RU2097848C1 - Method for dry disposal of used fuel assemblies - Google Patents

Abstract

FIELD: disposal of used fuel assemblies. SUBSTANCE: method involves installation of reinforced-concrete container in damping casing provided with end cover followed by charging it with used fuel assemblies. Casing is split structure so as to minimize height of container lifting when placing it in damping casing. Charged container is conveyed in damping casing to disposal site where it is removed from damping casing. Empty casing is turned for next charging with spent fuel assemblies. EFFECT: facilitated procedure. 2 cl, 3 dwg

Description

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

 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 / Edited by V. A. Legasov. M. Energoatomizdat, 1989, p. 494 496). The known method of dry storage offers a specific 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. This can be a surface mine, a dry well, or an air-cooled chamber.

 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. Dry storage facilities can be expanded gradually in small portions with minimal initial capital outlay.

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

 There is a method of intermediate and final storage of fuel elements of a nuclear reactor (German patent, N 3500999, class G 21 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 the camera. 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 nuclear power plants, as a rule, industrial centers with a concentration of the population and consumers of electricity, reduces the safety of operation of nuclear power plants. At the same time, the capacities of the on-site storage facilities are limited. In addition, the construction of a special structure is very expensive and leads to relatively long periods of storage creation.

 Closest to the invention in terms of essential features is a method for dry storage of highly radioactive waste (German patent N 3708234, CL G 21 F 9/34, 1988).

 The known method provides for the dry 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 involves transporting the chill mold to the storage place. The method consists in loading radioactive waste into the chill molds, placing the last in several tiers in a metal shipping container, and then using the means of ground transportation, the said containers are delivered to the final disposal area, where the chill molds are transferred into metal production containers in portions and transported to places final 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 in the field of final fuel disposal, which in itself complicates the method. At the same time, in relation to long-length spent fuel assemblies, the use of multi-tier transportation seems to be impractical for structural reasons.

 The objective of the invention is to reduce costs when implementing the concept of dry storage of spent nuclear fuel.

 The problem is solved due to the fact that in the method of dry storage of spent fuel assemblies, in which the spent fuel assemblies are inserted into the container and stored in a storage location including transporting the container to the storage location, according to the invention, before loading the spent fuel assemblies into the container, the latter is placed in a fitted end cover a damping casing in which a loaded container is transported to a storage location. At the storage location, the container is freed from the damping casing and installed at the storage location. An unloaded container is placed in the damping casing and the casing is returned for subsequent loading of the container.

 In addition, before loading into the container, each spent fuel assembly is placed in a pencil case and the latter 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 protect the container with SFAs from destruction in case of emergency situations during transportation to the storage site, which must be taken into account in accordance with IAEA requirements, and increases radiation protection of personnel during transportation.

 Figure 1 schematically shows the loading of the SFA in a metal container placed in a damping split casing; figure 2 damping detachable casing with a metal-concrete container placed in it, a longitudinal section; figure 3 damping detachable casing, General view.

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

 The spent fuel assemblies 1 withstand a certain period of time in the pool of water 2. Then, the SFA is delivered individually to the protective chamber 3, where each SFA is divided into two bundles of fuel rods. The bundles of fuel rods are installed in the accumulator 4, from which they are loaded into groups of 4 in groups of 4 prepared for loading.

 In another embodiment of the invention, before loading into the container, each spent fuel assembly is placed in a pencil case (not shown in the drawing) and the latter is sealed. This solution enhances radiation protection.

 The shipping container 5 comprises an inner and outer reservoir. The inner tank itself, container 6 is intended for loading SFAs and is made in the form of a metal-concrete structure with two caps: outer 7 and inner 8, located one above the other and mounted on a single base. The outer tank is a damping casing 9 of detachable elements. In general, the casing is made in the form of a shell 10 with diaphragms 11 and 12 at the ends. Under each diaphragm there are installed radially arranged tubular elements 13, fastened respectively with the diaphragm, the casing with each other. The inner surface of the shell is provided with ribs 14. Moreover, along the generatrix of the shell around the circumference, other tubular elements 15 are mounted, fastened respectively to the shell by the said ribs and to each other. The tubular elements are filled with porous energy-absorbing material, for example, cement-sand concrete with aggregate in the form of expanded expanded clay. The shell and ends of the casing are lined with reinforced concrete on the inside. In an embodiment of the invention, the casing is made of three detachable elements 16, 17 and 18, one of which is made in the form of an end cover of the casing. With the metal-concrete container 6, the casing 9 is fastened by means of pin devices (not shown in the drawing).

 Such a solution provides reliable protection of the container for any type of accidental fall, increases radiation protection due to additional shielding and reduces the structural reserves of the container's strength, which, in turn, allows to reduce the cost of the container. Moreover, the implementation of the casing is detachable to minimize the required height of the container when the latter is placed in the casing and released from the casing, which increases the safety of handling SFA.

 Previously, before loading the SFA, the metal-concrete container 6 is placed in a damping casing 9, which is fixed on the vehicle 19. At the same time, on the vehicle, the casing 9 is fastened with a tilter 20 with the possibility of installation in a vertical position when loading the SFA in the transport corridor 21 of the storage at the gas station and to horizontal position during transportation.

 The transport container 5 is horizontally delivered to the transport corridor of the nuclear power plant and installed under the loading window 22. By means of a cover removal device 23 mounted with the possibility of longitudinal movement on the vehicle platform, the end cover 18 of the damping casing is removed, after which the casing with the container by means of a tilter 20 is transferred in vertical position.

 Through the loading window using lifting means 24 remove the outer and inner lids of the container. After that, the loading window 22 is blocked by a guide-orienting device 25, which is connected to the upper end of the container.

 After loading the container, the latter is closed in the reverse order with lids, after which the damping casing with the container is put into transport position and the end cover 18 is installed on the damping casing 18. The casing with the loaded SFA container is transported to the storage place where the container 6 is released from the damping casing 9 and installed on storage.

 An unloaded container located in the storage location is placed in the damping casing 9, and the casing with the container is returned to the NPP for subsequent loading with spent fuel assemblies.

 In the case of the fall of the shipping container from the vehicle, at any possible angle of incidence, including falling onto the pin, the casing of the container with its tubular elements and the force set connecting them is deformed, absorbs the kinetic energy of the fall and dampens the shock.

 In addition, equipping a metal-concrete container with an SFA with a volumetric enclosure completely covering it provides additional radiation protection during transportation in accordance with the requirements of regulatory documents (Basic Safety and Physical Protection Rules for the Transport of Nuclear Materials. OPBZ 83. Moscow. 1984).

 Providing the “Radiation Safety Standards NRB 76/87 and basic sanitary rules. OSP 72/87”, taking into account additional shielding structures in the storage container for spent nuclear fuel, the requirements for the radiation-protective properties of a metal-concrete container can be lowered (Radiation Safety Standards NRB-76 / 87 and basic sanitary rules for working with radioactive substances and other sources of ionizing radiation OSP 72/87, Ministry of Health of the USSR, 3rd ed. Revised and revised M. Energoatomizdat, 1988). This makes it possible to reduce weight and reduce the cost of manufacturing a metal-concrete container as the main (base) and replicable element in the concept of dry storage of spent nuclear fuel and, accordingly, reduce the cost of implementing this concept.

 Thus, due to the design features, the proposed method provides protection of the metal concrete container with SFAs from destruction in case of emergency during transportation to the storage place, increases the radiation protection of personnel during transportation and makes it possible to reduce the cost of implementing the concept of dry storage of spent nuclear fuel when using metal concrete containers for SNF transportation and / or storage.

Claims (2)

 1. The method of dry storage of spent fuel assemblies, in which the spent fuel assemblies are inserted into a container and stored in a storage location, including transporting the container to the storage location, characterized in that the spent fuel assemblies are loaded into a metal-concrete container, while before loading the fuel assemblies into the container the latter is placed in a damping casing provided with an end cover, for which the casing is made detachable in such a way as to minimize the lifting height of the contour when placing it in a damping casing, and after loading the container, the latter in the damping casing is transported to the storage place where the container is freed from the damping casing, after which the casing with the container not loaded is returned for subsequent loading of the latter.  2. The method according to p. 1, characterized in that before loading into a metal container, each fuel assembly is placed in a pencil case and the latter is sealed.

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