ML25258A238
| ML25258A238 | |
| Person / Time | |
|---|---|
| Site: | Abilene Christian University |
| Issue date: | 09/15/2025 |
| From: | Abilene Christian University (ACU), Nuclear Energy eXperimental Testing Lab |
| To: | Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML25258A234 | List: |
| References | |
| Download: ML25258A238 (1) | |
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PROPRIETARY Degradation Management Program Implementation Update Report Introduction This document summarizes the initial implementation of the Degradation Management Program (DMP) as of September 2025 and describes the use of the associated DMP Database. This implementation enables Abilene Christian University (ACU) to establish a structured, iterative approach to degradation management for the Molten Salt Research Reactor (MSRR).
The report outlines methods for applying the DMP across the design, construction, and operational phases. It includes details on the in-scope components, the degradation mechanisms (DMs) considered, and both available and recommended mitigation strategies. Additionally, the report includes a sample showing how the DMP process is applied to selected Reactor System components, with each step documented in the DMP Database (Appendices A & B).
De"nitions DMP: The formal report that de"nes the DMPs overall structure, objectives, and requirements necessary to manage degradation for the MSRR. In accordance with permit condition 3.D(b), ACU submitted its DMP to the NRC on December 5, 2024 (ML24341A135). To date, no changes to the DMP have been issued. The DMP establishes a scope and expectations, including key principles, roles, responsibilities, and procedural framework. Unlike the DMP Database, the DMP is a static document since it establishes the foundational requirements. It is not expected to change over time unless a formal revision is warranted.
DMP Database (or the Database): The dynamic, living component of the DMP. It tracks the application of the degradation management strategies throughout the MSRRs lifecycle, capturing results and decisions from each step of the process. It serves as a centralized repository for component assessments, DM evaluations, and mitigation strategies, with references to supporting documentation. The DMP Database generates speci"c requirements (referred to as DMP Requirements) for the components within the DMP.
Currently maintained as an Excel spreadsheet, it may evolve as the DMP matures. Its primary purpose is to document and maintain the DMP Database Results and support ongoing updates as new data and research become available.
DMP Database Results: The results include the disposition (applicable or not applicable) and mitigation strategies for all considered DMs and Component Groups. Where full Page 1 of 15
PROPRIETARY disposition is not possible due to insufficient data (gaps), the results identify work needed to complete the disposition (actions).
Component Groups: To simplify organization and improve the usability of the DMP Database, the DMPs components are organized into groups of elements with similar properties and considerations. This grouping helps streamline the process, reduce duplication, and manage requirements more effectively.
DMP Requirements: Each mitigation strategy in the DMP Database Results corresponds to a requirement for the evaluated component group. These requirements are maintained by the DMP Database and are tailored to the speci"c groups identi"ed in the DMP. The requirements extend beyond design considerations to include fabrication and operational aspects.
DMP Design Speci"cations: The DMP Requirements can be extracted from the DMP Database to generate DMP Design Speci"cations for each component group. These speci"cations must be maintained throughout the components lifetime and updated as necessary. If a DMP Design Speci"cation con"icts with a prior requirement in the designers requirements tracking tool, the more conservative requirement shall apply. The tracking tool is referred to as the Requirements Traceability Veri"cation Matrix (RTVM).
Research: The systematic investigation, either through literature search or an experimental program, required to evaluate the considered degradation mechanism.
Figure 1 shows the relationship between the different terms.
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PROPRIETARY Figure 1: DMP Database De"nitions Page 3 of 15
PROPRIETARY Consequential Failure The DMPs mitigation strategies are selected according to the consequences of failure. The potential failure is determined to be consequential if it can impair or impede a safety function, such as leading to the release of radioactive material, inadequate heat removal from the reactor, or inadequate reactivity control. Moreover, failures may also be considered consequential if they compromise components that are critical to the mission and operation of the system.
Even if a DM is fully mitigated for a component through design, fabrication, or operational strategies, but the failure is evaluated as consequential, the DMP requires monitoring to detect failure. If the DM is not fully mitigated and the failure is consequential, the component requires monitoring to prevent failure.
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DMP Components Table 1 summarizes the MSRR systems included in the DMP, the relevant components, their classi"cation, and other bases for inclusion in the DMP.
Table 1: Systems and Major Components Included in the DMP System / Component Safety-Related (SR)
Key Asset or Mission-Critical Fuel Handling System (FHS)
Fuel Transfer Enclosure Fuel Storage Enclosure Fuel Salt Puri"cation & Storage Vessel Piping & Valves 5, 6 Reactor System (RX)
Reactor Vessel Reactor Drain Tank Page 4 of 15
PROPRIETARY System / Component Safety-Related (SR)
Key Asset or Mission-Critical Reactor Access Vessel (RAV)
Reactor Enclosure Reactor Thermal Management Liner (RTML)
Reactor Pump 1 Reactor Loop Piping Primary Heat Exchanger (shell and tube sides)
Moderator Internals - Supporting Grid Piping & Valves 3, 6 Coolant Salt System (CSS)
Coolant Salt Puri"cation Vessel Coolant Salt Drain Tank 1 Coolant salt Expansion Tank 1 Coolant Salt Pump 1 Radiator 1 Coolant Loop Piping & Valves 1, 5, 6 Auxiliary Heat Removal System (AHRS)
Louvers 1, 2 Gas Management System (GMS)
Helium (He) Vessels (Medium and Low Pressure Only)
He Piping & Valves (SR Only) 4, 6 He Heat Exchanger He Vacuum Vessel and Associated SR Piping &
Valves He Compressor Hydrogen Fluoride Piping & Valves (SR Only) 4, 6 Nitrogen Piping & Valves (SR Only) 4, 6 Off-Gas System (OGS)
Off-Gas Enclosure & Outer Piping Piping & Valves 5, 6 Fuel Salt Chemical Management (SCM) System (part of FHS)
Fuel Salt Sampling Enclosures Sample Holder Wire Valves & Piping 5, 6 Notes:
- 1. Component is SR because it is part of a pressure boundary. Other component functions are non-safety-related.
- 2. Excludes ducting between louvers and Reactor Cell, as well as ducting and louvers for the South Cell.
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PROPRIETARY System / Component Safety-Related (SR)
Key Asset or Mission-Critical
- 3. The RX includes reactor protection system (RPS) piping and valves, which refer to three (3) separate He lines connecting the Reactor Drain Tank and the Reactor Access Vessel, each with two (2) normally closed isolated valves. RPS piping and valves are owned by RX, while RPS owns the valve controls.
- 4. Such piping may be partially or entirely owned by other systems (e.g., FHS, CSS, RX, SCM, or OGS).
- 5. Includes all SR piping and valves attributed to this system. It may include a variety of process conditions and pipe and valve materials.
- 6. Includes one or more engineered safety features actuation system (ESFAS) valves.
Degradation Mechanisms Table 2 provides a list of the identi"ed DMs grouped into seven categories.
Table 2: Identi"ed Degradation Mechanisms Category ID Degradation Mechanism DM Index
- 1. Gross Structural Deformation PC Plastic collapse 1
DEF Excessive deformation and excess strain 2
- 2. Fatigue HCF High-cycle fatigue 3
LCF Low-cycle fatigue 4
EAF Environmentally-assisted fatigue 5
- 3. High-Temperature Mechanisms CRE Creep cracking 6
CRF Creep-fatigue 7
THA Thermal aging 8
DTE Differential thermal expansion 9
- 4. Embrittlement EMB Embrittlement 10
- 5. Corrosion SCC Stress corrosion cracking 11 IAC Irradiation-assisted corrosion 12 DAL Corrosion: dealloying 13 GAL Galvanic corrosion 14 COR General corrosion (includes HF reaction and decarburization) 15
- 6. Flow-Induced Degradation FRT Fretting 16 AER Abrasion and erosion 17 CAV Cavitation 18
- 7. Stress Relaxation Cracking SRC Stress relaxation cracking 19 Page 6 of 15
PROPRIETARY Component Groups The DMPs components are divided into Groups to streamline organization and improve the overall usability of the Database and associated processes. Grouping serves the following purposes:
- Make the Process Practical: By clustering related components together, the grouping approach simpli"es navigation and data handling. It allows users to focus on a speci"c subset of components during assessments or updates, reducing complexity and making the overall process more manageable and efficient.
- Avoid Repetitions: Components that share common characteristics, functions, or requirements can be grouped together. This eliminates the need to repeat the same information or apply identical requirements multiple times across similar components. Instead, requirements can be applied at the group level and inherited by all components within that group, saving time and reducing the potential for inconsistencies or errors.
- Manage Requirements More Easily: Grouping enables more effective requirement management by allowing users to assign, track, and update requirements for a collection of components simultaneously. This structure is particularly helpful when reviewing compliance, performing updates, or assessing impacts, since changes can be applied uniformly across all relevant components within a group. It also supports better traceability and simpli"es version control. Since each group is associated with a unique set of DMP Requirements, the total number of design speci"cations produced by the DMP directly corresponds to the number of groups, signi"cantly reducing the volume of documentation to manage.
Groups are created based on criteria to ensure consistency and relevance among the components they contain. Grouping criteria include:
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Table 3 lists all currently identi"ed groups. A sample of a group description for the reactor system is provided, which includes a list of applicable monitoring strategies. Ultimately, the Database describes which of these strategies are used to monitor or prevent component failure. For most groups, only a subset of the listed monitoring strategies will be required. The available monitoring strategies listed in the next section may change as the design progresses.
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Sample: Reactor System Group - RX01 RX01 includes the reactor vessel, the reactor vessels supporting grid for the graphite moderator, the RAV, and the drain tank. These components are made of 316H, are designed to be operated at high temperature, and are in contact with the fuel salt. Their failure is expected to be consequential.
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Conclusion & Next Steps To date, the speci"c inspection strategies required to proactively prevent component failures have not been formally de"ned. Although strategies to detect failure have been identi"ed for the different groups, many groups lack monitoring strategies to prevent failure. The de"nition of monitoring strategies to prevent failure will require coordination between different design groups and a clear de"nition of acceptance criteria to determine the inspection interval.
Several details remain to be evaluated before the Database can be considered comprehensive. For instance, the precise failure criteria for some assemblies (e.g., the reactor enclosure and the RTML) have not yet been established and should be de"ned in terms of performance degradation or loss of function. To close these gaps, a review team could:
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Although this is an initial assessment of components whose failure is considered consequential, these preliminary determinations must be validated. An analysis will demonstrate that, in the event of each components failure, the resulting radiation dose remains below the established threshold. This can be achieved by analyzing the component within each group that yields the highest dose and expanding the analysis to additional components if needed. Once con"rmed, these classi"cations can be used to focus inspection, monitoring, and mitigation efforts on the most safety-critical elements.
An independent review will be carried out to verify the DMPs technical rigor, identify any gaps or inconsistencies, and con"rm that all methodologies and data inputs meet industry best practices. This review will include a detailed assessment of the inspection strategy Page 10 of 15
PROPRIETARY proposals. The DM selection and grouping logic is considered reviewed during the workshop in April 2025, although it can still be modi"ed if needed.
Once the DMP has developed DMP Requirements and DMP Speci"cations for each component group, the DMP Speci"cations will be communicated to the design teams to ensure the identi"ed requirements can be met. After these requirements are addressed, the DMPs documentation will be updated to re"ect how each requirement has been satis"ed. This documentation includes detailing the design features, operational controls, inspection strategies, or material selections that ful"ll each requirement. The documentation will clearly articulate how the requirement is met, the mitigation strategies applied, and any ongoing monitoring or inspection activities. This level of traceability ensures that all stakeholders, such as designers, operators, regulators, and independent reviewers, have a clear understanding of how the DMPs objectives are being achieved.
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PROPRIETARY Appendix A DMP Database Format Appendix A provides a description of the DMP Database format. The Database, currently maintained as an Excel spreadsheet, has columns that correspond to speci"c steps in the DMP Process:
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Appendix B
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Appendix B
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