Inspectors have discovered flood seals were missing at the Vermont Yankee nuclear plant in Vernon.
BRATTLEBORO — For the third time in 18 months, inspectors have uncovered missing flood seals at the Vermont Yankee nuclear plant, a problem that could compromise the plant’s ability to operate electrical safety systems.
Inspecting for flood seals has been a Nuclear Regulatory Commission priority ever since the nuclear disaster in Fukushima, Japan, when floodwater from a tsunami inundated several nuclear plants similar in design to Vermont Yankee.
The most recent problem was discovered Wednesday during an annual inspection of the manholes at the Vernon plant, according to NRC spokesman Neil Sheehan.
In Wednesday’s instance, plant owner Entergy Nuclear failed to correct missing and faulty flood seals that were discovered last spring in underground pipes, Sheehan said.
He said Entergy Nuclear had hired a contractor to replace the missing seals, but the contractor had failed to do the job. He said Entergy was held accountable for the work of the contractor.
Flood seals have become a higher priority in the nuclear industry after the flooding at the Fukushima nuclear reactors.
If water is able to leak into underground conduit or pipes carrying electrical systems, Yankee’s safety could be compromised, according to a report posted by the NRC.
In the most recent case, a missing conduit flood seal between an outside manhole and the west “switchgear room compromised the flooding design of both the east and west switchgear rooms,” the NRC reported.
Entergy Nuclear spokesman Jim Sinclair said the problems had prompted Entergy to review its inspection program.
“We are reviewing the circumstances that resulted in the condition we found and will be doing an extensive review to identify the root cause and any enhancements we need to make to our inspection program,” Sinclair said late Friday.
He said after this week’s inspection turned up the problem, a new seal was immediately installed.
“We are also re-inspecting all similar manholes to verify that all necessary seals are in place,” he said.
Sheehan said that in March, a manhole identified as S2 was discovered to have problems with three conduit seals. He said two had incorrect screw plug seals and one had a missing seal. One of the two screw plugs was dislodged, he said.
“A work order was generated at that time to correct the deficiencies and the company believed the work order was completed and that all three conduits were corrected by installing a poured sealant,” he said.
But he said during Wednesday’s annual inspection, “workers again found problems in manhole S2.”
He said that once the problem was discovered Wednesday, Entergy reviewed the work order for the March problem. “It believes the contract workers who did the work in manhole S2 back in March most likely misinterpreted the instructions,” Sheehan said.
In March, the workers corrected the one faulty screw plug but didn’t realize there were two other faulty seals, he said.
According to NRC event reports about the March 19, 23 and 27 issues at Yankee, water from a dredging operation March 19 did leak into two electrical manholes which led to “vital switchgear rooms.” Yankee was shut down at the time for refueling, the report stated.
On March 23, a “partially dislodged seal” was discovered, and on March 27, another pathway for flood or rainwater into the manholes was discovered via an abandoned sump pump.
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