IMC 2515, App D (Plant Status) has been revised to require inspectors to monitor and trend RCS leakage indications. The change requires inspectors to review licensee procedures and action plans to identify sources of RCS unidentified leakage. In addition, guidance and techniques necessary for assessing potential adverse trends and action levels in response to increasing levels of RCS unidentified leakage have been provided as an attachment to this Appendix (Ref. DBLLTF Item 3.2.1(2)).
Specifically, the attachment states that:
1. The inspector should obtain the mean value ( µ ) for the past three months of RCS unidentified leakage rate and the corresponding standard deviation ( s ) from the licensee, on a monthly basis, representing a 3-month rolling data set.
2. Once a month, the inspector should use the mean value ( µ ) and the standard deviation ( s ) from the previous three months to calculate the three action level triggers ( µ, m + 2s, m + 3s ).
3. During the daily plant status review, the inspector should obtain the RCS unidentified leakage rate value.
4. The inspector should compare the licensee calculated RCS unidentified leakage rate value to the following three action level triggers to determine if there is a potential adverse trend and take appropriate actions. If the licensee performs the RCS leakage rate calculations several times a day, the inspector should compare only the highest value per day to the action level triggers. If the licensee, following their TS, only performs a RCS leakage rate calculation once per 72 hours, then the inspector should perform this comparison once per 72 hours.
Action Level I: Nine (9) consecutive leakage measurements above the mean m
Action Level II: Two (2) of three (3) consecutive measurements exceed the m + 2s
Action Level III: One (1) measurement of leak rate exceeds the m +3s
5. The inspector should take actions specified in this attachment if any of the action level trigger level criteria are exceeded.
IMC 0308, Att 2 (Technical Basis for the Inspection Program) “Figure 47 IMC 2515, Appendix D Basis Summary Sheet,” has been revised to reflect the changes made to IMC 2515, App D, ”Plant Status,” pertaining to RCS unidentified leakage trending and action levels to trigger increasing levels of NRC interaction with the licensee.