Abstract
The study of the effects behind the degradation of components and materials is becoming increasingly important for the safe operation of aged plants especially when it comes to life-extension. Since the Russian nuclear community began to examine life extension issues nearly fifteen years ago, there is much to learn from these Russian pioneering studies, a portion of which were performed under the TACIS (Technical Assistance for Commonwealth of Independent States) international collaboration program with EU countries. At the Ninth International Conference, recent data were introduced regarding the ageing effects of mechanical properties of various kinds of steel and the welding joints of Russian NPP components. The full title of the conference was Material Issues in Design, Manufacturing and Operation of Nuclear Power Plants Equipment. The meeting was organized by the Central Research Institute of Structural Materials (CRISM) "Prometey" in cooperation with the IAEA and JRC-EU. In reviewing the recent data presented at the Ninth Conference, the authors think that the paradigms of structural integrity issues in aged plants are now reasonably well established in (1) fracture mechanics and irradiation hardening of reactor vessels and core internals and (2) thermal ageing and annealing effects. Yet even when considering these well established paradigms, the current direction of study is not adequately addressing the effects of a corrosive environment. The first author believes that the current approach of low cycle fatigue is far from able to prevent and predict environmentally assisted cracks. This fundamental flaw stems from design codes, which do not incorporate the basic knowledge of corrosion mechanisms. Our focus in researching aged plants should be re-directed toward environmentally assisted cracking, typically the film rupture-slip dissolution mechanism of crack propagation under the effect of long cell action on local cells, as discussed by the first author in the other article which will also be presented at this conference (ICONE15-10559). The local cell action corrosion hypothesis is a practical application of the more fundamental theory of corrosion mechanism (called cathodic de-polarization theory) developed by a Russian academician Akimov as early as in 1945. Without finding a way to mitigate this corrosion process, the first author believes that the most current mechanical approaches towards the assurance of structural integrity are basically flawed as they do not take into consideration the electrochemical processes of corrosion.
