JP2012247384A - Abrasive water jet cutting method and apparatus therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an abrasive water jet cutting method with which a fuel storage rack and a fuel assembly can be cut while maintaining a subcritical state.SOLUTION: Boric acid water in a boric acid water tank 11 is boosted to about 400 MPa by a high-pressure pump 13 and supplied to a cutting head 4. Boron carbide particles (abrasives) 26 in an abrasive tank 14 are guided to the cutting head 4 by a hose 10 together with compression air supplied from a press-feed air supplying device 27. The boric acid water 7 and the boron carbide particles 26 are mixed, become a high-pressure water stream 28 to be jetted out of a cutting nozzle 5 of the cutting head 4 toward a fuel storage rack storing therein used fuel assemblies 3. The fuel storage rack and the used fuel assemblies 3 are cut by action of the boron carbide particles 26. Even if a nuclear fuel material is diffused in cooling water and a concentration of the nuclear fuel material in the cooling water is increased, a subcritical state is maintained by the boron carbide particles 26 diffused in the cooling water.

Description

  The present invention relates to an abrasive water jet cutting method and apparatus therefor, and more particularly to an abrasive water jet cutting method and apparatus suitable for cutting a fuel storage rack installed in a fuel pool and containing a fuel assembly. .

  In a nuclear power plant, when performing periodic inspection, a control rod is inserted into the core of the reactor to stop the operation of the reactor. After the reactor is shut down, periodic inspections are performed, and preventive maintenance work for reactor internals in the reactor pressure vessel is performed. Before starting the preventive maintenance work, all fuel assemblies loaded in the core are taken out of the reactor pressure vessel and stored in the fuel storage rack installed in the fuel pool. Stored.

  As preventive maintenance work, for example, a core shroud that is a structural member of a nuclear power plant installed in a reactor pressure vessel is replaced. Japanese Laid-Open Patent Publication No. 2007-24586 proposes a method of cutting the core shroud taken out from the reactor pressure vessel using an abrasive water jet in the replacement operation of the core shroud. In this cutting method, alumina is used as an abrasive.

JP 2007-24586 A

  If the fuel assembly is stored in the fuel storage rack installed in the fuel pool and the fuel assembly is damaged for any reason, the damaged fuel assembly It is not easy to remove it from the fuel pool in order to carry it to a predetermined place outside the fuel pool.

  Therefore, the inventors considered cutting the fuel storage rack containing the fuel assembly in the fuel pool, and examined performing this cutting by ejecting an abrasive water jet from the nozzle. As a result, when the inventors cut the fuel storage rack containing the fuel assembly using the abrasive water jet, the plurality of fuel rods constituting the fuel assembly are also cut and the fuel rod A part of the nuclear fuel material leaks into the cooling water in the fuel pool, and the particles of the nuclear fuel material leaked by the jet of high-pressure water injected from the nozzle are agitated together with the cooling water in the fuel pool. As a result, the concentration of nuclear fuel material has increased, and it has been recognized that a critical reaction may be caused.

  An object of the present invention is to provide an abrasive water jet cutting method and apparatus capable of cutting a fuel storage rack and a fuel assembly while maintaining a subcritical state.

  A feature of the present invention that achieves the above-described object is that a water stream containing particles of a neutron absorbing material is injected from a nozzle toward a fuel rack that contains a fuel assembly that is disposed in water, and the injected neutron absorbing material The purpose is to cut the fuel rack and the fuel assembly in the fuel rack by the particles.

  Since the fuel rack for storing the fuel assembly disposed in the water and the fuel assembly are cut using the neutron absorber particles which are abrasive, the neutron absorber diffused into the water used for cutting is cut. Due to the action of the particles, even if the concentration of the nuclear fuel material contained in the fuel assembly leaked into the water due to cutting increases in water, it can be prevented from becoming recritical by the nuclear fuel material. For this reason, the fuel rack and the fuel assembly can be cut in water while maintaining the subcritical state.

  The above-mentioned purpose is to inject a water stream including an abrasive containing no neutron absorbing material and an aqueous solution containing the neutron absorbing material toward a fuel rack that houses the fuel assembly disposed in water from the nozzle, and the injected abrasive This can also be achieved by cutting the fuel rack and the fuel assembly.

  According to the present invention, the fuel storage rack and the fuel assembly can be cut in water while maintaining the subcritical state.

It is explanatory drawing which shows the abrasive water jet cutting method of Example 1 which is one preferable Example of this invention. It is a block diagram of the abrasive water jet cutting device used for the abrasive water jet cutting method shown in FIG. It is a detailed longitudinal cross-sectional view of the cutting head shown in FIG. It is a block diagram of the abrasive water jet cutting device used for the abrasive water jet cutting method of Example 2 which is another Example of this invention. It is a block diagram of the abrasive waterjet cutting device used for the abrasive waterjet cutting method of Example 3 which is another Example of this invention.

  Examples of the present invention will be described below.

  An abrasive water jet cutting method according to embodiment 1 which is a preferred embodiment of the present invention will be described with reference to FIGS. 1 and 2.

  An abrasive water jet cutting device 8 used in the abrasive water jet cutting method of the present embodiment will be described with reference to FIGS. 1, 2, and 3. The abrasive water jet cutting device 8 includes a cutting head 4, a boric acid water tank 11, a high-pressure pump 13, an abrasive tank 14, and a purification device 18.

  The cutting head 4 has a mixer 6 and a cutting nozzle 5. The cutting nozzle 5 is attached to the mixer 6 and has an injection hole 25 connected to the mixer 6 (see FIG. 3). A boric acid water tank 11 filled with boric acid water 7 is connected to a switching valve (three-way valve) 12 by a hose 16. A hose 9 provided with a high-pressure pump 13 is connected to the cutting head 4 and communicated with the mixer 6. The abrasive tank 14 filled with abrasive boron carbide particles 26 is connected to the cutting head 4 by the hose 10. The hose 10 is connected to the mixer 6. A pressurized air supply device 27 is connected to the hose 10. A suction pump (submersible pump) 29 and a purification device 18 are provided in a hose 32 connected to the suction nozzle 17 and connected to the switching valve 12.

  The abrasive water jet cutting method of the present embodiment using the abrasive water jet cutting device 8 will be described.

  A plurality of spent fuel assemblies 3 taken out from the core in the reactor pressure vessel during the periodic inspection period of the nuclear power plant are installed in the fuel pool 1 in the reactor building (not shown). Each is stored in the storage rack 2 (see FIG. 1). The fuel storage rack 2 is arranged in the cooling water filled in the fuel pool 1, and the spent fuel assembly 3 stored in the fuel storage rack 2 circulates while being stored in the fuel pool 1. Cooled by cooling water.

  It is assumed that a part of the spent fuel assembly 3 stored in the fuel storage rack 2 is damaged for some reason as described above.

  Since the spent fuel assembly 3 damaged in the fuel storage rack 2 cannot be taken out from the fuel storage rack 2, the spent fuel assembly 3 is stored using the abrasive water jet cutting device 8. The fuel storage rack 2 is cut in the fuel pool 1. When cutting the fuel storage rack 2, the cutting head 4 of the abrasive water jet cutting device 8 is attached to the mast 21 of the fuel exchanger 20. The boric acid water tank 11, the high-pressure pump 13, the abrasive tank 14, and the pressurized air supply device 27 are installed on an operation floor 22 that surrounds the fuel pool 1 and is formed in the reactor building. The suction nozzle 17, the suction pump 29 and the purification device 18 are arranged in the cooling water in the fuel pool 1.

  The fuel changer 20 is also disposed on the operation floor 22. The refueling machine 20 has a traveling carriage 30 and a traversing carriage 31. The traveling carriage 30 is arranged across the fuel pool 1 and moves along the guide rail 24 provided on the operation floor 22. The traversing carriage 31 is installed on the traveling carriage 30 and moves on the traveling carriage 30 in a direction orthogonal to the moving direction of the traveling carriage 30. The mast 31 is attached to the traverse carriage 31 so as to be movable in the vertical direction.

  In a state where the cutting head 4 attached to the mast 21 is immersed in the cooling water in the fuel pool 1, the traveling is performed so that the cutting nozzle 5 is located immediately above the cutting start position of the fuel storage rack 2 to be cut. The carriage 30 and the traversing carriage 31 are moved to position the cutting nozzle 5 in the horizontal direction. Thereafter, the mast 21 is lowered, and the cutting nozzle 5 is lowered to a cutting position in the vertical direction of the fuel storage rack 2 (for example, a position half the height of the fuel storage rack 2). When the cutting nozzle 5 is lowered to the cutting position in the vertical direction, the lowering of the mast 21 is stopped. Thereafter, the cutting nozzle 5 is moved in the horizontal direction along one side surface of the fuel storage rack 2 while facing the one side surface. The horizontal movement of the cutting nozzle 5 is performed, for example, by moving the traversing carriage 31, and the fuel storage rack 2 is placed at a position half the height with the spent fuel assembly 3 stored. Disconnect.

  The fuel storage rack 2 and the spent fuel assembly 3 are cut by injecting high-pressure water containing abrasive from the injection holes 25 of the cutting nozzle 5. The high-pressure water is injected from the injection hole 25 as follows.

  The switching valve 12 is operated to connect the hose 16 and the hose 9 to drive the high-pressure pump 13 and the pressurized air supply device 27. The boric acid water 7 in the boric acid water tank 11 is led to the high pressure pump 13 by the hoses 16 and 9, is pressurized to about 400 MPa by the high pressure pump 13, and is supplied to the mixer 6 of the cutting head 4 through the hose 9. Is done. Boron carbide particles 26 in the abrasive tank 14 are supplied into the mixer 6 of the cutting head 4 through the hose 10 along with the compressed air supplied into the hose 10 from the pressurized air supply device 27. In the mixer 6, the boric acid water 7 and the boron carbide particles 26 are mixed, and a high-pressure (about 400 MPa) water flow 28 of the boric acid water 7 containing the boron carbide particles 26 is supplied from the injection holes 25 to the fuel storage rack to be cut. 2 is injected and collides with the fuel storage rack 2. The abrasive boron carbide particles 26 contained in the water stream 28 collide with the fuel storage rack 2 at a high speed. The fuel storage rack 2 is cut at a position where the boron carbide particles 26 collide by the action of the colliding boron carbide particles 26. Each spent fuel assembly 3 housed in the fuel storage rack 2 is also cut at the same cutting position in the vertical direction in conjunction with the cutting of the fuel storage rack 2.

  While spraying the high-pressure water stream 28 of the boric acid water 7 containing the boron carbide particles 26 from the injection holes 25 of the cutting nozzle 5, as described above, the traversing carriage 31 is moved so that the cutting nozzle 5 is moved in the horizontal direction. Move along one side of the fuel storage rack 2. When the horizontal movement of the cutting nozzle 5 (injecting the water stream 28 containing the boron carbide particles 26) along one side surface of one fuel storage rack 2 is completed at the vertical cutting position, the fuel storage rack 2 And the cutting | disconnection of each spent fuel assembly 3 accommodated in this fuel storage rack 2 is complete | finished.

  The boric acid water 7 contained in the water flow 28 injected from the cutting nozzle 5 diffuses into the cooling water in the fuel pool 1. In this embodiment, the concentration of boric acid in the cooling water in the fuel pool 1 is measured using an analyzer. The boric acid concentration is measured by collecting cooling water in the fuel pool 1 at predetermined time intervals, analyzing the collected cooling water, and measuring the boric acid concentration contained in the cooling water. When the measured boric acid concentration in the cooling water exceeds the set concentration, the switching valve 12 is switched to connect the hose 32 and the hose 9. This set concentration is obtained by supplying boron carbide particles 26 contained in the cooling water in the fuel pool 1 and boric acid water 7 supplied without boric acid water 7 from the boric acid water tank 11 to the cutting nozzle 5. This is the concentration of boric acid that can prevent acid from causing recriticality due to nuclear fuel material in the cooling water.

  When the hose 9 and the hose 32 are communicated with each other through the switching valve 12, the suction pump 29 is driven, and the cooling water containing boron carbide particles 26 and boric acid in the fuel pool 1 is sucked from the suction nozzle 17 and is supplied to the hose 32. Flows in. The cooling water containing boron carbide particles 26 and boric acid flowing into the hose 32 is pressurized by the suction pump 29 and guided to the purification device 18. In the purification device 18, the boron carbide particles 26 contained in the cooling water, the cutting powder of the fuel storage rack 2, the cladding originally contained in the cooling water in the fuel pool 1 and the like are removed. The cooling water containing boric acid purified by the purification device 18 is guided to the high-pressure pump 13 through the hoses 32 and 9 and is pressurized to about 400 MPa by the high-pressure pump 13. When the cooling water in the fuel pool 1 sucked from the suction nozzle 17 is supplied to the high-pressure pump 13, the boric acid water 7 in the boric acid water tank 11 is not supplied to the high-pressure pump 13.

  Cooling water containing high-pressure boric acid pressurized by the high-pressure pump 13 is introduced into the mixer 6 of the cutting head 4 and mixed with boron carbide particles 26 supplied through the hose 10. The high-pressure cooling water containing the boron carbide particles 26 is guided from the mixer 6 to the injection hole 25 and becomes a water flow 28 and is injected toward each fuel storage rack 2 to be cut. The fuel storage rack 2 and the spent fuel assembly 3 housed in the fuel storage rack 2 are cut by the action of the boron carbide particles 26 contained in the injected water stream 28.

  If the water stream 28 containing the cooling water sucked from the suction nozzle 17 is injected, the concentration of boric acid contained in the cooling water in the fuel pool 1 is changed to the boron carbide particles 26 contained in the cooling water in the fuel pool 1 and When the boric acid concentration is lower than the concentration of boric acid, which can prevent recriticality caused by nuclear fuel material in the cooling water, the switching valve 12 is switched to mix the boric acid water 7 in the boric acid water tank 11. The water stream 28 supplied to the vessel 6 and containing the boric acid water 7 is jetted from the cutting nozzle 5.

  When the fuel rods included in the spent fuel assembly 3 are cut by the boron carbide particles 26 injected from the cutting nozzle 5, the water flow 28 in which the nuclear fuel material present in each fuel rod is injected at the cutting position, It is blown off into the cooling water in the fuel pool 1. Further, the spent fuel assembly 3 is impacted by the collision of the high-speed water flow 28 with the fuel storage rack 2 and the spent fuel assembly 3 at the time of cutting, and the spent fuel assembly 3 vibrates. For this reason, a part of the nuclear fuel material in the fuel rod leaks into the cooling water from the cut portion of the fuel rod. As the cutting of the fuel storage rack 2 and the spent fuel assembly 3 proceeds, the concentration of the nuclear fuel material contained in the cooling water of the fuel pool 1 from the spent fuel assembly 3 increases for the reason described above. When the concentration of nuclear fuel material in the cooling water increases, the possibility of recriticality of nuclear fuel material in the worst case cannot be denied. However, in the present embodiment, boron carbide particles 26 that are neutron absorbers are used as abrasives used for cutting the fuel storage rack 2 and the like, and the boron carbide particles 26 injected from the cutting nozzle 5 are contained in the fuel pool 1. Since it exists by diffusing in the cooling water, even if the concentration of the nuclear fuel material in the cooling water in the fuel pool 1 is increased by the above-described cutting operation, recriticality is prevented from occurring due to the action of the boron carbide particles 26. Can do. That is, even if the concentration of the nuclear fuel material in the cooling water is increased by cutting the fuel storage rack 2 and the spent fuel assembly 3, the subcritical state can be maintained.

  Further, in this embodiment, the water flow 28 ejected from the cutting nozzle 5 at the time of cutting includes the boric acid water 7, and the boric acid water 7 ejected from the cutting nozzle 5 is also diffused in the cooling water in the fuel pool 1. To do. Since boron (neutron absorber) contained in the boric acid water 7 also absorbs neutrons, similarly to the boron carbide particles 26, recriticality due to the nuclear fuel material contained in the cooling water can be prevented.

  In this embodiment, the subcritical state is maintained, and the fuel storage rack 2 and the spent fuel assembly 3 accommodated in the fuel storage rack 2 are cut in the cooling water in the fuel pool 1 using an abrasive water jet. be able to. Since the fuel storage rack 2 and the spent fuel assembly 3 housed in the fuel storage rack 2 are cut using an abrasive water jet, the cutting can be easily performed.

  In this embodiment, the cooling water in the fuel pool 1 containing boric acid is injected from the cutting nozzle 5 as the water flow 28 by switching the switching valve 12 and used for cutting the fuel storage rack 2 and the like. The amount of the boric acid water 7 in the boric acid water tank 11 to be used can be reduced.

  In this embodiment, hafnium particles may be used as the abrasive in addition to the boron carbide particles 26 that are boron compounds. The boron carbide particles 26 and the hafnium particles are neutron absorber particles.

  In this embodiment, in the fuel storage rack 2, a fuel assembly that has been removed from the core at the regular inspection and has not reached the end of its life is stored in the fuel storage rack 2 or before being loaded into the core. Even when a fuel assembly having a burnup of 0 GWd / t is stored in the fuel storage rack 2 and these fuel assemblies are damaged as described above, the fuel storage rack and the fuel assembly The fuel assembly in the storage rack can be cut.

  Also in Examples 2 and 3 to be described later, in the fuel storage rack 2, a fuel assembly that has been removed from the core at the regular inspection and has not reached the end of its life is housed in the fuel storage rack 2 or in the core. The fuel storage rack and the fuel assembly in the fuel storage rack can be cut in a state where the fuel assembly having a burnup of 0 GWd / t before loading is stored in the fuel storage rack 2.

  An abrasive water jet cutting method according to embodiment 2, which is another embodiment of the present invention, will be described with reference to FIG.

  The abrasive water jet cutting device 8A used in the abrasive water jet cutting method of the present embodiment replaces the boric acid water tank 11 with the water tank 33 in the abrasive water jet cutting device 8 used in the first embodiment, and switches the switching valve 12 and suction. The nozzle 17, the purification device 18, and the suction pump 29 have a configuration in which the hose 32 is removed. A water tank 33 filled with water 34 not containing boron, which is a neutron absorber, is connected to the high-pressure pump 13 by a hose 9. Other configurations of the abrasive water jet cutting device 8A are the same as those of the abrasive water jet cutting device 8.

  In this embodiment, when the fuel storage rack 2 and the spent fuel assembly 3 housed in the fuel storage rack 2 are cut, the water flow 28 injected from the cutting nozzle 5 is supplied from the boron carbide particles 26 and the water tank 33 to the hose 9. A water stream comprising boron-free water 34 fed through.

  According to this embodiment, since the water stream 28 containing the boron carbide particles 26 and the water 34 is injected toward the fuel storage rack 2, the fuel storage rack 2 and the fuel storage rack are operated by the action of the boron carbide particles 26 contained in the water stream 28. The spent fuel assembly 3 housed in 2 can be cut. Boron carbide particles 26 contained in the water stream 28 and used for the cutting thereof diffuse into the cooling water in the fuel pool 1. For this reason, even if the concentration of the nuclear fuel material contained in the cooling water increases due to the cutting of the spent fuel assembly 3, the recriticality occurs in the same manner as in the first embodiment due to the action of boron carbide 26 diffused in the cooling water. Can be prevented, and a subcritical state can be maintained.

  An abrasive water jet cutting method according to embodiment 3, which is another embodiment of the present invention, will be described with reference to FIG.

  The abrasive water jet cutting device 8B used in the abrasive water jet cutting method of the present embodiment has a configuration in which the abrasive tank 14 is replaced with the abrasive tank 35 in the abrasive water jet cutting device 8 used in the first embodiment. The abrasive tank 35 is filled with alumina particles 36 instead of the boron carbide particles 26 as an abrasive. The hose 10 is connected to the abrasive tank 35. Other configurations of the abrasive water jet cutting device 8B are the same as those of the abrasive water jet cutting device 8.

  In this embodiment, the water flow 28 injected from the cutting nozzle 5 when the fuel storage rack 2 and the spent fuel assembly 3 housed in the fuel storage rack 2 are cut is supplied from the abrasive tank 35 to the cutting head 4 through the hose 10. A water stream including the alumina particles 36 and the boric acid water 7 supplied through the hose 16 and the hose 9. In the present embodiment, the water stream 28 ejected from the cutting nozzle 5 is not abradable and does not contain particles of neutron absorbers (for example, boron carbide and hafnium), and the alumina particles 36 contained in the water stream 28 also absorb neutrons. Contains no material.

  According to the present embodiment, since the water stream 28 containing the alumina particles 36 and the boric acid water 7 is injected toward the fuel storage rack 2, the fuel storage rack 2 and the fuel storage rack are operated by the action of the alumina particles 36 contained in the water stream 28. The spent fuel assembly 3 housed in 2 can be cut. The boric acid contained in the injected water stream 28 diffuses into the cooling water in the fuel pool 1 as in the first embodiment. For this reason, even if the concentration of the nuclear fuel material contained in the cooling water increases due to the cutting of the spent fuel assembly 3, recriticality is caused in the same manner as in Example 1 due to the action of boric acid diffused in the cooling water. This can be prevented and a subcritical state can be maintained. As in the first embodiment, the cooling water containing boric acid sucked from the suction nozzle 17 can be jetted from the cutting nozzle 5 together with the alumina particles 36 as the water flow 28. For this reason, the usage-amount of the boric-acid water 7 in the boric-acid water tank 11 can be reduced.

  In Example 3, instead of the alumina particles 36, particles of cast steel may be used as abrasives. The alumina particles 36 and the cast steel particles are abrasives that do not contain boron.

  DESCRIPTION OF SYMBOLS 1 ... Fuel pool, 2 ... Fuel storage rack, 3 ... Used fuel assembly, 4 ... Cutting head, 5 ... Cutting nozzle, 6 ... Mixer, 7 ... Boric acid water, 8, 8A, 8B ... Abrasive water jet cutting Device: 9, 10, 16, 32 ... hose, 11 ... boric acid water tank, 12 ... switching valve, 13 ... high pressure pump, 14, 35 ... abrasive tank, 17 ... suction nozzle, 18 ... purification device, 20 ... fuel changer , 21 ... mast, 22 ... operating bed, 26 ... boron carbide particles, 27 ... pressurized air supply device, 33 ... water tank, 34 ... water, 36 ... alumina particles.

Claims (11)

  A water stream containing neutron absorber particles that are abradable toward a fuel rack that houses a fuel assembly disposed in water is injected from a nozzle, and the fuel rack and the fuel are injected by the injected neutron absorber particles. Abrasive water jet cutting method for cutting an assembly.   2. The abrasive water jet cutting method according to claim 1, wherein the particles of the neutron absorber are either boron compound particles or hafnium particles.   The abrasive water jet cutting method according to claim 1 or 2, wherein the water stream ejected from the nozzle includes an aqueous solution containing a neutron absorber.   4. The abrasive water jet cutting method according to claim 3, wherein the aqueous solution containing the neutron absorber is supplied to the nozzle from a tank in which the aqueous solution is stored.   The aqueous solution containing the neutron absorber supplied to the nozzle is the water containing the neutron absorber present around the fuel storage rack, and the aqueous solution containing the neutron absorber from the tank to the nozzle The abrasive water jet cutting method according to claim 4, wherein the supply of water is stopped.   The abrasive water jet cutting method according to claim 3, wherein the aqueous solution containing the neutron absorber is an aqueous solution containing boron.   A water stream containing an abrasive containing no neutron absorbing material and an aqueous solution containing a neutron absorbing material is jetted from a nozzle toward a fuel rack containing a fuel assembly disposed in water, and the fuel rack and An abrasive water jet cutting method for cutting the fuel assembly.   The abrasive water jet cutting method according to claim 7, wherein the aqueous solution containing the neutron absorber is an aqueous solution containing boron.   A first tank filled with particles of a neutron absorber, a second tank filled with water, a pump for boosting the water, the particles of the neutron absorber in the first tank and the pump An abrasive water jet cutting apparatus comprising: a nozzle that injects the water in a mixed state.   The abrasive water jet cutting apparatus according to claim 9, wherein the second tank is a second tank filled with the water containing a neutron absorber.   A first tank filled with an abrasive that does not contain a neutron absorber, a second tank filled with an aqueous solution containing a neutron absorber, a pump for boosting the aqueous solution, the abrasive in the first tank, and the pump An abrasive water jet cutting apparatus, comprising: a nozzle that injects the aqueous solution whose pressure has been increased in a mixed state.

Images