The Effect of Fuel Thermal Conductivity Degradation With Burnup on PWR Licensing Limits

Abstract

Most fuel modeling computer codes of a decade ago did not explicitly account for fuel thermal conductivity degradation with burnup. The overestimation of thermal conductivity is compensated by other code adjustments. Following the approval of the legacy fuel thermal codes, the quantity, quality and comprehensiveness of fuel measurement data have increased dramatically. Recently, the US NRC has informally requested the nuclear industry review the thermal performance codes with the consideration of thermal conductivity degradation. This paper compares the legacy thermal conductivity models with the most recent available models that are published publicly and may have been incorporated into present generation fuel performance codes. Also included in this paper is one method which AREVA NP Inc. developed to evaluate the thermal conductivity degradation effect. The effect of thermal conductivity degradation on the PWR licensing limits, such as centerline fuel melt and strain, is demonstrated.