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 aging reactors has been growing because the three units at the Fukushima Dai-ichi 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 coming years.

The government said Friday that it plans to introduce legislation in the coming months to require reactors to stop running after 40 years. Japan does not currently have a limit on years of operation.