Aging Management Programs Research Articles

Characterization of spent nuclear fuel canister surface roughness using surface replicating molds

In this study we present a replication method to determine surface roughness and to identify surface features when a sample cannot be directly analyzed by conventional techniques. As a demonstration, this method was applied to an unused spent nuclear fuel dry storage canister to determine variation across different surface features. In this study, an initial material down-selection was performed to determine the best molding agent and determined that non-modified Polytek PlatSil23-75 provided the most accurate representation of the surface while providing good usability. Other materials that were considered include Polygel Brush-On 35 polyurethane rubber (with and without Pol-ease 2300 release agent), Polytek PlatSil73-25 silicone rubber (with and without PlatThix thickening agent and Pol-ease 2300 release agent), and Express STD vinylpolysiloxane impression putty. The ability of PlatSil73-25 to create an accurate surface replica was evaluated by creating surface molds of several locations on surface roughness standards representing ISO grade surfaces N3, N5, N7, and N8. Overall, the molds were able to accurately reproduce the expected roughness average (Ra) values, but systematically over-estimated the peak-valley maximum roughness (Rz) values. Using a 3D printed sample cell, several locations across the stainless steel spent nuclear fuel canister were sampled to determine the surface roughness. These measurements provided information regarding variability in normal surface roughness across the canister as well as a detailed evaluation on specific surface features (e.g., welds, grind marks, etc.). The results of these measurements can support development of dry storage canister ageing management programs, as surface roughness is an important factor for surface dust deposition and accumulation. This method can be applied more broadly to different surfaces beyond stainless steel to provide rapid, accurate surface replications for analytical evaluation by profilometry.

Nuclear Facilities Maintenance Culture Development Study

Maintenance is an essential part of the assets and facilities in the organization/company. This deserves serious attention because it is necessary for organizational/company resources, especially for aging nuclear facilities/installations. Maintenance is the main program used to manage company assets and facilities. A lack of asset and facility maintenance culture increases management and maintenance costs. A maintenance culture is needed to improve maintenance skills, tenacity, and perseverance. Maintenance culture is recognized as an essential aspect to improve the quality of maintenance work to maintain structures, systems, and components (SSC) so that they are ready for use at any time/when needed, as well as part of the implementation of aging management programs to extend the life of assets and facilities. This paper will discuss the development of the maintenance culture and review poor maintenance cultures and their solutions. This paper aims to develop a maintenance culture to prevent premature aging and extend the life of assets and facilities. Factors developing maintenance culture include leadership, communication, rewards and recognition, responsibility, rules and standards, empowerment, motivation, involvement, policies, work strategy and planning, teamwork, training and education, awareness, and organizational structure. Corruption, poor leadership, attitude problems, and lack of policy cause poor maintenance culture. The solution to a poor maintenance culture is selecting the right people, improving job skills and knowledge, repairing equipment, ensuring machine/equipment readiness, good planning, scheduling, and general organization, measuring performance, motivating and encouraging desire, and providing sufficient funding. Maintenance culture has an impact on facility performance. Keywords: maintenance culture, nuclear organization, assets, nuclear facility

A Study on One-Time Inspection for Aging Management of Operating Nuclear Power Plants

One-time inspection is used to confirm the effectiveness of nuclear power plant aging management programs such as water chemistry, fuel oil chemistry, and selective leaching program that is designed to prevent or minimize aging degradation during the plant operation. This paper represents one-time inspection experience of selected components and susceptible locations within the scope of water chemistry and fuel oil chemistry aging management programs. Prior to performing one-time inspection, sample sizes of components to be inspected were determined based on combination of materials, environment and aging effect. Examination techniques and relevant operating experience were analysed to obtain technical basis for further implementation of one-time inspection aging management programs. Existing correlation curves between sample size and total population number were reviewed to prepare further inspections for entire operating plants and ensure safety level of components subject to one-time inspection program.

Development of Risk Informed Aging Management Program in Decommissioning

Abstract This paper proposes to solve the issues related to aging management program (AMP) during the decommissioning phase by using risk information. The AMP for the decommissioning plants has not been established while the number of permanently shut down and decommissioned nuclear power plants are increasing in the world. The first issue is the change of the functional importance of the safety systems at the beginning of decommissioning. We propose to evaluate the importance using the probabilistic risk assessment (PRA) model with the change of specification in the decommissioning plant and to determine new importance grade. The second issue is to make the maintenance based on the appropriate risk information. This risk information should be based on the progress of decommissioning, reflected and evaluated in the PRA model, as well as information obtained from maintenance inspections, including the ROP process, and failure experience during routine operation. To address these issues, the maintenance program in decommissioning that uses the evaluation of risk information according to the decommissioning phase is proposed in this paper.

Turbulent Particle Flow in Spent Nuclear Fuel Storage Systems

Deposition models are being developed with the commercial computational fluid dynamics software STAR-CCM+ to evaluate particulate deposition on spent nuclear fuel (SNF) canisters. The primary particulate of concern is chloride salts, which are dispersed in the atmosphere and then deposited onto the canisters. During dry storage, the primary degradation process is likely to be chloride-induced stress corrosion cracking (CISCC) at the heat-affected zones of the canister welds. It is known that stainless steel canisters are susceptible to CISCC; however, the rate of chloride deposition onto the canisters is poorly known, based on sparse field data from a small number of sites. This paper describes work looking at various approaches to modeling turbulence, such as Reynolds-averaged Navier Stokes (RANS) and large eddy simulation (LES), and its impact on particle flow and deposition within a ventilated SNF storage system. The deposition rate is determined for a vertical canister system and a horizontal canister system. LES has the potential to simulate turbulent flows more accurately versus RANS, but is much more computationally expensive. A k-omega version of the RANS turbulence model was used for this study. The computational efficient RANS steady-state model predicted a similar canister deposition result as the LES simulation for a vertical canister storage system. For a horizontal storage system, the RANS steady-state model predicted more particles depositing on the canister than the LES simulation, providing a conservative estimation for particle deposition. A wall correction factor was added to the RANS model to dampen the turbulence fluctuation normal to a surface that left undamped, leads to the RANS model overpredicting deposition along a surface for smaller particles. This work was done to further development of deposition models that could be used to plan and inform SNF canister aging management programs with predictive models for the timing and occurrence of canister CISCC. This work is part of a larger effort tasked with understanding the likelihood of canister degradation due to CISCC. These models are still under development, and testing is needed for validation. However, these models are being presented now to demonstrate to canister vendors, utilities, regulators, and stakeholders the value of this type of modeling.

I-LAMP: Global, Industrywide Learning Aging Management Program for Neutron-Absorber Materials in Spent Fuel Pools

Neutron-absorber materials are used in spent fuel pool (SFP) storage racks to increase storage capacity while maintaining criticality safety margins. Previously, the Electric Power Research Institute (EPRI) proposed a global, industrywide learning aging management program (i-LAMP) as an alternative monitoring program as part of an aging management program. This proposal, along with other EPRI work, was accepted as a concept to close the issued generic letter by the regulator. Since then, EPRI has been working with EPRI-member utilities around the world on data collection. Furthermore, recently, a utility removed two neutron-absorber panels from an operating SFP to meet a regulatory commitment made prior to the i-LAMP proposal. Because of their age and unique history, these panels provided a unique opportunity not only to analyze the conditions of the panels, but also to potentially bound i-LAMP. This paper presents i-LAMP development to date with a focus on BORAL analysis results for these two unique panels, pilot pools as case studies to demonstrate the i-LAMP implementation, and a proposal for a path forward.

Operational Experience in Degradation (Ageing Effects) and Implementation of Ageing Management Programmes for Dry Storage Systems in Ukraine

The Coordinated Research Projects (CRPs) of International Atomic Energy Agency (IAEA) is a power tool to engage simultaneously a lot of different countries that operate Spent Fuel Storage Facilities for solving important safety issues at a deep level of competence and expertise. One of the topics that needs thorough research is behavior and state assessment of spent fuel assemblies and fuel rods during long/very long term storage in spent fuel storage facilities. It is naturally that over a long period, special attention is drawn to degradation mechanisms, ageing effects and ageing management programs that should be implemented in order to avoid and mitigate the impact of degradation mechanisms on spent fuel elements. This article describes the first step of implementing new IAEA CRP project “T13019. Performance Assessment of Storage Systems for Extended Durations (PASSED)” with contribution from the State Scientific and Technical Center for Nuclear and Radiation Safety (SSTC NRS), which conducts research regarding the “Operational experience on degradation (ageing effects) of dry storage systems” during the first stage” at the first stage. The overall objective of the research proposed by the SSTC NRS is to strengthen technical knowledge, experience and understanding of the long-term behavior of the dry spent fuel storage systems, and of the currently applied inspection and monitoring technologies. At the same time, a specific objective of involving the SSTC NRS in this project was not only to present national experience and practices, but also to study the existing experience of the participating countries, which also joined the CRP proposed by the IAEA. The article considers the existing storage systems for spent nuclear fuel at the Chornobyl and Zaporizhzhya NPP sites, provides examples of the aging management system for components and structures, as well as examples of the issues that require development, implementation and maintenance of aging management programs.

The information system concept for thermal monitoring of a spent nuclear fuel storage container

The paper notes that the most common way of handling spent nuclear fuel (SNF) of power reactors is its temporary long-term dry storage. At the same time, the operation of the dry spent fuel storage facilities almost never use the modern capabilities of information systems in safety control and collecting information for the next studies under implementation of aging management programs. The author proposes a structure of an information system that can be implemented in a dry spent fuel storage facility with ventilated storage containers. To control the thermal component of spent fuel storage safety, a database structure has been developed, which contains 5 tables. An algorithm for monitoring the thermal state of spent fuel was created for the proposed information system, which is based on the comparison of measured and forecast values of the safety criterion, in which the level of heating the ventilation air temperature was chosen. Predictive values of the safety criterion are obtained on the basis of previously published studies. The proposed algorithm is an implementation of the information function of the system. The proposed information system can be used for effective thermal monitoring and collecting information for the next studies under the implementation of aging management programs for spent fuel storage equipment, permanent control of spent fuel storage safety, staff training, etc.

AGING MANAGEMENT OF CABLES OF NUCLEAR POWER PLANTS

Cable aging management is an integral and mandatory requirement for continuous safety and reliable operation of nuclear power plants due to the extension of their service life. The research of the scientific community is focused on the adaptation of electrical non-destructive methods of monitoring cable samples in laboratory conditions to determine the state of their electrical insulation. The performed analysis of NPP cable aging management programs proves the need for new representative results of cable research to determine characteristics using special control methods and appropriate equipment. Emphasis is placed on the strategy of cable aging management with the involvement of scientists with professional experience in conducting complex diagnostic examinations with qualified analysis of the obtained results based on the most modern technologies. Effective methods, techniques, and modern techniques for the assessment of the technical condition of NPP cables are presented.

Cable Aging Management Program Implementation in Krško NPP-NEK

As a requirement for plant life extension for more than 40 years some additional Aging Management Programs (AMP) for passive equipment have to be implemented. The article presents overview of Cable Aging Management Program (CAMP) implementation. Program defines basic rules and initial activities for identification of adverse operation environment parameters that could lead to accelerated aging of specific materials. Samples of cables are selected based on nuclear safety and electrical equipment criticality for inspection and testing, to check functionality and prevent unexpected failure during normal operation. Acceptance criteria for environment parameters and diagnostic testing have been set. Initial visual inspection of cables condition in adverse environment and testing of sampled cables and environment are giving results for in time preventive measures. First cable aging management program is implemented since 2010 and its experience could be accommodated to other companies with cables recognized as key components.

Medium and Low Voltage Cable Measurements - TD, PD, LIRA

Elmont d.o.o. Krško – We have spread our main scope of the services from electrical maintenance, modifications implementations and quality control to cable testing area. The main reason for expanding our scope was to support Nuclear Power Plant Krško Cable Aging Management program and the world trend of LTE (Life Time Extension) in power plants. Scope of work – We are identifying potential downgraded conditions for safety and operational important cables in special areas (heat, water, radiation). Our main scope is visual control, and testing with analysis. For low voltage cables the main testing method is Line Resonance Analysis (LIRA). LIRA technology is based on the transmission line theory, through the estimation and analysis of the complex line impedance as a function of the applied signal frequency. We can monitor the global, progressive degradation of the cable insulation due to harsh environment conditions (high temperature, humidity, radiation) and detect local degradation of the insulation material due to mechanical impacts or local abnormal environmental conditions. For medium voltage cables we are using new methods with a power generator that uses Very Low Frequency – 0,1Hz (VLF). The main reason for this is that the measurement unit needs 500 times less energy than the unit which uses 50Hz frequency (50/0,1=500). With this power source we are performing dielectric loss measurements – Tan delta (TD) and Partial discharge measurements (PD). TD measurements show the severity of Water treeing in the measured cable. Water trees mainly come from moisture and are therefore present in cables that lie in manholes filled with water or they submerged in any other way. PD measurements show the severity of voids or other types of defects in cable insulation. These defects can arise during the manufacturing of the cable or they can arise during the installation of the cable or from an accident with the cable during the operational time.

International case survey and literature review of maintenance strategy for decommissioning nuclear power plant during transition period

The Chinshan nuclear power plant in Taiwan has currently shutdown when the operating license expired in 2018. However, because the operation license of the independent spent nuclear fuel dry storage facility has not been approved yet, and the fuel storage racks of Spent Fuel Pool (SFP) has almost saturated, there is not enough space to accommodate all irradiated fuels from the reactor core during the transition period. Therefore, part of the mechanical systems, plant structures and electrical equipment of the plant still have to meet the functional requirements for maintaining the safety under the pre-decommissioning activities.In this article, we introduce the international cases of permanent shutdown but the fuel still in the reactor core, and also describe the actions of the Taiwan Power Company in response to this situation. For the providing regulatory advice, we have also proposed a framework of the maintenance strategy associated with important issues for the transition period since 2018, including a revised Aging Management Program (AMP) for keeping the safety of spent nuclear fuel. From the knowledge level and important issues related to the topic, the Phenomena Identification and Ranking Table (PIRT) is quoted to complete the understanding level of requirements during the transition period.

Ageing management review for reactor license renewal

Abstract The Nuclear Regulatory Commission (NRC) issues licenses for commercial power reactors to operate for up to 40 years and allows these licenses to be renewed for additional periods of 20 years. In 1995 the Commission issued Part 54 of Title 10 of the Code of Federal Regulations (10 CFR Part 54) specifying the regulatory requirements for license renewal. The license renewal rule focuses on managing the adverse effects of ageing of plant structures and components. The NRC staff has developed license renewal rule implementation guidance documents. The NRC staff uses a systematic approach in evaluating the adequacies of ageing management programs. The NRC has approved several license renewal applications to date and will likely be asked to approve dozens more over the next 10 to 15 years.

Ageing management within British Energy in support of safe, reliable operation and lifetime extension objectives

Abstract British Energy has established a comprehensive suite of ageing/obsolescence asset management programmes. Through these programmes, the company has developed a thorough understanding of all the potentially significant degradation mechanisms which could affect the systems structures and components (SSCs) which are essential to the safe, reliable operation of their NPPs. The results from these ageing management programmes underwrite the existing design basis safety case, provide trending information for Safety System Reviews (SSRs) and Periodic Safety Reviews (PSRs) and provide data in support of extending the operating lifetimes of the NPPs. This paper describes te UK regulatory framework with respect to ageing management, British Energy’s overall approach to ageing management, The various ageing/obsolescence management programmes established by BEG, including examples of potentially significant ageing issues which have been successfully addressed by these programmes and the manner in which the results from the programmes are used in support of continued operation, SSRs, PSRs, lifetime extension and general performance enhancement.

Aging management experience to support reliability of RSG-GAS operation and future NPP in Indonesia

The aging process will cause a decrease in the reliability and safety performance of the nuclear reactor operation. As a consequence, the quality of service to stakeholders will decline. In order to keep nuclear reactor reliable, systematic activities are needed to manage the aging process that occurs at the GA Siwabessy multi-purpose reactor (RSG-GAS), in Serpong. The activity includes 4 main elements, i.e.: understanding and evaluating the aging process, using aging prevention methods, detection and surveillance methods, and aging mitigation methods. Aging management is carried out at RSG-GAS through routine and periodic maintenance, repair, replacement and monitoring mechanisms. Aging management must be planned from design, construction and commissioning activities to reactor operation. RSG-GAS aging management is carried out in accordance with safety guidelines from the international atomic energy agency (IAEA) and nuclear power regulatory body (BAPETEN) regulations, as well as various vendor documents. The success of aging management is demonstrated by operating parameters that meet operating limit conditions (OLC), and is evaluated through periodic safety assessments. This paper aims to convey the experience of RSG-GAS in aging management, in order to support the reliable operation of RSG-GAS. Experience in the aging management program of the RSG-GAS as long as 34 years, is an important asset in developing the aging management program of future Indonesian nuclear power plants.

Methodology for Determining the Thermal and Thermal-Stress States of a Concrete Storage Container for Spent Nuclear Fuel for Assessment of Its Service Life

The work is devoted to the development of methodologies for determining the thermal and thermal-stress states of the main equipment in dry container storage facilities for spent nuclear fuel. Storage facilities of this type are most common for spent fuel of nuclear power reactors. The safety of storage equipment in terms of assessing its service life is not covered widely enough in the world scientific literature. In particular, there are no effective methods for calculating the thermal and thermal-stress states of the equipment that would take into account the influence of many external factors throughout the life of a storage facility. To assess the thermal state of the containers, forward conjugate heat transfer problems, accounting for the mutual heat transfer in both a solid body and in the fluid environment (air), are proposed to be solved. Based on the solution of the conjugate heat transfer problems, the boundary conditions are to be determined to further assess the thermal-stress state of storage containers using inverse heat transfer problems. The proposed approach to determining the thermal and thermal-stress states of a concrete spent fuel container will promote more effective methods for assessing the service life of dry spent fuel storage facilities, which is, in turn, necessary in the development of ageing management programs for storage equipment and long-term safe operation.

Ageing management of research reactors instrumentation using neutron radiography applications

This paper introduces the applications of neutron radiography and tomography to improve maintenance and aging management programs in research reactors. Egypt second research reactor (ETRR-2) has an advanced neutron radiography/tomography facility and it is used to shoot and test different objects such as concerning antiquities, industry and applied research in various fields. Neutron radiography/tomography (NR/T) techniques offer ideal opportunities for nondestructive testing (NDT) evaluations. It has been possible to benefit from the applications and use of radiography to help improve maintenance of components and systems as well as aging management programs for the ETRR-2. This work proposes successful applications of NR/T to inspect and test different safety and safety related components such solenoid valves and the shielding tube of the defective fuel instrument to predict both damage and edging of these systems. Also, the NR technique monitored successfully the behavior efficiency of an air filtering unit (AFU) for dust removal from ventilation system in the research reactors. Additionally, we measured the capability of protective maintenance procedures to remove impurities or blockage from a stainless steel filter (SSF) used in water treatment system. NR/T techniques are successfully applied and enhanced both maintenance and ageing management programs of ETRR-2 instrumentation, equipment and systems.

Corrosion surveillance program for tank, fuel cladding and supporting structure of 30 MW Indonesian RSG GAS research reactor

Abstract The objective of this research is to understand the condition of the structural material of the 30 MW RSG-GAS research reactor as input for the aging management program. Furthermore, this should enable a prediction of the remaining life of the components. In the current experiment, corrosion surveillance was carried out at Interim Storage for Spent Fuel (ISSF), that has similar water quality as in reactor pool by using a corrosion probe which is made of aluminum alloy and stainless steel. The probe set is designed to understand the effect of water quality in the ISSF pond. The corrosion processes observed were pitting, crevice and galvanic corrosion. Two sets of corrosion probes were immersed into the ISSF pool in 2007, hanging by steel wire, 1-meter height from the bottom surface. One probe set consists of horizontal and vertical positions. The soaking time was 7 years. The observations made were water chemical content, corrosion rate and visual analysis, macro and micro. For macro visual observations an optical microscope was used, for micro-observations SEM-EDX. From the results of macro-observations, information on the presence of galvanic corrosion, crevice and pitting was obtained. SEM-EDX provides information on the influence of chloride ions on corrosion products. This experience will be very useful in dealing with the aging process of Indonesia’s nuclear power plants in the future.

ASME in-service inspection and in-service testing programs for Angra 1

The in-service inspection program of the Angra 1 plant is updated every 10 years, according to applicable standards - designer (American Project - are followed NRC requirements) and Cnen. NRC approves the use of ASME Section XI (In-service Inspection of Nuclear Power Plant Components). The object of in-service inspection of components in nuclear power plants is to provide a continuing assurance that they are safe. To provide this assurance for those components that are subject to the requirements of the ASME Boiler and Pressure Vessel Code, a set of rules has been formulated to provide assurance that the functional requirements of the components are available when required. The rules have been arranged to provide appropriate levels of assurance according to the importance of the component in its relationship to plant safety. The classifications that are established during design and manufacturing have been adopted to provide the levels of importance for the components. The types of components typically found in the various classifications have then been identified and rules formulated for each type. For each type of component in each classification, the functions have been considered and methods of inspecting, testing, or monitoring each component is specified. These rules include methods of determining the limits of acceptance of the results. Should it be necessary to take corrective action to repair various components, rules have been provided to establish acceptable methods of repair or replacement. Angra 1 started the Renewal License and Long-term Operation project and there are three important Aging Management Programs (AMP) that are based on ASME section XI. This article will discuss the ASME section XI subsections that are important for the License Renewal and Long-term Operation for Angra 1.

Results of Analysis of Aging Related Events at Ukrainian NPPs

The design lifetime (30 years) of Ukrainian NPPs has already been expired or will be expired soon. One of the priority areas for the development of nuclear energy is long-term operation (LTO) based on the results of periodic safety review. At present, eleven Ukrainian NPP units are operated under LTO conditions, which in turn causes certain features of operation related to wear, fatigue and general aging of components and structures.
 An issue of aging management is considered one of the main factors to ensure the safety of a nuclear installation, both in the design lifetime and in the long-term operation. The primary purpose of aging management is to ensure the safety and maximum efficiency of operation through the implementation of technically and economically feasible measures aimed at timely detection and keeping of degradation of NPP components caused by aging within the limits.
 One way to determine the efficiency of implemented measures and aging management programs is to analyze operational experience and, in particular, analyze the number of NPP operational occurrences during the design and long-term operation period and that are directly related to the aging effects. This paper presents the results of the analysis of the events at Ukrainian NPPs caused by aging processes, compares the results of national and international experience.