A fuel design being proposed by Framatome includes an annular fuel rod that consists of a 50 wt.% Zr uranium-zirconium (U-50Zr) alloy enriched to less than 20% U235 with an external zircaloy cladding while maintaining other aspects of the typical LWR fuel rod design. The rods are in a rectangular array supported and positioned by spacers within the fuel assembly bundle that maintains the position and location of the 24 guide tubes plus an instrument tube of the current U.S. pressurized-water reactor (PWR) 17 × 17 design UO2 fuel assembly. Top and bottom nozzles maintain the interfaces with the reactor control components and core internals. Design requirements are to be developed for the new design early in the design process. Using a combination of approved Nuclear Regulatory Commission (NRC) methodologies (i.e., ARCADIA ANP10297P-A & Supplement 1, ANP-10311P-A COBRA-FLX, ANP-10338P-A AREA – ARCADIA Rod Ejection Accident, etc.) and, if needed, new or supplemented codes and methods, compliance with the requirements will then be demonstrated by interested parties. The creation of design requirements, the establishment of specified acceptable fuel design limits (SAFDLs), and demonstration of design compliance is an iterative process that starts during the development of the design, through testing and irradiation of leads, up to the creation of the mechanical design topical report submitted for approval by the NRC. A topical report allows for a single NRC staff review of a safety-related topic applying to multiple nuclear power plants. The establishment of the design requirements and the SAFDLs is predicated on establishing design criteria. These design criteria for UO2 fuel have been refined over time through NRC licensing reviews of fuel design as part of the safety analysis reports (SARs). The NRC has established regulatory guidance for the review of SARs within the standard review plan (SRP). The NRC reviews focus on the nuclear fuel design as it relates to safety during normal operating conditions, anticipated operating occurrences (AOOs), and accident conditions. New fuel designs, new operating limits (e.g., rod burnup and power), and the introduction of new materials to the fuel system require a review to verify that existing design-basis limits, analytical models, and evaluation methods remain applicable for the specific design for normal operation, AOOs, and postulated accidents. Nuclear facilities must be designed and built to withstand loss to structures, systems, and components to ensure public health and safety (i.e., postulated accidents). The SRP is written with UO2 in mind. There are a number of phenomena associated with U-50Zr fuel co-extruded within zircaloy cladding that will be different when compared to typical UO2 fuel. The different material properties of U-50Zr, melting temperature, fission gas transport and release, decay heat, and thermal conductivity will introduce new phenomena associated with the failure mechanisms, defining the failure modes and fuel system damage mechanisms that challenge the design criteria. Since the SRP was developed for zirconium-clad UO2 fuel, new design-specific criteria and design-basis limits will need to be established for the U-50Zr fuel design. Failure modes and the associated failure mechanism specific to the U-50Zr fuel design will have to be developed. The available experience base for U-50Zr fuel is very limited in comparison to the experience base with UO2 fuels and other U-Zr fuels (e.g., U-10Zr). In addition, the majority of alloy fuel experience is limited to the use of alloy fuels in sodium fast reactors where the neutronic and thermal-hydraulic conditions are appreciably different than those of an LWR. New phenomena may require new methods development, and transient testing may be needed to help establish operating margins and fuel failure characteristics. In order to assess the fuel design, Framatome performed a failure mode effects and analysis (FMEA) and phenomena identification ranking table (PIRT) exercise to determine the relevant concerns for the new fuel design. Fuel performance researchers at Idaho National Laboratory (INL) then provided professional, technical opinion on the results of Famatome’s FMEA and PIRT. This document summarizes INL’s review of the FMEA and PIRT as well as some general commentary based upon its experience and role as the nation’s leading fuel development laboratory.
