JPH0631883B2 - Radioactive waste disposal methods and filling materials - Google Patents

Description

The present invention relates to a method for disposing of radioactive waste discharged from nuclear facilities such as nuclear power plants, nuclear fuel manufacturing plants, and laboratories related to nuclear power, and particularly solidification treatment. The present invention relates to a method of disposing low-level radioactive waste in a shallow land and a filler after being subjected to the above.

[Prior art] Among low-level radioactive waste discharged from nuclear facilities, those discharged in a liquid state are subjected to volume reduction treatment such as ion exchange and evaporation, and then solidified with cement, alfalto or plastic. It is stored in a container such as a drum. What is discharged in the solid state is
After being subjected to volume reduction processing such as combustion and compression molding, it is stored as it is or after solidification in a drum or a concrete container. At present, the majority of the containers containing these low-level radioactive wastes are stored in the storage facility inside the generating facility.

The radioactive waste stored in the storage facility inside the generating facility is to be disposed outside the generating facility when the storage capacity of the generating facility reaches the limit.

Disposal of radioactive waste means placing the radioactive waste outside the living environment of the person and removing it from the person's management, and is a measure opposite to the storage under the person's control. In principle, the disposed radioactive waste is left semi-permanently without returning to the control of human beings, so during the period when the radioactive waste contained in it leaks to the outside, its radioactivity decays. It must be made harmless.

In Japan, low-level radioactive waste disposal methods include ocean disposal by submersion of containers along the deep ocean floor and a concrete storage facility constructed at a shallow location isolated from groundwater. Disposal is being considered.

In Japan, it is decided to perform ocean disposal on the deep sea floor in the Pacific Ocean, but due to opposition from the Pacific countries near this area, it is not possible to carry out at present, and shallow land disposal is being promoted.

In shallow land disposal, after placing a container containing radioactive waste in a concrete storage facility and filling the gap with sand or soil as a backfill material, or by filling with mortar or concrete and solidifying, A method of sealing is considered.

The backfill material has a function of extending the time it takes for the water to reach the container when a crack occurs in the concrete wall of the storage facility for some reason and external water enters through the crack, or the water causes the wall of the container When the inside is corroded and the radioactive substance inside is eluted, the movement of the radioactive substance,
It is used with the expectation that it will be delayed by adsorbing it.

In addition, solidification with concrete or mortar extends the time it takes for water infiltrated from the outside to reach the container by covering the container storing radioactive waste with a layer of concrete or mortar that is difficult to pass water through. It is intended to delay the corrosion of the container due to its alkalinity, and further to extend the time until the radioactive substance eluted from the solidified body due to the corrosion of the container reaches the outside of the facility, that is, the living environment of people.

[Problems to be Solved by the Invention]

When disposing low-level radioactive waste in shallow land, in the method of filling the gap in the concrete storage facility where the container storing the radioactive waste is stacked with sand or soil,
Due to the large permeability of sand and soil, the time it takes for water infiltrated through cracks in concrete walls to reach a container containing radioactive waste is relatively short. Therefore, the container containing the radioactive waste is corroded, the time until the radioactive substance is eluted is short, and the radioactive substance may leak to the outside, that is, the human environment in a relatively short period of time.

Also, in the method of filling and solidifying mortar or concrete, due to the brittleness of the hardened material, for example, when a crack occurs in the concrete of the storage facility, there is a possibility that a crack will occur in the mortar or concrete that is the filler. Is strong. If this happens, the cracks will serve as water conduits, and water from the outside will quickly reach the container containing the radioactive waste, which may corrode the container and elute radioactive substances within a short period of time after disposal. On the contrary, the radioactive substance eluted along the route may easily leak to the outside.

[Means for Solving the Problems]

The present invention has been made in order to solve the above-mentioned problems of the conventional art, and replaces the conventional filler with 1 to 30 parts by weight of a hydraulic substance containing calcium and dry sand and / or dry soil 70. A filling material composed of about 99 parts by weight is filled in the space between the containers and the space between the containers and the storage facility made of concrete in which the container storing the radioactive waste is stored.

In the present invention, a hydraulic substance containing calcium and Portland cement, a mixed cement, other cements containing calcium, or a clinker of these cements, a lime and a metallurgical slag containing calcium, one of these powders and granules Alternatively, it is a mixture of two or more kinds.

Alternatively, a blast furnace slag slag, fly ash, or other pozzolan-reactive substance or the like may be added to the hydraulic substance containing calcium.

In the present invention, among the hydraulic substances containing calcium, those obtained by crushing clinker of Portland cement together with plain or blast furnace granulated slag can be preferably used. In this case, the size of the crushed product is 1 mm for all particles
It is desirable that the amount of particles is 10% or more and 70% or more. More desirably, all particles are 0.5 mm or less 1
90% or more of particles of 0 μm or more are preferable.

The clinker of Portland cement is an intermediate product for producing Portland cement, and is industrially manufactured at low cost in large quantities. Therefore, it is easily available, and it can be industrially pulverized in large quantities with plain or blast furnace granulated slag.

On the other hand, granulated blast furnace slag is a slag of a blast furnace, which is a pig iron manufacturing furnace, which is rapidly cooled with water, and a large amount of the crushed slag is used as a raw material for blast furnace cement. Therefore, this is also inexpensive and available in large quantities.

Generally, clinker is crushed by a ball mill etc. together with gypsum, which is a setting regulator, into cement. However, even by itself, the hardening ability is equivalent to that of cement, and the strength of the hardened material is also about the same.

Generally, a hydraulic substance containing calcium such as Portland cement or a clinker thereof is a fine powder, for example, a particle having a particle size of several μm or less, and when it comes into contact with water even if it is temporary, the Most will end the hydration reaction. However, if the particles are large enough, hydration will remain only on the surface upon temporary contact with water and the interior will remain unhydrated. Therefore, if the particles are large to some extent, it is possible to maintain the state of being unhydrated in the air for a long period of time, that is, the state where the curing ability is left.

It is desirable that the hydraulic substance containing calcium used in the present invention has a large particle size to some extent, but if it is too large, it will not cure even if it causes a hydration reaction in contact with water, and if it is too small, it will have a long storage period. A moisture hydration that occurs in the air or moisture brought in by sand causes a hydration reaction, which may not solidify when water enters through the cracks in the concrete wall of the storage facility. It is necessary to select the particle size appropriately according to the structure of the storage facility or the properties of sand and soil added at the same time.

In the present invention, dry sand or soil is used as the filler. The dried material is one that has a water content equal to or less than the water content in the air at that time, and it is possible to bring sand or soil into this state by drying by a usual method.

The purpose of drying sand or soil used as a filler is to facilitate mixing with hydraulic substances containing calcium to make a homogeneous filler, and to improve the fluidity to store radioactive waste. This is because it is possible to sufficiently fill the space between the containers containing the radioactive waste in the above facility.
Still another purpose is to minimize water entering the facility during storage and prevent corrosion of the container.

Also, when sand or soil used as a filler is dried as described above, the amount of water that enters the facility during storage is extremely small, and since it is sealed, there is almost no water brought in, and a hydraulic substance containing calcium is included. Hydration does not proceed for a long time.

Sand used in the present invention is not particularly limited, naturally occurring river sand, land sand, dune sand, sea sand without salt,
Alternatively, river gravel, crushed sand obtained by crushing crushed stone, water slag, other metallurgical slag, or a crushed product thereof can be used.

In the present invention, the soil is an aggregate of relatively fine mineral particles existing near the ground surface, and the main cause thereof is a material such as rock due to weathering.

All of the fillers used in the present invention may be filled in a pre-mixed storage facility, or each material may be added at the same time and mixed at the time of filling.

The mixing ratio of the filler used in the present invention is 1 to 30 parts by weight of a hydraulic substance containing calcium and 70 to 99 parts by weight of dry sand and / or soil. When the hydraulic substance containing calcium is 1 part by weight or less, the curing power is small and the object of the present invention cannot be achieved, and when it is 30 parts by weight or more, the cost as a filler becomes high.

In the present invention, clinker alone of Portland cement or a mixture of clinker of Portland cement and granulated blast furnace slag can be preferably used as the hydraulic substance containing calcium.

Regarding the particle size of the hydraulic material, it is desirable that all particles are 1 mm or less, and that 70% by weight or more of particles of 10 μm or more are contained. More desirably, all particles are 0.5 mm or less 10
90% by weight or more of particles having a size of μm or more is preferable.

It is considered that a very long period of time is required until the concrete wall of the facility for storing radioactive waste cracks and water penetrates through it. Therefore, in order for the filler according to the present invention to exhibit hydraulic properties even at that time, it is desirable that the filler itself has low activity and can maintain the ability to cure even after a long period of time.

That is, it is desirable that the hydraulic substance containing calcium used in the present invention contains a large amount of large particles that do not impair the hardening ability after hydration. Further, granulated blast furnace slag and pozzolan-reactive substances are substances that have low hydration activity per se, but exhibit hydraulic properties when they come into contact with moisture together with hydraulic substances containing calcium. Is a suitable substance.

Hydraulic material containing calcium and granulated blast furnace slag and /
Alternatively, the mixing ratio with the pozzolanic reactant may be arbitrary,
In order to efficiently exhibit the hydration activity or the hydraulic property of the granulated blast furnace slag, the ratio of the hydraulic substance containing calcium is preferably 20% or more.

[Action]

In the present invention, a mixture of a hydraulic substance containing calcium and sand and / or soil as a filler in the space between the containers of the concrete storage facility storing the container storing the radioactive waste or the space between the container and the facility. To fill.

When the filler according to the present invention is used, such as when the outer wall of the concrete facility storing the container containing the radioactive waste has a crack, when water enters the facility through the crack, calcium in the filler is present. A hydraulic substance containing is reacted with water and solidifies together with sand and soil, and prevents the infiltration of water from the part.

In addition, even when water further penetrates and reaches the container containing the radioactive waste, the corrosion of the container is significantly delayed because the surrounding atmosphere is alkaline due to the action of calcium caused by the hydraulic substance. . Further, most of the radioisotopes contained in the radioactive waste are metal elements that become hydroxides that are hardly soluble in an alkaline atmosphere, and therefore, even if they are eluted from the solidified body, it is difficult to move to the outside.

In addition, sand and soil filled with a hydraulic substance containing calcium have a function of adsorbing the eluted radioactive waste and delaying its movement.

It is a well-known fact that the toxicity of radioactive waste, or radiation, decays over time.

Therefore, radioactive waste can be rendered harmless by suppressing its leakage to the outside, that is, the human living environment for a certain period of time.

In the present invention, the reason for delaying the leakage of radioactive material by using hydraulic material containing calcium and dry sand and / or soil as a filler in the concrete storage facility containing radioactive waste is at this point, The main aim of the invention is to delay the leakage of radioactive waste into the environment and consequently render it harmless.

The radioactive substances contained in low-level radioactive waste are often those in which the metal forming the nuclear reactor is dissolved in reactor water and activated by the action of neutrons. The half-life of substances activated by these neutrons is generally short, with the longest ⁶⁰ Co being 5.3 years and ⁵⁴ Mn being 0.9 years. ⁹⁰ Sr (half-life: 28.8 years), which is a part of so-called fission material produced by nuclear fission of nuclear fuel in a nuclear reactor, ¹³⁷ Cs
Isotopes with a relatively long half-life such as (half-life of 30.2 years) are also included, but the amount is small.

Therefore, the method of the present invention is applied to a facility that disposes low-level radioactive waste, delays the intrusion of water from the outside of the facility, suppresses corrosion of the container, and further delays leakage of radioactive substances eluted by corrosion to the outside. This is a very effective means for preventing leakage of radioactive materials to the outside in shallow land disposal, that is, preventing contamination of human living environment with radioactive materials.

As described above, the filling material of the present invention is excellent in the property of preventing the movement of water infiltrating into the facility storing radioactive waste from the outside and protecting the container containing the radioactive waste from corrosion. Also, since it has a great effect of blocking the movement of radioactive substances eluted by water that has entered from the outside,
However, it is not limited to concrete storage facilities, but can be suitably used for general radioactive waste shallow land disposal.

〔The invention's effect〕

According to the radioactive waste disposal method of the present invention, a mixture of hydraulic material containing calcium and sand and / or soil is used as a filler when the radioactive waste is stored in a concrete storage facility for disposal in shallow ground. By doing
It is possible to expect the effect of suppressing the leakage of radioactive substances to the outside and thereby preventing the pollution of human living environment by radioactive substances.

Claims (2)

[Claims] 1. A radioactive waste contained in a container is piled up in a concrete storage facility, and the total particles are 1 mm or less in the space between the containers and the space between the container and the concrete storage facility. And particles of 10 μm or more
A filler comprising 1 to 30 parts by weight of a crushed body of Portland cement clinker containing 0% or more, or a crushed body of a mixture of the Portland cement clinker and granulated blast furnace slag, and 70 to 99 parts by weight of dry sand and / or dry soil. A method of disposing of radioactive waste, characterized by filling with. 2. All particles are 1 mm or less and 10 μm
1 to 30 parts by weight of a Portland cement clinker pulverized product containing 70% or more of the above particles or a mixture of the Portland cement clinker and blast furnace granulated slag, and dry sand and / or dry soil 70 to 9
9 parts by weight of filling material for radioactive waste shallow land disposal.