NRC's RIC: A clear line of sight for accident tolerant fuel deployment

“In my plenary speech I talked about my three priorities,” Hanson said. “They’re what I call the three A’s, the first being advanced reactors, the second being accident tolerant fuel, and the third being academic programs. Those all tie into this session together. As I learn more about what is being done at the NRC, I’m consistently impressed with the way the staff are adapting and using risk-informed techniques and really working together across the agency.”

Hanson, when he was a staff member on the Senate Appropriations Committee’s Energy and Water Subcommittee, supported the establishment of the Accident Tolerant Fuel (ATF) program in 2012.

Since then, the term ATF has become something of a catch-all for new and proposed LWR fuels and claddings, going beyond the selection of materials that can demonstrate reduced corrosion and hydrogen pickup under accident conditions. Broader goals for new fuels were evidenced by the scope of the session discussion, which included what it will take to deploy fuels enriched to about 5–10 percent uranium-235, within the category of high-assay low-enriched uranium (HALEU).

The potential benefits of ATF and higher enrichment levels include improved safety margins, improved economics for power reactors, and a reduction in spent fuel volumes of about 20 percent. Those benefits are closely linked: New fuel claddings lead to improved safety margins, which permit the use of higher density fuels, which in turn allow a reactor to generate the same power using less fuel by volume.

Presenters: What began as a research and development program within the Department of Energy and the NRC has grown to include related work and collaborative programs of uranium enrichers, fuel fabricators, research organizations such as the Electric Power Research Institute, and utilities that are irradiating lead test assemblies and considering placing commercial orders for fuel reloads of ATF. All were represented during the session.

• Marilyn Diaz, an NRC project manager and the session coordinator, described recent NRC work to build a regulatory infrastructure for ATF, including approving uranium enrichment by Urenco’s Louisiana Energy Services of up to 5.5 percent U-235 and opening discussions about the transportation of fuel products containing uranium enriched above 5 percent. The agency is emphasizing early and frequent communication and is ready to use innovative approaches to efficiently review submittals, Diaz said.
• Steve Cowne, chief nuclear officer at Urenco USA, described his company’s plans for enriching uranium to between 5 and 10 percent weight U-235. Preparing the company’s gaseous centrifuge plant in Eunice, N.M., to support that production would primarily mean licensing and analysis work, he said. “Transport is a big challenge,” Cowne said, adding that the industry will need either a different transportation package or new licensing to permit the transport of HALEU using existing packages.
• Zach McDaniel, ATF technology manager at Westinghouse Electric Company, described Westinghouse’s EnCore fuel program, which includes near-term products of chromium-coated zirconium cladding and ADOPT pellets, and longer-term development work on silicon carbide composite cladding and uranium nitride fuel pellets.
• John Williams, nuclear fuel and analysis director at Southern Nuclear Operating Company, said that his company is prepared to accelerate ATF deployment. ATF fuel rods developed by Global Nuclear Fuels have been irradiated in Southern’s Hatch-1, and samples have been extracted and sent to Oak Ridge National Laboratory for detailed examination. By the end of 2021, eight operating reactors under four different utilities will be hosting lead test assemblies of nine different ATF technologies, Williams said.
• Robert Daum, a senior technical executive at the Electric Power Research Institute, described EPRI's research into safety, performance, and economic analyses of LWR advanced fuel technologies to support timely research and confirm the business case for ATF. According to Daum, high-priority research needs include severe accident behavior; fuel fragmentation, relocation, and dispersal; criticality; fuel reliability; and spent fuel storage, transportation, and disposal.

Who will be first? Hanson asked Williams how utilities will make the decision to order ATF fuel for a plant or fleet, given how far in advance plant managers must plan outages.

“I’ve referred to this as the greatest chicken and egg problem we’ve ever faced,” Williams said. “If I’m an enricher or a fabricator I’m not going to make capital investments or licensing investments in my facility until I know that I have a customer that’s going to take my product.” Williams said that an estimated 15 units will have to express interest in the fuels to trigger enrichers to commit to investment. In turn, utilities need to see clear benefits and a clear path to regulation.

“For utilities to continue to move forward,” Williams said, “it is imperative that we see a successful licensing path for this innovative fuel technology and a successful licensing path for the implementation of the benefits. Specifically, we need a line of sight to the resolution of the challenges to the implementation of higher burnups.”

Cowne concurred. “We often use the phrase ‘Who’s going to jump first?’” he said. Enrichers such as Urenco are arguably the first link in the supply chain, but they don’t want to go it alone. “What we’re trying to encourage the industry to do is to hold hands and jump together off the end of that pier,” Cowne said.

The drivers: “There are different industry drivers that are pushing for the accident tolerant fuels in the different regions of the world,” McDaniel explained. “In the United States we are looking for that improved safety analysis but also the economic benefit. Economic benefits are key and that’s really pushing us toward how we can enable the higher burnup and higher enrichment product.”

Longer-term fuel products such as silicon carbide claddings are set to increase both safety and economic benefits. “When you really drive to ultimate accident tolerant benefits, you’re going to get to silicon carbide,” McDaniel said. “That’s the end product that delivers all the benefits that this program set out to do.” While technology development is still needed, the use of silicon carbide in LWR fuels could provide useful experience for advanced reactor deployments. “What we learn here for the existing fleet could help support the U.S. future fleet as well,” McDaniel said.

Facilities in high demand: Daum said that from the research perspective, “There have been challenges in terms of various facilities being shut down over the years, particularly irradiation test reactors, as well as the hot cell facilities for conducting post irradiation examination [PIE]. Those facilities are very much needed to help fill those material behavior data needs, as well as those material property needs.” Access to irradiation within the Transient Reactor Test (TREAT) Facility, the Advanced Test Reactor, and the High Flux Isotope Reactor have helped to test fuel samples with sufficient neutron fluence and burnup. “As more materials become available from the commercial reactor irradiations, there will be challenges in performing all the PIE that is needed,” Daum said.