The former president of Fukushima plant operator Tokyo Electric Power Co faces questioning for the first time on Friday by a high profile investigative panel seeking to uncover the causes of the world's worst nuclear disaster since Chernobyl.

Members of the panel appointed by parliament will likely grill Masataka Shimizu over whether he planned to abandon the tsunami-devastated Fukushima plant at the height of the crisis in March 2011, as reactors melted down and the situation was in danger of spinning out of control, threatening Tokyo itself.

Then-prime minister Naoto Kan and two other ministers handling the disaster response have told the panel that Shimizu had planned to withdraw all of his utility's workers as explosions rocked the plant and three reactors melted down, spewing radiation across northeast Japan.

Shimizu, 67, was also widely criticized for vanishing from public view three days after the disaster struck.

He was later hospitalised for dizziness and high blood pressure leaving the utility's chairman to supervise operations during his absence.

Shimizu's testimony coincides with efforts by Prime Minister Yoshihiko Noda's government to restart two idled nuclear reactors in western Japan to cope with possible power shortages when electricity demand peaks in July and August.

All of Japan's 50 reactors have gone offline since the crisis and Tokyo has been trying to win local communities' agreement for the restarts despite persistent public concerns about safety and delays in setting up a new nuclear regulator.

The government is also thrashing out a new energy strategy after scrapping a 2010 plan that would have boosted nuclear power's share of electricity to more than 50 per cent by 2030 from around 30 per cent before the disaster.

UNPREPARED FOR RISKS

Shimizu, who stepped down in June last year as president of the utility, known as Tepco, has been questioned in parliament but Friday is the first time he appears publicly in front of one of the three main inquiries that have looked into the disaster.

He and other Tepco executives had said repeatedly that the scale of the natural disaster was unpredictable, but company documents have shown the utility was well aware of the risk.

Kan, who himself resigned last year after harsh criticism of his handling of the crisis, told the panel last week he had rushed to Tepco headquarters on March 15 to order Shimizu not to withdraw all the utility's workers.

Tepco, however, has denied it planned a full-scale pullout from the plant, which lost power and cooling capacity after a massive earthquake and the tsunami devastated the facility.

Shimizu quickly became a target of public outrage in the early days and weeks of the crisis.

The governor of Fukushima prefecture, where the stricken plant is located, on two occasions refused to meet him when the president visited to apologize.

But in a sign of the close ties that bind corporate Japan, Shimizu will later this month become an outside board member of Fuji Oil Co., which is owned by AOC Holdings Inc., a firm in which Tepco has an 8.7 per cent stake.

Tepco itself, burdened with massive compensation and clean-up costs from the disaster, will be taken over by the government through a 1 trillion yen ($12.6 billion) injection of public funds to be approved at a shareholders' meeting this month.

The eventual cost of the disaster has been estimated at more than $100 billion. Last week, Tepco said the radiation release from Fukushima's meltdowns was more than twice initial estimates.