JP2500408B2 - Continuous melting device for nuclear fuel - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for continuously melting nuclear fuel scrap powder generated in a nuclear fuel manufacturing process or nuclear fuel powder in a spent nuclear fuel reprocessing process.

[0002]

2. Description of the Related Art Nuclear fuel scrap powder generated in a nuclear fuel manufacturing process is refined and recycled. For this refining, the scrap powder is dissolved in a cylindrical batch type dissolution tank. In the reprocessing of spent nuclear fuel, a so-called “shear reach method” is generally performed in the pretreatment step of the reprocessing in order to separate and recover unburned fissile material and newly generated fissile material. The shear reach method is a method in which a spent nuclear fuel rod is cut into a length of several cm along with a cladding tube in the diameter direction of a fuel assembly by a shear blade and put into an aqueous nitric acid solution as it is to leach and dissolve the nuclear fuel. . The nuclear fuel processed by the shear reach method is melted in a cylindrical melting tank, or is a screw type continuous melting tank (for example, JP-A-58-176107, 64-64).
65497) or a water turbine bucket type continuous melting tank (for example, Japanese Examined Patent Publication No. 60-41318, Japanese Utility Model Publication No. 64-52533). As another continuous dissolution treatment device,
The inside of the tank is partitioned by a partition wall, and the dissolution treatment liquid starts from one end of the partition.
In a dissolution tank that supplies the above into the tank and discharges from the other end.
Multiple fuel-loaded cages loaded with spent nuclear fuel shear fragments
And place the lower part of the fuel-loaded cage in the dissolution treatment liquid.
Use to dissolve and process spent nuclear fuel by dipping
A continuous dissolution processing apparatus for spent nuclear fuel is disclosed
(1-141399) . Furthermore, as a semi-continuous melting device, gold
Collection of finely cut strips of nuclear fuel coated with metal
Change the height position of the barrels that receive the baskets.
Side by side, and the bottom of each barrel is pulsated.
To the top of the reservoir via the dissolution liquid supply pipe.
Store the lowest barrel in the barrel via the dissolution liquid discharge pipe.
The above strips can be used as a solution by connecting them to the tank respectively.
A nuclear fuel melting device that dissolves more is disclosed (Japanese Patent Laid-Open No. Sho 61-135).
61-270695).

[0003]

However, the cylindrical melting tank is premised on batch processing, and in order to use this as a continuous processing apparatus, at least two batch type melting tanks are provided and these are alternately arranged. It is necessary to switch and use, or to increase the capacity of the one-time processing by increasing the capacity of the cylindrical dissolution tank and the storage tank of the dissolution liquid. In the former case, the switching operation becomes complicated, and in the latter case, there is a problem that the melting apparatus becomes large. Further, in both the screw type continuous dissolution tank and the water turbine bucket type continuous dissolution tank, the shaft for driving the screw or the water turbine bucket is provided so as to penetrate the dissolution tank. Sealing property is required to prevent leakage. In order to maintain the sealing property of the drive shaft, the continuous melting tank requires regular maintenance work. Also, in Japanese Patent Laid-Open No. 1-141399.
Continuous melt processing equipment using multiple fuel-loaded cages shown
In the installation, multiple fuels loaded with spent nuclear fuel shear fragments
You need to move the loading basket. Carry out this move
In order to support the fuel loading cage support plate, rotary lifting device, reversing device
It is necessary to install equipment such as
Dissolving tank with fuel loaded basket containing undissolved residue
Elevate from inside and then invert to expel internal shear fragments
After that, it is lowered again and returned to the dissolution tank.
Work is required. Also, JP-A-61-270695
The dissolution device indicated in the report also determined that the dissolution reaction was completed.
In the barrel is a basket to remove undissolved residue
Requires a device to remove and replace the
A little work is needed. Furthermore, the equipment that handles nuclear fuel, including the dissolution tank for nuclear fuel, is limited in terms of critical safety management in terms of the amount of nuclear fuel handled and the size and shape of the equipment such as diameter, thickness, width, etc. Both have a limited processing capacity.

An object of the present invention is to provide a continuous melting apparatus for nuclear fuel which has a compact shape, can be arbitrarily set with a processing capacity without causing a problem in criticality safety management, and is easy to maintain. Another object of the present invention is the unmelted nuclear fuel.
Providing a continuous melting device for nuclear fuel that can easily remove solution residues
To do.

[0005]

In order to achieve the above object, the structure of the present invention will be described with reference to FIGS. 1 and 2 corresponding to the embodiments. Continuous melting apparatus of the nuclear fuel of the present invention, nuclear
A dissolution tank 11 capable of storing a nitric acid solution of fuel and a plurality of reaction chambers 15a to 15e are formed in the dissolution tank 11, and the nitric acid solution flows from the upper reaction chamber to the lower reaction chamber. A lower partition plate 12 provided on the bottom surface of the dissolution tank 11 facing upward, a nuclear fuel supply port 13 provided in the uppermost reaction chamber 15a, and a lowermost reaction chamber 15e. And a nitric acid supply means 16 for supplying nitric acid to the reaction chambers 15a to 15e.
Gas introducing means 19 provided in the reaction chambers 15a to 15e for introducing gas into the reaction chambers and stirring the nitric acid solution, and temperature control means 22 for controlling the temperature of the reaction chambers 15a to 15e.
And a melting device for nuclear fuel. Its characteristic structure
Has a bottom surface 11a where the dissolution tank 11 is inclined and
Nuclear fuel is flat and has a thickness that does not make it critical.
A plurality of reaction chambers 15 a to 1 of the dissolution tank 11 formed by being closed.
5e on the bottom surface 11a of each of the reaction chambers 15a-15e
Residue removal pipe for removing undissolved residue of nuclear fuel that has settled to the bottom
17 is connected via a valve 24, and the lowest reaction chamber 1
From the upper side to the lower side in the reaction chambers 15a to 15e except 5e.
The nitric acid solution from the upper reaction chamber to the lower reaction chamber.
An upper partition plate 18 is installed to prevent gating and
Waste gas discharge means for discharging waste gas from the chambers 15a to 15e
21 is provided.

When the nuclear fuel supplied to the supply port 13 is made into a slurry in which nuclear fuel powder and water are kneaded, the reaction chamber 1
5a is preferable because no dust is generated and troubles due to blockage of the nuclear fuel supply port 13 are reduced. In addition, when NOx gas is introduced into each reaction chamber instead of air as a gas for stirring the nitric acid solution in the reaction chamber, the dissolution reaction is promoted in addition to the stirring effect, and iodine is expelled, which is preferable. .

[0007]

[Operation] The nuclear fuel supplied from the supply port 13 is the melting tank 11
Dissolved in nitric acid stored in the reaction chambers 15a to 15e.
The nitric acid-dissolved liquid flows from the upper reaction chamber to the lower reaction chamber without being short-passed by the upper partition plate 18 and given sufficient reaction time with the lower partition plate 12 to be discharged from the discharge port 14. To be done. Reaction chambers 15a-15
The nitric acid solution of e has its nitric acid concentration adjusted by the nitric acid supplied from the nitric acid supply means 16, and is stirred by the gas introduced from the gas introduction means 19. Also, the temperature control means 2
The reaction temperature is controlled by 2. The insoluble residue produced by the reaction is taken out by the residue take-out pipe 17, and the waste gas is discharged by the waste gas discharge means 21.

[0008]

An embodiment of the present invention will be described in detail with reference to the drawings. As shown in FIGS. 1 and 2, the dissolution tank 11 of the continuous processing apparatus has an inclined bottom surface 11a. Dissolution tank 1
1 is capable of storing a nitric acid solution of nuclear fuel and is formed in a flat plate shape having a thickness such that the stored nuclear fuel does not become critical. In this example, the thickness A (FIG. 2) is about 23 cm. The height B of the dissolution layer 11 is about 3 m and the length C is about 2 m (FIG. 1). In this example, four lower partition plates 12 forming five reaction chambers 15a, 15b, 15c, 15d and 15e are provided in the dissolution layer 11 vertically on the bottom surface 11a of the dissolution tank 11 at intervals. . These partition plates 1
2 has approximately the same height so that the nitric acid solution of nuclear fuel flows from the upper reaction chamber to the lower reaction chamber. A nuclear fuel chute 13a is provided above the uppermost reaction chamber 15a.
Is attached, and a supply port 13 is provided at the upper end of the chute. In this example, the nuclear fuel supplied to the supply port 13 is a slurry obtained by kneading nuclear fuel powder and water. A discharge pipe 14a for the nitric acid solution is attached to the upper part of the reaction chamber 15e located at the lowest position. The discharge pipe 14a has a discharge port 14.

A supply pipe 16 for nitric acid is provided outside the dissolution layer 11. The supply pipe 16 is introduced into the upper portions of the five reaction chambers 15a to 15e via the valve 23. Reaction chamber 15a
A residue extraction pipe 17 for extracting the undissolved residue of the nuclear fuel from the reaction chamber is connected to each bottom of each of ~ 15e via a valve 24,
It is arranged along the bottom surface of the dissolution tank 11. In the four reaction chambers 15a to 15d except the lowest reaction chamber 15e, four upper partition plates 18 are provided from the upper side to the lower side at intervals on the top surface of the dissolution tank 11. The lower ends of these partition plates 18 extend to a position lower than the upper ends of the lower partition plates 12 to prevent a short path of the nitric acid solution from the upper reaction chamber to the lower reaction chamber. Also, the reaction chambers 15a-1
5e is provided with a gas introducing pipe 19 penetrating each bottom thereof, and a gas ejecting portion 26 is provided at the end of the introducing pipe protruding into each reaction chamber.
Is connected. This gas introduction pipe 19 has NO in this example.
The x gas is pumped by a compressor (not shown). A waste gas discharge pipe 21 for discharging the waste gas generated by the reaction is connected to the top of the dissolution layer 11 above the reaction chambers 15a to 15e. Further, a heater 22a for raising the temperature of each reaction chamber is provided on the outer surface of the melting tank 11. The heater 22a is controlled by the controller 22 so that the temperature of the nitric acid solution is constant.

The operation of the apparatus thus configured will be described. First, an aqueous nitric acid solution adjusted to a predetermined nitric acid concentration is supplied to the reaction chambers 15a to 15e through the nitric acid supply pipe 16,
Store up to the water level shown. Also the controller 22
Controls the heater 22a to maintain the temperature of the reaction chambers 15a to 15e near the boiling point of the nitric acid aqueous solution. Next, the nuclear fuel powder is kneaded with water to form a slurry, which is supplied from the supply port 13 to the reaction chamber 15a. The nuclear fuel powder may be nuclear fuel scrap powder generated in the nuclear fuel manufacturing process, or nuclear fuel powder generated in the spent nuclear fuel reprocessing process. By converting the nuclear fuel powder into a slurry, the reaction chamber 1
No dust is generated at 5a, and the chute 13a is not clogged with the nuclear fuel powder.

The NOx gas pressure-fed to the gas introduction pipe 19 is introduced into the reaction chamber 15a from the gas injection portion 26, the nuclear fuel slurry and the nitric acid aqueous solution are agitated, and the nuclear fuel powder starts to dissolve. By introducing this NOx gas, iodine contained in the spent nuclear fuel can be expelled. If radioactive iodine is mixed with uranium or protonium extracted after this dissolution step, it will be difficult to handle uranium or protonium, and it will be converted into an undesired gaseous compound at the time of final calcination of reprocessing. Conventionally, an iodine purging tank was conventionally provided, but the introduction of this NOx gas makes the iodine purging tank unnecessary.

When the nitric acid concentration of the nitric acid solution changes due to the dissolution of the nuclear fuel powder, the valve 23 is opened and nitric acid is added to the nitric acid solution to adjust the concentration. The nitric acid solution flows from the reaction chamber 15a through the lower partition plate 12 into the reaction chamber 15b. Here, by the upper partition plate 18, the nitric acid solution does not short-pass from the upper reaction chamber 15a to the lower reaction chamber 15b, and the reaction is carried out for a sufficient time. Then, the nitric acid solution in an overflow state from the upper reaction chamber sequentially flows over the lower partition plate 12 and flows down to the lower reaction chamber. In this lower reaction chamber as well, as in the case of the upper reaction chamber, the NOx gas is introduced from the gas ejection portion 26 and the concentration thereof is adjusted by the nitric acid supplied from the supply pipe 16. The nuclear fuel powder is completely dissolved in nitric acid in the lowest reaction chamber 15e, and is discharged from the discharge pipe 14a. This device can continuously dissolve 4 tons of nuclear fuel per day. The undissolved residue settled in the reaction chambers 15a to 15e gathers at the outlet of the residue outlet pipe 17 by its own weight along the inclined bottom surface, and is intermittently opened through the outlet pipe 17 to the outside of the dissolution tank 11 by opening the valve 24 intermittently. Is discharged. The waste gas generated in the reaction chambers 15a to 15e is discharged through the discharge pipe 21.

In the above example, the nuclear fuel powder was previously kneaded with water to form a slurry, but if the dissolution treatment amount is small,
It is also possible to supply the powder as it is from the supply port without making it into a slurry. Moreover, although NOx gas was mentioned as a gas for stirring the nitric acid solution, if only for stirring,
It may be air. Further, although the heater and the controller are illustrated as the temperature control means, a cooling means for the nitric acid solution may be provided in addition to the heater in order to avoid an overheated state.

[0014]

As described above, the present invention has the following many excellent effects. Since the supplied nuclear fuel moves and is discharged from the upper reaction chamber to the lower reaction chamber in order of increasing solubility, the nuclear fuel can be continuously dissolved. Since the dissolved layer is a flat plate shape that does not make the stored nuclear fuel critical, there is no problem in criticality safety management. Even if the length C (Fig. 1) of the melting tank is extended, its thickness A
Since the criticality safety is maintained unless (Fig. 2) is changed, the length of the dissolution tank is changed and the number of reaction chambers is increased or decreased to create a continuous processing device that matches the residence time and processing capacity required for the dissolution reaction. Easy to make. The upper partition plate gives a sufficient reaction time in each reaction chamber until the nitric acid solution containing undissolved nuclear fuel powder flows into the lower reaction chamber without short-passing. Since the nitric acid concentration, the concentration or amount of air or NOx gas, or the temperature of the nitric acid solution of nuclear fuel can be controlled for each reaction chamber, the dissolution reaction in each reaction chamber can be accurately controlled. Since the dissolution tank has a sloping bottom surface, it is possible to easily and intermittently take out the settling undissolved residue from the bottom of each reaction chamber. The maintenance of the device is easy because there is no driving part as in the conventional continuous melting device. When the nuclear fuel is supplied to the reaction chamber in the form of a slurry in which nuclear fuel powder is kneaded with water, no dust is generated and troubles such as blocking the supply port are reduced. In the conventional reprocessing process, an iodine purging tank was installed next to the nuclear fuel dissolving device. However, if NOx gas is blown into the nitric acid dissolving liquid in the reaction chamber, iodine contained in the nuclear fuel can be expelled. It eliminates the need for iodine discharge tank.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a continuous melting apparatus for nuclear fuel according to an embodiment of the present invention.

FIG. 2 is a sectional view taken along the line DD.

[Explanation of symbols]

 11 dissolution tank 11a bottom surface of dissolution tank 12 lower partition plate 13 supply port for nuclear fuel 14 discharge port for nitric acid dissolved solution 15a to 15e reaction chamber 16 nitric acid supply pipe (nitric acid supply means) 17 residue extraction pipe (residue extraction means) 18 upper partition Plate 19 Gas introduction pipe (gas introduction means) 21 Waste gas discharge pipe (waste gas discharge means) 22 Controller (temperature control means) 22a Heater

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-63-61194 (JP, A) JP-A-1-141399 (JP, A)

Claims (3)

(57) [Claims] 1. A dissolution tank capable of storing a nitric acid solution of nuclear fuel (1
1) and a plurality of reaction chambers (15a, 15b, 15c, 15) inside the dissolution tank (11).
d, 15e), and a lower partition plate (12) provided upward on the bottom of the dissolution tank (11) so that the nitric acid solution flows from the upper reaction chamber to the lower reaction chamber. A supply port (13) for the nuclear fuel provided in the reaction chamber (15a) located at the top, and a discharge port (14) for the solution provided in the reaction chamber (15e) located at the bottom, Nitric acid supply means (16) for supplying nitric acid to the reaction chamber (15a, 15b, 15c, 15d, 15e), and the reaction chamber (15a, 15b, 15c, 15d, 15e) is provided, the reaction chamber is a gas Dissolution of nuclear fuel provided with gas introduction means (19) for introducing and stirring the nitric acid solution, and temperature control means (22) for controlling the temperature of the reaction chambers (15a, 15b, 15c, 15d, 15e) In the device, the melting tank (11) has an inclined bottom surface (11a) and
Nuclear fuel is flat and has a thickness that does not make it critical.
A plurality of reaction chambers (15a, 15b, 15c, 15d, 15e) of the dissolution tank (11) that are formed by being closed.
On the bottom surface (11a) of each of the reaction chambers (15a, 15b, 15c, 15d,
Take out the undissolved residue of the nuclear fuel settled at the bottom of 15e)
The residue extraction pipe (17) is connected through a valve (24), and the reaction chambers (15a, 15b, 15c, 15) except the lowest reaction chamber (15e) are connected.
d) Inside the upper reaction chamber from the upper reaction chamber to the lower reaction chamber
The upper part that prevents the short path of the nitric acid solution to the reaction chamber
A partition plate (18) is provided to discharge waste gas from the reaction chambers (15a, 15b, 15c, 15d, 15e).
An apparatus for continuously melting nuclear fuel, characterized in that a waste gas discharge means (21) is provided. 2. The continuous melting apparatus for nuclear fuel according to claim 1, wherein the nuclear fuel supplied to the supply port (13) is a slurry prepared by kneading nuclear fuel powder and water. 3. The continuous melting apparatus for nuclear fuel according to claim 1, wherein the gas introduced into the reaction chamber by the gas introducing means (19) is air or NOx gas.