Does California shutdown mean the end of nuclear power? Not so fast.

The debate around the closing of the Diablo Canyon nuclear power plant in San Luis Obispo County, Calif., signals a broader conversation around power sources that could be crucial to the nation's energy future.

When California’s largest electric utility announced last week that it would close the state’s last operational nuclear power plant, supporters were quick to call the moment a potential game changer for America’s energy future.

The basic message, after all, is that officials in America’s most populous state, while eager to battle against climate change, have decided that nuclear reactors aren’t needed in the fight.

And the move, in which state regulators nudged Pacific Gas & Electric Co. toward a plan to close its Diablo Canyon reactor, comes as other states have also been closing nuclear plants or planning to do so. Solar and wind power are surging, and PG&E said the Diablo Canyon power will be replaced by renewables.

Could the end of the line be coming into view for a power source that used to be hailed by some as the future of clean power?

Actually, it looks far too early to draw that conclusion. The reality is that a battle still rages and may go on for some time. Some new reactors are being built. Some governors even in other politically liberal states are trying to save old reactors rather than scrap them. And though cheap natural gas may have called the economics of nuclear plants into question, environmentalists are divided over whether a nuclear phaseout would be wise.

“I think the stakes are becoming higher as these closures are happening,” says Jesse Jenkins, a researcher at the Massachusetts Institute of Technology's Energy Initiative. “We have a pretty big decision to make as a country about whether or not we’re going to give up this source of power or to build on that foundation. That could be one of the biggest decisions we’ll have when it comes to our targets and climate goals.”

Opponents of nuclear power point to the plants’ safety risks, the problem of their radioactive waste, and the fast-falling costs of cleaner alternatives.

The other side says there’s still a key hurdle in deploying more solar arrays and wind turbines: They only provide power when the sun is shining or the wind blowing – unless it gets much cheaper to store that power to be used on demand.

For his part, Mr. Jenkins recently published a paper, with co-authors from the Argonne National Laboratory, noting this challenge of bringing storage costs down.

“The least-cost generation mix includes a diverse mix of resources,” they write, envisioning a future in which “wind, solar, and flexible nuclear technologies co-exist.”

Another argument made by supporters of nuclear power: Today’s reactors aren’t the same as yesterday’s. Newer ones can be smaller, less costly, and leave behind less radioactive waste.

This battle, in short, is far from settled by the move to close Diablo Canyon. The news has simply brought the debate into sharper relief.

A nuclear-free future?

Proponents of the shutdown plan say it’s a step toward ending both nuclear hazards and carbon emissions – and a model of long-term planning.

The landmark Diablo Canyon proposal, supported by a coalition of environmental groups and labor unions, calls for replacing the plant’s 2,200-megawatt capacity with a blend of renewable sources, efficiency upgrades, and energy storage. It includes a commitment from PG&E to source 55 percent of its overall energy sales from renewables. It also provides $350 million for existing workers’ severance, retention, and retraining, as well as $49.5 million to compensate the county for lost taxes and jobs.

Though still subject to approval by the state land commission, the agreement represents “a big step in the transition in California’s clean energy future, in which the grid is dominated by [power] generation from renewables,” says Peter Miller, senior scientist with the Natural Resources Defense Council, one of the groups that has lobbied for the Diablo Canyon shutdown.

“It shows it’s possible to develop [renewable] sources at a scale and speed that allow states to replace retiring resources,” he says.

The deal’s success, Mr. Miller and others contend, would make a strong case for the existing shift away from nuclear power – a movement that has gained momentum over the past few years.

Between 2013 and 2014, energy companies across the country pulled the plug on four nuclear power plants. This month, Exelon Corp. announced plans to shutter two nuclear plants in Illinois by 2017 and 2018, respectively.

In general, companies questioned the economics: The costs of maintaining aging reactors could not hold up against the declining price of natural gas and growing subsidies for renewables. The two Illinois plants ranked among Exelon’s top performers, for instance, yet they lost a combined $800 million over the past seven years, the company reported.

Safety has also been an issue. Less than two years after the Fukushima accident in Japan in 2011, a generator leak at the San Onofre nuclear plant in California drew domestic attention to the public health and environmental risks of such facilities.

The persistence of such concerns, along with unease around the use of a power source that could double as a weapon of mass destruction, suggests that the time is ripe to put an end to nuclear energy, some environmentalists say. And with renewables becoming cheaper than ever, a carbon-free and nuclear-free energy future may be within the nation’s grasp, they say.

The nuclear industry “is in reverse, it’s going down the drain,” says Daniel Hirsch, director of the environmental and nuclear policy program at the University of California, Santa Cruz. “Diablo Canyon shows that we can get rid of the risks of nuclear [power] without adding to the risk of global warming. It tells the world what we all need to do.”

'A viable option'

But that worldview on energy, if gaining in California, isn’t necessarily sinking in nationwide. In another politically liberal state, New York, Democratic Gov. Andrew Cuomo (D) has been trying to save some of the state’s economically squeezed reactors  

Indeed, plans to launch reactors that use safer, more efficient technology are already under way in Georgia and South Carolina – though concerns over delays and cost remain.

Innovators around the country have also been working on even more advanced nuclear technology that would address problems associated with traditional reactors, such as size, inflexibility, and cost. The engineers behind Silicon Valley-based Oklo, for instance, envision a nuclear reactor small enough to manufacture in a factory – like cars or prefab houses.

“We want to get the cost down, get them out the door really quickly,” says nuclear engineer Jacob DeWitte, the company’s co-founder and chief executive. “We want to show that this is a viable option.”

“Nationally, it’s a mixed bag,” notes Ali Mosleh, a professor of engineering at the University of California, Los Angeles and a former appointee of the US Nuclear Waste Technical Review Board. “Plants are shutting down, but there’s also construction here and there. And there’s momentum for small reactors and next-generation reactors.”

And maybe, some say, that’s the way it needs to be.

Nuclear energy provides 20 percent of the nation’s power, while renewables – wind, solar, geothermal, biomass, and hydroelectricity – produce 13 percent combined. Cutting nuclear from the equation could leave the US with a bigger challenge in terms of achieving its climate goals, says Kerry Emanuel, a climate scientist and meteorologist at the Massachusetts Institute of Technology

“The numbers just don’t add up,” he says. “In the last two years we have shut down prematurely more nuclear energy than we have added solar and wind.”

At the same time, the need for carbon-free energy is growing. To prevent dangerous levels of global warming, the world’s nations must achieve net-zero greenhouse gas emissions between 2060 and 2075, the United Nations reports. As the world’s second-largest energy consumer, the US plays a key role in implementing practices toward that goal.

And so some advocate the need to consider the use of multiple sources of clean energy – including the nation’s existing fleet of nuclear power – at least until the necessary climate targets are achieved.

“The way I view it, the best way of success is by thinking about deploying all those things,” says Armond Cohen, co-founder and executive director of the Clean Air Task Force, a Boston-based research and public advocacy nonprofit. “That’s the future we want to create. We want to have those options.”