Most of today’s operating nuclear plants that were originally designed for 30 or 40-year life are facing the long-term operation issues. Therefore, it is of meaningful importance to assess the time-dependent degradation and the ageing of the relevant nuclear systems, structures, and components (SSCs) because of resulting loss of structural capacity.

In this framework, the inverse method is implemented starting from temperatures at an accessible boundary, which are measured through a monitoring system. The reconstruction technique uses the elaborated signal provided by the monitoring system to determine temperature at inaccessible surface: this is the so-called inverse heat transfer problem (IHTP).

The inverse space marching method is applied.

Analytical and numerical studies are performed taking into account thermal transient conditions in order to determine thermal loads. In particular, the developed code demonstrates to be able to reconstruct temperature and stress profiles in any section of the pipe with a good accuracy.

In addition, the thermal loads obtained suggest that the investigated transient condition is not able to jeopardise the integrity of NPP, confirming the possibility of the plant extension of life.

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