CA1105623A - High exposure control rod finger - Google Patents
High exposure control rod fingerInfo
- Publication number
- CA1105623A CA1105623A CA313,067A CA313067A CA1105623A CA 1105623 A CA1105623 A CA 1105623A CA 313067 A CA313067 A CA 313067A CA 1105623 A CA1105623 A CA 1105623A
- Authority
- CA
- Canada
- Prior art keywords
- pellets
- rod
- sleeve
- control rod
- lead end
- 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
- G21C7/06—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
Abstract
Abstract of the Disclosure A nuclear reactor control rod containing a stack of B4C
absorber pellets in which the pellets in the lower end have a radius smaller than that of the other pellets and are wrapped with a sleeve having a linear compressibility sufficient to accommodate exposure-induced radial expansion of the end pellets without producing excessive clad strain and having a thermal conductivity sufficient to keep the centerline temperature of the end pellets below the melting point of B4C. One such sleeve material is a type 347 stainless steel having 22.5% theoretical density.
absorber pellets in which the pellets in the lower end have a radius smaller than that of the other pellets and are wrapped with a sleeve having a linear compressibility sufficient to accommodate exposure-induced radial expansion of the end pellets without producing excessive clad strain and having a thermal conductivity sufficient to keep the centerline temperature of the end pellets below the melting point of B4C. One such sleeve material is a type 347 stainless steel having 22.5% theoretical density.
Description
3L~ 3 Background of the Invention This invention relates to control rods for a nuclear reactor and more particularly to cylindrical control rods containing a stack of neutron absorbing pellets.
It is common, particularly in nuclear reactors of the pressurized water type (P'~R), to control the power output and power distribution in ;
the reactor core with control rods insertable from the top of the reactor into the fuel assemblies. These control rods are typically hollow metal tubes containing stacked pellets of uniformly shaped neutron absorbing poison material, usually B4C. In the core, the control rods reciprocate within control rod guide tubes, which provide an unobstructed path within the core while helping maintain the structural dimensions of the fuel assemblies.
The inner diameter of the guide tubes is usually chosen to be the maximum permitted by the fuel assembly lattice in order that the maximum possible diameter control rod can be inserted therein. It is desirable to maximize the diameter of the B4C pellets in the control rod because the absorption effectiveness of the rods is very strongly dependent, particularly in thermal neutron reactors, on the surface area of the pellets. For this reason, and to promote heat transfer, there usually are narrow clearances between the B4C pellets and the control rod clad, and between the control rod and its guide tube. The gap between the B4C pellet and the clad must be large enough, however, to accommodate the swelling the pellets experience when they are irradiated while in the reactor core. It is very important that the swollen pellets not press too strongly against the clad wall because significant clad deformation can result in the control rod jamming in its guide tube.
But if the gap is too large, chips that are dislodged from the ~4C
pellets as a result of the control rod reciprocation will settle in the gap in the lower tip of the rod and quickly deform the clad as the pellets in the tip swell.
;
,770090 - 2 - ~
~L3~g~S 6 ~3 The effective lifetime of a control rod is determined by the average cumulative radiation exposure over the length of the rod, and by the peak exposure at any point in the rod. The average exposure l;m;tation relates to the integrated destruction of the B-10 absorber isotope ;n the B4C, wh;ch can eventually render even a fully inserted rod ineffective in controlling the reactor. The peak radiation limit relates, as described above, to the local clad strain and the possibility of the control rod jamming in its guide tube. A major problem in the design of control rods for use in power reactors has been the economically unfavorable fact that the control rod peak exposure limit is experienced in the end of the control rod nearest the core well before the rod average exposure limit is approached. This results from the h;gh ;rradiation the leading t;p exper;ences even when the ent;re rod ;s out of the core and in the withdrawn position. To make the reactor vessel longer so that the tip of the rod can be farther from the core when in the w;thdrawn pos;tion, is too costly.
One prlor art solution is to fill the lower end of the control rod with a slug of silver-indium-cadm;um (Ag-In-Cd), which does not experience the high rate of swelling characteristic of B4C. Ag-In-Cd is much more expensive than B4C, however, and has slightly lower neutron absorpt;on strength.
Summary of the Invention It is an object of the present invention to increase the useful lifetime of control rods containing a column of neutron absorbing poison pellets that experience rad;at;on ;nduced expansion, w;thout significantly increasing the fabricat;on cost, or decreasing the neturon absorbing properties, relative to rods filled with a uniform column of such pellets. It is another object of the invention to utilize B4C
pellets in the lower end of top-mounted control rods in a manner that will mitigate the costly effect of having the peak radiation exposure in the lower end be the limiting factor in control rod life, yet will ;770090 3 . , .
6;~
retain sufficient neutron absorbing strength in the lower end.
It is a further object to prevent pellet chips from becoming lodged between the pellets in the lower encl and the adjacent clad.
Accordingly, in a broad aspect, the invention resides in a nuclear reactor control rod having a sealed cylindrical cladding o-f inside radius ~1 within which are stacked a plurality of poison absorber pellets haviny outside radius R2 substantially equal to ~1, the rod being mounted above the reactor core, wherein the improvement comprises: at least one of the pellets at the lead end of the rod having a radius R3 less than R2; and a sleeve circumferentially wrapped around the pellets at the lead end of the rod, said sleeve having a thick-ness sufficient to prevent dislocated pellet chips Erom lodging between the pellets at the lead end of the rod and said clad, and a compressibility sufficient to accommodate exposure-induced radial expansion of the pellets at the lead end of the rod with-out producing excessive clad strain.
In the preferred embodiment, the pellets are made of ~4C, and the sleeve has a minimum thermal conducti~ity sufficient to keep the pellet centerline temperature below the melting point of B4C when the control rod tip is located in the highest allowable full power peak neutron flux in the reactor core. One satisfactory sleeve material is type 347 stainless steel in the form of 22.5~ theoretical density porous metal.
B ef Description of the Drawings Figure 1 shows in cross section the lower end of a control rod containing the preferred embodiment of the invention.
Figure 2 shows the integral circumferential sleeve prior to being wrapped around the end pellets of the control rod.
Description of the Preferred Embodiment Figure 1 shows a control rod 10 comprising a cylindrical clad 12 in ~hich are stacked B4C absorber pellets 14l 16. In a typical nuclear reactor the stack of pellets 14 extends upward for 12 feet or more, but only the lower portion of the rod 10 is of concern in the present embodiment.
Approximately 10 inches of the lower portion of the rod 10 contains B4C pellets 16 having a smaller radius than the r~main-der of the pellets 14. Depending on the particular reactor deslgn, the smaller rad~us pellets .' ~ -4a-~ ~L~ 6 ~2 3 may extend over a distance of up to about 18 inches. The pellets 14 and 16 are sealed within the clad 12, the lower seal 20 being welded to the clad 12 and separated from the end pellets 16 by a spacer 18 having a radius substantially that of the clad inner radius. The end pellets 16 are circumferentially wrapped with a metallic integral sleeve 22 which, in the preferred embodiment, substantially fills the space between the end pellets 16 and the clad 12.
Figure 2 shows the sleeve 22 prior to insertion in the control rod 10. The pellets 16 are wrapped with the sleeve 22 and the com-bination is inserted into the clad 12 before the end cap 20 and spacer 1~ are welded in place. As shown in Figure 1, the upper portion 24 of the sleeve 22 abuts the bottom surface 26 of the lowermost regular pellets 16 and is thereby restricted from sliding out of proper position.
When the control rod 10 is in the withdrawn position relative to the reactor core (not shown) the end cap 20 is only a few inches ~rom the fuel, and the lower end of the rod 10 is irradiated by a substantial neutron flux. The flux decreases sharply with distance from the reactor core such that at a point in the control rod 10 about a foot from the end cap 20, the problem to which the invention is addressed ; 20 becomes of minimal importance. When exposed to a neutron flux, the B4C
pellets expand at a rate approximately proportional to the number of neutron absorptions occurring in the B4Ct pellets. Thus, even with the control rod withdrawn above the reactor core, neutrons continue to be absorbed at a sign;ficant rate in the lower end pellets 16. The sleeve 22 accommodates this expansion by compressing as the end pellets 16 expand so that little of the pellet expansion Force is transmitted to the clad 12. As described above, the clad 12 is not permitted to expand significantly because of the possibility it will jam in its control rod guide tube (not shown). The maximum permitted clad strain is determined for each reactor during the licensing proceedings.
Use of the present invention therefore permits the end pellets :770090 5 t ~L~ Ç~3 16 in the lower portion of the control rod lO to experience a sub-stantially higher integrated exposure than the remainder of the control rod pellets 14, without unduly limiting the useful lifetime of the rod lO. The upper portion of the control rod lO receives significant exposure only when the rod lO is inserted in the reactor core, but the lo~ler portion receives radiation not only when it is in the reactor core, but also as discussed above, when the rod 10 is withdrawn from the core.
Some control rods in nuclear reactors are used not only for quickly shutting down the reactor by means of rapid and full length insertion, but also for regulating the shape of the neutron flux and the power output in the core. These control rods are frequently manipulated into and out of the reactor core as part of normal plant operating procedures. This manipulation causes small chips and particles of B4C
from the stack of pellets 14 to work their way down into the lower portion of the rod 10 and, in -the absence of an effective barrier, to fill portions of the gap between the lower pellets 16 and adjacent clad 12. Such entrapped chips quickly deform or perforate the clad 12 upon expansion of the pellet after relatively little neutron exposure. As shown in Figure l, the sleeve 22 can be si~ed to serve as an effective barr;er to prevent significant movement o~ any matter from the regular pellets 14 to the end pellets 16.
Control rods used for regulating the power must be capable of withstanding the heat generated in the B4C pellets when they are exposed to the maximum permitted full power neutron fluxes. It is likely that the control rod end region will in some cases be in the peak neutron flux of the reactor core, and thus the sleeve 22 must have thermal conducting propert1es that will enable the heat generated in the end pellets 16 to be dissipated through the clad 12, without the temperature of the end pellets exceeding design limit values, typically the melting temperature of B4C~ A problem arises in this connection since materials having the desirable compressibility for sleeve 22 usually lack the ~a~ 3 desired thermal conductivity.
In the preferred embodiment of the invention, sleeve material made from 22.5~ theoretical density type 347 stainless steel has been found to provide the minimum acceptable thermal conducti~ity and also to provide satisfactory compressibility. In a typical control rod design wherein the stainless steel clad inner diameter is 0.745 inches and the clad thickness is 0.036 inches, a sleeve thickness of 0.032 inches and end pellet diameter of 0.674 inches have been found to give satisfactory results. Assuming a design limit on clad stress of 65,000 psi ~hot unirradiated yield strength), 65% of the B-10 atoms may be consumed by neutron absorption with a resulting 6.5% ;ncrease in pellet diameter, before this stress limit is reached. Destruction of all B-10 atoms would produce about 10% increase in pellet radius. The B4C pellet centerline temperature under the assumption that a new control rod is inserted into the reactor core such that the end region is exposed to a steady state thermal reactor total flux of 3.0 x 1014 neutrons per second per square centimeter, is 2,200F, which is below the B4C
melting temperature of 2,500F. The compressibility of the 22.5%
theoretical density type 347 stainless steel sleeve 22 is characterized by approximately 50 percent continuous load deflection for an applied stress of 5,000 to 6,000 psi. This material has a minimum thermal conductivity of 3.5 BTU per hour per square foot per degree F. For the particular embodiment shown in Figure 1, improvement in rod lifetime can be expected with any sleeve material having a thermal conductivity of at least 3.00 BTU per hour per square foot per degree F and a minimum linear compression rate of 1.0 percent per 1,000 psi continuous load deflection. Type 347 stainless steel having a range of theoretical density between 15 percent and 30 percent has been found to be a satis-factory material for most P~IR applications. Satisfactory sleeves can also be made from essentially pure fibrous nickel. Porous type 347 stainless steel is available from commercial sources such as the :770090 - 7 -3L~a~ 3 Technetics Division of the Brunswick Corporation. The compress;b;lity and thermal conductiv;ty required in specific reactors w;ll depend on the neutron flux in the core and at the core boundary, the desired lifetime of the control rod, the reactivity worth required in the rod, and the dimensions of the rod. The balancing of these factors in order to choose the optimum sleeve is well ~ithin the ordinary skill of practitioners of this art.
It is common, particularly in nuclear reactors of the pressurized water type (P'~R), to control the power output and power distribution in ;
the reactor core with control rods insertable from the top of the reactor into the fuel assemblies. These control rods are typically hollow metal tubes containing stacked pellets of uniformly shaped neutron absorbing poison material, usually B4C. In the core, the control rods reciprocate within control rod guide tubes, which provide an unobstructed path within the core while helping maintain the structural dimensions of the fuel assemblies.
The inner diameter of the guide tubes is usually chosen to be the maximum permitted by the fuel assembly lattice in order that the maximum possible diameter control rod can be inserted therein. It is desirable to maximize the diameter of the B4C pellets in the control rod because the absorption effectiveness of the rods is very strongly dependent, particularly in thermal neutron reactors, on the surface area of the pellets. For this reason, and to promote heat transfer, there usually are narrow clearances between the B4C pellets and the control rod clad, and between the control rod and its guide tube. The gap between the B4C pellet and the clad must be large enough, however, to accommodate the swelling the pellets experience when they are irradiated while in the reactor core. It is very important that the swollen pellets not press too strongly against the clad wall because significant clad deformation can result in the control rod jamming in its guide tube.
But if the gap is too large, chips that are dislodged from the ~4C
pellets as a result of the control rod reciprocation will settle in the gap in the lower tip of the rod and quickly deform the clad as the pellets in the tip swell.
;
,770090 - 2 - ~
~L3~g~S 6 ~3 The effective lifetime of a control rod is determined by the average cumulative radiation exposure over the length of the rod, and by the peak exposure at any point in the rod. The average exposure l;m;tation relates to the integrated destruction of the B-10 absorber isotope ;n the B4C, wh;ch can eventually render even a fully inserted rod ineffective in controlling the reactor. The peak radiation limit relates, as described above, to the local clad strain and the possibility of the control rod jamming in its guide tube. A major problem in the design of control rods for use in power reactors has been the economically unfavorable fact that the control rod peak exposure limit is experienced in the end of the control rod nearest the core well before the rod average exposure limit is approached. This results from the h;gh ;rradiation the leading t;p exper;ences even when the ent;re rod ;s out of the core and in the withdrawn position. To make the reactor vessel longer so that the tip of the rod can be farther from the core when in the w;thdrawn pos;tion, is too costly.
One prlor art solution is to fill the lower end of the control rod with a slug of silver-indium-cadm;um (Ag-In-Cd), which does not experience the high rate of swelling characteristic of B4C. Ag-In-Cd is much more expensive than B4C, however, and has slightly lower neutron absorpt;on strength.
Summary of the Invention It is an object of the present invention to increase the useful lifetime of control rods containing a column of neutron absorbing poison pellets that experience rad;at;on ;nduced expansion, w;thout significantly increasing the fabricat;on cost, or decreasing the neturon absorbing properties, relative to rods filled with a uniform column of such pellets. It is another object of the invention to utilize B4C
pellets in the lower end of top-mounted control rods in a manner that will mitigate the costly effect of having the peak radiation exposure in the lower end be the limiting factor in control rod life, yet will ;770090 3 . , .
6;~
retain sufficient neutron absorbing strength in the lower end.
It is a further object to prevent pellet chips from becoming lodged between the pellets in the lower encl and the adjacent clad.
Accordingly, in a broad aspect, the invention resides in a nuclear reactor control rod having a sealed cylindrical cladding o-f inside radius ~1 within which are stacked a plurality of poison absorber pellets haviny outside radius R2 substantially equal to ~1, the rod being mounted above the reactor core, wherein the improvement comprises: at least one of the pellets at the lead end of the rod having a radius R3 less than R2; and a sleeve circumferentially wrapped around the pellets at the lead end of the rod, said sleeve having a thick-ness sufficient to prevent dislocated pellet chips Erom lodging between the pellets at the lead end of the rod and said clad, and a compressibility sufficient to accommodate exposure-induced radial expansion of the pellets at the lead end of the rod with-out producing excessive clad strain.
In the preferred embodiment, the pellets are made of ~4C, and the sleeve has a minimum thermal conducti~ity sufficient to keep the pellet centerline temperature below the melting point of B4C when the control rod tip is located in the highest allowable full power peak neutron flux in the reactor core. One satisfactory sleeve material is type 347 stainless steel in the form of 22.5~ theoretical density porous metal.
B ef Description of the Drawings Figure 1 shows in cross section the lower end of a control rod containing the preferred embodiment of the invention.
Figure 2 shows the integral circumferential sleeve prior to being wrapped around the end pellets of the control rod.
Description of the Preferred Embodiment Figure 1 shows a control rod 10 comprising a cylindrical clad 12 in ~hich are stacked B4C absorber pellets 14l 16. In a typical nuclear reactor the stack of pellets 14 extends upward for 12 feet or more, but only the lower portion of the rod 10 is of concern in the present embodiment.
Approximately 10 inches of the lower portion of the rod 10 contains B4C pellets 16 having a smaller radius than the r~main-der of the pellets 14. Depending on the particular reactor deslgn, the smaller rad~us pellets .' ~ -4a-~ ~L~ 6 ~2 3 may extend over a distance of up to about 18 inches. The pellets 14 and 16 are sealed within the clad 12, the lower seal 20 being welded to the clad 12 and separated from the end pellets 16 by a spacer 18 having a radius substantially that of the clad inner radius. The end pellets 16 are circumferentially wrapped with a metallic integral sleeve 22 which, in the preferred embodiment, substantially fills the space between the end pellets 16 and the clad 12.
Figure 2 shows the sleeve 22 prior to insertion in the control rod 10. The pellets 16 are wrapped with the sleeve 22 and the com-bination is inserted into the clad 12 before the end cap 20 and spacer 1~ are welded in place. As shown in Figure 1, the upper portion 24 of the sleeve 22 abuts the bottom surface 26 of the lowermost regular pellets 16 and is thereby restricted from sliding out of proper position.
When the control rod 10 is in the withdrawn position relative to the reactor core (not shown) the end cap 20 is only a few inches ~rom the fuel, and the lower end of the rod 10 is irradiated by a substantial neutron flux. The flux decreases sharply with distance from the reactor core such that at a point in the control rod 10 about a foot from the end cap 20, the problem to which the invention is addressed ; 20 becomes of minimal importance. When exposed to a neutron flux, the B4C
pellets expand at a rate approximately proportional to the number of neutron absorptions occurring in the B4Ct pellets. Thus, even with the control rod withdrawn above the reactor core, neutrons continue to be absorbed at a sign;ficant rate in the lower end pellets 16. The sleeve 22 accommodates this expansion by compressing as the end pellets 16 expand so that little of the pellet expansion Force is transmitted to the clad 12. As described above, the clad 12 is not permitted to expand significantly because of the possibility it will jam in its control rod guide tube (not shown). The maximum permitted clad strain is determined for each reactor during the licensing proceedings.
Use of the present invention therefore permits the end pellets :770090 5 t ~L~ Ç~3 16 in the lower portion of the control rod lO to experience a sub-stantially higher integrated exposure than the remainder of the control rod pellets 14, without unduly limiting the useful lifetime of the rod lO. The upper portion of the control rod lO receives significant exposure only when the rod lO is inserted in the reactor core, but the lo~ler portion receives radiation not only when it is in the reactor core, but also as discussed above, when the rod 10 is withdrawn from the core.
Some control rods in nuclear reactors are used not only for quickly shutting down the reactor by means of rapid and full length insertion, but also for regulating the shape of the neutron flux and the power output in the core. These control rods are frequently manipulated into and out of the reactor core as part of normal plant operating procedures. This manipulation causes small chips and particles of B4C
from the stack of pellets 14 to work their way down into the lower portion of the rod 10 and, in -the absence of an effective barrier, to fill portions of the gap between the lower pellets 16 and adjacent clad 12. Such entrapped chips quickly deform or perforate the clad 12 upon expansion of the pellet after relatively little neutron exposure. As shown in Figure l, the sleeve 22 can be si~ed to serve as an effective barr;er to prevent significant movement o~ any matter from the regular pellets 14 to the end pellets 16.
Control rods used for regulating the power must be capable of withstanding the heat generated in the B4C pellets when they are exposed to the maximum permitted full power neutron fluxes. It is likely that the control rod end region will in some cases be in the peak neutron flux of the reactor core, and thus the sleeve 22 must have thermal conducting propert1es that will enable the heat generated in the end pellets 16 to be dissipated through the clad 12, without the temperature of the end pellets exceeding design limit values, typically the melting temperature of B4C~ A problem arises in this connection since materials having the desirable compressibility for sleeve 22 usually lack the ~a~ 3 desired thermal conductivity.
In the preferred embodiment of the invention, sleeve material made from 22.5~ theoretical density type 347 stainless steel has been found to provide the minimum acceptable thermal conducti~ity and also to provide satisfactory compressibility. In a typical control rod design wherein the stainless steel clad inner diameter is 0.745 inches and the clad thickness is 0.036 inches, a sleeve thickness of 0.032 inches and end pellet diameter of 0.674 inches have been found to give satisfactory results. Assuming a design limit on clad stress of 65,000 psi ~hot unirradiated yield strength), 65% of the B-10 atoms may be consumed by neutron absorption with a resulting 6.5% ;ncrease in pellet diameter, before this stress limit is reached. Destruction of all B-10 atoms would produce about 10% increase in pellet radius. The B4C pellet centerline temperature under the assumption that a new control rod is inserted into the reactor core such that the end region is exposed to a steady state thermal reactor total flux of 3.0 x 1014 neutrons per second per square centimeter, is 2,200F, which is below the B4C
melting temperature of 2,500F. The compressibility of the 22.5%
theoretical density type 347 stainless steel sleeve 22 is characterized by approximately 50 percent continuous load deflection for an applied stress of 5,000 to 6,000 psi. This material has a minimum thermal conductivity of 3.5 BTU per hour per square foot per degree F. For the particular embodiment shown in Figure 1, improvement in rod lifetime can be expected with any sleeve material having a thermal conductivity of at least 3.00 BTU per hour per square foot per degree F and a minimum linear compression rate of 1.0 percent per 1,000 psi continuous load deflection. Type 347 stainless steel having a range of theoretical density between 15 percent and 30 percent has been found to be a satis-factory material for most P~IR applications. Satisfactory sleeves can also be made from essentially pure fibrous nickel. Porous type 347 stainless steel is available from commercial sources such as the :770090 - 7 -3L~a~ 3 Technetics Division of the Brunswick Corporation. The compress;b;lity and thermal conductiv;ty required in specific reactors w;ll depend on the neutron flux in the core and at the core boundary, the desired lifetime of the control rod, the reactivity worth required in the rod, and the dimensions of the rod. The balancing of these factors in order to choose the optimum sleeve is well ~ithin the ordinary skill of practitioners of this art.
Claims (11)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. In a nuclear reactor control rod having a sealed cylindrical cladding of inside radius R1 within which are stacked a plurality of poison absorber pellets having outside radius R2 substantially equal to R1, the rod being mounted above the reactor core, wherein the improvement comprises:
at least one of the pellets at the lead end of the rod having a radius R3 less than R2; and a sleeve circumferentially wrapped around the pellets at the lead end of the rod, said sleeve having a thickness sufficient to prevent dislocated pellet chips from lodging between the pellets at the lead end of the rod and said clad, and a compressibility sufficient to accommodate exposure-induced radial expansion of the pellets at the lead end of the rod without producing excessive clad strain.
at least one of the pellets at the lead end of the rod having a radius R3 less than R2; and a sleeve circumferentially wrapped around the pellets at the lead end of the rod, said sleeve having a thickness sufficient to prevent dislocated pellet chips from lodging between the pellets at the lead end of the rod and said clad, and a compressibility sufficient to accommodate exposure-induced radial expansion of the pellets at the lead end of the rod without producing excessive clad strain.
2. The control rod of claim 1 wherein said sleeve is integral.
3. The control rod of claim 1 wherein the pellets at the lead end of the rod are made of B4C.
4. The control rod of claim 3 wherein said sleeve has a compressibility sufficient to accommodate up to 10 percent exposure induced radial expansion of said end pellets without producing excessive clad strain.
5. The control rod of claim 3 wherein said sleeve is type 347 stainless steel having a density between 15% and 30%
of theoretical.
of theoretical.
6. In a nuclear reactor control rod having a sealed cylindrical metal cladding of inside radius R1 the strain on which cannot exceed S, and within which are stacked a plurality of B4C absorber pellets having an outside radius R2 substantial-ly equal to R1, the rod being mounted for reciprocal movement into and out of the reactor core, the core having a maximum allowable peak neutron flux F, wherein the improvement comprises:
at least one of said pellets in the lead end of the rod having a radius R3 less than R2; and an integral sleeve circumferentially wrapped around the pellets in the lead end of the rod, said sleeve having a linear compressibility sufficient to accommodate exposure-induced radial expansion of the pellets in the lead end of the rod without producing clad strain exceeding S.
at least one of said pellets in the lead end of the rod having a radius R3 less than R2; and an integral sleeve circumferentially wrapped around the pellets in the lead end of the rod, said sleeve having a linear compressibility sufficient to accommodate exposure-induced radial expansion of the pellets in the lead end of the rod without producing clad strain exceeding S.
7. The control rod of claim 6 wherein said sleeve has a thermal conductivity sufficient to keep the centerline temperature of the pellets in the lead end of the rod below the melting point of B4C when the pellets in the lead end of the rod are located in flux F.
8. The control rod of claim 7 wherein said sleeve has a thickness substantially equal to R2-R3.
9. The control rod of claim 8 wherein said sleeve has a minimum thermal conductivity of 3.0 BTU per hour per square foot per degree F.
10. The control rod of claim 8 wherein said sleeve has a minimum linear compressibility of 1.0% per 1,000 psi continuous load deflection.
11. The control rod of claim 8 wherein said sleeve material is type 347 stainless steel having a density between 15% and 30% of theoretical.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US05/871,061 US4172762A (en) | 1978-01-20 | 1978-01-20 | High exposure control rod finger |
| US871,061 | 1978-01-20 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1105623A true CA1105623A (en) | 1981-07-21 |
Family
ID=25356639
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA313,067A Expired CA1105623A (en) | 1978-01-20 | 1978-10-11 | High exposure control rod finger |
Country Status (5)
| Country | Link |
|---|---|
| US (1) | US4172762A (en) |
| JP (1) | JPS5858037B2 (en) |
| CA (1) | CA1105623A (en) |
| DE (1) | DE2900801C2 (en) |
| SE (1) | SE450741B (en) |
Families Citing this family (25)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4522744A (en) * | 1982-09-10 | 1985-06-11 | Westinghouse Electric Corp. | Burnable neutron absorbers |
| JPS60121831U (en) * | 1984-01-25 | 1985-08-16 | 庄源 清治 | TV stand for bed |
| US4642216A (en) * | 1984-03-12 | 1987-02-10 | Westinghouse Electric Corp. | Control rod cluster arrangement |
| US4624827A (en) * | 1984-07-23 | 1986-11-25 | Westinghouse Electric Corp. | Nuclear reactor control rod having a reduced worth tip |
| US4798699A (en) * | 1984-07-26 | 1989-01-17 | Westinghouse Electric Corp. | Wear sleeve for a control rod end plug |
| US4631165A (en) * | 1984-08-03 | 1986-12-23 | Westinghouse Electric Corp. | Boiling water reactor control rod |
| FR2570214B1 (en) * | 1984-09-13 | 1986-11-14 | Commissariat Energie Atomique | ABSORBENT NEEDLE FOR ABSORBENT ASSEMBLY OF FAST NEUTRAL NUCLEAR REACTOR |
| FR2570213A1 (en) * | 1984-09-13 | 1986-03-14 | Commissariat Energie Atomique | Absorber needles for an absorber assembly of a fast-neutron nuclear reactor |
| US4699756A (en) * | 1985-08-08 | 1987-10-13 | Westinghouse Electric Corp. | Full length control rod employing axially inhomogeneous absorber materials for zero reactivity redistribution factor |
| US4678628A (en) * | 1986-03-03 | 1987-07-07 | Westinghouse Electric Corp. | Nuclear reactor control rod cluster for enthalpy rise compensation |
| DE3835711A1 (en) * | 1988-10-20 | 1990-04-26 | Bbc Reaktor Gmbh | CONTROL STAFF TO INFLUENCE THE REACTIVITY OF A CORE REACTOR AND ARRANGEMENT OF SEVERAL THESE STEERING STEELS TO A CONTROL UNIT |
| US5064607A (en) * | 1989-07-10 | 1991-11-12 | Westinghouse Electric Corp. | Hybrid nuclear reactor grey rod to obtain required reactivity worth |
| FR2710778B1 (en) * | 1993-09-29 | 1995-12-01 | Framatome Sa | Control cluster for nuclear reactor and reactor when applied. |
| FR2726393B1 (en) * | 1994-11-02 | 1997-01-17 | Framatome Sa | SILVER-BASED ALLOY CONTAINING INDIUM AND CADMIUM FOR THE REALIZATION OF NEUTRON ABSORBING ELEMENTS AND USE |
| JPH11281784A (en) * | 1998-03-26 | 1999-10-15 | Mitsubishi Heavy Ind Ltd | Control rod |
| US7460632B2 (en) * | 2004-09-22 | 2008-12-02 | Areva Np Inc. | Control rod absorber stack support |
| US20060176995A1 (en) * | 2005-02-10 | 2006-08-10 | Arizona Public Service Company | Control arrangement for use with nuclear fuel |
| DE102005037966A1 (en) | 2005-07-29 | 2007-02-01 | Areva Np Gmbh | Control rod for pressurized water nuclear reactor has absorber rod in cover tube that has recesses in its lower section as round or linear grooves |
| US20090034674A1 (en) * | 2007-07-30 | 2009-02-05 | Burger Joseph M | Nuclear reactor control rod |
| US8532246B2 (en) * | 2007-08-17 | 2013-09-10 | Westinghouse Electric Company Llc | Nuclear reactor robust gray control rod |
| FR2961624B1 (en) * | 2010-06-16 | 2014-11-28 | Commissariat Energie Atomique | OPEN POROSITY SOLID INTERFACE SEAL FOR NUCLEAR FUEL PEN AND NUCLEAR CONTROL BAR |
| US9153349B2 (en) * | 2012-03-12 | 2015-10-06 | Areva Inc. | Method for recycling nuclear control rods and recycled control rod section |
| US9424832B1 (en) | 2014-07-02 | 2016-08-23 | Ronald Isaac | Method and apparatus for safely and reliably sending and receiving messages while operating a motor vehicle |
| US11478977B2 (en) | 2018-04-24 | 2022-10-25 | Irwin Research And Development, Inc. | Thermoforming apparatus having deformation sensor and method |
| CN114913997A (en) * | 2022-03-31 | 2022-08-16 | 中广核研究院有限公司 | Control rod and control rod assembly |
Family Cites Families (10)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB835257A (en) * | 1956-05-18 | 1960-05-18 | Parsons C A & Co Ltd | Improvements in and relating to nuclear reactors |
| GB926133A (en) * | 1958-10-28 | 1963-05-15 | Atomic Energy Authority Uk | Improvements in or relating to nuclear reactors |
| NL113500C (en) * | 1959-08-14 | |||
| US3255092A (en) * | 1961-03-24 | 1966-06-07 | Gen Dynamics Corp | Control rods |
| US3365368A (en) * | 1964-07-10 | 1968-01-23 | Atomic Energy Authority Uk | Telescopically arranged nuclear reactor control elements |
| GB1112946A (en) * | 1965-08-10 | 1968-05-08 | Atomic Energy Authority Uk | Improvements relating to nuclear reactors |
| US3407117A (en) * | 1967-02-15 | 1968-10-22 | Combustion Eng | Nuclear reactor control rod with guide members |
| US3507748A (en) * | 1967-06-07 | 1970-04-21 | Henri Fenech | Control and safety device for nuclear reactors |
| US3510398A (en) * | 1967-06-23 | 1970-05-05 | Phillip M Wood | Burnable poison rods |
| JPS5055794A (en) * | 1973-09-13 | 1975-05-16 |
-
1978
- 1978-01-20 US US05/871,061 patent/US4172762A/en not_active Expired - Lifetime
- 1978-10-11 CA CA313,067A patent/CA1105623A/en not_active Expired
-
1979
- 1979-01-11 DE DE2900801A patent/DE2900801C2/en not_active Expired
- 1979-01-17 JP JP54003104A patent/JPS5858037B2/en not_active Expired
- 1979-01-19 SE SE7900514A patent/SE450741B/en not_active IP Right Cessation
Also Published As
| Publication number | Publication date |
|---|---|
| US4172762A (en) | 1979-10-30 |
| DE2900801A1 (en) | 1979-07-26 |
| JPS5858037B2 (en) | 1983-12-23 |
| JPS54109593A (en) | 1979-08-28 |
| SE450741B (en) | 1987-07-20 |
| SE7900514L (en) | 1979-07-21 |
| DE2900801C2 (en) | 1983-07-07 |
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Legal Events
| Date | Code | Title | Description |
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| MKEX | Expiry |