I actually was mistaken. The photo is from an earlier project: TES-3, from 1960. It was a system with 4 mobile units and a reactor that needed to be buried for shielding.

https://www.ixbt.com/live/offtopic/pervaya-v-mire-peredvizhn... (German Wiki also has an article with an image: https://de.wikipedia.org/wiki/TES-3 ).

I remember reading about it in an encyclopedia as a child.