05000454/LER-2005-005
| Docket Numbersequential Revmonth Day Year Year Month Day Yearnumber No. Byron Station 0500455 | |
| Event date: | 06-01-2005 |
|---|---|
| Report date: | 10-14-2005 |
| 4542005005R00 - NRC Website | |
Background
The Ultimate Heat Sink (UHS) at Byron Station is a common system to both units and consists of two mechanical draft cooling towers with a diverse Makeup system. Three non-safety related circulating water makeup pumps provide normal makeup to the towers. In addition, there are two safety related diesel driven makeup pumps (i.e., OA and OB Essential Service Water (SX)[BS] Makeup Pumps) and two deep well pumps [BS] with safety related power sources. The UHS is governed by Technical Specification (TS) 3.7.9, "Ultimate Heat Sink." Action Condition C of this TS provides the required actions to be taken when one SX Makeup Pump is inoperable and Action Condition D provide actions when two SX Makeup Pumps are inoperable. Both conditions allow seven days to restore the SX Makeup Pumps to operable status.
B. Description of Event:
On August 16, 2005, Operations personnel took a scheduled diesel fuel sample for the OA SX Makeup Pump.
Visual examination of the sample showed high water and sediment content. Based on the condition of the sample, at 1206 hours0.014 days <br />0.335 hours <br />0.00199 weeks <br />4.58883e-4 months <br />, the OA SX Makeup Pump was declared inoperable and TS 3.8.9 Action Condition C was entered. This was the first oil sample drawn since the diesel fuel oil tank had been cleaned and refilled on June 21, 2005. Furthermore, since the OB SX Diesel Fuel Oil Storage tank was cleaned and refilled on June 1, 2005, a similar condition was considered to potentially exist for the fuel oil of the OB SX Makeup Pump. A sample was taken and the OB SX Makeup Pump Diesel Oil Storage Tank sample showed similar results. The OB SX Makeup Pump was also declared inoperable at 1452 hours0.0168 days <br />0.403 hours <br />0.0024 weeks <br />5.52486e-4 months <br /> and TS 3.8.9 Action Condition D was entered.
Evaluation of the oil samples indicated the contamination was iron oxide particulate and an aqueous solution typical for cleaning diesel fuel storage tanks. This analysis indicated the June 2005 tank cleaning activities as the source of contamination for both fuel tanks.
Consequently, the OA SX Makeup Pump was cons dered inoperable since June 21, 2005 until August 16, 2005 (i.e., 56 days) and the OB SX Makeup Pump was considered inoperable since June 1, 2005 until August 16, 2005 (i.e., 77 days). This is in excess of the allowed 7 days of TS 3.7.9 and thus reportable to the NRC in accordance with 10 CFR 50.73 (a)(2)(i)(B) as a condition prohibited by TS. In addition, this is a condition where a single cause caused two independent trains in a single system to become inoperable and also reportable in accordance with 10 CFR 50.73 (a)(2)(vii).
FACILITY NAME (1) DOCKET NUMBER (2) LER NUMBER (6) PAGE (3) (If more space is required, use additional copies of NRC Form 366A)(17)
C. Cause of the Event
The root cause of this event was determined to be inadequate work instructions and post maintenance testing (PMT) for the tank cleaning activity. The work instructions contained insufficient scope and technical details to ensure tank cleanliness following the cleaning process. Iron oxide particles and aqueous cleaning agent solution remained in the tank when fuel oil was added. In addition, the PMT did not require an oil sample to be taken and analyzed.
A vendor who has successfully performed many tank cleaning activities in the past performed the tank cleaning work. However, a tank cleaning procedure did not exist nor were detailed work instructions provided. The Maintenance Planner believed the vendor, who specializes in tank cleaning, would have the expertise to perform the activity correctly. Consequently, detailed work instructions were not provided.
D. Safety Analysis
The SX Makeup Pump's fuel oil tanks are sized such that they would need refilling after three and half days of continuous running. An engineering evaluation concluded there is a high degree of confidence that both pumps would be fully capable of starting and operating for approximately three and one half days each without issue. The inoperability concern from a design basis standpoint is due to the inability to prove that during refilling of the SX Makeup Diesel Fuel Oil Tank turbulence would not cause sediment and/or water to mix into the suction line to the SX Makeup Pump engine. Since both SX Makeup Pump engines had successfully run for two monthly surveillances after the tank cleanings, it is reasonable to conclude that an SX Makeup pump engine would have run until it was refilled. The suction line to the SX M/U pump engine is approximately three inches off the bottom of the tank. Based on the review of the amount of contaminated oil removed from both storage tanks and the inspections performed on the day tanks and engine fuel filters, there is no concern that sediment or water migrated to the diesel engines or would have been capable of migrating to the engines until the point at which the tanks would need refilling (i.e. — three and one half days into the design basis accident).
The UHS design basis for Byron Station has a 30-day requirement for operability and the SX Makeup Pumps are credited as the source of water for the UHS. Therefore, since it cannot be demonstrated that either SX Makeup Pump would have been capable of operating for 30 days, the conclusion regarding inoperability was made. However, from a margin and risk standpoint, there is a negligible impact due to this historical condition.
The water inventory makeup requirements after three and one half days into the design basis accident are minimal. In addition, there are two trains of non-safety related deep well pumps that were always available during the time period in question. Even though the deep well pumps are considered non-safety related, they are seismically qualified and are capable of being powered from safety related power sources. They are also credited in the Byron licensing and design basis. This is not considered a loss of a safety function
E. Corrective Actions
As an immediate corrective action, the tanks were drained, cleaned, flushed, refilled with new fuel oil and sampled before returning to service.
The diesel engine fuel filters were replaced and the removed filters examined. The results showed no signs of sediment or water associated with the tank contamination.
FACILITY NAME (1) DOCKET NUMBER (2) LER NUMBER (6) PAGE (3) (If more space is required, use additional copies of NRC Form 366A)(17) Interim controls were established to ensure proper re-cleaning of the SX Makeup Pump fuel oil tanks and the cleaning of other fuel oil tanks. In addition, all tank cleaning PMTs will require an oil sample to be taken and analyzed. These controls will be developed into a permanent procedure.
A review of other vendor related activities will be conducted review of open contract releases and corresponding work instructions for vendor-supported activities planned to ensure adequate level of detail is provided for scope of work, work sequence, and work closeout criteria delineated in both the contract and associated work instructions.
F. Previous Occurrences
There have been no previous occurrences of this nature.