Rossi-α Experiment in the IPEN/MB-01 Research Reactor: Validation of Two-Region Model and Absolute Measurement of βeff and Λ

A new method for absolute measurement of the effective delayed neutron fraction, βeff, and the prompt neutron generation time, Λ, based on Rossi-α experiments and the Two-Region Model was developed at the IPEN/MB-01 Research Reactor facility. In contrast with other techniques like the Slope Method, Nelson-Number Method and 252 CfSource Method, 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. In this way, Rossi-α experiments for validation of this method were performed at the IPEN/MB-01 facility. The final results agree well with values from frequency analysis experiments and show uncertainties of 1.46% and 0.97% for βeff, and Λ respectively. This work supports the reduction of the 235 U thermal yield as proposed by Okajima and Sakurai.