## 3 Information Requirements Development  
The term 'information requirements' in our study refers to the general sets of information that are required by the operators to carry out their tasks. Specifically, in the event of severe accidents, the operators need to get certain information to perform the mitigation strategies, these are the target information requirements developed throughout this study. Additionally, the information requirements discussed here have a broader scope than the information requirements that are often developed together with display requirements, namely, the information required to be displayed. Our proposed information requirements can contribute to the work domain in various forms, not only as an information item in a system display but also might be in the personnel knowledge through training programs, in the content of the guidelines, and so on. Information requirements generation is an important process for designing not only the decision support displays but also for the overall decision support systems, or any complex system, especially at an early stage of development [34; 35]. A systematic approach is required to ensure that all the required information items are considered and implemented efficiently to achieve the desired performance of productivity, efficiency, safety, and so on [34]. The quality of decision-making depends on the information available to the decision-makers [44]. Nevertheless, by simply presenting more information, the quality of decision-making does not necessarily improve [42]. The correct information required by the tasks or functions being currently carried out shall support efficient decision-making. **Information requirements table. ** We collected the information requirements by taking the functions' aspects from the FRAM model and the states of knowledge from the decision ladder model. The information requirements are arranged in tabular form. Table 4 shows the information requirements related to the 'F2 Perform control guideline (select mitigation strategy)'. Besides the basics of information requirements, we included 'Knowledge type' and 'Information provider' to support the DSS development. The information requirements table contains the following information:  
* Function: the functions from the FRAM model;
* Information requirements: the information requirements for each function. An information requirement can be repeated for multiple functions;
* Information requirements source,'model' column: FRAM or decision ladder (DL) model where the information requirements are acquired. The 'details' column contains which aspects of FRAM function or which state of knowledge of decision ladder the information requirements are obtained;
* Knowledge type: the knowledge type of the information requirement. We defined the knowledge type as follows: Plans, Goals, Possibilities, Means, History, Relations, Procedures, Variables, States, Criteria, and Environments. An information requirement may have a different knowledge type depending on the functions;
* Information provider: the _assumed_ place where the operators can obtain the information requirements. We defined the information provider as follows: Self (knowledge), Communications, Display, Information support systems, and Guidelines and procedures. **Information requirements elicited from the FRAM model. ** In the following, we explain the information requirements of 'F.2 Perform control guideline (select mitigation strategy)' as a representative of our analysis method. Function F.2 is one of the key functions in severe accident management and it covers the observation of NPP parameters and the selection of a mitigation strategy based on predetermined conditions. From the FRAM model, we obtained 6 information requirements, and from the decision ladder model, we obtained 13 information requirements, where 4 of them are duplicated, leading to a total of 15 information requirements.