JPS63118693A - Spent fuel storage rack - Google Patents

Abstract

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

Description

Detailed Description of the Invention [Object of the Invention] (Industrial Application Field) The present invention relates to a spent fuel storage rack for storing spent fuel taken out from the core of a nuclear reactor, and particularly relates to a spent fuel storage rack for storing spent fuel taken out from the core of a nuclear reactor. This relates to a spent fuel storage rack with an improved rectangular cylindrical body that houses the spent fuel.

(Prior art) In general, in a nuclear power plant, a spent fuel storage rack is installed at the bottom of a fuel storage pool, and the spent fuel removed from the reactor core is stored in this rack and cooled, and its decay heat I am trying to remove it.

10 to 12 respectively illustrate conventional spent fuel storage racks, and the one shown in FIG. 10 has a plurality of rectangular cylinders 1 for storing spent fuel arranged in a lattice pattern. The bottom of each is welded to a rectangular plate-shaped base 2 to stand upright.

The outer periphery of the rectangular cylinder 1 placed on the outermost periphery of the base 2 is the upper part,
In the middle part, the lower part, and the like, reinforcing plates 3 in the shape of flat rectangular cylinders are welded and bundled into a bundle to be integrated.

The spent fuel storage rack shown in FIG. 11 has a plurality of rectangular cylinders 1 arranged vertically and horizontally in a staggered pattern on a rectangular plate-shaped base 2, and oriented toward the outermost periphery on the base 2. The openings on the outer surfaces between adjacent rectangular cylinders 1 are closed by vertical plates 5.

It is used within each rectangular cylinder 1, a rectangular cylindrical space surrounded by each rectangular cylinder 1, and a rectangular cylindrical space surrounded by each rectangular cylinder 1 and the vertical plate 5. fuel is stored.

In addition, an angle 6 is attached along the axial direction in the corner formed by the outer wall of the adjacent rectangular cylinder 1 phase U, as necessary, to enhance the bonding strength between the adjacent rectangular cylinders 1. ing.

The spent fuel storage rack shown in FIG. 12 has a plurality of rectangular cylinders 1 for storing spent fuel arranged in a lattice shape with required gaps in the vertical and horizontal directions, and their bottoms are fixed on a base 2. death,
The outer surfaces of each rectangular cylinder 1 are welded and integrated at the upper, middle, and lower parts by straight reinforcing plates 7.

The material of the conventional rectangular cylinder 1 of the spent fuel storage rack shown in FIGS. 10 to 12 is generally chromium 18
An austenitic stainless steel plate containing 8% nickel and 8% nickel is used.

That is, each rectangular cylinder 1 is a plate material 1 made of austenitic stainless steel and having a thickness of about 5 mm, as shown in FIG.
It is formed by forming a pair of sheets a and 1a, bending them into a mouth shape, and fixing the abutting portions 1b and ib of their end faces by welding.

(Problems to be Solved by the Invention) However, since such a conventional rectangular tube body 1 is made of an austenitic stainless steel plate, due to the characteristics of the material, its corrosion resistance against water and workability are limited. Although this is satisfactory, there are problems in that the neutron absorption capacity is small and the shielding effect of neutrons released from spent fuel is insufficient.

Therefore, in a conventional spent fuel storage rack incorporating rectangular cylinders 1, in order to enhance the neutron shielding effect between the spent fuel, for example, as shown in FIGS. As a result, there is a problem that the spent fuel storage rack becomes large and the spent fuel storage efficiency decreases.

Therefore, in recent years, in order to increase the storage density of spent fuel storage racks, austenitic stainless steel sheets doped with boron (10B), which has a high neutron absorption capacity, are used as the constituent material of the square cylinder 1, and boron carbide Methods are being considered that include using a material with an aluminum base material coated with aluminum, or using a neutron absorbing material made of an amorphous alloy containing boron and phosphorus.

However, boron-added austenitic stainless steels generally have poor weldability due to the appearance of polide (Fe1Cr)2B during welding, resulting in embrittlement (decreased elongation) of the welded part.

In addition, since amorphous alloys cannot be welded, they must be joined mechanically, supported by weldable materials such as stainless steel plates, and stainless steel plates can be joined together, or they can be welded. It is necessary to create a sandwich structure using materials, which increases the thickness of the material and prevents miniaturization and weight reduction.

Therefore, the present invention has been made in view of the above-mentioned circumstances, and an object thereof is to provide a spent fuel storage rack with significantly improved fuel storage density.

[Structure of the invention]

(Means for Solving the Problems) The present invention consists of a rectangular cylinder of a spent fuel storage rack made of hafnium plates with high neutron absorption capacity, thereby making the rectangular cylinder denser. It is configured as follows.

In a spent fuel storage rack provided with a plurality of rectangular cylinders for storing spent fuel, the rectangular cylinders are formed into a rectangular cylinder shape by a hafnium plate made of hafnium, and the welded portion of the hafnium plate is Welded by electron beam welding or laser beam welding.

(Operation) Spent fuel is stored inside each of the plurality of rectangular cylinders of the spent fuel storage rack.

These rectangular cylinders are made of hafnium plates with high neutron absorption capacity, so even when multiple rectangular cylinders are densely arranged, the spent fuel contained therein can be maintained in a subcritical state, and the spent fuel can be It is possible to increase the amount of melons stored in the fuel storage rack.

(Example) Embodiments of the present invention will be described below based on the drawings.

FIG. 1 is a perspective view of a rectangular cylinder incorporated in an embodiment of the present invention. In the figure, the rectangular cylinder 10 has a welded portion 11 of a pair of mouth-shaped hafnium plates 10a, 10a butted together. It is welded to form a rectangular cylinder.

That is, the hafnium plates 10a, 10a are made of hafnium (
Hf ) is formed into a plate shape with a thickness of, for example, about 2.5rItlR, and then each is bent into a cross-sectional shape, and the U-shaped end surfaces of these hafnium plates 108° 10a are butted against each other, The welded portion 11 on the outer surface of this abutting surface is electron beam welded or laser beam welded in a vacuum to form the rectangular tube body 10.

Although hafnium does not necessarily have a large thermal neutron absorption cross section, it has many absorption peaks in the resonance energy region, so it has properties suitable as a neutron absorbing material for the prismatic cylinder 10 that stores spent fuel.

Figure 2 shows hafnium plate 1 with a thickness of 5 m. The neutron absorption characteristics of Oa and 10a are shown by solid lines, and the neutron absorption capacity of these hafnium plates 10a and 10a is 3w higher than that of stainless steel.
Plate thickness 5 in which 10B (boron) of t (weight a)% is dispersed
It is shown that it is almost the same as that of the boron-added stainless steel of m (indicated by a dashed line in the figure).

In addition, the dotted line in Figure 2 is 1wt (weight) for titanium (T1).
% of 10B is added.

In addition, 0.1~Q, 2wt% of 10B was added, and the plate thickness was 5.
If the rectangular tube body 10 of the spent fuel storage rack is made of boron-added stainless steel plates of M, the rectangular tube body 10 can be arranged densely by the hafnium plates 10a, 10a. When formed, the thickness of the hafnium plates 10a, 10a is approximately 0.0 mm according to the following formula.
The thickness can be reduced to 3HR, and the arrangement of the rectangular cylinders can be made more dense.

3wt% 15 However, if the thickness of the hafnium plates 10a, 10a is too thin, the deformation will be large and it may not be possible to satisfy the seismic design conditions in strength calculations, etc. , for example, about 2.5 m+.

By the way, the metal structure of hafnium (Hf) constituting the hafnium plates ioa and ioa is shown in Figure 3 (f5 ratio 200 times).
As shown in the figure, hafnium exhibits an α structure with extremely fine crystal grain size, and when the crystal grain size becomes finer than 4, hafnium exhibits soundness in mechanical properties such as tensile strength, bending, and hardness.

Therefore, in order for the hafnium plates 10a, 10a to exhibit such sound mechanical strength, it is necessary for welding to have a small welding line width and a high welding speed.

Although welding the hafnium plates 10a, 10a is relatively easy, hafnium exhibits high reactivity in high temperature regions and reacts with nitrogen, oxygen, carbon, and hydrogen, so for example, Kungestin inert gas (TrG) welding When welding the hafni-cum plates 10a, 10a at a slow speed such as that shown in FIG. become

However, the welded portion 11 of the hafnium plates 10a, 10a,
For example, when performing electron beam welding or laser beam welding in a high vacuum of 1O-3 torr or more, or in an inert gas atmosphere such as argon or helium, the hafnium plate 1 is
The metal structure of 0a and 10a becomes a β structure with crystal grains fi4 or more, and it is possible to escape from the extreme growth of crystal grains in the welded part 11, so that embrittlement of the welded part 11 can be prevented.

In this embodiment, a plurality of rectangular cylinders 10 formed in this manner are replaced with conventional rectangular cylinders 1 shown in FIGS. 10, 11, and 12, respectively, to store each spent fuel. Since it can be assembled into a rack and these square tube bodies 10 can be made denser, it is possible to increase the storage capacity of spent fuel.

Further, according to this embodiment, since the plate thickness of the rectangular cylinder 10 can be made thinner, the spent fuel storage rack can be made smaller and made of pumice.

FIG. 6 shows another embodiment of the present invention, and this embodiment consists of a pair of mouth-shaped hafnium plates 10a shown in FIG.
When electron beam welding or laser beam welding is performed on the welded portion 11 of 10a in a high vacuum, a prismatic mantle 20 made of austenitic stainless steel is placed inside the prismatic cylinder 10.
It subverts the

The mantle 20 has grooves 21.21 of a required width recessed toward the axis on two sides corresponding to the two welds 11 of the rectangular cylinder 10. When a required gap is set between the inner surface of the mantle 20 and the groove 21.21, and when welding each welding part 11.11 against the outer surface of the rectangular cylinder 10, the melting total bending is applied to the outer surface of the mantle 20. Attach and
This prevents welding to the rectangular tube body 10. mantle 20
An eye bolt-shaped locking tool 22 is fixed to one end of the holder.

With this mantle 20 inserted into the rectangular tube body 10, after welding each welding part 11, the mantle 20 is hung by tying a lobe or the like to its locking tool 22, as shown in FIG. ,
The lower end of the rectangular cylinder 10 is supported by a stopper 23.

In this state, the rectangular tube body 10 is then heated to a temperature of, for example, about 540° C. to perform thermal expansion molding.

Since the mantle 20 is made of austenitic stainless steel, the square cylinder 10 has a thermal expansion coefficient of hafnium.
For example, it is about three times as large as that of 10.20, and a difference in thermal expansion occurs during heating of these 10.20 mm, and the rectangular tube body 10 is thermally expanded to the required diameter.

Furthermore, if a metal plate with high thermal conductivity, such as a copper plate, is interposed between the mantle 20 and the welded part 11 of the rectangular tube body 10, the cold W of the welded part 11 is accelerated, so that the above-mentioned Since it is possible to prevent the structure of the welded part 11 and its vicinity from becoming coarse, and to suppress reactions with various elements, the welded part 11 can be beautifully processed.

FIG. 8 shows still another embodiment of the present invention, in which the rectangular tube body 30 of this embodiment has an outer IF 130b made of an austenitic stainless steel plate on the outer periphery of an inner IF 30a made of a hafnium plate. It is fitted into a double tube.

In other words, the rectangular cylinder 30 has an inner cylinder 30a made of hafnium plate,
For example, it is inserted into an outer cylinder 3Ob made of an austenitic stainless steel plate that has been heated to about 540°C, and then cooled to room temperature to form a double cylinder.

FIG. 9 is a longitudinal sectional view showing another embodiment of the present invention, and in the figure, the rectangular tube body 40 of this embodiment is attached to both upper and lower ends of the rectangular tube body 30 of the embodiment shown in FIG. It is constructed by welding +=p41a, 41a made of austenitic stainless steel in the shape of a mouth.

As described above, the rectangular cylinder 10.3 of each embodiment shown in FIGS. 6 to 9
Similarly to the embodiment shown in FIG. 1, for example, the conventional rectangular cylinders 1 shown in FIG. 10, FIG. 11, and FIG. This makes it possible to achieve a denser arrangement of the rectangular cylinders 10, 30, 40, and to improve the spent fuel storage capacity.

[Effects of the Invention] As explained above, in the present invention, the rectangular cylinders of the general-purpose fuel storage rack are formed of hafnium plates with high neutron absorption capacity, so the arrangement of the rectangular cylinders can be made denser. As a result, the spent fuel storage capacity can be expanded.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of a rectangular cylinder incorporated in an embodiment of the aircraft fuel storage rack according to the present invention, and FIG. 2 is a neutron of a hafnium plate constituting the rectangular cylinder incorporated in the embodiment shown in FIG. 1. Graphs showing absorption capacity, Figures 3, 4 and 5
The figures are micrographs showing the metal structure of hafnium at 200x magnification, Figures 6, 7, and 8 are perspective views showing other embodiments of the present invention, and Figure 9 is a micrograph showing the metal structure of hafnium at 200 magnification. Furthermore, FIGS. 10, 11, and 12 are perspective views illustrating conventional spent fuel storage racks, and FIG. 13 is a half-cut vertical sectional view showing another embodiment. FIG. 2 is a cross-sectional view of a conventional rectangular tube body that is incorporated into a spent fuel storage rack (not shown). 10.30.40... Square cylinder, 10a... Hafnium plate, 11... Welded part, 20... Mantle, 30a
... Inner tube made of hafnium plate, 30b... Outer tube made of austenitic stainless steel plate. Representative Patent Attorney Noriyuki Nori Yudo Hiroshi Mimata Neutron Energy -<eV) Thickness 5 Shot Collection Material Chinawate Nakazumi v1 Combined Fig. 2 Fig. 3 Fig. 4 86 Fig. 7 Fig. 0a Figure 8 Figure 9 Figure Hemp 11

Claims (1)

[Claims] 1. A spent fuel storage rack having a plurality of rectangular cylinders for storing spent fuel, wherein the rectangular cylinders are formed into a rectangular cylinder shape by a hafnium plate made of hafnium, and the hafnium A spent fuel storage rack characterized in that the welded parts of the plates are welded by electron beam welding or laser beam welding in a vacuum. 2. The prismatic cylinder is formed by bending two hafnium plates made of hafnium into a U-shape, and then butting and welding the end faces of these U-shaped hafnium plates to each other. The spent fuel storage rack according to claim 1, wherein an austenitic stainless steel mantle is inserted into a rectangular tube and expanded by heating at a required temperature. 3. The spent fuel storage rack according to claim 1, wherein the rectangular cylinder is formed by fitting an outer cylinder made of an austenitic stainless steel plate around the outer periphery of an inner cylinder made of a hafnium plate that accommodates the spent fuel. . 4. The spent fuel storage rack according to claim 1, wherein the rectangular cylinders are arranged and fixed in a staggered pattern on the base. 5. The spent fuel storage rack according to claim 1 or 2, wherein the laser beam welding is performed in an inert gas atmosphere.