ML22320A004
| ML22320A004 | |
| Person / Time | |
|---|---|
| Site: | 99902049 |
| Issue date: | 12/05/2022 |
| From: | Holtec, SMR |
| To: | Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML22320A002 | List: |
| References | |
| 160-USNRC-029, SECY-94-084 | |
| Download: ML22320A004 (1) | |
Text
NRC Meeting:
SECY-94-084 Safe Shutdown Criteria December 5, 2022
Meeting Agenda
Introductions
Purpose & Outcome Overview of SMR-160 PCCS PCCS Performance and Safe Shutdown Condition Questions provided to N RC Open Forum holtec.com I smrllc.com I Page 2 H O LTEC I
T[K NA T I ONAL
Introductions
NRC staff Holtec staff o ec.com smr c.com I Page 3 HOLTEC I N.I [RNATIONr\\L
Purpose & Outcome PURPOSE: To provide a description of Passive Core Cooling System (PCCS) for non-LOCA events and describe some unique challenges in meeting the safe shutdown guidance per SECY-94-084.
OUTCOME: To obtain feedback from the NRC Staff on the safe shutdown guidance for SECY-94-084 and how it applies to SMR-160.
holtec.com I smrllc.com I Page 4
SMR-160 Passive Core Cooling PCCS is comprised of the following sub systems Prima ry Decay Heat Removal (PDHR)
Secondary Decay Heat Removal (SDHR)
HOLTEC I N °I [ I< N A T I O N,\\ l Automatic Depressurization System (ADS) - Only used for LOCA Passive Core Makeup Water System (PCMWS) - Only used for LOCA holtec.com I smrllc.com I Page 5
PDHR Consists of two closed loops Loop 1 pulls RCS coolant from the hot leg and returns cooler water to the SG lower head Loop 2 rejects Loop 1 energy to annular reservoir Primary function is to remove decay heat during non-LOCA events Capable of removing all decay heat without SOHR holtec.com I smrllc.com I Page 6 HOLTEC I N'! [RN A TION A L Note this figure does accurately show elevations, scales, or PDHR-RCS connections
SDHR Consists of one closed loop Removes core decay heat using the SG and rejects it to AR Steam from the SG enters the SOHR HX Steam rejects heat to AR and condenses in SOHR HX tubes Condensate returned to bottom of SG secondary side Primary function is to remove decay heat for non-LOCA or non-secondary side breaks Capable of removing all decay heat without POHR holtec.com I smrllc.com I Page 7 PROTECTED VENT CONTAINMENT ENCLOSURE STRUCTURE CONTAINMENT
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STRUCTURE SOHR Configuration HOLTEC I NT[KNAT I ONAL
PCCS Performance and Safe Shutdown Condition HOLTEC I N.I [R NA rlO Nrl l Per SECY-94-084, safe shutdown conditions for a passive design is defined as bringing the reactor coolant temperature to 420 °F or below within 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br />.
Following a LOCA, the SMR-160 will satisfy the safe shutdown requirement since the RCS becomes a saturated system operating at a pressure below 60 psia (saturation temperature
=293 °F).
For the non-LOCAs (Main Steam Line Break (MSLB) or Feedwater Line Break (FWLB) excluded) the SMR-160 will satisfy the safe shutdown requirement using the PDHR and SOHR systems.
holtec.com I smrllc.com I Page 8
MSLB and FWLB Safe Shutdown Performance For MSLB and FWLB events the SOHR is inoperable as the SG secondary side empties due to the break.
RCS coolant in the SG tubes is at an elevation above the RCS-PDHR nozzles.
With an empty SG secondary and RCS-PDHR nozzles being below the SG tubes, the RCS coolant in the SG tubes does not significantly circulate or cool.
Reactor core Specified Acceptable Fuel Design Limits (SAFDLs) are not challenged during MSLB or FWLB.
holtec.com I smrllc.com I Page 9
SECY-94-084 Safe Shutdown Questions Does 420 °F RCS temperature refer to RCS Average Temperature (Tavg)?
SMR-160 hot leg temperature is measured at bottom of the hot leg, thus the "RCS Average Temperature" will be below 420 °F within 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br /> for MSLB and FWLB events.
RCS coolant in the SG tubes would still be higher than the hot leg temperature (>550 °F). Would this violate the intent of the SECY-94-084 safe shutdown conditions, even if SAFDLs are met?
holtec.com I smrllc.com I Page 10
Open Forum o ec.com smr c.com I Page 11 HOLTEC I N l [ K NAT I ON,\\L