ML23355A163

Enclosure 1: Changes to Hermes 2 PSAR Chapter 4

ML23355A163
Person / Time
Site:	05000611, 05000612
Issue date:	12/21/2023
From:	Kairos Power
To:	Office of Nuclear Reactor Regulation
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ML23355A161	List: ML23355A162 ML23355A163
References
KP-NRC-2312-002
Download: ML23355A163 (1)

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KP-NRC-2312-002 Enclosure 1 Changes to Hermes 2 PSAR Chapter 4 (Non-Proprietary)

Preliminary Safety Analysis Report Reactor Description a coolable core geometry and adequate coolant flow through the core ensures the vessel wall temperature is below design limits, which prevent vessel failure. Dynamic behavior of the reactor, its support, and its internals are analyzed and designed to ensure vessel integrity and core geometry are maintained in a design basis earthquake to a degree sufficient to ensure passive heat removal. The vessel, as part of the reactor coolant boundary, ensures the containment of radionuclides by ensuring the coolant is confined and the TRISO particles in the fuel pebbles are protected from damage. These features demonstrate conformance to PDC 10.

To demonstrate compliance with PDC 14, the reactor vessel is fabricated, erected, and tested so as to have an extremely low probability of leakage, rapidly propagating failure, and gross rupture. The reactor vessel materials and weld metal will be qualified for use as described in Kairos Power topical report Metallic Materials Qualification for the Kairos Power Fluoride Salt-Cooled High-Temperature Reactor, KP-TR-013-P-A (Reference 3). The 316H SS of the reactor vessel as fabricated and tested in accordance with Reference 1 standards has a high fracture toughness at reactor operating conditions, thus reducing the likelihood of crack propagation. Table 4.3-3, Table 4.3-4, Table 4.3-5, and Table 4.3-6 provide the qualification tests required for a test reactor with an 11-year lifetime for 316H SS and weld materials.

These tables also present (for information only) qualification tests for both a test reactor with a lifetime of 5 years, and a commercial power reactor, which are described in Reference 3. The design of the reactor vessel and vessel internals support an 11-year lifetime. This is accomplished by operating the reactor vessel within the as-designed operational and transient condition stresses and by monitoring for changes (e.g., irradiation and thermally induced degradation, corrosion, creep) to the reactor vessel during in-service inspection and testing. . The RVSS-reactor vessel bottom head interface is designed to allow access for weld inspections. The reactor vessel top head supports in-service inspection of attachments and penetrations.

The reactor vessel shell and bottom head maintain a coolant pathway for cooling the reactor core and ensure submergence of fuel pebbles in the core. The reactor vessel is fabricated, erected, and tested in accordance with Reference 1 as a Class A component to account for thermal and physical stresses during normal operation and postulated events. The vessel is fabricated from 316H SS base metal and ER16-8-2 weld metal using a gas tungsten arc welding process. Reference 1 provides for weldment stress rupture factors up to a temperature of 650°C for ER16-8-2 weld metal with 316H base metal. Testing provides stress rupture factors up to 750°C for weld material with 316H base metal (Reference 3). The plant control system will detect leakage from the reactor vessel with catch basins, as described in Section 4.7, that are used to detect leaks in nearby coolant-carrying systems. These features demonstrate compliance with PDC 30.

Reactor vessel stress rupture factors are determined up to 750°C to encompass transient conditions.

The stress rupture factors are determined by a creep-rupture test on the vessel base material with weld metal under the gas tungsten arc welding process. The vessel design accounts for expected thermal, mechanical, and hydraulic stresses, and precludes failure via material creep, fatigue, and interactions of these phenomenathermal, mechanical, and hydraulic stresses. The leak tight design of the reactor vessel head minimizes air ingress into the cover gas and precludes corrosion of the internals. The high temperature, high carbon grade 316H SS of the core barrel and reflector support structure have high creep strength and are resistant to radiation damage, corrosion mechanisms, thermal aging, yielding, and excessive neutron absorption. Load combinations for the reactor vessel system and the RVSS are provided in Table 4.3-2 and Table 4.7-1. Vessel fluence calculations, as described in Section 4.5, confirm adequate margin relative to the effects of irradiation. The fast neutron fluence received by the reactor vessel from the reactor core and pebble insertion and extraction lines is attenuated by the core barrel, the reflector, and the reactor coolant. Coolant purity design limits are also established in consideration Kairos Power Hermes 2, Units 1 and 2 4-34 Revision 0

Preliminary Safety Analysis Report Reactor Description These features and capabilities demonstrate conformance to PDC 36 and PDC 37. Additional functions performed by the DHRS to support passive decay heat removal are described in Section 6.3.

The reactor vessel reflector blocks permit insertion of the reactivity control and shutdown elements. The ET-10 grade graphite of the reflector blocks is compatible with the reactor coolant chemistry and will not degrade due to mechanical wear, thermal stresses and irradiation impacts during the reflector block lifetime. The graphite reflector material is qualified as described in the Kairos Power topical report Graphite Material Qualification for the Kairos Power Fluoride Salt-Cooled High-Temperature Reactor, KP-TR-014-P-A (Reference 4). Table 4.3-7 and Table 4.3-8 provide the qualification tests required for a test reactor with an 11-year lifetime for graphite materials. These tables also present (for information only) qualification tests for both a test reactor with a lifetime of 5 years, and a commercial power reactor which are described in Reference 4. No additional testing programs, beyond those required for a non-power reactor as described in Reference 4, are anticipated for molten-salt infiltration, oxidation, abrasion, and erosion to support qualifying the graphite material for an 11-year lifetime. To preclude damage to the reflector due to entrained moisture in the graphite, the reflector blocks are baked (i.e.,

heated uniformly) prior to coming into contact with coolant. The reflectors, which act as a heat sink in the core, are spaced to accommodate thermal expansion and hydraulic forces during normal operation and postulated events. The gaps between the graphite blocks also allow for coolant to provide cooling to the reflector blocks. The reactor vessel permits the insertion of the reactivity control and shutdown elements as well. The vessel is classified as SDC-3 per ASCE 43-19 and will maintain its geometry to ensure the RCSS elements can be inserted during postulated events including a design basis earthquake.

These features demonstrate compliance with PDC 74.

4.3.4 Testing and Inspection The reactor vessel and internals will be included in an in-service inspection program, which will be submitted at the time of the Operating License Application.

4.3.5 References

1. American Society of Mechanical Engineers, ASME Boiler & Pressure Vessel Code, Section III, Division 5, High Temperature Reactors. 2017.

2. ASCE 43-19, Seismic Design Criteria for Structures, Systems, and Components in Nuclear Facilities.

3. Kairos Power, LLC, Metallic Materials Qualification for the Kairos Power Fluoride Salt-Cooled High-Temperature Reactor, KP-TR-013-P-A, April 2023.

4. Kairos Power, LLC, Graphite Material Qualification for the Kairos Power Fluoride Salt-Cooled High-Temperature Reactor, KP-TR-014-P-A, April 2023.

Kairos Power Hermes 2, Units 1 and 2 4-36 Revision 0

Preliminary Safety Analysis Report Reactor Description Table 4.3-3: Testing Requirements to Extend the ASME Qualification of ER 16-8-2 Test Program Non-power reactor Non-power reactor Commercial power (5-year lifetime) (11-year lifetime) reactor (20-year lifetime)

Tensile Testing Test matrix in Table 3 No additional testing* No additional testing*

of Reference 3 Creep Fatigue Test matrix in Table 3 Test matrix in Table 3 No additional testing**

Testing of Reference 3 to 760ºC of Reference 3 to 816ºC Creep Testing*** Up to 10,000 hours0 days <br />0 hours <br />0 weeks <br />0 months <br /> Up to 20,000 hours0 days <br />0 hours <br />0 weeks <br />0 months <br /> Up to 40,000 hours0 days <br />0 hours <br />0 weeks <br />0 months <br />

• No additional testing is required beyond that already specified for the non-power reactor (5-year lifetime)

• • No additional testing is required beyond that already specified for the non-power reactor (11-year lifetime)

• • • See information provided in Section 3.1 of Reference 3 Kairos Power Hermes 2, Units 1 and 2 4-39 Revision 0

Preliminary Safety Analysis Report Reactor Description Table 4.3-4: Testing Requirements for Reactor Design Test Program Non-power reactor Non-power reactor Commercial power (5-year lifetime) (11-year lifetime) reactor (20-year lifetime)

Test matrix in Table 4 No additional testing* No additional testing*

Tensile Testing of Reference 3 Stress Relaxation Test matrix in Table 5 No additional testing* No additional testing*

Testing of Reference 3 Test matrix in Table 6 No additional testing* No additional testing*

Stress Dip Testing of Reference 3 Uniaxial and Test matrix in Tables 7 No additional testing* No additional testing*

Notched Bar Creep and 8 of Reference 3 Testing Creep-Fatigue Test matrix in Table 9 No additional testing* No additional testing*

Testing of Reference 3 Test matrix in Table 10 Test matrix in Table 10 No additional testing**

Stress Relaxation of Reference 3 for Non- of Reference 3 for Cracking Power Test Reactor Commercial Power Reactor

• No additional testing is required beyond that already specified for the non-power reactor (5-year lifetime)

• • No additional testing is required beyond that already specified for the non-power reactor (11-year lifetime)

Kairos Power Hermes 2, Units 1 and 2 4-40 Revision 0

Preliminary Safety Analysis Report Reactor Description Table 4.3-5: Environmental Compatibility Testing of Metallic Materials 1 Test Program Non-power Non-power reactor Commercial power reactor (5-year (11-year lifetime) reactor (20-year lifetime) lifetime) 600 - 650°C, up to 600 - 650°C, up to 600 - 650°C, up to Effect of 3,000 hours0 days <br />0 hours <br />0 weeks <br />0 months <br />; 5,000 hours0 days <br />0 hours <br />0 weeks <br />0 months <br />; 750°C, 10,000 hours0 days <br />0 hours <br />0 weeks <br />0 months <br />; 750°C, up Temp.

750°C, up to 250 up to 250 hours0.00289 days <br />0.0694 hours <br />4.133598e-4 weeks <br />9.5125e-5 months <br /> to 250 hours0.00289 days <br />0.0694 hours <br />4.133598e-4 weeks <br />9.5125e-5 months <br /> hours Welding 650°C, up to 3,000 650°C, up to 5,000 650°C, up to 10,000 hours0 days <br />0 hours <br />0 weeks <br />0 months <br /> hours hours Plastic Strain 650°C, up to 3,000 650°C, up to 5,000 650°C, up to 10,000 hours0 days <br />0 hours <br />0 weeks <br />0 months <br /> hours hours Aging 650°C, up to 3,000 650°C, up to 5,000 650°C, up to 10,000 hours0 days <br />0 hours <br />0 weeks <br />0 months <br /> hours hours Corrosion Contamination Air ingress tests Flibe + int. coolant Flibe + int. coolant tests Testing in with Flibe + air at tests at 650°C at 650°C Nominal 650°C Flibe2 Redox Control Nominal Flibe + Nominal Flibe + Be, Nominal Flibe + Be, Be, 650°C up to 650°C up to 5,000 650°C up to 10,000 3,000 hours0 days <br />0 hours <br />0 weeks <br />0 months <br /> hours hours Occluded Evaluated using sample and sample cage geometry in all corrosion Geometry tests.

Erosive Flow Flibe + graphite Flibe + graphite Flibe + graphite particles, 650C, particles, 650C, up particles, 650C, up to up to 3,000 hours0 days <br />0 hours <br />0 weeks <br />0 months <br /> to 5,000 hours0 days <br />0 hours <br />0 weeks <br />0 months <br /> 10,000 hours0 days <br />0 hours <br />0 weeks <br />0 months <br /> Occlusion of Assessment of test systems after above testing Test System Full test matrix on Full test matrix on No additional testing**

HAZ samples only HAZ, Base Metal, Slow Strain Rate Testing and Weld Metal samples Full test matrix on Full test matrix on No additional testing**

Corrosion Fatigue and Stress HAZ samples only HAZ, Base Metal, Corrosion Cracking and Weld Metal samples Kairos Power Hermes 2, Units 1 and 2 4-41 Revision 0

Preliminary Safety Analysis Report Reactor Description Test Program Non-power Non-power reactor Commercial power reactor (5-year (11-year lifetime) reactor (20-year lifetime) lifetime) 500 - 750C, No further testing No additional testing**

testing up to 2,000 unless Environmental Creep Testing hours environmental degradation observed Corrosion 3,000-hour 5,000-hour 10,000-hour exposure exposure exposure SSRT 5x10-8 in/in tests No additional No additional testing*

Metallurgical testing*

Effects In-Situ Creep N/A Flibe + graphite + Flibe + graphite + redox redox control, 550 - control, 550 - 650C 650C Notes:

1. Test matrix requirements specified for the 5-year non-power reactor and 20-year power reactor are from Tables 12-17 of Reference 3

2. For corrosion testing in a non-power reactor with an anticipated 11-year lifetime, the total duration of corrosion tests is approximately half of the planned duration relative to the commercial power reactor because the 11-year lifetime of the non-power reactor is approximately half the lifetime of the commercial power reactor.

• No additional testing is required beyond that already specified for the non-power reactor (5-year lifetime)

• • No additional testing is required beyond that already specified for the non-power reactor (11-year lifetime)

Kairos Power Hermes 2, Units 1 and 2 4-42 Revision 0

Preliminary Safety Analysis Report Reactor Description Table 4.3-6: Irradiation Effects Testing of Metallic Materials Test Program Non-power reactor Non-power reactor Commercial power (5-year lifetime) (11-year lifetime) reactor (20-year lifetime)

Irradiation Induced Test matrix in Table No additional testing* No additional testing*

Embrittlement 11 of Reference 3 Test matrix in Table N/A, assessed based N/A, assessed based on Irradiation-Affected 11 of Reference 3 on inspection and inspection and Corrosion monitoring program monitoring program Irradiation-Assisted Test matrix in Table Also assessed via Also assessed via Stress Corrosion 11 of Reference 3 inspection and inspection and Cracking monitoring program monitoring program

• No additional testing is required beyond that already specified for the non-power reactor (5-year lifetime)

Kairos Power Hermes 2, Units 1 and 2 4-43 Revision 0

Preliminary Safety Analysis Report Reactor Description Table 4.3-7: Qualification Requirements of Unirradiated Graphite Mechanical and Thermal Properties 1 Test Program Non-power reactor Non-power reactor Commercial power reactor (5-year lifetime) (11-year lifetime) (20-year lifetime)

Mechanical and Based on ASME Sec No additional No additional testing*

Thermal Properties III Div 5 Code testing*

Property Variation HHA-III-5000 No additional No additional testing*

testing*

Purity ASTM D7219-08 No additional No additional testing*

and ASTM C1233 testing*

Molten Salt Confirmatory No additional Additional testing only if Flibe Infiltration testing testing* infiltration of ET-10 is observed at higher pressure of the commercial power reactor. Additional testing would be then included post-infiltration strength testing.

Oxidation ASTM D7542 No additional No additional testing*

testing*

HHA-III-3200 Note:

1. See information provided in Section 3.0, Table 5 and Table 6 of Reference 4.

• No additional testing is required beyond that already specified for the non-power reactor (5-year lifetime)

Kairos Power Hermes 2, Units 1 and 2 4-44 Revision 0

Preliminary Safety Analysis Report Reactor Description Table 4.3-8 Qualification Requirements for Graphite Irradiation1 Test Non-power reactor Non-power reactor Commercial power reactor Program (5-year lifetime) (11-year lifetime) (20-year lifetime)

Basic Use of existing Use of data within the existing Use of data within the Properties irradiation data for ETU-10 irradiation envelope. existing ETU-10 irradiation ETU-10 If graphite exceeds existing envelope. If graphite envelope for ETU-10, then exceeds existing envelope new irradiation data will be for ETU-10, then new obtained for ET-10. irradiation data will be obtained for ET-10.

Irradiation Relies on Relies on irradiation creep Irradiation creep data for ET-Creep irradiation creep data for other graphite 10 will be obtained to data for other grades. Based on turnaround support 20-year reactor graphite grades estimates from ORNL ETU-10 lifetime.

data and conservative fluence estimates for Hermes 2, 11 years of life is expected to remain pre-turnaround.

Uncertainties will be included in the analysis to allow margin. If final design data and turnaround analysis shows that graphite exceeds turnaround fluence, then irradiation creep data for ET-10 will be obtained and used.

Note:

1. See information provided in Section 4.3 of Reference 4.

Kairos Power Hermes 2, Units 1 and 2 4-45 Revision 0