CA1132728A - Control component structure - Google Patents
Control component structureInfo
- Publication number
- CA1132728A CA1132728A CA329,872A CA329872A CA1132728A CA 1132728 A CA1132728 A CA 1132728A CA 329872 A CA329872 A CA 329872A CA 1132728 A CA1132728 A CA 1132728A
- Authority
- CA
- Canada
- Prior art keywords
- spider
- stem
- bore
- burnable poison
- rod
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- G—PHYSICS
- G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
- G21C—NUCLEAR REACTORS
- G21C7/00—Control of nuclear reaction
- G21C7/02—Control of nuclear reaction by using self-regulating properties of reactor materials, e.g. Doppler effect
- G21C7/04—Control of nuclear reaction by using self-regulating properties of reactor materials, e.g. Doppler effect of burnable poisons
-
- G—PHYSICS
- G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
- G21C—NUCLEAR REACTORS
- G21C7/00—Control of nuclear reaction
- G21C7/06—Control of nuclear reaction by application of neutron-absorbing material, i.e. material with absorption cross-section very much in excess of reflection cross-section
- G21C7/08—Control of nuclear reaction by application of neutron-absorbing material, i.e. material with absorption cross-section very much in excess of reflection cross-section by displacement of solid control elements, e.g. control rods
- G21C7/10—Construction of control elements
- G21C7/117—Clusters of control rods; Spider construction
-
- G—PHYSICS
- G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
- G21C—NUCLEAR REACTORS
- G21C7/00—Control of nuclear reaction
- G21C7/06—Control of nuclear reaction by application of neutron-absorbing material, i.e. material with absorption cross-section very much in excess of reflection cross-section
- G21C7/08—Control of nuclear reaction by application of neutron-absorbing material, i.e. material with absorption cross-section very much in excess of reflection cross-section by displacement of solid control elements, e.g. control rods
- G21C7/10—Construction of control elements
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E30/00—Energy generation of nuclear origin
- Y02E30/30—Nuclear fission reactors
Landscapes
- Physics & Mathematics (AREA)
- Engineering & Computer Science (AREA)
- Chemical & Material Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Plasma & Fusion (AREA)
- General Engineering & Computer Science (AREA)
- High Energy & Nuclear Physics (AREA)
- Monitoring And Testing Of Nuclear Reactors (AREA)
- Catalysts (AREA)
- Working Measures On Existing Buildindgs (AREA)
- Clamps And Clips (AREA)
- Mutual Connection Of Rods And Tubes (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
A technique is provided for engaging and dis-engaging burnable poison rods from the spider in a fuel assembly. The cap on the end of each of the burnable poison rods is provided with a shank that is received in the respective bore formed in the spider. In one illustrative embodiment, the shank is deformed to firmly secure the rod and attached shank in the spider bore. Pressing the shank in the direction of the bore axis overcomes the deforma-tion to release the particular rod from the spider.
A technique is provided for engaging and dis-engaging burnable poison rods from the spider in a fuel assembly. The cap on the end of each of the burnable poison rods is provided with a shank that is received in the respective bore formed in the spider. In one illustrative embodiment, the shank is deformed to firmly secure the rod and attached shank in the spider bore. Pressing the shank in the direction of the bore axis overcomes the deforma-tion to release the particular rod from the spider.
Description
7~Z~
TECHN _AL FIELD
This invention is directed to improvements in nuclear reactor fuel assemblies, and, more particularly, to methods and apparatus for securing and removing burnable poison rods from the spider in a fuel assembly, and the like.
BACKGROUND ART
_ To produce useful power from nuclear processes i~ is necessary to assemble a sufficient concentration of fissionable uranium, or other suitable material, in a physical configuration that will sustain a con-tinuous sequence of energy-producing reactions. This assembly, or reactor core, transfers the heat tha~
is generated in the fission reactions to a working fluid. Frequently, pressurized water flowing through the core at high velocities is used for this purpose.
Because the heat, vibration and radiation tha~
is generated within a power reactor core creates a generally hostile environment, the structural integrity of the core components is an important consideration.
Consequently, pressurized water power reactor cores frequently are comprised of groups of fuel assemblies that are arranged in a generally right circular cylindrical configuration. Each fuel assembly, moreover usually comprises an array of about two hundred long slender fuel rods that are parallel ~o and spaced from each other.
.
.. - - '.
~' ` ~ ' ' , .-. ..
7~
TECHN _AL FIELD
This invention is directed to improvements in nuclear reactor fuel assemblies, and, more particularly, to methods and apparatus for securing and removing burnable poison rods from the spider in a fuel assembly, and the like.
BACKGROUND ART
_ To produce useful power from nuclear processes i~ is necessary to assemble a sufficient concentration of fissionable uranium, or other suitable material, in a physical configuration that will sustain a con-tinuous sequence of energy-producing reactions. This assembly, or reactor core, transfers the heat tha~
is generated in the fission reactions to a working fluid. Frequently, pressurized water flowing through the core at high velocities is used for this purpose.
Because the heat, vibration and radiation tha~
is generated within a power reactor core creates a generally hostile environment, the structural integrity of the core components is an important consideration.
Consequently, pressurized water power reactor cores frequently are comprised of groups of fuel assemblies that are arranged in a generally right circular cylindrical configuration. Each fuel assembly, moreover usually comprises an array of about two hundred long slender fuel rods that are parallel ~o and spaced from each other.
.
.. - - '.
~' ` ~ ' ' , .-. ..
7~
-2- CASE 4100 Each of these fuel rods contains a stack of generally cylindrical uranium dioxide pellets in which the uranium provides the fissionable fuel for the power reactor.
These fuel assemblies are no~ limited to fuel rods but also support a number of other components.
For example, instrumentation tubes for observing temp-erature and neutron flux conditions within the core;
end fittings and fuel element grids for stabilizing the fuel assembly components; and control rods and control rod guide tubes for regulating the power out-put from the reactor through the selective absorption of fission inducing neu~rons within the reactor core often are made a part of the fuel assembly structure.
Clearly, the neutron distribution will vary from place-to-place within the reactor core. Illustrative ly, near the core perimeter it can be expected that the neutron population will be small relative to the center of the reactor core because the concentration of neutron producing uranium is lower at the core perimeter than it is in the center of the core. Neutrons at the core perimeter can "escape" from the core more readily through the core surface than they can from the center of the core, further tending to reduce the neutron concentration near the reactor core surface. Because heat generation within any specific portion of the reactor core is related to the neutron population within that portion) there is a definite tendency to produce higher tempera-tures at the center of the reactor core than at itsmargin. This înclination ~oward producing local tempera-ture maxima in different regions within the reactor core is generally undesirable for a number of reasons.
Primarily, the reactor is designed for core operation that will not exceed a predetermined temperature. If this core temperature is reached in just one or in a t72~
These fuel assemblies are no~ limited to fuel rods but also support a number of other components.
For example, instrumentation tubes for observing temp-erature and neutron flux conditions within the core;
end fittings and fuel element grids for stabilizing the fuel assembly components; and control rods and control rod guide tubes for regulating the power out-put from the reactor through the selective absorption of fission inducing neu~rons within the reactor core often are made a part of the fuel assembly structure.
Clearly, the neutron distribution will vary from place-to-place within the reactor core. Illustrative ly, near the core perimeter it can be expected that the neutron population will be small relative to the center of the reactor core because the concentration of neutron producing uranium is lower at the core perimeter than it is in the center of the core. Neutrons at the core perimeter can "escape" from the core more readily through the core surface than they can from the center of the core, further tending to reduce the neutron concentration near the reactor core surface. Because heat generation within any specific portion of the reactor core is related to the neutron population within that portion) there is a definite tendency to produce higher tempera-tures at the center of the reactor core than at itsmargin. This înclination ~oward producing local tempera-ture maxima in different regions within the reactor core is generally undesirable for a number of reasons.
Primarily, the reactor is designed for core operation that will not exceed a predetermined temperature. If this core temperature is reached in just one or in a t72~
-3- CASE 4100 few local points within the reactor core, the over-all heat generating potential of the core can not be realized. This effect results because the temperatures elsewhere in the core must be kept to lower values in order not to exceed the design temperature at those limited points or "hot spots"
in which the maximum design temperature has been reached.
Accordingly, in the simplified example under consideration, o~er-all reactor power can be increased if the neutron population (and hence, hea~) in ~he central portion o~ the core is depressed and the neutron population in the larger volume that characterizes the peripheral reactor core annulus is allowed to increase. In this way, by "flattening" the power distri-bution in the reactor core, the core actually is able to generate more power than it would be able to generate if the neutron concentration, temperature and power was allowed to reach a peak in the center of the core, or in some other location, as the case may be. In order to achieve this "flat" power distribution, it has been the practice to in~ert "burnable poison" rods in the fuel assemblies. Typically, a burnable poison rod is a tube filled with a material that has a very high probability for absorbing neutrons. For example, a sintered dispersion of boron carbide in an alumina matrix is suitable for this purpose.
Neutrons, absorbed in this manner by means of the material within the rod are, in effect, withdrawn ~rom the fission and power generation process. And so, to "flatten" the power distribution with a reactor core, burnable poison rods are concentrated in those fuel assemblies that are located in the central portion o~ the reactor core.
3'~
in which the maximum design temperature has been reached.
Accordingly, in the simplified example under consideration, o~er-all reactor power can be increased if the neutron population (and hence, hea~) in ~he central portion o~ the core is depressed and the neutron population in the larger volume that characterizes the peripheral reactor core annulus is allowed to increase. In this way, by "flattening" the power distri-bution in the reactor core, the core actually is able to generate more power than it would be able to generate if the neutron concentration, temperature and power was allowed to reach a peak in the center of the core, or in some other location, as the case may be. In order to achieve this "flat" power distribution, it has been the practice to in~ert "burnable poison" rods in the fuel assemblies. Typically, a burnable poison rod is a tube filled with a material that has a very high probability for absorbing neutrons. For example, a sintered dispersion of boron carbide in an alumina matrix is suitable for this purpose.
Neutrons, absorbed in this manner by means of the material within the rod are, in effect, withdrawn ~rom the fission and power generation process. And so, to "flatten" the power distribution with a reactor core, burnable poison rods are concentrated in those fuel assemblies that are located in the central portion o~ the reactor core.
3'~
-4- CASE 4100 Depending on a number of subtle effects it also might be advisable to provide burnable poison rod concentrations in other portions of the reactor core in which specific design or operational features produce large local neutron populations.
Not only must the fuel assembly support all of these diverse structural components in spite of the generally hostile environment within a reactor core, but the fuel assembly also must be capable of the somewhat conflicting need for swift and easy disassembly. For instance, it should be noted that fuel assemblies become radioactive after exposure in an operating reactor core. This radiation is so intense 1~ that inspection and repair can be accomplished only with remote handling equipment behind adequate radiation shielding.
Consequently, because disassembly procedures are expensive and time consuming, the need for a sturdy, yet readily dismountable structure is of considerable commercial importance.
The burnable poison rods that are used in many fuel assemblies are a part of this s~ructural picture.
Generally, the burnable poison rods that have characterized ~5 the prior art are mounted for movement in a direction that is parallel to the longitudinal orientation of the fuel rods. A "spider", in the form of a centrally disposed hub from which a number of arms radiate often is used to couple the burnable poison rods together ~or longitudinal movement relative to the balance of the fuel assembly. This motion is required to permit the power reactor operator to insert or withdraw the burnable poison rods from the reactor core in response to power flattening needs.
- s -Eventually, lumped burnable poison rods must be removed from operation, packayed i,n a cask that provides adequate radi,ation shieldiny and then shipped for dispo~al at a suitable site. It is desirable to remove each of the rods from the spider in order to gconomize on the volume of the shipping cask. Unfortunately, removing the burnable poison rods from the spider is complicated and potentially hazardous for a number of reasons. The irradiated poison rods have developed, after sufficient irradiation in the re-actor core, an internal gas pressure. The cladding ortubing in which the burnable poison has been loaded also becomes qui~e brittle as a result of a period of irradiation.
The burnable poison rods usually are joined to their res-pective spider arms by means of threaded fasteners. In these circumstances, the most frequently suggested techni-ques for removing the rods from the spider are by means of shearing or sawing. Sawing the rods permits these rods to be handled more gently - an important consideration in view of the gas pressure within the rods - but the sawing process generates radioactive chips. Shearing overcomes this prob-lem to a large extent,' but does nevertheless result in un-desirably rough handling.
There is, then a need for some suitable means -Eor joining burnable poison rods to the spider arms in a manner that is proof against the reactor core environment but per-mits these rods to be removed from the spider simply, swiftly and delicately.
According to the invention, there is pr~vided a control component structure comprising a spider having a . .
. . .
;~
plurality of arms, at least onc spider bore forrned in said plurality of arms, sa:id spider bore including an enlarged recess and a small recess with an upright truncated conical section forming a transition from the enlaryed recess to the small recess, and a burnable poison rod includiny a tube terminating in transverse end, a plug with a chamfered end that leads into a cylindrical portion, said cylindrical por-tion of the plug snugly fitting ~J.ithin the tube and termina-ting in a radially protruding shoulder which engages the transverse end of the tube to which it is welded, and a stem protruding in the longitudinal direction from the central portion of the shoulder having a longitudinal stem bore ex-tending through about half of the length of the stem, a~
least part, of the stem which defines the stem bore being fixed within the truncated conical section, the enlarged re-cess and the small recess of the spider by outward deforma-tion of that part of the stem in order to releasably attach the rod to the spider, said stem being adapted to substant.i-ally reshape itself by movement of the rod in a longitudinal direction with respect to the spider bore, while maintaining the structural integrity of the poison rod and maintaining the structural integrit~ of the spider.
The invention also extends to a method oE assemb-ling and disassembling a control component structure for a nuclear reactor comprising the steps of providing a spider having a plurality of arms, at least one spider bore formed in said plurality of arms for receiving a burnable poison rod having a deformable stem protruding from one end thereof, -6a-insertiny the stem into the spider bore, fasten:iny the stem within the spider bore by deforminy a port,ion of the stem into engagement with a taper in said bore t and separating the burnable pOiSOTI rod from the spider by applyiny a longitudi-nal force to the stem of the burnable poison rod sufficientto extrude the deformed portion through the taper while maintaining structural unityof the burnable poison rod and maintaining structural unity of the spider. Preferably the stem has an axial bore, and a mandrelo~'smaller diameterthan the spider bore is inserted within the stem bore to apply the longitudinal force.
In these circumstances, although considerable force J~
may be applied to press the stem through the spider a~m bore~
it will be noted ~hat the force i8 applied in a longitudin~l direction relative to ~h~ stem ThiS feature of ~he in~ention not only protects the brittle, pressurized burnable poison rod from risk of fracture or other damage due to the rough hand-ling that characterizes shearing but also avoids producing a mass of radioactive chips if the rod is to be sawed free from the spider.
There are a number of more subtle advantages that accrue through the practice of the invention. Manufacturing costs, for example, are relatively low in comparison to the threaded fasteners that have characterized the prior art. Joint performance, moreover, is superior at the temperatures commonly reachedwithin nuc~earrea~tor cores. For instance, the greater thermal expansion of the spider arm (frequently made from stainless steel) relative to a zircalloy pin on the burnable poison end plug causes undesirable axial stress that must be compensated for by other means. This is achieved in the inven-tion by a corresponding radial loosening, thereby reducing the chance for generating undesirahle thermal stresses in this region. Without this automatically provided stress relief, these thermally induced forces otherwise might cause the stem to shear and thus permit the burnable poison rod to become an undesirable loose object within the reactor core.
The various features o novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, its operating advantages and specific objects attained by its use, reference should be :~ A
3272~
-7~-had to the accompanying drawiny and descriptive matter in which there is illustrated and descri~ea a preferxed embodiment of the invention.
BRIEF DESC~IPTION OF THE D~AWING
Fig. 1 shows a typical spidex and burnable poison rod combination, to which the invention may be applied;
FigO 2 illustrates in full section a typical embodi-ment of a portion of a stem of a rod in a partially assèmbled condition in accordance with the invention;
Fig. 3 shows in broken section the stem fully assem-bled in a portion of a spider of the invention; and Fig. 4 is a drawing in broken section illustrating a technique for disassemoling the stem from the ~t~ _ t ~
//
'' . ' 3~
DETAILED DESCRIPTION OF T~ PREFERRED EM~ODIMENTS
For a more detailed understanding of the invention, attention is invited to ~ig. 1. As illustrated, a spider 10, formed from stainless steel, or the like, is provided with a centrally disposed,generally cylindrical hub 11 that has a longitudinal axis 12. The spider 10 has a number of spider arms that extend radially from the hub 11 in a plane that is perpendicular to the axis 12. For purposes of simplified description, only spider arms 13, 14, 15, 16, 17, 20 and 21 which are viewed in the plane of of Fig. 1 of the drawing are shown.
A group of burnable poison rods 22, 23, 24, 25, 26, 27 and 30 are attached to their respective spider arms. All of these burnable poison rods are long, slender tubes in which the longitudinal axis of each of these tubes is parallel with the longitudinal axis 12 of the hub 11. As illustrated in more detail with respect to the burnable poison rod 30, a hollow tube 31 forms the outer surface of the rod. On longitudinal end of the tube 31 is sealed by means of a solid plug 32 that is welded or otherwise secured in the open tube end. Within the tube 31 and bearing against the plug 32 is a stack of short cylindrical burnable poison pellets 33. The individual cylindrical pellets in the stack 33 are pressed together in a longitudinal direction by means of a spring 34 which is lodged between the last pellet in the stack 33 and a plug 35 that is secured in the other open end of the hollow tube 31.
Turning now to Fig. 3, it can be seen that the plug 35 is provided with a chamfered end 36 that provides a lead in for a cylindrical portion 37. The inside diameter of the hollow tube 31 matches the outside diameter of the cylindrical portion to an extent that a snug fit is achieved.
~.3~
As shown in the drawing, ~he cylindrical portion, 37 terminates in a radially protruding shoulder 40 that engages the transverse end of the hollow tube 31 to which it is welded. In the illustr~tive erabodiment of the invention, the diameter of the hollow tube 31 in order to establish a flush rela~ionship between an exposed cylindrical portion 41 of the plug 35 that extends beyond ~he transverse end of the tube 31 and the outer surface of the tube.
A ~ransverse flange 42 that is spaced longi-tudinally from the shoulder 40 terminates the exposed cylindrical portion 41 of the plug 35. A stem 43 pro-trudes in a longitudinal direction from the central portion of the transverse flange 42. Most of the shank that forms the stem 43 is formed from solid metal stock. A longitudinal bore 44 is formed, however, in the stem 43 for a depth that extends from the free end of the stem through a distance that is about half of the stem length.
A portion of a stem 45 as manufactured, and before full installation on a spider arm 46, is shown in ~ig. 2. Thus the stem 45 has a generally cylindrical exterior configuration. Bore 47, that extends from the free end of the stem 45 to about half its length, also is of a generally cylindrical shape with the excep-tion of the bottom of the bore which is formed into the shape of a shallow cone.
It will be recalled that the stem 45 is received in the spider arm 46. To accomplish this end, the spider arm 46 is provided with a generally cylindrical passage-way 50 ~hat has a longitudinal axis 51 which is essentially coincident with the longitudinal axis of the stem 45 and the burnable poison rod tnot shown in Fig. 2). In accordance with a characteristic feature of the invention, an enlarged recess 52 is formed within the passageway 50.
Note in this respect, that the recess 52 overlaps only a portion of the bore 47 in the stem 45.
A truncated conical surface 53 affords a transition from the recess 52 to a bore 54 which forms the balance of the passa~eway 50. As shown in Fig. 2, the bore 54 has a slightly larger diameter than the outside diameter of the stem 45 that is lodged in the passageway 50.
In operation, the stem 45 is inserted into the appropria~e passageway 50. The stem is mechanically de~ormed through hydroforming 9 mechanical flaring or other suitable means, to match the contour of the truncated conical surface 53 and the enlarged recess 52 and to pro-vide a designed "weak point" for poison rod removal, as illustrated in Fig. 3. In this manner, ~he burnable poison rod is secured to the associated spider arm with-out making use of costly and difficult to handle weldfittings, and the like.
It will be recalled, moreover, that different metals often are used for the spider arm and for the burnable poison rod. The truncated conical surface 55, however, provides a tapered surface that alleviates the effect of the different coefficients of thermal ex-pansion. Typically, as the temperature increases, the exemplary stainless steel spider arm expands in an axial dire~tion more than the poison rod end plug 35 (usually Zircalloy). In this manner, ~he axial stresses ~hat otherwise would have been generated are alleviated because of the radial loosening of the parts. Thus, because the spider arm also expands radially more than the plug 35, the conical interface between the adjacent deformed portion of the stem 43 and the conical surface 53 shifts axially downward. The two parts remain in intima~e contact radially and axially, but the strain in the stem 45 has been materially reduced Tela~ive to the stresses that otherwise would have been generated.
Thus, although a tight joint is maintained throughout the entire range of reactor operating temperatures, the structure nevertheless provides a predetermined design "weak point" to facilitate removal of the burnable poison rod as described subsequently in more complete detail.
A further salient fea~ure of the invention is shown in Fig. 4. As illustra~ed, a plug 56 seals an end of a burnable poison rod 57. The plug 56 has a stem 60, the longitudinal axis OI which is coincident with longi-tudinal axis 61 of the burnable poison rod 57.
A bore 62 extends longitudinally through about half the length of the stem 60. As shown in the draw-ing, this bore has been expanded or upset through about half of its length to produce an enlarged cavity that enables the outer diameter of the adjacent portion of the stem 60 to bear against an enlarged recess 64 in a spider arm 65.
The bore 62 has a truncated conical taper 63 that also provides a transition to a smaller diameter bore portion 66. The smaller diameter bore portion 66, more-over, terminates in a cone 67.
In accordance with a salient feature of ~he in-vention, a mandrel 70 is pressed into the bore 62 in ; 25 the direction of arrow 71. The mandrel 70, preferably formed inthe shape of a slender, cylindrical metal shaft, has a diameter that is slightly smaller than the diameter of the smaller diameter bore portion 66.
The longitudinal axis of the mandrel 70 is generally - 30 coincident with the longitudinal axis 61 of the burnable poison rod 57.
To ~emove the burnable poison rod 57 from the spider arm 65 in a manner that will avoid undesirable shearing or sawing proceduTes it is only necessary to press the mandrel 70 in the direction of the arrow 71 with ~L~32~
force sufficient to extrude the stem 60 through small diame~er recess 72, threby freeing the stem 60 from the spider arm 65.
Naturally although not shown in the drawing, a group of mandrels can be ganged together on a plate These mandrels, aligned with and inserted into corres-ponding bores on respective burnable poison rods mounted in a spider, can press all of the rods out of the spider in one operation. In this way, a potentially hazardous, expensive and tedious process of shearing or sawing each burnable poison rod from the spider is avoided.
. .
~ ' ' ' . - .
Not only must the fuel assembly support all of these diverse structural components in spite of the generally hostile environment within a reactor core, but the fuel assembly also must be capable of the somewhat conflicting need for swift and easy disassembly. For instance, it should be noted that fuel assemblies become radioactive after exposure in an operating reactor core. This radiation is so intense 1~ that inspection and repair can be accomplished only with remote handling equipment behind adequate radiation shielding.
Consequently, because disassembly procedures are expensive and time consuming, the need for a sturdy, yet readily dismountable structure is of considerable commercial importance.
The burnable poison rods that are used in many fuel assemblies are a part of this s~ructural picture.
Generally, the burnable poison rods that have characterized ~5 the prior art are mounted for movement in a direction that is parallel to the longitudinal orientation of the fuel rods. A "spider", in the form of a centrally disposed hub from which a number of arms radiate often is used to couple the burnable poison rods together ~or longitudinal movement relative to the balance of the fuel assembly. This motion is required to permit the power reactor operator to insert or withdraw the burnable poison rods from the reactor core in response to power flattening needs.
- s -Eventually, lumped burnable poison rods must be removed from operation, packayed i,n a cask that provides adequate radi,ation shieldiny and then shipped for dispo~al at a suitable site. It is desirable to remove each of the rods from the spider in order to gconomize on the volume of the shipping cask. Unfortunately, removing the burnable poison rods from the spider is complicated and potentially hazardous for a number of reasons. The irradiated poison rods have developed, after sufficient irradiation in the re-actor core, an internal gas pressure. The cladding ortubing in which the burnable poison has been loaded also becomes qui~e brittle as a result of a period of irradiation.
The burnable poison rods usually are joined to their res-pective spider arms by means of threaded fasteners. In these circumstances, the most frequently suggested techni-ques for removing the rods from the spider are by means of shearing or sawing. Sawing the rods permits these rods to be handled more gently - an important consideration in view of the gas pressure within the rods - but the sawing process generates radioactive chips. Shearing overcomes this prob-lem to a large extent,' but does nevertheless result in un-desirably rough handling.
There is, then a need for some suitable means -Eor joining burnable poison rods to the spider arms in a manner that is proof against the reactor core environment but per-mits these rods to be removed from the spider simply, swiftly and delicately.
According to the invention, there is pr~vided a control component structure comprising a spider having a . .
. . .
;~
plurality of arms, at least onc spider bore forrned in said plurality of arms, sa:id spider bore including an enlarged recess and a small recess with an upright truncated conical section forming a transition from the enlaryed recess to the small recess, and a burnable poison rod includiny a tube terminating in transverse end, a plug with a chamfered end that leads into a cylindrical portion, said cylindrical por-tion of the plug snugly fitting ~J.ithin the tube and termina-ting in a radially protruding shoulder which engages the transverse end of the tube to which it is welded, and a stem protruding in the longitudinal direction from the central portion of the shoulder having a longitudinal stem bore ex-tending through about half of the length of the stem, a~
least part, of the stem which defines the stem bore being fixed within the truncated conical section, the enlarged re-cess and the small recess of the spider by outward deforma-tion of that part of the stem in order to releasably attach the rod to the spider, said stem being adapted to substant.i-ally reshape itself by movement of the rod in a longitudinal direction with respect to the spider bore, while maintaining the structural integrity of the poison rod and maintaining the structural integrit~ of the spider.
The invention also extends to a method oE assemb-ling and disassembling a control component structure for a nuclear reactor comprising the steps of providing a spider having a plurality of arms, at least one spider bore formed in said plurality of arms for receiving a burnable poison rod having a deformable stem protruding from one end thereof, -6a-insertiny the stem into the spider bore, fasten:iny the stem within the spider bore by deforminy a port,ion of the stem into engagement with a taper in said bore t and separating the burnable pOiSOTI rod from the spider by applyiny a longitudi-nal force to the stem of the burnable poison rod sufficientto extrude the deformed portion through the taper while maintaining structural unityof the burnable poison rod and maintaining structural unity of the spider. Preferably the stem has an axial bore, and a mandrelo~'smaller diameterthan the spider bore is inserted within the stem bore to apply the longitudinal force.
In these circumstances, although considerable force J~
may be applied to press the stem through the spider a~m bore~
it will be noted ~hat the force i8 applied in a longitudin~l direction relative to ~h~ stem ThiS feature of ~he in~ention not only protects the brittle, pressurized burnable poison rod from risk of fracture or other damage due to the rough hand-ling that characterizes shearing but also avoids producing a mass of radioactive chips if the rod is to be sawed free from the spider.
There are a number of more subtle advantages that accrue through the practice of the invention. Manufacturing costs, for example, are relatively low in comparison to the threaded fasteners that have characterized the prior art. Joint performance, moreover, is superior at the temperatures commonly reachedwithin nuc~earrea~tor cores. For instance, the greater thermal expansion of the spider arm (frequently made from stainless steel) relative to a zircalloy pin on the burnable poison end plug causes undesirable axial stress that must be compensated for by other means. This is achieved in the inven-tion by a corresponding radial loosening, thereby reducing the chance for generating undesirahle thermal stresses in this region. Without this automatically provided stress relief, these thermally induced forces otherwise might cause the stem to shear and thus permit the burnable poison rod to become an undesirable loose object within the reactor core.
The various features o novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, its operating advantages and specific objects attained by its use, reference should be :~ A
3272~
-7~-had to the accompanying drawiny and descriptive matter in which there is illustrated and descri~ea a preferxed embodiment of the invention.
BRIEF DESC~IPTION OF THE D~AWING
Fig. 1 shows a typical spidex and burnable poison rod combination, to which the invention may be applied;
FigO 2 illustrates in full section a typical embodi-ment of a portion of a stem of a rod in a partially assèmbled condition in accordance with the invention;
Fig. 3 shows in broken section the stem fully assem-bled in a portion of a spider of the invention; and Fig. 4 is a drawing in broken section illustrating a technique for disassemoling the stem from the ~t~ _ t ~
//
'' . ' 3~
DETAILED DESCRIPTION OF T~ PREFERRED EM~ODIMENTS
For a more detailed understanding of the invention, attention is invited to ~ig. 1. As illustrated, a spider 10, formed from stainless steel, or the like, is provided with a centrally disposed,generally cylindrical hub 11 that has a longitudinal axis 12. The spider 10 has a number of spider arms that extend radially from the hub 11 in a plane that is perpendicular to the axis 12. For purposes of simplified description, only spider arms 13, 14, 15, 16, 17, 20 and 21 which are viewed in the plane of of Fig. 1 of the drawing are shown.
A group of burnable poison rods 22, 23, 24, 25, 26, 27 and 30 are attached to their respective spider arms. All of these burnable poison rods are long, slender tubes in which the longitudinal axis of each of these tubes is parallel with the longitudinal axis 12 of the hub 11. As illustrated in more detail with respect to the burnable poison rod 30, a hollow tube 31 forms the outer surface of the rod. On longitudinal end of the tube 31 is sealed by means of a solid plug 32 that is welded or otherwise secured in the open tube end. Within the tube 31 and bearing against the plug 32 is a stack of short cylindrical burnable poison pellets 33. The individual cylindrical pellets in the stack 33 are pressed together in a longitudinal direction by means of a spring 34 which is lodged between the last pellet in the stack 33 and a plug 35 that is secured in the other open end of the hollow tube 31.
Turning now to Fig. 3, it can be seen that the plug 35 is provided with a chamfered end 36 that provides a lead in for a cylindrical portion 37. The inside diameter of the hollow tube 31 matches the outside diameter of the cylindrical portion to an extent that a snug fit is achieved.
~.3~
As shown in the drawing, ~he cylindrical portion, 37 terminates in a radially protruding shoulder 40 that engages the transverse end of the hollow tube 31 to which it is welded. In the illustr~tive erabodiment of the invention, the diameter of the hollow tube 31 in order to establish a flush rela~ionship between an exposed cylindrical portion 41 of the plug 35 that extends beyond ~he transverse end of the tube 31 and the outer surface of the tube.
A ~ransverse flange 42 that is spaced longi-tudinally from the shoulder 40 terminates the exposed cylindrical portion 41 of the plug 35. A stem 43 pro-trudes in a longitudinal direction from the central portion of the transverse flange 42. Most of the shank that forms the stem 43 is formed from solid metal stock. A longitudinal bore 44 is formed, however, in the stem 43 for a depth that extends from the free end of the stem through a distance that is about half of the stem length.
A portion of a stem 45 as manufactured, and before full installation on a spider arm 46, is shown in ~ig. 2. Thus the stem 45 has a generally cylindrical exterior configuration. Bore 47, that extends from the free end of the stem 45 to about half its length, also is of a generally cylindrical shape with the excep-tion of the bottom of the bore which is formed into the shape of a shallow cone.
It will be recalled that the stem 45 is received in the spider arm 46. To accomplish this end, the spider arm 46 is provided with a generally cylindrical passage-way 50 ~hat has a longitudinal axis 51 which is essentially coincident with the longitudinal axis of the stem 45 and the burnable poison rod tnot shown in Fig. 2). In accordance with a characteristic feature of the invention, an enlarged recess 52 is formed within the passageway 50.
Note in this respect, that the recess 52 overlaps only a portion of the bore 47 in the stem 45.
A truncated conical surface 53 affords a transition from the recess 52 to a bore 54 which forms the balance of the passa~eway 50. As shown in Fig. 2, the bore 54 has a slightly larger diameter than the outside diameter of the stem 45 that is lodged in the passageway 50.
In operation, the stem 45 is inserted into the appropria~e passageway 50. The stem is mechanically de~ormed through hydroforming 9 mechanical flaring or other suitable means, to match the contour of the truncated conical surface 53 and the enlarged recess 52 and to pro-vide a designed "weak point" for poison rod removal, as illustrated in Fig. 3. In this manner, ~he burnable poison rod is secured to the associated spider arm with-out making use of costly and difficult to handle weldfittings, and the like.
It will be recalled, moreover, that different metals often are used for the spider arm and for the burnable poison rod. The truncated conical surface 55, however, provides a tapered surface that alleviates the effect of the different coefficients of thermal ex-pansion. Typically, as the temperature increases, the exemplary stainless steel spider arm expands in an axial dire~tion more than the poison rod end plug 35 (usually Zircalloy). In this manner, ~he axial stresses ~hat otherwise would have been generated are alleviated because of the radial loosening of the parts. Thus, because the spider arm also expands radially more than the plug 35, the conical interface between the adjacent deformed portion of the stem 43 and the conical surface 53 shifts axially downward. The two parts remain in intima~e contact radially and axially, but the strain in the stem 45 has been materially reduced Tela~ive to the stresses that otherwise would have been generated.
Thus, although a tight joint is maintained throughout the entire range of reactor operating temperatures, the structure nevertheless provides a predetermined design "weak point" to facilitate removal of the burnable poison rod as described subsequently in more complete detail.
A further salient fea~ure of the invention is shown in Fig. 4. As illustra~ed, a plug 56 seals an end of a burnable poison rod 57. The plug 56 has a stem 60, the longitudinal axis OI which is coincident with longi-tudinal axis 61 of the burnable poison rod 57.
A bore 62 extends longitudinally through about half the length of the stem 60. As shown in the draw-ing, this bore has been expanded or upset through about half of its length to produce an enlarged cavity that enables the outer diameter of the adjacent portion of the stem 60 to bear against an enlarged recess 64 in a spider arm 65.
The bore 62 has a truncated conical taper 63 that also provides a transition to a smaller diameter bore portion 66. The smaller diameter bore portion 66, more-over, terminates in a cone 67.
In accordance with a salient feature of ~he in-vention, a mandrel 70 is pressed into the bore 62 in ; 25 the direction of arrow 71. The mandrel 70, preferably formed inthe shape of a slender, cylindrical metal shaft, has a diameter that is slightly smaller than the diameter of the smaller diameter bore portion 66.
The longitudinal axis of the mandrel 70 is generally - 30 coincident with the longitudinal axis 61 of the burnable poison rod 57.
To ~emove the burnable poison rod 57 from the spider arm 65 in a manner that will avoid undesirable shearing or sawing proceduTes it is only necessary to press the mandrel 70 in the direction of the arrow 71 with ~L~32~
force sufficient to extrude the stem 60 through small diame~er recess 72, threby freeing the stem 60 from the spider arm 65.
Naturally although not shown in the drawing, a group of mandrels can be ganged together on a plate These mandrels, aligned with and inserted into corres-ponding bores on respective burnable poison rods mounted in a spider, can press all of the rods out of the spider in one operation. In this way, a potentially hazardous, expensive and tedious process of shearing or sawing each burnable poison rod from the spider is avoided.
. .
~ ' ' ' . - .
Claims (6)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A control component structure comprising:
a spider having a plurality of arms, at least one spider bore formed in said plurality of arms, said spider bore including an enlarged recess and a small recess with an upright truncated conical section forming a transi-tion from the enlarged recess to the small recess, and a burnable poison rod including a tube termina-ting in transverse end, a plug with a chamfered end that leads into a cylindrical portion, said cylindrical portion of the plug snugly fitting within the tube and terminating in a radially protruding shoulder which engages the trans-verse end of the tube to which it is welded, and a stem pro-truding in the longitudinal direction from the central por-tion of the shoulder having a longitudinal stem bore exten-ding through about half of the length of the stem, at least part of the stem which defines the stem bore being fixed within the truncated conical section, the enlarged recess and the small recess of the spider by outward deformation of that part of the stem in order to releasably attach the rod to the spider, said stem being adapted to substantially reshape itself by movement of the rod in a longitudinal direction with respect to the spider bore, while maintaining the structural integrity of the poison rod and maintaining the structural integrity of the spider.
a spider having a plurality of arms, at least one spider bore formed in said plurality of arms, said spider bore including an enlarged recess and a small recess with an upright truncated conical section forming a transi-tion from the enlarged recess to the small recess, and a burnable poison rod including a tube termina-ting in transverse end, a plug with a chamfered end that leads into a cylindrical portion, said cylindrical portion of the plug snugly fitting within the tube and terminating in a radially protruding shoulder which engages the trans-verse end of the tube to which it is welded, and a stem pro-truding in the longitudinal direction from the central por-tion of the shoulder having a longitudinal stem bore exten-ding through about half of the length of the stem, at least part of the stem which defines the stem bore being fixed within the truncated conical section, the enlarged recess and the small recess of the spider by outward deformation of that part of the stem in order to releasably attach the rod to the spider, said stem being adapted to substantially reshape itself by movement of the rod in a longitudinal direction with respect to the spider bore, while maintaining the structural integrity of the poison rod and maintaining the structural integrity of the spider.
2. The control component structure according to Claim 1, wherein the spider is made of material which has a greater coefficient of thermal expansion than that of the stem.
3. The control component structure according to Claim 2, wherein the material of the spider is stainless steel.
4. The control component structure according to Claim 2, wherein the material of the stem is zircalloy.
5. A method of assembling and disassembling a control component structure for a nuclear reactor comprising the steps of:
providing a spider having a plurality of arms, at least one spider bore formed in said plurality of arms for receiving a burnable poison rod having a deformable stem protruding from one end thereof, inserting the stem into the spider bore, fastening the stem within the spider bore by defor-ming a portion of the stem into engagement with a taper in said bore, and separating the burnable poison rod from the spider by applying a longitudinal force to the stem of the burnable poison rod sufficient to extrude the deformed portion through the taper while maintaining structural unity of the burnable poison rod and maintaining structural unity of the spider.
providing a spider having a plurality of arms, at least one spider bore formed in said plurality of arms for receiving a burnable poison rod having a deformable stem protruding from one end thereof, inserting the stem into the spider bore, fastening the stem within the spider bore by defor-ming a portion of the stem into engagement with a taper in said bore, and separating the burnable poison rod from the spider by applying a longitudinal force to the stem of the burnable poison rod sufficient to extrude the deformed portion through the taper while maintaining structural unity of the burnable poison rod and maintaining structural unity of the spider.
6. A method according to Claim 5, wherein the stem has an axial bore, and a mandrel of smaller diameter than the spider bore is inserted within the stem bore to apply the longitudinal force.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US95252278A | 1978-10-18 | 1978-10-18 | |
| US952,522 | 1978-10-18 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1132728A true CA1132728A (en) | 1982-09-28 |
Family
ID=25492987
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA329,872A Expired CA1132728A (en) | 1978-10-18 | 1979-06-15 | Control component structure |
Country Status (9)
| Country | Link |
|---|---|
| JP (1) | JPS5928875B2 (en) |
| CA (1) | CA1132728A (en) |
| CH (1) | CH650352A5 (en) |
| DE (1) | DE2929465C2 (en) |
| ES (2) | ES484631A0 (en) |
| FR (1) | FR2439457A1 (en) |
| GB (2) | GB2032163B (en) |
| IT (1) | IT1124381B (en) |
| MX (1) | MX6683E (en) |
Families Citing this family (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE3337636C1 (en) * | 1983-10-15 | 1987-01-02 | Brown Boveri Reaktor GmbH, 6800 Mannheim | Process and device for exchanging neutron absorber rods |
| US4576787A (en) * | 1983-12-21 | 1986-03-18 | Westinghouse Electric Corp. | Burnable absorber assembly |
| EP0159509B1 (en) * | 1984-03-30 | 1989-01-04 | Westinghouse Electric Corporation | An improved control rod spider assembly for a nuclear reactor fuel assembly |
| JPS60163566U (en) * | 1984-04-02 | 1985-10-30 | ソニー株式会社 | disc cassette |
| US4640813A (en) * | 1984-09-26 | 1987-02-03 | Westinghouse Electric Corp. | Soluble burnable absorber rod for a nuclear reactor |
| FR2599884B1 (en) * | 1986-06-10 | 1988-10-07 | Fragema Framatome & Cogema | ADJUSTMENT GRAPPLE WITH REMOVABLE PENCILS FOR NUCLEAR FUEL ASSEMBLY |
| FR2633435B1 (en) * | 1988-06-28 | 1990-11-09 | Framatome Sa | ADJUSTABLE PENCIL ADJUSTING CLUSTER FOR NUCLEAR FUEL ASSEMBLY |
Family Cites Families (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR633615A (en) * | 1927-04-30 | 1928-02-01 | Soc Fr Constr Babcock & Wilcox | Process for chucking tubular parts into holes in other parts |
| US3314859A (en) * | 1963-12-05 | 1967-04-18 | Combustion Eng | Nuclear reactor fuel assembly-control rod organization |
| GB1152003A (en) * | 1965-08-17 | 1969-05-14 | Atomic Energy Authority Uk | Improvements relating to Nuclear Reactors |
| GB1112946A (en) * | 1965-08-10 | 1968-05-08 | Atomic Energy Authority Uk | Improvements relating to nuclear reactors |
| FR2208730B1 (en) * | 1972-12-05 | 1978-03-10 | Kerjean Yves | |
| FR2233587A1 (en) * | 1973-06-14 | 1975-01-10 | Chausson Usines Sa | Tube bundle heat exchanger - has tube ends shaped as complementary polygons |
-
1979
- 1979-06-15 CA CA329,872A patent/CA1132728A/en not_active Expired
- 1979-07-20 DE DE2929465A patent/DE2929465C2/en not_active Expired
- 1979-08-08 GB GB7927621A patent/GB2032163B/en not_active Expired
- 1979-08-08 GB GB8121246A patent/GB2077483B/en not_active Expired
- 1979-09-25 CH CH8628/79A patent/CH650352A5/en not_active IP Right Cessation
- 1979-09-25 MX MX798399U patent/MX6683E/en unknown
- 1979-09-28 IT IT09548/79A patent/IT1124381B/en active
- 1979-10-01 ES ES484631A patent/ES484631A0/en active Granted
- 1979-10-16 FR FR7925657A patent/FR2439457A1/en active Granted
- 1979-10-17 JP JP54133043A patent/JPS5928875B2/en not_active Expired
-
1980
- 1980-09-08 ES ES494899A patent/ES8302345A1/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| GB2077483B (en) | 1983-04-27 |
| JPS5557188A (en) | 1980-04-26 |
| FR2439457A1 (en) | 1980-05-16 |
| JPS5928875B2 (en) | 1984-07-16 |
| IT7909548A0 (en) | 1979-09-28 |
| IT1124381B (en) | 1986-05-07 |
| GB2077483A (en) | 1981-12-16 |
| DE2929465A1 (en) | 1980-04-24 |
| GB2032163B (en) | 1982-09-15 |
| FR2439457B1 (en) | 1984-06-08 |
| ES494899A0 (en) | 1982-12-16 |
| GB2032163A (en) | 1980-04-30 |
| MX6683E (en) | 1985-10-08 |
| ES8101803A1 (en) | 1980-12-16 |
| ES8302345A1 (en) | 1982-12-16 |
| ES484631A0 (en) | 1980-12-16 |
| DE2929465C2 (en) | 1983-12-01 |
| CH650352A5 (en) | 1985-07-15 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| US7668284B2 (en) | Tube-in-tube threaded dashpot end plug | |
| US4208248A (en) | Fuel assembly with a removable end fitting | |
| US12002593B2 (en) | Deforming a portion of a nut threaded on a guide tube end plug to lock the nut to a lower end fitting of a nuclear reactor fuel assembly | |
| CA1134961A (en) | Control component structure and its removal from fuel assembly | |
| US4381283A (en) | Control component structure | |
| JPH02196997A (en) | Exchange of defective fuel rod for fuel assembly of light water reactor | |
| US4284475A (en) | Wear sleeve for control rod guide tube | |
| CA1132728A (en) | Control component structure | |
| US4321111A (en) | Industrial technique | |
| US4418462A (en) | Method of assembling and disassembling a control component structure | |
| US4928291A (en) | Control cluster provided with removable control elements for a nuclear fuel reactor | |
| Walton | Control component structure | |
| Walton | Spider and burnable poison rod combinations | |
| Walton | Methods of assembling and disassembling spider and burnable poison rod structures for nuclear reactors | |
| GB2233812A (en) | Support pin assembly for control-rod guide tubes. | |
| Edwards et al. | Control component structure and its removal from fuel assembly | |
| Edwards et al. | Methods of assembling and disassembling spider and burnable poison rod structures for nuclear reactors | |
| Edwards et al. | Spider and burnable poison rod combinations | |
| KR820001574B1 (en) | Apparatus for securing and removing burnable poisonrods from the spider in a fuel assembly | |
| CA1136676A (en) | Grapple for manipulating end fitting for fuel assembly | |
| EP0151920B1 (en) | Method of processing a control element to be immersed in coolant of a nuclear reactor | |
| CA1129565A (en) | Control rod guide tube assembly | |
| KR820001724B1 (en) | Method for securing and removing burning poison rods from the spider in a fuel assembly | |
| Mishima | An improved testing device for measuring tangential expandability of beryllium tube | |
| US20020106049A1 (en) | Control element for a nuclear reactor |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |