Safety Assessment

In developing the decommissioning plan of "Fugen," the public effective dose assessment at a normal time and sky-shine dose by the gas waste and liquid waste releases in the dismantlement work period *1) we evaluate the safety of the decommissioning by considering the assessment and the public effective dose assessment of an assumed accident event.
For the public effective dose assessment, we evaluate it by mainly considering the following points.

●We have conservatively evaluated the amount of radioactivity to use in the assessment by uniformly using the values of 4.5 years after stopping the operation of the reactor regardless of the decommissioning process.
●We have conservatively evaluated it by taking into account all the assumed exposure pathways.
●We have conservatively evaluated the exposure dose on the assumption that all the dismantlement works have been conducted in one year

The outline of the safety assessment is shown below.

In addition, the evaluation results are as follows.

(1) Neighboring public radiation exposure evaluations in the normal condition

▶The effective dose received by the general public due to the radioactive gas waste and radioactive liquid waste became not only less than the dose limit: 1 mSv/y stipulated in laws and regulations, but also lower than the dose target value: 50 μSv/y described in the Nuclear Safety Commission guidelines.

▶The spatial radiation dose at the site boundary by direct and sky-shine radiations became sufficiently below the reference dose value: 50 μGy/y described in the Nuclear Safety Commission guidelines.

▶The total exposure dose of radiation workers became almost the same as the total exposure dose at the time of periodic inspection during the operation of the reactor.

(2) Neighboring public radiation exposure evaluations at the time of the accident

▶The effective dose at the highest radioactivity level when assuming a local filter damage accident of the contamination preventing enclosure during the reactor body demolition became sufficiently lower than the reference value: 5 mSv described in the Nuclear Safety Commission guidelines, having confirmed that it does not give a risk of significant radiation to the surrounding public.

*1) The sky-shine dose is the amount of radiation, which has transmitted through a building concrete with a thin shielding thickness, scattered with the substance in the air of the sky and fallen on the ground, and becomes maximum at the position away from the building.