The Energy Department shut down a weapons production reactor at the federal Savannah River Plant due to safety concerns raised by an unexpected power surge during startup operations last week, officials said Thursday.,

In particular, department officials expressed concern that Savannah River officials decided to continue running the reactor even though they did not understand why the power surge had occurred.Anson Franklin, an Energy Department spokesman, said the 2 percent power surge did not present a significant safety threat, but that sufficient caution was not exercised by officials of DuPont Corp. Du Pont runs the Savannah River plant for the government.

"They were not sufficiently safety conscious," Franklin said. "They should have been more alarmed."

The incident occurred last week as the "P" Reactor, one of three used in production of tritium and plutonium for the U.S. nuclear weapons program, was being returned to service following a four-month maintenance shutdown.

Officials said operators sought to boost power during the startup in an effort to sustain a balky nuclear reaction, unaware that chemical conditions within the reactor were acting against them.