Part 21 Report - 1997-872

 
 

ACCESSION #:  9711040085

                       LICENSEE EVENT REPORT (LER)



FACILITY NAME:  River Bend Station                        PAGE: 1 OF 6



DOCKET NUMBER:  05000458



TITLE:  Cracked Emergency Diesel Generator Valve Adjusting Screw

        Assembly Swivel Pads



EVENT DATE:  09/26/97   LER #:  97-007-00   REPORT DATE:  10/23/97



OTHER FACILITIES INVOLVED:                          DOCKET NO:  05000



OPERATING MODE:  5   POWER LEVEL:  0%



THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR

SECTION:

50.73(a)(2)(v), 50.73(a)(2)(vii), OTHER: 10 CFR 21



LICENSEE CONTACT FOR THIS LER:

NAME:  D.N. Lorfing, Supervisor - Licensing TELEPHONE:  (504) 381-4157



COMPONENT FAILURE DESCRIPTION:

CAUSE:  B   SYSTEM:  EK   COMPONENT:  CPLG MANUFACTURER:  C634

REPORTABLE NPRDS:  N



SUPPLEMENTAL REPORT EXPECTED:  NO



ABSTRACT:



On September 26, 1997, at 1715 hours, with the plant in mode 5

(refueling) and the reactor at 0% power, the Division I (Div II) and

Division II (Div II) emergency diesel generators (EDGs) were declared

inoperable.  Multiple valve adjusting screw assembly swivel pads

(VASASPs) in the Div I EDG were found to be cracked, and was attributed

to a manufacturing defect.  Although the EDG would have been able to

start and run following a loss of offsite power, an engineering

evaluation conservatively postulated that in the event of a gross failure

of the VASASP, the EDG may not have be able to run for the 30 days

assumed in the accident analysis.  Since the VASASPs in both the Div I

and the Div II EDGs were manufactured from the same material lot, the

condition was suspected to exist in both EDGs.  Subsequent inspection of

the Div II EDG on September 28, 1997, confirmed that four VASASPs were

cracked.  Based on the results of this inspection, the condition was

reported at 1000 hours pursuant to 10 CFR 50.72(b)(2)(iii) as a condition

which alone could have prevented the fulfillment of a safety function.

This report is submitted pursuant to 10 CFR 50.73(a)(2)(v).  Because the

same manufacturing defect caused the VASASP cracks in both EDGs, this

event is also reportable pursuant to 10 CFR 50.73(a)(2)(vii).  Core

alterations were suspended while both EDGs were inoperable, and the

VASASPs in the Div I and Div II EDGs were replaced with improved

components.  VASASPs removed from the two EDGs will be returned to the

vendor for analysis.  A review of the vendor's failure analysis report

will be performed to determine the need for additional corrective

actions.  Because the EDGs did not experience a gross failure of the

VASASPs, the safety significance of this event is considered low.



END OF ABSTRACT



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Reported Condition



On September 26, 1997, at 1715 hours, with the plant in mode 5

(refueling) and the reactor at 0% power, the Division I (Div I) and

Division II (Div II) emergency diesel generators (EDGs) (EK) were

declared inoperable.  Multiple valve adjusting screw assembly swivel pads

(VASASPs) (CPLG) in the Div I EDG were found to be cracked, and was

attributed to a manufacturing defect.



The valve adjusting screw assembly (VASA) is a threaded screw which

allows a fine adjustment of the valve clearance or lash.  The VASA

transmits the rocker arm motion to the valve stem, thereby opening and

closing the intake and exhaust valves at the specified timing.  At the

base of the VASA, where it meets the valve stem, is the VASASP.  The

VASASP is a mushroom-shaped socket which connects to the VASA.  The

VASASP rotates and tilts on the ball end of the VASA in order to keep

itself properly aligned with the valve stem through the cyclic motion of

the rocker arm (see Figure I for a photograph of a VASA).



Although the EDG would have been able to start and run following a loss

of offsite power, an engineering evaluation conservatively postulated

that in the event of a gross failure of the VASASP, the EDG may not be

able to run for the 30 days required by the accident analysis.  Since the

VASASPs in both the Div I and Div II EDGs were manufactured from the same

material lot, the condition was suspected to exist in both EDGs.

Subsequent inspection of the Div II EDG on September 28, 1997, confirmed

that four VASASPs were cracked.  Based on the results of this inspection,

the condition was reported at 1000 hours pursuant to 10 CFR

50.72(b)(2)(iii) as a condition which alone could have prevented the

fulfillment of a safety function of a system required to mitigate the

consequences of an accident.  This report is submitted pursuant to 10 CFR

50.73(a)(2)(v).  Because the same manufacturing defect caused the VASASP

cracks in both EDGs, this event is also reportable pursuant to 10 CFR

50.73(a)(2)(vii) as an event where a single cause or condition caused two

independent trains or channels to become inoperable in a single system

designed to mitigate the consequences of an accident.



Investigation



On September 15, 1997, at 2359 hours, during an inspection of the Div I

EDG, the VASASP for the cylinder number 5 exhaust valve was found to be

cracked.  Other Div I EDG VASASPs were inspected and no additional cracks

were found.  A metallurgical analysis determined that the failure of the

VASASP was due to a high strength, low toughness material being subjected

to a low magnitude impact in the presence of a notch.  The cracked VASASP

was replaced.  Following a post-maintenance run of the Div I EDG on

September 26, 1997, at 0830 hours, two additional cracked VASASPs were

identified.  Both the Div I and the Div II EDG were declared inoperable

at 1712 hours, on September 26, 1997.  The VASASPs on the Div I EDG were

replaced with improved assemblies.  The Div I EDG was tested and returned

to operable status at 1544 hours on September 27, 1997.



TEXT                                                          PAGE 3 OF 6



The Div II EDG was inspected on September 28, 1997, at 0959 hours and

four additional valves were found to have cracked screw assembly swivel

pads.  VASASPs on the Div II EDG were replaced on October 1, 1997, with

improved assemblies, and the EDG was returned to operable status.



The cracked VASASPs were material lot number VV64 with 1F26 screws.  The

vendor (Cooper-Enterprise) stated that lot VV64 swivel pads had waivers

for discrepancies identified during the manufacturing process.  The

waivers had been dispositioned within the vendor's 10 CFR 50, Appendix B

program prior to the material's shipment to River Bend Station (RBS).

The vendor indicated that, among other discrepancies, the material was

harder than specifications allowed.  RBS examined questionable VASASPs

removed from service, using liquid dye penetrant.  A total of ten cracked

VASASPs were found, each with a 1F26 screw and a lot VV64 swivel pad.

Forty-five of the 64 VASASPs removed from service were of this

configuration; none of the remaining VASASPs (with different

configurations) experienced any cracks.  The cracks were confined to the

upper or swaged area of the VASASP.  No VASASP cracked to the point of

being unrestrained by the adjusting screw.



Root Cause



The root cause of this event is a manufacturing defect.  Specifically,

the swivel pad portion of the VASASP (which forms the socket portion of a

ball-and-socket joint) was over-swaged (rolled) around the VASASP

adjusting screw.  The over-swaged condition made the joints too tight and

restricted motion of the assemblies, resulting in small impacts as the

valves were opened.



Two additional contributing causes were identified, as follows:



o    The VASASPs were manufactured from an inappropriate material.  The

     VASASPs should be manufactured from AISI 8620.  The VASASPs removed

     from service were manufactured from a material equivalent to

     SAE/AISI 8660, which is harder and more brittle than 8620.



o    The ball portion of the VASASP adjusting screw (which forms the ball

     portion of a ball-and-socket joint) was machined incorrectly.  The

     ball should be machined smooth.  The adjusting screws removed from

     service exhibited a machined cutback around the horizontal

     centerline of the ball.  This cutback formed an edge that was

     cutting a groove into the upper area inside of the swivel pad.



These three factors, combined, are judged to have caused the VASASPs to

crack.  Because the VASASP could not travel freely through its required

range of motion, the adjusting screw would strike the swivel pad at the

edge of the swaged area.  This repetitive impingement on the swivel pad

caused cracks to initiate at the groove cut by the improperly machined

screw (second contributing cause, above).  The cracks were brittle

fractures due to the high strength, low toughness material used in the

manufacturing process.



Previous Occurrences



No other cracking of the VASASPs has been experienced at RBS.



TEXT                                                          PAGE 4 OF 6



The VASASPs have been previously replaced because of abnormal wear of the

valve stems.  The VASASPs in both the Div I and Div II EDGs were replaced

in April 1994.  The abnormal wear was attributed to the design of the

VASA.  The vendor redesigned the VASASP by enlarging the base of the

swivel pad, and the new models were installed.



Corrective Actions



Core alterations were suspended while the two EDGs were inoperable.



The VASASPs in the Div I and Div II EDGs were replaced with new

components.  The vendor informed RBS that the replacement VASASPs were

manufactured from SAE/AISI 8620 material.  The vendor also stated that

the adjusting screws were visually inspected by the vendor to ensure

there were no sharp edges on the ball, and that the swivel pads were

manufactured with a special tool that precludes over-swaging.  The

replacement VASASPs were functionally inspected by extending the ball

joint and rotating the joint by hand.  The VASASPs exhibited proper range

of motion which was smooth and even, indicating no sharp edges or over-

swaging.



The VASASPs removed from the two EDGs will be returned to the vendor for

analysis, by October 31, 1997.  RBS management will review the vendor's

failure analysis report to determine if additional corrective actions are

needed.  Entergy Operations will monitor the vendor initiatives to ensure

effective corrective actions for the nonconformances and generic

implications identified through the investigation of this event.  These

will both be completed by April 30, 1998.



Safety Significance and Implications



The as-found condition of the VASASPs did not affect the past operation

of the EDGs.  In all of the observed cracks, the swivel pads remained

fixed to the adjusting screws.  The cracks in the swivel pads were not

360 degree circumferential cracks.  It is reasonable to expect that the

EDGs could have started at least one additional time without causing the

adjusting screws and the swivel pads to become disengaged.  Although

brittle fracture of the upper region of the VASASPs could cause small

pieces of metal to break off, the small pieces would be carried through

the cam region and into the oil sump of the EDG.  A protective screen in

the oil sump and an oil filter and oil strainer in the pump discharge

line protect the vital engine components from foreign material.  Thus,

the EDGs would have been able to mitigate the immediate consequences of

an accident.  The EDGs did not experience a gross failure of the VASASPs,

and so the safety significance of this event is considered low.



While RBS did not experience a complete failure of the VASASPs, it is

postulated that under highly unlikely conditions, the swivel pads could

fail.  The swivel pads could become disengaged from the adjusting screws

as a result of the brittle fracture of the upper region.  If the valves

were to open out of sequence, the existing clearances and rocker arm

motion would not prevent the unrestrained VASASPs from being displaced

off of the top of the valve stem.  This could possibly impact the 30-day

post-accident operation of the EDG.



TEXT                                                          PAGE 5 OF 6



Additional Information



The Div I and the Div II EDGs are both Transamerica Delaval, Incorporated

(TDI) model Delaval-DSR 48.



Note: Energy Industry Identification codes are identified in the text as

(*XX*)



TEXT                                                          PAGE 6 OF 6



Figure 1.  "Photograph of a Valve Adjusting Screw Assembly"



ATTACHMENT TO 9711040085                                      PAGE 1 OF 2



                                   Entergy Operations, Inc.

                                   River Bend Station

                                   5485 U. S. Highway 61

                                   P.O.  Box 220

Entergy                            St.  Francisville, LA 70775

                                   Tel 504 336 6225

                                   Fax 504 635 5068



                                   Rick J.  King

                                   Director

                                   Nuclear Safety & Regulatory Affairs



October 23, 1997



U. S. Nuclear Regulatory Commission

Document Control Desk, OP1-17

Washington, DC 20555



Subject:  River Bend Station - Unit 1

          Docket No. 50-458

          License No. NPF-47

          Licensee Event Report 50-458/97-007-00



File Nos.  G9.5, G9.25.1.3



RBG-44275

RBF1-97-0400



Ladies and Gentlemen:



In accordance with 10CFR50.73, enclosed is the subject report.



Sincerely,



RJK/BFT/bft

enclosure



ATTACHMENT TO 9711040085                                      PAGE 2 OF 2



Licensee Event Report 50-458/97-007-00

October 23, 1997

RBG-44275

RBF1-97-0400

Page 2 of 2



cc:  U.  S.  Nuclear Regulatory Commission

     Region

     IV 611 Ryan Plaza Drive, Suite 400

     Arlington, TX 76011



     NRC Sr.  Resident Inspector

     P.  O.  Box 1050

     St.  Francisville, LA 70775



     INPO Records Center

     700 Galleria Parkway

     Atlanta, GA 30339-3064



     Mr.  G.  Dishong

     Public Utility Commission of Texas

     1701 N.  Congress Ave.

     Austin, TX 78711-3326



     Louisiana Department of Environmental Quality

     Radiation Protection Division

     P.  O.  Box 82135

     Baton Rouge, LA 70884-2135

     ATTN.: Administrator



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