Don’t like much about LWRs,
Molten salt doesn’t thrill me at all.
Sodium makes me want to run,
But helium looks cool.
I’ve seen what may be the future of civilian nuclear power, thanks to Dr. Christina Back at General Atomics in San Diego. I hope it works. It isn’t going to be easy.
GA is a legendary name in nuclear power history. The company was the creator of the most important nuclear reactor ever, the TRIGA (Training, Research, Isotopes, General Atomics) non-power research machine. It was the result of a collaboration of Edward Teller and Freeman Dyson. Teller and Dyson started the design of TRIGA in 1956 and had an actual reactor in hand by 1958. The key to TRIGA: it can’t be crashed, making it the ideal training vehicle for budding nuclear physicists and engineers.
For about 50 years, GA has been pushing high-temperature helium-cooled power reactors, first successfully at Philadelphia Electric’s Peach Bottom site in a 40-MW demonstration unit. The technology failed to scale up at Public Service of Colorado’s Fort St. Vrain station. Subsequent attempts to combine helium-cooled, high-temperature reactors with ceramic-coated, graphite-moderated fuels (pebble-bed reactors) failed in the U.S. and South Africa.
GA is back with what looks like both an evolutionary and a revolutionary approach, relying on new ceramics technologies that also could have implications for conventional light-water reactors and high-temperature, non-nuclear manufacturing industries such as oil and gas. GA’s Back, with a B.S. in physics from Yale and a Ph.D. in plasma physics from the University of Florida, offered a description of the technology in recent testimony to a Senate committee, and a telephone interview with me.
Back explains that GA’s new reactor design, the “Energy Multiplier Module” or EM could be characterized as an “advanced small modular reactor.” It’s a fast neutron reactor, designed for 265-MWe and 53% efficiency. The reactor itself is only 12 meters high and 4.7 meters across. In terms of efficiency, according to GA, the reactor is equivalent of six of NuScale’s 65-foot-high proposed SMRs.
GA’s machine is designed to sit underground. Components would be built off site and trucked to the site. That’s pretty much what every SMR has proposed, including NuScale. But Back notes that the much smaller size of the GA reactor offers considerable cost savings. “It’s quite expensive to dig big holes,” she told me.
The advantage of inert helium as a coolant was a key to the Peach Bottom, Fort St. Vrain, and pebble-bed projects. The reactors don’t need to be near water opening up siting opportunities. Water can be a problem. High-temperature steam can react with hot metal-clad conventional fuel rods in a high-neutron environment. That can be an explosive combination in a severe accident. See Fukushima.
The key to GA’s new machine is not helium coolant (and gas turbine power generation), but new ceramic materials the San Diego firm is developing for fuel cladding and other reactor internals. GA has developed silicon carbide ceramics capable of surviving temperatures far higher than the zirconium alloys in conventional LWR fuel cladding. Combined with advanced fuels, the GA machines should be able to operate at much higher temperatures than LWRs or molten salt reactors, while offering a much greater thermal margin between the operating temperature of the reactor and the failure point of the cladding and surrounding equipment.
But ceramics are brittle. GA, with some $40 million of its own funds, has developed a way to engineer silicon carbide components with silicon carbide fibers to produce a ductile ceramic. “It doesn’t break,” said Back. The new materials can be used in LWRs, as well as in GA’s helium machine.
Getting these new materials in use will require ASTM approval, and GA is pursuing that standards certification process.
More daunting is U.S. Nuclear Regulatory Commission approval for the new GA design. As Back noted, the NRC is understandably LWR-centric. “There is going to be a need for a prototype because this is very different,” she said. Back said GA is talking to the NRC early in the process, and hoping to plant the notion that regulations can be performance-and-risk-based, as well as specific to a particular technology (LWRs). The NRC is holding a June 7-8 workshop in Bethesda, Md., looking at advanced, non-light water reactors.
The GA design offers other advantages, including safety, waste-management, and non-proliferation (the fuel is in the reactor for 30 years), too detailed for this blog posting.
A former NRC safety engineer once advised me, “Paper reactors always work perfectly. It’s when you try to build them that you get into trouble.” GA’s Energy Multiplier Module not only looks promising on paper, but the company has put a good deal of money on the table to develop the new ceramic technology. I’m paying attention.