VERLIFE – “Unified Procedure for Lifetime Assessment of Components and Piping in WWER NPPs during Operation” was initiated and co-ordinated by the Czech and was developed within the 5th Framework Program of the European Union in 2003 and later upgraded within the 6th Framework Program “COVERS – Safety of WWER NPPs” of the European Union in 2008. This Procedure had to fill the gap in original Soviet/Russian Codes and Rules for Nuclear Power Plants (NPPs) with WWER (Water-Water-Energetic-Reactor = PWR type) type reactors, as those codes were developed only for design and manufacture and were not changed since their second edition in 1989.
VERLIFE Procedure is based on these Russian codes but incorporates also new developments in research, mainly in fracture mechanics, and also some principal approaches used in PWR codes.
Last upgrading and principal extending of this VERLIFE Procedure was realized within the 3-years IAEA project (in close co-operation with another project of the 6th Framework Program of the European Union “NULIFE – Plant Life Management of NPPs”) that started in 2009 with final approval and editing in 2013.
As all versions of the VERLIFE procedure were coordinated by the Czech and first version was based on the Czech version of the NTD ASI, there have been simultaneously incorporated into the Czech NTD ASI (Normative Technical Documentation of the Czech Association of Mechanical Engineers) guidelines that are accepted by the Czech State Office for Nuclear Safety for the use in evaluation of Czech NPPs.
This document has several parts: Section IV – “Evaluation of Residual Lifetime of Components and Piping in WWER type NPPs” deals with the evaluation during NPP operation. Main part of the document is divided into four main parts:
- Evaluation of resistance of components and piping against non-ductile failure
- Evaluation of resistance of component and piping against fatigue damage,
- Evaluation of resistance of components and piping against corrosion-mechanical damage
- Evaluation of residual lifetime of components and piping with defects found during in-service inspections
Additionally, several appendices are included for detailed description of individual parts of evaluation, e.g.
- Determination of neutron fluences in reactor pressure vessel and internals
- Determination of degradation of materials during operation
- Requirements for evaluation of pressurized thermal shock regimes
- Evaluation of corrosion-errosion effects in piping
- Environmental fatigue evaluation
- Evaluation of reactor pressure vessel failure probability
Finally, the following appendices dealing with components integrity have been included:
- Lifetime of reactor pressure vessel internals
- Leak-before-break concept for WWER piping
- No-break-zone for WWER piping
The paper will describe structure and main principles of this Section IV.
