STRENGTH DESIGN
Design of components in line with strength
The requirements on nuclear components and the associated safety aspects are becoming more and more diverse and complex. This applies equally to various vessels, pumps, valves and the piping belonging to systems either required for generating power or having safety functions. Outside normal operation, components with safety functions have to fulfil their respective tasks during anticipated operational occurrences and accidents, which in turn are either caused by external impact, such as earthquakes or airplane crashes, or by internal events, like component failure etc.
TÜV NORD Nuclear experts perform independent calculations to verify whether all applicable loads and load combinations placed on the components can be accommodated, thereby ensuring the appropriate component function when required.
TÜV NORD Nuclear also offers longstanding experience in the fields of strength and stability design for non-nuclear engineering purposes. This encompasses e.g. non-nuclear power plant technology, general plant construction and engineering, as well as railway technology and automotive engineering.
Stress and fatigue analyses
TÜV NORD Nuclear uses the finite element programmes ANSYS and ABAQUS for stress and fatigue analyses of complex component geometries. For preparing the finite element (FE) models, the TÜV NORD Nuclear experts make use of suitable CAD tools, such as CAE, PATRAN, DesignModeler, or Autodesk Inventor.
The ROHRII programme is applied for piping calculations. In addition, TÜV NORD Nuclear uses the Dimy programme as well as its own programmes for standardised components, such as supports, flanges, screws, etc.
Creep strength/creep calculations
TÜV NORD Nuclear has expanded the area of application of the FE programmes by implementing separate subroutines for creep strength and developed an assessment concept for creep strength for selected materials. The numeric analyses are based on a modified Graham-Walles material law.
Fracture mechanics
Leak-before-break analyses for piping and vessels are carried out using analytical and numerical calculation procedures. Furthermore, crack growth calculations for defective components enable the estimation of their expected remaining service life, i.e. until failure would occur.
Functional aspects
The functional performance of valves is analysed in the context of system assessments. For this purpose, the closing behaviour of e.g. valves and sliders is reviewed based on the theoretical determination of the required actuation force and by using specific test results. In this context, the various influencing factors, such as the friction coefficient of the drive mechanism (stem) or between the slider plates and casing guide, are taken into consideration to ensure that the valve fulfils its opening and closing task when needed.
Assessment criteria and committee work
TÜV NORD Nuclear experts are familiar with national and international codes and standards; furthermore, they are continuously updating their specific knowledge by information from the most recent publications on strength design. Such information would be considered as assessment criteria for their analyses. Part of the TÜV NORD Nuclear experts in strength design are members of working groups deriving e.g. codes and standards. This would ensure a reasonable consideration and implementation of newly developed requirements.
