ML12061A249

ANP-3067, Rev. 1, St. Lucie, Unit 1 EPU - Information to Support NRC Review of RCS Depressurization with Pressurizer Overfill

ML12061A249
Person / Time
Site:	Saint Lucie
Issue date:	02/29/2012
From:	AREVA NP
To:	Office of Nuclear Reactor Regulation
References
L-2012-072 ANP-3067, Rev 1
Download: ML12061A249 (25)

Text

L-201.2-072 Attachment 2 ATTACHMENT 2 EXTENDED POWER UPRATE -RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION IDENTIFIED DURING AUDIT OF THE SAFETY ANALYSES CALCULATIONS ANP-3067 Revision I St. Lucie Unit 1 EPU Information to Support NRC Review of RCS Depressurization with Pressurizer Overfill (Cover page plus 24-pages)

Controlled Document ANP-3067 Revision 1 St. Lucie Unit 1 EPU -Information to Support NRC Review of RCS Depressurization With Pressurizer Overfill February 2012 A AREVA NP Inc. A R EVA Controlled Document AREVA NP Inc.ANP-3067 Revision 1 St. Lucie Unit I EPU -Information to Support NRC Review of RCS Depressurization With Pressurizer Overfill Copyright

© 2012 AREVA NP Inc.All Rights Reserved Controlled Document.A AR EVA St. Lucie Unit I EPU -Information to Support NRC Review of RCS Depressurization With Pressurizer Overfill ANP-3067 Revision 1 Paqe 3 Nature of Changes Item Page Description and Justification Rev. 0 1. All Rev. 1 1. 5 Initial Release Added acronyms to Nomenclature Added disposition of HFP vs. HZP 2. 10 and 11 Controlled Document A AREVA ANP-3067 St. Lucie Unit 1 EPU -Information to Support NRC Revision 1 Review of RCS Depressurization With Pressurizer Overfill Page 4 Table of Contents 1.0 Introd uctio n ..........................................................................................................

.....7 2.0 RCS Depressurization

-Pressurizer Overfill Analysis .................................................

8 2.1 Identification of Causes and Accident Description

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8 2.2 Description of Analyses and Evaluations

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8 2.3 Input Parameters and Assumptions

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9 2.4 A cceptance C riteria .......................................................................................

..11 2 .5 R e su lts ..........................................................................................................

..12 3 .0 R e fe re nce s ......................................................................................................................

2 4 List of Tables Table 1 RCS Depressurization

/ Pressurizer Overfill:

Initial Conditions and Biasing ...........

13 Table 2 RCS Depressurization

/ Pressurizer Overfill:

Sequence of Events .........................

15 List of Figures Figure 1 RCS Depressurization

/ Pressurizer Overfill -Pressurizer PORV Flow Rate ...... 16 Figure 2 RCS Depressurization

/ Pressurizer Overfill -Pressurizer Pressure .....................

17 Figure 3 RCS Depressurization

/ Pressurizer Overfill -RCS Coolant Temperatures

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18 Figure 4 RCS Depressurization

/ Pressurizer Overfill -RCS Subcooling

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19 Figure 5 RCS Depressurization

/ Pressurizer Overfill -Total RCS Flow Rate .....................

20 Figure 6 RCS Depressurization

/ Pressurizer Overfill -Indicated Reactor Power ................

21 Figure 7 RCS Depressurization

/ Pressurizer Overfill -Total HPSI and Charging Flow R a te s ...........................................................................................................................

2 2 Figure 8 RCS Depressurization

/ Pressurizer Overfill -Pressurizer Liquid Volume .............

23 Controlled Document A AR EVA ANP-3067 St. Lucie Unit 1 EPU -Information to Support NRC Revision 1 Review of RCS Depressurization With Pressurizer Overfill Page 5 Nomenclature AFAS auxiliary feedwater actuation signal AFW auxiliary feedwater ANP Advanced Nuclear Power AOO anticipated operational occurrence BOC beginning-of-cycle DNBR departure-from-nucleate-boiling ratio DTC Doppler temperature coefficient EPU Extended Power Uprate ESFAS engineered safety features actuation system FPL Florida Power and Light HFP Hot Full Power HPSI high-pressure safety injection HZP Hot Zero Power LAR Licensing Amendment Request LOOP loss of offsite power LR Licensing Report MFW main feedwater MSSVs main steam safety valves MTC moderator temperature coefficient NP Nuclear Power NR narrow range NRC Nuclear Regulatory Commission PORV(s) power-operated relief valve(s)PZR pressurizer RCPs reactor coolant pumps RCS reactor coolant system RPS reactor protection system RTP rated thermal power RWT refueling water tank SAFDLs specified acceptable fuel design limits SBCS steam bypass control system SG steam generator SIAS safety injection actuation signal Controlled Document A AR EVA St. Lucie Unit 1 EPU -Information to Support NRC Review of RCS Depressurization With Pressurizer Overfill ANP-3067 Revision 1 Pace 6 Nomenclature (Continued) thermal margin / low pressure technical specifications TM/LP TS Controlled Document A AR EVA ANP-3067 St. Lucie Unit 1 EPU -Information to Support NRC Revision 1 Review of RCS Depressurization With Pressurizer Overfill Page 7 1.0 Introduction The analysis described herein provides supplementary information to support the Nuclear Regulatory Commission's (NRC's) review of the St. Lucie Unit 1 Extended Power Uprate (EPU)License Amendment Request's (LAR's) Attachment 5 Licensing Report (LR), Section 2.8.5.6.1, Inadvertent Opening of Pressurizer Pressure Relief Valve.The information contained herein is specific to the St. Lucie Unit 1 EPU LAR submittal.

Controlled Document A AR EVA ANP-3067 St. Lucie Unit 1 EPU -Information to Support NRC Revision 1 Review of RCS Depressurization With Pressurizer Overfill Page 8 2.0 RCS Depressurization

-Pressurizer Overfill Analysis 2.1 Identification of Causes and Accident Description The Inadvertent Opening of Pressurizer Pressure Relief Valve, or Reactor Coolant System (RCS) Depressurization, event is defined, for St. Lucie Unit 1, as an accidental opening of one or both of the pressurizer power-operated relief valves (PORVs), due to a mechanical failure, spurious actuation signal, or unanticipated operator action.The event results in a loss of RCS fluid and a fairly rapid RCS depressurization.

If the moderator temperature coefficient (MTC) is positive, positive moderator density reactivity feedback caused by the depressurization leads to an increase in core power. The specified acceptable fuel design limits (SAFDLs) challenge is soon terminated, when the reactor trips on a thermal margin / low pressure (TM/LP) signal, but the RCS fluid loss and depressurization continue.The pressurizer liquid level begins to decrease significantly after the reactor trip, and this actuates the RCS charging pumps and minimizes RCS letdown. A low-low pressurizer pressure signal subsequently actuates high-pressure safety injection (HPSI). The HPSI and charging serve to restore the pressurizer level, but if the HPSI and charging flows are not throttled or terminated, the pressurizer will begin to overfill.

To prevent liquid discharge through the open PORV(s), the operators will have to close the open PORV(s) or the corresponding block valve(s) prior to the pressurizer dome becoming liquid-filled.

2.2 Description

of Analyses and Evaluations The purpose of this analysis was to evaluate the pressurizer overfill consequences of the RCS Depressurization event. Detailed analyses were performed using the S-RELAP5 code (Reference 1). The S-RELAP5 code was used to model the key primary and secondary system components, reactor protection system (RPS) and engineered safety features actuation system (ESFAS) trips, and core kinetics.

The calculations were performed to determine the operator Controlled Document A AR EVA ANP-3067 St. Lucie Unit 1 EPU -Information to Support NRC Revision 1 Review of RCS Depressurization With Pressurizer Overfill Page 9 action time necessary for precluding liquid relief through a single accidentally opened pressurizer PORV.a 2.3 Input Parameters and Assumptions Parameter biasing and assumptions (listed in Table 1, and discussed below) were designed to ensure conservatively high HPSI and charging flow rates, maximize initial pressurizer level, provide maximum reactivity feedback, and maximize the post-reactor-trip RCS heatup.Assumptions regarding mitigating systems and functions, along with a limiting single-failure, produce the most challenging scenario regarding pressurizer overfill." Initial Conditions

-The event was initiated from rated-power-plus-uncertainty conditions, with a maximum pressurizer level, minimum pressurizer pressure, and minimum technical specifications (TS) RCS flow. Both maximum- and minimum-initial-RCS-temperature cases were analyzed.* Reactivity Feedback -Beginning-of-cycle (BOC) moderatorb and Doppler feedback were assumed for this event. Minimum scram worth with the most reactive rod stuck out of the core was assumed.* Steam Generator Tube Plugging -Maximum steam generator tube plugging was assumed.* PORV Relief -Full open-single-PORV flow rate and steam-only relief were assumed.* Pressurizer Heaters -Both pressurizer-heaters-available and pressurizer-heaters-unavailable cases were analyzed.According to the NRC Standard Review Plan, NUREG-0800, Section 15.6.1, an accidental depressurization of the RCS could be caused by the inadvertent opening of a pressurizer PORV, which in turn could be caused by a spurious electrical signal or by an operator error. Florida Power and Light (FPL) letter to the NRC, L-2011-448, dated October 31, 2011 (Reference 2, Attachment 1, page 10) addressed the conditions which could cause both pressurizer PORVs to open and concluded that only a spurious energization of the 63X1P-1102 relay due to a short circuit would cause both PORVs to open. This spurious relay energization, however, is not considered to be a spurious electrical signal; therefore, consistent with the requirements of NUREG-0800, it is reasonable and acceptable to assume only one stuck open PORV for this event.b As a bounding assumption, moderator density feedback corresponding to the most-positive zero-power TS MTC limit was used.

Controlled Document-A A R EVA ANP-3067 St. Lucie Unit I EPU -Information to Support NRC Revision 1 Review of RCS Depressurization With Pressurizer Overfill Page 10" RPS and ESFAS Trips and Delays -RPS and ESFAS trip setpoints and delay times were biased to conservatively estimate the operator action time.* Loss of Offsite Power (LOOP) -Cases assuming either LOOP at reactor trip (with the reactor coolant pumps [RCPs] beginning to coast down at that time, and the main steam safety valves [MSSVs] subsequently removing heat transferred from the primary side) or offsite power remaining available throughout the event (with the RCPs remaining in operation, and either the steam bypass control system [SBCS] [if assumed available]a or the MSSVs providing post-trip primary-side heat removal) were analyzed.* Main Feedwater (MFW) -MFW was terminated at reactor trip-either due to LOOP (for LOOP cases), or as a conservative assumption (for no-LOOP cases)." HPSI and Charging -Maximum HPSI and charging flow rates, early actuation times, and a minimum refueling water tank (RWT) source temperature were assumed, to ensure the most limiting conditions for the event. No credit for automatic termination of charging, after restoration of pressurizer level, was taken." Letdown -No credit for automatic actuation of RCS letdown, after restoration of pressurizer level, was taken.* Auxiliary Feedwater (AFW) -Minimum AFW flow rate, maximum actuation time, and maximum temperature were assumed.* Single-Failure

-The assumed single-failure is loss of the turbine-driven AFW pump.The event analysis for EPU was initiated from hot full power (HFP) initial conditions.

The HFP overfill analysis bounds the event from hot zero power (HZP) conditions as follows: The HFP analysis assumed a moderator density feedback based on the most positive Technical Specification MTC limit (+7 pcm/°F). Increased core power from moderator feedback and higher core inlet temperatures result in an earlier TM/LP trip. From HFP a For scenarios with offsite power remaining available, the following cases were analyzed:

(1)maximum-capacity SBCS available, (2) minimum-capacity SBCS available, and (3) SBCS unavailable.

Controlled Document A AR EVA ANP-3067 St. Lucie Unit 1 EPU -Information to Support NRC Revision 1 Review of RCS Depressurization With Pressurizer Overfill Page 11 conditions, subsequent to reactor trip, the pressurizer pressure decreases at a faster rate due to increasing density of the fluid in the core relative to HZP. An earlier reactor trip and higher rate of depressurization after reactor scram initiates an earlier safety injection actuation signal (SIAS), an earlier initiation of the high pressure safety injection on SIAS and an earlier actuation of the charging pumps on SIAS or on pressurizer level deviation after scram all of which decrease the time to overfill.A bounding high initial pressurizer level assumed in the HFP case bounds the level at HZP initial conditions.

A bounding high initial pressurizer level will tend to decrease the time to pressurizer overfill making the HFP case more limiting.2.4 Acceptance Criteria This event is classified as an anticipated operational occurrence (AOO). The acceptance criteria for this event are: 1. Pressures in the reactor coolant and main steam systems should be maintained below 110% of the design values, 2. Fuel cladding integrity should be maintained by ensuring that the minimum departure from nucleate boiling ratio (DNBR) remains above the 95/95 DNBR limit, and 3. The event should not generate a more serious plant condition without other faults occurring independently.

The principally challenged acceptance criterion for this analysis is to demonstrate that the event does not generate a more serious plant condition a The analysis objective is to determine the minimum time for the pressurizer dome to become liquid-filled.

A transient-termination operator action time based on this analysis result will ensure that no liquid is relieved through the accidentally opened PORV.a The challenges to the overpressure limits and SAFDLs (e.g., DNBR) are addressed in the St. Lucie Unit 1 EPU LAR's Attachment 5 LR, Section 2.8.5.6.1, Inadvertent Opening of Pressurizer Pressure Relief Valve.

Controlled Document A AR EVA St. Lucie Unit 1 EPU -Information to Support NRC Review of RCS Depressurization With Pressurizer Overfill ANP-3067 Revision 1 Paqe 12 2.5 Results The sequence of events for the limiting casea is shown in Table 2. The system response is presented in Figure 1 to Figure 8.The analysis showed that the minimum time from the event initiation to the pressurizer dome becoming liquid-filled is 7 minutes.b Thus, the operators will have no more than 7 minutes from the inadvertent opening of a pressurizer PORV to terminate the event, by closing the PORV or its block valve.a The limiting case is initiated with maximum RCS temperatures and assumes that the pressurizer heaters are unavailable and that a LOOP occurs at reactor trip-which, in turn, renders the SBCS unavailable.

b The pressurizer is considered to be full when the liquid fraction in the dome reaches 1.00.

Controlled Document A AR EVA St. Lucie Unit 1 EPU -Information to Support NRC Review of RCS Depressurization With Pressurizer Overfill ANP-3067 Revision 1 Paqe 13 Table 1 RCS Depressurization

/ Pressurizer Overfill:

Initial Conditions and Biasing Parameter Value Initial Reactor Power 3029.06 MWt Initial Core Inlet Temperature Range 532 0 F -554oF Initial RCS Flow Rate (total) 375,000 gpm Initial Pressurizer Pressure 2185 psia Initial Pressurizer Level 68.6%Moderator Reactivity Moderator density feedback corresponding to +7.0 pcm/°F MTC Doppler Temperature Coefficient (DTC) -0.80 pcm/°F Scram Reactivity 6017.22 pcm Steam Generator Tube Plugging 10% (both steam generators)

Open Pressurizer PORV Flow Rate (single Sized to relieve 154,530 Ibm/hr PORV) at 2400 psia (steam only)TM/LP Reactor Trip Setpoint PPZR : 2061 psia x A 1 a x QR 1 b+ 15.85 psia/°F x Tiniet -8950 psia, or PPZR -1847 psia TM/LP Reactor Trip Signal-Processing Delay 0.9 s MFW Status Initially on auto, then terminated at reactor-trip Actuation of All Charging Pumps At reactor tripc Charging Flow Rate (total) 147 gpm RWT Temperature 51 °F SBCS Capacity Range 24% -58%SBCS Secondary System Pressure Setpoint 910 psia MSSV Setpoints Open on pressures higher than 1030.0 psia (for Bank 1) and 1060.8 psia (for Bank 2)Low-Low Pressurizer Pressure Safety Injection 1640 psia Actuation Signal (SIAS) Setpoint Safety Injection Availability Delay After SIAS 0.0 s HPSI Flow Rate Maximum, for both HPSI pumps a A 1 (of the TM/LP reactor trip function) was conservatively assumed to be 1.0 in the S-RELAP5 model.b QR 1 (of the TM/LP reactor trip function) is 1.0 at power levels above 97.2% of the rated thermal power (RTP).C For LOOP cases, no charging flow delay after LOOP (for emergency diesel generator startup and sequencing) was credited.

Controlled Document A AREVA St. Lucie Unit 1 EPU -Information to Support NRC Review of RCS Depressurization With Pressurizer Overfill ANP-3067 Revision 1 Paqe 14 Table 1 RCS Depressurization I Pressurizer Overfill:

Initial Conditions and Biasing (Continued)

Parameter Value Automatic Termination of Charging and Actua- Not credited tion of Letdown (after pressurizer level restored)Low-Low Steam Generator Level Auxiliary 14% narrow range (NR)Feedwater Actuation Signal (AFAS) Setpoint AFW Actuation Delay After AFAS 330 sa AFW Flow Rate (total) 2 electric pumps x 296 gpm / pump AFW Temperature 104°F a This maximum AFW actuation delay, which includes time for emergency diesel generator startup and sequencing, was used not only for LOOP cases but also-as an additional conservatism-for no-LOOP cases.

Controlled Document A AREVA St. Lucie Unit 1 EPU -Information to Support NRC Review of RCS Depressurization With Pressurizer Overfill ANP-3067 Revision 1 Page 15 Table 2 RCS Depressurization I Pressurizer Overfill:

Sequence of Events Event Time (s)Event initiation

-single pressurizer PORV inadvertently opens 0.0 Pressurizer pressure reaches TM/LP setpoint 60.2 TM/LP signal actuates reactor trip, offsite power is assumed to be lost, MFW is lost, 61.1 RCPs begin to coast down, turbine trips, and all RCS charging is assumed to begin Lowest steam generator (SG) level reaches AFAS setpoint 66.1 MSSVs first open 66.5 Pressurizer pressure reaches SIAS setpoint 107.2 HPSI begins 110.1 AFW flow to SG-1 and SG-2 begins 396.1 Pressurizer dome becomes liquid-filled 444.7 Controlled Document A AR REVA ANP-3067 St. Lucie Unit 1 EPU -Information to Support NRC Revision 1 Review of RCS Depressurization With Pressurizer Overfill Page 16 50 40 u 30 E 20 LL 10 0 0 I...100 200 300 400 Time (s)500 600 Figure 1 RCS Depressurization

/ Pressurizer Overfill -Pressurizer PORV Flow Rate Controlled Document A AR EVA St. Lucie Unit 1 EPU -Information to Support NRC Review of RCS Depressurization With Pressurizer Overfill ANP-3067 Revision 1 Paae 17 2400 2200 2000 1800 1600 a)1400 1200 1000 800 600 0 100 200 300 400 500 Time (s)600 Figure 2 RCS Depressurization

/ Pressurizer Overfill -Pressurizer Pressure Controlled Document A A R EVA St. Lucie Unit 1 EPU -Information to Support NRC Review of RCS Depressurization With Pressurizer Overfill ANP-3067 Revision 1 Paqe 18 620 600 580 U-S560 C.E I--540 520 500 0 100 200 300 400 500 Time (s)600 Figure 3 RCS Depressurization

/ Pressurizer Overfill -RCS Coolant Temperatures Controlled Document A AR EVA St. Lucie Unit 1 EPU -Information to Support NRC Review of RCS Depressurization With Pressurizer Overfill ANP-3067 Revision 1 Paqe 19 70 60 50 40 40 0 0 20 (I)130_0 7-20 10 0 100 200 300 400 500 Time (s)600 Figure 4 RCS Depressurization

/ Pressurizer Overfill -RCS Subcooling Controlled Document A AREVA St. Lucie Unit I EPU -Information to Support NRC Review of RCS Depressurization With Pressurizer Overfill ANP-3067 Revision 1 Page 20 110 100 90 80 0 M, 70 60 50 40 30 20 10 0 0 100 200 300 400 500 Time (s)600 Figure 5 RCS Depressurization

/ Pressurizer Overfill -Total RCS Flow Rate Controlled Document A AR EVA St. Lucie Unit 1 EPU -Information to Support NRC Review of RCS Deoressurization With Pressurizer Overfill ANP-3067 Revision 1 Paae 21 120 100 Indicated Power 0-0 0 CU ('D C: 80 60 40 20 0 , , I , I ...I I , , , , ...., , , , .I ..0 100 200 300 Time (s)400 500 600 Figure 6 RCS Depressurization

/ Pressurizer Overfill -Indicated Reactor Power Controlled Document A AR EVA St. Lucie Unit I EPU -Information to Support NRC Review of RCS Depressurization With Pressurizer Overfill ANP-3067 Revision 1 Page 22 140 120 100 E 0 LL 80 60 40 20 0 300 Time (s)600 Figure 7 RCS Depressurization

/ Pressurizer Overfill -Total HPSI and Charging.Flow Rates Controlled Document A AREVA St. Lucie Unit 1 EPU -Information to Support NRC Review of RCS Deoressurization With Pressurizer Overfill ANP-3067 Revision 1 Paoe 23 2000 1800 1600 1400 1200 1000> 800 600 400 200 0 0 100 200 300 400 500 Time (s)600 Figure 8 RCS Depressurization

/ Pressurizer Overfill -Pressurizer Liquid Volume Controlled Document A AR EVA ANP-3067 St. Lucie Unit I EPU -Information to Support NRC Revision 1 Review of RCS Depressurization With Pressurizer Overfill Page 24 3.0 References

1. EMF-231 0(P)(A) Revision 1, SRP Chapter 15 Non-LOCA Methodology for Pressurized Water Reactors, Framatome ANP, May 2004.2. L-2011-448, Response to NR C Reactor Systems Branch and Nuclear Performance Branch Request for Additional Information Regarding Extended Power Uprate License Amendment Reguest, FPL letter to NRC, dated October 31, 2011.