Japan’s Nuclear Regulatory Authority presented a draft outline of new safety standards for nuclear power plants in the wake of the Fukushima Daiichi nuclear disaster, including countermeasures against severe accidents and criteria for evacuating areas around nuclear power plants during an emergency this week. The new draft outline requires nuclear plant operators to take steps aimed at preventing damage to reactor core and containers and limiting releases of radioactive substances to a minimum if they are hit by massive natural disasters or other direct attacks.
Nuclear plant operators will be required to follow the standards as a precondition to get their reactors restarted, but implementing many of these measures would involve a very costly major revamp of existing facilities.
In order to be prepared for a loss of external power supplies in the wake of tsunami and earthquakes, the outline mandates that nuclear plant operators to deploy movable alternative equipment such as power supply vehicles in various places so that the plants can be operated safely for at least seven days without outside help.
The authority has also proposed that alternative control rooms to monitor reactors be built away from the reactor buildings. This would reduce the risk of plant workers being irradiated in an emergency.
Another of the proposed measures is a vent system equipped with filters to reduce levels of radioactive exhaust in case of an accident. Still other requirements are being considered, like a powerful water injection facility that could cool a damaged reactor from a safe distance.
The revised evacuation criteria define three stages of emergency, based on the state of affected nuclear reactors.
- Areas within 5 kilometers from nuclear plants will be evacuated immediately, regardless of radiation levels, in the worst stage, or if nuclear plants face a severe accident such as a station blackout that hit the Fukushima Daiichi complex.
- Evacuations of areas beyond 5 kilometers will be determined in accordance with radiation levels, and will be evacuated immediately once dosimeters hit 500 microsieverts per hour.
- If radiation levels reach 20 microsieverts per hour, such areas will be evacuated gradually, taking around one week.
The authority is expected to compile the final draft by the end of this month, which will be reviewed by the public, and then officially confirm the new standards by July.
Source: JiJi Press