I imagine that, at the time of this test, it would have been the place formerly known as Windscale, and renamed as Sellafield at some point after the eponymous

I imagine that, at the time of this test, it would have been the place formerly known as Windscale, and renamed as Sellafield at some point after the eponymous Windscale fire/disaster/WTFWTT/cover-up. It is on the coast, but does not appear to have any sort of harbor. I see it stopped reprocessing fuel in 2022, so if Britain's spent fuel is going anywhere these days, it probably spends some time on a ship.