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At least 235 records · Page 13

Toward integrating high-fidelity CFD approaches in the thermal-hydraulic analysis of turbulent dry cask systems

Nuclear power plants have been supplying resilient and reliable electricity for decades, contributing to energy independence of the U.S.. However, nuclear waste management remains one of the most significant challenges in the industry. The safety of dry cask storage systems relies heavily on their thermal-hydraulic performance. Computational Fluid Dynamics (CFD) simulations are often used to demonstrate this performance and ensure that the system design meets safety standards. This study presents reduced numerical models for various types of dry cask systems. These numerical models can produce efficient and fast results based on the employed modeling strategies. Additionally, the study uses a novel approach to high-fidelity simulations to evaluate modeling assumptions in dry cask modeling. Large Eddy Simulations (LES) are used for this purpose, particularly in regions where fluid velocity is relatively high and the turbulence characteristics become important. Furthermore, the results of these high-fidelity simulations will enhance the interpretation of outcomes produced from a lower-fidelity CFD model.

CFD↗

ASSESSING MATERIAL DEGRADATION EFFECTS ON LONG TERM STORAGE STRUCTURAL ANALYSES

PNNL staff are currently working to conduct analyses, integrate experimental data, and develop the technical basis for extended long term storage and subsequent transportation of used nuclear fuel. Analyses will serve to augment the experimental work by addressing degradation phenomena not readily obtainable through experimentation, such as low temperature creep over very long periods of time. Analyses can also address issues such as concrete degradation that may not require a comprehensive R&D program to resolve, as well as evaluation of engineering design solutions that can be implemented to mitigate the amount and extent of experimental data needed. Most importantly, analyses are necessary to determine how much degradation any structure, system, or component can experience and still maintain its ability to meet its safety functions. This paper focuses on various structural modeling issues that are affected by material degradation in extended long term storage scenarios. Typical storage cask and transportation package designs have a safety basis that includes a number of structural static or dynamic finite element analysis (FEA) models. Some of the features of these standard models need to be reconsidered when the fuel is in an extended long term storage state. In this paper, a number of standard safety basis FEA models are discussed and evaluated for their applicability to long term storage scenarios. A vertical handling drop analysis is used to illustrate a case where additional modeling is needed to define the loads and loading history needed to properly evaluate material degradation in long term storage scenarios.

Klymyshyn, Nicholas A.↗

Instrumentation: Nondestructive Examination for Verification of Canister and Cladding Integrity. FY2014 Status Update

This report documents FY14 efforts for two instrumentation subtasks under storage and transportation. These instrumentation tasks relate to developing effective nondestructive evaluation (NDE) methods and techniques to (1) verify the integrity of metal canisters for the storage of used nuclear fuel (UNF) and to (2) verify the integrity of dry storage cask internals.

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Monitoring of helium gas leakage from canister storing spent nuclear fuel: Radiological consequences and management

Chloride-induced stress corrosion cracking (CISCC) of canisters has been identified as a potential degradation mechanism requiring ageing management — especially in a marine air environment. Methods for monitoring helium gas leakage from canisters have been developed on the basis of a phenomenon that the bottom temperature of the canister increases as the top temperature of the canister decreases when helium gas leaks during storage. In this paper, we consider the radiological consequences of CISCC based on two scenarios of helium gas leakage and propose effective management that includes a timeline for monitoring and mitigation. Monitoring helium gas leakage by measuring the difference in temperature between canister surfaces in the dry cask storage of spent fuel (SF) can detect leakage before SF undergoes oxidation as a result of air ingress and before country-specific regulatory limits of off-site doses are exceeded, thereby enabling mitigatory action.

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Characteristics of Muon Computed Tomography of Used Fuel Casks Using Algebraic Reconstruction

Cosmic raymuons passing through matter lose energy from inelastic collisions with electrons and are deflected from nuclei due to multiple Coulomb scattering (MCS). The recent developments in position sensitive muon detectors that can measure incoming and outgoing trajectories of individual muons indicate that MCS could be an excellent candidate for spent nuclear fuel imaging. The main purpose of this paper is to evaluate tomographic scanning of spent nuclear fuel stored within vertical and horizontal dry storage casks. A quantitative analysis of the characteristics of images obtained with filtered back projection (FBP) and algebraic reconstruction techniques (ART) are presented herein, as such a comparison has not been carried out in the past. FBP is a fast tool to determine object boundaries. ART can include muon path models and prior knowledge that can improve resolution and reduce measurement time. The results demonstrate that missing fuel assemblies can be identified with more than 5 projections and that use of muon momentum significantly increases image resolution. It is expected that MCS can be used to successfully reconstruct the dry cask contents and allow identification of all described scenarios in hours. It is also expected that when total variation minimization and a non-local mean filter are applied, ART may yield much better image quality than FBP.

Liu, Zhengzhi↗

Evaluation of Neutron Absorber Panels from Zion Spent Fuel Pool

In spent fuel pools (SFPs), fixed neutron absorber materials are used to increase storage capacity while maintaining criticality safety margins. BORAL{sup R} is a commonly used neutron absorber material for both wet (SFPs) and dry storage (casks). The specific questions surrounding fixed neutron absorber materials include the following: 1. What are the conditions of the neutron absorber panels in SFPs? Is there any gross degradation that could cause potential concern for criticality safety of the pools? 2. Is the coupon monitoring approach adequate for monitoring the conditions of the panels as part of an aging management program? 3. For plants that do not have coupons, do current in situ measurement approaches provide accurate results? Could such in situ approaches be used as an alternative monitoring approach? In order to shed light on these technical questions using actual plant data, EPRI initiated the Zion comparative analysis project at the decommissioning Zion Nuclear Power Plant in late 2014. An overview of the Zion plant, SFP, and project was described in a previous publication. (authors)

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Detailed SCALE Dose Rate Evaluations for a Consolidated Interim Spent Nuclear Fuel Storage Facility

This paper presents a confirmatory dose rate calculation for a proposed consolidated interim spent nuclear fuel (SNF) storage facility (CISF). The proposed CISF was modeled in detail using SCALE 6.2.1 to determine the radiation dose map of the surrounding areas of the facility and determine the location of the controlled area boundary based on 10 CFR 72.104 requirements. The spatial dose rate distribution was determined as the total dose rate contributions by each of the 467 storage casks comprising the CISF. A rectangular boundary outside of which no dose rate exceeds 25 mrem/yr has the dimensions of 1.25 km x 1.25 km. It denotes the smallest rectangle that could serve as the controlled area boundary. The results (dose map) show the unique capability of the SCALE code system for a high-resolution radiation dose simulation of a large SNF storage facility.

Radulescu, Georgeta↗

Modeling of Particulate Behavior in Pinhole Breaches

A model is presented for calculating depressurization time for and particulate release from used nuclear fuel dry storage containers that have developed a pinhole breach. Particular attention is given to particulate deposition and transmission within the breach pathway. The model is modular in nature and is developed in a way that allows for more advanced treatments of internal temperature, internal component geometry, or aerosol flow to be readily incorporated. The model can be treated as a basis for addressing concerns associated with monitoring and verification efforts during long-term dry cask storage

Dry Storage↗

A Misload Analysis Methodology Supporting Criticality Analysis of Spent Nuclear Fuel Canisters Using As-Loaded Configurations

This paper presents an assembly misload analysis methodology developed to support criticality safety analysis of spent nuclear fuel (SNF) dual-purpose canisters (DPCs) using as-loaded configurations. The misload analysis approach is based on Interim Staff Guidance 8 “Burnup Credit in the Criticality Safety Analyses of PWR Spent Fuel in Transportation and Storage Casks” (ISG 8 rev. 3), but extended to support as-loaded configurations. The two misload scenarios analyzed included; (1) the correct assemblies are selected from the pool but placed incorrectly into the most reactive configuration inside the canister, and (2) the incorrect, most reactive assembly/assemblies in the pool is/are placed into the most reactive position(s) in the canister. Results from this misload analysis approach can be combined with misload probability to support criticality safety assessment of SNF during storage, transportation, and disposal. The misload analysis has been applied to 67 loaded DPCs at two sites using a disposal scenario. The analyzed sites include both PWR and BWR reactors and two canister variants—MPC-32 and MPC-68.

Liljenfeldt, Henrik↗

Using temperature and flow fields to detect gas leakage from canisters containing spent nuclear fuel: Applications to RAMM-TM

The multi-physics STAR-CCM+ code has been used to simulate the temperature and flow fields in canister gas leakage experiments conducted by using a 1/4.5-scale model storage cask. The simulations were conducted at Argonne National Laboratory’s Laboratory Computing Resource Center, utilizing high-performance computing resources. Development of STAR-CCM+ simulation models for the 1/4.5-scale model cask is described herein, followed by validation of the simulation results against experimental data. Canister depressurization and thermal response during gas leakage are discussed, along with analyses of the leakage path and allowable leakage rate. The insights gained from the STAR-CCM+ simulations and leakage analyses will help guide future experiments and actual industry applications of Argonne’s Remote Area Modular Monitoring system for canister surface temperature measurement (RAMM-TM) to enable effective aging management of spent fuel during extended dry storage, as well as help reduce risks to public safety and health and protect the environment.

Canister gas leakage↗

Simulated Gamma Doses to Coating Materials for Use in High Level Waste Packages

An outer shield barrier for spent nuclear fuel is being developed in order to improve dry cask performance under mechanical, chemical, and radiological degradation and stresses. The materials proposed for the outer shield barrier are titanium nitride (TiN), a composite oxide layer consisting of ZrO{sub 2}, TiO{sub 2}, and Al{sub 2}O{sub 3}, and a final layer of molybdenum disulfide (MoS{sub 2}). The ultimate aim of this research is to develop a multi component shield material either as multiple layers or a multi material composite that will improve the performance of steel used in long-term storage casks. Two approaches are being examined through this research effort: multilayer and composite. The composition of the oxide layer is crucial to optimizing the shield's properties and performance. At equal oxide compositions the mixture of these specific oxides is commonly known as zirconolite. This material has been shown to provide a water barrier and to provide substantial corrosion resistance to the dry cask. In order to optimize the radiological performance of this layer the compositions of each oxide have been varied and analyzed for chemical, mechanical, and radiological effects on performance. Through the course of this research effort materials performance changes after gamma and neutron exposure as well as gamma and neutron attenuation of the potential shield materials have been measured and correlated to coating composition. As it is particularly difficult to design a novel, five component material with the goal of improving corrosion, wear behavior, heat tolerance, radiation tolerance, and general survivability, it is necessary to understand which coating components contribute to each property enhancement, and which are critical to design and eventual coating survivability. To compliment the experimental research effort, a study of gamma radiation doses using the relevant zirconolite constituent oxides and assorted combinations off all three, ZrO{sub 2}-TiO{sub 2}-Al{sub 2}O{sub 3}, has been conducted in order to gain insight into which, if any, ratios of the three constituent oxides may provide optimal gamma radiation shielding. Analyzing and comparing the oxides to each other it is apparent that the outer shield barrier with no zirconia has the highest absorbed dose rate at 4.88 E6 mrad/hr. The simulations run with no alumina and no titania are remarkably similar in absorbed dose rates. Alumina and titania compositions increase the absorbed dose rate increase. This is to be expected as during these simulations the zirconia composition is decreasing.

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Code of Record: DOE Standard Canister (DOESC)

The United States Department of Energy (DOE) Spent Nuclear Fuel (SNF) Packaging Demonstration seeks to develop and demonstrate the designs, technology, processes, and regulatory framework for packaging DOE SNF for road-ready dry storage (RRDS); and establish the processes that will be used in a future production facility. The Packaging Demonstration will utilize the DOE Standard Canister (DOESC) for packaging select DOE-managed SNF types for interim storage, transportation and disposal as part of RRDS. Placing DOE-managed SNF into RRDS is part of the strategic framework for SNF on the Idaho National Laboratory (INL) site. To comply with DOE, INL and Nuclear Regulatory Commission (NRC) requirements, this Code of Record establishes the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code (BPVC), Section III, Division 3 as the Code that will govern DOESC and internal support structure constructioni, with certain clarifications. This Code of Record establishes a rationale for proceeding without construction certification of the DOESC (i.e., “N-stamping) and the extent to which a Registered Professional Engineer is required for the DOE Spent Fuel Packaging Demonstration. Given the (i) standard industry practice to pursue independent licensure of commercial storage casks and transportation packages by the NRC in lieu of ASME certification and (ii) guidance provided by 10 CFR 830, DOESC construction activities need not be certified (i.e., “stamped”) to the ASME BPVC. However, additional quality assurance requirements will apply as outlined in this Code of Record.

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History and Status of DOE’s Standardized Canister

[Poster] The U.S. Department of Energy (DOE) is responsible for managing spent nuclear fuel (SNF) currently in its possession, as well as SNF that will come into its possession in the future. DOE will rely upon the standardized canister to confine radionuclides and precluding the moderator in order to ensure safe, long-term management and disposition of SNF in its possession. This strategy helps minimize characterization costs (i.e., funds and exposure) and other technical challenges associated with the traditional approach of relying on fuel-specific properties to demonstrate compliance with the regulator. The use of the standardized canister offers the following benefits: • The standardized canister design is complete. It has been tested under a variety of drop and accident scenarios and was subsequently licensed under 10 CFR 72 as a storage system as part of the Foster Wheeler Environmental Corporation (FWENC) Facility. It is also part of the license submittal for Yucca Mountain. • There is high confidence that the standardized canister design can be stored within commercially-available storage casks and licensed as part of a transportation-system package. • A robust standardized canister simplifies accident analyses and does not rely on characterization of the contained waste. This simplifies safety analysis, provides a greater level of confidence with stakeholders and reduces cost and risk. • A common design for the associated packaging, closure, and loadout facilities results in significant savings. • The DOE standardized canister would simplify design efforts, procurement, and fabrication. • Standardizing handling activities and associated training, procedures, equipment, and tooling leads to enhanced safety and surety of operations. The standardized canister is the preferred package for these materials. It withstood scrutiny by the Yucca Mountain Repository License Application, the Nuclear Regulatory Commission’s (NRC) Advisory Committee on Nuclear Waste, the Nuclear Waste Technical Review Board, an American Society of Mechanical Engineers peer review, and the FWENC storage license application. This evaluation summarizes and documents the status of the design and rationale for the DOE standardized canister, and outlines remaining needs before deployment. In addition, it discusses the factors that have the potential to influence storage, transportation, and disposal of DOE SNF.

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History and Status of DOE’s Standardized Canister – 19657

The U.S. Department of Energy (DOE) is responsible for managing spent nuclear fuel (SNF) that is currently in, or will in the future come into, its possession. The DOE standardized canister will be relied upon to confine radionuclides and preclude moderator in order to ensure safe, long-term management and disposition of DOE SNF. This strategy offers an avenue for avoiding the characterization costs (i.e. funds and exposure) and other technical challenges associated with the traditional approach of relying on fuel-specific properties as the basis for demonstrating compliance with the regulator. The use of the standardized canister offers the following benefits: • The standardized canister design is complete. It has been tested under a variety of drop and accident scenarios and was subsequently licensed under 10 CFR 72 as a storage system as part of the FWENC Facility. It is also part of the license submittal for Yucca Mountain. • There is high confidence that the standardized canister design can be stored within commercially available storage casks and licensed as part of a transportation-system package. • The robustness of the standardized canister simplifies accident analyses and does not rely on characterization of the contained waste. This simplifies safety analysis, provides a greater level of confidence with stake holders and reduces cost and risk. • Significant savings result from a common design for the associated packaging, closure, and loadout facilities. • Design efforts, procurement, and fabrication are simplified • Safety and surety of operations are enhanced by standardizing handling activities and associated training, procedures, equipment, and tooling. The standardized canister is the preferred package for these materials and has withstood scrutiny by the Yucca Mountain Repository License Application, the NRC’s Advisory Committee on Nuclear Waste, the Nuclear Waste Technical Review Board, an American Society of Mechanical Engineers peer review, and the Foster Wheeler Environmental Corporation storage license application. This evaluation summarizes and documents the status of the design and rationale for the DOE standardized canister and outlines the remaining needs to allow deployment. In addition, it discusses the factors that have the potential to influence storage, transportation, and disposal of DOE SNF.

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History and Status of DoE's Standardized Canister - 19657

The U.S. Department of Energy (DOE) is responsible for managing spent nuclear fuel (SNF) currently in its possession, as well as SNF that will come into its possession in the future. DOE will rely upon the standardized canister to confine radionuclides and precluding the moderator in order to ensure safe, long-term management and disposition of SNF in its possession. This strategy helps minimize characterization costs (i.e., funds and exposure) and other technical challenges associated with the traditional approach of relying on fuel-specific properties to demonstrate compliance with the regulator. The use of the standardized canister offers the following benefits: - The standardized canister design is complete. It has been tested under a variety of drop and accident scenarios and was subsequently licensed under 10 CFR 72 as a storage system as part of the Foster Wheeler Environmental Corporation (FWENC) Facility. It is also part of the license submittal for Yucca Mountain. - There is high confidence that the standardized canister design can be stored within commercially-available storage casks and licensed as part of a transportation-system package. - A robust standardized canister simplifies accident analyses and does not rely on characterization of the contained waste. This simplifies safety analysis, provides a greater level of confidence with stakeholders and reduces cost and risk. - A common design for the associated packaging, closure, and loadout facilities results in significant savings. - The DOE standardized canister would simplify design efforts, procurement, and fabrication. - Standardizing handling activities and associated training, procedures, equipment, and tooling leads to enhanced safety and surety of operations. The standardized canister is the preferred package for these materials. It withstood scrutiny by the Yucca Mountain Repository License Application, the Nuclear Regulatory Commission's (NRC) Advisory Committee on Nuclear Waste, the Nuclear Waste Technical Review Board, an American Society of Mechanical Engineers peer review, and the FWENC storage license application. This evaluation summarizes and documents the status of the design and rationale for the DOE standardized canister, and outlines remaining needs before deployment. In addition, it discusses the factors that have the potential to influence storage, transportation, and disposal of DOE SNF. (authors)

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Assessing the release, transport, and retention of radioactive aerosols from hypothetical breaches in spent fuel storage canisters

Interim dry storage of spent nuclear fuel involves storing the fuel in welded stainless-steel canisters. Under certain conditions, the canisters could be subjected to environments that may promote stress corrosion cracking leading to a risk of breach and release of aerosol-sized particulate from the interior of the canister to the external environment through the crack. Research is currently under way by several laboratories to better understand the formation and propagation of stress corrosion cracks, however little work has been done to quantitatively assess the potential aerosol release. The purpose of the present work is to introduce a reliable generic numerical model for prediction of aerosol transport, deposition, and plugging in leak paths similar to stress corrosion cracks, while accounting for potential plugging from particle deposition. The model is dynamic (changing leak path geometry due to plugging) and it relies on the numerical solution of the aerosol transport equation in one dimension using finite differences. The model’s capabilities were also incorporated into a Graphical User Interface (GUI) that was developed to enhance user accessibility. Model validation efforts presented in this paper compare the model’s predictions with recent experimental data from Sandia National Laboratories (SNL) and results available in literature. We expect this model to improve the accuracy of consequence assessments and reduce the uncertainty of radiological consequence estimations in the remote event of a through-wall breach in dry cask storage systems.

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Preliminary Design of Critical Experiments Involving Commercially Available B 4 C Neutron Absorber Plates with Low-Enriched UO 2 Fuel

The International Criticality Safety Benchmark Evaluation Project (ICSBEP) is an initiative to provide high-quality benchmark data in a standardized format for criticality safety analysts to use to validate calculational tools and nuclear data. In the last released 2022 version, the ICSBEP handbook contains over 5,000 critical experiment descriptions, results, and associated models. This paper describes the critical configurations proposed and calculations performed as part of the conceptual design phase of Integral Experiment Request (IER) 554 (IER-554). The goal of IER-554 is to add to the benchmark experiments available to the criticality safety community by designing critical experiments that can analyze how adding commercially available Boralcan plates to an assembly of low-enriched UO2 fuel rods affects the effective neutron multiplication factor (k eff ). Boralcan, a neutron absorber product developed by Rio Tinto, is made of B4C in an Al 1100 matrix and is commonly used for criticality suppression in fuel storage pools. In the current version of the ICSBEP handbook, only a few dated critical experiments involve B4C materials, and none involve Boralcan in a thin plate shape. The experiments designed as part of IER-554 are intended to be performed at the Sandia Pulsed Reactor Facility/Critical Experiments (SPRF/CX) apparatus at Sandia National Laboratories. SPRF/CX is a well-characterized assembly considered trustworthy by the benchmarking community because of the numerous high-quality evaluations with very low experimental uncertainties included in the ICSBEP handbook. Figure 1 illustrates the assembly for a particular configuration from LCT-078, one of the published benchmarks in the ICSBEP handbook. The experiments will be moderated and reflected by light water at ambient atmospheric pressure. Before the plates are inserted in the critical assembly, they will be characterized with x-ray computed tomography (XCT) to identify the sizes and distribution of the B 4 C powder particles inside the plates. The preliminary design calculations were performed with SCALE 6.3.0 using the KENO V.a sequence for the criticality calculations, the CE-TSUNAMI-3D sequence for the sensitivity and uncertainty studies, and the ENDF/B-VII.1 Continuous Energy cross section library. All the calculation results presented have 10 pcm statistical uncertainties. A set of critical experiments with Boralcan plates could increase the confidence of the criticality safety community in its modeling methods when using this type of neutron absorber material. Experiments would also help validate k eff calculations, and the industry could use these validations to change the B loading credit limits from the US Nuclear Regulatory Commission standard review plan for dry cask storage of spent nuclear fuel. This paper summarizes only part of the analysis documented in the preliminary design report.

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Progress on the decommissioning of Zion nuclear generating station

The decommissioning of the twin 1040 MWe PWRs at Zion, near Chicago USA is a ground breaking programme. The original owner, Exelon Nuclear Corporation, transferred the full responsibility for reactor dismantling and site license termination to a subsidiary of EnergySolutions. The target end state of the Zion site for return to Exelon will be a green field with the exception of the dry fuel storage pad. In return, ZionSolutions has access to the full value of the decommissioning trust fund. There are two potential attractions of this model: lower overall cost and significant schedule acceleration. The Zion programme which commenced in September 2010 is designed to return the cleared site with an Independent Spent Fuel Storage Installation (ISFSI) pad in 2020, 12 years earlier than planned by Exelon. The overall cost, at $500 M per full size power reactor is significantly below the long run trend of $750 M+ per PWR. Implementation of the accelerated programme has been underway for nearly three years and is making good progress. The programme is characterised by numerous projects proceeding in parallel. The critical path is defined by the inspection and removal of fuel from the pond and transfer into dry fuel storage casks on the ISFSI pad and completion of RPV segmentation. Fuel loading is expected to commence in mid- 2013 with completion in late 2014. In parallel, ZionSolutions is proceeding with the segmentation of the Reactor Vessel (RV) and internals in both Units. Removal of large components from Unit 1 is underway. Numerous other projects are underway or have been completed to date. They include access openings into both containments, installation of heavy lift crane capacity, rail upgrades to support waste removal from the site, radiological characterization of facilities and equipment and numerous related tasks. As at February 2013, the programme is just ahead of schedule and within the latest budget. The paper will provide a fuller update. The first two years of the Zion programme offer some interesting learning opportunities. The critical importance of leadership and project control systems will be emphasised in the paper. Strong supplier relationships and good community cooperation are essential. A learning and adaptable team, incentivised to meet schedule and budget, drives affordability of the whole programme. Our key lessons so far concern organisation and people as much as engineering and technology. (authors)

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