JP3534591B2 - Method and apparatus for replacing fluid in a spent fuel transport container - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for displacing a fluid in a spent fuel transportation container, that is, boric acid water.

[0002]

2. Description of the Related Art A fuel assembly used in a nuclear power plant is housed in a spent fuel transportation container (hereinafter also referred to as a cask) which is usually called a cask, and is transported to a reprocessing plant. . In the cask, the spent fuel assemblies generate heat and are at high temperature, and since they emit radiation, they are filled with several thousand ppm of boric acid water to protect them.

Before the reprocessing in the reprocessing factory, it is necessary to discharge the boric acid water in the cask. However, if the drainage boric acid water treatment facility is not in the reprocessing factory, before the transportation to the reprocessing factory. It is necessary to replace with pure water in the nuclear power plant, and it is also important to carry out this replacement efficiently and in a short time because the target is radioactive.

FIG. 3 (a) shows an example of a conventional substitution method by mixing / diluting, in which a top portion 2 is provided inside a cask 1.
Water is supplied from the bottom part 3 and diluted with the internal boric acid water by convection and mixing, and then drained from the bottom part 3 and collected.

[0005]

However, in such a method, as can be seen from FIG. 3B, both the temperature and the concentration decrease slowly, and a long substitution time is required until the desired degree is reached. There is a problem. Accordingly, it is an object of the present invention to provide a method and apparatus that allows the fluid inside a shipping container to be replaced relatively quickly.

[0006]

To this end, claim 1
According to the present invention, a fluid having a temperature relatively lower than that of the internal fluid is injected from a vertically lower portion of the spent fuel transportation container containing the internal fluid, and the fluid is injected between the internal fluid and the injected cryogenic fluid. A spent fuel transport that forms a stratified interface in the inner layer and replaces the internal fluid with the injected fluid by the ascending effect of the stratified interface due to the density difference between the internal fluid and the cryogenic fluid above and below the stratified interface. A method of replacing a fluid in a container is provided.

Further, in order to achieve this object, claim 2
In the present invention according to, for replacing the internal fluid in the spent fuel transportation container having the drain valve in the lower part and the vent valve and the pressurizing valve in the upper part with the replacement fluid having a relatively lower temperature than the internal fluid, The apparatus includes a storage tank for storing the replacement fluid, a replacement fluid supply line connecting the storage tank to the drain valve of the spent fuel transportation container, and the storage tank interposed in the replacement fluid supply line. A pump for feeding the replacement fluid in the tank to the spent fuel transportation container, and a discharge line for discharging the internal fluid to the outside, which is connected to the vent valve and the pressure valve of the spent fuel transportation container. And a recovery tank connected to the discharge line.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Next, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the drawings, the same reference numerals indicate the same or corresponding parts. In FIG. 1, since the spent fuel transportation container 10 itself may have a well-known structure, it will be briefly described.
And a heat dissipation fin assembly 12 surrounding it, and the top and bottom of the shielding layer 11 are upper and lower lid assemblies 13, 1.
It is sealed by 4. A plurality of channels 16 for vertically accommodating each fuel assembly 15 are vertically provided inside the shielding layer 11, and the channels 16 are supported by a large number of support rings 17 which are axially separated from each other. There is.

Further, the drain valve 2 is attached to the lower lid assembly 14 of the transport container 10 in order to discharge the fluid therein.
6 is provided, the upper lid assembly 13 is provided with a vent valve 29 for adjusting the fluid level, and a pressurizing valve 30 for injecting pressurized gas so that the fluid does not boil. ing. Before the replacement, the transportation container 10 is filled with boric acid water (not shown) having a concentration of several 1000 ppm at 100 ° C. or less. INDUSTRIAL APPLICABILITY The replacement method and apparatus of the present invention efficiently replace high temperature and high concentration boric acid water in the transportation container 10 with pure water.

In FIG. 1, the fluid displacement device or system 20 supplies pure water into the transport container 10,
It is equipped with a pure water tank 21 of a capacity suitable for the transport container,
In order to accommodate the boric acid water recovered from the transport container 10,
The recovery tank 22 having the same capacity is provided. The pure water tank 21 is in fluid communication with the pure water supply line 25 including the pure water supply pump 23 and an appropriate valve 24 from the lower lid assembly 14 to the inside of the transportation container 10 through the drain valve 26. 22 is in fluid communication with the interior of the shipping container 10 from the upper lid assembly 13 via a vent valve 29 by a drain line 28 including a valve 27. Also,
The drainage line 28 communicating with the recovery tank 22 includes the valve 3
It communicates also with the pressurizing valve 30 mentioned above via 1.

In this fluid displacement system 20, when each valve is opened and the pure water supply pump 23 is operated, the pure water in the pure water tank 21 is injected into the transportation container 10 through the pure water supply line 25, and the inside The boric acid water is vent valve 2
The water is recovered in the recovery tank 22 by the buoyancy effect via the drain line 28 including the water level adjusting line including 9 and the pressurizing line including the valves 30 and 31.

FIG. 2A is a diagram for explaining this buoyancy effect. At the start of the replacement process, the shipping container 10 is full of hot boric acid water,
The specific weight of water is small. Under such circumstances,
When the vent valve 29 and the pressurizing valve 30 are opened and pure water of relatively low temperature (large specific weight) is injected from the drain valve 26 at the bottom of the transport container 10, the injected pure water PW is generated due to the difference in specific gravity. A stratified interface A is formed at the boundary between the high temperature boric acid water BW and the high temperature boric acid water BW. Although heat is exchanged in the vicinity of the stratified interface A, the stratified interface itself gradually rises as indicated by symbols A ′ and A ″ in FIG. However, as a whole, it forms a piston flow that flows as if the piston were moving.

Therefore, the high temperature boric acid water BW in the upper part is pushed out of the transport container 10 by the pure water PW from the lower part and is drained to the recovery tank 22 in FIG. 1 through the vent valve 29 and the pressurizing valve 30.

According to such a substitution system of the present invention, when the stratified interface passes through a certain position in the height direction of the transportation container,
Since the temperature and the concentration in the vicinity of that position drop sharply, as can be understood from FIG. 2B, the time required for replacement is significantly shortened as compared with the conventional example of FIG. 3B. it can.

Although the present invention has been described above with reference to its preferred embodiment, the present invention is not limited to this, and various modifications such as the following are possible. 1) The internal fluid of the transportation container is boric acid water having a concentration of 1000 ppm, but any fluid including the concentration may be used as long as it has a cooling / control function, and the replacement fluid is not limited to pure water. 2) Since it is cost effective to use the drain valve, the vent valve, and the pressurizing valve, which are provided in the transport container, for injecting the replacement fluid and discharging the internal fluid, the embodiment has such a configuration. Depending on the form of the transportation container to which the present invention is applied, for example, those corresponding to the drain valve, the vent valve and the pressurizing valve may be used,
If no counterpart exists, a separate valve device may be installed. 3) Although it is preferable to use both the vent valve and the pressurizing valve for discharging the internal fluid, it is not essential to use them, and only one of them may be used. 4) In the embodiment, the spent fuel is a fuel assembly,
The spent fuel may be other fuels, radioactive material or radioactive waste, as long as the fluid in the shipping container needs to be replaced.

[0016]

As described above, in the method invention according to claim 1, a fluid having a temperature relatively lower than that of the internal fluid is injected from the vertically lower portion of the spent fuel transportation container containing the internal fluid, A stratified interface is formed between the internal fluid and the injected low temperature fluid, and the internal layer is increased due to a difference in density between the internal fluid and the low temperature fluid above and below the stratified interface. In the device invention according to claim 2, the fluid is replaced with the injected fluid, and the internal fluid in the spent fuel transportation container having the drain valve in the lower portion and the vent valve and the pressurizing valve in the upper portion is An apparatus for replacing a replacement fluid having a temperature relatively lower than that of a fluid includes a storage tank for storing the replacement fluid and a replacement fluid supply connecting the storage tank to the drain valve of the spent fuel transportation container. A line, a pump interposed in the replacement fluid supply line for feeding the replacement fluid in the storage tank to the spent fuel transport container, the vent valve and the pressurization valve of the spent fuel transport container And a recovery tank connected to the exhaust line for exhausting the internal fluid to the outside, and a recovery tank connected to the exhaust line. Therefore, in the inventions of claims 1 and 2, the relatively low-temperature substitution fluid is injected from the lower portion of the transportation container, and the internal fluid of the transportation container is discharged from the upper portion. A stratified interface is formed between the displacement fluid and the internal fluid above due to the buoyancy effect or the density difference effect. This stratified interface gradually rises by continuing the injection of the displacement fluid. Since there is a large temperature difference between the two fluids above and below the stratified interface, and consequently a large concentration difference, even in a transport container with a complicated internal structure, the internal fluid is replaced with the replacement fluid in a relatively short time. be able to. Further, the inside of the transport container can be effectively decontaminated by the effect of the piston flow in which the stratified interface rises as described above.

[Brief description of drawings]

FIG. 1 is a system diagram illustrating a replacement method and a replacement device for carrying out the replacement method according to an embodiment of the present invention.

FIG. 2 (a) is a schematic diagram for explaining a piston flow caused by a buoyancy effect according to the present invention, and FIG.
It is a graph which shows temperature / concentration change of a specific part in a transportation container in which a piston flow has occurred.

FIG. 3 (a) is a schematic diagram for explaining a conventional mixed dilution method, and FIG. 3 (b) is a graph showing changes in temperature / concentration of a specific portion in a transportation container when the mixed dilution method is performed. is there.

[Explanation of symbols]

10 ... Spent fuel transportation container, 15 ... Fuel assembly (spent fuel), 20 ... Replacement device or system, 21 ...
Pure water tank (storage tank), 22 ... Recovery tank, 23 ...
Pure water supply pump, 25 ... Pure water supply line (displacement fluid supply line), 26 ... Drain valve, 28 ... Drain line (discharge line), 29 ... Vent valve, 30 ... Pressurization valve,
A ... Stratified interface, PW ... Pure water (displacement fluid), BW ... Boric acid water (internal fluid).

─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Shozo Taguchi 1-1-1, Wadazaki-cho, Hyogo-ku, Kobe-shi, Hyogo Mitsubishi Heavy Industries, Ltd. Kobe Shipyard (72) Inventor Kenji Usawa Kobe-shi, Hyogo 1-1 1-1 Wadasaki-cho, Hyogo-ku Mitsubishi Heavy Industries, Ltd. Kobe Shipyard (56) References Japanese Patent Laid-Open No. 9-80196 (JP, A) Japanese Patent Laid-Open No. 9-197083 (JP, A) (58) Survey Areas (Int.Cl. ⁷ , DB name) G21C 19/32

Claims (2)

(57) [Claims] 1. A stratification between the internal fluid and the injected cryogenic fluid by injecting a fluid having a temperature relatively lower than that of the internal fluid from a vertically lower portion of a spent fuel transportation container containing the internal fluid. A spent fuel transport container that forms an interface and replaces the internal fluid with the injected fluid by the ascending effect of the stratified interface due to the density difference between the internal fluid and the cryogenic fluid above and below the stratified interface. Fluid replacement method. 2. An apparatus for replacing an internal fluid in a spent fuel transportation container having a drain valve at a lower portion and a vent valve and a pressurizing valve at an upper portion with a replacement fluid having a temperature lower than that of the internal fluid. A storage tank for storing the replacement fluid, a replacement fluid supply line connecting the storage tank to the drain valve of the spent fuel transport container, and the replacement fluid supply line interposed therebetween. A pump for supplying the replacement fluid in the storage tank to the spent fuel transportation container, and a discharge for discharging the internal fluid to the outside, which is connected to the vent valve and the pressurization valve of the spent fuel transportation container. A device for displacing a fluid in a spent fuel transportation container, comprising a line and a recovery tank connected to the discharge line.