Large release frequency

The core damage and large release frequencies are low despite the conservative assumptions made in specifying success criteria for the passive systems. The success criteria have been developed in a more systematic, rigorous manner than typical PRA success criteria. The baseline success criteria are bounding cases for a large number of PRA success sequences. The baseline success sequences, in most cases, have been defined with ... 

Over the next several years, the PRA was detailed to the point it included detailed fault trees of the mechanical, electrical, and instrumentation and control systems and the scope was expanded to include shutdown, fire, flood events, and large release frequency and off-site dose quantifications. Core damage frequency PRA was supported by extensive plant thermal-hydraulic analysis to justify success criteria. Extensive testing and thermal-hydrauUc analysis, to support containment integrity during core melt sequences, underpirmed the large release PRA. 

Large Release Frequency for Internal Initiating Events at Power... 

The contributions to large release frequency from the late containment failure and intermediate containment failure release categories are negligible. The total frequency of the first two categories is 1.8 x 1 O events per year. These two categories make up 92 percent of the AP 1 OOO s... 

The large release frequency results are not very sensitive to the treatment of the steam generator tube rupture (SGTR) events for laige release frequency. 

The large release frequency is dominated by containment failures or bypasses due to steam generator tube rupture, and high primary pressure core damage sequences. The remaining containment failures ate dominated by an early containment failure due to reactor cavity flooding failure. 

The large release frequency is sensitive to the operator action to flood the reactor cavity in a short time following core damage. This operator action has been moved to the beginning of the appropriate Emergency Response Guideline, to increase its likelihood of success. 

Core Damage Frequency and Large Release Frequency for Plant Initiating Events while Shutdown... 

The PRA results (Section 19.59.5 of Reference 8.21) show that the overall APIOOO shutdown core damage frequency is very small, at 1.23 x 10 per year. The estimated large release frequency... 

Evaluating the Core Damage Frequency and the Large Release Frequency... 

Events Core Damage Frequency, per year Large Release Frequency, per year ... 

Similarly, the 3BE end state contributes 14% of the frequency of the at power large release frequency of 0.195xl0 per year, and 77.4% of the shutdown large release frequency of 0.205 X10 per year. Summing the two values results in the component of the frequency of large release due to 3BE Events being 1 86x 10 per year. The monetary benefit of this is 372. 

The 3BP end state contributes 14% of the fi equency of the at power large release frequency of... 

The diversified functions are selected on the basis of PRA insights to reduce the core damage frequency and to reduce the conditional probability of large-release frequency, given core damage. 

PRA calculations of large release frequencies have large uncertainties, and... 

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