Chapter 53: Predisposal of Radioactive Waste – Transportation – Part 2

This chapter was published on “Inuitech – Intuitech Technologies for Sustainability” on April 22, 2013.

4.     TYPES OF US RADIOACTIVE WASTE NEED TRANSPORTATION:

There are various types of nuclear waste materials that arise from the operation of commercial nuclear power plants and U.S. government defense activities that will need to be transported for further processing and/or permanent disposal. Commercial nuclear waste includes: SNF assemblies and associated non-fuel hardware, limited quantities of commercial High Level Waste (HLW) from the West Valley Demonstration Project, and GTCC waste. U.S. government defense waste includes: naval reactor Spent Nuclear Fuel (SNF), Department of Energy (DOE)-owned SNF, DOE HLW, and DOE Greater-than-Class C Low-Level (GTCC)-like waste. If the nuclear fuel cycle policy of the U.S. evolves from the current once-through fuel cycle to an alternative fuel cycle, additional waste streams might include commercial vitrified HLW and GTCC waste from reprocessing activities – primarily the activated fuel assembly hardware.

4.1       Commercial HLW and other Reprocessing Waste Streams:

Commercial reprocessing operations at the Nuclear Fuel Services plant near West Valley, New York, generated a small amount of HLW between 1966 and 1972, at which time reprocessing operations ceased. That site is presently owned by the New York State Energy Research and Development Authority. In 1980, Congress passed the West Valley Demonstration Project Act. This Act authorized DOE to conduct, in cooperation with the New York State Energy Research and Development Authority, a demonstration of solidification of HLW for disposal and the decontamination and decommissioning of demonstration facilities.

The West Valley Demonstration Project generated 275 canisters of HLW.  The solidified HLW is the result of a vitrification process, which can be used to convert a material into a glass or glassy substance. This is usually accomplished by a thermal process. The resulting glass is a rigid, non-crystalline material that has a relatively low porosity.  The stainless-steel canisters in which the HLW is stored have a nominal outside diameter of 2 feet (0.61 meters) and a nominal height of 10 feet (3 meters).

They contain approximately 7,060 cubic feet (ft3) (200 cubic meters [m3]) of vitrified HLW. According to DOE, the estimated total mass of this HLW is between 595 and 694 tons (540 and 630 metric tons).  DOE estimates that 5 canisters of HLW can be transported in a rail cask. Thus, it is estimated that 55 rail cask shipments will be needed to transport the HLW from the West Valley site.

A 2009 presentation regarding reprocessing waste streams by Areva identified the waste streams that would result from reprocessing of SNF in a reprocessing and recycling facility with an annual throughput of 800 MTU per year. Processing 800 MTU of commercial SNF per year would result in 560 canisters of vitrified HLW (with a nominal height of 1.34 meters [4.4 ft] and a diameter of 0.43 meters [1.4 ft]), 560 canisters of irradiated fuel assembly hardware which would be classified as GTCC waste, and other low-level radioactive waste (LLW).  TN International has two casks for transport of HLW, the TN-81 and TN-85. These HLW transport casks can transport 28 canisters of HLW. Thus, the 560 canisters of HLW and 560 canisters of GTCC waste produced annually could be transported for disposal in 40 TN-85 transport cask shipments.

4.2       Commercial GTCC Waste:

NRC regulations for the land disposal of radioactive waste are contained in Title 10, U.S. Code of Federal Regulations, Part 61 (10CFR61), and Licensing Requirements for Land Disposal of Radioactive Waste. Within 10CFR61, Section 61.55 classifies LLW for near surface land disposal. The waste classifications for LLW are determined by the specific radionuclides and the radionuclide concentration in the waste requiring disposal and are defined as: Class A, Class B, Class C, and GTCC waste, with Class A waste having the lowest concentrations of radionuclides and GTCC waste having the highest. Class A, B and C wastes are generally acceptable for near-surface disposal. According to Section 61.55, GTCC waste is “not generally acceptable for near-surface disposal” and therefore, it may require disposal in a geologic repository.

GTCC waste that is generated by commercial nuclear power plants arises primarily from metal components from reactor internals that become activated due to exposure to neutron flux during nuclear power plant operation. These components can include the core shroud, top fuel guide assembly components, core support plates, the lower core barrel, thermal shields, and lower grid plate components. GTCC waste from these reactor components would be generated as nuclear power plants are dismantled as part of the decommissioning process. [SNL 2007] Minimal quantities of commercial GTCC waste may also be generated during operation of nuclear reactors; items such as contaminated filters and resins, and irradiated “non-fuel components” (e.g., control rods and other incore components) may be classified as GTCC waste.

The overall quantities of GTCC waste at shutdown nuclear power plants and projected quantities of GTCC waste from operating plants have been estimated by DOE contractors to support an Environmental Impact Statement (EIS) regarding the disposal of GTCC waste that is being prepared by DOE’s Office of Environmental Management (DOE EM).  In a study released in 2007 to support this EIS, Sandia National Laboratories (SNL), a DOE contractor, estimated the maximum volume of GTCC waste arising from commercial nuclear power plants, when these plants eventually are shut down and dismantled, was estimated to be 30,760 ft3 (871 m3) according to SNL.  According to a report by DOE EM, if the approximate 871 m3 of GTCC waste were packaged in Transport, Aging and Disposal (TAD) canisters, which are similar in size to the dual-purpose canisters that are being used to store SNF, then a total of 398 TAD canisters would be needed, requiring approximately 398 shipments of commercial GTCC from nuclear power plant sites.

4.3       DOE Spent Nuclear Fuel:

In addition to commercial SNF, there will be approximately 2,750 tons (2,500 metric tons) of heavy metal of DOE-owned SNF, including naval reactor SNF that will require permanent disposal. [DOE 2002b] DOE presently stores most of its spent nuclear fuel at three primary locations: the Hanford Site in Washington State, the Idaho National Laboratory (INL) in Idaho, and the Savannah River Site (SRS) in South Carolina.  In addition, some DOE-owned SNF is stored at the Fort St. Vrain dry storage facility in Colorado. DOE and its predecessor agencies have generated approximately 250 different types of spent nuclear fuel from weapons production, nuclear propulsion, and research missions.

DOE and naval reactor SNF will be packaged in standard canisters. INL reports that it would use a combination of 18- and 24-inch (46- and 61-centimeter)-diameter stainless steel canisters for its disposition of SNF. SRS reports that it would use 18-inch canisters, and Hanford would use 25.3 inch (64 centimeter) multi-canister overpacks and 18-inch canisters. There are two conceptual canister designs for naval fuel: one with a length of 212 inches (539 centimeters) and one with a length of 187 inches (475 centimeters). Both canisters would have a maximum diameter of 67 inches (169 centimeters).  DOE estimates that a total of 784 rail cask shipments will be needed to remove DOE owned SNF from DOE sites.

4.4       DOE HLW:

The majority of HLW in storage in the U.S. is a result of the reprocessing of navy nuclear propulsion fuel and DOE nuclear materials related to plutonium and tritium production.  DOE stores high-level radioactive waste at the Hanford Site, SRS, and INL. DOE is in the process of immobilizing its HLW into a solid matrix within metal canisters.

DOE plans to vitrify the HLW that is at Hanford into a borosilicate glass matrix and pour it into stainless-steel canisters prior to shipment to a repository. DOE estimated the volume of Hanford HLW will require as many as 9,700 canisters, nominally 15 feet (4.5 meters) long with a 2 foot (0.61 meter) diameter.  Most of the HLW at INL is in the form of calcined solids. INL plans to use a hot isostatic pressing (HIP) process to transform the calcined solids into a glass-ceramic matrix.  DOE expects to load approximately 6,600 canisters with HLW from INL, with a nominal height of 10 feet (3 meters) and a diameter of 2 feet (0.51 meter).

The HLW at the SRS consists of wastes generated from the reprocessing of SNF. SRS is expected to generate an estimated 6,300 canisters of HLW, with a nominal height of 10 feet (3 meters) and a diameter of 2 feet (0.61 meters).  DOE expects that a total volume of 21,000 m3 of HLW from the three sites, which will be stored in approximately 22,600 canisters, will require transport and disposal.   DOE estimates that 5 canisters of HLW can be transported in a rail cask. Thus, it is estimated that 4,520 rail cask shipments will be needed to transport the HLW from the Hanford, INL, and SRS sites.

4.5       DOE GTCC-Like Waste:

DOE possesses wastes with characteristics that are similar to GTCC LLW and are referred to as “DOE GTCC-like waste.” This waste includes activated metals, sealed sources and other waste, such as LLW and transuranic waste. The total volume for the existing and projected inventory of DOE GTCC-like waste is 105,950 ft3 (3,000 m3).  If DOE’s GTCC-like waste were packaged in TAD canisters, a total of approximately 816 canisters would be needed, requiring approximately 816 cask shipments of DOE GTCC like waste from DOE sites.

4.6       Other GTCC Waste:

GTCC waste that does not originate at commercial nuclear power plants or DOE sites, includes sealed sources and waste from generators such as industrial research and development firms, fuel fabrication and irradiation research (burnup) laboratories, research nuclear reactors, and sealed source manufacturers, including sealed source waste, glove boxes. The total projected volume of this other GTCC waste is approximately 63,570 ft3 (1,800 m3) and it would require approximately 460 TAD canisters to transport this material for disposal.

5.       US TRANSPORTATION CASKS:

5.1       Description of Typical SNF Transport Casks:

SNF and HLW shipped in sturdy containers that provide physical protection, containment, shielding, heat management, and nuclear criticality safety for the SNF and HLW contained within. These containers are referred to as transport casks. In the U.S., the NRC is responsible for certification of SNF and HLW casks in accordance with NRC regulations contained in 10CFR71, Packaging and Transport of Radioactive Materials.  SNF and HLW transport casks are designed in a variety of different sizes and configurations in order to best handle the characteristics of the different types of SNF and HLW that will be transported and the mode of transportation (e.g., rail or truck transport – Figure 53-01).  Slide1Typical specifications for a truck cask that will be used for SNF shipment are:

  • Gross Weight (including fuel): 50,000 pounds (25 tons);
  • Cask Diameter: 4 feet;
  • Overall Diameter (including Impact Limiters): 6 feet;
  • Overall Length (including Impact Limiters): 20 feet; and
  • Capacity: Up to 4 PWR or 9 BWR fuel assemblies.

Typical specifications for a rail cask that will be used for SNF transport are:

  • Gross Weight (including fuel): 250,000 pounds (125 tons);
  • Cask Diameter: 8 feet;
  • Overall Diameter (including Impact Limiters): 11 feet;
  • Overall Length (including Impact Limiters): 25 feet; and
  • Capacity: Up to 37 PWR or 87 BWR fuel assemblies.

Typically, a SNF cask is comprised of a package body consisting of an inner and outer stainless steel structure (e.g., thick-walled cylinder), which encloses heavy metal (e.g., lead or depleted uranium) gamma shielding. However, some designs use a monolithic thick-walled steel cylinder that provides both gamma shielding and structure. Within the package body is a structure referred to as a “basket” that provides support, positioning, criticality safety, and heat management for the SNF or HLW canisters. Neutron shielding is generally exterior to the outer cylinder of the package body and consists of hydrogenous material such as polyethylene held in place by a thin-walled stainless steel structure. In some cask designs, the basket structure is part of a thin-walled sealed canister that is separate from the main shielding and containment package. Metallic and/or elastomeric seals and a bolted, shielded lid are used in cask closure mechanisms. In cask designs that employ inner sealed canisters, the canisters are seal-welded.  All contemporary SNF transport casks are equipped with removable external protective structures called impact limiters (also called energy absorbers) that reduce the mechanical forces imposed on the package under accident conditions. Helium is used to fill interior void spaces in the cask. Use of an inert gas such as helium improves heat transfer and also creates a non-oxidizing environment for the SNF.Slide2Packages designed for railroad transportation and/or intermodal barge shipping weigh up to 125 tons. SNF transport casks designed for highway transportation can weigh up to 26 tons and still meet the highway weight limits for legal weight shipping (i.e., gross vehicle weight (GVW) of 80,000 pounds). Over-weight truck (OWT) shipping with a GVW of about 110,000 pounds (i.e. 40-ton cask) is possible, but this mode requires special permits and may restrict vehicle movement on some roads. The overall weight of SNF casks must also be compatible with the lifting capability of the cask handling crane at the nuclear power plant site and at the facility to which the SNF is being shipped. There is roughly a 6 to 1 fuel capacity advantage of rail casks over highway casks.

5.2       Dual-Purpose Storage and Transport Casks:

The first dry storage systems licensed in the U.S. were storage-only technologies, licensed under NRC regulations.    In the late 1990s, nuclear operating companies began to consider dualpurpose storage and transport technologies to meet their onsite SNF storage requirements. Dualpurpose technologies are certified by NRC for storage. One of the benefits of dry storage using dual-purpose technologies for onsite dry storage is that, once SNF has been loaded into the sealed dual-purpose casks or canisters, it is hoped that the individual SNF assemblies would not have to be handled again prior to their eventual transport offsite to a Federal waste management system. SNF loaded into dual-purpose storage and transport technologies may have to be repackaged for disposal.

With a storage-only system, SNF is transferred from the SNF storage pool to a dry storage system; the SNF is stored in an onsite dry storage facility for an indefinite period of time; the storage system may need to be transferred back to the pool to be unloaded; and SNF is then reloaded into a transportation cask for transport offsite. If storage-only systems are relied on for onsite dry storage, the SNF storage pool may need to be maintained in operating condition in order to transfer fuel from storage-only systems to transportation casks for transport off-site at some point in the future. The development of dual-purpose dry storage technologies has been particularly important for shutdown nuclear power plants that have off-loaded SNF to dry storage, allowing those nuclear power plants, including the SNF storage pools, to be to dismantled and decommissioned.

With the prospect of very long-term dry storage at nuclear power plant sites, the majority of onsite dry storage facilities that have been commissioned since 2000 have loaded SNF into dualpurpose dry storage technologies. Even those companies that began dry storage facility operation in the 1980s and 1990s have transitioned from storage-only technologies to dual-purpose technologies. There are two primary types of dual-purpose technologies – cask based systems and canister based systems. Dual-purpose casks are similar in design to the rail cask designs. The basket that holds the individual fuel assemblies is generally integral to the cask assembly. Dual-purpose casks are certified.  Canister-based dual-purpose technologies utilize a sealed metal canister that is certified.  The dual-purpose storage system includes the DPC, a storage overpack, and related equipment. The dual-purpose transport system includes the same DPC, a transport overpack (e.g. transport cask), and related equipment.  As noted above, nuclear operating companies are expected to continue to utilize high-capacity dual-purpose technologies for onsite storage for the foreseeable future.

6.       US EQUIPMENT FOR TRANSPORTING RADIOACTIVE WASTE:

6.1       Description of Equipment:

Several modes of transport are available to ship SNF and HLW: highway, railroad, barge or ship.Slide3 In the U.S., shipping by barge would be conducted in conjunction with one of the other land based transport modes, often referred to as multi-modal shipments. The transfer of a SNF or HLW cask from one mode of transport to another, such as from heavy-haul truck or barge shipment to rail transport is referred to as inter-modal transfer.Slide4Specially designed trailers that provide integral tiedowns to fasten the cask to the conveyance are used for highway transport. There is an incentive to keep the gross weight of a truck cask, trailer, and tractor below 80,000 pounds, which is the legal weight limit for interstate highway transport.  Shipment weights that fall within the legal weight limit would not require heavy-load permits. To stay within this legal-weight limit, specialized tractor and trailer designs are often required.  Figure 53-03 shows a schematic of a truck cask loaded onto a truck for highway transport. Shipment weights that are over this legal-weight limit require that the shipper receive heavy load permits from the States and local jurisdictions with responsibility for the roads over which the shipment will be transported. Receipt of heavy load permits to support SNF shipments is an area of potential delay that should be considered in the transportation planning process.Slide5

Railroad transport also requires specialized equipment. Transport of the 125-ton SNF cask requires more than a 4-axle railcar due to the weight. Additionally, the Association of American Railroads (AAR) has prescribed unique design and testing requirements for railcar certification, as shown in Figure 53-04 a cask loaded onto a rail car along with a personnel barrier.

In some designs the cask may be mounted on a transport skid that has integral tie-downs. The skid may be moved with its attached cask from one mode of conveyance to another, for example, from a barge to a railcar. This eliminates the need to actually handle the cask separately at an off-site intermodal transfer facility. An example of intermodal transfer from rail to truck is shown in Figure 53-05.

For rail transport, in addition to the cask transport system (cask, impact limiters, transport skid, and auxiliary equipment), special rail equipment will be needed to ship loaded SNF casks from nuclear power plant sites to a central waste management facility: rail locomotives, rail cask cars, rail escort cars, and rail buffer cars (i.e., flatbed rail cars that are required by regulation to separate SNF cask cars from the locomotive and escort cars).  Each rail shipment is assumed to include one locomotive, one escort car, and two buffer cars and cask cars. The number of cask cars will depend upon the number of SNF casks that are being shipped. Slide6All of these transport mode and equipment designs have been used to some extent over the past four decades, both domestically and internationally.

Resources:

  1. The World Nuclear Association;
  2. IAEA Regulations for the Safety of Transport of Radioactive Material;
  3. US Nuclear Regulatory Commission; and
  4. Overview of High-Level Nuclear Waste Material Transportation by Energy Resources International Inc.

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