Proceedings of PVP2009 2009 ASME Pressure Vessels and Piping Division Conference July 26-30, 2009, Prague, Czech Republic Draft-PVP2009-77911 Copyright © 2009 by ASME 1 1 ASSESSMENT AND MANAGEMENT OF AGEING OF CIVIL STRUCTURES OF PAKS NPP Tamás Katona Paks NPP Fax: +36 75 50 7940 E-Mail: katonat@npp.hu Sándor Rátkai Paks NPP Fax: +36 75 50 7036 E-Mail: ratkai@npp.hu Péter Gősi VEIKI Institute for Electric Power Research Co. Fax: +36 1 461 3060 E-mail: peter.gosi@veikihed.hu István Móga ETV-ERŐTERV Co. Fax: +36 1 455 3638 E-Mail: moga.istvan@etv.hu ABSTRACT Ageing management review is an essential element of the licence renewal process. Proper ageing management has to ensure that ageing effects will be discovered and handled before the loss of the intended functions of the structures. This practice, the most important and the most frequent degradation mechanisms and effects with the involved concrete structures and structural elements, are presented and summarised in this paper. Two types of ageing management programmes are applied at Paks NPP. Programmes “A” are related to the different structural elements of the buildings or to typical ageing problems (e.g., settlement) which occur at many buildings. Programmes “B” specify the exact methods and conditions of the application of the necessary “A” programmes for the different buildings. Altogether 31 buildings are involved in the ageing management system of Paks NPP. The majority of the identified degradation problems were comparatively minor and involved mainly concrete cracking, leaching, chemical attack, corrosion of carbon steel liners, degradation of sealing and coating materials, and settlement. The main results of monitoring and theoretical analyses (in the fields of heavy-concrete structures, effect of elevated temperature, forecasting of settlement for the end of the extended lifetime, etc.) are also presented. INTRODUCTION Paks NPP operates four WWER-440/213 type reactor units, which provides ~38% of domestic power production. A power up rate programme resulting in ~500 MWe per unit will be completed in 2009. The units of Paks NPP were put into operation between 1982 and 1987 with a designed lifetime of 30 years. A detailed feasibility study demonstrated the possibility of the extension of operational lifetime by an additional 20 years, thanks to the operational and maintenance practice and the robustness of structures and components. Pre-conditions of a long-term operation (LTO) decision were: compliance with Current Licensing Basis (CLB), well defined and updated design basis information, implementation of ageing management programmes, and programme for identification and resolution of safety issues. Renewal of the operational licence is required for the extension of operational lifetime. According to the Hungarian regulation, the licence renewal is a two-step process. First the plant has to prepare its programme for long-term operation (LTO Programme) and submit it for regulatory control not later than 4 years before the expiration of the operational licence. LTO Programme means: