# Team-Communication Modeling Framework for Multi-Unit Nuclear Power Plant Accident Analysis
## 2 Methods and Data  
### Background and Related Works  
Especially in countries with multiple reactor units per NPP site, multi-unit accidents have been under intense study since the Fukushima accident proved its possibility and massive consequences [12]. A descriptive study was carried out by interviewing the employees who were directly involved in the accident, and five multi-unit risk factors were identified [11]. Although this study's results were highly specific to the Fukushima NPP design and accident characteristics, the insights can be generalized for other NPPs. Also, the suggestions pointed at both technical and non-technical aspects, such as maintaining operator knowledge, personnel planning, training personnel, improving communication capabilities, planning for emergencies, etc. We found that 13 of the 29 suggested activities were non-technical. Another study analyzing the three severe accidents found that, although the causes of accidents and accident sequences were different, the root causes were in the \"system deficiencies indicative of poor safety management and poor safety culture\" [8]. Thus, the non-technical aspects are as important as the technical ones in multi-unit NPP accidents. A part of the non-technical aspects mentioned above can be categorized as the non-technical skills (NTS) of the operators. The significance of operator NTS has been mentioned for at least 20 years [10]. Especially in high-risk domains such as NPP, safe accident countermeasures are very dependent on the NTS of the operators. Failures of NTS were reported to be the causes of most of the aviation, medical, and industrial accidents [13]. Likewise, in the nuclear industry, the lack of NTS contributed to most accidents, either directly or indirectly [14]. The skills listed as NTS varied between studies; however, the following skills were included most of the time: situation awareness, leadership, teamwork, and communication [10; 15; 16]. Various recent studies have reported the significance of NTS [14; 17; 18; 19]. In multi-unit accidents, one of the two most critical factors was the shared safety features between units, and the most common shared feature was the organizational aspects [3]. Another study classified the risks of multi-unit NPP into six classes, and two of them were human and organizational dependencies [20]. For organizations to perform safely during emergencies, accurate communications must be guaranteed. In the Fukushima accident, reduced communication seriously hindered the accident response, which amplified the accident consequences [11]. The failures in communication were reported to be responsible for nearly 60% of mistakes in safety-critical domains [16]. Especially in emergency response, there were times when the interactions between team members were more important than their domain knowledge [16]. Thus, communication is of the utmost importance; there is no alternative to safety management, and it is the basis of operator interactions [14]. In this study, we focused on the team communication of NPPs' emergency-response teams (ERTs) during emergencies since multiple teams must cooperate and the possibility for poor team performance is particularly high during stressful situations [21]. The necessity to investigate communication under a stressful environment such as an accident is also mentioned in other studies [21; 22; 23]. Moreover, even highly trained teams were found to function ineffectively, with significant variability in their performance during emergencies [24]. Effective communication was first mentioned as the first principle of effective emergency response in 1990 [10]. In the nuclear industry, the concerns of verbal communication during accidents have been raised since the 1990s [25; 26]. When a control room is modified, its impact on team communication is analyzed [27]. However, communication failures and the accidents caused by them were still reported and unresolved as recently as 2020 [17; 28].