05000338/LER-2003-002
| Document Number | |
| Event date: | 04-13-2003 |
|---|---|
| Report date: | 06-05-2003 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 3382003002R00 - NRC Website | |
FACILITY NAME (1) DOCKET LER NUMBER 16) � REVISION 1 NUMBER NUMBER NORTH ANNA POWER STATION UNIT 1 05000 - 338 1.0 DESCRIPTION OF THE EVENT On April 13, 2003, at 0300 hours0.00347 days <br />0.0833 hours <br />4.960317e-4 weeks <br />1.1415e-4 months <br /> with Unit 1 in Mode 5, containment personnel air lock (ENS System - NH, Component - AL) leakage testing was being performed as part of the start-up activities following a refueling outage. The total flow rate for the containment personnel air lock was measured at 22 standard cubic feet per hour (scfh). The periodic test procedure has a limit of La, which equates to personnel air lock outer door and none were found. Attempts were then made to locate the leakage on the personnel air lock inner door without success since the containment was under vacuum. The measured value of 22 scfh was subsequently factored in to the total containment local leakage rate and the total maximum path leakage rate. A decision was made to continue with unit start-up activities since the total maximum leakage rate was calculated at 42.319 scfh well below the TS acceptance criteria of The Technical Specification (TS) require two containment airlocks (i.e., equipment airlock and personnel airlock) be operable in Modes 1 through 4. Both the inner and outer air lock doors must be operable for the airlock to be operable. The TS LCO 3.6.2 surveillance requirement delineates air lock leakage rate testing in accordance with the "Containment Leakage Rate Testing Program". The acceptance limits of the program, Section 5.5, Programs and Manuals. While evaluating the test results and TS requirements, the specific criteria for containment personnel air lock leakage was overlooked. The requirements of TS were not properly verified resulting in an incorrect assumption that the overall containment leakage value (total maximum path leakage) was the limit.
On April 13, 2003, at 1114 hours0.0129 days <br />0.309 hours <br />0.00184 weeks <br />4.23877e-4 months <br /> Unit 1 entered Mode 4 with an inoperable containment personnel air lock. This event is reportable in accordance with 10CFR50.73(a)(2)(i)(B) for a condition prohibited by TS.
2.0 SIGNIFICANT SAFETY CONSEQUENCES AND IMPLICATIONS No significant safety consequences resulted from this event since containment was operating under vacuum and no leakage escaped to the atmosphere. The total maximum leakage rate was calculated to be 42.319 scfh well below the acceptance criteria of lock door is: a) verified closed within one hour, b) locked within twenty four hours, and c) verified locked closed once every thirty one days.
Appendix J to 10 CFR 50, Primary Reactor Containment Leakage Testing for Water Cooled Power Reactors, does not delineate specific acceptance criteria limits for containment air locks but rather containment leakage as a whole. The design limit of FACILITY NAME (1) � DOCKET � LER NUMBER 16) � PAGE (3) NORTH ANNA POWER STATION UNIT 1 � 05000 - 338 2003 —002 — allowable containment leakage during an accident is called La based on 0.1 percent of containment volume leakage per day. To allow margin for meeting the La limit, a fraction of that limit, measured leakage must be integrity.
Since containment penetrations have double barriers, leakage is tracked in three categories: a) As Left Maximum Path Leakage, b) As Left Minimum Path Leakage, and c) As Found Minimum Path Leakage. Maximum path leakage is the larger leak rate of two valves in series and minimum path leakage is the smaller leak rate of two valves in series.
Each of the three categories must be conditions such as start-up, refueling outages and operating. A running total is modified based on the measurement of new leakage sources and elimination of existing leaks by repair. The unit La is local leak rate including instrument error for the Unit 1 containment was:
As Left Maximum Path Leakage As Left Minimum Path Leakage As Found Minimum Path Leakage 42.319 scfh 19.023 scfh 17.406 scfh The calculated Total Maximum Path Leakage of 42.319 scfh is well below the acceptance criteria of 3.0 CAUSE The apparent cause is attributed to human en-or. The TS LCO 3.6.2 surveillance requirement delineates air lock leakage rate testing in accordance with the "Containment Leakage Rate Testing Program". The acceptance limits of the program are delineated in the TS Administrative Controls Section 5.5, Programs and Manuals. The requirements of TS were not properly verified resulting in an incorrect assumption that the containment personnel air lock leakage numbers specified in the periodic test procedure were administrative limits.
4.0 IMMEDIATE CORRECTIVE ACTION(S) Upon discovery of the condition prohibited by TS a station deviation report was initiated.
At the time of discovery Unit 1 had already been placed in Mode 5 as a result of reactor coolant leakage from the number 4 core exit thermocouple nozzle assembly.
5.0 ADDITIONAL CORRECTIVE ACTIONS Repairs were made to the containment personnel air lock inner door. Subsequent leakage rate testing was performed with satisfactory results.
U.S. NUCLEAR REGULATORY COMMISSION FACILITY NAME (1) NORTH ANNA POWER STATION UNIT 1 DOCKET L LER NUMBER 16) 1 NUMBER NUMBER 6.0 ACTIONS TO PREVENT RECURRENCE The periodic test procedures for containment personnel air lock leakage and total containment leakage testing are being revised to specifically reference TS Section 5.5 including a clarification that the limits for the containment personnel air lock are required by the TS and not an administrative limit.
7.0 SIMILAR EVENTS None 8.0 ADDITIONAL INFORMATION Unit 2 was not affected by this event. A review of Unit 2 containment personnel air lock leakage test results from the February 2003 start-up indicated 5.5 scfh.