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Use of Irradiated Fracture Toughness Values in Nuclear Vessel and Component Design Specifications for Fitness-for-Service Analysis using The Unified Curve Method

[+] Author and Article Information
Waleed Ishaque

Ontario Power Generation, Bowmanville, Canada
waleed.ishaque@gmail.com

1Corresponding author.

ASME doi:10.1115/1.4042498 History: Received August 01, 2018; Revised December 22, 2018

Abstract

The ASME Section III Rules for Construction of Nuclear Facility Components sub-section NB-2331 Material for Vessels requires that the effects of irradiation shall be considered on material toughness properties in the core belt line region of the reactor vessel. The code also states that "the Design Specifications shall include additional requirements, as necessary, to ensure adequate fracture toughness for the service lifetime of the vessel". In the cases of fitness-for-service assessment for component flaws (prevalent with age of component), irradiated material properties become highly relevant. An example of a fitness-for-service is that of a beyond design basis reactor vessel head drop accident in a Pressurized Water Reactor with a nozzle junction flaw. As a case-study, critical size of a postulated external surface semi-elliptical circumferential crack in a PWR nozzle-vessel junction is calculated using ANSYS Workbench with the applied impact load from the vessel head drop accident. Failure Assessment Diagrams for numerous crack depths and lengths were developed for the irradiated reactor vessel steel. The results were compared with the available finite-element and the American Petroleum Institute (API) standard API 579 analytical solutions for validation, showing good agreement. From this case-study, it is demonstrated that the effects of irradiation on fracture toughness become prominent. Using the Unified Curve Method, the irradiated fracture toughness data in design specification can be supplied so that it may be used in fitness-for-service analysis to account for component aging.

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