An assessment of prompt neutron reproduction time in a reflector dominated fast critical system: ELECTRA

•Prompt neutron reproduction time of ELECTRA is evaluated.•Static and dynamic reproduction times are distinguished for ELECTRA.•Avery-Cohn’s two-region prompt neutron theory is applied.

In this paper, an accurate method to evaluate the prompt neutron reproduction time for a reflector dominated fast critical reactor, ELECTRA, is discussed. To adequately handle the problem, explicit time dependent Monte Carlo calculations with MCNP, applying repeated time cut-off technique, are used and compared against the σ∼1/vσ∼1/v time dependent absorber method, applying artificial cross-section data in the Monte Carlo code SERPENT. The results show that when a reflector plays a major role in criticality for fast neutron reactor, the two methods predict different physical parameters (Λ=69±2Λ=69±2 ns and Λ=83±1Λ=83±1 ns for time cut-off and the 1/v method respectively). The reason is explained by applying Avery-Cohn’s two-region prompt neutron model.