Practical experience of failure analysis on nuclear facility or how I learned to love a well-structured FMEA

Abstract

The safety assessment principles for nuclear facilities, produced by the Office for Nuclear Regulation (ONR), define Engineering Principles which require a formal and structured analysis to be undertaken to identify all potential failure modes for structures, systems and components important to safety within a nuclear facility.It has been widely publicised, for example in “Mitigating the Loss of Critical Knowledge” by Bell (2014), that there is a skills shortage in engineering design assurance in highly regulated industries within the UK. This paper presents examples and lessons learnt from 5 years of practical experience in performing structured failure analysis, particularly Failure, Modes and Effects Analysis (FMEA), on nuclear facility design: these lessons learnt are considered applicable to all highly regulated industries. It is hoped that the following examples included in this report, might inspire and guide others in the development of FMEA in support of design assurance activities:Tailoring the level at which FMEA is undertaken to the nuclear classification of the safety function; detailed component level FMEA for higher level safety functions, and high level functional FMEA for lower level safety functions;Running the FMEA in parallel with design development and working with the design engineers to ensure results from the FMEA can influence the design at the appropriate time;Using FMEA to identify design mitigation and Examination, Maintenance, Inspection and Test (EMIT) recommendations during early phases of the design;Using FMEA to identify redundancy within a design to reduce the maintenance burden through life;Inclusion of component failure mode failure rate data to calculate the Probability of Failure on Demand (PFD) of safety functions;Inclusion of dependability analysis between systems to calculate the PFD of a higher level function;The positive impact of integrating Human Factors (HF) assessors in the development of the failure analysis.