JP2012198105A - Preparation operation method for radioactive material transport storage container, and lid part auxiliary shield body for preparation operation thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent an operator from being exposed to radiation in preparation operation for a radioactive material transport storage container.SOLUTION: A lid part auxiliary shield body 4 is attached to an outer surface of a primary lid 2 put to cover a container body 1 before preparation operation, and the attached lid part auxiliary shield body 4 is detached right before a secondary lid is attached to sufficiently blocks radiation such as gamma rays and neutrons from inside the container body 1 during the preparation operation such as bolt fastening operation for the primary lid 2 and drain operation for water in the container, thereby reducing exposure of the operator to the radiation during the preparation operation.

Description

  The present invention relates to a method for tailoring a radioactive substance transport storage container, and a tailing work lid auxiliary shield.

  Radioactive materials such as nuclear fuel used at nuclear power plants are cooled and stored for a certain period in the water pool at the power plant, then stored in radioactive material transport storage containers called casks, and transported directly to reprocessing plants. Or temporarily stored and then transported to a reprocessing plant. In this radioactive material transport storage container, the primary lid and the secondary lid are attached to the inside and outside of the cylindrical container body having a bottom plate to confine the contained radioactive material, and gamma rays, neutrons, etc. emitted by these radioactive materials This shields radiation (for example, see Patent Document 1). In the device described in Patent Document 1, a tertiary lid for transportation is attached to the outside of the secondary lid in order to prevent radiation leakage during transportation.

  One of the primary lid and secondary lid of this radioactive material transport storage container is made of a metal material such as steel having a high gamma ray shielding ability, and the other is made of a polymer material containing a large amount of hydrogen having a high neutron shielding ability. There are many. Some primary and secondary lids have the ability to partially shield gamma rays and neutrons, and both shield lids shield gamma rays and neutrons to assist each other. Moreover, the upper end part of the container main body of a radioactive substance transport storage container is normally provided with the level | step-difference part which made the inner peripheral side low, and an outer peripheral part is attached to this step part with a volt | bolt with a primary cover.

  When a radioactive material is stored in such a radioactive material transport storage container, and a tailoring operation for attaching a primary lid and a secondary lid to the container body is performed, first, the container body is placed in a water pool in which the radioactive material is stored. Submerge, store radioactive material in container, and cover with primary lid in water. After that, the container body covered with the primary lid is carried out of the water pool by a crane or the like, attached to the primary lid by bolting, and the water in the container body is discharged from the water outlet provided in the primary lid. Usually, the inside of the container body from which water has been discharged is vacuum-dried and then filled with an inert gas such as helium gas. The gas pressure in the container main body is set to a negative pressure of about 0.8 atm so that radiation-carrying gas does not leak to the outside. Finally, the tailoring operation is completed by attaching the secondary lid by bolting. A positive pressure space is provided between the primary lid and the secondary lid, and this positive pressure space is filled with helium gas or the like. The gas pressure in the positive pressure space is about 4 atm so that even if the gas in the container leaks from the seal portion of the primary lid, it does not leak to the outside.

JP-A-11-287893

  Since the conventional radioactive substance transport storage container described in Patent Document 1 needs to perform tailoring work such as bolting work of the primary lid and draining water in the container with only the primary lid covered, There is a problem that the amount of radiation exposure of workers increases. When the primary lid mainly shields gamma rays, the worker mainly receives neutrons, and when the primary lid mainly shields neutrons, the worker mainly receives gamma rays. In addition, when the primary lid partially shields gamma rays and neutrons, the operator receives both gamma rays and neutrons, although the respective exposure doses are reduced.

  In order to prevent such radiation exposure of workers, it is conceivable that the thickness of the primary lid can be increased so that both gamma rays and neutrons can be shielded. When installed, it must be designed within the lifting weight limit of the crane, and in order to provide a positive pressure space between the primary and secondary lids, the primary and secondary lids can withstand the pressure between the lids. However, if only the thickness of the primary lid is increased from the viewpoint of shielding design, there is a problem that the thickness of the secondary lid cannot withstand the pressure between the lids. Then, both gamma rays and neutrons cannot be shielded sufficiently. As another limit weight, the container may be lifted from the water pool. In this case, the total weight of the container body, the primary lid, and the water in the container after loading with radioactive material will be limited. If the thickness of the lid is increased, this limit weight cannot be satisfied.

  Therefore, an object of the present invention is to prevent the radiation exposure of workers in the work of tailoring the radioactive substance transport storage container.

  In order to solve the above-described problems, a method for tailoring a radioactive substance transport storage container according to the present invention is provided in a container body of a bottomed cylindrical radioactive substance transport storage container in water of a water pool in which the radioactive substance is stored. After storing the radioactive material, the container body is covered with a primary lid and taken out of the water pool. The covered primary lid is attached to the container body, and the water in the container body is drained. In a method for tailoring a radioactive material transport storage container in which a secondary lid is attached to the outside of the container, a lid auxiliary shield is attached to the outer surface of the primary lid and the secondary lid is attached before the primary lid is attached to the container body. Previously, a method of removing the attached lid auxiliary shield was adopted.

  That is, before attaching the primary lid to the container body, attach the lid auxiliary shield to the outer surface of the primary lid, and before attaching the secondary lid, remove the attached lid auxiliary shield so that the primary lid is bolted. During tailoring work such as work and draining water in the container, the primary lid and the auxiliary cover shield cover the gamma rays and neutron radiation from the container body sufficiently, and the radiation of the worker in the tailoring work Made it possible to prevent exposure.

  By attaching the lid auxiliary shield to the primary lid before the primary lid is put on the container body, the lid auxiliary shield can be easily removed outside the water pool in a safe state where radiation is not exposed. Can be attached to the primary lid.

  Further, the lid auxiliary shield for tailoring work of the radioactive substance transport storage container of the present invention is a radioactive substance in the container body of the bottomed cylindrical radioactive substance transport storage container in the water of the water pool in which the radioactive substance is stored. The container body is covered with a primary lid and taken out of the water pool. The covered primary lid is attached to the container body, and the water in the container body is discharged, and then the outside of the primary lid. A lid auxiliary shield for tailoring work used at the time of tailoring a radioactive material transport storage container to which a secondary lid is attached, wherein the lid auxiliary shield is attached to the primary lid before the primary lid is attached to the container body. The structure which was attached to the outer surface of a lid | cover and was removed before attaching the said secondary lid | cover was employ | adopted.

  That is, the lid auxiliary shield is attached to the outer surface of the primary lid before the primary lid is attached to the container body, and is removed before attaching the secondary lid, so that the primary lid and the lid auxiliary during the tailoring operation. With the shield, the radiation from inside the container body is sufficiently shielded so that the operator can be prevented from being exposed to radiation during the tailoring operation.

  The lid auxiliary shield has an opening so as to surround a discharge port for discharging the water in the container body provided in the primary lid, thereby facilitating the discharge operation of the water in the container. Can be done. In addition, using this opening, vacuum drying in the container and gas filling operation into the container can be suitably performed.

  When the primary lid is attached to the upper end of the container body by a plurality of bolts on the same pitch circle, the outer diameter of the lid auxiliary shield is set to a plurality of bolts on the same pitch circle. By making it smaller than the diameter of the circle connecting the inner ends of the bolts, the bolting operation of the primary lid can be easily performed.

  When the primary lid is provided with a handling jig mounting portion at the center of the outer surface thereof, the lid auxiliary shield is provided with an opening so as to surround the handling jig mounting portion. Thus, the primary lid can be easily handled with the lid auxiliary shield attached.

  The primary lid is attached to a stepped portion having a lower inner peripheral side provided at the upper end of the container body, and the height position of the outer surface when attached is lower than the upper end of the container body. In this case, when the lid auxiliary shield is attached to the outer surface of the primary lid, the upper surface position of the lid auxiliary shield is higher than the upper end of the container body. If the lid auxiliary shield is attached to the primary lid in advance and put on the container body, the amount of water collected on the lid carried out of the water pool will be reduced, and the water draining work on the lid will be reduced. Can do.

  The method for tailoring the radioactive material transport storage container according to the present invention includes the step of attaching the lid auxiliary shield to the outer surface of the primary lid and attaching the secondary lid before attaching the secondary lid before attaching the primary lid to the container body. Since the auxiliary shield is removed, it is possible to prevent the radiation exposure of the worker in the tailoring work.

  Further, the lid auxiliary shield for tailoring work of the radioactive material transport storage container according to the present invention is attached to the outer surface of the primary lid before the primary lid is attached to the container body, and is removed before attaching the secondary lid. Therefore, it is possible to prevent the radiation exposure of the worker in the tailoring work.

The conceptual diagram explaining the tailoring work method of the radioactive material transport storage container concerning this invention Fig. 1 is an exploded vertical side view showing the radioactive substance transport storage container and the lid auxiliary shield shown in Fig. 1. (A) is a top view which shows the state which attached the cover part auxiliary shield to the primary lid of FIG. 2, (b) is sectional drawing along the IIIb-IIIb line | wire of (a). FIG. 3 is a partially omitted vertical side view showing a state where the primary lid of FIG. 3 is attached to the container body of FIG. 4 is a partially omitted vertical side view showing a state in which the lid auxiliary shield shown in FIG. 4 is removed and the secondary lid shown in FIG. 2 is attached.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a conceptual diagram showing a method for tailoring a radioactive material transport storage container according to the present invention. In the preparation of the radioactive material transport storage container, first, the container body 1 of the bottomed cylindrical radioactive material transport storage container is placed in the water pool 31 in which the radioactive material M such as nuclear fuel used in the nuclear power plant is stored. The radioactive substance M is stored in the container main body 1. After that, the primary lid 2 with the lid auxiliary shield 4 attached to the outer surface is suspended by the crane 32 and placed on the container body 1, and the container body 1 covered with the primary lid 2 is placed outside the water pool 31 by the crane 32. It is lifted and carried on the work deck 33.

  Next, on the work deck 33, the operator attaches the primary lid 2 covering the container body 1 by bolting, and discharges the water in the container body 1 by the water discharge device 34. Although not shown, the water discharge device 34 inserts a double pipe into the container from a water discharge port 2b of the primary lid 2 described later, supplies compressed air from the outer pipe of the double pipe, The water in the container is discharged. A separate air supply port may be provided in the primary lid 2, a compressed air supply pipe may be inserted into the air supply port, and water may be discharged from the water discharge pipe inserted into the water discharge port 2b. After that, the inside of the container from which water has been discharged is vacuum-dried by the vacuum drying device 35 using the water discharge port 2b and filled with helium gas by the helium filling device 36. The gas pressure in the container filled with helium gas is a negative pressure of about 0.8 atm.

  Finally, the container body 1 to which the primary lid 2 and the lid auxiliary shield 4 are attached and filled with helium gas is attached with the secondary lid 3 after the lid auxiliary shield 4 is removed, which will be described later. The positive pressure space 11 between the primary lid 2 and the secondary lid 3 is filled with helium gas, and the tailoring operation is completed. The gas pressure in the positive pressure space 11 is about 4 atmospheres. The radioactive material transport and storage container for which the tailoring work has been completed is transported to the reprocessing plant as it is, or temporarily stored and then transported to the reprocessing plant.

  As will be described later, the primary lid 2 is made of carbon steel having a high gamma ray shielding ability, and the lid auxiliary shielding body 4 is made of a polypropylene resin containing a large amount of hydrogen having a high neutron shielding ability. The upper worker can reduce exposure to gamma rays and neutrons during tailoring operations such as bolting the primary lid 2 and discharging water in the container.

  As shown in FIG. 2, the container body 1 of the radioactive substance transport storage container is provided with, for example, an epoxy resin neutron shielding material 1c between a cylindrical inner cylinder 1a and an outer cylinder 1b made of carbon steel. A bottom plate 1d formed of carbon steel and an epoxy resin neutron shielding material is attached. The primary lid 2 is made of carbon steel having a high gamma ray shielding capability, and the secondary lid 3 and the lid auxiliary shield 4 are made of a polypropylene resin having a high neutron shielding capability containing a large amount of hydrogen.

  The material forming the lid auxiliary shield 4 can be a resin material such as polyethylene resin, epoxy resin, polyester resin, or a rubber material such as silicon rubber, ethylene propylene rubber, fluorine rubber, and the like. You can also When the primary lid 2 is made of a material having a high neutron shielding ability, the lid auxiliary shielding body 4 is made of carbon steel, stainless steel, aluminum, aluminum alloy, tungsten, lead, copper, high gamma ray shielding ability, It may be formed of a metal material such as a copper alloy. When the primary lid 2 partially shields gamma rays and neutrons, the lid auxiliary shield 4 is made of a resin-based material or rubber-based material containing a large amount of hydrogen. A combination of a material and a metal material may be used.

  3A and 3B show a state in which the lid auxiliary shield 4 is attached to the outer surface of the primary lid 2. A plurality of bolt holes 2a for bolts 5a to be attached to the container body 1 are provided on the same pitch circle on the outer peripheral portion of the primary lid 2, and a water discharge port 2b is provided at one place on the inner peripheral side thereof. A seat member 6 for fixing the double pipe of the water discharge device 34 is attached to the outer surface around the water discharge port 2b, and a positioning pin 6a for positioning the double pipe is provided on the upper surface of the seat member 6. Is provided. Moreover, the screw hole 2c is provided in four places in the center part of the primary lid 2, The handling jig | tool 7 for suspension etc. is attached to these screw holes 2c with the volt | bolt 5b. On the lower surface of the handling jig 7, leg portions 7a are provided at four locations, and bolts 5b are passed through bolt holes of these leg portions 7a.

  The outer diameter of the lid auxiliary shield 4 is formed smaller than the diameter of a circle connecting the inner ends of the bolts 5a attached to the plurality of bolt holes 2a on the same pitch circle, and around the water discharge port 2b. An opening 4a surrounding the seat member 6 is provided. Further, four openings 4b are provided at the center of the lid auxiliary shield 4 so as to surround the legs 7a of the handling jig 7. The lid auxiliary shield 4 is attached to the handling jig 7 with bolts 5c from the lower surface side at four positions that are 45 ° out of phase with the opening 4b, and is then attached to the handling jig 7 with the bolts 5b. It is attached to the primary lid 2 together.

  FIG. 4 shows a state in which the primary lid 2 to which the lid auxiliary shield 4 is attached is attached to the container body 1. The upper end portion of the inner cylinder 1a of the container body 1 is provided with a stepped portion 8 whose inner peripheral side is lowered, and the outer peripheral portion of the primary lid 2 is connected to a plurality of screw holes 9a provided in the stepped portion 8 with bolts 5a. It is attached. A ring-shaped neutron shielding member 10 made of polyethylene resin is mounted on the outer peripheral side of the upper end portion of the inner cylinder 1a. As described above, the outer diameter of the lid auxiliary shield 4 is formed smaller than the diameter of the circle connecting the inner ends of the plurality of bolts 5a attached to the bolt holes 2a. The bolting operation of the bolt 5a can be performed.

  Moreover, the thickness dimension of the cover part auxiliary | assistant shielding body 4 attached to the outer surface of the said primary cover 2 is formed in the thickness from which the upper surface becomes higher than the upper end of the container main body 1. FIG. Therefore, when the container main body 1 covered with the primary lid 2 is unloaded from the water pool 31, the amount of water that accumulates on the lid can be reduced, and the water removal work on the lid can be reduced.

  FIG. 5 shows a state in which the lid auxiliary shield 4 is removed from the primary lid 2 and the secondary lid 3 is attached to the container body 1. The secondary lid 3 is attached by bolts 5d to a plurality of screw holes 9b provided on the upper end surface of the inner cylinder 1a of the container body 1 on the outer peripheral side of the primary lid 2. A positive pressure space 11 filled with helium gas is formed between the primary lid 2 and the secondary lid 3.

As an example, the neutron dose equivalent rate above the lid auxiliary shield during the tailoring operation of the radioactive substance transport storage container using the lid auxiliary shield described above was calculated. As a comparative example, the neutron dose equivalent rate above the primary lid when the lid auxiliary shield was not used was also calculated. The calculation conditions are as follows.
(Radioactive material)
・ Type: BWR 8 × 8 STEP II fuel ・ Maximum burnup: 43000 MWD / tU
Average burnup: 40000 MWD / tU
・ Cooling years: 16 years (shielding calculation code)
-Calculation code: Two-dimensional transport calculation code (DOT3.5)
・ Cross sectional area library: Neutron 22 group, gamma ray 18 group DLC23 cask library

  Table 1 shows the calculation result of the neutron dose equivalent rate. From this calculation result, the neutron intensity per unit time is 1090 μSv / h in the comparative example not using the lid auxiliary shield, whereas the neutron intensity is 7 μSv in the embodiment using the lid auxiliary shield. / H. Therefore, the method for tailoring the radioactive substance transport storage container according to the present invention can suppress the exposure dose of the worker to a level that is not problematic for safety.

  In the embodiment described above, the lid auxiliary shield is attached to the primary lid before the primary lid is placed on the container body. However, after the container body covered with the primary lid is taken out of the pool, the lid portion An auxiliary shield can also be attached to the primary lid.

M radioactive substance 1 container main body 1a inner cylinder 1b outer cylinder 1c neutron shielding material 1d bottom plate 2 primary lid 2a bolt hole 2b water discharge port 2c screw hole 3 secondary lid 4 lid auxiliary shield 4a, 4b opening 5a, 5b, 5c, 5d Bolt 6 Seat member 6a Positioning pin 7 Handling jig 7a Leg 8 Stepped portion 9a, 9b Screw hole 10 Neutron shielding member 11 Positive pressure space 31 Water pool 32 Crane 33 Work deck 34 Water discharge device 35 Vacuum drying device 36 Helium filling equipment

Claims (7)

  After storing the radioactive material in the container body of the bottomed cylindrical radioactive material transport storage container in the water of the water pool where the radioactive material is stored, put the primary cover on the container body and carry it out of the water pool In the method for tailoring the radioactive material transport storage container, the primary lid is attached to the container body, drains the water in the container body, and then attaches the secondary lid to the outside of the primary lid. Before attaching to a container main body, the cover part auxiliary shield is attached to the outer surface of the primary lid, and the attached cover part auxiliary shield is removed before attaching the secondary lid. How to tailor the transport storage container.   The method for tailoring a radioactive substance transport storage container according to claim 1, wherein the lid auxiliary shield is attached to the primary lid before the primary lid is put on the container body.   After storing the radioactive material in the container body of the bottomed cylindrical radioactive material transport storage container in the water of the water pool where the radioactive material is stored, put the primary cover on the container body and carry it out of the water pool The lid for the tailoring work used in the tailoring work of the radioactive material transport storage container in which the covered primary lid is attached to the container main body and the water in the container main body is discharged and then the secondary lid is attached to the outside of the primary lid. A secondary auxiliary shield, wherein the lid auxiliary shield is attached to an outer surface of the primary lid before the primary lid is attached to a container body, and is removed before attaching the secondary lid. An auxiliary shield for tailoring containers.   The said lid part auxiliary | assistant shield is a lid | cover for tailoring work of the radioactive substance transport storage container of Claim 3 provided with an opening part so that the discharge port which discharges | emits the water in the said container main body provided in the said primary cover may be enclosed. Auxiliary shield.   The primary lid is attached to the upper end of the container body by a plurality of bolts on the same pitch circle, and the outer diameter of the lid auxiliary shield is set to the inside of the plurality of bolts on the same pitch circle. The lid auxiliary shielding body for tailoring work of the radioactive substance transport storage container according to claim 3 or 4, wherein the diameter is smaller than a diameter of a circle connecting the ends.   6. The primary lid includes a handling jig mounting portion at a center portion of an outer surface thereof, and the lid auxiliary shield includes an opening so as to surround the handling jig mounting portion. The lid auxiliary shield for tailoring work of the radioactive substance transport storage container according to any one of the above.   The primary lid is attached to a stepped portion having a lower inner peripheral side provided at the upper end portion of the container body, and the height position of the outer surface when attached is lower than the upper end of the container body. The upper surface position of the lid auxiliary shielding body is higher than the upper end of the container main body when the lid auxiliary shielding body is attached to the outer surface of the primary lid. A cover auxiliary shield for tailoring of the radioactive material transport storage container according to 1.

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