Errors in Perturbation Calculations

Exact and first-order perturbation formulas that give changes in the eigenvalue of the discrete multigroup neutron diffusion equation are obtained. Various errors arising during the evaluation of these formulas are discussed. It is shown that for exact theory to give greater precision than first-order theory the fluxes must be sufficiently well converged to display the changes in them due to the perturbation. The reader is encouraged to assess the likely outcome of errors in his own calculations.