JPH03231199A - Reducing method of volume of chopped piece of spent fuel - Google Patents

Abstract

PURPOSE:To improve the rate of reduction of volume and to reduce the cost for disposal of chopped pieces of spent fuel by a method wherein the chopped pieces of the fuel are exposed to an arc discharge of high-voltage and high- current plasma in water, heated to a high temperature and made to react with the water and water vapor. CONSTITUTION:Chopped pieces 1 of fuel subjected to compression molding are put on a frame 2 in an underwater discharge treatment vessel 7 and disposed between two electrodes 3. Next, water is sent into the vessel 7 from a water supply pipe 9, and after the chopped pieces 1 are covered sufficiently with the water, a discharge of high voltage and high current is generated between the two electrodes 3 and the chopped pieces 1 by operating a discharge power source 5. By this discharge, the chopped pieces 1 are heated instantaneously and turn to be zirconium oxide powder in the chemical reaction with the water, generating hydrogen simultaneously. This hydrogen is introduced into a hydrogen refining device 11 through a reaction gas discharge pipe 10 and it is caught in a hydrogen collecting vessel 13. The oxide zirconium powder produced in the vessel 7 is collected after the underwater discharge treatment and stored in a hermatically sealed vessel made of metal.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for reducing the volume of spent nuclear fuel sheared fragments in nuclear power generation.

[Prior Art] The conventional method for disposing of fuel shear fragments in nuclear power generation involves dissolving and removing the spent fuel in the fuel shear fragments in a dissolving tank, and then taking out the empty fuel shear fragments from the melting tank, washing them, and disposing of them. After that, it was placed in a metal container and sealed for storage.

[Problems to be solved by the invention] In the conventional treatment method, the bulk density of the fuel sheared pieces is small (
In order to process a large amount of fuel shear fragments (large volume),
A large amount of metal sealed containers were required, and therefore a large space for storage was required.

Since it is difficult to secure a large space for this storage, the volume of waste after volume reduction treatment needs to be as small as possible.

[Means for solving the problem] The present invention exposes spent fuel sheared pieces in water to a high voltage, high current plasma arc discharge, heats them to high temperatures, and reacts them with water and steam to form metal oxides. It is characterized by being made into powder, and the hydrogen generated at that time can be recovered and used at the same time.

[Operation] When the fuel sheared pieces are exposed to a plasma arc in water and steam, the metal instantly turns into high-temperature molten metal fine particles,
Immediately a chemical reaction occurs with surrounding water and steam, forming metal oxide powder and generating hydrogen. That is, Z r + H20 - Z r02 + H2 [Example] An example of the present invention will be described using FIG. 1.

FIG. 1 is a conceptual diagram of underwater discharge treatment of fuel sheared pieces.

In Fig. 1, 1 is a compression-molded used fuel shear piece for a light water reactor, 2 is a pedestal made of insulating material on which the fuel shear piece 1 is placed, 3 is an electrode for high voltage and high current discharge, and 4 is a An electric wire for supplying power to the electrode 3, which extends from the power source 5 as a bundle of two electric wires 4, and branches in the middle to form two wires.
The two electrodes 3 are connected to each other. 5 is a power source for the high voltage, high current discharge device; 6 is a floor for installing the power source 5; 7 is a floor for installing the power source 5;
is an underwater discharge treatment vessel, 8 is water in the treatment vessel, 9 is a water supply pipe, 10 is a reaction gas discharge pipe, 11 is a hydrogen purification device, 12
13 is a hydrogen collection container, and 14 is a hydrogen discharge pipe.

In FIG. 1, a compression-molded fuel shear piece 1 is placed on a pedestal 2 within an underwater discharge treatment vessel 7 and placed between two electrodes 3. At this time, the electrode 3 and the fuel shearing piece 1 may or may not be in contact with each other. Next, water is poured into the underwater discharge treatment container 7 from the water supply pipe 9.

After the water sufficiently covers the fuel shearing piece 1, the discharge power source 5
is activated to generate a high voltage and high current discharge between the picture electrode 3 and the fuel shear piece 1.

Due to this discharge, the space between the picture electrodes 3 becomes a high-temperature arc plasma state, and the fuel sheared pieces 1 are instantaneously heated and cause a chemical reaction with water, resulting in Z r + H20 - Z r 02 + H2,
It becomes zirconium oxide powder (Zr02) and simultaneously generates hydrogen. This hydrogen is led to the hydrogen purification device 1] through the reaction gas discharge pipe 10 and collected in the hydrogen collection container 13.

The zirconium oxide powder generated in the underwater discharge treatment container 7 is collected after the underwater discharge treatment and stored in a closed metal container. In addition, in the present invention, although the processing in water has been described, the present invention also applies when the inside of the processing container 7 is filled with water vapor.

[Effect of the invention] According to the present invention, the spent fuel sheared pieces become oxidized powder,
The volume reduction rate is significantly improved, and therefore less metal containers are required for storage and processing, and the space required for storage and processing (site, etc.) is also reduced.
This greatly reduces the cost of processing spent fuel shear fragments.

[Brief explanation of drawings]

FIG. 1 is a conceptual diagram of the underwater discharge treatment of the sheared fuel fragments for use in light water reactors. 1... Fuel shearing piece, 2... Frame, 3... Electrode, 4...
... Electric wire, 5... Power source, 6... Floor, 7... Underwater voltage detection/processing container.

Claims (1)

[Claims] A fuel shearing piece is placed between the electrodes of a high voltage discharge generating device in water or water vapor, and a high voltage and high current discharge is generated between the electrodes to heat and burn the fuel shearing piece between the electrodes. , a method for reducing the volume of used fuel shear pieces, which comprises converting the fuel shear pieces into metal oxide powder.