Examination and long term assessment of nuclear power plant structures Final report

This report describes the work that has been jointly carried out, based on a common and complementary programme by Taywood Engineering Ltd (TEL), Stangenberg Schnellenbach und Partner (SSP) and National Nuclear Corporation (NNC) on the long-term integrity of nuclear power plant structures. Currently deferral is considered as a preferred option for the dismantling of nuclear installations. There is, however, the need to determine the measures required for maintaining shutdown plants in a safe condition and to assess the radiological consequences and costs. TEL and SSP have worked on similar aspects of the examination and long-term assessment of nuclear power structures. This included substantiation of predictive models on the mode and pace of deterioration of nuclear plant structures and theoretical analyses of the destressing options available for both nonded and unbonded prestressing tendons. NNC has separately assessed the risk of rapid stress corrosion cracking of carbon/low ally steels and intergranular attack of stainless steel components. The study concludes that: after 150 years from construction, a majority of all areas could still be passive. Predicted times for the carbonation front to reach reinforcement positions range from 44 years to well in excess of 1000 years. Predictions based on measured levels to chloride within the concrete indicate that a substantial percentage of steel is unlikely to become depassivated within 150 years. During decommissioning, prestress levels can be safely reduced on both bonded and unbonded prestressed concrete pressure vessels in a controlled manner. The predictions have shown that it is only in the worst cases of complete destressing that comparatively small levels of tensile stresses are obtained in parts of the pressure vessels. Measurements made of the quantities of nitric acid concentration in the atmosphere within reactor R1 at Berkeley show quantities much lower than the predictions had indicated. Limited video inspections of the insides of Berkeley and Latina show no evidence of serious corrosion. (orig.)SIGLEAvailable from TIB Hannover: F95B2268 / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekBundesministerium fuer Bildung, Wissenschaft, Forschung und Technologie, Bonn (Germany); European Union (Euro), Brussels (Belgium)DEGerman