Diablo Canyon licence extension delayed for studies

12 April 2011

Pacific Gas & Electric (PG&E) has asked the US nuclear regulator to delay its final decision on the renewal of the operating licence of the Diablo Canyon nuclear power plant in California until comprehensive seismic studies are completed.


Diablo Canyon
Diablo Canyon (Image: NRC)
PG&E says that it is the only US utility that has a seismic department, which continually studies earthquake faults in the region of the power plant and global seismic events as part of Diablo Canyon's safety program.


In November 2008, the department, working in partnership with the US Geological Survey, discovered a new shoreline fault zone. PG&E's evaluation of the safety risk to the plant presented by the newly-discovered fault concluded that Diablo Canyon has adequate safety margin to withstand maximum ground motions assumed to occur from faults in the region.


The utility plans to undertake high-energy offshore 3-D studies of the shoreline fault's deeper regions as soon as it obtains necessary permits from various regulatory agencies.


"In the wake of the tragic accident at Japan's Fukushima Daiichi nuclear plant, we know that many of our customers and government partners are concerned and want to know more about the seismic characteristics surrounding the Diablo Canyon nuclear power plant," said John Conway, PG&E's senior vice president of energy supply and chief nuclear officer.


He added, "Because we live in a seismically active region, PG&E takes care in all its operations, especially at Diablo Canyon, to analyse and address seismic risks. In the aftermath of the Japanese earthquake and the resulting tsunami, we are working even more closely with various governmental permitting agencies to accelerate the plant's advanced seismic research."



NRC approves Limerick uprate
The US Nuclear Regulatory Commission has approved Exelon's request to increase the generating capacity of units 1 and 2 of the Limerick nuclear power plant in Pennsylvania.
Exelon plans to increase the capacity of each boiling water reactor (BWR) by 1.65%, from 1189 MWe to 1205 MWe. The utility intends to implement unit 1's uprate within 90 days, and unit 2's uprate within 90 days of the completion of its refuelling outage in spring 2011.

The NRC determined that Exelon could safely raise the reactors' power output primarily through more accurate means of measuring feedwater flow.


Conway stated, "As PG&E works towards this objective, we are asking the Nuclear Regulatory Commission (NRC) to withhold issuance of PG&E's renewed operating licences, if approved, until after this research is completed and the findings are submitted to the commission."


PG&E is "seeking to expeditiously complete the 3-D seismic studies and provide those findings to the commission and other interested parties so that they may have added assurance of the plant's seismic integrity," he said.


"Even after we have completed these advanced studies, our geoscientists will continue their ongoing seismic research to give us, our regulators and the public confidence that the plant remains safe," Conway added.


PG&E has operated the two power reactors at Diablo Canyon nuclear power plant since 1984 and 1985 respectively. Both units are 1100 MWe, Westinghouse-designed four-loop pressurized water reactors (PWRs) and generate about 32% of the utility's output, which serves northern and central California.


PG&E submitted its licence renewal application for both Diablo Canyon units to the NRC in November 2009. A 20-year extension to the plant operating licence would allow unit 1 to operate until 2044 and unit 2 to 2045.


Researched and written

by World Nuclear News


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