Sodium-Water Reaction approach and mastering for ASTRID Steam Generator design

The Steam Generator Unit (SGU) is one of the key components in the Sodium-cooled Fast Reactor system for it provides an interface between sodium and water. The objective for the SGU is related to the elimination or to the improvement of mastering of Sodium-Water Reaction (SWR). A first measure of prevention is the presence of the intermediate sodium circuit to separate chemical risk and radiological risk and to avoid pressure loadings inside the primary circuit in case of SWR. Modular SGU concept is selected, which limits the mechanical consequences on the secondary loop and on the intermediate heat exchanger of a postulated large SWR characterised by simultaneous guillotine failure of all the tubes of an SGU module (accidental envelope case). In addition, protection against large SWR is ensured by passive fast draining of the sodium loop using rupture disks. The redundancy and performance of the leak detection systems is reinforced. Supporting work includes SWR studies (modelling, pressure loading in the SGU, in the secondary loop and in the intermediate heat exchanger). SGU concepts are reviewed. (author)