Physics of Plutonium Recycling - Volume III

Volume III: Void Reactivity Effect in Pressurised Water Reactors

ISBN : 92-64-14591-5

The quality of the isotopic composition of plutonium fuel degrades as the number of recycles increases in thermal reactors, requiring an increase in the total loading necessary in mixed plutonium-uranium oxide fuel. With an increasing load of such poor-quality plutonium, the void coefficient in mixed UOX/MOX lattices becomes eventually positive. This factor is of particular relevance since the reactivity feedback associated with steam formation should always remain negative for inherent safety reasons. It is therefore important to be able to estimate with adequate precision the concentration at which the void coefficient changes sign.

This report describes such a benchmark study in which the performance of nuclear data libraries and codes currently available are compared with regard to the void reactivity effect calculations in such UOX/MOX pressurized-water reactor lattices.