JPH0687080B2 - Storage facility for spent nuclear fuel in gas - Google Patents

Description

TECHNICAL FIELD The present invention relates to a facility for storing spent nuclear fuel in gas, and more particularly to decay heat removal from nuclear fuel.

(Prior art and its problems) As a method of storing spent fuel until reprocessing, a method of immersing spent nuclear fuel assemblies in highly heat-removing water or liquid metal has been generally used. However, recently, a method of storing in a gas such as an inert gas or air has been proposed as an alternative.

This is, for example, as shown in FIG. 1, a radioactive dust removal filter (2), a gas cooler (3), a circulation blower (4) communicating with a fuel storage cell (1) formed of concrete of a required thickness. By providing a gas cooling circulation system consisting of, etc., a storage rack (6) in the cell (1) by the transfer machine (5), that is, a top and bottom having gas flow paths (6a) as shown in the partial view of FIG. A spent nuclear fuel assembly (7) (hereinafter referred to as a spent nuclear fuel (7)) held on a storage rack (6) including a support plate (6b) (6c) and a partition plate (6d).
A cooling gas (8) is circulated from the lower side to the upper side through a common gas passage (6e). Then, the decay heat generated in the spent nuclear fuel (7) by this cooling gas flow is carried away to the outside of the cell (1) for safe storage.

This method has attracted attention as a rational storage method because it can simplify the equipment compared to the liquid storage method, and its introduction in the future is under consideration.

However, as is well known, the heat removal performance of gas is inferior to that of liquid, so in order to maintain the temperature at which the spent nuclear fuel (7) is safe for storage, a gas cooling system with a correspondingly large capacity must be installed and cooling must be performed. It is necessary to take measures such as reducing the number of spent nuclear fuels (7) to be stored according to the capacity of the system, which leads to an increase in storage cost.

(Object of the Invention) The present invention provides a storage facility for spent nuclear fuel capable of increasing the storage capacity only by providing a simple means in the storage cell, and further improves the gas storage property superior to the liquid storage. It was made possible.

(Means of the Present Invention for Solving Problems) The features of the present invention are as follows. That is, as shown in the longitudinal sectional view and sectional plan view of FIGS. 3 (a) and 3 (b) showing one embodiment (the same reference numerals as those in FIGS. 1 and 2 denote the same parts), the spent nuclear fuel A cylindrical high void porous body having a diameter larger than that of (7) and having openings (9a) and (9b) at both ends, for example, a porous body having a porosity of 90% or more or layered wire mesh. The cylindrical porous body (9) is supported by the upper and lower support plates (6b) (6c) of the storage rack (6) and provided in the cooling gas passage of each storage unit. Then, the spent nuclear fuel (7) to be stored is inserted into the inside thereof to wrap around the peripheral surface so that the heat transfer mechanism shown in FIG. 4 is formed.

In this way, in addition to the natural convection from the lower side to the upper side, which is caused by the heating of the spent nuclear fuel (7) in the channel box or the wrapper tube (7a) by the fuel decay heat (a) shown in A of FIG. As shown by B in the figure, active natural convection on the peripheral surface of the cylindrical high void porous body (9) is generated, which is heated by the radiant heat (b) based on the fuel decay heat (a) to reach a high temperature. That is, the highly void porous body (9) has a surface area with an extremely high magnification as compared with the surface area of a normal plate material, has a large area to receive radiation from a high temperature surface, and promotes heat transfer by radiation. It has a three-dimensionally random mesh structure, and the direction of the surface is not constant, so due to the effect of diffuse reflection, the amount of radiation reflected in the direction of the high temperature surface is small compared to a plate with a flat surface, and as a result, the radiation is absorbed. This has the effect of making it easier (increasing the emissivity). Then, these heats rise between the spent nuclear fuel (7) and the high void porous body (9), and between the high void porous body (9) and the partition plate (6d) of the storage rack (8). ) Is carried away from the storage cell (1). Further, by promoting heat transfer by natural convection, the temperature on the high void porous body (9) side decreases, the temperature difference with the spent nuclear fuel (7) side increases, and heat transfer by radiation is increased. It also has the effect of being further promoted. Therefore, high void porous body (9)
With the provision of, it becomes possible to improve the heat removal function of decay heat more than the conventional one.

Fig. 5 shows the relationship between the heat flux and the surface temperature of the spent nuclear fuel (7) during storage of spent nuclear fuel assemblies with the same heating value, in the presence or absence of the cylindrical high void porous body (9). It is the figure asked for. In this case, the high void porous material (9) used was made by Sumitomo Electric Industries, Ltd. Celmet (trade name).

This celmet is a nickel-based alloy molded into a three-dimensional skeleton structure, and is characterized by being lightweight and having a large surface area per unit volume. That is, in the case of Celmet having a plate thickness of 5 mm, the surface area is about 15 times as large as that of a normal plate material, and if the thickness is increased, this ratio is further increased.

As is clear from this, the heat flux (8KW / cm ² ) corresponding to the heat value of typical spent nuclear fuel assemblies during gas storage.
The surface temperature of the spent nuclear fuel assembly in the above is about 370 ° C from the curve A in the figure when the high void porous body is not installed,
When installed, the temperature is about 320 ° C. from the curve B in the figure, and the surface temperature of the spent nuclear fuel assembly stored by using the high void porous body can be significantly reduced to about 50 ° C. Therefore, the increase in gas cooling capacity can be reduced accordingly. In addition, since the highly voided porous body is cheap and lightweight, has a simple structure, and is easy to implement, according to a trial calculation, the cost required is much higher than the increase in the gas cooling capacity required to lower the same surface temperature. It is cheap. In addition, the high void porous body does not require any driving power, so less power is required compared to the case where the cooling gas is used to lower the surface temperature due to the high void porous body, and the operating cost can be reduced. Becomes

Although the present invention has been described with reference to one embodiment, the heat removal effect can be enhanced by providing a plurality of highly void porous bodies (9) in a plurality of stages (two stages in the figure) as shown by a dotted line in FIG.

(Effects of the Invention) As is clear from the above description, according to the present invention, the excellent effect of providing a gas spent nuclear fuel storage facility having better storage performance than the conventional one can be obtained.

[Brief description of drawings]

1 and 2 are explanatory views of a spent nuclear fuel storage facility for gas, FIG. 3 is an explanatory view of an embodiment of the present invention, FIG. 4 is its heat transfer mechanism diagram, and FIG. 5 is heat transfer. It is an experimental example figure which shows a promotion effect. (1) ... storage cell, (2) ... dust filter, (3)
…… Gas cooler, (4) …… Circulation blower, (5) ……
Transfer device, (6) …… Storage rack, (6a) …… Gas flow path,
(6b) (6c) …… Support plate, (6d) …… Partition plate, (6e)…
… Common gas passage, (7) …… Spent nuclear fuel assembly,
(7a) …… Channel box, wrapper tube, etc. (8)
…… Cooling gas, (9) …… Cylindrical high void porous body, (9a)
(9b) …… Aperture.

Claims (1)

[Claims] 1. A facility for storing a spent nuclear fuel by supplying a cooling gas into a spent nuclear fuel storage cell,
A storage facility for spent nuclear fuel in a gas, characterized in that a cylindrical high void porous body is provided in a cooling gas passage around the spent nuclear fuel so as to surround the spent nuclear fuel.