JPS6122277B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a coolant leak detection device that can detect coolant leaks from a reactor vessel of a nuclear reactor and piping leading thereto with high responsiveness.

If a large amount of coolant leaks from the main piping of a nuclear reactor, it will lead to a serious accident. Therefore, it is necessary to detect coolant leakage early by some means and to take appropriate measures when leakage occurs.

By the way, in order to satisfy such a demand, for example, in light waterways, attempts have been made to generally monitor the change in humidity within the reactor containment vessel, or to monitor it by attaching an acoustic sensor to the piping.

However, although such leakage detection means are effective against large amounts of leakage, they are ineffective against extremely small amounts of leakage. In recent years, attempts have been made to detect the above-mentioned leaks by detecting the concentration value of gas floating in the reactor vessel and its rate of change, but there are problems such as poor S/N and lack of reliability. Ta.

The present invention was made in view of the above circumstances, and its purpose is to develop a nuclear reactor that can detect even a very small amount of coolant leak with good responsiveness and contribute to the prevention of accidents. An object of the present invention is to provide a device for detecting coolant leakage from a furnace vessel and piping communicating therewith.

In order to achieve the above object, the present invention focuses on the following points. In other words, when manufacturing fuel pins for a reactor core, even if strict controls are carried out, it is difficult to prevent fissile materials (uranium, plutonium, etc.) from adhering to the surface of the pins, albeit in very small amounts. be. When the fissile material attached to the surface of the fuel pin is irradiated with neutrons in the reactor, it generates fission products. Fission products include rare gases that do not chemically react with other substances,
In other words, it contains radioactive isotopes of Xe and Kr. These rare gases are mixed into the coolant and circulated together with the coolant. In a nuclear reactor, the above-mentioned rare gas exists only in the coolant circulation path. Therefore, if it is possible to detect whether or not the rare gas is leaking to the outside by some means, it should be possible to know whether or not the coolant is leaking. The present invention is based on this basic idea.

Hereinafter, details of the present invention will be explained with reference to illustrated embodiments. Note that the figure shows an example in which the present invention is applied to a light water reactor.

In FIG. 1, reference numeral 1 indicates a nuclear reactor, and this nuclear reactor 1 has a reactor vessel 3 housed within a containment vessel 2. As shown in FIG. A reactor core 4 is disposed inside the reactor vessel 3, and the heat generated by the reactor core 4 is cooled by water led through a pipe 5, and the steam generated by this cooling is led to the outside of the containment vessel 2 through a pipe 6. I have to.

A gas discharge pipe 7 and a gas return pipe 8 are provided in the wall of the containment vessel 2 to airtightly penetrate the wall, and these pipes 7 and 8 are connected to a leak detection device 11 according to the present invention. ing. This leak detection device 11
is structured as follows.

That is, a dehumidifier 12 for removing water vapor, a filter 13 for removing dust and mist, a flow meter 14, a fission product collector 15, and a pump 16 are connected in series between the gas exhaust pipe 7 and the gas return pipe 8. Connected. Note that as the dehumidifier 12 and the filter 13, those whose removal efficiency is known are used.

The fission product collector 15 is specifically constructed as shown in FIG. That is, the openings at both ends of the metal cylindrical body 17 are connected to the insulating members 18a, 18.
b, and a gas introduction pipe 19 and a gas discharge pipe 20 made of an insulating material are connected to both ends of the cylindrical body 17 in an airtight manner. Further, a core wire 2 is provided between the center portions of the insulating members 18a and 18b.
1, and connect this core wire 21 to the terminal 22,
Further, the cylindrical body 17 is connected to the terminal 23 and also connected to the terminal 25 via a resistor 24. A DC voltage is applied between the terminals 22 and 25 from a power supply device 26 in a relationship to be described later.

In the vicinity of the dehumidifier 12 and filter 13, there is a radiation detector 27 for detecting radiation in the gas flow flowing through the dehumidifier 12 and filter 13.
28 are provided. The outputs of these radiation detectors 27 and 28, the output of a pressure gauge 29 for detecting the pressure in the gas passage, and the output of the flowmeter 14 are introduced into an interfering radiation concentration measuring device 30. This interfering radiation concentration measuring device 30 calculates the radiation concentration per unit flow rate and unit pressure of the gas flow passing through the filter 13 from each output and the removal efficiency of the dehumidifier 12 and filter 13 that is known in advance. It is configured as follows.

On the other hand, a fission product concentration measuring device 31 is provided which controls the fission product collector 15 and determines the radiation concentration within the fission product collector 15. This fission product concentration measuring device controls the power supply device 26 to control the fission product collector 15.
A DC voltage V ₁ is applied between the terminals 22 and 25 of the terminal 22 for a predetermined period, and then the terminal 2
2 and 25, terminal 22 is positive and the V ₁
A larger DC voltage V ₂ is applied to cause discharge between the core wire 21 and the circular body 17. Then, the number of discharges is detected from the voltage drop between the terminals 23 and 25, and the number of discharges is converted into the number of discharges at a unit flow rate and unit pressure based on the outputs of the pressure gauge 29 and the flow meter 14, and the number of discharges is converted into the number of discharges at a unit flow rate and unit pressure. unit flow rate of gas flowing through the fission product collector 15 from
The radiation concentration value per unit pressure is calculated. This operation is repeated.

However, the fission product concentration measuring device 31
and the output of the interfering radiation concentration measuring device 30 are input to the notification device 32. Notification device 32
is configured to subtract the output of the interfering radiation concentration measuring device 30 from the output of the fission product concentration measuring device 31, and to perform a notification operation when this subtracted value exceeds a predetermined value.

Next, the operation of the apparatus configured as described above will be explained.

While the nuclear reactor 1 is in operation, if corrosion holes or cracks occur in the reactor vessel 3 or the pipes 5 and 6 leading thereto, water as a coolant will be released to the outside regardless of the scale. As mentioned above, the leaked coolant contains fission products produced when the fissile material attached to the surface of the fuel pins that make up the reactor core 4 is irradiated with neutrons in the reactor, i.e. radioactive isotopes of Xe and Kr. It is included. When these rare gases leak, they leak together with the coolant, but once they leak, there is no phase change like water, and the containment vessel 2
disperse within. On the other hand, the gas in the containment vessel 2 has
It contains large amounts of radioactive isotopes such as iron, manganese, cobalt, and iodine that are generated during the steady operation of the nuclear reactor 1, and these are also dispersed within the containment vessel 2.

When the pump 16 is operated, the gas in the containment vessel 2 is discharged from the gas discharge pipe 7 to the dehumidifier 12 to the filter 13 to the flow meter 14 to the fission product collector 1.
5 to the pump 16 to the gas return pipe 8. If the gas contains water vapor, dust, mist, etc., these are removed by a dehumidifier 12 and a filter 13. At this time, the radioactive isotopes such as iron, manganese, and cobalt adhere to moisture in the gas, and most of them are removed by the dehumidifier 12. Furthermore, most of radioactive isotopes such as iodine are removed by the filter 13.
However, these are not normally removed 100%, and only the amount determined by the removal efficiency of the dehumidifier 12 and filter 13 is removed. Here, fission products consisting of Xe and Kr resulting from coolant leakage are not normally removed by the dehumidifier 12 or filter 13. Therefore, the filter 13
Further downstream, gas containing radioactive isotopes such as iron, manganese, cobalt, and iodine that could not be removed by the dehumidifier 12 and filter 13, or the radioactive isotopes and fission products that appeared due to coolant leakage. Gas containing will flow.

However, now, the fission product concentration measuring device 31 is activated, and a DC voltage is applied between the terminals 22 and 25 of the fission product collector 15 at which the terminal 22 becomes negative.
V ₁ is applied, and the gas flowing through the fission product collector 15, that is, the cylindrical body 17, contains radioactive isotopes of fission products Xe and Kr; These Xe and Kr are the core wire 2
It adheres to the surface of 1. That is, when a rare gas undergoes β decay and becomes an alkali metal, it becomes positively charged. Therefore, it will be electrostatically attached to the surface of the negative voltage core wire 21. In this way, the fission products Xe and Kr are added to the gas extracted from the containment vessel 2.
, these Xe and Kr are collected on the surface of the core wire 21.

Then, after a predetermined period of time has elapsed, the fission product concentration measuring device 31 controls the power supply device 26 to
DC high voltage with terminal 22 positive between 2 and 25
Apply _V2 . As a result, the core wire 21 and the cylindrical body 1
7, a discharge occurs between the two. This discharge is caused by the core wire 2
This is an ionization effect caused by β rays emitted by fission products attached to the surface of 1. The ionizing current is usually
It depends on the amount of fission products attached. Furthermore, the above-mentioned discharge is performed in a pulsed manner due to the presence of the resistor 24, and the number of discharges per unit time depends on the amount of deposit. Then, the fission product concentration measuring device 31 determines the discharge circuit per unit time from the voltage drop across the resistor 24, and further converts the number of times into a radiation concentration value per unit flow rate and unit pressure. Then, a signal corresponding to this concentration level is output.

However, even if an attempt is made to measure the concentration of fission products with the fission product concentration measurement device 31 as described above, in reality, the dehumidifier 12 and filter 13 have a predetermined removal efficiency, A small amount of other radioisotopes also flows into the material collector 15, and the ionization current is affected by the influence of these radioisotopes. Therefore, the fission product concentration measuring device 31 detects the radiation concentration of the fission products and other components. In extreme cases, the amount of components other than fission products may exceed the amount of fission products. For this reason, the components of the fission products that are the object of measurement may be buried in other components. Therefore, it is necessary to selectively extract only the radioactive components of the fission products by some means, and for this purpose, the present device does the following.

That is, the radiation detectors 27 and 28 provided near the dehumidifier 12 and the filter 13 detect the radiation of radioactive isotopes of iron, manganese, cobalt, and iodine removed by the dehumidifier 12 and the filter 13, and the removed radiation. The radioactive isotope radiation that is not detected is detected, as is the fission product radiation that passes through the dehumidifier 12 and filter 13 as it is. In this case, the fission products are generated from the minute amount of fissile material adhering to the surface of the fuel pin, so the amount is compared to the amount of radioactive isotopes such as iron, manganese, cobalt, and iodine. Much less. Therefore, the radiation detector 27,
The detected value of 28 can be regarded as the detected value of substances other than fission products, that is, radioactive isotopes such as iron, manganese, cobalt, and iodine. The outputs of the radiation detectors 27 and 28 are input to a disturbing radiation concentration measuring device 30. This interference radiation concentration measurement device 30 introduces the outputs of the radiation detectors 27 and 28, the pressure gauge 29, and the flowmeter 14, and combines these outputs with the previously known removal efficiency of the dehumidifier 12 and filter 13. is used to calculate the radiation concentration value per unit flow rate and unit pressure of the gas after passing through the filter 13, and output a signal corresponding to this radiation concentration value. As mentioned above, the detection values of the radiation detectors 27 and 28 are the detection values of radioactive isotopes other than nuclear fission products, such as iron, manganese, cobalt, and iodine. Therefore, the radiation concentration value calculated by the interfering radiation concentration measuring device 30 is the radiation concentration value of radioactive isotopes other than fission products in the gas after passing through the filter 13. The output of the interfering radiation concentration measuring device 30 and the output of the fission product concentration measuring device 31 are input to the notification device 32. The notification device 32 subtracts the output signal of the device 30 from the output signal of the device 31, and performs a notification operation when this value is greater than a predetermined value. The reason for determining the difference between the output signals of both devices 31 and 30 in this way is that when determining the concentration of fission products due to discharge, the fission products remaining in the gas flowing in the fission product collector 15 are This is to remove the effects of other radionuclides. This cancels out the concentration of components other than fission products in the radiation concentration detected by the device 31. The notification device 32 performs a notification operation when the radiation concentration value of the fission product is above a predetermined value. Therefore,
By operating the notification device 32, it is possible to immediately know whether or not coolant is leaking from the furnace vessel 3 or the pipe 6 leading thereto.

In this way, whether or not coolant leakage has occurred is detected depending on whether radioactive isotopes such as Xe and Kr, which are nuclear fission products, are present in the containment vessel 2. Since nuclear fission products diffuse rapidly into the containment vessel 2 after a leak, the time required from the leak to the detection can be shortened, which is preferable from the standpoint of accident prevention. In addition, since it skillfully utilizes a phenomenon unique to nuclear fission products, it is possible to detect even the slightest leakage, making early detection possible. Also,
Unlike conventional methods that simply detect the radiation concentration of the gas inside the container 2, iron, manganese, and
Since it is not affected by radiation from radioactive isotopes such as cobalt and iodine, the radiation concentration of fission products is not buried by these disturbing and noise radiation concentrations, and therefore S/
N can be detected with high reliability. Therefore,
Even if the leakage of the coolant mentioned above is small, it can be detected reliably, greatly contributing to the safe operation of the nuclear reactor.

In the embodiments described above, fission products are detected using an ionization chamber method, but the method is not limited to this detection means, and detection may be performed based on the radioactivity of attached fission products. Moreover, the present invention is of course applicable not only to light waterways but also to liquid metal coolant furnaces.

As described in detail above, according to the present invention, coolant leakage can be detected early and with good response, and leakage from the reactor vessel and piping connected thereto can contribute to safe operation of the reactor. A coolant leak detection device can be provided.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of the present invention, and FIG. 2 is a longitudinal sectional view of a fission product collector in the same embodiment. 1... Nuclear reactor, 2... Containment vessel, 3... Reactor vessel, 4...
Reactor core, 12...Dehumidifier, 13...Filter, 15...Fission product collector, 30...Interference radiation concentration measuring device, 31...Fission product concentration measuring device, 32...Notification device.

Claims (1)

[Claims] 1. A gas passage provided with both ends communicating in the reactor containment vessel, a dehumidifier and a filter inserted in series in this gas passage, and a dehumidifier and a filter installed in the gas passage and floating in the reactor containment vessel. a pump that circulates the gas flowing through the dehumidifier and the filter in this order; a radiation detector that detects radiation in the gas flow flowing through the gas passage at a position where the dehumidifier and the filter are provided; and the gas passage. A flow meter and a pressure gauge detect the gas flow rate and gas pressure in the air, and the output of the radiation detector, flow meter, and pressure gauge and the removal performance of the dehumidifier and filter are used to detect the gas flow through the filter. an interfering radiation concentration measuring device for determining a radiation concentration value per unit flow rate and unit pressure; a fission product collector inserted in series at a position downstream of the filter in the gas passage; and the fission product collector. A collection operation is performed at fixed time intervals, and radiation inside the fission product collector is detected from the time the collection operation ends until the next collection operation is performed, and this detected value and a fission product concentration measuring device that calculates a radiation concentration value per unit flow rate and unit pressure of gas flowing through the fission product collector from the outputs of the flowmeter and the pressure gauge; and the fission product concentration. and a notification device that performs a coolant leak notification operation when a value obtained by subtracting the radiation concentration value determined by the interfering radiation concentration measuring device from the radiation concentration value determined by the measuring device is equal to or higher than a predetermined value. A system for detecting coolant leakage from the reactor vessel of a nuclear reactor and the piping connected to it.