ML24220A062
| ML24220A062 | |
| Person / Time | |
|---|---|
| Site: | 99902094 |
| Issue date: | 08/07/2024 |
| From: | Paulette Torres NRC/NRR/DANU |
| To: | Brooks C University of Illinois |
| References | |
| L-2024-NFN-0003 | |
| Download: ML24220A062 (7) | |
Text
From:
Paulette Torres Sent:
Wednesday, August 7, 2024 8:54 AM To:
Brooks, Caleb Cc:
Edward Helvenston; Holly Cruz (She/Her/Hers); Dan Beacon (He/Him); Ben Adams; Ayesha Athar; Greg Oberson (He/Him); Donna Williams; Grunloh, Timothy P; Foyto, Les; Nicolas, Michael; Devitt, Peter; Conlon, Kelly; Vary, Beth; Tim.Parkes@onr.gov.uk; Ivaylo Stanev
Subject:
Regulatory Audit Questions for the "University of Illinois Urbana-Champaign High-Temperature Gas-Cooled Research Reactor: Fuel Qualification Methodology" Topical Report (EPID: L-2024-NFN-0003)
Attachments:
UIUC Fuel Qualification Methodology Topical Report Regulatory Audit Questions.pdf Caleb S. Brooks, Ph.D.
Associate Professor University of Illinois at Urbana-Champaign Department of Nuclear, Plasma, and Radiological Engineering Talbot Laboratory, Room 111C, MC-234 104 South Wright St, Urbana, IL 61801
Dear Dr. Brooks,
On June 14, 2024, the NRC staff issued a regulatory audit plan (Agencywide Documents Access and Management System (ADAMS) Package Accession No. ML24166A223) for the University of Illinois at Urbana-Champaign (UIUC) related to the UIUC Fuel Qualification Methodology (FQM) Topical Report Release 1 (ML24071A237). Attached is a list of questions the NRC and CNSC staff have prepared. The NRC and CNSC staff would like to discuss these audit questions within the scope of the audit plan and is providing these questions in advance to facilitate discussion during the audit meetings. The audit questions contain proprietary and export-controlled information and are therefore separately being securely transmitted to UIUC via NRC BOX. We will add this email, with the attached redacted version of the questions, to public ADAMS.
If you have any questions, please contact Paulette Torres at (301) 415-5656 or by electronic mail at Paulette.Torres@nrc.gov, or Edward Helvenston at (301) 415-4067 or by electronic mail at Edward.Helvenston@nrc.gov.
Respectfully, Paulette A. Torres Non-Power Production and Utilization Facility Licensing (UNPL)
Division of Advanced Reactors and Non-Power Production and Utilization Facilities (DANU)
Office of Nuclear Reactor Regulation (NRR)
(301) 415-5656 paulette.torres@nrc.gov Project No.: 99902094 EPID: L-2024-NFN-0003
Enclosure:
As stated
Cc: GovDelivery Subscribers
Hearing Identifier:
NRR_DRMA Email Number:
2572 Mail Envelope Properties (SA0PR09MB703609E1BB01A532D854C9C6FEB82)
Subject:
Regulatory Audit Questions for the University of Illinois Urbana-Champaign High-Temperature Gas-Cooled Research Reactor Fuel Qualification Methodology Topical Report (EPID L-2024-NFN-0003)
Sent Date:
8/7/2024 8:54:18 AM Received Date:
8/7/2024 8:54:00 AM From:
Paulette Torres Created By:
Paulette.Torres@nrc.gov Recipients:
"Edward Helvenston" <Edward.Helvenston@nrc.gov>
Tracking Status: None "Holly Cruz (She/Her/Hers)" <Holly.Cruz@nrc.gov>
Tracking Status: None "Dan Beacon (He/Him)" <Daniel.Beacon@nrc.gov>
Tracking Status: None "Ben Adams" <Christopher.Adams@nrc.gov>
Tracking Status: None "Ayesha Athar" <Ayesha.Athar@nrc.gov>
Tracking Status: None "Greg Oberson (He/Him)" <Greg.Oberson@nrc.gov>
Tracking Status: None "Donna Williams" <Donna.Williams@nrc.gov>
Tracking Status: None "Grunloh, Timothy P" <tgrunloh@illinois.edu>
Tracking Status: None "Foyto, Les" <lfoyto@illinois.edu>
Tracking Status: None "Nicolas, Michael" <michael.nicolas@cnsc-ccsn.gc.ca>
Tracking Status: None "Devitt, Peter" <Peter.Devitt@cnsc-ccsn.gc.ca>
Tracking Status: None "Conlon, Kelly" <Kelly.Conlon@cnsc-ccsn.gc.ca>
Tracking Status: None "Vary, Beth" <beth.vary@cnsc-ccsn.gc.ca>
Tracking Status: None "Tim.Parkes@onr.gov.uk" <Tim.Parkes@onr.gov.uk>
Tracking Status: None "Ivaylo Stanev" <Ivaylo.Stanev@onr.gov.uk>
Tracking Status: None "Brooks, Caleb" <csbrooks@illinois.edu>
Tracking Status: None Post Office:
SA0PR09MB7036.namprd09.prod.outlook.com Files Size Date & Time MESSAGE 1853 8/7/2024 8:54:00 AM UIUC Fuel Qualification Methodology Topical Report Regulatory Audit Questions.pdf 133128
Options Priority:
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Official Use Only - Proprietary and Export-Controlled Information Official Use Only - Proprietary and Export-Controlled Information Questions for audit discussions related to:
UNIVERSITY OF ILLINOIS AT URBANA-CHAMPAIGN TOPICAL REPORT - UNIVERSITY OF ILLINOIS URBANA-CHAMPAIGN HIGH-TEMPERATURE GAS-COOLED RESEARCH REACTOR: FUEL QUALIFICATION METHODOLOGY (EPID:L-2024-NFN-0003)
Note: The questions below, which are provided within the scope of the audit plan dated June 14, 2024 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML24166A223), are intended to aid NRC and CNSC staff in understanding and reviewing the University of Illinois at Urbana-Champaign (UIUC) Micro Modular Reactor (MMR) Fuel Qualification Methodology (FQM) topical report (TR). Although the questions are not considered requests for additional information (RAIs) at this time, they may be used to help identify information that will require docketing to support the development of the TR safety evaluation.
Questions:
- 1. Clarify the differences (manufacturing, final product properties, dimensions, etc.) ((between the test specimens that will be tested and the as-designed Fully Ceramic Micro-encapsulated (FCM) fuel pellet.
- a. ((Specifically, TR Table 6.1 and Figure 6.1 appear contradictory. In the table, the outer diameter of the surrogate pellet is listed to be smaller, while the inner diameter is larger (the surrogate is a thinner walled annular cylinder). However, the depiction in Figure 6.1 doesnt appear to reflect the larger inner diameter of the test specimen.}}
- b. How will ((these differences}} be accounted/adjusted for during data acquisition, determination of mechanical properties, and/or modelling, if necessary? ((If differences exist}} that are not necessary to model/disposition, explain the supporting rationale.
- i. ((Will the thinner-walled test specimen generate internal stresses in a comparable (or conservative) manner with respect to the as-designed FCM pellets? How will this be shown/justified?}}
ii. How will the effective silicon carbide (SiC) matrix densities vary ((between the test specimens and as-designed pellets}}? (((Specifically, this question was formed from the context that SiC density resulting from the chemical vapor infiltration process is dependent on penetration depth, and the surrogate pellets are thinner (and therefore have a lower penetration depth on average.)}}
- 2. ((How will the unirradiated pressure testing be performed? How will internal pressure of the test specimens be manipulated and controlled? What is the extent of integrity testing? Will unirradiated specimens be tested until pellet fracture/failure?}}
- 3. Will pellet-to-pellet vibration/wear and/or pellet-graphite vibration/wear in the MMR core over the period of operation be considered when assessing outer dense surface layer (ODSL) performance? If the intent will be to justify that vibration/wear will not meaningfully impact pellet performance or radionuclide diffusion/transport phenomena, how will this be justified?
- 4. High levels of surface roughness and high levels of adhesion between individual tristructural isotropic (TRISO) layers, and/or at the TRISO-particle-to-pellet-matrix interfaces, could contribute to TRISO particle failures if the pellet matrix material fractures. Specifically, potential exists for pellet fractures to propagate through strongly-bonded TRISO particles, causing the particles to fail. ((TR Section 4.4.2 states that the effectiveness of the crack-deflection layers
Official Use Only - Proprietary and Export-Controlled Information Official Use Only - Proprietary and Export-Controlled Information (CDLs) will be confirmed by testing, and Section 6.2.5 states that pellets will be tested to and beyond failure. However, subsequent TR sections dont appear to mention how CDL effectiveness will be examined. How will CDL effectiveness be tested/examined?}}
- 5. Is FCM pellet fracture considered or expected during MMR operating or accident conditions, or will it be precluded by associated testing and analysis and establishment of appropriate operating limits?
- 6. TR Section 4.3 explains that SiC matrix and ODSL materials may exhibit higher swelling rates and swelling saturation levels at lower temperatures.
- a. Will the effects of irradiation at low temperatures be quantified during testing?
- b. Will temperature (and temperature gradient) be varied/controlled/monitored during the short-duration irradiation testing described in TR Section 6.2.5?
- c. The following sub-questions may require completion of testing, development of an evaluation model, and/or performance of analyses to be fully answered/bounded, and are therefore not expected/required to be fully addressed at this time for this TR review, but are included below to provide context for the above questions and for general consideration and discussion.
- i. Could irradiation at low temperatures be challenging/limiting with respect to internal stresses created in FCM pellets due to expansion of SiC and/or TRISO particle materials?
ii. Could initial MMR start-up/heat-up from cold temperatures challenge pellet integrity? (i.e., Given the thermal mass of core constituents (graphite, etc.) that would need to be heated and the amount of fission heat/irradiation necessary to do so, could steep thermal gradients develop in pellets during startup and result in differential thermal expansion and irradiation swelling rates within the pellets?) Will a start-up rate limit or required pre-heating approach to start-up be considered or required, operationally? iii. How will time/temperature/thermal gradient differences between actual UIUC MMR start-up/operation and the steady state irradiation testing conditions be modelled/dispositioned when justifying initial MMR startup?
- 7. Will high-temperature safety testing include specimens that are damaged/fractured during the irradiation tests (for instance, from short-duration irradiation testing)? (i.e., if pellet fracture/failure is predicted to occur during postulated accident conditions, how will the resultant fission product release rate quantification method be supported by the safety testing data obtained?)
- 8. How much time (decay time) will pass between completion of irradiation testing and performance of high-temperature safety testing? Will any meaningful short-lived radioactive isotopes effectively decay away prior to the safety testing/measurement? If so, how will they be accounted for when assessing dose consequences of postulated accident conditions?
- 9. How will testing and/or modelling be used to justify the predicted core operational period (((20 years)}}, specifically, with respect to phenomena that occur slowly and/or may not necessarily be challenging/limiting during the planned time-accelerated experimental testing? For example:
- a. Chemical attack of the ODSL will likely occur ((at very low rates for the predicted operating temperature of FCM in the MMR and the effects of chemical attack during planned testing may therefore be minimal}}. Will the reaction rate be quantified and will the potential for long-term (((~20 years)}} cumulative effects be examined to determine
Official Use Only - Proprietary and Export-Controlled Information Official Use Only - Proprietary and Export-Controlled Information whether this phenomenon may meaningfully challenge ODSL performance near the fuels end-of-life?
- b. What other time-at-temperature effects were considered and/or dispositioned (and how were they dispositioned?) with the long-term timeframe in mind?
- 10. Which of the parameters in TR Table 2.2 are the limits in Table 2.2 referred to in TR Section 6.7 (TR Table 6.3, first criterion)? Do the limits include all values with an equivalency expression (e.g., <, >, etc.), or a subset? If they include nominal values without equivalency expressions, how are tolerances defined?
- 11. How will the thickness of FCM pellet ODSLs be confirmed during manufacturing? How will hermeticity be tested during manufacturing? Will every FCM pellet be tested/confirmed, or will a statistical sampling be used to estimate that FCM pellets are being manufactured to the appropriate thickness and that no defective ODSLs exist?
- 12. Were other potential fuel acceptance criteria considered for inclusion to TR Tables 2.5 and 2.6 (and by reference, TR section 6.7)? Specifically, in Advanced Gas Reactor (AGR) program documentation (Electric Power Research Institute (EPRI), Uranium Oxycarbide (UCO)
Tristructural Isotropic (TRISO)-Coated Particle Fuel Performance, Topical Report EPRI-AR-1(NP)- A, 2020, ML20336A052), envelopes are described based on temperature, burnup, and fluence (akin to the parameters specified in the TR tables), but also power density and particle packing fraction (which are not included in the acceptance criteria in the TR). Explain why power density and particle packing fraction are not included/needed to adequately define fuel acceptance criteria.
- 13. Sections 1.2.3 and 7.2 of the TR state that meeting the acceptance criteria in Section 6.7 of the TR qualifies the fuel for use. It is not expected that a final determination regarding the fuels qualification for use would be made until after the data/testing/modelling are complete. Should these statements be revised to not imply that this TR will grant final fuel qualification?}}