(Adds details)

TOKYO, March 19 (Reuters) - More Japanese utilities admitted on Monday they had failed to report past incidents in which nuclear fuel rods were mishandled at their reactors.

Industry experts said even more past nuclear lapses might come to light because Japan's Trade Ministry in November ordered all utilities to investigate power plant records and report the findings to the government by the end of March, a process the ministry said would help improve the industry's safety controls.

"I would not think this is the end of the story," said an industry analyst who asked not to be named. "It is quite possible we will see more of these cases."

Japan's third-largest utility, Chubu Electric Power Co. <9502.T>, said the mishandling happened at the No. 2 nuclear reactor at its Hamaoka plant, western Japan, in May 1991 while it was shut for regular inspections.

Fourth-ranked Tohoku Electric Power Co. <9506.T> said it had a similar case at the No. 1 unit at its Onagawa nuclear power plant in July 1988. It was also shut for inspections at the time, a company official said.

Utilities are now required to report all such incidents to the authorities, although that was not the case in 1991 and 1988.

The admissions follow a disclosure last week by another Japanese utility, Hokuriku Electric Power Co. <9505.T>, that it had covered up a similar incident in 1999.

Chubu Electric said that there was no coverup at the 1991 incident.

"There was no concealing act or falsification (of data) for this incident," Mitsunori Ueda, a Chubu Electric manager, told a news conference. He said it was too minor an incident to be called a problem "so we did not report it."

"We only decided to make it public after Hokuriku Electric's announcement."

Officials at the government's nuclear safety agency were not available to comment.

In the Hokuriku Electric incident the mishandling of fuel rods caused "criticality", an unintended self-sustaining nuclear fission chain reaction, that lasted for 15 minutes.

The unit was shut down manually after an automatic shutdown function failed.

The Chubu and Tohoku officials said their cases did not lead to criticality.

Public confidence in Japan's nuclear power industry, which supplies about 30 percent of its electricity needs, has been undermined by a series of safety scandals over the past decade.

Hokuriku Electric said it had cancelled a bond issue because it would have been difficult to find investors after its coverup admission.

A spate of recent discoveries has also fanned public concern that Tokyo may again face the risk of a blackout as it did after Tokyo Electric Power Co <9501.T>.'s coverups of safety blunders in 2003.

However, this scandal was unlikely to repeat itself and the recent findings would not shut all of Japan's more than 50 nuclear units, which supply about 30 percent of electricity needs in the world's second-largest economy, analysts said.

"Most likely, we will see limited impact. But psychologically, to many Japanese consumers it is as though the (1986) Chernobyl nuclear reactor disaster might happen again," said Masanori Maruo, an industry analyst at Deutsche Securities.

So far only Hokuriku's nuclear unit has been shut down by the trade ministry since its November order, for a thorough check of safety measures.

AlertNet news is provided by