Challenges for the Nuclear Regulatory Commission in Licensing Accident Tolerant Fuel
After the meltdowns at Japan’s Fukushima Daiichi nuclear plant in March 2011, Congress directed the Department of Energy (DOE) to support development of new fuel designs that could tolerate loss-of-cooling and other accident scenarios far longer than the current uranium dioxide-zirconium alloy nuclear fuel system. Among other benefits, such accident tolerant fuel (ATF) could resist the zirconium-steam reaction that led to the hydrogen explosions at Fukushima and generated additional heat that hastened the meltdowns.
A variety of ATF designs have been proposed by DOE-funded groups and other manufacturers. Both new fuel-rod cladding materials and new fuel types are under development, including an advanced silicon carbide (SiC) composite fuel-rod cladding being developed by General Atomics. This effort has the support of multiple stakeholders across the nuclear industry, from fuel suppliers and DOE national laboratories to the Electric Power Research Institute, utilities, and plant owners.
In addition to avoiding severe accidents, ATF can add margin to normal operation, anticipated operational occurrences, and design-basis accidents. This would improve fuel-cycle economics and increase both fuel reliability and operational flexibility. The ATF program is currently on track, despite an aggressive schedule calling for first commercial use by the early 2020s.
A Challenging Path Ahead
The Nuclear Regulatory Commission (NRC) must approve new fuel designs before they can be loaded into a commercial reactor. This is a traditionally lengthy process that requires extensive testing of Lead Test Assemblies (LTAs) in operating reactor cores. To collect accurate data, the LTAs must be left in the core for at least two years. The licensing process also requires validation of fuel performance codes, thermal hydraulics, neutronics, safety margins, and other factors. Data must be collected and tools created that allow the NRC to analyze the performance of ATF under steady-state, design-basis accident (DBA), and beyond DBA conditions. ATF will also need new processes for fuel fabrication, transport, and spent-fuel storage, all of which require NRC approval.
Testing began this year on the first LTAs at plants owned by Southern Co. and Exelon. Both companies are enthusiastic supporters of the ATF program because of the substantial benefits ATF offers in enhanced safety, reduced operating costs, and extended plant lifetimes. The Nuclear Energy Institute has estimated that ATF has the potential to yield hundreds of millions of dollars in annual savings for the nuclear industry. In an environment in which many nuclear plants face existential economic challenges, and a number have already retired prematurely, ATF is a lifeline that can reach the market none too soon.
Nimble Licensing Is Necessary
To its credit, the NRC is well aware of this issue and has taken concrete steps to prepare for certification of ATF designs. Chairman Kristine L. Svinicki has expressed the need for the commission to become more nimble and responsive, and she clearly understands that the licensing process must adequately and efficiently accommodate advanced technologies if nuclear energy is to have a future in the U.S.
In late 2017, the NRC published a draft project plan for expedited ATF licensing. This plan has a number of encouraging elements, such as a commitment to working closely with the DOE to speed the collection of data and avoid duplication of efforts. But it also estimates that the process of analytical code development will require three to six years for all proposed ATF designs, with the more innovative approaches, such as SiC-based ATF, taking the longest. If past performance is any guide, some of these reviews could take longer than estimated, given that new fuels have typically taken a decade or longer to reach the market.
While the NRC’s commitment to performing a thorough validation of ATF is laudable, past efforts relied heavily on procedures drafted decades ago when computers had a fraction of their current capabilities, and modeling and simulation (M&S) tools were far less sophisticated. Fortunately for the NRC, some of the most advanced M&S capabilities are possessed by the DOE national labs, which have substantial experience in testing advanced nuclear technologies. The NRC should continue its close cooperation with DOE on ATF and take full advantage of these capabilities.
Engaging the NRC in ATF
As part of this process, the NRC also needs proactive engagement from industry to ensure it has the expertise to qualify advanced ATF designs. To that end, General Atomics has already initiated discussions with the NRC on its EM2 advanced reactor design (the project that was the genesis of SiC ATF), and it is planning to engage with the commission on qualification and licensing of its SiC cladding, as well as advanced uranium carbide fuel.
The stakes for the nuclear industry could not be higher. FirstEnergy recently announced plans to retire another three nuclear plants early because of economic challenges. It is impossible to say if ATF might have made the difference for FirstEnergy, but in this environment, nuclear energy needs every advantage it can get. If licensing ATF takes too long, it may arrive too late for many current plants. ■
—Christina Back, PhD is vice president, Nuclear Technologies and Materials, and Thomas W. Overton, JD is science editor with General Atomics in San Diego.