Determination of the equilibrium composition of cores with continuous fuel feed and removal using MOCUP

Algorithms and scripts were developed for determining, using MOCUP, the equilibrium fuel composition in cores operating with continuous fuel feeding and removal. Two types of Generation-IV systems are considered: Molten Salt Reactors and Pebble Bed Reactors. The methodology developed for the Molten Salt Reactor required limited modifications to the MOCUP functions and was widely applied and tested. A novel methodology is proposed for the Pebble Bed Reactor to determine the pebble composition as a function of its residence time and the resulting core average composition. This methodology uses a detailed full core model to properly account for the fuel double heterogeneity. (authors)