ML19256B558
| ML19256B558 | |
| Person / Time | |
|---|---|
| Site: | Turkey Point, Saint Lucie  |
| Issue date: | 07/26/1979 |
| From: | James O'Reilly NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II) |
| To: | Robert E. Uhrig FLORIDA POWER & LIGHT CO. |
| References | |
| NUDOCS 7908070754 | |
| Download: ML19256B558 (2) | |
Text
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NUCLEAR REGULATORY COMMISSION
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101 MA RIE T T A ST, N W SulT E 3100
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In Reply Refer To:
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_251 Florida Power and Light Company ATTN:
R. E. Uhrig, Vice President Advanced Systems and Technology P. O.
Box 529100 Miami, FL 33152 Gentlemen:
The enclosed Bulletin 79-17 is forwarded to you for action.
A written response is r2 quired.
If you desire additional information regarding this matter, please contact this office.
Sincerely,
' ~ ~ ~ - ~
(4 James P. O'Rei y Director Enclosure IE Bulletin 79-17 7908070754
JUL 2 61979 Florida Power and Light Company cc w/cocl:
C. M. Vetby, Plant Mana ge r Post Office Box 128 Ft. Pierce, Florida 33450 Nat Verms, Assistant QA Manager Post Office Box 128 ft. Pierce, Florida 33450 H. E. Yaeger, Plant Manager Post Office Box 013100 Miami, Florida 33101
i UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF INSPECTION AND ENFORCEMENT WAsillNGTON,
D. C.
20555 July 26, 1979 IE Bulletin No. 79-17 PIPE CRACKS IN STAGNANT BORATED WATER SYSTEMS AT PWR PLANTS Description of Circumstances:
During the period of November 1974 to February 1977 a number of cracking incidents have been experienced in safety-related stainless steel piping systems and port tons of systems which contain oxygenated, stagnant or essentially stagnant borated water.
Metallurgical investigations revealed these cracks occurred in the weld heat affected zone of 8-inch to 10-inch type 304 material (schedule 10 and 40), initiating on the piping 1.D.
surface and propagating in either an intergranular or transgranular mode typical of Stress Corrosion Cracking.
Analysts indicated the probable corrodents to be chloride and oxygen contami-nation in the affected systems.
Plants affected up to this time were Arkansas Nuclear Unit 1, R. E, Ginna, }{.B. Robinson Unit 2, Crystal River Unit 3, San Onofre Unit 1, and Surry Units 1 and 2.
The NRC issued Circular 76-06 (copy attached) in view of the apparent generic nature of the problem.
During the refueling outage of Three Mile Island Unit I which began in February this year, visual inspections disclosed five (5) through-wall cracks at welds ofin the spent fuel cooling system piping and one (1) at a weld in the decay heat removal system. These cracks were found as a result of local boric acid build-up and later confirmed by liquid penetrant tests. This initial identification of cracking was reported to the NRC in a Licensee Event Report (LER) dated May 16, 1979. A preliminary metallurgical analysis was performed by the licensee on a section of cracked and leaking weld joint from the spent fuel cooling system.
The conclusion of this analysis was that cracking was due to Intergranular St ress Corrosion Cracking (IGSCC) originating on the pipe 1.D.
The cracking was localtzed to the heat af fected zone where the type 304 stainless steel is sensitized (precipitated carbides) during welding.
In addition to the main through-wall crack, incipient cracks were observed at several locatic.. in the weld heat affected zone including the weld root fusion area wher-a miniscule lack of fusion had occurred. The stresses responsible for cracking are believed to be primar tly residual welding st resses in as much as the calculated applied stresses were found to be less than code design limits. There is no conclusive evidence at this time to identify those aggressive chemical species which promoted this IGSCC attack. Further analytical efforts in this area and on other system welds are being pursued.
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