RU2711078C1 - Dual-purpose container for transportation and storage of spent nuclear fuel - Google Patents

Abstract

FIELD: nuclear energy.SUBSTANCE: dual-purpose container for transportation and storage of spent nuclear fuel includes cast housing, neutron protection. Wall of cast housing is filled with solid-wall-forming neutron-protective barrier from material with melting point higher than melting temperature of material of housing, coefficient of thermal conductivity higher than that of cast housing material, density lower than that of cast housing material, capable of slowing and absorption of neutrons. In neutron-protective barrier there are longitudinal channels, longitudinal channels are filled with material characterized by shorter free path of fast neutrons than material of neutron-protective barrier.EFFECT: invention increases fabricability of production, reduces weight of liquid cast iron.5 cl, 1 tbl, 9 dwg

Description

The invention can be used in nuclear energy for transportation and temporary storage of spent nuclear fuel and other radioactive materials.

Cases of containers for transportation and storage of spent nuclear fuel, made of ductile iron (ductile iron), are usually cylindrical in shape and of considerable size. For example, the TUK 141O container has a maximum container diameter of 2390 mm, a maximum dimension for cargo trunnions of 2430 mm, a height of 5860 mm, a wall thickness of the container body of about 500 mm, a loaded container weighs 112,000 kg, an unloaded container weighs 98,000 kg [Romanova C Packed fuel in a new thing // Atomic Expert, No. 7 (58), 2017. URL: atomicexpert.com/page1776738.html]. To ensure radiation safety of transportation, inserts of neutron-protective material are built into the wall of the cylindrical body, which protect the environment and maintenance personnel from neutron radiation. Also, the container body must provide good heat dissipation to prevent overheating of the contents of the container, which can lead to the launch of a spontaneous nuclear reaction.

Currently, the designs of industrially produced containers operated as part of transport and packaging sets require increasing the manufacturability of the design to reduce the complexity of the work in their manufacture and assembly. In this case, additional complexity is caused by the need to ensure the requirements for radiation protection and heat transfer characteristics that comply with the IAEA requirements.

A known container for transporting and storing radioactive waste of nuclear power plants, containing a two-layer shell made of materials with different coefficients of thermal expansion, between which an additional sectional intermediate layer is introduced, in the sections of which there are through holes filled with neutron protection material [Description of the invention to patent RU 2054205] .

A disadvantage of the known container is the complexity of the manufacture and installation of an additional intermediate layer consisting of sections having through holes filled with neutron protection material.

A known container for transporting and / or storing spent nuclear fuel, comprising a metal housing including a bottom, outer and inner cylindrical shells, the cavity between which is filled with material for neutron absorption. Elements with high thermal conductivity, made in the form of radial longitudinal sheet elements, which are attached to the outer and inner cylindrical shells of the housing with compression by means of threaded elements, are passed through the neutron absorption material. Radial longitudinal sheet elements have through holes and / or discontinuous edges with the formation of recesses [Description of the invention to patent RU 2348085].

A disadvantage of the known container is the difficulty of mounting elements with high thermal conductivity passing through the material for neutron absorption during Assembly of the container.

A known container for transporting and / or storage of spent nuclear fuel containing metal inner and outer cylindrical shells with bottoms, the cavity between which is filled with heavy concrete [Description of the invention to patent RU 2084975].

A disadvantage of the known container is the high complexity of filling the cavity between the shells and the reinforcement with heavy concrete, as well as the thermal conductivity of concrete insufficient for highly active fuel.

A known construction of a container for storing radioactive materials (Radioactive material storage container) consisting of two coaxial inner and outer cylinders, which are interconnected by jumpers that act as heat-removing elements, the spaces formed in this case are filled with neutron-absorbing material. Jumpers are attached to the cylinders by means of a welded joint [Description of the invention to JP 2008082906].

A disadvantage of the known container design is the need for a welding operation to connect the jumpers. In addition, it is possible that fast neutrons can enter the environment through heat-removing elements connecting the outer and inner shells and passing through the neutron-absorbing material.

The closest in nature and taken as a prototype is the well-known TUK 141O container [Romanova S. Packed the fuel in a new thing // Atomic Expert, No. 7 (58), 2017. URL: atomicexpert.com/page1776738.html] including a housing made of high-strength cast iron with spherical graphite, stainless steel and boron steel case. In the walls of the housing on concentric diameters in a checkerboard pattern, with displacement in the radial and angular directions, so that they overlap along the radial lines, two rows of longitudinal blind holes are made by machining. These holes are filled with rods of solid neutron protective material (polyethylene), which provides neutron protection, which is an integral part of the radiation protection of the container. The remaining jumpers between the holes provide heat removal from the cover to the outer surface of the device.

A disadvantage of the known container TUK 141O using fuel assemblies (FA) with an increased level of burnout and initial enrichment is the low adaptability of its design, due to the complexity of its manufacture. In view of the fact that the material of the case does not provide adequate protection against neutron radiation, holes have to be made to accommodate the neutron protection with staggered arrangement in two rows on concentric diameters. This is required to exclude the possibility of a "direct backbone" of neutrons. The manufacture of holes by deep drilling (up to several meters) with their indicated location in high-strength cast iron is a very difficult technological operation of machining. In addition, increasing fuel activity leads to the need to increase the diameter of the holes and, accordingly, the wall thickness of the housing. And due to the limited maximum overall size of the container, the characteristics of the technological equipment used when handling it, an increase in wall thickness will lead to a decrease in the internal net volume in which the cover with heat-generating assemblies is located.

The technical result of the proposed dual-purpose container for transportation and storage of spent nuclear fuel is to increase the manufacturability of production, reduce the mass of molten iron required for the manufacture of casting the housing, improve the degree of neutron protection and heat transfer characteristics without increasing overall dimensions, wall thickness of the housing.

The technical result is achieved by the fact that in a dual-purpose container for transporting and storing spent nuclear fuel, including a molded case, neutron protection, a neutron-protective barrier of a material with a melting temperature higher than the melting temperature of the case material and a large thermal conductivity coefficient is poured into the wall of the cast body. than the material of the molded case, the density is lower than that of the material of the molded case, which has the ability to slow down and absorb neutrons into neutrons longitudinal channels are made of the o-protective barrier, longitudinal channels are filled with material characterized by a shorter mean free path of fast neutrons than the material of the neutron-protective barrier.

In FIG. 1 is a sectional view of a dual-purpose container for transporting and storing spent nuclear fuel.

In FIG. 2 shows a section AA of a dual-purpose container for transporting and storing spent nuclear fuel.

In FIG. Figure 3 shows type B of a dual-purpose container for transporting and storing spent nuclear fuel in which the longitudinal channels in the neutron-protective barrier are made by machining by drilling.

In FIG. Figure 4 shows type B of a dual-purpose container for transporting and storing spent nuclear fuel in which the longitudinal channels in the neutron-protective barrier are formed by metal pipes.

In FIG. 5 shows a mold for manufacturing a casting of a body of a dual-purpose container for transporting and storing spent nuclear fuel.

In FIG. 6 shows a view In a mold for manufacturing a casting of a body of a dual purpose container for transporting and storing spent nuclear fuel.

In FIG. 7 shows a case for a dual-purpose container for transporting and storing spent nuclear fuel in axial section.

In FIG. 8 is a cross-sectional view of a GH cover for a dual-purpose container for transporting and storing spent nuclear fuel.

In FIG. 9 is a view D of a case for a dual-purpose container for transporting and storing spent nuclear fuel.

The housing 1 of a dual-purpose container for transporting and storing spent nuclear fuel is cast. As a material for the manufacture of a cast body, for example, high-strength spheroidal cast iron, which has proven itself for these purposes, can be used. Case 7 is installed inside the molded case. Case 7 is used to accommodate fuel assemblies with spent nuclear fuel.

A neutron-protective barrier of material with a melting temperature higher than the melting temperature of the material of the molded body, a thermal conductivity coefficient greater than that of the material of the molded body and lower density than the material of the molded body, which has the ability to slow down and absorb neutrons, is poured into the wall of the cast housing 1.

The neutron-protective barrier is made of blocks 2, forming a continuous wall, preventing the free passage of neutrons in radial directions. In this case, the neutron-protective barrier from the blocks 2 is formed in such a way as to ensure, during the manufacture of the molded case 1, jumpers 3 from the material of the case in its bottom part.

Due to the fact that the neutron-protective barrier is not installed along the entire length of the cast housing 1, the integrity and strength of the cast housing 1 is ensured due to its monolithicity in the upper part. The presence of metal jumpers 3 at the level of the bottom of the casting of the body ensures the strength of the molded body of a dual-purpose container for transporting and storing spent nuclear fuel in its bottom.

At present, solid hydrogen-containing materials have been found to be predominantly used as neutron protection for transport and packaging kits for transporting spent nuclear fuel, among which polyethylene and polypropylene have the highest concentration of hydrogen. The disadvantage of materials based on polyethylene and polypropylene is that when exposed to elevated temperatures, they soften and have low thermal conductivity.

The mean free path of fast neutrons in various materials are given in table 1 [Radiation. - Electronic resource. URL: portal.tpu.ru/SHARED/a/ALEXTPUFTF/uchebnye-mat/iinph/Tab1/radiation.pdf].

A comparative analysis of neutron protection from polyethylene and graphite shows that polyethylene slows down neutrons 1.7 times better than pure graphite, but with the addition of graphite in the form of boron and gadolinium, its neutron-protective abilities will increase, reducing the difference in efficiency in compared to polyethylene.

Graphite can be used as a neutron-protective barrier in the design of the cast housing of a dual-purpose container for transporting and storing spent nuclear fuel, a material that has been widely used in thermal neutron reactors as a neutron moderator. Boron-containing (boron) graphite, graphite with the addition of gadolinium, graphite with the addition of boron and gadolinium in a total volume of 0-10%.

The advantages of graphite include a high melting point (3890 ° C, compared to the VChShG - 1200 ° C), high strength, good malleability (density 2.23 g / cm ³ , compared to the VChShG - 7.2 g / cm ³ ), high thermal conductivity and slight thermal expansion. Graphite has a thermal conductivity coefficient (100-354 W / (m * C)) significantly higher than that of nodular cast iron (25-42 W / (m * C)) of which the casing is made. Graphite is a good heat conductor, which will provide improved heat dissipation from the inner surface of the housing to its outer surface.

Boric graphite has good neutron-absorbing properties and low residual activity. Due to the presence of boron, boron graphite has a more perfect structure, increased strength, and better ability to absorb neutrons. Boric graphite is prepared from a mixture of graphite and any boron compound (B4C, B203, etc.). A sheet of boron graphite 2.5 cm thick (with a mass content of boron of up to 4%) weakens the density of the flux of thermal neutrons by 400 times [Protection from ionizing radiation. - Electronic resource. URL: http://zinref.ru/000_uchebniki/05300_tehnika_bezopasnosti/010_00_00_voprosi_dozimetria_nosovski_1998/007.htm].

In atomic engineering, gadolinium has found application for protection against neutron radiation, since this element has the highest ability to capture neutrons from all stable isotopes. Its cross section is 46,000 barn. Of all the gadolinium isotopes, the highest ability to capture neutrons is possessed by its gadolinium-157 isotope (capture cross section exceeds 150,000 barns) [Handbook of a chemist. - Electronic resource. URL: http://chem21.info/page/005059191229237063075030088004015245202249173107/].

The longitudinal channels 18 are made in the neutron-protective barrier 18. The longitudinal channels in the neutron-protective barrier can be made in various ways, for example, by machining by drilling (Fig. 3). Another way to perform longitudinal channels is to install metal pipes 24 (Fig. 4) into the neutron-protective barrier at the stage of its formation in the preparation of the mold.

The longitudinal channels 18 are filled with material characterized by a shorter mean free path of fast neutrons than the material of the neutron-protective barrier. This will enhance the neutron protection efficiency of the cast housing of a dual-purpose container for transporting and storing spent nuclear fuel.

In the proposed design of the cast body of a dual-purpose container for transporting and storing spent nuclear fuel using graphite as a neutron-protective barrier 3, the longitudinal channels 18 can be filled with polyethylene, a material characterized by a shorter fast-neutron mean free path than the material of the neutron-protective barrier ( Table 1).

The proposed invention works as follows.

In the molded case 1 of the dual-purpose container for transporting and storing spent nuclear fuel by press-fit, a cover 7 is installed or a cover 7 is installed on the landing, which provides close contact of the mating surfaces as a result of thermal expansion of the material when loading fuel assemblies with spent nuclear fuel into the container. On the outside, on the bottom of the container, a lid 9 is installed under which the neutron-protective material 8 is preliminarily placed. In the channels of the lid, fuel assemblies are installed, the container is closed with the inner 6 and outer 4 lids forming two airtight barriers, and neutron-protective material is placed between the lids 6 and 4 5.

During operation of the dual-purpose container for transporting and storing spent nuclear fuel, the heat emitted by the fuel assemblies is transferred to the surface of the container body in contact with the case 7 and through the neutron-protective barrier to the outer surface of the container and then transferred to the environment. In this case, the radiation emitted by the fuel assemblies consisting of gamma radiation is delayed by the volume of the HFG, and the neutron radiation is delayed by the neutron-protective barrier in which the longitudinal channels 18 are filled, filled with a material characterized by a shorter free path of fast neutrons than the material of the neutron-protective barrier.

The neutron-protective barrier can be made of blocks 2, tightly laid in relation to each other and forming a continuous wall.

The invention is implemented as follows.

Collect the mold. For this, a pallet 14 is installed on the bottom flask 11. A rod 13 is mounted on the pallet 14, forming a seating surface under the cover of the casting of the body. On the pallet 14 set the lower 15 and upper 16 chill mold. A cover 17 is mounted on top of the chill mold 16.

Blocks 2, for example, of graphite with a neutron absorber, are installed in the mold as cores of the mold, setting them in such a way as to form a continuous wall. At one end, the blocks 2 extend beyond the casting of the casing and pass through the holes in the cover 17. They are fixed at the desired height level, for example, by means of nuts 12. A mold cover 17 with blocks 2 fixed to it is mounted on the top 16 chill mold.

A load 10 is installed on top of the lid 17, preventing the ascent of the blocks 2 due to the buoyancy when filling the mold with a molten metal. Blocks 2 have such a geometric shape that when they are installed in the mold on the landing surface under the cover, they create a solid wall that prevents the free passage of neutrons in radial directions. That part of the blocks 2, which extends beyond the landing surface under the cover and passes through the holes in the cover 17, has a thinning that provides on the one hand the strength of the blocks 2 when they are suspended in the cover 17 and the mold is filled with molten metal, on the other hand, free space between the blocks 2 at the level of the bottom of the casting of the body to enable the filling of this space with a molten metal and the formation of partitions 3, thereby ensuring the strength of the casting.

The mold is filled through the gating system with a molten metal, for example, ductile iron with spherical graphite. As the metal melt cools, the neutron-protective barrier formed by blocks 2 is poured into the casting of the body. The material of the blocks 2 of the neutron-protective barrier does not form a solid wall over the entire casting height, but only at the level of the corresponding landing surface under the cover, so that its integrity and strength are ensured in the upper part of the casting. In the bottom of the casting of the body, the strength is ensured by the presence of jumpers 3.

According to the invention, the design of a molded case of a dual-purpose container for transporting and storing spent nuclear fuel provides an increase in the degree of neutron protection while maintaining the external dimensions of the container body, which is regulated by the requirements for the sizes of container loading places at Russian-designed nuclear power plants.

The improvement of protection against neutron radiation is provided due to the fact that a neutron protective barrier made of a material with the ability to slow down and absorb neutrons is poured into the wall of the molded case. Due to the fact that the neutron-protective barrier is made of a material with the ability to slow down and absorb neutrons, the longitudinal channels in the case are placed in one row, and not two, as in the prototype, this eliminates the “direct” lumbar of the neutrons through the bridges between the longitudinal channels. This circumstance contributes to the increase of neutron protection of the container without increasing the external overall dimensions of the container body, wall thickness compared to the prototype.

The value of the thermal conductivity of the material of which the neutron-protective barrier is made greater than that of the material of the molded case, guarantees improved, in comparison with the prototype, heat dissipation from the inner surface of the body to its outer surface through jumpers between the longitudinal channels 18.

Due to the fact that a part of the wall of the container body will be made of a neutron-protective barrier, the volume, and, consequently, the mass of molten iron required for the manufacture of the casting of the body is reduced.

The melting temperature of the material from which the neutron-protective barrier is made is higher than the temperature, the melting of the body material ensures that when the casting of the body of the dual-purpose container for transportation and storage of spent nuclear fuel is molten, the material from which the neutron-protective barrier is made is molten.

The lower density of the material of the neutron-protective barrier in comparison with the density of the material of the case helps to increase the manufacturability of its manufacture by simplifying the machining operation — manufacturing longitudinal channels 18 by deep drilling.

As a material for the manufacture of a neutron-protective barrier that meets the distinguishing features stated in the claims, graphite with a neutron absorber can be used, for example, boron-containing (boron) graphite, graphite with the addition of gadolinium, graphite with the addition of boron and gadolinium, as well as other additives that improve the ability to absorb neutrons.

The presence of longitudinal channels in the neutron-protective barrier filled with material characterized by a shorter mean free path of fast neutrons than the material of the neutron-protective barrier enhances the effectiveness of protection against neutron radiation. As such a material, a hydrogen-containing material, polyethylene, can be used.

The proposed construction of a dual-purpose container for transportation and storage of spent nuclear fuel will be most effective when the container body is used in combination with a cover of the following design, which is not removable with respect to the container

The case includes a molded case 19 with channels for installing fuel assemblies. The channels are formed by poured profile metal pipes 20 with flat faces. Pipes 20 are mounted in annular rows close to each other with mating along flat faces around the central pipe. The outer surfaces of the mating flat faces of the pipes 20 are lined with copper sheets 21, which provide improved heat dissipation from the pipes 20 to the case body 19. Bottom to the cover by mechanical connection, for example, bolted, a tray 22 is attached with holes located in accordance with the pipes 20. The tray 22 serves as a support for fuel assemblies during operation of the cover and provides the possibility of draining the decontamination solutions during its disinfection. At the upper end of the case there is a lid 23, which in turn is the inner lid of a dual-purpose container for transporting and storing spent nuclear fuel.

Such a cover is installed in a dual-purpose container for transporting and storing spent nuclear fuel by press fit, which ensures tight contact between the mating surfaces of the cover and the container, guaranteeing good heat transfer between them. The presence of a side wall housing cover made of ductile iron with spheroidal graphite, a material with the ability to retain gamma radiation, will improve the radiation protection of a dual-purpose container for transporting and storing spent nuclear fuel from gamma radiation.

The advantages of a dual-purpose container for transporting and storing spent nuclear fuel with a removable cover from the VChShG over the closest analogue of TUK 141O are as follows:

- when using graphite with a neutron absorber content in the design of the neutron protective barrier, improved mechanical properties of the resulting casting of the body are ensured due to the fact that the graphite used as a refrigerator in the manufacture of castings will conditionally divide the cylindrical surface of the casting into two parts - internal and external thereby reducing the wall thickness of the casting, which positively affects the casting process;

- when using graphite with the content of a neutron absorber in the design of the neutron protective barrier poured into the wall of the cast housing of a dual-purpose container for transporting and storing spent nuclear fuel, improved protection against neutron radiation is ensured, the "direct" neutron cross through the bridges between the longitudinal channels is excluded, which makes it possible to reduce the number of longitudinal channels by placing them in one row, and not in two as is done in the closest analogue of TUK 141O;

- a smaller number of longitudinal channels and their drilling not in the VChShG, but in graphite, a material less durable than the VChShG, simplifies the machining, and, consequently, increases the manufacturability of the structure;

- due to the fact that graphite has good thermal conductivity, it provides improved heat removal from the cover with the fuel assemblies located in it to the outer surface of the container body in comparison with the closest analogue of TUK 141O;

- due to the fact that the cover is made of cast iron from a ductile iron, such a container in its design will have a large mass of ductile iron which is larger than that of the TUK 141O analogue, which provides better protection against gamma radiation, which is one of the components of radiation compared with the closest analogue TUK 141O;

- the overall dimensions of the dual-purpose container for transporting and storing spent nuclear fuel meet all the requirements stipulated by the size of the container loading places at Russian-designed nuclear power plants;

- a dual-purpose container for transportation and storage of spent nuclear fuel allows the transportation of spent nuclear fuel of fuel assemblies (FA) with an increased level of burnup and initial enrichment, increased heat generation and is promising for nuclear power plants with VVER-1200, VVER-TOI power units.

Claims (5)

1. A dual-purpose container for transporting and storing spent nuclear fuel, including a molded case, neutron protection, characterized in that a neutron protective barrier made of a material with a melting temperature above the melting temperature of the body material, the thermal conductivity is large, is poured into the wall of the cast body than the material of the cast shell, with a density lower than that of the material of the cast shell, which has the ability to slow down and absorb neutrons, in the neutron-protective barrier The longitudinal channels are filled, the longitudinal channels are filled with material characterized by a shorter mean free path of fast neutrons than the material of the neutron-protective barrier. 2. A dual-purpose container for transporting and storing spent nuclear fuel according to claim 1, characterized in that the neutron protective barrier is made of graphite with a neutron absorber content. 3. A dual-purpose container for transporting and storing spent nuclear fuel according to claim 2, characterized in that the longitudinal channels made in the neutron-protective barrier are filled with polyethylene. 4. A dual-purpose container for transporting and storing spent nuclear fuel according to claim 1, characterized in that the longitudinal channels in the neutron-protective barrier are made by machining by drilling. 5. A dual-purpose container for transporting and storing spent nuclear fuel according to claim 1, characterized in that the longitudinal channels in the neutron-protective barrier are formed by metal pipes.

Images