ML011490303
| ML011490303 | |
| Person / Time | |
|---|---|
| Issue date: | 05/21/2001 |
| From: | Tim Reed NRC/NRR/DRIP/RGEB |
| To: | NRC/NRR/DRIP/RGEB |
| Reed T, NRR/DRIP/RGEB, 415-1462 | |
| References | |
| Download: ML011490303 (2) | |
Text
May 21, 2001 MEMORANDUM TO: File FROM: Timothy A. Reed, Sr. Reactor Systems Engineer/RA/
Generic Issues, Environmental, Financial &
Rulemaking Branch Division of Regulatory Improvement Programs, NRR
SUBJECT:
SUMMARY
OF PHONE CALL WITH NEI ON THE ISSUE OF LONG-TERM CONTAINMENT INTEGRITY The staff held a telecon with NEI on May 17, 2001 to clarify the staffs position regarding the need for incorporating guidance into NEI 00-04 to address the issue of long term containment integrity.
The staff provided the following information regarding long-term containment integrity to NEI:
ÿ In accordance to RG 1.174, proposed changes to the licensing basis have to be consistent with the defense-in-depth philosophy.
ÿ In meeting the defense-in-depth principle, a licensee should demonstrate that the function of the containment as a barrier (including fission product retention and removal) is not significantly degraded when SSCs that support the functions are moved to RISC-3.
ÿ One way to do this would be to show that these SSCs are not relied on to prevent late containment failure during core damage accidents.
ÿ An alternative method would be to demonstrate that a potential decrease in reliability of RISC-3 SSCs that support the containment function does not have significant impact on the estimate of late containment failure probability.
The RILP believes that the containment and its systems are important in the preservation of the defense-in-depth philosophy (in terms of both large early and large late releases). In essence, what we are asking is for a plant-specific understanding of the effects of containment systems on large late releases and an understanding of the credit given to these systems in keeping the conditional probability of these releases small. A licensee can qualitatively argue that an SSC is not relied upon to prevent large late containment failure and is thus LSS from this standpoint.
If an SSC plays a role in supporting containment function in terms of large late releases, and if the licensee wants to categorize these SSCs as LSS (for example, because of available redundant systems or trains or because failure is dominated by factors not related to the SSC),
then sensitivity studies should be performed to show that the effects on (i.e., change in) the late containment failure probability is small and that factors such as common cause failures or other dependencies are not important.
Note that the above approach is consistent with the categorization of SSCs for external events and low power and shutdown modes of operation, i.e., conservative categorization if no PRA exists and qualitative arguments are used, and more realistic treatment is permitted if quantification using a PRA is done to show that risk increases are small.
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