JPS5814100A - Method of cleaning structure adhered with alkali metal - 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 relates to a method for cleaning sodium-contaminated equipment used as a coolant.

Sodium U melts at about 98°0, about 30]~5
Used as a coolant in fast breeder reactors in the range of 50'0.

Flows through reactor vessels, pumps, heat exchangers, steam generators, etc.

Equipment such as the pumps and heat exchangers mentioned above are used for quite a long time, and during that time they may be inspected and repaired periodically or as necessary. Preferably, the device is then reused.

Since the above-mentioned inspections and repairs are generally carried out in the atmosphere, the liquid sodium is discharged beforehand, but the parts that have been in contact with the sodium are discharged.

Note that sodium is attached. The internal structure of the device may have sodium adhering to its outer surface, or sodium hydroxide may remain on the surface, which is undesirable for inspection and repair.

For this reason, cleaning (removal of adhering lium) is performed before exposing internal structures with sodium adhesion to the atmosphere.
Perform rough cleaning (primary cleaning) using water vapor, humidified gas, alcohol, etc.

The conventional general cleaning process has been to immerse the structure in pure water and rinse it as a secondary cleaning.

However, the internal structure has a complicated structure, and usually has a narrow entrance of about 20071772 mm on its surface and a slightly wider chamber space (hereinafter referred to as a clevis) inside. If there is such a leak, sodium will remain deep inside it even after the above-mentioned cleaning, and an aqueous solution of sodium hydroxide will likely remain at the inlet.

When inspecting and repairing internal structures in the atmosphere.

The aqueous sodium hydroxide solution at the clevis inlet reacts with carbon dioxide gas to become sodium carbonate, but the sodium carbonate acts as a seal, leaving unreacted hydroxide inside.
An IJum aqueous solution remains.

As mentioned above, an aqueous solution of thorium hydroxide remains in the crevices on the surface of internal structures.

During preheating for reuse, a problem arises in that alkaline stress corrosion cracking occurs.

The present invention was made in order to prevent the above-mentioned alkali stress corrosion cracking during reuse.

As the final cleaning, secondary cleaning, thorium hydroxide inside the crevice is completely removed by using a combination of physical removal of boiling bubbles by reduced pressure and chemical conversion to harmless carbonate by reaction with carbon dioxide gas. The purpose of this invention is to provide a cleaning method that can be used.

The method of the present invention will be explained below with reference to specific examples.

FIG. 1 is a system diagram of an apparatus for implementing the method of the present invention.

In FIG. 1, a porous support plate 11 on which the internal structures of two devices, that is, objects to be cleaned 1 are mounted, is installed at the bottom of a bot-shaped cleaning tank 10, and a heater 13 is attached to the outer periphery of the support plate 11.

After the object 1 to be cleaned is inserted and placed, the upper opening of the cleaning tank 10 is not closed with a lid 15, but an exhaust pipe 22 equipped with a valve 21 is connected to the lid 15. A drain pipe 25 with a valve 24 is connected to the bottom of the washing tank 10, while a vacuum tJI trachea 29 with a vacuum pump 27 and a valve 28 is connected to its top.

Also, a supply pipe 31 for introducing a cleaning agent such as steam or pure water;
33 are connected as shown, and valves 35 and 36 are provided respectively.

In the illustrated apparatus, for the first cleaning of the object 1 to be cleaned, the valve 28 is first opened, the vacuum pump 27 is started, the air in the cleaning tank 10 is discharged through the vacuum exhaust pipe 29, and then the valve 28 is opened. After closing, the cleaning tank 10 is heated by the heater 13.
Preheat the inside. The corresponding vent valves 35 and 36 are opened, and steam or the like is injected from the supply pipes 31 and 33. Water vapor containing hydrogen gas is continuously exhausted from the exhaust pipe 22. After the operation is completed.

The condensed water containing IJum (compound) is discharged through the drain pipe 25 to a waste water tank (not shown).

Note that the primary cleaning may be performed using humidified gas, alcohol, or the like instead of water vapor.

Next, the secondary cleaning will be explained with reference to FIG. 2 showing the state inside the clevis of the object 1 to be cleaned.

After the first cleaning, the supply pipe 31 is connected to a carbon dioxide supply source by being switched by a valve (not shown).

After that, (a) close valves 21, 24, 35, and 36, and close valve 2.
8 starts the vacuum pump 27 to evacuate the inside of the cleaning tank 10 and reduce the pressure to the target value.

FIG. 2(a) is an enlarged polar diagram showing the inside of the clevis 3 of the object to be cleaned 1 when the pressure is reduced in step (a). That is, due to the reduced pressure, so-called reduced pressure boiling occurs, and bubbles are generated in the aqueous solution A of thorium hydroxide, which escapes to the outside of the clevis 6. At the same time, part of the aqueous solution A is also pushed out.

(b) After reducing the pressure, close the valve 28 and open the valve 36 to connect the supply pipe 3.
3, pure water is poured into the cleaning tank 10, and the cleaning product 1 is held therein for a suitable period of time.

When water is being filled under reduced pressure.

Due to the supply of water from the outside of the clevis 3, the remaining thorium B also reacts with the water and changes into hydrogen gas and sodium hydroxide.

Hydrogen gas escapes to the outside in the same way as water bubbles.

In this manner, at the end of step (B), only the considerably diluted low concentration sodium hydroxide aqueous solution A remains in the clevis B, as shown in FIG. 2(B). However, since the concentration diffusion to the outside of the clevis 3 is performed only at a low speed, the sodium hydroxide concentration is hardly reduced even if it takes a long time.

(c) Open the valve 24 to discharge pure water from the cleaning tank 10, and at the same time open the valve 35 to discharge carbon dioxide (
A mixture of carbon dioxide and inert gas may be used. ) to cleaning tank 1
0 and held at 1 filled with carbon dioxide gas.

After performing the operation in step 7b (c), the procedure is generally as shown in Figure 2 (
In the situation of c), carbonic acid (IJum C) is produced in one part of the population, but IJum water solution A (which is still hydroxylated) remains in the deeper part.

If you perform step (a) again.

As shown in Figure 2), water bubbles are generated and separated.
Most of the thorium hydroxide aqueous solution A and sodium carbonate C are also extruded, and in the state of step (b), a small amount of thorium carbonate C and a -゛ layer are diluted as shown in Figure 2 (e). The resulting sodium hydroxide aqueous solution A remains. When step (c) is further performed here, as shown in FIG.

this is.

In Fig. 2 (e), the concentration of aqueous fluid A is already dilute, so
This is because the evaporation of water into the carbon dioxide atmosphere precedes the reaction between sodium hydroxide and carbon dioxide gas in the operation of step (N). In this way, repeating steps (a) to (c).

In the end, only a small amount of sodium carbonate C remains in the clevis B, as shown in Figure 2 □ (f), and it is hydroxylated.)
It has been confirmed that there is no IJum aqueous solution A, and even if preheating is performed before reuse, if Altep (a), (b), and (c) are repeated at least once, the state shown in Figure 2 (f) will be reached. Ta.

In step (c) of the above specific example, after introducing carbon dioxide gas, the above ``!-'' was held, but after the completion of draining, the vacuum pump 2
7, the pressure inside the cleaning tank 10 is once reduced by suctioning and discharging the carbon dioxide gas, and then carbon dioxide gas is introduced again from the supply pipe and maintained, resulting in a depressurized Buddha in the state shown in Figure 2 (b). It is also possible to quickly eliminate the sodium hydroxide aqueous solution A to achieve the state shown in FIG.

[Brief explanation of the drawing]

Figure 1 is a system diagram of installation for carrying out the method of the present invention;
Figures (A) to (F) are state explanatory diagrams at each step of the method of the present invention. 1...Object to be cleaned, 10...Cleaning tank, 15...Lid,
2+, 24°28, 35.36...valve, 22...t
J14 trachea, 25...fJI water tube, 27...vacuum pump, 29...vacuum υ1 trachea, 31.33...supply pipe. A...Sodium hydroxide aqueous solution, +1...Residual sodium, 0...Sodium carbonate, D...Water vapor foam agent Akira Sakama procedural amendment (method) Indication of case 1982 Patent Application No. 113103
Name of the No. Invention Relationship to the Case of Person Amending the Method of Cleaning Structures Adhered to Alkali Metals Patent Applicant Address 2-5-1 Marunouchi, Chiyoda-ku, Tokyo Name (62(1) Agent of Mitsubishi Heavy Industries, Ltd.) Address: Mitsubishi Heavy Industries, Ltd., 2-5-4 Marunouchi, Chiyoda-ku, Tokyo (Den 2+2-3111) 1982
November 24th, 2017, page 10, line 3 of the specification [Figure 2 (a) ~ (・→])
Figure 2 (・)～(g)” is corrected. (2)

Claims (1)

[Claims] After the object to be cleaned stored in the cleaning tank is primarily cleaned, the cleaning waste liquid is discharged, the pressure inside the tank is reduced, and the object to be cleaned is then submerged and held in pure water injected into the tank. . A method for cleaning an alkali metal-adhered structure, further comprising replacing and retaining the pure water in the tank with carbon dioxide gas.