Incorrectly installed clamps must be fixed before reactor starts up again

PLYMOUTH — Another equipment snafu at Pilgrim Nuclear Power Station was discovered on Sunday, this time in the critical safety system used to stop fission from occurring in the plant’s reactor during an emergency.

It marked the third mechanical problem at the 45-year-old beleaguered plant in as many weeks. The reactor is going into its fourth week of shutdown.

During a check on Sunday, a Pilgrim engineer found the support clamps for nine pipes that are part of the hydraulic control rod system appeared to be incorrectly installed.

The control rods are a key component in getting a reactor to shut down. They contain a powdered form of neutron-absorbing boron, slowing or stopping the fission process as the rods are inserted into the reactor core.

In an event such as an earthquake, the shaking could affect the pipes with the faulty clamps and result in a failure of the connected control rods to insert in Pilgrim’s reactor. Nuclear fission would then continue to occur.

Operators might even have to resort to injecting a so-called “poison” solution into the reactor to get nuclear fission to stop, according to Neil Sheehan, spokesman for the Nuclear Regulatory Commission.

The solution is made of a liquid boron.

While plants are equipped with the backup pump system to “poison” neutrons, it has yet to be used in the United States.

David Lochbaum, director of the Nuclear Safety Program for the Union of Concerned Scientists, recalled one reactor where the “poison” system almost came into play.

“Browns Ferry had 76 rods that didn’t insert in the 1980s,” Lochbaum said. “The operator reached for the switch but didn’t have to use it.”

The control rods fully inserted on the operator’s fourth try.

The discovery of the incorrectly installed clamps at Pilgrim does have a positive side, in Lochbaum’s opinion. “The catch indicates that workers haven’t turned a blind eye toward conditions as they wait out the time until permanent shutdown,” he said.

Entergy Corp. has announced Pilgrim will be permanently shuttered by May 31, 2019.

Pilgrim operators shut down the reactor on March 6 because of a suspected leak in a system needed to heat water before it is pumped into the reactor. While workers addressed this problem, the reactor lost off-site power at the height of the March 13 blizzard, and safety systems were powered by emergency diesel generators.

During testing prior to starting up the reactor, operators discovered the start-up transformer had sustained extensive damage during the storm and had to be replaced.

Entergy filed its event report on the clamps with the Nuclear Regulatory Commission on Monday, just one day before its yearly assessment meeting with federal regulators. The meeting, historically both heavily attended and contentious, is set for 6 p.m. today at the 1620 Hotel in Plymouth. Pilgrim has been classified as one of the three worst performing reactors in the country by federal regulators since 2015.

Entergy spokesman Patrick O’Brien confirmed nine pipes were found with what appeared to be clamps that were not correctly installed, but plant engineers are calculating whether the pipes would have held up in an earthquake. If so, they will ask to rescind their reports on the clamps, he said.

While Sheehan called an earthquake “a low probability event,” he said Entergy Corp., the plant’s owner and operator, will have to fix the incorrectly installed clamps before the reactor starts up again.

– Follow Christine Legere on Twitter: @ChrisLegereCCT.