1986

Norros, Leena; Sammatti, Pekka

The study consists of a series of two experiments. In experiment I "leak in the live steam manifold" was the test transient. Altogether 8 of the 12 crews took part in the test. In experiment II an even more difficult LOCA-transient of "partial breakdown of plate fixing bolts of the primary manifold of the steam generator" was used. All the 12 crews participated in the second experiment. The aim of varying the difficulty of the test transients was successful. The total number of errors in the first experiment was 57, in the second it was 155. It is to note that the method used does not include an evaluation of the fatality of the committed errors. The distribution of errors along the decision function was first analysed. In both experiments the majority of errors concentrated on the decision and execution functions. The distributions are not statistically different. In regard to the error causes the distributions differed significantly. In experiment I deficiencies in knowledge and action control and problems related to procedures were the major causes of errors. In the more difficult transient the knowledge and action control problems arose considerably accounting for of the total error causes and problems in cooperation within the crew have increased. We speak of a new error profile in the more complicated task. In experiment II a comparison of the distributions of the high error group and the low error group was also carried out. Neither in this case did the decision function distributions show a significant difference. However, again the error causes distribute significantly differently. The low error distribution is very sharp in the sense that most of the errors are in the knowledge and action control domain. The high error group has much more errors related to procedures and problems in collective operational strategy. Thus, the new error profile is more pronounced among the high error crews. For both experiments the errors were also analysed concerning the frequency of their occurrence in the action sequence. In the case of the second experiment also error type profiles in action sequence were constructed for each crew. The consistency of the crews performance in the two experiments was fairly high, which made it plausible to assume habitual features behind the observed differences. Preliminary hypothesis of the different forms of the operators diagnostic judgement were formulated on the basis of this analysis. In the study we could detect a distinct need for conceptual tools in operating difficult transients. Not only more process knowledge and better instructions are needed, but above all collectively formed strategic plans for organising the group and individual activity in an unexpected, new and complicated situation. This becomes more critical the higher the complexity of the demands. This constitutes a problem because in real situations psychic stress certainly tends to hinder such a rational and controlled communication.