ML20086Q406
| ML20086Q406 | |
| Person / Time | |
|---|---|
| Site: | Peach Bottom  |
| Issue date: | 07/19/1973 |
| From: | Boyer V PECO ENERGY CO., (FORMERLY PHILADELPHIA ELECTRIC |
| To: | Knuth D US ATOMIC ENERGY COMMISSION (AEC) |
| Shared Package | |
| ML20086Q397 | List: |
| References | |
| SDR-6, NUDOCS 8402270537 | |
| Download: ML20086Q406 (5) | |
Text
{{#Wiki_filter:.. . 9 9 PHILADELPHIA ELECTRIC COMPANY 2301 MARKET STREET PHILADELPHI A. PA.19101 V.S.BOYER vica rnssioant July 19, 1973 x Dr. D.F. Knuth, Director Directorate of Regulatory Operations United States Atomic Energy Commission Washington, D.C. 20545
Subject:
Significant Deficiency Report - Blistering of Coating on Unit #2 Torus Peach Bottom Atomic Power Station - Units 2 and 3 AEC Construction Permit Nos. CPPR-37 and CFPRe-38 File: QUAL 2-10-2 SDR No. 6 Dear Dr. Knuth In compliance with 100FR50 55, paragraph (e) attached is the Significant Deficiency Report concerning subject Blistering of Coating on Unit No. 2 Torus. This item was reported to AEC DRO I by telecon on June 8,1973 We trust that this satisfactorily resolves this item. If further information is required, please do not hesitate to contact us. We appreciate yc,ur extending the time for our response to July 23, 1973 as agreed by telecon of July 9, 1973 between our Mr. H. B. Winitsky and Mr. J. Allentuck, USAEC DRO I. Sincerely, ff./1 y% Attachment Copy to: J. P. O'Reilly, USAEC V
\ p h 8402270537 790813 gDRADOCK 05000277 D PDR 3 0670
- '. ATTACHMENT 1
- Significant Deficiency Report - SDR No. 6 Torus Coating Failure in Unit No. 2
; Peach Bottom Atomic Power Station - Units 2 and 3 AEC Construction Permit Nos. CPPR-37 and CPPR-38 i
INTRODUCTION AND BACKGROUND The Torus is located below and encircles the Drywell (see attached sketch) with a centerline diameter of approximately 111 feet and a cross-
; sectional diameter of 31 feet.
To provide protection against corrosion, the internal surfaces of the structural steel plates for the Torus were shop coated with inorganic zine over a pickled steel surface preparation. l During 1969 and 1970 a phenolic finish coat was. applied over all . interior surfaces of the #2 Torus. The decision to apply a top coat i over inorganic zine stemmed from a concern within the industry of hydrogen evolution from inorganic zine exposed to deionized water and steam atmos-phere. It was subsequently determined by independent testin contribution of hydrogen would be minimal (about 0.28 vol.).%gHowever, that the all hydrogen content will be kept below the lower explosive limit of 4% j via the Containment Atmospheric Dilution System. The selection of a phenolic topcoat was based on test results of various combinations of coating systems for the Peach Bottom Design Basis Accident Criteria. In March, 1971, during a routine inspection of the #2 Torus, failure of the phenolic coating was found below the waterline. On February 10,
- 1972 it was decided to repair the Torus interior coating.as follows
1 4 1. Below water line: Cand blast to white metal and apply inorganic zine (one coat) only. I
- 2. Water line level: Sand blast to white metal in 2 ft. band
! and apply one coat of inorganic zine and one top coat of phenolic.
4 3 Vapor Zone (above water line): Repair defective areas only. The rationale for retention of the top coating in the vapor zone was that the condition of coating was essentially good. Coating adhesion tests performed during the re-coating investigation substantiated this rationale. At the present time the Torus is costed with one coat of inorganic zine in the immersion zone with a-two foot wide phenolic band at the water line and the original coating system in the vapor zone. On May 31, 1973 after the Torus underwent a relatively severe dynamic ,, steam test (demineralized water heated to 1800F, held at this temperature for
~
i approximately 48 hours or more and then subjected to a " fast" cool down) , ~ blister formation was observed in the vapor zone area of the Torus. 1 PB-SDR-6
.-. . .-, . .. .. , .. ., . - . ~ . . - - --
~
O O 1 l DESCRIPTION OF DEFICIENCY A thorough inspection revealed that the phenolic finish coat blistered in localized areas. The blistering or delamination occurred at the phenolic 1 waterline band and in 16calized areas in the vapor zone as large as six feet in diameter, but mainly in smller areas of concentrated blisters no more than approximately one foot in diameter. Also, clusters of individual blisters one , half inch or less in diameter were found at scattered locations. These blister clusters averaged about one foot in diameter. - It is estimated the total phenolic failure amounted to less than 1% of the surface area. The inorganic zine base coat, in failure areas, was found to be
; in excellent condition.
Preliminary analysis of the blistered areas indicated that in general the blistering or delamination occurred in the areas where a two-coat phenolic system existed because of unavoidable overlapping during application. This determination was made by measuring tha paint chips and visual examination of
, exposed areas where phenolic still exists. The examination also showed that the bonding between inorganic zine and the metal surface is still intact.
ANALYS~S OF SAFMPY IMPLICATIONS l Blistering and subsequent delamination of the phenolic top coat may occur l during a " loss of coolant" accident. However, this material is of the thermo setting type and has a melting point of about 1100 F, therefore the material i will harden, become more brittle and not react with the deionized water. Also, since the phenolic is heavier than water, it will settle to the bottom of the Torus. Plu ' the Torus.(gging of strainers segmented is notring by structural likely, considering girders) the configuration and realizing of that typical Core
- Spray and HPCI strainers are connected to 16-inch pipe and the RHR strainer to
, 24-inch pipe, and the strainers are truncated cones with areasiof 4 7 and 7 i square feet respectively. They are mounted one foot above the Torus invert and . have 1/8" holes. Further, the strainer flow area is conservatively designed-
~
with twice the area requred to pass the design flow at design pressure drop. CORRECTIVE ACTION On June 1, 1973 all loose, phenolic finish coat was removed and care was taken not to disturb the condition of inorganic zine primer. After removal of loose material, a testing program was initiated on June 1 and completed on June 14,-1973 to determine the integrity of the remaining phenolic top coat, including steam dynamic testa simulating the conditions
- experienced on May 31, 1973 The results of inspections made after conclusion of these tests clearly indicated that the inorganic zine primer was performing its corrosion resistance function and that the vast majority of the remaining phenolic finish coat was firmly adherred and is satisfactory from'a performance standpoint. .
PB-SDR-6 l l l
( CORRECTIVE ACTION - Continued The cafety analysis design basis includes suppression pool cooling to preclude operation outside of the containment design temperature and pressure for all modes of planned operation, abnormal operational transients and accidents, with the exception of the monthly surveillance testing of the High Pressure Coolant Injection System and Reactor Core Isolation Cooling System turbines. Steps are being taken to incorporate operation of a Residual Heat Removal heat exchanger (with high pressure service water) to cool and circulate the water during monthly surveillance testing of the High Pressure Coolant Injection System and Reactor Core Isolation Cooling System turbines. This procedure will preclude localized high temperature on the vessel wall and eliminate thermal stress on the coating (such as was experienced on the May 31, 1973 l coating failure) during normal plant operation. ADDITIONAL INFORMATION In view of the foregoing, we have initiated the necessary procedure to recoat. thit #3 Torus as follows:
- a. Below water line: Sand blast to white metal and apply one coat of inorganic zine only.
- b. Vapor Zone: Repair defective areas in present inorganic zine coating.
This procedure will provide an inorganic zine coating on the entire internal surfaces of the Torus. PWS/dhm PB-SDR-6
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