Mechanical design issues and resolutions of a dual cooled fuel for the OPR-1000

A dual cooled fuel is recently brought into focus due to its potential of considerable power uprating. The purpose of present work is to realize the innovative concept of a dual cooled fuel to be a fuel assembly structure compatible with the OPR-1000 system. Under the framework, the critical issues such as the outer cladding thickness and the growth difference of the inner and outer cladding tubes are dealt with in this paper. We designed the thickness of outer cladding tube by using the elastic buckling criterion and safety factor analysis. From the concern of the inner cladding's bowing during irradiation, it was suggested that the outer cladding would grow more than the inner one by applying different microstructures to the inner and outer cladding tubes. It was noted that the gap between fuel rods would not be narrowed further during the different irradiation growth. The structural components such as fuel rod supporting structure, top and bottom end pieces and guide tubes could be designed without a drastic change of those of the conventional fuel. Candidate designs of the components are also presented.

► Thickness of outer cladding tube is determined by using the elastic buckling criterion.
► Growth difference of the inner and outer claddings will not cause fuel rod bowing.
► Structural components are designed without a drastic change of the conventional ones.