Plans are being drawn up to rate Japan’s nuclear power plants for safety to better monitor risk-prone plants and reduce inspection costs.

The Nuclear and Industrial Safety Agency said the new policy marks a turning point in its safety monitoring system. In the past, equal weight has been given to all nuclear power plants on the question of ensuring safety.

Under the new policy, all plants will be rated in terms of their operating performance, including radiation management and the number of failures at reactors, officials said.

Those rated at the lower end of the scale will be subject to increased monitoring, while those with higher ratings will receive minimal inspections, they said.

The officials said the rating system would enable the agency to focus on risk-prone plants and reduce reactor mishaps.

It would cut inspection costs, they said, if operating performance at plants are kept above average, while also raising safety awareness among power companies and plant workers.

The policy is the result of a multiyear project by the nuclear watchdog, which is under the Ministry of Economy, Trade and Industry. The agency will seek amendments to the Electric Utility Law — the law governing nuclear power operations — and other legislation to implement the new system within the next few years.

The United States introduced a similar rating system in 2000, assigning to nuclear power plants four grades in 18 categories, such as the number of unexpected reactor shutdowns and malfunctions in plant safety features.

When rating 103 nuclear reactors between January and March, U.S. regulators found problems at 31 of facilities, attesting to the usefulness of the rating-based safety system.

Japanese nuclear regulators said they intend to modify the U.S. system to suit the conditions of nuclear reactors in Japan. They will develop original standards and evaluation methods over the next four to five years.

To prevent complacency from compromising safety standards at higher-rated plants, the nuclear agency intends to complement the new system with surprise inspections, the officials said.

To date, the agency has merely inspected the main facilities of nuclear power plants, leaving it up to individual power companies to inspect the rest of their facilities.

A pipe rupture caused by a hydrogen explosion at Chubu Electric Power Company’s Hamaoka nuclear power plant last November occurred in an area not covered by state inspections.

The agency has decided to introduce the new system, incorporating such new concepts as quality assurance and security audits, “to look into the safety-enhancing efforts among operators,” a senior agency official said.

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