Chris Lohse Archives

By: Christopher Lohse

There have been several industry initiatives to support optimization of examination requirements for various items/components (both Class 1 and Class 2 components) in lieu of the requirements in the ASME Code, Section XI. The ultimate objective of these initiatives is to optimize the examination requirements (through examination frequency reduction, examination scope reduction, or both) while maintaining safe and reliable plant operation. There are various examples of examination optimization for both boiling water reactors (BWRs) and pressurized water reactors (PWRs). Each of these technical bases for examination optimization relies on a combination of items. The prior technical bases have relied on: (1) operating experience and prior examination results as well as (2) some form of deterministic and/or probabilistic fracture mechanics. For BWRs, the two main technical bases that are used are BWRVIP-05 and BWRVIP-108. These technical bases provide the justification for scope reduction for RPV circumferential welds, nozzle-to-shell welds, and nozzle inner radius sections. For PWRs, the main technical basis for RPV welds is WCAP-16168. These technical bases are for the RPV welds of BWRs and PWRs which represent just a small subset of the examinations required by the ASME Code, Section XI. Therefore, the industry is evaluating whether technical bases can be optimized for other components requiring examinations.

By: Tim Griesbach and

For the past several years baffle-former bolt (BFB) cracking in pressurized water reactors has become a significant concern for of PWR plants. In 2016, three similar Westinghouse designed plants (Indian Point 2, Salem 1, and D. C. Cook Unit 2) experienced significant numbers of cracked BFBs, attributed to irradiation-assisted stress corrosion cracking (IASCC). These plants had common characteristics that included the 4-loop plant design, downflow configuration, and Type 347 stainless steel bolting material. BFB cracking is not an entirely new phenomenon as it was initially detected in the French PWR fleet in the 1990s. However, the extent of cracking found in some of the US plants has greatly exceeded prior cracking. Extensive industry programs have identified and categorized by tier group the most susceptible plants, and the EPRI Materials Research Program (MRP) has published guidance regarding baffle-former bolt UT inspections for PWR plants for detection of degraded and cracked bolts in the baffle-former assembly (MRP-2017-009).

News & Views, Volume 46 | Application of Probabilistic Flaw Tolerance Evaluation Optimizing NDE Inspection Requirements

News & Views, Volume 46 | Baffle-Former Bolt Management: Cost/Benefit Studies