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Non-destructive testing for ageing management of nuclear power components

: Dobmann, G.

Volltext urn:nbn:de:0011-n-1836206 (2.9 MByte PDF)
MD5 Fingerprint: 6512aa011dc0c6312a48933ded4c997c
Erstellt am: 26.11.2011

Tsvetkov, P. (Ed.):
Nuclear power - Control, reliability and human factors
Rijeka: InTech, 2011
ISBN: 978-953-307-599-0
Kap.17, S.311-338
Aufsatz in Buch, Elektronische Publikation
Fraunhofer IZFP ()
3MA; NDT; structural health monitoring (SHM)

Worldwide a renaissance of the nuclear industry is obviously taken place and many countries favour nuclear power as one reliable opportunity to generate electrical energy at very low CO2 generating rates in order to avoid the green house effect in the earth atmosphere. However, since 1986 when the Tschernobyl accident was happening, nearly
nowhere new nuclear power plants were established. The People Republic of China, India and in the last decade Japan, Finland and France are the exception. In other words, existing supply chains of former manufacturers were mainly destroyed or have changed its technical application field. Furthermore, a lot of technical expertise was lost as younger generations were influenced politically to find its interest in other scientific areas other than in nuclear
physics or nuclear engineering.
Even if we can observe today a change in mind in many countries concerning the acceptance of nuclear power the question seriously is to answer: Will we find enough well skilled technicians to reliably build all the planned nuclear power plants in the future? Therefore, life extension of existing plants the more plays an important role. This is truer as we have learnt in the last decades how many potential we have for life time extension even if we take into account ageing phenomena concerning the materials as thermal ageing, fatigue and neutron embrittlement when we think at steel components in the primary circuit; as there are the reactor pressure vessel, heat exchangers, surge line, pressurizer vessel, main cooling pumps and pipe lines. However, as in different countries life extension
to an over all life time of 80 years is in discussion in future we have to take into account the infrastructure, i.e. bridges nearby, important for fluid traffic, emergency current generators, the concrete components of the containment and the cooling towers but also ageing phenomena of electric cable insulation, etc.
Within these life time extension strategies the methodology of a continuously applied ageing management worldwide is seen as an important measure to guarantee nuclear safety. Besides the application of standardised non-destructive testing (NDT) technology during inservice inspection trials in order to perform a diagnosis of the material states online structural health monitoring of components by enhanced and intelligent NDT-sensors
and sensor-networks will play a forthcoming future role. In Germany actually code-accepted procedures to perform ageing management were finally discussed and approved by the authorities. However, research and development in the last decade in the Nuclear Safety Research Programme of the German Ministry for Economy and Technology was continuously performed in order to develop and qualify NDT-technology for characterisation of ageing phenomena. The here presented chapter describes the objectives of this research and the final results
obtained. In any case, the methodology of the micromagnetic NDT procedures was especially developed. This methodology is suitable for materials characterisation of magnetisable steels in terms of determination of mechanical properties. There are many similarities between movements of dislocations under mechanical loads and pinning of this lattice defects at vacancies, precipitates, grain and phase boundaries, contributing to the
strength of the material and the movement of magnetic domains under magnetic loads, i.e. when the material is magnetised in a hysteresis loop. The methodology of the Micromagnetic, Multiparameter, Microstructure and Stess Analysis (3MA) is discussed which on a wide basis of different diverse as well as redundant information allows the sensitive materials characterisation. In case of a Cu-rich steel alloy precipitation hardening is discussed in combination with thermal ageing. It is shown that superimposed fatigue loads will enhance the thermal
ageing effect. Fatiguing of austenitic stainless steel under some conditions is combined with phase
transformation from the face-centred-cubic (fcc) lattice to body-centred-cubic (bcc) martensitic phase which is ferromagnetic of nature. Where the carbon content is low enough to avoid the phase transformation other NDT techniques based on electric conductivity effects or ultrasonic wave propagation phenomena have to be applied.
3MA is sensitive to characterise neutron embrittlement in pressure vessel materials. Material of western pressure vessel design as well as of Russian design were characterised which shows that a new NDT technology for inservice inspection of the pressure vessel wall from the id-surface can be developed.