The French Generation IV sodium cooled Fast Reactor (SFR) is designed with a large pool-type vessel and equipment (pumps, heat decay removal) which are sensitive to horizontal seismic accelerations. It is necessary to design these components with an appropriate seismic isolation system depending on the site seismic conditions.

For ASTRID, the SFR industrial demonstrator project under development by the CEA, the preliminary study has concluded to the necessity to isolate horizontally all the buildings of the nuclear island on a para-seismic raft equipped with seismic pads. At the current Basic Design phase, the project takes into account the lessons learnt from the recent Jules Horowitz Reactor (JHR) and ITER research reactor projects under construction and equipped with seismic isolators.

Seismic isolation allows to decrease the horizontal building accelerations from 5 to 10 times. Positive aspects consist in reducing the average reinforcement ratio of these buildings and to ease the design of the main reactor block components, with in the end, an expected gain of cost.

ASTRID partners aims also to improve and innovate with this isolation technology. Based on the European standards, previous solutions used elastomeric rubber with metallic parts pads. BOUYGUES Company (CEA’s partner for ASTRID), associated to CNIM Company, has chosen to change the raw material, using polyurethane material instead of natural rubber. Several advantages are expected. With ageing, the polyurethane is softening whereas natural rubber is hardening (and potentially reducing seismic isolation capacity).

The main conclusion is that these new pads respect the dynamic behavior of the buildings, give better margin in seismic condition and allow modifying easily the pads stiffness.

The next step is that a complete qualification program will be implemented in order to validate the one scale dynamic characteristics of the isolators at full scale and to justify the requested 90 years lifetime.