ML18037A020
| ML18037A020 | |
| Person / Time | |
|---|---|
| Site: | Nine Mile Point  |
| Issue date: | 07/19/1984 |
| From: | Vassallo D Office of Nuclear Reactor Regulation |
| To: | Hooten B NIAGARA MOHAWK POWER CORP. |
| Shared Package | |
| ML17054A907 | List: |
| References | |
| NUDOCS 8407300435 | |
| Download: ML18037A020 (6) | |
Text
Docket No. 50-220 July 19, 1984 Mr. B.
G., Hooten Executive Director, Nuclear Operations Niagara Mohawk Power Corporation 300 Erie Boulevard West
- Syracuse, New York 13202
Dear Mr. Hooten:
SUBJECT:
SAFETY EVALUATION, CRACK - 12" CORE SPRAY SYSTEM - LOOP 11 Re:
Nine Mile Point Nuclear Station, Unit No.
1 We have completed the review of the cracking in the core spray system pipe at Nine Mile Point, Unit No. 1.
We, as you, have concluded that the cracking was caused by chloride transgranular stress corrosion cracking.
We have also reviewed your repair procedure, and concluded that the repair mode was satisfactory.
The repaired area should be volumetrically inspected at the next refueling outage and be included as a part of your In-service Inspection (ISI) program.
Our Safety Evaluation is enclosed.
Sincerely, Original signed by/
Enclosure:
As stated Domenic B. Vassallo, Chief Operating Reactors Branch ¹2 Division of Licensing cc w/enclosure:
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Mr. B. G. Hooten Niagara Mohawk Power Corporation Nine Mile Point Nuclear Station, Unit No.
1 CC:
Troy B. Conner, Jr.,
Esquire Conner 5 Wetterhahn Suite 1050 1747 Pennsylvania
- Avenue, N.
W.
Washington, D. C.
20006 Robert P. Jones, Supervisor Town of Scriba R. D.
P4
- Oswego, New York 13126 Niagara Mohawk Power Corporation ATTN:
Mr. Thomas Perkins Plant Superintendent Nine Mile Point Nuclear Station Post Office Box 32
- Lycoming, New York 13093 U. S. Environmental Protection Agency Region II Office Regional Radiation Representative 26 Federal Plaza New York, New York 10007 Resident Inspector U. S. Nuclear Regulatory Commission Post Office Box 126
- Lycoming, New York 13093 John W. Keib, Esquire Hiagara Mohawk Power Corporation 300 Erie Boulevard West
- Syracuse, New York 13202 Thomas A. Murley Regional Administrator Region I Office U. S. Nuclear Regulatory Commission 631 Park Avenue King of Prussia, Pennsylvania 19406 hlr. Jay Dunkleberger
~
Division of Policy Analysis and Planning New York State Energy Office Agency Building 2 Empire State Plaza
- Albany, New York 12223
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SAFETY VALUATION NIAGARA~IA I PIIRARINN NINE MILE P INT N LEAR STATION UNIT 1 0
K T NO.
50-220 REPAIR OF CRACKED 12 CORE SPRAY SYSTEM PIPING " LOOP"
1.0 INTRODUCTION
2.0 Inservice Inspection results of ultrasonic and surface examinations of loop ll - 12" core spray piping between the drywell penetration and internal isolation valve - detected the presence of a crack.
The crack was located adjacent to a longitudinally oriented welded attachment lug.
The crack turned circumferentially from the lug, is approximately 90X around the pipe, and had a depth (by ultrasonics) of approximately 50K of the wall thickness.
The crack appeared to have started at the OD surface.
Penetrant indications were reported as spaced intermittently at approximately 7'ntervals with a 454 orientation of the pipe axis.
Subsequent excavation of the crack by grinding confirmed the depth to be between 0.250 and 0.398 inches.
.This confirmed the ultrasonic examination results.
~ N EVALUATION The licensee repaired the defective piping by local grinding to remove the flaw and tungsten gas welding (TIG) to restore the pipe'all to its original thickness.
Liquid penetrant and ultrasonic examinations were performed on the excavated cavity prior to repair welding to ensure that the defect was completely removed.
The weld repair was accomplished by the TIG process using SFA 5.9 -
ER 309, 3/32" filler wire to fill the cavity in the P-8, ASTOR - A-358, Class 1 pipe.
Liquid penetrant and ultrasonic examinations were performed following the repair to verify that the weldment and heat affected zone were sound.
The welding process utilized by the licensee to effect the repair is a low heat input process
.and minimizes sensitization of the P-8, 304 austenitic stainless steel base material.
Further, the inter-pass temperature was maintained less than 300 F during the repair.
The filler wire is compatible with the base material.
The non-destructive examinati'ons performed verified that the base material was free of cracking prior to repair welding and that the final weldment was sound.
Preliminary results from the licensee in analyzing the boat sample removed from the cracked pipe indicate the crack is transgranular in nature.
EDAX analysis by the licensee has identified the presence of chlorides on the fracture face.
The mode of failure has 4een identified by the.licensee as transgranular stress corrosion cracking.
Preliminary analysis by Brookhaven Laboratories, our contractor, has verified the licensee'indings.
3.0 CONCLUSION
We find the repair performed by the licensee to be acceptable.
The repair was performed in a manner to minimize sensitization of the base material and should not affect performance of the pipe since it was similar to a repair that would have been performed on an initial fabrication defect.
Region I has verified that the repair was performed in an acceptable manner.
The stress corrosion was most likely caused by contamination on the pipe surface acting with stress from the installation of the lug and/
or other operating or residual stresses.
We recommend that a volumetric examination of the repaired area be performed at the next scheduled refueling outage.
Oated:
July 19, 1984