The Nuclear Regulation Authority (NRA) plans to require that highly radioactive waste generated when nuclear reactors are decommissioned be buried underground at least 70 meters deep for about 100,000 years until the waste becomes no longer hazardous.
Moreover, disposal sites for such waste should not be built in areas that could be affected by active faults or volcanoes.
The plan is part of the proposed regulatory standards on disposal sites for radioactive waste from dismantled nuclear reactors, which the NRA approved on Aug. 1. The NRA will hear opinions from power companies operating nuclear plants and other entities before finalizing the regulatory standards.
Low-level radioactive waste generated when reactors are dismantled is graded by three ranks in descending order from L1 to L3.
The proposed regulatory standards cover L1 waste, such as containers for control rods and fuel assemblies.
There have been no regulatory standards for L1 radioactive waste even though a growing number of nuclear reactors are bound to be decommissioned under the regulatory standards for nuclear plants that have been stiffened following the outbreak of the Fukushima nuclear crisis in March 2011.
Under the proposed regulatory standards for L1 waste, electric power companies would be required to build disposal sites on stable ground. Such facilities should not be built near faults at least 5 kilometers in length. Moreover, utilities would be mandated to confirm from records or geological surveys that there has been no volcanic activity over the past 2.6 million years or so near where they plan to build the disposal sites.
Power companies would also be obligated to avoid building disposal sites near oil or mineral deposits because areas with such natural resources may be excavated in the future.
Such radioactive waste must be regularly monitored over a roughly 300- to 400-year period following its disposal to see if the waste contaminates nearby groundwater. The owners of disposal sites would then be banned from digging areas surrounding the facilities without permission from the central government.
The proposed standards also require that additional radiation exposure dosages from disposal sites be limited to 0.3 millisieverts or less a year in accordance with international standards. It is also required to confirm whether radiation doses would be below that limit even if the functions for shielding radiation were partially lost, such as the container holding radioactive waste being broken, by analyzing doses under such scenarios.
(Japanese original by Ei Okada, Tokyo Science & Environment News Department)