JPH0634082B2 - Reactor facility caispit - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a cask handling method in a nuclear power plant, and more particularly to a cask pit suitable for decontamination work of a cask.

[Background of the Invention]

Spent fuel, radioactive solid waste such as control rods generated in the nuclear reactor is extracted from the core and then stored in the water in the spent fuel pool. After that, these radioactive solid wastes are sent to the reprocessing plant for spent fuel, and to the site bunker equipment, which is a dedicated storage facility for other radioactive solid wastes. A dedicated transfer container (hereinafter referred to as a cask) having the above is used.

The cask handling method conventionally used around the spent fuel pool in the reactor building is shown in Figs. 7 and 8 below.
It will be described with reference to the drawings. FIG. 7 is a plan view showing the arrangement of equipment on the fuel handling floor in a boiling water reactor building, and FIG. 8 is a vertical sectional view thereof.

The cask 7 is carried into the reactor building by a dedicated truck, and is lifted by the overhead crane 8 from the large object entrance 4 to the fuel handling floor. After that, the cask 7 is washed in the cask decontamination pit 3, and the lid, the valve, and the seal portion are inspected for leaks. After removing the cask lid, a submersible hanger is attached and suspended in the cask pit 2. Caskpit 2 is installed in a corner of spent fuel pool 1, and canal 5
It is connected to the pool 1 via.

Next, the gate 6 is removed, and the radioactive solid waste stored in the spent fuel pool 1 is moved to the cask pit 2 through the canal 5 and loaded into the cask 7. Then, the cask 7 is covered with a lid, hoisted by an overhead crane 8, conveyed to the cask decontamination pit 3, the lid bolts are tightened, the cask outer surface is decontaminated, and various inspections such as a leak test are performed. To carry out.

In the above conventional procedure, the cask 7 is moved to the cask pit 2
Cask decontamination work to prevent water pollution in the pit 2 before it is carried into the building, and work to remove radioactive substances adhering to the outer surface of the cask in the cask pit 2 before being carried out outside the building, Is performed by wiping with a cloth waste in the cask decontamination pit 3.
This is a tedious task. In particular, in the case of a cask for transferring spent fuel, fins are attached to the outer surface of the cask to increase the effect of dissipating the heat generated by the stored spent fuel. Is needed.

Also, when suspending the cask in the cask pit 2, and
Since the vertical hanger 10 connected to the hook 9 of the overhead crane is immersed in water when it is carried out from the cask pit 2, it is necessary to decontaminate it.

In addition, the cask pit 2 with spent fuel loaded into the cask
When carrying out from the cask decontamination pit 3 to the cask decontamination pit 3, there is a work of washing a cask (weight of about 70 tons) above the cask pit 2 while hanging it in the air, and a work of installing a safety stand and temporarily tightening four bolts. It is necessary and is bothersome in terms of work and unfavorable for safety. Further, since the cask 7 is carried out from the water in the cask pit 2 and washed while being suspended, when the cask 7 is transferred to the cask decontamination pit 3, vinyl or poly sheet or the like 11 is used to prevent contamination of the operation floor.
Therefore, secondary work such as curing work and decontamination or disposal of the living creatures occurs to some extent.

Furthermore, it is important to note that the conventional cask pits did not take care to prevent the cask from tipping over.

Japanese Patent Laid-Open Publication No. Sho 55 is a patent document which describes in detail the method of operating the cask pit in the conventional spent fuel loading / unloading operation.
-36753 and JP-A-55-36754.

[Object of the Invention]

An object of the present invention is to provide a cask pit capable of preventing the cask from falling over in the cask pit and simplifying the cask handling work.

[Outline of Invention]

The cask pit of the present invention has an auxiliary pit at the bottom for accommodating the cask, and the sectional size of the auxiliary pit is the cask when the cask placed in the auxiliary pit is tilted by an external force and comes into contact with the wall of the auxiliary pit. The maximum tilt angle of the cask is set to be smaller than the critical tilt angle at which the cask falls, so that when the cask is tilted by an external force, it can be restored and become self-supporting. Is equipped with a cask decontamination device.

Example of Invention

An embodiment of the present invention will be described below with reference to FIGS. 1 to 6.

FIG. 1 is a plan view showing the equipment arrangement of a fuel handling floor according to the present embodiment, FIG. 2 is a vertical sectional view thereof, and FIG. 3 is a side view of a cask with a partial cross section.

The cask 7 carried to the reactor building by the trailer was lifted from the large cargo port 4 to the fuel handling floor by the main hook of the ceiling crane that was unloaded from the fuel handling floor, and the lower cushion pair 14 provided in preparation for cask lowering was installed. After being removed, it is carried into the cask inspection pit 13. Cask inspection pit 1
3 corresponds to the conventional cask decontamination pit 3,
In the present invention, the inspection is performed in the pit 13, but the decontamination work is not performed.

In the cask inspection pit 13, a cask fall prevention device (not shown) is attached in consideration of the fall of the cask 7 in the unlikely event.
Radioactivity of the cask 7 at the time of acceptance is measured. Next, a leak test of the vent valve 15 for adjusting the internal pressure of the cask and the drain valve 16 for draining water from the cask is performed to confirm the hermeticity of the cask.

After the leak test is completed, the lid 18 of the cask 7 is removed, and the radioactivity inside the cask is measured. After that, the main hook 9 of the overhead crane 8 is set on the vertical hoisting tool 10, the hoisting tool 10 is attached to the trunnion 19 of the cask, the cask fall prevention device is removed, and the hoisting crane 10 is carried into the cask pit 12 in the spent fuel pool 1.

Cask pit 12 has an upper pit 12 _1, provided at the bottom, consisting of smaller diameter auxiliary pits 12 _2. To cask 7 to minimize the damaging fall down by the earthquake or the like, the cross-sectional dimension of the auxiliary pits 12 _2, when in contact with the auxiliary pits 12 _second wall inclined cask placed in the auxiliary pit The maximum tilt angle is determined to be smaller than the critical tilt angle that causes the cask to fall, and
Even if the contact cask is nodding to its fall event to the auxiliary pit 12 ₂ of the wall it is as recover and restore again. The diameter _{D p} of the auxiliary pits 12 ₂ for this To be Here, H _p is the depth of the auxiliary pit, D _c is the diameter of the cask, and H _c is the height of the cask.

Before loading the cask 7, the cask pit 12 has a gate 6 having a water sealing function installed in a canal 5 between the spent fuel pool 1 and the cask pit 12, and then drains water from the cooling purification system drainage pipe 20. Keep it. In this state, to carry the cask 7 to cask pit cylindrical 12 auxiliary pits 12 _2. In this case, since the cask 7 is carried in with the water drained as described above, the vertical suspension 10 is not immersed in water and is not contaminated by pool water.

After confirming that the cask 7 descended to the bottom of the auxiliary pits 12 _2, as shown in FIG. 4, it is placed an auxiliary pit lid 21 to the opening of the auxiliary pits 12 _2. The auxiliary pit lid 21 by contacting through the pit opening the seat surface 22 and the gasket 23 has a function of isolating the upper pit 12 ₁ of the cask pit 12.

Upper cask pit 1 auxiliary pit 12 ₂ by a cover 21
2 ₁ and after isolation, Figure 4 which is installed in the auxiliary pits 12 _2, cask by decontamination apparatus 24 shown in FIG. 5 7
To wash. The decontamination device 24 may be replaced by a nozzle that ejects high-pressure jet water, but in the present embodiment, the cask 7 is provided so as to surround the cask 7 in the vertical direction, and the cask is attached to the drive shafts 25 arranged at equal intervals. 7 is installed so as to rotate in the direction along the fin 17, and the decontamination is performed by the brush 26 that is installed over the entire length of the cask 7 having bristles slightly longer than the radial length of the fin 17. ing. Cask 7 is cleaned under running pure water by a spray 30 provided near the auxiliary pits 12 ₂ opening. Wash water is drained from the drain pipe 27 provided in the auxiliary pit 12 ₂ bottom.

After the decontamination work is completed, the auxiliary pit lid 21 is removed, and the cask pit 12 is fed through the cooling and purification system water supply pipe 41 shown in FIG.
The inside is filled with water until it reaches the same water level as that of the spent fuel pool 1. However, the order to meet the water, first the cask 7 after the full water slowly filled with water between the auxiliary pits 12 ₂ and cask 7, then water in the upper pit 12 _1. At this time, it is necessary to be careful to supply water after confirming that the valves 29 and 28 attached to the drain pipe 27 and the cooling and purification system drainage pipe 20 are closed.

After the water depth is secured by filling the water in this way at the time of fuel transfer, the spent fuel is loaded into the cask 7 through the canal 5, and the cask pit 12 is filled with water. Cover the cask 7 with a lid 18. After confirming that the lid has been completely closed, the canal 5 is closed at the gate 6, the valve 28 of the cooling and purification system drainage line 20 is gradually opened, and water in the cask pit 12 is drained. When the water is finished completely drained and after isolating the upper pit 12 ₁ is mounted an auxiliary pit lid 21 performs decontamination of the cask 7 the outer surface by the decontamination device 24. After the decontamination work for a predetermined time is completed, the auxiliary pit lid 21 is opened and radiation measurement is performed to confirm the degree of decontamination, and after confirming that sufficient decontamination has been performed, the auxiliary pit 122 ₂ After drying the outer surface of the cask 7 by blowing dry air from the nozzles 31 installed at an appropriate pitch, the cask lid 18 is tightened while controlling the torque.

In this state, drop the vertical suspension 10 from the overhead crane 8,
After moving the cask 7 loaded with the spent fuel to the cask inspection pit 13 and attaching a cask tipping prevention device (not shown), after performing radiation measurement, surface dose rate measurement, water level adjustment, temperature measurement and leak test, It is taken out of the reactor building and transferred to the subsequent processing facility.

FIG. 6 shows the water supply, drainage and cooling purification system in this embodiment.

According to this embodiment, decontamination of a complicated portion having a shape such as the fin 17 of the cask 7 can be easily performed, and the work efficiency is improved.

Further, since water is not poured into the cask pit when the cask 7 is carried in and out of the cask pit 12, the vertical hoisting gear 10 connected to the hook 9 of the overhead crane 8 is not immersed in water, and thus the vertical hoisting gear 10 No need for decontamination work, secondary work can be reduced, and man-hours for handling cask can be reduced.

Further tightening of the lid 18 of the cask 7, because perform the cask 7 while set stably in the auxiliary pits 12 _2,
Unlike the conventional case, the cask 7 is lifted to the middle in the cask pit 2 and stopped, and the work of temporarily installing the safety stand and temporarily tightening is unnecessary, and the number of work steps can be reduced.

Further, since the cask 7 can be moved from the cask pit 12 to the cask inspection pit 13 in a dried state, there is no need for curing for preventing contamination of the floor which is the path of the cask 7, reducing the number of work steps and secondary waste. Occurrence can be reduced.

Of course, there is an effect that the cask can be prevented from falling in the auxiliary pit.

〔The invention's effect〕

 The present invention has the following effects.

(1) Even if the cask tilts in the auxiliary pit due to an external force such as an earthquake, it can be restored and self-supporting without falling, so damage to the cask due to falling can be prevented, and the reliability of cask handling in the reactor plant is improved. be able to.

(2) Since the cask can be decontaminated within the limited area of the auxiliary pit, it is possible to minimize radioactivity scattering during decontamination, and at the inspection pit after it has been carried into the cask inspection pit. Exposure during various inspection work is reduced.

(3) When the cask is moved to the cask inspection pit, no curing is required to prevent contamination of the floor surface, which is a route, and the number of man-hours for secondary work can be greatly reduced.

(4) When the cask is carried out to the cask pit, it is possible to prevent the vertical lifting device from being immersed in water, so the decontamination work of the vertical lifting device is not required.

[Brief description of drawings]

FIG. 1 is a plan view showing the arrangement of equipment on a fuel handling floor according to an embodiment of the present invention, FIG. 2 is a vertical sectional view thereof, FIG. 3 is a side view of a cask with a partial cross section, and FIG. FIG. 5 is a vertical sectional view showing an auxiliary pit and its internal device in the example, FIG. 5 is a plan view of FIG. 4, and FIG.
A cooling purification system diagram, FIG. 7 and FIG. 8 are a plan view and a vertical sectional view, respectively, showing the equipment arrangement of a conventional fuel handling floor. 1 …… Spent Fuel Pool 2 …… Cask Pit 3 …… Cask Decontamination Pit 4 …… Large Carrying Port 5 …… Canal 6 …… Gate, 7 …… Cask 8 …… Overhead Crane, 9 …… Hook 10 ... Vertical lifting tool 11 ... Vinyl or poly sheet 12 ... Cask pit, 12 ₁ ...... Upper pit 12 ₂ ...... Auxiliary pit 13 ...... Cask inspection pit 14 ...... Lower buffer, 15 ...... Vent valve 16 …… Drain valve, 17 …… Fin 18 …… Cask lid, 19 …… Trunnion 20 …… Cooling purification system drainage pipe 21 …… Auxiliary pit lid, 22 …… Seat surface 23 …… Gasket, 24 …… Decontamination equipment 25 ... Drive shaft, 26 ... Brush 27 ... Drain pipe, 28 ... Drain valve 29 ... Cooling purification system drain valve 30 ... Spray pipe 31 ... Dry air nozzle 32 ... Ski Surge tank 33 …… Condensate storage tank, 34 …… Residual heat removal system 35 …… Fuel pool pump 36 …… Makeup water system, 37 …… Diffuser 38 …… Reactor auxiliary equipment cooling system 39 …… Fuel pool heat exchanger 40 ... Fuel pool filtration desalination equipment 41 ... Cooling purification system water supply piping 42 ... Liquid level gauge, 43 ... Pump 44 ... Waste treatment system

Claims (4)

[Claims] Claims: 1. Adjacent to a pool for storing spent fuel and other radioactive solid waste generated in a nuclear reactor in water, the pool is connected via a canal so as to be separable by a gate, and In a cask pit of a nuclear reactor facility having a space where a cask for carrying in and out of fuel and other radioactive solid waste can be placed, the cask pit has an auxiliary pit capable of accommodating the cask at the bottom, The cross-sectional dimensions are such that the maximum tilt angle of the cask when it comes into contact with the wall of the auxiliary pit leads to the fall of the cask so that the cask placed in the auxiliary pit is restored and becomes independent even if it leans due to external force. It is set to be smaller than the critical tilt angle, and a cask decontamination device for cask decontamination equipment is provided in the auxiliary pit. . 2. A cask pit for a nuclear reactor facility according to claim 1, wherein the auxiliary pit can be provided with a sealable lid. 3. The cask decontamination device comprises a plurality of rotating brushes surrounding the cask and nozzle means for pouring washing water toward the cask.
Cascade of the nuclear reactor facility described in the paragraph. 4. The auxiliary pit comprises cask drying means for blowing air to the cask.
The cask pit of the nuclear reactor facility according to the paragraph 2, 3 or 3.