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ACRS Subcommittee Presentation: NuScale Topical Report- Loss-of-Coolant Accident Evaluation Model, PM-0220-68917, Revision 0
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Issue date:	02/17/2020
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To:	; Office of Nuclear Reactor Regulation
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"ACRS Subcommittee Presentation: NuScale Topical Report- Loss-of-Coolant Accident Evaluation Model," PM-0220-68917, Revision 0 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 Subcommittee Presentation N uScale Topical Report I ,

j Loss-of-Coolant Accident

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Presenters Matthew Presson Licensing Project Manager Dr. Pravin Sawant Supervisor Code Validation and Methods Dr. Selim Kuran Thermal Hydraulic Analyst 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)

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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 50.46Appendix K Compliance(Section 2.2.3 of LTR)

RG 1.203 EMDAP (Section 2.1 of LTR)

Element 1 Establish Requirements for EM Capabilities LOCA PIRT (LTR Ch. 4)

Element3 Element2 Develop Evaluation Model Develop Assessment Base N RE LAPS Code (L TR Ch. 6)

SET and IET Assessment (LTR Ch. 7) Evaluation model (LTR Ch. 5)

Break spectrum and sensitivity calcs. (LTR Ch. 9)

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NPM Safety Systems

ECCS

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

- Reactor Recirculation Valves (RRV): 2 valves

- Reactor Vent Valves (RW) : 3 valves

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

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

Inadvertent Actuation Block (IAB)

Reactor Vent V es 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 Reaculation Valves

- Passive, boiling-condensation system

- Removes heat from RCS through SG via MO 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, NRELAP5 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 -

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Slowdown ECCS Actuation Flow Reversal at RRVs C7 ~

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NRELAPS 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 1D 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 NRELAP5:

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

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

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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 Nu Scale SETs

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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

Scaling Basis PowerNolume Scaling Reduced height and reduced volume scale

- Full Pressure and Temperature

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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

LOCA break spectrum

- Break location and sizes

- Single failures

- Power availability

Methodology sensitivity calculations

- Required by Appendix K

- Phenomena-specific

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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 NRELAP5 scalability

Scaling and distortion analysis

Differences and distortions between NPM and NIST can be accounted using NRELAPS 18 PM-0220-68917 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-0220-68917 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 Development Approach

- Compliancewith 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 LOCAPIRT addressed IORV

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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)

Conservatisms 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

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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-0220-68917 Copyright 2020 by NuScale Power, LLC.

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Acronyms 1-D one-dimensional HP high pressure 3D 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 minimum 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-0220-68917 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-0220-68917 Copyright 2020 by NuScale Power, LLC.

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Portland Office Richland Office 6650 SW Redoood Lane, 1933 JadVvin 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:IIIMNW. nuscalepower.com

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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 ~

';j;' 1000 Control rods begin to fall 2.7 =i UJ 800

~

Peak steam generator pressure is reached 64 0.. 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 ~

established 0 30

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RPV, Riser --+-

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TAF Ref. Elevation at O ft -

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RVV Opening Results 1800 Sequence of Events Time (s) 1600 RWopens 0 1400 Containment pressure reaches analytical limit 0.3 1200 ti Minimum CHFR occurs 0.3 ~ 1000

~ 800 Control rods begin to fall 2.3 :,

Ill Ill

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

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TAF Ref. Elevation at O ft - + -

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ML20054A406

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