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
  • G21C7/113—Control elements made of flat elements; Control elements having cruciform cross-section
• • 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

Definitions

• the present invention relates generally to control rods for nuclear reactors having an upper, generally cruciform cross-section and a lower velocity limiter secured to the upper section and particularly relates to apparatus and methods for selectively adjusting the weight of the velocity limiter whereby the overall control rod weight can be adjusted.
• Control rods in nuclear reactors form dual functions of power distribution shaping and reactivity control.
• the rods enter from the bottom of the reactor and are typically connected to bottom-mounted, hydraulically-actuated drive mechanisms to allow axial positioning for reactivity regulation or rapid SCRAM insertion.
• the control rods are generally cruciform in cross-sectional shape, with each blade or wing of the rod typically containing tubes filled with a nuclear poison such as boron carbide or hafnium.
• the lower portion of the control rod comprises a velocity limiter disposed in a guide tube.
• Velocity limiters are conventionally designed to limit he drop velocity to a selected velocity, for example, 3.11 feet per second, minimize drag resistance during a SCRAM event, provide an interface between the control rod and control rod guide tube and provide a coupling between the control rod blade absorber sections and the control rod drive.
• a velocity limiter for a control rod for a nuclear reactor which can be adjusted in weight within a predetermined range such that the velocity limiter with a selectively adjusted weight can be used with any one of the various and different control rod absorber section designs.
• the specific weight of the ve.ocity limiter is determined by the weight of the neutron absorber section, i.e., with a heavier absorber section, a lighter velocity limiter is provided and, conversely . with a lighter absorber section, a heavier velocity limiter is provided.
• the present invention provides, as part of the velocity limiter, a standard vane, a set of light or heavy transition pieces, a socket and a set of light or heavy fins.
• a standard vane By selecting one or the other of the light or heavy transition pieces and combining the selected transition piece with one or the other of a selected one of the light or heavy sets of fins, an approximation of the desired weight for the velocity limiter and, hence, the overall control rod, can be obtained.
• the heavy transition piece can be modified such that its weight lies within a range from approximately the weight of the light transition piece to the weight of the heavy transition piece without modification.
• Each transition piece includes an enlarged diameter central section having a bore therethrough.
• the heavier transition piece has a small bore whereas the light transition piece has a radially enlarged bore.
• a method of adjusting the weight of a control rod for use in a nuclear reactor having an upper, generally cruciform absorber section and a lower velocity limiter attached to the section and including a vane, a transition piece and fins, comprising the steps of providing first and second sets of fins with the second set of fins being heavier than the first set of fins, providing first and se c ond transition pieces, with the second transition piece being heavier than t first transition piece, selecting one of the first and second sets of fins and one of the first and second sets of transition pieces and forming a velocity limiter for the control rod containing the vane and the selected ones of the f ⁇ s and the transition pieces thereby selectively adjusting the weight of the control rod.
• apparatus for selectively adjusting the weight of a control rod for use in a nuclear reactor comprising an upper control rod body, a lower velocity limiter including a vane, a first set of fins, a second set of fins heavier than the first set of fins, a first transition piece, a second transition piece heavier than the first transition piece, the control rod being formed with one of the first and second sets of fins secured to the vane and one of the first and second transition pieces secured to the vane whereby a control rod of selected adjusted weight is formed.
• FIGURE 1 is a side elevational view of a control rod constructed in accordance with the present invention.
• FIGURES 2 and 3 are enlarged portions of light and heavy velocity limiters, respectively, parts being broken out and in cross-section for ease of illustration;
• FIGURE 4 is an enlarged side elevational view of a vane employed in the velocity limiter hereof with parts broken out and in cross-section;
• FIGURES 5A and 5B are fragmentary side elevational views with parts broken out and in cross-section of light and heavy transition pieces, respectively, for selective use in the velocity limiter hereof;
• FIGURE 6 is a ⁇ ross-sectional view of a socket employed in the present invention.
• FIGURES 7A and 8A are ide elevational views of light and heavy sets of fins, respectively, with Figures 7B and 8B illustrating corresponding respective halves of those fins.
• a control rod constructed in accordance with the present invention and including an upper cruciform absorber section or body 12 and a lower velocity limiter section 14.
• the blades or wings 16 of the upper section 12 typically include tubes filled with a neutron poison such as boron carbide, the tubes conventionally extending vertically within each of the blades 16.
• the lower velocity limiter is typically mounted in a control rod guide tube, not shown, for movement in a vertical direction between the correspondingly-shaped cruciform portions in the interstices of the core among the fuel bundle assemblies.
• the control rod is typically under hydraulic fluid control for movement vertically to allow axial positioning of the absorber section adjacent to the fuel bundle assemblies in the event of a SCRAM or for reactivity regulation.
• the 14 include a set of fins 18 aligned vertically with the blade 16 of the upper section of the control rod and transition piece 20 and a vane 22, the transition piece mounting a socket 24 at its lower end.
• the socket 24 is adapted for connection to a control rod drive, not shown, whereby the control rod can be vertically positioned relative to the fuel bundle assemblies.
• the vane 22 is illustrated in Figure 4 and includes a generally frustoconical section having a hollow interior 26 open at its bottom for receiving the coolant/moderator.
• An annular turning vane 28 is disposed in the vane 22 and defines an annular flow channel 30 between the vane 28 and the upper portion of vane 22.
• the vane 28 mounts a plurality of lugs 32 which mount rollers, not shown, for engaging along the interior surfaces of the control rod guide tube whereby the control rod can be displaced vertically.
• transition piece 20a is generally in the form of a hollow cylinder having a sleeve 34 projecting from its upper end.
• the cylinder of the transition piece is of a relatively thin wall.
• the lower end of the transition piece 20a is secured, for example, by welding to the upper end of the socket 24.
• transition piece 20b is similar in external configuration to the transition piece 20a.
• transition piece 20b is formed of a substantially solid interior with a small axial passageway 36.
• An imaginary outline 38 of the interior wall of the lighter transition piece 20a is illustrated in the heavier transition piece 20b to indicate the extent of the increase in material and, hence, weight of the heavier transition piece 20b as compared with the lighter transition piece 20a.
• Transition pieces are preferably formed of a stainless steel material.
• the first set of fins 18a comprise four fin halves which have short, vertically extending side edges 39 followed by long, downwardly inclined outer edges 40 terminating at their lower ends in contoured edges 42 for connection to the transition piece 20.
• the fins 18b are similarly formed except that the outside vertical edge 41 of each fin extends vertically downwardly to a greater extent than the outside vertical edge 39 of each of fins 18a of Figures 7A and 7B.
• the inclined edge 44 which transitions between the vertical edge and the contoured edge 42 for seating on the transition piece is at a greater downwardly inclined angle to the vertical.
• the thickness of the fins shown in Figures 8A and 8B is substantially greater than the thickness of the set of fins shown in Figures 7A and 7B. It will be appreciated that upon comparing the configurations of the fin sets of Figures 7A and 7B with those of Figures 8A and 8B, the second sets of fins 18b are heavier than the first set of fins 18a. The increase in weight is due solely to the increase in material forming the fins. While there is an increased surface area for the heavier fins 18b a ; compared with the lighter fins 18a, the external geometry is not altered sufficiently to have significant extent on the fluid mechanical properties of the velocity limiter. It will also be appreciated that four fin halves of the selected set are used at right angles to one another for each control rod.
• the weight of the velocity limiter is determined by the weight of the neutron absorber section, i.e., upper section 12.
• the total weight of the control rod will be the combined weight of the upper section 12 and the velocity limiter 14.
• the total control rod weight can be adjusted to meet the target or licensing weight by adjusting the weight of the velocity limiter. To accomplish this for a given known weight of the control rod absorber section, a combination of the selected transition pieces and fins will be made to approximate the desired weight.
• the lightest of the transition pieces, i.e., transition piece 20a, and the lightest of the fin sets 18, i.e., fin set 18a may be selected for combination with the vane 22 and socket 24. This affords the lightest control rod for the given heavy weight of absorber section.
• the heavier velocity limiter 20b may be selected and combined with the heavier set of fins 18b. This affords the heaviest control rod for the given light weight of absorber section.
• the weight of the velocity limiter can be varied between a maximum and minimum range and with a mix of the light and heavier fin sets and transition pieces. That is, to meet weights in-between the maximum and minimum weights of the velocity limiter, a different combination of fin sets and transition pieces can be utilized, i.e., a heavy transition piece with a set of light fins or a light transition piece with a set of heavy fins.
• the weight of the heaviest transition piece can be adjusted, i.e., lowered.
• a weight between it and the weight of the lighter transition piece can be provided by removing material from within the bore of the transition piece 20b. From a review of Figure 5B, it will be appreciated that more or less of the material within the bore 36 of the heaviest transition piece 20b can be removed, down to the weight of the lightest transition piece 20a. The extent of passable removal of the material is illustrated in Figure 5B by the material volume between bore 36 and the dashed lines 38.

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• 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)
• Luminescent Compositions (AREA)

Priority Applications (2)

Applications Claiming Priority (2)

Publications (1)

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Family Applications (1)

Country Status (4)

Cited By (1)

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Citations (3)

Family Cites Families (12)

• 1999
  • 1999-10-27 US US09/427,937 patent/US6396893B1/en not_active Expired - Lifetime
• 2000
  • 2000-10-25 WO PCT/US2000/029402 patent/WO2001035420A1/en not_active Ceased
  • 2000-10-25 JP JP2001537074A patent/JP4624627B2/ja not_active Expired - Lifetime
• 2001
  • 2001-06-26 SE SE0102250A patent/SE519499C2/sv not_active IP Right Cessation
• 2002
  • 2002-04-23 US US10/127,459 patent/US20020122527A1/en not_active Abandoned

Patent Citations (3)

Non-Patent Citations (2)

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