After the war Cockcroft became the director of the Atomic Energy Research Establishment ( AERE ) at Harwell , where the low-powered , graphite-moderated GLEEP became the first nuclear reactor to operate in western Europe when it was started on 15 August 1947 . This was followed by BEPO in 1948 . Harwell was involved in the design of the reactors and the chemical separation plant at Windscale . Under his direction it took part in frontier fusion research , including the ZETA program . His insistence that the chimney stacks of the Windscale reactors be fitted with filters was mocked as '' Cockcroft 's Folly '' until the core of one of the reactors ignited and released radionuclides during the Windscale fire of 1957
Windscale fire
Windscale fire
John Cockcroft