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{{#Wiki_filter:LGS UFSAR APPENDIX 15B Limerick Generating Station, (LGS) Units 1 and 2 15B.0          INTRODUCTION This appendix summarizes the analyses performed in support of the LGS Units 1 and 2 operating power/flow map expansion and the contingency mode of operation with selected individual equipment out-of-service. The maximum extended operating domain consists of the maximum extended load line region and the increased core flow region. The equipment out-of-service analyses include turbine bypass system, feedwater heaters, end-of-cycle recirculation pump trip and single recirculation loop operation. The power/flow map expansion and equipment out-of-service analyses assume the rerate thermal power of 3458 MWt (References 1 through 6).
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TRACG implementation analyses results (References 7 and 8) are based on a thermal power of 3,515 MWt.
15B.1          MAXIMUM EXTENDED OPERATING DOMAIN AND PARTIAL FEEDWATER HEATING ANALYSIS This analysis justifies the operation of LGS Units 1 and 2 in the maximum extended operating domain described in Figure 15.0-1. The safety impact evaluation of this extended region was performed with partial feedwater heating.
15B.1.1        MAXIMUM EXTENDED LOAD LINE LIMIT REGION The maximum extended load line limit (MELLL) region is defined as a power/flow operating domain bounded by:
: a.      100% rated power.
: b.      the load line which intercepts 100% power, and
: c.      100% rated rod line.
MELLL improves operational flexibility during power ascension by providing additional operating room above the original rated load line. It also provides a lower core flow condition at a rated power to allow for flow control reactivity compensation due to fuel burnup during an operating cycle and for improved fuel cycle economics.
The extended power/flow region has been created to provide relief from the operating restrictions inherently imposed during ascension to power by the previous power/flow region. The MELLL boundary (% core flow at the 100% rerated core power) was determined generically, based on safety and evaluations performed to meet required thermal and reactivity margins for BWR plants.
When compared to the initial power/flow operating domain, operating in the MELLL region results in plant operation at a higher load line, which allows for higher core power at a given core flow.
This condition increases the fluid subcooling in the downcomer region of the reactor vessel which affects the power distribution in the core and potentially affects steady-state operating thermal limits and transient accident/performances. The impact of this operating mode was evaluated to ensure safe plant operation.
The evaluations to support this operational domain at the rerated condition of 3458 Mwt are documented in Reference 1 and 6. The MELLL analyses also considered the equipment out-of-service assumptions.
APPENDIX 15B                                15B.1                    REV. 20, SEPTEMBER 2020
 
LGS UFSAR 15B.1.2          INCREASED CORE FLOW/FINAL FEEDWATER TEMPERATURE REDUCTION REGION The increased core flow (ICF) region (Figure 15.0-1) is defined as a power/flow operating domain bounded by:
: a.      100% rated power.
: b.      110% rated core flow, and
: c.      100% rated core flow.
The ICF region is a feature that improves operational flexibility during power ascension by providing additional flow range at rated power to compensate for xenon variations during power changes. The ICF capability provides reactivity compensation due to fuel burnup during an operation cycle and additional reactivity to extend an operating cycle to improve fuel cycle economics.
The safety evaluation addresses ICF operation throughout the cycle, and ICF with Final Feedwater Temperature Reduction (FFWTR) during end-of-cycle extension and power coastdown. The amount of FFWTR considered in the analysis corresponds to a reduction of 105F from the nominal feedwater temperature conditions.
Limiting transients events were performed at the bounding condition of 110% of rated core flow, and the results are documented in Reference 3. These ICF/FFWTR evaluations also included various equipment out-of-service such as the turbine bypass system, and the end-of-cycle recirculation pump trip.
15B.1.3          FEEDWATER HEATING OUT-OF-SERVICE Feedwater heating out-of-service (FWHOOS) is defined as operation with feedwater heaters out-of-service, corresponding to operation with a reduction in feedwater temperature of up to 60F from nominal.
The FWHOOS feature provides potential improved plant availability by allowing continued unrestricted plant operation with feedwater heaters out-of-service.
The FWHOOS analysis was performed for a core thermal power of 3458 MWt, using the LGS expanded operating domain. The results are described in References 4 and 5.
15B.2            ARTS PROGRAM The ARTS program is a performance improvement feature which updates fuel thermal limits administration at partial power/flow conditions, improves instrumentation response and increases plant operating flexibility and efficiency.
ARTS provides limits for MCPR and MAPLHGR as a function of power and flow to better ensure fuel cladding integrity. It also modifies the basis of rod block monitor trips to terminate excessive reactivity insertions during rod withdrawal error events. The original flow-biased rod block monitor trips are replaced by local power biased trips.
APPENDIX 15B                                15B.2                    REV. 20, SEPTEMBER 2020
 
LGS UFSAR The ARTS analyses (References 2 and 6) were performed at the rerated power level of 3458 MWt and a maximum core flow of 110% of rated. The analysis also assumes equipment out-of-service such as turbine bypass and end-of-cycle recirculation pump trip and single loop operation. The results are summarized in Reference 2 for all equipment in-service and in Reference 6 for the equipment out-of-service conditions.
15B.3            SINGLE LOOP OPERATION Single Loop Operation (SLO) at a reduced power is a valuable feature from a plant availability/outage standpoint. The capability to operate with a single recirculation loop is highly desirable in the event that a recirculation pump or other component renders one loop inoperable.
The analyses necessary to justify SLO operation are evaluated in Reference 2.
15B.4            OTHER EQUIPMENT OUT-OF-SERVICE In addition to the FWHOOS feature, LGS also has the turbine bypass system out-of-service (TBSOOS) and the end-of-cycle recirculation pump trip out-of-service (EOC-RPTOOS) features.
Subsequent to the analysis supporting power/flow map expansion, an additional equipment out-of-service feature, power load unbalance out-of-service (PLUOOS), was implemented.
15B.4.1          TURBINE BYPASS SYSTEM OUT-OF-SERVICE Turbine bypass operation has a significant impact on the severity of fast pressurization events. Of these AOOs, the turbine trip no bypass (TTNBP) and load rejection no bypass (LRNBP) events already exclude the turbine bypass operation from their licensing event basis assumptions. The feedwater controller failure (FWCF) normally evaluated with an operable bypass system is therefore re-analyzed without the turbine bypass function.
The TBSOOS option was integrated in the power/flow map expansion and performance improvement programs (including power rerate) previously described. The results of the Anticipated Operating Occurrences (AOO) analysis with TBSOOS are described in Reference 1.
Turbine Bypass System OOS may be referred to as Turbine Bypass Valve (TBVOOS) in some documentation. Starting with Limerick 2 Cycle 14, "TBVOOS" was changed to be referred to as "TBSOOS" to reflect that the bypass valves are assumed to be unable to provide pressure control, and so transients that rely on the bypass system for pressure control (e.g., rod withdrawal error),
are analyzed accordingly for the TBSOOS condition.
15B.4.2          END-OF-CYCLE RECIRCULATION PUMP TRIP OUT-OF-SERVICE The purpose of the end-of-cycle recirculation pump trip (EOC-RPT) is to protect the integrity of the fuel cladding during fast pressurization transients, especially turbine generator trips.          It supplements the reactor scram function during these events. The trip of the reactor recirculation pumps early in these transient events decreases the magnitude of the power excursion by adding negative reactivity to the core, consequently resulting in lower thermal operating limits.
For the power/flow map expansion and equipment-out-of-service features previously described, both the limiting TTNBP and FWCF events are analyzed with the EOC-RPTOOS option. The results of these analyses are described in Reference 1.
APPENDIX 15B                                15B.3                      REV. 20, SEPTEMBER 2020
 
LGS UFSAR 15B.4.3          POWER LOAD UNBALANCE OUT-OF-SERVICE The purpose of the power load unbalance (PLU) is to prevent turbine over-speed in the event of a load rejection. The PLU prompts the fast closure of the turbine control valves when an unbalance is detected while operating above 55% power. With the PLUOOS, a load rejection event will not cause fast closure of the TCVs. A backup trip from the generator protection system logic is credited and results in a turbine trip signal.
15B.4.4          PRESSURE REGULATOR OUT-OF-SERVICE The purpose of the Pressure Regulator Out-of-Service (PROOS) is to support operation when one pressure regulator is out-of-service and the system is no longer single failure proof. Failure of a pressure regulator downscale, when there is no second pressure regulator operable will cause slow closure of the turbine control valves. This event can require more limiting thermal limits.
The results of these analyses are described in References 7 and 8 and/or included as part of the cycle-specific reload analysis.
15B.5           
 
==SUMMARY==
AND CONCLUSION Specific analyses have been performed to determine the impact of LGS plant operation with the above specified reactor performance improvements. The results demonstrate that all licensing basis criteria for the required safety analyses are acceptable. These include the following analysis evaluations.
: a.      Anticipated Operational Occurrences (AOOs) Analysis
: b.      Loss-Of-Coolant Analysis
: c.      Containment Response
: d.      Reactor Vessel and Internals Mechanical Integrity
: e.      Miscellaneous Impact Verifications (e.g. Anticipated Transients Without Scram).
The AOOs analyses are cycle-specific and are reanalyzed during subsequent fuel cycles as part of the reload licensing scope of work. The LOCA analysis is fuel type specific and is evaluated or reanalyzed as required. The containment dynamic loads, reactor internal components structural integrity and the miscellaneous analyses are cycle-independent. These tasks are performed during the initial application of the performance improvement programs and remain valid for subsequent fuel reloads, unless the analyses boundaries and/or analytical assumptions are subsequently changed.
15B.6 REFERENCES
: 1.      GE Nuclear Energy, "Power Rerate Safety Analysis Report" for Limerick Generating Station Units 1 and 2, Licensing Topical Report NEDC-32225P, Class III (Proprietary), September 1993.
APPENDIX 15B                                  15B.4                  REV. 20, SEPTEMBER 2020
 
LGS UFSAR
: 2. GE Nuclear Energy, "Maximum Extended Load Line Limit and ARTS Improvement Program Analyses" For Limerick Generating Station Units 1 and 2, NEDC-32193P (Revision 2), October 1993.
: 3. GE Nuclear Energy, "Safety Review for Limerick Generation Station Units 1 and 2- 110%
Increased Core Flow Operation and Final Feedwater Temperature Reduction' NEDC-32224P (Revision 1), October 1993.
: 4. GE Nuclear Energy, "Increased Core Flow and Partial Feedwater Heating Analysis" for Limerick Generation Station Unit 1 Cycle NEDC-31323, October 1986.
: 5. GE Nuclear Energy, "Impact of Power Rerate and Final Feedwater Temperature Reduction (FFWTR) or Limerick Feedwater Nozzle Fatigue," GE-Ne-523-102-0793, July 27, 1993.
: 6. GE-NE letter/Report transmittal to PECO, (G93-PEPR-327) Subject "Limerick ARTS Application with Equipment Out-of-service (EOOS)", December 10, 1993.
: 7. GE Hitachi Nuclear Energy, "Limerick Generating Station Units 1 and 2 TRACG Implementation for Reload Licensing Transient Analysis," 0000-0137-9500-R1, October 2017.
: 8. GE Hitachi Nuclear Energy, "Limerick Generating Station (LGS) Units 1 and 2 TRACG Cycle-Independent PROOS Analysis Report," 002N4397-R1, January 2016.
APPENDIX 15B                            15B.5                REV. 20, SEPTEMBER 2020}}

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