By Jim Shilander
Southern California Edison officials publicly outlined the company’s response to the Nuclear Regulatory Commission’s Confirmatory Action Letter Friday in Laguna Hills but received some tough questions about the utility’s conclusions on what happened at the San Onofre Nuclear Generating Station from NRC personnel, as well as members of the public.
NRC SONGS Special Project Team Manager Art Howell indicated that the commission’s review of Edison’s conclusions would likely take at least a few more months, since he indicated that he was considering putting out information on the “status” of the work in mid-February.
Approximately 300 people attended the meeting at The Hills Hotel, which only had about 45 minutes of public questions and comment. The majority of the meeting was given over to Edison officials to explain the technical details of what had happened in Unit 3 and the steps taken to maintain safety in Unit 2.
Thomas Palmisano, a vice president of engineering at Edison, largely presented the results of the company’s investigation and its proposal for how to avoid future problems at Unit 2. Palmisano said the problems with Unit 3 of the plant had been the result of a type of tube-to-tube wear that had been previously unseen in plants elsewhere in the United States.
“Edison recognized the significance of Unit 3′s condition, and recognized the same susceptibility in Unit 2,” Palmisano said. Unit 2, he noted, could have been started up after refueling was completed, but the company had delayed restart in order to be sure it was safe to restart. The company had actually sought help from Mitsubishi Heavy Industries, which designed and manufactured the replacement generators for Units 2 and 3, as well as several of Mitsubishi’s competitors and independent utility experts to look at the design of the steam generators and determine what might have been the problem.
Palmisano said, in a response to a question from Howell, that the type of tube wear experienced in Unit 3 had been thought of as theoretically possible, but hadn’t been seen in the field, at least until the failure of Unit 3. He explained that the rows of tubes were separated from one another by anti-vibration bars, but were not designed to prevent the type of vibrations that caused the wear.
“This has not been seen before,” Palmisano said.
The root cause, he said, had been a design flaw at Mitsubishi, which had used thinner anti-vibration bars than it had used in other designs, due to the size of the generators being built.
Palmisano said that several hundred tubes had experienced significant wear in Unit 3. Upon inspection of Unit 2, he said, two tubes were found to have similar amounts of wear as in Unit 3, and were preventatively plugged, as were approximately 182 other tubes in the same area where wear had been found in Unit 3.
“The phenomenon in Unit 3 is unpredictable and rapid,” Palmisano said. The tubes that were plugged, he said, would likely be subject to the same type of wear experienced in Unit 3 if Unit 2 were to operate at 100 percent capacity. “It’s a similar set of tubes,” Palmisano noted.” But Unit 3 is behaving differently than Unit 2.”
Peter Dietrich, Edison’s Chief Nuclear Officer, noted that the support structures for the tubing had been much more effective in Unit 2. He and Palmisano then explained that company had arrived at its proposal for operating Unit 2 at 70 percent power based on the evidence gathered during the work. Operating at that level would not generate the same type of “dry steam,” flowing at high velocities that caused the majority of the wear in Unit 3, they noted.
The company had also installed additional safeguards, they said, and had increased their ability to catch minor leaks and the ability to monitor vibrations. Dietrich also reiterated that safety was, in his mid, the paramount issue for the plant.
“We will not restart either Unit 2 or Unit 3 until we and the NRC are satisfied it is safe to do so.”
San Clemente anti-nuclear advocate Gene Stone said he was worried that Edison and the NRC were engaged in “group-think” with regard to what was fixing the problems at the plant. Restarting Unit 2, he said, was asking for trouble after what happened at Unit 3.
Dietrich said the utility was trying to apply lessons learned. “We’re applying the lessons learned in Unit 3 directly to Unit 2,” Dietrich noted. “Unit 2 operated at 100 percent power for 21 months.”
The meeting had been preceded by a press conference featuring a number of advocates against restarting the plant. Activist Donna Gilmore of San Clemente noted the history of workers at SONGS making complaints about safety to the NRC should give the commission pause about Edison’s claims to have found the problems in the steam generators.
“Their plan is to start it up and see what happens,” Gilmore said.