Comparison between real and design thermal transient in the charge-line nozzle of a pressurized water reactor

During plant operation, some reactor coolant system components are subjected to important thermal shocks. For example the charge-line nozzle is strongly affected by variations in the charge and discharge line flow induced by: - large injection or dilution of boran - volume adjustment Thus, the design cumulation low cycle fatigue index has a very high value, in the most affected zone and the allowed small number of the most severe transients (mainly created by tempory interruption of the chemical and volume control systems) is restrictive for the plant's operators and it would be very useful to know the real damage undergone by the component, particularly in the case of an excessive number of transients. For that reason a particular instrumentation of the charge-line nozzle of a French P.W.R. plant has been set up. This on line instrumentation is composed of thermocouples fixed on the external surface of the nozzle. These thermocouples measure the profile of all the transients 'seen' by the charge-line, during the pre-operation tests and the first commercial operation year of the plant. (orig./GL)