PRA improves IRIS plant safety-by-design™

The International Reactor Innovative and Secure (IRIS) NSSS has used Safety-by-Design™ from its inception. NSSS design features have either eliminated or significantly reduced the consequences of 7 of the 8 Class IV design basis events. Concurrent with the IRIS design effort, PRA teams have performed preliminary PRAs for the IRIS plant. The PRA team has worked with the IRIS design team to implement design changes that improved plant reliability The initial PRA study resulted in a CDF of 1.2×10-8 for internal events. A second PRA team has 1) addressed ATWS impact on CDF; 2) evaluated potential fire, flood and seismic external events; 3) performed a preliminary Human Reliability Analysis (HRA) and 4) developed a preliminary Large Early Release Frequency (LERF) model that included assumptions on containment response following core damage. The net result of these studies increased to IRIS CDF from 1.2×10^-8 to 2×10^-8. Future PRA work will require closely following the detailed IRIS design effort 1) to assure assumptions made during the PRA analysis are confirmed or 2) to revise the PRA accordingly.