A new concept of Monte Carlo kinetics parameter calculation using complex-valued perturbation

A new Monte Carlo method to calculate two types of kinetics parameters, the effective delayed neutron fraction (eff) and the prompt neutron generation time (), is proposed in this paper. The new method uses perturbation techniques in which extra delayed neutrons or a fictitious 1/v absorber is added to the unperturbed system to calculate the eff or , respectively. In the new method, the perturbation is added as a complex-valued perturbation. This paper conjectures that the change in the eigenvalue due to the perturbation is accurately approximated by the imaginary part of the eigenvalue of the complex-valued perturbed equation. The conjecture is corroborated by certain numerical tests presented in this paper. A Monte Carlo calculation algorithm is established to solve the complex-valued perturbed eigenvalue equation. One single Monte Carlo calculation to solve the complex-valued eigenvalue equation yields highly accurate approximations of the exact kinetics parameters with much less computational costs compared with the previously proposed method that uses multiple Monte Carlo * Corresponding author. Tel: +81 72 451 2414; Fax: +81 72 451 2658 E-mail address: [email protected] (T. Yamamoto)