JPH1130689A - Leakage fuel assembly detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a leakage fuel assembly detector that can continuously monitor fluctuation of radioactive nuclide of a gas waste disposal system so as to be able to positively detect the occurrence of leakage fuel. SOLUTION: A radiation detector 8 with performance of being able to discriminate gamma rays from radioactive nuclide emitted from leakage fuel, from gamma rays from other radioactive nuclide is installed near piping or equipment of a gas waste disposal system of a nuclear reactor. An energy discriminating means 9 is provided to energy-discriminate gamma rays of specific energy from a detection signal of the radiation detector 8, and a counting rate computing means 10 is provided to compute the counting rate of gamma rays continuously without a lack of counting on the basis of a signal from the energy discriminating means 9.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a leaked fuel assembly detection device for detecting gamma rays near piping or equipment in a gaseous waste treatment system of a nuclear reactor.

[0002]

2. Description of the Related Art When a defect occurs in a nuclear fuel during the operation of a nuclear reactor, radionuclides may be released from the inside of the nuclear fuel. Means are provided for detecting the leakage of radionuclides from.

[0003] For example, when a defect occurs in a fuel cladding tube during operation of a boiling water reactor, means conventionally used for detecting the occurrence of the defect include the following two methods.
There is one.

[0004] 1) Process radiation monitor This is a means for installing an ionization chamber type detector in a part of a sampling pipe branched from a pipe for gaseous waste treatment and continuously monitoring the intensity of all gamma rays from the current output. 2) Nuclide analysis by sampling A gas vial sampling device is installed in a part of the sampling pipe branched from the gas waste treatment system pipe, and the radionuclide collected in the vial bin is analyzed by a germanium detector and a pulse height analyzer, and radioactivity is analyzed. This is a means for calculating the concentration for each nuclide.

[0005]

However, while the above process radiation monitor can perform continuous and continuous monitoring, it detects all gamma rays, so that the radioactive rare gas from the leaked fuel and its interfering components are not detected. discrimination and made ¹³ N was impossible.

In the nuclide analysis by sampling,
The radioactivity concentration of each radionuclide can be calculated,
Continuous monitoring was not possible due to the time required for sampling.

Accordingly, an object of the present invention is to provide a leaked fuel assembly detection device capable of continuously monitoring the fluctuation of radionuclides in a gas waste treatment system and reliably detecting the generation of leaked fuel.

[0008]

According to the leaked fuel assembly detection device of the present invention, the leaked fuel assembly is installed near the piping or equipment of the gaseous waste treatment system of the nuclear reactor and released from the leaked fuel. A radiation detector having the ability to discriminate gamma rays from radionuclides from gamma rays from other radionuclides, and energy discriminating means for discriminating gamma rays of specific energy from detection signals of the radiation detector, And a counting rate calculating means for calculating the counting rate of gamma rays without fail and continuously based on a signal from the energy discriminating means.

According to a second aspect of the present invention, there is provided the leaked fuel assembly detecting apparatus, further comprising a result display means for displaying a calculation result by the counting rate calculation means.

According to the third aspect of the present invention, the counting rate calculating means further receives a process signal related to a reactor output from a process computer for monitoring the operation of the nuclear reactor. It is characterized in that a change in the signal is compared with a change in the gamma ray counting rate.

According to the leaked fuel assembly detection device of the present invention, the process signal is one of a control rod operation signal, an average output area monitor signal, and a local output area monitor signal. Or a plurality of signals.

[0012] According to the leaked fuel assembly detection device of the invention, the counting rate calculating means may further continuously calculate the counting rate of a specific radioactive rare gas or the counting rate ratio of a plurality of radioactive rare gases. Is calculated.

According to the leaked fuel assembly detecting apparatus of the present invention, the counting rate calculating means further comprises a gamma ray from ¹³ N having a specific energy based on a total gamma ray counting rate from all radionuclides. The present invention is characterized in that the count rate obtained by subtracting the count rate is continuously calculated.

According to the leaked fuel assembly detection device of the present invention, the counting rate calculating means further transmits an alarm signal when the gamma ray counting rate exceeds an alarm threshold value. It is characterized by the following.

According to the leaked fuel assembly detection device of the present invention, the counting rate calculating means may further include a gamma ray counting rate based on a temporal change of the gamma ray counting rate. The time until the value is reached is calculated.

According to the leaked fuel assembly detection device of the ninth aspect, the counting rate calculating means further calculates each radioactivity concentration from each gamma ray counting rate for a plurality of radioactive rare gases. The radioactivity concentration ratio of a plurality of radioactive rare gases is calculated from the radioactivity concentration, and the burnup of the leaked fuel assembly is calculated based on the radioactivity concentration ratio.

[0017] According to the leaked fuel assembly detection device according to the tenth aspect of the present invention, the counting rate calculating means further comprises:
The recoil, diffusion,
It is characterized in that an equilibrium component ratio is calculated.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment Hereinafter, a leaked fuel assembly detection device according to a first embodiment of the present invention will be described with reference to FIG.

FIG. 1 is a schematic diagram showing a gas waste treatment system of a boiling water reactor and a leaked fuel assembly detection apparatus according to the present embodiment applied to the gas waste treatment system.
As shown in FIG. 1, the gaseous waste treatment system of a boiling water reactor includes an air extractor 1, a recombiner 2, an exhaust gas condenser 3, a rare gas hold-up tank 4, and a stack 5 which are sequentially connected. Further, a rare gas monitor chamber 6 is branched and connected between the exhaust gas condenser 3 and the rare gas hold-up tank 4. When a defect occurs in the fuel cladding of the fuel rod and a radionuclide (fission product) containing a radioactive rare gas is released into the reactor from inside the fuel rod, one of the released radionuclides is released. The part reaches the rare gas monitoring chamber 6.

The leaked fuel assembly detection device according to the present embodiment includes a shield 7 disposed near the rare gas monitoring chamber 6 and a gamma ray detector 8 disposed inside the shield 7. Here, the gamma ray detector 8 has a capability of distinguishing gamma rays from radionuclides released from leaked fuel from gamma rays from other radionuclides. The shield 7 is provided with a gamma ray detector 8
Is installed when the contribution of gamma rays scattered by surrounding structures cannot be ignored.

A wave height analyzer 9 is connected to the gamma ray detector 8. The wave height analyzer 9 discriminates a gamma ray having a specific energy from the detection signal of the gamma ray detector 8, and counts each energy. Is stored internally. The crest analyzer 9 is connected to a counting rate calculation device 10.
The measurement and control of the pulse height analyzer 9 are continuously performed without missing at an arbitrary time interval, and the count rate of the gamma ray of the target radionuclide is measured from the energy spectrum information 9a from the pulse height analyzer 9 without fail and continuously. Is calculated. A display device 11 is connected to the count rate calculation device 10, and the display device 11 displays the time series information 10b of the count rate from the count rate calculation device 10.

As described above, according to the leaked fuel assembly detection device of the present embodiment, fluctuations of radionuclides in the gas waste treatment system can be continuously monitored. Leaks from nuclear fuel can be found very early and reliably without any work.

Further, the leaked fuel assembly detection device according to the present embodiment is provided with a gamma ray detector 8 having a performance capable of discriminating gamma rays from radionuclides released from leaked fuel from gamma rays from other radionuclides. Therefore, radionuclides from leaked fuel can be detected separately from radionuclides that fluctuate due to other factors, and leaks from nuclear fuel can be detected with high sensitivity and high reliability.

Second Embodiment Next, a leaked fuel assembly detection device according to a second embodiment of the present invention will be described with reference to FIG. The leaked fuel assembly detection device according to the present embodiment is obtained by partially changing the configuration of the first embodiment, and in the following description, portions common to the first embodiment will be described. Is omitted.

As shown in FIG. 2, in the leaked fuel assembly detection device according to the present embodiment, a process computer 12 for monitoring the operation of the nuclear reactor is connected to the counting rate calculation device 10. Various process signals 12 a relating to the operation of the nuclear reactor are sent to the process computer 12, and a process signal as reactor output information 12 b is sent from the process computer 12 to the count rate calculation device 10. Here, the process signal as the furnace output information 12b is a control rod operation signal, an average output area monitor signal (monitor instruction value), or a local output area monitor signal when a change occurs in the furnace output due to control rod operation or the like. (Monitor instruction value) is one signal or a plurality of signals.

Then, upon receiving the process signal as the furnace output information 12 b from the process computer 12, the counting rate calculation device 10 generates the furnace output information 12 b and the counting rate time-series information 10 b
Comparing the change in the process signal with the change in the gamma count rate, thereby determining the location of the fuel assembly containing the failed fuel rod in the reactor.

That is, if there is a defect in the fuel cladding tube, if the average power of the reactor fluctuates or local power fluctuates in the vicinity of the fuel rod, the radioactivity released from the leaked fuel with this power fluctuation is generated. Since the gamma ray counting rate of the nuclide also changes, the position of the fuel assembly including the damaged fuel rod in the reactor can be identified by analyzing the correlation between the local power fluctuation and the gamma ray counting rate change. .

As described above, according to the leaked fuel assembly detection device according to the present embodiment, the process signal is transmitted from the process computer 12 to the count rate calculation device 10, and the change in the process signal And the change in the gamma ray counting rate, the position of the fuel assembly including the damaged fuel rod in the reactor can be specified.

Third Embodiment Next, a leaked fuel assembly detection device according to a third embodiment of the present invention will be described with reference to FIG. In addition, the leaked fuel assembly detection device according to the present embodiment is the same as the first or second fuel assembly.
The configuration is partially modified from the embodiment,
In the following description, description of parts common to the first and second embodiments will be omitted.

As shown in FIG. 3, the gamma ray counting rate does not change when the furnace power changes near a healthy fuel rod, but when the furnace power changes near a leaking fuel rod, After a predetermined delay time after the start of the furnace power fluctuation, a significant change in the gamma ray counting rate occurs. The delay time here is determined by the performance and operating state of the gaseous waste treatment system of the nuclear reactor.

Therefore, in the leaked fuel assembly detection device according to the present embodiment, the counting rate calculating device 10 continuously calculates the counting rate of a specific radioactive rare gas or the counting rate ratio of a plurality of radioactive rare gases. To In other words, the counting rate calculating unit 10, ¹³³ Xe and ¹³⁵ relatively long half-life of the count rate change of radioactive noble gases such as Xe, or ¹³³ X the long half-life
The change in the ratio between e and the count rate of ¹³⁸ Xe with a short half-life is continuously calculated without interruption and monitored.

As described above, according to the leaked fuel assembly detection device according to the present embodiment, the count rate or count rate ratio of a specific radioactive rare gas is continuously and continuously monitored without any measurement. If a radioactive nuclide leaks due to a break in the tube, the change can be detected as soon as the radioactive rare gas reaches the measurement point. Therefore, the presence or absence of breakage of the fuel cladding tube and the position of the leaked fuel rod in the reactor can be reliably detected.

Further, according to the leaked fuel assembly detection device of the present embodiment, it is possible to not only detect a leak quickly but also to monitor the expansion of damage after the leak occurs.

Fourth Embodiment Next, a leaked fuel assembly detection device according to a fourth embodiment of the present invention will be described with reference to FIG. Note that the leaked fuel assembly detection device according to the present embodiment includes the first to third fuel assemblies.
The configuration is partially modified from the embodiment,
In the following description, description of parts common to the first to third embodiments will be omitted.

In the leaked fuel assembly detection device according to the present embodiment, the counting rate calculation device 10 (see FIG. 1 or FIG. 2).
Is designed to continuously calculate a count rate obtained by subtracting a gamma ray count rate from ¹³ N having a specific energy (511 keV) from a total gamma ray count rate from all radionuclides.

That is, in the leaked fuel assembly detection device according to the present embodiment, the wave height analyzer 9 (see FIG. 1 or FIG. 2) of the entire energy spectrum signal shown in FIG.
The leak is detected by continuously monitoring the count value obtained by subtracting the net count value ^{13 of 13} N which depends only on the furnace power without depending on the presence or absence of the leaked fuel from the count value 14 of the total energy which can be detected by the above. I have to.

As described above, according to the leaked fuel assembly detection device of the present embodiment, the total energy count value 14
¹³ N that does not depend on the presence or absence of leaking fuel but only on the reactor power
Since the count value obtained by subtracting the count value 15 is continuously monitored, the leakage of the radionuclide from the nuclear fuel can be detected with high accuracy.

Fifth Embodiment Next, a leaked fuel assembly detection device according to a fifth embodiment of the present invention will be described with reference to FIG. The leaked fuel assembly detection device according to the present embodiment includes the first to fourth fuel assemblies.
The configuration is partially modified from the embodiment,
In the following description, description of parts common to the first to fourth embodiments will be omitted.

As shown in FIG. 5, in the leaked fuel assembly detection device according to the present embodiment, an alarm device 13 is connected to a counting rate calculation device 10. Then, the counting rate calculation device 10
Compares the preset warning threshold value 10a with the gamma ray counting rate, and issues a warning signal 10c when the gamma ray counting rate exceeds the warning threshold value 10a. Warning signal 10
c is an alarm device 1 operating in the central control room or on-site monitoring panel
3 to activate the alarm device 13.

Here, it is possible to set not only one alarm threshold value 10a but also a plurality of alarm levels according to the stage of leakage.
It is also possible to provide an alarm device 13 that performs an operation corresponding to each.

As described above, since the leaked fuel assembly detection device according to the present embodiment is provided with the alarm device 13, the occurrence of the leak from the nuclear fuel can be immediately notified.

Sixth Embodiment Next, a leaked fuel assembly detection device according to a sixth embodiment of the present invention will be described with reference to FIG. Note that the leaked fuel assembly detection device according to the present embodiment includes the first to fifth fuel assemblies.
The configuration is partially modified from the embodiment,
In the following description, description of parts common to the first to fifth embodiments will be omitted.

After the occurrence of a defect in the fuel cladding tube, the gamma ray counting rate increases when the amount of leakage from the damaged fuel increases, and when the gamma ray counting rate reaches a preset reactor shutdown reference value, the operation of the reactor is started. Need to stop.

Therefore, in the leaked fuel assembly detection device according to the present embodiment, the counting rate calculation device 10 (see FIG. 1 or FIG. 2) changes the gamma ray counting rate based on the time-dependent change of the gamma ray counting rate to shut down the reactor. The time until the reference value is reached (date) is calculated.

That is, in the leaked fuel assembly detection device according to the present embodiment, the reference value of the reactor operation stop is inputted in advance to the count rate calculating device 10 and the count rate calculating device 1
0 is, for example, the extrapolation rate is obtained from the differential value of the change in the gamma ray counting rate in an arbitrary time range based on the time course of the gamma ray counting rate shown in FIG. Calculate and predict the time (date) until the value is reached.

As described above, according to the leaked fuel assembly detection device of the present embodiment, it is possible to predict the time until the gamma ray counting rate reaches the reactor shutdown reference value, so that leakage from the nuclear fuel occurs. After that, the appropriate action can be taken.

Seventh Embodiment Next, a leaked fuel assembly detection device according to a seventh embodiment of the present invention will be described with reference to FIGS. In addition,
The leaked fuel assembly detection device according to the present embodiment includes the first
The configuration is partially modified from the first to sixth embodiments, and in the following description, the description of the parts common to the first to sixth embodiments will be omitted.

As shown in FIG. 7, the leaked fuel assembly detection device according to the present embodiment is provided with two systems of measurement units 16 and 17 including a shield 7, a gamma ray detector 8 and a wave height analyzer 9. The measurement unit 16 in the former stage includes the exhaust gas condenser 3 and the rare gas hold-up tank 4 as in the above-described embodiments.
The gamma ray near the rare gas monitor chamber 6 which is branched and connected between the gamma rays is measured. The latter measuring unit 17 measures the gamma ray near the rare gas monitor chamber 6 which is branched and connected between the rare gas hold-up tank 4 and the stack 5, and the vicinity of the rare gas monitor chamber 6. , A shield 7 and a gamma ray detector 8 are provided.

In the leaked fuel assembly detection device according to the present embodiment, the counting rate calculator 10 calculates each radioactivity concentration from each gamma ray counting rate for a plurality of radioactive rare gases, and calculates each radioactivity concentration from each radioactivity concentration. The radioactivity concentration ratio of the plurality of radioactive rare gases is calculated, and the burnup of the leaked fuel assembly is calculated based on the radioactivity concentration ratio.

That is, the counting rate calculation device 10 calculates the ¹³³ Xe counting rate from the spectrum obtained from the measuring section 16 at the preceding stage, calculates the ¹³³ Xe radioactivity concentration from the previously calibrated conversion count, and The counting rate and the radioactivity concentration of ⁸⁵ Kr are calculated from the spectrum obtained from the measuring unit 17. Here, by keeping the gas containing the radionuclide in the rare gas hold-up tank 4 for a certain period of time, the ¹³ N which interferes with the spectrum measurement of ⁸⁵ Kr can be sufficiently attenuated.
Gamma rays from ⁸⁵ Kr can be measured with high accuracy.

Further, the counting rate calculation device 10 continuously monitors the two radioactivity concentrations, and calculates the ratio of the radioactive rare gas corresponding to the sudden release of the radioactive rare gas. Then, as shown in FIG.
A value of 0 calculates the burnup of the leaked fuel assembly from the ratio of the radioactive concentrations of ¹³³ Xe and ⁸⁵ Kr.

As described above, according to the leaked fuel assembly according to the present embodiment, the burnup of the leaked fuel assembly can be calculated from the ratio of the radioactivity concentration of ¹³³ Xe to ⁸⁵ Kr, so The position of the fuel assembly in the reactor can be specified very accurately.

Eighth Embodiment Next, a leaked fuel assembly detection device according to an eighth embodiment of the present invention will be described with reference to FIG. Note that the leaked fuel assembly detection device according to the present embodiment includes the first to seventh fuel assemblies.
The configuration is partially modified from the embodiment,
In the following description, description of parts common to the first to seventh embodiments will be omitted.

In the leaked fuel assembly detection device according to the present embodiment, the counting rate calculation device 10 uses the correlation between the gamma ray counting rates of a plurality of radioactive rare gases at each measurement time point as an index of the emission form. Calculate the component ratio of jump, diffusion and equilibrium.

That is, the counting rate calculation device 10 can calculate the radioactivity concentrations of up to seven types of radioactive rare gases from the measured spectrum of the radioactive rare gas, ¹³³ Xe,
¹³⁵ Xe, ^{135 m} Xe, ¹³⁸ Xe, ^{85 m} Kr, ⁸⁷ Kr and
The emission rates of the seven ⁸⁸ Kr radioactive rare gases per unit time can be calculated from the spectra stored in the pulse height analyzer 9.

Then, as shown in FIG. 9, the counting rate calculator 10 calculates each component ratio of recoil, diffusion and equilibrium from the correlation between each calculated noble gas release rate and the decay constant of each radionuclide. I do.

As described above, according to the leaked fuel assembly detection device according to the present embodiment, the count rate calculator 10 calculates the respective component ratios of recoil, diffusion, and equilibrium. It is possible to estimate the presence / absence of fuel damage or the degree of damage from, and further, by continuously calculating the transition of the three components, from the occurrence of defects in the fuel cladding, the degree of damage, In addition, it is possible to monitor the extension of damage due to the reactor operation.

[0058]

As described above, according to the leaked fuel assembly detection device of the present invention, the fluctuation of radionuclides in the gaseous waste treatment system can be continuously monitored.
Leaks from nuclear fuel can be detected very early and reliably without any artificial work such as sampling.

Further, according to the leaked fuel assembly detection device of the present invention, there is provided a radiation detector having a capability of discriminating gamma rays from radionuclides released from leaked fuel from gamma rays from other radionuclides. Therefore, the radionuclide from the leaked fuel can be discriminated and detected from the radionuclide fluctuating due to other factors, and the leak from the nuclear fuel can be detected with high sensitivity and high reliability.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a schematic configuration when a leaked fuel assembly detection device according to a first embodiment of the present invention is installed in a gas waste treatment system of a boiling water reactor.

FIG. 2 is a schematic diagram showing a schematic configuration when a leaked fuel assembly detection device according to a second embodiment of the present invention is installed in a gas waste treatment system of a boiling water reactor.

FIG. 3 is a graph for explaining an operation of the leaked fuel assembly detection device according to the third embodiment of the present invention.

FIG. 4 is a graph for explaining an operation of the leaked fuel assembly detection device according to the fourth embodiment of the present invention.

FIG. 5 is a schematic diagram showing a schematic configuration when a leaked fuel assembly detection device according to a fifth embodiment of the present invention is installed in a gas waste treatment system of a boiling water reactor.

FIG. 6 is a graph for explaining the operation of the leaked fuel assembly detection device according to the sixth embodiment of the present invention.

FIG. 7 is a schematic diagram showing a schematic configuration when a leaked fuel assembly detection device according to a seventh embodiment of the present invention is installed in a gas waste treatment system of a boiling water reactor.

FIG. 8 is a graph for explaining the operation of the leaked fuel assembly detection device according to the seventh embodiment of the present invention.

FIG. 9 is a graph for explaining the operation of the leaked fuel assembly detection device according to the eighth embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 6 rare gas monitor chamber 7 shield 8 gamma ray detector 9 wave height analyzer 10 count rate calculator 10a alarm threshold 11 display 12 process calculator 12b furnace output information (process signal) 13 alarm

Claims (10)

[Claims] 1. A gamma ray from a radionuclide released from a leaked fuel is installed in the vicinity of piping or equipment of a gaseous waste treatment system of a nuclear reactor, and has a capability of distinguishing gamma rays from other radionuclides from energy. A radiation detector, energy discriminating means for energy discriminating a gamma ray having a specific energy from a detection signal of the radiation detector, and a count rate of the gamma ray based on the signal from the energy discriminating means without fail and continuously. And a counting rate calculating means for calculating the leaked fuel assembly. 2. The leaked fuel assembly detection device according to claim 1, further comprising a result display means for displaying a calculation result by said counting rate calculation means. 3. The count rate calculating means further receives a process signal related to the reactor power from a process computer monitoring operation of the reactor, and compares a change in the process signal with a change in the gamma ray count rate. The leaked fuel assembly detection device according to claim 1 or 2, wherein: 4. The system according to claim 3, wherein the process signal is one or more of a control rod operation signal, an average output area monitor signal, and a local output area monitor signal. Leakage fuel assembly detection device. 5. The apparatus according to claim 1, wherein said counting rate calculating means continuously calculates a counting rate of a specific radioactive rare gas or a counting rate ratio of a plurality of radioactive rare gases. The leaked fuel assembly detection device according to claim 4. 6. The counting rate calculating means may further continuously calculate a counting rate obtained by subtracting a gamma ray counting rate from ¹³ N having a specific energy from a total gamma ray counting rate from all radionuclides. The leaked fuel assembly detection device according to any one of claims 1 to 5, wherein: 7. The apparatus according to claim 1, wherein said counting rate calculating means further transmits an alarm signal when the gamma ray counting rate exceeds an alarm threshold value. The leaked fuel assembly detection device according to claim 1. 8. The method according to claim 1, wherein the counting rate calculating means calculates a time required for the gamma ray counting rate to reach a predetermined reactor operation stop reference value based on a temporal change of the gamma ray counting rate. The leaked fuel assembly detection device according to any one of claims 1 to 7, wherein: 9. The counting rate calculating means further calculates each radioactivity concentration from each gamma ray counting rate for a plurality of radioactive rare gases, and calculates a radioactivity concentration ratio of the radioactive rare gases from each radioactivity concentration. The leaked fuel assembly detection device according to any one of claims 1 to 8, wherein the calculated burnup of the leaked fuel assembly is calculated based on the radioactivity concentration ratio. 10. The counting rate calculating means further calculates a recoil / diffusion / equilibrium component ratio which is an index of the emission form based on the correlation of the gamma ray counting rates of a plurality of radioactive rare gases at each measurement time point. 2. The method according to claim 1, wherein the calculation is performed.
The leaked fuel assembly detection device according to any one of claims 9 to 9.