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Nuscale - Dhrs and ECCS Logic Changes, PM-0219-64563, Revision 0
	ML19053A518
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Site:	NuScale
Issue date:	02/19/2019
From:	; NuScale
To:	; Office of New Reactors
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L0-0219-64591 Enclosure 1:

"DHRS and ECCS Logic Changes," PM-0219-64563, Revision 0 I

NuScale Power, LLC 1100 NE Circle Blvd., Suite 200 Corvallis, Oregon 97330 Office 541.360-0500 Fax 541.207.3928 www.nuscalepower.com

NuScale Noriproprietary DHRS and ECCS Logic Changes Brian Arnholt l&C Supervisor Ross Snuggerud Operations Supervisor Ben Bristol Safety Analysis Supervisor 2/19/2019 PM-0219-64563 Revision: O Copyright 2019 by NuScale Power, LLC.

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DHRS and ECCS MPS Changes

Decay Heat Removal System (DHRS) signal modified to support plant operations

Existing DHRS signal split into two signals

- DHRS actuation

- Secondary System Isolation (SSI)

Remove uncredited ECCS actuation on reactor pressure vessel (RPV) level

Minimal impact to safety analysis

Some Technical Specifications changes

Conforming changes required throughout DCA

No change to Module Protection System (MPS) architecture 2

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Decay Heat Removal System M a in M a in S team S team MSI V M S IV Containme nt Ins ul ated In s ul a ted V e s s el Insula ted In su lated Rea ctor Non insulated Non insulated Pres sure Non insulated Non insulated Passive Pass ive Condenser Conde n ser Core Reactor Pool 3

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Operational Insights.

NuScale operation and safety philosophy are unique

- The module protection system ensures that passive cooling is in service or available in all required modes

- Operators are not expected to override safety signals (can not override DHRS)

- Interlocks are designed to remove actuation signals when plant conditions no longer require automatic protective actions

DHRS during startup (Current Design)

- With the existing design, the low superheat signal cannot be cleared during initial plant startup preventing closure of the DHRS actuation valves and preventing heatup on module heating system 4

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Operational Insights

Secondary System Isolation Actuation (New \Design)

- New Secondary System Isolation (SSI) signal isolates Main Steam and Feedwater to the Steam Generators through an automatic protective action .

. - SSI signals are a subset of the current DHRS actuation signals.

Allows for a reduction in the current number of DHRS actuation signals (13 to 4)

- New configuration bypasses SSI low superheat actuation when one steam generator isolated by a closed feedwater isolation ~valve and less than 15% reactor power

Ensures passive cooling, allows operator control during startup

Revised DHRS actuation signals and add S,SI signals

- Allows for additional operator maneuverability of the plant at low power/shutdown conditions within the safety analysis 5

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Safety Analysis Impacts

Most events not impacted by DHRS logic changes

Cooldown events that trip on SG overfill or inventory loss conditions will not immediately actuate DHRS upon SSI

- - Increase in FW Flow transient will trip the reactor and isolate the SGs on low superheat but does not actuate DHRS until high steam pressure reached

- Steam Line Breakwill isolate the SGs on low steam pressure but does not actuate DHRS until high RCS temperature or steam pressure signals are reached

Small delays in DHRS actuation are not expected to impact safety analysis margins 6

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Licensing Chapter 15 Impacts

/

Chapter 15 Impact

- No impact on MCHFR because reactor trip signals are unaffected

- Small effect on primary and secondary pressure margins for some

events

- Event descriptions will have changes in the timing of DHRS and Secondary System Isolation signals (i.e~, sequence of events

. -tables will have separate entries)

~ Section 15.1 Primary Cooldown events will have some timing delay between Secondary System Isolation and DHRS actuation*

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l&C Impacts

No changes to MPS architecture or fundamental design

ESF Function Changes

- New ESF function for Seconda~y System Isolation (SSI)

Isolates main feedwater (FW) and main steam to protect steam generator (SG) inventory without an unnecessary cooldown

Adds new operating bypass

Adds new manual actuation switches for SSI actuation

FW isolation valve position switches are re-classified as safety-related to support operating bypass logic

- Simplify automatic DHRS actuation ,

Many events requiring SG isolation do not need DHRS cooling

13 signals reduced to 4 signals 8

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ECCS Actuation on RPV Level

ECCS Actuation on Reactor Pressure Vessel (RPV) Leve*I Removed from MPS Logic

Safety analysis only credits automatic ECCS actuation on High Containment (CNV) Water Level (no change) *.

Removal, of uncredited ECCS actuation on RPV level has no impact on risk*

(core damage frequency or large e*arly release frequency)

RPV level indication retained as nonsafety-related sensor and remains a Post Accident Monitoring Type B, C, and D variable

ECCS automatic actuation occurs on High Containment Water Level or Low AC Voltage after 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> 9

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Licensing Impacts

FSAR Tier 1

FSAR Tier 2 *

Part 4 Technical Specifications

Advanced Sensor Technical Report* (TR-0316-22048)

Instrument Setpoint Methodology Technical Report (TR-0616-49121)

. .

Changes will be included in DCA Revision 3 (August 2019) 10 PM-0219-64563 Revision: 0 Copyright 2019 by NuScale Power, LLC.

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Technical Specification Impacts

No new Technical Specifications

- New MPS function

- SSI ESF function and associated operating bypasses will require some renumbering and bases descriptive changes.

Technical Specifications Changes

- Substantive changes are in LCOs

3.3.1 MPS Instrumentation,

3.3.3 ESFAS Logic and Actuation,

3.3.4 Manual Actuation Functions, and

3.5.2 DHRS

- Bases updates to the above areas, and in LCOs

3.5.1 ECCS,

3.7.1 MSIV, and

3. 7 .2 Feedwater Isolation 11 PM-0219-64563 Revision: 0 Copyright 2019 by NuScale Power, LLC.

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Summary

DHRS signal needs to be modified to support plant operations

Existing DHRS signal split into two signals

- DHRS actuation

- Secondary System Isolation

Remove uncredited ECCS actuation on RPV Level

Minimal impact to safety analysis

Introduces no new Technical Specifications, but does require some Technical Specifications *changes

Conforming ch~nges required throughout DCA

No change to MPS architecture 12 PM-0219-64563 Revision: 0 Copyright 2019 by NuScale Power, LLC.

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Portland Office Richland Office 6650 SW Redwood Lane, 1933 Jadwin Ave., Suite 130 Suite 210 Richland, WA 99354 Portland, OR 97224 541.360.0500 971.371.1592 Arlington Office .

Corvallis Office 2300 Clarendon Blvd., Suite 1110 1100 NE Circle Blvd., Suite 200 . Arlington, VA 22201 Corvallis, OR 97330 541.360.0500 London Office 1st Floor Portland House Rockville Office Bressenden Place 11333 Woodglen Ave., Suite 205 London SW1 E 5BH .

Rockville, MD 20852 United Kingdom 301.770.0472 . +44 (0) 2079 321700 Charlotte Office 2815 Coliseum Centre Drive, Suite 230 Charlotte, NC 28217 980.349.4804 http://www.nuscalepower.com

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ML19053A518

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