ML19226A334
| ML19226A334 | |
| Person / Time | |
|---|---|
| Site: | Nuclear Energy Institute |
| Issue date: | 08/14/2019 |
| From: | Holtzman B Nuclear Energy Institute |
| To: | John Marshall Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| Download: ML19226A334 (7) | |
Text
BENJAMIN HOLTZMAN Senior Project Manager, Fuel and Radiation Safety 1201 F Street, NW, Suite 1100 Washington, DC 20004 P: 202.739.8031 bah@nei.org nei.org August 14, 2019 Ms. Jane E. Marshall Director, Division of Safety Systems (Acting)
Office of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission Washington, DC 20555-0001
Subject:
Comments on Draft Interim Staff Guidance on the Chromium-Coated Zirconium Alloy Fuel Cladding Accident Tolerant Fuel Concept Project Number: 689
Dear Ms. Marshall:
On behalf of the nuclear energy industry, the Nuclear Energy Institute (NEI) 1 submits the attached comments on the draft Interim Staff Guidance (ISG) on the Chromium-Coated Zirconium Alloy Fuel Cladding Accident Tolerant Fuel Concept (ATF-ISG-01). NEI has been working with the Nuclear Regulatory Commission (NRC) to establish regulatory guidance that may be used by NRC staff reviewing industry applications involving chromium-coated zirconium alloy clad fuel products. The ISG also provides insights on staff expectations for vendor topical submittals for accident tolerant fuel (ATF). This ISG supplements the guidance in NUREG-0800, Standard Review Plan. We appreciate the staffs early publication of the draft ISG and the opportunity to present our initial views of the document during the public meeting on August 6, 2019.
The attachment represents our initial comments based on a short timeframe review.
While there are several areas of agreement, as noted in our comments, the attachment highlights key differences between industrys and NRCs expectation for how the ATF coated cladding applications should be assessed. Additionally, we would like to reiterate one main concern related to the inclusion of the manufacturing process into the ISG that was discussed in industrys presentation at the public meeting.
Industrys concern is that the draft ISG significantly expands the traditional licensing scope and attempts to regulate the manufacturing process through fuel qualification. NUREG-0800 is a performance-based standard and the manufacturing process is not part of the current regulations. Furthermore, the coated cladding fuel concepts are not conceptually different from the current fuel products (same base substrate 1
The Nuclear Energy Institute (NEI) is responsible for establishing unified policy on behalf of its members relating to matters affecting the nuclear energy industry, including the regulatory aspects of generic operational and technical issues. NEIs members include entities licensed to operate commercial nuclear power plants in the United States, nuclear plant designers, major architect and engineering firms, fuel cycle facilities, nuclear materials licensees, and other organizations involved in the nuclear energy industry.
Ms. Jane E. Marshall August 14, 2019 Page 2 material with a 10-30 µm thick coating) and as such, the existing manufacturing oversight framework is considered to be adequate. Other NRC regulations and oversight, such as 10 CFR Part 50 Appendix B and vendor quality assurance inspections, are in place to review the manufacturing process. Therefore, manufacturing processes should not be included in the ISG as part of the staffs fuel qualification review.
Thank you for your consideration of our comments. We look forward to continue working with the NRC through the ISG publication process and industrys ATF activities as we work to deploy batch reloads by 2023. If you have any questions or require additional information, please contact me.
Sincerely, Ben Holtzman Attachment c: Andrew Proffitt, NRR, NRC Jason Drake, NRR, NRC Josh Whitman, NRR, NRC Dennis Morey, NRR, NRC Robert Lukes, NRR, NRC NRC Document Control Desk
Comment # Location Comment Proposed Change Although this ISG mainly focuses on the metallic chromium coatings on Zirconium based cladding, at some places NRC tried to include some discussion on chromium Industry recommends to remove discussion on Crbased ceramic based ceramic coatings and emphasized their influence on the properties of coatings and consider only metallic Crcoating for this ISG. Or better underlying base cladding . This inclusion of discussion on ceramic coatings has only 1 General explain how the ISG denotes information applicable to any coated complicated the report and is not helpful, since many thermophysical properties of cladding concept and where information is only relevant to a the Crbased ceramic coated cladding are expected to be significantly different than specific cladding concept.
base cladding and requires substantial experimental data for developing models and licensing justification.
If the ISG is intending to specifically denote the phenomena as being important for coating cladding concepts, the ISG should discuss the relative importance regarding Please revise ISG text to be consistent with intent and if specifically the existing phenomena and new mechanisms. The current text equivocates the 2 General denoting phenomena as being important for coating cladding impact of all mechanisms such as defects and embrittlement. Defining importance or concepts denote importance as per the PIRT report.
concentration of defects may allow for important issues to be more easily separated from the noise.
The use of 'chrome' and 'chromium' interchangeably in several places is incorrect.
3 General Please revise text to properly use chrome and chromium
'Chrome' refers to a method of industrial electroplating, not the element chromium Main Section Industry appreciates the ability to provide input on the ISG but what is the benefit in 4 Remove unnecessary text Lines 2326 noting the feedback mechanism in the ISG itself?
Main The publication date for Reference 3 appears to be in error. The ATF Project Plan 5 Document Please revise text was published in September 2018, not September 2019.
References The ISG should clearly state whether it's denoting the specific The ISG calls out that it is not attempting to set standards for review of any credit or Appendix A content needed for a fuel topical report or providing additional 6 benefit applicants may request, but many of the phenomena noted in Appendix C are Lines 1833 guidance on how industry will need to realize prospective benefits.
specifically tied to benefits and not licensing criteria.
The confidence level to which the proposed property improvements must be Appendix A 7 demonstrated by the applicant to satisfy the NRC reviewer(s) is not explicitly stated in Please include information related to the required confidence level.
Lines 3139 the document Please revise text as shown:
"Finally, if an applicant wishes to take credit for coating behavior up Appendix A Industry agrees that benefits should be allowed when supported by data, but please to a certain burnup, or during certain accident conditions, it is 8
Lines 3439 indicate that the data must support the 'full operating domain.' necessary for the adherence of that coating to the substrate to have been demonstrated to that burnup and during those conditionsjustified for the full operating domain."
Please revise text as shown:
The structure of the sentence strongly implies that high burnup data is a "Finally, if an applicant wishes to take credit for coating behavior up requirement. This could have impacts on initial implementations and/or conditional Appendix A to a certain burnup, or during certain accident conditions, it is 9 topical approvals as the statement implies that coatings on the rods must be Lines 3839 necessary for the adherence of that coating to the substrate to have prototypical to demonstrate adherence at high burnup before batch loading and that been demonstrated to that burnup and during those it may not be possible to use all available data.
conditionsjustified for the full operating domain."
Appendix A Industry agrees that SAFDLs can be addressed in multiple ways and that no specific 10 None Lines 5758 testing requirements should be denoted.
Appendix A 11 What does the word sufficiently exactly mean? Please clarify the expectation.
Line 70 The ISG text references PIRT Section 6.4.2 and states that the applicant should ensure the performance concerns referenced in the PIRT Section are addressed. The PIRT section states that all data (for some performance concerns) need to be provided Please rephrase the ISG text to be clear that a manufacturing Appendix A 12 from tubes that come from a qualified process. However, it does not provide any process doesn't require NRC qualification before data acquisition Lines 6772 guidance to the reviewer as to what it means for a process to be qualified. The ISG can begin.
should be clear that it is not regulation manufacturing processes nor should be requiring an applicant to get data from an approved/qualification process.
The ISG text references PIRT Section 6.4.2 and states that the applicant should ensure the performance concerns referenced in the PIRT Section are addressed. The PIRT section states that all data (for some performance concerns) need to be provided Please rephrase the ISG text to be clear that a manufacturing Appendix A from tubes that are manufactured in a prototypic manner. However, it does not 13 process doesn't require NRC qualification before data acquisition Lines 6772 provide any guidance to the reviewer as to what it means for a process to be can begin.
considered prototypic. The ISG should be clear that it is not regulation manufacturing processes nor should be requiring an applicant to get data from an approved/qualification process.
Comment # Location Comment Proposed Change The ISG text discussing the current 50.46 regulatory limit (1204°C/17%ECR) is likely inappropriate and needs to be corrected. The referenced PNNL PIRT section 6.2.6 does not really talk about why 1204°C is not appropriate. The discussion on why 17%
ECR may not be appropriate for a coated rod appears to be based on mix up of calculated ECR (that is regulated) with measured ECR (that is not regulated). The fact that there is a mismatch between calculated CPECR (or BJ according actual 50.46) The section should be revised to state that current 50.46 regulatory and measured ECR is a reflection of the ATF effectiveness of the coating. limit (1204°C/17%ECR for uncoated cladding) can be applied on a conservative basis to coated cladding if supported by test data, and Appendix A 14 The argument in ISG appears to be that for extended time at 1200°C (read this to that if the applicant wishes to have a different licensing calculated Line 7390 mean for times far exceeding needed to reach the limit based on calculated ECR for the coated rod, then justification must be made. Moreover CP/BJECR, i.e. no longer in DBA space), the coated rod could be embrittled even that no exemption to 50.46 would be needed in the former case, though the measured ECR is low (because of ATF benefit); and because the and an exemption would be needed in the latter option.
embrittling mechanism is not understood this becomes a problem and so 17% ECR is not protecting the cladding. This argument only makes sense if 50.46 is based on measured ECR, but it is not. The current 50.46 regulatory limit, based on calculated ECR (CP or BJ) from time and temperature, actually continues to serve the purpose of protecting the cladding.
Potential regulatory changes are introduced related to extensions of the existing fuel burnup limits. Such burnup limit extensions are currently being evaluated by the Appendix A Remove regulatory changes for increasing burnup limits from the 15 industry and were the subject of a 2018 workshop that included NRC staff. However, Lines 97101 ISG on coated cladding.
this comment seems inappropriate for the ISG since burnup limit changes were not within the review scope for the ATF PIRT.
" may be to ignore the coating (for purposes of TM analyses) and use the properties of the underlying substrate" > this wording carries the risk of not considering where "may be to demonstrate that the coating will have a negligible Appendix A 16 the coating results in a changed behavior. It could be shown that the coating does not impact on the property and use the properties of the underlying Lines 113115 result in more than a negligible change, and thus use the model of uncoated cladding, substrate."
but that is not ignoring the coating Appendix A Industry appreciates that flexibility is provided for the applicant in addressing each 17 None Lines 115117 damage mechanism Appendix A the use of the word may should be clarified to indicate that the described test data Revise text to indicate "provides a list of test data that may could 18 Line 138 is one of many options to satisfy the data needs. be used in code assessment."
Appendix A This statement pertains to geometric uncertainties resulting from fabrication.
19 Please clarify the expectation.
Lines 163166 Presumably, this will also apply to uncertainties in coating thickness.
If cracking and delamination of the coating are ruled out by results from the LTA Appendix A program and the surface roughness of the coated clad is shown to be similar to that 20 Please clarify the expectation.
Lines 185187 for the uncoated clad, does the applicant need to do any CHF testing with coated cladding?
The addition of a 30 µm thick coating to RFA fuel decreases the hydraulic diameter of interior subchannels by less than 2% [1.7% for 30 µm and 1.1% for 20 µm]. This should have a negligible impact on the thermalhydraulics. Please ensure consistency in ISG regarding treatment of coating Appendix A impact on TH. Specifically, whether the ISG is indicating this as an Lines 185187 21 Additionally, the statement that for AOOs and postulated accidents involving a important area for an applicant to address because TH scope is a and Lines 246 decrease in reactor coolant flow the presence of the chromium coating will not topic in the traditional scope of licensing fuel topicals or because it's 248 change the systems response implies NRCs recognition that the coating will have important to coated cladding applications negligible impact on core thermalhydraulics. Industry agrees that a 1030 µm coating will have a negligible impact on TH.
This paragraph presumes that models (TM, Nuclear physics and TH) will be changed Recommend to change each of the sentences to should be Appendix A 22 to capture the impacts of chroming coating. This does not acknowledge alternative captured considered in the {fuel rod performance/nuclear physics /
Lines 221226 approaches such as ignore the coating as discussed in Line 113 - 115. thermal hydraulics} model evaluation.
This section discusses many expected benefits relative to advertised features of a general product as opposed to providing guidance to review the material changes for It is suggested the ISG focus only the material changes and their a specific product submission, which may later result in benefits via the incorporation associated specific LOCA phenomena benefit, e.g. reduced external to analyses. A LOCA result, such as PCT, is the due to a wide variety of integrated reaction with steam reduces energy release and oxygen generation Appendix A, 23 properties and phenomena. A predicted PCT change should not be relied upon since and associated loss of ductility; reduced operational hydrogen Lines 249255 it will be very plant and product specific. minimizes hydrogen enhanced embrittlement; etc. Any change in results would be justified by the combination of changes, positive Additionally, the change in liberated hydrogen should be restricted to the reduced or negative, to the product.
external surface reaction.
The text says that the parameters that are affected during LOCA are presented in the Appendix A, 24 table below, however the draft does not contain a table listed below. This statement Please provide table for review.
Line 251 should be corrected or the table added.
Comment # Location Comment Proposed Change Statement indicates that the scope of work needed to complete the Chapter 15 demonstration increases significantly if the application is accompanied with (among other things) an increase in allowable fuel rod burnup or increased 235U enrichment.
This is a blanket statement that needs to be clarified.
Appendix A The idea that the Chapter 15 Safety Analyses work would increase significantly is not NRC should explicitly define the additional scope needed to 25 Lines 264268 consistent with how industry confirms safety analyses on a reload and bounding complete Chapter 15 analyses for coated cladding applications.
analysis basis. Only if the coated cladding implementation changes part of the bounding envelopes currently used by safety analyses would work then need to be addressed. However, the idea that a single parameter deviating from its noncoated value would automatically SIGNIFICANTLY increase the Chapter 15 safety analyses needs clarification.
Industry recognizes the importance of process controls in manufacturing but Appendix B disagrees that the NRC should license specific manufacturing processes. The ISG and Statements concerning processing conditions and/or coating 26 Lines 32, 79, its application should focus on the critical material performance characteristics, technique should be removed or rewritten.
8384 regardless of the manufacturing process.
Suggest adding a caveat to the statement: "Table 5.1 in the PIRT report provides a Appendix B, 27 summary of the tests that could be performed to quantify the material properties Please revise text as noted.
Lines 3940 discussed below but should consider the updated text in the following sections."
Thermal expansion section it is not clear what the NRC's expectations are. Are we Justification for thermal expansion models should be provided as Appendix B, 28 supposed to justify the models/ show data? Address the stresses from thermal well as a demonstration that thermal cycling does not lead to Lines 59 85 expansion mismatch? Something else? coating damage.
Industry believes that Crcoated cladding will have an impact on emissivity by Therefore the impact on emissivity values should be evaluated and Appendix B, 29 reducing oxide thickness - emissivity strongly correlates to oxide thickness, increasing accounted for in accident analyses comment also provided to NRC Lines 86101 with increased oxide until it stabilizes consistent with an opaque surface. for PIRT report section 5.1.3.
The ISG says that the coating will not result in any improvement in the strength of the substrate, and is also assumed to have zero load bearing capability. This was not Appendix B Please remove statement "Generally, coating is assumed not to 30 unequivocally stated in the PIRT. If supported by data, Industry wants to retain the Lines 131146 offer any load bearing capability."
ability to realize benefits in this area and so the ISG should not preempt them at this early stage.
Appendix B, The NRC does not state their expectations. Do they want FR growth data? Evaluation Verification of growth models with inreactor data or a commitment 31 Lines 173185 of strain mismatch and resulting stresses? to collect data can be used.
Please revise text to indicate that if the coated cladding will be as Inreactor data is recommended for oxidation rate, including cracked specimens.
good as or better than current fuel products for oxidation, and Appendix B This does not seem necessary if only conservative oxidation benefits are claimed, and 32 industry can provide supporting justification of this fact it is Lines 199202 also does not seem necessary if other exreactor measures are taken to show that the conservative to use the current oxidation rate without additional cracks (if present) do not result in aggressive corrosion at edges.
test data.
Appendix B inreactor data from rods with cracked coatings be evaluated to assess if there is Revise text to state "the interface between coated and uncoated 33 regions inreactor be evaluated to assess if there is aggressive Lines 201202 aggressive corrosion at cracks or interfaces is more specific than necessary.
corrosion at cracks or interfaces Corrosion typically refers to the operational process, not the high temperature oxidation reaction. Additionally, while thinning of the cladding is important, high Appendix B, 34 temperature steam oxidation results in diffusion of oxygen into the betasubstrate It is suggested that this section be clarified.
Lines 236245 which is the mechanism for clad embrittlement. It is suggested that this section be clarified.
Most of the items in this section are not new failure mechanisms but rather performance characteristics which need to be accounted for in the current failure mechanisms. The exception is C.4.9 eutectic formation, which in fact is a new failure 35 Appendix C mechanism. Galvanic corrosion is a more specific example of corrosion that is None required by NUREG0800, S4.2 to be factored into the other fuel damage mechanisms, but could be treated as a new damage mechanism, since it conceivably could itself cause a fuel failure.
Appendix C 36 The word siting should be replaced with "citing" Please replace text as noted.
Line 7 Appendix C It is not clear how nonuniformity in coating thickness could lead to rod bow. The text 37 Please clarify this section.
Lines 916 may be confusing Rod Bow and Channel Bow in BWR applications.
Appendix C There is no SAFDL listed for DNB or CPR? Should be included in this section and 38 Please add text as noted.
Section C.2 guidance provided.
There is too much presumption about what happens in Crcoatings due to a crack in Appendix C This should be phrased so that the issue is addressed, but not 39 the initial, asbuilt coating. But this is only adverse if credit is taken for oxidation rate Lines 5367 assuming that there's an adverse consequence.
reduction postballooning during a LOCA.
Comment # Location Comment Proposed Change In the same way NRC should not be licensing/regulation the specific manufacturing Appendix C process, the inspection processes and controls should not be part of the licensing Please remove text it may be desirable to add crack detection 40 Line 66 process. It is incumbent on the vendor to implement process controls that ensure criteria..
material performance and properties are consistent with what is licensed.
Please revise text to the impact of the coating and associated oxide Appendix C Limits should be proposed that preclude environmental damage to the protective 41 layer on oxidation, hydriding, and crud should be predicted and Lines 9495 Cr2O3 layer can be written more generally.
evaluated.
Appendix C Reference to Appendix A is incorrect and should reference ISG Appendix B since the 42 Please revise as noted.
Line 141 original PIRT text crossreferences PIRT Section 5.1 Appendix A lines 213 216 refer to 10CFR50.46c and DG1327 as potential positive Appendix C, impact of the Crcoatings related to these requirements. This is inconsistent with lines 43 Lines 144 It is suggested that this section be clarified.
144 146 which states that this ISG will only deal with current regulations and staff 146 guidance.
Please revise the text "This thermal margin should not be exceeded Appendix C For BWRs, this is not actually an accurate representation of dryout phenomena, nor is 44 for normal operation and AOOs." to be consistent with language Line 151152 it actually articulated this way in NUREG0800, Chapter 4.4.
currently in NUREG0800.
This failed to draw any parallels between the incore Zr fuel rod and the excore Inconel heater rod differences. Is there an understanding that the performance of Appendix C 45 these two are the same, and that only a coating (whether on Zr or Nibased alloy) may Industry requests that NRC review text for consistency.
Lines 169177 influence CHF? Also, CPR and CHF are not equivalent, and the physics may result in sensitivities not being the same between DNBR and CPR estimations for coated rods.
Appendix A lines 181 - 194 appears to give applicants discretion to appropriately account for the impact of coatings on CHF, including the impact of coating Appendix C The two appendices should be reconciled so that applicants have a 46 degradation. In contrast, Appendix C appears to require CHF testing for each coating Line 181 clear, crisp understanding of expectations.
and assembly type rather than allowing discretion. In addition, Appendix C appears to cast doubt on the veracity of typical CHF testing using Inconel assemblies.
Appendix C Revise impact on the uniform elongation relative to the reference Zr with impact 47 Please revise as noted.
Line 195 on the pelletcladding mechanical interaction relative to the reference Zr.
If the alternate approach is followed and the current limits are concluded to be Appendix C Please revise text to indicate that RIA testing is not required with 48 acceptable then RIA testing on irradiated material or a commitment to do so should Lines 197199 acceptable justification.
not be required.
Industry believes that coated cladding will be as good as or better than current fuel Appendix C products during an RIA, and as long as industry can provide supporting justification of 49 Please revise as noted.
Lines 200203 this fact it is conservative to use current RIA assumptions for a coated cladding RIA analysis. Assuming that all rods would fail creates unnecessary conservatism.
Rather than repeating the LOCA embrittlement testing program, including irradiated Appendix C cladding tubes as proposed, a limited subset of testing on unirradiated and pre Please revise text to indicate there are additional methods of 50 Lines 243251 hydrided tubes should be sufficient to confirm adequacy of the existing limits or attaining test data.
reasonableness of a new set of conservative limits.
The subsections have statements about basing accident behavior using the term Appendix C 51 based on. This term should be revised to with consideration of the potential Please revise as noted.
Section C.4 impact.
Coating cracking isn't a new failure mechanism; it does not inherently cause a Appendix C Cracking of the coating is not a failure mechanism itself and 52 cladding failure, but changes the behavior to be accounted for when evaluating other Lines 307328 shouldn't be part of the ISG's performance criteria.
damage mechanisms Delamination is not a new failure mechanism itself; it does not inherently cause a cladding failure, except for the potential creation of debris, which affects other Appendix C Delamination is not a failure mechanism itself and shouldn't be part 53 systems. It affects the fuel cladding response in the OTHER failure mechanisms and Lines 329357 of the ISG's performance criteria.
will be included in the performance assessment of the cladding when evaluating other failure mechanisms In general, ceramic coatings will be more susceptible to delamination than metallic Consider revising to state Metallic and ceramic coatings may Appendix C coatings. - this statement is not consistent with other places in the ISG where 54 behave differently in this regard. Or remove, as there is no specific Line 331332 metallic and ceramic coatings are noted as being different in that this statement does assistance to the reviewer on the topic.
not provide the reviewer references for the information.
An improvement would be to add that the interdiffusion could be implicitly or Please revise text to indicate "CrZr interdiffusion should be Appendix C explicitly considered in the development of SAFDLs. For example, if more limits on 55 considered either implicitly or explicitly in the development of limits Lines 386391 timeattemperature are set such that interdiffusion does not become limiting, it on" would be implicitly covered and nothing further would be needed.
The ISG should direct the applicant to review the impact to source The current ISG text indicates that Cr51 will cause the source term for ATF coated term holistically, and determine whether the ATF source term is cladding to be worse than current fuel products. While Cr51 is a radioisotope not more limiting source term or if the current source term values Appendix C currently present in current fuel products, the statement that the source term will be bound the ATF coated cladding source term. In many cases, the 56 Lines 392417 more limiting ignores the beneficial contributions the more robust accident tolerant coated cladding application will be as good as or better than current attributes of the ATF fuel concept provide. The source term is unrelated to SAFDLs, fuel products, and if industry can provide supporting justification of safety, or the PIRTdefined damage mechanisms and performance concerns. this fact it is conservative to use the current values without additional test data.
Comment # Location Comment Proposed Change The ISG assumes the impact of irradiation will have a negative impact on the strength Appendix C 57 and ductility of the coating; however, It could also improve properties as The ISG should simply advise the reviewer to consider the impact.
Line 403406 cladding/coating systems can be complex.
Appendix C There are other methods for obtaining galvanic corrosion properties besides LTA 58 Please revise text to consider the impact.
Line 440 examination.
Defects are not a new damage mechanism. They do not inherently cause a cladding Appendix C failure, just as defects in current cladding do not inherently cause cladding failure. Defects are not a failure mechanism itself and shouldn't be part of 59 Lines 441449 They are part of the properties in any cladding or coating and will be included in the the ISG's performance criteria.
performance assessment of the cladding when evaluating other failure mechanisms.
The quality assurance steps or processes associated with making the cladding should not be licensed as part of the product. Product licensing is based on components that Appendix C Statements concerning processing conditions and/or coating 60 are representative of typical manufacturing processes and the vendor quality control Lines 441449 technique should be removed or rewritten.
processes will be established to identify the presence of defects that would degrade the performance below the licensed performance level.
The lowest temperature eutectic for the CrZr system is noted as occurring at 1332 C, which is noted beyond the current DBA temperature limit of 1200 C. Is this being Appendix C noted because it is an important finding for coated cladding that needs to be 61 Please clarify the expectation.
Lines 450456 addressed even though it is beyond traditional licensing scope? Or is this being included for future applications where industry may try to extend the DBA temperature range?