Are Small Nuclear Reactors Safer?

In the wake of the deadly earthquake and tsunami that struck northeastern Japan on Friday which now threatens the possibility of partial or full reactor meltdowns at several Japanese nuclear power plants, many anti-nuclear campaigners are using the opportunity to posit that nuclear power is neither clean, green nor safe, even in the context of its potential to reduce greenhouse gas emissions contributing to global warming. And at the very least, that is a conversation worth having.

But what about the much-hyped small modular reactors (SMRs) that are being touted as one possible way to scale-up the low-carbon electricity generating-potential of nuclear power, and to do so at a much lower cost than traditional utility-scale nuclear power plants? Are the much smaller SMRs any safer than large nuclear power plants? And can they withstand the kind of thrashing that Japanese plants endured on Friday without melting down? From what I can gather, the answer to both of those questions is yes.

In the United States, Nuclear Regulatory Commission regulations require that every plant be built to survive an earthquake larger than the strongest ever recorded in the area. And when the NRC does finally produce a regulatory regime governing SMRs, the same rule will likely be put in place. But what happens when a major earthquake and tsunami event not only prevents a nuclear power plant from operating properly but also prevents the emergency back-up systems from operating properly, or at all? In the case of SMRs, because of the size of the reactors and the passive cooling systems used, a loss of back-up power or access to fresh water would be irrelevant.

“They are smaller, so the amount of radioactivity contained in each reactor is less,” writes John Wheeler at This Week in Nuclear. “So much less,” he writes, “that even if the worse case reactor accident occurs, the amount of radioactive material released would not pose a risk to the public.”

Not only do smaller reactors contain less fuel, which slows down the progression of reactor accidents, most SMRs are small enough that they cannot over heat and melt down.

“Where operators in large reactors have minutes or hours to react to events, operators of SMRs may have hours or even days. This means the chance of a reactor damaging accident is very, very remote,” writes Wheeler.

A 2010 report by the American Nuclear Society (pdf) seems to back that up. According to the report, many of the safety provisions required in large reactors are not necessary in the many new small reactor designs.

In particular, most SMRs are not water cooled, they use passive systems of gas, liquid salt, or liquid metal coolants that operate at low pressures, meaning that if radioactive gasses build up inside the containment building, like they did inside the reactors at the Fukushima nuclear power plant, there is less pressure to expel radioactive gasses into the environment.

The fact that they don’t need fresh water to cool the reactors mean there is no need for pumps to move the water, and perhaps more importantly, they do not require access to electrical power via the grid or via backup diesel generators to provide active cooling support.

“They get all the cooling they need from air circulating around the reactor,” writes Wheeler. “This is a big deal because if SMRs can’t melt down, then they can’t release radioactive gas that would pose a risk to the public.”

In addition to not requiring access to electricity to support an active cooling system, SMRs are small enough that they can be built underground. Doing so certainly wouldn’t protect them from the damaging effects of earthquakes, per se, but it would prevent them from being lifted off their foundations by a powerful tsunami and floated away like matchboxes, as we saw was the case with so many large, heavy structures on the northeastern coast of Japan last Friday afternoon.

As someone who has personally and publicly wrestled with the nuclear power issue for a very long time, I would like to believe that we have the ability to generate safe, reliable, clean nuclear power. And while I still believe there is a place for new nuclear capacity in the U.S. and elsewhere, I’m not so sure that new capacity should come in the form of large, capital-intensive, utility-scale nuclear power plants — plants that obviously are not impervious to environmental threats.

Article by Timothy B. Hurst, appearing courtesy Celsias.