Development of a High Thermal Conductivity SiC Cladding Using a Method for Predicting Tubular Thermal Properties

Zirconium alloys have been the fuel cladding material of choice for light water reactors (LWR) since the 1960s. However, zirconium oxidation at high temperatures has been a major concern after the Fukushima nuclear incident on March 11, 2011. In a loss of coolant accident (LOCA), the reactorĺs coolant temperature can rise significantly, thus causing an exothermic reaction between zirconium and steam that, in turn, produces highly flammable hydrogen gas as a byproduct. Monolithic silicon carbide (SiC) materials are being considered for accident tolerant fuel (ATF) applications due to their excellent thermal properties, creep resistance, low neutron absorption, and lack of producing an explosive hydrogen byproduct in the case of a LOCA. In this proposed work, the brittle fracture of monolithic SiC ceramics are addressed by manufacturing a fracture resistance multilayer SiC composite. However, major drawbacks of SiC composite materials are their low and anisotropic thermal conductivities and the lack of a method to measure and/or predict its thermal conductivity accurately. Ceramic Tubular Products (CTP) proposes to develop an ATF cladding for LWRs based on a multilayer SiC composite design. In this work, a method for accurately predicting the thermal properties of the anisotropic SiC multilayer composites will be developed and compared with the experimental measurement of thermal conductivity of curved multilayer SiC composites. During Phase I, a method for predicting the anisotropic thermal properties of multilayer tubular SiC composites at various temperatures and irradiation based on a steepest-entropy-ascent quantum thermodynamic (SEAQT) analytical code will be developed. A multilayer tubular SiC composite will be designed and manufactured to validate the SEAQT code and understand the relationship between matrix crystallinity and thermal conductivity. In Phase II, the development of the SEAQT code will be complete, which will be used to design and manufacture tubular multilayer SiC composites with high thermal conductivity for LWR cladding with an expected thermal conductivity improvement of >50%. In Phases II and III, CTP and Idaho National Laboratory (INL) will collaborate in fuel production and the performance evaluation of SiC multilayer claddings under irradiation. The project is successful, the product will be an ATF cladding based on a multilayer SiC composite for LWRs, which will be more oxidation and corrosion resistant and will not produce an explosive hydrogen byproduct in case of a severe accident. A second product of this project, if successful, will be a SEAQT code, which gives CTP and other LWR cladding designers the necessary tool to predict the thermal conductivity of anisotropic multilayer tubular SiC composites at various temperatures and neutron irradiations.