Long discussion: https://www.worksinprogress.news/p/why-british-nuclear-flopp...

Magnox: un-enriched fuel, designed for weapons, low operating temperature.

AGR: too complicated, can't be refuelled without complete shutdown.

PWR has emerged as the only viable design, and even that is too complicated compared to solar+batteries.

Basically, plumbing is the enemy. Every joint is a potential failure. If what's in the pipe is radioactive or corrosive or explosive (in the case of molten sodium, all three), that's extra bad. So there's tremendous cost of inspections.

Something about AGR in this great Stross piece https://www.antipope.org/charlie/blog-static/rants/nothing-l...