ML20090M509

Provides Addl Info Re Cracked Studs on Recirculation Pumps

ML20090M509
Person / Time
Site:	Monticello
Issue date:	05/31/1974
From:	Mayer L NORTHERN STATES POWER CO.
To:	Oleary J US ATOMIC ENERGY COMMISSION (AEC)
References
NUDOCS 9105030429
Download: ML20090M509 (3)

Text

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(TDiPORARY FOPJt) CONTROL NO:__ fD 8 7 FILE:__ N'3 0 =

M: DATE OF DOC DATE PIC ' D LTR MDiO RPT OT!!ER erthern States Power Company tinneapolis, Minnesota 55401 5-31-74 6-7-74 X

! L, 0, Mayer TO: ORIG CC OTliER SENT AEC PDR X J . F . O ' Le a ry 1 signed SENT LOCAL PDR X CLASS UNCLASS PROP INFO INPUT NO CIS REC'D DOCKET NO:

XXX 40 50-263 DESCRIPTION: ENCLOSURES:

Ltr re their 4-15-74 Itr, furnishing addl info concerning cracked studs on recirculation --

Pumps..... ACI(NOWLEDGED 9105030429 740331

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NORTHERN STATES POWER COMPANY hiinrwapolis, hiinnesota 55401 s7-

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,N e w ,, " '[p biay 31, 1974 MP' h h l; htr. J. F. O' Leary, Director '4 -

• Q"i s Directorate of Licensing s

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Office of Regulation y United States Atomic Energy Co:mtission Washington, D. C. 20545

Dear bir. O'Leaty:

hDNTICELLO NUCLEAR GENERATING PIM Docket No. 50-263 License No. DPR-22 Additional Information Concerning Cracked Studs on Recirculation Pumps In our April 15, 1974 letter it was reported that investigation into the

( cause of the cracked recirculation panp stuffing box holddown cover studs and possible corrective actions had not been completed. This letter reports the resolution of the problem.

l Metallurgical examination revealed that the major factor contributing to the stud fsilure was that the studs were improperly heat treated causing ti. m to be susceptible to stress corrosion cracking. The stress corrosion cracking mechanism was accelerated by a concentration cell effect of an elongation pin cavity and, possibly, by the presence of fluoride containing 0-rings in the pump gland seal assembly.

l l To prevent recurrence, the following steps were taken:

i

a. The elongatior. pin cavity of the spare studs used in No.12 Recirculation Pump was seal welded to eliminate the possibility of the cavity acting as a corrosion concentration cell,

b. New studs used in No. 11 Recirculation Pump were purchased without the elongation pin cavity.

c. liardness tests were performed on the newly purchased studs to verify that they had been properly heat treated.

d. Previously installed 0-rings were replaced with halogen frec 2.la-N 0-rings.

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2-The recirculation ptrnp main studs were ultrasonically examined and found satisfactorv.

Very truly yours, hY W L. O. 1byer, PE Director of Nuclear Support Services IIWmrn ec: J G Keppler G Charnoff Minnesota Pollution Control Agency Attn: E A Pryzina L