ML20206P651
| ML20206P651 | |
| Person / Time | |
|---|---|
| Site: | Davis Besse  |
| Issue date: | 06/30/1986 |
| From: | C-E OPERATING PLANTS OWNERS GROUP |
| To: | |
| Shared Package | |
| ML20206P641 | List: |
| References | |
| IEB-85-003, IEB-85-3, PROC-860630, NUDOCS 8607020184 | |
| Download: ML20206P651 (17) | |
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l CE Owners Group Action Plan As a Result of The Davis-Besse Event June 1986 l
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Table of Contents Page A. Background 1 B. Davis-Besse Event Evaluation 3 C. CE0G Davis-Besse Event Action Plan 5 l
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A. Background The Davis-Besse Nuclear Power station experienced a loss-of-main feed-water event on June 9, 1985. As a result of numerous equipment failures and an operator error, the plant experienced a temporary loss of all feedwater. Manual initiation of the startup feedwater pump and the auxiliary feedwater system allowed the plant to be brought to a cold shutdown condition. Subsequent investigation by the NRC indicates that this event was significant. Their findings were published in NUREG-1154.
The NUREG's findings clearly illustrate that equipment failures and human errors contributed to the severity of the Davis-Besse event.
The CE Owners Group (CE0G) agreed at its September, 1985 meeting to form a Review Group for evaluating the Davis-Besse event with respect to its impact on plants with C-E Nuclear Steam Supply Systems (NSSS). The Review Group held its initial meeting on October 29, 1985. The Review Group's objectives were to:
o Review the Davis-Besse event o Determine generic concerns applicable to CE0G plants, and o Develop an action plan to address these concerns The Ruiew Group is composed of the following representatives:
T. Cogburn Arkansas Power & Light - Chairman J. Price Florida Power & Light - Vice Chairman C. Olvera Southern California Edison M. Meisner Louisiana Power & Light J. Reardon Northeast Utilities R. Mehaffey Omaha Public Power District B. Sullivan Baltimore Gas & Electric R. Vosburgh Washington Public Power Supply System P. Nelson Arizona Public Services G. Whittier Maine Yankee Their initial review on October 29, 1985 identified several potential areas of concern for CEOG plants.
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The Review Group met again January 8 - 9, 1986. The Review Group considered in detail the specific NUREG 1154 findings to determine their applicability to CEOG plants. A draft action plan was formulated for those items considered generic to CE0G plants.
The Review Group held its third meeting on March 13-14, 1986. The Review Group revised and finalized the action plan. The final action plan for CE0G plants is contained in Section C of this report.
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B. Davis-Besse Event Evaluation l
This section discussed the inherent design differences of a typical CE0G plant and the Davis-Besse plant. Several major design features favorably affect the NSSS response of a CE0G plant following a total loss of feedwater event.
- 1. Steam Generator Design C-E U-tube recirculating steam generators operate with considerably more secondary water inventory during full power operation than do the once-through steam generators. Minimum boil dry time after a total loss of feedwater event for a CE0G plant is typically 20 minutes, while the boil dry time after a total loss of feedwater event for a plant with once-through steam generators is typically 5 minutes. This additional boil dry time provides an adequate secondary side heat sink to remove decay heat while operators are trying to restore alternate sources of feedwater.
- 2. Reactor Trip on Low SG Level CE0G plants have a reactor trip on low steam generator water level.
For a total loss of feedwater event, the steam generator low level reactor trip occurs very early in the event (approximately 20 seconds after initiation of the event from full power). Reactor Coolant system (RCS) fluid conditions are still within the Reactor Protective System (RPS) temperature and pressure setpoints at time of reactor trip on low steam generator level. This reactor trip scheme terminates reactor power earlier in the event and preserves more steam generator secondary inventory for decay heat removal.
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- 3. Auxiliary Feedwater System Diversity i CE0G plants have AFW systems with diverse power sources. As j recomended by SRP 10.4.9 and BTP-ASB-10-1, CE0G plants have all !
I installed at least one motor driven and one turbine driven AFW pump. i
- 4. AFW Control Logic The automatic AFW activation logic in CEOG plants differs from the i Davis-Besse design. Unlike the Steam and Feed Rupture Control System (SFRCS) employed at Davis-Besse, CE0G AFW automatic activa-tion logic does not allow one operator action to result in a common mode failure of the AFW. Separate operator actions must be taken to manually overide each AFW component.
Sumary There are significant design differences between CE0G plants and Davis-Besse. These design differences ensure that the specific sequence of events that occurred at Davis-Besse could not occur at a CE0G plant.
A major factor identified by this evaluation is that all CEOG plants have a more reliable AFW system than the Davis-Besse design. While the actual design of the ArW system is plant specific, all CEOG plants share comon l design features that would prevent a similar sequence of events from rendering the AFW system inoperable. Diverse pump drivers (at least one l
motor and one turbine) are utilized at all CE0G plants ensuring that they
! are not vulnerable to comon cause failure. Additionally, the AFW actuation controls do not allow a single operator error to terminate all l
AFW flow. Separate, deliberate operator action must be taken to manually override each AFW component. These two features make it highly unlikely that a CE0G plant would sustain a complete loss of feedwater event.
Additionally, two design features of the CE0G NSSS also provide for a better plant response to a loss of feedwater event. In the unlikely 4
I event that a complete loss of feedwater event occurs at a CE0G plant these design features help mitigate the severity of the event.
- 1. CE0G plants have significantly larger secondary steam generator inventory. CE0G plants have typically 20 minutes before steam generator dryout while plants with once-through steam generators have approximately five minutes before dryout occurs for a total loss of feedwater event. The CE0G plants afford significantly longer operator response times to correct abnormal equipment performance before the NSSS experiences a significant heat-up or rise in pressure. In addition, the AFW actuation setpoints for CE0G plants are reached with much more secondary inventory remaining than the corresponding Davis-Besse SFRCS low level setpoint.
- 2. CE0G plants have a reactor trip scheme based on steam generator level. This reactor trip terminates reactor power early in the event preserving steam generator inventory for decay heat removal following a total loss of feedwater event.
C. CE Owners Group Davis-Besse Event Action Plan The action plan developed by the Review Group is intended to address all the generic concerns identified in NUREG 1154. Since there are significant design differences between the Davis-Besse plant and CE0G plants, several of the concerns in NUREG 1154 are not applicable to CE0G plants. The final action plan includes the generic concerns considered applicable to CE0G plants.
- 1. Action Plan Development The Review Group reviewed the issues and concerns raised by the Davis-Besse event. The following input documents were considered during the review: NUREG 1154, Generic Letter 85-13, B&W Owners Group 1154 Task Force Report, and the Westinghouse Owners Group Davis-Besse Evaluation Program. Each identified item from this 5
review was evaluated to determine the response required. These responses can be summarized as follows:
o No Action Required - The issue is only applicable to plants with Babcock & Wilcox NSSSs. These items are not contained in the CEOG action plan.
o CE0G Members Exchange Informatio_n - The issue is generic to CEOG plants. The CE0G will be used to facilitate communication and information exchange.
o Resolution Required by Individual Utility - The issue is generic to CE0G plants, but the solution is plant specific and should be addressed by each utility.
o CE0G to Investigate Generic Solution - The issue is generic to CE0G plants and a generic study is desirable and feasible.
The action plan is contained in this section. Each action item is presented on a separate sheet containing:
- Action Item Number
- Title
- Statement of Issue
- Responsibility
- Schedule of Completion Date All items are scheduled to be completed by September 1986.
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C-E Owners Group Davis-Besse Event Reviev 1
Action Item No: 1
Title:
Root Cause Determination Sectement of Issue: The Davis-Besse Incident indicated the need to evaluate root ccure determination methods to ensure that analyses of equipment failures and system trcusients are sufficient to initiate appropriate corrective action to prevent recurrence.
Scheduled D3tniled Action Steps Responsibility Completion
- 1. Initiate exchange of information. Each Utility Complete by providing descriptions of root cause determination and correction methods in current use.
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- 2. Review root cause determination CE July 1, 1986 methods used by CEOG members (site visits as required).
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4 C-E Owners Group Davis-Besse Event Review 1
Action Iten No: 1
Title:
Root Cause Determination (Continued)
Scheduled Litr.iled Action Stepe Responsibility Completion l
- 4. Solicit input from the B&W Review Group July 1, 1986 Owners Group on the results from their activities addressing this issue.
- 5. Evaluate the results obtained Review Group September 1, 1986 i
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in steps 1-4 and provide these l results and recommendations to the Operations Subcommittee for consideration.
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C-E Owners Group Davis-Besse Event Review Action Item No: 2
Title:
Review of Systems Performance and Testing Str.tement of Issue: The Davis-Besse event indicated that there may be inadequacies in past performance and testing of safety related systems. These inadequacies are b31ng partially addressed in conjunction with utility responses to IE Bulletin 85-03 (sco action item 3). Recommendations from the Davis-Besse review of the past p:rformance of selected systems and of testing associated with these systems may be cpplicable to C-E Owners.
Scheduled Datailed Action Steps Responsibility Completion
- 1. Ifonitor the results of the D-B Review Group July 1, 1986 review of systems performance. (contingent upon completion of test program at Davis-Besse.)
- 2. Inform C-E Owners of D-B items Review Group September 1, 1986 which may be generic concerns and determine if further action is needed.
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C-E Owners Group Davis-Besse Event Review Action Item No: 3
Title:
Reliability of Selected Safety Related Motor-Operated Valves Statement of Issue: Ensure that the maintenance, testing and operability checks of cciccted actor operated safety related valves are such that the valves are capable of p:rforming their safety related function.
Scheduled Ditniled Action Steps Responsibility Completion
- 1. Provide information for Review Group Complete individual utility consideration in responding to IE Bulletin 85-03.
- 2. A CEOG task has been approved Review Group Ccmplete to arsist utilities in responding to action item a of IE Bulletin 85-03.
Information from this task has been used by licensees in their individual submittals to the NRC in responce to IE Bulletin 85-03.
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C-E Owners Group Davis-Besse Event Review i
, Action Item No: 4
Title:
Reliability of the PORV Str.tement of Issue: The Davis-Besse event indicated that the reliability of PORVs to rcccat may be inadequate.
j Scheduled Responsibility Completion Detailed Action Steps Review Group Complete
- 1.. Review the D-B event for
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implications of PORY reliability and determine if industry-wide actions are needed.
l Although some C-E plants utilize PORVs, the response of th3 C-E plant design to events similar to the Davis-Besse event are much less likely i
to result in unplanned relief valve lifts. Cyclic operation of PORVs is not a sp:cified mode in Energency Procedure Guidelines for C-E plants. Further all C-E plcnts with PORVs have PORV block valves and acoustic monitoring instrumentation.
Providad that each affected utilii:y has adequately addressed the human engineering of indication and alarms, the reliability of PORVs should not be of concern to C-E plants. Each affected utility is considering this concern; no further generic cetion is needed.
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l C-E Owners Group Davis-Besse Event Reviev Actien Item No: 5 Titin: AFW Pump Turbine Overspeed Trips Stat ment of Issue: All C-E plants have both turbine and electric driven AFW pumps, thst: fore common mode failures of the type identified by the D-B event are not a prsblem. However, the D-B event indicates that the potential for overspeed tripa on steem driven pumps may exist.
Scheduled Datniled Action Steps Responsibility Completion
- 1. Review past opera' ting experience Each Utility July 1, 1986 and identify the causes and corrective actions for over-speed turbine trips. Identify manufacturer and model number of turbines and governor.
- 2. Consolidate, review, and Review Group September 1, 1986 i
distribute the information
, provided by each utility.
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C-E Owners Group Davis-Besse Event Review Action Item No: 6
Title:
Effect of Physical Security and Administrative Restrictions on Operations Sectement of Issue: The Davis-Besse event highlighted the potential adverse effect of plant physical security and administrative restrictions on the operator's cbility to gain timely access and operate equipment to mitigate accidents.
Scheduled Dsteiled Action Steps Responsibility Completion
- 1. Discuss the effect of security Review Group Complete
- or other administrative features on the operator's ability to gain access and control of critical equipment in an emergency to determine if further actions are necessary.
- The Review Group concluded that any potential adverse effect of Plant Physical Security and Administrative Restrictions can be accommodated during normal plant operations. However, should security systems fail to operate properly, the operators' ability to gain access and operate equipment to mitigate accidents may be severely restricted. The review group believes that the NRC should place added emphasis on resolving the conflicting requirements placed on nuclear power l plants to facilitate response to emergency conditions without undue impact of administrative requirements such as security, fire protection, etc.
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C-E Owners Group Davis-Besse Event Review Action Item No: 7
Title:
Review of criteria for initiating Feed and Bleed Strtement of Issue: The Davis-Besse event identified the need to ensure that the criteria used by the operator for initiating feed and bleed mode of operation are cicar and concise.
Scheduled Ditniled Action Steps Responsibility Completion
- 1. Review the feed and bleed Operations July 1, 1986 criteria in the CEOG Emergency Subcommittee Procedure Guidelines and identify any needed changes.
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l C-E Owners Group Davis-Besse Event Review Action Item No: 8
Title:
Reducing Feedwater Initiated Trips Statement of Issue: The Davis-Besse event identified the need to reduce feedwater transients resulting in plant trips thereby reducing challenges to safety systems.
Scheduled Detailed Action Steps Responsibility Completion '
- 1. The incidence of feedwater Operations Ongoing initiated trips and potential Subcommittee l corrective actions needed to
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address them are part of the CEOG Scram Reduction Program.
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