The Humboldt Bay plant site, owned by Pacific Gas and Electric Company, consists of two fossil fueled units, two mobile gas turbines, and a nuclear unit -- Unit No. 3. The site consists of approximately 143 acres, located on the shore of the bay, just southwest of Eureka, California. The generating unit had a net electrical output of 65 MWe.

The nuclear steam supply system consists of a single cycle, natural circulation, boiling water reactor (BWR) and the associated control and support systems. The primary containment is located entirely below grade and consists of a drywell vessel and a suppression chamber, both located within a reinforced concrete caisson. The drywell vessel is centrally located and serves as the primary containment vessel. The suppression chamber is constructed of reinforced concrete lined with carbon steel plate. The turbine-generator consists of a tandem, compound, double-flow, condensing turbine, directly connected to a hydrogen-cooled, synchronous generator. The turbine consists of a single flow, high pressure section and a double flow, low pressure section with a crossover pipe connecting the two.

Commercial operation for the nuclear unit began in August 1963 and continued until July 1976, when it was shut down for refueling. The alternative option of decommissioning the unit was debated and ultimately selected in July 1983; the mode selected was custodial SAFSTOR for a period of up to 30 years. Although the lack of a source for accepting the spent fuel was the primary reason for selecting the SAFSTOR mode, there were additional benefits resulting from this option -- benefits that have been recognized by many stations with multiple units. Since Unit 3 shares the plant site with two operating fossil units, operations and maintenance personnel would be available to provide the necessary custodial surveillance for the entire period. Secondly, the 30-year period would allow radiation levels to decay, resulting in about a 25% reduction in radiation exposures, and thereby simplify the handling and disposal of highly irradiated components. And finally, 30 years of industry developments and experience might result in lower costs and higher safety levels.

The active work to place the unit into the SAFSTOR mode began in late 1983 with the unloading of the reactor core, followed by the flushing and draining of piping systems and then isolating them from those systems still in operation. Physical removal of equipment was performed only where this would contribute to lower radiation exposures during SAFSTOR. Interconnected systems were either removed or blanks installed. All radioactive wastes were processed and shipped for burial, including cleaning the spent fuel storage pool and processing contaminated water from the suppression chamber. Significant modifications changed the facility from one designed to operate to one supporting long-term fuel storage. These modifications included upgrading the pool and stack monitoring systems, modifying the security system, and enclosing the radwaste treatment systems.

Preparation for SAFSTOR was completed in July 1988, following the NRC's approval of the Decommissioning Plan. The plant has been maintained in custodial storage since that time, retaining 390 fuel assemblies that will eventually be shipped to a federal burial facility, estimated to take 2 or 3 years. A major dismantling project began in September 1998, when public concerns over seismic vunerability motivated PGE's removal of the unit's 250-foot tall, concrete vent stack. The utility has also been preparing the regulatory documents and applications to transfer its spent fuel to dry cask storage.