Modeling Shock and Vibration on Used Nuclear Fuel During Normal Conditions of Transportation

In 2017, the United States Department of Energy (DOE) collaborated with Spanish and Korean organizations to perform a multimodal transportation test to measure shock and vibration loads imparted to used nuclear fuel (UNF) assemblies. This test used real fuel assembly components containing surrogate fuel mass to approximate the response characteristics of real, irradiated used nuclear fuel. Pacific Northwest National Laboratory was part of the test team and used the data collected during this test to validate numerical models needed to predict the response of real used nuclear fuel in other transportation configurations. This paper summarizes the modeling work and identifies lessons learned related to the modeling and analysis methodology. The modeling includes railcar dynamics using the NUCARS software code and explicit dynamic finite element modeling of used nuclear fuel cladding in LS-DYNA. The NUCARS models were validated against railcar dynamics data collected during captive track testing at the Federal Railroad Administration’s Transportation Technology Center in Pueblo, CO. The LS-DYNA models of the fuel cladding were validated against strain gage data collected throughout the test campaign. One of the key results of this work was an assessment of fuel cladding fatigue, and the methods used to calculate fatigue are detailed in this paper. The validated models and analysis methodologies described in this paper will be applied to evaluate future UNF transportation systems.

Identification of Key Factors of Fire Risk of Oil Depot Based on Fuzzy Clustering Algorithm

With the rapid development of the national economy, the demand for oil is increasing. In order to meet the increasing energy demand, China has established a number of oil depot in recent years, whose largest capacity reaching up to tens of millions of cubic meters. Due to the flammable and explosive nature of the stored medium, the risk of fire in the oil depot area has increased dramatically as the tank capacity of the storage tank area has increased. The intensification of the oil depot and the development of large-scale oil storage tanks have brought convenience to the national oil depot, but also brought many catastrophic consequences. In recent years, there have been many fires and explosions in the oil depot, causing major casualties and property losses, which seriously endangered the ecological environment and public safety. Based on the constructed oil depot fire risk index system, the fuzzy C-means algorithm (FCM) and fuzzy maximum support tree clustering algorithm is introduced. Through the two fuzzy clustering mathematical models, key factors in the established index system are identified. Firstly, the expert scoring method is used to evaluate the indicators in the oil depot fire risk index system, and the importance degree evaluation matrix of oil depot fire risk factors is constructed through the fuzzy analysis of expert comments. Then, the fuzzy C-means algorithm (FCM) and the fuzzy clustering tree algorithm are used to cluster the various risk indicators, and the key factors of the oil depot fire risk are identified. Through the comparative analysis and cross-validation of the results of the two fuzzy clustering methods, the accuracy of the recognition results is ensured. Finally, using an oil depot as a case study, it is found that passive fire prevention capability and emergency rescue capability are key factors that need to be paid attention to in the oil depot fire risk index. The fuzzy clustering algorithm used in this paper can digitize the subjective comments of experts, thus reducing the influence of human subjective factors. In addition, by using two fuzzy clustering algorithms to analyze and verify the key factors of the oil depot fire risk, the reliability of the clustering results is guaranteed. The identification of key factors can enable managers to predict high-risk factors in advance in the fire risk prevention and control process of the oil depot, so as to adopt corresponding preventive measures to minimize the fire risk in the oil depot, and ensure the safety of the operation of the oil depot.

International Civil Ageing Management and Assessment Methodology of Concrete

For many nuclear power plants worldwide the operation period will be extended to 60 or 80 years in the coming years. As the operation period increases, the importance of knowledge of ageing mechanisms increases. In the framework of LTO there is limited knowledge about ageing and structural integrity of concrete structures. Knowledge about the strength of concrete structures and modelling thereof can be improved for a more complete knowledge base on ageing and degradation mechanism in nuclear facilities. Therefore, effort is required to improve the knowledge of concrete, material models and finite element modelling techniques as well as the assessment method. Recent developments have shown that ageing of civil structures receive more attention internationally (E.g. concrete degradation in bunker building Doel). Traditionally a large part of the research and development is focused on mechanical issues like piping and vessels. In order to increase the knowledge in the field of civil structures, the focus is on investigation of ageing of concrete and determining analysis methods. This paper focuses on the development of a practical assessment method for ageing of civil structures. As a first step information from international publications and other sources on civil structures ageing issues and management thereof, will be gathered. Well known international standards taking care of ageing phenomena based on problem areas and good practices are IGALL and GALL. IGALL and GALL contain information tables based on international experience. This is the starting point of the research in finding an assessment methodology for civil ageing management. It will be shown that IGALL and GALL contain very similar elements. Sorting on the AMPs results in a practical set of datasheets with summarizing information per AMP, including the underlying international experience. The datasheets are of limited size, presenting an helpful overview of the relevant structures or components, materials, environment and mechanisms. A method for civil ageing management is proposed which will be applied and developed in more detail in future research. Further research is necessary to develop a specific assessment methodology for concrete.

Proposal for Improving Insulation Installation Practice for Superheated Steam Line

Insulation is widely used in process plants to reduce heat loss of process fluids in piping and pressure vessels. However, insulation is often not installed around Normally No Flow (NNF) line pipe. In a refinery plant, a steam leak incident happened due to a through-wall crack, which was found around the connection between an insulated superheated steam line with insulation and an uninsulated safety valve line. The through-wall crack was identified to be a fatigue crack initiated at the inner surface by fractography. An unsteady Computational Fluid Dynamics (CFD) analysis was performed to identify mechanism of the through-wall crack initiation. Based on the observation of fractography and the CFD analysis, it is inferred that the through-wall crack was induced by a high cycle thermal fatigue phenomenon, so-called thermal striping, due to incomplete mixing of hot and cold fluids. Many thermal striping incidents in nuclear plants and process plants have been reported. In view of the above fact, it is suggested that conventional insulation installation practice for NNF line pipe, in particular superheated steam line, may cause cracks due to thermal striping around the connection between main superheated steam pipe and branch dead-end leg. In this paper, a convenient guideline for insulation installation is proposed for a dead-end leg of superheated steam line to prevent cracks caused by thermal striping. The guideline can be used to judge the necessity of insulation installation, based on degree of superheat of steam.

Prediction of Flow-Accelerated Corrosion/Erosion in High-Speed Ejectors Using a CFD Model

In high-velocity ejector systems containing liquid droplets, ejector walls are sometimes damaged by flow-accelerated corrosion/erosion. Velocity, droplet size, impact angle etc. are the most important parameters affecting flow-accelerated (FA) corrosion/erosion. In our plant operation, we had experienced FA corrosion/erosion and consequent failure even with very low impact angle. To understand the leak/ failure, we have adopted the Euler-Euler multiphase model-based CFD approach. In the Euler-Euler multiphase model, the liquid droplets are modelled as dispersed phase while the gas-steam is modelled as a continuous phase. To capture the droplet dynamics very accurately, appropriate correlations for drag, lift and wall lubrication force have been chosen. In CFD simulations we have observed liquid film formation at the ejector wall. The liquid film moves along the ejector wall creates a very high wall shear-stress. In the location of high wall shear-stress, one can expect high FA corrosion/erosion and consequent leak. Qualitative comparison of the X-ray image of the actual equipment with the CFD results for wall-shear stress shows very good agreement in terms of predicting leak location. Moreover, we have varied the droplet size and the liquid fraction in the upstream of the ejector. Qualitatively we have observed that with increase in droplet size the material removal rate increases, however, the affected area of the leak decreases. The more liquid in the system increases the wall-shear stress very rapidly. The present CFD model is useful for predicting the leak-prone location and taking predictive actions (e.g. cladding the wall with a high-grade material).

Fitness for Service Assessment of Carbon Steel Vessel With Localized Deformation During PWHT

Post weld heat treatment (PWHT) is applied to welded pressure vessels and piping to relieve residual stress built up during welding. During the PWHT, pressure vessel made of carbon steel is heated up to a minimum temperature of 595 °C for a holding period as required based on the thickness (Refer ASME Section VIII, Division 1, UCS 56) [1]. However, for equipment susceptible to carbonate stress corrosion cracking, PWHT is required irrespective of thickness at a temperature range of 649 °C to 663 °C as per WRC 452 [2]. A process column built in 1983 and operating in carbonate stress corrosion cracking environment was observed to have widespread corrosion under insulation at reboiler supports. Material of construction for the column was SM41B (Japanese Industry Standards Carbon Steel). Four Insert plates of various sizes were welded at same circumferential band during turnaround. The insert plate repair sizes were relatively large. Local PWHT was required to be performed with the equipment in vertical condition. Due to risk of uneven temperature distribution and resultant local thermal stresses, spot PWHT or Bulls-eye method of PWHT was not considered. Full circumferential local PWHT was considered for this equipment. During the actual PWHT process, localized overheating occurred, and some areas of deformation were observed in the equipment. A multi discipline review was performed to understand the root cause of the localized overheating and subsequent deformation. This paper describes the methodology and results of the fitness-for-service (FFS) assessments that were performed based on API 579-1/ ASME FFS-1, 2016 [3] to assess the integrity of the column. Based on the assessment performed, the equipment was found to be fit for service and continued safe operations.

Boron Injection Tank Repair at Indian Point Unit 3

In the Fall of 2018 Westinghouse designed a welded plug to repair a leak around a previously capped nozzle in the Boron Injection Tank at Indian Point Unit 3. The leak was caused by weld cracking around the nozzle. In order to complete the repair, the existing nozzle and weld needed to be removed by boring into the tank so that a custom plug could be installed. Due to site procedures, welding could not be performed inside the tank, so a single weld on the outside of the tank needed to be designed to meet ASME B&PV Code, Section III requirements. In addition, the tank was manufactured from carbon steel with a stainless steel cladding, so future corrosion of the carbon steel needed to be assessed. The leak was an outage related incident, which required the design to be expedited. This paper will discuss the technical challenges in designing the welded plug to meet the site and code requirements.

Thermal Analysis of the 9977 Package Used for Nuclear Material Storage

The 9977 is a US Department of Energy (DOE) shipping package used to transport plutonium bearing materials. The package utilizes a single 6 inch diameter containment vessel and a foam overpack to protect against fire and impact events. A storage facility fire, hotter and longer than the regulatory transportation fire, is evaluated to ensure radioactive material containment is maintained. A sensitivity analysis of foam degradation is also considered to conservatively simulate potential aging effects of the foam during storage. A minimum foam thickness needed to maintain containment during the hypothetical facility fire is determine.

Comparative Risks of Hydrostatic and Pneumatic Pipeline Testing

An important step in a pipeline-construction project is confirming that the piping and facilities are adequate for the expected operating pressures. This confirmation is done via a static strength test using a test fluid. All fluids have mass and internal energy. Fluids under pressure have significantly elevated internal energy. All fluids are compressible to some greater or lesser extent, and the fluid added to raise the pressure of the fluid in the bulk volume adds significant energy. The raw mass of a fluid must be considered when evaluating terrain elements and support elements (i.e., pipe stands and pipe racks). The selection process for a test fluid should always endeavor to minimize the total risk of the entire process. There is guidance in the primary pipeline design/construction codes (e.g., ASME B31 series) for many of the important considerations for managing the risk associated with the tests required to perform this confirmation of fitness for purpose. This code-guidance has historically not shown a clear preference for the selection of one particular test-medium over another. Some jurisdictions have written regulations that step away from ASME guidance and do show a clear preference for hydrostatic testing over pneumatic testing. This preference manifests itself in several ways, but the primary representation is the requirement in statutes and regulations that a pneumatic test have an “exclusion zone” around the test to reduce the risk of injury during the test. These documents tend to not have an exclusion-zone requirement for hydrostatic tests. This paper is undertakes to demonstrate the relative risks of liquid vs. gaseous test media and presents a background of why pneumatic tests have been singled out by regulators as higher risk and shows why this regulatory preference can result in actually increasing risk rather than decreasing it.

Study on Hydrate Formation and Dissociation in the Presence of Fine-Grain Sand

During the solid fluidization exploitation of shallow non-diagenetic NGHs (Natural Gas Hydrates) in the deep-water, hydrates together with mineral sand, natural gas, seawater and drilling fluids flow in the production pipeline. Natural gas released from hydrates during the process of solid fluidization will reform hydrates under the suitable conditions. Therefore, research on the formation and dissociation of methane hydrates in the presence of fine-grain sands is of great significance for ensuring the flow assurance of solid fluidization exploitation of shallow non-diagenetic NGHs in the deep-water field. In this paper, a high-pressure autoclave was used to carry out the experiments of hydrate formation and dissociation under different initial pressures and particle sizes of the fine-grain sand, for investigating into the hydrate induction time, formation amount, rate and dissociation affected by the presence of the fine-grain sand. Results indicated that hydrate formation kinetics in the presence of fine-grain sand was supposed to be also affected by mass/heat transfer, thermodynamics and kinetics. The fine-grain sand would be dispersed in the water phase under the effect of buoyancy, gravity and shearing force. Besides, the fine-grain sand at the gas-water interface would hinder the mass transfer of the methane gas into the water, inhibiting the nucleation of the hydrates, which was more obviously at the lower pressure. When the driving force for hydrate formation was larger, hydrate formation amount increased with the decrease of the particle size of the fine-grain sand. However, hydrate formation amount decreased with the decrease of the particle size of the fine-grain sand when the driving force for hydrate formation was lower. The average growth rate in the presence of fine-grain sand with 2.9 μm was larger than that of 9.9 μm. However, hydrates grew rapidly and subsequently tended to grow at a lower rate in the presence of fine-grain sand with 2.9 μm at 8.0 MPa initial pressure, which was assumed to be affected by the unconverted water wrapped inside the hydrate shell. The changing trends of gas emission during the dissociation process between the sand-containing system and the pure water system were nearly the same. The amount of gas emission reached a peak value within 15 minutes and then tended to stabilize. The difference in the amount of gas emission mainly depended on the formation amount before hydrate dissociation. Hydrates grew rapidly once methane hydrates nucleated in the presence of the fine-grain sand at the lower pressure, which would increase the plugging risk during the process of the solid fluidization exploitation. Further study of the fine-grain sand on flow assurance during hydrate dissociation process should be done in the future. The results of this paper provided an important theoretical basis and technical support for reducing the risk in the process of the solid fluidization exploitation of shallow non-diagenetic NGHs in the deep-water field.