An Extended Rod Drop Method Applicable to Subcritical Reactor System Driven by Neutron Source

Abstract

Control rod drop method based on the integral count technique and the extrapolation one was extended to apply to a subcritical reactor system driven by a neutron source. Similarly to the conventional method, the extended method is capable of rapid estimation of rod reactivity worth and is essential from the educational viewpoint. For the demonstration of the applicability, a series of rod drop experiments was carried out in subcritical and critical states of a reactor system, and rod reactivity worth and effective neutron source strength were determined from the counting data of a neutron detector. In addition, the time-sequence count data were acquired and the least-squares inverse kinetics analysis was made to justify the present extended method. The rod worth and source strength obtained by the present method were consistent with those obtained by the least-squares inverse kinetics method.

Subcriticality

“…First, the theory of the least-squares inverse kinetics method (LSIKM) [31][32][33] is briefly described. Assuming the zero-power and one-point kinetics model, the timedependent neutron behavior of a subcritical reactor system driven by an external neutron source can be described as…”

“…The integral count technique has been frequently employed to determine the subcriticality from a source jerk experiment and a rod drop one [31,36]. When a neutron source is rapidly taken out of a subcritical reactor core or a control rod is dropped into a critical core at t = 0, the reactivity of the core can be expressed as…”