JPH0658435B2 - How to clean the piping - Google Patents

Description

Description: TECHNICAL FIELD OF THE INVENTION The present invention relates to a method for cleaning piping used in a nuclear power plant, a nuclear fuel reprocessing plant or the like, through which a radioactive fluid flows.

[Technical background of the invention and its problems]

Since radioactive fluids are handled in nuclear power plants and nuclear fuel reprocessing plants, radioactive materials adhere to the pipes used in these facilities, resulting in high doses. Therefore, the piping is regularly cleaned to remove radioactivity.

Various methods have been attempted as cleaning methods for these pipes, and they are roughly classified into a chemical decontamination method and a mechanical decontamination method. The chemical decontamination method is a method of decontaminating a radioactive substance by using a chemical agent, and the mechanical decontamination method is an ultrasonic wave,
Method using brush, pig, etc., air bubble mixed flow cleaning,
Jet cleaning, sand blast cleaning, etc.

Now, the forms of radioactive substances attached to pipes are as follows.

When entering the composition of the corrosion resistant oxide film (stainless steel pipe, carbon steel pipe) on the surface of the pipe and integrating with the film. In this case, the radioactive substance is present only in the thickness of the film, and the amount of the substance is small.

When radioactive material particles are stuck in the valley of the rough surface of the pipe.

When scale or adhesion (due to electrostatic attractive Van der Waals force, adhesive force) is applied to the surface of the pipe.

 If the pipe is stuck in the rust tank.

 If it has accumulated at the bottom of the pipe.

 When it has entered the gap of the pipe.

The chemical decontamination method is effective in the above cases 1 and 2, but in other cases, it is not suitable because the amount of waste increases or remains undissolved. On the other hand, the mechanical decontamination method is effective when radioactive substances are deposited and adhered, or when it enters the rust layer, but it removes the substances taken in the oxide film. Can not. Also, those that adhered to oil stains or hard scales, those that entered valleys or gaps on rough surfaces, or those that easily re-attached did not succeed only by mechanical decontamination method, and were used in combination with chemical decontamination agents. In many cases, it is more successful.

In addition, mechanical decontamination methods generally spread radioactive contamination, and they are disadvantageous in that they are large in size, are easily exposed to radiation because they are difficult to operate remotely, and are subject to restrictions on the piping structure, etc. There are many points. For these reasons, the mechanical decontamination method is not generalized, and it is desired to combine the advantages of both with the chemical decontamination method.

Among the mechanical decontamination methods, the waterflushing method is easy to use together with the chemical decontamination method. The water-flushing method is a method in which water and air are well stirred by a mixer and flowed in a pipe as a gas-liquid multiphase flow. Due to the turbulent effect, sediment and soft deposits (sludge, slime and soft (Scale) is to be removed. If a chemical solution is used as the solution, the advantages of the chemical decontamination method can be incorporated.

[Object of the Invention]

An object of the present invention is to improve a conventional water flushing method in a method for cleaning a pipe through which a radioactive fluid flows so that the pipe can be cleaned more effectively.

[Outline of Invention]

A detailed examination of the conventional water flushing method for cleaning the pipe shows that even if air and water are mixed in advance and fed into the pipe, the air bubbles are separated after several meters and the flow velocity is insufficient. It was found that air bubbles accumulated upwards and flowed as it was. That is, the gas-liquid multiphase flow does not flow stably. Upon further testing, the effect of raising sludge and slime is large when the boundary surface between the gas phase and the water phase passes, and larger bubbles are generated in the pipe diameter than the flow containing fine bubbles. It was also found that the flow like this is more effective. In other words, when the liquid plug passes after the air column, the liquid plug directly collides with the deposit in the pipe, and by repeating the collision intermittently,
The effect of peeling off adhered substances is great. Further, when the mixed state of the gas-liquid mixed phase was investigated in more detail, it was found that the plug flow and the slag flow were more effective in the case of the horizontal pipe, and the slag flow and the floss flow were better in the case of the vertical pipe. In the gas and liquid plug flow, slug flow, and floss flow, when the holdup amount of gas is large, the pressure loss is small, so the flow velocity of the water plug can be increased, and the sludge carrying capacity is increased. The advantages of being able to do this have also been found.

Judging from the results of these investigations, it is not necessary to previously stir and mix gas and liquid before pipe feeding as in the past, but rather gas and liquid are alternately fed into the pipe at high pressure and high speed at arbitrary intervals. It has been found that the inclusion is more effective in various respects.

That is, the present invention relates to a method for cleaning a pipe for radioactive fluid, characterized in that a cleaning chemical liquid and air are alternately press-fitted into a pipe column at arbitrary intervals so that a liquid plug and an air column pass alternately. .

In the above, the interval between the cleaning chemical liquid and the air is set such that the length of the water plug is at least 10 times the pipe diameter and the length of the air column is 10 pipe diameters.
It is effective to make it more than double.

The cleaning liquid may be water, or any of those conventionally used as a cleaning liquid, such as sulfuric acid, oxalic acid, citric acid, and sulfamic acid, as long as the cleaning effect is expected. However, foaming materials are not preferable.

Example of Invention

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

FIG. 1 is a flow sheet showing an example of the cleaning method of the present invention. The chemical liquid tank 1 and the compressed air tank 2 are separately prepared, and the chemical liquid is fed into the pipe 5 to be cleaned by the liquid feed pump 3 through the check valve 4 at a constant flow rate. When the chemical liquid flows through the pipe 5 at a constant flow rate, the scale and sludges are dissolved, softened, and dispersed to some extent. Here, high pressure compressed air is pressed into the pipe to form a water plug and a fairly long air column. The air volume and the air feeding time are controlled by a valve, while the chemical liquid is automatically stopped by the check valve when this air flow flows.

Next, the experimental results comparing the liquid plug cleaning according to the present invention and the conventional cleaning method will be described with reference to FIG. The conventional cleaning methods that have been tested are liquid flow cleaning in which only liquid is vibrated and liquid cleaning is performed in a gas-liquid mixed phase. The experiment was performed by depositing magnetite powder and hematite powder inside the pipe and then cleaning the inside of the pipe by the above-mentioned three kinds of cleaning methods. In FIG. 2, the vertical axis represents the effect ratio of each cleaning method with respect to the cleaning effect of liquid flow cleaning. Further, a is an effect on magnetite powder, and b is an effect on hematite powder. As is clear from this figure, the effect of the liquid plug cleaning of the present invention is 1.5 times or more as large as the effect of the conventional liquid flow cleaning and the effect of mixed bubble cleaning.

In this way, the chemical liquid and the air flow are alternately flowed through the pipe at an appropriate interval to lift the sludges,
Transport at high speed.

The chemicals, air, and sludges discharged from the pipe enter the cyclone 6, where the chemicals and the sludges are separated from the air stream.
Next, the sludges are separated from the chemical liquid by the hydroclone 7 and stored in the sludge tank 8. The chemical solution is returned to the chemical solution tank 1 by the return pump 10 via the surge tank 9,
To be reused. The airflow separated by the cyclone 6 is connected to the exhaust system via the silencer 11, and is connected to the exhaust system through a filter or cyclone having higher performance if necessary.

〔The invention's effect〕

According to the cleaning method of the present invention, the sludge, slime, and soft scale deposited and adhered to the pipe can be effectively removed, and the air column can be lengthened by increasing the interval between the water plugs. Therefore, the pressure loss can be reduced. Therefore, the flow velocity at the same pressure becomes large, and the conveying ability of the sludge and the like that has peeled off becomes large.

In addition, since radioactive substances are removed in the form of sludge, clad, etc., the consumption of chemicals is reduced, but the amount of secondary waste is also reduced.

Furthermore, the method of the present invention does not require agitation and mixing of gas and liquid in advance, so the apparatus is simple. The amount of gas and fluid, the interval, etc. can all be easily adjusted by adjusting the valve.
And it can be applied to piping of any structure.

Further, unlike the conventional water fracturing method, since it is not a gas-liquid mixed phase flow, there is little foaming by a surfactant or the like, and therefore sludges can be easily separated.

Furthermore, since remote control is easy, there is no risk of radiation exposure.

[Brief description of drawings]

FIG. 1 is a flow sheet showing an embodiment of the present invention,
FIG. 2 is a diagram showing an experimental result comparing the effect of the cleaning method of the present invention with the effect of the conventional cleaning method. 1 ... Chemical liquid tank, 2 ... Compressed air tank, 3 ... Liquid feed pump, 4 ... Check valve, 5 ... Piping, 6 ... Cyclone, 7 ... Hydroclone, 8 ... Sludge tank, 9 ... Surge tank, 10 …… Return pump 11 …… Silencer

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Jun Yoshikawa 4-1 Ukishima-cho, Kawasaki-ku, Kawasaki-shi, Kanagawa Nihon Nuclear Power Company Ltd. (72) Hideji Seki 4 Ukishima-cho, Kawasaki-ku, Kawasaki-shi, Kanagawa No. 1 In the Research Institute of Japan Nuclear Power Company (72) Inventor Akira Kikuchi 1-6 of Uchisaiwaicho, Chiyoda-ku, Tokyo Inside Tokyo Shibaura Electric Co., Ltd. (56) Reference JP-A-57-117379 (JP , A)

Claims (4)

[Claims] 1. A method for cleaning a radioactive fluid pipe, comprising alternately inserting a cleaning liquid and air into a pipe at an arbitrary interval so that a liquid plug and an air column pass alternately. 2. The cleaning liquid and air are introduced at intervals such that the length of the liquid plug is at least 10 times the pipe diameter and the length of the air column is at least 10 times the pipe diameter. A method for cleaning a pipe for radioactive fluid according to claim 1. 3. The method for cleaning a radioactive fluid pipe according to claim 1, wherein the cleaning liquid is water. 4. The method for cleaning a pipe for radioactive fluid according to claim 1, wherein the cleaning liquid is a chemical cleaning chemical liquid.