"Given the current situation of Japan's high dependency on nuclear power, and the fact that switching to thermal power would be bad for the environment, it's hard to think that the government will change its policy," said Takeshi Shigemoto, an associate director who follows the industry at Fitch Ratings.

A strong earthquake struck the coast of central Japan last month near the site of a nuclear power plant, although the operator said it was prepared for big tremors.

"Not enough steps in general have been taken against quakes, so now fears are stronger than ever," said Masako Sawai, at the Citizens' Nuclear Information Centre.

Earthquakes are not the only thing rattling consumer confidence in the nuclear power industry this year.

Since mid-March, two separate electric power firms have admitted that mishandling nuclear fuel rods caused "criticality" incidents -- unintended self-sustaining nuclear fission chain reactions -- one in 1978, one in 1984 and one in 1999.

Hokuriku Electric Power Co. has confessed to covering up the 1999 mishap at its Shika plant, near the site of last week's earthquake, while Tokyo Electric Power Co. (TEPCO) said the same about the other two incidents, including the one in 1978 -- which may have gone on for as long as 7- hours.

None of the incidents led to any radiation leak, but there have been reports of other fuel rod mishaps, as well as emergency reactor stoppages that were never reported, five years after a scandal over long-term falsification of safety records by TEPCO.

FATAL ACCIDENTS

One of the nation's worst nuclear accidents took place in September 1999, when workers at a nuclear facility in Tokaimura, northeast of Tokyo, set off an uncontrolled chain reaction by using buckets to mix nuclear fuel. Two workers were killed.

"People have to have electricity, so the companies can't be punished in a significant way, such as shutting down plants," said Hideyuki Koyama, from an anti-nuclear group in western Japan.

In 2004, four workers at a nuclear power plant were killed by a leak of high-pressure steam from a pipe. Prosecutors recently said negligence was involved in their deaths but that management had been lax for so long it was impossible to prove those at higher levels had failed to take action, media reports say.

Despite these mishaps, Japan still plans to boost its nuclear power supply to 40 percent of total energy supply from the current roughly 30 percent, while power firms have announced plans to build 13 new generators on top of the existing 55 plants.

Officials say the incidents emerging now are the result of trade ministry orders to go through power plant records and report all mishaps by the end of March, an effort to restore public trust.

"These are all old incidents," said Hisanori Nei, director of the Trade Ministry's Nuclear Plant Inspection Division. "It's much harder to hide such problems now."

In 2003, inspection standards were tightened so inspectors work in teams instead of solo. Fines for cover-ups of 300,000 to 1 million yen (US$2,500 to $8,500) a person, and 100 million yen (US$850,000) per company were introduced, along with the possibility of up to a year in prison.

Other changes are afoot.

Reporting rules may be tightened further, and TEPCO said that it will delay three of its four new nuclear projects. Hokuriku Electric also said it would keep its nuclear units shut through the business year that started on April 1.

Activists remain sceptical.

"The government standards are way too soft, and there's nothing there to intimidate the power firms at all," said Sawai at the Citizens' Nuclear Information Centre.