Evaluation of Detector-Efficiency and Source-Worth Corrections for Subcritical Reactivity Measurements in a Fast Critical Assembly

Analytical corrections for the effect of subcritical reactivity on /βeff, detector efficiency, and ²⁴⁰Pu source worth in control-rod-group worth measurements in zero-power plutonium reactor Assembly 3 have been evaluated. Calculations of each factor were performed for a number of subcritical configurations in Phases 1B and 2; the results are presented and compared to the critical reference case. An evaluation of the method is included to establish a logical and efficient procedure for determining such corrections for future assemblies, which shows that extrapolations between similar configurations can be made accurately on the basis of only one or two rod patterns.