ML11279A251

Slides for Forthcoming Meeting with Oconee Nuclear Station, Units 1 ,2 and 3 Regarding Proposed Tornado Mitigation Strategy

ML11279A251
Person / Time
Site:	Oconee
Issue date:	10/06/2011
From:	Duke Energy Carolinas
To:	Office of Nuclear Reactor Regulation
Stang J
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ML11279A250	List: ML11279A251 ML11279A252 ML11279A253
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Download: ML11279A251 (24)

Text

Presented by Oconee Nuclear Station October 11, 2011

Introduction Purpose of revised strategy is to credit the minimum number of SSCs required to place and maintain the affected unit(s) at approximately 250 deg F.

Utilizing only these SSCs minimizes the post tornado recovery actions that must be accomplished within the first 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> of the event.

Proposed strategy is modeled using ONS NFPA 805 compliance strategy for the Auxiliary Building Fire Area.

Procedural actions denoted by an asterisk (*) have not yet been developed.

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Compliance Strategy Affected unit(s) maintained safe and stable in mode 3

[hot standby] with RC temperature 525 deg F from SSF for up to 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> (unless the initiating event causes the unit(s) to be driven to a lower temperature).

Recovery actions restore SSCs required to transition affected unit(s) from mode 3 to an RC temperature of approximately 250 deg F.

A natural circulation cool down is performed and affected unit(s) are maintained safe and stable long term at approximately 250 deg F in natural circulation.

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Method of Accomplishment for Maintaining Unit @ Hot Standby Reactivity Control Function o Shutdown margin initially established by the insertion of the control rods prior to SSF activation.

o Shutdown margin maintained by RCS makeup with borated water from the Spent Fuel Pool (SFP) using SSF RC Makeup pump with letdown back to the SFP.

Reactor Coolant Inventory Control Function o SSF control of RCP seal injection using the SSF Reactor Coolant Makeup Pump supplied from the SFP with Letdown back to the SFP.

4

Method of Accomplishment for Maintaining Unit @ Hot Standby Reactor Coolant Pressure Control Function o SSF control of RCS Pressure via Group B & C Pressurizer Heaters and Pressurizer Safety Relief Valves.

o Pressure control is partially satisfied by those systems associated with RC Inventory Control and Decay Heat Removal Control.

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Method of Accomplishment for Maintaining Unit @ Hot Standby Decay Heat Removal Control Function o Following loss of RCPs, DHR established by SSF control of natural circ between the core and SG A & B.

o SSF ASW pump feeds SG A & B for reactor coolant heat removal.

o MS pressure is regulated using MS isolation and steam release through the SRVs.

o The SSF Submersible pump provides water to the CCW system for supplying the SSF ASW pump.

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Method of Accomplishment for Maintaining Unit @ Hot Standby Process Monitoring Function o The following system process variables are monitored from the SSF:

• Pressurizer pressure and level,

• RCS pressure and temperature,

• SSF RC Makeup flow and suction/discharge pressure,

• SSF ASW flow

• S/G level.

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Method of Accomplishment for Maintaining Unit @ Hot Standby Vital Auxiliaries o SSF electrical distribution system is separated from normal plant power to SSF power systems. SSF Diesel Generator provides power for AC and DC power systems.

o SSF cooling credited for SSF control room, battery rooms, computer room, and response room. SSF ventilation equipment credited for SSF diesel generator, HVAC, SWGR, and pump rooms.

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Method of Accomplishment for Transition to Mode 4 Reactivity Control Function o Shutdown margin maintained by adequate concentration of borated water from the BWST via local operation of HPI Pump A or B and RC letdown through local operation of the RV head vent valves.

Reactor Coolant Inventory Control Function o RC makeup via local operation of HPI Pump A or B for makeup via RCP seal injection and A RC makeup header with suction aligned from the BWST and RC letdown through local operation of the RV head vent valves.

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Method of Accomplishment for Transition to Mode 4 Reactor Coolant Pressure Control Function o Local operation of PZR PORV and operation of Pressurizer Heaters from SSF CR credited for controlling system pressure during natural circulation cooldown.

Decay Heat Removal Function o DHR provided by natural circulation between core and SGs using the SSF Auxiliary Service Water Pump taking suction from CCW intake piping.

o RCS cooldown control provided by local operation of the Main Steam atmospheric dump valves.

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Method of Accomplishment for Transition to Mode 4 Process Monitoring Function o Following system process variables are monitored from the SSF CR: Pressurizer pressure and level, RCS pressure and temperature, SSF ASW flow, and SG level.

o Following system process variables are monitored locally following repair: RCP seal injection flow and BWST level.

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Method of Accomplishment for Transition to Mode 4 Vital Auxiliaries o Credited electrical power path for HPI Pump A or B is PSW 4KV SWGR supplied from either Keowee Hydro Generator through underground power path or 100KV transmission line.

o Credited electrical power path for SSF ASW Pump is PSW 4KV power aligned to SSF 4KV SWGR and supplied from either Keowee Hydro Generator through underground power path or 100KV transmission line.

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Event Sequence Tornado Watch is declared.

o Operating crews enter AP/06, Natural Disaster.

Tornado Warning is declared.

o One licensed operator (either RO or SRO) proceeds to SSF and establishes communications with control rooms.

o All operations shift personnel report to assigned unit CR.

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Event Sequence continued Tornado strikes site resulting in:

o Three unit blackout.

o Tornado related damage disables TD emergency feedwater pump on each unit.

This is assumed worst case scenario.

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Event Sequence continued All three units trip.

o CR SRO on each unit enters EP/01, EOP.

o Reactor operators perform immediate manual actions and symptoms check of EOP and determine that a loss of RCP seal cooling and SG DHR function has occurred.

o Licensed operator at SSF directed to establish RCP seal cooling via reactor coolant makeup system on one unit (existing 20 minute TCA), aligns SSF ASW for all affected units and establishes SG DHR via SSF ASW system (existing 14 minute TCA) on one unit.*

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Event Sequence continued Two additional licensed operators (LO) proceed to SSF and establish SG DHR and RCP seal cooling.*

o LOs proceed via current credited travel path.

o If travel path blocked LOs proceed via alternate egress points from auxiliary building.

o LOs enter SSF via north or south entrance.

SPOC is notified to deploy SSF submersible pump.

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Event Sequence continued Affected unit(s) maintained in natural circulation hot standby conditions (typically 555 deg F/2155 psig) from SSF for up to 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />.

TSC is activated. RP/1000/22, Procedure for Major Site Damage Assessment and Repair, is entered to coordinate site assessment and repair activities.*

OP/1102/24, Plant Assessment and Alignment Following Major Site Damage, is entered to assess availability of systems required for unit cool down and make necessary alignments once repairs are completed.*

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Recovery Actions 13.8 KV line from PSW substation to PSW building is restored.*

A & B HPI discharge headers assessed for damage and repaired as necessary.*

RCP seal injection header assessed for damage and repaired as necessary.*

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Recovery Actions continued (Existing) portable valve control panel installed.

o Panel is placed outside WPR in yard area.

o Panel is connected to PZR PORV, RV head vent valves and CFT isolation valves at reactor building penetration in WPR.

o Panel receives 600 vac, 120 vac and 125 vdc power from SSF.

TSC arranges for fire truck to replenish SFP inventory per RP/1000/22 (existing 36 hour4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br /> TCA) via installed connection.

PSW power aligned to SSF and SSF D/G shutdown.*

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Post Recovery Action Event Sequence OP/1102/25, Cooldown Following Major Site Damage, is entered and RCS cool down is performed with command and control from SSF CR.*

o PSW booster pump is locally started to supply HPI pump cooling.

o HPI pump A or B is locally started.

o RCP seal injection control valve is locally throttled to establish RCP seal injection.

o SSF RCMU System secured from SSF CR.

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Post Recovery Action Event Sequence o PZR heaters de-energized from SSF CR.

o RV head vent valves opened by local operation from portable valve control panel.

o Cool down initiated by local operation of Main Steam atmospheric dump valves.

o RC letdown to SFP secured from SSF CR.

o RCS pressure reduction is initiated by local operation of PZR PORV from portable valve control panel.

o CFT isolation valves closed by local operation from portable valve control panel.

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Post Recovery Action Event Sequence o Affected unit(s) stabilized in natural circulation hot shutdown conditions at approximately 250 deg F/300 psig.

o RV head vents are closed.

o HPI system is secured.

o Long term RC pressure provided by SSF powered PZR heaters.

o Long term DHR provided by SGs fed from SSF ASW.

o SSF submersible pump maintains SSF ASW pump suction inventory.

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Acronyms AP - Abnormal (Operating) Procedure ASW - Auxiliary Service Water BWST - Borated Water Storage Tank CCW - Condenser Circulating Water CFT - Core Flood Tank CR - Control Room D/G - Diesel Generator DHR - Decay Heat Removal EOP - Emergency Operating procedure HPI - High Pressure Injection HSB - Hot Standby HVAC - Heating, Ventilation and Air Conditioning Mode 3 - reactor subcritical with RC temperature 250 deg. F.

MS - Main Steam NC - Natural Circulation OP - Operating Procedure PORV - Power (Pilot) Operated Relief Valve PSW - Protected Service Water PZR - Pressurizer 23

Acronyms continued RC - Reactor Coolant RCP - Reactor Coolant Pump RCS - Reactor Coolant System RO - Reactor Operator RP - (Emergency) Response Procedure RV - Reactor Vessel SFP - Spent Fuel Pool SG - Steam Generator SPOC - (Maintenance) Single Point of Contact SRO - Senior Reactor Operator SRV - Safety Relief Valves SSC - Structures, Systems and Components SSF - Standby Shutdown Facility SWGR - Switchgear TCA - Time Critical Action TD - Turbine Driven TORMIS - Tornado Missile Analysis Program TSC - Technical Support Center WPR - West Penetration Room 24