TOKYO (AP) — A Japanese utility sought government approval Monday to restart two nuclear reactors even though some key upgrades to prevent another nuclear crisis will take three years.

All but one of Japan's 54 reactors are offline for regular safety checks, and the last will be shut down in May. Residents fear another disaster like the Fukushima crisis, but Japan faces a severe power shortage if reactors are not restarted.

The government issued new safety guidelines to address residents' worries, but it gave no deadline for when the improvements must be finished. Utility officials say the full upgrades will take three years.

Kansai Electric Power Co. submitted its safety plans for two reactors at the Ohi plant in Fukui prefecture, and the government's final decision on whether to restart the reactors is reportedly expected later this week.

"We'll aim to achieve the world's top-class safety at our plants," said Kansai Electric President Makoto Yagi as he handed the safety improvement roadmap to Economy and Industry Minister Yukio Edano.

However, more than one third of the necessary upgrades on the list are still incomplete, utility officials said.

Filtered vents that could substantially reduce radiation leaks in case of an accident threatening an explosion, a radiation-free crisis management building, and fences to block debris washed up by a tsunami won't be ready until 2015. This means the plant, as well as plant workers and residents, won't be fully protected from radiation leaks if a Fukushima-level accident occurs while the measures are being taken.

Currently, the crisis management headquarters at the Ohi plant is in the basement, which would be flooded in case of a major tsunami, Kansai Electric officials said. The plant is relocating the function to a room next to the control room for the two reactors.

The Fukushima Dai-ichi completed a similar building at a slightly elevated area on the complex just a year before the disasters — though it was meant for quakes. It was the key crisis management center after surviving the March 11, 2011, tsunami that washed into the plant, destroying the plant's power and cooling systems, causing three reactor cores to melt. Plant officials have said the building was key to their survival.

None of Japan's 54 nuclear reactors are equipped with filtered vents, although their operators are moving to install them in coming years.

"The operators are expected to take initiative to improve safety and reliability, and never dwell on the safety myth," Edano told Yagi, urging the utility to expedite the process.

Ohi town mayor Shinobu Tokioka called the roadmap a "step forward," but urged the central government and nuclear regulators to carefully review the reactors' safety.

The startup guidelines are based on recommendations adopted last month by the Nuclear and Industrial Safety Agency. The most crucial measures to secure cooling functions and prevent meltdowns as in Fukushima were incorporated in the government's guidelines, but the rest were not.

Some experts said a resumption without these key protections would leave the plant vulnerable.

Tadahiro Katsuta, a Meiji University associate professor who was on a government panel that produced nuclear safety recommendations, said the upgrades completed are "mostly quick-fix measures," and that more important ones, such as a crisis management center, have been put off.

"I doubt if this would suffice to carry out the lessons from Fukushima in the case of another accident," Katsuta told public broadcaster NHK.