Study about effective photoneutron coefficient in HWZPR

In Heavy Water Zero Power Reactor (HWZPR), the photoneutron coefficient is a parameter of special significance for reactor safe operation and accurate measurement of the reactor power ascending period. Although, in the stable power operation, the fission delayed neutrons and the delayed photoneutrons are only the small fractions of the total neutrons in the reactor, but the certain time after the reactor shutdown they become the main neutron source. In order to measuring the effective photoneutron coefficient, the decay curve of the neutron intensity in the HWZPR was obtained as a function of time after shutdown. The experiment was repeated in the different reactor powers, lower than 40 W. The reactor was in the stable power for 40 min, before shutdown. By analyzing the decay curve into a sum of decreasing exponentials and using the theory of point kinetics, the effective photoneutron coefficient was measured. The delayed neutron and photoneutron counts were corrected to infinite irradiation time. According to the experimental results, the effective delay photoneutron coefficient is equal to 0.31. In continue, this parameter was calculated by MCNPX code. The comparison of the experimental and calculated results show that the relative difference between them is less than 4% and the MCNPX calculated results is verified.