05000382/LER-2011-001
| Waterford 3 Steam Electric Station | |
| Event date: | 02-16-2011 |
|---|---|
| Report date: | 04-16-2011 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 3822011001R00 - NRC Website | |
REPORTABLE OCCURRENCE
This condition meets 10 CFR 50.73(a)(2)(i)(B) reporting criteria because Waterford 3 operated in a condition prohibited by the plant's Technical Specifications (TS). TS 3/4.11.2.5 requires that the concentration of oxygen in the waste gas holdup system [WEI shall be limited to less than or equal to 2 percent by volume at all times whenever the hydrogen concentration exceeds 4 percent by volume. TS 3/4.11.2.5 Action 'a' requires that in the event that oxygen concentration is greater than 2 percent by volume, but less than 4 percent by volume, oxygen concentration must be reduced to 2 percent or less within 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br />. Contrary to this requirement, Gas Decay Tank (GDT) C oxygen concentration exceeded the allowed concentration for a period exceeding 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br />.
INITIAL CONDITIONS/BACKGROUND
The Gaseous Waste Management System [WEI consists of a Gas Surge Tank (GST), two Waste Gas Compressors (WGC), three Gas Decay Tanks (GDT), and the associated piping and valves required to collect gaseous waste and allow for release through the plant stack.
At the time of the event, the plant was in Mode 1, operating at 100% power. There were no Technical Specifications (TS) LCO Actions in effect impacting the event. The following equipment conditions affected the event. Waste Gas Compressor A was out of service. Gas Decay Tanks A and B pressures were operating equalized due to leakage past each tank's nitrogen inlet valve, NG-230A and NG-230B ILKI respectively; this condition is being addressed in Condition Report CR-WF3-2008-00093.
EVENT DESCRIPTION
On 2/14/11, during a trend review of the gas decay tanks, it was discovered that GDTs A, B, and C pressures unexpectedly equalized on 2/6/11. As part of the investigation for the pressure equalization, GDT C was sampled by an automated Waste Gas Analyzer with results of 4.9 percent oxygen and 19.7 percent hydrogen and by the Gas Chromatogram with results of 4.49 percent oxygen and 22.47 percent hydrogen. Both indications were greater than the TS 3/4.11.2.5 requirements and Condition Report CR-WF3-2011-00854 was initiated to address this condition.
On 2/14/11, at 10:50 a.m., TS 3/4.11.2.5 Action `13' was entered because the oxygen concentration exceeded 4 percent in GDT C. TS 3/4.11.2.5 Action 'If states "with the concentration of oxygen in the WASTE GAS HOLDUP SYSTEM greater than 4 percent by volume and the hydrogen concentration greater than 4 percent by volume, immediately suspend all additions of waste gases to the system and immediately reduce the concentration of oxygen to less than or equal to 4 percent by volume and then take the ACTION in 'a' above.
To immediately lower GDT C oxygen concentration, the plant aligned nitrogen to the Gas Surge Tank and placed GDT C in service to receive the nitrogen. In a further effort to immediately lower GDT C oxygen concentration, the plant began adding nitrogen gas directly to G DT C using bypass features of the nitrogen system and returned WGC A to service.
On 2/14/11, at 4:10 p.m., GDT C oxygen concentration reached less than 4 percent oxygen, and the plant exited TS 3/4.11.2.5 Action 'b.'
ICI
EVENT DESCRIPTION (continued) Actions taken to restore compliance per TS 3/4.11.2.5 Action 'a' included adding nitrogen directly to GDT C by bypassing the in-line nitrogen system regulators, aligning nitrogen to the Gas Surge Tank, and placing GDT C in service to receive the nitrogen.
On 2/18/11, at 10:47 p.m., GDT C was confirmed to be concentration and TS 3/4.11.2.5 Action 'a' was exited.
CAUSAL FACTORS
An apparent cause evaluation determined that the equalization among the GDTs was most likely due to seat leakage past GDT A nitrogen inlet valve NG-230A and inadvertent opening of GDT C nitrogen inlet valve NG-230C. Opening this valve created an equalizing flow path with GDTs A and C. Regarding detection of the event from 2/6/11 through 2/14/11, the Waste Gas Analyzer Panel was not aligned to GDT C because the normal practice is to only monitor the in-service GDT.
GDT C was not in service during this time period.
The initiating cause of the event is attributed to seat leakage on NG-230A and seat leakage/opening on NG-230C. This seat leakage is a result of corrosion product deposition on valve seats from high velocity flow through ball valves. The high velocity gases transport corrosion particles to,the valve seats resulting in seat damage, both from initial impact at high velocity and subsequent operation of the valve with corrosion particles embedded in the seats. The corrosion particles are the result of moisture in the gaseous waste management system that causes corrosion of carbon steel components such as piping, valves, and tanks.
Exceeding the 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> allowed outage time for TS 3/4.11.2.5 Action 'a' was contributed to by various issues. First, maintaining nitrogen gas directly to the GDT C using bypass features of the nitrogen system was pressure constricted to ensure the nitrogen system relief valve did not lift. Second, there were delays in aligning nitrogen gas directly to the GDT C using bypass features of the nitrogen system and in placing GDT C into service to add nitrogen via the GST. Third, GDT C inlet isolation valve GWM-206C [WEI was unable to be opened, which delayed adding nitrogen to GDT C via the GST.
CORRECTIVE ACTIONS
Completed actions include:
GDT C inlet valve GWM-206C has been rebuilt. A human performance evaluation was completed and determined that ineffective communication contributed to the delay. Applicable department personnel discussed interdepartmental communications and the need to ask for clarity when instruction provided is determined to be lacking or conditions have changed Planned actions include:
GDTs A and C nitrogen inlet valves are scheduled to be reworked. Corrective actions have been assigned to investigate the need for additional changes to address equipment issues contributing to this event.
SAFETY SIGNIFICANCE
There were no safety consequences as a result of this event. TS 3/4.11.2.5, Radioactive Effluents, Explosive Gas Mixture is provided to ensure that the concentration of potentially explosive gas mixtures contained in the Waste Gas Holdup system is maintained below the flammability limits of hydrogen and oxygen. Hydrogen gas is flammable at a concentration of 4 percent to 75 percent in air. During this event, concentrations of 4.9 percent oxygen and 19.7 percent hydrogen were present in GDT C based upon monitoring performed on 2/14/11. It is suspected that an out of specification mixture of oxygen and hydrogen may have been present when GDT C and GDT A pressures were equalized on 2/6/11, but its value is unknown. GDT C was returned to 2 percent oxygen concentration with greater than 4 percent hydrogen at 10:47 p.m. on 2/18/11. During this event GDT C contained a gas mixture that was potentially hazardous both from an industrial safety and radiological safety perspective. If there had been a catastrophic release of all of the GDT's contents to the environment, the total off site dose would have been —5.7E-1 curies. This is significantly less than the TS 3/4.11.2.6 LCO limit of 8.5E+4 curies for a single GDT.
SIMILAR EVENTS
There have been no previous similar licensee events reported in the last three years.
ADDITIONAL INFORMATION
Energy industry identification system (EIIS) codes are identified in the text within brackets I I.