Benchmarks on effective delayed neutron parameters and reactivity: a Brazilian IPEN/MB-01 contribution to the IRPhE project

The purpose of this work is to present the experimental results of the in-pile experiments performed at the IPEN/MB-01 Reactor for the determination of the effective delayed neutron parameters and reactivity. The methodologies employed were the macroscopic noise in the frequency domain, where the very low frequency range (< 1.0 Hz) was also exploited and analyzed, and the microscopic noise, which is based on the measurement of Rossi-α and Feynmann-α distributions at several subcritical levels. In this last case, a Two- Region Model was developed. The main advantage of these methodologies is to obtain the effective delayed neutron parameters in a purely experimental way, eliminating all parameters that are difficult to measure or calculate. Consequently, the uncertainties associated with these parameters are eliminated and the accuracy in the effective delayed neutron parameters is improved. Both techniques are claimed to be well defined and produce experimental data of very high quality. Finally, it is proposed to assign benchmark-values to βeff (the effective delayed neutron fraction), to Λ (the prompt neutron generation time), to their ratio (βeff/Λ) and also for the first time to the reactivity by means of the in-hour equation. It is concluded that the experiments are acceptable benchmarks. (authors)