JPS5918398Y2 - Underwater transport device for spent nuclear fuel assemblies - Google Patents

Description

[Detailed explanation of the idea] Spent nuclear fuel at a nuclear power plant is extracted from the reactor, temporarily stored in a spent nuclear fuel pool, and then sent to a reprocessing plant after a prescribed cooling period. .

Special containers are used to transport spent nuclear fuel to this reprocessing plant, but spent nuclear fuel has radioactivity of several hundred Curies and is likely to be scattered in the air.
Loading of the transport container must be done underwater.

In other words, a transportation container is submerged in a spent nuclear fuel pool, and the spent nuclear fuel stored in a rack at the bottom of the pool is lifted underwater using a lifting tool attached to a crane, and then loaded into the transportation container. It had been taken.

In this case, the height of the nuclear thermal fuel being transported underwater must be less than the water depth required for radiation shielding, and generally the height of the spent nuclear fuel being transported is lower than the height required when passing over the transport container. Since this is the highest point, the depth of the pool is usually set at a height that provides the depth necessary for shielding the spent nuclear fuel at its highest point.

However, recently, in this spent nuclear fuel removal work,
As a hypothetical accident based on the assumption that a crane or other equipment has malfunctioned, countermeasures against falling transport containers are now required.

One of these hypothetical accidents is a fall accident when a transport container is taken in and out of a pool, but the transport container usually weighs over 70 tons, and the fall distance from the floor to the bottom of the pool is 10. Since it is normal for the fall to be several meters long, the impact force that the bottom of the pool receives from this accident is enormous. Especially in the case of a structure with a space below the pool, if some kind of countermeasure is not taken, Many of them have difficulty maintaining their structural strength.

One of the countermeasures, which has been put to practical use both inside and outside the country, is to install a shock absorber at the position where the transport container is submerged in the pool, that is, at the position where the transport container is expected to fall.

This is relatively easy and inexpensive compared to other measures, and is especially advantageous when carried out as a modification work after completion.
If there is not enough depth in the pool, radiation shielding problems will occur.

In other words, the height of the shock absorber is determined by the strength of the pool bottom structure and the efficiency of the absorber itself, and in the past, it was often around 600 mm, but when nuclear fuel is loaded, the transport container is placed on top of this shock absorber. Therefore, the radiation shielding water layer becomes thinner by that height.

Since the area of a pool is quite large, it is rare for the water depth to be determined with this much leeway.

Therefore, even if consideration was given to the use of shock absorbers from the initial planning stage, when remodeling the pool, major work had to be done to increase the depth of the pool in order to avoid insufficient radiation shielding.

This proposal relates to an improvement of an underwater transportation device for spent nuclear fuel assemblies that overcomes these difficulties, and includes a trolley movably installed above the spent nuclear fuel pool, a hoist installed on the trolley, and a hoist attached to the hoist. It has a lifting operating member that is suspended and supported so that it can be hoisted up, and a radiation shielding cover that is slidably fitted to the lifting operating member and suspended on the trolley, and the shielding cover is installed near the water surface in the water of the pool. The purpose is to provide an underwater transportation device for spent nuclear fuel that can reduce the water depth of a nuclear fuel pool as much as possible.

As described above, the present invention includes a trolley movably provided above the spent nuclear fuel pool, a hoist disposed on the trolley, a lifting operation member suspended from the hoist so as to be able to be hoisted up, and the lifting member. It has a radiation shielding cover that is slidably fitted to the operating member and is suspended on the trolley, and the shielding cover is located near the water surface of the pool, so that the upper part of the spent nuclear fuel assembly is not exposed to the surface of the spent nuclear fuel assembly. The nuclear fuel assembly can be shielded by the radiation shielding cover, and the nuclear fuel assembly can be lifted above the limit water depth and placed in a transportation container in the pool without increasing the radiation on the water surface of the spent nuclear fuel pool. In addition, since the lifting member moves up and down underwater to connect to or detach from the spent nuclear fuel assembly, highly accurate position control is required. Since it is slidably fitted to the lifting actuating member and does not move up or down, there is no water resistance and highly accurate position control is possible (aligned with the aggregate,
(can be combined).

In addition, since the shielding cover is located in a shallow part of the water, it does not obstruct the view when viewing the joint between the lifting member and the spent nuclear fuel assembly from diagonally above. When moving horizontally underwater, since the shielding cover is located in a shallow area, there is less shaking due to water resistance, there is less risk of interference with other objects, and it can come to rest quickly, allowing horizontal movement and transport inside the transport container. This makes it easy to store and operate accurately.

Therefore, according to this proposal, even if the upper end of the transport container is set at a shallower position than the water depth limit as a result of installing a shock absorber as a measure to prevent transport containers from falling, there is no need to increase the pool water depth, and the pool construction cost can be reduced. It can be lowered to a large extent.

The present invention will be described below with reference to the illustrated embodiment. Reference numeral 1 denotes a rod-shaped lifting tool which is a lifting operation member. At the lower end of the lifting tool 1, there is a metal fitting 2 for gripping the nozzle part of the spent nuclear fuel assembly 13. The lifting tool 1 is attached and detached from the water using a bundle 3 provided at the upper end of the lifting tool 1.

Further, a radiation shielding cover 4 made of steel or lead is slidably fitted to the shaft portion of the lifting tool 1, and a water depth 11 required for shielding the target spent nuclear fuel assembly 13 during transportation.
The shielding cover 4 is formed to have a length and thickness sufficient to cover the more protruding portion and to keep the radiation dose on the water surface within a specified value in that case.

Further, two eyes 5 are provided on the upper part of the shielding cover 4, and one end of a cable 6 of an appropriate length is tied to the eyes 5.
so that the lower end of the shielding cover 4 is located at the water depth 11,
The other end of the cable 6 is tied to an eye 9 of a trolley 7 that runs horizontally on a vertically movable horizontal beam (not shown).

Furthermore, the upper end of the lifting tool 1 is engaged with a hook of a hoist 8 disposed on the trolley 7, and is suspended and supported so as to be able to be hoisted up.

A storage rack 12 is installed on the bottom surface 15 of the pool where the pool water level is raised to a height of 10, and a transport container body 14 is placed via a shock absorber 16.

Since the illustrated embodiment is constructed as described above, the lifting tool 1 is lifted upwardly as shown in FIG.
is lowered by driving the hoist 8 as shown in FIG. The spent nuclear fuel assembly 13 is hoisted to the height required for loading by driving in the opposite direction, moved horizontally onto the transport container body 14 to the state shown in FIG. 4, and the hoist hook is lowered again to lift the spent nuclear fuel assembly 13 to the height required for loading. By storing the body 13 in a predetermined position within the transport container main body 14 and releasing the connection with the lifting tool 1, the spent nuclear fuel assembly 13 in the storage rack 12 can be stored within the transport container main body 14.

In this manner, according to the embodiment, only the lifting operating member, that is, the lifting tool 1 moves up and down, and the shielding cover 4 does not move up and down, so water resistance is small and the spent nuclear fuel assembly 13 can be lifted and hung smoothly. can be carried out, and the shielding cover 4
is maintained at a predetermined height underwater, preventing excessive lifting and allowing highly accurate position control, making it safe.
In addition, since the attachment and detachment of the spent fuel assembly 13 by the lifting tool 1 is performed below the shielding cover 4, it is visible and safe operation is possible. Since it is carried out at a fixed position, it has the advantage of having little water resistance and being able to come to rest quickly.

In addition, as shown in FIG. 4, a shock absorber 16
Even if the water depth necessary for radiation shielding is insufficient when loading the spent nuclear fuel assembly 13 into the transportation container 14 for additional installation, etc., the upper part of the spent nuclear fuel assembly 13 can be shielded with the shielding cover 4, The radiation dose on the water surface 10 can be kept within a predetermined value.

Furthermore, if this method is adopted from the initial planning stage, the water depth of the pool can be reduced, the construction cost of a vast pool can be greatly reduced, and it is also possible to avoid mistakes while operating the spent nuclear fuel assembly 13. In this case, the danger of being exposed to radiation by lifting the cable 6 higher than the limit height can be easily prevented by the operator being careful about slack in the cable 6.

Although the above embodiment is for a nuclear power plant, it can of course also be applied to a refactory that receives spent nuclear fuel.

[Brief explanation of drawings]

FIG. 1 is a longitudinal sectional side view illustrating an embodiment of an underwater transport device for spent nuclear fuel assemblies according to the present invention, and FIGS. 2 to 4 are side views illustrating the usage state of the embodiment.

Claims (1)

[Scope of utility model registration request] A trolley movably disposed above the spent nuclear fuel pool, a hoist disposed on the trolley, a hoisting member suspended from the hoist so as to be able to be hoisted up, and a hoisting member movably mounted on the hoisting member. 1. An underwater transportation device for spent nuclear fuel assemblies, characterized in that the device has a radiation shielding cover fitted to the trolley and suspended from the trolley, and the shielding cover is located near the water surface of the pool.