JPH09304597A - Cushioning material for disposal of radioactive waste - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to combine waterstop and venting performance by setting the proportion of constituents at a specific ratio of bentonite, ganister sand and iron powder respectively with a specific granularity. SOLUTION: A cushioning-material block 17 which separates a container housing hole 6 and a disposition overpack 14 made in underground bedrock 2 is constituted of bentonite of 40 to 20wt.%, ganister sand of 40 to 60wt.% and iron powder of 10 to 20wt.%, and the grain diameters of bentonite and iron powder are set at several to dozens μm and that of ganister sand at dozens to a hundred and dozens μm. The bentonite swells by absorbing the groundwater to prevent it from intruding, and the iron powder prevents the overpack 14 from corroding by consuming the oxygen in the groundwater and densifies the block 17. The ganister sand lets the heat of the overpack 14 escape to the bedrock 2 and can secure a measure of an air space in the block 17 because the grain diameter of the ganister sand is large. This makes it possible to store in the air space a gas such as hydrogen evolved owing to the reducing corrosion of the overpack 14 and prevent the block 17 from cracking due to gas pressure.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a buffer material for radioactive waste disposal which enables geological disposal of radioactive waste after use in a nuclear reactor such as a nuclear power plant in a stable state. is there.

[0002]

2. Description of the Related Art Radioactive wastes (radioactive waste liquids, radioactive substances, spent fuels, etc.) of high, medium and low radioactive levels are classified according to their radioactivity levels (high, medium and low), and they are applicable. It is stored and stored in a special sealed container.

In order to store and dispose of radioactive waste in a deep underground and isolate it from the living sphere, a storage container obtained by vitrifying the radioactive waste is surrounded by an overpack material such as metal and ceramics. Therefore, the geological disposal is carried out to the geological disposal site, and the geological disposal is performed by loading these into the disposal hole and filling a buffer material such as bentonite around the disposal hole.

As the cushioning material, 80 to 90% by weight of swelling bentonite and 10 to 20% by weight of silica sand having a high thermal conductivity are mixed and hardened in a block form. Is being considered.

In the above-mentioned block of cushioning material, bentonite, which is the main component, absorbs groundwater and expands, thereby eliminating the gap between the overpack and the cushioning material and the gap between the cushioning material and the container accommodating hole. The structure of densifies and prevents the intrusion of groundwater, and silica sand, which has a high thermal conductivity, releases the heat of the overpack to the underground rock, resulting in the temperature of the overpack contained in the cushioning material increasing. Is expected to function.

[0006]

However, in the cushioning material having the above components, when bentonite is swollen and the block is densified, a gas generated when the overpack is corroded (such as hydrogen gas due to reductive corrosion). There will be no route to escape to the underground rock side, and when gas accumulates around the overpack and the pressure of the gas becomes high, the gas will try to escape and the block will crack, stopping the block. May destroy water performance.

In view of the above situation, it is an object of the present invention to provide a cushioning material for radioactive waste disposal, which has both water stopping performance and degassing performance.

[0008]

SUMMARY OF THE INVENTION According to the present invention, a swelling bentonite of 40 to 40 is used as a component of a cushioning material inserted to separate a container accommodating hole formed in underground rock and an overpack for disposal. The present invention relates to a cushioning material for radioactive waste disposal, which comprises 20% by weight, 40 to 60% by weight of silica sand having high thermal conductivity, and 10 to 20% by weight of iron powder.

In this case, the particle size of bentonite and iron powder is several μm to several tens μm, and the particle size of silica sand is several tens μm.
˜100 to 10 μm may be used.

According to the above means, the following effects can be obtained.

When the disposal overpack is accommodated in the container accommodating hole, the penetration of groundwater into the buffer material block separating the container accommodating hole and the disposal overpack proceeds.

Then, since the block made of cushioning material contains 40 to 20% by weight of swelling bentonite, the bentonite absorbs groundwater and swells, and a gap between the container accommodation hole and the cushioning material, and There is no gap between the cushioning material and the disposal overpack, and the structure of the block is densified to prevent the entry of groundwater.

Then, the block made of cushioning material contains 1 part of iron powder.
Since it contains 0 to 20% by weight, oxygen content in groundwater (groundwater is originally reducible and contains almost no oxygen content, but oxygen is mixed during excavation of the underground disposal site. When the iron powder is oxidized by (due to being eroded), the oxygen content contained in the groundwater is exhausted, the oxidative corrosion of the disposal overpack is prevented, and the volume is expanded by the oxidation. The block structure is further densified to prevent groundwater intrusion more completely.

Further, since the block made of cushioning material contains 40 to 60% by weight of silica sand having a high thermal conductivity, the silica sand allows the heat of the disposal overpack to escape to the underground rock, and Prevents the disposal overpack contained therein from becoming hot.

Then, over a period of several years and time, the disposal overpack causes reductive corrosion, which progresses at a very slow rate, due to groundwater that has soaked in the buffer block. Hydrogen gas etc. is generated by the above, but since the block made of a cushioning material contains a large amount of 40 to 60% by weight of silica sand having a particle size larger than that of bentonite or iron powder by about one order of magnitude, swelling of bentonite or In the block densified by the volume expansion of iron powder,
It is possible to secure a certain amount of voids between the particles that make up the block by the particles of silica sand, and to store gas such as hydrogen gas generated by the reducing corrosion of the disposal overpack in the above voids. It will be possible.

As a result, it is possible to prevent the block from cracking due to the pressure of the hydrogen gas generated by the reducing corrosion of the disposal overpack, and to prevent the water blocking performance of the block from being destroyed.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

1 and 2 show an example of an embodiment of the present invention.

First, the underground disposal site will be described with reference to FIG.

A vertical hole 3 is drilled from the ground 1 to the underground rock 2 at a position of about 1000 m underground,
At the bottom, a container housing space 4 extending from the lower end of the vertical hole 3 in a substantially horizontal direction is formed, and a plurality of cylindrical container housing holes 6 are formed on a floor surface 5 of the container housing space 4 to form an underground disposal site 7.

Then, a building 8 is installed on the ground 1 so as to surround the vertical hole 3, and a winding device 9 such as a winch is provided in the building 8 so that the wire rope 10 wound by the winding device 9 is installed. Elevator 1 whose tip is arranged in a vertical hole 3 so that it can be raised and lowered.
1 to form a lifting mechanism 12.

Further, in the ceiling portion 13 of the container housing space 4,
Although not shown in detail in particular, an insertion device 15 such as an overhead crane is provided which can move and insert the disposal overpack 14 into each container housing hole 6 by moving in the front-rear direction, the left-right direction, etc. Mechanism 12 and insertion device 15
A delivery device such as a carrier truck 16 capable of delivering the disposal overpack 14 is provided therebetween.

Further, a block 17 made of a cushioning material is arranged in the container receiving hole 6 to separate the underground rock 2 and the disposal overpack 14.

In the present invention, the component of the cushioning material forming the block 17 is swelling bentonite.
0 to 20% by weight, silica sand with high thermal conductivity is 40 to 60% by weight, and iron powder is 10 to 20% by weight.

At this time, the bentonite and iron powder have a particle size of several μm to several tens of μm, and the silica sand has a particle size larger than these by about one digit, several tens of μm to hundreds of tens μm, preferably two. It is set to 10 μm to 30 μm.

In the figure, reference numeral 18 denotes a buffer hole cover for closing the container hole 6.

Next, the operation will be described.

A vitrified body obtained by encapsulating and solidifying radioactive waste in glass is housed in a disposal overpack 14 on the ground.

When the disposal overpack 14 is formed in this way, as shown in FIG. 1, the disposal overpack 14 is placed on the elevator 11 of the elevating mechanism 12 and the winding device 9 such as a winch is unwound to rewind the ground 1. From building 8 to vertical hole 3
Underground rock bed located approximately 1000 m underground through
It is sent to the container accommodating space 4 of the underground disposal site 7 which is formed in the horizontal direction and extends in the horizontal direction.

Then, the disposal overpack 14 sent to the container accommodating space 4 is received by a delivery device such as a transport carriage 16 and is delivered from the transport carriage 16 to an insertion device 15 such as an overhead crane.

Then, by moving the insertion device 15 such as an overhead crane that has received the disposal overpack 14 in the front-rear direction and the left-right direction, the container is transported to the target container-accommodating hole 6 and is then transferred to the container-accommodating hole 6. Insert the disposal overpack 14.

Here, in the container receiving hole 6, the inside of
A block 17 made of a cushioning material containing bentonite as a main component is arranged, and the disposal overpack 14 inserted into the container housing hole 6 is stored separately from the underground rock 2.

Then, when the disposal overpack 14 is inserted into the container accommodation hole 6, the container accommodation hole 6 is covered with the accommodation hole lid 18, and the accommodation hole lid 18 is flush with the floor surface 5 of the container accommodation space 4. To do so.

When the disposal overpack 14 is accommodated in the container accommodating hole 6 in this manner, the permeation of groundwater into the buffer block 17 separating the container accommodating hole 6 and the disposal overpack 14 proceeds. go.

Then, since the block 17 made of cushioning material contains 40 to 20% by weight of bentonite having a swelling property, the bentonite absorbs groundwater and swells, and a gap between the container housing hole 6 and the cushioning material, Also, there is no gap between the cushioning material and the disposal overpack 14, and the block 17
The organization of is blocked to prevent intrusion of groundwater.

Since the block 17 made of cushioning material contains 10 to 20% by weight of iron powder, the oxygen content contained in the groundwater (groundwater is originally reducing and contains almost no oxygen content). However, oxygen is mixed in during the excavation of the underground disposal site 7) and the iron powder is oxidized, so that the oxygen content contained in the groundwater is exhausted and the disposal overpack 14 is oxidized. In addition to preventing corrosion, the expansion of the volume by oxidation further densifies the structure of the block 17 to more completely prevent the entry of groundwater.

Furthermore, since the block 17 made of cushioning material contains 40 to 60% by weight of silica sand having a high thermal conductivity, the silica sand allows the heat of the disposal overpack 14 to escape to the underground rock 2. , It is possible to prevent the temperature of the disposal overpack 14 contained in the cushioning material from rising.

After a few years and time, the disposal overpack 14 causes reductive corrosion, which has a very slow progressing rate, due to groundwater or the like infiltrating the block 17 made of cushioning material. Although hydrogen gas is generated by the corrosion of the bentonite, since the block 17 made of the cushioning material contains a large amount of 40 to 60% by weight of silica sand having a particle size larger than that of bentonite or iron powder by about one digit, bentonite. Even in the block 17 that has been densified due to the swelling of the powder and the volume expansion of the iron powder, it is possible to secure a certain amount of voids between the particles that configure the block 17 by the particles of silica sand, and the overdisposal A gas such as hydrogen gas generated by the reducing corrosion of the pack 14 can be stored in the void.

This prevents the block 17 from cracking due to the pressure of the hydrogen gas generated by the reducing corrosion of the disposal overpack 14 and destroying the water blocking performance of the block 17.

It should be noted that the present invention is not limited to the above-described embodiment, and various changes can be made without departing from the scope of the present invention.

[0041]

As described above, according to the present invention,
It is possible to obtain an excellent effect that it is possible to have both the water stopping performance and the degassing performance.

[Brief description of drawings]

FIG. 1 is a schematic side cross-sectional view of an underground disposal site according to an example of an embodiment of the present invention.

FIG. 2 is a partially enlarged view of FIG.

[Explanation of symbols]

 2 Underground rock 6 Container accommodation hole 14 Overpack for disposal 17 Block made of cushioning material

Claims (2)

[Claims] 1. A component of a cushioning material that is inserted to separate a container accommodating hole formed in underground rock and an overpack for disposal, 40 to 20% by weight of swelling bentonite, and a thermal conductivity of A cushioning material for radioactive waste disposal, characterized by containing 40 to 60% by weight of high silica sand and 10 to 20% by weight of iron powder. 2. The buffer material for radioactive waste disposal according to claim 1, wherein the particle size of bentonite and iron powder is several μm to several tens μm, and the particle size of silica sand is several tens μm to several hundred tens μm.