Design flaws at Pilgrim date back at least 7 years

By Christine Legere
clegere@capecodonline.com
April 08. 2015
Plant owner Entergy Corp. has issued a post-event report on the Jan. 27 forced shutdown of the Pilgrim Nuclear Power Station in Plymouth.  Merrily Cassidy/Cape Cod Times
Plant owner Entergy Corp. has issued a post-event report on the Jan. 27 forced shutdown of the Pilgrim Nuclear Power Station in Plymouth. Merrily Cassidy/Cape Cod Times

Pilgrim Nuclear Power Station’s switchyard — which connects the Plymouth plant to the electrical grid — has design flaws dating back to at least 2008 that have yet to be fixed.

The flaws can cause electrical arcing, which has led to the loss of power at the plant and the unplanned shutdown of the reactor when severe weather hits, according to an explanation provided Tuesday to federal regulators by Entergy Corp., the facility’s owner and operator, in its required post-event report on the Jan. 27 forced shutdown of the plant.

“The root cause of the event is that the design of the switchyard does not prevent flashover when impacted by certain weather conditions experienced during severe storms,” according to the report. Heavy winds were blowing in off the ocean, which added to the problems, according to the report.

Entergy’s long term solution is to modify the switchyard design. Meanwhile, the company will look at other measures, “including the requirement to place the reactor in cold shutdown prior to the anticipated arrival of certain severe winter storms,” according to the 7-page report.

Loss of off-site power during the Jan. 27 blizzard caused the reactor to automatically shut down. A series of post-shutdown mechanical glitches then occurred, including the failure of an air compressor that powers several non-essential systems. In its report this week, Entergy wrote that it determined the compressor wouldn’t start because of a low battery.

The high-pressure coolant injection system, used to cool the reactor, was shut down after its overload alarm sounded. The system had become waterlogged because valves that would have been draining the water weren’t working, according to the report. The valves would normally be powered by the failed air compressor.

Another valve used to cool the reactor failed to open or only partially opened. That valve was disassembled and found to contain damaged parts, according to Entergy. The company wrote that the manufacturer of the valve will be asked to determine the cause of the problem.

Several area watchdog groups had called on federal regulators to shut down Pilgrim prior to the January storm, based on a similar blizzard in February 2013 that knocked out offsite power and forced the reactor into an unplanned shutdown.

The request to power down the reactor was not granted, but the plant was ultimately forced into shutdown under circumstances similar to the 2013 storm.

Arcing electricity in the switchyard was identified as the root cause both times. Similar shutdowns related to switchyard problems took place twice during a winter storm on Dec. 19 and Dec. 20, 2008, according to Entergy’s report.

An Entergy spokeswoman said the company has made efforts to address switchyard issues.

“In 2008 and 2013, modifications were made to our switchyard hardware, storm preparations and mitigation procedures were updated based upon new learnings from specific weather conditions,” Entergy spokeswoman Lauren Burm wrote in an email. “Further modifications to the switchyard are planned to address the issues more recently identified. Pilgrim has and always will operate safely in all weather conditions.”

David Lochbaum, Director of the Nuclear Safety Project for the Union of Concerned Scientists, said equipment such as the high-pressure coolant system are routinely tested at all plants, and he would assume that was true at Pilgrim. Tests are done in “milder” conditions, he said, such as when there is no loss of electrical power.

“Test efforts are well-intended but come up short,” he said. “Hopefully that’s one of the lessons learned.”

The same was likely true of the air compressor.

“They test compressors routinely but maybe didn’t test the battery,” he said.

Not true, according to Burm, who said the battery was regularly checked.

The Nuclear Regulatory Commission sent inspectors to Pilgrim to investigate the January shutdown, but their report has not been released.

“We are continuing to review a number of these issues, most notably the functioning of the safety relief valves during the shutdown and the company’s plans to make modifications to the switchyard to prevent flashover (electrical arcing) during winter storms,” NRC spokesman Neil Sheehan wrote in an email. “We will evaluate all of the information in this submittal as part of our broader assessment of the event.”

Mary Lampert, chairwoman of the advocacy group Pilgrim Watch, has frequently blamed equipment breakdowns on the age of Pilgrim, which has operated since 1972.

Lampert cited Harwich’s Democratic state senator: “As Senator Dan Wolf says, ‘How many people have a 40-year-old appliance operating in their house?'”

“After a while, things wear out.”

— Follow Christine Legere on Twitter: @chrislegereCCT

Timeline of recent activity at Pilgrim

  • January 25: Nuclear Regulatory Commission announces Pilgrim Nuclear Power Station failed a December inspection and will remain among bottom five plants in country based on performance, requiring more oversight.
  • January 27: Reactor forced to shut down due to problems in the switchyard which connects the plant to the electric grid.
  • February 2: NRC sends inspectors to Pilgrim to investigate the shutdown.
  • February 5: Entergy submits an event notice to NRC saying a generator that would power instruments measuring levels in seawater intake bays had failed during the January storm. Worker had been sent to shed to make sure tides weren’t driving water levels too high.
  • February 9: Reactor powers back up.
  • February 14: Reactor shut down due to storm forecast.February 18: Pilgrim brought back online.
  • March 6: NRC tells Entergy, in its annual assessment letter, Pilgrim will remain categorized at a degraded level of performance. The plant will be inspected again in July.
  • April 7: Entergy issues post-event report on the Jan. 27 shutdown.
  • NRC inspection report on Jan. 27 incident still not issued.
Tagged , , , , , . Bookmark the permalink.

Comments are closed.