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July 14, 2011 

Nuclear Expert Dispels Myths about Small Modular Nuclear Reactors in Senate Testimony

WASHINGTON (July 14, 2011) -- A physicist from the Union of Concerned Scientists (UCS) today testified before a Senate subcommittee that small modular nuclear reactors are not necessarily any safer or more secure than conventional size reactors and could be more dangerous. Companies vying to sell small reactors, he said, are overstating their benefits and downplaying their potential pitfalls.

“Although some light water [small modular reactor] concepts may have desirable safety characteristics,” Edwin Lyman, a senior scientist with UCS’s Global Security Program, told the Senate Appropriations Committee’s Energy and Water Development Subcommittee, “unless they are carefully designed, licensed, deployed and inspected, [they] could pose comparable or even greater safety, security and proliferation risks than large reactors.”

Lyman was one of six panelists testifying today on the safety and economics of light water small modular reactors. The other speakers included two government representatives—Peter Lyons, the assistant secretary for nuclear energy at the Department of Energy, and William Magwood IV, a commissioner at the Nuclear Regulatory Commission (NRC)—and three industry representatives—Kathryn Jackson, chief technology officer at Westinghouse Electric; Christopher Mowry, president of Babcock and Wilcox Nuclear Energy; and Paul Lorenzini, CEO of NuScale Power. A video clip of the hearing is available on the committee’s website.

Unlike large, convential reactors that generate 1,000 megawatts or more, small modular reactors, which generate less than 500 megawatts, can be built at a factory, delivered to a site fully constructed, and then placed underground, either singly or in multiples.

Lyman argued that siting them underground would not make them safer. “While underground siting could enhance protection against certain events, such as aircraft attacks and earthquakes, it could also have disadvantages…,” he said. He reminded the subcommittee that the Fukushima Daiichi reactors’ diesel generators and electrical switchgear were underground, increasing their vulnerability to flooding. Likewise, he said, emergency crews would have a more difficult time accessing an underground reactor in the event of a serious accident.

Lyman also dispelled the industry myth that small modular reactors are “passively safe.” “[N]o credible reactor design is completely passive and can shut itself down and cool itself in every circumstance without the need for intervention,” he said. “…Small reactors may have an advantage because the lower the power of a reactor, the easier it is to cool through passive means such as natural convection cooling with water or even with air. However, accidents affecting multiple small units may cause complications that could outweigh the advantages of having lower heat removal requirements per unit. Moreover, ‘passively safe’ reactors require some equipment, such as valves, that are designed to operate automatically but are not 100 percent reliable.”

Passive systems may not work in the event of a serious accident that the reactor was not designed to withstand, he added, so they “should also be equipped with highly reliable, active backup systems and associated instrumentation and control systems.”

More backup systems, he pointed out, would drive up the cost of small reactors, which already have a sizable economic disadvantage compared with large reactors. Because of economies of scale, the capital cost per kilowatt for a small reactor would be approximately 250 percent more than that for a large conventional reactor.

To offset this disadvantage, Lyman said, the industry is trying to cut its operating and maintenance costs by pressuring the NRC to weaken regulatory requirements for modular reactors for emergency planning, control room staffing, and security staffing. Modular reactors contain smaller amounts of radioactive materials than conventional reactors, so the nuclear industry argues they pose less risk to the public and therefore should be treated differently.

“[S]mall reactors will not necessarily be safer than large reactors on a per-megawatt basis,” Lyman countered. “Simply put, the risk to the public posed by one 1,200-megawatt reactor will be comparable to that posed by six 200-megawatt reactors—assuming that all units are independent—unless the likelihood of a serious accident is significantly lower for each smaller reactor.” However, given that the NRC does not require new reactors, large or small, to be any safer than the reactors currently operating, Lyman said, “new reactor designs that have inherent safety features not present in current reactors may not actually end up being safer … if designers compensate by narrowing safety margins in other areas” to cut costs.

Finally, Lyman warned about allowing the industry to site small modular reactors in remote areas or developing countries that have no nuclear experience or emergency planning infrastructure. “UCS believes that [small modular reactors] are only suitable for deployment where there is an established infrastructure to cope with emergencies, and if sufficient numbers of trained operator and security staff can be provided,” he said. “… Even within the U.S., small utilities with little or no experience in operating nuclear plants need to fully appreciate the unique challenges and responsibilities associated with nuclear power and should not expect that small modular reactors will provide any relief in this regard.”


The Union of Concerned Scientists puts rigorous, independent science to work to solve our planet's most pressing problems. Joining with citizens across the country, we combine technical analysis and effective advocacy to create innovative, practical solutions for a healthy, safe, and sustainable future.

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