A law enabling nuclear reactors in Japan to operate beyond 60 years took effect Friday, scrapping a limit imposed after the Fukushima crisis, with the government viewing the power source as vital to the country's energy mix.

Under the new system, the life of a reactor will, in principle, be extended beyond 60 years by no longer including offline periods for safety reviews or suspensions ordered by courts that are not due to the inappropriate actions of an operator.

The law replaces rules allowing the operation of reactors for up to 40 years, with extensions up to 60 years possible if approved by regulators. The rules were introduced in 2013 following the Fukushima nuclear disaster that was triggered by a massive earthquake and tsunami in March 2011.

The legislation was enacted in 2023 after the government led by then Prime Minister Fumio Kishida shifted from the previous policy of reducing reliance on nuclear power, saying in 2022 that the country will fully utilize nuclear plants to cut carbon dioxide emissions and realize a stable energy supply amid Russia's war in Ukraine.

The No. 1 reactor at Kansai Electric Power Co's Takahama nuclear plant, the country's oldest unit that began operating in November 1974, could be granted permission to continue for 72 years as it was offline for about 12 years due to a safety assessment by the Nuclear Regulation Authority and other reasons.

The offline periods to be exempted from total service life do not include suspensions due to inappropriate actions by operators, such as when Tokyo Electric Power Company Holdings Inc was slapped with an effective ban on operating the Kashiwazaki-Kariwa plant in Niigata Prefecture for insufficient antiterrorism measures.

The Ministry of Economy, Trade and Industry will assess the extension periods of nuclear reactors beyond 60 years.

The law also stipulates that operators of nuclear plants that have been running for 30 years or more must compile long-term plans for facility management at least every 10 years and obtain approval from the Nuclear Regulation Authority.

The regulator will assess the soundness of nuclear reactors and the concrete used in such facilities as well as the feasibility of operators' plans to address parts shortages.