Perturbation of General Boundary Condition for an Eigenvalue Change in the Neutron Boltzmann Transport Equation

First-order perturbation formalisms, representing a change in the eigenvalue of the neutron Boltzmann transport eigenvalue equation due to the boundary condition change, are derived. The same expression for first-order perturbations is also obtained using Rahnema’s procedure. The formalisms obtained are applicable to the general boundary condition. These formalisms are verified, and their accuracy is estimated by applying the formalisms to systems whose boundary conditions deviate slightly from the standard vacuum and white boundary conditions.