ML20220A202
| ML20220A202 | |
| Person / Time | |
|---|---|
| Site: | Watts Bar  |
| Issue date: | 08/07/2020 |
| From: | Tennessee Valley Authority |
| To: | Kimberly Green NRC/NRR/DORL/LPL2-2 |
| Green K | |
| References | |
| EPID L-2020-LRM-0064 | |
| Download: ML20220A202 (27) | |
Text
Watts Bar Nuclear Plant (WBN)
Proposed License Approach Regarding a Change for the WBN Units 1 and 2 Technical Specification (TS) 3.3.2 Table 1 Function 6.e Auxiliary Feedwater Auto - Start from Loss of Main Feedwater Pumps August 11, 2020
Opening Remarks
Background
Need for Change Proposed design change Proposed TS changes License Amendment Request (LAR) Schedule Milestones Closing Remarks Agenda l 2
Opening Remarks Purpose of the meeting is to discuss a proposed change to WBN Units 1& 2 TS 3.3.2 Table 1 Function 6.e Auxiliary Feedwater Auto
- Start from Loss of Main Feedwater Pumps.
Similar presentation provided to NRC on May 27, 2020.
Proposed TS change will allow the use of the standby main feedwater pump (SBMFWP) as the normal means for starting up and shutting down the plant.
Proposed design change to the AFW Auto-start Logic to support the LAR. Design change will be implemented during the WBN 1 Cycle 17 Refueling Outage (U1R17) scheduled for October 2021.
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Background===
WBN TS 3.3.2 Table 1 Function 6.e, Trip of all Turbine Driven Main Feedwater Pumps (TDMFWPs), for Auxiliary Feedwater (AFW) auto-start function is an anticipatory function that provides early actuation of the AFW system to mitigate the consequences of a loss of normal feedwater For the WBN Loss of Normal Feedwater event, the credit AFW safety function actuation is from the AFW auto-start on low-low steam generator (SG) level (TS 3.3.2 Table 1 Function 6.b). This engineered safety feature actuation system (ESFAS) meets all requirements for reliable power supplies, separation, redundancy, testability, seismic and environmental qualifications as specified in 10 CFR 50.55a(h)(2), Protection Systems.
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Background===
The WBN main feedwater system (MFW) is designed to supply a sufficient quantity of feedwater to the SG secondary side during plant normal operating conditions.
The WBN MFW system consists of two TDMFWPs arranged in parallel with a single SBMFWP, two injection water pumps, three (parallel string) high-pressure FW heaters, and associated piping and instrumentation.
The TDMFWPs are variable speed feed pumps with each pump can provide up to 67% capacity The two TDMFWPs variable speed main feedwater pumps are capable of delivering feedwater to the four SGs under all expected operating conditions.
The electric motor-driven SBMFWP can provide approximately 15% to 18%
capacity During certain times of the year, to improve plant efficiency, the standby main feedwater pump is used to supplement MFP flow at high plant loads.
The SBMFP will automatically start if one of the TDMFPs trip above 67%
power.
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Background===
l 6 The electric motor driven SBMFWP does not interface with the MFP Trip for AFW Auto-Start Logic The original design basis for WBN allowed the electric motor driven SBMFWP to be used for normal plant startup and shutdown (up to 15% thermal power) while a TDMFWP(s) were being placed or removed from service.
NUREG 0847, Safety Evaluation Report Related to the Operation of Watts Bar Nuclear Plant Units 1 and 2 Docket Nos. 50-390 and 50-391, dated June 1982 (ML072060490),Section 10.4.7:
The use of the standby feedwater pump is the normal means for starting up and shutting down the plant. This pump is also automatically activated in the event of the loss of one main feedwater pump. This is accompanied by an automatic turbine runback to 85 percent of load if the power level is above 80 percent of full power. Should main feedwater flow continue to decrease, the auxiliary feedwater system will automatically activate when the low-low steam generator level is reached. The auxiliary feedwater system (see Section 10.4.9) automatically provides flow to the steam generators for decay heat removal upon the loss of normal feedwater supply.
Additional Regulatory Background at the end of the presentation
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Background===
NRC documented concerns on the use of the SBMFWP for reactor startup beginning in 2006 since the SBMFWP does not interface to the auxiliary feedwater water (AFW) automatic start logic.
TS change 08-07 denoted that the SBMFWP pump was originally designed to provide feed flow during startup and shutdown conditions below 15%
rated thermal power (RTP) and to accommodate loss of one TDMFP above 67% RTP. Due to the non-compliance issues addressed in NRC Inspection Reports 2006-004 and 2008-003, the AFW motor driven pumps and the TDMFPs would be used for normal plant startup and shutdown in compliance with the proposed change.
The AFW motor driven pumps and the TDMFWPs are used for normal plant startup and shutdown in compliance with TS 3.3.2 Table 1 Function 6.e PLACE THE TITLE OF THE PRESENTATION HERE l 7
Need for Change Presently, the AFW motor driven pumps and the TDMFWPs are used for normal plant startup and shutdown in compliance with TS 3.3.2 Table 1 Function 6.e During startup, with the use of the AFW motor driven pumps, steam generator water level and feedwater control at low reactor thermal power (2-3%) power can be challenging Feedwater swings affect temperature and power which is not ideal at low powers with tight control bands A TDMFWP is placed in service at low reactor thermal power (~4%). However, it is ideal for a steam driven pump, which impacts reactivity, to be placed in service at a higher RTP (>5% Mode 1).
With the use of the SBMFWP for startup activities SBMFWP would be placed in service to control SG level from Mode 3 to Mode 1 ~15% power.
At 10% -15% rated thermal power, a TDMFP would be placed in service in Mode 1 to control SG water levels Once the TDMFP is operating, the SBMFP would be removed from service.
The use of the SBMFWP during start up activities would simplify startup activities with the elimination of the need to swap between AFW level control valves and MFW bypass valves in Mode 2 (2-3% RTP).
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Proposed Design Approach Revise the AFW Auto-start Logic The addition of SBMFWP power supply breaker contact interface to the AFW Auto-start Logic The breaker contact will close when breaker is open.
This will make the AFW auto-start logic initiate from the trip of all MFW pumps both TDMFPs and the SBMFP The SBMFP trip channel will be provided with a handswitch that allows the operations staff to place the channel in trip when the SBMFP is not operable.
The revised circuitry will remain as an anticipatory AFW auto-start function and will not be credited in the WBN accident analyses.
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Proposed Design Change Existing AFW Auto-Start initiation Logic l 10
Proposed Design Change Proposed design for AFW auto-start initiation logic with the addition of the Standby Main Feedwater Trip channel l 11
Proposed Design Change Design for AFW auto-start initiation logic when the SBMFP is supplying feedwater to the SGs l 12
Proposed TS Changes TS 3.3.2 Table 1 Function 6.e will be revised to denote the AFW Automatic start will include:
The Trip of all MFW Pumps
>> The trip of both TDMFPs
>> And
>> The trip of the SBMFP The applicability of the SBMFP trip channel would be Modes 1 and 2.
A new TS 3.3.2 condition will be added to address inoperability of the SBMFP trip function.
Associated changes to the TS Bases l 13
Proposed TS Changes for WBN 1 (markup) l 14
Proposed TS Changes for WBN 1 (markup) l 15
Proposed TS Changes for WBN 2 (markup) l 16
Proposed TS Changes for WBN 2 (markup) l 17
Proposed TS Changes for WBN 2 (markup) l 18
Proposed TS Changes for WBN 1 (final) l 19
Proposed TS Changes for WBN 1 (final) l 20
Proposed TS Changes for WBN 2 (final) l 21
Proposed TS Changes for WBN 2 (final) l 22
Proposed TS Changes for WBN 2 (final) l 23
LAR Schedule Milestones August 4, 2020 - LAR pre-submittal meeting with NRC September 1, 2020 - LAR submittal.
NRC approval of LAR within one year from the date of the submittal (Requested). 30-day implementation period October 2021 - Scheduled start of WBN U1R17 outage l 24
26 Regulatory Background 2004
- TVA submits TS-04-013
- Clarification of AFW start from TDMFP 2006
- TVA withdraws TS-04-013
- NRC issues NCV 05000390/2006004-04 for failing to have AFW start signal
- NRC Integrated Inspection Report 05000390/20060004 and 05000391/2006004 2008
- NRC issues NCV 05000390/2008003-1 for violation of TS 3.0.4
- NRC Integrated Inspection Report 05000390/20080003 and 05000391/2008003
- NRC issues License amendment 75 for TS 3.3.2.Table 1 Function 6.e
- Present License condition
- NRC Issues IN 2015-05 INOPERABILITY OF AUXILIARY AND EMERGENCY FEEDWATER AUTO-START CIRCUITS ON LOSS OF MAIN FEEDWATER PUMPS
- WBN Issue discussed
Regulatory Background NRC documented concerns on the use of the SBMFP for reactor startup beginning in 2006 since the SBMFP does not interface to the auxiliary feedwater water (AFW) automatic start logic.
Due to the non-compliance issues addressed in NRC Inspection Reports 2006-004 and 2008-003, TVA submitted TS Change 08-07 AFW Auto-start Upon Trip of the Turbine Driven Main Feedwater Pumps TS change 08-07 denoted that the SBMFP pump was originally designed to provide feed flow during startup and shutdown conditions below 15% rated thermal power (RTP) and to accommodate loss of one TDMFP above 67% RTP. Due to the non-compliance issues addressed in NRC Inspection Reports 2006-004 and 2008-003, the AFW motor driven pumps and the TDMFPs would be used for normal plant startup and shutdown in compliance with the proposed change.
The AFW motor driven pumps and the TDMFPs are used for normal plant startup and shutdown in compliance with TS 3.3.2 Table 1 Function 6.e PLACE THE TITLE OF THE PRESENTATION HERE l 27