Europe needs hyperscalers (lots of them)

> I remember our AGR reactor technology got overwhelmed by the American PWR reactors, despite being much safer.

Don't know if they were safer, but it's clear they were more expensive.

> Iirc it used deuterium (heavy water) as the moderator

No, graphite for moderator, CO2 as coolant. They used control rods to control the reactivity.

> "to see what will happen"

There are very conflicting stories about the details, but it is clear that it was a pre-planned test, deemed necessary to verify correct operation. It was supposed to be done by the day-shift, but it was delayed, so the unprepared night-shift got the job.