05000498/FIN-2007007-08
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Finding | |
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| Title | Combined Adverse Conditions Not Considered in Fuel Oil Storage Tank Sizing |
| Description | The team identified an unresolved item involving accounting for the combined effect of vortexing and standby diesel generator frequency variations in fuel oil storage tank sizing. Calculation MC-6256, Sizing of Standby Diesel Generator Fuel Oil Storage Tank, Revision 4, determined a total 7-day fuel oil requirement of 51,500 gallons, comparing this value with a technical specification requirement of 60,500 gallons. However, this calculation did not consider the effects of vortexing or generator frequency variations. Condition Record 97-14434-10 included an evaluation of fuel oil vortexing completed as part of a Review of Safety Related Tanks (other than Refueling Water Storage Tank & Auxiliary Feedwater Storage Tank) for Vortexing Concerns. Separately, Calculation EC-5100, Standby Generator Transient Response Model, Revision 2, contained an evaluation performed under Condition Record 97-13089-1 in order to Perform Evaluation of Electrical Frequency Variations on Mechanical Fluid Systems. The vortexing evaluation determined that 13.5 inches of fuel oil volume would be susceptible to excessive air entrainment, representing 4120 gallons of unusable fuel oil with a 7-day fuel oil requirement of 55,360 gallons (referencing Calculation MC-6038, Standby Diesel Generator Fuel Oil Storage Tank Level Setting Calculation. The total required volume would therefore be 59,480 gallons. The frequency effects evaluation determined that Standby Diesel Generator load would increase by roughly 6% because the majority of load consists of pumps and fans with primarily friction system loads. The evaluation then compared this 6 percent increase in load with the standby diesel generator fuel oil storage tank calculated margin of more than 10 percent. However, the vortexing evaluation had already effectively reduced the majority of the analyzed margin with a remaining 1020 gallons of fuel oil between 59,480 gallons and the technical specification requirement of 60,500 gallons. Therefore, applying a 6 percent increase in standby diesel generator load in addition to considering vortexing effects would have exceeded the technical specification requirement under those analyzed conditions. In addition, the most recent fuel oil storage tank sizing calculation determined a 7 day fuel oil requirement of 51,500 gallons. As discussed in the finding Manual Loads not Considered for Fuel Oil Storage Tank Sizing Calculation, this requirement neglected manual loads during the 7 days for which provision would be made to use during a design basis event. A bounding analysis considering the actual anticipated manual loads, in addition to the vortexing reduction and increased load frequency effect, exceeds the minimum technical specification requirement. The fuel oil storage tank sizing calculation included additional conservative assumptions regarding expected pump operation during design basis accident scenarios. For example, the calculation assumed auxiliary feedwater, high-head safety injection, and containment spray pumps would be run continuously for 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> following a large break loss-of-coolant accident. The licensee recalculated the fuel oil storage tank sizing using more realistic assumptions with respect to load profile and determined sufficient fuel oil margin does exist with all design basis conditions considered. This issue was entered into the licensees corrective action program as Condition Request 07-14398 and 07-15592. After further discussions with staff from the NRC Office of Nuclear Reactor Regulation, the team concluded that this issue of failure to account for the combined effect of vortexing and standby diesel generator frequency variation in the fuel oil storage tank sizing would remain open as an unresolved item. Additional NRC staff review was necessary to determine whether the issue was acceptable, whether it was a finding, or whether it constituted a deviation or violation. Pending completion of this review, this item is unresolved: URI 05000498; 499/2007007-08, Combined Adverse Conditions not Considered in Fuel Oil Storage Tank Sizing. |
| Site: | South Texas  |
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| Report | IR 05000498/2007007 Section 4OA5 |
| Date counted | Mar 31, 2008 (2008Q1) |
| Type: | URI: |
| cornerstone | No Cornerstone |
| Identified by: | NRC identified |
| Inspection Procedure: | |
| Inspectors (proximate) | H Anderson B Henderson S Rutenkroger W Sifre R Bywater J Chiloyan M Chambers G Apger S Makorb Tharakanw Walker A Fairbanks J Kramer S Hedger C Denissen L Micewski J Dixon G Guerra P Elkmann |
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Finding - South Texas - IR 05000498/2007007 | |||||||||||||||||||||||||||||||||||||||||
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Finding List (South Texas) @ 2008Q1
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