How to disable tile expiration?

I have managed to install osm on my machine and pre render tiles for every zoom until zoom 17 only for France (which is the only part which interests me)
When i access the tiles (with openlayer for example) until zoom 9 it gives me the cached version of the tile. However if I go deeper, it regenerates the tile. My server has a really low config and I want it to use the cache always. How can i disable the automatic regeneration of tiles for level > 9 ?

I looked in the apache configuration of mod_tile or in renderd configuration but i couldn’t find the proper parameter to set!

Thanks a lot for your help.
Best regards