Electric Power Development Co. said Friday that it has decided to postpone its plan to start operating its Oma nuclear power plant by two years to fiscal 2024 due to longer-than-expected safety tests by the nuclear regulatory body.

The company, known as J-Power, has delayed the schedule for the second time after it applied for the safety check of the plant, which will be the world's first reactor to run solely on plutonium-uranium mixed oxide fuel, in December 2014, with an initial plan aimed at starting operation in fiscal 2021.

But it put off the original schedule in September last year to around fiscal 2022 due to the prolonged screening process by the Nuclear Regulation Authority after the company was asked to provide further explanations of the plan to build the plant in Aomori Prefecture.

"We would like to continue responding appropriately to (requests from) the regulation authority for safety screening," said Shosaku Kusunose, executive managing officer in charge of the Oma plant project.

Nuclear power plant operators in Japan need to obtain safety clearance from the NRA under tougher regulations adopted after the Fukushima nuclear crisis in 2011, which led to a nationwide halt of nuclear power plants.

Following the 2011 Fukushima disaster, the city of Hakodate in neighboring Hokkaido sued the company and government in April 2014, demanding a halt to the plant's construction.