ML19141A186
| ML19141A186 | |
| Person / Time | |
|---|---|
| Site: | PROJ0728, 99902041 |
| Issue date: | 06/03/2019 |
| From: | Dennis Morey NRC/NRR/DLP/PLPB |
| To: | Peters G Framatome |
| Rowley J, NRR/DLP/PLPB, 415-4053 | |
| Shared Package | |
| ML19141A179 | List: |
| References | |
| CAC MF9716, EPID L-2017-TOP-0031 | |
| Download: ML19141A186 (7) | |
Text
FINAL SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION BAW-10227P, REVISION 1, SUPPLEMENT 1P EVALUATION OF ADVANCED CLADDING AND STRUCTURAL MATERIAL (M5)
IN PWR REACTOR FUEL FRAMATOME INC, PROJECT NO. 728; DOCKET NO. 99902041
1.0 INTRODUCTION
By letter dated May 4, 2017 (Reference 1), Framatome Inc. (Framatome, formerly known as AREVA Inc.) submitted BAW-10227, Revision 1, Supplement 1P, Evaluation of Advanced Cladding and Structural Material (M5) in PWR Reactor Fuel, for U.S. Nuclear Regulatory Commission (NRC) review and approval. Framatomes motivation for the supplement is to re-establish the iron (Fe) concentration limit [ ''''''''''''''''' ''''''''''''''''''' ''' ''''''''''''' ''''''''''
'''''''''''''' '''' ' ''''''''''''''''''''' '''''''''''' ' ''''''''''' ''''''''' ''''''''''']. Framatome states that the current state of the art Zr production allows reliable production of ingots with iron concentrations no greater than ['''] parts per million (ppm). Therefore, modification of the iron impurity concentration from [''''] to [''''] ppm is being requested. All other impurity concentration limits remain as specified by the tables in Section I.20 of Reference 5.
2.0 REGULATORY EVALUATION
Regulatory guidance for the review of fuel system materials and designs and adherence to General Design Criteria (GDC)-10, GDC-27, and GDC-35 is provided in NUREG-0800, Standard Review Plan for the Review of Safety Analysis Reports for Nuclear Power Plants (SRP), Section 4.2, Fuel System Design (Reference 6). In accordance with SRP Section 4.2, the objectives of the fuel system safety review are to provide reasonable assurance that: (1) the fuel system is not damaged as a result of normal operation and anticipated operational occurrences, (2) fuel system damage is never so severe as to prevent control rod insertion when it is required, (3) the number of fuel rod failures is not underestimated for postulated accidents, and (4) coolability is always maintained. A not damaged fuel system is defined as fuel rods that do not fail, fuel system dimensions that remain within operational tolerances, and functional capabilities that are not reduced below those assumed in the safety analysis.
Objective 1, above all, is consistent with GDC-10 in Title 10 of the Code of Federal Regulations (10 CFR) Part 50, Appendix A, and the design limits that accomplish this are called specified acceptable fuel design limits. Fuel rod failure means that the fuel rod leaks and that the first fission product barrier (the cladding) has, therefore, been breached. However, the NRC staff recognizes that it is not possible to avoid all fuel rod failures during normal operation, and reactor coolant cleanup systems are installed to deal with a small number of leaking rods. Fuel rod failures must be accounted for in the dose analysis required by 10 CFR Part 100 for postulated accidents. Coolable geometry means, in general, that the fuel assembly retains its rod-bundle geometrical configuration with adequate coolant channels to permit removal of residual heat following a design basis accident. The general requirements to maintain control rod insertability and core coolability appear repeatedly in the GDC, but are most explicit in Enclosure 2
GDC-27 and GDC-35. Specific coolability requirements for the loss-of-coolant accident are given in 10 CFR 50.46.
3.0 TECHNICAL EVALUATION
The main objective of BAW-10227, Revision 1, Supplement 1P, is to demonstrate that the slight increase in maximum allowable iron concentration does not significantly impact the performance of M5. As such, no revisions to any approved M5 models or correlations related to Reference 5 have been proposed. The other impurity concentration limits remain as specified by the tables in Section I.20 of Reference 5.
Since the supplement does not revise any models or correlations, citations of the original topical report in technical specifications and core operating limits reports are sufficient; a specific reference to BAW-10227, Revision 1, Supplement 1P, is not required.
Audit of BAW-10227, Revision 1, Supplement 1P Supporting Documents The NRC staff completed its acceptance review on October 18, 2017, and found that the material presented was sufficient to begin its review (Reference 2). After an initial review, the NRC staff identified some areas requiring further discussion, and determined it necessary to review documents supporting BAW-10227, Revision 1, Supplement 1P, analyses to resolve the NRC staff concerns. The scope and objectives were defined in an audit plan (Reference 3).
Sections 3 and 4 of BAW-10227, Revision 1, Supplement 1P, reference a technical paper presented at the ASTM B10 Zirconium in the Nuclear Industry Symposium for a vast amount of data and analysis to support this topical report. The technical paper is cited 31 times. The technical paper, Impact of Iron in M5TM, was authored by representatives from several different Framatome organizations in France, Germany, and USA. This technical paper lacks the pedigree necessary to support an NRC safety finding. Consequently, the underlying Framatome testing and research reports were audited to verify that the information cited from the technical paper is accurate.
The NRC staff audit report describes in detail both relevant Framatome quality assurance procedures reviewed including a summary of all audit documents reviewed supporting each of the respective technical paper citations (Reference 4).
All of the audit objectives listed in Section 2 of the audit report were covered and all audit items (8 total) were closed as documented in Section 3 of the audit report. No errors or negative findings were identified during the audit. No requests for additional information were needed to provide further information.
Material Properties Evaluation Section 3 of BAW-10227, Revision 1, Supplement 1P, describes potential effects of the change in allowable iron concentration on microstructure and metallurgical texture. M5 has a fully recrystallized microstructure, characterized by an alpha-Zr (-Zr) matrix with two types of uniformly distributed precipitates: body-centered cubic beta-niobium (-Nb) precipitates and hexagonal Laves phase (Zr(Nb,Fe)2) intermetallic precipitates. Metallurgical evaluations were performed on M5 cladding samples with varying iron concentrations up past the requested limit.
Based on these studies, Framatome concludes that mean second phase particle sizes do not
evolve significantly with the iron content. Likewise, metallurgical texture, as expressed by the basal plane Kearns factors, does not exhibit significant dependence with the iron content.
Section 4 of BAW-10227, Revision 1, Supplement 1P, describes potential effects of the change in allowable iron concentration on material properties. Material properties can be separated into physical properties and mechanical properties. Impurities are expected to have very little influence on physical properties, such as density, so a simple treatment based on the rule of mixtures is used to assess the impact. In contrast, mechanical properties could be affected by impurities, so experimental results were presented to demonstrate that modifying the iron concentration limit will not have a significant effect.
Structure-Insensitive Properties The following structure-insensitive physical properties were evaluated using the rule of mixtures:
- Density
- Coefficient of thermal expansion
- Specific-heat capacity
- Emissivity
- Poissons ratio
- Modulus of elasticity These evaluations concluded that the magnitude of change as a result of the small increase in allowable iron concentration was smaller than the reported uncertainty in the measured physical property.1 In the case of structure-insensitive properties (i.e., those that dont depend strongly on the material matrix/precipitate distribution), Framatome explains that these properties are not affected by the proposed increase in the iron concentration limit, which can be seen by applying the rule of mixtures. In these cases, Framatome explains that the change in iron concentration results in a change in property that is much smaller than the uncertainty associated with the given property - the smallest ratio of uncertainty-to-change across all structure-insensitive properties was observed to be 30, which is sufficiently large to indicate the smallness of impact of these types of material property changes.
Based on the above discussion, Framatome ultimately found no evidence that any of the structure-insensitive material properties are adversely affected in a meaningful way by increasing the M5 iron concentration limit from ['''''] ppm to [''''] ppm.
1 NRC staff reviewed Framatome provided references for reported uncertainties cited in BAW-10227, Revision 1, Supplement 1P, during the audit and found them to be reasonable. Additional details are provided in Audit Item #3 in Reference 4.
Structure-Sensitive Properties The following structure-sensitive properties were evaluated by Framatome:
- Thermal conductivity
- Oxidation resistance
- Aqueous corrosion (important during normal operation and reactivity insertion accidents (RIA))
- High temperature oxidation (important during loss-of-coolant accidents)
- Ultimate tensile strength
- Yield strength (0.2 percent offset)
- Ductility
- Ramp temperature test data was used to suggest that equivalent cladding ductility would be maintained during a RIA for a range of M5 iron concentration between
[''''] ppm and [''''] ppm.
- Creep resistance
- Fuel rod cladding (out-of-pile and in-pile2)
- Guide tubes3
- Meyers hardness
- Growth rate
- Free growth
- Growth of fuel assembly (FA) components
- Data shows that at worst, guide tube (GT) growth may increase very slightly with irradiation at an iron concentration of 1000 ppm relative to the current M5 iron concentration limit of [''''] ppm; other data shows no significant increase. However, since the requested increase is from [''''] ppm to
['''''] ppm, it is reasonable to expect little to no observable increase in GT growth.
- In general, an increase in iron concentration to 1000 ppm relative to the current M5 iron concentration limit shows a decrease in fuel rod (FR) growth.4 Therefore, no change in GT growth, which dictates FA growth, and 2
Necessary because out-of-pile tests only measure thermal creep, which is a relatively small contributor to overall in-reactor creep.
3 Section 4.10.2 of BAW-10227, Revision 1, Supplement 1P, describes the evaluation for guide tube creep. During the audit, Framatome discussed relevant testing with NRC staff. The NRC staff reviewed Framatome calculations supporting guide tube creep modeling. Additional details documenting NRC staff observations are provided in Audit Item #4 in Reference 4.
4 The NRC staff noted that a decrease in fuel rod growth would have a negative impact on predicted void volume and rod internal pressure, therefore the impact of the re-defined M5 depends on whether the application methods credit fuel rod growth in those predictions. However, high iron content M5 measurements in Framatomes fuel rod growth database show that the higher iron content M5 being proposed in BAW-10227, Revision 1, Supplement 1P, is within the scatter of the database implying valid void volume and rod internal pressure predictions for the proposed higher iron content M5. Additional details are provided in Audit Item #5 in Reference 4.
a general decrease in FR growth, would tend to lead to an increased gap between the FRs and the upper tie plate, which increases design margin and likewise safety margin.
- Resistance to hydriding (important during RIA)
- Stress corrosion cracking resistance
- Alpha beta transformation temperature5
- Fatigue strength For some structure-sensitive properties, qualitative assessments showed either insignificant or relatively minor effects due to the proposed increase in the iron concentration limit. In these cases (e.g., thermal conductivity), the small relative impact of the change in iron concentration was assessed in relation to the small magnitude of the increase in iron concentration relative to the other alloying element concentrations.
However, experimental testing was performed - out-of-pile, and specifically in-pile - to validate important structure-sensitive properties that are less straightforward to address qualitatively, and that have traditionally been tracked as part of ongoing surveillance programs.6 High burnup lead test assembly (LTA) data was collected and analyzed supporting Framatomes assessment of the effects on the various material properties discussed in Section 4 of the supplement due to an increase in the iron concentration limit.7 This LTA data, although limited, further validates Framatomes claim that an increase in the M5 iron concentration limit from ['''''] ppm to
[''''] ppm will have no adverse impact on the material properties that were assessed.
Framatome summarizes in Section 2 of BAW-10227, Revision 1, Supplement 1P, by stating:
['''''''''''''''''''' '''''''''''''''''''' ' ''''''''''''''''''''''' ''' ''''' '''''' '''''''''' '' '''' '''''''' '''''' '''']
demonstrates that the combination of the experience and [Framatomes] normal product surveillance is sufficient to ensure safe operation.
Based on the above discussion, Framatome ultimately found no evidence that any of the structure-sensitive material properties are adversely affected in a meaningful way by increasing the M5 iron concentration limit from ['''''] ppm to [''''] ppm.
5 Section 4.17 of BAW-10227, Revision 1, Supplement 1P, describes the evaluation of phase transition temperature. Iron has been identified as a beta-stabilizer in Zr alloys. As such, the NRC staff expects the
-Zr to -Zr plus -Zr phase transition temperature should be slightly reduced at the higher iron concentrations. During the audit, Framatome presented the Zr-Fe phase diagram. The beta phase transition temperature initially decreases with increasing iron then drops from about [''''''''' '''''''''' '''']
down to ['''''''''' ''''' ''''' ''''']. The phase transition temperature remains constant after the iron solubility limit ([''''''''''''' '''']). Hence, there is no impact on the phase transition temperature by raising the maximum iron content up to the proposed value.
6 The original approval of M5 in BAW-10227P-A, Revision 1, discussed continued growth measurement and model updates. During the audit, Framatome mentioned that their M5 growth models have been refined and updated as more data is collected. The NRC staff supports these continued improvements and data collection. Consequently, BAW-10227, Revision 1, Supplement 1P, does not need to further define an update process.
7
[''''''''''''''''''''] total fuel rods amongst ['''''''] total LTAs - ['''''] LTAs from a commercial German reactor and ['''''] from a commercial French reactor - form the current database. The iron concentration of this M5 variant was 1000 ppm and encompasses the requested change.
Consequently, based on the justifications given in addition to the demonstrated insignificant impact of the higher allowable iron impurity concentration on cladding performance, the NRC staff finds the higher allowable iron impurity concentration to be acceptable.
M5 Definition Section 1 of BAW-10227, Revision 1, Supplement 1P, provides the following justification for maintaining the name M5 for the cladding alloy at the higher allowable iron concentration:
Limits on alloying elements (niobium, oxygen, and sulfur for M5) are established to determine the behavior of the alloy, whereas limits on impurities are established to ensure product uniformity. Because the modification is an adjustment to the concentration limit for one impurity element, the name "M5" will be retained.
Based on the demonstrated insignificant impact of the higher allowable iron impurity concentration on cladding performance and continued applicability of approved models and correlations, the NRC staff accepts the justification to maintain M5 for the higher allowable iron impurity concentration.
4.0 CONCLUSION
The NRC staff has reviewed BAW-10227, Revision 1, Supplement 1P, that describes an update to the M5 iron concentration impurity limit previously defined in BAW-10227P-A, Revision 1 (the base topical report). The NRC staff concludes that any downstream safety calculations relying on M5 material properties will not be adversely affected in a meaningful way with an iron concentration limit of either [''''] ppm or ['''''] ppm based on Framatomes assessment of the iron concentration change with respect to relevant material properties as characterized in the base topical report. While the quantitative evidence was based on both out-of-pile and in-pile data, the in-pile data is the most applicable and is essential to the NRC staffs approval of the change. Furthermore, Framatomes continuing normal product surveillance is sufficient to provide the NRC staff with reasonable assurance that safe operation will continue for reactors using M5 at the higher iron concentration limit.
Consequently, in the context of limiting M5 iron concentration as an impurity, Framatome has demonstrated that an M5 iron concentration limit of either [''''] ppm or ['''''] ppm is functionally equivalent, therefore the NRC staff agrees that either can be used to represent M5 for the purpose of performing downstream safety analyses.
5.0 REFERENCES
- 1. Request for Review and Approval of BAW-10227, Revision 1, Supplement 1P, Evaluation of Advanced Cladding and Structural Material (M5) in PWR Reactor Fuel, NRC:17:021, May 4, 2017 (Agencywide Document and Management System (ADAMS)
Accession No. ML17130A708).
- 2. Acceptance for Review of AREVA Inc. Topical Report BAW-10227, Revision 1, Supplement 1P, Evaluation of Advanced Cladding and Structural Material (M5) in PWR Reactor Fuel (CAC NO. MF9716), October 18, 2017 (ADAMS Accession No. ML17283A261).
- 3. Regulatory Audit Plan for January 30-31, 2019, Audit for Framatome Inc. Topical Report BAW-10227, Revision 1, Supplement 1P, Evaluation of Advanced Cladding and Structural Material (M5) in PWR Reactor Fuel (CAC MF9716/
EPID L-2017-TOP-0031), January 15, 2019 (ADAMS Accession No. ML18355A980).
- 4. Audit Report: BAW-10227P, Revision 1, Supplement 1P, Evaluation of Advanced Cladding and Structural Material (M5) in PWR Reactor Fuel, Lynchburg, VA, January 30-31, 2019 (ADAMS Accession No. ML19035A120).
- 5. BAW-10227P-A, Revision 1, Evaluation of Advanced Cladding and Structural Material (M5) in PWR Reactor Fuel, June 2003 (ADAMS Accession No. ML15162B052).
- 6. NUREG-0800, Standard Review Plan for the Review of Safety Analysis Reports for Nuclear Power Plants (SRP), Section 4.2, Fuel System Design, Revision 3, March 2007 (ADAMS Accession No. ML070740002).
Attachment:
Resolution of Comments Principle Contributors: A. Patel, NRC/NRR/DSS P. Clifford, NRC/NRR/DSS Date: June 3, 2019