Multigroup diffusion theory with directional group constants for narrow resonances

Sikander Majid Mirza, Purdue University

Abstract

This study addresses the problem of neutron physics calculations in transition regions. Directional effects in the reaction rate calculations that are lacking in the standard methods are incorporated. Direction dependent group constants have been developed for narrow actinide resonances. These group constants were generated by using detailed integral transport theory fluxes which reflect the transitional effects. It was found that for narrow resonances, these group constants exhibit a linear dependence on $\mu$, the cosine of the polar angle in the slab geometry. An improved one-dimensional multigroup diffusion approach was developed that uses the direction dependent group constants. The "augmented diffusion equation" reduces to standard diffusion theory in the absence of directional effects. The improved approach was implemented in a multigroup diffusion theory code which is used iteratively. In practical applications, a single "uptake" appears to be adequate. The improved methodology was applied to the problem of blanket neutron transmission. The use of directional group constants in augmented diffusion theory yields a considerably increased neutron transmission in LMR blankets and thus improves the flux and reaction rate predictions. This eliminates about one third of "C/E drop-off."

Degree

Ph.D.

Advisors

Ott, Purdue University.

Subject Area

Nuclear physics|Nuclear physics

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