JPH0431792A - Ring shaped storage tank of nuclear fuel material and its neutron shielding body - Google Patents

Abstract

PURPOSE:To enable easy manufacturing of a ring shaped storage tank of nuclear material solution in short time by filling a plurality of polyethelene blocks for neutron shielding inside an inner cylinder of main body of the tank which stores the nuclear fuel material solution. CONSTITUTION:a ring shaped storage tank 10 in this invention, consists of a main body of the ring shaped storage tank formed by an inner cylinder 12, an outer cylinder 14 and a bottom plate 16, and a neutron shielding body which is filled into an inside of the inner cylinder 12. A solution state nuclear fuel material 20 is stored in a ring shaped space of a main body of the ring shaped storage tank. This neutron shielding body consists of a plurality of polyethelene blocks 22 having outer shape corresponding to breadthwise cross-sectional shape of the inner cylinder 12. Since the polyethelene has the same or much more hydrogen atom content than a paraffin, enough neutron shielding effect can be expected. The polyethelene blocks shield neutrons generated from the stored nuclear fuel material stored at the ring shaped part of the ring shaped storage tank, and therewith criticality can be well prevented.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an annular storage tank for storing nuclear fuel material in solution form;
and a neutron shield made of a polyethylene block filled in the center thereof.

[Prior art] In order to prevent criticality when storing nuclear fuel material in solution form,
A container filled with neutron shielding material is used inside the inner cylinder of the annular storage tank. In the prior art, paraffin was used as this neutron shielding material.

In order to fill the inner cylinder of the annular storage tank with paraffin, paraffin blocks are heated and melted, and the paraffin blocks are poured into the inner cylinder of the annular storage tank and cooled and solidified.
Since it is necessary to prevent any air bubbles from remaining inside, a small amount of molten paraffin is poured into the inner cylinder of a heated annular storage tank, and the process of gradually cooling and solidifying is repeated until the top of the inner cylinder is filled. The production process is extremely complicated.

[Problem B to be Solved by the Invention] The above-mentioned conventional techniques usually have the disadvantage that manufacturing takes a long time (about two weeks). Furthermore, since the entire annular storage tank must be heated, the production equipment becomes large-scale, and there are manufacturing problems in that it is difficult to fill paraffin without missing parts.

Furthermore, when cutting the annular storage tank body with an electric nibbler or the like during disassembly, there was a risk that the paraffin would catch fire due to the sparks generated.

The purpose of the present invention is to solve the above-mentioned drawbacks of the prior art, to create a nuclear fuel material that can be easily manufactured in a short period of time, allows checking for defects in the neutron shield in advance, and can be easily dismantled. An object of the present invention is to provide an annular storage tank and a neutron shield for use therein.

[Means for Solving the Problems] In order to achieve the above object, the present invention uses a polyethylene block as a neutron shield. That is, the present invention is an annular storage tank for nuclear fuel material in which a plurality of polyethylene blocks for neutron shielding are densely packed inside the inner cylinder of an annular tank main body for storing nuclear fuel material in solution form. It is desirable that the polyethylene blocks have an outer shape that matches the cross-sectional shape of the inner cylinder, and that they can be stacked in multiple stages.

[Working copolyethylene has a hydrogen atom content equal to or higher than that of paraffin, so it has a sufficient neutron shielding effect. The polyethylene block blocks neutrons generated from the nuclear fuel material stored in the annular part of the annular storage tank and prevents criticality.

[Example] Fig. 1 is an exploded perspective view showing an embodiment of an annular storage tank according to the present invention, and Fig. 2 is a longitudinal sectional view.

This annular storage tank 10 includes an inner cylinder 12, an outer cylinder 14, and a bottom plate 1.
It consists of an annular tank main body 18 consisting of 6, and a neutron shielding body filled inside the inner cylinder 12. Nuclear fuel material 20 in solution form is stored in the annular space of the annular tank body 18 .

The present invention is significantly different from the prior art in the material and structure of the neutron shield filled in the inner cylinder 12. This neutron shield consists of a plurality of polyethylene blocks 22 having an outer shape that matches the cross-sectional shape of the inner cylinder 12.

Here, three through holes 24 are formed in the polyethylene block 22, and about three polyethylene blocks 22
are combined with polyethylene bolts 26, stacked in multiple stages, and filled into the inner cylinder 12. The polyethylene block 22 is manufactured into a predetermined shape by machining.

In FIG. 2, reference numeral 28 indicates an inlet nozzle for nuclear fuel material, and reference numeral 30 indicates an outlet nozzle.

The reason why a plurality of polyethylene blocks are combined as described above is that there is a limit to how many polyethylene blocks can be manufactured without causing defects. This limit depends primarily on the volume of the polyethylene block to be manufactured. With current technology, for example, the diameter is 450■
In this case, the height limit is about 700 cm. The larger the diameter, the lower the height limit.

The number density of hydrogen atoms in paraffin is 8.01×10°/
CC, whereas that of polyethylene is 8.63X
1 ton of nuclear fuel in solution form with 10" particles/cc, which has performance equivalent to or better than paraffin, and has a sufficiently large neutron shielding effect.
Since neutrons generated from 20 are shielded by the internal neutron shield, criticality accidents can be prevented from occurring.

According to the results of criticality safety analysis, it has been found that if the gap between the mating surfaces of the polyethylene blocks 22 is within about 1 mm, there will be no safety problem at all.

To further prevent neutron transmission through the gap, Figure 3A
, B, it is also effective to form concave grooves 32 and protrusions 34 that fit into each other at corresponding positions on the mating surfaces (upper surface and lower surface) of the polyethylene block 22.

Although the preferred embodiments of the present invention have been described above, the present invention is not limited to such a configuration.If the polyethylene block is small relative to the inner cylinder dimension of the annular tank, only the height direction can be used. In addition, multiple pieces are combined and filled into the inner cylinder even in the horizontal direction. However, it goes without saying that it is desirable to manufacture a polyethylene block as large as possible without causing defects. The shape of the polyethylene block can be changed as appropriate to match the shape of the inner cylinder of the annular tank body. The shapes of the concave portions and convex portions formed on the upper and lower surfaces may also be modified as appropriate.

[Effects of the Invention] As described above, the present invention has a structure in which a plurality of polyethylene blocks are combined as a neutron shield to be filled inside the inner cylinder of the annular storage tank, so that the following effects can be obtained. With the conventional structure of melt-filling paraffin, it took about two weeks to manufacture an annular storage tank, but with the present invention, polyethylene blocks can be manufactured by machining, so the annular storage tank can be manufactured in a short period of time (about two days). In the present invention, since it can be put in and taken out in the form of a block, there is no need to cut it when dismantling the annular storage tank, it can be easily dismantled by lifting it, and there is no risk of ignition due to sparks etc. during disassembly. Furthermore, since the appearance, dimensions, presence or absence of defective parts, etc. of the polyethylene block can be thoroughly inspected before filling, safety and reliability are improved.

[Brief explanation of the drawing]

Fig. 1 is an exploded perspective view showing an embodiment of the annular storage tank according to the present invention, Fig. 2 is a vertical sectional view after assembly, and Figs. 3 A and B.
is a perspective view showing another example of a polyethylene block. DESCRIPTION OF SYMBOLS 10... Annular storage tank, 12... Inner cylinder, 14... Outer cylinder, 16... Bottom plate, 18... Annular tank body, 20...
- Nuclear fuel material in solution form, 22... Polyethylene block, 26... Polyethylene bolt, 32... Concave groove, 34... Convex strip. Patent applicant: Power Reactor and Nuclear Fuel Development Corporation Representative, Shigeru Miyoshi Hito Figure 1 121!1 Figure 3

Claims (1)

[Scope of Claims] 1. An annular storage tank for nuclear fuel material in which a plurality of polyethylene blocks for neutron shielding are densely packed inside the inner cylinder of an annular tank main body for storing nuclear fuel material in solution form. 2. A neutron shield made of polyethylene blocks having an outer shape matching the cross-sectional shape of the inner cylinder of the annular storage tank according to claim 1, and stacked and filled in the inner cylinder. 3. The neutron shielding body according to claim 2, wherein recesses and projections that fit into each other are formed at corresponding positions on the upper surface and the lower surface.