Monticello / Nuclear plant starts up again after repairs

01/27/2007

Welding problem caused Jan. 10 shutdown


BY DENNIS LIEN
Pioneer Press


After almost a two-week shutdown, the reactor at the Monticello, Minn., nuclear power plant was started up Tuesday and should be running at full power in a couple of days.

The plant operator, Nuclear Management Co., took the step after an internal investigation cited a welding problem that caused the automatic shutdown Jan. 10. Repairs have since been made, and a search found no similar problems elsewhere.

The investigation confirmed early speculation focusing on a large control box that regulates steam flow to the plant's steam turbine-generator. It determined the box fell 6 inches, causing connecting linkages to open four turbine control valves. That caused steam pressure to drop and the plant's safety system to automatically shut down the reactor.

The support structure for the box was welded to other steel. But the investigation found that the design for the structure was inadequate and some of its welds were undersized or done poorly. Other structures in the turbine and reactor buildings were checked, and no problems were found.

Saying the 600-megawatt plant's safety systems operated properly, the Nuclear Regulatory Commission stressed that the reactor was never threatened and there was no danger to the public or plant employees.

Nuclear Management Co. operates the plant for Minneapolis-based Xcel Energy. Last fall, Xcel's license for the plant, which began operating in 1970, was renewed until 2030.