This is the first look at what happens to uranium fuel during a nuclear meltdown

Dec 11, 2014

Image: Corium lavas. Credit: U.S. Department of Energy via ABC Science

By Fiona MacDonald

A team of researchers in the US has performed a world-first experiment that will help them work out how uranium dioxide fuel behaves in its molten state – something that generally only occurs at the start of a nuclear meltdown.

This is the first time scientists have managed to get an up-close view of what happens to the fuel as it heats up to more than 3,000 degrees Celsius. Their results have been published in Science, and will help researchers improve safety at nuclear power plants.

“In extreme events like Fukushima and Chernobyl, the uranium dioxide literally melts, and we wanted to study the material to really understand it,” the paper’s lead author Lawrie Skinner from Stony Brook University in New York told Stuart Gary from ABC Science.

“We can now pin down a little bit more accurately what the properties and temperature of the melt will be. Any sensible reactor design should take into account the real structure, physical properties, and behaviour of this melt.”

The reason it’s taken so long for scientists to study this phenomenon is that it’s extremely tough to find a furnace that can withstand heats of 3,000 degrees Celsius – most will begin to melt and react with the uranium at such a high temperature, which interferes with the results. (Well, that, and the fact that generally people want to be as far away from a nuclear reactor as possible.)


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6 comments on “This is the first look at what happens to uranium fuel during a nuclear meltdown

  • 1
    NearlyNakedApe says:

    This is the first time scientists have managed to get an up-close view of what happens to the fuel as it heats up to more than 3,000 degrees Celsius. Their results have been published in Science, and will help researchers improve safety at nuclear power plants.

    I don’t understand how this constitutes “research”. What happens to the Uranium fuel as it heats up to more than 3000 deg. C ?…

    It melts!! That’s what happens. And we already know why it melts: the water coolant in the reactor core evaporates and if the core cannot be refilled fast enough with water (power failure, damaged pumps, etc.) the fuel rods get so hot that they start melting and eventually punch a hole in the reactor vessel.

    Not exactly rocket science here.

    In order to make nuclear reactors safer, we have to go back to the drawing board and stop using inefficient, wasteful and badly obsolete 1950’s technology nuclear reactors. How about spending time and energy on designing and building LFTR reactors instead and make the laws of physics work for you instead of always having to keep them in check to prevent a meltdown. Kirk Sorensen has described these problems in detail:

    1- Using water as a coolant is a bad idea to begin with. The boiling point is too low. Using molten salt even if we keep using the same fuel is already an order of magnitude safer.

    2- Uranium oxide fuel rods contain less than 1% of actual fuel. They have to be replaced every 18 months and the fission of uranium 235 produce tons of transuranic toxic waste that will remain radioactive for up to 10,000 years.

    Instead of trying to study “how uranium dioxide fuel behaves in its molten state”, why don’t we eliminate solid fuel rods altogether and prevent the problem from occurring in the first place by using a liquid Uranium 233 fluoride fuel (bred from Thorium 232) mixed with the lithium fluoride coolant. If the fuel/coolant mixture gets too hot, the solid salt plug at the base of the reactor core melts and the liquid fuel is drained into a cooling tank designed to dissipate heat quickly.



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  • LFTR = Liquid Flouride Thorium Reactor, a type of breeder reactor.

    http://en.wikipedia.org/wiki/Liquid_fluoride_thorium_reactor

    Two of the problems I don’t normally see addressed with nuclear power are:

    nuclear fuels in general are not exactly abundant. That is not a sustainable solution.
    it takes so much conventional fossil fuel energy to extract and process it.

    Another general problem is you have so much quite old nuclear technology still in service. The economics don’t let you keep everything up to date with the latest controls.

    Then there is a working giant fusion reactor, complete with fuel, sufficient for all
    energy needs for the foreseeable future, located safely distant from the earth. It
    beams its energy to earth mostly in the safe 580 nanometer band. We call it the sun.

    Surely that is the long-range solution. Even small scale space collection would provide so much energy it would interfere with climate.

    I think it is discounted because of the difficulty negotiating exclusive resource rights. It is too free.



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  • Roedy Dec 12, 2014 at 4:29 am

    LFTR = Liquid Flouride Thorium Reactor, a type of breeder reactor.

    Two of the problems I don’t normally see addressed with nuclear power are:

    nuclear fuels in general are not exactly abundant. That is not a sustainable solution.
    it takes so much conventional fossil fuel energy to extract and process it.

    There is a lot of info. on thorium here:-

    http://www.itheo.org/thorium-energy-conference-2012

    The Chinese initiated action to find viable energy sources significant enough to wean the country off its dependence on carbon-based energy. The large amounts of Thorium being produced as a by-product of its rare earth mining operations, is a further incentive. ThEC12 was partnered by the Shanghai Institute of Applied Physics (SINAP) – a senior academic institution of the Chinese Academy of Science (CAS), which has been given specific responsibility for the Thorium Energy utilization programme in China.



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  • I don’t understand how this constitutes “research”. What happens to the Uranium fuel as it heats up to more than 3000 deg. C ?… It melts!! That’s what happens.

    I don’t think this attitude is particularly beneficial, if you don’t mind me saying so. In the source post, on Science Alert, there are some interesting clues about what they actually observed -they didn’t just take nice pictures.

    Furthermore, we do have this kind of reactors around the world: knowing more details about the going-badly-wrong process is for sure something worthy, since you can’t send those old reactors into high orbit at the push of a button and, as you said, there are objects which use old technology, which for sure augments the probability of them going-badly-wrong.

    2- Uranium oxide fuel rods contain less than 1% of actual fuel. They have to be replaced every 18 months and the fission of uranium 235 produce tons of transuranic toxic waste that will remain radioactive for up to 10,000 years.

    This statement looks, to me, riddled with faults. And, actually, the information I have been gathering lately seems to agree with me.

    Fuel rods usually have an higher content in 235U, to make things easier. You range from 3-5% for commercial reactors to 10-20% for research reactors. Oh you can produce vastly more enriched Uranium, but you usually need it to make bombs. And you don’t want your reactor to turn into a bomb.

    What exactly do you mean by “transuranic waste”? Is it an institutionalized misnomer or are you trying to refer to the breeding of 239Pu from 238U in reactors? Because in nuclear fission what you get are lighter elements. Here you can find a list of what fission yelds, and in what percentage. Of course it’s radioactive and dangerous, but I wouldn’t call it neither “toxic” nor “transuranic”.

    How about spending time and energy on designing and building LFTR reactors instead

    I read about it and it’s an interesting technoloy -more elegant than the classical, solid fueled reactor. But a much as I love the physics underlying nuclear fission, I doubt it can be a viable, long term alternative. If I’d prefer to see efforts around nuclear fusion increased, actually. But that doesn’t mean to stpo researching metdowns: the more we know, the better, since the world is peppered with reactors that can go wrong in that way and, as I said earlier, we cannot eject them into outer space at the first sign of troubles.



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  • Lorenzo Dec 13, 2014 at 6:00 am

    How about spending time and energy on designing and building LFTR reactors instead

    I read about it and it’s an interesting technoloy -more elegant than the classical, solid fueled reactor. But a much as I love the physics underlying nuclear fission, I doubt it can be a viable, long term alternative.

    It could be viable for many decades while we sort out other carbon replacement systems including fusion. Interestingly, LFTR reactors can in addition to burning thorium, be used to burn up other nuclear waste.

    If I’d prefer to see efforts around nuclear fusion increased, actually.

    Indeed so! .. . .But while this is developed, LFTR reactors could work alongside renewables to get the CO2 emissions down.



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  • 6
    NearlyNakedApe says:

    @ Lorenzo:

    Re: What happens to the Uranium fuel as it heats up to more than 3000 deg. C ?… It melts!! That’s what happens.

    I don’t think this attitude is particularly beneficial, if you don’t mind me saying so. In the source post, on Science Alert, there are some interesting clues about what they actually observed -they didn’t just take nice pictures.

    Ok so I was being sarcastic about it. Sorry about that. I guess you can chalk it up to my impatience and anger with the people who built and run these monsters in such an irresponsible way. Their legacy to this world are the nuclear disasters of Chernobyl (the worst ever IMO) and Fukushima (a close second). People died and suffered in the worst imaginable way and that makes me upset.

    So when somebody tells me we need to spend valuable resources to study how the fuel rods melt in reactors that are inherently flawed, it tends to strike a bad chord with me. I just think that spending money and time on how to avoid meltdowns in the first place would be far more useful.

    And the best way to do that is to scrap this hopelessly flawed reactor design and go back to the drawing board (like any competent, responsible engineer would do) and resume the very promising research on molten salt reactors that was canned at Oak Ridge in the late sixties (because of politics courtesy of the infamous Tricky Dick). That’s where we need to focus our resources (at least for now, more on this below).

    Re: Uranium oxide fuel rods contain less than 1% of actual fuel.

    Fuel rods usually have an higher content in 235U, to make things easier. You range from 3-5% for commercial reactors to 10-20% for research reactors.

    You’re right. Worse part is I already knew this but somehow got my facts mixed up. It’s the uranium ore that yields uranium which contains about 0.7% U235 and 98.3% U238, not the fuel rods. Guess I should never post late at night with a few beers under my belt…

    They (fuel rods) have to be replaced every 18 months

    This I’m sure of though. Thorium based nuclear fuel could burn for years without needing to be replenished.

    Re: the fission of uranium 235 produce tons of transuranic toxic waste that will remain radioactive for up to 10,000 years.

    What exactly do you mean by “transuranic waste”? Is it an institutionalized misnomer or are you trying to refer to the breeding of 239Pu from 238U in reactors? Because in nuclear fission what you get are lighter elements. Of course it’s radioactive and dangerous, but I wouldn’t call it neither “toxic” nor “transuranic”.

    Ok, since I am not Deepak Chopra I hitherto promise to never use technical jargon with which I am not 100% familiar ever again. BUT….. The essence of what I said is what really matters and that is, I believe, correct. Radioactive waste from conventional enriched uranium reactors can remain radioactive for up to 10,000 years. And they can contaminate the water, soil and crops which would then become toxic.

    The fission products of Thorium bred U233 can be recycled for the most part (83% I think, not sure) and the remainder is a small amount of waste that can decay in about 100 years. Now of course, I WOULD prefer no waste at all but if it comes down to a choice between lots of waste for 10,000 years and a little waste for 100 years, I’ll choose the latter thank you very much.

    Oh and like Alan mentioned, thorium reactors could be used to recycle decades worth of fission by-products from those water cooled monsters. In my book, that’s a win-win situation.

    If I’d prefer to see efforts around nuclear fusion increased, actually.

    Me too. Fusion is the perfect solution. But a self-sustained fusion reaction is sooooo much harder to attain than fission that it’s likely to require hundreds of billions in research and be decades away. I’m afraid it may come too late to make a difference. Right now, our most urgent priority is to eliminate coal plants and find a way to produce carbon-free electricity cheaply. The technology for LFTR is already here and could be working within a few years. China BTW is lining up its crosshairs on LFTR technology.

    Another incentive: the future of motor vehicles belongs to hydrogen fuel cell technology but the main obstacle is that producing hydrogen requires electrical energy. If that energy comes from a coal plant then it’s not clean energy at all. It kind of defeats the whole idea behind hydrogen. If it comes from a thorium plant, then it is carbon free. Thorium power plants could be a major factor in drastically reducing the amount of CO and CO2 we pour into the atmosphere in the decades to come.

    But that doesn’t mean to stop researching meltdowns: the more we know, the better, since the world is peppered with reactors that can go wrong in that way and, as I said earlier, we cannot eject them into outer space at the first sign of troubles.

    I agree. We are stuck with those monsters but what if we found a way to convert (at least partially) those power plants to thorium based plants? After all, the electrical infrastructure is already in place and that would be a major logistical and economical advantage wouldn’t it?

    Anyway, sorry for the long post but these issues are important and deserve that we spend time discussing them. Thank you for your time Lorenzo.



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