Uncertainty and global sensitivity analysis of neutron survival and extinction probabilities using polynomial chaos

The underlying deterministic results of the model are found to closely match analytical benchmarks and, once uncertainty is introduced, the GPC results match both Monte Carlo simulations and analytical results for polynomial order greater than two. The GPC method is found to require significantly less computational time to achieve a given accuracy on the survival and extinction probabilities than the Monte Carlo method. It is found that, the probabilities are most sensitive to χi for lower i and have a significant sensitivity to χ2 in all cases. A chain's survival probability is moderately sensitive to the neutron lifetime early in simulation. In the subcritical case this sensitivity increases as the simulation continues whilst it decreases in the supercritical case. The extinction probability is sensitive to the source strength.