The Nuclear Regulatory Commission yesterday put a temporary hold on a 20-year license extension for the controversial Vermont Yankee nuclear power plant. The commission had instructed its staff to issue the renewal last Thursday, the day before the massive earthquake and tsunami in Japan.

Spokesman Neil Sheehan attributed the delay to the fact that manpower is short while the agency focuses resources on helping Japan deal with the unfolding nuclear crisis triggered by the natural disaster.

But opponents of the nearly 40-year-old plant, who note it is the same design as the most compromised reactor in Japan, said the delay should be far longer — until the agency can assure the public the plant is safe.

Vermont Yankee, in Vernon near the Massachusetts border, has suffered a series of problems in recent years that have frayed the public trust, including the collapse of a cooling tower and leaks of tritium into groundwater from underground pipes that company officials initially said were not there.

“I think it is prudent to take a step back and say this reactor design is having serious problems in Japan,’’ said James Moore, clean energy program director for the Vermont Public Interest Research Group. “The last thing we should do is say it is good to go for another 20 years past its expiration date.’’

Germany yesterday shut down seven aging plants until they can be assessed for safety following the Japanese crisis. In Russia, Prime Minister Vladimir Putin ordered a review at all Russian nuclear facilities. India’s plants are also undergoing a review.

The Obama administration, however, has not ordered any similar review and has continued to back nuclear power through the crisis, saying it would learn lessons from Japan’s nuclear problems. President Obama has embraced nuclear power, requesting $36 billion for government-backed loans to help the nuclear industry build additional plants.

While the delay has given some hope to opponents of the Yankee plant, it is unclear whether there is any possibility, legally, of the commission reversing the decision it made last week, when it allowed staff to issue the license.

A spokesman for Senator Bernie Sanders of Vermont, who has been calling for a delay in the issuing of the plant’s license because of the nuclear crisis in Japan, said last night that the short-term delay is welcome, even if it appears to be for bureaucratic reasons such as staffing shortages.

But the spokesman, Michael Briggs, said the senator still is hoping for a full reevaluation of the plant in light of the events in Japan.

He said officials from the Nuclear Regulatory Commission are scheduled to appear at a Senate oversight hearing today and Sanders hopes to get more answers then.

Yesterday, Vermont Yankee spokesman Larry Smith said it was his understanding the delay was merely a temporary one and the license would be issued soon.

The timing of the Japanese crisis couldn’t be worse for the nuclear industry, as it attempts a broad rebirth as a green energy source to combat global warming; the reactors do not emit greenhouse gases that cause the atmosphere to warm.

Vermont Yankee provides roughly one-third of the Green Mountain State’s electricity, for the most part inexpensively.

That low cost, and the more than 600 jobs the plant provides, has won it some support in the state.

Still, antinuclear sentiment, always an undercurrent in this liberal state because of the dangers of radioactive releases and waste, grew stronger in 2006 after the plant received NRC permission to increase its power output by 20 percent.

Donovan Slack contributed to this story. Beth Daley can be reached at bdaley@globe.com.

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