The Nuclear Regulation Authority proposed stricter criteria Thursday for evacuation and other protective actions against radiation exposure as part of efforts to flesh out atomic disaster mitigation guidelines.
According to a draft of revised guidelines, the NRA said people living outside a 5-km radius from a nuclear power plant should expect to evacuate immediately if a radiation dose of 500 microsieverts per hour is detected, while people living within the 5-km radius will be instructed to evacuate much earlier.
The radiation level is tougher than the international standard. The Vienna-based International Atomic Energy Agency sets the benchmark at 1,000 microsieverts.
The NRA plans to finish revising the guidelines, initially compiled last October to deal with the Fukushima No. 1 nuclear plant triple-meltdown disaster that started in March 2011, possibly in February.
If radiation readings reach 20 microsieverts, people will be advised to refrain from consuming local food and told to relocate within a week, and if the level reaches 0.5 microsievert, they will be advised to not eat local foods until a thorough study of their radiation levels clears them of risk.
Residents living within a 5-km radius of a stricken plant will be effectively subject to judgment calls based on the danger level.
The state and local governments will be urged to start gathering information when an area where a plant is located is hit by an earthquake registering 6 or higher on the Japanese seismic intensity scale to 7.
If a reactor coolant leak occurs, local governments will have to prepare for evacuations and the distribution of iodine tablets to mitigate the threat of thyroid cancer. If the affected utility can’t control the situation, a general evacuation will be ordered.
The NRA also plans to distribute iodine tablets in advance to households living within the 5-km radius of an atomic plant. For those living farther away, local governments are basically expected to keep iodine on hand, but details still need to be worked out.
In the Fukushima crisis, residents living within a 20-km radius of the plant and areas beyond had to flee from their homes.
The evacuation process caused significant chaos and the central government’s instructions regarding the use of iodine pills were delayed.