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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 OSTI2020

Deposition Behavior of Supersaturated Silicic Acid on the Surfaces of Chlorite and Sericite around Geological Repository - 20138

Around the repository for HLW underground, cementitious materials used for the repository may complicate the migration of radionuclides in the host rock by the alteration of groundwater to a high alkaline condition. Specially, the alkaline groundwater dissolves silicate minerals of host rocks but the plenty of silicic acid dissolved from host rocks in groundwater will become supersaturated and deposit on the surface of flow-paths after decreasing the pH value to about 8 with dispersion and dilution. The deposition of silicic acid is presumed to recover and improve the barrier performance of host rocks for the radionuclide migration because of the narrowing of flow paths and the decrease of the permeability. In this study, the deposition behavior of supersaturated silicic acid was examined by the deposition experiments and the deposition rate constants, k [m/s], were evaluated from the experimental data. As the minerals of the surface of flow-paths, this study focused on chlorite and sericite, hydrothermally-altered minerals distributed to fill fractures of granite. In the experiments, deposition behavior of silicic acid on the powder of chlorite or sericite was observed after the pH of the solution was adjusted to 8 in order to make the silicic acid supersaturated. The solution of CaCl{sub 2} and NaCl were added into a silicic acid to simulate Ca{sup 2+} from the cementitious materials of the repository, Na{sup +} of the saline groundwater in Japan. From the results, the value of k was estimated to be about the order of 10{sup -10}∼10{sup -9} m/s for both chlorite and sericite and the value was almost the same as those for amorphous silica in the previous study. Therefore, the deposition of silicic acid may be assessed by similar apparent deposition rate constants even in actual underground containing various silicate minerals. Moreover, the Damkoehler number which is the dimensionless number expressed by the ratio of characteristic time of mass transfer and chemical reaction was calculated to be 10{sup 4} or more from the value of k. This value shows that the deposition reaction of silicic acid was estimated as much more predominant than the groundwater flow under the situation simulated in this study. These results suggest that the deposition of supersaturated silicic acid on the flow paths composed with various silicate minerals will be able to retard the migration of radionuclides because of narrowing micro flow-paths. (authors)

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DOE OSTI2020

Dual-Purpose Canister Filling Demonstration Project Progress Report

This report discusses the initial progress made at the Oak Ridge National Laboratory to support direct disposal of dual-purpose canisters (DPCs) using filler materials to demonstrate that the probability of criticality in DPCs during disposal to be below the probability for inclusion in a repository performance assessment. In the initial phase of a multi-phase effort that will result in a full-scale demonstration, a computational fluid dynamics (CFD) model was developed to gauge the filling process and to uncover any unforeseen issues. The initial filling simulations of the lower region (mouse holes) of a prototypic DPC show successful removal of the inner space voids and smooth, even progression of the liquid level. In the initial phase, flow through a pipe that is similar to the drain pipe in a DPC will be investigated separately to gain valuable insight of flow regime inside a pipe. The initial experimental setups for validating the computational filling model have been designed, and the various assembly parts are being procured. The experience gained from the initial experiments will be applied to the next steps toward a full-scale demonstration and to the validation of multiphysics filling simulation models.

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DOE OSTI2019

Evaluation of Engineered Barrier Systems (Mid-year Status Report)

This document is a summary of the R&D activities associated with the Engineered Barrier Systems Work Package. Multiple facets of Engineered Barrier Systems (EBS) research were examined in the course of FY19 activities. This report is focused on delivering an update on the status and progress of modelling tools and experimental methods, both of which are essential to understanding and predicting long-term repository performance as part of the safety case. Specifically, the work described herein aims to improve understanding of EBS component evolution and interactions. Ultimately, the EBS Work Package is working towards producing process models for distinct processes that can either be incorporated into performance assessment (PA), or provide critical information for implementing better constraints on barrier performance. The main objective of this work is that the models being developed and refined will either be implemented directly into the Geologic Disposal Safety Assessment (GDSA) platform, or can otherwise be indirectly linked to the performance assessment by providing improved bounding conditions. In either the case, the expectation is that validated modelling tools will be developed that provide critical input to the safety case.

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DOE OSTI2015

Performance assessment modernization at WIPP - 15077

To aid in WIPP PA calculations, the US DOE has undertaken a broad modernization effort that includes: 1) updating the hardware and operating system used; 2) moving the current PA (performance assessment) codes to the new system; and 3) adding a database to store results essential for the analysis of assessments; 4) integrating run-control scripts with a web site to facilitate monitoring of performance assessment calculations; and 5) adding new capabilities via implementation of the PFLOTRAN code to replace multiple codes currently in use. The majority of codes were migrated from an Open VMS/Alpha processor system to a Unix/Intel processor system. Most codes were upgraded to use the dynamic allocation features of Fortran 95 and double precision variables. A few codes were migrated from Linux/Intel systems to the Unix/Intel systems and these code required nearly no changes to the source code. All of the migrated codes were re-qualified under Sandia's WIPP QA program. The implementation of some of the conceptual models using PFLOTRAN is being driven by the expectation that changes in the configuration of the repository will require a 3-dimensional representation of the mined areas. Symmetry in the current configuration of the repository made a 2-D representation adequate. PFLOTRAN is an open-source, state-of-the-art massively parallel subsurface flow and reactive transport code. A version of this code is being developed specifically for WIPP PA in order to maintain the capabilities of the current flow and transport codes, as well as add the capabilities of a parallel code that will treat additional processes, including: 1) miscible multi-phase flow; and 2) heat transfer. PFLOTRAN will replace the two codes (i.e. BRAGFLO and NUTS) currently used for flow and transport calculations, simplifying the PA code structure and speeding up calculations by simultaneously solving for flow and transport with a single code. To ensure that PFLOTRAN reproduces the results of the current code suite, existing test cases have been used for verification purposes. Additional test cases have been developed to establish the new capabilities for WIPP PA. The result of the modernization effort will be a state-of-the-art subsurface flow and transport capability that will serve WIPP PA into the future. (authors)

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DOE OSTI2024

An introduction to Spent Nuclear Fuel decay heat for Light Water Reactors: a review from the NEA WPNCS

This paper summarized the efforts performed to understand decay heat estimation from existing spent nuclear fuel (SNF), under the auspices of the Working Party on Nuclear Criticality Safety (WPNCS) of the OECD Nuclear Energy Agency. Needs for precise estimations are related to safety, cost, and optimization of SNF handling, storage, and repository. The physical origins of decay heat (a more correct denomination would be decay power) are then introduced, to identify its main contributors (fission products and actinides) and time-dependent evolution. Due to limited absolute prediction capabilities, experimental information is crucial; measurement facilities and methods are then presented, highlighting both their relevance and our need for maintaining the unique current full-scale facility and developing new ones. The third part of this report is dedicated to the computational aspect of the decay heat estimation: calculation methods, codes, and validation. Different approaches and implementations currently exist for these three aspects, directly impacting our capabilities to predict decay heat and to inform decision-makers. Finally, recommendations from the expert community are proposed, potentially guiding future experimental and computational developments. One of the most important outcomes of this work is the consensus among participants on the need to reduce biases and uncertainties for the estimated SNF decay heat. If it is agreed that uncertainties (being one standard deviation) are on average small (less than a few percent), they still substantially impact various applications when one needs to consider up to three standard deviations, thus covering more than 95% of cases. The second main finding is the need of new decay heat measurements and validation for cases corresponding to more modern fuel characteristics: higher initial enrichment, higher average burnup, as well as shorter and longer cooling time. Similar needs exist for fuel types without public experimental data, such as MOX, VVER, or CANDU fuels. A third outcome is related to SNF assemblies for which no direct validation can be performed, representing the vast majority of cases (due to the large number of SNF assemblies currently stored, or too short or too long cooling periods of interest). A few solutions are possible, depending on the application. For the final repository, systematic measurements of quantities related to decay heat can be performed, such as neutron or gamma emission. This would provide indications of the SNF decay heat at the time of encapsulation. For other applications (short- or long-term cooling), the community would benefit from applying consistent and accepted recommendations on calculation methods, for both decay heat and uncertainties. This would improve the understanding of the results and make comparisons easier.

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DOE OSTI2020

D and D Research on KM-IT Platform - 20494

The Knowledge Management Information Tool (KM-IT) is a web-based system developed to maintain and preserve the Department of Energy's (DoE's) knowledge base. The system was developed by Florida International University's Applied Research Center (FIU-ARC) with the support of the D and D community including the DOE Office of Environmental Management, and with the collaboration and support of the DoE's Energy Facility Contractors Group (EFCOG) and the former ALARA Centers at Hanford and Savannah. The KM-IT system is a community driven system tailored to serve the technical issues faced by the workforce across the DOE Complex. This KM-IT web-based interactive system is operational and available for use at www.dndkm.org and is currently comprised of the following modules: Web Crawler, Hotline, Technology, Hanford's ALARA Center Reports, Specialist Directory, Lessons Learned, Best Practices, Video/Picture Library, Vendors and Industry News. The Web Crawler dynamically searches through the KM-IT repository as well as the web and displays search results based on the search criteria. The Hotline allows registered users to post questions/problems related to D and D and to receive solutions from a subject-matter specialist. The Technology module serves as repository of D and D technologies and contains technology/ demonstration fact sheets and vendor information. D and D community members can add Lessons Learned, Best Practices, and Pictures/Videos to the D and D repository, after a formal approval process. The Vendor module provides a directory of commercial vendors who provide D and D related technologies, supplies, and services. KM-IT makes an excellent use of the knowledge that exists within the D and D community by allowing D and D project managers around the DOE complex to collaborate by sharing innovative ideas, past experiences, and practices and by maintaining a directory of subject matter specialists. FIU has developed the dedicated module on KM-IT platform to publish D and D research being performed at FIU. This module highlights current EM research efforts and activities in support of D and D being performed at FIU/SRNL associated with fixatives and intumescent products. FIU will expand this module to include the recent and current D and D research being performed across multiple DOE EM sites, national labs and universities. FIU will collaborate with SRNL, INL, ANL and other universities to explore and publish D and D research activities on KM-IT. As a result, the user community will have a centralized location to review new D and D related research across the DOE EM complex. (authors)

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DOE OSTI2017

A Bottom's-Up Model for Siting and Developing Consent-Based Disposal Solutions for SNF and HLW in the USA - 17332

At the end of 2016, the licensing and continued development of the USA's only candidate HLW-repository since 1987 at the Yucca Mountain (YM) site in Nevada had been on hold since 2010 pending the enactment of enabling legislation for one or more of the following paths forward: 1. Re-start of the YM HLW repository. 2. Consent-based siting and development (S and D) of new HLW-repositories for commingled disposal of commercially- (CHLW) and defense-generated (DHLW) HLW. 3. Consent-based S and D of a repository and/or deep boreholes for DHLW only. Public trust in the implementing and regulating entities and a definitive say in an apolitical S and D process by the directly affected parties (DAPs) are historical imperatives for gaining public acceptance and maintaining sustained support of any or all of them. However, due to the widespread negative legacy currently attributed to past politically-controlled S and D organizations, an even more politically controlled organizational structure and an amorphous, 'consent-based', S and D model like that introduced twice in proposed Senate bills since June 2013 will exacerbate, rather than mitigate, the main root causes to past contentions, lawsuits, delays, and cost-increases. We therefore recommend: 1) Assigning the responsibility for safe disposal of CHLW to an independent, chartered public corporation with requisite subject-matter expertise and adequate financial resources. 2) Enacting a related law that: a. Defines 'consent-based' in measurable terms; b. Assigns irrevocable veto rights to facility host state(s) based upon the majority opinion of its legal residents at pre-determined S and D milestones. c. Requires Congressional approval before the facility can open and close. (authors)

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DOE OSTI2020

Opportunities for an Integrated Web-Based Workbench for Data Access and Analysis - 20244

Management of environmental issues can require integration of multiple types of data and information, conducting data analysis and interpretation, and providing data visualization for effective communications. These data elements are important for site management to support regulator interactions and provide defensibility for remedial decisions. Databases and information repositories are core elements of managing data; however, efficient data access and analysis also enable effective site management. The U.S. Department of Energy (DOE) Hanford Site is an example of a complex site with a voluminous quantity of environmental data and a need for efficient site management. Different tiers of data and information tools have been developed and deployed to address site needs. These tools are configured for ready access via the web site interfaces and meet the rigorous quality requirements for environmental site management. Evolving efforts are focused on an integrated platform to meet site environmental management needs. In this platform, users can access site information at multiple levels of detail based on their need and permissions, so that data and associated analyses are presented within the context of the site mission and the user's management or technical needs. This concept is not only applicable at individual sites like Hanford but also applicable at other sites within the DOE complex. An integrated web-based architecture that links data visualization, data analytics, and management tools can provide holistic access to large data sets, minimize complexity, and maximize interactivity and technical communication. (authors)

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DOE OSTI2015

Status of HLW disposal in the USA and rational, progressive, paths forward based upon lessons learned in the USA and abroad since 1973 - 15103

The development of the USA's only candidate (since 1987) HLW-repository at the Yucca Mountain (YM) site, Nevada, was halted by the Obama administration in 2009. Four years later, the Obama administration proposed a new strategy for the back end of the nuclear fuel cycle that would open a consent-based HLW repository 'by 2048'. At the end of 2014, both the YM HLW repository and the new HLW-disposition (storage and disposal) strategy remain on hold due to lack of enabling legislation. With this as background, and based upon our active involvement in, monitoring of, and reporting on HLW management programs in the USA and abroad since 1973, we submit that: 1. Politics, political will, and legal actions and outcomes will continue to govern progress. 2. Public acceptance and sustained support (PASS) may influence politics and political will. 3. PASS is time-dependent and governed by: a. Ideologies; b. Perceived benefits and risks; c. Level and equity of radiation protection provided by applicable regulations; d. Perceived robustness/safety of the proposed disposition concept; and e. Perceived credibility and competency vested in the involved organizations and their respective leaders (= TRUST). We therefore recommend that the USA concurrently pursues at least two, 'centralized' HLW-storage and -disposal solutions based upon best-available relevant knowledge and majority-PASS at facility-host locations. Furthermore, safe(r) and more secure disposal of defense/government-generated HLW could probably commence at least 15 years earlier than 'by 2048' in/at: 1. The YM repository/site. 2. The WIPP repository/site. 3. 'Local' deep boreholes. (authors)

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DOE OSTI2015

Development of flaw acceptance criteria for aging management of spent nuclear fuel multi-purpose canisters

A typical multipurpose canister (MPC) is made of austenitic stainless steel and is loaded with spent nuclear fuel assemblies. The canister may be subject to service-induced degradation when it is exposed to aggressive atmospheric environments during a possibly long-term storage period if the permanent repository is yet to be identified and readied. Because heat treatment for stress relief is not required for the construction of an MPC, stress corrosion cracking may be initiated on the canister surface in the welds or in the heat affected zone. An acceptance criteria methodology is being developed for flaw disposition should the crack-like defects be detected by periodic in-service Inspection. The first-order instability flaw sizes has been determined with bounding flaw configurations, that is, through-wall axial or circumferential cracks, and part-through-wall long axial flaw or 360° circumferential crack. The procedure recommended by the American Petroleum Institute (API) 579 Fitness-for-Service code (Second Edition) is used to estimate the instability crack length or depth by implementing the failure assessment diagram (FAD) methodology. The welding residual stresses are mostly unknown and are therefore estimated with the API 579 procedure. It is demonstrated in this paper that the residual stress has significant impact on the instability length or depth of the crack. The findings will limit the applicability of the flaw tolerance obtained from limit load approach where residual stress is ignored and only ligament yielding is considered.

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DOE OSTI2016

Deposition Behavior of Supersaturated Silicic Acid on Ca-type Bentonite in Geological Disposal System - 16033

For backfilling tunnels in geological disposal systems, the degradation of the low permeability of Na-type bentonite by ion-exchanging to Ca-type is a concern. The deposition of silicic acid around a repository with the dramatic change in pH due to the use of cement causes the clogging of the flow-path and pore space. Such effect may contribute to a more effective barrier performance for radionuclide migration in the backfill. As a first step to clarifying the clogging effect in the backfill, this study examined the deposition of supersaturated silicic acid on Ca-type bentonite. In the deposition experiments, the supersaturated silicic acid solution (250 ml, 4-10 mM, pH>10) was poured into a polyethylene vessel containing Ca-type bentonite (2.5-10.0 g). The deposition of silicic acid was started by setting the pH to 8. As a result, supersaturated silicic acid significantly deposited on Ca-type bentonite under all experimental conditions of supersaturated silicic acid concentration. The experimental results showed that the deposition rate-constants were in the order of 10-11 m/s. Our previous study showed the clogging effect in rocks by using numerical simulation with the same order rate-constants. These findings suggest that the deposition of supersaturated silicic acid on Ca-type bentonite causes the retention of low permeability and the retardation effect for radionuclides by the clogging effect in backfilled tunnels. (authors)

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DOE OSTI2021

An Alternative Conceptual Model for the Spent Nuclear Fuel–Water Interaction in Deep Geologic Disposal Conditions

For the long-term safety assessment of direct disposal of spent nuclear fuel in deep geologic repositories, knowledge on the radionuclide release rate from the UO 2 matrix is essential. This work provides a conceptual model to explain the results of leaching experiments involving used nuclear fuel or simulant materials in confirmed reducing conditions. Key elements of this model are: direct effect of radiation from radiolytic species (including defects and excited states) in the solid and in the first water layers in contact with its surface; and excess H 2 may be produced due to processes occurring at the surface of the spent fuel and in confined water volumes, which may also play a role in keeping the spent fuel surface in a reduced state. The implication is that the fractional radionuclide release rate used in most long-term safety assessments (10 -7 year -1 ) is over estimated because it assumes that there is net UO 2 oxidation caused by radiolysis, in contrast with the alternative conceptual model presented here. Furthermore, conventional water radiolysis models and radiation chemical yields published in the literature are not directly applicable to a heterogeneous system such as the spent fuel–water interface. Suggestions are provided for future work to develop more reliable models for the long-term safety assessment of spent nuclear fuel disposal.

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DOE OSTI2021

Dual-Purpose Canister Filling Demonstration Project Progress Report

This report discusses the progress made at the Oak Ridge National Laboratory to support direct disposal of dual-purpose canisters (DPCs). Acceptable filler materials should demonstrate that the probability of criticality in DPCs during the disposal timeframe is below the probability threshold for inclusion in a repository performance assessment. This effort, which will ultimately result in a full-scale demonstration, includes computational fluid dynamics (CFD) modelling developed to gauge the filling process and to uncover any unforeseen issues. Filling simulations of the lower region (mouse holes) of a prototypic DPC show successfully simulate filling of the void space inside the canister and a smooth, even progression of the liquid level. Flow through a pipe that is similar to the drainpipe in a DPC is being investigated separately to gain valuable insight of the flow regime inside a pipe. Three physical experiments validating the computational filling model have been completed using surrogate liquids. One experiment using molten metal has been completed and the results demonstrate adequate filling of the canister void spaces. Although the scale experiment observed some void spaces related to shrinkage of the metal during cooling, the volume filled is expected to be sufficient to meet the purpose of moderator exclusion. Further experiments will scale up the geometry, moving towards a full-sized DPC demonstration, and provide a more rigorous investigation of candidate filler materials.

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DOE OSTI2024

Drop Analysis of Department of Energy Standard Canister with Fort Saint Vrain SNF

DOE manages over 300 types of SNF, most of which are located at the INL site. The Idaho Cleanup Project and INL are collaborating on the Road-Ready Capability Demonstration Project, which will develop and demonstrate the designs, technology, processes, and regulatory framework for packaging DOE-managed SNF at the INL site for ?road-ready dry storage?. ?Road-ready dry storage? is a SNF management concept where SNF is packaged into dry and sealed canisters, which are then placed in on-site storage in anticipation of later transportation. The forward-looking goal of the Demonstration is establishing the foundation for a large-scale road-ready dry storage program at the INL site. The Demonstration will first package Fort Saint Vrain SNF currently stored at INL into several DOE Standard Canisters. These Standard Canisters will then be loaded into another commercial transportation or storage containment system (e.g., storage cask or transportation package). The Standard Canister is a class of standardized canisters designed for containing the large variety of DOE-managed SNF during interim storage, transportation and/or disposal at a geological repository. One critical aspect of road-ready dry storage is the ability to license the DOE Standard Canisters and its associated transportation package to 10 CFR 71. Depending on the SNF and transportation strategy, the Standard Canisters may have to maintain structural integrity under normal conditions of transport and hypothetical accident scenarios (i.e., drop events). The Standard Canisters have been tested and analyzed under various SNF loading configurations and accident drop events in support of the Idaho Spent Fuel Facility and other DOE programs. However, no analysis has been completed to support the recent Demonstration. This analysis will consider the Ø0.5 m × 5.1 m Standard Canister under drop scenario(s) considered in previous INL tests and analyses, including the 9 m drop at 80 degree off vertical. However, this analysis will consider the more recent Fort Saint Vrain loading configurations proposed for the Demonstration. This analysis will performed using strain-based acceptance criteria established by the American Society of Mechanical Engineers Boiler and Pressure Vessel Code, Section III, Division 3. It will be compared to previous analyses and form the foundation of further formal calculations that will be used to support licensing efforts of the road-ready dry storage system at INL.

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DOE OSTI2015

Outcomes of the full scale seal experiment: a seal industrial prototype for the Cigeo project - 15207

The Full Scale Seal (FSS) Experiment is one of various experiments implemented by Andra, within the frame of the French HLW and IL-LLW Deep Geological Repository Project (aka Cigeo) development, to demonstrate the technical feasibility and check the performance of the seals which will be constructed in the shafts, ramps, drifts and disposal vaults, at time of Cigeo underground facilities progressive closure. The FSS experimental objectives, principles and rationale were presented at WM'2013 (Paper 1306): FSS is a technological demonstrator built on surface, inside a concrete made horizontal drift model (also called the 'test box'). FSS is part of the European DOPAS (Demonstration of Plugs and Seals) [2] project, under the umbrella of the Implementing Geological Disposal - Technology Platform (IGD-TP) [3] project. FSS construction activities started in July 2012 and were completed in September 2014. The construction compliance assessment work activities are now ongoing (and will be continued until mid-2015). This paper presents the construction and monitoring story of the FSS components, starting with the construction of a first containment wall based on a low pH self-compacting concrete (SCC), followed by the swelling clay core backfilling sequence and finishing with the erection of a second containment wall based on a low pH shotcrete. The FSS experiment also enabled to qualify the commissioning methods applicable to an industrial sealing work at time of underground operations in the Repository. These commissioning methods are described and the results discussed. The equipment and methods used for the purpose of seal component construction and monitoring are presented. The physical characteristics obtained for each component of the seal are detailed and the compliance of measured values with the initial requirements is commented. The post-mortem work planned (e.g. coring and wire sawing of low pH concrete containment walls, use of penetrometer for the swelling clay core...) is also explained. FSS is a first of a kind experiment, by its size, by the technical choices made. The first technical outcomes were presented to the French Nuclear Authority and to its Technical Support Organization. The successful implementation of the work carried out in the FSS drift model was positively assessed by the evaluators and deemed representative of the real underground conditions (industrial feasibility is proven). This article concludes with a critical analysis of the methods and equipment used, of the results obtained and provides some perspectives of improvement for the construction of the first Cigeo industrial prototype seals scheduled around 2030 in ramps and horizontal drifts (provided the Cigeo construction is authorized in late 2020, and following the licensing request filing scheduled in late 2017). (authors)

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DOE OSTI2013

Testing of a Transport Cask for Research Reactor Spent Fuel - 13003

Since the beginning of the last decade three Latin American countries that operate research reactors - Argentina, Brazil and Chile - have been joining efforts to improve the regional capability in the management of spent fuel elements from the TRIGA and MTR reactors operated in the region. A main drive in this initiative, sponsored by the International Atomic Energy Agency, is the fact that no definite solution regarding the back end of the research reactor fuel cycle has been taken by any of the participating country. However, any long-term solution - either disposition in a repository or storage away from reactor - will involve at some stage the transportation of the spent fuel through public roads. Therefore, a licensed cask that provides adequate shielding, assurance of subcriticality, and conformance to internationally accepted safety, security and safeguards regimes is considered a strategic part of any future solution to be adopted at a regional level. As a step in this direction, a packaging for the transport of irradiated fuel for MTR and TRIGA research reactors was designed by the tri-national team and a half-scale model equipped with the MTR version of the internal basket was constructed in Argentina and Brazil and tested in Brazil. Three test campaigns have been carried out so far, covering both normal conditions of transportation and hypothetical accident conditions. After failing the tests in the first two test series, the specimen successfully underwent the last test sequence. A second specimen, incorporating the structural improvements in view of the previous tests results, will be tested in the near future. Numerical simulations of the free drop and thermal tests are being carried out in parallel, in order to validate the computational modeling that is going to be used as a support for the package certification. (authors)

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DOE OSTI2017

Modeling of Radiolytic Production of Oxidants Relevant to Corrosion of a Used Fuel Container in Deep Geologic Repository Environments - 17641

The Canadian used nuclear fuel disposal concept involves a deep geological repository using a multi-barrier system. A key barrier is the used fuel container (UFC). It consists of an inner vessel of carbon steel, which provides the structural strength to withstand repository loads, and an outer coating of copper acting as an external corrosion barrier. Relative to other design concepts, coated containers have thinner walls that provide less shielding for γ-radiation, raising the possibility of radiolysis-induced corrosion on the exterior of the container. Also, any trapped aerated water inside the container or in the bentonite clay may condense on the container surface, be exposed to γ-radiation and influence the container corrosion. Understanding the effect of radiation on container corrosion is one key factor to consider in the assessment of the integrity and longevity of the UFC. Humid air radiolysis produces HNO{sub 3} as the dominant oxidizing species. A conservative hemispherical water droplet model was developed to predict the accumulation of HNO{sub 3} and its impact on corrosion. Radiolysis of groundwater in the presence of Cl{sup -} mainly produces H{sub 2}O{sub 2} and HOCl. The concentration of these species is <10 mM and their sum remains almost constant. Radiation exposure tests showed radiation-induced corrosion on carbon steel and Cu. A systematic study of the Cu corrosion and the corrosion rate as a function of [H{sub 2}O{sub 2}], [HOCl], pH and γ-radiation is on-going. (authors)

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