ML25293A458

From kanterella
Jump to navigation Jump to search
2 - Control of Heat Generation
ML25293A458
Person / Time
Site: Kemmerer File:TerraPower icon.png
Issue date: 10/20/2025
From: Reed Anzalone
Advisory Committee on Reactor Safeguards, NRC/NRR/DANU/UTB2
To:
References
Download: ML25293A458 (1)
v • d • e


Text

NRC Review of Kemmerer Unit 1 Construction Permit Application Control of Heat Generation Reed Anzalone NRR/DANU/UTB2 ACRS Subcommittee Meeting October 22-23, 2025

Topics

  • Reactor core components
  • Fuel assemblies, control assemblies, other core assemblies
  • Compressive assemblies R&D item
  • Interfacing systems
  • Core design
  • Reactivity control system design
  • Supporting functions from control systems 2
  • Described in PSAR sections 3.11 and 7.1.1, includes:
  • Fuel assemblies
  • Control assemblies
  • Other assemblies
  • RCC safety-significant functions
  • DL3-RR2 cladding barrier
  • DL3-HR5 - HR10, DL3-HR13 passive heat removal in various SSCs 3

Reactor core components (RCC)

Fuel assemblies PSAR section 3.11 incorporates by reference TR NAT-2806-A, Fuel and Control Assembly Qualification (ML24354A191) which was reviewed by ACRS in May and June 2024

  • U-10Zr in HT9 cladding, with wire wrap in hexagonal assemblies
  • Assemblies in hexagonal HT9 ducts with inlets that interface with lower core plate and load pads that interface with adjacent assemblies 4

PSAR figure 7.1.1-1

Control assemblies

  • Design consistent with NAT-2806-A
  • Control rod assemblies (CRAs) move up and down in ducts in locations shown
  • Primary and secondary control assemblies
  • Geometric differences to account for CCF of assembly-to-duct binding
  • Either primary or secondary assemblies sufficient to shut down reactor
  • Secondary assemblies used for fine reactivity control 5

PSAR figure 7.1.1-2

Other reactor core assemblies Described in PSAR section 7.1.1

  • Reflector assemblies
  • Shield assemblies
  • Compressive assemblies
  • Subject of R&D program as described in PSAR chapter 13
  • LDAs/LTAs
  • Other 6

PSAR figure 7.1.1-2

Interfacing components Reactor internal structures are part of reactor enclosure system (RES) and described in PSAR section 7.1.2

  • Core inlet plenum, core barrel 7

PSAR figure 7.1.2-5

Review of fuel design (PSAR section 3.11)

  • DANU-ISG-2022-01, Review of Risk-Informed, Technology-Inclusive Advanced Reactor Applications Roadmap (ML23297A158) states that staff review at CP stage should focus on the role of the fuel in the safety analysis and adequacy of the fuel qualification plan
  • These issues were covered by the approved TR NAT-2806-A
  • Fuel qualification plan described in NAT-2806-A
  • Role of fuel in safety analysis
  • Fuel cladding has radionuclide retention function (DL3-RR2) but can fail in accident scenarios
  • Dominant failure mechanism is thermal creep rupture with contribution from FCCI/eutectic
  • When cladding is breached, fuel plenum contents assumed to release instantaneously; matrix retains some radionuclides as modeled in source term analysis 8

Review of RCC (PSAR section 7.1.1)

  • Fuel and control assemblies are SR to support reactivity control, heat removal, and radionuclide retention functions.
  • Structural elements of all other core assemblies are SR to limit deflection to ensure control rod insertability and coolability.
  • PDC 2 - Protected from external hazards by RES, and all assemblies are seismically qualified
  • PDC 10, 11, 12, 16, 26, 28, 29, 80
  • Addressed by TR, safety analysis, and core design 9

Core Design

  • Described in PSAR sections 3.12 and 3.13 and TP-LIC-RPT-0011, Core Design and Thermal Hydraulic Technical Report (ML25276A289 )
  • Staffs review at CP stage focused on ensuring core design supports applicable PDCs and that associated analytical methods are appropriate
  • Staff review was supported by contractors from ANL 10 PSAR figure 7.1.1-2

Applicable PDCs

  • PDC 10 - core designed with appropriate margin to assure SARRDLs are not exceeded during normal operation and AOOs
  • Demonstrated through PSAR chapter 3 safety analysis of AOOs
  • PDC 11 - prompt inherent feedback must compensate for increase in reactivity in the power operating range
  • Preliminary reactivity feedback parameters provided in TP-LIC-RPT-0011
  • PDC 12 - power oscillations that result in conditions exceeding SARRDLs are not possible or can be detected and suppressed
  • Demonstrated using approved TR NAT-9393-A, Reactor Stability Methodology (ML25211A275) reviewed by ACRS in March and April 2025
  • PDC 26 - provides requirements related to reactivity control 11

Methods

  • Neutronics: uses a mix of ANL suite of reactor simulation tools and TerraPower-specific tools
  • MC2-3 for cross sections, DIF3D for diffusion and transport
  • Other tools to support flux calculations, depletion analyses, core assembly bowing, fuel phenomena, etc.
  • Staff considered tools to be appropriate for intended applications with modeling selections generally consistent with expectations for this kind of reactor
  • Thermal-hydraulics: uses TerraPower-specific tools
  • Modeling consistent with established subchannel codes using appropriate correlations from literature for key phenomena
  • Hot channel factors: consistent with usage in historic SFR applications
  • Staff concluded codes and modeling choices specified are adequate for preliminary analyses
  • Code V&V needs to be demonstrated as part of OL application
  • Uncertainty quantification approach is reasonable, but analyses need refinement and further confirmation at OL 12

Key core design parameters

  • Staff worked with NRC/RES and ANL and ORNL to perform confirmatory analyses for key core design parameters
  • Depletion calculations performed using ANL code suite, kinetics parameters and reactivity coefficients calculated using SCALE
  • Staff confirmatory analyses are consistent with KU1 preliminary analysis
  • Preliminary kinetics parameters and reactivity coefficients are reasonable compared to publicly available data on other reactors (both operated and designed) as documented in SE
  • Use of HALEU fuel and other factors may provide benefits for key core parameters relative to historic HEU or U-Pu cores 13

Control rod drive system (CRD)

  • Key components
  • CRD motor drive assembly & controller
  • Scram valve and cylinder assembly
  • Safety-significant functions
  • DL3-RC2 Reactor scram on loss of power
  • DL3-RR1 Primary coolant boundary 14

Gravity scram functions

  • Reactor trip breakers are opened by RPS, scram SOVs de-energize, pressure from scram cylinder vents, gripper disengages from CRA, CRA falls into core by gravity
  • Scram on loss of power (DL3-RC2)
  • After RTBs open, same as above
  • Alternative shunt trips (DL4-RC6 and subfunctions)
  • AST provides alternate means of tripping RTBs via shunt trip feature 15

Design to support gravity scram functions

  • All elements supporting DL3-RC1 and RC2 are SR, designed with materials consistent with ASME Section III Division 5 (III-5), and subject to SR mechanical and electrical EQ
  • CRD driveline assembly has some components made of Alloy 718 which is approved in III-5 for bolting applications only
  • Sodium aerosol effect on CRD components mitigated by inert cover gas flow and bellows
  • Scram system consists of 3 SOVs configured such that single failure would not cause loss of scram function
  • Common cause failure considered in PRA and drives DL3-RC1 failure 16

CRD driveline scram follow

  • RPS issues control signal (separate and independent from scram signal) to initiate motor drive in when any automatic or manual scram occurs
  • Supported by NSRST motor drive and associated controllers
  • Drive motors located on top of CRDM housing, motor controllers located in substructure of NI control building (NCB)
  • Functions independently of gripper release 17

Review of CRD

  • Safety functions
  • Design supports safety functions as discussed on previous slides with SR and NSRST components
  • PDCs related to quality and protection from phenomena (1, 2, 4, 80)
  • Designed to III-5, qualified under electrical/mechanical EQ for environmental conditions, and seismically qualified (SCS1 for SR and SCN1 for NSRST)
  • Reactivity control and primary coolant boundary PDCs described on subsequent slides 18

PDC 26 - Reactivity Control Systems PDC 26 Minimum of two reactivity control systems or means must provide capability to:

1) insert negative reactivity at sufficient rate and amount to ensure SARRDLs are not exceeded and safe shutdown is achieved and maintained for AOOs; 2) independent and diverse from (1), (3), and (4),

control the rate of reactivity changes during planned, normal power changes to ensure SARRDLs are not exceeded; 3) cool the core, shut down the reactor, and maintain safe shutdown following a postulated accident; 4) maintain the reactor shutdown during fuel loading, inspection and repair activities Credited Capability 1)

Delatch and gravity scram of primary and secondary CRA. Reactor can be shut down with both banks assuming highest worth rod stuck out, or either bank. RPS or AST can cause a scram.

2)

Motor drive control, with diversity provided by separate sets of CRAs. Secondary CRAs provide regulating function for small reactivity changes.

3)

Same means as (1) 4)

Primary and secondary CRA insertion plus administrative controls for managing shutdown margin.

19 Based on the independence of the motor drive function from the gravity scram function, the diversity of CRA designs to mitigate common cause failures, and the use of AST, staff found the approach to PDC 26 acceptable.

PDC 28 - Reactivity Limits

  • PDC 28 requires limits on amount and rate of reactivity increase to ensure primary coolant boundary and core are not damaged
  • CRA worth available for withdrawal is limited by core design and administratively by identification of appropriate rod insertion limits
  • RILs not identified at CP but expected at OL
  • Limit on CRA withdrawal rate is provided by physical design of CRD motor drives and interlocks that only enable one rod to be withdrawn from the core at a time 20

Primary coolant boundary PDCs (14, 15, 30, 31, 32)

  • CRDM housing attaches to rotatable plug assembly (RPA) on reactor head (RH) and forms portion of primary coolant boundary
  • CRDM housing is designed consistent with III-5, with overpressure protection provided by sodium cover gas system (SCG)
  • Sodium aerosol effect on primary coolant boundary and potential for sodium-air interaction managed through cover gas flow and use of bellows as discussed previously 21

Acronyms ACRS - Advisory Committee on Reactor Safeguards ANL - Argonne National Laboratory AOO - Anticipated Operational Occurrence ASME - American Society of Mechanical Engineers AST - Alternative Shunt Trip CCF - Common Cause Failure CP - Construction Permit CRA - Control Rod Assembly CRD - Control Rod Drive CRDM - Control Rod Drive Mechanism DANU - Division of Advanced Reactors and Non-Power Production and Utilization Facilities EQ - Equipment Qualification FCCI - Fuel-Cladding Chemical Interaction HALEU - High Assay Low Enriched Uranium HEU - High Enriched Uranium ISG - Interim Staff Guidance KU1 - Kemmerer Unit 1 LDA - Lead Demonstration Assembly LTA - Lead Test Assembly NCB - Nuclear Island Control Building NRC - Nuclear Regulatory Commission NRR - Office of Nuclear Reactor Regulation NSRST - Non-Safety-Related with Special Treatment OL - Operating License ORNL - Oak Ridge National Laboratory PDC - Principal Design Criterion PRA - Probabilistic Risk Assessment PSAR - Preliminary Safety Analysis Report Pu - Plutonium R&D - Research and Development RCC - Reactor Core Components RES - Office of Research RH - Reactor Head RIL - Rod Insertion Limit RPA - Rotatable Plug Assembly RPS - Reactor Protection System RTB - Reactor Trip Breaker SARRDL - Specified Acceptable System Radionuclide Release Design Limit SCG - Sodium Cover Gas SCN1 - Non-Safety-Related Seismic Class 1 SCS1 - Safety-Related Seismic Class 1 SFR - Sodium Fast Reactor SOV - Solenoid Operated Valve SR - Safety-Related SSC - Structure, System, or Component TR - Topical Report U - Uranium UTB2 - Advanced Reactor Technical Branch 2 V&V - Verification and Validation Zr - Zirconium 22

Retrieved from "https://kanterella.com/w/index.php?title=ML25293A458&oldid=5535195"