Optimal fuel utilization in a BWR with once-through uranium cycles

Methods of better utilization of first core fuel that has been or will be discharged with a rather low burnup and stored at the plant, has been investigated. This includes options like reinsertion of fuel assemblies in later cycles into the same reactor or into another reactor at the same station, and reconstitution or ''spiking'' of old assemblies, i.e., replacing some of the fuel rods within the assembly by fresh rods. The analysis has been performed with the Fuel Management System - FMS, (Ref. 1), which provides a systematic tool for fuel cycle optimization in LWR's. It includes several code modules performing lattice burnup calculations for cross-section generation, fuel cycle optimization, 1-D and 3-D reactor simulations with coupled neutronics- and thermal-hydraulics calculations. FMS has been in use on a production level for several years, and can be considered as a proven, well-tested tool for applications of this type. The computer code system is described in some detail in Appendix A