The algorithm and experimental measurement of subcritical system prompt neutron decay fundamental parameters

In light water moderated subcritical system, accounting for the number of secondary neutrons produced by fission reactions, the total number of 99% neutrons is prompt neutron which plays a dominant role. Prompt neutron decay parameter a is an important parameter in nuclear systems, accurate measurement of this value is much more important for nuclear criticality safety. Based on one group thermal neutron diffusion theory, depending on the generation time of secondary neutrons in fission reaction, as the effect of higher harmonic fluxes of prompt neutron and delayed neutron is eliminated, we obtained a attenuation curve originating from the fundamental prompt neutron decay constant. Algorithm was written and verified with the help of data acquisition parameters and standard data. In experiments, based on the characteristic decay constant method, the integral reactivity of one control rod was obtained by measuring the prompt neutron decay parameters in each segments. For comparison, we calibrated the same control rod' integral reactivity by neutron generation method, both measurements agree well. The symmetrical control rods' integral reactivity were measured by the characteristic decay constant method, which put in order group P, group A, group B, and group E in four different cores. Data analysis shows that the standard deviation is ± 0.042 million, corresponding to the percentage deviation of 0.6%. (authors)