DERIVATION OF CONSISTENT REACTIVITY WORTH AND EIGENVALUE SEPARATION FROM SPACE-DEPENDENT ROD WORTHS ON THE BASIS OF MODAL APPROACH

A method is proposed to infer the consistent reactivity worth and the lambda-mode eigenvalue separation from space-dependent control rod worths in loosely-coupled reactors. Using the modal expansion approximation for a transient flux, we derive a two-mode version of the formula for an integral-count rod drop measurement. The formula is very simple and there is no need for the theoretical correction factor. The experimental procedures are convenient as well as standard rod drop measurements. Furthermore, the present formula is more general, compared with the previous two-point formula, and is anticipated to be applicable even to large single-core reactors. The applicability of the formula is confirmed by a demonstration in the UTR-KINKI reactor, a light-water moderated and graphite-reflected reactor.