Quantification of Core Barrel Motion Using an Analytically Derived Scale Factor and Statistical Reactor Noise Descriptors

A method was developed for quantitative inference of core barrel motion from the following statistical descriptors using an analytically derived scale factor (SF): cross-power spectral density (CPSD), auto-power spectral density, and amplitude probability density (APD). The proper frequency band over which to compute the statistical descriptors is conveniently determined from the coherence and phase information from two ex-core power range neutron monitors positioned diametrically across the reactor vessel Core barrel motion can then be quantified from the integral of the band-limited CPSD of two diametrically opposed excore monitors or, if the coherence between the pair is ≳0.7, from a properly band-limited APD function. Wide-band APD and CPSD functions were both demonstrated to yield erroneous estimates for the magnitude of core barrel motion.