NRC-89-0191, Provides Staff W/Results of Inps & Repairs of Primary Containment/Torus Coatings During First Refueling Outage. Suppression Chamber Air Space Will Be Inerted During Plant Operation

Provides Staff W/Results of Inps & Repairs of Primary Containment/Torus Coatings During First Refueling Outage. Suppression Chamber Air Space Will Be Inerted During Plant Operation

ML19324B639
Person / Time
Site:	Fermi
Issue date:	10/31/1989
From:	Sylvia B DETROIT EDISON CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
CON-NRC-89-0191, CON-NRC-89-191 NUDOCS 8911070237
Download: ML19324B639 (4)

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'E4 October 31, 1989 NIC-89-0191 U. S. !bclea ' Degulatory Ccanission Attn Document Control Desk l

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'."eferences: 1) Fermi 2 NIC Docket No. 50-341 NIC License No. t@F-43 2)' Detroit Fdison Letter to NIC, " Coatings Inside 4

Contal.' ment," EF2-72778, dated August 28, 1984.

3) Detroit Fdison Letter to NIC,'" Primary Containment Coatings Evaluation - Transmittal of Additional g g Information," 2F2-72271, dated October 11, 1984.

4). Detroit Edison Letter to NIC, " Responses to Six Moltional NIC Staff Questions," EF2-72045, datcd January 10, 1985.

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5) Detroit Fdison Letter to NIC, " Primary Containment Coatings, Mditional Inforaation," NE-85-0048, dated January 24,~1985.

6) Detroit Fdison Letter to NIC, " Primary Containnent Coatings Transmittal of Final Report No.

DICo-12-2191, Pevision 4, ' Evaluation of Containment Coatings'", VP-85-0140, dated June 28, 1985.-

Subject:

Results of Inspectionn and Repairs of Primary CJntalDnent/ Torus Cont 1ngs Durina First Refuellno Outagg.

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. Poferencen 2 - 6 provided the NIC staff with various correspondence on y

. Detroit E31 son Conpany's (DICo's) ovaluation of containment coatings at Fermi 2.

The purpose of this letter is to provide the NBC staff with the results of inspections and rcpairs of these coatings for your i-

'information as ccxnmitted in the reference correspondence.

-. n. c During the current (first) refuelirg outage,100% of the interior anS exterior of' the Torus was inspected.

I.: general, the Torus and 1

' related structures were found to be in good condition. Although sone y(

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UStHC li October 31, 1989 15C-89-0191 Pagc 2 earface ruct was found as described belcv, there wre no neasurable pits or corrosion found on the Torus shell. Minor touchup of the coatings was empleted on the exterior of the Torus.

For the interior Torus work, S. G. Pjnney and Associates, Inc., was contrtetcd by DICo to corduct underwater inspection, desludging ard coating repair. This work and the results consJsted of the following:

o All instrunentation and associated wires installed for the Safety g

Relief Valve. (SRV) blow-down tests were rtsnoved ard relatEd areaD recoated. No neasurable pittingcorrosion was fwnd.

o Minor nochanical damage to the coatirs was fourd ar.3 rcpaired.

o Small blisters, characterized as #4 to 66 medium-dense blisters as rated on the AS'IM scale (i.e.,1/32" to 1/4"), were fourd on the suppression chenber imnersion phase protective coating system.. They are locatcd between 4:00 and 8:00 o' clock on the bottom invert of the Tonic shell.

There was no evidence of spontanecosly ruptured blisters, i.e.,

the blisters are intact and exhibit film cohesive strength.

Selectcd areas of the blisteral coating were rcstovcd, inspectcd and recoated. During the inspections, no corrosion / pitting was found under the blistero.

The cordition of the blistered area was further evaluatcd by nuclear engineering and the coating consultants. A review of the DECO records indicates that the Plasite 7155 coating materials originally used were mixed and applied in accordance with the manufacturer's instructions ard DECO's specificaticn, including a force-heat cure of the original coating following 4pplication.

liowever, due to subsequettt Mark I containnont nodification work, repairs of the original coating were required for sone areas.

3 Per the manufcoturer, it was sufficient to only air dry the repair coating. 'Ihus, forced heat curing of the repcir caating was not requircd. The root cause of the blistering was solvent en'taoment. This occurs when the coatings are not force-heat curcd. This phonmenon is coranon with epoxy enanels used in iratersion service. if post-curing is not utilized to " bake out" any residual solvents in the coating film. The epoxy enanels are a densely cross-linked polyner film and, as such, it is difficult for the coating solvents to escape after application. The blisters are estimated to have developed within the first year after coating application.

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MC-89-0191 Page.3 l

Based on the inspections of the Torus shell surface where the

blisters were removed, active corrosion is not expected to occur under the rmaining intact blistered coating. In Mdition, the Fermi-2 containnent is kept inerted with nitrogen gas during plant operation. This further redaces the potential for corrosion of the Torus shell. These opoxy enamels have been usM E

successfully in supproccion pool service for.many years at various other stations. Blistering of the coating has also been discovered at other stations and has been shown to have no p

negative inpact on safe operation. Specifically, DECO's evaluations have concluded that the blisters found at Fermi 2 will not affect corrosion of the suppression chanber nor will they come off and plug Emergency Core Cooling Systs strainers during a Design Basis Accident cr normal plant operation.

To monitor the blister areas, photogr@hs of selected arem were taken.- These areas will be inspected during subsequent refueling outages, new photos will be taken and conpared with the original photos to detecteny changes in the blistering. These inspections will be documentcd. An engineering evaluation will then be made to tecept the coatings for continued operation or make rcpairs, as appropriate.

o Inspection of the coatings in the vapor phase area of the Torus L

chcll were conpleted and repairs performad as needed. Some areas were not rcpaired due to ina:cessibility and/or based on evaluations which did not justify the need for repairs as follows:

The surface of the vacuum breaker flanges are slightly corroded. This light rusted surface will have no inpact on the operability of the vacuum breakers.-

Minor mechanical damage to the coating surface of the vent hooder and down-convrers was not repaired. The corrosion in the damaged areas is very light with no L

apparent pitting. Leaving these areas uncoatcd will have no inpact on vent system operability.

The eight vent header deflectors were not coatcd. These steel deflectors are approxinately 1-1/2" thick and provide no structural requirment. Deflectors will rust approxinat'ely 1 mil per year. If painting would have been needed, blasting of these surfaces would have been required. During this tin' the def3ectors were partially subnerged in the 'ater. It was not feasible to pa' int them during this refueling outage since the

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blasting would have presented a potential airborne

'>1 contaminants concern and may have required' cleanup of

[. 3 the ruppression pool water.

The surpression chanber air space will be. inerted during plant F.

Z operation. Therefore, any additional corrosion.to the above 6P areas is expected to be minimal. DBCo will inspect and reair as needed those areas not repaired, as noted above, at the Second c.

Refueling Outage.

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If you should have any questions regarding this information, please l

1t contact Terry L. Riley, Supervisor of Coupliance and Special Projects, Nuclear Licensing, at (313) 586-4041' (or x-1684).

His TRajr i-Sincerely.

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R. C. Knop W..G.' Rogers J..F. Stang t

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