Reliability in an imperfect world: inspecting critical systems

title:Reliability in an imperfect world: inspecting critical systems
topics:Dependability, security and performance
contact:E.J.J. Ruijters MSc & dr. M.I.A. Stoelinga


RAMS (Reliability, Availability, Maintenance, Safety) requirements are of utmost importance for safety-critical systems like nuclear power plants, power grids, and railroad infrastructure. Proper maintenance is crucial to keeping these systems as reliable as they need to be, leading to questions such as: How much maintenance is enough? What if an inspection overlooks a developing problem?

A widely used standard for RAMS analysis is fault tree analysis (FTA), which we have recently extended to include maintenance through fault maintenance trees (FMTs). The current models assume that inspections are carried out perfectly and find all problems that can be found. In practice, however, inspections are often carried out in difficult conditions (low light, awkward angles) that result in potential problems being overlooked in some inspections. Therefore, we want to extend the model to include such imperfect inspections.

Your tasks will include:

  • Study of maintenance practices, with emphasis on inspections
  • Integration of imperfect inspections in the FMT framework
  • Case study to validate the extended model

As part of this project, you will visit NedTrain who will assist with the case study.


  1. W.E. Vesely, F.F. Goldberg, N.H. Roberts, D.F. Haasl, Fault Tree Handbook, Office of Nuclear Regulatory Research, US Nuclear Regulatory Commision, 1981 (Digital version available here)
  2. E. Ruijters, D. Guck, P. Drolenga, M. Stoelinga, Fault maintenance trees: reliability centered maintenance via statistical model checking. (Digital version available here)