Rossi-{alpha} experiment in the IPEN/MB-01 research reactor: Validation of two-region model and absolute measurement of {beta}{sub eff} and {Lambda}

A new method for absolute measurement of the effective delayed neutron fraction, {beta}{sub eff}, and the prompt neutron generation time, {Lambda}, based on Rossi-{alpha} 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 {sup 252}Cf- Source 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-{alpha} 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 {beta}{sub eff}, and {Lambda} respectively. This work supports the reduction of the {sup 235}U thermal yield as proposed by Okajima and Sakurai. (authors)