Measurement of k eff by delayed neutron multiplication in subcritical systems

In this paper, we build on the concept of equivalent fundamental-mode source to propose using delayed neutrons as a neutron source in multiplication experiments to acquire the effective multiplication factor k eff of subcritical systems, which is difficult to acquire directly from conventional neutron source multiplication method. We analyzed the difference between a fundamental-mode fission source and delayed neutron source, then adopted a factor to convert delayed neutron distribution to an equivalent fundamental-mode source distribution, and employed Monte Carlo code to acquire this factor. The delayed neutron multiplication measurement method was established for the first time, and corresponding experiments were conducted in subcritical systems. The multiplication of delayed neutrons was measured based on Chinese Fast Burst Reactor-II (CFBR-II) at subcritical states, and k eff was acquired from delayed neutron multiplication successfully (0.9921 and 0.9969, respectively). The relative difference between k eff obtained by the new method and previous values acquired by the positive period method is less than 1% for these two studied cases.