ML20090L849
| ML20090L849 | |
| Person / Time | |
|---|---|
| Site: | Monticello  |
| Issue date: | 09/06/1974 |
| From: | Mayer L NORTHERN STATES POWER CO. |
| To: | Oleary J US ATOMIC ENERGY COMMISSION (AEC) |
| References | |
| NUDOCS 9102130466 | |
| Download: ML20090L849 (3) | |
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MSIs NORTHERN STATES POWER COMPANY M lN N E A PO L.t m. M I N N E S OTA 8 8 40 0 September 6, 1974
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Mr. J F O' Leary, Director Directorate of Licensing D SEP101974 " 5
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U S Atomic Energy Commis:, ion h', CCCC 4 4y/
Washington, DC 20545
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Dear Mr. O' Leary:
MONTICELLO NUCLEAR GENERATING PLANT Docket No. 50-263 License No. DPR-22 Additional Infomation Concerning Cracked Studs on Recirculation Pumps Following submittal of our May 31, 1974 letter, additior.a1 information became available concerning reactor recirculation pump stuffing box holddown cover studs.
This information was subsequently reviewed by Regulatory Operatier.s inspectors during an inspection conducted on July 16-18, 1974. At that time it was agreed to submit the infomation to your office.
The following information is submitted in accordance with that agreement:
1.
Abnormal sensitivity to stress corrosion can result if che stud material, ASTM A 193, Grade B6 Type 410 martensitic stainless steel, is improperly heat treated or tempered.
Characteristic data from material suppliers indicate that the hardness for 3
hardened and terpered (1100 F) 410 martensitic stainless steel should range from Rockwell C20 to C28. The hardness readings for the failed studs were in the range of Rockwell C31 to C32, 2.
Two sets of stuffing box holddown cover studs have been ordered from the manufacturer having the following specifications:
a.
Maximum hardness Rockwell C25.
l b.
Rolled threads, i
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110 Kpsi minimum tensile strer.gth, d.
No elongation hole.
I e.
Material heat number to be indicated on the end of each stud.
9102130466 740906 PDR ADOCK 05000263 a
t NORTHk.RN OTATED POWER COMPANY Mr. J F O' Leary Sept.cmber 6, 1974 Page 2 3.
Hardness value of each stud will be verified by NSP upon receipt.
4.
It is planned to replace the existing studs during the Fall 1975
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refueling outage.
It is also planned at that time to subject the existing studs to non-destructive examination to detect any de teriora ti on.
Yours very truly, Y
7 L 0 Mayer, PE Director of Nuclear Support Services LOM/kn ec:
J G Keppler G Charnoff Minnesota Pollution Control Agency Aten. E A Pryzina 1
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CCNTROL NO: 9313 4
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FRoti DATE OF LCC DATE F.IC'D LTR nX py -
- T;-;R Northern States Power Co Minneapolis, Minn 55401
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9-6-74 9-10-74 XX L 0 Mayer 103 ORIG CC CT:-2R SENT AIO I':3 XXXX Mr. O' Leary 1 signed SENT LOCAL ?.' ^^^
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50-263 DESCP.I?;IO:i:
ENCLCSL7ES :
Ltr re Abnormal Occurrence submitted on 5-31,74 EMEDED.
re additional information concerning cracked acuds on recirculation pumps.
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