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Editorial: Gov't must clarify SPEEDI's status in event of nuclear accident

The government has decided to allow local governments to exercise their own discretion in utilizing the System for Prediction of Environmental Emergency Dose Information (SPEEDI) -- which forecasts the diffusion of radioactive materials in the event of a nuclear accident -- when evacuating their residents to safety.

The decision, made at a meeting of Cabinet ministers whose work relates to the nuclear power issue, came in response to a request filed by the National Governors' Association. Niigata Gov. Hirohiko Izumida, who chairs the association's Special Committee for Risk Management and Disaster Control, hailed the central government's decision, saying, "It has paved the way for us to map out our evacuation plans."

However, the Nuclear Regulation Authority (NRA), the central government's nuclear watchdog, has decided not to use SPEEDI when evacuating residents on the grounds that the reliability of the prediction system is low and its use would "bring about many adverse effects."

The NRA's decision has bewildered residents in areas surrounding nuclear power plants and left them wondering whether SPEEDI will be of help or not at all. It also raises concerns that unnecessary confusion may occur in the event of a nuclear accident, when the NRA and local governments clash in their decisions over whether to evacuate residents or not.

The SPEEDI system forecasts the extent of the dispersion of radioactive materials and their airborne concentration based on the amount of radioactive substances released into the air, the timing of those emissions and weather conditions, among other factors. However, the system failed to make an accurate prediction in the wake of the Fukushima No. 1 nuclear plant disaster because the amount of radioactive materials released from the complex and other data were unavailable.

Under the NRA's revised nuclear disaster response guidelines, residents within a 5-kilometer radius of a nuclear plant will be ordered to evacuate in the event of an emergency even before the release of radioactive materials. Residents within a 5- to 30-kilometer radius, meanwhile, will be ordered to stay indoors while officials determine from local radiation dose measurements whether evacuation is necessary.

Technology to accurately predict the time when radioactive materials will be released in the air has yet to be developed. Calculations based on assumptions may be inaccurate because of different wind directions when the actual emissions of radioactive materials occur. It is therefore understandable that the NRA has pointed to the lack of reliability of advance estimates.

The Niigata Prefectural Government is concerned that immediate evacuation of residents would be difficult as roads could be cut off in the event of multiple disasters such as an earthquake followed by a nuclear accident at the Kashiwazaki-Kariwa nuclear plant operated by Tokyo Electric Power Co. The prefectural government thus believes that under such a scenario the use of SPEEDI predictions along with actual measurements would be valuable when considering evacuation routes and other measures.

The Meteorological Society of Japan has also recommended to the NRA that prediction data such as SPEEDI be put to use in nuclear emergencies.

How much can SPEEDI's credibility be enhanced, and can the system be utilized after radioactive substances are emitted into the air? The central government should take responsibility and specify how it is going to use SPEEDI.

The NRA's safety screening of the Kashiwazaki-Kariwa plant has entered its final stage. As reactivation of the nuclear station ultimately requires approval from Gov. Izumida, the central government's latest decision to leave the use of SPEEDI up to local governments -- a decision made at the initiative of the Ministry of Economy, Trade and Industry, which oversees nuclear plant operators -- apparently gave consideration to Izumida's assertions.

The conflict of opinions between the NRA and the National Governors' Association stems from the fact that nuclear accident evacuation planning is not subject to the NRA's safety screenings and is instead left up to each local government. The central government should be responsible for overseeing resident evacuation plans in an integrated manner.

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