JPS61144597A - Square cylindrical body for absorbing neutron - Google Patents

Abstract

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

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a neutron absorbing rectangular cylinder with excellent neutron absorbing ability used in a spent fuel storage rack.

[Technical aspects of the invention and its problems] The rectangular cylindrical body for a spent fuel storage rack for a nuclear reactor, which uses both a conventional neutron absorbing material and a strength member, has a vertical length as shown in Fig. 5. It is formed of an inner cylinder 1 and an outer cylinder 2 with a square cross section, and a neutron absorbing material 3 is inserted between the inner cylinder 1 and the outer cylinder 2.

Spacers 4 are interposed at the four corners. The inner cylinder 1 and outer cylinder 2 in this rectangular cylinder each have strict dimensional tolerances and have poor workability. Moreover, the neutron absorbing material 3 does not contribute to the strength of the cylinder. As a result, the wall thickness of the rectangular cylinder increases and the space factor increases, making it difficult to achieve high density as a fuel storage rack.
However, it has the disadvantage that the Ic weight is heavy.

In a nuclear couplant, spent fuel removed from a nuclear reactor core is temporarily stored until it is reprocessed. In recent years, in order to effectively utilize the space within a spent fuel pool (hereinafter referred to as a pool), improvements have been made to narrow the spacing between stored fuels, and racks based on this idea are referred to as high-density racks. It is necessary to form the storage rack in such a structure that the fuel does not reach criticality due to mutual influence, but in order to narrow the distance between the fuels to be stored, as mentioned above, there is a neutron absorbing structure between the inner cylinder 1 and the outer cylinder 2. Material 3 is being inserted.

Also, storage racks are for storing fuel, so
It is also an important piece of equipment from the standpoint of earthquake resistance, and must have sufficient strength. However, as is clear from Fig. 5, in the conventional storage rack, the neutron absorbing material 3 is inserted between the inner cylinder 1 and the outer cylinder 2, so the wall thickness of the rectangular cylinder becomes large and the density is high. High density racks cannot be expected.

It is also possible to construct the rectangular tube using an alloy itself containing an element with a large neutron absorption cross section, but this type of alloy is generally brittle and has low elongation, making it extremely difficult to form it into a rectangular tube. It has drawbacks such as being difficult.

[Objective of the Invention 1 The object of the present invention has been made to solve the above-mentioned drawbacks, and has excellent workability and weldability, does not cause crevice corrosion, has sufficient strength, and can be easily thinned. An object of the present invention is to provide a neutron absorbing rectangular cylinder suitable for a spent fuel storage rack that can be made to have a high density.

[Summary of the Invention] The neutron absorbing rectangular cylinder of the present invention is formed by rolling cladding of austenitic stainless steel with an alloy added with an element having a large neutron absorption cross section so that the austenitic stainless steel is on the outside. It is characterized by

The alloy that serves as the neutron absorber is subject to compression during bending, making it less likely to crack. Furthermore, since the alloy serving as the neutron absorbing material and the austenitic stainless steel are metallically bonded by rolling, no gaps are created, so there is no concern about selective corrosion in this part.

Furthermore, since the neutron absorbing material is an alloy that contributes to strength, there is no need to increase the wall thickness of the rectangular cylinder, and as a result, it is possible to significantly increase the density of the rack.

Elements with large neutron absorption cross sections include hafnium,
There are europium, etc., but boron is preferable because it is available at low cost. In addition, as an alloy to which these elements are added, N
There are i-base alloys, austenitic stainless steels, etc.
It is desirable to choose austenitic stainless steel from the viewpoints of workability, corrosion resistance, and price of the rolled clad steel plate.

By selecting the amount of boron added to the austenitic stainless steel to be 1% or more, it is possible to obtain the thinner thickness necessary to maintain subcriticality.

[Embodiment of the Invention] An embodiment of the neutron absorbing rectangular cylinder according to the present invention will be described below with reference to FIGS. 1 to 4.

FIG. 1 shows a cross section of a rectangular cylinder according to the present invention.
The outer tube 05 of the vertical tube is made of austenitic stainless steel (hereinafter referred to as 304), and the vertical inner tube 6 is made of boron-added austenitic stainless steel (hereinafter referred to as 304B). Both of these are formed into a rectangular tube shape using rolled clad steel plates.

304B is 8-14% Ni, 16-20% by weight
Boron (8) in 304 consisting of Cr remainder Fe and impurities
2% by weight was added. Clad steel plates are made by cleaning the surfaces of these 304 plates and 304B plates, and then
Laminated, each end sealed by welding, 900~i, os
It is rolled to a desired thickness at a temperature range of 0°C.

The rectangular cylinder is formed by bending this rolled clad steel plate into desired dimensions as shown in FIG. 2, which shows only one corner. If the ductility of the 304B portion is insufficient during bending, a groove 7 is previously formed in the inner cylinder 6 material of 304B as shown in FIG. 3 before bending. This groove 7 allows easy bending.

When a rack is constructed by stacking rectangular cylinders formed in this manner, sufficient neutron absorption capacity must be maintained to prevent the fuel from reaching criticality. A- Containing a large amount of boron in stenitic stainless steel reduces ductility and is not preferable from the viewpoint of workability. It has to be bigger.

However, increasing the plate thickness too much goes against the trend of increasing rack density as described above. Therefore, in the present invention, this problem is solved by cladding the high boron-containing 304B with ordinary boron-free 304 which has good workability.

The neutron absorption capacity of boron-added stainless steel exhibits the characteristics shown in FIG.

In addition, in the figure, a indicates 0% boron content, and b indicates 0%.
．． 5% by weight, C is 1.0% by weight, d is 1.5% by weight, and e is 2.0% by weight.

As is clear from this figure, it is recognized that the plate thickness can be made thinner by increasing the boron content.

If the boron content is less than 1%, the plate thickness for maintaining subcriticality is too thick, and the effect of increasing density is small. Therefore, it is desirable that the boron content of 304B, which is a cladding, is 1% or more.

In addition, in this example, the boron content is 2%,
The plate thickness of 304B is 2.8 mm.

When constructing a spent fuel rack from rectangular cylinders, it is necessary to stack the rectangular cylinders and attach a bottom plate and reinforcing beams, but if the cladding is made of 304, which has good weldability, these parts can be welded to form the fuel rack. It is possible to assemble.

Note that in the conventional triple structure shown in Fig. 5, the outer cylinder 2, neutron absorber 3, and inner cylinder 1 are not connected, and in order to ensure sufficient strength, the inner cylinder 1 and the outer cylinder 2 must be connected. It needed to be somewhat thicker. In contrast, in the present invention, the neutron absorbing material, that is, 304B, and the base material 304 are integrally bonded with each other through complete metal bonding, so that the overall thickness can be reduced.

[Effects of the Invention] As described above, according to the present invention, the rectangular cylinder constituting the fuel storage rack for a nuclear reactor is formed from a steel plate rolled and clad with 304B added with an element having a large neutron absorption cross section. By doing so, the workability and weldability of the rectangular cylinder are improved, and the groove can be made smaller and smaller, and a rectangular cylinder for neutron absorption suitable for a high-density fuel storage rack can be provided.

Note that the present invention is not limited to the above embodiments, but includes, for example, 3
Effects similar to those of the above embodiment can also be obtained by forming a rectangular tube from steel plates laminated with 048 alloy in the form of a sandwich inch and rolled and clad.

Further, the austenitic stainless steel used in the present invention is not limited to 304 described in the embodiment.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing an embodiment of the rectangular tube for neutron absorption according to the present invention, and FIG. 2 is a partial cross-sectional view showing an enlarged view of the rectangular tube shown in FIG. 1 with its corners bent. , Fig. 3 is a partial cross-sectional view showing the state of the crat plate in Fig. 2 before bending, Fig. 4 is a characteristic diagram showing the relationship between the amount of boron added to austenitic stainless steel, plate thickness, and neutron absorption capacity. FIG. 5 is a cross-sectional view showing a conventional neutron absorbing rectangular cylinder. 1...Inner tube 2...Outer tube 3...Neutron absorbing material 4...Spacer 5 ......Austenitic stainless steel outer cylinder 6...Boron-added austenitic stainless steel inner cylinder 7...Full

Claims (3)

[Claims] (1) Austenitic stainless steel is laminated on one side of an alloy plate containing an element with a large neutron absorption cross section to form a rolled cladding, and from this rolled cladding, an alloy plate containing an element with a large neutron absorption cross section is placed on the inside. A rectangular cylinder for neutron absorption, characterized in that it is formed into a rectangular cylinder shape. (2) The rectangular cylinder for neutron absorption according to claim 1, wherein the alloy to which an element having a large neutron absorption cross section is added is an austenitic stainless steel to which boron is added. (3) The rectangular cylinder for neutron absorption according to claim 1, wherein the boron content of the austenitic stainless steel is 0.1% or more by weight.