Month: September 2014

The Latest Chapter in Diablo Canyon’s Seismic Saga

Lara Uselding
Public Affairs Officer, Region IV
 
Scott Burnell
Public Affairs Officer, HQ
 

Today, the NRC is looking over a 1,400-page report produced by the owners of the Diablo Canyon nuclear power plant for California state officials who had asked for new seismic information about the plant.

Specifically, Pacific Gas & Electric produced the report to meet part of a 2006 California law, California Assembly Bill 1632. PG&E shared the report with the NRC as they’re required to do as part of the plant’s existing long-term seismic research program.

diabloEarlier research examined the Shoreline fault, just offshore of Diablo Canyon. Both PG&E and the NRC had previously concluded, in 2009 and 2012, the fault could only generate a quake weaker than one from the Hosgri fault, which Diablo Canyon is designed to safely withstand.

For the new report, PG&E performed state-of-the-art surveys of faults near the plant, including the Shoreline fault. The new report’s more detailed information and updated analysis indicates the Shoreline fault is both longer than previously thought and able to produce a slightly stronger earthquake.

As part of its NRC requirements, PG&E must assess the report’s impact on plant operations. NRC Resident Inspectors and Region IV staff experts have already looked at PG&E’s assessment and so far the information provides confidence the plant can keep the public safe after a seismic event.

While PG&E’s new seismic information adds detail about the faults in the plant’s immediate vicinity, the company’s evaluation claims an earthquake generated by movement on the Shoreline fault would not be as energetic as previous studies say a Hosgri-generated earthquake would be.

Just as with the earlier Shoreline fault reports, the NRC will thoroughly review the new information through our existing oversight methods. The agency will take whatever action is appropriate if our review questions PG&E’s conclusions.

PG&E will also use this new information as it re-evaluates its overall seismic hazard as part of the NRC’s response to the 2011 Fukushima nuclear accident. PG&E’s re-evaluation is due to the NRC in March 2015. The NRC remains committed to integrating new information into our understanding of safety at all reactors.

Part II: Ensuring Safety in the First Temple of the Atom

Thomas Wellock
NRC Historian
 

https://www.lib.ncsu.edu/specialcollections/digital/text/engineAs noted in Part I of this story on the NC State research reactor, the Atomic Energy Commission (AEC) was very anxious to promote the world’s first civilian reactor. But its enthusiasm was tempered by the challenge of placing a reactor safely on a busy college campus and developing an approval process for non-AEC reactors.

The AEC turned to its Reactor Safeguard Committee, the forerunner of today’s Advisory Committee on Reactor Safeguards. The Committee was formed in 1947 to evaluate the safety of new reactors proposed by AEC laboratories and contractors.  “The committee was about as popular—and also necessary—as a traffic cop,” recalled Safeguard Committee Chairman Edward Teller.

The Committee’s most significant contribution was establishing a conservative approach to safety given the engineering uncertainty of that era. “We could not follow the usual method of trial and error,” Teller said. “The trials had to be on paper because the actual errors could be catastrophic.” The Committee developed a “simple procedure” of challenging a reactor designer to write a “hazard summary report” that imagined the worst “plausible mishap”—soon known as a “maximum credible accident”—and demonstrate the reactor design could prevent or mitigate it.

Five NC Stte physics professors designed the reactor. Here, in the reactor control room (left to right front row) are Clifford K. Beck and Arthur C. Menius, Jr. Standing is Newton Underwood, three unidentified students, Arthur Waltner and Raymond L. Murray.
Five NC State physics professors designed the reactor. Here, in the reactor control room, (left to right front row) are Clifford K. Beck and Arthur C. Menius, Jr. Standing is Newton Underwood, three unidentified students, Arthur Waltner and Raymond L. Murray.

The Committee focused on several hazards, including a surge in the chain reaction called a reactor “runaway,” a catastrophic release of radioactive material from fire, sabotage, or an earthquake, and hazards from routine operation that might result from leaks or inadvertent exposures. The Committee asked NC State to address these concerns in a “hazards summary report.”

To meet the Committee’s desire for inherent safety, NC State proposed a “water boiler” reactor, which was believed to have “student-proof” safety margin given its strongly “negative coefficient” of reactivity that limited greatly the possibility of a runaway. NC State also developed interlocks and an extremely dense concrete shielding to discouraged sabotage.

In order for NC State to commit the funds to such a long-term project, it needed an early approval. This created a dilemma since the college did not yet have a detailed, complete design.  The AEC used a two-step conditional approval that was similar to its later construction permit/operating license process. In step one, construction did not begin until NC State addressed the most important design safety issues. When it did, the AEC agreed by contract to supply enriched fuel. The fuel was not delivered, however, until NC State resolved all outstanding safety questions and a final inspection took place. With that, the first civilian reactor in history went critical in September 1953.

The AEC approach to safety at NC State foreshadowed many later regulatory practices. As important as the 1954 Atomic Energy Act is to current regulatory practice, it is interesting to see that many of the critical elements have even deeper roots back toward the beginning of the atomic era.

 

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