A DFM/Fuzzy/ATHEANA Human Failure Analysis of a Digital Control System for a Pressurizer

A methodology comprising Dynamic Flowgraph Methodology (DFM) and A Technique for Human Error Analysis (ATHEANA) is applied to a digital control system proposed for the pressurizer of current pressurized water reactor plants. The methodology consists of modeling this control system and its interactions with the controlled process and operator through an integrated DFM/ATHEANA approach. The results were complemented by the opinions of experts in conjunction with fuzzy theory. In terms of human reliability, DFM, along with ATHEANA, can model equipment failure modes, operator errors (omission/commission), and human factors that, combined with plant conditions, influence human performance. The results show that the methodology provides an efficient fault analysis of digital systems identifying all possible interactions among components. Through prime implicants, the methodology shows the event combinations that lead to system failure. Quantitative results obtained are in agreement with literature data, with a few percentage value discrepancies.