The timeline for restarting the San Onofre Nuclear Generating Station in the wake of unexpected wear on new components is still unclear, plant and Nuclear Regulatory officials said Thursday.
Southern California Edison won’t get the go-ahead from the feds to restart the plant until the NRC figures out what caused the component failures and unexpected wear, said NRC spokeswoman Lara Uselding.
The NRC has sent an extra team of inspectors to the plant in addition to the two on-site - NRC staffers Greg Warnick and John Reynoso who work there year-round. The team, which arrives Monday, will be led by Greg Warner out of the NRC’s Arlington, Texas, office, Uselding said.
The unplanned shutdown is costing Edison $600,000 to $1 million per day, one energy expert said. Meanwhile, local anti-nuclear groups have seized on the problem to illustrate their assertion that nuclear energy is unsafe.
Three of the 129 new heat-exchanger tubes were found to have had unexpected wear after a radioactive steam leak in January. This week, they failed a pressure test and will have to be taken out of service, Southern California Edison said in a news release.
Testing the remaining tubes will take an additional eight days, Uselding said.
During normal functioning, superheated, radioactive water runs through the tubes in question—there are tens of thousands of tubes at the plant—and transfers the heat to pure water, creating steam to turn massive turbines that generate the electricity.
One of the tubes in Unit 3 sprung a leak in late January, squirting out radioactive steam before it was isolated. If any radiation escaped into the atmosphere, it was at undetectable levels, said plant officials and some outside experts.
Though the damaged tubes are only a year or so old and were replaced as part of $674-million upgrades to the plant, Uselding said it’s not unusual for the tubes to see some wear after even their first cycle.
What is unusual is the amount of wear and the number of tubes involved at San Onofre, she said. The team of experts will be studying the design, installation, shipping and operation of the new heat exchangers to determine the exact cause of the extensive wearing and will present those findings at a future public meeting, Uselding said.
Tube Testing and Operation
Though Southern California Edison will likely have to plug a number of tubes and take them out of service, Uselding said the plant could still operate at 100 percent with up to 700 tubes, or 8 percent of the tubes taken out of service.
“Some plants can operate with more than 30 percent of the tubes plugged,” Uselding said. “It’s a plant-specific evaluation.”
So hypothetically, the San Onofre plant could be up and running even if technicians stopped up all 129 tubes in question, Uselding said. But they won’t be allowed to fire up the reactors again until the Nuclear Regulatory Commission figures out what happened to cause all the wear and tear in the first place and Edison proves they addressed the problem, she said.
According to literature provided by Southern California Edison, tubes are inspected using three different methods and three different devices.
Inspectors start by running two types of “eddy current” tests, both of which work by shooting an electric current through the tube walls to measure the thickness.
First, inspectors thread a “bobbin probe” into each tube to measure overall wear. Then, they use a more precise “rotating probe” to more thoroughly map out the areas in the tubes that showed substantial wear.