Nuclear power plant shift supervisor's decision making during microincidents

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Abstract

The aim of this paper is to examine the cognitive processes through which operators make decisions when dealing with microincidents during their actual work, and to determine whether they use a naturalistic or normative decision making strategy. That is, do they try to recognize a microincident as familiar and base decisions on pattern recognition, tacit knowledge, or condition–action rules (naturalistic), or do they need to concurrently compare and contrast options, before selecting the best possible according standard operating procedures (normative)? The method employed for data collection was a cognitive task analysis (CTA) based on operators’ activities. The main finding of this research was that decision making is primarily based on naturalistic strategies. These findings contrast the normative behavior prescribed by the organization's work design and their standards of competency for training and evaluation operators work.

Relevance to industry

This study presents a situated method to describe how sharp end operators make decisions during microincidents that occurs in normal operation, emphasizing how the sociotechnical environment affects their cognitive strategies, which is one of the basic steps for an organization that wants to enhance the safety culture.

Introduction

Nuclear power plants (NPPs) are hazard environments where emergencies can have devastating effects as seen in the Chernobyl disaster in 1996. In overall command of control room crew and of handling any incident encountered, is the Shift Supervisor (SS). The outcome of a crisis is consequently dependent on the SS's judgement, decision making and situation awareness.

The aim of this study was to examine the cognitive processes through which experienced Shift Supervisors make decisions during microincidents in normal plant operation, and to determine whether they use a naturalistic or normative decision making strategy. That is, do they recognize the situation as familiar and base decisions on condition–action rules (naturalistic), or do they need to concurrently compare and contrast options before selecting the best possible (normative). Emphasis was on the individual Shift Supervisors’ understanding of the situation and the meaning he attached to the information or events taking place. The method employed to achieve this objective, was a cognitive task analysis (CTA) based on field studies.

Investigations based on field studies during NPPs normal operation are rare. Mumaw et al. (1996) had already noticed this situation, indicating that the focus of the research has been on emergency operations. They claimed that because most abnormalities are preceded by normal operating regimes, an understanding of people performance during normal operation is critical. After a set of field studies carried out in Canadian nuclear power plants, Mumaw et al. (1996), and Vicente et al. (1997) found that what makes monitoring difficult is not the need to identify subtle abnormal indications in a quiescent background, but rather the need to identify relevant information against a noisy background. Their findings emphasized the active problem-solving nature of monitoring in NPPs, and highlight the use of strategies for knowledge-driven and the proactive adaptation of the man–machine interface (control room) to support monitoring. Since most of the operators’ adaptive strategies depends on the SS's authorization, to investigate the SS's decision making process can be seen as a complement of Mumaw, Vicente and colleagues’ studies.

Another issue to justify this investigation is that the risk organizations performance criteria for decision making (OPITO, 1997; INPO, 1997) present elements that suggests a normative decision making model based on information gathered from all available sources, appropriate resource utilization, valid interpretation of information, and valid action selection based on this information. Additionally, a review of potential consequences and probabilities against possible response actions, the development of a plan of action, and quick interventions are required. The normative approach described by the industry contrasts with research evidence that has indicated that in emergencies, decision making is often based on condition–action rules (Rasmussen, 1983) or recognition (Klein, 1989). However, in normal operation conditions, what happened with the decision making processes?

Section snippets

Naturalistic decision making

Naturalistic decision making (NDM) is a comparatively new term, referring to how people make decisions in complex real world settings. The study of NDM asks how experienced people, working as individuals or groups in dynamic, uncertain, and often fast paced environments, identify and assess their situation, make decisions and take actions whose consequences are meaningful to them and to the larger organization in which they operate (Zsambok and Klein, 1997; Klein et al., 1993). The research

Methodological framework

Considering the ecological and holistic approach of the NDM research, the cognitive task analysis (CTA) based on field studies is the natural methodological framework for this research. CTA is a ubiquitous description for a number of methods used to elicit knowledge from workers in specific domains. Seamster et al. (1997) defined CTA as methods to identify and describe cognitive structures such as knowledge base organization and representational skills, and processes such as attention, problem

The field studies

The research was based on a set of field studies carried out in one nuclear power plant. Our first field study was an exploratory study with two aims: (1) to break the ice between researchers and operators; (2) to get a preliminary understand of the strategies that operators use to overcome the work environment constraints. Pilot study results set the basis to the second study, carried out during NPP startup and shutdown. In this studies our aim were to classify Shift Supervisor decision making

Shift Supervisors decision making style

Clear examples (20%) of multiple generation and concurrent evaluation of options were found in the protocols (and were backed up in the debrief sessions) which suggested that the design of the study did not suppress evidence of such a decision making strategy. These decisions occurred during the Reactor Heat Removal Blockade MI, and during the Incompatibility Procedures MI. In these two MIs time pressure were not important: in the Reactor Heat Removal Blockade, the refrigeration process was

Conclusions

There were several methodological problems associated with the use of verbal protocols in this field studies. Firstly, the complexity of NPP control room operators’ activities and the large number of personnel involved made it difficult to distinguish between what would in fact be Shift Supervisors decisions and decisions made by other team members, only authorized by SSs. Secondly, the use of an actual work scenario also complicated the matter as a number of questions arose where the answer

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      Similarly, it is evident that detailed PSFs included in the social aspect (or cultural characteristics such as roles, responsibilities, norms and attitudes of human operators) are also important for explaining the variability of human performance. Actually, the influence of cultural variability on the performance of operating personnel seems to be even natural because they have to accomplish the required tasks by making a complicated decision with a high degree of uncertainty, which is caused by one or more features expected from a real situation including: (1) ill-structured problems, (2) uncertain dynamic environments, (3) shifting, ill-defined or competing goals, (4) actions with feedback and/or feedforward loops, (5) time stress, (6) multiple decision makers, (7) organizational goals and norms, and (8) poorly defined procedures [8]. In other words, as it is really subjective to decide something under such conditions, it is anticipated that the cultural characteristic of operating personnel could be one of the most radical factors resulting in the variability of their performance [32,49,50,56].

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