Ensuring the Safety of Spent Fuel in Storage

Mark Lombard
Director, Office of Spent Fuel Storage and Transportation
Spent fuel dry casks
Spent fuel dry casks

While no one can say with certainty today where spent nuclear fuel will ultimately go for long-term storage or disposal, one thing is clear: the current methods of spent fuel storage are safe.

Managing the “back end” of the nuclear fuel cycle – what happens to the fuel after it is taken out of a reactor – may never be completely separated from political and economic considerations. But the technical challenges are fairly straightforward. Spent fuel is hot. And it is extremely radioactive. It must be kept cool and it must be shielded to protect workers, the public and the environment. It must also be properly controlled to prevent it from achieving a sustained nuclear chain reaction, also known as going critical.

The NRC has updated its Storage of Spent Nuclear Fuel fact sheet, which explains the two major ways spent fuel is managed – in pools and in dry cask storage. The fact sheet explains the regulatory requirements, inspections and monitoring that ensure spent fuel is managed safely. It also details improvements the NRC has made to address concerns raised by the accident at Japan’s Fukushima plant and the 9/11 terrorist attacks.

An NRC backgrounder, Dry Cask Storage of Spent Nuclear Fuel, provides more detail on how this management strategy evolved, the basic requirements for dry storage, different licensing options and opportunities for public input.

A great deal more information on spent nuclear fuel storage is also available on the NRC’s website. We encourage you to read about our activities in this area and post your questions, comments and concerns below.

Author: Moderator

Public Affairs Officer for the U.S. Nuclear Regulatory Commission

18 thoughts on “Ensuring the Safety of Spent Fuel in Storage”

  1. The dry storage casks typically have an inner sealed metal canister, several inches thick, that provides containment for the spent nuclear fuel. One of the many requirements for licensing a spent fuel storage system is that it must prevent a nuclear chain reaction. Cask designers can do this by putting “poisons” inside the canister—materials that absorb the neutrons necessary to cause fissioning. They can also space the fuel assemblies far enough apart that they will not fission. Another protection against criticality is the fact that the fuel is “spent,” which means it can no longer efficiently sustain a chain reaction even in the reactor core. Spent fuel is much less reactive than fresh fuel. Spent fuel has much less of the U-235 isotope that fissions than is present in fresh nuclear fuel. There are also more fission products, which become more stable (less reactive) the longer the fuel remains in the reactor core. The buildup of fission products slows down the chain reaction at the same time that the U-235 is being depleted, which is why the fuel is eventually removed from the core. Finally, the canisters are designed to keep out any water. A chain reaction in a spent fuel storage cask could not begin without the presence of water.

    The spent fuel could not burn inside these sealed metal containers. A fire requires oxygen. All oxygen is removed from these casks and they are filled with an inert (nonreactive) gas. Even if oxygen were present, there is no ignition source inside the canisters.

    Mark Lombard

  2. Dry storage casks usually consist of a sealed metal cylinder to contain the spent fuel placed inside a metal or concrete outer shell to provide radiation shielding. The casks must also manage the heat and prevent nuclear fission. They are designed to withstand earthquakes, projectiles, tornadoes, floods, temperature extremes and other scenarios. The heat and radioactivity from the spent fuel decrease over time without the need for fans or pumps. The casks are under constant monitoring and surveillance. More details about dry cask storage can be found in this backgrounder: http://www.nrc.gov/reading-rm/doc-collections/fact-sheets/dry-cask-storage.html

    Mark Lombard

  3. Hi John, here’s a reactor engineer response:
    Spent fuel has lifetime limits and burnup limits. Lifetime is straightforward, the fuel is only allowed so many years at reactor temperature and pressure. Burnup limits are what you are talking about, and has to do with how much energy was extracted from the fuel (this causes changes inside the rod), and neutron/radiation exposure. For the most part, the fuel rod cladding (zircalloy) is transparent to neutrons, the bigger issue with the rods is generally the changes to the chemistry of the fuel INSIDE the rod, which reduces the heat conductivity of the rod. For a BWR, a fuel rod can typically transfer something like 12 kw of heat per foot of rod, but after a couple years, it can only transfer about 5 kw per foot. For PWRs, they tend to start in the 20-22 kw/ft range, and decrease to around 12 kw/ft. In either case, this limits how much power you are allowed to get out of the rod and is another reason they are replaced.

    The thing which USUALLY drives replacement, is actually the depletion of fuel, and not the thermal and age limits of the fuel rod. However, sometimes you end up in cases where you have a fuel assembly which spent too much time in hot spots of the core and needs to be discharged early. The plant’s core monitoring systems keep track of these parameters for every individual fuel rod and calculates this continuously.

  4. I can’t speak for all plants, but the plants i have worked at have boron plated fuel racks for spent fuel. it is basically a permanantly installed control rod which ensures the fuel cannot go critical in the spent fuel pool.

    There are requirements to maintain the spent fuel pool criticality less than 0.95 dk/k of reactivity at all times. For plants that do not have boron plated racks, they need to do calculations to prove this every time they move a spent fuel bundle.

    With regards to Ft. Calhoun, the spent fuel rods are well above the flood plane. I know this much for fact.

  5. This is something indeed very remarkable. I was unaware that fuel can be extracted from a nuclear reactor. Totally agree with you Susan, tanks are specifically manufactured for highly flammable and radioactive fuels. By updating its fact sheet, NRC has done a wonderful job.

  6. I’ll take the coal particulate matter over fallout like that from Fukushima any day, thank you. I’m also wondering if the wood fiber substrate photovoltaic technology (1/100,000th the cost of glass substrate to produce), will be allowed to flourish, or if we will stick with the Global Genome Destruction means of producing power.

  7. Is it true spent fuel also is removed and replaced because the intense radioactivity damages the cladding enough to make integrity a concern?

  8. Why is spent fuel not stored in containment structures? Is is not an uncontained nuclear reaction waiting to happen in the event of meltdown? Is a fire not just as bad? Fort Calhoun, did those rods get exposed to river water? Would the NRC or the industry have told us if they did? Your industry risks the entire freaking corn belt just from one spent fuel pool at Calhoun. More flooding this year is predicted. Does the COE have a plan to blow levees if needed to prevent further ‘incidents’ in Nebraska or with other reactors in flood plains? Or would that be too embarassing to the economy or the administration?

  9. Yes, i agree, its truly very important task of storing fuel..Cask storage, what is this storage medium? can you explain?

  10. Talk about FUD

    You can go to every plant’s operating license on the NRC webpage. If you go to technical specifications, usually in chapter 3.8.1 (for improved standard technical specifications, which many plants use), a condition of operability for the plant is to perform monthly testing for each diesel generator. There are also reliability requirements for diesel generators (most plants are over 95%, many over 97.5%), requirements for cold quick starts, 24 hour run requirements, and rebuild maintenance requirements, that are required as part of the plant’s operating license.

    I know my plant in particular performed 300 start tests on each diesel during startup testing, and we perform at least 12 start tests per year, per diesel, with at least two of those cold quick starts, and at least 1 every 2 years is a full 24 hour after major maintenance. We also rebuild our generators every 10 years to keep them in like new condition. I’ve personally witnessed many of these tests on the generators. When things wrong with them are discovered we have a clock which starts which requires us to fix it or shut the plant down, then re-test the generator after it has been fixed. Additionally we have to evaluate “past operability”, and perform common mode evaluations to ensure the other generators are not out of service due to the same problem.

    I’m not sure why things from 30 years ago somehow mean the nuclear industry isn’t doing the right thing today. This is nothing more than conjecture/conspiracy/FUD.

  11. NPPs and SFPs are not safe if the diesel generators aren’t checked and made sure they are not a joke:

    Back in the day, when we checked the emergency back-up diesels in America, a mind-blowing number flunked. At the New York nuke, for example, the builders swore under oath that their three diesel engines were ready for an emergency. They’d been tested. The tests were faked, the diesels run for just a short time at low speed. When the diesels were put through a real test under emergency-like conditions, the crankshaft on the first one snapped in about an hour, then the second and third. We nicknamed the diesels, “Snap, Crackle and Pop.” from http://enenews.com/emergency-declared-at-u-s-nuclear-plant-after-lightning-strike-venting-of-the-unit-1-primary-containment-normal-radiation-levels-have-been-reported-nrc-mobilizes-incident-response-ce

    Come on nuclear industry, you threaten half the country with every plant and pool.

  12. The NRC, as an independent regulatory agency, does not promote nuclear programs. NRC ensures public health and safety through regulatory programs on any fuel cycle facility the country pursues. At this time, there has not been sufficient commitment by industry to license, construct and operate a reprocessing facility.

    The Department of Energy plays a leading role in setting nuclear policy. DOE is researching advanced nuclear fuel technologies, including reprocessing, fuel designs and advanced reactors.

    The NRC has done some investigations to better understand reprocessing technologies, should the Commission task the staff with developing regulations for licensing an advanced reprocessing facility. The NRC staff is due to report to the commissioners this summer on recommendations as to whether NRC should proceed toward developing a regulatory framework for reprocessing.

    Mark Lombard

  13. Anonymous — We do not have any unapproved comments pending, nor have any been “not approved.” If you still do not see your comment, please resubmit it.


  14. Because nuclear fuel loses efficiency over time, commercial nuclear reactors routinely remove the oldest fuel from their cores every 18 to 24 months and load fresh fuel in its place. These loading/unloading operations must be done in compliance with NRC regulations to ensure that the public and plant workers are adequately protected from the spent fuel’s radioactivity. The fuel is then placed in large pools of water to cool and shield it. Commercial spent fuel is not used to make nuclear weapons.

    The fact sheet and backgrounder linked to the blog post explain spent fuel storage in more detail.

    Mark Lombard

  15. I stated the same thing, but for some reason, my comment did not post. My point was that so much research and development has gone into the reuse of spent fuel. Additionally, we can mention Yucca Mountain–which could, rather be used for long term storage–be a facility where spent fuel is stored and reprocessed. New technologies could be developed there too. Many things are being developed here all the time–with other countries taking advantage of our technology and expertise. Remember West Valley?

  16. You know if there was a way people could see physically in one place the mass of ,material emitted in the atmosphere (hence hourly into their babies lungs) by fossil fuels in the country just in one week they’d be having grave second thoughts.about how “big” a problem siting sealed-up nuclear waste is.

    James Greenidge
    Queens NY

  17. That’s interesting because I had no idea that you could take the fuel out of a nuclear reactor. Most fuels that help highly destructive weapons like that is usually extremely hot and very radioactive.

    I do know they have specialized tanks for that. Tanks are built for the highly flammable and radioactive fuels.

  18. Why not pursue “closing” the fuel loop by finding alternatives for reuse of the spent fuel. France has been reprocessing for years. We had reprocessing available to us in the 1960’s and early 1970’s and then West Valley was abruptly shut down. Although reprocessing may not be a complete answer,there are alternatives that decrease the amount of spent fuel and storage requirements. Research and development is being conducted now, yet nothing has resulted from it. It seems as what is being developed here is used in other countries. We have one of the best nuclear programs in the world, yet we fall behind in implementing the technologies we develop here in the United States. How do we benefit here at home? How do we communicate the future of nuclear as being a safe and sound energy alternative? Moreso, how are we closing the fuel cycle rather than just allowing the spent fuel to sit? I understand that money has a lot to do with it, but if Yucca Mountain is not even on the list of alternatives, then that money should be redirected to something that will work in the near future. Even private corporations have explored these alternatives.

Comments are closed.

%d bloggers like this: