ML25010A115
| ML25010A115 | |
| Person / Time | |
|---|---|
| Site: | 99902069 |
| Issue date: | 01/10/2025 |
| From: | NRC |
| To: | NRC/NRR/DANU |
| References | |
| Download: ML25010A115 (6) | |
Text
From:
Brian Bettes Sent:
Friday, January 10, 2025 8:09 AM To:
Delaney Simmons; Drew Peebles Cc:
Cayetano Santos; Josh Borromeo
Subject:
Audit Questions Related to Kairos Safety Analysis Methodology Topical Report Attachments:
3rd set of audit questions Kairos KP-SAM TR FINAL Public Version_Redacted.pdf Delaney and Drew, Attached is the third set of audit questions related to the NRC staffs audit of Kaiross safety analysis methodology topical report. This is the public version in which the proprietary and export-controlled information has been redacted. The non-public version has been shared with Kairos via the Box secure portal.
Please let me know if you have any questions.
Brian Bettes Brian L. Bettes Project Manager, Advanced Reactor Licensing Branch 1 Division of Advanced Reactors and Non-Power Production and Utilization Facilities Office of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission
Hearing Identifier:
KairosPower_PreApp_Public Email Number:
20 Mail Envelope Properties (SA1PR09MB110993B3B043F924EE9BF2E2F9C1C2)
Subject:
Audit Questions Related to Kairos Safety Analysis Methodology Topical Report Sent Date:
1/10/2025 8:08:36 AM Received Date:
1/10/2025 8:08:00 AM From:
Brian Bettes Created By:
Brian.Bettes@nrc.gov Recipients:
"Cayetano Santos" <Cayetano.Santos@nrc.gov>
Tracking Status: None "Josh Borromeo" <Joshua.Borromeo@nrc.gov>
Tracking Status: None "Delaney Simmons" <simmons@kairospower.com>
Tracking Status: None "Drew Peebles" <peebles@kairospower.com>
Tracking Status: None Post Office:
SA1PR09MB11099.namprd09.prod.outlook.com Files Size Date & Time MESSAGE 643 1/10/2025 8:08:00 AM 3rd set of audit questions Kairos KP-SAM TR FINAL Public Version_Redacted.pdf 640744 Options Priority:
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Official Use Only - Proprietary and Export Controlled Information UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 KAI ROS POWER, LLC - SAFETY ANALYSIS METHODOLOGY FOR THE KAI ROS POWER FLUORIDE SALT-COOLED HIGH-TEMPERATURE TEST REACTOR TOPICAL REPORT THIRD SET OF AUDIT QUESTIONS (EPID NO. L-2024-TOP-0022)
[Question GEN-6] Section 1.2, "Regulatory Background," of the topical report (TR) states that "[t]he development of this safety analysis methodology is consistent with the applicable portions of the evaluation model development and assessment process (EMDAP) described in Regulatory Guide [RG] 1.203, 'Transient and Accident Analysis Methods'
[ML053500170]." Please provide information on plans for addressing each step in the RG 1.203 process in the electronic Reading Room (eRR).
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[Question 4.3-1) In the KP-SAM base model, does each core node have both fuel and moderator pebble heat structures? How many types of fuel pebble heat structures are defined (e.g., average, hot)? How is power deposited or distributed within these heat structures?
[Question 4.3-2) Please explain how the radial flow from the core to reflector is represented in the KP-SAM base model.
[Question 5-1] Please discuss the process for identification of the limiting event for the different event categories in section 5, "Event-Specific Methods." Please discuss the sensitivity calculations that will be performed, and the figures-of-merit (FOMs) used for the identification of the limiting event.
[Question 5-2) Please explain how the safety analysis methodology accounts for undesirable impacts due to availability of the non-safety related plant control system and operator actions. Please discuss specific examples.
[Question 5-3) Please describe the core design inputs and reactor physics parameters (reactivity coefficients and other neutronic data) for the core model to calculate reactivity response and the power distribution. In addition, please explain how the conservative biases/uncertainties are applied to these parameters in safety analysis calculations?
[Question 5.1-1] Section 5.1.1, "Bias Application," describes conservative biases for different parameters used in the analysis of an increase in heat removal event. In general, it appears that the parameters are biased to maximize the heat-up.
o Please justify why maximizing the heat-up would be the bounding event for the reactivity response.
o Please explain how the direction of bias is determined for different parameters considering the multiple FOMs. Specifically, please identify if there is any FOM for which the required bias direction for conservative analysis is different than the biasing prescribed in section 5.1.1 to maximize the heat-up.
[Question 5.1-2) Section 5.1.2, "Sensitivities", describes sensitivity studies proposed for the analysis of an increase in heat removal event. The material property sensitivity analysis includes only the properties of the coolant.
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Please discuss how the impact of uncertainties in properties of other materials is accounted for in the methodology. For example, heat capacities of reflector, fuel and moderator pebbles, reactor vessel, and other internal structures which could significantly affect the total stored energy in the model.
o Please discuss how the uncertainties in total mass and heat transfer surface areas of different structures in reactor vessel (e.g., reflector, fuel and moderator pebbles) and primary system are accounted for in the methodology.
[Question 5.4-1) Section 5.4.1, "Bias Application," states that "[a] transient radial peaking factor is not applied because the withdrawal of all control elements results in a symmetric reactivity insertion. Transient radial and pebble peaking factors are applied for the single element withdrawal events to account for axial and radial changes in the power shape during the reactivity-initiated event. A hot pebble factor, which conservatively treats the power shape and associated uncertainties, is applied to calculate the highest temperature fuel pebble." Please discuss how three-dimensional power distribution or asymmetry in power response is accounted for in a single element withdrawal event. In addition, discuss the differences between the transient radial peaking factor, transient pebble peaking factor, and hot pebble factor, and their physical importance for the methodology.
[Question 5.5-2) Section 5.5.2, "Sensitivities," states that the limiting salt spill event is conservatively modeled as a combination of the most limiting break conditions rather than a single break scenario. Please describe how this is achieved.
[Question 5.6-3) Please describe how the temperature distribution of pebbles in the pebble extraction line and the pebble insertion line is determined in section 5.6, "Pebble Handling and Storage System Malfunction."
[Question 5.7-1) Section 5.7, "Radioactive Release from Subsystem or Component," states that the limiting event in this group is expected to be a seismic event, which results in failure of the subsystems and components not designed to withstand the design basis earthquake.
o Please clarify if the radioactive material at risk of release (MAR) for the seismic event is only located in the subsystems and components that fail (i.e., are not designed to withstand the design basis earthquake), or if there are releases from other systems or components that communicate with the failed subsystems and components, potentially with a delayed or protracted release.
o Section 5.7 states that the evaluation model for this event group is composed of establishing MAR inventories, combining releases from multiple subsystem or component failures, and the gas space transport model. Please explain in detail how the gas space transport model will be used.
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[Question A-1) Please provide the analytical limits or reactor protection system setpoints used for the example calculations in appendix A, "Example Calculations" of the TR.
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