Tokyo: Japan says it will soon require atomic reactors to be shut down after 40 years of use to improve safety following the nuclear crisis set off by last year's tsunami.

Concern about ageing reactors has been growing because the three units at the Fukushima Daiichi plant in northeastern Japan that went into meltdown following the tsunami in March were built starting in 1967. Among other reactors at least 40 years old are those at the Tsuruga and Mihama plants in central Japan, which were built starting in 1970.

Many more of the 54 reactors in Japan will reach the 40-year mark in the near future, though some were built only a few years ago.

The government said on Friday that it plans to introduce legislation in the coming months to require reactors to stop running after 40 years. Japanese media reported that the law may include loopholes to allow some old nuclear reactors to keep running if their safety is confirmed with tests.

The proposal could be similar to the law in the US, which grants 40-year licences and allows for 20-year extensions. Such renewals have been granted to 66 of 104 US nuclear reactors. That process has been so routine that many in the industry are already planning for additional licence extensions that could push the plants to operate for 80 years or even 100.