Some Implications of a Stochastic Neutron Population Model with Feedback

Abstract

A derivation of the time-dependent forward stochastic equation is sketched for a point reactor with linear feedback and an arbitrary finite fission neutron frequency distribution. Certain pathological characteristics of possible stochastic trajectories are discussed, and limiting conjectures are made based on physical considerations. The time-independent forward stochastic equation with negative reactivity feedback is solved in the classical manner, leading to a recursion relation for the long-run probabilities. Next, all factorial moments of the long-run distribution are shown to be finite, and the corresponding probabilities, P(N,∞), are thus o(N^−k) for any integer k. Following this, a more tractable recursion relation is presented for the simpler case of binary fission. For this simpler model, the equivalence to an independent analysis of the Kolmogorov forward matrix equations, as presented in a previous paper, is demonstrated. Finally, a simple recursion relation among factorial moments of the long-run distribution is derived for the binary fission model.