|ŠTĚPÁNEK Ivo||University of West Bohemia|
|Spoluautoři TENGLER Marek, SLADKÁ Jana|
The subject of this paper is to describe the practical use of micro-indentation methods, i.e. measurement of material characteristics by low loads indentation tests, for the preparation a standardized procedure of the conditional monitoring of selected system components of the safety-related systems to ensure their long-term exploitation. With regard to the requirements for long-term operation nuclear power plants that follow from legislation, it is necessary for the important equipment to demonstrate their adequacy for all design basis events and for the whole period of their service. This is one of the basic principles of nuclear safety of the defense against common cause failures. This concept is called the equipment qualification and is characterized by the systematic documentation of equipment performance capability and their components that are, so called, classified items of the plant safety-related systems. The equipment must be qualified for all postulated conditions arising from long-term operation, as well as required assessment for conditions under severe accident regime. Such conditions include effects of degradation due environmental conditions (temperature, humidity, radiation, etc.) inflict equipment parts made of non-metallic materials. As a typical example of the relevant representatives of such elements are cable systems. Newly published a series of standards IEC / IEEE 62582 reflects the requirement of the introduction of condition monitoring, which implies of updated standards IEC 60780 (IEEE Std 323-2004) and to efficiently extend the equipment qualified life, generally limited in active equipment of safety-related systems, exactly for non-metallic materials. Condition monitoring presents a feasible method of continuous monitoring of aging indicators and subsequent extrapolation and determination of qualified life, respectively its continuous extension. The observation results presented here show, that standardized conservative methods of measurement of material properties, such as monitoring of changes of the relative elongation at break or OIT (Oxidation-Induction Time), which defines the aging rate, and can be supplemented or fully replaced by methods of micro-indentation measurements. These methods can be effectively determine parameters of the dynamic hardness significantly more accurately and consequently identify local indicators of aging with significantly higher populations of measurements. Herewith, there is guaranteed realistically determine values of the indicators of aging and eliminate uncertainty measurement and considerably precise a prediction of service lifetime. The indisputable advantage is also non-destructive nature of the tests and demands to the size of samples.