New Problem at Diablo Nuclear Plant’s Unit 2 Causes 3rd Shut Down

7 Jan 2021

Correction made Jan. 21

Half of California’s sole remaining nuclear plant, Diablo Canyon, is offline for the third time in six months, and it’s not expected to be back in continuous service for several more weeks. The plant’s 1,150 megawatt Unit 2 went down Dec. 2.

Both of the unit’s two unplanned outages earlier last year were due to a hydrogen leak from an electric component at Pacific Gas & Electric’s plant. The latest shutdown for Unit 2 was caused by vibration issues in the main electric generator in the non-nuclear side of the plant, PG&E spokesperson Suzanne Hosn told Current in a Jan. 7 email. She added that the utility has “been focused on conducting in-depth inspections of the main electrical generator and making repairs with Siemens—the vendor—and other industry experts.”

PG&E’s Diablo Plant: the red rectangular facility houses the electric generator

“What is going on?” David Weisman, Alliance for Nuclear Responsibility spokesperson, asked. “It started as a hydrogen leak and now it’s unexplained vibrations.” He said the state grid operator and energy regulators must pay attention now because the earliest the plant will be back online is May 31. “Summer will be here before we know it.”

The California Independent System Operator is “monitoring the outage closely and coordinating with PG&E,” Anne Gonzales, CAISO spokesperson, said.

Hosn said PG&E plans to start a series of tests in which the unit is put on online and then taken offline several times over a number of weeks to gather operational data. After the tests, Diablo is scheduled for its Spring refueling, she said.

With refueling comes a planned outage set for mid March that’s expected to last 35 days. That means Unit 2 won’t be fully back online before the middlle to end of April, if all goes smoothly.

Last July and October, PG&E said the issue that caused the sudden outages at Unit 2 was a hydrogen leak from a problematic electrical component, called a stator, which cools a very hot spinning generator.  The stator was recently rebuilt in 2019 at a cost of $100 million.

The California Public Utilities Commission on Dec. 3 approved ratepayer recovery of the stator rebuild, noting that PG&E’s inspection found it was necessary. PG&E insisted that a stator rebuild was required because of “progressive degradation of certain components likely to lead to the eventual failure of the generator stator which could lead to an unplanned outage of 100 days or more.” As it happened, that charge to ratepayers was okayed just as Unit 2 was taken offline a third time last year, on Dec. 2.

Weisman is concerned about more unplanned outages at Unit 2. Those stress the facility and could cause the nuclear reactor to trip. The Nuclear Regulatory Commission puts nuclear facilities on its watch list if there are three unexpected trips in a year.

The current outage has not impacted “energy supplies to California ISO” because the loads are currently low, Gonzales said.

The troubled Diablo plant is slated for permanent closure by 2025.

Elizabeth McCarthy

The correction reflects PG&E’s expected date for refueling, which is mid-March. Current previously reported the refueling start date as April 25

Comments are closed.


Please share California's Energy Policy news source with your friends