The Effect of Thermal Conductivity on the Central Temperature Safety Criteria in a Typical WWER-1000 Nuclear Reactor

To ensure safe operation of nuclear power plants, regulatory bodies legislates numbers of safety criteria, one of which is to preserve fuel centerline temperature below specified limit (melting point of oxide UO2 type fuel). It guarantees safe operation since the clad integrity will be maintained. In this regard, Thermal hydraulic models and simulations are utilized, to estimate such temperature. An important parameter which affects temperature distribution in the fuel (and core) is thermal conductivity of fuel itself. It is, however, influenced by different parameters, i.e. fuel irradiation and temperature of the fuel, which varies during operating cycles. This study takes the heed to the effect of variation of thermal conductivity on so-called safety criteria. Neutronic calculations are done via coupling WIMS and CITATION codes, to obtain reactivity for operating cycles of a typical WWER-1000 nuclear power plant core. CFD model of the core is conducted, then, to estimate required thermal-hydraulic parameters. Fuel centerline temperature and DNBR are estimated, and compared for two possible fuel element configurations, i.e. solid, annular with internal and external coolant passage. The results reveal that the sensitivity of fuel centerline temperature and DNBR to variation in burnup rate.