P Boiling Water Reactor Vessel and Internals Program (BWRVIP)

Transcription

1 2018 Research Portfolio P Boiling Water Reactor Vessel and Internals Program (BWRVIP) Program Description As boiling water reactors (BWRs) age, various types of materials degradation mechanisms can challenge the reliable operation of the BWR primary system. Stress corrosion cracking, for example, first appeared in recirculation piping in the early 1960s and was then shortly thereafter discovered in reactor pressure vessel internal components. Materials performance issues across the nuclear fleet were dealt with on a case-by-case basis, focusing on site-specific components, systems, and materials management philosophies. This nearterm, reactive approach resulted in costly unplanned outages and expensive weld-by-weld mitigation and repair methods that lacked a comprehensive fundamental understanding of the degradation and how to effectively deal with it. A longer-term, strategic approach to materials aging management helps ensure that safe and reliable functionality is maintained throughout the life of BWR plants. The Boiling Water Reactor Vessel and Internals Project (BWRVIP) provides an integrated and proactive approach for managing materials-related degradation issues in reactor coolant system components in boiling water reactors. The program has developed reliable and cost-effective detection, inspection, mitigation, and repair guidance to address the safety-significant facets of operation resulting from materials degradation issues. The Program is now looking to optimize the guidance using the information gained from 20+ years of implementation. This continuous improvement will sharpen the engineering judgements and technical bases associated with aging management and support the plant s continued safe operation. Research Value The BWRVIP is a mature program that has been addressing materials integrity issues related to the BWR reactor pressure vessel and internals since Research results lead to proven solutions for managing materials degradation, optimized inspection scopes, improved understanding of structural integrity during operation, reduced personnel radiation exposure, and improved models to better characterize the degradation of internals components that can be used by BWR utilities. Program participants gain access to the following: Strategic roadmaps outlining research gaps associated with key issues such as jet pump flow-induced vibration, intergranular stress corrosion cracking, and irradiation assisted stress corrosion cracking (IASCC), and mitigation of internals degradation and other activities needed to address these gaps The technical bases documents for guidance that improves plant reliability Cost-effective techniques to mitigate stress corrosion cracking of reactor internal components Options and design criteria for replacing or repairing reactor components Optimized internals inspection guidelines and solutions to BWR technical issues Global BWR industry operating experience Technical insights for inspection options that can help reduce outage critical path times, address new degradation phenomena, and provide data to inform regulatory decisions Approach The BWRVIP Program takes an integrated approach to degradation management encompassing assessment, repair, mitigation, and inspection. Continuous learning from research and development (R&D) of ongoing agerelated damage using state-of-the-art materials testing and analysis tools improves understanding of materials aging mechanisms. This knowledge is used to develop the technical basis for guidelines related to the inspection 1

2 and assessment of materials-related issues in BWR reactor vessels and internals. BWRVIP activities lead to innovative, efficient ways to manage degradation without compromising safety. Operational experience, inspection data and techniques are evaluated to identify best practices that can be deployed to enhance boiling water reactor reliability and alert stakeholders to new or unexpected issues. The BWRVIP works closely with other Electric Power Research Institute (EPRI) materials related programs, including the Materials Reliability Program (MRP), Nondestructive Evaluation (NDE), Primary Systems Corrosion Research (PSCR), Chemistry, and Fuel Reliability Program (FRP) to ensure appropriate technologies and technical guidance are effectively integrated into BWRVIP research activities. The program focuses on improving the understanding of materials performance in areas such as fracture toughness and crack growth of stainless steel exposed to high fluence levels as well as the weldability of irradiated materials for repair. Because these factors impact materials aging on all reactor types, enhanced understanding of their interactions and their impact on materials performance are essential. Research results are provided in the form of guidelines that help ensure prompt detection of material degradation; technical reports to support materials performance assessments; and cost-effective tools that identify and enable degradation management over the life of the plant. The BWRVIP program encompasses research related to assessment, inspection, repair, and mitigation. Assessment: Develop inspection and evaluation guidelines that provide the scope for what needs to be inspected and a methodology for evaluating or repairing any indications. Inspection: Develop advanced nondestructive evaluation techniques to improve detection of indications in internal components. Repair: Develop technically based repair criteria for degraded components and compile information needed to safely plan and implement repairs. Mitigation: Provide guidance for implementing effective chemistry-based countermeasures for stress corrosion cracking of reactor internal components. The program also manages the Integrated Surveillance Program (ISP) for the U.S. BWR fleet, which monitors changes in reactor pressure vessel materials properties due to neutron irradiation for the current licensing period of the U.S. fleet. A new ISP for second license renewal is now being developed to support plants that decide to operate beyond 60 years. The BWRVIP uses the Materials Degradation Matrix (MDM) tool along with the BWR Issue Management Tables (BWRVIP-167, Rev. 3) to identify damage mechanisms and the associated knowledge gaps needed to resolve technical issues. Tasks that are developed to address the issues are grouped into Research Focus Areas (RFAs) to help communicate the annual work plans. The BWRVIP has 12 RFAs: Reactor Pressure Vessel Thermal and Irradiation Effects on Stainless Steel Reactor Internals Management of Jet Pump Flow-Induced Vibration Mitigation of BWR Material Degradation BWR Irradiated Materials Welding Management of High Strength Alloys BWR-Related Corrosion Research BWR Inspection & NDE Technology Guideline Management Fatigue Management Steam Dryer Management Page 2 of 5

3 Alloy 182 / 600 Management To resolve complex issues that may stretch across multiple focus areas or involve multiple external stakeholders, roadmaps have been developed to address jet pump flow-induced vibration, intergranular stress corrosion cracking and mitigation, irradiation assisted stress corrosion cracking (IASCC), and welding of materials due to irradiation degradation. Nuclear plant owners can participate separately in a project aimed at maintaining and improving the BWR Vessel and Internals Application (BWRVIA) software code, which performs radiolysis analysis and electrochemical corrosion potential calculations for boiling water reactors. Continued maintenance of this code ensures that the latest industry operating experience is reflected in BWR radiolysis analysis to aid in mitigation efforts and asset preservation associated with water chemistry control. Selected reports and products may be prepared in whole or in part in accordance with the EPRI Quality Program Manual that fulfills the requirements of 10 CFR 50 Appendix B and 10 CFR 21. The quality assurance status of reports and products will be marked and identified. Accomplishments BWRVIP research informs the assessment and implementation of effective approaches for managing materials degradation issues in reactor internal components. Research results provide nuclear plants with the information necessary to maintain safe operation and make cost-effective decisions for managing degradation of BWR vessel and internal components. Received safety evaluation for Optimized Core Spray Inspection and Evaluation Guidance based on operational experience and technical data. Published a report that provides updated load terms, definitions and combinations for flaw evaluation and repair design criteria of reactor pressure vessel internal components to support utility implementation of BWRVIP guidance. This resolved issues associated with GE-Hitachi Safety Communications regarding postulated recirculation line break and annulus pressurization loads for BWR internals. Developed a methodology that can be used to assess the technical viability of a requirement to examine core plate bolting. Published Revision 20 of the examination guidelines for reactor pressure vessels and internals. Evaluated irradiated BWR internals to advance the understanding of the relationship between fracture toughness and neutron fluence in highly irradiated stainless steel materials. Developed data on crack growth of irradiated austenitic stainless steels in support of a methodology to evaluate the operability of internal components in BWRs to end-of-life fluence levels. Data will be used to extend crack growth models to higher neutron doses associated with longer term service. Conducted metallurgical evaluations of off-axis indications removed from a utility s core shroud. This information will be used to develop and improve the technical bases for optimizing BWRVIP-76. Demonstrated online noble metal chemical addition as a mitigation technique for stress corrosion cracking. Analysis of service removed components indicate that the technique is effective in reducing electrochemical corrosion potentials and has no adverse plant impacts. Because the application is performed during operation, 60 critical path hours can be saved versus the classic noble metal application. Remote visual round robin testing performed jointly by the industry and NRC Research confirmed the reliability of BWRVIP In-Vessel Visual Inspection guidance to adequately identify surface flaws to ensure damage can be effectively managed. Received safety evaluation on technical basis for screening irradiation and thermal embrittlement in cast austenitic stainless steel materials. Reviewed the adequacy of BWRVIP aging management programs for second license renewal (60-80 years). Page 3 of 5

4 Developed an integrated surveillance plan to monitor materials behavior for longer time periods and support effective aging management through second license renewal. Developed a screening approach to help manage efficient implementation of revised and new BWRVIP guidelines. Key Activities BWRVIP research and development for 2018 will continue to focus on the technical gaps defined in the BWR Issue Management Tables (BWRVIP-167 Rev. 3). Highest-priority gaps include the impacts of fluence on the material properties of BWR materials and mitigation of intergranular and irradiated assisted stress corrosion cracking. Specific efforts will include the following: Reviewing the MDM and BWR Issue Management Tables to ensure clear high priorities are known IASCC research and inspection guidance Environmental effects on fatigue properties and fatigue crack growth curves for BWRs Crack growth testing, fracture toughness evaluations, and metallurgical examinations of highly irradiated materials Quantification of the effect of chemistry transients on stress corrosion cracking of low-alloy reactor pressure vessel steels and updated associated guidance Extension of the BWR Integrated Surveillance Program from 60 years to 80 years Development of technical basis on BWRVIP materials aging to inform decisions regarding second license renewal in the United States and license extension outside the United States. Continue to optimize the guidance using inspection results and operational experience from the global fleet. Estimated 2018 Program Funding $13.2M Program Manager Andrew McGehee, , amcgehee@epri.com Page 4 of 5

5 BWRVIP Online Noble Chem Tech Summary of Projects The On-Line NobleChem (OLNC) process is used to deposit small particles of Pt on BWR internals and piping surfaces to mitigate IGSCC. The process is applied over10-14 days annually or several times during a cycle. The Pt catalyst recombines excess hydrogen and oxygen in the water and decreases the electrochemical corrosion potential (ECP) of the surface resulting in mitigation of IGSCC of internal components. However, there are several issues regarding demonstration and modeling of Pt deposition in the vessel and piping and effective implementation of OLNC that still remain to be resolved. These issues are being addressed by this project. BWRVIP-62 Revision 1 was prepared in 2011 to address mitigation effectiveness and submitted to the NRC for review. After reviewing the report, the NRC requested additional information (RAIs) on noble metal deposition in BWR internals. The responses to these questions have been prepared based on additional data and will be used to develop BWRVIP-62 Rv.2. ECP of Coupons from OLNC Plants On-line NobleChem (OLNC) process involves periodic injection small amounts of Pt in the feedwater in the presence of dissolved hydrogen and is widely used by BWRs to mitigate IGSCC of reactor internals and piping. Pt deposition on internal surfaces catalyzes the recombination of hydrogen and oxygen leading to a decrease in ECP and IGSCC mitigation. A correlation between Pt loading, particle size/density, catalytic activity and ECP is needed to demonstrate the effectiveness of OLNC and to support the technical basis of BWRVIP-62 Rv1 report on inspection optimization of BWR internals. Mitigation/BWR-VIP This project includes the review of the BWR Water Chemistry Guidelines and collection of all U.S. BWR s and several international BWR s chemistry and performance data into a centralized database each year. This task also includes the analysis of operating data to support Guidelines reviews and revisions and utility requests as well as the collection of operating experience with hydrogen water chemistry, noble metal chemical application (NMCA) and On-line NobleChem (OLNC) technologies used by BWRs to mitigate intergranular stress corrosion cracking (IGSCC) of BWR internals and piping. P : BWRVIA - BWR Vessel and Internals Application for Radiolysis/ ECP Various technologies including moderate hydrogen injection, known as hydrogen water chemistry, and noble metal chemical addition or online NobleChem (OLNC) have been applied in boiling water reactors (BWRs) to mitigate intergranular stress corrosion cracking (IGSCC) by lowering primary water electrochemical corrosion potential (ECP). Analytical capabilities that determine the appropriate injection concentrations for maintaining ECP values at appropriate levels can help mitigate corrosion. This users group provides information and training on the use of the radiolysis and ECP models used in EPRI s Boiling Water Reactor Vessel and Internals Application (BWRVIA) software program. Ongoing development of the codes is also discussed through the users group. Page 5 of 5