Nuclear Microreactors (SMRs—small modular reactors)

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Small modular reactors (SMRs) are part of a new generation of nuclear power plants being designed all over the world. The objective of these SMRs is to provide a flexible, cost-effective energy alternative.  A micro nuclear reactor is a small version of a nuclear reactor (approximately a few tens of meters). It is often so small it can be shipped or flown in.

Small reactors are defined by the International Atomic Energy Agency as those with an electricity output of less than 300 MWe, although general opinion is that anything with an output of less than 500 MWe counts as a small reactor.  Micro nuclear reactors could be used to power large vessels, production facilities (e.g. water purification, or mines), or small (remote) villages.

Modular reactors are manufactured at a plant and brought to the site fully constructed. They allow for less on-site construction, increased containment efficiency, and heightened nuclear materials security.

A plethora of small designs and business models are emerging. A 25-megawatt reactor is 1/64 the size and complexity of a standard large 1.6 gigawatt reactor from Westinghouse or AREVA. It costs $25 million (Hyperion says) instead of $6-9 billion and could power a small town.

There are a variety of different types of SMR. Some are simplified versions of current reactors, others involve entirely new technologies.

Licensing for SMRs has been an ongoing discussion. There was a workshop in October 2009 about licensing difficulties and another in June 2010, with a congressional hearing in May 2010. With growing worries about climate change and greenhouse gas emissions, added to problems with hydrocarbon supplies from foreign countries and accidents like the BP oil rig explosion in the Gulf of Mexico, many government agencies are working to push the development of different licensing for SMRs. 


Name Power Technology Producer
CAREM 27 MWe PWR CNEA & INVAP, Argentina
FUJI 100 MWe MSR ITHMSO, Japan-Russia-USA
Hyperion Power Module[1] 25 MWe SMR Hyperion Pwr Gen – Santa Fe, NM USA
KLT-40 35 MWe PWR OKBM, Russia
MRX[disambiguation needed] 30 – 100 MWe PWR JAERI, Japan
IRIS-100 100 MWe PWR Westinghouse-led, international
SMART[disambiguation needed] 100 MWe PWR KAERI, S. Korea
NP-300 100 – 300 MWe PWR Technicatome (Areva), France
VK-300 300 MWe BWR Atomenergoproekt, Russia
PBMR 165 MWe HTGR Eskom, South Africa, et al
GT-MHR 285 MWe HTGR General Atomics (USA), Minatom (Russia) et al
BREST 300 MWe LMR RDIPE (Russia)
4S 10 – 50 MWe FNR Toshiba – Japan
TerraPower 10 MWe TWR Intellectual Ventures – Bellevue, WA USA
E-Cat 10 KWe LENR Andrea Rossi – Italy

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

VIDEO 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 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.”

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