Feds Issue Safety Violation Notice to SONGS' Manufacturer

By City News Service

The U.S. Nuclear Regulatory Commission announced today that the inadequate design of steam generators at the San Onofre Nuclear Generating Station was a safety violation, and that a Notice of Nonconformance was sent to the manufacturer, Mitsubishi Heavy Industries.

An investigation into a small, non-injury leak in one of the two reactors at the nuclear power plant in northern San Diego County in January 2012 found that the cause was vibrations in steam pressure tubes.

The other reactor was undergoing scheduled maintenance at the time -- and both units remained shut down. In June, the plant's operator and majority owner, Rosemead-based Southern California Edison, announced the reactors would be retired.

The steam generators were installed in 2010 and 2011.

The safety violation was one of low to moderate safety significance, according to an NRC statement.

The agency said its actions against Mitsubishi, which has 30 days to respond, are designed to prevent an occurrence in steam generators installed at U.S. nuclear plants in the future. The design flaw resulted from faulty computer modeling, according to the statement.

Edison -- which has 10 days to formally respond to the NRC's findings -- contends that computer codes used by the manufacturer in the design of the steam generators inaccurately predicted thermal hydraulic conditions, leading to tube vibration, wear, and ultimately the leak.

The NRC also found that MHI embedded the same computer modeling error in the design of steam generators at four other nuclear plants, although none developed the fluid elastic instability that caused San Onofre to shut down, according to the utility.

"Mitsubishi designed the system," said Pete Dietrich, Edison's senior vice president and chief nuclear officer. "Mitsubishi built the system. Mitsubishi's system failed. They are the experts. SCE was the customer."

Edison questioned MHI about its computer models during the design process, he said.

Dietrich said it is normal for a plant operator to be cited even though the violation was caused by a vendor or contractor.

A public forum hosted by the NRC on the decommissioning of the reactors at San Onofre for 6 p.m. Thursday at the Omni La Costa Resort and Spa in
Carlsbad.