Power, 11/01/2015 | Kennedy Maize
eneration III nuclear reactors have not shown much ability to overcome the weaknesses of conventional Gen-II light-water reactor technology, offering at best evolutionary approaches. Is there room for a more revolutionary approach? Many parties are exploring new technologies, but it’s impossible to tell which, if any, will succeed.
Last August, Andy Revkin, The New York Times’s “Dot Earth” blogger, waxed enthusiastic about a new fusion reactor design from a team of students and researchers at the Massachusetts Institute of Technology (MIT). Revkin reported (based mostly on the MIT press release) that the team had come up with a plan for a “demonstration-scale fusion energy power plant that could actually produce a fusion energy machine that is affordable, robust, compact.”
MIT claimed that the new design takes the long-disappointing “tokomak” donut-shaped fusion reactor and shrinks it with new materials. This would allow the use of a much higher magnetic flux to contain the superhot plasma needed to fuse hydrogen atoms, which would produce heat far exceeding any conventional fission reactors, yet with a much smaller footprint. The hype suggested a 10-year time frame.
Despite the credulous coverage of MIT’s dream machine, there are important skeptics, many of whom note that fusion is a technology whose horizon has receded despite years of research and billions of dollars of government investment. Robert Hirsch, who ran the fusion program for the Atomic Energy Commission (AEC, the predecessor of the Nuclear Regulatory Commission) and the Energy Research and Development Administration in the 1970s, told POWER, “Higher magnetic field tokamaks have been around since the early 1970s, but high magnetic fields contain high stored energy, which can be released when [superconducting] magnets quench, which the regulators will be very sensitive to.” Magnet quenching—abrupt termination of the magnetic field—can result in destructive forces inside the machine and considerable damage.
The MIT reactor design, which MIT is calling the ARC, hits all the proper notes to attract attention: small, modular, and efficient. But it’s just one of a number of “new” (actually mostly old but previously discarded) reactor models various engineers and entrepreneurs are advancing as the solutions to the well-known woes of conventional, large-scale light-water reactors (LWRs).
A Nuclear Gen-X
Call them “Gen-Next” reactors, as they do away with the conventional numerical nomenclature of Gen-I (small, early plants such as Indian Point I in New York, now long closed), Gen-II (most of the large plants ordered in the 1970s and operating today), and Gen-III (today’s designs, such as the Westinghouse AP1000 and AREVA’s EPR, under construction but not yet operating). Gen-IV, the industry’s label for advances over Gen-III designs, implies more of the same, while Gen-Next implies radically different approaches, with much promise and plenty of risk (see sidebar).
The Fabulous Flying Fusion Machine
Last summer, a team of Boeing engineers got a U.S. patent for a laser-fusion-powered aircraft engine. The conceptual design (Patent No. US 9,068,562 B1) has high-power lasers aimed at a target of deuterium and tritium, a simplified concept similar to the much larger research on laser fusion under way at the Department of Energy’s National Ignition Facility at Lawrence Livermore National Laboratory in California.
In the Boeing patent, the lasers cause the hydrogen isotopes to fuse into helium, producing a thermonuclear explosion (Figure 2). As described by Business Insider, the helium and hydrogen byproducts shoot out of the back of the engine at enormous pressure, yielding thrust. The inside of the “thrust chamber,” coated in natural uranium (mostly U238), reacts with the neutrons from the thermonuclear reaction, generating immense heat.
2. A flying reactor? Boeing engineers have received a patent for this concept for a fusion-powered jet engine. Courtesy: Boeing
Coolant flowing along the outside of the combustion chamber captures the heat and is sent through a turbine generator to produce electricity to power the engine’s lasers. According to the patent application, the engine could power rockets, missiles, and spacecraft.
Fusion expert Robert Hirsch was dismissive of the design. He told POWER that Lawrence Livermore “seems to have failed to ignite pellets, and a laser to do the suggested job at the needed energies isn’t even on anyone’s drawing board, as far as I know. But you never know, so you submit a patent.”
“As of now, the engine lives only in patent documents,” notes Business Insider.
Earlier conventional reactor designs are being phased out. The Gen-Is are gone. Many Gen-IIs are nearing retirement. But Gen-IIIs have not met stated goals for plants that are cheaper and easier to build, feature much greater standardization, and offer modular construction advantages over the prior generation.
Investment portfolio manager Henry Hewitt wrote in Greentech Media recently that Gen-III reactors “have been a disappointment.” None are currently operational, and many of the plants under construction have seen delays and budget overruns—some of them huge, as with the EPR. The latest World Nuclear Industry Status Report (a publication that is skeptical of nuclear power) attributes these delays, including those at the four Westinghouse units under construction in the U.S., to “design issues, shortage of skilled labor, quality control issues, supply chain issues, poor planning either by the utility and/or equipment suppliers, and shortage of finance.”
Those looking to nuclear power as a long-term component of a plan to limit carbon dioxide emissions have for more than a decade been examining and touting new generations of nuclear concepts that escape the limits of the LWR (see “Nuclear Industry Pursues New Fuel Designs and Technologies” in the March 2015 issue). These new technologies include designs that rely on thermal (slow) neutrons, fast neutron breeder reactors, various cooling approaches, higher-temperature machines that are more efficient, and the ability to burn spent nuclear fuel from those conventional LWRs, which look to be around for a very long time.