The Maine Yankee nuclear plant had been running at its highest level ever and had had a string of emergency shutdowns in the months before it was crippled by a fire, a spokesman said.

The plant operated at record levels through March and April, said spokesman Duggan Kimball. Its capacity has been increased from 825 megawatts to 880 megawatts over the past few years.The Maine Nuclear Referendum Committee, an anti-nuclear group, claimed the plant had been running at levels that stressed profits over safety and that it was ripe for an accident after having shut down nine times in nine months.

"Possibly it's time for people to reconsider the nuclear experiment here in Maine," said Tom Coffins, spokesman for the group.

After years of relatively trouble-free operation, the plant was shut down to repair leaks in the reactor steam generator system, to correct a problem controlling the steam turbine and to fix gauges and monitors.

However, Kimball said the frequent shutdowns proved plant operators made safety their primary concern.

"It really is a sign of our conservative operating philosophy. If anything, we are overcautious," he said.

Monday's fire in the plant's non-nuclear section was the most serious incident in its 19-year history.