JPH04335196A - Abnormality diagnosis device for reactor - Google Patents

Abstract

PURPOSE:To defect immediately small leakage of primary coolant from heat conduction tubes in a steam generator of a pressurized water reactor. CONSTITUTION:In addition to an existing monitor 18 of turbine exhaust gas line provided in the exhaust gas line pipe 17 to sample a part of steam (gas) from a water condenser 12, a first radiation detector 19 of <16>N is installed on the secondary main steam pipe 13 from a steam generator 8. The first radiation detector 19 and the second radiation detector 21 for the monitor 18 of the turbine exhaust gas line are connected to an arithmetic processor 20.

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 7 and flows into the heat exchanger tubes 9 in the steam generator 8 . The secondary coolant in the steam generator 8 exchanges heat with the heat exchanger tubes 9 and is heated to become high-temperature, high-pressure steam, which flows through the secondary main steam piping 13 and flows into the turbine 14 . The turbine 14 rotates and drives the generator 15 to generate electricity. The steam that has completed its work in the turbine 14 flows into the condenser 12, where it is cooled and becomes condensed water. This condensate flows through the secondary water supply pipe 16 to the steam generator 8.
Water is supplied to the system as a secondary coolant. On the other hand, steam generator 8
The primary coolant flowing through the heat transfer tubes 9 is cooled by exchanging heat with the secondary coolant, and is cooled from the primary main cooling pipe 11 to the pump 1.
0, it returns to the reactor vessel 3 and is heated in the reactor core 4.

In the figure, 5 is a control rod, 6 is a pressurizer, and 17 is a control rod.
indicate exhaust gas system piping. Further, 18 is a turbine exhaust gas system monitor, which is equipped with a radiation detector for measuring radioactive substances in the exhaust gas.

By the way, in the steam generator 8, a large number of heat transfer tubes 9 made of inverted U-shaped thin tubes are attached to a tube plate, and all of these heat transfer tubes 9 are inspected during periodic inspections. The soundness has been confirmed. If the heat transfer tubes 9 are damaged during reactor operation and the primary coolant leaks, the radioactive materials in the leaked primary coolant will be transferred to the secondary main steam pipe 13.
The water passes through the turbine 14, and then passes through the condenser 12 and returns to the water supply system. In the PWR, some steam (gas) is extracted from the condenser 12 through the exhaust gas system piping 17, and if the extracted steam contains radioactive substances exceeding the alarm set value, the turbine exhaust gas system monitor 18 The system is configured so that an alarm will be issued.

[0006]

[Problem to be Solved by the Invention] The exhaust gas system monitor 18 of the exhaust gas system is used to continuously monitor radioactivity leaked into the secondary system of the primary coolant due to damage to the heat transfer tube 9 in the steam generator 8. There is. The radioactivity concentration in the PWR secondary system piping during normal operation is almost zero, so the measurement results for damage monitoring of the heat transfer tubes 9 sometimes have peak-like fluctuations due to fluctuations in natural radiation or noise in the measurement system. may appear. Currently, there is no way to determine whether this is a significant signal. In addition, it is difficult to understand the situation of the damaged part when the damage is significant and the dose rate increases further.

That is, in a conventional PWR, when the primary coolant leaks, the leakage of radionuclides (rare gases, corrosion products, fission products, etc.) targeted by the turbine exhaust gas system monitor 18 causes the alarm set value to be exceeded. An alarm will be issued when the amount exceeds. However, the turbine exhaust gas system monitor 18 is also located at the terminal end of the secondary system, and 16N (7 seconds), which is the main source nuclide of the primary coolant that leaks into the secondary system due to leakage of the heat exchanger tubes 9, is located at the end of the secondary system. Ya1
Short half-life nuclides such as 5C (2 seconds) are attenuated until they reach the turbine exhaust gas system monitor 18 and are hardly counted. Therefore, the radionuclides targeted by the turbine exhaust gas system monitor 18 due to primary coolant leakage include rare gases, corrosion products, nuclear fission products, and the like. However, these radionuclides present in the primary coolant are originally small in amount compared to 16N and 15C, and the part that leaked into the main steam is extracted and measured, so it is difficult to detect when a small amount leaks. is difficult to detect. Furthermore, due to background fluctuations due to natural radiation, the device cannot determine abnormal signs due to trace leakage as significant values. Another 16N
The amount of 16N and 15C produced in the reactor changes depending on the operating status of the reactor (reactor output, core flow rate, etc.), so a temporary increase in the dose rate may be an expansion of an abnormality or 16N or 15C.
It is not possible to determine whether this is due to a change in the amount of production.

[0008] As a countermeasure, if there is a change, the secondary system water is sampled and radioactivity measurement is carried out. For this reason, if there is a leak, it will take up to 3 days until the results are available.
There is a risk that a time delay of 0 to 60 minutes will occur, leading to an escalation of the accident. As described above, there are problems such as difficulty in determining abnormal symptoms due to trace leakage.

The present invention has been made to solve the above problems, and is a nuclear reactor that can quickly detect a small amount of leakage of primary coolant from a heat transfer tube in a steam generator in a pressurized water reactor. The purpose of the present invention is to provide an abnormality diagnosis device. [Structure of the invention]

0010

[Means for Solving the Problems] The present invention provides an exhaust gas monitor equipped with a radiation detector that detects radioactivity leaking into the secondary system of the primary coolant due to damage to the heat transfer tube in the steam generator of a pressurized water reactor. and 1 installed on the upstream side of the secondary main steam piping.
Radiation detectors targeting 6N and the signals detected by these radiation detectors are processed in time series to determine whether the processed signals are significant signals due to leakage, fluctuations in natural radiation, or noise in the measurement system. It is characterized by consisting of an arithmetic processing system.

[0011]

[Operation] The abnormality diagnosis device of the present invention uses a conventional exhaust gas system monitor installed in the exhaust gas bleed pipe of the exhaust gas system;
By comparing the output signals of the radiation detector installed in the secondary main steam piping and measuring 16N in time series,
When a change appears in the output of each radiation detector, it is possible to determine whether the change is due to background fluctuation, noise in the measurement system, or leakage. This is because both the radioactivity measured in the exhaust gas system (for example, 13N, rare gas) and the 16N measured in the secondary main steam piping are generated within the reactor core, and damage to the heat transfer tubes occurs within the steam generator. If this happens, both nuclides are likely to migrate to the secondary system at the same time. Therefore, if a change occurs in the radiation detector in the exhaust gas system due to a leak, a similar change will occur in the detector in the secondary main steam piping upstream within the time taken into account the arrival time of the steam. There should be. If the change is due to background fluctuations or noise in the measurement system, temporal correspondence will not be established even if only one radiation detector or both change.

[0012] In this way, a radiation detector measuring 16N was installed upstream of the secondary main steam piping, and the radiation dose fluctuations of the measurement system of this radiation detector and the radiation dose installed in the exhaust gas bleed piping were measured. If the variation in the radiation dose of the measurement system of the radiation detector appears in response to the time delay of steam between measurement points, it can be determined that the variation in the radiation dose is due to the same radioactive substance. Each measurement data is transferred in real time to a processing system consisting of a processing unit equipped with calculation functions, and the fluctuations in radiation dose are checked at a time that takes into account the arrival time at both the upstream and downstream detectors. If measured, it is determined that the variation in radiation dose is due to the passage of the same radioactive material, and the system quickly detects that the variation in radiation dose is due to a small leakage of the primary coolant and the time of its occurrence, and compares it with plant data. By doing so, it is possible to diagnose abnormalities in the reactor.

[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 7 and flows into a large number of heat transfer tubes 9 in the steam generator 8 . The secondary coolant in the steam generator 8 exchanges heat with the heat exchanger tubes 9 and is heated to become high-temperature, high-pressure steam, which flows through the secondary main steam piping 13 and flows into the turbine 14 . The turbine 14 rotates and drives the generator 15 to generate electricity. The steam that has completed its work in the turbine 14 flows into the condenser 12, where it is cooled and becomes condensed water. This condensate flows through the secondary system water supply pipe 16 and is supplied to the steam generator 8 as a secondary system coolant. On the other hand, the primary coolant flowing through the heat transfer tubes 9 in the steam generator 8 is cooled by exchanging heat with the secondary coolant, and is returned to the reactor vessel 3 from the primary main cooling pipe 11 by the pump 10 into the reactor core 4. is heated. In addition, in the figure, 5 indicates a control rod, and 6 indicates a pressurizer.

In the embodiment of the present invention, in addition to the turbine exhaust gas system monitor 18 provided at the downstream measurement point A of the exhaust gas system piping 17 that extracts some steam (gas) from the condenser 12, A first radiation detector 19 that targets 16N is installed at the upstream measurement point B of the secondary main steam pipe 13 of the steam generator 8. Note that a second radiation detector 21 is incorporated into the turbine exhaust gas system monitor 18. This first
The second radiation detectors 19 and 21 are connected to an arithmetic processing system 20 via measurement systems A and B, as shown in FIG.

FIG. 2 shows a block diagram of the measurement system and arithmetic processing system 20 in the present invention. In FIG. 2, a first radiation detector 19 is installed in the secondary main steam piping 13 as an upstream measurement point B, and a second radiation detector 21 is installed in the exhaust gas system piping 17 as a downstream measurement point A. is set up. The first and second radiation detectors 19 and 21 are connected to power supplies 22 and 23, respectively, to which a voltage is applied, and are also connected to measurement system A and measurement system B via signal cables 24 and 25. The measurement system A and the measurement system B are connected to the arithmetic processing system 20 and also to the first and second data output devices 26 and 27. The arithmetic processing system 20 receives data from a plant data output device 28 and is connected to a third data output device 29 .

FIG. 3 is a graph showing the relationship between dose and time at the upstream measurement point B, and FIG. 4 is a graph showing the relationship between the dose and time at the upstream measurement point A.
This shows a graph of . In the figure, A, B, and C indicate single signals, and D-D', E-E', and F-F' indicate the same signal.

As mentioned above, in this embodiment, the exhaust gas system piping 1
In order to detect the cause of fluctuations in the radiation dose rate of the turbine exhaust gas system monitor 18 installed in the exhaust gas system piping 1
A first radiation detector 19 for 16N is provided in the turbine exhaust gas system monitor 18 installed at 7 and in the secondary main steam pipe 13 on the upstream side thereof. The turbine exhaust gas system monitor 18 and the first radiation detector 19 are connected to the arithmetic processing system 20 by signal cables 24 and 25.

The first radiation detector 19 uses an ionization chamber type or NaI (Tl) scintillation detector or the like to continuously measure the dose rate or count rate in the same manner as the turbine exhaust gas system monitor 18. The measurement data is transferred in real time from measurement system B of the first radiation detector 19 and measurement system A of the turbine exhaust gas system monitor 18 to the processing system 20 via signal cables 24 and 25, and is measured by the first radiation detector 19. The variation in the radiation dose rate determined by the arrival time of the steam between measurement points (
After the steam delay time), the turbine exhaust gas system monitor 18 determines whether there has been a change in the radiation dose rate, and detects the presence or absence of leakage. If a leak is detected in the measurement system, plant data is imported from the plant data output device 28 and compared, thereby diagnosing an abnormality in the reactor.

In the above embodiment, an example was explained in which radiation detectors were installed at two locations, but the present invention is not limited to this, and an arbitrary number of radiation detectors may be installed in the secondary main steam pipe 13 and the exhaust gas system pipe 17. can.

[0020]

[Effects of the Invention] According to the present invention, even if a small amount of primary coolant leaks into the secondary coolant, it is possible to distinguish between fluctuations in the radiation dose due to the leakage and fluctuations in the background of natural radioactivity. In addition to being able to detect system coolant leaks early,
By processing measurement data as changes over time, it is possible to diagnose the occurrence and transition of abnormalities.

[Brief explanation of drawings]

FIG. 1 is a system diagram showing an embodiment of the present invention together with an outline of a pressurized water nuclear power plant.

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

FIG. 3 is a characteristic diagram showing the relationship between the dose at the upstream measurement point in FIG. 2 and the passage of time.

FIG. 4 is a characteristic diagram showing the relationship between the dose at the downstream measurement point in FIG. 2 and the passage of time.

[Explanation of symbols]

1... Reactor building, 2... Reactor containment vessel, 3... Reactor vessel, 4... Reactor core, 5... Control rod, 6... Pressurizer, 7... Primary system piping, 8... Steam generator, 9... Heat exchanger tube, 10...pump, 11...
Primary system main cooling piping, 12... Condenser, 13... Secondary system main steam piping, 14... Turbine, 15... Generator, 16... Secondary system water supply pipe, 17... Exhaust gas system piping, 18... Turbine exhaust gas system monitor , 19...first radiation detector, 20...computation processing system,
21... Second radiation detector, 22, 23... Power supply, 24,
25... Signal cable, 26, 27, 29... First to third data output devices, 28... Plant data output device.

Claims (1)

[Claims] 1. An exhaust gas monitor equipped with a radiation detector for detecting leakage radioactivity of a primary coolant into a secondary system due to damage to a heat transfer tube in a steam generator of a pressurized water reactor; A radiation detector targeting 16N is installed upstream of the steam pipe, and the signals detected by these radiation detectors are processed in time series to determine whether the processed signal is a significant signal due to leakage or fluctuations in natural radiation. 1. A nuclear reactor abnormality diagnosis device comprising: an arithmetic processing system that determines whether noise is caused by measurement system noise or measurement system noise.