Seismic monitoring instruments from the 1970s, such as the equipment used at a Dominion Resources Inc. nuclear-power plant in Virginia, may not provide accurate readings, a U.S. earthquake scientist said.
Dominion’s monitors at the North Anna plant are “an older system from the 1970s and it is probably not accurate within 10 percent” and possibly as much as 20 percent, William Leith, earthquake hazards program coordinator at the U.S. Geological Survey, said today at a Nuclear Regulatory Commission meeting.
“Modern systems can certainly provide much faster information, much more accurate information, than these older systems that are in many of the nuclear-power plants in the Eastern U.S.,” he said.
Twin reactors at the North Anna plant, about 11 miles (18 kilometers) from the epicenter of a 5.8-magnitude temblor on Aug. 23, are shut while the company and NRC inspectors examine the earthquake’s effects on the facility. Dominion officials have said that they have found no damage to safety-related equipment and plan to have the Unit 1 reactor ready for re-start by Sept. 22, pending regulatory approval.
“It is our experience that ‘70s technology is robust, more than some newer technologies,’’ Dominion spokesman Richard Zuercher said in an e-mail today.
Dominion at North Anna relied on tape recorders and ‘‘scratch plates’’ to record ground movement. The plant was struck by jolts as much as twice its design limit, NRC staff estimated.
The company calculated that the shaking exceeded the plant’s design by less, ‘‘something between 10 and 20 percent,’’ Eugene Grecheck, vice president for nuclear development, told reporters Sept. 8. Dominion is ‘‘absolutely confident’’ in its readings from the equipment at North Anna, he said.
Every nuclear plant should ‘‘at a minimum have a free-field instrument’’ that records seismic movement away from buildings, Leith said.
Dominion is installing free-field instruments today, and it has an ‘‘uninterruptible power supply system’’ for its seismic equipment in power-plant buildings, Zuercher said. The plant’s scratch plates are in a reactor containment building and an auxiliary building.
The lack of modern instrumentation ‘‘hinders a quick, well-informed decision-making’’ by reactor owners and the NRC, Leith said. It also ‘‘severely limits an engineer’s ability to understand’’ how plant components react to ground movement, he said, citing Dominion’s assessment of nuclear-waste storage casks at North Anna that moved during the earthquake.
Guidelines established by the Electric Power Research Institute based in Palo Alto, California, show that for an earthquake of ‘‘this level of intensity and duration, you should expect to see no significant damage,’’ Zuercher said. ‘‘And that is what we are seeing.’’