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The Incredible Shrinking Reactor

Small is beautiful for nuclear developers.

Fortnightly Magazine - May 2010

the class of SMRs.

One is labeled integral pressurized water reactors. These are light-water cooled and light-water moderated reactors. The NRC currently is studying three of these: B&W’s mPower design; Westinghouse’s IRIS; and a third called NuScale, being developed by NuScale Power. “We are having some limited pre-application discussions with all three of these vendors,” Mayfield says, adding that NuScale and B&W have been most active recently. “We’ve had discussions with Westinghouse over a longer period of time,” he explains. “During all of these discussions, we become more familiar with the technologies, and the vendors better understand the regulatory requirements and how they might apply to that technology.”

A second technology area is labeled high-temperature gas-cooled reactors. Westinghouse, General Atomics, PBMR Ltd., and Areva are working on these designs. Instead of using water as the coolant and moderator, this technology uses high-temperature helium. “We are currently looking at the pre-conceptual designs and conceptual designs of these,” Mayfield says. “Under the Energy Policy Act of 2005 , the notion is that the prototype reactor would be built and licensed in the U.S.” The DOE is working on the specifics, and the NRC is working with DOE on generic aspects of these reactors, looking at policy issues, and discussing the early pre-application process without choosing a specific design, because DOE hasn’t yet made that selection.

A third technology category involves liquid-metal reactors. “There are a number of variations of designs on these,” Mayfield says. “The more common ones are liquid-sodium cooled.” Toshiba is advancing one such design called the Super-Safe, Small and Simple (4S) reactor, and GE Hitachi Nuclear is backing the Power Reactor Innovative Small Modular (PRISM). “We’re having very limited pre-application discussions with them,” Mayfield says. ( For more information, see “Pocket Nukes Come On Strong,” Fortnightly.com .)

Technical Benefits

SMRs have a number of technical benefits compared to full-size nuclear reactors. For one, most of them can be manufactured quickly. For example, while traditional built-on-site plants can take about five years to construct, the mPower units that would be built in B&W factories are estimated to take about half that time, and then be shipped by rail or barge to the sites.

Another particularly appealing feature of SMRs is their lower requirements for cooling water, and even the ability to use air-cooled condensers. “This could offer a unique application for us in locations where water may be a limitation,” says Ashok Bhatnagar, TVA nuclear’s senior vice president, nuclear generation development and construction.

Additionally, plant safety is an appealing feature. Most of the SMRs utilize a simpler design than standard-sized reactors, and have fewer moving parts that could fail. They also contain a smaller nuclear reaction and generate less heat. All of this means they are designed to be easier to shut down if malfunctions occur.

Security benefits also make SMRs an attractive option. “These are as safe as existing large plants,” Mowry says. “We can also make some enhancements to the technology to make these units even more secure.” For example, all the safety systems and reactor containment would be located