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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Deep Borehole Disposal Safety Case

The safety case for deep borehole disposal of nuclear wastes contains a safety strategy, an assessment basis, and a safety assessment. The safety strategy includes strategies for management, siting and design, and assessment. The assessment basis considers site selection, pre-closure, and post-closure, which includes waste and engineered barriers, the geosphere/natural barriers, and the biosphere and surface environment. The safety assessment entails a pre-closure safety analysis, a post-closure performance assessment, and confidence enhancement analyses. This work outlines the assessment basis and safety assessment aspects of a deep borehole disposal safety case. The safety case presented here is specific to deep borehole disposal of Cs and Sr capsules, but is generally applicable to other waste forms, such as spent nuclear fuel. The safety assessments for pre-closure and post-closure are briefly summarized from other sources; key issues for confidence enhancement are described in greater detail. These confidence enhancement analyses require building the technical basis for geologically old, reducing, highly saline brines at the depth of waste emplacement, and using reactive-transport codes to predict their movement in post-closure. The development and emplacement of borehole seals above the waste emplacement zone is also important to confidence enhancement.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2019

Deep Borehole Disposal Safety Case

This report describes the current status of the safety case for the deep borehole disposal (DBD) concept. It builds on the safety case presented in Freeze et al. (2016), presenting new information and identifying additional information needs for specific safety case elements. At this preliminary phase of development, the DBD safety case focuses on the generic feasibility of the DBD concept. It is based on potential system designs, waste forms, engineering, and geologic conditions; however, no specific site or regulatory framework exists. Updated information is provided for the following safety case elements: (1) pre-closure basis and safety analysis, (2) post-closure basis and performance assessment, and (3) confidence enhancement. This research was performed as part of the deep borehole field test (DBFT). Based on revised U.S. Department of Energy (DOE) priorities in mid-2017, the DBFT and other research related to a DBD option was discontinued; ongoing work and documentation were closed out by the end of fiscal year (FY) 2017. This report was initiated as part of the DBFT and documented as an incomplete draft at the end of FY 2017. The report was finalized by Sandia National Laboratories in FY2018 without DOE funding, subsequent to the termination of the DBFT, and published in FY2019.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2016

Actinide Containment Safety Case in a TRU/HLW Repository in Salt - 16369

The safety case for the permanent isolation of actinides in a salt nuclear repository is discussed. The need for actinide and brine chemistry research is driven by the regulatory process that requires an accounting of low-probability 'worst case' scenarios to show that the release criteria are met under these unexpected conditions. An overview of the WIPP approach to establish the actinide source term, which is defined by the oxidation state distribution, solubility and tendency to form colloidal species, is presented for the key actinides. This approach is then discussed in the context of extending the salt repository concept to defense high level waste (HLW) and possibly spent fuel (SF) to identify key needs and gaps. It is an overall conclusion of this review that the WIPP serves as a good template for the HLW/SF case and the safety case can be readily extended to this repository concept with proper repository design and supporting experimental results. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2016

Evaluation of Current Knowledge for Building the Dutch Salt Safety Case - 16024

This paper provides an overview of an evaluation for building the Safety Case of geological disposal of radioactive waste in rock salt in the Netherlands. The evaluation comprises the present knowledge about the safety and feasibility of geological disposal designs considered in the past, thereby classifying the information taking into account the methodology and structure of a Safety Case. The evaluation is performed as part of the Dutch research programme OPERA (OnderzoeksProgramma Eindberging Radioactief Afval - Dutch acronym for Research Programme into Geological Disposal of Radioactive Waste) by a consortium consisting of GRS from Germany, and TNO and NRG from the Netherlands. Basis of the evaluation is the available Dutch and international scientific-technical information about geological disposal in rock salt, especially from the German and US programmes. The evaluations have shown that although much knowledge on the topic exists, the available information need to be integrated in order to develop a Dutch Safety Case on rock salt. For example, the characteristics of the Dutch radioactive waste investigated for disposal have changed considerably since the last Dutch research programme ended in 2000. This implies that the previously considered Dutch facility concepts for geological disposal in rock salt need to be adapted to the newly regarded waste types such as spent fuel from research reactors and large amounts of LLW, including depleted uranium. Introducing these aspects into the iteration towards a salt Safety Case would also require an update of the post-closure safety assessment. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2016

Safety Case Considerations for Deep Borehole Disposal of Cs/Sr Capsules - 16294

The U.S. Department of Energy Office of Nuclear Energy (DOE-NE) performed an assessment of disposal options that recommended the consideration of deep borehole disposal of smaller DOE-managed waste forms, such as cesium (Cs) and strontium (Sr) capsules. To assess the feasibility of the deep borehole disposal concept for Cs/Sr capsules, safety case considerations are identified and examined. A safety case includes quantitative (e.g., safety assessments) and qualitative information related to both pre-closure (operational) and post-closure safety. For deep borehole disposal of Cs/Sr capsules, pre-closure safety considers potential hazards associated with waste package surface handling and downhole emplacement activities; post-closure safety considers scenarios for long-term radionuclide transport to the biosphere. A preliminary list of qualitative indicators of pre-closure and post-closure safety is presented. Research, development, and demonstration (RD and D) activities that can provide a quantitative basis for these indicators are discussed. In particular, DOE-NE has initiated a Deep Borehole Field Test, using surrogate test packages without radioactive waste, to further investigate various aspects of site characterization, deep drilling, and waste package handling and emplacement that would be needed for a full-scale disposal facility for Cs/Sr capsules or other DOE-managed waste forms. Finally, preliminary results from pre-closure hazard analyses and post-closure performance assessment (PA) calculations are presented as examples of supporting information for the quantitative safety case considerations. These preliminary results suggest that a favorable safety case can be developed for deep borehole disposal of Cs/Sr capsules. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2016

The Importance of Getting it Right - Lessons from the Failure and Subsequent Approval of the LLWR Environmental Safety Case - 16691

The Low Level Waste Repository (LLWR) in the UK submitted an Environmental Safety Case in 2002 which was rejected by the Environment Agency 3 years later. Almost a decade after the rejection, the LLWR submitted a completely different document which was approved in November 2015. This paper looks at the lessons learned from the failed submission and documents the strategy employed by the Site's new contractor to overcome both the challenging technical issues that led to the initial rejection and overcome the resistance to long term disposal by the local community. It will describe the journey it has taken to move from a flawed safety case, to a technically sound safety case, to one that is approved by the regulator, and accepted by the community. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2015

ORNL Evaluation of Electrabel Safety Cases for Doel 3 / Tihange 2: Final Report

Oak Ridge National Laboratory (ORNL) performed a detailed technical review of the 2015 Electrabel (EBL) Safety Cases prepared for the Belgium reactor pressure vessels (RPVs) at Doel 3 and Tihange 2 (D3/T2). The Federal Agency for Nuclear Control (FANC) in Belgium commissioned ORNL to provide a thorough assessment of the existing safety margins against cracking of the RPVs due to the presence of almost laminar flaws found in each RPV. Initial efforts focused on surveying relevant literature that provided necessary background knowledge on the issues related to the quasilaminar flaws observed in D3/T2 reactors. Next, ORNL proceeded to develop an independent quantitative assessment of the entire flaw population in the two Belgian reactors according to the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code, Section XI, Appendix G, Fracture Toughness Criteria for Protection Against Failure, New York (1992 and 2004). That screening assessment of all EBL-characterized flaws in D3/T2 used ORNL tools, methodologies, and the ASME Code Case N-848, Alternative Characterization Rules for QuasiLaminar Flaws . Results and conclusions from the ORNL flaw acceptance assessments of D3/T2 were compared with those from the 2015 EBL Safety Cases. Specific findings of the ORNL evaluation of that part of the EBL structural integrity assessment focusing on stability of the flaw population subjected to primary design transients include the following: ORNL s analysis results were similar to those of EBL in that very few characterized flaws were found not compliant with the ASME (1992) acceptance criterion. ORNL s application of the more recent ASME Section XI (2004) produced only four noncompliant flaws, all due to LOCAs. The finding of a greater number of non-compliant flaws in the EBL screening assessment is due principally to a significantly more restrictive (conservative) criterion for flaw size acceptance used by EBL. ORNL s screening assessment results (obtained using an analysis methodology different from that of EBL) are interpreted herein as confirming the EBL screening results for D3/T2. ORNL s independent refined analysis demonstrated the EBL-characterized flaw 1660, which is non-compliant in the ORNL and EBL screening assessment, is rendered compliant when modeled as a more realistic individual quasi-laminar flaw using a 3-D XFEM analysis approach. ORNL s and EBL s refined analyses are in good agreement for the flaw 1660 close to the clad/base metal interface; ORNL is not persuaded that repeating this exercise for more than one non-compliant flaw is necessary to accept the EBL conclusions derived from the aggregate of EBL refined analysis results. ORNL General Conclusions Regarding the Structural Integrity Assessment (SIA) Conducted by EBL for D3/T2 Based on comparative evaluations of ORNL and EBL SIA analyses and on consideration of other results, ORNL is in agreement with the general conclusions reported by Electrabel in their RPV D3/T2 Technical Summary Note of April 14, 2015: More than 99 percent of flaws in D3/T2 meet the defined screening criterion, rendering them benign with respect to initiation in the event of a design transient. Refined analyses of non-compliant flaws from the screening assessment indicate that only 11 of the 16196 detected flaws have a critical reference-temperature material index (designated RTNDT) that implies the possibility of the initiation of cleavage fracture at some future time. For those 11 2 flaws, the calculated margin in RTNDT (a measure of acceptable embrittlement relative to end-ofservice-life conditions) is significant, being greater than 80 C. Fatigue crack growth is not a concern in the flaw-acceptability analyses. Primary stress re-evaluation confirms that the collapse pressure is more than 1.5 times the design pressure in the presence of defects detected in D3/T2. Sufficient conservatisms are built into the input data and into the different steps of the SIA; in some cases, those conservatisms are quantified and imply that additional margins exist in the SIA. Taken as a whole, the foregoing results and conclusions confirm the structural integrity of Doel 3 and Tihange 2 under all design transients with ample margin in the presence of the 16196 detected flaws.

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗
DOE OSTI2020

Deep Isolation-Development of the Safety Case for Disposal of Radioactive Wastes in Horizontal Boreholes - 20028

Deep Isolation has developed a safe, secure, and permanent geological disposal method for high-level waste, including spent nuclear fuel as well as sealed sources and other highly radioactive materials. The method leverages well established directional drilling technology to create horizontal repositories deep underground. The combination of great depth (1-3 km) and the ability to precisely position repositories in a horizontal orientation provides access to geologic strata that are inaccessible for typical mined and deep vertical borehole repositories. A number of potential direct and indirect safety benefits accrue including:1) greater depth below regional freshwater aquifers; 2) increased flexibility and more geologic options for siting; 3) access to deep formations with persistent and sustained reducing conditions. In addition there are a number of safety elements related specifically to the horizontal repository geometry including: 1) passive direction of thermally driven fluid and radionuclide movement away from the vertical access hole and toward the 'dead end' portion of the repository; 2) mitigation of seismic hazards by orienting repositories parallel to local and regional fault structures. In this paper we explore and discuss some of the key technologic, geologic and hydrologic elements that support the deep horizontal borehole safety case. The stalemate seen across the globe on the disposal of spent nuclear fuel and high-level waste can be broken. Deep Isolation offers a novel option for safe, secure, and permanent deep geological disposal of nuclear waste that can be developed as centralized repositories or adapted to smaller regional or site-specific repositories located near waste sources. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2016

The Approach of the Environmental Consequences and Impacts during Transport of Radioactive Materials (RAM)-A Safety Case - 16420

International Atomic Energy Agency (IAEA) works, together with Member States (MS), to provide a strong, sustainable and visible global nuclear safety and security framework, protecting people and the environment from the harmful effects of ionizing radiation. In the announcement of this IAEA Conference it is underlined that 'nuclear safety and security are to a great extent scientific in nature, a regulatory body with responsibilities for nuclear facilities and other licensed activities involving radioactive material needs to have permanent access to supporting expertise'. This can be provided internally to the regulatory body or through an external entity such as a TSO in order to provide a competent and timely response to regulatory needs, and the development and maintenance of an appropriate knowledge base and associated tools and services, including training and tutoring services, are the main areas on which the conference will focus. This paper presents certain results obtained during carrying out the IAEA-Romanian Scientific Research Contract entitled: 'Romanian Contribution to the Development of Methodology for Risk Assessment and State Management of Nuclear Security Regime (Risk and Radiological Consequences)' where the author served as CSI (Chief Scientific Investigator) a part of the IAEA CRP-(Coordinated Research Project) on the: 'Development of Methodology for Risk Assessment and State Management of Nuclear Security Regime'. Also, potential risks and their possible radiological consequences to peoples and environment must not be underestimated. However, the assessment of risk must be realistic and quantified, and the requirements placed on the appropriate. The IAEA regulations for the Safe Transport of Radioactive Material, 2012 Edition, Specific Safety Requirements, SSR-6, are applicable to the national and international carriage of radioactive material by all modes of transport- by road, by rail, by air, by sea or by inland waters. The Radioactive Material to be transported must be categorized on the basis of its activity concentration, total activity, fissile characteristics (if any) and other relevant subsidiary characteristics. Packaging and package requirements are then specified on the basis of the hazard of the contents and range from normal commercial packaging (for low hazard contents) to strict design and performance requirements (for higher hazard contents). (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2025

Bayesian Optimized Deep Ensemble for Uncertainty Quantification of Deep Neural Networks: a System Safety Case Study on Sodium Fast Reactor Thermal Stratification Modeling

Deep neural networks (DNNs) are increasingly important to scientific computing and engineering system simulations. Accurate uncertainty quantification (UQ) for DNNs is critical in safety-sensitive engineering domains. Traditional Deep Ensemble (DE) methods, while easy to implement, frequently suffer from poorly calibrated uncertainty estimates and limited predictive accuracy due to reliance on fixed architectures with varied weight initializations. To address these issues, we introduce a workflow that combines Bayesian Optimization (BO) and DE. The workflow is modular, scalable, and integrates parallel BO initialized with Sobol sequences to individually optimize the hyperparameters of each ensemble member. This method enhances ensemble diversity, improves predictive accuracy, and provides reliable uncertainty estimates. We evaluate the proposed BODE approach in a sodium fast reactor thermal stratification modeling case study, where we used a densely connected convolutional neural network to predict turbulent viscosity during the reactor transient with consideration of data noise. We benchmark its performance against several optimization approaches, including baseline deep ensemble, evolutionary algorithm-optimized ensemble, ensemble formed via random search combined with greedy selection, and a BO ensemble using random initialization. Here, our results demonstrate superior performance of the developed BODE approach. In noise-free scenarios, BODE notably reduces incorrect aleatoric uncertainty and significantly enhances predictive accuracy. Under conditions of 5% and 10% Gaussian noise, BODE adaptively quantifies uncertainty proportional to data noise, achieving up to an 80% reduction in root mean square error compared to baseline methods and producing well-calibrated prediction intervals.

Bayesian optimization↗