John Large’s working life was split into two halves, the first spent designing civil and military nuclear reactors and the second trying to make sure the industry was kept safe from accidents, nuclear waste and security threats. In this later role as a consulting engineer John was a dangerous opponent for the secretive nuclear establishment because his inside knowledge gave him the ability to ask difficult questions and expose weaknesses. He was never afraid to speak truth to power, although it took courage to take on such a powerful industry.
Despite his chosen role as an outsider, John’s abilities meant he had an astonishing list of clients ranging from the Russian Federation, the British government, the International Atomic Energy Agency (IAEA) and Greenpeace International. He was invited by the IAEA to China, North Korea and Iran, and by others to the US and Japan, to give advice on their nuclear programmes and the risks they posed.
John was still the leading independent analyst of safety and security in the nuclear industry at the time of his death, aged 75, from a heart attack. He was working on a report pressing for the permanent closure of Hunterston B nuclear plant in north Ayrshire, currently offline while cracks in the graphite bricks at the rare investigated.
While John often gave the impression that he had just stepped off the floor of an engineering works and was too busy to talk, he was in fact generous with his time and patient enough to explain a point of nuclear physics to an inquiring reporter.
He insisted on accuracy. As a result journalists who were faced with a secretive industry frequently turned to him to see if a possible story was credible, and for background information. Once I asked him how he knew about a serious problem with refuelling Britain’s fleet of advanced gas-cooled reactors, including Hunterston B, and he replied it was because he had helped design them.
He rarely talked about his achievements, but he was proud of his role in 2001 in overseeing nuclear safety for the successful raising of the Russian nuclear-powered K-141 submarine, the Kursk, which had sunk a year earlier with the loss of all 118 crew. He was the main nuclear adviser to the Dutch salvage company Mammoet-Smit and the Russian Federation, for which the Russians gave him a medal.
But it was his detailed reports for governments, MPs and campaigning organisations that had the most influence. They were always written in the same easy to understand but precise style and detail. Though many of the reports made uncomfortable reading for governments and the industry, nobody ever suggested his facts or interpretation were wrong, even though they often tried to ignore them. Some of his latest reports on the danger of terrorism to nuclear installations in Britain and elsewhere have been kept secret to avoid revealing the industry’s weakest points.
His immense knowledge stemmed from working in the 1960s and 70s as a senior research fellow with the UK Atomic Energy Authority while a member of the department of mechanical engineering at Brunel University in west London. At the time the UKAEA was responsible for Britain’s intertwined civil and military nuclear programmes and only employed the brightest and best brains. Much of his early work is still classified as secret.
In the late 60s John worked for a time at Windscale (now Sellafield), where plutonium for Britain’s nuclear weapons programme was produced and then transferred to the US in the early 70s as part of the 1958 US/UK Nuclear Cooperation Agreement. A curious attempt by the US military to get him to serve in Vietnam led John to take a sudden fishing holiday in Canada before returning directly to the UK and resuming work at Brunel University and the UKAEA.
John’s background as the son of a Fleet Street printer, Henry Large, and his wife, Rose (nee Hampshire), the landlady of the Neptune pub in Bermondsey, gave him a quick wit and ability to get to the point. His direct approach made a big impact in many court appearances as an expert witness, before committees of MPs, and in television studios.
He was born in Woking, Surrey, but grew up in London, where he went to Wilson’s grammar school in Peckham, and spent a year at Camberwell School of Art, before studying engineering at Imperial College. He was appointed a research assistant at Brunel in 1968, promoted to lecturer in 1971, and remained on the staff there until 1986.
He began the second phase of his career that year when he set up Large & Associates, consultant engineers that at one time employed up to 40 people. It was when things went wrong at nuclear power plants that John found himself in greatest demand. His first technical assessment of the Fukushima accident in Japan in 2011 confirmed a triple reactor meltdown within two weeks, well before it was officially acknowledged.
As well as his work, he applied his skills to restoring the 18th-century Robert Adam home he shared with his partner, Jenny Sherrell (known to everyone, including John, as AP, because she was from Alexandra Palace). This was in Ha-Ha Road overlooking the military barracks in Woolwich, an address that delighted him. There he kept bees and over 40 years took a leading role in the running of Oxleas Wood Apiary, located at Shooters Hill, a remnant of old London countryside. For many years he taught with great enthusiasm a 10-week summer course for aspiring beekeepers.
He is survived by Jenny, his daughter, Joanna, from an earlier relationship, and his brother, Bob.
• John Henry Large, consulting engineer, born 4 May 1943; died 3 November 2018