A valve that failed during three inspections over the last five years was cited in a Nuclear Regulatory Commission report as the reason for water leaking into an electrical equipment room after the transformer explosion and fires at Indian Point Energy Center in May.
About half an inch of water was found on the floor of the switchgear room ”“ used to house breakers that power safety-related equipment ”“ warranting a special inspection by the NRC that has resulted in a green-level violation, which is considered of low safety significance.
“Engineers replaced the problematic valves prior to the unit”™s return to service on May 25 and put in place robust testing procedures to ensure the valves operate as designed in the future,” according to a statement from Patricia Kakridas, a spokeswoman for the plant”™s owner, Entergy Corp. A pressure switch was also repaired, Kakridas said.
The flooding occurred after the Buchanan-based nuclear power plant experienced a rupture of one of its main transformers, causing an automatic shutdown of the Unit 3Â reactor May 9. The reactor was put back online May 25. The transformer rupture caused two fires that activated the water deluge system and other fire protection systems, including alerting the on-site fire brigade, to extinguish the flames using foam and water.
In the report released Thursday evening, the NRC said, “Based on the design of the deluge system for the transformer yard, only one deluge system actuation is anticipated.” But the heat generated from the fires caused other nearby deluge systems to activate, creating more water than anticipated, which clogged the drain in the switchgear room.
The deluge valves are designed to open and create water flow, but “they did not close once system pressure reached 6 psig (pounds per square inch gauge)” ”“ as designed ”“ “and continued to port water to the floor,” according to the report. In addition, a water-sensing pressure switch, which is supposed to detect when the water reaches 6 pounds per square inch gauge, was found to have had a “buildup of corrosion products,” the report said.
During the investigation of the flooding incident, NRC inspectors found that one of the valves was “documented to have opened during its 2-year deluge activation tests on April 7, 2011, April 2, 2013, and March 24, 2015, but did not close as designed after the deluge system actuated.”
Entergy attempted to fix the valve in 2013 ”“ two years after a work order and condition report were filed following the first inspection failure and shortly before the second failed inspection ”“ but did not correctly identify the problem and did not follow up with any additional repairs. Following the third valve closure failure earlier this year, a corrective action plan was created but was not completed before the transformer failure May 9, according to Entergy.
NRC officials said in the report that the valve problem “was a performance deficiency that was reasonably within Entergy”™s ability to foresee and correct, and should have been prevented.”
The report said that within four minutes the flood area had been isolated and that the water had drained completely within 30 minutes of isolating it.
An investigation by Entergy and an independent engineering firm determined in June that faulty insulation caused the transformer to combust. Further analysis is being conducted off-site by an engineering expert.
The NRC inspectors assigned to the plant will also be releasing a findings report next month about the failure of the transformer, according to Neil Sheehan, an NRC spokesman.
