05000416/LER-2015-002
| Grand Gulf Nuclear Station, Unit 1 | |
| Event date: | 10-01-2015 |
|---|---|
| Report date: | 11-30-2015 |
| Initial Reporting | |
| 4162015002R00 - NRC Website | |
At the time of the event, Grand Gulf Nuclear Station (GGNS) Unit 1 was operating in MODE 1 at 100 percent rated core thermal power. There were no systems, structures, or components that were inoperable at the start of the event that contributed to the event.
B. Description of Event
On October 1, 2015, Standby Gas Treatment System (SGTS)[BH] B failed Technical Specification (TS) Surveillance Requirement (SR) 3.6.4.1.3. This surveillance procedure requires the SGTS B train to drawdown Secondary Containment [NG] to >t= 0.311 inches of vacuum water gauge at 180 seconds and maintain that pressure with the SGTS B Filter Train flow rate not exceeding 4000 cfm for the duration of the surveillance (1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br />). The configuration being tested involved opening inner doors to test the boundary created by the outer doors. Standby Gas Treatment System B was able to drawdown Secondary Containment to >/= 0.311 inches of vacuum water gauge in 60.6 seconds, steady state. The vacuum reading at 180 seconds, during the short term transient period of testing when fans and dampers were modulating, was 0.25 inches of vacuum water gauge. The rest of the steady state test readings were greater than 0.41 inches of vacuum water gauge with the average surveillance reading being 0.43 inches of vacuum water gauge. The filter train flow was at 3850 cfm for the length of the surveillance Secondary Containment boundary was immediately returned to a previously known operable configuration to maintain Secondary Containment integrity after the configuration tested during the October 1, 2015 surveillance failed. Troubleshooting performed by Maintenance between October 1, 2015 and October 5, 2015 identified and documented there was inleakage through four Secondary Containment isolation doors. After three of the door seals were replaced, TS SR 3.6.4.1.3 was performed for the configuration being tested, which previously failed, and passed with satisfactory results.
C. Extent of Condition In the past 3 years, it was documented in three separate condition reports the drawdown surveillance testing failed to meet the requirements of TS SR 3.6.4.1.3. These events are also being reported under this Licensee Event Report (LER). The following events were not reported prior to this LER because they were not previously identified as a loss of safety function. The conditions are as follows:
1. June 17, 2014: During SGTS B drawdown testing, the required vacuum criteria at 180 seconds after initiation was not met as required by the surveillance (all other vacuum readings were satisfactory). The cause was determined to be inleakage through the 166' Elevation Railbay Floor Plugs. Railbay floor plugs were repaired and the retest was performed with satisfactory results.
2. October 31, 2014: During SGTS A drawdown testing, the required vacuum criteria at 180 seconds after initiation was not met as required by the surveillance (all other vacuum readings were satisfactory).
The cause was determined to be inleakage through a Railbay Door. The Railbay door was repaired and the retest was performed with satisfactory results.
3. August 2, 2015: During SGTS A drawdown testing, the first 10 minute interval of data taken did not pass the >1= 0.311 inches of vacuum water gauge criteria as required by the surveillance (all other vacuum readings were satisfactory). The cause was determined to be inleakage though two door seals.
Both door seals were repaired and the retest was performed with satisfactory results.
During these tests, the drawdown testing requirements of TS SR 3.6.4.1.3 were not met for the configuration being tested, rendering Secondary Containment inoperable during the testing. Immediately after the failed tests, the system was placed in a previously known operable configuration and the identified inleakage was corrected. All retests performed after inleakage corrections for the configuration being tested, which previously failed, were passed with satisfactory results.
D. Event Cause The cumulative inleakage through four secondary containment door seals was the cause of the reduced vacuum in the Enclosure Building.
E. Corrective Actions
To correct for the inleakage through the secondary containment doors during the surveillance testing, three of the leaking door seals were replaced. Upon replacement of the door seal, the surveillance was performed with satisfactory results.
F. Safety Significance
F.1 Nuclear Safety There were no actual nuclear safety consequences related to this event.
F.2 Radiological Safety There was no radiological consequence during this event.
The potential for a radiological consequence occurred on October 1, 2015 between 0324 hours0.00375 days <br />0.09 hours <br />5.357143e-4 weeks <br />1.23282e-4 months <br /> and 0440 hours0.00509 days <br />0.122 hours <br />7.275132e-4 weeks <br />1.6742e-4 months <br />, approximately 116 minutes. There was no abnormal release during this time; therefore, no radiological consequences occurred.
F.3 Industrial Safety This event did not have any actual or potential impacts on industrial safety.
G. Basis of Reportability This LER is being submitted pursuant to Title 10 Code of Federal Regulations (10 CFR) 50.73(a)(2)(v)(C) for an event or condition that could have prevented the fulfillment of the safety function of structures or systems that are needed to: (C) control the release of radioactive material. Telephonic notification was made to the U.S Nuclear Regulatory Commission (NRC) Emergency Notification System (ENS) on October 7, 2015, pursuant to 10 CFR 50.72(b)(3)(v)(C).