Signal Fluctuation and Neutron Source in Inverse Kinetics Method for Reactivity Measurement in the Sub-critical Domain

Abstract

This paper presents numerical experiments on reactivity measurement by the inverse kinetics method in the sub-critical domain or at low power. The increase in the fluctuation of the neutron signal at low power levels will cause difficulties in the evaluation of reactivity. And the effect of direct emission from the external neutron source to the detector may not be neglected at lower power.

Two cases are discussed: a large reactivity change as in a rod drop experiment and the reactivity change when the neutron signal is affected by direct emission from the neutron source. These cases have been studied with numerical simulations, and optimal ways to evaluate the reactivity under such conditions have been discussed.

KEYWORDS:

• numerical experiment
• inverse kinetics equation
• external neutron source strength
• sub-criticality
• neutron noise
• least squares approximation