RU2580817C1 - Method of non-cavity filling of reactor spaces when decommissioning uranium-graphite nuclear reactor - Google Patents

Abstract

FIELD: processing and recycling of waste.

SUBSTANCE: invention relates to technology of operation of uranium-graphite nuclear reactors. In compliance with method of no-cavity filling reactor spaces at reactor decommissioning as per version of on-site disposal selected is path of process channel, through which cavity will be filled in. Preliminarily prepared paths for free movement of screw. In selected channel screw pipe is inserted and screw is placed coaxially inside pipe. In nearest path of process channel vibrating boom is installed. Loose barrier material is fed into top of screw pipe. By means of screw under pressure barrier material is advanced in filled cavity. Simultaneously with help of vibration oscillations of vibrating boom and operation of screw conditions created for separation of formed "hill", material compaction, flotation around obstacles and walls.

EFFECT: possibility to form solid security barriers with sufficient meagreness for sorption and limitation of migration of radionuclides at decommissioning of uranium-graphite nuclear reactor as per on-site version of disposal.

2 cl, 1 dwg

Description

The invention relates to the nuclear industry, and in particular to the technology for decommissioning uranium-graphite reactors, and can be used to create continuous safety barriers by filling the reactor spaces with barrier-free bulk materials.

A known method of fixing the soil and a device for its implementation (Patent RU 2330141, IPC E02D3 / 12, published. 07.27.2008), selected as an analogue. According to this method, a well is drilled by a hollow auger drill stand containing at least one perforated auger. Fixing substances are pumped into the ground by means of a supply line, with the overlapping of the top of the discharge zone during drilling. Loosened soil is moved and compacted above the perforated screw. Depending on the properties and condition of the soil, additional portions of aggregate are supplied to the well in the form of drill cuttings or sand. The fixing substance is injected simultaneously over the entire thickness of the discharge zone around the perforated screw.

The specified method has disadvantages:

- low efficiency of filling wells with cavities formed during drilling;

- the inability to fill the reactor spaces through the curved paths of technological channels.

There is a method of filling reactor spaces with bulk barrier material during decommissioning of reactors according to the option of on-site disposal (Patent RU 2534228, IPC G21C11 / 00, published on November 27, 2014), selected as an analogue. According to the specified method, the barrier material is fed through the pipe under its own weight into the space to be filled. The barrier material is moved horizontally by a stream of compressed air through the duct. The duct is located inside the feed pipe. The jets of compressed air are deployed in the horizontal direction using nozzles located below the end of the supply pipe.

The specified method has disadvantages:

- the supply of compressed air in the horizontal direction through the nozzles contributes to the release of radioactive dust from the reactor structures to the surface;

- the achieved density of the barrier material does not provide complete sorption of radionuclides.

A known method of filling reactor spaces, developed by OJSC "SCC" and described in the report "Technology of cavity-free filling of reactor spaces with barrier material" inv. No. TO-5304/90 [K. Yushitsin. Decommissioning of industrial uranium-graphite reactors of SCK OJSC. 11.2012, p. 15-22, http://www.osatom.ru/mediafiles/u/files/V_reg_forum_2012/VE_PUGR_SXK.pdf], selected as a prototype. To create safety barriers in the reactor space, a screw of the required length is chosen. The selected screw is introduced into one of the tracts of the technological channels to a predetermined depth. Using an electric motor, the auger is driven. Dry barrier material is fed from above into the auger funnel. Create safety barriers by moving material in the vertical and horizontal direction.

The specified method has disadvantages:

- when creating safety barriers, the formation of cavities is possible;

- limited application, since during the operation of the reactor, the channel paths bend, which impedes the advancement of the screw.

The objective of the invention is to develop a method for creating in reactor spaces internal safety barriers that limit the entry of radionuclides into the environment.

The problem is solved due to the fact that in order to create continuous safety barriers by filling the reactor spaces with barren materials without barriers, the screw of the required length is chosen in the same way as in the prototype. The selected screw is introduced into one of the paths of the technological channels of the reactor to a predetermined depth. The previously used path and the paths closest to it align. Install a funnel in the screw pipe. Using an electric motor, the auger is driven. A vibrating rod is installed in the nearest path of the process channel, granular barrier material is fed to the top of the screw pipe, with the help of a screw rotating with a rotation period of 1.2-0.4 seconds, the barrier material is moved under pressure into empty reactor spaces, the material is evenly distributed and compacted in the filled cavities by exposure fluctuations from the operation of the vibrating rod with a frequency of 15-25 Hz.

A positive effect is achieved due to the fact that a screw is used to fill the reactor spaces with bulk barrier materials during the decommissioning of a uranium-graphite reactor according to the option of on-site disposal. The auger is selected so that it moves freely in the path of the technological channel of the reactor.

To ensure free movement of the screw, preliminary preparation of the technological channel path is carried out. Using visual-diagnostic diagnostics, places of curvature of the technological channel are identified. Curved paths are bored by the drill rod in several passes. Similarly, the paths closest to the selected channel are prepared.

After preparing the paths of the technological channels, a screw pipe of the appropriate length is assembled. Dimensions are selected individually, based on the size of the reactor. With the help of a crane, a screw pipe is installed in the path of the technological channel. A screw is placed inside the screw pipe, a funnel is mounted on top. The shank of the auger is connected to the motor chuck.

A vibrating rod is installed in the adjacent tract of the technological channel to a depth in accordance with the length of the screw. The vibratory bar is selected with such an external diameter to exclude the possibility of contact with the side walls of the technological channel.

Using an electric motor, the auger is driven. At the same time, the vibrating rod is included in the operation. Dry fine material, for example clay-containing backfill, is fed from above into the auger funnel. Due to the rotation of the screw, the clay moves to the lower end of the screw pipe and enters the filled cavity. Overpressure is maintained by constant rotation of the screw. The spreading of the formed “hill”, compaction of the material, flow around obstacles and walls in the filled cavity is ensured by the joint operation of the screw and the vibrating rod.

Therefore, filling the reactor spaces with bulk materials using screw devices and vibrating rods during decommissioning of a uranium-graphite reactor allows the creation of barrierless safety barriers that ensure the sorption of radionuclides.

Figure 1 presents a diagram of the cavityless filling of the subreactor space. When decommissioning a uranium-graphite reactor according to the option of safe disposal in place, free cavities are formed, for example, between the lower metal structures 1 and 2. The screw pipe 3 is located inside one of the tracts of the technological channel 4. Inside the screw pipe 3, screw 5 is placed coaxially. Vibro rod 6 located in the nearest path of the technological channel 4.

After preparatory work related to concreting the lower metal structures 2, they begin to create internal safety barriers. Select the path of the technological channel 4 for visual inspection diagnostics. If the curvature of the channel path impedes the advancement of the screw, align it. Alignment is carried out, for example, using a mobile drilling machine. If alignment is not possible, choose another technological channel. Similarly, prepare the nearest path of the technological channel 4.

A screw pipe 3 is installed in the prepared path of the technological channel 4. The length of the screw pipe 3 is selected equal to the length of the technological channel path to the lower metal structures 1. A screw 5 is placed coaxially inside the screw pipe. A vibration rod 6 is placed in the nearest channel of the technological channel 4. The length of the vibration rod is selected in accordance with screw length 5.

The bulk barrier material in the form of clay-containing backfill 7 is fed into the screw pipe 3. Under its own weight, the clay-containing backfill moves along the axis of rotation of the screw 5 along the screw pipe 3 to the cavity being filled. Overpressure is maintained by constant rotation of the screw 5. Using vibration from the vibrations of the vibrating rod 6 and the operation of the screw 5 create the conditions for spreading the "hill", flow around obstacles and walls, and compaction of the material.

It is allowed to use the combined action of the rotating auger 5 and the vibrating rod 6 to create continuous safety barriers by filling the voids between the walls of the shaft and the side metal structures of the reactor, in auxiliary rooms and technological shafts.

An example embodiment of the invention is given below.

A mine prepared for decommissioning of an industrial uranium-graphite reactor (PUGR) of JSC "UDC UGR" was selected as an object for the cavity-free filling of reactor spaces. Internal safety barriers were created between the lower supporting metal structures. For this, one of the paths of technological channels was selected. A visual examination of the tract was performed for curvature. In the case of detecting curvature up to 200 mm, boring and alignment of the technological channel path was carried out using a mobile drilling power plant. If the curvature was more than 200 mm, then another channel was selected. Similarly, the nearest tract of the technological channel was prepared.

After the preparation operations, a screw pipe made of stainless steel with an external diameter of 58 mm was inserted into the path of the technological channel. A screw with an external diameter of 54 mm was coaxially mounted inside the screw pipe. A vibrating rod was placed in the adjacent technological channel. The auger and vibration rod were driven by separate electric motors. Electrical installations were supplied with a voltage of 380 V from an alternating current network. The screw rotational speed was 100 rpm. The vibration rod vibration frequency is about 20 Hz.

Bulk barrier material was fed into the upper part of the screw tube. Dry mixtures based on clay rocks after preliminary grinding (grinding) were used as a barrier material. The content of the silt fraction in the barriers was up to 28% wt., Fine dust fraction up to 50% of the mass. A significant part of the rock consisted of finely divided material with a cation exchange capacity of more than 30 mEq / 100 g of rock. Under its own weight, the clay-containing material was pushed along the axis of rotation of the screw into the cavity being filled. A “hill” formed in the cavity being filled. With the help of vibration from vibrations of the vibrating rod 6 and the operation of the screw 5, conditions were created for spreading the resulting "hill", compaction of the material, flow around obstacles and walls.

To fill the entire volume between the metal structures, a similar sequence of operations was performed through other paths of the technological channels.

The specified method was also used to create continuous safety barriers by blanket-free filling of voids between the walls of the shaft and the side metal structures of the reactor, in former auxiliary rooms and technological shafts, for example ШТ-2.

The implementation of the present invention makes it possible to form continuous safety barriers of sufficient density to limit the migration of radionuclides during decommissioning of a uranium-graphite nuclear reactor according to an on-site disposal option

Claims (2)

1. A method for blanketing the reactor spaces during decommissioning of a uranium-graphite nuclear reactor, including selecting a screw of the required length, introducing the selected screw into one of the paths of the technological channels of the uranium-graphite reactor to a predetermined depth, rotating the screw with an electric motor, and supplying a dry barrier material from above into the auger funnel, creating safety barriers by moving the material in the vertical and horizontal direction, characterized in that the paths of those Urological channels are prepared for free movement of the screw, a screw pipe is inserted into the selected path and a screw is placed coaxially into the pipe, a vibrating rod is installed in the nearest path of the technological channel, granular barrier material is fed to the top of the screw pipe using a screw rotating with a rotation period of 1.2-0.4 sec push the barrier material under pressure into the empty reactor spaces, evenly distribute and compact the material in the filled cavities by the action of vibrations from the operation of the vibro rod per hour total 15-25 Hz. 2. The method according to p. 1, characterized in that they pre-prepare the technological channel by boring and aligning the path.

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