Speaker
Description
Delayed neutron data is essential in inherent reactor safety and in reactor control since it is used to estimate the reactivity. The quantities of interest related to delayed neutrons are the average delayed neutron yield, and the group constants that define the kinetics of delayed neutron emission.
Discrepancies among the evaluated data as well as missing covariance in most of international databases result in excessive conservatism in the safety margins. In order to improve this status, a collaboration among CEA and CNRS was settled to produce high-quality delayed neutron data for several fissioning systems of interest in GEN-II & III reactors.
Following successful campaigns at ILL (Institut Laue-Langevin) in 2018 and 2019, devoted to 235U, a new campaign was realized in march 2021, focusing on the thermal fission of 239Pu. The experiment consists of a cold neutron beam hitting a fissile target, placed at the center of a long-counter made of a polyethylene matrix in which 16 helium-3 tubes are introduced. After a defined irradiation length, during which fissions occur and precursors buid up, the beam is quickly interrupted and the delayed neutrons emitted by the precursors' is detected. First estimations of the delayed neutron yield and group constants are proposed and discussed in this paper, in comparison with data from the literature.