ML20248B888
| ML20248B888 | |
| Person / Time | |
|---|---|
| Site: | Vermont Yankee File:NorthStar Vermont Yankee icon.png |
| Issue date: | 05/28/1998 |
| From: | Reid D VERMONT YANKEE NUCLEAR POWER CORP. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| BVY-98-78, NUDOCS 9806020010 | |
| Download: ML20248B888 (11) | |
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VERMONT YANKEE y
NUCLEAR POWER CORPORATION 185 Old Ferry Road, Brattleboro, VT 05301-7002 (802) 257-5271 May 28,1998 BVY 98-78 United States Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555
References:
(a)
Letter, USNRC to VYNPC, NVY 98-35, dated March 11,1998.
(b)
Letter, VYNPC to USNRC, BVY 98-61, dated May 1,1998.
(c)
Generic Letter 91 18, Revision 1.
Subject:
Vermont Yankee Nuclear Power Station License No. DPR-28 (Docket No. 50-271)
Supplement to Letter BVY 98-61, Additional Bases for Maintaining Operation (BMOs) scheduled for final resolution following the 1998 RFO.
Reference (a) documents a meeting between Vermont Yankee and the USNRC to discuss the status of BMOs that were scheduled for final resolution following the 1998 refuel outage (RFO). At that time it was projected that thirteen BMOs would be open at plant start-up.
On May 1,1998, at the NRC's request, Vermont Yankee submitted letter BVY 98-61 (Reference (b)),
l providing information on the ten BMOs that were, at that time, scheduled for final resolution following start-up from the 1998 RFO. Since that time, an additional six BMOs have been scheduleA for resolution j
following the RFO. Two of the six are issues we previously had scheduled to be resolved and four are new issues that we have identified as part of our efTorts to resolve design basis issues.
This letter is being written as a supplement to Reference (b). This letter provides information on the six additional BMOs, in addition to the ten discussed in Reference (b), that are also scheduled for final resolution following start-up from the 1998 refueling and maintenance outage.
l The integrated assessment of the BMOs discussed in hference (b) has been updated to include the
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additional BMOs discussed in this letter. This revised assessment investigated the integrated impact on plant operations personnel and the ability to mitigate design basis events. The methodology included identification of the impact of open BMOs on coincident Design Basis Events including accidents and I
natural phenomena. The assessment examined potential interface issues to ensure there was no impact on the ability to mitigate these events. In summary, the revised integrated assessment did not identify any l
unacceptable interaction or operator action that was found to be impractical. There are no additional manual operator actions required to mitigate design basis events that resuhed from the additional six BMOs.
Based on this, the BMOs planned to be open following the 1998 RFO, as discussed in this letter and in Reference (b), do not impact Vermont Yankee's ability to operate the facility in a safe manner.
. Appendix A provides a summary of the six additional BMOs and the resolution status and schedule. A summary of the Vermont Yankee BMO process was provided in Reference (b).
There are currently sixteen BMOs (including the six BMOs discussed in this letter and the ten BMOs discussed in Reference (b)) scheduled for final resolution following start-up from the 1998 RFO. Vermont Yankee believes that our efTorts to resolve these self-identified issues have been continuous and aggressive since the issues were identified and that the schedule for resolving these issues is consistent with the 9906020010 990529' PDR ADOCK 05000271
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expectations of Reference (c). Since a plant start-up is scheduled shortly, after May 27,1998, Vermont l
Yankee will update the NRC Senior Resident inspector should there be additional changes to the number of BMOs planned to be open at startup.
We trust that the enclosed information is responsive to your request; however, should you have any questions or require additional information, please do not hesitate to contact us.
Sincerely, VERMONT YANKEE NUCLEAR POWER CORPORATION s
Donald A. Reid Senior Vice President, Operations cc:
USNRC Region i Administrator USNRC Resident inspector-VYNPC USNRC Project Manager-VYNPC VT Department of Public Service I
DVY 98-78 May 28,1998 Page 2 0f 2
Vrnuon har Nrcu:An Powr.n CoswouxuoN APPENDIX A BMO SUMMARIES BMO 96-18 " STEAM TUNNEL PRESSURE RELIEF PANELS
DESCRIPTION OF CONDITION In December 19%, while performing a reconstitution of the High Energy Line Break (HELB) model that l.
supports the Equipment Qualification (EQ) program, Vermont Yankee identified that the model did not account for uncertamtics in the actuation point for some relief panels. He relief panels actuate following Main Steam Line, High Pressure Coolant Injection (HPCI) line, Reactor Core Isolation Cooling (RCIC),
Reactor Water Cleanup (RWCU), or Feedwater line breaks that are postulated to occur in the steam tunnel.
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Further, during an. April 1997 unplanned shutdown, Vermont Yankee used the shutdown as an opportunity i
to obtain as-built data on the relief panels. Analysis was performed and the need for additional field information was identified. Since the areas of the steam tunnel and turbine building required access to obtain field information, the 1998 outage presented the next opporttmity to obtain the necessary field data.
IMMEDIATE ACTIONS TAKEN Upon discovery, the issue was entered into the Event Report (ER) process as ER %-1199. Additionally, BMO %-18 was developed.
Key factors that mitigate this event include:
- 1) Evaluations have been completed using the as-built data obtained during the 1998 outage, to identify the resultant temperature that is expected due to the postulated breaks.
- 2) An assessment of the impact of the resultant temperatures on EQ equipment has been completed and the equipment has been determined acceptable at the higher temperatures (fmal EQ program document changes are still required).
- 3) A modification was made to the facility during 1997 that provides a dedicated pressure relief path for the large Main Steam Line Break (MSLB).
- 4) A dedicated temporary vent path has been identified in the turbine building to mitigate the smaller HPCI and RCIC line breaks and will be implemented as a temporary modification prior to startup.
IMPACT ON OPERATORS Dere are no additional manual operator actions required to mitigate this condition.
This BMO is available in the control room for operator resiew, BASIS FOR DEFFERAL BEYOND 1998 REFUELING OUTAGE (RFO)
Vermont Yankee does not view the 1998 RFO as an opportunity to fully resolve this issue.
This BMO was planned for closure prior to stant-up from the 1998 RFO, however, as part of the final closcout, additional inspections and evaluations were detennined to be required. %csc additional
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inspections and evaluations identified additional issues requiring resolution that have impacted the ability to fully resolve this BMO prior to start-up.
APPENDIX A BVY 98-78 Page I of 9
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Venuov Y.mn Nrcuan l'owm Com onwos BMO 96-18 " STEAM TUNNEL PRESSURE RELIEF PANELS" (continued)
- Ihese additionalissues include:
- 1) Concems were identified about the effects (resultant temperature increase) of smaller line breaks (i.e.,
HPCI and RCIC) that do not immediately isolate. The effects of these breaks were determmed to be more limiting than the MSLB and additional dedicated temporary venting capacity was required.
Additional time will be required to install permanent modifications such that this issue can be resolved.
- 2) The inspections identified concems about the structural load carrying capabilities of additional components (back draA damper in HVAC ducts) and the analysis needs to be finalized.
- 3) Resultant EQ documentation cannot be fully updated prior to completion of the analyses.
Based on the information obtained during the 1998 RTO, complation nf the required analysis and a resultant permanent plant modification, as necessary, are required to fully reso!ve this issue. These conditions do not pose an operability concern since the current BMO is based on the actual field conditions identified during the 1998 RFO.
ACTION PLAN FOR FINAL RESOLUTION / CURRENT SCHEDULE
'Ihe current plan for final resolution is to complete the required analysis, finalize the EQ program changes and detennine the scope of the resultant design change.
Vermont Yankee plans to complete the required analysis and determine the scope of any required modifications by August 1998.
Ifit is determined that the required modifications can be performed with the plant operating, they will be completed by January 1999. If the resultant modification is determined to require the plant to be shutdown, it will be installed prior to start-up from tiu: 1999 RFO.
APPENDIX A BVY 98-78 Page 2 of 9
Vanum Y.mi.r. Nrcu:.Au l'own:n Commxium BMO 97-58 " SERVICE WATER STRAINERS" DESCRIPTION OF CONDITION In November 1997, while performing ultrasonic inspections of the station Service Water System strainer shells, localized pitting below the code minimum wall thickness was noted. nese inspections are performed as part of Vermont Yankee's Senice Water System monitoring program to identify these types of conditions and initiate repair efforts.
His BMO was initially scheduled for closure based on the as is condition being considered acceptable, however, upon reevaluation, it was considered more conservative to leave the BMO open until the scheduled maintenance effont is completed.
IMMEDIATE ACTIONS TAKEN Upon discovery, the issue was entered into the Event Report process as ER 97-1645. Additionally, BMO 97-58 was developed.
Key factors that mitigate this event include:
- 1) ne impact of the localized wall thinning on structural integrity was evaluated and it was determmed that the structural integrity is not affected.
- 2) Ultrasonic Testing (UF) inspections are being performed on a monthly basis and evaluations of the data have not revealed a substantial degradation since the issue was identified. nese inspections shall continue until the strainer shells are replaced.
- 3) Since cach senice water strainer is designed to pass full senice water flow, one affected strainer could be isolated should a leak occur without impacting the system's ability to perform its design function (s).
- 4) Should minor leakage occur, it is expected to be less than three gpm which is well within system design flow requirements.
- 5) Safety related equipment that could be impacted by spray are protected from tir potential effects of water spray.
j IMPACT ON OPERATORS l
There are no additional manual operator actions or procedure changes required to mitigate this condition.
j This BMO is available in the control room for operator resiew, BASIS FOR DEFFERAL BEYOND 1998 REFUELING OUTAGE (RFO) 1 Vermont Yankee does not view the 1998 RFO as an opportunity to fully resolve this issue.
The current plan for resolution includes the purchase of replacement shells for both of the senice water strainers. These parts are on order and could not be obtained in time for replacement during the 1998 RFO.
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ACTION PLAN FOR FINAL RESOLUTION / CURRENT SCHEDULE The current plan for final resolution is to obtain the required replacement component parts and schedule the
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APPENDIX A BVY 98-78 Page 3 of 9 j:
l V :nm>Ns YAwu Ni cu-:Au iSiwr.n C<>iu <inxinos BMO 97-58 " SERVICE WATER STRAINERS"(continued)
Ifit is deternuned that the required maintenance can be performed with the plant operating, it will be l-completed by January 1999. If the resultant modification is determined to require the plant to be shutdow11, I
it will be installed prior to start-up from the 1999 RFO.
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l APPENDIX A BVY 98-78 Page 4 of 9 l
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1 vi:nuosr vrwi.i:. Ni ci.i.an i'ows:n conronriins BMO 98-01 "HPCI/RCIC VACUUM BREAKERS" DESCRIPTION OF CONDITION 1
In January 1998, while developing the HPCI and RCIC Design Basis Documents, a concern about the l
placement of the installed turbine exhaust line vacuum breakers was noted. It was identified that the HPCI l
and RCIC turbine exhaust lines could be subject to a water hammer when the lines depressurize following i
turbine operation with an elevated drywell pressure. An elevated drywell pressure is expected for some postulated Loss of Coolant Accident (LOCA) conditions.
l During the 1998 outage, a modification to the facility was implemented which resolves this condition.
Additionally, the HPCI and RCIC exhaust check valves, which are now required to meet the requirements of 10 CFR 50 Appendix J, were successfully inspected, refurbished, and tested.
This BMO will remain open to support final closure of all required analysis and paperwork.
IMMEDIATE ACTIONS TAKEN Upon discovery, the issue was entered into the Event Report process as ER 98-0057. Additionally, BMO 98-01 was developed.
Key factors that mitigate this event include:
- 1) During the 1998 outage, a modification to the facility was implemented, which resolves this condition.
Additionally, the HPCI and RCIC exhaust check valves, which are now required to meet the requirements of 10 CFR 50 Appendix J, were successfully inspected, refurbished, and tested. All affected systems, including the modification, will be declared operable prior to startup.
IMPACT ON OPERATORS There are no additional manual operator actions required to mitigate thi; condition.
This BMO is available in the control room for operator resiew.
BASIS FOR DEFFERAL BEYOND 1998 REFUELING OUTAGE (RFO)
Vermont Yankee does not view the 1998 RFO as an opportunity to fully resolve this issue.
The need for a modification was identified just prior to the refueling outage and efforts to fully resolve have been aggressive. A6ditional administrative time is required to support final closure of the required analysis and paperwork.
ACTION PLAN FOR FINAL RESOLUTION / CURRENT SCIIEDULE The current plan for final resolution is to complete the required paperwork and closcout the BMO.
l This BMO is planned to be closed by August 1998.
I APPENDIX A r
BVY 98-78 Page 5 of 9
Vrnuosi Yawn. Nrcu:.ru Powut Com onu.os
.BMO 98-14 " REACTOR BUILDING PRESSURE RELIEF PANELS" DESCRIPTION OF CONDITION In April 1998, during inspections beit.3 performed to support resolution of BMO 96-18," Steam Tunnel Pressure Relief Panels," concerns about the reactor building prercure relief panels, which are assumed in the analysis to relieve at 0.25 psig, were identified. Evaluations have determined that the panels will relieve at a calculated nominal value of 0.47 psig. The 0.25 psig value has been used to support other engineering evalur.tions (i.e., block wall program input).
IMMEDIATE ALTIONS TAKEN Upon discovery, the issue was entered into the Event Report process as ER 98-1013. Additionally, BMO 98-14 will be approved prior to plant start-up.
Since the plant was shutdawn when this i:: sue was discovered, no other immediate actions were necessary.
Key factors that mitigate this event include:
- 1) Evaluations, which have assessed the impact on structural elements (i.e., block walls, doors, etc.), have concluded '.nat the resultant increase in stresses are within code allowances for the components in question.
- 2) ne increased relief setpoint has been used in evaluations to support BMO % *.8 and BMO 98-18,
" Equipment Qualification Temperatures for the HPCI High Energy Line Break," and it has been determined that there is no impact on safety related equipment qualification.
IMPACT ON OPER ATORS There are no additional manual operator actions or procedure changes needed to mitigate this condition.
He BMO is available in the control room for operator resiew.
BASIS FOR DEFFERAL BEYC ND 1998 RFO Vermont Yankee does not vi:r.ne 1998 RFO as an opportunity to fully resolve this issue.
His issue was identified during the 1998 outage and resolution will require significant engineering analysis that will not be completed by start-up. These analysis include finalizing the assessment of the impact on the EQ/HELB program and the Block Wall program.
ACTION PLAN FOR FINAL RESOLUTION / CURRENT SCHEDULE The current plan for final resolution is to complete the required analyses to address this issue and closcout the BMO by September 1998.
APPENDIX A BVY 98-78 Page 6 of 9
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I BMO 98-15 "DRYWELL PRESSURE" DESCRIPTION OF CONDITION In April 1998, during development of the Cycle 20 Reload Design Change Package, a potential for exceeding the calculated por U % containment peak accident pressure was identified. This was due to a recalculation of drywell and wmwel! volumes which resulted in a total contamment volume that was less than that previously identified, as well as a failure to account for the effects of operation in Extended Load i
Line Limit Analysis (ELLLA) conditions.
IMMEDIATE ACTIONS TAKEN Upon discovery, the issue was entered into the Event Repost process as ER 98-1031. A root cause analysis of this issue is being performed and will be factored into the final resolution. A task force has also been fornel to resolve this issue. Additionally, BMO 98-15 will be approved prior to plant start-up.
Since um plant was shutdown when this issue was discovered, no other immediate actions were necessary Key factors that mitigate this event included:
- 1) It is Vermont Yankee's engineeringjudgement that peak post-LOCA containment pressure continues to be within the 44 psig maximum identified in the plant's Technical Specifications and used as a basis for the Appendix J testing. Hisjudgement is based on review of containment re-analysis reports for
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other plants and discussion with the reactor vendor. A number of other Boiling Water Reactors l
(BWRs) have performed power up-rate containment analyses and calculated lower peak contaimnent 1
pressures. De principal conservatism in the original analysis methods is related to the high initial mass flow from the primary system pipe break. Thisjudgement has been validated by a Vermont Yankee specific evaluation perforned using a more realistic contamment analysis methodology that demonstrates that containment peak pressure would be approximately 41-42 psig for Vermont Yankee.
This methodology has been approved by the NRC for similar uses at other plants.
- 2) The FSAR analysis calculating the radiological effects of a Design Basis Accident (DBA) LOCA assumes a leakage from the containment at the design leakage rate for 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />. The actual duration of tie peak pressure following design basis events is on the order of 2 to 3 seconcis (FSAR Figure 14.6-5).
- 3) Here is adequate margin within the existing Icak rate testing program results (10 CFR 50, Appendix J Type A, B and C testing) to account for the maximum possible increase in containment peak accident Pressure
- 4) The potential effect on Mark I containment loads has been evaduated. De predicted increase in loads is small and well within the consenatism of the Mark I prcgram. -
IMPACT ON OPERATORS Dere are r2 additional manual operator actions or operating procedure changes needed to mitigate this condition.
BASIS FOR DEFFERAL BEYOND 1998 RFO Vermont Yankee does not view the 1998 RFO as an opportunity to fully resolve this issue.
This issue was identified during the 1998 outage and resolution will require significant engineering analysis that cannot be completed by start-up. Margin evaluations have concluded that final peak pressure will be APPENDIX A BVY 98-78 l
Page 7 of 9
Vruuosi Yante Nect.Eru Powtu Couron.mos BMO 98-15 DRYWELL PRESSURE"(continued) less than 44 psig. Final resolution includes completing the a'ulysis to verify the final peak contaimnent pressure is below 44 psig.
ACTION PLAN FOR FINAL RF. SOLUTION / CURRENT SCliEDULE This new methodology, once approved, will become part of our licensing basis.
Vermont Yankee plans to discuss use of this methodology with the NRC and establish the tinal methodology in the near ternt Once begun, the new analysis is expected to be completed within approxinutely six months. The final analysis will become the new analysis of record.
'Ile BMO will be closed once the analysis is completed.
I-APPENDIX A BVY 98-78 Page 8 of 9
Wusso n nWI Nmuu l'onu %.oum e*
BMO 98-18 " EQUIPMENT QUALIFICATION TEMPERATURES FOR TIIE IIPCI IIIGII l
ENERGY LINE BREAK" DESCRIPTION OF CONDITION in May 1998, during the development of Reactor Building block wall differential pressure calculations being performed to support resolution of BMO 96-18, it was identified that the resultant post-HELB temperatures for the HPCI Steam Line Break in the torus room were higher than those presiously calculated in a 1984 analysis. 'Ilds has been attributed to modeling changes and upgrades to the facility since 1984.
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IMMEDIATE ACTIONS TAKEN Upon discovery, the issue was entered into the Event Report process as ER 98-1232. Additionally, I
BMO 98-18 will be approved prior to plant start-up.
Since the plant was shutdown when this issue was discovered, ne other immediate actions were necessary.
Key factors that mitigate this event include:
- 1) An evaluation, using the Uchida 1. dysis option (endorsed in NUREG 0588) in RELAP4/ MODS, has determined that actual temperature profiles are acceptable from an equipment qualification standpoint.
The Uchida approach is a more realistic assessment for a steam line break with condensation.
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- 2) Additionally, conservatism in the initial assumptions relative to Reactor Building initial conditions and l
conservative mass and energy release assumptions provide added margin to support operability.
- 3) An assessment of the impact of the resultant temperatures on EQ equipment has been completed and the equipment has been determined to be acceptable at the temperatures shown in the evaluation.
IMPACT ON OPERATORS There were no additional manual operator actions or operating procedure changes needed to mitigate tids condition.
l The BMO is available in the control room for operator resiew.
BASIS FOR DEFFERAL BEYOND 1998 RFO Vermont Yankee does not consider the 1998 RFO as an opportunity to fully resolve this issue.
This issue was identified during the 1998 outage and will require completed analysis and documentation in the Vermont Yankee EQ program manual. His effort will not be completed prior to start-up.
ACTION PLAN FOR FINAL RESOLUTION / CURRENT SCIIEDULE Vermont Yankee plans to complete the required analysis to resolve this issue, update the required documentation, and close tids BMO by January 1999.
l APPENDIX A BVY 98-78 Page 9 of 9 l
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