Abstract. The status of the Joint Evaluated Fission and Fusion file (JEFF) is described. JEFF-3.1 comprises a significant update of actinide evaluations, materials evaluations that have emerged from various European nuclear data projects, the activation library JEFF-3.1/A, the decay data and fission yield sub-libraries, and fusion-related data files from the EFF project. The revisions were motivated by the availability of new measurements, modelling capabilities and trends from integral experiments. Validations have been performed, mainly for criticality, reactivity temperature coefficients, fuel inventory and shielding of thermal and fast systems. Compared with earlier releases, JEFF-3.1 provides improved performance with respect to a variety of scientific and industrial applications. Following on from the public release of JEFF-3.1, the French nuclear power industry has selected this suite of nuclear applications libraries for inclusion in their production codes.

Accurately quantifying the transmutation rate of tungsten (W) under neutron irradiation is a necessary requirement in the assessment of its performance as an armour material in a fusion power plant. The usual approach of calculating average responses, assuming large, homogenised material volumes, is insufficient to capture the full complexity of the transmutation picture in the context of a realistic fusion power plant design, particularly for rhenium (Re) production from W. Combined neutron transport and inventory simulations for representative spatially heterogeneous models of a fusion power plant show that the production rate of Re is strongly influenced by the local spatial environment. Localised variation in neutron moderation (slowing down) due to structural steel and coolant, particularly water, can dramatically increase Re production because of the huge cross sections of giant resolved resonances in the neutron-capture reaction of 186 W at low neutron energies. Calculations using cross section data corrected for temperature (Doppler) effects suggest that temperature may have a relatively lesser influence on transmutation rates.

The European Activation File (EAF) project has been an ongoing process performed through European and world-wide cooperation that has led to the creation of succeeding EAF versions. The latest release, EAF -99, has benefited from the generation and maintenance of comprehensive activation files and the maturing of the processing code SYMPAL. Recently, for the first time, results of integral experiments have been used to adjust data. Validation of activation code predictions, and thereby of cross section and decay data, has been performed by means of direct comparison with measurements of sample structural material under fusion-relevant neutron spectra. The EAF-99 library contains 12,468 excitation functions involving 766 different targets from IH to 257Fm, atomic numbers 1 to 100, in the energy range 10. 5 e V to 20 Me V. The 1,500,000 lines that make up the pointwise file are then processed into numerous groupwise files with different micro-flux weighting spectra to meet various user needs. Uniquely, an uncertainty file is also provided that quantifies the degree of confidence placed on the data for each reaction channel.