Yucca Mountain – Packaging and Storing Radioactive Waste

t1larg.casks.nrcSo – thus far we’ve gone over a little of the history of the Yucca Mountain project and how both geology and hydrogeology can affect waste disposal. What I thought could be interesting today would be to talk a little about how the spent reactor fuel is packaged – both for transport and for disposal – because this is a third factor that has a profound impact on how well the waste can be isolated from the environment. Then, for the last installment in this series (next week) I’ll try to examine some of the claims both for and against the site to see how well they hold up.

To recap a little bit – fissioning a uranium atom splits it into 2 radioactive fission products. These accumulate as the reactor operates – adding more radioactivity as time goes on. As the reactor operates, though, the fuel “burns” up the uranium – after a few years the concentration of fissionable atoms drops to the point where it’s time to swap out the spent fuel rods for new ones. The spent rods are intensely radioactive so they’re normally stashed in spent fuel pools until they can cool off a bit – and in this case, “cooling off” means thermally as well as radiologically since the energy given off by the decaying fission products causes the spent fuel to heat up. But after a long enough time the fuel will cool off to the point at which it can be removed from the water and placed into huge casks that are placed in storage yards at the reactor sites – this is called dry cask storage.

At some point – if Yucca Mountain or some other high-level waste repository opens up – either the dry casks will be used for transport or the spent fuel will be transferred to transport casks that will be loaded onto rail cars or trucks and relocated to their final resting place. It’s these casks that will also be the penultimate barrier between the radioactivity within and the environment so they warrant a description.

First of all the things are huge. I saw some in Lithuania about a decade ago and they looked to be at least 10 feet tall and 5 feet in diameter. And since the physics of uranium fission are the same around the world (reactor design changes somewhat from place to place, but not enough to make a huge difference for commercial reactors) the characteristics of spent reactor fuel are reasonably similar as are the characteristics of the casks. In other words, the spent fuel casks in the US are huge as well.

In addition to providing protection to the spent fuel they are also designed to reduce radiation dose rates to an acceptable level – low enough to pose no risk to those sharing the road with the casks if they are transported by truck. But there’s a lot more to safely shipping waste than keeping rad levels down – the spent fuel casks must also be able to protect the waste while it’s in transit to the final disposal site, not to mention protecting it during its long millennia in storage. We’ll tackle these one at a time.

Spent fuel casks have to meet some stringent requirements to ensure that they don’t release highly radioactive fission products while they’re in transit to the final disposal site. Casks must be able to pass these tests without suffering a failure:

  • A 9-meter (30 foot) fall onto a hard surface
  • Puncture test where the container falls 1 meter onto a 6” steel rod
  • 30 minutes of being engulfed in an 800 degree C (1475 degree F) fire
  • 8 hours of immersion beneath 3 feet of water
  • 1 hour of immersion beneath 200 meters (655 feet) of water

These requirements are more than theoretical – in the 1970s Sandia National Laboratories tested some spent fuel containers with full-scale crashes to confirm that what looked good on paper and in the laboratory would work in real life. The most dramatic test was running a locomotive engine into a flatbed truck carrying a cask on it – the locomotive was pretty much destroyed while the cask, while damaged, survived and would not have leaked radioactivity into the environment. There’s a nice video on YouTube showing the locomotive test and others – these videos alone ought to allay any doubts about the ability of these casks to protect spent fuel while it’s en route to the disposal site.

Physical ruggedness is nice, but there’s more to keeping radioactive waste safe than protecting it from collisions – once delivered to the site the casks have to help keep the waste isolated from the environment for up to a million years and that takes a lot more than strength. Rust and corrosion will attack the strongest container – all they need are the right conditions and enough time to work. Not only that, but metals behave differently (and chemical reactions proceed more quickly) at higher temperatures – such as those produced by the decay of fission products. So the thermal effects also have to be factored in when designing the things.

So here’s the bad news about long-term disposal of spent reactor fuel – and the containers meant to hold it. Nobody knows how a container is going to hold up over even 100,000 years, let alone a million years (the time span required by EPA). We can do our best to design something with the lowest possible corrosion rate and we can do our best to design in a high level of structural strength – but no matter how we try to artificially age these materials in the lab we can only guess at their long-term performance. Let’s face it – all of human history is only about 5000 years and the Pyramids are younger than that. We can assert the longevity of our designed structures all we want, but we have no direct experience with anything so long-lived. Of course we can put other barriers in place as well – and likely will – but anything artificial suffers the same drawback, that all of human history is far shorter than the period of time for which we’re hoping to isolate the waste.

On the other hand, the engineered packages aren’t the only barrier between the radioactive waste and the environment – and we actually do have one data point about the ability of rock to hold radioactive waste for prolonged periods of time. In fact, what we have is the remnants of a natural nuclear reactor that achieved criticality in what is now the nation of Gabon (in Western Africa) about two billion years ago. The details of how the reactor (called the Oklo reactor) formed and operated are fascinating, but there’s not enough room in this posting to go into the details. For the purposes of this, let it suffice to say that in two billion years, virtually all of the fission products have remained in place. This is in spite of the reactor zone being located in fractured and porous sandstone that was below the water table more often than not – in fact, if the reactor zone were not completely saturated with water the reactor could never have operated. So – remembering the last two posts – porous and water-saturated rock are not well-suited for waste disposal. But in spite of this, the fission products have remained in place for two billion years. This bodes well for the ability of Yucca Mountain (or whatever location ends up with the spent fuel repository) to safely isolate the waste until it decays to stability.

So here’s the bottom line with regards to the waste containers. First, they certainly seem capable of safely storing spent reactor fuel for the length of time that they’re stored at the reactor plants and multiple tests have shown they can protect the waste while it’s en route to wherever it will be disposed of. But no matter how well we design the containers – no matter how convincing our computer models and calculations might be, there’s no guarantee that they’ll last the million years that is the current standard for the waste site. But that doesn’t mean that Yucca Mountain is incapable of storing radioactive waste safely for that length of time – the natural nuclear reactor in Oklo shows that even radioactive waste that’s stored in porous and water-saturated sandstone can remain in place for the eons. This bodes well for the Yucca Mountain site’s ability to retain our radioactive waste for a paltry million years or so.

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4 Responses to “Yucca Mountain – Packaging and Storing Radioactive Waste”

  1. Mark September 16, 2013 at 7:54 AM #

    They recently did another test of the casks where they shot a missile at it:

    http://www.youtube.com/watch?v=jBp1FNceTTA

    You can’t see much in the video, but it’s pretty cool. It’s supposed to simulate an airplane crashing into one of these things.

    Regarding the longevity of the waste, any chance of a post on fast breeders as an option for disposal of the transuranics? They have their problems, I know – and they obviously still leave the fission products. But they seem like an option worth considering.

  2. J. Boling September 16, 2013 at 9:00 PM #

    “[T]he million years that is the current standard,” assumes there is no advancement in technological means of rendering this material less hazardous, or even benign. Given the 5000 year history of man’s development, from throwing rocks at one another to the ability to throw mega-tons, I think it’s safe to say that well before the million-year horizon, alternatives will be available. Yucca Mountain, or any other site, only has to suffice until that day.

    • Mark September 23, 2013 at 6:42 AM #

      Alternatives are available now, they just don’t work very well yet. The vast majority of the waste lasting more than 300 years is transuranics produced by neutron absorption in U-238. A fast breeder reactor can burn those off entirely, leaving only the fission products – and is also about 100x as fuel efficient as a conventional reactor, which is another nice feature. This isn’t future technology, the US built a prototype in the 50s. Unfortunately, the units built so far have all been too expensive to be competitive, and many have had safety issues. (Also, they can crank out gobs and gobs of plutonium, which some see as a downside (note: humorous understatement). It’s reactor-grade rather than weapons-grade, though, so it’s entirely unclear to me how useful it would be to building a weapon.)

      There are a couple of groups claiming to have designs that solve the cost and safety problems – most notably the advocates of the Integral Fast Reactor – but there hasn’t been any money to build prototypes in the US since the 80s. But, as far as I can tell – and I am not an expert on these matters – there doesn’t seem to be any reason intrinsic to the idea why a fast reactor couldn’t be safe and cost-effective, and both the Chinese and the Russians are going ahead with their own experimental models. I’ll be very curious to see how those work out for them.

  3. Mark J Carter September 19, 2013 at 11:00 PM #

    How Do We Meet the Challenge of Spent Nuclear Fuel and High Level Waste?: by Mark J. Carter

    As of December 2011 more than 67,000 metric tons of Spent Nuclear Fuel (SNF) was in temporary storage within the United States. This SNF is stored onsite at both operating and decommissioned plants. This is expected to increase at a rate of about 2,000 metric tons per year. (1)

    The initial Nuclear Waste Policy Act (NWPA) was passed in 1982 and was amended in 2008.

    The 1982 NWPA established the intent and method of funding for the Yucca Mountain Nuclear Waste Repository which was never opened. (1,2)

    Under the initial Nuclear Waste Policy Act of 1982 the Nuclear Power Plant Operators pay 1 tenth of one cent into The Nuclear Waste Fund for each kilowatt hour of energy sold.(3) In return the US taxpayer, through their agent, the Department of Energy, takes financial and physical responsibility for the security, transportation, processing, and storage of all SNF and all High Level Waste (HLW) related to commercial operations. (4) This includes plant infrastructure that meets the definition of High Level Waste at the end of plant life cycle. (5)

    Although the 1982 law allowed the government to review the adequacy of the one mil per KWH payments into the Nuclear Waste Fund; the “NWPA Amendment Act 2008” forbids raising these fees above one mil per KWH. (6)

    The “NWPA Amendment Act of 2008” also eliminates consideration of environmental impact of onsite storage when it concerns the issuance, amendment, or renewal of a license to construct or operate a facility. In addition, it exempts the plants from state mandated clean air standards. (7)

    Under the contracts provided for by law, the US Tax Payer was to begin taking possession of SNF and HLW materials in 1998. Since the United States of America, as well as all other nations, has failed to develop permanent repositories for these wastes, the United States Tax Payers were forced to breach their contractual agreement to take possession of these materials. Since 1998 the Nuclear Power Plant operators have been suing the United States Taxpayer to recover the costs of storing the SNF and HLW. (4)

    A single Nuclear Power Plant Operator in Minnesota recently settled for 100 million dollars to cover the cost of storing SNF and HLW generated by two reactors. This settlement covered a 10 year period of storage with further litigation and settlements expected. This 100 million dollar judgment is a small percentage of what has already been paid, or is under appeal, regarding other Nuclear Plant Operations. (8)

    These judicatory awards are not paid out of the Nuclear Waste Fund; but out of the U.S. Treasury Judgment Fund. This Judgment “has no fiscal year limitations, and there is no need for the Congress to appropriate money to replenish it.” (9)

    As of July 31, 2012 the Nuclear Waste Fund balance was $49,474,000,000 which includes interest payments to the fund. (10)

    Is permanent onsite storage a better solution than centralized sites? If so, then could the Nuclear Waste Fund rather than the Judgment Fund be used to finance current storage?

    Would repealing the Nuclear Waste Policy Act, returning the funds with accrued interest, and requiring the industry to pay this very significant business cost encourage the industry to accelerate new technologies and processes promised by industry pundits?

    Would this result in a more economically efficient Nuclear Power Industry?

    Does the Nuclear Waste Policy Act give the Nuclear Energy Industry an unfair competitive advantage over other forms of energy production?

    Was the court ruling requiring settlement funding be made from the U.S. Treasury Judgment Fund instead of the Nuclear Waste Fund a fair and equitable ruling for the American Tax Payer?

    Would bringing the Nuclear Power Industry to a business competitive level of self support be in everyone’s long term interest?

    References:

    1. Congressional Reporting Service Report to Congress – U.S. Spent Nuclear Fuel Storage – May 24, 2012.
    2. Nuclear Waste Policy Act of 1982 – section 111 (b) (1)
    3. Nuclear Waste Policy Act of 1982 – section 302
    4. Congressional Budget Office Testimony – Statement of Kim Cawley Chief, Natural and Physical Resources Cost Estimate Unit – The Federal Governments Liabilities Under The Nuclear Waste Policy Act. October 4, 2007
    5. Amendment to NWPA 2008 – section 105 – 12 ( C )
    6. NWPA Amendment Act 2008 – section 204
    7. Amendment to NWPA 2008 – Section 104 (2) and Section 201
    8. Before The Minnesota Public Utilities Commission – Docket Number – E-002/M-11-807 – December 16, 2011 – Section II.
    9. Congressional Budget Office Testimony – Statement of Kim Cawley Chief, Natural and Physical Resources Cost Estimate Unit – The Federal Governments Liabilities Under The Nuclear Waste Policy Act. October 4, 2007 – Section – “The Judgment Fund.”
    10. U.S. Treasury Monthly Statement of Public Debt of The United States – July 31, 2012

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