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A Sensitivity Analysis of Nuclear Assembly Extinction Probabilities: Application to Reevaluated Fission Multiplicity Data

Scott D. Ramsey, Roy A. Axford

Nuclear Science and Engineering / Volume 166 / Number 1 / September 2010 / Pages 48-57

Technical Paper /

We implement direct and approximate local sensitivity analysis techniques within the context of stochastic point kinetics neglecting delayed neutrons and external neutron sources. After reviewing the derivation of certain probabilities that the neutron population in a nuclear assembly is exactly zero [probabilities of extinction (POEs)], we consider their dependence on physical data. We subsequently focus on fission number distribution dependence and draw comparisons between two different data sets. As various POEs are dependent upon these data through the solution of a nonlinear ordinary differential equation, local sensitivity analysis provides a useful means through which to assess the effects of data reevaluation. We first conduct this analysis generally (though approximately) using Gâteaux-derivative methodology. Following the generalized developments, exact and approximate results for 235U are presented with a discussion concerning important consequences related to criticality safety.

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