JPS61223700A - Method of storing low-level radioactive waste - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a storage method for safely storing low-level radioactive waste packed in drums or concrete containers for a long period of time.

[Technical background of the invention and its problems] Nuclear power plants, nuclear fuel reprocessing plants, and other nuclear facilities generate large amounts of low-level radioactive waste, although the radioactivity concentration is small. These are usually packed in drums or concrete containers, but as there is currently no established permanent disposal method, it is necessary to store and manage them for long periods of time, such as several decades.

The elements required for such a storage facility are that it has the capacity to store tens of thousands of bottles of waste, that it can be stored stably and safely over a long period of time, that it is easy and rational to manage, and that the equipment is rational. These include the fact that it is easy to disassemble and remove.

This is because the stored materials are generated in large quantities and are waste materials, so it is important to reduce costs as long as safety is not compromised. - Conventionally, methods have been considered or implemented to store these wastes as they are, giving priority to storage efficiency, but this method is vulnerable to damage to the waste during storage, so radioactivity is constantly released inside and outside the facility. It becomes necessary to pay attention to this. For example, in a facility that stores 20,000 pieces of waste, if each piece has radioactivity of IOCi, assuming a 1% breakage rate, then 20000
There is a risk of radioactivity being released. Actual damage is thought to be minimal corrosion or cracking, so it is unlikely that such radioactivity will be released from the goldmine. In some cases, ventilation equipment that has the ability to remove energy may be required.

At the same time, there is a risk that the inside of the facility will be contaminated, so there is a strong possibility that large-scale decontamination will be necessary during demolition and that a large amount of radioactive waste will be generated. In addition, since a large amount of waste is stored as it is, the II volume rate in the facility is relatively large, several + mR.
/h or more. This is 1 person per person for radiation exposure management purposes.
They are allowed to enter the facility for no more than 20 to 30 minutes a day.

Therefore, in consideration of unforeseen circumstances, it is necessary to have enough maintenance personnel available for a long period of several decades, and with conventional technology, when considering the long-term operation of the facility, it is not necessarily rational and uncertain. You can see that the element is included.

[Object of the Invention] An object of the present invention is to provide a method for storing low-level radioactive waste, which can be safely stored for a long period of time using reasonable equipment, and which is relatively easy to manage and dismantle.

[Summary of the Invention] A method for storing low-level radioactive waste according to the present invention is to store a plurality of low-level radioactive wastes packed in drums or concrete containers in a storage volume having a predetermined volume, by storing them on the side, top, or The waste is stored so as to maintain a certain distance between each other, and the gap between the above-mentioned intervals in the storage container is filled with sand, and the waste is buried in sand of a preset thickness. , and then the storage container is transported into a storage building and stored.

[Embodiments of the Invention] The method for storing low-level radioactive waste according to the present invention has an important feature of storing low-level radioactive waste in a state where it is buried in sand. Characteristics can be fully utilized.

(1) Acts as a barrier to the diffusion of radioactive materials. Sand itself acts as a physical barrier and is known to have adsorption properties, and is also used as a filter in radioactive waste treatment systems at nuclear power plants. ``These effects are greater as the grain size of the sand becomes smaller, but it is thought that the sand normally used in concrete production will have sufficient effects.

(2) Provides a shield from radiation. The radiation emitted from low-level radioactive waste mainly has an energy of 0.5Me■ to 2M
It is eV gamma rays, and in order to reduce the dose rate to 1/2, it is necessary to extend the sand plain to about 10 cm, and to reduce it to 1/4, it is necessary to extend about 20 cm.

(3) The price is relatively low and economical.

Next, a process example of the method for storing low-level radioactive waste according to the present invention will be explained with reference to FIG. First, the low-level radioactive waste 1 is inspected for appearance and Iil rate by the inspection equipment 2, and after the inspection is stored in the storage container 4 by the crane 3. At this time, the distance between the side surface of the storage container 4 and the waste material 1 is set to a predetermined distance to secure a sand plain. still,
In order to prevent the storage efficiency from decreasing due to this sandy field, the storage container 4
Put multiple pieces of waste into. After the storage is completed, the sand 6 in the hopper 5 is filled into the gap between the side of the storage container 4 and the waste 1, the gap between the wastes, and the top surface of the waste, and the waste is placed in the specified sand. Bury it. The sand 6 is filled from the top surface of the waste until it reaches a preset thickness.

Although the above steps are normally performed in an inspection building (not shown), it is more convenient for the hopper 5 to be installed outside the building for replenishing sand, etc. The storage container 4 that has been filled with sand 6 is transferred from the inspection building to the storage building 7 by an oak lift 8 and stored therein. In addition, transportation methods are not limited to forklifts.
It may also be the lane where you run. Furthermore, since the transfer is performed automatically or remotely and manually, people only enter the storage building when an unexpected situation such as an accident occurs.

Next, an example of the storage container 4 used in the present invention will be explained with reference to FIG. In FIG. 2, a storage container 4 capable of storing four pieces of low-level radioactive waste 1 is shown. Storage container 4
is assembled from rust-proof iron plates, etc., and its bottom plate 1
The collar 11 provided at 0 serves as a guide when storing the waste 1 and also serves to maintain the distance between the side of the storage container 4 and the waste 1 at a set value. The distance between the waste materials 1 may be as long as there is clearance for handling. Since the waste 1 will not move if it is filled with sand, additional measures to fix the position of the waste 1 are usually not necessary.

In this embodiment, an overlap margin 12 is provided so that the storage containers 4 can be stacked in multiple stages during storage, and the structure is such that the overlap margin 12 of the upper storage container 4 fits into the side plate of the lower storage container 4. Can be stored in a stable state. Also, from this, the height of the storage container is the height of the waste 1 plus the overlap with the sand plain above the waste 1.

The sand plain above the waste is set in advance and indicated by a marker 13. If the sand is filled up to this mark 13, the sand field between the side of the container and the waste and above the waste is determined by the radiation blocking effect and the 111 tA diffusion barrier effect. As mentioned above, the former can reduce the dose rate to 1/2 to 1/4 with a thickness of 10 cm to 20 cm. The latter is considered to have a thickness that exceeds that normally required for drying, as the damage to the waste will not be large-scale, the radioactivity diffusion will be quasi-static, and most of the damage can be done by sand near the surface of the waste. Never.

Note that due to this sand field, the storage efficiency is lower than when storing the waste 1 as it is, but even when storing the waste 1 as it is, the clearance for handling is approximately several cm to 10c+n per piece of the waste 1. It may become 10
Storage efficiency does not decrease significantly in ~20cm sand flats. Furthermore, in the present invention, the number of wastes to be placed in the storage container is not limited to four as shown in Figure 2, but the storage efficiency can be adjusted because the storage container can hold more wastes. .

Furthermore, the sand plain can also be optimized according to goals and conditions.

As explained above, in the present invention, by forming a sand layer of about 10 to 20 cm around the low-level radioactive waste 1, the AM rate in the storage building can be reduced to 1/2 to 1/4. can reduce maintenance staff margin by 1/2 for unforeseen situations.
It can be reduced to ~1/4. In addition, due to this decrease in the dose rate, the shielding thickness of the ceiling and walls of the storage building will be reduced to 5 to 10 cm 1 l.
(can do.

Furthermore, the possibility of radioactivity leaking into the storage building is sufficiently small, making it possible to significantly reduce or eliminate ventilation equipment capable of removing radioactivity.

Furthermore, since the inside of the storage building is not contaminated with TLI radioactivity, the facility can be easily dismantled and removed. To dispose of the sand during demolition and removal, it is sufficient to sample the radioactivity of the sand in each storage container and dispose of only those that are confirmed to be contaminated, taking radioactivity into consideration. Since the breakage rate of the waste is considered to be small, such sand is a small part of the total. Moreover, this method is advantageous because it allows prediction of the state of damage to the waste in the storage container.

In addition, in the present invention, since a plurality of wastes are integrated in a storage container, the container has good stability even when stacked in multiple stages, and is suitable for long-term storage due to its earthquake resistance and large margin against overturning. on the other hand,
Although the present invention requires sand and sand filling equipment and storage containers, they are fully compensated for by providing decades of safety and greatly reducing uncertainty during demolition. It is something that

[Effects of the Invention] As described above, the method for storing low-level radioactive waste according to the present invention makes use of the properties of sand to enable safe storage for a long period of time with rational equipment, and facilitates management and dismantling. It is.

[Brief explanation of drawings]

FIG. 1 is a process diagram showing a method for storing low-level radioactive waste according to the present invention, and FIG. 2 is a perspective view showing an embodiment of a storage container used in the present invention. 1...Low level radioactive waste 4...Storage container, 5...Hopper 6...Sand, 7...Storage building 11...Color,
12... Weight allowance 13... Sand filling mark (7317) Representative Patent attorney Noriyuki Chika (Baka 1)
Figure 1 Figure 2

Claims (1)

[Claims] A plurality of low-level radioactive wastes packed in drums or concrete containers are stored in a storage container with a predetermined volume so as to maintain a certain distance between the sides and top surfaces or between the wastes, and burying the waste in sand of a predetermined thickness by filling the gaps at intervals with sand;
A method for storing low-level radioactive waste, characterized in that the storage container is then transported and stored in a storage building.