RU2796637C1 - Spent nuclear fuel storage facility - Google Patents

Abstract

FIELD: nuclear energy.

SUBSTANCE: invention relates to chamber type dry storage facilities for spent nuclear fuel (SNF) and is intended for temporary storage of spent nuclear fuel. The storage of spent nuclear fuel comprises a storage chamber with monolithic reinforced concrete protective walls, canisters designed to accommodate spent fuel assemblies, upper and lower floors, and a natural ventilation system. The natural ventilation system includes vertical outlet and inlet air ducts with air intakes, horizontal inlet and outlet manifolds, between which there is a lower ceiling with installed embedded pipes; embedded pipes are also installed in the upper ceiling, coaxially with the embedded pipes of the lower ceiling. Plugs are inserted into the embedded pipes of the upper floor, separating the storage from the room with the floor machine. Canisters are inserted into the embedded pipes of the lower ceiling, either a canister with SNF or an empty canister with a plug is installed in each pipe. All embedded pipes of the lower floor are closed before loading.

EFFECT: cold air intake is made at a height that makes it impossible for surface water to enter the air manifold.

7 cl, 3 dwg

Description

Technical field

SUBSTANCE: invention relates to nuclear power engineering, namely, to chamber-type dry storage facilities for spent nuclear fuel (SNF) and is intended for temporary storage of spent nuclear fuel in order to reduce residual heat release of fuel before being sent for storage in an on-site storage facility or for reprocessing.

State of the art

From patent document RU2273067C1, a storage facility for spent nuclear fuel is known, containing a vertical well with a bridge in the upper part of the well, containers (nests) with canisters with spent nuclear fuel placed in the well, and a well ventilation system. The containers are made in the form of cylinders with perforated sections in the lower part and are installed vertically on the bottom of the well. Canisters with spent nuclear fuel are located in containers one above the other. In this case, at least one free container is installed in the well, and the jumper in the upper part of the well is installed below the upper ends of the containers. Containers with canisters with spent nuclear fuel are located along the perimeter of the well, and a free container is installed between them in the center of the well.

In the described storage, canisters are loaded into containers (nests) one on top of the other in the form of a garland and are held in containers at a given height with the help of spacers, and in the center with the help of centralizers. The heat released during storage of spent nuclear fuel is removed to the atmosphere by natural ventilation. Cold air through the perforated sections of the containers enters the interior of the containers and, being heated, rises and is discharged into the atmosphere. If it is necessary to remove the lower canister, the upper canisters with SFAs are reloaded into a free container without being taken to the surface, and the lower canister is removed for repair or processing.

The disadvantages of the known storage include the fact that atmospheric air will descend along the well in the space between the containers, moving downstream at low speed, due to the significant cross section of the space between the containers. Based on this, air will enter the perforated sections of the containers already preheated from the walls of the containers, which will lead to a decrease in its density and, accordingly, to a decrease in the natural draft created due to the difference in air densities in the lower and upper parts of the well.

As a result, especially in summer, a decrease in natural draft can lead to an increase in the temperature of the canisters with SFAs, also taking into account that the heat transfer from the fuel assemblies to the atmospheric air has a low efficiency, since the heat flow overcomes thermal resistance from the air inside the canister to the air in the container and from the air in the container to atmospheric air.

The presence of perforated sections in the lower part of the nests (cells) does not allow the nests (cells) to be used as an additional safety barrier.

From patent document RU2572361C1, a storage facility for spent nuclear fuel is known. The storage contains a storage chamber with monolithic reinforced concrete protective walls, in which nests are installed between its upper and lower floors. The nests are equipped with protective plugs that are installed in the nests during welding after loading two canisters and equipped with sampling tubes connecting the internal cavity of the nest with the serviced area through a shut-off valve. The storage chamber is equipped with equipment that ensures remote loading of canisters with spent nuclear fuel into storage nests and installation of protective plugs in them. The natural ventilation system contains embedded pipes installed in the lower ceiling of the chamber, connecting the chamber with the under-chamber space, connected, in turn, with air intake devices. The upper part of the chamber is connected by exhaust channels with exhaust pipes located on the roof of the chamber.

The disadvantages of the known storage include the air flow through the nests (channels) of storage with empty canisters, which reduces the cooling efficiency of canisters with SFAs.

The main requirements for SNF storage facilities include the following:

- ensuring nuclear safety during storage and transport and technological operations with spent fuel;

- ensuring the radiation safety of personnel and protecting the environment;

- control of residual heat removal, guarantee of the integrity of the fuel cladding and the safety of the fuel in the storage.

The radiation safety of the spent nuclear fuel storage depends significantly on the state of the fuel cladding.

The key characteristic for the integrity of SNF in the dry storage method is the temperature of the fuel cladding, which makes the task of increasing the efficiency of SNF cooling in storage relevant.

Disclosure of invention

The problem to be solved by the invention is to improve the safety of SNF storage.

The technical result obtained by implementing the invention is to increase the efficiency of cooling canisters with SNF in the storage facility and to improve radiation safety.

The specified technical result is achieved by the fact that in the storage of spent nuclear fuel, containing a storage chamber with monolithic reinforced concrete protective walls, canisters designed to accommodate spent fuel assemblies, upper and lower floors, a natural ventilation system, which includes vertical outlet and inlet air ducts with air intake devices, horizontal inlet and outlet manifolds, between which there is a lower ceiling with installed embedded pipes to ensure that the air flow is directed only through the embedded pipes, in the upper ceiling, coaxially with the embedded pipes of the lower ceiling, embedded pipes are installed, into which plugs are inserted that separate the storage from the room with the refueling machine, canisters are inserted into the embedded pipes of the lower ceiling, either a canister with SNF or an empty canister with a plug is inserted into each pipe, the cold air intake is made at a height that makes it impossible for surface water to enter the air collector.

All embedded pipes of the lower floor are closed before loading.

Prior to loading, all embedded pipes of the lower floor are covered with empty canisters with plugs.

Either a canister with SNF or an empty canister with a plug is installed in the embedded pipe of the lower ceiling.

The canisters are placed with a step that ensures nuclear safety of storage.

The canisters have a cylindrical shape, the body of the canisters has ribs, which increases the area of the canister's heat exchange surface and, accordingly, increases its cooling efficiency.

The upper surface of the cork is equipped with a gripping device closed with a lid, there is a seal on the shoulders of the cork, and the lower part of the cork is provided with thermal insulation.

The canister in which SNF is loaded is filled with lead, which increases the efficiency of heat removal from fuel rods. The lower narrow part of the canister is a damper, the bottom of the canister body is equipped with a collet gripper for fixing SNF, the canister cover has a fungus for the gripping device.

Immersion of SNF into a canister preliminarily filled with liquid lead is carried out by standard refueling equipment. Prevention of ascent provides a collet grip of the pencil case.

The inlet part of the lower air collector can have a U-shape, in the lower part of which a ladder is installed, designed to drain water in case it enters the U-shaped collector.

The space between the casing of the canister and the laying pipe of the lower floor forms vertical air channels through which cooling air flows. An empty canister with a plug, installed in the embedding pipe of the lower ceiling, closes the embedding pipe, thereby increasing the flow of cooling air in the embedded pipes with canisters with SNF.

Embedded pipes ensure the movement of air flow only through the space between the canister body and the embedded pipe.

Brief description of the drawings

The invention is illustrated by drawings, which show one of the possible embodiments of the invention.

In FIG. 1 shows a general view of the SNF storage facility.

In FIG. 2 shows a canister with spent nuclear fuel.

In FIG. 3 shows a canister with spent nuclear fuel with a temporary plug.

The storage contains a storage chamber with monolithic reinforced concrete walls forming inlet and outlet air ducts, upper and lower ceilings, in which embedded pipes are installed coaxially.

To cool the canisters with SNF installed in the embedded pipes of the lower ceiling, the storage facility is equipped with a cooling system based on natural air circulation.

Implementation of the invention

The following describes a possible, but not the only, embodiment of the claimed invention.

The repository may consist of several SNF storage compartments. Each compartment (Fig. 1) includes vertical outlet air ducts 1, inlet air ducts 2, horizontal inlet 3 and outlet 4 manifolds, upper 5 and lower 6 floors with embedded pipes 7, canisters 8 with SNF, empty canisters 9 for SNF with plugs 10, plugs 11. In the lower part of the air duct, ladders 12 are installed to drain water that has fallen into the U-shaped collector. Each pencil case has its own cell.

Embedded pipes 7 of the lower floor 6 are intended for orderly placement of canisters with spent nuclear fuel in the storage facility, and for directing the flow of cooling air along the ribs of canisters 8 with spent nuclear fuel.

Plugs 11 are intended for biological protection of personnel from ionizing radiation from canisters 8 with spent nuclear fuel installed for storage, and to prevent the exit of cooling air into the central hall (CH). Plugs 11 are installed in the upper ceiling of the storage compartments above the cells for canisters 8 with SNF.

Plug 11 is a metal cylinder with shoulders for installation in the upper ceiling 5. Plug 11 may have filler inside. The upper surface of the cork 11 is equipped with a gripping device (not shown in Fig.), closed by a lid, similar to the gripping device for the lid of the canister 8. There is a seal on the shoulders of the plug 11. The lower part of the plug 11 is provided with thermal insulation.

Canister 8 (9) for SNF 21 (Fig. 2) is a metal pipe 14 closed from below, filled with lead 15. The lower narrow part of the canister 8 (9) is a damper 16 that protects the fuel in the canister from damage when SNF is loaded into the canister . The bottom of the canister body 8 (9) is equipped with a collet gripper 17 intended for fixing the SFA 21 in the canister 8 (9) from floating up. The cover 18 of the canister 8 (9) has a fungus 19 for the gripper. To increase the heat exchange surface, the canister body 8 (9) has fins 20.

Canisters 8 with SNF are placed in embedded pipes 7 installed in the lower floor 6.

The plug 10 on the empty canister 9 for SNF (Fig. 3) is a removable metal structure, consisting of two identical elements, put on the empty canister 9 for SNF to block the air flow through the embedded pipe 7 of the lower ceiling 6.

The proposed repository is operated as follows.

Before loading canisters 8 with SNF, empty canisters 9 with plugs 10 must be inserted into all embedded pipes of the lower floor, except for one, to ensure that the air flow is directed only through the embedded pipes into which canisters 8 with SNF will be installed.

The water that has entered the lower U-shaped part of the duct 2 is removed by gravity through the ladder 12.

In the process of further loading of the storage, empty canisters 9 with plugs 10 are alternately removed and canisters 8 with SNF are installed instead. For the period of these operations, the plug 11 is removed from the upper ceiling 5, and after the installation of the canister 8 with SFA is installed in place.

Transportation of canisters 8 with SNF to the storage facility is carried out using floor-standing machine 13. The use of floor-standing machine 13 provides biological protection for personnel and prevents fuel from heating above the permissible temperature during fuel transportation and in case of emergencies.

In the room located above the upper floor 5, excess pressure is maintained to prevent air from the storage from entering it.

After welding of the cover 18, the tightness of the canister 8 with SNF is checked.

When SNF is stored in the near-reactor storage facility, the air temperature in the exhaust air ducts is monitored.

The technical solution according to the invention can be used for dry storage of spent nuclear fuel before being sent for long-term storage in an on-site storage facility or for reprocessing.

Claims (7)

1. Spent nuclear fuel storage containing a storage chamber with monolithic reinforced concrete protective walls, canisters designed to accommodate spent fuel assemblies, upper and lower ceilings, a natural ventilation system, which includes vertical outlet and inlet air ducts with air intakes, horizontal inlet and outlet manifolds, between which there is a lower ceiling with installed embedded pipes, characterized in that in the upper ceiling, coaxially with the embedded pipes of the lower floor, embedded pipes are installed into which plugs are inserted that separate the storage from the room with a floor machine, canisters are inserted into the embedded pipes of the lower ceiling , either a canister with SNF or an empty canister with a plug is installed in each pipe, while all the embedded pipes of the lower ceiling are closed before loading, the cold air intake is made at a height that makes it impossible for surface water to enter the air collector. 2. Storage of spent nuclear fuel according to claim 1, characterized in that the canisters are placed with a step that ensures nuclear safety of storage. 3. Spent nuclear fuel storage according to claim 1, characterized in that the canisters have a cylindrical shape and the case of the canisters has ribs. 4. Spent nuclear fuel storage according to claim 1, characterized in that before the start of loading, all embedded pipes of the lower ceiling are covered with empty canisters with plugs. 5. Storage of spent nuclear fuel according to claim 1, characterized in that the upper surface of the plug is equipped with a gripping device closed by a lid, there is a seal on the shoulders of the plug, and the lower part of the plug is provided with thermal insulation. 6. Spent nuclear fuel storage according to claim 1, characterized in that the canister into which the SNF is loaded is filled with lead. 7. The storage of spent nuclear fuel according to claim 1, characterized in that the lower narrow part of the canister is a damper, the bottom of the canister case is equipped with a collet gripper for fixing spent nuclear fuel, the canister cover has a fungus for the gripping device.

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