ML24282A733

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Enclosure - NRC Staff Feedback on Acu MC&A White Paper
ML24282A733
Person / Time
Site: Abilene Christian University
Issue date: 10/10/2024
From:
NRC/NRR/DANU/UAL2
To:
Abilene Christian University (ACU)
Richard Rivera, NRR/DANU
Shared Package
ML24282A730 List:
References
EPID L-2024-NFO-0005
Download: ML24282A733 (1)
v • d • e


Text

ABILENE CHRISTIAN UNIVERSITY - U.S NUCLEAR REGULATORY COMMISSION STAFFS FEEDBACK REGARDING ABILENE CHRISTIAN UNIVERSITYS WHITE PAPER:

MATERIAL CONTROL AND ACCOUNTING AT THE ABILENE CHRISTIAN UNIVERSITY MOLTEN SALT RESEARCH REACTOR (MSRR) (EPID: L-2024-NFO-0005)

SPONSOR INFORMATION

Sponsor: Abilene Christian University (ACU)

Sponsor Address: ACU Box 28208, Abilene, Texas 79699-8208

Docket/Project No.: 05000610

DOCUMENT INFORMATION

Submittal Date: April 26, 2024

Submittal Agencywide Documents Access and Management System (ADAMS) Accession No.: ML24117A070

Purpose of the White Paper: ACU stated that the purpose of this white paper is to provide a foundation regarding the material control and accounting (MC&A) approach for the Molten Salt Research Reactor (MSRR) to be built at Abilene Christian University (ACU).

Action Requested: ACU requested the U.S. Nuclear Regulatory Commission (NRC) staffs feedback and observations regarding the information discussed in white paper: Material Control and Accounting at the ACU MSRR, and specifically regarding measurement methods and, considering the nature of molten fuel, what level of uncertainty is acceptable.

FEEDBACK AND OBSERVATIONS

1. General
a. The NRC staff notes that the review of this document was limited to the items identified in the white paper, based on the scope of the request and the nature of the white paper.

No observations regarding items that were not included in the white paper are provided as part of this feedback.

b. ACU should be aware of the applicability of Title 10 of the Code of Federal Regulations (10 CFR) Part 74, Material Control and Accounting of Special Nuclear Material, subpart B, General Reporting and Recordkeeping Requirements, regarding general reporting and recordkeeping requirements. This includes the following regulations:

Enclosure

  • 10 CFR 74.11, Reports of loss or theft or attempted theft or unauthorized production of special nuclear material, regarding the 1-hour reporting requirement for loss, theft, or diversion;
  • 10 CFR 74.13, Material status reports, regarding the submittal of material status reports to the Nuclear Materials Management and Safeguards System (NMMSS);
  • 10 CFR 74.15, Nuclear material transaction reports, regarding the submittal of nuclear material transaction reports;
  • 10 CFR 74.19, Recordkeeping, regarding recordkeeping, where applicable.
c. The NRC staff notes that the MC&A requirements in 10 CFR Part 74, were written primarily for the light-water reactor (LWR) fuel cycle. As such, some features of non-LWR types of operations may need alternative approaches to demonstrate meeting the regulation. Specific control and accounting requirements are provided in subpart C, Special Nuclear Material of Low Strategic Significance, subpart D, Special Nuclear Material of Moderate Strategic Significance, and subpart E1, Formula Quantities of Strategic Special Nuclear Material, of 10 CFR Part 74 for certain licensees based on the strategic significance, or category, of the special nuclear material (SNM). The NRC staff notes that these subparts contain exclusions for licensees governed by 10 CFR Part 50, Domestic Licensing of Production and Utilization Facilities, which include nuclear power and non-power (research and test) reactors. For the current licensees of LWR facilities and research and test reactors, the SNM is usually maintained in the form of readily identifiable fuel assemblies that are managed on a per-item basis, and 10 CFR Part 74, subpart B (excluding 10 CFR 74.17), contains the appropriate MC&A program requirements. Regulatory Guide 5.29, Special Nuclear Material Control and Accounting Systems for Nuclear Power Plants (ML13051A421), provides American National Standard Institute publication, N15.8-2009, as an acceptable approach to the NRC staff for complying with the applicable MC&A requirements in subpart B for power reactors.

However, the NRC staff understands that certain non-LWR designs (including for power and non-power reactors) may include closer integration of the fuel cycle with the reactor and may require new MC&A approaches which may include additional control and accounting requirements to those contained in subpart B.

d. The NRC staff notes that for a molten salt reactor (MSR), the SNM may be in both item form (fresh fuel and used fuel in containers) and bulk form during reactor operations. As such, an adequate MC&A program for an MSR may have some aspects that resemble a fuel cycle facility, where applicable general reporting and recordkeeping requirements in subpart B would still apply, but additional MC&A requirements may also apply based on the category of SNM, the nature of the fuel, any required fuel processing or handling, and the reactor design features that are relative to MC&A. The NRC staff notes that the existing regulatory framework could be applied on a case-by-case basis to adjust to the practical differences of the design from the existing LWR designs.

1 Subpart C - Special Nuclear Material of Low Strategic Significance, also known as Category III; subpart D - Special Nuclear Material of Moderate Strategic Significance, also known as Category II; and subpart E - Formula Quantities of Strategic Special Nuclear Material, also known as Category I.

e. ACU states that the white paper is based on a preliminary design of the MSRR and the fuel form to be utilized. ACU notes that since the form of uranium that will be provided by the Department of Energy has not yet been determined, the MC&A approach described in the white paper may be changed and adjusted as detailed design changes dictate.

The NRC staff acknowledges the preliminary nature of the white paper and appreciates early engagement regarding this topic.

2. Adequacy of the Proposed MC&A Approach
a. ACU states that the format of the white paper follows the guidance in NRCs NUREG-2159, Revision 1, Acceptable Standard Format and Content for the Fundamental Nuclear Material Control Plan Required for Special Nuclear Material of Moderate Strategic Significance (ML22143A963). Additionally, ACU provides information in figure 1, MC&A Relevant Design Parameters for MSRR, which indicates that the MSRR fuel will contain high assay low enriched uranium (HALEU) at less than 20 weight percent in the uranium-235 isotope (wt percent U-235). The NRC staff notes that NUREG-2159 provides a structure and information as one means of facilitating compliance with the MC&A requirements for licensees authorized to possess and use SNM of moderate strategic significance, or a category II quantity of material. The guidance applies to applicants and licensees subject to the category II MC&A requirements in 10 CFR Part 74, subpart D, Special Nuclear Material of Moderate Strategic Significance. The NRC staff notes that HALEU containing uranium enriched to greater than 5 and less than 20 wt percent U-235 is considered category II SNM. As the NRC staff noted above in item 1.c., 10 CFR Part 74 contains exclusions for licensees governed by 10 CFR Part 50, including non-power reactors. The NRC staff also notes that while facilities licensed under 10 CFR Part 50 are generally excluded from the MC&A requirements in subpart D of 10 CFR Part 74, due to the nature of the MSR technology, some of the guidance in NUREG-2159 for fuel cycle facilities possessing and utilizing category II SNM may be appropriate to apply to an MC&A program at an MSR utilizing HALEU.
b. The ACU white paper contains sections that correspond to the chapters of NUREG-2159 regarding the various MC&A program elements. ACU provided high-level descriptions for each section/MC&A program element, including pertinent design elements of the MSRR. As such, the NRC staff could only provide general feedback regarding the current approach described in the ACU white paper. The sections describe the following:
i. Introduction ii. General Performance Objectives, Related Requirements, Commitments and Acceptance Criteria iii. Management Structure iv. Measurements
v. Measurement Control Program vi. Statistics vii. Physical Inventories viii.Item Control ix. Shipper-Receiver Comparisons
x. Assessment and Review of the MC&A Program xi. Tamper-Safing xii. Resolving Indications of Loss, Theft, Diversion, or Misuse of SNM xiii.Recordkeeping

The NRC staff acknowledges that ACU provided preliminary information considering guidance in NUREG-2159 and would review information regarding each of these MC&A elements in detail during its review of a future MSRR operating license application.

3. Additional Feeback Regarding Specific Areas as Requested by ACU:
a. ACU states that because molten fuel presents unique MC&A challenges, it is seeking particular feedback, as possible, regarding: (1) measurement methods; and (2) considering the nature of molten fuel, what level of uncertainty is acceptable. The NRC staff agrees that there are MC&A challenges with respect to a MSR and provides the following feedback regarding the requested items.
b. Measurement Methods
i. The NRC staff notes that ACU defines four material control boundaries: a research bay item control area (ICA), a radiochemistry lab ICA, a systems pit material balance area (MBA) and a reactor MBA. These areas will be delineated by material control boundaries and are established to localize losses to specific areas. The NRC staff notes that in NUREG-2159, an ICA is defined as an identifiable physical area for the storage and control of SNM items. Control of items moving into or out of an ICA is by item identity and SNM quantity as determined from previous measurement.

Additionally, NUREG-2159 defines an MBA as an identifiable physical area for the physical and administrative control of nuclear material such that the quantity of nuclear material moved into or out of the MBA is represented by measured values.

The NRC staff notes that an MBA is established to conduct material balance evaluations and determine an inventory difference (ID) for that MBA for each material balance period. Each MBA must have measurement points to enable measurement of SNM as it is received or shipped from the MBA. Any ID is determined and localized to a particular MBA. The NRC staff notes that for each MBA, the suite of measurement systems should be chosen to meet the desired total standard error of the inventory difference (SEID) value for the MBA. The NRC staff also notes that NRC Form 327, Special Nuclear Material (SNM) And Source Material (SM) Physical Inventory Summary Report, is filed on a plant basis, with a plant being a set of operations coordinated into a single manufacturing or research effort. Given the information above, the NRC staff notes that the preliminary ACU structure appears consistent with the definitions, however, ACU may consider encompassing the two designated ICAs in an additional MBA which may allow for the further localization of any loss, such that the entire plant is subdivided into MBAs.

ii. The NRC staff notes that the regulatory framework has flexibility for a reactor system with a novel design that requires a different approach in measuring SNM than a LWR or existing research and test reactors. An applicant can identify and request approval of alternate measurements or systems that demonstrate equivalent control.

iii. The NRC staff understands that some of the national laboratories are currently undertaking research regarding measurement systems for some of the material to be measured in an MSR (e.g., salt fuel, radioactive waste). The NRC staff notes that an applicant would be expected to demonstrate that the chosen analysis methods are sufficient, depending on the material form. For example, destructive analysis plus volume determination from a calibrated tank may be needed to provide sufficient SEID values, whereas gamma measurement plus weighing might be sufficient for uranium tetrafluoride (UF4) measurement. The NRC staff notes that the choice of the suite of measurement systems and the measurement points should demonstrate the ability for valid MBA determinations and control points for, particularly, the reactor MBA. Additionally, shipper-receiver difference (SRD) evaluations should be performed, and transfers of fuel to the reactor MBA should be measured.

c. Measurement Systems Uncertainty Requirements
i. The NRC staff notes that it appears that for all material control areas except the reactor MBA, the material will be available for measurement. As such, the sum of the uncertainty of the measurement systems, the SEID, may meet category II requirements (as specified in 10 CFR 74.43 (c)(8)(iii)). However, if this is not possible or appropriate for the chosen measurement, an applicant can propose an equivalent standard error.

ii. ACU states that it will rely on shipper values for SNM received. The NRC staff notes that the final product shipped to the reactor MBA is expected to be known (e.g.,

measurement, verification of shipper value). If the material balance evaluation for the reactor MBA results in a statistically significant ID, the SRD is typically an integral part of a licensees assessment to determine if the ID is due to an inaccurate shippers value.

iii. The NRC staff notes that based on current information from ACU discussed during a public meeting held on August 20, 2024 (see the meeting summary: ML24267A253),

the reactor would be shut down and material transferred to the drain tank at the time of the physical inventory. Therefore, it is anticipated that the measurement of SNM in molten fuel salt in the drain tank should be achievable. As such, the NRC staff understands that the material in the reactor MBA would be measured as part of the physical inventory. Measurement control points with measurement systems for any transfer points (off gas, sampling, or drainage) could be established. The NRC staff notes that a measurement point regarding the piping between the reactor and the drain tank could be established to demonstrate additional confidence. At this time, the NRC staff is not certain whether it is achievable or necessary to establish provisions similar to category II requirements regarding ID and SEID in the reactor MBA. The NRC staff notes that since the material is measured upon receipt into this MBA, and if it is not significantly processed prior to feeding it into the reactor, it may be considered as static, and therefore, measurements may not be necessary for physical inventory. This would depend on the accuracy of the measurement systems and whether the reactor has been accessed between physical inventories, which may create a possible unmonitored removal. Additionally, the NRC staff notes that the measurement systems used to determine values of transfers into and out of the MBA, if they achieve category II accuracy, could provide the statistical confidence in the ID value alone.

REFERENCES

  • Abilene Christian University (ACU). Material Control and Accounting at the Abilene Christian University Molten Salt Research Reactor (MSRR), dated April 26, 2024 (ML24117A070).

PRINCIPAL CONTRIBUTORS

John Russell (NMSS/DFM/MCAB)

Suzanne Ani (NMSS/DFM/MCAB)

Glenn Tuttle (NMSS/DFM/MCAB)

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