ML20070A518
| ML20070A518 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  |
| Issue date: | 01/17/1991 |
| From: | Wallace E TENNESSEE VALLEY AUTHORITY |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| TAC-76429, TAC-76430, NUDOCS 9101230150 | |
| Download: ML20070A518 (4) | |
Text
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,O TENNESSEE VALLEY AUTHORITY CH ATT ANOOG A, TENNESSEE 374o1 5B Lookout Place JAN 171991 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D.C.
20555 Gentlemen In the Matter of
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Docket Nos. 50-327 Tennessee Valley Authority
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50-328 SEQUOYAH NUCLEAR PLANT (SQN) - MINIMUM ACCEPTABLE TIME FOR CLEANING DIESEL GENERATOR (DG) FUEL-CIL STORAGE TANKS (TS 90-08) (TAC 76429/76430)
Reference NRC letter to TVA dated April 27, 1990, " Exigent Changes for Cleaning Diesel Generator Fuel-011 Storage Tanks (TAC 76429/76430)
(TS 90-08) - Sequoyah Nuclear Plant, Units 1 and 2" By the referenced letter, NRC approved TVA's exigent Technical Specification (TS) Change 90-08 to allow an additional 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> (144 hours0.00167 days <br />0.04 hours <br />2.380952e-4 weeks <br />5.4792e-5 months <br /> total) for performing TS Surveillance Requirement (SR) 4.8.1.1.2.F.1, 10-year DG fuel-oil
-storage tank cleaning.
Ir. the referenced letter, NRC also requested that TVA review the scope of work required for cleaning SQN's DG fuel-oil storage tanks to determine the " minimum acceptable time" needed to clean the tanks.
Upon completion of the tank cleaning on August 2, 1990. TVA conducted an evaluation of the cleaning process in' order to ascertain the minimum acceptable time needed to clean the tanks, lacluding other possible methods of cleaning the tanks. Enclosed are a complete description of the cleaning process and the results of TVA's evaluation of this process.
Lased on the results of TVA's evaluation, it is recommended that the existing TS allowable time of 144 hours0.00167 days <br />0.04 hours <br />2.380952e-4 weeks <br />5.4792e-5 months <br /> not be reduced.
Please direct questions concerning this issue to t'. A. Cooper at (615) 843-PA22.
Very truly yours.
TENNESSEE VALLEY AUTHORITY k
, JtM tt E.G.blallac Mana r Nuclear Licensing and Regulatory Affairs Enclosure cc:
See page 2 9101230150 910117 ADOCK0500gg7 An Equel opportunity Employer DR Ie
, U.S. Nuclear Regulatory Commission JAN 17 F391 cc (Enclosure):
Ms. S. C. Black, Deputy Director Project Directorate 11-4 U.S. Nuclear Regulatory Commission One White Flint, North 11555 Rockville Pike Rockville. Maryland 20852 Mr. J. N. Donohew Project Manager U.S. Nuclear Regulatory Commission One White Flint, North i
11555 Rockville Pike Rockville, Maryland 20852 NRC Resident Inspector Sequoyah Nuclear Plant 2600 Igou Ferry Road Soddy Daisy. Tennessee 37379 Mt. B. A. Wilson, Project Chief U.S. Nuclear Regulatory Commission Region II 101 Marietta Street. NW. Suite 2900 Atlanta. Georgia 30323-w
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l l-ENC 1,0SURE i
i A train of diesel generators (DGs) at Sequoyah Nuclear Plant (SQN) consists of two DG sets with each set having four underground fuel-oil storage tanks.
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Storage tank cleaning is completed on a single DG set while the remaining set j
(f rom the af fected DG train) provides (through tenporary industrial hoses) the i
fuel supply for both DG sets of the affected train.
The utilization of temporary hoses allows both DG sets of the affected train to remain functional j
throughout the tank cleaning process.
Only two of four tanks associated with a DG set are cleaned simultaneously.
This is becauce of limited workspace, i
personnel safety while working in a confined space, and tank design limitations for draining from one tank to the next.
Before the cleaning i
process, all necessary equipment is prestaged at the jobsite and personnel are
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briefed as to their responsibility and expected start time. New tuel is available and contingency plans are in place to minimize cleaning time.
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Following the c1 caning process for two tanks, the tanks are isolated using temporary bladders and allowed to dry while tank cleaning continues on the remaining two tr.nks. Attempting to clean four tanks simultaneously in an i
i elfort to reduce cleaning duration is not feasible because of reasons l
described above.
l The first stage of c1 caning involves connection of temporary industrial hose j
to the fuel-oil pump suction and overflow lines.
Hoses are then primed and l
flow verification tests run to ensure that no leaks exist and that required DG j
fuel consumption rates can be achieved.
I The second stage involves removal of the existing fuel-oil. The existing i
fuel-oil transfer system is utilized to pump most of the fuel-oil to one of the two yard storage tanks. The remaining fuel (approximately 2,000 gallons) j is then pumped (using temporary pumps) to a waste oi* tanker or $5-gation drums.
Following fuel-oil removal, tank cleaning is begun. The tanks are flushed using the existing fire protection system.
Any accuolated water is l
removed using temporary pumps. Cleaning is accomplished using steam, followed by repeated flushes. The tanks are then dried using air movers.
Following a TVA quality control inspection, each tank is hand wiped with a sodium i
hypochlorite solution.
Tank manvey covers are then placed back in position.
Following the completion of tank cleaning and restoration, the tanks are i
i111ed with new fuel-oil using the permanent fuel-oil transfer system.
The third stage involves removal of temporary hoses, restoration of permanent i
pump suction and overflow lines, and completion of DG operability surveillance requirements.
y The shortest completion time for the recently performed cleaning sequence was i
i 65.5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br />. The longest completion time required 90.5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br />.
(It should be noted that the longest completion time was associated with the first set of tanks, and the shortest completion time was associated with the last set of tanks.)
The first and last stages of the cleaning process involve hook-up/ disconnect of tempcrary industrial hoses to allow the DG set being cleaned to remain functional. This process encompasses approximately 15 percent of the total clening duration. Although this process could be deleted to reduce total l
duration, maintaining the DG functional throu6 out the cleaning evaluation is h
considered to be of greater value in the interest of maximizing overall se(e operation of the SQN units. As previously stated, duration of the first
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a
.se -
l cleaning sequence was 90.5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br />, and the duration of the last cleaning sequence was 65.5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br />.
Based on the long interval between cleaning (approximately 10 years), the difference in durations between first and last sequence, as well as the duration itself, would not be expected to change
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significantly for future cleanings.
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TVA's TS Change 90-08 request described a cleaning duration of 100 hours0.00116 days <br />0.0278 hours <br />1.653439e-4 weeks <br />3.805e-5 months <br /> with an additional 44 hours5.092593e-4 days <br />0.0122 hours <br />7.275132e-5 weeks <br />1.6742e-5 months <br /> for contingency allowances to resolve any equipment i
problems and unforeseen problems while working in severe environmental conditions, and to correct minor problems that might be found inside the tanks. During the recen cleaning process, no unforeseen contingencies were encountered.
Permanent and temporary equipment functioned properly and backup equipment was readily available. No tank repairs were required and no material procurement problems were encountered.
TVA considers the 44-hour timeframe to be an appropriate contingency for future tank cleanings where unforeseen problems may be encountered.
a In conclusion. TVA reconnends that the existing TS allowable time of 144 hours0.00167 days <br />0.04 hours <br />2.380952e-4 weeks <br />5.4792e-5 months <br /> not be reduced.
Experience indicates that this time is appropriate for j
allowing well-planned cemoletion of the cleaning process with reasonable
-J contingency for unforeseen problems.
TVA's conclusions are based on the t
followings j
1.
The 10-year interval for the cleaning requirement limits the probability that SQN's DGs would be required for accident mitigation during the cleaning process.
2.
The affected train of DGs renatn functional during the cleaning process.
3.
The unaffected train of DGs is maintained operable during the cleaning process.
4.
The extensive contingency measures taken provide good assurance that the DGs would be able to perform the required function Pi the event of demand-during_the tank cleaning process.
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