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Smaller, cheaper reactor aims to revive nuclear industry, but design problems raise safety concerns

Engineers at NuScale Power believe they can revive the moribund U.S. nuclear industry by thinking small. Spun out of Oregon State University in 2007, the company is striving to win approval from the U.S. Nuclear Regulatory Commission (NRC) for the design of a new factory-built, modular fission reactor meant to be smaller, safer, and cheaper than the gigawatt behemoths operating today. But even as that 4-year process culminates, reviewers have unearthed design problems, including one that critics say undermines NuScale’s claim that in an emergency, its small modular reactor (SMR) would shut itself down without operator intervention.

The issues are typical of the snags new reactor designs run into on the road to approval, says Michael Corradini, a nuclear engineer at the University of Wisconsin, Madison. “I don’t think these things are show-stoppers.” However, M. V. Ramana, a physicist who studies public policy at the University of British Columbia, Vancouver, and has been critical of NuScale, says the problems show the company has oversold the claim that its SMRs are “walk-away safe.” “They have given you the standard by which to evaluate them and they’re failing,” Ramana says.

Passive safety?

Normally, convection circulates water—laced with boron to tune the nuclear reaction—through the core of NuScale’s reactor (left). If the reactor overheats, it shuts down and valves release steam into the containment vessel, where it conducts heat to a surrounding pool and condenses (center). The water flows back into the core, keeping it safely submerged (right). But the condensed water can be low in boron, and reviewers worried it could cause the reactor to spring back to life.