ML23102A241
| ML23102A241 | |
| Person / Time | |
|---|---|
| Site: | 99902069, Hermes |
| Issue date: | 04/19/2023 |
| From: | Kairos Power |
| To: | Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML23102A238 | List: |
| References | |
| KP-NRC-2304-004 | |
| Download: ML23102A241 (1) | |
Text
KP-NRC-2304-004 Enclosure 2 Presentation Slides for the April 19, 2023 ACRS Kairos Power Subcommittee Meeting (Non-Proprietary)
Hermes PSAR Chapter 13 Accident Analysis DR. MAT THEW DENMAN - DISTINGUISHED ENGINEER, RELIABILITY DR. TIMOTHY DRZEWIECKI - MANAGER, SAFETY ANALYSIS ACRS KAIROS POWER SUBCOMMIT TEE MEETING APRIL 19, 2023 Copyright © 2023 Kairos Power LLC. All Rights Reserved.
17 No Reproduction or Distribution Without Express Written Permission of Kairos Power LLC.
Safety Case Summary
- 10 CFR 50.34(a)(4) requires a preliminary safety analysis to assess the risk to public health and safety from operation of the facility, including determination of the margins of safety
- To demonstrate compliance with 10 CFR 100.11 dose reference values, a Maximum Hypothetical Accident (MHA) that bounds the postulated events is analyzed for dose consequences by challenging the performance of functional containment The Hermes MHA approach is consistent with guidance in NUREG-1537 The Hermes MHA is not physical The Hermes MHA includes conservatisms that maximize source term The Hermes MHA includes a postulated release of radionuclides
- To ensure that the postulated events are bounded by the MHA:
The list of postulated events is comprehensive to ensure that any event with the potential for significant radiological consequences has been considered Initiating events and scenarios are grouped, so that a limiting case for each group can be qualitatively described in CPA (quantitative results will be provided with OLA)
Acceptance criteria are provided for the important figures of merit in each postulated event group to ensure the potential consequences of that event group remain bounded by the MHA as the design progresses Prevention of an event initiator is justified in the PSAR Copyright © 2023 Kairos Power LLC. All Rights Reserved.
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Relationship between Dose Limits, the Maximum Hypothetical Accident, and Postulated Events
- The Maximum Hypothetical Accident (MHA) 100.11(a)(1-2) Reference Values is constructed to:
Be conservatively non-physical to overestimate Margin potential off-site dose consequences To EAB/LPZ Dose (relative)
Provide confidence that sufficient Dose Ref.
safety margin exists Values Ensure that reasonable design constraints will result in bounded postulated event doses MHA Dose Hypothetical Conservatism
Quantitatively evaluated Ensures that sufficient margin exists to 10 CFR Design Basis 100.11 dose reference values Potential Postulated Event Doses Conservatism Copyright © 2023 Kairos Power LLC. All Rights Reserved.
19 No Reproduction or Distribution Without Express Written Permission of Kairos Power LLC.
Postulated Event Analysis Methodology
- Postulated events are identified in Chapter 13 of the PSAR Postulated events include any potential upset to plant operations, within the plant design basis, that causes an unplanned transient to occur Justification is provided for those events excluded from the design basis (Prevented Events, PSAR Section 13.1.10)
- Figures of merit provide the means to measure and demonstrate that the resulting dose of a postulated event is bounded by the dose consequences of the MHA
- The preliminary methods and sample calculations of the postulated event groups are provided in KP-TR-018, Rev. 2. The methodology describes:
How to analyze figures of merit for each postulated event group How the acceptance criteria ensure that the off-site dose consequences of postulated events are bounded by the MHA
- The final safety analysis results will be provided with the Operating License Application (including verification and validation of the evaluation models used)
Copyright © 2023 Kairos Power LLC. All Rights Reserved.
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Postulated Event Analysis Methodology (cont.)
- The evaluation model development activities for the postulated events follow a process similar to the Evaluation Model Development and Assessment Process (EMDAP) from Reg. Guide 1.203
- Postulated events with similar characteristics and modeling approaches are grouped into categories, consistent with NUREG-1537
- The limiting event for each event category is identified and qualitatively assessed from event initiation until a safe state is reached
- The safe state is defined in the methods for each category of events as a point where the transient figures of merit have stabilized in a safe condition Copyright © 2023 Kairos Power LLC. All Rights Reserved.
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Input Parameters for Postulated Event Analysis
- Input parameters considered for postulated event analysis include a range of values to be evaluated for the final design (Table 4-4 of KP-TR-018)
- A range of values are assessed to identify the limiting scenario for each postulated event
- Key model uncertainties and initial conditions are conservatively applied to the methods to ensure figures of merit are conservatively predicted Copyright © 2023 Kairos Power LLC. All Rights Reserved.
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Limiting Postulated Events (1 of 3)
- Loss of Forced Circulation Pump seizure disables the primary salt pump Reactor protection system detects high coolant temperature and initiates a reactor trip Grouped events include locked rotor and loss of normal heat sink
- Insertion of Excess Reactivity Control system or operator error causes highest worth control element to withdraw continuously at the maximum control element drive speed Reactor protection system detects the reactivity insertion due to a high neutron flux or high coolant temperature and initiates a reactor trip Grouped events include fuel loading error, reflector shifting, and venting of gas bubbles
- General Challenges to Normal Operation Includes challenges to normal operation not covered by another event category that require automatic or manual shutdown of the reactor Bounded by the limiting loss of forced circulation postulated event Grouped events include spurious trips, operator errors, and equipment failures Copyright © 2023 Kairos Power LLC. All Rights Reserved.
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Sample Transient Analysis - Loss of Forced Circulation (Overheating)
KP-TR-018, Figure A4-1 Adapted from KP-TR-018, Figure A4-1
- Loss of forced circulation initiated by pump seizure/locked rotor
- Reactor trip on high plenum temperature reached ~30 seconds into event
- A second peak occurs ~20 hours into event followed by monotonic temperature decrease Copyright © 2023 Kairos Power LLC. All Rights Reserved.
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Limiting Postulated Events (2 of 3)
- Mishandling or Malfunction of Pebble Handling and Storage System Break in a fuel transfer line during removal from the core results in a spill of pebbles within the transfer line to the room The reactor protection system detects this condition and initiates a pebble handling and storage system trip Grouped events include transfer line break when pebbles are inserted into empty core, core at power, storage canisters, and mishandling of fuel outside the reactor
- Radioactive Release from a Subsystem or Component Limiting event assumed to be a seismic event that results in a failure of all systems containing radioactive material that are not qualified to maintain structural integrity during a design basis earthquake Design requirement on the amount of MAR for SSCs to be below the amount of MAR derived from the MHA Grouped events include releases from the tritium management system, inert gas system, chemistry control system, and inventory management system Copyright © 2023 Kairos Power LLC. All Rights Reserved.
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Limiting Postulated Events (3 of 3)
- Salt Spills A hypothetical double-ended guillotine break occurs in the PHTS hot leg piping Reactor protection system detects the salt spill due to a low coolant level and initiates a reactor trip Grouped events include spurious draining of the PHTS, leaks from other Flibe containing systems, mechanical impact or collision of Flibe bearing SSCs, and HRR tube breaks
- Internal and External Hazard Events Internal and external events include internal fire, internal water flood, seismic event, high wind, toxic release, mechanical impact or collision with SSCs, and external flood as described in Chapter 2 Events in this category are bounded by or considered as initiators in other event categories Copyright © 2023 Kairos Power LLC. All Rights Reserved.
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Summary Postulated events within the design basis are identified and grouped by characteristics and modeling approaches
- Design features which are credited with mitigating the effects of postulated events are described
- Figures of merit are derived for the postulated events to provide surrogate metrics which demonstrate that the resulting doses are bounded by the dose consequences of the MHA analysis
- The acceptance criteria for these figures of merit represent design limits that ensure the MHA is bounding Copyright © 2023 Kairos Power LLC. All Rights Reserved.
27 No Reproduction or Distribution Without Express Written Permission of Kairos Power LLC.