A new method for absolute measurement of βeff based on Microscopic Noise Experiments and the Two-Region model in the IPEN/MB-01 research reactor

A new method for absolute measurement of the effective delayed neutron fraction, βeff, based on Microscopic Noise Experiments and the Two-Region Model was developed at the IPEN/MB-01 Research Reactor. In contrast with other techniques, the main advantage of this new methodology is to obtain the parameters in a purely experimental way, eliminating all parameters that are difficult to measure or calculate. Consequently, the uncertainties associated to these parameters are eliminated and the accuracy in βeff is improved. Experimentally, several Rossi-α and Feynman-α measurements were performed in the IPEN/MB-01 in a large subcritical interval. By adopting the present approach, the final results show that uncertainties of 0.67% and 0.97% on, respectively, βeff and Λ are achievable. The theory/experiment comparison of βeff shows that among the available nuclear data libraries JENDL3.3 has the best performance.