Levels of Automation for a Computer-Based Procedure for Simulated Nuclear Power Plant Operation: Impacts on Workload and Trust

Nuclear power plants increasingly utilize digitalized systems, including computer-based procedures (CBPs) and automation. These novel technologies require human factors’ evaluation to ensure safety. Potentially, automation contributes to safety by reducing workload, but automation may also induce a loss of situation awareness and trust miscalibration. The current study investigated workload during a simulated nuclear power plant (NPP) emergency operation procedure (EOP) executed using a CBP supported by automation. Two levels of automation (LOA) were compared within subjects: management-by-consent (lower LOA) and management-by-exception (higher LOA). Subjective workload and trust were assessed, together with objective psychophysiological and performance-based workload measures. LOA effects varied across the different workload measures. The hypothesis that workload would be reduced at the higher LOA was confirmed for a behavioral measure (secondary task response time). However, other metrics, including instantaneous self-assessment (ISA) and heart rate variability (HRV), showed increased workload at the higher LOA. Different LOAs may produce differing operator strategies that require multivariate workload assessment to evaluate. Effect sizes for the impact of LOA on workload were indexed by Cohen’s d. Several of these effect sizes were in the 0.4–0.6 range, indicating effects of medium magnitude. In addition, subjective workload data were compared with those from a previous study that simulated conventional NPP operations. As anticipated, workload tended to be lower with the automated procedure. The study suggests future directions for human factors research on plant modernization.