Interpretation of Noise Coherence Function Measurements in Liquid-Metal Fast Breeder Reactor Critical Assemblies

An improved technique for inferring the eigenvalue separation, which is important in spatial stability analysis, was developed using the noise coherence function. It was applied to fast reactor critical assemblies of various sizes and compositions that exhibited a wide range of spatial decoupling. In each experiment, four lithium-glass detectors were used to measure noise coherence functions. Various ratios of the coherence functions were used to obtain the first two modes of separation considering higher modes and variations in detector efficiencies. The eigenvalue separation obtained by noise analysis agreed well with calculation.