JPH04324398A - Abnormality diagnostic device for reactor - Google Patents

Abstract

PURPOSE:To diagnose the operation status of a reactor by detecting quickly the leak of primary coolant due to the rupture of heat conduction pipe in a steam generator in a pressurized water reactor. CONSTITUTION:In a secondary main steam pipe 8 to send steam generated in a steam generator 6 to a turbine 9, a neutron detector 18 is provided. Radiation rate or count rate is constantly measured with the neutron detector 18. By sending the measured data to an arithmetic processing system 19 and comparing it to a normal value, the existence of a leak is diagnosed.

Description

[Detailed description of the invention]

[Object of the invention]

0002

[Industrial Application Field] The present invention relates to a pressurized water nuclear reactor (hereinafter referred to as
The present invention relates to a nuclear reactor abnormality diagnosis device for diagnosing leakage of primary coolant from a broken part of a heat transfer tube in a steam generator in a nuclear reactor (hereinafter referred to as PWR).

0003

2. Description of the Related Art A conventional pressurized water nuclear reactor will be schematically explained with reference to FIG. In the figure, reference numeral 1 indicates a reactor building, 2 indicates a reactor containment vessel, and 3 indicates a reactor vessel. The primary coolant heated in the reactor core 4 in the reactor vessel 3 flows through the primary system piping 5 and flows into the heat transfer tube 7 in the steam generator 6 . The secondary coolant in the steam generator 6 is heated by exchanging heat with the heat exchanger tube 7 , becomes high-temperature, high-pressure steam, flows through the secondary main steam pipe 8 , and flows into the turbine 9 . The turbine 9 rotates and drives the generator 10 to generate electricity. The steam that has completed its work in the turbine 9 flows into the condenser 11, where it is cooled and becomes condensed water. This condensate flows through the secondary water pipe 12 and is supplied to the steam generator 6 as a secondary coolant. On the other hand, the primary coolant flowing through the heat transfer tubes 7 in the steam generator 6 is cooled by exchanging heat with the secondary coolant, and is returned to the reactor vessel 3 from the primary main cooling pipe 13 by the pump 14 into the reactor core 4. is heated.

[0004] In the figure, 15 is a control rod, 16 is a pressurizer,
Reference numeral 17 indicates a spray tube. In addition, 21 is an exhaust gas system bleed pipe, 22 is a turbine exhaust gas system monitor,
It measures radioactive substances in exhaust gas.

By the way, in the steam generator 6, a large number of heat transfer tubes 7 made of inverted U-shaped thin tubes are attached to a tube plate, and all of these heat transfer tubes 7 are inspected during regular inspections. The soundness has been confirmed. If the heat transfer tubes 7 are damaged during reactor operation and the primary coolant leaks, the radioactive materials in the leaked primary coolant will pass through the secondary main steam piping 8 and transfer to the turbine 9. Furthermore, it passes through the condenser 11 and returns to the water supply system. In the PWR, some steam (gas) is extracted from the condenser 11 through the exhaust gas extraction piping 21, and if the extracted steam contains radioactive substances exceeding the alarm set value, the exhaust gas monitor 22 detects It is configured to issue an alarm.

[0006]

[Problems to be Solved by the Invention] In conventional PWRs, when the primary coolant leaks, an alarm is set on the exhaust gas monitor 22 to detect the leakage of targeted radionuclides (rare gases, corrosion products, nuclear fission products, etc.). An alarm will be issued when the amount exceeds the value. However, the amount of these radionuclides present in the primary coolant is small to begin with, and the measurement is performed by extracting a portion of the leakage into the main steam, making it difficult to detect when a small amount leaks. There is. In addition, there are other problems such as the inability to grasp the status of leaked radioactive materials and changes in the scale of leakage from damaged parts of heat exchanger tubes.

The present invention has been made to solve the above problems, and is capable of quickly detecting a small amount of leakage of primary coolant from a heat transfer tube in a steam generator in a pressurized water reactor, and reducing the scale of the damaged part. It is an object of the present invention to provide a nuclear reactor abnormality diagnosis device that can perform estimation and predict the transition of leakage amount. [Structure of the invention]

[0008]

[Means for Solving the Problems] The present invention provides a dose rate measurement system in which a neutron detector is installed in the secondary main steam system of a pressurized water reactor, the secondary main steam piping, or the turbine, and the The data obtained from the rate measurement system is compared with normal conditions to determine whether there are any abnormal signs due to leakage, and the radioactivity concentration in the main steam at the measurement point is calculated from the dose rate to predict the transition of the leakage. , and an arithmetic processing system that measures the damage over time.

[0009]

[Operation] The present invention uses a dose rate measurement system in which a neutron detector is installed in the secondary main steam system of a pressurized water reactor, and compares data obtained from this measurement system with data obtained under normal conditions. The arithmetic processing system then determines whether there are any abnormal signs due to the leak, calculates the radioactivity concentration in the main steam at the measurement point from the dose rate, predicts the course of the leak, and estimates the scale of the damaged part based on changes over time. conduct. If the heat transfer tube in the steam generator were to break, the radioactive substances in the primary coolant would reach the neutron detector within a few seconds. The nuclide to be measured is 17N, which emits neutrons, and since neutrons are measured, it can be detected without being affected by natural radiation or gamma rays emitted by source nuclides that exist in other primary systems. , the output of the neutron detector changes significantly.

[0010] Furthermore, a neutron detector is installed on the upstream side (closer to the steam generator) along the flow path of the main steam, facing the vicinity of the secondary main steam piping that connects the steam generator and the turbine of the pressurized water reactor. If a system is installed, the data obtained from the dose rate measurement system can be compared with normal conditions to determine whether there are abnormal signs due to leakage, and the radioactivity concentration in the main steam at the measurement point can be calculated from the dose rate. The leakage trend is predicted and the scale of the damaged area is estimated based on changes over time. Furthermore, since the object to be measured is neutrons and the attenuation effect of the main steam pipe (inner thickness 2 to 3 cm) is small, even a small amount of leakage can be sufficiently detected.

Furthermore, when a neutron detector is installed in the turbine of a pressurized water reactor, the data obtained from the dose rate measurement system is compared with normal conditions to determine the presence or absence of abnormal signs due to leakage, and to determine the dose rate. The radioactivity concentration in the main steam at the measurement point is calculated from the rate, the leakage transition is predicted, and the scale of the damaged part is estimated based on changes over time.

In the abnormality diagnosis device of the present invention, 17N, which is a neutron-emitting nuclide and is generated by the 17O(n,p)17N reaction, is sent to the secondary main steam system, near the main steam piping of the secondary system, or to the turbine. It will be continuously monitored by the installed neutron detector. This makes it possible to perform measurements without being affected by fluctuations in natural radiation or by other gamma-ray-emitting nuclides, allowing early detection of small amounts of radioactive material leaking from damaged heat exchanger tubes. In addition to estimating the scale of damage, it is also possible to predict changes in the amount of leakage as the damage expands.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Examples of the present invention will be described with reference to the drawings. FIG. 1 schematically shows a pressurized water nuclear power plant including an embodiment of the present invention. In the figure, code 1 is the reactor building, 2
3 indicates the reactor containment vessel, and 3 indicates the reactor vessel. The primary coolant heated in the reactor core 4 in the reactor vessel 3 flows through the primary system piping 5 and flows into a large number of heat transfer tubes 7 in the steam generator 6 . The secondary coolant in the steam generator 6 is heated by exchanging heat with the heat exchanger tube 7 , becomes high-temperature, high-pressure steam, flows through the secondary main steam pipe 8 , and flows into the turbine 9 . The turbine 9 rotates and drives the generator 10 to generate electricity. The steam that has completed its work in the turbine 9 flows into the condenser 11, where it is cooled and becomes condensed water. This condensate flows through the secondary system water supply pipe 12 and is supplied to the steam generator 6 as a secondary system coolant. On the other hand, the primary coolant flowing through the heat transfer tubes 7 in the steam generator 6 is cooled by exchanging heat with the secondary coolant, and is returned to the reactor vessel 3 from the primary main cooling pipe 13 by the pump 14 into the reactor core 4. is heated. In the figure, 15 is a control rod, 16 is a pressurizer, and 17 is a control rod.
indicate the spray tubes, respectively.

In the first embodiment, a neutron detector 18 is provided in the secondary main steam system in order to measure the neutrons released due to β-decay of 17N in the secondary main steam system. ing. This neutron detector 18 is an arithmetic processing system 1
9 by a signal cable 20.

FIG. 2 shows a block diagram of the measurement system and arithmetic processing system in the present invention. In FIG. 2, a neutron detector 18 is installed at the measurement point of the secondary main steam pipe 8.
is installed, and a preamplifier 23 is installed in the neutron detector 18.
is connected. The preamplifier 23 is connected to a high-voltage/low-voltage power source 24 via a signal cable 20, and a voltage is applied thereto. On the other hand, the signal cable 20 is branched to the arithmetic processing system 19.
is connected. The arithmetic processing system 19 includes a converter 25, a multichannel scaling (MCS) 26, and an arithmetic processing unit 27. A plant data output device 28 and a data output device 29 are connected to the arithmetic processing device 27 .

The neutron detector 18 uses a REM counter, a Bonner ball, a liquid scintillator, etc., and calculates the dose rate or count rate using MCS26 (multichannel scaling).
Measure continuously in mode. Measured data is transferred in real time via a signal cable 20 such as a coaxial cable or an optical cable to an arithmetic processing system 19 comprising an arithmetic processing unit 27, such as a personal computer, equipped with data input/output and arithmetic functions.

Since the 17N to be measured is a neutron-emitting nuclide, the background of neutrons in natural radiation is zero, so when a neutron is detected by the neutron detector 18, the heat transfer tube breaks and the primary coolant is immediately turned off. It is determined that the leak has occurred to the next main steam system, the dose rate is converted to radioactivity concentration, the value and the amount of change are output, and the progress of the leak is predicted based on the results.

According to the first embodiment, the neutron detector 1 is installed in the secondary main steam system connecting the steam generator 6 and the turbine 9.
Based on the data obtained from this measurement system and the data obtained from this measurement system, the data obtained from this measurement system is compared with normal conditions to determine the presence or absence of abnormal signs due to leakage, and the radiation in the main steam at the measurement point is determined from the dose rate. It is comprised of an arithmetic processing system 19 that can calculate the concentration of energy and process changes over time. Note that the 17N to be measured is generated by the 17O(n,p)17N reaction.
It is a nuclide that emits approximately 1 Mev of neutrons with a half-life of 4.2 seconds. Since neutrons are measured during measurement, they can be detected without being affected by natural radiation or gamma rays emitted by source nuclei present in other primary systems, and the output of the neutron detector changes significantly.

Next, in the second embodiment of the present invention, in order to measure the neutrons released due to β-decay of 17N in the secondary main steam pipe 8, a neutron detection device is installed facing the pipe 8. A container 18 is provided. This neutron detector 1
8 is connected to an arithmetic processing system 19 via a signal cable 20.

Neutron detector 1 in this second embodiment
The position of 8 is the steam generator 6 from the viewpoint of the source strength of 17N.
It is desirable to be closer to the exit 6a. The neutron detector 18 uses a REM counter, a Bonner ball, a liquid scintillator, etc., and calculates the dose rate or count rate using MCS (multichannel system).
Perform continuous measurements in (scaling) mode. Measured data is transferred in real time via a signal cable 20 such as a coaxial cable or an optical cable to an arithmetic processing system 19 comprising an arithmetic processing device (such as a personal computer) 27 equipped with data input/output and arithmetic functions.

Since the 17N to be measured is a neutron-emitting nuclide, the background of neutrons in natural radiation is zero, so when a neutron is detected by a detector, the primary system coolant immediately changes to the secondary system due to a heat exchanger tube breakage. It is determined that there has been a leak into the main steam pipe, the dose rate is converted to radioactivity concentration, the value and the amount of change are output, and the transition of the leak is predicted based on the results. In addition, by determining in advance the radioactivity concentration of the radionuclide to be measured in the primary system coolant and the transfer rate from the steam generator 6 to the secondary system main steam piping 8, it is possible to The scale of the damaged portion of the heat exchanger tube 7 can be estimated from the value of the radioactivity concentration in the steam. Furthermore, by determining the proportion of radioactive nuclides (17N, 16N, 15C, rare gases, fission products, corrosion products, etc.) in the primary coolant through calculations and measurements in advance, it is possible to The total leaked radioactivity concentration can be estimated.

According to the second embodiment, a position on the upstream side along the main steam flow path, facing the secondary main steam piping 8 connecting the steam generator 6 and the turbine 9, for example, a position close to the steam generator 6 A dose rate measurement system with a neutron detector 18 installed at It consists of an arithmetic processing system that calculates the radioactivity concentration in steam and processes changes over time. If the heat transfer tube 7 in the steam generator 6 is damaged, the radioactive substances in the primary coolant will reach the neutron detector 18 in a few seconds.

Note that 17N to be measured is 17O(n
, p) Produced in a 17N reaction, approximately 1 in a 4.2 second half-life
It is a nuclide that emits Mev neutrons. During measurement, it can be detected without being affected by natural radiation or gamma rays emitted by source nuclides that exist in other primary systems.
The output of the detector changes significantly. In addition, since it is a neutron, the attenuation effect by the main steam pipe (inner thickness 2 to 3 cm) 8 is small, so even a trace amount of leakage can be sufficiently detected.

Next, in a third embodiment of the present invention, a neutron detector 18 is provided on the turbine floor in the turbine building. This neutron detector 18 is connected to an arithmetic processing system 20 by a signal cable 21.

Neutron detector 1 in this third embodiment
It is desirable that the position of 8 be closer to the turbine body from the viewpoint of the radiation source strength of 17N. The neutron detector 18 continuously measures the dose rate or count rate in MCS (multichannel scaling) mode using a REM counter, Bonner ball, liquid scintillator, or the like. Measurement data is transmitted in real time via signal cable 20 such as coaxial cable or optical cable.
Then, the data is transferred to an arithmetic processing system 19 comprising an arithmetic processing device (such as a personal computer) equipped with data input/output and arithmetic functions.

Since the 17N to be measured is a neutron-emitting nuclide, the background of neutrons in natural radiation is zero, so when a neutron is detected by a neutron detector, the primary coolant is immediately damaged due to damage to the heat transfer tube 7. It is determined that the leak has leaked into the secondary main steam piping 8 and transferred to the turbine 9, and the dose rate is converted to radioactivity concentration and the value and amount of change are output, and the transition of the leak is determined based on the results. Predict.

According to the above-mentioned embodiment, the dose rate measurement system in which the neutron detector 18 is installed inside the turbine building and the data obtained from this measurement system are compared with the normal state to detect abnormalities due to leakage. It consists of an arithmetic processing system that determines the presence or absence of symptoms, calculates the radioactivity concentration in the main steam at the measurement point from the dose rate, and processes changes over time.

Note that 17N to be measured is 17O(n
, p) Produced in the 17N reaction with a half-life of 4.2 seconds and approximately 1
It is a nuclide that emits Mev neutrons. During measurement, since neutrons are measured, detection is possible without being affected by natural radiation or gamma rays emitted by source nuclides present in other primary systems, and the output of the neutron detector changes significantly.

[0029]

[Effects of the Invention] According to the present invention, the nuclide to be measured is 17N, which emits neutrons, and since neutrons are measured, natural radiation and source nuclides present in other primary systems emit neutrons. It can be detected without being affected by gamma rays, and it is possible to quickly and accurately diagnose minute leaks of primary system cooling to the secondary system due to damage to heat transfer tubes in the steam generator, as well as fluctuations in the amount of leakage.

[Brief explanation of the drawing]

FIG. 1 is a block diagram schematically showing a pressurized water nuclear reactor including an embodiment of the present invention.

FIG. 2 is a block diagram of a measurement system and an arithmetic processing system in the present invention.

[Explanation of symbols]

1...Reactor building, 2...Reactor containment vessel, 3...Reactor vessel, 4...Reactor core, 5...Primary system piping, 6...Steam generator, 7...Heat transfer tube, 8...Secondary system main steam piping, 9 ... Turbine, 10 ... Generator, 11 ... Condenser, 12 ... Secondary system water supply pipe, 13 ... Primary system main cooling pipe, 14 ... Pump, 15 ... Control rod, 16 ... Pressurizer, 17 ... Spray pipe, 18 ...neutron detector, 19...
Arithmetic processing system, 20... Signal cable, 21... Exhaust gas system extraction piping, 22... Turbine exhaust gas system monitor, 23... Preamplifier, 24... High voltage/low voltage power supply, 25... Converter, 26... MC
S, 27... Arithmetic processing unit, 28... Plant data output device, 29... Data output device.

Claims (1)

[Claims] [Claim 1] Secondary main steam system of a pressurized water reactor,
Alternatively, a dose rate measurement system with a neutron detector installed in the main steam piping of the secondary system or the turbine is used, and the data obtained from this dose rate measurement system is compared with normal conditions to determine whether there are abnormal signs due to leakage. A nuclear reactor characterized by comprising an arithmetic processing system that calculates the radioactivity concentration in the main steam at a measurement point from judgment and dose rate, predicts the transition of leakage, and measures the damage over time. Abnormality diagnosis device.