AVS 60th International Symposium and Exhibition
    Actinides and Rare Earths Focus Topic Tuesday Sessions
       Session AC+AS+EN-TuA

Invited Paper AC+AS+EN-TuA1
Prospects for Accident Tolerant Fuels in Light Water Reactors

Tuesday, October 29, 2013, 2:00 pm, Room 102 C

Session: Actinides and Rare Earths: The Nuclear Fuel Cycle and Critical Materials
Presenter: S.J. Zinkle, Oak Ridge National Laboratory
Authors: S.J. Zinkle, Oak Ridge National Laboratory
K.A. Terrani, Oak Ridge National Laboratory
L.L. Snead, Oak Ridge National Laboratory
Correspondent: Click to Email
Further enhancement of safety margins in current and next generation commercial fission reactors in general requires an integrated engineering systems design approach. However, tangible gains in safety margin (and performance) may be achievable by utilizing one or more materials science modifications to the fuel system. In this paper the specific attributes of what would constitute accident tolerant (or enhanced safety margin) fuels will be presented. There are four key metrics to be considered for such a fuel under transient accident conditions: reduced enthalpy production, reduced hydrogen production, improved resistance to clad ballooning and rupture (maintaining coolability of the core), and suppressed fission product release. There are a variety of materials science approaches that can be considered to address one or more of these four metrics for accident tolerant fuels, ranging from relatively incremental modifications to the cladding material to dramatic alternatives to the historical monolithic UO2 ceramic fuel pellets surrounded by seamless Zr alloy tubing. For example, solute modifications and/or highly adherent coatings that improve the high temperature steam oxidation resistance of Zr alloy cladding would directly lead to reduced enthalpy and hydrogen production. For extended high temperature transient conditions, deployment of high thermal-creep strength, oxidation-resistant cladding (e.g. advanced steels, coated molybdenum, or SiC/SiC) would maintain the coolant channel geometry and significantly suppress the rate of enthalpy and hydrogen production in the core compared to current Zr alloy cladding. This will effectively delay the threshold for fission product release from the fuel while providing longer time periods for emergency core cooling systems to become activated to halt core degradation processes. In addition, the critical heat removal limit in the core to prevent severe degradation would be lowered. Utilization of microencapsulated fuel forms (i.e., triple-encapsulated fuel kernels) within a high thermal conductivity matrix (i.e. SiC) would reduce the stored energy under normal operating conditions compared to standard fuels, resulting in suppressed fuel temperature increase under loss of coolant accident conditions that could limit fuel cladding ballooning and burst. Improved fission product retention within the fuel during high temperature accidents would also be anticipated. This presentation will review several potential fuel system options and outline key feasibility challenges that need to be resolved, along with briefly discussing potential impact on reactor neutronics and overall electricity production costs.