

The linked PDF (page 14) has a few diagrams that can help infer vessel size, and the Wikipedia page for TSMR-LF1 also includes a decent floor plan and links to satellite images. Looks like a typical research reactor footprint, which means it may scale to be similar to existing LWRs at higher power. https://esfr-smart.eu/wp-content/uploads/2021/04/S53_1_Paul_Gauthe_Overview_MSR_Gauthe.pdf
For reference, a typical PWR may be ~3000 MWth.
Here’s a more measured take on it, particularly the Update section - though it’s written by the company creating the long-term waste repository in Switzerland so there’s some obvious bias.
It appears the modeling/simulation code Transmutex developed is heavily based on the open-source Geant4 toolkit.