ML23115A480

NRR E-mail Capture - Hermes Audit Reports

ML23115A480
Person / Time
Site:	99902069, Hermes
Issue date:	04/25/2023
From:	Matthew Hiser NRC/NRR/DANU
To:	Gardner D, Peebles D Kairos Power
References
Download: ML23115A480 (30)

Text

From: Matthew Hiser Sent: Tuesday, April 25, 2023 3:43 PM To: Drew Peebles; Darrell Gardner Cc: Andrew Proffitt; Benjamin Beasley; Samuel Cuadrado de Jesus; Edward Helvenston

Subject:

Hermes Audit Reports Attachments: Report for Audit Kairos Hermes CP PSAR Chapter 2 Site Characteristics.pdf; Report for Audit Kairos Hermes CP Decay Heat Removal System.pdf; Report for Audit Kairos Hermes CP PSAR Chapter 7 I&C.pdf

Dear Darrell and Drew:

Attached are summaries of three audits conducted by U.S. Nuclear Regulatory Commission (NRC) staff (the staff) of the Hermes test reactor site characteristics, decay heat removal system, and instrumentation and controls as presented in the Preliminary Safety Analysis Report (PSAR). By letter dated September 29, 2021, Kairos Power LLC (Kairos) applied for a construction permit (CP) under Title 10 of the Code of Federal Regulations (10 CFR) Part 50 for its Fluoride Salt-Cooled, High Temperature Non-Power Reactor (Hermes); the application included a preliminary safety analysis report (PSAR) (Agencywide Documents Access and Management System (ADAMS) Accession No. ML21272A375). PSAR Chapter 2, Site Characteristics, describes the site location, including a discussion of the population in the vicinity, the distribution of infrastructure and natural features, as well as the basis for selection of the Hermes reactor site. PSAR Chapter 6, Engineered Safety Features, Section 6.3, Decay Heat Removal System (DHRS), describes the DHRS and its safety function of removing decay heat when the normal heat rejection system is unavailable. PSAR Chapter 7, Instrumentation and Control Systems, describes the instrumentation and control (I&C) systems that monitor and control plant operations during normal operations and planned transients and also monitor and actuate protection systems in the event of unplanned transients.

These audits allowed the staff to gain a better understanding of Kaiross PSAR through review and discussion of underlying supporting documentation and aided in assessing the safety of the proposed test reactor. Enhanced understanding and communications provided detailed information to the staff and supported effective and efficient development of information needs.

The staff reviewed information through the Kairos Electronic Reading Room (ERR) and held discussions with Kairos staff to understand and resolve questions. In many cases, Kairos updated the Hermes PSAR to resolve items discussed in the audit.

Sincerely, Matt Matthew Hiser Senior Project Manager Advanced Reactor Licensing Branch 1 (UAL1)

Division of Advanced Reactors and Non-Power Production and Utilization Facilities (DANU)

Office of Nuclear Reactor Regulation (NRR)

US Nuclear Regulatory Commission Phone: 301-415-2454 l Office: OWFN 6C53 Matthew.Hiser@nrc.gov

Hearing Identifier: NRR_DRMA Email Number: 2053 Mail Envelope Properties (BLAPR09MB6563B02EB9EF6F19DE00C899E8649)

Subject:

Hermes Audit Reports Sent Date: 4/25/2023 3:42:31 PM Received Date: 4/25/2023 3:42:00 PM From: Matthew Hiser Created By: Matthew.Hiser@nrc.gov Recipients:

"Andrew Proffitt" <Andrew.Proffitt@nrc.gov>

Tracking Status: None "Benjamin Beasley" <Benjamin.Beasley@nrc.gov>

Tracking Status: None "Samuel Cuadrado de Jesus" <Samuel.CuadradoDeJesus@nrc.gov>

Tracking Status: None "Edward Helvenston" <Edward.Helvenston@nrc.gov>

Tracking Status: None "Drew Peebles" <peebles@kairospower.com>

Tracking Status: None "Darrell Gardner" <gardner@kairospower.com>

Tracking Status: None Post Office: BLAPR09MB6563.namprd09.prod.outlook.com Files Size Date & Time MESSAGE 2484 4/25/2023 3:42:00 PM Report for Audit Kairos Hermes CP PSAR Chapter 2 Site Characteristics.pdf 201955 Report for Audit Kairos Hermes CP Decay Heat Removal System.pdf 177438 Report for Audit Kairos Hermes CP PSAR Chapter 7 I&C.pdf 160871 Options Priority: Normal Return Notification: No Reply Requested: No Sensitivity: Normal Expiration Date:

SUMMARY

REPORT FOR THE REGULATORY AUDIT OF KAIROS POWER LLC HERMES CONSTRUCTION PERMIT PRELIMINARY SAFETY ANALYSIS REPORT SITE CHARACTERISTICS (CHAPTER 2)

June 2022 - August 2022

1.0 BACKGROUND

AND PURPOSE By letter dated September 29, 2021, Kairos Power LLC (Kairos) applied for a construction permit (CP) under Title 10 of the Code of Federal Regulations (10 CFR) Part 50 for its Fluoride Salt-Cooled, High Temperature Non-Power Reactor (Hermes); the application included a preliminary safety analysis report (PSAR) (Agencywide Documents Access and Management System (ADAMS) Accession No. ML21272A375). PSAR Chapter 2, Site Characteristics, describes the site location, including a discussion of the population in the vicinity, the distribution of infrastructure and natural features, as well as the basis for selection of the Hermes reactor site.

This audit enabled the U.S. Nuclear Regulatory Commission (NRC) staff (the staff) to gain a better understanding of Kaiross PSAR Chapter 2 through review and discussion of underlying supporting documentation. Enhanced understanding and communications supported effective and efficient development of information needs.

2.0 AUDIT REGULATORY BASES The bases for the audit are the regulations in 10 CFR Part 50, Sections 50.34(a), Preliminary Safety Analysis Report, specifically 50.34(a)(1)(i) and 50.34(a)(4).

3.0 AUDIT OBJECTIVES The primary objective of the audit was to enable a more effective and efficient review of PSAR Chapter 2 through the staffs review and discussion of supporting documentation with Kairos. Gaining access to underlying documentation and engaging in audit discussions about site characteristics facilitated the staffs understanding of the Hermes application and aided in assessing the safety of the proposed test reactor. The audit improved communication and provided detailed information for the staff.

4.0 SCOPE OF THE AUDIT AND AUDIT ACTIVITIES The audit was conducted from June to August 2022, via the Kairos electronic reading room (ERR). The staff conducted the audit in accordance with the Office of Nuclear Reactor Regulation (NRR) Office Instruction NRR-LIC-111, Revision 1 Regulatory Audits (ML19226A274).

Members of the audit team, listed below, were selected based on their detailed knowledge of the subject. Audit team members included:

1. Amitava Ghosh, NRR (Technical Reviewer)

2. Yuan Cheng, NRR (Technical Reviewer)

3. Jenise Thompson, NRR (Technical Reviewer)

4. David Heeszel, NRR (Technical Reviewer)

5. Jason White, NRR (Technical Reviewer)

6. Benjamin Beasley, NRR (Project Manager)

7. Edward Helvenston, NRR (Project Manager)

Prior to the audit, the audit team reviewed PSAR Chapter 2 and provided preliminary questions on site characteristics by e-mail on January 10, 2022 (ADAMS Accession No. ML22024A492).

Kairos responded to the preliminary questions on February 3, 8, and 9, 2022 (ML22041A337, ML22040A142, ML22040A338). In the audit plan (ML22143B016), the staff provided a series of remaining questions (following the preliminary questions and responses) to be addressed and focused on during the audit.

During the audit, meetings were held between the staff and Kairos on June 9, July 27, and August 4, 2022.

The staff reviewed the following documents via the ERR:

• Report of Geotechnical Exploration K-33 Site Due Diligence (Geotech report)

• Guide to Classification of Soil for Field Boring Logs

• PSAR pages indicating changes proposed by Kairos in response to various audit questions 5.0

SUMMARY

OF AUDIT OUTCOME The staffs audit focused on the review of supporting documents associated with the questions identified in the audit plan (ML22143B016). The staff reviewed information through the Kairos ERR and held discussions with Kairos staff to understand and resolve questions. In many cases, Kairos updated the Hermes PSAR to resolve items discussed in the audit. The tables below summarize the resolution of the audit questions.

Resolution of Questions on Nearby Facilities Question Question Resolution Number 2.2-1 In Section 2.2.1.3, the last sentence of the middle paragraph reads " the The typographical error was annual average daily vehicle count at TN 58 north of the intersection with TN corrected to change the 58 was 12,641 in 2018." Should the first reference to TN 58 in this portion of second reference to TN 58.

the sentence refer to TN 327?

2.2-2 The last paragraph of Section 2.2.2.3 states, "The average flight distance of Kairos performed an additional 37 miles is selected based on the generic flight length provided in Table B-43 sensitivity analysis to show of DOE-STD-3014-2006." However, the DOE Standard value of 37 miles is this value is conservative.

provided as an example; it is not generic. Please clarify the justification for the average flight distance of 37 miles, or revise PSAR Section 2.2.2.3 and Tables 2.2-8 and 2.2-9 as appropriate.

2.2-3 Section 2.2.3.1 does not identify specific stored chemical explosion risks for Kairos verified that other nearby facilities. Please provide a basis for not considering these explosions or nearby facilities were far provide assessments of the potential explosion hazards for the chemicals enough away and modified the identified in Tables 2.2-3 and 2.2-4. PSAR accordingly.

2.2-4 PSAR Section 2.2.3.1 states that the proposed Oak Ridge Airport will include Kairos analyzed the hazard two 10,000 gallon above-ground tanks for aviation fuels. The PSAR discusses from the jet fuel tanks and potential explosive hazard from jet fuel tanks but does not appear to consider found significant margin based potential BLEVE. Would potential BLEVE of two jet fuel tanks at the proposed on the distance of Hermes Oak Ridge Airport be a credible hazard to the proposed facility? If not, please from the airport. The PSAR explain. If so, please provide an analysis of this hazard in the PSAR. was modified accordingly.

2.2-5 In PSAR Table 2.2-8, based on footnote (b), it appears Kairos based the x Kairos indicated that the distance and y distance values on an assumption that all flights either taking coordinate system is based on off or landing use the same runway end (i.e., all flights take off or touch down distance from the center of the at the same point at the same end of the runway). However, the NRC staff runway and made corrections notes that it is not clear whether this assumption is correct. Please explain the to the Table. The PSAR was coordinate system used in assessing x distance and y distance of the modified accordingly.

proposed facility from the proposed runway and discuss and justify whether Kairos used an assumption that all flights use the same runway end.

Resolution of Questions on Hydrology Question Question Resolution Number 2.4-4 In PSAR Section 2.4, the applicant used different vertical datum, mean sea level (msl), PSAR modifications NGVD29 and NAVD88, to indicate flood elevations and the Hermes site grade, were made to clarify the respectively. Please provide the elevations using a consistent vertical datum or justify elevations in Tables 2.4-why the provided data are adequate. 2 and 2.4-3.

2.4-5 With respect to consideration of potential floods, PSAR Section 2.4 states, River Factors affecting blockage on the Clinch River arm of the Watts Bar Reservoir, and flow diversion on flooding hazards, such Poplar Creek and the Clinch River are also considered. Additional information will be as river blockage and provided with the application for the Operating License. PSAR Tables 2.4-2 and 2.4-3 flow diversion events, show the flood elevations for various flood events resulting from river hydraulic will be analyzed further computations. Please clarify whether the river blockage and flow diversion as indicated and addressed in the in the quoted statement from Section 2.4 were included in the computations to support FSAR. Analysis will the flood elevations shown in the Tables 2.4-2 and 2.4-3. If the Tables are not the result include a blockage of considering the blockage and diversion, please clarify where the computational result assessment for nearby of considering the blockage and diversion may be found in the PSAR. Also, according to bridges and possible PSAR Figure 2.4-1, there are three bridges crossing Poplar Creek. Are blockages on the sediment buildup as stream due to potential failures of these bridges included in the river flood computations appropriate.

in Tables 2.4-2 and 2.4-3 or elsewhere in the PSAR?

2.4-6 PSAR Section 2.4.1 states, The November 28, 1973, and April 4, 1977, [East Fork Kairos modified the Poplar Creek] floods were about equal in magnitude. These floods reached an elevation PSAR to clarify that of 770.2 feet NGVD with a recurrence interval of approximately 30 years at 3.3 miles these floods would have upstream of the confluence with Poplar Creek. Only minor damage occurred as a result no impact to the Hermes of these floods (Reference 5). The staff notes that the distance from the confluence to site.

the Hermes site is approximately 2 miles. Based on the 2 miles of distance, it appears that floods at the recorded flood elevation of 770.2 feet (based on NGVD29) in the East Fork Poplar Creek may have an impact at the Hermes site, with a grade elevation at 765 feet (based on NAVD88). Please discuss what the potential inundation at the Hermes site could be, if the recorded 1973 and 1977 flood events extended to the Poplar Creek flow near the Hermes site.

2.4-7 PSAR Section 2.4.3 indicates a site-specific PMF analysis will be discussed with the Kairos modified the application for an Operating License. However, the details and basis of this site- PSAR to clarify the specific PMF are not clear. Please clarify whether the site-specific PMF is a flood relevant statement and event resulting from a local intense precipitation (LIP) event as PSAR Section 2.4.3.3 will consider maximum appears to indicate, which the staff notes is different from the PMP used to estimate the

PMF in Section 2.4.2.1. Are the meanings of the local PMP event and local intense credible precipitation as precipitation [LIP] event interchangeable as used in Section 2.4.3.3? appropriate in the operating license application.

2.4-8 PSAR Section 3.3.2, External Flooding Events, states, The meteorological Kairos modified PSAR characterization from Section 2.3 provides a probable maximum precipitation Section 3.3.2 to clarify accumulation of water. As stated in PSAR Section 2.3.2.6, Precipitation, For the site how external flooding area, using a 100-year return period, the PMP for 6, 12, 24, and 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> is 5.0, 6.0, 6.8, events are considered in and 8.0 inches, respectively (see Table 2.3-20). Comparing these two quoted terms of hydrological statements from Sections 3.3.2 and 2.3.2.6, the staff notes that, given how a PMP is loads on safety-related otherwise described in Section 3.3.2, the statement in Section 3.3.2 appears to be structures.

inconsistent with the meteorological information from Section 2.3 because Section 2.3 describes a PMP that is based on a storm with a 100-year return period. Please clarify the quoted statement in Section 3.3.2 to confirm that the storm with a 100-year return period is different from the PMP event used in Sections 2.4 and 3.3.2 for evaluation of external floods. In addition, please clarify that the storm with a 100-year return period discussed in Section 2.3 is not applicable to Section 3.3.2, in which Kairos assumed the PMP is an event causing a PMF event with equal probability (see the assumption in Section 2.4.2.1).

Resolution of Questions on Geology, Seismology, and Geotechnical Question Question Resolution Number 2.5-1 PSAR Section 2.5.2 discusses borings and observation trenches used to Kairos modified the PSAR to add explore subsurface conditions at the Hermes site, but some details of detailed information on borings results of the borings and trenches do not appear to be provided in the from the Geotech report. The PSAR. Please provide details of observations from the borings, including actual design will be informed by standard penetration test (SPT) N-values, as well as the trenches. In additional borings that are addition, please discuss how the information has been used in the design planned and will be discussed in of the Hermes facility. the operating license application.

2.5-2 PSAR Section 2.5.2 discusses soil types encountered at the Hermes site, Kairos provided the Geotech but some details of the soils are not clear from the PSAR. Please provide report to the staff for viewing in soil classification, different index properties, measured strengths, and the ERR. Kairos also stated that stiffness properties (modulus and Poissons ratio) for each soil type. additional information and

analysis on soil stiffness and strength properties affecting soil/backfill lateral pressure on the reactor building will be provided in the FSAR.

2.5-3 PSAR Figure 2.5-1 shows the boring plan for the Hermes site. Given that Kairos modified PSAR Section Figures 2.5-2 and 2.5-3 state that [i]nformation between borings is 2.5.4.3 to clarify that the location assumed and actual conditions may vary and given that the precise of the Hermes reactor to be footprint of the reactor building is not determined and there are no approximately 100 feet north of boreholes in the close vicinity of the anticipated location, NRC staff needs Boring B-5. Kairos modified PSAR additional information to assure that the site is appropriately characterized. Section 2.5.5.2 to clarify that the Will the foundation of the safety related portion of the reactor building foundation of the safety-related (basemat) be different than the foundation for the non-safety related portion of the Reactor Building will portions of the building? Please explain the differences, if any. rest on concrete fill down to the bedrock.

2.5-4 PSAR Figures 2.5-2 and 2.5-3 provide subsurface profiles for the Hermes Kairos modified PSAR section site, but do not appear to indicate the location of the reactor building. 2.5.5.2 to clarify that the location Describe the location of the reactor foundation in Figures 2.5-2 and 2.5-3. of the Hermes reactor will be approximately 100 feet north of Boring B-5.

2.5-5 Section 2.5.5.2.1 states that the underlying rock has adequate bearing Kairos provided the Geotech capacity. To allow staff to confirm the bearing capacity of the rock, please report to the staff for viewing in provide rock fracture network characteristics, such as, number of joint sets the ERR. Kairos modified PSAR and their orientations (dip and dip direction), open or filled joints, degree of Section 2.5.5.2.1 to indicate that weathering of the joints, and spacing of the joint sets. Also provide intact additional details on bearing rock strength and stiffness properties (modulus and Poissons ratio) and capacity, settlement, and lateral the rock mass strength and modulus estimation for each rock type along pressure will be provided in the with the method used. FSAR.

2.5-6 Based on the information in Figures in 2.5-2 and 2.5-3, the staff notes the Kairos provided clarifications to high water table. The water table is not discussed in the text of the PSAR. PSAR sections 2.4.1.2 and 2.4.4 Provide a discussion on what actions would be taken to address the high on how the high water table and water table. Also discuss the seasonal variation of the water table and how seasonal variations in water table the water table at the proposed site location would affect the bearing will be addressed.

capacity and settlement of the reactor foundation.

2.5-7 PSAR Section 2.5.2.3.2 states that the north portion of the Hermes site is underlain by the Mascot Formation, which is medium to thickly bedded.

Please clarify what is meant by medium to thickly bedded.

2.5-8 PSAR Section 2.5.2.3.2 states that the midsection of the Hermes site is underlain by the Pond Springs formation, which is medium bedded and medium jointed. Please clarify what is meant by medium bedded and Kairos provided access to Guide medium jointed. to Classification of Soil for Field 2.5-9 PSAR Section 2.5.2.3.2 states that the south end of the Hermes site is Boring Logs describing soils and underlain by the Murfreesboro dolomitic limestone, which is light gray, rocks that Kairos used.

medium, close jointed. Please clarify what is meant by this description.

2.5-10 PSAR Table 2.5-1 includes a description of Bedrock Murfreesboro that states it is 60 [degree], and has clay filled fracture at 30.5 [feet]. Please clarify what is meant by this description, including what type of clay the description is referring to.

PSAR Section 2.5.2.1 states that the geotechnical investigation at the Kairos modified PSAR Section Hermes site encountered indications of karstic activity. PSAR Section 2.5.2.1 to indicate that additional 2.5.4.3 states that the geotechnical subsurface investigation encountered tests and surveys will be limited evidence of voids or karstic dissolution at or near the reactor performed and documented in the building location. PSAR Section 2.5.4.3 discusses borings on the Hermes FSAR, including site site, but it is not clear how the investigations confirmed that there are no reconnaissance, analysis of 2.5-11 unacceptable karst features at the site. However, it is not clear how Kairos LiDAR imaging, inventory of plans to thoroughly evaluate the site for karst features. The staff notes that surface depressions in the site boring may not comprehensively identify karst features, and moreover, area, deeper borings at the there are no boreholes within the reactor footprint that might identify small- reactor location, laboratory scale karst features. How does Kairos propose to evaluate the subsurface analysis of rock cores and rock mass for karst features? Does Kairos propose to use ground- elaboration of the karst model for penetrating radar (GPR), or perform other geophysical measurements? Hermes.

2.5-12 PSAR Section 2.5.4.2 states that the Hermes safety-related reactor Kairos modified the PSAR to foundation basemat would be placed on bedrock, and surrounding clarify the plans for constructing structures would be placed either on bedrock or engineered soil. However, the foundation of the safety-Kairos response dated February 9, 2022 (ML22040A336), to Question related portion of the Reactor 2.5-2 which the staff sent to Kairos by email dated January 10, 2022 Building (ML22024A492), states that the Hermes foundation will be placed over an engineered crushed stone or lean concrete fill placed directly over sound rock. Please clarify the apparent discrepancy, especially with respect to the foundation of the safety-related portions of the reactor building.

In addition, to allow the staff to confirm the adequacy of engineered soils/backfill, please provide characteristics of engineered soils, crushed stone, and lean concrete proposed to be placed between the foundations of the reactor and surrounding structures and the bedrock. Also, please identify the source(s) of these soils and crushed stones and show that both of these materials are available in adequate quantities; clarify whether the lean concrete would be consistent with any standard; and justify why the engineered backfill would not be susceptible to liquefaction.

2.5-13 Based on the location of the weathered limestone in PSAR Figure 2.5-2 Kairos corrected the elevations and given that PSAR Section 2.5.4.2 states that the reactor building and scale in Figure 2.5-22 to foundation basemat is deployed at bedrock, the staff notes that the reactor address the question and ensure foundation would be below an elevation of 745 feet (below the weathered consistency with other portions of zone of limestone). Kairos notes in response to NRC question 2.5-2 the PSAR.

(ADAMS No. ML22040A338) that [t]he excavation is planned to reach the approximately 30 ft depth, exposing the surface of the foundation rock.

The scale on the left of PSAR Figure 2.5-22 shows that the reactor building foundation would be at an elevation of 760 feet. Figure 2.5-22 also shows an excavation depth of about 20 ft below the existing surface.

Please clarify the excavation depth for the proposed site, the depth to sound rock, and the correct elevation of the reactor building.

2.5-14 Regarding Section 2.5.5.2.1, provide an analysis of the estimated bearing Kairos provided the Geotech capacity (static and dynamic) and foundation settlement. Describe the report to the staff for viewing in method(s) used along with the assumptions. Provide the estimated bearing the ERR. Kairos modified PSAR capacity and elastic settlement including the factor of safety against Section 2.5.5.2.1 to indicate that bearing failure. Describe why long-term consolidation settlement is not a additional details on bearing concern. Justify why any potential sliding along the interface between capacity, settlement, and lateral Murfreesboro limestone and Pond Springs Formation (Figure 2.5-2) due to pressure will be provided in the the load imposed by construction of the reactor would not affect the FSAR.

stability of the proposed reactor site.

2.5-15 Regarding Figure 2.5-22, it appears that there is backfill to the side of the Kairos corrected the elevations safety related portion of the reactor building. Please discuss how the and scale in Figure 2.5-22 to lateral pressure from the backfill placed at side of the reactor building address the question and ensure would be assessed. consistency with other portions of the PSAR. Kairos modified PSAR Section 2.5.5.2.1 to indicate that additional details on bearing

capacity, settlement, and lateral pressure will be provided in the FSAR.

2.5-16 Liquefaction potential is discussed in Section 2.5.4.2. Section 2.5.2.3 Kairos modified PSAR section discusses standard penetration tests (SPT) of the soils of different 2.5.4.2 to clarify that the safety-boreholes at the site. The staff notes that the SPT N-values are not related reactor foundation will be corrected, for example, in accordance with Youd, et. al., 2001 for each on a concrete fill placed directly hole with depth. It is not clear how the liquefaction potential can be on competent bedrock. Therefore, assessed with uncorrected values. The reference is Youd, T.L, et al. liquefaction is not an issue.

(2001), Liquefaction Resistance of Soils: Summary Report from the 1996 NCEER and 1998 NCEER/NSF Workshops on Evaluation of Liquefaction Resistance of Soils, American Society of Civil Engineers Journal of Geotechnical and Geoenvironmental Engineering, October 2001, pp. 817-833.

2.5-17 The staff reviewed revised PSAR Figure 2.5-3 as well as the geologic Kairos indicated that profile provided in the Environmental Report (ER Figure 3.3-3), which Environmental Report Figure 3.3-appears to follow a similar trendline across the site as the profile shown in 3 is a more general regional revised PSAR Figure 2.5-3. The staff observed that ER Figure 3.3-3 shows depiction of conditions rather than slightly different subsurface thicknesses of several units over the similar based on detailed site-specific cross-section to revised PSAR Figure 2.5-3. Specifically, revised PSAR measurements. For the safety Figure 2.5-3 shows approximately 20 ft of clay fill underlain by a thin lens review, site-specific information of alluvial clay that thickens towards the center of the profile and a thick that is the best representation of layer of residuum clay to the northwest (B) section of the profile that thins the site subsurface based on the towards the center. Bedrock is encountered below the residuum clay at actual boreholes at the site can be elevation 710 ft and as high as elevation 740 ft at the base of the alluvial found in PSAR Figures 2.5-2 and clay. In contrast, ER Figure 3.3-3 shows a thin layer of fill underlain by a 2.5-3.

layer of clay that thickens from the northwest (A) towards the center of the profile before encountering bedrock between about elevation 745 and 730 ft. The staff is requesting the applicant to clarify the spatial relationship between the profile shown in ER Figure 3.3-3 and that shown in revised PSAR Figure 2.5-3 and confirm the subsurface units between the two profiles, including the types of clay and the approximate thicknesses of these units.

6.0 EXIT BRIEFING The staff conducted an audit closeout meeting on August 23, 2022. At the exit briefing the staff reiterated the purpose of the audit and discussed their activities. Additionally, the staff stated that they did not identify areas where additional information would be necessary to support the review.

There were no deviations from the audit plan.

7.0 ADDITIONAL INFORMATION RESULTING FROM AUDIT No RAIs were generated as a result of this audit. However, Kairos voluntarily updated the Hermes PSAR as seen in Revision 2 (ML23055A672) to address several items discussed during the audit.

8.0 OPEN ITEMS AND PROPOSED CLOSURE PATHS Not applicable.

SUMMARY

REPORT FOR THE REGULATORY AUDIT OF KAIROS POWER LLC HERMES CONSTRUCTION PERMIT PRELIMINARY SAFETY ANALYSIS REPORT SITE CHARACTERISTICS (CHAPTER 2)

DATED: APRIL 2023 OFFICE NRR/DANU/UAL1:PM BC: NRR/DEX/EHB BC: NRR/DANU/UAL1 NAME MHiser BHayes* AProffitt*

DATE 2 / 8 /2023 2 / 13 /2023 4 / 25 /2023

• concurred by email

SUMMARY

REPORT FOR THE REGULATORY AUDIT OF KAIROS POWER LLC HERMES CONSTRUCTION PERMIT PRELIMINARY SAFETY ANALYSIS REPORT DECAY HEAT REMOVAL SYSTEM (CHAPTER 6, SECTION 6.3)

February 2022 - October 2022

1.0 BACKGROUND

AND PURPOSE By letter dated September 29, 2021, Kairos Power LLC (Kairos) applied for a construction permit (CP) under Title 10 of the Code of Federal Regulations (10 CFR) Part 50 for its Fluoride Salt-Cooled, High Temperature Non-Power Reactor (Hermes); the application included a preliminary safety analysis report (PSAR) (Agencywide Documents Access and Management System (ADAMS) Accession No. ML21272A375). PSAR Chapter 6, Engineered Safety Features, Section 6.3, Decay Heat Removal System (DHRS), describes the DHRS and its safety function of removing decay heat when the normal heat rejection system is unavailable.

This function is credited in the safety analyses of PSAR Chapter 13, Accident Analysis, to maintain acceptable reactor vessel and fuel temperatures.

This audit enabled the U.S. Nuclear Regulatory Commission (NRC) staff (the staff) to gain a better understanding of Kaiross PSAR Chapter 6, Section 6.3 through review and discussion of underlying supporting documentation. Enhanced understanding and communications supported effective and efficient development of information needs.

2.0 AUDIT REGULATORY BASES The bases for the audit are the regulations in 10 CFR Part 50, Sections 50.34(a), Preliminary Safety Analysis Report, specifically 50.34(a)(1)(i), 50.34(a)(3), and 50.34(a)(4).

3.0 AUDIT OBJECTIVES The primary objective of the audit was to enable a more effective and efficient review of PSAR Chapter 6, Section 6.3 through the staffs review and discussion of supporting documentation with Kairos. Gaining access to underlying documentation and engaging in audit discussions about the DHRS facilitated the staffs understanding of the Hermes application and aided in assessing the safety of the proposed test reactor. The audit improved communication and provided detailed information for the staff.

4.0 SCOPE OF THE AUDIT AND AUDIT ACTIVITIES The audit was conducted from February to October 2022, via teleconference and the Kairos electronic reading room (ERR). The staff conducted the audit in accordance with the Office of Nuclear Reactor Regulation (NRR) Office Instruction NRR-LIC-111, Revision 1 Regulatory Audits (ML19226A274).

Members of the audit team, listed below, were selected based on their detailed knowledge of the subject. Audit team members included:

1. Alex Siwy, NRR (Technical Reviewer)

2. Jeff Schmidt, NRR (Technical Reviewer)

3. Ben Adams, NRR (Technical Reviewer)

4. Alexander Chereskin, NRR (Technical Reviewer)

5. Benjamin Beasley, NRR (Project Manager)

6. Edward Helvenston, NRR (Project Manager)

Prior to the audit, the audit team reviewed PSAR Chapter 6, Section 6.3 and provided a series of topics in the audit plan, dated February 17, 2022 (ML22039A226), to be addressed during the audit. On June 16, 2022, the staff transmitted an additional list of questions to be addressed during the audit (ML22167A117).

During the audit, meetings were held between the staff and Kairos on June 28, August 2, August 9, and August 16, August 30, 2022.

The staff reviewed the following documents via the ERR:

• Hermes Decay Heat Removal System Design Description

• Performance Predictions for the DHRS During Postulated Event Conditions (Reference 4 of Hermes Decay Heat Removal System Design Description)

• Document discussing DHRS qualification testing programs

• Onset to Freezing - Results from a Preliminary Analysis document

• Draft change pages for the PSAR and for technical report KP-TR-018, Postulated Event Analysis Methodology, indicating changes proposed by Kairos in response to various audit questions 5.0

SUMMARY

OF AUDIT OUTCOME The staffs audit focused on the review of supporting documents associated with the topics identified in the audit plan and subsequently transmitted questions. The staff reviewed information through the Kairos ERR and held discussions with Kairos staff to understand and resolve questions. In many cases, Kairos updated the Hermes PSAR to resolve items discussed in the audit. The table below replicates specific audit questions 6.3-1 through 6.3.12 transmitted by email dated June 16, 2022, and summarizes the resolution of the questions. In addition, the table lists and summarizes the resolution of additional follow-up questions the staff asked Kairos during the audit.

Question Question Resolution Number 6.3-1 The NRC staff would like to review Reference 4 Kairos provided Reference 4 for staff audit.

(Performance predictions for the DHRS during nominal Kairos stated that the purpose of this reactor scram conditions) of the Hermes Decay Heat document is to provide the basis for scoping Removal System Design Description. Please make this out heat transfer limits for the DHRS, and reference available for NRC audit. ensure it is consistent with the Hermes design.

6.3-2 Does Reference 4 (see #1) support the KP-SAM model During an audit meeting, Kairos confirmed results for reactor vessel temperature? If not, is there that yes, Reference 4 supports the model another reference that does, and may the NRC staff audit it? results by establishing a temperature boundary condition.

6.3-3 The NRC staff would like more information about how the During an audit meeting, Kairos noted that DHRS is modeled in KP-SAM. Is a document that explains the DHRS is modeled by a boundary the detailed modeling and associated assumptions available condition in KP-SAM. Reactor vessel heat for audit? removal is relatively insensitive to DHRS temperature, but KP-SAM uses a correlation to account for the relationship.

Kairos stated that KP-SAM doesnt explicitly model the heat transfer resistance term due to the gas gap in the double-walled structure of the DHRS. However, it is accounted for by using information from Reference 4 to inform the input to the KP-SAM model.

6.3-4 Please further explain why the net heat removal Kairos stated that net heat transfer is not performance of the thimbles is not affected if a float valve affected because the temperature of DHRS fails open. (E.g., do the thimbles in the affected train surfaces do not change, so radiative heat continue to remove the same integrated amount of heat as transfer does not significantly change. Kairos they would if they were not affected; do the other DHRS stated it plans to do testing to confirm this trains compensate for any degradation in the affected train; understanding of system performance.

or is there some other explanation?)

In response to further staff questions during audit discussion about potential steam cooling in the axially higher parts of the

thimbles, Kairos noted that steam in the thimbles is mixed phase, i.e., never completely steam.

6.3-5 Please explain how the thimbles are oriented in each steam Kairos stated that each DHRS train has six separator and the overall orientation around the reactor thimbles and the thimbles (from all four vessel. trains) are evenly distributed around the vessel with each train covering one quarter of the vessel circumferentially.

6.3-6 Please confirm the location of the equipment and structure Kairos stated that the ESCS is located cooling system (ESCS) relative to the DHRS and insulation. immediately outside the insulation, while the DHRS thimbles are between the insulation and the reactor cavity.

6.3-7 The design description states that ESCS operation post- Kairos stated that the ESCS does not shutdown will result in increased cooling rate relative to interfere with view factors for the DHRS DHRS operation alone. Has ESCS operation been thimbles because insulation separates the considered in the analysis of overcooling events? thimbles and the ESCS. Kairos noted that it will consider the effects of ESCS operation and insulation in sensitivity studies for the FSAR. Kairos also noted that for overcooling analyses in Chapter 13 (i.e., relating to analyses of potential accidents) for an operating license application, it would need to consider maximum DHRS performance as well as parasitic heat losses to capture the most challenging overcooling event.

6.3-8 Have sensitivity studies been performed to quantify the Kairos noted that the PSAR indicates that effects of uncertainties in view factors (e.g., due to the Hermes will be designed to mitigate factors reactor thermal management system heaters)? that could affect heat removal between the vessel and the DHRS. Kairos also noted that the reactor thermal management system heaters will not have a significant impact on DHRS function as they will simply absorb and re-emit heat like the vessel wall.

6.3-9 The design description acknowledges that loss of function Kairos clarified that a credible failure path over time is a credible failure path due to accumulation of

fouling within the separator float valves; however, does not mean failure is likely or expected.

redundancy of the four separate DHRS loops prevents loss The DHRS will be subject to technical of the required safety function. The NRC staff notes that if specifications (i.e., limiting conditions for one train fails in this mode, the other trains may be prone to operation and surveillances) to ensure fail in this manner around the same time. How will this type operability and identify any failure or of scenario be prevented? degradation that could prevent DHRS from performing its safety function.

Kairos also stated that the DHRS will have appropriate design features to prevent fouling, and there will be testing to further evaluate potential failure modes and ensure float valves function properly.

6.3-10 Has any analysis been performed to evaluate the magnitude Kairos noted that radiation heat transfer and impact of thermal gradient asymmetry in the event of would be reduced in that scenario. However, loss of inventory in one DHRS train? a final analysis will be provided in the FSAR.

Kairos also noted that PSAR Section 4.3.2 (specifically, the discussion of PDC 31) indicates that the reactor vessel design will account for transient stresses in analyzing reactor vessel integrity.

6.3-11 If a leak occurs in one DHRS train and water enters the leak Kairos indicated that it expects the effect barrier, what is the impact on DHRS performance in the would be limited. Kairos noted that boil-off of affected train? the water may actually cause slightly increased heat removal for the affected thimble. Kairos stated that during normal operations, a leak would be detected and addressed.

6.3-12 PSAR Subsection 7.3.1.2, "Decay Heat Removal System," Kairos confirmed that the figure and states that the water tank isolation valves fail open upon description in PSAR Chapter 6 is correct.

loss of power. However, PSAR Figure 6.3-1, "Functional PSAR Chapter 7 referred to the DHRS Diagram of the DHRS," shows that the isolation valve fails in orientation when the DHRS is operating.

the last position. Similarly, the Hermes Decay Heat Removal System Design Description states that the isolation valves Kairos provided proposed revisions to PSAR fail in place (in an as-is state). Please clarify the apparent Chapter 7 to clarify that the valves fail in discrepancy in the PSAR and make any necessary changes. place (which, during normal operation above

the threshold power, is open). Kairos subsequently submitted the PSAR changes to the docket by letter dated June 30, 2022 (ML22181B053).

Follow-up A (Primarily follow-up to questions 6.3-1, 6.3-2, and 6.3-3) Kairos provided a document discussing DHRS qualification testing programs for staff As a follow up, the staff asked Kairos to provide further audit. The staff indicated that it would require information regarding DHRS qualification testing programs. the information to be docketed to support its The staff requested that this include information on review. Kairos submitted the document to the physical phenomena (e.g., heat loading) and discussion of docket by letter dated September 1, 2022 how the physical phenomena are evaluated, or why they (ML22244A235).

are precluded. The staff also specifically asked if DHRS qualification testing included low pressure quenching tests to ensure that stable heat removal can be established because the guide thimble and evaporator tube will initially be empty and hence relatively hot prior to its startup (upon reaching the threshold power). In addition, the staff specifically asked if a thimble feedwater float valve failing to close as heat demand decreases was included in the DHRS qualification testing.

Follow-up B (Primarily follow-up to questions 6.3-1, 6.3-2, and 6.3-3) Kairos confirmed that the final DHRS sizing will be informed by final design calculations As a follow up to its review of Reference 4 during the audit, to ensure acceptance criteria are met on the staff asked Kairos whether the preliminary calculations both ends (i.e., overheating and for DHRS sizing conservatively consider the possibility for overcooling). The calculation in Reference reactor overcooling (e.g., incorporating assumptions such as 4 was primarily intended as a scoping calculation.

a fresh core and maximum DHRS performance).

In response to discussion with the staff regarding whether it would be possible to provide preliminary analyses of a more conservatively modeled overcooling event, Kairos provided the document Onset to Freezing Preliminary Analysis for staff audit.

In response to discussions following staff review of this document, Kairos provided for

audit proposed revisions to KP-TR-018 and PSAR Chapter 13 to reflect that Kairos plans to design the DHRS to preclude core freezing by design for at least 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> following a reactor shutdown. Kairos stated that it could change this commitment in an OL application but understands it would need to provide justification for such a change. In response to further audit discussions with the staff, Kairos provided for audit updated proposed revisions to KP-TR-018 and PSAR Chapter 13 to further clarify the prevention of Flibe freezing for 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> and make additional conforming changes.

Kairos subsequently submitted the KP-TR-018 and PSAR Chapter 13 changes to the docket by letter dated October 13, 2022 (ML22286A240).

Follow-up C (Primarily follow-up to questions 6.3-1, 6.3-2, and 6.3-3) Kairos stated that the correlation is used for the preliminary analysis because it is a Regarding Appendix B of Reference 4, the staff noted that scoping calculation and Kairos considers a the correlation used for critical heat flux analysis is for a flat flat plate analysis to be more conservative.

plate and asked whether Kairos considered a correlation Kairos clarified that the value of constant C more consistent with the evaporator tube geometry. In was obtained from a paper referenced in the Reference 4 document.

addition, the staff asked where Kairos obtained the value of the constant C.

Follow-up D (Primarily follow-up to questions 6.3-1, 6.3-2, and 6.3-3) The DHRS system design description document that Kairos provided for staff audit The staff requested that Kairos provide figure(s) better included some DHRS figures with additional describing the design of the DHRS. detail.

Following audit discussions, Kairos indicated that it would add 2 additional figures to the PSAR to show steam separator and float

valve geometries relative to each other, and how fluid flows through guide tube and up evaporator tube. Kairos provided for audit proposed revisions to PSAR Chapter 6, and subsequently submitted these changes to the docket by letter dated August 24, 2022 (ML22236A593).

Follow-up E (Primarily follow-up to questions 6.3-1, 6.3-2, and 6.3-3) During an audit meeting, Kairos confirmed that Equation 5.1-9 contains a typo, but it The staff noted that the Reference 4 provided for audit does not carry over to underlying appeared to contain a typographical error in its Equation calculations.

5.1-9. The staff asked Kairos to clarify whether the typo carried over to underlying calculations in the document.

Follow-up F Regarding instrumentation to ensure DHRS operability, the Kairos stated that it has not yet determined staff asked Kairos how ensuring DHRS operability would be what parameters will need to be monitored, accomplished and whether additional measurements or because it is still looking into what the instrumentation would be needed for this. complete set of potential DHRS failure mechanisms is. However, Kairos confirmed that there will be specific instrumentation to show the DHRS is performing as expected.

6.0 EXIT BRIEFING The staff conducted an audit closeout meeting on October 11, 2022. At the exit briefing, the staff reiterated the purpose of the audit and discussed their activities. Additionally, the staff stated that they did not identify areas where additional information would be necessary to support the review.

There were no deviations from the audit plan.

7.0 ADDITIONAL INFORMATION RESULTING FROM AUDIT No RAIs were generated as a result of this audit. However, Kairos voluntarily updated the Hermes PSAR (ML22181B053, ML22286A240, and ML22236A593) and a technical report (ML22286A240) and submitted additional information on the docket (ML22244A235) to address several items discussed during the audit.

8.0 OPEN ITEMS AND PROPOSED CLOSURE PATHS Not applicable.

SUMMARY

REPORT FOR THE REGULATORY AUDIT OF KAIROS POWER LLC HERMES CONSTRUCTION PERMIT PRELIMINARY SAFETY ANALYSIS REPORT DECAY HEAT REMOVAL SYSTEM (CHAPTER 6, SECTION 6.3)

DATED: APRIL 2023 OFFICE NRR/DANU/UAL1:PM BC: NRR/DANU/UTB2 BC: NRR/DANU/UAL1 NAME MHiser CDeMessieres* AProffitt*

DATE 4 / 13 /2023 4 / 24 /2023 4 / 25 /2023

• concurred by email

SUMMARY

REPORT FOR THE REGULATORY AUDIT OF KAIROS POWER LLC HERMES CONSTRUCTION PERMIT PRELIMINARY SAFETY ANALYSIS REPORT INSTRUMENTATION AND CONTROL (CHAPTER 7)

April 2022 - July 2022

1.0 BACKGROUND

AND PURPOSE By letter dated September 29, 2021, Kairos Power LLC (Kairos) applied for a construction permit (CP) under Title 10 of the Code of Federal Regulations (10 CFR) Part 50 for its Fluoride Salt-Cooled, High Temperature Non-Power Reactor (Hermes); the application included a preliminary safety analysis report (PSAR) (Agencywide Documents Access and Management System (ADAMS) Accession No. ML21272A375). PSAR Chapter 7, Instrumentation and Control Systems, describes the instrumentation and control (I&C) systems that monitor and control plant operations during normal operations and planned transients and also monitor and actuate protection systems in the event of unplanned transients.

This audit enabled the U.S. Nuclear Regulatory Commission (NRC) staff (the staff) to gain a better understanding of Kaiross PSAR Chapter 7 through review and discussion of underlying supporting documentation. Enhanced understanding and communications supported effective and efficient development of information needs.

2.0 AUDIT REGULATORY BASES The bases for the audit are the regulations in 10 CFR Part 50, Sections 50.34(a), Preliminary Safety Analysis Report, specifically 50.34(a)(1)(i), 50.34(a)(3), and 50.34(a)(4).

3.0 AUDIT OBJECTIVES The primary objective of the audit was to enable a more effective and efficient review of PSAR Chapter 7 through the staffs review and discussion of supporting documentation with Kairos. Gaining access to underlying documentation and engaging in audit discussions about the I&C design facilitated the staffs understanding of the Hermes application and aided in assessing the safety of the proposed test reactor. The audit improved communication and provided detailed information for the staff.

4.0 SCOPE OF THE AUDIT AND AUDIT ACTIVITIES The audit was conducted from April to July 2022, via the Kairos electronic reading room (ERR) and in person at the Kairos facility in Albuquerque. The staff conducted the audit in accordance with the Office of Nuclear ReactorRegulation (NRR) Office Instruction NRR-LIC-111, Revision 1 Regulatory Audits (ML19226A274).

Members of the audit team, listed below, were selected based on their detailed knowledge of the subject. Audit team members included:

1. Joe Ashcraft, NRR (Technical Reviewer)

2. Calvin Cheung, NRR (Technical Reviewer)

3. Benjamin Beasley, NRR (Project Manager)

Prior to the audit, the audit team reviewed PSAR Chapter 7 and provided a series of questions in the audit plan (ML22089A166) to be addressed during the audit.

During the audit, meetings were held between staff and Kairos in Alameda, California and Albuquerque, New Mexico on April 12 and 13, 2022, respectively.

The staff reviewed the following documents:

• Draft PSAR pages indicating changes proposed by Kairos in response to various audit questions 5.0

SUMMARY

OF AUDIT OUTCOME The staffs audit focused on the review of supporting documents associated with the questions identified in the audit plan (ML22089A166). The staff reviewed information through the Kairos ERR and held discussions with Kairos staff to understand and resolve questions. In many cases, Kairos updated the Hermes PSAR to resolve items discussed in the audit. The table below summarizes the resolution of the audit questions.

Question Question Resolution Number 7.1-1 Section 7.1, Reference 2, states the version used for Kairos indicated that the 2003 version was selected Institute of Electrical and Electronics Engineers (IEEE) 7- because it is the current NRC-endorsed version in 4.3.2 is 2003. Clarify why the 2003 version is used instead of RG 1.152.

a more recent version.

7.1-2 Section 7.1.2 states that for both plant control system (PCS) Kairos modified the PSAR to remove use of the and reactor protection system (RPS) "activation and term activation to avoid confusion.

actuation" setpoints are calculated. What is the difference between "activation" and "actuation" setpoints?

7.1-3 Describe the methodology and rigor used to establish non- Kairos modified the PSAR to remove reference to safety setpoints. setpoints for non-safety systems, which are not needed for a safety finding.

7.2-1 Is there any redundancy in the PCS platform or non-safety Kairos indicated that the level of redundancy will be sensors? This is in conjunction with request number 7.2-5 in informed by the reliability design requirements of this section, concerning PCS failure modes. the PCS hardware selected. The PCS hardware and its reliability will be provided in the FSAR.

7.2-2 Figure 7.1-1 does not identify the subsystems in the PCS to Kairos modified PSAR Section 7.2.3 to clarify that which the RPS sensors input. the PCS is designed to not be able to interfere with the RPSs ability to perform its safety functions.

Kairos indicated that PCS has dedicated sensors equivalent to the sensors in RPS with additional sensors that are only provided to PCS.

7.2-3 For the one-way data diode shown in Figure 7.1-1, there is Kairos modified PSAR Figure 7.1-1 and PSAR no information that discusses how the data diode is Section 7.3.3 to clarify that the data diode is implemented into the architecture and whether it will be integrated into the RPS hardware platform.

controlled via hardware or software.

7.2-4 The four subsystems of the PCS shown in Figure 7.1-1 do Kairos modified PSAR Table 7.2-3 but will need to not reflect the reactor auxiliary heating system (RAHS) and further clarify the RAHS description in Table 7.3-2 there is no discussion of the RAHS in Section 7.2. Update and Section 7.3 for the OL application.

Figure 7.1-1 and provide a discussion for the RAHS in Section 7.2.

7.2-5 Section 7.2 does not discuss PCS failure modes. Please Kairos modified PSAR Section 7.2.3 to clarify that describe the PCS failure modes. the PCS is designed to not be able to interfere with the RPSs ability to perform its safety functions.

The PCS hardware and a reliability evaluation, consistent with the safety classification of the PCS, will be provided in the FSAR.

7.3-1 Regarding Section 7.3, clarify if the RPS technology platform Kairos will provide the technology platform in the will be based on an NRC-approved topical report platform FSAR.

and if plant-specific action items will be addressed.

7.3-2 Figure 7.1-1 shows safety-related isolation devices. A bullet The typographical error in the bullets of PSAR in Section 7.3.1 lists the gateways as two non-safety RPS Section 7.3.1 was corrected to change the bullet on gateways. The gateways are shown in Figure 7.1-1 as part gateways to RPS isolation hardware.

of the main control room (MCR) and the PCS. Please clarify whether the gateways provide isolation from the RPS and if so, why are the gateways not safety related.

7.3-3 There is no discussion of function allocation in Section 7.3, Kairos will provide additional specificity in the which needs to be considered for defense in depth. Please FSAR, either by referencing the Highly Integrated describe RPS function allocation. Protection System (HIPS) topical report (ML17256A894) or explaining functional allocation if not referencing the topical report.

7.3-4 Regarding Figure 7.1-1, it is not clear if the post-accident Kairos corrected the typographical error in PSAR monitoring (PAM) displays in the remote onsite shutdown Figure 7.1-1 to clarify that the ROSP is non-safety panel are non-safety related or safety related (based on the related. Kairos indicated isolation as a separate color in the figure). As stated in Section 7.4, the remote device is not needed because it will be built into the onsite shutdown panel (ROSP) is not safety related. Later in platform technology.

Section 7.4, it is stated that no operator actions are needed, thus no PAM A variables are provided and PAM displays can be non-safety related and should have a diode to isolate them from the RPS. This topic should be addressed by Kairos as part of the application for an Operating License.

Specifically, the final safety analysis report needs to discuss how they are planning to implement this one-way communication.

7.3-5 The isolation between manual trips and RPS seems to Kairos modified PSAR Figure 7.4-1 to match Figure conflict with how it is shown in 7.4-1. (In Figure 7.1-1 an 7.1-1 with the intent to shown that no separate

isolation device is shown and Figure 7.4-1 shows a isolation is needed because isolation occurs at the gateway.) The arrow that shows that the signal goes both point of generation.

ways from the RPS in Figure 7.4-1. Please clarify.

7.3-6 Regarding Figure 7.1-1, if PAM displays in the ROSP are Kairos indicated isolation as a separate device is non-safety related, then please clarify why they arent not needed because it will be built into the platform isolated from the RPS. technology.

7.4-1 PSAR Section 7.4.3.1 states that the MCR is located at a Kairos indicated that the I&C architecture is distance from the Reactor Building such that the radiological designed to allow control room location flexibility.

consequences of unfiltered air in the MCR during postulated Kairos modified the PSAR, including Section events does not exceed 5 rem TEDE for the duration of the 7.4.3.1, to clarify the MCR will be in a separate event. PSAR Section 3.5.1 states that the main control stand-alone building away from the Reactor and building is a standalone building on the site that contains the Auxiliary Buildings. The location of the building plant control system and reactor protection system human housing the MCR and the MCR HVAC intakes and system interface consoles (main control room). However, access openings will be provided in the FSAR PSAR Table 3.6-1 indicates that the main control room is in designed to keep doses below 5 rem TEDE. The the Auxiliary Building and PSAR Section 7.4 also states that only radiological release location will be the the main control room is in the Auxiliary Building. Reactor Building. Table 3.6-1 will need to be Environmental Report Figure 2.2-3 gives the expected site updated with the OL application to confirm the layout and shows that the location of the Auxiliary Building is MCR location consistent with Section 7.4.3.1.

attached to the Reactor Building. Clarify the location of the main control room and relationship to the Reactor Building.

Provide information on potential radiological release locations and control room HVAC intakes and access openings for the MCR.

7.5-1 Section 7.3.2 states that the RPS is designed in accordance Kairos indicated that based on the final selection of with IEEE Std 603-2018. Please discuss the use of IEEE sensors, appropriate failure analysis will be Std 603-2018 for safety sensors rather than other versions. conducted and documented in the FSAR, including Also, if there are any digital safety-related sensors, then common cause failure for digital sensors if they are common cause failure needs to be addressed along with used in combination with a HIPS platform.

other IEEE criteria.

6.0 EXIT BRIEFING The staff conducted an audit closeout meeting on July 8, 2022. At the exit briefing the staff reiterated the purpose of the audit and discussed their activities. Additionally, the staff stated that they did not identify areas where additional information would be necessary to support the review.

7.0 ADDITIONAL INFORMATION RESULTING FROM AUDIT No RAIs were generated as a result of this audit. However, Kairos voluntarily updated the Hermes PSAR as seen in Revision 2 (ML23055A672) to address several items discussed during the audit.

8.0 OPEN ITEMS AND PROPOSED CLOSURE PATHS Not applicable. There were no deviations from the audit plan.

SUMMARY

REPORT FOR THE REGULATORY AUDIT OF KAIROS POWER LLC HERMES CONSTRUCTION PERMIT PRELIMINARY SAFETY ANALYSIS REPORT INSTRUMENTATION AND CONTROL (CHAPTER 7)

DATED: APRIL 2023 OFFICE NRR/DANU/UAL1:PM BC: NRR/DEX/EICB BC: NRR/DANU/UAL1 NAME MHiser MWaters* AProffitt*

DATE 4 / 13 /2023 4 / 14 /2023 4 / 25 /2023

• concurred by email