In July 2006 the NEA/Data Bank made available upon request the JEFF-3.1 library in ACE format (NEA-1768 ZZ-MCJEFF3.1NEA). This library contains continuous energy neutron cross section data files for use in the Monte Carlo program MCNP. The nuclides processed are all the evaluations of the General Purpose Library and Thermal Scattering JEFF-3.1 Library, including the important light nuclei, structural materials, fission products, control rod materials and burnable poisons, all major and minor actinides. This library was generated with the NJOY-99.90 nuclear data processing system plus some specific updates required for correct processing. The library has undergone strict Q&A procedures. All inputs used for processing JEFF3.1 with NJOY99.90 and the documented derived version are provided. The validations made, using benchmark experiments for criticality (ICSBEP) and shielding (SINBAD) are documented in the report
