ML20069A969

ACRS Full Committee Presentation: NuScale Topical Report, Loss-of-Coolant Accident Evaluation Model, PM-0320-69138, Revision O

ML20069A969
Person / Time
Site:	NuScale
Issue date:	03/05/2020
From:	NuScale
To:	Office of Nuclear Reactor Regulation
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LO-0320-69139 PM-0320-69138, Rev 0
Download: ML20069A969 (30)

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L0-0320-69139

Enclosure:

"ACRS Full Committee Presentation: NuScale Topical Report, Loss-of-Coolant Accident Evaluation Model," PM-0320-69138, Revision O NuScale Power,LLC 1100 NE Circle Blvd., Suite 200 Corvallis, Oregon 97330 Office 541.360-0500 Fax 541.207.3928 www.nuscalepower.com

NuScale Nonproprietary ACRS Full Committee Presentation N uScale Topical Report Loss-of-Coolant Accident Evaluation Model March 5, 2020 PM-0320-69138 Copyright 2020 by NuScale Power, LLC.

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Presenters Matthew Presson Licensing Project Manager Dr. Pravin Sawant Supervisor Code Validation and Methods Dr. Selim Kuran Thermal Hydraulic Analyst Ben Bristol Supervisor System Thermal Hydraulics 2

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Agenda

• Methodology Overview

- Background

- Regulatory Requirements

- Methodology Roadmap

• NPM Safety Systems Overview

• Element 1: PIRT

• Element 2: Assessment Base

• Element 3: NRELAPS Evaluation Model

• Element 4: Applicability Evaluation

• Extension of LOCA EM to IORV

• Conclusions 3

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Background

• Unique NPM Design Features

- Integrated design eliminates piping and limits potential breaks

- Coolant captured completely in containment, cooled and returned to RPV using a large pool as ultimate heat sink

• Simple LOCA Progression with Well-Known Phenomena

- Choked/un-choked flow through break and ECCS valves

- Core decay heat and RCS stored energy release

- CNV heat transfer to pool (condensation, conduction, convection)

• EM Development Approach

- Follows Regulatory Guide 1.203 EMDAP (Table 2-1)

- Compliance with 10 CFR 50.46 and Appendix K requirements (Table 2-2) 4 PM-0320-69138 Copyright 2020 by NuScale Power, LLC.

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Regulatory Requirements

• 10 CFR 50.46 Acceptance Criteria

- Max. clad temperature< 2200 °F

- Cladding oxidation > 0.17 times thickness

- Hydrogen generation < 0.01 times total hydrogen from oxidation of all cladding

- Core remains amenable to cooling

- Long-term cooling maintained

• Maximum PCT at steady state, no clad heat up

• Conservative LOCA EM Acceptance Criteria (FOMs)

- Core remains covered: collapsed level > TAF

- MCHFR > CHFR Limit (1.29)

- Containment pressure and temperature below design limit 5

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Methodology Roadmap

• 10 CFR 50.46 Appendix K Compliance (Section 2.2.3 of LTR)

• RG 1.203 EMDAP (Section 2.1 of LTR) r Element 1 Establish Requirements for EM Capabilities LOCA PIRT (LTRCh. 4) r Element3 Element2 Develop Evaluation Model Develop Assessment Base SET and IET Assessment (L TR Ch. 7)

• NRELAP5 Code (LTR Ch. 6)

Evaluation model (LTR Ch. 5)

\... ~ "'" Break spectrum and sensitivity calcs. (LTR Ch. 9) ~

Element4 Assess EM Adequacy Top-down and Bottom-up evaluation (LTR Ch. 8) 6 PM-0320-69138 Copyright 2020 by NuScale Power, LLC.

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NPM Safety Systems

• ECCS

- Opens a boiling/condensing circulation flow path to transfer decay and residual heat to reactor pool

- Reactor Recirculation Valves (RRV) : 2 valves

- Reactor Vent Valves (RVV) : 3 valves

- Actuation Signals: High C NV level, 24-hour loss of AC power

- Fail safe: ECCS trip valves open on loss of DC power

• Inadvertent Actuation Block (IAB)

Reactor Vent Valves

- Prevents inadvertent opening of ECCS valves at high RCS pressure

- Actuation based on differential pressure between RPV and CNV

• Module Protection System (MPS)

- Reactor scram

- Steam Generator (SG) and Containment (CNV) Isolation

- Passive safety system activation (ECCS and DHRS)

• Decay Heat Removal System (DHRS)

- ---+-+- Reactor Recirculation Valves

- Passive, boiling-condensation system

- Removes heat from RCS through SG via two trains

- Each trains capable of removing 100% decay heat

- Not credited in LOCA EM NOTTO SCALE 7

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Element 1 PIRT 8

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PIRT Process

• Assessment of relative importance of phenomena

- Unique phases

- Key components

• PIRT panel included recognized experts and NuScale subject matter experts

• State-of-knowledge, design description, LOCA description, NRELAPS calculations

• Figures-of-Merit

- CHF, Collapsed level above top of the active fuel , CNV P & T

• Rankings

- Importance: High, Low, Medium, Inactive

- Knowledge: Well known (small uncertainty), Known (moderate uncertainty, partially known (large uncertainty), very limited 9

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Spatial and Temporal Decomposition

• Phenomena identified for Systems , Structure, Components (SSCs) and LOCAphases o Phase 1a: Slowdown o Phase 1b: ECCS activation (opening)

RCS-CNV -e-ti Phase 1a hase 1b Phase 2 0

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Slowdown ECCS Actuation Flow Reversal at RRVs

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il F OD

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Time System/Subsystem/Module decomposition Distinct phases of a typical NPM LOCA 10 PM-0320-69138 Copyright 2020 by NuScale Power, LLC.

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Element 2 Assessment Base 11 PM-0320-69138 Copyright 2020 by NuScale Power, LLC.

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NRELAP5 Code

• RELAP5-3D©v4.1.3 used as a baseline code o Two-fluid model (thermal and mechanical non-equilibrium)for hydrodynamics with

• Non-condensable gases with gas phase

• Semi-implicit scheme for time integration o Heat conduction across 1 D geometries (slab, cylinder, sphere) o Neutron Kinetics with thermal hydraulic feedback o Special Process Models o Comprehensive control/trip system modeling

• Code configuration control and development consistent with NuScale's NQA-1 2008 / 2009a QA program

• Modifications for NRELAPS:

- NuScale specific components (e.g., helical coil SG)

- Regulatory requirements (i.e., Appendix K)

- Error correction 12 PM-0320-69138 Copyright 2020 by NuScale Power, LLC.

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IET and SET Data

• Extensive database with adequate coverage of all high-ranked phenomena

• Integral effects tests (IET)

- Six (6) NIST-1 tests

• Separate effects tests (SET)

- Two (2) NIST-1 SETs

- Four (4) other NuScale SETs

- Nine (9) Legacy SETs 13 PM-0320-69138 Copyright 2020 by NuScale Power, LLC.

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NIST-1 Facility

• Primary source of NuScale-Specific IET and SET data

• Design Features

- Integral Reactor Vessel with electrically heated rod bundle core, helical coil steam generator, and pressurizer Containment with HTP and Cooling Pool

- DHRS, ECCS, eves lines represented

- 700 instruments

• Sca ling Basis Power/Volume Scaling Reduced height and reduced volume scale

- Full Pressure and Temperature Same Time Scale (isochronicity) 14 PM-0320-69 138 Copyright 2020 by NuScale Power, LLC.

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Element 3 NRELAP5 NPM LOCA 15 *~ !NUSCALE .

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NPM LOCA Model Overview

• Analysis and Justifications

- NRELAP5 model nodalization and input options

- Time-step control

- Initial and boundarycondition biases

- Treatment of setpoints and trips

• LOCAbreak spectrum

- Break location and sizes

- Single failures

- Power availability

• Methodology sensitivity calculations

- Required by Appendix K

- Phenomena-specific

- To establish conservative biases 16 PM-0320-69138 Copyright 2020 by NuScale Power, LLC.

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Element 4 Applicability Evaluation 17 PM-0320-69138 Copyright 2020 by NuScale Power, LLC.

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Applicability Evaluation

• Evaluated models and correlations (bottom-up)

- Identified dominant models/correlations for 'H' phenomena (Table 8-1 of LTR)

- Identified key model/correlation parameters and phenomenological domain where models/correlations are used (Tables 8-2 and 8-4)

- Reviewed models/correlations (Table 8-18 of LTR)

• Pedigree, Applicability range, Fidelity to SET data, Scalability

• Evaluated integral performance of EM (top-down)

- Reviewed code governing equations and numerics

- Evaluated integral performance of code using IET data (Table 8-19 of LTR)

- Evaluated IET data applicability and NRELAPS scalability

• Scaling and distortion analysis

• Differences and distortions between NPM and NIST can be accounted using NRELAP5 18 PM-0320-69138 Copyright 2020 by NuScale Power, LLC.

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Conclusions

• Number of conservatisms built into the NuScale LOCA EM

- 10 CFR 50 Appendix K

- Other methodology conservatisms

• Cycle independent bounding LOCA analysis

• Supported by extensive experiment database, well qualified code, and several sensitivity calculations

• Applicability evaluation consistent with RG 1.203

• CHF not challenged

• Collapsed level in RPV remains above TAF

• No clad or fuel heat-up

• CNV P& Tremain below design limits 19 PM-0320-69138 Copyright 2020 by NuScale Power, LLC.

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Appendix B to LOCALTR Extension to IORV Event 20 PM-0320-69138 Copyright 2020 by NuScale Power, LLC.

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IORV Background

• LOCA EM Extended to IORV

- Liquid space (RRV) and steam space (RVV, RSV) discharge

- Similartransient phenomena and progression

• EM Developr11ent Approach

- Compliance with DSRS for NuScale SMR Design 15.6.6

- Follows RG 1.203 EMDAP

- Element 1 (PIRT), Element 2 (Assessment), and Element4 (Applicability) remains same as LOCA EM

• Initial LOCJ~ PIRT addressed IORV

- Element 3 (NRELAPS Model) unique due to event classification 21 PM-0320-69138 Copyright 2020 by NuScale Power, LLC.

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Differences from LOCA EM

• Minor methodology differences given AOO classification

• Key Acceptance Criteria

- MCHFR ~ Lim it(~ 1.13 high flow range, ~ 1.37 low flow range)

• Conservatisrns same as LOCA with exceptions:

- Fuel properties still biased to maximize stored energy, but additional 15°/o bias removed

- Limiting axial power shapes and radial peaking based on subchannel analysis

- Moody choked flow model for 2-phase flow choking applied to initiating valve

- Initial conditions biased to minimize MCHFR 22 PM-0320-69138 Copyright 2020 by NuScale Power, LLC.

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Conclusions

_* IORV is an extension of LOCA EM given similar transient phenomena and progression

- PIRT, Assessment, and Applicability same as LOCA

• Minor methodology differences for AOO classification

- Focused on conservative CHFR evaluation

• MCHFR occurs early in transient, then rapidly rises given increasing flow to power ratio

• Collapsed level in RPV remains above TAF 23 PM-0320-69138 Copyright 2020 by NuScale Power, LLC.

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Acronyms 1-0 one-dimensional HP high pressure 30 three-dimensional HS heat sink AC alternating current HTP heat transfer plate ANS American Nuclear Society H2TS hierarchical two-tiered scaling CCFL counter current flow limitation IAB inadvertent actuation block CHF critical heat flux IET integrated effects test CNV containment vessel INL Idaho National Laboratory eves chemical and volume control system KATHY Karlstein thermal-hydraulic test facility DC direct current kW kilowatt DCA Design Certification Application LOCA loss-of-coolant accident DHRS decay heat removal system LTR Licensing Topical Report ECCS emergency core cooling system Max maximum EM evaluation model MCHFR minim um critical heat flux ratio EMDAP evaluation model development and Min minimum assessment process Mlb/ft2 *hr pounds mass per square foot per hour FW feedwater MPS module protection system FSAR Final Safety Analysis Report MSIV main steam isolation valve FOM figure of merit NIST-1 NuScale Integral System Test Facility HL hot leg NPM NuScale Power Module 24 PM-0320-69138 Copyright 2020 by NuScale Power, LLC.

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Acronyms P&T pressure and temperature PCT peak cladding temperature PIRT phenomena identification and ranking table psi pounds per square inch psia pounds per square inch absolute PZR pressurizer QA Quality Assurance RCS reactor coolant system RG Regulatory Guide RRV reactor recirculation valve RPV reactor pressure vessel RW reactor vent valve SG steam generator SET separate effects test SIET Societa lnformazioni Esperienze Termoidrauliche StDev standard deviation TAF top of active fuel 25 PM-0320-69138 Copyright 2020 by NuScale Power, LLC.

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Portland Office Richland Office 6650 SW Red'AOOCI Lane, 1933 Jadv,in Ave., Suite 130 Suite 210 Richland, WA 99354 Portland, OR 97224 541. 360. 0500 971.371.1592 Charlotte Office Corvallis Office 2815 Coliseum Centre Drive, 1100 NE Circle Blvd., Suite 200 Suite 230 Corvallis, OR 97330 Charlotte, NC 28217 541.360. 0500 980. 349. 4804 Rockville Office 11333 Woodglen Ave., Suite 205 Rockville, MD 20852 301. 770.0472 http:l!WvVW.nuscalepowercom W Twtter: @NuScale_Pov..er NUSCALE TM Powe r for al l hu m ankind 26 PM-0320-69138 Copyright 2020 by NuScale Power, LLC.

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Backup IORV Slides 27 PM-0320-69138 Copyright 2020 by NuScale Power, LLC.

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RRV Opening Results Sequence of Events Time (s) 1800 RRVopens 0 1600 1400 Minimum CHFR occurs 0.5

? 1200 Containment pressure reaches analytical limit 0.7 <I) a.

- 1000

~

Control rods begin to fall 2.7  ::J

l 800

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Peak steam generator pressure is reached 64 Cl.. 600 400 Remaining ECCS valves open 161 200 Minimum collapsed liquid level above the core 170 50 100 150 200 250 300 Peak containment pressure is reached 171 Time (sec)

RPV Pressure - - CNV Pressure -

Natural circulation from containment to RPV is g 35 197 ~

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Time_{sec)

RPV, R1ser -+--

CNV -

TAF Ref. Elevation at O ft -

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RW Opening Results 1800 Sequence of Events Time (s) 1600 RWopens 0 1400 Containment pressure reaches analytical limit 0.3 1200

~

Minimum CHFR occurs 0.3 -~ 1000 Cl)

5 800 Control rods begin to fall 2.3

"'"'~ 600 Peak steam generator pressure is reached 25 a..

400 Peak containment pressure is reached 52 200 Remaining ECCS valves open 3925 Natural circulation from containment to RPV is 4072 RPV Pressure --+- Time (sec) CNV Pressure -

established

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35 Minimum collapsed liquid level above the core 4192 ...

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RPV, Riser - -

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TAF Ref. Elevation at Oft -

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