A roughly 700,000-pound steam generator removed from a boiler at the San Onofre Nuclear Generating Station was en route to a disposal site in Utah today on a specially configured truck trailer.

The unit, which was part of an assembly inside a boiler, emits about as much radiation as a dental X-ray, according to Southern California Edison, which operates the idled plant.

The steam generator was put on the trailer Sunday night and will be hauled to Clive, Utah, over the next three weeks -- via Las Vegas and Salt Lake City. The exact route is not being disclosed. The shipment is the third of its kind.  

One of two in-service reactor units was already offline for refueling and maintenance when a leak in a tube in a steam generator in the other reactor unit prompted SCE to shut down the second reactor Jan. 31. The cause of the premature wear is the subject of an investigation.

New steam generators, shipped from Japan's Mitsubishi Heavy Industries, are awaiting installation.

Last week in a third-quarter financial reported filed by parent Edison International, SCE said costs associated with the shutdown exceeded $300 million. As of Sept. 30, inspection and repair costs totaled about $96 million, while the costs of replacing the electricity normally generated at the came to about $221 million.

The U.S. Nuclear Regulatory Commission is reviewing a proposal from Edison to restart one of the reactors at 70 percent power for a trial period of five months, at which time more inspections would take place to ensure its safety. There are no immediate plans to restart the other reactor.

On Oct. 25, the California Public Utilities Commission voted to initiate a formal investigation into problems at San Onfore.