Stuck steam valve triggers SCRAM shutdown at Brattleboro, VT nuke plant

[Ian David]

GLIDE Number: NC-20070831-13163-USA
Date / time: 31/08/2007 07:55:33
Event: Nuclear Event
Area: North-America
Country: USA
State/County: State of Vermont
City: Brattleboro
Number of Deads: None or unknow
Number of Injured: None or unknow
Damage level: Minor

Description:

A sticking steam valve forced an automatic shutdown of the boiling water reactor at Vermont Yankee nuclear power plant Thursday afternoon.The shutdown, which is also called a SCRAM, occurred during turbine steam valve testing, said Yankee spokesman Rob Williams.

"Plant technicians are in the process of investigating the cause of the automatic shutdown," wrote Williams in a press release. "The plant remains in a safe and stable condition and will be restarted after a thorough evaluation of the shutdown is completed."Prior to the shutdown, which occurred at 3:12 p.m., the plant had been running at 62 percent of capacity. The plant has been powered down from 100 percent since Aug. 21, when one of 22 cooling towers at the plant collapsed."We have plant technicians here that check the operations of plant systems," said Williams, late Thursday afternoon. The technicians were checking the steam valves, he said, which allow steam to move from the plant's turbine to the generator, when the reactor shut down.The steam valve problem is probably not related to the cooling tower collapse, said Howard Shaffer, a retired nuclear engineer and the chairman of the Northeast Section of the American Nuclear Society.

"The cooling towers are not even operating right now," he said. "This is purely an event that has to do with the valves."Once the problem has been resolved, he said, it could take technicians a day or two to get the plant back up to 62 percent.During the valve testing, "binding" was noticed, said Williams, and the reactor, which sensed the disruption, automatically shutdown."Nuclear power plants have very complex plumbing systems," said Uldis Vanags, Vermont's state nuclear engineer. Because of the number of valves and the miles of piping in a nuclear plant, technicians "are constantly checking the valves, especially critical ones like these steam valves."Last year, the NRC authorized Entergy to increase the power level of the reactor from 540MWe to 650MWe, a 20 percent increase. Entergy is in the process of requesting a 20-year license extension, from 2012 to 2032.Since the plant's uprate, it has had "more than the ordinary number of shutdowns," said Ray Shadis, technical consultant for the anti-nuclear group New England Coalition on Nuclear Pollution. The reason for this, he said, is that some maintenance was deferred to a recent refueling shutdown while plant technicians readied it for its power uprate.In 2003, Yankee shut down due to a blown recirculation pump seal. In 2005, an electrical insulator in the plant's switchyard broke, also forcing a shutdown, as did two fires in 2006, one in a transformer and the other in a pump motor.

Vermont Emergency Management "stepped up activation of its Emergency Operations Center after notification and will continue to monitor the status at the plant," according to a press release from the Department of Public Safety in Waterbury.In the early days of nuclear power, SCRAM was an acronym for Safety Control Rod Ax Man. Boron moderator rods were raised and lowered on ropes to control the level of activity in the reactor. In the event of a runaway chain reaction, a man with an ax would chop the rope and drop the rods into the nuclear pile to stop the reaction.

More:
http://hisz.rsoe.hu/alertmap/woalert_read.php?lang=eng&cid=13163

[lonestarnot]

1. What happened with this?