On this day October 10, 1957

The Windscale fire in Cumbria, U.K. is the world’s first major nuclear accident when the graphite core of a British nuclear reactor at Windscale, Cumberland (now Sellafield, Cumbria), caught fire, releasing substantial amounts of radioactive contamination into the surrounding area.

Sellafield

Sellafield

The event, known as the Windscale fire, was considered the world’s worst reactor accident until Three Mile Island in 1979. Both incidents were dwarfed by the magnitude of the Chernobyl disaster in 1986.

Early in the morning on 10 October, it was suspected that something unusual was going on. The temperature in the core was supposed to gradually fall as Wigner release ended, but the monitoring equipment showed something more ambiguous was going on and one thermocouple indicated that core temperature was instead rising.

In an effort to help cool the pile, more air was pumped through the core. This lifted radioactive materials up the chimney and into the filter galleries. It was then that workers in the control room realised that the radiation monitoring devices which measured activity at the top of the discharge stack were at full scale reading. In accordance with written guidelines, the foreman declared a site emergency. No one at Windscale was now in any doubt that Pile Number 1 was in serious trouble.

Operators tried to examine the pile with a remote scanner but it had jammed. Tom Hughes, second in command to the Reactor Manager, suggested examining the reactor personally and so he and another operator went to the charge face of the reactor, clad in protective gear. A fuel channel inspection plug was taken out close to a thermocouple registering high temperatures and it was then that the operators saw that the fuel was red hot.

“An inspection plug was taken out,” said Tom Hughes in a later interview, “and we saw, to our complete horror, four channels of fuel glowing bright cherry red.” There was no doubt that the reactor was now on fire, and had been for almost 48 hours.

Reactor Manager Tom Tuohy donned full protective equipment and breathing apparatus and scaled the 80 feet to the top of the reactor building, where he stood atop the reactor lid to examine the rear of the reactor, the discharge face. Here he reported a dull red luminescence visible, lighting up the void between the back of the reactor and the rear containment.

Red hot fuel cartridges were glowing in the fuel channels on the discharge face. He returned to the reactor upper containment several times throughout the incident, at the height of which a fierce conflagration was raging from the discharge face and playing on the back of the reinforced concrete containment—concrete whose specifications insisted that it must be kept below a certain temperature to prevent its disintegration and collapse

On the morning of Friday 11 October and at its peak, 11 tonnes of uranium were ablaze. Temperatures were becoming extreme (one thermocouple registered 1,300 degrees Celsius) and the biological containment around the stricken reactor was now in severe danger of collapse. Faced with this crisis, the operators decided to use water.

This was incredibly risky: molten metal oxidises in contact with water, stripping oxygen from the water molecules and leaving free hydrogen, which could mix with incoming air and explode, tearing open the weakened containment. But there was no other choice. About a dozen hoses were hauled to the charge face of the reactor; their nozzles were cut off and the lines themselves connected to scaffolding poles and fed into fuel channels about a meter above the heart of the fire.

Tom Tuohy then ordered everyone out of the reactor building except himself and the Fire Chief. All cooling and ventilating air entering the reactor was shut off. Tuohy once again hauled himself atop the reactor shielding and ordered the water to be turned on, listening carefully at the inspection holes for any sign of a hydrogen reaction as the pressure was increased.

Tuohy climbed up several times and reported watching the flames leaping from the discharge face slowly dying away. During one of the inspections, Tuohy found that the inspection plates—which were removed with a metal hook to facilitate viewing of the discharge face of the core—were stuck fast. This, Tuohy reported, was the fire trying to suck air in from wherever it could.

“I have no doubt it was even sucking air in through the chimney at this point to try and maintain itself,” he remarked in an interview. Finally he managed to pull the inspection plate away and was greeted with the unfathomable sight of the fire dying away.

“First the flames went, then the flames reduced and the glow began to die down,” he described, “I went up to check several times until I was satisfied that the fire was out. I did stand to one side, sort of hopefully,” he went on to say, “but if you’re staring straight at the core of a shut down reactor you’re going to get quite a bit of radiation.”

Water was kept flowing through the pile for a further 24 hours until it was completely cold.

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