Risk-Informed Safety Analysis for Accident Tolerant Fuels

Accident tolerant fuels (ATFs) are being tested by different nuclear vendors and research organizations, and their introduction into the U.S light water reactor fleet is planned for the second half of the 2020s. Under the framework of the U.S. Department of Energy Light Water Reactor Sustainability (LWRS) Program, as part of the LWRS Risk-Informed Systems Analysis Pathway, research is being conducted at the Idaho National Laboratory (INL) to develop tools and methods that can help the industry to quantify the benefits from adopting ATF technology. In this paper we describe the developed risk-informed methodology including the safety analysis code improvements, and we present some results for selected accident scenarios. The developed methodology combines the INL state-of-the-art deterministic Best Estimate code RELAP5-3D and the probabilistic risk analysis tools RAVEN and SAPHIRE. The analyses are performed on a three-loop pressurized water reactor, simulating station blackout and large-break loss-of-coolant accidents and considering near-term ATFs or iron-chromium-aluminum and chromium-coated clads. Finally, we show how, applying our methodology, the new core damage frequency (CDF) can be assessed. The results indicate that the main benefit in introducing near-term ATFs is a significant reduction in hydrogen production during accident conditions. No significant CDF reduction was found.