Criticality predictions in the Hanford reactors

The purpose of this study was to examine the general area of criticality prediction errors at the smaller (``pre-K``) reactors. Such errors evolve from a number of uncertainties which are difficult if not impossible to eliminate with present measuring and accounting techniques; the magnitude of these uncertainties in aggregate was indicated in an earlier study about 1.5 milli-k, which, at the time of the study, represented an ``inherent`` prediction error that constituted a practical limit on accuracy. Present day computer usage has improved considerably upon this. Predictions at the various Hanford reactors are made on the basis of a fundamental pile variable known as cold clean reactivity. This variable may be qualitatively defined as the ultimate reactivity of the room temperature reactor with all poisons and poisonous short-term fission products removed. The quantity CCR may be determined during operation by properly evaluating the temperature-reactivity coefficients C{sub m} and C{sub g}, or it may alternatively be determined at startup, when these effects are zero and the equation reduces to CE = R + {rho}{tau} + L + P4. The latter equation serves as the basis for the uniform calculational approach used herein.