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Kairos Power LLC, Presentation Slides for the April 18, 2023 ACRS Kairos Power Subcommittee Meeting
	ML23102A240
Person / Time
Site:	99902069, Hermes
Issue date:	04/18/2023
From:	; Kairos Power
To:	; Office of Nuclear Reactor Regulation
Shared Package
ML23102A238	List: ML23102A239; ML23102A240; ML23102A241;
References
	KP-NRC-2304-004
	Download: ML23102A240 (1)
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KP-NRC-2304-004 Enclosure 1 Presentation Slides for the April 18, 2023 ACRS Kairos Power Subcommittee Meeting (Non-Proprietary)

Hermes PSAR 12.9 Quality Assurance J O R D A N H A G A M A N - D I R E C TO R O F R E L I A B I L I T Y E N G I N E E R I N G A N D Q UA L I T Y A S S U R A N C E ACRS KAIROS POWER SUBCOMMITTEE MEETING APRIL 18, 2023 Copyright © 2023 Kairos Power LLC. All Rights Reserved.

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12.9 Quality Assurance

10 CFR 50.34 (a)(7) A description of the quality assurance program to be applied to the design, fabrication, construction, and testing of the structures, systems, and components of the facility.

The Quality Assurance Program Description (QAPD) for the design, construction, and operation of the Hermes reactor is based on ANSI/ANS 15.8-1995 (R2005), Quality Assurance Program Requirements for Research Reactors Endorsed by NRC Regulatory Guide 2.5, Quality Assurance Program Requirements for Research and Test Reactors (RG 2.5)

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Quality Assurance Program Description

The Hermes QAPD applies to design-phase, construction-phase, and operations-phase activities affecting the quality and performance of safety-related structures, systems, and components (SSCs).

Safety-related SSCs within the scope of the Hermes QAPD are identified by design documents.

Technical aspects are considered when determining program applicability including, as appropriate, the SSCs design safety function.

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Quality Assurance Program Description

The Hermes QAPD includes discussion of eighteen design, construction, and modifications program elements:

Organization Inspections Quality Assurance Program Test Control Design Control Control of Measuring and Test Equipment Procurement Document Control Handling, Storage, and Shipping Procedures, Instructions, and Drawings Inspection, Test, and Operating Status Document Control Control of Non-Conforming Items and Services Control of Purchased Items and Services Corrective Actions Identification and Control of Items Quality Records Control of Special Processes Assessments Copyright © 2023 Kairos Power LLC. All Rights Reserved.

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Hermes PSAR Chapter 13 Accident Analysis DR . M AT T HEW DE N M AN - DI ST INGU ISHED E N G INEER, R E L I ABI LITY ACRS K A I RO S P OW E R S U BCO M M I T TEE M E E TING APRIL 18, 2023 Copyright © 2023 Kairos Power LLC. All Rights Reserved.

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Safety Case Summary

10 CFR 50.34(a)(4) requires a preliminary safety analysis to assess the risk to public health and safety from operation of the facility, including determination of the margins of safety

To demonstrate compliance with 10 CFR 100.11 dose reference values, a Maximum Hypothetical Accident (MHA) that bounds the postulated events is analyzed for dose consequences by challenging the performance of functional containment The Hermes MHA approach is consistent with guidance in NUREG-1537 The Hermes MHA is not physical The Hermes MHA includes conservatisms that maximize source term The Hermes MHA includes a postulated release of radionuclides

To ensure that the postulated events are bounded by the MHA:

The list of postulated events is comprehensive to ensure that any event with the potential for significant radiological consequences has been considered Initiating events and scenarios are grouped, so that a limiting case for each group can be qualitatively described in CPA (quantitative results will be provided with OLA)

Acceptance criteria are provided for the important figures of merit in each postulated event group to ensure that the potential consequences of that event group remain bounded by the MHA as the design progresses Prevention of an event initiator is justified in the PSAR Copyright © 2023 Kairos Power LLC. All Rights Reserved.

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Relationship between Dose Limits, the Maximum Hypothetical Accident, and Postulated Events

The Maximum Hypothetical Accident (MHA) 100.11(a)(1-2) Reference Values is constructed to:

Be conservatively non-physical to overestimate Margin potential off-site dose consequences To EAB/LPZ Dose (relative)

Provide confidence that sufficient safety margin Dose Ref.

exists Values Ensure that reasonable design constraints will result in bounded postulated event doses MHA Dose Hypothetical Conservatism

At the PSAR stage, only the MHA dose is:

Quantitatively evaluated Needed to ensure that sufficient margin exists to Design Basis 10 CFR 100.11 dose reference values Potential Postulated Event Doses Conservatism Copyright © 2023 Kairos Power LLC. All Rights Reserved.

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Maximum Hypothetical Accident: Narrative (1 of 2)

The shutdown and heat removal systems are assumed to perform their safety functions but are not modeled. Instead, hypothetical temperature curves are used to conservatively drive radionuclide movement through the functional containment. Individual release pathways are discussed on the next slide.

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Maximum Hypothetical Accident: Narrative (2 of 2)

Radionuclides are postulated to diffuse from TRISO particles The distribution of TRISO particles account for both manufacturing defects and in-service failures Pre-transient diffusion of radionuclides from the fuel kernels are hypothetically and conservatively not modeled to maximize fuel inventory for release

Radionuclides are postulated to evaporate and degas from the Flibe driven by conservative natural convection boundary conditions. No holdup of gases in Flibe is credited.

Tritium is conservatively assessed to maximize both its inventory and release The initial inventory of tritium is conservatively assessed The release of tritium is conservatively postulated to:

desorb from in-vessel graphite as a function of temperature instantaneously release from both steel and Flibe

The Ar-41 inventory that is held up by closed graphite pores is instantaneously released Copyright © 2023 Kairos Power LLC. All Rights Reserved.

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MHA: Methodology (1 of 3)

The Hermes MHA uses the methodology from the approved KP-FHR Mechanistic Source Term Methodology Topical (KP-TR-012-P-A). The following concepts directly leverage the topical report:

Radionuclide grouping and transport approaches for the TRISO Fuel and Flibe coolant

Mass transfer correlations for tritium into graphite reflectors and pebbles

The gas space is not credited for confinement of the radionuclides that release from the Flibe free-surface

Two-hour holdup assumptions for radionuclides transporting through the reactor building

Conservative, unfiltered, ground level releases are modeled to maximize offsite doses Copyright © 2023 Kairos Power LLC. All Rights Reserved.

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MHA: Methodology (2 of 3)

The following non-physical conditions provide additional hypothetical challenges to the functional containment (beyond what is described in KP-TR-012-P-A):

Prescribed hypothetical temperature histories are applied to the transient. This ensures that the MHA will bound the system temperatures from the postulated event groups.

Pre-transient diffusion of radionuclides from the fuel in the reactor core is neglected.

This ensures that the maximum inventory is available for release at the initiation of the transient.

A bounding vessel void fraction is assumed to facilitate the release of low volatility species in the vessel via bubble burst.

Additional conservatism in tritium modeling to address limitations associated with tritium modeling in graphite is described in KP-TR-012-P-A.

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MHA: Methodology (3 of 3)

1. Identify and account for the sources of material at risk (MAR) and the barriers to release

2. Evaluate release fractions for every combination of barrier, radionuclide group, and time interval

3. RADTRAD and ARCON evaluate dose consequences at the exclusion area boundary (EAB) and the low population zone (LPZ)

Three sources of MAR and associated release barriers Fuel kernels Legend: Circulating Structural MAR activity Sources Tritium Argon-41 TRISO layers Barriers Flibe Graphite grains Graphite pores for non-Flibe tritium Gas space Copyright © 2023 Kairos Power LLC. All Rights Reserved.

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Maximum Hypothetical Accident:

Sources of MAR (1 of 2)

1. TRISO Fuel Serpent 2 evaluation provides fuel inventory Pre-transient depletion of radionuclides from the fuel is neglected to maximize inventory available for release

2. Circulating Activity Bounding value of circulating activity is assumed in the analysis Expected to be a variable controlled by technical specification Copyright © 2023 Kairos Power LLC. All Rights Reserved.

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Maximum Hypothetical Accident:

Sources of MAR (2 of 2)

3. Structural (steel, reflector, pebbles)

Tritium The inventory conservatively bounds the operating lifetime at full capacity factor with margin while accounting for differential uptake rates for pebbles and reflector Transfer from Flibe to structures Born in the Flibe but transferred to and sorbed in structures (primarily graphite)

Transport speciation is conservatively assigned as tritium fluoride to maximize tritium sorption Transfer from Flibe to structures determined by mass transfer coefficients from Flibe flow characteristics Sorption within structures Sorbed solely as a function of mass transfer from the Flibe to structures (i.e., no diffusion resistance)

Retained without modeling steady state release mechanisms (i.e., perfect absorber)

Argon-41 Produced via neutron activation of Ar-40 to Ar-41 The inventory available for release consists of Ar-41 contained within the graphites closed porosity Copyright © 2023 Kairos Power LLC. All Rights Reserved.

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Maximum Hypothetical Accident:

Release models for the TRISO Fuel

Transport through TRISO fuel layers is modeled using Ficks laws of diffusion Fuel Fuel The CORSOR model is used for kernel diffusion IAEA correlations are used for layer diffusion

Diffusion is driven by the fuels hypothetical temperature curve

Transient diffusion of fission products:

Is negligible if even a single PyC layer remains intact Total releases are thus dominated by releases from exposed kernels Fuel Particle

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Maximum Hypothetical Accident:

Release models for the Flibe Coolant

Flibe provides a secondary functional containment barrier to:

Bounding circulating activity In-transient release of fission products from TRISO

Two release mechanisms are modeled for Flibe Impurities Bubble burst Evaporation

Certain radionuclide groups bypass the Flibes functional containment No credit for gas retention High volatility noble metals evaporate near instantaneously Copyright © 2023 Kairos Power LLC. All Rights Reserved.

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Maximum Hypothetical Accident:

Release models for the Structural MAR

Tritium in graphite grains No-holdup of tritium in the Flibe instantly drops the concentration of tritium outside of graphite grains drops to zero Tritium rapidly diffuses out of the graphite grain due to the non-physical concentration gradient

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Maximum Hypothetical Accident:

Release models for the Gas/Atmospheric Transport

RADTRAD:

Input: Mobilized material-at-risk activities Source RADTRAD Depletion mechanisms Radioactive decay Conservative and Prescriptive Values ARCON96 Aerosol settling (i.e., Henry correlation)

Environment Leakage rates (two-hour holdup) Reactor Building Reactor Building to Environment

ARCON96:

Inputs ARCON96 Hourly Meteorological Data Distance from the reactor building to the following areas:

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Maximum Hypothetical Accident:

Dose Consequences Dose results meet 10 CFR 100.11 reference values at the EAB and LPZ with significant margin Whole Body Dose (rem) Thyroid Dose (rem)

Location and Duration 10 CFR 100 MHA Result 10 CFR 100 MHA Result Exclusion Area Boundary (First 2 hrs at 250m) 25 0.227 300 0.235 Low Population Zone 25 0.059 300 0.081 (30 days at 800m)

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Summary

The MHA dose consequence results meet the site dose reference values in 10 CFR 100.11(a)(1-2) at the EAB and LPZ with significant margin

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ML23102A240

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