The method of packaging of spent nuclear fuel

 

(57) Abstract:

The inventive method includes loading of spent nuclear fuel (SNF) through the spacer elements in the container from corrosion resistant metal, welded to the container top cover, heating the container, fill SNF molten low-melting metal and holding solidification of the melt. Loading spent fuel is carried out by filling the greater part of the free space in the container massive elements of the fusible metal. Fill the spent fuel is carried out at the fusion of these elements directly in the container. The technical effect is to reduce the release of radioactive substances from the spent fuel in the exercise of its packaging. 6 C.p. f-crystals, 4 Il.

The invention relates to nuclear technology and can be used for packaging of spent nuclear fuel for its transportation and/or long-term storage.

There is a method of storing cassettes containing spent nuclear fuel (hereinafter - the spent fuel in cooling pools under a layer of water.

The disadvantage of this method is the high probability of release of radionuclides due to the relatively high speed corros does not exceed several tens of years after the cartridges have been removed from a nuclear reactor [1].

There is a method of dry spent fuel storage by placing it (after soaking for several years in water) in a thick-walled concrete or metal containers filled with inert gas [2].

The disadvantage of this method is not sufficiently effective heat removal from the surface of structural elements tapes, high temperature heating and, consequently, a relatively high rate of corrosion of the fuel cladding. Therefore, the method does not allow for safe storage of SNF in a long time (over 100 years) and cannot prevent the selection of radionuclides from spent nuclear fuel. In addition, the implementation of the method in most cases is only possible with the implementation of the forced ventilation of the container, which further reduces the reliability of spent fuel storage.

There is a method of packaging containing SNF cassettes or bundles of fuel rods by placing them with the spacer elements in the thin-walled container made of corrosion resistant metal, welding to the container top cover with holes for pouring molten metal and ventilation, heat the container with spent fuel, fill the container through the top opening of molten lead or fusible alloy is the introduction of the operation of the current and final control of tightness of the container of spent nuclear fuel [3, 4]. This method is the closest to the invention on the achieved result and the technical nature.

The advantage of this method is the increased reliability of long-term storage of SNF at the expense of creating additional highly effective corrosion barrier between the SNF and the environment, ensure the retention of radioactive products inside the container, the weakening of the radiation from the spent fuel efficiency of cooling of spent fuel, as well as the possible use of the method not only for long-term storage, but also for transportation of spent fuel.

The disadvantages of this method are the high probability of leaks in the fuel cladding by heating them in the process of pouring the melt or in preparation for filling and release significant amounts of radioactive gases into the gas purification system or in the environment, as well as the multistage and the complexity of the process of filling the container.

The aim of the invention is to reduce the likelihood of leaks in the fuel cladding and the reduction of the release of radioactive substances from the spent fuel in the exercise of its packaging.

This objective is achieved in that in the known method of packaging of spent fuel (including downloading the soda is korrozionnostojkoj metal, welding to the container top lid, heat the container with spent fuel, fill the spent molten metal holding solidification of the melt in the container and sealing the container with SNF) when loading the container it is additionally put massive elements of a low-melting metal and pouring SNF molten metal is carried out by melting these massive elements when they are heated in the container.

In one of the private options of how this goal is achieved by the fact that the massive melting of the elements in the container is carried out after the welding of the lid and the complete sealing of the container.

Another private variant of the method in the container place additional material, is made of metal more fusible than the massive metal elements, and fill the spent fuel is carried out at the melting of this additional material. In this embodiment, the additional material may be placed in the lower part of the container, and the melting of the additional element and the melt flow in the gas cavity in the area of spent fuel in the container is accompanied by the movement of massive elements and SNF from top to bottom. In this embodiment, the SPO is not placing the spent fuel in the container. In this variant of the method after fusion of the additional element and fill SNF spending massive melting and homogenization of the melt.

Another private variant of the method after solidification of the melt spend depressurization gas cavity in the upper part of the container and filling it with molten lead or an alloy based on it.

Another private variant of the method in the upper part of the container place getter to absorb radioactive and/or chemically active gases.

The essence of the invention lies in the fact that the fill SNF molten metal is carried out by melting pre-placed in the container massive elements of the fusible metal, such as lead or an alloy based on it. This raises the opportunity to spend a fill with a minimum release of radioactive elements from spent fuel and prevareni the lid of the container, i.e., without the release of radioactive substances into the environment. To ensure a complete fill of SNF massive amount of items loaded in a container, choose with regard to full fill SNF and fill all gaps and voids in the area of the spent fuel inside the container. Using the basic blocks of material, there is a possibility to significantly reduce the temperature of the fill SNF and even more to reduce the disclosure of damaged membranes and the release of radioactive substances outside the SNF and the volume of the container.

In Fig. 1 shows a longitudinal section of a filled container with welded lid before heating to melt blocks of lead or alloy on the basis of Fig. 2 is a longitudinal section of the container after melting the blocks and fill the SNF; Fig. 3 is a longitudinal section of a filled container with welded lid before heating to melt additional element placed at the bottom of the container; Fig. 4 is a longitudinal section of the container after the melting of the additional element and fill the SNF.

Example 1. In a container, comprising (see Fig. 1) of the cylindrical shell 1 and welded to the bottom part 2, download SNF 3 in the form of bundles of fuel elements and solid elements 4 and 5 are executed, respectively, in the form of a cylindrical ingot with 4 cavities for placement of spent fuel and fasteners - continuousy elements 7 and the bottom plate 5. The container 1 and 2 are made of corrosion-resistant alloy 06X18H10T and massive elements 4 and 5 are made of lead brand C2, which contains Myung is carried out with the help of structural elements, performed, respectively, in the form of a base plate 6 and centrifuge-fastening elements 7. After loading of spent fuel and solid elements in the container, it is sealed by welding thereto of a cover 8 made of a corrosion resistant alloy. The container is placed in a heating furnace and conducting heating the surface to a temperature of 350oC. In the heating process massive elements 4 and 5 is melting and filling a molten metal gas cavities and gaps 9 and pouring the melt of the gaps between the elements of the SNF. Elements SNF refrain from surfacing using clamps (not shown). After melting and casting the melt SNF, the container is cooled and carry out the crystallization of the melt with the formation in the upper part of the container of the gas cavity (see Fig. 1). In the gas cavity may be placed getter to absorb corrosive and radioactive gases (not shown).

Example 2. In a container, comprising (see Fig. 2) of the cylindrical shell 1 and welded to the bottom part 2, download SNF 3 in the form of bundles of fuel elements and solid elements 4 and 5. Massive element 4 is made in the form of a cylindrical ingot 4 with cavities to accommodate SNF 3 and the fixing - centering elements 7. E is fusible, than the massive metal elements. The amount of the additional element is selected such that when it is melting, you could fill all gas cavity in the area of the spent fuel in the container. The container 1 and 2 are made of corrosion-resistant alloy 06X18H10T, massive elements 4 and 5 are made of lead brand C2 (contains not less than 99.9% Pb and has a melting point 327,4oC) and the secondary element 6 is made from an alloy of low melting eutectic of 44.5%Pb - 55.5%of Bi with a melting point 123,5oC. Loading and placement of SNF 3, items 4, 5 and 6 in the container 1 and 2 is carried out with the help of structural elements, made, respectively, in the form of a support plate 7 and centrifuge-fastening elements 8. After loading the SNF and massive elements 4, 5 and additional element in the container, it is sealed by welding thereto of a cover 9 made of a corrosion resistant alloy. The container is placed in a heating furnace and conducting heating the surface to a temperature of approximately 130oC. In the heating process additional element 6 is melting and filling a molten metal gas cavities and gaps 10 and 11, and pouring the melt of the gaps between the elements of the SNF. In the process of fusion will complement and massive elements 4 from top to bottom. Elements SNF refrain from surfacing special screws which are not shown in Fig. 2, 3, 4. After melting and casting the melt SNF, the container is cooled and carry out the crystallization of the melt with the formation in the upper part of the container of the gas cavity (see Fig. 4). In the gas cavity may be placed getter to absorb corrosive and radioactive gases (not shown).

Example 3. Conduct loading SNF 3 and massive elements 4 and 5 in the container as in example 1 (see Fig. 1). Welded to the container lid, equipped with a sealed tube. Spend pouring molten SNF as in example 1 and the crystallization of the melt. After solidification of the melt nozzle connected to the gas treatment system and conduct its depressurization, and then through the pipe are filled with molten lead gas cavity 10 (see Fig. 2). After a full or partial fill cavity 10 melt conduct its crystallization and seal the pipe.

Using the proposed method can improve the reliability of long-term storage of SNF at the expense of creating additional highly effective corrosion barrier between the SNF and the environment, to provide a hold of the SNF, and also allows you to use not only for long-term storage, but also for transportation of spent fuel. Furthermore, the method can significantly reduce the likelihood of leaks in the fuel cladding by heating them in the process of pouring the melt or in preparation for filling and release significant amounts of radioactive gases into the gas purification system or in the environment. The method also allows to significantly simplify the process of filling the spent fuel melt.

Sources of information

1. Tikhonov N. S. and others About the status of the storage of spent fuel. The second interdisciplinary conference on the problem of storage and transportation of processed nuclear fuel. Leningrad, October 1990, S. 23-26.

2. Nuclear Europe Worldscan, N 3,4 - 1990, p.36.

3. Second interim assessment of the Canad. conceptfor Nucl.fuel waste disposal, AECL-8373-2, 1984.

4. International Symposium on Sptnt Fuel Storage Safety Engineering and Environmental Aspects. Velyukhanov V. P., Ioltukhovsky A. G., Polykov A. C. and others. Concept of long-term safe storage of RBMK Leaky Spent Fuel in Metal Matrix. Vienna, 10-14 October, 1994.

1. The method of packaging of spent nuclear fuel (SNF), including its load by using the spacer elements in the container from corrosion resistant metal, welded to the container upper cover characterized in that what a load of spent fuel is carried out by filling the greater part of the free space in the container massive elements of the fusible metal, and fill the spent fuel is carried out at the fusion of these elements directly in the container.

2. The method according to p. 1, characterized in that as the fusible metal for massive items use a lead or an alloy based on it.

3. The method according to p. 1, characterized in that the upper part of the container placed a getter to absorb radioactive and/or chemically active gases.

4. The method according to p. 1 or 2, characterized in that the lower part of the container, an additional element is made of a more fusible metal than the metal of massive elements, and fill the spent fuel is carried out at the melting of this additional element and filling formed by melt gas cavities between spent nuclear fuel and solid elements.

5. The method according to p. 4, characterized in that the additional element is selected equal to or greater than the amount of gas cavities in the container in the area of the spent fuel.

6. The method according to p. 4 or 5, characterized in that after deposition of additional elements, ASS="ptx2">

7. The method according to p. 4, characterized in that the solid elements made of lead, and an additional element from an alloy based on it.

 

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