JP2008134102A - Boiling water reactor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To attain the easy removal, reinstallation and disposal of core shrouds by setting up the structures of the core shrouds which automatically become coaxial with the space between mutual core shrouds split in the assembly of them and joints between the core shrouds and a reactor pressure vessel and, at the same time, constrain radial and axial displacements due to external force such as an earthquake. <P>SOLUTION: The core shrouds are split structures consisting of ring-shaped members along the axial direction. The ring-shaped members are placed in the reactor pressure vessel by stacking each of those ring-shaped members on a shroud support and joint them in the axial direction with support rods 20 so that the ring-shaped members can be installed and removed. A fitting section whose cross section is shaped like an approximate trapezoid to constrain radial movements is formed in a jointed end of each of the ring-shaped members along the axial direction. The structure is set up where each of the ring-shaped members are joined through the fitting section. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a boiling water nuclear reactor, and more particularly to a boiling water nuclear reactor in which a core shroud in a reactor pressure vessel is replaced with a split structure to facilitate work such as replacement and removal.

  A structure in a reactor pressure vessel in a conventional boiling water reactor will be described by taking an improved boiling water reactor called ABWR as an example. FIG. 9 is a longitudinal sectional view showing the structure in the reactor pressure vessel of this improved boiling water reactor.

  As shown in FIG. 9, the reactor pressure vessel 101 is configured as a closed vessel having a reactor wall 101 a and an upper lid 101 b, and a cylindrical core shroud 103 that houses a reactor core 102 is installed in the reactor pressure vessel 101. Has been. The core shroud 103 is supported by a shroud support 104 and a pump deck 105 standing from the lower part of the reactor pressure vessel 101 by welding and has an integrated structure with the reactor pressure vessel 101.

  A core support plate 106 and an upper lattice plate 107 are installed at the lower part and the upper part of the core shroud 103, respectively, and a large number of fuel assemblies 108 are loaded therebetween to constitute the core 102.

  Further, a shroud head 109 is disposed at the upper end of the core shroud 103, and an air / water separator 111 is installed above the shroud head 109 via a stand pipe 110. A steam dryer 112 is installed above the steam separator 111.

  A main steam pipe 113 that guides steam generated in the core 102 to a turbine (not shown) is connected to the wall of the reactor pressure vessel 101 on the side of the steam dryer 112. A water supply pipe 114 for supplying cooling water to the reactor pressure vessel 101 is connected to the side of the standpipe 110 of the reactor pressure vessel 101.

  Below the core support plate 106, a control rod guide tube 116 that houses the control rod 115 inserted into the core 102 and a control rod drive mechanism 117 for driving the control rod 115 are installed. A plurality of internal pumps 118 are arranged in the circumferential direction below 101.

  In the conventional boiling water reactor configured as described above, during operation, cooling water is supplied from a cooling water supply system (not shown) into the reactor through the water supply pipe 114, and is supplied to the reactor pressure vessel 101 and the core shroud 103. A downward flow is caused by the internal pump 118 from the enclosed annular space, is led to the core 102 through the bottom of the furnace, and is heated by the core 102 to become steam.

  The steam passes through the stand pipe 110, the steam separator 111 and the steam dryer 112, and is sent to the turbine through the main steam pipe 113. The steam used for work in the turbine is cooled by a main condenser (not shown), and returns to the upper portion of the reactor pressure vessel 101 from the water supply pipe 114 as circulating water.

  By the way, in the conventional boiling water reactor described above, the core shroud 103 is assembled by a welding configuration, and is welded to the shroud support 104 at the lower end, and the shroud support 104 is welded to the lower mirror portion of the pressure vessel 101. . Therefore, when the core shroud 103 has deteriorated over time and needs to be replaced, a large-scale work such as cutting has been required.

In recent years, the lower end of the core shroud is detachably attached to the shroud support and pump deck via fasteners such as bolts and nuts, and the work for removing the core shroud from the bottom of the reactor is facilitated. (See Patent Documents 1 and 2, etc.).
JP-A-8-254591 JP 2005-195461 A

  In a conventional general boiling water reactor, a core shroud is assembled by a welding configuration, welded to a shroud support at a lower end, and the shroud support is welded to a mirror part under a pressure vessel. Therefore, even when the core shroud has deteriorated over time and needs to be replaced, there is a problem that it cannot be easily removed.

  On the other hand, in the case where the shroud support and the core shroud are joined with bolts and nuts, the core shroud can be easily attached / detached, but other operations such as division of the core shroud and removal of each part thereof, etc. There were still difficulties.

  The reactor pressure vessel is made of carbon steel, and the core shroud is made of stainless steel. For this reason, since the thermal expansion coefficient of stainless steel is higher than that of carbon steel at the operating temperature of the reactor (about 300 ° C.), it is necessary to absorb the difference in elongation in the radial direction.

  Furthermore, since the core shroud is formed by welding a plurality of ring-shaped member structures that are welded together to form a cylindrical integrated structure, an extremely large number of cuttings are required when the core shroud is replaced or discarded afterwards. There was a problem that required time and effort.

  The present invention has been made in view of such circumstances, and has a structure that automatically becomes a coaxial core between the core shrouds divided at the time of assembling the core shroud and a connection portion with the reactor pressure vessel, Thus, a boiling water reactor capable of achieving simple core shroud removal, reattachment and disposal is provided.

  In the present invention, the boiling water type is capable of restraining radial and axial displacements due to external forces such as earthquakes and absorbing the difference in radial expansion based on the difference in thermal expansion coefficient between different materials of the core shroud. Provide a nuclear reactor.

  In order to achieve the above object, according to the present invention, a cylindrical core shroud is erected from a lower part in a reactor pressure vessel via a shroud support and a pump deck, and a core installed at a lower part and an upper part of the core shroud. In a boiling water reactor in which a fuel assembly is loaded between a support plate and an upper lattice plate to constitute a core, the core shroud is divided into a plurality of ring-shaped members along the axial direction, and each of these ring-shaped reactors A boiling water nuclear reactor is provided in which members are stacked on the shroud support and are axially connected by a plurality of support rods, and are detachably installed in the reactor pressure vessel.

  Further, in the present invention, the connection end portion along the axial direction of each ring-shaped member is provided with a fitting portion having a substantially trapezoidal cross section that restrains the movement in the radial direction, and each ring shape is interposed via the fitting portion. The boiling water reactor according to claim 1, wherein the members are connected to each other.

  Further, according to the present invention, the relative movement in the lateral direction is restricted between the upper end portion of the shroud support and the lower end portion of the core shroud joined on the shroud support, but the thermal expansion deformation in the radial direction is allowed. A boiling water nuclear reactor according to claim 1 or 2, wherein a fitting portion having an uneven structure is provided.

  According to the present invention, the core shroud is divided into a split structure, and the core shrouds divided at the time of assembling and the connecting portion with the reactor pressure vessel automatically become coaxial cores, and at the same time, radial and axial directions due to external forces such as earthquakes. The displacement is constrained so that simple core shroud removal, reattachment and simple disposal can be achieved.

  Hereinafter, an embodiment of the present invention will be described with reference to FIGS. In this embodiment, an improved boiling water reactor (ABWR) will be described as an example, but the present invention can also be applied to other boiling water reactors (BWR).

  FIG. 1 is a longitudinal sectional view showing the entire configuration of a reactor pressure vessel. As shown in FIG. 1, the reactor pressure vessel 1 of the present embodiment is configured as a closed vessel having a reactor wall 1 a and an upper lid 1 b, and a shroud support 4 and a pump deck 5 are formed from the lower part in the reactor pressure vessel 1. A cylindrical core shroud 3 is erected through the. A core support plate 6 and an upper lattice plate 7 are respectively installed at the lower part and the upper part of the core shroud 3, and a large number of fuel assemblies 8 are loaded therebetween to constitute the core 2.

  A shroud head 9 is disposed at the upper end portion of the core shroud 3, and an air / water separator 11 is installed on the upper portion of the shroud head 9 via a stand pipe 10. A steam dryer 12 is installed above the steam separator 11. A main steam pipe 13 that guides steam generated in the core 2 to a turbine (not shown) is connected to the wall of the reactor pressure vessel 1 on the side of the steam dryer 12. A water supply pipe 14 for supplying cooling water to the reactor pressure vessel 1 is connected to the side of the standpipe 10 of the reactor pressure vessel 1.

  Below the core support plate 6, a control rod guide tube 16 that houses a control rod 15 inserted into the core 2 and a control rod drive mechanism 17 for driving the control rod 15 are installed. A plurality of internal pumps 18 are arranged in the circumferential direction at the lower part of 1.

  In the boiling water reactor of the present embodiment configured as described above, the core shroud 3 has a divided configuration including a plurality of ring-shaped members 31 to 36 along the axial direction. That is, the core shroud 3 is divided from the upper part into a shroud upper ring 31, a shroud upper cylinder 32, a shroud intermediate ring 33, a shroud intermediate cylinder 34, a shroud lower ring 35 and a shroud lower cylinder 36.

  The divided ring-shaped members 31 to 36 are stacked on the shroud support 4, and the vertical direction which is the axial direction of the core shroud 3 is provided by the vertically long support rods 20 arranged along the furnace wall 1 a. Are coupled along.

  FIG. 2 is a cross-sectional view showing a state in which only the plurality of ring-shaped members 31 to 36 are installed in the reactor pressure vessel 1 of the core shroud 3. As shown in FIG. 2, three ring-shaped members arranged at the upper stage, that is, the shroud upper ring 31, the shroud upper trunk 32 and the shroud intermediate ring 33 are assembled by a connector 37, and the furnace wall 1 a is fixed by a fixing member 38. It is abuttingly arranged on the inner surface side of and positioned and fixed. The upper grid plate 7 is assembled on the shroud intermediate ring 33.

  A shroud intermediate cylinder 34, a shroud lower ring 35 and a shroud lower cylinder 36 are sequentially connected to the lower part of the shroud intermediate ring 33, and the lowermost shroud lower cylinder 36 is supported by the upper end of the shroud support 4. . The core support plate 6 is assembled on the shroud lower ring 35.

  A plurality of vertically long support rods 20 are arranged at regular intervals around the outer periphery of the core shroud 3 made of such connecting members. A threaded portion is formed at the lower end of each support rod 20, and this threaded portion is inserted downward through a mounting hole 41 formed in the pump deck 5, and a nut provided on the lower surface of the pump deck 5. Etc., and is fixed to the lower fastening tool 40 such as a screw.

  Further, an upper clamp 39 made of a bolt, a nut, or the like is provided at the upper end of each support rod 20, and the upper end of the support rod 20 is inserted above the connecting member 37 and the fixing member 38. The upper shroud upper ring 31 can be pushed down by the upper fastener 39. As a result, the ring-shaped members are stacked on the shroud support 4 in the reactor upper space, and are connected in the axial direction so as to be detachably installed in the reactor pressure vessel 1.

  FIG. 3 is an enlarged cross-sectional view for explaining the connection configuration of each component of the core shroud 3. As shown in FIG. 3, the shroud upper ring 31 is configured as a ring-shaped member that constitutes the uppermost portion of the core shroud 3, and includes a shroud head mounting portion 31a and a ring member 31b. On the lower surface of the ring member 31b, a downward groove 31c having a substantially reverse trapezoidal cross-section with an opening widening downward is formed.

  A shroud upper body 32 is disposed below the shroud upper ring 31. The shroud upper body 32 has a predetermined axial length, constitutes the peripheral wall portion of the uppermost end portion of the core shroud 3, and supports the shroud upper ring 31. The upper and lower end portions of the shroud upper body 32 are formed with an upward convex portion 32a and a downward convex portion 32b each having a substantially cross-sectional trapezoidal shape that narrows toward the upper and lower portions, and these upward convex portion 32a and downward convex portion 32b. Is fitted into the downward groove 31c of the shroud upper ring 31 and receives a pressing force.

  A shroud intermediate ring 33 is disposed below the shroud upper body 32. The shroud intermediate ring 33 is configured by connecting a ring member 33a to a lower side of the peripheral portion of the upper grid plate 7 by a connecting tool 33b such as a bolt or a nut. An upward groove 33c having a substantially trapezoidal cross-sectional shape is formed, and a downward groove 33d having a substantially cross-sectional trapezoidal shape similar to the above is formed on the lower surface of the ring member 33a. The downwardly projecting portion 32b of the shroud upper body 32 is fitted into the upward groove 33c and receives a pressing force.

  A shroud intermediate body 34 is disposed below the shroud intermediate ring 33. The shroud intermediate cylinder 34 has a predetermined axial length, constitutes the peripheral wall portion of the upper and lower intermediate portions of the core shroud 3, and supports the shroud intermediate ring 33. The upper and lower end portions of the shroud intermediate cylinder 34 are formed with an upward convex portion 34 a and a downward convex portion 34 b each having a substantially cross-sectional trapezoidal shape that narrows toward the upper and lower portions. The upward convex portion 34 a is formed on the shroud intermediate ring 33. It is fitted into the downward groove 33d and receives a pressing force.

  A shroud lower ring 35 is disposed below the shroud intermediate cylinder 34. The shroud lower ring 35 is configured such that a ring member 35a is connected to a lower side of the peripheral portion of the core support plate 6 by a connecting tool 35b such as a bolt or a nut. An upward groove 35c having a substantially trapezoidal cross-sectional shape similar to that described above is formed on the upper surface of the outer peripheral position of the ring member 35a, and a downward groove 35d having a substantially trapezoidal trapezoidal shape similar to that described above is formed on the lower surface of 35a. A downward projection 34b of the shroud intermediate cylinder 34 is fitted into the upward groove 35c and receives a pressing force.

  A shroud lower body 36 is disposed below the shroud lower ring 35. The shroud lower body 36 has a predetermined axial length, constitutes the lowermost peripheral wall portion of the core shroud 3, and supports the shroud lower ring 35. At the upper end of the shroud lower body 36, an upward convex portion 36a having a substantially cross-sectional trapezoidal shape narrowing upward is formed, and the upward convex portion 36a is fitted into a downward groove 35d of the shroud lower ring 35. , Receive the pressing force.

  Further, at the lower end portion of the shroud lower body 36, uneven portions 36b are formed radially from the center portion at regular intervals. The downward convex portion 36b is adapted to be fitted to the concave and convex portion 4a formed radially from the central portion at the upper end portion of the four. The uneven portions 36b and 4a will be described later with reference to FIGS.

  According to the above configuration, the core shroud is divided into a plurality of ring-shaped members along the axial direction, and the ring-shaped members are stacked on the shroud support and connected in the axial direction by the plurality of support rods. In the reactor pressure vessel, it is installed so as to be detachable, and the connecting end portion along the axial direction of each ring-shaped member is provided with a fitting portion having a substantially trapezoidal cross section for restraining radial movement. Since each ring-shaped member is configured to be connected via a portion, each ring-shaped member has a fitting portion composed of a trapezoidal groove portion and a convex portion, and the inclined portions are fitted to each other so that each ring-shaped member is The center alignment is automatically achieved, and a lateral load can be transmitted.

  FIGS. 4A and 4B are explanatory views showing a removal procedure when the core shroud 3 is replaced. The core shroud 3 needs to be replaced. When the core shroud 3 is replaced, first, the top cover of the reactor pressure vessel 1 is removed, and the steam dryer 12, the steam separator 11, the fuel assembly 8, the control rod 15, and the control rod guide tube 16 are removed. Remove.

  Thereafter, the support rod 20 is removed, and the core shroud divided into a plurality of ring-shaped members (a shroud upper ring 31, a shroud upper cylinder 32, a shroud intermediate ring 33, a shroud intermediate cylinder 34, a shroud lower ring 35, and a shroud lower cylinder 36). 3 is removed. With this configuration, it is possible to replace the core shroud 3 that has been a conventional welding structure and has been very difficult to remove very easily.

  In addition, each ring-shaped member of the core shroud 3 is divided into a plurality of circumferential directions and machine-fastened, so that it is divided without troublesome work such as cutting at the time of disposal after removal, and is discarded after being reduced in size. It becomes possible.

  FIGS. 5 and 6 are enlarged views of the fastening structure in the vertical direction by the support rod 20 described above. As shown in these drawings, in the present embodiment, the members below the shroud upper ring 31, the shroud upper body 32, and the shroud intermediate body 33 are fixedly screwed to the support rod 20 via the connecting portion 37 and the fixing member 38. On the other hand, the lower end of the support rod 20 is inserted into the mounting hole 41 and screwed into the lower fastening member 40, so that the shroud upper ring 31 or the shroud lower body 36 faces the shroud support 4. It can be pressed and held downward. Further, by loosening the upper fastener 39, the core shroud can be disassembled by sequentially transferring the members upward upward as shown in FIG. 4b. In addition, after repair, replacement of parts, etc., the in-furnace structure can be easily reconfigured by a method reverse to the above.

  FIG. 7 is a cross-sectional view of the core shroud 3 fitting portion and the connecting portion of the core shroud 3 and the shroud support 4, and FIG. 8 is a cross-sectional view taken along line BB of FIG. As shown in these drawings, in this embodiment, while restraining the relative movement in the lateral direction between the upper end portion of the shroud support 4 and the lower end portion of the core shroud joined on the shroud support 4, A fitting portion having a concavo-convex structure that allows thermal expansion deformation in the radial direction is provided.

  That is, the shroud lower body 36 is provided with radial downward convex portions 36b, and the shroud support 4 is provided with radial upward concave portions 4a. And the downward convex part 36b of the shroud lower trunk | drum 36 and the radial upward recessed part 4a of the shroud support 4 are mutually fitted.

  The reactor pressure vessel 1 is made of carbon steel, and the core shroud 3 is made of stainless steel. At the operating temperature of the reactor (about 300 ° C.), stainless steel has a higher thermal expansion coefficient than carbon steel. It is necessary to have a structure that absorbs the difference in elongation between the two.

  For this reason, the core shroud 103 is constrained in the lateral direction of the reactor pressure vessel 101, but it is necessary to provide a groove-type fitting structure that is movable in the radial direction from the center of the core shroud. The core shroud 103 absorbs about 2 mm (one side) of elongation in the radial direction, and tightening by the shroud support rod 130 is necessary to restrain the floating of the core shroud 103 due to the differential pressure in the core.

  According to the above configuration, if the core shroud 3 is damaged, it can be repaired by replacing the core shroud 3 or taking it out from the reactor pressure vessel 1 by a simple method. And while restraining the lateral relative movement between the upper end portion of the shroud support and the lower end portion of the core shroud joined on the shroud support, the thermal expansion deformation in the radial direction is subjected to the fitting portion of the concavo-convex structure. Can be tolerated.

  In the present invention, in addition to the above configuration, the core shroud divided in the axial direction can be further divided into a plurality of portions in the circumferential direction and coupled by mechanical fastening. With such a configuration, the parts can be further subdivided, and handling at the time of disposal of the removed core shroud becomes easier.

  Further, the present invention can be applied not only to the new nuclear reactor as in the above embodiment, but also as an in-core structure replacement technique including a core shroud of an existing boiling water reactor.

1 is a longitudinal sectional view showing the overall configuration of a reactor pressure vessel according to an embodiment of the present invention. Sectional drawing which shows the state which installed the ring-shaped member in the said embodiment in the reactor pressure vessel. The expanded sectional view for demonstrating the connection structure of each component of the core shroud in the said embodiment. (A), (b) is an effect explanatory view in the embodiment. The expanded sectional view for demonstrating the connection structure of each component of the core shroud in the said embodiment. Explanatory drawing which expands and shows the fastening structure of the up-down direction by the support rod in the said embodiment. AA sectional drawing of FIG. BB sectional drawing of FIG. Explanatory drawing which shows a prior art example.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Reactor pressure vessel, 1a ... Reactor wall, 1b ... Top cover, 2 ... Core, 3 ... Core shroud, 4 ... Shroud support, 5 ... Pump deck, 6 ... Core support plate, 7 ... Upper lattice plate, 8 ... Fuel Aggregate, 9 ... shroud head, 10 ... stand pipe, 11 ... steam separator, 12 ... steam dryer, 13 ... main steam pipe, 14 ... water supply pipe, 15 ... control rod, 16 ... control rod guide tube, 17 Control rod drive mechanism, 18 Internal pump, 20 Support rod, 31 Shroud upper ring, 31a Shroud head mounting part, 31b Ring member, 31c Downward groove, 32 Shroud upper body, 32a Upward convex , 32b... Downwardly projecting portion, 33... Shroud intermediate ring, 33 a... Ring member, 33 b .. coupling member, 33 c .. upward groove, 33 d. ... Upward convex portion, 34 b. Downward convex portion, 35... Shroud lower ring, 35 a. Ring member, 35 b. Fastener, 35 c. Upward groove, 35 d. Concavo-convex portion, 37 coupling, 38 fixing member, 39 upper clamp, 40 lower clamp, 41 mounting hole.

Claims (4)

A cylindrical core shroud is erected from the lower part of the reactor pressure vessel via a shroud support and a pump deck, and a fuel assembly is loaded between the core support plate and the upper lattice plate installed at the lower and upper parts of the core shroud. In the boiling water reactor in which the core is configured, the core shroud is divided into a plurality of ring-shaped members along the axial direction, and the ring-shaped members are stacked on the shroud support, The boiling water nuclear reactor is characterized in that it is axially connected by a support rod and is detachably installed in the reactor pressure vessel. The connecting end portion along the axial direction of each ring-shaped member is provided with a fitting portion having a substantially trapezoidal cross section that restrains radial movement, and the ring-shaped members are connected via the fitting portion. The boiling water reactor according to claim 1. Between the upper end portion of the shroud support and the lower end portion of the core shroud joined on the shroud support, a concavo-convex structure that restricts the relative movement in the lateral direction and allows the thermal expansion deformation in the radial direction is fitted. The boiling water reactor according to claim 1 or 2, wherein a joint is provided. The boiling water reactor according to any one of claims 1 to 3, wherein the core shroud divided in the axial direction is further divided into a plurality of circumferential directions and can be coupled by mechanical fastening.

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