Proactive Management of Materials Degradation - A Review of Principles and Programs

Abstract

Executive SummaryThe response of the nuclear industry and regulators to issues of materials degradation in the past generally has been to develop and approve mitigation actions after the degradation has occurred. These mitigation actions have involved increases and improvements in in-service inspection, changes in designs, materials, and operating conditions, and replacement of degraded components. This reactive approach has maintained the safety of operating reactors but has proved to be an inefficient and expensive way of managing materials degradation issues for the industry.To address the issue of "reactive management of materials degradation", the NRC has initiated a program to assess the potential to identify early the components that are potentially susceptible to future degradation, so that mitigation and/or monitoring and repair actions can be proactively developed, assessed, and implemented before the degradation process could adversely impact structural integrity or safety. Two processes can be envisioned for the Proactive Management of Materials Degradation (PMMD) programs. The processes are (a) implementation of actions to mitigate or eliminate the susceptibility to materials degradation, and (b) implementation of effective inspection, monitoring, and timely repair of degradation. This study concentrated on an identification of components susceptible to future degradation and an assessment of the existing knowledge level for potential development of mitigation actions, that is, process (a) only. The Pacific Northwest National Laboratory conducted the research to find and develop the PMMD information contained in this technical letter report. This technical letter report concisely explains the basic principles of PMMD and its relationship to prognostics, provides a review of programs related to PMMD being conducted worldwide, and provides an assessment of the technical gaps in PMMD and prognostics that need to be addressed.Degradation and aging are terms used to describe both the deterioration and aging of components, but it is useful to distinguish between them. Degradation is immediate or gradual deterioration of characteristics of systems, structures, and components (SSCs) that could impair their ability to function within acceptance criteria. Aging is a general process in which characteristics of an SSC gradually change with time or use. When aging processes are known, they can be monitored through an appropriate aging management program and plant life management (PLiM) program and potentially mitigated.Aging degradation mechanisms are usually classified into two main categories, which are those that (1) affect the internal microstructure or chemical composition of the material and thereby change its intrinsic properties (thermal aging, creep, irradiation damage, etc.), and (2) impose physical damage on the component either by metal loss (corrosion, wear) or by cracking or deformation (stress-corrosion, deformation, cracking). As can be seen above, the phenomenon of aging degradation in nuclear p...

Proceedings of the Inaugural Meeting of the International Forum for Reactor Aging Management (IFRAM)

“…1 and 2;NRC 2005a, b). Pacific Northwest National Laboratory (PNNL) recently issued a report on the review of various international activities in PMMD (PNNL-17779; Bond et al 2008). There have also been initiatives by Electricite de France (EdF), Tokyo Electric Power Company (TEPCO), EPRI, and others to establish a -Materials Aging Institute.‖ Within the materials degradation research community, there are also networks and technical meetings focused on some elements of PMMD.…”

Report from the Light Water Reactor Sustainability Workshop on On-Line Monitoring Technologies

“…In some cases, the degradation may involve phenomena not yet experienced in the operating fleet, but which laboratory data and/or a mechanistic understanding indicate it may be pertinent to future reactor operations. PMMD includes the methodology and actions needed to manage both active and passive elements in the NPP systems throughout their existence to minimize the impact of degradation, maintain safety, and potentially enable extensions to system operating life [30].…”

“…To date, the identified technical gaps are in the areas of basic science, engineering, and regulator, code and standards application. The full scope of these needs is still being defined [38].…”

Light Water Reactor Sustainability (LWRS) Program ? Non-Destructive Evaluation (NDE) R&D Roadmap for Determining Remaining Useful Life of Aging Cables in Nuclear Power Plants

“…Attention is now turning to the potential for a second round of license extensions (Chockie et al 1991;Bond 1999;Gregor and Chockie 2006;Bond et al 2008). A challenge to safe, longterm operations is the life-limiting nature of materials aging and degradation, as such aging and associated degradation in the structural response of the material can limit safety margins.…”