July-August 2019 NPJ

(Continued on page 30) Nuclear Plant Journal, July-August 2019 NuclearPlantJournal.com 29 Reliability & Integrity Management By A. Thomas Roberts, Pomo18 Consult LLC. A. Thomas Roberts A. Thomas Roberts has over thirty five years’ experience in the nuclear power industry. His career started with nuclear plant construction at various sites in the 1970’s. It proceeded to the operation phase of the business at a utility in the northeast with two Pressurized Water Reactors and one Boiling Water Reactor for over twenty eight years. His career has involved a wide span of engineering management responsibilities, including Site Engineering, Quality Assurance, Maintenance Engineering, Welding Engineering, Construction Management and Engineering Programs Manager. After his retirement from the utility, Mr. Roberts moved onto his second career at MPR Associates where he was a engineering consultant and project manager. Recently, he has transitioned into a semi retried status working part time for MPR Associates Inc. and establishing his own consulting firm (i.e., Pomo18 Consult LLC). He is a current Chairman of ASME Section XI Sub-Group RIM – ASME XI Division 2 Welds Focus Group. The ASME Code Section XI Standards Committee has just published ASME Code Section XI, Division 2, entitled Reliability and Integrity Management (RIM) to address future advanced reactor designs that are currently in development. ASME Code Section XI, Division 2, is a “technology neutral” inservice code that may be applied to any advanced reactor designs. Included inDivision 2 are technology-specific appendices intended to account for different reactor designs with regard to inservice inspection (ISI) parameters. In order to understand how RIM will be applied to nservice inspections, n overview of the echnical basis for Division 2 and some f the processes it mploys is provided elow. The foundations f ASME Codes Section XI, Division and Section XI, Division 2, are u n d a m e n t a l l y different. In order to understand these differences, it is important to acknowledge the original technical foundation for ASME XI, Division 1. The explanation is summarized well from a quote by one of the founding chairmen of ASME XI, Division 1: “The philosophy of Section XI is to mandate a sufficient number of examinations and tests ( selected deterministically ) to provide assurance that the original safety that was designed and built into the plant is maintained throughout its service life.” – L.J. Chockie (1975) - Chair, Section XI. In contrast to ASME Code Section XI, Division 1, which was founded on deterministic criteria, ASME Code Section XI, Division 2, is built on a concept known as System Based Code (SBC) for its technical basis. This approach was chosen because it evaluates all structures, systems and components for their relative importance in maintaining overall plant safety and then establishes appropriate monitoring parameters to assure long term reliability. This is opposed to the prescriptive approach used by Division 1 which uses the Class 1 (e.g., reactor coolant system), Class 2 (emergency core cooling systems) and 3 (e.g., tertiary systems) approach to ISI with each Class having less rigorous criteria for ongoing inservice inspections. At a high level, RIM provides a framework to permit increased flexibility to:  Give a rational method for safety margin(1) optimization(2) in order to increase inservice inspections and monitoring and operational maintenance flexibility.  Enable optimization of safety margin integrity for the entire life cycle of structures, systems, and components (SSCs).  Continuously evaluate safety margin integrity through initial design to plant decommissioning as a “living” program. A simplified description of the process employed by RIM, which is employed by ASME Code Section XI, Division 2 follows: 1. Determine scope of SSCs for the RIM Program. 2. Evaluate SSC damage mechanisms. 3. Determine plant and SSC level reliability requirements. 4. Evaluate RIM strategies to achieve reliability targets. 5. Evaluate uncertainties in SSC reliability performance. 6. Determine scope and parameters for the specific SSC in the RIMProgram. 7. Continuously monitor (i.e., monitoring and NDE- MANDE) SSC reliability performance and update the revisions to a RIM Program over the entire life of a reactor facility. In RIM, a total required safety margin is first defined and then it is distributed to each individual requirement in a rational manner. As noted previously, this approach contrasts with conventional construction and inservice codes which are based on deterministic approaches. Each of the seven steps outlined below provides a high level overview of the RIM process and summarizes various evaluations involved, each of which fulfill different objectives. 1. At the onset, a structural design oriented evaluation considers SSCs structural integrity. In other words, the probability of failure based on design conditions. i a t o e b o 1 f