ML18059A913

LER 94-006-00:on 940217,plant Shutdown Per TSs Due to Leak on Asme,Section Xi,Class 2 saftey-related Check Valve. Caused by Through Wall Defect on Valve CK-ES3166.Check Valves CK-ES3166 & CK-ES3188 replaced.W/940321 Ltr

ML18059A913
Person / Time
Site:	Palisades
Issue date:	03/21/1994
From:	Rogers D, Young B CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.)
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-94-006, LER-94-6, NUDOCS 9404010017
Download: ML18059A913 (6)

Text

11.

consumers Power David W. Rogers Plant Safety and Licensing Director POWERIN&

NtlCHlliAN'S PRO&RESS Palisades Nuclear Plant

27780 Blue Star Memorial Highway, Covert, Ml 49043 March 21,- 1994 i

• Nuclear Regulatory Commis.sion*

.Document Control Desk

Washington, DC 20555

. 'DOCKET SQ-255 ~ LICENSE DPR-2.0 -- PAL.ISADES PLANT LICENSEE EVENT REPORT 94~006 - PLANT SHUTDOWN IN ACCORDANCE WITH PLANT TECHNICAL SPECIFICATIONS BECAUSE OF A LEAK ON AN ASME, SECTION XI, CLASS 2, SAFETY-RELATED CHECK VALVE .

1 Licensee Event Report (LER)94-006 is attached. This event is reportable in*

. accordance with 10CFR50.73(a)(2)(i)(A) as th~ completion of a nuclear plant

'shutdown required by the plant's technical .

specifications.

David WRogers Plant Safety and Licensing Direct6r CC Admi.nistrator, .Region III,. USNRC NRC Resident Inspector - *Palisades

• 1 Attachment A CMS' ENERGYCOMPANY

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U.S. NUCLEAR REGUV..TORY COMMIS510N

-OVED OMB NO. 31~10.

EXPIRES: 8/3 1196 '

LICENSEE EVENT REPORT (LERI FACILITY NAME 111 DOCKET NUMBER 121 PAGE 131 Palisades Plant 0 I 5 I 0 I 0 I 0

• 1 2 I 5 I* 5 1 I OF 0 I 5 TITLE 141 ONLA~I ~~~JDOW~-f~_ACfOTRD~~9E WITH PLANT TECHNICAL SPECIFICATIONS BECAUSE OF A LEAK P llN ll :Mk" -.Kl:TlllN x ,., ,,c::;c;: ? C:::Al<'F'T'V-l)i;'T ATl'n r"u1<rv UATUJ<

EVENT DATE 161 lER NUMBER 181 REPORT DATE 181 OTHER FACILITIES INVOLVED Ill SEQUENTIAL REVISION FACILITY NAMES MONTH DAY YEAR YEAR NUMBER NUMBER MONTH DAY YEAR N/A 012 II 7 9 4 914 o Io 16 010 013 211 91 4 N/A ol&lololol I THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR I: IC,_...,..°',,_. of ttw fo/Jow/ngl 1111 OPERATING N

I 20.4061cl 60.731all21Pvl 73.711bl 20.4021bl MOOE 181 20.4061all1 IOI 60.381cll11 - 60.731all21M -* 73.711*1

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60. 7 31aH2HviiiHBI 60.731all21bcl below Incl tn Text, NRC Form 388AI LICENSEE CONTACT FOR THIS LER 1121 NAME TELEPHONE NUMBER Barry N. Young, Staff Licensing Engineer COMPLETE ONE LINE FOR EACH COMPONENT FAILURE DESCRIBED IN THIS REPORT 1131 MANUFAC* REPORTABLE MANUFAC* REPORTABLE CAUSE SYSTEM COMPONENT TURER TO NPROS CAUSE SYSTEM COMPONENT TURER TO NPRDS I I I I I I I I I I I I I I I I I I I I I I I I I I I I

- SUPPLEMENTAL REPORT EXPECTED 1141 MONTH DAY YEAR EXPECTED

- - - , YES IJfYN. _,,,,.,,. EKPECTED SVBMSSIONOATEI -""Fxl NO SUBMISSION DATE 1161 I I I ABSTRACT (L.4onlr ID 1400 _ .. i.*.* -~II'-~- fYP9WritfM h*I 1181 On February 17, 1994, at 1538 hours0.0178 days <br />0.427 hours <br />0.00254 weeks <br />5.85209e-4 months <br />; with the plant operating at 100% power, an accumulation of boric acid on the valve body of check;valve CK-ES3166 was confirmed to be caused by a through wall defect. The 24-inch austenitic stainless steel check valve is located between the containment sump and the suction piping for one train of Engineered Safeguards System (ESS) pumps. The check*valve is considered an ASME, Class 2 component in the Section XI program. The valve was declared inoperable. A Plant shutdown was initiated at 1634, February 17, 1994 and the plant was taken to cold shutdown.

Inspection of the comparable ch~ck valve in the other ESS train~ CK-ES3181, identified indications of a similar nature in the casting of that valve.

The cause of this event was a through wall defect in the body of an ASME, Class 2, check valve, CK-ES3166, due to .preferential corrosion at the grain boundaries in a weld repaired region of the valve casting. The code does not.allow operation of an ASME Class 2 component with a through wall leak.

Corrective action for this event.will be the repair of both check valves, CK-ES3f66 and CK-ES3181.

NRC Form 388A U.S. NUCLEAR REGULATORY COMMISSION (9*831 APPROVED OMB NO. 3.160-0104 EXPIRES: 8/31 /86 LICENSEE EVENT REPORT (LERI TEXT CONTINUATION FACILITY NAME 111 DOCKET NUMBER 121 LER NUMBER 131 PAGE (41 SEQUENTIAL REVISION YEAR NUMBER NUMBER Palisades Plant 0 I 5 I0 I0 I0 I2 I5 I5 9 I4 - 0 I 0I 6 - 0 I0 0 I2 OF 0 I5 EVENT DESCRIPTION On February 17, 1994, at 1538 hours0.0178 days <br />0.427 hours <br />0.00254 weeks <br />5.85209e-4 months <br />, with the plant operating at 100% power, an accumulation of boric acid on the valve body of check valve CK-ES3166 [BQ;ISV] was confirmed to be caused by a through wall defect. The 24-inch austenitic stainless steel check valve is located between the containment sump [BP;ISV] and the suction piping for one train of Engineered Safeguards System (ESS) pumps. The check valve is considered an ASMEJ Class 2 compohent in the Section XI program. The valve was declared inoperable because the Code does not allow operation of a Class 2 component with a through wall leak. A Plant shutdown was initiated at. 1634; February 17, 1994 and the plant was taken to cold shutdown.

Inspection of the comparable check valve in the other ESS train, CK-ES3181, identified indications -0f a similar nature in the casting of that valve.

This event is reportable to the NRC in accordance with 10CFR50.73(a)(2)(i)(A) as the completion of a nuclear plant shutdown required by the plant's technical specifications.

CAUSE OF THE EVENT The.cause of this event was a through wall defect in the body of an ASME, Class 2, check valve, CK-ES3166, due to preferential corrosion at the grain boundary in a weld repaired region of the valve casting. The valve.b~dy material in the area of the defect had been ~

extensively sensitized as it is in the heat affected zone of a number of welding operations that have been performed on the valve. This sensitization at the grain boundary followed by intergranular corrosion caused the leak to surface. A possible contributor to the leak going through wall was that it could have traveled along an existing defect to go entirely through wall.

ANAL VS.IS OF THE EVENT CK-ES3166 and CK-ES3181 are*Chapman A351-CF8M 316 Cast Stainless Steel 24-inch tilting disk check valves. They are located in the West and East Engineered Safeguards Rooms, respectively. The valves are part of the Engineered Safeguards Systems (ESS) pumps suction header. The valve inlet flow is from the containment sump, and thus the outlet supplies the ESS pumps following a Containment Sump Recirculation Actuation Signal. The inlets have bolted flanges and the outlets are butt welded to the ESS pump suction*

piping.

• On Monday, February 14, 1994, a dry boric acid deposit was identified on the CK-ES3166 outlet weld. After numerous inspections a boric acid spot about the size of a pen tip was ,observed on Thursday, February 17, 1994. .The spot was roughly 3/4-inch from the toe

q c,

'l NRC Form 388A 19-831 U.S. NUCLEAR REGULATORY COMMISSION APPROVEO OMB NO. 3150-0104 EXPIRES: 8/31185 LICENSEE EVENT REPORT (LERI TEXT CONTINUATION FACILITY NAME 111 DOCKET NUMBER 121 LER NUMBER 131 PAGE 141 SEQUENTIAL . REVISION YEAR . NUMBER NUMBER Palisades Plant 0 I 5 I.0 I 0 I 0 I ? I 5 I 5 9 I4 - 0 I 0 1- 6 - 0 I0 0 I3 OF 0 I5 of the butt weld and was located on the check valve body. Dye penetrant examination results were inconclusive until light hand filing was performed on the suspected area which resulted in positive identification.of a 3/32-inch long defect. The check valve was declared inoperable and plant shutdown was commenced.

The through wall flaw was in a heat affected zone created by casting weld repairs and the adjacent butt weld. The existence of the repair welds was determined during the surface replication and macro etching activities.

Additional inspection of the same area on the second containment sump check valve, CK-ES3181, has revealed subsurface indications that we have con~ervatively decided to repair.

The history_ of the valves is tha't both check valv,es were originally welded into place, but during initial plant startup test (circa 1969) seat leakage problems were identified and the valves were cut out and sent back to the manufacturer for repairs. While at the manufacturer, the internals of the check valves were repaired and weld repairs were made to the buttweld ends of the valves.

The check valves were .returned to the plant and welded into place. The through wall leak on CK-ES3166 and additional NDE determined that indications were present in an area where the valve body had seen significant*prior heat input. Casting weld repairs by the vendor, and two butt weld operations to install the valve (original and following valve removal for seat leakage repaiTs), created a highly sensitized heat altered zone on CK-ES3166. The continuously sensitized grain boundaries near the buttweld pipe connection and valve casting weld repair areas were observed via several surface replications performed on CK-ES3166.

The leak mechanism was determined by non-destructive examination '(NDE) and surface replication metallography. Interpretation of the results indicated that inter-granular corrosion attack was occurring in sensitized weld heat affected zones initiating on the valve inside diameter.

SAFETY SIGNIFICANCE Analysis, based on the methodology' of Appendix C of the 1989 ASME,Section XI, code and the proposed Standard Review Plan 3.6.3, "Leak Before Break Procedures," performed after the flaw had been characterized determined that adequate margin between the Allowable Stress Index (SI) and the ~pplied Stress In_dex (ASl 0 and ASl 8 ) , such that failure of the valve would not occur during a safe shutdown earthquake event. The presence of the through wall defect, although not allowed by code requirements, had no impact on safety.

i l

'~

NRC Form 388A U.S. NUCLEAR REGULATORY COMMISSION

}7 19-831 APPROVED OMB NO. 3150-0104 EXPIRES: 9/31 /85 LICENSEE EVENT REPORT (LERI TEXT CONTINUATION FACILITY NAME 111 DOCKET NUMBER 121 LER NUMBER 131 PAGE 141 SEQUENTIAL REVISION YEAR NUMBER NUMBER Palisades Plant o 5I Io Io Io I2 I 5 I5 *s 14 - o I oI 6 - o Io o 4I oF

• I o s CORRECTIVE ACTION 1 1

Near Term Actions: I li.

Corrective action for this event continues, with the weld repair or replacement of both check valves, CK-ES3166 and CK-ES3181. The ASME Code Case N-504-1, "Alternate Rules For Repair of Class 1, 2, and 3 Austenitic Stainless Steel Piping,Section XI, Division l,"

is being used to repair the valves. We have r~quested and received approval for the use of this Code Case from the NRC.

VT-2 examinations on both containment sump outlet valves and both SIRW tank outlet valves revealed no additional boric acid deposits or leaks of the pressure boundary material.

VT -2 examinations were also completed on 18 similar cast.stainless steel butt welded valves in the -ESS system to determine the existence of any similar boric acid buildup on welded ends. No additional indications .were observed.

Longer Term Actions: '.

Review the importance of reporting observed conditions which could indicate through wall leakage of components with those personnel who perform system walkdowns.

Assess existing.welding practices to ensure that controls exist to minimize sensitization of stainless steel components and the resulting long term intergranular corrosion.

Revise the Palisades Augmented Inspection Progr~m to include periodic examinations required for code case N-504-1 repairs on valves CK-ES3166 and CK-ES3181.

Develop a ranked list of valves with similar intergranular corrosion {IGC} susceptible welds and develop actions to inspect and evaluate higher risk components for existence of IGc*defects. *

• If CK~ES3166 or CK-ES3181 is removed d~ring the 1995 REFOUT, perform further metallurgical examinations of weld areas to further characterize the through wall flaw and other nondestructive examination indications.

Perform destructive examinatfons on similarly susceptible valves that are removed for replacement in 1994 or 1995 to determine further existence of _intergranular attack in heat-affected zones.

Use the Tesults of *planned inspections on CK-ES3181 and CK-ES3166 and other IGC inspections on Palisades' valves to develop a programmatic control mechanism to prevent excessive repairs on components that could lead to excessive sensitization.

NRC Form 388A U.S. NUCLEAR REGULATORY COMMISSION

~ 18-831 AP!'ROVED OMB NO. 3160-0104 r EXPIRES: 8/31186 LICENSEE EVENT REPORT (LERI TEXT CONTINUATION FACILITY NAME 111 DOCKET NUMBER 121 LER NUMBER 131 PAGE 141 SEQUENTIAL REVISION YEAR NUMBER NUMBER Palisades Plant I 0 I 5 I0 I0 I0 I2 I5 I5 9 I4 - 0 I0I6 - 0 I0 0 I5 OF 0 I5 ADDIT~ONAL INFORMATION The details of the valve defects, the associated analyses, and a root cause analysis are contained in a M~rch 6, 1994 Consumers Power Company letter to the NRC entitled, "Code Case N-504-1 Update Approval For Leak Repair 6f Containment Sump Check Valves."