Concept of the Core for a Small-to-Medium Sized BWR that does not Use Control Rods during Normal Operation

Abstract

A small-to-medium-sized boiling water reactor (BWR) with a natural circulation system is being developed for countries where initial investment funds for construction are limited and electricity transmission networks have not been fully constructed. To lighten operators’ work load, a core that does not use control rods during normal operation (control rod-free core) was developed. To evaluate the natural circulation type core performance, a neutronics calculation system coupled with core flow evaluation that considered the divided chimney above the core was developed. The control rod-free core with power level fluctuation control to less than 10% was developed using the system.