ML23138A403
| ML23138A403 | |
| Person / Time | |
|---|---|
| Site: | Hermes File:Kairos Power icon.png |
| Issue date: | 05/18/2023 |
| From: | NRC |
| To: | NRC/NRR/DANU |
| References | |
| Download: ML23138A403 (7) | |
Text
From:
Samuel Cuadrado de Jesus Sent:
Thursday, May 18, 2023 6:05 PM To:
KairosPower-CPDocsPEm Resource
Subject:
NRC General Audit Questions-Reactor Fuel, Reactor Vessel, Thermal Hydraulic Design, Reactor Coolant System Attachments:
NRC General Audit Questions Regarding Hermes CP PSAR_Redacted.pdf Samuel Cuadrado de Jesús Project Manager Advanced Reactor Licensing Branch (UARL)
Division of Advanced Reactors and Non-Power Production and Utilization Facilities (DANU)
U.S. Nuclear Regulatory Commission Phone: 301-415-2946 Samuel.CuadradoDeJesus@nrc.gov
Hearing Identifier:
KairosPower_CPDocs_Public Email Number:
39 Mail Envelope Properties (SA1PR09MB73920B20252E7A95330EF46A887F9)
Subject:
NRC General Audit Questions-Reactor Fuel, Reactor Vessel, Thermal Hydraulic Design, Reactor Coolant System Sent Date:
5/18/2023 6:04:59 PM Received Date:
5/18/2023 6:05:03 PM From:
Samuel Cuadrado de Jesus Created By:
Samuel.CuadradoDeJesus@nrc.gov Recipients:
"KairosPower-CPDocsPEm Resource" <KairosPower-CPDocsPEm.Resource@nrc.gov>
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SA1PR09MB7392.namprd09.prod.outlook.com Files Size Date & Time MESSAGE 333 5/18/2023 6:05:03 PM NRC General Audit Questions Regarding Hermes CP PSAR_Redacted.pdf 158363 Options Priority:
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NRC General Audit Questions Hermes Construction Permit (CP) Application Preliminary Safety Analysis Report (PSAR)
Reactor Fuel Item #
Question 4.2-13
- 1.
Beyond that described in PSAR, Section 4.2.1.1, is there a description of the moderator pebble design?
- 2.
Is there information in a licensing submittal which describe the specific graphite matrix material and end-state attributes of the pebble (e.g., grain size)?
- 3.
Is there a testing program to ensure buoyancy, wear characteristics, crush and impact loading tests (e.g., due to shutdown element insertion) including the effects of irradiation?
In short, is a document available for staff audit which has content similar to the fuel qualification topical report and addresses the moderator pebble, or does Kairos plan on evaluating the various failure modes in Chapter 13?
4.2-14 KP-TR-018, Section 3.4.2.2., TRISO Failure Probability, references Section 4.2. The staff has the following questions:
The staff understands the first paragraph to determine the failure fractions of the five states (and the fraction of intact particles) for both pre-transient (high and low temperature profiles) and transient using event specific power and temperatures. Is KP-BISON only used to determine failure fractions (weighing of cohorts) for the MHA or are KP-BISON transient particle releases (failed and intact) also determined for input into the MST?
4.2-15 The second paragraph of Section 3.4.2.2 describes an alternative method. The staff takes assuming MHA fuel temperature profiles to mean setting the kernel temperature vs time to Figure 2.1 and setting the pebble surface (Tfilm) to a conservative value based on the Flibe MHA temperature profile plus various uncertainties. KP-BISON would be used to determine incremental, transient failure fractions. These KP-BISON determined incremental failure fractions will be bounding if postulated event temperatures stay below the MHA temperature-time curve. These are show to be negligible to compared to the pre-transient failure fractions.
Reactor Vessel Item #
Question
4.3-10 Provide piping arrangement and anti-siphon device drawings that show how the anti-siphoning works following a pipe break.
Thermal-Hydraulic Design 4.6-1
- a.
The fluidic diode is identified as a research and development item in PSAR Section 1.3.9. Since the fluidic diode supports a key safety function, the staff needs to determine the feasibility of developing such a device for Hermes. Therefore, the staff is requesting additional information such as existing industry applications or research that would indicate there is reasonable assurance this device can be successfully developed to perform its Hermes safety function.
- b.
In the PSAR, please provide a description of, and schedule for, the research and development program for the fluidic diode, as required by 50.34(a)(8).
4.6-2
- a.
Staff has questions about how some of the heat transfer correlations fit together in the Hermes models.
- i.
((
)) is discussed in KP-TR-017-P, Section 5.3.1, Porous Media Modeling, and ((
))
- 1.
In KP-SAM, how do these correlations fit together to calculate the heat transfer from the fuel centerline to the bulk reactor coolant? The staff understands the KP-SAM model calculates core average coolant temperature. ((
))
Is the staffs understanding correct? To determine the average coolant conditions in KP-SAM how are pebble bed conduction, convection and pressure drop determined?
- 2.
In KP-SAM, is ((
)) the same ((
)) from KP-TR-017-P?
- 3.
In KP-SAM, is the ((
)) used to account for pebble-to-pebble convective heat transfer?
- 4.
In KP-SAM, how is heat transfer to the graphite reflector calculated (I.e radiative, conductive, and convective heat transfer from pebbles and coolant)?
ii.
Are these correlations in KP-SAM consistent across all Hermes thermal-hydraulic models (i.e., STAR-CCM+)?
iii.
What modifications are made to the heat transfer correlations in SAM, if any?
Please provide justifications for the heat transfer correlations used in KP-SAM, regardless of whether they are different or the same as the correlations in SAM.
4.6-3 KP-TR-017-P, Section 5.3.1, Porous Media Modeling, states ((
)) Is this ((
))
used in all the Hermes models, and what is the justification for choosing it? What other ((
)) if any, are used in the Hermes models, and what are the justifications for choosing them?
4.6-4 In Section 4.6, Thermal-hydraulic Design, please reference discussions on computer codes and evaluation models. Staff would be satisfied with references to KP-TR-017 and KP-TR-018 (e.g., Thermal-hydraulic computer codes and evaluation models are discussed in KP-TR-017 Sections 4 and 5 and KP-TR-018 Section 4).
Reactor Coolant System 5.1-1 PSAR Section 5.1.1.5 indicates that auxiliary heating may be needed to prevent coolant freezing in certain areas of the plant where insulation alone may not be adequate.
Describe where this auxiliary heating may be needed and whether Flibe freezing may impair the ability of a system, structure, or component (SSC), to perform its safety function. Additionally, describe scenarios in which auxiliary heating may be needed to prevent Flibe from freezing.
5.1-2 What subsystem provides the thermal management function described in Section 5.1.1.3? The reactor auxiliary heating system described in Section 9.1.5.1.2 doesnt appear to include primary heat transfer system (PHTS) components such as the Heat Rejection Radiator (HRR).
5.1-3 The interface between the primary and intermediate system is now separating Flibe from air. Part of Principal Design Criteria (PDC) 73 states that a single barrier between the systems may be appropriate provided that postulated leakage doesnt result in failure of the safety function of safety related SSCs. Describe how air leakage through the HRR barrier may impact the safety functions of safety related SSCs and whether a single passive barrier is appropriate to meet PDC 73.
5.1-4 Section 5.1.3 states that significant air ingress is excluded by design basis. How much is significant air ingress in this instance? Additionally, describe how trips of the primary salt pump and air blowers prevents a large quantity of air from reaching the PHTS. Section 5.1.1.3 states that this prevents forced air ingress but doesnt discuss natural convection air ingress. How will the upper bound limit for air in the reactor coolant be determined and measured?
5.1-5 Section 5.1.3 states that design features such as trip of the PSPs and air blowers help to meet PDC 33. However, PDC 33 is not cited in Section 5.1.2. Clarify whether this should be added to Section 5.1.2. Additionally, clarify whether the PSPs need to be tripped to maintain reactor coolant inventory in the event of a leak in the reactor coolant boundary, if only the anti-siphon feature is relied upon, or if a combination of both are needed to maintain coolant inventory.
5.1-6 NUREG-1537 Section 5.2, "Primary Coolant System," states that the primary coolant system should maintain high quality coolant to limit corrosion of fuel cladding, control rods, the vessel, and other essential components. The PSAR does not appear to state the required coolant purity to limit corrosion of SSCs other than the reactor vessel.
Describe how coolant purity will be maintained to limit corrosion of SSCs other than the reactor vessel (e.g. TRISO, control rods, pump components).
5.1-7 Section 5.1.1.1, "Reactor Coolant," states that a description of the reactor coolant can be found in KP-TR-005, Reactor Coolant for the Kairos Power Fluoride-Salt Cooled High Temperature Reactor. However, the PSAR doesnt appear to state that the LiF to BeF2 stoichiometry needs to be maintained in order to keep thermophysical properties within appropriate bounds. 10 CFR 50.36(c)(2)(ii)(B), "Criterion 2," states an operating restriction that is an initial condition for a DBE or transient analysis which could challenge integrity of a fission product barrier must be a technical specification (TS). Does Kairos plan to include a proposed TS in the OL to maintain the LiF:BeF2 ratio for Flibe?
5.1-8 Identify the materials of construction used in the PHTS in order to provide reasonable assurance that no significant galvanic corrosion of safety related SSCs will occur.
5.1-9 Section 5.1.1 states that the PHTS system functions include Provide for in-service inspection, maintenance and replacement activities". Clarify if this refers to ISI, maintenance and replacement activities for the PHTS or if this statement is referring to support for these activities for safety related systems.
5.1-10 Section 5.1.1 states that the PHTS system functions include Provide capability to drain the PHTS to reduce parasitic heat loss during over-cooling transients. A description of this does not appear to be included in Chapter 5. Provide a description of this capability and the cases when draining would be necessary.
5.1-11 Section 5.1.1.3 provides a description of the HRR blower and states that the blower will be tripped concurrent with the primary salt pump to prevent air ingress. However, there is not a description of other potential blower malfunctions. Provide a description of potential malfunctions of the heat rejection subsystem blower and how under/over cooling events could affect the temperature of the Flibe and other system performance.
5.1-12 How will an appropriate in-service testing program for the active components in the PHTS be determined? Will the in-service inspection program be performed under a reliability and integrity management (RIM) program as discussed in Ch 6.3.4?
5.1-13 Section 5.1.1.1 of the Hermes PSAR references topical report KP-TR-005 for a description of the reactor coolant. Limitations and Conditions of that topical report require an applicant to perform work to ensure coolant properties are in the applicants QA program which Kairos is pursuing (see the regulatory audit summary at ADAMS Accession No. ML21364A106). Provide and discuss the status of the thermophysical property data confirmation for the Flibe coolant.