The UK Space Agency, on 2021 Jan 12, announced a research contract with Rolls-Royce for nuclear propulsion of spacecraft, based on R-R's experience with nuclear power for submarines. The press release is bereft of any tangible details; it merely promises faster travel to Mars than chemical propulsion (duh). It ends by disparaging Project Orion, so presumably R-R won't be duplicating that.
The press release has been quoted by many news agencies, but none of these even guess at technical details. What might R-R be planning to investigate?