Session: OAC-07-01 Plant Life Extension: Aging & Life Management-1

Paper Number: 151662

151662 - Review of Operating Experience Involving Material Degradation in Periods of Extended and Long-Term Operation 

Abstract: 

The Nuclear Energy Agency (NEA) Component Operational Experience, Degradation and Ageing Programme (CODAP) is the continuation of the 2002-2011 OECD/NEA Pipe Failure Data Exchange Project (OPDE) and the 2006-2010 OECD/NEA Stress Corrosion Cracking Project. In December 2023, 14 nations entered into an agreement for CODAP’s fourth term (2024-2026). The CODAP project periodically prepares topical reports on the results of systematic evaluations of the international operating experience with piping and selected non-piping passive components. An overriding objective of these reports is to foster technical cooperation, to deepen the understanding of national differences in plant ageing management, and to preserve the institutional knowledge with respect to material degradation phenomena. This paper presents the results of an evaluation material degradation in periods of extended operation (PEO) and long term operation (LTO) of commercial nuclear power plants. The results, conclusion and recommendations of this evaluation were obtained using a five-step approach:

1.     The results from a questionnaire on long term operation served as a basis for determining to what extent the CODAP Event Database could be used to assess LTO trends in material performance. In preparing the CODAP LTO Study a comparison was made between the content of the CODAP event database and the results of the questionnaire.

2.     A review of the results of two expert panels on material degradation issues during LTO. In preparing the CODAP LTO Study a comparison was made between the CODAP event database and the results of the expert panels.

3.     In 2019 the U.S. Nuclear Regulatory Commission organized an international workshop on age-related degradation of reactor vessels and internals. The technical information included in the workshop presentations and the workshop summary report was used to augment the country-specific overviews of material degradation issues in CODAP LTO Study.

4.     Detailed review of the material degradation issues as recorded in the CODAP Event Database. This review included reactor vessel internals and safety-related and non-safety-related piping system components. Different technical approaches were explored in the examination of trends and patterns in the operating experience data.

5.     Formulation of a synthesis of the PEO/LTO material degradation insights based on the results of Steps 1 through 4.

High-cycle mechanical fatigue continues to cause operational challenges. Hence, no fundamental difference between early life operation and PEO/LTO. An increasing failure trend is observed for Safety Class 3 raw water cooling water piping, however. In contrast, flow-accelerated corrosion (FAC) monitoring programs and stress corrosion cracking (SCC) mitigation processes have had a significant positive impact on the longer-term material performance.

 

Presenting Author: Keiko Chitose OECD NEA

Presenting Author Biography: Dr Keiko CHITOSE, Nuclear Safety Specialist at OECD/Nuclear Energy Agency - since September 2021.
In her present role, Dr Chitose is primarily managing and providing support to the Working Group on Integrity and Ageing of Components and Structures (WGIAGE) and its subgroups. She has more than 35 years of experience in nuclear safety research, engineering and safety assessment for licensing application. Prior to her current position she had worked at Japan Nuclear Safety Institute as Senior Manager of risk management department, Mitsubishi Heavy Industries as section head of risk assessment engineering section. She is an ASME member, a member of American Nuclear Society and member of Atomic Energy Society of Japan.
Dr. Chitose holds a PhD in Nuclear Engineering from Tokyo City University and Waseda University.

Authors:

Keiko Chitose OECD NEA
Bengt Lydell SIGMA-PHASE INC.
Eric Focht U.S. Nuclear Regulatory Commission