The objective of HYTHEC-HYdrogen THErmo-chemicat Cycles-is to investigate the effective potential for massive hydrogen production of the S-I thermo-chemical cycle, and to compare it with the hybrid S Westinghouse (WH) cycle. The project aims to conduct flow-sheeting, industrial scale-up, safety and costs modelling, to improve the fundamental knowledge and efficiency of the S-I cycle H-2 production step, and to investigate a solar primary energy source for the H2SO4 decomposition step which is common to both the cycles. Initial reference flow-sheets have been prepared and compared. First data and results are available now on the coupling of S-I cycle with a very high temperature nuclear reactor, scale-up to industrial level and cost estimation, improvement of the knowledge of the HIx mixture (S-I cycle) and membrane separation, splitting of sulphuric acid using a solar furnace, and plant concepts regarding the WH process. (C) 2006 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.