The sulphur based thermochemical cycles are considered as the most promising and mature process for their potentiality to produce massively hydrogen at competitive cost, coupled with nuclear heat source. Many laboratory-scale experiments have been successfully performed in particular through European funded Programs. The major challenge remains the simultaneity of high temperature (beyond 800 °C) and corrosive sulphuric environments.
Theses conditions are requiring advanced materials and special design for the process components. And technological feasibility at pilot scale has still to be demonstrated.

In 2006, CEA has initiated a pluriannual development program called “HYPRO”, for one of the key component of this thermochemical process : the SO3 decomposer.
HYPRO project focuses on pilot scale mock-up development, coupled with a heat source representative of a Gas Cooled High Temperature Reactors.

After a brief recall of the project development since 2006, This paper is presenting the recent achievements mainly in the following areas :
- the main theoretical results on materials assessment in term of :
* corrosion resistance,
* catalysts efficiency
- the preliminary design of a small SO3 decomposer dedicated to kinetic studies,
- the realisation and test of a small plate compact SiC heat exchanger.

Furthermore, CEA, has now set this development work within the new European Project HYCYCLES (7th PCRD Energy), which aims, among others, at the qualification of a pilot-scale heat exchanger for SO3 decomposition. This part of HYCYCLES program is presented either in this paper.