By Sharryn Dotson, Editor
Just a few short years ago, small modular reactor (SMR) technology was gaining increased attention from not just the nuclear industry, but also the power generation industry as a whole. Following the accident at Fukushima, and at a time when it looked like new large-scale nuclear power would be too expensive and time-consuming to build, SMRs were seen as the next big thing to bring safe and reliable power to the U.S. grid as utilities planned retirements of both nuclear and fossil-fueled power plants.
While countries such as Russia, India, Pakistan and China have all made great strides in developing and using SMRs either for research or in innovative projects like floating power plants, the U.S. has lagged behind in SMR development.
The US Department of Energy defines SMRs as reactors that are 300 MW or smaller in capacity, and can be manufactured in a factory and delivered and installed at the site in modules. The NuScale design includes an integrated steel containment vessel with the reactor vessel inside, and no field-built containment building. It is installed underground, within a reactor building designed to protect against aircraft impact, and inside an 8-million gallon pool, along with as many as 11 additional 50-MW NuScale Power Modules. The pool serves as the ultimate heat sink and all normal operation and emergency cooling operations are accomplished with natural circulation to drive the coolant flow. In a Fukushima-like station blackout event the NuScale plant can shut down and self-cool indefinitely with no operator action, no additional water and no source of electricity (AC nor DC).
NEI breaks down SMRs into three reactor designs: light water, high-temperature gas-cooled, and liquid metal and gas-cooled fast reactors. Each design has its own benefits, and reactors of each type have been developed with varying degrees of success.
|A cutout of the 45-MW NuScale small modular reactor. Photo Courtesy: NuScale|
Light Water Reactors
NEI notes that light water reactors (LWR) are typically smaller than 300 MW. LWR designs under development include Babcock & Wilcox's 180-MW Generation mPower SMR, Westinghouse's 225-MW reactor, NuScale Power 45-MW reactor and Holtec's 160-MW Inherently Safe Modular Underground Reactor (HI-SMUR).
B&W's Generation mPower SMR technology was the first to win a cost-sharing funding initiative with the U.S. Department of Energy (DOE) and project partners Tennessee Valley Authority (TVA) and engineering, procurement, and construction firm, Bechtel. TVA and Generation mPower, an alliance between B&W and Bechtel, have teamed on a project to build two 180-MW Generation mPower reactors at TVA's Clinch River site in Tennessee. The project is scheduled for completion in 2021.
Though Generation mPower has scaled back its development and funding of the technology, both B&W and TVA continue to pursue the Clinch River project and the cost-sharing initiative with the DOE. B&W CEO Jim Ferland said in an article in the Charlotte Business Journal that the company has not abandoned the development of the SMR or the Generation mPower business unit.
Chief Commercial Officer Mike McGough said the NuScale design differs from other SMR designs that use either vertical or horizontal reactor coolant pumps. The NuScale design uses the physics of natural circulation—convection, conduction and gravity—to drive the flow of coolant through the core, eliminating the need for reactor coolant pumps and the associated costs and maintenance challenges.
With proposed and implemented emissions regulations, McGough said NuScale is in position to boost the U.S. grid when the technology becomes commercially available.
"With proposed EPA regulations, it is only going to drive people with carbon-generated baseloads to find methods of non carbon-generated electricity," McGough said.
McGough said NuScale remains "bullish" on U.S. prospects, and also believes there will be a growing market overseas, particularly in Japan and the United Kingdom.
Westinghouse has also scaled back development of its 225-MW SMR design to focus more on its growing AP1000 market. A spokesperson for Westinghouse said a team of engineers and business staff remains assigned to the SMR development to ensure its availability when market conditions improve.
High-Temperature Gas-Cooled Reactors
NEI says these reactors are best suited for providing process heat for industrial purposes, as well as in the development of tar sands, oil shale and coal-to-liquids applications. Reactors include General Atomics' Gas Turbine Modular Helium Reactor (GT-MHR) and the Pebble Bed Modular Reactor Ltd.
In September 2010, the 165-MW Pebble Bed Modular Reactor in South Africa was forced to end development due to lack of funding and an inability to gain new investors. Westinghouse had signed on to invest in the project, but withdrew in May 2010. The project had investments of $1.3 billion by the time it ceased operations, and 80 percent of those funds were from the South African government. However, government officials said they would not support the project if developers could not find outside investors because the project might have cost an additional $4.2 billion.
The reactor would have used helium as a coolant and repurposed its waste heat for other industrial processes.
General Atomics' (GA) GT-MHR can generate 285 MW of electricity and is being developed in partnership with Russia's OKBM Afrikantov and supported by Fuji Industries of Japan. The company aims to produce hydrogen from a demonstration high-temperature reactor to be built at the Idaho National Laboratory.
According to UXC, GA plans to have an operating GT-MHR prototype in Russia and then a completed and licensed demo plant in the U.S.
|General Atomics' EM2 is a 265-MW reactor designed to burn spent fuel and depleted uranium. Photo Courtesy: General Atomics|
Liquid Metal and Gas-Cooled Fast Reactors
NEI includes GE Hitachi Nuclear Energy's Power Reactor Innovative Small Module (PRISM), General Atomics Energy Multiplier Module (Em2), Gen4 Energy's Gen4 Module (G4M) and the Toshiba 4S (Super-Safe, Small and Simple) in this reactor category.
GA's Em2 reactor has a capacity of 265 MW. The reactor is designed to burn spent fuel and depleted uranium. GA said the company is in the research and development phase of a new high-performance fuel, and that it is still on track for a 12- to 14-year plan to deploy an Em2 prototype deployment.
"We are currently focused on fuel development, which has far-reaching implications for current LWRs and other advanced reactor designs. This can enable much better reactor performance and dramatically improve the economics of nuclear energy while meeting all safety requirements," said Dr. John Parmentola, senior vice president of the Energy and Advanced Concepts Group at GA.
Though the Em2 was not picked as a winner in either round of cost-sharing funding by the DOE, workers have continued to develop the reactor.
"We strongly believe this will be the future of nuclear energy," Parmentola said. "We are currently working with a foreign country on the development of Em2."
GE-Hitachi (GEH)'s 311-MW PRISM reactor is considered a "fast spectrum reactor" that can be configured to use plutonium stockpiles as fuel. The reactor can also run on used nuclear fuel, depleted uranium, and other used fuels, said Eric Loewen, chief consulting engineer – Advanced Plants with GEH.
The company looked into developing a sodium-cooled reactor that was small and factory-built.
Loewen said the initial concept was first developed by GE in 1981 and was picked up at the U.S. Advanced Liquid Reactor Program, which ran from 1984 to 1994. The initial design was further refined and eight other U.S. firms helped with the development of the PRISM.
"All reactor designs have benefits, but for a lot of technical reasons, they're not ready to go to market," Loewen said. "Sodium-cooled technology is ready. Every major component has been tested and inspected by the NRC."
By cooling with sodium, the reactor can make fissile material. PRISM can be employed to utilize stockpiles of plutonium as seen at the Sellafield site in the United Kingdom and spent nuclear fuel here in the U.S.
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