ML18136A133
| ML18136A133 | |
| Person / Time | |
|---|---|
| Site: | Surry  |
| Issue date: | 10/17/1979 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML18136A132 | List: |
| References | |
| NUDOCS 7911050020 | |
| Download: ML18136A133 (3) | |
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Introduction UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D. C. 20555 SAFETY EVALUATION REPORT OF ACTIONS TAKEN TO ELIMINATE FEEDWATER PIPING CRACKS AT SURRY POWER STATION, UNIT NO. T On June 22, 1979, in response to IE Bulletin 79-13, the licensee performed radiographic inspections of the reducer to feedwater nozzle weld areas in the feedwater piping on loops "A", "B" and "C".
The radiography revealed circumferential cracks in the base metal at the nozzle to reducer counterbore regions of all three steam generators.
A meeting was held with the licensee on August 8, 1979 to discuss the following items regarding feedwater piping cracks:
- l. Nature and extent of the cracking
- 2. Metallurgical evaluation of the cracking including identification of the mode of failure.
- 3. Stress analyses
- 4.
Operating history
- 5.
Feedwater chemistry
- 6.
Corrective actions
- 7.
Safety implications By letter dated August 31, 1979, the licensee provided details of the inspection and corrective actions taken.
Discussion and Evaluation The licensee performed volumetric examinations of all the feedwater p1 ping welds inside the containment and found rejectable fabrication related discontinuities in four welds in loop "A", two welds in loop "B" and six welds in loop "C".
No service induced cracking was identifi.ed in the piping except as previously ~entioned in the nozzle to reducer region..
The results of the metallographic evaluation and further ultrasonic examinations of the reducer from Loop B confirmed the deepest cracks were at the counterbore at the 64° and at the 121° locations.
The maximum crack depth was 0.080 inches. Smaller cracks were also found
/
/
- in the tapered section between the counterbore and schedule 80 pipe.
In addition, heavy machining marks were 0bserved on the**reducer, ID.
Some cracking which was observed as a spike filled with oxide appeared to have initiated from the bottom of the machining marks.
Beachmarks were observed on the fracture faces of the most severe cracks.
The mode of failure was identified by the licensee as corrosion assisted fatigue.
The licensee performed stress analyses in an effort to identify any anomalies which could cause the observed cracks.
The analyses were:
- 1. Structural analyses using a 30 finite element model of the feedwater line including the effects of thermal, deadweight and pressure (does not include stratification conditions).
The licensee reports that results show th~ stresses are within the allowable code limits.
- 2.
20 finite element fatigue analysis of the feedwater nozzle/elbow configuration.
The licensee reports that the results show an acceptable usage factor using the allowable cycJes for a peak stress range from the ASME design S/N curves
- 3.
Frequency analysis of the feedwater line and steam generator.
The licensee reports that the results of the analysis indicate that feedwater line/steam generator resonances are possible but consider this unlikely based on testing performed at their similar faci 1 i ti es that have been instrumented.
The reducers were removed and replaced on all steam generators.
Any cracks identified by the 1 iquid penetrant examination of the nozzle bore ID or OD were removed and, if required, repaired.
Repairs to fabrication related discontinuities in welds in the feedwater lines have been completed.
The nozzle.to fitting welds were fully radiographed and ultrasonically inspected following completion of the welding and stress relieving operations.
We conclude that the actions taken by the licensee are sufficient to ensure that the piping integrity will be maintained.
The licensee will be replacing the steam generators at the next refueling outage.
Should further actions be required based on the results of studies and research*
under progress, we will inform the licensee what actions, if any, are deemed necessary.
We have determined that this action does not authorize a change in effluent types or total amounts nor an increase in power level and will not result in any significant environmental impact.
Having made
- / this determination~ we have further concluded that the action involves
'an action which is insignificant from the standpoint of environmental impact and, pursuant to 10 CFR i51.5(d)(4), that an environmental impact statement, or negative declaration and environmental impact appraisal need not be prepared in connection with this action.
Camel us ion We have concluded, based on the considerations discussed above, that:
(1) because this action does not involve a significant increase in the probability or consequences of accidents previously considered and does not involve a significant decrease in a safety margin, the action does not involve a significant hazards consideration, (2) there is reasonable assurance that the health and safety of the public will not be endangered by operation in the proposed manner, and (3) such activities will be conducted in compliance with the Commi*ssion's regulations and this action will not be inimical to the common defense and security or to the health and safety of the public.
Date: October 17, 1979