Neutron flux shape dependent temperature distribution in a fuel pellet

Fuel centerline temperature is an important parameter in a fuel pin performance analysis. The quantitative measure of fuel centerline temperature depends on coolant temperature, thermal conductivity of the fuel and heat generation rate in the fuel pin. In general, fuel performance studies are carried out by assuming uniform volumetric heat generation across the fuel pin. However, fission rate is not uniform across the fuel pin. Due to self shielding effect, the thermal neutron flux shows a depression in the central region of the fuel pellet. Hence, more heat is generated in the peripheral region as compared to the central region. It is observed that in a thermal reactor, assumption of uniform heat generation across pellet gives a conservative value of fuel centerline temperature as compared to the centrally depressed heat generation for same linear heat rate. In this paper the variation of temperature distribution for various spatial shapes of the heat generation is brought out. The effect of enrichment on the heat generation profile and the difference between fuel centerline temperatures, with and without the assumption of uniform heat generation, has also been brought out. (author)