ML18052A939

LER 86-040-02:on 861217,dye Penetrant Insps Identified Transgranular Stress Corrosion Cracking of CRD Mechanism Seal Housing.Cause Undetermined.Benefit of Addl Dye Penetrant Tests Being evaluated.W/870416 Ltr

ML18052A939
Person / Time
Site:	Palisades
Issue date:	12/17/1986
From:	Johnson B, Kozup C CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.)
To:	NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM)
References
LER-86-040, LER-86-40, NUDOCS 8704210430
Download: ML18052A939 (4)

Text

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!X..ICTIO IUIM!SllON OATl 1111 I I With the Plant in hot shutdown condition (ie, 530 degrees, 2150 psia), engineering walkdowns identified control rod drive mechanism (CRDM) number 25 to be exhibiting primary coolant system leakage of approximately 0.12 gallons per minute. The CRD seal housing [SEAL;AA] was removed and, during bench testing, exhibited leakage from the drive shaft tube penetration. On December 17, 1986, dye penetrant inspections identified positive circumferential indications around the inner drive shaft housing.

Subsequent investigations indicated that CRD seal housing 25 was one of three seal housings procured in 1977. The two other CRD seal housings were identified to be installed in positions 23 and 28. On January 7, 1987, they were removed, and dye penetrant inspections indicated similar cracking. ASME Section XI inspection requirements were exceeded by testing an additional eleven installed CRD seal housings. No similar indications were noted.

Vendor analyses indicate that axial and circumferential cracks found on CRD seal housings 23, 25 and 28 were the result of transgranular stress corrosion cracking.

Records indicate the three CRD seal housings were manufactured from the same materials and co~prised the entire manufacturing lot. This is believed to b.e an isolated

• incident and not to represent a safety hazard.

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NRC Forll\'"3'eA 19-831 LICENSEE EVENT REPORT CLER) TEXT CONTINUATION U.11. NUCLEAR REGULATORY COMMISSION APPROVED OMS NO. 3150-0104 EXPIRES: 8/31185 FACILITY NAME (11 DOCKET NUMBER 121 LEll NUMIEll 1111 'AGE 131 PALISADES NUCLEAR PLANT 0 j5jOjOjOl21515 8j6 - 01410 - 0(2 012OF013 TEXT l l f - - ii '9qUlir8d, u* ~ NllC Fann .-.*111171 Description With the Plant in hot shutdown condition (ie, 530 degrees, 2150 psia), engineering walkdowns identified control rod drive mechanism (CRDM) number 25 (serial number:

2966-101) to be exhibiting primary coolant system [PCS] leakage of approximately 0.12 gallons per minute. The CRD seal housing [SEAL;AA] was removed from the reactor head and, during bench testing, exhibited leakage from the drive shaft tube penetration. Subsequently, on December 17, 1986, dye penetrant inspections identified positive circumferential indications around the inner diameter of the motor tube sleeve.

On December 17, 1986, due to positive dye penetrant indications on CRD seal housing 25, an additional six seal housings were dye penetrant tested per ASME Section XI. No similar positive indications were noted.

On December 19, 1986, CRD seal housing 25 was sent to Combustion Engineering to determine the primary failure mechanism via destructive and metallurgic examination.

A records search initiated by both the licensee and vendor indicated that CRD seal housing 25 was one of three spare CRD seal housings procured from Combustion Engineering in 1977. Also indicated was that the seal housings were manufactured from the same materials and comprised the entire manufacturing lot. The remaining seal housings were determined to be on the reactor head in positions 23 and 28.

On January 7, 1987, CRD seal housings 23 and 28 (serial numbers 2966-103 and 2966-102, respectively) were removed and dye penetrant tested. Both seal housings exhibited positive indications similar to CRD seal housing 25. Subsequently, both seal housings were sent to Combustion Engineering for further examination.

On January 9, 1987, due to the additional findings on seal housing 23 and 28, and per ASME Section XI, five additional CRD seal housings were removed and dye penetrant tested. No similar positive indications were noted.

The Combustion Engineering destructive and metallurgical analyses indicate that the axial and circumferential cracking existing on the inner diameter of the motor tube I

sleeve is a result of transgranular stress corrosion cracking.

Cause of the Event The exact cause of the transgranular stress corrosion cracking could not be determined. There is evidence of a contaminant being present on the fracture surface; however, the specific contaminant could not be determined. Metallurgical analyses of the contaminant indicate that the primary elements identified are consistent with those found in Type 304 stainless steel and dye penetrant fluid and developer.

Additional elements were identified which are known to promote transgranular stress corrosion cracking (ie, potassium) in stainless steel; however, no explanation for their presence could be determined. Nor could an exact correlation be derived between their existence and the cracking.

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NRC For.,.,3MA U.S. NUCLEAR REGULATORY COMMISllON 19-831 LICENSEE EVENT REPORT (LEA) TEXT CONTINUATION APPROVED OMB NO. 3150-0104 EXPIRES: 8/31185 FACILITY NAME 111 DOCKET NUM8Ell 121 LEll NUMIE R Ill PAGE 131 PALISADES NUCLEAR PLANT 0 I 5 I 0 I 0 I 0 I 2 I 5 I5 81 6 - 0 14 I 0 - 0 I 2 0 I3 OF 0 I3 Text' 111--lr~. 11#-NllC Fonnl11M'1I 1171 The presence of the contaminant and evidence of transgranular stress corrosion cracking appears to be an isolated case, associated with the entire manufacturing lot comprised of CRD seal housings 23, 25 and 28 (serial numbers 2966-103, 2966-101 and 2966-102). Although the lot of three spare CRD seal housings detailed above were manufactured to the same specifications as the original seal housings, differences exist between the two lots that make the spare unique. These differences include:

different heats of materiall manufacturing location, tooling and personnel.

Analysis of the Event The significance of a total failure (ie, 360 degrees through wall crack of the motor tube*sleeve) would have been a resultant small line break loss of coolant accident equivalent to a two and a quarter inch diameter pipe break. Loss of coolant accidents due to pipe break have been analyzed from small breaks up to a complete double-ended severance of a 42 inch diameter PCS pipe break and are compensated by the*Emergency Core Cooling System and it 1 s associated limiting condit.ions of operation.

Since it has been demonstrated that this occurrence is isolated to the three CRD seal housings manufactured and procured in the same lot, that the three affected CRD seal housings have been removed and destroyed during testing and that all original CRD seal housings dye penetrant tested per ASME Section XI requirements showed no reportable indications, it is concluded that this problem is unique to the lot of these spares and that there is no evidence to suggest that the 48 original seal housings are in any danger of developing a similar problem. Therefore, this item is not considered a safety concern for continued operation.

Corrective Actions All ASME Section XI code inspection requirements have been exceeded to date with th~

subsequent dye penetrant testing of eleven additional CRDM seal housings from the original manufacturing lot, with no positive indicatio'ns. Combustion Engineering was contracted, and has completed, destructive and metallurgical examinations upon the faulty seal housings.

Consumers Power Company is currently evaluating the benefit which may be gained by performing additional dye penetrant tests as part of the inservice inspection program.

No further examinations are required by ASME Section XI.

Additional Information Failed components: Control Rod Drive Mechanism seal housings manufactured by Comb"ustion Engineering - Serial numbers 2966-101, 2966-102 and 2966-103.

No previously submitted LERs were identified where a similar root cause determination was made.

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April 16, 1987 Nuclear Regulatory Commission Document Control Desk Washington, DC 20555 DOCKET 50-255 - LICENSE DPR PALISADES PLANT -

LICENSEE EVENT REPORT 86-040 - REVISION 2 (CRACKING OF CONTROL ROD DRIVE SEAL HOUSING)

Licensee Event Report (LER)86-040, Revision 2 (Cracking of Control Rod Drive Seal Housing) is attached. This event was reportable to the NRC per 10CFR50.73(a)(2)(ii). This revision reports the final results of the failure analysis performed by Combustion Engineering as committed to in Revision 01 to this LER.

Brian D Johnson Staff Licensing Engineer CC Administrator, Region III, NRC NRC Resident Inspector - Palisades OC0487-0041-NL02