Identification of Potential Operator Burden Through Systematic Assessment of Actual Plant Transients

Abstract

Recent events in U.S. operating nuclear power stations have raised questions as to whether control room operators might be unnecessarily burdened in their response to unusual events. To respond to these questions a team of plant control room operators, system design experts, and a human reliability analyst were assembled by the plant owners to investigate the issue of operator burden. The approach taken focused upon the review of all significant transients which had occurred in one plant type since 1980. The system design organization had previously analyzed each of these events as part of their Transient Assessment Program (TAP). These TAP reports represent a significant data set related to actual transient conditions and operator responses. The reports constituted the primary data base upon which the study was based.The thrust of the effort was the utilization of a multi-disciplinary team to become familiar with the transients and specifically with the operator and equipment responses. This information was then used to indicate generic areas where operator overburden might have occurred. Next information was elicited from the operations staff at each participating facility. In this way plant specific information was obtained which attempted to identify when and in which stations each of the previously identified generic overburdened conditions might apply.The study first required the development of a clear and concise definition of what operator burden was, and the development of generic examples of when it was likely to be observed in actuality. The definition chosen relates the extent of burden to the probability of operator error using an information processing paradigm of operator decision making. The developed definition was then applied to the review of 6 significant transients. This application allowed for the development of 5 generic qualitative categories of operator burden.In a parallel effort, the systems design team members developed detailed scenarios of each transient in a format designed to highlight the key operator decision points. The developed scenarios included a combined presentation of an operator action event tree (von Herrmann, 1983), and an operator concern event timeline. For each of the key decision points identified, a set of questions was developed and correlated to actual plant conditions at that point. These decision point packages were then circulated for response to participating operators and the responses led to a qualitative evaluation of the level of operator burden associated with specific aspects of transient integration.