2023

Liinasuo, Marja; Karanta, Ilkka; Kling, Terhi

Heavy lifting is critical to the safety of a nuclear power plant. The lifting of the protective tube unit (PTU) is reported here, from the HRA perspective; PTU was chosen because its lifting procedure is complex, and the related potential damage is severe due to its weight. The goal of this research report is to provide detailed and systematic information about the nature of heavy lifting and the possibilities of the related human errors.<br/>As methods, seven crane operators and crane operator assistants were interviewed. Firstly, an earlier interview was reanalysed for the identification of dynamic, error-inducing factors related to heavy lifting. Secondly, hierarchical task analysis was used for the identification of the main tasks and sub tasks for the lifting of the PTU. Also, some error-related issues were identified during the hierarchical task analysis.<br/>Five dynamic factors were identified related to lifting during outage. These potentially error-affecting factors are shift extension, working for a long time without a pause, background noise, constant haste, and multitasking, all lowering threshold for human error.<br/>The proceeding of the PTU lifting was analysed, using hierarchical task analysis during the interviews. As a result, 13 main tasks and the related subtasks were identified. Along with the task-analysis process, possibilities for human error were sought for. Various sources for errors were found: human communication related issues, procedure related issues, human resource related issues, malfunction of machine of device, difficult lifting circumstances, and timing related issues. In the study, the proceeding of the lifting session was focused on, and the identified errors serve more like examples of possible errors. The identified errors are related to human injury, weakened situation awareness of crane operator and crane operator assistant, faulty operation of crane, outsiders in the reactor hall during lifting, and insufficient of matters in finishing meeting.<br/>Even this sample of dynamic features and other issues related to human error show that the reasons for human error can be a complex combination of factors, some affecting constantly and some occasionally, in a more unique manner. A more thorough understanding on issues increasing error possibility, as well as the possibility of the errors themselves, could be reached by the same methodology as used in this study, with just more resources.