JPS6361195A - Continuous melter for spent nuclear fuel - Google Patents

Abstract

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

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an apparatus for dissolving nuclear fuel in heated nitric acid and separating it from an insoluble coating material in a reprocessing process of spent ceramic nuclear fuel. In particular, the present invention relates to an apparatus suitable for continuously dissolving nuclear fuel with a high concentration of fissile material with high efficiency.

[Conventional technology]

As a nuclear fuel melting device, the so-called batch method is used, in which the necessary amount of acid is added into a container loaded with nuclear fuel, the melting is completed by heating, and then the melting liquid and the insoluble coating material are separated and taken out. There is a so-called continuous method in which the nuclear fuel and acid are loaded into a container while the solution and coating material are taken out respectively.

It takes a certain amount of time to melt the fuel, and it takes a certain fraction of the hourly loading amount.
If it is assumed that the continuous melting device is melted in batches, it is calculated that the average fuel loading of the continuous melting device will not be more than 1.5 of the initial fuel loading of the batch melting tank with the same daily processing capacity. In reality, it is estimated to be about one-quarter.

As described above, continuous melting equipment requires only a small fuel loading capacity and is highly efficient, but there is a problem in removing undissolved materials from the coating material.
``Apparatus for continuously processing a processed material in a liquid'' described in Japanese Patent No. 94297 has been proposed.

However, since this device continuously loads fuel into a limited area within the device, it is difficult to ensure criticality safety when melting fuel with a high concentration of fissile material such as fast reactor fuel. There were disadvantages.

[Problem that the invention seeks to solve]

The purpose of the present invention is to maintain a large processing capacity while maintaining criticality safety when dissolving nuclear fuel with a high concentration of fissile material in a dissolution treatment solution, to complete the progress of the dissolution process, and to load and coat sheared fragments. It is an object of the present invention to provide a continuous nuclear fuel melting and processing device that does not spread contamination when extracting materials, maintains mechanical durability in a highly corrosive atmosphere, and is easy to maintain even in the event of failure.

[Means for solving problems]

The continuous melting device of the present invention allows the cages loaded with nuclear fuel to be freely arranged in a continuous manner within the annular container that holds the dissolution treatment liquid, and arranges the cages loaded with fuel as evenly as possible within the annular container. , avoid uneven distribution of fuel-loaded cars.

This makes it possible to ensure criticality safety up to a higher fissile material concentration even when using the same nuclear fuel loading basket.

The above functional features are that the annular container holding the dissolution treatment liquid is divided into upper and lower halves, the upper part rotates relative to the fixed lower liquid storage part, and the nuclear fuel loading basket is installed at the top of the container. This is achieved by structural features that allow the lifting device to be moved to any position within the annular container.

[Effect]

In the continuous melting device of the present invention, by using a plurality of fuel loading cages, it is possible to set the distribution of nuclear fuel material within the device, which depends on the amount of fuel loaded into the cages and the reduction in melting thereof, to the optimal conditions for ensuring criticality safety. It is.

In reality, fuel loading means that every other one in the annular container is
After one round, the gaps are filled in, and after all the cars have been placed, the sheathing material is discharged in order from the car placed furthest ahead, and a new fuel shear piece is loaded.

〔Example〕

Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

The continuous melting device for spent nuclear fuel is mainly composed of a fixed part 1 having an annular shape and serving as a base, and a rotating part 2 mounted on the fixed part 1.

The fixed part 1 has a heating jacket 3 at its bottom.

Storage tank for dissolving treatment liquid 4. It consists of a rack 6 supporting a fuel loading tank 5.

All pipes connected to the melting device are connected by fixed parts. The piping is: fuel shear piece loading pipe 7° acid supply pipe 8.
Dissolving treatment liquid overflow pipe9. Dissolved exhaust gas extraction pipe 10. Covering material extraction pipe 11. It consists of a heating medium supply pipe 12, a drain pipe 13, etc.

The fixed part 1 and the rotating part 2 are kept airtight at the sliding connection part by a pair of water seal devices 14 provided on the inside and outside.

The rotating part 2 includes a guide rail 15 that constitutes a part of the fixed part 1.
A plurality of drive rollers 16 forming part of the rotating section are mounted on the
It is supported by and gives rotational motion.

The rotating part 2 includes a lifting device 1 for raising and lowering the fuel loading basket.
7 is installed, and the tip of the lifting bag W117 is the rotation holding mechanism 1.
8, and can hold the fuel loading basket, raise and lower it, and rotate it. There is an extension 19 in a part of the rotating part 2 to allow the fuel loading and the rotating part 5 to rotate.

There is a circular water tank 20 inside the circular fixed part 1,
A cadmium plate 21 is provided around the outer periphery of the water tank 20 as a thermal neutron absorbing material.

The continuous melting device for spent nuclear fuel according to the present invention is supported by a rack 6 in the fixed part 1 and is placed in advance with the required number of fuels for normal operation.

The fuel loading container 5 has a fan-shaped horizontal cross section, and its upper portion forms an edge so that it can be supported by a rack 6.

The continuous melting device first supplies acid from the acid supply pipe 8, fills it to the height of the overflow pipe 9, and heats it.
is placed under the loading pipe 7, and the fuel shear pieces are loaded into the basket.

Among the spent fuel loaded in the car 5, the fuel material crushed by the shearing operation rapidly dissolves in the solution. When the rapid melting has subsided, the rotating part 2 is rotated, and the lifting device 1
117 lifts up the cage 5 at the position of the loading pipe 7, rotates the rotating part 2, and moves the car loaded with fuel to the empty space in the liquid storage part 4 and places it there.

A device that lifts and lowers empty cars in positions that are not adjacent to the placement position of the car loaded with fuel! ! 17, place it under the loading pipe 7, and repeat the above operation.

When there are no empty cages in the liquid storage tank 4, the first loaded and arranged cage is lifted by the lifting device, moved onto the coating material extraction pipe 11, and rotated by the rotation holding mechanism. , the dressing material in the basket is discharged into the dressing material extraction pipe.

After the covering material is discharged, the empty basket is moved to the loading pipe 7 for the next loading.

During the above operations, acid is supplied so that the concentration of nuclear fuel material in the dissolution solution does not exceed a certain value, and the dissolution solution equivalent to the supplied amount flows out from the overflow pipe 9, thereby continuously supplying acid. A good dissolution is achieved.

Exhaust gas generated from the melting of spent nuclear fuel is extracted from extraction pipe 1.
The pressure inside the device made of 0 is kept slightly lower than the outside pressure to prevent radioactive substances from diffusing outside the device.

Criticality safety can be maintained even at higher fissile material concentrations by arranging the fuel loading basket so that it is not adjacent to any consecutive loading.

In the continuous melting device according to the present invention, a fixed part 1 is connected to all the pipes, and a rotary part 2, which is made of highly corrosion-resistant material and does not require maintenance over a long period of time, has a roller for rotational drive. 16. Lifting bag! 17. The zero-rotation part 2, in which drive parts such as the rotation holding mechanism 18 are integrated, is connected to the fixed part 1 by an annular water seal device 14, so the rotating part 2 can be easily attached to the fixed part 1 by lifting vertically.
The drive part can be easily maintained.

The present invention is achieved by controlling the rotational movement of the one-rotation unit 2 using a computer, and thereby controlling the arrangement of the nuclear fuel loading cage, regardless of the above-described embodiment, and also by installing a radiation measuring device outside the device. The amount of remaining fuel in the fuel loading basket is measured, and the dissolving treatment liquid is pumped up from the bottom of the container and circulated inside the fuel loading basket. This can be achieved by adding a method such as spraying water or a dilute acid aqueous solution to remove the adhering dissolving treatment liquid.

According to this example.

(1) Since the fuel loading baskets can be freely arranged, consecutively loaded baskets are not placed next to each other, so criticality safety can be ensured even in the continuous melting of spent fuel with a high concentration of fissile material. .

(2) The reliability of the device can be increased because the main drive mechanism is located outside the device, where there is no risk of it coming into contact with acid or fuel shear dust.

(3) During the process of continuous dissolution operation, the inside of the device is always kept at a reduced pressure compared to the outside, so there is no risk of radioactive substances diffusing outside the device.

(4) All drive parts that require periodic maintenance are integrated into a fixed part and a rotating part that can be easily separated, making maintenance easy.

〔Effect of the invention〕

According to the present invention, the nuclear fuel loading basket loaded with nuclear fuel with a high concentration of fissile material can be freely placed in the continuous melting device, so the loading of nuclear fuel means arranging it so as to minimize the neutron multiplication factor in the device. Therefore, it is possible to increase the processing capacity while maintaining criticality safety when dissolving nuclear fuel with a high concentration of fissile material in the dissolution processing solution.

In addition, all the mechanisms involved in loading the fuel shear pieces, removing the sheathing material, and lifting and lowering and moving the fuel loading basket are installed in a sealed container with a water-sealing device, so there is no possibility that radioactive materials will spread outside the device. In addition, since all drive mechanisms are provided outside the sealed container, reliability is high even when handling highly corrosive solutions, and maintenance is easy even in the event of a failure.

[Brief explanation of the drawing]

The figure is a longitudinal cross-sectional view of a continuous melting device for spent nuclear fuel according to an embodiment of the present invention. 1...Fixed part, 2...Rotating part, 3...Heating jacket, 4...Liquid storage tank, 5...Fuel loading, 6...
・Rack, 7... Loading pipe, 8... Acid supply pipe, 9...
- Overflow pipe, 10...Dissolved exhaust gas extraction pipe, 11...Coating material extraction pipe, 12...Heating medium supply pipe, 13...Drain pipe, 14...Water seal device, 15 ... Guide rail, 16... Drive roller.

Claims (1)

[Claims] 1. A plurality of corrosion-resistant nuclear fuel loading baskets are placed at arbitrary positions in a corrosion-resistant annular container that holds a dissolution treatment liquid, and the lower part of the nuclear fuel loading basket is filled with the dissolution treatment liquid. A continuous melting device for spent nuclear fuel, characterized by immersing it in a spent nuclear fuel. 2. The annular container is divided into a fixed lower part consisting of a liquid storage part and an upper part capable of rotational movement, and the upper structure has an elevating device for a nuclear fuel loading cage. The device for continuously melting spent nuclear fuel described above. 3. The annular container is kept airtight by a water sealing device except for the inlet for nuclear fuel sheared pieces and the outlet for exhaust gas generated during the melting process of spent nuclear fuel. The continuous melting device for spent nuclear fuel according to item 1 or 2. 4. In the annular container, the cage loaded with the nuclear fuel sheared pieces is arranged adjacent to the nuclear fuel loading cage arranged furthest in advance. The continuous melting device for spent nuclear fuel according to item 3. 5. Loading the nuclear fuel sheared pieces into the fuel loading basket and removing the insoluble cladding material from the fuel loading basket are carried out at respective set locations in the annular container, The continuous melting device for spent nuclear fuel according to item 2, 3, or 4. 6. In the annular container, a radiation detection device is installed directly facing the fuel loading basket that is lifted by the lifting device, and the radiation generated by the fuel loading basket before and after the melting treatment is measured. Claim 1
The continuous melting device for spent nuclear fuel according to item 1, 2, 3, 4 or 5. 7. In the annular container, the dissolving treatment liquid is pumped up from the bottom of the container and circulated within the fuel loading basket, Claims 1, 2, 3, and 4;
The continuous melting device for spent nuclear fuel according to item 5 or 6.