PISA

PISA, Pressure Vessel Integrity and Safety Analysis: in connection with the long-term operation of the Swiss nuclear power plants, it must be proven that the integrity of the reactor pressure vessel (RPV) continues to be guaranteed during normal operation and also in case of operating faults and postulated incidents. The PISA project was launched in 2009 as the successor to the Diagnostics project. It aims to analyse the state of knowledge in the area of brittle fracture safety proof for RPVs. Extended measurements and model calculations will then be carried out to determine the structural integrity of the RPV under long-term conditions.

The project comprises the following sections:

• Investigations of advanced measurement methods for the non-destructive determination of the degree of embrittlement of the RPV material. The measurement of the thermoelectric effect (Seebeck coefficient) that was assessed as promising in the predecessor project is to be improved in respect of measurement technology. Initial adaptations to the experimental set-up in 2009 yielded a significant reduction in the spread of measurements, and greater reproducibility for individual measurements.
• Studies of the literature were initiated to examine the current level of knowledge regarding damage mechanisms and models of microstructural processes during neutron irradiation of RPV steels.
• Finally, studies were launched on probabilistic methods that can be used for the purposes of demonstrating safety and brittle fracture safety for the RPV. Comparative tests were carried out to evaluate software modules in respect of their suitability for safety analyses on material ageing.