Application of stochastic diffusion theory to the interpretation of the 252Cf source-driven noise analysis method for subcriticality determination

The 252Cf source-driven noise analysis (CSDNA) method is an experimental technique, which makes use of noise analysis to determine the multiplication factor, k, in subcritical multiplying media. In this work, a stochastic diffusion description was used to interpret the CSDNA experiment in an infinite, homogeneous medium in order to shed light on the practicality of this experimental procedure in determining the multiplication factor. By defining such a benchmark problem an exact solution is obtained for the subcritical multiplication factor in which the locations of the 252Cf source and neutron detectors are explicitly taken into account. The expression relating reactivity to the measured data was found to depend implicitly on k itself. Through a numerical analysis of this expression, certain limiting conditions were identified in which the expression for the reactivity became essentially independent of k, hence demonstrating some possibility for the viability of this technique. However, under more realistic experimental conditions, i.e. for finite systems in which diffusion theory is not applicable, the measurement of the subcritical multiplication factor from the measured data, without extensive transport calculations, becomes doubtful. (Author)