JPH0124252B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a system for detecting the location of damaged nuclear fuel in a fast breeder reactor by detecting a tag gas sealed in a nuclear fuel rod. The present invention relates to a concentrator for a detection system.

Generally, in a fast breeder reactor, if the cladding of the nuclear fuel loaded in the reactor core is ruptured, the temperature distribution of the reactor core will change, resulting in a dangerous situation. Therefore, when operating a nuclear reactor, it is necessary to constantly monitor whether or not the nuclear fuel is damaged by some means, and if damage occurs, the location of the damage must be promptly detected and appropriate measures such as removing the nuclear fuel must be taken. It is necessary to take measures.

By the way, as a means of detecting damage to nuclear fuel in a nuclear reactor, basically, when a nuclear fuel rod is damaged, fission products leak from the damaged area, and this leaks into the coolant or the cover gas (cover gas) that covers the coolant. The main component of is argon gas, so it will be referred to as argon gas hereafter).
There are means to check whether gaseous fission products are mixed in argon gas, and these devices are called FFD (Failed Fuel Detection).

Next, as a means of detecting the location of damaged fuel,
A tag gas (generally a different combination of isotopes such as Xe (xenon) for each fuel) that is not produced as a fission product is sealed in the nuclear fuel rod in advance. Therefore, when a fuel rod breaks, these tag gases leak out and mix with the argon gas. There is a method of detecting the location of damaged fuel by detecting tag gas in argon gas.
This collection of detection devices is called FFDL (Failed Fuel).
Detection and Location).

By the way, the FFD and FFDL are installed as shown in FIG. In other words, the argon gas covering the upper space 2 of the reactor 1 is transmitted through the pipes 3, 12,
It passes through 13 and 14 and is sucked into the circulation pump 7, and returns to the upper space 2 of the reactor 1 via piping 15.
This system is called a primary argon gas system. An FFD 4 is installed in parallel with the pipe 12 by pipes 16 and 17 branching from the pipe 3 of this system. FFDL40
is installed in parallel with the FFD, with a pipe 18 branching from the pipe 16, a compressor 11, a concentrator 5 connected to the compressor 11, an analyzer 6 connected to the concentrator 5, and a pipe 18 connected to the analyzer 6. The pipes 19 are connected to each other in order.
FFD4 is constantly operated and monitors for fuel damage. The concentrator 5 has a function of concentrating the cover gas to the point where the tag gas can be analyzed.
FFDL40 is designed to start immediately after fuel damage is detected by FFD4, so it is not always in operation.

An example of the conventional concentrating device 5 is a device that cools activated carbon to an extremely low temperature (about -180° C.) and uses it (this is called a cryogenic method). However, even when the FFDL40 is not operating, the activated carbon must be constantly cooled to an extremely low temperature. In addition, when adsorbing argon gas led from reactor 1 through piping to an adsorption bed using the cryogenic method, if the temperature of the argon gas is high, a large amount of refrigerant (generally liquid nitrogen) is used to cool the adsorption bed. , it is necessary to control the temperature. For this reason, a low temperature heat exchanger is provided at the inlet of the adsorption bed to lower the temperature of the argon gas flowing into the adsorption bed. However, during adsorption operation, the amount of heat that cannot be reduced by the low-temperature heat exchanger is absorbed by supplying liquid nitrogen and adjusting it with the heater. Furthermore, liquid nitrogen requires a rectifier because the air in the room is used to produce liquid air, which is rectified for use. Furthermore, a liquid nitrogen tank is required between the rectifier and the adsorption bed in order to constantly and stably supply a refrigerant. In this way, a rectifier for liquid nitrogen, which is a refrigerant, and a liquid nitrogen tank for storage are required, and a low-temperature heat exchanger is also required to reduce the amount of liquid nitrogen used during adsorption operation. required. Furthermore, since argon gas cannot be cooled to extremely low temperatures, temperature control of the adsorption bed is required even during adsorption operation.

Another example of the conventional concentration device 5 is a device that is always on standby at room temperature and causes activated carbon to adsorb tag gas at room temperature (this is called a room temperature method). However, due to the temperature dependence of the adsorption capacity of activated carbon (as shown in Figure 3, the adsorption capacity is extremely small at high temperatures), the adsorption amount is extremely small at room temperature, so a very large amount of activated carbon is required, and the concentration is also low. Since the concentration does not increase, multiple concentrators are required.

The present invention has been made in view of the above, and is simplified by providing a low temperature generator upstream of the adsorption bed of the concentrator, which has two functions: cooling the adsorption bed and cooling the argon gas containing the tag gas. An object of the present invention is to obtain a concentrator for a damaged fuel position detection system that is a simple facility and easy to operate and control.

An embodiment of the present invention will be described below with reference to the drawings.

As mentioned above, the FFDL is composed of the compressor 11, the concentrator 5, the analyzer 6, and the pipes 18 and 19. FIG. 2 shows an embodiment of a concentrator according to the invention. While the FFDL is on standby, fresh argon gas (argon gas from an argon gas cylinder, etc., not from the reactor) flows into the low temperature generator 20 (a general term for refrigerators that produce liquid air, nitrogen, etc.) from the inlet valve 21. The liquid is liquefied, passes through a valve 22 attached to a pipe 33 having a heat insulating structure 34, and is sprayed by a sprayer 24 attached to an adsorption tower 23 to cool an adsorption bed 25. Temperature control at this time includes on-off control of the sprayer 24 and control of the heater 26.
This is done by on-off control. Further, a stirrer 27 is attached to cool the adsorption bed 25 uniformly and efficiently. Fresh argon gas sprayed from the sprayer 24 cools the adsorption bed 25 and is then discharged to an exhaust gas system (not shown) through an outlet pipe 28 on the upper side of the adsorption tower 23.

Furthermore, if liquid argon gas accumulates at the bottom of the adsorption tower 23, the temperature of the adsorption tower 23 is raised to increase the temperature of the adsorption tower 23.
3 is discharged from the outlet pipe 28 on the bottom side.

In addition, in order to efficiently cool and heat the adsorption bed 25 and maintain its temperature, the adsorption tower 23 has a heat insulation structure 29.
has.

When fuel damage is detected by FFD, the inlet valves 21 and 22, which were in the open state, are closed, and the inlet valve 30, which was in the closed state, is opened. The argon gas containing the tag gas flows into the low temperature generator 20 through the inlet valve 30 by the compressor 11, is cooled, enters the adsorption bed 25 through the inlet pipe 31 having a heat insulating structure 35, and flows out through the outlet pipe 32. Argon gas cooled by the low temperature generator 20 is transferred to the adsorption bed 2.
Adsorption bed 25 with fresh argon gas flowing into the adsorption bed 25
There is no need to cool it down. Activated carbon 38 is filled inside the adsorption bed 25 .

The operation of the FFDL equipped with the concentrator of the present invention in the above configuration will be explained below. When no fuel damage occurs, the concentrator of the present invention is on standby with the adsorption bed 25 cooled to about -180°C.
This cooling is maintained by operating the low-temperature generator 20 for liquefying fresh argon gas, and spraying the generated liquid argon gas into the adsorption tower 23 with the atomizer 24.
The adsorption bed 25 is uniformly and efficiently cooled by stirring with the stirrer 27, and the temperature is controlled by the heater 26.

Further, cooling and temperature maintenance can be performed very efficiently by the heat insulation structure 29.

Therefore, by closing the inlet valves 21 and 22 and opening the inlet valve 30 at the same time that fuel damage is detected by the FFD, the argon gas in the reactor containing the tag gas is sent to the low temperature generator 20. Here, the argon gas is cooled to a temperature (approximately -180°C) at which it has a large adsorption capacity (see Figure 3), and is
1, it flows into the adsorption bed 25, which has already been cooled to about -180°C, and is adsorbed by the activated carbon 38.

Furthermore, -180 during FFDL operation (adsorption operation)
The primary argon gas cooled to about 0.degree. C. continuously flows into the adsorption bed 25, and since the adsorption tower 23 is sufficiently insulated by the heat insulation structure 29, temperature control of the adsorption bed 25 is almost unnecessary.

Next, the remaining argon gas with the tag gas adsorbed by the activated carbon 38 is discharged from the outlet pipe 32 to the analyzer 6. By continuously performing this flow of inflow, adsorption, and discharge, the tag gas is
8 will be adsorbed and retained and concentrated. Naturally, all of the tag gas flowing into the adsorption bed 25 during this operation is adsorbed by the activated carbon 38. When the adsorption operation is completed, the argon gas adsorption bed 2
5 is stopped and the adsorption bed 2 is heated by the heater 26.
5, the tag gas concentrated by the activated carbon 38 is desorbed. By sending this to the analyzer 6 and analyzing it, the position of the damaged fuel can be detected.

The concentrator of the present invention cools the adsorption bed and the primary argon gas with valves 21 and 2 before the activated carbon adsorption tower.
By installing a low temperature generator that can be switched by 2 and 30, the following effects can be obtained when compared with the conventional device. Since the refrigerant for cooling the adsorption bed can be supplied by a low-temperature generator, a rectifier, liquid nitrogen tank, etc. are unnecessary, and the equipment can be simplified. Furthermore, the operational control of the low-temperature generator for refrigerant production is simplified because a rectifier is not required. Further, since the argon gas is also cooled by the low temperature generator 20, a low temperature heat exchanger is not required, and the equipment can be simplified. Further, since the argon gas is cooled to an extremely low temperature and flows into the adsorption bed, it is not necessary to control the temperature of the adsorption bed 25 during adsorption operation, and operation control is easy.

Furthermore, the adsorption bed 25 is completely cooled when FFDL is started, and the argon gas cooled by the cooler 20 to a state where the adsorption capacity is large flows into it, so that the tag gas can be completely adsorbed and retained (concentrated).

Therefore, the accuracy of detecting the position of damaged fuel is improved, and the safety of nuclear reactor operation can be improved.

[Brief explanation of drawings]

Figure 1 is a system configuration diagram of the primary argon gas system, FFD and FFDL in a nuclear reactor, Figure 2 is a configuration diagram of an embodiment of the present invention, and Figure 3 is a diagram of adsorption characteristics of xenon on activated carbon. It is. 5... Concentrator, 6... Analyzer, 20... Low temperature generator, 25... Adsorption bed, 27... Stirrer.

Claims (1)

[Claims] 1. In the concentrator of the nuclear reactor's damaged fuel position detection system, there is a pipe that leads fresh gas to the low-temperature generator, an inlet valve for this pipe to the low-temperature generator, and a cover gas inside the reactor that leads to the low-temperature generator. piping and an inlet valve of the piping to the cryogenic generator, and the cryogenic generator cooling fresh gas and cover gas;
A piping with an adiabatic structure that guides fresh gas cooled from the low-temperature generator to the atomizer in the adsorption tower and a valve attached to this piping, and a piping with an adiabatic structure that guides the cover gas cooled by the low-temperature generator to the adsorption bed. , a heater for controlling the temperature of the adsorption bed, an agitator for stirring fresh gas in the adsorption tower, an adsorption tower with an adiabatic structure containing the atomizer and the adsorption bed, the heater and the agitator, and A concentrator for a damaged fuel position detection system, comprising a pipe that leads cover gas to a detector and a pipe that discharges fresh gas from an adsorption tower.