JPS582798A - Method of decontaminating equipment contaminated with radioactive material - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is applicable to atomic couplants, secondary equipment, piping, etc., which have a surface containing a radioactive substance such as "kh" or "Co."

equipment that is contaminated with radionuclides such as Co, Cr, and iFe.

Fast breeder reactor power plant2. During operation, the fuel cladding and tube core structural materials are irradiated with neutrons, producing large amounts of radioactive substances such as long-half-life radionuclides such as CG, Ic0, and 14Mn. , elutes into the coolant due to corroded core structural materials and fuel cladding materials.

These radioactive substances eluted into the coolant flow together with the coolant in the primary cooling system and deposit on the surfaces of the equipment and pipes of the primary cooling system. These radioactive l1lllll
can cause radiation exposure to workers performing maintenance, inspection, and repair of nuclear reactors.

For example, in the case of a demonstration-scale large-dust fast breeder reactor, it is expected that the radiation intensity near the pipes in the main equipment will reach about 10 V notogen/hour two to three years after the start of operation.

Therefore, during repairs, it is necessary to remove radionuclides from such aircraft IIIm. Also, some l! Even when the 9-SS is disposed of as I11 Qin because it becomes unnecessary due to new construction, it is important to decontaminate it and reduce the amount of attached radiation.

In general, methods for decontaminating radioactive substances attached to Class S machines include (1) rubbing the surface with a pusher, (2)
Examples include ultrasonic cleaning and (3) chemical decontamination.

Considering the decontamination of the primary system equipment of fast breeder reactors used in high-temperature metallic sodium coolant of 500℃ or higher,
Radioactive substances attached to the surface of equipment materials are not only attached to equipment materials, but also penetrate into the grain boundaries of the materials.In decontamination by steam cleaning or alcohol cleaning, largely! #! I can't help it. Similarly, methods such as scrubbing with a brush and ultrasonic cleaning are used in most cases.
Acid cleaning methods using chlorine/acid, citric acid, etc. have been studied.

However, regarding these chemical removals,
II141I #lI is strongly corroded, making it impossible to reuse the bridge*si, and there are also problems such as processing large amounts of tumor fluid.
Accompanied by JI.

The metal used as a coolant in the primary cooling system of the rapid growth reactor reacts with chemical cleaning in water, so these nine decontamination VCTos are sufficient to clean the metal and thorium. Decontamination work cannot begin until after this has been carried out.

For this reason, system decontamination that decontaminates part or the whole of the reactor, as currently being developed in the light water reactor power generation plan, is not possible using the above chemical cleaning method. .

In this invention, the radioactive substances attached to the cooling system of the fast breeder reactor, such as 'MO, 'Co, 'Co,
“Cr.

Decontamination of radioactive nuclides such as 69F@9 can be performed remotely, and the equipment materials are decontaminated without the corrosion rate that occurs when cleaning with acid.It is also possible to reuse the equipment, making it more effective and requiring less manpower. Our objective is to provide a method that can easily decontaminate radioactive substances without applying any heat.

Honji @Hiro: A tank for storing the striped material is installed in the highest temperature part of the gold-sodium circulation system, and a decontamination machine is inserted into ζζ to circulate metallic sodium. Then, the length of the covered body is 1m! Since the radioactive substances adhering to the surface are gradually released from the metal sodium, we will use a method that can remove the husk by precipitating and removing them at a low temperature of the metal sodium.

　　　：・ A negative example of the present invention will be described in detail below.

11111i111 shows an embodiment of the present invention. In the figure, it is a container made of 1-wire stainless steel, etc.] The upper part is written as 7 Tsunji 2! @ structure. A table 3 on which objects to be decontaminated are placed is provided at the bottom of this container. An object 4 to be decontaminated is placed on one of the machines 10. This is 7Tsunji 2) It is put in and taken out. The capacity is at the top, and the pipe S is used to exchange the hook.
After passing I6, go to Pipe BK again υto 2 tubes IFII 7km
! @ is being done. This trap container 7 is a container similar to that of a station/resistance, etc., and is filled with metal metal rings, etc. It is designed to send a filter to cool the trap volume 1B7. This trap capacity @7 is filled with a pop-up 10 by pipe 5. Heat exchanger 6
．． The heater 9 is connected again to the container 1 to form a metal sodium oli's device.

9, tank 1 is connected to pipe IIK through pulp 10]
It is connected to the drainer/receptor 12. 13.15 is the metal sodium 9.l) When the apparatus is stopped, the metal sodium 13 in the circulation system is drained into the "drain" tank 12.

14.16 is the cover gas for each tank, which is filled with h>argon gas.

Insert the equipment to be decontaminated from the flage 2 into the tank 1, and then 7 lunges 2. ? *Close and 1111! After evacuating the existing gas through a cover gas supply/exhaust system (not shown), the pulp 10 t II is filled with sodium 15 in the drain tanker into the uniform circulation device.

Thereafter, the pump 10 is activated to pump sodium metal through the circulation system at a predetermined flow rate.

After that, 7 Ann 8. Apply electricity at 119tl1 and set the temperature conditions of the metal sodium circulation system. The higher the temperature inside Menta 1, the faster it can be removed.
The temperature of the part 1 of the trap 7 is increased to 400 t) by @OOυ or more. Maintain the ζO state for a certain period of time.

In this case, round metallic sodium heated to a high temperature by the heating SS flows from the lower part of the tank 1. This metal powder flows upward while contacting the surface of the object 40 to be decontaminated, dissolving the composition of the surface of the equipment material. At the same time, the liK emits 411 radionuclides attached to the surface. These ejected radioactive substances are sent from the upper part through a pipe 5 to a trap 7 while being cooled by a heat exchanger 6. It is then cooled down again.

OSS such as Fe, Cr, Mn, Co, etc. in sodium
The temperature is smaller at low temperatures than at high temperatures. These metal elements eluted in this container 1 are deposited on mesh crystals in the trap. At this time, radioactive substances are also precipitated and removed. Metal impurities and radioactive substances are precipitated, and the reduced amount of metallic sodium is pumped to pump 1G and heat exchanger I.
After passing through S6, the temperature is raised in heating 1I19 and returned to the tank IK again.

As the above waste is returned, the radioactive substances on the surface of the object to be decontaminated are gradually removed and collected in the trap 7KII.

After a certain period of time has elapsed, open the tank 10 and store all the metal sodium 13 in the drain tank 12, then cool the tank 1 to room temperature and close the flange 2 to remove the object to be decontaminated. Take out.

The magnitude of the decontamination effect by the method of the present invention is as follows: 1. The temperature of the trap 7 [conditions] depends on the oxygen impurity concentration in the metal sodium and the decontamination time, but to give an example, the temperature of the tank 1 is 600°C, the trap part 7 is 400°C, and the S in the metal sodium is ! When the elemental concentration was 10 ppm, decontamination for 240 hours resulted in 85% of Mn and 5ac.
80% for O, IOC, 9 for LLC
0%, and 89% decontamination was achieved regarding Fe.

This decontamination tends to be completed in a shorter time as the IJ rim temperature is higher.

The present invention is similar to the conventional Kl! Decontamination can be easily and efficiently carried out without using any cleaning solution such as by simply immersing it in metallic sodium, the same coolant used in fast breeder reactors.

This not only allows for easy decontamination without requiring much manpower, but also prevents equipment from being corroded and rolled up, which is extremely advantageous in reusing the equipment after maintenance.

Furthermore, since the method of the present invention can be performed with extremely simple operation, it is suitable for remote control and can greatly contribute to reducing the radiation exposure of workers.

The present invention is effective not only for decontaminating high-speed secondary equipment, but also for decontaminating radioactively contaminated equipment in light water reactors and reprocessing facilities.

l... Evening.

4...9 equipment contaminated with radioactive materials (objects to be decontaminated).

6... Heat exchanger.

7... Trap container.

9... Heater.

1st I1 5

Claims (1)

[Claims] This circulation is created by creating a temperature difference while circulating metallic sodium! A device whose surface is contaminated with a radioactive substance is placed in the high-temperature metal sodium in the circulation path and brought into contact with the metal sodium, and the radioactive substance is eluted into the metal sodium. A method of decontaminating equipment contaminated with radiation and Ik substances, which involves depositing radioactive substances in low-temperature areas.