International evaluation Co-operation. Delayed neutron data for the major actinides

Subgroup 6 was set up in 1990 with the task of coordinating activities aimed at reducing the discrepancies, which then existed, between calculated and measured nuclear reactor reactivity scales based on reactor kinetics. The main aim has been to reduce the uncertainties in the delayed neutron data for the major actinides, 235U, 238U and 239Pu. In this final report of the subgroup recommended delayed neutron data are proposed for these isotopes and the state of the art in the field of delayed neutron data is reviewed. Recommended data for the time dependence of delayed neutron emission and for the associated energy spectra for fission in 20 isotopes are also proposed. The report is accompanied by a CD-Rom which contains a number of documents providing more detail about the derivation of the recommended data. In addition, papers describing the measurements made at IPPE Obninsk concerning total yields and tune dependence, as well as associated studies of semi-empirical models, are also available on the CD-ROM. The report presents an overview of the state of the art. Short descriptions are given of the different activities, together with bibliographic references. Some recent results are also reported. The report is organised in four sections. The first section summarises general analyses of the available delayed neutron data. The remaining three sections summarize activities carried out to measure, evaluate and validate delayed neutron data. (author)