ML20084C876
| ML20084C876 | |
| Person / Time | |
|---|---|
| Site: | Dresden  |
| Issue date: | 05/21/1971 |
| From: | Brian Lee COMMONWEALTH EDISON CO. |
| To: | Morris P US ATOMIC ENERGY COMMISSION (AEC) |
| Shared Package | |
| ML20084C878 | List: |
| References | |
| 13024, NUDOCS 8304080279 | |
| Download: ML20084C876 (5) | |
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Commonwealth Edison Company ONE FIRST NATIONAL PLAZA
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POST OPPICE sor 747
- C H I C A G O, ILL4HOls 40490 May 21, 1971
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Dr. Peter A. Morris, Director
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Subject:
Additional Information Concerning the
- I Operation of Dresden Unit 2
Dear Dr. Morris:
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On April 24, 1971,y f
Reports Numbers 10 through 13.we submitted to you Dresden Special discussed the torus paint problem and the status of that problem 1
Report Number 12 of that series as of April 21, 1971.
Attached hereto is a Report entitled, Supplemental Infor-nation to Special Report #12 - Torus Paint Problems, Dresden - Unit 2.
This Report discusses all of the torus paint problems which have been
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found and the solution which has been taken to solve these problems.
In addition, the Report indicates that during the next refueling outage of Dresden Unit 2, the Dresden 2 torus will be drained and an inspection made of the torus paint.
l In addition to three signed originals, 19 copies of this submittal are also being transmitted.
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Very truly yours, f
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Byron Lee, Jr.
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Assistant to the President SUB8CRIBED and SWORN to before me this j/3' day of 4 to 1971.
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Supplomontal Infonmation to Special Report #12 Torus Paint Problems Drosden - Unit 2 The submittal "Special Reports" dated April 21, 1971, included Roport No. 12, Torus Paint.
This report stated that an inspection of the torus paint abovo water level revenlod three types of coating distress:
pinpoint rust to metal substrato, blisters ranging in size from 1/8 inch to li inch in diumo tor, and small areas of dolem-ination betwoon the finish coat and the prime coat.
On April 29, 1971 thoso paint problems woro explained further to the ACRS Subcommittee and the AEC Staff.
Subsequent to the dato.of the report and the presentation in Wnshington and immediately after the reactor core was reconstitutod, the torus was emptied of water nnd a thorouch inspection made of the paint bolou the water. level.
This inspection revealed additional paint problems.
Conside rable delamination, sepa, ration of the paint between the two primer coats, on the inboard torus wall in an area around the torus betwoon h and $ o' clock, representing % of the painted surface a wall width of approxi-mately 8 foot, was found.
Approximately 10 in this area, or about.5% of the total coated surfaces, was affected.
Mejor delnminatinn nocurrnd in 6 of the 16 bnys.
Minor delsminobinns in two or three arons por bay, each aron affected representing less than 1 sq.ft. were found in 4 bays.
The paint in the remaining 6 buys was found to be in excellent condition.
The delaminated areas were discolored and a thin, continuous film of water was found behind the coating.
All areas of dolamination showed the delaminated coating was intact and evidenced a very tough surface.
Only with considerable effort with sharp knives was it possible to cut through the coating to initiato removal of the de-laminated matorial.
Small delaminated areas be twoon 7 end 8 o'. clock on the outboard torus walls wero found in 2 bays.
Each delmuination was less than 1 f t.sq. and represent only a few isolated casos.
The romaindor of the conting in this area is in excellent condition.
There are.no delaminations of this type on internal surfaces such as baffles, the I-foot dinmotor vent header, douncomers, grating, etc.
t Aftor the bottom of the torus had dried, four small cracks in tho paint wero found at 6 o ' clock.
The cracks involved the finish coat and second primer coat, the first primer coat, on the metal, shouod no crack indications.
The cracks ranged in length from 6 inchos to 18 inchos.
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Small blistei-a, generally varying in size from 1/8 inch to 1/2 inch, woro ibund over much of the lower half of the torus.
A few blistors up to lh inch sizo were also found.
Those blisters are the same type found in the upper half of the torus in which the separation occurred by shearing or pulling apart of the primo coats.
These blistors are firm and tight with a mnall amount of liquid underneath each blister.
In no instance was any coating missing from a blister.
In summary, the torus paint problems which have occurred both abovo and below the water are as follows:
1.
Pinpoint rust to motal - These areas aro small and isolated and were undoubtodly caused by holidays in the coating which for some reason were not dotected during inspection of the completed coat-ing work or wore caused by too thin a coating over some sharp metal projections or over sand particles.
2.
Blistering - Two types of blistors, all of which were lh inch or less in diamotor, were found.
/h) B11stors caused by separation betwoon tha-prime and finish coats.
These blistors were few in n6mber and probably caused by isolated cases of improperly prepared surface, b) Blisters caused by shearing or the pulling apart of the finish coat and the second primo coat from the first. prime coat.
The fnilurn modo of bhis problem is, at present, unknown.
3 Largo Delaminated Areas - These delaminations occurred on the in-board torus wall and the cause of failure is unknown.
However, the paint exports who are trying to determino the cause of this mode of failure all agree that the coating materials and application, including preparation of the stool surfaces, are not probable causes of the doleminations.
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Small Dolmninated Arcas - Those delaminations occurred on the outboard torus wall and the cause of failure is unknown.
Cracking of coating at bottom of torus - The cause of this failure is unknown, however it has been detonnined that those small cracka did not open up until after the coating dried out.
After complotion of the inspection, we reviewed the various paint problems and decided to make the following ;intertm repairs:
1.
The small isolated areas of pinpoint rusting havo been ground down to bare metal, cleaned, and recoated with the originally spocified Phenolino 368.
2.
The blistors caused by separation of the coats have been ground down to bare metal, cleanod, and reconted with the.
originally specified Phonolino 368.
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Blisters caused by shearing of the primer coats having a diameter greater than d inch and above the water level were removed, the remaining portion of the primer coat cleaned, and recoated with the originally specified Phenoline 368.
The remaining blisters, above water, are all very small, tight, and firm.
These blisters were left undisturbed.
3 The delaminated areas and the blisters on the inboard torus wall have been shot blasted to remove the separated material.
The surface was then gone over thoroughly to remove the small pieces of remaining delaminated material.
The shot blasting did not disturb the first prime coat which in all cases is firmly adhered to the metal surface.
The perimeters of the delaminated areas, where removal of the delaminated material exposed the edges'of the coating still in place, were ground down, cleaned and scaled with a 4 inch to 6 inch wide strip of Phenoline 368 to prevent water seepage under the_ paint coats.
In addition to the interim repairs, the following listed tests are being conducted to establish the failure causes:
1.
Tests, presently in process, are being carried out by the' Carboline Company and the paint contractor to try to duplicate the failures and thereby establish the causes.
2.
Numerous coating samples have been removed and are being analyzed.
3 Fifteen test coupons, each 2 inch by 4 inch, painted on both sides to a Lhickness of 15 mils with Phenoline 368 have been installed in various locations of the torus.
This test is to determine if increased' coating thickness (original ' coating.about 10 mils) will retard the failures.
4.
Small isolated areas on the torus walls were sandblasted to bare metal to determine corrosion rates below and above the water.
5 Instrumentation is being installed in the torus which will con-tinually measure the torus air temperature and the suppression pool water temperature.
Seven additional areas are being monitored, one above water and six below water at various levels and locations.
6.
Facilities have been installed, through two unused drain flanges on the bottom of the torus, to periodically remove ~ samples'of the torus water to analyze for chemicals and cleanliness.
The repairs made to the torus paint are, in our opinion, those which give us the highest confidence level that the paint in the torus will remain intact during the next operatingLcycle.
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-g-Wo are convinced through numerous inspections of the blistors that the coating over the blisters will not deteriorate during the next oporating cycle.
Although the blistors might increase in size by a small amount, they will remain firm, tight, and intact.
The exposed prime coat remaining af ter removal of the separated material in the areas of large delaminations under water will gradu-ally reduce in thickness.
Leaving the primer exposed in this manner, and at this point in timo, 18 considorably more roassuring than if thoso relatively large areas were recoated before the cause of the delsminations is dotormined.
However, we are confident that the small patched areas will not separate because similer patching of small arons mad,o previously remain in excellent condition.
During the next scheduled refueling outage we will drain the torus and make a thorough taspection of the paint.
In the interim period, the AEC, both Staff and Complianco, will be kept informed of all developments regarding the torus paint.
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