ML20084G682

Torus Coating Insp on Dresden 2 Reactor, Rept 17

ML20084G682
Person / Time
Site:	Dresden
Issue date:	05/09/1972
From:	COMMONWEALTH EDISON CO.
To:
Shared Package
ML20084G655	List: ML20084G653 ML20084G657 ML20084G660 ML20084G666 ML20084G682 ML20084G724
References
NUDOCS 8304220215
Download: ML20084G682 (4)

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J REPORT NO. 17 TORUS COATING INSPECTION ON THE i

DRESDEN 2 REACTOR May 9, 1972 o

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I l Commonwealth Edison Company l .

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9 9 REPORT NO. 17

1. History During the spring 1971 Unit 2 refueling outngo, inspection of the Torus revenlad some pinpoint rusting, blistering and dolnninntion of the Phonoline 366 conting system above the water linn. The Torus wns then drained end sin 11ar - -

w arens of paint distress were rovenled in the undorwater portion. A detailed discussion of these preblems nnd the action tnken nre presented in "Supplomontal Infornntion to Specini Report F12 - Torus Point Prob 1cas - Unit ?2", trons-mitted in a letter from Fyron Lee, Jr. to T,r. Morris, dated May 21. 1971.

2. Status as found durinr, innpcetions in c'ebruary and March of 1 1972.

The continc system abovo normal water level was found to bo e in good condition. However, the costing below normal water  ;

lovel showed continued dotoriorntion. The general condition ~ 1.

was similar to that found in the previous outngo with some .l additionn1 pinpoint rusting, due to primer damogo fron shot biceting during the previoun repnirs.

3 Current Progrcm

1. It uns dncided to remove the presont conting system from the torus shell nnd ring girders below the normnl wnter line end replace it uith en inorgnnic zinc conting (Onrholino "nrbo Zinc "11). "'ho bnfr1ns will not be reconted but any dis-tressed top cont noterin1 will bo removed. A t the present stato of the nrt, we bellovo thnt the inorganic zine coating has a botter potential for troublo-free service. 'i'ho primary reasons nre:

a. Although the mnnufacturer has no long term ense histories in dominerr,112nd voter services, the coeting has pro-vided antinfnctory protnetion in sc1t wnter nnd fresh water immercion, for periods of nore thnn five years.

The postulcted service life in dontnarnlized unter is seven to cirht years.

b. Carbo "inc '11 is not a filn forming polymer such as nn epoxy resin. With this type conting it is physically impoesible for n fniluro such tha t the conting is romoved in shcots or plocca uhich mis.,ht block the ".CCS strainers. j Should Cnrbo Zinc "11 foil, it uill deconpoco into minIte perticles (micron sire) of the size of finely ground zinc.

In other words, should "crbo Zinc "11 foil, the pnrticle size of the fniled conting uould be no irrger than the rust pnrticles from the unconted stnol piping system.

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c. Should repairs become nocessnry, the system of one coat of Cnrbo Zinc fil would be the easiest protectivo coating system to repair during a normal outage of a nuclear power plant.

d. Should the addition of inhibitors or pu control be desired, they will be compatible with the Cnrbo Zinc

1. 11 system.

e. This conting is being utilized as the initial cooting system in severn1 pinnts presently under construction and is also beinC used to repair / replace previous coating systems at other Lnstallotions.

4 On Going Progran Two programs have boon initin ted to monitor tho performance of the conting:

a. A test sample program - 21 samples hrve been prepared to be as similar to the newly reconted torus shell as is possible. These will be placed in the torus and three will be renoved for evnlantion nnd testing ooch refueling outnge.

b. A torus wall thickness Monitoring program - thirty areas have been selected such thnt 25 are in areas of maximum coating deterferntion end 5 oro in areas

, of good conting performance. Those areas will be monitored from the outsid o ot' the torus, utilizing ultrasonic testing equipment. 0his will provido a surveillance technique for nonitoring coating loss of protection vnd subsequent corrosion of the tcrus ,

shell. '2hc system will detect a shell thickness reduction of epproxima tely 3 mils or greater. Base lino shell thickness readings woro modo at the thirty i

sample arons after removnl of the old conting system.

5. conclusions '

Although extensivo laboratory testing hns been dono in an effort to duplicato the inilure of the phonoline 368 coating systen, no conclusive results no to the ceuse of fn11ure have been ascertnined. Some npecimenn performed well and other failed es in the torus for no clonrly detectable reason. The fnilure phenomenn hns been further studied through chemical enclysis of failed conting specimons taken from the Unit 2 torus. The results of these snelysos were also inconclusive in identifying the fnilure mechanism.

o 3 O The phenolino 368 conting has proved satisfactory in the abovo water environment and will remain in pince for further ovnluntion.

Below water level the phonoline 366 conting system has been replaced with Carbo-2inc 911 as described above. The lack of success with the phenoline system below water end in identifying the failure mechonism was the motivation for changing to a completely different type of conting system.

The advantages of the Carbo-Zine 511 system selected are listed above.

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