ML20150C881
| ML20150C881 | |
| Person / Time | |
|---|---|
| Site: | NuScale |
| Issue date: | 05/29/2020 |
| From: | Rad Z NuScale |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| LO-0620-70348 PM-0620-70244, Rev 0 | |
| Download: ML20150C881 (27) | |
Text
LO-0620-70348 NuScale Power, LLC 1100 NE Circle Blvd., Suite 200 Corvallis, Oregon 97330 Office 541.360-0500 Fax 541.207.3928 www.nuscalepower.com May 29, 2020 Docket No.52-048 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk One White Flint North 11555 Rockville Pike Rockville, MD 20852-2738
SUBJECT:
NuScale Power, LLC Submittal of Presentation Materials Entitled ACRS Full Committee Presentation: NuScale Topic - Boron Redistribution and Associated Design and DCA Changes, PM-0620-70244, Revision 0 The purpose of this submittal is to provide presentation materials to the NRC for use during the upcoming Advisory Committee on Reactor Safeguards (ACRS) NuScale Full Committee Meeting on June 3, 2020. The materials support NuScales presentation of boron redistribution and associated design changes in the NuScale Design Certification Application.
The enclosure to this letter is the nonproprietary presentation entitled ACRS Full Committee Presentation: NuScale Topic - Boron Redistribution and Associated Design and DCA Changes, PM-0620-70244, Revision 0.
This letter makes no regulatory commitments and no revisions to any existing regulatory commitments.
If you have any questions, please contact Matthew Presson at 541-452-7531 or at mpresson@nuscalepower.com.
Sincerely, Zackary W. Rad Director, Regulatory Affairs NuScale Power, LLC Distribution: Robert Taylor, NRC Michael Snodderly, NRC Christopher Brown, NRC Gregory Cranston, NRC Prosanta Chowdhury, NRC Michael Dudek, NRC
Enclosure:
ACRS Full Committee Presentation: NuScale Topic - Boron Redistribution and Associated Design and DCA, PM-0620-70244, Revision 0
LO-0620-70348 NuScale Power, LLC 1100 NE Circle Blvd., Suite 200 Corvallis, Oregon 97330 Office 541.360-0500 Fax 541.207.3928 www.nuscalepower.com
Enclosure:
ACRS Full Committee Presentation: NuScale Topic - Boron Redistribution and Associated Design and DCA Changes, PM-0620-70244, Revision 0
NuScale Nonproprietary Revision:0 Template #: 0000-21727-F01 R6 ACRS Full Committee Presentation Boron Redistribution and Associated Design and DCA Changes June 3, 2020 NuScale Topic Copyright 2020 by NuScale Power, LLC
Copyright 2020 by NuScale Power, LLC.
Revision:0 Template #: 0000-21727-F01 R6 Presenters Matthew Presson Licensing Project Manager Paul Infanger Licensing Specialist Ben Bristol Supervisor, System Thermal-Hydraulics Hannah Rooks Supervisor, NSSS Systems Analysis Sarah Bristol Supervisor, Probabilistic Risk Assessment
Copyright 2020 by NuScale Power, LLC.
Revision:0 Template #: 0000-21727-F01 R6 Agenda
- Boron Redistribution Background
- Boron Dilution Analysis
- Event Scenarios
- Design Changes
- Safety Analysis
- Mechanical Analysis
- DCA and Conforming Changes
- Conclusions
Copyright 2020 by NuScale Power, LLC.
Revision:0 Template #: 0000-21727-F01 R6 Boron Redistribution Background
- During ACRS subcommittee meetings in February 2020, scenarios were discussed that could lead to dilution of fluid in reactor pressure vessel (RPV) downcomer
- Under certain conditions, ECCS actuation or restoration of natural circulation flow could transport diluted coolant to the reactor core
- Postulated reactivity event could be outside those previously evaluated
- Return to power (FSAR 15.0.6)
- Boron dilution (FSAR 15.4.6)
- Boron redistribution (RAI 8930)
- NuScale initiated an evaluation of the postulated scenarios in accordance with Corrective Action Program
Copyright 2020 by NuScale Power, LLC.
Revision:0 Template #: 0000-21727-F01 R6 Boron Dilution Analysis Existing methods used bounding assumptions or assumed perfect mixing Large analysis conservatisms lead to unrealistic results Large boron loss term for fluid in containment (CNV) below reactor recirculation valves (RRVs)
Boron lost in vapor through reactor vent valves (RVVs) due to volatility No mechanism for boron recovery No methodology approved by the NRC exists for detailed boron mixing in downcomer or core Determined that the postulated boron redistribution scenarios could be eliminated through several minor design changes NRC initiated an audit (ML20059N687) to review the resolution of the postulated boron redistribution scenarios and associated changes to the NuScale Design Certification Application (DCA)
Daily interactions to support NRC staff review
Copyright 2020 by NuScale Power, LLC.
Revision:0 Template #: 0000-21727-F01 R6 Event Scenarios
- Potential events that required further evaluation for boron dilution LOCAs Condensation of water in CNV from RVVs Condensation of unborated water in downcomer ECCS actuation can transport unborated water to core DHRS operation can shrink RCS inventory below top of riser Condensation of unborated water in downcomer Unborated water can enter core when restoring natural circulation or after ECCS actuation (24-hour timer on loss of AC power)
Anticipated Transient Without Scram (ATWS)
Condensation of unborated water in downcomer and CNV after RCS fluid lost through reactor safety valves (RSVs)
Unborated water can enter core when restoring natural circulation or opening ECCS valves
Copyright 2020 by NuScale Power, LLC.
Revision:0 Template #: 0000-21727-F01 R6 Design Changes
- Design Considerations
- Ensure early actuation of ECCS for postulated LOCA events
- Actuates ECCS while pressure and level in RPV are higher than CNV establishes flow out of RPV when ECCS valves open
- After outflow, flow stagnates and slowly reverses through RRVs so that no large influx of unborated water can occur
- Provide mechanism for boron mixing in the unlikely event that RCS level drops below riser
- Eliminates potential dilution from restored natural circulation following analyzed DHRS cooldown scenarios or ATWS events
- Eliminates potential dilution from operator action to restore natural circulation or manual ECCS actuation
Copyright 2020 by NuScale Power, LLC.
Revision:0 Template #: 0000-21727-F01 R6 Design Changes (continued)
- ECCS actuation prevented by either of following interlocks
- CNV pressure less than 1 psia
- RCS Thot less than 475 ºF
- Interlocks prevent ECCS actuation for Non-LOCA events
- RCS is subcooled in DHRS cooldown events (lower than 475 ºF) and have no increase in CNV pressure
- Main steam line breaks and feedwater line breaks
Copyright 2020 by NuScale Power, LLC.
Revision:0 Template #: 0000-21727-F01 R6 Design Changes (continued)
- Lowered ECCS CNV level actuation setpoint
- 252 inches (from 282 inches)
- Level setpoint range remains above RRV
- Actuates ECCS while RCS level and pressure greater than CNV level and pressure
- Ensures initial flow out of RPV into CNV
- Establishes boron mixing before ECCS flow into RPV
PM-0620-70244 10 Copyright 2020 by NuScale Power, LLC.
Revision:0 Template #: 0000-21727-F01 R6 Design Changes (continued)
- Diverse flowpaths added to RPV riser
- Provide a flow path from riser through the downcomer to the core to ensure boron mixing even if level drops below top of riser
- Four 3/4 inch holes located at midpoint of SG
- Impact to normal operation is minimal
- Flow through holes is small (2 kg/s) compared to minimum 100% flow (535 kg/s)
- Holes located below RCS contracted level from extended DHRS cooldown
- Holes are above equilibrium riser level after ECCS actuation (no impact on LOCA cooling)
- Additional detail about this design change included in proprietary closed presentation
PM-0620-70244 11 Copyright 2020 by NuScale Power, LLC.
Revision:0 Template #: 0000-21727-F01 R6 Safety Analysis
- Return to Power (FSAR 15.0.6)
- End of cycle conditions remain limiting
- No impact to the postulated limiting return to power scenario
- Flow through riser holes maintains downcomer greater than critical boron concentration for events earlier in cycle
- Modifications maintain assumptions in redistribution analysis
- Some postulated events would actuate ECCS on low RCS pressure (most steam space LOCAs and some liquid space LOCAs)
- No change to limiting event MCHFR or collapsed liquid level
- Minor changes to some non-limiting events
PM-0620-70244 12 Copyright 2020 by NuScale Power, LLC.
Revision:0 Template #: 0000-21727-F01 R6 Safety Analysis (continued)
- No impact to limiting events (Loss of DC power events actuate ECCS on IAB threshold)
- RVV opening events with power available, remaining ECCS valves open on RCS pressure or low valve P
- RRV events not affected (remaining valves open on CNV level)
- RSV events remain bounded by inadvertent ECCS valve opening
PM-0620-70244 13 Copyright 2020 by NuScale Power, LLC.
Revision:0 Template #: 0000-21727-F01 R6 Mechanical Analysis
- Mechanical design and analysis impacts of the riser holes
- Negligible impact on full power RCS flow rate ( approximately 0.1 kg/s)
- Does not introduce structural integrity concerns due to flow-induced vibration
- No update needed to CVAP Technical Report
- Negligible impact to DHRS cooldowns
PM-0620-70244 14 Copyright 2020 by NuScale Power, LLC.
Revision:0 Template #: 0000-21727-F01 R6 Mechanical Analysis (Continued)
- Flow Induced Vibration (FIV) Evaluation
- The riser holes have been evaluated for FIV mechanisms turbulent buffeting (TB)
>> Holes are small (volume reduction of upper riser approximately 1/26,000) -
no impact to riser structural properties and TB evaluations not affected
- vortex shedding (VS)
>> Riser holes not expected to generate vortices due to continuous flow through the holes
>> If vortices did form, would not be coincident with riser acoustic modes
- Reviewed Operating Experience for fuel pin vibration due to baffle gap cross-flow
>> Normal flow through holes produces minimal force and no resonance with nearby components
PM-0620-70244 15 Copyright 2020 by NuScale Power, LLC.
Revision:0 Template #: 0000-21727-F01 R6 Probabilistic Risk Assessment
- PRA Evaluation
- Thermal hydraulic evaluation
- PRA models
- Risk significance and results
PM-0620-70244 16 Copyright 2020 by NuScale Power, LLC.
Revision:0 Template #: 0000-21727-F01 R6 Beyond Design Basis Thermal Hydraulic Impacts
- Design changes incorporated into best estimate NRELAP5 PRA thermal hydraulics model
- riser holes credited for preventing significant boron redistribution (per Chapter 15 analyses)
- new ECCS actuation logic modeled
- Impact to postulated event progression
- cycling RSV sequences now reach the new low RCS pressure ECCS actuation
- DHRS credit to reduce rate of coolant loss of unisolated injection line pipe breaks outside containment mitigated with core flood and drain system (CFDS)
- no impact to remaining sequences or assessments
PM-0620-70244 17 Copyright 2020 by NuScale Power, LLC.
Revision:0 Template #: 0000-21727-F01 R6 PRA Model Impacts
- Negligible effect on ECCS fault tree model
- fault tree does not credit all sensors/signals
- Negligible effect on ECCS initiating events
- requires three sensors to spuriously actuate
- Success criteria
- RSV cycling
- DHRS credited to mitigate unisolated injection line pipe break
- Negligible effect on operator actions
- modeled cues are unchanged
PM-0620-70244 18 Copyright 2020 by NuScale Power, LLC.
Revision:0 Template #: 0000-21727-F01 R6 PRA Results
- Internal events
- negligible change in the core damage frequency (CDF) and large release frequency (LRF)
- negligible change in the conditional containment failure probability (CCFP)
- no change in candidate risk-significant structures, systems, or components (SSCs)
- no change in candidate risk-significant initiating events or human actions
- no change in the significant core damage cutsets (FSAR Table 19.1-18)
- no change in the significant large release cutsets (FSAR Table 19.1-26)
- External events
- negligible effect
- Low power and shutdown
- negligible effect
- CVCS remains available during the plant cooldown to respond to RCS volume changes, as well as maintain adequate shutdown margin
- holes in the riser will maintain RCS recirculation independent of operator action
PM-0620-70244 19 Copyright 2020 by NuScale Power, LLC.
Revision:0 Template #: 0000-21727-F01 R6 PRA Summary
- Implementing the design changes to ECCS actuation, and the addition of riser bypass flow holes have a negligible effect on PRA results and insights
- some PRA sequences that involve cycling the RSV will now result in ECCS actuation
- riser holes credited to prevent significant boron redistribution
- Event tree logic has been updated to reflect the new event progressions for affected sequences.
PM-0620-70244 20 Copyright 2020 by NuScale Power, LLC.
Revision:0 Template #: 0000-21727-F01 R6 DCA and Conforming Changes
- DCA Revision 4, Errata 2, submitted May 20, 2020
- Tier 1 Chapter 2
- add new ECCS signal on low RCS Pressure
- FSAR Chapters
- riser holes and structural evaluations (Sections 3.9, 5.4)
- new ECCS actuation, interlocks and setpoint changes, passive ECCS valve opening, RCS wide range pressure instrumentation (Sections 3.2. 6.2, 6.3, 7.1, 7.2, 15.0, 15.6, 17.4)
- downcomer boron dilution mechanism (Sections 4.3, 15.0)
- LOCA analysis changes, sequence of events (Section 15.6.5)
- PRA event sequences for new ECCS actuation and riser holes (Section 19.1)
- Technical Specifications and Bases
- LCOs 3.3 Instrumentation and 3.5 ECCS
PM-0620-70244 21 Copyright 2020 by NuScale Power, LLC.
Revision:0 Template #: 0000-21727-F01 R6 DCA and Conforming Changes (continued)
- Technical Reports (submitted May 20, 2020)
- Instrument Setpoint Methodology (TR-0616-49121) - added ECCS Setpoint and Actuation range design changes
- NSSS Advanced Sensor (TR-0316-22048) - added ECCS Setpoint and Actuation range design changes
- Containment Response (TR-0516-49084) - added ECCS Setpoint and Actuation range design changes
- Long-Term Cooling Methodology (TR-0916-51299) - added ECCS Setpoint and Actuation range design changes
- Technical Specification Regulatory Conformance and Development (TR-1116-52011) - incorporated associated changes in instrumentation and bases
- GDC 33 Exemption - Possible revision to exemption basis being discussed with NRC staff. Not included in DCA Revision 4, Errata 2.
PM-0620-70244 22 Copyright 2020 by NuScale Power, LLC.
Revision:0 Template #: 0000-21727-F01 R6 DCA Conforming Changes
- Topical Reports (submitted May 27, 2020)
- LOCA Methodology (TR-0516-49422) - added ECCS Setpoint and Actuation range design changes. Added the Riser Hole design change.
No change to limiting cases for MCHFR and collapsed liquid level above TAF Non-limiting cases remain non-limiting
- Non-LOCA Methodology (TR-0516-49416) - added ECCS Setpoint and Actuation range and the Riser Hole design changes Results for RCS pressure, core inlet temperature, RCS flow, and steam generator pressure confirmed to have negligible differences under DHRS cooling
PM-0620-70244 23 Copyright 2020 by NuScale Power, LLC.
Revision:0 Template #: 0000-21727-F01 R6 Summary and Conclusions
- Design changes preclude boron redistribution for postulated design basis and beyond design basis events
- ECCS actuation on low RCS pressure or high CNV level
- Assures initial flow out of RPV to preclude influx of unborated water from CNV or downcomer
- Riser holes assure boron mixing in downcomer and core
- when DHRS cools and shrinks RCS level below the riser
- Analyses demonstrate no significant changes to results and that acceptance criteria continue to be met
- The evaluation and resolution of this topic involved the evaluation of a broad scope of postulated scenarios, extensive calculations, analyses and related document changes to develop and implement the design changes
PM-0620-70244 24 Copyright 2020 by NuScale Power, LLC.
Revision:0 Template #: 0000-21727-F01 R6 Acronyms MCHFR - minimum critical heat flux ratio NPM - NuScale Power Module P - differential pressure Psia - pounds per square inch absolute RAI - Request for Additional Information RCS - reactor coolant system RPV - reactor pressure vessel RRV - reactor recirculation valve RSV - reactor safety valve RTP - return to power RVV - reactor vent valve
/s - per second SAFDL - specified acceptable fuel design limits SDM - shutdown margin SG - steam generator TB - turbulent buffering TAF - top of active fuel VS - vortex shedding AC - alternating current ACRS - Advisory Committee on Reactor Safeguards AOO - Anticipated Operational Occurrences ATWS - anticipated transient without scram CCFP - conditional containment failure probability CDF - core damage frequency CFDS - core flood and drain system CHF - Critical Heat Flux CNV - containment vessel COL - Combined License CVAP - Comprehensive Vibration Assessment Program CVCS - chemical and volume control system DCA - Design Certification Application DHRS - decay heat removal system ECCS - emergency core cooling system EOC - end of cycle
ºF - degree Fahrenheit scale FIV - flow induced vibration FSAR - Final Safety Analysis Report GDC - General Design Criteria IAB - inadvertent actuation block kg - kilogram LCO - Limiting Condition for Operation LOCA - loss-of-coolant accident LRF - large release frequency
PM-0620-70244 25 Copyright 2020 by NuScale Power, LLC.
Revision:0 Template #: 0000-21727-F01 R6 http://www.nuscalepower.com Twitter: @NuScale_Power Portland Office 6650 SW Redwood Lane, Suite 210 Portland, OR 97224 971.371.1592 Corvallis Office 1100 NE Circle Blvd., Suite 200 Corvallis, OR 97330 541.360.0500 Rockville Office 11333 Woodglen Ave., Suite 205 Rockville, MD 20852 301.770.0472 Richland Office 1933 Jadwin Ave., Suite 130 Richland, WA 99354 541.360.0500 Charlotte Office 2815 Coliseum Centre Drive, Suite 230 Charlotte, NC 28217 980.349.4804