ESTIMATION AND INTERPRETATION OF K(EFF) CONFIDENCE-INTERVALS IN MCNP

The Monte Carlo code MCNP has three different, but correlated, estimat ors for calculating k(eff) in nuclear criticality calculations: collis ion, absorption, and track length estimators. The combination of these three estimators, the three-combined k(eff) estimator, is shown to be the best k(eff) estimator available in MCNP for estimating k(eff) con fidence intervals. Theoretically, the Gauss-Markov theorem provides a solid foundation for MCNP's three-combined estimator. Analytically, a statistical study, where the estimates are drawn using a known covaria nce matrix, shows that the three-combined estimator is superior to the estimator with the smallest variance. Empirically, MCNP examples for several physical systems demonstrate the three-combined estimator's su periority over each of the three individual estimators and its correct coverage rates. Additionally, the importance of MCNP's statistical ch ecks is demonstrated.