ML15125A319

3/18/2015, Meeting Slide for Tennessee Valley Authority Presentation on GDC 5 Strategy for Watts Bar Unit 2

ML15125A319
Person / Time
Site:	Watts Bar
Issue date:	03/18/2015
From:	Tennessee Valley Authority
To:	Plant Licensing Branch II
Minarik A, NRR/DORL/LPLWB, 415-6185
Shared Package
ML15125A344	List: ML15125A314 ML15125A319 ML15125A331
References
Download: ML15125A319 (12)

Text

General Design g Criterion 5 Licensing Open Item 91 - GDC-5

• TVA TVA should update the FSAR with information describing how WBN Unit 2 meets GDC 5, assuming the worst case single failure and a Loss of Offsite Power

• GDC 5 - Sharing of structures, systems, and components.

Structures, systems, Structures systems and components important to safety shall not be shared among nuclear power units unless it can be shown that such sharing will not significantly impair their ability to perform their safety functions, including, in the event of an accident in one unit, an orderly shutdown and cooldown of th remaining the i i units.

it 1

General Design Criterion 5

• Design Basis WBN designed as a Hot Standby plant

• One unit in accident

• Second unit can remain safely f l iin H Hott St Standby db WBN has the capability to safely handle one unit in an accident and bring second unit to cold shutdown within approx 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> 2

General Design Criterion 5

• ERCW system has 8 pumps serving two units 4 train A, 4 train B Two pumps (on one train) required to safely shutdown two units Provides cooling to CCS, Containment Spray, Safety related HVAC, diesel generators, etc.

g

• CCS system has 5 pumps and three heat exchangers Provides cooling to Emergency core cooling systems, Residual heat removal heat exchangers exchangers, spent fuel pool cooling cooling, etc etc.

3

General Design g Criterion 5 4

General Design g Criterion 5

• Two principal scenarios for GDC5 One unit proceeding to Shutdown, Second unit undergoes LOCA One unit proceeding to Shutdown, Second unit has emergency Shutdown

• Example Limiting LOCA scenario for GDC 5 LOCA in one unitunit, second unit progressing to cold shutdown Loss of Offsite Power Failure of both train A diesels (train A power single failure)

Loss of Downstream dam 85oF river water temperature (Technical Specification limit)

Heat exchangers - max fouling ECRW and CCS Pumps at minimum performance

• This results in the single B train CCS heat exchanger (HX-C) serving both the accident and non-accident unit using the C-S CCS pump 5

General Design g Criterion 5

• Analysis of this limiting event shows Accident unit can be cooled safely Non-accident unit can be brought to cold shutdown in 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> for GDC 5 compliance Limitation is non-accident unit remains in Hot Standby y ((safe shutdown state) for 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> prior to entering RHR cooling Auxiliary feedwater to steam generators Steaming from Steam Gen PORV or safeties If non-accident unit is already on RHR in less than 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> it may be necessary to return unit to Hot Standby Allows decay heat to subside prior to adding load to CCS 6

General Design g Criterion 5

• Final Safety Analysis Report was revised describing compliance

• Staff RAIs were answered

• Open item closed by NRC in SSER 27

• Remaining action Technical Specification revision to allow return to Mode 3 for non-accident non accident unit for 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> Rejected by NRC Tech Spec Branch 7

General Design Criterion 5 Options

1. Do nothing 2

2. Credit UHS temperature below 85oF

3. Credit parallel B CCS pump for non-accident unit with C-S pump

4. Credit adding second ERCW pump to shutdown unit B EDG 8

General Design Criterion 5 Options

5. Credit adding second ERCW pump to shutdown unit A EDG R

Results lt

• After reviewing options and several combination of options, the following was selected selected.

• 3+4+5-No delay in RHR cooldown. Revised Design Basis. Acceptable p Margin g for Diesel generator while 3rd ERCW pump loaded 9

General Design Criterion 5 10

General Design Criterion 5

• Option 3+4+5 gives plant most flexibility

• Things g to do

• Diesel Generator loading and margin calcs (prelim OK)

• Develop Licensing Approach for 3 out of 4 ERCW in Mode 5 (Need both train A and both Train B pumps operable for non-accident unit)

• Procedure changes (parallel B CCS pump, 3rd ERCW available in Mode 5 for 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br />)

• 20 minute action outside control room (override ERCW interlock) 11

General Design Criterion 5

• Mission dose for operator action

• FSAR changes (Three ERCW pumps required required))

• System Description changes

• U1 and U2 revised Containment Analysis (U2 in-work, initial QA results 3/13/15.)

• Revise ERCW and CCS flow analyses

• Confirm X-tie Valves are useable DCN to Implement new ERCW / CCS Flow Requirements

• DCN to install ERCW interlock override (online)

• Provides side benefit of 90% ERCW acceptability 12