WO2003034442A1

WO2003034442A1 - Method and device for liquid coolant nuclear reactor fuel rod assembly handling and leakage monitoring

Info

Publication number: WO2003034442A1
Application number: PCT/RU2002/000423
Authority: WO
Inventors: Pavel Slavyagin; Leonid Pervushin; Valery Seredkin; Vladimir Yakovlevich Gecha
Original assignee: Pavel Slavyagin; Leonid Pervushin; Valery Seredkin; Vladimir Yakovlevich Gecha
Priority date: 2001-10-19
Filing date: 2002-09-12
Publication date: 2003-04-24
Also published as: RU2186429C2

Abstract

The present invention relates to nuclear power industry, in particular, to the operation of liquid coolant nuclear reactors, and can be used for the production, utilization, reprocessing and storage of nuclear fuel loaded into fuel rod assemblies. The liquid coolant reactors FA handling and leakage monitoring method comprises the steps of lifting the FA from the reactor area cell, placing the FA into a device comprising an outer, middle and an inner sections, clamping the handled and monitored FA together with the gas feeding and gaseous radionuclide monitoring system. The method comprises the handling the FA. Objective of the present invention is to provide for simultaneous FA handling and leakage monitoring procedures.

Description

Method and Device for Liquid Coolant Nuclear Reactor Fuel Rod Assembly Handling and Leakage Monitoring

The present invention relates to nuclear power industry, in particular, to the operation of liquid coolant nuclear reactors, and can be used for the production, utilization, reprocessing and storage of nuclear fuel loaded into fuel rod assemblies (FA).

Known is nuclear reactor FA handling device (SU Inventor's Certificate 1820763 G 21 C 19/10, 1996). Said device comprises a handling pipe with a shutoff valve driven via a tie rod by the motor located on the top of the handling pipe, and a retractable arm with catchers and a clamp. The shutoff valve tie rod and the catcher arm have stops that interact during the lifting of the shutoff valve, and the retractable arm stop is kinematically connected with the retractable arm catchers such that the catchers are released when the stop is lifted.

Said handling device allows fuel rod handling by applying an elevated starting force and lifting the spent FAs, including the peripheral ones, from their seats in nuclear power plant reactors with natural circulation of the first loop coolant. However, said device is not suitable for fuel rod leakage monitoring.

Also known is a fuel rod leakage monitoring method (RU Patent 2094861 G 21 C 17/06, 1997). Said method comprises the steps of reducing the test volume pressure relative to the fuel rod pressure and probing the radionuclide outflow. Preliminarily for this method, the outer volume pressure is increased to within the maximum allowed reactor pressure, kept for a certain time and then dropped to the initial level. The presence of leakage in the fuel rod is indicated by the radionuclide release peak that accompanies the pressure drop.

Disadvantage of said solution is the risk of fuel rod case damage by the abrupt changes in pressure and the necessity of separating the element removal and leakage monitoring procedures.

The closest counterpart of the present invention is the FA handling and leakage monitoring device and method for liquid metal coolant nuclear reactor (SU Inventor's Certificate 490376 G 21 C 17/06, 1977). Said device comprises a catcher arm with a catcher and a motor for clamping and removing fuel rod assemblies from the reactor area, a guide pipe with a motor, and gas feeding and removal channels for FA fuel rod leakage monitoring, wherein one gas feeding channel is inside the catcher arm and leads to the FA head, and the lower end of the catcher arm has a sealing sleeve.

The device operates as follows. The motor brings the catcher arm down to the FA head, and the sealing sleeve acts to prevent leakage below the intake windows. After that the blowing gas is fed through the gas feeding channel and, wherever the fuel rod case is leaking, removes gaseous radionuclides by bubbling through the liquid coolant. The radionuclide containing gas is fed through the gas removal channel to the monitoring system that calculates the extent of fuel rod case leakage by the gas flow radioactivity level.

Disadvantages of said technical solution is the separation of the fuel rod or FA handling and monitoring procedures, the risk of fuel rod case damage during said handling and monitoring procedures due to their long duration, and the incompleteness of gaseous radionuclide collection that affects the leakage measurement accuracy.

Therefore the objective of the present invention is to provide for simultaneous FA handling and leakage monitoring procedures.

Another objective of the present invention is to reduce the reactor maintenance and overhaul downtime, thereby reducing the overall electric power costs.

Said objectives are achieved by using the liquid coolant reactor FA handling and leakage monitoring method that comprises the steps of lifting the FA from the reactor area cell, placing the FA into a device comprising an outer, a middle and an inner sections, clamping the handled and monitored FA together with the gas feeding and gaseous radionuclide monitoring system, blowing the gas through the coolant to probe the radionuclide concentration in the gas and conclude upon the presence and extent of leakage in the FA and final handling of the FA. Preliminarily or during the FA handling procedure, gas is pumped into a gas container to a preset pressure, fed via the pipeline and the injectors to under the open bottom portion of the device sections in an amount of within 50 dm³, and then a gas sample is taken from the gas volume above the liquid coolant between the inner and the middle sections and analyzed for radionuclide concentration. Preferably, the amount of gas fed at this stage is within 40 dm³. Usually, gas is sampled from the volume in the vicinity of the coolant surface.

Said objectives are also achieved by using the liquid coolant reactor FA handling and leakage monitoring device that comprises said outer section, wherein said outer section comprises said inner and said middle sections, a catch for clamping the handled and monitored FA said gas feeding and gas radionuclide concentration measurement system and a control unit. Said catch is located in the bottom portion of said inner section that is connected to the drive motor. Said gas feeding system comprises a compressor, a gas container, an injector and pipelines, wherein said compressor is connected to said control unit, the output of said compressor is connected to said gas container, the output of said gas container is connected via a valve to the input of said pipeline and the output of said pipeline is connected to said injector that is installed such as to allow gas feeding from said gas container to the bottom portion of said outer section. Said gaseous radionuclide monitoring system comprises a pipeline, a probing device and a gas feeder, wherein the input of said pipeline is located in the above-coolant volume between said middle and said inner sections, the output of said pipeline is connected to the input of said measuring device, and the output of said probing device is connected to the input of said gas feeder. The pipeline that connects said inner section to said probing device comprises an outer portion and an inner portion installed such as to allow their movement relative to each other without affecting the leak proofhess of said pipeline. Said valve is mechanically or electromagnetically driven and controlled by said control unit. Preferably, said gas container is capable of storing within 50 dm of the gas. Said gas feeding system may further comprise a pressure gage installed between said gas container and said valve. Said radionuclide concentration probing system may further comprise a data processing and displaying unit connected to the output of said probing device. The top portion of the pipeline that connects said inner section to said probing device can extend above the top flange of said middle section and fitted to the inner surface of said outer section, whereas the bottom portion of said pipeline is fitted to the inner surface of said middle section. Also, the top portion of said pipeline that connects said inner section and said probing device can extend above the top flange of said middle section and fitted to the inner surface of said outer section, whereas the bottom portion is fitted to the outer surface of said middle section and enters inside said middle section through an opening in the wall of said middle section above the water level. Said device may further comprise a bridge for carrying said sections and said drive motor. Preferably, said injector is rigidly fixed on said outer section such that not to restrict the movement of said inner sections and the coolant. However, said injector can also be in the form of a rotary device activated by the compressed air fed to said injector, wherein said air turns said injector to the position in which the opening of said injector is inside the lower cross-section of said outer section. Preferably for this embodiment, said injector is installed such that the air can be only fed when said sections are assembled.

The preferred embodiment of the device according to the present invention for a VVER series reactor is shown in the drawing.

Said device comprises a retractable working arm that comprises the outer section (a metallic pipe) 1 connected to the bridge of the handling machine 2. Inside said outer section there is the middle section (a metallic pipe) 3, inside which there is the inner section 4. The handled assembly of fuel rods is clamped with the catch 6 to the inner section 4 of said retractable working arm, and in the transportation position as shown in the drawing, it is inside the middle section 3 and completely submerged into the reactor water 7. The outer section 1 has the pipeline 8 with the injector 9. The air stored in the container 10 at the preset pressure is fed to under the fuel rod assembly 5 via the pipeline 8 and the injector 9, this being activated by the solenoid valve 11 actuated from the controlled unit 12, or by the manual valve 13. The amount of air fed to the FA is within 40 1 and is determined by the air pressure in the container 10 and the container volume. The air pressure in the container 10 is produced by the compressor 14, probed by the pressure gage 15 and adjusted by the safety valve 16. The container 10 is filled before the opening of the valves 11 or 13. The compressor 14 is inactive when the air is fed from the contained 10 to the pipeline 8. When the FA 5 is lifted from the reactor area cell or the cooling pond to the transportation position, the water pressure around the FA 5 decreases. If some fuel rods of the FA 5 are leaking, the fission products contained in the gas gap between the fuel and the leaking fuel rod case flow out to the surrounding water, because the outer pressure is lower than the inner one. The air fed through the injector 9 produces bubbles that float to the surface of the middle section 3 with the assembly inside and further through the water in the gap 17 between the middle section 3 and the inner section 4. The gaseous fission products carried over to the water from the leaking fuel rods are taken on by the gas bubbles. When the bubbles float up to the water surface (the water level 7) the air and the gaseous fission products are released from the bubbles and flow to the above-water volume 18 between the middle section 3 and the inner section 4 of the working retractable arm. The air is pumped from this section with the air pump 20 through the pipeline 19 the intake opening of which is located exactly above the water level 7 in the above-water volume

18 between the middle section 3 and the inner section 4 of the working retractable arm, and further the air is passed through the radioactivity measuring device 21, again through the air pump 20 and released to the reactor room. The air pump 20 is either activated by a control signal of the control unit 12 or working permanently during the control of all the reactor FAs. The radioactivity of the gaseous fission products in the intake air is permanently measured probed by the detector of the probing device 21. The sensor signal is sent to the data processing and displaying unit 22. The presence or absence of leaking fuel rods in the tested FA 5 is concluded on the basis of the signal level. The system elements 10 through 18 and

20 through 22 are arranged on a rack installed on the bridge 2 of the handling machine.

The leakage monitoring of fuel rod assembly 5 is performed as follows. The FA is lifted into the working rod to reach the transportation position. Previously or simultaneously, the required air pressure is developed in the container 10 with the compressor

14, following which the compressor 14 is switched off. Air is fed from the container 10 through the pipeline 8 and the injector 9 to under the FA bottom by opening the valves 11 or 13. The air bubbles float up in the water inside the working arm with the FA 5 to remove radioactive fission products and carry them to the above- water volume 18 between the middle section 3 and the inner section 4 of the working retractable arm. After that air is pumped with the compressor 20 from the above-water volume 18 through the pipeline 19 and the probing device 21, the sensor of which constantly measures the radioactivity of the passing air. The presence of leaking fuel rods in the tested FA 5 is concluded on the basis of the measured radioactivity level.

To increase the authenticity of leakage monitoring due to reduction of the flow dilution, one should keep the volume of air injected into the device within 40 1 and pump air from the above- water volume 18 from the layer right above the water surface.

In one embodiment of the present invention, the FA case leakage monitoring duration is within 3 minutes, wherein the monitoring process is simultaneous with handling, the risk of case damage is completely excluded because no additional handling of the cases is involved, and almost the entire amount of gaseous fission products released from the FA case leaks are removed from the liquid coolant, this resulting in an at least tenfold increase in the method accuracy (the signal-to-noise ratio).

Claims

What is claimed is a

1. Liquid coolant reactor FA handling and leakage monitoring method that comprises the steps of lifting the FA from the reactor area cell, placing the FA into a device comprising an outer, a middle and an inner sections, clamping the handled and monitored FA together with the gas feeding and gaseous radionuclide monitoring system and handling the FA, wherein, preliminarily or during the FA handling procedure, gas is pumped into a gas container to a preset pressure, fed via the pipeline and the injectors to under the open bottom portion of the device sections in an amount of within 50 dm , and passed through the coolant inside the middle section, and then a gas sample is taken from the gas volume above the liquid coolant between the inner and the middle sections and analyzed for radionuclide concentration to conclude upon the presence of leaks in the FA.

2. Method according to Claim 1, wherein gas is fed in an amount of within 40 dm³.

3. Method according to Claim 1, wherein gas is sampled in the gas volume in a close vicinity of the liquid coolant surface.

4. Liquid coolant reactor FA handling and leakage monitoring device that comprises an outer section, a middle section and an inner section, a catch for clamping the handled and monitored FA located in the bottom portion of said inner section connected to the drive motor, a control unit and a gas feeding and gas radionuclide concentration measurement system, wherein said gas feeding system comprises a compressor, a gas container, an injector and pipelines, wherein said compressor is connected to said control unit, the output of said compressor is connected to said gas container, the output of said gas container is connected via a valve to the input of said pipeline, the output of said pipeline is connected to said injector that is installed such as to allow gas feeding from said gas container to the bottom portion of said outer section, said gaseous radionuclide monitoring system comprises a pipeline, a probing device and a gas feeder, wherein the input of said pipeline is located in the above-coolant volume between said middle and said inner sections, the output of said pipeline is connected to the input of said probing device, the output of said probing device is connected to the input of said gas feeder, the pipeline that connects said inner section to said probing device comprises an outer portion and an inner portion installed such as to allow their movement relative to each other without affecting the leak proofhess of said pipeline.

5. Device according to Claim 4, wherein said valve is mechanically driven.

6. Device according to Claim 4, wherein said valve is electromagnetically driven and controlled by said control unit.

7. Device according to Claim 4, wherein said gas container is capable of storing within 50 dm of the gas.

8. Device according to Claim 4, wherein said gas feeding system further comprises a pressure gage installed between said gas container and said valve.

9. Device according to Claim 4, wherein said radionuclide concentration probing system further comprises a data processing and displaying unit connected to the output of said probing device.

10. Device according to Claim 4, wherein said device further comprises a bridge for carrying said sections and said drive motor.

11. Device according to Claim 4, wherein said injector is rigidly fixed on said outer section.

12. Device according to Claim 4, wherein said injector is in the form of a rotary device activated by the compressed air fed to said injector, wherein said air turns said injector to the position in which the opening of said injector is inside the lower cross-section of said outer section.