JPS60132630A - Dissolving apparatus - Google Patents

Abstract

PURPOSE:To prevent corrosion caused by conc. nitric acid, by forming a dissolving apparatus of used nuclear fuel from a double structure consisting of an inner barrel and an outer barrel while filling the ring shaped space between both barrels with a heating medium. CONSTITUTION:The lower part of a barrel 2 is formed of a double structure consisting of an inner barrel 2a for receiving used nuclear fuel and conc. nitric acid and an outer barrel 2b to which a heating jacket 9 for receiving steam 10 used in heating is welded and the ring shaped space 8 between both inner and outer barrels 2a, 2b is filled with a heating medium such as water or oil. By this structure, there is no contact with concentrated nitric acid and a heat affected part is prevented from corrosion due to concentrated nitric acid.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a melting device used to melt spent nuclear fuel.

The oxide has uranium-268 in lett partially converted to plutonium-269.

This type of melting device has the function of melting the four materials used in a nuclear reactor using high-temperature concentrated nitric acid in order to easily separate them from nuclear fission products for reprocessing.

An example of a conventional melting device is shown in Figure 1, in which a slab (1) with a rectangular cross section and a cylindrical barrel (2) are connected to a connecting pipe (3).
connected with. Shredded spent nuclear fuel is stored in barrels (
2) into the basket (4). After that, the slab (1) is filled with concentrated nitric acid, and heating steam is flowed into the jacket (5) welded to the outside of the barrel (2) to heat the concentrated nitric acid inside the device and simultaneously circulate it. It looks like this.

Because this melting device is filled with high-temperature concentrated nitric acid, there is a risk of corrosion and pinholes. Also, since the jacket (5) is attached to the barrel (2) by welding, there is a high possibility of corrosion from the heat-affected zone (and if the wetted parts inside the jacket (5) corrode, it must be repaired. There was no way to do this, and the entire device had to be replaced.

The present invention was invented to solve the above-mentioned drawbacks.
The gist is that in a spent nuclear fuel melting device consisting of a slab filled with concentrated nitric acid, a cylindrical barrel into which spent nuclear fuel is charged, and a connecting pipe connecting the slab and barrel, the barrel The whole or part of the shell has a double structure consisting of an inner shell that receives spent nuclear fuel and concentrated nitric acid, and an outer shell that is equipped with a heating jacket that receives the heating steam. A melting device characterized in that a space is filled with a heat medium.

In the present invention, since the above structure is provided, the outer shell equipped with the heating jacket is isolated from the high-temperature concentrated nitric acid in the inner shell by the heat medium in the inner shell and the annular space, and is in contact with the concentrated nitric acid. Therefore, even if the heating jacket is welded and attached to the outer shell, its heat-affected zone will not be corroded by concentrated nitric acid. Furthermore, since the inner shell that receives concentrated nitric acid has an integral structure without being welded, there is less risk that the inner shell will be corroded by concentrated nitric acid.

Furthermore, the inner and outer shells can be made of different materials and have different structures depending on their functions, so even if one of them is damaged, it will be a hassle to replace just one.

One embodiment of the invention is shown in FIG. 2, which is a partial cross-sectional view of the nozzle barrel. As shown in Figure 2, the lower part of the barrel (2) consists of an inner shell (2α) that receives spent nuclear fuel and concentrated nitric acid, and an outer shell (101'4) that is welded with a heating jacket (9) that contains heating steam (101'4). It has a double structure consisting of a shell (2h), and the annular space (8) between the inner shell (2α) and the outer shell (2h) is filled with a heat medium such as water or oil.Inner shell (It is made of 2α stainless steel, and its main body has an integrated structure to reduce the number of welded parts, and only the joint part with nozzle 01) is welded.Although not shown, the inner body of the barrel (2α It is connected to the slab via a one-piece connecting pipe.

The outer shell (2b) is heated by the steam passing through the heating jacket (9), and then the inner shell (2α) is heated by heat conduction through the heat medium filling the annular space (8).
) is heated, and then the concentrated nitric acid inside the inner shell (2α) is heated. If the inside of the annular space (8) is brought to atmospheric pressure, 100
In order to heat concentrated nitric acid to a temperature above C, it is desirable to fill the tank with oil having a high boiling point as a heat medium. Concentrated nitric acid may pass through the grain boundaries of the stainless steel inner shell (2α) and seep into the outer surface of the inner shell (2α), albeit in a small amount.
Even in that case, the concentrated nitric acid is diluted by the heat medium filling the annular space (8) and does not directly reach the welded part of the outer shell (2h). In addition, the PH of the heat medium filled in the annular space (8) is measured, and if there is any abnormality, immediately remove the inner shell (2).
It would also be possible to replace α).

[Brief explanation of the drawing]

FIG. 1 is a front view of a conventional melting device, and FIG. 2 is a front view of a conventional melting device.
FIG. 3 is a partial vertical cross-sectional view of the barrel in the example. Slab...m Barrel...(2) Connecting pipe...(
3) Inner shell...(2α) Outer shell...(2h) Heating jacket...(9) Annular space...(8) Sub-Agent Patent Attorney Shige Okamoto Figure 1 Figure 2

Claims (1)

[Claims] In a spent nuclear fuel melting device consisting of a slab filled with concentrated nitric acid, a cylindrical barrel into which spent nuclear fuel is charged, and a connecting pipe that connects the slab and the nozzle, the whole or part of the barrel is It has a double structure consisting of an inner shell that receives spent nuclear fuel and concentrated nitric acid, and an outer shell that is equipped with a heating jacket that receives heating steam, and a heat medium is filled in the annular space between the inner shell and the outer shell. A dissolving device characterized by: