Diablo Canyon Nuclear Plant: Solid as a Rock or Ready to Crumble?

Although the official title of the U.S. Senate Environment and Public Works Committee hearing on Dec. 3 was “[Nuclear Regulatory Commission’s] Implementation of the Fukushima Near-T­erm Task Force Recommendations and other Actions to Enhance and Maintain Nuclear Safety,” much of the testimony focused on possible seismic problems in and around the Diablo Canyon nuclear power plant.

In Sen. Barbara Boxer’s (D-Calif.) opening statement, she set the stage by saying “Even after learning of newly discovered strong earthquake faults close to the power plant, the NRC has declined to act on its senior inspector’s warning—its own senior inspector’s warning—that the reactor should be shut down if it did not come back into compliance with its seismic licensing requirements.”

“Diablo Canyon is the only nuclear power plant in the nation operating at the highest seismic risk area as determined by the NRC,” said Rep. Lois Capps (D-Calif.), who attended the hearing to provide a statement. She noted that the Hosgri offshore fault was discovered less than three miles from the facility during construction, and that the Shoreline Fault was found in 2008 less than half a mile from the plant.

Pacific Gas and Electric Co. (PG&E), owner of Diablo Canyon, claims that the facility is seismically safe and able to withstand the largest potential earthquakes in the region. The company completed extensive scientific research, and on Sept. 10 it released a report that it says demonstrates that the plant remains safe.

“Vast resources have been devoted to examine onshore and offshore fault systems in the region of interest to better understand potential hazards,” Neal Driscoll, a professor of geology and geophysics at the Scripps Institution of Oceanography at the University of California, San Diego, said in a PG&E press release. “In my opinion, outside of oil and gas exploration, the offshore areas by Diablo Canyon are one of the most studied continental regions in the world.”

The PG&E research used state-of-the-art 3-D PCable equipment to survey fault systems offshore. The technology provides detailed imaging of steeply dipping faults that are difficult to image using traditional 2-D multichannel seismic data. The 3-D data provide measurements of fault offsets, both vertically and horizontally. Offset information is said to be very important in the hazard assessment process.

“This research effort, utilizing the latest technologies, demonstrates Diablo Canyon continues to be seismically safe,” said Ed Halpin, senior vice president and chief nuclear officer at PG&E. “These studies provide scientists and regulators an unprecedented scientific analysis of the seismic characteristics near Diablo Canyon.”

But Sam Blakeslee, PhD, former California state senator and California seismic safety commissioner, was skeptical of PG&E’s analysis. In his testimony, Blakeslee said “The utility has a long and remarkable history of producing sanguine technical reports that get the seismic hazard analysis at Diablo exactly wrong.”

In addition to the troubling history that Blakeslee alleged, he noted the following other concerns about the company’s seismic report: disregard of double design earthquake basis, weakening of Hosgri Evaluation basis, lack of transparency, rapidly evolving analytical methods, and the possibility of more seismic threats to come. While Blakeslee said he is a lifelong Republican, a scientist, and is not anti-nuclear, he feels that Diablo should be forced to complete the license amendment process, so that technical arguments can be made in a public, independent setting rather than behind closed doors.

Tony Pietrangelo, senior vice president and chief nuclear officer at the Nuclear Energy Institute, offered a more optimistic view of the Diablo situation. “Nuclear plants have several aspects of seismic protection, including safety factors applied to the reactor designs, conservative requirements in engineering codes and standards, and specific requirements for the strength of steel and concrete used to build the plants. These design and construction practices are above and beyond the protection needed to safely withstand significant ground motion,” he said in his testimony.

He noted that engineering and materials design, and seismic study technologies and methodologies have evolved significantly over time, which allows for more certainty as to how a nuclear power plant’s structures, systems, and components will react to a seismic event, and diminishes the reliance on overly conservative techniques and assumptions.

According to Pietrangelo, Diablo is unique in the industry in that it is licensed for three earthquake designs: the Design Earthquake, Double Design Earthquake (equivalent to the Safe Shutdown Earthquake), and the Hosgri Earthquake. Diablo has continually studied the geologic features surrounding the plant through its long-term seismic program.

“I realize this issue is even more complex because some staff at the NRC filed a differing professional opinion on issues related to Diablo Canyon and the Shoreline fault. Differing professional opinions do occur among the 4,000 staff at the NRC, and the NRC has a process for addressing them,” Pietrangelo testified.

However, Daniel Hirsch, lecturer at the University of California, Santa Cruz, presented a grimmer picture. “A Fukushima-type disaster is just waiting to happen here. All it takes, just as at Fukushima, is an earthquake larger than the plant was designed to withstand. It could happen tomorrow,” Hirsch said.

Aaron Larson, associate editor (@AaronL_Power, @POWERmagazine)

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