NUHOMS - The Horizontal Difference in Used Nuclear Fuel Storage
When used nuclear fuel is placed in dry storage, it is typically transferred from the used fuel pool to metal canisters, which are then loaded into heavy concrete overpacks. These canister and overpack dry fuel storage “systems” do not require any power supply for active heat removal systems and have no moving parts. "Wet" storage in the used fuel pool, however, requires a constant supply of power to keep the cooling water pumps going.
AREVA TN provides superior quality dry storage systems, including dry shielded canisters that are built of durable stainless steel at our American fabricator, Columbiana Hi Tech, or at one of our QA-qualified fabricators around the world. Our concrete overpacks are called Horizontal Storage Modules, and are either cast on site or built at our American manufacturer and shipped to the site for installation.
Expert Team Delivers more than just Technology
Safe used fuel management is not just about purchasing a storage system … It is about a coordinated team of construction specialists, engineers, and trained and practiced “industry best” used fuel loading teams. AREVA's safe used fuel management program features state-of-the-art aging management technologies and services, and a reliable and safe transport system to move the fuel offsite.
With these capabilities and custom design, AREVA offers all services needed to manage used nuclear fuel safely and efficiently from start to finish.
Dry storage systems store the used fuel in either a horizontal or vertical position. Initially, dry storage systems were vertical, until AREVA developed a less risky and innovative solution: Horizontal systems cannot tip over, and onsite handling of these heavy systems is simple and safer in the horizontal position. Plus, the horizontal orientation during storage avoids the significant temperature difference between the two canister ends of a vertical system, reducing the possibility of thermally induced stresses in the material. Horizontal systems are easy to inspect and transport. Most importantly, AREVA's horizontal storage modules are arranged gap-free, side-by-side, which all but eliminates radiation emissions and results in minimal exposure to plant workers and the public.
NUHOMS® Horizontal Storage offers:
- Best shielding due to gap-free, side-by-side arrangement
- Highest level of safety
- Highly corrosion-resistant stainless steel canisters, plus the duplex stainless steel option for marine environments
- Massive concrete storage modules for a fortress like protection of the used fuel
- Lowest risk in moving fuel on-site due to horizontal orientation
- Highest seismic performance of any system
- NRC-licensed cask to transport canisterized high burn-up fuel
- Surest path to moving used fuel away from nuclear plants to the WCS Interim Storage Facility
- Major safety features as a result of conservative design and conduction of heat, rather than relying on convection.
Offering the highest shielding, transparent pricing and low lifecycle costs … NUHOMS® is the dry storage solution of choice for nuclear facilities around the world.
Removal of Fuel from Nuclear Plants Sites – Waste Control Specialists (WCS)
While government entities are still working on providing a final storage repository for used nuclear fuel, there is already an interest in removing fuel from sites, especially from permanently shut down ones.
AREVA is partnered with Waste Control Specialists (WCS) in the development of a License Application for an Interim Storage Facility (ISF) for Used Nuclear Fuel at their facility in Andrews County, TX. The License will allow the storage of Used Nuclear Fuel from select reactors at shut down sites, and from Texas. The goal is to begin receiving fuel from shut down reactors in the 2020 - 2022 timeframe.
AREVA is well positioned to support shipments from nuclear plant sites. With its NRC-licensed transport cask for canisterized High Burn-Up fuel and unparalleled global experience in transporting used fuel, AREVA TN offers technologies and expertise for the ultimate answer to the U.S. challenge of safely storing used nuclear fuel.
Our horizontal NUHOMS® used fuel storage system has the best demonstrated shielding in the industry. The NUHOMS® system offers significant life cycle cost savings in plant integration, low risk in the pool transfer process and infrastructure savings when compared to other available systems.
State-of-the-art, high-performance stainless steel canisters are engineered to extremely conservative technical specifications for heat conductivity that take into account all possible risks, no matter how farfetched. The canisters feature redundant welded lids, state-of-the-art precision welding procedures, low risk horizontal transfer processes, and a massive concrete module for housing. These aspects of the system combine to make NUHOMS®, by far, the safest system that has been proven to be safe and low-risk … at more than 30 plant sites across the nation.
NUHOMS® is engineered for 1.5g horizontal acceleration and 1.0g vertical acceleration. Its low profile and array structure and horizontal position ensure stability, thus the NUHOMS® system is the highest seismically qualified dry fuel storage system in the world.
NUHOMS® canisters are made of high-performance stainless steel that is corrosion-resistant and up to 5/8" thick. For oceanside marine environments, the duplex stainless steel option provides a robust barrier against chloride-induced stress corrosion cracking, pitting and crevice corrosion. The state-of-the-art engineering and precision fabrication ensure long-term integrity of the shielding properties … keeping communities and workers safe!
Flooding and Tornado Low Risk
NUHOMS® has successfully and safely operated through two tornado events. Our impact design analysis criteria examples include a 276 pound wooden utility pole traveling more than 200 MPH, a 1500 pound steel pipe traveling more than 140 MPH and a 4000 pound automobile traveling more than 195 MPH!
Accessible and Retrievable
Horizontal, above-ground storage modules are the easiest to access and monitor long-term and are less costly to maintain. Our aging management technologies are setting the standard for the industry and are key to ensuring continuous safety of canisters for the long-term. NUHOMS® canisters are easy to retrieve and are the least risky to move due to their more stable horizontal orientation. This drives lower doses during the fuel loading process as it take less time to move the canister, and it enables future easy retrieval and transport of the fuel off site.
Extended Storage (EOS)
NUHOMS EOS 37PTH and 89BTH Dry Shielded Canisters
The next advanced evolution of our proven, high-performance dry shielded canister offers:
- Higher capacity
- Higher heat load
- Superior shielding
- Low plant risk
- Low life cycle costs
AREVA TN’s NUHOMS® EOS 37PTH and 89BTH Dry Shielded Canisters (DSC) provide customers with a high-capacity, high-burnup, and high-heat load system for PWR and BWR dry used fuel storage needs. The 37PTH DSC is designed to store and transport 37 PWR fuel assemblies with or without channels. The 89BTH is designed to store 89 BWR fuel assemblies.
The EOS 37PTH and EOS 89BTH baskets are constructed using alloy steel, aluminum, and metal matrix composite (MMC) plates configured into an egg crate design, allowing for a more cost-efficient fabrication. The compartment assemblies are connected to perimeter aluminum transition rail assemblies. Geometric spacing, fixed neutron absorbers and soluble burn are used to maintain criticality control for enrichments up to 5.0% U235.
The EOS 37PTH and EOS 89BTH DSCs are optimized for plants with minimum crane capacity of 125 tons and have a 108 ton option available. The EOS canisters will be transferred in the new NUHOMS® EOS TC series transfer cask to gain the benefit of being fully shielded. EOS 37PTH and EOS 89BTH DSCs are transferred and stored in a horizontal configuration using the NUHOMS® EOS HSM concrete modules. The EOS HSM is a new and improved HSM-H, with redesigned vents for a higher capacity heat load while maintaining the same overall footprint. The EOS 37PTH and 89BTHDSC assemblies incorporate the proven NUHOMS® welded closure design that has been used in numerous loaded canisters in the United States.
NUHOMS® has four primary components
Dry Shielded Canister (DSC, #9 in the illustration)
The NUHOMS® Dry Shielded Canister (DSC) is a state-of-the-art canister that AREVA TN has designed and licensed for safe storage and transport of used fuel. The NUHOMS® canister has a strong containment shell that is made up of up to 5/8" thick highly corrosion-resistant stainless steel. The canister has uninterrupted aluminum heat conductive pathways and crisscrossed slotted plates. The slotted plates enable heat conduction so that the heat from the fuel assemblies on the interior of the canister can easily conduct to the sides of the canister where the heat is then dissipated by the air flow. The horizontal configuration allows for the heat to be removed from the fuel more efficiently over a large area and also distributes weight more evenly for maximum safety and stability during transfer or transport.
Horizontal Storage Module (HSM, #8)
NUHOMS® systems have the highest seismic capability available, due to the fortress-like HSMs. In addition, HSMs have proven flood performance and have high tornado wind and missile tolerances. Each HSM has internal heat shields and a shield door. The HSMs are arranged in an array that offers added shielding through the side-by-side configuration. The ends of each array include additional shielding and the roof of the concrete reinforced module is four feet thick. This heavy shielding results in no measurable dose to the public.
Transfer Cask (TC, #10)
The NUHOMS® Transfer Cask (TC) is used to safely move the horizontal loaded Dry Shielded Canister (DSC) from the fuel building to the storage site for insertion of the loaded DSC into the Horizontal Storage Module (HSM). AREVA TN’s experienced and practiced team of experts -- who have consistently demonstrated industry-best performance -- can manage this “pool to pad” process for the site. NUHOMS® University offers real-time training with full-size components and equipment to ensure the pool to pad transfer is completed incident-free, on-time and on-budget.
MP197HB Transport Cask
The NUHOMS® MP197HB transportation cask is used to transport canisterized used fuel offsite, and is the only transportation cask licensed to transport canisterized high burn-up used fuel in the United States. The MP197HB is a shielded cask that consists of a containment boundary, structural shell, gamma shielding material, and solid neutron shield. Impact limiters are attached to each end of the NUHOMS® MP197HB cask during shipment.
Top 10 FAQs
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
1. 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 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.
AREVA’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.
In fact, if horizontal storage modules (HSMs) are added to a site with existing vertical systems, the minimal dose to the public can be further reduced.
What happens when a tornado 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, even when impacted by an aircraft.
3. Can the storage system leak radioactive material?
Nuclear fuel is in the form of solid ½” ceramic pellets contained in metal rods, so the radioactive material cannot leak out. No AREVA dry fuel storage systems have ever leaked radioactive material.
4. 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 at least 5 years after the fuel’s last operation in the reactor core. Available AREVA TN designs allow for storage after as short a time as 3 years.
5. How would a utility transport containers loaded with high burnup fuel from the utility site?
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.
6. 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!
7. 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 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.
8. 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!
9. Is fuel that is less than 45 GWD/MTU safer?
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, AREVA has safely and successfully transported more than 75,000 used nuclear fuel assemblies, including 15,000 high burnup fuel assemblies.
10. 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.
Other systems, including underground systems, are difficult to access and inspect, and require more risky maneuvers to extract a compromised canister.
AREVA TN leases its NUHOMS® Transfer System and NUHOMS® Ancillary Equipment including the NUHOMS® Transfer Trailer, the NUHOMS® Transfer Casks (OS 200 and OS199), the NUHOMS® Vacuum Drying System (VDS) and the NUHOMS® AREVA Automated Welding system (AAWS). Leasing is one flexible option for customers to accommodate budget restraints, as needed.
AREVA TN includes in its leasing offer the use of AREVA TN technicians to ensure the safe and streamlined operation of the equipment during the loading campaign.
While most AREVA TN customers do purchase their NUHOMS® Transfer System, leasing the NUHOMS® Transfer System or its components can offer a more economical route for some nuclear power plants, depending their loading programs.