Standard Article

Fatigue Monitoring in Nuclear Power Plants

Other Applications

  1. Wilhelm Kleinöder,
  2. Christian Pöckl

Published Online: 15 SEP 2009

DOI: 10.1002/9780470061626.shm203

Encyclopedia of Structural Health Monitoring

Encyclopedia of Structural Health Monitoring

How to Cite

Kleinöder, W. and Pöckl, C. 2009. Fatigue Monitoring in Nuclear Power Plants. Encyclopedia of Structural Health Monitoring. .

Author Information

  1. AREVA NP GmbH, Erlangen, Germany

Publication History

  1. Published Online: 15 SEP 2009

Abstract

During design phase, stress and fatigue analyses are made in order to design safety-related components of the pressure-retaining boundary in nuclear power plants. The design transients are based on the planned operation procedures for the different nuclear primary and auxiliary systems. These design transients are always assumed conservatively with respect to the temperature differences and the expected thermal gradients.

A measurement program carried out in a German nuclear power plant in 1982 showed that the real operating conditions of the plant partly differed from the assumptions and predictions. It was quite clear that this insight will also have a significant influence on the fatigue calculations made so far; however, more detailed analyses on the basis of the measured data showed that fatigue limits were not exceeded. This experience also revealed the big potential of making fatigue analyses on the basis of measured data.

Within the following years, the first developments were made for the permanent monitoring of component fatigue. Meanwhile, fatigue monitoring plays an important role in structural health monitoring in nuclear power plants. Particularly for utilities, which are planning lifetime extension for their plants, it is an invaluable advantage if they have measured data of the real operating behavior of their systems and components available. With such data, the current real fatigue usage factor can be easily calculated for most cases and therefore an extrapolation for future development can be made.

This article shows the development of such a fatigue monitoring system till the current state and deals with the benefits for the units that have implemented such systems. It also describes the studies that are necessary for the definition of the locations to be monitored. Furthermore, the current state of the technical devices used for monitoring is described. These include the mechanical components as well as the electronic systems needed for the acquisition of data. It is also necessary to mention the procedures used for evaluation of the data. Different methodologies from cycle counting to fatigue analyses based on monitored data are described and examples are given. Also, existing alternative fatigue monitoring systems from other engineering companies and manufacturers are briefly outlined. Finally, new developments that may come up in the future are also discussed.

Keywords:

  • fatigue monitoring;
  • fatigue mechanism;
  • fatigue-causing phenomena;
  • thermocouples;
  • measurement section;
  • measurement electronic system;
  • evaluation;
  • cycle counting;
  • stress-based fatigue;
  • NPP operation;
  • direct measurement