Edison revealed this morning its plan to restart Unit 2, one of two reactors at San Onofre that have been shut down since January after premature damage was discovered to the tubes in the steam generators.
The company said the cause of the damage to the tubes was “fluid elastic instability,” a condition caused by several factors. The term refers to the vibration of the tubes inside a support structure. The excess vibration is caused by high steam velocity and low moisture around the tubes - and secondly by ineffective tube supports.
The proposal to be considered by the NRC is to restart Unit 2 at reduced power (70 percent). Edison said that would generate about 800 MW of power.
After about five months, the unit would be shut down again and checked for tube wear.
On a one hour phone call to explain the proposal to media and investors this morning, company head Peter Dietrich said the reason there was more tube wear in Unit 3 after a shorter period of operation than Unit 2 was the slight differences in the tube support structure assembly. He said the tube support in Unit 3 allows a “looser bundle,” allowing the tubes to vibrate more and permitting "tube to tube" wear.
“An obvious question here is : why is Unit two different than Unit three?" Dietrich said, "We now know that, although all of the steam generators were constructed with the same basic design, there were slight differences in the manufacturing and assembly of the Unit two steam generators that caused the tubes in the Unit thee steam generators to be much more susceptible to the vibration that resulted in the tube to tube wear. “
Dietrich said tube wear against support structures is not unusual in nuclear steam generators and the industry has techniques to investigate and correct this condition. However the "tube to tube" wear is more serious and less common.
Edison officials said any proposal to bring Unit 3 back online will not happen before next summer. That unit is currently defueled.
In a Frinds of the Earth telephone conference following Edison's announcement, Arnie Gundersen of Fairewinds Associates said running the plant at 70 per cent power would not solve the problems and Edison's plans to restart Unit 2 amount to a science experiment.
He said no nuclear plant in the United States has modified the design of the steam generators to the extent that Edison did when it replaced them in recent years. Gunderson believes those design changes have compromised the safety of both Units 2 and 3. He conceded that Unit 3 is more dangerous than Unit 2, but he and Daniel Hirsch of the "Committee to Bridge the Gap" said the underlying problems at both units are more serious than steam generator problems anywhere else in the country.
Dietrich said Edison is committed to “getting it right” and to running the plant safely. He said the company cannot restart Unit 2 without approval from the NRC.
The ball is now in NRC’s court. The regulatory agency will hold a public meeting next Tuesday, October 9 at 6 p.m. in Dana Point.
The meeting will start with a roundtable, including an NRC representative, Edison's chief nuclear officer, members of the California Energy Commission and the state's Public Utilities Commission plus concerned members of the pubic. It will conclude with a question and answer session.
Senator Barbara Boxer, Chair of the Environment and Public Works Committee, today called on the head of the NRC, Allison Macfarlane, to live up to a commitment the commission made not to approve the restart of San Onofre until the NRC has completed its investigation and the public has been assured of its safety.