269 NUCLEAR ENGINEERING AND TECHNOLOGY, VOL.40 NO.4 JUNE 2008 EXTENSION OF OPERATIONAL LIFE-TIME OF WWER- 440/213 TYPE UNITS AT PAKS NUCLEAR POWER PLANT TAMÁS JÁNOS KATONA * , SÁNDOR RÁTKAI Nuclear Power Plant Paks 7031, Paks, P.O. Box. 71, Hungary * Corresponding author. E-mail : katonat@npp.hu Received April 10, 2008 1. INTRODUCTION The four WWER-440/213 units at Paks NPP, Hungary are approaching to their last decades of licensed and designed term of operation. Design life-time of WWER- 440/213 type reactors/plants is 30 years and the operational licence had been limited to that term. Detailed feasibility study demonstrates the possibility of extension of operational lifetime by additional 20 years, thanks to operational and maintenance practice, and robustness of design of the structures and components. Enhancement of the reactor thermal power by 8% will increase the net power output (from 460MWe to 500MWe), consequently, it improves the competitiveness of the plant and makes the long-tem operation (LTO) even more reasonable. Long- term operation of Paks NPP is widely supported by the public in Hungary. According to Hungarian regulations, a formal license renewal (LR) is required for prolongation of operation. However safe and economically reasonable prolongation of operation of Paks WWER-440/213 type plant and any other old vintage plans should be considered in broader context. It requires: a) a comprehensive engineering practice, which integrates - up-to-date knowledge on ageing phenomena, - vigilance through condition monitoring /ageing management, - ability to recognise the unexpected phenomenon when it arises, - a consequent application of best practices, - feed-back of experiences, - proper consideration of WWER-440/V213 features, - graded approach in accordance with safety relevance and plant lifetime limiting character of the given structure/component and ageing process; b) a regulatory framework for controlling the safety both in the act of licence renewal and continuously during the operation. Consequent application of these attributes will result in a gapless system of plant practice, applied engineering tools, methodologies and regulatory control processes. A “gapless” plant system/approach means: - all systems, structures and components (SSCs) have to be covered by certain plant programme, - all ageing processes have to be considered, - all plant activities have to be considered, i.e. the routine activities should be integrated with those specific to LTO utilizing the synergy between them. Above criteria are valid for the regulatory frame as well. Operational license of WWER-440/213 units at Paks NPP, Hungary is limited to the design lifetime of 30 years. Prolongation by additional 20 years of the operational lifetime is feasible. Moreover, enhancement of the reactor thermal power by 8% will increase both the net power output and the competitiveness of the plant. Paks NPP is a pioneer considering the power up-rate and preparation of long-term operation of WWER-440/213 design. Systematic preparatory work for long- term operation of Paks NPP has been started in 2000. A regulatory framework and a comprehensive engineering practice have been developed. According to the authors view, creation of a gapless engineering system via consequent application of best practices, and feed-back of experiences together with proper consideration of WWER-440/V213 features are the decisive elements of ensuring the safety of long-term operation. That systematic engineering approach is in the focus of recent paper. Key elements of justification and measures for ensuring the safety of long-term operation of Paks NPP WWER-440/213 units are identified and discussed. These are the assessment of plant condition and review of adequacy of ageing management programmes, also the review, validation and reconstitution of time limited ageing analyses as core tasks of licence renewal. KEYWORDS : Long-Term Operation, Power Up-Rate, Time Limited Ageing Analyses, Ageing Management, WWER-440/213