Review and validation of TLAAs is a rather complex task for the majority of VVER plants. The issue is related to the availability of design base infor­mation and incompleteness of the delivered design documentation. Often only the final results of the analyses are known; in some cases, the analyses are presumably obsolete. For the majority of VVER plants outside Russia the TLAAs have to be performed anew using state-of-the-art methods in accordance with the recent requirements. In comparing the practice of dif­ferent VVER operating countries, the most complex cases are probably the Eastern-European VVER-440/213 plants since these plants have to over­come this issue. For instance, in the case of the Rivne NPP in Ukraine, full scope stress calculation and fatigue analysis had to be performed for the VVER-440/213 type units.

The case of Paks NPP Hungary will be discussed below on the basis of Katona, Ratkai and Pammer (2007), Katona et al. (2010) and Katona, Ratkai and Pammer (2011). TLAAs have to be reviewed and verified for the most important structures and components (SCs). Developing a methodology for TLAA reconstitution and defining the method of adaptation of ASME BPVC for a Soviet designed plant has been reported by Katona, Ratkai and Pammer (2007) and Katona, Ratkai and Pammer (2011). Hungarian regu­lations require application of state-of-the-art methods and standards in the time-limiting ageing analyses. ASME Boiler & Pressure Vessel Code, Section III, edition 2001 (ASME BPVC) had been selected for the reconstitution of TLAAs and associated strength verification. The code selection requires understanding of both the Russian (Soviet) design standards and the ASME BPVC code. Different studies were performed for ensuring the adequacy of ASME BPVC implementation for VVER-440/213. Calculations were per­formed for a 50 year extended operational lifetime with an additional margin of 10 years. The use of ASME BPVC is not a generic approach used by VVER operators. In some VVER operating countries the conservative PNAE G-7- 002-86 standard is used by the operators and accepted by the regulators.