The OSMOSE Experimental Program for the qualification of integral cross sections of actinides

The need of better nuclear data on minor actinides has been stressed by various organizations throughout the world. It especially deals with the studies on plutonium management and waste incineration in existing systems and transmutation of waste or Pu burning in future nuclear concepts. To address this issue, a Working Party of the OECD has been concerned with identifying these needs and has produced a detailed High Priority Request List for Nuclear Data. The first step in obtaining better nuclear data consists in measuring accurate integral data and comparing them to integrated energy dependent data: this comparison provides a direct assessment of the effect of deficiencies in the differential data. Several international programs have indicated a strong desire to obtain accurate integral reaction rate data for improving the major and minor actinides cross sections. Data on major actinides (i.e. 235U, 236U, 238U, 239Pu, 240Pu, 241Pu, 242Pu and 241Am) are reasonably well-known and available in the Evaluated Nuclear Data Files (JEFF, JENDL, ENDF-B). However information on the minor actinides (i.e. 232Th, 233U, 237Np, 238Pu, 242Am, 243Am, 242Cm, 243Cm, 244Cm, 245Cm, 246Cm and 247Cm) is less well-known and considered to be relatively poor in some cases, having to rely on model and extrapolation of few data points. In this framework, the ambitious OSMOSE program between the Commissariat a l'Energie Atomique (CEA), Electricite de France (EDF) and the U.S. Department of Energy (DOE) has been undertaken with the aim of measuring the integral absorption rate parameters of actinides in the MINERVE experimental facility located at the CEA Cadarache Research Center. The OSMOSE Program (Oscillation in Minerve of isOtopes in 'Eupraxic' Spectra) includes a complete analytical program associated with the experimental measurement program and aims at understanding and resolving potential discrepancies between calculated and measured values. The OSMOSE program began in 2005 and will continue until 2010. The reactivity worth of samples having been fabricated in CEA Marcoule from 2001 to 2005, and containing separated actinides (232Th, 233U, 234U, 235U, 236U, 238U, 237Np, 238Pu, 239Pu, 240Pu, 241Pu, 242Pu, 241Am, 243Am, 244Cm and 245Cm), will be measured by an oscillation technique with an overall expected accuracy better than 3%. The measurements will cover a wide range of neutron spectra: over-moderated thermal spectrum, PWR UOx standard spectrum, PWR 100% MOX spectrum and epithermal HCLWR type spectrum. The paper has the following structure: I. Introduction; II. Main goals and major stakes; III. Experimental conditions; 1. The MINERVE facility; 2. The experimental lattices; 3. The oscillation technique of measurement; 4. Calibration curves for samples measurement; 5. OSMOSE samples; IV. Conclusion. To summarize, this paper has described the OSMOSE experimental program that will be performed between 2005 and 2010 in the MINERVE facility of CEA Cadarache. It covers the majority of the actinides that concern in the reactor physics and the fuel cycle, from 232Th up to 245Cm and is therefore highly valuable for every domain of neutron study. Indeed it will allow to determine by an oscillation technique the reactivity of samples containing the separated studied actinides with an accuracy that takes into account the uncertainties on the experiments, on the calculations and on the material balance of the samples. As a consequence, the OSMOSE program will involve an improvement - at least by a factor 2 - on the main nuclear data (integral resonance, capture cross section, reproduction factor) of the studied actinides, and on a large range of neutron spectra (thermal and epithermal). A single and accurate experimental database for heavy nuclides will thus be obtained and will enrich the JEFF3 project. It will also contribute to complete the database on burn up credit studies that currently only takes into account the fission products created during the fuel cycle