A three-dimensional time-dependent multigroup SPN method for unstructu
red tetrahedral meshes is developed. The SPN equations are expressed i
n a canonical form that allows them to be solved using standard diffus
ion solution techniques in conjunction with source iteration, diffusio
n-synthetic deceleration, and fission-source acceleration. A computati
onal comparison of this SPN method with an even-parity S-N method is g
iven.