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Testing Spent Fuel Transport Casks Using Scale Models

Bernard White
Senior Project Manager
Division of Spent Fuel Storage and Transportation

Before casks can be used to transport the most radioactive cargo—including spent nuclear fuel—the NRC requires them to undergo a thorough safety evaluation. Casks are evaluated for their ability to withstand vibration, water spray, free fall, stacking, penetration and fire. A cask must be able to contain and shield the spent fuel and keep it in a safe configuration under both normal and accident conditions. Typically, spent fuel casks are certified through a combination of engineering analyses and scale model or component testing.

People often ask why the NRC allows designers to test scale models instead of requiring tests on full-sized casks. The bottom line is scale-model testing provides the necessary information for the NRC staff to know that a cask loaded with spent fuel can be transported safely, even in the event of an accident.

scalemodel2First, it is important to understand what information comes out of these tests. Test casks are fitted with sensors to measure acceleration. These accelerometers are similar to the ones used in smart phones, video game remotes and pedometers to respond to the movements of the user. Knowing the cask’s acceleration allows designers and the NRC to understand the forces different parts of the cask will experience in different types of impacts. The design engineer generally calculates these impact forces first by hand or by computer. Tests on a scale model can be used to check the accuracy of these analyses.

Engineers follow a similar process to safety-test airplanes, ships, bridges, buildings and other large structures. Scale-model testing is a proven and accepted practice across engineering disciplines, and may be one of the oldest engineering design tools. (Ancient Egyptian, Greek, and Roman builders are known to have built small models to assist in planning structures.) Today, models allow oversized structures to be examined in wind tunnels, under different weight loads and on shake tables to provide key inputs into design and safety reviews.

Cost savings is a factor, but not the most important one. The biggest reason for using scale models is practicality. Transport casks for spent nuclear fuel are typically in the 25-ton to 125-ton range. There are very few testing facilities in the world that can put a 125-ton cask through the required tests.

For example, during 30-foot drop test, the test cask must strike the surface in the position that would cause the most severe damage. Cask designers often perform several drops to ensure they identify the correct position. After the 30-foot drop, the cask is dropped 40 inches onto a cylindrical puncture bar, then placed in a fully-engulfing fire for 30 minutes. Casks are also immersed in water to ensure they don’t leak. Measurements from these tests are plugged into computer programs that analyze the cask structure in great detail.

This analysis can determine the stresses placed on cask closure bolts, canisters and baskets that hold the spent fuel in place, and the spent fuel assemblies themselves. Computer simulations can be run for different scenarios, providing maximum flexibility to designers in understanding how best to design different parts of a cask’s structure.

In addition, NRC regulations specify that in the 30-foot drop test, the cask must hit an “unyielding” surface. This means the cask itself, which may be fitted with “impact limiters,” has to absorb all the damage. The impact limiters work much like the bumper that protects a car in a collision. The target surface cannot dent, crack or break in any way. In a real-world accident, a 125-ton cask would damage any surface significantly. It requires considerably more engineering work to achieve an unyielding surface for a full-sized cask than for a scale model, with no measurable advantage. The rule-of-thumb for testing is the impact target should be 10 times the mass of the object that will strike it. So a 125-ton cask would need to hit a 1,250 ton surface. A 30-ton cask would only need a 300-ton target.

Scale models are easier to handle and can be used efficiently for many drop orientations to meet the multiple test requirements. If a test needs to be run again, it can be done much more easily with a scale model. Design changes are also more easily tested on models. Together with extensive analyses of a cask’s ability to meet our regulatory requirements, the information from these tests allows the NRC to decide whether a cask can safely transport the radioactive contents.

11 responses to “Testing Spent Fuel Transport Casks Using Scale Models

  1. Erica Gray June 30, 2015 at 9:44 am

    We still do not know how High Burnup fuel will be behave in storage or transport!
    This casks being used were NOT designed to hold high burnup fuel…read Dominions convincing statement to the NRC.
    As usual the NRC putting the cart before the horse!
    2003 ~ Currently, the TS for the North Anna ISFSI limit the fuel to be stored in the TN-32 to the following: initial enrichment of <=3.85% (wt U-235), assembly average burnup of <=40,000 MWD/MTU, and heat generation of <=0.847 Kw/assembly. This amendment requests the limits be amended as follows: initial enrichment of <=4.35% (wt U-235), assembly average burnup <=45,000 MWD/MTU, and heat generation of <=1.02 Kw/assembly.
    Need for the Proposed Action: The proposed action is necessary to allow continued storage of spent fuel in dry casks at the North Anna ISFSI. Without this amendment, North Anna will be unable to load spent fuel in TN-32 casks because the remaining spent fuel at the site has the higher enrichment and burnup. If unable to store spent fuel in TN-32 casks, North Anna will not be able to retain full core offload capability. North Anna would eventually have to find an alternate means to store fuel, or shut down.
    http://www.gpo.gov/fdsys/pkg/FR-2003-06-11/html/03-14683.htm

    and NOW Dominion has volunteered VA to become a test site for an experimental cask.

    All in the VA seismic zone, on an earthquake fault.

  2. zona nokia June 30, 2015 at 1:17 am

    Good very good

  3. Bob Tripathi June 22, 2015 at 7:06 am

    Bernie: nice summary of 10 CFR Part 71 requirements. Cheers👍

  4. NukePuke June 19, 2015 at 9:39 am

    If We Could Only Have Learned From Models of Nuclear Power Plants
    Interesting article about shipping casks for spent but still highly radioactive fuel. (BTW, is the word “casks” short for “caskets”?!) NRC, when might we expect to have a permanent High Level Waste (HLW) repository so we can actually use these “transportation” casks?
    Glad the NRC is using cask models to save us taxpayer’s money. How does this savings stack up against all the costs taxpayers and utility ratepayers are being assessed to store all this HLW at 94 sites all over the country? Let alone the potential costs to humanity if terrorists attack these vulnerable sites and cause a public Armageddon.
    If only nuclear power plant models were used in the earliest days of nuclear power. Such models may have given us valuable insights into just how deadly nuclear power could be. We then could have avoided the nuclear nightmare that has ensued.
    Come to think of it though “models” called nuclear research facilities and nuclear power plant prototypes were used in the early days. Sadly they were not used to carefully consider whether or not nuclear power was really the safe or wise thing to do. They were used only to figure out the best way to foist this new energy source on the public.
    Just take a look at all the nuclear accidents that have occurred in the United States involving just those nuclear “models”. There is a long list provided at: http://www.lutins.org/nukes.html
    The handwriting was on the wall a half-century ago: nuclear power technology is fraught with uncertainty and danger.
    But big business and big money trumped concerns for public safety.
    Full speed ahead, damn the torpedoes!

    • Frank June 19, 2015 at 5:09 pm

      Your anti nuke bias does not mean you should close your eyes to it. How many (civilian) nuclear accidents have we really had, and how many people died of nuclear radiation? Google how safe is your Kilowatt.
      In Fukushima we really had a worst of a kind case, not one melt down but three, and yet nobody was killed by radiation and nobody is likely to die from it. Chernobyl which was not really an accident of course stands out.
      It is people with your agenda that prevent the opening a permanent repository at Yucca mountain. It, like the NRC have been paid for by the electricity consumers at a rate of 0.1 cent per kWh and not the taxpayers.
      If terrorists attack the HLW containers at their scattered sites, and really cause a problem, blame Harry Reid. He and the rabid anti nukes are the cause that the material is not at a safe centralised facility, where it could be protected and guarded much easier.

      Moderator Note: Some verbiage removed to adhere to comment guidelines.

      • Erica Gray June 30, 2015 at 9:32 am

        Frank, you obviously don’t realize the situation.
        Yucca is not suitable and even if it had been….it would already be full.
        It’s already been stated we would need several deep geological sites, but since that’s not going to happen any time soon..the NRC is going to allow interim/temporary storage.
        Hence the reason for all this talk about transportation.
        Shipping high level nuclear waste around the country to temporary sites is ridiculous and NOT a solution.
        The solution starts with the discontinued production of this dangerous waste in the first place!
        http://www.energy.senate.gov/public/index.cfm/hearings-and-business-meetings?ID=ad6d1de1-c2e9-41a5-aef8-2238bee5162c

    • Engineer-Poet June 21, 2015 at 5:32 pm

      Witness this:

      (BTW, is the word “casks” short for “caskets”?!)

      As I said, fear-mongering, trying to create an association with death.  Almost any native English speaker knows that there is nothing in common between cask (a container made and shaped like a barrel) and casket (a. a coffin; b. a small chest or box) and hasn’t been since the back-formation almost 600 years ago.

      Let alone the potential costs to humanity if terrorists attack these vulnerable sites and cause a public Armageddon.

      The stationary storage casks are even more heavily-built than transport casks, and transport casks can withstand impact from a speeding locomotive at 80 MPH.  You would have to be paranoid to believe that terrorists could come up with anything remotely as damaging, and a shameless fear-monger to try to make the public believe there’s any possible danger.

      If only nuclear power plant models were used in the earliest days of nuclear power. Such models may have given us valuable insights into just how deadly nuclear power could be. We then could have avoided the nuclear nightmare that has ensued.

      If only the public had been educated in the earliest days of nuclear energy.  Such education could have immunized the public against the fear-mongering still pushed by the anti-nuclear (and implicitly pro-fossil) forces to this day.  The formation of the NRC might have been done differently or avoided completely, nuclear power could have continued to be cheaper than coal, and millions of people whose lives were cut short by fossil-fuel extraction, transport and combustion would have enjoyed better life and health.

      But big business and big money trumped concerns for public safety.

      Yes, that is exactly what the coal and gas industries have managed to do, by sidelining nuclear power for several decades.  Nuclear power is far safer than what’s kept the grid going in the mean time, even 4x safer than wind.

      Just take a look at all the nuclear accidents that have occurred in the United States involving just those nuclear “models”. There is a long list provided at: http://www.lutins.org/nukes.html

      And there have been exactly zero radiation-related fatalities at commercial nuclear power plants in all that time (the 1961 SL-1 incident was an experimental military reactor, the Peabody accident involved highly-enriched uranium not even produced for commercial nuclear power plants).  Everything else on the list is either non-nuclear (and would be considered not newsworthy if it occurred at a fossil-fired plant) or harmed nothing and no one.  In other words, it is ALL fear-mongering.

      The handwriting was on the wall a half-century ago: nuclear power technology is fraught with uncertainty and danger.

      I have learned that the “true believers” and those who simply post for pay have no shame.

      Moderator Note: Some verbiage removed to adhere to blog comment guidelines.

  5. CaptD June 18, 2015 at 8:40 pm

    More on long term low cost ☢ storage first suggested in 2012

    I’ve suggested that the NRC offer a Million Dollar Prize for the best way to “solve” the nuclear waste storage problem” for the next 50 years, so please consider this idea as my “low cost” solution to America’s “long term” radioactive waste storage problem:

    Make use of our Military Testing Bases and or our MOA’s (Military Operation Area’s) out west, which are really huge tracts of land (think tens of thousands of acres) used ONLY by the military and already secured by them 24/7!

    Placing these very large (heavy) concrete casks in a poke-a-dot pattern will allow for at least 50 to 100 years of storage, safe from everything except a War, (in which case every reactor is just as vulnerable) and then revisit the storage problem then; at which time, probably a future solution will allow for an even better, lower cost “final solution”…

    Because these casks would be very large and all look alike nobody would know what was in any one of them, which would be yet another level of security for the casks containing even higher levels of nuclear waste! An ideal outside coating for these casks would be similar to the spray-on “bed liner” used for pickup trucks that not only prevents rusting and or damage for the life of the vehicle but would also seal the casks to prevent leakage of any kind!

    Hopefully these casts would be similar in size to a large shipping container so that existing material handling equipment could be used to load, unload and or move them about without “inventing” a mega hauler vehicle. By keeping the “footprint” of these casks similar to a large 40 foot container, the stacking and or placement of them might also be semi or fully automated which would not only save money but again keep the exact location of any specific cask secret! The monitoring of these casks 24/7/365 could even be done via satellite since these casks are similar in size to rocket launchers which are easily seen from space.

    In another 50 to 100 years, storage technology will be such that, yet another lower cost solution for all this waste will be found, and then it can be considered verses continuing to using the above storage plan… Perhaps sometime In the future, a safe low cost solution like lifting it all into space via a space elevator* and then shoving it in an orbit that will send it into the SUN for final recycling will present itself…

    BTW: Area 51 (which now officially finally exists) contains huge tracts of land that has already been used as a nuclear testing site (which is now still contaminated and is now off limits to all but a few forever) so it would allow all this material to effectively disappear into an already highly remote and ultra secure site…

    * The Space Elevator Project is something that the NRC should help fund ASAP, because it represents the best way to actually “recycle” ☢ by eliminating the storage of nuclear waste on Earth!

    • Frank June 19, 2015 at 5:12 pm

      Place it at Yucca mountain, an already contaminated test site, and leave it there until you either decide to use it in a different type of reactor or forget it for a couple of million years.

  6. CaptD June 18, 2015 at 8:33 pm

    Model testing cannot duplicate actual long term testing since what happens in a test chamber does not really indicate what will happen in real life, things like design flaws, manufacturing flaws and other “mistakes” only become know with time, not models.

    Since these casks will become highly radioactive, if they start leaking ☢ it will become a very BIG deal!

    Why not instead aim for a cask system that is designed to last say 50 years then be inserted into yet another larger cask thereby encasing the entire original cask in a new cask that is good for yet another 50 years or longer as determined by actual real life testing?
    +
    Surprise: High Burnup fuel delays decommissioning & raises cost!
    Containing the Edison and Mitsubishi Heavy Nuclear Energy Dispute Proves Problematic https://shar.es/12P746 #NukeFreeCal

    The NRC said the “high burnup” fuel which has been used at San Onofre (a surprise to almost everyone) and the problems it causes in decommissioning:

    Much longer periods to “cool down” before caste storage is possible.

    Different castes required for high burnup fuel.

    Incomplete NRC/DOE testing on length of time that the caste will survive storing high burnup fuel!

    Expect to hear much more about this issue since it directly affects the cost to decommission San Onofre and stay tuned to find out who will pay the “extra” amount ratepayers or SCE?
    +
    NRC symposium on high burn-up spent fuel:

    http://www.nrc.gov/public-involve/conference-symposia/ric/past/2013/docs/abstracts/sessionabstract-24.html

  7. Nikohl Vandel June 18, 2015 at 1:00 pm

    Reblogged this on Niki.V.all.ways.My.way. and commented:
    My initial thought is that scale model testing is like as good as full size testing so long as compounding impact of more nuclear fuel vs. the scaled amount is not a factor. I hope they also do random just got thrown off the truck, rolling down a hill kind of testing. The random rather than expected impacts are likely the most probable kind of accident.

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