Utilization of light water reactors for plutonium incineration

Abstract

In this work a potential of incineration of excess Pu in LWR's is investigated. In order to maintain the economic viability of the Pu incineration option it should be carried out by the existing power plants without additional investment for plant modifications. Design variations are reduced to the fuel cycle optimization, i.e. fuel composition may be varied to achieve optimal Pu destruction. Fuel mixtures considered in this work were based either on uranium or thorium fertile materials and Pu as a fissile component. The slightly enriched U fuel cycle for a typical pressurized water reactor was considered as a reference case. The Pu content of all fuels was adjusted to assure the identical cycle length and discharged burnup values. An equilibrium cycle was simulated by performing cluster burnup calculations. The material composition data for the whole core was estimated based on the core, fuel and cycle parameters. The annual production of Pu of a standard PWR with 1100 MWe output is about 298 kg. The same core completely loaded with the MOX fuel is estimated to consume 474 kg of Pu, mainly fissile isotopes. The MOX-239 fuel type (pure PU-239) shows a potential to reduce the initial total Pu inventory by 220 kg/year and fissile Pu inventory by 420 kg/year. The following two fuel types: TMOX and TMOX-239 are based on Th-232 as a fertile component of the fuel, instead of U-238. The amount of Pu destroyed per year for both cases is significantly higher than that of U-based fuels. Especially impressive is the reduction in fissile Pu inventory: more than 900 kg/year. The safety related reactivity coefficients were found negative, which indicates that the basic behaviour of a reactor core utilizing Pu and Pu-Th based fuel types will be quite similar to that of a standard PWR core utilizing slightly enriched U fuel. It was also found that the reactivity control of a core based on Pu fuel as a fissile component will be more difficult due to a reduced reactivity worth of the soluble boron and control rod control mechanisms.