KINETIC STUDY OF TRR CORE IN FUEL CONVERSION FROM HEU TO LEU

Abstract

In the conversion of fuel in the Tehran Research Reactor core from Highly- Enriched Uraniutn to Low-Enriched Uranium fuel neutronics analysis, thermal hydraulic calculations and kinetic performance of the core have to be studied. In this study, static and dynamic core performance for HEU and LEU fuels were investigated. In static conditions, two groups of neutron flux distributions in axial direction were obtained by solving diffusion equations. In transient cases, the slow and fast transient phenomena, small reactivity and large reactivity insertion effect, were investigated. To find the temperature feedback effect on core reactivity, such as coolant drainage tnalfunction, the effective tnultiplication factor was calculated for two different temperatures, namely 293? K and 373? K, using the cotnputer code WIMS-D/4. From here, the average temperature coefficient of reactivity was obtained. It should be pointed out that the coefficient dependence on temperature is approximately a linear function. In fast transient study, for HEU fuel $1.510.5 reactivity and for LEU fuel $1.3510.5 reactivity were considered. In slow transient study, a reactivity equivalent to $0.0085/s for HEU fuel and $0.0034/s and $0.00851~ in the case of LEU fuel was introduced into the core. The result of calculations show that in fast transient in the case of LEU fuel, reactor power drops sharply before the scram time set is reached. It seems as if the overall performance of the LEU core is comparable with that of the HEU fuelled core