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BNFL plant at Sellafield

  1. Hi
    The BNFL plant at Sellafield in the UK is reported to have ‘lost’ 30kg of plutonium in the reprocessing nuclear fuel. It is reported as a paper loss due to the limits of accurate measurement within the process. Due to the lack of information in the news reports I am left a little confused. Are they saying then had x kg ± y kg at the start of the process now they have x-30 kg where 30kg is within the boundaries of the margin of error. Or is the 30Kg more then one expect to have to account for given the problems of measurement in the process

    Kieron
     
  2. jcsd
  3. brewnog

    brewnog 2,793
    Science Advisor
    Gold Member

    Depending on which newspaper you read, between 30 and 80kg was unaccounted for. Officially, it hasn't been lost or stolen, but apparently fuel can occasionally get misplaced during handling routines (!), and the 'paper loss' claim was also used. Apparently at various stages in the process, the amount of plutonium has to be calculated rather than measured, and this has also been reported as a cause of the error.

    This 'misplaced' plutonium has been reported more than once (in 2001 5.6kg was unaccounted for, in 1999 24.9kg), and these amounts are totals for the entire year and not just overnight. Newspapers and action groups argue "how can BNFL say that it hasn't been stolen?", a question which is easily answered merely by looking at the amount of security around Sellafield.

    Morbius?
     
  4. Astronuc

    Staff: Mentor

    Here is some background on Sellafield.

    http://www.bellona.no/en/energy/nuclear/sellafield/wp_5-2001/21736.html

    The question is how many tonnes of spent fuel has been reprocessed. Then how much of that was Pu. In 1 metric ton (1000 kg of spent fuel) there might be 10 to 30 kg Pu. If several hundred (or thousands) of metric tons of spent fuel was reprocessed, it is conceivable that an uncertainty of 30 kg's of Pu might accumulate through a combination of book-keeping errors and simple loss into the waste stream a few grams at a time.

    Records keeping between 1950 and up to the end of the 1970's was largely paper, which was then transferred to computer (perhaps). The was before the digital age of PCs and large networks.
     
  5. Morbius

    Morbius 1,160
    Science Advisor

    Kieron,

    Given that the BNFL plant at Sellafield has reprocessed many, many
    TONS of spent nuclear fuel - 30 Kg is not a lot. One full core load for
    a single reactor is about 100 tons. So each full core load has about
    2 tons of plutonium.

    Sellafield has reprocessed many, many full core equivalents of spent
    nuclear fuel over the few decades that it has been in operation.
    I would tend to think 30 Kg/yr is well within the margin of error.

    In fact, I would have expected an even larger number than 30 Kg. If it's
    that low - they must be doing a very good job.

    Dr. Gregory Greenman
    Physicist
     
    Last edited: Feb 17, 2005
  6. Morbius

    Morbius 1,160
    Science Advisor

    brewnog,

    You've summarized it pretty well.

    One has to remember that when you "assay" the material - to find out
    how much you have - you weigh it. Put a sample of plutonium on your
    scale and the scale tells you it weighs 2.5 Kilograms. However, that
    sample may really weigh 2.5000001 Kilograms. The scale isn't showing
    you that 0.1 milligram overage - it's not 100% accurate. So you just
    "lost" 0.1 milligram of plutonium.

    It's not really lost - your scale just didn't report it properly. There are
    only so many digits on the display. Or when you wrote it in the books,
    you rounded the number off to 2.500 Kg.

    That's how you can "lose" 0.1 milligrams. Now do that over and over
    again, day in and day out for a year - multiplied by many people doing
    the measuring - and you can well lose 30 Kg "on paper".

    However, the plant has a lots of security because it handles plutonium.
    All the operations with plutonium are done in "hot cells", or "caves" or
    "glove boxes". Even though your balance makes a small error - that
    plutonium hasn't gotten out of the "hot cell" or "glove box". It's still
    there - you just lost track of it on paper.

    So it's doubtful that anyone has smuggled that material out of the
    plant - the 30 Kg is just the accumulation of all the uncertainties.

    Dr. Gregory Greenman
    Physicist
     
  7. brewnog

    brewnog 2,793
    Science Advisor
    Gold Member

    Judging by the strict controls they have there (and after Sept 11th I noticed they got a *lot* stricter) there's no way that someone could have stolen anything at all from Sellafield, without them noticing.
     
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