RU2273903C1 - Method for dry storage of spent fuel assemblies in container - Google Patents

Abstract

FIELD: transport and storage of spent nuclear fuel.

SUBSTANCE: proposed method includes placement of fuel assemblies in transport package incorporating container and split damping casing designed so as to minimize lift of container when inserting it in split damping casing. Transport package is conveyed to storage place where container is freed of casing, whereupon spent fuel assemblies are kept in storage place. In the process spent fuel assemblies are first placed in container and then the latter is inserted in vertical position into split damping casing made in the form of removable drum with butt-end covering and base that functions as end lid of this drum. Charged container is installed on base, covered on top with removable drum, and the latter is fastened to base. Then split damping casing is secured to container, whereupon transport package is conveyed in transport position to storage place.

EFFECT: enhanced reliability of storage and transportation.

6 cl, 5 dwg

Description

The invention relates to nuclear technology, in particular to the storage of spent fuel, and more specifically, to dry container storage of spent fuel assemblies (SFA) of nuclear power plants (NPPs), and can be used to improve reliability in handling SFA.

The dry storage of spent nuclear fuel is known (Handbook of Nuclear Energy Technology. Translated from English by F. Ran, A. Adamantiades, J. Kenton, C. Brown / Ed. By V. A. Legasov. M.: Energoatomizdat, 1989, p. .494-496). The known method of dry storage involves a certain initial exposure time in a pool of water. After that, the spent fuel is loaded into a container, which is stored in a storage location. It can be a surface mine, a dry well, or an air-cooled chamber.

If the method of dry container storage is considered enlarged, it can be noted that in the general case it involves the following set of operations:

- SFAs withstand a certain period of time in a pool of water;

- load the SFA into the container;

- the loaded container is transported to the place of intermediate storage (in the territory of the nuclear power plant or in the closest storage facility). The use of intermediate storage allows you to obtain a delay in relation to the decision on the final disposal of spent nuclear fuel (Janberg K. Storage of spent fuel in Germany. Journal of Thermal Engineering, No. 11, 1996, p. 70-76);

- store the container in an intermediate storage place for 20-50 years;

- a container with SFA is transported to the place of final storage;

- the container with the SFA is installed in the place of final storage (burial).

It can be noted that the operation of transporting SFAs to the storage location is always inherent in the technological process that makes up the method of dry container storage, i.e. the content of the concept of “method for dry container storage of SFAs” includes “transportation of SFAs to the storage location”.

Compared to other approaches to spent nuclear fuel (SNF) storage, dry storage has potential economic benefits. With this storage, based on passive cooling, very simple systems are used that do not require significant maintenance. The capacities of dry storage plants can be increased gradually, in small portions with capital minimum initial costs.

The disadvantage of this method is that during the construction of an off-line SNF storage facility, safety is required during transportation, i.e. it is necessary to increase the radiation-protective properties of the container and reduce the loads in case of possible emergency situations during transportation, which must be taken into account in accordance with the IAEA recommendations. This, in turn, determines the cost of the method. The construction of special facilities for storing containers, such as surface mines, wells, or underground chambers, also requires large capital investments.

A known method for the intermediate and final storage of fuel elements of a nuclear reactor (DE patent No. 3500999, G 24 C 19/32, 19/06, 1986), which consists in the fact that the spent fuel elements are inserted into metal bushings and stored in a shielded cooled chamber. In this case, the spent fuel elements are inserted into the bushings on the reactor and together with them are transported to the input technological position of the specified chamber in a transport tank mounted on a trolley that allows the tank to rotate into a vertical position in which the upper end side of the tank is on the upper platform of the trolley. The fuel elements are taken away with bushings and transferred to a store accessible for a loading machine serving the said chamber.

A disadvantage of the known method for storing spent nuclear fuel is that it involves the construction of an on-site storage facility. The concentration of nuclear fuel in one place, and the location of the NPP is usually industrial centers with a concentration of the population and consumers of electricity, reduces the safety of operation of the NPP. At the same time, the capacities of the reactor storage facilities are limited. In addition, the construction of a special structure is very expensive and leads to a relatively long time for the creation of the storage.

A known method of dry storage of high level radioactive waste (DE patent No. 3708234, G 21 F 9/34, 1988). The known method involves the storage of radioactive waste loaded into the chill molds by storing the chill molds in the wells, calculated for individual chill molds and made at the final waste disposal site, and includes transporting the chill mold to the storage place. The method consists in the fact that the radioactive waste is loaded into chill molds, the last one is placed in several tiers in a metal shipping container, after which the said containers are delivered to the final disposal area by means of ground transportation, where the chill molds are transferred into metal production containers in portions and transported to the final places burial calculated for individual chill molds. After unloading the chill molds to the places of final burial, operational containers are returned to load the next portion of chill molds from the transport container.

The disadvantage of this method of dry storage is the relatively large metal consumption and the need for the construction of special wells under the chill mold, which requires large investments. In addition, in the known storage method, including the operation of transporting chill molds with radioactive waste to the storage location, the latter is relatively laborious. The mentioned operation involves the use of two types of containers - transportation and production and reloading of fuel from one container to another, which in itself complicates the method. At the same time, in relation to long-length spent fuel assemblies, the use of multi-level transportation seems to be inappropriate for design reasons.

A known method of container storage of radioactive waste, in which radioactive waste is stored or transported in a steel container surrounded by the walls of several containers made of concrete, steel and lead (GB patent No. 2132814, G 21 F 9/34, 5/00, 1984). The containers are inserted one into the other, and each is sealed with at least one lid. In this case, the outer container is detachable in the form of a base, onto which removable coaxial rings and an end overlap are successively installed. This embodiment of the outer container (casing) allows, when loading, to minimize the lifting height of other containers inserted one into the other and, thus, improves the safety of handling radioactive waste placed in a steel container. The outer container is essentially reinforced concrete blocks with end faces installed on top of each other, which serve as a means of additional shielding from radiation. The division of the outer container into parts is due to the requirement of ease of installation.

However, the known method of container storage does not imply damping of a steel container with radioactive waste during possible emergency situations during transportation of radioactive waste, i.e. the steel container is not protected from shock loads, which reduces radiation safety, for example, during transportation.

A known method of dry container storage of spent nuclear fuel and similar materials, in which a steel container with NLD during the intermediate storage period at the nuclear power plant in a vertical position is placed in a protective and ventilation casing, which can be assembled from annular reinforced concrete elements mounted on top of each other (patent US No. 5852643, G 21 F 005/00, 1998). In this case, a steel container with SNF is installed on a round base, on which annular coaxial reinforced concrete elements and a round lid (end overlap) are subsequently installed. The mentioned base and ring-shaped elements are provided with guide protrusions, so that when the elements of the protective and ventilation casing are joined around the steel container, an annular channel of a given width is formed. This channel contributes to the creation of defocusing geometry in the event of a cumulative charge (for example, an anti-tank armor-piercing projectile) entering the protective casing. Thus, the protective and ventilation cover protects against possible radioactive contamination in the event of a terrorist attack at a nuclear power plant.

However, the protective and ventilation casing in the known method does not imply the protection of the steel container during transportation of the latter, because casing elements are not bonded to each other and the casing itself is not bonded to a steel container.

A known method of dry container storage of long (up to 14 m) SFAs, in which the housing (internal reservoir) with SFA is placed in a split casing (patent RU No. 2148864, G 21 F 5/008, 2000). According to the known method, SFAs are first kept for a certain period in a pool of water, and then SFAs are loaded into a container for transportation and long-term storage (up to 50 years). The container contains an outer casing with a lid (detachable casing), a case with slots for long SFAs, and shock absorbers. In this case, the container is equipped with an inner case (inner reservoir) with a cover covering the cover with SFA sockets, containing means for fastening with the outer case (detachable casing) and resting on shock absorbers uniformly located and rigidly fixed at the bottom of the horizontally mounted outer casing (detachable casing ) and on the inner surface of the cover of the outer casing. The container is loaded as follows. Tilter grab the container and set in a vertical position on the installation site. Unlock the cover of the outer casing (detachable casing), hook the inner casing (inner reservoir) with a crane and transfer it to the platform for loading the cover. Undock the lid of the inner casing, load the case with long SFAs and dry the SFA by drying with hot air. After drying, the SFA tightly closes the inner case (inner reservoir) with a lid and is filled with inert gas through the corresponding valve. The inner case is returned to the container, the outer case (detachable casing) is hermetically closed, and the container is set to a horizontal position. In this position, the container is transported by rail to the storage location.

The known method of dry storage of long SFA assumes the adoption of measures to ensure minimization of the height of the loaded container (internal tank) when placed in a protective casing. However, the solution to this problem is not disclosed in a well-known source of information.

A known method of dry container storage, which ensures minimization of the lifting height of the loaded container (inner tank) when placing the latter in a protective damping casing (patent RU No. 2105364, G 21 F 5/008, 1998), for which the casing is made in the form of a split drum with end walls and a shell, including the Central element and end elements (areas adjacent to the end walls). In this case, the shell is divided into four parts: two cylindrical adjacent to the corresponding end walls and two half-cylinders. As a result of the division into components, the damping casing in the embodiment is a detachable structure consisting of a base, a top cover and two end caps, respectively interconnected by means of flange connections. According to the known method, before transporting a container with spent nuclear fuel from the nuclear power plant to a place for further storage or disposal, the base of the damping casing is installed in the horizontal position in the form of a half-cylinder on a support foundation or a special storage frame. Then, by means of lifting means, an internal SNF tank is installed in a horizontal position on the supports of the said base. The height of the tank above the floor does not exceed 300 mm, i.e. permissible value under the conditions of a possible emergency fall of the tank. After that, the upper cover of the damping casing is mounted, which is connected to the base. Then the inner tank is fixed inside the damping casing using threaded stops. After that, two end caps of the damping casing are successively installed, which are connected to its base and top cover. Then the inner tank is fixed in the axial direction using the corresponding threaded stops. After that, the installation of the container containing the inner and outer reservoirs on the vehicle is carried out. The container is transported in a horizontal position.

However, in the known method, the installation of the container with SNF in the protective damping casing is carried out in a horizontal position, which involves the preliminary tilting of the container with SNF and complicates the handling of the container when it is placed in the protective damping casing. In addition, the relatively large number of connectors of the protective damping casing increases the complexity of the dry container storage method.

Closest to the invention in terms of essential features is a method for dry storage of spent fuel assemblies according to patent RU No. 2097848 (G 21 F 5/008, 1997). The known method includes the following operations:

a) a metal-concrete container (inner tank) is placed in a damping demountable casing provided with an end cap (outer tank). Moreover, the specified casing is made detachable in such a way as to minimize the required lifting height of the metal-concrete container (MBC) when the latter is placed in an upright position in the casing and released from the casing. Thus, MBK (inner reservoir) together with a damping casing (outer reservoir) form a shipping container. Along with ensuring that the MBC is protected against damage during transportation accidents and providing additional radiation protection during the transportation of MBCs, the damping casing makes it possible to reduce the weight and reduce the cost of manufacturing MBCs, and since MBC is the main (basic) and replicated element for a dry container solution storage, then, due to the placement of MBK for the period of transportation in the damping casing, the cost of the method of dry container storage as a whole is reduced;

b) load the SFA into the shipping container (the SFA is loaded into the MBC located in the damping casing).

In an embodiment of the method, each SFA before loading into the MBC is placed in a pencil case and the latter is sealed;

C) close the shipping container, including the outer (damping casing) and inner (MBK) tanks.

In an embodiment of the method, the damping casing and the MBC are rigidly fastened to each other;

d) the loaded shipping container is transported to the storage location;

e) MBK (inner reservoir) is freed from the damping casing (outer reservoir);

f) MBK are installed at the place of storage;

g) the shipping container is returned for subsequent loading (having previously placed in the damping casing an unloaded MBK located in the storage location). Thus, the MBK is protected from destruction in case of possible emergency situations when it is transported in an unloaded condition. The damping casing, being designed to protect against the destruction of the loaded MBK, moreover, provides protection for the empty MBK.

The known method for dry storage of spent fuel assemblies allows using concrete containers for transportation and / or storage of spent nuclear fuel to protect the container with spent fuel assemblies from destruction during possible emergency situations during transportation to the storage site, which must be taken into account in accordance with the IAEA recommendations, and increases the radiation protection of personnel during transportation .

However, the placement of a metal-concrete container in the damping casing prior to the loading operation in the SFA container significantly increases the dimensions of the serviced (i.e., loaded) structure (the complete assembly with the damping casing). Given that the container is loaded with spent fuel assemblies, as a rule, it is carried out in the transport corridor of the reactor workshop of the nuclear power plant, whose dimensions are limited, then under the conditions of ensuring the possibility of movement in it of this design, it is necessary to reduce the dimensions of the damping casing and, accordingly, the dimensions of the container. As a result, the number of SFAs placed in the container is reduced. In total, this leads to the need to increase the required number of containers and to increase the cost of implementing the concept of dry container storage of spent nuclear fuel. In addition, used in the known method, the damping casing has a relatively large number of connectors, which increases the complexity of the method of dry storage of SFA.

The present invention solves the problem of providing, under the existing infrastructure, the possibility of using metal-concrete containers with optimal overall mass characteristics (in terms of the number of SFAs placed in the container) while ensuring the protection of containers with SFAs from destruction during possible emergency situations during transportation to the storage place.

The problem is solved due to the fact that in the method of dry container storage of spent fuel assemblies, comprising placing the fuel assemblies in a transport and packaging set consisting of a container and a detachable damping casing, made detachable so as to minimize the height of the container when placed in a detachable damping casing , and transporting the transport packaging to the storage location where the container is free from the casing, after which spent fuel the assemblies are stored in the storage place, according to the invention, the spent fuel assemblies are first loaded into the container, after which the container is placed in a vertical position in a detachable damping casing made in the form of a removable drum with an end cover (top cover) and a base acting as an end (bottom) removable drum covers. In this case, the loaded container is installed on the base, covered with a removable drum (like a cap), which is fastened to the base, and then the detachable damping casing is fastened to the container, after which the transport and packaging set is transported to the storage place in the transport position.

Along with this, in the embodiment, before loading the spent fuel assemblies into the container, they are installed in a multi-seat case.

In another embodiment, before installing the loaded container on the base, the latter is installed in a recess made at the site of the work site.

In addition, in the above-described embodiments, on-site storage after releasing the container from the casing, the container is freed from spent fuel assemblies.

At the same time, in another embodiment, when the container is released from spent fuel assemblies, they are reinstalled in another container (storage container), intended only for storage of spent fuel assemblies.

In an embodiment, when the spent fuel assemblies are installed in a multi-seat case, after loading the spent fuel assemblies into the case, its internal cavity is sealed.

The technical result of the use of the invention is that it allows the use of metal-concrete containers for transportation and / or storage of spent nuclear fuel to ensure that the container with SFAs does not deteriorate in case of emergency situations during transportation to the storage site, which must be taken into account in accordance with IAEA recommendations and increases the radiation protection of personnel during transportation and at the same time allows using concrete containers with optimal overall mass characteristics from the point of view of the number of SFAs being placed (loaded), which reduces the required number of containers and thereby makes it possible to reduce the cost of implementing the concept of dry storage of spent nuclear fuel when using MBC for transportation and / or storage of spent nuclear fuel.

Figure 1 schematically shows the overload of canisters with SFAs from the holding pool into a metal-concrete container mounted on an in-station trolley inside the transport corridor of the reactor workshop of the nuclear power plant; figure 2 - unloading the in-house truck at the place of intermediate storage of containers with SFA; figure 3 - metal container with SFA, placed in a damping casing, and a lifting means with a tipping device at the place of intermediate storage before loading the transport and packaging set on a railway platform (railway conveyor); figure 4 - installation of a transport and packaging set on a railway platform (railway conveyor); figure 5 - detachable damping casing with a metal-concrete container placed in it, a longitudinal section.

In an embodiment of the invention, the method is carried out using a transportation container 1, which contains internal and external tanks 2, 3. Internal tank 2 - the container itself is designed to load SFA 4 and is made in the form of a cylindrical metal-concrete structure with two airtight covers: external 5 and internal 6 located one above the other and mounted on a single base 7. Covers 5 and 6 form two circuits (barriers) of protection. In addition, the design of the inner tank 2 (i.e., the container itself) allows the installation of an additional sealing cap (for example, in the form of a sheet), which is welded around the perimeter to the base 7 (not shown). The installation of an additional sealing cover is due to the possibility of reducing the tightness of the seals of the covers 5 and 6 under conditions of prolonged radiation and thermocyclic exposure during storage of spent nuclear fuel and - the requirement to ensure the reliability and environmental safety of the method of dry container storage.

The outer tank 3 is a damping casing of detachable elements. In general, the casing is made in the form of a removable drum 8 with end overlap and a base 9, designed to support the removable drum 8 and acting as the lower end cover of the removable drum. In an embodiment of the invention, the end-overlapping drum 8 and the base 9 comprise shock-damping elements, for example, in the form of a set of tubes, having sufficient strain energy. The base 9 with the drum 8 is mounted in the form of a bolted flange connection, while the inner cylindrical surface of the drum 8 is associated with a corresponding mating surface made on the base. This eliminates the possibility of loading the bolts 10 of the aforementioned flange joints with shear (transverse) forces upon impact. In the cylindrical wall of the drum and the end face of the drum, threaded elements 11 interacting with the body of the inner tank 2 are installed, which exclude the possibility of moving the inner tank 2 (the container itself) relative to the outer tank 3 (damping casing) under the effect of overloads during transportation. Thus, thanks to the threaded elements 11, the possibility of collisions of the container and the damping casing during transportation is excluded.

The proposed method for dry storage of spent fuel assemblies is implemented as follows.

Spent fuel assemblies 4 withstand a certain period in the pool 12 with water. In an embodiment of the method, SFAs are placed (installed) in multi-seat cases 13, which simplifies handling of SFAs.

In the embodiment, after installing the SFA in the canister 13, the latter is sealed, for example by "welding" its cover. Sealing the can allows you to significantly increase environmental safety in case of possible emergency situations during the transportation and storage of spent nuclear fuel. The use of multi-seat cases compared to single-seat cases can reduce the total number of cases and their sealing elements.

After a certain period of exposure in the pool of water and, accordingly, a decrease in the level of activity of the SFA, they are unloaded from the pool 12 of the exposure and loaded into the container 2 for further storage. The SFA can be loaded into the container when the container 2 is located in the transport corridor 14 of the reactor workshop on a special in-plant trolley 15 having a minimum cargo area height. Cases 13 with SFAs are installed in the corresponding slots of the spacer grid 16, which is previously placed in the container 2. It is basically possible to load the SFA directly into the container 2 or in the spacer grid 16 installed in the loading chamber, which is then installed together with the SFA in the container 2. B In the latter case (in the absence of pencil cases), the nests of the spacer grid can be made isolated from the space of the internal cavity of the container and can be covered by lids (not Zano). Loading, in-plant transportation of container 2 and storage of the container at nuclear power plants are carried out with the container vertical. After loading the container, it is closed, as a rule, with two sealed covers 5.6 and the loaded container is transported to the place of intermediate storage 17 (in the territory of the nuclear power plant or in the adjacent storage). At the same time, the container is moved and the container is installed at an intermediate storage place with a speed limit and a container lifting height, as well as with the use of additional safety devices, which eliminates the possibility of emergency situations in which the SFA loaded into the container could be destroyed and could be the container is damaged or depressurized.

In the place of intermediate storage 17, the loaded container may be for a long time. Then the loaded container 2 is transported to the place of final storage.

Before transporting the container with the SFA from the nuclear power plant to the place of final storage (for example, in a regional repository or at a radiochemical plant for reprocessing SNF), the container 2 is placed in a split damping casing 3. In this case, the container 2 with the SFA is installed on a horizontally exposed base by means of standard lifting equipment 9, then cover with a removable drum 8 from above, which, for example, with bolts, is rigidly fastened to the base 9. Then, using threaded elements 11, the damping casing 3 is scratched lyayut container 2. This eliminates the possibility of moving the latter within the enclosure during transport. The threaded elements 11 fastening the damping casing to the container are at the same time distance and damping elements and, in addition, serve as thermal bridges. This technical solution provides reliable protection of the container 2 for any type of accidental fall, increases radiation protection due to additional shielding and allows to reduce structural reserves of the container's strength, which, in turn, allows to reduce the cost of the container. Moreover, the implementation of the damping casing 3 is detachable with a detachable base 9, when the container with SFA is installed on the base 9 of the casing and covered with a removable drum 8 with end overlap, it allows to minimize the height of the container when the latter is placed in the casing and freed from the casing, which increases the safety of handling SFA (SNF). In another embodiment (not shown), an additional reduction in the height of the container with the SFA when placed in a damping casing can be achieved by installing the base 9 of the casing in the pit (a recess made at the site of the work site, in particular, at the place of intermediate storage).

After the container is assembled with a damping casing (transport and packaging set) by means of lifting means 18 and the tilting device 19 is transferred to a horizontal position. In this position, the transport and packaging set (TUK) is installed on the vehicle, for example, a railway platform (railway conveyor) 20 and the position of the TUK relative to the latter is fixed.

The transport and packaging set (damping casing with a container) in the transport position is transported to the place of final storage (burial). A detachable damping casing, equipped with shock absorbing elements (for example, pipes, a set of ribs in the form of frames and stringers, etc.), reduces the overloads acting on the container to an acceptable level in all possible emergency situations regulated by regulatory documents of the Russian Federation and IAEA recommendations , at any, including the most unfavorable angles of incidence of the TUK (for example, a drop at the angle of the TUK). At the same time, placing the container in a damping casing significantly increases the strength characteristics of the transport and packaging set when it falls on the pin, heat-shielding properties when it enters the fire zone, and radiation-shielding properties.

After the container is transported to the regional storage, it is released in the storage location from the damping casing in the reverse order. Then the damping casing is returned to the NPP for transportation of the subsequent container with the SFA, and the container with the SFA is installed in the storage place.

In another embodiment, at the storage location after releasing the container 2 from the damping casing 3, the container is freed from the SFA 4. In this embodiment, the SFA 4 at the storage location from the container 2 is reloaded (reinstalled) into another container intended only for storage of the SFA (storage container ), the requirements for which can be significantly lower than for the container 2 intended for storage and / or transportation (the requirements associated with possible emergency transport situations are excluded). This allows you to significantly simplify the storage container and reduce its cost compared to container 2 and, accordingly, to reduce the cost of implementing the method of dry container storage.

Thus, due to the design features, the proposed method allows the use of metal-concrete containers for SNF transportation and / or storage to ensure that the container with SFAs does not deteriorate in case of emergency situations during transportation to the storage site, which must be taken into account in accordance with IAEA recommendations and increases radiation protection personnel during transportation and at the same time allows using concrete containers with optimal overall mass characteristics from the point of view of the number of SFAs being placed (loaded), which reduces the required number of containers and thereby makes it possible to reduce the cost of implementing the concept of dry storage of spent nuclear fuel when using MBC for transportation and / or storage of spent nuclear fuel.

Claims (6)

1. The method of dry container storage of spent fuel assemblies, comprising placing the fuel assemblies in a transport and packaging set consisting of a container and a detachable damping casing, made detachable so as to minimize the height of the container when placed in a detachable damping casing, and transportation a packaging set to a storage location where the container is freed from the casing, after which the spent fuel assemblies are stored in a storage location, characterized in that the spent fuel assemblies are first loaded into the container, after which the container is placed in a vertical position in a detachable damping casing made in the form of a removable drum with an end overlap and a base acting as the end cover of the removable drum, while the loaded container is installed on the base, the top is covered with a removable drum, which is fastened to the base, and then a detachable damping casing is fastened to the container, after which the transport and packaging set transport position transported to the storage location. 2. The method according to claim 1, characterized in that before loading the spent fuel assemblies into the container they are installed in a multi-seat case. 3. The method according to claim 1, characterized in that before installing the loaded container on the base, the latter is installed in a recess made at the site of the work site. 4. The method according to any one of claims 1 to 3, characterized in that at the storage location after releasing the container from the casing, the container is freed from spent fuel assemblies. 5. The method according to claim 4, characterized in that when the container is released from the spent fuel assemblies, they are reinstalled in another container. 6. The method according to claim 2, characterized in that after loading the spent fuel assemblies into the pencil case, its internal cavity is sealed.

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