Last week, the agency announced that the plant located between San Diego and Los Angeles will remain off-line while investigators determine why tubing in its massive steam generators is eroding at an unusual rate and repair the problem.
Operator Southern California Edison has said 321 tubes with excessive wear will be plugged and taken out of service at the two reactors, well within the margin to allow them to keep operating.
In a four-page letter to Edison last week, NRC Regional Administrator Elmo E. Collins scrolled out a series of steps the utility must take before restarting the seaside reactors.
"The agency is very concerned," NRC spokesman Victor Dricks said. "The steam generators are a vital and very important piece of plant equipment, so ensuring their integrity is important" to the company and the NRC.
Jaczko will be joined by Sen. Dianne Feinstein (D., Calif.), her office confirmed.
The plant's four steam generators each contain nearly 10,000 alloy tubes that carry hot, pressurized water from the reactors. The Unit 2 reactor was shut down for maintenance when workers discovered extensive wear on its tubing.
The tubes are a critical safety barrier - if one or more break, there is the potential that radioactivity could escape into the atmosphere. Also, serious leaks can drain cooling water from a reactor. If a leak becomes serious, a plant is required to shut down.
The steam generators were manufactured by Japan-based Mitsubishi Heavy Industries.
Authorities in California have been scrambling to find additional power in case the reactors remain idled through summer, when energy use typically peaks. That could include restarting retired plants in Huntington Beach in northern Orange County.
Last week, an environmental group said the utility misled the NRC about design changes that it said are the likely culprit in excessive tube wear. The report by nuclear consultants Fairewinds Associates, and produced for nuclear watchdog Friends of the Earth, warned that a more detailed study is needed on the tubing before the reactors are restarted.