International Conference on Research Reactors:
Safe Management and Effective Utilization

14-18 November 2011, Rabat, Morocco

Subcritical measurements were performed for the first time at the RA-3 research and production reactor in order to obtain relevant kinetic parameters for the safe operation of the reactor. Measurements were made during the shut-down period in presence of high background gamma radiation (greater than 106 R/h) and xenon. At each stationary subcritical state, the neutron source was assumed to come from photoneutron precursors produced during the normal operation of the reactor. Kinetic parameters were estimated using both neutron noise and inverse kinetics techniques. It was possible to estimate the photoneutron effectiveness of the RA-3 reactor, giving a value of (1.11 ± 0.05) 10-4. Using the least squares inverse kinetics method the neutron source strength was estimated and then used in the inverse kinetics equation in order to get the reactivity evolution during the change of core configuration of the reactor. The study of the obtained experimental values shows the existence of spatial effects in the reactivity estimation, which were confirmed by numerical simulations carried out with the diffusive neutron code PUMA.

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