In-service monitoring of piping and vessels in nuclear power plants: report on BMU Study SR 2218

The BMU-Study SR 2218 is made with a view to describing and assessing fatigue monitoring as commonly applied today to piping and vessels in nuclear power plants. First, the fundamentals with regard to strain, instrumentation and calculation of fatigue are compiled and the current regulations listed. With reference to the available literature, own experience and a survey conducted among operators and manufacturers of the now common types of installations, the points of measurement, the methods of measuring, the acquisition systems for measured data and the methods of analysis are described, as are the results obtained from the measurements so far. After a careful review of these results, proposals are presented for improving the acquisition of measured data and, most important of all, for analysis and assessment. In the nuclear power plants in Germany those areas which are of relevance to fatigue have been identified by means of temperature measurements taken in the recent past in the various types of installations. Many thorough analyses have been made on the basis of transients measured in order to assess the relevance of the areas in terms of fatigue. The degrees of fatigue established are normally D=0.2-0.3. that is < D = 0.5 for loads occurring in service. It can be stated, in summary, that the degrees of fatigue obtained from fatigue monitoring systems are more realistic than those obtained from the approach adopted in the design stage. As the requirements of the nuclear power plants are specific and varied, there can be no universal and flexible system that is adequate for all applications. That is why it will always be necessary to find solutions for each individual case. This paper gives an overview about the content and the results of the study. © 1999 Elsevier Science S.A. All rights reserved.