Peach Bottom Unit 2 Level 2 PRA Model Implementation and Enhancements with SAPHIRE 8 for ICM

This letter report documents the work performed under JCN V6225, Task 5A. Task 5A requires INL to complete the conversion of the ICM Level 2 model, i.e., Peach Bottom Unit 2 Level 2 PRA Model, from SAPHIRE 7 to SAPHIRE 8, and ensure the functionality of SAPHIRE 8 for solving the Level 2 model utilizing Version 8 enhancements over previous versions. One of the enhancements is to ensure the functionality of the ability to solve for a selected phase. The INL will also assess the feasibility of using SAPHIRE 8 decomposition event tree functionality and make SAPHIRE 8 enhancements based on NRC user comments for using Level 2 models. Section 2 discusses the implementation of Peach Bottom Unit 2 Level 2 model in SAPHIRE 8, as well as the unique features in the SAPHIRE Level 2 model. Sections 3 to 5 documents the INL efforts to enhance the SAPHIRE Level 2 model by simplifying the complex partitioning quantification approach, and investigating the usage of phase feature and decomposition event tree in SAPHIRE model. Section 3 describes the developing of a streamlined, simplified Level 2 quantification approach that does not use the partition rules. Since the partitioning approach is not continued to be used for Level 2 model quantification, the requirement in Task 5A to make the partition rules phase-aware is no longer applicable. Section 4 presents the using of the phase feature in the Level 2 model. Section 5 develops the decomposition event trees that would be used for Peach Bottom Unit 2 Level 2 model.