In nuclear power plants operated by E.ON, thermocouples have been installed since commissioning of the plants at fatigue relevant locations, especially at primary circuit components. Temperature measurement planes have been retro-fitted, further developed and the positions of the measurement planes have been reassigned and optimized continuously based on operational lessons learned. Comprehensive surveillance activities yield to a significant amount of information which is used to analyze the component specific health status. Additionally this information can be used to optimize plant’s behavior in the context of operational excellence.

An evaluation of temperature measurement is needed from the regulatory point of view and reported periodically in the context of long term fatigue evaluation being a significant part of the German ageing management process and break preclusion concept. Beyond that, the detailed information of temperature transients, gained by these measurements, allows the engineer to analyze thermal loadings of monitored components. Subsequently this information is used to optimize operation of the plants by minimizing fatigue relevant transients. The more detailed the temperature transient information is the more complex analytical and numerical models have to be in order to comprehensively consider relevant effects. Therefore numerical Finite-Element models of primary circuit components have been developed allowing the engineer to analyze temperature loading (e.g. stratification or plug-flow events) in detail and to draw conclusions being used to optimize the plant.

In the context of this publication examples of pressurized light water reactors will be discussed in detail showing the ability of the detailed evaluation process and the effectiveness of the evaluation procedure:

• Operational lessons learned from temperature measurement evaluation.

• Minimizing stratification events in the surge line by optimizing the point in time when main coolant pumps are turned off.

• Temperature loading of the auxiliary spray line during start-up phase.

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