Heavy water reactor fuel rod bundle in-pile damage monitoring method

Abstract

The invention belongs to the technical field of nuclear fuel, and particularly relates to a heavy water reactor fuel rod bundle in-reactor damage monitoring method. Comprising the following steps: 1, carrying out online monitoring by using a fission gas monitoring system; 2, chemical sampling analysis of the coolant; and 3, performing data analysis by using a damaged fuel positioning system. The method has the beneficial effects that the method solves the problems that the monitoring means for the damage in the heavy water reactor fuel rod bundle is single, and the time for intervening in searching the damaged fuel is late, the fuel damage phenomenon can be found in the first time, and the work for searching the damaged fuel is started in the first time. The damaged fuel searching work is involved in advance, the searching time of the damaged fuel can be shortened, and the influence of coolant nuclide on personnel and the environment after damage can be reduced.

Description

Technical Field

[0001] This invention belongs to the field of nuclear fuel technology, specifically relating to a method for monitoring in-core damage to fuel rod bundles in heavy water reactors. Background Technology

[0002] In the past, heavy water reactors were judged to have broken fuel in the reactor by referring to pressurized water reactors and using WANO's Fuel Reliability Index (FRI). When the FRI was greater than 19 Bq / g, it was considered that there was broken fuel in the reactor, and only then was the broken fuel search work initiated.

[0003] This method has its shortcomings. When the FRI index of the unit exceeds 19 Bq / g, the I-131 nuclide in the coolant of the heavy water reactor unit has often increased by about ten times. At this time, it is relatively late to start the search for damaged fuel. The high level of nuclide in the coolant will cause the radioactivity level in the plant to increase, increase the collective dose to personnel, and increase the emission of radioactive gases into the environment.

[0004] Therefore, heavy water reactors need to establish a new method for monitoring damaged fuel to detect fuel damage as soon as possible and initiate the damaged fuel search operation immediately, so as to strengthen the monitoring of the fuel integrity of the fuel rod bundles in heavy water reactors. Summary of the Invention

[0005] The purpose of this invention is to provide a method for monitoring fuel rod bundle damage within the heavy water reactor, so as to detect fuel damage as soon as possible, intervene in the damaged fuel search work immediately, and reduce the impact of fuel damage on the unit, personnel and environment.

[0006] The technical solution of the present invention is as follows: a method for monitoring in-core damage of heavy water reactor fuel rod bundles, comprising the following steps:

[0007] Step 1: Conduct online monitoring using a fission gas monitoring system;

[0008] Step 2: Coolant chemical sampling and analysis;

[0009] Step 3: Use the damaged fuel location system to perform data analysis.

[0010] Step 1 includes:

[0011] Step 11: Use a fission gas monitoring system to continuously monitor the nuclides Xe-133, Xe-135, I-131, Kr-88 and total gamma in the coolant online to monitor the overall fuel integrity in the reactor. Check the online monitoring status of nuclides by the fission gas monitoring system daily.

[0012] Step 12: If Xe-133, Xe-135, I-131, Kr-88 and total gamma are continuously rising or abnormally increasing, or if an operator reports an Xe-133 alarm, immediately retrieve the nuclide data from chemical sampling analysis and compare their trends. If the trends of the two nuclide changes are consistent, there may be damaged fuel in the reactor.

[0013] Step 13: For minor damage, extract the nuclide concentration values ​​by copying the energy spectrum file from the fission gas monitoring system, analyze the nuclide increase trend and the time of abnormal nuclide increase, and compare the change trend with the nuclide data from chemical sampling analysis. In the case of low coolant nuclide concentration, determine whether there is damage to the fuel in the reactor.

[0014] Step 14: According to the technical specifications, in unit modes 1, 2, and 3:

[0015] If the Xe-133 radioactivity is less than 200 MBq / kg, otherwise reduce the power to 80% FP within 8 hours;

[0016] If the I-131 radioactivity is less than 500 MBq / kg, otherwise enter mode 2 within 8 hours and mode 4 within 24 hours.

[0017] Step 15: If a malfunction or abnormal data is detected in the fission gas monitoring system, a work request is issued, requiring maintenance personnel to inspect and repair it.

[0018] Step 2 includes:

[0019] Samples of coolant from the two loops of the reactor core were taken and analyzed to monitor the trends in the concentrations of Xe-133, Xe-135, I-131, I-134, and Kr-88 nuclides, in order to monitor for a continuous increase or abnormal rise in the concentration of coolant nuclides.

[0020] Step 21: Under normal circumstances, the coolant in the two loops of the reactor core is sampled and analyzed alternately twice a week;

[0021] Step 22: Conduct weekly trend tracking analysis on chemical analysis data. If the overall trend is upward or there is a significant increase in nuclides, the coolant nuclides are abnormal. Analyze the reasons for the increase, which may indicate fuel damage within the reactor.

[0022] Step 23: After the coolant nuclide anomaly is detected, during the period of slow increase and stability of coolant nuclide, the sampling frequency of chemical analysis is increased from twice a week to three times a week to monitor the trend of coolant nuclide.

[0023] Step 24: If the concentration of coolant nuclides is detected to be continuously rising or abnormally increasing, compare it with the data from the fission gas monitoring system. If the two show the same trend, immediately start the search for damaged fuel.

[0024] The damaged fuel location system determines whether there is damaged fuel in the channel by measuring the delayed neutrons generated by the decay of fission products I-137 and Br-87 in the coolant at the outlet of each of the 380 fuel channels and the trend of the delayed neutron count rate and the background count rate.

[0025] Step 31: Under normal circumstances, the unit will conduct a delayed neutron scan of the damaged fuel location system on all 380 fuel channels of the reactor core every 6 months to establish a normal background count of delayed neutrons over a long period of time. At the same time, the unit will check whether there is damaged fuel in the 380 fuel channels based on the periodic scan data.

[0026] Step 32: If the scan results of the damaged fuel location system show an upward trend or an abnormal increase in the delayed neutron count of a channel, check whether there is high noise signal interference in the detector of that channel. If so, issue a work request to repair the detector circuit; otherwise, perform a single-channel manual scan on the channel showing an upward trend or an abnormal increase to confirm the actual situation of the signal. If it is true, arrange for refueling of the suspected damaged fuel channel according to the core condition.

[0027] Step 33: After the coolant nuclide shows abnormality, increase the scanning frequency as needed;

[0028] Step 34: After detecting a 25% increase in I-134 nuclide in the coolant, a delayed neutron scan of the damaged fuel location system is performed on all 380 fuel channels in the reactor core. If a fuel channel with an abnormal count rate is found, a single-channel scan is performed on that channel to monitor for damaged fuel based on the change in count rate.

[0029] The continuous increase or abnormal rise of total gamma in step 12 specifically means that the monitoring data has continuous spikes and is higher than 0.4 MBq / kg, or the monitoring data continues to rise and the rate of increase is greater than 0.

[0030] In step 14, mode 1 is power operation, mode 2 is low-power hot pressurization, mode 3 is heating or cooling, and mode 4 is extremely low-power cold depressurization.

[0031] The delayed neutron count in step 32 shows an upward trend or an abnormal increase, specifically meaning that the delayed neutron count rate in each scan is higher than the previous one or 20% higher than the background count rate, or the delayed neutron count rate is more than twice the background count rate.

[0032] The beneficial effects of this invention are as follows: This invention solves the problems of limited monitoring methods for fuel rod bundle damage in heavy water reactors and late intervention in the search for damaged fuel. It enables the immediate detection of fuel damage and the immediate initiation of the damaged fuel search operation. Early intervention in the search for damaged fuel can shorten the search time and reduce the impact of coolant nuclides on personnel and the environment after damage. Detailed Implementation

[0033] The present invention will be further described in detail below with reference to specific embodiments.

[0034] The method for monitoring in-core damage to fuel rod bundles in heavy water reactors includes the following steps:

[0035] The fission gas monitoring system used in this invention is used to continuously monitor the concentrations of Kr-88, I-131, Xe-133 and Xe-135 in the coolant, as well as the total gamma activity, in order to monitor the total radioactivity level in the coolant. It can also be used to determine whether there is fuel damage in the reactor core, which is existing technology.

[0036] The damaged fuel location system uses the principle of measuring delayed neutrons associated with I-137 and Br-87. It determines whether there is damaged fuel in each fuel channel by sampling and measuring the number of delayed neutrons in each of the 380 fuel channels. This is a prior art technology.

[0037] Step 1: Apply a fission gas monitoring system for online monitoring, as detailed below:

[0038] A fission gas monitoring system is used to continuously monitor the nuclides Xe-133, Xe-135, I-131, Kr-88, and total gamma in the coolant online to monitor the overall fuel integrity within the reactor. The online nuclide monitoring system is checked daily to promptly detect any abnormal increases in nuclide levels. Under normal circumstances, the monitored nuclide data appear as a straight line.

[0039] Step 12: If Xe-133, Xe-135, I-131, Kr-88 and total gamma are continuously increasing or abnormally increasing (monitoring data has continuous spikes and is higher than 0.4 MBq / kg, or monitoring data continues to rise and the rate of increase is greater than 0), then the presence of damaged fuel in the pile is suspected.

[0040] If an operator reports an Xe-133 alarm (2 MBq / kg), the nuclide data from the chemical sample analysis should be retrieved immediately and compared with its trend. If the nuclide trends of the two are consistent, it indicates that the fission gas monitoring system measurement data is normal, and the presence of damaged fuel in the reactor is suspected.

[0041] Step 13: For minor damage, where the increase in nuclide concentration does not reach the detection limit of the fission gas monitoring system (0.4 MBq / kg), it is necessary to copy the energy spectrum file from the fission gas monitoring system and extract the nuclide concentration value to analyze the nuclide increase trend. The time of abnormal nuclide increase can be analyzed based on the inflection point of the nuclide increase curve. At the same time, the change trend can be compared with the nuclide data from chemical sampling analysis to determine whether there is damage to the fuel in the reactor when the coolant nuclide concentration is low.

[0042] Step 14: According to the technical specifications, in unit modes 1, 2, and 3:

[0043] If the Xe-133 radioactivity is less than 200 MBq / kg, otherwise reduce the power to 80% FP within 8 hours;

[0044] If the I-131 radioactivity is less than 500 MBq / kg, otherwise enter mode 2 within 8 hours and mode 4 within 24 hours.

[0045] Step 15: If a malfunction or abnormal data is detected in the fission gas monitoring system, a work request is issued, requiring maintenance personnel to inspect and repair it.

[0046] Note: Mode 1: Power operation; Mode 2: Low-power hot pressurization; Mode 3: Temperature rise or fall; Mode 4: Very low-power cold depressurization; Mode 5: Ensure reactor shutdown.

[0047] Step 2: Coolant chemical sampling and analysis

[0048] Samples of coolant from both loops of the reactor core were taken and analyzed to monitor the concentration trends of Xe-133, Xe-135, I-131, I-134, and Kr-88 nuclides. This was done to monitor for sustained or abnormal increases in coolant nuclide concentrations (typically manifested in the following situations: ① each analysis shows a higher concentration than the previous one; ② each analysis shows a concentration more than 20% higher than normal; ③ a single analysis shows a concentration more than twice the normal concentration, with subsequent analyses showing a continued increase).

[0049] Step 21: Under normal circumstances, the coolant in the two loops of the reactor core is sampled and analyzed alternately twice a week.

[0050] Step 22: Perform trend tracking analysis on the chemical analysis data weekly. If the overall trend is upward or there is a significant increase in nuclide levels (each analysis data is higher than the previous analysis data, or a certain analysis data is more than twice the normal data, and subsequent analysis data continues to rise), then the coolant nuclide is abnormal, and fuel damage in the reactor is suspected.

[0051] Step 23: After an anomaly is detected in the coolant nuclide, during the period of slow increase in coolant nuclide levels (usually manifested as each analysis data being higher than the previous one, but not doubling) and nuclide stability, the frequency of chemical analysis sampling is increased from twice a week to three times a week to strengthen the monitoring of coolant nuclide trends.

[0052] Step 24: If the concentration of coolant nuclides is detected to be continuously rising or abnormally increasing, compare it with the data from the fission gas monitoring system. If the two show the same trend, immediately start the search for damaged fuel.

[0053] Step 3: Data Analysis of Damaged Fuel Locator System

[0054] The principle behind the damaged fuel location system is as follows: It measures the delayed neutrons produced by the decay of fission products I-137 and Br-87 in the coolant at the outlet of each of the 380 fuel channels. Based on the trend of the delayed neutron count rate relative to the background count rate, it determines whether damaged fuel is present in the channel. For example, if the delayed neutron count rate in a certain channel is between 1.2 and 10 times the background count rate, damaged fuel is suspected in that channel, and further investigation through refueling is needed to determine if damaged fuel is present in that channel.

[0055] Step 31: Under normal circumstances, the unit will conduct a delayed neutron scan of all 380 fuel channels in the reactor core every 6 months to establish a normal background count of delayed neutrons over a long period of time. At the same time, the unit will check whether there is damaged fuel in the 380 fuel channels based on the periodic scan data.

[0056] Step 32: If the scan results of the damaged fuel location system indicate that the delayed neutron count in a channel is trending upward or abnormally increasing (i.e., the delayed neutron count rate in each scan is higher than the previous one or 20% higher than the background count rate, or the delayed neutron count rate is more than twice the background count rate), then check whether the detector in that channel is experiencing high noise signal interference. If so, issue a work request to repair the detector circuit; otherwise, perform a single-channel manual scan on the channel showing an upward trend or abnormal increase to further confirm the true situation of the signal. If the single-channel scan data is consistent with the full-core scan data, it is determined to be a real signal. At this time, refueling of the suspected damaged fuel channel can be arranged according to the core condition.

[0057] Step 33: If the coolant nuclide is abnormal, the scanning frequency can be increased as needed.

[0058] Step 34: After detecting a 25% increase in I-134 nuclide in the coolant, a delayed neutron scan of the damaged fuel location system is performed on all 380 fuel channels in the reactor core. If a fuel channel with an abnormal count rate is found, a single-channel scan is performed on that channel to monitor for damaged fuel based on the change in count rate.

Claims

1. A method for monitoring in-reactor damage of fuel rod bundles in heavy water reactors, characterized in that, Includes the following steps: Step 1: Conduct online monitoring using a fission gas monitoring system; Step 2: Coolant chemical sampling and analysis; Step 3: Use the damaged fuel location system to perform data analysis.

2. The method for monitoring in-core damage of heavy water reactor fuel rod bundles as described in claim 1, characterized in that, Step 1 includes: Step 11: Use a fission gas monitoring system to continuously monitor the nuclides Xe-133, Xe-135, I-131, Kr-88 and total gamma in the coolant online to monitor the overall fuel integrity in the reactor. Check the online monitoring status of nuclides by the fission gas monitoring system daily. Step 12: If Xe-133, Xe-135, I-131, Kr-88 and total gamma are continuously rising or abnormally increasing, or if an operator reports an Xe-133 alarm, immediately retrieve the nuclide data from chemical sampling analysis and compare their trends. If the trends of the two nuclide changes are consistent, there may be damaged fuel in the reactor. Step 13: For minor damage, extract the nuclide concentration values ​​by copying the energy spectrum file from the fission gas monitoring system, analyze the nuclide increase trend and the time of abnormal nuclide increase, and compare the change trend with the nuclide data from chemical sampling analysis. In the case of low coolant nuclide concentration, determine whether there is damage to the fuel in the reactor. Step 14: According to the technical specifications, in unit modes 1, 2, and 3: If the Xe-133 radioactivity is less than 200 MBq / kg, otherwise reduce the power to 80% FP within 8 hours; If the I-131 radioactivity is less than 500 MBq / kg, otherwise enter mode 2 within 8 hours and mode 4 within 24 hours. Step 15: If a malfunction or abnormal data is detected in the fission gas monitoring system, a work request is issued, requiring maintenance personnel to inspect and repair it.

3. The method for monitoring in-core damage of heavy water reactor fuel rod bundles as described in claim 1, characterized in that, Step 2 includes: Samples of coolant from the two loops of the reactor core were taken and analyzed to monitor the trends in the concentrations of Xe-133, Xe-135, I-131, I-134, and Kr-88 nuclides, in order to monitor for a continuous increase or abnormal rise in the concentration of coolant nuclides. Step 21: Under normal circumstances, the coolant in the two loops of the reactor core is sampled and analyzed alternately twice a week; Step 22: Conduct weekly trend tracking analysis on chemical analysis data. If the overall trend is upward or there is a significant increase in nuclides, the coolant nuclides are abnormal. Analyze the reasons for the increase, which may indicate fuel damage within the reactor. Step 23: After the coolant nuclide anomaly is detected, during the period of slow increase and stability of coolant nuclide, the sampling frequency of chemical analysis is increased from twice a week to three times a week to monitor the trend of coolant nuclide. Step 24: If the concentration of coolant nuclides is detected to be continuously rising or abnormally increasing, compare it with the data from the fission gas monitoring system. If the two show the same trend, immediately start the search for damaged fuel.

4. The method for monitoring in-core damage of heavy water reactor fuel rod bundles as described in claim 1, characterized in that, Step 3 includes: The damaged fuel locating system measures the delayed neutrons generated by the decay of fission products I-137 and Br-87 in the coolant at the outlet of each of the 380 fuel channels, and determines whether there is damaged fuel in the channel based on the trend of the delayed neutron count rate and the background count rate. Step 31: Under normal circumstances, the unit will conduct a delayed neutron scan of the damaged fuel location system on all 380 fuel channels of the reactor core every 6 months to establish a normal background count of delayed neutrons over a long period of time. At the same time, the unit will check whether there is damaged fuel in the 380 fuel channels based on the periodic scan data. Step 32: If the scan results of the damaged fuel location system show an upward trend or an abnormal increase in the delayed neutron count of a channel, check whether there is high noise signal interference in the detector of that channel. If so, issue a work request to repair the detector circuit; otherwise, perform a single-channel manual scan on the channel showing an upward trend or an abnormal increase to confirm the actual situation of the signal. If it is true, arrange for refueling of the suspected damaged fuel channel according to the core condition. Step 33: After the coolant nuclide shows abnormality, increase the scanning frequency as needed; Step 34: After detecting a 25% increase in I-134 nuclide in the coolant, a delayed neutron scan of the damaged fuel location system is performed on all 380 fuel channels in the reactor core. If a fuel channel with an abnormal count rate is found, a single-channel scan is performed on that channel to monitor for damaged fuel based on the change in count rate.

5. The method for monitoring in-core damage of heavy water reactor fuel rod bundles as described in claim 2, characterized in that: The continuous increase or abnormal rise of total gamma in step 12 specifically means that the monitoring data has continuous spikes and is higher than 0.4 MBq / kg, or the monitoring data continues to rise and the rate of increase is greater than 0.

6. The method for monitoring in-core damage of heavy water reactor fuel rod bundles as described in claim 2, characterized in that: In step 14, mode 1 is power operation, mode 2 is low-power hot pressurization, mode 3 is heating or cooling, and mode 4 is extremely low-power cold depressurization.

7. The method for monitoring in-core damage of heavy water reactor fuel rod bundles as described in claim 4, characterized in that: The delayed neutron count in step 32 shows an upward trend or an abnormal increase, specifically meaning that the delayed neutron count rate in each scan is higher than the previous one or 20% higher than the background count rate, or the delayed neutron count rate is more than twice the background count rate.