JPH0465999B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a spent nuclear fuel melting location, and in particular, to a spent nuclear fuel melting location that is improved so that the distribution of an acid solution for dissolving the spent nuclear fuel is smooth. Regarding equipment.

[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 travels 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 ₂ +2HNO ₃ +1/2O ₂ →UO ₂ (NO ₃ ) ₂ +H ₂ O Although not shown, the slab 16 includes a means for extracting the acid solution in which the nuclear fuel is dissolved, a means for supplying a new acid solution, and a means for supplying the new acid solution. A means for extracting soluble sludge is installed. Uranium oxide nuclear fuel is usually inserted into pipes made of stainless steel, etc.
This cutting waste and insoluble 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 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 a very small slope, which causes the problem that sludge tends 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 that has 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, etc., the melting tube 12
The communication pipe 18 between the slab 16 and the slab 16 is a straight pipe or a straight pipe shape, and the communication pipe 18 is installed at an angle.

In the first invention, as shown in FIG. 1, the lower communication pipe 18 is provided with a downward slope from the slab 16 toward the melting tube 12, and the liquid is passed from the slab 16 to the melting tube 12. flows towards. Further, a gas blowing pipe 26 is provided at the bottom of the melting pipe 12.
is provided at the lower part of the melting tube 12,
A sludge receiver 34 is provided at a position below the connection position of the lower communication pipe 18.

In the second invention, as shown in FIG. 3, the liquid flows from the slab 16 toward the dissolution tube 12 in the lower communication tube 18.

Further, a gas blowing pipe 26 is provided at the lower part of the melting pipe 12 or the lower communication pipe 18, and the slab 16 is provided with a gas blowing pipe 26.
A sludge collection part 16a is provided at a lower part or lower part of the sludge collection part 16a, which is below the connection position of the communication pipe 18.

[Function] When gas is blown from the lower part of the melting tube 12, the gas rises in the melting tube 12, and along with this, the melting tube 1
The acid solution in 2 flows upward, and after dissolving the uranium oxide in the spent nuclear fuel on the way, it flows through the communication pipe 2.
2 and enters the slab 16. Within the slab 16, the acid solution flows downward and from the communication pipe 18 to the melting pipe 1.
2 Return to the bottom.

In the spent nuclear fuel melting apparatus of the present invention, the communicating pipe 18 is installed as a straight pipe or in the shape of a straight pipe and inclined, and there is no part with a small slope as in the conventional case. is not accumulated.

In the first invention, the liquid containing sludge descends in the lower communication pipe 18 and changes its direction directly upward when it enters the melting pipe 12. At this time, the sludge contained in the liquid efficiently settles downward and falls into the sludge receiver 34 at the bottom of the dissolving tube 12. Therefore, the sludge is reliably separated from the liquid and the liquid is circulated smoothly.

In the second invention, before the liquid enters the lower communication pipe 18 from the slab 16, the sludge in the liquid settles and falls into the sludge collection part 16a, and the sludge is reliably collected in the collection part 16a. . Therefore, the amount of sludge entering the lower communication pipe 18 is reduced, and the accumulation of sludge in the lower communication pipe 18 can be further reduced.

[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 tapered portion 12a is provided at an intermediate level on the inner circumferential surface of the melting tube 12, and the housing 1
4 is hooked to this tapered portion 12a. A gas blowing pipe 26 is connected to the lower part of the melting pipe 12 .

The housing 14 may be a low cylindrical body made of acid-resistant wire mesh made of stainless steel or the like, or a low cylindrical body with a number of holes bored in the peripheral wall surface and the bottom surface, etc. In short, the liquid can be absorbed into 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.

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 pipe 24 is provided at a level above the melting tube 12, and the communication pipe 22 is provided at a level slightly above the top of the housing 14.

In this embodiment, jackets 28, 30, and 32 are provided on the side circumferential surface of the dissolution tube 12, and cooling water or heated water is passed through the jackets 28, 30, and 32 to cool or heat the acid solution or gas as required.

Further, a cup-shaped sludge receiver 34 is inserted into the bottom of the dissolving tube 12 in order to make it easier to take out the settled sludge.

In this embodiment, the slab 16 is cylindrical,
Its lower part is tapered, and a communicating pipe 18 is connected to the bottom of this slab 16. This slab 16 is also provided with a jacket 35, and cooling water or heating water is supplied as necessary to cool or heat the acid solution. In addition, a drain pipe 3 is installed on the slab 16.
6 and an exhaust gas pipe 38 are provided.

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 melting pipe 12, the acid solution rises inside the melting pipe 12, and the casing rises. 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 then supplied to the slab 1 from the communication pipe 22.
The sludge enters the melting tube 12 through the communicating tube 18 and settles in the sludge receiver 34 at the bottom of the melting tube 12. (Please note that slab 16
A portion of the acid solution that has entered is drained from the slab 16 by a drain 36 and replaced with fresh acid solution. ) Furthermore, the gas desorbed from the acid solution in the dissolution tube 12 enters the slab 16 through the communication pipe 24, and is discharged from the exhaust gas pipe 38 together with the gas desorbed from the acid solution in the slab 16, to the exhaust gas treatment system. Sent.

In this first embodiment, since the communication pipe 18 slopes downward from the slab 16 toward the melting pipe, almost no sludge accumulates in the communication pipe 18. In the present invention, the communication pipe 18 may be provided so as to have a downward slope from the melting pipe 12 to 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.

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

In this embodiment, the bottom of the slab 16 is squeezed into a cone shape to form a thin tube-shaped sludge collection portion (hereinafter referred to as "the thin tube") 16a that extends downward, and the lowermost end of the thin tube 16a A sludge extraction pipe 40 is connected to.

The other end of this sludge extraction coffin 40 is connected to a separator 44 whose inside is kept under negative pressure by an ejector 42.
The sludge settled in the slab 16 is extracted from the sludge extraction pipe 40 together with the acid solution, introduced into the settling tank 46 through the separator 44, and settled at the bottom thereof. The acid solution, which is the supernatant liquid in the sedimentation tank 46, is introduced into the lower part of the thin tube 16a through a pipe 48. In this way, the acid solution is poured into the capillary tube 16.
The sludge is introduced into the thin tube 16a by reducing the concentration of the sludge in the thin tube 16a or loosening the sludge so that the sludge that has settled in the thin tube 16a can be smoothly extracted into the sludge extraction tube 40. This is to do so. (Note that fresh water or air may be blown in instead of the recovered acid solution.) In the figure, 50 is a condenser that cools the working fluid of the ejector 42, and the condensed liquid flows from the separator 52 to the piping 54. The gas enters the sedimentation tank 46 through the pipe 5.
6 to the gas processing system.

Note that the sludge extraction pipe 41 may be inserted from the upper part of the slab 16, as shown by the two-dot chain line in FIG.

FIG. 4 shows the main parts of a third embodiment of the present invention.

In this embodiment, a perforated tube 58 is installed upright in the casing 14 inserted into the dissolving tube 12, and the lower end of the perforated tube 58 is opened at the bottom of the casing 14, and the upper end of the perforated tube 38 is opened at the bottom of the casing 14. is sealed with a plug 60.

In the spent nuclear fuel dissolution tube according to this embodiment, a part of the acid solution flowing upward in the dissolution tube 12 enters the casing 14 from the lower part of the casing 14. The remainder of the acid solution enters the porous tube 58 from the lower end opening of the porous tube 58 and flows upward. On the way, it passes through holes in the peripheral wall of the porous tube 58 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 circulated to the slab 16 through the communication pipe 22, as in the above embodiment.

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 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. 6 shows the main parts of a spent nuclear fuel melting apparatus according to a fifth 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 the housing step portion 14d is hooked onto this ring 13, so that the housing 14 is held within 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. 6, 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 58. 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.

In the embodiment of FIGS. 4-6, the upper end of the perforated tube 58 is sealed with a plug 60. In the embodiment of FIGS. This means that the acid solution rising inside the porous tube 58
This is to allow the spent nuclear fuel to pass through the holes in the peripheral wall of No. 8 and evenly flow into the housing 14, but if the spent nuclear fuel is also charged to the upper part of the porous pipe 58, as long as such an inflow is ensured, Small holes may be drilled in the plug 60 to allow some of the acid solution in the perforated tube 58 to flow through the holes in the plug 60 and onto its top.
That is, the upper end of the porous tube 58 may be sealed, or the opening area may be smaller than that of other portions of the porous tube 58.

FIG. 7 is a longitudinal sectional view of a spent nuclear fuel melting apparatus according to a sixth embodiment of the present invention.

In this embodiment, a plurality of (two in the illustrated example)
) melting tubes 12, 12 are installed. The bottom surface of the slab 16 is inclined toward the center, and a vertical pipe 62 is connected to the bottom thereof, and a sludge collecting section 64 is provided at the lower end of this vertical pipe. That is, a collection can having a large diameter part 64a, a tapered part 64b, and a small diameter part 64c is used, and the large diameter part 64a is connected to the vertical pipe 62.
is fixed so as to cover the lower part of the vertical pipe 62, and a gap is formed between the lower end edge of the vertical pipe 62 and the tapered part 64b of the collecting can.
A liquid introduction pipe 66, a sludge extraction pipe 68, and a gas blowing pipe 70 are provided at the lower part of the narrow diameter portion 64c.

Thus, the straight communicating pipe 18 has a large diameter portion 64a.
and the bottom of the melting tube 12, and is installed so as to slope upward from the large diameter portion 64a toward the communicating tube 12. A gas blowing pipe 26 is installed in the middle of this communication pipe 18.

When gas is blown from the gas blowing pipe 26, the bubbles rise in the communication pipe 18 and the dissolution pipe 12, and along with this, the acid solution also rises in the communication pipe 18 and the dissolution pipe 20, dissolving the nuclear fuel. Then, it enters the slab 16 from the communication pipe 22, then enters the vertical pipe 62, goes around the lower edge of the vertical pipe 62, and enters the large diameter part 64.
a and is introduced into the communication pipe 18 again.

As the lower edge wraps around, the sludge in the acid solution is separated from the liquid and settles to the bottom of the collecting can.

This settled sludge is removed by the gas and liquid introduced into the bottom of the collection can by the gas blowing pipe 70.
Due to the stirring effect of the liquid introduced from 6, the sludge is loosened and extracted from the sludge extraction pipe 68.

Note that the other parts in FIG. 7 can adopt any of the configurations of the embodiments in FIGS. 1, 3 to 6, and the same effects can be obtained.

[Effects] As described above, according to the present invention, sludge does not accumulate in the communication pipe between the melting pipe and the lower part of the slab, the acid solution flows smoothly, and good operation can be performed at all times. .

[Brief explanation of the drawing]

1, 3, 4, and 7 are vertical sectional views showing a spent nuclear fuel melting device according to an embodiment of the present invention, FIG. 2 is a vertical sectional view showing a conventional example, and FIG. 5 and FIG. 6 are sectional views of main parts according to different embodiments of the present invention. 12...Dissolution tube, 14...Casing, 16...Slab, 18, 20, 22, 24...Communication tube, 26...
...Gas blowing pipe, 28,64...Sludge collection section,
28, 30, 32, 35...Yatsuketo, 58...
... Porous pipe, 60 ... Plug, 40, 41 ... Sludge extraction pipe, 42 ... Ejector, 46 ... Sedimentation tank.

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 slab that is installed vertically adjacent to the melting tube. , communicating the lower part of the melting tube and the lower part of the slab,
A straight pipe or a substantially straight lower communicating pipe through which liquid flows from the slab toward the melting tube, and at least one communicating pipe that communicates the melting pipe with the slab at a level above the lower communicating pipe. In the spent nuclear fuel melting apparatus, a gas blowing pipe is connected to the lower part of the melting pipe, and the lower communication pipe is installed so as to slope downward from the slab toward the melting pipe. A spent nuclear fuel melting apparatus characterized in that a sludge receiver is provided at a lower part of the melting pipe and below a connection position of the lower communication pipe. 2. A melting tube that is installed vertically and has a housing for holding spent nuclear fuel to be melted inside it, a slab that is installed vertically adjacent to the melting tube, and a lower part of the melting tube. and the bottom of the slab,
A straight pipe or a substantially straight lower communicating pipe through which liquid flows from the slab toward the melting tube, and at least one communicating pipe that communicates the melting pipe with the slab at a level above the lower communicating pipe. In the spent nuclear fuel melting apparatus, a gas blowing pipe is connected to a lower part of the melting pipe or a lower communication pipe, and the lower communication pipe is installed at an angle, and the lower part of the slab is connected to the lower part of the slab. An apparatus for melting spent nuclear fuel, characterized in that a sludge collection section is provided at a position below the connection position of the lower communication pipe.