RU2287194C1 - Method for dismounting defective spent fuel assemblies - Google Patents

Abstract

FIELD: nuclear power engineering; handling nuclear wastes stored in dry storage depots including in those of submarine fleet.

SUBSTANCE: proposed method that can be used to dismount defective spent fuel assemblies disposed in dry storage depots of nuclear submarines and surface craft and provides for shielding environment from gamma and neutron rays in the course of handling defective fuel assemblies includes removal of safety plug, cutting and extraction of fuel assembly cans. Movable-portal frame is installed on dry-storage depot floor; at least one movable shielding pressure unit provided with video and radiation monitoring systems is mounted on portal, and safety plug is removed by means of lifting crane of floor; shielding pressure unit is installed above tube seat holding defective fuel assembly and let down on shielding cushion while tilting space suit, if necessary; can holding spent fuel assembly is cut out by means of face milling cutter, end part of mentioned assembly being held in the process by means of grip disposed in rod; can holding defective fuel assembly is extracted by means of pressure-unit handler grips; end parts of can holding defective fuel assembly are cut off by means of side mills and then they are placed in solid radioactive waste reservoir; pressure unit is displaced by means of portal within cavity accommodating shipping casks; axis of defective assembly active part is aligned with that of one of shipping casks; the latter is lifted and placed in pressure unit, active part of assembly is placed in the latter, pressure unit holding shipping cask is displaced to drying seat accommodating magazine with compartments to receive shipping casks; shipping cask is placed in one of magazine compartments; operations for extracting other defective fuel assemblies and for delivering shipping casks to magazine are repeated until magazine is filled up with shipping casks, whereupon magazine is closed with bayonet lid communicating through flexible pipeline with evacuating and dry-gas filling systems; active parts of defective fuel assemblies are dried out, then magazine holding shipping casks is loaded in shipping-and-packing set. This method provides for dismounting defective spent fuel assemblies whose deviation from vertical position exceeds permissible value.

EFFECT: enhanced efficiency and environmental friendliness, enlarged functional capabilities.

2 cl, 5 dwg

Description

The invention relates to nuclear energy, in particular to methods for the management of nuclear waste stored at dry storage bases (BSH), and can be used to dismantle defective spent fuel assemblies (SFA) stored in the BSH of an atomic submarine fleet.

On BSH SFAs are placed in canisters, which are installed vertically in cascades of tube plates. The number of pencil cases in the cascade is 5-7 pieces. Cases are attached to tube sheets with welded rings. The assemblies thus obtained are installed in steel pipes with a diameter of about 250 mm, called tube sockets. A bottom is welded to the bottom of each pipe. Pipe sockets are placed in boxes and are welded together by jumpers. The space between the nests is filled with concrete with the formation of a pillow made of concrete over them, which is a protection against gamma and neutron radiation. Holes with a diameter exceeding the outer diameter of the pipes are made in the concrete cushion above the nests. These openings are covered with protective plugs.

As a result of established practice, BSHs were located near the coastline of the sea, which led to the effect of sea water on the walls of the boxes for storing SFAs. Over time, the walls of the boxes corroded, which led to cracking of the concrete pouring and corrosion of the pipes of the nests in which the SFA was placed. The canisters in which the SFAs were inserted were also corroded and swollen, which caused the gaps between the SFAs and the canisters to fill with corrosion materials. As a result, the extraction of SFA in the standard version became impossible. Such defective assemblies are called unrecoverable. The situation was also aggravated by the fact that part of non-recoverable assemblies was installed with deviations from the vertical exceeding the permissible deviation, which complicates the dismantling of assemblies.

The proposed invention is aimed at solving the problem of dismantling defective SFAs stored on a storage tank of nuclear submarine and surface fleets.

There is a method of dismantling defective SFA placed in individual canisters in storage facilities of floating technical bases, described in the journal "Atomic Equipment Abroad", No. 3, 1997, p.20-21, "Floating storage" Lepse ". By a known method, the protective plug of the loading hole of the rotary plate located above the SFA canisters is removed. Rotating the rotary plate, center the loading hole relative to the SFA canister, assess the condition of the upper parts of the SFA. Further, according to one of the options, the rotary plate is removed to provide access to the SFA. Then the pencil cases are removed entirely using remotely controlled dismantling tools.

The disadvantages of this method are:

- high complexity of removing the rotary plate;

- the possibility of release into the environment of radioactive products released from the SFA, since after removing the turntable, access to all SFA is open;

- the difficulty of dismantling defective SFAs installed with deviations from the vertical exceeding the permissible deviation.

A known method of dismantling SFAs from temporary storage facilities located on floating technical bases, according to patent RU 2154864, selected by the applicants as a prototype.

According to the known method, canisters with SFA are welded to the bushings inserted along the landing path into the holes of the tube plate, which in turn are welded to the tube plate.

To implement the known method, remove the protective plug of the loading hole of the rotary plate that is joined to the defective SFA, then, rotating the rotary plate, center this hole relative to the case with the defective SFA. Through the loading hole of the rotary plate in the tube plate and in the flange of the passage sleeve, an annular groove is made using a cutter mounted on the rod, the inner diameter of which is slightly larger than the outer diameter of the passage sleeve and the depth of which exceeds the penetration in the tube plate. Then, using the gripper located in the container, they capture the pencil case by the technological grooves in its upper part, and draw the pencil case together with the bushing into the container through the loading hole of the turntable.

The disadvantages of the prototype are:

- the impossibility of applying the known method in cases where the SFA canisters are installed in the cascade of tube plates due to the fact that the tool post holder cannot have sufficient rigidity due to its large outreach required when cutting the middle and lower tube plates;

- the difficulty of dismantling defective SFAs in cases where the cases with SFAs are installed with deviations from the vertical exceeding the permissible deviation;

- the known method does not include segments at the SFA end parts and placing them in containers for solid radioactive waste, as well as placing the active parts in canisters, closing them with lids, which complicates the subsequent preparation of SFA for drying and transportation for storage or processing;

- the method does not solve the issue of protecting the environment from gamma and neutron radiation generated by defective SFAs during their dismantling.

The technical result of the proposed invention is to eliminate the disadvantages of the prototype, namely:

- the creation of the ability to dismantle defective SFAs located on the base station of nuclear submarine and surface fleets;

- improving the effectiveness of the method due to the dismantling of defective SFAs having deviations from the vertical exceeding the permissible deviation;

- expanding the functionality of the method by preparing the dismantled SFA for drying and transportation to storage or processing;

- ensuring environmental protection from gamma and neutron radiation during the dismantling of defective SFAs.

The technical result is achieved by the fact that in the method of dismantling defective spent fuel assemblies, comprising removing the protective plug, cutting and removing canisters, according to the invention, a frame with a portal that can be moved in two mutually perpendicular directions is installed on the site of the dry storage base, where defective assemblies are located in the horizontal plane, at least one protective spacesuit is placed on the portal, which can be rotated about its longitudinal axis of symmetry and Moving vertically up and down relative to the portal, as well as tilting relative to it, equipped with video surveillance and radiation control systems, technological equipment, removing the protective plug is carried out using a crane, which is equipped with a platform, install a protective suit over the pipe socket with a defective assembly and lower it to a protective cushion, if necessary, tilting the spacesuit at an angle that ensures alignment or parallelism of the longitudinal axis of symmetry of the socket and the spacesuit, is cut out a canister with a spent fuel assembly using an end mill, the diameter of the inner hole of which exceeds the outer diameter of the canister, mounted on a hollow rod, the inner diameter of which also exceeds the outer diameter of the canister, while holding the defective assembly by the end part of the grip located in the rod, remove the canister from defective assembly using the grips of the manipulators located in the spacesuit, cut off the end parts of the pencil case with a defective assembly using disk cutters, then place them in a container for solid radioactive waste, with the help of the portal, the spacesuit is moved to the shaft in which the transport cases are located, the axis of the active part of the defective assembly is aligned with the axis of one of the transport cases, the transport case is raised inside the spacesuit, the active part of the assembly is placed in it, the spacesuit with the transport case is moved to the drying slot, in which the cassette with cells for pencil cases is located, the transport case is installed in one of the cells of the cartridge, operations for removing other defective assemblies and delivery of transport cases the cartridge is repeated until the cartridge is completely filled with canisters, the cartridge is closed with a sealed bayonet cap connected by a flexible conduit to vacuum systems and filled with dry inert gas, the active parts of the defective assemblies are dried, then the cartridge with transport canisters is loaded into the shipping and packing kit to send the defective assemblies to processing or storage.

In addition, for the destroyed defective spent fuel assemblies, the storage socket pipe is cut using the second suit, then the entire cartridge is removed, if necessary, the end parts of the cartridge are cut, the active part is loaded into the transport case, drying is carried out for subsequent loading of the transport case with the cartridge into the transport -packing kit for shipment for processing or storage.

The proposed technical solution provides for the dismantling of the SFA located on the BSH due to the fact that the cutting of canisters from the cascade of tube plates is carried out by a cylindrical end mill mounted on a hollow rod equipped with a gripper for the end part of the defective assembly, as well as due to the use of a protective suit, having the ability to tilt relative to the portal, allows you to position the hollow bar with the cutter at an angle equal to the angle of inclination of the defective assembly, and remove the pencil case with the assembly with the direction of the pulling force at the same angle.

Cutting off the end parts of the canisters and SFAs, placing them in containers for solid waste, placing the active parts of the SFAs in transport canisters with subsequent transfer to the drying sockets, drying and packing them in a transport and packaging complex expands the functionality of the method, ensures the continuity of the process for preparing defective SFAs for processing or storage.

The use in the proposed method of a protective suit equipped with video surveillance and radiation control systems, technological equipment and located above the tube sockets with defective SFAs, protects the environment and operators from gamma and neutron radiation generated by defective SFAs.

The proposed method is illustrated by the following drawings.

Figure 1 shows a frame 1 with a portal 2 mounted on it, with the ability to move along the guides 3 and 4 of the frame 1, a protective suit 5 is installed on the portal.

Figure 2 shows a scheme for cutting a canister with a SFA, including a protective suit 5, a milling machine 6 installed inside the suit 5 with a hollow rod 7, equipped with an end mill 8 and a gripper 9 SFA. The suit is also equipped with a hydraulic lift 10 and is mounted on a protective pillow 11 made of concrete coaxially with the hole 12 in the pillow, below which there is a tube socket 13, in which an assembly 14 is located, consisting of a cascade of tube plates 15 and canisters 16 welded with ring seams to the tube plates 15, in canisters 16 posted SFA 17.

Figure 3 shows a diagram of the segments of the shanks of the defective SFA 17 (cases 16 are not shown) using disk milling cutters 18 of the cutting machine 19. The defective assembly is held in this case by the grippers 20, 21 and 22.

Figure 4 shows the layout of the active part of the SFA 17 in the transport case 23 located in the slot 24, using the capture 21 and the elevator 25 of the manipulator.

Figure 5 shows a diagram of the installation of transport canisters 23 using the lift 26, located in the suit 5, in the cassette 27. To close the cassette 27, a bayonet cover 28 with a flexible pipe 29 is provided. 30 indicates a case of the transport and packaging complex located in the drying slot 31.

The proposed method for dismantling defective SFA is as follows.

Using a crane, remove the protective plug of the tube socket 13. Determine the state of the SFA using a dynamometer installed in the power circuit: crane - gripping device - SFA. If the lifting force of the SFA exceeds the regulated one, this means that the assembly has become unrecoverable in the standard version due to corrosion of the canisters and SFA.

Above the defective assembly 14, a protective suit 5 is installed using the portal 2 and lowered onto a protective cushion 11, combining the longitudinal axis of the suit with the longitudinal axis of the pencil case. If the assembly 14 is installed with a deviation from the vertical by an angle exceeding the allowed one, the spacesuit 5 is tilted to this angle in order to combine or parallelize the longitudinal axes of the assembly 14 and the spacesuit 5. Then the defective SFA 17 is cut out together with the canister 16 from the cascade of tube plates 15, using a milling machine installed in a spacesuit 5. Cutting out is carried out using an end mill 8 attached to a hollow rod 7. The internal openings of the mill 8 and rod 7 exceed the outer diameter of the canister 16, which will ensure that the canisters are cut out over the entire height a cascade of tube plates 15. To hold the SFA 17 with a canister 16 inside the hollow rod 7 when cutting the lower tube plate 15, use a gripper 9 mounted in the rod 7 at a height from the cutting end of the milling cutter 8 equal to the distance from the lower tube plate to the head of the SFA.

After the lower tube plate 15 has been cut, the rod 7 is raised up to the lower end of the pencil case 16 inside the spacesuit 5, then a support (not shown) is brought under the pencil case 16, the gripper 9 that holds the head of the SFA 17 is opened, the rod 7 is lifted up, and the case 16 is fixed using the grippers 20, 21 and 22 of the manipulators. The end parts of the canister 16 are cut off together with the SFA 17 using disk milling cutters 18, the rod 7 is lifted upward, freeing the head of the SFA 17. The upper and lower manipulators, equipped with grippers 22 and 20, move the end parts to the side and, unclenching the grips, first the lower, then upper, dump the end parts into a container for solid radioactive waste.

Next, the suit 5 is moved to the shaft 24, in which the transport canisters 23 are placed, the axis of one of the canisters 23 is aligned with the axis of the active part of the SFA 17, the transport canister 23 is fed into the suit 5 using the lift 24 and the active part is laid into it. After that, the suit 5, loaded with a transport case 23, is moved to the drying slot 31, in which the cartridge 27 with cells for the cases is placed. The case 23 is installed in one of the cells of the cartridge 27. The operations to remove other SFAs and the delivery of transport cases to the cartridge is repeated until the cartridge is completely filled with cases.

Then the cassette 27 is closed with a sealed bayonet cap 28, connected by a flexible pipe 29 to vacuum systems and filled with dry inert gas, the active parts of the SFA are dried. After that, the cassette 27 with transport cases 23 is loaded into a transport and packaging set (not shown) for sending defective assemblies for processing or storage.

EFFECT: invention allows to carry out sequentially technological operations for the extraction of defective SFAs, their preliminary preparation before being sent for storage or processing, while protecting operators from gamma and neutron radiation. If the list of technological operations carried out with the help of one spacesuit is not enough for the full technological cycle, a second spacesuit can be installed on the portal, with which you can perform the remaining operations.

For example, for damaged defective spent fuel assemblies, the tubes of the storage slot are cut out with the help of a second suit, then the entire cartridge is removed, if necessary, the ends of the cartridge are cut, the active part is loaded into the transport case, drying is carried out for subsequent loading of the transport case with the cartridge into the transport -packing kit for shipment for processing or storage.

Claims (2)

1. A method for dismantling defective spent fuel assemblies, comprising removing a protective plug, cutting and removing canisters, characterized in that a frame with a portal is installed on the site of the dry storage base where the defective assemblies are located, having the ability to move in two mutually perpendicular directions in the horizontal plane , at least one protective spacesuit is placed on the portal, having the ability to rotate about its longitudinal axis of symmetry and move vertically up and down relative to the portal, as well as the inclination relative to it, equipped with video surveillance and radiation monitoring systems, technological equipment, the removal of the protective plug is carried out using a crane, which is equipped with a platform, install a protective suit over a tube socket with a defective assembly and lower it onto a protective pillow, if necessary tilting the spacesuit at an angle that ensures alignment or parallelism of the longitudinal axis of symmetry of the nest and the spacesuit, cut out the pencil case from the spent fuel assembly with a face mill, the diameter of the inner hole of which exceeds the outer diameter of the canister, mounted on a hollow rod, the inner diameter of which also exceeds the outer diameter of the canister, while holding the defective assembly by the end part of the grip located in the rod, remove the canister with the defective assembly using the grippers of the manipulators located in the suit, cut off the end parts of the pencil case with a defective assembly using disk cutters, then place them in a container for solid radioactive waste, using of the portal, the spacesuit is moved to the shaft in which the transport cases are located, the axis of the active part of the defective assembly is aligned with the axis of one of the transport cases, the transport case is raised inside the spacesuit, the active part of the assembly is placed in it, the spacesuit with the transport case is moved to the drying slot in which it is located a cassette with cells for pencil cases, a transport pencil case is installed in one of the cells of the cartridge, the operation to remove other defective assemblies and the delivery of transport pencil cases to the cartridge is repeated until completely filled Asset canisters, the cassette lid is closed airtight bayonet associated flexible piping systems with evacuation and filling a dry inert gas by drying the active parts of defective assemblies, then the cassette to transport loaded canisters in transport and packaging for shipment of defective assemblies for processing or storage. 2. The method for dismantling defective spent fuel assemblies according to claim 1, characterized in that for the destroyed defective spent fuel assemblies, the storage socket pipe is cut using a second suit, then the entire cartridge is removed, the end parts of the cartridge are cut off, if necessary, the active part is loaded into transport case, carry out dehydration for subsequent loading of the transport case with a cartridge into the transport and packaging kit for shipment for processing or storage.

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