JP2012083255A - Spent fuel storage container and rust prevention treatment method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve such problems that there is a possibility that water cannot be removed by vacuum drying because there is a gap in a fitting part between a lid and an inner cylinder, and water enters the inner cylinder when fuel is loaded in a pool, and moreover, there is a possibility of corrosion in a gap in a fitting part between a side surface of a secondary lid of the outside of a lid bolt and the inner cylinder because of being exposed to the atmosphere during a long storage period.SOLUTION: In a spent fuel storage container in which an opening is provided at an upper part of a cylindrical body drum, and the inside of the body drum is tightly sealed by mounting a plurality of lids such as primary lid and secondary lid on this opening, an anti-corrosion treatment is applied to the fitting parts between the body drum and the lids.

Description

  The present invention relates to a spent fuel storage container used for transporting and storing spent fuel generated from a nuclear power plant.

  In general, fuel that has been used in the core of a nuclear power plant is taken out of the core and temporarily stored in a pool or the like as spent fuel. Thereafter, spent fuel is reprocessed at a reprocessing plant, whereby uranium and plutonium are recovered as resources.

  On the other hand, the amount of spent fuel generated at nuclear power plants is increasing with the demand for power generation, and is expected to exceed the amount processed at reprocessing plants in the near future. In that case, spent fuel needs to be stored appropriately in consideration of safety until it is reprocessed. Depending on the relationship between the amount of spent fuel generated and the amount of reprocessing, the storage period may be assumed to be about 50 years.

  Examples of the spent fuel storage system include a dry storage system and a wet storage system. Among them, the dry storage system is low in cost and excellent in storage stability over a long period of time. Conventionally, a metal cask is known as a spent fuel storage container used in a dry storage system.

  The metal cask is provided with an inner cylinder in the outer cylinder constituting the container, and heat transfer fins made of a metal plate such as copper having high thermal conductivity are attached to the outer side of the outer cylinder at intervals in the circumferential direction. A metal basket is provided inside the inner cylinder, and spent fuel is stored therein.

  Between the inner cylinder and the outer cylinder is a cured resin that is a neutron shield. The inner cylinder is a carbon steel cylinder having an upper opening and is a γ-ray shield. A primary lid for preventing leakage of radioactive material is attached to the opening of the inner cylinder, and a secondary lid is attached to the outside thereof. The inner cylinder and the lid are sealed with a metal gasket.

  In the case of a metal cask, spent fuel is loaded into the cask in the fuel pool, the water inside the cask and the gasket part is drained in the decontamination pit, and then vacuum drying is performed to remove moisture. After this, a secondary lid is attached and transported and stored. The reason for vacuum drying is to prevent water from corroding each part and to suppress an increase in internal pressure during storage.

  For example, Patent Document 2 describes a method of vacuum drying inside a cask. Patent Document 3 describes a structure and a corrosion prevention method for preventing corrosion of the gasket part.

Japanese Patent Laid-Open No. 2001-141884 Japanese Patent Laid-Open No. 2002-243888 JP 2006-125905 A

  The fitting portion between the lid and the inner cylinder has a slight gap in order to make the fitting of the lid smooth. This gap is considered to be desirable to prevent the occurrence of corrosion during long-term storage for the following reasons.

  There is a gap between the primary lid side surface outside the lid bolt and the fitting portion of the inner cylinder, so that water enters when fuel is loaded in the pool and may not be completely removed by vacuum drying. Further, since the gap between the side surface outside the lid bolt of the secondary lid and the fitting portion of the inner cylinder is exposed to the atmospheric atmosphere during long-term storage, there is no possibility of corrosion here.

  If corrosion occurs in the fitting portion between the primary lid or the secondary lid and the inner cylinder during long-term storage, it may be difficult to reopen the lid after storage. While the method described in Patent Document 3 can effectively prevent corrosion around the sealing portion of the metal gasket, what is an essential countermeasure against corrosion between the lid side surface and the inner cylinder? Don't be.

  The objective of this invention is providing the spent fuel storage container which prevented the corrosion of the fitting part of a primary lid or a secondary lid, and an inner cylinder.

  In the spent fuel storage container that seals the inside of the main body cylinder by attaching an opening having an upper part of the cylindrical main body cylinder and a plurality of lids such as a primary lid and a secondary lid to the opening. This is achieved by subjecting the fitting portion between the main body cylinder and the lid to rust prevention treatment.

  Moreover, the said objective WHEREIN: It is preferable to apply the inorganic coating material at normal temperature for the said rust prevention process.

  For the above purpose, the inorganic coating material is preferably an inorganic coating material such as carbon fine particles or zinc fine particles.

  Another object of the present invention is to provide a spent fuel storage container that seals the inside of the main body barrel by attaching an opening at the top of the cylindrical main body cylinder and a plurality of lids such as a primary lid and a secondary lid to the opening. In the rust-proofing method for rusting the fitting portion between the main body cylinder and the lid, the rust-proofing is achieved by applying a rust-proof carbon fine particle-based coating material at room temperature.

  According to the present invention, there is provided a spent fuel storage container that can suppress the occurrence of rust at the fitting portion between the lid and the inner cylinder and prevent biting when the lid is opened after long-term storage. it can.

It is a perspective view which shows a general spent fuel storage container. It is a figure equivalent to the AA line cross section of FIG. 1 used as one Example of this invention. It is sectional drawing which shows the fitting part of the lid | cover and inner cylinder of the spent fuel storage container of this invention. It is an expanded sectional view of the fitting part of the lid | cover and inner cylinder of the spent fuel storage container of this invention.

  Before describing an embodiment of the present invention, an outline of a spent fuel storage container will be briefly described with reference to FIG.

FIG. 1 is a perspective view of a part of a spent fuel storage container.
In FIG. 1, a spent fuel storage container 1 is composed of an inner cylinder 2, an outer cylinder 4, and a bottom plate 5 that serve as a fuel storage 1a. A space is formed between the inner cylinder 2 and the outer cylinder 4, and the space is filled with a resin 3 serving as a neutron shield. Similarly, the bottom plate 5 is filled with a bottom resin 3b serving as a neutron shield in the space between the outer plate 5a and the inner plate 5b. A cylindrical top steel plate 7 projects from the upper surface of the outer cylinder 4. The top steel plate 7 extends from the bottom plate 5. Fins 6 (shown in FIG. 2) are provided between the inner cylinder 2 and the outer cylinder 4 so as to cross the resin 3. The fins 6 transmit heat from the inner cylinder 2 to the outer cylinder 4 and also serve as a reinforcing material for the space filled with the resin 3.

  Reference numeral 8 denotes a lid for closing the upper opening of the spent fuel storage container 1. The lid 8 is composed of a primary lid 8a and a secondary lid 8b. A space is formed inside the primary lid 8a, and the inside thereof is filled with a lid resin 3a serving as a neutron shield. The spent fuel storage container 1 is stored in the spent fuel storage pool for a predetermined cooling period.

  However, as described above, when the spent fuel storage container 1 storing the spent fuel is stored and stored for a long time, the primary lid or the secondary lid and the fitting portion of the inner cylinder 2 of the spent fuel storage container 1 are fitted. Corrosion may occur. If corrosion occurs, it may be difficult to open the lid 8 again after storage.

  Therefore, the inventors of the present invention have considered that the contact portion between the lid and the inner cylinder is subjected to rust prevention treatment.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

FIG. 2 is a cross-sectional view of the spent fuel storage container taken along the line AA (in FIG. 2, the partial cutout of FIG. 1 is deleted).
FIG. 3 is a longitudinal sectional view of a spent fuel storage container showing a fitting portion with the lid.
In FIG. 1, carbon fine particles are coated on the side surfaces of the primary lid 8a and the secondary lid 8b and the edges of the bottom surface of the lid. Further, the coating process is similarly performed on the portions of the inner cylinder 2 facing the side surfaces of the primary lid 8a and the secondary lid 8b and the edge surface of the lid bottom surface. At this time, it is preferable that the peripheral portion of the application surface is masked in advance so that no excessive coating material is attached.

  The application work may be performed by brushing or spraying. The number of times of coating or the spraying time per unit area is determined in advance, and the coating thickness is managed. For example, it should be 0.1 mm or less. Thereafter, the organic solvent is removed by drying at room temperature. After confirming that there is no coating unevenness by visual inspection, remove the masking and complete the construction.

FIG. 4 is an enlarged cross-sectional view of the fitting portion of the lid and the inner cylinder of the spent fuel storage container of the present invention.
In FIG. 4, the lid 8 is separated into a primary lid 8a and a secondary lid 8b. The primary lid 8 a is fixed to the top steel plate 7 with primary lid bolts 9. The secondary lid 8 b is fixed to the top steel plate 7 with secondary lid bolts 10. Reference numeral 12 denotes a metal gasket in which the primary lid 8a and the secondary lid 8b are sealed against the top steel plate 7, respectively. Reference numeral 11 denotes a rust preventive film treated on the top steel plate 7 side or at least one of the primary lid 8a and the secondary lid 8b.

  By applying this rust preventive film, corrosion of the fitting portion between the primary lid or the secondary lid and the inner cylinder can be prevented, so that the lid can be prevented from being opened.

  When the cask 1 is subjected to a rust prevention treatment around the fitting portion between the secondary lid and the inner cylinder 2 rather than the primary lid, various methods can be considered as the rust prevention treatment. The following requirements must be satisfied from the viewpoint of application.

  Since this part is close to the sealing part of the metal gasket, the sealing part of the secondary lid and the inner cylinder 2 is subjected to precise machining in order to exhibit the performance of the metal gasket. For this reason, it is necessary to avoid the thermal effect on this part during the rust prevention treatment, and a method of rust prevention treatment at room temperature, which is not thermal spraying, is desirable.

  Further, from the viewpoint of cost, it is important that construction can be easily performed without using a special device. From the viewpoint of construction management, it is desirable that the range to be rust-proofed can be easily managed. Furthermore, it is essential that the antirust effect is stable for a long period of time even in a high temperature and radiation environment.

  From the above, rust prevention treatment with an inorganic rust prevention paint is preferred, but an example of an inorganic rust prevention paint is rust prevention treatment using a coating material mainly composed of carbon fine particles. This coating material is applied in such a manner that fine particles of graphite or carbon are dispersed in an organic solvent, and the organic solvent is volatilized to form a coating. It can be easily applied by brushing or spraying at room temperature. It is easy to adjust the thickness of the coating, and even if it is applied outside the application area, it can be easily removed with alcohol or the like, so that the construction management is easy.

  Furthermore, according to the tests conducted by the inventors of the present invention, the coating is excellent in heat resistance and radiation resistance, and it is significantly altered even when heating at a temperature exceeding 200 ° C. or irradiation with γ rays. There is no. Based on the test results, it was evaluated that the rust prevention function would not deteriorate during long-term storage when applied to the relevant part of the metal cask. As an inorganic coating material other than the carbon fine particle-based coating material, an aluminum-based coating material such as a zinc dust-based coating material or an aluminum phosphate film can be applied.

  As described above, the inventors of the present invention apply an inorganic coating material such as carbon fine particles that can be applied at room temperature to the side surface on the outer side of the primary lid and the secondary lid, and to the portion of the inner cylinder facing the fitting portion. It is intended to be constructed.

  As described above, according to the present invention, rust generation at the fitting portion of the lid and the inner cylinder is suppressed, and the rust prevention treatment can be easily performed at room temperature without using a special device.

  DESCRIPTION OF SYMBOLS 1 ... Used fuel storage container main body, 1a ... Fuel storage part, 2 ... Inner cylinder, 3 ... Resin, 3a ... Lid resin, 3b ... Bottom resin, 4 ... -Outer cylinder, 5 ... bottom plate, 5a ... inner plate, 5b ... outer plate, 6 ... fin, 7 ... top steel plate, 8 ... lid, 8a ... primary lid, 8b ... secondary lid, 9 ... primary lid, 10 ... secondary lid bolt, 11 ... rust preventive film, 12 ... metal gasket.

Claims (4)

In a spent fuel storage container that seals the inside of the main body cylinder by attaching an opening part on the upper part of the cylindrical main body cylinder and a plurality of lids such as a primary lid and a secondary lid to the opening part,
A spent fuel storage container, wherein a fitting portion between the main body body and the lid is subjected to rust prevention treatment. The spent fuel storage container according to claim 1,
A spent fuel storage container, wherein the rust prevention treatment is performed by applying an inorganic coating material at room temperature. The spent fuel storage container according to claim 2,
The spent fuel storage container, wherein the inorganic coating material is an inorganic coating material such as carbon fine particles or zinc fine particles. An opening provided on an upper portion of a cylindrical main body, and the main body cylinder of the spent fuel storage container that seals the inside of the main body cylinder by attaching a plurality of lids such as a primary lid and a secondary lid to the opening; and In the rust prevention method to rust the fitting part with the lid,
The rust prevention method is a rust prevention treatment method characterized in that a rust prevention carbon fine particle coating material is applied at room temperature.

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