JP2002022893A - Method for making radioactive waste disposal facility low permeable - Google Patents

Abstract

PROBLEM TO BE SOLVED: To maintain low permeability of a structure by suppressing tension stress generated in a concrete structure. SOLUTION: After setting radioactive waste 2 inside an underground concrete structure 1, cement filler material 3 with high gas permeability and low water permeability is charged to solidify in one body for a radioactive waste disposal facility. The initial water addition amount for the filler material 3 is made 0 or minimum necessity and a hydration reaction is gradually caused accordingly to the permeation of underground water after closing the facility.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for reducing water permeability of a radioactive waste disposal facility.

[0002]

2. Description of the Related Art Since wastes have various properties depending on their types, there are various methods of storing the wastes, and the wastes have been put into practical use. Among these, there is a hollow cylindrical underground concrete structure as a disposal facility for radioactive waste. When stored inside this, after the waste is placed in place, high air permeability that allows gas generated from the waste to safely pass through the internal gap,
2. Description of the Related Art Materials that require low water permeability that can suppress infiltration of groundwater are filled and quickly solidified. As the material having high air permeability and low water permeability, inorganic porous mortar and the like are mentioned, and by filling these,
There is a method of storing radioactive waste while degassing.

[0003]

However, according to this method, a rapid heat of hydration is generated in the filler at the time of construction, the rigid cement-based filler thermally expands, and the internal pressure acts on the concrete structure. Tensile stress is generated, which causes cracking. In addition, the pressure of the gas generated from the waste also acts as an internal pressure on the structure, which also generates a tensile stress and causes cracks. As a result, when groundwater is present, there is a problem that it penetrates into the structure through cracks and causes water leakage.

An object of the present invention is to solve the above-mentioned problems, and an object of the present invention is to suppress the tensile stress generated in a concrete structure so that a radioactive material capable of maintaining a low water permeability of the concrete structure can be maintained. It is intended to provide a method for reducing water permeability of a waste disposal facility.

[0005]

In order to achieve the above object, the method of the present invention comprises: placing a plurality of radioactive wastes in an internal space of an underground concrete structure having a closed section; In a radioactive waste disposal facility that is filled with a highly air-permeable and low-water-permeability cement-based filler and solidified integrally, the initial amount of water added to the filler is reduced to 0 or a necessary minimum. The hydration reaction is caused gradually according to the infiltration of groundwater. Therefore, in the method of the present invention, the hydration reaction is slow, large heat generation does not occur, and it is possible to prevent the occurrence of problems such as temperature cracks in the structure due to thermal stress.

[0006] The method of the present invention also includes a method of placing a plurality of radioactive wastes in an internal space of an underground concrete structure having a closed cross section, and then filling a gap between the wastes with a cement-based filler having high air permeability and low water permeability. In a radioactive waste disposal facility that is filled and solidified integrally, a projection made of steel or the like is projected in advance on the inner surface of the concrete structure, and is integrated with the filler. It is. Therefore, in the method of the present invention, since the protrusions are pulled inward by the shrinkage of the filler and the concrete structure is compressed as a whole, a prestress directed toward the inside is introduced, so that the tensile stress generated by the gas pressure is generated. Can be suppressed.

[0007]

Preferred embodiments of the present invention will be described below in detail with reference to the accompanying drawings. Figure 1
Indicates a waste disposal facility to which the method of the present invention is applied, and is composed of a hollow cylindrical underground concrete structure 1 built in a surrounding rock E, and inside the structure 1, for example, a cube Many solidified radioactive wastes 2
Are arranged in the form of a matrix, and the operation of filling the gaps between the wastes 2 with the filler 3 is repeated in order from the bottom to fill the inside of the structure 1, thereby closing the facility.

As the filler 3, a cement-based filler having high air permeability and low water permeability, such as porous concrete, is used. In addition, in the method of the present invention, the amount of water to be mixed with the filler 3 is smaller than that of the conventional method in that a water: cement ratio of a material kneaded or a dry powder of a mortar component is such that the hydration reaction does not immediately occur. The operation of filling as it is is repeated until it is full.

In the initial state in the above method,
As shown in FIG. 2 (a), even if the interior expands due to the heat generated by the waste 2 (the internal expansion pressure is indicated by an arrow), the filler 3 has not been sufficiently hardened yet, and accordingly, the concrete structure on the outer periphery thereof No harmful internal pressure is generated in the object 1. Further, when the groundwater pressure in the bedrock E acts on the concrete structure 1 (groundwater pressure is indicated by an arrow), the waste storage portion has low rigidity because it does not infiltrate to the filler 3. ), A compressive stress is introduced.

[0010] From this state, as the groundwater sequentially permeates into the structure 1 due to a change with time (illustration of the permeation state is indicated by an arrow), as shown in FIG. A hydration reaction occurs. At this time, the calorific value is extremely small as compared with the related art, and in addition, due to hydration shrinkage, a prestress directed inward is introduced into the structure, thereby making it difficult to generate cracks.

By forming a plurality of projecting members (not shown) such as steel materials in advance inside the structure 1 at appropriate intervals (preferably projecting in the normal direction), the filling material 3 is formed. With the hardening of the material, a force for pulling the protruding material toward the inside acts, and prestress toward the inside is introduced into the structure 1, so that the internal pressure generated by the gas pressure can be suppressed.

Further, the minute water permeation that has passed through the structure 1 is as follows:
In the process of passing through the filler 3, it is consumed by the hydration reaction, and further as shown in an enlarged part of FIG. Since the water is retained at 3a, it is difficult for the center to permeate.

After the above-mentioned hardening accompanied by the extremely slow hydration reaction of the filler due to the infiltration of the groundwater is completed, the filler becomes highly rigid, and the contraction deformation of the structure 1 due to the external pressure is suppressed,
Cracks hardly occur. On the contrary, there is an excellent effect that the tensile stress due to the pressure of the gas generated from the waste 2 is suppressed.

[0014]

As is apparent from the above description, in the method for reducing water permeability of a radioactive waste disposal facility according to the present invention, the occurrence of water stoppage defects is achieved by introducing external pressure and suppressing internal pressure. And maintain low water permeability of concrete structures.

[Brief description of the drawings]

FIG. 1 is a plan sectional view of a radioactive waste disposal facility to which the method of the present invention is applied.

FIGS. 2 (a) to 2 (c) are explanatory plan views showing temporal changes in the same method.

[Explanation of symbols]

 1 Underground concrete structure 2 Radioactive waste 3 Cement-based filler

Claims (2)

[Claims] After a plurality of radioactive wastes are set in an internal space of an underground concrete structure having a closed section, a gap between the wastes is filled with a cement filler having high air permeability and low water permeability. In a radioactive waste disposal facility that is solidified integrally, the initial amount of water added to the filler is reduced to 0 or a necessary minimum, and a hydration reaction is gradually generated according to the infiltration of groundwater after the facility is closed. Characteristic low-permeability method for radioactive waste disposal facilities. 2. After placing a plurality of radioactive wastes in the interior space of an underground concrete structure having a closed cross section, filling the gaps between the wastes with a cement filler having high air permeability and low water permeability. In a radioactive waste disposal facility that is solidified integrally, a radioactive waste disposal facility characterized in that a protrusion made of steel or the like is projected in advance on the inner surface of the concrete structure and integrated with the filler. Low water permeability method.