ML20215F769
| ML20215F769 | |
| Person / Time | |
|---|---|
| Site: | Quad Cities  |
| Issue date: | 12/18/1986 |
| From: | Johnson I COMMONWEALTH EDISON CO. |
| To: | Harold Denton Office of Nuclear Reactor Regulation |
| References | |
| 2503K, NUDOCS 8612240058 | |
| Download: ML20215F769 (3) | |
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g m m,y Chca00. IIinois 60000 0767 December 18, 4.986 i
i Mr. Harold R. Denton, Director Office of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission Washington, DC 20555 i
subject: Quad Cities Station Units 1 and 2 i
Thickness Checks Performed on Drywell Shells NRC Docket Nos. 50-254 and 50-265 i
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Dear Mr. Denton:
This letter documents Commonwealth Edison's response to a concern i
identified at Oyster Creek in November of this year regarding errosion of the Mark I containment drywell. Both units of Quad cities have been inspected and no thining degradation was detected on either unit.
j A thickness check was completed on certain areas of the Unit 1 and 2 drywell shells. The thickness readings were completed using ultrasonic j
testing. The inspections were performed certified Level II UT inspectors employed by Conam Inspection, which is our outage inspection contractor for the balance of plant work. The UT inspectors were accompanied and directed i
by Quad cities Station Quality Control inspectors.
i The initial inspection was performed on Unit 2 on December 4, 1986, j
and was ccnducted as we described below:
The thickness was measured in eight locations coinciding with each vent header penetration. The location of the target spot for getting the readings
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were planned and completed at approximately 2" above the concrete basement floor directly under each penetration. The average readings ranged from 1.24" to 1.27".
The original shell thickness was, by design, required to be j
nominally one to one-eighth inches. Each location was checked in three to four spots to achieve the average and the comment was documented that there j
wasn't more than.003" difference in any of the readings from high to low in each inspection area. This inspection was done through the painted surface.
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/ 4 H. R. Denton December 18, 1986 The completed inspection results were reviewed by the authorizied Nuclear Inspector. Additionally, the results were discussed with the NRC Region III Inspector who normally reviews any NDE related work at the site during refuel outage.
Subsequent to this initial inspection, it was discovered that our design includes a reinforcing plate on the outside of the shell at these locations which would possibly isolate this plate from the outside shell environment. Therefore, it was decided to reconduct the inspection at the midpoint, but asinuth, between the vent headers at the floor concrete level. The plate material wouldn't be isolated from the outside shell environment and there was no external plates in this area. When performing this second inspection, we encountered some difficulty witht he point in these areas, so we had the areas cleaned to bare metal prior to performing these inspections. The results ranged from 1.161" through 1.226", which is well over the nominal 1.125" nominal design requirement. Additionally, per a request from the General Electric Site Representative, additional readings were taken above the floor level at one location (approximately 4' up and 6' up from the floor) to see if any significant shell thickness differences were noted. This was done at the location between vent header penetration X-5E and X-5F (approx. asinuth 225 degrees). The results recorded a thickness rang from 1.210" to 1.220", which appears to be essentially the same as the lower readings. This inspection was completed on December 6, 1986.
Unit I was also inspected on December 6, 1986. This inspection was performed using a different UT inspection device which allow the use of higher sound energies. This machine has more capabilities and was able to penetrate the paint coating and give us accurate thickness readings. The areas inspected coincide with the areas picked for the second Unit 2 inspec-tion. The UT machine was set up on its CRT screen which does not utilize a digital display for readings, therefore, readings are not achieved in the thousandth-of-an-inch" detail. However, it is accurate as a technique to identify any shift over +/- (plus or minus).010".
With this in mind, the readings all fell within the 1.25" range with approximately 1.20" to 1.30" on the low /high end. Additionally, we inspected an area above the floor with the same results.
As with the earlier inspection, the results were reviewed by the authorized Nuclear Inspector and the results discussed with the NRC Region III Inspector.
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H. R. Denton December 18, 1986 CONCLUSION: Commonwealth Edison feels that this inspection confirms that there doesn't appear to be any thinning degradation ongoing on the Quad Cities Units 1 and 2 drywell shells at this time.
If there are any further questions regarding this matter, please contact this office.
Very truly yours, LL h
I. M. Johnso Nuclear Licensing Administrator la cc: Resident Inspector - Quad Cities T. S. Rotella - NRR 2503K