JPS6028000Y2 - Transport container for spent nuclear fuel - Google Patents

Description

[Detailed explanation of the idea] The present invention relates to an improvement in a spent nuclear fuel transport container.

A container for transporting spent nuclear fuel (hereinafter simply referred to as a cask).

), when storing spent nuclear fuel in a fluid-tight manner in its storage space, there are two types: one in which it is stored with water, and the other in which it is not, and these are called wet type and dry type respectively. .

Of these types, in the former wet type, the water (cooling water) filled around the spent nuclear fuel is used to conduct heat to dissipate the decay heat generated from the spent nuclear fuel outside the cask. It also has the effect of shielding radiant heat emitted from nuclear fuel.

The typical spent nuclear fuel transported in wet casks is from light water-cooled nuclear reactors.

Spent light water reactor fuel is made up of long and narrow bundles of fuel, with a type of metal fitting for attachment or handling arranged at both ends of the bundle.

Radiation and heat are primarily emitted by the fuel rods.

On the other hand, even if there is a virtual fire accident in the cask,
Sufficient airtightness is required, but in the event of an accident, the inside of the cask would reach a considerable high temperature, so if the storage space is filled with cooling water, its thermal expansion force may cause damage in the event of a fire. The cooling water becomes compressed water and has an abnormally high pressure, and it is usually difficult to keep it safely sealed inside the cask due to the strength of the cask.

Therefore, in wet casks, cooling water is usually filled in the storage space with a small amount of air to prevent the cooling water from reaching the state of compressed water even under high temperatures during a fire accident. It is generally designed to.

However, although this method prevents the outer shell of the cask from being destroyed due to abnormally high pressure in the storage space in the event of a fire accident, on the other hand, during normal transportation of spent nuclear fuel (the cask It is stacked horizontally on top of the transport vehicle.

), the upper part of the fuel rods in the storage space is not filled with cooling water.

A gas phase portion is created above.

Therefore, the above-mentioned effect of radiation shielding by the cooling water cannot be expected in the gaseous portion near the fuel rods of the spent nuclear fuel since the radiation is emitted from the fuel rods.

Also, heat transfer to the cask body where the cooling fins are located is impeded.

Therefore, there is a problem in that it is necessary to take measures such as increasing the thickness of the shielding material.

The present invention was proposed with the aim of solving the above-mentioned problems of the conventional methods. Spent nuclear fuel is inserted into a storage space surrounded by radiation shielding material, and the water inside the cylindrical container is sealed and transported. At the top and bottom of the filling area, a closed container having a reduced pressure gas phase space and configured to be easily destroyed due to an abnormal temperature rise of the water in the water filling area is provided, and further This relates to a container for transporting spent nuclear fuel, which has a large number of fins protruding from the outer peripheral surface of the body of the cylindrical container.

Hereinafter, the present invention will be described in detail with reference to embodiments shown in the accompanying drawings.

In the figure, 1 is a cylindrical outer shell of the cask, and 2 is its lid. By fitting and fixing 2 to the cask outer shell 1 as shown in the figure, the inside of the cask outer shell 1 is sealed fluid-tightly. It is now possible to do so.

The members 1 and 2 are made of a radiation shielding material such as copper or copper and lead to form a radiation shielding material.

3 is a neutron shielding water layer filled in the space formed between the outer periphery of the cask outer shell 1 and heat dissipation fins 4, which will be described later, as shown in the figure; A heat dissipation fin 5 attached to the cask shell 1 is a storage space surrounded by radiation shielding material, and the storage space 5 is filled with cooling water and used to load spent nuclear fuel. A basket 6 is incorporated, and spent nuclear fuel 7 is loaded into the basket 6.

8', 8'' are airtight containers having a reduced pressure gas phase space inside, and these airtight containers 8', 8'' are connected to the basket 6.
are disposed at the upper and lower portions of the storage space in the longitudinal direction, that is, at the top and bottom portions within the water-filled region of the storage space surrounded by the radioactive shielding material.

In this case, the outer periphery of the closed containers 8', 8'' is covered with cooling water.

Further, the gas phase space inside the closed containers 8', 8' is evacuated or filled with reduced pressure air.

Total volume of these airtight containers 8' and 8'' (width of gas phase space)
is equal to the volume that the cooling water in the storage space 5 expands while rising from the temperature at the time of normal spent nuclear fuel transportation to the temperature at the time of a fire accident, and the temperature or pressure of the cooling water is equal to the temperature at the time of normal use. If the nuclear fuel rises abnormally beyond that during transportation, the sealed containers 8', 8'' will be easily destroyed,
The structure is such that the airtightness is lost.

For example, the airtight containers 8', 8'' may be configured to have a structure and strength that allow them to be easily buckled or destroyed by an increase in external pressure, and may also be configured to have a structure and strength that allows them to be easily buckled or destroyed when a certain temperature is exceeded. It may be made of an alloy material having a melting point such that it melts.

The present invention is characterized in that the sealed containers 8' and 8'' having such a structure are respectively disposed at the top and bottom of the water-filled region of the cask sealed with radiation shielding.

When using the cask according to the present invention, spent nuclear fuel 7
When loading the water into the basket 6 built into the storage space 5 and sealing it together with cooling water, the volume of the storage space 5 must be adjusted to within a range that does not result in abnormally high pressure compressed water under the temperature conditions during transportation. Fill in enough cooling water to fill the

Therefore, when transporting spent nuclear fuel in vertical casks,
The cooling water expands due to the heat generated by the spent nuclear fuel and fills the storage space 5, but its pressure remains close to the saturated vapor pressure at that temperature and does not show any abnormal rise.

Therefore, during normal transportation of spent nuclear fuel, the closed container 8',
8" will not be destroyed.

Furthermore, even if the sealed container 8'' at the bottom is destroyed for some reason during suspended transportation within the power plant, and the water level of the cooling water in the storage space 5 drops, in such a case, the spent nuclear fuel 7 together with the basket 6, the storage space 5 is reduced by its own weight.
As the spent nuclear fuel 7 descends downward, the upper end of the spent nuclear fuel 7
No exposure to cooling water.

Therefore, there is no gas phase in the storage space 5 of the cask, or there is almost no gas phase, so that the heat dissipation and radiation shielding effects of the cooling water extend to the entire circumference of the cask.

On the other hand, if the Koshimoto cask encounters a fire accident while being transported off-road outside the power plant, the temperature and pressure of the cooling water will naturally rise, resulting in an airtight container 8', 8'' with a gas phase space.
will be destroyed.

Therefore, the volume occupied by the cooling water in the storage space 5 is the volume occupied by the airtight container 8.
'.

Therefore, by appropriately setting the volume of the sealed containers 8' and 8'', even if the cooling water reaches the maximum temperature at which a fire occurs and expands considerably, There is no case of abnormally high pressure compressed water, and the pressure resistance of the cask shell is sufficient to be close to the saturated vapor pressure at the maximum temperature.

In addition, since the inside of the airtight containers 8', 8'' is evacuated or filled with reduced pressure air, compared to the case where air at atmospheric pressure is sealed inside, the airtight container 8', 8'' This has the advantage of lowering the pressure rise of the cooling water.

Since the spent nuclear fuel transport container of the present invention has the above-mentioned structure and function, the present invention solves all the above-mentioned conventional problems. If so, the gas phase inside the storage space 5 of the transport container will be non-existent, or there will be a very small amount close to it, so the heat emitted from the fuel rods of the spent nuclear fuel is transferred to the finned body by cooling water. The heat is transmitted through, and the heat is dissipated appropriately.

Furthermore, radiation emitted from the fuel rod portion in the radial direction is also suitably shielded.

Furthermore, in the event of a fire accident, the airtight containers 8' and 8'' are destroyed, and the volume occupied by the cooling water in the storage space 5 increases by that volume, so that the cooling water does not turn into abnormally high-pressure compressed water. Moreover, there is an advantage that the sealed containers 8', 8'' at the top and bottom of the storage space 5 provide an impact protection effect for the stored spent nuclear fuel 7.

In other words, the spent nuclear fuel transportation container is required to have sufficient safety even if it is subjected to a free fall impact from a height, but in this case, the present invention When the spent nuclear fuel container falls in the axial direction, the airtight container 8' at the top and bottom of the storage space 5
, 8'' function as a shock absorber for the stored spent nuclear fuel, which has the advantage of ensuring its nuclear safety.

[Brief explanation of the drawing]

The accompanying drawing is a schematic vertical sectional view of an embodiment of the present invention. 1: Spent nuclear fuel container (cask) outer shell, 2: Lid, 3:
Neutron shielding water layer, 4: Cooling fins, 5: Storage space, 6
: Basket, 7: Nuclear fuel, 8', 8'': Closed container having a reduced pressure gas phase space inside.

Claims (1)

[Scope of utility model registration request] A cylindrical container in which spent nuclear fuel is inserted into a storage space surrounded by radiation shielding material and transported in a sealed manner has a depressurized gas phase space at the top and bottom of a water-filled region, and the water-filled region Each of the cylindrical containers has a closed container configured to be easily destroyed due to an abnormal temperature rise of the water inside the container, and a large number of fins are provided protruding from the outer peripheral surface of the body of the cylindrical container. Container for transporting spent nuclear fuel.