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nuclear_patents

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claims
1. An EUVL multilayer structure, comprising: alternating layers of an absorber layer and a spacer layer; and an interface layer placed between each absorber layer and each spacer layer, wherein said interface layer comprises a material that controls interfacial reactions between said absorber layer and said spacer layer subsequent to fabrication of said multilayer, wherein said material is selected from the group consisting of boron carbide and carbon with boron based compounds. 2. The EUVL multilayer structure of claim 1 , wherein said material is characterized as having a low absorption of EUV and X-ray wavelengths. claim 1 3. The EUVL multilayer structure of claim 1 , wherein said absorber layer comprises molybdenum and said spacer layer comprises silicon. claim 1 4. The EUVL multilayer structure of claim 3 , wherein said interface layer controls interfacial reactions, increases the reflectance of EUV and X-ray wavelengths and increases the thermal stability. claim 3 5. The EUVL multilayer structure of claim 1 , wherein said introduced interface layer comprises B 4 C. claim 1 6. The EUVL multilayer structure of claim 3 , wherein the thickness of an interface layer between molybdenum on silicon has a thickness within a range from 0.1 nm to 1.0 nm and wherein an interface layer between silicon on molybdenum has a thickness within a range from 0.1 nm to 0.5 nm. claim 3 7. The EUVL multilayer structure of claim 1 , wherein said absorber layer comprises molybdenum and said spacer layer comprises beryllium. claim 1 8. The EUVL multilayer structure of claim 1 , wherein said interface layer results in the formation of smoother more stable interfaces between all layers of said multilayer structure as compared to a multilayer structure that does not have said interface layer. claim 1 9. A method of making an EUVL multilayer structure, comprising: providing alternating layers of an absorber layer and a spacer layer; and placing an interface layer between each such absorber layer and each such spacer layer, wherein said interface layer comprises a material that controls interdiffusion between said absorber layer and said spacer layer, wherein said material is selected from the group consisting of boron carbide and carbon with boron based compounds. 10. The method of claim 9 , wherein said material is characterized as having a low absorption of EUV and X-ray wavelengths. claim 9 11. The method of claim 9 , wherein said absorber layer comprises molybdenum and said spacer layer comprises silicon. claim 9 12. The method of claim 11 , wherein said interface layer controls the formation of interfacial layers, increases the reflectance and increases thermal stability. claim 11 13. The method of claim 9 , wherein said interface layer comprises B 4 C. claim 9 14. The method of claim 11 , wherein the thickness of an interface layer between molybdenum on silicon has a thickness within a range from 0.1 nm to 1.0 nm and wherein an interface layer between silicon on molybdenum has a thickness within a range from 0.1 nm to 0.5 nm. claim 11 15. The method of claim 9 , wherein said interface layer is deposited using a method selected from the group consisting of magnetron sputtering, ion beam sputtering and electron evaporation. claim 9 16. The method of claim 9 , further comprising annealing said multilayer structure to reduce its residual stress. claim 9 17. The method of claim 16 , wherein said multilayer structure is annealed at about 150 degrees Celsius for about 3 hours. claim 16 18. The method of claim 9 , wherein said interface layer results in the formation of smoother more stable interfaces between all layers said multilayer structure as compared to a multilayer structure that does not have said interface layer. claim 9 19. An EUVL multilayer structure, comprising: alternating layers of an absorber layer and a spacer layer; and a non-hydrogenated interface layer placed between each absorber layer and each spacer layer, wherein said interface layer comprises a material that controls interfacial reactions between said absorber layer and said spacer layer subsequent to fabrication of said multilayer. 20. The EUVL multilayer structure of claim 19 , wherein said material is selected from the group consisting of boron carbide and carbon with boron based compounds. claim 19
046577262
summary
CROSS REFERENCE TO RELATED APPLICATIONS Reference is hereby made to the following copending applications dealing with related subject matter and assigned to the assignee of the present invention. 1. "An Improved Water Displacer Rod Spider Assembly For a Nuclear Reactor Fuel Assembly" by Trevor A. Francis; U.S. Ser. No. 595,154; filed Mar. 30, 1984. 2. "Control Rod For Nuclear Reactor" by Trevor A. Francis and John F. Wilson; U.S. Ser. No. 556,576; filed Nov. 30, 1983. BACKGROUND OF THE INVENTION The present invention relates generally to nuclear reactors, and more particularly is directed to an apparatus used with a fuel assembly for controlling the nuclear reactivity by varying the volume of the moderator/coolant associated with the fuel rods of the assembly and, at the same time, adding a burnable poision gas in thereby improving the fuel utilization, thus allowing for lower fuel enrichments. In most nuclear reactors the core portion is comprised of a large number of elongated fuel elements or rods grouped in and supported by frameworks referred to as fuel assemblies. The fuel assemblies are generally elongated and receive support and alignment from upper and lower transversely extending core support plates. Conventional designs of these fuel assemblies include a plurality of fuel rods and hollow tubes or guide thimbles held in an organized array by grids spaced along the fuel assembly length and attached to the guide thimbles. The guide thimbles are structural members which also provide channels for neutron absorber rods, burnable poison rods or neutron source assemblies which are all vehicles for controlling the reactivity of the reactor. Top and bottom nozzles on opposite ends thereof are secured to the guide thimbles in thereby forming an integral fuel assembly. Generally, in most reactors, a moderator/coolant such as water, is directed upwardly through aperatures in the lower core support plate and along the various fuel assemblies to receive the thermal energy therefrom. An example of such a fuel assembly structure can be seen in U.S. Pat. No. 4,326,419; granted to Donald J. Hill. Since the nuclear industry's inception, core component design improvements have evolved in response to changes in regulatory requirements, manufacturing considerations, and power generation costs. Increasingly, utilities and fuel suppliers have focused ever more strongly on neutron economy and reduced power generation costs. These effects have been motivated by increased fuel and fuel enrichment costs. In response to these demands, designers have been working hard in developing new designs and in modifying existing designs to improve fuel utilization, as well as, in increasing safety margins in reactors. It is known that improved fuel economy can be achieved in a PWR (Pressurized Water Reactor) by initially operating with a reduced H/U (hydrogen/uranium) ratio and then returning the ratio to normal somewhat later in the core cycle. The initial H/U reduction has the effect of increasing the epithermal part of the neutron spectrum at the expense of the thermal part. This results in increased breeding and decreased fission and fuel depletion rates. Since reactor fuel starts off with excess reactivity, this spectral shift represents no problem early in the core life; however, if the decrease in H/U were maintained through the entire core cycle, nothing would be gained because the higher fertile material absorption and lower fission rate would more than balance the gains from the increased breeding and lower burnup. Consequently, in order to properly take advantage of the increased breeding and lower burnup, it is necessary to return the H/U ratio back to its normal value. The net result would allow a reactor to be operated for a full core cycle with a reduced initial uranium enrichment. One of the ways of altering the H/U ratio which has been investigated involves the use of displacer rods. As the name implies, these rods are placed in the core to initially displace some of the moderating water and decrease the H/U ratio, and then, at some point during the core cycle, the displacement associated with these rods would be removed. One approach considered for removing this displacement is through the use of movable mechanisms, similar to those associated with control rods. Such an approach is described in the above cross-referenced copending application of Trevor A. Francis, entitled "An Improved Water Displacer Rod Spider Assembly For A Nuclear Reactor Fuel Assembly". Among other unfavorable conditions, movable control mechanisms are expensive. Another approach contemplated for removing the displacement is to have membranes provided on the ends of the displacer rods which are penetrated at some point in time to allow the rods to be filled with water. The basic idea makes use of a small heating element surrounding a specially indented end cap on the hollow displacer rod. At an appropriate time, the heater is turned on and the indented part of the end cap is weakened to the point where the external water pressure opens the end cap and fills the rod with water. The basic idea was expanded to include a manifold for each fuel assembly which would be constructed very similar to the spider-like control rod clusters presently used in reactors. All the rods in the cluster would be controlled by a single end-cap in the cluster head. The end-cap on each cluster would have an external plug connected to the heater inside. The procedure for changing the H/U ratio during a reactor cycle would be as follows: first, the reactor would be reduced to lower power or placed in a hot shut-down condition; the heaters in all the displacer rod clusters would be activated through heater power cables until all the end-caps have blown; and then, the reactor would be started up again. With the increased reactivity resulting from the higher H/U ratio, an elevated concentration of boron shim would have to be reintroduced into the primary coolant. Some of the problems anticipated with such an approach would be the reliability of the connectors and wiring when exposed to the pressure and corrosive capabilities of the reactor water, the potential failure of the rods themselves, what to do with the burst displacer rods after use since they are contaminated and thus inconvenient and impractical to transport and/or discard, and lastly, there is concern as to what would happen to such a displacer rod system in the case of LOCA (Loss of Coolant Activity) or other reactor problems. The present inventors were aware of the teachings of the above described works and their shortcomings when they developed their alternative approach which is the subject of the present invention. SUMMARY OF THE INVENTION The present invention provides a moderator control apparatus for a nuclear reactor fuel assembly so as to improve fuel utilization and thereby reduce fuel cycle costs. The apparatus is designed to displace a portion of the moderator/coolant for a reduced H/U ratio at initial start-up and then later, on a gradual basis, remove the displacement in shifting the energy spectrum by returning the H/U ratio to normal. The displacer rods are initially filled with a gaseous burnable poison to prevent large positive moderator temperature coefficients so as to insure a negative moderator temperature coefficient and to help in power shaping. Near the end of the cycle, with the reintroduction of the moderator/coolant, any remaining burnable poison gas is released into the system and taken away in the off gas system. The design is such that the removal of the moderator/coolant displacement, as well as, the release of the burnable poison gas is carried out on a slow and independently controlled basis in thereby insuring safety against accidental release or large change of reactivity during any single occurrence or transient. The system also increases an operator's flexibility in relieving unexpected power tilts during the operating cycle. This spectral shift, burnable poison, apparatus additionally alleviates the utilities concern over disposal of spent burnable poisons that are presently used to hold down excess reactivity. Further, the design of the apparatus allows for last minute power distribution adjustment. Since the poison gas can be loaded at the plant site and therefore it is possible to change the poison loading up until the time when the apparatus is placed in the core. Such flexibility greatly aids in finding acceptable loading patterns if after shutdown a utility decides not to use assemblies previously planned to be loaded. Still further, the design is such that maintenance and repair can easily be performed in the spent fuel pit. Another highly advantageous feature of the invention is that the control apparatus is reusable simply by recharging or refilling with a poison gas. This refilling operation can easily take place on-site, thus eliminating the expense of discarding the rods or the inconvenience and high costs in transporting them off-site due to their contaminated condition. Accordingly, the present invention sets forth in a fuel assembly for a nuclear reactor including an organized array of upstanding fuel rods, a number of elongated guide thimbles strategically located within the fuel rod array, and a moderator/coolant flowing upwardly along the fuel rods, an apparatus to control the nuclear reactivity for improved fuel utilization in thereby reducing fuel cycle costs. The control apparatus includes: (a) a plurality of hollow displacer rods adapted to be inserted into respective ones of the guide thimbles for displacement of a predetermined volume of the moderator/coolant associated with the fuel rods to decrease the hydrogen/uranium ratio from a given level; (b) a manifold adapted to be disposed on the top of the fuel assembly and having a plurality of inlet ports and a plurality of exit ports connected to and in fluid flow communication with respective ones of the displacer rods and with each of the inlet ports being in fluid flow communication with at least one of the exit ports; and (c) valve means operably associated with the manifold inlet ports for selectively controlling the flow and non-flow of the moderator/coolant into the displacer rods, flow of the moderator/coolant through the inlet ports and into the displacer rods increasing the moderator/coolant volume to thereby shift the hydrogen/uranium ratio back to its given level. The invention further includes the displacer rods being filled with a burnable poison gas which is released into the moderator/coolant as it flows into the rods so as to insure a negative moderator temperature coefficient and to assist in power shaping. More particularly, in the preferred embodiment, the manifold takes on the form of a hub defining a central opening and a plurality of hollow tube-like vanes mounted on and extending radially outwardly from the hub. The inward ends of the vanes defining the inlet ports which are circumferentially spaced about and disposed adjacent to the central opening. The valve means is selectively movable between a non-flow mode, wherein all inlet ports are closed to the flow of moderator/coolant therethrough, and a sequential flow mode, wherein some of the inlet ports are open to flow while other ones are closed to flow of the moderator/coolant therethrough. In the preferred embodiment, the valve means is in the form of an elongated hollow pipe or stem having at least one aperature or orifice, and preferably two, defined in the lower section thereof. The valve stem is rotatably mounted in the manifold with its lower orificed section being disposed in the central opening of the manifold and with its exterior wall being in abutting contact with the inlet ports so as to prevent flow of the moderator/coolant therethrough. Flow of the moderator/coolant, and the release of the burnable poison gas simultaneously therewith, through the inlet ports only occurs when the orifices are aligned with the inlet ports which is accomplished through rotation of the valve stem. These and other advantages and attainments of the present invention will become apparent to those skilled in the art upon a reading of the following detailed description when taken in conjunction with the drawings wherein there is shown and described an illustrative embodiment of the invention.
summary
048256471
abstract
A thruster assembly is disclosed which includes a removable filament mounted in a heat exchange cavity which isolates propellant from the filament and transfers energy from the filament to the propellant. The filament may comprise a single winding of wire or may, if desired, comprise a bifilar wound helix. Also disclosed are a number of ways of powering the filament including a plurality of power supplies provided for redundancy as well as variability of operation. The thruster assembly housing includes sophisticated heat conduction structure including a tortuous internal heat conduction path which minimizes heat loss from the thruster for a variety of disclosed purposes. Also disclosed is structure for providing energy transfer to propellant both through radiation and emission. Several techniques for improving the performance of the thruster assembly and particularly related to the nozzle structure as well as to the fuel supply structure and heat exchange structure form the main basis for this disclosure. Further, a test bed facility for testing the inventive thruster assembly is set forth.
summary
summary
summary
claims
1. A nuclear fuel assembly having an elongated dimension and comprising: a plurality of interconnected components wherein at least some of the interconnected components comprise:a top nozzle;a bottom nozzle;a plurality of guide thimbles extending between the top nozzle and the bottom nozzle;a plurality of fuel rods extending between the top nozzle and the bottom nozzle; anda plurality of grids arranged in a tandem spaced relationship that extends between the top nozzle and the bottom nozzle along the elongated dimension, with each of the grids having a plurality of cells some of which support fuel rods and others through which the guide thimbles respectively pass and attach to the plurality of grids;wherein at least one grid of the plurality of grids comprises a peripheral surface area that extends in a plane a distance along the elongated dimension; andwherein the at least one grid of the plurality of grids comprises a bimetallic spring that moves between a first and second position relative to the plane as the fuel assembly transitions from a reactor core shutdown temperature to a reactor core operating temperature, with the second position placing the bimetallic spring in contact with a corresponding grid of an adjacent nuclear fuel assembly located in a reactor core. 2. The nuclear fuel assembly of claim 1 wherein the bimetallic spring has an elongated dimension and the elongated dimension of the bimetallic spring extends transverse to the elongated dimension of the nuclear fuel assembly. 3. The nuclear fuel assembly of claim 2 wherein the bimetallic spring is continuous and extends across several of the grid cells. 4. The nuclear fuel assembly of claim 1 wherein the at least one grid of the plurality of grids is a mid-grid. 5. The nuclear fuel assembly of claim 1 wherein the at least one grid of the plurality of grids is one of an upper grid or a lower grid or both an upper grid and a lower grid. 6. The nuclear fuel assembly of claim 1 wherein the bimetallic spring is configured in a rectangular shape having an elongated dimension. 7. The nuclear fuel assembly of claim 6 wherein the elongated dimension of the bimetallic spring extends substantially parallel to the elongated dimension of the nuclear fuel assembly. 8. The nuclear fuel assembly of claim 1 wherein the bimetallic spring comprises stainless steel and either FeNi36 or 64FeNi. 9. The nuclear fuel assembly of claim 8 wherein the bimetallic spring is formed on each corner of the at least one grid of the plurality of grids. 10. The nuclear fuel assembly of claim 1 wherein the peripheral surface area of the at least one grid of the plurality of grids comprises a base metal, and wherein the bimetallic spring is formed by coating the base metal with a material having a lower coefficient of thermal expansion than the base metal. 11. The nuclear fuel assembly of claim 1 wherein the bimetallic spring is formed on a corner of the at least one grid of the plurality of grids. 12. The nuclear fuel assembly of claim 1 wherein the bimetallic spring does not protrude outwardly from the plane in the first position and protrudes outwardly from the plane in the second position to contact the corresponding grid of the adjacent nuclear fuel assembly. 13. The nuclear fuel assembly of claim 1 wherein the bimetallic spring is configured in a round disc shape. 14. The nuclear fuel assembly of claim 13 wherein the bimetallic spring has a dome when exposed to the reactor core operating temperature. 15. The nuclear fuel assembly of claim 13 further comprising relief holes spaced around the circumference of the bimetallic spring. 16. The nuclear fuel assembly of claim 1 wherein the bimetallic spring comprises a base material coated with a material having a different coefficient of thermal expansion than the base material. 17. The nuclear fuel assembly of claim 1 wherein the bimetallic spring comprises a lamination of a first material and a second material, wherein the first material has a different coefficient of thermal expansion than the second material.
summary
summary
claims
1. A canister for spent nuclear fuel storage comprising:a longitudinal axis;an elongated shell extending along the longitudinal axis, the shell including a top end and a bottom end;a cavity extending along the longitudinal axis inside the shell for storing spent nuclear fuel;a baseplate attached to the bottom end of shell and enclosing a lower portion of the cavity;a closure lid detachably fastened to the top end of the shell and enclosing an upper portion of the cavity;a plurality of mounting bolts extending longitudinally through the lid and threadably engaging the top end of the shell; wherein the canister is configured for placement inside an outer overpack with radiation shielding; andwherein the lid has a circular lid body comprising a lower portion inserted into the cavity of the shell, an upper portion, and an intermediate annular mounting flange protruding radially outwards beyond the lower and upper portions, the bolts extending longitudinally through respective vertical bolt holes in the mounting flange to engage the top of the shell. 2. The canister according to claim 1, wherein the mounting flange does not protrude radially outwards beyond the top of the shell. 3. The canister according to claim 1, wherein the lid includes an annular step-shaped upper shoulder at a transition between the mounting flange and upper portion, and an annular step-shaped lower shoulder at a transition between mounting flange and the lower portion. 4. The canister according to claim 1, further comprising an upper circumferential seal disposed at an interface between the upper shoulder and the top of the shell, and a lower circumferential seal disposed at an interface between the lower portion and the shell. 5. The canister according to claim 1, wherein the lid body has a monolithic unitary construction which includes the upper portion, the lower portion, and the mounting flange. 6. The canister according to claim 1, wherein the lid is hermetically seal welded to the top of the shell and does not protrude radially outwards beyond the top of the shell. 7. The canister according to claim 1, wherein the bolts each define a bolt axis which is spaced by a first radial distance from the longitudinal axis of the canister which is less than a second radial distance between an outer surface of the shell and the longitudinal axis. 8. The canister according to claim 1, wherein the bolts each threadably engage a corresponding upwardly open threaded bore formed in the top of the shell. 9. The canister according to claim 8, wherein the threaded bores penetrate an upward facing annular end surface of the top of the shell. 10. The canister according to claim 9, when the bolts are arranged in a circumferentially and uniformly spaced apart bolt pattern extending a full 360 degrees around the annular end surface of the top of the shell. 11. The canister according to claim 8, wherein the fastening portion has a greater first wall thickness than a second wall thickness of the lower portion of the shell between the fastening portion and the bottom end of the shell, and the fastening portion having a height greater than at least three times its first wall thickness. 12. The canister according to claim 11, wherein the fastening portion protrudes radially outwards beyond the lower portions of the shells and defines an outwardly open recessed area extending longitudinally between the fastening portion and the baseplate of the canister. 13. The canister according to claim 12, further comprising a plurality of longitudinally-extending cooling fins protruding radially outwards from the shell in the recess. 14. The canister according to claim 13, wherein the fins do not protrude radially outwards beyond the upper reinforced fastening portion of the shell. 15. The canister according to claim 11, wherein the baseplate protrudes radially outwards beyond the lower portion of the shell. 16. A canister for spent nuclear fuel storage comprising:a cylindrical shell extending along the longitudinal axis, the shell including a top end, a bottom end, and an outer surface;an internal cavity extending between the top and bottom ends of the shell along the longitudinal axis for storing spent nuclear fuel;a baseplate attached to the bottom end of shell and enclosing a lower portion of the cavity;a closure lid detachably fastened to the top end of the shell and enclosing an upper portion of the cavity, the lid having a circular body comprising a first upper portion and a second mounting flange portion protruding radially outwards beyond the first upper portion;a plurality of mounting bolts extending longitudinally through the second mounting flange portion of the lid and threadably engaging the top end of the shell; wherein the second mounting flange portion of the lid does not protrude radially outwards beyond the outer surface of the shell;wherein the canister is configured for placement inside an outer overpack with radiation shielding; andwherein the lid further comprises a third lower portion inserted into the cavity of the shell, the second mounting flange portion protruding radially outwards beyond the third lower portion. 17. The canister according to claim 16, wherein the bolts each threadably engage a corresponding upwardly open threaded bore formed in the top of the shell. 18. The canister according to claim 16, further comprising an annular circumferential seal disposed at an interface between an upward facing annular end surface of the top of the shell and a downward facing annular surface defined by the mounting flange portion of the lid. 19. The canister according to claim 18, further comprising a circular radiation shield plate received in an upper portion of the cavity and supported therein by the shell, the shield plate disposed between the mounting flange portion of the lid and the cavity. 20. The canister according to claim 19, further comprising a circular diaphragm seal interspersed between the shield plate and the mounting flange portion of the lid. 21. The canister according to claim 16, further comprising a plurality of longitudinally-extending cooling fins protruding radially outwards from the shell, the fins spaced perimetrically apart around the shell. 22. The canister according to claim 21, wherein the fins do not protrude radially beyond the lid of the canister. 23. The canister according to claim 22, wherein the fins do not protrude radially beyond the baseplate of the canister.
claims
1. A clamp apparatus stiffening a riser brace assembly fixedly attached between a riser pipe in a nuclear reactor and a wall of the reactor for stabilizing the riser pipe, the riser brace assembly composed of a riser brace block attached to the wall, an upper riser brace leaf and a lower riser brace leaf, the upper and lower riser brace leaves in spaced vertical relation from each other and attached between the riser brace block and to the riser pipe via a riser brace, the clamp apparatus comprising: a first plate engaging a top surface of the upper riser brace leaf; a second plate engaging a bottom surface of the lower riser brace leaf; and a wedge assembly arranged between the first and second plates and engaging a bottom surface of the upper riser brace leaf and a top surface of the lower riser brace leaf. 2. The clamp apparatus of claim 1 , wherein claim 1 the first plate and second plate apply clamping forces on the riser brace leaves, and the wedge assembly applies counter-forces to the clamping forces on opposing surfaces of the riser brace leaves so as to fixedly secure the clamp apparatus to the riser brace assembly. 3. The clamp apparatus of claim 2 , wherein the wedge assembly is expandable so as to apply forces countering the clamping forces. claim 2 4. The clamp apparatus of claim 2 , further comprising a plurality of mechanical fasteners adapted to provide clamping forces to the first plate, second plate and wedge assembly. claim 2 5. The clamp apparatus of claim 1 , wherein the wedge assembly further includes a plurality of wedge components, said wedge components adapted to evenly distribute stress on the riser brace assembly. claim 1 6. The clamp apparatus of claim 5 , wherein one of the wedge components includes a key that engages a slot in the first or second plate, aligning the wedge assembly between the first and second plates. claim 5 7. clamp apparatus of claim 1 , wherein the first and second plates engage each other via a tongue and groove interface. claim 1 8. The clamp apparatus of claim 1 , wherein; claim 1 the first plate includes one or more tongue portions, and the second plate includes one or more protrusions containing a recessed groove engaging a tongue portion of the first plate, aligning the first and second plates at the riser brace assembly. 9. The clamp apparatus of claim 1 , wherein the first plate, second plate and wedge assembly are positioned near an interface attaching the riser brace block to the riser brace leaves. claim 1 10. A clamp apparatus supporting a riser brace assembly fixedly attached between a riser pipe in a nuclear reactor and a wall of the reactor for stabilizing the riser pipe, the riser brace assembly having a riser brace block attached to the wall, an upper riser brace leaf and a lower riser brace leaf, the upper and lower riser brace leaves in spaced vertical relation from each other and attached between the riser brace block and to the riser pipe via a riser brace, the clamp apparatus comprising: a top plate in contact with a surface of the upper riser brace leaf; a support plate in contact with a surface of the lower riser brace leaf; and a wedge assembly provided between the top plate and support plate applying tension against surfaces of the upper and lower riser brace leaves that are opposite the surfaces in contact with the top plate and support plate. 11. The clamp apparatus of claim 10 , further comprising a plurality of fasteners applying clamping forces to fixedly secure the top plate and support plate to the riser brace leaves. claim 10 12. The clamp apparatus of claim 10 , wherein the top plate and support plate engage each other via a tongue and groove interface. claim 10 13. The clamp apparatus of claim 12 , wherein claim 12 the top plate includes one or more tongue portions, and the support plate includes one or more protrusions containing a recessed groove for engaging a tongue portion of the support plate aligning the top plate and support plate at the riser brace assembly. 14. The clamp apparatus of claim 1 , wherein claim 1 the upper riser brace leaf is sandwiched between a wedge assembly top surface and a first plate bottom surface, and the lower riser brace leaf is sandwiched between a wedge assembly bottom surface and a second plate top surface. 15. The clamp apparatus of claim 10 , wherein claim 10 the upper riser brace leaf is sandwiched between a wedge assembly top surface and a top plate bottom surface, and the lower riser brace leaf is sandwiched between a wedge assembly bottom surface and a support plate top surface.
summary
047160179
claims
1. In a nuclear reactor fuel assembly having a structural tube with a predetermined inside diameter, a generally cylindrical insert of an axial length substantially smaller than the axial length of said structural tube and having a generally cylindrical passageway of a predetermined diameter smaller than said predetermined inside diameter for providing an effectively reduced inside diameter for said structural tube, said insert comprising: means, having an outside diameter approximately equal to said predetermined inside diameter, for coaxially centering said insert within said structural tube; forming lobes, operable when expanded to locally deform against said structural tube thereby locking said insert within said structural tube. 2. The insert of claim 1, further comprising projections extending radially into the passageway of said insert and operable to cooperate with an expansion tool to accurately position said expansion tool with respect to said forming lobes. 3. The insert of claim 3, wherein said projections are expandable with said forming lobes and wherein said projections are operable, in an unexpanded configuration, to pass an expansion tool moving in a first direction through said passageway and to register said expansion tool when moving in a direction opposite to said first direction, with said forming lobes. 4. The insert of claim 1, wherein said coaxial centering means comprises a pair of centering lobes, each having an outside diameter approximately equal to said predetermined inside diameter, disposed at ends of said insert. 5. The insert of claim 4, wherein said coaxial centering means is provided with a plurality of circumferentially spaced axial slots. 6. The insert of claim 1, wherein said coaxial centering means comprises an elongated central lobe formed on said insert and having an outside diameter approximately equal to said predetermined inside diameter. 7. The insert of claim 6, wherein said coaxial centering means is provided with a plurality of circumferentially spaced axial slots. 8. The insert of claim 1, wherein said coaxial centering means comprises a pair of lobes disposed at ends of said insert and a central lobe, all of said lobes having an outside diameter approximately equal to said predetermined inside diameter. 9. The insert of claim 8, wherein said coaxial centering means is provided with a plurality of circumferentially spaced axial slots. 10. The insert of claim 1, wherein said forming lobes comprise a pair of annular lobes having generally arcuate cross-sections formed at axially spaced apart locations along said insert, said annular lobes having a nominal thickness, said insert having reduced thickness portions axially disposed on either side of said annular lobes to facilitate expansion of said lobes. 11. The insert of claim 10, further comprising a plurality of axially extending expansion slots formed in said insert in a region of said forming lobes, said expansion slots being circumferentially spaced about said forming lobes.
summary
abstract
A garment for protection from ultraviolet radiation, having a torso garment with a front side and a rear side that extend from a first edge to an end. Further having first and second lateral sides and first and second shoulder sections. Extending from the first and second lateral sides and the first and second shoulder sections are first and second sleeves. First and second hand covers extend from the first and second sleeves respectively. The first and second hand covers each have an elastic band. The elastic band, a distal end, and third and fourth lateral sides define an interior face. The interior face has a thumb loop and at least first and second finger loops. The elastic band, the distal end, and the third and fourth lateral sides also define an exterior face.
052157067
abstract
A method and apparatus for eliminating erroneous test readings during ultrasonic testing of nuclear fuel rods is disclosed. The method and apparatus employ the use of an alignment guide to effect temporary alignment of the fuel rods during testing in order to overcome mechanical deviations of the rods. The alignment guide includes elongated, parallel guide bars for insertion into an array prior to ultrasonic testing. The bars are mounted on a base which, in turn, is movably mounted on a support element. A fixed guide maintains the relative position of the guide bars with respect to one another. A hydraulic element causes the guide bars to be inserted and removed from the fuel array. In a preferred arrangement, the alignment guide may be removably mounted on a frame containing the ultrasonic testing equipment.
description
This application is a National Phase of PCT/EP2009/067443, filed Dec. 17, 2009, entitled, “METHODS FOR PREPARING AN ACTINIDE OXALATE AND FOR PREPARING AN ACTINIDE COMPOUND”, and which claims priority of, French Patent Application No. 08 58860, filed Dec. 19, 2008, the contents of which are incorporated herein by reference in their entirety. The present invention relates to a method for preparing an actinide(s) oxalate. It also relates to a method for preparing an actinide(s) compound and, in particular, an actinide(s) oxide, carbide or nitride using said method. The invention makes it possible to obtain powders of simple or mixed actinides oxalates provided with remarkable properties, particularly as regards their aptitude to be handled, to be filtered and to be poured, and, from said oxalate powders, powders of simple or mixed actinides compounds that have said same properties. The invention finds application in the field of processing and recycling of spent nuclear fuels where it has a quite particular interest for the preparation of actinides compounds suited to serving in the manufacture of nuclear fuel pellets of oxide, carbide or nitride type and, more specially, of mixed actinide oxides. These mixed actinides oxides may in particular be mixed oxides of uranium and of plutonium with if appropriate neptunium ((U,Pu)O2 or (U,Pu,Np)O2), mixed oxides of uranium and of americium with if appropriate curium ((U,Am)O2 or (U,Am,Cm)O2), mixed oxides of uranium and of curium ((U,Cm)O2), or instead mixed oxides of uranium, of plutonium and of americium with if appropriate curium ((U,Pu,Am)O2 or (U,Pu,Am,Cm)O2) and/or neptunium ((U,Pu,Np,Am)O2 or (U,Pu,Np,Am,Cm)O2). The nuclear fuel cycle as implemented by AREVA NC in France includes steps that consist in converting uranyl nitrate and plutonium nitrate into oxides that are then used to manufacture nuclear fuel pellets and, in particular, MOX fuels. In this way are produced uranium oxide UO2, plutonium oxide PuO2 and mixed oxides of uranium and of plutonium (U,Pu)O2. In the latter case, this is known as coconversion. The (co)conversions of uranyl nitrate and plutonium nitrate are currently achieved by methods that are all based on a same principle, namely that uranium, plutonium or these two elements are firstly (co)precipitated in the form of an insoluble salt by bringing into contact one of these nitrates or a mixture of the two with a precipitation agent then the resulting (co)precipitate is, after filtration, washing and spinning, calcinated to be transformed into an oxide. For the preparation of uranium oxide, the precipitation agent is typically aqueous ammonia so that the uranium precipitates in the form of ammonium uranate, which leads by calcination to uranium sesquioxide U3O8, which is then reduced into UO2. For the preparation of plutonium oxide or a mixed oxide of uranium and plutonium, the precipitation agent is typically oxalic acid so that the (co)precipitate obtained is an oxalate. In all cases, it is essential that the (co)conversion method used leads to obtaining an oxide powder that has characteristics compatible with use in the different operations used during the manufacture of nuclear fuel pellets. In particular, said powder must be easy to handle, have a good aptitude to filtration and flow. Moreover, it is desirable that it generates the least possible dust to avoid disseminating radioactive materials in the confined enclosures in which the nuclear fuel pellets are manufactured and reduce the risks of external contamination in the event of rupture of confinement. It is thus important that the (co)precipitates from which the UO2, PuO2 and (U,Pu)O2 powders are obtained have, themselves, such characteristics and that consequently the granulometric and morphological aspects resulting from interactions between the processes of nucleation, crystalline growth, agglomeration and splintering that occur during (co)precipitation are taken into account during the preparation of said (co)precipitates. Precipitating actinides is traditionally carried out in stirred reactors. However, the use of this type of reactor leads to precipitates being obtained that have a dispersed granulometric distribution, with the presence of very fine dust generating particles. Precipitation in a rotating disc reactor generally makes it possible to obtain precipitates with narrower granulometric distribution but poses problems of scaling and accumulation of materials due to the large diameter of the disc. Optimisation studies are thus necessary to limit as best as possible the deposits of crystals on the walls in what is known as the nucleation zone which these reactors comprise. The problems of scaling are all the more acute in the case of actinide oxalates given that the nuclei that form are particularly sticky. In certain adaptations of this technology, the disc is replaced by a Rushton turbine, which leads to increasing the shear rate. The problems of scaling may then prove to be less important but to the detriment of the granulometry due to attrition phenomena. Precipitation in Vortex effect reactor does not have these drawbacks. This type of reactor is moreover employed with success in the nuclear industry for the oxalic precipitation of plutonium. Having said that, it does not represent an entirely satisfactory solution in so far as the production capacity of (co)precipitates of actinides in Vortex effect reactor is limited for reasons of criticality. Yet, in the perspective of building new plants for processing spent nuclear fuels in which it is envisaged to produce fluxes containing several purified actinides, amenable to beneficiation into mixed actinide oxides, carbides or nitrides, it would be desirable to have available a method that makes it possible to produce actinides oxalates and, in particular, mixed oxalates at high rates. Furthermore, it would be desirable that this method makes it possible to obtain actinides oxalates in the form of powders, the granulometric and morphological characteristics of which and, consequently, the properties of handleability, filterability and flowability are, if possible, even more interesting than those presented by actinides oxalate powders prepared in Vortex effect reactor. The Inventors have thus set themselves the aim of providing such a method. This aim is attained by the invention which proposes, in the first instance, a method for preparing an oxalate of one or more actinides, which comprises: the precipitation of said actinide or the coprecipitation of said actinides in the form of oxalate particles by bringing into contact an aqueous solution containing the actinide(s) with an aqueous solution of oxalic acid or of an oxalic acid salt; and the collection of the resulting oxalate particles; and which is characterised in that the precipitation or coprecipitation is carried out in fluidised bed. For reasons of simplicity, the term “(co)precipitation” serves to designate, in what precedes and follows, a precipitation or a coprecipitation, whereas the term “(co)precipitate” serves to designate a precipitate or a coprecipitate. In a similar manner, the term “(co)conversion” serves to designate, in what precedes and follows, a conversion or a co-conversion. Furthermore, the expressions “solution of actinide(s)” and “oxalic solution” serve to designate respectively, in what follows, the aforementioned aqueous solution containing the actinide(s) and the aqueous solution of oxalic acid or of oxalic acid salt. It is recalled that precipitation in fluidised bed is a precipitation technique known to those skilled in the art. Indeed, its use has already been described in the literature to precipitate a certain number of salts such as calcium, nickel, zinc, lead or copper carbonates (see for example, Van Ammers et al., Wat. Supply, 1986, 4, pp 223-235; Schöller et al. 1987, Proceedings of the Second Conference on Environmental Technology, Production and the Environment, pp 294-303; Nielsen et al. 1997, Water Sci. Techno., 36, pp 391-397; Zhou et al. 1999, Water Research, 33(8), pp 1918-1924), calcium, iron or zinc phosphates (see, for example, Seckler et al. 1996, Water Research, 30(7), pp 1585-1596), sulphur or copper or instead sodium perborate tetrahydrate (Frances et al. 1994, Chemical Engineering Science, 49(19), pp 3269-3276). The reader may thus, if necessary, refer to these documents to learn the principle of this technique and its different implementation methods. According to the invention, the solution of actinide(s) typically has a total concentration of actinide(s) of 0.01 to 300 g/L and, preferably, of 10 to 100 g/L whereas the oxalic solution typically has a concentration of oxalic acid or oxalic acid salt of 0.05 to 1 mole/L and, preferably, of 0.4 to 0.8 mole/L. The volume ratio of the solution of actinide(s) to the oxalic solution is preferentially chosen so that the oxalic acid or oxalic acid salt is in excess compared to the stoichiometric conditions of the precipitation reaction of the actinide or actinides, this excess being, preferably, from 0.01 to 0.5 mole/L and, better still, from 0.05 to 0.2 mole/L. Preferably, the aqueous solution of actinide(s) contains the actinide(s) in the form of nitrate(s), since it is in this form that these elements are generally produced by spent nuclear fuel processing plants. Furthermore, the solution of actinide(s) is preferentially an acid solution and, more specially, a nitric acid solution, in which case it contains generally from 0.1 to 4 moles/L and, better still, from 1 to 2 moles/L of nitric acid. This solution and/or the oxalic solution may contain in addition a monocharged cation, which is constituted uniquely of atoms of oxygen, carbon, nitrogen and hydrogen, and which is capable of favouring the formation of a homogeneous actinide oxalate, particularly (but not necessarily) by stabilising this or these actinide(s) at the oxidation state in which they are initially present in said solution. The use of such a cation, which has a quite particular interest when it is wished to coprecipitate several actinides of which one at least is in the oxidation state IV whereas another of said actinides is in the oxidation state III—which is, for example, the case for the preparation of a mixed oxalate of uranium(IV) and of plutonium(III) or of a mixed oxalate of uranium(IV) and of americium(III)—is described in detail in the international application PCT published under the number WO 2005/119699. If the monocharged cation has the vocation of stabilising the actinide(s) in their oxidation state and, in particular, in the IV and III oxidation states respectively, then said cation is present in the aqueous solution containing this or these actinide(s) and is, preferably, chosen from the hydrazinium ion and hydrazinium ions comprising one or more alkyl groups, the most preferred ion of all being the hydrazinium ion. In which case, said hydrazinium ion is advantageously provided by the presence of hydrazinium nitrate in the solution of actinide(s), for example at a concentration of 0.01 to 0.2 mole/L, said hydrazinium nitrate being obtained beforehand by reacting nitric acid with hydrazine, pure or diluted in water. If the monocharged cation is not specially destined to stabilise the actinide(s) in their oxidation state, then said cation may be present in one or the other of the solution of actinide(s) and the oxalic solution and is, preferably, chosen from the ammonium ion and substituted ammonium ions such as alkylammonium ions, more particularly from quaternary substituted ammonium ions such as tetraalkylammonium ions, the most preferred ion of all being the ammonium ion. In which case, said ammonium ion may be provided either by the presence of aqueous ammonia in the solution of actinide(s), or by carrying out the coprecipitation by means of an aqueous ammonium oxalate solution. The method according to the invention is, preferably, used in a fluidised bed reactor which, being of vertical main axis, comprises: an intermediate part allocated to the fluidisation of particles of (co)precipitate, in other words actinide(s) oxalate; an upper part allocated to the decantation of particles of (co)precipitate; and a lower part allocated to the sedimentation of particles of (co)precipitate. In which case, the method comprises: the bringing into contact, in the fluidised bed reactor, of the solution of actinide(s) with the oxalic solution by introducing said solutions into said reactor, one at least of said solutions being introduced into the lower part of the reactor so as to create an ascending current of liquid; as a result of which, a fluidised bed of particles of (co)precipitate is formed in the intermediate part of the reactor; the decantation of the particles of (co)precipitate in the upper part of the reactor; as a result of which, two phases are formed, namely a solid phase constituted of the particles of (co)precipitate and a liquid phase which corresponds to the mixing of the aqueous solutions introduced into the reactor but which is depleted into actinide(s) and into oxalic acid or oxalic acid salt; and the sedimentation of particles of (co)precipitate in the lower part of the reactor. According to the invention, the formation of particles of (co)precipitate in the fluidised bed reactor results uniquely from bringing into contact, in said reactor, the solution of actinide(s) and the oxalic solution. Nevertheless, it is also possible to facilitate the formation of this (co)precipitate by injecting into the reactor, simultaneously with its filling with solution of actinide(s) and with oxalic solution or at the end of this filling, a suspension of fine actinide(s) oxide particles—in other words particles having typically a size of 5 to 20 μm—which are going to play the role of seeds (or nuclei). These seeding particles will most usually be particles having been obtained previously by a conventional “batch” method of precipitation in reactor, dried and stored with a view to their subsequent use as seeds. Nevertheless, they may also be particles that are obtained during the preparation of an actinide(s) oxalate by the method according to the invention, for example by supplying, with solution of actinide(s) and oxalic solution, a (co)precipitation vessel which is independent of the fluidised bed reactor but which is connected to it by a pipe, advantageously provided with a pump, suited to enabling the transfer, at a selected rate, of said particles into said reactor. Furthermore, it is entirely possible, according to the invention, to provide that the finest particles of (co)precipitate—in other words, in practice, those that measure less than 10 μm—present in the upper part of the fluidised bed reactor are withdrawn and transferred into the lower part of said reactor during the (co)precipitation. This is then termed “recycling loop”. This method of implementation is besides that which is preferred in the case of the preparation of a mixed oxalate such as a mixed oxalate of uranium(IV) and of plutonium(III) or a mixed oxalate of uranium(IV) and of americium(III). In all cases, the (co)precipitation may be carried out at a temperature ranging from 10 to 80° C., this temperature being that which reigns in the fluidised bed reactor. An ideal temperature is typically of the order of 20 to 35° C. Although the actinide(s) from which it is wished to prepare an oxalate may, according to the invention, be chosen from all known actinides, it is typically uranium, plutonium, neptunium, thorium, americium and/or curium. In particular, it is uranium, plutonium, neptunium, americium and/or curium that it is wished to obtain in the form of a simple or mixed oxalate suited to being transformed secondarily into an actinide compound useful for the manufacture of nuclear fuel pellets, of the oxide, carbide or nitride type. Such an oxalate is advantageously a mixed oxalate, in which case it is, preferably, an oxalate of uranium(IV) and of plutonium(III), an oxalate of uranium(IV) and of americium(III), an oxalate of uranium(IV) and of curium(III), an oxalate of uranium(IV), of plutonium(III) and of neptunium(IV), an oxalate of uranium(IV), of plutonium(III) and of americium(III), an oxalate of uranium(IV), of americium(III) and of curium(III), an oxalate of uranium(IV), of plutonium (III), of americium(III) and of curium(III) or instead an oxalate of uranium(IV), of plutonium(III), of neptunium(V), of americium(III) and of curium(III) from which may be produced respectively the mixed oxides (U,Pu)O2, (U,Am)O2, (U,Cm)O2, (U,Pu,Np)O2, (U,Pu,Am)O2, (U,Am,Cm)O2, (U,Pu,Am,Cm)O2 and (U,Pu,Np,Am,Cm)O2. Among these oxalates, preference is given to the oxalates of uranium(IV) and of plutonium(III), to the oxalates of uranium(IV) and of americium(III), as well as to the oxalates of uranium(IV), of plutonium(III) and of americium(III). In this respect, it goes without saying that, in the case where the method according to the invention is used to prepare a mixed actinides oxalate which is intended to be transformed then into mixed oxide, the respective proportions of the actinides in the aqueous solution that is brought into contact with the oxalic solution are chosen as a function of the proportions in which these actinides must be found in the mixed oxide and the precipitation yield obtained for each of them. As mentioned previously, the method according to the invention also comprises collecting the particles of (co)precipitate, which is typically carried out by decanting off the particles having sedimented in the lower part of the fluidised bed reactor. This collection may be followed by solid-liquid separation operations of the filtration, centrifugation or analogous type, to remove the particles of (co)precipitate from the liquid phase likely to have been decanted with them, as well as operations of washing and/or drying. The method for preparing an actinide(s) oxalate according to the invention has numerous advantages. Indeed, it makes it possible to obtain powders of simple or mixed actinides oxalates which are constituted of spherical or quasi spherical particles (as may be seen in appended FIGS. 3A and 3B), of average size greater than the average size of particles of actinides oxalates obtained to date (including those obtain in Vortex effect reactors), and which have a narrow and controlled granulometry, exempt of easily dispersible fine particles. It ensues that these powders have remarkable properties of filterability and flowability, their flowability after drying being, in fact, comparable to that of dry sand. It also ensues that these powders are easy to handle and do not generate dust, thus reducing the risks of dissemination and contamination in the event of rupture of confinement. Furthermore, the use of a fluidised bed having, among other advantages, that of offering a large contact surface between the liquid and solid phases, the method according to the invention makes it possible in addition to prepare actinides oxalate powders at high rates while using fluidised bed reactors of reduced dimensions, which is particularly interesting in terms of managing risks of criticality. In addition, since a fluidised bed can be used according to very varied methods, the method according to the invention has great flexibility of use with the possibility of perfectly adapting said method as a function of the actinide or actinides from which it is wished to obtain an oxalate and the use for which said oxalate is intended and, thus, the characteristics of size, composition or other that it has to have. Moreover, the problems of scaling and accumulation of materials encountered during the use of certain types of reactor, such as rotating disc reactors, do not exist with fluidised bed reactors, which are easy to empty and to clean, which makes it possible to simplify maintenance operations. The method according to the invention is thus particularly adapted to the preparation of actinides oxalates intended to be transformed secondarily into actinides compounds suited to serving in the manufacture of nuclear fuel pellets, of the oxide, carbide or nitride type. Another object of the invention is a method for preparing an actinide(s) compound of the oxide, carbide or nitride type, which comprises: the preparation of an oxalate of one or more actinides by a method as defined previously; and the calcination of this oxalate. The calcination of actinides oxalates into actinides oxides, carbides and nitrides is well known to those skilled in the art. It is thus simply recalled that it is generally carried out at temperature and under an atmosphere that may be oxidising, inert or reducing depending on whether it is wished to obtain an oxide, a carbide or a nitride of actinide(s). Thus: for the synthesis of oxides, the temperature is generally of the order of 600 to 800° C. and the atmosphere is an inert atmosphere, typically of nitrogen or argon, or oxidising, typically of air, according to the actinides considered; for the synthesis of carbides, the temperature is generally of the order of 1500 to 1800° C. and the atmosphere is an inert atmosphere, typically of nitrogen or argon, or reducing, typically a mixture of hydrogen and nitrogen or argon; whereas for the synthesis of nitrides, the temperature is generally of the order of 1500 to 1800° C. and the atmosphere is a reducing atmosphere, composed of nitrogen and hydrogen. For the synthesis of carbides and nitrides, the source of carbon necessary for carbothermic reduction is either added to the aforementioned atmospheres, in which case it is typically methane, or present in the actinide(s) oxalate in molecular form. According to the invention, the actinide(s) oxalate is advantageously a mixed oxalate, in which case it is, preferably, an oxalate of uranium(IV) and of plutonium(III), an oxalate of uranium(IV) and of americium(III), an oxalate of uranium(IV) and of curium(III), an oxalate of uranium(IV), of plutonium(III) and of neptunium(IV), an oxalate of uranium(IV), of plutonium(III) and of americium(III), an oxalate of uranium(IV), of americium(III) and of curium(III), an oxalate of uranium(IV), of plutonium(III), of americium(III) and of curium(III) or instead an oxalate of uranium(IV), of plutonium(III), of neptunium(V), of americium(III) and of curium(III), the calcination of which makes it possible to obtain respectively mixed oxides (U,Pu)O2, (U,Am)O2, (U,Cm)O2, (U,Pu,Np)O2, (U,Pu,Am)O2, (U,Am,Cm)O2, (U,Pu,Am,Cm)O2 and (U,Pu,Np,Am,Cm)O2. In particular, it is a mixed oxalate of uranium(IV) and of plutonium(III), an oxalate of uranium(IV) and of americium(III) or of an oxalate of uranium(IV), of plutonium(III) and of americium(III). Other characteristics and advantages of the invention will become clear on reading the remainder of the description that follows and which relates to two embodiment examples of the invention, one for the preparation of a neodymium(III) oxalate decahydrate and, from this, an neodymium oxide, and the other for the preparation of a mixed oxalate of uranium(IV) and cerium(III). Obviously, these examples are only given by way of illustration of the object of the invention and do not constitute in any way a limitation of this object. It should be noted that neodymium(III) and cerium(III) are not actinides but lanthanides which have chemical properties extremely similar to those of trivalent actinides (namely, plutonium(III), americium(III) and curium(III)), particularly in terms of solubility and complexation, but which, unlike the latter, are not radioactive. It is thus conventional to use them instead of trivalent actinides in the elaboration of methods intended to be used on these actinides. In FIGS. 1 and 6, identical references are used to designate identical components. In this example, firstly a neodymium(III) oxalate decahydrate is prepared by bringing into contact, in a fluidised bed reactor, a 30 g/L aqueous solution of neodymium(III) nitrate, acidified between 0.5 and 2 moles/L by addition of nitric acid, with an aqueous solution comprising 0.7 mole/L of oxalic acid. To do this, the installation 10, which is represented schematically in FIG. 1, is used. This installation comprises, as essential component, a fluidised bed reactor 11 of vertical main axis, which is composed of three parts: an intermediate part 12, which is allocated to the fluidisation of neodymium(III) oxalate decahydrate particles, which then form following the bringing into contact of the aqueous solutions of neodymium(III) nitrate and oxalic acid; an upper part 13, which is allocated to the decantation of neodymium(III) oxalate decahydrate particles; and a lower part 14, which is allocated to the sedimentation of their particles and to their collection. The intermediate part 12 of the reactor 11 is constituted of a cylinder, typically of circular straight section and with double walls 15, inside of which flows a thermo-fluid, for example water, making it possible to maintain the temperature reigning in this reactor constant. In this particular case, the temperature used is 25° C. The upper part 13 is constituted of a cone frustrum, the small base of which originates at the upper end of the intermediate part 12 and the large base of which extends by a cylinder, typically of circular straight section like the intermediate part 12 but of diameter greater than that of said intermediate part 12. It is, furthermore, provided with an overflow 25 making it possible to eliminate from the reactor 11 the liquid phase, depleted in neodymium(III) nitrate and in oxalic acid, which results from the decantation of neodymium(III) oxalate decahydrate particles. The lower part 14 is, for its part, constituted of a cone, the base of which originates at the lower end of the intermediate part 12 and the summit of which (which forms the lower end of the reactor 11) is provided with a system 16 of the tap, valve or analogous type, making it possible to collect, by decantations, the neodymium(III) oxalate decahydrate particles having sedimented. The reagents, in other words the aqueous solution of neodymium(III) nitrate and the aqueous solution of oxalic acid, are introduced into the reactor 11, above the limit between the intermediate 12 and lower 14 parts of this reactor, by means of two injection pipes, respectively 17 and 18, which go down into the reactor 11 passing through its upper 13 and intermediate 12 parts. The injection pipe 17 is connected to a reservoir 19 of aqueous solution of neodymium(III) nitrate via a pipe 20, which is provided with a pump 21 making it possible to regulate the feed rate of the reactor 11 via the injection pipe 17. As for the injection pipe 18, it is connected to a reservoir 22 of aqueous solution of oxalic acid via a pipe 23, which is also provided with a pump 24 making it possible to regulate the feed rate of the reactor 11 via the injection pipe 18. The feed rates of the reactor 11 via the injection pipes 17 and 18 are adjusted so as to obtain in this reactor an excess of oxalic acid compared to the stoichiometric conditions of the precipitation reaction of 0.05 to 0.2 mole/L. The reactor 11, the reservoirs 19 and 22 and the pipes 20 and 23 are provided with different types of sensors (pH indicators, temperature indicators, flow rate indicators, etc.) which are not represented in FIG. 1 for reasons of clarity. As may be seen in FIG. 1, the reactor 11 does not comprise an agitator, or recycling loop, the homogenisation of the mixture of reagents and the fluidisation of the neodymium(III) oxalate decahydrate particles being ensured uniquely by the feed rates of said reactor with these reagents. The capacity of the intermediate part 12 of the reactor 11 is 1 liter. After 4 hours of operating in continuous mode of the reactor 11, by carrying out decantations by means of the system 16 situated at its lower end, are collected particles of neodymium(III) oxalate decahydrate, which is filtered on a Buchner filter, then is washed and dried to obtain a powder. The volume size distribution (measured by means of a MALVERN Mastersizer® X model particle size analyser) of the particles constituting said powder (curve 1) as well as that of neodymium(III) oxalate decahydrate particles obtained by precipitation in a Vortex effect reactor (curve 2), using identical chemical conditions (same reagents, same initial concentrations, same acidity, same oxalic excess, same temperature) to those mentioned above, are represented in FIG. 2. As may be seen in this figure, the curve corresponding to the neodymium oxalate particles prepared according to the invention is shifted towards the right of the graph, in other words towards higher particle diameters compared to that corresponding to the neodymium oxalate particles obtained in the Vortex effect reactor. Thus, the diameter D43 (average diameter) of neodymium oxalate particles prepared according to the invention is 161 μm whereas it is only 72 μm for the neodymium oxalate particles obtained in the Vortex effect reactor. In addition, the neodymium oxalate prepared according to the invention does not comprise particles whose diameter is below 9 μm and has a diameter D10 of 31 μm (which signifies that there are only 10% of particles of said oxalate that have a size below 31 μm), whereas the neodymium oxalate obtained in the Vortex effect reactor comprises 6% of particles, the diameter of which is below 10 μm and its diameter D10 is 17 μm (which signifies that 10% of the particles of this oxalate have a size below 17 μm). Furthermore, as shown in FIGS. 3A, 3B, 4A and 4B, which correspond to photographs taken with a scanning electron microscope of particles of these two types of oxalate, the neodymium oxalate particles prepared according to the invention (FIGS. 3A and 3B) have a spherical or quasi spherical morphology, with a volumic shape factor Φv of the order of 0.5, which is not the case of neodymium oxalate particles obtained in the Vortex effect reactor (FIGS. 4A and 4B) which, for their part, appear in the form of agglomerates of elongated sticks and are characterised by a shape factor Φv of the order of 0.02. Furthermore, a neodymium oxide is prepared by calcinating under air, at 700° C. for 1 hour, the neodymium oxalate prepared according to the invention. The volume size distribution (measured by means of a MALVERN Mastersizer® X model particle size analyser) of the particles constituting said oxide (curve 1) as well as that of neodymium oxide particles obtained by calcinating, under the same conditions, a neodymium(III) oxalate decahydrate prepared by precipitation in a Vortex effect reactor (curve 2) are represented in FIG. 5. This figure shows that the improvement in the granulometric characteristics of an oxalate is found in the oxide obtained from this oxalate since the diameters D43 (average diameter) and D10 of particles of the oxide obtained by calcination of the neodymium oxalate prepared according to the invention are respectively 46 μm and 15.5 μm, whereas they are only 12.7 μm and 2.1 μm for the oxide particles obtained by calcination of the neodymium oxalate prepared by precipitation in a Vortex effect reactor. A mixed oxalate of uranium(IV) and of cerium(III) is prepared by bringing into contact, in a fluidised bed reactor, an aqueous solution with 20 g/L of uranyl nitrate and with 10 g/L of cerium(III) nitrate, acidified between 0.5 and 2 moles/L by addition of nitric acid, with a 0.7 mole/L aqueous solution of oxalic acid. To do this, the installation 10, which is represented schematically in FIG. 6, is used. This installation is substantially identical to that represented in FIG. 1 as regards the fluidised bed reactor 11. On the other hand, it differs from it by the fact that the intermediate part 12 of the reactor 11 is provided with a stirrer 26, for example with blades, which is driven in rotation by a motor 27, for example at a speed of 20 rpm, and which is intended to facilitate the homogenisation of the mixture of reagents that are introduced into the reactor. It also differs from it by the fact that the reactor 11 is equipped with a recycling loop 28, in other words a pipe that originates in the upper part 13 of said reactor, substantially at the level of the overflow 25, and ends in its lower part 14, near to the decantation system 16, and the flow rate of which is regulated by a pump 29, for example of peristaltic type. This recycling loop makes it possible to maintain the fluidisation and to withdraw the fine particles of mixed oxalate of uranium(IV) and of cerium(III) present in the upper part 13 of the reactor 11 and to re-inject said particles into the lower part 14 of said reactor. Moreover, it differs from it by the fact that the supply of the reactor 11 with reagents is not ensured by injection pipes but by two pipes, respectively 30 and 31, one of which joins up with said reactor whereas the other joins up with the recycling loop 28. The pipe 30 is connected to a reservoir 32 of aqueous solution of uranyl and cerium(III) nitrates and is provided with a pump 33 making it possible to regulate the feed rate of the reactor 11 via the pipe 30. In a similar manner, the pipe 31 is connected to a reservoir 34 of aqueous solution of oxalic acid and is provided with a pump 35 making it possible to regulate the supply of the recycling loop 28 via the pipe 31. The feed rates of the reactor 11 via the pipe 30 and the recycling loop via the pipe 31 are adjusted so as to obtain in this reactor an excess of oxalic acid compared to the stoichiometric conditions of the precipitation reaction of 0.05 to 0.2 mole/L. The capacity of the intermediate part 12 of the reactor 11 is, furthermore, much greater than that of the reactor 11 of the installation shown in FIG. 1, since it is 80 liters. The temperature that reigns in the reactor 11 is 25° C. After 80 hours of operation in continuous mode of the reactor 11, by carrying out decantations by means of the system 16 situated at its lower end, particles are collected of a mixed oxalate of uranium(IV) and of cerium(III), which is filtered on a Buchner filter, then is washed and dried to obtain a powder. The volume size distribution (measured by means of a MALVERN Mastersizer® X model particle size analyser) of the particles constituting said powder (curve 1) as well as that of the particles of a mixed oxalate of uranium(IV) and of cerium(III) prepared by precipitation in a Vortex effect reactor (curve 2), using the same reagents and the same flow rates as those mentioned above, are represented, in the form of curves, in FIG. 7. As shown in this figure, the curve corresponding to the particles of the mixed oxalate of uranium and of cerium prepared according to the invention is, once again, shifted towards the right of the graph, in other words towards particles of higher diameter, compared to that corresponding to the particles of the mixed oxalate of uranium and of cerium obtained by precipitation in the Vortex effect reactor. The diameter D43 (average diameter) of the particles of the mixed oxalate of uranium and of cerium prepared according to the invention is 90 μm, whereas it is only 45 μm for the particles of the mixed oxalate of uranium and of cerium obtained in the Vortex effect reactor. In addition, the diameter D10 of the particles of the mixed oxalate of uranium and of cerium prepared according to the invention is of the order of 25 μm (which signifies that there is only 10% of particles of this oxalate that have a size below 25 μm) whereas the diameter D10 of particles of the mixed oxalate of uranium and of cerium obtained in the Vortex effect reactor is 9 μm (which signifies that 10% of particles of this oxalate have a size below 9 μm). [1] Van Ammers et al. 1986, Wat. Supply, 4, pp 223-235 [2] Schöller et al. 1987, Proceedings of the Second Conference on Environmental Technology, Production and the Environment, pp 294-303 [3] Nielsen et al. 1997, Water Sci. Techno., 36, pp 391-397 [4] Zhou et al. 1999, Water Research, 33(8), pp 1918-1924 [5] Seckler et al. 1996, Water Research, 30(7), pp 1585-1596 [6] Frances et al. 1994, Chemical Engineering Science, 49(19), pp 3269-3276 [7] International patent application PCT WO 2005/119699
claims
1. Process for filling drums containing dangerous waste, said process comprising the following stages: assembly of an intermediary lid on a drum containing dangerous waste, said lid comprising an opening closed in a sealed fashion by a cap; providing a containment hood overhanging one end of the drum closed by the intermediary lid, applying negative pressure to the drum and the containment hood until the end of the process; perforation of the cap by a toothed crown carried by said containment hood; injection of a blocking material into the drum, by means of an injection tube located inside the toothed crown. 2. Process according to claim 1 , in which the end of filling the drum by the blocking material is detected and the injection is stopped. claim 1 3. Process according to claim 2 , in which the end of filling the drum is detected by at least one bubble tube opening inside the toothed crown. claim 2 4. Process according to claim 3 , in which the end of the bubble tube is positioned at a predetermined level below the cap, after perforation of the cap. claim 3 5. Process according to claim 1 , in which the drum is made to vibrate during injection of the blocking material. claim 1 6. Process according to claim 1 , in which, before injection of the blocking material, the material is made to circulate continuously in a closed circuit. claim 1 7. Process according to claim 1 , in which, after injection of the blocking material into the drum, the drum is separated from the containment hood and an external lid is placed on the drum, on top of the intermediary lid. claim 1 8. Process for filling drums containing dangerous waste, said process comprising the following stages: assembly of an intermediary lid on a drum, said lid comprising an opening closed in a sealed fashion by a cap; perforation of the cap by a toothed crown carried by a containment hood overhanging one end of the drum closed by the intermediary lid; injection of a blocking material into the drum, by means of an injection tube located inside the toothed crown; negative pressure application to the drum and the containment hood, as soon as the drum is set in place and during perforation and injection; in which the cap is equipped with ballast means ensuring evacuation into the drum, by gravity, of a disc cut out in the cap at the time of its perforation. 9. Process for filling drums containing dangerous waste, said process comprising the following stages: assembly of an intermediary lid on a drum, said lid comprising an opening closed in a sealed fashion by a cap; perforation of the cap by a toothed crown carried by a containment hood overhanging one end of the drum closed by the intermediary lid; injection of a blocking material into the drum, by means of an injection tube located inside the toothed crown; negative pressure application to the drum and the containment hood, as soon as the drum is set in place and during perforation and injection; in which the cap is perforated by displacing the drum upwards, in relation to a fixed containment hood. 10. Process for filling drums containing dangerous waste, said process comprising the following stages: assembly of an intermediary lid on a drum, said lid comprising an opening closed in a sealed fashion by a cap; perforation of the cap by a toothed crown carried by a containment hood overhanging one end of the drum closed by the intermediary lid; injection of a blocking material into the drum, by means of an injection tube located inside the toothed crown; negative pressure application to the drum and the containment hood, as soon as the drum is set in place and during perforation and injection; in which, after injection of the blocking material into the drum, cleaning of the means of injection is carried out. 11. Installation for filling drums containing dangerous waste, said installation comprising: an intermediary lid able to be mounted on a drum, said lid comprising an opening closed in a sealed fashion by a cap; a containment hood able to overhang an end of the drum closed by the intermediary lid, said hood having a toothed crown able to perforate the cap; means of injection of a blocking material, opening inside the toothed crown; and means of negative pressure application for the drum and the containment hood; means for detecting the end of filling the drum with the blocking material, in which the means for detecting the end of filling the drum comprise at least one bubble tube opening inside the toothed crown; means for positioning the end of the bubble tube at a predetermined level below the cap, in which the means for positioning the end of the bubble tube comprise a laser detector mounted on the containment hood and able to measure the distance between the containment hood and the intermediary lid. 12. Installation for filling drums containing dangerous waste, said installation comprising: an intermediary lid able to be mounted on a drum, said lid comprising an opening closed in a sealed fashion by a cap; a containment hood able to overhang an end of the drum closed by the intermediary lid, said hood having a toothed crown able to perforate the cap; means of injection of a blocking material, opening inside the toothed crown; and means of negative-pressure application for the drum and the containment hood; in which the lid is provided with ballast means in a part able to be perforated by the toothed crown. 13. Installation for filling drums containing dangerous waste, said installation comprising: an intermediary lid able to be mounted on a drum, said lid comprising an opening closed in a sealed fashion by a cap; a containment hood able to overhang an end of the drum closed by the intermediary lid, said hood having a toothed crownable to perforate the cap; means of injection of a blocking material, opening inside the toothed crown; and means of negative pressure application for the drum and the containment hood; in which the intermediary lid comprises, on a face able to be turned towards the interior of the drum, at least one anti-float organ able to rest on the radioactive wastes around the opening, to provide a free space between these wastes and the intermediary lid. 14. Installation for filling drums containing dangerous waste, said installation comprising: an intermediary lid able to be mounted on a drum, said lid comprising an opening closed in a sealed fashion by a cap; a containment hood able to overhang an end of the drum closed by the intermediary lid, said hood having a toothed crown able to perforate the cap; means of injection of a blocking material, opening inside the toothed crown; and means of negative pressure application for the drum and the containment hood; in which the means of injection of the blocking material comprise a closed circuit linked to the injection head of said material, opening inside the toothed crown. 15. Installation according to claim 14 , in which a deflector is placed beneath the injection head, so as to direct the blocking material towards a peripheral region of the drum. claim 14 16. Installation according to claim 14 , in which the closed circuit comprises: claim 14 a hopper for filling and storing the blocking material; and pumping means able to make the blocking material circulate from the hopper to the injection head and continuously in the closed circuit. 17. Installation according to claim 16 , in which the closed circuit comprises in addition means for cleaning said circuit and the injection head. claim 16
claims
1. A propellant transport structure apparatus for a spacecraft comprised of:a transport layer having an elongated shape and a plurality of openings;a substantially transparent back cover, corresponding in size to said transport layer;a plurality of containment border structures sandwiched between said transport layer and said substantially transparent back cover; anda membrane affixed to a front side of said transport layer such that said membrane overlays said plurality of openings of said transport layer,wherein each of said plurality of openings is surrounded by one of said plurality of containment border structures,wherein each of said plurality of openings further includes a propellant material, said propellant material being affixed to said substantially transparent back cover and contained by one of said plurality of containment border structures,wherein one of said plurality of containment border structures encloses said propellant material along a length and a width of said transport layer,wherein each containment border structure is separated by a discrete distance from any other containment border structure,wherein said containment border structure is affixed to a back side of said transport layer and to a front side of said substantially transparent back cover,wherein said membrane is sufficiently thin that an ignited propellant material bursts through said membrane to propel a spacecraft,wherein said membrane comprises a material which is not flammable. 2. The apparatus of claim 1 wherein said substantially transparent back cover is transparent to a laser beam. 3. The apparatus of claim 1 wherein said transport layer is comprised of a highly resilient material. 4. The apparatus of claim 1 wherein said transport layer is nonconductive. 5. The apparatus of claim 1 wherein said transport layer is reinforced with reinforcing members. 6. The apparatus of claim 5 wherein said reinforcing members are metallic. 7. The apparatus of claim 5 wherein said reinforcing members are non-metallic. 8. The apparatus of claim 5 wherein said reinforcing members are comprised of a material selected from a group consisting of aluminum, titanium, steel, stainless steel, Kevlar®, nylon, and synthetic fibers. 9. The apparatus of claim 1 wherein said membrane is a material selected from a group consisting of plastic film, polyimide film, plastic foil, aluminum foil, and tin foil. 10. The apparatus of claim 1 wherein said containment border structures are uniformly spaced. 11. The apparatus of claim 1 wherein said containment border structures are non-uniformly spaced. 12. The apparatus of claim 1 wherein spacing of said containment border structures is dependent on said propellant material, amount of said propellant material, amount of thrust required, and scale of system in which said apparatus is used. 13. The apparatus of claim 1 wherein said containment border structures are spaced so that said propellant material contained in said containment border structure is isolated from propellant material contained in adjacent containment border structures. 14. The apparatus of claim 1 wherein said propellant material is ablation material and is placed continuously along said transport layer. 15. A laser ignition/ablation propulsion system comprised of:a laser;a laser ignition/ablation chamber having a window, said window being transparent to a laser beam, and at least one containment wall seal;propellant material; anda transport structure for transporting said propellant material into said laser ignition/ablation chamber, said transport structure comprised of:a transport layer having an elongated shape and a plurality of openings;a substantially transparent back cover, corresponding in size to said transport layer;a plurality of containment border structures sandwiched between said transport layer and said substantially transparent back cover; anda membrane affixed to a front side of said transport layer such that said membrane overlays said plurality of openings of said transport layer,wherein each of said plurality of openings is surrounded by one of said plurality of containment border structures,wherein each of said plurality of openings further includes a propellant material, said propellant material being affixed to said substantially transparent back cover and contained by one of said plurality of containment border structures,wherein one of said plurality of containment border structures encloses said propellant material along a length and a width of said transport layer,wherein each containment border structure is separated by a discrete distance from any other containment border structure,wherein said containment border structure is affixed to a back side of said transport layer and to a front side of said substantially transparent back cover,wherein said membrane is sufficiently thin that an ignited propellant material bursts through said membrane to propel a spacecraft,wherein said membrane comprises a material which is not flammable. 16. The system of claim 15 wherein said transport structure is rigid. 17. The system of claim 15 wherein said transport structure is flexible. 18. The system of claim 15 wherein said transport structure is adapted for mounting on a reel. 19. The system of claim 15 wherein said window is comprised of a material selected from a group consisting of glass, thick glass, plastic, resin, quartz, silicon, and polycarbonate resin thermoplastic. 20. The system of claim 15 wherein said transport structure further includes optional filler material. 21. A laser ignition/ablation propulsion system comprised of:a laser;a laser ignition/ablation chamber having a window, said window being transparent to a laser beam, and at least one containment wall seal;a transport structure for transporting said propellant material into said laser ignition/ablation chamber comprised of:a transport layer having an elongated shape and a plurality of openings;a substantially transparent back cover, corresponding in size to said transport layer;a plurality of containment border structures sandwiched between said transport layer and said substantially transparent back cover; anda membrane affixed to a front side of said transport layer such that said membrane overlays said plurality of openings of said transport layer,wherein each of said plurality of openings is surrounded by one of said plurality of containment border structures,wherein each of said plurality of openings further includes a propellant material, said propellant material being affixed to said substantially transparent back cover and contained by one of said plurality of containment border structures,wherein one of said plurality of containment border structures encloses said propellant material along a length and a width of said transport layer,wherein each containment border structure is separated by a discrete distance from any other containment border structure,wherein said containment border structure is affixed to a back side of said transport layer and to a front side of said substantially transparent back cover,wherein said membrane is sufficiently thin that an ignited propellant material bursts through said membrane to propel a spacecraft,wherein said membrane comprises a material which is not flammable;a feed reel; anda takeup reel. 22. The system of claim 21 wherein said feed reel and said takeup reel are comprised of a material selected from a group consisting of high strength plastic, polyimide, carbon composite, aluminum, beryllium, and combinations thereof. 23. The system of claim 21 wherein speed of said feed reel and said takeup reel is variable. 24. The system of claim 21 wherein speed of said feed reel and said takeup reel is synchronized to pulsing of said laser beam. 25. The system of claim 21 wherein said speed of said feed reel and said takeup reel is proportionate to burn rate of said propellant targets. 26. The system of claim 21 which further includes a controller. 27. The system of claim 21 wherein said ignition chamber further includes a plurality of containment walls.
RE0315834
claims
1. In a nuclear fuel assembly including, .Iadd.a plurality of .Iaddend.longitudinally extending rigid support .[.means.]. .Iadd.tubes.Iaddend.; upper and lower end fittings supported by said support .[.means.]. .Iadd.tubes .Iaddend.at opposite ends thereof; a plurality of elongated fuel elements in parallel relationship and extending substantially between said upper and lower end fittings and supported by said support .[.means.]. .Iadd.tubes.Iaddend., hold-down apparatus for said fuel assembly in which said upper end fitting comprises: an end plate supported by said support .[.means.]. .Iadd.tubes .Iaddend.against downward motion relative thereto and extending transversely thereof; .[.alignment means.]. .Iadd.a plurality of hollow cylindrical posts .Iaddend.projecting longitudinally upward from and supported against upward motion relative to said end plate, .Iadd.each of .Iaddend.said .[.alignment means.]. .Iadd.posts .Iaddend.having an outwardly enlarged shoulder affixed thereto and spaced upwardly from said end plate.[.;.]..Iadd., said posts and end plate including passageways extending vertically therethrough in registry with said tubes whereby a control element may be inserted therewithin into said fuel assembly; .Iaddend. force transmitting means slidably mounted on said .[.alignment means.]. .Iadd.posts .Iaddend.and movable therealong between said shoulder and said end plate.Iadd., and including a hold-down plate having at least one hub portion, an aperature in and extending through said hub portion for relative slidable passage therethrough of said posts, .Iaddend.and .[.having a portion thereof.]..Iadd.leg portions .Iaddend.extending laterally beyond said .[.shoulder.]. .Iadd.shoulders .Iaddend.for receiving a downward force applied to said .Iadd.leg .Iaddend..[.portion.]. .Iadd.portions.Iaddend.; and spring means .Iadd.coaxially disposed about a plurality of said posts and being .Iaddend.interposed .Iadd.in compression .Iaddend.between said force transmitting means and said end plate for biasing said force transmitting means upwardly from said plate whereby a said downward force on said force transmitting means is yieldably transmitted to said fuel assembly. .[.2. The apparatus of claim 1 wherein said force transmitting means comprise a hold-down plate having at least one hub portion; an aperture in and extending through said hub portion for relative slidable passage therethrough of said alignment means; and leg means extending substantially radially outward from said hub portion beyond said enlarged shoulder on said alignment means..]. 3. The apparatus of claim .[.2.]. .Iadd.1 .Iaddend.wherein said .[.alignment means comprise a plurality of cylindrical posts extending upwardly from said end plate and.]. .Iadd.posts are .Iaddend.symmetrically disposed about the vertical axis passing through the center of gravity of said fuel assembly; and said hold-down plate includes said same plural number of apertured hub portions for relative insertion therethrough of said .[.alignment.]. posts, said hub portions being joined and positioned relative to one another .[.and.]. by said leg .[.means.]. .Iadd.portions.Iaddend.. .[.4. The apparatus of claim 1 wherein said spring means comprise a coil spring, said coil spring being in compression and coaxially disposed about said alignment means..]. . The apparatus of claim 3 wherein said spring means comprise coil springs, said coil springs being in compression and coaxially disposed about a plurality of said .[.alignment.]. posts. .[.6. The apparatus of claim 1 wherein said fuel assembly includes a hollow tube open at its upper end and extending at least the full extent of said fuel elements parallel thereto and in vertical alignment with said alignment means; and said alignment means and said end plate include a passageway extending vertically therethrough in registry with said hollow tube whereby a control element may be inserted therewithin into said fuel assembly..]. .[.7. The apparatus of claim 3 wherein said fuel assembly includes hollow tubes open at their upper ends and extending at least the full extent of said fuel elements thereto and in vertical alignment with alignment posts; and said alignment posts and said end plate include passageways extending vertically thereto in registry with said hollow tubes whereby a control element may be inserted therewithin into said fuel assembly..]. .[.8. The apparatus of claim 7 wherein said hollow tubes comprise said support means extending between said fuel assembly end fittings..]..Iadd. 9. The apparatus of claim 5 wherein the posts are rigidly secured to the end plate. .Iaddend.
claims
1. A metrology system, comprising:an x-ray illumination source configured to generate an amount of soft x-ray radiation including multiple illumination wavelengths within a desired photon energy range from 80 electronvolts to 3,000 electronvolts and an undesired photon energy range below 80 electronvolts;an x-ray detector configured to detect an amount of x-ray radiation scattered from a semiconductor wafer in response to the amount of soft x-ray radiation;a plurality of x-ray optical elements each having at least one optical surface disposed in an optical path between the x-ray illumination source and the detector;an integrated optical filter fabricated over the optical surface of at least one of the plurality of x-ray optical elements, the integrated optical filter including one or more material layers that absorb radiation in the undesired photon energy range and transmits radiation in the desired photon energy range; anda computing system configured to determine a value of a parameter of interest characterizing a structure disposed on the semiconductor wafer based on the detected amount of x-ray radiation. 2. The metrology system of claim 1, wherein the metrology system is a soft x-ray reflectometry system. 3. The metrology system of claim 2, wherein the soft x-ray reflectometry system operates in a grazing incidence mode. 4. The metrology system of claim 2, wherein the metrology system operates in an imaging mode. 5. The metrology system of claim 1, wherein the integrated optical filter is disposed over a multilayer x-ray reflecting structure fabricated over the optical surface of the at least one of the plurality of x-ray optical elements. 6. The metrology system of claim 5, further comprising:a diffusion barrier layer, the diffusion barrier layer disposed between the one or more material layers of the integrated optical filter and the multilayer x-ray reflecting structure, disposed between the optical surface and the multilayer x-ray reflecting structure, or disposed over the one or more material layers of the integrated optical filter. 7. The metrology system of claim 1, wherein the optical surface of the at least one of the plurality of x-ray optical elements is curved. 8. The metrology system of claim 1, wherein a thickness of the integrated optical filter varies as a function of location on the optical surface of the at least one of the plurality of x-ray optical elements. 9. The metrology system of claim 1, further comprising:a stand-alone optical filter disposed in the optical path between the x-ray illumination source and the detector.
claims
1. A method for regulating operational parameters of the core of a pressurized water nuclear reactor, the nuclear reactor having:a core which is divided into an upper zone and a lower zone, and produces thermal power;a plurality of groups of rods for controlling the reactivity of the core, each of which occupies, in the core, a plurality of insertion positions which are stepped vertically starting from an upper position;means for inserting each group of rods in the core vertically;a primary circuit which assures the circulation of a primary cooling fluid through the core;means for adjusting the concentration of a neutron-absorbent component in the primary cooling fluid; andmeans for acquiring values which are representative of the conditions of operation of the core of the reactor,wherein the regulation method comprises:a step of acquiring values representative of (1) thermal power produced in the upper and lower zones of the core, (2) temperatures of hot and cold branches, and (3)flow of primary cooling fluid, which are representative of the conditions of operation of the core of the reactor;a step of evaluation of actual values of (i) mean temperature of the primary cooling fluid in the core, (ii) axial distribution of thermal power between the upper and lower zones of the core, and (iii) a parameter representative of capacity to increase power of the reactor corresponding to the thermal power which is produced by the core when the groups of rods are raised to the vicinity of the upper position, which values (i)-(iii) are collectively the operational parameters, this evaluation being performed at least as a function of the values acquired;a step of selection of either a first control law or a second control law to control (a) the concentration of the absorbent component, and (b) positions of insertion of the groups of rods, the first control law being different from the second control law, wherein the first control law is selected as soon as at least one group of rods is in an insertion position lower than a predetermined position, and the second control law is selected as soon as all the groups of rods are in respective insertion positions above said predetermined position;a step of calculating set points of the operational parameters at least as a function of control set points; anda step of regulation of the operational parameters as a function of set points relating to said parameters and of the actual values evaluated, by means of the selected control law,wherein the first control law comprises the following steps, in any order:modifying the positions of insertion of the groups of rods as a function of the deviation of the mean temperature of the primary cooling fluid in the core with regard to its set point, in order to regulate the mean temperature of the primary cooling fluid in the core to its set point;modifying the positions of insertion of the groups of rods as a function of the deviation of the axial distribution of power with regard to its set point, in order to regulate the axial distribution of power to its set point; andadjusting the concentration of the neutron-absorbent component in the primary cooling fluid as a function of the deviation from its set point of the parameter which is representative of the capacity to increase power of the reactor corresponding to the thermal power produced by the core when the groups of rods are raised to the vicinity of the upper position, which is representative of the capacity to increase the power of the reactor to its set point, in order to regulate the said increase power capacity to its set point; andwherein the second control law comprises the following steps, in any order:modifying the positions of insertion of the groups of rods as a function of the deviation of the mean temperature of the primary cooling fluid in the core with regard to its set point, in order to regulate the mean temperature of the primary cooling fluid in the core to its set point;adjusting the concentration of the neutron-absorbent component in the primary cooling fluid as a function of the deviation of the axial distribution of power with regard to its set point, in order to regulate the axial distribution of power to its set point; andmodifying the positions of insertion of the groups of rods as a function of the deviation from its set point of the parameter which is representative of the capacity to increase power of the reactor corresponding to the thermal power produced by the core when the groups of rods are raised to the vicinity of the upper position, which is representative of the capacity to increase the power of the reactor to its set point, in order to regulate the said increase power capacity to its set point. 2. The method according to claim 1, wherein the step of calculating set points of the operational parameters further comprises a sub-step of calculation of the mean temperature set point of the primary cooling fluid in the core, on the basis of a value which is representative of the power provided to an electricity network which is supplied by the reactor. 3. The method according to claim 2, wherein the step of calculating set points of the operational parameters further comprises a sub-step of distribution of the groups of rods into a sub-set for control of the mean temperature of the primary cooling fluid in the core, and a heavy sub-set which assures substantially the control of the axial distribution of power, the groups of rods of the heavy sub-set being inserted less far than those of the other sub-set. 4. The method according to claim 3, wherein the heavy sub-set is always positioned in the upper half of the core. 5. The method according to claim 3, wherein the parameter which is representative of the capacity to increase the power of the reactor is determined at least on the basis of the positions of insertion of the group(s) of rods of the control sub-set, the step of calculating set points of the operational parameters comprising a sub-step of calculation of a position set point for the group(s) of rods of the control sub-set as a function of a set point for the capacity to increase the power and to values acquired. 6. The method according to claim 5, wherein the step of regulation by means of the first control law further comprises:a sub-step of calculation of a displacement to be carried out for the group(s) of rods of the control sub-set as a function of the set point and to the actual value of the mean temperature of the primary cooling fluid in the core; anda sub-step of modification of the position(s) of insertion of the group(s) of rods of the control sub-set as a function of the displacements calculated for the purpose of regulating the mean temperature of the primary cooling fluid in the core to the set point. 7. The method according to claim 5, wherein the step of regulation by means of the first control law further comprises:a sub-step of calculation of the displacements to be carried out for the set(s) of rods of the control sub-set and of a displacement to be carried out for the heavy sub-set as a function of at least the set point and the actual value of the axial distribution of thermal power; anda sub-step of modification of the position(s) of insertion of the group(s) of rods of the control sub-set and/or of the heavy sub-set as a function of the displacements calculated for the purpose of regulating the axial distribution of thermal power to the set point. 8. The method according to claim 7, wherein, when the mean temperature of the cooling fluid is in a dead band around its set point, the control sub-set and the heavy sub-set are displaced in inverse directions in order to regulate the axial distribution of thermal power to its set point. 9. The method according to claim 5, wherein the step of regulation by means of the first control law further comprises:a sub-step of calculation of the concentration of the neutron-absorbent component as a function of the set point and to the actual value of the parameter representative of the capacity to increase the power of the reactor; anda sub-step of adjustment of the concentration of the neutron-absorbent component in the primary cooling fluid to the concentration calculated in order to regulate the parameter representative of the capacity to increase the power of the reactor to its set point. 10. The method according to claim 5, wherein the step of regulation by means of the second control law further comprises:a sub-step of calculation of the displacement(s) to be carried out for the group(s) of rods of the control sub-set and of the displacement to be carried out for the heavy sub-set as a function of the set point and to the actual value of the mean temperature of the primary cooling fluid in the core, and as a function of the set point and the actual position of the group; anda sub-step of modification of the position(s) of insertion of the group(s) of the control sub-set and/or of the heavy sub-set as a function of displacements calculated, for the purpose of regulating the mean temperature of the primary cooling fluid in the core to the set point. 11. The method according to claim 10, wherein the control sub-set is displaced first in order to regulate the mean temperature of the primary cooling fluid in the core, the heavy sub-set being displaced when the control sub-set has reached the limits of a dead band centered on its position set point. 12. The method according to claim 5, wherein the step of regulation by means of the second control law further comprises:a sub-step of calculation of the concentration of the neutron-absorbent component as a function of the set point and to the actual value of the axial distribution of thermal power; anda sub-step of adjustment of the concentration of the neutron-absorbent component in the primary cooling fluid at the concentration calculated in order to regulate the axial distribution of thermal power to the set point. 13. The method according to claim 5, wherein the step of regulation by means of the second control law further comprises:a sub-step of calculation of the displacement(s) to be carried out for the group(s of rods of the control sub-set and of the displacement to be carried out for the heavy sub-set as a function of at least the set point and to an actual value of the positions of insertion of the group(s) of rods of the control sub-set; anda sub-step of modification of the positions of insertion of the group(s) of the control sub-set and/or of the heavy sub-set as a function of the displacements calculated, in order to maintain the group(s) of the control sub-set in a dead band around the insertion position set point. 14. The method according to claim 13, wherein, when the mean temperature of the cooling fluid is in a dead band around its set point, the control sub-set and the heavy sub-set are displaced in inverse directions in order to keep the group(s) of the control sub-set in the said dead band around its insertion position set point. 15. The method according to claim 3, wherein the groups of rods of the control sub-set are inserted or extracted sequentially when the thermal power produced by the core varies, two groups which are inserted or extracted in succession, each group having respective insertion positions which are separated from one another by a difference which is constantly less than a predetermined limit. 16. The method according to claim 1, wherein the regulation method is automatic. 17. The method according to claim 1, wherein the set point of the parameter representative of the capacity to increase the power of the reactor is a set point for the positions of insertion of several groups of rods, calculated based on a set point of capacity to increase the power of the reactor and on an actual value of a primary thermal power of the core.
047675926
description
DETAILED DESCRIPTION OF THE INVENTION The invention involves a protective surface or wall for energy deposition inside a vacuum vessel, such as used in a tokamak type reactor system exemplified by the Doublet III magnetic confinement fusion reactor. The protective surface or wall involves at least one array of connected plates mounted on the inside walls of the vessel. The protective surface utilizes an array of small rectangular plates attached with threaded fasteners to the existing walls. The protective surface enables safe operation of divertor discharges with high neutral beam power. Divertor plasma operation in the Doublet III, for example, is substantially different from the operation of classical divertor tokamak type reactor systems, such as Poloidal Divertor Experiment (PDX) and Axisymmetric Divertor Experiment (ASDEX). In those devices, plasma energy flow is guided to a sacrificial neutralizer plate by coils inside the vacuum vessel. In the Doublet III type system there are no coils inside the vacuum vessel; the plasma energy is guided by the external coils to the vessel wall itself. The flux surface geometry for the expanded boundary diverter mode of the Doublet III type system is shown in FIG. 1. The power flow in the expanded boundary divertor mode is as follows: Ohmic and neutral beam power (up to about 5MW to date) is deposited inside the closed flux surfaces (see FIG. 1). Typically about one-third of this power is radiated by impurities uniformly and harmlessly to the walls of the vacuum vessel. The remaining two-thirds of this power flows radially across the closed flux surfaces into the scrape-off layer. The scrape-off layer (see FIG. 1) is about 0.60 in. (2 cm) thick and consists of those field lines which are not closed but run to the divertor areas on the wall. The heat transport in the scrape-off layer is mainly parallel to the field lines. Because of high plasma density buildup just in front of the divertor areas, much of the power is radiated from this divertor region or area before it impinges on the wall. The wall protection system of this invention is made up of discrete uncooled Inconel plates but offers about 86% of the toroidal coverage of the prior known continuous belt limiter. Future power loadings should be down from the previous 1.0 to 1.7 kW/cm.sup.2 by a factor of 16 (245XO.86/13). Since the projected energy load will increase four times, a net reduction of a factor of 4 in power loading should be realized. The plate array wall protection system of this invention, as opposed to the prior continuous belt limiter, has no continuous toroidal current path which would carry large currents during disruptions and plasma breakdown. The small plates minimize forces and torques produced by eddy currents induced during normal plasma operation and disruptions. Since the system is uncooled, relying primarily on radiative cooling between shots, thermal cycling and stress and provision for thermal expansion were important factors in the design of the plate array system. The protective wall system also requires that inherent material strength be sufficient to resist applied loads, and that the cross-sectional area at attachment points be large enough to ensure proper electrical grounding and physical anchoring of each plate. Other goals accomplished by the protective wall of this invention are to: Minimize the quantity of different kinds of plates; minimize the number of new studs required for attaching the plates to the walls; and reduce the amount of welding, machining, and bending needed to fabricate the plates. In addition, the plate array system interfaces with existing diagnostics and is easy to install, while distortion effects due to thermal expansion are minimal. The primary areas of the inside surface of the pressure vessel walls to be protected by the protective plate arrays or heat shields, indicated generally at 10, are illustrated in FIG. 2. These areas are all potential areas of impingement by diverted field lines, depending on the exact configuration of the flexible plasma field shaping coil system of the reactor (Doublet III in this embodiment). For example, the expanded boundary divertor of FIG. 1 may be operated such that it produces heat loads on both the inboard (inner) and outboard (outer) walls indicated at 11 and 12, respectively, at or below the midplane 13, as shown in FIG. 2, or the divertor configuration may be operated such that heat loads are produced only on the inboard (inner) wall 11 at two sites, above and below midplane 13. Also, when the expanded boundary diverter is operated with highly triangular plasmas, such produce diverted field line impingement in an upper inner corner of the vacuum vessel, indicated at 14, as shown in FIG. 2. The divertor heat shield or protective wall of this invention consists of an array of rectangular shaped plates, generally indicated at 15, as shown in FIGS. 5a-5c. Each plate 15, as shown in FIG. 3 may, for example, be 8.times.6 in. (20.times.15 cm) fabricated from 1/8 in. thick Inconel 625 sheet. The basic plate design is a folded `mailbox` configuration, which allows an external face or main body surface or section 16 of the plate to protect both the vessel wall and the hardware which attaches the plates to the wall, as seen in FIGS. 5a-5c. As seen in FIG. 3 edge portions along the longer side of plate 15, indicated at 17 and 18 of the plate face or surface 16 are each bent downward at two places to obtain greater rigidity and to minimize bending and distortion of the plates due to uneven heating and thermal expansion. Note that the outer ends of edge portions 17 and 18 are bent so as to be substantially perpendicular with respect to the main body portion of surface 16. The plate 15 includes two end flange-like portions 19 and 20 which are each bent at two points at an angle of about 90.degree. with respect to the main body portion of surface 16, and form surfaces 21, 22 and 23, 24, respectively. Each of the surfaces 22 and 24 of flange-like portions 19 and 20 is provided with a pair of protuding sections or attachment members 25, 26 and 27, 28, respectively, which include cut-aways 29, 30, 31 and 32 respectively, by which the plate 15 is mounted to the vessel wall 11 or 12, as described hereinafter. Note that surfaces 22 and 24 of flange portions 19 and 20 are bent in a direction toward each other, with the cut-aways 29-32 being located in the lower side or end of each of protuding sections 25-28. By way of example, the edge portions have a width of 0.75 in.; flange-like portions 19 and 20 have a width of 2.07 in. and length of 7.38 in., with surfaces 21 and 23 having a width of 4.25 in. and surfaces 22 and 24 having a width of 2.0 in.; protuding sections 25-28 having a length of 1.56 in. and width of 2.0 in., with cut-aways 29-32 having a depth of 1.0 in. and width of 0.75 in. An array 10 of protective plates 15 covers the selected areas of the vessel walls 11 and/or 12 and the void volume, indicated at 33, between the plates and the wall is an area where neutral particles can accumulate. To prevent these neutral particles from influencing the plasma as they move upward beyond the plate array 10, the top course or section of plates 15 on both inner and outer walls 11 and 12 are fitted with a series of gas-seal sheets or plates (not shown) which extend across the adjacent edges 17 and 18 of the adjacent plates 15. This series of gas-seal sheets or plates effectively blocks particle migration out of the top of the plate array 10. The protective plates 15 are mounted on the inner walls 11 and 12 of the vacuum vessel by fasteners or mounting hardware assemblies or structure illustrated in FIGS. 4 and 5a-5c. The fasteners, or mounting hardware assemblies, generally indicated at 35, each consist of a stud 36, a centrally apertured standoff 37, a centrally apertured spool 38, clamping washer 39, lock washer 40 and nut 41. The central aperture of standoff 37 includes a tapered section 42. The studs 36 are welded to the vessel wall 11, as indicated at 43, and are, for example, 0.312 in. (0.79 cm) diameter Inconel, with a length of 1.50 in. The spool 38 is provided with an outer annular groove 44 having an outer tapered edge 45, and with a reduced diameter projecting section 46. For example, the standoff 37 is fabricated of stainless steel, with a diameter of 1.25 in. and length of 0.675 in. with the tapered central aperture 42 at an angle of 45.degree.; the spool 38 is fabricated of silver plated stainless steel, with an overall length of 0.50 in., an outer diameter of 1.25 in., with groove 44 having a depth of 0.315 in., width of 0.15 in., with tapered edge 45 being at an angle of 30.degree., and with projecting section 46 having a length of 0.10 in. and diameter of 0.62 in. The clamping washer 39 is fabricated of silver plated stainless steel with an outer diameter of 1.25 in. and thickness of 0.125 in. with lock washer 40 and nut 41 being fabricated of silver plated stainles steel. Each plate 15 is anchored by four studs 36, with the tapered central opening 42 of standoff 37 extending around the weld 43, as shown in FIGS. 5b and 5c. Two tight, electrically sound anchors are made on one side of each plate, as illustrated in FIG. 4 by plate attachment member 25 being clamped tight between spool 38 and clamping washer 39, projecting section 46 of spool 38 serving as a support and abutment point with cut-away 29 of attachment member 25. This complete electrical circuit from plate 15 through stud 36 to wall 11 does not intercept poloidal magnetic flux and so no major disruption-caused current should flow in the plate 15 or studs 36. The two remaining studs 36 are designed as slip joints (poor electrical contact), as illustrated in FIG. 4 by plate attachment member 26 being loose in groove 44 of spool 38, with cut-away 30 being supported by spool 38. These slip joints restrain normal loading, are easy to assemble, and accommodate thermal expansion. Plates 15 will not be overstressed if the slip joint (spool groove 44 and attachment member 26) cannot slip due to friction or misalignment. The spool 38 accommodates thermal expansion. The spool 38 can be installed with projecting section 46 facing outwardly or inwardly. Either way, it allows one plate to be tightened (via clamping washer 39) while the neighboring plate, attached at the same point, slides in oversized groove 44 of spool 38, as shown in FIG. 5b. A space, indicated at 47, between plates 15 is held to a nominal 0.18 in. (0.46 cm), see FIG. 5a-5c. Also, as shown at 48 in FIG. 5b, the surfaces 16 of adjacent plates 15 are at an angle of 7.0.degree. (8:1 pitch line) with respect to each other, which is the maximum angle of plasma incidence. In view of the fact that Inconel and stainless steel are prone to galling (especially under vacuum conditions), and to minimize friction between sliding surfaces, the spools 38, washers 39 and 40, and nuts 41 are silver plated. The silver plating also enhances the electrical conduction between the plates 15 and the vessel wall 11 and/or 12. The studs 36 carry the mechanical loads on the plates 15 and the electrical currents flowing from the plate to the wall, and each has, for example, a minimum axial load capability of 300 lb. (135 kg). For further detailed discussion of the stud loading, thermal analysis, stress analysis, etc., of the protective wall plate array of this invention, attention is directed to Report No. GA-A17192, Protective Interior Wall For The Doublet III Vacuum Vessel, R. D. Phelps et al, December 1983. It has thus been shown that the present invention provides a protective inner wall for vacuum vessels, such as used in fusion reactors. The protective wall utilizes a series of small plates attached to the wall and installed so as to effectively conceal and protect the mounting hardware, while providing a substantial surface area that will absorb plasma energy. The invention also involves mounting hardware which ensures proper electrical grounding and physical anchoring of each of the protective plates, while allowing for distortion effects due to thermal expansion. While a particular embodiment of the protective plates and mounting hardware therefor has been illustrated and described, modifications will become apparent to those skilled in the art, and it is intended to cover in the appended claims also such modifications as come within the scope of the invention.
claims
1. A Thorium fuel rod comprising:a fuel element containing solid Thorium, the fuel element having a length and defining a central bore extending along at least a majority of the length; andan inner core element positioning within the central bore defined by the fuel element, the inner core having a length that extends along at least 75% of the length of the fuel element, the inner core defining an interior cavity, the interior cavity defining a void space, wherein the void space of the interior cavity is subject to a vacuum; andan end cap sealed to the inner core element in such a manner that the vacuum within the void space is maintained, the end cap being formed of a material capable of passing particles through the end cap such that the particles can impinge upon an nucleus forming the inner core, wherein the particles are of a sufficient energy that impingement of a particle upon an nucleus forming the inner core can induce a (p, n) reaction resulting in the emission of a neutron having an energy level of 0.7 MeV or greater. 2. The Thorium fuel rod of claim 1 wherein the fuel element comprises Thorium Dioxide and an outer cladding. 3. The Thorium fuel rod of claim 1 wherein the outer surface of the fuel element defines a plurality of fins. 4. The Thorium fuel rod of claim 3 wherein the fins are spiral shaped. 5. The Thorium fuel rod of claim 1 wherein the inner core element comprises Beryllium. 6. The Thorium fuel rod of claim 1 wherein the inner core element is formed such that a portion of the void space within a first radial cross-section of the inner core element is eclipsed by a portion of the inner core within a second radial cross-section of the inner core element wherein the first and second radial cross-sections are taken at different locations along the axial direction of the Thorium fuel rod. 7. The Thorium fuel rod of claim 1 wherein the inner core element is configured such that the void space within a first radial cross-section of the inner core element is aligned with the void space within a second radial cross-section of the inner core element wherein the first and second radial cross-sections are taken at different locations along the axial direction of the Thorium fuel rod.
description
This application claims the benefit of priority to U.S. Provisional Patent Application Nos. 60/534,027, filed 2 Jan. 2004, and 60/550,618, filed Mar. 4, 2004; both of these applications are incorporated herein by reference. Near-field scanning optical microscopes (“NSOMs”) operate by scanning an optical probe (“probe”) over a sample. Depending on the mode of operation of an NSOM, the probe may illuminate or collect light, or both. The probe passes light through an aperture smaller than the wavelength of the light. The probe and/or sample are scanned such that the aperture passes over the area to be imaged. An image so constructed occurs on a line-by-line or point-by-point basis. Typical NSOMs use piezoelectric transducers to perform the scanning motions. The spatial resolution achievable by an NSOM is not limited by the wavelength of the light, as in standard microscopy, but rather by the dimension of the aperture through which the light passes (i.e., a smaller aperture produces a higher resolution image) and by the spacing of the points or lines that make up the image. An NSOM may also act as a light source to produce subwavelength images in photoresist. A substrate is coated with photoresist and placed on an NSOM stage. The NSOM probe and/or the substrate are scanned to move the probe's aperture over an area of photoresist to be imaged, to expose the photoresist line-by-line or point-by-point. Photoresist image resolution depends upon the dimension of the aperture and on the spacing of the points or lines during scan. Existing electron beam tools for direct writing exposure of photoresist on a substrate expose the substrate to vacuum conditions and high energy electrons. Imaging of surface features (i.e., alignment features) in electron beam tools also unavoidably exposes photoresist over such features. Images produced by existing conventional lithography tools such as mask projection or contact aligners expose entire regions simultaneously through photomasks. The images produced by conventional lithography tools are also subject to the effects of diffraction. A near-field scanning optical microscope system exposes photoresist on a substrate. The system includes an NSOM probe, and translational stages capable of moving one of the probe and the substrate such that the probe traverses, in continuous motion, over the entire substrate. Another near-field scanning optical microscope system exposes photoresist on a substrate using an array of NSOM probes. Methods for exposing photoresist on a substrate include the steps of translating a surface of the substrate across an NSOM probe (or an array of NSOM probes) in continuous motion. FIG. 1 shows an embodiment of an NSOM lithography system 5, which has a control computer 10, a fiber optic subsystem 30, and an NSOM 50. Control computer 10 is configured by software 20 to perform various tasks as described herein. Control computer 10 and fiber optic subsystem 30 interface through a shutter control line 130, an ultraviolet (“UV”) laser power control line 132, and a red laser power control line 134. Fiber optic subsystem 30 generates light, transmitted by optical fiber 72 to NSOM 50. Control computer 10 also interfaces with certain components of NSOM 50 as follows: a piezoelectric (“piezo”) assembly 68, through piezo control line 108; a tuning fork assembly 70, through tuning fork line 104; a stage assembly 61, through stage control line 102; a stage photodiode 88, through stage photodiode output line 110; and a main photodiode 120, through main photodiode output line 124. As used herein, “line” may comprise multiple lines or buses as a matter of design choice. NSOM 50 may also include other components as described below. FIG. 2 shows a side view of NSOM 50. Certain features of FIG. 2 have been exaggerated for clarity and are not drawn to scale. NSOM 50 includes a base 52, a support member 54, and an enclosure 56. A Y translation stage 62 mounts with base 52; an X translation stage 64 mounts with Y translation stage 62. A rotational stage 86 mounts with X translation stage 64. A substrate holder 80 mounts with rotational stage 86; a stage photodiode 88 is integrated with substrate holder 80. A substrate 82 is placed on substrate holder 80. A Z translation stage 66 mounts with support member 54. Piezo assembly 68 mounts with Z translation stage 66. Tuning fork assembly 70 mounts with piezo assembly 68. Optical fiber 72 mounts with one side of tuning fork assembly 70. An end of optical fiber 72 passes through opening 58 in enclosure 56, to connect with fiber optic subsystem 30, FIG. 1. Another end of optical fiber 72, just below the point at which optical fiber 72 mounts with tuning fork assembly 70, is part of optical probe 74. Through microscope 60, mounted with support member 54, a user may view an area of substrate 82 adjacent to optical probe 74. FIG. 3 shows exemplary detail of NSOM 50. Each of X translation stage 64 and Y translation stage 62 is, for example, a high precision, long travel, granite air bearing stage, (e.g., a granite air bearing stage capable of 2 nm step sizes over 300 mm travel in its axis of motion). Rotational stage 86 is, for example, a rotary stage with 0.0001 degree resolution. Y translation stage 62, X translation stage 64, and rotational stage 86 are shown connected with stage control lines 102(a, b, c) respectively. Tuning fork assembly 70 is shown connected with tuning fork control line 104(a) and tuning fork measurement line 104(b). Piezo assembly 68 is shown connected with piezo control line 108; a voltage supplied by piezo control line 108 to piezo member 68 controls the length of piezo member 68, to control separation between optical probe 74 and sample 82. Light entering stage photodiode 88 generates an electrical current that is sent into stage photodiode output line 110; the electrical current is proportional to the intensity of the light. Stage photodiode 88 thus enables calibration of light intensity emitted from optical probe 74, and enables transmission imaging of small samples. Collection optics 120 operate to collect light from substrate 82 and to focus the collected light into main photodiode 122, which in turn connects with main photodiode output line 124. FIG. 4 shows exemplary detail of fiber optic subsystem 30. UV laser power supply 32 adjusts electrical power supplied to UV laser 36, in response to signals from control computer 10 on UV laser power control line 132. UV laser 36 emits UV light (with light intensity proportional to the electrical power supplied) towards shutter 38. Shutter control line 130 operates shutter 38 to block or alternatively transmit UV light into coupling optics 40. When shutter 38 is open, coupling optics 40 collect UV light into fiber 42. Red laser power supply 34 adjusts electrical power supplied to red laser 44, in response to signals from control computer 10 on red laser power control line 134. Red laser 44 emits red light (with light intensity proportional to the electrical power supplied) into fiber 46. Fiber 42 and fiber 46 connect with a dichroic fiber combiner 48, which combines the UV and red light into optical fiber 72. NSOM lithography system 5 may operate as an imaging tool, a photoresist exposure tool, or both. When NSOM lithography system 5 operates as an imaging tool, control computer 10 (as configured by software 20) sends a signal through tuning fork control line 104(a) to tuning fork assembly 70, causing tuning fork assembly 70 to dither optical probe 74 in the Y direction (i.e., in the direction of arrow 84 of FIG. 2), adjacent to a surface of substrate 82. Tuning fork assembly 70 returns an oscillation amplitude measurement through tuning fork measurement line 104(b) to control computer 10. A measured oscillation amplitude indicates a shear-force interaction between probe 74 and substrate 82, with a dampened oscillation amplitude indicating proximity of probe 74 to substrate 82. Control computer 10 uses the oscillation amplitude measurement to adjust a voltage supplied to piezo member 68, in order to maintain a constant probe-to-substrate separation. Referring to FIG. 3, light entering optical fiber 72 passes into optical probe 74; a portion of the light is emitted through a subwavelength aperture in optical probe 74 towards substrate 82. In one example of generating image data, collection optics 120 collect reflected light from sample 82 and focus the reflected light into main photodiode 122, which sends an electrical current (proportional to the reflected light) into main photodiode output line 124. Control computer 10 receives the electrical current from main photodiode output line 124 and converts it to digital data. In another example of generating image data, stage photodiode 88 may collect light transmitted through sample 82 and send an electrical current (proportional to the transmitted light) into stage photodiode output line 110. Control computer 10 receives the electrical current from stage photodiode output line 110 and converts it to digital data. Control computer 10 moves substrate 82 in a raster scan under optical probe 74 by generating and sending signals through stage control lines 102(a, b, c) to stages 62, 64, and 86, respectively. The distance traveled by substrate 82, from one point to the next in the raster scan, is less than the wavelength of light emitted through optical probe 74. Simultaneously, control computer 10 enables and/or controls (1) the determination and adjustment of probe-to-substrate separation, (2) light emission through optical probe 74, (3) collection of light by main photodiode 122 or stage photodiode 88, and (4) conversion of the electrical current signal from main photodiode output line 124 or stage photodiode output line 110 to the digital data. By building a database wherein the digital data is associated with the position of substrate 82 at each point of the raster scan, control computer 10 builds an image of substrate 82. The resolution of the image is not limited by the wavelength of light, but by the distance between measurement points, and by the size of the aperture in optical probe 74. The image produced by NSOM lithography system 5 may be used, for example, to generate NSOM image data identifying the location of NSOM optical probe 74 with respect to features on substrate 82 (given the known positions of X and Y translation stages 64 and 62, and rotational stage 86). The NSOM image data may then be used to implement software corrections, allowing NSOM optical probe 74 to align to features on substrate 82 with high precision. When NSOM lithography system 5 operates as a lithography exposure tool, UV light emitted through optical probe 74 exposes photoresist on substrate 82. FIG. 5 is a flowchart of a lithographic process 300 employing NSOM lithography system 5 to expose photoresist. The lithographic process begins at step 310. An optional step 312 dilutes photoresist with ethyl lactate, to enable application of the photoresist as a thin film. Step 314 applies the (optionally diluted) photoresist to a substrate (e.g., substrate 82). Steps 350 and 355 are described further below. Step 316 transfers the photoresist coated substrate to the NSOM (i.e., places it on substrate holder 80). Step 320 performs a coarse rotation alignment (e.g., using NSOM optical microscope 60). Step 322 turns on a red light source into the NSOM fiber probe for imaging during alignment (i.e., control computer 10 transmits a signal into red laser power control line 134, causing red light to be emitted into optical fiber 72, as described in FIG. 4). Step 322 also adjusts the intensity of the light obtained at the fiber tip (i.e., by evaluating the light received at photodiode assembly 88 and appropriately adjusting the signal into red laser power control line 134). Step 324 takes NSOM image data, calculates a fine rotation alignment correction based on this data, and performs a fine rotation alignment (i.e., by sending a signal into stage control line 102(c) to move rotational stage 86 by the amount of the correction). The use of red light at step 324 avoids exposure of photoresist as image data is taken, as photoresist is insensitive to red light. Step 326 also takes NSOM image data (again using red light) and calculates registration correction factors (i.e., pattern registration and/or image scaling factors that direct the motions of NSOM 50 during exposure). Step 330 turns off the red light (i.e., by sending appropriate signals into red laser power control line 134), and selectively opens a shutter to couple UV light into the NSOM fiber probe for photoresist exposure (i.e., by sending appropriate signals into UV laser power control line 132 and shutter control line 130, the UV light emitted being coupled into optical fiber 72, as described in FIG. 4). Step 330 also adjusts the intensity of the light obtained at the fiber tip (i.e., by evaluating the light received at photodiode assembly 88 and sending appropriate signals into UV laser power control line 132). The use of UV light enables the exposure of photoresist in step 332, described below. Steps 320, 322, 324, 326 and 330 above may be fully automated, that is, performed by control computer 10 under the control of software 20 without human intervention, or they may be performed with the assistance of a human (e.g., to perform rotation alignment step 320, to validate fine alignment step or registration step 326, and/or to adjust the light sources). Step 332 performs vector or raster scan exposure of the photoresist. A computer (e.g., control computer 10) reduces pattern information from a pattern database to a series of lines to be exposed in the photoresist. In vector scan exposure, the lines to be exposed are referred to as vectors, and may point in any direction over the surface being imaged (i.e., when substrate 82 is an X-Y plane, any vector may have both X and Y components). Vector scan exposure is thus analogous to the operation of a pen type plotter. In raster scan exposure, the lines to be exposed are in either the X or Y direction, and the substrate being exposed is scanned past a writing tool in one of the X or Y directions before its position is incremented in the other of the X or Y directions. Raster scan exposure is thus analogous to the operation of an ink jet type printer (using a single ink jet). In either of vector or raster scanning, the photoresist is selectively exposed through the NSOM probe. Control computer 10 coordinates operation of an electromechanical shutter (e.g., shutter 38 of FIG. 4) to block UV light during connecting moves (e.g., as optical probe 74 passes over areas wherein exposure is undesirable). Step 334 removes the exposed substrate from the NSOM (e.g., from substrate holder 80 of FIG. 3). Step 336 develops the exposed photoresist in a standard developer. Step 340 completes the lithographic process. The high precision and long travel of X translation stage 64 and Y translation stage 62, combined with the other features of NSOM lithography tool 5, may provide advantages relative to existing direct write lithography tools. For example, tools which employ piezo members for fine positioning of substrates have a motion range of tens of microns. Larger motions involve a combination of coarse motions (provided by, for example, translation stages) and fine motions provided by the piezo members. This can lead to “stitching errors” in which large individual shapes include gaps due to a calibration mismatch between the fine and coarse movements. The use of Y and X translation stages 62 and 64 (as shown in FIG. 2 and FIG. 3) with travel limits sufficient to traverse an entire substrate 82 past an optical probe 74 in a single continuous motion, enables an NSOM 50 to expose large feature sizes without the stitching errors of the prior art. “Entire substrate,” in this context, means from any given point on one of the edges of the substrate to any other point on an opposing edge of the substrate. An advantage of NSOM lithography tool 5 relative to conventional (i.e., mask based, projection or contact) lithography tools is the ability to control the dimensions of individual exposed features by varying the scan speed during exposure. For example, when a mask based lithography tool of the prior art is used to expose photoresist, it is common practice to vary the exposure time to control the dimensions of exposed features. When positive photoresist is used, a longer exposure results in slightly wider exposed areas. However, the simultaneous exposure of all the mask features causes the dimensions of all the exposed areas to vary according to the exposure. When an application requires changes to specific dimensions within a layer (leaving other dimensions unchanged), implementing the changes requires generation of a new design database and generation of a new photomask from the new design database. Generating a photomask costs from several hundred dollars up to about three thousand dollars, and can take days or weeks. By contrast, when NSOM lithography tool 5 is used, the exposure scan speed may be varied (by control computer 10, under the control of software 20) on a feature by feature basis, with slower scan speed resulting in wider exposed areas (in positive photoresist). Thus, once a new design database is generated, the change can be tested immediately, resulting in savings of both money and time compared to the prior art. Other advantages of NSOM lithography tool 5, relative to existing direct write lithography tools, may include the ability to image substrate features for alignment purposes, without exposing photoresist, and to avoid certain conditions that may cause substrate damage. Prior art electron beam tools cannot selectively generate an image of a substrate for alignment purposes without exposing photoresist in the imaged areas. Fiber optic subsystem 30 of NSOM lithography tool 5 is a light source that alternates between the use of red light (which does not expose photoresist) for generating data for alignment and registration purposes, and UV light for photoresist exposure. Electron beam tools also require the substrate to be subjected to a vacuum, and exposure of the substrate to beams of electrons with energy on the order of one thousand to one hundred thousand electron volts. Either of these conditions may cause damage to certain types of substrates. NSOM lithography tool 5 exposes the substrate only to atmospheric conditions and relatively low energy photons. In another embodiment of an NSOM lithography tool as described herein, an array of optical probes is used to simultaneously expose photoresist at multiple points on a substrate. A single probe in a probe array may be coupled alternately to red light and UV light sources to facilitate imaging for alignment and registration. Alternatively, a single probe (i.e., a probe that is not part of an array) may be coupled alternately to red light and UV light sources to facilitate imaging for alignment and registration; offsets may be implemented in software to correct for the difference in position between the single probe and the probes of a probe array. FIG. 6 is a schematic illustration of an array 75 of NSOM probes coupled with optical fiber 72. The number of probes shown in FIG. 6 is illustrative only, it will be appreciated that an array of NSOM probes may have more or fewer probes than are shown in FIG. 6. In another exemplary use of an NSOM lithography tool as described herein, coarse features may be patterned on a substrate using a conventional lithography tool, and fine features may be written using NSOM lithography. In one embodiment, a substrate (e.g., substrate 82) may be coated with photoresist and exposed using a conventional lithography tool. In FIG. 5, after a substrate is coated with diluted photoresist in step 314, step 350 selectively exposes photoresist through a photomask using the conventional lithography tool. In step 355, the photoresist is developed to fix a first image, after which the substrate is placed on a substrate holder (e.g., substrate holder 80) in step 316. In this example, the NSOM lithography tool may align either to the developed photoresist image, or to features created on the substrate by previous process steps. After exposure in the NSOM lithography tool, the photoresist is developed again to fix a second image. In another embodiment, a substrate (e.g., substrate 82) is coated with photoresist, and a first image is exposed using a conventional lithography tool. Subsequently, the substrate is placed on a substrate holder (e.g., substrate holder 80) without development of the photoresist. A latent photoresist image is generally present after photoresist is exposed but before it is developed. The NSOM lithography tool may align either to a latent photoresist image, or to features created on the substrate by previous process steps. After exposure of a second image by the NSOM lithography tool, the photoresist is developed to fix the first and second images simultaneously. Changes may be made in the above methods and systems without departing from the scope hereof. It should thus be noted that the matter contained in the above description or shown in the accompanying drawings should be interpreted as illustrative and not in a limiting sense. The following claims are intended to cover all generic and specific features described herein, as well as all statements of the scope of the present method and system, which, as a matter of language, might be said to fall there between.
048266493
description
Referring now to the figures of the drawings in detail and first, particularly, to FIG. 1 thereof, there is seen a diagrammatic illustration of a heating reactor having an internal, substantially cylindrical reactor pressure vessel 1 and an external safety vessel 2 enveloping the pressure vessel with an interspace 3 spacing them apart. The two vessels have respective lower vessel parts 1.1, 2.1, caps 1.2 and 2.2 that are spherically arched toward the outside, and vessel bottoms 1.3 and 2.3 that are spherically arched toward the outside. The lower vessel parts 1.1 and 2.1 and the caps 1.2 and 2.2 are each provided with vessel flanges 1.10, 2.10 and 1.20 and 2.20 having a reinforced wall thickness, and the flanges 1.10-1.20 and 2.10-2.20 are each clamped together in a pressure-tight manner by means of cap screw 1.4 and 2.4, respectively. Supported in the interior of the pressure vessel 1 is a cylindrical core vessel 4 which is open at the bottom and the top and a reactor core 5 on a non-illustrated supporting structure in the core vessel. The reactor core may, for example, be constructed as shown in German Published, Non-Prosecuted Application DE-OS No. 33 45 099 or European Published, Non-Prosecuted Application No. 0 173 767. The reactor core 5 includes a fuel element field 5.0 with fuel elements disposed upright, only two of which, 5.1, 5.2 are shown. Control rods 6 are supported in such a way that they are insertable and retractable in interspaces between the fuel elements 5.1, 5.2, which are cross-shaped in the present case due to a rectangular cross section of the fuel elements. Control rod guide rods 6.1 shown in phantom, control rod guide tubes 6.2 guided on the guide rods 6.1 and cross-shaped projecting or spaced apart absorber plates 6.3 secured to the control rod guide tubes 6.2, are part of the control rods 6; the length of the absorber plates 6.3 is at least as great as the core height h.sub.k and preferably somewhat greater than the core height, as shown. A piston/cylinder system combined with each of the control rods 6 enables an incremental raising or lowering of the control rods out of or in to the reactor core 5 and permits the control rods 6 to be retracted upward out of the core 5 with the absorber rod plates or parts 6.3 thereof, which means that the neutron flux density in the core increases to a greater or lesser extent, or they can be inserted once again to a more or less complete extent into the core 5 by lowering the fluid pressure, which means that the neutron flux density in the core decreases to a more or less pronounced extent, up to the point of the complete shutdown of the nuclear reaction (except for the so-called after-heat of decay). In the present case it is assumed that each of the control rods 6 is equipped with such a piston/cylinder system (such as described, for example, in German Published, Non-Prosecuted Application DE-OS No. 33 45 099 or in greater detail in European Published, Non-Prosecuted Application No. 0 173 767) and the cooling water of the reactor serves as the working fluid. The reactor pressure vessel 1 is filled up to a level 1.5 with cooling water, which serves at the same time as a moderator. During rated operation of the nuclear fission reaction in the nuclear reactor core 5, the cooling water KW takes it course upward along vertically extending cooling canals of the fuel elements 5.1, 5.2, etc. as indicated by outlined arrows f.sub.kw, due to the principle of natural circulation, without requiring internal cooling water pumps, and in so doing cools the fuel elements; the heated cooling water, which has a lower specific gravity, then laterally enters an annular chamber 7 between the core vessel 4 and the lower part 1.1 of the pressure vessel, specifically entering heat exchangers 8 disposed therein, only one of which is diagrammatically outlined. Reference symbol KW is also used to represent the reservoir or drain for the cooling water, as well as the water itself. A U-shaped coil of pipes is disposed in the heat exchangers 8 and the secondary coolant, which once again is water in particular, circulates in the coil and the reactor cooling water KW flows outside past the U-shaped pipes and in so doing cools down and then flows farther downward in the annular chamber 7 into a chamber 7.0 underneath the reactor core 5 because its specific gravity increases as it cools, after which the circulation begins again. A wall/ceiling construction of the heating reactor building is shown at reference numeral 9. A wall 9.1 of the building is in the form of an annular or polygonal wall that encompasses both vessels 1, 2 with an interspace 100 therebetween. The annular or polygonal wall at the same time serves as a biological shield and the outer safety vessel 2 is mounted on a non-illustrated upright frame or the like on a foundation construction, which is also not shown. The internal pressure vessel 1 is also supported by means of vertical ribs and by means of spacer ribs disposed on the outer jacket thereof in a radially central and axially thermally movable manner coaxially within the safety vessel; the support elements are again not shown, because they are unnecessary for an understanding the invention. The hydraulic control rod drive, which is the actual subject of the invention, is identified as a whole by reference symbol CD. The hydraulic control rod drive includes the aforementioned non-illustrated piston/cylinder systems on the control rods 6 and a fluid line 10 internal to the reactor (only one of the lines is shown, but it is understood that a plurality of lines is provided, each of which is associated with one of the control rods 6). The fluid line 10 supplies the cooling water serving as the working fluid from below to the piston/cylinder system of the respective control rod 6. The control rod drive CD also includes a control valve assembly 11, disposed on the outside of the reactor pressure vessel and secured in a pressure-tight manner, which is intended for influencing the fluid quantity on the pressure side of a fluid pump 12 in order to adjust the control rod 6 in the "raising" or "lowering" direction, or for holding the control rod position that has been assumed; the one representative internal fluid line 10 extends downward, for instance, as shown in the annular chamber 7, from the control valve assembly 11 through a pressure-tight line duct 13 that passes through the cap 1.2. Finally, the aforementioned fluid pump 12 external to the reactor is also part of the control rod drive CD; the pump is secured on the ceiling 9.2 of the building and the pump communicates with the piston/cylinder systems of the control rods 6 on the pressure side through the aforementioned control valve assembly 11 and with the cooling water reservoir KW in the reactor pressure vessel 1 on the suction side through a pressure line 12.1 and a suction line 12.2 as well as through another pressure-tight line duct 14 in the jacket wall of the safety vessel 2 and a further pressure-tight line duct 15 in the flange portion of the lower part 1.1 of the pressure vessel. Inside the pressure vessel 1, an internal line segment 12.1a of the pressure line 12.1 extends from the line duct 15 as far as the line duct 13 of the control valve assembly 11. The working fluid is withdrawn from the cooling water reservoir KW by the fluid pump 12 through the other internal suction line segment 12.2a. FIGS. 1 and 2 show that the fluid pump 12 has a pressure connector 121 and a suction connector 122, to which the respective pressure line 12.1 and suction line 12.2 are connected, and FIG. 2 shows that two fluid pumps 12A and 12B are individually provided, which are connected in parallel with one another, each being separately constructed for accommodating the entire fluid flow; that is, each of the two fluid pumps 12A and 12B connected in parallel with one another is constructed for 100% of the rated output. The two pumps are each incorporated in a respective pump branch Z.sub.A, Z.sub.B, the branch Z.sub.A having a series circuit of the following components: a pump control valve V11 on the suction side, the pump 12A itself, a check valve R1 and a pump control valve V12 on the pressure side. Correspondingly, the series circuit of a suction-side pump control valve V21, the pump 12B itself, a check valve R2 and a pressure-side pump control valve V22 is provided in the pump branch Z.sub.B. In the pressure line 12.1 external to the reactor and upstream of the line duct 14, two motor-actuated isolating valves 16a, 16b are disposed in line with one another, and in the suction line 12.2 external to the reactor, two motor-actuated isolating valves 17a and 17b are disposed shortly upstream of the line duct 14. Advantageously, at least two fluid pumps 12A, 12B operating parallel with one another are provided and if one pump malfunctions the other one automatically begins to function, so that the first pump can be isolated by means of its two valves on the pressure and suction sides and then inspected and repaired as needed. In order to increase the serviceability of the entire reactor plant, it may be useful to provide three pump branches Z.sub.A, Z.sub.B and Z.sub.C connected in parallel with one another, because in that case two pumps that are capable of functioning will always be available in the event of a pump malfunction. The control valve assembly 11 for the control rod drive CD shown in detail in the form of a circuit diagram in FIG. 3, has the following control branches for each control rod 6 to be actuated: 1. A holding branch A communicating on the inlet side with the pressure line 12.1a and on the outlet side with the pressure side (fluid line 10) of the piston/cylinder system. The branch A has a first fluid throttle a1 and a bypass fluid throttle a2 connected upstream in terms of the gradient of the first fluid throttle a1 and it discharges into a drain through a bypass line A1. The throttle cross sections of the first fluid throttle a1 and of the bypass fluid throttle a2 are dimensioned in such a way that when the fluid pump 12 is operating they allow the passage of a fluid flow that is sufficient for maintaining a particular control rod 6 in its particular position. When the pump 12 is pumping in a circulatory flow through the bypass fluid throttle a2, a pressure level is produced at the line point 17, and a partial flow is then fed into the holding branch A through the first fluid throttle a1. The bypass fluid throttle also serves the function of ejecting bubbles (venting the hydraulic lines). 2. A raising branch B has a series circuit of a raising valve assembly H and a second fluid throttle b1, wherein two branch ends of the raising branch B are connected to the holding branch A at a connecting point 17 upstream of the first fluid throttle a1 and at a connecting point 18 downstream of the first fluid throttle a1. 3. A lowering branch C has a series circuit of a lowering valve SV and a third fluid throttle c1, wherein the lowering branch C is connected to the holding branch A with one end of the branch C downstream in terms of the drop of the first fluid throttle a1 at the connecting point 18, and with the other end of the branch C discharging into the interior of the pressure vessel 1 like the bypass line a1, that is into the drain or the cooling water reservoir KW, in the form of an outflow line extending through corresponding pressure-tight line ducts 13 through the cap 1.2. According to a first provision (a), the control valve assembly 11 includes means for automatically opening the lowering valve SV in the associated lowering branch and/or the respectively operative raising valve assembly H, in the event that an opened raising valve of the raising valve assembly H in one of the raising branches should stick .The automatic opening means are in the form of at least two raising valves H1-H2 in FIG. 5; H10-H2 in FIGS. 6, 10 and 11; H10-W01-H2 in FIG. 7; or W100-H2 in FIG. 12. According to a second provision (b), the raising valves are connected in series with one another so as to reduce the fluid flow through the particular malfunctioning raising branch B, B.sub.i at least far enough so that further raising of the triggered control rod 6 is prevented. By definition, in the simplest case the raising valve assembly H shown in FIG. 3 can also include only a single raising valve, or as shown in the further drawings may include double or triple series circuits having a plurality of raising valves. In the embodiments of FIGS. 10 and 11, double series circuits each including two raising valves H10-H2 are augmented by a turbulence chamber valve W10, which controls the raising fluid flow into the drain KW in the case of a malfunction. In order to provide the first provision (a), the raising valves H are equipped with position indicators which furnish electrical monitoring signals that are available to the control room. These signals may be obtained, for example, by means of limit switches, which operate inductively or by means of ultra-sound and emit an electrical signal, especially a signal voltage, for both the closing position and the opening position of the raising valve and signals for intermediate positions can be derived as well. In order to monitor the function of the entire control valve assembly 11, it may be useful to provide the lowering valves SV with position indicators as well. Particularly in heating reactors or heavy water moderated pressurized water reactors of relatively high output, of approximately 10 MW.sub.th and up, in which the change in the neutron flux density in the core 5 dictated by an undesirable retraction of a control rod or of a small control rod group of up to three control rods remains within allowable limits, the following provision is recommended; The opening time of the particular raising valve is compared with its desired or set-point opening time that is required to attain the desired control rod raising increment. To this end, as shown schematically in FIG. 4, the actual value for the period of time that elapses between the signal "raising valve open" and "raising valve closed", with the actual value being generally symbolized as t.sub.a-z, is compared with a threshold value .DELTA.t.sub.1 for a desired or set-point opening time period. If this set-point opening time period is exceeded by a predetermined proportion k.(.DELTA.t.sub.1), where 0<k<1, the associated lowering valve SV is opened. In the diagram shown, the period of time t.sub.a-z1 is below the set-point opening time period .DELTA.t.sub.1 ; in other words, a proper closure of the raising valve is taking place. On the other hand, the actual value t.sub.a-z2 is approximately 30% above the set-point opening time period .DELTA.t.sub.1, and an associated electronic monitoring circuit which is associated with the control valve assembly 11 is set in such a way that after the set-point opening time period .DELTA.t.sub.1 has been exceeded by the proportion k.(.DELTA.t.sub.1) and thus the tripping SV is opened, the raising command is at least equalized, so that the applicable control rod cannot be retracted farther but instead remains in its position that it has just reached. Naturally, by actuating a larger group of lowering valves SV or all the lowering valves, it is possible to reduce the fluid pressure on the pressure side of the piston/cylinder systems far enough so that all the control rods drop to their lowermost position, that is including the control rod having the raising valve which was malfunctioning in its open position. It is readily possible to set the response threshold time far enough above the set-point opening time period .DELTA.t.sub.1, for example 20-40% higher, that the control rod having the raising valve which is malfunctioning in the open position cannot be retracted significantly farther but instead can be intercepted very quickly. In the illustrated embodiment, a factor k of 0.3 was used. Preferably, 0.3<k<1. The second embodiment illustrated in FIG. 5 is provided for a hydraulic control rod drive CD01, which is used in heating reactors or heavy water moderated pressurized water reactors of lesser capacity, up to approximately 10 MW.sub.th. In such relatively small heating reactors or nuclear reactors, the absorber cross section of an individual control rod contributes notably to the entire neutraon capturing cross section, so that an undesirable retraction of even a single control rod must be avoided under all circumstances. This can be accomplished according to FIG. 5 by providing that every control branch assembly, which is shown at reference symbol CV in FIG. 3 and each of which is associated with one control rod 6 in the context of the entire assembly of the hydraulic control rod drive CD, has a series circuit in the raising branch B thereof including at least two raising valves H1, H2, so that if one raising valve H1 or H2 sticks in its open position, the interruption of the raising fluid flow is effected by the other raising valve H2 or H1, and vice-versa. Only two control branch assemblies CV1, CV2 are shown in FIG. 5; it will be understood that a number of control branch assemblies is also to be provided which corresponds to the number of control rods 6. In logical relationship with FIG. 3, the individual holding, raising and lowering branches are correspondingly indicated as A.sub.I , B.sub.I and C.sub.I in the control branch assembly CV1 and as A.sub.II, B.sub.II and C.sub.II in the control branch assembly CV2. In general, the holding, raising and lowering branches can be designated as A.sub.i, B.sub.i and C.sub.i, where i (1,2 . . . i) identifies the particular individual branch. In this case, reference symbol A.sub.0 designates a distributor line common to all of the holding branches and reference symbol A represents the holding branch assembly as an entity. The circuitry structure is otherwise as shown in FIG. 3 and the outflow lines discharging into the plenum or cooling water reservoir are labelled at the ends thereof with a hydraulic symbol D. The likelihood that both of the raising valves H1, H2 connected in series with one another will stick in their open position is very slight; in any case, if this malfunction should occur, all the lowering valves SV would be opened. This need not be done if a so-called turbulence chamber valve is provided as a third raising valve, as a diverting valve or as a turbulence throttle for the respective raising branch B, B.sub.I, B.sub.II, and so forth, as described below referring to FIGS. 7-11. As already noted, the working flow principle is at the basis of the control rod drive; that is, retraction is possible only if the necessary hydraulic pilot pressure is furnished by the pump 12 or pump assembly. That is, if the pump is reduced in its rpm or shut off, the pressure of the working fluid drops and all the control rods reach the inserted position thereof or automatically drop into the inserted position thereof. As shown in FIG. 6, each control rod of a control rod drive CD02 is assigned one control branch assembly CV1, CV2 etc., in accordance with FIG. 5; however, a pilot raising valve (H1 in FIG. 5) is not provided for each individual control branch assembly, or in other words it is not present in multiple or numerous form; instead, only one such valve is provided, in the form of a master raising valve H10 connected to the input side which is common to all the control branch assemblies CV1, CV2, etc. A fluid throttle b10 is connected in series with the master raising valve H10, in such a manner that when the valve H10 is opened, it allows the fluid flow to pass to each of the individual raising valves H2 downstream thereof, so that whenever a particular control rod is to raised, the applicable raising valve H2 downstream thereof is opened. If that valve were to stick in its open position, or in other words if it could not be closed or it could only be closed after a considerable delay, the master raising valve H10 would be closed and thus all the control rods would remain in the position they have assumed; further movement in the "raising" direction by any one control rod is no longer possible. The designation of the other hydraulic components and lines is the same as in FIG. 5, but a separate connection point 18.1 is provided for each raising branch B.sub.I, B.sub.Ii and a separate connection point 18.2 is provided for each lowering branch C.sub.I, C.sub.II, respectively, forming connections with the holding branches A.sub.I or A.sub.II. The symbols for the fluid throttles a1, a2, b1, c1 are shown somewhat differently in FIG. 5 than in FIGS. 3 and 6, but their meaning is the same. In the embodiment of the control rod drive of FIG. 6, n-1 fewer raising valves are thus needed, if n is the number of control branch assemblies or control rods to be triggered. It may be useful to combine the control circuit of FIG. 6 with the provisions explained with reference to FIG. 4 for monitoring the position of the raising valves, so that the the precise raising valve which is malfunctioning can be recognized in the control room and in this case an automatic opening of the associated lowering valve can also be provided, so that in the event of the already-closed master raising valve H10, the applicable control rod is lowered into its zero position (inserted position). The hydraulic control branch assemblies provided for the control rod drives CD, CD01 and CD02 shown in FIGS. 3, 5 and 6 undergo further substantial augmentation by means of embodiments of hydraulic control branch assemblies for control rod drives CD03, CD1, CD2 and CD3 shown in FIGS. 7-13. If the circuit of FIG. 7 is compared with that of FIG. 6, it can be seen that the circuit of FIG. 7 agrees with that of FIG. 6 in terms of the embodiment of the control branch assemblies CV1, CV2 etc. (once again, only two control branch assemblies are shown) associated with each individual control rod drive. An expansion and further development of the circuit is provided with respect to the master raising valve H10. The valve H10 is followed by a turbulence chamber valve W01, which has three hydraulic connections s.sub.o, c.sub.o, e.sub.o for three types o f fluid flows, namely a supply flow f1, a control flow f2 and an outlet flow f3. As the drawing shows, the internal, controllable flow path s.sub.o -e.sub.o of the turbulence chamber valve W01, which is located between the supply flow inlet s.sub.o thereof and the valve outlet e.sub.o thereof, is disposed in the raising branch B. Reference symbol B.sub.0 is once again the distribution line that is common to all of the raising branches B.sub.I, B.sub.II, etc. The control flow f2 of the turbulence chamber valve W01 is supplied thereto through a fluid throttle b2. The throttle b2 is located in the fluid line C, which is connected at a connecting point 17.2 to the line branch A10, which turn is connected at a connecting point 17.1 to the distributor line A of the holding branch. The series circuit formed of the line branch A10, the fluid throttle a21 and the fluid throttle a22 together produce the bypass branch A1, which discharges into a drain D and provides for the defined adjustment of a fluid flow that keeps the particular control rod in its holding position together with the first fluid throttles A1 in the respective individual holding branches. However, the bypass branch A1 also has the task of assuring a certain pressure level between the two fluid throttles a21 and a22 thereof, that is the pressure level is approximately 5-10% lower at the connecting point 17.3 than the pressure level that is carried on from the connecting point 17.2 through the control flow line C and the fluid throttle b2 to the control flow connection c.sub.o of the turbulence chamber valve W01. Before giving a detailed discussion of the function of the turbulence chamber valve W01 in the context of the circuit of FIG. 7, an individual turbulence chamber valve shown in FIG. 8 will first be explained. The hydraulic connections s.sub.o, c.sub.o and e.sub.o and fluid flows, namely the supply flow f1, the control flow f2 and the outlet flow f3, are designated in the same way as in FIG. 7. Turbulence chamber valves are purely fluidic elements, which operate solely on the basis of hydraulic effects, having no moving parts and requiring no auxiliary energy external to the system. In this regard, see the article, "Konstruktion und Leistung von Wirbelgeraten" (Construction and Output of Turbulence Devices) by H. Brombach in the journal "Messen - Steuern - Regelm" [measurement - control - regulation], VEB Verlag Technik, Berlin, No. 11. November 1978, pages 638-642, in particular pages 641 and 642. The radial turbulence chamber valve shown by way of example in FIG. 8 (axial and conical turbulence chamber valves also exist) is formed of a flat hollow cylindrical turbulence chamber housing 21, which contains a turbulence chamber 21' in the interior thereof, a connector for the supply connection s.sub.o discharging radially into the turbulence chamber 21, a connector for the control flow connection c.sub.o discharging at a tangent into the turbulence chamber 21, and a connector for the outlet flow connection e.sub.o disposed axially with respect to the axis of rotation of the housing 21 or with respect to the turbulence chamber 21'. The connector for the outlet flow f3 may be in the form of a nozzle or Venturi nozzle, as shown, to keep the pressure loss as low as possible. The supply flow f1, shown in dotted lines and supplied through the radially disposed connector s.sub.o, leaves the turbulence chamber 21' through an axial connector e.sub.o, on the initial condition that no control flow f2 is flowing as yet. The throttling effect of the turbulence chamber valve is then relatively slight, and the supply flow f1 is equal to the outlet flow f3. If a control flow f2 with a control pressure approximately 5-10% higher than the pressure of the supply flow f1 is sent through the tangential connector c.sub.o, then an increasingly intensive swirl flow is generated in the turbulence chamber 21' with increasing control flow quantity. If centrifugal force causes the buildup of a counterpressure in the turbulence chamber 21', this causes the inflow of the supply flow f1 to be reduced (or if the control flow decreases again causing the inflow to increase again) so that it can be controlled. A relatively low maximum control flow throughput of approximately 10-20% of the maximal supply flow throughput f1 is sufficient to stop the supply flow f1. The control flow f2 which is represented by dashed lines, flows in spirals from the tangential inlet to the axial connector e.sub.o and propagates the spiral flow in the connector. The arrow f3 of the outlet flow is shown in dot-dash lines in the FIG. 8 embodiment, in order to represent that it includes components of both the control flow f2 and the supply flow f1. However, if the control flow throughput f2 attains the intended maximum of approximately 10-20% of the supply flow f1, then the supply flow comes to a stop. The outlet flow f3 then contains only a control flow, so that the flow then is approximately 20% of the throughput of the blocked-off supply flow f1. In order to explain the functioning of the circuit of FIG. 7, it is first assumed that the preceding master raising valve H10 is closed and that the raising valves H2 downstream thereof are closed as well. It is also assumed that the control rod drive triggered by the hydraulic control branch CV1 is to be raised by a predetermined number of increments. Specifically, the hydraulic pulse that can be generated by the simultaneous opening of the raising valve H2 downstream and the master raising valve H10 upstream should be sufficient for performing a raising increment that may amount to 20 mm, for example. in other words, the master raising valve H10 and the raising valve H2 downstream thereof are opened at the same time; as a result, the supply flow f1 flows through a line S from the master rising valve through the turbulence chamber valve W01 into the raising branch B, and from there through the raising valve H2 downstream thereof and the fluid throttle b1 (partial branch B.sub.I) thereof into the fluid line 10 that is internal to the reactor, to the associated control rod drive. The connection points of the raising branch B.sub.I and of the lowering branch C.sub.I with respect to the fluid line 10 of the holding branch A.sub.I are shown in FIG. 7 with reference symbols 18. 1 and 18.2, respectively. For the ensuing explanation, reference is first made to the diagram of FIG. 9. In FIG. 9, the point t.sub.a on the abscissa represents the opening instant of the two raising valves H10 and H2 mentioned above, at which point the turbulence chamber valve is simultaneously triggered as well, so that an outlet flow f3(t) flows at the outlet e.sub.o thereof. The turbulence chamber valve W01 has a characteristic causing the outlet flow f3(t) to behave as indicated by the curve drawn in heavy solid lines, which is to first rise up to a maximum f3.sub.max (curve segment f31) and then to drop to a minimal outlet flow f3.sub.min (curve segment f32), whenever the control flow f2 begins to have an effect. The period of time from the beginning of flow of the outlet flow f3(t) until the outlet flow drops to the value f3.sub.min is shown as .DELTA..tau.. This period of time .DELTA..tau. can also be referred to as the time constant of the turbulence chamber valve W01. The curve segment f30(t) is intended to clarify the proper closing function of the two raising valves H10 and H2. In other words, if these two raising valves are given a closure command at or shortly after the maximum of the curve f3(t), because the intended raising increment of the control rod has been performed, then the fluid flow as indicated by the curve segment f30(t) drops to zero in accordance with the closing time constant of the two raising valves, so that the set-point opening time period of .DELTA.t.sub.1, for example, is adhered to. This curve course f30(t) would also result if only one of the two valves were to close upon actuation of the two raising valves H10 and H2 in the closing direction. On the other hand, if the inherently very unlikely situation should arise that both of the activated raising valves H10, H2 located in series with one another should stick in their open position even though the closing command had been given from the time t.sub.z on, then the turbulence valve W01 comes into play, and because of the control flow f2 that has its effect with the time constant .DELTA..tau., the outlet flow f3(t) drops as represented by the curve segment f32 from the value of f3.sub.max to the value of f3.sub.min, the latter value being approximately 10-20% of the original supply flow f1. This value of 10-20% of the supply flow f1 is too low for it to have any effect on the control rod drives in the raising direction. The result is therefore that the outlet flow f3 of the turbulence chamber valve W01 is capable of being reduced to such a fraction of its value in the open position due to the application of a control flow f2, that the operation of raising the control rods is reliably interrupted, that is with a margin of safety as well, due to the thus-reduced fluid flow f3(t) in the raising branch B, B.sub.I or B.sub.II. The term "margin of safety" is understood in this context to mean that for instance an operation of raising the control rod be cannot triggered until 50% of the normal supply flow throughput f1, so that with the lower value of 10-20% of the normal supply flow for the minimum outlet flow f3.sub.min, one is on the safe side. It will furthermore be understood that the time constant .DELTA..tau. of the turbulence chamber valve, that is the period of time that elapses from the onset of the control and supply flow f2, f1 at a time .DELTA..tau.=0 or t=t.sub.a until throttling off the supply flow f2, is matched to the set-point opening time period .DELTA.t.sub.1 of the raising valves H10, H2. This period of time is required for performing a desired maximal allowable raising increment of the applicable control rod, in such a way that in event that both raising valves H10, H2 should stick in their open position after or shortly after attaining the set-point opening time, the raising branch B is automatically throttled off hydraulically, in the direction of interrupting the raising operation, by reducing the outlet flow f3(t) of the turbulence chamber valve W01 to its throttled-off value f3.sub.min . The turbulence chamber valve W01 could also be used for each of the individual raising branches B.sub.I, B.sub.II of the embodiment illustrated in FIG. 5, or in other words multiple turbulence chamber valves could be provided; however, it is particularly advantageous if it is only associated with the master raising valve H10 of FIG. 7 and if it is accordingly dimensioned like the valve H10 for a greater fluid flow. This simplifies the hydraulic circuit considerably, without having to accept sacrifices in terms of safety. FIG. 7 thus shows a preferred hydraulic circuit of the turbulence chamber valve W01, in which the internal, controllable flow path s.sub.o -e.sub.o thereof is located between the outlet of a pilot raising valve, in the form of a master raising valve H10, and the inlet of one of the raising valves H2 downstream thereof of which a multiplicity are connected in parallel with one another. The turbulence chamber valve W01 can easily be dimensioned in such a way that the time constant .DELTA..tau. thereof is, for example, in the range between 150 and 250 ms. These are also practical delay times, which arise in the execution of control rod raising increments in hydraulic control drives. In the diagram of FIG. 9, the turbulence chamber valve already throttles down whenever the set-point opening period of time .DELTA.t.sub.1 is exceeded by approximately 20%. Depending on the construction of the control rod drive, .DELTA..tau. can also be made up to approximately 3 times greater than the value .DELTA.t.sub.1, because the descending segment f32 of the outlet flow course in any case can no longer effect notable shifts of the control rod in the raising direction. In FIGS. 1 and 2, the fluid pumps 12 are shown as fluid pumps which are external to the reactor. However, it is also possible to structurally unite the fluid pumps with the control valve assembly 11, in which case they would be seated in a pressure-tight housing, encapsulated on the outside of the cap 1.2 of the reactor pressure vessel 1, as is shown in FIG. 2 of German Published, Non-Prosecuted Patent Application DE-OS No. 34 35 584. The length of the pressure and suction lines 12.1, 12.2 can be shortened. However, in the context of the present invention a placement of the fluid pumps 12 external to the reactor is preferred, because of better accessibility and ease of maintenance. The invention also preferably relates to fuel element and control rod assemblies of the kind in which the control rods have cross-shaped absorber plates which engage the correspondingly cross-shaped interspaces between four adjoining fuel elements, as shown in German Published, Non-Prosecuted Application DE-OS No. 33 45 099. The control rods can also engage interspaces that are provided between the fuel rods inside the fuel elements, for example as shown in U.S. Pat. No. 3,379,619 in a version of pressurized water reactors. The embodiments described below in connection with FIGS. 10 and 11 are based on the recognition that not only can such turbulence chamber valves be connected in series with the raising the valves in the particular raising branch of the control rods (in which case they block or throttle the raising fluid flow after a predetermined period of time, that is if a raising valve should stick in its open position), but safety circuits for the raising branches of control rod drives of this generic type can also be provided to accomplish a great advantage, in which the turbulence chamber valves in the response situation divert fluid flows from the main fluid flow and direct it into a drain. It will be understood that in FIG. 10, hydraulic elements or components identical to those in FIGS. 3-8 are identified by the same reference numerals, so that the basic function of the circuit of FIG. 10 is readily apparent. Unlike FIGS. 3-8, two control rods 6 are provided, which symbolically stand for a plurality or multiplicity of such triggered control rods. The outer tube 6.2 of the tubes which are shown as being coaxial with one another is the movable control rod guide tube in each case, which can be moved upward and downward by a non-illustrated piston, and the inner tube is the control rod guide rod 6.1. Reference symbol CV1 indicates the entire control branch assembly associated with the upper control rod, while reference symbol CV2 is the entire control branch assembly associated with the lower control rod 6. One common holding branch A belongs to both control branch assemblies CV1, CV2, etc. The branch A is bifurcated in other partial holding branches A.sub.I or A.sub.II for each control branch assembly. The partial holding branches are connected to the partial raising branches B.sub.I or B.sub.II at the connecting points 18.1 or 18.2. The holding branch designated as a whole by reference symbol B has a line segment common to all of the holding branch segments, which has the pilot raising valve H10 and the fluid throttle b10 connected to the inlet side of the valve. The entire raising branch B then divides into the individual raising branch segments B.sub.I, B.sub.II, etc. at a circuit point 19, each of these branch segments having a separate raising valve H21, H22, etc. downstream thereof, with an associated fluid throttle b2 upstream thereof. Finally, each control branch assembly CV1, CV2, etc. has a respective lowering branch C.sub.I or C.sub.II, the latter being respectively connected at connecting points 18.3 and 18.4 to the raising branch segments B.sub.I .sub.and B.sub.II and through a remote-controlled lowering valve SV establishing communication with the hydraulic drain D if needed, in this case with the cooling water plenum (KW) of the reactor pressure vessel 1. The fluid line 10 shown in FIG. 1, which is internal to the reactor, is also subdivided in accordance with the multiple assembly shown in FIG. 10, where it is identified by reference symbols 10.1 and 10.2. Once the fluid flow supplied to the drives of the control rods 6 through the holding and raising branches A, A.sub.I, A.sub.II and B, B.sub.I, B.sub.II, has performed its work n the piston/cylinder systems thereof, it is drained out of the control rods into the cooling water plenum, as indicated by respective fluid lines 20.1 and 20.1. The fluid throttles in the holding branch segments A.sub.I, A.sub.II are again designed by reference symbol a1. The turbulence chamber valve W01, with the supply line s thereof being connected to the raising branch B at a circuit point 22 between the two raising valves H10 and H2, is connected to the already-explained series circuit H10-H2 including the pilot raising valve and the respective raising valve downstream thereof (as noted, H2 is represented by a multiplicity of separate raising valves H21, H22, etc. downstream thereof). The turbulence chamber valve W01 generally functions in such a way that it reduces the fluid flow in the raising branch B, or in the respective raising branch segment B.sub.I, B.sub.II, etc., whenever the fluid flow flows out for longer than the set-point opening time period .DELTA.t.sub.1 and cannot be blocked off by the series circuit of the raising valves H2-H10 because of a valve malfunction. In this case, the operation of raising the triggered control rod 6 is interrupted immediately. This function of the turbulence chamber valve in a series circuit, with respect to the pilot raising valve and the raising valve downstream thereof, has been described in detail while referring to FIGS. 3-9. This serial connection sets as a precondition for response of the turbulence chamber valve preventing the fluid to flow through the two raising valves in line with one another from being interrupted after the set-point opening time period .DELTA.t.sub.1 has elapsed. On the other hand, in the context of the present invention it is possible to make the turbulence chamber valve respond as soon as one of the two series-connected raising valves H10-H2 malfunctions, particularly the pilot raising valve H10. Before describing the connection and functioning of the turbulence chamber valve W01 in detail, some supplementary remarks are in order regarding the mode of operation of the turbulence valve of FIG. 8. The functions of the control flow f2 and the supply flow f1 can be reversed, so that if the pilot pressure of the supply flow f1 is greater than the pressure of the control flow f2 by a few per cent, for instance 3 to 10%, the supply flow can cancel the blocking swirl flow of th control flow f2 in the turbulence chamber 21' and the inherently blocked turbulence chamber valve then becomes open once again. This last-mentioned function of controlling the degree of opening of the turbulence chamber valve with a dominating supply flow f1 is utilized in the context of the following two embodiments. The arrow f3 of the outlet flow is shown in dot-dash lines, to indicate that it contains components of both the control flow f2 and the supply flow f1, as noted above. Once the control flow throughput f2 reaches the intended maximum of approximately 10 to 20% of the supply flow f1, the supply flow f1 is overcome, and the turbulence chamber valve closes. The outlet flow f3 therefore contains only the control flow f2, so that by that point approximately 20% of the throughput of the supply flow f1 which is then blocked off is flowing. For example, in accordance with the circuit of FIG. 10, the supply line s of the turbulence chamber valve W01 in the version shown in FIG. 8 is connected to the raising branch B at the connecting point 22, that is between the pilot and the raising valves H10, H2 downstream thereof. The outlet line e discharges into a drain or into the cooling water reservoir KW of the pressure vessel 1 and the control line c thereof is connecting to the raising branch B upstream of the pilot raising valve H10 through at least one fluid throttle A21 for generating a hydraulic pressure level p.sub.c. As the drawing shows, in order to adjust the control pressure p.sub.c in the control line c, a bypass A10 which discharges into the drain KW and is formed of a series circuit of least two fluid throttles a21, a22, is connected to the raising branch B at the connecting point 17 upstream of the pilot raising valve H10 or of the pressure line 12.1 of the pump 12 The control line begins at a branching point 23 between the two fluid throttles a21 and a22. The pressure level p.sub.c is adjusted in such a way that when the pilot raising valve H10 is closed, the pressure is greater than the pressure level p.sub.s in the supply line s, so that the pressure level p.sub.c thus maintains a blocking swirl flow in the turbulence chamber valve W01. On the other hand when the pilot raising valve H10 is opened, the pressure level p.sub.c in the control line c is lower than the pressure level p.sub.s in the supply line s, so that after a time constant .DELTA..tau. of the turbulence chamber valve W01 elapses, corresponding to a time period .DELTA.t.sub.2, which is equal to or somewhat greater than the set-point opening time period .DELTA.t.sub.1 of the raising valves H10, H2 for performing a desired maximally allowable raising increment, the blocking effect of the control flow f2 is cancelled by the supply flow f1, and the majority of the fluid flow in the raising branch B is diverted as a supply flow f1 through the opened turbulence chamber valve W01 into the drain KW so as to interrupt the raising operation. The remaining mass flow, which can therefore continue to flow through the raising branch B for driving the applicable control rod 6 (on the condition that an associated following raising valve H2 is also malfunctioning), is no longer sufficient to maintain or initiate a raising operation. The various states will be described below once again, for the sake of a better understanding of the mode of operation. (a) Floating or Holding Status (Normal Operation): Both raising valves H10 and H2 (or the applicable raising valve H21 or H22 downstream thereof) are closed. The fluid flow necessary for holding the control rod 6 flows through the holding branch A. In the bypass branch A10, the throttles a21 and a22 are selected in such a way that a slightly higher pressure p.sub.c is established in the control line c than in the supply line s (pressure p.sub.s) and the fluid flow through the turbulence chamber valve W01 from the tangential inlet c.sub.o to the axial outlet e.sub.o is sufficient to establish the required blocking state. As already noted, the meaning of the term "blocking state" is an follows: flow turbulence is built up and no fluid flow occurs from the supply line s to the outlet line e. If an overpressure which may be present from the closed-off tubular volume between the two raising valves H10 and H2 has been reduced or relieved through the turbulence chamber valve from s to e, then a swirl flow or turbulence can built up in the turbulence chamber 21' (see FIG. 8) and the turbulence chamber valve W01 performs a blocking function. (b) Raising Operation (Normal Operation): The valves H10 and H2 are opened simultaneously and are kept open for a short period of time .DELTA.t.sub.1 <.DELTA.t.sub.2 (.DELTA.t.sub.2 is the time after which the blocking state in the turbulence chamber valve is cancelled), until such time as the raising mass flow necessary for raising into the next stage has flowed long enough, in addition to the floating or holding mass flow. During this time period .DELTA.t.sub.1, although the pressure p.sub.s in the supply line s is greater than the pressure p.sub.c in the control line c, is not in a position to completely dissipate the turbulence in the turbulence chamber 21' (which is the cause for the blocking state). (c) Raising Operation (Assuming a Defect in the Two Valves H10 and H2): The two series-connected valves H10 and H2 remain opened for a period of time .DELTA.t.sub.2 >.DELTA.t.sub.1. At the onset of a raising operation, a pressure p.sub.s is established in the supply line s, which is very much higher than the pressure p.sub.c in the control flow line c. If this pressure p.sub.s can act for a relatively long period (which is at least .DELTA.t.sub.2 or more) upon the s.sub.o inlet of the turbulence chamber valve W01 the blocking state will then build up more or less rapidly. Finally, if the turbulence previously built up in the floating state (see the above-described operating state a) can no longer be maintained, then a flow path from the supply line s through the turbulence chamber to the outlet line e is opened up. This path, with its radial inflow and axial outflow, has a very low pressure-loss coefficient and as a result of the ensuing slight flow resistance, it enables the majority of the raising mass flow to flow out into the drain or into the plenum KW. The pressure loss at the throttle b10 and at the valve H10 increases through the bypass s.sub.o -e.sub.o which is now open, because of an increased mass flow of the fluid. The pressure p.sub.s in the supply line s can drop to slightly below the pressure p.sub.c in the control line c (even then it is still greater than the pressure at the connecting point 18.1 downstream of the following raising valve H2, but it is possible to construct the turbulence chamber valve W01 in such a way as to prevent a turbulence from building up once again in this state through the inlet c.sub.o. Thus a further raising operation is now no longer possible. (d) Pilot Raising Valve H10 Defective and Following Raising Valve H2 Closed: If the valve H10 continuously remains open, then after a period of time .gtoreq..DELTA.t.sub.2, the turbulence in the turbulence chamber 21' can be broken down by means of the pressure p.sub.s prevailing in the supply line s, which is higher than the pressure p.sub.c in the control line c, and the flow path s.sub.o -e.sub.o through the turbulence chamber is opened up. If the valve H2 is then opened, no raising operation is possible. (e) Following Raising Valve H2 Defective and Pilot Raising Valve H10 Closed: If the raising valve H2 continuously remains open, then the pressure from the outlet of the raising branch segments A.sub.1 or A.sub.2 (connecting point 18.1) or a lower pressure will be established in the supply line s. Depending on the valve construction, the turbulence chamber valve W10 will remain in the blocking state or will allow a small proportion of the floating volume flow or holding mass flow to flow out. In the second embodiment illustrated in FIG. 11, the control flow line c and the supply line s of the turbulence chamber valve W01 are connected to the raising branch B directly upstream and downstream of the pilot raising valve H10 through respective fluid throttles d2 and d1, which serve the purpose of pressure equalization. A further fluid throttle d3 that suitably serves the purpose of pressure equalization is also disposed in the outlet line e of the turbulence chamber valve W01, as shown. Otherwise, the hydraulic control rod drive CD2 of FIG. 1 does not differ from the control rod drive CD1 shown in FIG. 6. The special feature of this embodiment of the control rod drive CD2 is that during the raising operation, with an assumed defect of the two raising valves H10 and H2 after the period of time .gtoreq..DELTA.t.sub.2, the pressure difference between the control flow line c and the supply line s is substantially determined only by the valve H10 and thus is quite small; the fluid throttles d1, d2 and d3 serve only to provide fine equalization. As a result, the pressure ratio (p.sub.c -p.sub.e)/(p.sub.s -p.sub.e), which is important for the valve construction and where p.sub.e is the pressure in the outlet line downstream of the turbulence chamber valve W01, remains virtually constant from the first moment in which the two serial raising valves H10, H2 are opened (at which time the turbulence valve W01 is still in the blocking state) until the state of a completely dissipated turbulence or swirl flow (bypass s.sub.o -e.sub.o fully opened). Otherwise the function of the turbulence chamber valve W01 along with its hydraulic circuitry is like that described above in connection with the circuit CD1 of FIG. 10. Since the segment c-e of the turbulence chamber valve W01 is opened in the circuit CD2 of FIG. 11 in the floating or holding state (normal operation), as described in paragraph (a) of the description of FIG. 10 (that is, a control flow f2 flows into the outlet line 3), the pressure drop at the fluid throttles d2 and d3 and the pressure drop at the fluid throttle b10 upstream thereof and the internal pressure drop in the segment c.sub.o -e.sub.o within the turbulence chamber 21' must be taken into account for the hydraulic dimensioning of the holding or floating segment a. This means that in this kind of normal operation, the turbulence chamber W01 functions like a normal fluid throttle inside a bypass branch leading to the drain KW in series with the fluid throttles b10, d2 and d3. In FIGS. 10 and 11, only one fluid pump 12 is shown, in order to illustrate that the hydraulic control rod drive CD1 or CD2 according to the invention functions with one fluid pump. However, it is more advantageous to improve the redundancy with at least two parallel-connected fluid pumps as already shown and explained in connection with FIG. 2. In the final embodiment illustrated in FIGS. 12 and 13, the valve W100 of at least two series-connected raising valves W100 and H2 of the raising valve assembly H seen in FIG. 12, is a turbulence throttle. The basic layout of the control branch assembly CV for the control rod drive identified as a whole in FIG. 12 by the reference symbol CD3, is like that explained above in connection with FIG. 3 or FIG. 6; that is, once again a main holding branch A having holding branch segments A.sub.i and a main raising branch B having raising branch segments B.sub.i are provided. A single main lowering branch C is also provided in this case, which is common to all of the control branch assemblies CV.sub.i. A single representative and diagrammatically illustrated control rod is shown in two positions, that is, a lower inserted position I of absorber plates 6.3 thereof and a retracted or partially retracted upper position II. Once again, reference symbol 6.1 represents a control rod guide rod, and 6.2 represents a control rod guide tube, the latter having a non-illustrated piston/cylinder assembly associated therewith, as already explained in connection with FIG. 1. FIG. 13 shows the turbulence throttle W100 on a larger scale and in a diagrammatic form, with a housing surrounding a cylindrical turbulence chamber 21', a connection or connector c.sub.o discharging through a tangential nozzle c.sub.o1 into the turbulence chamber 21' and being connected to a circumferential housing wall 21.3, the connector being intended for a control flow line c, and a connecting line e and a connector e.sub.o communicating with the turbulence chamber 21' through an axial nozzle e.sub.o1 and being connected to the end wall 21.2 of the housing (the lower wall as seen in the drawing). The upper end wall of the housing in the figure is shown at reference symbol 21.1. A further outlet line e.sub.1 with a smaller cross section than the outlet line e is connected to the end wall of the housing opposite the axial nozzle e.sub.o1 of the outlet line e. The further outlet line e.sub.1 serves as a vent line for removing expansion water. The other non-illustrated end of the line communicates with a hydraulic drain, in other words with the cooling water reservoir KW of the reactor pressure vessel 1. This kind of turbulence throttle W100 is a passive fluidic resistor. A swirl flow is imposed on the fluid in the turbulence chamber 21', through the tangential control line c coming from the pump pressure line 12.1 or 12.1a in FIG. 12. Such a swirl is also referred to as turbulence. The flow paths of the this kind of turbulence are logarithmic spirals. Due to the low-loss acceleration of the fluid particles, high tangential speeds and therefore high centrifugal forces are produced near the axial outlet nozzle e.sub.o1. The centrifugal force generates a counterpressure, which keeps the flow into the turbulence chamber small. The turbulent core of a fluid-driven turbulence throttle of this kind, which is subject to negative pressure, fills with vapor or gas. The flow resistance of the turbulence throttle W100 from c.sub.o to e.sub.o with the turbulence built up is designated by reference symbol Z.sub.2. The flow resistance Z.sub.2 is greater by a factor k' than the flow resistance Z.sub.1 of the turbulence throttle that is present when the fluid flow through the control line c has just ben initiated and a turbulence has not yet built up. This kind of turbulence throttle W100 can be constructed in such a way that the factor k' may, for instance, be located in the range between 5 and 20. The flow arrows shown in FIG. 13 symbolize a state in which a turbulence is just building up, so that the still relatively low flow resistance Z.sub.1 is present. In other words, the majority of the arriving control flow f2 flows as an outlet flow f3 to the raising valve H2. Once the turbulence has built up in the turbulence chamber 21', approximately 10 to a maximum of 20% of the control flow f2 flows through the axial outlet line e to the raising valve H2; this quantity of fluid is not sufficient to bring about further raising of the control rod 6 (FIG. 6) with its absorber plates 6.3. The function of the circuit shown in FIG. 12 is as follows: if one of the selected control rods 6 is to be raised by one increment or incremental unit, then its associated raising valve H2 in the associated raising branch segment B.sub.i is opened. The fluid flow which therefore begins to be fed from the top pressure line 12.1, 12.1a, causes a flow to be produced from the control connection c.sub.o to the outlet e.sub.o in the turbulence throttle W100, and this internal flow in the turbulence throttle is driven by the pressure drop (p.sub.c -p.sub.3)>0. Since a turbulence has not yet completely built up inside the turbulence throttle W100 during the set-point opening time period .DELTA.t.sub.1 of the raising valve H2, which may, for instance, amount to 200 ms, the flow resistance of the turbulence throttle is at the relatively low value Z.sub.1. The control rod 6 thus is lent a sufficiently large impetus or receives a sufficiently large fluid flow amount to execute the desired raising increment. Once the set-point opening time period .DELTA.t.sub.1 has elapsed, the normal situation is that the raising valve H2 closes. Thus the outlet flow f3 of the turbulence throttle is interrupted, and the turbulence that is in the process of being created collapses, so only air or gases and possibly some expansion water can then flow through the second outlet line e.sub.1]l . On the other hand, if the raising value H2 is still in its opening position after the elapse of a set-point opening time period .DELTA.t.sub.1, despite a command to close, or in other words if it is sticking, then the fluid flow f3 (which is shown in brackets to symbolize this abnormal state) can continue to flow until the time period .DELTA.t.sub.2 has elapsed, which is somewhat longer than .DELTA.t.sub.1, such as by 20-30%. After the time period .DELTA.t.sub.2 has elapsed, the turbulence inside the turbulence chamber 21' seen in FIG. 13 has fully developed, so that the increased flow resistance Z then prevails, by means of which the outlet flow f3 is reduced, for instance, to 10% of its maximal value; thus this outlet flow is no longer suitable, or is ineffective for raising the control rod 6. In the control room, the remote position indicator shows that the associated raising valve H2 has not assumed its closing position, so that suitable repair measures or a change of the malfunctioning raising valve can be performed. Similar to the serial turbulence chamber valve W01, the turbulence throttle W100 is preferably also common to a multiplicity of control branch assemblies CV.sub.i and a correspondingly multiplicity of raising branch segments B.sub.i. In the case of the turbulence throttle W100, a relatively simple series circuit results, because this turbulence throttle combines both the function of a normal pilot raising valve and the function of the controllable flow resistance within itself. The redundant series circuit is accordingly formed by the "pilot" turbulence throttle and one of each of the raising valve H2 downstream thereof in the associated raising branch segments B.sub.i located parallel to one another .
051289750
abstract
An X-ray exposure system for exposing a semiconductor wafer to a mask with X-rays contained in synchrotron radiation, is disclosed. In this system, the mask and the wafer are held on a main frame so that their surfaces extend substantially parallel to a vertical axis. The main frame suspends from a supporting frame through a plurality of air mounts, each being vertically displaceable. The supporting frame is placed on the same reference surface as that of an SOR ring that produces synchrotron radiation. By using these air mounts, any tilt of the mask and the wafer relative to the irradiation region of the synchrotron radiation, as well as the position of the mask and the wafer in the vertical direction, with respect to the irradiation region, can be controlled and maintained constant. Thus, accurate pattern printing is ensured.
claims
1. A method for treating nuclear sludge comprising subjecting the nuclear sludge to a plasma treatment in a plasma chamber, in the presence of an oxidant, to melt at least some of the inorganic components of the sludge, wherein the plasma chamber comprises a crucible having a cooled inner surface, this surface cooled sufficiently such that the inorganic components in contact with the inner surface are in a solid state and form a barrier between the part of surface of the crucible with which they are in contact and the molten inorganic components of the sludge;wherein the plasma chamber comprises two graphite electrodes; andwherein the electrodes are operated in one or both of:(i) a first mode in which an electric arc is passed between the electrodes above the level of the nuclear sludge (remotely coupled); or(ii) a second mode in which an electric arc is passed between the electrodes through the inorganic components of the sludge (transferred). 2. A method according to claim 1, wherein the plasma is generated by DC electricity. 3. A method according to claim 1, wherein the inner surface of the crucible comprises copper. 4. A method according to claim 1, wherein during the plasma treatment the internal surface of the crucible is maintained at a temperature below the solidus temperature of the inorganic components of sludge. 5. A method according to claim 4, wherein the inner surface of the crucible is at a temperature of 50° C. or below. 6. A method according to claim 1, wherein the crucible is water-cooled. 7. A method according to claim 1, wherein the method further comprising transferring the molten components of the sludge to a container for the storage of nuclear waste. 8. A method according to claim 1, wherein the sludge contains one or more materials selected from magnesium hydroxide, silicon dioxide, uranium oxide, magnesium carbonate, aluminium oxide, sodium oxide and magnesium oxide. 9. A method according to claim 1, wherein the method produces a solid product that contains one or more materials selected from forsterite, cordierite, albite and clinoptilolite and other zeolites. 10. A method according to claim 1, wherein the plasma treatment is carried out at a temperature of 1000° C. or more. 11. A method according to claim 1, wherein the plasma treatment is carried out at a temperature of 1800° C. or less. 12. A method according to claim 1, wherein the oxidant present within the plasma chamber comprises air. 13. A method according to claim 1, wherein gases selected from nitrogen, argon and air are fed to the plasma chamber. 14. A method according to claim 1, wherein the sludge is mechanically agitated during the plasma treatment. 15. A method according to claim 1, wherein at least one of the two graphite electrodes has a coating comprising alumina. 16. A method according claim 1, wherein the plasma chamber is further provided with:(i) a water-cooling system for cooling at least part of the inner surface of the crucible, wherein water can be passed between an outer wall and an inner wall of the crucible in order to cool the inner wall;(ii) an inlet for an oxidant adapted such that the oxidant and waste are mixed before or upon entry into the interior of the plasma chamber;(iii) an upper chamber and a lower chamber, the upper chamber being adapted to allow molten material in the upper chamber to flow by gravity into the lower chamber; and/or(iv) one or more electrodes having a coating comprising alumina.
claims
1. A method for the generation of 223Ra of pharmaceutically tolerable purity comprisingi) preparing a generator mixture comprising 227Ac, 227 Th, and 223Ra in a first aqueous solution comprising a first mineral acid;ii) loading said generator mixture onto a diglycolamide DGA separation medium;iii) eluting said 223Ra from said DGA separation medium using a second mineral acid in a second aqueous solution to give an eluted 223Ra solution; andiv) stripping the DGA separation medium of said 227Ac and 227Th by flowing a third mineral acid in a third aqueous solution through the DGA separation medium in a reversed direction, wherein said 223Ra of pharmaceutically tolerable purity comprises less than 45 Bq 227Ac per 1 MBq 223Ra. 2. The method as claimed in claim 1 wherein at least 99.5% of the 227Ac loaded onto the resin in step ii) is regenerated in step iv). 3. The method as claimed in claim 1 wherein at least 95% of the 227Th loaded onto the resin in step ii) is regenerated in step iv). 4. The method of claim 1 additionally comprising the step of:y) storing said mixture of 227Ac and 227Th for a period sufficient to allow ingrowth of 223Ra by radioactive decay, whereby to re-form a generator mixture comprising 227Ac, 227Th, and 223Ra. 5. The method as claimed in claim 1 wherein the generator mixture has an 227Ac activity of at least 1 GBq. 6. The method as claimed in claim 1 wherein the generator mixture is stored as a salt and contacted with a separation medium only when separation of 223Ra is required. 7. The method of claim 6 wherein said contacting occurs for no more than 1 day every 1 to 8 weeks. 8. The method as claimed in claim 1 wherein the DGA separation medium is a DGA resin. 9. The method as claimed in claim 1 wherein the DGA separation medium comprises N,N,N′,N′-tetrakis-2-ethylhexyldiglycolamide binding groups. 10. The method as claimed in claim 1 wherein said first mineral acid is an acid selected from the group consisting of H2SO4, HNO3, and HCl. 11. The method of claim 10 wherein said first mineral acid is HCl. 12. The method as claimed in claim 1 wherein said second mineral acid is an acid selected from the group consisting of H2SO4, HNO3, and HCl. 13. The method of claim 12 wherein said second mineral acid is HCl. 14. The method as claimed in claim 1 wherein the eluted 223Ra solution has a contamination level of no more than 45 Bq 227Ac per 1 MBq 223Ra. 15. The method as claimed in claim 1 wherein the steps of loading the generator mixture onto the DGA separation medium and eluting the eluted 223Ra solution provide a separation ratio of 223Ra to 227Ac of at least 10,000:1. 16. The method as claimed in claim 1 wherein said third mineral acid is an acid selected from the group consisting of H2SO4, HNO3, and HCl. 17. The method of claim 16 wherein said third mineral acid is HCl.
048760625
summary
BACKGROUND OF THE INVENTION The present invention relates to a fuel assembly, and particularly to a fuel assembly which has a water rod and is suitable for use in a boiling water reactor. A conventional assembly for installation in a boiling water reactor comprises a channel box having a quadrangular cylindrical form and a fuel bundle which is received in the channel box. This fuel bundle comprises an upper tie plate and lower tie plate which are respectively provided at the upper and lower ends of the channel box, a plurality of spacers which are axially arranged at given distances in the channel box, a plurality of fuel rods which are regularly arranged in a square lattice form and pass through the spacers, and a water rod serving as a neutron moderating rod. In such a boiling water reactor, the phase change of a coolant takes place in a fuel assembly and serves to remove heat. Therefore, the coolant flowing in the upwardly direction of the fuel assembly has a lower density at its upper position. Gap water, which is a region of saturated water, is present around the circumference of the channel box so that a control rod or a tube equipped with a neutron detector can be inserted therein. In this way, the fuel assembly arrangement is such that coolant is unevenly distributed through the fuel assembly in the horizontal and vertical direction during operation. Light water serving as a coolant acts as a moderator for neutrons, and, in a conventional fuel assembly, the ratio of fuel to moderator, an important factor in determining nuclear properties, depends upon the position of the moderator in the fuel assembly. A water rod which is disposed at the center of the fuel assembly improves the nuclear properties, as well as improving the stability of a reactor core. However, the heterogeneity described above has more influence in the case of a fuel assembly where an attempt is made to increase the average enrichment thereof view to increasing the degree of burn-up, thereby to realize more effective use of uranium resources and a reduction in the powder cost of generating power. Examples of fuel assemblies which have been proposed to solve the above-described problem include a fuel assembly in which the number of neutron moderating rods is increased, a fuel assembly as disclosed in Japanese Patent Laid-Open No. 65792/1984 in which a large-diameter moderating rod having a diameter that is greater than the side of a fuel lattice unit is disposed, and a fuel assembly as disclosed in Japanese Patent Laid-Open Nos. 40986/1975 and 178387/1984 in which a moderating rod having a square cross section is disposed SUMMARY OF THE INVENTION It is an object of the present invention to provide a fuel assembly which allows the degree of thermal allowance to be increased and the fuel economy to be improved. It is another object of the present invention to make the power distribution in the cross-sectional plane of a fuel assembly even. The first object of the present invention can be achieved by controlling a ratio A.sub.M /A.sub.C representing the ratio between the area A.sub.M of a moderator region in a moderating rod in a cross-sectional plane in which a moderator is present and the area A.sub.C of a coolant passage in a fuel assembly and the area A.sub.M. The ratio A.sub.M /A.sub.C is controlled to take a value within the range of 0.07 to 0.11, and the area A.sub.M is controlled to take a value equivalent to 75% or more of the total area of fuel lattice units in which a moderating rod is arranged, but in which no fuel rods are disposed. Each fuel lattice unit has a square shape obtained by connecting the axes of four adjacent fuel rods in the fuel rods which are arranged in a lattice form, and represents a region defined by four lines which pass through the intermediate points between a fuel rod and four adjacent fuel rods arranged around it and which are parallel with the lines of arrangement of the fuel rods. A typical example is the S-shaped form shown in FIG. 4 described below. Since the ratio A.sub.M /A.sub.C of the area A.sub.M of a moderator region to the area A.sub.C of a coolant passage in a fuel assembly is within the range of 0.07 to 0.11, the fuel assembly enables savings to be made in terms of both uranium consumption and fuel economy. In addition, since the area A.sub.M is 75% or more of the total area of a plurality of fuel lattice units in which no fuel rods are arranged, but in which a moderator is arranged, the rate of increase in the critical power and the degree of thermal allowance are increased.
046844996
claims
1. In combination with an elongated nuclear reactivity control member, a releasable latching structure useful for releasably attaching said control member at an end thereof to a top nozzle adapter plate of a nuclear fuel assembly, comprising: (a) a mounting body including an inner plug portion attached to said end of said control member and an outer end portion disposed axially outward from said inner plug portion and said end of said member; and (b) a spring latch disposed about said mounting body and being attached to said outer end portion thereof, said spring latch having at least one latch finger extending toward said inner plug portion of said body and being movable toward and away from said body between an outer latching position in which said finger is adatped to engage a fuel assembly top nozzle adapter plate and retain said elongated member in a stationary relationship with respect to the adapter plate and an inner unlatching position in which said finger is adapted to disengage from the adapter plate and allow removal of said member from the adapter plate. (a) a mounting body having (b) a generally cylindrical spring latch having (a) engagable means defined in said adapter plate; (b) a mounting body attached to said end of said absorber rod and extending axially upward therefrom through said passageway and above said adapter plate; (c) a string latch disposed about said mounting body above said adapter plate and having at least one latch finger extending downwardly toward said adapter plate, said latch finger being deflectible toward and away from said mounting body between an outer latching position in which said finger engages said engagable means on said adapter plate and retains said absorber rod disposed in said guide thimble and an inner unlatching position in which said finger disengages from said engagable means on said adapter plate and allows removal of said absorber rod from said guide thimble; and (d) means defined on said mounting body and string latch for attaching said spring latch to said body. said engagable means is in the form of a recess formed in said adapter plate within said passageway therein; and said latch finger extends into said adapter plate passageway for engaging with and disengaging from said passageway recess when said finger is deflected between its respective latching and unlatching positions. said mounting body has a portion generally coextensive with said latch finger and defining a recessed region along said mounting body; and said latch finger is disposed generally outside of said recessed region when in its latching position and generally within said recessed region when in its unlatching position. 2. The latching structure as recited in claim 1, wherein said outer end portion of said mounting body has a groove defined therein. 3. The latching structure as recited in claim 2, wherein said spring latch includes an outer ring portion disposed about said outer end portion of said mounting body and having a bulge formed therein which extends into said groove in said outer end portion so as to connect said spring latch to said mounting body. 4. The latching structure as recited in claim 3, wherein said mounting body includes a middle body portion having a configuration which generally defines a recessed region surrounding said mounting body at said middle body portion thereof. 5. The latching structure as recited in claim 4, wherein said spring latch includes a plurality of circumferentially spaced apart latch fingers connected at their outer ends to said outer ring portion in cantilever fashion and extending along said middle body portion of said mounting body, said fingers being radially deflectible toward and away from said middle body portion between said outer latching positions in which said fingers are adapted to engage said adapter plate and are generally disposed outside of said recessed region surrounding said mounting body middle portion and said inner unlatching positions in which said fingers are adapted to disengage from said adapter plate and are generally disposed within said recessed region surrounding said mounting body middle portion. 6. The latching structure as recited in claim 5, wherein each of said latch fingers includes a latching key defined on an inner end thereof being configured to engage with and disengage from said adapter plate when said finger is deflected between its respective latching and unlatching positions. 7. In combination with an elongated nuclear reactivity control member, a releasable latching structure useful for releasably attaching said control member at an end thereof to a top nozzle adapter plate of a nuclear fuel assembly, comprising: 8. In a fuel assembly including a top nozzle having an adapter plate with at least one passageway defined therethrough, at least one guide thimble connected to said adapter plate, and a burnable absorber rod disposed within said guide thimble, a releasable latching structure for releasably interconnecting an end of said absorber rod to said adapter plate, comprising: 9. The fuel assembly as recited in claim 8, wherein: 10. The fuel assembly as recited in claim 9, wherein said latch finger has a latching key defined on its lower end being configured to engage said adapter plate within said recess formed in said passageway of said plate. 11. The fuel assembly as recited in claim 9, wherein:
053965345
abstract
A shutter mechanism for collimating x-rays uses a frame to define an opening with two opposing interior edges. An elongated flexible band extends in sliding engagement about at least a portion of the periphery of the frame opening. A first shutter member made of an x-ray opaque material has a first end attached to the flexible band along the first interior edge of the frame. Similarly, a second shutter member made of an x-ray opaque material has a first end attached to the flexible band along the second interior edge of the frame. A drive means, such as a stepper motor, translates the flexible band relative to the frame to control the positions of the shutter members and the shutter aperture. In the preferred embodiment, the interior edges of the frame also include tracks that slidably engage the opposing edges of the shutter members for support. Two or more of these frame assemblies can be stacked in a rotated orientation about a common axis to provide two-dimensional control of the size of the shutter aperture.
claims
1. A hybrid optic comprising:a capillary optic for receiving x-rays from an x-ray source at an entrance portion of the capillary optic and configured to provide substantially parallel or substantially diverging x-rays at an exit portion of the capillary optic; anda grazing incidence multi-shell optic (GIMSO) coupled, at an entrance portion of the GIMSO, to the exit portion of the capillary optic to receive the substantially parallel or substantially diverging x-rays emerging from the exit portion of the capillary optic, the GIMSO comprising an exit portion for providing x-rays. 2. The hybrid optic of claim 1, wherein the capillary optic is configured to receive substantially diverging x-rays at the entrance portion and configured to provide substantially diverging x-rays at the exit portion of the capillary optic. 3. The hybrid optic of claim 2, wherein the GIMSO is directly coupled to the capillary optic and configured to receive the substantially diverging x-rays directly from the exit portion of the capillary optic and configured to provide substantially converging x-rays at the exit portion of the GIMSO. 4. The hybrid optic of claim 1, wherein the capillary optic is configured to receive substantially diverging x-rays at the entrance portion and configured to provide substantially parallel x-rays at the exit portion of the capillary optic. 5. The hybrid optic of claim 4, wherein the GIMSO is directly coupled to the capillary optic and configured to receive the substantially parallel x-rays directly from the exit portion of the capillary optic and to provide substantially converging x-rays at the exit portion of the GIMSO. 6. The hybrid optic of claim 1, wherein the acceptance angle of x-rays at the entrance portion of the capillary optic is greater than 3 degrees from a central axis of the capillary optic. 7. The hybrid optic of claim 1, wherein the acceptance angle of x-rays at the entrance portion of the capillary optic is greater than 6 degrees from a central axis of the capillary optic. 8. The hybrid optic of claim 1, wherein the capillary optic has a focal length less than or equal to 60 mm and the GIMSO has a focal distance greater than 100 mm. 9. The hybrid optic of claim 1, wherein the GIMSO comprises a single reflection optic. 10. The hybrid optic of claim 1, wherein the GIMSO comprises a double reflection optic. 11. The hybrid optic of claim 1, wherein the GIMSO comprises a cylindrical spiral geometry. 12. The hybrid optic of claim 1, wherein the GIMSO comprises a conical spiral geometry. 13. The hybrid optic of claim 1, wherein the GIMSO comprises a nested cylinder geometry. 14. The hybrid optic of claim 1, wherein the GIMSO comprises a metal coated foil capable of being shaped into a desired geometry. 15. The hybrid optic of claim 1, wherein the GIMSO comprises a machined metal surface rigidly manufactured into a desired geometry. 16. The hybrid optic of claim 14, wherein the metal comprises at least one of nickel, gold and iridium and the foil comprises at least one of a plastic foil, aluminum foil and quartz ribbon. 17. The hybrid optic of claim 10, wherein the GIMSO includes a first surface positioned to reflect x-rays provided by the capillary optic and a second surface to reflect x-rays reflected from the first surface. 18. The hybrid optic of claim 17, wherein the first surface includes a first parabolic surface and the second surface includes a second parabolic surface. 19. The hybrid optic of claim 17, wherein the first surface includes a parabolic surface and the second surface includes a hyperbolic surface. 20. The hybrid optic of claim 1, wherein the capillary optic comprises a bundle of glass capillary tubes.
041815696
claims
1. A nuclear reactor having a reactivity control system comprising: at least one control rod of neutron absorbing material arranged for vertical displacement between a first fixed operable position wherein the neutron absorbing material is disposed above the reactor core and a variable second operable position wherein the neutron absorbing material is disposed within the core, means for monitoring an operating parameter of the core and initiating a trip signal in response to a predetermined condition, a fixed first latching device for securing the control rod in the first operable position, the device being responsive to the monitoring means whereby on initiation of a trip signal the device can release the control rod, a second latching device for variably arresting fall of the control rod in the variable second operable position, and means for adjusting the variable second operable position relative to the reactor core while said rod is held by either of said first and second latching devices, the adjusting means being responsive to reactivity within the reactor core, whereby the initial position of arrest of a released rod and subsequent controlled insertion in the reactor core can be varied. 2. A nuclear reactor according to claim 1, wherein the means for adjusting the second operable position of the control rod is optionally capable of operation by alternative control means whereby the control rod can be returned to the first operable position. 3. A nuclear reactor according to claim 2 wherein the latching devices are of the electro-magnetic kind releasable by interruption of the power supply to the latching devices. 4. A nuclear reactor according to claim 3 having a plurality of second latching devices arranged in series, each second latching device being responsive to a discrete reactor parameter.
040452867
summary
This invention relates to a nuclear reactor in which the fuel is provided in the form of a molten salt and is more particularly concerned with an arrangement of the reactor block which serves to limit to strictly necessary values both the length and bulk of the circuit followed by the high-temperature molten salt which is discharged from the reactor core and consequently to reduce the thermal stresses and chemical corrosion of metallic components employed in the construction of the reactor. The conceptual design and technology of molten salt reactors are already known. These reactors make use of a fuel in liquid form which is brought to a high temperature of the order of at least 600.degree. C. as a result of nuclear fission within the reactor core. As a general rule, this fuel consists of plutonium or uranium fluoride or alternatively a mixture of uranium and thorium fluoride dissolved in fluorides of lithium-7 and beryllium; the eutectic mixture thus formed consequently has a relatively low melting point, suitable fluidity and low vapor tension. In a reactor of this type, provision is made within the core for a mass of suitable neutron-moderating material usually consisting of graphite in which are formed ducts for the flow of the fuel salt; the heat gained by this latter as it passes through the reactor core is exchanged in at least one primary heat exchanger with another molten salt or so-called buffer salt such as sodium fluoborate, for example. Said buffer salt in turn exchanges its heat in a secondary circuit comprising a steam generator, the steam being finally expanded in an electric power generating plant. Reactors of this type are capable of operating with a flux of thermal neutrons or a flux of fast neutrons according to the composition of the salt, the distribution of the salt within the reactor core and the nature of the moderator. The fuel salt can be burnt in the reactor core with a periodic readjustment of the fuel concentration whilst processing of this latter and in particular the extraction of fission products are carried out only after a predetermined period of operation. In another design concept, the fission products and especially the gaseous products are continuously withdrawn by a method of chemical bubbling with concomitant adjustment of the fuel salt concentration. Finally, in the case of operation as a breeder reactor, the fuel salt is processed so as to permit continuous removal of protactinium-233 by liquid bismuth followed by metallic reduction by thorium and intermediate storage so as to permit radioactive decay and conversion to uranium-233 in the state of fluoride which is then returned to the main primary circuit (Revue Energie Nucleaire -- vol. 13 No 2 -- March, 1971 -- "Les reacteurs a sels fondus" -- (Molten-salt reactors) -- M. Grenon and J-J. Geist). In these conventional design concepts, the three essential components of the primary molten fuel-salt circuit, namely the reactor core, the primary heat exchangers and the pumps for circulating the fuel within said circuit are connected to each other by means of piping systems forming one or a number of loops located outside the vessel which contains the reactor core. These piping systems must have a sufficient degree of flexibility in order to maintain thermal stresses at an acceptable level. Moreover, in designs of this type which are at present known, the pumps are placed either in the hot branch of said loops for collecting the molten fuel salt at the outlet of the reactor core or in the cold branch at the outlets of the primary heat exchangers. In point of fact, these solutions have a disadvantage in that a substantial portion of the primary circuit is placed in contact with the fuel salt at its maximum temperature; this accordingly produces not only an increase in thermal stresses but also an aggravation of the problems presented by chemical corrosion of structures by the molten salt since the corrosive action of this latter increases very rapidly as the temperature rises. The present invention relates to a nuclear reactor of the type aforementioned in which the primary circuit is directly integrated in the vessel containing the reactor core, thus circumventing the disadvantages outlined in the foregoing. In particular, said primary circuit is provided within a common vessel containing the reactor core and a neutron-moderating mass pierced by passages for the circulation of the molten fuel salt with at least one primary heat exchanger which is located as close as possible to the reactor core and through which the hot fuel salt passes immediately after discharge from said core and with pumps for circulating the cold molten fuel salt which is discharged from the heat exchangers and returned into the reactor core. In accordance with the invention, the molten fuel salt reactor of the type described above is distinguished by the fact that the free spaces defined within the reactor vessel between the core, the heat exchangers and the pumps are filled with an inert material which is compatible with the molten fuel salt except for the passages in which the fuel salt is circulated. The arrangement adopted consists especially in mounting within a common vessel both the reactor core, the heat exchangers and the pumps for circulating the fuel salt which is discharged from said heat exchangers and returned to the core. Accordingly, the useful volume of the molten fuel salt which is heated to the maximum temperature of the cycle can be reduced to the strict minimum; the primary heat exchanger or exchangers or the separate units constituting said exchangers can be connected directly to the core outlet by means of passages of small dimensions while the assembly formed by the reactor, the heat exchangers and the pumps is placed within a single container or vessel which surrounds the entire primary circuit. In consequence, the metallic structures or other structures which are subjected to the most arduous operating conditions and placed in particular in contact with the hot fuel salt are limited to the greatest possible extent. Thus most of the primary circuit is only in contact with the cold fuel salt for which connecting passages are also provided, the dimensions of said passages being calculated as a function of the requirements of hydraulic operation of the system. Moreover, the integrated reactor concept results in containment of the molten fuel salt within a vessel of simple shape which is conducive to cooling and heat insulation. In a particular embodiment of the invention, the reactor core is placed within the central portion of an open vessel having a vertical axis and is surrounded by a lateral reflector which defines an annular region with the internal vessel wall, the pumps for the circulation of molten fuel salt and the heat exchangers being placed within said annular region, said pumps and said heat exchangers being disposed at uniform intervals around the reactor core. In accordance with a particular feature of the first embodiment aforementioned, the pumps and heat exchangers are suspended within the annular space beneath a horizontal vault roof extending above the reactor vessel, said vault roof being provided with a central access opening placed opposite to the reactor core and closed by a removable shield plug. In another alternative embodiment which permits a further reduction in overall length and dimensions of the connecting passages provided for the molten fuel salt discharged from the reactor core, each circulating pump is directly mounted beneath a heat exchanger within the annular space so as to constitute a pump-exchanger unit, the passages providing a connection with the reactor core being constituted by ducts formed radially from the axis of the reactor vessel and placed in the top and bottom portions of the reactor core. Whatever design may be adopted for the primary circuit and whatever in particular may be the relative arrangement of the components of said circuit, the inert material which is compatible with the molten fuel salt and fills the spaces left free between the reactor core, the heat exchangers and the pumps in order to limit the useful volume in circulation is constituted by expanded graphite. The use of graphite within a molten-salt reactor vessel has already been contemplated. However, in known designs, this material is provided in the form of impregnated blocks but this is attended by two disadvantages: on the one hand, said blocks are costly and, on the other hand, they result in local temperature rises which are liable in some cases to be prohibitive. In fact, when the free spaces formed for example within the annular region around the reactor core between the pumps and the heat exchangers are filled with graphite blocks, it is not possible to prevent the presence of thin layers of fuel salt which lie stagnant between the adjacent faces of said blocks, especially as a result of clearance-spaces formed at the time of assembly and operation. Under these conditions, the nuclear components of said salts which are exposed to the environmental neutron radiation give rise to nuclear reactions, thus releasing thermal energy which cannot be removed by conduction through the graphite since this latter usually has low heat conductivity. In some cases, the temperatures attained can be of a high order and prove detrimental to the good operation of the installation since they are liable to result in serious damage to some reactor vessel structures or the internal components of said vessel. The utilization of expanded graphite makes it possible on the contrary to overcome these disadvantages. This graphite is preferably obtained from grains of lamellar complexes of graphite abruptly subjected to a substantial temperature rise so as to produce a thermal shock which results in the conversion of said grains to flakes. Said flakes are then compacted so as to form blocks or graphite agglomerates having a density which can range from 0.1 to 2 according to the compacting pressure adopted. In particular, the compacting can be carried out by isostatic or unidirectional compression, depending on the nature of the end product to be obtained and the design of the fabrication means employed. One remarkable advantage of expanded graphite results from the possibility of forming lightweight compact blocks or masses, the faces of which are practically impermeable to liquids which have a high surface tension. This is precisely the case of the molten fuel salt which is circulated within the reactor in contact with said blocks and fills the free spaces in the reactor vessel. It is worthy of note that these free spaces, in particular in the annular region provided within the reactor vessel between this latter and the reactor core, can be occupied by expanded graphite which is compacted in situ to a predetermined density without preliminary annealing and especially in zones of complex shape, for example around the connecting passages through which the molten fuel salt is circulated. Said passages which connect the reactor core to the heat exchangers and to the circulating pumps can be formed in the mass of expanded graphite either by forming spaces having the requisite size at the time of filling of the reactor vessel or by employing tubes of dense graphite around which the graphite packing is then compacted. It should finally be noted that the use of expanded graphite does not introduce any dimensional limitation in the mass of graphite employed and consequently makes it possible to dispense with joints between blocks in those zones in which the neutron flux density would result in unacceptable temperatures in the fuel salt which is trapped in said joints. If necessary, said mass can be arranged so as to permit slight circulation of the fuel salt and thus prevent stagnation of this latter.
046719202
summary
BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to ice condenser containments, also known as ice baskets, employed for condensing steam generated from the primary water of a nuclear reactor in the event of an accidential loss of coolant and, more particularly, to a maintenance screw drill/conveyor tool and method for maintenance of ice beds of ice condenser containments, for filling sublimated ice voids within each of the plurality of ice baskets, without having first to remove any of the existing charges of ice within the baskets. 2. State of the Relevant Art Ice condenser containments, also known as ice baskets, are employed with nuclear reactors for condensing the steam from the primary water of the reactor in the event of an accidental loss of coolant. In a typical installation, there are provided approximately 2,000 ice baskets, each of which is approximately one foot in diameter and 48 feet in height and is filled with approximately 1,500 pounds of ice. The sidewalls of the ice basket, substantially cylindrical in configuration, are perforated to permit rapid exposure of the steam to the ice and corresponding, rapid cooling. Each such ice basket incorporates, at spaced intervals therein, stiffening rings comprising structural elements which provide lateral rigidity and support, to accommodate not only the weight of ice contained therein but also seismic and other disturbances. Conventional ice baskets furthermore include elements known as cruciforms, comprising generally x-shaped metal straps which extend diametrically across the interior of the basket and are welded at the ends of the straps to the interior sidewalls of the basket, typically at or adjacent the stiffening rings. Typically, the cruciforms are formed of 1/8 inch thick metal, and are 11/2 inches in height. Further, typically, seven (7) such cruciforms are assembled within the basket, spaced at approximately six (6) foot vertical intervals. While not structural members of the baskets and thus not necessary to add radial stiffness to the ice basket cross-section, the cruciforms are necessary elements for satisfying various requirements of the ice bed within the basket. For example, cruciforms are necessary to assure that the geometry of the ice bed within the basket is contained during the entire meltout period of a postulated loss of coolant accident. Specifically, as the ice melts upwardly and away from the bottom of the ice baskets, ice contained therein at higher elevations cannot be permitted to fall down into the bottoms of the baskets, since this presents the potential of creating bypass flow routes for the emerging steam which would accompany the loss of coolant. The cruciforms also serve to prevent large masses of ice from falling during seismic disturbances; falling masses of ice could impose unacceptable impact loads on the ice basket and related, underlying supporting structure. The presence of the cruciforms, however, compounds a maintenance problem which exists in the operation of nuclear power systems employing such ice condenser containments. Particularly, due to sublimation of the ice, the initial volume and weight thereof decreases with time and thus the ice must be replenished, or replaced. Typically, a minimum of at least 1,200 pounds of ice is required for each ice basket, for assuring its effectiveness for counteracting the accidental loss of coolant, as above referenced. The cruciforms impose a substantial obstacle to replenishing the supply of ice, as the latter is depleted due to sublimation. For example, the successively lower compartments of the basket, as delineated by the cruciforms, may contain inadequate charges of ice due to sublimation loss, which charges remain spaced apart due to the presence of cruciforms. Thus, while access may be had to the upper, open end of the ice basket for recharging the first and possibly the second upper compartments, the lower compartments are inaccessible, yet may contain an inadequate charge of ice due to sublimation voids. The ice basket thus loses its required cooling capability, presenting a potentially serious deficiency. Known methods and related apparatus for replenishing sublimated ice voids in the ice baskets all effectively require the complete removal of all remaining ice and the cruciforms, as well, before the compartments may be successively reloaded with new charges of ice and replacement cruciforms installed, to the required capacity of the entire basket. There thus exists a significant requirement, for which no solution has appeared heretofore, of satisfying this critical maintenance operation without having to remove remaining ice or existing cruciforms. SUMMARY OF THE INVENTION The present invention affords a maintenance screw drill/conveyor tool, and related method of operation, for maintaining ice beds of ice condenser containments, in accordance with which an axially extending hole is drilled longitudinally down through the ice condenser containment, or basket, typically to a depth of from 42 feet to 43 feet from the open, upper end of the basket (i.e., for a typical basket of a height of 48 feet). The tool is then selectively operated to feed ice downwardly through the drilled hole and into the voids, while gradually being retracted, or withdrawn, from the hole as the voids are filled, from the lowermost to the uppermost compartment of the basket. In more detail, each ice basket initially is weighed to determine the net weight, or content of the borated ice therein and thus establish whether the ice content thereof must be replenished. Suitable equipment for accomplishing that weighing function is disclosed in the copending application, entitled "COMPACT ICE BASKET WEIGHING TOOL," of which the coinventors herein are among the coinventors thereof and which application is assigned to the common assignee hereof. Once an ice basket is identified as requiring replenishment of the ice, it is isolated and enclosed by installing and inflating elongated plastic inflatible bags about the exterior surface of, and between, the selected ice basket and those of adjacent rows and columns, to prevent spillage of the ice out of the holes in the sidewalls of the ice basket. This isolation technique is a part of the ice loading procedure as typically is employed both in initial charging of ice and subsequent replenishment of ice, in accordance with known procedures. The screw drill/conveyor tool of the present invention includes a support frame which is mounted on the lattice frame surrounding a selected ice basket and locked in place thereon. A drill is mounted for selectively controlled, vertically reciprocating movement relative to a support frame by an electrically driven winch which selectively raises and lowers the drill in a vertical direction. An auger shaft of plural sections interconnects the drill and a rotary bit. Initially, the winch raises the drill to its uppermost position and a first auger shaft section is connected to the drill at its upper end and to a rotary bit at its other end. The drill is turned on and the auger and bit rotated thereby and the winch turned on to permit the drill to progress downwardly in a parallel axial relationship within the ice basket, until approximately one foot of the upper end of the shaft section remains above the top of the ice basket. A clamping device pivotally mounted on the support frame then is rotated into position to capture the protruding end of the drill shaft section to prevent it from dropping into the ice basket. The drill then is disconnected and raised by the winch to the uppermost position of its travel in the support frame. A subsequent drill shaft section then is coupled to the first, and connected to the drill. The operation then is repeated until the coupled drill shaft sections have advanced the bit to the aforementioned desired depth, typically some 42 feet to 43 feet below the top of the basket. At the conclusion of the drilling operation, a final shaft section is coupled in place, so as to dispose the electrically driven drill at the uppermost travel position relative to the platform and as controlled by the winch. The clamping device then is disengaged to release the drill shaft section, and a funnel pivotally mounted on the frame is rotated into position adjacent the protruding drill shaft section. The winch motor is maintained in an off condition, thereby locking the drill and the coupled shaft sections at the established elevation. The drill then is switched to rotate in a reverse direction and granular ice chips or flakes are fed into the funnel. By virtue of a continuous, helical spiral fin on the auger shaft sections, the reverse rotation thereof pulls the loose ice downwardly through the drilled hole and fills the lowermost, and the successive, next higher voids. As the voids become full, the ice compacts about the rotating drill shaft section, as evidenced by a tendency of the rotational speed of the drill to decrease and of the auger to attempt to back out of the ice basket. When these conditions are observed, further ice conveying operations are halted and one or more drill shaft sections are removed, by a reverse sequence of the drilling operation, and then the ice feeding, or conveying, operation is repeated. These operations continue until the successive compartments of the ice basket are filled. Upon completion of filling a given ice basket, the plastic blowout bags are deflated and removed and the ice basket is lifted and weighed to verify the new weight and confirm that it satisfies the requisite content of ice. If not, the foregoing procedures are repeated for that ice basket. If the measured weight confirms the adequacy of the ice replenishing operations, the operations are performed for a next successive ice basket. Accordingly, the screw drill/conveyor tool and maintenance method in accordance with the present invention overcomes significant limitations of prior art mechanisms and procedures, greatly facilitating the important maintenance function of replenishing sublimation voids in ice baskets employed with the nuclear reactor systems. These and other advantages of the apparatus and method of the present invention will be more apparent from the following drawings and detailed description.
description
1. Field of the Invention The present invention relates to nuclear reactor fuel assemblies and more particularly to an array for supporting fuel rods wherein the array, or support assembly, consists of a matrix of substantially flat members forming a grid-like frame assembly and a plurality of helically fluted tubular members. 2. Background Information In a typical pressurized water reactor (PWR), the reactor core is comprised of a large number of generally vertically, elongated fuel assemblies. The fuel assemblies include a support grid structured to support a plurality of fuel rods. The fuel assembly includes a top nozzle, a bottom nozzle, a plurality of the support grids and intermediate flow mixing grids, and a plurality of thimble tubes. The support grids are attached to the plurality of elongated thimble tubes which extend vertically between the top and bottom nozzles. The thimble tubes typically receive control rods, plugging devices, or instrumentation therein. A fuel rod includes a nuclear fuel typically clad in a cylindrical metal tube. Generally, water enters the fuel assembly through the bottom nozzle and passes vertically upward through the fuel assembly. As the water passes over the fuel rods, the water is heated until the water exits the top nozzle at a very elevated temperature. The support grids are used to position the fuel rods in the reactor core, resist fuel rod vibration, provide lateral support for the fuel rods and, to some extent, vertically restrain the fuel rods against longitudinal movement. One type of conventional support grid design includes a plurality of interleaved straps that together form an egg-crate configuration having a plurality of roughly square cells which individually accept the fuel rods therein. Depending upon the configuration of the thimble tubes, the thimble tubes can either be received in cells that are sized the same as those that receive fuel rods therein, or can be received in relatively larger thimble cells defined in the interleaved straps. The straps are generally flat, elongated members having a plurality of relatively compliant springs and relatively rigid dimples extending perpendicularly from either side of the flat member. Slots in the straps are utilized to effect an interlocking engagement with adjacent straps, thereby creating a grid of “vertical” and “horizontal” straps which form generally square cells. The location of the springs and dimples are configured such that each cell typically has a spring on each of two adjacent sides. On each of the sides of the cell opposite the springs there are, typically, two dimples. The springs must be disposed opposite the dimples so that the fuel rod is biased against the dimples by the springs. The springs and dimples of each cell engage the respective fuel rod extending through the cell thereby supporting the fuel rod at six points (two springs and four dimples) in each cell. Preferably, each spring and/or dimple includes an arcuate, concave platform having a radius generally the same as a fuel rod. This concave platform helps distribute the radial load on the sides of the fuel rods. The perimeter straps have either springs or dimples extending from one side and peripherally enclose the inner straps of the grid to impart strength and rigidity to the grid. During assembly, the straps must be assembled in a specific configuration to ensure that each cell has the springs and dimples in the proper position. As such, assembly of the prior art frame assembly is a time consuming process. It would be advantageous to have a support assembly that is more easily constructed. The straps may include one or more mixing vanes formed thereon that facilitate mixing of the water within the reactor to promote convective heat exchange between the fuel rods and the water. This motion, along with the elevated temperatures, pressures, and other fluid velocities within the reactor core tend to cause vibrations between the grids and the fuel rods. As with the proper positioning of the straps, care must be used to ensure that the mixing vanes are disposed at the proper locations. Additionally, the action of the water flow impinging on the mixing vanes cause both a pressure drop in the pressure vessel and creates torque in the frame assembly, neither of which are desired. Since the grids support the fuel rods within the fuel cell, such vibrations therebetween can result in fretting of the fuel rods. Such fretting, if sufficiently severe, can result in breach of the fuel rod cladding with resultant nuclear contamination of the water within the reactor. It is desired to provide an improved grid designed to minimize fretting wear between the grids and the fuel rods while maintaining a mixed flow of water through the reactor core. It is also desired to have a support assembly that is easily assembled. There is, therefore, a need to provide a support grid for a nuclear fuel assembly wherein the fuel rods are supported by a tubular member having a helical, fluted fuel rod contact portion. There is a further need for a support assembly that is easily assembled. There is a further need for a nuclear fuel assembly wherein a support grid includes a tubular member having a helical, fluted fuel rod contact portion for supporting fuel rods. These needs, and others, are met by the present invention which provides a support grid for a nuclear fuel assembly, wherein the fuel rod is a generally cylindrical fuel rod with a diameter, and the support grid includes a frame assembly having a plurality of generally uniform cells, each cell having at least one sidewall and a width, and at least one generally cylindrical tubular member. The tubular member has a cell contact portion with a greater diameter and at least one fluted helical fuel rod contact portion with a lesser diameter. As used herein, a “fuel rod contact portion” is typically, but is not limited to, an arcuate line extending at least partly around the cylinder that is a fuel rod. The cell contact portion and the fuel rod contact portion are joined by a transition portion. The greater diameter is generally equivalent to the cell width, and the lesser diameter is generally equivalent to the fuel rod diameter. In this configuration, a fuel rod disposed in the tubular member would engage the inner diameter. The tubular member is disposed in one cell of the plurality of generally square cells so that the cell contact portion engages the at least one cell sidewall. In this manner, the fuel rod is held by the helical fuel rod contact portion and the tubular member is held by the frame assembly. In a preferred embodiment, the tubular member has a wall of uniform thickness so that the helical fuel rod contact portion defines a passage with a helical shape on both the side adjacent to the fuel rod and the side adjacent to the cell wall. These helical shaped passages act to mix the water so that mixing vanes are not required. There are at least two advantages to using the helical shaped passages; first, the water flow does not impinge on the shaped passage, so there is a minimal pressure drop created by the mixing structure. Second, by reversing the direction of the helical passage in selected cells, the amount of torque exerted on the frame assembly may be controlled. The helical fuel rod contact portion may be formed in various configurations. For example, there may be a single (or multiple) helical fuel rod contact portion having an angular displacement of 360 degrees, that is, extending 360 degrees around the tubular member. However, given the relatively short height of a typical cell, the pitch (radial distance/height) of the helical fuel rod contact portion may be too great thereby restricting the flow of water through the helical portion of the passage. Alternatively, there may be at least two helical fuel rod contact portions each extending 180 degrees around the tubular member. However, in a preferred embodiment, there are four helical fuel rod contact portions each extending 90 degrees around the tubular member. While these examples have used a number (N) of helical fuel rod contact portions and an angular displacement (A) that equals 360 (N*A=360), this is not required. That is, virtually any number of helical fuel rod contact portion(s) may be used with any angular displacement. It is further noted that, while a symmetrical helical contact portion is preferred, a helical contact portion may be an asymmetrical helix; that is the pitch may be variable along the tubular member. The tubular members, preferably, have a smooth transition between the cell contact portion and the helical fuel rod contact portion. Where there are four helical fuel rod contact portions, the shape of the tubular member is similar to the perimeter of a flower with four petals. Alternatively, the tubular member may include extended platform sections structured to engage either the wall of the frame assembly and/or the fuel rod. Where there is a platform, the transition section will typically be a sharp curve. In another embodiment, the greater portion of the length of the transition portion is generally flat and the ends are sharply angled. The frame assembly includes a plurality of cells typically structured to contain a nuclear fuel rod. As noted above, some cells are adapted to enclose a thimble rod or other device. However, the non-fuel rod cells are not relevant to this invention and, while noted, will not be discussed hereinafter. In the preferred embodiment, the frame assembly is made from a plurality of substantially flat, elongated strap members disposed in two interlocked sets, a “vertical” set and a “horizontal” set. The vertical set of strap members is disposed generally perpendicular to the horizontal strap members. Also, the strap members in each set are generally evenly spaced. In this configuration, the cells are generally square. In an alternate embodiment, the frame assembly is made from tubular members that have been welded together, preferably at 90 degree intervals. As used herein, directional terms, such as, but not limited to, “upper” and “lower” relate to the components as shown in the Figures and are not limiting upon the claims. As shown in FIG. 1, there is a fuel assembly 20 for a nuclear reactor. The fuel assembly 20 is disposed in a water vessel (not shown) having an inlet at the bottom and an outlet at the top. The fuel assembly 20 comprises a lower end structure or bottom nozzle 22 for supporting the fuel assembly 20 on the lower core plate (not shown) in the core region of a reactor (not shown); a number of longitudinally extending control rod guide tubes, or thimbles 24, projecting upwardly from the bottom nozzle 22; a plurality of transverse support grids 26 axially spaced along the guide thimbles 24; an organized array of elongated fuel rods 28 transversely spaced and supported by the grids 26; an instrumentation tube 30 located in the center of the assembly; and an upper end structure or top nozzle 32 attached to the upper ends of the guide thimbles 24, in a conventional manner, to form an integral assembly capable of being conventionally handled without damaging the assembly components. The bottom nozzle 22 and the top nozzle 32 have end plates (not shown) with flow openings (not shown) for the upward longitudinal flow of a fluid coolant, such as water, to pass up and along the various fuel rods 28 to receive the thermal energy therefrom. To promote mixing of the coolant among the fuel rods 28, a mixing vane grid structure, generally designated by the numeral 34, is disposed between a pair of support grids 26 and mounted on the guide thimbles 24. The top nozzle 32 includes a transversely extending adapter plate (not shown) having upstanding sidewalls secured to the peripheral edges thereof in defining an enclosure or housing. An annular flange (not shown) is secured to the top of the sidewalls and suitably clamped to this flange are leaf springs 36 (only one of which being shown in FIG. 1) which cooperate with the upper core plate (not shown) in a conventional manner to prevent hydraulic lifting of the fuel assembly caused by upward coolant flow while allowing for changes in fuel assembly length due to core induced thermal expansion and the like. Disposed within the opening defined by the sidewalls of the top nozzle 32 is a conventional rod cluster control assembly 38 having radially extending flukes, being connected to the upper end of the control rods, for vertically moving the control rods in the control rod guide thimbles 24 in a well known manner. To form the fuel assembly 20, support grids 26 and a mixing vane grid structure 34 are attached to the longitudinally extending guide thimbles 24 at predetermined axially spaced locations. The bottom nozzle 22 is suitably attached to the lower ends of the guide thimbles 24 and then the top nozzle 32 is attached to the upper ends of guide thimbles 24. Fuel rods 18 are then inserted through the grids 26 and grid structure 34. The fuel rods 18 are generally elongated cylinders having a diameter. For a more detailed description of the fuel assembly 20, reference should be made to U.S. Pat. No. 4,061,536. The fuel assembly 20 depicted in the drawings is of the type having a square array of fuel rods 28 with the control rod guide thimbles 24 being strategically arranged within the fuel rod array. Further, the bottom nozzle 22, the top nozzle 32, and likewise the support grids 26 are generally square in cross section. In that the specific fuel assembly 20 represented in the drawings is for illustrational purposes only, it is to be understood that neither the shape of the nozzles or the grids, or the number and configuration of the fuel rods 18 and guide thimbles 24 are to be limiting, and the invention is equally applicable to different shapes, configurations, and arrangements than the ones specifically shown. For example, as shown in FIGS. 2 and 4, the support grid 26 includes a frame assembly 40 and at least one generally cylindrical tubular member 50. The frame assembly 40 includes a plurality of cells 42 defined by cell walls 43. Each cell 42 has a width as indicated by the letter “w.” In one embodiment, the cells 42 and cell walls 43 are formed from a plurality of substantially flat, elongated strap members 44 disposed in two interlocked sets, a vertical set 46 and a horizontal set 48. The strap members 44 in the vertical and horizontal sets 48 of strap members 44 are generally perpendicular to each other. Additionally, the strap members 44 in each set are generally evenly spaced. In this configuration, the strap members 44 form generally square cells 42A. Thus, each cell 42A has two diagonal axes “d1” and “d2,” which are perpendicular to each other and extend through the corners of the cell 42A, as well as two normal axes “n1” and “n2,” which are perpendicular to each other and extend through the center of the cell 42A and which intersect perpendicularly with the cell walls 43. The points on the cell wall 43 that the two normal axes pass through are the closest point, “cp,” between the cell wall 43 and the center of the cell 42. As shown in FIG. 3, the frame assembly 40 also has a height, indicated by the letter “h,” wherein the height is substantially less than the width or length of the frame assembly 40. Further, the frame assembly 40 has a top side 47 and a bottom side 49. It is notable that the strap members 44 of the present invention do not include protuberances, such as springs and dimples, as did strap members of the prior art. The lack of additional support structures makes the construction of the frame assembly 40 very easy. The tubular member 50 of the support grid 26 is shown in FIGS. 4 and 5. The tubular member 50 includes at least one helical fluted portion or fuel rod contact portion 52, a cell contact portion 54, and a transition portion 56 disposed therebetween. As shown in FIGS. 4-6, the tubular member 50 has four fuel rod contact portions 52, which is the preferred embodiment. Other configurations are discussed below. The cell contact portion 54 has a greater diameter being generally equivalent to said cell width and is structured to snugly engage the cell 42. The fuel rod contact portion 52 has a lesser diameter, being generally equivalent to said fuel rod 28 diameter. Thus, the tubular member 50 may be disposed in a cell 42 and a fuel rod 28 may be disposed in the tubular member 50. In a preferred embodiment, the tubular member 50 is made from a material having a uniform thickness. Thus, the helical fuel rod contact portion 52 defines an outer passage 60 between the outer side of the tubular member 50 and the cell wall 43. Additionally, the cell contact portion 54, which is spaced from the fuel rod 28, defines an inner passage 62. Water which flows through either the outer or inner passages 60, 62 is influenced by the shape of the helical fuel rod contact portion 52 resulting in the water being mixed. The tubular member 50 may be constructed with any number of helical fuel rod contact portions 52 which may have any degree of pitch. For example, as shown in FIG. 7, a tubular member 50 has a single helical fuel rod contact portion 52 that extends 360 degrees about the tubular member 50. As shown in FIG. 8, a tubular member 50 has a two helical fuel rod contact portions 52 that each extend 180 degrees about the tubular member 50. As shown in FIG. 9, a tubular member 50 has a two helical fuel rod contact portions 52 that each extend 360 degrees about the tubular member 50. As noted above, FIG. 5 shows a tubular member 50 having a four helical fuel rod contact portions 52 that each extend 90 degrees about the tubular member 50. Preferably, the helical fuel rod contact portions 52 are spaced evenly about the tubular member 50, but this is not required. These examples have used a number (N) of helical fuel rod contact portions 52 and an angular displacement (A) that equals 360 degrees or a multiple of 360 degrees. This configuration is especially adapted for use in a square cell 42A. That is, the cell contact portion 54 will only contact the cell wall 43 at the closest point on the cell wall 43. At other points eg., the corner of the cell 42A, the tubular member 50 greater diameter, that is the cell contact portion 54, will not contact a cell wall 43. Thus, as shown best in FIG. 6, where there are four evenly spaced, helical fuel rod contact portions 52 that each extend 90 degrees about the tubular member 50, there are four corresponding cell contact portions 54, each disposed between a helical fuel rod contact portions 52. To ensure the greatest amount of surface area contact between the tubular member 50 and the cell wall 43, the tubular member 50 is disposed with each helical fuel rod contact portion 52 generally aligned with a diagonal axis at the top side 47 of the cell and aligned with a different diagonal axis at the bottom side 49 of the cell. In this orientation, the cell contact portion 54 is aligned with a cell wall 43 closest point at the top side 47 and at the bottom side 49. A similar configuration may be made with cells 42 of any shape. That is, the number (N) of helical fuel rod contact portions 52 is preferably equal to the number of sides (S) to the cell 42, and the angular displacement (A) is preferably 360 degrees/S. Thus, the tubular member may be positioned with each helical fuel rod contact portion 52 generally aligned with an axis passing through the corner of the cell 42 at the top side 47 of the cell and aligned with a different axis passing through the corner of the cell 42 at the bottom side 49 of the cell. Thus, the cell contact portion 54 is aligned with the cell wall 43 closest point at the top side 47 and at the bottom side 49. In another embodiment, the frame assembly 40 includes a plurality of cylindrical cells 42B defined by a plurality of connected tubular frame members 70. As shown in FIG. 10, the frame assembly 40 may have a plurality of densely packed tubular frame members 70, however, as shown in FIG. 11, a pattern of aligned tubular frame members 70 is preferred. That is, the tubular frame members 70 are coupled to each other at 90 degree intervals about the perimeter of each tubular frame member 70. The tubular member 50 is disposed within the cylindrical cells 42B. As shown in FIG. 12, the combination of the tubular member 50 and the cylindrical cell 42B again creates an inner passage 62 between the fuel rod 28 and the tubular member 50 and an outer passage 60 between the tubular member 50 and the tubular frame member 70. The cylindrical cell 42B of the tubular frame member 70 has the additional advantage that the entire cell contact portion 54 abuts the cell wall 43. That is, the diameter of the cylindrical cell 42B is the same as the cell width, which is also the same as the closest point, and, as such, the cell contact portion 54 will engage the cell wall 43 along the entire height of the cell wall 43. This is unlike a square cell 42A wherein the cell contact portion 54 does not contact the cell wall 43 at the corners. In another embodiment, shown in FIG. 13, the functions of the tubular member 50 and the tubular frame member 70 have been combined in a helical frame member 80. That is, the frame assembly 40 includes a plurality of helical frame members 81 disposed in a matrix pattern. The helical frame member 80, like the tubular member 50 includes at least one helical fuel rod contact portion 52, however, instead of a cell contact portion 54, the outer side of the helical frame member 80 is a contact portion 55 structured to be directly coupled to the contact portion 55 of an adjacent helical frame member 80. As with the tubular frame member 70 embodiment of the frame assembly 40, the helical frame members 80 are coupled to each other at 90 degree intervals about the perimeter of each helical frame member 80. Additionally, in this embodiment the frame assembly 40 preferably includes a plurality of outer straps 82 structured to extend about the perimeter of the plurality of helical frame members 81. The outer straps 82 are coupled to the contact portions 55 of the helical frame members 80 disposed at the outer edge of the plurality of helical frame members 81. A fuel rod 28 is disposed through at least one helical frame member 80. As shown best in FIG. 12, as viewed as a cross-section, the tubular member 50 components, i.e., the helical fuel rod contact portion 52, the cell contact portion 54, and the transition portion 56, preferably, are shaped as smooth curves. This configuration gives the tubular member 50 a compressible, spring-like quality. However, as shown in FIG. 14, the cell contact portion 54 may include an extended planar length or platform 90. The platform 90 is structured to provide a greater surface area which engages the cell wall 43. The greater length of the platform 90 will necessitate the transition portion 56 having a sharp curve. Similarly, as shown in FIG. 15, the helical fuel rod contact portion 52 may include a concave platform 92 adapted to extend radially about the fuel rod 28. As before, greater length of the concave platform 92 will necessitate the transition portion 56 having a sharp curve. A tubular member 50 may also include both a platform 90 at the cell contact portion 54 and a concave platform 92 at the helical fuel rod contact portion 52. Finally, the tubular member 50 may also be constructed with a generally flat transition portion 56 with angled ends 94. As shown in FIG. 16, in this embodiment the transition portion 56 is generally planar in a cross-sectional top view. It is understood that, due to the helical nature of the fuel rod contact portion 52, the transition portion 56 is not flat in the direction of the height of the frame assembly 40. While specific embodiments of the invention have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular arrangements disclosed are meant to be illustrative only and not limiting as to the scope of invention which is to be given the full breadth of the claims appended and any and all equivalents thereof.
summary
claims
1. A characterisation system comprising:a characterisation cell for smoke analysis by optical spectrometry, comprising:a reaction chamber;an inlet orifice for the inlet of smoke into the reaction chamber;an outlet orifice for the evacuation of smoke from the reaction chamber;an analysis window for entry of a laser beam intended to form the plasma inside the reaction chamber;a fan for ensuring scanning of inert gas in the vicinity of the analysis window; anda shielding injector coaxially aligned with the inlet orifice configured to coaxially inject smoke shielded by a jet of inert gas around the smoke into the reaction chamber;a collector downstream of the outlet orifice of the cell configured to recover the smoke after its analysis;a pressure regulator for keeping the pressure constant in the reaction chamber of the cell,wherein the pressure regulator comprises a regulation valve placed downstream of the collector to compensate for a loss of charge due to clogging of filters of the collector,wherein the regulation valve is connected to a pressure probe placed in the cell for measuring the pressure therein for its servo-control, andwherein the regulation valve is servo-controlled as a function of the pressure measured inside the cell and which is adapted to open progressively as the collector gets clogged;a reactor for the generation of smoke;a second collector positioned downstream of the reactor;a second regulation valve for regulating the pressure inside the reactor;wherein the second regulation valve is placed downstream of the second collector,wherein the second regulation valve is connected to a second pressure probe placed in the reactor for measuring the pressure therein for its servo-control, andwherein the second regulation valve is servo-controlled as a function of the pressure measured inside the reactor and which is adapted to open progressively as the second collector gets clogged. 2. The system of claim 1, wherein the cell further comprises an arm extending between the reaction chamber and the analysis window, the arm being formed in two parts of different cross-sections, the larger cross-section part being arranged nearer the analysis window and the smaller cross-section part being arranged nearer the reaction chamber to form a Venturi and to ensure overpressure nearer the window. 3. The system of claim 1, wherein the flow rate of inert gas generated by the fan is adjustable. 4. The system of claim 1, wherein the flow rate of inert gas generated by the coaxial shielding injector is adjustable. 5. The system of claim 1, wherein the injector is a circular double nozzle having first and second coaxial orifices, the first orifice having a disc-shaped cross-section for the inlet of smoke, and the second orifice having a ring-shaped cross-section which encloses the first orifice for the inlet of inert gas. 6. The system of claim 1, wherein the cell further comprises a viewing window for observation of the plasma produced inside the reaction chamber during its operation. 7. The system of claim 1, wherein the fan also ensures scanning of inert gas in the vicinity of the viewing window. 8. The system of claim 1, wherein the flow rate of inert gas generated by the Venturi is adjustable. 9. The system of claim 1, wherein the cell further comprises an arm extending between the reaction chamber and the inlet orifice. 10. The system of claim 1, wherein the cell further comprises an arm extending between the reaction chamber and the outlet orifice. 11. The system of claim 1, wherein the cell further comprises a first arm extending between the reaction chamber and the inlet orifice, a second arm extending between the reaction chamber and the outlet orifice, and a third arm extending between the reaction chamber and the analysis window. 12. The system of claim 11, wherein the first and second arms extend along a first axis, and the third arm extends along a second axis that is perpendicular to the first axis. 13. The system of claim 11, wherein the third arm is formed in two parts of different cross-sections, the larger cross-section part being arranged nearer the analysis window and the smaller cross-section part being arranged nearer the reaction chamber to form a Venturi and to ensure overpressure nearer the window. 14. The system of claim 1, wherein the smoke is a smoke of nanoparticles. 15. The system of claim 1, wherein the second regulation valve regulates the pressure inside the reactor so as to keep said pressure constant. 16. The system of claim 1, wherein the second regulation valve is placed at the outlet of the second collector. 17. The system of claim 1, wherein the second regulation valve is adapted to open progressively as filters of the second collector gets clogged due to nanoparticles. 18. The system of claim 1, wherein an outlet of the reactor is connected to a pump which creates a flow of smoke.
abstract
A portable test and certification unit for laser-based speed measuring devices (e.g., traffic laser guns) is provided. The test and certification unit is capable of performing manual, semi-automatic and automatic measurements on laser guns, ensuring no “missed” steps in the certification process. The unit is optionally supported by a general-purpose digital computer such as a “PC,” which may, in turn, record test results and print certification documents. The test and certification unit allows for fast and accurate certification of laser guns in a laboratory or in the field by operators of only minimal technical skill, thereby saving expense and time, as laser guns no longer must be removed from vehicles and/or shipped to a remote certification facility.
description
This application claims priority under 35 U.S.C. §119 to Japanese Patent Application Nos. JP2006-094116 filed Mar. 30, 2006 and JP2007-028448 filed Feb. 7, 2007, the entire content of which is hereby incorporated by reference. 1. Field of the Invention The present invention relates to a fluorescent X-ray analysis apparatus which performs an element analysis and a composition analysis of a sample by irradiating a primary X-ray to the sample and detecting a fluorescent X-ray generating from the sample. 2. Description of the Related Art In recent years, a cadmium pollution of a food, and the like become a problem, and a quantitative determination of a cadmium content in the food, and the like are performed. Hitherto, in the quantitative determination of cadmium, although there have been performed an ICP (inductively coupled plasma spectrometry) and the like, there have been problems that, in addition to the fact that a time is necessary for such a pretreatment as to make the sample into a solution, a dispersion occurs in a measurement result in dependence on an operator. From the background like this, as a measurement method substituted for the ICP, a fluorescent X-ray analysis is noted. The fluorescent X-ray analysis is one in which a kind and a quantity of an element contained in the sample is specified by irradiating the primary X-ray to the sample and detecting the generated fluorescent X-ray, and hitherto it has been utilized mainly in an analysis of the sample, such as Cu alloy or Fe alloy, whose main component is a heavy element, and the like. Since the fluorescent X-ray has an intensity and an energy which are inherent to the element, it is possible to specify the element having been contained in the sample and its quantity by detecting an intensity and an energy of the generated fluorescent X-ray. In the fluorescent X-ray analysis, there suffices if the primary X-ray is directly irradiated to the sample, and there are advantages that a measurement is possible even if the sample is not pretreated and, also as to an analysis result, a reproducibility is good in comparison with the ICP. A detection lower limit denoting an accuracy of the fluorescent X-ray analysis like this is determined by the following expression.Detection lower limit=3×(√Background intensity/Measurement time)/Sensitivity Here, the background intensity means mainly an intensity of a scattered X-ray or the like other than the fluorescent X-ray generating from an aimed element having been contained in the sample. Further, the sensitivity is a magnitude of an X-ray intensity obtainable in a detector. That is, by decreasing the background intensity and further raising the sensitivity, the detection lower limit is improved, and it becomes possible to realize the quantitative determination of a trace element. As the fluorescent X-ray analysis apparatus capable of performing the fluorescent X-ray analysis like this, for example, there is proposed one having possessed an X-ray source irradiating the primary X-ray to the sample, a detector detecting the fluorescent X-ray generated from the sample to which the primary X-ray has been irradiated, and a primary filter having plural filter components, or the like (e.g., refer to JP-A-2004-150990 Gazette). According to the fluorescent X-ray analysis apparatus like this, by absorbing the primary X-ray of plural energy bands by the primary filter and irradiating the primary X-ray of a necessary energy band, it is possible to decrease the background intensity, thereby improving the detection lower limit. However, the primary X-ray having been irradiated to the sample excites the sample to thereby generate the fluorescent X-ray (primary fluorescent X-ray) and, by the sample, scatters to a periphery as a primary scattered ray. And, between the primary fluorescent X-ray and the primary scattered ray, one part having been not detected by the detector generates, by the fact that it is irradiated to an X-ray source, an outer periphery face of the detector or the like, a secondary X-ray. That is, by the fact that it scatters in the X-ray source, the outer periphery face of the detector or the like, a secondary scattered ray generates and, further by the fact that it excites elements forming the X-ray source, the outer periphery face of the detector or the like, a secondary fluorescent X-ray generates. And, one part of the X-ray having been generated secondarily scatters directly or again in the sample and is detected by the detector. That is, by the fact that the unnecessary X-ray having generated subsidiarily, which is the X-ray other than the primary fluorescent X-ray to be detected originally, is detected by the detector, a count (intensity) of the X-ray entering into the detector increases. In a case like this, since there is a limit in the count of the X-ray capable of being detected by the detector, although it is necessary to suppress the intensity of the primary X-ray irradiated from the X-ray source, the intensity of the primary fluorescent X-ray capable of being detected lowers as well, so that there has been a problem the detection lower limit deteriorates as a result. Further, by placing a member (hereafter, called a collimator), which has a through-hole, in a front face of the detector, although it is possible to suppress the count of the X-ray entering into the detector, since the secondary fluorescent X-ray generating from a hole wall of the through-hole of the collimator is detected in its most by the detector, the count of the X-ray is increased by this X-ray generating secondarily, so that it is impossible to fundamentally reduce the X-ray other than the primary fluorescent X-ray to be detected originally. Further, in a count circuit, by the fact that the count increases in such a degree that the X-rays having generated subsidiarily cannot be discriminated as separate ones, a count error (hereafter, called a pileup) occurs. The pileup exerts two adverse effects on a spectrum obtainable. One is a deterioration (a peak width of the spectrum becomes thick) of an energy resolving power. The other one is the fact that a pseudo-peak called “sum-peak” is formed. Both increase the background intensity, thereby deteriorating the detection lower limit. From the problem like this, as mentioned above, although there is noted the quantitative determination of the trace aimed element such as the cadmium content in the food, due to these X-rays generating subsidiarily, there has not led to obtain the detection lower limit under which the quantitative determination of the trace aimed element is possible. This invention is one having been made in view of the above-mentioned circumstances, and one providing a fluorescent X-ray analysis apparatus in which the detection lower limit has been improved by reducing the X-ray generating subsidiarily and detected. In order to solve the above problems, this invention proposes the following means. The present invention is a fluorescent X-ray analysis apparatus which possesses an X-ray source irradiating a primary X-ray, and a detector in which a collimator having a through-hole in its center part has been placed in a front face, and in which, when the primary X-ray has been irradiated to a sample from the X-ray source, a primary fluorescent X-ray generating from the sample and passing through the through-hole of the collimator is detected by the detector, wherein the X-ray source and the detector are disposed while adjoining the sample, and an irradiated face of the X-ray source or the detector, to which a primary scattered ray having generated by the fact that the primary X-ray scatters in the sample and the primary fluorescent X-ray having generated from the sample are irradiated, is covered by a secondary X-ray reduction layer reducing a secondary scattered ray and a secondary fluorescent X-ray, which generate by irradiations of the primary scattered ray and the primary fluorescent X-ray. According to the fluorescent X-ray analysis apparatus concerned with this invention, while the primary X-ray having been irradiated to the sample from the X-ray source excites the sample to thereby generate the primary fluorescent X-ray, it scatters by the sample to a periphery as the primary scattered ray. One parts of the primary fluorescent X-ray and the primary scattered ray pass through the through-hole of the collimator, and are detected by the detector. And, since the primary fluorescent X-ray having been detected has an energy inherent to an element contained in the sample, it is possible to quantify the element contained in the sample by that energy and the intensity. On this occasion, since the X-ray source is disposed while adjoining the sample, the primary X-ray is effectively irradiated at a high density from the X-ray source without being attenuated. Additionally, since the detector is disposed while adjoining the sample as well, the primary fluorescent X-ray having generated is effectively detected at a high density without being attenuated. On the other hand, one parts of the primary scattered ray and the primary fluorescent X-ray, which don't pass through the through-hole, are irradiated to the above-mentioned irradiated face. On this occasion, by the fact that the irradiated face is covered by the secondary X-ray reduction layer, these X-rays are absorbed to the secondary X-ray reduction layer, and it is possible to reduce a scattered ray (hereafter, referred to as a secondary scattered ray) generating secondarily by scattering in the irradiated face, and a fluorescent X-ray (hereafter, referred to as a secondary fluorescent X-ray) generating secondarily by the fact that an element forming the irradiated face is excited. That is, the secondary scattered ray and the secondary fluorescent X-ray, which generate, or a scattered ray (hereafter, referred to as a tertiary scattered ray) generating by the fact that the former rays are irradiated again to the sample and scatter in the sample pass or passes through the through-hole of the collimator, and thus it is possible to reduce the intensity of the X-ray detected by the detector. Therefor, it is possible to suppress the pileup resulting from an increase in the X-ray having generated subsidiarily, such as the secondary scattered ray, the secondary fluorescent X-ray and the tertiary scattered ray, thereby reducing a background. Further, by reducing the intensities of the secondary scattered ray, the secondary fluorescent X-ray and the tertiary scattered ray, which are detected by the detector, it is possible to reduce the count (intensity) of the unnecessary X-ray entering into the detector. Therefor, it is possible to increase the intensity of the primary X-ray irradiated to the sample and, by this, it is possible to increase the intensity of the primary fluorescent X-ray generating from the sample, thereby raising the sensitivity. Further, it is deemed to be more desirable that, in the above fluorescent X-ray analysis apparatus, the secondary X-ray reduction layer is formed by an element whose energy of a fluorescent X-ray generating in maximum from the secondary X-ray reduction layer is lower than an energy of a fluorescent X-ray generating in maximum from an irradiated face having been covered by the secondary X-ray reduction layer. That is, according to the fluorescent X-ray analysis apparatus concerned with this invention, by the fact that the primary scattered ray and the primary fluorescent X-ray are irradiated to the secondary X-ray reduction layer, the secondary X-ray reduction layer is excited, so that the secondary fluorescent X-ray generates also from the secondary X-ray reduction layer. However, since the secondary fluorescent X-ray generating from the secondary X-ray reduction layer is lower in its energy than the secondary fluorescent X-ray generating from the irradiated face, the secondary fluorescent X-ray generating from the secondary X-ray reduction layer is suppressed as mentioned above. Further, there can be made a lower energy with respect to the primary fluorescent X-ray becoming an object of a measurement, so that it is possible to reduce the background intensity. Additionally, it is deemed to be more desirable that, in the above fluorescent X-ray analysis apparatus, the secondary X-ray reduction layer is constituted by at least two layers of a base layer and a surface layer covering the base layer, and the surface layer is formed by an element whose energy of a fluorescent X-ray generating in maximum from the surface layer is lower than an energy of a fluorescent X-ray generating in maximum from the base layer. According to the fluorescent X-ray analysis apparatus concerned with this invention, by being constituted by at least two layers of the base layer and the surface layer, the primary scattered ray and the primary fluorescent X-ray, which are irradiated to the irradiated face, are absorbed stepwise by the surface layer and the base layer whose absorption efficiency is higher. Additionally, by covering the base layer by the surface layer, since the energy of the secondary fluorescent X-ray generating from the secondary X-ray reduction layer can be made a lower energy, the secondary fluorescent X-ray generating from the secondary X-ray reduction layer is suppressed as mentioned above. Further, there can be made the lower energy with respect to the primary fluorescent X-ray becoming the object of the measurement, so that it is possible to reduce the background intensity. Further, it is deemed to be more desirable that, in the above fluorescent X-ray analysis apparatus, the secondary X-ray reduction layer covers a hole wall of the through-hole of the collimator. According to the fluorescent X-ray analysis apparatus concerned with this invention, the primary fluorescent X-ray and the primary scattered ray, which have entered into the through-hole of the collimator, pass through the through-hole and are directly entered into the detector, and their one parts are irradiated to the hole wall of the through-hole. On this occasion, since the secondary X-ray reduction layer is provided in the hole wall of through-hole, it is possible to reduce the secondary fluorescent X-ray generating from the hole wall of the through-hole, thereby reducing the count of the unnecessary X-ray entering into the detector. Further, it is deemed to be more desirable that, in the above fluorescent X-ray analysis apparatus, the secondary X-ray reduction layer covers an outer periphery face of the collimator. According to the fluorescent X-ray analysis apparatus concerned with this invention, the primary fluorescent X-ray and the primary scattered ray, which have been irradiated to the outer periphery face of the collimator, are absorbed to the secondary X-ray reduction layer, and thus it is possible to reduce the secondary scattered ray and the secondary fluorescent X-ray, which are irradiated again to the sample. Therefor, it is possible to reduce the tertiary scattered ray generating by the fact that the secondary scattered ray and the secondary fluorescent X-ray scatter in the sample, so that the background intensity can be reduced, and the count of the unnecessary X-ray entering into the detector can be reduced. According to the fluorescent X-ray analysis apparatus of the present invention, by covering the irradiated face by the secondary X-ray reduction layer, it is possible to absorb the primary fluorescent X-ray and the primary scattered ray, which are irradiated to the irradiated face, thereby reducing the X-ray generating subsidiarily, such as the secondary scattered ray and the secondary fluorescent X-ray. Therefor, it is possible to suppress an increase in the count of the detector, which results from these unnecessary X-rays generating subsidiarily, increase the intensity of the primary fluorescent X-ray obtainable with respect to the X-ray generating subsidiarily, and raise the sensitivity, thereby contriving an improvement in the detection lower limit. FIG. 1 to FIG. 4 show an embodiment concerned with this invention. As shown in FIG. 1, a fluorescent X-ray analysis apparatus possesses an X-ray source 2 disposed while adjoining one face S1 of a sample S and irradiating a primary X-ray A to the sample S, and a detector 3 disposed adjoining the other face S2 of the sample S and detecting a primary fluorescent X-ray B generating from the sample S. The sample S is a solid or as liquid, which has a fluidity, and enclosed in a container 4 having been formed by a material capable of transmitting an X-ray. More detailedly, in the present embodiment, the sample S is a granular rice, and it is one attempting to quantify Cd contained in the rice. The X-ray source 2 is an X-ray tube bulb for instance, and one irradiating the primary X-ray A having been constituted by a characteristic X-ray and a continuous X-ray of a target of the X-ray tube bulb. In the present embodiment, an outer hull of the X-ray source 2 is formed by brass having been composed of Cu and Zn. In front of the X-ray source 2, a primary filter 5 is provided in a position through which the irradiated primary X-ray A passes. The primary filter 5 is one absorbing only the X-ray of a specified energy within the primary X-ray A irradiated from the X-ray source 2. And, by absorbing the X-ray of the same energy range as the fluorescent X-ray B generating from the aimed element (element to be quantified) having been contained in the sample S, it is possible to improve the detection lower limit by suppressing an increase in the count and an increase in the background intensity due to the fact that the X-ray other than the fluorescent X-ray B is detected. The detector 3 can detect an energy and an intensity of the fluorescent X-ray B generating from the sample S. A collimator 6 is covered to a tip part 3a of the detector 3. The collimator 6 is one suppressing an increase in the count of the X-ray entered into the detector 3, and a member in which a through-hole 7 has been formed in its center part. The collimator 6 is formed by such a heavy element that the X-ray other than that entered from the through hole 7 is not transmitted, and it is Mo for instance. Further, a secondary filter 8 is provided in an inside opening 7a of the through-hole 7 of the collimator 6, and the X-ray having been entered into the through-hole 7 passes through the secondary filter 8 and is detected by the detector 3. The secondary filter 8 is one absorbing, within the X-ray entered into the through-hole 7, only an X-ray of a specified energy range. And, by absorbing an X-ray of an energy range different from the fluorescent X-ray B generating from the aimed element having been contained in the sample S, the detector 3 can detect a fluorescent X-ray of a specified energy, and it is possible to suppress the count of the X-ray to be detected, thereby raising a detection efficiency. By the fact that the primary X-ray A is irradiated to the sample S from the X-ray source 2, the primary X-ray A is absorbed in its one part to the sample S, scattered in its one part by the sample S, and its one part excites the sample S to thereby generate the fluorescent X-ray. And, these X-rays pass through the through-hole 7 of the collimator 6 to thereby be detected by the detector 3, and are irradiated to an irradiated face 9 that is other exposed portion. As the irradiated face 9, there are an outer periphery face 2a of the X-ray source 2, an outer periphery face 6a of the collimator 6, and a hole wall 7a of the through-hole 7 of the collimator 6. And, these irradiated faces 9 are covered respectively by secondary X-ray reduction layers 10, 11 and 12. The secondary X-ray reduction layer 10 covering the hole wall 7a of the through-hole 7 of the collimator 6 is constituted by two layers of a base layer 10a covering the hole wall 7a of the through-hole 7 of the collimator 6 and a surface layer 10b covering the base layer 10a. The base layer 10a is formed by an element whose energy of the fluorescent X-ray generating in maximum is lower than an energy of the fluorescent X-ray generating in maximum (in highest intensity) from Mo forming the collimator 6, and it is Cu for instance. Here, there is explained about a reason why, in a case where the collimator is formed by Mo, Cu (copper) is used as the base layer 10a of the secondary X-ray reduction layer 10. There are known the facts that, in a certain element, a generation efficiency of the fluorescent X-ray generating from the sample by the primary X-ray having been irradiated from the X-ray source becomes higher the more an energy of the primary X-ray having been irradiated is than an absorption end energy of the element generating the fluorescent X-ray and nearer to the absorption end energy, and that, if the energy of the primary X-ray having been irradiated is lower than the absorption end energy of the element generating the fluorescent X-ray, the generation efficiency becomes zero (0). Here, the absorption end energy of a K shell of Cu is 8.98 keV, and the absorption end energy of an L shell is LI absorption end 1.100 keV, LII absorption end 0.953 keV and LIII absorption end 0.933 keV. And, in a case where an energy of the primary X-ray having been irradiated to Cu is higher than the absorption end energy of the K shell of Cu, e.g., in a case where it is 50 keV, from the above conditions of the generation efficiency, a K ray that is the fluorescent X-ray from the K shell generates more than an L ray that is the fluorescent X-ray from the L shell. On the other hand, in a case where the energy of the X-ray having been irradiated to Cu is lower than the absorption end energy of the K shell of Cu, and higher than the absorption end energy of the L shell of Cu, e.g., in a case where it is 7 keV, it follows that the K ray does not generate and only the L ray generates. In a case where the energy of the primary X-ray having been irradiated to Cu is lower than the absorption end energy of the L shell, both of the K ray and the L ray don't generate. Further, the absorption end energy of a K shell of Mo is 17.4 keV, and the absorption end energy of an L shell is LI absorption end 2.88 keV, LII absorption end 2.62 keV and LIII absorption end 2.52 keV. Whereupon, like the present embodiment, by the fact that a surface of the collimator 6 composed of Mo is covered by the base layer 10a of the secondary X-ray reduction layer composed of Cu, the primary scattered and the primary fluorescent X-ray, which generate in the sample, are absorbed to the base layer 10a of the secondary X-ray reduction layer and, by that fact that the primary scattered ray and the primary fluorescent X-ray which excite the collimator 6 reduce, the secondary fluorescent X-ray and the secondary fluorescent X-ray which generate from the collimator 6 reduce. In addition, the secondary fluorescent X-ray generating from the collimator 6 is absorbed by passing again through the base layer 10a of the secondary fluorescent X-ray reduction layer, and thus the secondary fluorescent X-ray generating from the collimator 6 is additionally reduced. By the above processes, although the secondary fluorescent X-ray and the secondary scattered ray, which generate from the collimator 6, are reduced, instead of it, the secondary fluorescent X-ray and the secondary scattered ray generate from the base layer 10a of the secondary X-ray reduction layer. However, in a case where the energies of the primary scattered ray and the primary fluorescent X-ray are higher than the absorption end energy of the K shell of Mo, e.g., in a case where they have been made 50 keV, from the above conditions of the generation efficiency, since the generation efficiency of the secondary fluorescent X-ray generating from the base layer 10a of the secondary X-ray reduction layer becomes lower than the secondary fluorescent X-ray generating from the collimator 6 when there is no base layer 10a of the secondary X-ray reduction layer, it is possible to reduce the secondary fluorescent X-ray. By this, by the fact that the secondary X-ray reduction layer is formed by an element whose absorption end energy of the fluorescent X-ray generating in maximum from the secondary X-ray reduction layer is lower than the absorption end energy of the fluorescent X-ray generating in maximum from the irradiated face having been covered by the secondary X-ray reduction layer, it is possible to effectively reduce the secondary fluorescent X-ray in a case where the primary fluorescent X-ray and the primary scattered ray, which have generated from the sample, are larger than the absorption end energy. Further, as to the detector, although the secondary fluorescent X-ray is absorbed during a time till it enters into a detection element, it becomes more difficult to be detected the lower becomes the energy of the secondary fluorescent X-ray. Therefor, like the above conditions relating to the element forming the secondary X-ray reduction layer, by using the element of the secondary X-ray reduction layer so as to lower the energy of the fluorescent X-ray generating by the secondary X-ray reduction layer, it is possible to additionally reduce the secondary fluorescent X-ray. Further, the surface layer 10b is formed by an element whose energy of the fluorescent X-ray generating in maximum is lower than the energy of the fluorescent X-ray generating in maximum from Cu forming the base layer 10a, and it is Al for instance. Further, also the secondary X-ray reduction layer 11 covering the outer periphery face 6a of the collimator 6 is constituted similarly by two layers of a base layer 11a and a surface layer 11b. And, similarly, the base layer 11a is formed by Cu, and the surface layer 11b is formed by Al which is the element whose energy of the fluorescent X-ray generating in maximum is lower than the energy of the fluorescent X-ray generating in maximum from Cu forming the base layer 11a. Further, the secondary X-ray reduction layer 12 covering the outer periphery face 2a of the X-ray source 2 is constituted by one layer, and formed by an element whose energy of the fluorescent X-ray generating in maximum is lower than the energy of the fluorescent X-ray generating in maximum from Cu and Zn, which form the outer periphery face 2a of the X-ray source 2, and it is formed by Al for instance. Next, there are explained about actions of the fluorescent X-ray analysis apparatus 1. As shown in FIG. 1, the primary X-ray A having been irradiated from the X-ray source 2 passes through the primary filter 5, and is irradiated to the sample S while having a predetermined solid angle. On this occasion, since the X-ray source 2 is disposed while adjoining the sample S, the primary X-ray A can be irradiated to the sample S at a high density without attenuating. And, as to the primary X-ray A having been irradiated to the sample S, its one part excites an element contained in the sample S to thereby generate the fluorescent X-ray (hereafter, referred to as a primary X-ray) inherent to the element, and one part of the primary X-ray A is scattered to a periphery by the sample S as a primary scattered ray C. And, one parts of the primary fluorescent X-ray B and the primary scattered ray C pass through the through-hole 7 of the collimator 6, and are detected by the detector 3. Within the X-ray having been detected, from an energy and an intensity, which show a component of the primary fluorescent X-ray, an element contained in the sample S is specified. For example, as shown in FIG. 3 and FIG. 4, in a case where Cd of a predetermined quantity is contained in the sample S, it is possible to detect a peak Y1 of the intensity near 23 keV that is an energy range of the fluorescent X-ray of Cd. Incidentally, within the X-ray having been detected, a component of the primary scattered ray C is detected as a characteristic X-ray whose peak is formed in other energy band and a continuous X-ray continuously detected in the whole energy band of the X-ray. Further, the other primary fluorescent X-ray B and the primary scattered ray C, which don't pass through the through-hole 7 of the collimator 6, scatter to a periphery, or are irradiated to the outer periphery face 2a of the X-ray source 2, the outer periphery face 6a of the collimator 6, or the hole wall 7a of the through-hole 7, that is the irradiated face 9. As shown in FIG. 2, a primary fluorescent X-ray B1 and a primary scattered ray C1, which are irradiated to the hole wall 7a of the through-hole 7 of the collimator 6, are absorbed stepwise by the surface layer 10b and the base layer 10a, which constitute the secondary X-ray reduction layer 10. More detailedly, first, one parts of the primary fluorescent X-ray B1 and the primary scattered ray C1 are absorbed to the surface layer 10b, and the other one parts transmit through it and irradiate the base layer 10a. Additionally, as to the primary fluorescent X-ray B1 and the primary scattered ray C1, which have been irradiated to the base layer 10a, their one parts are absorbed to the base layer 10a. Since the base layer 10a is formed by the element generating the fluorescent X-ray whose energy is higher than the surface layer 10b, it is possible to absorb the primary fluorescent X-ray B1 and the primary scattered ray C1 at a high absorption efficiency. Finally, only one parts of the primary fluorescent X-ray B1 and the primary scattered ray C1, which have transmitted through the base layer 10a, are irradiated to the hole wall 7a of the through-hole 7. That is, by the fact that many of the primary fluorescent X-ray B1 and the primary scattered ray C1, which are irradiated, are absorbed to the base layer 10a and the surface layer 10b, which constitute the secondary X-ray reduction layer 10, it is possible to reduce intensities of a secondary scattered ray D1 generating by scattering in the hole wall 7a of the through-hole 7 and a secondary fluorescent X-ray E1 generating by the fact that the element forming the hole wall 7a of the through-hole 7 is excited. Further, since the secondary fluorescent X-ray E1 having generated from the hole wall 7a of the through-hole 7 is additionally absorbed in the base layer 10a and the surface layer 10b, it is possible to additionally reduce the intensity of a secondary fluorescent X-ray E2 generating from the hole wall 7a of the through-hole 7. Further, by the fact that the primary fluorescent X-ray B1 and the primary scattered ray C1 are irradiated, the base layer 10a and the surface layer 10b are excited as well, so that the secondary fluorescent X-ray E1 generates from each of these layers. However, since the base layer 10a and the surface layer 10b are formed by the element (Cu, Al) generating the fluorescent X-ray whose energy is lower than the element (Mo) forming the collimator 6, the energy of the secondary fluorescent X-ray E1 which generates can be made a lower energy. Further, as to the secondary fluorescent X-ray E1 generating from the base layer 10a, it is reduced by being absorbed in the surface layer 10b. Like the above, by the fact that the hole wall 7a of the through-hole 7 is covered by the secondary X-ray reduction layer 10, the primary fluorescent X-ray B1 and the primary scattered ray C1 are absorbed, and it is possible to reduce the intensities of the secondary scattered ray D1 and the secondary fluorescent X-ray E1, which generate, and the energy of the secondary fluorescent X-ray E1 which generates can be made the lower energy. One of reasons why the energy of the secondary fluorescent X-ray is made the low energy is for the fact that it is possible to suppress the secondary fluorescent X-ray generating subsidiarily, because an excitation efficiency becomes worse the more the energy of the secondary fluorescent X-ray generating by the primary scattered ray and the primary fluorescent X-ray is separated to a low energy side from the energies of the primary scattered ray and the primary fluorescent X-ray. The other one is for the fact that it is possible to suppress the detection of the secondary fluorescent X-ray generating subsidiarily, because a detection efficiency of the detector becomes worse the lower becomes the energy of the X-ray. Further, as shown in FIG. 1, a primary fluorescent X-ray B2 and a primary scattered ray C2, which are irradiated to the outer periphery face 6a of the collimator 6, are similarly absorbed stepwise in the surface layer 11b and the base layer 1a, which constitute the secondary X-ray reduction layer 11, to thereby reduce the intensities of a secondary scattered ray D2 and the secondary fluorescent X-ray E2, which generate, and the secondary fluorescent X-ray E2 can be made the lower energy. The secondary scattered ray D2 and a secondary fluorescent X-ray E2, which have generated, scatter again by the sample S, so that a tertiary scattered ray F generates. And, although one part of the tertiary scattered ray F passes through the through-hole 7 of the collimator 6 and is detected, it is possible to reduce an intensity of this tertiary scattered ray F and make it a lower energy. Reason why an energy of the tertiary scattered ray is made the low energy is because it is possible to suppress a detection of the tertiary scattered ray generating subsidiarily, since the detection efficiency of the detector becomes worse the lower becomes the energy of the X-ray. Additionally, as shown in FIG. 1, a primary fluorescent X-ray B3 and a primary scattered ray C3, which are irradiated to the outer periphery face 2a of the X-ray source 2, are similarly absorbed by the secondary X-ray reduction layer 12. Although the secondary X-ray reduction layer 12 is constituted by one layer having been formed by Al, it is formed by the element (Al) generating the fluorescent X-ray whose energy is lower than the element (Cu, Zn) forming the outer periphery face 2a of the X-ray source 2. Therefor, similarly, it is possible to reduce intensities of a secondary scattered ray D3 and a secondary fluorescent X-ray E3, which generate, and make the secondary fluorescent X-ray E3 a low energy. As to the secondary scattered ray D3 and the secondary fluorescent X-ray E3, which have generated, their one parts directly pass through the through-hole 7 of the collimator 6 and are detected by the detector 3. Further, the other one parts scatter in the sample S and become the tertiary scattered ray F. Although one part of the tertiary scattered ray F passes through the through-hole 7 of the collimator 6 and is detected, by the fact that intensities of the secondary scattered ray D3 and the secondary fluorescent X-ray E3 are reduced and they are low energies, also the tertiary scattered ray F is additionally reduced in its intensity, and it can be made a low energy. Like the above, by covering the outer periphery face 2a of the X-ray source 2, the outer periphery face 6a of the collimator 6 and the hole wall 7a of the through-hole 7 of the collimator 6, which are the irradiated faces 9, by the secondary X-ray reduction layers 10, 11 and 12, it is possible to reduce the intensities of the secondary scattered ray D and the secondary fluorescent X-ray E, which generate form each irradiated face 9, and further the tertiary scattered ray F generating by the fact that the formers scatter again, thereby making them low energies. These X-rays generating subsidiarily are unnecessary X-rays differing from the primary fluorescent X-ray B generating from the element contained in the sample S, and bring about an increase in a useless count. That is, by reducing the intensities of these X-rays generating subsidiarily and making them the low energies, it is possible to suppress the increase in the count to thereby reduce the background intensity, and it is possible to contrive an improvement in the detection lower limit. FIG. 3 and FIG. 4 are measurement results in a case where the sample S containing Cd has been measured by the fluorescent X-ray analysis apparatus 1, and FIG. 5 and FIG. 6 are measurement results in a case where, as a comparative example, there has been made a constitution in which the secondary X-ray reduction layers 10, 11 and 12 are not provided. As shown in FIG. 3 and FIG. 4, the fact is seen that the fluorescent X-ray (Kα ray) of Cd can be confirmed while having the peak Y1 in the energy range of 23 keV. On the other hand, as shown in FIG. 5 and FIG. 6, in the case where the secondary X-ray reduction layers 10, 11 and 12 are not provided, as mentioned above, since the background intensity increases by the pileup in the count circuit, the peak Y1 is buried in the background, so that it becomes difficult to confirm an accurate intensity of the primary fluorescent X-ray B. Further, by reducing the intensity of the X-ray generating subsidiarily, such as the secondary scattered ray D, the secondary fluorescent X-ray E and the tertiary scattered ray F, it is possible to reduce a count of the unnecessary X-ray detected by the detector. And, by a quantity in which the count of the unnecessary X-ray has been reduced, it is possible to increase the intensity of the primary X-ray A to thereby increase the intensity of the primary fluorescent X-ray B generating from the sample. Therefor, it is possible to raise the intensity, i.e., the sensitivity, of the primary fluorescent X-ray B, which can be obtained by the detector 3, thereby additionally improving the detection lower limit. Additionally, in the secondary X-ray reduction layer 10 and the secondary X-ray reduction layer 11, there can be constituted by the two layers of the base layers 10a and 11a, and the surface layers 10b and 11b. Therefor, it is possible to effectively absorb the primary fluorescent X-ray B and the primary scattered ray C, which are irradiated, and the energy of the secondary fluorescent X-ray E can be made the lower energy with respect to the energy of the primary fluorescent X-ray B. Like the above, by covering the secondary X-ray reduction layers 10, 11 and 12 to the irradiated faces 9, it is possible to improve the detection lower limit, and realize the quantitative determination of the trace aimed element, such as the quantitative determination of Cd contained in the food. Especially, in the case where the X-ray source 2 and the detector 3 have been disposed while adjoining the sample S, effects of a reduction in the background intensity and a reduction in the count of the X-ray by the secondary X-ray reduction layers 10, 11 and 12 become remarkable, so that it is possible to more effectively contrive an improvement in the detection lower limit in cooperation with an effect by being provided while adjoining. In the above, although there has been detailedly mentioned about the embodiment of the present invention by referring to the drawings, a concrete constitution is not one limited to this embodiment, and there is included also a design modification or the like in a scope not deviating from a gist of the present invention. Incidentally, in the present embodiment, as the irradiated faces 9, although there have been enumerated the outer periphery face 2a of the X-ray source 2, the outer periphery face 6a of the collimator 6 and the hole wall 7a of the through-hole 7 of the collimator 6, there is not limited to these. By providing the secondary X-ray reduction layer in at least a portion to which there are irradiated the primary scattered ray C and the primary fluorescent X-ray B, which generate by the primary X-ray A, it is possible to expect the similar effect. Further, although there have been made such that, about the secondary X-ray reduction layers 10 and 11, they are constituted by the two layers of Cu and Al and, about the secondary X-ray reduction layer 12, by the one layer of Al, there is not limited to these. There suffices if it is constituted by at least one layer having been formed by the element generating the fluorescent X-ray whose energy is lower than the element forming the irradiated face 9, and it may be made a constitution of three or more layers. Further, in the present embodiment, as the sample S, although one in which the solid (rice) having the fluidity has been enclosed in the container 4 has been enumerated in the example, there is not limited to this. For example, it may be other food having a certain regular shape, or other one whose main component is a light element, and it is possible to expect the effect also in a sample whose main component is a heavy element. Further, in the fluorescent X-ray analysis apparatus 1, although there has been made one in which the primary filter 5 and the secondary filter 8 are provided, there may be made a constitution in which they are not provided and, further, there may be made a constitution in which filters of different kinds can be switched at a suitable time.
045254966
summary
BACKGROUND OF THE INVENTION This invention relates to self-inverting water-in-oil emulsions of water-soluble polymers wherein emulsions invert immediately upon the addition of sufficient water. This invention also relates to processes for preparing such emulsions. Various water-soluble polymers such as polyacrylamide and copolymers of acrylamide with other monomers are well-known to be effective flocculants for many substrates including sewage, cellulosic fibers and fines for retention and freeness, metal or treatment, plating waste, coal tailings, and the like. Such polymers are also known to exhibit superior thickening properties when said polymers are dissolved in aqueous media. Particularly well-known for this purpose are the anionic carboxamide polymers such as acrylamide/acrylic acid copolymers, including those prepared by hydrolysis of polyacrylamide. Such polymers are very useful as fluid mobility control agents in enhanced oil recovery processes. In the past, such polymers have been made available commercially as powders or finely divided solids which must be subsequently dissolved in an aqueous medium in order to be used. Because such dissolution steps are sometimes time consuming and often require rather expensive mixing equipment, it has become a common practice to formulate the water-soluble polymer in a water-in-oil emulsion wherein the polymer is dissolved in the dispersed aqueous phase. Such emulsions, a well as a method for preparing them, are described in U.S. Pat. No. 3,284,393 to Vanderhoff et al. Unfortunately for many applications, these emulsions do not invert as readily as desired. In order to accelerate the inversion rate of such emulsions, it has been a common practice, e.g., as shown in U.S. Pat. No. Re. 28,474, to add a water-soluble surfactant just prior to inversion. While the addition of an inverting surfactant in this manner does increase the rate of inversion, the resulting emulsions often do not exhibit the activity or ability to pass through porous structures (so-called screen factor or filterability) that is desired for fluid mobility control agents. More importantly, it is found that such practices are generally not satisfactory when it is necessary to invert the emulsion in aqueous medium containing dissolved salts as is often the case for enhanced oil recovery practices. In view of the foregoing deficiencies of conventional emulsions and methods for inverting them, it is highly desirable to provide a self-inverting water-in-oil emulsion that will invert quickly into an aqueous medium that may contain significant quantities of dissolved salts. It is also desirable to provide an emulsion that has a reduced oil content and increased polymer solids. SUMMARY OF THE INVENTION The present invention is such an emulsion that comprises (1) a discontinuous aqueous phase containing a water-soluble polymer which aqueous phase is dispersed as colloidal-sized particles or droplets in (2) a continuous oil phase wherein the emulsion contains an inverting amount of an inverting surfactant and an emulsifying amount of a water-in-oil emulsifier. By an "inverting amount" is meant that the amount of inverting surfactant is such that the water-in-oil emulsion will invert in a reasonably short period of time when the emulsion is combined with sufficient water. In the emulsion of this invention, it is critical that (1) at least a portion of the inverting surfactant be added at some point prior to the completion of polymerization and (2) at least a portion of the inverting surfactant be added to the emulsion after polymerization, but prior to inversion. In another aspect, the present invention is a method for preparing the aforementioned emulsion which comprises (1) forming a stable water-in-oil emulsion (monomeric precursor) containing at least one water-soluble monomer in the aqueous phase which is dispersed in a continuous oil phase, said emulsion containing an emulsifying amount of a water-in-oil emulsifier and an amount of an inverting surfactant that is sufficient to increase the degree of inversion when the emulsion of water-soluble polymer is inverted, but less than that which destabilizes the monomeric precursor or the emulsion of polymer; (2) subjecting the monomeric precursor to conditions to polymerize the monomer; and (3) adding a remaining amount of inverting surfactant which will enable the resulting water-in-oil emulsion of water-soluble polymer to invert upon the addition of sufficient water. Surprisingly, it is found that, by having a portion of the inverting surfactant present in the monomeric precursor prior to polymerization and by adding an additional portion of the inverting surfactant to the emulsion subsequent to polymerization, an emulsion is obtained which is superior to emulsions obtained by either adding all of the inverting surfactant to the monomeric precursor prior to polymerization or by adding all of the inverting surfactant to the emulsion subsequent to the polymerization. The emulsions of this invention are superior to conventional emulsions in that they have increased polymer solids, reduced oil content, lower bulk viscosity and less inverting surfactant than is employed in conventinal emulsions. These emulsions, although self-inverting upon the addition of water, are stable in that they can be stored for long periods of time and/or can undergo several freeze-thaw cycles without irreversible coagulation or precipitation. Most surprising is the ability of such emulsions to invert readily into aqueous media containing substantial quantities, e.g., from about 0.0001 to about 20 weight percent, of dissolved salts which are commonly present in subterranean brines. In addition to their utility as drilling muds, fracturing fluids, and fluid mobility control agents in oil recovery methods, the emulsions of the present invention are also useful as flocculating agents for sewages, industrial wastes, mining streams such as coal slurries and mining effluents, gas thickeners for coating formulations and as additives for the manufacture of paper. DETAILED DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENTS The present invention is practiced in the preparation of water-in-oil emulsions of any water-soluble polymer. Such emulsions are those wherein the dispersed phase is an aqueous phase having dissolved therein a water-soluble polymer and the continuous oil phase is a water-immiscible inert organic liquid. The ratio of the aqueous phase to the oil phase is suitably any ratio that permits the formation of a water-in-oil emulsion. Preferably, however, based on the total weight of the water-in-oil emulsion, the disperse phase constitutes from about 50 to about 90, more preferably from about 65 to about 80, weight percent of the emulsion. The continuous oil phase preferably constitutes from about 10 to about 50, more preferably from about 20 to about 35, weight percent of the emulsion. For the purposes of this invention, the water-soluble polymer contained in the aqueous phase of the emulsion is one which forms a thermodynamically stable mixture when combined with water. These mixtures form spontaneously and include true solutions in which the individual polymer molecules are dispersed as well as micellular or colloidal solutions wherein the polymer molecules are aggregated to some extent but wherein such aggregates are no larger than colloidal size. Accordingly, the water-soluble polymers are generally homopolymers and copolymers of water-soluble ethylenically unsaturated monomers. Suitable water-soluble monomers include those that are sufficiently water-soluble to form at least a 10 weight percent solution when dissolved in water and readily undergo addition polymerization to form polymers that are water-soluble. Exemplary water-soluble monomers include ethylenically unsaturated amides such as acrylamide, methacrylamide and fumaramide; their N-substituted derivatives such as 2-acrylamide-2-methylpropane sulfonic acid (AMPS), N-(dimethylaminomethyl)acrylamide as well as N-(trimethylammoniummethyl)acrylamide chloride and N-(trimethylammoniumpropyl)methacrylamide chloride; ethylenically unsaturated carboxylic acids such as acrylic acid, methacrylic acid, itaconic acid and fumaric acid. Ethylenically unsaturated quaternary ammonium compounds such as vinylbenzyl trimethyl ammonium chloride, sulfoalkyl esters of unsaturated carboxylic acids such as 2-sulfoethyl methacrylate; aminoalkyl esters of unsaturated carboxylic acids such as 2-aminomethyl methacrylate and 2-(N,N-dimethylamino)ethyl methacrylate as well as the quaternized derivatives thereof such as acryloylethyl trimethyl ammonium chloride; vinyl amines such as vinyl pyridine and vinyl morpholine, diallyl amines and diallyl ammonium compounds such as diallyl dimethyl ammonium chloride; vinyl heterocyclic amides such as vinyl pyrrolidone; vinylaryl sulfonates such as vinylbenzyl sulfonate as well as the salts of the foregoing monomers. Of the foregoing water-soluble monomers, acrylamide and combinations of acrylamide and acrylic acid are preferred. Acrylamide and combinations thereof with up to 50 mole percent of other water-soluble monomers, based on total water-soluble monomer, are more preferred. Most preferred are polymers wherein the water-soluble monomer is acrylamide and a mixture of from about 60 to about 99 mole percent of acrylamide with from about 1 to about 40 mole percent of other water-soluble monomers. The molecular weight of the water-soluble polymer is not particularly critical and may vary over a wide range from about 1 to about 25 million. Preferred polymers have weight average molecular weight in the range from about 2 to about 10 million. The water-immiscible oil phase of the emulsion generally comprises at least one inert hydrophobic liquid. Usually such liquid is an organic liquid such as a liquid hydrocarbon or substituted hydrocarbon. Preferred organic liquids are the halogenated hydrocarbons such as perchloroethylene, methylene chloride and the like as well as liquid hydrocarbon having from 4 to 15 carbons per molecule including aromatic and aliphatic hydrocarbons and mixtures thereof, e.g., benzene, xylene, toluene, mineral oils, liquid paraffins such as kerosene, naptha and the like. Of the foregoing organic liquids, the hydrocarbons are the more preferred, with aliphatic hydrocarbons being most preferred. In general, the water-in-oil emulsions of the present invention are prepared by following the general procedure described in the prior art as exemplified in U.S. Pat. Nos. 3,284,393; 3,624,019 and 3,734,873, which are hereby incorporated by reference. In such methods, an aqueous solution of water-soluble, ethylenically unsaturated monomer(s) is dispersed in the inert hydrophobic organic liquid containing a sufficient amount of a water-in-oil emulsifying agent to form a water-in-oil emulsion of the water-soluble monomer (monomeric precursor). At some point prior to or during the polymerization of such monomer, an inverting surfactant is incorporated in an amount that is sufficient to increase the degree of inversion of the emulsion of the water-soluble polymer when the emulsion is subjected to inverting conditions, provided that said amount is less than that which destabilizes the monomeric precursor or the emulsion. In accordance with this invention, the initial portion of inverting surfactant may be added to the monomeric precursor, or it may be added to the aqueous phase or oil phase prior to formation of the monomeric precursor so long as it is present in the monomeric precursor prior to the completion of polymerization. By "degree of inversion" is meant the percentage of polymer that completely dissolves in the aqueous phase upon inversion based on the total polymer that could dissolve. By "destabilizing the emulsion" is meant that the monomeric precursor or the water-in-oil emulsion of water-soluble polymer separates into two phases having a single interface or inverts into an oil-in-water emulsion. Preferably, said amount of inverting surfactant that is added prior to polymerization is in the range from about 0.05 to about 5 percent based on monomer weight, most preferably from about 0.2 to about 2 weight percent. The resulting stable water-in-oil emulsion of monomer is then heated under free-radical forming conditions in order to polymerize the monomer in the dispersed phase to form a water-in-oil emulsion of the water-soluble polymer. Subsequent to polymerization and prior to inversion, this water-in-oil emulsion is combined with additional inverting surfactant which may or may not be the same as the inverting surfactant added prior to polymerization. This post-added inverting surfactant is added in an amount sufficient to cause inversion when the water-in-oil emulsion is combined with sufficient water to form a continuous aqueous phase. Preferably, such post-added amount of inverting surfactant is in the range from about 0.5 to about 10, most preferably from about 3 to about 7, weight percent based on the weight of the polymer. Emulsifiers suitably employed for purposes of emulsifying the aqueous phase containing the water-soluble monomer in the organic liquid are those emulsifiers that promote the formation and stabilization of water-in-oil emulsions. Normally such emulsifiers have a hydrophilic-lipophilic balance (HLB) in the range from about 2 to about 9, most preferably from about 3 to 6. Preferably, the emulsifying agent is sorbitan monooleate, the reaction product of oleic acid with isopropanolamide or a mixture thereof. Other suitable emulsifying agents include hexadecyl sodium phthalate, decyl sodium phthalate, octadecyl sodium phthalate, sorbitan monooleate, sorbitan stearate, glycerine mono- or distearate and combinations of such emulsifying agents. Generally, the emulsifier is used in amounts sufficient to provide the desired water-in-oil emulsion. This amount is normally in the range from about 0.1 to about 20, preferably from about 3 to about 5, weight percent based on the weight of monomer. Inverting surfactants suitably employed in the practice of this invention are generally those that promote the formation of oil-in-water emulsions or dispersions when the water-in-oil emulsion is combined with sufficient water to form a continuous aqueous phase. Generally, such inverting surfactants are water-soluble compounds having an HLB in the range from about 6.5 to about 20, preferably from about 10 to about 14. Examples of such inverting surfactants include nonionic, anionic, cationic or amphoteric surfactants with nonionic surfactants being preferred. Preferred nonionic surfactants include (1) alkyl polyethyleneoxy compounds such as alkyl polyethyleneoxy alcohol represented by the formula: EQU R--(EO).sub.n --H wherein R is C.sub.4 -C.sub.20 alkyl, EO is ethyleneoxy and n is a number from 1 to 10 and (2) nonionic surfactants such as the reaction products of ethylene oxide or mixtures of ethylene oxide and higher alkylene oxide with active hydrogen compounds such as phenols, alcohols, carboxylic acids and amides, e.g., alkylphenoxyethyleneoxy alcohols and alkylphenoxy polyethyleneoxy alcohols. Also suitable are anionic compounds represented by the formula: EQU R--X wherein R is as defined hereinbefore and X is SO.sub.3 H, CO.sub.2 H or PO.sub.3 H and salts thereof. Examples include long chain carboxylates such as potassium oleate, sodium laurate, potassium stearate, potassium caprolate, sodium palmatate and the like; alkali metal alkylbenzene sulfonates such as sodium nonylbenzene sulfonate and potassium dodecylbenzene sulfonate; alkali metal alkyl sulfates such as sodium dodecyl sulfate and alkali metal dialkyl sulfosuccinates such as sodium dihexyl sulfosuccinate and sodium dioctyl sulfosuccinate; salts of resin acids such as abietic acid and dihydroabietic acid. Also suitable are cationic surfactants such as alkyl ammonium or quaternary ammonium salts, e.g., dodecyl ammonium hydrochloride, dodecyl trimethyl quaternary ammonium chloride and the like, and ethoxylated fatty amines. Other suitable surfactants are described in McCutcheon's Detergents and Emulsifiers, North American Edition, 1980 Annual. Also included in the aforementioned surfactants are oligomeric and polymerizable surfactants described at pages 319-322 of Blackley, Emulsion Polymerization, Halsted Press (1975). Examples of such oligomers include ammonium and alkali metal salts of functionalized oligomers sold by Uniroyal Chemical under the trade name "Polywet" and copolymers of acrylonitrile and acrylic acid having molecular weights less than 2000 which are prepared in the presence of chain terminating agents such as n-octyl mercaptan. Examples of polymerizable surfactants include sodium salts of 9- and 10-(acryloylamido)stearic acid and the like. Of the foregoing surfactants, the nonionic types are preferred, with ethoxylated alkyl phenols and ethoxylated fatty alcohols being most preferred. As mentioned hereinbefore, polymerization of the water-in-oil emulsion of the water-soluble monomers is advantageously effected under conventional conditions such as described in U.S. Pat. No. 3,284,393. Normally such polymerization is practiced in the presence of a polymerization initiator capable of generating free-radicals. Preferably, this free-radical initiator is employed in amounts from about 0.01 to about 0.1 weight percent of initiator based on the monomers. Exemplary polymerization initiators include the inorganic persulfates such as potassium persulfate, ammonium persulfate and sodium persulfate, azo catalysts such as azobisisobutyronitrile and dimethylazoisobutyrate; organic peroxygen compounds such as benzyl peroxide, t-butylperoxide, diisopropylbenzene hydroperoxide and t-butyl hydroperoxide. Of these initiators, the organic types such as t-butyl hydroperoxide are preferred. In addition to the aforementioned ingredients, the emulsion polymerization recipe optionally includes chain transfer agents, chelating agents, buffers, salts, and the like. The emulsions of this invention are self-inverting in that they invert readily when dispersed into water without adding additional inverting surfactant. They are particularly effective for inversion in aqueous media containing from about 0.001 to about 10, especially from about 0.05 to about 5, weight percent of dissolved salts such as sodium chloride, calcium chloride, magnesium chloride and the like that are normally present in subterranean brines. The following examples are given to illustrate the invention and should not be construed as limiting its scope. Unless otherwise indicated, all parts and percentages are by weight.
claims
1. A method for improving productivity of an ion implanter having an ion source chamber, the method comprising the steps of:supplying a gaseous substance to the ion source chamber, the gaseous substance comprising one or more reactive species for generating ions for the ion implanter;stopping the supply of the gaseous substance to the ion source chamber; andsupplying a hydrogen containing gas to the ion source chamber for a period of time after stopping the supply of the gaseous substance. 2. The method according to claim 1, further comprising:generating a plasma in the ion source chamber based on the one or more reactive species, thereby generating the ions. 3. The method according to claim 1, wherein the gaseous substance comprises reactive species selected from a group consisting of carbon dioxide (CO2), carbon monoxide (CO), oxygen (O2), and any type of hydrocarbon. 4. The method according to claim 1, further comprising:generating a plasma in the ion source chamber based on the hydrogen containing gas, thereby reconditioning the ion source chamber. 5. The method according to claim 1, wherein the hydrogen containing gas comprises one or more materials selected from a group consisting of phosphine (PH3), ammonia (NH3), arsine (AsH3), methane (CH4), and hydrogen (H2). 6. The method according to claim 1, wherein the hydrogen containing gas further comprises a sputtering agent. 7. The method according to claim 6, wherein the sputtering agent comprises one or more inert gases. 8. The method according to claim 1, wherein the period of time for supplying the hydrogen containing gas is determined based at least in part on an amount of time during which the gaseous substance is supplied to the ion source chamber. 9. The method according to claim 1, further comprising:stopping supplying the hydrogen containing gas to the ion source chamber after the period of time; andsupplying a second gaseous substance to the ion source chamber after stopping supplying the hydrogen containing gas;wherein the period of time is determined based at least in part on a composition of the second gaseous substance. 10. The method according to claim 9, wherein the second gaseous substance comprises one or more boron containing reactive species. 11. The method according to claim 1, wherein the period of time for supplying the hydrogen containing gas is determined based on one or more endpoint detection methods selected from a group consisting of mass spectrometry, residual gas analysis, emission spectroscopy, and absorption spectroscopy. 12. A method for improving productivity of an ion implanter having an ion source chamber, the method comprising the steps of:supplying a gaseous substance to the ion source chamber, the gaseous substance comprising one or more reactive species for generating ions for the ion implanter;stopping the supply of the gaseous substance to the ion source chamber; andsupplying a chlorine containing gas to the ion source chamber for a period of time after stopping the supply of the gaseous substance. 13. The method according to claim 12, wherein the chlorine containing gas comprises one or more materials selected from a group consisting of chlorine (Cl2), hydrochloride (HCl), boron trichloride (BCl3) and indium trichloride (BCl3). 14. A method for improving productivity of an ion implanter having an ion source chamber, the method comprising the steps of:supplying the ion source chamber with a gaseous mixture of a hydrogen containing gas and one or more reactive species; andgenerating a plasma in the ion source chamber based on the gaseous mixture, wherein the plasma contains ions generated from the one or more reactive species for use in the ion implanter, and wherein the plasma further removes one or more compounds from the ion source chamber. 15. The method according to claim 14, wherein the gaseous mixture further comprises a sputtering agent. 16. The method according to claim 15, wherein the sputtering agent comprises one or more inert gases. 17. The method according to claim 14, wherein the hydrogen containing gas comprises one or more materials selected from a group consisting of phosphine (PH3), ammonia (NH3), arsine (AsH3), and hydrogen (H2). 18. The method according to claim 14, wherein the hydrogen containing gas accounts for 5-40% of a volume of the gaseous mixture. 19. A method for improving productivity of an ion implanter having an ion source chamber, the method comprising the steps of:supplying a gaseous substance to the ion source chamber, the gaseous substance comprising one or more reactive species for generating carbon ions for the ion implanter;stopping the supply of the gaseous substance to the ion source chamber;supplying a hydrogen containing gas to the ion source chamber for a period of time after stopping the supply of the gaseous substance, the hydrogen containing gas also comprising at least one sputtering agent; andgenerating a plasma based on the hydrogen containing gas, wherein the plasma removes one or more metal compounds from the ion source chamber.
061455830
claims
1. A device for inspecting the interior of a steam generator, comprising: a first boom; a second boom having a first end pivotally attached to the first boom and a second end; a head assembly attached to the second end; registration guides mounted to the head assembly which extend away from and retract to the head assembly, the registration guides sized and configured to press against tubes of the steam generator in an extended position; a drive assembly attached to the head assembly; and a movable sensing wand attached to the drive assembly at a proximal end and having a sensor probe at a distal end, the sensor probe comprising a light source and a camera. providing an inspection device comprising a first boom, a second boom having a first end pivotally attached to the first boom and a second end, a head assembly attached to the second end, a drive assembly attached to the head assembly, and a movable sensing wand attached to a drive mechanism in the head assembly at a proximal end and having a sensor at a distal end; inserting the inspection device through an access port in the generator; positioning the first boom and the second boom in the tube lane perpendicular to the tube rows; uprighting the inspection device within the generator in the tube lane to a position generally parallel to the tube rows; locating the device at a predetermined location; extending registration guides away from the head assembly against adjacent tubes, each of the registration guides having a major length which is aligned in parallel with the longitudinal axes of the adjacent tubes of the steam generator; moving the wand to position the sensor at a desired location; illuminating from the distal end of the wand; and recording and displaying visual images at a display located remotely from the device. a first boom; a second boom having a first end pivotally attached to the first boom and a second end; a head assembly attached to the second end; a drive assembly attached to the head assembly; a plurality of pneumatically actuated registration guides attached to the head assembly, the registration guides having a major length which is aligned in parallel with longitudinal axes of the steam generator tubes, the registration guides sized and configured to press against the steam generator tubes in an extended position so as to stabilize the head assembly, the registration guides being coated so as to prevent damage to the steam generator tubes; and a movable sensing wand attached to the drive assembly at a proximal end and having a sensor probe at a distal end, the sensor probe comprising a light source and a camera. a first boom; a second boom having a first end pivotally attached to the first boom and a second end; a head assembly attached to the second end; a plurality of registration guides attached to the head assembly, the registration guides having a major length oriented so as to be in alignment with the longitudinal axes of tubes of the steam generator, the registration guide being sized and configured to press against the steam generator tubes in an extended position; a drive assembly attached to the head assembly; and a telescopingly extendible sensing wand attached to the drive assembly at a proximal end and having a sensor probe at a distal end. a first boom; a second boom having a first end pivotally attached to the first boom and a second end; a head assembly attached to the second end; a plurality of registration guides attached to the head assembly, the registration guides having a major length oriented so as to be in alignment with the longitudinal axes of tubes of the steam generator, wherein the registration guides include two pairs of registration guides which are alternately actuated; a drive assembly attached to the head assembly; and a telescopingly extending sensing wand attached to the drive assembly at a proximal end and having a sensor probe at a distal end. 2. The device according to claim 1, comprising a pneumatic actuator for extending and retracting the registration guides. 3. The device according to claim 1, wherein the second boom comprises a telescoping boom. 4. The device according to claim 1, wherein the sensing wand comprises a telescoping wand. 5. The device according to claim 1, further comprising additional cameras. 6. The device according to claim 2, wherein the registration guides comprise a plurality of pneumatic actuators. 7. The device according to claim 1, wherein the head assembly comprises at least one additional sensor for measuring relative position. 8. The device according to claim 7, wherein the sensor comprises a counter. 9. The device according to claim 1, wherein the first boom comprises a pivoting means for engaging the second boom. 10. A method for inspecting the interior of a steam generator comprising: 11. The method according to claim 10, further comprising pneumatically actuating the registration guides. 12. The method according to claim 10, further comprising feeding positioning data from the registration guides such that the precise location of the device within the generator is known. 13. A device for inspecting the interior of a steam generator, comprising: 14. The device of claim 13, the light source comprising two lamps. 15. The device of claim 13, the plurality of pneumatically actuated registration guides comprising two pairs of registration guides which are alternately actuated. 16. The device of claim 13, where the sensing wand is a telescoping wand. 17. The device of claim 13, further comprising a tilt sensor, a proximity sensor, an air pressure sensor, and a hydraulic sensor. 18. The device of claim 14, wherein the camera is located between the two lamps. 19. A device for inspecting the interior of a steam generator, comprising 20. The device of claim 19, wherein the registration guides are pneumatically actuated. 21. The device of claim 19, wherein the sensing wand is a pivotable wand. 22. The device for inspecting the interior of a steam generator, comprising: 23. The device of claim 22, wherein the registration guides extend away from the head assembly and retract toward the head assembly.
abstract
A method of multileaf collimator (MLC) leaf positioning in tracking-based adaptive radiotherapy is provided. The method includes determining a radiotherapy beam pattern by transforming a treatment beam plan into radiotherapy beam coordinates, determining a dose discrepancy between the radiotherapy beam pattern and a deliverable MLC aperture, where the dose discrepancy includes a sum of an overdose cost and an underdose cost to a treatment volume, and minimizing the dose discrepancy, where the dose discrepancy minimization provides a determined deliverable MLC aperture for the radiotherapy beam.
047440996
description
DETAILED DESCRIPTION In the drawing an x-ray diagnostic apparatus for the preparation of mamma radiographs is illustrated including an x-ray source 1 and a support table 2 for the radiography subject 3. Serving the purpose of compression of the radiography subject 3 is a compression device comprising a compression localizer 4 which is mounted on a compression carriage 5 and which is pressed by means of an electromotor 6 against the radiography subject 3. When the localizer engages the radiography subject 3 and attains a specific specified compression force, the motor 6 is shut off. With the compression localizer 4 resting against the radiography subject 3, a spring 7 is tensioned corresponding to the respective compression force, which spring is secured to one end of a lever 8 which is pivotally mounted about a shaft 9, and which, at the other end, supports the compression localizer 4. The spring 7, in conjunction with an actual value transducer 10, forms an electric signal corresponding to the compression force exerted by the localizer 4. In the illustrated apparatus, in addition, the respective compression path s is detected by a path length transducer 11 and converted into an electric signal. The transducer may be coupled wtih the output drive train driven by motor 6 as indicated by the dash line 11a. The motor 6 (which is secured to carrage 5) positions the carriage 5 via a toothed wheel 12 which has rolling engagement with a fixedly mounted toothed rack 13 which is fixed relative to support table 2. The actual value signals for the compression force and compression paths are supplied via lines 14a and 15a to inputs 14 and 15 of the density computer 16 which determines therefrom the density of the radiography subject 3 and hence the respectively required radiation filter. A signal corresponding to the required filter is connected to the output 17 of the density computer 16. The provided radiation filters can be arranged in the manner described in U.S. Pat. No. 3,976,889 on a disc 19 rotatably mounted in an eccentric fashion relative to the central ray of the x-radiation 18. In order to rotate the disc 19 an electromotor 20 is provided which forms an actual value signal on the line 21 which corresponds to the filter respectively shifted into the ray path 18 (in the example a filter 19a is shown in the operating position). This actual value signal on the line 21 is compared with the desired value signal on the line 17. If the filter disposed in the ray path does not agree with the required filter, an amplifier 22 will deliver a signal at its output 23 which switches on the motor 20 until the signals on the lines 17 and 21 correspond. Instead of the detection of the compression force and of the compression path, in the case of simple apparatus with a fixedly adjusted compression force, it can be sufficient to detect only the respective compression path. The density signal on the line 17 can also be supplied via an interface to the x-ray high voltage generator supplying the x-ray source 1 and in this fashion an automatic adjustment of the x-ray tube voltage can take place as described, for example, in U.S. Pat. No. 3,991,314. It will be apparent that many modifications and variations may be made without departing from the scope of the teachings and concepts of the present invention.
description
The present teachings relate to refrigeration systems and, more particularly, to monitoring a condenser in a refrigeration system. Produced food travels from processing plants to retailers, where the food product remains on display case shelves for extended periods of time. In general, the display case shelves are part of a refrigeration system for storing the food product. In the interest of efficiency, retailers attempt to maximize the shelf-life of the stored food product while maintaining awareness of food product quality and safety issues. The refrigeration system plays a key role in controlling the quality and safety of the food product. Thus, any breakdown in the refrigeration system or variation in performance of the refrigeration system can cause food quality and safety issues. Thus, it is important for the retailer to monitor and maintain the equipment of the refrigeration system to ensure its operation at expected levels. Refrigeration systems generally require a significant amount of energy to operate. The energy requirements are thus a significant cost to food product retailers, especially when compounding the energy uses across multiple retail locations. As a result, it is in the best interest of food retailers to closely monitor the performance of the refrigeration systems to maximize their efficiency, thereby reducing operational costs. Monitoring refrigeration system performance, maintenance and energy consumption are tedious and time-consuming operations and are undesirable for retailers to perform independently. Generally speaking, retailers lack the expertise to accurately analyze time and temperature data and relate that data to food product quality and safety, as well as the expertise to monitor the refrigeration system for performance, maintenance and efficiency. Further, a typical food retailer includes a plurality of retail locations spanning a large area. Monitoring each of the retail locations on an individual basis is inefficient and often results in redundancies. A method for monitoring a condenser in a refrigeration system is provided. The method comprises calculating a thermal efficiency of a condenser of a refrigeration system based on operation of the condenser and arranging said thermal efficiency over a predetermined period. Further, the method comprises comparing the average to an efficiency threshold and generating a notification based on the comparison. In other features, a controller is provided that executes the method. In still other features, a computer-readable medium having computer-executable instructions for performing the method is provided. Further areas of applicability of the present teachings will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the teachings. The following description is merely exemplary in nature and is in no way intended to limit the present teachings, applications, or uses. As used herein, computer-readable medium refers to any medium capable of storing data that may be received by a computer. Computer-readable medium may include, but is not limited to, a CD-ROM, a floppy disk, a magnetic tape, other magnetic medium capable of storing data, memory, RAM, ROM, PROM, EPROM, EEPROM, flash memory, punch cards, dip switches, or any other medium capable of storing data for a computer. With reference to FIG. 1, an exemplary refrigeration system 100 includes a plurality of refrigerated food storage cases 102. The refrigeration system 100 includes a plurality of compressors 104 piped together with a common suction manifold 106 and a discharge header 108 all positioned within a compressor rack 110. A discharge output 112 of each compressor 102 includes a respective temperature sensor 114. An input 116 to the suction manifold 106 includes both a pressure sensor 118 and a temperature sensor 120. Further, a discharge outlet 122 of the discharge header 108 includes an associated pressure sensor 124. As described in further detail hereinbelow, the various sensors are implemented for evaluating maintenance requirements. The compressor rack 110 compresses refrigerant vapor that is delivered to a condenser 126 where the refrigerant vapor is liquefied at high pressure. Condenser fans 127 are associated with the condenser 126 to enable improved heat transfer from the condenser 126. The condenser 126 includes an associated ambient temperature sensor 128 and an outlet pressure sensor 130. This high-pressure liquid refrigerant is delivered to the plurality of refrigeration cases 102 by way of piping 132. Each refrigeration case 102 is arranged in separate circuits consisting of a plurality of refrigeration cases 102 that operate within a certain temperature range. FIG. 1 illustrates four (4) circuits labeled circuit A, circuit B, circuit C and circuit D. Each circuit is shown consisting of four (4) refrigeration cases 102. However, those skilled in the art will recognize that any number of circuits, as well as any number of refrigeration cases 102 may be employed within a circuit. As indicated, each circuit will generally operate within a certain temperature range. For example, circuit A may be for frozen food, circuit B may be for dairy, circuit C may be for meat, etc. Because the temperature requirement is different for each circuit, each circuit includes a pressure regulator 134 that acts to control the evaporator pressure and, hence, the temperature of the refrigerated space in the refrigeration cases 102. The pressure regulators 134 can be electronically or mechanically controlled. Each refrigeration case 102 also includes its own evaporator 136 and its own expansion valve 138 that may be either a mechanical or an electronic valve for controlling the superheat of the refrigerant. In this regard, refrigerant is delivered by piping to the evaporator 136 in each refrigeration case 102. The refrigerant passes through the expansion valve 138 where a pressure drop causes the high pressure liquid refrigerant to achieve a lower pressure combination of liquid and vapor. As hot air from the refrigeration case 102 moves across the evaporator 136, the low pressure liquid turns into gas. This low pressure gas is delivered to the pressure regulator 134 associated with that particular circuit. At the pressure regulator 134, the pressure is dropped as the gas returns to the compressor rack 110. At the compressor rack 110, the low pressure gas is again compressed to a high pressure gas, which is delivered to the condenser 126, which creates a high pressure liquid to supply to the expansion valve 138 and start the refrigeration cycle again. A main refrigeration controller 140 is used and configured or programmed to control the operation of the refrigeration system 100. The refrigeration controller 140 is preferably an Einstein Area Controller offered by CPC, Inc. of Atlanta, Ga., or any other type of programmable controller that may be programmed, as discussed herein. The refrigeration controller 140 controls the bank of compressors 104 in the compressor rack 110, via an input/output module 142. The input/output module 142 has relay switches to turn the compressors 104 on an off to provide the desired suction pressure. A separate case controller (not shown), such as a CC-100 case controller, also offered by CPC, Inc. of Atlanta, Ga. may be used to control the superheat of the refrigerant to each refrigeration case 102, via an electronic expansion valve in each refrigeration case 102 by way of a communication network or bus. Alternatively, a mechanical expansion valve may be used in place of the separate case controller. Should separate case controllers be utilized, the main refrigeration controller 140 may be used to configure each separate case controller, also via the communication bus. The communication bus may either be a RS-485 communication bus or a LonWorks Echelon bus that enables the main refrigeration controller 140 and the separate case controllers to receive information from each refrigeration case 102. Each refrigeration case 102 may have a temperature sensor 146 associated therewith, as shown for circuit B. The temperature sensor 146 can be electronically or wirelessly connected to the controller 140 or the expansion valve for the refrigeration case 102. Each refrigeration case 102 in the circuit B may have a separate temperature sensor 146 to take average/min/max temperatures or a single temperature sensor 146 in one refrigeration case 102 within circuit B may be used to control each refrigeration case 102 in circuit B because all of the refrigeration cases 102 in a given circuit operate at substantially the same temperature range. These temperature inputs are preferably provided to the analog input board 142, which returns the information to the main refrigeration controller 140 via the communication bus. Additionally, further sensors are provided and correspond with each component of the refrigeration system and are in communication with the refrigeration controller 140. Energy sensors 150 are associated with the compressors 104 and the condenser 126 of the refrigeration system 100. The energy sensors 150 monitor energy consumption of their respective components and relay that information to the controller 140. Referring now to FIG. 2, data acquisition and analytical algorithms may reside in one or more layers. The lowest layer is a device layer that includes hardware including, but not limited to, I/O boards that collect signals and may even process some signals. A system layer includes controllers such as the refrigeration controller 140 and case controllers 141. The system layer processes algorithms that control the system components. A facility layer includes a site-based controller 161 that integrates and manages all of the sub-controllers. The site-based controller 161 is a master controller that manages communications to/from the facility. The highest layer is an enterprise layer that manages information across all facilities and exists within a remote network or processing center 160. It is anticipated that the remote processing center 160 can be either in the same location (e.g., food product retailer) as the refrigeration system 100 or can be a centralized processing center that monitors the refrigeration systems of several remote locations. The refrigeration controller 140 and case controllers 141 initially communicate with the site-based controller 161 via a serial connection, Ethernet, or other suitable network connection. The site-based controller 161 communicates with the processing center 160 via a modem, Ethernet, internet (i.e., TCP/IP) or other suitable network connection. The processing center 160 collects data from the refrigeration controller 140, the case controllers 141 and the various sensors associated with the refrigeration system 100. For example, the processing center 160 collects information such as compressor, flow regulator and expansion valve set points from the refrigeration controller 140. Data such as pressure and temperature values at various points along the refrigeration circuit are provided by the various sensors via the refrigeration controller 140. Referring now to FIGS. 3 and 4, for each refrigeration circuit and loop of the refrigeration system 100, several calculations are required to calculate superheat, saturation properties and other values used in the hereindescribed algorithms. These measurements include: ambient temperature (Ta), discharge pressure (Pd), condenser pressure (Pc), suction temperature (Ts), suction pressure (Ps), refrigeration level (RL), compressor discharge temperature (Td), rack current load (Icmp), condenser current load (Icnd) and compressor run status. Other accessible controller parameters will be used as necessary. For example, a power sensor can monitor the power consumption of the compressor racks and the condenser. Besides the sensors described above, suction temperature sensors 115 monitor Ts of the individual compressors 104 in a rack and a rack current sensor 150 monitors Icmp of a rack. The pressure sensor 124 monitors Pd and a current sensor 127 monitors Icnd. Multiple temperature sensors 129 monitor a return temperature (Tc) for each circuit. The analytical algorithms include common and application algorithms that are preferably provided in the form of software modules. The application algorithms, supported by the common algorithms, predict maintenance requirements for the various components of the refrigeration system 100 and generate notifications that include notices, warnings and alarms. Notices are the lowest of the notifications and simply notify the service provider that something out of the ordinary is happening in the system. A notification does not yet warrant dispatch of a service technician to the facility. Warnings are an intermediate level of the notifications and inform the service provider that a problem is identified which is serious enough to be checked by a technician within a predetermined time period (e.g., 1 month). A warning does not indicate an emergency situation. An alarm is the highest of the notifications and warrants immediate attention by a service technician. The common algorithms include signal conversion and validation, saturated refrigerant properties, pattern analyzer, watchdog message and recurring notice or alarm message. The application algorithms include condenser performance management (fan loss and dirty condenser), compressor proofing, compressor fault detection, return gas superheat monitoring, compressor contact monitoring, compressor run-time monitoring, refrigerant loss detection and suction/discharge pressure monitoring. Each is discussed in detail below. The algorithms can be processed locally using the refrigeration controller 140 or remotely at the remote processing center 160. Referring now to FIGS. 5 through 15, the common algorithms will be described in detail. With particular reference to FIGS. 5 and 6, the signal conversion and validation (SCV) algorithm processes measurement signals from the various sensors. The SCV algorithm determines the value of a particular signal and up to three different qualities including whether the signal is within a useful range, whether the signal changes over time and/or whether the actual input signal from the sensor is valid. Referring now to FIG. 5, in step 500, the input registers read the measurement signal of a particular sensor. In step 502, it is determined whether the input signal is within a range that is particular to the type of measurement. If the input signal is within range, the SCV algorithm continues in step 504. If the input signal is not within the range an invalid data range flag is set in step 506 and the SCV algorithm continues in step 508. In step 504, it is determined whether there is a change (Δ) in the signal within a threshold time (tthresh). If there is no change in the signal it is deemed static. In this case, a static data value flag is set in step 510 and the SCV algorithm continues in step 508. If there is a change in the signal a valid data value flag is set in step 512 and the SCV algorithm continues in step 508. In step 508, the signal is converted to provide finished data. More particularly, the signal is generally provided as a voltage. The voltage corresponds to a particular value (e.g., temperature, pressure, current, etc.). Generally, the signal is converted by multiplying the voltage value by a conversion constant (e.g., ° C./V, kPa/V, A/V, etc.). In step 514, the output registers pass the data value and validation flags and control ends. Referring now to FIG. 6, a block diagram schematically illustrates an SCV block 600. A measured variable 602 is shown as the input signal. The input signal is provided by the instruments or sensors. Configuration parameters 604 are provided and include Lo and Hi range values, a time Δ, a signal Δ and an input type. The configuration parameters 604 are specific to each signal and each application. Output parameters 606 are output by the SCV block 600 and include the data value, bad signal flag, out of range flag and static value flag. In other words, the output parameters 606 are the finished data and data quality parameters associated with the measured variable. Referring now to FIGS. 7 through 10, refrigeration property algorithms will be described in detail. The refrigeration property algorithms provide the saturation pressure (PSAT), density and enthalpy based on temperature. The refrigeration property algorithms further provide saturation temperature (TSAT) based on pressure. Each algorithm incorporates thermal property curves for common refrigerant types including, but not limited to, R22, R401a (MP39), R402a (HP80), R404a (HP62), R409a and R507c. With particular reference to FIG. 7, a refrigerant properties from temperature (RPFT) algorithm is shown. In step 700, the temperature and refrigerant type are input. In step 702, it is determined whether the refrigerant is saturated liquid based on the temperature. If the refrigerant is in the saturated liquid state, the RPFT algorithm continues in step 704. If the refrigerant is not in the saturated liquid state, the RPFT algorithm continues in step 706. In step 704, the RPFT algorithm selects the saturated liquid curve from the thermal property curves for the particular refrigerant type and continues in step 708. In step 706, it is determined whether the refrigerant is in a saturated vapor state. If the refrigerant is in the saturated vapor state, the RPFT algorithm continues in step 710. If the refrigerant is not in the saturated vapor state, the RPFT algorithm continues in step 712. In step 712, the data values are cleared, flags are set and the RPFT algorithm continues in step 714. In step 710, the RPFT algorithm selects the saturated vapor curve from the thermal property curves for the particular refrigerant type and continues in step 708. In step 708, data values for the refrigerant are determined. The data values include pressure, density and enthalpy. In step 714, the RPFT algorithm outputs the data values and flags. Referring now to FIG. 8, a block diagram schematically illustrates an RPFT block 800. A measured variable 802 is shown as the temperature. The temperature is provided by the instruments or sensors. Configuration parameters 804 are provided and include the particular refrigerant type. Output parameters 806 are output by the RPFT block 800 and include the pressure, enthalpy, density and data quality flag. With particular reference to FIG. 9 a refrigerant properties from pressure (RPFP) algorithm is shown. In step 900, the temperature and refrigerant type are input. In step 902, it is determined whether the refrigerant is saturated liquid based on the pressure. If the refrigerant is in the saturated liquid state, the RPFP algorithm continues in step 904. If the refrigerant is not in the saturated liquid state, the RPFP algorithm continues in step 906. In step 904, the RPFP algorithm selects the saturated liquid curve from the thermal property curves for the particular refrigerant type and continues in step 908. In step 906, it is determined whether the refrigerant is in a saturated vapor state. If the refrigerant is in the saturated vapor state, the RPFP algorithm continues in step 910. If the refrigerant is not in the saturated vapor state, the RPFP algorithm continues in step 912. In step 912, the data values are cleared, flags are set and the RPFP algorithm continues in step 914. In step 910, the RPFP algorithm selects the saturated vapor curve from the thermal property curves for the particular refrigerant type and continues in step 908. In step 908, the temperature of the refrigerant is determined. In step 914, the RPFP algorithm outputs the temperature and flags. Referring now to FIG. 10, a block diagram schematically illustrates an RPFP block 1000. A measured variable 1002 is shown as the pressure. The pressure is provided by the instruments or sensors. Configuration parameters 1004 are provided and include the particular refrigerant type. Output parameters 1006 are output by the RPFP block 1000 and include the temperature and data quality flag. Referring now to FIGS. 11 through 13, the data pattern recognition algorithm or pattern analyzer will be described in detail. The pattern analyzer monitors operating parameter inputs such as case temperature (TCASE), product temperature (TPROD), Ps and Pd and includes a data table (see FIG. 11) having multiple bands whose upper and lower limits are defined by configuration parameters. A particular input is measured at a configured frequency (e.g., every minute, hour, day, etc.). As the input value changes, the pattern analyzer determines within which band the value lies and increments a counter for that band. After the input has been monitored for a specified time period (e.g., a day, a week, a month, etc.) notifications are generated based on the band populations. The bands are defined by various boundaries including a high positive (PP) boundary, a positive (P) boundary, a zero (Z) boundary, a minus (M) boundary and a high minus (MM) boundary. The number of bands and the boundaries thereof are determined based on the particular refrigeration system operating parameter to be monitored. If the population of a particular band exceeds a notification limit, a corresponding notification is generated. Referring now to FIG. 12, a pattern analyzer block 1200 receives measured variables 1202, configuration parameters 1204 and generates output parameters 1206 based thereon. The measured variables 1202 include an input (e.g., TCASE, TPROD, Ps and Pd). The configuration parameters 1204 include a data sample timer and data pattern zone information. The data sample timer includes a duration, an interval and a frequency. The data pattern zone information defines the bands and which bands are to be enabled. For example, the data pattern zone information provides the boundary values (e.g., PP) band enablement (e.g., PPen), band value (e.g., PPband) and notification limit (e.g., PPpct). Referring now to FIG. 13, input registers are set for measurement and start trigger in step 1300. In step 1302, the algorithm determines whether the start trigger is present. If the start trigger is not present, the algorithm loops back to step 1300. If the start trigger is present, the pattern table is defined in step 1304 based on the data pattern bands. In step 1306, the pattern table is cleared. In step 1308, the measurement is read and the measurement data is assigned to the pattern table in step 1310. In step 1312, the algorithm determines whether the duration has expired. If the duration has not yet expired, the algorithm waits for the defined interval in step 1314 and loops back to step 1308. If the duration has expired, the algorithm populates the output table in step 1316. In step 1318, the algorithm determines whether the results are normal. In other words, the algorithm determines whether the population of each band is below the notification limit for that band. If the results are normal, notifications are cleared in step 1320 and the algorithm ends. If the results are not normal, the algorithm determines whether to generate a notice, a warning, or an alarm in step 1322. In step 1324, the notification(s) is/are generated and the algorithm ends. Referring now to FIG. 14, a block diagram schematically illustrates the watchdog message algorithm, which includes a message generator 1400, configuration parameters 1402 and output parameters 1404. In accordance with the watchdog message algorithm, the site-based controller 161 periodically reports its health (i.e., operating condition) to the remainder of the network. The site-based controller generates a test message that is periodically broadcast. The time and frequency of the message is configured by setting the time of the first message and the number of times per day the test message is to be broadcast. Other components of the network (e.g., the refrigeration controller 140, the processing center 160 and the case controllers) periodically receive the test message. If the test message is not received by one or more of the other network components, a controller communication fault is indicated. Referring now to FIG. 15, a block diagram schematically illustrates the recurring notification algorithm. The recurring notification algorithm monitors the state of signals generated by the various algorithms described herein. Some signals remain in the notification state for a protracted period of time until the corresponding issue is resolved. As a result, a notification message that is initially generated as the initial notification occurs may be overlooked later. The recurring notification algorithm generates the notification message at a configured frequency. The notification message is continuously regenerated until the alarm condition is resolved. The recurring notification algorithm includes a notification message generator 1500, configuration parameters 1502, input parameters 1504 and output parameters 1506. The configuration parameters 1502 include message frequency. The input 1504 includes a notification message and the output parameters 1506 include a regenerated notification message. The notification generator 1500 regenerates the input notification message at the indicated frequency. Once the notification condition is resolved, the input 1504 will indicate as such and regeneration of the notification message terminates. Referring now to FIGS. 16 through 40, the application algorithms will be described in detail. With particular reference to FIGS. 16 through 21, condenser performance degrades due to gradual buildup of dirt and debris on the condenser coil and condenser fan failures. The condenser performance management includes a fan loss algorithm and a dirty condenser algorithm to detect either of these conditions. Referring now to FIGS. 16 and 17, the fan loss algorithm for a condenser fan without a variable speed drive (VSD) will be described. A block diagram illustrates a fan loss block 1600 that receives inputs of total condenser fan current (ICND), a fan call status, a fan current for each condenser fan (IEACHFAN) and a fan current measurement accuracy (δIFANCURRENT). The fan call status is a flag that indicates whether a fan has been commanded to turn on. The fan current measurement accuracy is assumed to be approximately 10% of IEACHFAN if it is otherwise unavailable. The fan loss block 1600 processes the inputs and can generate a notification if the algorithm deems a fan is not functioning. Referring to FIG. 17, the condenser control requests that a fan come on in step 1700. In step 1702, the algorithm determines whether the incremental change in ICND is greater than or equal to the difference of IEACHFAN and δIFANCURRENT. If the incremental change is not greater than or equal to the difference, the algorithm generates a fan loss notification in step 1704 and the algorithm ends. If the incremental change is greater than or equal to the difference, the algorithm loops back to step 1700. Referring now to FIGS. 18 and 19, the fan loss algorithm for a condenser fan with a VSD will be described. A block diagram illustrates a fan loss block 1800 that receives inputs of ICND, the number of fans ON (N), VSD speed (RPM) or output %, IEACHFAN and δIFANCURRENT. The VSD RPM or output % is provided by a motor control algorithm. The fan loss block 1600 processes the inputs and can generate a notification if the algorithm deems a fan is not functioning. Referring to FIG. 19, the condenser control calculates and expected current (IEXP) in step 1900 based on the following formula:IEXP=N×IEACHFAN×(RPM/100)3 In step 1902, the algorithm determines whether ICND is greater than or equal to the difference of IEXP and δIFANCURRENT. If the incremental change is not greater than or equal to the difference, the algorithm generates a fan loss notification in step 1904 and the algorithm ends. If the incremental change is greater than or equal to the difference, the algorithm loops back to step 1900. Referring specifically to FIGS. 20 and 21, the dirty condenser algorithm will be explained in further detail. Condenser performance degrades due to dirt and debris. The dirty condenser algorithm calculates an overall condenser performance factor (U) for the condenser which corresponds to a thermal efficiency of the condenser. Hourly and daily averages are calculated and stored. A notification is generated based on a drop in the U averages. A condenser performance degradation block 2000 receives inputs including ICND, ICMP, Pd, Ta, refrigerant type and a reset flag. The condenser performance degradation block generates an hourly U average (UHRLYAVG), a daily U average (UDAILYAVG) and a reset flag time, based on the inputs. Whenever the condenser is cleaned, the field technician resets the algorithm and a benchmark U is created by averaging seven days of hourly data. A condenser performance degradation analysis block 2002 generates a notification based on UHRLYAVG, UDAILYAVG and the reset time flag. Referring now to FIG. 21, the algorithm calculates TDSAT based on Pd in step 2100. In step 2102, the algorithm calculates U based on the following equation: U = I CMP ( I CND + Ionefan ) ⁢ ( T DSAT - T a ) To avoid an error due to division by 0, a small nominal value Ionefan is added to the denominator. In this way, even when the condenser is off, and ICND is 0, the equation does not return an error. Ionefan corresponds to the normal current of one fan. The In step 2104, the algorithm updates the hourly and daily averages provided that ICMP and ICND are both greater than 0, all sensors are functioning properly and the number of good data for sampling make up at least 20% of the total data sample. If these conditions are not met, the algorithm sets U=−1. The above calculation is based on condenser and compressor current. As can be appreciated, condenser and compressor power, as indicated by a power meter, or PID control signal data may also be used. PID control signal refers to a control signal that directs the component to operate at a percentage of its maximum capacity. A PID percentage value may be used in place of either the compressor or condenser current. As can be appreciated, any suitable indication of compressor or condenser power consumption may be used. In step 2106, the algorithm logs UHRLYAVG, UDAILYAVG and the reset time flag into memory. In step 2108, the algorithm determine whether each of the averages have dropped by a threshold percentage (XX %) as compared to respective benchmarks. If the averages have not dropped by XX %, the algorithm loops back to step 2100. If the averages have dropped by XX %, the algorithm generates a notification in step 2110. Referring now to FIGS. 22 and 23, the compressor proofing algorithm monitors Td and the ON/OFF status of the compressor. When the compressor is turned ON, Td should rise by at least 20° F. A compressor proofing block 2200 receives Td and the ON/OFF status as inputs. The compressor proofing block 2200 processes the inputs and generates a notification if needed. In step 2300, the algorithm determines whether Td has increased by at least 20° F. after the status has changed from OFF to ON. If Td has increased by at least 20° F., the algorithm loops back. If Td has not increased by at least 20° F., a notification is generated in step 2302. High compressor discharge temperatures result in lubricant breakdown, worn rings, and acid formation, all of which shorten the compressor lifespan. This condition can indicate a variety of problems including, but not limited to, damaged compressor valves, partial motor winding shorts, excess compressor wear, piston failure and high compression ratios. High compression ratios can be caused by either low suction pressure, high head pressure or a combination of the two. The higher the compression ratio, the higher the discharge temperature. This is due to heat of compression generated when the gasses are compressed through a greater pressure range. High discharge temperatures (e.g., >300 F) cause oil break-down. Although high discharge temperatures typically occur in summer conditions (i.e., when the outdoor temperature is high and compressor has some problem), high discharge temperatures can occur in low ambient conditions, when compressor has some problem. Although the discharge temperature may not be high enough to cause oil break-down, it may still be higher than desired. Running compressor at relatively higher discharge temperatures indicates inefficient operation and the compressor may consume more energy then required. Similarly, lower then expected discharge temperatures may indicate flood-back. The algorithms detect such temperature conditions by calculating isentropic efficiency (NCMP) for the compressor. A lower efficiency indicates a compressor problem and an efficiency close to 100% indicates a flood-back condition. Referring now to FIGS. 24 and 25, the compressor fault detection algorithm will be discussed in detail. A compressor performance monitoring block 2400 receives Ps, Ts, Pd, Td, compressor ON/OFF status and refrigerant type as inputs. The compressor performance monitoring block 2400 generates NCMP and a notification based on the inputs. A compressor performance analysis block selectively generates a notification based on a daily average of NCMP. With particular reference to FIG. 25, the algorithm calculates suction entropy (sSUC) and suction enthalpy (hSUC) based on Ts and Ps, intake enthalpy (hID) based on sSUC, and discharge enthalpy (hDIS) based on Td and Pd in step 2500. In step 2502, control calculates NCMP based on the following equation:NCMP=(hID−hSUC)/(hDIS−hSUC)*100In step 2504, the algorithm determines whether NCMP is less than a first threshold (THR1) for a threshold time (tTHRESH) and whether NCMP is greater than a second threshold (THR2) for tTHRESH. If NCMP is not less than THR1 for tTHRESH and is not greater than THR2 for tTHRESH, the algorithm continues in step 2508. If NCMP is less than THR1 for tTHRESH and is greater than THR2 for tTHRESH, the algorithm issues a compressor performance effected notification in step 2506 and ends. The thresholds may be predetermined and based on ideal suction enthalpy, ideal intake enthalpy and/or ideal discharge enthalpy. Further, THR1 may be 50%. An NCMP of less than 50% may indicate a refrigeration system malfunction. THR2 may be 90%. An NCMP of more than 90% may indicate a flood back condition. In step 2508, the algorithm calculates a daily average of NCMP (NCMPDA) provided that the compressor proof has not failed, all sensors are providing valid data and the number of good data samples are at least 20% of the total samples. If these conditions are not met, NCMPDA is set equal to −1. In step 2510, the algorithm determines whether NCMPDA has changed by a threshold percent (PCTTHR) as compared to a benchmark. If NCMPDA has not changed by PCTTHR, the algorithm loops back to step 2500. If NCMPDA has not changed by PCTTHR, the algorithm ends. If NCMPDA has changed by PCTTHR, the algorithm initiates a compressor performance effected notification in step 2512 and the algorithm ends. Referring now to FIGS. 26 and 27, a high Td monitoring algorithm will be described in detail. The high Td monitoring algorithm generates notifications for discharge temperatures that can result in oil beak-down. In general, the algorithm monitors Td and determines whether the compressor is operating properly based thereon. Td reflects the latent heat absorbed in the evaporator, evaporator superheat, suction line heat gain, heat of compression, and compressor motor-generated heat. All of this heat is accumulated at the compressor discharge and must be removed. High compressor Td's result in lubricant breakdown, worn rings, and acid formation, all of which shorten the compressor lifespan. This condition can indicate a variety of problems including, but not limited to damaged compressor valves, partial motor winding shorts, excess compressor wear, piston failure and high compression ratios. High compression ratios can be caused by either low Ps, high head pressure, or a combination of the two. The higher the compression ratio, the higher the Td will be at the compressor. This is due to heat of compression generated when the gasses are compressed through a greater pressure range. Referring now to FIG. 26, a Td monitoring block 2600 receives Td and compressor ON/OFF status as inputs. The Td monitoring block 2600 processes the inputs and selectively generates an unacceptable Td notification. Referring now to FIG. 27, the algorithm determines whether Td is greater than a threshold temperature (TTHR) for a threshold time (tTHRESH). If Td is not greater than TTHR for tTHRESH, the algorithm loops back. If Td is greater than TTHR for tTHRESH, the algorithm generates an unacceptable discharge temperature notification in step 2702 and the algorithm ends. Referring now to FIGS. 28 and 29, the return gas superheat monitoring algorithm will be described in further detail. Liquid flood-back is a condition that occurs while the compressor is running. Depending on the severity of this condition, liquid refrigerant will enter the compressor in sufficient quantities to cause a mechanical failure. More specifically, liquid refrigerant enters the compressor and dilutes the oil in either the cylinder bores or the crankcase, which supplies oil to the shaft bearing surfaces and connecting rods. Excessive flood back (or slugging) results in scoring the rods, pistons, or shafts. This failure mode results from the heavy load induced on the compressor and the lack of lubrication caused by liquid refrigerant diluting the oil. As the liquid refrigerant drops to the bottom of the shell, it dilutes the oil, reducing its lubricating capability. This inadequate mixture is then picked up by the oil pump and supplied to the bearing surfaces for lubrication. Under these conditions, the connecting rods and crankshaft bearing surfaces will score, wear, and eventually seize up when the oil film is completely washed away by the liquid refrigerant. There will likely be copper plating, carbonized oil, and aluminum deposits on compressor components resulting from the extreme heat of friction. Some common causes of refrigerant flood back include, but are not limited to inadequate evaporator superheat, refrigerant over-charge, reduced air flow over the evaporator coil and improper metering device (oversized). The return gas superheat monitoring algorithm is designed to generate a notification when liquid reaches the compressor. Additionally, the algorithm also watches the return gas temperature and superheat for the first sign of a flood back problem even if the liquid does not reach the compressor. Also, the return gas temperatures are monitored and a notification is generated upon a rise in gas temperature. Rise in gas temperature may indicate improper settings. Referring now to FIG. 28, a return gas and flood back monitoring block 2800, receives Ts, Ps, rack run status and refrigerant type as inputs. The return gas and flood back monitoring block 2800 processes the inputs and generates a daily average superheat (SH), a daily average Ts (Tsavg) and selectively generates a flood back notification. Another return gas and flood back monitoring block 2802 selectively generates a system performance degraded notice based on SH and Tsavg. Referring now to FIG. 29, the algorithm calculates a saturated Ts (Tssat) based on Ps in step 2900. The algorithm also calculates SH as the difference between Ts and Tssat in step 2900. In step 2902, the algorithm determines whether SH is less than a superheat threshold (SHTHR) for a threshold time (tTHRSH). If SH is not less than SHTHR for tTHRSH, the algorithm loops back to step 2900. If SH is less than SHTHR for tTHRSH, the algorithm generates a flood back detected notification in step 2904 and the algorithm ends. In step 2908, the algorithm calculates an SH daily average (SHDA) and Tsavg provided that the rack is running (i.e., at least one compressor in the rack is running, all sensors are generating valid data and the number of good data for averaging are at least 20% of the total data sample. If these conditions are not met, the algorithm sets SHDA=−100 and Tsavg=−100. In step 2910, the algorithm determines whether SHDA or Tsavg change by a threshold percent (PCTTHR) as compared to respective benchmark values. If neither SHDA nor Tsavg change by PCTTHR, the algorithm ends. If either SHDA or Tsavg changes by PCTTHR, the algorithm generates a system performance effected algorithm in step 2912 and the algorithm ends. The algorithm may also calculate a superheat rate of change over time. An increasing superheat may indicate an impending flood back condition. Likewise, a decreasing superheat may indicate an impending degraded performance condition. The algorithm compares the superheat rate of change to a rate threshold maximum and a rate threshold minimum, and determines whether the superheat is increases or decreasing at a rapid rate. In such case, a notification is generated. Compressor contactor monitoring provides information including, but not limited to, contactor life (typically specified as number of cycles after which contactor needs to be replaced) and excessive cycling of compressor, which is detrimental to the compressor. The contactor sensing mechanism can be either internal (e.g., an input parameter to a controller which also accumulates the cycle count) or external (e.g., an external current sensor or auxiliary contact). Referring now to FIG. 30, the contactor maintenance algorithm selectively generates notifications based on how long it will take to reach the maximum count using a current cycling rate. For example, if the number of predicted days required to reach maximum count is between 45 and 90 days a notice is generated. If the number of predicted days is between 7 and 45 days a warning is generated and if the number of predicated days is less then 7, an alarm is generated. A contactor maintenance block 3000 receives the contactor ON/OFF status, a contactor reset flag and a maximum contactor cycle count (NMAX) as inputs. The contactor maintenance block 3000 generates a notification based on the input. Referring now to FIG. 31, the algorithm determines whether the reset flag is set in step 3100. If the reset flag is set, the algorithm continues in step 3102. If the reset flag is not set, the algorithm continues in step 3104. In step 3102, the algorithm sets an accumulated counter (CACC) equal to zero. In step 3104, the algorithm determines a daily count (CDAILY) of the particular contactor, updates CACC based on CDAILY and determines the number of predicted days until service (DPREDSERV) based on the following equation:DPREDSERV=(NMAX−CACC)/CDAILY In step 3106, the algorithm determines whether DPREDSERV is less than a first threshold number of days (DTHR1) and is greater than or equal to a second threshold number of days (DTHR2). If DPREDSERV is less than DTHR1 and is greater than or equal to DTHR2, the algorithm loops back to step 3100. If DPREDSERV is not less than DTHR1 or is not greater than or equal to DTHR2, the algorithm continues in step 3108. In step 3108, the algorithm generates a notification that contactor service is required and ends. An excessive contactor cycling algorithm watches for signs of excessive cycling. Excessive cycling of the compressor for an extended period of time reduces the life of compressor. The algorithm generates at least one notification a week to notify of excessive cycling. The algorithm makes use of point system to avoid nuisance alarm. FIG. 32 illustrates a contactor excessive cycling block 3200, which receives contactor ON/OFF status as an input. The contactor excessive cycling block 3200 selectively generates a notification based on the input. Referring now to FIG. 33, the algorithm determines the number of cycling counts (NCYCLE) each hour and assigns cycling points (NPOINTS) based thereon. For example, if NCYCLE/hour is between 6 and 12, NPOINTS is equal to 1. if NCYCLE/hour is between 12 and 18, NPOINTS is equal to 3 and if NCYCLE/hour is greater than 18, NPOINTS is equal to 1. In step 3302, the algorithm determines the accumulated NPOINTS (NPOINTSACC) for a time period (e.g., 7 days). In step 3304, the algorithm determines whether NPOINTSACC is greater than a threshold number of points (PTHR). If NPOINTSACC is not greater than PTHR, the algorithm loops back to step 3300. If NPOINTSACC is greater than PTHR, the algorithm issues a notification in step 3306 and ends. The compressor run-time monitoring algorithm monitors the run-time of the compressor. After a threshold compressor run-time (tCOMPTHR), a routine maintenance such as oil change or the like is required. When the run-time is close to tCOMPTHR, a notification is generated. Referring now to FIG. 34, a compressor maintenance block 3400 receives an accumulated compressor run-time (tCOMPACC), a reset flag and tCOMPTHR as inputs. The compressor maintenance block 3400 selectively generates a notification based on the inputs. Referring not to FIG. 35, the algorithm determines whether the reset flag is set in step 3500. If the reset flag is set, the algorithm continues in step 3502. If the reset flag is not set, the algorithm continues in step 3504. In step 3502, the algorithm sets tCOMPACC equal to zero. In step 3504, the algorithm calculates the daily compressor run time (tCOMPDAILY) and predicts the number of days until service is required (tCOMPSERV) based on the following equation:tCOMPSERV=(tCOMPTHR−tCOMPACC)/tCOMPDAILY In step 3506, the algorithm determines whether tCOMPSERV is less than a first threshold (DTHR1) and greater than or equal to a second threshold (DTHR2). If tCOMPSERV is not less than DTHR1 or is not greater than or equal to DTHR2, the algorithm loops back to step 3500. If tCOMPSERV is less than DTHR1 and is greater than or equal to DTHR2, the algorithm issues a notification in step 3508 and ends. Refrigerant level within the refrigeration system 100 is a function of refrigeration load, ambient temperatures, defrost status, heat reclaim status and refrigerant charge. A reservoir level indicator (not shown) reads accurately when the system is running and stable and it varies with the cooling load. When the system is turned off, refrigerant pools in the coldest parts of the system and the level indicator may provide a false reading. The refrigerant loss detection algorithm determines whether there is leakage in the refrigeration system 100. Refrigerant leak can occur as a slow leak or a fast leak. A fast leak is readily recognizable because the refrigerant level in the optional receiver will drop to zero in a very short period of time. However, a slow leak is difficult to quickly recognize. The refrigerant level in the receiver can widely vary throughout a given day. To extract meaningful information, hourly and daily refrigerant level averages (RLHRLYAVG, RLDAILYAVG) are monitored. If the refrigerant is not present in the receiver should be present in the condenser. The volume of refrigerant in the condenser is proportional to the temperature difference between ambient air and condenser temperature. Refrigerant loss is detected by collectively monitoring these parameters. Referring now to FIG. 36, a first refrigerant charge monitoring block 3600 receives receiver refrigerant level (RLREC), Pd, Ta, a rack run status, a reset flag and the refrigerant type as inputs. The first refrigerant charge monitoring block 3600 generates RLHRLYAVG, RLDAILYAVG, TDHRLYAVG, TDDAILYAVG, a reset date and selectively generates a notification based on the inputs. RLHRLYAVG, RLDAILYAVG, TDHRLYAVG, TDDAILYAVG and the reset date are inputs to a second refrigerant charge monitoring block 3602, which selectively generates a notification based thereon. It is anticipated that the first monitoring block 3600 is resident within and processes the algorithm within the refrigerant controller 140. The second monitoring block 3602 is resident within and processes the algorithm within the processing center 160. The algorithm generates a refrigerant level model based on the monitoring of the refrigerant levels. The algorithm determines an expected refrigerant level based on the model, and compares the current refrigerant level to the expected refrigerant level. Referring now to FIG. 37, the refrigerant loss detection algorithm calculates Tdsat based on Pd and calculates TD as the difference between Tdsat and Ta in step 3700. In step 3702, the algorithm determines whether RLREC is less than a first threshold (RLTHR1) for a first threshold time (t1) or whether RLREC is greater than a second threshold (RLTHR2) for a second threshold time (t2). If RLREC is not less than RLTHR1 for t1 and RLREC is not greater than RLTHR2 for t2, the algorithm loops back to step 3700. If RLREC is less than RLTHR1 for t1 or RLREC is greater than RLTHR2 for t2, the algorithm issues a notification in step 3704 and ends. In step 3706, the algorithm calculates RLHRLYAVG and RLDAILYAVG provided that the rack is operating, all sensors are providing valid data and the number of good data points is at least 20% of the total sample of data points. If these conditions are not met, the algorithm sets TD equal to −100 and RLREC equal to −100. In step 3708, RLREC, RLHRLYAVG, RLDAILYAVG, TD and the reset flag date (if a reset was initiated) are logged. Referring now to FIG. 38, the algorithm calculates expected daily RL values. The algorithm determines whether the reset flag has been set in step 3800. If the reset flag has been set, the algorithm continues in step 3802. If the reset flag has not been set, the algorithm continues in step 3804. In step 3802, the algorithm calculates TDHRLY and plots the function RLREC versus TD, according to the function RLREC=Mb×TD+Cb, where Mb is the slope of the line and Cb is the Y-intercept. In step 3804, the algorithm calculates expected RLDAILYAVG based on the function. In step 3806, the algorithm determines whether the expected RLDAILYAVG minus the actual RLDAILYAVG is greater than a threshold percentage. When the difference is not greater than the threshold percentage, the algorithm ends. When the difference is greater than the threshold, a notification is issued in step 3808, and the algorithm ends. Ps and Pd have significant implications on overall refrigeration system performance. For example, if Ps is lowered by 1 PSI, the compressor power increases by about 2%. Additionally, any drift in Ps and Pd may indicate malfunctioning of sensors or some other system change such as set point change. The suction and discharge pressure monitoring algorithm calculates daily averages of these parameters and archives these values in the server. The algorithm initiates an alarm when there is a significant change in the averages. FIG. 39 illustrates a suction and discharge pressure monitoring block 3900 that receives Ps, Pd and a pack status as inputs. The suction and discharge pressure monitoring block 3900 selectively generates a notification based on the inputs. Referring now to FIG. 40, the suction and discharge pressure monitoring algorithm calculates daily averages of Ps and Pd (PsAVG and PdAVG, respectively) in step 4000 provided that the rack is operating, all sensors are generating valid data and the number of good data points is at least 20% of the total number of data points. If these conditions are not met, the algorithm sets PsAVG equal to −100 and PdAVG equal to −100. In step 4002, the algorithm determines whether the absolute value of the difference between a current PsAVG and a previous PsAVG is greater than a suction pressure threshold (PsTHR). If the absolute value of the difference between the current PsAVG and the previous PsAVG is greater than PsTHR, the algorithm issues a notification in step 4004 and ends. If the absolute value of the difference between the current PsAVG and the previous PsAVG is not greater than PsTHR, the algorithm continues in step 4006. In step 4006, the algorithm determines whether the absolute value of the difference between a current PdAVG and a previous PdAVG is greater than a discharge pressure threshold (PdTHR). If the absolute value of the difference between the current PdAVG and the previous PdAVG is greater than PdTHR, the algorithm issues a notification in step 4008 and ends. If the absolute value of the difference between the current PdAVG and the previous PdAVG is not greater than PdTHR, the algorithm ends. Alternatively, the algorithm may compare PdAVG and PsAVG to predetermined ideal discharge and suction pressures. The description is merely exemplary in nature and, thus, variations are not to be regarded as a departure from the spirit and scope of the teachings.
claims
1. A method for monitoring an operating condition of a wind turbine, comprising:capturing measurement data and operating condition parameters by various sensors and recording in memory;assigning the captured measurement data to a correct one of a plurality of bins by:selecting a subset of the operating condition parameters by a processing unit;calculating a set of n characterizing moments based on the selected subset of the operating condition parameters by the processing unit, wherein the n characterizing moments comprise a set of values that characterize operational states of the turbine;defining a finite n-dimensional space, each of the n-dimensional space representing possible values for one of the n characterising moments by the processing unit;sub-dividing the n-dimensional space into the plurality of bins by the processing unit, each of the bins representing a n-dimensional interval and defining an acceptable range for the set of the n characterizing moments that characterize operational states of the turbine;defining the n-dimensional interval by n one-dimensional intervals by the processing unit, each of the n one-dimensional intervals representing an interval in one of the n-dimensional space;determining if the set of the characterising moments falls within the acceptable range for one of the bins by the processing unit;accepting the set of the characterising moments and the captured measurement data if the set of the characterising moments belongs to the one of the bins by the processing unit;assigning the captured measurement data to the correct one of the bins based on the acceptable range determination to correlate the captured measurement data with the operational state of the turbine represented by that bin; anddetermining if required input values are available for a selected evaluation method from the captured measurement data and evaluating the captured measurement data correlated with operational state of the turbine by bin according to the selected evaluation method. 2. The method as claimed in claim 1, wherein if the set of the characterizing moments does belong to the one of the bins, processed data of the captured measurement data and the set of the characterising moments are determined whether to be stored in a long-term storage. 3. The method as claimed in claim 2, wherein an alarm status is detected for checking whether the alarm status has changed with respect to the processed measurement data and characterising moments contained in the long-term storage and the processed measurement data and characterising moments are to be stored in the long-term storage if the alarm status has changed. 4. The method as claimed in claim 3, wherein a given time is determined for checking whether the given time has passed since a last storing of the processed measurement data and characterising moments in the long-term storage and the processed measurement data and characterising moments are to be stored in the long-term storage if the given time has passed. 5. The method as claimed in claim 4, wherein the given time is determined for checking whether the given time has passed since the last storing of processed measurement data in the long-term storage only when the alarm status has not changed. 6. The method as claimed in claim 1, wherein the captured measurement data and the operating condition parameters are evaluated based on evaluating a rule definition. 7. The method as claimed in claim 6, wherein the rule definition comprises a rule expression defining a type of an evaluation method, a time of evaluating the measurement data, a frequency of evaluating the measurement data, a type of data to be used for evaluating the measurement data, and an amount of data to be used for evaluating the measurement data. 8. The method as claimed in claim 1, wherein an index of the one of the bins is provided and an evaluation of the captured measurement data is tagged with the index of the one of the bins to which the set of the characterising moments belongs. 9. The method as claimed in claim 1, wherein if the set of the characterizing moments does not belong to the one of the bins, the set of the characterising moments is determined again. 10. The method as claimed in claim 1, wherein the captured measurement data and the operating condition parameters are continuously captured. 11. The method as claimed in claim 1, wherein the captured measurement data and the operating condition parameters comprise measurement data captured from a condition monitoring system, a vibration measurement value, a strain gauge measurement value, a wind speed measurement value, a rotor rotational speed value, a generated power value, a temperature measurement value, and a measurement value representative of an amount of metal particles detected in a lubricating oil of the wind turbine. 12. The method as claimed in claim 1, wherein the characterizing moments are calculated by calculating a root mean square or a mean value of the operating condition parameters. 13. The method as claimed in claim 1, wherein the measurement data is evaluated by processing the captured measurement data and comparing the processed captured measurement data with previously processed captured measurement data associated to the set of the characterising moments which belongs to the same bin. 14. The method as claimed in claim 1, wherein the captured measurement data is processed in real time for pulse-counting on oil-debris monitoring equipment, safety critical monitor of general vibration level, tower sway detection, and over speed detection. 15. The method as claimed in claim 1, wherein the captured measurement data is stored in a memory and is subsequently processed offline for autospectra, time series, and envelopes. 16. A wind turbine monitoring system for monitoring an operating condition of a wind turbine, comprising:a memory that comprises captured measurement data and operating condition parameters and a plurality of bins; anda processing unit that:selects a subset of the operating condition parameters;calculates a set of n characterizing moments based on the selected subset of the operating condition parameters, wherein the n characterizing moments comprise a set of values that characterize operational states of the turbine;defines a finite n-dimensional space, each of the n-dimensional space representing a possible value for one of the n characterising moments;sub-divides the n-dimensional space into the plurality of bins, each of the bins representing a n-dimensional interval and defining an acceptable range for the set of the n characterizing moments that characterize operational states of the turbine;defines the n-dimensional interval by n one-dimensional intervals, each of the n one-dimensional intervals representing an interval in one of the n-dimensional space;determines if the set of the characterising moments falls within the acceptable range for one of the bins;accepts the set of the characterising moments and the captured measurement data if the set of the characterising moments belongs to the one of the bins;assigns the captured measurement data to a correct one of the bins based on the acceptable range determination in order to correlate the captured measurement data with operational state of the turbine represented by that bin; anddetermines if required input values are available for a selected evaluation method from the captured measurement data and evaluates the captured measurement data correlated with operational state of the turbine by bin according to the selected evaluation method.
050358537
summary
The invention relates to a nuclear reactor fuel assembly including at least one uprightly disposed spacer having a grid of intersecting sheet-metal struts defining meshes therebetween, mutually parallel rods each being disposed in a respective one of the meshes, and strip-like contact springs parallel to the rods, each of the contact springs being disposed in a respective one of the meshes and having two strip ends both being retained on one of the struts, each of the contact springs having a contact location being resilient relative to the strut for contacting a rod, the contact location being spaced apart from both of the strip ends, each of the contact springs having an undulatory transverse curve at the contact location, and the contact springs being continuously smooth and flat from the contact location to the strip ends resting on the strut. A fuel assembly of the type mentioned above is known from Swiss Patent No. 499 850. The contact spring of the known nuclear reactor fuel assembly is located on one side of one strut of the spacer and is secured at both strip ends to the strip ends of an identically constructed contact spring located on the other side of the strut. The undulating transverse curve at the contact locations of the strip-like contact springs for the associated rod is located on the side of the associated strip-like contact spring facing away from the strut. In a nuclear reactor, the fuel assembly is longitudinally exposed to the flow of a coolant, which therefore also flows through the individual meshes in the spacer. This leads to a relatively high resistance to the flow of coolant through the individual meshes of the spacer and therefore through the overall fuel assembly. It is accordingly an object of the invention to provide a nuclear reactor fuel assembly, which overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type and which keeps the flow resistance for the coolant passing through the individual meshes of the spacer and therefore through the overall fuel assembly optimally low. With the foregoing and other objects in view there is provided, in accordance with the invention, a nuclear reactor fuel assembly, comprising at least one uprightly disposed spacer having a grid of intersecting sheet-metal struts defining meshes therebetween, mutually parallel rods, especially fuel rods containing nuclear fuel, each being disposed in a respective one of the meshes, and strip-like contact springs being parallel to the rods and each having a side facing toward and a side facing away from a respective one of the struts, each of the contact springs being disposed in a respective one of the meshes and having two strip ends both being retained on the one strut, each of the contact springs having a contact location being resilient relative to the one strut for contacting a rod, the contact location being spaced apart from both of the strip ends, each of the contact springs having an undulatory transverse curve disposed at the contact location on the side of the contact spring facing toward the one strut, and the contact springs being continuously smooth and flat from the contact location to the strip ends resting on the one strut. As a result, a gap is formed between the rod and the contact spring resting thereon for the coolant flowing through each individual mesh in the longitudinal direction of the fuel assembly in a nuclear reactor, which narrows and widens uniformly. The overall result is an optimally low flow resistance for the coolant of the nuclear reactor fuel assembly. In accordance with a concomitant feature of the invention, the undulatory transverse curve is in the form of a single curve disposed at the contact location, and the contact spring has transition locations adjacent the undulatory transverse curve being unequally spaced apart from the one strut on which the contact spring is retained. Other features which are considered as characteristic for the invention are set forth in the appended claims. Although the invention is illustrated and described herein as constructed in a nuclear reactor fuel assembly, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
abstract
A neutron generator and method of constructing the same. The generator includes a grid configured to produce an ionizable gas when heated by electrons impinging thereon. A cathode emits electrons to heat the grid and to collide with produced ionizable gas atoms to generate ions. Neutrons are generated from a collision of ions impinging on a target in the generator. A tool for subsurface use incorporating the neutron generator.
summary
description
In the Figures, corresponding reference symbols indicate corresponding parts. FIG. 1 schematically depicts a lithographic projection apparatus 1 according to an embodiment of the invention. The apparatus 1 includes a base plate BP; a radiation system Ex, IL constructed and arranged to supply a projection beam PB of radiation (e.g. EUV radiation), which in this particular case also comprises a radiation source LA; a first object table (mask table) MT provided with a mask holder that holds a mask MA (e.g. a reticle), and connected to a first positioning device PM that accurately positions the mask with respect to a projection system or lens PL; a second object table (substrate table) WT provided with a substrate holder that holds a substrate W (e.g. a resist-coated silicon wafer), and connected to a second positioning device PW that accurately positions the substrate with respect to the projection system PL. The projection system or lens PL (e.g. a mirror group) is constructed and arranged to image an irradiated portion of the mask MA onto a target portion C (e.g. comprising one or more dies) of the substrate W. As here depicted, the apparatus is of a reflective type (i.e. has a reflective mask). However, in general, it may also be of a transmissive type, for example (with a transmissive mask). Alternatively, the apparatus may employ another kind of patterning device, such as a programmable mirror array of a type as referred to above. The source LA (e.g. a discharge or laser-produced plasma source) produces a beam of radiation. This beam is fed into an illumination system (illuminator) IL, either directly or after having traversed a conditioning device, such as a beam expander Ex, for example. The illuminator IL may comprise an adjusting device AM that sets the outer and/or inner radial extent (commonly referred to as "sgr"-outer and "sgr"-inner, respectively) of the intensity distribution in the beam. In addition, it will generally comprise various other components, such as an integrator IN and a condenser CO. In this way, the beam PB impinging on the mask MA has a desired uniformity and intensity distribution in its cross-section. It should be noted with regard to FIG. 1 that the source LA may be within the housing of the lithographic projection apparatus (as is often the case when the source LA is a mercury lamp, for example), but that it may also be remote from the lithographic projection apparatus, the radiation beam which it produces being led into the apparatus (e.g. with the aid of suitable directing mirrors). This latter scenario is often the case when the source LA is an excimer laser. The present invention encompasses both of these scenarios. The beam PB subsequently intercepts the mask MA, which is held on a mask table MT. Having traversed the mask MA, the beam PB passes through the lens PL, which focuses the beam PB onto a target portion C of the substrate W. With the aid of the second positioning device PW and interferometer IF, the substrate table WT can be moved accurately, e.g. so as to position different target portions C in the path of the beam PB. Similarly, the first positioning device PM can be used to accurately position the mask MA with respect to the path of the beam PB, e.g. after mechanical retrieval of the mask MA from a mask library, or during a scan. In general, movement of the object tables MT, WT will be realized with the aid of a long-stroke module (coarse positioning) and a short-stroke module (fine positioning), which are not explicitly depicted in FIG. 1. However, in the case of a wafer stepper (as opposed to a step and scan apparatus) the mask table MT may just be connected to a short stroke actuator, or may be fixed. The mask MA and the substrate W may be aligned using mask alignment marks M1, M2 and substrate alignment marks P1, P2. The depicted apparatus can be used in two different modes: 1. In step mode, the mask table MT is kept essentially stationary, and an entire mask image is projected at once, i.e. a single xe2x80x9cflash,xe2x80x9d onto a target portion C. The substrate table WT is then shifted in the X and/or Y directions so that a different target portion C can be irradiated by the beam PB; 2. In scan mode, essentially the same scenario applies, except that a given target portion C is not exposed in a single xe2x80x9cflash.xe2x80x9d Instead, the mask table MT is movable in a given direction (the so-called xe2x80x9cscan directionxe2x80x9d, e.g., the Y direction) with a speed v, so that the projection beam PB is caused to scan over a mask image. Concurrently, the substrate table WT is simultaneously moved in the same or opposite direction at a speed V=Mv, in which M is the magnification of the lens PL (typically, M=xc2xc or ⅕). In this manner, a relatively large target portion C can be exposed, without having to compromise on resolution. FIG. 2 illustrates the substrate table WT and the second positioning device PW in more detail. The second positioning device PW is a planar magnetic positioning device having a stator 10 comprising a plurality of magnets (not illustrated) arranged in rows and columns in a single plane. The magnets in the stator 10 may be arranged according to a Halbach array, i.e. the magnetic orientation of successive magnets in each row and each column rotates 90xc2x0 counterclockwise. The substrate table WT is provided with an electric coil system in its base. The electric coil system comprises two types of coils, one type having an angular offset of +45xc2x0, and the other having an offset of xe2x88x9245xc2x0 with respect to the checker board configuration of the magnets. The substrate table WT may be moved relative to the stator 10 by driving current through the electric coil system in the base of the substrate table WT. A mechanical limiter 100 limits rotation of the substrate table WT about a direction orthogonal to the stator 10. As shown in FIG. 2, reference number 12 denotes the X-axis and reference number 14 denotes the Y-axis and the mechanical limiter 100 limits rotation around the Z-axis (i.e. Rz). The mechanical limiter 100 includes an actuator 20 which moves in a direction 16 in the plane of the stator 10. The actuator 20 moves in direction 16 which is parallel to the Y-axis 14 along a guide or track 25. An elongate member 110 is fixedly attached to the actuator 20. A sleeve 120 which at least partly surrounds the elongate member 110 is fixedly attached to the substrate table WT. The sleeve 120 is slidable along the elongate member 110. In use, movement of the substrate table WT in the X-direction 12 results in the sleeve 120 sliding along the elongate member 110. If the substrate table WT moves in the Y-direction, the actuator 20 is also moved a corresponding amount in the Y-direction 14 so that the substrate table WT may move freely unhindered by the mechanical limiter 100. This is achieved by having a sensor for measuring the position of the actuator 20 with respect to the substrate table WT and which initiates the actuator 20 to follow the substrate table WT in the Y-direction. The substrate table WT can be moved by the second positioning device PW without interference from the mechanical limiter 100. Frictionless bearings such as air bearings may be used between the sleeve 120 and the elongate member 110. The mechanical limiter 100 may be provided with incremental or linear encoders 125, 127 to aid in alignment and control of the substrate table WT. Only one encoder is illustrated in FIG. 2. The encoder is of an interferometer type consisting of a sensor 125 attached to the sleeve 120 and a diffraction grating 127 attached to the elongate member 110. Other types of encoders, such as rotational potentiometers, can be used and the position in the Y-direction may also be measured. The position at which the encoders are fixed may also be different. Should the substrate table WT experience a rotational force about the Z-axis, engagement of the sleeve 120 and the elongate member 110 will substantially prevent rotation of the substrate table WT. Upon rotation of the substrate table WT around the Z-axis, each end of the sleeve 120 will come in contact on opposite sides of the elongate member 110. The amount of rotation of the substrate table WT about the Z-axis allowed before rotation is stopped by the mechanical limiter 100 may be adjusted by a choice of the length of the sleeve 120 in the elongate direction of the elongate member 110 and by a choice of difference in external dimension of the elongate member 110 and the internal dimension of the sleeve 120. Alternatively, the elongate member 110 and sleeve 120 may be attached such that some limited rotation relative to the actuator 20 or substrate table WT is possible. The mechanical limiter 100 may be designed to substantially prevent any rotation or may be designed to allow for rotation of up to 3xc2x0, 5xc2x0 or 10xc2x0. Software may be provided to limit the rotation around the Z-axis. However, mechanical solutions may also be provided as software may fail. Conduits 30 provide the substrate table WT with utilities. The conduits 30 may be attached between the substrate table WT and the actuator 20. In an alternative embodiment, the conduits 30 may be guided by the mechanical limiter 100 from the actuator 20 to the substrate table WT. In this way large mechanical loads on the conduits 30 can be substantially prevented as only one degree of freedom of the conduits is then required. The actuator 20 may be mounted on the track 25 and driven by a suitable device, such as a liner electric motor or a worm drive. Referring to FIG. 3, a mechanical limiter 200 includes at least one pair of crossed elongate arms 210, 220, 230. Each pair of crossed elongate arms are pivoted relative to each other at a median portion 211, 221, 231. A first pair 210 of the at least one pair of crossed elongate arms is an outer pair of elongate arms. An outer end 212 of one arm of the outer pair of arms 210 is rotatably attached to the substrate table WT. An outer end 216 of the other elongate arm of the pair 210 is in sliding engagement with a slot 214 in the substrate table WT. The slot 214 is parallel to the Y-axis 14. A second pair 220 of the at least one pair of crossed elongate arms is an outer pair of elongate arms. An outer end 222 of one arm of the outer pair of arms 220 is rotatably attached to the actuator 20. An outer end 226 of the other elongate arm of the pair 220 is in sliding engagement with a slot 224 in the actuator 20. The slot 224 is parallel to the slot 214 on the substrate table WT. Between the first pair 210 and the second pair 220 of crossed elongate arms, a third pair 230 of elongate arms is situated. The ends of the elongate arms of the first pair 210 and the second pair 220 not attached to the substrate table or actuator 20, are attached to ends of the elongate arms of the third pair 230. The invention also works with only a single pair of elongate arms in which case one end of each elongate arm will be attached to the actuator 20 and the other end to the substrate table WT. Alternatively only two pairs may be used, or any other number. In use, the mechanical limiter 200 is similar to the mechanical limiter 100 for movement in the Y-direction. For movement of the substrate table WT in the X-direction, the pairs of crossed elongate arms 210, 220, 230 pivot relative to each other in a scissor action to extend and retract. The ends 216, 226 engaged in slots 214 and 224 (which are parallel) allow this freedom to expand and contract and ensure that the limiter 200 can limit rotation. Dimensioning of the thickness of the elongate slots 214, 224 and the engagement portion of ends 216, 226 results in the desired degree of rotatability of the substrate table WT before limitation of rotation. The limiter 200, and the limiter 300 described below, may also have incremental or linear encoders attached to substrate table WT or the mechanical limiter 200, 300 (or the actuator in the case of the limiter 200) to measure the position of the substrate table WT and may have conduits 30 guided by the mechanical limiter 200, 300 to the substrate table WT. Referring to FIGS. 4a and 4b, a mechanical limiter 300 may be used in a lithographic apparatus having only one substrate table WT. The range of movement of the single substrate table WT in such an apparatus is small compared to the range of movement required of the substrate tables WT in an apparatus with dual substrate tables WT. Thus, the mechanical limiter 300 is more suited to an apparatus with only a single substrate table WT. The difference in the mechanical limiter 300 and the mechanical limiters 100 and 200 is that one end of the mechanical limiter 300 is fixed in a position relative to the stator 10 of the second positioning device PW rather than being movable in a direction of the plane of the stator 10. The required two degrees of freedom of the end of the mechanical limiter 300 attached to the substrate table WT is achieved by use of two four-bar mechanisms 301 and 302. These replace the elongate member 110 and slide 120 of the limiter 100. The first four-bar mechanism 301 includes of a first pair of elongate arms 310, 315 of equal length which are attached between the substrate table WT and a joining member 340. The first pair of elongate arms 310, 315 are pivotably attached at each end and the separation distance between their attachment portions on the substrate table WT and on the joining member 340 are equidistant such that the elongate arms 310, 315 always remain parallel. The second four-bar mechanism 302 includes a second pair of elongate arms 320, 325 of equal length. The second pair of elongate arms 320, 325 are attached at one end to the joining member 340 and at another end fixedly in relation to the stator 10 on a platform 330. Again, the ends of the second pair of arms 320, 325 are rotatably fixed equidistant from each other at each end. The first arm 310 of the first pair of arms and the first arm 320 of the second pair of arms are pivoted about the same point on the joining member 340. However, the arms 310, 320 may pivot at different positions on the joining member 340. The positioning of the ends of the elongate arms and the fact that both of the first pair of arms are the same length and that both of the second pair of arms are the same length means that when the substrate table WT moves the substrate table WT will be constrained in its rotation about the Z-axis by the mechanical limiter 300. If a wider range of rotation is required, the platform 330 may be attached to an actuator (i.e. actuator 20) such that a larger range of motion of the substrate table WT is possible. While specific embodiments of the invention have been described above, it would be appreciated that the invention may be practiced otherwise than as described. The description is not intended to limit the invention.
summary
claims
1. An electron beam apparatus comprising:(a) a beam source to generate a radiation beam; (b) a photocathode comprising an electron-emitting material composed of activated alkali halide having a minimum electron emission energy level that is less than 75% the minimum electron emission energy level of the un-activated alkali halide, whereby the electron-emitting material emits electrons when the radiation beam is incident thereon; (c) electron beam elements to form an electron beam from the emitted electrons and direct the electron beam onto a workpiece; and (d) a support to support the workpiece. 2. An apparatus according to claim 1 wherein the electron-emitting material is composed of activated alkali halide having a minimum electron emission energy level that is less than 50% of the minimum electron emission energy level of the un-activated alkali halide. 3. An apparatus according to claim 1 wherein the activated alkali halide comprises a minimum electron emission energy level that is less than about 5 eV. 4. An apparatus according to claim 1 wherein the un-activated alkali halide absorbs a first level of a radiation capable of creating color centers to form the activated alkali halide, and the activated alkali halide absorbs a second level of the same radiation to emit electrons. 5. An apparatus according to claim 1 wherein the activated alkali halide comprises an interior region having a first alkali concentration, and a surface region having a second alkali concentration that is higher than the first alkali concentration. 6. An apparatus according to claim 5 wherein the second alkali concentration is higher than the first alkali concentration by at least a fraction of a monolayer of alkali atoms. 7. An apparatus according to claim 1 wherein the alkali halide comprises cesium halide. 8. An apparatus according to claim 7 wherein the cesium halide comprises cesium bromide or cesium iodide. 9. An apparatus according to claim 1 wherein the beam source comprises (i) a diode-pumped laser or argon-ion laser, and (ii) a frequency multiplier crystal. 10. An apparatus according to claim 1 wherein the beam source comprises a laser having a wavelength of from about 190 to about 532 nm. 11. An electron beam pattern generator to generate a pattern of electrons on a workpiece, the pattern generator comprising:(a) a laser beam source to generate a laser beam having a wavelength of from about 190 to about 532 nm; (b) a beam modulator to modulate the intensity of the laser beam according to a pattern and direct the modulated laser beam onto a photocathode; (c) a photocathode comprising an electron-emitting material composed of activated alkali halide having a minimum electron emission energy that is less than about 5 eV, such that the electron-emitting material emits electrons when the modulated laser beam is incident thereon; (d) electron beam elements to form an electron beam from the emitted electrons and direct the electron beam onto a workpiece; and (e) a support to support the workpiece. 12. An electron beam inspection apparatus to inspect a workpiece with electron beams, the apparatus comprising:(a) a beam source to generate a laser beam having a wavelength of from about 190 to about 532 nm; (b) a photocathode comprising an electron-emitting material composed of activated alkali halide having an electron emission minimum energy that is less than about 5 eV, such that the electron-emitting material emits electrons when the laser beam is incident thereon; (c) electron beam elements to form an electron beam from the emitted electrons and direct the electron beam onto a workpiece; (d) a support to support the workpiece; and (e) an electron detector to detect electrons backscattered from the workpiece to inspect the workpiece. 13. An electron generating method comprising:(a) providing an electron-emitting material composed of alkali halide; (b) activating the alkali halide to form an activated alkali halide having a minimum electron emission energy level that is less than 75% of the minimum electron emission energy level of the un-activated alkali halide; and (c) directing a radiation beam on the activated alkali halide, the radiation beam having photons with an energy level that is higher than the minimum electron emission energy level of the activated alkali halide to cause electrons to be emitted therefrom. 14. A method according to claim 13 wherein (b) comprises directing the radiation beam onto the alkali halide material for a sufficient time period that the alkali halide develops an interior region having a first alkali concentration and a surface region having a second alkali concentration. 15. A method according to claim 14 comprising directing the second radiation onto the alkali halide for from about 120 to about 240 minutes. 16. A method according to claim 13 wherein (c) comprises modulating the radiation beam according to a pattern to generate modulated electron beams. 17. A method according to claim 13 further comprising:(d) detecting electrons backscattered from the workpiece to inspect the workpiece. 18. A method of manufacturing a photocathode for an electron beam apparatus, the method comprising:(a) providing a substratum in a process zone; (b) evacuating the process zone; (c) evaporating an alkali halide in the process zone to deposit alkali halide on the workpiece; and (d) activating the deposited alkali halide to have a minimum electron emission energy level that is less than half the electron emission minimum electron emission energy level of the un-activated alkali halide by directing radiation onto the deposited alkali halide for a sufficient time period to develop an interior region having a first alkali concentration and a surface region having a second alkali concentration that is higher than the first alkali concentration. 19. A method according to claim 18 wherein the radiation comprises a laser beam having a wavelength of from about 190 to about 532 nm. 20. A method according to claim 18 wherein (c) comprises evaporating an alkali halide material comprising cesium bromide or cesium iodide. 21. An electron beam pattern generator according to claim 11 wherein the electron-emitting material is composed of activated alkali halide having a minimum electron emission energy level that is less than 50% of the minimum electron emission energy level of the un-activated alkali halide. 22. An electron beam pattern generator according to claim 11 wherein the activated alkali halide comprises an interior region having a first alkali concentration, and a surface region having a second alkali concentration that is higher than the first alkali concentration. 23. An electron beam pattern generator according to claim 11 wherein the alkali halide comprises cesium halide. 24. An electron beam pattern generator according to claim 23 wherein the cesium halide comprises cesium bromide or cesium iodide. 25. An electron beam pattern generator according to claim 11 wherein the laser beam source comprises (i) a diode-pumped laser or argon-ion laser, and (ii) a frequency multiplier crystal. 26. An electron beam inspection apparatus according to claim 12 wherein the electron-emitting material is composed of activated alkali halide having a minimum electron energy level that is less than 50% of the minimum electron emission energy level of the un-activated alkali halide. 27. An electron beam inspection apparatus according to claim 12 wherein the activated alkali halide comprises an interior region having a first alkali concentration, and a surface region having a second alkali concentration that is higher than the first alkali concentration. 28. An electron beam inspection apparatus according to claim 12 wherein the alkali halide comprises cesium halide. 29. An electron beam inspection apparatus according to claim 28 wherein the cesium halide comprises cesium bromide or cesium iodide. 30. An electron beam inpsection apparatus according to claim 12 wherein the laser beam source comprises (i) a diode-pumped laser or argon-ion laser, and (ii) a frequency multiplier crystal.
053655559
abstract
A system for measuring water level includes a reactor pressure vessel containing a core and steam separator assembly, with the vessel being filled with water to a nominal level above the core. A reference leg contains a column of water having a reference level disposed above the nominal level, and a first variable leg has a first tap disposed in the vessel below the reference and nominal levels. A first monitor is disposed between the reference leg and the first leg for determining differential pressure therebetween to indicate level of the water in the vessel above the first tap. A second variable leg includes a second tap in the vessel below the first tap, and a second monitor is disposed between the first and second legs for determining differential pressure therebetween to indicate level of water in the vessel between the first and second taps when the water level falls below the first tap.
description
The present application is a continuation of U.S. patent application Ser. No. 15/634,408 filed Jun. 27, 2017, which claims the benefit of priority to U.S. Provisional Application No. 62/355,057 filed Jun. 27, 2016. The foregoing applications are incorporated herein by reference in their entireties. The present invention generally relates to storage of nuclear fuel, and more particularly to an improved nuclear fuel storage rack system for use in a fuel pool in a nuclear generation plant. A conventional free-standing, high density nuclear fuel storage rack is a cellular structure typically supported on a set of pedestals from the floor or bottom slab of the water-filled spent fuel pool. The bottom extremity of each fuel storage cell is welded to a common baseplate which serves to provide the support surface for the upwardly extending vertical storage cells and stored nuclear fuel therein. The cellular region comprises an array of narrow prismatic cavities formed by the cells which are each sized to accept a single nuclear fuel assembly comprising a plurality of new or spent nuclear fuel rods. The term “active fuel region” denotes the vertical space above the baseplate within the rack where the enriched uranium is located. High density fuel racks used to store used nuclear fuel employ a neutron absorber material to control reactivity. The commercially available neutron absorbers are typically in a plate or sheet form and are either metal or polymer based. The polymeric neutron absorbers commonly used in the industry were sold under trade names Boraflex and Tetrabor, with the former being the most widely used material in the 1980s. The neutron absorber panels have been typically installed on the four walls of the storage cells encased in an enveloping sheathing made of thin gage stainless steel attached to the cell walls in the active fuel region. Unfortunately, the polymeric neutron absorbers have not performed well in service. Widespread splitting and erosion of Boraflex and similar degradation of Tetrabor have been reported in the industry, forcing the plant owners to resort to reducing the density of storage (such as a checkered board storage arrangement) thereby causing an operational hardship to the plant. A neutron absorber apparatus is desired which can be retrofit in existing fuel racks suffering from neutron absorber material degradation in order to fully restore reactivity reduction capacity of the storage cells. Embodiments of the present invention provide a neutron absorber insert system which can be readily added in situ to existing storage cells of the fuel rack having degraded neutron absorbers and reduced reactivity reduction capacity. The system comprises a plurality of neutron absorber apparatuses which may be in the form of absorber inserts configured for direct insertion into and securement to the fuel storage cells. The inserts have a low-profile small and thin cross sectional footprint which does not significantly reduce the storage capacity of each storage cell. A fuel assembly may be inserted into a central longitudinally-extending cavity of the insert and removed therefrom without first removing the insert. The inserts include a locking feature which is automatically deployed and secures the insert in the cell, as further described herein. Advantageously, the absorber insert may utilize an available edge surface on an existing storage tube of the fuel rack which can be engaged by the locking feature of the absorber tube. This eliminates the need for modifying the existing fuel rack in order to accommodate the insert, thereby saving time and expense. In one embodiment, the edge surface may be part of an existing neutron absorber sheathing structure on the fuel storage tube. The inserts may advantageously be deployed in the existing fuel rack storage cells via remote handling equipment such as cranes while the rack remains submerged underwater in the spent fuel pool. In one aspect, a neutron absorber apparatus for a nuclear fuel storage system includes: a fuel rack comprising a vertical longitudinal axis and plurality of longitudinally-extending storage cells, each cell comprising a plurality of cell sidewalls defining a cell cavity configured for storing nuclear fuel therein; a sheath integrally attached to a first cell sidewall of a first cell and defining a sheathing cavity configured for holding a neutron absorber material; an absorber insert comprising plural longitudinally-extending neutron absorber plates each comprising a neutron absorber material, the insert disposed in the first cell; and an elastically deformable locking protrusion disposed on one of the absorber plates, the locking protrusion resiliently movable between an outward extended position and an inward retracted position; the locking protrusion lockingly engaging the sheath to axially restrain the insert and prevent removal of the insert from the first cell. In another aspect, a neutron absorber apparatus for a nuclear fuel storage system includes: a fuel rack comprising a vertical longitudinal axis and plurality of longitudinally-extending storage tubes each defining a cell, each storage tube comprising a plurality of tube sidewalls defining a primary cavity; an absorber insert insertably disposed in the primary cavity of a first storage tube, the absorber insert comprising a plurality of absorber plates arranged to form a longitudinally-extending neutron absorber tube having an exterior and an interior defining a secondary cavity configured for storing a nuclear fuel assembly therein, each absorber plate formed of a neutron absorber material; an upper stiffening band extending perimetrically around an upper end of the absorber tube, the upper stiffening band attached to the exterior of the absorber tube and protruding laterally outwards beyond the absorber plates to engage the tube sidewalls of the first storage tube; a lower stiffening band extending perimetrically around a lower end of the absorber tube and disposed at least partially inside the secondary cavity, the lower stiffening band attached to the interior of the absorber tube; wherein the absorber plates of the insert assembly are spaced laterally apart from the tube sidewalls of the first storage tube by the upper stiffening band forming a clearance gap therebetween. In another aspect, a neutron absorber apparatus for a nuclear fuel storage system includes: a fuel rack comprising a plurality of longitudinally-extending storage cells, each cell comprising a plurality of cell walls defining a cell cavity for storing nuclear fuel; a longitudinally-extending absorber tube insertably disposed in a first cell of the fuel rack and having an exterior and an interior, the absorber tube comprising: an elongated chevron-shaped first absorber plate comprising a first section and a second section angularly bent to the first section along a bend line of the first absorber plate; an elongated chevron-shaped second absorber plate comprising a third section and a fourth section angularly bent to the third section along a bend line of the second absorber plate; an upper stiffening band extending perimetrically around upper ends of the first and second absorber plates and coupling the first and second absorber plates together. Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. All drawings are schematic and not necessarily to scale. Parts shown and/or given a reference numerical designation in one figure may be considered to be the same parts where they appear in other figures without a numerical designation for brevity unless specifically labeled with a different part number and described herein. The features and benefits of the invention are illustrated and described herein by reference to exemplary embodiments. This description of exemplary embodiments is intended to be read in connection with the accompanying drawings, which are to be considered part of the entire written description. Accordingly, the disclosure expressly should not be limited to such exemplary embodiments illustrating some possible non-limiting combination of features that may exist alone or in other combinations of features. Furthermore, all features and designs disclosed herein may be used in combination even if not explicitly described as such. In the description of embodiments disclosed herein, any reference to direction or orientation is merely intended for convenience of description and is not intended in any way to limit the scope of the present invention. Relative terms such as “lower,” “upper,” “horizontal,” “vertical,”, “above,” “below,” “up,” “down,” “top” and “bottom” as well as derivative thereof (e.g., “horizontally,” “downwardly,” “upwardly,” etc.) should be construed to refer to the orientation as then described or as shown in the drawing under discussion. These relative terms are for convenience of description only and do not require that the apparatus be constructed or operated in a particular orientation. Terms such as “attached,” “affixed,” “connected,” “coupled,” “interconnected,” and similar refer to a relationship wherein structures are secured or attached to one another either directly or indirectly through intervening structures, as well as both movable or rigid attachments or relationships, unless expressly described otherwise. It will be appreciated that any numerical ranges that may be described herein shall be understood to include the lower and upper numerical terminus values or limits of the cited range, and any numerical values included in the cited range may serve as the terminus values. Referring to FIGS. 1-5, a nuclear facility which may be a nuclear generating plant includes a fuel pool 40 according to the present disclosure configured for storing a plurality of nuclear fuel racks 100. The fuel pool 40 may comprise a plurality of vertical sidewalls 41 rising upwards from an adjoining substantially horizontal bottom base wall or slab 42 (recognizing that some slope may intentionally be provided in the upper surface of the base slab for drainage toward a low point if the pool is to be emptied and rinsed/decontaminated at some time and due to installation tolerances). The base slab 42 and sidewalls 41 may be formed of reinforced concrete in one non-limiting embodiment. The fuel pool base slab 42 may be formed in and rest on the soil sub-grade 26, the top surface of which defines grade G. In this embodiment illustrated in the present application, the sidewalls are elevated above grade. The base slab 42 may be located at grade G as illustrated, below grade, or elevated above grade. In other possible embodiments contemplated, the base slab 42 and sidewalls 41 may alternatively be buried in sub-grade 26 which surrounds the outer surfaces of the sidewalls. Any of the foregoing arrangements or others may be used depending on the layout of the nuclear facility and does not limit of the invention. In one embodiment, the fuel pool 40 may have a rectilinear shape in top plan view. Four sidewalls 41 may be provided in which the pool has an elongated rectangular shape (in top plan view) with two longer opposing sidewalls and two shorter opposing sidewalls (e.g. end walls). Other configurations of the fuel pool 40 are possible such as square shapes, other polygonal shapes, and non-polygonal shapes. The sidewalls 41 and base slab 42 of the fuel pool 40 define an upwardly open well or cavity 43 configured to hold cooling pool water W and the plurality of submerged nuclear fuel racks 100 each holding multiple nuclear fuel bundles or assemblies 28 (a typical one shown in phantom view seated in a fuel rack cell in FIG. 5). Each fuel assembly 28 contains multiple individual new or spent uranium fuel rods. Fuel assemblies are further described in commonly assigned U.S. patent application Ser. No. 14/413,807 filed Jul. 9, 2013, which is incorporated herein by reference in its entirety. Typical fuel assemblies 28 for a pressurized water reactor (PWR) may each hold over 150 fuel rods in 10×10 to 17×17 fuel rod grid arrays per assembly. The assemblies may typically be on the order of approximately 14 feet high weighing about 1400-1500 pounds each. The fuel racks 100 storing the fuel assemblies are emplaced on the base slab 42 in a high-density arrangement in the horizontally-abutting manner as further described herein. The fuel pool 40 extends from an operating deck 22 surrounding the fuel pool 40 downwards to a sufficient vertical depth D1 to submerge the fuel assemblies 28 in the fuel rack (see, e.g. FIG. 6) beneath the surface level S of the pool water W for proper radiation shielding purposes. The substantially horizontal operating deck 22 that circumscribes the sidewalls 41 and pool 40 on all sides in one embodiment may be formed of steel and/or reinforced concrete. In one implementation, the fuel pool may have a depth such that at least 10 feet of water is present above the top of the fuel assembly. Other suitable depths for the pool and water may be used of course. The surface level of pool water W (i.e. liquid coolant) in the pool 40 may be spaced below the operating deck 22 by a sufficient amount to prevent spillage onto the deck during fuel assembly loading or unloading operations and to account to seismic event. In one non-limiting embodiment, for example, the surface of the operating deck 22 may be at least 5 feet above the maximum 100 year flood level for the site in one embodiment. The fuel pool 40 extending below the operating deck level may be approximately 40 feet or more deep (e.g. 42 feet in one embodiment). The fuel pool is long and wide enough to accommodate as many fuel racks 100 and fuel assemblies 28 stored therein as required. There is sufficient operating deck space around the pool to provide space for the work crew and for staging necessary tools and equipment for the facility's maintenance. There may be no penetrations in the fuel pool 40 within the bottom 30 feet of depth to prevent accidental draining of water and uncovering of the fuel. In some embodiments, a nuclear fuel pool liner system may be provided to minimize the risk of pool water leakage to the environment. The liner system may include cooling water leakage collection and detection/monitoring to indicate a leakage condition caused by a breach in the integrity of the liner system. Liner systems are further described in commonly owned U.S. patent application Ser. No. 14/877,217 filed Oct. 7, 2015, which is incorporated herein by reference in its entirety. The liner system in one embodiment may comprise one or more liners 60 attached to the inner surfaces 63 of the fuel pool sidewalls 41 and the base slab 42. The inside surface 61 of liner is contacted and wetted by the fuel pool water W. The liner 60 may be made of any suitable metal of suitable thickness T2 which is preferably resistant to corrosion, including for example without limitation stainless steel, aluminum, or other. Typical liner thicknesses T2 may range from about and including 3/16 inch to 5/16 inch thick. Typical stainless steel liner plates include ASTM 240-304 or 304L. In some embodiments, the liner 60 may be comprised of multiple substantially flat metal plates or sections which are hermetically seal welded together via seal welds along their contiguous peripheral edges to form a continuous liner system completely encapsulating the sidewalls 41 and base slab 42 of the fuel pool 40 and impervious to the egress of pool water W. The liner 60 extends around and along the vertical sidewalls 41 of the fuel pool 40 and completely across the horizontal base slab 42 to completely cover the wetted surface area of the pool. This forms horizontal sections 60b and vertical sections 60a of the liner to provide an impervious barrier to out-leakage of pool water W from fuel pool 40. The horizontal sections of liners 60b on the base slab 42 may be joined to the vertical sections 60a along perimeter corner seams therebetween by hermetic seal welding. The liner 60 may be fixedly secured to the base slab 42 and sidewalls 41 of the fuel pool 40 by any suitable method such as fasteners. With continuing reference to FIGS. 1-5, the fuel rack 100 is a cellular upright module or unit. Fuel rack 100 may be a high density, tightly packed non-flux type rack as illustrated which is designed to be used with fuel assemblies that do not require the presence of a neutron flux trap between adjacent cells 110. Thus, the inclusion of neutron flux traps (e.g. gaps) in fuel racks when not needed is undesirable because valuable fuel pool floor area is unnecessarily wasted. Of course, both non-flux and flux fuel rack types may be stored side by side in the same pool using the seismic-resistant fuel storage system according to the present disclosure. The invention is therefore not limited to use of any particular type of rack. Fuel rack 100 defines a vertical longitudinal axis LA and comprises a grid array of closely packed open cells 110 formed by a plurality of adjacent elongated storage tubes 120 arranged in parallel axial relationship to each other. The rack comprises peripherally arranged outboard tubes 120A which define a perimeter of the fuel rack and inboard tubes 120B located between the outboard tubes. Tubes 120 are coupled at their bottom ends 114 to a planar top surface of a baseplate 102 and extend upwards in a substantially vertical orientation therefrom. In this embodiment, the vertical or central axis of each tube 120 is not only substantially vertical, but also substantially perpendicular to the top surface of the baseplate 102. In one embodiment, tubes 120 may be fastened to baseplate 102 by welding and/or mechanical coupling such as bolting, clamping, threading, etc. Tubes 120 include an open top end 112 for insertion of fuel assemblies, bottom end 114, and a plurality of longitudinally extending vertical sidewalls 116 (“cell walls”) between the ends and defining a tube or cell height H1. Each tube 120 defines an internal cell cavity 118 extending longitudinally between the top and bottom ends 112, 114. In the embodiment shown in FIG. 2A-B, four tube sidewalls 116 arranged in rectilinear polygonal relationship are provided forming either a square or rectangular tube 120 in lateral or transverse cross section (i.e. transverse or orthogonal to longitudinal axis LA) in plan or horizontal view (see also FIG. 3). Cells 110 and internal cavities 118 accordingly have a corresponding rectangular configuration in lateral cross section. The top ends of the tubes 120 are open so that a fuel assembly can be slid down into the internal cavity 118 formed by the inner surfaces of the tube sidewalls 116. Each cell 110 and its cavity 118 are configured for holding only a single nuclear fuel assembly 28. Tubes 120 may be made of any suitable preferably corrosion resistant metal, such as without limitation stainless steel or others. Baseplate 102 may be made of a similar or different corrosion resistant metal. It will be appreciated that each tube 120 can be formed as a single unitary structural component that extends the entire desired height H1 or can be constructed of multiple partial height tubes that are vertically stacked and connected together such as by welding or mechanical means which collectively add up to the desired height H1. It is preferred that the height H1 of the tubes 120 be sufficient so that the entire height of a fuel assembly may be contained within the tube when the fuel assembly is inserted into the tube. The top ends 112 of tubes 120 may preferably but not necessarily terminate in substantially the same horizontal plane (defined perpendicular to longitudinal axis LA) so that the tops of the tube are level with each other. The baseplate 102 at the bottom ends 114 of the tubes defines a second horizontal reference plane HR. As best shown in FIGS. 2A-B, tubes 120 are geometrically arranged atop the baseplate 102 in rows and columns along the Z-axis and X-axis respectively. Any suitable array size including equal or unequal numbers of tubes in each row and column may be provided depending on the horizontal length and width of the pool base slab 42 and number of fuel racks 100 to be provided. In some arrangements, some or all of the fuel racks 100 may have unequal lateral width and lateral length as to best make use of a maximum amount of available slab surface area as possible for each installation. For convenience of reference, the outward facing sidewalls 116 of the outboard tubes 120A may be considered to collectively define a plurality of lateral sides 130 of the fuel rack 100 extending around the rack's perimeter as shown in FIGS. 2A-B. Referring to FIGS. 1-5, each fuel rack 100 comprises a plurality of legs or pedestals 200 which support rack from the base slab 42 of the fuel pool 40. Pedestals 200 each have a preferably flat bottom end 204 to engage the pool base slab 42 and a top end 202 fixedly attached to the bottom of the baseplate 102. The pedestals 200 protrude downwards from baseplate 102. This elevates the baseplates 102 of the rack off the base slab 42, thereby forming a gap therebetween which defines a bottom flow plenum P beneath rack 100. The plenum P allows cooling water W in the pool to create a natural convective circulation flow path through each of the fuel storage tubes 120 (see e.g. flow directional arrows in FIG. 5). A plurality of flow holes 115 are formed in the rack through baseplate 102 in a conventional manner to allow cooling water to flow upwards through the cavity 118 of each tube 120 and outward through the open top ends 112 of the tubes. Commonly owned U.S. patent application Ser. No. 14/367,705 filed Jun. 20, 2014 shows fuel rack baseplates with flow holes, and is incorporated herein by reference in its entirety. The pool water W flowing through the tubes is heated by the nuclear fuel in fuel assemblies, thereby creating the motive force driving the natural thermal convective flow scheme. Referring now then to FIGS. 3 and 5, flow holes 115 create passageways from below the base plate 102 into the cells 110 formed by the tubes 120. Preferably, a single flow hole 115 is provided for each cell 110, however, more may be used as needed to create sufficient flow through the tubes. The flow holes 115 are provided as inlets to facilitate natural thermosiphon flow of pool water through the cells 110 when fuel assemblies having a heat load are positioned therein. More specifically, when heated fuel assemblies are positioned in the cells 110 in a submerged environment, the water within the cells 110 surrounding the fuel assemblies becomes heated, thereby rising due to decrease in density and increased buoyancy creating a natural upflow pattern. As this heated water rises and exits the cells 110 via the tube open top ends 112 (see FIG. 1), cooler water is drawn into the bottom of the cells through the flow holes 115. This heat induced water flow and circulation pattern along the fuel assemblies then continues naturally to dissipate heat generated by the fuel assemblies. Pedestals 200 may therefore have a height selected to form a bottom flow plenum P of generally commensurate height to ensure that sufficient thermally-induced circulation is created to adequately cool the fuel assembly. In one non-limiting example, the height of the plenum P may be about 2 to 2.5 inches (including the listed values and those therebetween of this range). To facilitate lateral cross flow of cooling water between cells 110 in the fuel rack 100, a minimum of two lateral flow holes 115A may be provided proximate to the lower or bottom end 114 of each tube 120 (see, e.g. FIGS. 4 and 5). Each hole defines top, bottom, and side edges in tube material. In one embodiment, the flow holes 115A may be formed by a punching operation. Pedestals 200 may have any suitable configuration or shape and be of any suitable type. Each fuel rack 100 may include a plurality of peripheral pedestals 200 spaced apart and arranged along the peripheral edges and perimeter of the baseplate 102, and optionally one or more interior pedestals if required to provide supplemental support for the inboard fuel assemblies and tubes 120B. In one non-limiting embodiment, four peripheral pedestals 200 may be provided each of which is located proximate to one of the four corners 206 of the baseplate. Additional peripheral pedestals may of course be provided as necessary between the corner pedestals on the perimeter of the baseplate. The pedestals are preferably located as outboard as possible proximate to the peripheral edges 208 of the baseplates 102 of each fuel rack or module to give maximum rotational stability to the modules. With continuing reference to FIGS. 1-5, each fuel rack storage tube 120 in some embodiments may include a longitudinally-extending absorber sheath 300 disposed on one or more tube sidewalls 116. The sheath 300 extends at least over the active zone or height of the fuel rack tubes 120 where the fuel is positioned in the fuel rack 100 (see, e.g. FIG. 5). Sheath 300 has a raised profile or projection from the tube sidewall 116. Sheath 300 has a vertically elongated and generally flat body including top end 310 defining a top lip or edge, bottom end 311 defining a bottom lip or edge 436, and a sidewall 312 extending axially between the top and bottom ends. The top and bottom ends 310, 311 terminate at a point spaced apart from the top and bottom ends 112, 114 of the storage tube 120 as shown. The sheath 300 may be attached to the tube sidewall 116 via welding or another suitable technique. Sheath sidewall 312 is spaced laterally apart from the sidewall 116 of the tube 120 such that each “picture frame” sheath 300 forms an envelope defining a sheathing cavity 301 between the sheath and tube sidewall which is configured for receiving neutron absorber material 302 therein (e.g. in sheet or panel form as represented in FIGS. 4 and 5). The sheath body is therefore configured and laterally offset from the tube sidewall 116 by a distance commensurate with the dimensions and thickness of the absorber sheet or panel inserted therein. The boron-containing material or “poison” may be Boraflex, Tetrabor, (both previously mentioned) or another. In some existing used fuel rack installations, the absorber material 302 may be in a degraded condition thereby requiring augmentation with a neutron absorber apparatus disclosed herein to restore fuel neutron reactivity control to the fuel rack. FIGS. 6-13 show a neutron absorber apparatus according to the present disclosure. The apparatus may be in the form of a shaped neutron absorber insert 400 configured to be slidably insertable into one of the tubes 120 and cells 110 of the fuel rack 110 shown in FIGS. 1-5 discussed above. Absorber insert 400 includes a plurality of longitudinally-extending neutron absorber walls or plates 402 each comprising a neutron absorber material operable to control reactivity of the fuel stored in the fuel rack cells. The absorber plates 402 may be made of a suitable boron-containing metallic poison material such as without limitation borated aluminum. In some embodiments, without limitation, the absorber plates 402 may be formed of a metal-matrix composite material, and preferably a discontinuously reinforced aluminum/boron carbide metal matrix composite material, and more preferably a boron impregnated aluminum. One such suitable material is sold under the tradename METAMIC™. Other suitable borated metallic materials however may be used. The boron carbide aluminum matrix composite material of which the absorption plates 402 are constructed includes a sufficient amount of boron carbide so that the absorption sheets can effectively absorb neutron radiation emitted from a spent fuel assembly, and thereby shield adjacent spent fuel assemblies in a fuel rack from one another. The absorption plates may be constructed of an aluminum boron carbide metal matrix composite material that is about 20% to about 40% by volume boron carbide. Of course, other percentages may also be used. The exact percentage of neutron absorbing particulate reinforcement which is in the metal matrix composite material, in order to make an effective neutron absorber for an intended application, will depend on a number of factors, including the thickness (i.e., gauge) of the absorption plates 402, the spacing between adjacent cells within the fuel rack, and the radiation levels of the spent fuel assemblies. In one configuration, absorber insert 400 may comprise an assembly formed by two bent and chevron-shaped angled plates (designated 402A and 402B for convenience of reference), which are held together by metallic upper and lower stiffening bands 404, 406. Each plate 402A, 402B has the shape of a common structural angle sized to fit within the interior dimensions of each fuel rack storage tube 120/cell 110. Absorber plates 402A, 402B may each be formed of a generally flat or planar plate or sheet of neutron absorber material which is mechanically bent along a linear longitudinal bend line BL extending the plate's length L2 to form first and second half-sections 408, 410. The bend line BL may be located midway between the two side edges 412 of the plates 402A or 402B so that each half-section 408, 410 has an equal width W2. In other possible embodiments, the half-sections may have unequal widths. Half-sections 408 and 410 may be arranged mutually perpendicular to each other at a 90-degree angle around the bend line BL in one embodiment as shown. When the absorber plates 402A, 402B are fastened together via the stiffening bands 404, 406, they collectively form a tubular box frame comprising a four-sided rectilinear absorber tube 424 having a vertical centerline IC and defining an exterior surface 418 and interior surface 420. Interior surface 420 in turn defines a longitudinally-extending and completely open central cavity 422 configured for insertably receiving and holding a nuclear fuel assembly 28 therein (typical fuel assembly shown in FIG. 5). Cavity 422 extends from upper end 414 to lower end 416 of the absorber tube 424. The ends 414 and 416 of the tube are open. Absorber tube 424 and concomitantly cavity 422 may have a square cross sectional shape in one embodiment as shown. Rectangular or other cross sectional tube and cavity shapes may be used in some embodiments depending on the cross sectional shape of the fuel storage tubes 120. The mating longitudinal edges 426 of the absorber tube plates 402A and 402B may laterally spaced apart in some embodiments forming an axially extending slot 412 for the entire length of the absorber tube assembly (see, e.g. FIG. 6). The slot width is fixed by the upper and lower stiffening bands 404, 406 to which the absorber plates are fastened. In other embodiments, the longitudinal edges 426 of the absorber plates 402A, 402B may be abutted without any appreciable gap. Upper and lower stiffening bands 404, 406 may be annular ring-like structures having a complementary configuration to the absorber tube 424. Stiffening bands 404, 406 may have a square configuration in the non-limiting illustrated embodiment. The upper and lower bands are attached to the upper and lower extremities of the absorber tube plates 402A, 402B, respectively. Methods used to secure the bands 404, 406 to the upper and lower ends 414, 416 of the plates include for example without limitation welding, riveting, threaded fasteners, or other techniques. The stiffening bands may be made of a corrosion resistant metal, such as stainless steel in one embodiment. Referring to FIGS. 6-10, the upper stiffening band 404 extends perimetrically around the upper end 414 of the absorber tube 424. The upper stiffening band 404 is sized to closely fit inside the upper region of the fuel storage cell 110/tube 120 with a very small clearance between interior surfaces of the fuel rack storage tube sidewalls 116 and the band, thereby giving the absorber tube 424 structural rigidity and rotational fixity of position in the storage cell at the upper end of the absorber tube. In one embodiment, the upper stiffening band is preferably attached to the exterior surfaces 418 of the absorber tube plates 402A, 402B at the upper end 414 of absorber tube 424. The upper stiffening band may be disposed precisely at the upper end 414 of absorber tube 424 as illustrated, or in other embodiments may be proximate to but spaced vertically downwards apart from the upper end 414. In either case, upper stiffening band 404 is preferably located at an elevation at least above the top end 310 of the absorber sheath 300 on storage tube 120 to prevent interference with the sheath when inserting the absorber tube into the fuel storage cell 110. Upper stiffening band 404 projects laterally and transversely outwards from and beyond the exterior of the absorber tube 424 to engage the sidewalls 116 of the storage tube. When the absorber tube 424 is installed in one of the fuel rack cells 110 as shown in FIG. 5, the outwards projection of upper stiffening band 404 laterally spaces the absorber tube 424 apart from the interior cell side walls 116. This creates a clearance gap G1 between the exterior surfaces 418 of the absorber tube 424 (formed by tube absorber plates 402A, 402B) and interior surfaces of the cells 110 (formed by the sidewalls 116 of the fuel storage tubes 120). Gap G1 is preferably sized commensurate to the lateral projection depth D2 of the sheaths 300 on the fuel storage tubes 120 to receive the sheaths in the gap when installing the absorber tube 424 in the fuel storage cell 110. This allows the absorber tube 424 to be slideably inserted into the fuel storage cell 110 without interference from the projection of the sheaths 300 outwards from the sidewalls 116 of the storage tube 120 (see, e.g. FIG. 5). Because the sheaths 300 have a longitudinal length which terminates short of the upper and lower ends of the fuel storage tubes 120 as shown in FIG. 4, the upper stiffening band 404 may be fully seated inside the upper end of the storage tube without interference from the sheath (see, e.g. FIG. 9). To further avoid interference with the sheaths 300 when the absorber tube 424 is slid into the fuel storage tube 120 through the open top end 112 of the storage tube, the lower stiffening band 406 is instead mounted in the interior or cavity 422 of the absorber tube in one embodiment as best shown in FIG. 10. Lower stiffening band 406 extends perimetrically around the lower end 416 of the absorber tube 424 in cavity 422. The lower stiffening band provides structure rigidity and rotationally fixity in position to the lower end portion of the absorber tube 424 when seated in the fuel storage cell 110. Lower stiffening band 406 may be completely recessed inside the absorber tube 424 within central cavity 422 wherein the lower end of the tube 424 engages the baseplate 102 of the fuel rack when the absorber insert is fully inserted therein. In alternative embodiments, the lower stiffening band may have an extended length and protrude downwards beyond the lower end 416 of the absorber tube 424 to engage the baseplate 102. If the storage tube 120 has optional lateral flow holes 115A as shown in FIGS. 4 and 5, matching flow holes (not shown) may be provided at corresponding locations in the lower stiffening band 406. When the absorber tube 424 is fully seated in the storage tube 120, the flow holes in absorber tube would become concentrically aligned with the lateral flow holes 115A of the storage tube to preserve fuel pool cooling water cross flow between cells 110. According to another aspect, the absorber tube 424 may include one or more axial restraints to lock and axially fixate the tube in longitudinal position within the storage cell 110 of the fuel rack 100. Referring to FIGS. 6-11, the axial restraints in one non-limiting embodiment may be formed by elastically deformable locking protrusions comprised of metal leaf spring clips 430. Spring clips 430 each have an elongated body formed of corrosion resistant spring steel. Clips 430 include a lower fixed end portion 432 rigidly attached to the exterior surface 418 of the absorber tube 424 and an opposite resiliently movable cantilevered upper free-end locking portion 434. Fixed end portion 432 may be substantially flat and fixedly attached to absorber tube plates 402A, 402B by any suitable means, such as without limitation welding, riveting, or fasteners in some embodiments. Locking portion 434 extends upwardly from fixed end portion 432 and is obliquely angled thereto forming a space between the locking portion and the absorber tube 424. Locking portion 434 thus projects laterally outwards from the absorber tube 424 (i.e. absorber plates 402A, 402B). When the absorber tube 424 is installed in the fuel rack storage tube 120, locking portion 434 is also obliquely angled to the vertical longitudinal axis LA of the fuel rack (identified in FIG. 2). The locking spring clips 430 are positioned on the lower half of absorber tube 424 and arranged to engage an available edge disposed on the lower half of the fuel storage tubes 120. In one embodiment, the spring clips may be positioned to engage a free bottom edge 436 of the sheaths 300 which is laterally spaced away from sidewall 116 of the storage tube 120, (see, e.g. FIGS. 4, 5, and 11). The free bottom edges 436 are often formed near the lateral end portions 438 of the bottom end 430 of the sheath 330 where the sheath is not welded or otherwise attached to the storage tube 120. In such configurations, the spring clips 430 may be disposed proximate to the corners 428 of the lower half of the absorber tubes 424 to engage the bottom edges 436 of the sheaths 300. Any suitable number of spring clips 430 may be provided. In one embodiment, at least two spring clips 430 may be provided preferably on different sides of the absorber tube 424. In other embodiments, each of the four sides of the absorber tube may have at least one spring clip. Preferably, at least one spring clip 430 is located to engage one available bottom edge 436 of a sheath 300 of the storage cell 110 in which the absorber tube is installed to lock the absorber tube axially in place in the cell. It bears noting that at least one of the four storage tube sidewalls 116 inside of each fuel storage cell 110 includes a sheath 300 for engagement by a locking spring clip 430. This single engagement is sufficient to lock the absorber tube 424 in position within the storage cell. The locking protrusion or spring clip 430 is resiliently movable between an outward an inward deflected and retracted position for sliding the absorber tube 424 into the fuel storage tube 120 or cell 110, and an outward undeflected and extended position for engaging the sheath 300 and locking the absorber tube in position in the fuel rack 100. Operation of the locking protrusion or spring clip 430 will become evident by describing a method for installing a tubular neutron absorber insert 400 in a storage cell 110 of a fuel rack. A suitable cell 110 may first be selected having at least one available absorber sheath 300 for locking the insert in the fuel rack 100. In one example, cell 110A identified in FIG. 3 may be selected. The fuel rack 100 may be still submerged in the fuel pool 40 and radioactively active. Preferably, a fuel assembly 28 if already present in cell 110A may be removed first. An absorber insert 400 which may be in the form of absorber tube 424 described above is then positioned over and axially aligned with cell 110A. The locking spring clip or clips 430 are initially in their outward undeflected and extended position (see, e.g. FIG. 11). An overhead hoist or crane may be used to deploy the absorber insert 400. The insert 400 is then slowly lowered into the cell 110A through open top end 112 of the cell. After the lower end 416 of the absorber insert 400 passes through the cell top end 112, at least one of the locking spring clips 430 slideably engages the top end 310 of at least one absorber sheath 300. The spring clip 430 compresses and folds inward to the deflected and retracted position against the absorber tube 424. As the absorber insert 400 continues to be lowered farther into the cell 110A, the locking portion 434 of the spring clip 430 slides along the sidewall 312 of the sheath 300 and remains in the compressed retracted position. When the spring clip 430 eventually passes beneath and reaches a lower elevation in cell 110A below the bottom end 311 of the sheath, the spring clip 430 will snap open via its elastic memory returning to the initial extended position of the spring clip thereby catching and lockingly engaging the bottom edge 436 of sheath 300 (see, e.g. FIGS. 5 and 11). This locking engagement between the sheath 300 and locking portion 434 of spring clip 430 prevents the absorber insert 400 from being axially withdrawn from the fuel rack cell 110A, thereby locking the insert in axial position in the fuel rack. Advantageously, reactivity control to cell 110A is fully restored despite the degraded original boron-containing neutron absorber material which may still be present in the sheath. The open cavity 422 of the low profile absorber insert 400 is configured to allow a fuel assembly 28 to be inserted into cell 110A following the absorber restoration process, and to be removed from the storage cell without requiring removal of the insert. It bears noting that while the upper stiffening band 404 rotationally and laterally stabilizes the upper portion of the absorber insert 400 in the storage tube 120, the sheath 300 on the tube sidewall and the spring clips 430 act to rotationally and laterally stabilize lower portions of the insert by preventing excessive movement even during a seismic event. The absorber insert 400 may also be used in some embodiments with a fuel storage tube 120 that does not include an absorber sheath 300 on at least one sidewall 116 for engagement by the spring clip 430, but instead includes an optional flow hole 115A as shown in FIG. 4. In such a case, the spring clip 430 may be configured and arranged on the absorber insert 400 to engage a top edge of the flow hole 115A for locking the insert axially in place in the tube. The insertion process and action of the spring clip 430 is the same as described above, except that the surface of the storage tube sidewall 116 engages the spring clip 430 to fold the clip inwards in the retracted position until it passes below the flow hole 115A. At that elevation, the clip springs or snaps back to the outward undeflected and extended position to lockingly engage the hole. FIG. 12 shows an alternative construction of an absorber insert 400 according to the present disclosure. In lieu of the upper and lower stiffening bands 404, 406 coupling two chevron-shaped or angled absorber plates 402A, 402B together as shown in FIG. 6, each absorber plate 402C, 402D may be shaped as a structural channel. A longitudinal slot 412 may be formed between mating edges 426 of the plates 402C and 402D as shown in FIG. 12. All other element of construction including spring clips 430 and stiffening bands 404, 406 may otherwise be the same as absorber plates 402A, 402B described herein. While the foregoing description and drawings represent exemplary embodiments of the present disclosure, it will be understood that various additions, modifications and substitutions may be made therein without departing from the spirit and scope and range of equivalents of the accompanying claims. In particular, it will be clear to those skilled in the art that the present invention may be embodied in other forms, structures, arrangements, proportions, sizes, and with other elements, materials, and components, without departing from the spirit or essential characteristics thereof. In addition, numerous variations in the methods/processes described herein may be made within the scope of the present disclosure. One skilled in the art will further appreciate that the embodiments may be used with many modifications of structure, arrangement, proportions, sizes, materials, and components and otherwise, used in the practice of the disclosure, which are particularly adapted to specific environments and operative requirements without departing from the principles described herein. The presently disclosed embodiments are therefore to be considered in all respects as illustrative and not restrictive. The appended claims should be construed broadly, to include other variants and embodiments of the disclosure, which may be made by those skilled in the art without departing from the scope and range of equivalents.
abstract
An underground nuclear power reactor having a hollow blast tunnel which extends from one end of a containment member which houses a nuclear reactor, heat exchanger, generator, etc. A hollow blast tunnel extends from one end of the containment member with a normally closed door positioned therebetween. The blast tunnel defines a blast chamber having a plurality of spaced-apart debris deflectors positioned therein. The blast chamber has an upper wall with a roof opening formed therein which is selectively closed by a roof portion. If the reactor needs to be repaired or replaced, the door is opened so that the reactor will pass therethrough into the blast chamber and outwardly through the roof opening. If the reactor explodes, the blast therefrom drives the debris therefrom through the door and into the blast chamber where the deflectors reduce the blast force as the debris passes through the blast chamber.
summary
summary
055240402
summary
FIELD OF THE INVENTION This invention relates generally to an x-ray monochromator and is particularly directed to a high energy resolution, high angular acceptance crystal monochromator such as used with high energy experimental physics apparatus. BACKGROUND OF THE INVENTION High energy radiation such as that from x-ray undulators and multipole wigglers installed in high energy photon sources such as synchrotrons are increasingly being used in applications of ultra-monochromatic radiation in various fields of science and technology. Monochromatization of the hard x-ray component (5-30 keV) of synchrotron radiation down to the .mu.eV-neV level may be achieved via coherent nuclear resonant scattering. This technique involves a nuclear resonant medium having a coherent response for producing an energy bandpass of .mu.eV-to-neV. However, the nuclear resonant medium also has a non-resonant response (viz. Rayleigh scattering) which, if not suppressed, will generally overwhelm the detection system and lead to a prohibitively poor signal-to-noise ratio. Despite available techniques to suppress non-resonant scattering, it is extremely beneficial to reduce the energy bandpass of the x-ray beam as much as possible before it is incident on the nuclear resonant medium. It is possible to arrange the resonant atoms in a crystal lattice in such a way that for certain reflections only the resonant nuclei scatter in phase. Thus, a perfect sample of such a crystal can suppress a large fraction of the unwanted electron scattering. It is well known in the prior art that high brightness undulators provide high flux in the resonant bandwidth in the form of a very low divergence beam. Thus, an appreciable portion of the intensity of the incident x-ray beam can be captured before it is made to diverge from a single crystal with a vertical divergence of only .apprxeq.25 microradians. Using dispersive geometry, researchers at Brookhaven National Laboratory have used Si(8 4 0) crystals to achieve 0.09 eV resolution with an angular acceptance of 6 microradians. However, the apparatus employed to achieve this is of considerable size, i.e., 60" high and 24" long. The divergence of x-rays coming from current radiation sources is typically on the order of 100 microradians. The divergence of x-rays from the next generation of synchrotron radiation sources such as the Advanced Photon Source at Argonne National Laboratory will be approximately 25 microradians. Current monochromators are of only limited use in capturing the full intensity of the less diverging x-rays of the next generation of high energy photon sources. A diffractometer for nuclear Bragg scattering is disclosed in "Construction of a Precision Diffractometer for Nuclear Bragg Scattering at the Photon Factory" in Rev. Sci. Instrum., 63(1), January 1992, by Ishikawa et al. The disclosed diffractometer includes a nested pair of crystals in fixed relation with no energy tuning capability. A monochromator system for use in nuclear Bragg scattering is disclosed in "New Apparatus for the Study of Nuclear Bragg Scattering", Nuclear Instruments and Methods in Physics Research, A266 (1988), 329-335, by Siddons et al. The present invention addresses the aforementioned limitations of the prior art by providing an x-ray monochromator employing, in combination, an asymmetrical channel-cut single crystal of lower order reflection and a symmetrical channel-cut single crystal of higher order reflection in a novel nested geometry which allows for the incident x-ray beam to be collimated by the asymmetrically cut crystal before undergoing high order reflection by the symmetrically cut crystal in an arrangement which affords precise energy tuning. OBJECTS AND SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a high energy resolution, high angular acceptance crystal monochromator for use in nuclear Bragg scattering studies. It is another object of the present invention to provide an x-ray monochromator employing, in combination, an asymmetrical channel-cut single crystal of low order reflection and a symmetrical channel-cut single crystal of higher order reflection in a novel nested geometry. Yet another object of the present invention is to provide a 4-bounce dispersive crystal monochromator capable of reducing the bandpass of synchrotron radiation to a 10-50 meV level, without sacrificing angular acceptance, and which is also capable of precise energy tuning. The present invention comprises a highly asymmetrically cut (.alpha.=20) outer silicon crystal (4 2 2), with low order reflection combined with a symmetrically cut inner silicon crystal (10 6 4), with high order reflection. The asymmetrically cut crystal collimates the diverging x-rays, while the symmetrically cut crystal reduces the energy bandpass. Compactness and high resolution are achieved by combining the asymmetrically and symmetrically cut crystals in a novel "nested" geometry, so that the beam is collimated by the asymmetrically cut crystals before undergoing high order reflection by the symmetrically cut crystals. Rotational displacement drives coupled to the two crystals permit precise energy tuning of the monochromator. The nested monochromator was designed for use with high energy synchrotron radiation sources, but also has application in anomalous diffraction studies of atomic structure of large molecules like protein crystals, anomalous small angle scattering studies, and inelastic x-ray scattering from polymers and biological systems.
044029047
abstract
A method for testing the clad integrity of a nuclear fuel rod, comprising the first step of fabricating a sealed fuel rod with a wad of electrically conducting material mounted therein. The material is of a type that undergoes a permanent change in electrical conductivity when exposed to water. The next step is to establish an eddy current signal characteristic of the moisture-free rod. The rod is then loaded into the core as part of a fuel assembly. After the producing power, the assembly is removed for inspection, and an eddy current signal is again obtained from the rod. The eddy current signals are compared to determine whether inleakage of moisture has oxidized or otherwise altered the conductivity of the wad enough to significantly change the characteristic signal.
055442064
abstract
Apparatus for inspecting the nuclear reactor comprising a boom rotatably connected by a pivot point to the top of a reactor head, a mechanism for rotating the boom with respect to said pivot point, a camera affixed to said boom and being slidingly affixed thereto such that the camera may be slidably adjusted in a longitudinal direction with respect to said boom.
abstract
When the electrode potential of a charge control electrode above a wafer is reduced, image brightness is reduced. A point of change in the image brightness is a switching point between a positively charged state of the image and a negatively charged state of the image, showing the weakly charged state of the image. By setting this point of change as an inspecting condition, the amount of electric charges on the surface of the wafer can be reduced, and stable wafer inspection can be performed. It is estimated that an applied voltage V1 in FIG. 14 corresponds to the point of the change and is roughly included in the voltage range of a region enclosed by a broken line in the vicinity of the applied voltage V1. Within this voltage range, the influence of charge on an inspection under the inspecting condition can be reduced.
summary
047284870
summary
CROSS REFERENCE TO RELATED APPLICATIONS Reference is hereby made to the following copending U.S. applications dealing with related subject matter and assigned to the assignee of the subject application: 1. "Light Water Moderator Filled Rod For A Nuclear Reactor" by P. K. Doshi et al, assigned U.S. Ser. No. 654,709 and filed Sept. 26, 1984. 2. "Soluble Burnable Absorber Rod For A Nuclear Reactor" by P. K. Doshi et al, assigned U.S. Ser. No. 654,625 and filed Sept. 26, 1984. BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates generally to nuclear reactors and, more particularly, is concerned with a unique design concept for burnable absorber rods which provides rods of an overall standardized length while simulating conventional custom-designed rods which have a variety of reduced lengths. 2. Description of the Prior Art In a typical nuclear reactor, the reactor core includes a large number of fuel assemblies each of which is composed of top and bottom nozzles with a plurality of elongated transversely spaced guide thimbles extending between the nozzles and a plurality of transverse grids axially spaced along the guide thimbles. Also, each fuel assembly is composed of a plurality of elongated fuel elements or rods transversely spaced apart from one another and from the guide thimbles and supported by the grids between the top and bottom nozzles. The fuel rods each contain fissile material and are grouped together in an array which is organized so as to provide a neutron flux in the core sufficient to support a high rate of nuclear fission and thus the release of a large amount of energy in the form of heat. A liquid coolant is pumped upwardly through the core in order to extract some of the heat generated in the core for the production of useful work. Since the rate of heat generation in the reactor core is proportional to the nuclear fission rate, and this, in turn, is determined by the neutron flux in the core, control of heat generation at reactor start-up, during its operation and at shutdown is achieved by varying the neutron flux. Generally, this is done by absorbing excess neutrons using control rods which contain neutron absorbing material. The guide thimbles, in addition to being structural elements of the fuel assembly, also provide channels for insertion of the neutron absorber control rods within the reactor core. The level of neutron flux and thus the heat output of the core is normally regulated by the movement of the control rods into and from the guide thimbles. Also, it is conventional practice to design an excessive amount of neutron flux into the reactor core at start-up so that as the flux is depleted over the life of the core there will still be sufficient reactivity to sustain core operation over a long period of time. In view of this practice, in some reactor applications burnable absorber or poison rods are inserted within the guide thimbles of some fuel assemblies to assist the control rods in the guide thimbles of other fuel assemblies in maintaining the neutron flux or reactivity of the reactor core relatively constant over its lifetime. The burnable poison rods, like the control rods, contain neutron absorber material. They differ from the control rods mainly in that they are maintained in stationary positions within the guide thimbles during their period of use in the core. The overall advantages to be gained in using burnable poison rods at stationary positions in a nuclear reactor core are described in U.S. patents to Rose (U.S. Pat. No. 3,361,857) and to Wood (U.S. Pat. No. 3,510,398). U.S. Pat. Nos. 4,169,759 and 4,169,760 to Bevilacqua describe the use of a first group of full length control rods insertable into a nuclear reactor core for normal control of reactor power and of a second group of part length control rods insertable into the core for control of power oscillations. The part length control rod has first and second ends with a first neutron absorbing material at its first end, a second neutron absorbing material at its second end spaced from the first neutron absorbing material by a distance less than the length of the core, and a third intermediate portion connecting the first and second neutron absorbing material, the intermediate material being substantially non-neutron absorbing. The first neutron absorbing material is normally positioned outside of the reactor core where it has little or no effect on the neutron flux of the reactor core, while the second neutron absorbing material is normally positioned in the central region of the core for control of power oscillation. Upon the requirement for a rapid reactor shutdown, the part length control rod is scrammed or inserted into the core so that both first and second ends of the control rod are present in the core. The current trend in reactor core power distribution control is toward the use of burnable absorber rods having reduced lengths for the maximization of peaking factor margin. This approach involves the provision of custom-designed lengths and placements of the reduced length burnable absorber or poison rods. However, such approach presents some potentially significant manufacturing and handling difficulties. First, it precludes the manufacturing facility from being able to build rods from a standard inventory and can require a significant additional non-standard inventory (to cover manufacturing yield problems) that is unusable after completion of the reduced lenght rods for one particular reload region of the core. Second, handling of reduced length burnable absorber rod clusters when loading or unloading the reactor core entails considerable difficulty. Because of the design of the burnable absorber rod cluster handling tool, it is a very difficult task to be able to deal with clusters of a length different from that originally assumed in the design of the tool. It is doubly difficult because the cluster is sufficiently delicate that handling it improperly can result in damage, which could result in a delay in restarting the reactor. Consequently, a need exists for a different approach to burnable absorber rod design which will retain the flexibility of custom-designed reduced length burnable absorber rods in terms of maximizing reactor core power distribution control capability while, if not eliminating, at least reducing the above-described difficulties encountered in the manufacturing and handling of these custom-designed rods. SUMMARY OF THE INVENTION The present invention provides a standardized length burnable absorber rod designed to satisfy the aforementioned needs. The standardized rod is composed of three separate parts which, when assembled from standardized pre-manufactured parts, provides the reactor core power distribution control capability of the custom-designed reduced length burnable absorber rod that has been available heretofore. The standardized design concept of the present invention provides several advantages over the custom-designed or custom-fit concept. First, the absorber section, which is typically the most expensive part, can be provided as a small set of standard lengths, enabling the manufacturing facility to build from standardized inventory without sacrificing the peaking factor margin of the custom-fit design. Second, all burnable absorber rods will always be of the same overall length, eliminating any problems with handling. Third, providing the right kind of reduced length burnable absorber rod in an emergency situation becomes a matter of the assembly, rather than the manufacture, of the rod which drastically reduces emergency response time. Accordingly, the present invention sets forth for use in a fuel assembly for a nuclear reactor a standardized reduced length burnable absorber rod, comprising: (a) an upper end plug; (b) a lower end plug; (c) an elongated middle tubular section having opposite upper and lower ends and a chamber defined therein between the opposite ends; (d) a burnable absorber material disposed in the chamber of the middle tubular section; (e) an elongated upper tubular extension extending between and rigidly interconnecting the upper end plug and the upper end of the middle tubular extension; and (f) an elongated lower tubular extension extending between and rigidly interconnecting the lower end plug and the lower end of the middle tubular section. Still further, the standardized rod includes a pair of upper and lower end caps, the upper end cap being attached to the upper end of the middle tubular section so as to seal the same and the lower end cap being attached to the lower end of the middle tubular section so as to seal the same. More particularly, the upper tubular extension of the standardized rod has a hollow chamber formed therein which defines an upper space extending between the upper end plug and the upper end cap on the upper end of the middle tubular section. Similarly, the lower tubular extension of the standardized rod has a hollow chamber formed therein which defines a lower space of a predetermined axial length extending between the lower end plug and the lower end cap on the lower end of the middle tubular section. Each of the upper and lower tubular extensions and the middle tubular sections has one of a plurality of known different standard axial lengths being selected so that the upper and lower tubular extensions and middle tubular section when interconnected together will have a combined standard axial length which is the same from rod to rod. The present invention also relates to a cluster of standardized reduced length burnable absorber rods for use in a fuel assembly of a nuclear reactor, comprising: (a) a plurality of middle rod sections having a multiplicity of different axial lengths and containing burnable absorber material; (b) a plurality of upper end spacer sections having a multiplicity of different axial lengths; and (c) a plurality of lower end spacer sections having a multiplicity of different axial lengths; (d) each of the rods being formed of one middle rod section tandemly arranged between and rigidly interconnecting one upper end spacer section and one lower end spacer end section, the rigidly interconnected sections which form each rod being selected so as to provide the same standard combined axial length for each of the rods although the axial lengths of the middle rod sections can vary from rod to rod whereby the axial location of the burnable absorber material along the rod can also vary from rod to rod. Also, each of the middle rod sections has a sealed chamber defined therein for containing the burnable absorber material. Additionally, each of the rods has an upper end plug on the upper end spacer section and a lower end plug on the lower end spacer section. Each of the upper end spacer sections defines an upper empty space between the upper end plug and the middle rod section of the rod, while each of the lower end spacer sections defines a lower empty space between the lower end plug and the middle rod section of the rod.
abstract
An instrument removal system for removing detector cables from a nuclear reactor includes a removal cart and a disposal cask. in an exemplary embodiment, the removal cart includes a base including a plurality of wheels coupled thereto, a motor mounted on the base, and a drive shaft operatively coupled to the motor. A disposal spool is removably mounted on the drive shaft, and the disposal spool includes a notch sized to receive the detector cable. A housing is mounted on the base, with the housing enclosing the disposal spool. Also, an entrance port is located in the housing to permit the detector cable to enter the housing.
041529189
description
DETAILED DESCRIPTION OF THE INVENTION Shown in FIGS. 2 and 3 is one embodiment of the present invention. This vertical rolling mill 1 shown therein is, as is obvious from the drawings, composed of a frame 2 and a stand 3. The frame 2 is provided with a sole plate 4 disposed horizontally in order to mount the stand 3 thereon and an upright portion 5 extends upwardly at one side of said sole plate 4. Below the sole plate 4 are juxtaposed a pair of spindles 6 and 6' having vertical axes of rotation, and these spindles 6 and 6' consist of universal couplings. These universal couplings 6 and 6' are constructed in the same manner and of a self-standing and short length type respectively. They are each comprised of an outer cylinder 21, a cylindrical lower portion 22 accommodated within the lower part of said outer cylinder 21 and a cylindrical upper portion 23 accommodated within the upper part of the outer cylinder 21 as shown in FIGS. 4 and 5. In the lower portion 22 there is provided an opening the inner circumference of which is splined. On the other hand the upper portion 23 has an opening the cross-sectional configuration of which is non-circular as shown in FIG. 5. In the inside of the tubular cylinder 21 connecting the lower portion 22 and the upper portion 23 in axially displaceable fashion, there is provided a spring 24 which shortens the length of the coupling by narrowing the distance between the upper and lower parts thereof along the axial direction whenever the coupling is subjected to external force working along practically an axial direction. The universal couplings 6 and 6' have their lower portions 22 fixed on a pair of splines 25 and 25' extending upwardly perpendicularly from an intermeshed pair of gears 7 and 7' along the axis of rotation thereof respectively. These gears 7 and 7' constitute a member of the gear drive mechanism 9 connected to a motor 8. Accordingly, the couplings 6 and 6' are devised to rotate in opposite directionsin response to operation of the motor 8. The upper portions 23 of the couplings 6 and 6', when the couplings are fixed on the splines, 25 and 25' extend through an opening formed in the sole plate 4, and the upper extremities thereof are so disposed as to project slightly above the level of the surface of the sole plate 4 when the stand 3 is not mounted on the sole plate 4. On the upright portion 5 of the frame 2 there is provided a pair of overhung portions 10 and 10' for holding one side of the sole plate 4 therebetween. These overhung portions 10 and 10' are provided with perpendicular guide faces 11 and 11' respectively extending parallel to the direction of inserting the material-to-be-rolled between the rolling rolls. A pair of holding members 12 and 12' forming a pair of confronting are provided both on the upper part and the lower part of the overhung portions 10 and 10'. The holding members 12 and 12' face each other. The inwardly confronting fore ends of these holding members 12 and 12' are equipped with projections 13 and 13' respectively. These projections 13 and 13' are retracted in the holding members 12 and 12' respectively at the time when the holding members are not in operation, while at the time when the holding members are operated by a fluid they project from the holding members 12 and 12' respectively and toward each other between the confronting wall surfaces of the overhung portions 10 and 10'. On the stand 3 are rotatably installed the rotary shafts 14 and 14' which extend vertically and are located adjacent each other leaving a space therebetween. On the intermediate portions of these rotary shafts 14 and 14' there is installed a pair of rolling rolls 15 and 15' respectively at identical elevations. The lower ends of the rotary shafts 14 and 14' are configured such that when the stand 3 is mounted on the sole plate 4, they face the afore described opening of the sole plate 4 and fit closely in the non-circular openings formed in the upper portion 23 of the universal couplings 6 and 6' and are disposed therein, whereby the shafts 14 and 14' are interconnected so as to rotate in opposite directions with the rotation of the couplings 6 and 6'. The pair of rolling rolls 15 and 15' are made short in dimension just long enough to form a single caliber thereon, and they define a single caliber 16. On one side of the stand 3 is provided a pair of shoulders 17 and 17' at both the upper part and the lower part. The shoulders are so configured as to fit on the corners of the overhung portions 10 and 10' of the upright portion 5 of the frame 2. On these shoulders 17 and 17' are formed perpendicular guide faces 18 and 18' which are useful at the time of mounting the stand 3 on the sole plate 4 in cooperation with the guide faces 11 and 11' formed on the overhung portions 10 and 10'. The adjusting screws 19 and 19' are provided on the stand 3 for the purpose of advancing and retracting the guide faces 18 and 18' and thereby adjusting the horizontal position of the caliber 16 at the time when the stand 3 has been mounted on the sole plate 4. The shoulders 17 and 17' are further provided with perpendicularly extending grooves 20 and 20', respectively, for the purpose of accommodating the projections 13 and 13' adopted to project from the fore ends of the holding members 12 and 12' between the confronting wall surfaces of the overhung portions 10 and 10' at the time when the stand 3 has been mounted on the sole plate 4 and thereby fixing the stand 3. Next, in the following will be explained the mode of the operation of the foregoing embodiment. On the occasion of placing the stand 3 on the frame 2, the stand 3 is lifted by a machine such as crane and the like and is let down from above the sole plate 4 while making the guide faces 18 and 18' run along the guide faces 11 and 11'. By closely fitting the lower ends of the rotary shafts 14 and 14' in the openings provided in the upper portions 23 of the universal couplings 6 and 6', the stand 3 is made to stand still on the sole plate 4, and further the projections 13 and 13' are fitted in the perpendicular grooves 20 and 20' by actuating the holding members 12 and 12'. By so doing, the central position of the caliber 16 is defined by the vertical elevation above the sole plate 4 and the horizontal distance from the guide faces 11 and 11' and it is set to coincide with a prescribed pass line. When the motor 8 is driven under such conditions, the universal couplings 6 and 6' rotate in opposite directions through the gear drive mechanism 9. The rotary shafts 14 and 14' interlocked with couplings 6 and 6' rotate in concert with the couplings, whereby the rolling rolls 15 and 15' rotate in opposite directions to perform the rolling of the rod-shaped material-to-be-rolled inserted in the caliber 16. Adjustment of the horizontal position of the caliber 16 is performed by advancing or retracting the guide faces 18 and 18' through the operation of the adjusting screws 19 and 19' and thereby adjusting the distance between the caliber 16 and the guide faces 11 and 11'. On the occasion of dismounting the stand 3 from the frame 2 in order to replace it, the motor 8 is stopped, the projections 13 and 13' are disengaged from the perpendicular grooves 20 and 20' by actuating the holding members 12 and 12' in a direction opposite to the foregoing, the stand 3 is thereafter moved to another place by lifting with a machine such as crane, etc., and successively a new stand 3' is positioned on the frame 2 in the same way as described above. Inasmuch as a vertical rolling mill according to the present invention is of such a construction as described above, at the time of replacing the stand thereof, said stand can be directly lifted by a crane or the like from the prescribed position for rolling. Consequently, it does not require any conventional mechanism for the purpose of moving the stand sideways as well as up and down and the stand can be of a small size and light weight. Accordingly, it can be placed on a site of limited area with a relatively simple, ordinary foundation. A vertical rolling mill according to the present invention is also advantageous in that the rolling rolls employed therein, which are of the single-caliber type, are made shorter and lighter than rolls of the multi-caliber type. Therefore, a vertical rolling mill according to the present invention is advantageous compared with the conventional rolling mills in that the stand per se is of light weight, a machine such as crane, etc. for use in lifting the stand suffices to be of a relatively small size. As a result, the size and weight of the rolling mill as a whole can be further reduced, thereby facilitating the operation of machine such as crane, etc., and further simplifying such works as the settling of rolling mill, the replacing of stand, and so forth. Although a particular preferred embodiment of the invention has been disclosed in detail for illustrative purpose, it will be recognized that variations or modifications of the above disclosed apparatus, including the arrangement of parts, lie within the scope of the present invention.
abstract
A UV light irradiating apparatus for irradiating a semiconductor substrate with UV light includes: a reactor in which a substrate-supporting table is provided; a UV light irradiation unit connected to the reactor for irradiating a semiconductor substrate placed on the substrate-supporting table with UV light through a light transmission window; and a liquid layer forming channel disposed between the light transmission window and at least one UV lamp for forming a liquid layer through which the UV light is transmitted. The liquid layer is formed by a liquid flowing through the liquid layer forming channel.
abstract
The coated nanotube surface signal probe constructed from a nanotube, a holder which holds the nanotube, a coating film fastening a base end portion of the nanotube to a surface of the holder by way of adhering the base end portion on the surface of holder in a range of a base end portion length with an electric contact state and covering a specified region including the base end portion with the coating film maintaining the electric contact state between the nanotube and the holder, a tip end portion of the nanotube being caused to protrude from the holder; and the tip end portion is used as a probe needle so as to scan surface signals. The coated nanotube surface signal probe can be used as a probe in AFM (Atomic Force Microscope), STM (Scanning Tunneling Microscope) other SPM (Scanning Probe Microscope).
description
This Application is a Nonprovisional of and claims the benefit of priority under 35 U.S.C. §119 based on U.S. Provisional Patent Application No. 62/288,598 filed on Jan. 29, 2016. The Provisional Application and all references cited herein are hereby incorporated by reference into the present disclosure in their entirety. The present invention relates to imaging, sensing and optical source technologies based on infrared (IR) emitters, specifically IR emitters fabricated from polaritonic material structures. Infrared (IR) signaling with the aid of night vision and/or thermal imaging technology for detection has provided a means towards relatively covert free-space signaling and communications applications. In addition, IR signaling can serve as a means of free-space communications within the various atmospheric windows, and can denote a change in sensor status (e.g. the detection of chemical agent). However, current approaches use either high-power IR lasers (FIG. 1A) or spectrally broad, highly diffuse emitters (FIG. 1B). As can be seen from FIG. 1A, in the case of high-power IR lasers, the high power of the laser produces a high-visibility signal under the appropriate imaging conditions; however such laser-based sources tend to be highly directional, such that outside of a narrow cone of angles between the detector and the source, an optical signal from such a high-power laser will not be readily observed. The high output power can also cause a “halo” effect whereby the detected signal saturates multiple pixels washing out part of the image. In addition, such systems have a large power requirement that limits battery life, making them unsuitable for many field uses. In the case of diffuse emitters as shown in FIG. 1B, the source may be observed over a broader range of angles; however, this comes at the cost of being spectrally broad and weak in amplitude, making their observation outside of close ranges difficult. In addition, because they are spectrally broad, such emitters may clearly advertise the location of the source, since they may be observable not only to authorized observers having thermal imagers in a specified wavelength range, e.g., 3 μm thermal imagers, but also to anyone having conventional near-IR night vision goggles. Thus, these sources are very easy to replicate and intercept. Thus, despite substantial advancements in technology, significant issues with these applications persist. To ameliorate these issues, new technological approaches are required. Polar dielectric crystals experience an imbalance of the partial ionic charges of the atomic species in the crystal. For example, in the exemplary silicon carbide polar dielectric illustrated by the block diagram in FIG. 2A, a charge imbalance exists between the partial positive charge “δ+” of the Si ions in the lattice and the partial negative charge “δ−” of the C ions. The presence of this partial ionic charge imbalance enables stimulation of surface phonon polaritons (SPhPs) in such polar dielectric materials. In addition, the sub-diffractional confinement of light can be observed using metallic and highly doped semiconductor species (including many of the polar dielectric SPhP crystals when a high density of free carriers are present), providing similar behavior in the higher frequency regimes. In these cases, the incident light couples to free electrons or holes (“carriers”) in the material in a manner illustrated by the block schematic in FIG. 2B, providing the mechanism for the sub-diffractional confinement of light. Incident light at wavelengths corresponding to frequencies w between the frequency ωTO of the transverse optic (TO) and the frequency ωLO of the longitudinal optic (LO) phonons of a polar dielectric material, e.g., as shown by 4H—SiC Raman spectrum curve 301 shown in FIG. 3A, induces coherent oscillations of the crystal lattice of the material. Because of the presence of the positive and negative atomic charges δ+ and δ−, these oscillations induce a large surface electromagnetic field that causes a normally transparent dielectric to become highly reflective within this spectral band, referred to as the “Reststrahlen” band, as seen by dashed IR reflectance curve 302 for 4H—SiC shown in FIG. 3A (and also shown in FIG. 3B). See Joshua D. Caldwell, Lucas Lindsay, Vincenzo Giannini, Igor Vurgaftman, Thomas L. Reinecke, Stefan A. Maier and Orest J. Glembocki, “Low-loss, infrared and terahertz nanophotonics using surface phonon polaritons,” Nanophotonics 2015; 4: 44-68. Correspondingly, the real part of the dielectric function (permittivity) becomes negative, as shown by solid curve 303 shown in FIG. 3B, which enables the confinement of resonant light within sub-diffractional volumes through the nanostructuring of these polar dielectrics or at interfaces and surfaces of such materials. A plot illustrating the wide range of surface plasmon (NIR to MWIR) and surface phonon (MWIR to FIR) polariton materials, often referred to collectively as “polaritonic” materials, is provided in FIG. 4, with standard plasmonic metals (e.g. silver, gold, aluminum and copper) that support surface plasmons in the ultraviolet and visible and other more exotic types of polaritons (e.g. exciton polaritons) being omitted for simplicity; however, one skilled in the art will readily recognize that the materials shown in FIG. 4 are merely exemplary and by no means constitute an exhaustive and complete list of available polaritonic materials. It was recently demonstrated by researchers that the Naval Research Laboratory (NRL) that nanoscale structures fabricated out of silicon carbide (SiC) and hexagonal boron nitride (hBN) result in spectrally narrow resonances within the mid-infrared (10.3-12.5 um for SiC; 6.2-7.3 um and 12.1-13.2 um for hBN), with resonance linewidths as narrow as 3 cm−1, on par with well-defined crystal vibrations. See Joshua D. Caldwell, Orest J. Glembocki, Yan Francescato, Nicholas Sharac, Vincenzo Giannini, Francisco J. Bezares, James P. Long, Jeffrey C. Owrutsky, Igor Vurgaftman, Joseph G. Tischler, Virginia D. Wheeler, Nabil D. Bassim, Loretta M. Shirey, Richard Kasica, and Stefan A Maier, “Low-Loss, Extreme Subdiffraction Photon Confinement via Silicon Carbide Localized Surface Phonon Polariton Resonators,” Nano Lett. 2013, 13, 3690-3697 (SiC); and Joshua D. Caldwell, Andrey V. Kretinin, Yiguo Chen, Vincenzo Giannini, Michael M. Fogler, Yan Francescato, Chase T. Ellis, Joseph G. Tischler, Colin R. Woods, Alexander J. Giles, Minghui Hong, Kenji Watanabe, Takashi Taniguchi, Stefan A. Maier, and Kostya S. Novoselov, “Sub-diffractional volume-confined polaritons in the natural hyperbolic material hexagonal boron nitride,” NATURE COMMUNICATIONS (2014) 5:5221 (hBN). See also U.S. Pat. No. 9,195,052 to Long et al, entitled “Actively Tunable Polar-Dielectric Optical Devices” (Nov. 24, 2015); U.S. Pat. No. 9,244,268 to Long et al., entitled “Actively Tunable Polar-Dielectric Optical Devices” (Jan. 26, 2016); U.S. Pat. No. 9,274,532 to Long et al., entitled “Actively Tunable Polar-Dielectric Optical Devices” (Mar. 1, 2016); and U.S. Patent Application Publication No. 2016/0103341 by Long et al. These nano-scale polaritonic structures, such as the SiC bowtie antenna arrays whose reflectances are illustrated by the plots shown in FIG. 5A, can provide passive polarization- and frequency-selective infrared reflection spectra due to the sub-diffractional resonance modes supported within the nano-scaled structures. In addition, the IR emission spectra of such SiC bowtie antenna arrays at T=350° C. shown in FIG. 5B demonstrate that by heating the structures to modest temperatures, tailored IR emission can be produced, with the emission retaining the polarization and narrow spectral bandwidth of the resonances observed in the reflection spectra shown in FIG. 5A. It has been observed within our lab that heating even to small temperatures such as 50° C. is sufficient to induce a measurable emission. This phenomenon was originally demonstrated for SiC micron-scale gratings and microwires. See Jean-Jacques Greffet, Rémi Carminati, Karl Joulain, Jean-Phillipe Mulet, Stéphane Mainguy, and Yong Chen, “Coherent emission of light by thermal sources,” Nature 2002, 416, 61-64; and Jon A. Schuller, Thomas Taubner, and Mark L. Brongersma, “Optical antenna thermal emitters,” NATURE PHOTONICS, Vol. 3 (November 2009), pp. 658-661. If a device comprising a plurality of nano-scale emitters is fabricated on a substrate homogeneous with the nano-scale emitters (e.g. SiC bowties on a SiC substrate), the IR emission from the nano-scale emitters will be superimposed upon the broadband high reflectivity (low emission) of the underlying substrate, providing a large optical contrast. On the other hand, if the nano-scale structures are fabricated (or grown) on a dissimilar substrate material, the IR emission from those structures will be superimposed upon the IR emission of the underlying substrate and will result in a broad gray-body radiation spectrum with the narrow-band IR emission signature from the nano-scale structures superimposed thereon. While the IR emission from localized SPhP resonators discussed in the literature has primarily focused on SiC structures, see Greffet, supra, and Schuller, supra, in principle, any polar dielectric crystal can be used, provided the Reststrahlen band is in an appropriate frequency range for IR emission at the temperature of operation. This is equally applicable to surface plasmon polaritons. In the case of the latter, such materials will operate over a broader spectral range, but the resonance linewidths will be significantly broadened with respect to the lower-frequency SPhP materials. Although use of most plasmonic metals (e.g. gold and silver) would be cost-prohibitive and would require excessive temperatures, even in excess of their melting points, to achieve emission near their resonances in the visible spectral region, a significant effort has also been focused on developing alternative lower-loss plasmonic materials. For instance, developments from Prof. Jon-Paul Maria's group at North Carolina State University have led to a low-loss plasmonic material in the form of dysprosium-doped cadmium oxide that would offer the potential for IR emitters in the 2-8 μm range. See E. Sachet, C. T. Shelton, J. S. Harris, B. E. Gaddy, D. L. Irving, S. Curarolo, B. F. Donovan, P. E. Hopkins, P. A. Sharma, A. L. Sharma, J. F. Ihlefeld, S. Franzen, and J.-P. Maria, “Dysprosium-doped cadmium oxide as a gateway material for mid-infrared plasmonics” Nature Materials 14, 414-420 (2015). Additional materials such as transparent conducting oxides would provide opportunities in the 1-5 um region. See Gururaj V. Naik, Vladimir M. Shalaev, and Alexandra Boltasseva, “Alternative Plasmonic Materials: Beyond Gold and Silver,” Adv. Mater. 2013, 25, 3264-3294. While the optical losses (efficiency) of these plasmonic materials is higher than in their phonon polariton counterparts, which will result in broader emission linewidths, they do offer the potential for tailored IR emitters in a spectral range where currently no known phonon polaritons exist (λ<6 μm). As noted above, a wide array of these polaritonic materials is presented in FIG. 4. It should be noted that all of those presented are in various states of commercial maturity, but successful synthesis of all has been demonstrated. Further, it should be stated that this list is not meant to be exhaustive, but that this approach is equally applicable to tailored IR emitters of all kinds, for instance SPhP, surface plasmon and dielectric resonators. This summary is intended to introduce, in simplified form, a selection of concepts that are further described in the Detailed Description. This summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter. Instead, it is merely presented as a brief overview of the subject matter described and claimed herein. The present invention utilizes the properties of polaritonic materials to provide IR emission devices that can be frequency- and/or amplitude-modulated to provide spectral, temporal and spatial patterns that can be recognized only under the appropriate filtering and/or demodulation conditions. The IR emission devices comprise one or more arrays of fabricated polaritonic infrared emitters arranged on a substrate, where the arrays of emitters are coupled to a heater configured to provide heat to one or more of the emitter arrays in the device. When the fabricated infrared emitters are heated, they produce an infrared emission that can be polarized and whose spectral emission range, emission wavelength, and/or emission linewidth can be tuned by the material used to form the elements of the array and/or by the size and/or shape of the emitters. In some embodiments, the nanoscale emitters are formed from or are coated with a ferroelectric polaritonic material which is used to modulate the frequency response of the polaritonic IR emitters through the application of a piezoelectric strain that changes the material's polarization state and can be induced by the application of an external bias. In other embodiments, the polaritonic IR emitters are formed from or are coated with a phase change material such as vanadium dioxide (VO2), vanadium pentoxide (V2O5), germanium-antimony-tellurium (GeSbTe), or tungsten trioxide (WO3), which can change the infrared reflection of the emitters by the application of a thermal, electrical, or optical pulse which changes the material from a “metallic” to a “dielectric” state, thereby enabling the amplitude of the emission from the IR emitters to be modulated. In other embodiments, the polaritonic IR emitters are coated with a thermal dissipation layer such as nanodiamond. Such materials can serve to conduct the heat rapidly away from the emitting material, therefore “shutting off” the IR emission or spectrally tuning the emission energy. The aspects and features of the present invention summarized above can be embodied in various forms. The following description shows, by way of illustration, combinations and configurations in which the aspects and features can be put into practice. It is understood that the described aspects, features, and/or embodiments are merely examples, and that one skilled in the art may utilize other aspects, features, and/or embodiments or make structural and functional modifications without departing from the scope of the present disclosure. The present invention utilizes the properties of polaritonic materials to provide IR emission devices that can be frequency- and/or amplitude-modulated to provide spectral, temporal and spatial patterns that can be easily recognized under the appropriate filtering and/or demodulation conditions. Aspects of the means by which the infrared emission signals can be imaged or detected for potential applications will be described below in the context of the FIGURES, which form a part of the disclosure of the present invention. It will be noted that in the FIGURES and in the description herein, where a structural element appears in more than one FIGURE, those elements are denoted by the same reference numeral, with only the first digit being changed to reflect the FIGURE in which they are shown. For example, IR emitter array 700 shown in FIGS. 7A/7B corresponds to IR emitter array 800 shown in FIGS. 8A/8B, IR emitter array 900 shown in FIGS. 9A/9B, and IR emitter array 1100 shown in FIG. 11. As noted above, if a device comprising an array of polaritonic nano-scale structures is fabricated on a substrate homogeneous with the nano-scale structures (e.g. SiC bowties on a SiC substrate), the nano structure's IR emission will be superimposed upon the broadband high reflectivity (low emission) of the underlying substrate, providing a high optical contrast, whereas if the nano-scale structures are fabricated (or grown) on a dissimilar substrate material, the IR emission from those nano-scale structures will be superimposed upon the IR emission of the underlying substrate and will result in a broad gray-body radiation spectrum with the narrow-band IR emission signature from the nano-scale structures superimposed thereon. This difference in the IR emission of a such a device, depending on the substrate on which it is formed, provides a great deal of flexibility in the design of such IR emission devices, enabling a device to be designed to hide the presence of the signal in a broadband infrared source, to provide a high degree of contrast relative to the background substrate, or to provide a signal that can only be observed if the nanostructured device is illuminated by an external source having a certain frequency or at high temperatures by an IR imager configured to detect certain frequencies. In addition, the material and structure of the device can be tuned to provide more or less thermal contrast vis a vis the substrate, thereby permitting the device to be more or less visible as desired. FIGS. 6A/6B and 6C/6D illustrate the way in which an array of nano-scale polaritonic IR emitters can be used to produce a desired thermal image. FIG. 6A depicts thermal images of a metal chuck and a SiC substrate that have a measured temperature (as measured by, e.g., a thermocouple) of 75° C., and shows that the metal chuck has a thermally imaged “apparent” temperature of 76° C., while the SiC substrate—while having the same measured temperature as the chuck—appears to be much cooler, with an apparent temperature of 66° C.; FIG. 6C shows a similar difference in apparent temperatures of a metal chuck and a SiC substrate both having a measured temperature of 120° C., with the metal chuck having an apparent temperature of 121° C. and the SiC substrate exhibiting a much cooler apparent temperature of 103° C. In addition, as shown in FIGS. 6B and 6D, SiC in the form of one or more arrays of nano-scale IR emitters can appear “warmer” to a thermal imager than the solid slab of SiC used as a substrate for the array, where all of which exhibit apparent temperatures that are cooler than the measured temperature, but range in actual apparent temperatures with variations due to spectral shifts in the SPhP resonance frequencies. Thus, as shown in FIG. 6B, a SiC nano-scale structure array having a measured temperature of 75° C. has an apparent temperature in the range of about 63 to about 65° C., while a SiC nano-scale structure array having a measured temperature of 120° C. (FIG. 6D) has an apparent temperature in the range of about 105 to about 109° C. This difference between the measured and apparent temperatures occurs due to the method by which a thermal camera is calibrated. Because a thermal camera determines the apparent temperature based on the total integrated intensity collected over a spectral bandwidth of the camera and assumes it to be a gray-body, mirrors, which do not emit, can appear much cooler than their actual measured temperature. By making appropriately designed SPhP or SPP nano-scaled structures, one can tailor the apparent temperature of an object without changing its true measured temperature. As described in more detail below, in accordance with the present invention, the present invention takes advantage of these thermal properties of polaritonic materials to provide an IR emission device comprising arrays of fabricated IR emitters formed from polaritonic materials that exhibit phonon or plasmon polariton resonances when they are heated above room temperature and/or are illuminated by light having wavelengths within their Reststrahlen band, where the devices can be modified to provide a desired thermal response. In many embodiments, the polaritonic IR emitters in devices in accordance with the present invention will be in the form of nanoscale emitters such as polaritonic nanoantennas and often will be referred to as such in the description below, but one skilled in the art will readily recognize that other configurations of the polaritonic emitters such as one- or two-dimensional gratings, meshes, etc., can also be used, and all such emitter configurations are deemed to be within the scope of the present disclosure. FIGS. 7A and 7B provide a side and a top view, respectively, of an exemplary general configuration of an IR emission device in accordance with one or more aspects of the present invention. Thus, as can be seen from FIGS. 7A and 7B, an IR emission device in accordance with the present invention comprises one or more arrays 700 of nanoscale polaritonic IR emitters arranged on a substrate 703, with an intermediate dielectric membrane 702 disposed between the substrate 703 and the emitter array to provide mechanical stability and thermal isolation to the heated nanoscale IR emitter arrays to reduce power consumption. The arrays of IR emitters are coupled to a heater 704 that is configured to provide heat to one or more of the emitter arrays in the device. Boron-doped nanocrystalline diamond is especially suited for use as a heater in an IR emission device in accordance with the present invention because it is optically transparent and will not interfere with the thermal signal from SiC; however, one skilled in the art will recognize that other heating systems (e.g. serpentine metal resistive heaters) can be used as appropriate. While omitted from the FIGURE for simplicity, in such cases, electrical contacts would be utilized to drive a current through the heater. As described above, when the nanoscale IR emitters are heated by heater 704, they produce an IR emission that can be polarized using careful design of the IR emitter structure. In addition, in accordance with the present invention, the spectral emission range, emission wavelength, and/or emission linewidth of the IR emission can be tuned by varying the any one or more of the polaritonic material used, the size of the emitters, and/or their shape. In some cases the IR emission of the emitters can be tuned so as to cause the array of emitters to have a different “perceived” temperature than that of the underlying substrate. Thus, in accordance with the present invention, by tailoring the characteristics of the device, an IR emission device formed from such a polaritonic material nano-scale structure array can be tailored to provide a desired IR emission response. For example, by selecting an appropriate material for the substrate and/or the IR emitters, the IR emission from the device can cause the device to have a desired IR emission spectrum that can be used as a tailored optical source or beacon or can be used to modify the perceived temperature of the device in a manner as described above. In some embodiments, the device can be designed to be “hidden” from view unless the device is illuminated by light having an appropriate frequency, e.g., a frequency spectrally close to the resonance of the nanoscale IR emitters. In other embodiments, a heater can be configured to apply heat to selected IR emitter arrays or to produce variations in the actual temperatures applied to different IR emitter arrays on the same device, thereby producing a spatially patterned IR emission signature that can identify a source of the IR emitters. It will be noted here that one skilled in the art will recognize that the device design illustrated in FIGS. 7A/7B is merely exemplary, and other designs can be used in implementing the key features of the invention, i.e., the use of nano-scale structures of nanophotonic and photonic materials for tailored narrow-band and polarized IR emitters which can provide a source of IR emission for a wide range of applications and the use of various mechanisms by which the IR emission from the emitters can be frequency- or amplitude-modulated over a wide range of modulation frequencies and modulation depths. In addition, while these features are described primarily in the context of IR emitters that are heated to provide an IR emission, one skilled in the art will recognize that in many cases one or more of these features can also be used to provide modulated absorption/reflection/transmission from similar devices at ambient temperatures. One way in which the IR emitters in a device in accordance with the present invention can be tuned and/or modulated is through the use of specific kinds of emitter materials or coatings on the emitters. Thus, the polaritonic resonances can be tuned by using ferroelectric materials (e.g. lead zirconate titanate), phase change materials (e.g., vanadium pentoxide or germanium telluride), and/or fast thermal dissipation materials (e.g. nanodiamond or boron arsenide) to induce fast changes in the amplitude or free-space wavelength of the resonances. As discussed above, any change in the amplitude or wavelength corresponding to the resonance frequency will result in a commensurate change in the IR emission spectrum. As described below, in many cases, these ferroelectric, phase change, or fast thermal dissipation materials can be used as a coating for multi-layered IR emitters formed from polaritonic materials. However, many of these phase change and ferro/piezoelectric materials are also semiconductors and/or polar dielectric materials in their own right and so in some embodiments can be used in devices where a single material provides both the plasmonic/SPhP-based IR emitter/sensor and the material for transduction, simultaneously. While we mention only single-material or bi-material iterations of this invention, it should be noted that one skilled in the art will also recognize that more complicated multilayered and/or metamaterial-based structures with various polaritonic, ferroelectric, phase change, and/or fast-thermal dissipation materials to achieve these aims within a user-defined frequency range are also within the scope of this patent. FIGS. 8A-8C illustrate aspects of an exemplary embodiment of an IR emission device in accordance with the present invention in which ferroelectric materials are used to obtain a frequency-modulated thermal response of the polaritonic IR emitters. As with the embodiment illustrated in FIGS. 7A and 7B described above, in the exemplary embodiment illustrated in FIGS. 8A and 8B, an IR emission device in accordance with the present invention includes an array 800 of nanoscale polaritonic IR, or thermal, emitters (labeled as “TE” in the FIGURE) arranged on a silicon substrate 803, with an intermediate dielectric membrane 802 disposed between the substrate 803 and the emitter array 800. In the embodiment illustrated in FIG. 8A, each of the individual polaritonic IR emitters 801 in the array 800 comprises an IR emitter core 801a formed from a polaritonic material such as silicon carbide (SiC) that is coated with an outer layer 801b of a ferroelectric (FE) material such as aluminum nitride (AlN) or barium strontium titanate (BST). In some cases, e.g., AlN or BST, the ferroelectric material is also a polar dielectric capable of supporting phonon polaritons, so that in some embodiments, as shown in FIG. 8B, the ferroelectric material is used to form the IR emitters 801 themselves rather than simply be used as a coating. In some embodiments, all of the emitters are coated with or formed from the same ferroelectric material, while in other embodiments, a subset of the emitters can be coated with or formed from a different ferroelectric material so as to produce a spatially varying strain, and thus a spatially varying IR emission pattern, e.g., one that can identify the owner of the IR emitters to a reader of the thermal signal. In still other embodiments, one or more of the emitters can be formed from a ferroelectric material core with a coating of a phase change material; while in other embodiments, one or more of the emitters can be formed from a phase change material core with a coating of a ferroelectric material. Whether coated with a ferroelectric material or formed from one, the emitters 801 are coupled to a heater 804 that is configured to provide heat to one or more of the emitters in the array so as to produce an IR emission in a manner described above, where the IR emission can serve as a narrow-band infrared optical source or beacon or that may cause the heated array of emitters to have a different “perceived” temperature than that of the underlying substrate and/or surrounding environment. In addition, in this embodiment of an IR emitter in accordance with the present invention, the emitters are coupled to electrical contacts 805 and a voltage source which can apply a bias across the ferroelectric material. The ideal configuration of the contacts will be dictated by the IR emitter design and the orientation of the ferroelectric crystal planes in the device. The voltage source can be any suitable source capable of applying a bias to the device, e.g., a battery or other power pack. When a voltage pulse is applied to the coated or solid ferroelectric IR emitters 801, the voltage reorients the spontaneous polarization of the ferroelectric material, thereby inducing a strain in the ferroelectric coating or emitter material. This change in strain modifies the frequency or frequencies of the optical phonons of the polar dielectric material forming the IR emitters, thus modifying the spectral frequency of their sub-diffractional resonances. Thus, in accordance with the present invention, the output frequency of the IR emitters as well as their “perceived” temperature can be tuned by selecting an appropriate ferroelectric material to obtain the desired response and/or by choosing an appropriate electrical bias to be applied to an existing ferroelectric array. In some embodiments, the polarization of the ferroelectric material can also be changed through the injection of free carriers (electrons and/or holes) into one or more of the IR emitters or into an area of the IR emission device adjacent to the IR emitters. See U.S. Pat. Nos. 9,195,052; 9,244,268; and 9,274,532, supra, and U.S. Patent Application Publication No. 2016/0103341, supra. Such polarization changes can be implemented in ferroelectric and piezoelectric crystals (e.g. AlN) and may be induced through electrical, mechanical or thermal stimuli as well. This change in polarization of the ferroelectric material enables the IR emission frequency of the nanoscale array to be shifted spectrally as shown in FIG. 8C, where the initial resonance curve 810a is spectrally shifted to the position illustrated by curve 810b through the application of a compressive strain via an applied bias to the ferroelectric coating or nano-scale structure, while the application of a tensile strain would induce a spectral shift in the opposite direction. This spectral shift is transient, and is maintained only as long as the strain is applied. Therefore, if the strain is applied for short timescales, for instance sub-microseconds, a frequency modulated thermal source can be realized. If such a thermal source can be made to have an apparent temperature similar to that of the local background it would only be observed if someone demodulates the signal at the correct modulation frequency. In other embodiments, use of phase change materials such as vanadium dioxide (VO2), vanadium pentoxide (V2O5), germanium-antimony-tellurium (GeSbTe), or tungsten trioxide (WO3), offers another avenue towards drastically changing the infrared reflection by the application of a thermal, electrical, or optical pulse. FIGS. 9A and 9B illustrate exemplary aspects of IR emission devices in accordance with the present invention in which such phase change materials are used to tune the device and produce a desired IR emission response. Thus, as with the previous embodiments described above, in the exemplary embodiment illustrated in FIGS. 9A and 9B, an IR emission device in accordance with the present invention includes an array 900 of individual nanoscale IR emitters (TE) 901 arranged on a substrate 903, with an intermediate dielectric membrane 902 disposed between the substrate 903 and the emitter array. As with the embodiments described above, the emitters 901 are coupled to a heater 904 that is configured to provide heat to one or more of the emitter arrays on a given device when an electrical bias is applied to the heater contacts 905. In the embodiment illustrated in FIG. 9A, each of the IR emitters 901 in the array comprises an IR emitter core 901a formed from a polaritonic material such as silicon carbide that is coated with an intermediate layer of a dielectric material 901b and an outer layer 901c of a phase change material such as vanadium oxide (VO2), vanadium pentoxide (V2O5), germanium-antimony-tellurium (GeSbTe), or tungsten trioxide (WO3). Intermediate layer 901b can thermally isolate the phase change and polaritonic materials so that they can be held at different temperatures; however, the device can also operate without the presence of this intermediate layer, with the phase change and polaritonic materials operating at the same temperature. In addition, some phase change materials such as vanadium dioxide (VO2) or vanadium pentoxide (V2O5) are also polar dielectric materials capable of supporting SPhPs, so that in some embodiments, as shown in FIG. 9B, the phase change material can be used to form the IR emitters 901 themselves rather than merely be used as a coating. In either case, the IR emitters can be heated by heater 904 to provide an IR emission in a manner described above, where the IR emission can be used as a narrow-band infrared source or beacon or may cause the array of emitters to have a different “perceived” temperature than that of the underlying substrate or local environment. In addition, the phase change material changes properties when the IR emitters are heated. For example, vanadium oxide changes from a dielectric i.e., electrically transparent, state to a metallic, i.e., reflective state. This change in state can also be induced in some embodiments by driving a small current through the phase change material, e.g., through electrical contacts 905, while in other embodiments it can be induced by the use of fast optical laser pulses applied to the phase change material. Thus, as illustrated by the plot in FIG. 9D, in one state, where the IR emitters are at a temperature T above the critical temperature (T>Tc), the phase change material has “metallic” properties and becomes highly reflective and/or absorptive depending on the magnitude of the imaginary part of the permittivity of the PCM in the metallic state, such that IR emission from the underlying nano-scale structure is suppressed. In such cases, the IR emission from the devices will be dominated by the IR emission of the metallic phase change material. If the material is a high quality metal, with low loss, it will be highly reflective with minimal to no IR emission, whereas if it is a poor, lossy metal, it will act as a gray-body and provide a broad IR emission, dictated by its own emissivity, rather than by the underlying polaritonic nano-scale structure array. In a second state, where the IR emitters are at a temperature T less than some critical temperature Tc (T<Tc), the phase change material has “dielectric” properties, i.e., is transparent or only weakly absorbing, therefore enabling the IR emission from the underlying nano-scale structures to be transmitted and thus, observed. In such a case, the IR emission will be dictated by the underlying polaritonic nano-scale structure emissivity, and thus will provide the narrow-band, potentially polarized IR emission signature described above. This change from “metallic” to “dielectric” states is ideal for amplitude modulation. Thus, as illustrated in the plot shown in FIG. 9C, an IR emission device according to this embodiment of the present invention can be turned “on” and “off” at a rapid rate, or can be induced to vary in amplitude to intermediate values depending on the device design and the properties of the phase change and polaritonic materials used. Such an approach can be quite useful for communications using infrared beacons since the device can be designed so that its emission(s) has an apparent temperature similar to their surroundings and will blend into the thermal background, but can be observed clearly if the observer demodulates the imaged scene at the appropriate frequency. The metallic-to-dielectric phase change materials such as vanadium dioxide (VO2) are a good candidate for this type of operation. The plot in FIG. 9D illustrates the optical response of a vanadium dioxide film grown by atomic-layer epitaxy and shows the change in reflectivity of the material depending on whether its temperature T is above or below a critical temperature Tc, i.e., that it can be in a low-reflectance dielectric state at T<Tc and in a high-reflectance metallic state at T>Tc. Note that large contrasts in the infrared reflectivity can be achieved over a broad spectral range, making VO2 a particularly suitable material for this embodiment. Of course, many other alternative phase change materials exist, and any suitable material may be used as appropriate. Other aspects of phase change materials also make them highly suitable for use in IR emitters in accordance with the present invention. The phase change exhibited in the entire class of phase change materials is accompanied by a substantial contrast in refractive index. Large changes in the local refractive index can also be used to induce a spectral shift in the resonance frequency of the sub-diffractional resonator, therefore providing a mechanism towards frequency modulation as well, provided the phase change material still exhibits sufficient transmission at the wavelength of the IR emission in its metallic state. Phase change materials alternating between crystalline and non-metallic amorphous states would be good candidates for such approaches. In addition, as with the ferroelectric materials described above, the polarization of such phase change materials can also be changed through the injection of free carriers (electrons and/or holes) into one or more of the IR emitters or into an area of the IR emission device adjacent to the IR emitters. Moreover, in a manner similar to that described above with respect to emitters formed from ferroelectric materials, in some embodiments, all of the emitters are coated with or formed from the same phase change material, while in other embodiments, a subset of the emitters can be coated with or formed from a different phase change material so as to produce a spatially varying change in dielectric function, and thus a spatially varying IR emission pattern, e.g., one that can identify the owner of the IR emitters to a reader of the thermal signal. In still other embodiments, some of the plurality of emitters in the array can be formed from ferroelectric materials while others are formed from phase change materials, with their respective IR emission being tuned as described herein so as to provide a predetermined spatially varying IR emission pattern. In other embodiments, aspects of which are illustrated in FIGS. 10A and 10B, the polaritonic IR emitters can be coated with a thermal dissipation layer. In such embodiments, the thermal dissipation layer can serve to conduct the heat rapidly away from the emitting material, therefore “shutting off” the IR emission or spectrally tuning the emission energy. Many of these emitters (e.g. SiC) also exhibit high thermal conductivities, so will naturally lend themselves to faster thermal cycling. Thus, as illustrated in FIG. 10A, an IR emission device in accordance with this embodiment of the present invention includes an array 1000 of polaritonic nanoscale IR emitters (TE) 1001 arranged on a substrate 1003, with an intermediate dielectric membrane 1002 disposed between the substrate 1003 and the emitter array. As with the embodiments described above, the emitters 1001 are coupled to a heater 1004 that is configured to provide heat to one or more of the arrays of emitters on the device. In addition, in the embodiment illustrated in FIG. 10A, at least some of the IR emitters 1001 in the array have an IR emitter core 1001a formed from a polaritonic material that is coated with an outer thermal dissipation layer 1001b of a thermal dissipation material. By overcoating the emitters with a high thermal conductivity layer 1001b, applied heat used to induce the IR emission can be rapidly dissipated, thereby lowering the temperature of the IR emitter nano-scale structure 1001a, which in turn will reduce the amplitude of the IR emission. In some embodiments, the emitters can be formed from a ferroelectric material or from a phase change material as described above with respect to FIGS. 8B and 9B, respectively, with the emitters then coated with the thermal dissipation layer 1001b. In other embodiments, the thermal dissipation layer can be placed as the underlying dielectric spacer layer 1002 or can be in the form of a via created through the backside of the substrate 1003. Such TDL-based IR emitters provide an ideal approach for amplitude modulation. Thus, an IR emission device according to this embodiment of the present invention can be turned “on” and “off” at a rate as described above in the case of emitters and/or coatings made from phase change materials, or, as illustrated in the plot shown in FIG. 10B, can be induced to vary in amplitude to intermediate values depending on the device design and the temperature of the IR emitter at any given time. As the IR emitter can be controlled by understanding the interplay between the thermal dissipation rate of the TDL and the heat applied to the IR emitter array, this can serve as a means to modulate the amplitude of the IR emission signature. Such an approach can be quite useful for simple signaling with infrared beacons as it can be designed to have an apparent temperature similar to its surroundings and so be hidden in the thermal background, but can be observed clearly if the observer demodulates the imaged scene at the appropriate frequency. One exemplary TDL material that can be incorporated into an IR emitter in accordance with this embodiment of the present invention would be nanocrystalline diamond (NCD), but any other suitable material can be used. Alternatively, as in the embodiments described above with respect to ferroelectric and phase change materials, in some embodiments of an IR emitter having a TDL layer incorporated therein, the nano-scale structures can be formed from a high thermal conductivity material, for instance SiC, which can simultaneously serve as both the IR emitter and the TDL. While the above device implementations have focused on resonant IR emitters, these modulation approaches can also be used to modulate the throughput of an optical signal within a waveguide fabricated from a polaritonic material. In such cases, the propagation length and subdiffractional confinement of polaritonic waveguides is directly tied to the permittivity of the polaritonic material. By inducing a local strain through the use of a waveguide fabricated from a polaritonic ferroelectric material or from phase change material or a polaritonic waveguide coated with a ferroelectric or phase change material, the permittivity of the waveguide material can be modified, thus providing again a means for modulating the transmitted and/or reflected optical signal. Advantages and New Features The devices outlined in this disclosure would serve to provide a spectrally narrow, polarized light source that is also semi-diffuse, low-power, light-weight, with minimal electronic and mechanical components that could induce failure, potentially low-cost and can be amplitude and/or frequency modulated. This provides the benefits of both wide-viewing angles and long battery life, visibility over long ranges, while also providing spectral and polarization specific behavior with frequency and/or amplitude modulation of the response that can enable covert operation and/or modulated optical sources for beacons or optical communications devices. The divergence of the source can in principle also be tailored by modifying the periodicity of the nano-scale structure array, the shape of the nano-scale structures, or incorporation of dispersive elements/optics with those structures. One could envision a large area (mm to cm size scale) single array that could be used to provide a spectral signature that could be superimposed upon either the IR emission of a broad band infrared source or the IR emission from the background to hide the signal in plain sight. Another alternative would be to fabricate a series of thermally isolated IR emitter arrays that could be individually addressed. This approach would also provide the benefits of the single array design, while also providing the opportunity to create unique spatial patterns that could be more readily discerned with imaging technology, albeit with the additional cost of the more complicated fabrication. Another possible alternative is to use these sources in conjunction with chemical sensors or as Surface Enhanced Raman or Surface Enhanced Infrared Absorption sensors themselves that can emit the covert pattern only when a change of status occurs (e.g. detection of chemical species of interest). Furthermore, these emitters can provide narrow-band sources of a defined frequency and polarization that can operate over a broad spectral range where solid-state narrowband sources (LEDs and laser diodes) are currently limited or completely absent (MWIR to THz). These emitters can potentially provide a low-power, low-cost, polarized IR source where commercial sources are not currently available (λ>13 um) and/or for gas-phase sensing. The modulated signal could be used for many potential signaling or communications applications. For example, an array of nanoscale IR emitters in accordance with the present invention can be arranged in a predetermined pattern to provide an identifying signal that is visible only to someone having appropriate imaging and filtering equipment. In other embodiments, the modulated emission(s) source could be used to identify sensors that have had a change of status (e.g. a chemical sensor detecting a dangerous gas) or to perform chemical spectral analysis. Or in another embodiment, the devices could be worn or held by personnel and be used for communications or to identify the personnel as being of a specific origin or belonging to an authorized organization. They could also serve as an alternative, modulated, solid-state infrared light source with narrow spectral band, polarized emission whereby depending on the polaritonic material chosen (e.g. plasmonic or phonon polariton species) the emission wavelength could be designed anywhere from the near-infrared (e.g. highly doped transparent conducting oxides), into the MWIR (e.g. dysprosium doped cadmium oxide) into the LWIR (e.g. silicon carbide and III-Nitrides) and FIR (e.g. phosphide-, antimonide-, arsenide- and telluride-based semiconductors). Finally, these emitters are also strong absorbers of light on resonance, and highly reflective off-resonance and therefore can be used as a passive device that when illuminated by an external light source or by the thermal energy of the local environment can provide a similar narrow-band and polarized response, but in this case could be covert even in areas where minimal background emission is anticipated. These and other applications derived from these modulated IR emitters also benefit from the atmospheric windows (e.g. the 3-5 and 8-12 μm windows, denoted by gray cross-hatched regions in FIG. 4), whereby light with these wavelengths can be transmitted over long distances with minimal absorption or scattering of light within the atmosphere. Alternatives Many additional uses in both the military and commercials spheres could be realized from this invention. Such modulated thermal sources could be used for molecular sensing, as the basis for free space communications, as on-chip sources for infrared nanophotonic devices or lab-on-a-chip approaches or for spectroscopy. Although particular embodiments, aspects, and features have been described and illustrated, one skilled in the art would readily appreciate that the invention described herein is not limited to only those embodiments, aspects, and features but also contemplates any and all modifications and alternative embodiments that are within the spirit and scope of the underlying invention described and claimed herein. The present application contemplates any and all modifications within the spirit and scope of the underlying invention described and claimed herein, and all such modifications and alternative embodiments are deemed to be within the scope and spirit of the present disclosure.
046876200
description
DESCRIPTION OF THE PREFERRED EMBODIMENT In the operation of a commercial pressurized water reactor it is desirable to be able to prolong the life of the reactor core to better utilize the uranium fuel and to be able to effectively change the reactor core power output in response to load follow requirements. The invention described herein provides a means to control a spectral shift reactor during load follow. Referrring to FIG. 1, the nuclear reactor is referred to generally as 20 and comprises a reactor vessel 22 with a removable closure head 24 attached to the top end thereof. An inlet nozzle 26 and an outlet nozzle 28 are connected to reactor vessel 22 to allow a coolant such as water to circulate through reactor vessel 22. A core plate 30 is disposed in the lower portion of reactor vessel 22 and serves to support fuel assemblies 32. Fuel assemblies 32 are arranged in reactor vessel 22 and comprise reactor core 34. As is well understood in the art, fuel assemblies 32 generate heat by nuclear fissioning of the uranium therein. The reactor coolant flowing through reactor vessel 22 in heat transfer relationship with fuel assemblies 32 transfers the heat from fuel assemblies 32 to electrical generating equipment located remote from nuclear reactor 20. A plurality of control rod drive mechanisms 36 which may be chosen from those well known in the art are disposed on closure head 24 for inserting or withdrawing control rods (not shown) from fuel assemblies 32. In addition, a plurality of displacer rod drive mechanisms 38 are also disposed on closure head 24 for inserting or withdrawing displace rods 40 from fuel assemblies 32. Displacer rod drive mechanism 38 may be similar to the one described in copending U.S. patent application Ser. No. 217,055, filed Dec. 16, 1980 in the name of L. Veronesi et al. entitled "Hydraulic Drive Mechanism" and assigned to the Westinghouse Electric Corporation. For purposes of clarity, only a selected number of displacer rods 40 are shown in FIG. 1. However, it should be understood, that the number of displacer rods 40 are chosen to correspond to the number of displacer rod guide tubes in fuel assemblies 32. A plurality of displacer rod guide structures 42 are located in the upper section of reactor vessel 2 with each being in alignment with a displacer rod drive mechanism 38 for guiding the movement of displacer rods 40 through the upper section of reactor vessel 22. A calandria 44 may be arranged between fuel assemblies 34 and displacer rod guide structures 42 and comprises a multiplicity of hollow stainless steel tubes arranged in colinear alignment with each displacer rod and control rod for providing guidance of the displacer rods and control rods through the calandria area and for minimizing flow induced vibrations in the displacer rods and control rods. Referring now to FIGS. 2-4, fuel assemblies 32 comprise fuel elements 48, grids 50, bottom nozzle 52, top nozzle 54, and guide tubes 56. Fuel elements 48 may be elongated cylindrical metallic tubes containing nuclear fuel pellets and having both ends sealed by end plugs. Fuel elements 48 may be arranged in a substantially 20.times.20 rectangular array and are held in place by grids 50. Guide tubes 56 which may number 25 are arranged in a generally 5.times.5 array within each fuel assembly 32. Each guide tube 56 occupies the space of about four fuel elements 48 and extend from bottom nozzle 52 to top nozzle 54 and provide a means to support grids 50, top nozzle 54 and bottom nozzle 52. Guide tubes 56 may be hollow cylindrical metallic tubes manufactured from Zircaloy and capable of accommodating rods such as displacer rods 40 or control rods. Displacer rods 40 and control rods are manufactured to be approximately the same size so that each guide tube 56 can equally accommodate either a displacer rod or a control rod. When not occupied by a rod, guide tubes 56 are filled with reactor coolant; however, when displacer rods 40 are inserted in guide tubes 56 displacer rods 40 displace the coolant therein. Grids 50 are positioned at various locations along the length of fuel assembly 32 and serve to space fuel elements 48 and guide tubes 56 at appropriate distances from each other and to allow the reactor coolant to circulate in heat transfer relationship with fuel elements 48. A more detailed description of a similar grid may be found in U.S. Pat. Nos. 3,379,617 and 3,379,619, both issued in the name of H. N. Andrews et al. As can be seen in FIG. 4, displacer rods 40 are elongated cylindrical substantially hollow rods which can be manufactured out of Zircaloy and may be of the type described in copending U.S. patent application Ser. No. 217,052 entitled "Displacer Rod For Use In A Mechanical Spectral Shift Reactor" filed Dec. 16, 1980 in the name of R. K. Gjertsen et al. and assigned to the Westinghouse Electric Corporation. Displacer rods 40 may also contain ZrO.sub.2 or Al.sub.2 O.sub.3 pellets for weighting the rod and enhancing its lowerability. Displacer rods 40 are arranged so as to be in colinear alignment with guide tube 56 so that displacer rods 40 may be inserted in guide tubes 56 when it is desired. Displacer rods 40 are supported from a common attachment known as a spider 58. Spider 58 comprises a body 60 with struts 62 radially extending from body 60. Displacer rods 40 are individually attached to each strut 62 to form an array corresponding to the array of guide tubes 56 into which displacer rods may be inserted. Spider 58 is attached to drive shaft 64 which is connected to displacer rod drive mechanism 38. Activation of displacer rod drive mechanism 38 causes drive shaft 64 to be either lowered or raised thereby inserting or withdrawing displace rods 40 from fuel assemblies 32 or core 34. It is important to note that each spider 58 is arranged to be able to insert displacer rods 40 into more than one fuel assembly 32. For example, as shown in FIG. 4, spider 58 is capable of inserting 25 displacer rods in center fuel assembly 32 and 4 displacer rods in each of the adjacent 4 fuel assemblies. In this manner displacer rods 40 can be moved in and out of fuel assemblies 32 without increasing the number of spiders and drive mechanisms. Referring now to FIGS. 5 and 6, displacer rod guide structures 42 comprise a plurality of split tube guides 70 which are designed to allow rods such as displacer rods or control rods to pass therethrough. Displacer rod guide structures 42 are located between calandria 44 and closure head 24 as shown in FIG. 1 and are arranged to correspond to each displacer rod drive mechanism 38. A number of spacers 72 are located at various locations along split tube guides 70 and together with split tube guides 70 serve to guide displacer rods 40 through the upper section of reactor vessel 22. As can be seen in FIG. 6, 8 split tube guides 70 may be provided for guiding displacer rods 40. The "split" in split tube guides 70 along with slots 74 in spacers 72 allow spider 58 to pass therethrough while maintaining alignment of the rods with guide tubes 56 in fuel assemblies 32. A center slot 76 is also provided for accommodating drive shaft 64 so that spider 58 may be moved therethrough. Referring again to FIG. 1, calandria 44 which comprises a multiplicity of tubes provides guidance for the rods such as displacer rods 40 through the calandria area. In general, the tubes in calandria 44 are not split tubes, as are split tube guides 70, so that spider 58 stops its descent when spider 58 nears the top of the tubes in calandria 44. When stopped at the top of calandria 44 all rods extend through the calandria tubes and are fully inserted in fuel assembly 32. While inserted in the calandria tubes, the rods are protected from the flow of reactor coolant thereby minimizing vibrations that would otherwise be induced by the high velocity of the reactor coolant in that area. In the invention as described herein, at least three different types of rods are capable of being inserted into guide tubes 56. For example, displacer rods, control rods, and gray rods may be arranged to be inserted in guide tubes 56. All of the rods are approximately the same size and configuration, but because of the materials with which they are made serve different purposes. Displacer rods 40 which may be either a hollow thick walled tube or may contain a low neutron absorbing material such as ZrO.sub.2 or Al.sub.2 O.sub.3 pellets are used to displace reactor coolant and thereby control reactor moderation. Control rods contain neutron absorbing material as is well understood in the art and serve to control core reactivity in a commonly understood fashion. Gray rods are similar to displacer rods 40 but are made of a an intermediate neutron absorbing material such as stainless steel so that their reactivity worth per rod is greater than than of displacer rods 40. Referring now to FIGS. 7-11, the quarter core arrangement of fuel elements 48, displacer rods 40, control rods 80, gray rods 82, and unrodded locations 84 are shown. It is to be understood that the full reactor core configuration can be established by extrapolating the quarter core shown in FIG. 7. Actually, the quarter core shown in FIG. 7 is a mirror image of the eighth core taken along line A--A of FIG. 7. However, the quarter core of FIG. 7 is being shown for clarity. As can be seen in FIG. 10, each fuel assembly 32 comprises an array of fuel elements 48 and an array of guide tubes 56. Generally, control rods 38 and gray rods 82 are used only in the diagonally arranged guide tubes 56 while displacer rods 40 are generally used in all guide tubes 56 of a given fuel assembly. In addition, an instrument tube 88 is provided near the center of each fuel assembly 32 for accommodating data instrumentation. While each fuel assembly 32 is essentially identical to the one shown in FIG. 10, each fuel assembly 32 can produce a different function depending on whether guide tubes 56 are occupied by reactor coolant, displacer rods 40, control rods 80, or gray rods 82. Displacer rods 40 and gray rods 82 are generally chosen to be approximately the same size so as to displace approximately the same volume of water. However, gray rods 82 can be thick walled stainless steel cylindrical rods which gives each individual gray rod a higher reactivity worth than a single displacer rod. The wall thickness of the gray rods may be approximately 0.065 inches. But since the gray rods are usually arranged in clusters of 9 as opposed to clusters of 41 displacer rods, each gray rod cluster has a smaller reactivity worth than a displacer rod clusters. Thus, by proper selection of materials and by proper selection of the number of rods, a balanced reactivity worth can be attained for the gray rods and displacer rods. In addition, since the reactivity worth of a gray rod cluster may be approximately 25% of a displacer rod cluster, various combinations of movements of gray rods clusters and displacer rod clusters can yield numerous reactivity worths throughout the core. Referring now to FIG. 11, a fuel assembly 32 in which no control rods 80 or gray rods 82 are used and in which only displacer rods 40 are used in guide tubes 56 is referred to generally as displacer assembly 90. A fuel assembly 32 in which both displacer rods 40 and control rods 80 are employed (but no gray rods) is referred to as control assembly 92. Similarly, fuel assembly 32 in which both displacer rods 40 and gray rods 82 are used is called a gray assembly 94. It should be noted that in FIG. 11 fuel elements 48 have been omitted for clarity and that those fuel assemblies are similar to those shown in FIG. 10. Still referring to FIG. 11, each of the control rods 80 and gray rods 82 are attached to a spider (not shown) similar to spider 58 except that the spider for the control rods 80 or gray rods 82 generally only effects one fuel assembly. In this manner, all control rods 80 or gray rods 82 in a given fuel assembly can be raised or lowered by a single drive mechanism. Furthermore, since each displacer rod spider 58 can extend into the adjacent fuel assemblies (as illustrated in the center portion of FIG. 11 and in FIG. 4), the displacer rod spider's 58 movement effects the control on five fuel assemblies and reduces the number of displacer rod drive mechanisms needed. Of course, on the periphery of the quarter core (as shown in FIG. 7) the particular spiders may move less than the usual number of rods because there are no adjacent fuel assemblies or there are unrodded locations 84. Referring again to FIGS. 8 and 9 which comprise FIG. 7, a quarter core arrangement. Each row or partial row is numbered 100-114 and each column or partial column is numbered 116-130 and comprises: Fuel Assembly (100,116) quarter displacer assembly PA0 (100,118) half control assembly PA0 (100,120) half displacer assembly PA0 (100,122) half control assembly PA0 (100,124) half displacer assembly PA0 (100,126) half control assembly PA0 (100,128) half displacer assembly PA0 (100,130) half gray assembly PA0 (102,116) half control assembly PA0 (102,118) full displacer asembly PA0 (102,120) full gray assembly PA0 (102,122) full displacer assembly PA0 (102,124) full gray assembly PA0 (102,126) full displacer assembly PA0 (102,128) full control assembly PA0 (102,130) full displacer assembly PA0 (104,116) half displacer assembly PA0 (104,118) full gray assembly PA0 (104,120) full displacer assembly PA0 (104,122) full control assembly PA0 (104,124) full displacer assembly PA0 (104,126) full control assembly PA0 (104,128) full displacer assembly PA0 (104,130) partial control-unrodded assembly PA0 (106,116) half control assembly PA0 (106,118) full displacer assembly PA0 (106,120) full control assembly PA0 (106,122) full displacer assembly PA0 (106,124) full control assembly PA0 (106,126) full displacer assembly PA0 (106,128) full control assembly PA0 (106,130) full displacer assembly PA0 (108,116) half displacer assembly PA0 (108,118) full gray assembly PA0 (108,120) full displacer assembly PA0 (108,122) full control assembly PA0 (108,124) full displacer assembly PA0 (108,126) full control assembly PA0 (108,128) full displacer assembly PA0 (110,116) half control assembly PA0 (110,118) full displacer assembly PA0 (110,120) full control assembly PA0 (110,122) full displacer assembly PA0 (110,124) full control assembly PA0 (110,126) full displacer assembly PA0 (110,128) partial displacer unrodded asembly PA0 (112,116) half displacer assembly PA0 (112,118) full control assembly PA0 (112,120) full displacer assembly PA0 (112,122) full control assembly PA0 (112,124) full displacer assembly PA0 (112,126) partial displacer unrodded assembly PA0 (114,116) half gray assembly PA0 (114,118) full displacer assembly PA0 (114,120) partial control unrodded assembly PA0 (114,122) full displacer assembly As can be seen from the above description of the quarter core, the core configuration based on this concept can be illustrated generally as shown in FIG. 11. Basically, the fuel assembly in the center of the full core as represented by fuel assembly (100,116) in FIG. 7 can be chosen to be either a control assembly 92 or preferably a displacer assembly 90. Once this is chosen, the four fuel assemblies immediately adjacent to the flat sides of the center fuel assembly are chosen to be the other type and the fuel assemblies on the diagonal are chosen to be the same type as the center assembly. This pattern is then continued in an alternating fashion. For example, the center fuel assembly (100,116) in FIG. 7 was chosen to be a displacer assembly 90 so that the fuel assemblies on its adjacent flat sides are chosen to be either control assemblies 92 or gray assemblies 94 while those on the diagonal are chosen to be displacer assemblies 90. This pattern is repeated in alternating fashion until the periphery of the core is reached where the end fuel assemblies may be chosen to be hybrid assemblies based on the nuclear physics of the particular core. Whether a particular assembly is chosen to be a control assembly 92 or a gray assembly 94 is determined by first selecting the number and location of control assemblies needed based on conventional core design. The remainder of the assemblies not chosen to be control assemblies 92 are then used as gray assemblies 94. Thus, substantially the entire core can be arranged on an alternating pattern of displacer assemblies and control or gray assemblies with practically all the fuel assemblies being served by at least one displacer rod spider 58 and with each displacer rod spider 58 serving generally 5 fuel assemblies. Moreover, each fuel assembly is served by at least one drive mechanism for either displacer rods, control rods or gray rods. The illustrated core arrangement provides a means by which the neutron spectrum can be controlled in a "spectral shift" fashion by controlling the moderator volume in the core. This can be accomplished by displacing and replacing the water coolant in the core at appropriate times thereby changing the moderation of the core. In the present invention, displacer rods 40 and gray rods 82 can be used to effect this moderation change. In operation, all displacer rods 40 and gray rods 82 are inserted in core 34 at the beginning of the core life. However, none of the control rods 80 need be inserted at that time. The insertion of displacer rods 40 and gray rod 82 is done by activating the appropriate drive mechanism such as displacer rod drive mechanism 38. When the drive mechanism is activated, displacer rods 40 and gray rods 82 fall into the appropriate guide tubes 56 in fuel assemblies 32. The displacer rods and gray rods will displace their volume of coolant (water) thus reducing the volume of moderator in core 34. The reduction of moderator hardens the neutron spectrum of the core and increases plutonium production. This hardening of the neutron spectrum is generally referred to as "spectral shift". The harder neutron spectrum reduces boron chemical shim requirements, results in a more negative moderator temperature coefficient, and reduces or eliminates burnable poison requirements. As the uranium fuel in the core is depleted over the life of the core, a certain number of displacer rods 40 and/or gray rods 82 may be withdrawn from the core by activating their respective drive mechanisms. The withdrawal of the rods allows more water-moderator into the core region and increases moderation of the core. This, in effect, introduces reactivity worth at a time when fuel depletion is causing a reactivity worth depletion. Thus, the reactivity of the core can be maintained at appropriate levels for a longer time. The withdrawal of the rods can continue at a selective rate (depending on core conditions) until, near the end of core life, all displacer rods 40 have been withdrawn from the core. In addition to the use of displacer rods 40 and gray rods 82 for the purpose of "spectral shift", these rods can also be used for load follow purposes. For example, when the concentration of boron in the reactor coolant falls below approximately 100 ppm the capability of a boron bleed-and-feed operation to compensate for the xenon transient during load follow may not be practical. However, by withdrawing or inserting selected displacer rods 40 or gray rods 82, a proper reactivity change can be made to compensate for the xenon transient. Moreover, such a maneuver can be performed to adjust overall power requirements or to adjust radial power distributions. Since gray rods 82 have a different reactivity worth than displacer rods 40 and since gray rods 82 and displacer rods 40 are located in different core locations, proper selection and movement of the rods can accomplish delicate reactor control. Calculations of the reactivity worth of a 41-rod displacer rod cluster indicates that such a cluster may have a reactivity worth of approximately 75 pcm. That is, core reactivity is expected to increase by about 75 pcm when a single 41-rod displacer rod cluster is moved from fully inserted to fully withdrawn when fuel burnup is about 11,000 MWD/MTU. At the same time, the moderator temperature coefficient of reactivity is predicted to be about -35 pcm/.degree.F. Hence, withdrawal of a single 41-rod displacer rod cluster, with no associated change in control rod position or power level, will result in a reactor coolant average temperature increase of about 2.degree. F. with the temperature change lagging behind displacer rod movement by about 10-20 seconds (one loop transit time). Since the coolant average temperature changes in response to displacer movement are small and occur slowly, coolant temperature change can be used to "cushion" the effect of displacer movement on overall core reactivity. That is, due to the negative moderator temperature coefficient, the reactor coolant temperature change will tend to offset a portion of the reactivity change caused by the displacer rod movement thus providing a smooth transition in core reactivity when a displacer rod cluster is moved. Since displacer rod cluster reactivity worth and the absolute value of the moderator temperature coefficient change in the same direction and at comparable fractional rates with changing boron concentration and hydrogen-to-uranium ratio in the core, the temperature change per unit displace rod cluster movement is generally independent of core conditions throughout the latter part of the core life. Referring to FIG. 12, utilizing these concepts for reactor control two reactor coolant temperature bands can be selected for reactor operating purposes. These bands may be different from and wider than the conventional operating bands. One band, band A, is the wide band and is selected to be approximately 4.degree. F. wide, 2.degree. F. on either side of the reactor coolant average temperature set point, T.sub.s. T.sub.s is chosen to be the reactor coolant average temperature at which it is desired to operate the reactor. As an alternative, the average cold leg temperature may be used. An administrative guidance limit or narrow band, band B, may be chosen to be approximately 3.degree. F. wide, 1.5.degree. F. on either side of set point temperature T.sub.s. Band A is chosen so that is the reactor coolant temperature reaches this limit automatic systems are initiated to reverse the temperature drift. Band B is chosen as a working guide limit so that as the reactor coolant temperature approaches this limit either operator or automatic selection and initiation of displacer rod movement may begin to avoid reaching the band A limit. In this manner as the reactor coolant temperature drifts downwardly such as during xenon accumulation as illustrated between t.sub.0 and t.sub.1, withdrawal of a particular displacer or gray rod cluster is initiated. Between t.sub.1 and t.sub.2 the cluster is withdrawn which takes approximately 15 minutes to achieve complete withdrawal. The withdrawal of a cluster allows additional water-moderator to enter the core which increases core reactivity and results in the reactor coolant temperature drifting upwardly. As the xenon continues to accumulate the coolant temperature begins to drop again as illustrated between t.sub.2 and t.sub.3. As t.sub.3 is approached it again becomes necessary to select and withdraw the next cluster, either a 41 rod displace cluster or a 9 rod gray cluster depending on the reactivity addition needed. The time frame between t.sub.4 and t.sub.5 indicates the time frame in which the next cluster should begin to be withdrawn to avoid reaching band A's limit. In this manner reactor coolant temperature variations such as those due to xenon transients can be compensated for without adjusting the boron concentration in the coolant and while prolonging the core life. In addition to determining when a particular cluster should be moved, it is also necessary to determine which cluster or group of clusters should be moved and whether they should be moved in or out of the core. In this regard it can be appreciated that since a displacer rod cluster effects a larger core area than does a gray rod cluster and since individual gray rods have different reactivity worth than do individual displacer rods, a proper selection and movement of various clusters can effect core reactivity levels and radial power distribution. Referring now to FIG. 13, a power sharing fraction calculator 100 determines the fraction of the total core power that is attributed to each fuel assembly. This can be ascertained in conventional manner by having a sufficient number of in-core radiation detectors to determine local neutron flux or nuclear power level magnitudes. For example, about 60 fuel assemblies may be equipped with about 5 radiation detectors such as gamma detectors. The 5 radiation detectors can be axially spaced along the fuel assembly so that in all about 300 in core detectors can provide instantaneous reactivity levels for 60 core zones. These readings, together with calibration and weighting factors, can be fed to power sharing fraction calculator 100 for determining the power sharing fraction borne by each core zone. At the same time, current condition compiler 102 compiles other core conditions such as boron concentration, hydrogen-to-uranium fraction, and present cluster positions. This information together with the information from power sharing fraction calculator 100 is transmitted to displacer movement effect predictor 104 which determines the reactivity change and power sharing fraction change that would occur by moving each cluster. It has been found that the reactivity change associated with a particular fuel assembly by moving the corresponding cluster is related to the present fuel assembly power density. The correlation can be expressed as follows: EQU .DELTA.R=m.times.APD where .DELTA.R=reactivity change of the fuel assembly by inserting or withdrawing the corresponding cluster (displace rods or gray rods); PA1 APD=fuel assembly power density before moving the cluster; and PA1 m=straight line slope PA1 NPD=new fuel assembly power density PA1 OPD=old fuel assembly power density PA1 BU=burnup in MWD/MTU It has also been determined that the slope, m, can be related to burnup as illustrated by the following data: ______________________________________ Burnup Slope, m (MWD/MTU) (pcm per cluster/unit power density) ______________________________________ 1,000 5.4 6,000 32.8 11,000 60.0 ______________________________________ yielding a relation of slope to burnup of: EQU m=0.0054.times.BU where BU=burnup in MWD/MTU. Therefore, EQU 1/W2/R=0.0054.times.BU.times.APD By using this relationship, movement effect predictor 104 can predict the reactivity change to be expected from moving the cluster corresponding to that fuel assembly. This information is then transmitted to cluster selector 106. It has also been found that the post-withdrawal power density of a particular fuel assembly can be related as follows: EQU NPD=(1.17+0.000033.times.BU).times.OPD where Thus the power density change in a particular fuel assembly can be found based on its power density prior to cluster movement. This information is then transmitted to cluster slector 106. A requirements predictor 108 which may be chosen from those well known in the art is arranged to determine and transmit cluster selector 106 the amount of reactivity increase or decrease that is anticipated to be needed. This can be based on data such as coolant average temperature, power level, band limits, and set point considerations. Power sharing fraction calculator also feeds the power sharing fraction for each fuel assembly to cluster selector 106. Cluster selector 106 accepts the power sharing fraction for each fuel assembly prior to a cluster movement, the reactivity change to be expected if a cluster were moved, the present fuel assembly power density (OPD) for each fuel assembly, the predicted fuel assembly power density (NPD) for each fuel assembly, and the reactivity change required. From this, a new power sharing fraction for each fuel assembly can be determined. Based on this information and the current position of each cluster, cluster selector 106 can select the one or more grouping of cluster movements that will achieve the desired reactivity change without distorting the overall power sharing profile. In general, this search may include predicting the next reactivity change and the movement required thereby so as to prevent making a cluster movement that could hinder latter cluster movements. The selected cluster groupings can be transmitted directly to power distribution verifier 110, operator readout 112, and automatic system control 114. Power distribution verifier can check the predicted power sharing fractions to the old power sharing fractions and can trip alarm 116 if the predicted change is outside set limits. The operator can view operator readout 112 and select which of the selected cluster groupings to use or the selection can be made automatically by cluster selector 106 and transmitted to automatic system control 114 for implementation of the cluster movement. Thus, based on these criteria, various movements (insertions or withdrawals) of numerous combinations of available displacer rod or gray rod clusters can be evaluated and implemented for controlling a pressurized water reactor such as during load follow. Therefore, the invention provides a method of operating a pressurized water nuclear reactor in which the reactor power level can be changed without making control rod or chemical shim changes.
summary
047926929
description
The lamp 10 shown in the drawing includes a substantially point-shaped source of radiation 11 disposed at one focus of an ellipsoidal reflector 12. The lamp 10 produces a convergent beam of radiation the angle .alpha.E of which measures about 30.degree. with respect to the optical axis 13. At or close to the second focus of the reflector 12, the entrance surface 14 of an optical waveguide 15 is dispoeed. The optical axis of the waveguide 15 at the entrance surface 14 coincides with the optical axis 13 of the reflector 12. The waveguide 15 has a crowned exit surface 16, a bent portion 17 of constant diameter close to the exit surface 16, and a portion 18 having a steeper tapering than exists between the entrance surface 14 and the bent portion 17. The portion 18 is disposed immediately before the exit surface 16. The optical waveguide 15 has an overall conical shape of circular cross-section with the following dimensions: ______________________________________ diameter d1 of the entrance surface 14: 10 mm diameter d2 of the exit surface 16: 3 mm length of the waveguide measured along approx. 100 mm its optical axis: length of the straight portion of the approx. 75 mm waveguide between the entrance surface 14 and the beginning of the bent portion 17: diameter of the waveguide in the bent 4 mm portion 17: radius of the center line of the bent 20 mm portion 17: angle of curvature: approx. 75.degree. length of the portion 18 of steeper 5 mm tapering, within which the dia- meter decreases from 4 mm to 3 mm: ______________________________________ The waveguide 15 is made of quartz having a refractive index of approximately 1.46, which approximately equals .sqroot.2. The waveguide may be formed as a solid rod or composed of a plurality of discrete radiation conducting fibers. Glass or synthetic material may be used instead of quartz. Given the above values, a beam of radiation incident on the entrance surface 14 at an angle .alpha.E of approximately 22.degree. is transmitted through the waveguide 15 to the exit surface 16 which it hits at the limit angle of total reflection, leaving the exit surface at an angle of 90.degree. with respect to the optical axis. Beams incident on the entrance surface 14 at smaller angles leave the exit surface 16 at correspondingly smaller angles. This results in an overall semi-spherical lobe of radiation from the exit surface 16. Beams incident on the entrance surface 14 within an angular range of approximately 22.degree. to 30.degree. leave the waveguide laterally before reaching the exit surface 16 substantially within that region in which the diameter is smaller than about 3.6 mm. It is therefore preferable to select the entrance angle .alpha.E greater than that value (approximately 22.degree.) at which all radiation is transmitted to the exit surface, thus ensuring that radiation of sufficient intensity is available at the exit surface 16 even under large angles with respect to the optical axis. Since the portion 18 disposed immediately before the exit surface 16 has a steeper tapering than the remaining waveguide, any radiation which does not reach the exit surface 16 will leave the waveguide very shortly before the same, thereby enhancing the useful radiation in case the rod is laterally applied. If the ratio of the refractive index of the optical waveguide to that of the environment has the above value of .sqroot.2, any beam carried by the waveguide will reach the exit surface 16, and the largest exit angle will be 90.degree.. With a smaller refractive index ratio, the maximum exit angle will be smaller than 90.degree.. If, in this case, the angle of incidence .alpha.E is increased, radiation will be emitted from the peripheral wall of the waveguide. If the refractive index ratio is made greater than .sqroot.2 part of the radiation transmitted through the waveguide will be totally reflected at the exit surface 16; while this may be avoided by reducing the angle of incidence .alpha.E, a corresponding portion of the radiation emitted by the lamp 10 will be lost, or th ellipsoidal reflector 12 must be shaped so that it surrounds the source of radiation 11 more completely with the result that the reflector must have a greater axial length, thereby incressing the overall dimension of the lamp 10. If the exit surface 16 is made planar, in contrast to the above-described embodiment, it will be seen that the radiation intensitydecreases and a dark zone is produced in a range of about 85 to 90.degree. with respect to the optical axis. This dark zone is avoided by the crowned or rounded shape of the exit surface 16.
039487237
claims
1. In combination a nuclear reactor and a fuel subassembly and isolating device for the reactor, said reactor including a vessel containing a coolant, a core surrounded by said coolant, said core containing a plurality of fuel subassemblies, said fuel subassemblies including handle means on the upper ends thereof, each of said handle means being configured to form a camming surface, and a closure head for said vessel containing an access port positionable above the various fuel subassembly locations; said centering and isolating device comprising: plug means for insertion into said access port, said plug having means for limiting penetration thereof into said port and further including a longitudinally extending opening therethrough of a size to permit passage of a fuel subassembly; an elongated structural tube attached to the lower end of and extending downwardly from said plug means; a downwardly extending camming tube vertically disposed under said structural tube; means for interconnecting said structural tube and said camming tube, said means permitting limited radial movement of said camming tube relative to said structural tube and being capable of raising and lowering said camming tube relative to said structural tube; said camming tube having a larger internal cross section than the external cross section of said fuel subassemblies and being configured to engage said camming surfaces of adjacent fuel subassemblies which lowered about a selected subassembly to bring said camming tube into axial alignment with said selected subassembly; whereby upon lowering said camming tube into said reactor core to isolate a selected fuel subassembly radial movement of said camming tube occurs if said tube is misaligned with said subassembly to thereby bring said tube and said subassembly into axial alignment with one another. 2. The combination of claim 1 wherein said means for interconnecting said structural tube and said camming tube comprises: axially movable rod means extending downward from within said structural tube; a substantially cylindrical housing connected to the end of said rod means for axial movement therewith; a first annular plate disposed within said housing said plate being restrained from radial or axial movement with respect to said housing, the inner diameter of said first plate being larger than the outer dimension of said camming tube; a second annular plate disposed within said housing in overlying relation with said first annular plate, the inner diameter of said second plate being larger than the outer dimension of said camming tube; a third annular plate disposed within said housing in overlying relation with said second annular plate, said third annular plate comprising an integral outward extension of the upper end of said camming tube, said camming tube extending downward through said annular plates to a level below the bottom of said first plate; means for preventing relative rotational motion between said first annular plate and said second annular plate while permitting limited motion of said second plate relative to said first plate along a single diametrical axis of said first plate; means for preventing relative rotational motion between said second annular plate and said third annular plate while permitting limited motion of said third plate relative to said second plate along a diametrical axis of said second plate perpendicular to said axis of said first plate. 3. The combination of claim 2 wherein said first annular plate is mounted for relative rotational movement with respect to said housing and including rotational drive means extending downward from within said structural tube and carried at its lower end by said housing for operationally engaging and selectively rotating said first plate, whereby upon actuating said rotational drive means said camming tube is caused to rotate. 4. The combination of claim 2 wherein said means for preventing relative rotational motion between said first annular plate and said second annular plate comprises key means longitudinally coincident with said diametrical axis of said first plate, extending from one of said first and second annular plates and a mating keyway on the other of said annular plates; and wherein said means for preventing relative rotational motion between said second annular plate and said third annular plate comprises key means longitudinally coincident with said diametrical axis of said second plate, extending from one of said second and third annular plates and a mating keyway on the other of said annular plates.
abstract
Systems and methods for obtaining and displaying a collimated X-ray image are described. The methods can include providing an X-ray device having an X-ray source, a square or rectangular X-ray detector, and a collimator. The collimator can be sized and shaped to collimate an X-ray beam from the X-ray source that exposes a receptor region on the detector. The collimator can allow the X-ray image received by the X-ray detector to have any suitable shape that allows a relatively large view of the image to be displayed and rotated on the display device without changing the shape or size of the image as it rotated. In some instances, the collimator provides the image with superellipse shapes or cornerless shapes having four substantially straight edges with a 90 degree corner missing between at least two edges that run substantially perpendicular to each other. Other embodiments are described.
058728252
abstract
When hydrogen is generated within the containment of a nuclear power station, its containment atmosphere must be inerted. An undesired pressure buildup within the containment is prevented during such inerting with the apparatus and the method. It is possible to vent and inert the containment atmosphere simultaneously. A reversible activity holdup device is provided, which makes it possible to vent the containment atmosphere, without radioactive material being released into the surroundings. It is thereby also possible for the containment of a nuclear power station to be inerted even as a preventive measure, so that the safety of the nuclear power station plant is markedly increased.
description
1. Field of the Invention The invention relates to an extreme UV radiation focusing mirror for focusing of extreme UV radiation which is emitted by a high density and high temperature plasma, and an extreme UV radiation source device using this extreme UV radiation focusing mirror. The invention relates especially to an extreme UV radiation focusing mirror which focuses extreme UV radiation of the above described plasma with high efficiency and which, moreover, can make the far-field distribution of the light beam at the focus point uniform, and an extreme UV radiation source device using this extreme UV radiation focusing mirror. 2. Description of the Prior Art According to the miniaturization and increased integration of integrated semiconductor circuits, an increase in resolution is required in a projection exposure device for its manufacture. To meet this requirement, the wavelengths of the exposure radiation source are being increasingly shortened. As a semiconductor exposure radiation source of the next generation in succession to an excimer laser device, an extreme UV radiation source device (hereinafter also called an EUV radiation source device) is being developed which emits extreme UV radiation (extreme ultra violet radiation; hereinafter also called EUV radiation) with wavelengths from 13 nm to 14 nm, especially with a wavelength of 13.5 nm. A primary goal of the invention is to eliminate the above described disadvantages in the prior art. Therefore, a primary object of the invention is to devise an EUV focusing mirror in which the far-field distribution of the EUV radiation which has been focused by the EUV focusing mirror can be made advantageous and the nonuniformity (scattering) of the illuminance can be suppressed, and to devise an EUV radiation source device using such an EUV focusing mirror. The EUV focusing mirror in accordance with the invention, like a conventional EUV focusing mirror, has several concave mirrors in a rotation shape with different diameters. The concave mirrors comprising the EUV focusing mirror are coaxially arranged such that their axes of revolution agree with one another such that the focus positions essentially agree with one another. The EUV focusing mirror is made such that the EUV radiation with a grazing incidence angle from 0° to 25° can be advantageously reflected, and moreover, focused by this arrangement of the interlaced high precision concave mirrors. The above described object is also achieved in accordance with the invention as follows: (1) For an extreme UV radiation focusing mirror of the grazing incidence type in which there are several nested concave mirrors with different diameters, on the end of the respective concave mirror on the side which is not the reflection surface, a bevel is formed such that it has a given angle with respect to the radiation reflection surface. This means that a bevel is formed on the end on the radiation incidence side of the respective concave mirror of the EUV focusing mirror and/or on the end on the radiation exit side thereof. Specifically, on the end on the radiation incidence side and on the end on the radiation exit side of the respective concave mirror, a bevel is formed such that the end on the radiation incidence side and/or the end on the radiation exit side of the above described concave mirror drops out of the away region of the incidence EUV radiation which is focused by the EUV focusing mirror, and of the away region of the exit radiation thereof. The area which contains this bevel is called the edge area. Furthermore, the state in which on the end a bevel is formed such that its thickness becomes smaller, the more it approaches the tip, is called a knife edge type. Also, the end on which this bevel is formed is called the knife edge part. (2) In (1), the shape of the reflection surface of the above described concave mirror is one of the shapes of an ellipsoid of revolution, a paraboloid of revolution, or a Wolter shape. In this connection, the focal points of the respective concave mirrors essentially coincide with one another. (3) In (1) and (2), the angle of the bevel on the radiation incidence side of the end of the above described concave mirror is set such that it is a positive angle in the clockwise direction with respect to the running direction of the extreme UV radiation which is incident on the above described radiation incidence end. (4) In (1) and (2), the angle of the bevel on the radiation exit side of the end of the above described concave mirror is set such that it is a negative angle in the clockwise direction with respect to the running direction of the extreme UV radiation which emerges from the above described radiation exit end. (5) In (1) and (2), the angle of the bevel on the radiation incidence side of the end of the above described concave mirror is set such that it is a positive angle in the clockwise direction with respect to the running direction of the extreme UV radiation and furthermore the angle of the bevel on the radiation exit side of the end of the above described concave mirror is set such that it is a negative angle in the clockwise direction with respect to the running direction of the emerging UV radiation. (6) In an extreme UV radiation device which comprises the following: a vessel; a raw material supply means for supply of raw material which contains an extreme UV radiation fuel and/or a compound of an extreme UV radiation fuel to this vessel; a means for heating and excitation which heats and excites the supplied raw material in the above described vessel and in which a plasma is produced that emits radiation which contains extreme UV radiation; a focusing optical means which is located in the above described vessel to focus the radiation which has been emitted from the above described plasma; and a radiation extracting part from which the focused radiation is extracted from the vessel,the above described focusing optical system is the extreme UV radiation focusing mirror which was described in (1) to (5).Action of the Invention As was described above, the following effects can be obtained in accordance with the invention. (1) By the measure that, on the side of the end on the radiation incidence side and/or of the end on the radiation exit side which does not constitute the reflection surface of the respective concave mirror of the EUV focusing mirror, a bevel in the form of a knife edge is formed, the disadvantage of formation of nonuniformity/scattering of the illuminance on the workpiece by the shielded region can be prevented by the amount of thickness of the substrate material of the respective concave mirror. (2) By the measure that the angle of the bevel on the radiation incidence side of the end of the concave mirror is set such that it is a positive angle in the clockwise direction with respect to the running direction of the extreme UV radiation which is incident on the radiation incidence end and that the angle of the bevel on the radiation exit side of the end of the concave mirror is set such that it is a negative angle in the clockwise direction with respect to the running direction of the extreme UV radiation emerging from the radiation exit end, the shielding ratio of the grazing incident EUV radiation onto the end of the respective concave mirror can be reduced to a dramatic degree and the region with reduced light intensity for far-field distribution can be reduced. It becomes possible to reduce the nonuniformity of the illuminance on the workpiece. The invention is further described below with reference to the accompanying drawings. FIGS. 1 & 2 schematically show the arrangement of a focusing mirror in accordance with the invention, FIG. 1 being a cross section of the focusing mirror through a plane which passes through the optical axis (A-A cross section as shown in FIG. 2). FIG. 2 shows the focusing mirror as viewed from the radiation exit side. In the figures, a case is shown in which the above described shape of the reflection surface is of the Wolter type. However, the reflection shape can also be an ellipsoid of revolution, a paraboloid of revolution or the like. FIGS. 1 & 2 show an arrangement in which there are, for example, five nested Wolter mirrors a, b, c, d, and e of different diameters. The reflection surface of the respective Wolter mirrors a, b, c, d, and e, proceeding from the radiation incidence side, have the shape of a hyperboloid and the shape of an ellipsoid. Furthermore, knife edge parts are formed by bevels on the ends of each of the Wolter mirrors b through e on the sides which do not constitute the reflection surfaces. As is shown in FIG. 2, on the radiation exit sides of the respective Wolter mirror a to e, there is a spider 2a which is comprised, for example, of a spider flange 2b of copper and spokes 2c. The ends of the respective Wolter mirrors a to e, on the radiation exit side, as shown in FIG. 1, are installed in a groove of the spoke 2c, and for example, are attached by means of a cement or a fixing brace or the like. FIG. 3(a) is a schematic of the geometric locations of the light beams of one embodiment of the focusing mirror in accordance with the invention. In the figure, as also in FIG. 7(a), the solid lines a1, b1, c1, d1 and e1 show the geometric locations of the light beams which pass proceeding from the plasma position through the radiation incidence ends and radiation exit ends of the respective Wolter mirrors a, b, c, d, and e. This means that the solid lines a1, b1, c1, d1 and e1 represent the geometric locations of the light beams in the case of the maximum incidence angle on the respective Wolter mirrors a, b, c, d, and e of the radiation which has been focused by the respective Wolter mirrors a, b, c, d, and e onto given sites. On the other hand, the double dot-dash lines a3, b3, c3, d3 and e3, as also in FIG. 7(a), are the geometric locations of the light beams in the case of reflection on the boundaries between the hyperbolas and the ellipsoids for the respective Wolter mirrors a, b, c, d, and e. This means that the double dot-dash lines a3, b3, c3, d3 and e3 are the geometric locations of the light beams in the case of the minimum incidence angle of the radiation which is being focused by the respective Wolter mirrors a, b, c, d and e onto given sites, into the respective Wolter mirrors a, b, c, d and e. It also means that the rays which have been focused by the respective Wolter mirrors a, b, c, d and e pass through a space between the solid lines a1, b1, c1, d1, e1 and the double dot-dash lines a3, b3, c3, d3 and e3. The radiation which has been focused by the Wolter mirror e passes through a space between the light beams e1 and the light beams e3 while the light beams which pass outside this space are not focused. The geometric locations of the light beams which are focused by the respective Wolter mirrors a, b, c, d, e therefore appear as follows. The light beams proceeding from the plasma emission point until incidence on the hyperbolas of the respective Wolter mirrors a, b, c, d, e pass through the region which is formed by the following: the distance between the plasma and the incidence ends of the respective Wolter mirrors a, b, c, d, and e for the solid lines a1, b1, c1, d1, and e1; the distance between the plasma and the boundaries between the hyperbolas and the elliptical surfaces of the respective Wolter mirrors a, b, c, d, and e for the double dot-dash line a3, b3, c3, d3 and e3, and a hyperbola. Light beams which pass outside this region are not focused. On the other hand, the light beams which are reflected by the elliptical surfaces of the respective Wolter mirrors a, b, c, d, and e pass through a region which is formed by the following: a distance after reflection from the elliptical surfaces for the solid lines a1, b1, c1, d1, and e1; a distance after reflection from the boundaries between the hyperbolas and the elliptical surfaces for the double dot-dash lines a3, b3, c3, d3 and e3; and solid lines a1, b1, c1, d1, and e1; double dot-dash lines a3, b3, c3, d3 and e3; an elliptical surface. Light beams which pass outside the region are not focused. Conventionally, the above described double dot-dash lines a3, b3, c3, and d3 were shielded by the thick parts of the incidence ends of the respective Wolter mirrors b, c, d, e. The geometric locations of the light beams in the case of a minimum incidence angle on the respective Wolter mirrors a, b, c, d, e were therefore the dot-dash lines a2, b2, c2 and d2, as is shown in FIG. 7(b). For the EUV focusing mirror in accordance with the invention, the sides of the radiation incidence ends of the respective Wolter mirrors b to e which do not constitute reflection surfaces, are made in the form of knife edges so that the above described double dot dash lines a3, b3, c3, and d3 are not shielded by the thick parts of the ends on the radiation incidence sides (radiation incidence ends) of the respective Wolter mirrors b, c, d, e. This means that, on the radiation incidence ends of the respective Wolter mirrors b, c, d, e, there are knife edge parts bin, cin, din, ein, as is shown in FIG. 3(b). The angle of the edge side of the knife edge part (plane including the bevel) is set such that it becomes an identical or positive angle with respect to the directions in which the light beams a3, b3, c3, d3 (shown using the double dot-dash lines run), when the clockwise direction is considered positive. Likewise, the radiation exit ends of the respective Wolter mirrors b, c, d, e are made in the form of a knife edge so that the above described double dot-dash lines a3, b3, c3, and d3 are not shielded. This means that, on the radiation exit and incidence ends of the respective Wolter mirrors b, c, d, e, there are knife edge parts bout, cout, dout, eout, as is shown in FIG. 3(c). The angle of the edge side of the knife edge part (plane including the bevel) is set such that it becomes an identical or negative angle with respect to the directions in which the light beams a3, b3, c3, d3 (shown using the double dot-dash lines) run when the clockwise direction is considered positive. FIG. 4 shows the far-field distribution when using the EUV focusing mirror in accordance with the invention in an EUV radiation source device. When the far-field distribution which is shown in the figure is compared to the far-field distribution when using a conventional EUV focusing mirror for an EUV radiation source device (see, FIGS. 7(a) and (b)), the degree of reduction of the light intensity is smaller than in the conventional case, even if regions with reduced light intensity are present isolated. In FIG. 4, the regions with reduced light intensity are regions which depend on the thickness of the tip areas of the knife edge parts on the radiation incidence and exit end of the respective Wolter mirrors b, c, d, e. FIG. 5 shows the arrangement of one example when using the invention for a focusing mirror in the form of an ellipsoid of revolution. FIG. 5 is a cross section of the focusing mirror through a plane through the optical axis. In FIG. 5 only the arrangement of the mirrors to one side with respect to the optical axis is shown, the mirrors being arranged symmetrically to the optical axis. FIG. 5 shows that, for example, there are four nested mirrors a, b, c, d with different diameters. The reflection surfaces of the respective Wolter mirrors a, b, c, d are in the form of an ellipsoid. In this embodiment, as in the above described embodiment, the ends on the sides of the respective mirrors b to d which do not constitute reflection surfaces, are made in the form of a knife edge at the radiation incidence side and the radiation exit side. In this way, it is possible to prevent the disadvantage that nonuniformity/scattering of the illuminance is formed by the shielded regions as a result of the thickness of the substrate material of the respective concave mirror on the workpiece. In the case of a conventional EUV focusing mirror, for adequate cooling, a thickness of roughly 1 mm of the substrate material of the respective concave mirror of the EUV focusing mirror is needed. The grazing incident EUV radiation is shielded by this amount of thickness, as a result of which a region with an extremely reduced light intensity occurs for the far-field distribution. The nonuniformity of the illuminance on the workpiece is therefore increased. On the other hand, in the case of an EUV focusing mirror in accordance with the invention, on the two ends of the respective concave mirror of the EUV focusing mirror there are knife edge parts. The bevel of the above described knife edge part is set such that the grazing incident EUV radiation is not shielded. Furthermore, the thickness of the tip of the knife edge part can be fixed to the μm order, therefore very thin. Therefore, the ratio of the shielding of the grazing incident EUV radiation from the ends of the respective concave mirror can be made very small, by which a reduction in the size of the region with a reduced light intensity occurs for the far-field distribution. As a result, it becomes possible to reduce the nonuniformity of the illuminance on the workpiece.
description
This application claims the priority of Korean Patent Application No. 10-2004-0107222, filed on Dec. 16, 2004, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference. 1. Field of the Invention The present invention relates to a micro-column electron beam apparatus with a reduced size (20 mm×20 mm×30 mm) that can be mounted in an ultra high vacuum chamber. 2. Description of the Related Art Efforts have been made world wide to miniaturize micro-column electron beam apparatuses. Micro-column electron beam apparatuses are applied to scanning tunneling microscopes, which align an emission tip, which is an electron beam source essential to all electron beam apparatuses, along an optical axis and operate the emission tip in a field emission mode. Also, micro-column electron beam apparatuses are used to ensure a high throughput of electron beam lithography systems. FIGS. 1 and 2 are respectively a perspective view and an exploded perspective view of a conventional micro-column electron beam apparatus, illustrating a micro-column stage that allows an electron beam source tip module to be aligned in the X, Y, and Z axes. A stage module 100 employed in the conventional micro-column electron beam apparatus functions as a three-axis positioner. The stage module 100 includes four stainless steel stages, that is, a base frame 101, an Y-axis slider stage 110, an X-axis slider stage 120, and a Z-axis slider stage 130. However, this structure is instrumentally complex and physically requires various additional functions, and each additional function causes operational problems. Also, a slow motion of a piezoelectric (PZT) actuator 102 results in friction between the stages, and a fast motion of the PZT actuator 102 causes the stages to slip from desired positions due to their inertia. In general, the PZT actuator 102 moves the stages by approximately 10 μm at a voltage of 100 V. To make the moving stages sliding, both a rigid bearing and a smooth sliding surface should be used. Steel and sapphire, which have a smooth sliding surface in a general stage environment, may be used for the smooth sliding bearing. There may be used a guide bearing which has V-grooves 112 of several millimeters attached in the moving base frame 101 at an angle of 90 degrees. Ball sliding bearings may be placed in the V-grooves 112 to act as guiding bearings. In the conventional stage module, a great force is applied to contact surfaces so that the V-grooves 114 over a half rod 114 can slide and reduce friction generated in the contact surfaces. However, this structure has disadvantages of poor alignment caused when the V-grooves 112 are mechanically processed. In addition, as the contact surfaces increase, a pressure higher than the ball bearings is produced. A spring of the base frame 101 for pressing the moving stages is a leaf spring 113, not a coil spring. The leaf spring 113 is fairly stiff in a direction perpendicular to a direction in which it is flexible. The present invention provides a micro-column electron beam apparatus which is structurally simple to permit integrated packaging and reliably align a micro electron lens module of an electron beam source tip module. According to an aspect of the present invention, there is provided a micro-column electron beam apparatus comprising: a base; an electron lens bracket on which an electron lens module can be fixed, mounted in a central portion of the base; an electron beam source tip module vertically disposed on the electron lens module; a pan spring plate stage module that is mounted over the base, supports the electron beam source tip module at a central portion thereof, and includes a three-coupling pan spring plate portion including first through third spring units that are coupled to the electron beam source tip module in three directions on a plane perpendicular to the vertical axis, which vertically passes the center of the electron beam source tip module, to elastically support the electron beam source tip module in three directions; a first piezoelectric actuator coupled to the pan spring plate stage module to move the electron beam source tip module along a first axis perpendicular to the vertical axis; and a second piezoelectric actuator coupled to the pan spring plate stage module to move the electron beam source tip module along a second axis perpendicular to the vertical axis and the first axis. The first spring unit may be disposed along the first axis, the second spring unit may be disposed along the second axis, and the third spring unit may be spaced 135 degrees apart from each of the first and second spring units. The first piezoelectric actuator may be disposed on a first straight line parallel to the first axis, and the pan spring plate stage module may include a first support member that is disposed between the first axis and the first straight line, closer to the first straight line, and a first lever that contacts both the first piezoelectric actuator and the electron beam source tip module and rotates about the first support member, wherein, when the first piezoelectric actuator is lengthened and moved, the electron beam source tip module is moved a distance equal to the distance the fist piezoelectric actuator is lengthened and moved times the ratio of the distance between the first axis and the first support member to the distance between the first support member and the first straight line, wherein the second piezoelectric actuator is disposed on a second straight line parallel to the second axis, and the pan spring plate stage module includes a second support member that is disposed between the second axis and the second straight line, closer to the second straight line, and a second lever that contacts both the second piezoelectric actuator and the electron beam source tip module and rotates about the second support member, wherein, when the second piezoelectric actuator is lengthened and moved, the electron beam source tip module is moved a distance equal to the distance the second piezoelectric actuator is lengthened and moved times the ratio of the distance between the second axis and the second support member to the distance between the second support member and the second straight line. A portion of the first lever for pushing the electron beam source tip module may be vertically divided into two portions and the first spring unit may be disposed between the vertically divided portions of the first lever, and a portion of the second lever for pushing the electron beam source tip module may be vertically divided into two portions and the second spring unit may be disposed between the vertically divided portions of the second lever. The micro-column electron beam apparatus may further comprise a metal ball disposed between the first piezoelectric actuator and the first lever and a metal ball between the second piezoelectric actuator and the second lever to transfer a force through a spot contact. The micro-column electron beam apparatus may further comprise: a third piezoelectric actuator coupled to the pan spring plate stage module and vertically separated from the electron beam source tip module; a third lever having a first end connected to the third piezoelectric actuator and a second end coupled to the electron beam source tip module; and a hinge unit disposed closer to the first end of the third lever than the second end of the third lever, wherein, when the third piezoelectric actuator is moved, the electron beam source tip module is moved along the vertical axis a distance equal to the distance the third piezoelectric actuator is moved times the ratio of the distance between the first end of the hinge unit and the hinge axis to the distance between the hinge axis and the second end of the hinge unit. The second end of the third lever may have a through-hole through which the electron beam source tip module can pass. The pan spring plate stage module may include at least one vertically perforated wire path through which a plurality of wires connected to the electron lens module and the first and second piezoelectric actuators can pass. The micro-column electron beam apparatus may further comprise a land board that is mounted on an upper portion of the pan spring plate stage module and has a plurality of upwardly protruding electrical connectors to which the plurality of wires passing through the wire path are connected. The micro-column electron beam apparatus may further comprise heat pipe coupling units disposed on the land board to couple heat pipes for exhausting heat generated in the electron beam source tip module. The present invention will now be described more fully with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. FIG.3 is a perspective view of a micro-column electron beam apparatus according to an embodiment of the present invention. Referring to FIG. 3, the micro-column electron beam apparatus 1 includes a base 10, an electron lens bracket 20, an electron beam source tip module 30, a pan spring plate stage module 40, first, second, and third piezoelectric (PZT) actuators 50, 52, and 54, first, second, and third levers 60, 64, and 68, and a land board 70. FIG. 4 is an exploded perspective view illustrating a state where the micro-column electron beam apparatus is rotated 90 degrees clockwise. Referring to FIG. 4, the base 10 has fixed stays 12 formed at four corners. Accordingly, the base 10 is separated from the bottom of the electron lens bracket 20 by the height of the fixed stays 12. Also, an inner space is formed by the fixed stays 12, and the bottom surface of the base 10 has a through-hole. The electron lens bracket 20 is centered over the hole in the bottom surface of the base 10 and fixed to the base 10. An electron lens module 22 is horizontally fixed to the electron lens bracket 20. The electron lens module 22 is made of silicon or glass. The electron lens module 22 is formed by stacking and aligning an object lens module for focusing a beam, a single or double deflection system, and an electrostatic source lens module for extracting and accelerating electrons. A tip of the electron lens module 22 is aligned along an optical axis to be aligned with a source tip module operated in a field emission mode. The electron beam source tip module 30 is longitudinally disposed on the electron lens module 22. The electron beam source tip module 30 is coupled to the pan spring plate stage module 40 by a holder 302. So, it can move horizontally and vertically. The pan spring plate stage module 40 is mounted over the base 10, and is made of STS 314. The pan spring plate stage module 40 supports the electron beam source tip module 30 at a central portion thereof. The pan spring plate stage module 40 has a three-coupling pan spring plate unit 44 formed at the center thereof as shown in FIG. 6. The three-coupling pan spring plate unit 44 may be integrally formed with the pan spring plate stage module 40. As shown in FIG. 6, the three-coupling pan spring plate unit 44 includes first, second, and third spring units 41, 42, and 43 such that the three springs 41 through 43 can be moved vertically and can also be moved along first and second axes 94 and 96 perpendicular to each other and to the vertical direction. Here, FIGS. 6 and 7 illustrate a state where the three-coupling pan spring plate unit 44 is rotated 90 degrees clockwise to the three-coupling pan spring plate unit 44 shown in FIG. 5. The first spring unit 41 is disposed on the first axis 94, and the second spring unit 42 is disposed on the second axis 96. The third spring unit 43 is spaced 135 degrees apart from each of the first and second spring units 41 and 42. The three-directional spring units 41, 42, and 43 prevent distortion. The electron beam source tip module 30 is vertically coupled to a place where the three spring units 41, 42, and 43 meet. Accordingly, the first through third spring units 41 through 43 can elastically support the electron beam source tip module 30 so that the electron beam source tip module 30 can be moved in three perpendicular directions. The pan spring plate stage module 40 has vertically perforated wire paths 45 through which a plurality of wires (not shown) connected to the electron lens module 22 and the first, second, and third PZT actuators 50, 52, and 54 can pass. Accordingly, 22 or less enamel copper wires connected to the electron lens module 22 and wires connected to the PZT actuators 50, 52, and 54 can be connected to electrical connectors of the land board 70 disposed at the top of the apparatus 1 without being exposed to the outside of the apparatus 1. Accordingly, the entire size of the apparatus 1 is reduced, thereby contributing to the miniaturization of the apparatus 1. The first PZT actuator 50 and the second PZT actuator 52 are coupled to the pan spring plate stage module 40, and respectively move the electron beam source tip module 30 along the first axis 94 and the second axis 96. In the present embodiment, the pan spring plate stage module 40 includes the first lever 60 and the second lever 64 to increase the movement of each actuator, thereby increasing the movement of the electron beam source tip module 30. FIG. 8 is a plan view of the pan spring plate stage module. Referring to FIG. 8, the first PZT actuator 50 extends along a first straight line 95 that is parallel to the first axis 94. A first support member 62 is a cylindrical pin disposed between the first axis 94 and the first straight line 95, closer to the first straight line 95. The first lever 60 contacts both the first PZT actuator 50 and the electron beam source tip module 30 and rotates about the first support member 62. In this structure, a method of moving the electron beam source tip module 30 along the first axis 94 will now be explained. If the first PZT actuator 50 is turned on, the first PZT actuator 50 is elongated, thereby pushing one end of the first lever 60. Then, according to the lever rule, the distance the other end of the first lever 60 is moved along the first axis 94 is equal to the distance the end of the first lever 60 pushed by the first PZT actuator 50 is moved times the ratio of the distance between the first axis 94 and the first support member 62 to the distance between the first support member 62 and the first straight line 95. Here, the movement of the first PZT actuator 50 may be increased fivefold. The other end of the first lever 60, that is, a portion 61 of the first lever 60 pushing the electron beam source tip module 30, is vertically divided into two portions. The first spring unit 41 is disposed between the vertically divided portions. Accordingly, the first lever 60 with the first spring unit 41 therein can uniformly push the electron beam source tip module 30. The second PZT actuator 52 extends along a second straight line 97 that is parallel to the second axis 96, and a second support member 66 is disposed between the second axis 96 and the second straight line 97, closer to the second straight line 9. The second lever 64 contacts both the second PZT actuator 52 and the electron beam source tip module 30. As the second PZT actuator 52 is lengthened and moved, the movement is magnified five times by the second lever 64 to move the electron beam source tip module 30 along the second axis 96. The end of the second lever 64 for pushing the electron beam surface tip module 30 is divided into two portions, and the second spring unit 42 is disposed between the divided portions of the second lever 64. Meanwhile, in the present embodiment, the micro-column electron beam apparatus 1 includes a third PZT actuator 54, a third lever 68, and a hinge unit 69. The third PZT actuator 54 is coupled to the pan spring plate stage module 40 as shown in FIG. 4, and is separated vertically from the electron beam source tip module 30. The third PZT actuator 54 vertically moves the electron beam source tip module 30. The third lever 68 has one end connected to an upper end of the third PZT actuator 54 and another end 682 coupled to the electron beam source tip module 30. In the present embodiment, the other end 682 of the third lever 68 has a through-hole 680 through which the electron beam source tip module 30 can pass. The through-hole 680 does not permit the holder 302 of the electron beam source tip module 30 to pass therethrough, such that the other end 682 of the third lever 68 applies a force to an upper end of the holder 302. The hinge unit 69 is a pin passing through the pan spring plate stage module 40 and the third lever 68. The hinge unit 69 is disposed on the one end of the lever 68 connected to the third PZT actuator 54. If the third PZT actuator 54 is turned on, the third PZT actuator 54 is elongated and moved, thereby pushing the end of the third lever 68 connected to the third PZT actuator 54. The third lever 68 is rotated about the pin-shaped hinge unit 69, and the other end 682 of the third lever 68 moves the electron beam source tip module 30 downwardly. Here, the distance the electron beam source tip module 30 is moved along the vertical axis is equal to the distance to the third PZT actuator 54 is moved times the ratio of the distance between the end of the third lever 68 connected to the third PZT actuator 54 and the hinge axis 69 to the distance between the hinge axis 69 and the other end 682 of the third lever 68. Here, the movement of the third PZT actuator 54 may be increased fivefold. FIG. 7 depicts a computer simulation results illustrating expected movements of the three spring units 41, 42, and 43 included in the three-coupling pan spring plate unit 44. Although not shown, a metal ball may be disposed between contact surfaces of the first PZT actuator 50 and the first lever 60 to transfer a force through a spot contact. In this case, irrespective of the angle or area of the contact surfaces, the first PZT actuator 50 can uniformly push the first lever 60. Metal balls may also be disposed between the second PZT actuator 52 and the second lever 64 and between the third PZT actuator 54 and the third lever 68. The land board 70 is mounted on the upper portion of the pan spring plate stage module 40. As depicted in FIG. 4, a plurality of electrical connectors 72 are disposed on the land board 70. However, the electrical connectors 72 are not shown in FIG. 3. The electrical connectors 72 are mounted on a plate member that forms the land board 70, and the wires passing through the wire paths 45 are electrically connected to the electrical connectors 72. Specifically, the electrical connectors 72 pass through the plate member such that the internal wires of the apparatus 1 are connected to the portions of the electrical connectors below the plate member and electric plugs are connected to the portions of the electrical connectors 72 above the plate member. Heat pipe coupling units 74 (see FIG. 10) may be disposed on the land board 70 to couple heat pipes (not shown) for transferring heat generated in the electron beam source tip module 30 outside of the apparatus 1. The temperature of the apparatus 1 can be increased to approximately 1000 to 1800 K due to the heat generated in the electron beam source tip module 30. If the high heat is not properly dissipated, the heat is conducted to components inside the apparatus 1, thereby adversely affecting the lifespan and operation of the components. Accordingly, heat pipes with high heat transfer capacity may be used to dissipate the heat. The apparatus 1 uses the heat pipe coupling units 74 to couple such heat pipes. FIG. 10 is a perspective view of a micro-column electron beam apparatus assembly 2 employing a plurality of micro-column electron beam apparatuses 1 according to an embodiment of the present invention. Referring to FIG. 10, nine micro-column electron beam apparatuses are assembled in a 3×3 array formed on a plane. To this end, the micro-column electron beam apparatus assembly 2 includes an upper flange 82, a lower flange 84, and assembly stays 86. The upper flange 82 and the lower flange 84 are vertically separated from each other and are fixed to each other by the four assembly stays 86. Through-holes are formed in the upper flange 82 so that upper portions of the micro-column electron beam apparatuses 1 can be exposed upwardly. Through-holes are also formed in the lower flange 84 so that lower portions of the micro-column electron beam apparatuses 1 can be exposed downwardly. As described above, since the micro-column electron beam apparatus uses the three-coupling pan spring plate unit and the PZT actuators the structure of the apparatus is simple and thus the entire size of the apparatus can be reduced, and the electron beam source tip module can be controlled with a high precision in three directions. Additionally, if the levers are additionally used in the micro-column electron beam apparatus, the movement of the PZT actuators can be increased. Furthermore, if the heat pipe coupling units for coupling the heat pipes are used, the temperature of the apparatus can be reduced as desired. While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.
abstract
A reuse apparatus of eutectic salt waste produced in an electro refining process and a method thereof is a technology that in order to collect the eutectic salt of the eutectic salt waste, oxidizes/precipitates nuclides (rare earth and TRU) within the eutectic salt waste, an oxygen dispersing method is used to perform a layer separation into the eutectic salt layer and the precipitate layer. Then, the precipitate layer and eutectic salt layer are separated and collected, so that the eutectic salt layer is directly reused and the eutectic salt within the precipitates is reused by separating and collecting it using distillation/condensation processes. The reuse apparatus of the eutectic salt waste and a method thereof thereby increases the collecting efficiency of the eutectic salt and allows the compositions of the collected eutectic salt to have the same compositions as the eutectic salt used in the electro refining process.
claims
1. A gas sensor comprising:a semiconductor substrate, which has an opening; anda sensing membrane, which is located at an end of the opening to make up a recess in combination with the opening and includes:a gas sensitive film;a heater made of polycrystalline silicon;a pair of gas-sensitive-film extension electrodes made of polycrystalline silicon, wherein a first end of each gas-sensitive-film extension electrode is in electric contact with the gas sensitive film and a second end of each gas-sensitive-film extension electrode extends outward from the sensing membrane; anda pair of heater extension electrodes made of polycrystalline silicon, wherein a first end of each heater extension electrode is in electric contact with the heater and a second end of each heater extension electrode extends outward from the sensing membrane,wherein the gas-sensitive-film extension electrodes and the heater are provided on a same layer of the semiconductor substrate. 2. The gas sensor in claim 1 including a plurality of circuit electrodes, which are made of a metal and located outside the sensing membrane, wherein the gas-sensitive-film extension electrodes and the heater extension electrodes are in electric contact with the circuit electrodes outside the sensing membrane. 3. The gas sensor in claim 2, wherein the circuit electrodes are made of aluminum or aluminum alloy. 4. The gas sensor in claim 2 further comprising circuit components, which are located outside the sensing membrane and are in electric contact with the circuit electrodes, wherein the circuit components electrify the heater through the circuit electrodes and are configured to facilitate processing an electric signal that is generated at the gas sensitive film to provide an output signal. 5. The gas sensor in claim 4, wherein the circuit components include a C-MOSFET. 6. The gas sensor in claim 5, wherein gate electrodes of the C-MOSFET are made of polycrystalline silicon. 7. A gas sensor comprising:a semiconductor substrate, which has an opening;a sensing membrane, which is located at an end of the opening to make up a recess in combination with the opening and includes:a gas sensitive film, which extends to an outside of the opening;a heater made of polycrystalline silicon; anda pair of heater extension electrodes made of polycrystalline silicon, wherein a first end of each heater extension electrode is in electric contact with the heater and a second end of each heater extension electrode extends outward from the sensing membrane; anda plurality of circuit electrodes, which are made of a metal and located outside the sensing membrane,wherein the heater extension electrodes are in electric contact with the circuit electrodes outside the sensing membrane, andwherein the gas sensitive film is provided with a pair of film electrodes positioned entirely outside the sensing membrane, which are directly connected to the circuit electrodes. 8. The gas sensor in claim 7, wherein the circuit electrodes are made of aluminum or aluminum alloy. 9. The gas sensor in claim 7 further comprising outside electric circuit components, which are located outside the sensing membrane and are in electric contact with the circuit electrodes, wherein the outside components electrify the heater through the circuit electrodes and are configured to facilitate processing an electric signal that is generated at the gas sensitive film and to produce an output signal. 10. The gas sensor in claim 9, wherein the outside electric components include a C-MOSFET. 11. The gas sensor in claim 10, wherein gate electrodes of the C-MOSFET are made of polycrystalline silicon. 12. The gas sensor in claim 7, wherein the gas sensitive film has a dimension in an extending direction, which is larger than a dimension of the sensing membrane in the extending direction. 13. The gas sensor in claim 1, wherein the sensing membrane includes a plurality of layers. 14. A gas sensor comprising:a semiconductor substrate, which has an opening portion;a gas sensitive film provided to cover at least a part of the opening portion;a heater made of polycrystalline silicon;a pair of film electrodes made of polycrystalline silicon, wherein each film electrode has a first end electrically connected to the gas sensitive film and a second end extending outward from the opening; anda pair of heater electrodes made of polycrystalline silicon, wherein each heater electrode has a first end electrically connected with the heater and a second end extending outward from the opening,wherein the film electrodes and the heater are provided on a single layer on the semiconductor substrate.
06188748&
summary
This invention relates to a contour collimator for radiotherapy, comprising a plurality of plate-shaped diaphragm elements movably arranged with respect to each other in a guiding block to form a contour diaphragm for a radiation beam emitted by a radiation source towards the collimator, and at least one drive for moving the diaphragm elements. Such a contour collimator is known from EP 0 387 921 B1. In radiotherapy, such contour collimators serve for forming a diaphragm whose opening corresponds to the contour of the area of the human body to be irradiated, so that the high-energy rays emanating from the radiation source only impinge on this area and the surroundings of this area are shielded from the radiation. The known contour collimator provides for each group of a given number of plate-shaped diaphragm elements a common adjusting part which serves for serially moving one select diaphragm element each relative to the remaining diaphragm elements. For this purpose, a gear of the adjusting part meshes with a rack provided at the diaphragm element and a non-rotary, toothed area of the adjusting part meshes with the rest of the diaphragm elements to fix them. In order to accelerate the adjusting step, the prior art proposes to provide two such adjusting parts on either side of the contour collimator. For moving the individual diaphragm elements, the prior art makes necessary that the respective adjusting part is initially moved translatorily and transversely to the diaphragm elements, so that the adjusting gear comes into engagement with the rack of a select diaphragm element. Then, a rotation is applied to the gear to move the associated diaphragm element. This process has to be repeated for each diaphragm element of a group. It is the object of the present invention to create a contour collimator of the generic kind, which can be adjusted more rapidly and altogether has a simpler and thus operationally more reliable design requiring less maintenance. According to the characterizing part of claim 1 this object is achieved in that a drive is associated with each diaphragm element, that the drives of one group of diaphragm elements are substantially adjacent to one another and that a driving transmission is provided between each drive and the associated diaphragm element. In spite of the distance which is laterally very narrow between the individual diaphragm elements and corresponds approximately to the thickness of a diaphragm, e.g. 1 mm, it is possible with this design to equip each diaphragm element with a drive of its own thus actuating it separately. This serves for considerably accelerating the adjusting time for a contour collimator, so that the irradiation time for each patient is reduced in one respect, which is a relief for the patient and is also simultaneously accompanied by an increase in economic efficiency. In an advantageous embodiment, the drives are arranged substantially as a semicircle. This serves for obtaining an especially simple and clearly arranged design in which the driving transmissions have substantially equal length, so that equal components can be used for the design. In a further advantageous embodiment, each driving transmission has a flexible towards tension-resistant and pressure-resistant power-transmitting element, one end of which is connected with the associated diaphragm element and the other end of which is connected with the associated drive and which is movably supported in translatory fashion in a moving guide. Such a power-transmitting element permits an especially flexible arrangement of the drives. When each power-transmitting element is detachably coupled to its associated diaphragm element via a coupling linkage, this creates a simple design of the contour collimator, which also permits the rapid exchange of individual elements without any difficulties. The same advantage occurs when each power-transmitting element is detachably coupled to its associated drive via a coupling linkage. Each power-transmitting element advantageously comprises a spring band. Each drive is preferably formed by a linearly acting motor. This renders possible an especially slim or narrow design of the arrangement of drives, so that the arrangement of drives can be very compact. In this connection, the motor is preferably an electric linear motor. As an alternative, the motor is an electric motor having a linearly acting gearing, preferably a rack-and-pinion gear or a spindle gearing. When the guiding block has upper and lower guide plates each of which is provided with a plurality of upper guide grooves and lower guide grooves, respectively, for the diaphragm elements, an especially reliable and fail-safe adjustability of the diaphragm elements is guaranteed. In a preferred embodiment, the upper and lower guide plates are each provided with a preferably rectangular opening, which determine the maximum diaphragm opening and have a common middle plane extending substantially rectangularly with respect to the longitudinal direction of the guide grooves. When the moving guides are arranged substantially side by side in a moving guide block and have moving guide gaps which diverge in bent and fan-shaped fashion and each of which accommodates a power-transmitting element in translatorily movable fashion, safe guidance of the power-transmitting elements is achieved, so that an accurate translatory adjustment of the diaphragm elements is possible, since undesired bulging of the power-transmitting elements is prevented by the gap walls tightly abutting against the respective power-transmitting element. An especially compact arrangement will be formed when two superposed planes of drive arrangements are associated with each moving guide block, two superposed drives each being applied to one power-transmitting element accommodated in contiguous moving guides. By this, the overall width of the contour collimator can be limited effectively in spite of a plurality of movable diaphragm elements. When two opposite groups of translatorily drivable diaphragm elements are provided in the guiding block, two opposite diaphragm elements each being guided in upper and lower common guide grooves, on the one hand, the provision of the opposite groups of diaphragm elements creates the possibility of adjusting contours rotating about an angle of 360.degree. and, on the other hand, it is made possible to achieve complete screening in the area of said guide groove by contact of two opposite diaphragm elements. When each diaphragm element of a pair of opposite diaphragm elements is movable with its free edge facing away from the respective drive beyond the common middle plane of the openings in the lower and upper guide plates, contours can be produced which have strong constrictions on one side as is the case e.g. with kidney-shaped contours. It is preferred to associate with each drive a displacement pickup, preferably a potentiometer, for detecting the current position of the corresponding diaphragm element. This serves for enabling an accurate control of the diaphragm element positions, so that e.g. the contour can automatically be adjusted by a computer program. This embodiment is especially reliable and inexpensive when the displacement pickup has a moving potentiometer which can be actuated translatorily. If at least one of the diaphragm elements disposed within the region of the central middle ray of the radiation beam is provided with at least one thickening rib extending in the translational direction, reliable shading of the central middle ray will be achieved, since the thickening rib shades the middle ray extending parallel to the diaphragm element. As an alternative, the diaphragm elements can be inclined towards the ray. Moreover, the top of a middle diaphragm element can alternatively be thicker than its bottom. This shading effect is even intensified when each thickening rib meshes with a corresponding groove in the adjacent diaphragm element.
046631089
description
DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawings, a vacuum liner for a high energy plasma device 20 (FIG. 1), is best shown in FIG. 2 at reference numeral 22. While the liner 22 is exemplarily shown as a torus, it will be appreciated that it can be formed into any desired shape. The device includes a frame 24 for supporting the liner and a magnet system 26 which could be made up of toroidal, poloidal, helical and other coils or windings which may be either of superconductive or normal material. The purposes of the magnetic system are to produce and confine the plasma inside the vacuum liner 22. The liner 22 includes a vacuum tight liner wall 28 made up of a number of bellows sections 30 having corrugations forming interior ridges 32 and grooves 34 (see FIG. 3), and a number of port or gore sections 36 having generally smooth interiors. Each section has a closed peripheral wall defining an interior 38 with open ends. Adjacent interiors of adjacent sections form a plasma path 40. The corrugations of the bellows sections extend transversely to the axis of the plasma path. The bellows sections are preferably formed of stainless steel and have a relatively thin wall thickness, e.g., 20 mils. They have sufficient loop resistance that the penetration times for the magnetic fields provided by the magnet system, are acceptably short. The port sections, also made of stainless steel, are preferably somewhat thicker and have ports 42 and associated piping 44 for passage of the constituents of the plasma and for applying a vacuum. The various sections carry mating collars 46 at their ends so that the sections can be welded together to complete the vacuum tight wall 28. Theoretically, a properly designed magnet system would provide sufficiently homogeneous magnetic fields that the plasma is contained in the liner out of contact with the liner inner surface. However, available magnet systems do not provide such ideal fields and the plasma contacts the liner inner surface. When the plasma contacts the inner surface of a bellows, energetic particles from the plasma impinge on the bellows wall resulting in localized heating and causing melting and loss of vacuum integrity. Additionally metal ions from the sections enter and contaminate the plasma. These metal ions might have a charge of 10, whereas the electrons and hydrogen ions typically found in the plasma have a charge of 1. The introduction of the metal ions into the plasma causes increased radiation resulting in power loss in the plasma. In order to protect the bellows sections from the plasma, the vacuum liner of the present invention includes means for keeping the plasma from contacting the liner wall 28. This limiting means comprises a ring 48 made up of beads 50 nested in the interior groove 34 formed by each corrugation, as best shown in FIG. 3. The beads 50, which could be shaped as small right circular cylinders, each have an aperture 52 therethrough. A fastening means in the form of a wire 54 made of a material having resistance to high temperature and appropriate spring characteristics, such as a nickel-chromium-iron alloy, is laced through the beads, as shown in FIG. 4. The ends 56 of the wire are overlapped inside beads of the ring. The beads are formed of a material having a higher melting temperature than the material from which the liner wall 28 is formed. The beads are preferably formed of silicon carbide coated carbon, ceramic material or a nickel-chromium-iron alloy, with high density carbon being most preferable. The liner wall 28, with all its bellows sections 30, can include over 400 corrugations with each ring including 100 or more beads. Thus the installation of the rings must be simple to keep the cost low. The as-formed length of each ring is preferably slightly greater than the circumference of the groove portion to be filled. The ring can be fitted into the groove with an inwardly protruding remaining bulge of a few beads. By pressing the bulge outwardly into the groove, all the beads in the ring slightly compress and the bellows slightly stretches, allowing the bulged portion to snap into the groove. By the "keystone effect" the ring is firmly held in its groove. Each bead is in compression and the material forming the groove prevents expansion of the loop while the flanking ridges preclude lateral movement of the ring. Thus the ring is installed simply and quickly with strong mechanical retention, all without any need to weld or otherwise fasten the beads to the bellows section. As shown in FIG. 3, the beads 50 extend from their respective grooves 34 past the apices of the interior ridges toward the plasma path. Although the rings of beads do not overlie the inner ridges of the bellows sections, under many operating conditions they substantially protect the ridges from impingement by high energy charged particles which leave the plasma and give up their energy to the first surface they strike. This is because these particles predominantly follow the direction of the composite magnetic field. Typically the radial component of the composite magnetic field is much smaller than the toroidal component. Thus the paths taken by most of the escaping charged particles intersect the bellows section wall at shallow angles. These angles are so shallow that most charged particles strike the portions of the beads disposed above the level of the ridges and not the ridges. Put another way, although the ridges are visible in plan, they are in the shadow of the beads in view of the direction of the plasma. Besides the right circular cylindrical bead 50 of FIG. 6A, the beads could be made into other shapes. A T-shaped bead 50A includes a stem 58 for reception in the groove and oppositely extending arms 60 which at least partially overlie the ridges 32 flanking the groove 34 in which is disposed the stem 58. A bead 50B which is elliptical in cross section is shown in FIG. 6C. Because this bead configuration extends further toward the plasma path, it casts a longer shadow with respect to the escape trajectories of the charged particles. Thus, rings formed using the beads 50B could, under certain circumstances, be placed in every other groove with the remaining grooves left empty. The elliptical beads would then cast a shadow over all the ridges. Referring to FIG. 5 a bead configuration is shown which protects portions of the wire extending between the beads. Each bead 50C has a tail portion 62 with a central recess 64, and a pointed nose portion 66 sized for reception in the recess 64 of the next bead. Accordingly wire portions between the beads are shadowed by components of the tail portions 62. Referring to FIG. 7, bead configurations are shown which substantially fully cover the ridges with respect to the plasma. A ring formed of a first type of bead 50D is disposed in every other groove. The beads 50D are in the form of split or one half cylinders and are disposed so that the flat side of the bead faces the plasma path. The remaining grooves are fitted with rings formed of modified T-shaped beads 50E, each having a stem 58E and oppositely extending arms 60E of sufficient length and elevation to overlie the ridges flanking their groove and to overlap the beads 50D in adjacent grooves. Although melting and consequential vacuum loss is usually not a problem with the thicker port sections 36, introduction of metal ions therefrom into the plasma can be a problem. Thus it is preferable to cover also the interiors of the port sections with a limiter ring 66 shown in FIG. 8. The limiter ring for the port sections includes a plurality of T-shaped tiles 68 with each tile having a pair of spaced apertures 70, one adjacent each side, for receiving wires to form the tiles 68 into the ring 66. Spaced annular end stops 72 are welded to the interior of the port sections to locate the ring 66. The limiter ring is installed in a manner similar to the installation of the ring 48 described above. Note that two wires 74 are used to hold the limiter ring. These wires are positioned to flank any ports 42 formed in the port section. Thus the wires are positioned to hold remaining tile portions even through a central portion of a tile is removed to accommodate the port. FIGS. 9A-9D illustrate tile configurations 68A, 68B, 68C and 68D, respectively, for formation into rings to be fitted between various sections. These tiles include various arms and removed portions for overhanging the end ridge of a bellows section or for providing space to accommodate a welding bead. Through the use of bellows section rings 48, limiter rings 66 and other rings formed by tiles 68A-68D, substantially the entire inner surface of the liner wall 28 can be covered with a plasma limiter. The carbon limiter material is in intimate contact with the liner wall to preclude arcing. However the carbon limiter does not appreciably reduce the loop resistance of the vacuum liner 22. Even if adjacent rings touch, the carbon joint formed is of high resistance. In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained. As various changes could be made in the above constructions without departing from the scope of the invention, it is intended that all matter contained in the above description shall be interpreted as illustrative and not in a limiting sense.
050664514
claims
1. A method of movably repositioning a control rod cluster assembly of a nuclear reactor relative to a plurality of fuel assemblies in the nuclear reactor within a maximum displacement composed of a multiplicity of separate successive single steps, said method comprising the steps of: (a) performing a single-step repositioning of a control rod cluster assembly in a nuclear reactor by moving the control rod cluster assembly through soley a single step of such displacement; and (b) repeating said single-step repositioning at a plurality of separate times during a given fuel cycle of the reactor to perform a sequence of at least more than one of the separate single-step repositionings of the control rod cluster assembly during the given fuel cycle of the nuclear reactor, the separate times being spaced from one another by periods of time during which the control rod cluster assembly remains stationary; (c) said single-step repositioning being repeated at most once every month during a twelve month fuel cycle. (a) operating a control rod drive mechanism of a nuclear reactor to perform a single step repositioning of a control rod cluster assembly in a nuclear reactor by moving the control rod cluster assembly through solely a single step of such displacement; and (b) repeating said operating of the control rod drive mechanism at a plurality of separate times during a given fuel cycle of the reactor to perform a sequence of separate singlestep repositionings of the control rod cluster assembly during the given fuel cycle of the nuclear reactor, the separate times being spaced from one another by periods of time during which the control rod cluster assembly remains stationary; (c) said operating of the control rod drive mechanism being repeated at most once every month during a twelve month fuel cycle. (a) operating a control rod drive mechanism of a nuclear reactor to perform a single step repositioning of a control rod cluster assembly in a guide tube assembly in a nuclear reactor by moving the control rod cluster assembly through solely a single step of such displacement; and (b) repeating said operating of the control rod drive mechanism at a plurality of separate times during a given fuel cycle of the reactor to perform a sequence of separate singlestep repositionings of the control rod cluster assembly in the guide tube assembly during the given fuel cycle of the nuclear reactor, the separate times being spaced from one another by periods of time during which the control rod cluster assembly remains stationary; (c) said operating of the control rod drive mechanism being repeated at most once every month during a twelve month fuel cycle. 2. The method as recited in claim 1, wherein said single-step repositioning is repeated at most once every four months in a twelve month fuel cycle. 3. A method of movably repositioning a control rod cluster assembly of a nuclear reactor relative to a plurality of fuel assemblies in the nuclear reactor within a maximum displacement composed of a multiplicity of separate successive single steps, said method comprising the steps of: 4. The method as recited in claim 3, wherein said operating of the control rod drive mechanism is repeated at most once every four months in a twelve month fuel cycle. 5. A method of movably repositioning a control rod cluster assembly in a guide tube assembly of a nuclear reactor within a maximum displacement composed of a multiplicity of separate successive single steps, said method comprising the steps of: 6. The method as recited in claim 5, wherein said operating of the control rod drive mechanism is repeated at most once every four months in a twelve month fuel cycle.
abstract
In accordance with the present invention, there is provided a strainer system for use in a nuclear sump. The strainer system of the present invention includes at least one primary strainer module which defines a primary strainer/filter surface. In the strainer system, the primary strainer surface of the primary strainer module has a debris interceptor which is cooperatively engaged thereto, and may be outfitted with one or more pressure released or activated membranes. In a loss of coolant accident, the debris interceptor, alone or in combination with the pressure activated membrane(s), is adapted to reduce the differential pressure experienced across the strainer system in nuclear power plants with medium to high fiber loads.
description
This application is related to U.S. patent application Ser. No. 13/495,069, filed concurrently herewith. 1. Field This invention pertains generally to small modular pressurized water reactors and, more particularly, to a system for passively cooling a small modular reactor after the reactor has been tripped. 2. Related Art In a nuclear reactor for power generation, such as a pressurized water reactor, heat is generated by fission of a nuclear fuel such as enriched uranium, and transferred into a coolant flowing through a reactor core. The core contains elongated nuclear fuel rods mounted in proximity with one another in a fuel assembly structure, through and over which the coolant flows. The fuel rods are spaced from one another in co-extensive parallel arrays. Some of the neutrons and other atomic particles released during nuclear decay of the fuel atoms in a given fuel rod pass through the spaces between fuel rods and impinge on fissile material in adjacent fuel rods, contributing to the nuclear reaction and to the heat generated by the core. Movable control rods are dispersed throughout the nuclear core to enable control of the overall rate of the fission reaction, by absorbing a portion of the neutrons, which otherwise would contribute to the fission reaction. The control rods generally comprise elongated rods of neutron absorbing material and fit into longitudinal openings or guide thimbles in the fuel assemblies running parallel to and between the fuel rods. Inserting a control rod further into the core causes more neutrons to be absorbed without contributing to fission in an adjacent fuel rod; and retracting the control rods reduces the extent of neutron absorption and increases the rate of a nuclear reaction and the power output of the core. FIG. 1 shows a simplified conventional nuclear reactor primary system, including a generally cylindrical pressure vessel 10 having a closure head 12 enclosing a nuclear core 14 that supports the fuel rods containing the fissile material. A liquid coolant, such as water or borated water, is pumped into the vessel 10 by pump 16 through the core 14 where heat energy is absorbed and is discharged to a heat exchanger 18 typically referred to as a steam generator, in which heat is transferred to a utilization circuit (not shown) such as a steam driven turbine generator. The reactor coolant is then returned to the pump 16 completing the primary loop. Typically, a plurality of the above described loops are connected to a single reactor vessel 10 by reactor coolant piping 20. Commercial power plants employing this design are typically on the order of 1,100 megawatts or more. More recently, Westinghouse Electric Company LLC has proposed a small modular reactor in the 200 megawatt class. The small modular reactor is an integral pressurized water reactor with all primary loop components located inside the reactor vessel. The reactor vessel is surrounded by a compact, high pressure containment. Due to both the limited spaced within the containment and the low cost requirement for integral pressurized light water reactors, the overall number of auxiliary systems needs to be minimized without compromising safety or functionality. For that reason, it is desirable to maintain most of the components in fluid communication with the primary loop of the reactor system within the compact, high pressure containment. Typical conventional pressurized water reactor designs make use of active safety systems that rely on emergency AC power after an accident to power the pumps required to cool down the reactor and spent fuel pool. Advanced designs, like the AP1000®, offered by Westinghouse Electric Company LLC, make use of passive safety systems that only rely on natural circulation, boiling and condensation to remove the decay heat from the core and spent fuel pool. It is desirable to apply these passive safety system principals to a small modular reactor design and preferably simplify the design, while still maintaining the safety margins. Accordingly, it is an object of this invention to provide a passive safety system for a small modular reactor that can identify the occurrence of a loss of coolant accident or a main steam line break and initiate a series of events within a pressurized containment of the small modular reactor to cool the reactor over an extended period of approximately five to seven days without outside intervention. It is a further object of this invention to provide such a passive safety system that has a simplified design, which consolidates components over that previously employed in advanced larger reactor designs. These and other objects are achieved by a modular nuclear reactor system having a reactor pressure vessel with a removable head; a primary coolant loop of a nuclear reactor enclosed within the reactor pressure vessel; and a containment pressure vessel enclosing the reactor pressure vessel, with the containment pressure vessel being substantially submerged in a liquid pool. In one embodiment, the modular nuclear reactor system includes an in-containment pool system comprising a sump for collecting reactor coolant escaping from the primary system. The in-containment pool system is located within the containment pressure vessel outside of the reactor pressure vessel and includes means for passively recirculating reactor coolant within the in-containment pool system and the sump into the reactor pressure vessel in the unlikely event of a loss of coolant accident. Preferably, the in-containment pool system is connected to a cold leg of the primary coolant loop through a check valve. The in-containment pool system may further include an in-containment reservoir of reactor coolant which is connected to the sump by check valves which open automatically when the sump level is higher than the water level in the in-containment pool system. Desirably, the modular nuclear reactor system includes a depressurization system to equalize the pressure within the reactor pressure vessel and the containment pressure vessel to facilitate the passive recirculation of reactor coolant during the unlikely event of a loss of coolant accident. Preferably, the depressurization system is connected to the hot leg of the primary coolant loop. The in-containment pool system may further include one or more in-containment pool tanks containing reactor coolant, which are supported at an elevation above a reactor core within the reactor pressure vessel, wherein the in-containment tanks are connected in fluid communication with the in-containment reservoir. The modular nuclear reactor system may also include one or more core make-up tanks containing reactor coolant at a pressure substantially equal to the pressure within the reactor pressure vessel. The core make-up tanks are desirably supported within the containment pressure vessel at an elevation above the reactor core and are connected at an upper portion of the core make-up tanks to a hot leg of the primary coolant loop and at a lower portion of the core make-up tanks to a cold leg of the primary coolant loop with an isolation valve between the lower portion of the core make-up tanks and the cold leg to isolate the lower portion from the cold leg of the primary coolant loop during normal reactor operation. A second depressurization subsystem is connected to the top of the core makeup tanks. A modular nuclear reactor system may also include a passive residual heat removal system for cooling the reactor coolant within the core make-up tanks when the isolation valve is in an open condition. Preferably, the passive heat removal system has a first heat exchanger with a primary side and a secondary side. The primary side of the first heat exchanger is in fluid communication with the reactor coolant in the core make-up tank and the secondary side of the first heat exchanger is in fluid communication with a primary side of a second heat exchanger having a secondary side in fluid communication with an ultimate heat sink pool; with the ultimate heat sink pool extending to an elevation above the containment pressure vessel. In one embodiment, the ultimate heat sink pool is in fluid communication with means for replenishing the liquid pool that the containment pressure vessel is substantially submerged in, when the liquid in the pool drops below a preselected level. A modular nuclear reactor system may also include a protection and safety monitoring system which is configured to monitor the occurrence of any design basis event including a loss of coolant accident or a steam line break and upon such occurrence issue a control signal to open the isolation valve associated with the core make-up tanks. The protection and safety monitoring system may additionally monitor the reactor coolant level within the core make-up tanks and when the reactor coolant within the core make-up tanks goes below a pre-selected level, the protection and safety monitoring system issues a control signal to activate the depressurization system. Desirably, activation of the depressurization system also activates vent valves on the in-containment pool tanks that vent an interior of the in-containment pool tanks to the interior of the containment pressure vessel. The in-containment pool tanks are configured to drain into the core through the in-containment reservoir when the pressure in the reactor pressure vessel substantially equals the pressure in the containment pressure vessel. In still another embodiment, the reactor pressure vessel includes a steam generator heat exchanger having a primary side as part of the primary coolant loop of the nuclear reactor and a secondary side connected in a closed loop with a steam drum located outside of the containment pressure vessel. The secondary side of the steam generator heat exchanger has steam generator isolation valves for isolating the secondary side of the steam generator heat exchanger from the steam drum. The protection and safety monitoring system is additionally configured to monitor for a primary or secondary side break and when the break is detected, the protection and safety monitoring system issues a safeguards signal to the steam generator isolation valves that isolate the steam generator heat exchanger from the steam drum in response to the safeguards signal. FIGS. 2, 3, 4 and 5 illustrate a small modular reactor design which can benefit from the passive heat removal system, high head water injection system and recirculation system claimed hereafter. FIG. 2 shows a perspective view of the reactor containment of a modular reactor design to which this invention can be applied. The reactor containment illustrated in FIG. 2 is partially cut away, to show the reactor pressure vessel and its integral, internal components. FIG. 3 is an enlarged view of the reactor pressure vessel shown in FIG. 2. FIG. 4 is a schematic view of one embodiment of the reactor and some of the reactor auxiliary systems, including an ultimate heat sink and secondary heat exchange loop of the combined passive heat removal system and high head water injection system of one embodiment of this invention. FIG. 5 is a schematic view of another embodiment of the passive safety system of this invention, which includes the major components of the extended passive core cooling and coolant recirculation system of this invention. Like reference characters are used among the several figures to identify corresponding components. In an integral pressurized water reactor such as illustrated in FIGS. 2, 3, 4 and 5, substantially all of the components typically associated with the primary side of a nuclear steam supply system are contained in a single reactor pressure vessel 10 that is typically housed within a high pressure containment vessel 34 capable of withstanding pressures of approximately 250 psig, along with portions of the safety systems associated with the primary side of the nuclear steam supply system. The primary components housed within the reactor pressure vessel 10 include the primary side of a steam generator, reactor coolant pumps 28, a pressurizer 22 and the reactor itself. The steam generator system 18 of a commercial reactor, in this integral reactor design, is separated into two components, a heat exchanger 26 which is located in the reactor vessel 10 above the reactor upper internals 30 and a steam drum 32 which is maintained external to the containment 34 as shown in FIGS. 4 and 5. The steam generator heat exchanger 26 includes within the pressure vessel 10/12, which is rated for primary design pressure and is shared with the reactor core 14 and other conventional reactor internal components, two tube sheets 54 and 56, hot leg piping 24 (also referred to as the hot leg riser), heat transfer tubes 58 which extend between the lower tube sheet 54 and the upper tube sheet 56, tube supports 60, secondary flow baffles 36 for directing the flow of the secondary fluid medium among the heat transfer tubes 58 and secondary side flow nozzles 44 and 50. The heat exchanger 26 within the pressure vessel head assembly 12 is thus sealed within the containment 34. The external-to-containment steam drum 32 is comprised of a pressure vessel 38, rated for secondary design pressure. The external-to-containment steam drum 32 includes centrifugal type and chevron type moisture separation equipment, a feed water distribution device and flow nozzles for dry steam, feed water, recirculating liquid and wet steam, much as is found in a conventional steam generator design 18. The flow of the primary reactor coolant through the heat exchanger 26 in the head 12 of the vessel 10 is shown by the arrows in the upper portion of FIG. 3. As shown, heated reactor coolant exiting the reactor core 14 travels up and through the hot riser leg 24, through the center of the upper tube sheet 56 where it enters a hot leg manifold 74 where the heated coolant makes a 180° turn and enters the heat transfer tubes 58 which extend through the upper tube sheet 56. The reactor coolant then travels down through the heat transfer tubes 58 that extend through the lower tube sheet 54 transferring its heat to a mixture of recirculated liquid and feedwater that is entering the heat exchanger through the sub-cooled recirculation input nozzle 50 from the external steam drum 32, in a counterflow relationship. The sub-cooled recirculating liquid and feedwater that enters the heat exchanger 26 through the sub-cooled recirculation input nozzle 50 is directed down to the bottom of the heat exchanger by the secondary flow baffles 36 and up and around heat exchange tubes 58 and turns just below the upper tube sheet 56 into an outlet channel 76 where the moisture-laden steam is funneled to the wet steam outlet nozzle 44. The wet saturated steam is then conveyed to the external steam drum 32 where it is transported through moisture separators which separate the steam from the moisture. The separated moisture forms the recirculated liquid which is combined with feedwater and conveyed back to the sub-cooled recirculation input nozzle 50 to repeat the cycle. Both conventional pressurized water reactor designs and advanced pressurized water reactor designs (such as the AP1000® offered by the Westinghouse Electric Company LLC, Cranberry Township, Pa.) make use of both decay heat removal systems and high head injection systems to prevent core damage during accident scenarios. In the Westinghouse small modular reactor design, illustrated in FIGS. 2, 3, 4 and 5, cost and space constraints limit the capability of these systems as currently implemented in the larger pressurized water reactors. This invention combines the passive decay heat removal, high head water injection and recirculation functions into a single, simple, integrated system. This combined safety system greatly simplifies the integral reactor design as compared to the larger pressurized water reactor safety systems, and allows for comparable reactor protection capabilities during accidents at a decreased cost and with lower spatial requirements. The embodiment of the invention claimed hereafter which is described herein includes a novel recirculation system design that can continuously cool the reactor core for approximately seven days without operator action or the use of external power. The initial passive cooling time may be further extended by replenishing the water in an ultimate heat sink pool outside the containment as will be described hereafter. As can be viewed from FIGS. 2-5, the safety system of this invention includes three basic functions: a high head water injection function in which water under pressure is forced into the core in a recirculation loop through the core make-up tank; a residual heat removal system which cools the reactor coolant circulating through the core make-up tank; and a core recirculation system that continually recirculates coolant through the core. The combined high head water injection function and residual passive heat removal function can be understood by referring to FIGS. 2-4, which show a combined core make-up tank/passive residual heat removal heat exchanger 40/42 located within the containment vessel 34, with the passive residual heat removal heat exchanger 42 located within the core make-up tank 40. The passive residual heat removal heat exchanger 42 includes an inlet plenum 43 at the top end of the core make-up tank and an outlet plenum 46 at the lower end of the core make-up tank. An upper tube sheet 48 separates the upper inlet plenum 43 from a secondary fluid plenum 64 and a lower tube sheet 52 separates the lower outlet plenum 46 from the secondary fluid plenum 64. A tube bundle 62 of heat exchange tubes extends between the upper tube sheet 48 and the lower tube sheet 52. Accordingly, primary fluid from the hot leg of the core 82, supplied through the inlet piping 84 enters the inlet plenum 43, is conveyed through the tube bundle 62 to the outlet plenum 46 and is returned to the cold leg 78 of the core 14 through the outlet piping 88. The coolant passing through the tube bundle 62 transfers its heat to a secondary fluid in the secondary fluid plenum 64 between the tube sheets 48 and 52. A secondary fluid enters the secondary fluid plenum 64 through the secondary fluid inlet piping 66, absorbs the transferred heat from the tube bundle 62 and exits through the secondary fluid outlet piping 68. The height of the core make-up tank 40, i.e., the elevation at which the core make-up tank is supported, is maximized in order to facilitate high natural circulation flows. During steady state operation, the core make-up tank 40 and the primary tube side of the passive residual heat removal heat exchanger 42 is filled with cold, borated water at the same pressure as the reactor coolant. This water is prevented from flowing into the reactor pressure vessel 40 by a valve 80 on the exit piping 88 on the bottom of the core make-up tank 40. During accident conditions, the reactor protection and safety monitoring system signals the opening of the valve 80, allowing the cold, borated core make-up tank water to flow down through the exit piping 88 and into the cold leg 78 of the reactor pressure vessel 10. Concurrently, hot reactor coolant then flows from the core exit region 82 into the core make-up tank 40 through the inlet piping 84, and then into the core make-up tank inlet plenum 43. The hot reactor water then flows down through the tubes within the tube bundle 62 of the passive residual heat removal heat exchanger 42, and is cooled by cold secondary water flowing through the shell side of the passive residual heat removal heat exchanger in the secondary fluid plenum 64. The secondary water which is pressurized to prevent boiling, then flows upward through piping 68 to a second heat exchanger 72 in the ultimate heat sink tank 70, where it transfers heat to the cold water in the tank 70. The now cooled secondary water flows down through the return piping 66, and into the core make-up tank shell side 64 of the heat exchanger 42 to repeat the process. Both the ultimate heat sink loop and the core make-up tank primary loop are driven by natural circulation flows. The core make-up tank primary loop flow continues to remove heat from the reactor even after steam enters the core make-up tank inlet piping 84. During an accident in which coolant is lost from the reactor pressure vessel 10, the water level in the reactor vessel drops as the passive residual heat removal heat exchanger 42 removes decay heat from the reactor 10. When the water level drops below the core make-up tank inlet piping entrance at the core exit region 82, steam enters the inlet piping and breaks the natural circulation cycle. At this point, the inventory of the core make-up tank (excluding the secondary shell side 64 of the passive residual heat removal heat exchanger) flows downward through the outlet piping under the steam pressure and into the reactor pressure vessel cold leg 78, effectively serving as a high head injection. This combined high head injection from the core make-up tank and residual heat removal heat exchanger combination is more fully described in application Ser. No. 13/495,069, filed concurrently herewith. The embodiment illustrated in FIG. 5 combines the features of the combined core make-up tank high head injection and residual heat removal system with an in-containment reactor recirculation system that provides core cooling, without outside power, over an extended period. In one preferred embodiment of the small modular reactor safety system, illustrated in FIG. 5, the integral reactor vessel 10 is inside a small high pressure containment vessel 34 as previously mentioned with regard to FIG. 4. The containment vessel 34 is substantially submerged in a pool of water 90 to provide external cooling to the vessel. Inside the vessel is an in-containment pool system 92 that comprises in-containment pool reservoirs 94 connected to in-containment pool tanks 96 located at an elevation above the reactor core 14. The in-containment pool reservoir 94 is split in two halves, each connected to one in-containment pool tank 96. The core make-up tanks 40, of which there can be one or more, are also located inside the containment, as previously mentioned, at an elevation above the core. The top of each core make-up tank is coupled to the hot leg at the core exit region 82 of the reactor vessel above the core 14, while the bottom of the core make-up tank is connected to the direct vessel injection nozzle 100 in the cold leg of the reactor primary coolant loop downstream of the reactor coolant pumps 28. Residual heat removal heat exchangers 42 are included within the core make-up tanks 40 to conduct heat out of the system as heretofore described. The primary side of the residual heat removal heat exchangers are coupled to the core exit region 82 and cold leg 78 of the reactor pressure vessel 10. The residual heat removal heat exchanger secondary side is connected to heat exchangers in the ultimate heat sink pools 70. The ultimate heat sink pools 70 are placed at a higher elevation than the containment 34. This secondary side cooling loop of the residual heat removal system heat exchangers is pressurized using accumulators. Automatic depressurization system valves 102 are connected to independent lines to the hot leg 82 of the reactor vessel 10. A second set of depressurization valves is connected to the top of each core makeup tank. The purpose of these valves is to depressurize the reactor and equalize the pressure between the containment volume and the reactor vessel volume. This is necessary to recirculate water into the reactor from the containment pressure vessel under gravity. On each core make-up tank cold leg 88, a normally closed, fail open valve 80 prevents flow through the core make-up tank during normal operation. After an accident, these valves will open to allow cold, borated water that is inside the core make-up tank during normal operation to flow into the reactor through natural circulation. This natural circulation is initiated by the temperature difference between the hot leg connection line and the cold borated water initially in the core make-up tank during normal operation. It should be noted that the core make-up tank, i.e., the primary side of the residual heat removal heat exchanger 42, is pressurized to a level substantially equal to that encountered within the reactor vessel 10. The recirculation of coolant through the core is sustained by the cooling of the water that flows into the core make-up tank primary side by the secondary natural circulation loop of the residual heat removal heat exchanger that is cooled by the ultimate heat sink pool 70. Flow through the secondary loop of the residual heat removal heat exchanger is initiated by heating of the secondary water inside the core make-up tank and sustained by the cooling of the secondary water in the ultimate heat sink heat exchanger. The in-containment pool system 92 is connected through the in-containment pool reservoirs 94 to sump injection nozzles through check valves 104. The check valves allow flow from the in-containment pool system through the in-containment pool reservoirs 94 to the reactor coolant system. The in-containment pool system 92 is also connected to a lower portion of the containment interior volume or containment sump 98 through check valves and normally closed, in-vessel retention valves 106. The check valves allow flow from the containment sump 98 to the in-containment pool system 92. The in-vessel retention valves 106 allow the water in the in-containment pool system 92 to flow into the reactor vessel cavity and cool the exterior of the reactor vessel preventing the core from melting through the reactor vessel wall. The steam generator secondary side 108 is connected to an external steam drum 32 that separates the wet steam coming from the steam generator heat exchanger into dry steam and water. The heat removal capability of the water in the steam drum may also be used after an accident. The operation of the steam generator is more fully described in application Ser. No. 13/495,050, filed concurrently herewith. The steam drum 32 can be isolated by closing off the isolation valves 110 and 112. The operation of the safety system can be demonstrated through a review of the sequence of events that will occur following a postulated loss of coolant accident. A loss of coolant accident occurs when a primary pipe breaks inside the containment. As there are no large primary pipes in an integral reactor, the primary pipe break will be on auxiliary connections to the reactor like the pressurizer spray line on the pressurizer 22 or the connections to the core make-up tanks 40. These lines will be limited in diameter to under six inches. The first step in a loss of coolant accident sequence is the diagnosis by the protection and safety monitoring system 114 that an event is in progress. The protection and safety monitoring system then generates a protection system signal which results in the insertion of the control rods into the core 14 and a trip of the reactor coolant pumps 28. The steam drum 32 will be isolated from the turbine by closing off the main steam line 116 and the feedwater recirculation line from the steam drum to the Steam Generator. The second step is opening the valves 80 below the core make-up tanks 40 which results in the cold, borated water in the core make-up tanks being forced into the core, cooling it and keeping the core covered. The residual heat removal heat exchangers are also activated, and this initiates the natural circulation cooling flow from the hot leg, through the heat exchanger and into the cold leg. The secondary side cooling loop of the residual heat removal heat exchangers will transfer the heat to the ultimate heat sink pools 70. This cooling will continue until the water level in the reactor has dropped below the hot leg residual heat removal inlet connections in the reactor vessel 10. At this point, the water in the core makeup tanks starts to drain into the cold leg. A low water level in the core make-up tanks or another actuation signal will actuate the automatic depressurization system valves 102, equalizing the pressure between the reactor volume and the containment volume. As soon as the pressure in the reactor is low enough, the in-containment pool tanks 96 (only one of which is shown) will drain into the reactor under gravity through the in-containment pool reservoirs 94 and the check valves 106. The vent valves 120 on the in-containment pool tanks 96 will open with the automatic depressurization system valves 102 permitting the tanks to drain. The water in the in-containment pool tanks 96 will replenish the water in the core, keeping the core covered as the water in the reactor boils off, releasing steam into the containment 34 through the automatic depressurization system valves 102. The steam inside the containment 34 then condenses on the cold containment vessel, which is submerged in the water pool 90 which is covered by a vented removable radiation shield 124. The condensed steam will collect in the bottom of the containment in the sump 98, with the water level rising as more steam is condensed on the cold containment vessel wall. When the water level in the in-containment pool tanks 96 reaches a sufficient level, check valves will open allowing the water inside the containment to flow from the sump 98 into the in-containment pool reservoirs 94 and back into the reactor through sump injection nozzles 100. This creates a continuous cooling loop with water in the reactor boiling off and the steam released into the containment through the automatic depressurization system valves 102. The steam condensate then flows back into the reactor through the in-containment pool system 90 under natural circulation. Through this process, the decay heat is transferred from the core to the water outside the containment 34. The water pool 90 outside the containment may boil off but can be replenished from the ultimate heat sink pool 70 through float valves 122. The combined water in the ultimate heat sink pools 70 and outside containment pool 90 is sufficient to cool the reactor for at least seven days. After that, either the ultimate heat sink water should be replenished via connections in the ultimate heat sink pools that allow for the addition of inventory to extend the cooling operation, or AC power should be restored to cool the ultimate heat sink pools. The postulated main steam line break inside the containment event makes use of additional features of the safety systems of the embodiments described herein. In this case, the protection and safety monitoring systems will diagnose that a main steam line break event is in progress and send a signal to isolate the steam drum 32 from the containment 34 by closing the steam drum isolation valves 110 and 112, preventing the steam drum water inventory from entering the containment or interacting with the steam generator tubes within the reactor vessel head 12. A reactor trip signal will also be generated, if the reactor is operating at power. The valves 80 below the core make-up tanks will then be opened, starting the delivery of borated water to the core 14. Any reactivity excursion will be terminated by the delivery of borated water to the core. The decay heat will be transferred by way of the residual heat removal heat exchangers 42 to the ultimate heat sink pools 70, which will increase in temperature until they boil. The volume of the ultimate heat sink pools is enough to cool the reactor for at least seven days. After that, either the ultimate heat sink water should be replenished or AC power should be restored to cool the ultimate heat sink pools. The protection and safety monitoring system 114, the in-vessel retention valves 106, the steam drum isolation valves 110, 112, the in-container pool tank vent valves 120, the automatic depressurization valves, and the core make-up tank isolation valve do not rely on the availability of AC power. While specific embodiments of the invention have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular embodiments disclosed are meant to be illustrative only and not limiting as to the scope of the invention which is to be given the full breadth of the appended claims and any and all equivalents thereof.
claims
1. A dynamically reconfigurable mixed-signal device, comprising:a semiconductor substrate;a first gateway conductor integrated on the semiconductor substrate;a plurality of solid-state switching devices integrated on the semiconductor substrate, including a first group wherein each of the switching devices of the first group is coupled to the first gateway conductor; anda plurality of bidirectional contacts, each coupled to one of the plurality of switching devices, including a first set and a vehicle set, wherein each of the contacts of the first set is coupled to one of the switching devices of the first group, and wherein each of the contacts of the vehicle set correlates to one of a plurality of vehicle interface connector pins;wherein any one of the first set of contacts can be linked to any other one of the first set of contacts by closing a first corresponding switch of the first group of switching devices that links the any one of the first set of contacts to the first gateway conductor and closing a second corresponding switch of the first group of switching devices that links the any other one of the first set of contacts to the first gateway conductor;thereby facilitating dynamically reconfigurable interconnection of any one of the plurality of vehicle interface connector pins that correlates to any one of the first set of contacts to any other one of the first set of contacts. 2. The dynamically reconfigurable mixed-signal device of claim 1, further comprising a switch control module integrated on the semiconductor substrate, the switch control module being coupled to the plurality of switching devices to control the plurality of switching devices. 3. The dynamically reconfigurable mixed-signal device of claim 2, further comprising a bus interface module integrated on the semiconductor substrate, the bus interface module being coupled to the switch control module to provide a communications interface between the switch control module and at least an interconnect bus. 4. The dynamically reconfigurable mixed-signal device of claim 1, wherein each of the plurality of switching devices is coupled to one and only one of the plurality of contacts. 5. The dynamically reconfigurable mixed-signal device of claim 1, wherein each of the contacts of the vehicle set correlates to one and only one of a plurality of vehicle interface connector pins. 6. The dynamically reconfigurable mixed-signal device of claim 1, wherein each of the contacts of the vehicle set correlates to one and only one of a plurality of pins on a vehicle interface connector configured substantially in accordance with a Society of Automotive Engineers (SAE) J1962 standard. 7. The dynamically reconfigurable mixed-signal device of claim 1, wherein the plurality of solid-state switching devices and the plurality of bidirectional contacts are configured to transmit an electrical signal having an electrical potential equal to that of a vehicle electrical system. 8. The dynamically reconfigurable mixed-signal device of claim 1, wherein the plurality of contacts further includes a tool set, and each of the contacts of the tool set correlate to one of a plurality of vehicle communication network protocol interface circuits in a vehicle diagnostics tool, and the vehicle set and the tool set are mutually exclusive;thereby facilitating dynamically reconfigurable interconnection of any one of the plurality of vehicle interface connector pins that correlates to any one of the first set of contacts to any one of the plurality of vehicle communication network protocol interface circuits in the vehicle diagnostics tool that correlates to any other one of the first set of contacts. 9. The dynamically reconfigurable mixed-signal device of claim 8, wherein at least one contact of the tool set correlates to a vehicle-based controller area network (CAN) protocol interface circuit in a vehicle diagnostics tool. 10. The dynamically reconfigurable mixed-signal device of claim 8, wherein at least one contact of the tool set correlates to a Chrysler Collision Detection (CCD) protocol interface circuit in a vehicle diagnostics tool. 11. The dynamically reconfigurable mixed-signal device of claim 8, wherein at least one contact of the tool set correlates to a vehicle-based communication network protocol interface circuit in a vehicle diagnostics tool, the communication network protocol being substantially in accordance with an International Standards Organization (ISO) 9141-2 standard. 12. The dynamically reconfigurable mixed-signal device of claim 8, wherein at least one contact of the tool set correlates to one of the following vehicle-based communication network protocol interface circuits: Society of Automotive Engineers (SAE) J1850 Variable Pulse Width (VPW), SAE J1850 Pulse Width Modulation (PWM), International Organization for Standardization (ISO) 9141-2, Controller Area Network (CAN), Ford Standard Corporate Protocol (SCP), Chrysler Collision Detection (CCD), DaimlerChrysler Scalable Coherent Interface (SCI), General Motors (GM) 8192 Universal Serial Receiver/Transmitter (UART) or Assembly Line Diagnostic Link (ALDL), Bosch Controller Area Network (CAN), Ford Data Communication Link (DCL). 13. The dynamically reconfigurable mixed-signal device of claim 8, further comprising a second gateway conductor integrated on the semiconductor substrate, the plurality of switching devices further including a second group wherein each of the switching devices of the second group is coupled to the second gateway conductor, the first group and the second group being mutually exclusive, and the plurality of contacts further including a second set wherein each of the contacts of the second set is coupled to one of the switching devices of the second group;wherein any one of the second set of contacts can be linked to any other one of the second set of contacts by closing a third corresponding switch of the second group of switching devices that links the any one of the second set of contacts to the second gateway conductor and closing a fourth corresponding switch of the second group of switching devices that links the any other one of the second set of contacts to the second gateway conductor;thereby further facilitating dynamically reconfigurable interconnection of any one of the plurality of vehicle interface connector pins that correlates to any one of the second set of contacts to any one of the plurality of vehicle communication network protocol interface circuits in the vehicle diagnostics tool that correlates to any other one of the second set of contacts. 14. The dynamically reconfigurable mixed-signal device of claim 13, wherein each of the contacts of the vehicle set is coupled to one of the switching devices of the first group and to one of the switching devices of the second group, such that any one of the contacts of the vehicle set can be linked either to the first gateway conductor or to the second gateway conductor by closing either a fifth corresponding switch of the first group of switching devices or a sixth corresponding switch of the second group of switching devices, respectively;thereby facilitating dynamically reconfigurable interconnection of any one of the plurality of vehicle interface connector pins to any one of the plurality of vehicle communication network protocol interface circuits in the vehicle diagnostics tool that correlates either to any one of the first set of contacts or to any one of the second set of contacts. 15. The dynamically reconfigurable mixed-signal device of claim 14, wherein each of the contacts of the tool set that is coupled to one of the switching devices of the first group is paired with one of the contacts of the tool set that is coupled to one of the switching devices of the second group, and each such pair of contacts of the tool set correlates to a pair of transmission lines coupled to one of the plurality of vehicle communication network protocol interface circuits in the vehicle diagnostics tool;thereby facilitating dynamically reconfigurable interconnection of any two of the plurality of vehicle interface connector pins to any one pair of transmission lines coupled to any one of the plurality of vehicle communication network protocol interface circuits in the vehicle diagnostics tool. 16. A dynamically reconfigurable mixed-signal device, comprising:a semiconductor substrate;a first gateway conductor integrated on the semiconductor substrate;a second gateway conductor integrated on the semiconductor substrate;a plurality of pairs of solid-state vehicle-side switching devices integrated on the semiconductor substrate, each such pair consisting of a first vehicle-side switching device coupled to the first gateway conductor and a second vehicle-side switching device coupled to the second gateway conductor;a plurality of pairs of solid-state tool-side switching devices integrated on the semiconductor substrate, each such pair consisting of a first tool-side switching device coupled to the first gateway conductor and a second tool-side switching device coupled to the second gateway conductor;a switch control module integrated on the semiconductor substrate, the switch control module being coupled to the vehicle-side switching devices and to the tool-side switching devices to control the vehicle-side switching devices and the tool-side switching devices;a bus interface module integrated on the semiconductor substrate, the bus interface module being coupled to the switch control module to provide a communications interface between the switch control module and at least an interconnect bus;a plurality of bidirectional vehicle-side contacts, each correlating to one and only one of a plurality of vehicle interface connector pins and each being coupled to the first and second vehicle-side switching devices of one of the plurality of pairs of vehicle-side switching devices; anda plurality of pairs of bidirectional tool-side contacts, each tool-side contact being coupled to one and only one of the tool-side switching devices, and each pair of tool-side contacts correlating to a first transmission line and to a second transmission line, the first and second transmission lines being coupled to one of a plurality of vehicle communication network protocol interface circuits in a vehicle diagnostics tool;wherein any two of the plurality of vehicle-side contacts can be linked to any one of the plurality of pairs of tool-side contacts by closing the first and second tool-side switching devices coupled to the any one of the plurality of pairs of tool-side contacts, closing the first vehicle-side switching device coupled to one of the any two of the plurality of vehicle-side contacts and closing the second vehicle-side switching device coupled to another of the any two of the plurality of vehicle-side contacts;thereby facilitating dynamically reconfigurable interconnection of any two of the plurality of vehicle interface connector pins to the first transmission line and to the second transmission line of any one of the plurality of vehicle communication network protocol interface circuits in the vehicle diagnostics tool. 17. A dynamically reconfigurable mixed-signal device, comprising:first means for receiving a first electrical signal, the first means for receiving correlating to a first vehicle interface connector pin;second means for receiving a second electrical signal, the second means for receiving correlating to a second vehicle interface connector pin;integrated-circuit means for selectively linking the first means for receiving either to a first gateway conductor or to a second gateway conductor;integrated-circuit means for selectively linking the second means for receiving either to the first gateway conductor or to the second gateway conductor;first means for sending the first electrical signal, the first means for sending correlating to a first transmission line coupled to a vehicle communication network protocol interface circuit in a vehicle diagnostics tool;second means for sending the second electrical signal, the second means for sending correlating to a second transmission line coupled to a vehicle communication network protocol interface circuit in the vehicle diagnostics tool;integrated-circuit means for selectively linking the first gateway conductor to the first means for sending; andintegrated-circuit means for selectively linking the second gateway conductor to the second means for sending;thereby facilitating dynamically reconfigurable interconnection of the first and second vehicle interface connector pins to the first and second transmission lines of the vehicle communication network protocol interface circuit in the vehicle diagnostics tool. 18. The dynamically reconfigurable mixed-signal device of claim 17, further comprising integrated-circuit means for controlling the means for selectively linking the first means for receiving, the means for selectively linking the second means for receiving, the means for selectively linking the first gateway conductor, and the means for selectively linking the second gateway conductor. 19. The dynamically reconfigurable mixed-signal device of claim 18, further comprising communication means for connecting the means for controlling to at least an interconnect bus. 20. A method of adapting a vehicle diagnostics tool interface, comprising the steps of:receiving a first electrical signal, correlating to a first vehicle interface connector pin;receiving a second electrical signal, correlating to a second vehicle interface connector pin;selectively switching the first electrical signal to a first gateway conductor;selectively switching the second electrical signal to a second gateway conductor;selectively switching the first gateway conductor to a first transmission interface contact correlating to a vehicle communication network protocol interface circuit in a vehicle diagnostics tool; andselectively switching the second gateway conductor to a second transmission interface contact correlating to the vehicle communication network protocol interface circuit in the vehicle diagnostics tool;thereby facilitating dynamically reconfigurable interconnection of the first and second vehicle interface connector pins to the vehicle communication network protocol interface circuit in the vehicle diagnostics tool. 21. The method of claim 20, further comprising the step of receiving control signals from at least an interconnect bus.
abstract
A system of monitoring a black cell environment using sensors is presented, in which the sensors can be easily replaced during a sealed period of the black cell environment. The black-cell monitoring system includes at least one sealed vessel that is disposed within the black cell environment. The vessel is configured to store a hazardous mixed substance and is sealed from the external environment for a pre-determined amount of time. The black-cell monitoring system also includes at least one tubing that extends from the outside of the vessel to the inside of the vessel. The black-cell monitoring system also includes a fiber optic cable that is disposed within the lumen of the tubing. At least a portion of the fiber optic cable is disposed within a portion of the tubing located inside the sealed vessel.
claims
1. A control rod drive for a nuclear reactor, comprising:a drive housing;a throttle bush disposed at least partially in said drive housing;a drive unit; anda control rod carrying element disposed in said drive housing and moveable between a basic position and a moved-in end position, a part of said control rod carrying element being guided in said throttle bush and said control rod carrying element having a lower end cooperating with said drive unit, said control rod carrying element and said throttle bush defining there-between a flow path for a pressure fluid, said flow path leading beyond said throttle bush and having a free flow cross section varying in dependence on a position of said control rod carrying element. 2. The control rod drive according to claim 1, wherein said free flow cross section increases when the control rod carrying element moves from the basic position to the moved-in end position. 3. The control rod drive according to claim 1, wherein said control rod carrying element has a length and an outer diameter varying over said length of said control rod carrying element. 4. The control rod drive according to claim 3, wherein said control rod carrying element has a lower region facing said drive unit and an upper region, said outer diameter of said control rod carrying element is smaller in said lower region than said outer diameter in said upper region resulting in a reduced outer diameter in said lower region. 5. The control rod drive according to claim 4, wherein said outer diameter of said control rod carrying element has a narrowing region that narrows continuously to said reduced outer diameter. 6. The control rod drive according to claim 4, wherein said reduced outer diameter extends constantly over a part of a length of said control rod carrying element. 7. The control rod drive according to claim 5, wherein said control rod carrying element is a hollow piston having a wall with at least one bypass orifice formed in said wall. 8. The control rod drive according to claim 7, wherein said bypass orifice is disposed one of in a region upstream of said narrowing region and in a region of said narrowing region of said control rod carrying element. 9. The control rod drive according to claim 4, wherein said control rod carrying element has, in said lower region having said reduced outer diameter, an outer web, said outer web disposed within said throttle bush when said control rod carrying element is positioned in the moved-in end position. 10. The control rod drive according to claim 9, wherein said throttle bush having an inside diameter, and said outer web is a peripheral annular web having an outer diameter corresponding approximately to said inside diameter of said throttle bush. 11. The control rod drive according to claim 4, further comprising longitudinal webs disposed in a region of said reduced outer diameter on said control rod carrying element.
abstract
An improved nuclear shielding material that is flexible so as to effectively fill voids in radiation containment structures. Under very high temperatures the material is designed to undergo pyrolysis and transform into a strong ceramic material. The material contains a number of components, the first of which is a polymeric elastomer matrix such as a two part self-polymerizing system like RTF silicone rubber. Additional components include: a compound to shield gamma radiation like tungsten carbide powder, a neutron absorbing/gamma blocking compound such as boron carbide powder, a heat conducting material such as diamond powder, a high temperature resistant compound such as silicon dioxide powder, a second neutron absorbing compound which also imparts electrical conductivity, namely barium sulfate powder, and a hydrogen gas surpassing component which readily absorbs hydrogen such as sponge palladium.
summary
summary
043269214
abstract
A design of fuel assembly control rod guide thimble which includes insets or indentations which project inwardly from the upper end of the guide thimble and extend longitudinally of the thimble for about the same distance traversed by a control rod movable therein. These preferentially formed discrete indented areas or insets within the guide thimble provide for controlled localized control rod to guide thimble wear. The insets minimize wear at the control rod-guide thimble interface by lowering the normal load and encouraging the control rod into a line contact wearing mode. Additional insets may be remotely installed after irradiation if desired.
062018477
description
DETAILED DESCRIPTION OF THE INVENTION FIG. 1 is a top sectional view of a boiling water nuclear reactor pressure vessel 10. Reactor pressure vessel 10 includes a vessel wall 12 and a shroud 14 which surrounds the reactor core (not shown) of pressure vessel 10. An annulus 16 is formed between vessel wall 12 and shroud 14. The space inside annulus 16 is limited with most reactor support piping located inside annulus 16. Cooling water is delivered to the reactor core during a loss of coolant accident through core spray distribution header pipes 18 and 20 which are connected to downcomer pipes 22 and 24 respectively. Downcomer pipes 22 and 24 are connected to shroud 14 through lower T-boxes 26 and 28 respectively, which are attached to shroud 14 and internal spargers 30. Distribution header pipes 18 and 20 diverge from an upper T-box assembly 32. Particularly, T-box 32 includes, in one embodiment, a T-box housing 34 having first, second, and third ends 36 (shown in FIG. 2), 38, and 40. First end 36 of T-box housing 34 is coupled to a safe end 42 of core spray nozzle 44. Ends 38 and 40 are configured to be in substantial alignment and configured to couple to core spray line header pipes 18 and 20 respectively. Header pipes 18 and 20 are coupled to second and third ends 38 and 40 by pipe connectors 46 and 48 respectively. Pipe connectors 46 and 48 may be any pipe connectors known in the art, but preferably, are pipe connectors such as described in co-pending U.S. patent application Ser. No. 08/909,283, entitled PIPE CONNECTOR ASSEMBLY, filed Aug. 11, 1997, and assigned to the present assignee. FIG. 2 is a sectional side view with parts cut away of T-box assembly 32. In one embodiment, T-box assembly 32 includes in addition to T-box housing 34, a cruciform wedge 50 and a draw bolt 52. T-box housing 34 is configured to be positioned so that first end 36 is located inside core spray nozzle 44 and engages core spray nozzle safe end 42. Particularly, safe end 42 includes a first end 54, a second end 56, and a bore 58 extending between ends 54 and 56. Bore 58 includes a tapered portion 60 located between ends 54 and 56. First end 36 of T-box housing 34 engages core spray nozzle safe end 42 at first end 54 forming a metal-to-metal interface 62. T-box housing 34 also includes a cover opening 64 that is in substantial alignment with first end 36, and is configured to receive a T-box cover plate 66. T-box cover plate 66 includes a draw bolt opening 68 configured to receive draw bolt 52. First end 36 of T-box housing 34 also includes a plurality of positioning lugs 70 (one shown) configured to engage core spray nozzle 44 to center T-box housing 34 in core spray nozzle bore 72. Draw bolt 52 is configured to extend through a bore 74 of a central member 76 of cruciform wedge 50. Draw bolt 52 comprises a cap portion 78 located at a first end 80 configured to be larger than the diameter of bore 74 through central member 76 of cruciform wedge 50. A second end 82 of draw bolt 52 is configured to extend through draw bolt opening 68 in T-box cover plate 66 and to threadenly engage a draw bolt nut 84. Referring to FIG. 3, cruciform wedge 50 includes central member 76 having bore 74 extending therethrough. First, second, third and fourth web members 86, 88, 90, and 92 extend from central member 76. Web members 86, 88, 90, and 92 are configured so as to form an X shaped configuration. Support members 94 and 96 extend between ends 98, 100, 102, and 104 of adjacent web members 86, 88, 90, and 92. Particularly, support member 94 extends between first and second web members 86 and 88, and support member 96 extends between third and fourth web members 90 and 92. Support members 94 and 96 are configured to conform to bore 58 of core spray nozzle safe end 42. Particularly support members 94 and 96 are configured to engage tapered portion 60 of safe end bore 58 (shown in FIG. 2). Additionally, web members 86, 88, 90, and 92 are configured to be contoured to minimize flow resistance. To replace a core spray line in nuclear reactor pressure vessel 10, the existing T-box/thermal sleeve combination is removed from core spray nozzle safe end 42 by conventional underwater plasma arc cutting and/or electric discharge machining (EDM). Typically, a small portion of end 54 of safe end 42 is also removed. First end 54 is then prepared, usually by EDM, to mate with first end 36 of T-box housing 34. Particularly, first end 54 of safe end 42 is machined so as to form a metal-to-metal interface 62 with first end 36 of T-box housing 34. T-box assembly 32 is used to connect core spray lines 18 and 20 to safe end 42 of core spray nozzle 44 by coupling first end 36 of T-box housing 34 to safe end 42 and coupling ends 38 and 40 to core spray distribution header pipes 18 and 20. Particularly, to couple first end 36 of the T-box housing 34 to safe end 42, cruciform wedge 50 and draw bolt 52 are inserted into safe end bore 58. Cruciform wedge 50 is configured with webs 86, 88, 90, and 92 in an X-shaped configuration and only two support members 94 and 96 connecting web members 86, 88, 90, and 92 to permit wedge 50 to be inserted into safe end bore 58. Wedge 50 is inserted in an orientation that positions the axis of bore 74 of central member 76 of wedge 50 perpendicular to the axis of bore 58 of nozzle safe end 42. Wedge 50 is then tilted so as to move central member bore 74 into co-axial alignment with safe end bore 58, and support members 94 and 96 into engagement with tapered portion 60 of safe end bore 58. Draw bolt 52 is then inserted through bore 74 of wedge central member 76 with threaded end 82 of draw bolt 52 extending away from safe end 42 and towards T-box housing 34. This may be accomplished by attaching a thin wire (not shown) to threaded end 82 of bolt 52 and threading the wire through wedge central member bore 74 before inserting wedge 50 and draw bolt 52 into safe end 42. After wedge 50 has been tilted to its operational position the wire may be pulled through central member bore 74 which in turn pulls threaded end 82 of draw bolt 52 through wedge bore 74 and into position with cap portion 78 of bolt 52 engaging central member 76 of wedge 50. T-box housing 34 is then positioned with the alignment lugs 70 engaging the inside surface of core spray nozzle 44 and first end 36 of housing 34 engaging first end 54 of safe end 42. T-box cover plate 66 is then positioned over cover opening 64 with threaded end 82 of draw bolt 52 extending through draw bolt opening 68 in cover plate 66. Draw bolt nut 84 is then threaded onto bolt 52 and tightened to a predetermined torque. Core spray header pipes 18 and 20 are then coupled to ends 38 and 40 of T-box housing 34 to complete the installation. The above described T-box assembly 32 facilitates replacing core spray lines 18 and 20 without removing core spray nozzle safe end 42 or draining reactor 10. In addition T-box assembly 32 facilitates attaching core spray lines 18 and 20 to safe end 42 without welding. From the preceding description of various embodiments of the present invention, it is evident that the objects of the invention are attained. Although the invention has been described and illustrated in detail, it is to be clearly understood that the same is intended by way of illustration and example only and is not to be taken by way of limitation. Accordingly, the spirit and scope of the invention are to be limited only by the terms of the appended claims.
summary
050341855
summary
BACKGROUND OF THE INVENTION This invention relates generally to reactor control blades for controlling the power of a light-water nuclear reactor such as a boiling water reactor and relates more particularly to a high-reactivity-worth, long-lived nuclear reactor control blade designed to increase the reactor shut-down margin and extend the lifetime. In general, conventional boiling water reactor control blades have a construction such that a multiplicity of neutron absorbing rods are inserted in a plurality of wings formed of elongated U-shaped sheaths fixed to a central tie rod. Each of the neutron absorbing rods is constituted by, for example, a stainless steel cover tube filled with boron carbide (B.sub.4 C) grains provided as a neutron absorber. While this reactor control blade is inserted in a core section of a nuclear reactor such as a boiling water reactor, the neutron absorber which fills the sheaths is irradiated with neutrons and gradually loses neutron absorbing ability. The nuclear reactor control blade is therefore changed after being used for a predetermined operation period. Each wing of the control blade used in the core section of a nuclear reactor is not irradiated with neutrons uniformly over the entire area. An insertion end region and an outer edge region of each wing, for example, are irradiated with neutrons more intensely. Part of the neutron absorber which fills each of those region therefore absorbs neutrons at a higher rate, becomes worn faster and reaches the nuclear lifetime faster. Consequently, the whole of the reactor control blade must be scrapped even though the nuclear lifetime of the rest of the neutron absorber in the other region is sufficient. The conventional control blade is thus disadvantageous in terms of economy. In addition, an increase in the frequency of replacement of the reactor control blades means an increase in the total period of time taken for replacement operations, resulting in a reduction in the plant factor and, hence, a considerable economical demerit. There is also a risk of increasing the rate at which operators are exposed to radiation. To prevent this problem and risk, the inventors of the present invention have already proposed a type of nuclear reactor control blade in which a neutron absorber having a comparatively long lifetime such as hafnium is provided in some sections of the control blade where the intensity of neutron irradiation is high. This reactor control blade has, as disclosed in Japanese Patent Laid-Open No. 53-74697, a hybrid structure in which a long-lived neutron absorber is provided in top end portions and blade edge portions of the wings. This hybrid type of reactor control blade has a lifetime twice as long as that of an ordinary type of control blade. In the conventional reactor control blades, the wing is filled with a neutron absorber with a density distribution uniform over the entire region of the wing, and sections of the wing divided in the axial direction are equalized with respect to neutron absorbing ability or reactivity. This arrangement, however, allows a certain dispersion of reactivity with passage of time owing to non-uniformity of the neutron irradiation rate such as mentioned above. There is therefore a possibility of a local deterioration in terms of reactor shut-down margin at the last stage of the operating cycle of the reactor. The reactor shut-down margin distribution (or subcriticality) in the axial direction in the case of operation of the reactor for a predetermined period of time using the above-described type of reactor control blade varies slightly depending upon the design specification of the fuel assembly or the method of operating the reactor, but this distribution is always substantially the same. That is, the reactor shut-down margin is high with respect to the upper and lower ends of the core and is minimum with respect to a position slightly lower than the upper end. This phenomenon can be explained by the following reason. If the effective axial length of the reactor core is L, the void coefficient during operation is particularly high in a section close to the upper end of the core ranging between this upper end and a position at a distance of 3/4.L from the lower end of the core. In this section, the power density of the reactor is relatively low and the amount of remaining uranium of a mass number of 235 (U-235) which is a fissile material is comparatively large Neutron spectrum hardening takes place by the effect of generating voids. As a result, the plutonium generation reaction (neutron absorption reaction) is promoted. For this reason, the enrichment of fissile materials in an upper section of the core becomes relatively high after the operation of the reactor, so that the reactor shut-down margin becomes relatively reduced with respect that region. In the present circumstances, the nuclear fuel burn-up extension and the operating cycle extension will inevitably be promoted because of demands for improvements in the reactor in terms of operation economy. To satisfy such demands, fuels of high enrichment factors are increasingly adopted and, correspondingly, reactor control blades having a long nuclear lifetime and improved in the reactor shut-down margin are urgently required. If the conventional reactor control blades are applied to a reactor loaded with a nuclear fuel of a high enrichment factor, the reactor shut-down margin becomes relatively reduced and it is necessary to periodically replace the reactor control blades with a short operating cycle. To replace the reactor control blades, it is necessary to perform complicated operations of shutting down the reactor and preliminarily removing from the core a multiplicity of fuel assemblies disposed around the control blades which are to be replaced. The period of time during which the reactor is shut down is thereby extended, resulting in a considerable reduction in the operation efficiency of the reactor and, hence, a deterioration in terms of economy. There is also a possibility of a considerable increase in the amount of working for management. To satisfy demands for extension of the lifetime of control blades, the applicant of the present invention has developed a long-lived reactor control blade greatly improved. As disclosed in Japanese Patent Laid-Open No. 58-55887, this reactor control blade is constituted by inserting neutron absorbing plates formed from a long-lived neutron absorbing material, e.g., hafnium in wings formed from stainless steel. As a result of the use of long-lived neutron absorbing plates formed from hafnium or the like, the lifetime of the control blade has been increased to a large extent. This reactor control blade, however, is considerably heavy and expensive as a whole since it makes use of hafnium in the form of a plate which is more expensive than ordinary neutron absorbers and which also has a high density. This control blade cannot be applied to units using conventional control blade driving mechanisms without condition since the design of the mechanism for driving this control blade must be changed to enable the mechanism to withstand the heavy load. SUMMARY OF THE INVENTION In view of these problems of the conventional art, an object of the present invention is to provide a high-reactivity-worth, long-lived type of control blade for a nuclear reactor designed to increase the reactor shut-down margin as well as the lifetime by providing an optimum amount of a long-lived neutron absorber in a region where the reactor shut-down margin tends to become smaller to specially increase the reactivity worth thereof. Another object of the present invention to provide a control blade for a nuclear reactor designed to be improved in the total reactivity worth as well as to extend the lifetime by devising means to cope with swelling of a neutron absorber. Still another object of the present invention is to provide a control blade for a nuclear reactor designed to be reduced in the total weight by forming a neutron absorber from a special light-weight alloy. A further object of the present invention is to provide a control blade for a nuclear reactor designed to extend the nuclear, mechanical lifetime and to become backfittable to existing reactor units as well as to attain the above objects. To attain these objects, the present invention provides one of its aspects a control blade for a nuclear reactor, having: a plurality of wings each in the form of a generally rectangular plate having an longitudinal axis extending in the longitudinal direction of the control blade, the wings being closed at their widthwise ends to each other so as to form a cross-shaped cross section of the control blade; an upper end structural member fixed to an upper end of each of the wings inserted into a core of the reactor; a lower end structural member fixed to a lower end of the wing inserted into the reactor core; a central connection member connecting the upper end structural member and the lower end structural member so as to support the wing; and a packing means formed in the wing, a neutron absorber being packed in the packing means; wherein the wing is formed of a diluted alloy obtained by diluting a long-lived neutron absorber such as hafnium with a diluent. More specifically, the neutron absorber packing means is formed as a multiplicity of aligned neutron absorber housing holes extending in the widthwise direction of the wing, and some of these housing holes formed in a region where the subcriticality becomes smaller or shallower during shut-down of the reactor are enlarged so as to have an elongated cross section while the structure including these elongated holes is formed with means to cope with swelling. The present invention also provides in another of its aspects a control blade for a nuclear reactor based on the above construction wherein the neutron absorber packing means is formed as a neutron absorber packing space section which is divided into a first region on the side of the inserted upper end and a second region on the side of the inserted lower end and adjacent to the first region. The first region includes a high-reactivity-worth region in which a diluted alloy obtained by diluting a long-lived neutron absorber with a diluent is packed. A plurality of lateral holes extending in the widthwise direction of the wing are arranged in a row over the region where the long-lived neutron absorber is contained, and a neutron absorber different from the long-lived neutron absorber is packed in these lateral holes. The present invention also provides in still another of its aspects a control blade for a nuclear reactor wherein the neutron absorber packing space section is divided into a first region on the side of the inserted upper end where the neutron irradiation rate is particularly high, a second region next to the first region, where the subcriticality becomes smaller during shut-down of the reactor, and a third region bordering the second region on the side of the inserted lower end, a long-lived neutron absorber being packed in housing holes formed in the first region, a neutron absorber such as boron carbide being packed in housing holes formed in the second and third regions, at least one of the housing holes formed in the third region being formed as a gas plenum. In these control blades also, some of the housing holes formed in a region where the subcriticality becomes smaller during shut-down of the reactor are enlarged so as to have an elongated cross section while the structure including these elongated holes is formed with means to cope with swelling. In the thus-constructed control blades for nuclear reactors, each wing is formed from a diluted alloy containing an optimum amount of hafnium having a long lifetime and a high density, and this diluted alloy is formed of a solid solution containing zirconium or titanium having a low density. It is therefore possible to manufacture a light-weight control blade having a smaller weight and stable physically and chemically. This control blade can therefore be adopted for use in conventional reactors without changing design specifications relating to load withstanding performance of the existing control blade driving mechanisms. The reactivity worth of the reactor control blade is increased by the complementary neutron absorption effects of hafnium contained as a long-lived neutron absorber in the diluted alloy forming each wing and of the neutron absorber packed in the housing holes in each region, thereby improving the reactor shut-down margin and increasing the nuclear lifetime to a large extent. In the control blades of the above constructions, a larger amount of the neutron absorber is provided in a portion where the subcriticality becomes smaller during shut-down of the reactor while a long-lived neutron absorber is provided in a portion where the neutron irradiation rate is particularly high, gas plenums are disposed in an optimized fashion in the other portions to receive gasses such as helium generated by the reaction between the neutron absorber and neutrons, thereby limiting the increase in the gas pressure and improving the mechanical strength. In the control blades for nuclear reactors in accordance with the present invention, housing holes are formed in each wing in such a manner that they extend in the widthwise direction of the wing and that they are arranged in a row in the longitudinal direction of the wing. A long-lived neutron absorber is disposed at least in accommodation holes which are formed in the inserted upper end section of the wing and which contribute to the reactivity worth. Therefore the neutron absorbing ability of the inserted upper end section which is exposed to neutron irradiation when inserted in the core during operation of the reactor or even when drawn out is maintained for a long period of time, thus improving the nuclear lifetime. When the control blade is used by being fully inserted into the core, nuclear reaction of the interior of the fuel assembly is restricted by the void phenomenon with respect to the second region which is formed next to the first region of the control blade in the longitudinal direction and where the subcriticality becomes smaller. In this event, therefore, the amount of remaining nuclear fuel with respect to the second region is large. Besides, the density of fissile materials becomes relatively increased by the plutonium generation reaction. However, the present invention has optimized the amount of the neutron absorber packed in the second region by changing the pitch, shape and dimensions of the housing holes formed in the second region so as to increase the hole capacity per unit length in the lengthwise direction of the wing compared with the other regions. The desired reactivity worth of the neutron absorber in the second region can be thereby maintained even during a long-term operation of the reactor. In consequence, it is possible to ensure a sufficient overall reactor shut-down margin while the control blade is fully inserted in the reactor core. The portion of the wing in which the elongated holes are formed is constructed to cope with swelling in such a manner that a neutron absorber which does not swell by neutron absorption reaction is provided in the extreme end portions of each housing hole closer to the adjacent holes, or that the thicknesses of the wing wall portions on opposite sides of the hole are increased at the extreme end portions to increase the mechanical strength. Instead, inner tubes filled with a neutron absorber may be fitted in the elongated holes, an inner sleeve is fitted in each elongated hole while a neutron absorber containing boron is packed in this inner sleeve, or dimples are formed in the outer surfaces of the wing wall portions. The control blade is thus designed to reduce the degree of stress around the elongated hole caused by swelling, delay the time at which the stress starts generating, or prevent the generation of the stress, thus extending the mechanical lifetime.
claims
1. A computer tomography medical examination device, comprising:a radiation source for x-raying an object being medically examined from a projection direction with a radiation energy associated to the projection direction;a detector for detecting a radiation from the radiation source and recording a projection image of the object;a data memory for storing a predetermined correction value; andan evaluation unit connected downstream of the detector for correcting a radiation hardening of the projection image,wherein an operating parameter of the radiation source is applied to determine the radiation energy associated to the projection direction which depends on an absorption characteristics of the object,wherein the evaluation unit is provided with the operating parameter and reads the predetermined correction value allocated to the operating parameter and corrects a radiation hardening on the projection image. 2. The device as claimed in claim 1, wherein the radiation source is an x-ray tube and the detector is an x-ray detector. 3. The device as claimed in claim 1, wherein a variable of the operating parameter is an x-ray tube voltage. 4. The device as claimed in claim 1, wherein the evaluation unit reads the predetermined correction value relative to the x-ray tube voltage from the data memory and carries out a water correction on the projection image by the predetermined correction value. 5. The device as claimed in claim 1, wherein the evaluation unit performs a post-reconstructive correction of an hardening on the projection image that is caused by an attenuation which is different than a water-equivalent material in the object. 6. The device as claimed in claim 5, wherein the post-reconstructive correction of the hardening of the projection image is carried out iteratively by the evaluation unit. 7. The device as claimed in claim 5, wherein the post-reconstructive correction of the hardening of the projection image is carried out by the evaluation unit with a spatial resolution that is less than a spatial resolution of the projection image. 8. The device as claimed in claim 1,wherein an object model differentiated according to the absorption characteristics of the object is determined by the evaluation unit from the projection image,wherein an object data record derived from the object model is allocated by the evaluation unit to a pixel of the projection image,wherein the correction value for the projection image is determined by the evaluation unit using the object data record and the x-ray tube voltage. 9. The device as claimed in claim 1, wherein the object is a live animal or human patient. 10. A method for correcting a radiation hardening on a projection image of an object being medically examined, comprising:x-raying the object by a radiation source from a projection direction with a radiation energy associated to the projection direction;detecting a radiation from the radiation source and recording a projection image of the object by a detector;storing a predetermined correction value in a data memory;correcting the radiation hardening of the projection image by an evaluation unit connected downstream of the detector; andproviding a corrected projection image,wherein an operating parameter of the radiation source is applied to determine the radiation energy associated to the projection direction which depends on an absorption characteristics of the object,wherein the evaluation unit is provided with the operating parameter and reads the predetermined correction value allocated to the operating parameter and corrects a radiation hardening on the projection image. 11. The method as claimed in claim 10, wherein the radiation source is an x-ray tube and the detector is an x-ray detector and the projection image is generated by the x-ray tube and the x-ray detector. 12. The method as claimed in claim 10, wherein the tube voltage is used as a variable of the operating parameter. 13. The method as claimed in claim 10, wherein a water correction on the projection image is carried out by the evaluation unit by reading a predetermined correction value from the data memory relative to the tube voltage applied. 14. The method as claimed in claim 10, wherein a post-reconstructive correction of the radiation hardening on the projection image is performed by the evaluation unit relative to the tube voltage, the hardening caused by a material having a different attenuating effect than a water-equivalent material. 15. The method as claimed in claim 14, wherein the post-reconstructive correction of the hardening is performed iteratively by the evaluation unit. 16. The method as claimed in claim 14, wherein the post-reconstructive correction of the hardening is performed with a spatial resolution that is less than a spatial resolution of the project image data. 17. The method as claimed in claim 10,wherein a three-dimensional object model differentiated according to an absorption characteristics of the object is determined by the evaluation unit from the projection image,wherein an object data record is derived from the object model and is allocated to the project image,wherein the object data record and the tube voltage are used to determine a correction value for the projection image from the data memory. 18. The method as claimed in claim 10, wherein the object is a live animal or human patient.
summary
claims
1. A nuclear power plant comprising a primary coolant circuit, a steam-water circuit separated from the primary coolant circuit and a steam generator connected to the primary coolant circuit and the steam-water circuit to transfer heat from the primary coolant circuit into the steam-water circuit, wherein the steam-water circuit has:at least one dosing point to introduce a reducing agent that is an organic compound consisting of carbon, hydrogen and oxygen and set a predetermined oxygen concentration in the steam-water circuit and reducing conditions within the steam generator;at least one potential sensor located in the steam generator and configured to measure a redox potential of water in the steam-water circuit, andat least one TOC flowmeter configured to measure the concentration of the reducing agent in the steam-water circuit. 2. The nuclear power plant according to claim 1, wherein the reducing agent acts as an oxygen scavenger when exposed to gamma radiation. 3. The nuclear power plant according to claim 1, wherein the reducing agent is selected from the group consisting of C1-C6 alcohols, aldehydes, ketones and mixtures thereof. 4. The nuclear power plant according to claim 3, wherein the reducing agent is a C1-C6 alcohol. 5. The nuclear power plant according to claim 4, wherein the reducing agent is methanol. 6. The nuclear power plant according to claim 1, wherein the steam-water circuit has a condenser and a main condensate pump, and the dosing point is located between the condenser and the main condensate pump. 7. The nuclear power plant according to claim 1, wherein the steam-water circuit has a feed water container, and the dosing point is located downstream from the feed water container. 8. A method for operating a nuclear power plant comprising a primary coolant circuit, a steam-water circuit separated from the primary coolant circuit and a steam generator connected to the primary coolant circuit and the steam-water circuit to transfer heat from the primary coolant circuit into the steam water circuit, the method comprising introducing an organic reducing agent consisting of carbon, hydrogen and oxygen into the steam-water circuit by means of a dosing device,measuring a redox potential of water in the steam-water circuit with at least one potential sensor located in the steam generator,measuring a concentration of the reducing agent in the water of the steam-water circuit with at least one TOC flowmeter and;adjusting the concentration of the reducing agent with the dosing device based on the measured redox potential and reducing agent concentration such that a predetermined oxygen concentration is set in the steam-water circuit and reducing conditions are set within the steam generator. 9. The method according to claim 8, further comprising setting a pH of greater than 7 in the steam-water circuit. 10. The method according to claim 8, wherein the concentration of the reducing agent is continuously measured. 11. The method according to claim 8, wherein the steam-water circuit comprises a main condensate portion leading a main condensate from a condenser to a feed water container, where the main condensate and water from a water separator are collected and maintained for supply as feed water and a feed water portion leading from the feed water container to a feed water supply line at the steam generator, the method further comprising analyzing and controlling the oxygen content in the main condensate and/or the feed water with the concentration of the reducing agent. 12. The method according to claim 8, wherein the steam generator has a circulation space in which circulating water circulates to absorb heat from the primary coolant circuit, with the concentration of the reducing agent in the circulating water being in a range from 10E-7 mol/kg to 10E-3 mol/kg. 13. The method according to claim 12, wherein the concentration of the reducing agent in the circulating water is in the range of 3×10E-7 to 3×10E-4 mol/kg. 14. The method according to claim 8, wherein the steam-water circuit has a feed water portion comprising a feed water supply line, and that the steam generator comprises a circulation space in which circulating water circulates to absorb heat from the primary coolant circuit, and wherein the concentration of the reducing agent is determined in the feed water and/or in the circulating water by means of the TOC flowmeters. 15. The method according to claim 8, wherein the steam generator further comprises a circulation space in which circulating water circulates to absorb heat from the primary coolant circuit, and wherein the redox and/or corrosion potential is measured in the circulating water by means of the potential sensor. 16. The method according to claim 8, wherein the steam generator further comprises a circulation space in which circulating water circulates to absorb heat from the primary coolant circuit, and wherein the redox potential in the circulating water is measured continuously and used as a control parameter for adjusting the concentration of the reducing agent. 17. The method according to claim 8, wherein the steam generator comprises a circulation space in which circulating water circulates to absorb heat from the primary coolant circuit, and wherein the redox and/or corrosion potential in the steam-water circuit is/are measured to adjust oxidizing conditions in the steam-water circuit and wherein, at the same time, the redox and/or corrosion potential in the circulating water is/are measured to adjust the reducing conditions of the circulating water. 18. The method according to claim 8, wherein the steam generator further comprises a circulation space in which circulating water circulates to absorb heat from the primary coolant circuit and wherein the concentration of the reducing agent in the circulating water is maintained in a range from 5×10E-6 mol/kg to 5×10E-2 mol/kg. 19. The method according to claim 8, wherein the predetermined oxygen concentration is not more than 0.1 mg/kg.
056446071
description
DETAILED DESCRIPTION OF THE EMBODIMENTS Hereinafter, details of the present invention will be explained with reference to embodiments shown in the drawings. FIG. 8(a) is a transverse cross-sectional view for explaining a composition of the core of a boiling water reactor. In the figure, there is shown fuel assemblies 36, control rods 40 and LPRMs (Local Power Range Monitors) 41, respectively. And, as shown in FIG. 8(b), four bundles of fuel assemblies around one control rod 40 compose a fuel cell. A handle 36A of the bundle 36 faces the control rod 40 at an angle of 45 degrees. Since the reactivity of a reactor core continues to decrease during operations of a nuclear reactor, it is necessary for old fuel assemblies to be periodically exchanged with new fuel assemblies. And, the period between the fuel exchanges is called an operation cycle, the old and the new fuel assemblies being exchanged at the end of each operation cycle. In a nuclear power plant of 1100 MWe class, about 800 bundles of fuel assemblies are loaded in a reactor core, and one fourth to one third of all loaded fuel assemblies have to be exchanged in every regular inspection. Since the fuel assembly exchange (refueling) work is the critical part in a regular inspection, reduction of the time of refueling gives rise to reduction in the number of days required for the regular inspection, and furthermore improves the availability factor of the nuclear power plant. In the following, an existing refueling apparatus will be explained. First, an example of an existing refueling apparatus and the composition of a fuel assembly grappling apparatus are shown in FIGS. 9 and 11, respectively. The refueling apparatus shown in FIG. 9 consists of main parts of a travel carriage 1, a traverse carriage 2, an extension pipe 3, a grapple 4 and a hoist 5. And, as shown in FIG. 11, the fuel assembly grappling apparatus is composed of the extension pipe 3, the grapple 4, and grapple driving motors 10 and 11. The travel carriage 1 is moved by a driving motor 8 on a pair of rails 6 provided at the side parts of each one of a fuel pool 32 and a reactor core pool 30, which will be explained later. The traverse carriage 2 including the grapple 4, the extension pipe 3 and the hoist 5, is moved by a driving motor 9 on a pair of rails 7 provided on the travel carriage 1. The grapple 4 is lifted and lowered by the hoist 5, and rotated around the vertical axis by a driving motor 11 for adjusting the angle of a grappled fuel assembly. Further, the grapple 4 is attached at the bottom of the extension pipe 3. Hereafter, the moving directions of the travel carriage 1 and the traverse carriage 2, the elevating direction of the grapple 4, and the rotating direction of the grapple 4, will be referred to as the x, Y, Z and .theta. directions, respectively. The travel carriage 1, the traverse carriage 2 and the hoist 5 of the refueling apparatus are driven by the direct current motors, and the motions in the x-Y directions are controlled by a control system having a calculation unit as shown in FIG. 10. The control system of the existing refueling apparatus shown in FIG. 10 is composed of the travel carriage driving motor 8, the traverse carriage driving motor 9, the calculation unit 50, speed controllers 51A and 51B and speed sensors 52A and 52B. In the figure, there are also shown a signal for instructing the target position of fuel assembly transfer 53, position signals 54A and 54B representing the positions of the carriages 1 and 2, speed control signals 55A and 55B, and speed signals 56A and 56B. An operator inputs the destination ID address in a fuel pool or a reactor core for a fuel assembly to be transferred as the signal for instructing the target position of fuel assembly transfer 53, into the calculation unit 50. The calculation unit 50 takes in a signal representing the present position X.sub.1 (position signal 54A) of the travel carriage 1, and a signal representing the present position Y.sub.1 (position signal 54B) of the traverse carriage 2, and calculates each of the speed control signals 55A and 55B for the travel and the traverse carriages 1 and 2, based on a relation between each present position and the target position, and then inputs the calculated speed control signals 55A and 55B to the speed controllers 51A and 51B. The speed controller 51A (51B) compares the speed control signal 51A (51B) with the sensed speed signal 56A (56B) and further generates the speed control signal 51A (51B) for controlling the voltage in a control circuit of the direct current motor for the travel carriage 1 (the traverse carriage 2) so that the difference between the speed control signal and the sensed speed signal is reduced to zero, and then the positioning of a transferred fuel assembly is accomplished by continuous control operations of the carriages 1 and 2. In the above-explained existing control method, the X-Y simultaneous control is adopted for reducing the time of fuel transfer between the present position and the target position, but reducing the time of fuel transfer by executing a multidimensional control including Z-.theta. simultaneous control is not considered. In the following, an automatic refueling apparatus forming an embodiment of the present invention will be explained, by referring to FIG. 1-FIG. 4. The composition of an automatic refueling apparatus including a control system is shown in FIG. 1. Position signals indicating position change amounts in the X, Y, Z and .theta. directions are sensed by synchro transmitters, each of which is provided for a respective driving axis (not shown in a figure), and the signal are input to a process input/output unit 13. The process input/output unit 13 converts the position signals to digital signals, and outputs them to a computer, namely, a central processing unit 14. The central processing unit 14 calculates the moving amounts in the X, Y, Z and .theta. directions by comparing the present position with the target position, which has been given by a demand of an operator via an operator console 16, and generates control signals based on the calculated moving amounts and sends them to the driving motors 8, 9, 10 and 11 via the process input/output unit 13 and a control panel 12. FIG. 2(a) is a perspective view of the apparatus, in which the arrangement of position sensors used in the embodiment is shown. And, FIG. 2(b) is an enlarged fragmentary view showing the hoist part 5 illustrated in FIG. 2(a), which shows also the arrangement of position sensors attached at the hoist part 5. The position sensing system shown in FIGS. 2(a) and 2(b) includes an actuator 60 for detecting the position of the travel carriage 1, a limit switch 61 for detecting the position of the travel carriage 1, a limit switch 62 for detecting the elevation position of the grapple 4, a synchro transmitter 63 for indicating the elevation position of the grapple 4, a synchro transmitter 65 for detecting the position of the travel carriage 1, a synchro transmitter 66 for detecting the position of the traverse carriage 2, and a hoist 64 for elevating the fuel assembly grappling apparatus. The computer system used in the control system is composed of the central processing unit 14, the process input/output unit 13, the operator console 16, and peripheral devices, such as a memory unit 15, an input/output typewriter 18, a printer 17, a data reader 19 and so forth. Through the relay panel 20 and the process input/output unit 13, the central processing unit 14 takes in information indicating the position of the automatic refueling apparatus shown in FIG. 3, that is, the position in the X direction over a reactor core region, detected by detection means, such as a limit switch (c), (located in the interval between two chain double-dashed lines parallel to the Y axis shown in FIG. 3), the gate position through which the traverse carriage 2 passes, (the Y coordinate value of a chain double-dashed line parallel to the X axis, passing through the fuel pool 31, a gate 30 and the reactor core pool 32), detected by detection means, such as a limit switch (D), the upper limit position of the grapple 4 detected by detection means, such as a limit switch (E), an intermediate position detected by detection means, such as a limit switch (F), the seating position of a fuel assembly in the fuel pool, detected by detection means, such as a limit switch (G), the seating position of a fuel assembly in the reactor core, detected by detection means, such as a limit switch (G'), the position permitted for the travel and traverse motions during operations without a load in the fuel pool, detected by detection means, such as a limit switch (H), the position permitted for the travel and traverse motions during operations without a load in the reactor core, detected by detection means, such as a limit switch (B), and the position permitted for the travel and traverse motions during operations with a load in the reactor core, detected by detection means, such as a limit switch (A). Then, the central processing unit 14 controls the positioning of a fuel assembly to be transferred and monitors the fuel assembly transferring operations. Meanwhile, the Z coordinate value indicates the bottom position of the grapple 4. In the following, automatic operations in the refueling work, to which the present invention is applied, will be explained in detail with reference to FIG. 3-FIGS. 6(a) and 6(b). As shown in FIGS. 3 and 4, the automatic refueling apparatus is installed at a region over both the fuel pool 30 and the reactor core pool 32, and is moved between both pools. When the refueling is carried out, the gate 31 is opened, and the space over both of the pools and the gate part is filled with water. In the fuel pool 30, a fuel assembly rack 33 is provided. Usually, the fuel assembly exchanging operations are carried out between the fuel assembly rack 33 and the reactor core 34. For this purpose, the coordinate values, data indicating the presence of a fuel assembly and data of an assembly positioning angle, for each lattice of the fuel assembly rack 33, or for each cell of the reactor core 34, are stored in the computer system. By referring to FIG. 3, FIGS. 5(a) and 5(b), the fuel assembly exchanging operations will be explained for a case in which a fuel assembly is transferred from a position P at the fuel assembly rack 33 to a position Q at the reactor core 34. Let the coordinates of the present position P and the target terminal position Q be (X.sub.P, Y.sub.P, Z.sub.P, .theta..sub.P) and (X.sub.Q, Y.sub.Q, Z.sub.Q, .theta..sub.Q), respectively. At first, an operator inputs a pair of ID numbers IQ.sub.X and IQ.sub.Y in the X and Y directions corresponding to the coordinates (X.sub.Q, Y.sub.Q) of the target position Q, using the operator console 16. Then, the operator commands the computer system to judge the possibility of starting the required automatic operations, that is, the required fuel assembly transfer. If an automatic start is permitted, the operator initiates automatic start by pushing a button for starting the automatic operations. Then, after the required fuel assembly is grappled, a Z direction lifting control 1 is first executed, and then the grappled fuel assembly is temporally stopped at the upper limit position detected by the limit switch (E). Then, a X-Y simultaneous control 2 is executed. In the X-Y simultaneous control, the shortest route (P.fwdarw.b.fwdarw.c) for the prescribed points b and c, is calculated, and the computer system outputs control signals for controlling the motions in the x and y directions of the two carriages so that the grapple 4 moves along the calculated route (P.fwdarw.b.fwdarw.c). That is, in turn for the intermediate target points b and c, the deviations of the present position from each intermediate target point .DELTA.X and .DELTA.Y are calculated. Then, a constant speed control is executed for the direction corresponding to a larger deviation, and a deviation ratio (.DELTA.X/.DELTA.Y or .DELTA.Y/.DELTA.X) speed control is executed for the direction corresponding to a smaller deviation. Further, when the grapple 4 reaches the prescribed point c and the limit switch (C) is turned on, the X-Y-Z-.theta. simultaneous control 3 is started. In the angle .theta. control, an angle control signal is obtained based on the deviation of the angle .theta..sub.P from the angle .theta..sub.Q, and is output to the driving means. In the lowering control of the X-Y-Z-.theta. simultaneous control 3, the lowering of a fuel assembly is continued until the limit switch (A) for detecting the position permitted for the travel and traverse motions during operations with a load in the reactor core is turned off. Then, the lowering of the grapples 4 is stopped at the point where the limit switch (A) is turned off, and the control system executes a swing attenuation waiting control in which the grapple motion is stopped for a predetermined time to wait for the swing attenuation of the transferred fuel assembly 36. After finishing the swing attenuation control, a Z direction lowering control 4 is executed, and the transferred fuel assembly 36 is inserted into the reactor core 34 and the bottom of the grapple 4 is stopped at the seating position of a fuel assembly cell in the reactor core, detected by a limit switch (G'). FIG. 5(a) is a flow chart of the controlling operations for transferring the fuel assembly 36 held by the grapple 4 from the fuel pool 30 into the reactor core 34. And, FIG. 5(b) is a flow chart of the controlling operations for moving the fuel assembly grappling apparatus without a fuel assembly from the fuel pool 30 to the reactor core 34 to take out a fuel assembly. Next, the operations for transferring fuel assembly 36 from the reactor core 34 to the fuel pool 30, will be explained by referring to FIG. 4, FIGS. 6(a) and 6(b). FIG. 6(a) is a flow chart of the controlling operations for transferring the fuel assembly 36 held by the grapple 4 from the reactor core 34 into the fuel pool 30. FIG. 6(b) is a flow chart of the controlling operations for moving the fuel assembly grappling apparatus without a fuel assembly from the reactor core 34 to the fuel pool 30 to take out fuel assembly. In the following, the fuel assembly exchanging operations will be explained for a case wherein a fuel assembly is transferred from a position Q at the reactor core 34 to a position P at the fuel assembly rack 33. Let the coordinates of the present position Q of the grapple 4 and the target terminal position P be (X.sub.Q, Y.sub.Q, Z.sub.Q, .theta..sub.Q) and (X.sub.P, Y.sub.P, Z.sub.P, .theta..sub.P), respectively. At first, an operator inputs a pair of ID numbers IP.sub.X and IP.sub.Y in the X and Y directions corresponding to the coordinates (X.sub.P, Y.sub.P) of the target position P, using the operator console 16. Then, the operator commands the computer system to judge for the possibility of starting the required automatic operations, that is, the required fuel assembly transfer. If the automatic start is permitted, the operator initiates automatic start by pushing a button for starting the automatic operations. Then, after the required fuel assembly is grappled, a Z direction lifting control 1 is first executed, and then the grappled fuel assembly is temporally stopped at the upper limit position detected by the limit switch (A). Then, a X-Y-Z-.theta. simultaneous control 2 is executed. In the X-Y-Z-.theta. simultaneous control, the shortest route (Q.fwdarw.c) for the prescribed point c is calculated, and the computer system outputs control signals for controlling the motions in the x, y, z and .theta. directions of the grapple 4 so that the grapple moves along the calculated route (Q.fwdarw.c). That is, for the intermediate target point c, the deviations of the present position from the intermediate target point c, .DELTA.X and .DELTA.Y are calculated. Then, a constant speed control is executed for the direction corresponding to a larger deviation, and a deviation ratio (.DELTA.X/.DELTA.Y or .DELTA.Y/.DELTA.X) speed control is executed for the direction corresponding to a smaller deviation. Further, at the same time that the x-y control is started, the X-Y-Z-.theta. simultaneous control is started. In the angle .theta. control, an angle control signal is obtained based on the deviation of the angle .theta..sub.Q from the angle .theta..sub.P, and is output to the driving means. Then, a X-Y simultaneous control 3 is executed. In the X-Y simultaneous control, the shortest route (c.fwdarw.b.fwdarw.P) for the prescribed points b and c is calculated, and the computer system outputs control signals for controlling the motions in the x and y directions of the two carriages so that the grapple 4 moves on the calculated route (c.fwdarw.b.fwdarw.P). After finishing the X-Y control, the control system executes a swing attenuation waiting control. When the swing attenuation control is completed, a Z direction lowering control 4 is executed, and the transferred fuel assembly 36 is inserted into the fuel assembly rack 33 and the bottom of the grapple 4 is stopped at the seating position of a fuel assembly in the fuel pool, detected by a limit switch (G). As mentioned above, in the automatic fuel assembly transferring control, the control modes 1-4 are cyclically carried out. Further, the following control pattern is also carried out in the above cyclic control, that is, a control pattern of operations for moving the automatic refueling apparatus from the fuel pool 30 to the reactor core 34 to take out a fuel assembly 36 from the reactor core. This control pattern is executed in accordance with the control flow as shown in FIG. 5(b). And, as safety countermeasures, a prohibition logic against the moving of the grapple 4 in the X, Y and Z directions, as shown in FIG. 7, is also provided in the embodiment. Therefore, with the embodiment, X, Y, Z and .theta. axis simultaneous control can be safely executed, which can further considerably reduce the time for refueling. Furthermore, the same control method as mentioned above can be also applied to an automatic refueling apparatus with a fuel assembly grappling apparatus capable of holding a plurality of fuel assemblies. Such an automatic refueling apparatus also greatly improves the reduction of the refueling time. Thus, since the four-dimensional X, Y, Z and .theta. axis simultaneous control is made possible for the operations of transferring and taking out a fuel assembly in the fuel pool or the reactor core, by using the present invention, the time of 70 s for every fuel assembly exchanging operation cycle requiring about 10 m can be saved, which also equals a saving of one day for a 12-day refueling operation presently required in a regular inspection of a 1100 WMe class of a Boiling Water Reactor.