05000423/LER-2002-001
| Event date: | 01-25-2002 |
|---|---|
| Report date: | 03-14-2002 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(v), Loss of Safety Function |
| 4232002001R00 - NRC Website | |
I. Event Description
On January 25, 2002, with reactor power at 100 percent, it was identified that the ventilation system flow measurements obtained to satisfy the monthly Technical Specification surveillance requirement for the Control Room Emergency Ventilation System (CREVS) [VI] had been corrected twice for the density effects of local pressure. The current surveillance data for both trains, adjusted to remove the extra pressure correction, was verified to be within the required range. However, a review of historical surveillance data identified several cases where the recorded Train A surveillance data, adjusted to remove the extra pressure correction, resulted in recorded system flows outside the required range. As a result, Train A of the CREVS was left in an inoperable, but available condition after the completion of the historical surveillance tests. The time Train A was in this condition exceeded the 7 day allowed outage time.
The CREVS consists of two redundant trains both of which are required to be operable in all Modes by Technical Specification 3.7.7, Control Room Emergency Ventilation System. Restoration of an inoperable ventilation train when the plant is operating in Modes 1 through 4 is required within 7 days, or a plant shutdown to Mode 3 is required within the next 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />, and Mode 5 the following 30 hours3.472222e-4 days <br />0.00833 hours <br />4.960317e-5 weeks <br />1.1415e-5 months <br />.
Since the Train A CREVS was inoperable due to historical surveillance data outside the acceptance criteria for time periods approximately equal to the monthly surveillance interval, which is greater than the allowed outage time (7 days) plus shut down time to Mode 3 (6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />), this condition is reportable in accordance with 10 CFR 50.73(a)(2)(i)(B), Operation or Condition Prohibited by Technical Specifications.
The same procedural error existed on Train B CREVS. Any historical surveillance data outside the acceptance criteria for Train B would have resulted in an inoperable, but available ventilation train.
II. Cause of Event
The procedure used to perform the surveillance tests was not correctly revised in 1992 when new test equipment was purchased. The cause of this condition is attributed to weak interdisciplinary review requirements for procedure changes during that time period. The current procedure change process contains rigorous interdisciplinary review requirements, and it has been evaluated to ensure it contains the necessary controls to properly account for test equipment changes.
III. Analysis of Event
The CREVS will mitigate the consequences of an accident by protecting the control room operators approximately one hour after the event. Protection for the control room operators immediately following an event is provided by the Control Room Envelope Pressurization System. Mitigating the consequences of an accident is one of the four safety functions of structures and systems listed by 10 CFR 50.72(b)(3)(v) and 10 CFR 50.73(a)(2)(v), Event or Condition That Could Have Prevented Fulfillment of a Safety Function. During the time period that Train A of the CREVS was inoperable, no work was done that would have affected system flow rate. Train A was only inoperable due to the ventilation flow calculation error, Train A would have been capable of performing its accident mitigation function, as demonstrated by subsequent monthly testing which produced acceptable flow rates. This event did not result in the loss of any safety function, and is of low safety significance.
IV. Corrective Action Procedure changes have been completed to remove the pressure correction factor when this test instrument is used.
Other surveillance procedures were reviewed for proper usage of test equipment and no additional issues were identified.
U.S. NUCLEAR REGULATORY COMMISSION NRC FORM 366A (7-2001) FACILITY NAME (1) DOCKET (2) LER NUMBER 6) I PAGE (3) Millstone Nuclear Power Station - Unit 3 05000423 YEAR SEQUENTIAL REVISION
V. Previous Occurrences
No previous similar events/conditions were identified.
Energy Industry Identification System (EIIS) codes are identified in the text as [XX].