Preliminary Safety Performance Assessment of ESFR CONF-2 Sphere-Pac-Fueled Core

A preliminary safety assessment of the CONF-2 version of the European Sodium Fast Reactor core loaded with both pellet and sphere-pac fuels was performed. The reference Unprotected Loss Of Flow (ULOF) and an Unprotected Transient Over-Power (UTOP) accidents were simulated, along with a set of sensitivity studies aimed at evaluating the influence of uncertainties affecting both safety coefficients and the fuel thermal conductivity. Among the major outcomes, it could be preliminarily concluded that the use of sphere-pac fuel may bring some disadvantages from the safety point of view in the event of a UTOP accident, whereas no concerns are raised for a ULOF scenario. Consistently, uncertainties in the determination of the fuel thermal conductivity and Doppler constant were found to have no significant impact on the ULOF transient predictions, but to influence the UTOP simulations, making their accurate determination critical for the system safety assessment. (author)