An empirical investigation of operator performance in cognitively demanding simulated emergencies

Abstract

This report documents the results of an empirical study of nuclear power plant operator performance in cognitively demanding simulated emergencies. During emergencies operators follow highly prescriptive written procedures. The objectives of the study were to understand and document what role higher-level cognitive activities such as diagnosis, or more generally 'situation assessment,' play in guiding operator performance, given that operators utilize procedures in responding to the events. The study examined crew performance in variants of two simulated emergencies: (1) an Interfacing System Loss of Coolant Accident and (2) a Loss of Heat Sink scenario. Data on operator performance were collected using training simulators at two plant sites. Up to 11 crews from each plant participated in each of two simulated emergencies for a total of 38 cases analyzed. Crew performance was videotaped and partial transcripts were produced and analyzed. The results revealed a number of instances where higher-level cognitive activities such as situation assessment and response planning enabled operators to handle aspects of the situation that were not fully addressed by the procedures. This report documents these cases and discusses their implications for the development and evaluation of training and control room aids, as well as for human reliability analyses.

Development of New Taxonomy of Inappropriate Communication and Its Application to Operating Teams in Nuclear Power Plants

“…The ISLOCA scenario is referred from nuclear regulation/control room-6208 (NUREG/CR-6208) [28]. The ISLOCA scenario was designed to be difficult from the point of view of situation assessment.…”

An overview of the evolution of human reliability analysis in the context of probabilistic risk assessment.

“…Following these developments, and continuing experience with human actions associated with misunderstandings by operators in responding to unusual plant conditions, developments took place to create newer HRA models that use as their basis a more complete understanding of the interactions between people and the systems. For example, later work by Woods et al [22], Hollnagel [23,24], Roth, et al [25] and Reason [18] all added significantly to the explanation of how people can be led to misunderstand the nature of events. This explanation underlies several of the more recent methods like ATHEANA [3] and CAHR (Sträter [26]; Sträter and Bubb [27]).…”

“…While procedures (whether written or memorized through training) provide a structured support to operators, experiments (Roth et al [25]) have shown that they are, at best, an initial basis for action but operators must reassess the guidance in light of the actual plant conditions; even for the symptom-based procedures developed after Three Mile Island. In other words, while procedures are written using certain assumptions about the course that an off-normal condition will take, there are many opportunities for the plant to behave differently from the assumptions underlying the procedures.…”

“…This is true even for the so-called symptom-based procedures that provide basic steps to be followed once certain symptoms appear, regardless of the cause of the symptoms. However, experience has shown, both in simulators and in real events, that the symptoms can mislead operators into taking the wrong actions as discussed in Roth, et al [25]) and Kauffman [36]. During the development of the ATHEANA HRA method, several of these events were examined in detail to identify the kinds of failures that led to the wrong actions being taken (Barriere, et al [37]).…”

Operator Behaviors Observed in Following Emergency Operating Procedure Under a Simulated Emergency

“…prescribed tasks in EOPs) and a dynamic process (i.e. the nature of an on-going situation) [1]- [3]. From the existing human reliability analysis (HRA) method, the effect of procedures on human performance has been recognized as one of the most important performance shaping factors (PSF) [4]- [6].…”