Demonstration of Fatigue for LTO

Do you need to revalidate your fatigue analyses in the framework of LTO? Long Term Operation (LTO) of nuclear power plants (NPPs) requires revalidation of the structural integrity of safety relevant structures and components including  fatigue. The basis is generally formed by a set of fatigue analyses.

NRG has developed the methodology for the revalidation of fatigue TLAAs (Time Limited Ageing Analyses) for the successful LTO license change of NPP Borssele in the Netherlands.

LTO demonstration for fatigue TLAAs starts with an independent scoping survey to determine the components and locations that require a fatigue analysis. The scope is defined by engineering judgment and assessment against international practice and guidelines. Next, a methodical review is performed of all existing fatigue TLAAs. This also includes the latest international developments regarding environmental effects and high cycle thermal fatigue. In order to reduce excessive conservatism, a comparison is made of the number of cycles in the analyses and the number of cycles projected to the end of the intended period of LTO. The loading conditions used in the analyses are assessed by means of temperature measurements by a fatigue monitoring system.

As a result of the review, further fatigue assessment or assessment of environmental effects is necessary for certain locations. New analyses are performed using state-of-the-art calculation and assessment methods. The management of fatigue is ensured by means of the fatigue concept where load monitoring, transient counting and fatigue assessment are coupled through an integrated approach during the entire period of LTO.