the suppression pool, and a header sequentially connecting each of the spargers. The spargers are configured in such a way that when steam is vented into the header from the nuclear reactor, pressure disturbances arising at any two successive spargers to optimize at substantially the relation ##EQU3## where .phi..sub.i and .phi..sub.i-1 represent phase angles of the disturbances at two successive spargers, i is an integer greater than one and less than or equal to N and denotes the serial position of the sparger, and m is a positive integer greater than or equal to zero. |
claims | 1. A method, operable in the presence of an ambient flux of cosmic rays, of braking an asteroid upon approach to a lunar or planetary surface, comprising:projecting deuterium-containing particle fuel material in a specified direction outward from a landing site on a lunar or planetary surface toward an approaching asteroid, the asteroid having a mass of not more than 100 metric tons, the asteroid also provided with its own onboard propulsion system,dispersing the material as a cloud directly in an incoming flight path of the asteroid, the material interacting with the ambient flux of cosmic rays to generate products having kinetic energy; andreceiving by the asteroid of at least some portion of the generated kinetic-energy-containing products to produce thrust directed generally away from the lunar or planetary surface that decelerates the asteroid as it approaches the landing site at a specified trajectory. 2. The method as in claim 1, wherein the deuterium-containing particle fuel material is projected from a pre-positioned system at the landing site to a specified location outward from the asteroid such that the generated kinetic-energy-containing products pushing against the asteroid produce braking thrust according to a desired asteroid trajectory toward the landing site. 3. The method as in claim 2, wherein the pre-positioned landing site further includes radar tracking equipment for determining position, velocity, and trajectory of the asteroid as it approaches the landing site and directs the projecting of the fuel material to a calculated location in relation to the approaching asteroid. 4. The method as in claim 2, wherein the pre-positioned system also disperses a cloud of the deuterium-containing particle fuel material in the immediate vicinity of the landing site such that generated kinetic-energy-containing products create a braking cushion at the landing site. 5. The propulsion system as in claim 1, wherein the deuterium-containing particle fuel material comprises Li6D. 6. The propulsion system as in claim 1, wherein the deuterium-containing particle fuel material comprises D2O. 7. The propulsion system as in claim 1, wherein the deuterium-containing particle fuel material comprises D2. 8. The propulsion system as in claim 1, wherein the deuterium-containing particle fuel material is in solid powder form. 9. The propulsion system as in claim 1, wherein the deuterium-containing particle fuel material is in pellet form. 10. The propulsion system as in claim 1, wherein the deuterium-containing particle fuel material is in frozen form. 11. The propulsion system as in claim 1, wherein the deuterium-containing particle fuel material is in liquid droplet form. 12. The propulsion system as in claim 1, wherein the deuterium-containing particle fuel material also contain up to 20% by weight of added particles of fine sand or dust. 13. The propulsion system as in claim 1, wherein the deuterium-containing particle fuel material is projected outward from the landing site as successive packages. 14. The propulsion system as in claim 13, wherein each package is configured to disperse the deuterium-containing particle fuel material as localized cloud at a specified distance from the asteroid. 15. The propulsion system as in claim 1, wherein each landing site has at least one gun and a set of shell projectiles to be shot from the at least one gun to target areas for fuel material dispersal. 16. The propulsion system as in claim 15, wherein the shell projectiles contain a chemical explosive and a fuse configured to disperse the fuel material as a localized cloud at a specified distance from the asteroid. 17. The propulsion system as in claim 15 wherein each shell projectile comprises a shell wall encasing the fuel material with a fuse and chemical explosive charge activated by the fuse. 18. The propulsion system as in claim 17, wherein the shell projectile further comprises a cartridge case containing a propellant for projecting the shell to a targeted location. 19. The propulsion system as in claim 17, wherein the fuse comprises a timer for activating the explosive charge at a specified time after projection of the shell. 20. The propulsion system as in claim 17 wherein the fuse comprises a location detection system for activating the explosive charge when the shell reaches a targeted location. |
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050531883 | claims | 1. A reactor system of a boiling water type atomic power plant including a reactor pressure vessel, a primary containment vessel containing the reactor pressure vessel, a main turbine, a main steam piping extending through the primary containment vessel between the reactor pressure vessel and the main turbine, and inside and outside main steam isolation valves provided on the main steam piping inside and outside the primary containment vessel, respectively, at least the outside main steam isolation valve being disposed nearer to a wall of the containment vessel than other valves provided on the main steam piping outside of the containment vessel, at least one of the inside and outside main steam isolation valves being a quick closure valve enabling closure within a period of time of less than 3 seconds required for protection of a turbine at a time of interruption of turbine load, and a volume of the reactor pressure vessel allotted for accommodating steam being sufficient to permit the quick closure valve to quickly close and to mitigate a transient phenomenon associated with a pressure rise in the reactor pressure vessel due to the quick closure of the quick closure valve so as to insure safety and stability of the reactor system. 2. A reactor system as set forth in claim 1, wherein the inside main steam isolation valve is the quick closure valve. 3. A reactor system as set forth in claim 1, wherein the outside main steam isolation valve is the quick closure valve. 4. A reactor system as set forth in claim 1, wherein the reactor pressure vessel, is for a natural circulation reactor. 5. A reactor system as set forth in claim 1, wherein the quick closure valve enables closure within a period of time of about 0.1 second. |
041727606 | summary | BACKGROUND In known types of nuclear power reactors, for example as used in the Dresden Nuclear Power Station near Chicago, Ill., the reactor core comprises a plurality of spaced fuel assemblies arranged in an array capable of self-sustained nuclear fission reaction. The core is contained in a pressure vessel wherein it is submmerged in a working fluid, such as light water, which serves both as coolant and as a neutron moderator. Each fuel assembly comprises a tubular flow channel, typically of approximately square cross section, surrounding an array of elongated, cladded fuel elements or rods containing suitable fuel material, such as uranium or plutonium oxide, supported between upper and lower tie plates. The fuel assemblies are supported in spaced array in the pressure vessel between an upper core grid and a lower core support plate. The lower tie plate of each fuel assembly is formed with a nose piece which fits in a socket in the core support plate for communication with a pressurized coolant supply chamber. The nose piece is formed with openings through which the pressurized coolant flows upward through the fuel assembly flow channels to remove heat from the fuel elements. A typical fuel assembly of this type is shown, for example, by D. A. Venier et al. in U.S. Pat. No. 3,654,077. An example of a fuel element or rod is shown in U.S. Pat. No. 3,378,458. A plurality of control rods, containing neutron absorbing material, are selectively insertable in the spaces or gaps among the fuel assemblies to control the reactivity of the core. In a known core arrangement, such as shown for example in U.S. Pat. No. 3,020,888, the control rod blades have a cross or cruciform trasversel cross section shape whereby the "wings" of the blades of each control rod are insertable in the spaces between an adjacent four fuel assemblies. Suitable mechanisms are provided, as shown in the above-mentioned U.S. Pat. No. 3,020,888, to selectively move the control rods into and out of the core whereby the neutron population and hence the core power level can be controlled by the non-fission capture of neutrons by the neutron absorbing material in the control rods. Suitable such neutron absorbing materials, including commonly used boron, are set forth in the above-mentioned U.S. Pat. No. 3,020,888. During initial operation of the first core of a reactor, temporary, removable control curtains may be used to augment the moveable control rods. Such curtains may be formed of a boron stainless steel alloy and be suspended from the upper core support grid in the water gaps opposite the control blade tips. Additional information on nuclear power reactors may be found, for example, in "Nuclear Power Engineering," M. M. El-Wakil, McGraw-Hill Book Company, Inc., 1962. While the various reactor components are thoroughly factory tested before being placed in the reactor, there is a continuing need for in-service inspection equipment which can rapidly and conveniently verify the integrity of or detect any anomalies in such components at the reactor site, particularly after such components have been subjected to reactor service and have, therefore, become radioactive. Such radioactive condition of used components requires remotely operable equipment which can scan such components under water to protect the test equipment operators from radiation. Furthermore, known component testing techniques using photographic film, such as X-ray techniques, are not useful for radioactive components because the film is exposed by the radiation therefrom. It is known that neutrons can be detected in the presence of radiation from radioactive components. It is also known that the transmission of neutrons through a component is a function of the neutron absorbing properties of the component. Therefore, it is an object of the invention to verify the quality of or detecting anomalies in radioactive components by comparing the neutron transmission characteristics thereof with the neutron transmission characteristics of a similar component of known quality, for example, with a factory tested and verified standard component. Another object is to determine the neutron transmission characteristics of a component. Another object is to remotely scan a radioactive component submerged in a body of water for neutron transmission therethrough along its length. Another object of the invention is to provide test equipment including a neutron source and neutron detectors for directing neutrons into and detecting the neutron transmission through a selected dimension of a component. SUMMARY These and other objects of the invention are achieved by providing a small, high intensity neutron source removably contained in a shielded enclosure having an opening along one side to direct neutrons into an adjacent component under test. A second shielded enclosure is located on the other side of the component under test with an apertured neutron collimating plate adjacent the component. Neutron detectors are positioned behind the apertures of the collimating plate to detect the neutrons which are transmitted through the transverse dimension of the component. Means are provided to move the testing device along the component (or vice versa) and the signals from the neutron detectors are recorded (for example, on a strip chart) to provide a profile of the neutron transmission through the component along its length. This neutron transmission profile can then be compared to a neutron transmission profile which is similarly obtained from a standard component of known quality. |
043057861 | claims | 1. In a system wherein radioactive neutron-emitting elements are placed in succession in a liquid-filled tank and wherein the addition of each successive fuel element will cause a sub-critical multiplication factor, k, to approach a critical value of unity in accordance with the equation: EQU CR.sub.2 /CR.sub.1 =(.alpha..sub.2 /.alpha..sub.1).(1-k.sub.1)/(1-k.sub.2) providing a neutron flux from a source in said tank; counting the rate of neutron delivery (CR) to a detector location spaced from said source; storing electrical signals indicative of the quantity CR at said detector location before and after each successive fuel element is added to the tank; storing a value indicative of .alpha..sub.2 /.alpha..sub.1 for each said fuel element added to the tank based upon a given geometric positioning of fuel elements already in the tank; and computing k.sub.2 after the insertion of each successive fuel element in the tank from the equation: EQU Cr.sub.2 /CR.sub.1 =(.alpha..sub.2 /.alpha..sub.1).(1-k.sub.1)/(1-k.sub.2) |
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047524383 | abstract | A tubular cluster guide for use in a nuclear reactor having upper internals comprising a lower plate formed with flow openings is fixed to an upper plate of the intervals and provided with a device for guiding and centering its lower part in the lower core plate. The centering device has a plurality of rigid blades carried by the lower part of the guide, spaced apart angularly about the axis of the guide and engagable in an opening of the lower plate with a radial clearance and a plurality of flexible blades between the rigid blades. The flexible blades bear on the edge of the opening and exert a radially directed force thereon. Bridges may be formed in the lower plate to retain a broken resilient blade. |
description | FIG. 1 schematically shows a major part of an exposure device using X-ray according to Embodiment 1 of the present invention. In this embodiment, the exposure device is shown as a proximity type semiconductor device manufacturing apparatus, using the X-ray as the exposure radiation. In FIG. 1, designated by 1 is a X-ray source; 2 is a light blocking plate for limiting the exposure view angle; and 3 is a mask for the X-ray exposure which has a predetermined transfer pattern thereon. The radiation blocking plate is movable to a given position by driving means 20. Designated by 4 is a photosensitive substrate in the form of a wafer; 5L, 5R are X-ray absorbing materials disposed outside the exposure view angle of the mask 3, which normally define a frame, but for the simplicity of explanation, the left side is indicated as absorbing material 5L, and the righthand side is indicated as absorbing material 5R in the Figure. Designated by 6 is a strength distribution of the exposure X-ray in one direction on the wafer 4. FIG. 1 schematically illustrates the one-to-one exposure and transfer from the mask 3 onto the wafer 4 using the X-ray. The exposure device of this embodiment comprises an alignment portion for alignment between the mask 3 and the wafer 4, stages for supporting a shutter, the wafer 4, the mask 3 and the like, but they are omitted for simplicity. The positional relation is schematically shown in the FIG. 1, and, for example, when the X radiation source is a synchrotron radiation, the X radiation source 1 is far away from the mask 3, whereas the mask 3 and the wafer 4 are spaced only by several tens micron. The light blocking plate 2 for limiting the exposure view angle is supported on the exposure apparatus and is disposed approx several mm to several tens mm away from the surface of the mask 3 to permit movement thereof. As shown in FIG. 1, when the X-ray is projected onto the mask 3 from the X-ray source 1, the light blocking plate 2 blocks the X-ray. At this time, a penumbra (blurrness) 3a of the X-ray is generated at the edge of the exposure view angle on the mask. According to this embodiment, the penumbra portion 3a is overlapped with the absorbing material region (5R, 5L) of the mask 3, so that amount of the X-ray is limited at the edge of the penumbra. FIG. 2 shows in detail the region 7 in which the strength distribution is changing at the edge of the exposure view angle, that is, the area enclosed by a circle in FIG. 1. FIGS. 2, (A), (B) and (C) show an example in which the strength distribution 6 of the exposure X-ray on the wafer 4 changes due to the relation between the position in which the strength distribution changes due to the penumbra 3a and the position of the X-ray absorbing material 5R disposed at the outer peripheral of the transfer pattern region on the mask 3. Ideally, the projection intensity is 100% in the exposure area and 0% in the other area, but actually this is difficult. Practically, therefore, the intensity in the exposure area is 98%, and the non-exposed portion is 2%, on the basis of which the exposure area and the non-exposure area are defined. In other words, the tolerance of the exposure amount relative to the target level is plus and minus 2% in this example. In FIGS. 2, (A), (B) and (C), the lines indicated by 98% and 2% are threshold lines. The values used here are only examples, and proper values are selected properly by one skilled in the art, depending on the exposure process, the sensitivity of the resist. As shown in FIG. 2, (A), the exposure area (pattern region) 21, the boundary region 22 and the non-exposure area (next pattern region) 23 are divided by the intersection point 21a, 22a points 21a, 22a between the thresholds (98% and 2%) and the intensity distribution curve. The non-exposure area 23 shown in the Figure may be an exposure area of the next shot area. FIG. 2, (A) shows a conventional example of a distribution of the X-ray projection intensity onto the mask 3. The X-ray absorbing material 5R outside the exposure view angle on the mask 3 is formed on the portion on which the X-ray is not projected in FIG. 2, (A), the same applies to the case where it is not formed. The boundary region 22 existing between the exposure area 21 and the non-exposure area (next exposure area) 23 in this case is the area in which the intensity is 98% to 2% of the intensity distribution curve 6. Conventionally, the portion of the width has not been used for the exposure since it is the non-usable area peculiar to the X-ray exposure device. FIG. 2, (B) shows the case in which the X-ray absorbing material 5R outside the exposure view angle on the mask 3 is formed extended to the pattern region 21 which is exposed to the X-ray. Here, the intensity distribution curve 8 is similar to the curve 6 shown in FIG. 2, (A). The intensity distribution curve 6 shown in FIG. 2, (B) represents the intensity distribution when the absorbing material 5R absorbs a part of the projection X-ray. FIG. 2, (B) shows the case in which the absorbing material 5R is formed to the pattern region 21 so that intensity distribution curve 8 is changed to the intensity distribution curve 6. If the design is on the safety side in order to avoid the influence of the area in which the intensity distribution changes while the variation in the exposure amount in the exposure area 21, the exposure is prevented in the penumbra region 22. In such case, the boundary region 22 existing between the exposure area 21 and the exposure area 23 has the width shown in the Figure. FIG. 2, (C) illustrates an embodiment of the present invention. The difference between the FIG. 2, (C) and FIGS. 2, (A), (B) is in that inner edge of the X-ray absorbing material 5R outside the exposure view angle on the mask 3 is made to overlap with the penumbra region 22. The inner edge 5Ra of the X-ray absorbing material 5R which is the boundary of the exposure view angle of the X-ray mask 3 is placed in the area which is the boundary region 22 outside the proper exposure amount area described in conjunction with FIG. 2, (A), that is, which involves non-uniform intensity distribution. As will be understood from comparison among (A), (B) and (C) in FIG. 2, by placing the inner edge 5Ra of the X-ray absorbing material 5R within the penumbra region 22, the width of the boundary region 22 is smaller than in (A) and (B) in FIG. 2. By decreasing the width of the boundary region 22 in this manner, the exposure area can be expanded in the exposure system according to this embodiment. As described in the foregoing, according to the present invention, the use is made with the mask having a light blocking portion or a low intensity regions 5R, 5L of the X-ray absorbing material which is similar to the transfer pattern, in a predetermined portion or portions outside the transfer pattern region 21, so that region 22 of the penumbra provided by the light blocking plate for limiting the exposure view angle of the exposure device is placed by the light blocking plate 2 moved by driving means such that region 22 contains the inner edge portion of the light-blocked area 5R, 5L. By doing so, the light blocking plate of the apparatus assures the exposure area of the transfer pattern, and the low intensity region 5R, 5L of the mask sufficiently reduces the X-ray intensity in the penumbra provided by the light blocking plate to suppress the entering into the adjacent pattern region. FIGS. 3, 4 are schematic illustration of the major part in Embodiment 2 of the present invention. In this embodiment, the gap between the transfer pattern region and the light blocking portion or low intensity region is selected in accordance with the property of the resist useed in the transfer step, the order of the steps or the material of the film to be processed; and the portion of the penumbra provided by the light blocking plate for limiting the exposure view angle is projected to the light blocking portion or the low intensity region; and the exposure and the non-exposure of the boundary region of the outer periphery of the transfer pattern is selected using the penumbra. Particularly, in this embodiment, the selection between the exposure and non-exposure of the boundary region 22 depending on the exposure step and the resist is enabled; and the corresponding X-ray absorbing materials 5L, 5R outside the exposure area on the X-ray mask 3. In FIGS. 3, (A) and (B), the case of the necessary exposure of the boundary region is shown when the adjacent exposure areas are exposed. As shown in FIG. 3, (A), the left side pattern region 21 is exposed. The solid line 6 shows the influence of the penumbra provided by the light blocking plate (not shown) and the distribution of the projection X-ray intensity on the wafer provided by the X-ray absorption pair 5R disposed outside the transfer pattern of the mask 3. Then, as shown in FIG. 3, (B), right side pattern region 23 is exposed. Similarly to the foregoing case, the exposure occurs to the boundary region 22, and the intensity distribution of the projection X-ray on the wafer is as indicated by the solid line 6 in FIG. 3, (B). In the boundary region 22 the exposure amount distribution 9 is a sum of the two exposures. Thus, in order to exposegg the boundary region 22, the light blocking plate 2 is moved by the driving means such that X-ray absorbing materials 5R, 5L outside the exposure area which defines the exposure area on the mask is disposed outside the center 10 of the penumbra region. As indicated by the total exposure amount 9, the exposure amount at the center portion (boundary region 22) is excessive, but the exposure amounts at the both sides thereof (pattern region 21, 23) are proper. Since the boundary region 22 does not include the fine pattern, and therefore, the resist is assuredly exposed if the exposure amount is larger, so that there is no practical problem. The case that boundary portion is required to be exposed, occurs, for example, when the resist in the boundary region is to be removed during the development in the process using positive-type resist or when the resist in the boundary region is to be retained during the development in the process using negative type resist. FIGS. 4, (A) and (B) show the position of the X-ray absorbing material 5R in the case that it is not necessary to expose the boundary region 22. Similar to the case of FIG. 3, the curve 6 represents the distribution of the exposure amount on the wafer provided by the exposure of the first left side pattern region 21. The curve 9 represents a distribution of the integrated exposure amount when the righthand side pattern region 23 is exposed. In order to prevent the exposure of the boundary region 22, the light blocking plate 2 is moved by the driving means 20 such that X-ray absorbing materials 5L, 5R outside the exposure area defined on the mask 3 is disposed inside the center line 10 of the penumbra region (boundary region 22), as shown in the Figure. Particularly, by setting such that absorbing material 5R is covered all over the boundary region 22 from the position very close to the outside of the necessary exposure area (pattern region 21), the distribution 9 of the total exposure amount which is the sum of the exposures from both sides is less than the threshold of the photosensitivity of the resist, and therefore, the resist remains there, as shown in Figure. However, as indicated by a solid line 9 in the Figure, the amount of the exposure is not zero, but is several percent to 30% approx, which is not large though. For this reason, an adjustment relative to the threshold of the photosensitivity of the resist is desirable. By the development, the thickness of the resist may be reduced in a case, but it occurs outside the fine pattern region (21, 23), and therefore, the tolerance is relatively large. The case that boundary portion is required to be exposed, occurs, for example, when the resist in the boundary region is to be retained during the development in the process using positive-type resist or when the resist in the boundary region is to be removed during the development in the process using negative type resist. It has been decided before or during the mask design how to process the resist in the boundary region, and therefore, the absorbing materials 5R, 5L are placed at either of the above positions accordingly. When the device is manufactured, using the exposure method of Embodiment 1 or 2, the process includes a step of relative positional alignment between the mask and wafer and a developing step of developing the wafer after the pattern on the surface of the mask is projected and transferred onto the wafer surface. According to the present invention, there is provided an exposure method and an exposure device wherein the width of the boundary region influenced by the penumbra when the device is manufactured using the X-ray, so that devices can be manufactured with high efficiency and stability. Additionally, according to the present invention, the width of the boundary region existing between the pattern region to be transferred and the next pattern region can be reduced, so that exposure area can be expanded, and therefore, the devices can be manufactured efficiently. Furthermore, by providing an absorbing material at a predetermined position outside the exposure area of the mask and projecting the penumbra of the light blocking plate to the position, it is possible to make selection whether to retain the resist or not, and therefore, the stability of the process can be improved. While the invention has been described with reference to the structure disclosed herein, it is not confined to the details set forth and this application is intended to cover such modifications or changes as may come within the purposes of the improvements or the scope of the following claims. |
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abstract | An improved particle beam treatment system optionally includes exchangeable particle beam nozzles. These particle beam nozzles may be automatically moved from a storage location to a particle beam path or between particle beam paths for use in medical applications. Movement may be achieved using a conveyance, gantry, rail system, or the like. The improved particle beam treatment system optionally also includes more than two alternative particle beam paths. These alternative particle beam paths may be directed to a patient from a variety of different angles and in different planes. |
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044249039 | description | FIG. 1 shows a molecular sieve 1 consisting of a molecular sieve filling 1a surrounded by a cartridge 2 made of pure aluminum and provided with quick-connect seals 3, 4. The cartridge 2 is enclosed in a wax partition layer 5 so as to be isolated from the filler 6 into which the molecular sieve 1 is embedded. The outer jacket is formed by a container 7, for instance also made of pure aluminum, which is closed by a lid 8. The seal is made hermetic by a welding seam 9. FIG. 2 shows another container for storing tritium, and includes three molecular sieves 10, 11, 12 in cartridge form embedded therein. These molecular sieves 10, 11, 12 each are enclosed by a wax partition layer 13 and by a filler means 14, for instance plastic or plaster, and by a container 15 made of pure aluminum. The container 15 additionally is encased by a multi-ply glass-fiber reinforced plastic layer 16 and is sealed by means of a blind flange with a metal seal 17. The plastic layer 16 seals the container 15 hermetically against gases and liquids and provides good protection against corrosive liquids. If subsequently the container must be separated or reopened, this may be done by sawing, the molecular sieves 10, 11, 12 being then exposed. To facilitate this separation, reference rupture sites 18, 19 may be provided on the container 15. The moment the molecular sieves 10, 11, 12 are exposed, the quick-connect seals 10 may be hooked up to a gas or rinsing line. By passing an inert gas through the tritium, it can be dissolved out of the molecular sieves 10, 11, 12. These seals are designed as the so-called quick-connect seals which open automatically when the mating connectors are set on them, while otherwise they seal in absolutely vacuum-tight manner. While this invention has been described as having a preferred design, it will be understood that it is capable of further modification. This application, is therefore, intended to cover any variations, uses, or adaptations of the invention following the general principles thereof and including such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains, and as may be applied to the essential features hereinbefore set forth and fall within the scope of this invention or the limits of the claims. |
048225258 | claims | 1. A process for preparing a cartridge for disposal of a radioactive waste liquid, which comprises filling glass fibers in a mold, heat-treating the fibers for partial fusion and molding them into a molded product of a predetermined shape, wherein at least one member selected from the group consisting of boric acid, silicic acid, lithium borate, lithium silicate, zinc borate, zinc silicate, an organic silane, a silica sol, an oil emulsion, and an alumina sol, is applied to the glass fibers or to the molded product. 2. The process according to claim 1, wherein at least one member selected from the group consisting of aqueous solutions of boric acid, silicic acid, lithium borate, lithium silicate, zinc borate and zinc silicate, an organic silane, an oil emulsion, and an alumina sol, is impregnated to the glass fibers or to the molded product, followed by drying. 3. The process according to claim 1, wherein said at least one member is applied in an amount of from 0.01 to 2% by weight as solid content relative to the glass fibers. 4. The process according to claim 1, wherein the organic silane is a .gamma.-alkylaminotriethoxysilane, and the oil emulsion is an emulsified mineral oil. 5. The process according to claim 1, wherein the glass fibers are composed essentially of 50 to 75% by weight of SiO.sub.2, 0 to 15% by weight of B.sub.2 O.sub.3, from 0 to 10% by weight of Li.sub.2 O, from 0 to 10% by weight of BaO, from 0 to 25% by weight of CaO, from 0 to 10% by weight of ZnO and from 0 to 15% by weight of Alhd 2O.sub.3. 6. The process according to claim 5, wherein boric acid, silicic acid, lithium borate, lithium silicate, zinc borate, zinc silicate, an alumina sol or a mixture thereof is applied to bring the final composition of the molded product to be 55 to 65% by weight of SiO.sub.2, 2 to 6% by weight of B.sub.2 O.sub.3, from 2 to 6% by weight of Li.sub.2 O, from 0 to 6% by weight of BaO, from 2 to 6% by weight of CaO, from 2 to 6% by weight of ZnO and from 2 to 8% by weight of Al.sub.2 O.sub.3. 7. The process according to claim 1, wherein the organic silane or the oil emulsion is applied in an amount of from 0.001 to 1% by weight, relative to the glass fibers. 8. The process according to claim 1, wherein the glass fibers have an average diameter of from 8 to 18 .mu.m. |
summary | ||
047909609 | abstract | A process for the stripping of cesium ions from an aqueous solution in which a precipitation agent is added to the aqueous solution and the resulting precipitate, containing the CS.sup.+ ions is stripped from the solution. Sodium or lithium tetraphenylborates, carrying electron-attracting substituents on the phenyl rings are employed as precipitation agent. |
description | The invention relates to nuclear power industry and nuclear reactor plants, and more particularly to nuclear reactor plants with liquid-metal coolants. At the same time, this invention may also be applied to various non-nuclear reactor plants. One of the key problems of nuclear reactor plants with liquid-metal coolants is corrosion of reactor structural materials. To prevent corrosion, the technique for formation of protective oxide coatings is used. The corrosion resistance of reactor structural materials, for example, steel, depends on the integrity of these coatings. It should be noted that the mentioned problem may occur both in nuclear reactor plants with non-liquid-metal coolants and in non-nuclear reactor plants. Although, this invention is described in relation to nuclear reactor plants with liquid-metal coolants, it also can be used both in nuclear reactor plants with non-liquid-metal coolants and in non-nuclear reactor plants. Oxygen can be applied for the purpose of formation of oxide coatings. Patent RU2246561 (issued on Feb. 20, 2005) discloses the method for increasing the oxygen concentration in the coolant by way of injecting the oxygen gas directly into the coolant, or supplying oxygen to the coolant surface, for example, into the gas chamber close to the coolant—in the latter case oxygen penetrates the coolant by way of infusion. Due to the fact that iron, chrome, and other components of structural materials have higher chemical affinity for oxygen, than coolant components, such as lead and/or bismuth, oxygen, inserted into the liquid metal coolant in the form of oxides of the coolant components, will oxidize components of structural materials and, at adequate oxygen concentration, will form protective oxide coatings on the surface of reactor walls. To ensure this kind of effect, oxygen concentration in the coolant is to be maintained within specified limits which depend on the reactor design and structural materials, as well as on the type and composition of coolant. Besides oxygen the other gases may be injected into the coolant. One of the disadvantages of such method is that gas injection into the coolant results in formation of bubbles floating to the coolant surface and gas from these bubbles enters the above-coolant space. While being in the coolant the dust, solidphase particles and components dissolved in the coolant may penetrate the gas bubbles. Therefore, gas injected into the coolant becomes contaminated by dust, solidphase particles and components after staying in the coolant and entering above-coolant space. Reuse of such gas, in particular, its reinjection into the coolant, results in contamination of the coolant and reactor equipment and, therefore, causes equipment faults and reduction of operating life of the equipment and reactor as a whole. The purpose of this invention is to provide the method and control system for gas injection into coolant and reactor plant, which are free from disadvantages intrinsic to the background of the invention. In particular, it is necessary to prevent contamination of the reactor coolant, vessel and equipment due to presence in the above-coolant space and reuse of the gas that was previously injected into the coolant and contaminated therein, while providing the possibility of gas reuse. The purpose of this invention is achieved by using the method of gas injection into the reactor coolant. The reactor is connected to the gas system and comprises device intended for injection of gas into the coolant installed partially in the coolant and partially in the above-coolant space and adapted to gas supply from the above-coolant space to the coolant. The gas system is connected to the reactor and adapted to gas supply/removal to/from the above-coolant space. The method includes the following steps: gas to be injected into the coolant is supplied from the gas system to the above-coolant space; gas is injected into the coolant by maintaining the gas pressure higher than coolant pressure in the device intended for injection of gas into the coolant; gas is injected into the gas system from the above-coolant space. In one of the possible embodiments of invention, gas is continuously supplied to the above-coolant space from the gas system and is continuously removed from the above-coolant space to the gas system during the gas injection into the coolant. In another possible embodiment of invention, gas is injected into the coolant for not longer than it is required for gas injected into the coolant to reach the coolant surface. Gas removed from the above-coolant space to the gas system is preferably filtrated and reinjected into the above-coolant space. In some embodiments, gas pressure in the device intended for injection of gas into the coolant is maintained higher than the coolant pressure by increasing gas pressure in the near-coolant space. In other embodiments, gas pressure in the device intended for injection of gas into the coolant is maintained higher than the coolant pressure by local reduction of the coolant pressure near the device intended for injection by rotating at least part of the device intended for injection of gas into the coolant. The purpose of this invention is also achieved by using the control system for gas injection into the reactor coolant. The reactor is connected to the gas system and comprises device intended for injection of gas into the coolant installed partially in the coolant and partially in the above-coolant space and adapted to gas supply from the above-coolant space to the coolant. The gas system is connected to the reactor and adapted to gas supply/removal to/from the above-coolant space ensured. Control system includes the following: control modulus of the gas system adapted to control the gas system ensuring gas supply to the above-coolant space of the reactor and ensuring gas removal from the above-coolant space of the reactor; and control modulus of the device intended for injection of gas into the coolant adapted to control the device intended for injection of gas into the coolant ensuring gas injection from the above-coolant space into the coolant. In some embodiments, control modulus of the gas system may be adapted to ensure continuous gas supply to the above-coolant space and/or continuous gas removal from the above-coolant space. In other embodiments, the system may include timer and the control modulus of the device intended for injection of gas into the coolant may be adapted to ensure gas injection into the coolant for not longer than it is required for gas injected into the coolant to reach the coolant surface. The purpose of this invention is also achieved by using the nuclear reactor plant which includes: a reactor, a coolant located in the reactor, a gas system connected to reactor and adapted to supply and remove gas to/from the above-coolant space and the device intended for injection of gas into the coolant installed partially in the coolant and partially in the above-coolant space and adapted to gas supply from the above-coolant space to the coolant. The gas system and device intended for injection of gas into the coolant are adapted to function in compliance with the method for any of the embodiments described above and/or under control of the system for any of the embodiments described above. In the preferable embodiment, the gas system comprises pipes, gas filter and pump connected into the loop, origin of which is adapted to receive gas from the above-coolant space of the reactor and end of which is adapted to supply gas to the above-coolant space of the reactor. The present invention provides the method and device (system) for control of gas injection into the coolant and reactor plant, which are free from disadvantages intrinsic to the background of the invention. Such technical result as prevention of contamination of the reactor coolant, vessel and equipment is accomplished. In particular, removal of gas contaminated while being in the coolant from the above-coolant space is ensured by way of airing of this space, which allows to improve safety, reliability, and extend the operating life of the reactor plant. This invention applies to a reactor plant (for example, nuclear reactor plant) which includes, as per one of the examples in FIG. 1, reactor 101 that comprises coolant 104 connected with the gas system by means of pipes 108 and 114 that are equipped with isolation valves 109 and 115 respectively. Besides, reactor may also include circulation pump 110 with an impelling propeller 111, disperser 112 with power and control terminal 113. A reactor 101 is a tank, the walls 102 of which are made of structural materials with adequate mechanical, thermal, radiation and other types of durability necessary for safe operation of a reactor plant, such as steel. Safe operation of reactor plants is of particular importance due to the fact that the core 103 of reactor 101 contains radioactive materials which release energy in the course of radioactive fission. At least a certain quantum of this energy in the form of heat is transferred to the coolant 104 located in the reactor and contacting with the core (i.e. the radioactive materials are located primarily in the coolant), and further transported to the heat exchanger 107 where the heat energy is transferred to other materials (for example, water, steam and other heat-absorptive materials), at a distance from the radiation source. In some embodiments of the invention the heat exchanger can be a steam generator designed to generate steam which can be used for heating of other media or activation of turbines. Downstream of the heat exchanger 107, the heat energy is transferred through the utilities outside the reactor without hazard of radiation contamination which, therefore, is concentrated within the reactor. In connection to this, due to drastic, undesired and long-term effects of radiation contamination of surrounding areas the special emphasis is placed on the strength and safe operation of the reactor. It is preferable to circulate the coolant in the reactor 101, in the circuit covering the core and the heat exchanger, for long-term and efficient transfer of heat from the core 103 to the heat exchanger 107 of the reactor. In order to ensure circulation the pump 110 with impelling propeller is preferably used. One of the important factors to retain strength of the reactor 101 through time is prevention or mitigation of corrosion of structural materials of reactor walls 102, its reinforcing, fixture, strength and other elements to the admissible level. The mentioned factor must also be considered when a coolant consisting of liquid metals such as sodium, lithium, lead, bismuth and etc. is used as the coolant 104. Heavy metals (lead, bismuth) have an advantage over light-weight metals because of their increased safety, particularly, in terms of low fire hazard. Besides, the coolants made of heavy metals have such an advantage as stability of their properties in case of water ingress. Naturally, the physical and chemical properties of such coolant will change in case of water ingress, but such changes will be insignificant and allow further operation. This can be useful for improving safety of a reactor plant in view of possible accidents or leakages of equipment where water is present or flows in the liquid form or in the form of steam, for example, heat exchangers or steam generators. Even if a heat exchanger or steam generator is faulty (have a leakage), the reactor plant can be operated until repair or replacement of faulty (leaking) equipment, as the coolant made of heavy metals allows such operation mode due to the insignificant (uncritical) dependence of its physical and chemical properties on injection of liquid or vaporous water. In order to reduce corrosion action on structural materials of the reactor, it is considered advantageous to create oxide coatings on the boundary between the coolant and structural material, for example, by supplying oxygen to the coolant surface (with subsequent infusion of oxygen into the coolant) or into the coolant; upon that the oxygen can be transferred by the coolant towards the reactor walls where oxygen can react with the structural materials (for example, steel) and form an oxide in the form of oxide coating on the surface of the structural material. An additional advantage of such anticorrosion protection is reduction of heat-exchange rate between the coolant and reactor walls due to low thermal conductivity of oxides. Injection of oxygen into the coolant and increase of oxygen concentration can be provided by means of supply of oxygen gas or oxygen-bearing gas from the gas system into the reactor to the near-coolant space and/or their injection into the coolant. If oxygen concentration value in coolant is too high, it may cause oxygen-type corrosion of structural materials, which leads to reduction of the reactor operating period, formation of a coolant leakage risk, excessive accumulation of solid-phase deposits in the coolant, etc. To reduce excessive oxygen concentration in the coolant, which could be caused by, for example, reactor depressurization and penetration of atmospheric air therein, or by scheduled maintenance, which resulted in excessive increase of oxygen concentration in the coolant, or to ensure coolant purification, it is allowed to use hydrogen gas or hydrogen-containing gas, supplied to the near-coolant space or injected into the coolant. When hydrogen gas is injected into the coolant, oxygen concentration in the coolant is reduced due to interaction of hydrogen with oxygen in the coolant and/or recovery of oxides of the coolant components. Reduction of excessive oxygen concentration in the coolant is a process important to reactor safety since extremely high oxygen concentration leads to the hazard of oxygen corrosion of reactor walls. Oxygen or hydrogen can be injected in the pure state or as a gas mixture, for example, mixtures with inert gases, neutral gases, with moisture vapor or other gases. Furthermore, in some cases it is required to inject gases, which do not contain oxygen or hydrogen, but which consist, for example, of inert gases only (for example, for flotation cleaning of reactor internal surfaces). Three-stage circuit can be used for gas injection into the coolant. At the first stage oxygen or hydrogen (or other gas) can be injected into the near-coolant space by means of the gas system, being the part of the reactor plant, with an outlet to reactor 101 space 106 above coolant 104 by means of pipe 108. Coolant 104 occupies only a part of the reactor tank to reduce the hazard of reactor depressurization due to thermal expansion of the coolant during heating. Upper part 106 of the reactor tank located above surface 105 (“level”) of coolant 104 is usually filled with inert gas (He, Ne, Ar) or a mixture of inert gases to prevent corrosion and undesired chemical reactions. To supply gas to the reactor (into the near-coolant space, as shown in FIG. 1) there is pipe 108 of the gas system. Furthermore, the gas system contains pipe 114, equipped with breather 115, for gas outlet from the reactor into the gas system. The purpose of pipes (pipelines) 108 and 114 is gas supply into or outlet from the reactor (is interchangeable). Furthermore, the reactor plant may be provided with other pipes (pipelines) for supply/outlet of gas from the reactor. The gas system, detailed in FIG. 2, can include pipelines (pipes) 108, 114, 216 and other, mixers/distributors, isolation valves 109, 114, 211-215 (breathers, valves, etc.), filter 204, pumps 202 and 203 and other equipment, not shown in FIG. 2, commonly used in gas systems and known from the background of the invention. The gas system can be connected with source 201 or a variety of gas sources or include them respectively, and can perform gas mixing by means of mixers and/or distribute gas or gas mixture by means of distributors, the function of which can be performed by the mixers themselves. Gas supply from the source to the gas system is controlled by isolation valves 211. The gas sources intended for supply to the reactor or for use in the gas system can be represented by facilities for gas generation and purification, for example, facilities for water electrolysis into oxygen and hydrogen. Gas main lines or gas cylinders or cylinder systems, which contain compressed gas, can also be the sources. Gas supply can be performed by means of high pressure inside the gas cylinders or by pumps provided for gas supply from the capacitors wherein the gas is stored. FIG. 2 outlines gas cylinder 201 that contains high pressure high-purity gas. At outlet from the sources or inside them gas filters can be provided, intended for gas purification from particles of various sizes, which without the filters would damage the gas system and/or the reactor, and lead to gas and/or coolant contamination. In order to control the movement of the gases though the pipes, pipelines, mixers/distributors and different equipment of the gas system there are isolation valves 109,115,211-215. Isolation valves can be presented by breathers, valves, switches, cocks, gate valves, shutoffs and other types of equipment that can be used for fluid/gas flow control. Primarily isolation valves are adapted to provide remote control, for example, by means of electric, hydraulic, lever drives and other types of drives. Remote control ensures safety of the personnel performing reactor services, scheduled maintenance or operation. Furthermore, remote control allows for control of a great number of isolation valves from one place, for example, from a panel, thus allowing for monitoring the whole condition and faster response to the changing state, making it possible to carry out a range of operations, which require performance of complex operation mode sequences, and improving reactor safety in general. Mixers/distributors are presented by a connection of several pipes/pipelines, through which various gases can be supplied for mixing and/or distribution into various pipes/pipelines and various equipment. For example, mixers/distributors can be represented by pipe connections, passing between valves 109, 211, 212 or between valves 213, 214 and filter 204, shown in FIG. 2. Mixing can be performed either directly in place of pipe/pipeline connection due to high diffusibility of gases and ability to penetrate each other and mix, or in a capacitor specially intended for mixing, to which pipes/pipelines are connected. The result of gas mixing can be transported by one or more pipes/pipelines, i.e. transported to one destination point or distributed into several destination points. Furthermore, the same gas can be led from one or several pipelines and supplied to several pipelines, which transport the gas to relevant consumers or destination points—in such case the gas is distributed. In some cases mixer/distributor can operate in the mode of a common pipe/pipeline, wherein the gas is supplied into one pipe and removed from the other. The operation mode of gas system in controlled by means of isolation valves, the state of which (open/closed, flow rate, etc.) determines the direction of gas flow. For example, for gas supply from source 201 to pipe 108, and therefore into above-coolant space 106, with an outlet to the above-coolant space through wall 102 of the reactor, breathers 211 and 109 are opened, and breather 212 must be closed. In case when gas removal from above-coolant space is impossible, i.e. if breather 115 is closed or breathers 213 and 214 are closed, gas will be transported to the reactor to the above-coolant space till it is equal to gas pressure in the source or till it is equal to pressure that can be created by a force pump, if such is used for gas supply to the reactor. Alternatively, if gas removal from above-coolant space is possible, i.e. if breathers 115, 214 and 215 are open, and breathers 212 and 213 are closed, then the gas, supplied from source 201 to the reactor into the above-coolant space by means of pipe 108, will be removed from the above-coolant space into the gas system through pipe 114. Then the gas will pass through filter 204, being purified from contamination, and will be removed into the atmosphere or space intended for storage (for example, spent gas storage) through pipe 216. In such case the ventilation of the above-coolant space will be performed. Above-coolant space ventilation is also possible without supply of gas from source 201. Gas system loop that contains filter 204 and pump 202 can be used for this purpose. In order to arrange a loop in the gas system it is necessary to open breathers 109, 115, 212 and 213, and close breathers 211 and 214. When activating (switching on) pump 202 the gas system loop sucks the gas in from above-coolant space 106 through pipe 114, the gas passes through filter 204 and pump 202 and is resupplied to space 106 through pipe 108. If pump 202 is capable to supply gas in opposite direction, then gas will be removed from space 106 through pipe 105, and reenter space 106 through pipe 114. However, in such case contamination by small particles, suspension and/or dust of pump 202 is possible, since gas filtration is performed after gas passes the pump. Therefore a preferred option of gas circulation arrangement in space 106 and gas loop is the option, where at first gas passes through filter 204 and then through pump 202, since in such case the risk of pump contamination is reduced and its lifetime is extended without the need for repair. Gas circulation in the space and in the gas loop with such configuration allows filtering gas in space 106 and ensuring the required degree of purity depending on filter 204. As a result, the above-coolant space is vented with pure gas without gas consumption from external sources. Filter 204 is a device that allows for breathing and retention of dust, solidphase and/or liquid and/or jelly-like particles and other gas contaminating impurities. The filter may contain fibrous materials, such as fiber glass, fiber felt, etc. which ensure retention of impurities. It is also possible to use various screens, gauzes etc. Furthermore, the filter may contain, be coupled with or designed as centrifugal or gravitational dust collectors for example, in the form of a cyclone filter. Furthermore, the filter may contain be coupled with or designed as a cooler, that allows for gas purification from air steam by means of their cooling and turning into water while the purified gas is removed from the filter. In some configurations cases of above-coolant ventilation are possible, where gas is removed from the above-coolant space by means of a pump, placed in the discharge pipe (preferably downstream of filter) and is vented to atmosphere or spent gas storage or processing equipment. In FIG. 2 pump 203, that removes gas from space 106 through pipe 114 and filter 204 and supplies it to the discharge pipe can be used as such equipment. In order to provide such configuration it is required that breathers 115, 214 and 215 are open, and breather 213 is closed. In such case there is no need to supply any gas to the above-coolant space by means of any gas source. It is sufficient to provide connection of intake pipe with the gas storage or atmosphere, and the gas from the storage will be sucked into above-coolant space (preferably through a filter) by means of gas rarefaction (decreased pressure) in above-coolant space, created for example by output pump. In gas system option shown in FIG. 2, there is no pipe, that would allow for connection with atmosphere or gas storage not by means of a pump and not with high pressure gas source and would have connection with the above-coolant space, however in other embodiments such pipes and their connections with atmosphere or gas sources can be provided. In the above configurations of gas system the above-coolant space ventilation is provided in several ways. Firstly, gas from the gas source can be supplied to the above-coolant space through a feed pipe or under pump head, passing through the above-coolant space and independently be transported to the pipe for removal from the space. Secondly, gas can be removed from the space through an outlet pipe by means of an extraction pump, independently flowing into space from inlet pipe and passing through the above-coolant space to the outlet hole. Thirdly, there is a combined version, in which gas is simultaneously supplied to the above-coolant space through a feed pipe (by means of a pump and/or from the gas source) and is removed from the space through an outlet pipe by means of a pump. There is also an option where a pump same as pump 202 in the loop configuration, performs gas removal from the space and supplies the gas to the space again. All the versions of configuration provide for ventilation of the above-coolant space by means of supply and/or removal of gas into/from the above-coolant space. After gas was injected into the above-coolant space, the second stage of injection of gas into the coolant is realized, which is injection of gas directly into the coolant from the above-coolant space. To inject gas into the coolant, the reactor is equipped with a device intended for injection of gas into the coolant. The device is installed partially in the coolant and partially in the above-coolant space. The device makes it possible to supply gas from above-coolant space to the coolant through the holes of the device interconnected by channel. One hole is located in the above-coolant space, the other one is in the coolant. In one of the embodiments, the device can be a tube that has a channel inside which connects holes at the ends of the tube, while one end is located above the coolant and the other end is in the coolant. In another embodiment, a similar tube can be equipped with a pump that injects gas from the above-coolant space into the tube, and thereby into the coolant. Device intended for injection of gas into the coolant can be executed in the form of disperser, configuration and operation principle of which are described further below, or it can be a combination of these or other devices (as well as a different device) that make it possible to inject gas into the coolant. Gas can be injected into the coolant, for instance, in two ways. The first way consists in creating increased pressure in the above-coolant space as compared to inside-the-coolant pressure (for instance, when the gas in the above-coolant space does not press on the whole of the surface of the coolant, and/or in case when the coolant can flow to space where there is no increased pressure which is created in the above-coolant space), that can cause forced penetration of gas into the coolant which has lower internal pressure than the device intended for injection of gas into the coolant. Pressure value can be determined by means of pressure sensors in this space or space connected to it with the gas system pipeline, or according to the amount of gas pumped to this gas space which can be determined with the use of flow rate meters. The disadvantage of this method consists in proneness of the device intended for injection of gas into the coolant to clog the outlet hole (holes) located in the coolant due to formation of coatings and solidphase particles or penetration of solidphase impurities, dust from gas over the coolant into the device intended for injection of gas into the coolant. To prevent clogging of disperser outlet holes, the hole is mainly done on the moving elements of the device intended for injection of gas into the coolant. These elements are installed in the coolant, for example, on the lower end of the rotating element of the device intended for injection of gas into the coolant. The other way consists in creating a local zone of low pressure in the coolant, for example, near the device intended for injection of gas into the coolant (entrainment of gas with coolant). For instance, it can be done with the help of elements of the device intended for injection of gas into the coolant that rotate or move in the coolant. In one of the embodiments, this can be achieved with the use of discs in the lower part of the disperser which may have blades. When rotating, the discs create a low-pressure area in the coolant under the action of centrifugal forces. The gas passing from the above-coolant space to the lower holes near or in the discs through the longitudinal channel goes to the mentioned low-pressure area. Due to the gradient of coolant velocity near the device intended for injection of gas into the coolant (disperser, for instance), in particular, the discs, i.e. when the coolant near the disperser moves faster than in the area away from it, the gas entering the coolant in the form of bubbles is fragmented to smaller bubbles, thereby creating the finely-divided two-component suspension of gas-coolant. Due to the fact that the device intended for injection of gas into the coolant has moving (rotating) elements, the coolant moves (flows over) near the surfaces of the device intended for injection of gas into the coolant, which washes the solid particles and oxide coatings away from the device intended for injection of gas into the coolant, thereby ensuring its automatic self-purification. This property increases the operating life of the device intended for injection of gas into the coolant as well as the operating life and safety of operation of the reactor plant in general. In individual embodiments of this invention intended for injection of gas into the coolant, the disperser 112 is installed in the function of the device intended for injection of gas into the coolant 104 from the space 106 above the coolant in the reactor 101. For this purpose, the disperser 112 is installed partially in the coolant 104 and partially in the space 106 near the coolant 104 Gas containing oxygen or hydrogen can be injected into the coolant directly from the gas system pipeline, but in this case the pipeline will be sunk in the coolant, which may lead to plugging and clogging of the pipeline, thereby affecting safety and decreasing the operating life of the reactor plant. The disperser 112 is installed vertically, in this case the disperser 112 is set to position extending its operating life, as the coolant and the solid-phase oxides do not penetrate into the disperser (which would require that they move upwards) or cause its clogging, which extends its operating life. As the disperser is able to supply gas from the near-coolant space to the coolant, the gas entrained through the hole in the upper part of disperser located, in a particular case, in the above-coolant space passes through a channel in the disperser (for example, in the shaft) downward and comes out of its lower part located in the coolant (the names of directions change accordingly at other layouts of disperser). In the embodiment shown in FIG. 3 the disperser can have two discs, one of which rotates and another one does not. Such a combination creates a low-pressure area of the coolant between the discs; gas may get to this area from the holes in the shaft or in one or two discs. As it is possible to provide a sufficiently small distance between the discs, and one of the discs rotates relative to another, the pressure drops faster compared to the case when both discs rotate. As a result, the efficiency of gas injection into the coolant is improved and the gas bubbles become even smaller, i.e. the dissolution efficiency of gas in the coolant is improved. The solid electrolyte oxygen sensor shown in FIG. 3 consists of the following main elements: the disperser housing 301 with a stationary upper disc; the hollow shaft 302 connected to the lower rotating disc 303; the flange 304 fastening the disperser to the reactor vessel; the electric motor 307 with the drive magnetic half-coupling 306 transferring rotation to the hollow shaft 302 with the use of a driven magnetic half-coupling 305. The electric motor 307 with the half-coupling 306 is installed on the outside of the reactor wall 102, and the half-coupling 305 is installed on the inside of the reactor wall 102. In the preferable option shown in FIG. 3 the upper disc (stator) of the disperser is rigidly connected to the disperser housing 301. The lower rotating disc 303 is connected to the rotating shaft 302. The lower disc and the shaft are hollow, their cavities are interconnected. In the upper part the shaft cavity is connected to the gas circuit through holes. The holes of small diameter (at least 12 holes) are punched on the surface of the lower disc forming a clearance; these holes are located in a circumferential direction. The upper disc can also have small holes for injection of liquid metal into the cavity between the discs. In the upper part the rotating shaft is connected to the shaft of the sealed electric motor 307 powered from the frequency converter by means of magnetic half-couplings 305 and 306. The disperser is immersed in the coolant so that the holes in the upper part of the shaft are above the liquid level, and the upper and lower discs are below the liquid level. When the sealed electric motor is run, the lower disc rotates with the prescribed angular velocity. As a result of coolant movement relative to the lower disc, a low-pressure area is formed in the clearance, which provokes the injection of gas into the clearance from the cavity of the lower disc through the holes in its upper part. Due to the velocity gradient of coolant the bubbles in the clearance are fragmented and the finely-divided gaseous phase together with the coolant comes from the clearance to the main flow of the coolant. In other embodiments of the disperser, the lower disc can be stationary, and the upper disc can be a rotating one. Besides, the cavity connecting the near-coolant space and the hole in the disc can be placed both in the shaft and in the housing. The holes can be made both in the rotating disc and in stationary one (or both). As mentioned above, the operation principle of the gas disperser is based on the fragmentation of gas bubbles in liquid upon being injected into the flow with high velocity gradient. Due to the irregularity of Q force applied to the surface elements, the large bubbles in such a flow are broken down into small ones. In the preferable option of the disperser, high-gradient flow of liquid in the gas disperser is formed in the clearance between rotating and stationary discs. The degree of gaseous phase dispersion with all other conditions being equal depends on velocity gradient in the flow. The velocity gradient is increased by reducing the clearance between the discs or increasing the linear speed of the discs' relative motion. The injection of gas into the coolant can be regulated due to the capability of controlling gas system operation which can inject essential gas in the near-coolant space, and/or create increased pressure in the near-coolant space, as well as due to the capability of controlling disperser operation which does not inject gas into coolant from the above-coolant space in passive state (without rotation of discs), and injects oxygen-containing gas into the coolant from the above-coolant space in active state (with rotation of discs), and the rate (efficiency) of gas injection into coolant may depend on the disc rotation speed. Application of dispersers with rotating discs is more reasonable, because it does not require to create increased pressure to inject gas to the coolant from the near-coolant space, but it is sufficient to actuate (activate) the disperser, which simplifies and thereby enhances the reliability of control system operation. To actuate (“activate”) the disperser, it is required to rotate the shafts and discs (or one of the shafts and one of the discs). This may be done with the use, for example, of an electric motor. To reduce the destructive effect of high temperatures and vapors of the coolant on the electric motor and, consequently, to extend its operating life, the motor shall be located outside the reactor (although, in some embodiments it can be located inside). To rotate the disperser parts, the shaft may be passed through the reactor wall from the electric motor. For this purpose, the wall shall have an opening. However, to improve the reactor structural strength and thereby its operational safety, the preferable embodiment allows the rotation to be transferred from the electric motor to the disperser elements with the use of magnetic coupling the parts of which are installed opposite each other on the different sides of the reactor wall. The magnetic field formed by a magnetic half-coupling can transfer the rotary force to another half-coupling located on the other side of the reactor wall, thereby actuating the disperser. If the disperser motor is located outside the reactor, it can be controlled through a wire (cable) 113 shown in FIG. 1 designed for the supply of electric power to the electric motor by supplying or not supplying the power voltage or changing its parameters. In this invention the actuation of disperser by means of an electric motor is designated as “activation” of the disperser and the shutdown of an electric motor when the disperser stops operating is designated as its “deactivation”. Rotation speed of the electric motor can be controlled in different ways: in a binary way (cut-off/cut-in), at different rotation speeds or with a possibility to set any rotation speed within the specified range. Consequently, the higher rotation speed is, the more gas (including oxygen) is dissolved in the coolant and the smaller gas bubbles are formed. As mentioned above, the gas (including oxygen-containing gas) can be injected into the coolant even when the increased gas pressure is created in the above-coolant space and the disperser is not activated. But in this case, the outlet hole (holes) of the disperser may be clogged. Therefore, to increase reliability and extend the operating life of reactor equipment (which leads to improving safety and reactor plant operating life extension), when applying this method of gas supply into the coolant (due to the increased pressure of the gas in the near-coolant space), the device intended for injection of gas into the coolant shall be activated in any case, so that the outlet hole (holes) at the lower end immersed in the coolant is flown around with the coolant which prevent accumulations of oxides, deposits, films etc. in/on it. Furthermore, the very control of gas pressure in the near-coolant space performed in such a way that the gas penetrates into the coolant through a device intended for injection of gas into the coolant even without its activation, may be undesired due to formation of large-sized bubbles which, for example, are less effective at flotation cleaning of inner surfaces of reactor, and provide for much lower accuracy of gas concentration (e.g. oxygen or hydrogen) in the coolant due to less precision of pressure control in the gas system than the control of disperser rotation speed, and, consequently, local decrease of pressure in the coolant near the rotating end (discs) of the disperser; therefore, it is preferable to perform gas injection into the coolant with the use of an activated disperser. After the gas is injected into the coolant in the form of bubbles, it will attempt to float to the surface as the density of the gas is much lower than the one of the coolant. The coolant is a liquid (in general, the invention may be used for air injection not only to the coolant, but to any other liquid) where bubbles can move. According to the Archimedes' principle, they will flow upwards, i.e. emerge. In case the coolant is circulated in the reactor, i.e. the coolant is moving in a closed circuit, for example, by the action of a circulation pump such as pump 110, and coolant velocity is higher than the one of the bubbles in the coolant, the bubbles may be entrained by the coolant, move over the entire circuit and float to the surface of the coolant only when the volume of the coolant with the floating bubbles is close to the surface of the coolant in reactor (i.e. to the surface 105 of separation of two media: coolant 104 and gas 106 in the above-coolant space), or when the circulation stops. In both cases at the movement of gas in the coolant such flow of bubbles cleans the surface of reactor walls of sediments, solidphase particles, dust, etc. Such sediments, solidphase particles and dust accumulate in gas bubbles and eventually are lifted out on the surface of the coolant from where they get into the gas in the above-coolant space. Such effect may be used for flotation cleaning of reactor structures exposed to the coolant (in such case inert gases, moisture vapor or gas mixtures, such as the mixture of inter gas with hydrogen and moisture vapor, may be injected). Due to the abovementioned phenomena, upon injection of gas in the form of bubbles into the coolant after a certain period of time defined by the rise rate of the bubbles and time of their circulation in the coolant, these gas bubbles filled with the above contaminants which may penetrate the bubbles not only from reactor walls but also from the coolant itself, float to the surface of the coolant, and the gas in the above-coolant space becomes contaminated with dust, solidphase particles, etc. In the meantime injection of gas into the coolant may be continued. As the gas in the above-coolant space became contaminated, the coolant is injected with contaminated gas, and thus the coolant is not cleaned and contaminants may again be deposited on the walls and structures of reactor. Aside from that, due to the fact that the device intended for injection of gas into the coolant has a channel through which the gas is injected into the coolant, the flow of contaminated gas through this channel may result in clogging of the device and loss of its efficiency (capacity). Furthermore, as there is a high probability of formation of deposits and clogs at the output of the device intended for injection of gas into the coolant, that is near the hole at the end of the device submerged in the coolant, contaminated gas enhances such probability and tendency to contamination of outlet holes. In case a disperser with two discs rotating relative to one another is used as a device intended for injection of gas into the coolant, the space between the discs may also be contaminated reducing the capacity of the disperser and in extreme cases may knock it out of service and/or clog outlet holes. All of this suggests that injection of contaminated gas into the coolant must be avoided. For this purpose, at the third stage after the gas is injected into the coolant, the contaminated gas is removed from the above-coolant space. Gas removal may be performed, for example, by means of an extraction pump removing the gas from reactor through the outlet pipe (usually there is a filter mounted at the front of the pump allowing filtering contaminants in the gas and prevent the pump from contamination which could knock it out of service or degrade its performance). In case the inlet pipe is open, the gas at the same time will be supplied (injected) to the above-coolant space. It can be either the purified gas from the atmosphere or pure gas storage, or the same gas which was removed from the above-coolant space and filtered. Gas may also be removed by supplying pure gas to the above-coolant space which will force the contaminated gas out through the open outlet pipe. Due to the availability of the third stage, the contaminated gas is removed from the above-coolant space and replaced by pure (purified) gas; therefore, the coolant is injected with pure uncontaminated gas preventing deterioration of coolant characteristics and necessity of its replacement, protecting structures of reactor against corrosion by removing contaminants from its walls and preventing their origination, thus preventing contamination and clogging of the device intended for injection of gas into the coolant as well as extending its life and increasing operation time duration with no need of repair. At injection of gas into the coolant with the purpose of preventing injection of contaminated gas into the coolant, operation of reactor plant and, more specifically, of its gas system components and device intended for injection of gas into the coolant, may be performed, for example, in accordance with the method shown in FIG. 4. Gas supply control can be performed by means of a single control device or control system consisting of several modules. In one embodiment, the control system for gas injection into the coolant may contain the module for control of the gas system and module for control of device intended for injection of gas into the coolant. The module for control of the gas system controls the gas system and, in particular, its equipment, pumps, valves, etc. so as to provide for supply of gas to the above-coolant space in the reactor or cutting-off of this supply as well as to ensure removal of gas from the above-coolant space of the reactor and cease of gas removal. With this purpose the module for control of the gas system is able to control the gas system in such a way so that its configurations provide for supply/removal of gas or their cease, for example, in accordance with configurations which refer to FIG. 2. Module for control of the device intended for injection of gas into the coolant controls the device intended for injection of gas into the coolant so as to ensure supply of gas from the above-coolant space to the coolant or cutting-off of this supply. For example, a disperser as well as the methods of its activation and deactivation which refer to FIG. 3 can be used for this purpose. When using the method shown in FIG. 4, at first during step 401 it should be checked whether gas injection into the coolant is required. If gas injection is not required, the standby mode is continued and the check of step 401 is periodically repeated or a command indicating the necessity of gas injection into the coolant is awaited. Step 401 can be performed by the module for control of the gas system and/or module for control of device intended for injection of gas into the coolant or a certain general control module. In such case, if it was determined at step 401 that gas injection into the coolant is needed, then at step 402 the module for control of the gas system and/or module for control of device intended for injection of gas into the coolant can check whether the gas is supplied to the above-coolant space. If gas is not supplied, then the module for control of the gas system provides for gas supply to the above-coolant space at step 403, for example, by means of arrangement of one of configurations of the gas system at which the gas is supplied to the above-coolant space (examples of such configurations are described with reference to FIG. 2). If it was determined at step 402 that the above-coolant space is supplied with gas (an additional check may also be conducted to verify the conformance of the supplied gas to the one that is required to be supplied to the coolant) or upon completion of step 403 the module for control of device intended for injection of gas into the coolant performs step 404 activating the device intended for injection of gas into the coolant. Immediately after completion of step 404 or in the course of its execution, a timer, counting the specified time interval at step 405, is started. The timer can be included in the control system in the form of a separate module or be a part of other modules, for example, included in the module for control of device intended for injection of gas into the coolant. During the time period counted by the timer, the device intended for injection of gas into the coolant continues to inject gas into the coolant. The time interval set for the timer may be defined as time required for floating of gas bubbles to the surface of the coolant upon their injection to the coolant. In case the coolant circulation is not performed, this time can be quite short and defined as a distance from the surface of the coolant (depth) where holes for gas injection into the coolant of the device intended for injection of gas into the coolant are situated, divided by the rise rate of the gas bubbles. In case there is circulation of the coolant in the reactor, which is induced, for example, by circulation pump 110 shown in FIG. 1, and bubbles of the injected gas are entrained by the coolant (for this purpose, for example, in FIG. 1 disperser 112 is located near pump 110, and propeller 111 is rotating so that the coolant moves downward from the propeller), the gas bubbles may float up to the surface of the coolant after passing the whole circuit; in such case the time set by the timer may be equal to the length of the circulation circuit or the path of the bubbles prior to emergence, divided by the coolant circulation velocity. On expiration of the time interval, counted by the timer, the module for control of device intended for injection of gas into the coolant may react in several ways. In the first instance, it may just stop the injection of gas into the coolant in order to prevent injection of contaminated gas irrespective of whether the above-coolant space is ventilated with pure gas or not. In the second instance, it may leave it as it is and continue to inject gas into the coolant in case the module for control of the gas system provides uninterruptible (continuous) ventilation of the above-coolant space with pure gas; in such case the gas injected to the coolant by means of the device intended for injection of gas into the coolant will be pure and the damaged caused by contaminated gas will be prevented. In the third instance, the module for control of device intended for injection of gas into the coolant may act in accordance with the method shown in FIG. 4, which is a combination of the first two methods. At step 406 following the end of the counting by the timer of set time at step 405, the module for control of device intended for injection of gas into the coolant can check whether the gas is supplied to the above-coolant space (whether its ventilation is performed). If gas continues to be supplied, the device intended for injection of gas into the coolant may continue injection of the gas and the module for control of device intended for injection of gas into the coolant proceeds to step 405, i.e. the set time interval is counted again. In case the gas is not supplied, the module for control of device intended for injection of gas into the coolant deactivates the device intended for injection of gas into the coolant at step 407 and proceeds to step 401, and the same method is used again. Due to the method repeatability, its repetition and automatic control of gas injection into the coolant can be ensured, which allows to lessen the necessity for intervention of qualified personnel and, to a certain extent, exclude their participation in reactor plant operation control. In the embodiment of the method shown in FIG. 4 the duration of uninterruptible injection of gas into the coolant is defined by the duration of gas supply to the above-coolant space. Depending on the mode of gas supply controlled by the module for control of the gas system, the whole system can operate in two modes. In case the module for control of the gas system provides for uninterruptible supply of gas to the above-coolant space for a long period of time (more than the time interval counted at step 405), gas injection into the coolant in accordance with the method shown in FIG. 4 will also be uninterruptible and its duration will be defined by the duration of gas supply from the gas system which may be set, for example, by an additional timer being a part of the module for control of the gas system, or a command sent from other devices or control board. In case the module for control of the gas system provides for supply of gas to the above-coolant space for a short period of time (less than the time interval counted at step 405), gas injection into the coolant in accordance with the method shown in FIG. 4 will be single-shot or noncontinuous (repeated) if gas injection to the coolant is still required after a single cycle performed in accordance with the method shown in FIG. 4 upon completion of step 407. The method steps are preferably implemented in the shown and described sequence, but in some embodiments, whenever possible, the steps can be performed in a different sequence or simultaneously. It should be noted that the interrelation between the operation of the module for control of the gas system and the module for control of device intended for injection of gas into the coolant may differ from the one described above with relation to the implementation of the method shown in FIG. 4. For example, gas supply to the above-coolant space and gas injection into the coolant may start and end jointly, simultaneously or with a certain time difference. Furthermore, where gas supply to the above-coolant space is mentioned in FIG. 4 and in description of the invention as a whole, it may be considered equivalent to removal of gas from the above-coolant space or simultaneous injection of gas into the space and removal of gas from the above-coolant space, as these modes can be performed simultaneously provided that there is no need, for example, for pressure increase in the above-coolant space. The main criterion is the provision of ventilation of the above-coolant space with the purpose of forcing out/replacement of contaminated gas with pure gas either continuously or at the time when the gas is not injected into the coolant. Pure gas can be supplied to the space above the coolant from the gas source in order to be newly (for the first time) supplied gas each time. In another case, gas circulation is possible when pure gas supplied to the space above the coolant is obtained from the contaminated gas removed from the space above the coolant by filtration. For this purpose, it is possible to use the gas system configuration, forming a loop, which includes a filter and a pump (see above). If method of creating a pressure in near-coolant space (and, hence, in device intended for injection of gas into the coolant) which exceeds the value of pressure in the coolant is used to inject gas into the coolant, the ventilation of the space above the coolant can be carried out either in intermittent mode, when after injection of gas into the coolant by the action of increased gas pressure within the allowed time interval, the gas pressure is reduced by bleeding into the discharge pipe and the space above the coolant is vented or in continuous mode, when gas is discharged from the space at a rate that prevents the pressure drop in order to maintain increased gas pressure in the near-coolant space. The gas outlet rate can be controlled by the size of the isolation valve bores or, for example, by the resistance to the gas flow created by the filter or other equipment. The gas outlet rate and ventilation of the space above the coolant can be determined by the state (configuration) of the gas system or by means of flowmeters for example. The modules controlling the gas system and the device intended for injection of gas into the coolant can exchange information among themselves, for example in binary form, informing, for example, that the gas is supplied or not supplied, or that it is necessary to stop gas injection, or it is possible to start the gas supply (in some cases a signal can be given that directly prohibits the supply of gas or regulates the supply of power or sending of control signals to equipment controlled by another module). In another embodiment, the modules can exchange information about the equipment operation modes and the gas system state, changes in modes and parameters of operation and changes in the gas system operation and state—for example, about device activation or deactivation or the isolation valve opening or closing at a certain rate, which can be determined in instantaneous values or in the variation value for a specific, single, partial or total time interval. In some embodiments, the modules controlling the gas system and the device intended for injection of gas into the coolant can obtain information about the activation or deactivation (or degree of activity) of the equipment or valves controlled by adjacent modules (in particular, the modules controlling the device intended for injection of gas into the coolant and the gas system, respectively), directly from equipment or valves or from drivers or drives or cards that control this equipment or valves. Thus, for example, the module controlling the gas system and the device intended for injection of gas into the coolant can receive and/or exchange information about the disperser state (activated, deactivated and/or activation degree) and/or about the state of the equipment controlling or diagnosing the gas system, such as sensors, isolation valves (valves, breathers, etc.), pumps, etc. (state of this equipment can be expressed in the closed/open position, capacity, flow rate, activated/deactivated state and/or activation degree) directly from the disperser and/or gas system equipment (power supply terminals or sensors) and/or form boards/drivers/control cards of the specified equipment, as well as from the output of the module controlling the device intended for injection of gas into the coolant and the gas system that controls the equipment. In some embodiments, the modules controlling the gas system and the device intended for injection of gas into the coolant may give a signal for light, sound or another indication showing that it is necessary to perform some of the operations required in accordance with the present invention. Such indication can be perceived by the personnel monitoring and controlling the reactor plant, and this personnel can carry out activation/deactivation of equipment and/or valves or issue commands on activation/deactivation of equipment and/or valves to the modules controlling the gas system and the device intended for injection of gas into the coolant, for example, on the basis of decisions taken after the perception of such indication. The control system may contain a warning signal module designed so as to form a warning signal informing of the necessity to deactivate the disperser and/or termination of gas supply and/or supply/removal of gas to/from the space above the coolant, if operation in current mode may lead to equipment and coolant contamination. The structure of the control device (control system) as per this invention may have other configurations which may be the alternatives obtained by means of addition, exclusion or replacement. The block scheme of control method shown in FIG. 4, as well as examples of implementation of the reactor plant, apparatus and devices in FIG. 1-3 are given for illustrations only and can limit the breadth of protection of this invention, defined in the claims. Any actions, objects, modules, elements, equipment and other attributes indicated in singular can also be considered as used if there are many of them in the plant or method, and on the opposite, if plurality is indicated, one object or action may be sufficient for the use of such attribute. The control system can be automatic, i.e. the system can independently take and implement all decisions based on the data received and processed by the system. The advantage of such automatic method of gas injection in the coolant is that the necessity for the qualified personnel to take part in reactor plant control may be eliminated. However, it may cause the risk of reactor plant functioning conditions exceeding the permissible limits due to the closedness of the control cycle in case of unlimited positive feedback, wherein an attempt to control the undesired deviation of a parameter results in a greater deviation of the parameter in the undesired direction (this may occur due to imperfection of processing algorithms and equipment failures). In another embodiment, the control system of gas injection into the coolant can be implemented with personnel involved in data processing and/or decision-making. This option requires involvement of highly qualified specialists. This will ensure the consideration of all possible parameters and exclude the reactor plant switch to hazardous or critical operation modes, as a human being, in contrast to an automatic device, is able to adaptively estimate the current situation and change action plans taking into account security and long-term operation issues. To enable the personnel to receive data and interact with the control system, the reactor plant may have a control board equipped with indicating means such as light indicators (light panels, displays, information boards etc.), audio indicators (loud speakers, buzzers, alert systems etc.) and other, such as tactile displays. Furthermore, the control board can be equipped with input devices for requesting necessary information, testing and input of control commands. The input devices can be buttons, toggle switches, levers, keyboards, sensors, touch pads, trackballs, mouse, sensor panels and other input devices known in the prior art. Considering the variety of information equipment, the control board can be extended, for the personnel to use the board more conveniently. The equipment may include a rolling chair which, apart from operational comfort, ensures quick and easy access to remote parts of the control board and the operator can easily push off the current position and quickly get to the desired position due to progressive motion of the chair rolls. However, it should be noted that both embodiments of the control system, the automatic one and the one involving personnel, have certain disadvantages. The manual control may have such a disadvantage as low speed of data processing and decision-making by personnel compared to the requirements of the reactor plant. On the other hand, the fully automated control system may be unsafe in case of failures or incomplete algorithms of data processing. As a result, the combined embodiment of the control system may be implemented, i.e. data processing and control are performed in automatic mode, but the data are displayed with the use of indicating means and, if any parameter exceeds the permissible limits (or approaches to the permissible limits) or upon any necessity the qualified personnel can adjust the operation of the automated control system or control it manually. The modules of the control system can be executed in hardware on the basis of discrete electronic components, integrated microcircuits, processors, assemblies, racks etc. The control system can be analog, digital or combined. Modules which are electrically connected to equipment located in the reactor or in the control board and which control its operation or process the data may include the converters of voltage, current, frequency, analog signals to digital ones and contrariwise, drivers, sources of current or voltage and control elements. All these elements and modules can be located on one or several mounting plates, can share one board or component or be separated accordingly, or can be executed and installed without the use of mounting plates. The control system modules may also be executed in software. For this purpose, integrated microcircuits with programmable logic, controllers, processors and computers can be used as hardware; while software will include programs with commands and codes executed by means of the indicated microcircuits, controllers, processors, computers etc. connected to the reactor devices and equipment. The programs shall be stored in memory units which can be executed in various forms known in the prior art and can be data carriers read by computer: read-only memory, hard drives and floppy disks, flash-drives, optical disks, frame memory etc. The programs may include chains of codes or commands for implementation of method and algorithms as per this invention, in whole or in part. Microcircuits, controllers, processors and computers can be connected to the input/output devices which may be located separately or be included into the control board. Separate modules of the control system can be software modules or be combined into one or several programs as well as into one or several software packages or elements. The control system and its modules may be executed as both hardware and software, i.e. part of the modules or all the modules may be executed in hardware, and part of the modules or control devices may be made as software. In the preferable embodiment, the control modules of reactor equipment (gas system, device intended for injection of gas into the coolant) and the modules for conversion of sensors can be made in hardware, and the modules for processing of data and commands, information display and control of processing parameters (such as threshold and permissible values) can be made as software on the basis of a computer, processor or controller. Additionally, specialized microcircuits can be produced. Such circuits shall contain all the necessary hardware elements with programs or parameters of data processing to be downloaded into these circuits. In the preferable embodiment, all electronic and other elements and components shall be made radiation-resistant to allow for operation of components and operability of the system in the whole as part of a nuclear reactor plant, which may be a source of ionizing radiation, and to preserve the capability of reactor operation control even in accident conditions and prevent possible adverse effects, thereby ensuring the enhanced safety and long operating life. |
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claims | 1. In an ion implanter apparatus including a source for the generation of charged ions as an ion beam, means for directing the ion beam in a desired direction, and a surface for the implantation of charged ions in the ion beam into a prepared workpiece,the improvement of an assembly for adjusting and controlling particles in the ion beam, said assembly comprising:a multi-coil array comprised of (i) a first ferromagnetic bar, and (ii) a plurality of wire coils disposed on said bar;a second ferrogmagnetic bar having a planar surface which is positioned to lie parallel to and spaced from said multi-coil array;controlled power supplies for providing electric current independently to each of said coils, such that each of said coils produces an individually controllable magnetic field;and a region for applying the magnetic fields produced by said coils to an ion beam traveling therethrough, said region being dimensionally circumscribed in an x-axis direction by said multi-coil array and in a y-axis direction by the distance separating said multi-coil array from said planar surface. 2. In an ion implanter apparatus including a source for the generation of charged ions as an ion beam, means for directing the ion beam in a desired direction, and a surface for the implantation of charged ions into a prepared workpiece,the improvement of an assembly for adjusting and controlling charged ions in an ion beam, said assembly comprising:a first multi-coil array comprised of(i) a first ferromagnetic bar, and(ii) at least two wire coils wound independently and positioned along said first bar;a second multi-coil array which is positioned parallel to the first coil array and at a preset distance from the first multi-coil array, said second multi-coil array being comprised of(a) a second ferromagnetic bar, and(b) at least two wire coils wound independently and positioned along said second bar;power supplies for providing current independently through said wire coils such that said wire coils generate individually adjustable magnetic fields;a region between said first and second multi-coil arrays for applying magnetic fields from said coils to an ion beam traveling therethrough, the region extending in an x-axis direction the length of said first and second multi-coil arrays, and in a y-axis direction the distance separating said first multi-coil array from said second multi-coil array. 3. The regulator apparatus as recited by claim 1 or 2 wherein said ion beam is a ribbon-shaped beam. 4. The regulator apparatus as recited by claim 1 or 2 wherein the number of said wire coils wound on a core ranges between nine and twenty-three. 5. The regulator assembly recited by claim 1 or 2 further comprising a means of measuring the profile of the current density of the ion beam in its long dimension at the plane where the workpiece is to be implanted, by measuring the current density at a plurality of positions. 6. The regulator assembly as recited by claim 5 wherein the current is adjusted in response to the measurement of the current density profile, so as to modify the observed ion beam density until that density conforms to a desired profile. 7. A method for adjusting and controlling charged particles in an ion beam,said method comprising the steps of: obtaining an assembly comprised of a multi-coil array comprised of (i) a bar of ferromagnetic material, and (ii) at least two wire coils disposed on said bar,a ferromagnetic element having a planar surface which is positioned to lie parallel to and spaced from said multi-coil array,power supplies for providing current independently through said wire coils that said wire coils generate individually adjustable magnetic fields,and a region for applying magnetic fields from said cores to an ion beam traveling therethrough, the region extending in an x-axis direction said length of said bar of said multi-coil array and in a y-axis direction by said distance separating said multi-coil array from said planar surface of said ferromagnetic element;directing an ion beam through said region of said assemblypassing current independently through said wire coils, whereby wire coils independently generate individually adjustable magnetic fields;and adjusting and controlling the degree of uniformity for the ion beam passing through said assembly. 8. A method for adjusting and controlling the uniformity of charged particles in an ion beam, said method comprising the steps of:obtaining an assembly comprised of: a first multi-coil array comprising (i) a first ferromagnetic bar, and (ii) a plurality of wire coils wound independently and positioned along the length of said bar,a second multi-coil array which is positioned parallel to the first coil array, and at a preset distance from said first multi-coil array, said second multi-coil array comprising (a) a second ferromagnetic bar, and (b) at least two wire coils wound independently and positioned along said second bar,power supplies for providing current independently through wire coils on said each of said bars of said first and second multi-coil arrays, such that the wire coils generate individually adjustable magnetic fields, anda region between said first and second multi-coil arrays for applying magnetic fields from said coils to an ion beam traveling therethrough, the region extending in an x-axis direction the length of said bars of said first and second multi-coil arrays, and in a y-axis direction the distance separating said first multi-coil array from said second multi-coil array;directing the ion beam through said region of said assembly;passing current independently and concurrently through said wire coils on each of said bars of said first and second multi-coil arrays, whereby said wire coils independently and concurrently generate orthogonally extending and individually adjustable magnetic fields of limited breadth between said first and second multi-coil arrays,and whereby said plurality of adjacently extending magnetic fields of limited breadth collectively form a contiguous magnetic field between said first and second multi-coil arrays; andadjusting and controlling the uniformity of an ion beam passing through said assembly. 9. In an apparatus for implanting charged ions including an ion source for the generation of charged ions to be implanted, means for directing the ion beam, and a surface for the implantation of charged ions in the ion beam into a prepared workpiece,the improvement being an apparatus for correcting variations in ion density or shape of the ion beam, said apparatus comprising:a structure manufactured from a magnetic material, said structure being comprised of an upper magnetic core member and a lower magnetic core member, each having a long dimension between its ends, the lower core member having a planar surface parallel to and spaced from said upper core member, anda plurality of coil units distributed along said upper core member, each coil unit comprising a single continuous electrical circuit that surrounds a core member; andpower supplies connected to the coils such that each of said coils may be independently excited to produce a magnetic field;a region existing between said upper and lower magnetic core members, wherein said region is dimensionally circumscribed in a x-axis direction by said upper and lower magnetic core members, and in a y-axis direction by the gap distance separating said upper and lower magnetic core members, and wherein the degree of uniformity for the charged particles of a ion beam is adjusted and controlled. 10. In an apparatus for implanting charged ions including an ion source for the generation of charged ions to be implanted, means for directing the ion beam, and a surface for the implantation of charged ions in the ion beam into a prepared workpiece,the improvement being an apparatus for correcting variations in ion density or shape of the ion beam, said apparatus comprising:a first multi-coil array comprising(i) an upper core member of magnetic material having a long dimension between its ends, and(ii) a plurality of independently excitable coil units distributed along said upper core member; anda second multi-coil array comprising(i) a lower core member of magnetic material having a long dimension between its ends, and(ii) a plurality of independently excitable coil units distributed along said lower core member;power supplies such that each of said coils may be independently excited by current in one direction for said coil units distributed along said upper magnetic core member and in the opposite direction for said coil units distributed along said lower magnetic core member when viewed from one end of said upper and lower core members to produce a magnetic field between said upper and lower magnetic core members;a region between said first and second multi-coil arrays for applying a magnetic field to an ion beam traveling therethrough, wherein said region is dimensionally circumscribed in a x-axis direction by said first and second multi-coil, and in a y-axis direction by the gap distance separating said first multi-coil array from said second multi-coil array, and wherein the degree of uniformity for the charged particles of an ion beam is adjusted and controlled. 11. The regulator apparatus as recited by claim 10, further comprising additional members of magnetic material connected between respective ends of said upper and lower magnetic core members to form the short dimensions of a rectangular frame, said additional members having independently excitable coil units distributed along said members, each said coil unit comprising a single continuous electrical circuit that surrounds an additional member, andmeans for independently exciting said coil units distributed along one or both of the additional magnetic members. 12. The regulator apparatus as recited by claim 10, wherein said ion beam is a ribbon beam. 13. The regulator apparatus as recited by claim 10, wherein the number of said coil units distributed along each of said upper and lower core member ranges between nine and twenty-three. 14. The regulator apparatus as recited by claim 13, wherein the number of said coil units is nine, sixteen or twenty-three. 15. The regulator apparatus as recited by claim 13, wherein three independent winding sections are on each magnetic core member, wherein each winding section comprises at least two individually excited coils. 16. The regulator assembly recited by claim 10 further comprising a means for monitoring the current ion density or shape of the ion beam at the workpiece to be implanted. 17. The regulator assembly as recited by claim 16, further comprising a current controller for independently changing the current passing through said individual coil units to produce a controllable magnetic field configuration between said upper and lower magnetic core members to introduce aberration correction and deflection. 18. The regulator apparatus as recited by claim 11, wherein equal and opposite ampere-turns are generated by coils on said additional magnetic core members forming the short dimensions of a rectangular frame and by coils on said magnetic members forming the long axes of the rectangular structure. 19. The regulator apparatus as recited by claim 10, wherein the individual coils are sufficiently close together to allow the magnetic field on the axis of beam region to vary smoothly. 20. A method for implanting a plurality of charged particles into a semiconductor material thereby modifying properties of said semiconductor materials, said method comprising the steps of:obtaining an apparatus comprised of a first multi-coil array comprising(i) an upper magnetic core member having a long dimension between its ends, and(ii) a plurality of coil units distributed along said upper core member, each coil unit comprising a single continuous electrical circuit that surrounds the upper core member; anda second multi-coil array parallel to said first comprising(i) a lower magnetic core member having a long dimension between its ends, and(ii) a plurality of coil units distributed along said lower core member, each coil unit comprising a single continuous electrical circuit that surrounds the lower core member;means for independently exciting said upper and lower coil units by currents which are in one direction for the coil units distributed along said upper magnetic core member and in the opposite direction for the coil units distributed along said lower magnetic core member when viewed from one end of said upper and lower magnetic core members; anda region between said first and second multi-coil arrays for applying a magnetic field to an ion beam traveling therethrough;passing electrical energy of variable current independently and concurrently through each of said upper and lower coil units, whereby each adjacently positioned and energized coil unit independently and concurrently generates a magnetic field between said first and second multi-coil arrays,and whereby said plurality of adjacently extending magnetic fields collectively form a magnetic field between said first and second multi-coil units, and whereby each magnetic field can be individually and concurrently altered to yield an adjustable and controllable magnetic field gradient over said contiguous magnetic field; andadjusting and controlling the degree of uniformity for the charged particles of an ion beam passing through said apparatus. 21. The method as recited by claim 20, wherein the apparatus obtained further comprises additional magnetic members each of which is connected between respective ends of said upper and lower magnetic core members to form the short dimensions of a rectangular frame, said members having a plurality of independently excitable coil units distributed along said members, each said coil unit comprising a single continuous electrical circuit that surrounds an additional magnetic member, andsaid method further comprising the step of passing electrical energy of variable current independently and concurrently through each adjacently positioned coil unit on each of said additional magnetic members forming the short dimensions of the rectangular frame, and controlling the energy of variable current to further adjust and control the degree of uniformity for the charged particles of the ion beam passing through said apparatus. 22. The regulator apparatus as recited by claim 9 wherein said ion beam is a ribbon-shaped beam. 23. The regulator apparatus as recited by claim 9 wherein the number of said wire coils wound on a core member ranges between nine and twenty-three. 24. The regulator assembly recited by claim 9 further comprising a means of measuring the profile of the density of the ion beam in its long dimension at the plane where the workpiece is to be implanted, by measuring the density at a plurality of positions. 25. The regulator assembly as recited by claim 24 wherein the current is adjusted in response to the measurement of the density profile, so as to modify the observed ion beam current density until that density conforms to a desired profile. 26. The apparatus as recited by claim 2, further comprising a current controller configured to actively adjust current passing through said wire coils to produce a controllable magnetic field in the region between said first and second multi-coil arrays for correcting aberrations of the ion beam passing through the region. 27. The apparatus as recited by claim 2, further comprising a current controller configured to actively adjust current passing through said wire coils to produce a controllable magnetic field in the region between said first and second multi-coil arrays in response to a condition of the ion beam passing through the region. 28. The apparatus as recited by claim 27, wherein the condition of the ion beam is an ion density of the ion beam. 29. The apparatus as recited by claim 27, wherein the condition of the ion beam is a shape of the ion beam. 30. The apparatus as recited by claim 27, wherein the controller is further configured to make active adjustments on a time scale limited only by a decay rate of eddy currents in said first and second ferromagnetic bars. 31. The apparatus as recited by claim 27, further comprising:faraday cups to measure an intensity and angle distribution of the ion beam passing through the region between said first and second multi-coil arrays, and wherein the current controller is further configured to actively adjust the controllable magnetic field in response to the intensity and the angle distribution of the ion beam measured by the faraday cups, and wherein the current controller is further configured to make active adjustments on a time scale limited only by a decay rate of eddy currents in said first and second ferromagnetic bars. |
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050858254 | claims | 1. A multiple liquid standby safety injection system for nuclear reactor plants, comprising the combination of: a nuclear reactor plant including a reactor pressure vessel containing a core of fissionable nuclear fuel: a first water tank for containing cooling water and gas under pressure for propelling the water through an injection system including a valve controlled conduit making fluid communication from said first tank to the nuclear reactor pressure vessel above the fuel core for supplying cooling water to the fissionable fuel during an emergency; a second solution tank for containing a water solution of a soluble neutron absorbent compound and gas under high pressure for propelling the neutron absorbent water solution through an injection system including a valve controlled conduit making fluid communication from said second tank to the nuclear reactor pressure vessel for supplying neutron absorbent solution to the core of fissionable fuel during an emergency; a source of high pressure compressed propelling gas having a valve controlled conduit making fluid communication therefrom to each the first water tank and the second solution tank to provide pressurized gas to the tanks for propelling their contents through their respective injection systems into the nuclear reactor pressure vessel by means of their respective valve controlled conduits; sensing means monitoring the nuclear reactor pressure vessel operating the valves controlling flow in the conduits making fluid communication between the first water tank and the pressure vessel, and between the second solution tank and the pressure vessel; and a propellant pressurized gas supply and distribution system comprising a fluid conveying conduit having a flow controlling valve making fluid communication between the first water tank and the second solution tank and having pressure monitoring and sensing means in both the first water tank and second solution tank for regulating an actuating mechanism operating the flow controlling valve whereby fluid flow of pressurized gas between the first water tank and the second solution tank is determined by their relative pressures. a nuclear reactor plant including a reactor pressure vessel containing a core of fissionable nuclear fuel; a first water tank for containing cooling water and gas under pressure for propelling the cooling water through an injection system including a valve controlled conduit making fluid communication from said first tank to the nuclear reactor pressure vessel above the fuel core contained therein for supplying supplemental cooling water to the fissionable fuel during an emergency; a second solution tank for containing a water solution of a soluble neutron absorbent compound and a gas under high pressure for propelling water solution through an injection system including a valve controlled conduit making fluid communication from said second tank to the nuclear reactor pressure vessel adjacent to the fuel core for supplying neutron absorbent solution to the core of fissionable fuel during a emergency; a source of high pressure compressed propelling gas having a valve controlled conduit making fluid communication therefrom to each the first water tank and the second solution tank for providing pressurized gas to each tank for propelling their liquid contents through their respective injection systems into the nuclear reactor pressure vessel by means of their respective valve controlled conduits; sensing means monitoring conditions in the nuclear reactor pressure vessel for operating the valves controlling flow through the conduits making fluid communication between the first water tank and the pressure vessel; a propellant pressurized gas supply and distribution system comprising a fluid conveying conduit having a flow controlling valve making fluid communication between the first water tank and the second solution tank and having pressure monitoring and sensing means in both the first water tank and second solution tank for regulating an actuating mechanism operating the flow controlling valve in the fluid conveying conduit making fluid communication between the first water tank and the second solution tank whereby fluid flow of pressurized gas between the first water tank and the second solution tank is determined by their relative pressures; and liquid level measuring means for monitoring the level of a liquid within each the first water tank and the second solution tank and regulating valve activating mechanisms operating a first flow control valve in the conduit making fluid communication from said first tank to the nuclear reactor pressure vessel, and a second flow control valve in the conduit making fluid communication from said second solution tank to the nuclear reactor pressure vessel, said first and second flow control valves terminating fluid flow from said tanks to the pressure vessel when a predetermined low level of liquid within the respective tank occurs. a nuclear reactor plant including a reactor pressure vessel containing a core of fissionable nuclear fuel; a first water tank for containing cooling water and gas under pressure for propelling the water through an injection system including a valve controlled conduit making fluid communication from said first water tank to the nuclear reactor pressure vessel above the fuel core for supplying cooling water to the fissionable fuel during an emergency; a second solution tank for containing a water solution of a soluble neutron absorbent comprised compound and gas under high pressure for propelling the neutron absorbent water solution through an injection system including a valve controlled conduit making fluid communication from said second solution tank to the nuclear reactor pressure vessel for supplying neutron absorbent solution to the core of fissionable fuel during an emergency; a source of high pressure compressed propelling gas having a valve controlled conduit making fluid communication therefrom to each the first water tank and the second solution tank to provide pressurized gas to the tanks for propelling their contents through their respective injection system into the reactor pressure vessel by means of their respective valve controlled conduits; sensing means monitoring the nuclear reactor pressure vessel and operating the valves controlling fluid flow in the conduits making fluid communication between the first water tank and the reactor pressure vessel, and between the second solution tank and the reactor pressure vessel; a propellant pressurized gas supply and distribution system comprising a fluid conveying conduit having a flow controlling valve making fluid communication between the first water tank and the second solution tank and having pressure monitoring and sensing means in both the first water tank and second solution tank for regulating an actuating mechanism operating the flow controlling valve in the fluid conveying conduit making fluid communication between said first and second tanks whereby fluid flow of pressurized gas between the first water tank and the second solution tank can be determined by their relative pressure; liquid level measuring means for monitoring the level of a liquid within each of the first water tank and the second solution tank, a regulating valve activating mechanism operating a flow control valve in the conduit making fluid communication from said first water tank to the reactor pressure vessel, and a regulating valve activating mechanism operating a flow control valve in the conduit making fluid communication from said second solution vessel to the reactor pressure vessel for selectively terminating fluid flow from said tanks to the pressure vessel when a predetermined low level of liquid occurs within a tank; and, said first water tank and second solution tank each being provided with a liquid level measuring float valve for closing off the respective conduits making fluid communication from each tank to the nuclear reactor pressure vessel when a predetermined low level of liquid occurs within each tank. 2. A multiple liquid standby safety injection system for nuclear reactor plants of claim 1, wherein the first water tank is provided with a liquid level measuring means for monitoring the level of a liquid within the tank and regulating a valve activating mechanism operating a flow control valve in the conduit making fluid communication from said first tank to the nuclear reactor pressure vessel for terminating fluid flow from the first water tank to the pressure vessel. 3. A multiple liquid standby safety injection system for nuclear reactor plants of claim 1, wherein the second solution tank is provided with a liquid level measuring means for monitoring the level of a liquid within the tank and which regulates a valve actuating mechanism operating a flow control valve in the conduit making fluid communication from said second tank to the nuclear reactor pressure vessel for terminating fluid flow from the second solution tank to the pressure vessel. 4. A multiple liquid standby safety injection system for nuclear reactor plants of claim 1, wherein the terminal end of the conduit making fluid communication from the first water tank to the nuclear reactor pressure vessel is provided with a flow check valve in a normally closed state thereby preventing back-flow. 5. A multiple liquid standby safety injection system for nuclear reactor plants, comprising the combination of: 6. The multiple liquid standby safety injection system for nuclear reactor plants of claim 5, wherein the terminal end of the conduit making fluid communication from the first water tank to the nuclear reactor pressure vessel is provided with a flow check valve in a normally closed state thereby preventing back-flow of fluid from the nuclear reactor pressure vessel into the conduit. 7. A multiple liquid standby safety injection system for nuclear reactor plants of claim 5, wherein the first water tank is provided with a liquid level measuring float valve for closing off the conduit making fluid communication from said first water tank to the nuclear reactor pressure vessel. 8. A multiple liquid standby safety injection system for nuclear reactor plants of claim 5, wherein the second solution tank is provided with a liquid level measuring float valve for closing off the conduit from said second solution tank to the nuclear reactor pressure vessel. 9. A multiple liquid standby safety injection system for nuclear reactor plants of claim 5, wherein the valve controlled conduits making fluid communication respectively from the first and second tanks to the nuclear reactor pressure vessel each include dual parallel control valves. 10. A multiple liquid standby safety injection system for nuclear reactor plants, comprising the combination of: 11. A multiple liquid standby safety injection system for nuclear reactor plants of claim 10, wherein the valve controlled conduits making fluid communication respectively from the first water tank and the second solution tank to the reactor pressure vessel each include dual parallel control valves. 12. A multiple liquid standby safety injection system for nuclear reactor plants of claim 10, wherein the terminal end of the conduit making fluid communication from the first water tank to the nuclear reactor pressure vessel is provided with a flow check valve located entirely within said reactor vessel and which prevents back-flow of fluid from the nuclear reactor pressure vessel into the conduit. 13. A multiple liquid standby safety injection system for nuclear reactor plants of claim 10, wherein the valve controlled conduit making fluid communication from the first water tank and the second solution tank includes a squib-type valve. 14. A multiple liquid standby safety injection system for nuclear reactor plants of claim 10, wherein the conduit making fluid communication from the first water tank and the second solution tank comprises at least one squib-type flow controlling valve operated by a logic system signal. 15. A multiple liquid standby safety injection system for nuclear reactor plants of claim 10, where the conduit making fluid communication from the first water tank to the second solution tank comprises multiple flow control valves with at least one explosive operated valve. 16. A multiple liquid standby safety injection system for nuclear reactor plants of claim 12, wherein the flow check valve in the terminal end of the conduit making fluid communication from the first water tank to the nuclear reactor pressure vessel is in a normally closed state. |
description | The present invention relates to a strip for a nuclear fuel assembly spacer grid comprising interlaced strips defining a lattice of cells for receiving fuel rods and allowing flow of a coolant in a flow direction, the strip being of the type comprising a wall portion for delimiting a cell, a spring formed in the strip and provided on the wall portion for biasing the fuel rod extending through the cell away from the wall portion, the spring being cut out in the strip and delimited by a slot, and a motion limiter formed in the strip on the wall portion to limit motion of the fuel rod received in the cell towards the wall portion against action of the spring. U.S. Pat. No. 4,879,090 illustrates on FIG. 5 thereof a peripheral strip for a nuclear fuel assembly spacer grid, the peripheral strip comprising wall portions to delimit cells and on each wall portion a spring formed by a tab cut out in the strip and motion limiters formed as a pair of bosses embossed in the strip at a distance from the tab. In operation, a coolant fluid (e.g. water) flows axially upwardly through the cells of the spacer grid. The spring and the motion limiters provided on each wall portion protrude from the plane of the wall portion towards the center of the same cell delimited by the wall portion and partially obstruct the coolant fluid flow channel. An object of the invention is to provide a strip for a nuclear fuel assembly spacer grid limiting the flow resistance of the spacer grid whilst allowing suitable support for the nuclear fuel rods during the whole fuel assembly lifetime and good manufacturability. To this end, a strip for a nuclear fuel assembly spacer grid of the above-mentioned type is provided, wherein the motion limiter is located on an edge of the slot opposite the spring and defines a risen portion on the edge. In other embodiments, the strip comprises one or several of the following features, taken in isolation or in any technically feasible combination: the motion limiter is provided upstream the spring in the coolant flow direction through the cell delimited by the wall portion; the motion limiter enlarges towards the edge of the slot; the motion limiter rises from the wall portion towards the edge of the slot; the motion limiter is a bulge; the spring comprises a cantilevered tab; the tab extends downwardly in cantilevered fashion towards an upstream lower edge of the strip; the slot is an elongated curved slot, the tab being delimited between the slot and a connection line joining two opposite ends of the slot; the spring comprises a contact portion at least partially formed in the tab to contact the fuel rod received in the cell; and the contact portion is elongated in the flow direction. The invention also relates to a spacer grid comprising interlaced strips defining a lattice of cells for receiving fuel rods and allowing flow of a coolant axially upwardly through the spacer grid, at least one of the interlaced strips being a strip as defined above. The invention further relates to a nuclear fuel assembly comprising a bundle of fuel rods and an armature for supporting the fuel rods, the armature comprising at least one spacer grid as defined above. The nuclear fuel assembly 2 for a pressurized water reactor (PWR) illustrated on FIG. 1 comprises a bundle of nuclear fuel rods 4 and an armature 6 for supporting the fuel rods 4. The PWR fuel assembly 2 is elongated along an assembly axis L extending vertically when the fuel assembly 2 is disposed inside a nuclear reactor. The armature 6 comprises a lower nozzle 8, an upper nozzle 10, a plurality of guide-tubes 12 and a plurality of spacer grids 14. The guide-tubes 12 extend parallel to assembly axis L and connect the lower nozzle 8 to the upper nozzle 10 and maintain a predetermined spacing along assembly axis L between the nozzles 8, 10. Each guide-tube 12 opens upwards through the upper nozzle 10 for allowing insertion of a control rod into the guide-tube 12. The nuclear fuel assembly 2 for a boiling water reactor (BWR) illustrated on FIG. 2 is also elongated along an assembly axis L extending vertically when the fuel assembly 2 is disposed inside a nuclear reactor. The BWR fuel assembly 2 comprises a bundle of nuclear fuel rods 4, an armature for maintaining the fuel rods 4 and a tubular fuel channel 15 surrounding the bundle of fuel rods 4. The armature typically comprises a lower nozzle and an upper nozzle spaced along assembly axis L, at least one water channel 13 arranged within the bundle of fuel rods 4 and a plurality of spacer grids 14 distributed along the bundle of fuel rods 4. The fuel rods 4, the water channel 13 and the fuel channel 15 extend between the lower nozzle and the upper nozzle, with the water channel 13 and the fuel channel 15 connecting the lower nozzle and the upper nozzle. The water channel 13 extends parallel to the fuel rods 4. The water channel 13 is arranged for channeling a coolant/moderator flow separately from the bundle of fuel rods 4. The fuel channel 15 extends parallel to the fuel rods 4. The fuel channel 15 encases the bundle of fuel rods 4 and the water channel 13. The fuel channel 15 is arranged for channeling a coolant/moderator flow between and about the fuel rods 4. The PWR and BWR spacer grids 14 are distributed in spaced relationship along the fuel rods 4. Each spacer grid 14 extends transversely to the assembly axis L. Each fuel rod 4 comprises a tubular cladding, pellets of nuclear fuel stacked inside the cladding and caps closing the ends of the cladding. Each fuel rod 4 extends parallel to assembly axis L through the spacer grids 14 with being supported transversely and longitudinally relative to assembly axis L by the spacer grids 14. In operation, the fuel assembly 2 is placed in a nuclear reactor with the lower nozzle 8 resting on a bottom plate of the reactor and the assembly axis L being substantially vertical. A coolant flows upwardly along the fuel assembly 2 with flowing between the fuel rods 4 and through the nozzles 8, 10 and the spacer grids 14 as illustrated by arrows F on FIGS. 1 and 2. The spacer grids 14 may be similar to each other and one spacer grid 14 according to the invention will be further described with reference to FIGS. 3-7. As illustrated on FIG. 3, the spacer grid 14 comprises a plurality of interlaced metallic strips 16 defining a lattice of cells 18 each for receiving one fuel rod 4, only a few cells 18 being illustrated on FIG. 3. In a known manner, in the case of a spacer grid for a PWR fuel assembly, the interlaced strips 16 also define a plurality of cells for receiving PWR guide-tubes 12, the spacer grid 14 being secured to the guide-tubes 12, e.g. by welding. Similarly, in the case of a spacer grid for a BWR fuel assembly, the at least one BWR water channel 13 typically replaces one or several fuel rods 4 in the lattice, the interlaced strips 16 define an aperture for the water channel 13 and the spacer grid 14 is secured to the water channel 13, e.g. by welding. Only cells 18 for receiving fuel rods 4 are illustrated on FIG. 3 and in the following, the term “cell” refer to the cells 18 for receiving fuel rods 4. Each cell 18 is tubular and extends along a cell axis A. The cell axis A is to be parallel to the assembly axis L (perpendicular to FIG. 3) when the spacer grid 14 is assembled in the fuel assembly 2 (FIGS. 1 and 2). The cell axes A of the different cells 18 are parallel. Each cell 18 is delimited by four wall portions 20 of two pairs of intersecting strips 16, the strips 16 of each pair extending parallel to one another. One wall portion 20 of each pair of opposite wall portions 20 delimiting a cell 18 has an elastic spring 22 formed in the wall portion 20 and protruding in a free state towards the center of the cell 18, and the other wall portion 20 of each pair of opposite wall portions 20 has a rigid dimple 24 formed in the wall portion 20 and protruding towards the center of the cell 18. The springs 22 and dimples 24 provided on the wall portions 20 of each cell 18 are arranged such that a fuel rod 4 extending through the cell 18 is biased transversely by the springs 22 against the dimples 24 to support the fuel rod 4 transversely and longitudinally relative to the cell axis A. Each wall portion 20 delimiting two adjacent cells 18 (one on each side of the strip 16) has a spring 22 protruding on a face of the wall portion 20 in one of the cells 18 and a dimple 24 protruding on the opposite face of the wall portion 20 in the other cell 18. Each wall portion 20 delimiting only one cell 18 has either a spring 22 or a dimple 24. FIG. 4 illustrates a plurality of the wall portions 20 of a strip 16, each of these wall portions 20 being adapted to delimit two cells 18, one on each side of the strip 16. In operation, the coolant flows upwardly through each cell 18 in the flow direction F represented on FIG. 4 from an upstream lower edge 26 to a downstream upper edge 28 of the strip 16. The flow direction F is parallel to the cell axis A. Each wall portion 20 extends from the lower edge 26 to the upper edge 28. The wall portions 20 are separated by slits 30 provided on the lower edge 26 and extending substantially to the half-height of the strip 16 for engagement with a series of corresponding slits 30 provided on the upper edge 28 and extending substantially to the half-height of an intersecting strip 16. The strip 16 optionally comprises fins 32 protruding upwardly from the upper edge 28, each fin 32 being inclined relative to the cell axis A for imparting helical motion to the coolant fluid flowing through the cells 18 and enhancing heat exchange between the coolant and the fuel rods 4. The strip 16 comprises on each of the illustrated wall portions 20 a spring 22, a dimple 24 and a motion limiter 34 each formed in the strip 16 and thus integrally one-piece with the strip 16. The spring 22 and the motion limiter 34 provided on each wall portion 20 protrude on the same face of the strip 16, whereas the dimple 24 protrudes on the opposite face of the strip 16. The dimples 24 are alternately disposed below and above the springs 22 on the adjacent wall portions 20. Interlaced strips 16 thus can be arranged such that a spring 22 provided on a wall portion 20 of a strip 16 delimiting a cell 18 faces a dimple 24 provided on the opposite wall portion 20 of another strip 16 delimiting the cell 18. The springs 22 of the strip 16 are identical and one spring 22 is further described with reference to FIGS. 5-7. The spring 22 illustrated on FIG. 5 comprises a flexible cantilevered tab 36 and a contact portion 38 cut out in the strip 16. The tab 36 is delimited in the strip 16 by an elongated curved slot 40 of closed contour. The tab 36 is delimited between the slot 40 and the connection line 46 joining the opposed ends 48 of the slot 40. The ends 48 are preferably circular and enlarged to limit local mechanical peak stresses. The line 46 is perpendicular to the cell axis A. The tab 36 is connected to the wall portion 20 along the line 46. The tab 36 extends downwardly in cantilevered fashion towards the upstream lower edge 26 and has an upper base 42 connected to the wall portion 20 and a lower free tip 44. The tab 36 is converging towards the free tip 44. The slot 40 is generally U-shape with diverging branches (or V-shape with a rounded tip). In a free state of the spring 22, the tab 36 is inclined relative to the wall portion 20 and extends downwardly and away from the wall portion 20 towards the center of the cell 18 delimited by the wall portion 20. The tab 36 is elastically flexible by elastic deformation of the tab 36 with rotation of the tab 36 around a rotation axis substantially coinciding with the line 46. The flexibility of the tab 36 can be adjusted by adjusting the diameter of the ends 48 of the slot 40. The contact portion 38 is formed exclusively in the tab 36 and protrudes from the tab 36 opposite the wall portion 20 and towards the center of a cell 18 delimited by the wall portion 20. The contact portion 38 is integrally one-piece with the tab 36. The contact portion 38 is provided in the form of an arched bridge cut out in the tab 36. The contact portion 38 is elongated in the direction of the cell axis A, the two ends of the contact portion 38 connected to the tab 36 being aligned in the direction of the cell axis A. The contact portion 38 is formed as a lancing 50 delimited between two openings 52 extending substantially parallel to each other in the direction of the cell axis A. The motion limiter 34 associated to the spring 22 is formed in the strip 16 along the edge 54 of the slot 40 opposite to the tab 36. The motion limiter 34 defines a risen portion 56 on the edge 54 of the slot 40. The motion limiter 34 is a bulge formed in the strip 16 and protruding from the wall portion 20 on the same side than the corresponding spring 22. The motion limiter 34 is disposed below the spring 22 and is thus upstream the spring 22 in a cell 18 delimited by the wall portion 20. The motion limiter 34 is profiled to define a fluid deflector for diverging coolant away from the spring 22 disposed in the slipstream of the motion limiter 34. To this end, the motion limiter 34 is profiled to rise from the wall portion 20 and to enlarge transversely to the cell axis A towards the edge 54 in the downstream upward direction. The motion limiter 34 comprises e.g. a lower tip-like nose pointing upstream and raising end enlarging downstream, and an upper section of constant cross section extending the nose in the downstream direction up to the edge 54. As illustrated on FIG. 7, the contact portion 38 contacts the outer surface of a fuel rod 4 extending through a cell 18 delimited by the wall portion 20 with the tab 36 being elastically deformed towards the wall portion 20. The spring 22 thus biases the fuel rod 4 away from the wall portion 20 (toward the right on FIG. 7) in contact with a dimple 24 provided on the opposite wall portion 20 delimiting the cell 18. In this configuration, the free tip 44 of the tab 36 extends substantially in the plane of the wall portion 20 and the height H of the contact portion 38 relative to the wall portion 20 is superior to the height h of the apex 62 of the motion limiter 34. There is a gap D between the apex 62 and the outer surface of the fuel rod 4. In operation, the coolant flows through the cell 18 and around the fuel rod 4 upwardly at high speed in the flow direction F parallel to the cell axis A. This causes transverse vibration of the fuel rod 4 inside the cell 18. Transverse vibrations may also occur during transportation from manufacturing plant to power plant and during handling of the fuel assembly 2. The motion limiter 34 is rigid and limits movements of a fuel rod 4 towards the wall portion 20 against the action of the spring 22. The motion limiter 34 thus avoids overstress of the spring 22 and namely plastic deformation thereof. The spring 22 formed in the strip 16 with a flexible cantilevered tab 36 and a rigid contact portion 38 enables to bias the fuel rod 4 with an appropriate transverse force while limiting the flow resistance. The tab 36 furnishes the biasing force when the free tip 44 of the tab 36 is retracted in the plane (or nearly) of the wall portion 20; in this position only the contact portion 38 protrudes from the wall portion 20. The contact portion 38 being elongated in the flow direction F enables to further limit the flow resistance and to provide an elongated contact zone with the fuel rod 4 for limiting fretting risks. The spring 22, and namely the contact portion 38, is in the slipstream of the motion limiter 34. The motion limiter 34 disposed on the edge 54 at the nearest possible position to the spring 22 and profiled to limit fluid flow resistance contributes to limiting the overall flow resistance of the strip 16. The motion limiter 34 provided on an edge 54 is obtainable by punching with limited energy to deform the strip 16. The strip 16 thus possesses a good manufacturability. The spring 22 including the tab 36 and the contact portion 38 and the motion limiter 34 are obtainable in a single punching and stamping operation to manufacture the strip 16 at low cost. In a free state of the spring 22 (FIG. 6) the tab 36 is inclined relative to the wall portion 20 with the height E of the free tip 44 of the tab 36 relative to the wall portion 20 inferior to the height h of the apex 62 of the motion limiter 34. The motion limiter 34 serves as a guide during upwardly inserting the fuel rod 4 through the cell 18 on assembling the fuel assembly 2. The motion limiter 34 thus avoids damaging the spring 22 and/or the fuel rod 4 upon insertion of the fuel rod 4 and enhances manufacturability of the fuel assembly 2. The alternative embodiment of FIGS. 8 and 9 differ from that of FIGS. 5 and 6 by the feature that the contact portion 38 is formed partially in the tab 36 and partially in the wall portion 20. The contact portion 38 is more elongated and steps over the line 46 joining the ends 48 of the slot 40 delimiting the tab 36. This increases the stiffness of the spring 22 as biasing the spring 22 causes simultaneous deformation of the upper base 42 of the tab 36 and of the upper end of the contact portion 38 about two parallel but different axes. In the alternative embodiment of FIG. 10, the upstream lower edge 26 of the strip 16 is zigzag-shaped such that it is low at the center of each wall portion 20 and high at the junction between the wall portions 20 where interlaced strips 16 intersect each other. As a result, a spacer grid 14 may be formed with interlaced strips 16 crossing at cross points 66 at a level higher than the lower points 64, whereby debris possibly present in the coolant fluid are guided transversely towards the cross points 66 at corners of the square shaped cells 18 where the space between the inner surface of the cells 18 and the fuel rods 4 is larger. The debris are thus prevented from damaging the fuel rods 4. In an alternative embodiment, the lower edge 26 of the strip 16 is zigzag-shaped such that the upstream lower edge 26 is alternatively at a high level and at a low level at the junction between the wall portions 20. As a result, the interlaced strips 16 may be assembled to provide cross points 66 at a high level and cross points 66 at a low level arranged in staggered rows, with the same benefit. The lower edge 26 may present a wave shape instead of a zigzag shape. The invention is applicable to spacer grids for a PWR (Pressurized Water Reactor) fuel assembly or to spacer grids for a BWR (Boiling Water Reactor) fuel assembly as illustrated and also to spacer grids for a VVER (Water-Water Energetic Reactor) fuel assembly. |
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claims | 1. A method of controlling the amount of energy to reach a breast cancer patient undergoing intraoperative electron radiation therapy, comprising:providing an intraoperative electron radiation therapy machine having a head for producing a monoenergetic beam;selecting a bolus made of a material having substantially the same density as human breast tissue and placing the bolus between the head of the machine and the patient to change the energy of a monoenergetic beam after the monoenergetic beam has left the part of the machine that accelerates the electrons to the desired energy, the bolus being chosen to reduce the energy traveling through the tube to a desired amount of energy to treat the patient. 2. The method of claim 1, wherein the bolus is integral with a collimator tube which attaches to the head of the intraoperative electron radiation therapy machine. 3. The method of claim 2, wherein the tube is made of poly(methyl methacrylate). 4. The method of claim 1, wherein the bolus comprises at least one material from the group consisting of isodense materials made up primarily or entirely of carbon, oxygen, and hydrogen, such as PMMA, Delrin brand acetal resin, UHMW (ultra-high molecular weight polyethylene), polyethylene, polypropylene, ABS, acrylic, Bakelite, CPVC, fiberglass, Kynar brand plastic, Lexan brand plastic, Micarta brand plastic, PVC, Ryton brand plastic, and Teflon brand polytetrafluoroethylene. 5. The method of claim 1, wherein the bolus comprises poly(methyl methacrylate). 6. The method of claim 1, further comprising calibrating the intraoperative electron radiation therapy machine after it is moved and before it is used to treat a patient. 7. A method of controlling the amount of energy to reach a breast cancer patient undergoing intraoperative electron radiation therapy, comprising:providing an intraoperative electron radiation therapy machine having a head for producing a beam;controlling the intraoperative electron radiation therapy machine such that the head produces a monoenergetic beam during calibration of the machine and treatment of the patient;calibrating the intraoperative electron radiation therapy machine after it is moved and before it is used to treat a patient;selecting a bolus made of a material having substantially the same density as human breast tissue and placing the bolus between the head of the machine and the patient to change the energy of a monoenergetic beam after it has left the machine, the bolus being chosen to reduce the energy traveling through the tube to a desired amount of energy to treat the patient. 8. The method of claim 7, wherein the bolus is integral with a collimator tube which attaches to the head of the intraoperative electron radiation therapy machine. 9. The method of claim 8, wherein the tube is made of poly(methyl methacrylate). 10. The method of claim 7, wherein the bolus comprises at least one material from the group consisting of isodense materials made up primarily or entirely of carbon, oxygen, and hydrogen, such as poly(methyl methacrylate), Delrin brand acetal resin, UHMW (ultra-high molecular weight polyethylene), polyethylene, polypropylene, ABS, acrylic, Bakelite, CPVC, fiberglass, Kynar brand plastic, Lexan brand plastic, Micarta brand plastic, PVC, Ryton brand plastic, and Teflon brand polytetrafluoroethylene. 11. The method of claim 7, wherein the bolus comprises poly(methyl methacrylate). 12. Apparatus for performing electron radiation therapy on a patient, the apparatus comprising:a plurality of boluses for use with an intraoperative electron radiation therapy machine having a head for producing an energy beam, the boluses made of a material having substantially the same density as human tissue for placement between the head of the machine and the patient to change the energy of a beam after it has left the machine, the bolus being chosen to reduce the energy traveling through the tube to a desired amount of energy to treat the patient. 13. The apparatus of claim 12, wherein the boluses comprise at least one material from the group consisting of isodense materials made up primarily or entirely of carbon, oxygen, and hydrogen, such as poly(methyl methacrylate), Delrin brand acetal resin, UHMW (ultra-high molecular weight polyethylene), polyethylene, polypropylene, ABS, acrylic, Bakelite, CPVC, fiberglass, Kynar brand plastic, Lexan brand plastic, Micarta brand plastic, PVC, Ryton brand plastic, and Teflon brand polytetrafluoroethylene. 14. The apparatus of claim 12, wherein the boluses comprise poly(methyl methacrylate). 15. The apparatus of claim 12, further comprising a collimator tube. 16. The apparatus of claim 15, wherein the tube is made of at least one material from the group consisting of isodense materials made up primarily or entirely of carbon, oxygen, and hydrogen, such as poly(methyl methacrylate), Delrin brand acetal resin, UHMW (ultra-high molecular weight polyethylene), polyethylene, polypropylene, ABS, acrylic, Bakelite, CPVC, fiberglass, Kynar brand plastic, Lexan brand plastic, Micarta brand plastic, PVC, Ryton brand plastic, and Teflon brand polytetrafluoroethylene. 17. The apparatus of claim 15, wherein the tube is made of poly(methyl methacrylate). 18. The apparatus of claim 12, wherein at least some of the boluses are integral with collimator tubes. 19. The apparatus of claim 12, further comprising the intraoperative electron radiation therapy machine. 20. Apparatus for performing electron radiation therapy on a breast cancer patient, the apparatus comprising:an intraoperative electron radiation therapy machine having a head for producing a beam of energy;an intraoperative electron radiation therapy collimator tube connected to the intraoperative electron radiation therapy machine;a plurality of boluses made of a material having substantially the same density as human breast tissue to change the energy of a beam after the beam has left the head of the machine, allowing a bolus to be chosen to reduce the energy traveling from the head to a desired amount of energy to treat the patient. 21. The apparatus of claim 20, wherein the boluses comprise at least one material from the group consisting of isodense materials made up primarily or entirely of carbon, oxygen, and hydrogen, such as poly(methyl methacrylate), Delrin brand acetal resin, UHMW (ultra-high molecular weight polyethylene), polyethylene, polypropylene, ABS, acrylic, Bakelite, CPVC, fiberglass, Kynar brand plastic, Lexan brand plastic, Micarta brand plastic, PVC, Ryton brand plastic, and Teflon brand polytetrafluoroethylene. 22. The apparatus of claim 20, wherein the boluses comprise poly(methyl methacrylate). 23. The apparatus of claim 20, wherein the tube is made of at least one material from the group consisting of isodense materials made up primarily or entirely of carbon, oxygen, and hydrogen, such as poly(methyl methacrylate), Delrin brand acetal resin, UHMW (ultra-high molecular weight polyethylene), polyethylene, polypropylene, ABS, acrylic, Bakelite, CPVC, fiberglass, Kynar brand plastic, Lexan brand plastic, Micarta brand plastic, PVC, Ryton brand plastic, and Teflon brand polytetrafluoroethylene. 24. The apparatus of claim 20, wherein the tube is made of poly(methyl methacrylate). 25. The apparatus of claim 20, wherein at least some of the boluses are integral with collimator tubes. 26. The apparatus of claim 20, wherein the head produces a beam of a single energy. 27. The method of claim 7, wherein the intraoperative electron radiation therapy machine produces a beam of a single energy. 28. The method of claim 7, wherein the intraoperative electron radiation therapy machine produces a beam of about 10 MeV. |
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description | This invention relates to the electronic component reliability. In particular, the present invention relates to field reliability monitoring of electronic components. Electronic systems and circuits have made a significant contribution towards the advancement of modern society and are utilized in a number of applications to achieve advantageous results. Numerous electronic technologies such as digital computers, calculators, audio devices, video equipment, and telephone systems facilitate increased productivity and cost reduction in analyzing and communicating data, ideas and trends in most areas of business, science, education and entertainment. Often these advantageous results are achieved through the use of electronic components. To obtain desired performance results from electronic components it is usually critical for the components to operate reliably. Without reliable operation an electronic component usually does not perform properly and results are suspect. The importance of information processed and communicated by modern electronic systems is increasing and can result in significant economic impact if the processing and communication operations are not reliable. Accurately establishing the reliability of increasingly complex and sophisticated electronic components and systems is difficult. For example, an almost insatiable desire for increased communication bandwidth and information processing capacity has led to a tremendous demand for advanced capabilities. However, even advanced electronic components usually have some probability of failure and the probability of failure typically increases as the components are used and operating conditions cause stress over time. Traditionally, a reliability indication is estimated before a component is shipped and is typically based upon testing of a component simulating an anticipated “average condition”. For example, a Medium Time Between Failures (MTBF) value estimated before shipment is based upon “average condition” assumptions. However, the “average condition” assumptions do not usually provide an accurate representation of actual in field conditions for a particular use. When a component is shipped, control over operating conditions is lost and users (e.g., customers) typically expose the electronic components to a wide variety of operating conditions. Operating conditions have a significant impact on reliability. There are a variety of environmental and operational stresses that can detrimentally impact failure rates and reliability. For example, typically the number of “operations” electronic components perform (e.g., transistors turning on and off as data traffic passes through a communications component), the higher the likelihood of a failure because the operations usually electrically stress the components. A high temperature environmental condition also contributes to stressing the components in a detrimental manner and increases the likelihood of a failure. As a component participates in greater operational activities and diverse environments, accurately establishing the reliability of network components becomes more difficult. Inaccurate reliability values can have numerous detrimental impacts including diminished confidence in a component. Customers often treat the reliability of a component as an asset. Components with higher reliability usually do not adversely impact revenue generating operations as often as low reliability components and high reliability components typically do not result in repair or replacement expenses as often. Customers also sometimes utilize reliability values in maintenance decisions and inaccurate reliability values can adversely impact maintenance operations. Reliability values are often utilized as a fundamental manufacturing and/or service parameter. The reliability values can be used to predict the number of components returned for service and/or repair and the support required to address the service and/or repair demand. For example, reliability values are often utilized to forecast the amount of “spare parts” inventory to manufacture and maintain for servicing and repair operations. Furthermore, when a component is returned for servicing or repair and a component failure is identified, attempts at factoring the failure in reliability estimates are sometimes made. However, the operational and environmental conditions are not usually tracked and impacts associated with the conditions are not included in attempts to factor the failure in future pre-shipment failure estimates. Traditional attempts at establishing reliability do not usually include actual field usage information and can result in erroneous assumptions on the quality of the system, statistical behavior and future predictions. The present invention systems and methods facilitate automated efficient and effective electronic component and system failure prediction and reliability determination. A present invention electronic component reliability determination system and method includes adjustments for actual operating and environmental conditions and stress impacts on failure analysis. In one embodiment, operational and environmental conditions are monitored and a reference failure rate is adjusted (e.g., by an acceleration/deceleration factor) to compensate for impacts associated with the monitored conditions. The conditions are monitored at predetermined intervals and an adjusted determination of an “instantaneous” failure rate is made. The instantaneous failure rate is utilized to ascertain a reliability index value. An electronic component reliability determination system and method can also account for infant mortality and aging effects in the determination of the reliability index value. In addition, reliability index values for both a component and a system in which the component is included can be ascertained. The present invention includes a variety of features that facilitate flexible and advantageous implementation. In one embodiment, a present invention electronic component reliability determination system and method also reports the operational condition measurements, environmental condition measurements, “instantaneous” failure analysis values and/or reliability determination results in a convenient format both locally (e.g., via a user graphical interface) and/or remotely (e.g., to a centralized manufacturing database). Electronic component reliability determination systems and methods of the present invention are also capable of utilizing background processing capabilities to perform many of the operational and environmental condition measurement controls, instantaneous failure rate determinations and reliability analysis. Present invention background processes have minimal or no interference with other runtime activities. The present invention can also facilitate conservation of memory and communication resources by implementing intelligent data gathering and a variety of compression techniques. In one exemplary implementation, an electronic component reliability determination system and method senses environmental condition indication values at regular intervals and saves environmental condition indication values that have more than a minor impact. For example, an environmental condition (e.g., temperature) can be sensed at 15 minute intervals and sensed temperature values stored if the sensed temperature value indicates a statistically relevant change (e.g., more that 2 degrees) or if numerous intervals pass without recording the sensed values (e.g., save a temperature indication value every 2 hours regardless of temperature change). Reference will now be made in detail to the preferred embodiments of the invention, an electronic component reliability determination system and method, examples of which are illustrated in the accompanying drawings. While the invention will be described in conjunction with the preferred embodiments, it will be understood that they are not intended to limit the invention to these embodiments. On the contrary, the invention is intended to cover alternatives, modifications and equivalents, which may be included within the spirit and scope of the invention as defined by the appended claims. Furthermore, in the following detailed description of the present invention, numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, it will be obvious to one ordinarily skilled in the art that the present invention may be practiced without these specific details. In other instances, well known methods, procedures, components, and circuits have not been described in detail as not to unnecessarily obscure aspects of the current invention. The present invention facilitates efficient and effective component and system failure and reliability prediction. In one embodiment, operational and environmental conditions are monitored and a reference failure rate is adjusted (e.g., by an acceleration/deceleration factor) to compensate for impacts associated with the monitored conditions. The adjusted failure rate can be referred to as an “instantaneous” failure rate. The instantaneous failure rate is utilized to determine a reliability index value. In addition, infant mortality and aging effects can be accounted for in the reliability index value determination. The instantaneous failure rates and reliability index values can be utilized to provide a more accurate indication of a component failure probability than traditional reliability pre-shipment estimate attempts. Information provided by a present invention electronic component reliability determination system and method can also be utilized to provide an indication of system quality and statistical behavior information for use in forecasting appropriate resource levels (e.g., spare parts, labor, etc.) for maintenance, service and/or repair operations. FIG. 1 is a flow chart of electronic component reliability determination method 100, in accordance with one embodiment of the present invention. Electronic component reliability determination method 100 determines an instantaneous failure rate and reliability index value. Compensations or adjustments for operational and/or environmental conditions, infant mortality issues and aging are factored into the determination of a reliability index value. The instantaneous failure rate and reliability index values can be ascertained on an individual electronic component basis and/or a cumulative system basis. In step 110, an initialization process is executed. The initialization process includes installing initial settings associated with a reliability indicator. There are number of different initial settings that can be incorporated in implementations of the present invention. For example, settings can include a reference failure rate value, reference condition values, (e.g., a reference temperature, an electrical stress reference value, etc.), a condition sampling period (e.g., 15 minutes, 24 hours, etc.), and a data saving interval (e.g., how often temperature data is saved). The values of the initial settings can be determined before shipment and stored in a nonvolatile memory location (e.g., nonvolatile random access memory, flash memory, electrically erasable programmable read only memory, etc.). The integrity of the nonvolatile memory can be checked during initialization. In one exemplary implementation, the initial setting values are retrieved from the nonvolatile memory and loaded in another memory (e.g., volatile random access memory, etc.) during initialization. The initialization process can also include sensing and tracking the first startup time of a component after leaving the manufacturer (e.g., an indication of the first time a customer starts up a system). In one embodiment of the present invention, an initialization process includes starting background tasks (e.g., background tasks can include tasks performed in steps 120 and 130). In step 120, a field condition determination process is implemented. A field condition determination process determines field conditions (e.g., environmental conditions, operational conditions, etc.) of components and systems when deployed after first customer shipment (e.g., “in the field”). In one exemplary implementation of the present invention, a field condition determination is performed at predetermined times or at regular intervals (e.g., temperature is measure at 15 minutes intervals). In one embodiment, the field condition determination process monitors field condition indication information (e.g., temperature, communication traffic, etc.) associated with a reliability indicator. The field condition information can be represented by operational parameters and there can be a number of different operational parameters associated with a reliability indicator. For example, the operational parameters can include measurements of things that cause stress on a component or system. The present invention is capable of monitoring a variety of different stresses that can impact reliability, including environmental stresses (e.g., temperature, location, altitude, humidity, etc.) and electrical stresses (e.g., switching components on and off, power surges, electromagnetic interference, etc.). The operational parameter information can also include a measurement of the time a component is in operation. In one exemplary implementation, a measurement of the time since the electronic component first powered up after shipment from a manufacturer is tracked. A timer keeps track of timing intervals (e.g., a predetermined number of minutes) which are summed to provide a total period of time the component has been in operation. In one embodiment of the present invention, the intervals are also utilized to determine when various activities are performed (e.g., sampling a temperature reading, saving a field condition value, determining communication traffic flow, etc). Referring still to step 120 of FIG. 1, field condition indication information can be obtained in a variety of ways. The field condition indication information can be measured directly by measuring or sensing components (e.g., temperature sensors, traffic byte counters, etc.). The field condition indication information can be obtained indirectly by deriving the information from measured information. For example, differences of temperature measurements at an air intake and an air exhaust provide an indication of how much heat the component is dissipating which in turn can provide an indication of the number of operations the component is performing. In a communication device, the number of operations a component performs can provide an indication of the amount of traffic being communicated through the device. For example, if the temperature is determined for varying ranges of communication traffic (e.g., 0% to 100% of communication capacity) at different ambient temperatures, the “field” measured values of a component temperature (e.g., “case” temperature) and the temperature read from an air intake sensor can be utilized to approximate the percent of traffic passing through the electronic component. In step 130, a field condition reliability analysis process in preformed. A present value or “instantaneous” value of a reliability indicator is determined at a predetermined time (e.g., at regular predetermined intervals). Alternatively, the reliability indicator value can be determined if a predetermined field condition occurs (e.g., if a temperature measurement varies greater than 2 degrees, traffic communication value exceeds a predetermined value, etc). The present value or “instantaneous” value of the reliability indicator is adjusted for impacts associated with field conditions. In one embodiment of the present invention, various different values associated with reliability determination are ascertained including a field condition failure adjustment factor (e.g., an acceleration/deceleration factor), an instantaneous failure rate for components and/or a system, and a cumulative reliability index value for a component and/or system. In one exemplary implementation, a field condition failure adjustment factor (e.g., a temperature stress adjustment factor, an electrical stress adjustment factor, etc.) is utilized to determine an instantaneous failure rate which is in turn utilized to ascertain an indication of a component and a system reliability (e.g., a cumulative reliability index value). The field condition reliability analysis process can also provide a probability of failure and reliability index indication that is adjusted for life cycle stage (e.g., infant mortality boundaries, end of life boundaries, etc.) considerations and aging issues. In step 140, a reliability information management process is performed. The reliability information management process manages the disposition of reliability related information. In one exemplary implementation, the reliability related information (e.g., field condition information, instantaneous failure rates, cumulative reliability index information, etc.) is stored in a memory location. For example, a non-volatile memory (e.g., a Flash EProm) can be utilized to store various different operational parameter information. The reliability related information is communicated remotely to a centralized resource (e.g., a manufacturing database) via a network for analysis and interpretation in one embodiment of the present invention. Alternatively, the information can be downloaded from memory when a system is removed from deployment (e.g., when the system is returned to a manufacturer). The reliability related information can be utilized to project or estimate maintenance, service and/or repair demand (e.g., spare parts inventory, etc.). The reliability related information can also be utilized to “update” various reliability statistics and reference values. A reliability information management process can also forward reliability related information (e.g., temperature measurements and other reliability related information or temperature measurements alone) to an interface in a user interface process. In step 150, a user interface process is implemented. The user interface process presents reliability related information in a convenient and correlated manner. A customer can utilize an interface provided by the interface process to examine the impact of operating conditions on reliability and to project maintenance timing. A manufacturer can also utilize the information to provide services and/or support to a customer. An interface process can also include changing the values of initialized settings for a variety of items, including field condition sampling intervals and reference temperatures. In one embodiment of the present invention, performing a field reliability analysis includes a system reliability analysis. The failure rates of the components are utilized in the system reliability analysis to provide a system reliability indicator. In determining the reliability index of the system in terms of the system components, the present invention can include compensations for the configuration (e.g., redundancy) of the components within the system. In one exemplary implementation in which the components are arranged with a serial structure and the failure of one of the components stops processing through the serial structure or “chain” (e.g., the components are not redundant), a system reliability index value at a particular time is the product of reliability index values of the components. For example: R ( t ) = ∏ i = 1 n R i ( t ) where the system reliability index at a particular time t is R(t), reliability index value of a component i at time t is Ri(t) and n is number of non-redundant components. This is a simple relation between the system MTBF and the components' MTBF. If system components are arranged in a configuration in which the failure of one of the components does not stop the chain, the analysis of the system redundant value is different. For example, the value is defined by: R ( t ) = 1 - ∏ i = 1 n ( 1 - R i ( t ) ) In addition, the reliability index can be calculated for the redundant components and resulting values can be used in the serial calculation above. FIG. 2 is a block diagram illustration of an electronic component reliability determination system 200 in accordance with one embodiment of the present invention. Electronic component reliability determination system 200 comprises sensor 210, reliability processing component 220, memory 230 and communication bus 250. Electronic component reliability determination system 200 determines the “instantaneous” failure rates and cumulative reliability of operation components 241 and 242. Communication bus 250 communicatively couples sensor 210, reliability processing component 220, memory 230, and operational components 241 and 242. Sensor 210 participates in sensing operational parameter information. In one embodiment, the operational parameter information is associated with operational environmental conditions. For example, sensor 210 can sense temperature. Sensor 210 is readily adaptable for a variety of configurations. For example, sensor 210 can include a diode inside a component (e.g., inside a component's case) and the diode is utilized to measure temperature. The temperature is derived based upon resistance encountered in passing a current through the diode and measuring the resulting voltage. Sensor 210 can be an ambient temperature measuring device that measures ambient temperature. The sensor 210 can also include air intake and exhaust temperature measuring components. It is appreciated that sensor 210 can be configured to sense a variety of operational parameter information. For example, sensor 210 can be configured to sense altitude. Alternatively sensor 210 can be configured to sense electrical stress related measurements. For example, sensor 210 can be configured to sense a variety of electrical stress related items, including voltage, current, processing activities, and communication activities (e.g., sense the number of bytes of communication traffic, etc.). Reliability processing component 220 performs instructions associated with ascertaining a field condition adjusted reliability value (e.g., an instantaneous reliability value). In one embodiment, a field adjusted reliability index value is defined by: R j ( t ) = 1 - ∫ 0 ∞ λ j β β s β - 1 exp [ - ( λ j s ) β ] ⅆ s where λ is the instantaneous failure rate coefficient and β is a life cycle shape factor. Reliability processing component 220 can also perform instructions to obtain a cumulative reliability indication value. For example, a cumulative reliability indication value can be defined by: R j ( t ) = 1 - ∑ M k = 1 λ jk β β δ ( k δ ) β - 1 exp [ - ( λ jk k δ ) β ] where δ is a time interval (e.g., a sampling interval). The life cycle stage shape factor beta (β) defines boundary conditions for the life stages of a component or system. In one embodiment, β takes into account reliability impacts associated with infant mortality issues and system aging issues. One exemplary definition of β is given by: β = { V a + 1 - V a T 1 t t < T 1 1 T 1 < t < T 2 1 - 1 - V b T ∞ - T 2 t > T 2 where the infant mortality interval or stage is 0 to time T1 and the end of life interval or stage is the interval from T2 to T infinity. The operational life cycle stage is the interval time T1 to time T2. In one exemplary implementation of the present invention, the value of β is less than 1 for the infant mortality stage, 1 for the operational life cycle stage and greater than one for the end of life stage. In one embodiment, the value of β is stored in a nonvolatile part of memory 230. Reliability processing component 220 also performs instructions for determining an instantaneous failure rate (λi). In one exemplary implementation of the present invention, the instantaneous failure rate is defined by:λi=AiSiΛi where λi is the instantaneous failure rate, Ai is the temperature stress adjustment value, Si is the electrical stress adjustment value and Λi is a base or reference failure rate. It is appreciated that there can be a variety of different stress adjustment factors. For example, there can be a stress adjustment factor for each measured field condition (e.g., temperature, humidity, altitude, etc.) In one exemplary implementation, the temperature stress adjustment factor is established in accordance with the following definition: A i = λ i Λ j = exp [ E a k ( 1 T ref - 1 T op ) ] where Ea is a thermal activation energy for a defect (eV), k is Boltzmann's constant (8.63 10−5 eV/K), Tref is a reference temperature and Top is an operating temperature (e.g., measured by sensor 210). In one exemplary implementation, the activation energy is specific for the defect considered. An electrical stress adjustment factor can be established in accordance with the following definition:Si=exp[mi(Pop−Pref)]where Pop is the percent of the stress applied (e.g., traffic calculated) and Pref is a percent (e.g., 50%) used in the reference measurement of the MTBF. The variable mi is an electrical stress parameter characteristic of the component and can be predetermined (e.g., saved in memory 230 as a reference value). In one exemplary implementation in which the reference temperature is 313 degrees Kelvin, the operating temperature is 333 degrees Kelvin and the activation energy is 0.4 eV (e.g., an average value for silicon or oxide defects), the temperature stress adjustment factor is 2.4. Therefore, the instantaneous failure rate for the electronic component is 2.4 times higher than the reference failure rate. Alternatively, this can also be expressed by indicating that these two hours are like 4.8 effective hours at MTBF or that the MTBF for these two hours is 2.4 times less than the given MTBF. Memory 230 can include a variety of configurations. In one embodiment, memory 230 includes nonvolatile memory for storing static reference information and historical data. FIG. 3 is block diagram illustration of illustration of nonvolatile memory structure 300, one embodiment of a nonvolatile portion of present invention memory 230. Nonvolatile memory structure 300 comprises static information section 310, historical data section 320, and scratch section 330. Static information section 310 stores static information including reference values and sampling interval duration values. In one embodiment, static information section 310 includes block identification section 311, constants section 312, sensor description section 313 and component description section 314. Historical data section 320 stores historical data including results of a field condition determination process (e.g., temperature, location, altitude, humidity, switching components on and off, power surges, electromagnetic interference, etc.). The historical data can also include values resulting from a field condition reliability analysis process (e.g., an “instantaneous” value of a reliability indicator adjusted for impacts associated with field conditions can be received). Scratch section 330 stores information during erase/write of data (e.g., a data sector). FIGS. 4A and 4B are block diagram illustrations of nonvolatile Flash EProm memory structure 400, one exemplary implementation of a present invention memory 230. FIGS. 5A and 5B is block diagram illustration of one embodiment of a RAM structure 500, an embodiment of a volatile portion of memory 230 after being loaded with values from a nonvolatile memory structure, in accordance with one embodiment of the present invention memory. In one embodiment of the present invention, information associated with reliability determination is saved in a condensed format. FIG. 8 is a flow chart of reliability information condensing process 800, in accordance with one embodiment of the present invention. In one exemplary implementation, the condensed format includes saving a reference value and the difference between the reference value and a measured value. For example, a reference temperature (e.g., 40 degrees C.) is saved and then the difference (e.g., 20 degrees C.) from a measured value (e.g., 40 degrees C.) at a particular sampling time is saved. In one embodiment, the temperature differences that exceed a predetermined value are saved and differences that do not exceed the predetermined difference are not saved. In step 810, a reliability related reference value is saved. It is appreciated that the present condensation method is readily applicable to a variety of reliability related references values. For example, a possible related reference values include a reference temperature, an initial start up time after shipment from the manufacturer, a communication traffic reference value, a humidity reference value, and/or an altitude reference value. In step 820, an updated reliability related value is received. In one embodiment, the updated reliability related value is a result of implementing a field condition determination process (e.g., results of step 120 of electronic component reliability determination method 100). For example, the results of the field condition determination process can be expressed as operational parameters which can include measurements of things that cause stress on a component or system (e.g., temperature, location, altitude, humidity, switching components on and off, power surges, electromagnetic interference, etc.). In addition, a count of the sampling periods can be received. In one exemplary implementation, the updated reliability related value can include values resulting from a field condition reliability analysis process (e.g., results of step 130 of electronic component reliability determination method 100). For example, a present value or “instantaneous” value of a reliability indicator adjusted for impacts associated with field conditions can be received. The updated reliability related value can including a field condition failure adjustment factor, an instantaneous failure rate for components and/or a system, and a cumulative reliability index value for a component and/or system. In step 830, a storage relationship value is determined. The storage relationship value is value associated with a relationship between the updated reliability related value and the reliability related reference value. The relationship is a predetermined relationship. For example, the storage relationship value can be the difference between the updated reliability related value and the reliability related reference value. The difference can be direct or incremental. For example, if a reliability related reference value is a reference temperature of 40 degrees Celsius and an updated reliability related value is a measured temperature of 60 degrees Celsius the storage relationship value can be 20 degrees Celsius. Alternatively, a predetermined incremental differential can be established (e.g., 5 degrees Celsius) and the storage relationship value (e.g., 4) is based upon an incremental count (e.g., an increment count of 4 instead of a difference of 20 degrees Celsius). The storage relationship value can also be a count of sampling periods. In step 840, the storage relationship value is saved. The storage relationship value can be stored in a non-volatile memory location. In one exemplary implementation, the storage relationship value is stored in a reliability information table “format”. The reliability information tables can be utilized to store a variety of measured values (e.g., temperature measurements, humidity values, altitude values, etc.). The stored values (e.g., temperature measurements) can also be utilized in the determination of the other reliability information (e.g., instantaneous failure rates, reliability index values, etc.) which can also be saved in a present invention compression format (e.g., a base or reference value and differential increments). FIG. 9A is an illustration of a reliability information table 910, one example of information that can be condensed in accordance with an embodiment of the present invention. The columns represent different updated reliability related information (e.g., measurement from sensors, sampling time intervals) and the rows represent the values of the different updated reliability related information. For example, the first, second and third columns are measurements from sensor 911, 912, and 913 respectively and the forth column is a time interval count 914. The rows of data (second, third and forth rows of the illustration) are the measured values from the respective sensors at different times. In one embodiment, the first row of data is a base measurement from which the following rows are measured from The first time can be an absolute time designated in month/day/year and hours, minutes and seconds (mm/dd/yy hh:mm:ss). For example the time 6/10/03 10:20:00 can be expressed as the number of minutes elapsed from 1/1/70 00:00:00 which is 211217140 or in hexidecimal form is OC987194. FIG. 9B is another illustration of condensed reliability information table 910 in accordance with one embodiment of the present invention. The values stored in the second and third rows of data (the third and forth row of the illustration) are the differences in the sensed values from the previous time interval. Alternatively, the values can be the difference from the reference value. In the present example, the sampling interval time is fifteen minutes. The present invention is readily adaptable for storing a combination of regular or clear data and compressed data. For example, the first row of data can be clear values (e.g., an absolute value, an actual measurement, a fully expressed time, etc.) and the second and third row of data (third and forth row of the illustration) can be compressed values (e.g., the difference of a measured value from the previous value). FIG. 9C is an illustration of a condensed reliability information table 910 with binary values in accordance with one embodiment of the present invention. The condensing conserves memory space. For example, in the first column third row, instead of using 8 bits to represent the value 28, 4 bits are used to represent the difference from 27. The first bit of the values in the third and forth row indicate whether the difference is positive or negative. For example, a logical 0 can represent positive and a logical 1 can represent negative, or vise versa. In the illustrated example the time does not have a sign value as it is assumed to be positive (e.g., the increments do not go back in time). FIG. 6 is a block diagram of a communication device 600 in accordance with one embodiment of the present invention. It is appreciated that communication device 600 is readily adaptable for a variety of communication activities including routing communication information. Communication device 600 includes controller 620, ports 611 through 615, and reliability determination system 650. Controller 620, ports 611 through 615, and reliability determination system 650 are communicatively coupled. Controller 620 controls supervisory and non-supervisory communication activities for communication ports 611 through 615. Reliability determination system 650 determines the “instantaneous” failure rates and cumulative reliability of controller 620 and ports 611 through 615. In one embodiment of the present invention, reliability determination system 650 includes instructions for determining the “instantaneous” failure rates and cumulative reliability. Alternatively, instructions for determining the “instantaneous” failure rates and cumulative reliability can be stored in memory 622 and processed by processing component 621 in addition to instructions for controlling communications through communication device 600. In one embodiment, an electronic component reliability determination hierarchy is established for directing reliability determination activities. FIG. 7 is a block diagram illustration of reliability determination hierarchy 700 in accordance with one embodiment of the present invention. Reliability determination hierarchy 700 includes initialization module 710, background module 720 and run time module 730. The components of reliability determination hierarchy 700 cooperatively operate to direct reliability determination activities. Initialization module 710 directs implementation of an initialization process. In one embodiment, initialization module 710 includes instructions for checking the integrity of non volatile memory, initializing random access memory (RAM) with previously stored values (e.g., initial settings stored in a nonvolatile memory), defining a reliability sampling period or interval and starting background tasks. Background module 720 directs reliability determination background operations. For example, background module 720 can direct background operations associated with a field condition determination process and a field condition reliability analysis process. In one embodiment, background module 720 includes instructions for implementing reliability associated firmware activities. Background module 720 can divide background tasks into multiple background threads that operate separately and do not interfere with one another. For example, one background task thread is started to gather field condition information (e.g., perform a field condition determination process) and a secondary background task is started to analyze data (e.g., performing a field condition reliability analysis process). In one exemplary implementation, the secondary background task can be performed in an time less than a first background task interval (e.g., a temperature measuring interval). The fist background process can run without interference from the secondary background process (e.g., the first background task does not have to wait for a processor to complete the secondary background task). Runtime module 730 provides an interface to an operating system and messaging features. For example, field condition information and/or reliability indication information can be communicated to a remote resource. In one exemplary implementation, reliability determination activities (e.g., calculation of instantaneous failure rates, etc,) can be performed by the runtime module 730 also. In one embodiment, the instructions of reliability determination hierarchy 700 are stored on a computer readable medium and cause a processor to implement reliability determination operations. Thus, the present invention provides a convenient and accurate indication of failure rates and reliability indications. A highly relevant field adjusted indication of the mean time between failure (MTBF) is also provided. The present invention facilitates increased accuracy in predicting and estimating maintenance, service and repair activities and resources. For example, better indications of spare part inventories can be forecasted with reliability information provided by the present invention. The reliability information made available by the present invention can also be used to modify existing reference values and/or in future design decisions. The foregoing descriptions of specific embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the invention and its practical application, to thereby enable others skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the Claims appended hereto and their equivalents. |
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claims | 1. A gas field ion source, comprising:a housing,an electrically conductive tip within the housing,a gas supply configured to supply a gas to the housing, the gas comprising neon or a noble gas with atoms having a mass larger than neon, andan extractor electrode having a hole to permit ions generated in the neighborhood of the tip to pass through the hole,wherein a surface of the extractor electrode facing the tip comprises a material selected to have a negative secondary ion sputter rate of less than 10−5 per incident neon ion so that, during use of the gas field ion source, the extractor electrode produces a relatively low rate of negative secondary ions that are accelerated from the extractor to the tip. 2. The gas field ion source of claim 1, wherein the extractor comprises at least one material selected from the group consisting of carbon, iron, molybdenum, titanium, vanadium, tatalum. 3. The gas field ion source of claim 1, wherein at least the surface of the extractor facing the tip comprises a metal that does not form oxides. 4. The gas field ion source of claim 1, wherein the hole has a vacuum conductance of less than 1 liter per second. 5. The gas field ion source of claim 4, wherein the hole has a vacuum conductance of less than 0.2 liter per second. 6. The gas field ion source of claim 4, wherein a gas pressure on one side of the hole is in the range 10−2 to 10−3 torr, and a gas pressure on another side of the hole is in the range 10−5 to 10−7 torr. 7. The gas field ion source of claim 4, wherein a gas pressure on one side of the hole is in the range 10−2 to 10−3 mbar, and a gas pressure on another side of the hole is in the range 10−5 to 10−7 mbar. 8. The gas field ion source of claim 1, wherein a distance between the tip and the extractor electrode is such that the extractor hole subtends a half angle of 15 to 40 degrees in angle. 9. The gas field ion source of claim 8, wherein the distance between the tip and the extractor electrode is such that the extractor hole subtends a half angle of 20 to 25 degrees in angle. 10. The gas field ion source of claim 8, wherein the distance between the tip and the extractor electrode is such that the extractor hole subtends a solid angle in the range between 0.38 steradians and 0.59 steradians. 11. The gas field ion source of claim 1, further comprising a cryogenic cooling system configured to cool at least an output tube of the gas supply to a cryogenic temperature. 12. The gas field ion source of claim 11, further comprising a heater configured to heat the output tube of the gas supply. 13. The gas field ion source of claim 1, further comprising a heater configured to heat the housing. 14. The gas field ion source of claim 1, further comprising a chemical getter within the housing. 15. The gas field ion source of claim 1, further comprising a flapper valve at the housing. 16. The gas field ion source of claim 1, further comprising a bypass line of the gas delivery system to a space outside the housing. 17. A gas field ion source, comprising:an external housing,an internal housing within the external housing,an electrically conductive tip within the internal housing,a gas supply configured to supply a gas to the internal housing, the gas supply comprising a tube terminating within the internal housing,an extractor electrode having a hole to permit ions generated in the neighborhood of the tip to pass through the hole into the external housing, anda flapper valve between the internal and the external housing, the flapper valve being configured to increase a flow of gas from the internal housing to the external housing when the flapper valve is opened,wherein a surface of the extractor electrode facing the tip comprises a material selected to have a negative secondary ion sputter rate of less than 10−5 per incident neon ion so that, during use of the gas field ion source, the extractor electrode produces a relatively low rate of negative secondary ions that are accelerated from the extractor to the tip. 18. The gas field ion source of claim 17, wherein the gas supply is configured so that:in a first mode of operation of the gas field ion source, the gas supply supplies a first noble gas; andin a second mode of operation of operation of the gas field ion source, the gas supply supplies a second noble gas. 19. The gas field ion source of claim 18, wherein the first gas is helium, and the second gas is neon. 20. A method, comprising:providing a gas field ion source, comprising:an external housing,an internal housing within the external housing,an electrically conductive tip within the internal housing,a gas supply configured to supply first and second gases to the internal housing, the gas supply comprising a tube terminating within the internal housing,an extractor electrode having a hole to permit ions generated in the neighborhood of the tip to pass through the hole into the external housing, a surface of the extractor electrode facing the tip comprises a material selected to have a negative secondary ion sputter rate of less than 10−5 per incident neon ion so that, during use of the gas field ion source, the extractor electrode produces a relatively low rate of negative secondary ions that are accelerated from the extractor to the tip, anda flapper valve arranged between the internal and the external housing configured to increase a flow of gas from the internal housing to the external housing when the flapper valve is opened,operating the gas field ion source while keeping the flapper valve closed, andopening the flapper valve when changing between operation of the charged particle beam source with the first gas and the second gas,wherein the first gas is different from the second gas. |
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abstract | Systems and methods are provided for scanning an item utilizing an X-ray scanner in order to facilitate a determination of whether the X-ray radiation penetrated through the entirety of the scanned item. Various embodiments comprise a conveying mechanism, an X-ray emitter, a detector, and an X-ray penetration grid (XPG). The XPG may comprise a radiopaque grid that may serve as a reference for determining whether radiation passes through the scanned item, the grid oriented such that the grid members are neither parallel nor perpendicular to the direction of travel. Such orientation may minimize or eliminate “ghosted” radiation signals included in a visual display of the radiation received by the detector. A scanned item may be oriented with the XPG such that radiation emitted by the X-ray emitter that passes through a portion of the scanned item must also pass through the XPG before being received by the detector. |
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summary | ||
claims | 1. An X-ray optical device, comprising:an X-ray source configured to emit X-rays;an X-ray optics configured to image a beam of X-rays generated by the X-ray source onto a sample to be analyzed;a beam blocking unit arranged for selectively blocking off at least a portion of the X-ray beam output by the X-ray optics;the beam blocking unit comprising a rotating shaft and a beam blocking element, wherein the rotating shaft is rotatable by a driving unit around a rotating shaft axis and arranged laterally offset with respect to the X-ray beam output by the X-ray optics;wherein the beam blocking element is mounted eccentrically on the rotating shaft such that the beam blocking element is movable into different beam overlap positions for blocking off corresponding portions of the beam when the beam blocking element is eccentrically rotated around the rotating shaft axis;a sensor unit configured to measure an angle of rotation or angular position of the shaft rotated by the driving unit; anda control unit, wherein the control unit is in communication with the sensor unit, the driving unit and an external input device, wherein the control unit is configured to:determine an actual beam overlap position of the beam blocking element based on the angular position of the rotating shaft measured by the sensor unit;compare the actual beam overlap position with a set beam overlap position received from the input device; andbased on the comparison, generate a signal that controls the driving unit to drive the rotating shaft to an angular position that corresponds to the set beam overlap position. 2. The X-ray optical device according to claim 1, wherein the beam overlap position of the beam blocking element depends on the angle of rotation of the rotating shaft. 3. The X-ray optical device according to claim 1, wherein the beam blocking element is movable into any position between a predetermined minimum overlap position and a predetermined maximum overlap position by selecting a corresponding angle of rotation between 0° and 180°. 4. The X-ray optical device according to claim 1, wherein the beam blocking element is movable from a minimum overlap position to a maximum overlap position and from the maximum overlap position back to the minimum overlap position by turning the rotating shaft one full revolution. 5. The X-ray optical device according to claim 1, wherein the beam blocking element comprises a rotationally symmetric body with a lateral surface defining a beam blocking edge for the X-ray beam. 6. The X-ray optical device according to claim 1, further comprising:a bearing unit designed for rotatably bearing the rotating shaft; anda casing designed for receiving the bearing unit, the rotating shaft and the beam blocking element. 7. The X-ray optical device according claim 1, further comprising at least one sealing element designed for realizing an air-tight seal around the rotating shaft. 8. The X-ray optical device according to claim 1, wherein the driving unit comprises an electric motor configured to generate a torque and a belt drive configured to transmit the torque to the shaft. 9. The X-ray optical device according to claim 1, wherein the X-ray optics comprises at least one reflective element designed to image an X-ray beam with a predetermined focal length. 10. The X-ray optical device according to claim 1, further comprising a collimator configured to further refine the beam of X-rays in between the X-ray optics and the sample, wherein the beam blocking unit is either arranged after the X-ray optics, before the collimator or after the collimator. 11. A method of operating an X-ray optical device, the method comprising the steps of:generating X-rays by an X-ray source;imaging, by the X-ray optics, a beam of the X-rays from the X-ray source onto a sample to be analyzed;collimating, by a collimator, the beam of X-rays to be imaged to the sample, the collimator located between the X-ray optics and the sample;adjusting a divergence angle or intensity of the imaged X-ray beam in dependence of the sample to be analyzed, wherein the adjusting step comprises moving a rotating shaft and a beam blocking element towards a desired overlap position by rotating the rotating shaft by a predetermined angle of rotation, wherein the adjusting step is performed automatically by a control unit and a driving unit which is mechanically coupled to the rotating shaft. 12. An X-ray analysis system configured to analyze crystalline or powder samples, the system comprising:an X-ray source configured to emit X-rays;an X-ray optics configured to image a beam of X-rays generated by the X-ray source onto a sample to be analyzed;a beam blocking unit arranged for selectively blocking off at least a portion of the X-ray beam output by the X-ray optics;the beam blocking unit comprising a rotating shaft and a beam blocking element, wherein the rotating shaft is rotatable by a driving unit around a rotating shaft axis and arranged laterally offset with respect to the X-ray beam output by the X-ray optics;wherein the beam blocking element is mounted eccentrically on the rotating shaft such that the beam blocking element is movable into different beam overlap positions for blocking off corresponding portions of the beam when the beam blocking element is eccentrically rotated around the rotating shaft axis;a sensor unit configured to measure an angle of rotation or angular position of the shaft rotated by the driving unit;a control unit, wherein the control unit is in communication with the sensor unit, the driving unit and an external input device, wherein the control unit is configured to:determine an actual beam overlap position of the beam blocking element based on the angular position of the rotating shaft measured by the sensor unit;compare the actual beam overlap position with a set beam overlap position received from the input device; andbased on the comparison, generate a signal that controls the driving unit to drive the rotating shaft to an angular position that corresponds to the set beam overlap position;a sample stage configured to hold and orient the sample to be analyzed relative to the X-ray beam output by the X-ray optical device; andan X-ray detector configured to detect X-rays scattered by the sample. 13. The system according to claim 12, wherein the beam overlap position of the beam blocking element depends on an angle of rotation of the rotating shaft. 14. The system according to claim 13, wherein the beam blocking element is movable from a minimum overlap position to a maximum overlap position and from the maximum overlap position back to the minimum overlap position by turning the rotating shaft one full revolution. 15. The system according to claim 12, wherein the driving unit comprises an electric motor configured to generate a torque and a belt drive configured to transmit the torque to the shaft. 16. The system according to claim 12, further comprising a collimator configured to further refine the beam of X-rays in between the X-ray optics and the sample, wherein the beam blocking unit is either arranged after the X-ray optics, before the collimator or after the collimator. |
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053295625 | summary | BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a method of cutting and removing a nuclear reactor for dismantling and removing a used nuclear reactor. 2. Description of the Prior Art Generally, nuclear reactors reach a permanent operation termination period 30 to 40 years after the start of the operation. Even after a nuclear fuel is withdrawn, a nuclear reactor has residual radioactivity such as radioactivation products, and various regulations have been put in force to ensure safety management and disposal for decommissioning of such a nuclear reactor. Means for decommissioning a nuclear reactor comes in three types. First means closes a nuclear reactor facility and puts it under suitable management, second means executes work such as shielding of the nuclear reactor to tightly isolate radioactive materials form outside and third means dismantles and removes radioactive structures inside the reactor facility. Since only a limited environment for installation of the nuclear reactor is available, a new facility, too, is preferably set up inside the same facility as the existing facility and in this sense, the third means for dismantling and removing the used reactor is preferred among the means described above. Accordingly, the development of a method of dismantling and removing safely and efficiently the used reactor has been earnestly desired. As means for accomplishing the object described above, a method has been proposed which cuts vertically and horizontally the body base portion of the reactor, for example, by continuous core boring so as to cut off the base portion from a pressure vessel, and transports and preserves them under a sealed state in a large waste preservation warehouse. SUMMARY OF THE INVENTION The pressure vessel itself of the reactor, after the body base portion thereof has been removed, has a diameter of 5 to 8 m and a height of 12 to 18 m. The wall thickness of the pressure vessel made of an austenitic stainless steel is from about 150 to 200 mm. Since no method which divides the pressure vessel, being a large-scale facility, both horizontally and vertically has not yet been established, the pressure vessel has been preserved in the past in a large-scale sealed preservation warehouse. A technique which cuts such a pressure vessel in water by a remote-controlled plasma cutting method is now being developed but cutting of the structure inside the reactor by this method is extremely difficult, though this method can cut the pressure vessel and the outer peripheral portions. Nevertheless, the number of nuclear reactors the service life of which ends up shortly are acceleratingly increasing every year and hence, the development of a method which can dismantle and remove safely and efficiently the nuclear reactors has been strongly desired. As its dismantling technique, the Applicant of the present invention has developed a technique which pressure-feeds grouting material into a pressure vessel to integrally solidify them together, and then cuts them with a wire saw having diamond grains. When the pressure vessel is cut starting with its outer periphery, the technique described above can cut integrally all the structural members while preventing the scatter of radioactive appliances and base materials and can therefore carry out safely and reliably the dismantling operation. Moreover, since the grouting material isolates the internal materials having radioactivity, transportation and disposal can be carried out safely. In the technique described above, the outer periphery of the surface to be cut is made of a metal. Therefore, the development of a technique which can stabilize the initial cutting portion and can decrease wear of the grains of the wire saw during the cutting operation of the metal portions has been desired as a technique which further improves cutting efficiency. It is therefore a first object of the present invention to provide a method of safely and efficiently dismantling and removing a nuclear reactor, particularly its pressure vessel. It is a second object of the present invention to provide a method of cutting and removing a nuclear reactor which can stably cut the reactor when the reactor is cut with a wire saw, and can reduce the wear of the grains of the wire saw. To accomplish the first object, the method of cutting and removing the nuclear reactor according to the present invention pressure-feeds a grouting material into the pressure vessel and into peripheral members outside the pressure vessel so as to integrally solidify them together, and starts cutting with the outer periphery of the pressure vessel. When the cutting operation is carried out, the method of the invention uses a wire saw having diamond grains on the surface. Furthermore, when the cutting operation is carried out, the present invention executes double cutting by the use of a preceding cutting edge and a cutting groove width adjustment cutting edge, and in this way, the present invention can dismantle and remove safely and efficiently the pressure vessel, and the like, of the nuclear reactor. To accomplish the second object, the second means of the present invention comprises packing a cement grouting material or a synthetic resin material into the nuclear reactor, covering its outer periphery with a concrete, cutting the reactor into blocks starting with its outer periphery with a wire saw using diamond beads and carrying them out, and comprises packing a cement grouting material or a synthetic resin material into a nuclear reactor, cutting the outer portion of the reactor by a plasma, cutting then the inside of the reactor into blocks with a wire saw using diamond beads, and carrying them out, in order to cut and remove the nuclear reactor. When the nuclear reactor is cut with the wire saw, therefore, the present invention can stably cut the reactor, can reduce the wear of the grains of the wire saw and can improve cutting performance. A first means being constituted as described above, the present invention first pressure-feeds a grouting material into the pressure vessel and into the peripheral members outside the pressure vessel so as to integrate and solidify them together, then prevents radioactive appliances and materials from scattering when the cutting operation is started with the outer periphery of the pressure vessel, and makes it possible to carry out smoothly the cutting operation by using a wire saw, or the like. The present invention uses a wire saw having diamond grains on the surface and cuts integrally all the appliances and materials, conducts double cutting using a preceding cutting edge and a cutting width adjustment cutting edge, and keeps a predetermined cutting width by the cutting width adjustment cutting edge which compensates for a decrease in cutting groove width resulting from the wear of the preceding cutting edge. The second means being constituted as described above, the present invention first pressure-feeds a cement grouting material or synthetic resin material having high fluidity into the nuclear reactor before cutting of the reactor is started, and the cement grouting material or the synthetic resin material is packed even into fine spaces of internal appliances. Next, after the outer periphery of the reactor is covered with concrete, it is cut with the wire saw using the diamond beads. In this case, since the first cut portion is the concrete material, the cutting operation can be easily started with the wire saw using the diamond beads and when the cutting operation reaches the main body of the reactor made of a stainless steel, the wire saw can exhibit a stable cutting performance as it is guided by the cut concrete portion. Even when the sharpness of the cutting portion of the wire saw drops due to the wear of the surface of the bead material in the course of cutting of the stainless steel reactor, the concrete material which is cut from the metal portion by the wire saw functions as the grinding stone and polishes the wire saw. Therefore, the wire saw maintains its performance in cutting the stainless steel. |
abstract | A linear accelerator head for use in a medical radiation therapy system can include a housing, an electron generator configured to emit electrons along a beam path, and a microwave generation assembly. The linear accelerator head may include a waveguide that is configured to contain a standing or travelling microwave. The waveguide can include a plurality of cells that are disposed adjacent one another, wherein each of the plurality of cells may define an aperture configured to receive electrons therethrough. The linear accelerator head can further include a converter and a primary collimator. |
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claims | 1. A method of operating a propagating nuclear fission deflagration wave reactor, the method comprising:initiating a nuclear fission deflagration wave with a first nuclear igniter;propagating a propagating nuclear fission deflagration wave through a first region of a nuclear fission deflagration wave reactor to a second region of the nuclear fission deflagration wave reactor, the first region being contiguous with the second region, each one of the first and second regions configured to be critical independent of the other of the first and second regions;propagating the propagating nuclear fission deflagration wave through the second region; and after propagating the nuclear fission deflagration wave through the second region, re-propagating the propagating nuclear fission deflagration wave through the first region. 2. The method of claim 1, wherein re-propagating the propagating nuclear fission deflagration wave includes re-initiating the propagating nuclear fission deflagration wave with a second igniter. 3. The method of claim 1, wherein re-propagating the propagating nuclear fission deflagration wave includes at least one of decaying and removing fission products from the first region. 4. The method of claim 1, wherein re-propagating the propagating nuclear fission deflagration wave includes providing at least one of neutrons and fissile material to the first region. 5. The method of claim 1, wherein re-propagating the propagating nuclear fission deflagration wave includes controlling neutron modifying structures. 6. The method of claim 1, wherein:the propagating nuclear fission deflagration wave remains substantially spatially fixed; andthe first and second regions are moved relative to the propagating nuclear fission deflagration wave. 7. The method of claim 1, wherein:the first and second regions are stationary; and the propagating nuclear fission deflagration wave propagates through the first and second regions. |
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050650335 | claims | 1. A coupling apparatus for providing cable controls to a storage unit in a radiographic system for manipulating a quantity of radioactive material, in a radioactive capsule, between a stored position and a use position, the storage unit having a passage through it for storing said radioactive capsule in the passage and shielding the surrounding environment from the stored radioactive material, a flexible leader attached to said radioactive capsule adapted to be guided through said passage, and comprising: disconnectable coupling means having a connector assembly fixed to said storage unit at one end of said passage and a separable control cable assembly of tubular shape, said connector assembly having a tubular aperture for receiving said separable control cable assembly endwise therein, and means for releasably locking said control cable assembly to said connector assembly, said connector assembly having means responsive to movement of said flexible leader for automatic locking of said radioactive capsule in the stored position upon return of said radioactive capsule to the stored position within said storage unit, said responsive means comprising: a slide member and a sleeve, said sleeve having a hole defined therein, said slide member having a larger diameter aperture and a smaller diameter aperture defined therein, a mass attached to said source cable means for engagement with said sleeve hole and said small diameter aperture, said slide member having an open position during which said sleeve hole and said larger diameter aperture are in alignment, and a locked position during which said sleeve hole and said smaller diameter aperture are in alignment capturing said mass therebetween, biasing means for urging said slide member toward said locked position, and said slide member and said sleeve defining therebetween interlocking means for holding said slide member in said open position, said mass triggering the interlocking means to disengage upon return of said radioactive capsule to the stored position allowing said biasing means to move said slide member. said separable control cable assembly having means to receive said engagement means for locking said separable control cable assembly against withdrawal from said tubular aperture upon rotation of said dial; said means for preventing, including said one end of said slide member engaging sides of said aperture of said dial surface while said slide member is in said open position and said dial in said operate position, thereby preventing movement of said dial from said operate position until said slide member is slid from said operate position to said locked position. providing a connector assembly fixed to said storage unit at one end of said passage and a separable control cable assembly of tubular shape, attaching said control cable assembly to said storage unit, said connector assembly having a tubular aperture for receiving said separable control cable assembly endwise therein, and means for releasably locking said control cable assembly to said connector assembly, automatically locking said radioactive capsule in said stored position upon return of said radioactive capsule to the stored position within said storage unit, providing a slide member and a sleeve, said sleeve having a hole defined therein, said slide member having a larger diameter aperture and a smaller diameter aperture defined therein, providing a mass attached to said source cable means for engagement with said sleeve hole and said small diameter aperture, said slide member having an open position during which said sleeve hole and said larger diameter aperture are in alignment, and a locked position during which said sleeve hole and said smaller diameter aperture are in alignment capturing said mass therebetween, and providing biasing means for urging said slide member toward said locked position, and said slide member and said sleeve defining therebetween interlocking means for holding said slide member in said open position, said mass triggering the interlocking means to disengage upon return of said radioactive capsule to the stored position allowing said biasing means to move said slide member. said separable control cable assembly having means to receive said engagement means for locking said separable control cable assembly against withdrawal from said tubular aperture upon rotation of said dial. a slide member and a sleeve, said sleeve having a hole defined therein, said slide member having a larger diameter aperture and a smaller diameter aperture defined therein, a mass attached to said source cable means, said mass having a diameter too large to fit through said sleeve hole and said smaller diameter aperture and small enough to fit through said larger diameter aperture, said slide member having an open position during which said sleeve hole and said larger diameter aperture are in alignment allowing movement of said source cable means with attached mass in one direction through said larger diameter aperture, and a locked position during which said sleeve hole and said smaller diameter aperture are in alignment capturing said mass therebetween thereby preventing any movement of said source cable means, biasing means for urging said slide member toward said locked position, said slide member and said sleeve defining therebetween interlocking means for holding said slide member in said open position, said mass triggering the interlocking means to disengage upon return of said radioactive capsule to the stored position allowing said biasing means to urge said slide member from said open position to said locked position thereby safely storing said radioactive capsule in said stored position. a slide member and a sleeve, said sleeve having a hole defined therein, said slide member having a larger diameter aperture and a smaller diameter aperture defined therein, a mass attached to said source cable means for engagement with said sleeve hole and said smaller diameter aperture, said slide member having an open position during which said sleeve hole and said larger diameter aperture are in alignment, and a locked position during which said sleeve hole and said smaller diameter aperture are in alignment capturing said mass therebetween. biasing means for urging said slide member toward said locked position, said slide member and said sleeve defining therebetween interlocking means for holding said slide member in said open position, said mass triggering the interlocking means to disengage upon return of said radioactive capsule to the stored position allowing said biasing means to move said slide member. 2. A coupling apparatus according to claim 1 wherein said means for releasably locking includes a dial mounted in said connector assembly for concentric rotation about the axis of said tubular aperture, said dial having engagement means activated upon rotating said dial, 3. A coupling apparatus according to claim 2 wherein said mass and said radioactive capsule are attached to said flexible leader at substantially opposite ends thereof, said mass extending into said connector assembly when said radioactive capsule is stored in said storage unit. 4. A coupling apparatus according to claim 3 wherein said dial has a connect position during which said engagement means are inoperative and an operate position during which said engagement means are activated to engage said means for receiving said engagement means, thereby locking said separable control cable assembly against withdrawal. 5. A coupling apparatus according to claim 4 wherein said dial further includes means providing a dial surface, said dial surface having an aperture formed therein, said dial surface for engaging one end of said slide member when said slide member is in the locked position and said dial in said connect position, thereby preventing movement of said slide member from said locked position to said open position, said aperture to receive said one end of said slide member when said dial is in said operate position and said slide member in said open position. 6. A coupling apparatus according to claim 5 wherein said biasing means includes a spring. 7. A coupling apparatus according to claim 6 wherein said interlocking means comprises a recess defined in said slide member for receiving said sleeve. 8. A coupling apparatus according to claim 7 further including means for preventing detachment of said separable control cable assembly from said connector assembly until said radioactive capsule is stored in said stored position, 9. A method for providing cable controls to a storage unit on a radiographic system for manipulating a quantity of radioactive material, in a radioactive capsule, between a stored position and a use position, the storage unit having a passage through it for storing said radioactive capsule in the passage and shielding the surrounding environment from the stored radioactive material, a flexible leader attached to said radioactive capsule adapted to be guided through said passage, and comprising the steps of: 10. A method according to claim 9 wherein said means for releasably locking includes a dial mounted in said connector assembly for concentric rotation about the axis of said tubular aperture, said dial having engagement means activated upon rotating said dial, 11. A method according to claim 8 wherein said mass and said radioactive capsule are attached to said flexible leader at substantially opposite ends thereof, said mass extending into said connector assembly when said radioactive capsule is stored in said storage unit. 12. In a radiographic apparatus for manipulating a quantity of radioactive material between a stored position and a use position, including a capsule of said radioactive material, a storage unit with means defining a passage through it for storing the capsule in the passage and shielding the surrounding environment from the stored radioactive material, a source cable means attached to said radioactive capsule and adapted to be guided through said passage, said storage unit passage having respective inlet and outlet ports, a separable control cable means, connector means for receiving the control cable means and disposed at the inlet port of the storage unit, said separable control cable means adapted for releasable engagement with said source cable means, said source cable assembly in combination with the connector means comprising: 13. In a radiographic apparatus as set forth in claim 12 wherein said interlocking means comprises a recess defined in said slide member for receiving said sleeve. 14. In a radiographic apparatus as set forth in claim 13 wherein said mass comprises a ball on said source cable means, said ball being disposed at an end of said source cable remote from said radioactive capsule. 15. In a radiographic apparatus as set forth in claim 14 wherein said biasing means for urging comprises a spring. 16. In a radiographic apparatus for manipulating a quantity of radioactive material between a stored position and a use position, including a capsule of said radioactive material, a storage unit with means defining a passage through it for storing the capsule in the passage and shielding the surrounding environment from the stored radioactive material, a source cable means attached to said radioactive capsule and adapted to be guided through said passage, said storage unit passage having respective inlet and outlet ports, a separable control cable means, connector means for receiving the control cable means and disposed at the inlet port of the storage unit, said separable control cable means adapted for releasable engagement with said source cable means, said source cable assembly in combination with the connector means comprising: 17. In a radioactive apparatus as set forth in claim 16 wherein said interlocking means comprises a recess defined in said slide member for receiving said sleeve. 18. In a radioactive apparatus as set forth in claim 17 wherein said mass comprises a ball on said source cable means, said ball being disposed at an end of said source cable remote from said radioactive capsule. 19. In a radiographic apparatus as set forth in claim 18 wherein said biasing means for urging comprises a spring. |
claims | 1. A nuclear fuel rod with metal cladding having exterior burnable poison particles thereon in exterior contact with aqueous reactor coolant, the fuel rod having an axis, and an outer abraded surface on said metal cladding; an initial layer of burnable poison particles, having a particle size of from 1 micrometer to 250 micrometers, on said outer abraded, metal cladding surface of said nuclear fuel rod where the initial layer of the burnable poison particles are adhered to said outer surface of said metal cladding at a phase change interface caused by impact of the particles where said phase change interface is selected from the group consisting of molecular surface melting of the metal cladding, atom bonding due to crystal formation and inner atom diffusion between the burnable poison and cladding; additional layers of adhering burnable poison particles on said initial layer, where the exterior layer of the additional layers has a protective oxidation caused by contact with the aqueous coolant, wherein the burnable poison particles are selected from the group consisting of elemental boron, elemental gadolinium, elemental hafnium, elemental erbium, HfB2, ZrB2, Gd2O3, and mixtures thereof; the metal cladding is a zirconium based metal, and wherein fuel pellets are contained inside the metal cladding. 2. The nuclear fuel rod of claim 1, wherein the additional layers of burnable poison particles have a total thickness of from 0.001 mils to 10 mils. 3. The nuclear fuel rod of claim 1, wherein the burnable poison is ZrB2, and the phase change interface is on the exterior surface of the rod. 4. The nuclear fuel rod of claim 1, wherein the protective oxidation when initially formed, continuously protects the interior burnable poison particles from dissolving in the contacting reactor coolant, which coolant has a temperature of from about 200° C. to 360° C., and wherein said burnable poison particles are not dissolved. |
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claims | 1. A dry storage canister for storing and/or transporting spent nuclear fuel rods comprising:a pressure vessel forming a gas-tight containment boundary about a cavity; anda basket apparatus positioned in the cavity, the basket apparatus comprising;a plurality of disk-like grates, each disk-like grate having a plurality of cells formed by a gridwork of beams;the disk-like grates arranged in a spaced manner with respect to one another so that the cells of the disk-like grates are aligned;wherein the plurality of cells comprises fuel cells; anda plurality of ventilated tubes positioned within the fuel cells, each of the ventilated tubes comprising a tubular body portion, a closed bottom end, and a ventilated cap portion, the tubular body portion forming a cavity in which a plurality of spent nuclear fuel rods are positioned. 2. The dry storage canister of claim 1, wherein the plurality of cells further comprises poison rod cells, the fuels cells being larger than the poison rod cells. 3. The dry storage canister of claim 2, further comprising a plurality of poison rods extending through the poison rod cells of the disk-like grates. 4. The dry storage canister of claim 1, whereinthe disk-like grates further comprise a ring-like structure encompassing the gridwork of beams;the gridwork of beams comprising a first series of parallel beams, a second series of parallel beams and a third series of parallel beams; andwherein the first, second and third series of parallel beams are arranged in the ring-like structures so as to intersect and form the plurality of cells. 5. The dry storage canister of claim 2, whereinthe disk-like grates further comprise a ring-like structure encompassing the gridwork of beams; andthe gridwork of beams comprising a first series of parallel beams, a second series of parallel beams and a third series of parallel beams; andwherein the first, second and third series of parallel beams are arranged in the ring-like structures so as to intersect and form a plurality of hexagonal shaped cells and a plurality of triangular shaped cells. 6. The dry storage canister claim 5, wherein the poison rod cells are triangular shaped cells; andthe fuel cells are hexagonal shaped cells. 7. The dry storage canister of claim 1 wherein the disk-like grates are arranged in a spaced manner by a plurality of tie-rods having tubular spacers. 8. The dry storage canister of claim 1 wherein the beams are rectangular strips of metal having notches, the notches arranged on the rectangular strips so that when the strips are arranged in the desired gridwork, the notches of the strips are aligned and the strips slidably mate with one another. |
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053217322 | summary | BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to supports and, more particularly, to boiling water reactor control rod drive housing supports. Still more particularly, this invention relates to control rod drive housing support bars with radiation shields. 2. Description of the Prior Art In boiling water rectors the control rod drive housing supports are generally located underneath the reactor vessel near the control rod housings. The control rod drive housing supports limit the travel of and support a control rod in the event that a control rod drive housing is ruptured. The supports prevent a nuclear excursion as a result of a housing failure, thus protecting the fuel barrier. Typically, control rod drive housing supports consist of hanger rods that are attached and supported at their upper end at a beam structure immediately underneath the reactor pressure vessel and support bars which are bolted between the hanger rods below the control rod drives. Another grid of bars is installed on the support bars to transfer the load of a ruptured control rod drive housing to the support bars. Generally, a pair of grid bars support each control rod drive. Each pair of grid bars are held together by two grid clamps and a bolt. In this support system of the prior art, when it is necessary to change or replace a control rod drive, the grid bars must be removed. In order to remove the grid bars the operator must manually unscrew the grid clamp bolt, remove the two grid clamps and then remove the grid bars, each weighing approximately forty pounds. The number of grid bars which must be removed depends on the number of control rods which must be replaced. Furthermore, since the grid bars are interlocking, they must be removed starting from the outer peripheral row. Thus, if a large number of control rod drives must be replaced or if an inner control rod drive must be replaced, a large number of grid bars must be removed. The result is a time consuming and cumbersome process. Moreover, as the grid bars are heavy and awkward to handle, a dropped bar could result in serious injury. Further still, the persons handling the grid bars or working under the reactor pressure vessel are subject to substantial radiation doses. The more time a person must spend replacing the control rod drives, therefore, the more that person is subject to radiation. Thus it is a problem in the prior art to adequately support a control rod drive housing in a boiling water reactor while allowing for quick and easy replacement of control rod drives and reducing and minimizing the radiation exposure of a person working under the reactor pressure vessel. SUMMARY OF THE INVENTION It is an object of the present invention to support a control rod drive housing in the event that a control rod housing is ruptured while allowing for quick and easy replacement of a control rod drive. It is another object of the present invention to provide a control rod drive housing support which minimizes the amount of radiation which a person is subject to when replacing a control rod drive or working under the reactor pressure vessel. It is another object of the present invention to provide a control rod drive housing support which can be removed automatically. Additional objects, advantages and novel features of the invention will be set forth in the description which follows, and will become apparent to those skilled in the art upon reading this description or practicing the invention. The objects and advantages of the invention may be realized and attained by the appended claims. To achieve the foregoing and other objects, in accordance with the present invention, as embodied and broadly described herein, the control rod drive housing support of this invention may comprise a first means for supporting a control rod drive in the case of a housing failure; and second means for supporting the control rod drive in the case of a housing failure and shielding persons working under the reactor vessel from radiation, the second means being supported by the first supporting means, and wherein the second means can be automatically raised and lowered from a non-support position where the control rod drive is not supported to a support position where the control rod drive is supported. Further, the first supporting means may comprise a plurality of support members provided in rows on opposing sides of a lower portion of a plurality of control rod drives and the second supporting means may comprise a plurality of support cups, each of the support cups receiving, and shielding a lower portion of the control rod drive and supporting the control rod drive in the case of a housing failure. |
claims | 1. A charged particle beam writing apparatus which divides a predetermined region on which writing is effected by a charged particle beam into a plurality of region groups and writes a pattern on the predetermined region while compensating the CPB drift at regular time intervals in accordance with a time-profile, said time interval being determined for each region group, said charged particle beam writing apparatus comprising:grouping means for dividing said predetermined region into smaller regions each consisting of one or the same number of frames, obtaining data indicative of the areal density of a pattern to be written on each smaller region, determining the amount of change in pattern areal density between each two adjacent smaller regions, and grouping said smaller regions into region groups depending on whether or not said amount of change is greater than a predetermined value. 2. The charged particle beam writing apparatus according to claim 1, further comprising:areal density determining means for dividing said predetermined region into smaller regions each consisting of one or the same number of frames, and determining the areal density of a pattern to be written on each smaller region. 3. The charged particle beam writing apparatus according to claim 1, wherein:said predetermined region includes a first predetermined region and a second predetermined region, and said writing is to be performed on said first and second predetermined regions in that order; andthe amounts of change in pattern areal density determined by said grouping means include the amount of change in pattern areal density between the last smaller region of said first predetermined region on which said writing is to be performed and the first smaller region of said second predetermined region on which said writing is to be performed. 4. The charged particle beam writing apparatus according claim 3, further comprising:areal density determining means for dividing said predetermined region into smaller regions each consisting of one or the same number of frames, and determining the areal density of a pattern to be written on each smaller region. |
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claims | 1. A containment cask for storage or transport of a radioactive material comprising:a metallic inner shell;a metallic intermediate shell disposed on an outer side of the inner shell;an outer shell disposed so as to cover an outer side of the intermediate shell;lead solidified from a molten lead poured between the inner shell and the intermediate shell to serve as a gamma ray shielding material; anda low melting point metal filled in either one or both of (i) a first void layer formed at a boundary between the inner shell and the solidified lead or (ii) a second void layer formed at a boundary between the intermediate shell and the solidified lead. 2. A containment cask according to claim 1, wherein the low melting point metal has a melting point lower than the melting point of lead. 3. A containment cask according to claim 1, wherein the low melting point metal has a melting point lower than an allowable temperature of the containment cask for the radioactive material. 4. A containment cask according to claim 1, wherein the low melting point metal is a metal or an alloy in a liquid state at a normal temperature. 5. A containment cask for storage or transport of a radioactive material comprising:a metallic inner shell;a metallic intermediate shell disposed on an outer side of the inner shell wherein a homogenization treatment is performed on only one of either an outer surface of the inner shell or on an inner surface of the intermediate shell;an outer shell disposed so as to cover an outer side of the intermediate shell;lead solidified from a molten lead poured between the inner shell and the intermediate shell to serve as a gamma ray shielding material; anda low melting point metal filled in a void layer formed at a boundary between the solidified lead and either the outer surface of the inner shell or the inner surface of the intermediate shell, whichever surface was not homogenization treated. 6. A containment cask according to claim 5, wherein the low melting point metal has a melting point lower than the melting point of lead. 7. A containment cask according to claim 5, wherein the low melting point metal has a melting point lower than an allowable temperature of the containment cask for the radioactive material. 8. A containment cask according to claim 5, wherein the low melting point metal is a metal or an alloy in a liquid state at a normal temperature. 9. A containment cask for storage or transport of a radioactive material comprising:a metallic inner shell;a metallic intermediate shell disposed on an outer side of the inner shell;an outer shell disposed so as to cover an outer side of the intermediate shell;a plurality of lead bodies, formed beforehand into any desired shape and size and inserted into a space between the inner shell and the intermediate shell to serve as a gamma ray shielding material; anda low melting point metal filled in a void layer formed among the lead bodies. 10. A containment cask according to claim 9, wherein the low melting point metal has a melting point lower than the melting point of lead. 11. A containment cask according to claim 9, wherein the low melting point metal has a melting point lower than an allowable temperature of the containment cask for the radioactive material. 12. A containment cask according to claim 9, wherein the low melting point metal is a metal or an alloy in a liquid state at a normal temperature. 13. A containment cask according to claim 9, wherein the void layer formed among the lead bodies is filled with a good thermal conductivity oil, instead of using the low melting point metal. |
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abstract | A target device for a neutron generating device, an accelerator-excited neutron generating device, and a beam coupling method thereof are disclosed. The target device comprises a plurality of solid particles serving as a target body; and a target body reaction chamber for accommodating the solid particles. With the accelerator-excited neutron generating device and the beam coupling method according to the present invention, the solid particles which are being circulated and situated outside the target body reaction chamber are processed, thereby overcoming defects in the prior art such as low-efficiency heat exchange, a short life time, a bad stability and a narrow application range, and achieving the advantages of high-efficiency heat exchange, a long life time, a good stability and a wide application range. |
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047078464 | summary | BACKGROUND OF THE INVENTION It is known in the art that in order to provide shielding or filtration in association with radiation sources masking or shielding devices are required. Such shielding devices take on various configurations depending on the method of providing the shield, the size of the area to be shielded and the type of radiation source. Various radiation shielding configurations have been developed in connection with X-ray radiography to provide against the excessive exposure of the subject to radiation. It is also known in rhe art that filtration or diffusion of radiation provides against excessive exposure of the subject. Various devices have been developed to filter the radiation generated in connection with X-ray radiography. All of these devices need to be mounted in close association to the source of the radiation in order to provide maximum shielding against, or filtration of, the radiation. The prior developments of the inventors of the present invention are exemplary of the devices known in the art and teach the use of both a shielding means and a filtration means for providing either shield or a filter for the radiation generated in connection with X-ray radiography. These prior developments also teach the use of a specialized mounting means to cooperatively place the shield or filter in close association to the source of the radiation to provide maximum benefit to the subject in permitting the least amount of excessive exposure to unnecessary radiation. These developments are described in U.S. Pat. Nos. 4,266,139 and 4,472,637 and typify the present state of the art in this field. It is an object of the present invention to carry these developments one step further and to provide a masking device to block all radiation from the radiation source not needed to cause an image to appear on an X-ray film for the specific area of the subject to be observed or inspected. It is a further object of the present invention to provide a masking device which cooperates with the earlier developed shielding and filtering devices and the standard X-ray systems in use today. It is also an object of the present invention to provide a masking device which is compact, easy to use, versatile and resilient to continued use and not quickly subject to irradiation from an X-ray radiation generating source. SUMMARY OF THE INVENTION The masking device of the present invention relates generally to radiation shielding devices and more particularly to X-ray shielding devices having a shielding means to block entirely or confine radiation dosage to specific areas of a subject. Specifically, the present invention provides a shielding or masking means to confine or direct the X-ray radiation to a specific area under observation or inspection and to prevent unnecessary and excessive radiation dosages to the subject during full spine radiographs. The full spine shielding means is comprised of a metallic shield or mask constructed of lead or other radiopaque material, said shield being provided with a vertically oriented elongated slot or opening having a broader portion nearer its distal or lower end for permitting only the X-ray radiation necessary to cause an image to appear on the X-ray film for the specific area to be observed or inspected, the spinal column and the pelvic region, to pass through the slot or opening and for blocking the unnecessary radiation from contacting the subject and causing excessive exposure to such radiation. Said shield is laminated between two pieces of translucent plastic or other suitable material and is configured for positioning in close association with an X-ray radiation generating source, for example, on the front of the collimator of an X-ray machine. In the preferred embodiment of the present invention, the shield is located immediately adjacent to and in front of the collimator of an X-ray machine in cooperation with a mounting means having two sets of transverse tracks, one set for receiving and securing the shield of the present invention and the second set for receiving and adjustably securing a substantially rectangular transparent plate, wherein the transparent plate may be frictionally secured to the mounting means and, thus, to the X-ray radiation generating source. Other shielding means or filtering means may be adjustably positioned on the transparent plate to actively cooperate with the shield of the present invention in preventing excessive radiation to reach specific areas of the subject under observation or inspection. |
041622316 | description | DESCRIPTION OF THE PREFERRED EMBODIMENT These and other objects of the invention for recovering palladium and technetium values from an aqueous nitric acid nuclear fuel reprocessing waste solution containing these and actinide, rare earth and fission product values may be met by adjusting the concentration of the nitric acid in the waste solution to about 2.4 M to form a feed solution, contacting the feed solution with an organic extractant of about 0.1 M tricaprylammonium nitrate in a water-immiscible inert aliphatic or aromatic hydrocarbon diluent whereby the palladium and technetium values are selectively taken up by the extractant, and contacting the extractant containing the values with an aqueous strip solution about 8 M in nitric acid whereby the palladium and technetium values are stripped from the extractant. The feed solution may be any aqueous nitric acid solution containing these and any other values. The nitric acid concentration may vary from 0.5 to 3.0 M, preferably 2.0 to 2.5 M and most preferably 2.4 M, thus, a solution with a nitric acid concentration outside of these ranges will require adjustment. The process of the invention was developed specifically for the recovery of palladium and technetium values from aqueous nitric acid fuel reprocessing waste solutions resulting from the Purex Process. These solutions are commercially referred to as the HAW and the EEW waste and vary slightly in nitric acid and actinide concentrations. Both solutions typically contain about 0.24 gms palladium and 0.14 gms technetium per liter in addition to quantities of actinides, rare earths and fission products. Alternatively, the feed may be a nitric acid waste solution from which the actinide and other values have already been partitioned or removed. The extractant may range from about 0.05 to 0.5 M, preferably about 0.1 M, in tricaprylmethylammonium nitrate (TCA.NO.sub.3). The diluent may be any inert, water-immiscible aromatic or aliphatic hydrocarbon such as diethylbenzene (DEB), diisopropylbenzene, xylene, dodecane or kerosene or a chlorinated carbon such as carbon tetrachloride, or a hydrogen bonding diluent such as a water-immiscible carboxylic acid. Although the extractant is quite specific for palladium and technetium values under the prescribed conditions, some neptunium and plutonium values which may be present in the feed and which are in the +4 valence state will be coextracted. Thus about 5% of the neptunium values and 90% of the plutonium values present in the feed solution will be coextracted with the palladium and technetium values. The palladium and technetium values are then separated from the coextracted actinide values during the stripping step. Any actinide or other values remaining in the extractant after stripping has removed the palladium and technetium values may be scrubbed by contact with an aqueous solution of 1.0 M formic acid containing 0.1 M nitric acid before being recycled. Contact of the loaded extractant with an aqueous scrub containing 1.0 to 0.1 M nitric acid, preferably 0.44 M, may be necessary to remove any fission products such as zirconium and niobium which may become entrapped in the extractant. The aqueous strip solution may vary from about 4 to 15 M, preferably about 8 M, in nitric acid in order to selectively strip the palladium and technetium values from the loaded extractant and away from any plutonium and neptunium values which may have been coextracted and which will remain in the extractant. The palladium and technetium values may be recovered from the nitric acid strip solution and separated from each other by any method known to those skilled in the art. For example, the strip solution containing the palladium and technetium values may be evaporated to recover the nitric acid. The residue may then be dissolved in H.sub.2 SO.sub.4 and treated with a reducing agent to reduce the palladium to the metal which is then filtered to recover the palladium metal while the remaining solution is heated to volatilize the technetium which is recovered for further processing or disposal. The extraction temperature is not critical and may be carried out over a range of from about 25.degree. to 75.degree. C. with 50.degree. C. generally preferred for the stripping step due to the decrease in the distribution ratio at the higher temperature. The extractant-feed contact temperature of 25.degree. C. is slightly preferred over higher temperatures in order to improve distribution ratios. In general contact times are not critical, although 30 seconds was found satisfactory to ensure phase mixing. The actual extraction operation can be carried out in batch or continuous operation, using, for example, simple mixer-settlers, direct or countercurrent flow, centrifugal contactors, liquid-liquid extraction in a chromatographic column or using other similar conventional type equipment known to those skilled in the art. Phase ratios can be varied depending upon engineering considerations and economic factors. The TCA.NO.sub.3 extractant is capable of recovering about 98% of the palladium and greater than 99.9% of the technetium present in the feed solution using four extraction and two scrub stages along with about 5% of the neptunium and 90% of the plutonium when present in the +4 valence state. Stripping with four stages recovered about 96% of the palladium and greater than 99.9% of the technetium, giving an overall palladium recovery from the feed solution of about 94%. The following examples are given to illustrate the process of the invention and are not to be taken as limiting the scope of the invention which is defined in the appended claims. EXAMPLE I A synthetic waste solution was prepared by mixing nitric acid solutions of salts of nonradioactive isotopes of fission products and rare earths. The quantities of fission product elements used were for liquid light-water reactor fuel irradiated to 33,000 Mwd/metric ton of heavy metal. The products from 1 metric ton of the fuel are assumed to be present in 5600 liters of a 2.9 M HNO.sub.3 (HAW waste stream) or 5900 liters of a 2.4 M HNO.sub.3 (EEW waste stream from from exhaustive tributyl phosphate extraction of the HAW waste stream). Separate portions of the synthetic waste were spiked with palladium and technetium for testing. A countercurrent extraction process was set up using 0.1 M TCMA NO.sub.3 in DEB, synthetic EEW waste solution which was 2.4 M in nitric acid and a scrub of 0.44 M HNO.sub.3. The temperature was 25.degree. C. The phase ratio of feed:organic scrub was 1.0:1.43:0.43. After four extraction and two scrub stages the extractant contained 98.0% of the palladium and 99.9% of the technetium present in the feed. EXAMPLE II The extractant from Example I containing the palladium and technetium values was contacted with 8 M HNO.sub.3 strip solution at 25.degree. C. with an organic to aqueous phase ratio of 1:1. After four stages of contact, about 4.0% of the palladium remained in the extractant as did about 7% of the technetium. This gave an overall palladium recovery from the feed solution of about 94'. As can be seen from the preceding discussion and examples, the method of the invention provides a simple and effective method for the recovery of palladium and technetium values from nuclear fuel reprocessing waste solutions. It has been calculated that, by using the method of the invention, about 1.2 kg of palladium could be recovered from the waste resulting from the reprocessing of 1 metric ton of liquid light-water reactor fuel irradiated to 33,000 Mwd. |
047769823 | summary | BACKGROUND OF THE INVENTION The invention "NAGIVA Disposal Process" is a method for the storage of radioactive material, and particularly for the temporary storage of radioactive nuclear fuel from nuclear reactors and non-reprocessed radioactive material. The spent fuel contains products which are highly radioactive and it is therefore necessary to keep it separated from living organisms. Spent non-reprocessed fuel can be stored temporarily for a short or long time pending a decision to reprocess the material or to move it to permanent storage. The heat evolution of the fuel rods increases when they are lifted out of the reactor and, in the present state of the art, they must be placed in a pool for cooling. After this initial cooling it has been proposed that the spent fuel be converted into solid form for temporary container storage. It has also been proposed that the fuel be mixed with liquid glass to solidify it. The present invention provides a safe and practical method for the handling and storage of spent, nonreprocessed fuel from nuclear reactors. |
abstract | Disclosed herein are a novel phosphate compound by which a copper ion can be dispersed in a high proportion in a synthetic resin, thereby providing excellent visible ray-transmitting property and performance that near infrared rays are absorbed with high efficiency, a preparation process thereof, a phosphate copper compound obtained from the phosphate compound and a preparation process thereof, and a near infrared ray-absorbing acrylic resin composition which has both excellent visible ray-transmitting property and near infrared rays absorption capability. |
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claims | 1. In a nuclear reactor having a reactor vessel wall and a nozzle penetrating the wall for delivering a fluid into the reactor, the nozzle including an end portion of a sleeve within the nozzle and having a groove, a connection with piping internal to said reactor vessel, comprising: a thermal sleeve extending from within the reactor vessel wall and having an end adjoining said sleeve end portion within said nozzle; a generally cylindrical collet having a plurality of circumferentially spaced fingers with radially directed flanges adjacent one end thereof, said flanges engaging in said groove; said collet being connected to said thermal sleeve adjacent an end thereof opposite said one collet end; and a retention sleeve secured to said thermal sleeve and extending about said fingers to retain said flanges in said groove. 2. A connection according to claim 1 wherein said thermal sleeve terminates on the interior of said vessel wall in a T-connection. claim 1 3. A connection according to claim 1 wherein said groove lies along a radially interior surface of said sleeve end portion, said flanges of said collet projecting generally radially outwardly for engagement in said groove. claim 1 4. A connection according to claim 3 wherein said collet and said thermal sleeve are screwthreaded to one another at said opposite end of said collet. claim 3 5. A connection according to claim 3 wherein said retention sleeve overlies said fingers on radially inward sides thereof, said retention sleeve being screwthreaded to said thermal sleeve. claim 3 6. A connection according to claim 1 including a sealing washer between said sleeve end portion and said thermal sleeve end adjoining said sleeve end portion. claim 1 7. A connection according to claim 1 wherein said groove lies along a radially interior surface of said sleeve end portion, said flanges of said collet projecting generally radially outwardly for engagement in said groove, said collet and said thermal sleeve being screwthreaded to one another at said opposite end of said collet, said retention sleeve overlying said fingers on radially inward sides thereof, said retention sleeve being screwthreaded to said thermal sleeve, and a sealing washer between said sleeve end portion and said thermal sleeve end adjoining said sleeve end portion. claim 1 8. A connection according to claim 1 including a plurality of adjustable wedge blocks between said thermal sleeve and an interior wall surface of said nozzle for supporting said thermal sleeve, retention sleeve and collet within said nozzle. claim 1 |
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summary | ||
description | This application is a continuation of U.S. patent application Ser. No. 13/830,380, filed Mar. 14, 2013, now allowed, and titled TARGET FOR EXTREME ULTRAVIOLET LIGHT SOURCE, which is incorporated herein by reference in its entirety. The disclosed subject matter relates to a target for an extreme ultraviolet (EUV) light source. Extreme ultraviolet (EUV) light, for example, electromagnetic radiation having wavelengths of around 50 nm or less (also sometimes referred to as soft x-rays), and including light at a wavelength of about 13 nm, can be used in photolithography processes to produce extremely small features in substrates, for example, silicon wafers. Methods to produce EUV light include, but are not necessarily limited to, converting a material that has an element, for example, xenon, lithium, or tin, with an emission line in the EUV range into a plasma state. In one such method, often termed laser produced plasma (LPP), the plasma can be produced by irradiating a target material, for example, in the form of a droplet, plate, tape, stream, or cluster of material, with an amplified light beam that can be referred to as a drive laser. For this process, the plasma is typically produced in a sealed vessel, for example, a vacuum chamber, and monitored using various types of metrology equipment. In one general aspect, a method includes releasing an initial target material toward a target location, the target material including a material that emits extreme ultraviolet (EUV) light when converted to plasma; directing a first amplified light beam toward the initial target material, the first amplified light beam having an energy sufficient to form a collection of pieces of target material from the initial target material, each of the pieces being smaller than the initial target material and being spatially distributed throughout a hemisphere shaped volume; and directing a second amplified light beam toward the collection of pieces to convert the pieces of target material to plasma that emits EUV light. Implementations can include one or more of the following features. The EUV light can be emitted from the hemisphere shaped volume in all directions. The EUV light can be emitted from the hemisphere shaped volume isotropically. The initial target material can include a metal, and the collection of pieces can include pieces of the metal. The metal can be tin. The hemisphere shaped volume can define a longitudinal axis along a direction that is parallel to a direction of propagation of the second amplified light beam and a transverse axis along a direction that is transverse to the direction of propagation of the second amplified light beam, and directing the second amplified light beam toward the collection of pieces can include penetrating into the hemisphere shaped volume along the longitudinal axis. The majority of the pieces in the collection of pieces can be converted to plasma. The first amplified light beam can be a pulse of light having a duration of 150 ps and a wavelength of 1 μm. The first amplified light beam can be a pulse of light having a duration of less than 150 ps and a wavelength of 1 μm. The first amplified light beam can include two pulses of light that are temporally separated from each other. The two pulses can include a first pulse of light and a second pulse of light, the first pulse of light having a duration of 1 ns to 10 ns, and the second pulse of light having a duration of less than 1 ns. The first and second amplified light beams can be beams of pulses. The first amplified light beam can have an energy that is insufficient to convert the target material to plasma, and the second amplified light beam have an energy that is sufficient to convert the target material to plasma. A density of the pieces of target material can increase along a direction that is parallel to a direction of propagation of the second amplified light beam. The pieces of target material in the hemisphere shaped volume can have a diameter of 1-10 μm. In another general aspect, a target system for an extreme ultraviolet (EUV) light source includes pieces of a target material distributed throughout a hemisphere shaped volume, the target material including a material that emits EUV light when converted to plasma; and a plane surface adjacent to the hemisphere shaped volume and defining a front boundary of the hemisphere shaped volume, the front boundary being positioned to face a source of an amplified light beam. The hemisphere shaped volume faces away from the source of the amplified light beam. Implementations can include one or more of the following features. The hemisphere shaped volume can have a cross-sectional diameter in a direction that is transverse to a direction of propagation of the amplified light beam, and a maximum of the cross-sectional diameter can be at the plane surface. A density of the pieces of the target material in the hemisphere shaped volume can increase along a direction that is parallel to a direction of propagation of the amplified light beam. At least some of the pieces can be individual pieces that are physically separated from each other. The hemisphere shaped volume can be irradiated with an amplified light beam having sufficient energy to convert the individual pieces of the target material to plasma, and the hemisphere shaped target can emit EUV light in all directions. The target material droplet can be part of a stream of target material droplets that are released from a nozzle, and the target system also can include a second target material droplet that is separate from the target material droplet and released from the nozzle after the target material droplet. The target system also can include the nozzle. The source of the amplified light beam can be an opening in a chamber that receives the target material droplet. In another general aspect, an extreme ultraviolet (EUV) light source includes a first source that produces a pulse of light; a second source that produces an amplified light beam; a target material delivery system; a chamber coupled to the target material delivery system; and a steering system that steers the amplified light beam toward a target location in the chamber that receives a target material droplet from the target material delivery system, the target material droplet including a material that emits EUV light after being converted to plasma. The target material droplet forms a target when struck by the pulse of light, the target including a hemisphere shaped volume having pieces of the target material throughout the volume, and a plane surface positioned between the hemisphere shaped volume and the second source. Implementations can include the following feature. The pulse of light can be 150 ps or less in duration. Implementations of any of the techniques described above may include a method, a process, a target, an assembly for generating a hemisphere shaped target, a device for generating a hemisphere shaped target, a kit or pre-assembled system for retrofitting an existing EUV light source, or an apparatus. The details of one or more implementations are set forth in the accompanying drawings and the description below. Other features will be apparent from the description and drawings, and from the claims. Referring to FIG. 1A, a perspective view of an exemplary target 5 is shown. The hemisphere shape and gently sloped density profile of the target 5 enables the target 5 to provide additional EUV light, increased conversion efficiency, and EUV light that is radially emitted outward from the target in all directions. The hemisphere shape can be a half of a sphere or any other portion of a sphere. However, the hemisphere shape can take other forms. For example, the hemisphere shape can be a partial oblate or prolate spheroid. The target 5 can be used in a laser produced plasma (LPP) extreme ultraviolet (EUV) light source. The target 5 includes a target material that emits EUV light when in a plasma state. The target material can be a target mixture that includes a target substance and impurities such as non-target particles. The target substance is the substance that is converted to a plasma state that has an emission line in the EUV range. The target substance can be, for example, a droplet of liquid or molten metal, a portion of a liquid stream, solid particles or clusters, solid particles contained within liquid droplets, a foam of target material, or solid particles contained within a portion of a liquid stream. The target substance, can be, for example, water, tin, lithium, xenon, or any material that, when converted to a plasma state, has an emission line in the EUV range. For example, the target substance can be the element tin, which can be used as pure tin (Sn); as a tin compound, for example, SnBr4, SnBr2, SnH4; as a tin alloy, for example, tin-gallium alloys, tin-indium alloys, tin-indium-gallium alloys, or any combination of these alloys. Moreover, in the situation in which there are no impurities, the target material includes only the target substance. The discussion below provides examples in which the target material is a target material droplet made of molten metal. In these examples, the target material is referred to as the target material droplet. However, the target material can take other forms. Irradiating the target material with an amplified light beam of sufficient energy (a “main pulse” or a “main beam”) converts the target material to plasma, thereby causing the target 5 to emit EUV light. FIG. 1B is a side view of the target 5. FIG. 1C is a front cross-sectional view of the target 5 along the line 1C-1C of FIG. 1A. The target 5 is a collection of pieces of target material 20 distributed in a hemisphere shaped volume 10. The target 5 is formed by striking a target material with one or more pulses of radiation (a “pre-pulse”) that precede (in time) the main pulse to transform the target material into a collection of pieces of target material. The pre-pulse is incident on a surface of the target material and the interaction between the initial leading edge of the pre-pulse and the target material can produce a plasma (that does not necessarily emit EUV light) at the surface of the target material. The pre-pulse continues to be incident on the created plasma and is absorbed by the plasma over a period that is similar to the temporal duration of the pre-pulse, about 150 picoseconds (ps). The created plasma expands as time passes. An interaction between the expanding plasma and the remaining portion of the target material can generate a shock wave that can act on the target material non-uniformly, with the center of the target material receiving the brunt of the shock wave. The shock wave can cause the center part of the target material to break into particles that expand in three dimensions. However, because the center part also experiences force in an opposite direction from the expanding plasma, a hemisphere of particles can be formed instead of a sphere. The pieces of target material 20 in the collection can be non-ionized pieces or segments of target material. That is, the pieces of target material 20 are not in a plasma state when the main pulse strikes the target 5. The pieces or segments of target material 20 can be, for example, a mist of nano- or micro-particles, separate pieces or segments of molten metal, or a cloud of atomic vapor. The pieces of target material 20 are bits of material that are distributed in a hemisphere shaped volume, but the pieces of target material 20 are not formed as a single piece that fills the hemisphere shaped volume. There can be voids between the pieces of target material 20. The pieces of target material 20 can also include non-target material, such as impurities, that are not converted to EUV light emitting plasma. The pieces of target material 20 are referred to as the particles 20. Individual particles 20 can be 1-10 μm in diameter. The particles 20 can be separated from each other. Some or all of the particles 20 can have physical contact with another particle. The hemisphere shaped volume 10 has a plane surface 12 that defines a front boundary of the hemisphere shaped volume 10, and a hemisphere shaped portion 14 that extends away from the plane surface in a direction “z.” When used in a EUV light source, a normal 15 of the plane surface 12 faces an oncoming amplified light beam 18 that propagates in the “z” direction. The plane surface 12 can be transverse to direction of propagation of the oncoming amplified light beam 18, as shown in FIGS. 1A and 1B, or the plane surface 12 can be angled relative to the oncoming beam 18. Referring also to FIG. 1D, the particles 20 are distributed in the hemisphere shaped volume 10 with an exemplary density gradient 25 that has a minimum at the plane surface 12 of the target 5. The density gradient 25 is a measure of the density of particles in a unit volume as a function of position within the hemisphere shaped volume 10. The density gradient 25 increases within the target 5 in the direction of propagation (“z”) of the main pulse, and the maximum density is on a side of the target 5 opposite from the side of the plane surface 12. The placement of the minimum density at the plane surface 12 and the gradual increase in the density of the particles 20 results in more of the main pulse being absorbed by the target 5, thereby producing more EUV light and providing a higher conversion efficiency (CE) for a light source that uses the target 5. In effect, this means that enough energy is provided to the target 5 by the main pulse to ionize the target 5 efficiently to produce ionized gas. Having the minimum density at or near the plane surface 12 can increase the absorption of main beam by the target 5 in at least two ways. First, the minimum density of the target 5 is lower than the density of a target that is a continuous piece of target material (such as a target material droplet made of molten tin or a disk shaped target of molten tin). Second, the density gradient 25 places the lowest density portions of the target 5 at the plane surface 12, which is the plane where the amplified light beam 18 enters the target 5. Because the density of the particles 20 increases in the “z” direction, most, or all, of the amplified light beam 18 is absorbed by particles 20 that are closer to the plane surface 12 before the beam 18 reaches and is reflected from a region of high density within the target 5. Therefore, compared to a target that has a region of high density closer to the point of impact with the amplified light beam 18, the target 5 absorbs a higher portion of the energy in the amplified light beam 18. The absorbed light beam 18 is used to convert the particles 20 to plasma by ionization. Thus, the density gradient 25 also enables more EUV light to be generated. Second, the target 5 presents a larger area or volume of particles to the main pulse, enabling increased interaction between the particles 20 and the main pulse. Referring to FIGS. 1B and 1C, the target 5 defines a length 30 and a cross-section width 32. The length 30 is the distance in the “z” direction along which the hemisphere portion 14 extends. The length 30 is longer than a similar length in a target that is a continuous piece of target material because the hemisphere shaped volume 10 has a longer extent in the “z” direction. A continuous piece of target material is one that has a uniform, or nearly uniform, density in the direction of propagation of the amplified light beam 18. Additionally, because of the gradient 25, the amplified light beam 18 propagates further into the target 5 in the “z” direction while reflections are kept low. The relatively longer length 30 provides a longer plasma scale length. The plasma scale length for the target 5 can be, for example, 200 μm, which can be twice the value of the plasma scale length for a disk shaped target made from a continuous piece of target material. A longer plasma scale length allows more of the amplified light beam 18 to be absorbed by the target 5. The cross-section width 32 is the width of the plane surface 12 of the target 5. The cross-section interaction width 32 can be, for example, about 200 μm, when the target 5 is generated with a pre-pulse that occurs 1000 ns prior to the main pulse, and the pre-pulse has a duration of 150 ps and a wavelength of 1 μm. The cross-section interaction width 32 can be about 300 μm when the target 5 is generated with a 50 ns duration CO2 laser pulse. A pulse of light or radiation has a temporal duration for an amount of time during which a single pulse has an intensity of 50% or more of the maximum intensity of the pulse. This duration can also be referred to as the full width at half maximum (FWHM). Like the length 30, the cross-section width 32 is larger than a similar dimension in a target that is made of a continuous, coalesced piece of target material (such as a target material droplet made of coalesced molten metal). Because both the interaction length 30 and the interaction width 32 are relatively larger than other targets, the target 5 also has a larger EUV light emitting volume. The light emitting volume is the volume in which the particles 20 are distributed and can be irradiated by the amplified light beam 18. For example, the target 5 can have a light emitting volume that is twice that of a disk shaped target of molten metal. The larger light emitting volume of the target 5 results in generation of greater amounts of EUV light and a higher conversion efficiency (CE) because a higher portion of the target material (the particles 20) in the target 5 is presented to and irradiated by the amplified light beam 18 and subsequently converted to plasma. Further, the target 5 does not have a wall or high density region at a back side 4 that could prevent EUV light from being emitted in the direction of propagation of the main pulse. Thus, the target 5 emits EUV radially outward in all directions, allowing more EUV light to be collected and further increasing the collection efficiency. Moreover, radially isotropic EUV light or substantially isotropic EUV light can provide improved performance for a lithography tool (not shown) that uses the EUV light emitted from the target 5 by reducing the amount of calibration needed for the tool. For example, if uncorrected, unexpected spatial variations in EUV intensity can cause overexposure to a wafer imaged by the lithography tool. The target 5 can minimize such calibration concerns by emitting EUV light uniformly in all directions. Moreover, because the EUV light is radially uniform, errors in alignment and fluctuations in alignment within the lithography tool or upstream from the lithography tool do not also cause variations in intensity. FIGS. 2A, 2B, and 3A-3C show exemplary LPP EUV light sources in which the target 5 can be used. Referring to FIG. 2A, an LPP EUV light source 100 is formed by irradiating a target mixture 114 at a target location 105 with an amplified light beam 110 that travels along a beam path toward the target mixture 114. The target location 105, which is also referred to as the irradiation site, is within an interior 107 of a vacuum chamber 130. When the amplified light beam 110 strikes the target mixture 114, a target material within the target mixture 114 is converted into a plasma state that has an element with an emission line in the EUV range to produce EUV light 106. The created plasma has certain characteristics that depend on the composition of the target material within the target mixture 114. These characteristics can include the wavelength of the EUV light produced by the plasma and the type and amount of debris released from the plasma. The light source 100 also includes a target material delivery system 125 that delivers, controls, and directs the target mixture 114 in the form of liquid droplets, a liquid stream, solid particles or clusters, solid particles contained within liquid droplets or solid particles contained within a liquid stream. The target mixture 114 can also include impurities such as non-target particles. The target mixture 114 is delivered by the target material delivery system 125 into the interior 107 of the chamber 130 and to the target location 105. The light source 100 includes a drive laser system 115 that produces the amplified light beam 110 due to a population inversion within the gain medium or mediums of the laser system 115. The light source 100 includes a beam delivery system between the laser system 115 and the target location 105, the beam delivery system including a beam transport system 120 and a focus assembly 122. The beam transport system 120 receives the amplified light beam 110 from the laser system 115, and steers and modifies the amplified light beam 110 as needed and outputs the amplified light beam 110 to the focus assembly 122. The focus assembly 122 receives the amplified light beam 110 and focuses the beam 110 to the target location 105. In some implementations, the laser system 115 can include one or more optical amplifiers, lasers, and/or lamps for providing one or more main pulses and, in some cases, one or more pre-pulses. Each optical amplifier includes a gain medium capable of optically amplifying the desired wavelength at a high gain, an excitation source, and internal optics. The optical amplifier may or may not have laser mirrors or other feedback devices that form a laser cavity. Thus, the laser system 115 produces an amplified light beam 110 due to the population inversion in the gain media of the laser amplifiers even if there is no laser cavity. Moreover, the laser system 115 can produce an amplified light beam 110 that is a coherent laser beam if there is a laser cavity to provide enough feedback to the laser system 115. The term “amplified light beam” encompasses one or more of: light from the laser system 115 that is merely amplified but not necessarily a coherent laser oscillation and light from the laser system 115 that is amplified (externally or within a gain medium in the oscillator) and is also a coherent laser oscillation. The optical amplifiers in the laser system 115 can include as a gain medium a filling gas that includes CO2 and can amplify light at a wavelength of between about 9100 and about 11000 nm, and in particular, at about 10.6 μm, at a gain greater than or equal to 1000. In some examples, the optical amplifiers amplify light at a wavelength of 10.59 μm. Suitable amplifiers and lasers for use in the laser system 115 can include a pulsed laser device, for example, a pulsed, gas-discharge CO2 laser device producing radiation at about 9300 nm or about 10600 nm, for example, with DC or RF excitation, operating at relatively high power, for example, 10 kW or higher and high pulse repetition rate, for example, 50 kHz or more. The optical amplifiers in the laser system 115 can also include a cooling system such as water that can be used when operating the laser system 115 at higher powers. FIG. 2B shows a block diagram of an example drive laser system 180. The drive laser system 180 can be used as the drive laser system 115 in the source 100. The drive laser system 180 includes three power amplifiers 181, 182, and 183. Any or all of the power amplifiers 181, 182, and 183 can include internal optical elements (not shown). The power amplifiers 181, 182, and 183 each include a gain medium in which amplification occurs when pumped with an external electrical or optical source. Light 184 exits from the power amplifier 181 through an output window 185 and is reflected off a curved mirror 186. After reflection, the light 184 passes through a spatial filter 187, is reflected off of a curved mirror 188, and enters the power amplifier 182 through an input window 189. The light 184 is amplified in the power amplifier 182 and redirected out of the power amplifier 182 through an output window 190 as light 191. The light 191 is directed toward the amplifier 183 with fold mirrors 192 and enters the amplifier 183 through an input window 193. The amplifier 183 amplifies the light 191 and directs the light 191 out of the amplifier 183 through an output window 194 as an output beam 195. A fold mirror 196 directs the output beam 195 upwards (out of the page) and toward the beam transport system 120. The spatial filter 187 defines an aperture 197, which can be, for example, a circular opening through which the light 184 passes. The curved mirrors 186 and 188 can be, for example, off-axis parabola mirrors with focal lengths of about 1.7 m and 2.3 m, respectively. The spatial filter 187 can be positioned such that the aperture 197 coincides with a focal point of the drive laser system 180. The example of FIG. 2B shows three power amplifiers. However, more or fewer power amplifiers can be used. Referring again to FIG. 2A, the light source 100 includes a collector mirror 135 having an aperture 140 to allow the amplified light beam 110 to pass through and reach the target location 105. The collector mirror 135 can be, for example, an ellipsoidal mirror that has a primary focus at the target location 105 and a secondary focus at an intermediate location 145 (also called an intermediate focus) where the EUV light can be output from the light source 100 and can be input to, for example, an integrated circuit beam positioning system tool (not shown). The light source 100 can also include an open-ended, hollow conical shroud 150 (for example, a gas cone) that tapers toward the target location 105 from the collector mirror 135 to reduce the amount of plasma-generated debris that enters the focus assembly 122 and/or the beam transport system 120 while allowing the amplified light beam 110 to reach the target location 105. For this purpose, a gas flow can be provided in the shroud that is directed toward the target location 105. The light source 100 can also include a master controller 155 that is connected to a droplet position detection feedback system 156, a laser control system 157, and a beam control system 158. The light source 100 can include one or more target or droplet imagers 160 that provide an output indicative of the position of a droplet, for example, relative to the target location 105 and provide this output to the droplet position detection feedback system 156, which can, for example, compute a droplet position and trajectory from which a droplet position error can be computed either on a droplet by droplet basis or on average. The droplet position detection feedback system 156 thus provides the droplet position error as an input to the master controller 155. The master controller 155 can therefore provide a laser position, direction, and timing correction signal, for example, to the laser control system 157 that can be used, for example, to control the laser timing circuit and/or to the beam control system 158 to control an amplified light beam position and shaping of the beam transport system 120 to change the location and/or focal power of the beam focal spot within the chamber 130. The target material delivery system 125 includes a target material delivery control system 126 that is operable in response to a signal from the master controller 155, for example, to modify the release point of the droplets as released by a target material supply apparatus 127 to correct for errors in the droplets arriving at the desired target location 105. Additionally, the light source 100 can include a light source detector 165 that measures one or more EUV light parameters, including but not limited to, pulse energy, energy distribution as a function of wavelength, energy within a particular band of wavelengths, energy outside of a particular band of wavelengths, and angular distribution of EUV intensity and/or average power. The light source detector 165 generates a feedback signal for use by the master controller 155. The feedback signal can be, for example, indicative of the errors in parameters such as the timing and focus of the laser pulses to properly intercept the droplets in the right place and time for effective and efficient EUV light production. The light source 100 can also include a guide laser 175 that can be used to align various sections of the light source 100 or to assist in steering the amplified light beam 110 to the target location 105. In connection with the guide laser 175, the light source 100 includes a metrology system 124 that is placed within the focus assembly 122 to sample a portion of light from the guide laser 175 and the amplified light beam 110. In other implementations, the metrology system 124 is placed within the beam transport system 120. The metrology system 124 can include an optical element that samples or re-directs a subset of the light, such optical element being made out of any material that can withstand the powers of the guide laser beam and the amplified light beam 110. A beam analysis system is formed from the metrology system 124 and the master controller 155 since the master controller 155 analyzes the sampled light from the guide laser 175 and uses this information to adjust components within the focus assembly 122 through the beam control system 158. Thus, in summary, the light source 100 produces an amplified light beam 110 that is directed along the beam path to irradiate the target mixture 114 at the target location 105 to convert the target material within the mixture 114 into plasma that emits light in the EUV range. The amplified light beam 110 operates at a particular wavelength (that is also referred to as a source wavelength) that is determined based on the design and properties of the laser system 115. Additionally, the amplified light beam 110 can be a laser beam when the target material provides enough feedback back into the laser system 115 to produce coherent laser light or if the drive laser system 115 includes suitable optical feedback to form a laser cavity. Referring to FIG. 3A, a top plan view of an exemplary optical imaging system 300 is shown. The optical imaging system 300 includes an LPP EUV light source 305 that provides EUV light to a lithography tool 310. The light source 305 can be similar to, and/or include some or all of the components of, the light source 100 of FIGS. 2A and 2B. As discussed below, the target 5 can be used in the light source 305 to increase the amount of light emitted by the light source 305. The light source 305 includes a drive laser system 315, an optical element 322, a pre-pulse source 324, a focusing assembly 326, a vacuum chamber 340, and an EUV collecting optic 346. The EUV collecting optic 346 directs the EUV light emitted by converting the target 5 to plasma to the lithography tool 310. The EUV collection optic 346 can be the mirror 135 (FIG. 2A). Referring also to FIGS. 3B-3E, the light source 305 also includes a target material delivery apparatus 347 that produces a stream of target material 348. The stream of target material 348 can include target material in any form, such as liquid droplets, a liquid stream, solid particles or clusters, solid particles contained within liquid droplets or solid particles contained within a liquid stream. In the discussion below, the target material stream 348 includes target material droplets 348. In other examples, the target material stream can include target material of other forms. The target material droplets travel along the “x” direction from the target material delivery apparatus 347 to a target location 342 in the vacuum chamber 340. The drive laser system 315 produces an amplified light beam 316. The amplified light beam 316 can be similar to the amplified light beam 18 of FIGS. 1A-1C, or the amplified light beam 110 of FIGS. 2A and 2B, and can be referred to as a main pulse or a main beam. The amplified light beam 316 has an energy sufficient to convert the particles 20 in the target 5 into plasma that emits EUV light. In some implementations, the drive laser system 315 can be a dual-stage master oscillator and power amplifier (MOPA) system that uses carbon dioxide (CO2) amplifiers within the master oscillator and power amplifier, and the amplified light beam 316 can be a 130 ns duration, 10.6 μm wavelength CO2 laser light pulse generated by the MOPA. In other implementations, the amplified light beam 316 can be a CO2 laser light pulse that has a duration of less than 50 ns. The pre-pulse source 324 emits a pulse of radiation 317. The pre-pulse source 324 can be, for example, a Q-switched Nd:YAG laser, and the pulse of radiation 317 can be a pulse from the Nd.YAG laser. The pulse of radiation 317 can have a duration of 10 ns and a wavelength of 1.06 μm, for example. In the example shown in FIG. 3A, the drive laser system 315 and the pre-pulse source 324 are separate sources. In other implementations, they can be a part of the same source. For example, both the pulse of radiation 317 and the amplified light beam 316 can be generated by the drive laser system 315. In such an implementation, the drive laser system 315 can include two CO2 seed laser subsystems and one amplifier. One of the seed laser subsystems can produce an amplified light beam having a wavelength of 10.26 μm, and the other seed laser subsystem can produce an amplified light beam having a wavelength of 10.59 μm. These two wavelengths can come from different lines of the CO2 laser. Both amplified light beams from the two seed laser subsystems are amplified in the same power amplifier chain and then angularly dispersed to reach different locations within the chamber 340. In one example, the amplified light beam with the wavelength of 10.26 μm is used as the pre-pulse 317, and the amplified light beam with the wavelength of 10.59 μm is used as the amplified light beam 316. In other examples, other lines of the CO2 laser, which can generate different wavelengths, can be used to generate the two amplified light beams (one of which is the pulse of radiation 317 and the other of which is the amplified light beam 316). Referring again to FIG. 3A, the optical element 322 directs the amplified light beam 316 and the pulse of radiation 317 from the pre-pulse source 324 to the chamber 340. The optical element 322 is any element that can direct the amplified light beam 316 and the pulse of radiation 317 along similar paths and deliver the amplified light beam 316 and the pulse of radiation 317 to the chamber 340. In the example shown in FIG. 3A, the optical element 322 is a dichroic beamsplitter that receives the amplified light beam 316 and reflects it toward the chamber 340. The optical element 322 receives the pulse of radiation 317 and transmits the pulses toward the chamber 340. The dichroic beamsplitter has a coating that reflects the wavelength(s) of the amplified light beam 316 and transmits the wavelength(s) of the pulse of radiation 317. The dichroic beamsplitter can be made of, for example, diamond. In other implementations, the optical element 322 is a mirror that defines an aperture (not shown). In this implementation, the amplified light beam 316 is reflected from the mirror surface and directed toward the chamber 340, and the pulses of radiation pass through the aperture and propagate toward the chamber 340. In still other implementations, a wedge-shaped optic (for example, a prism) can be used to separate the main pulse 316, the pre-pulse 317, and the pre-pulse 318 into different angles, according to their wavelengths. The wedge-shaped optic can be used in addition to the optical element 322, or it can be used as the optical element 322. The wedge-shaped optic can be positioned just upstream (in the “−z” direction) of the focusing assembly 326. Additionally, the pulse of radiation 317 can be delivered to the chamber 340 in other ways. For example, the pulse 317 can travel through optical fibers that deliver the pulses 317 and 318 to the chamber 340 and/or the focusing assembly 326 without the use of the optical element 322 or other directing elements. In these implementations, the fiber can bring the pulse of radiation 317 directly to an interior of the chamber 340 through an opening formed in a wall of the chamber 340. Regardless of how the amplified light beam 316 and the pulses of radiation 317 and 318 are directed toward the chamber 340, the amplified light beam 316 is directed to a target location 342 in the chamber 340. The pulse of radiation 317 is directed to a location 341. The location 341 is displaced from the target location 342 in the “−x” direction. The amplified light beam 316 from the drive laser system 315 is reflected by the optical element 322 and propagates through the focusing assembly 326. The focusing assembly 326 focuses the amplified light beam 316 onto the target location 342. The pulse of radiation 317 from the pre-pulse source 324 passes through the optical element 322 and through the focusing assembly 216 to the chamber 340. The pulse of radiation 317 propagates to the location 341 in the chamber 340 that is in the “−x” direction relative to the target location 342. The displacement between the location 342 and the location 341 allows the pulse of radiation 317 to irradiate a target material droplet to convert the droplet to the hemisphere shaped target 5 before the target 5 reaches the target location 342 without substantially ionizing the target 5. In this manner, the hemisphere shaped target 5 can be a pre-formed target that is formed at a time before the target 5 enters the target location 342. In greater detail and referring also to FIGS. 3B and 3C, the target location 342 is a location inside of the chamber 340 that receives the amplified light beam 316 and a droplet in the stream of target material droplets 348. The target location 342 is also a location that is positioned to maximize an amount of EUV light delivered to the EUV collecting optic 346. For example, the target location 342 can be at a focal point of the EUV collecting optic 346. FIGS. 3B and 3C show top views of the chamber 340 at times t1 and t2, respectively, with time=t1 occurring before time=t2. In the example shown in FIGS. 3B and 3C, the amplified light beam 316 and the pulsed beam of radiation 317 occur at different times and are directed toward different locations within the chamber 340. The stream 348 travels in the “x” direction from the target material supply apparatus 347 to the target location 342. The stream of target material droplets 348 includes the target material droplets 348a, 348b, and 348c. At a time=t1 (FIG. 3B), the target material droplets 348a and 348b travel in the “x” direction from the target material supply apparatus 347 to the target location 342. The pulsed beam of radiation 317 irradiates the target material droplet 348a at the time “t1” at the location 341, which is displaced in the “−x” direction from the target location 342. The pulsed beam of radiation 317 transforms the target material droplet 348b into the hemisphere target 5. At the time=t2 (FIG. 3C), the amplified light beam 316 irradiates the target 5 and converts the particles 20 of target material into EUV light. Referring to FIG. 4, an exemplary process 400 for generating the hemisphere shaped target 5 is shown. The process 400 can be performed using the target material supply apparatus 127 (FIG. 2A) or the target material supply apparatus 347 (FIGS. 3B-3E). An initial target material is released toward a target location (410). Referring also to FIGS. 3B and 3C, the target material droplet 348a is released from the target material supply apparatus 347 and travels toward the target location 342. The initial target material is a target material droplet that emerges or is released from the target material supply apparatus 347 as a droplet. The initial target material droplet is a droplet that has not been transformed or altered by a pre-pulse. The initial target material droplet can be a coalesced sphere or substantially spherical piece of molten metal that can be considered as a continuous piece of target material. The target material droplet 348a prior to the time “t1” is an example of an initial target material in this example. A first amplified light beam is directed toward the initial target material to generate a collection of pieces of target material distributed in a hemisphere shaped volume (420) without substantially ionizing the initial target material. The collection of pieces of target material can be the particles 20 (FIGS. 1A-1C), which are distributed in the hemisphere shaped volume 10. The first amplified light beam can be the pulsed light beam 317 emitted from the source 324 (FIGS. 3A, 3D, and 3E). The first amplified light beam can be referred to as the “pre-pulse.” The first amplified light beam is a pulse of light that has an energy and/or pulse duration sufficient to transform the target material droplet 348a from a droplet that is a continuous or coalesced segment or piece of molten target material into the target 5, which is a hemisphere shaped distribution of particles 20. The first amplified light beam can be, for example, a pulse of light that has a duration of 130 ns and a wavelength of 1 μm. In another example, first amplified light beam can be a pulse of light that has a duration of 150 ps, a wavelength of 1 μm, an energy of 10 milliJoules (mJ), a 60 μm focal spot, and an intensity of 2×1012 W/cm2. The energy, wavelength, and/or duration of the first amplified light beam are selected to transform the target material droplet into the hemisphere shaped target 5. In some implementations, the first amplified light beam includes more than one pulse. For example, the first amplified light beam can include two pulses, separated from each other in time, and having different energies and durations. FIG. 9 shows an example in which the first amplified light beam includes more than one pulse. Further, the first amplified light beam can be a single pulse that has a shape (energy or intensity as a function of time) to provide an effect that is similar to that achieved by multiple pre-pulses. The second amplified light beam has energy sufficient to convert the target material droplet into a collection of pieces. A second amplified light beam is directed toward the collection of pieces to convert the particles 20 to plasma that emits EUV light (430). The second amplified light beam can be referred to as the “main pulse.” The amplified light beam 316 of FIG. 3A is an example of a second amplified light beam. The amplified light beam 316 has sufficient energy to convert all or most of the particles 20 of the target 5 into plasma that emits EUV light. Referring to FIG. 5, an example of a waveform 500 that can be used to transform a target material droplet into a hemisphere shaped target is shown. FIG. 5 shows the amplitude of the waveform 500 as a function of time. The waveform 500 shows a representation of the collection of amplified light beams that strike a particular target material droplet in a single cycle of operation of the EUV light source. A cycle of operation is a cycle that emits a pulse or burst of EUV light. The waveform 500 also can be referred to as a laser train 500 or a pulse train 500. In the waveform 500, the collection of amplified light beams includes a pre-pulse 502 and a main pulse 504. The pre-pulse 502 begins at time t=0, and the main pulse 504 begins at a time t=1000 ns. In other words, the main pulse 504 occurs 1000 ns after the pre-pulse 502. In the waveform 500, the pre-pulse 502 can have a wavelength of 1.0 μm, a duration of 150 ps, an energy of 10 mJ, a focal spot 60 μm in diameter, and an intensity of 2×1012 W/cm2. This is an example of one implementation of the waveform 500. Other parameter values can be used, and the parameter values of the pre-pulse 502 can vary by a factor of 5 as compared to this example. For example, in some implementations, the pre-pulse 502 can have a duration of 5-20 ps, and an energy of 1-20 mJ. The main pulse 504 can have a wavelength of 5-11 μm, a pulse duration of 15-200 ns, a focus spot size of 50-300 μm, and an intensity of 3×109 to 8×1010 W/cm2. For example, the main pulse 504 can have a wavelength of 10.59 μm and a pulse duration of 130 ns. In another example, the main pulse can have a wavelength of 10.59 μm and a pulse duration of 50 ns or less. In addition to the times t=0 and t=1000 ns, the times t1-t4 are also shown on the time axis. The time t1 is shortly before the pre-pulse 502 occurs. The time t2 is after the pre-pulse 502 ends and before the main pulse 504 begins. The time t3 occurs shortly before the main pulse 504, and the time t4 occurs after the main pulse 504. The times t1-t4 are used in the discussion below, with respect to FIGS. 6A-6D, of a transformation of a target material droplet to a hemisphere shaped target using the waveform 500. Although the waveform 500 is shown as a continuous waveform in time, the pre-pulse 502 and main pulse 504 that make up the waveform 500 can be generated by different sources. For example, the pre-pulse 502 can be a pulse of light generated by the pre-pulse source 324, and the main pulse 504 can be generated by the drive laser system 315. When the pre-pulse 502 and the main pulse 504 are generated by separate sources that are in different locations relative to the chamber 340 (FIG. 3A), the pre-pulse 502 and the main pulse 504 can be directed to the chamber 340 with the optical element 322. Referring also to FIGS. 6A-6D, interactions between a target material droplet 610 and the waveform 500 that transform the target material droplet 610 into a hemisphere shaped target 614 are shown. A target supply apparatus 620 releases a stream of target material droplets 622 from an orifice 624. The target material droplets 622 travel in the “x” direction toward a target location 626. FIGS. 6A-6D show the target supply apparatus 620 and the droplet stream 622 at the times t=t1, t=t2, t=t3, and t=t4, respectively. FIG. 5 also shows the times t=t1 through t=t4 relative to the waveform 500. Referring to FIG. 6A, the pre-pulse 502 approaches the target material droplet 610. The target material droplet 610 is a droplet of target material. The target material can be molten metal, such as molten tin. The target material droplet 610 is a continuous segment or piece of target material that has a uniform density in the “z” direction (the direction of propagation of the waveform 500). The cross-sectional size of a target material droplet can be, for example, between 20-40 μm. FIG. 7A shows the density of the target material droplet 610 as a function of position along the “z” direction. As shown in FIG. 7A, compared to free space, the target material droplet 610 presents a steep increase in density to the waveform 500. The interaction between the pre-pulse 502 and the target material droplet 610 forms a collection of pieces of target material 612 that are arranged in a geometric distribution. The pieces of target material 612 are distributed in a hemisphere shaped volume that extends outward from a plane surface 613 in the “x” and “z” direction. The pieces of target material 612 can be a mist of nano- or micro-particles, separate pieces of molten metal, or a cloud of atomic vapor. The pieces of target material can be 1-10 μm in diameter. A purpose of the interaction between the pre-pulse 502 and the target material droplet 610 is to form a target that has a spatial extent that is larger than the diameter of the main pulse 504 but without substantially ionizing the target. In this manner, as compared to a smaller target, the created target presents more target material to the main beam and can use more of the energy in the main pulse 504. The pieces of target material 612 have a spatial extent in the x-y and x-z planes that is larger than the extent of the target material droplet 610 in the x-y and x-z planes. As time passes, the collection of pieces 612 travels in the “x” direction toward the target location 626. The collection of pieces 612 also expands in the “x” and “z” directions while moving toward the target location 626. The amount of spatial expansion depends on the duration and intensity of the pre-pulse 502, as well as the amount of time over which the collection of pieces 612 is allowed to expand. The density of the collection of pieces 612 decreases as time passes, because the pieces spread out. A lower density generally allows an oncoming light beam to be absorbed by more of the material in a volume, and a high density can prevent or reduce the amount of light absorbed and the amount of EUV light produced. A wall of high density through which light cannot pass or be absorbed and is instead reflected is the “critical density.” However, the most efficient absorption by a material can occur near but below the critical density. Thus, it can be beneficial to for the target 614 to be formed by allowing the collection of pieces 614 to expand over a finite time period that is long enough to allow the collection of pieces 613 to expand spatially without being so long that the density of the pieces decreases to a point where the efficiency of laser absorption decreases. The finite time period can be the time between the pre-pulse 502 and the main pulse 504 and can be, for example, about 1000 ns. Referring also to FIGS. 8A and 8B, examples of the spatial expansion of the collection of pieces 612 as a function of time after the pre-pulse strikes a target material droplet for two different pre-pulses are shown, with FIG. 8A showing an example for a pre-pulse similar to the pre-pulse 502. The time after the pre-pulse strikes a target material droplet can be referred to as the delay time. FIG. 8A shows the size of the collection of pieces 612 as a function of delay time when the pre-pulse has a wavelength of 1.0 μm, a duration of 150 ps, an energy of 10 mJ, a focal spot 60 μm in diameter, and an intensity of 2×1012 W/cm2. FIG. 8B shows the size of the collection of pieces 612 as a function of delay time when the pre-pulse has a wavelength of 1.0 μm, a duration of 150 ps, an energy of 5 mJ, a focal spot 60 μm in diameter, and an intensity of 1×1012 W/cm2. Comparing FIG. 8A to FIG. 8B shows that the collection of pieces 612 expands more rapidly in the vertical directions (x/y) when struck by the more energetic and more intense pre-pulse of FIG. 8A. Referring again to, FIG. 6C the target material droplet 610 and the stream of droplets 622 are shown at the time=t3. At the time=t3, the collection of target material pieces 612 has expanded into the hemisphere shaped target 614 and arrives at the target location 626. The mail pulse 504 approaches the hemisphere shaped target 614. FIG. 7B shows the density of the hemisphere shaped target 614 just before the main pulse 504 reaches the target 614. The density is expressed as density gradient 705 that is density of particles 612 in the target 614a function of position in the “z” direction, with z=0 being the plane surface 613. As shown, the density is minimum at the plane surface 613 and increases in the “z” direction. Because the density is at a minimum at the plane surface 613, and the minimum density is lower than that of the target material droplet 610, compared to the target material droplet 610, the main pulse 504 enters the target 614 relatively easily (less of the main pulse 504 is absorbed). As the main beam 504 travels in the target 614, the particles 612 absorb the energy in the main beam 504 and are converted to plasma that emits EUV light. The density of the target 614 increases in the direction of propagation “z” and can increase to an amount where the main beam 504 cannot penetrate and is instead reflected. The location in the target 614 with such a density is the critical surface (not shown). However, because the density of the target 614 is initially relatively low, a majority, most, or all, of the main beam 504 is absorbed by the particles 615 prior to reaching the critical surface. Thus, the density gradient provides a target that is favorable for EUV light generation. Additionally, because the hemisphere shaped target 614 does not have a wall of high density, the EUV light 618 is radially emitted from the target 614 in all directions. This is unlike a disk shaped target or other target with a higher density, where the interaction between the main pulse and the target generates plasma and a shock wave that blows off some of the target as dense target material in the direction of propagation of the main pulse 504. The blown off material reduces the amount of material available for conversion to plasma and also absorbs some of the EUV light emitted in the forward (“z”) direction. As a result, the EUV light is emitted over 2π steradians, and only half of the EUV light is available for collection. However, the hemisphere shaped target 614 allows collection of EUV light in all directions (4π steradians). After the main pulse 504 irradiates the hemisphere shaped target 614, there is negligible or no dense target material left in the hemisphere shaped target 614, and the EUV light 618 is able to escape the hemisphere shaped target 614 radially in all directions. In effect, there is very little matter present to block or absorb the EUV light 618 and prevent it from escaping. In some implementations, the EUV light 618 can be isotropic (uniform intensity) in all directions. Thus, the hemisphere shaped target 614 provides additional EUV light by allowing EUV light 619, which is generated in the forward direction, to escape the hemisphere shaped target 614. Because the hemisphere shaped target 614 emits EUV light in all directions, a light source that uses the hemisphere shaped target 614 can have increased conversion efficiency (CE) as compared to a light source that uses a target that emits light over only 2π steradians. For example, when measured over 2π steradians, a hemisphere shaped target that is irradiated with a MOPA CO2 main pulse having a duration of 130 ns can have a conversion efficiency of 3.2%, meaning that 3.2% of the CO2 main pulse is converted into EUV light. When the hemisphere shaped target is irradiated with a MOPA CO2 main pulse having a duration of 50 ns, the conversion efficiency is 5% based on measuring the EUV light emitted over 2π steradians. When the EUV light is measured over 4π steradians, the conversion efficiency is doubled because the amount of EUV light emitted from the target is doubled. Thus, the conversion efficiency for the two main pulses becomes 6.4% and 10%, respectively. In the example of FIGS. 6A-6D, the waveform 500, which has a delay time of 1000 ns between the pre-pulse 502 and the main pulse 504, is used to transform the target material droplet 610 into the hemisphere shaped target 614. However, other waveforms with other delay times can be used for the transformation. For example, the delay between the pre-pulse 502 and the main pulse 504 can be between 200 ns and 1600 ns. A longer delay time provides a target with a larger spatial extent (volume) and a lower density of target material. A shorter delay time provides a target with a smaller spatial extent (volume) and a higher density of target material. FIG. 9 shows another exemplary waveform 900 that, when applied to a target material droplet, transforms the target material droplet to a hemisphere shaped target. The waveform 900 includes a first pre-pulse 902, a second pre-pulse 904, and a main pulse 906. The first pre-pulse 902 and the second pre-pulse 904 can be collectively considered as the first amplified light beam, and the main pulse 906 can be considered as the second amplified light beam. The first pre-pulse 902 occurs at time t=0, the second pre-pulse 904 occurs 200 ns later at time t=200 ns, and the main pulse 906 occurs at time t=1200 ns, 1200 ns after the first pre-pulse 902. In the example of FIG. 9, the first pre-pulse 502 has a duration of 1-10 ns, and the second pre-pulse 504 has a duration of less than 1 ns. For example, the duration of the second pre-pulse 504 can be 150 ps. The first pre-pulse 502 and the second pre-pulse 504 can have a wavelength of 1 μm. The main pulse 506 can be a pulse from a CO2 laser that has a wavelength of 10.6 μm and a duration of 130 ns or 50 ns. FIGS. 10A-10D show the waveform 900 interacting with a target material droplet 1010 to transform the target material droplet 1010 into a hemisphere shaped target 1018. FIGS. 10A-10D show times t=t1 to t4, respectively. Times t=t1 to t4 are shown relative to the waveform 900 on FIG. 9. The time t=t1 occurs just before the first pre-pulse 502, and the time t=t2 occurs just before the second pre-pulse 504. The time t=t3 occurs just before the main pulse 506, and the time t=t4 occurs just after the main pulse 506. Referring to FIG. 10A, a target material supply apparatus 1020 releases a stream of target material droplets 1022. The stream 1022 travels from the target material supply apparatus 1020 to a target location 1026. The stream 1022 includes target material droplets 1010 and 1011. The first pre-pulse 502 approaches and strikes the target material droplet 1010. The cross-sectional size of a target material droplet can be, for example, between 20-40 μm. Referring also to FIG. 11A, the density profile 1100 of the target material droplet 1010 is uniform in the direction of propagation “z” of the pre-pulse 502, and the target material droplet 1010 presents a steep density transition to the pre-pulse 502. The interaction between the first pre-pulse 502 and the target material droplet 1010 produces a short-scale plume 1012 (FIG. 10B) on a side of the target material droplet 1010 that faces the oncoming first pre-pulse 902. The plume 1012 can be a cloud of particles of the target material that is formed on or adjacent to the surface of the target material droplet 1010. As the target material droplet 1010 travels toward the target location 1026, the target material droplet 1010 can increase in size in the vertical “x” direction and decrease in size in the “z” direction. Together, the plume 1012 and the target material droplet 1010 can be considered as an intermediate target 1014. The intermediate target 1014 receives the second pre-pulse 504. Referring also to FIG. 11B, at the time t=t2, the intermediate target 1014 has a density profile 1102. The density profile includes a density gradient 1105 that corresponds to the portion of the intermediate target 1014 that is the plume 1012. The density gradient 1105 is minimum at a location 1013 (FIG. 10B) where the second pre-pulse 504 initially interacts with the plume 1012. The density gradient 1105 increases in the direction “z” until the plume 1012 ends and the target material 1010 is reached. Thus, the first pre-pulse 502 acts to create an initial density gradient that includes densities that are lower than those present in the target material droplet 1010, thereby enabling the intermediate target 1014 to absorb the second pre-pulse 504 more readily than the target material droplet 1010. The second pre-pulse 504 strikes the intermediate target 1014 and generates a collection of pieces of target material 1015. The interaction between the intermediate target 1014 and the second pre-pulse 504 generates the collection of pieces 1015, as shown in FIG. 10C. As time passes, the collection of pieces of target material 1015 continues to travel in the “x” direction toward the target location 1026. The collection of pieces of target material 1015 forms a volume, and the volume increases as the pieces expand with the passage of time. Referring to FIG. 10D, the collection of pieces expands for 1000 ns after the second pre-pulse 502 strikes the intermediate target 1014, and the expanded collection of pieces forms the hemisphere shaped target 1018. The hemisphere shaped target 1018 enters the target location 1016 at time t=t4. The hemisphere shaped target 1018 has density that is at a minimum at a surface plane 1019, which receives the main pulse 506, and increases in the “z” direction. The density profile 1110 of the hemisphere shaped target 1018 at a time just before the main pulse 506 strikes the target 1018 is shown in FIG. 11C. The hemisphere shaped target 1018 has a gentle gradient that is at a minimum at the surface plane 1019 that receives the main pulse 506. Thus, like the hemisphere target 614, the hemisphere target 1018 absorbs the main pulse 506 readily and emits EUV light 1030 in all directions. As compared to the hemisphere target 614, the maximum density of the target 1018 is lower and the gradient is less steep. Other implementations are within the scope of the following claims. For example, the shape of the target can vary from a hemisphere that has a rounded surface. The hemisphere shaped portion 14 of the hemisphere shaped target 5 can have one or more sides that are flattened instead of being rounded. In addition to, or alternatively to, being dispersed throughout the hemisphere shaped target 5, the particles 20 can be dispersed on a surface of the hemisphere shaped target 5. |
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summary | ||
060752505 | claims | 1. A radiation image storage panel having a composite comprising a transparent support of plastic film and a phosphor layer provided thereon containing stimulable phosphor particles, wherein the composite is covered on its top surface and back surface of said support with a protective film comprising a fluororesin whose scratch resistance is higher than that of the surface of the support and whose contact angle is larger than that of the surface of the support. 2. The radiation image storage panel of claim 1, wherein the thickness of the protective film on the phosphor layer side surface is thinner than that of the film on the support side surface. 3. The radiation image storage panel of claim 1, wherein the transparent support comprises plastic material selected from the group consisting of polyethylene terephthalate, polyethylene napthalate, polyamide and polyimidoamide. 4. The radiation image storage panel of claim 1, wherein the fluororesin is selected from the group consisting of polytetrafluoroethylene, polychlorotrifluoroethylene, polyfluorinated vinyl, polyfluorinated vinylidene, tetrafluoroethylene-hexafluoropropylene copolymer, and fluoroolefin-vinyl ether copolymer. 5. The radiation image storage panel of claim 1, wherein the protective film on the support side surface is formed by applying an organic solution of fluororesin directly onto the support side surface. 6. The radiation image storage panel of claim 1, wherein the protective film on the support side surface comprises a fluororesin and light-scattering particles. 7. The radiation image storage panel of claim 1, wherein the protective film on the support side surface comprises a fluororesin, light-scattering particles, and at least one coupling agent selected from the group of a titanate coupling agent and an aluminum coupling agent. 8. The radiation image storage panel of claim 1, wherein the protective film on the phosphor layer side surface is formed by applying an organic solution of fluororesin directly onto the surface of the phosphor layer. 9. The radiation image storage panel of claim 1, wherein the protective film on the phosphor layer side surface is composed of a transparent film and a protective layer provided thereon which is formed by coating a organic solution of fluororesin on the transparent film. 10. The radiation image storage panel of claim 1, wherein the storage panel is for double-side reading system radiation image recording and reproducing method. |
054715148 | description | DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGS. 1-3 show a fuel channel 1 of substantially square cross section. The fuel channel 1 surrounds, with no significant free space, an upper square portion 2a of a bottom part 2 which otherwise comprises a conical portion 2b and a cylindrical portion 2c. The bottom part 2 has a downwardly-facing inlet opening 3 for cooling water. Besides supporting the fuel channel 1, the bottom part 2 supports a supporting plate 4. At its lowermost part, the fuel channel 1 has a relatively thick wall portion which is fixed to the bottom part 2 and the supporting plate 4 by means of a plurality of horizontal bolts, indicated by dash-dotted lines 5. By means of a hollow supporting member 6 with cruciform cross section, the fuel channel 1 is divided into four vertical tubular parts 7 with at least substantially square cross section. The supporting member 6 is welded to the four walls 1a, 1b, 1c and 1d of the fuel channel 1 and has four hollow wings 8. The central channel formed by the supporting member 6 is designated 9 and is connected at the bottom to an inlet tube 10 for moderator water. Each tubular part 7 comprises a bundle 11 of twenty-five fuel rods 12. The rods 12 are arranged in a symmetrical lattice in five rows each containing five rods 12. Each rod 12 is included in two rows perpendicular to each other. Each bundle 11 is arranged with a bottom tie plate 13, a top tie plate 14 and a plurality of spacers 15. A fuel rod bundle 11 with bottom tie plate 13, top tie plate 14, spacer 15 and fuel channel 1 forms a unit which, in this application, is referred to as a sub-assembly, whereas the device illustrated in FIGS. 1-3 and comprising four such sub-assemblies is referred to as a fuel assembly. The four bottom tie plates 13 are supported in the fuel assembly by the supporting plate 4 and are each partially inserted into a corresponding square hole 16 therein. The holes for the passage of the water through the bottom tie plate 13 are designated 17a. According to the present invention, debris catchers 18 are arranged below the bottom tie plates 13 in the bottom part 2, that is, in the flow path for the water which flows to each one of the bottom tie plates 13. An example of debris catchers 18 according to the invention is shown in FIG. 1 and FIGS. 3-5. The debris-catching element consists of a plurality of helical springs 19 arranged in slots in a holder. In this embodiment the holder consists of three--a first 20, a second 21, and a third 22--substantially parallel plates where the two flat sides of the second plate 21 are provided with concentric, annular slots 23 whereas the first 20 and third 22 plates only have one flat side provided with such slots 23. Since the plates 20-22 are arranged with the flat sides adjoining each other, a parallelepiped is formed with annular channels 24 of circular cross section. The springs 19 are fixed in two levels between the plates 20-22 in these channels 24. The plates 20-22 are provided in the axial direction with through-holes 17 for the flow of cooling water through the fuel assembly. The plate 20 is provided with a flange 20a for fixing the debris catcher 18 in the bottom part 2. FIGS. 5 and 6 show an alternative embodiment in which the holder consists of concentric rings 25 fixed to each other in the axial and radial directions via a cruciform support member 26, to which the rings are fixed, for example, by welding. In an alternative embodiment (not shown), the rings 25 can be fixed by means of pins which extend through holes in several rings 25, to which pins the rings 25 are welded. The helical springs 19 are fixed between two layers of rings 25 in the spaces, slots 27, which are formed between the concentric rings 25. FIGS. 7-9 show a debris-catching element which consists of one single helical spring 19 adapted so as to form, per se, a plane spiral. FIG. 7 shows a holder seen in a section corresponding to 4--4 in FIG. 1. The holder comprises a plate 28 which is formed such that the slot 30 therein consists of a plane spiral corresponding to the plane spiral helical spring 19. In the axial direction the plate 28 is provided with through-holes 17 for the flow of cooling water through the fuel assembly. FIG. 8 shows a holder for the plane spiral helical spring 19 seen from above. The holder is formed in the same way as the holder shown in FIG. 5. The plane spiral helical spring is fixed, like the annularly arranged helical springs in FIG. 5, in the space, the slot 27 between the concentric rings 25. At the transition of the spring 19 between two slots 27, the spring 19 is stretched out such that a part of a winding turn is arranged around the ring 25 which lies between the slots 27 in question. FIG. 9 shows a holder which, like the plane spiral helical spring 19, is formed as a plane spiral 29. The spring 19 is arranged between the spiral turn of the plane spiral 29, that is, in the slot 30. The spiral is fixed radially and axially by means of a cruciform support member 26 corresponding to the support member shown in FIGS. 5, 6 and 8. The material in the holders consists, for example, of stainless steel or another material resistant to corrosion by the reactor water. The material in the springs 19 preferably consists of Inconel. The pitch of the helical springs 19 is determined by the demand for debris catching capacity. The helical springs 19 are made with tolerances which prevent the occurrence of a play between the springs 19 and the holders, thus eliminating the risk of abrasion caused by vibrations. To compensate for the pressure drop which arises across the debris catcher 18, the diameter of the through-holes 17a in the bottom plate 13 can be somewhat increased. According to a particularly preferred embodiment of the invention, the debris catcher 18 consists of a device which is parallel to the bottom tie plate 13 such that the symmetry axis of the helical springs 19 is horizontal. If the debris catcher 18 is arranged below the bottom tie plate 13, it has, in addition to the above-mentioned advantages, the advantage of being able to be inspected and cleaned. It is obvious that a debris catcher 18 of the kind described can be used in a fuel assembly which is not, as in the exemplified case, divided into sub-assemblies with separate bottom tie plates 13 but which consists of one single assembly with one single bottom tie plate 13 and is thus in analogous manner placed in the flow path of the water to the single bottom tie plate 13. The number of levels with helical springs 19 can, of course, be greater or smaller than what has been shown in the embodiments. It is also obvious that a debris catcher 18 of the kind described can be arranged below the bottom tie plate 13 of a pressurized-water reactor. In a pressurized-water reactor, because of the constructive design of the flow path of the water to the bottom tie plate, it is normally most suitable to allow the debris catcher 18 to make contact with the underside of the bottom tie plate. |
description | This application is a national stage application of PCT/CN2014/085811 filed on Sep. 3, 2014, which claims priority of Chinese patent application number 201310395436.0 filed on Sep. 3, 2013. The disclosure of each of the foregoing applications is incorporated herein by reference in its entirety. The invention relates to nuclear power plant reactivity control and control rod design for a modular pebble-bed high-temperature gas-cooled reactor and particularly relates to a reactivity control method and a telescoped control rod for a pebble-bed high-temperature gas-cooled reactor. A pebble-bed high-temperature gas-cooled reactor originated from an AVR experimental reactor in Germany Based on success of the AVR reactor experiment, in the 1970s, i.e. in the high-speed development period of world nuclear power, the thorium high-temperature gas-cooled reactor demonstration power plant (THTR-300) with electric power of 300 MW was built and operated in Germany. With occurrence of the nuclear power plant accidents of Three Mile Island in the USA and Chernobyl in the Soviet Union, the public and supervision authorities in various countries increasingly pay more attention to safety of nuclear power plants, and thus, the development trend of high-temperature gas-cooled reactor commercial power plant is changed into a modular high-temperature gas-cooled reactor with passive inherent safety from original large-scale direction. The high-temperature gas-cooled reactor nuclear power plant demonstration project (HTR-PM) of the HuaNeng ShanDong ShiDao Bay nuclear power plant, which has been constructed in China, is a typical modular pebble-bed high-temperature gas-cooled reactor. Due to high single-reactor power of the thorium high-temperature gas-cooled reactor (THTR-300), two sets of control rod systems are arranged, wherein one set of control rod system is provided with 36 regulating rods that are arranged on a lateral reflection layer and used for regulating rapid reactivity change and hot shutdown under the accident working condition; and the other set of control rod system is provided with 42 control rods and the 42 control rods are inserted into a reactor core pebble bed and are used for carrying out long-term cold shutdown and ensuring a certain cold shutdown depth. The operating experience of the thorium high-temperature gas-cooled reactor shows that the control rods inserted into the reactor core pebble bed require a huge driving force to overcome resistance of stacked spherical fuel elements, which causes damage to the fuel elements. Therefore, only the lateral reflection layer control rods are retained in the later design of the modular pebble-bed high-temperature gas-cooled reactor HTR-MODUL. The HTR-MODUL has single-reactor thermal power of 200 MW, a reactor core diameter of 3 m and a reactor core average height of 9.4 m. Reactivity control and Shutdown systems of the HTR-MODUL include a control rod system and an absorption sphere shutdown system, the control rod system is provided with six control rods in total, the six control rods are arranged at the lateral reflection layer, and each control rod corresponds to a set of driving mechanism for enabling the control rod to move up and down. Each control rod has an absorber length of 4,800 mm and a total length of 5,280 mm and is divided into ten sections in total, each control rod has an outer diameter of 10.5 mm, each control rod has a pore diameter of 130 mm, a cladding material adopted by the control rods is X8CrNiMoNb 1616, the total weight of each control rod is 104 kg, and the highest design temperature of each control rod is about 900 DEG C. The control rod system of the HTR-MODUL has the main functions of reactor power regulation and hot shutdown. Design parameters of the control rods show that the control rods are of a multi-section single-rod structure; since all the control rods need to be taken out of an active region when the reactor operates under the full power, the length of an absorber of each control rod is about half the height of the reactor core active region due to the limitation of the height of a reactor pressure vessel. Except for the control rod system, the other set of reactivity control and shutdown system of the HTR-MODUL is the absorption sphere shutdown system. The system is provided with 18 lines of absorption spheres which are also positioned at the lateral reflection layer of the reactor, the absorption spheres fall into pore passages of the lateral reflection layer by means of gravity and are returned to a sphere storage tank from the pore passages of the lateral reflection layer in a pneumatic conveying manner. The system has the main functions that: 1, when the reactor is started and operates under low power, the absorption sphere shutdown system works together with the control rod system to carry out reactivity control; and 2, the absorption sphere shutdown system separately achieves cold shutdown and ensures a certain cold shutdown depth. The above mentioned reactivity control of the HTR-MODUL has the following problems that: 1, the absorption sphere shutdown system has a great number of functional requirements, is complex in system design and has a high requirement for operation reliability; 2, when the reactor is started and operates under low power, a reactor operator not only needs to operate the control rod system, but also needs to blow the absorption spheres up in a pneumatic conveying manner from each absorption sphere pore passage, and the amount of the absorption spheres conveyed each time needs to be accurate and controllable, which brings great operation difficulty to the reactor operator and is likely to cause accidents. Therefore, design of the HTR-PM reactivity control and shutdown system adopts the following technical innovations that: two sets of mutually independent systems, the control rod system and the absorption sphere system, are still retained but the functions of the two sets of systems are regulated; the control rod system is divided into safety rod banks, regulating rod banks and shim rod banks, the safety rod banks are all taken out of the reactor active region when the reactor is started and operates under low power, the value of the safety rod banks is sufficient to ensure shutdown under any reactor working condition, the regulating rod banks perform reactor power regulation so as to flatten reactor core power distribution and compensate reactivity change of a reactor core during the normal operation, the shim rod banks are used for compensating reactivity change after the reactor operates for a long time; as actuating mechanisms of a reactor protection system, the safety rod banks and the regulating rod banks can rapidly achieve hot shutdown, assumed that one control rod with the highest reactivity value is in failure; and when the reactor is started and operates under low power, the regulating rod banks and the shim rod banks cooperate to carry out reactivity control. If all the control rods are put in. Cold shutdown can be separately achieved and a certain cold shutdown depth is ensured. As a standby shutdown system, the absorption sphere shutdown system does not participate in startup of the reactor and operation at all power levels and can be manually put into use as required; and when the control rod system and the absorption sphere shutdown system are put into use together, long-term cold shutdown or overhaul shutdown can be achieved. The invention aims to solve the technical problems that under the condition of keeping structural design parameters of a pressure vessel, reactor internals and the like of an existing modular pebble-bed high-temperature gas-cooled reactor unchanged essentially, only a control rod system is used to achieve cold shutdown and ensure a certain shutdown depth. The invention adopts the following technical scheme: a telescoped control rod for a pebble-bed high-temperature gas-cooled reactor comprises an inner rod, an outer rod and a guide cylinder assembly which are vertically and coaxially arranged, wherein the outer rod and the guide cylinder assembly are hollow cylindrical bodies; the top end of the inner rod can move up and down inside the outer rod and the other end of the inner rod moves up and down, along with the top end, inside a control rod passage which is positioned below the guide cylinder assembly and is coaxial with the guide cylinder assembly; and the top end of the outer rod can move up and down in the guide cylinder assembly and the other end of the outer rod moves up and down, along with the top end, inside the control rod passage. Preferably, the inner rod is of a multi-section structure and comprises a coupling head assembly, an anti-impact head assembly and a plurality of internal section rods connected in series by sphere articulated joints, wherein one end of the coupling head assembly is connected with the internal section rod at the first section and the other end of the coupling head assembly is connected with a loop chain of a control rod driving mechanism; and one end of the anti-impact head assembly is connected with the internal section rod at the tail section. Preferably, the coupling head assembly comprises a coupling head, a flat pin, a locking bead ring, a buffer pressure plate, a cylinder spring, a bearing pressure plate, a ceramic ball, a bearing bottom plate and a sphere joint; the coupling head is connected with the loop chain of the control rod driving mechanism by the flat pin and the locking bead ring is used for encircling and fastening the flat pin; and the buffer pressure plate is arranged on the cylinder spring to form a buffer structure, the buffer structure is externally arranged on the side wall of the coupling head, the sphere joint is in threaded connection with the bearing pressure plate and is in spherical fit with the upper end plate of the internal section rod, a thrust bearing structure is formed by the ceramic ball, the bearing pressure plate and the bearing bottom plate together, and the thrust bearing structure is externally sleeved by the coupling head. Preferably, each internal section rod comprises an outer sleeve, an upper end plate and a lower end plate respectively positioned at both ends of the outer sleeve, and a B4C pellet that is welded and packaged between the upper end plate and the lower end plate and is positioned in the outer sleeve; gaps are reserved between the B4C pellet and the outer sleeve and between the B4C pellet and the upper end plate; and a hold-down spring is arranged between the B4C pellet and the upper end plate. Preferably, the anti-impact head assembly comprises a buffer pressure plate, a disk spring and an anti-impact head, wherein a bulge is formed on the side wall of the anti-impact head and the disk spring is arranged between the bulge and the buffer pressure plate. Preferably, a top inner shrunk opening and a top outer shaft shoulder are formed at the top of the outer rod; and the outer rod is of a multi-section structure and comprises a sliding sleeve type shock absorber, hanging assemblies and a plurality of external section rods, the hanging assemblies are connected with the corresponding external section rods, and the sliding sleeve type shock absorber is connected with the external section rod at the head end. Preferably, each external section rod comprises an inner sleeve, an outer sleeve, an upper end plate, a lower end plate, a hold-down spring and a B4C pellet, wherein the B4C pellet is mounted in an annular space defined by the inner sleeve, the outer sleeve, the upper end plate and the lower end plate and gaps are reserved between the B4C pellet and the inner and outer sleeves as well as the upper end plate; the hold-down spring is arranged between the B4C pellet and the upper end plate; and the outer sleeve is provided with a vent hole. Preferably, all the hanging assemblies are the same in the number of hanger ring structures arranged. Each hanger ring structure comprises two sphere pendants, two cylindrical pins, a long hanger ring and two check rings; the sphere pendants are mounted in inner side grooves of the upper end plate and the lower end plate; the sphere pendants are connected with the long hanger ring by the cylindrical pins and the cylindrical pins are fixed with the check rings; and gaps are reserved among the sphere pendants, the cylindrical pins and the long hanger ring. The guide cylinder assembly comprises an upper segment, a middle segment and a lower segment; the upper segment and the middle segment are fixedly mounted on an upper bearing plate for the metal reactor internals together; the upper segment is positioned above the bearing plate and a gap is reserved between the upper segment and a reactor pressure vessel sealing head; the middle segment is positioned under the bearing plate and passes through a plurality of layers of reactor core pressure plates; the bottom of the middle segment is inserted into the lower segment; the lower segment is fixed to the upper bearing plate and a metal reactor internal positioning plate and can be inserted into a top carbon brick and a top reflection layer graphite brick by a certain depth according to a designed length; and a positioning ring is welded at the lower end of the lower segment. The invention further provides a reactivity control method for the pebble-bed high-temperature gas-cooled reactor. The reactivity control method for the pebble-bed high-temperature gas-cooled reactor comprises: a rod inserting process and a rod lifting process; in the rod inserting process, at the top half section of the control rod travel, the outer rod and the inner rod move together under the dragging action of the driving mechanism, when the top end of the outer rod descends to a reactor active region upper edge, the outer shaft shoulder of the outer rod is lapped to the positioning ring at the bottom end of the guide cylinder assembly and at this moment, the outer rod does not move downwards any more under the bearing action of the positioning ring of the guide cylinder assembly, i.e. the outer rod reaches the lower limit of the travel; the inner rod can be further inserted downwards along the inner sleeve of the outer rod under the drive of the driving mechanism and is separated from the outer rod, till reaching the lower limit of the travel, and at this moment, the outer rod and the inner rod cover a whole reactor core active region; in the rod lifting process, at the bottom half section of the control rod travel, only the inner rod moves upwards under the dragging action of the driving mechanism and is gradually inserted into the outer rod until the inner rod is in contact with the inner shrunk opening of the outer rod and the inner rod and the outer rod are completely overlapped; and the rod lifting operation is further carried out, the inner rod and the outer rod move upwards together and gradually enter the guide cylinder assembly, and when both the inner rod and the outer rod are positioned at the reactor active region upper edge, the rod lifting limit is reached. The telescoped control rod for the pebble-bed high-temperature gas-cooled reactor, which is provided by the embodiment of the invention, has the following beneficial effects: (1) technical conditions are created for the modular pebble-bed high-temperature gas-cooled reactor to carry out reactivity control and shutdown only by utilizing a control rod system; the startup and operating control operation of the modular pebble-bed high-temperature gas-cooled reactor is simplified; and functional requirements of an absorption sphere shutdown system are reduced and design complexity of the absorption sphere shutdown system is reduced. (2) due to limitation of the height of the reactor pressure vessel and the like, the length of each control rod of the existing modular pebble-bed high-temperature gas-cooled reactor is only about half the height of the reactor core active region, however, on the premise of not changing the height of the pressure vessel and other total design parameters of the existing modular pebble-bed high-temperature gas-cooled reactor, the spread length of the telescoped control rod provided by the invention can cover the height of the whole reactor core active region; so that reactivity value of the control rod system is improved to the greatest extent. (3) spring shock absorbers are arranged at multiple positions on the telescoped control rod provided by the embodiment of the invention, so that various impact loads can be effectively reduced and operation reliability of the control rod can be improved. (4) the telescoped control rod provided by the embodiment of the invention is of a detachable structure, which facilitates processing, manufacturing, packaging, transportation and nuclear power plant field installation. in the drawings, 1, inner rod; 2, outer rod; 3, guide cylinder assembly; 4, loop chain; 5, reactor core active region; 6, control rod graphite passage; 11, coupling head assembly; 12, sphere articulated joint; 13, internal section rod; 14, anti-impact head assembly; 21, sliding sleeve type shock absorber; 22, hanging assembly; 23, external section rod; 31, guide cylinder assembly upper segment; 32, guide cylinder assembly middle segment; 33, guide cylinder assembly lower segment, 34, positioning ring; 35, reactor internal upper bearing plate; 36, pressure plate; 37, reactor internal positioning plate; 38, top carbon brick; 51, active region upper edge; 52, active region lower edge; 53, pressure vessel sealing head; 61, cylindrical shell type shock absorber; 110, flat pin; 111, locking bead ring; 112, coupling head; 113, buffer pressure plate; 114, cylinder spring; 115, bearing pressure plate; 116, ceramic ball; 117, bearing bottom plate; 118, sphere joint; 120, upper sphere joint; 121, lower sphere joint; 122, flat pin; 123; locking bead ring; 124, auxiliary hole; 125, process tank; 130, upper end plate; 131, lower end plate; 132, hold-down spring; 133, outer sleeve; 134, B4C pellet; 135, internal section rod vent hole; 140, buffer pressure plate; 141, disk spring; 143, anti-impact head; 210, inner shrunk opening; 211, outer shaft shoulder; 212, pre-tightening pressure plate; 213, disk spring; 220, sphere pendant; 221, long hanger ring; 222, cylindrical pin; 223, check ring; 230, upper end plate; 231, lower end plate; 232, outer sleeve; 233, inner sleeve; 234, B4C pellet; 235, hold-down spring; 236, external section rod vent hole. The specific implementation of the invention is further described by combining the accompanying drawings and embodiments. The embodiments below are only used for illustrating the invention, but not used for limiting the scope of the invention. FIG. 1 and FIG. 2 show an operating principle diagram of a telescoped control rod according to one embodiment of the invention. The telescoped control rod comprises: an inner rod 1, an outer rod 2 and a guide cylinder assembly 3. The inner rod 1 is connected with a loop chain 4 of a control rod driving mechanism by a coupling head assembly and moves up and down under the dragging action of the driving mechanism in the guide cylinder assembly 3 and a control rod graphite passage 6; the movement lower limit of the inner rod 1 is limited by the maximum length of the loop chain 4 and reaches a reactor active region lower edge 52; the movement upper limit of the inner rod 1 is limited by the height of a reactor pressure vessel and is higher than a reactor active region upper edge 51; the inner rod I can be kept above an active region in a dynamic manner by the driving mechanism; and in the case of accident shutdown, a driving mechanism power supply is switched of and the inner rod 1 falls into a lateral reflection layer of the active region by means of the gravity, which meet the design principle of fault safety. The top of the outer rod 2 is provided with an inner shrunk opening 25 and an outer shaft shoulder 24, the inner rod 1 is inserted from the bottom of the outer rod 2, and by utilizing the inner shrunk opening 25, the outer rod 2 can be lapped to the inner rod 1. At the top half section of the control rod travel, the outer rod 2 and the inner rod 1 move together under the dragging action of the driving mechanism, when the integral outer rod 2 is positioned below the reactor active region upper edge 51, the outer shaft shoulder 24 of the outer rod 2 is lapped to a positioning ring 34 at the bottom end of the guide cylinder assembly 3 and at this moment, the outer rod 2 does not move downwards any more under the bearing action of the positioning ring 34 of the guide cylinder assembly 3, i.e. the outer rod 2 reaches the lower limit of the travel; and the inner rod 1 can be further inserted downwards along inner sleeves of the outer rod 2 under the drive of the driving mechanism and is separated from the outer rod 2, till reaching the lower limit of the travel, and at this moment, the outer rod 2 and the inner rod 1 cover a whole reactor core active region 5, and thus the reactivity value of the control rod is improved to a great extent. Conversely, in the rod lifting process, at the bottom half section of the control rod travel, only the inner rod 1 moves upwards under the dragging action of the driving mechanism and is gradually inserted into the outer rod 2 until the inner rod 1 is in contact with the inner shrunk opening 25 of the outer rod 2 and the inner rod 1 and the outer rod 2 are completely overlapped; then, the rod lifting operation is further carried out, the inner rod 1 and the outer rod 2 move upwards together and gradually enter the guide cylinder assembly 3, and when both the inner rod 1 and the outer rod 2 are positioned at the reactor active region upper edge 51, the rod lifting limit is reached; at this moment, a reactor can operate under full power. In conclusion, the spread length of the telescoped control rod according to the invention is gradually increased up to the whole reactor core active region 5 in the rod inserting process, and conversely, in the rod lifting process, the spread length of the telescoped control rod is gradually decreased and is finally only half the height of the reactor core active region 5. An operating passage of the outer rod 2 and the inner rod 1 is formed by the guide cylinder assembly 3 and the control rod graphite passage 6 together, the guide cylinder assembly 3 takes a guiding effect on operation of the outer rod 2 and the inner rod 1 and meanwhile, the outer rod 2 and the inner rod 1 are prevented from impacting with other reactor internals under the seismic condition; and the positioning ring 34 is welded at the lowermost end of the guide cylinder assembly 3 so as to limit the maximum inserting-down travel of the outer rod 2. wherein, in order to illustrate a multi-section structure clearly, a 10-section structure is illustrated as one example. The structural form of the multi-section inner rod 1 is as shown in FIG. 3 and the multi-section inner rod 1 comprises: a coupling head assembly 11, nine sphere articulated joints 12, ten internal section rods 13 and an anti-impact head assembly 13, wherein the coupling head assembly 11, as shown in FIG. 4, is composed of a flat pin 110, a locking bead ring 111, a coupling head 112, a buffer pressure plate 113, a cylinder spring 114, a bearing pressure plate 115, a ceramic ball 116, a bearing bottom plate 117 and a sphere joint 118; the coupling head 112 is connected with the loop chain 4 of the control rod driving mechanism by the flat pin 110 and the locking bead ring 111 is used for preventing the flat pin 110 from falling off; when the inner rod 1 is lifted upwards from the bottom of the control rod graphite passage 6, the moving inner rod 1 can be collided with the static outer rod 2 and the buffer pressure plate 113 and the cylinder spring 114 can buffer the collision; a thrust bearing structure is formed by the ceramic ball 116, the bearing pressure plate 115 and the bearing bottom plate 117 together and has the main effect of avoiding causing distortion of the loop chain 4 of the driving mechanism and influencing operation of the driving mechanism due to uneven weight distribution; the sphere joint 118 is in threaded connection with the bearing pressure plate 115, is spot-welded with the bearing pressure plate 115 and is in spherical fit with an internal section rod upper end plate 130 so as to ensure mutual flexible rotation between the coupling head assembly 11 and the corresponding internal section rod 13; each internal section rod 13, as shown in FIG. 6, is composed of an outer sleeve 133, the upper end plate 130, a lower end plate 131, a hold-down spring 132 and a B4C pellet 134; the B4C pellet 134 is a neutron absorber and is welded and packaged in the outer sleeve 133; gaps are reserved between the B4C pellets 134 and the outer sleeves 133 as well as the upper end plates 130 so as to compensate irradiation swelling of the B4C pellets 134; in order to prevent the B4C pellets 134 from being displaced, the hold-down springs 132 are arranged at the tops of the B4C pellets 134; the B4C pellets 134 can generate helium when being irradiated by neutrons and internal section rod vent holes 135 in the middles of the B4C pellets 134 are beneficial to discharge of neutrons; the total length of the B4C pellets 134 of ten internal section rods 13 is about half the height of the reactor core active region; each sphere articulated joint 12, as shown in FIG. 5, comprises an upper sphere joint 120, a lower sphere joint 121, a flat pin 122 and a locking bead ring 123; the sphere articulated joints 12 not only ensure reliable connection of the adjacent internal section rods 13, but also can ensure mutual flexible rotation between the adjacent internal section rods 13; auxiliary holes 124 and process tanks 125 are formed on the sphere joints so as to bring convenience to assembling and disassembling of the internal section rods 13; the anti-impact head assembly 14, as shown in FIG. 7, is welded with the internal section rod 13 at the bottommost end into one whole body and comprises a buffer pressure plate 140, a disk spring 141 and an anti-impact head 142; corresponding to the anti-impact head, a cylindrical shell type shock absorber 61 is arranged at the bottom of the control rod graphite passage 6; as shown in FIG. 1, the cylindrical shell type shock absorber 61 is used for relieving impact of fracture of the inner rod 1 to graphite reactor internals under the condition of an extreme accident and ensuring structural integrity of the graphite internals; and the buffer pressure plate 140 and the disk spring 141 relieve impact of fracture of the outer rod 2 to the inner rod 1 under the condition of the extreme accident, meanwhile, also guarantee the outer rod 2 not to be separated from the control rod driving mechanism, and are convenient to take out and replace the outer rod 2. In order to illustrate the multi-section structure clearly, the ten-section structure is illustrated as one example. The detailed structure of the outer rod 2 is as shown in FIG. 8 and the outer rod 2 comprises a sliding sleeve type shock absorber 21, nine hanging assemblies 22 and ten external section rods 23. wherein the sliding sleeve type shock absorber 21, as shown in FIG. 9, comprises an inner shrunk opening 210, an outer shaft shoulder 211, a pre-tightening pressure plate 212 and a disk spring 213; the inner shrunk opening 210 is combined with the upper end plate 230 of the corresponding external section rod 23 into one whole body and is welded with the inner sleeve 233 of the corresponding external section rod 23; the pre-tightening pressure plate 212 is in threaded connection with the inner shrunk opening 210 and applies a certain pre-tightening three to the disk spring 213; a certain gap is reserved between the outer shaft shoulder 211 and an outer sleeve 232 of the corresponding external section rod 23 and when the outer rod 2 is inserted down under the drive of the driving mechanism or the driving mechanism is powered off and the outer rod 2 falls down, the outer shaft shoulder 211 is collided with the positioning ring 34 at the lower end of a control rod guide tube and slides upwards and the disk spring 213 is deformed by the pressure, so that the gap between the outer shaft shoulder 211 and the outer sleeve 232 takes a shock absorbing effect and still guarantees the corresponding external section rod 23 not to be separated from the outer shaft shoulder 211 under the condition that the disk spring 213 generates the largest deformation; each external section rod 23, as shown in FIG. 11, is composed of the inner sleeve 233, the outer sleeve 232, an upper end plate 230, a lower end plate 231, a hold-down spring 235 and a B4C pellet 234; the B4C pellets 234 are also welded and packaged in an annular space between the inner and outer sleeves and the end plates and gaps are reserved between the B4C pellets 234 and the inner and outer sleeves as well as the upper end plate so as to compensate irradiation swelling of the B4C pellets 234; in order to prevent the B4C pellets from being displaced, the hold-down springs 235 are arranged between the tops of the B4C pellets 234 and the upper end plates 230; the outer sleeves 232 are provided with external section rod vent holes 236, so that helium generated by the B4C pellets 234 due to irradiation of neutrons can be discharged and jackets of the external section rods 23, which are formed by the inner and outer sleeves and the upper and lower end plates, are prevented from bearing an internal pressure or an external pressure; the B4C pellets 234 are sintered bodies, the required density of the B4C pellets 234 is 2.0 g/cm3 and is smaller than the theoretical density of the B4C pellets 234, and the B4C pellets 234 with high density are easy to irradiate by neutrons to be cracked; the total length of absorbers mounted in ten external section rods 23 is about half the height of the reactor core active region 5; wherein, each hanging assembly 22, as shown in FIG. 10, is provided with six same hanger ring structures; each hanger ring structure comprises two sphere pendants 220, two cylindrical pins 222, a long hanger ring 221 and two check rings 223; the insides of the upper and lower end plates of the external section rods 23 are slotted and the sphere pendants 220 can be laterally mounted into the upper and lower end plates; the sphere pendants 220 are connected with the long hanger ring 221 by the cylindrical pins 222 and the cylindrical pins 222 are fixed with the check rings 223; the sphere pendants 220 can swing relative to the end plates of the external section rods; gaps are reserved among the sphere pendants 220, the cylindrical pins 222 and the long hanger ring 221; and the check rings 223, the long hanger ring 221 and the cylindrical pins 222 of each hanging assembly 22 are all detachable, and thus, the outer rod 2 is packaged and transported in a form of single external section rods 23 without being integrally packaged and transported, which not only reduces difficulty, but also improves reliability and in addition, has benefits for nuclear power plant field control rod installation. As shown in FIG. 12, the guide cylinder assembly 3 is divided into upper, middle and lower segments and each segment has a short length and is convenient to manufacture, produce and install; the upper segment 31 and the middle segment 32 are fixedly mounted on a reactor internal upper bearing plate 35 for metal reactor internals together; the upper segment 31 is positioned above the bearing plate and a large gap is reserved between the upper segment 31 and a reactor pressure vessel sealing head 53 so as to compensate thermal expansion difference between the metal reactor internals and the pressure vessel; the middle segment 32 is positioned under the bearing plate and passes through a plurality of layers of reactor core pressure plates 36; the bottom of the middle segment 32 is inserted into the lower segment 33 of the guide cylinder assembly; the lower segment 33 of the guide cylinder assembly is fixed to a reactor internal positioning plate 37 for the metal reactor internals and is inserted into a top carbon brick 38 and a top reflection layer graphite brick; and a positioning ring 34 is welded at the lower end of the lower segment 33. The reasons of designing both the inner rod 1 and the outer rod 2 of the telescoped control rod into a multi-section hanging structural form are that the control rod graphite passage 6 is of a graphite piled structure and has the height of over 20 meters so as not to completely ensure straightness of the control rod graphite passage 6 in the mounting process and in addition, the control rod graphite passage 6 is possible to deform due to irradiation of neutrons in the reactor operating process. The multi-section hanging structure can effectively prevent the operation of the outer rod 2 in the control rod graphite passage 6 or the operation of the inner rod 1 in the outer rod 2 from being blocked or jammed. In addition, the sufficiently large gaps are reserved both between the outer rod 2 and the control rod graphite passage 6 and between the inner rod I and the outer rod 2, which facilitates movement of the outer rod 2 and the inner rod 1. The environmental temperature of the control rod reaches 560 DEG C. under the normal operation condition of the reactor and is close to 1,000 DEG C. under the accident condition, and thus, all metal structural materials of the control rod according to the invention adopt high-temperature resistance nickel-based alloy with good high-temperature endurance; and in order to prevent mutual engaged adhesion of metal contact surface materials in the high-temperature environment, the metal contact surface materials are different in trademarks and are all subjected to solid lubrication processing to keep flexibility of the sphere articulated joints and the hanging assemblies, so that the telescoped control rod has high industrial practicality. The above embodiments are only used for illustrating the invention, but not intended to limit the invention, and various variations and conversions can be carried out by those common skilled in the related technical fields within the spirit and principle of the invention, and thus, all equivalent technical schemes also belong to the scope of protection of the invention. |
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049884735 | abstract | A self-latching reactivity-reducing device contains neutron absorbing material and is installable in a guide thimble of a spent fuel assembly for reducing the reactivity of the assembly to allow its storage in an on-site fuel storage facility. The device includes an elongated rod which contains the neutron absorbing material and has a central passage extending between opposite ends of the rod. A self-latching mechanism is disposed on a leading end of the rod and engagable with a lower end portion of the guide thimble upon full insertion of the rod in the guide thimble so as to render the self-latching mechansim unlatchable from the guide thimble without the use of an independent tool inserted solely through the rod passage from a trailing end thereof. A closure plug is removably fastened to the trailing end of the rod for closing the passage therethrough. The self-latching mechanism includes a plurality of latch members being mounted for pivotal movement between displaced latching and releasing positions at the leading end of the rod and biased toward the latching position. |
summary | ||
051877260 | summary | FIELD OF THE INVENTION This invention pertains generally to the field of micro-electronic processing techniques, particularly to X-ray lithography and to X-ray lithography masks. BACKGROUND OF THE INVENTION In the formation of micro-electronic devices using photolithographic techniques, the wavelength of the "light" utilized to form the image on the target photoresist imposes a fundamental limit on the available image definition. The image resolution, or minimum linewidth that can be imaged, is limited by the diffraction of the light at the edges of the features of the masks through which the light is projected. The commonly used figure of merit is the Fresnel number f calculated as f=W.sup.2 /G.lambda., where G is the gap distance between the mask and the target surface, .lambda. is the wavelength of the light being utilized and W is the feature size. The Fresnel number f provides a guide in assessing the obtainable resolution, with f=0.5 corresponding to about what is usually considered the resolution limit. To allow the creation of smaller micro-electronic structures than are attainable utilizing visible or ultraviolet optical systems, X-ray sources are being utilized. Synchrotrons are particularly suitable as X-ray sources for X-ray lithography since the synchrotron provides an intense, steady beam of substantially collimated X-ray photons having a mixture of wavelengths spanning soft to hard X-rays. Because the wavelength .lambda. of X-rays is smaller than the wavelength of optical or ultraviolet light, X-ray lithography inherently allows smaller features to be created. However, the feature size for X-rays is also ultimately limited, as the Fresnel number criterion also applies to X-ray lithography systems. The formula for the Fresnel number is approximate since it does not include physical effects, and resolutions in X-ray lithography systems less than 1,000 Angstroms (A) have been demonstrated with gaps larger than those that might be expected from the Fresnel number calculated for such systems. Nonetheless, the Fresnel number provides an approximate criterion for determining the ultimate resolution. Using this criterion, for example, it is found that to image 0.25 micrometer (.mu.m) lines with one nanometer (nm) radiation would allow a maximum gap of only 12.5 .mu.m. Thus, as the required line resolution shrinks, so does the available working distance between the mask and the target surface. It is generally considered difficult to perform X-ray lithography exposures at distances between the mask and target of less than 10 .mu.m. It may be noted that there are two types of images that can be considered in determining the resolution in X-ray lithography, the aerial image (the X-ray intensity at the target surface) and the latent image (the image recorded in the target photoresist resist material). Phase shifting masks have been used to increase the image definition in projection optical systems, and their use has been proposed to allow extension of the resolution limit of conventional visible and ultra-violet light optical lithographic systems. The phase shift mask includes a transparent layer of suitable thickness defining certain features which introduces a half wavelength (.pi.) phase shift of the field E.sub.1 of the light transmitted through the layer relative to the field E.sub.2 of the light transmitted through an area without the transparent layer. The total field E.sub.t is obtained by addition of the two fields, i.e., E.sub.t =E.sub.1 +E.sub.2, so that at some position along the image plane, the total field must become zero because of the continuity requirement. This creates a sharp modulation in the intensity pattern. A judicious choice of the phase shifting overlayer can improve the image even for complex patterns, although the technique works best for regular and repetitive cases such as those used in the manufacture of dynamic random access memories (DRAMs). It has been suggested that an X-ray mask having an absorbent thickness appropriate for yielding a .pi. phase shift can improve image sharpness. See Y. C. Ku, et al., "Use of a Pi-Phase Shifting X-Ray Mask to Increase the Intensity Slope at Feature Edges," J. Vac. Sci. Technol. B, Vol. 6, No. 1, January/February 1988, p. 150-153. The masks described therein are absorbing masks, and the phase effects were used to refine the image rather than to define it. SUMMARY OF THE INVENTION In accordance with the present invention, a phase shift mask for X-ray lithography is provided having at least one phase shifting feature having at least one sharply defined sidewall which is upright with respect to the surface of the carrier on which the feature is supported. The material of the phase shifter feature introduces a half wavelength shift to X-ray photons passed therethrough compared to photons passed through a region of the mask having no phase shift material. The region of phase shift material is preferably of relatively low attenuation of X-rays passed through it, i.e., it is substantially "transparent" to X-rays, and is mounted on a carrier substrate which itself is substantially transparent to X-rays. The phase shift mask is placed in close proximity (e.g., preferably within five to ten micrometers) of a target structure which includes a layer of photoresist material. A beam of preferably collimated X-rays is then passed through the mask to expose the resist beneath the mask. Where a positive photoresist is used, the interaction of the X-ray photons with the photoresist causes the photoresist to be susceptible to dissolution in a developer. The target with the exposed photoresist thereon is then treated with a developer to remove all of the exposed photoresist, which leaves photoresist structures on the carrier which were not exposed to X-ray photons sufficiently to render such regions of the photoresist removable. Such structures occur underneath the intersection beneath the upright sidewalls of the phase shift features on the phase shift mask because of destructive interference of the spatially coherent X-rays which are passed through the mask. The interaction of the photons phase shifted by 1/2 of a wavelength and the photons that are not so phase shifted leaves a zone between the two regions where there is very little effective X-ray energy deposited, preferably at a level below a sharply defined resist exposure threshold so that the resist is left unremoved in those areas. The phase shift mask of the present invention allows very thin wall structures to be formed in the photoresist on the target substrate, in the range of a few hundred Angstroms wide. Typical X-ray photoresists such as polymethyl methacrylate (PMMA), may be utilized to provide such structures. It is found that the unexposed region is very sharply defined because of the rapid variation of the electrical field. The width of the region, i.e., the resolution, is dependent on the gap between the mask and the photoresist layer, while the modulation is not. In accordance with the present invention, closed figure structures can readily be formed by providing a feature comprising a bounded region of phase shift material on the mask carrier with sharply defined upright sidewalls. However, the structures of the present invention can also be formed in other than closed figures. For example, by combining a phase shift mask region with a pure absorber region, (which substantially blocks the X-rays), an exposure of the target resist can be carried out in such a way that the region covered by the absorber of the target resist, after developing, is connected to the lines formed by the phase shift feature mask. Unconnected lines may also be formed utilizing a phase shift mask having some side walls which are substantially upright and also slanting sidewalls in which the material of the phase shift mask at the sidewall slants inwardly or outwardly. When the X-ray beam is passed through such a phase shift mask, the phase shift effect will cause destructive interference of the X-ray beam at the region underneath the upright sidewalls, but the area under the slanting sidewalls will not have substantial cancellation of the X-ray beam thereunder, resulting in substantially total exposure of the photoresist under these regions. The result is isolated thin walls formed in the target resist which correspond to the upright sidewalls in the phase shift feature on the mask. The slanting sidewalls of the phase shift mask can be produced, for example, by exposing a PMMA photoresist material with a beam of X-rays passed at an angle through an X-ray mask having an absorber on it, so that the absorption of X-rays into the photoresist takes place at an angle. The width of the lines left unexposed on the target photoresist can also be selected as desired by varying the gap between the mask structure and the target photoresist, or by varying the gap between selected regions of phase shifter material on the carrier of the mask and the underlying target photoresist material. Further objects, features, and advantages of the invention will be apparent from the following detailed description when taken in conjunction with the accompanying drawings. |
claims | 1. A passive main control room habitability system in a nuclear reactor power plant having a generation system for converting stored energy of compressed air into electrical power when the main control room habitability system is activated during a loss of all AC power scenario comprising:at least one tank for storing the compressed air;a pressure regulator located downstream of the at least one tank and connected thereto to receive and to reduce pressure of the compressed air to produce lower pressure compressed air;an air-driven mechanism located downstream of the pressure regulator and connected thereto to receive and expand the lower pressure compressed air;an eductor located downstream of the air-driven mechanism; andpiping to connect the tank, pressure regulator, air-driven mechanism and eductor,wherein, the lower pressure compressed air corresponds to an inlet pressure of the air-driven mechanism and wherein, the air-driven mechanism is structured to provide at least one function selected from converting said lower pressure compressed air into the electrical power and providing the lower pressure compressed air to the eductor to receive and distribute air into a control room of the nuclear reactor power plant. 2. The passive main control room habitability system of claim 1 wherein the mechanism comprises an air-driven turbine and a generator. 3. The passive main control room habitability system of claim 1 wherein the mechanism comprises an air-driven pump. 4. The passive main control room habitability system of claim 1 wherein the mechanism compresses an air-driven turbine, generator, and air-driven pump. 5. The passive main control room habitability system of claim 1 wherein the maximum pressure of the compressed air in the at least one tank is about 4000 psi. 6. The passive main control room habitability system of claim 1 wherein the minimum pressure in the at least one tank is about 3333 psi. 7. The passive main control room habitability system of claim 1 wherein the stream of lower pressure compressed air is about 120 psi. 8. The passive main control room habitability system of claim 3 wherein a pressure differential of 25 psi between the stream of lower pressure compressed air and design pressure of the eductor is used to operate the pneumatic pump. 9. A method of generating electrical power by converting stored energy of compressed air in an activated, passive main control room habitability system in a nuclear reactor power plant during a loss of all AC power scenario, comprising:pressurizing the compressed air in at least one storage tank;passing the compressed air through a pressure regulator located downstream of the at least one tank and connected thereto for receiving and for reducing the pressure of the compressed air, and for producing lower pressure compressed air;delivering the lower pressure compressed air to an air-driven mechanism located downstream of the pressure regulator and connected thereto for receiving and expanding the lower pressure compressed air, which corresponds to an inlet pressure of the air-driven mechanism, and for providing at least one function selected from converting said lower pressure compressed air into the electrical power and providing the lower pressure compressed air to an eductor for receiving and distributing air into a control room of the nuclear reactor power plant. 10. The method of claim 9 wherein the mechanism comprises a turbine and a generator. 11. The method of claim 9 wherein the mechanism comprises an air-driven pump. 12. The method of claim 9, wherein the mechanism comprises a turbine, a generator, and an air-driven pump. |
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047956070 | description | Referring now to the FIGURE of the drawing, there is shown a cylindrical core 1 of a gas-cooled high-temperature nuclear reactor formed of a non-illustrated bed of numerous spherical fuel assemblies, which enter into the core 1 through a loading tube 2 and leave the core 1 through a discharge tube 3. The core 1 is surrounded initially by an inner layer of numerous graphite reflector blocks 4 which have a circular-sector or ring-segment shape or also a trapezoidal cross section and are surrounded by an outer layer of insulating stacked carbon blocks 5 which likewise have a circular-sector or ring-segment shaped cross section and are held together by a steel receptacle or jacket 6. The steel receptacle 6 is cooled by numerous vertical U-shaped tubes 7 which are uniformly distributed around the circumference thereof. In the two legs of the respective U-tubes 7, natural circulation is produced due to the different temperatures; this circulation leads the cooling water to an otherwise non-illustrated heat exchanger which is arranged outside the primary system of the reactor. The hot leg of these U-tubes is connected in heat transfer relationship to the steel receptacle 6 in order to absorb the after-heat from the reactor core. The graphite blocks 4 of the side or lateral reflector contain, in the vicinity of the core, a first set of several vertical channels 8, uniformly distributed over the circumference, for containing non-illustrated control rods, which can be inserted into the reflector from the top through guide tubes 9. These guide tubes 9 are spaced from one another by a ring plate 10. The ceiling of the reactor is formed, like in the AVR, of several layers of graphite or carbon blocks which are arranged on top of one another, have a sector-shaped cross section and are supported by the graphite blocks 4 and the carbon blocks 5 of the side or lateral wall. The uppermost blocks 11 of the reactor ceiling or cover are formed of carbon blocks and are closed except for holes provided for the absorber rod guides 9. The blocks 12, 13 and 14 of graphite which are located underneath are formed not only with a second set of channels 15 and the first channels 8 already provided in the reflector blocks 4, for receiving control rods therein, but also with several radial slots 16, through which the cooling gas enters into the core space. The blocks 11, 12 and 13 respectively support a rotary part 17 of graphite which is disposed in the longitudinal axis of the reactor and in which the loading tube 2 is guided. In the bottom of the reactor, the discharge tube 3 is surrounded by several bottom blocks 18 and 19 which form a funnel-shaped bottom and are formed with numerous vertical holes through which the hot coolant flows off through an intermediate space supported by columns 20 and through an annular space 21 surrounding the discharge tube 3. The receptacle 6 is provided with a base plate 22 which is formed with several holes 23 uniformly distributed over the circumference thereof and a central opening 24 which is protected from the emerging hot gas by insulation 25, which is not otherwise described in detail. The gas entering through the holes 23 flows through an second channels 15 vertically upwardly, then through an intermediate space between the blocks 11 and 12 and through the slots 16 in the blocks 12, 13 and 14 down into the core 1. In normal operation, the side or lateral and ceiling or cover reflector are cooled. In the normal shutdown procedure of this reactor, the control rods are inserted and the blower power is throttled; in the process, the temperature in the core rises and the core becomes subcritical due both to the high negative temperature coefficient of the reactivity and to the inserted rods. Thereafter, the reactor can be cooled down with reduced blower power to the cold, subcritical state. If the blowers fail, the reactor goes into the hot subcritical state due to the rising temperature, even without the control rods having been inserted. The heat stored in the fuel elements and the after-heat newly produced in them is thus distributed over the core and the reflector which subsequently gives off the heat through the insulation of carbon blocks 5 to the U-tubes 7. As long as the operating pressure in the primary loop of, for example, 50 bar is maintained, the heat exchange in the core is aided by internal convection. If the pressure drops, i.e. for example below 10 bar, this convection is no longer of great importance, so that the entire heat must and can be relinquished through conduction and radiation from the core, via the reflector and the insulation, to the U-tubes 7. The following table contains the main design data of the illustrated reactor. ______________________________________ Thermal power output MW 125 Height of core m 6.0 Diameter of core m 3.0 Average power density of the core MW/m.sup.3 2.94 Reflector thickness m 0.75 Single-zone core OTTO(once through, then out)loading Type of cycle Uranium/Plutonium Heavy-metal loading/fuel element g 7 Burn-up GWd/t 40 Average exit temperature of coolant .degree.C. 750 Average entrance temperature of coolant .degree.C. 250 Number of reflector rods 20 Thickness of reflector rods cm 8 Reactivity data: Temperature effect (20.degree. C. to 750.degree. C.) % 6 Xenon effect % 3 Maximum water break-in % 1 Effectiveness of reflector rods % 12 Effectiveness of one reflector rod % 0.5 Initial enrichment % 5 Temperature coefficient: Equilibrium core k/.degree.C. -7 .multidot. 10.sup.-5 Xenon-free core k/.degree.C. -10 .multidot. 10.sup.-5 Fuel element dwelling time d 500 Conversion rate 0.4 Radial temperature difference K 120 Maximum fuel element temperature in the .degree.C. 850 equilibrium core Maximum fuel element temperature after shutdown: Reactor at pressure .degree.C. 1200 Loss of pressure accident .degree.C. 1400 Thickness of carbon block insulation m 0.25 ______________________________________ |
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