ML19312C417
| ML19312C417 | |
| Person / Time | |
|---|---|
| Site: | Oconee  |
| Issue date: | 11/24/1976 |
| From: | Moseley N NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II) |
| To: | Parker W DUKE POWER CO. |
| References | |
| NUDOCS 7912130939 | |
| Download: ML19312C417 (1) | |
Text
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"4 NUCLEAR REGULATORY COMMISSION f.
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In Reply Refer To:
IE:II:NRC 50-269 50-270 50-287 I
Duke Pcver Cc=pany ATTN:
Mr. William O. Parker, Jr.
t Vice President of Steam Production j
h22 South Church Street P. O. Box 2178 Charlotte, North Carolina 28242 Gentlemen:
The enclosed Circular 76-06 is forwarded to you for action.
If there are any questions related to your under-1 standing of the actions required, please contact this office.
Sincerely,
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Norman C. Moseley Director
Enclosure:
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.s IE Circular 7606 Data: November 24, 1976 STRESS CORROSION CRACKS IN STAGNANT, LOW PRESSURE STAINLESS PIPING CONTAINING BORIC ACID SOLUTION AT PWR's DESCRIPTION OF CIRCUMSTANCES:
DURING THE PERIOD November 7,1974 to November 1,1975 several incidents of through-wall cracking.have occurred in the 10-inch, schedule 10 type 304 stainless steel piping of the Reactor Building Spray and Decay Heat Removal Systems at Arkansas Nuclear Plant No. 1.
On October 7, 1976, Virginia Electric and Power also reported through-wall cracking in the 10-inch schedule 40 type 304 stainless discharge piping of the "A" recirculation spray heat exchanger at Surry Unit No. 2.
A recent inspection of Unit 1 Containecnt Recirculation Spray Piping revealed crack-ing similar to Unit 2.
On October 8, 1976 another incident of similar cracking in 8-
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inch schedule 10 type 304 stainless piping of the Safety In-jection Pump Suction Line at the Ginna facility was reported by the licensee.
Information received on the metallurgical analysis conducted to date indicates that the failures were the result of inter-granular stress corrosion cracking that initiated on the in-side of the piping. A commonality of factors observed asso-iated with the corrosion mechanism were:
1.
The cracks were adjacent to and propagated along weld zones of the thin-walled low pressure piping, not part of the reactor coolant system.
2.
Cracking occurred in piping containing relatively stagnant boric acid solution not required for normal operating con-ditions.
3.
Analysis of surface products at this time indicate a chloride ion interaction with oxide formation in the re-latively stagnant boric acid solution as the probable cor-rodant, with the state of stress probably due to welding and/or fabrication.
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The source of the chieride ion is not definitely known.
However, at ANO-1 the chlorides and sulfide level observed in the surface tarnish film near welds is believed to have been introduced into the piping during testing of the sodium thiosulfate discharge valves, or valve leakage.
Similarly, at Ginna the chlorides and potential oxygen availability were assumed to have been present since original construction of the borated water storage tank which is vented to aenosphere.
Corrosion attack at Surry is attributed to in-leakage of chlo-rides through recirculation spray heat exchange tubing, allow-ing buildup of contaminated water in an otherwise normally dry spray piping.
ACTION TO BE TAKEN BY LICENSEE:
1.
DESCRIPTION OF YOUR PROGRAM FOR ASSURING CON-TINUED INTEGRITY OF THOSE SAFETY-RELATED' PIPING SYSTEMS WHICH ARE NOT FREQUENTLY FLUSHED, OR WHICH CONTAIN NON-FLOWING LIQUIDS.
This program should include consider-ation of hydrostatic testing in accordance with ASME Code Section XI rules (1974 Edition) for all active systems required for safety injection and containment spray, in-cluding their recirculation modes, from source of water supply up to the second isolation valve of the primary system. Similar tests should be considered for other safety-related piping systems.
2.
Your program should also consider volumetric examination of a representative number of circumferential pipe welds by nondestructive examination' techniques.
Such examina-tions should be performed generally in accordance with Appendix I of Section XI of the ASME Code, except that the examined area should cover a distance of approxi-mately six (6) times the pipe wall thickness (but not less than 2 inches and need not exceed 8 inches) on each Supplementary examination techniques, side of the weld.
such as radiography, should be used where necessary for evaluation or confirmation of ultrasonic indications re-sulting from such examination.
3.
A report describing your program and schedule for these inspections should be submitted within 30 days after re-ceipt of this Circular.
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The NRC Regional Office should be Laformed within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />, of any adverse findings resulting during nondestructive evaluation of the accessible piping welds identified above.
5.
A summary report of the examinations and evaluation of results should be submitted within 60 days from the date of completion of proposed testing and examinations.
This summary report should also include a brief descrip-tion of plant conditions, operating procedures or other activites which provide assurance that the effluent c' hem-i istry will maintain low levels of potential corrodants in such relatively stagnant regions within the piping.
Your responses should be submitted to the Director of this office, with a copy to the NRC Office of Inspection and En-forcesent, Division of Reactor Inspection Programs, Wash-ington, D.C.
20555.
Approval of NRC requirements for reports concerning possible generic problems has been obtained under 44 U.S.C 3152 from the U.S. General Accounting Office.
(GAO Approval B-180255 (R0062), expires 7/31/77).
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