JP2003075586A - Cask and cooling air flow regulation method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a corrosion-prone environment for canister by regulating the flow rate of cooling air to keep the surface temperature of a canister within a prescribed range. SOLUTION: In this cask 2, the flow regulation of cooling air is performed by use of a block 14 for partially blocking an inlet port 11 for introducing the cooling air for cooling the inner part of the cask 2 containing nuclear fuel into the cask 2 and a block 14 for partially blocking an outlet port 12 for discharging the cooling air introduced from the inlet port 11 out of the cask 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cask which is a container for storing a nuclear fuel assembly, and a cooling for cooling the cask by removing decay heat released from the stored nuclear fuel assembly. The present invention relates to a cooling air flow rate adjusting method for a cask that adjusts a flow rate of air.

[0002]

2. Description of the Related Art Spent nuclear fuel assemblies 1 generated in a nuclear power plant are stored in a dedicated container called a cask 2 for each predetermined number of bodies. That is, as shown in FIG. 2, the cask 2 is vertically arranged at a predetermined location of the nuclear power plant, and the upper lid 3 is removed. And
The long-shaped nuclear fuel assembly 1 hoisted by a fuel hoisting crane (not shown) is hoisted by a canister 4 having a predetermined hoisting hole for hoisting.

The cask 2 in which the nuclear fuel assembly 1 is stored in the nuclear power plant is horizontally hung by a crane (not shown), and is loaded on the bed of a dedicated trailer in a horizontally placed state. The cask 2 loaded on the bed of the dedicated trailer in this manner is further rigidly fixed so that the load does not collapse even while the dedicated trailer is moving. Thereafter, the cask 2 is transported to the cask storage building by this dedicated trailer.

As shown in FIG. 3, the cask storage building is equipped with an overhead crane 9, and the casks 2 carried into the building by a dedicated trailer 7 are vertically hung by the overhead crane 9 one by one. It is moved to a predetermined storage location 8 in the building.

The cask 2 thus moved to the predetermined storage location in the cask storage building stores the nuclear fuel assembly 1 therein until the nuclear fuel assembly 1 contained therein is subjected to reprocessing. It is stored in the cask storage building as it is.

[0006] The spent nuclear fuel assembly 1 contains fission products (hereinafter referred to as "FP" (abbreviation of Fission Products)), and decay heat is generated from these FPs. Therefore, as shown in FIGS. 2 and 4, the cask 2 is provided with an inlet 11 and an outlet 12.
Outside air (air) is introduced into the cask 2 through the inlet 11. This outside air is used as cooling air, and after cooling the canister 4 in which the nuclear fuel assembly 1 is stored, it is exhausted from the exhaust port 12.

As described above, the cooling air is continuously supplied to the canister 4 inside the cask 2 so that the decay heat is removed and the canister 4 is cooled.

[0008]

However, such a conventional cask cooling method has the following problems.

That is, most of the nuclear facilities in Japan, including the cask storage building, are constructed near the coast. When the cask 2 is stored in the cask storage building existing near the coast as described above, sea salt particles having high hygroscopicity are attached to the surface of the canister 4, so that the canister 4 removes moisture in the outside air. Absorbs and becomes more corrosive. As a result, the stress corrosion cracking (St
ress Corrosion Cracking) (hereinafter abbreviated as "SCC")
Is likely to occur. In addition, sea salt particles canister 4
Unless the relative humidity of the surface of the above is about 10% or more, it does not adhere to the surface of the canister 4.

FIG. 5 shows that the relative humidity on the surface of the canister 4 is 100% (x = 0) to the relative humidity on the surface of the canister 4 when the surface temperature of the canister 4 is increased (when x is increased). It is an analysis result figure showing (z) for every temperature (y).

From the analysis result of FIG. 5, since the temperature at which the relative humidity on the canister surface is high is on the high temperature side,
At a high temperature of 30 ° C. (y = 30 ° C.), the following is an examination of the condition that the relative humidity is 10% or less. That is, when the air temperature is 30 ° C., the surface temperature of the canister 4 where the relative humidity is 10% (z = 10%) or less is 50 ° C. (x = 50 ° C.) or more higher than the air temperature. Therefore, the surface temperature of the canister 4 is 80 ° C.
When the above is reached, the relative humidity (10
%), The corrosiveness becomes low.

Further, generally, the corrosive environment becomes more severe as the temperature becomes higher. Therefore, at about 500 ° C. or higher, the effect of severer corrosive conditions is more conquered than the effect of lowering relative humidity. In addition, it becomes corrosive again. However, the surface temperature of the canister 4 is
From the viewpoint of temperature limitation of the fuel cladding tube of the nuclear fuel assembly 1 housed in
Under such conditions, the higher the temperature, the more mild the corrosive environment.

As described above, the decay heat is released from the nuclear fuel assembly 1 housed in the canister 4, but the decay heat decays as the storage time elapses. Meanwhile, cask 2
The flow rate of the cooling air supplied to the inside is almost constant regardless of the storage time. Therefore, even if the flow rate of the cooling air is set so that the surface temperature of the canister 4 becomes 80 ° C. or higher at the initial stage of storage, the decay heat weakens after the storage time elapses, so the cooling effect is relatively high. Becomes higher, the surface temperature of the canister 4 becomes lower than in the initial storage,
There is a problem that the corrosiveness becomes severe.

The present invention has been made in view of such circumstances, and the flow rate of the cooling air supplied to the inside of the cask is adjusted so that the surface temperature of the canister is maintained within a predetermined range. An object of the present invention is to provide a cask and a cooling air flow rate adjusting method for the cask, which prevent the canister from being corroded easily.

[0015]

In order to achieve the above object, the present invention takes the following means.

That is, the cask according to the invention of claim 1 is
The inlet for introducing the cooling air for cooling the inside of the cask into the cask is provided with a cooling air flow rate control means such as a fan for controlling the flow rate of the cooling air.

In the cask according to the second aspect of the present invention, an inlet closing member for closing a part of the inlet for introducing the cooling air for cooling the inside of the cask containing the nuclear fuel into the cask, and the cooling introduced from the inlet. The flow rate of the cooling air is adjusted by using an exhaust port closing member that closes a part of the exhaust port that exhausts the air to the outside of the cask. For example, blocks are used as the introduction port closing member and the exhaust port closing member, and the flow rate of the cooling air is adjusted by appropriately adjusting the number and the insertion ratio of the blocks to be inserted into the introduction port or the exhaust port.

According to a third aspect of the present invention, in the cask according to the second aspect of the invention, the inlet closing member and the exhaust opening closing member are made of, for example, lead suitable for shielding γ rays, and further for shielding neutrons. By arranging a suitable resin on the outer periphery, it has a shielding function of shielding the radiation emitted from the nuclear fuel.

A cask according to a fourth aspect of the present invention comprises an inlet area adjusting means and an exhaust area adjusting means. The introduction port area adjusting means is capable of adjusting the flow rate of the cooling air introduced into the introduction port by adjusting the area of the introduction port for introducing the cooling air for cooling the inside of the cask into the cask. Further, the exhaust port area adjusting means can adjust the flow rate of the cooling air exhausted from the exhaust port by adjusting the area of the exhaust port that exhausts the cooling air introduced from the introduction port to the outside of the cask. is there.

According to a fifth aspect of the present invention, in the cask of the fourth aspect of the invention, the exhaust port is provided with a thermometer for measuring the temperature of the cooling air exhausted from the exhaust port to the outside of the cask. Based on this, the area of at least one of the introduction port and the exhaust port is adjusted so that this temperature falls within a predetermined range.

According to a sixth aspect of the cask of the fifth aspect of the invention, the predetermined range is 80 ° C. or higher and 300 ° C. or lower.
By setting the temperature to 80 ° C. or higher, the relative humidity (about 20%) in which the sea salt particles cannot absorb moisture is lowered, so that the corrosiveness can be lowered. Further, by setting the temperature to 300 ° C. or lower, the temperature limit of 300 ° C. of the fuel cladding tube of the nuclear fuel assembly housed in the canister is maintained.

According to a seventh aspect of the present invention, there is provided a method for adjusting a cooling air flow rate of a cask, wherein an inlet for introducing cooling air for cooling the inside of the cask equipped with a canister containing nuclear fuel as an inner container into the cask, and The flow rate of the cooling air flowing inside the cask is adjusted by closing a part of the exhaust air that exhausts the introduced cooling air to the outside of the cask, and the surface temperature of the canister is kept within a predetermined range.

[0023]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

It is to be noted that the reference numerals in the drawings used in the description of the following embodiments are designated by the same reference numerals as those in FIGS. 2 to 4.

An embodiment of the present invention will be described with reference to FIG.

The cask to which the cooling air flow rate adjusting method according to the embodiment is applied is the inlet 1 of the cask 2 of the prior art.
1 and the exhaust port 12 are partially closed by blocks 14 to adjust the cooling air flow rate. Therefore, the introduction port 11 and the exhaust port 1
The configuration other than 2 is the same as the configuration of the conventional cask 2 shown in FIG. 10 and FIG.

A cask to which the cooling air flow rate adjusting method according to this embodiment is applied will be described with reference to FIG.

FIG. 1 is a detailed configuration diagram showing an example of an inlet port and an exhaust port in a cask to which the cooling air flow rate adjusting method according to the embodiment is applied.

That is, the cask to which the cooling air flow rate adjusting method according to the embodiment is applied is shown in FIGS.
As shown in (b), block insertion guides 13 are provided on both sides of the introduction port 11 and the exhaust port 12. On the other hand, the block 14 is provided with a recess 16 corresponding to the block insertion guide 13. Then, the block insertion guide 13 is loosely fitted in the recess 16, and the block 14 is slid along the block insertion guide 13 toward the inner side of the introduction port 11 and the exhaust port 12 to introduce the introduction port 11 and the exhaust port 12. Is partially blocked.

When the cask 2 is stored in the predetermined storage place 8 of the cask storage building, the flow rate of the outside air circulating in the cask storage building is substantially constant. Therefore, as described above, the block 14 is inserted and the introduction port 11 is inserted.
By partially closing the exhaust port 12 and the exhaust port 12, the flow rate of the cooling air introduced into the cask 2 is reduced.

The introduction port 11 and the exhaust port 12 are respectively provided with block insertion guides 13 on the left and right sides, whereby two blocks 14 at maximum can be inserted. In this way, when the block 14 is inserted into the inlet 11 and the exhaust port 12 to adjust the flow rate of the cooling air, the block 14 may be inserted into the inlet 11 and the exhaust port 12 independently. For example, only one block 14 may be inserted into the introduction port 11 and two blocks 14 may be inserted into the exhaust port 12.

The block 14 is made of carbon steel 17 in which a neutron absorber 18 is embedded. The neutron absorber 18 may be made of any material that absorbs neutrons, such as resin, boron (B), gadolinium (Gd), and cadmium (Cd). Further, a part of the block 14 may be partially embedded with lead suitable for blocking γ rays. in this way,
The block 14 shields radiation emitted from the nuclear fuel assembly 1 housed in the canister 4. The depth dimension a of the block 14 is
And a value equal to the depth dimension b of the exhaust port 12 (a = b), which makes the flow of the cooling air smoother and prevents irregular flow as much as possible. Further, the block 14 is provided on the front side with a surface steel plate 19 having a height dimension n larger than the height dimension m of the introduction port 11 and the exhaust port 12 (m <n). As a result, the block 14 is erroneously placed in the inlet 11 and the outlet 12.
I try not to put it in too much.

The cask to which the cooling air flow rate adjusting method according to the embodiment is applied has a thermometer 15 installed at the exhaust port 12. The thermometer 15 measures the temperature of the cooling air exhausted from the exhaust port 12. As described in the prior art, under the condition that the surface temperature of the canister 4 is kept at 300 ° C. or lower, if it becomes 80 ° C. or higher, the corrosiveness becomes low. The temperature of the cooling air is measured, and the number of blocks 14 to be inserted is adjusted based on the measured temperature result.

That is, when the temperature measured by the thermometer 15 is 300 ° C. or lower and is sufficiently higher than 80 ° C., both the inlet port 11 and the exhaust port 12 are blocked.
The cooling air is introduced into the inside of the cask 2 at the maximum flow rate without inserting. On the other hand, when the temperature measured by the thermometer 15 is lower than 80 ° C., it is assumed that the surface temperature of the canister 4 is also lowered to about 80 ° C. Therefore, the inlet 11 and the outlet 12 The block 14 is appropriately inserted into the above to reduce the flow rate of the cooling air introduced into the cask 2. This lowers the cooling efficiency and raises the surface temperature of the canister 4.

Next, a cooling air flow rate adjusting method for a cask to which the cooling air flow rate adjusting method according to the embodiment having the above-mentioned configuration is applied will be described.

The nuclear fuel assembly 1 is housed in the cask 2 stored in the cask storage building. Decay heat is generated from this nuclear fuel assembly 1, but the value of this decay heat decays with the passage of storage time. That is, since the cask 2 that has just stored the nuclear fuel assembly 1 emits higher decay heat, the cask 2 shown in FIG. 1 (a1) and FIG.
As shown in (b1), the block 14 is not inserted into the introduction port 11 and the exhaust port 12, and the cooling air is introduced into the cask 2 at the maximum flow rate.

As the storage time elapses, the heat of decay decreases. As described above, the canister 4 becomes highly corrosive when the surface temperature thereof becomes 80 ° C. or lower. Therefore, when the temperature of the cooling air exhausted from the exhaust port 12 is measured to be 80 ° C. or lower by the thermometer 15,
As shown in (a2) or FIG. 1 (b2), the inlet 11
Alternatively, by inserting one block 14 into the exhaust port 12 or both, the flow rate of the cooling air introduced into the cask 2 is reduced. This reduces the cooling efficiency and raises the surface temperature of the canister 4 to 80 ° C. or higher.

Further, as the storage time elapses, the decay heat further decreases, and the temperature of the cooling air exhausted from the exhaust port 12 is again measured to be 80 ° C. or lower by the thermometer 15. . In this case, FIG. 1 (a3) or FIG.
As shown in (b3), the introduction port 11 or the exhaust port 12,
Alternatively, by further inserting one block 14 into both of them, the flow rate of the cooling air introduced into the cask 2 is further reduced. This further reduces the cooling efficiency,
The surface temperature of the canister 4 is raised again to 80 ° C. or higher.

Since the block 14 is made of carbon steel 17 and the neutron absorber 18 and lead (not shown) are embedded in a part of the block 14, when the block 14 is inserted into the introduction port 11 and the exhaust port 12. The radiation emitted from the nuclear fuel assembly 1 is blocked by the block 14. This reduces the air dose rate around the cask 2.

As described above, in the cask to which the cooling air flow rate adjusting method according to the embodiment is applied, the flow rate of the cooling air for cooling the inside of the cask 2 is set to the inlet 1 of this cooling air.
It can be adjusted by a simple method of inserting the block 14 into the 1 and the exhaust port 12. That is, since the outside air is flowing at a substantially constant flow rate inside the cask storage building, the block 14 is inserted into the inlet 11 and the outlet 12, and the area of the inlet 11 and the outlet 12 is reduced to reduce the outside air. The flow rate of the cooling air introduced into the cask 2 can be reduced. This also lowers the heat removal efficiency, so that the temperature of the canister 4, which is the inner container of the cask 2, can be increased.

Further, the exhaust port 12 is provided with a thermometer 15, and the temperature of the cooling air exhausted from the exhaust port 12 to the outside of the cask 2 can be measured by the thermometer 15. The surface temperature of the canister 4 can be estimated based on the temperature.

Therefore, the surface temperature of the canister 4 can be adjusted by adjusting the insertion amount of the block 14 and the cooling air flow rate based on the temperature measured by the thermometer 15.

As already described, the canister 4 becomes highly corrosive when the surface temperature thereof becomes 80 ° C. or lower. On the other hand, the decay heat emitted from the nuclear fuel assembly 1 housed in the canister 4 becomes lower as the storage time elapses.

Therefore, with respect to the cask 2 immediately after being stored in the cask storage building, cooling air is supplied without inserting the block 14 into both the inlet 11 and the outlet 12, and the measurement result of the thermometer 15 is monitored.
And, with the decay heat decay, from the monitor result,
When it is determined that the surface temperature of the canister 4 is about to be 80 ° C. or lower, the block 14 is appropriately inserted into the inlet 11 or the exhaust port 12 to reduce the cooling efficiency so that the surface temperature of the canister 4 reaches 80 ° C. ℃ or more 300 ℃
You can keep:

In the embodiment, the case where up to two blocks 14 can be inserted into each of the inlet 11 and the exhaust 12 has been described as an example, but it is possible to insert into each inlet 11 and each exhaust 12. The number of such blocks 14 is not limited. Further, the cask 2 is provided with, for example, four inlets 11 at its lower part and four outlets 12 at its upper part, and by sequentially inserting blocks 14 into them, a long period of time can be obtained. The surface temperature of the canister 4 can be maintained at 80 ° C. or higher and 300 ° C. or lower.

The block 14 may be made of any material as long as it does not allow cooling air to pass therethrough. Therefore, in this block 14, lead having an effect of shielding γ rays and neutron absorber 1 having an effect of shielding neutrons
8 is embedded, the radiation emitted from the nuclear fuel assembly 1 can be shielded by inserting the block 14 into the inlet 11 and the exhaust 12, and the air dose rate around the cask 2 can be reduced. it can.

The means for reducing the area of the inlet 11 and the outlet 12 is not limited to the block 14 described in the present embodiment, but a shutter, a louver or the like may be used. Any means may be used as long as the area of the inlet 11 and the outlet 12 can be narrowed.

The preferred embodiment of the present invention has been described above with reference to the accompanying drawings, but the present invention is not limited to such a configuration. Within the scope of the technical idea of the invention as claimed in the claims, those skilled in the art can come up with various modifications and modifications, and the modifications and modifications are also within the technical scope of the present invention. Be understood to belong to. For example, the block 14 for narrowing the area of the inlet 11 and the outlet 12 is not used, and instead, a fan that forcibly blows cooling air to the inlet 11 is used. Then, based on the measurement result by the thermometer 15,
The flow rate of the cooling air may be adjusted by adjusting the rotation speed of the fan.

[0049]

As described above, according to the present invention,
The flow rate of the cooling air supplied to the inside of the cask can be adjusted so that the surface temperature of the canister is kept within a predetermined range.

As described above, it is possible to realize the cask and the cooling air flow rate adjusting method for the cask, which can prevent the environment in which the canister is easily corroded.

[Brief description of drawings]

FIG. 1 is a detailed configuration diagram showing an example of an introduction port and an exhaust port in a cask to which a cooling air flow rate adjusting method according to an embodiment of the present invention is applied.

FIG. 2 is a perspective view showing a general structure of a cask.

FIG. 3 is a conceptual diagram showing a method of moving a cask in a cask storage building.

FIG. 4 is a vertical sectional view showing a general structure of a cask.

FIG. 5 is a correlation diagram showing the analysis results regarding the relationship between the amount of change in canister surface temperature, air temperature, and relative humidity.

[Explanation of symbols]

1 ... Nuclear fuel assembly 2 ... Cask 3 ... Top lid 4 ... Canister 7 ... Dedicated trailer 8 ... Storage location 9 ... Overhead crane 11 ... Inlet 12 ... Exhaust port 13 ... Block insertion guide 14 ... Block 16 ... Recess 17 ... Carbon steel 18 ... Neutron absorber 19 ... Surface steel plate

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Kazuo Asada             2-1-1 Niihama, Arai-cho, Takasago, Hyogo Prefecture             Takasago Laboratory, Mitsubishi Heavy Industries, Ltd. (72) Inventor Mitsuhiro Irino             2-19-13 Takanawa, Minato-ku, Tokyo Ryoyu Co., Ltd.             Within system technology

Claims (7)

[Claims] 1. A cask characterized in that a cooling air flow rate control means for controlling a flow rate of the cooling air is provided at an inlet for introducing cooling air for cooling the inside of the cask into the cask. 2. An inlet closing member for closing a part of an inlet for introducing the cooling air for cooling the inside of the cask containing the nuclear fuel into the cask, and the cooling air introduced from the inlet to the outside of the cask. A cask characterized in that the flow rate of the cooling air is adjusted by using an exhaust port closing member that closes a part of an exhaust port for exhausting air. 3. The cask according to claim 2, wherein the inlet closing member and the exhaust opening closing member have a shielding function of shielding radiation emitted from the nuclear fuel. . 4. An inlet opening area adjusting means for adjusting an area of an inlet for introducing cooling air for cooling the inside of the cask into the cask, and an exhaust outlet for exhausting the cooling air introduced from the inlet to the outside of the cask. And an exhaust port area adjusting means for adjusting the area of the cask. 5. The cask according to claim 4, wherein the exhaust port is provided with a thermometer for measuring a temperature of cooling air exhausted from the exhaust port to the outside of the cask, and a temperature measured by the thermometer. Based on the above, the cask is characterized in that the area of at least one of the introduction port and the exhaust port is adjusted so that this temperature falls within a predetermined range. 6. The cask according to claim 5, wherein the predetermined range is 80 ° C. or higher and 300 ° C. or lower. 7. An inlet for introducing cooling air for cooling the inside of a cask equipped with a canister containing a nuclear fuel as an inner container into the cask, and exhausting the cooling air introduced from the inlet to the outside of the cask. A method for adjusting the flow rate of cooling air for a cask, characterized in that the flow rate of the cooling air flowing inside the cask is adjusted by closing a part of the exhaust port and the surface temperature of the canister is kept within a predetermined range.