By Mike McMahon, Senior Vice President, AREVA TN Americas
The topic of safely transporting and storing used nuclear fuel at U.S. nuclear energy facilities is causing a lot of discussion in communities around the country. Questions about radiation shielding, safety, and seismic capabilities are prompting the most responses, but there are also persistent misunderstandings about safely managing used nuclear fuel that muddy the conversation.
Let’s clear that up…
During our nearly 50 years of experience safely managing used nuclear fuel, we have advanced safe used nuclear fuel storage technology significantly with AREVA’s NUclear HOrizontal Modular Storage (NUHOMS®) system.
Based on that experience, let’s take a look at the…
Top 10 Used Nuclear Fuel FAQs
- What is “high burnup fuel” and can it be safely transported and stored? “Burnup” is a term used to describe how much energy has been produced in a nuclear fuel assembly. Typical units are “Gigawatt-days per Metric Ton of Uranium” (GWD/MTU). Burnup can be thought of as the “gas mileage” for nuclear fuel because it tells us how much energy has been extracted from a given amount of uranium in the same way that “miles per gallon” tells us how far a car will go on one gallon of gas. The term “Gigawatt-days” is the amount of energy required to produce one gigawatt (1 billion watts) of power for one day (24 hours). It is similar to the more familiar term “kilowatt-hour” or “kW-hr” seen on a monthly electric bill (i.e., one kilowatt-hour is the amount of energy required to produce one kilowatt [1000 watts] of power for one hour). By way of comparison, since 1 Gigawatt is equal to 1,000,000 kilowatts, 1 Gigawatt-day is equal to 24,000,000 kilowatt-hours. Since nuclear fuel produces enormous amounts of energy, we need to use big units of measure!
The U.S. Nuclear Regulatory Commission (NRC) considers “High Burnup” Fuel to be any fuel with a burnup higher than 45 GWD/MTU. There is nothing magical about the 45 GWD/MTU number – it is a somewhat arbitrary limit to mark the boundary between “high burnup” and “low burnup” fuel. High burnup fuel can be and has been safely stored and transported. Since 1966, AREVA has safely and successfully transported more than 75,000 used nuclear fuel assemblies, including 15,000 high burnup fuel assemblies.
- How long can the storage system safely contain the high burnup fuel? The NRC issues a license for dry fuel storage systems for an initial period of 20 years. When the initial license ends, it does not mean that the system is no longer safe, it simply means it requires review and renewal – much like a driver’s license. At the end of 20 years, the NRC requires that a license renewal application be submitted, which, if approved, will extend the license for an additional increment of up to 40 years. The NRC does not place a limit on the number of 40-year renewals that can be obtained. The design life of AREVA’s NUHOMS® systems is 100+ years with an aging management program. Effective product life can be extended almost indefinitely through inspections, aging management programs, and maintenance. The NUHOMS® system’s horizontal above-ground fortress-like structure enables easy access for inspections, monitoring, and maintenance that may be needed for aging management and life extension programs.
- How would a utility transport containers loaded with high burnup fuel from the utility site? Is there an NRC-licensed container approved to safely transport high burnup fuel? Yes, AREVA’s NUHOMS® MP197HB Transport Package is NRC-licensed for transportation of canisterized high burnup fuel from the utility site to a repository, to another interim storage site, or to a recycling plant, whichever options are available to receive used nuclear fuel.
- Can “damaged” nuclear fuel be safely stored and then transported? Damaged fuel can unequivocally be safely stored and transported in our storage containers, just as undamaged or intact fuel can be safely stored and transported. The dry fuel storage container includes an internal basket structure that keeps the fuel assemblies separated and stable. When storing damaged fuel we either take an added step of inserting screened caps on either end of the basket compartment, or we place the fuel assembly in a separate ventilated container (called a “can”) before placing it in the basket. The damaged fuel can then be safely stored in exactly the same manner as intact fuel in our NUHOMS® system.
- How do you keep the used fuel safe in an earthquake? The AREVA’s NUHOMS® system securely stores the dry fuel storage containers in a horizontal position within a sturdy, low-profile, reinforced concrete structure. Our robust earthquake-resistant design achieves the highest seismic capability of any used fuel storage system in operation today. We offer NUHOMS® module designs that are engineered for 1.5g horizontal ground acceleration and 1.0g vertical acceleration. As a reference point, people have trouble standing at 0.02g acceleration!
- What happens when a tornado, or flood, or even an airplane strikes the used fuel storage site? The NUHOMS® system’s low profile, thick reinforced concrete design can weather the impact. It can withstand tornado-accelerated objects including telephone poles (13.5” diameter, 276 pounds traveling 200 mph), a steel pipe (12” diameter, 1,500 pounds, 140 mph), and an automobile (4000 pounds, 195 mph), and can safely maintain its sealed integrity when impacted by an aircraft. Flooding does not affect the above-ground NUHOMS® system’s safe operations.
- What are the radiation levels at a nuclear fuel storage site? All levels are well within the required limits. Immediately next to the closest publicly-accessible area boundary, the total dose received from a dry fuel storage facility containing sealed NUHOMS® containers is less than the regulatory limit of 25 mrem over the course of one year. By way of comparison, the average American receives a dose of about 310 mrem in one year from natural background sources of radiation, such as cosmic rays and radon.
- Can the storage system leak radioactive material? Nuclear fuel is in the form of solid ½” pellets contained in metal rods. No AREVA dry fuel storage systems have ever leaked radioactive material.
- How long does used fuel have to stay in the reactor’s used fuel pool before it is put in a dry cask storage system? Cooling time in the reactor’s used fuel pool before dry storage is typically 5 to 7 years after the fuel’s last operation in the reactor core. Some of AREVA TN’s designs allow for storage after as short a time as 3 years.
- What if a worst-case scenario actually happens inside a dry fuel canister or during the transport of a canister? We intentionally build-in design conservatism in our calculations to ensure that an AREVA dry fuel storage container is capable of safely storing fuel in the very worst case scenario. Containers are backfilled with inert Helium gas, and are designed to transfer the heat out of the fuel assemblies so that fuel will be safe during the storage period. One key way to do this is through the convection heat transfer from the fuel to the Helium in the container cavity. In our calculations, we do not credit this convection heat transfer (or cooling) inside the container cavity, so our containers are designed to manage the original higher heat levels. Our very conservative approach offers the most comprehensive, safest solution for storing fuel. In the licensing process for our transport cask, we made the worst case scenario assumption that the cladding had been damaged, and then did our calculations to ensure that the fuel would still be safe in spite of that occurrence!
Now that you have these answers, learn more about NUHOMS® and safe used fuel transport and storage (video) on our AREVA TN website, and watch the high-impact test video showing a 660-pound steel projectile impacting an AREVA storage container at 534 miles per hour.