JP2007064899A - Processing method for spent nuclear fuel container - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a processing method of spent nuclear fuel container capable of suppressing hydrogen gas generated during containing spent nuclear fuel in a basket of the spent nuclear fuel container called a cask, with a low cost and simple method. <P>SOLUTION: The processing method of a basket 5 made of aluminium alloy has a plurality of containing rooms 5a arranged in the containing space 2 of a cask 1 for containing spent nuclear fuel. In the method, after injecting ion exchanging water in the containing space 2, an electric heater 12 is arranged in the specific containing room 5a and the spent fuel is heated in 60 to 90°C range for at least one hour. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for treating spent nuclear fuel containers.

  Spent nuclear fuel generated at nuclear power plants, etc. is stored in storage facilities such as a spent nuclear fuel storage pool as it is, but due to its limited storage capacity, spent nuclear fuel is stored intermediately at regular intervals. It is necessary to transfer to facilities and reprocessing facilities.

During this transfer, the spent nuclear fuel is accommodated in a spent nuclear fuel container called a cask and transferred to an intermediate storage facility, a reprocessing facility, or the like.
The casks include those for transportation, storage, and transportation / storage. The storage space provided in the cask has a storage called a basket having a large number of storage chambers in which spent nuclear fuel can be stored. Members are arranged, and as a constituent material of the basket, an aluminum alloy having good thermal conductivity and sufficient strength is used (see Patent Document 1 and Patent Document 2).
JP-A-8-29584 Japanese Patent Laid-Open No. 9-159796

By the way, when the spent nuclear fuel is stored in the cask, the cask is immersed in the ion exchange water filled in the storage pool.
For this reason, when the spent nuclear fuel is stored in the cask, if the aluminum alloy, which is a constituent material of the basket, is exposed on the surface as it is, the ions will be ionized for several tens of hours to several days after being immersed in the storage pool. Hydration reaction between exchanged water and aluminum alloy occurs, and hydrogen gas is generated, causing safety problems, and the hydrated aluminum hydroxide floats in the water and the inside of the pool becomes cloudy, reducing workability. Problem arises.

  Conventionally, for such hydrogen gas generation, there were often no particular measures taken, but in order to suppress hydrogen gas generation, when aluminum alloy, which is a constituent material of the basket, is alumite treated, This leads to an increase in the cost of the basket components, and if a part of the coating is peeled off during the processing and assembly of the components, the repair becomes difficult and the generation of hydrogen gas may not be completely suppressed. It was.

  Accordingly, the present invention provides a method for treating a spent nuclear fuel container that can suppress hydrogen gas generated when the spent nuclear fuel is contained in a spent nuclear fuel container basket called a cask in a simple and low-cost manner. The purpose is to provide.

In order to solve the above-mentioned problems, a processing method of a spent nuclear fuel container according to the present invention is a treatment of an aluminum alloy basket having a plurality of storage chambers that are disposed in a storage space of a spent nuclear fuel container and store spent nuclear fuel. A method,
After injecting ion-exchanged water into the housing space, the ion-exchanged water is heated.
In addition, the heating means disposed in the storage chamber is used when the ion exchange water is heated.

  Furthermore, it is a method which makes heating temperature the range of 60-90 degreeC in the case of heating of ion-exchange water.

  According to the above processing method, a protective coating is formed on the surface of the aluminum alloy basket simply by filling the ion exchange water and heating with the heating means, so the spent nuclear fuel container is immersed in the ion exchange water in the storage pool. In this case, almost no hydration reaction takes place, that is, almost no hydrogen gas and hydrate are generated. Therefore, it is safe and easy to load spent nuclear fuel in the storage pool. It can be done by simple processing.

[Embodiment]
Hereinafter, the processing method of the spent nuclear fuel container which concerns on embodiment of this invention is demonstrated.
First, a schematic configuration of the spent nuclear fuel container will be described with reference to FIGS.

  The spent nuclear fuel container (hereinafter referred to as a cask) 1 generally includes a bottomed cylindrical cask body 4 having a cylindrical storage space 2 and a plurality of cooling fins 3 provided on the surface thereof, and the cask. A basket 5 made of an aluminum alloy in which a large number of storage chambers 5a are formed that can be accommodated in the accommodating space 2 of the main body 4 and can store a large number of spent nuclear fuel rod assemblies (prism-like columns); It is composed of

  Then, in the final assembly stage, as shown in FIG. 4, the basket 5 is assembled into the accommodating space 2 of the cask main body 4, and after this incorporation is completed, the processing according to the present invention is performed.

Hereinafter, the processing method of the cask 1, especially the basket will be described.
First, as shown in FIG. 5, deionized ion-exchanged water (also referred to as deionized water) is poured into the cask body 4 with the basket 5 incorporated in the accommodation space 2 until it is full. To do.

  Next, as shown in FIG. 6 to FIG. 7, for example, four storage chambers (only three are shown in the drawing) are included in the storage chamber at an appropriate location among the multiple storage chambers 5 a of the basket 5. An electric heater (an example of a heating means) 12 connected to the power source 11 is arranged in 5a, and heated with a heat amount (for example, about 17 kW, about 90 ° C. as a heating temperature) of the design heat generation amount in the cask. .

  As this electric heater 12, for example, a ceramic heating element (element) arranged in a sheath formed of a stainless steel pipe is used, and its length is the length of the heating part of the fuel assembly. Is almost equal to

  During this heating, the storage chamber 5a whose temperature is likely to be lowered is selected, and thermometers are arranged at appropriate multiple locations (for example, four locations such as the bottom, the top, and the middle) inside the ion exchange water. Measure the temperature (hereinafter referred to as water temperature).

And heating is continued for at least 1 hour from the time of the value of the thermometer which shows the minimum temperature among the thermometers arrange | positioned in multiple places exceeding 90 degreeC, for example.
By the way, since the movement of water in the basket 5 is performed only at the bottom of the storage chamber 5a and the vicinity of the upper end opening, the heat transfer between the adjacent storage chambers 5a is conducted through the basket 5 itself. Will be done. Of course, the heat transfer in the storage chamber 5a is performed by convection. Overall, the heat from the storage chamber 5a in which the electric heater 12 is disposed spreads slowly due to heat transfer.

Therefore, when the water temperature in the storage chamber 5a having the lowest temperature (or seems to be low) exceeds 90 ° C., it means that the entire water temperature of the basket 5 has exceeded 90 ° C.
When heated at this temperature for a predetermined time or at 90 ° C. for 1 hour or longer, a protective coating called boehmite is formed on the surface of the basket 5, that is, the surface of aluminum, and the surface is protected.

After 1 hour, the electric heater 12 is turned off and cooled by natural heat dissipation.
The hydrogen gas generated during the temperature rise is forcibly ventilated so that the hydrogen gas does not stay.

After cooling, the ion exchange water may be discharged and the inside may be dried.
As described above, since the protective coating is formed on the surface of the basket 5 made of aluminum alloy only by filling the ion exchange water and heating to a predetermined temperature by the electric heater 12, the cask 1 is replaced with the ion exchange water in the storage pool. Even when immersed in the storage pool, there is almost no hydration reaction, that is, almost no generation of hydrogen gas and hydrates, so that the spent nuclear fuel can be loaded safely and easily in the storage pool. It can be performed by an inexpensive process.

By the way, when the heating temperature is a little low, for example, even at 60 ° C., the same effect as that at 90 ° C. can be obtained, but the heating time requires a considerably long time.
In the graph of FIG. 8, the integrated generation amount of hydrogen gas generated according to the heating time is shown for the cases of 90 ° C. and 60 ° C.

  From the graph of FIG. 8, it can be seen that at 90 ° C., when the heating time is about 1 hour or longer, the amount of generated hydrogen gas is greatly reduced, and after 30 hours, the hydrogen gas is not generated. Moreover, in the case of 60 degreeC, when the heating time passes for about 30 hours or more, it turns out that the generation amount of hydrogen gas begins to fall, and when 70 hours pass, there will be almost no generation | occurrence | production of hydrogen gas.

  Further, in the graph of FIG. 9, when the heating temperature is 30 ° C., 60 ° C., 90 ° C., when immersed in ion-exchanged water heated to 60 ° C. and 90 ° C., respectively, for 168 hours, for example. Indicates the cumulative amount of hydrogen gas generated.

  From the graph of FIG. 9, in the case of 30 ° C., it can be seen that the formation of the protective film of aluminum is not sufficient and hydrogen gas is generated, and at 60 ° C. and 90 ° C., that is, 60 ° C. to 90 ° C. In the range, the formation of a protective film of aluminum is sufficiently performed, so that almost no generation of hydrogen gas is observed.

  From these results, the generation amount of hydrogen gas is so small that it is processed at a high temperature, that is, if it is heated at 90 ° C. or higher for 1 hour or longer (preferably 30 hours or longer), it can be immersed in heated water thereafter. It was found that the generation of hydrogen gas can be suppressed. Further, it has been found that if the treatment is performed at 60 ° C. or higher for a long time (for example, 30 hours or longer, preferably 70 hours or longer), the generation of hydrogen gas can be suppressed even if the substrate is immersed in heated water. In addition, although intermediate temperatures such as 70 ° C. and 80 ° C. were not described, naturally, by performing the treatment with a time between them (about 1 to 30 hours, preferably about 30 to 70 hours), Generation of gas can be suppressed. In addition, when ion-exchanged water boils, bubbles generated by boiling cause erosion of the protective coating on the aluminum surface, and a treatment with a large amount of water vapor (sealing of the container, etc.) is required, which is not preferable.

According to the processing method described above, the following effects can be obtained.
Since the above processing is performed after the basket and the cask main body are completed, no special consideration is required for the surface state during assembly, and the manufacture of the cask is facilitated.

  The only members required for this treatment are ion-exchanged water and an electric heater, and the ion-exchanged water is easily available, and the electric heater is used for a heat transfer test performed when the cask is completed. Can be used, and does not require special preparation.

In addition, since the ion-exchanged water after treatment has no composition change, it can be reused as it is, and no special treatment is required even when it is discarded.
By the way, in the said embodiment, although the long pipe-shaped thing of about 4.5 m was used as the electric heater 12, for example, about 1 m is submerged in the bottom part of the storage chamber 5a, is heated, and ion-exchange water is used. The entire storage chamber 5a may be heated by convection. In this case as well, the ion exchange water in the other storage chamber 5a where no electric heater is arranged is heated by the heat transfer of the basket 5 itself.

  Moreover, in the said embodiment, although the electric heater 12 has been arrange | positioned in the storage chamber 5a of the basket 5 as a heating means, while arrange | positioning an electric heater outside, ion-exchange water is supplied to this electric heater and the storage chamber 5a. It is also possible to heat by circulating between them. Further, high temperature steam (evaporated ion exchange water) may be used in place of the electric heater, and more specifically, the basket 5 may be filled with high temperature steam.

  Furthermore, in the above embodiment, the basket itself has been described as being processed. However, when an aluminum alloy is used for the inner wall surface of the accommodating space 2 of the cask main body 4, the inner wall surface of the accommodating space 2 is used. By performing the same process as that of the basket 5 described above, the generation of hydrogen gas on the cask body 4 side can be suppressed. When heating at least the inner wall surface of the cask main body 4, the same method as the heating method for the basket 5 described in the above embodiment may be used. That is, when the ion exchange water is heated, the cask main body 4 simultaneously with the basket 5 is used. The inner wall surface can also be heated to a predetermined temperature.

It is a schematic sectional drawing of the spent nuclear fuel container to which the processing method concerning an embodiment of the invention is applied. It is a schematic sectional drawing of the basket arrange | positioned in the used nuclear fuel container. It is a schematic plan view of the basket arrange | positioned in the used nuclear fuel container. It is a schematic sectional drawing which shows the procedure of incorporating a basket in the spent nuclear fuel container. It is a schematic sectional drawing explaining the processing method which concerns on embodiment of this invention. It is a schematic sectional drawing explaining the processing method. It is a schematic sectional drawing explaining the processing method. It is a graph which shows the relationship between the heating time for demonstrating the effect by the processing method, and the integrated generation amount of hydrogen gas. It is a graph which shows the relationship between the immersion time after heat processing for demonstrating the effect by the processing method, and the integrated generation amount of hydrogen gas.

Explanation of symbols

1 Spent nuclear fuel container (cask)
2 Storage space 4 Cask body 5 Basket 5a Storage chamber 12 Electric heater

Claims (3)

A method for treating an aluminum alloy basket having a plurality of storage chambers for storing spent nuclear fuel, which is disposed in a storage space of a spent nuclear fuel container,
A method for treating a spent nuclear fuel container, wherein ion-exchanged water is injected into the housing space and then the ion-exchanged water is heated.   The method for treating a spent nuclear fuel container according to claim 1, wherein heating means disposed in the storage chamber is used for heating the ion exchange water. The method for treating a spent nuclear fuel container according to claim 1 or 2, wherein the ion-exchanged water is heated in a range of 60 to 90 ° C.

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