I think that part of the Windscale design came over pretty much intact from the Hanford reactors which supplied plutonium for the Manhattan Project. Hanford was (slightly) safer in that they used water as coolant rather than air. But the lack of care inherent in every part of this project is terrifying - the UK was desperate to become a nuclear power after the US reneged on its promise of ongoing cooperation that it was prepared to do just about anything to get a bomb as quickly as possible despite the country being utterly bankrupt (like that could ever happen again!).
The really terrifying bit about the Windscale reactors was that the filters on the exhaust stacks were nearly omitted on the grounds of cost. Had they not been in place when Pile Number 1 became a barbecue, the UK would have come as a very credible runner up to Chernobyl.
I was a bit glib in my first posting, the Magnox reactors eventually settled down to become reliable generators and in some ways they were superior to the PWR in that it was pretty much impossible to melt one and even massive coolant leaks were survivable. The follow-on AGR was a masterpiece of pure engineering - hugely efficient and fuel didn’t need reprocessing (it still was for political reasons), but even more expensive, not helped by pretty much every one being a bespoke unit rather than a standard design.
Though there is one thing no one wants to talk about - there’s about 100,000 tonnes of intensely-irradiated graphite in the cores of the Magnox and AGR stations that no one has a clue how to make safe. As well as radioactive carbon, the blocks contain relatively-long lived isotopes including 60Co, 133Ba, 137Cs, 154Eu. Hoping ‘something will turn up’ is one of the reasons that the decommissioning of these stations is so expensive (at least £130 billion) and on such an incredibly long time scale (about a century).
