Space-Time Analysis of Reactivity Measurements.

Space-time changes in the neutron flux or shape function at the detector location should be considered in rod worth measurements through the inverse kinetics equation. The modal-local method proposed in this study calculates the shape function, representing the localized perturbations due to reactor parameter changes. Once the lambda modes and local functions for several intermediate rod locations are calculated, the shape function is very easily obtained for varying rod positions. This allows implementation of the modal-local method as a reactivity meter for on-line data analysis. A rod drop experiment in a high-temperature gas-cooled reactor test facility, KAHTER, has been simulated in two-dimensional geometry and two energy groups with the time-dependent diffusion theory code, FX2-TH. The modal-local method reproduces the time-dependent FX2-TH reactivity and shape function with an overal accuracy of a percent. A control rod calibration with thermal-hydraulic feedback included was simulated in one-dimensional geometry and two energy groups, with the modal-local results within 0.5% of both the control-rod and the feedback reactivities calculated with the FX2-TH code. The modal-local method reroduced equally well the perturbed steady state flux distributions for the KAHTER facility in three-dimensional geometry and six energy groups calculated with the CITATION code, providing accurate space-time analysis of the integral and differential rod worth measurements performed at the KAHTER facility. These static and transient studies indicate the applicability of the proposed method in accounting for space-time effects in detector signals.PhDNuclear engineeringUniversity of Michiganhttp://deepblue.lib.umich.edu/bitstream/2027.42/160188/1/8422293.pd