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An Infamous First

Storm_Clouds_over_Sellafield_-_geograph.org.uk_-_330062

The worst nuclear accident in Great Britain’s history happens to be it’s first, and one of the world’s first. Known as the Windscale Fire, it occurred at the Windscale, Cumberland (know called Sellafield, Cumbria) Pile No. 1. Luckily, a system that engineers did not want and deemed unnecessary may have saved the day.

Not wanting to be left behind in the post-WWII nuclear arms race, Britain hurriedly built a nuclear processing facility known as Windscale. Rather than water-cool the reactor, the graphite cores were air cooled. Air was drawn in by large fans, passed through channels in the reactor core, and then exhaust out a large chimney called a “Pile”. Two reactors were built, Pile 1 and Pile 2.

Late in construction, eminent British nuclear physicist Sir John Cockroft insisted filters be added to the top of the piles. Engineers tried to avoid changing the design after the piles had been constructed, but when you are on the line for a Nobel Prize, you can get your way. The filters, in fact, served no operational purpose during normal operations.

Britain, in a “keeping up with the Jones'” mode, switched the reactors from producing enriched plutonium to producing tritium after the US built and tested a tritium bomb. Rather than build a new plant for tritium production, they repurposed the Windscale plant. The problem is that the tritium production required higher temperatures than the plutonium production.

The graphite core was designed for even heating at the original energy level. When it was decided to increase the energy (heat) level in the reactor, the core began developing hot spots and uneven heating. After a test run, it was determined that the affect was minimal and they could start production.

The problem was the temperature sensors the engineers were reading weren’t necessarily in the hottest parts of the core.

On October 7, 1957, operators began an annealing cycle for the core. The process involved turning the cooling fans to lower power and running the core at a low power to develop enough heat to anneal the graphite core. Once the annealing process began, the control rods were lowered back into the core to control the reaction. The expected energy release did not appear to be spreading through the core properly, so the beginning steps were repeated.

What the operators and engineers didn’t realize that some parts of the core were dangerously hot and the application of another nuclear heat process was not on the list of Good Things.

A fire started in the core, but the instrumentation only showed a gentle increase in temperature. This gentle increase in temperature was expected and nothing seemed to be out of the normal. Early on October 10, engineers noticed that instead of peaking and gradually cooling, the reactor temperatures continued to climb. In order to try to cool the reactor, the fans were switched back to a higher speed. This just fed oxygen to the fire and helped it to spread. It also lifted radioactive material up the chimney and into the filters.

An inspection plug was opened and engineers saw their worst nightmare: fuel channels were glowing bright cherry red. They were definitely in the realm of Not Good.

In a panic, the operators switched the fans to full speed. Of course, this just made things worse. Then they tried using carbon dioxide that had been delivered for another reactor on site. They couldn’t, however, get enough CO2 to the reactor to be useful. Instead, the extreme heat stripped the oxygen from the CO2 that did make it to the reactor and further fueled the fire.

They then tried pouring water on the now blazing fire. The mode was one of desperation as measured temperatures now were dangerously high. The risk of pouring water on the fire was that the metals would oxidize and release hydrogen gas from the H2O and cause an explosion.

The water did nothing.

Finally, the reactor manager ordered everyone out but himself and the fire chief. He went to look through an inspection panel and decided to stop feeding the fire with the fans. After shutting them off he witnessed the fire starting to die down. The next time he went to have a look he couldn’t open the inspection panel. He believed, correctly this time, that the fire was sucking air in from everywhere it could to try and maintain itself. This caused a slight vacuum in the reactor chamber. It would have meant that the fire was trying to draw air in from the pile, but the filters would have restricted that flow.

Water continued to pour down for a further two days until it was verified the fire was out and the reactor was cooling down. The reactor was sealed. Pile 2 was considered too dangerous for use and shut down. No other air-cooled reactors have been built since.

As with any new technology, operators and engineers sometimes have to improvise when things don’t go quite right. Sure, in hind sight turning the fans on seems like a silly thing to do, but at the time it probably seemed the most reasonable. In the absence of experts, mistakes are made. Luckily, in this case, the mistake only resulted in a small release of radioactive material.

[Image Credit: Chris Eaton]

  • cruisintime

    One Century ago we lived on a fairly pristine Planet.
    We have poisoned our planet, radioactive waste, oceans filled with garbage.
    Fracking and drilling until all the Water is poison.
    But we have really big yachts and fancy cars.

    • PowerTryp

      And as technology progresses so too our ability.
      We will be able to clean our Water and someday harvest it from asteroids.
      Clean energy is available and becoming cheaper
      But hypocrites will complain (Constantly) using the products made with the materials they rail against.

      • cruisintime

        If you believe that load I feel sorry for you.

        • PowerTryp

          With a pessimistic outlook like that you would feel sorry.

          • cruisintime

            The word you were searching for was "Realistic".

          • Well, that's just Tandy.

          • cruisintime

            No Shack!

    • jeepjeff

      We have been cutting down and burning forests to make way for agriculture since before recorded history. England, the Middle East and Easter Island are but three quick, off the top of my head examples of places where human deforestation and worse happened before modern times. In the latter two cases, there were large associated ecosystem collapses. There may have been some climate effects in there, but we did not help.

      Radiation is a part of the natural world. Maybe we have done some pretty bad damage over the years, but you should look into what has become the Chernobyl Wildlife Preserve. PBS' Nature has a couple of good documentaries on it. Our toxic radioactive pollution might not be as bad as our CO2 emissions. (I'm more worried about global climate change than the long-term effects of Fukushima.)

      Pre-industrial cities were sanitation nightmares. Going back to pre-modern sewage systems with current population levels would cause algae blooms that make the current ones look like a non-issue. We'd see a return of old enemies like Cholera.

      As technology has marched forward, we've discovered new problematic things, but we've also learned to clean up after ourselves. We know more about ecosystem biology now than in the past, and we have some hope that we can save things. We do need to stop poisoning our planet, I am, at the end of the day, an environmentalist. But the way is forward. Backwards is a nightmare.

  • EdS

    Nice writeup!
    Let the nitpicking commence:
    I'm pretty sure a pile is the graphite core, not to be confused with a stack, which is a chimney.
    (You have an it's for its, and an affect for affect)

    • I was severely jet lagged when I wrote this.

    • You need a period after your own misspelling of effect.

  • highmileage_v1

    Slightly off topic but I've wondered if you could dispose of spent reactor fuel in a tectonic subduction zone. Lock the spent fuel in a matrix of some sort, drill into the plate, insert, and let nature take its course. Hmmm.

    • It's been considered and rejected. The motion is so slow that the waste would remain dangerously close to being exposed for at least tens of thousands of years, within a corrosive environment that is periodically subject to significant earthquakes and other hazards. It might be possible (although prohibitively expensive via current techniques) to drill deeply enough to avoid some of these issues, but a hole that deep could also be drilled in other equally promising areas far more easily than it could be at the bottom of the ocean, so at that point it would be needlessly wasteful to do the drilling and burial at a subduction zone.

  • monkey_tennis

    About 20 years ago I went to the Visitor Centre at the Sellafield plant. The ageing display materials had been produced in the early '80s when nuclar energy was probably at its most divisive and politically contentious (UK politics spanned from the Thatcherite, libertarian & privatising to the 'Atomkraft nein danke!"-stickered Greenpeace). The tone of the exhibition was an unbounded and slightly creepy enthusiasm about the wonders of atomic power; without any acknowledgement of the problems faced — what to do with all of the waste, how to stop Sellafield itself regularly spilling radioactively polluted cooling water into the Irish sea, etc..

    I wandered around the exhibition bored and jaded, but smiled wryly when one of the commentaries referred to Sellafield as being built on the site of "the famous Windscale reactor".

    "Why was Windscale famous?" was the question that was left hanging in the air…

    Ah yes; that would be because of the 'Windscale Disaster' wouldn't it!

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