This Rolls Royce design isn't all that "small." A RR SMR design is a 470MWe PWR. About half the size of a typical PWR reactor. Fukushima Daiichi Unit 1 was 460MWe. Calling this an "SMR" is a stretch, likely for PR purposes.

It's a rather conventional design, low enriched fuel, no exotic coolants. There is a paper on it at NRC[1]. And they've never built one, so if they get it running by the 2030's they'll be doing pretty well for a Western company.

[1] https://www.nrc.gov/docs/ML2521/ML25212A115.pdf