Using the MCNP Taylor Series Perturbation Feature (Efficiently) for Shielding Problems

摘要

The MCNP perturbation capability can be extremely accurate for shielding problems. This paper has demonstrated that it is not necessary to use a PERT card (or two PERT cards) for every perturbed point in a parameter study. Two PERT cards suffice to obtain the Taylor series coefficients, generate a continuous curve of the resulting perturbed response, and estimate the statistical uncertainty in the perturbed response. This paper has focused on cross-section and density perturbations. Material-substitution perturbations require special treatment [6], but it might be possible to apply the methods of this paper. The run times for the test problem increased by only ~20% of the rule of thumb quoted in the manual [3]. The PERT card must not be used to perturb problem parameters that would cause the source spatial, spectral, or angular distribution to be perturbed.