WO2024112228A1

WO2024112228A1 - Storage facility for spent nuclear fuel

Info

Publication number: WO2024112228A1
Application number: PCT/RU2023/000221
Authority: WO
Inventors: Георгий Ильич ТОШИНСКИЙ; Александр Владиславович ДЕДУЛЬ; Олег Геннадьевич КОМЛЕВ; Сергей Александрович ГРИГОРЬЕВ
Original assignee: Акционерное Общество "Акмэ - Инжиниринг"
Priority date: 2022-11-22
Filing date: 2023-07-21
Publication date: 2024-05-30

Abstract

The invention relates to depots for the dry storage of spent nuclear fuel. The present storage facility for spent nuclear fuel comprises a storage chamber with protective walls, canisters, an upper floor, a lower floor, and a natural ventilation system. The natural ventilation system includes vertical outlet ducts and inlet ducts with air intake devices, and a horizontal inlet header and a horizontal outlet header, between which the lower floor is disposed with receiving tubes mounted therein, the upper floor also having receiving tubes mounted therein in coaxial alignment with the receiving tubes of the lower floor. The receiving tubes of the upper floor have plugs installed therein which separate the storage facility from a space containing a floor-mounted machine for conveying filled spent fuel canisters into the storage facility. The receiving tubes of the lower floor have canisters installed therein, each tube containing either a filled spent fuel canister, or an empty canister with a closure. All of the receiving tubes of the lower floor are closed until loading begins. The invention provides for more effective cooling of spent fuel canisters in the storage facility.

Description

Spent nuclear fuel storage facility

Technical field

The invention relates to nuclear energy, 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 the residual heat release of the fuel before sending it for long-term 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 jumper 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 containing 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, pencil cases are loaded into containers (nests) one on top of the other in the form of a garland and are held in the containers at a given height using spacers, and in the center using centralizers. The heat released during storage of spent nuclear fuel is removed into the atmosphere by natural ventilation. Cold air enters the interior of the containers through the perforated sections of the containers and, when heated, rises and is released into the atmosphere. If it is necessary to remove the lower canister, the upper canisters with spent fuel assemblies are reloaded into a free container without being removed to the surface, and the lower canister is removed for repair or recycling.

The disadvantages of the known storage facility include the fact that atmospheric air will descend down the well in the space between the containers, moving in a downward flow at low speed, due to the significant cross-section of the space between the containers. Based on this, air will enter the perforated areas 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 canisters with spent fuel assemblies, taking into account also that the transfer of heat from fuel assemblies to atmospheric air has 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 the atmospheric air.

The presence of perforated areas 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 facility contains a storage chamber with monolithic reinforced concrete protective walls, in which nests are installed between its upper and lower ceilings. The nests are equipped with protective plugs that are installed in the nests by 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 allows for remote loading of canisters with spent fuel into storage slots 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 sub-chamber space, which is, in turn, connected to air intake devices. The upper part of the chamber is connected by exhaust ducts to exhaust pipes located on the roof of the chamber.

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

The main requirements for spent fuel storage facilities include the following:

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

- ensuring radiation safety of personnel and environmental protection;

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

The radiation safety of a spent fuel storage facility depends significantly on the condition of the fuel rod cladding.

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

Disclosure of the Invention

The problem to be solved by the invention is to improve the safety of spent nuclear fuel storage.

The technical result obtained by implementing the invention is to increase the cooling efficiency of canisters with spent nuclear fuel in storage and to increase radiation safety.

This technical result is achieved by the fact that in a spent nuclear fuel storage facility 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 floor with installed embedded pipes to ensure the direction of air flow only through the embedded pipes, in the upper ceiling coaxial with the embedded pipes of the lower floor, embedded pipes are installed into which plugs are inserted, separating the storage facility from the room with the reloading machine, canisters are inserted into the embedded pipes of the lower floor, either a canister with spent fuel or an empty canister with a plug is installed in each pipe, the cold air intake is made at a height that ensures impossibility of surface water entering the air collector.

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

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

Either a canister with spent fuel or an empty canister with a plug is installed in the embedded pipe of the lower floor.

The canisters are placed in increments to ensure nuclear safety of storage.

The canisters have a cylindrical shape, the body of the canisters has fins, which increases the heat transfer surface area of the canister and, accordingly, increases the efficiency of its cooling.

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

The canister into which the spent fuel is loaded is filled with lead, which increases the efficiency of heat removal from the 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 securing SNF, the canister cover has a mushroom for a gripping device.

Immersion of spent fuel into a canister previously filled with liquid lead is carried out using standard reloading equipment. Prevention of ascent is ensured by the collet grip of the pencil case.

The inlet part of the lower air manifold can be U-shaped, in the lower part of which a drain is installed, designed to drain water if it enters the U-shaped manifold.

The space between the canister body and the embedded pipe of the lower floor forms vertical air channels through which cooling air flows. An empty canister with a plug, installed in the embedded pipe of the lower floor, blocks the embedded pipe, thereby increasing the flow of cooling air in the embedded pipes with canisters containing spent nuclear fuel.

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

Brief description of drawings

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

In fig. Figure 1 shows a general view of the spent fuel storage facility.

In fig. Figure 2 shows a pencil case with spent nuclear fuel.

In fig. Figure 3 shows a canister containing spent nuclear fuel with a temporary plug. The storage facility contains a storage chamber with monolithic reinforced concrete walls forming inlet and outlet air ducts, upper and lower ceilings in which embedded pipes are coaxially installed.

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

Embodiment of the invention

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

The storage facility may consist of several compartments for storing spent nuclear fuel. Each compartment (Fig. 1) includes vertical exhaust 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. At the bottom of the air duct, drains 12 are installed to drain water that has entered the U-shaped collector. Each pencil case has its own cell.

The embedded pipes 7 of the lower floor 6 are designed for orderly placement of canisters with SNF in the storage facility, and for directing the flow of cooling air along the ribs of canisters 8 with SNF.

Plugs 11 are intended for biological protection of personnel from ionizing radiation of canisters 8 with SNF installed for storage, and to prevent the escape 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 plug 11 is equipped with a device for gripping (not shown in the figure), closed with a lid, similar to the device for gripping the lid of a pencil case 8. There is a seal on the shoulders of the plug 11. The lower part of the plug 11 is equipped with thermal insulation.

The canister 8 (9) for SNF 21 (Fig. 2) is a metal pipe 14 closed at the bottom, 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 loading SNF into the canister. . The bottom of the canister body 8 (9) is equipped with a collet grip 17, intended for fixing the spent fuel assemblies 21 in the canister 8 (9) from floating. The cover 18 of the pencil case 8 (9) has a mushroom 19 for the gripping device. To increase the heat transfer surface, the case body 8 (9) has fins 20.

Canisters 8 with spent fuel are placed in embedded pipes 7 installed in the lower ceiling 6.

The plug 10 for 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 floor 6.

The proposed storage facility 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 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 gets into the lower U-shaped part of the air duct 2 is removed by gravity through the ladder 12.

In the process of further loading of the storage facility, empty canisters 9 with plugs 10 are removed one by one and canisters 8 with SNF are installed instead. During these operations, plug 11 is removed from the upper ceiling 5, and after installing the canister 8 with the spent fuel assemblies, it is installed in place.

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

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

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

When storing spent fuel in a reactor storage facility, the air temperature in the exhaust air ducts is monitored.

Industrial applicability

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

Claim

1. Spent nuclear fuel storage facility, 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 output manifolds, between which there is a lower floor with installed embedded pipes, characterized in that in the upper floor, coaxially with the embedded pipes of the lower floor, embedded pipes are installed, into which plugs are inserted, separating the storage from the room with the floor machine; pencil cases are inserted into the embedded pipes of the lower floor , either a canister with spent fuel or an empty canister with a plug is installed in each pipe, while all embedded pipes of the lower floor are closed before loading, the cold air intake is made at a height that ensures that surface water cannot enter the air collector.

2. The spent nuclear fuel storage facility according to claim 1, characterized in that the canisters are placed in increments that ensure nuclear safety of storage;

3. The spent nuclear fuel storage facility according to claim 1, characterized in that the canisters are cylindrical in shape and the body of the canisters is finned.

4. The spent nuclear fuel storage facility according to claim 1, characterized in that before loading begins, all embedded pipes of the lower floor are covered with empty canisters with plugs.

5. The spent nuclear fuel storage facility 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 equipped with thermal insulation.

6. The spent nuclear fuel storage facility according to claim 1, characterized in that the canister into which the spent nuclear fuel is loaded is filled with lead.

7. The spent nuclear fuel storage facility according to claim 1, characterized in that the lower narrow part of the canister is a damper, the bottom of the canister body is equipped with a collet gripper for securing spent fuel, and the canister lid has a mushroom for a gripping device.

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