Precision Limitations in the Measurement of Small Reactivity Changes

Expected errors in reactivity measurements made with a servo control are discussed and compared with observation. The influence upon measurement statistics of a residual spurious reactivity drift, of variable detector efficiency, and of servo control parameters is examined and compared with results using a thermal reactor at 72 watts. Power limited precision is shown to be obtainable with a servo control over a broad range of operating configurations and with good discrimination against incoherent residual reactivity drift.