The nuclear regulator on Thursday began screening three Kansai Electric Power Co. reactors which the utility wants to bring back online and keep in service beyond their mandated 40-year life span. All three are now nearing that limit.

A regulation brought in after the March 2011 nuclear disaster forbids the operation of nuclear reactors for more than 40 years, although operators can secure a 20-year extension if the reactors are refitted and obtain safety clearance from the Nuclear Regulation Authority.

Before the nuclear crisis, Kansai Electric was heavily reliant on atomic power. It hopes to restart the No. 3 unit at its Mihama plant and Nos. 1 and 2 units at the Takahama plant, all located on the Sea of Japan coast in Fukui Prefecture.

But Kansai Electric faces the daunting task of upgrading old equipment and clearing regulator screening within certain time limits.

For example, the new regulations require utilities to install power cables made from fire-retardant materials. Kepco hopes to clear the NRA checks by coating existing cables with non-flammable paint.

The company has decided to scrap its Nos. 1 and 2 reactors at the Mihama plant, which are both over 40 years old, believing that it was not economical to invest in costly refits, given the reactors' comparatively small output.