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Method for recovering serviceability of nuclear reactor fuel assembly subchannel

IPC classes for russian patent Method for recovering serviceability of nuclear reactor fuel assembly subchannel (RU 2302671):

G21C3/02 - Fuel elements

G21C17 - Monitoring; Testing

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FIELD: nuclear engineering; retrofitting subchannels of high-power uranium-graphite tank reactor cores.

SUBSTANCE: proposed method for recovering serviceability of nuclear reactor fuel assembly subchannel includes reactor shutting down, dismounting of standard floor blocks from subchannel, and removal of fuel assembly. Process channel is checked for serviceability. Channel is visually inspected within reactor for integrity and channel inner diameter profile is measured. Then process channel pre-removal operations are made. Process channel is removed from subchannel and placed in storage. Construction clearance between process channel and graphite stacking is recovered by calibrating graphite column including finishing of central bore internal diameter to desired size and expansion device segment is installed between guard plate and top graphite block. Graphite column is checked for condition by inspecting inner surface of column. Telescopic joint height and inner diameter of graphite column central bore are measured. Then process channel removed earlier and found serviceable by its check results is reinstalled in fuel assembly subchannel. After that final mounting operations are conducted including welding of process channel to adjacent structures and formation of nuclear reactor subchannel.

EFFECT: ability of evaluating process channel life, reduced dose rate on attending personnel.

1 cl, 3 dwg

The invention relates to nuclear technology, in particular, to a method of recovery of the fuel cell nuclear reactor, and can be used for repair and restoration work and execution of works on reconstruction of the fuel cell active zones channel uranium-graphite nuclear large reactors (RBMK).

Fuel cell RBMK is a graphite column, collected from 14 graphite block with a Central hole in which is fitted with a channel (TC). Between TC and the column set graphite rings. After mounting the average value of the gas gap between the wall of the technological channel and graphite bricks that make up the system "TC-graphite, has a value equal to 3 mm. to compensate For thermal expansions in the fuel cell of the upper tracts is made in the form of a telescopic connection. The initial value is gearing 225 mm

During long-term operation of RBMK fuel cell is under constant influence of factors such as increased temperature and reactor irradiation. As a result of this constructive elements of fuel cells undergo irreversible changes both in axial and in radial directions, in particular, there is a reduction of the size of the gas gap in the system "TC-graphite, down is his complete exhaustion, and the reduction in the value of the telescopic connection of the upper tract of the technological channel (TSC)providing compensation for thermal expansion during operation of the reactor. This decrease in TST below the limit value (80 mm) can lead to disengagement of the upper tract and flange Assembly with a pipe, to the increase of internal stresses and damage to the main constructive elements of fuel cell technology channel and graphite columns).

Repair work on the restoration of the fuel cell nuclear reactor are necessary, responsible and complex technological operations associated with large labor and dose costs and require the use of remote devices.

Known methods of recovery of the fuel cell active zone of the nuclear reactor, in particular: 1 - "the Rules of the operational control of technological channels, CPS channels and graphite reactors RBMK-1000. BSR-To SD", (#E 040-2703), NEITHER of CIAT, 1993, 31 p and 2 - Laaland and other NPP safety with a channel reactors. Reconstruction of the active zone. M.: Energoatomizdat, 1997, str-189.

Method of recovery of the fuel cell nuclear reactor, described in the second source, received by the applicant as is rototype the claimed invention (copy source attached). The method includes the following operations: stopping reactor dismantling blocks slab flooring with a fuel cell, the discharge of the fuel Assembly (FA), a preparatory operation for extracting production channel, comprising: drying TC, installation in the drum separator (BS) a couple of plugs in the sockets steam communication (STC), the segment of the roll from TC, cutting the corner seam welding TC to the sleeve, housed "Usovo" weld TK-tract and undermining channel, clearance grooves tract chip, removing the technological channel, inserting it in the pool storage of solid radioactive waste (HTR) and the subsequent "cutting it" in TC and recycling, recovery of the technological gap between the channel and the graphite walls by installing in the design position of the protective plate blocks of graphite and bore the center hole of the inner diameter of the graphite column to the desired size, and then perform the cleaning of seats in the path of the new TC, cut the seam allowance on the lower part of the new TC and cutting edges for welding and then carry out the installation of new production channel and carry out final Assembly work, including welding of the established channel to adjacent structures and the formation of a fuel cell.

This method has the following disadvantages.

In the known method n which determine the suitability of reusing the extracted process channel; after removing the TC immediately disposed in the water storage pool and a fuel cell in the rehabilitation process establish a new TC. Thus, the method does not allow the possible operating life lessons technological channel and thereby increase its service life. The disadvantage of this method is that in the storage of solid radioactive waste is placed not only technological channels that are not suitable for further exploitation, but also those who have not yet exhausted their resources and could have a long time to be used for electricity generation. For storage of recycled TC requires additional amounts of HTR. In addition, the utilization of TK, suitable for operation, can lead to continuous accumulation of radioactive waste, thereby increasing negative effect, both on the technical support personnel and the environment and ecology of the region as a whole.

Objectives of the invention are: identification of potential re-use of technological channel, lifetime extension of the technological channel of the fuel cell, the reduction of harmful radioactive impact on the environment, reduction of radioactive waste and thereby harmful radioactive impact on the environment, C is the transport-technological operations with radioactive substances and the reduction of radiation exposure of personnel.

The essence of the proposed method of recovery of the fuel cell nuclear reactor is as follows.

Stop a nuclear reactor, carry out the disassembly blocks slab flooring with a fuel cell and discharging the fuel Assembly (FA), they control the status of the technological channel to identify its suitability for the job, which inside the reactor conduct a visual inspection of the LC, check its integrity and measure the profile of the inner diameter of the LC, carry out preparatory actions for the extraction process of the channel, as in the known method, and then from the fuel cell extract technological channel and set it in storage. Then restore the gap between technological channel and graphite walls through the Central bore hole inner diameter of the graphite column to the desired size and installation segment-compensator between the protective plate and the top graphite block, they control the state of the graphite column by a visual inspection of the inner surface, measuring tall sizes telescopic connection and the internal diameter of the Central hole of the graphite columns, after which the fuel cell set the technology channel, previously extracted from it and is suitable for its results to the of ntrolle, to re-operation, and then perform the final installation work, including welding channel to adjacent structures and the formation of a fuel cell.

Declared and known (prototype) methods have common features, in particular, in both methods of recovery of the fuel cell nuclear reactor is carried out by: stopping reactor dismantling blocks slab flooring with a fuel cell, the discharge of the fuel Assembly (FA), preparatory actions before removing the technological channel, removing the technological channel of the fuel cell and set it in the store, the restoration of the gap between technological channel and graphite masonry, by boring the internal diameter of the Central hole of the graphite column to the desired size, and then perform the installation in the fuel cell technology channel and perform final Assembly work, including welding channel to adjacent structures and the formation of a fuel cell.

Distinctive features of the declared and known methods are:

after unloading the fuel assemblies carry out condition monitoring of technological channel to identify its suitability for the job, which inside the reactor conduct a visual inspection of the LC, check its integrity and prof measure the l inner diameter,

- after the operation of boring the internal diameter of the Central hole of the graphite columns, set the segment-compensator between the protective plate and the top graphite block;

- exercise control condition graphite columns, which carry out a visual inspection of the inner surface, measure tall sizes telescopic connection and the internal diameter of the Central hole of the graphite columns;

as technological channel in the fuel cell set the channel previously extracted from it and is suitable according to the results of its control, to re-operation.

The proposed method of recovery of the fuel cell nuclear reactor allows to identify the resource technological channel, thereby extend its life, to carry out repair and restoration work of the fuel cell at this level that they allow you to ensure reliable operation of a nuclear reactor for a long time without stopping for repairs. The claimed method allows to reduce the accumulation of radioactive waste in HTR and thus reduce the harmful radioactive impact on the environment, reduce transport-technological operations with radioactive substances and to reduce radiation doses to personnel. The result of the technical achievements of the claimed method confirm ridesa information with the Kursk nuclear power plant, where restoration works were held fuel cell according to the claimed method.

The proposed method is illustrated in the drawings, figure 1 is a-3, where figure 1 shows the structural diagram of the fuel cells section (without fuel assemblies); figure 2 - structural diagram of the system "TC-graphite, in section, a fragment of a figure 1 and figure 3 - structural diagram of the installation of the segments of the joints in the fuel cell nuclear reactor, in section, a fragment of B figure 1.

Figure 1-3 shows the positions of the main structural elements of the fuel cell, where: 1 - pipe steam communication (STC) or steam-pipe; 2 - node telescopic connection tracts (TST); 3 - graphite column; 4 - technological channel (figure 1); 5 - inner graphite ring; 6 - graphite block; 7 - outer graphite ring (figure 2, detail a figure 1); 8 - tube telescopic connection after Assembly; 9 - flange telescopic connection after Assembly; 10 - protective plate; 11 - segment-the compensator (figure 3, detail B, figure 1).

Method of recovery of the fuel cell is as follows.

Stop a nuclear reactor. The initial state of the reactor before the beginning of the restoration works - he is in a subcritical state. Carry out the dismantling blocks slab flooring with fuel I the side, and from the fuel cell is discharged fuel Assembly (FA). Next remotely supervise the performance of the technology channel 4 (figure 1-3), thereby determining its suitability for continued service, which is carried out by: visual inspection technology channel 4 by the television camera; using ultrasonic flaw detector checks the integrity of the process channel; using diametrally measure the profile of the inner diameter of the technological channel.

When replacing the technological channel 4 (figure 1-3) there are a number of limitations, namely: for installation in the reactor allowed the TC, which corresponds to the results of the core monitoring operating limits. In addition, the extracted TC should not have damaged graphite rings 5 and 7 (figure 2) and bushing (item not shown). The result of control of technical condition of TC is returning to heat the cell TC having a high activity.

As in the known method, then hold preparatory work for future retrieval process channel, namely: are drying TC, installation in the drum separator (BS) a couple of plugs in the pipe 1 (Fig 1) steam communication (STC), the segment of the roll from TC, cutting the corner seam welding TC to the sleeve, housed "Usovo" weld TK-tract, and erosion of the channel, the cleaning groove tract chip.

Then use a crane to extract the technological channel of the fuel cell and install it into the pool. When removing TC from the reactor control while efforts extraction and status graphite rings 5, 6 (figure 2). In the pool are all extracted technological channels, i.e. channels that are determined suitable for continued service, and channels that are identified as not suitable for re-use.

Then restore the technological gap between TC 4 and the graphite walls.

in graphite blocks 6 (2, 3) by means of a pneumatic cutter (or firmware) are boring (calibration) of the Central hole of the inner diameter of the graphite column 3 (figure 1) to the desired size, namely, the inner diameter of the center hole should be at least 113,7 mm;

- special devices raise the protective plate 10 (Fig 3.) and set the segment-compensator 11 (figure 3) between the plate 10 and the top graphite block, which allows to increase the compensation ability of the TST 2 (figure 1) between the upper graphite block 6 (2, 3) and the protective plate 10 (Fig 3). In the result, the amount of engagement of the upper tracts increased by 70 mm

Then hold control condition of the graphite column 3 (figure 1), to thereby determine the validity of the stop in her technological channel, then:

using television cameras perform a visual inspection of the inner surface of the graphite blocks, detecting the presence on the surface of debris and crumbs between the graphite blocks;

using cameras and combined with her roulette measure tall sizes telescopic connection, thus determining the amount of gearing;

- remote diametera measure the inner diameter of the center hole of the graphite columns, thereby determine the actual size of the diameter of the hole defined by the project.

Control technology channel on the suitability of reuse, i.e. after determination of compliance of technical parameters of a channel specified operating limits, the extracted channel from the pool store with a crane installed in the fuel cell.

At the end of the recovery operations are responsible for final Assembly work, including welding technological channel to adjacent structures and the formation of a fuel cell of a nuclear reactor.

Method of recovery of the fuel cell nuclear reactor, namely, that stop a nuclear reactor, carry out the dismantling of blocks of standard flooring with a fuel cell and discharging the fuel Assembly is, they control the status of the technological channel to identify its suitability for the job, which inside the reactor perform a visual inspection of the channel, check its integrity and measure the profile of the inner diameter of the channel, then do the preparatory work for the extraction process of the channel, remove the technological channel of the fuel cell and set it in storage, restore the technological gap between technological channel and masonry by calibration of the graphite columns, including the internal bore diameter of the center hole to the desired size, and set the segment-compensator between the protective plate and the top graphite block, they control the state of the graphite column, which carried out the inspection of internal surfaces columns, measure tall sizes telescopic connection and the internal diameter of the Central hole of the graphite column, next to the fuel cell set the technology channel, previously extracted from it and is suitable according to the results of its monitoring, re-operation, and then perform the final installation work, including welding set technological channel to adjacent structures and the formation of a fuel cell of a nuclear reactor.