Evaluation of subcriticality from a modeled asymmetric rod-drop for the Clinch River Breeder Reactor

The proposed method for monitoring the subcriticality of the Clinch River Breeder Reactor (CRBR) is the modified source multiplication (MSM) method using ex-vessel detectors. The MSM method requires calibration by an alternate reactivity measurement technique, and present plans involve calibration from an inverse kinetics rod-drop (IKRD) calculation using the response of the source range flux monitors (SRFM) following a primary control assembly (PCA) insertion into the core. Past experiments have been performed to demonstrate the feasibility of the IKRD technique on small-scale mockups of the CRBR shield. These experiments have shown that the signal-to-noise ratio from the detector response is sufficient to perform IKRD calculations, but they do not correctly simulate the spatial effects that may be encountered in the full scale reactor. Therefore, a detailed analysis of the CRBR design is necessary to demonstrate the applicability of the IKRD method. The work performed for this dissertation generated a solution for the three-dimensional time-dependent angular flux in the shield following a simulated off-center rod drop and generated the SRFM detector response from this flux. The three-point IKRD technique was then applied to the detector response to calculate the subcritical reactivity (from the core model) to insure that spatial effects allowed the use of IKRD calculations to determine the core reactivity for actual reactor conditions. The results of comparing the direct calculation to the IKRD analyses showed that a maximum reactivity error of 1.3% was obtained from the IKRD analysis. These results indicate that the IKRD method can be used to calibrate the MSM method to monitor the subcriticality of the CRBR