05000333/LER-2009-001
| Docket Numbersequential Revmonth Day Year Year Month Day Yearnumber No. N/A 05000 | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 3332009001R00 - NRC Website | |
BACKGROUND
The Emergency Onsite Power Supply System [EIIS=EK] consists of two (2) redundant Emergency Diesel Generator (EDG) [EIIS=DG] subsystems along with 4160 V switchgear and interconnecting cabling. Each EDG subsystem consists of two (2) 2600kW EDG(s), associated piping, valves, instrumentation and controls. Each EDG is provided with an independent Fuel Oil Storage and Transfer System [EIIS=DE] consisting of a Diesel Fuel Oil Storage Tank (FOST) [EIIS=TK], a Diesel Fuel Oil Day Tank (FODT) [EIIS=TK] and two full-capacity motor-driven Fuel Oil Transfer Pumps [EllS=13]. The Fuel Oil Transfer Pumps provide the capability to transfer fuel from the FOST to the FODT.
Each EDG FOST has a storage capacity of 36,000 gallons. Each FODT has a storage capacity of 545 gallons.
Within each EDG subsystem's fuel oil transfer system, a cross-tie pathway, consisting of two normally closed manual valves, enables transfer of fuel from either FOST to either or both associated FODT(s).
FSAR Section 8.6.2.9 states, "The Fuel Oil System for each of the emergency AC power sources has the capacity to supply fuel to its respective emergency AC power source to operate it continuously at full load for seven days.
FSAR.Section 8.6.7 states, "The two diesel units comprising each emergency AC power source are capable of starting and operating continuously under postulated accident conditions for a period of seven days, using fuel stored in underground fuel storage tanks.
TS Bases 3.8.3 states, Each storage tank has a fuel oil capacity sufficient to operate one EDG for a period of 7 days while the EDG is supplying full load." TS Surveillance Requirement (SR) 3.8.3.1 requires verification every 31 days that the FOST contain at least 32,000 gallons of fuel oil when the EDG subsystem is required to be operable.
TS SR 3.8.3.3 requires verification that new and stored fuel are within the limits established in the Diesel Fuel Oil Testing Program. TS SR 3.8.3.3 Bases states, "Verify in accordance with the tests specified in ASTM D975-2006 (Ref. 6) that the sample has an absolute specific gravity at 60/60° F of greater than or equal to 0.83 and less than or equal to 0.89 or an API Gravity at 60°F of greater than or equal to 27° and less than or equal to 39° ...
The original analysis, by the licensee for the initial license and Technical Specifications, established the minimum seven (7) day fuel oil supply based on the manufacturer's fuel oil consumption data provided in the vendor manual„ which was stated as "approximately 3 gpm". At a consumption rate of 3 gpm the EDG would consume 30,240 gallons during 7 days of continuous operation. A Technical Specification limit of 32,000 gallons was considered to be sufficiently conservative to ensure 7 days of continuous operation. In 1990, in ,response to NRC Information Notice 89-50 "Inadequate Emergency Diesel Generator Fuel Supply", JAF performed EDG Fuel Oil Consumption Testing and determined that the actual fuel oil consumption rate was 3.08 gpm. Based on this consumption rate, it was calculated that actual consumption over a 7 day period would be 31,046.4 gallons. Again the Technical Specification limit of 32,000 gallons was considered to be sufficiently conservative to bound the calculated consumption.
In November 2006, calculation JAF-CALC-06-00114 was performed to analyze the potential affect of lower sulfur content in Ultra Low Sulfur Diesel (ULSD) Fuel Oil on fuel oil consumption rate. Since the only paiameter in the fuel oil specification that was changing was sulfur content the calculation only addressed the potential impact of the change in sulfur on fuel oil heat content. In May 2007, while revising the calculation to address an error in the application of the calculation methodology, it was determined that implementation of the methodology required assessing all of the specification parameters at their worst allolkable value. It was determined that the heat content of the fuel was significantly affected by the API Gravity and, based on the requirement in the calculation methodology to consider the worst case fuel oil properties, the current Low Sulfur Diesel (LSD) Fuel Oil might require greater than 32,000 gallons of fuel for a 7 day supply at API Gravities greater than 36 degrees. A condition report was written, initial operability was confirmed, and fuel oil level in the underground tanks was raised to greater than the new calculated minimum value. An analysis to determine if there was a past operability concern was performed.
In July 2007, while the past operability analysis was being conducted, additional conservatisms that had not been addressed in either the original analysis or subsequent engineering calculation, JAF-CALC-06-00114, were identified. These conservatisms included the tank geometry, operation at the upper end of the allowable frequency range, and the potential for vortexing in the FOST. When these additional conservatisms were added to the calculation it was determined that the TS required volume of 32,000 gallons was inadequate to support 7 days of continuous operation under full load conditions. It was further determined that there were several occasions during the period between July 2004 and July 2007 when the volume in the FOST was below the calculated 7 day volume for a time period longer than allowed by the TS. The past operability determination incorrectly allowed consideration of the FODT volume in determining if the EDG System could have performed its safety function.
EVENT DESCRIPTION
In May 2007, the engineering staff was revising calculation JAF-CALC-06-00114 Rev. 1 to address an error in the application of the calculation methodology. During the revision of the calculation it was determined that the TS minimum FOST inventory requirement of 32,000 gallons was not sufficiently conservative to ensure that an EDG will operate at full load for seven (7) days when using fuel oil with API gravity greater than 36 degrees. TS SR 3.8.3.3 Bases establishes the allowable API gravity for diesel fuel oil as ranging from 27 to 39 degrees. Neither the analysis, based on fuel oil consumption rate, nor engineering calculation JAF-CALC-06-00114 Rev. 1, dated March 27, 2007, considered the lower volumetric heat content at the upper end of the allowable API gravity range and its affect on EDG fuel oil consumption rate.
In July 2007, it was identified that calculation JAF-CALC-06-00114 Rev. 1 did not include conservatisms addressing operation of the EDG at the upper end of the allowable frequency band, tank geometry, and potential vortexing in the FOST. Engineering concluded that with these conservatisms, the calculated 7 day FOST volume requirement was greater than the current TS requirement of 32,000 gallons. At that time the available fuel inventories were below the new calculated FOST 7 day minimum inventory requirement but above the TS 6 day minimum inventory requirement. Additional fuel oil was added to the tanks and volume was raised to greater than the new calculated 7 day minimum within the TS LCO Completion Time. Review has determined that on several occasions between July 2004 and July 2007 the volume in the FOST was below the new calculated 7 day volume for a period of time greater than allowed by the Technical Specifications.
CAUSE OF EVENT
The apparent cause of the condition was an original analysis based on fuel oil consumption data that did not address fuel oil properties and design conditions that could affect the fuel oil consumption rate and the useable volume of the FOST and, a narrow focus when addressing a change in fuel oil properties.
The analysis based on fuel oil consumption testing did not address affects of varying fuel oil parameters and assumed that the current TS 7 day minimum inventory requirement of 32,000 gallons provided adequate margin for any unspecified conservatisms.
When calculation JAF-CALC-06-00114 was initiated to address a change in fuel oil sulfur content it was assumed that the existing analysis was sufficiently conservative and, that since the specifications for other parameters were unchanged they didn't have to be addressed in the calculation. Because these assumptions were not validated the cause of the condition is identified as inadequate work practices. The result was a non-conservative calculation.
When taken in aggregate the conservatisms that were not addressed in the original analysis and calculation JAF-CALC-06-00114 (worst case fuel oil parameters, operation at the upper end of the allowable frequency range, tank geometry, and potential vortexing in the FOST) resulted in a non-conservative Technical Specification 7 day minimum FOST volume.
EXTENT OF CONDITION
The narrow focus used in identifying the design inputs to calculation JAF-CALC-06-00114 was limited to this calculation. A review of quality related engineering products developed within the prior 6 months by the calculation preparer and the design verifier associated with calculation JAF-CALC-06-00114 concluded that the design inputs used were appropriate and correct, and that reviews were performed by personnel appropriately independent from the preparers of the documents.
FAILED COMPONENT IDENTIFICATION
There were no component failures as a result of this deficiency.
CORRECTIVE ACTIONS
Immediate Corrective Actions
1. Revised the engineering change documentation associated with calculation JAF-CALC-06-00114 justifying the use of ULSD fuel oil.
2. Developed administrative controls establishing new FOST inventory requirements consistent with the new calculated 7 day minimum requirement.
Completed Corrective Actions
1.Performed independent verification of the sampling of safety related products provided by the preparer and design verifier during the prior six (6) months of discovery.
2. Performed a Human Performance Evaluation and provided coaching to engineering personnel on the relevant "Human Performance Trap?, "Worker / Supervision Management Tools" and "Process / Programmatic / Organization Issues".
3. Developed a case study to be reviewed during continuing training sessions that highlights the principles and expectations for thoroughness in reviewing engineering work products.
4. Submitted a TS amendment revising the 7 day and 6 day FOST volume.
ASSESSMENT OF SAFETY CONSEQUENCES
The condition involves the determination that there were several occasions between July 2004 and July 2007 in which the available fuel inventory of a FOST was not sufficient to ensure continuous operation of the associated EDG for seven (7) days under full load conditions. The deficiency was caused by a failure to include appropriate conservatisms in both the original analysis of fuel oil inventory requirements and the subsequent calculation establishing the acceptability of ULSD fuel oil. The reduction in available EDG run time from the FOST did not impact plant risk and the safety significance of this deficiency is considered low. At the time of discovery, the FOST(s) inventories were less than the 7 day minimum but greater than the 6 day minimum (a condition allowed by the plant Technical Specifications), and were restored to greater than the 7 day minimum within the time allowed by the Technical Specifications. Administrative controls were established to maintain FOST volume greater than the new calculated 7 day minimum requirement. During the three (3) years preceding the discovery, (July 2004 thru July 2007), the combined inventories of Fuel Oil Storage Tanks and their associated Fuel Oil Day Tanks were sufficient to ensure seven (7) days of continuous EDG operation. Therefore, the EDG systems were available to perform their required safety function and there was no reduction in the margin of safety as a result of this condition.
SIMILAR EVENTS
There are no similar reportable conditions which have occurred at the JAF site within the preceding three (3) years.
REFERENCES
None