RFQUL . RY INFORMATION DISTRIBUTI, SYSTEM (RIDS)

ACCESSION NBRFAC IL: 50-275

AUTH. NAMFSISK. D. P.SHIFFERi J. D.

RECIP. NAME

8811010322 DOC. DATE: 88/10/27 NOTARIZED: NO . DOCKET 4Diablo Canyon Nuclear Power Planti Unit ii Pacific Ga 05000275

AUTHOR AFF 1LIATIONPacific Gas LD~ Electric Co.Paci f i'c Gas L4~ Electric Co.

RECIPIENT AFFILIATION

SUBJECT: LER 88-009-00: on 880720i two of eight steam generator manwagsdiscovered leaking 4 five manwags showed indications ofseepage. Caused bg Flexite Super gaskets experiencingcomprehensive creep. Gaskets replaced. Ij/881027 ltr.

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This report is being voluntarily submitted for information purposes only, as

described in item 19 of Supplement Number 1, to NUREG-1022.

Following a cooldown to Mode 5 after 12 months of operation at normal operatingtemperatures, two of eight steam generator manways were discovered to be

leaking'nd

five others showed indications of seepage. Investigation has revealed that theinception of leakage was during or after the cooldown following the manual reactortrip of July 17, 1988.

Subsequent discussion with the gasket manufacturer (Flexitallic) has disclosed thatthe gaskets being used, "Flexite Super" gaskets, experience compressive creep and

loss of resiliency due to changes in the filler material when exposed to hightemperatures (greater than 400 degrees Fahrenheit) for extended periods of time.

Examination of the "Flexite Super" gaskets showed a greater amount of permanentdeformation than the asbestos-filled gaskets called for in the initial design ofthe manways. This permanent deformation resulted in a loss of manway stud preloadand in leakage when the manway cooled. The "Flexite Super" manway gaskets have

been replaced with asbestos-filled gaskets in all four Unit 2 steam generators.

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Unit 2 was in Hode 5 (Cold Shutdown) and Unit,l was in Hode 1 at approximately50 percent power during this event.

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A. Event:

This report is being voluntarily submitted for information purposes onlyas described in item 19 of Supplement Number 1 to NUREG-1022.

On July 20, 1988, during a mechanical maintenance pre-outage leak-checkwalkdown inside the Unit 2 containment, a puddle (approximately 10 feetin diameter) of water was observed on the 91 foot level inside thebioshield area. The source of the water was traced to the bottom of theinsulation on steam generator (AB)(SG) 2-2.

On July 22, 1988, further investigation of the leak discovered on July 20disclosed the formation of crystals in the puddle and the flow path fromSG 2-2, indicating borated water. Close examination determined the leak-to be coming from the area of the two SG 2-2 primary manways (AB)(PEN).Removal of the insulation from the manways confirmed the source of theleakage. The-insulation was promptly removed from the other SGs, but noother indication of SG primary manway leakage was found.

On July 23, 1988, a formal investigation team was formed to develop anaction plan and determine the cause of the occurrence. Boric acidsamples were removed for chemical and radiochemical analysis. The vendorwas contacted for a history of similar occurrences and recommendationsfor corrective actions. Examination of the available data indicated thatthe leak had started during or after the cooldown following theJuly 17, 1988 transients. Observations supporting this determination areas follows:

1. No boric acid crystallization was observed when the leakage wasfirst discovered on July 20, 1988.

2. Chemical and radiochemical analysis of the samples showed thecrystals to be nearly identical in radioisotopes with that ofsamples from the RCS, therefore the crystals were fresh (less than aweek out of the RCS).

.3. The boric acid crystals found were soft. The presence of the hotdry ambient conditions indicated that the boric acid crystals hadformed recently.

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4. The unit had be'en at elevated temperatures from July 4, 1987, toJuly 18, 1988. Hestinghouse stated that due to differentcoefficients of expansion of the materials in the manway closure',the potential'or leakage is greater at low temperatures.

5. The leakage pattern around the two leaking manways showed a slowdownward liquid flow pattern. Had the leak been present when theunit was at an elevated temperature and pressure, a steam spraypattern would have been expected. In addition, the presence ofboric acid "snow" woul.d have been expected.

6. Containment activity levels since the last refueling showed nosignificant trends or step increases in activity.

On July 29, 1988, a followup examination of SGs 2-1, 2-3, and 2-4 manwaysidentified leakage on five of the six manways. This leakage had occurredafter the initial examination conduced on July 22, 1988. .

On July 30, 1988, all Unit 2 SG manway covers were removed andinspected. "Flexi te -Super" gaskets were replaced with asbestos-filledFlexitallic gaskets.

B. Inoperable structures, components, or systems that contributed to theevent:

None

C. Dates and approximate times for ma)or occurrences:

l. July 17, 1988, at 0717 PDT: A manual reactor trip was initiatedas reported in LER 2-88-008-00. Unitcooled down to Hode 4 (Hot Shutdown)-.

2. July 18, 1988, at 1313 PDT:

3. July 20, 1988, at 0130 PDT:

Unit 2 entered Hode 5 (Cold Shutdown)using natural circulation cooldown.

A puddle of water was observed duringa mechnical maintenance pre-outageleak-check walkdown inside the Unit 2containment.

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4. July 22, 1988: - During inspection to locate the leak source,crystallization was observed.

5. July 23, 1988: Boric acid crystal samples were removed from thevicinity of the SG 2-2 manways for chemical andradiochemical analysis.

6. July 29, 1988:

7. July 30, 1988:

Reinspection of SG manways on the other three SGs

revealed indication of leakage on five of the sixSG manways.

Initiated removal and inspection of all Unit 2 SG

manway covers. Replaced "Flexite Super" gasketswith asbestos-filled Flexitallic gaskets.

D.

8. August 11, 1988: Unit 2 entered Mode 1 (Power Operation). Hoindication of SG manway leakage.

Other systems or secondary functions affected:

None

E. Method of Discovery:

On July 20, 1988, during a mechanical maintenance pre-outage leak-checkwalkdown inside the Unit 2 containment, a pudd'le (approximately 10 feetin diameter) of water was observed on the 91 foot level inside thebioshield area. The source of the water was traced to the bottom of theinsulation on SG 2-2. On July 22, 1988, during an inspection to locatethe source of the leak, crysta11ization was observed. Furtherobservation determined the leak to be from the area of the SG 2-2 primarymanways. Removal of the insulation from the manway covers confirmed anapproximately 'two drop per second leak. The insulation was then removedfrom the other three Unit 2 SGs. Visual inspection of the manways on theother three SGs showed no evidence of leakage.

F. Operator actions:

None

G. Safety system responses:

None

A. Imnediate cause:

Examination of the gasket showed the "Flexite Super" gaskets to haveexperienced a greater amount of permanent deformation than the

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asbestos-filled flexftallfc gaskets called for fn the initial design ofthe manways. This permanent deformation caused a reduction fn manway

stud preload and resulted in leakage when the manway cooled.

B. Root Cause:

PG&E conducted an extensive investigation of the potential causes of thisevent using a multfdfscfplfnary Event'nvestigation Team.

Following a cooldown to Hode 5 after 12 months of operation at normaloperating temperatures, two of ei'ght steam generator manways werediscovered to be leaking and five others showed indications of seepage.Investigation has revealed that the inception of leakage was during or .

after the cooldown. Hestinghouse, the NSSS vendor, has indicated that,-due to the construction of the manway closure, leakage fs more likely tooccur fn a cooled condition than a hot condition. Subsequent discussionwith the gasket manufacturer (Flexftallfc) has disclosed that the gasketsbeing used, Flexitallic "Flexite Super" gaskets, experience compressivecreep and loss of resf lfency 'due to changes in the filler material

when'xposedto high temperatures (greater than 400 degrees Fahrenheit) for., extended periods of time. The Flexi tallfc UFlexi te* Super" manway gaskets

have been replaced wi th asbestos-filled gaskets fn all four Unit 2 steamgenerators.

The Event Investigation Team evaluated potential root causes as follows:

Material degradation

Examination of studs, gaskets, and the flange face failed to provideany indication of failure or degradation of these components.

However, examination of the gasket showed the "Flexite Super"gaskets to have experienced a greater amount of permanentdeformation than the asbestos-filled Flexftallic gaskets called forfn the initial design of the manways. This permanent deformationcaused a reduction in manway stud preload and resulted fn leakagewhen the manway cooled. Discussions with the gasket manufacturer,(F'lexitallfc) has disclosed that the gaskets being used, Flexftallfc"Flexite Super" gaskets, experience compressive creep and loss ofresiliency due to changes in the filler material when exposed tohigh temperatures (greater than 400 degrees Fahrenheit) for extendedperiods of time. The Flexftallfc "Flexite Super" gaskets have beenreplaced with asbestos-ff lied gaskets.

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Design

Investigation has shown that the initial design of the manway was

adequate. However, a design change was made to replace theoriginally designed asbestos-filled Flexitallic gasket with a new"superior .performing" replacement gasket, Flexite Super, alsomanufactured by Flexitallic. It has been the practice of the plantto purchase such gaskets as comnercial grade, and to applyappropriate dedication activities (in this case, verification ofreceipt of the purchased gasket, and verification of no leakage).

At the present time, Flexitallic Company has not been qualified as a

safety-related vendor under the PGIEE QA program; however,Flexi tallic has stated that they have been supplying gaskets toother utilities under their QA programs;

Flexitallic representatives had full knowledge and concurred withthe decision to install the "Flexite Super" gasket in the manwayclosures. However, their recent experience over the past year ortwo has'ed them to conclude that this type of gasket is unsuitablefor use in this type of closure, although it is an acceptablesubstitute for less flexible closures such as pipe flanges.

Moreover, the substitution of this gasket was not discussed with theNSSS vendor before the fact. The vendor manway installationprocedure was written specifically for using asbestos-filledgaskets. Westinghouse has stated that they would not now concur inthe installation of such replacement gaskets in the SG manways.

Installation

A review of the installation procedure and the as found conditiondid not indicate any problems with instal'latlon that could havecontributed to this event.

5. Maintenance

Preventive maintenance is not performed on the SG manways; however,this fact is not considered to be a contributor to this event.

Testing

This event was not caused by a missed, incomplete, or inadequatetesting.

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7. End of Life

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No component involved in this event deteriorates with age and thereare no moving parts to wear out. The compressive creep experiencedby the gasket is not considered normal wear.

8. Inappropriate Equipment Operation

The Event Investigation Team did not find any evidence of improperoperation of equipment. All temperature and pressure cycles werewithin Hestinghouse provided limits., Although a power-operatedrelief valve did lift during'he pressure transient on July 17, thisrelief lifts at 2335 psig which is well below the RCS safety i,imitpressure of 2735 psig.

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Y.

RCS leakage and containment activity are constantly monitored. This leak was

discovered before being significant enough to contribute to RCS leakage or. containment activity level. Hestinghouse has stated that heating up the

manway increases the stud loading, thus the most likely time for a leak wouldbe during or at the end of a plant cooldown.

Had the leak developed at full power, containment activity monitors would havedetected the leak and applicable procedures would have been followed prior tothe leak increasing sufficiently to affect the reactor coolant system. If theradiation monitors had failed to detect the increased activity, and the leakhad increased in volume from the maximum of two drops per second at the timeof discovery, the reactor coolant inventory monitoring system would havedetected the leak and the plant operators would have followed the applicableprocedure to place the unit in a safe shutdown condition. Thus, the healthand safety of the public were not affected by this event.

rr iv

A. The "Flexite Super" gaskets in all four Unit 2 SGs have been replacedwith asbestos-filled Flexitallic gaskets.

B. Other "Flexite Super" gaskets being used in systems heated over 400degrees were located and evaluated. All other "Flexite Super" gasketlocations were determined to be acceptable.

C. The SG manways in Unit 1 will be inspected during the next outage ofsufficient duration. A visual inspection of the Unit 1 SGs performed inJuly, 1988, did not show any sign of leakage.

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D. The SG manway gaskets 1n Unit 1 w)11 be replaced dur)ng the nextrefuel )ng outage.

VI. 1 1

A. Failed Components:

B.

Fl ex'all 3 c gasket:Manufacture:Part Number:Descr1pt1on:

Flexfte SuperFlex1tal11c Gasket Company390-A029-H01Gasket, Primary Manway Super Flex 2500

ps'rev1ous

LERs on s1m> lar events:

None

2338S/0064K4+C TO+M S49a19SJI

Pacific Gas and ElectricTompany 77 Beale Street

San Francisco, CA 94106

4f5I972.7000TAX 910.372 6587

James D. Shiffer

Vice PresidentNuclear Power Generation

October 27, 1988

PGhE Letter No. DCL-88-256.

U.S. Nuclear Regulatory CommissionAttn: Document Control DeskHashington, D.C. 20555

Re: Docket No. 50-275, OL-DPR-80Docket No. 50-323, OL-DPR-82Diablo Canyon Units 1 and 2Licensee Event Report 2-88-009-00 -(Voluntary)Steam Generator Hanway Leak Following Cooldown Due .To Use of-

'askets That Experienced Compressive Creep And Loss ofRes i 1 i ency

Gentlemen:

PGhE is submitting the enclosed voluntary Licensee Event Report (LER)regarding steam generator manway leaks that occurred during or after aunit cooldown. This report is being submitted for i nformation purposesonly, as described in item 19 of Supplement Number 1 to NUREG-1022.

This event has in no way affected the pub'lic's health and safety'.

Kindly acknowledge receipt of this material on the enclosed copy ofthis'etter and return it in the enclosed addressed envelope.

Sincerely,

f/. D. Sh'fer

cc: 3. B. HartinH. M. HendoncaP. P. NarbutB. NortonH. RoodB. H, VoglerCPUCDiablo *DistributionINPO

Enclosure

DC2-88-EH-N083

2338S/0064K/DY/2167

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