The Japanese government plans to limit the service life of nuclear reactors to 40 years, nuclear disaster minister Goshi Hosono said on Friday, according to the Kyodo news agency.

It will also require nuclear plant operators to take measures to prevent severe accidents that could result in serious damage to the reactor core and the massive release of radioactive material.

The plan is part of a bill drawn up in the wake of the nuclear disaster at the Fukushima Daiichi plant, based on the assumption that nuclear power should be used only when safety can be ensured, Hosono said.

The bill is expected to be submitted to parliament later this month.

Of Japan's 54 commercial reactors, three are at least 40 years old - the No. 1 reactors at Tokyo Electric Power Co.'s Fukushima Daiichi plant, Japan Atomic Power Co.'s Tsuruga plant in Fukui Prefecture, and Kansai Electric Power Co.'s Mihama plant also in Fukui.