JPH02236500A - Production of buffer material for disposition of 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] <Industrial Application Field> The present invention is a radioactive waste disposal device that is buried around a solidified body of radioactive waste buried underground and isolates the solidified body from the surrounding living area. The present invention relates to a method for manufacturing one of the HWy materials.

<Conventional technology> Radioactive waste generated by power generation at nuclear power plants can be broadly classified into low-level and high-level waste, but in any case, it contains radioactive materials, so it cannot be directly or indirectly introduced into the living area. In each country's radioactive waste plans, which must be disposed of without causing any adverse effects, high-level waste containing materials with high radioactivity and long half-lives, such as waste liquid from reprocessed spent fuel, must be disposed of. The most effective method for disposal is to solidify it, bury it in deep geological formations, and isolate it using human ebarium and the natural barrier of the strata, and there is a need for technological development of human ebarium materials.

FIG. 6 is a system diagram showing an example of these barriers.

Solid waste packages such as canisters and overpacks are buried around the solid waste.

Next, cushioning material, backfill material, etc. to secure these packages during burial are buried, and grouting, plugs, etc.
Seals and other items are buried to form the Human Evaria.

Outside of this, the living environment extends through a natural barrier.

<Problems to be solved by the present invention> Currently, bentonite is a promising candidate as one of the human barrier materials, and it is considered that it can be made into a buffer material with high density and sufficient barrier function and workability. It is being

When solidifying powder containing clay minerals for the purpose of increasing density, it is common to use cement and water as a binder to solidify the powder, or to add water and compact it with a rammer or roller. .

However, in any case, it is difficult to produce a high-density solidified body.

To solve this problem, the sample is placed in a cylindrical or cubic container and uniaxially compressed using a pressure plate to increase the density, but this method limits the shape of the solidified material and the friction of the container wall. There are manufacturing defects such as not being homogeneous because pressure is not transmitted uniformly.

<Objective of the present invention> The present invention was made to solve the above-mentioned problems. The purpose of the present invention is to provide a method for manufacturing a cushioning material for material disposal.

<Configuration of the Present Invention> An embodiment of the present invention will be described below with reference to the drawings.

<A> Soil buffer material The present invention uses a soil buffer material as a raw material for a buffer material for radioactive waste disposal site Evalia.

This soil buffer material shall have the following properties.

(1) Thermal conductivity The heat held by the solidified waste is released into the surrounding rock layer and dissipated, keeping the temperature near the solidified material below the allowable level, so it has good thermal conductivity.

(2) Physicochemical stability The material is stable so that it does not change physically or chemically under the temperature, pressure, and hydraulic environment of the disposal hole where solidified waste is buried underground. thing.

(3) B Water permeability and water stop property Water permeability should be as low as possible in order to retard the corrosion rate of the solidified waste package and reduce leaching of nuclides from the solidified waste.

(4) Swelling, self-sealing property, while propagating the stress from the package interposed between the solidified plastic waste and the cushioning material, while not directly transmitting the stress received from the outside due to displacement of the surrounding rock to the package; Having elasticity that relaxes.

(5) Mechanical strength The product must have mechanical strength to securely fix the package containing the solidified waste.

(6) Chemical buffering properties and nuclide adsorption properties In order to delay the transfer of nuclides to the surrounding strata after possible damage to the solidified waste package, the adsorption properties of radioactive nuclides should be good.

<Exposure> Manufacture of buffer block (Figures 2 to 5) In this example, a case will be explained in which bentonite having the above properties is used as the soil buffer material, but other general soil materials may also be used. .

First, bentonite is powdered and water is mixed in a ratio of bentonite powder:water=93±1=7±1 to prepare the fluid 11 so that the entire water distribution is homogeneous.

Note that the fluid also includes powder fluid.

Next, this fluid 11 is filled into a mold 2 of an arbitrary shape made of a flexible member such as rubber, and the lid of the mold 2 is tightened to seal it.

The mold 2 with the fluid 11 tightly sealed has a pressure of 2000 kgf/cn.
? It is placed in a pressurized container 3 having a structure capable of withstanding the above pressure.

Next, compressed liquid 31 is placed around the mold 2 in this pressurized container 3.
is injected, and the pressurized container 3 is covered and sealed.

A pressurizing means such as an oil jack 32 is attached to the pressurized container 3, and the compressed liquid 31 can be pressurized at an arbitrary pressure.

Then, using the compressed liquid 31 as a pressurizing medium, high pressure (1000 to 2000 k
g f /cJ) is added evenly to compress and solidify the fluid 11.

When there is no change in the amount of compressed liquid 31, compression is completed.

Thereby, a high-density buffer block body 1 can be manufactured.

If you want to change the shape of the block body 1, change the mold 2 to the desired shape, and use the same method as above to change the shape of the fluid 1.
By pressurizing 1, a block 1 of any shape can be obtained.

<How to use the buffer block body> As shown in FIG. 1, the buffer block body 1 manufactured as described above is stacked around the solidified waste body 4 to form a wall that seals the solidified waste body 4. Build your body.

Effects of the Present Invention> Since the buffer block body 1 produced by the above method is isotropically compressed, it has a higher density (2.2 to 2 Jg/co?) compared to the buffer material produced by the conventional method. ) and homogeneous.

In addition, it has all the properties necessary for the above-mentioned cushioning material, and its particularly excellent point is that it has extremely low water permeability (10~lo
cm/sec).

<Effects of the Present Invention> Since the present invention has been described above, the following effects can be expected.

In other words, conventional methods have been to increase the density by placing cushioning material in a cylindrical or cubic container and uniaxially compressing it with a pressure plate, but this limits the shape of the solidified material and reduces the friction of the container wall. Due to this, there are manufacturing defects such as pressure not being transmitted uniformly and therefore not being homogeneous.

In contrast, in the present invention, a flexible mold made of rubber or the like is filled with a fluid made of a mixture of soil cushioning material and water, and high pressure is applied evenly from the outside of the mold to the fluid inside. This method involves compressing and solidifying the material.

Therefore, by changing the shape of the mold, any desired shape of the buffer block can be obtained.

Further, since high pressure can be applied evenly to the fluid inside the mold, a very homogeneous buffer block body with low water permeability can be obtained.

Therefore, leakage of radioactive substances from the solidified waste can be effectively suppressed.

[Brief explanation of drawings]

Figure 1: An explanatory diagram of the buried state and state of the buffer block. Figures 2 to 5: An explanatory diagram of the manufacturing method of the buffer block. Figure 6: An explanatory diagram of the barrier system. Figure 1. Figure 2. Figure 6. Figure 1.

Claims (2)

[Claims] (1) In a method for manufacturing a buffer material for radioactive waste disposal, which is buried around a solidified body of radioactive waste buried underground and isolating the solidified body from the surrounding living area, soil buffer material powder and water are combined. Filling a flexible mold with a homogeneously mixed fluid, compressing and solidifying the fluid by applying equal pressure from the outside of the mold to the fluid inside, producing a block of high-density cushioning material. A method for producing a cushioning material for radioactive waste disposal, characterized by: (2) A method for manufacturing a buffer material for radioactive waste disposal as set forth in claim 1, using bentonite powder as the soil buffer material.