Smaller reactors may still have a major problem with nuclear waste

Lindsay Krall decided to study nuclear waste out of love for mystery. It’s not easy to figure out how to bury radioactive atoms – it requires a mixture of particle physics, careful geology and engineering, and a high tolerance for a lot of regulations. But the most insidious component of all is time. It will take thousands of years for nuclear waste from today’s reactors to become safer. So no solution can require too much stewardship. It has to work and it has worked for generations. Until then, there will be no tool to divide these atoms, nor will the company that designed the reactor. Who knows? The United States may not exist either.

The US does not have such a plan right now. This is the case since 2011, with regulators facing stiff local resistance pulling the plug out of decades of waste disposal efforts under Yucca Mountain, Nevada, stuck $ 44 billion in federal funds for the job. Since then, the nuclear industry has done a good job of temporarily storing its waste, which is one of the reasons why Congress has shown little interest in developing solutions for future generations. Long-term thinking is not their strong point. “In the US, it was a complete institutional failure,” says Krall.

But there is a new type of nuclear power plant on the unit: the small modular reactor (SMR). The US nuclear industry has been stagnant for a long time, largely due to the huge cost of building massive new power plants. In contrast, SMRs are small enough to be built in a factory and then transported elsewhere for energy production. Advocates hope that this will make them more cost-effective than today’s large reactors and offer an affordable, always-on complement to less predictable renewables, such as wind and sun. According to some, they should also produce less radioactive waste than their predecessors. A Department of Energy-sponsored report in 2014 estimated that the U.S. nuclear industry would produce 94 percent less fuel waste if large, old reactors were replaced by new smaller ones.

Krall was skeptical of the last part. “SMRs are generally marketed as a solution – you may not need a geological repository for them,” he says. And as a postdoctoral fellow at Stanford, she began rummaging with two prominent nuclear experts for patents, research documents, and license applications on two dozen proposed reactor designs, none of which had yet been built. Thousands of pages of edited documents, several requests for public records and an extensive appendix full of calculations were later given to Krall, who is now a scientist at the Swedish Nuclear Waste Society. more waste: more than five times the spent fuel per unit of output and up to 35 times for other forms of waste. The research was published in the Proceedings of the National Academy of Sciences earlier this week.

Startups seeking licenses to build SMR proposals have challenged the findings, saying they are ready for any waste that is generated while the US is dealing with permanent disposal. “Five times a small number is still a really small number,” says John Kotek, who heads politics and public affairs at the Institute of Nuclear Energy, a trade association.

However, the authors say that the “baseline” end of the fuel cycle, which includes waste and decommissioning, should be a major factor in what they see as the uncertain economy of new reactors. “The purpose of this document is to stimulate discussion,” said Allison Macfarlane, former chairwoman of the US Nuclear Regulatory Commission and co-author of the document. “We can’t figure out how much it will cost until we understand what we’re dealing with.”

Designing smaller reactors can facilitate their construction, but it also creates a problem: neutron leakage. The reactors produce energy by burning neutrons into uranium atoms, which causes them to split. This emits more neutrons, which in turn find more targets and cause a chain reaction. But some of these neutrons miss. Instead, they fly out of the core and encounter other parts of the reactor that are “activated” or radioactive. Inside the SMR, there is less room for neutrons to push there, so more are escaping. The problem cannot be bypassed. “Basically, we’re dealing with gravity, the laws of physics,” says Krall. “It’s something you have to prepare.”