05000271/LER-1993-005
| ML20056D941 | |
| Person / Time | |
|---|---|
| Site: | Vermont Yankee  |
| Issue date: | 08/13/1993 |
| From: | Wanczyk R VERMONT YANKEE NUCLEAR POWER CORP. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| LER-93-005, LER-93-5, NUDOCS 9308190039 | |
| Download: ML20056D941 (5) | |
| Event date: | |
|---|---|
| Report date: | |
| 2712093005R00 - NRC Website | |
text
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NERMONT YANKEE N'UCLEAR -POWER CORPORATION
~ .
h ' -] P O. Box 157, Governor Hunt Road 4 (' 9 ..:
Vernon, Verrnont 05354-0157 (802) 257-7711 i
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August 13, 1993 U.S. Nuclear Regulatory Commission Document Control Desk '
Washington, D.C. 20555
REFERENCE:
Operating License DPR-28 f Docket No. 50-271 Reportable Occurrence No. LER 93-05, Supplement 1 i
Dear Sire:
As defined by 10 CFR 50.73, we are reporting the attached Reportable ;
Occurrence as LER 93-05, Supplement 1. l t
Very truly yours, VERMONT YANKEE NUCLEAR POWER CORPORATION I
, d lc' A ~ / d Q :
p Robert J. Wanczyk Plant Manager 1
cc: Regional Administrator l USNRC <
Region I l 475 Allendale Road l King of Prussia, PA 19406 !
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17002G 9308190039 930913 o /
PDR ADOCK 05000271 E /'e S PDR f G \
1
- WRC Forp 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED OMS No. 3150-0104
. (6-89) EXP12ES 4/30/92 ,
ESTICtATED BURDEN PER RESPONSE TO CD4 PLY WITH THIS
]NFORMATION COLLECTION REQUEST: 50.0 HRS. FORWARD 1 COMMENTS REGARDING BURDEN ESTIMATE TO THE RECORDS AND REPORTS MANAGEMENT BRANCH (P-350), U.S. NUCLEAR REGULATORY COMMISSION, WASHINGTON DC 20555, AND 10 THE PAPERWORK REDUCTION PROJECT (3160-0104), OFFICE OF MANAGEMENT AND BUDGET, WASHINGTON, DC 20603.
1 FACILITY WAME (1) DOCKET NO. (2) PAGE (3)
VERMONT YANKEE NUCLEAR PO4 R STAT]ON Ol5l0l0l0l2l7l1 0 1 0F 0 4 TITLE (4) CONTROL ROD DRIVE SCRAM TIMES GREATER THAN THAT REQUIRED BY TECHNICAL SPECIFICATIONS DUE TO SCRAM SOLENDID I
PILOT VALVE COMPONENTS, SUPPLEMENT 1.
i EVENT DATE (5) LER NUMBER (6) REPORT DATE (7) OTHER FACILtTIES INVOLVED (B)
MONTH DAY YEAR YEAR SEQ # REV # MONTH DAY YEAR FACILITY NAMES DOCKET NO. ($)
0 5 0 0 0 0 4 0 6 9 3 9 3 -
0 0 5 -
0 1 0 8 1 5 9 3 0 5 0 0l0 _
OPERAlikG THIS REPORT IS SUBMITTED PURSUANT TO REQ'MTS OF 10 CFR i: CHECK ONE OR M3RE (11)
MODE (9)
N 20.402(b) 20.405(c) 50.73(a)(2)(iv) 73.71(b) i
< POWER 20.405(a)(1)(1) 50.36(c)(1) 50.73(a)(2)(v) 73.71(c)
LEVEL (10) l6l0 20.405(a)(1)(ii) 50.36(c)(2) 50.73(a)(2)(vil) OTHER:
.... ............. 20.405(a)(1)(lii) X 50.73(a)(2)(1) 50.73(a)(2)(vii i)( A)
.................. 20.405(a)(1)(iv) X 50.73(a)(2)(li) 50.73(a)(2)(viii)(B)
.................. 20.405(a)(1)(v) 50.73(a)(2)(iii) 50.73(a)(2)(x)
LICENSEE CONTACT FOR THIS LER (12) i j NAME TELEPHONE NO.
AREA
, CDDE ROBERT J. WANC2YK, PLANT MANAGER Bl0l2 2l5l7l-l7l7l1l1 COMPLETE ONE LINE FOR EACH COMPONENT FAILURE DESCRIBED IN THIS REPORT (13)
CAUSE SYST COMPONENT MFR REPORTABLE CAUSE SYST CoHPoNENT MFR REPORTABLE TO NPRDS .... TO NPRDS ....
B AlA lFl$lV Al4l9l9 Y .... NA l l l l l l l 4 ....
l A
- l- -j-l-l- -l-l-l+ N WA l l l l l l SUPPLEMENTAL REPORT EXPECTED (14) EXPECTED M3 DAY YR j SUCMIS$10N q DATE (15) j YES (If yes, conplete EXPECTED SU5 MISSION DATE) X NO l l l 1
- ABSTRACT (Limit to 1400 spaces, i.e., approx. fifteen single-space typewritten lines) (16)
On 4/6/93, following Control Rod Dnve scram time testing, it was concluded that the core average scram time and the
- scram times of seven (7) of the 2X2 control rod arrays at notch forty-six (46) were not in compliance with Technical
] Specifications (TS) Section 3.3.C. On 4/6/93, the plant was shutdown due to an unrelated minor leak in the Feedwater System. Subsequent fo!!aw-up investigation into paSt scram time testing revealed that on 10/15/92, the plant should have been shutdown when the *as-found" scram times for one 2X2 array, at notch forty-six (46), was found not to be in comphance with Technical Specifications.
The cause of the slow scram times has been attnbuted to deDraded performance of the Scram Solenoid Pilot Valves (SSPVs). The cause for the failure to comply with TS on 10/15/92 and shutdown the reactor was the result of an incorrect interpretation of a Technical Specification Limiting Condition for Operation.
Following the 4/6/93 shutdown, immediate corrective actions were to rebuild the Scram Solenoid Pilot Valves to address the slow scram times, and to no longer allow the use Of repeated scrams to determine TS compliance. Other a corrective actions included forming a task team to investigate the slow scram times, and a task team to investigate possible j programmatic issues associated with the event.
J t!RC Forn 366 1 (6-89)
ERC Fora 366A U.S. NUCLEA:t REGULATORY {.O N sSloN APPROVED OMS No. 3t50-0104 (6-89) EXPIRES 4/30/92 )
EST! MATED BURDEN PER RESPONSE TO COMPL7 WITH TH15 IkFORMATION COLLECTION REcuEST: 50.0 HRS. FORWARD 1 LICENSEE EVENT FEPORT (LER) COMMENTS REGARDING BURDEN ESTIMATE TO THE RECORDS AND TEXT C0hilWuATION REPORTS MANAGEMENT BRANCH (P-350), U.S. NUCLEAR REGULATORY I CoMM!sSION, WASHINGTON DC 20555, AND TO THE PAPERWORK REDUCTION PROJECT (3160-0104), OFFICE OF MANAGEMENT AND BUDGET, WASHINGTON, DC 20603.
FACILITY KAME (1) DOCKET NO (2) LER WUMBER (6) PAGE (3)
YEAR SEQ # REV #
VERMONT YANKEE NUCLEAR POWER CoRPORAT!oN 0l5j0l0j0l2l7l1 9 3 -
0 0 5 -
0 1 0l2 0F 0l4 TEXT (if more space is required, use additional NRC Form 366A) (17)
DESCRIPTIQN On 4/6/93, following Control Rod Drive (Ells = AA) scram time testing, it was concluded that the core average scram time and the scram times of seven (7) of the 2X2 control rod arrays, at notch forty-six (46) (*as found"), were not in compliance with TS Section 3.3.C scram time lirnits. Dunng the course of the 4/6/93 testing, certain control rods were immediately retested and all scram times met the TS requirements. The NRC subsequently granted an Enforcement Discretion for 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br />, beginning at 2200 hours0.0255 days <br />0.611 hours <br />0.00364 weeks <br />8.371e-4 months <br /> on 4/6/93, to preclude a plant shutdown as required by TS. The 48 hour5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> Enforcement Discretion was based on the f act that a new analysis had concluded that a scram time of 0.5 seconds, at notch forty-six (46),
still enveloped the worst case transient which is a turbine trip without bypass valves. On 4/6n3 at 2233 hours0.0258 days <br />0.62 hours <br />0.00369 weeks <br />8.496565e-4 months <br />, a plant shutdown was initiated due to a minor leak in the Feedwater System. Subsequent follow-up investigation into past scram time testing revealed that on 10/15/92 the plant should have been shutdown when the "as-found* scram times fo* one 2X2 array, at notch forty-six (46), was found not to be in compliance with Technical Specifications. The plant did not shutdown as required by TS Section 3.3.F. The control rods in the 2X2 array had been immediately retested and subsequent scram times (*as lef t*
l data I were within the applicable TS Limits. Prior to October 1992 Vermont Yankee's practice had been to allow scram time I retest data (*as lef t* data) to determine compliance with TS.
Following the determination of the slow scram times, a multi-discipline Task Force was formed of individuals from Reactor Engineering, instrument & Control, Mechanical Maintenance, Operations, a lead systems engineer for Control Rod Drive Systems from the General Electnc Co., as well as a representative from the Automatic Switch Co. to investigate the slow scram times and determine the root cause and subsequent necessary repairs. This included a sub-task force to acquire physical data from the Scram Solenoid Pilot Valve components. A second Task Force was also formed of Yankee Nuclear Service Division personnel to investigate any programmatic issues associated with the event.
i CAUSE OF EVENT i The root cause of the slow scram times is the degraded performance of the Scram Solenoid Pilot Valves (SSPVs).
Elastomeric aging during normal plant operation of SSPV subcomponents has been identified as having a direct affect on scram times. The cause of why the SSPV material had not been replaced prior to exhibiting slower than allowed scram times has been attributed to weaknesses in the previous trending program and in the scram timing measurement methodology. These weaknesses were aggravated by the use of as-lef t versus as-found data.
The root cause for the f ailure to comply with TS on 10/15/92 and shutdown the reactor was the result of an incorrect interpretation of a Technical Specification Limiting Condition for Operation.
ABIALYSIS OF EVENT The design basis of the Reactivity Control System is to provide sufficient nuclear reactivity control devices (control rods) to control the excess reactivity in the core and to provide for adjustment of the control rods to permit power generation.
The safety function of the Reactivity Control System, that applies to this event, is to provide sufficient rapid insertion of control rods so that no fuel damage resutts from any abnormal operating transient.
The limiting rtsign transient for this event is a turbine trip without bypass valves. This event was analyzed by the Yankee Nuclear Lrvices Transient Analysis Group using times that exceeded the TS limits. Although the scram times on 4/6/93 were not initially in compliance with TS, (core aversoe notch 46 time was 0.369 seconds (TS limit of 0.358 seconds) and seven of the sixty-eight 2X2 arrays were in the range of 0.380 to 0.418 seconds (TS limit of 0.379 seconds)), the conclusion of the analysis is that no present cycle operating limits would be affected if the notch 46 scram time was 0.5 seconds or less. Additionally, the scram time on 10/15/92 for the one 2X2 array that was nct in compliance with TS was 0.391 seconds, however, this scram time is also enveloped by the conclusion of the analysis.
NRC Form 366 (6-89)
ERC Form 366A U.S. WOCLEAR REcOLATORY CoPCIIS$loN APPROVED OMS Co. 3150-0104 (6-89) EXPlRES 4/30/92 ESilMATED BURDEN PER RESPONSE To COMPLY WITH THIS INFORMAT!oW COLLECT!oW REQUEST: 50.0 HRS, FORWARD LICENSEE EVENT REPORT (LER) COMMENTS RECARDING BURDEN ESTIMATE To THE RECORDS AND . ,
TEXT CONTINUAT!oW REPORTS MANAcEMENT sRANCH (P-350), U.S. NUCLEAR REGULA1oRY i CoMMISSloN, WASHINGTON DC 20555, AND to THE PAPERWORK REDUCT!oW PROJECT (3160-0104), OFFICE OF MANAGEMENT AND BUDcET, WASHINGTON, DC 20603.
1 FACILITY NAME (1) DOCKET NO (2) LER MUMBER (6) PACE (3) 1 YEAR SEQ # REV # i a
VERMoWT YAkKEE NUCLEAR POWER CORPORATloN 0l5l0l0l0l2l7l1 9 3 -
0 0 5 -
0 1 0l3 0F 0l4 j l
TEXT (if more space is required, use additional NRC Form 366A) (17) '
The 4/6/93 testing vwas conducted when the plant was at approximately 60% power. During the evaluation of the scram times the plant was held less than 75% power. The above analysis took into account the operating hmits at 100% !
power. i 1
As the scram times were enveloped by the analyzed times of 0.5 seconds, no safety consequences would have I resulted from the as-found scram insertion times for any operational transients. l Prior to startup, all Scram Solenoid Pilot Valves were rebuilt and the control rods were subsequently retested with j scram tirnes within the TS scram time hmits. i i The practice of using *as lef t" scram time data instead of *as found" data was investigated by an independent task l
[ force from Yankee Nuclear Services Division (YtJSD). Their review of plant records combined with interviews showed that this J approach to control rod surveillance testing had been an accepted practice since the plant began commercial operation in 1972. l 1 This practice had been employed for single rod scram testing during cold hydrostatic conditions as well as when testing at !
l power. The surveillance procedure used to conduct the testing has never specified the use of *as found* or *as lef t* data. The !
j practice of utilizing *as lef t* scram data has been perpetuated over the years through On the Job Training (OJT) within the ;
Reactor & Computer Engineering Department. As-found data was utihred to evaluate the scram times from the October 15, l 1992 scheduled surveillance of the control rod drive system. This will continue to be the methodology utilized at VY. ;
I At no time was there any threat to the health and safety of the pubbc.
CCRRECTIVE ACUONS Immediate Corrective Actions I l
- 1. Following the e/6/93 testing the data was evaluated to assess the safety significance of the event
!. and discussions were initiated with the NRC Concerning Enforcement Discretion. j a
Intermedete Corrective Actions I 1
4
- 1. Following the plant shutdown for the minor leak in the feedwater system, the immeciate actions were
! as f ohows:
- a. Two tasks teams were forrr ed, one to evaluate the slow scram times, and one to investigate i i
possible programmatic issues associated with failure to comply with TS. A sub-task team y
was also formeu to specihcally investigate the physical condition of the Scram Solenoid Pilot !
3 Valve components to determine the root cause and review previous test data. ,
e
- b. All 178 Scram Solenoid Pilot Valves were rebuilt with new component parts prior to plant startup. >
! 2. Cold hydrostatic tests of all 89 control rods were performed to ensure full compliance with TS.
l
- 3. Following plant startup, single rod scram testing was performed on 100% of the rods. Using *as !
found" data, the results were within TS hmits. f
- 4 The results of the scram time testing performed in June 1993 were compared to those times measured following the May SSPV rebuild and no degradation in scram times had occurred. !
]
tfRC Form 366 (6-89) .
b 4 i i
02C Forts 366A U.S. NUCLEAR REGULATORY COMMISSION APPSOVED OMS No. 3150-0104 (6 89) EXPIRES 4/30/92 EST! MATED BURDEN PER RESPONSE TO COMPLT WITH THIS INFORMATION COLLECTION REQUEST: 50.0 HRS. FORWARD LICENSEE EVENT REPORT (LER) COMMENTS REcARDING BURDEN ESTIMATE To THE RECORDS AND
- TEXT CONTINUATION REPORTS MAAACEMENT BRANCH (P-350), U.S. NUCLEAR REGULATORY COMMISSION, WASHINGTON DC 20555, AND TO THE PAPERWDRC REDUCTION PROJECT (3160-C104), of FICE OF MANAGEMENT AND BUDcET, WASHINGTON, DC 20603.
FACILITY NAME (1) DOCKET WO (2) LER NUMBER (6) Pact (3)
YEAR SEQ # REV #
9 0 0 VERMONT TANKEE NUCLEAR POWER CORPORAT!oN 3 5 0 1 0l4 0F 0l4 0l5l0l0l0l2l7l1 TEXT (if more space is required, use add:tional NRC Form 366Al (17)
- 5. The removed component parts of several of the Scram Solenoid Pilot Valves wer) sent to General Electric for further analysis to identify the root cause for the slow scram times, this report has been completed.
- 6. A memo was issued from the Plant Manager requiring all departments involved in TS surveillances to evaluate their current assessment practice to ensure margins to limits are monitored and maintained.
- 7. The Control Rod Scram Testing and Data Reduction Procedure OP 4424 has been revised to include the following improvements:
- a. Incorporation cf improved testing methodology as recommended in the YNSD Corrective Action Report, this includes clarification relative to utilging *as-found" versus *as-lef t* data.
- b. Inclusion of human f actor improvements.
- c. Performance of an administrative review of scram time test data, and the preparation of a CRD System Evaluation Report.
- 8. A Nuclear Network entry has been made summarizing this event to the industry.
Lono Term Corrective Actions
- 1. Vermont Yankee is in the process of incorporating significant changes for performance trending into the Control Rod Scram Testing and Data Reduction Procedure, these changes are scheduled to be completed by 9/24/93. In conjunction with the procedural improvements, the use of historical data and the development of an improved computer based trending program will result in an enhanced trending / performance monitoring program, changes are scheduled to be completed by 7/23/94.
- 2. Technical Specifications section 3.3 is being reviewed to determine if enhancements should be made to remove ambiguity. Based upon the results of the review, Technical Specification revisions may be suomitted, this activity is scheduled to be completed by 10/1/93.
- 3. Administrative Technical Specification Limits for the scram time setpoints will be established and included in OP 4424. These setpoints are currently in review and scheduled for completion by 9/24/93.
4 All personnel who interf ace with Technical Specifications section 3.3 (Control Rod Drive System) will receive training on this issue by 12/31/93.
- 5. In 1994 a self assessment will be performed to evaluate the corrective actions implemented relative to the scram timing issue and confirm that adequate response has been taken to preclude recurrence, this is scheduled to occur by 10/1/94.
ADDITIONAL INFORMATION No similar events have been reported to the Commission in the last five years.
The Scram Solenoid Pilot Valves that were rebui!1 are ASCO Model HVA 90-405 2A (Ells =FSV)
ERC Fora 366 (6-29)
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