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DOE OSTI2016

Impact of Corrections to the Spallings Volume Calculation on Waste Isolation Pilot Plant Performance Assessment - 16135

The numerical code DRSPALL (from direct release spallings) is written to calculate the volume of Waste Isolation Pilot Plant solid waste subject to material failure and transport to the surface (i.e., spallings) as a result of a hypothetical future inadvertent drilling intrusion into the repository. An error in the implementation of the DRSPALL finite difference equations was discovered and documented in a software problem report in accordance with the quality assurance procedure for software requirements. This paper describes the corrections to DRSPALL and documents the impact of the new spallings data from the modified DRSPALL on previous performance assessment calculations. Updated performance assessments result in more simulations with spallings, which generally translates to an increase in spallings releases to the accessible environment. Total normalized radionuclide releases using the modified DRSPALL data were determined by forming the summation of releases across each potential release pathway, namely borehole cuttings and cavings releases, spallings releases, direct brine releases, and transport releases. Because spallings releases are not a major contributor to the total releases, the updated performance assessment calculations of overall mean complementary cumulative distribution functions for total releases are virtually unchanged. Therefore, the corrections to the spallings volume calculation did not impact Waste Isolation Pilot Plant performance assessment calculation results. (authors)

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DOE OSTI2016

Regulatory Compliance Strategy For Recovery-Driven Underground Ventilation System Changes - 16355

The Waste Isolation Pilot Plant (WIPP) facility is managed and operated by Nuclear Waste Partnership LLC (NWP) for the U.S Department of Energy (DOE). On February 14, 2014, a radiological event occurred in the WIPP facility underground repository, which resulted in the release of transuranic isotopes contaminating a portion of the underground primarily along the ventilation path from Panel 7, the location of the incident. The release was initially detected by an underground continuous air monitor (CAM) which caused an automatic switch of the ventilation system to filtration mode and ventilation was directed through high-efficiency particulate air (HEPA) filtration banks located in the surface exhaust building. When the HEPA filtration was engaged, the underground normal ventilation was reduced from 425,000 standard cubic feet per minute (scfm) to 60,000 scfm. Since the event, all exhaust air is filtered through HEPA filters at 60,000 scfm to minimize the possibility of exposure to workers, the public and the environment. Ventilation of fresh air to the WIPP underground is a primary limitation to performing underground recovery activities; therefore, recovery-driven ventilation changes are needed. The safe recovery of the WIPP facility and resumption of normal waste emplacement activities require an increase in ventilation capacity to be accomplished in three phases: 1) Interim Ventilation System, 2) Supplemental Ventilation System and 3) Permanent Ventilation System. Each phase adds increased air flow to the underground and allows for underground activities to be performed concurrently. The regulatory strategy for ventilation recovery focuses on ensuring that needed changes to the WIPP facility are protective of human health and the environment. Recovery-driven ventilation changes are implemented using the procedures, processes, and regulations that are required by the two primary regulatory agencies for the WIPP facility: the U.S. Environmental Protection Agency (EPA) and the New Mexico Environment Department (NMED) as well as DOE requirements. Regulatory compliance is being achieved for the three ventilation phases to restore underground ventilation by providing the regulators and stakeholders opportunities for involvement during the design and development processes. A strategy for a tiered NMED permitting process and a plan for developing required EPA documentation are under consideration. The Project's objective is to resume normal waste emplacement activities with safety, protection of the public, the worker and the environment as the highest priorities. Important elements of ensuring that WIPP facility recovery and future waste emplacement activities occur as planned are transparency and communication with the regulatory community. (authors)

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DOE OSTI2017

Report on the Status of the SFWST Campaign International Activities in Disposal Research at SNL

The following summaries are provided as fulfillment of milestone M4SF-17SN080305022 and represent international coordination activities in disposal research funded by the US DOE Spent Fuel and Waste Storage and Technologies (SFWST) Campaign during Fiscal Year 2017: SFWST funded bi-lateral interactions with Taiwan, OECD-NEA Repository Metadata (RepMet) project, SFWST funded bi-lateral interactions with the Republic of Korea.

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DOE OSTI2025

Standard Analysis Report INV-SAR-81, Revision 0 Chemical and Cement Components 2023 Inventory Estimates for the Interim State Performance Assessment of the Waste Isolation Pilot Plant

This standard analysis report provides the estimates for the chemical (oxyanions and complexing agents) and cement components with a data collection cut-off date of December 31, 2023. These estimates will be included in a Performance Assessment Inventory Report developed for the U.S. Department of Energy (DOE) interim state repository configuration performance assessment (PA) for the 2026 Compliance Recertification Application (CRA).

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DOE OSTI2017

Swedish Solution for Reconditioning, Transport, Interim Storage and Final Disposal of Failed Fuel - 17024

Despite today's increasingly more reliable operation of nuclear power plants, failed fuel rods exist in all Swedish plants. Managing intermediate storage and sub-sequential final disposal of such rods has been a growing problem. The Swedish system for spent fuel management uses the principle of intermediate storage of the fuel in a central intermediate storage facility (CLAB) before disposal in a final repository according to the KBS-3 method. However, the intermediate storage facility does not allow storage of failed fuel and the final repository has limitations on moisture in the deposited fuel and hence failed or broken fuel rods cannot be accepted as-is. The nuclear power companies in Sweden have jointly established the Swedish Nuclear Fuel and Waste Management Co, SKB, to manage the spent fuel and the operational waste. To find a solution to transport the failed fuel to storage, SKB has established a project with the goal to have all currently failed fuel rods from all the Swedish nuclear power plants reconditioned and transported to the intermediate storage facility before the year of 2020. The project has established the acceptance criteria for reconditioned failed fuel in the final repository and evaluated a number of options for treatment, encapsulation and transportation of the failed fuel rods. Furthermore, two suppliers have developed reconditioning methods fulfilling the criteria and contracts were signed with both suppliers in May 2016. This paper outlines the details of the Swedish solution for treatment and storage of failed fuel including the technical requirements for the reconditioning method and transportability. (authors)

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DOE OSTI2016

Immediate Dismantling of a Large Fleet of LWR NPPs: Consequences for Spent Fuel and Waste Management - 16027

The experience feedback shows that the complete dismantling of one Light Water Reactor (LWR) unit is an activity now globally well under control (reactor pressure vessel and its internals removal and cutting included). However some specific industrial difficulties may arise in view of the dismantling of numerous LWR units simultaneously. Indeed more than 300 LWR units are currently operated worldwide, which have been commissioned these last 50 years. So in some countries, many units may be permanently shut down over a period of few years in the next decades. Such a situation addresses the issue of the overall management of large quantities of spent nuclear fuel (SNF) and decommissioning waste for the concerned units. For example, in France, the legislative and regulatory framework for the nuclear facilities favors their dismantling 'as soon as possible' after their permanent shutdown which implies as well to limit the duration of the transition period from operation to decommissioning. Furthermore 58 LWR units have been commissioned between 1977 and 1999 in France - on average more than 2 units per year. In this context, the operator (Electricite de France - EDF) plans to remove quickly the SNF then to perform dismantling actions immediately after the permanent shutdown of the LWR units. One issue is to remove the SNF from all the relevant units, even if this removal is simultaneous in many units (permanently shut down or still under operation). Similar issue has to be taken into account regarding the management of the radioactive waste (RW) produced by the dismantling and clean-up actions, notably the RW that cannot be disposed of in a near surface repository. One method followed by the French technical support organization (Institut de Radioprotection et de Surete Nucleaire - IRSN) to analyze these issues is the use of estimates of flows of SNF and RW. These estimates are based notably on a phasing-scenario and a planning template defined for the decommissioning of the units of one nuclear power plant (NPP) and coupled to an overall schedule for phase out all the units of the fleet. The estimates relative to the next decades can be compared to the current experience feedback of flows of SNF and RW for units under operation, in order to identify risks when facing decommissioning. The risks highlighted are driven by key parameters (as duration of the main dismantling actions) of the estimates which can be adapted to minimize their impact. On this basis, it is possible to identify the key-factors to dismantle each unit of NPPs and phase out the fleet regarding SNF and RW management. It is noteworthy that this work needs to be done in any case upstream the studies and the implementation of dismantling actions. Finally it can be underlined that another issue is the human resources (staff, skills and knowledge) necessary to perform all the decommissioning actions, but this aspect is not addressed in the present paper. (authors)

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DOE OSTI2022

Sensitivity analysis of generic deep geologic repository with focus on spatial heterogeneity induced by stochastic fracture network generation

Geologic Disposal Safety Assessment Framework is a state-of-the-art simulation software toolkit for probabilistic post-closure performance assessment of systems for deep geologic disposal of nuclear waste developed by the United States Department of Energy. This paper presents a generic reference case and shows how it is being used to develop and demonstrate performance assessment methods within the Geologic Disposal Safety Assessment Framework that mitigate some of the challenges posed by high uncertainty and limited computational resources. Variance-based global sensitivity analysis is applied to assess the effects of spatial heterogeneity using graph-based summary measures for scalar and time-varying quantities of interest. Behavior of the system with respect to spatial heterogeneity is further investigated using ratios of water fluxes. This analysis shows that spatial heterogeneity is a dominant uncertainty in predictions of repository performance which can be identified in global sensitivity analysis using proxy variables derived from graph descriptions of discrete fracture networks. New quantities of interest defined using water fluxes proved useful for better understanding overall system behavior.

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DOE OSTI2015

Multilateral Spent Fuel Management Efforts: Nonproliferation and Energy Implications in the Asia Pacific

Management of spent nuclear fuel in the Asia Pacific will be a growing challenge in coming decades as the region continues its rapid economic and nuclear energy expansion. Accompanying this growth has been skyrocketing energy demand. The capacity of nuclear energy in the Asia Pacific is expected to increase by approximately 50% by 2035. In fact, of the 66 reactors under construction worldwide, 47 are being built in the Asia Pacific region alone. In a sense, the area is experiencing the so-called ‘Nuclear Renaissance’, which could simultaneously increase proliferation risks while fueling economic growth and political stability. And because ‘Asia Pacific’ includes North America, Oceania, East Asia, Southeast Asia and, by some definitions, South and Central Asia as well as the Middle East, the demand for nuclear energy in particular is expected to continue. Consequently, the Asia Pacific region will soon face important decisions about how to support and implement the necessary infrastructure for nuclear energy expansion and deal with the waste, while also meeting all nonproliferation obligations under the Treaty on the Non-Proliferation of Nuclear Weapons (NPT). One option for dealing with spent nuclear fuel that should be considered is multilateral spent fuel management. Such an effort could help reduce risks associated with safety, proliferation and security of nuclear energy. While the original idea of multilateral spent nuclear fuel management is a decades-old concept, no official plan has been developed because of challenges related to cost, liability, transportation, export controls, international commerce, and nonproliferation, to name a few. Nonetheless, as more and more newcomer countries decide to develop nuclear energy, but do not yet have a strategic plan or the financial means to deal with the waste, the international community may need to take a more proactive approach in developing a multilateral effort, particularly with respect to geological repositories and interim dry storage. Risks and benefits will need to be analyzed, while the role of such an effort in the revival of the Nuclear Renaissance will need to be evaluated. This paper provides an overview of spent nuclear fuel management efforts in the Asia Pacific region and attempts to analyze the possible benefits and feasibility of a multilateral approach.

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DOE OSTI2019

Aluminum Clad SNF: Technical Considerations and Challenges for Extended (>50 years) Dry Storage - 1900y

The U.S. Department of Energy (DOE) manages a significant inventory (>13 MTHM) of aluminum clad spent nuclear fuel (ASNF) using a combination of wet and dry storage at three primary sites; Hanford, Idaho National Laboratory (INL), and Savannah River Site (SRS). The majority of this ASNF is generated from U.S. and international research test reactors (RTR), examples include Advanced Test Reactor (ATR) at INL and High-Flux Isotope Reactor (HFIR) at Oak Ridge National Laboratory (ORNL). The Obama Administration suspension of the Yucca Mountain repository, issuance of the January 2013 DOE 'Strategy for the Management and Disposal of Used Nuclear Fuel and High-Level Radioactive Waste,' delays in implementing the 'regionalization' SNF approach recommended in the 1995 'Department of Energy Programmatic Spent Nuclear Fuel Management and Idaho National Engineering Laboratory Environmental Restoration and Waste Management Programs Final Environmental Impact Statement,' and limited ASNF processing capability at SRS H-Canyon means that interim storage has become the de-facto strategy for managing ASNF. The 1995 Idaho Settlement Agreement requires the DOE to transfer all SNF stored at INL to interim dry storage prior to December 31, 2023 and wet storage capacity at the SRS is nearing capacity. This situation was recognized by the DOE Spent Nuclear Fuel Working Group (SNFWG) and at its June 2016 meeting formed a ASNF sub-working group comprised subject matter experts to evaluate this area and provide a report of findings. The ASNF sub-working group met many times over several month period to review the engineering and technical basis of existing and planned DOE ASNF dry storage facilities and additional studies on the behavior of ASNF under different conditions, including during reactor service. The ASNF sub-working group focused its review on RTR SNF. Based on these reviews, the ASNF sub-working group identified five knowledge gaps and technical data needs that should be addressed to ensure viability and safety of extended, greater than 50 years, sealed or vented interim dry storage of ASNF. These five areas include; behavior/chemistry of aluminum oxyhydroxide layer in dry storage, radiolytic gas generation properties of aluminum oxyhydroxide layers, effect of episodic breathing and radiolytic generation of corrosive gases during storage, performance of ASNF in existing dry storage systems, and effects of high temperature (>1000 C) drying on chemistry and behavior of aluminum oxyhydroxide layers. The ASNF sub-working group also recommended development of an action plan to identify technical and engineering activities needed to address the knowledge gaps and technical data needs. Results of the ASNF sub-working group are documented in 2017 report 'Aluminum Clad Spent Nuclear Fuel: Technical Considerations and Challenges for Extended (>50 years) Dry Storage,' DOE-ID/RPT-1575. The INL assembled a team comprised of twenty INL and Savannah River National Laboratory SNF management and subject matter experts to develop this action plan. Over the course of 2 months the team worked to develop the action plan. The plan identified and recommended six technical and engineering tasks needed to address the previously identified knowledge gaps and technical data needs. DOE Environmental Management Office of Technology Development is providing funding to the INL to execute these tasks. This paper will present and discuss the results of the ASNF sub-working group, tasks identified in the action plan, and experimental activities underway at INL and SRNL to address the action plan. (authors)

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DOE OSTI2019

Radiation Induced Corrosion of Copper in Deep Geological Repositories - 19493

This paper presents an overview of the Cu corrosion research being conducted by the Radiation Assisted Materials Performance Science (RAMPS) group at Western University, in collaboration with the Canadian Nuclear Waste Management Organization (NWMO) and Canada Natural Science and Engineering Research Council (NSERC). This paper presents an overview of our research in three areas to develop a high-fidelity copper corrosion model. Copper is an important candidate material for corrosion protection of used nuclear fuel containers (UFC). The UFC and its environment will be exposed to a continuous flux of γ-radiation. The three areas are chemical kinetics of γ-radiolysis of humid air and groundwater, the effects of solution parameters on Cu corrosion dynamics without γ-radiation and the effects of γ-radiation on Cu corrosion dynamics. These studies show that because of the strong feedback loops between processes occurring during copper corrosion, the overall corrosion mechanism may not follow linear dynamics. Presented here are our key findings, their implications for corrosion science in general, and the potential implications of these results for predictions of the adequacy of a UFC copper corrosion allowance. (authors)

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DOE OSTI2015

System-level logistics modeling of DPC direct disposal - 15511

The U.S. Department of Energy (DOE), Office of Used Nuclear Fuel Disposition, has been conducting a study of the technical feasibility of direct disposal of existing dual-purpose canisters (DPCs) loaded with commercial spent nuclear fuel (SNF). The system-level logistical modeling described here is a part of this study with the primary goals to project the inventory of DPCs in the future and to understand the timing of DPC disposal constrained by thermal power limits for disposal and other key parameters of the waste management system. The logistics simulations also allow for estimating fuel age at emplacement, an important consideration if storage time is limited. This analysis evaluated the effects on DPC direct disposal from uncertainty in repository emplacement power limits, the repository start date, and whether or when the nuclear industry could transition to loading SNF into the smaller capacity multi-purpose canisters (MPCs). MPCs implemented at a future date would likely contain the youngest fuel with highest burnup, but smaller MPCs would cool to the emplacement power limits relatively quickly. The results of this analysis demonstrate that DPC direct disposal could be complete by about 2070 to 2170 depending on the repository emplacement power limit. These completion dates can be expedited by approximately 10 to 40 years in some scenarios through the transition to MPCs. The greatest average SNF age at emplacement is 88 years in the scenarios with the smallest repository thermal power limit in which no transition to MPCs is considered. Transition to MPCs could decrease the average age at emplacement, to as low as 42 years in some scenarios. (authors)

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DOE OSTI2020

Modelling uranium dioxide corrosion under repository conditions: A pore-scale study of the chemical and thermal processes

This paper investigates the corrosion behaviors of spent uranium dioxide (UO 2 ) fuel when placed in geological repositories. We performed pore-scale reactive transport simulations of the UO 2 corrosion process in a defective fuel rod with different orientations of breach or fracture on its clad. It is found that the corrosion rate has strong dependency on the breach orientation. The highest corrosion rate of UO 2 is calculated when the angle between the groundwater flow direction and the clad fracture reaches 180°. UO 2 corrosion simulations with different flow rates are compared. The results show the higher flow rate accelerates the corrosion of UO 2 fuel. The effect of pH on the corrosion process is also determined. It is indicated that higher pH can limit the corrosion of UO 2 by reducing the reaction rate. The dependence of reaction rate and time on reactive surface area is explored. Spent fuel with lower surface area demonstrates longer lifetime under corrosion conditions. A numerical model coupling thermal conduction and chemical reactions is developed to assess the impact of temperature on the process of UO 2 corrosion. The results show that higher temperature leads to larger corrosion rates for UO 2 . Here, the predicted reaction rates are higher in comparison with the isothermal results. Hence, our results can help improve the fundamental understanding of UO 2 corrosion in geological repositories for long-term storage of spent nuclear fuels and provide guidance for the safe operations and selection of appropriate repositories.

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DOE OSTI2017

Storage, transportation and disposal system for used nuclear fuel assemblies

An integrated storage, transportation and disposal system for used fuel assemblies is provided. The system includes a plurality of sealed canisters and a cask sized to receive the sealed canisters in side by side relationship. The plurality of sealed canisters include an internal basket structure to receive a plurality of used fuel assemblies. The internal basket structure includes a plurality of radiation-absorbing panels and a plurality of hemispherical ribs generally perpendicular to the canister sidewall. The sealed canisters are received within the cask for storage and transportation and are removed from the cask for disposal at a designated repository. The system of the present invention allows the handling of sealed canisters separately or collectively, while allowing storage and transportation of high burnup fuel and damaged fuel to the designated repository.

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DOE OSTI2017

Storage, transportation and disposal system for used nuclear fuel assemblies

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DOE OSTI2017

Potential Cost Implications of an Interim Storage Facility for Commercial SNF+ - 17132

The question of whether or not consolidated interim storage of commercial spent nuclear fuel (SNF) should be part of the federal waste management system as an intermediate step before permanent disposal has been debated for more than four decades. This paper summarizes an evaluation of the cost implications of incorporating a consolidated interim storage facility (ISF) into the waste management system (WMS). In this study, the order-of-magnitude estimates of total system costs were calculated and tabulated. The analyzed scenarios involve shipment of SNF from reactors in dual-purpose storage and transportation canisters (DPCs) currently being used by utilities for dry storage at reactor sites. A number of pertinent conclusions can be drawn from this evaluation, including: - Delay in repository availability increases total system costs. Any delay in opening a repository increases total system costs, regardless of whether the system has an ISF or not. This is due to the increased cost associated with an extended duration for storage, whether at multiple independent spent fuel storage installations (ISFSIs) or at an ISF, until waste can be disposed of.- There is a potential total system lifecycle cost avoidance in realistic scenarios with an ISF when compared to scenarios with no ISF. However, most of the cost avoidance occurs several decades after the ISF is opened. The total WMS cost differential over the long term is mainly attributed to the reduced operational costs of storing the fuel in a consolidated facility rather than at individual reactor sites. - Earlier establishment of an ISF allows for more avoidance of post-shutdown at-reactor storage costs for any repository opening date. An ISF allows earlier acceptance of fuel from reactors, which reduces at-reactor costs from a total system perspective. - Transportation costs have little impact on a WMS with or without an ISF. These impacts range from 3-11% of the total cost in all scenarios. Therefore, transporting the fuel twice does not appear to be a significant cost concern driver relative to other system costs. In conclusion, designing, licensing, and constructing an ISF will require a large near-term financial investment. However, reduced annual operating and maintenance costs for an integrated waste management system with an ISF, compared to a system without an ISF, could eventually result in system-wide (integrated) cost avoidance due to reductions in at-reactor storage costs in the long term. The largest cost avoidances would not occur for several decades, so assumptions about inflation, escalation, and discount rates will have a significant effect on potential economic impacts of an ISF. It should be noted that other benefits associated with the investment of an ISF-such as earlier removal of SNF from shutdown reactor sites, earlier prospects for site re-utilization, and additional overall integrated waste management system flexibility-were not addressed in this study. (authors)

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DOE OSTI2019

DOE SFWST Campaign R&D Roadmap Update

The Spent Fuel and Waste Science and Technology (SFWST) Campaign of the U.S. Department of Energy (DOE) Office of Nuclear Energy (NE), Office of Spent Fuel and Waste Disposition (SFWD) is conducting research and development (R&D) on deep geologic disposal of spent nuclear fuel (SNF) and high-level nuclear waste (HLW). R&D addressing the disposal of SNF/HLW in the U.S. is currently generic (i.e., "non-site-specific") in scope, following the suspension of the Yucca Mountain Repository Project in 2010. However, to prepare for the eventuality of a repository siting process, the former Used Fuel Disposition Campaign (UFDC) of DOE-NE, which was succeeded by the SFWST Campaign, formulated an R&D Roadmap in 2012 outlining generic R&D activities and their priorities appropriate for developing safety cases and associated performance assessment (PA) models for generic deep geologic repositories in several potential host-rock environments in the contiguous United States. This 2012 UFDC Roadmap also identified the importance of re-evaluating priorities in future years as knowledge is gained from the DOE's ongoing R&D activities.

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DOE OSTI2018

Annual Transuranic Waste Inventory Report – 2018 (Data Cutoff Date 12/31/2017)

The purpose of this Annual Transuranic Waste Inventory Report – 2018 (ATWIR-2018) is to document the inventory estimate of transuranic (TRU) waste reported by the TRU waste generator sites as of December 31, 2017. This report also notes major changes to the inventory used for the Annual Transuranic Waste Inventory Report – 2017 (ATWIR-2017) (U.S. DOE 2017a) that had a cutoff date of December 31, 2016. This updated inventory information is provided to the U.S. Department of Energy (DOE) Carlsbad Field Office (CBFO) and is available to the DOE TRU waste complex, Waste Isolation Pilot Plant (WIPP) stakeholders, and regulators. The TRU waste inventory information is used for strategic planning, and supports DOE/CBFO’s input into documents (e.g., WIPP Documented Safety Analysis and National Environmental Policy Act analyses), planned changes, and other design changes that may take place in the repository. The DOE/CBFO has determined this report will provide the basis for the Performance Assessment Inventory Report for development of the 2019 Compliance Recertification Application (CRA) deferred performance assessment (PA) (Shrader 2018).

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DOE OSTI2016

Microstructural Characteristics of U-Zr Ingot Slug and Atomized Powder for SFR metal Fuel

Rod-type fuel slugs and spherical powder of U- 10wt.%Zr alloy was also fabricated and characterized in microstructure by injection casting, gravity casting and centrifugal atomization process. U grains became finer from ∼30μm in conventionally ingot rod to ∼2μm in atomized powder. Laminar structure became so fine from ∼0.2μm in conventionally cast ingot rod to 0.05∼0.1μm in atomized powder. Metallic fuels such as U-Zr and U-Pu-Zr alloys have been considered as a nuclear fuel for a sodium-cooled fast reactor (SFR), related to the closed fuel cycle for managing minor actinides and reducing a high radioactivity levels since the 1980's. Metallic fuel slugs of U-Pu-Zr alloys for SFR have conventionally been fabricated by an injection casting method. U-Pu-Zr alloy melts are injected and cast into quartz tube molds during injection casting. Metallic fuel slugs are collected by fracturing quartz tubes from the molds. Demolded quartz tubes are treated with radioactive wastes. Recently, management of minor actinides (MA) became an important issue because direct disposal of the long-lived MA can be a long-term burden for a tentative repository up to several hundreds of thousand years. The metallic fuel for SFR should be remotely fabricated under a radiation shielded environment such as a hot cell, because it contains highly radioactive MA such as Np, Am and Cm. The addition of MA in the fuel composition introduces new challenges in the manufacturing of a metallic fuel slug. Am has a high vapor pressure under a vacuum atmosphere at above a melting temperature of U-Zr or U-Pu-Zr. Used graphite crucibles and quartz molds cannot be recycled easily because of difficult decontamination of radioactive residues on their surfaces. It is necessary to minimize the vaporization of Am and volume of radioactive wastes. Atomized metallic fuel does not need these quartz molds during fabrication, as uranium alloys are prepared as a particle form. It is possible to reduce the formation of radioactive wastes by applying the fabrication process of a particulate metallic fuel. Metallic fuel having a fine microstructure, which originates from a rapid solidification effect during atomization process, results in a higher FG release rate during irradiation. In the case of applying a new forming method such as vibrocompaction in Zr sheath, the sheath can act as a reliable FCCI (fuel/cladding chemical interaction) barrier and a re-constraint for external elongation. In addition, atomized fuel powder, dispersed in a Na liquid metal having a high thermal conductivity, may have a lower temperature distribution during irradiation. In order to develop an efficient fabrication process of metallic fuel for SFR, U-Zr ingot rods were fabricated in a lab-scale with various casting methods. Rod-type U-Zr fuel slugs were fabricated by gravity casting and injection casting. Spherical powder of U-Zr alloy was also fabricated by centrifugal atomization. And then, the microstructural characteristics were investigated by using electron microscopes and energy-dispersive electron X-ray spectroscopy. Atomized U-10Zr powder generally showed spherical morphology of below 200 μm in particle size. U grains became finer from ∼30 μm in conventionally ingot rod to ∼2 μm in atomized powder. Laminar structure became so fine from ∼0.2 μm in conventionally cast ingot rod to 0.05∼0.1 μm in atomized powder. Atomized particulate metallic fuel for SFR has a fine microstructure, resulting in a higher fission gas release rate during irradiation. (authors)

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