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ACRS Full Committee Presentation: NuScale Topical Report, Loss-of-Coolant Accident Evaluation Model, PM-0320-69138, Revision O
	ML20069A969
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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
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"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 L0-0320-69139

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2 PM-0320-69138 Revision: 0 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 Copyright 2020 by NuScale Power, LLC.

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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 4

PM-0320-69138 Revision: 0 (Table 2-2)

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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 r

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

Element2 Develop Assessment Base SET and IET Assessment (L TR Ch. 7)

Element3 Develop Evaluation Model NRELAP5 Code (LTR Ch. 6)

Evaluation model (LTR Ch. 5)

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

6 PM-0320-69138 Revision: 0 Element4 Assess EM Adequacy Top-down and Bottom-up evaluation (LTR Ch. 8)

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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 CNV level, 24-hour loss of AC power Fail safe: ECCS trip valves open on loss of DC power

Inadvertent Actuation Block (IAB)

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)

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 7

Reactor Vent Valves

---+-+- Reactor Recirculation Valves NOTTO SCALE

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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 9

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Spatial and Temporal Decomposition

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

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Time System/Subsystem/Module decomposition Distinct phases of a typical NPM LOCA 10 PM-0320-69138 Revision: O

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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)

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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

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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 Power/Volume Scaling Reduced height and reduced volume scale Full Pressure and Temperature Same Time Scale (isochronicity) 14 PM-0320-69138 Revision : 0 Copyright 2020 by NuScale Power, LLC.

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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

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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 18 PM-0320-69138 Revision: 0

Scaling and distortion analysis

Differences and distortions between NPM and NIST can be accounted using NRELAP5 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 Revision: 0 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

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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

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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 Revision: 0 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 Revision: 0 Copyright 2020 by NuScale Power, LLC.

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Acronyms P&T PCT PIRT psi psia PZR QA RCS RG RRV RPV RW SG SET SIET StDev TAF 25 PM-0320-69138 Revision: 0 pressure and temperature peak cladding temperature phenomena identification and ranking table pounds per square inch pounds per square inch absolute pressurizer Quality Assurance reactor coolant system Regulatory Guide reactor recirculation valve reactor pressure vessel reactor vent valve steam generator separate effects test Societa lnformazioni Esperienze Termoidrauliche standard deviation top of active fuel Copyright 2020 by NuScale Power, LLC.

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Portland Office 6650 SW Red'AOOCI 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 Jadv,in Ave., Suite 130 Richland, WA 99354 541. 360. 0500 Charlotte Office 2815 Coliseum Centre Drive, Suite 230 Charlotte, NC 28217 980. 349. 4804 http:l!WvVW.nuscalepowercom W Twtter: @NuScale_Pov..er 26 PM-0320-69138 Revision: 0 Copyright 2020 by NuScale Power, LLC.

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RRV Opening Results Sequence of Events RRVopens Minimum CHFR occurs Containment pressure reaches analytical limit Control rods begin to fall Peak steam generator pressure is reached Remaining ECCS valves open Time (s) 0 0.5 0.7 2.7 64 161 Minimum collapsed liquid level above the core 170 Peak containment pressure is reached Natural circulation from containment to RPV is established 171 197 1800 1600 1400

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RW Opening Results Sequence of Events RWopens Containment pressure reaches analytical limit Minimum CHFR occurs Control rods begin to fall Peak steam generator pressure is reached Peak containment pressure is reached Remaining ECCS valves open Time (s) 0 0.3 0.3 2.3 25 52 3925 1800 1600 1400 1200

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