JP2006214749A - Decontamination method for inside of reactor pressure vessel - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and a device for effectively removing deposited crud in a core, hardly soluble crud, cut chips, etc. from the inside of a reactor pressure vessel. <P>SOLUTION: Before chemical decontamination, radioactive crud deposited and accumulated in the core underwater is removed with high pressure water and extruded. The radioactive crud extruded into core water and deposited at the bottom of the reactor is removed with a bottom suction device, filtrated and collected with a filter. Chemical decontamination is performed and the radioactive crud deposited on in-core walls and in-core structure is solved and removed. The in-core structure is cut underwater and removed. The hardly soluble radioactive crud remaining on the pressure vessel wall is brushed with an underwater washing machine, sucked, removed and filtrated and collected with the filter. The hardly soluble radioactive crud remaining at the reactor bottom is removed with the bottom suction device and filtrated and collected with the filter. A temporary shield is attached to core wall underwater. After draining well-pool water and pressure vessel water, flashing is conducted with an in-core sprinkler and remaining radioactive crud is washed and filtrated with the filter. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a decontamination method in a reactor pressure vessel, and more particularly, to a decontamination method in a reactor pressure vessel accompanying an internal structure replacement work in the reactor pressure vessel.

  In boiling water reactors, reactor internals have been replaced from the viewpoint of preventive maintenance of the plant, and core shroud 7, which is one of the reactor internals, has also been replaced or planned. Has been.

  The core shroud is a stainless steel structure shown in 7 of FIG. 1 and attached to the inside of the reactor pressure vessel, and has a cylindrical structure surrounding the fuel assembly (core) in the reactor pressure vessel. It has become. The core shroud 7 serves as a partition plate to separate the flow of cooling water in the nuclear reactor and guide water supplied to the nuclear reactor to the lower part of the fuel assembly.

  In the replacement of the core shroud 7, in-core equipment such as the feed water sparger 3, the core spray spargeer 5 and the jet pump 8 in addition to the core shroud 7 is cut and removed, and new equipment is attached.

  And when these equipments are replaced, work in the furnace where a high dose equivalent rate is expected will occur, so chemical decontamination in the furnace, installation of temporary shields, etc. in order to further reduce the dose of workers Measures to reduce the dose of workers in the reactor are being implemented.

  Conventionally, in such dose reduction measures, iron oxide scale called radioactive cladding, which causes a high dose equivalent rate, has been dissolved and removed mainly by chemical decontamination. Inner deposited cladding and the like remain after chemical decontamination, which hinders improvement of work in the furnace.

  The hardly soluble clad remaining after the chemical decontamination adheres to and remains on the wall 11 of the reactor pressure vessel, and this is dried to become radioactive dust, so that the working environment when the worker enters the furnace is significantly deteriorated. Let

  Moreover, it is desirable to remove the in-furnace deposited cladding and the like before chemical decontamination because it leads to an increase in the amount of chemicals used during chemical decontamination and an increase in work load in waste liquid treatment. In addition, leaving the in-furnace cladding is left in the process of cutting and removing in-furnace structures after chemical decontamination. Worsen.

  From the above background, in order to carry out chemical decontamination to improve the working environment in the reactor efficiently and in a short period of time, it is effective to effectively deposit the cladding in the reactor from the reactor pressure vessel. There has been a demand for a procedure, method and apparatus for removing clad, cutting chips and the like.

  The present invention has been made in view of the above problems, and in a method of chemically decontaminating the inside of a reactor pressure vessel and improving the working environment in the reactor, it is possible to efficiently decontaminate the inside of the reactor pressure vessel. The provision of procedures is the subject.

  As a result of diligent studies to solve the above problems, the present inventors have found that the reactor pressure vessel can be efficiently cleaned by combining various cleaning and removal methods according to the properties of various clads, The present invention has been completed.

That is, the present invention is a reactor pressure vessel decontamination method characterized by sequentially performing the following steps (A) to (H).
(A) Prior to chemical decontamination, high-pressure water is used to remove and discharge radioactive cladding deposited and deposited in the furnace in water.
(B) A step of sucking and removing the radioactive clad discharged into the water in the furnace in step A and the radioactive clad deposited on the bottom of the furnace with a bottom suction device, and filtering and collecting with a filter,
(C) A process of chemically decontaminating the furnace and chemically dissolving and removing the radioactive cladding adhering to the furnace wall and the furnace structure,
(D) cutting and removing the in-furnace structure in water;
(E) Brushing, sucking and removing the hardly soluble radioactive clad remaining on the reactor pressure vessel wall with an underwater brush washer, and filtering and collecting with a filter;
(F) A step of sucking and removing the hardly soluble radioactive clad remaining and deposited on the bottom of the furnace with a bottom suction device and collecting by filtration with a filter;
(G) a step of attaching a temporary shield to the furnace inner wall surface in water;
(H) The process of draining the well pool water and the reactor pressure vessel, flushing with a sprinkler in the reactor, washing away the remaining radioactive cladding, and filtering and collecting with a filter.

  According to the method of the present invention, it is possible to efficiently remove in-reactor deposited cladding, hardly soluble cladding, cutting chips, and the like, and chemical decontamination can be efficiently performed. It is possible to improve the working environment in the container.

  In addition, when the furnace shroud is replaced, the work environment in the furnace can be rationally improved by incorporating the decontamination method of the present invention.

  The reactor pressure vessel decontamination method of the present invention can be carried out by sequentially performing the steps (A) to (H). Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 shows a boiling water reactor pressure vessel structure, and FIG. 2 shows a series of decontamination work steps. FIG. 3 is an installation cross-sectional view of the water supply inlet nozzle 2 of the narrow part cleaning apparatus 20 used in the step (A), and FIG. 4 is a front view of the narrow part cleaning apparatus 20. 5 is a configuration diagram of the bottom suction device 30 in the step (B), FIG. 6 is a configuration diagram of the submersible brush cleaning machine 31 in the step E, and FIG. 7 is a configuration diagram of the in-furnace water spraying device 33 in the step H. FIG. 8 is a configuration diagram of the furnace bottom drainage device 39 in the process H.

  In carrying out the method of the present invention, first, high pressure water is used as the step (A), and the radioactive clad adhered and deposited in the furnace in water is removed and discharged.

  In the step (A) of the present embodiment shown in FIG. 2, the radioactive clad deposited in the narrow nozzle portion of the reactor pressure vessel 11 such as the feed water inlet nozzle 2 and the core spray nozzle 4 is discharged and removed with high-pressure water. It is. In this discharge removal, it is preferable to use the narrow part cleaning device 20. As shown in FIG. 3, the high-pressure water spray nozzles 51 and 52 of the narrow part cleaning apparatus 20 are attached in opposite directions, thereby canceling the balance of the jet reaction force of the narrow part cleaning apparatus 20 and underwater. It can be easily installed in the water supply sparger 3 or the core spray sparger 5, and the high-pressure water sprayed onto the nozzle narrow portion 50 can discharge and remove the radioactivity accumulated in the narrow portion. In addition, as high pressure water used in this process, the water of the pressure of about 15-30 MPa is used, for example, The temperature may be about 10-40 degreeC.

  The radioactive clad deposited on the nozzle narrow portion 50 is difficult to completely dissolve and remove in the chemical decontamination performed in the step (C). Cause work exposure and radioactive dust generation. Therefore, prior to chemical decontamination, it is important to discharge and remove the radioactive cladding deposited in the narrow part in the step (A).

  Subsequent to the step (A), the radioactive clad discharged into the furnace water in the step or the radioactive clad previously deposited on the bottom of the furnace, the radioactive clad and the furnace discharged into the furnace water in the step A The radioactive clad deposited on the bottom is removed by suction with the bottom suction device 30 shown in step (B) of FIG.

  The bottom suction device 30 used in this step (B) is composed of a suction tube 59 and a suction port 60, as shown in FIG. The bottom suction device 30 is operated from the fuel exchanger 16 installed on the reactor well 15 or the dedicated work carriage, and the radioactive clad and the reactor bottom sediment clad sucked thereby are sucked into the suction hose 26, underwater Via the pump 25 and the discharge hose 27, for example, it is filtered and collected by the filter 24 installed in the fuel pool 23. The filter 24 used in this step is preferably one that can filter particles having a size of about 0.4 to 1.0 μm, and the material is preferably polypropylene or the like.

  In addition to the step (B) performed prior to the chemical decontamination, this step is similarly performed as the step (F) in order to discharge and remove the radioactive cladding deposited after the steps (D) and (E). Is done.

  Next, chemical decontamination in the furnace is performed, and the radioactive cladding adhering to the furnace inner wall surface and the furnace internal structure is chemically dissolved and removed. This chemical decontamination may be performed under general conditions, for example, using a decontamination agent such as oxalic acid at a temperature of about 90 to 95 ° C. for about 100 hours.

  After the above chemical decontamination is completed, the in-furnace structure is cut and removed in water. This step is also performed by a conventional method. For example, the core internal shroud 7, the feed water sparger 3, the core spray sparger 5, the jet pump 8, etc. in FIG. Is carried out.

  After the above-mentioned reactor internals are carried out and removed, the hardly soluble loose radioactive clad remaining on the reactor pressure vessel wall in step (E) is brushed, sucked and removed with an underwater brush washer. Filter and collect with a filter.

  In this step (E), the hardly soluble radioactive clad is suspended from the wall brush washer 31 incorporating the underwater electric motor 62 and the underwater brush 64 shown in FIG. The cleaning device composed of the electric winch 28 that moves along and moves up and down is removed by operating from the fuel exchanger 16 installed on the upper portion of the reactor well 15 or the dedicated work carriage. In addition, the cutting chips generated in the previous step (D) are also removed together with the hardly soluble radioactive clad.

  By this process, the hardly soluble cladding and the cutting chips generated at the time of cutting the in-reactor structure water in the step (D) are removed from the reactor pressure vessel, and these remain and do not become a radiation source. Therefore, it is possible to prevent work exposure and radioactive dust generation in the in-furnace work performed thereafter.

  Further, following the step (E), the hardly soluble radioactive clad remaining and deposited on the bottom of the furnace (and the cutting chips deposited on the bottom of the furnace) are removed by suction with a bottom suction device and collected by filtration with a filter. Step (F) is performed.

  In the removal of the radioactive cladding in this step (F), a bottom suction device 30 composed of a suction tube 59, a suction port 60 and a suspension 58 as shown in FIG. 5 is used. It is operated from the fuel changer 16 installed on the upper portion of the well 15 or the dedicated work carriage. Then, the radioactive clad discharged in the steps (C) to (E), the cut swarf of the furnace internal structure, and the furnace bottom deposited clad are sucked, and the filter installed, for example, in the fuel pool 23 through the discharge hose 27 24, and can be collected.

  As described above, after removing the radioactive cladding or the like serving as a radiation source from the wall surface of the reactor well, a temporary shield is attached to the inner wall surface of the reactor in water as step (G). This temporary shield is provided for the purpose of preventing an operator from being exposed to the reactor wall of the reactor pressure vessel partially activated, and the reactor wall shield shown as 32 in step (G) of FIG. It is. As the material of the furnace wall shield 32, stainless steel, lead or the like is used, and the thickness thereof is about 100 mm.

  Finally, after draining the well pool water and the reactor pressure vessel, flushing is performed with a water spray device in the reactor, the remaining radioactive clad is washed away, and the step (H) of collecting by filtration with a filter is performed. .

  In this step, flushing is performed by the in-furnace sprinkler 33 as shown in step (H) of FIG. FIG. 7 shows an example of the structure of the in-furnace watering device 33. This device swings the injection nozzles 83 and 84 in the lower hemisphere by the rotation of the air motor or the electric motor 70.

  In this step (H), after draining the reactor well 15 pool water, an in-core water sprinkler 33 and a sprinkler gantry 34 are installed in the reactor pressure vessel flange 12 part, and at the same time, the reactor pressure vessel After installing the reactor bottom drainage device 39 for discharging the flushing water in a state where the reactor pressure vessel 11 is filled with water on the control rod drive mechanism housing 10 of the bottom portion 13, the reactor pressure vessel top lid 1 is installed and then the reactor pressure Water is drained from the vessel 11, water is supplied to the water sprinkler 33 from the watering pump 35 installed on the operation floor, and the inner surface of the reactor pressure vessel 11 is washed by flushing.

  The flushing flushes away the radioactive cladding remaining on the wall of the reactor pressure vessel 11 and the bottom 13, and the flushing wastewater containing the radioactive cladding generated at this time is submerged by a submersible pump 89 and a pump base 90 installed at the bottom of the reactor. And so on. Then, for example, only the radioactive cladding is filtered and collected by the filter 24 or the like installed in the fuel pool 23, and the filtered flushing water is again sprinkled in the furnace through the water supply tank 36 and the watering pump 35 installed in the operation area. Water is supplied to the device 33, and circulation use becomes possible.

  On the other hand, the above-described reactor bottom drainage device 39 is installed on the control rod drive mechanism housing 10 of the reactor pressure vessel bottom 13 as shown in FIG. 8, and is equipped with a submersible pump 89, a float switch 92, a pump suction pipe, and a pump base 90. And the like. The float switch 92 incorporated in the apparatus adjusts the water level at the bottom of the furnace, and the 360 ° rotating nozzle 95 incorporated in the apparatus injects pressure water in the entire 360 ° circumferential direction. The back surface of the baffle plate 14 that becomes a blind spot from the in-furnace sprinkler 33 is cleaned.

  The above step (H) includes the reactor pressure vessel chemical decontamination in the step (C) and the insoluble cladding and cutting of the inner surface of the reactor pressure vessel after the in-reactor structure water cutting in the step (D). Depending on the amount of deposited chips, it may be added between step (E) and step (F).

  According to such a configuration of the present invention, chemical decontamination that is performed to improve the working environment in the furnace is efficiently performed, and the in-furnace deposited cladding, the hardly soluble cladding, and the cutting chips are efficiently removed. Can be removed.

It is drawing which shows the structure of a boiling water reactor pressure vessel. It is drawing which shows a decontamination work process. It is installation sectional drawing of the water supply inlet nozzle of the narrow part washing | cleaning apparatus used at a process (A). It is a front view of the narrow part washing | cleaning apparatus used at a process (A). It is a block diagram of the bottom part suction device used at a process (B). It is a block diagram of the underwater brush washing machine used at a process (E). It is a block diagram of the in-furnace watering apparatus used at a process (H). It is a block diagram of the furnace bottom part drainage apparatus used at a process (H).

Explanation of symbols

1…… Reactor pressure vessel top 2…… Feed water inlet nozzle 3…… Feed water sparger 4…… Core spray nozzle 5…… Core spray sparger 6…… Upper grid plate 7…… Core shroud 8…… Jet pump 9…… Core support plate 10… Control rod drive mechanism housing 11…… Reactor pressure vessel 12…… Reactor pressure vessel flange 13…… Reactor pressure vessel bottom 14…… Baffle plate 15…… Reactor well 16…… Fuel changer 20 ... ... Narrow part cleaning device 21 ... ... High pressure pump 22 ... ... High pressure hose 23 ... ... Fuel pool 24 ... ... Filter 25 ... ... Submersible pump 26 ... ... Suction hose 27 ... ... Discharge hose 28 ... ... Electric winch 29 ... ... Wire 30…… Bottom suction device 31…… Underwater brush washer 32 ... Furnace wall shield 33 ... ... Sprinkler in furnace 34 ... ... Sprinkler stand 35 ... ... Sprinkler pump 36 ... ... Water supply tank 37 ... ... Discharge hose 38 ... ... Pressure hose 39 ... ... Furnace bottom drainage 50 ... ... Nozzle narrow part 51 ... ... Injection nozzle (1)
52 ... Injection nozzle (2)
53 ... Water jet (1)
54 ... Water jet (2)
55…… Guide plate 56…… Piping 57…… Horseshoe tube……
58 ... ... Suspension tool 59 ... ... Suction tube 60 ... ... Suction port 61 ... ... Suspension wire 62 ... ... Underwater electric motor 63 ... ... Gear box 64 ... ... Underwater brush 65 ... ... Mount 70 ... ... Air motor or electric motor 71 ... ... Spur gear (1)
72 ... ... Spur Gear (2)
73 ... ... Gearbox 74 ... ... Spur Gear (3)
75 ... ... Spur Gear (4)
76…… Inflow pipe 77…… Fixed shaft 78…… Rotating body 79…… Fixed gear 80…… Driven gear (1)
81…… Driven gear (2)
82…… Bearing 83…… Watering nozzle (1)
84…… Watering nozzle (2)
85 ... Equipment frame 86 ... ... Water supply 87 ... ... Water jet (1)
88 ... ... Water jet (2)
89…… Submersible pump 90…… Pump mount 91…… Pump suction pipe 92…… Float switch 93…… Foot valve 94…… Suspension 95…… 360 ° rotating nozzle
more than

Claims (7)

A reactor pressure vessel decontamination method characterized by sequentially performing the following steps (A) to (H).
(A) Prior to chemical decontamination, high-pressure water is used to remove and discharge radioactive cladding deposited and deposited in the furnace in water.
(B) A step of sucking and removing the radioactive clad discharged into the water in the furnace in step A and the radioactive clad deposited on the bottom of the furnace with a bottom suction device, and filtering and collecting with a filter,
(C) A process of chemically decontaminating the furnace and chemically dissolving and removing the radioactive cladding adhering to the furnace wall and the furnace structure,
(D) cutting and removing the in-furnace structure in water;
(E) Brushing, sucking and removing the hardly soluble radioactive clad remaining on the reactor pressure vessel wall with an underwater brush washer, and filtering and collecting with a filter;
(F) A step of sucking and removing the hardly soluble radioactive clad remaining and deposited on the bottom of the furnace with a bottom suction device and collecting by filtration with a filter;
(G) a step of attaching a temporary shield to the furnace inner wall surface in water;
(H) The process of draining the well pool water and the reactor pressure vessel, flushing with a sprinkler in the reactor, washing away the remaining radioactive cladding, and filtering and collecting with a filter.   The decontamination in a reactor pressure vessel according to claim 1, wherein the radioactive clad removal in the step (A) is performed using a nozzle in which the balance of the jet reaction force is offset by mounting the high-pressure water jet nozzle in opposite directions. Method.   The decontamination method in a reactor pressure vessel according to claim 1 or 2, wherein the bottom suction device used for suction removal of the radioactive cladding in the step (B) is composed of a submersible pump, a suction pipe and a suction port.   The underwater brush washer used for removing the hardly soluble radioactive cladding in step (E) is a wall brush washer incorporating an underwater electric brush and an electric winch that suspends this device and moves it vertically along the reactor pressure vessel wall. The reactor pressure vessel decontamination method according to any one of claims 1 to 3, wherein   The nuclear reactor according to any one of claims 1 to 4, wherein the bottom suction device used for removing the hardly soluble radioactive clad in the step (F) comprises a submersible pump, a suction pipe, and a suction port. Decontamination method in pressure vessel.   The decontamination method in a reactor pressure vessel according to any one of claims 1 to 5, wherein the flushing water after filtration and collection of the radioactive cladding is circulated and used as the flushing water used for the flushing in the step (H). In step (H), after draining the well pool water, an in-core water sprinkler is installed on the reactor pressure vessel flange, and the flushing water is discharged to the bottom of the reactor with the reactor pressure vessel filled with water. After installing the reactor bottom drainage system consisting of the submersible pump, float switch and piping to perform, drain the reactor pressure vessel after installing the reactor pressure vessel top lid, and spray water from the watering pump installed on the operation floor The reactor pressure vessel decontamination method according to claim 1, wherein water is supplied to the apparatus to clean the inner surface of the reactor pressure vessel.

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