JPH0467639B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a spent nuclear fuel melting device, and more particularly to a spent nuclear fuel melting device that has been improved so that spent nuclear fuel can be melted quickly.

[Prior Art] Conventionally, when dissolving spent nuclear fuel such as uranium oxide, the spent nuclear fuel is cut into short pieces and immersed in an acid solution such as nitric acid to dissolve the spent nuclear fuel.

FIG. 2 is a schematic cross-sectional view showing a conventional spent nuclear fuel melting device.

This spent nuclear fuel melting device consists of a cylindrical melting tube 12 and a casing 14 inserted into the melting tube 12. The casing 14 is porous, and is usually a cylindrical body made of wire mesh such as stainless steel, or a cylindrical body made of metal with a large number of holes. In each figure, the casing 14 is shown with a broken line to indicate that the casing 14 is porous.

A plurality of locations on the side surface of the melting tube 12 are connected to a liquid tank 16 called a slab through communication tubes 18, 20, 22, and 24. In addition, at the bottom of the dissolution tube 12,
An oxygen gas blowing pipe 26 is installed. and,
The melting tube 12 and the slab 16 are filled with an acid solution such as nitric acid.

When oxygen gas is blown from the blowing pipe 26, this gas rises in the melting pipe 12, and along with this, the liquid in the melting pipe 12 also rises and flows from the communicating pipe 22 to the slab 16.
It returns to the melting tube 12 through the communication tube 18 and circulates.

A portion of the liquid passes between the slab 16 and the melting tube 12 through a communication tube 20 installed at an intermediate level. The communication pipe 24 is for gas distribution,
Oxygen gas blown into the melting tube 12 from the blowing pipe 26 passes through the communication pipe 24 and enters the slab 16.

Spent nuclear fuel cut into short pieces is charged in the casing 14, and is gradually dissolved in an acid solution according to the following chemical reaction formula.

UO ₃ +2HNO ₃ +1/2O ₂ → UO ₂ (NO ₃ ) ₂ +H ₂ O Although not shown in the slab 16,
A means for extracting an acid solution in which nuclear fuel has been dissolved, a means for supplying a new acid solution, a means for extracting insoluble sludge, etc. are installed. Uranium oxide nuclear fuel is
Usually, it is inserted into a pipe made of stainless steel or the like, but the cutting waste and undissolved matter in the uranium oxide rod become sludge and are included in the acid solution.

Furthermore, the pipe itself into which the uranium oxide rod is inserted does not dissolve in the acid solution and remains in the case 14 even after the uranium oxide has dissolved, so after the melting is finished, the case 14 is pulled up and the remaining pipe is removed. Take it out.

[Problems to be solved by the invention] In the above-mentioned conventional spent nuclear fuel melting tube,
The acid solution entering the dissolution tube 12 from the communication tube 18 and rising therein passes through the bottom surface of the casing 14 and tries to rise further inside the casing 14 .

However, since a large amount of spent nuclear fuel that has been cut into short pieces is charged into the casing 14, even if an attempt is made to increase the rate of rise of the liquid by increasing the amount of oxygen gas blown, there is an upper limit to the amount of bubbles that can rise. However, it was not possible to inject more than a predetermined amount of oxygen gas.

Therefore, there is an upper limit to the flow rate of the acid solution that flows through the melting tube 12 and comes into contact with the spent nuclear fuel, resulting in the problem that it takes a considerably long time to melt the spent nuclear fuel.

In addition, in the above conventional example, the communication pipe 18 between the melting pipe 12 and the lower part of the slab 16 is curved, and there are parts where there is no slope or where the slope is extremely small.
Therefore, there was a problem that sludge was likely to accumulate.

[Means for Solving the Problems] In order to solve the above-mentioned conventional problems, the present invention provides that, as shown in FIGS. 1 and 3, the spent nuclear fuel casing to be melted is In a spent nuclear fuel melting device having a melting tube 12 charged into the melting tube 12 and a slab 16 connected to the melting tube 12 by a plurality of communication tubes 18, 22, 24, the slab 16 is cylindrical. Oxygen gas or a gas containing oxygen is blown into the bottom of the slab 16 to circulate the acid solution so that it flows upward within the slab 16 and flows downward within the melting tube 12. Also, the melting tube 12
A communication pipe 18 through which the liquid flows from the to the slab 16 is a straight pipe or a straight pipe shape, and the communication pipe 18 is installed at an angle. A sludge collection section 28 is provided connected to the lower part of the melting tube 12.

The bottom of the melting tube 12 is an opening, and a cylindrical container-like member 34 serving as a sludge collecting section 28 is fixed so as to cover this opening. The container-shaped member 34 consists of a large diameter part 34a, a small diameter part 34b, and a tapered part 34c, and a gap is formed between the tapered part 34c and the opening edge of the melting tube 12. Further, the upper end of the large diameter portion 34a is fixed to the lower outer peripheral surface of the melting tube. The communication pipe 18 is connected to this large diameter portion 3.
4a.

[Function] When the gas blown from the bottom of the slab 16 rises in the slab 16, the slab 16
The acid solution inside flows upward and enters the dissolution tube 12 through the communication tube 22. The acid solution flows downward in the melting tube 12, dissolves the uranium oxide of the spent nuclear fuel along the way, and after the sludge is separated in the sludge collection section 28, it returns into the slab 16 through the communication tube 18.

In the spent nuclear fuel melting apparatus of the present invention, gas is blown into the slab 16, so that a large amount of gas can be blown to increase the amount of acid solution circulated. Therefore, a large amount of acid solution comes into contact with the spent nuclear fuel, increasing the rate of dissolution of the spent nuclear fuel. Furthermore, since a large amount of gas is blown into the system, even if air is blown in instead of oxygen gas, the oxygen necessary for dissolving uranium oxide can be sufficiently supplied, and there is no need to use expensive oxygen gas.

In addition, the sludge that has come into contact with the spent nuclear fuel and is included in the liquid is immediately collected in the collection section located at the bottom of the melting tube 12, so the sludge content in the liquid is reduced. . Furthermore, since the communication pipe 18 is installed at an angle and there is no part with a small slope unlike the conventional system, sludge does not accumulate in the communication pipe 18.

[Example] Examples will be described below with reference to the drawings.

FIG. 1 is a schematic vertical sectional view of a spent nuclear fuel melting apparatus showing a first embodiment of the present invention.

In FIG. 1, a ring 13 is provided at an intermediate level on the inner circumferential surface of the melting tube 12, and a housing 14 is hooked onto this ring 13.

The melting tube 12 has its side surface connected to the slab 16 through communication tubes 18 , 22 , and 24 .
In this embodiment, the communication pipe 18 is a straight pipe, and is installed so as to have a downward slope from the slab 16 toward the melting pipe 12. The communication tube 24 is located at the upper level of the melting tube 12, and the communication tube 22 is connected to the housing 1.
4, respectively, at a level slightly above the top.

In this embodiment, jackets 30 and 32 are provided on the side circumferential surface of the dissolution tube 12, through which cooling water or heated water flows to cool or heat the acid solution as required.

In addition, a sludge collection section 2 is provided at the bottom of the melting tube 12.
8 is provided. The configuration of this collection section 28 will be explained next. The bottom of the dissolution tube 12 is an opening, and a cylindrical container-like member 3 is arranged to cover this opening.
4 is fixed. The container-shaped member 34 has a large diameter portion 3
4a, a narrow diameter portion 34b, and a tapered portion 34c, and a gap is formed between the tapered portion 34c and the opening edge of the melting tube 12. Further, the upper end of the large diameter portion 34a is fixed to the lower outer peripheral surface of the melting tube. The communication pipe 18 is connected to this large diameter portion 34a.

The acid solution flowing downward in the dissolution tube 12 is
The sludge goes around the opening edge of the lower end and enters the inside of the large diameter part 34a, and is separated when the acid solution goes around and settles at the bottom of the container-like member 34.

A cup-shaped sludge receiver 36 is inserted into the bottom of the container-shaped member 34 in order to facilitate taking out the settled sludge.

The housing 14 may be a bottomed cylindrical body made of acid-resistant wire mesh made of stainless steel or the like, or a bottomed cylindrical body with a number of holes bored in the peripheral wall surface and the bottom surface. A structure that can pass through and hold the cut pieces of spent nuclear fuel inside is used.

Further, the slab 16 is cylindrical, the lower part thereof is tapered, and the gas blowing pipe 26 is provided at the bottom of the slab 16. This slab 16 is also provided with jackets 42 and 44, and cooling or heating water is supplied as necessary to cool or heat the acid solution. Note that the slab 16 is provided with a drain pipe 46 and an exhaust gas pipe 48.

In the spent nuclear fuel melting apparatus according to the embodiment configured as described above, as the gas blown from the blowing pipe 26 rises inside the slab 16, the acid solution rises inside the slab 16 and flows from the communication pipe 22. It enters the melting tube 12, flows downward, flows into the casing 14, contacts the spent nuclear fuel in the casing 14, and the nuclear fuel is melted. Also, at this time, the sludge comes to be contained in the acid solution. This acid solution is collected in the collecting section 28.
After the sludge has been separated through the acid solution 18, it enters the slab 16 and is recycled. (Note that part of the acid solution that has entered the slab 16 is discharged from the slab 16 through the drain pipe 46, and new acid solution is supplied instead.) In addition, gas desorbed from the acid solution in the dissolution pipe 12 enters the slab 16 through the communication pipe 24 and is discharged from the exhaust gas pipe 48 together with the gas blown into the slab 16.

In this first embodiment, a straight communicating pipe 18 is shown, but in the present invention, a straight pipe, for example, a bent pipe in which a plurality of straight pipes are connected in a dogleg shape, may also be used. good. Even in this case, the pipe should be sloped along its entire length so that there are no areas with a small slope.

Further, in the present invention, the communication pipe 18 is arranged so that it has a downward slope from the melting pipe 12 toward the slab 16.
may be provided.

FIG. 3 shows the main parts of a spent nuclear fuel melting apparatus according to a second embodiment of the present invention.

In this embodiment, a perforated tube 38 is set upright in the casing 14 inserted into the dissolving tube 12, the upper end of the perforated tube 38 is opened at the upper part of the casing 14, and the lower end of the perforated tube 38 is opened at the upper part of the casing 14. is sealed with a plug 40. Further, the housing 14 is hooked onto a tapered portion 12a formed in the dissolving tube 12.

In the spent nuclear fuel melting tube according to this embodiment, a part of the acid solution flowing downward in the melting tube 12 enters the housing 14 from the upper part of the housing 14. The remainder of the acid solution enters the porous tube 38 from the upper end opening of the porous tube 38 and flows downward. On the way, it passes through holes in the peripheral wall of the perforated tube 38 and enters the housing 14 little by little. In this way, the spent nuclear fuel within the casing 14 comes into contact with the acid solution evenly, and the nuclear fuel is quickly dissolved.

The acid solution that has passed through the casing 14 and dissolved the nuclear fuel is separated into sludge in the collecting section 28 as in the first embodiment, and then passes through the communication pipe 18 to the slab 16.
is circulated.

FIG. 4 shows the main parts of a spent nuclear fuel melting apparatus according to a third embodiment of the present invention.

In this embodiment, the outer circumferential portion of the bottom surface of the housing 14 is tapered into a cone shape, and this tapered portion is engaged with the tapered portion 12a of the dissolving tube.
In this way, the housing 14 is stabilized and the melting tube 1
2.

FIG. 5 shows the main parts of a spent nuclear fuel melting apparatus according to a fourth embodiment of the present invention.

In this embodiment, the lower part of the housing 14 is a narrow diameter part 14a, and a stepped part 14d is formed at the boundary with the upper large diameter part 14b. A ring 13 is provided on the inner circumferential surface of the melting tube 12 , and a housing stepped portion 14 d is sealed in the ring 13 to hold the housing 14 inside the melting tube 12 .

Note that if the sloped portion 14c is provided on the upper surface side of the step portion 14d to form a cone shape, the spent nuclear fuel can be easily inserted into the narrow diameter portion 14a.

In the embodiment shown in FIG. 5, a large diameter portion 14b is provided, but this large diameter portion 14b is not provided, that is, the portion above the stepped portion 14d is eliminated, and instead, a wire is attached to the upper end of the porous tube 28. The housing 14 may be moved in and out of the melting tube 12 by connecting a thin rod or the like and pulling the wire or thin rod.

[Effects] As described above, according to the present invention, it is possible to increase the circulation amount of the acid solution, improve the contact between the acid solution and the spent nuclear fuel, and quickly dissolve the nuclear fuel. Moreover, sludge does not accumulate in the communication pipe between the melting pipe and the lower part of the slab. Furthermore, air can be used instead of the expensive oxygen gas.

[Brief explanation of the drawing]

1 and 3 are longitudinal sectional views showing a spent nuclear fuel melting apparatus according to an embodiment of the present invention, FIG. 2 is a longitudinal sectional view showing a conventional example, and FIGS. 4 and 5 are respectively in accordance with the present invention. FIG. 3 is a sectional view of a main part according to a different embodiment. 12...Dissolution tube, 14...Casing, 16...Slab, 18, 20, 22, 24...Communication tube, 26...
...Gas blowing pipe, 28...Sludge collection section, 30,
32, 42, 44... Jacket, 38... Porous pipe, 40... Plug.

Claims (1)

[Scope of Claims] 1. A melting tube that is installed vertically and has a casing for holding spent nuclear fuel to be melted inserted therein, and a cylindrical tube that is installed vertically adjacent to the melting tube. A lower communicating pipe that communicates the lower part of the melting tube with the lower part of the slab and allows liquid to flow from the melting tube to the slab, and communicates the melting tube and the slab at a level above the lower communicating pipe. A spent nuclear fuel melting device comprising at least one communication pipe, a gas blowing pipe connected to the bottom of the slab, and a sludge collection section connected to the bottom of the melting pipe. The lower communicating pipe is straight or almost straight,
The sludge collecting section has a substantially cylindrical shape with the cylindrical axis direction as the vertical direction, and has a large diameter part surrounding the outer periphery of the lower part of the melting tube, and a large diameter part surrounding the outer periphery of the lower part of the melting tube. a tapered part that continues to the lower end of the melting tube and whose diameter decreases downward; and a narrow diameter part that continues to the lower end of the tapered part, and the opening edge of the lower end of the melting tube and the tapered part are at the same height. A gap is formed between the tapered part and the opening edge at the lower end of the melting tube, and the upper end of the large diameter part is fixed to the outer peripheral surface of the lower part of the melting tube, and the lower communicating tube is connected to the large-diameter portion, a spent nuclear fuel melting device.