Emergency core cooling system criteria for triplex silicon carbide cladding

Operating criteria for Emergency Core Cooling System (ECCS) has been prescribed to maintain integrity of Zr-based fuel assemblies during a Loss of Coolant Accident (LOCA). With new Accident Tolerant Fuel (ATF) designs planned to replace current nuclear fuels, the ECCS criteria should be re-configured properly. This paper proposes a risk-informed approach to establishing the ECCS criteria for Silicon Carbide (SiC) cladding ATF. SiC failure modes were categorized into deterministic and stochastic. A methodology to calculate SiC stochastic tensile fracture probability was outlined. The cladding functional failure probability was formulated from the combination of fractures in each layer of SiC clad. ECCS performance, which includes mass flow rate and actuation timing of high and low pressure active injection, were varied to investigate clad failures. The SiC clad failure probability was found in the order of 1E-15 when it replaced Zr-clad while keeping ECCS criteria the same. A deterministic clad failure occurred when ECCS actuation exceeds 936 seconds after a large break LOCA, or when the ECCS mass flow rate was less than 4% of its designed capacity. When the likelihood of ECCS to perform beyond this criteria was less than 7E-4, the overall risk from deterministic and stochastic failures was less than ECCS risk in cooling Zr-clad of 1E-3. Results suggested that ECCS criteria for SiC may be relaxed compared to the criteria for Zr-clad. This relaxation may provide reductions in operational and maintenance costs.