Neutronic analyses of the FREYA experiments in support of the ALFRED LFR core design and licensing

During the EURATOM FP7 project FREYA, a number of experiments was performed in a critical core assembled in the VENUS-F zero-power reactor able to reproduce the ALFRED lead-cooled fast reactor spectrum in a dedicated island. The experiments dealt with the measurements of integral and local neutronic parameters, such as: the core criticality, the control rod and the lead void reactivity worth, the axial distributions of fission rates for the nuclides of major interest in a fast spectrum, the spectral indices of important actinides (U238, Pu239, Np237) respect to U235. With the main aim to validate the neutronic codes adopted for the ALFRED core design, the VENUS-F core and its characterisation measurements were simulated with both deterministic (ERANOS) and stochastic (MCNP, SERPENT) codes, by adopting different nuclear data libraries (JEFF, ENDF/B, JENDL, TENDL). This paper summarises the main results obtained and points out a general agreement between measurements and simulations, with few discrepancies for some parameters that are here discussed. Additionally, a sensitivity and uncertainty analysis was performed with deterministic methods for the core reactivity: it clearly indicates that the calculation accuracy of the different codes/libraries resulted to be lower than the uncertainties due to nuclear data.