Overview of In-Service Degradation Assessment
In nuclear power plants, numerous components are prone to degradation during operation or due to abnormal operating conditions. These degradation processes need to be evaluated to ensure continued safe operation, determine necessary repairs before reentering service, or decide on component replacement. Ideally, anticipating in-service degradation through a component's assessment or a comprehensive Life Cycle Management plan allows for the development of generic dispositions or Flaw Handbooks in advance to provide justification during inspections. However, when unexpected degradation occurs, time becomes a critical factor, necessitating a rapid and robust technical justification. BWX Technologies possesses a range of proven capabilities to conduct assessments of various in-service degradations during outage scenarios, often with minimal impact on the overall outage window.
Applications and Analyses
An essential aspect of condition assessment and life extension for existing vessels and tubing in nuclear facilities involves the evaluation of crack-like defects. BWX Technologies can provide analyses to determine the maximum allowable crack size, along with structural limits. These analyses address the findings of typical In-Service Inspection (ISI) pressure vessel inspections and specific inspections mandated by industry guidelines like EPRI MRP-139. While flaw evaluations can be conducted on a case-by-case basis, developing a component-specific Flaw Handbook allows for the advanced analysis of assumed flaws, enabling swift disposition of flaws during outages. Additionally, BWX Technologies can analyze various forms of in-service degradation such as general corrosion, Flow Accelerated Corrosion (FAC), wastage, or pitting of pressure vessels, tubing, or piping to determine necessary repairs or disposition as-found conditions.
Capabilities and Tools Offered by BWX Technologies
BWXT offers comprehensive engineering capabilities for conducting fracture mechanics-related analyses and testing on nuclear components and pressure vessels. Their fracture mechanics capabilities include finite element modeling of intricate geometries to determine stress intensity factors, welding and fabrication residual stress analyses, FE crack growth analysis, failure assessment diagrams, KIc, KIR, JIc, JIR testing, and developing crack growth rate curves. They are adept at ASME Section III Appendix-G analysis, ASME Section XI crack growth analysis, US NRC Regulatory Guide 1.121-based tube flaw analysis for steam generators, and utilizing finite element software like ANSYS®, ABAQUSTM, and ABACUSTM with VFD. BWX Technologies has extensive experience in applying ASME Code Section III and Section XI, US NRC Regulatory Guide 1.121, British Standards 7910, and R6 flaw assessment procedures. For tubing flaw evaluation, they adhere to EPRI Steam Generator Integrity Assessment Guidelines and the Flaw Handbook as per NEI 97-06. Moreover, BWX Technologies can analyze similar and dissimilar metal welded joints while considering residual stress effects in flaw analysis.