LT6740B - Method for dismantling of the graphite stack of nuclear reactor - Google Patents

Abstract

The invention relates to methods of protecting against X-rays, gamma rays, corpuscular radiation or particle bombardment; treating of radioactively contaminated materials; decontamination arrangements therefor. The method for dismantling of the graphite stack of nuclear reactor comprising pouring liquid into the reactor void with the graphite stack in it, then lifting up of the stack‘s blocks and transferring to a dedicated location outside the reactor. To simplify the dismantling technology of high irradiated graphite stack and the equipment for lifting up of the graphite stack, the graphite stack is flooded with a liquid with a density higher than the density of the reactor graphite, and this liquid is pumped into the reactor void so that the graphite stack exposed by Archimedes force is raised so much that the upper blocks and its parts, which are transferred by the controlled manipulator to a designated point outside the reactor, presently float at the top of the reactor void at the same level.

Description

Technical field

The invention relates to methods of protection against X-rays, gamma rays, particulate radiation or particle firing, as well as to the handling of radiation-contaminated materials and to decontamination devices therefor.

State of the art

From a technical point of view, the most complex and dangerous part of the decommissioning technology of a nuclear reactor is the dismantling of its core. The decommissioning of a nuclear reactor takes place in an environment of very high levels of ionizing radiation, so technical solutions for the dismantling of a nuclear reactor core, including graphite formwork, must reduce the potential exposure of workers and the release of radionuclides from reactor structures into the environment.

Known manual disassembly in an air environment. This technology was used to dismantle the GLEEP experimental nuclear reactor and is described in the article - Potter DJ, Jarvis RB, Banford AW, Cordingley L., and M. Grave, Selection of Retrieval Techniques for Irradiated Graphite during Reactor Decommissioning - 11587. WM2011 Conference, February 27 - March 3, 2011, Phoenix, AZ.

http: //www.wmsvm.orq/archives/2011/papers/11587.pdf/, reviewed June 17, 2015.

This dismantling method is not suitable when the reactor exposure is high, as in this case there is no shielding of ionizing radiation from the reactor structures.

Known disassembly in air by replacing the biological protection of the reactor top with a shielding platform and using a remote control system to take and lift a separate piece of graphite formwork. This technology was used to dismantle the WAGR Energy Nuclear Reactor and is described in Hallivvell C. The Windscale Advanced Gas Cooled Reactor (WAGR) Decommissioning Project A Close Out Report for WAGR Decommissioning Campaigns 1 to 10 - 12474. VVM2012 Conference, February 26 - March 1, 2012, Phoenix, Arizona, USA.

http://www.wmsvm.org/archives/2012/papers/12474.pdf/. reviewed on 06/17/2015.

This method of disassembly requires sophisticated remote control system manipulators to lift graphite formwork blocks at various heights from the bottom of the reactor from the reactor, with higher ionizing resistance of the remote control system manipulators! radiation, because the ionizing radiation of the reactor structures is not shielded in the area of operation of the manipulators, an additional ventilation system is required to remove air contaminated with radioactive aerosol particles, as well as additional equipment to remove cracked or highly brittle graphite blocks from the reactor.

Disassembly in air is known by dismantling a small part of the reactor top biosecurity and using a robot or a robot and remote control system to remove graphite from the reactor. This technology is described in the report - naaniOK A.O. TexHHHecKwe peujeHHsi w οπβιτ AO «OflLĮ ΥΓΡ» no očpaLųeHMio c očnyMeHHbiM ΓρβφιιτοΜ npn BbJBOfle M3 3KcnnyaTaųnn. MeJKąyHapoAHbiii očmecTBeHHbiii cpopyMflnajior u BbiCTaBKa «Ατομ3κο2017», MocKBa, 21-22 Hoiičpb, 2017.

http://www.atomeco.Org/mediafiles/u/files/2017/materials/06 ATOMEKO Pavlvk A.O .pdf., revised 04/09/2018.

This method of dismantling requires sophisticated remote control system manipulators to lift graphite formwork blocks at various heights from the reactor bottom, higher remote control system manipulators and robots with ionizing resistance! radiation, as ionizing radiation from reactor structures is not shielded in the area of operation of manipulators and robots, requires an additional ventilation system to remove air contaminated with radioactive aerosol particles, as well as additional equipment to remove cracked or highly brittle graphite blocks from the reactor.

The closest analogue to the technical solution is Fort St. A method of dismantling the graphite core of a high-temperature gas-cooled nuclear reactor at the Vrain Nuclear Power Plant by filling the dismantled graphite core with water to protect workers from ionizing radiation. During the work, water was circulated and the water was filtered and treated. Underwater, using a remote-controlled manipulator of a complex design, individual graphite blocks and parts were taken and lifted by transferring them and placing them in dedicated containers. This technology is described in Fisher, M. (1998). Fort st. Vrain decommissioning project (IAEA-TECDOC - 1043). International Atomic Energy Agency.

https://inis.iaea.orQ/collection/NCLCollectionStore/ Public / 29/059 / 29059907.Ddf, revised 2012-02-21.

This dismantling method requires complex remote control system manipulators to lift graphite formwork blocks at different heights from the reactor bottom, higher resistance of the remote control system manipulator to ionizing radiation, because the ionizing radiation of the reactor structures in the manipulator operation area is less, resistance to moisture due to the fact that the operations of the manipulator are performed not only in air but also in water, as well as additional equipment is needed to remove cracked or very fragile graphite blocks from the reactor.

Technical problem solved

The aim of the invention is to simplify the technology and equipment for the dismantling of highly irradiated graphite formwork, and at the same time to extend the service life of the equipment and to reduce the cost of this process.

Disclosure of the essence of the invention

The essence of the solution according to the proposed invention is that in the method of dismantling graphite formwork of a nuclear reactor, which involves flooding the graphite formwork in the reactor cavity with liquid, then sequentially lifting the formwork blocks and other graphite parts from above and transferring them to a manipulator. outside the reactor, to raise the graphite formwork, it is flooded with a liquid with a density higher than that of the reactor graphite, and this liquid is added to the reactor cavity so that the graphite formwork rises under Archimedean force so that its upper blocks float at the top of the reactor cavity. the floating graphite blocks, parts thereof and other graphite parts are transferred to a dedicated location outside the reactor by a controlled manipulator, and the reactor cavity is replenished with a quantity of said liquid having a density higher than that of the reactor to compensate for the volume of graphite already removed, and graphite formwork below the top If the blocks rise and float again at the top of the reactor cavity, which will be analogously transferred to said dedicated location outside the reactor, repeat the steps described until all the graphite formwork blocks and other floating parts thereof have been raised and transferred.

The liquid used to flood the graphite formwork of the reactor in the reactor cavity is an aqueous solution of salts.

The aqueous saline solution can be prepared from salts such as CsCOOH or ZnCl ₂ , or CaBr ₂ / CaCl ₂ .

Prior to dismantling the graphite formwork, the biological protection of the reactor top is dismantled, and before dismantling the biological protection of the reactor top, the reactor cavity is filled with such liquid that the upper level of graphite blocks in the reactor is at the lower level of said biological protection.

After dismantling the biological protection of the reactor top, the enlarged reactor cavity is replenished with said liquid to such a maximum level that said liquid does not escape from the reactor cavity when the graphite formwork rises.

At present, all the upper blocks of the graphite formwork and its other floating parts are raised to the same level at the top of the reactor cavity from which the transfer takes place to a dedicated location outside the reactor.

The graphite formwork can be reinforced before flooding {by allowing suitable dismantling guide structures into the existing channels.

Dismantling guides can be selected from channel equipment previously used in the reactor or special rods with such low sliding friction with the graphite blocks that they can be subjected to Archimedean force without additional steps to slide through the dismantling structures.

Utility of the invention

According to the invention, a method for dismantling graphite formwork in a nuclear reactor is proposed, in which the graphite parts are lifted using their buoyancy property by filling the reactor cavity with a liquid having a density higher than the reactor graphite parts, which greatly simplifies dismantling technology and equipment.

In addition, high ionizing radiation absorption in a high-density liquid significantly reduces the ionizing radiation dose rate due to the reactor structures in the space above the graphite formwork and in adjacent rooms during biological protection and graphite formwork dismantling. Filling the reactor cavity with liquid during the dismantling of the graphite formwork significantly reduces the formation of radioactive aerosol particles and thus significantly reduces the air pollution of adjacent rooms with radioactive aerosol particles. All this significantly reduces the cost of the technological process and the equipment required for it.

The invention is explained in detail by drawings, which do not limit the scope of the invention and which show:

FIG. 1 - nuclear reactor with graphite formwork installed therein;

FIG. 2 - nuclear graphite reactor formwork dismantling equipment.

Example of realization of the invention

A storage tank 3 with a pumping system is installed next to the nuclear reactor 1, in which the irradiated graphite formwork 2 is installed. The tank 3 is intended for storing a liquid 4 with a density higher than the graphite 2 of the reactor, such as an aqueous solution of CsCOOH with a density between 1800 kg / m ³ and 2500 kg / m ³ , and a pumping system for pumping the liquid 4 into the reactor cavity 1 and from her. Next to the reactor 1, a container 5 is also provided for accommodating the removed blocks of graphite formwork 2 and its parts. The container is equipped with a system for removing the above-mentioned graphite formwork parts.

The method of dismantling the formwork of a nuclear graphite reactor involves the following sequence of steps:

If necessary, reinforce the graphite formwork 2 {by allowing suitable dismantling guides into the existing channels, such as previously used duct equipment in the reactor or special rods with such low sliding friction with the graphite blocks that they can be exposed when immersed in the liquid. Archimedes' forces without additional action to scroll through these dismantling structures;

From the tank 3, the pumping system fills the cavity of the reactor 1 with an amount of liquid 4 such that the upper level of the graphite blocks is at the lower level of the biological protection of the top of the reactor; Completely or partially dismantles the biological protection of the top of a nuclear reactor;

From the tank 3, the pumping system replenishes the reactor 1 cavity with such an amount of liquid 4 that it fills the enlarged reactor cavity after dismantling the top of the reactor to the maximum level so that the liquid does not spill from the increased reactor cavity and the graphite formwork upper blocks are exposed.

Archimedean forces would rise and float at the top of cavity 1 of the reactor. Floating graphite blocks and parts from the reactor cavity 1, for example by a manipulator, are moved outside the reactor, for example to a container 5 adjacent to the reactor 5. The reactor 1 cavity is replenished with liquid 4 to compensate for the volume of graphite formwork blocks and parts dismantled and raised. so that the upper blocks below the graphite formwork float at the top of the reactor cavity at the same level as the previously raised blocks. The currently floating upper graphite blocks and their components are moved from the same upper level of the reactor 1 to a location outside the reactor, such as a container 5. The above steps are repeated until all the graphite formwork blocks and components are removed from the reactor 1 cavity;

After removing all the details of said graphite formwork, they are removed from the reactor dismantling guide structure, if used. The liquid is then pumped out of the reactor cavity 1 and the secondary radioactive waste generated during formwork dismantling is removed.

Claims (8)

Definition of the invention A method of dismantling a graphite formwork in a nuclear reactor, comprising flooding the graphite formwork in the reactor cavity with liquid, then sequentially lifting the formwork blocks and its other graphite components from above and transferring them to a designated location outside the reactor by a manipulator. that to raise the graphite formwork, it is flooded with a liquid of a density higher than that of the reactor graphite, and this liquid is added to the reactor cavity so that the graphite formwork rises under Archimedean force so that its upper blocks float at the top of the reactor cavity the floating graphite blocks, their parts and other graphite parts are transferred to a dedicated location outside the reactor by a controlled manipulator, and the reactor cavity is replenished with a quantity of said liquid with a density higher than that of the reactor to compensate for the volume of graphite already removed; the upper blocks below the formwork again p repeat the steps described above at the top of the reactor cavity, which will be analogously transferred to said dedicated location outside the reactor, until all the graphite formwork blocks and other floating parts thereof have been raised and transferred. 2. The process according to claim 1, characterized in that the liquid used for flooding the graphite formwork of the reactor in the reactor cavity is an aqueous solution of salts. 3. The method of claim 2, wherein the aqueous salt solution can be prepared from salts such as CsCOOH or ZnCl ₂ , or CaBr ₂ / CaCl ₂ . 4. A method according to any one of claims 1 to 3, characterized in that prior to disassembly of the graphite formwork, the reactor top biological protection is dismantled and before the reactor top biological protection is disassembled, the reactor cavity is filled with said liquid such that the graphite blocks in the reactor cavity. at the lower level of that biological protection. 5. A method according to any one of claims 1 to 4, characterized in that after the dismantling of the reactor top biological protection, the increased reactor cavity is replenished with said liquid to such a maximum level that no liquid escapes from the reactor cavity when the graphite formwork rises. 6. A method according to any one of claims 1 to 5, characterized in that all currently present upper blocks of the graphite formwork and other floating parts thereof are raised to the same level at the top of the reactor cavity from which the transfer takes place outside the reactor. 7. A method according to any one of claims 1 to 6, characterized in that the graphite formwork can be reinforced before it is flooded (by allowing suitable dismantling guide structures into the channels therein. 8. The method according to claim 7, characterized in that the dismantling guide structures can be selected from previously used reactor equipment or special rods, the sliding friction of which with graphite blocks is so low that they can be subjected to Archimedean force without further action. slip through these dismantling structures.