Neutron Data Measurements for Waste Transmutation at Gelina

Abstract

During the last decade there has been a growing interest in Partitioning and Transmutation technologies as a means of strongly reducing the long-term radiotoxic inventory of nuclear waste. Main emphasis has been placed on the burning of minor actinides (MA) and of long-lived fission products (LLFP). In order to contribute building a sound data base for the neutron induced reactions of the concerned isotopes, a collaboration has been started in 1995 between the Service de Physique Nuclaire of CEA France and the Institute for Reference Materials and Measurements of Geel, Belgium. In the frame of this co-operation, a mixed group of scientists carries out measurements and analysis of neutron capture and transmission cross sections at the GELINAtime-of-flight facility of the IRMM. An important preparatory activity is also the procurement of such radioactive isotopes and the production of gram-quantity samples, a work that is also carried out at the IRMM, Geel. The isotopes investigated so far are 99Tc, 129I and 237Np. Work on 99Tc, which is considered the most offending LLFP, is practically completed: a total of 659 resonances have been analyzed up to 10 keV neutron energy making use of both capture and transmission data. Spin has also been assigned to 51 s-wave levels. Quantities such as the average level spacing, the average capture width and the strength function for s- and p-wave levels have been derived from such a large sample of resonances. Average capture and transmission cross sections have also been determined in the unresolved region from 10 to 150 keV. The analysis of 237Np transmission data has allowed to determine the neutron widths, and at low energy also the capture widths, of some 570 resonances below 500 eV and preliminary data up to 1 keV are available. Preliminary results of 129I transmission measurements below 1 keV energy are presented at this conference in a separate contribution. 1)