2 Septembre 2016
September 2, 2016
By TAKASHI SUGIMOTO/ Staff Writer
Highly radioactive waste from the decommissioning of nuclear reactors should be buried at depths beyond 70 meters for 100,000 years, the Nuclear Regulation Authority has decided.
Under the decision made Aug. 31, nuclear waste that would mainly consist of the control rods used in nuclear reactors would be buried in areas where earthquakes and volcanoes pose a minimal threat.
Electric power companies would be responsible for managing the buried waste for periods between 300 and 400 years. The central government would then take over and restrict entry and digging in the burial sites for a period of 100,000 years.
The NRA divides nuclear waste from the decommissioning process into four major categories depending on the radiation level: extremely high, high (L1), comparatively low (L2) and extremely low (L3).
The Aug. 31 decision applies to L1 waste. Disposal methods had already been decided for the other categories.
Nuclear waste categorized as having extremely high radiation levels is mainly from spent nuclear fuel. L2 level waste would mainly come from part of the reactor pressure vessel while L3 waste would be from piping surrounding the pressure vessel.
The depths at which waste is buried differs according to the radiation level.
Nuclear waste with extremely high radiation levels has to be buried deeper than 300 meters for a period of 100,000 years.
L2 waste will be buried at a depth between 10 and 20 meters, while L3 waste will be buried several meters underground.
The Federation of Electric Power Companies of Japan had calculated that if all 57 nuclear reactors in Japan were decommissioned, a total of about 8,000 tons of L1 nuclear waste would be produced.
The NRA concluded that there was a necessity to encase L1 waste in concrete and bury it in bedrock deeper than 70 meters for at least 100,000 years.
The period in which electric power companies would manage the waste was set at between 300 and 400 years because a period of several tens of thousands of years is unrealistic.
Even though the burial methods have been decided on, the much more difficult task of deciding on which burial sites to use must still be resolved.
The electric power companies must acquire the sites to be used to bury nuclear waste.
Decommissioning work has begun at the Tokai reactor in Ibaraki Prefecture, once operated by the Japan Atomic Power Co.
The company received local approval in January 2016 for burying only L3 waste within the reactor grounds.
That is the only decision so far by any local community in Japan for accepting the burial of nuclear waste in their backyard. No local government has given the green light for a site to be used to bury L2 or L1 waste.
Consideration is also being given to possible burial sites for nuclear waste with extremely high radiation levels.
The sites have to be distant from volcanoes and active faults, but also in locations where transporting the waste would not be difficult.
That has led to the inclusion of a condition that the sites be within 20 kilometers of the coastline to be considered "highly appropriate" as a burial site.
The central government plans to present by the end of 2016 a map of possible sites that would be considered "scientifically promising" for the disposal of waste with extremely high radiation levels.