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DOE OSTI2018

The Need for Integrating the Back End of the Nuclear Fuel Cycle in the United States of America

Current practice for commercial spent nuclear fuel management in the United States of America (US) includes storage of spent fuel in both pools and dry storage cask systems at nuclear power plants. Most storage pools are filled to their operational capacity, and management of the approximately 2,200 metric tons of spent fuel newly discharged each year requires transferring older and cooler fuel from pools into dry storage. In the absence of a repository that can accept spent fuel for permanent disposal, projections indicate that the US will have approximately 134,000 metric tons of spent fuel in dry storage by mid-century when the last plants in the current reactor fleet are decommissioned. Current designs for storage systems rely on large dual-purpose (storage and transportation) canisters that are not optimized for disposal. Various options exist in the US for improving integration of management practices across the entire back end of the nuclear fuel cycle.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗

DOE OSTI2017

Materials and Dimensional Reference Handbook for the Boiling Water Reactor Dry Cask Simulator.

The performance of commercial nuclear spent fuel dry storage casks is evaluated through detailed analytical modeling of the system’s thermal performance. A recent investigation has been completed that produced a data set that can be used to test the validity of the modeling presently used to determine cladding temperatures in modern vertical dry casks. To produce these data sets under well-controlled boundary conditions, the dry cask simulator (DCS) was built to study the thermal-hydraulic response of fuel under a variety of heat loads, internal vessel pressures, and external configurations [Durbin and Lindgren, 2017]. The experiments were conducted in Albuquerque, New Mexico where the local ambient atmospheric pressure is typically 83 kPa. The purpose of this handbook is to document the pertinent geometric and material property information needed to perform model validation efforts.

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗

DOE OSTI2016

Simulation of Proposed Heat Treatment Methods for the Sister Rods

The High Burnup Spent Fuel Data Project (the 'project'), sponsored by the U.S. Department of Energy (DOE) Office of Nuclear Energy (NE), is focused on experimentally evaluating the effects of long-term dry storage and transportation on high burnup (HBU) pressurized water reactor (PWR) fuel (>45 gigawatt days per metric ton uranium). The goals of the project are to provide confirmatory data for analytical model validation and potential improvement; to provide input to future dry storage cask design; to support license renewals and new licenses for Independent Spent Fuel Storage Installation facilities; and to support transportation licensing for high burnup used fuel. In support of these project goals, an instrumented TN-32B bolted-lid cask (the Research Project Cask or RPC) at the North Anna reactor site will be loaded with intact, HBU PWR fuel assemblies (Project Assemblies) having four different kinds of cladding: standard Zircaloy-4, low-tin Zircaloy-4, ZIRLO{sup R}, and M5{sup R}. In approximately ten years, the instrumented cask will be opened for inspection and several fuel rods from the Project Assemblies will be characterized. The project has also removed 25 'sister rods' from assemblies at North Anna: 9 directly from the project assemblies and 16 from similarly constructed and operated HBU assemblies. The 25 sister rods are all high burnup and cover the range of domestically-used cladding alloys. The 25 sister rods were shipped to Oak Ridge National Laboratory (ORNL) in early 2016 for detailed non-destructive examinations (NDE) followed by destructive examination (DE). Examination of the sister rods will provide a baseline for comparison with the cask rods and will allow for separate effects testing. Dry storage canister loading is completed under water in a designated area of the plant's spent fuel pool. In preparation for dry storage, the fuel assemblies and canister cavity must be drained and dried. Typically, the highest temperatures experienced by the fuel during dry storage are encountered either during drying or transfer of the canister to the storage pad; therefore, as a part of the sister rod testing these temperatures will be simulated in the lab to produce samples that are representative of the peak cladding temperature the fuel experiences either during drying, transfer, or storage. (authors)

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DOE OSTI2018

Muon Tracing and Image Reconstruction Algorithms for Cosmic Ray Muon Computed Tomography

Cosmic ray muon-computed tomography (μCT) is a new imaging modality with unique characteristics that could be particularly important for diverse applications including nuclear nonproliferation, spent nuclear fuel monitoring, cargo scanning, and volcano imaging. The strong scattering dependence of muons on atomic number Z in combination with high penetration range could offer a significant advantage over existing techniques when dense, shielded containers must be imaged. However, μCT reconstruction using conventional filtered back-projection is limited due to the overly simple assumptions that do not consider the curved path caused by multiple Coulomb scattering prompting the need for more sophisticated approaches to be developed. Here, we argue that the use of improved muon tracing and scattering angle projection algorithms as well as an algebraic reconstruction technique should produce muon tomographic images with improved quality–or require fewer muons to produce the same image quality–compared to the case where conventional methods are used. We report on the development and assessment of three novel muon tracing methods and two scattering angle projection methods for μCT. Simulated dry storage casks with single and partial missing fuel assemblies were used as numerical examples to assess and compare the proposed methods. The reconstructed images showed an expected improvement in image quality when compared with conventional techniques, even without muon momentum information, which should lead to improved detection capability, even for partial defects.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2025

Non-destructive evaluation and machine learning methods for inspection of spent nuclear fuel canisters: A state-of-the-art review

Nuclear energy is among the cleanest and most efficient energy sources currently available. The operation of nuclear power plants (NPPs) produces large amounts of high-level radioactive waste known as spent nuclear fuel (SNF). Currently, large amounts of SNF is stored in dry cask storage systems (DCSSs) for extended interim storage until a permanent disposal solution becomes available. During the extended interim storage, the DCSS, particularly the SNF canisters, may degrade and abnormal conditions may occur. Therefore, non-destructive evaluation (NDE) and machine learning (ML) approaches are necessary for inspection of SNF canisters. This paper presents a state-of-the-art review of literature by summarizing recent progress made on the applications of NDE and ML for inspection of SNF canisters. Sixteen NDE methods are examined and compared: visual inspection, ultrasonic guided waves (UGWs), laser-based approaches, acoustic emission (AE), eddy current testing (ECT), non-invasive acoustic sensing, dynamic modal testing, cosmic ray muons tomography, neutron imaging, gamma rays detection, fiber optical sensors, through-wall communications, X-ray computed tomography (CT), vibrothermography, monoenergetic photon sources, and surface acoustic wave (SAW) sensors. The technology readiness level (TRL) for each method is assessed and compared. Recent publications on ML-enhanced visual inspection, AE, non-invasive acoustic sensing, dynamic modal testing, and neutron imaging for SNF canisters are summarized and future research needs are identified. In conclusion, this review article provides a convenient reference on the state-of-the-art applications of NDE and ML methods for inspection of SNF canisters.

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DOE OSTI2017

Optimization Scheme for Establishing Queues for Shipment of UNF from Shutdown Reactor Sites - 17554

Approximately 14, 815 used nuclear fuel assemblies (5,800 MTHM) are stored in 486 dry storage cask systems located at 12 independent spent fuel storage installations (ISFSIs) located at shutdown reactor sites located across the U.S. that have no access to spent fuel pools. A preliminary evaluation was performed by the University of North Carolina at Charlotte (UNCC) in collaboration with AREVA to establish optimization schemes for establishing queues for the removal of this used/spent nuclear fuel (hence forth identified as UNF) and Greater than Class C low level wastes (GTCC) found at these shutdown reactor sites. These queues assumed the major portion of the shipment of the UNF and GTCC would be by rail, with heavy haul truck or barge potentially utilized to move the UNF from the site to rail for sites not served directly by rail. The destination for these rail shipments were a hypothetical consolidated interim storage facility (CSF) located in West Texas. The queues were developed based on the total costs and time to finish all shipments needed to remove all the UNF from these shutdown sites. Results are presented for optimization schemes based on a continuous flow of shipments using 1, 2, and 3 crews dedicated to individual ISFSIs and discrete shipments using 2 crews capable of performing operations at multiple ISFSIs. (authors)

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DOE OSTI2015

High-level waste relocation requires use of new technology in aging nuclear facility - 15269

The West Valley Demonstration Project (WVDP) is preparing to relocate 278 canisters of vitrified high-level waste (HLW) from their current location inside the Main Plant Process Building (MPPB) to an outdoor pad for long-term, on-site storage. The waste was produced at the WVDP between 1996 and 2002 and was originally placed in interim storage inside the MPPB in anticipation of off-site shipment for disposal. Relocation of the canisters to a new on-site location is now necessary as part of WVDP Phase 1 Site Decommissioning work to enable pre-demolition activities inside the MPPB to proceed. The logistics of packaging and moving the HLW canisters within an aging facility to another on-site location has provided numerous technical challenges with subsequent innovations. Significant preparations have taken place to resolve structural inadequacies, including sub-surface soil subsidence issues, antiquated equipment, and facility reconfigurations to support up to 134 metric ton (148 ton) loads. To perform the transfer and storage of the HLW canisters, new equipment and fabrications were required including a robust storage system consisting of stainless steel canister overpacks within steel-reinforced concrete storage casks, three specialty cask transporters, a remotely operated welding system and construction of an outdoor engineered storage pad to store the 56 casks containing the relocated HLW canisters. Packaging and relocation of vitrified canisters is scheduled to begin in 2015. (authors)

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DOE OSTI2017

Thermal Analysis Capability of UNF-ST&DARDS

In the United States, approximately 2,500 casks are loaded with commercial spent nuclear fuel (SNF) that has transitioned from wet storage (spent fuel pools) to dry storage. The number of loaded dry storage casks is increasing by approximately 200 each year. Over time, cask designs have evolved to enhance safety and to accommodate more fuel and higher heat loads. Also, higher burnup fuel is being transitioned into dry storage. The SNF is being stored in dry casks for longer times than specified in the original certification period. Several degradation mechanisms related to fuel assemblies and canisters are affected by temperature. For the cladding, temperature-dependent phenomena include creep and annealing, hydride reorientation and embrittlement, and the ductile-to-brittle transition. Temperature can also influence phenomena that affect the long-term integrity of the storage system, including deliquescence, corrosion, and stress-corrosion cracking. Therefore, accurate determination of the temperatures of various components is needed to evaluate potential safety-related issues during transportation after extended storage and to ensure SNF retrievability. The Used Nuclear Fuel-Storage, Transportation & Disposal Analysis Resource and Data System (UNF ST&DARDS) is being developed for the US Department of Energy Office of Nuclear Energy to streamline analyses for the waste management system [1]. Lastly, the thermal analysis capability within UNF-ST&DARDS and example results are discussed herein.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗

DOE OSTI2016

Dry Canister Storage System Inspection and Robotic Delivery System Development

EPRI is working to develop and demonstrate technologies capable of inspecting welded stainless steel canisters used in dry cask storage systems in situ, without the need to remove them from their concrete casks. This involves the coupling of specialized cameras and inspection devices with small remotely operated vehicles (ROVs). The objective is to demonstrate the capability to identify any presence of (or precursors to) stress corrosion cracking (SCC) and other anomalies that may require additional investigation. (authors)

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DOE OSTI2018

Long-term Prediction of Spent Fuel Storage Canisters - Issues and Approaches - 18112

The considerations involved in aging management of stainless steel canisters used in dry cask storage of spent fuel are discussed in this paper in a probabilistic framework. The two important modes of degradation in the long-term performance of the casks are localized corrosion and stress corrosion cracking initiating from the external surface. These degradation modes are determined by the evolution of the electrochemical behavior and the strain rate of the stainless steel. Laboratory data suggest that Type 304L/316L stainless steels should suffer from localized corrosion and SCC under salt deposits. However, field inspection of the canisters has not indicated extensive pitting or stress corrosion cracking. This discrepancy can be understood in terms of the joint probabilities of various factors that must come together to cause these failure modes. A Bayesian network approach is suggested as the framework for modeling the probability of failure of canisters and long-term management of aging. The gaps in knowledge to conduct a Bayesian network analysis are discussed. (authors)

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DOE OSTI2016

Experimental Seismic Response of Scaled Storage Containments under Identical Loading Conditions - 16318

Dry Storage Casks (DSCs) store spent nuclear fuel (SNF), usually at sites contiguous to nuclear power plants known as Independent Spent Fuel Storage Installation (ISFSI). DSCs have been considered as a temporary storage solution, and are usually licensed for 20 years, which can be extended up to an operating periods of 60 years. Recently, however, DSCs have been considered as a potential mid-term solution for hundreds of years. This consideration requires reevaluation of DSC performance under a larger seismic hazard. That leads to larger horizontal and vertical accelerations. This study is a part of a research project evaluating the seismic response of free-standing DSCs under long return period seismic events. This article assess whether the response of free-standing structures under seismic excitation is repeatable. For this purpose, experimental tests were conducted using a six degree-of-freedom (6DOF) shake table. During the experimental tests, several ground motions were repeated multiple times to obtain the dynamic response under identical loading conditions. Scaled casks of four aspect ratios (radius to centroidal height ratio, r/h{sub cg}) were studied: 0.39, 0.43, 0.55 and 0.62. The specimens studied are considered to be 1:2.5 and 1:3.5 scaled model of generic prototype casks. The experimental results show that a small change in initial conditions leads to change in the boundary condition of moving bodies and in combination with acceleration being applied at different frequencies contained within the applied ground motions may lead to a large variation in the response. (authors)

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DOE OSTI2018

Sister Rod Nondestructive Examination Final Report

This report documents work performed under the Spent Fuel and Waste Disposition for the US Department of Energy (DOE) Office of Nuclear Energy (NE) Spent Fuel and Waste Science and Technology program. This work was performed to fulfill the Level 2 Milestone M2SF-17OR010201021, “Documentation of Non-destructive Tests on Sister Pins,” within work package SF-17OR01020102. The High Burnup Spent Fuel Data Project, sponsored by DOE-NE, is focused on understanding the effects of long-term storage and transportation on high burnup (HBU) (>45 gigawatt days per metric ton uranium) light water reactor fuel. The goals of the project are to “provide confirmatory data for model validation and potential improvement, provide input to future spent nuclear fuel (SNF) dry storage cask design, support license renewals and new licenses for Independent Spent Fuel Storage Installations (ISFSIs), and support transportation licensing for high burnup SNF". In support of project goals, 25 sister rods were removed from fuel assemblies at the North Anna Power Station. Nine rods were removed from the project assemblies, and 16 rods were removed from similar HBU assemblies. The 25 sister rods were shipped to Oak Ridge National Laboratory (ORNL) Irradiated Fuels Examination Laboratory (IFEL) in early 2016 for detailed nondestructive examination (NDE) and destructive examination (DE). The detailed examinations will provide essential information on the physical state of the HBU rods and the fuel contained in the rods prior to loading, drying, and long-term dry storage. Similar tests will be performed at the end of the long-term storage period to identify any changes in the fuel rods’ properties during the dry storage period.

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DOE OSTI2015

Higher harmonic ultrasonic guided waves for structural integrity assessment of dry storage canisters - 15381

Dry storage of used fuel from nuclear power plants has gone from an interim storage solution to a longer-term solution, which necessitates monitoring the integrity of the stainless steel canister that confines the used fuel. Since the storage facilities are located around the country in a variety of different environments there is a wide range of degradation mechanisms that could occur over time in the cylindrical canister. One potential degradation mode that has created significant concern is stress corrosion cracking. We propose using higher harmonic ultrasonic guided waves as a tool to nondestructively inspect used fuel canisters. Higher harmonics are generated when a wave propagates through a nonlinear elastic media. These higher harmonics have been shown to be quite sensitive to microstructural features such as dislocation substructures, persistent slip bands, precipitates, etc. The use of ultrasonic guided waves to inspect the canister is attractive due to the size of the canister and the ability of guided waves to inspect a reasonably large domain relative to traditional bulk wave ultrasonics. We will highlight our recent progress on theory, numerical simulations, and laboratory experiments to develop higher harmonic guided waves as a tool to detect microstructural changes that precede macro-scale damage. Analyzed structures include plates and hollow cylinders, and we focus on localized damage initiation, as is the case for stress corrosion cracking. Recent experiments focus on using magnetostrictive transducers in activating the fundamental shear horizontal mode (SH0) and the third harmonic that is generated due to the material nonlinearity. The magnetostrictive transducer comprises a thin iron-cobalt foil, a meandering electric coil, and a permanent magnet. These transducers are inexpensive, easy to use, and are very efficient at generating shear waves. In applications where the wavelength is larger than the plate thickness, the waves are guided by the traction free boundary conditions and propagate in the plane of the plate. For this canister application, the shear horizontal waves energize the entire thickness of the canister and propagate along the shell in the direction dictated by the meander coil. Experiments indicate that magnetostrictive transducers can generate waves that propagate in plate thicknesses of 1 mm to at least 16 mm. The SH0 mode is nondispersive and generates a third harmonic of the same mode that is shown to be sensitive to localized plastic strain and unseen fatigue damage. It has a strong potential to detect the very early stages of stress corrosion cracking. Due to the geometric configuration of dry storage casks, the transducers will need to be delivered to the inspection points by a robotic system that navigates through the cask ventilation system. (authors)

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DOE OSTI2017

Accident analysis of spent fuel storage and transportation cask with Gd based neutron absorber

The shortage of nuclear spent fuel storage pool has been issued. The spent fuel storage and transportation cask is one of the major alternatives for storing spent fuel. The use of advanced neutron absorber is important for effective storage of spent fuel in spent fuel cask. Gadolinium based neutron absorber is chosen since it has high neutron absorption cross section in thermal neutron region compared to boron and it does not produce any gas element when it reacts with a neutron. The major requirement for neutron absorbing materials in the spent fuel cask system is to maintain subcriticality in normal, off-normal and accident conditions. In this study, the criticality calculations under accident conditions are conducted to ensure the safety of spent fuel cask. Major accident conditions are flood and cask tip-over. The full and partial flooded condition is analyzed and 100% flooded condition has the highest reactivity. The water density is selected as 1 g/cm{sup 3} because k{sub eff} is highest at this condition. When the cask tip-over, the flux trap reduces. In this case, a huge increase in reactivity of 800 pcm takes place. (authors)

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DOE OSTI2015

System impacts of accelerated transfer of used nuclear fuel to dry storage - 15220

In the wake of the September 11, 2001 terror attacks, and again after the March 11, 2011, accident at the Fukushima Dai-Ichi station from the Great East Japan Earthquake/tsunami, concern was expressed regarding security of current spent fuel storage practices in the United States. An approach recurrently proposed to reduce the potential for fire and the release of radionuclides in an accident or sabotage scenario is to reduce the loading of the reactor fuel pools, which are frequently maintained near their full capacity at many reactor sites in the U.S. We assess the impact on the waste management system of different scenarios for accelerating the schedule of used nuclear fuel (UNF) transfer from reactor pools to dry storage casks. We consider scenarios where the spent fuel pools are drawn down to 50% or 25% of full capacity over 5- or 10-year schedules. The scenarios include status quo, where UNF continues to remain in dry storage at the reactor sites, as well as scenarios with UNF transfer to interim storage and eventually to a mined geologic repository. The primary purpose is to evaluate how the different scenarios for accelerating the transfer of UNF to at-reactor dry storage would affect the performance of the entire UNF management system. Areas that were considered include an estimate of the additional system costs that could be incurred and where the existing infrastructure at the reactor sites would come under stress from the transfer demands. This study considered only the fuel-handling logistics and rough-order-of-magnitude cost at reactor sites, interim storage facility, and operations to package UNF into disposal canisters. The effects of minimum fuel age that could be transferred and the accelerated transfer starting date are also examined, but found to have relatively little effect. Impacts on safety and worker dose are not evaluated quantitatively, although effects can be inferred from increases in handling operations, etc. from the scenarios considered. (authors)

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DOE OSTI2016

Overview of the U.S. Department of Energy, Office of Nuclear Energy's Nuclear Fuel Storage and Transportation Planning Project

The U.S. Department Energy, Office of Nuclear Energy (DOE-NE) is laying the groundwork for implementing interim storage, including associated transportation, per the Administration's Strategy for the Management and Disposal of Used Nuclear Fuel and High- Level Radioactive Waste, and to develop a foundation for a new nuclear waste management organization. The organization within DOE-NE that is responsible for this planning is the Office of Nuclear Fuels Storage and Transportation (NFST). The technical work to support this planning effort is being conducted by DOE's national laboratories. DOE's overarching goal is to develop options for decision-makers on the design of an integrated waste management system. The goal is to develop an integrated plan to (1) implement interim storage; (2) improve the overall integration of storage as a planned part of the waste management system; (3) prepare for the large-scale transportation of SNF and high-level waste (HLW), with an initial focus on removing SNF from the shutdown reactor sites; and (4) develop the foundational information, resources, and capabilities needed to support future implementation decisions and actions. Near-term objectives are to (1) develop and maintain an integrated plan to accomplish the Administration's Strategy goals, (2) improve integration of storage as a planned part of the waste management system, (including evaluating standardization of dry cask storage systems), (3) develop and evaluate design options for an integrated waste management system, (4) develop and apply systems analyses to provide quantitative estimates of system impacts of utility actions' impacts on the system and inform future decisions, (5) prepare for the large-scale transportation of SNF and HLW, (with an initial focus on removing SNF from the shutdown reactor sites), and (6) establish and maintain a unified, integrated SNF database and analysis system to characterize the input to the waste management system. (authors)

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗

DOE OSTI2023

Metallographic examinations and hydrogen measurements of high-burnup spent nuclear fuel cladding

In the US, commercial spent nuclear fuel (SNF) is transferred to interim dry storage casks where it will be stored for decades awaiting transport to a consolidated interim storage facility or a geologic repository. Because the fuel rod cladding is the first barrier against any radioactive material release, understanding the behavior of SNF cladding, particularly at high burnup (HBU), in dry storage conditions is crucial to safely store and transport the spent fuel. In this study, a series of metallographic examinations and cladding hydrogen measurements were conducted on HBU SNF cladding at Oak Ridge National Laboratory as a part of the High Burnup Spent Fuel Data Project, which is sponsored by the US Department of Energy (DOE) Office of Nuclear Energy (NE). Here, t o investigate the effect of simulated drying conditions on the cladding, three as-received fuel rods with different cladding materials—M5, ZIRLO, and Zircaloy-4—were heated to 400°C and then slow-cooled to room temperature. The pellet and cladding were then qualitatively and quantitatively analyzed and compared in terms of pellet crack morphology, HBU rim, waterside oxide, cladding H, and cladding hydride morphologies. This paper presents and discusses the results of these analyses in detail.

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DOE OSTI2016

Advanced Borobond™ Shields for Nuclear Materials Containment and Borobond™ Immobilization of Volatile Fission Products - Final CRADA Report

Borobond is a company-proprietary material developed by the CRADA partner in collaboration with Argonne, and is based on Argonne's Ceramicrete technology. It is being used by DOE for nuclear materials safe storage, and Boron Products, LLC is the manufacturer and supplier of Borobond. The major objective of this project was to produce a more versatile composition of this material and find new applications. Major target applications were use for nuclear radiation shields, such as in dry storage casks; use in immobilization of most difficult waste streams, such as Hanford K-Basin waste; use for soluble and volatile fission products, such as Cs, Tc, Sr, and I; and use for corrosion and fire protection applications in nuclear facilities.

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