Waterford - Millstone Power Station, like many nuclear complexes around the country, was not designed to withstand a combined earthquake and flood comparable to Japan's earthquake and tsunami, a federal task force has found.

In the first phase of information gathering at 104 reactors around the country, federal Nuclear Regulatory Commission inspections performed at Millstone last month by a new task force formed because of the crisis in Japan found the power station was not specifically built to withstand concurrent extreme disasters like an earthquake and flood.

Neil Sheehan, a spokesman for the NRC, cautioned that such a finding doesn't necessarily mean that the plant wouldn't be able to withstand such an event.

Despite the finding, Millstone operator Dominion is adequately prepared for such possible independent troubles as station blackouts, fires, floods and explosions, the same NRC inspection team found. Millstone has two operating reactors and one that is permanently shut down but still houses radioactive spent fuel.

In Japan, a combined earthquake and tsunami in March knocked out power and flooded equipment at the Fukushima Daiichi reactors, causing meltdowns and spent fuel fires that required evacuations and permanent plant shutdowns.

By comparison, the United States' Northeast region is historically an area of low seismic activity, Sheehan said, but given what happened in Japan, the NRC wants to be more prepared nationwide for such rare but plausible events.

At Millstone, the most extreme example of a vulnerable condition is the location of a valve needed to operate a water main used to suppress fires at the shutdown Unit 1 reactor. The valve would be under water and inaccessible following a major flood, inspectors found.

Sheehan pointed out that other sources of water and backup procedures would likely be found, but the vulnerability should be addressed.

Millstone meets existing federal licensing and design requirements for fire protection, explosions and flooding, Sheehan added, but such non-safety-related systems as sump pumps needed to mitigate flooding and fire protection mechanisms like fire pumps are not "seismically qualified" to withstand a combined earthquake and flood, inspectors found.

Some equipment necessary to combat fires was also found not to be housed in buildings that are resistant to a combined earthquake and flood, Sheehan said.

Since the occurrence of compounded, extreme natural disasters are "in the realm of low probability," Sheehan said, it's too early to say what steps would be needed to correct or combat site vulnerabilities at Millstone or other plants across the country.

"We haven't seen any immediate safety operability issues" at Millstone, he said.

"Many of these issues fall beyond the 'design basis' - what the plant was designed and built to withstand. These are extreme events like what we saw in Japan. We're just seeing a lot of issues surfacing that fall into a category beyond 'design basis.' The Japan reactor events are taking us into new territory."

The inspections will lead to reports in mid-July and further recommendations that could be site-specific or "generic" - that is, broadly applicable to multiple reactor sites, said Sheehan. Some of the recommendations, for instance, could include building "seismically rugged" structures to house equipment that are able to withstand a major earthquake and flood, he said.

"This was a valuable exercise for Millstone, reviewing our readiness for a beyond design basis accident in light of the events in Japan," said Dominion spokesman Ken Holt.

The company has identified areas where it can improve safety, specifically in response to multiple events occurring at the same time, and is evaluating the best way to do that, he said.

p.daddona@theday.com