ML19208D793
| ML19208D793 | |
| Person / Time | |
|---|---|
| Site: | Prairie Island  |
| Issue date: | 08/29/1979 |
| From: | Wachter L NORTHERN STATES POWER CO. |
| To: | James Keppler NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III) |
| References | |
| NUDOCS 7909290564 | |
| Download: ML19208D793 (3) | |
Text
fl NSP NORTHERN STATES POWER COMPANY M I N N E A PO LI S. M I N N E SOTA 55401 August 29, 1979 Er, James G. Keppler Director - Region III Office of Inspection and Enforcement United States Nuclear Regulatory Commission 799 Roosevelt Road Glen Ellyn, Illinois 60137
Dear Mr. Keppler:
PRAIRIE ISLAND NUCLEAR GENERATING PLANT Dockets No. 50-282 and No. 50-306 In further response to IE Bulletin 79-13, the following is offered:
All examinations required by IE Bulletin 79-13 were completed on Prairie Island Unit 1 feedwater piping during a July, 1979, turbine outage.
Radiographic examinations of the feedwater nozzle-to-piping welds and of adjacent pipe and nozzle areas were performed in accordance with Bulletin Item 1.a.
In addition, these areas were ultrasonically examined in accordance with Section XI, 1974 Edition, and Appendix 3 issued Winter, 1975. Further, these areas were examined visually and with magnetic particle in accordance with Section XI, 1974 Edition, Summer, 1975, Addenda. The results of these examirations showed no evidence of cracking or other unacceptable indications.
The Prairic Island design has a common nozzle for main and auxiliary systems with the auxiliary system connection in containment on the steam generator side of the main feedwater final check valve.
Radiographic examinations suggested by Bulletin Item 2.a in accordance with Item 1.a were therefore performed on all main feedwater piping circ.mferential butt welds in containment from the containment penetration to the icedwater nozzle on loop A and from the end of the encapsulation sleeve to t'.e feedwater nozzle on loop B.
The examinations included the auxiliary feedwater sweep-o-let connection welds to the main feedwater lines and the piping base metal from the auxiliary feedwater connections to the steam generator nozzles.
All these areas examined by radiography were also examined by visual, ultrasonic, and magnetic particle methods referenced above. The results of these examinations revealed no evidence of cracking or other unacceptable indications with one exception. Weld FW-139 showed an unacceptable slag inclusion in both RT and UT examinations; this indication was removed by hand grinding and repair welding and found acceptable by the original inspection methods after repair.
1054341l AUG3y1979 7909298 N k
NORTHERN STATES POWER COMPANY i
Mr. James G. Keppler August 29, 1979 Page 2 All main feedwater piping supports and restraints in containment were inspected in accordance with the requirements of Bulletin item 2.c.
Supports and restraints were visually inspected for operability,
~ hysical integrity, and conformance to design.
In addition, support pattachment weld connections to the feedwater piping were visually and magnetic particle inspected on loop A.
Minor discrepancies such as encapsulation pipe physical contact with support elements were corrected by grinding to increase clearances, and two loose nuts on restraints were tightened. All other inspection results were acceptable.
Several additional measures were implemented by Northern States Power Company concerning verification of feedwater piping integrity. One of the main feedwater final check valves was opened on Unit 1, and inspection of the accessible internal piping surfaces showed no indications of pitting corrosion. Strain gauge and thermal couple instrumentation was installed on the nozzle-to-pipe weld and feedwater piping system to gain further information on thermal and mechanical effects. Preliminary results obtained during Unit 1 heatup and return to power indicate thermal stratification exists; however, no dynamic response stresses were detected which provides -dditional confidence in the adequacy of the piping and piping support design.
Based on the favoralle results of the inspection program completed on Unit 1, and in accordance with the guidance provided by Item 3.0 of the Bulletin, Unit 2 inspections will be performed during the next refueling outage presently scheduled for January, 1980, or during the next extended outage should one occur prior to refueling.
Further justification for this position is based on the following:
1.
Unit 2 piping, support, and nozzle-to-pipe connection designs and materials are very similar to Unit 1.
2.
Unit 2 operating history indicates it has experienced only 15 heatup and cooldown cycles as compared to 23 such cycles on Unit 1.
3.
Unit 2 operating history indicates it has experienced only about 1200 hours0.0139 days <br />0.333 hours <br />0.00198 weeks <br />4.566e-4 months <br /> in the condition of at or near full temperature and supplied by auxiliary feedwater as compared with a history of approximately 2000 hours0.0231 days <br />0.556 hours <br />0.00331 weeks <br />7.61e-4 months <br /> in that condition for Unit 1.
4.
Examinations on Unit 1 give no indications of pitting corrosion, and preliminary results of test instrumentation on Unit 1 give no indication of mechanically-induced dynamic stresses.
5.
Unit 2 has operated on AVT chemistry since initial startup; and, because the secondary is an all-ferrous system, an elevated pH of 9.6 has generally been maintained since initial operation.
We believe this higher pH environment in the secondary system significantly reduces su+ceptibility to any corrosion-assisted 1054342$
NORTHERN STAT
- E POWER COMPANY Mr. James G. Keppler August 29, 1979 Page 2 cracking mechanism as evidenced by the total absence of any indications of steam generator tube denting or thinning.
-A supplemental response will ue submitted within 30 days of the examination of Unit 2.
Yours very truly, L. J. Wachter Vice President - Power Pr'oduction and System Operation cc:
Mr. G. Charnoff NRC Office of Inspection and Enforcement Washington, D.C.
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