A believer in solar power rarely has a good word to say about nuclear, though the sun generates light in a nuclear way via fusion. Of course, the zealotry works in the other direction as well. Almost any energy source boasts a cadre of ardent adherents: burning coal (it alleviates poverty!). Fracking for natural gas (we're better than coal!) Wind turbines (the fuel is always free!) Even fusion here on Earth. If you don't believe me, check the comments on this piece.

So it's no surprise that energy has proven a wedge issue among those who strive to save the world. Now along comes a new, intriguing documentary entitled Pandora's Promise that hits movie theaters on June 12 and promises to drive that wedge even deeper.

The story of the film is your basic conversion narrative, minus the conversion onscreen and geared to produce a hoped-for one in the audience. A band of five self-professed converts to the benefits of nuclear power—iconoclast Stewart Brand, author Gwyneth Cravens, climate activist Mark Lynas, nuclear weapons expert Richard Rhodes, and environmental thinker Michael Shellenberger—lay out their individual reasons for their newfound belief.

That newfound belief runs counter to that of the majority of environmentalists and environmental organizations from the beginnings of the movement in the 1970s. Much of that opposition stems from the original sin of nuclear power: it was used as a weapon first. Nuclear became synonymous with mushroom clouds at Hiroshima and Nagasaki and many other testing grounds and skies, mutually assured destruction, even nuclear winter and some kind of Armageddon, in the words of Whole Earth Catalog founder Brand.

What has cracked that catholic opposition for Brand and others is the invisible and invidious challenge of climate change. Simply put: nuclear power is one of the few technologies available today that can produce a lot of electricity, a lot of the time without a lot of greenhouse gases entering the atmosphere. To be anti-nuclear at this point means being for burning fossil fuels because energy sources such as solar and wind are too fickle and small to play a big role in providing clean electricity to the 7 billion people on the planet, according to this belief.

The film, through interviews with engineers and others, also notes that another original sin of nuclear power may have been the technology chosen by U.S. Admiral Hyman Rickover in the 1950s. The light water reactors the "Father of the Nuclear Navy" selected for commercial development may be simpler in design but they produce nuclear waste fairly rapidly and in quantity that still has no place to go. Safety is not an inherent feature of such reactors but instead has to be engineered around them with the cloak of containment vessels, redundant systems and other support and safety systems that add to the expense of nuclear power today. In fact, light water reactors are one of the few technologies to see little or no reduction in cost as more and more of them were built over the past several decades. Each one was, in essence, custom-designed to deal with the specific issues for a particular site and the specific version of the technology deployed.

That has left each reactor with its own unique flaws, as witnessed in the three nuclear catastrophes in Three Mile Island, Pennsylvania; Chernobyl, Ukraine; and Fukushima, Japan. Each reactor may be flawed in its own way, but the three milestone accidents did share one critical failing in common: the human factor. In all three, human oversight, omission, and/or flat-our error played a pivotal role in allowing the nuclear accidents to occur—so much so that engineers of new reactor systems have emphasized the removal of humans from their oversight in an accident entirely. So-called passive safety designs—such as the two new AP-1000 reactors being built at the Vogtle nuclear power plant in Georgia—require no human intervention to work. These systems intend to provide some insurance against human error leading to catastrophic meltdown.

And the world needs more and more power. Lifting hundreds of millions of Chinese people out of poverty in the last few decades required the construction of hundreds of coal-fired power plants, which has lead to China disappearing beneath a sulfurous haze of choking smog as well as surpassing the U.S. as the world leader in greenhouse gas pollution. Energy efficiency can't save us from that, according to the Breakthrough Institute's Shellenberger. As the global population heads toward 9 billion or even more potentially, energy use may double by 2050 and continue to increase. To stop adding yet more greenhouse gases to the atmosphere, all of that energy would have to be clean energy. And the only clean energy available is nuclear, according to Shellenberger and the other true believers of this film—in the absence of CO2 capture and storage for fossil fuel burners or some form of inexpensive electricity storage in the case of renewables like the wind and sun.

Size is an enduring totem for the proponents of nuclear power: the poster for the film above shows the actual size of the tiny cube of enriched uranium that could provide enough electricity for your entire life. And the filmmaker's own conversion experience came when he visited the single room in France, the size of a basketball court, beneath which much of that nation's nuclear waste is stored. Here is another size comparison: a pound of uranium contains as much energy as more than 2 million pounds of coal. Size matters and, since we face outsized problems from burning fossil fuels, an atomic-sized solution, with few emissions and well understood risks, can seem attractive.

That means we have to get over our overblown fears of radiation. Cravens, who wrote Power to Save the World about her own pilgrim's progress from nuclear opponent to proponent, notes that eating a single banana gives a higher dose of radiation than drinking water laced with tritium from the leaking Vermont Yankee nuclear power plant—as footage plays of anti-nuclear activists handing out bananas to their fellow protesters at Vermont Yankee. Why? Each and every banana bears radioactive potassium, which also happens to be a necessary nutrient. This is where the film is strongest, showing the ridiculousness embedded in the zealotry of those opposed to nuclear power. One sight gag shows radioactivity readings from a dosimeter in Chernobyl, high in the sky over the Pacific Ocean and at a naturally radioactive beach in Brazil, along with many other places. Those three are listed in order of size of dose by the way, yet we see a man being buried in these sands for a holistic treatment of his body pains.

And that's what it comes down to for these converts: the risks are smaller than people think since few have died directly from the meltdowns at Three Mile Island, Chernobyl and even Fukushima. Burning coal already kills thousands of people each year, and that's just premature deaths from polluted air. A recent paper by retired climate scientist James Hansen pegs the number of lives saved by nuclear power (via displaced fossil fuels) at 1.8 million people since the 1970s—and the technology has the potential to save millions more. Everyone in the film points to the French energy transition from burning oil to generate electricity to getting 80 percent of their power from nuclear within just a few decades as inspiration for what the world should undertake. And, though the existing global fleet of 400+ reactors mass produces the plutonium needed for nuclear weapons, it can also be used to rid the world of excess bombs. The U.S. and Russia have already proven that as the U.S. has turned old Russian nuclear warheads into the fuel for the U.S. fleet of 104 reactors under the "Megatons to Megawatts" program.

Besides, there are better, safer nuclear technologies that could be explored further, like the integral fast reactor that enjoyed, in a test, conditions similar to those that resulted in the Fukushima disaster—a total loss of electric power to run cooling pumps and other safety technology. This advanced reactor, instead of melting down, just shut down in the absence of electricity during a trial in Idaho in the 1980s. Similarly, there are enthusiasts for molten-salt reactors or the kind of small, modular reactor that could be built on an assembly line and finally make nuclear power at least cheaper. Even Microsoft billionaire turned global philanthropist Bill Gates, among others, thinks the nuclear industry is in desperate need of some innovation. Maybe the innovation for nuclear is to take the Homer Simpsons and Mr. Burns of the world and replace them with super-smart robots or sealed nuclear batteries.

Of course, the old adage in the nuclear business is that the best reactor is a paper reactor. Every nuclear power technology looks best when it exists only in drawings and schematics before real construction and operation begins, as Admiral Rickover observed (pdf) at the dawn of the nuclear age.

On the one hand, these five proponents note that nuclear is here today and available, but the technology that is so available to help combat climate change in the near term is this same decried light water reactor technology with all of its flaws (some of which have been remedied by better engineering). And we would need to build thousands in short order and at great expense to displace all the coal and natural gas fired power plants around the world. It might be cheaper to bolt on even inefficient CO2 capture and storage technology to each and every one of those power plants and bury the greenhouse gas if the goal is to prevent further climate change. We could even bury the CO2 in the same place that Craven's nuclear mentor, physicist Rip Anderson, suggested for nuclear waste: beneath the sea.

On the other hand, these proponents urge a new look at other technologies for generating electricity from fission: the fast-breeder reactors that work like a perpetual motion machine and require liquid sodium as a coolant, which has a propensity to burn in the presence of either air or water. Others propose a thorium fuel cycle, yet other alternative reactor designs or even fusion, which seems to always be 50 years in the future. All of them would take decades to develop and deploy and face the same hurdles as the dismissed renewable power from the sun, wind and the Earth's own heat. In fact, such advanced nuclear is well behind in the deployment race compared to all these other renewable technologies. As it stands, nuclear power struggles to grow fast enough to keep up with existing reactors that retire and only India and China seem keen on building a new fleet, primarily composed of light water reactors, albeit incorporating the latest in passive safety design.

This film springs from director Stone's dismay at the pessimism surrounding efforts to combat climate change and runs somewhat counter to his own first feature, Radio Bikini, which chronicled the horrors of nuclear weapons. But the main question around nuclear power is not answered by this visually compelling and interesting film Pandora's Promise: what if this is an example of a technology that people just cannot handle due to its complexity and unforgiving nature as well as its inability to gain widespread social acceptance?

Early in the film, we watch Lynas tour the aftermath of the multiple meltdowns at Fukushima Daiichi nuclear power plant in Japan and have his faith shaken. "There is no other energy source that does this, leaves huge areas contaminated by its strange invisible presence," he notes on camera while wearing a white Tyvek anti-contamination full body suit. "It's kind of eerie. I could say I'm having a wobble. I could see why we'd want to do without nuclear power."

By the calculus known as probabilistic risk assessment that governs nuclear power safety in the U.S. we should have one nuclear meltdown in 100,000 years. We've already had such a partial core meltdown at Three Mile Island in the first 50 years of the nuclear era, with at least three more even more drastic core meltdowns worldwide. For many, nuclear power remains more closely related to some of the other woes afflicting humankind that sprang from Pandora's mythical box than the hope that these converts require.