Part 21 Report - 1998-154

 
 

ACCESSION #: 9804270179



               South Carolina Electric & Gas Company   Gary J. Taylor

               P.O. BOX 88                             Vice President

               Jenkinsville, SC 29065                  Nuclear Operations

               (803) 345-4344

SCE&G

A SCANA Company               April 17, 1998

                              RC-98-0076



Document Control Desk

U. S. Nuclear Regulatory Commission

Washington, DC 20555



Gentlemen:



Subject:  VIRGIL C. SUMMER NUCLEAR STATION

          DOCKET NO. 50/395

          OPERATING LICENSE NO. NPF-12

          FINAL REPORT PURSUANT TO 10 CFR PART 21 (SSH 98-002)



Ref: (a)  Gary J. Taylor to Document Control Desk, RC-98-0045 dated March

          02, 1998.

     (b)  Darryl Hartley, Engine Systems, Inc. to George Robertson,

          SCE&G, 702115 dated March 18, 1998.



This final report for the potential 10 CFR Part 21 reportable issue

regarding the "A" Diesel Generator EG-B for the Virgil C. Summer Nuclear

Station (VCSNS) is submitted as a followup to reference (a), pursuant to

the requirements of 10 CFR 21.21(a)(2).  The results of the additional

troubleshooting and cause determination are attached.



The vendor provided their response to VCSNS on 3/18/98 (Ref (b)).  This

evaluation concludes that the failure of the EG-B unit is not reportable

under 10 CFR Part 21.



Should you have any questions, please call Mr. Michael J. Zaccone at

(803) 345-4328.



                              Very truly yours,



                              Gary J. Taylor



GJT/mjz



Enclosure



c:   Distribution



                NUCLEAR EXCELLENCE - A SUMMER TRADITION!



Document Control Desk

RC-98-0076

SSH 980002

Page 2 of 2



Distribution



     J. L. Skolds                  D. L. Abstance

     W. F. Conway                  R. J. Waselus

     R. R. Mahan                   R. L. Osborne

     R. J. White                   G. A. Robertson

     L. A. Reyes                   J. B. Knotts Jr.

     L. M. Padovan                 NRC Resident Inspector

     R. B. Clary                   INPO Records Center

     M. F. Miltner                 J & H Marsh & McLennan

     A. R. Koon                    NSRC

     G. E. Williams                RTS (SSH 980002)

     T. L. Matlosz                 Files (818.18)

     B. C. Williams                DMS (RC-98-0076)

     P. Ledbetter



Attachment to Document Control Desk

RC-98-0076

SSH 980002

Page 1 of 2



The Woodward governor hydraulic actuator (EG-B) unit was sent to Power

Control Services of Engine Systems Inc. for an as-found evaluation and

refurbishment following the speed oscillations which occurred during

surveillance testing on 12/30/97.  An interim report for 10 CFR Part 21

reportability was necessary due to additional troubleshooting and cause

determination efforts for this hydraulic actuator.



Speed oscillations occurred on the "A" diesel generator after opening the

DG output breaker during surveillance testing (STTS#9721373) on 12/30/97.

After extensive troubleshooting, it was determined that these speed

oscillations were due to a problem with the Woodward governor hydraulic

actuator (EG-B) unit.  The EG-B unit was replaced and the oscillations

disappeared.



The EG-B unit (Serial No. 1380933) was sent to Power Control Services

(Woodward representative) for a determination of the cause of the

instability and for refurbishment.



It was initially thought that several nicks found on the lower land area

of the main relay plunger could have caused the instability.  From the

vendor evaluation, the nicks on the land area of the main relay plunger

were a contributor to this problem; however, replacement of this plunger

did not totally resolve the instability in the unit.  Additional research

was conducted to: 1) perform hot bore dimensional checks on the sub-

governor power case, 2) replace parts in the unit to eliminate the

instability, and 3) locate and review the previous repair records for the

unit.



     1) The hot bore checks have been completed on the power case with no

     problems identified.  Also, the EG-B was reassembled using a new

     power case with the old relay plunger and instability was still

     observed.  Additionally, the EG-B was disassembled and reassembled

     several times with a new power case and relay plunger, but the unit

     continued to exhibit instability.



     2) Several other parts including bushings and seals were replaced,

     but the instability was still present.  A replacement subgovernor

     was then built from a core unit and was identical to the original

     design with the exception of installing a new, upgraded ballhead and

     heavy duty buffer springs.  With these changes the unit exhibited

     steadier operation.  The original subgovernor with the upgraded

     ballhead was tested, showing a better response, but the unit still

     exhibited hunting.  The original subgovernor containing both the

     heavy duty buffer springs and the upgraded ballhead was tested

     satisfactorily.



     The vendor stated in reference (b) that there was excessive gain on

     the mechanical part of the governor.  Compensation for the

     instability could only be made by replacement of the original

     ballhead with an updated version and by replacement of the original

     buffer springs with heavy duty ones.



Attachment to Document Control Desk

RC-98-0076

SSH 980002

Page 2 of 2



     3) Previous repair records for the EG-B unit were not located at the

     vendor's facility.  This was attributed to the 1985 repair being

     performed at the Fort Collins, Colorado facility (nuclear units are

     now repaired at the Rocky Mount, North Carolina facility) and to

     computer changes which occurred at Woodward in the early 1990s.



     Plant records indicate that this EG-B had a history of hunting

     problems.  The EG-B (Serial # 1380933) which failed during this

     event had been replaced in 1981, before initial plant criticality.

     Diesel setup and startup testing were occurring at this time, so

     this EG-B did not have any significant operating history.  This EG-B

     was apparently having problems due to hunting, but no additional

     details were documented.  It was stored in the warehouse until

     December, 1985, sent to Woodward for repair, and returned to VCSNS

     in April 1986.  It was again stored in the warehouse until being

     placed in service from 11/11/97 until the 12/30/97 event.



Essentially every subcomponent was inspected and compared against design

specifications, therefore, instability of this EG-B unit was not due to a

defect in design or hardware.  Additionally, this unit was operated and

maintained in the same manner as the other units onsite (which have an

extensive failure-free service history), therefore, this problem was not

due to improper operation or maintenance instructions.  Per discussions

with the vendor, instabilities experienced with EGBs in the past have

been attributable to an identified failure mechanism.  The instability

observed with this specific EG-B is not typical and appears to be an

isolated incident.



In conclusion, this problem appears to be unique to EG-B, Serial #

1380933, and has not been previously observed by the vendor or otherwise

reported by industry events.  Based on the above, the cause of the speed

oscillations has been determined to be a one-time, non-repeatable failure

of the EG-B, and therefore, not reportable under 10 CFR Part 21.



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