JP2010223844A - Shield louver with movable cascade slits - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve improvement in required countermeasures for such as the importance of radiation shielding design in an existing storage facility for radioactive material where (1) a large number of metal casks encapsulating spent fuel are stored in a relatively narrow site, and (2) in order to avoid an excessive rise in temperature of the metal casks, the facility is provided with large opening parts (an air intake opening and an exhaust tower) for efficiently releasing heat outside the facility by natural cooling. <P>SOLUTION: A shield louver composed of movable cascade slit plates is installed on the exhaust tower in order to reduce streaming through the air intake opening of the storage facility for radioactive material or spent fuel. The cascade slit plates are arranged in parallel with each other so as to minimize the obstruction of air flow. As for the slit plates, their angle can be changed corresponding to a target dose level so that the shielding effect can be adjusted. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a shielding louver in a radioactive material storage facility.

The current radioactive material storage facilities are characterized by the following: (1) A large amount of metal cask containing spent fuel is stored in a relatively small site.
(2) In order to avoid an excessive temperature rise of the metal cask, it is mentioned that a large opening (intake port and exhaust tower) for efficiently releasing heat to the outside of the facility by natural cooling is provided. In addition to the above features, the facility is closer to the site boundary than the existing nuclear power plant and nuclear fuel reprocessing facility, and neutrons and gamma rays generated from metal casks are required to comply with legal dose target values at the site boundary. Therefore, it is important to design shields against radiation.

  Japanese Patent Application Laid-Open No. 2002-40191 describes a technology provided with a blade unit regarding a duct radiation shielding structure.

JP 2002-40191 A

Journal of Japanese Society of Atomic Energy, vol.6, No.2, p.225-238 (2007)

  As described above, in the radioactive material storage facility, radiation streaming from the air inlet and the exhaust tower becomes a problem in order to comply with the target dose at the site boundary. In order to reduce radiation streaming, the louver may be arranged perpendicular to the direction of the exhaust tower axis. In this case, however, the flow of air is obstructed and the heat removal efficiency is lowered. Measures such as increasing are taken. Accordingly, an object of the present invention is to reduce streaming while ensuring air flow in the exhaust tower.

  The main feature of the present invention is that a shielding louver made of a movable blade row-type slit plate is installed in the exhaust tower in order to reduce streaming from the intake of a radioactive material or spent fuel storage facility. To do. About a cascade row type | mold slit, it arrange | positions in parallel so that it may not inhibit the flow of air as much as possible. The slit plate can adjust the shielding effect by changing the slit plate angle according to the target dose level.

  In addition, the slit has a two-layer structure of iron and resin, and the microscopic structure of the surface of the wing-shaped slit plate and the inner surface of the exhaust tower is a saw blade type process (FIG. 2).

  When adopting the movable blade row type slit of the present invention (FIG. 1), the streaming from the exhaust tower is reduced as compared with the current one shown in FIG. 3 without greatly hindering the air flow in the exhaust tower, It is possible to reduce the dose at the site boundary.

  In particular, it is the most characteristic that the shielding effect can be adjusted by changing the slit plate angle. Changing the shielding performance freely without changing the number of layers of the slit plate leads to standardization of the storage facility and can improve the economic efficiency.

  The following equation is established approximately for the leakage radiation dose.

  Dose ∝ S '/ S (See Fig. 4 for S and S').

Schematic diagram of a metal cask intermediate storage facility. Cascade-type slit inside the exhaust tower. FIG. Schematic diagram of a metal cask intermediate storage facility (flat slit). About leakage radiation dose. Schematic diagram of a metal cask intermediate storage facility (corrugated slit).

  Embodiments of the present invention will be described below with reference to the drawings.

  Facilities that store nuclear fuel that has been used for a certain period of time at nuclear power plants, etc. are designed to efficiently release heat outside the facility by natural cooling in order to avoid excessive temperature rise of the metal cask due to decay heat of spent fuel. A large opening (exhaust tower) is provided. In addition, since a large amount of metal cask filled with spent fuel is stored in a relatively narrow site, a shielding design against radiation streaming from the exhaust tower is required to comply with the target dose at the site boundary of the facility. Is important. Specifically, there is a need for a design that reduces radiation streaming while ensuring sufficient air flow in the exhaust tower.

  FIG. 1 is a schematic view of a cask-type intermediate storage facility that employs a shielding louver having a movable blade row type slit plate of the present invention. The facility stores a metal cask 2 filled with spent fuel 1 in the facility, and exhausts decay heat released from the intake ports 3 and 2 for taking air from outside into the facility. And an assembly 5 of movable blade row slit plates 6 is disposed inside the exhaust tower 4. The air around the metal cask heated by the metal cask rises and is discharged from the exhaust tower to the outside of the facility, and the outside air is taken in from the intake port. The cask is cooled by natural cooling by this air circulation. FIG. 2 is an enlarged view of a sectional view and a side view of the inside of the exhaust tower 4. Each slit plate 6 is connected to a rotating rod 7, and the rotating rod 7 is connected to the exhaust tower with a structure that can freely rotate. According to the measurement result of the radiation dose at the site boundary and the measurement result of the housing surface temperature of the storage facility, the angle of the slit plate is adjusted by rotating the rotating rod 7 from the management room outside the facility. If the measured radiation dose level is higher than the target value, tilt the slit plate so that it approaches perpendicular to the exhaust tower axis direction.If the measured enclosure temperature is high, increase the air flow rate. The amount of radiation leaked is adjusted by tilting it closer to the exhaust tower axis direction. In adjusting the angle of the slit plate, each slit plate is interlocked, and each slit plate always keeps parallel. This is to minimize the air flow obstruction effect (air pressure loss effect).

  It has been confirmed that the amount of radiation leaked by the radiation streaming from the facility is approximately ∝S ′ / S using S and S ′ shown in FIG. 5 (quantitative knowledge about air pressure loss, Although there is no evaluation result, the pressure loss tends to increase with the phenomenon of S ′ / S). The radiation dose adjustment function described above is very useful when considering the case where the same facility is expanded on the same site. The radiation dose at the site boundary is the total of the radiation doses from all the relevant facilities in the site, and when the present invention is applied, the radiation dose from existing facilities other than the newly established facility can be controlled. It is thought that the degree can be increased.

  The slit plate 6 has a two-layer structure of iron (shielding body effective for shielding gamma rays) and resin (shielding body effective for shielding neutrons), and a microscopic view of the surface of the slit plate 6 and the inner surface of the exhaust tower 4. The target structure can be further reduced by using the saw blade processing shown in FIG.

  As shown in FIG. 2, a cask-type intermediate storage facility having a shielding louver having a structure in which a plurality of flat plate slits are arranged parallel to each other.

  A cask-type intermediate storage facility having a shielding louver composed of corrugated slit plates as shown in FIG.

  [Embodiment 2] Regarding the effect of [Embodiment 3], the amount of radiation leaked from the facility can be approximately expressed as a dose ∝S '/ S as described above. It is possible to reduce the leakage dose as compared with the one arranged in parallel with. Compared with [Example 1], it can be constructed at a low cost because it is a fixed type and does not have a slit rotation function.

The ratio of the number of metal casks accommodated at that time to the maximum number of metal casks accommodated is adjusted so that the slit elevation angle θ shown in FIG.
(I) When 0 to 40% metal cask is stored: 20 degrees (ii) When 40 to 70% metal cask is stored: 30 degrees (iii) 70 to 90% metal cask is stored When it is: 40 degrees (iv) When 90 to 100% of the metal cask is stored: 50 degrees

  If the facility is expanded on the premises, the figures will be revised.

  As described above, the storage room for storing the sealed container containing the radioactive substance is provided, and the intake port for taking in the air taken from the outside into the storage room and the exhaust tower for discharging the air in the storage room to the outside. The radioactive material storage facility is provided with a radiation dose measuring device, and in the radioactive material storage facility provided with a slit plate in the exhaust tower, the slit plate is a movable blade row type, the movable blade is movable The flow of air in the exhaust tower according to the operation method of the radioactive substance storage facility, in which the dose measurement value is set to be a constant value from the ratio of the storage container in the storage chamber or the dose measurement value obtained from the radiation dose measuring device Is to reduce streaming while ensuring. This may be performed manually or may be performed by a control device that performs control based on the measurement values taken from the radiation dose measuring device.

  A radiation dose measuring device is provided in a radioactive material storage facility (for example, an exhaust tower), and the slit elevation angle θ is adjusted so that the dose measurement value is always a constant value regardless of the number of metal casks accommodated in the facility.

  A temperature measuring device is provided in the exhaust tower, and the slit elevation angle θ is adjusted so that the temperature of the air discharged outside the facility is always below a certain value regardless of the amount of radiation leaked.

1 Spent Fuel 2 Metal Cask 3 Inlet 4 Exhaust Tower 5 Assembly 6 Slit Plate 7 Rotating Rod

Claims (5)

A storage chamber for storing a sealed container containing a radioactive substance; an intake port for taking in air taken from the outside into the storage chamber; and an exhaust tower for discharging the air in the storage chamber to the outside,
In a radioactive material storage facility comprising a slit plate in the exhaust tower,
A radioactive substance storage facility, wherein the slit plate is of a movable blade row type. In the radioactive substance storage facility according to claim 1,
The said slit board has the shielding louver of the structure which has arrange | positioned the several flat plate slit so that it may become parallel for every step, The storage facility of the radioactive substance characterized by the above-mentioned. In the radioactive substance storage facility according to claim 1 or 2,
The said slit board has a shielding louver comprised from a waveform slit board, The storage facility of the radioactive substance characterized by the above-mentioned. In the radioactive substance storage facility according to any one of claims 1 to 3,
A radiation dose measuring device is installed in the radioactive substance storage facility,
The movement of the movable wing is set according to a ratio of the storage container in the storage chamber or a dose measurement value obtained from a radiation dose measuring device. A storage chamber for storing a sealed container containing a radioactive substance; an intake port for taking in air taken from the outside into the storage chamber; and an exhaust tower for discharging the air in the storage chamber to the outside,
A radiation dose measuring device is installed in the radioactive substance storage facility,
In a radioactive material storage facility comprising a slit plate in the exhaust tower,
The slit plate is a movable blade row type,
The movement of the movable wing is set so that the dose measurement value becomes a constant value from the ratio of the storage container in the storage chamber or the dose measurement value obtained from the radiation dose measuring device. How to operate the facility.

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