RU2773730C1 - Cover for placing, storing and transporting spent fuel assemblies - Google Patents

Abstract

FIELD: nuclear technology.

SUBSTANCE: invention relates to nuclear technology, in particular, to apparatus intended for placing spent fuel assemblies (SFA) of WWER reactors therein. Cover for placing, storing and transporting spent fuel assemblies consists of a pipe located in the central part of the cover, a base, at least two sections with SFA sockets, an upper, a lower, and intermediate plates. The SFA sockets are formed by borated aluminium sheets installed in the grooves of the upper, lower and intermediate plates. The borated aluminium sheets are made in the form of combs and form hexagonal sockets by crossing each other with the grooves. Segments made of a highly heat-conducting material and upper segments made of corrosion-resistant steel are installed along the outer diameter of the cover, and the sections of the cover are pulled together with pins, wherein compensating elements are installed on the pins under nuts. Hold-down apparatus are installed in each SFA socket in the lower plate and in the base. The hold-down apparatus are equipped with water drainage holes.

EFFECT: invention allows for an increase in the nuclear safety, heat sink, and strength of the cover.

8 cl, 5 dwg

Description

The invention relates to nuclear engineering, in particular to devices designed to accommodate spent fuel assemblies (SFA) of VVER 1000, VVER 1200, VVER 1300 reactors during transportation and storage in containers.

Such a device is known in the form of a cover for transporting and storing spent nuclear fuel (RF patent No. 2686476, G21F 5/00, publ. 29.04.2019).

The cover contains a cast body with cast-in profile metal pipes with flat edges, forming channels for installing fuel assemblies. The pipes in the case 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 surface of the pipes of the outer annular row and the inner surface of the cast body is filled with inserts of neutron-shielding material with a melting temperature higher than the melting temperature of the material of the cast body. The structure is immovably fixed due to the shrinkage that occurs during the crystallization of the metal melt during the manufacture of the casting of the cast body.

The disadvantages of this cover are as follows:

- the presence in the body of cast-in hexagonal pipes lined with copper sheets with inserts of neutron-shielding material. The use of materials with different coefficients of linear thermal expansion in a single rigid structure will lead to cracking of the joints between them. Which will lead to further difficulties in decontamination;

- pipes are installed in annular rows close to each other with conjugation 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. Impossible gap-free conjugation of pipes and lining with copper plates. And in the presence of minor gaps, it is difficult to ensure the drainage of water from the cover;

- it is inefficient to use a neutron-protective material based on graphite with absorbing materials in the design of the case; the dose rate on the surface of the container is determined not by thermal neutrons, but by neutrons of higher energies;

- dense arrangement of hexagonal tubes with SFA does not ensure the nuclear safety of the container.

Also known is a case for placing and storing spent fuel assemblies of the VVER-1000 reactor (RF patent No. 2593388, G21F 5/00, publ. 10.08.2016).

The case contains a central tube, spacer grids with hexagonal tubes, in which spent fuel assemblies are placed, installed relative to the axis of the central tube in two annular rows, separated by an intermediate tube, while the hexagonal tubes in a row are mated with each other by ribs, and part of the faces on the outside has radiation protection inserts. Spacer grids with hexagonal tubes are made in the form of sections fastened together, each of which is made of aluminum alloy and consists of a central tube, two spacer grids with hexagonal holes, in which hexagonal tubes are placed, having internal hexagonal grooves at the ends, hexagonal grooves are installed in the latter rails made of corrosion-resistant steel, the sections are mounted on a base consisting of a spacer support with holes along the axis of which clamping devices are installed on the outside, and a carrier pipe, the lower section and the carrier pipe are fixed to the support by fasteners, on the spacer grid of the upper section and between the spacer section gratings are equipped with diaphragms made of corrosion-resistant steel, the carrier pipe is also made of corrosion-resistant steel and has an adapter for a load gripping device.

The disadvantages of this cover are as follows:

- high labor intensity of manufacturing due to the complex design of the cover with a large volume of welded joints, fasteners, as well as with the installation of radiation protection inserts and the use of hexagonal pipes;

- since the cover determines the size of the container, the increased capacity of up to 20 spent fuel assemblies of the VVER-1000/1200 reactor increases the overall dimensions of the container, preventing the latter from fitting into the SNF handling scheme of the Russian Federation without significant costs;

- the cover is disassembled only into large sections, which makes it impossible to replace only defective structural elements during operation, which significantly increases the cost of maintaining the cover.

Also known is a cover for transporting and storing spent nuclear fuel (RF patent No. 2642853, G21F 5/00, publ. 01/29/2018).

The cover of the container contains a central bearing pipe made of corrosion-resistant steel, on which sections fastened together are installed, each of which is made of two spacer grids made of stainless steel, between them there are hexagonal pipes for accommodating fuel assemblies, having neutron protection and installed relative to the axis of the central pipe in two annular rows, sections are installed on a base consisting of a spacer support with holes, along the axis of which clamping devices are installed on the outside, the carrier pipe has an adapter for a load gripping device. Between the spacer grids, heat-removing disks are installed parallel to them, and steel racks are installed parallel to the hexagonal pipes, which together with the spacer grids form a load-bearing frame, neutron protection is installed inside each pipe face in the form of a plate made of a boron-containing composite, six pipes are placed in the first row relative to the axis of the carrier pipe, and in the second - twelve. The cover allows to place spent fuel assemblies of VVER-1000/1200 type reactors.

This cover is taken as a prototype, as the closest in technical essence to the claimed technical solution.

The disadvantages of this cover are as follows:

- high labor intensity of manufacturing a large number of heat-removing disks and spacer grids perforated with hexagonal holes;

- the absence in the Russian Federation of the mastered technology for the production of aluminum hexagonal pipes;

- high labor intensity of manufacturing and mounting of plates from boron-containing composite;

- a combination of materials with different coefficients of thermal expansion (corrosion-resistant steel and aluminum alloy) in the power frame can lead to a violation of the integrity of the cover design and the need to replace it in its entirety or its components.

These shortcomings do not allow the use of the prototype case in the SNF handling scheme of the Russian Federation for VVER-1000/1200/1300 type reactors.

The purpose of the present invention is to create a cover with the placement of the maximum number of spent fuel assemblies (18 pieces) of VVER-1000/1200/1300 reactors, which fits into the SNF handling scheme of the Russian Federation, while ensuring the safety parameters of storage and transportation, in particular nuclear safety, heat removal and cover strength .

The technical result is to increase nuclear safety, heat removal and strength of the casing, improve the maintainability of the casing and reduce the cost of manufacturing and maintaining the casing for placement, storage and transportation of spent fuel assemblies.

The technical result is achieved by the fact that in the case for placement, storage and transportation of spent fuel assemblies, consisting of a pipe located in the central part of the case, a base, at least two sections with nests for SFAs, an upper, lower and intermediate plates, the pipe is permanently attached to the bottom plate, the slots for SFAs are formed by borated aluminum sheets installed in the grooves of the upper, lower and intermediate plates, while the borated aluminum sheets are made in the form of combs and intersecting with each other through the grooves form hexagonal nests, segments of material of high thermal conductivity and the upper segments are made of corrosion-resistant steel, and the sections of the cover are pulled together by studs, while compensating elements are installed on the studs under the nuts.

Pressing devices are installed in the bottom plate and in the base in each slot for SFAs.

The base is made to provide free movement relative to the cover.

Guides are installed on the top plate along the perimeter of each slot for SFAs.

In the upper part, a head is fixed to the pipe for inserting/removing the cover into/from the container.

Two diametrically located grooves are made on the outer surface of the cover.

All plates and clamping devices are equipped with holes for draining water from the cover.

The slots for SFAs are linearly arranged in rows and connected to each other by ribs.

Hydrogenated titanium shot is placed in the upper part of the tube.

The use of hydrogenated titanium shot in the upper part of the pipe provides biological protection.

The use of baffles made of borated aluminum, firstly, ensures heat removal from SFAs, preventing the formation of overheating zones in them, secondly, ensures nuclear safety, and thirdly, reduces the cost of manufacturing the cover and increases its maintainability.

The formation of partitions from sheets of borated aluminum, made in the form of combs with grooves installed in the grooves of the plates, provides a quick disconnect connection and does not require the use of fasteners or welding.

SFA nests, linearly arranged in rows and mated with each other by ribs, provide higher nuclear safety.

Segments made of aluminum alloy, acting as guides for the pins, form the body of the case and the interior of the hexagonal shape, ensure the transfer of heat from the SFA to the container.

The use of compensating elements in the form of disc springs and the absence of a connection between the carrier pipe and the top plate compensate for the thermal expansion of the material (simultaneous use of corrosion-resistant steel (stud) and aluminum alloy).

The use of a movable base with clamping devices, firstly, provides additional biological protection along the bottom of the container, secondly, it reduces the impact load on the case when it is installed in the container, and thirdly, it allows the use of the case in a container for sealed canisters.

The use of two diametrically located grooves on the outer part of the cover ensures the orientation of the cover in the container and prevents its rotation in the container during transportation.

The proposed layout of the hexagonal cells makes it possible to fit into the existing SNF handling scheme for VVER-1000/1200/1300 type reactors for the Russian Federation.

The invention makes it possible to replace only defective parts of the structure during the maintenance of the cover, which reduces the time and cost of manufacturing.

The invention is illustrated by drawings, which show:

in fig. 1 - design of the cover for placement, storage and transportation of spent fuel assemblies of the reactor;

in fig. 2 – top view of the case;

in fig. 3 – section of one of the sections;

in fig. 4 - remote element And figure 1;

in fig. 5 is an axonometric projection of one of the baffles of the case socket before assembly from borated aluminum sheets and after assembly.

The case is a cylindrical structure with nests for installing SFAs.

Pipe 1 made of corrosion-resistant steel is located in the central part of the cover. In the upper part, a head 2 is attached to the threaded pipe for installing (removing) the cover into the container (from the container). The upper part of the tube is filled with shot of hydrogenated titanium 3, which serves as biological protection.

The cover is made in the form of three sections 4. The sections consist of partitions 5 with sheets of borated aluminum 6, top plates 7, bottom 8 made of corrosion-resistant steel and intermediate 9 made of aluminum alloy, as well as segments 10 made of aluminum alloy and top 11 segments made of corrosion-resistant steel. Partitions 5 made of borated aluminum sheets 6, which ensure nuclear safety, are installed in the grooves of the top 7, bottom 8 and intermediate 9 plates. rows. Nests 12 are mated with each other by ribs. Segments 10 made of high thermal conductivity material (aluminum alloy) are installed along the outer diameter of the case, providing efficient heat removal from SFAs to the container body, and upper segments 11 made of corrosion-resistant steel.

Sections 4 of the cover are pulled together by studs 13. To compensate for thermal expansion, compensating elements 15 are installed on studs 13 under nuts 14.

Pipe 1 and bottom plate 8 are interconnected by means of a welded joint.

In the lower part of the cover there is a base 16, which provides additional biological protection along the bottom of the container. The base has free play relative to the cover. In the bottom plate 8, and in the base 16 in each socket 12 for SFAs, clamping devices 17 are installed.

Guides 18 are installed on the top plate 7 along the perimeter of each nest 12 to compensate for misalignment of the loaded SFA being loaded out of alignment on nest 12.

On the outer part of the cover, two diametrically located grooves "a" are made, which provide orientation of the cover in the container body and prevent rotation of the cover in the container during its transportation.

All plates 7, 8, 9 and pressing devices 17 have holes 19 for draining water from the cover.

The case for placement, storage and transportation of spent fuel assemblies of the VVER-1000/1200/1300 reactor is operated as follows.

The cover together with the container (not shown in the drawings) is a transport packaging kit (TUK). The cover outside the container is in an empty state in a vertical position.

The cover with the help of a load gripping device (not shown in the drawings) attached to the head 2 is installed in a vertically standing container, aligning the grooves "a" in the cover with the guides in the container. TUK with the help of a load gripping device is installed at the place of SFA loading. SFAs are installed in the case in water. SFAs are loaded into hexagon sockets of 12 sections 4 of the case, one at a time in a given sequence, supported by clamping devices 17 using a special lifting device (not shown in the drawings). After loading the required amount of SFAs, the TUK is closed with the canister in the cask tightened and the SFA in the canister. Further, the TUK is dried and transported, as a rule, in a horizontal position, to the fuel regeneration facility.

The removal of SFAs from the TUK is carried out using a special lifting device at the appropriate service post. Extraction of the empty cover from the container is carried out with the help of a load gripping device attached to the head 2.

To carry out maintenance work with the cover and, if necessary, to repair it, it can be disassembled into its component parts by removing the appropriate fasteners.

The use of this invention makes it possible to create a case with the placement of the maximum number of spent fuel assemblies (18 pieces) of VVER-1000/1200/1300 reactors, which fits into the SNF handling scheme of the Russian Federation, while ensuring the safety of storage and transportation, in particular nuclear safety, heat removal and the strength of the case , as well as improve the maintainability of the cover and reduce the cost of its manufacture and maintenance.

Claims (8)

1. Case for placement, storage and transportation of spent fuel assemblies, consisting of a pipe located in the central part of the case, the base, at least two sections with slots for spent fuel assemblies, top, bottom and intermediate plates, characterized in that the pipe is permanently attached to the bottom plate, the slots for SFAs are formed by borated aluminum sheets installed in the grooves of the upper, lower and intermediate plates, while the borated aluminum sheets are made in the form of combs and, intersecting with each other through the grooves, form hexagonal nests; segments made of high thermal conductivity material and upper segments made of corrosion-resistant steel, and sections of the case are pulled together with studs, compensating elements are installed on studs under the nuts, clamping devices are installed in the bottom plate and in the base in each nest for SFAs, while all plates and clamping devices equipped with holes for draining water from the cover. 2. Case according to claim. 1, characterized in that the base is made with the provision of free play relative to the case. 3. Case according to claim 1, characterized in that guides are installed on the top plate around the perimeter of each slot for SFAs. 4. Cover according to claim 1, characterized in that a head is fixed to the pipe in the upper part for installing / extracting the cover into / from the container. 5. Cover according to claim 1, characterized in that two diametrically located grooves are made on the outer surface of the cover. 6. Case according to claim 1, characterized in that the slots for SFAs are linearly arranged in rows and connected to each other by ribs. 7. Cover according to claim 1, characterized in that biological protection in the form of hydrogenated titanium shot is placed in the upper part of the pipe. 8. Cover according to claim 1, characterized in that the sections of the cover are made without welded joints.

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