Tokyo: A Japanese government nuclear safety panel decided to legally require utilities to take measures to prevent severe nuclear accidents following the crisis at the Fukushima Daiichi atomic power plant.

The government had so far left it up to the nuclear plant operators to decide whether to take steps against accidents that result in severe damage to reactor cores, based on the assumption that such disasters cannot happen.

In a policy compiled in 1992, the Nuclear Safety Commission, an independent panel supervising the country's nuclear regulatory agency, said the possibility of severe accidents occurring is small enough that they "cannot happen in reality."

According to a draft plan compiled by the panel's secretariat and released on Monday, utilities would be obliged to design nuclear power plants that can deal with possible loss of power caused by natural disasters, and create operation manuals for such a situation.

As for severe accidents triggered by plane crashes or terrorist attacks, the panel said such actions should be maintained as voluntary efforts by the utilities.

The commission is expected to present a basic policy on the issue possibly later this year and seek to have it legislated.

The latest move is based on the lessons learned from the nuclear crisis at the Fukushima plant, which was hit by a magnitude 9.0 earthquake and tsunami on March 11.

The six-reactor complex lost nearly all of its power sources, causing the cooling functions of many of the reactors and pools storing spent nuclear fuel to fail.