ML20236A852
| ML20236A852 | |
| Person / Time | |
|---|---|
| Site: | Vogtle  |
| Issue date: | 10/15/1987 |
| From: | NRC |
| To: | |
| Shared Package | |
| ML20236A838 | List: |
| References | |
| IEC-77-15, NUDOCS 8710230180 | |
| Download: ML20236A852 (6) | |
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, SAFETY EVALUATION RELATED TO THE ZINC C0ATING 0F DIESEL FUEL OIL STORAGE TANKS V0GTLE ELECTRIC GENERATING PLANT, UNITS 1 AND 2 DOCKET NOS. 50-424 AND 50-425 INTRODUCTION License Condition 2.C(8) was included in the Vogtle Unit 1 full-power license (Facility Operating License NPF-68), dated March 16, 1987 because of staff concern that the reaction products of the acidic impurities in diesel fuel oil with the zinc inorganic coating of the storage tanks might cause plugging of lines and fuel injectors in diesel generators. The license condition states:
" Prior to restart following the first refueling, GPC shall (1) replace the zinc coating in the diesel generator fuel oil storage tanks with a coating which does not contain zinc or (2) by March 1, 1988 provide an acceptable justification to the staff that the present fuel oil storage tank zinc-based coating will not affect the operability and reliability of the diesel generators over the life of the plant as specified in IE Circular 77-15."
Also, Technical Specification Surveillance Requirement 4.8.1.1.2f requires sampling and analysis of new fuel oil and oil in the storage tanks to verify that the neutralization number is less than 0.2 and the mercaptan content is less than 0.01%.
By letters dated July 13, September 30, and Ocotber 15, 1987, the licensee coating oninformation provided justifying the continued use of the inorganic zinc the fuel tanks.
This information included the following items:
(1) The inorganic zinc coating substantially extends the life of steel storage tanks rate. by delaying the onset of corrosion and by reducing the corrosion The lowered corrosion rate results in less particulate contamination in the fuel oil.
(2) The staff concern arose in part because of the discussion in IE Circular No.Cooper the 77-15 of a clogged strainer in the fuel line to the diesel generator at Station.
The circular states that fuel oils are degraded by contact with metal such as zinc, which "has a tendency to form soluble soaps in the fuel oil which are deposited on the diesel engine's injector nozzles.
performance." A buildup of this deposit will eventually degrade the engine's The circular also states that "[t]he presence of water in the fuel oil promotes the growth of fungi or slime that also degrades the fuel and has the potential for clogging filters."
The licensee's letter of July 13, 1987 noted that the Cooper St~ation event could not have been caused by zinc because the steel Cooper tanks are not coated internally. According to the licensee, the diesel engine manufacturer makes no recommendations regarding the use of zinc coatings on storage tanks; it only specifies the use of No. 2 diesel fuel oil. The inorganic zinc coating manufacturer has stated that.the " coating can be used with diesel fuel as long as the neutralization number is no greater than 0.4 and 8710230100 871015 DR ADOCK 0500 4
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. the mercaptan content is no greater than 0.01%." Analyses by the licensee 1 of ten samples of fuel oil .in Vogtle Unit 1 storage tanks A and B ranged
.j from 0.06 to 0.10 for the neutralization number, with an average of 0.08. '
The average mercaptan content in ten samples was 0.0005%,
No water was visible in thirteen of fifteen fuel oil samples. Only a trace of water was visually detectable in the remaining two samples. The Technical Specifications require sampling of the fuel oil.in the storage tanks 'at.least once every 31 days to verify that the particulate contam-ination is less than 10 mg/ liter.
(3) Duplex fuel oil filters are installed in the fuel lire with provisions to measure the differential pressure across the filter in use. A high ,
differential pressure would be annunciated in the control room, and an I operator would switch from one filter element to the other, j
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(4) Diesel generator " pop" tests are perfomed on the fuel injectors every 18 I months to check the spray pattern from the fuel injectors. As part of i this test, all injectors are disassembled, cleaned, and inspected. Any l damaged or worn parts are replaced. .The inspection procedure will include i provisions for the analysis of any significant deposits of zinc.
(5) In accordance with the Technical Specifications, water is checked for and removed from the storage tank sumps at least once every 31 days. ,
I EVALUATION j The staff has reviewed the information provided in the licensee's letter of July 13, 1987, and found it to be consistent with information from other !
industry and literature sources. Protective coating experts consulted by the staff agree that the preferred coating to protect against the corrosion of steel storage tanks by fuel oil is inorganic zine without a top coat. The j staff's research has not uncovered any problems of plugging of diesel generator l fuel injectors, i
- Filter Clogging by Insolubles: With regard to the staff's original concern about clogging lines and filters with corrosion products or metallic soaps, i the licensee's provision of a duplex- filter with control room annunciation of
- excessive differential pressure across the filter element in operation is adequate to protect against a line clogging incident of the type that occurred at the Cooper Station. The Technical Specification requirements to monitor and control the neutralization number and concentrations of particulate, mercaptans, and water in fuel oil provide assurance that the rate of accumu-lation of filter-clogging corrosion products or oil degradation. products will be slow.
1 Fuel aboutInjector soluble Plugging zine soaps By(Soluble principally Zinc zine Compounds:
naphthenate)',With regard to the concern the chemical literature indicates that they have beneficial effects as combustion improvers and fungicides (Kirk-Othmer Encyclopedia of Chemical Technology, Third Edition, Vol. 15, pp. 7.49-752; Vol. 8, pp. 44-48, John Wiley and Sons, NY, 1978).
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.To provide a quantitative basis .for considering the problem of soluble zinc !
napthenates, .the staff-requested that the. licensee take samples of the fuel oil in the storage tanks and have them analyzed for soluble zinc. By letter dated September 30,:1987, the licensee reported the following results:
Date Tank A
Zinc (pom) 7.2
)
T/27/87- i 8/22/87 .B 6.6 .j 9/11/87 A 7.2 9/11/87 B 5.6 1 1 There are no specific ' standards for allowable limits on zine concentration j Lin fuel oil. The American Society for Testing and. Materials. (ASTM) .speci- J fication for allowable' total concentration of inorganic constituents in j No. 2 diesel' fuel is 10 ppm. -'The'licenseets; letter of September '30,1987 i stated that the total inorganic material', including the zinc, in the fuel j oil. tested was less than 10: ppm. l 1
References to the use.of. napthenates asL" combustion improvers " which . reduce i the concentrations of soot, smoke, and incompletely burned fuel', indicate that concentrations of metallic napthenatesi(usually mixtures) in the range of 5 to 40 ppm are effective (R. D.'Giammer et al., "The effect~of additives in reducing particulate emmissions from residual' oil combustion"i American Society of Mechanical Engineers rpapers),'1975: pp. 75-86; Japanese Patent 74 42, 886, i H. Ogawa, November 18, 1974; K. 1. Ivanov et al., "Effect of metal-containing I additives on the concentration of sulfur trioxide in products of the combustion I of liquid sulfur-containing fuels", Teoloenergetika,1973: pp. 85-87). Higher I concentrations of up to 1300 ppm are used for high sulfur fuels (0.9%). -
Unfortunately, these studies.do not provide any specific information on the o long-term plating or deposition behavior of these additives on injector nozzles.
It is likely however that more complete combustion with less soot and smoke would correspond to a lesser tendency toward deposition and plugging. In a conference telephone call on October 6, 1987, the lic'ensee stated that an inspection of the injection nozzles after several hundred hours'of diesel operation detected no signs of deposition or-plugging of the nozzles.
Fromthemeasuredneutralizationnumbers,theequivaientcoIdentrationof zinc, disso)ved as zinc naphthenate, can be. calculated. For'a neutralization number of 0.08, the corresponding dissolved zinc concentration would be _
approximately 47 ppm. The. fact that the zinc concentration in the fuel oil after storage in the Vogtle Unit 1 zinc-lined tanks for!approximately two years is only 6 to 7 ppm indicates either a very' slow reaction or a self-limiting one. It-may be that naphthenic acids react at appreciable rates only with oxidized zinc compounds such as Zn0'and Zn(OH), but not with zinc metal. l Another possibility is that the outer silicate layers.of the; coating protect ;
the zine in the inner coating layers'from contact with naphtheni.c. acids. t In sumarizing the considerations about dissolved zinc naphthenate, no evidence has been'found that dissolved concentrations.of 6 to 7 ppm zine would tend to deposit on~and plug diesel generator fuel injsetors. To the contrary, some literature studies indicate that these concentrations'of zinc naphthenate would act as combustion improvers with more complete combustion and >1ess e
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formation of soot and smoke. The Technical Specification limits placed on the allowable concentrations of acidic constituents and water in fuel oil serve to lessen the likelihood of the buildup of excessive concentrations of dissolved zinc. The ASTM standard of less than 10 ppm total inorganic material in No. 2 diesel fuel oil reflects industrial experience that this level of inorganic content is acceptable. In view of the high solubility of zinc naphthenate in fuel oil and its special property of improving combustion, the ASTM limit of l 10 ppm inorganic material may be unduly conservative in the case of zine naphthenate. On the basis of the new information on dissolved zinc available since the issuance of IE Circular No. 77-15, the staff concludes that the ;
current levels of dissolved zinc in the diesel fuel storage tanks are acceptable. l Corrosion: With regard to the effects of inorganic zinc coating on the corrosion of the steel storage tanks, the staff agrees with the analysis j provided by the licensee. In industrial practice, inorganic zine protective coatings are widely accepted as the most satisfactory way to provide long-term ]
protection of underground steel tanks against corrosive attack by the acidic l constituents of fuel oil. The Technical Specification limits on the allowable i concentrations of acidic constituents and of water prevent the accumulation of ;
high concentrations of these corrosion-enhancing materials in the fuel oil.
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The corrosion product zinc naphthenate is itself a corrosion inhibitor. It also has fungicidal activity and thus helps to control microbiological corrosion in any water phase which may collect in the storage tank sumps. These anti-corrosion activities are further advantages deriving from the presence of the inorganic zine tank lining.
CONCLUSION The staff has concluded, based on the considerations discussed above, that the ,
licensee has provided an acceptable justification that the inorganic zinc ,
coating on the fuel oil storage tanks will not adversely affect the operability and reliability of the diesel generators over the life of the plant. These considerations include: .
l new infonnation on industrial experience with fuel oil tanks I coated with inorganic zinc and on the combustion-improving l properties of zinc naphthenate, the addition of duplex fuel line filters to remove corrosion products or degradation products which could plug the fuel 1 line, and J surveillance procedures to check the quality of the fuel oil, to monitor the differential pressure across the fuel line !
filter, and to inspect the diesel generator fuel injectors !
for zinc deposits.
Accordingly, License Condition 2.C(8) to Operating License NPF-68,is considered resolved. This evaluation also applies to Vogtle Unit 2.
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To assure ~ that the fuel oil storage anCdelivery systems- remains operable bnd ;
reliable, the~ Technical Specifications related to fuel all qdility, including.
the limits' on neutralization- number and mercaptan ~ conteht', should remain in
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< -1 effect." In addition, the ' licensee should continue to monitod. the differential
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pressure across;the filter element in the fuel .line as stated in~its July 13,
.1987 letter.' .The proposed Vogtle Unit 2 Technical Specifications.,shcald- _
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'. i- include the s'ame Specificaticas rtgarding fuel oil quality, and Untt, 2 should- 1 also monitor. the differential pressure across the fuel line filter, . 3. .)
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- . Mr. J. P.-0'Reilly .
Georgia' Power Company Vogtle Electric Generating Plant i 1
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Mr. L'. T. Gucwa Resident Inspector '
. Chief Nuclear Engineer Nuclear Regulatory Conunission !
Georgia Power. Company P. O. Box 572 P.O. Box 14545 Waynesboro, Georgia 30830
' Atlanta, Georgia 30302-Mr. Ruble A. Thomas . Deppish Kirkland, III, Counsel j Vice President - Licensing _ Office.of the Consumers' Utility j Vogtie Project Council-GeorgiaLPower Company / Suite 225 Southern Company Services, Inc. 32 Peachtree Street, N.W.
P.O. Box 2625 Atlanta, Georgia 30303 i Binningham, Alabama 35202 James E. Joiner Mr. Paul D. Rice Troutman, Sanders, Lockerman, !
Vice President & Project General Manager & Ashmore i Georgia Power Company '
Candler Building Post Office Box 299A, Route 2 127 Peachtree Street, N.E.
Waynesboro, Georgia 30830 Atlanta, Georgia 30303 i
Danny Feig ;
Mr. J. A. Bailey 1130 Alta Avenue l Project Lic.ensing Manager Atlanta, Georgia. 30307 l Southern Company Services, Inc.
P.O. Box 2625 Carol Stangler Birmingham, Alabama. 35202 Georgians Against Nuclear. Energy 425 Euclid Terrace Ernest L. Blake, Jr. Atlanta,. Georgia 30307 Bruce W. Churchill, Esq.
Shaw, Pittman, Potts and Trowbridge
. 2300 N Street, N. W.
Washington, D. C. 20037 Mr. G. Bockhold, Jr.
Vogtle Plant Manager Georgia Power Company Route 2, Box 299-A Waynesboro, Georgia 30830 Regional Administrator, Region II U.S. Nuclear Regulatory Commission 101 Marietta Street, N.W., Suite 2900 Atlanta, Georgia 30323 Mr. R. E..Conway
. Senior Vice President and Project Director .
Georgia Power Company Rt. 2, P. O. Box 299A Waynesboro, Georgia 30830