RU2686476C1 - Container cover for spent nuclear fuel transportation and storage - Google Patents

Abstract

FIELD: nuclear energy.SUBSTANCE: invention relates to devices in which fuel assemblies with spent nuclear fuel are placed during their transportation and storage. Cover of container for transportation and storage of spent nuclear fuel includes cast housing with poured shaped metal tubes with flat faces forming channels for installation of fuel assemblies. Pipes in the jacket are installed with circular rows tightly to each other with conjugation along flat faces around the central pipe. Outer surfaces of conjugated flat tube faces are coated with copper sheets. Space between external surface of pipes of outer annular row and inner surface of cast housing is filled with inserts from neutron-protective material with melting point higher than melting point of material of cast housing. Structure is rigidly fixed due to shrinkage occurring during crystallisation of molten metal at cast cast housing casting.EFFECT: imparting high neutron protective properties to the case while providing improved heat removal from fuel assemblies installed in appropriate channels to the outer surface of the cast housing of the case.1 cl, 4 dwg, 1 tbl

Description

The invention relates to nuclear power engineering, in particular to distance devices, in which fuel assemblies with spent nuclear fuel are placed during their transportation and temporary storage in transport packaging kits (TUK).

A cover is known for housing and storing spent fuel assemblies of a VVER-1000 reactor (description of invention to patent RU 2593388, priority 08/04/2015, published 08/10/2016, bulletin No. 22) containing a central tube, spacer grids with hexagonal tubes. The spacer grids with hexagonal tubes are made in the form of sections fastened together. Each section is made of aluminum alloy and consists of a central tube, two spacer grids with hexagonal holes. Hexagonal tubes are placed in the holes. The pipes have internal hexagonal grooves at the ends. The grooves are fitted with hexagonal rails made of corrosion-resistant steel. The sections are mounted on a base consisting of a spacer support with holes. A clamping device is installed along the axis of the holes from the outside. Bearing pipe is made of corrosion-resistant steel and has an adapter for lifting device.

A disadvantage of the known cover for the placement and storage of spent fuel assemblies of the VVER-1000 reactor is the low manufacturability of the design, due to the many structural elements used, the complexity of their manufacture and the need to ensure high accuracy of their installation. Another disadvantage of the known cover for the placement and storage of spent fuel assemblies of the VVER-1000 reactor is its high cost associated with the complexity of manufacturing.

A well-known construction of a cover for the placement and storage of spent fuel assemblies of the VVER-1000 reactor (description of the invention to patent RU 2453007, declared 04/01/2011, published 10.06.2012) containing a central tube, spacer grids with twenty pipes in which the spent fuel assemblies are placed. The pipes are made in the form of a hexagon and are installed in two annular rows relative to the axis of the central pipe, separated by an intermediate pipe. The pipes in the row are mated with each other by the ribs, and some of the faces on the outside are lined with radiation protection plates.

A disadvantage of the known design of the cover for the placement and storage of spent fuel assemblies of the VVER-1000 reactor is the high complexity of the work, due to the complexity of the design of the cover, namely the need to install spacer grids, using central and intermediate pipes, installing hexagonal tubes with the formation of voids between them. As a result of the proposed arrangement of hexagonal tubes, the contact between adjacent hexagonal tubes is not carried out along its lateral surface, but only along an insignificant part of it, which limits the efficiency of the heat sink. In addition, the construction of a cover for accommodating and storing spent fuel assemblies of the VVER-1000 reactor does not provide protection against neutron radiation, which in turn requires embedding of the transport and packaging set of neutron protection into the container body, which leads to an increase in the wall thickness of the container body, and therefore and its diametral size.

A known design of the transport packaging for transporting and storing spent nuclear fuel (Description of the utility model to the patent RU 75496, priority 27.02.2008, published 10.08.2008, Bull. No. 22), including a body made of high-strength nodular cast iron, internal and external covers, case and dampers. The case has longitudinal channels filled with heat-resistant polyethylene. To increase the heat transfer surface between the cover, the container body and the surrounding air, the outer surface of the container body has annular chiseled ribs, and the inner surface of the container body and the outer surface of the case have mating cooling fins, which intensify the heat sink from spent fuel assemblies placed in the container case. container body and further into the environment. The case is made of metal cast with channels for the installation of fuel assemblies. At the same time, on the outer surface of the cover there are cooling fins mated with cooling fins on the inner surface of the case.

The disadvantage of the design of the known transport packaging kit for transportation and storage of spent nuclear fuel is the low manufacturability of the cover design, due to the need to manufacture, install and remove rods, forming channels for installing fuel assemblies in a molded case during its manufacture, as well as the need for accurate machining of channels installation of fuel assemblies. The disadvantages include the high cost of construction due to the high complexity of the work on its production. The disadvantages also include the absence in the case of protection against neutron radiation, which in turn requires the implementation of longitudinal channels in the case, filling them with neutron-protective material (heat-resistant polyethylene), which leads to an increase in the wall thickness of the container body, and, consequently, its diametrically size.

The closest and taken as a prototype is the well-known construction of a bimetallic cover for TUK (Description of the utility model to patent RU 171956, declared December 7, 2016, published on 06/22/2017), including a molded case in which the channels for the placement of fuel assemblies are formed by molded shaped metal pipes with flat edges fixed in a molded case due to shrinkage that occurs in the process of melt cast iron crystallization during the manufacture of a molded case casting.

A disadvantage of the known construction of a bimetallic cover for a TUK is its large diametral size, which is caused by the need to have channels for accommodating fuel assemblies at some distance from each other to provide thermal bridges to remove heat from the side surfaces of the central channels to the outer surface of the cover. In addition, high-strength cast iron provides protection against gamma radiation, but does not provide protection against neutron radiation, which in turn requires embedding in the container body of the transport and packaging neutron protection package, which leads to an increase in the thickness of the container body wall, and, consequently, its diametral size.

The technical result of the proposed container case for transporting and storing spent nuclear fuel consists in imparting to the case high neutron-protective properties while providing improved heat removal from the heat-generating assemblies installed in the respective channels to the outer surface of the molded case of the case.

The technical result is achieved by the fact that in the case of a container for transporting and storing spent nuclear fuel, including a molded case with poured metal pipes with flat edges that form channels for installing fuel assemblies, the pipes are installed in annular rows close to each other with matching along flat edges around the central tube, the outer surfaces of the flat faces of the pipes mating with each other are lined with copper sheets, the space between the outer surface of the tubes an annular row, and the inner surface of the cast case is filled with inserts of neutron-protective material with a melting temperature higher than the melting temperature of the material of the cast case, forming a solid wall preventing neutrons from flying in radial directions, the design is fixed by the shrinkage occurring during the process of melt metal crystallization in the manufacture of cast cast body.

FIG. 1 shows the case of a container for transporting and storing spent nuclear fuel in axial section.

FIG. 2 shows a section AA of a container cover for transporting and storing spent nuclear fuel.

FIG. 3 is a view of the cover of a container for transporting and storing spent nuclear fuel.

FIG. 4 shows a general view, combined with a cut, of a container for transporting and storing spent nuclear fuel with a sheath according to the invention.

The proposed container case for transporting and storing spent nuclear fuel includes a molded case 1 with channels for installing fuel assemblies. The channels are formed by molded shaped metal pipes 2 with flat edges. The pipes 2 are installed in annular rows close to each other with mating along flat faces around the central pipe. The outer surfaces of the flat faces of the pipes 2 mating with each other are lined with copper sheets 3, which provide improved heat removal from the pipes 2 to the casing 1.

Currently, in the nuclear industry, in order to prevent the occurrence of spontaneous nuclear chain reaction in fuel assemblies installed in the channels of the cover, boron steel CHS82 (04X14TZR1F) is used to manufacture shaped metal pipes 2, which has the property of neutron absorption due to boron content. Since the pipes 2 are made of a material with a low thermal conductivity and are installed in several annular rows close to each other with mating along flat edges around the central pipe, the lining of the outer surfaces of the flat faces mated to each other 2 copper sheets 3 will provide improved heat dissipation from the pipes 2 to the molded case 1. Due to the fact that the contact between the mating surfaces of the pipes 2 is carried out through the copper sheets 3, and, as is known, copper has a high coefficient of thermal conductivity, an improved heat removal from all pipes 2, including the central one, will be provided, and thus the occurrence of an uncontrolled nuclear reaction in the fuel assemblies installed in the channels of the case for transporting and storing spent nuclear fuel is excluded. In addition, copper is a material that can be easily machined, which helps to ensure high manufacturability of the structure.

In the manufacture of a molded body 1 of a container cover for transporting and storing spent nuclear fuel, for example, high-performance nodular cast iron (VChGH) can be used, which has proven itself as a material for the manufacture of containers for transporting and storing spent nuclear fuel -packing kits.

To give the case a container for transporting and storing spent nuclear fuel with neutron-protective properties, the space between the outer surface of the tubes of the outer ring row and the inner surface of the molded case 1 is filled with inserts 8, 9, 10 of the neutron-protective material with the melting temperature above the melting point of the material of the molded case forming a solid wall, preventing the free flight of neutrons in radial directions.

One example of the neutron protection is the implementation of inserts 8, 9, so that they form a closed ring in the cross section of the cover. Inserts 10 are installed in such a way as to overlap the joints between the inserts 8, 9. Inserts 10 are necessary to prevent the direct passage of neutrons through possible gaps in the junction of the faces of the inserts 8, 9 conjugated with each other.

Graphite can be used as a neutron-protective material, a material that has found wide application in thermal 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%. In the manufacture of casting the cast body 1, the pipe 2 and the inserts covering them from neutron-protective material 8, 9, 10 are fixedly connected due to the shrinkage that occurs during the crystallization of the molten metal casting the cast body 1. The inserts 8, 9, 10 have different shapes and the geometrical dimensions of the cross section and can be made of graphite with different content of additives of boron and gadolinium to ensure the same effectiveness of protection against neutron radiation, taking into account their shape and geometric dimensions of the sections.

At present, solid hydrogen-containing materials have found primary use as neutron protection for TUK, among which polyethylene and polypropylene have the highest hydrogen concentration. The disadvantage of neutron protection based on polyethylene and polypropylene is that when exposed to elevated temperatures, they soften, change their geometrical parameters and undergo partial destruction with evolution of gases and increase in pressure in the volume occupied by them to values that are dangerous for the outer shell of the TUK. In addition, the lack of neutron protection of polypropylene is that this material has a much higher compared with the metal coefficient of temperature linear expansion (more than 13 times) [Description of the invention to the patent RU 2522580, announced 31.07.2012, published 07/20/20141 .

Data on the mean free path of fast neutrons in various materials are given in Table 1 [Radiation. - Electronic Resource.URL: http://portal.tpu.ru/SHARED/a/ALEXTPUFTF/uchebnye-mat/iinph/Tab1 /radiation.pdf].

A comparative analysis of neutron protection from polyethylene and graphite shows that pure graphite slows down neutrons 1.7 times worse than polyethylene, but taking into account the additions to graphite in the form of boron and gadolinium, its neutron-protective abilities will increase, reducing the difference in efficiency compared with polyethylene. In addition, graphite has several advantages over materials containing hydrogen.

The advantages of graphite are high strength, good machinability, high thermal conductivity and low thermal expansion. Graphite has a coefficient of thermal conductivity significantly higher than that of nodular cast iron from which the body is made. Graphite is a good conductor of heat, which will ensure improved heat removal from the fuel assemblies installed in the channels formed by the pipes 2 to the outer surface of the molded case 1.

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, 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 up to 4%) weakens the flux density of thermal neutrons 400 times [Protection from ionizing radiation. - Electronic Resource.URL:

http://zinref.ru/000_uchebniki/05300_tehnika_bezopasnosti/010_00_00_voprosid_ozimetria_nosovski_1998/007.htm].

In the atomic technology, gadolinium has been used for protection against neutrons, since this element has the highest ability to capture neutrons from all stable isotopes. Its cross section is 46,000 barn. Of all gadolinium isotopes, its gadolinium-157 isotope has the highest neutron capture capacity (capture section exceeds 150000 barn) [Chemist Handbook. - Electronic resource. URL: http: //chem21.info/page/005059191229237063075030088004015245202249173107/].

Graphite inserts 8, 9, 10 are made from blanks obtained by the well-known production technology of graphite electrodes of electric arc furnaces with additions of boron and gadolinium oxides.

The bottom of the container cover for transporting and storing spent nuclear fuel is attached by mechanical connection, for example, bolted connection, a pallet 4 with openings arranged in accordance with pipes 2. The pallet 4 serves as a support for fuel assemblies during operation of the case as part of a transport packaging container for transportation and storage of spent nuclear fuel and provides the possibility of draining decontamination solutions during its disinfection.

At the upper end 6 of the cover of the container for transporting and storing the spent nuclear material on the inner surface of its body, a step is carried out to form the flange in order to allow the cover 7 to be installed.

On the inner surface of the upper end 6 of the container cover for transporting and storing spent nuclear fuel, a protective coating is used that is resistant to decontamination solutions, a cover 5 is installed that protects the ends of the inserts 8, 9, 10 from the effects of decontamination solutions and the upper cover 7, which in turn is the inner lid of the container for transporting and storing spent nuclear fuel as part of the transport and packaging kit.

Works the invention as follows. The case of a container for transporting and storing spent nuclear fuel is not removable in relation to the container body. The cover of the container for transporting and storing spent nuclear fuel is installed in the container body of a transport packaging package for fit with a fit, or installed in a mold as a core during the manufacture of a container body casting, as a result they will be interconnected by shrinking the metal during cooling casting the container body.

Neutron protection 13 is placed outside the cavity of the bottom part of the container body and cover 14 is installed. The fuel assemblies are installed in the cover channels, cover 7 is installed on the upper end of cover 6, neutron protection 11 is placed above it, and the outer cover of container 12 is installed.

During operation of the container cover for transporting and storing spent nuclear fuel, the heat emitted by the fuel assemblies is transferred to pipes 2, and is discharged from them through copper sheets 3, revetting pipes 2.

Implemented the invention as follows.

Metal pipes 2 and inserts made of neutron-protective material 8, 9, 10 are installed into the casting mold as casting rods, and the casting mold is filled with molten metal. As the molten metal cools, it crystallizes while the metal pipes 2 and inserts 8, 9, 10 are reliably fixed in the casting due to shrinkage resulting from the crystallization of the molten metal as it cools. The result is a casting of the cover of the container for transporting and storing spent nuclear fuel. Then, the resulting casting of the cover of the container for transporting and storing the spent nuclear fuel is sent for machining, then to the lower part by means of a mechanical connection, the pallet 4 is fixed. At the upper end of the cover of the container for the transportation and storage of the spent nuclear fuel a protective coating is made that is resistant to deactivating solutions and set the cover 5.

Due to the fact that the space between the outer surface of the copper sheets framing the pipes of the outer annular row and the inner surface of the cast case body is filled with inserts of neutron-protective material with a melting temperature above the melting temperature of the material of the cast body, it is possible to fix the structure due to shrinkage of the melt that occurs during crystallization metal in the manufacture of cast cast body. The advantages of the invention are: - lining the outer surfaces of the flat faces of the pipes mating with each other with copper sheets provides improved heat dissipation from all fuel assemblies installed in the channels of the cover and thereby prevents the occurrence of spontaneous chain reaction due to overheating of the fuel assemblies;

- provides a compact arrangement of channels to accommodate fuel assemblies due to the lack of free space between them, there are no additional fasteners in the form of spacer grids;

- predominant use as neutron protection has received the use of polyethylene, but its disadvantage is the low melting point (about 115 ° C), which requires its installation at a certain distance from the source of neutron radiation in a place that is heated to lower temperatures. Such a place is the wall of the container body, which leads to a complication of the design of the container body and an increase in the labor intensity of its manufacture. Neutron protection is installed in the container case wall of the transport and packaging set, for which concentric diameters are staggered, shifted in the radial and angular directions, so as to ensure their overlap along the radial lines, two rows of longitudinal blind holes with depth to 6 m. These holes are filled with rods of neutron-protective material - polyethylene. The remaining bridges between the holes provide heat removal from the cover to the outer surface of the device. In view of the fact that the outer diameter of the container is limited by the size of the technological equipment of storage facilities for spent nuclear fuel, the cooling fins on the outer surface of the case have a limited area, which is insufficient with increasing fuel assemblies for more than 18 pieces.

The use of a neutron-protective material with a high melting point makes it possible to install neutron protection in the vicinity of the neutron source directly in the container cover for transporting and storing spent nuclear fuel, and not in its case. Due to the fact that the space between the outer surface of the tubes of the outer annular row and the inner surface of the cast case body is filled with inserts made of neutron-protective material, forming a solid wall that prevents the free passage of neutrons in radial directions, it becomes possible to reduce the wall thickness of the container body for transporting and storing spent nuclear fuel and, accordingly, its overall size, or while maintaining the outer overall size, it is possible increase the size of the cooling fins on the outer surface of the container body and thereby improve the heat dissipation from it.

In addition, the placement of neutron protection in the case eliminates the time-consuming operation of drilling deep (up to 6 m) holes in the housing wall to accommodate neutron protection, and thereby improve the manufacturability of the container body for transporting and storing spent nuclear fuel.

- the use of neutron-protective material with a melting point higher than the melting temperature of the material of the cast body allows you to install neutron protection during the manufacture of the casting body and still fix the structure due to shrinkage of the molten metal during crystallization during the manufacture of the cast body casting exceptions additional assembly operations.

BIBLIOGRAPHY

1. Description of the invention to the patent RU 2593388, priority 08/04/2015, published 08/10/2016, bull. №22.

2. Description of the invention to the patent RU 2453007, declared 04/01/2011, published 10.06.2012.

3. Description of the utility model to the patent RU 75496, priority 27.02.2008, published 10.08.2008, Bull. №22.

4. Description of the utility model for patent RU 171956, announced 12/07/2016, published on 06/22/2017.

5. Description of the invention to the patent RU 2522580, declared 31.07.2012, published July 20, 2014.

6. Radiation. - Electronic resource. URL:

http://portal.tpu.ru/SHARED/a/ALEXTPUFTF/uchebnyemat/iinph/Tab1/radiation.pdf.

7. Protection against ionizing radiation. - Electronic resource.

URL: http: //zinref.ru/000_uchebniki/05300_tehnika_bezopasnosti/010_00_00_voprosi_dozimetria_nosovski_1998/007.htm.

8. Reference chemist. - Electronic resource.

URL: http://chem21.info/page/00505919122923 7063075030088004015245202249173107 /.

Claims (1)

Container case for transporting and storing spent nuclear fuel, including a molded case with infused metal pipes with flat edges that form channels for installing fuel assemblies, characterized in that the pipes are installed in annular rows close to each other with mating along flat edges around the central pipe, the outer surfaces of the flat faces of the pipes mating with each other are lined with copper sheets; the space between the outer surfaces of the pipes of the outer annular row and the inner The ground surface of the cast case is filled with inserts of neutron-protective material with a melting point higher than the melting temperature of the material of the cast case, forming a solid wall that prevents the free passage of neutrons in radial directions, the design is fixed by the shrinkage that occurs during the casting of cast metal enclosures.

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