Resulting in one of the largest mass arrests in US history, the standoff at Seabrook helped spark a national backlash against nuclear power that has reverberated for decades, playing a significant role in curbing federal ambitions to build hundreds of reactors across the country.

In all, about 2,000 demonstrators converged on what would become the Seabrook Nuclear Power Plant, preaching non-violence and carrying signs that read, “Split Wood, Not Atoms” and “Go Fishing, Not Fission.”

Forty years ago, Renny Cushing led hundreds of protesters through the front gates of perhaps the nation’s most controversial construction site, sprawled across a stretch of marshland along the New Hampshire coast.


What happened on that warm day on April 30, 1977, and the movement it galvanized, may have led to unforeseen consequences. Some environmental advocates now question whether their opposition to nuclear power paved the way for more coal, oil, and natural gas power plants, prime sources of greenhouse gases linked to global warming.

But for activists like Cushing, then a goateed carpenter who at 24 had already been arrested several times as a founding member of what became known as the Clamshell Alliance, there are no regrets.

“It’s a very unforgiving technology, and we saw what we were doing as an effort to stand up for social justice,” said Cushing, now 64, and a state representative from nearby Hampton, N.H.

As demonstration projects in the 1950s and 1960s showed the viability of nuclear power to generate vast amounts of electricity, political leaders vowed to build as many as 1,000 nuclear reactors by the end of the century.

That never materialized, in no small measure because of the anti-nuclear movement, crystallized by the occupation of Seabrook, said Tom Wellock, a historian at the US Nuclear Regulatory Commission, which was created in 1975 to oversee the growing number of reactors across the country.


“What happened with the Clamshell Alliance at Seabrook is that it really nationalized consciousness about nuclear power and inspired similar groups around the country,” he said. “Their influence on policy-makers certainly mattered.”

The number of reactors peaked in the 1990s at 112, and today, there are just 99. Seven more are slated to shut down in the coming decade, including the Pilgrim Nuclear Power Station in Plymouth.

A demonstrator waited outside the main gate of the Seabrook N.H. nuclear plant site in 1977. Bob Dean/Globe Staff/Globe Staff

Ultimately, it cost nearly $7 billion to complete Seabrook, which didn’t begin generating power until 1990 – 14 years after the formerly named Public Service Co. of New Hampshire received a construction permit. It was one of the last nuclear plants built in the United States, and produces only half the power that its founders envisioned. Only one of two planned reactors was built.

Economic pressures played a major role in dampening the ambition for more nuclear plants as well. Many plants, like Pilgrim, which began producing power in 1972, have struggled with financial challenges. It takes billions of dollars to build a nuclear plant, and tens of millions of dollars every year to keep them fueled, operating safely, and secure.

Those pressures were particularly acute in the 1970s and 1980s, when energy efficiency efforts during the oil embargo reduced demand for electricity, rising interest rates increased construction costs, and regulations were tightened in response to the 1979 meltdown at Three Mile Island, which stoked public fears about nuclear power.

In recent years, the economics have become harder still. A rush of cheap natural gas from hydraulic fracking has made many nuclear plants uncompetitive, especially in states like Massachusetts where energy prices aren’t subsidized.


Today, like other nuclear plants, Seabrook is contending with costly maintenance challenges. The plant is licensed to operate until 2030, but federal regulators have denied its bid to extend its license for another 20 years until they approve a plan to correct the degradation of the concrete walls and foundation of its containment building.

As part of their effort to sustain public support for the plant, which employs 550 people full-time and provides power to roughly 1.2 million homes and businesses, company officials now argue that Seabrook remains vital to the region’s ability to curb carbon emissions and address global warming.

“We absolutely believe nuclear energy is part of the solution to concerns about climate change,” said Alan Griffith, a spokesman for Seabrook, which is now owned by NextEra Energy, a Florida-based company. “We believe that states and countries won’t be able to meet their carbon mandates without nuclear power.”

Indeed, carbon emissions in 2015 rose in New England for the first time in five years, a spike that energy officials attributed to the Vermont Yankee nuclear plant’s closing the year before, because the closure forced the power grid to rely on plants run by dirtier fuels such as oil and natural gas. Without power from Seabrook, Massachusetts would struggle to comply with the state’s legal requirement of cutting its carbon emissions 25 percent below 1990 levels by 2020.


The challenges of reducing carbon emissions, especially under a Trump administration, have led some environmental groups to rethink their position on nuclear power. This month, the Environmental Defense Fund published an essay titled, “Why We Still Need America’s Nuclear Power Plants – At Least for Now.”

It urged states with competitively priced energy to provide subsidies to help nuclear plants remain in business.

“When a nuclear plant is retired today, there is a greater chance the plant will be replaced by a natural gas plant than a renewable energy plant,” wrote John Finnigan, a senior regulatory attorney for the group.

But few members of the Clamshell Alliance, which inspired a number of similar protest groups, have come around to supporting nuclear power.

The protesters 40 years ago occupied the property, about 40 miles north of Boston, for nearly a day before state troopers from five New England states intervened, holding more than 1,400 activists in National Guard armories for up to two weeks.

Robin Thompson spent 11 days in the National Guard armory in Manchester, N.H., eating canned peas and singing “We Shall Overcome.” Now 62, she doesn’t “have a moment of regret” about the protests, describing nuclear power as “outrageously dangerous.”

Like many of her fellow activists, she’s also deeply worried about the impact of emissions from fossil fuel-fired power plants.

“It does give me pause that carbon emissions are going up,” said Thompson, a 62-year-old who lives in Amherst, Mass. “But I still believe nuclear power is an absolute disaster waiting to happen.”


No one is known to have died from a radiation leak at a nuclear plant in the United States since an explosion at a test reactor in Idaho Falls killed three people in 1961. But radioactive waste from those plants will remain a threat to public safety for thousands of years, critics say. Much of that waste remains scattered at nuclear plants around the country, with no clear plan on how to dispose of it.

Building hundreds of additional nuclear plants would have substantially cut the US contribution to climate change, reducing the need for some 1,300 coal plants in the United States. But protesters contend that the country should have devoted the vast sums of money that went to nuclear power to developing renewable energy.

“This is my regret: that our larger society did not hear or heed our concerns fully and deeply enough,” said Thea Paneth, now 58 and from Arlington. She was 18 years old when she spent 12 days confined to an armory in Dover after being arrested at Seabrook.

“I have done all I could, for love of people and planet Earth,” she said. “I am thankful and grateful for the folks who showed me how to engage in struggle.”

Thea Paneth participated in the landmark protests 40 years ago against the Seabrook nuclear power plant. Suzanne Kreiter/Globe Staff/Globe staff

David Abel can be reached at dabel@globe.com. Follow him on Twitter @davabel.