Used or spent nuclear fuel is a dry, solid ceramic pellet, not a liquid. These pellets are about the size and shape of a large pencil eraser. They are stacked and sealed inside long metal-alloy rods, which are then securely bound into a rectangular bundle called a fuel assembly. After the radioactive used fuel assemblies are removed from a reactor and cooled underwater for a minimum of two years, they are loaded into large stainless steel canisters, which are vacuum dried to remove all liquid and air from the sealed canister, and welded shut. The canister is filled with an inert gas that prevents the fuel from degrading over time. The canisters are stored on site in large concrete casks or vaults.
No Orano dry fuel storage systems have ever leaked radioactive material, and in the 50+ years since commercial nuclear energy began, used nuclear fuel in dry storage has never caused harm to people or the environment.
The Orano 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 1.0g horizontal ground acceleration and 1.0g vertical acceleration. As a reference point, people have trouble standing at 0.02g acceleration. Our NUHOMS dry storage system has withstood actual earthquakes and maintained secure storage.
The NUHOMS system’s low profile, thick reinforced concrete design can weather the impact. Each concrete storage module is individually constructed to withstand extreme events, plus a multiple-module side-by-side installation makes it even more so.
The NUHOMS module is designed to withstand wind-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 individual sealed integrity, even when impacted by an aircraft or other external assault.
During a hurricane or other extreme flooding event, the NUHOMS module is designed to maintain its secure storage, stability and cooling, even when submerged underwater. The above-ground design also simplifies post-event inspection. Watch the NUHOMS Flooding video.
The secure dry storage of used nuclear fuel cannot be affected by a cyberattack. The used nuclear fuel is inside a metal canister, which is sealed inside a thick concrete storage module, which sits on a concrete pad in the storage site. It is a completely passive cooling system, which removes heat by conduction through the materials and/or heat convection through air vents. There are no electronics involved in storing the fuel or enabling the fuel to cool.
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 virtually undetectable and is well below 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.
Orano’s Nuclear Horizontal Storage system NUHOMS uses the effect of self-shielding with great success. The system, which reduces the emitted radiation by placing storage modules side-by-side without gaps, offers the highest level of shielding available today.
An added benefit: if Horizontal Storage Modules (HSMs) are added to a site with existing vertical systems, the minimal dose to the public can be further reduced.
Cooling time in the reactor’s used fuel pool before dry storage is typically at least 5 years after the fuel’s last operation in the reactor core. Available Orano designs allow for storage after as short a time as 2 years. Watch a video showing how used nuclear fuel is moved from a reactor used fuel storage pool to the onsite NUHOMS dry storage system.
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 shielded canister 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.
“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. Orano’s NRC license for the MP197HB Transport Cask includes transportation of canisterized high burnup fuel from a utility site to a repository, to another interim storage site, or to a recycling facility, whichever options are available to receive used nuclear fuel.
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. In fact, since 1966, Orano has safely and successfully transported more than 75,000 used nuclear fuel assemblies, including 15,000 high burnup fuel assemblies.
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 Orano’s NUHOMS dry storage 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 simplified access for inspections, monitoring, and maintenance that may be needed for aging management and life extension programs. Watch a video showing robots inside a NUHOMS storage module inspecting a used fuel canister.