ML22035A041
| ML22035A041 | |
| Person / Time | |
|---|---|
| Site: | 07109372 |
| Issue date: | 02/14/2022 |
| From: | Storage and Transportation Licensing Branch |
| To: | Framatome |
| P SAVEROT NRC/NMSS/DFM/STLB 3014157505 | |
| Shared Package | |
| ML22035A040 | List: |
| References | |
| Download: ML22035A041 (5) | |
Text
UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001
SAFETY EVALUATION REPORT Docket No. 71-9372 Model No. TN-B1 Package Authorization for Limited Shipments
BACKGROUND
On November 15, 2021, (ADAMS Accession No. ML21319A388), Framatome Inc. submitted a 10 CFR 71.95 report describing instances where shipments of unirradiated fuel assemblies were made while the conditions of approval in the Certificate of Compliance (CoC)
USA/9372/B(U)F-96 were not observed. As an example, Condition No. 5(b)1) states that the fuel channel side thickness is 0.254 cm while the maximum fuel channel side thickness was in fact measured at 0.260 cm. Framatome noted that the presence of the fuel channel on the fuel assembly slightly increases the reactivity with adjacent fuel assemblies but also performed a sensitivity study to confirm that the change in keff was within uncertainty values and remained within the approved safety basis of the package. This non-conformance was only associated with the 11 x11 fuel assembly and channel and Framatome has confirmed no similar issue exists with the other fuel designs (8x8, 9x9, and 10x10).
On December 17, 2021, Framatome Inc. (Framatome or the applicant) submitted a request for authorization to ship Framatome channeled Boiling Water Reactor (BWR) ATRIUM 11 (11x11) unirradiated fuel assemblies with the following changes: (i) increase of the allowable fuel channel side thickness, and (ii) introduction of new materials for the shock isolating system in the outer and inner containers of the TN-B1 packaging in order to prevent fretting on the fuel rods.
EVALUATION
MATERIALS EVALUATION
The applicant stated that the ATRIUM 11 fuel channel side thickness is increased to fully bound the channels nominal thickness dimension plus a fabrication allowance. The applicant stated that previous evaluations have shown a slight reactivity increase when the channel thickness is increased.
The applicant stated that the existing vibro-isolating rubber components are restrictively defined as natural rubber and to increase the vibration absorption performance of the packaging during normal conditions of transport (NCT), additional materials such as synthetic rubber are considered using a conservative bounding approach. Additionally, the applicant stated that the existing inner container cushioning material, previously labeled as shock absorber, does not protect against impact loads intended for NCT or hypothetical accident condition drops, and is now renamed as vibration absorber. In addition, this inner container cushioning material was restrictively defined as polyethylene foam, but to increase the vibration absorption 2
performance of the packaging during normal conditions of transport, additional materials such as synthetic rubber are considered using a conservative bounding approach.
The applicant stated that these modifications will improve the product quality for transportation over long distance and facilitate the sourcing of new components for package refurbishment.
The applicant stated that the additional rubber material selection options for cushioning or vibration reducing application are inherently stable products that can be easily monitored, and the package is not exposed to a harsh environment that could accelerate degradation of rubbers properties. The applicant stated that the rubber and the associated locations are inspected prior to each use. The applicant mentioned that a plastic sleeve is around the channel fuel assembly and any negative effect from the rubber is anticipated to be first identified by discoloration of the plastic sleeve. Furthermore, the applicant stated that fuel assemblies are not stored for extended periods of time, i.e., greater than 6 months, within the packaging without being re-packaged. The staff finds this explanation to be acceptable because the additional options for rubber material are very similar in kind for this application and visual inspections can identify any degradation that can then be addressed by the applicant.
Material Chemical, Galvanic or Other Reactions
The applicant stated that the materials added as an option to replace the existing natural rubber are regularly used as gaskets and seals in the packaging industry and that these types of rubbers are very stable and unreactive in their intended use of the TN-B1 package. The applicant also stated that the inner and outer containers do not form an air-tight seal, thereby allowing venting of any off-gassing material should it occur. The staff finds that the applicants justification is acceptable because the package is not exposed to any harsh conditions and is inspected periodically and before each use.
Thermal Evaluation
The applicant stated that the thermal properties of the polyethylene cushioning material were conservatively modeled in the thermal evaluation and there is no change to the existing thermal evaluation. The staff finds this to be acceptable because this material is not relied upon for any safety function during a thermal event.
Conclusion
These vibration isolation and shock absorption components reduce vibrational loading of the fuel assemblies during NCT. While the fuel assembles would not fail as a result of NCT vibrational loading, excessive vibrational loading could result in surface abrasion by contact between the fuel cladding and the assembly hardware. Fuel assemblies are inspected after receipt and even minor evidence of abrasion would need to be evaluated and dispositioned prior to use. By using improved vibration isolating materials, the amount of vibration induced abrasion is reduced and that reduces the need to evaluate and disposition minor abrasion.
Based on the discussion above, the staff concludes that the selected materials are acceptable.
CRITICALITY EVALUATION
The applicant requested a letter authorization to ship three TN-B1 packages with the following changes accounted for in the criticality safety evaluation: 1) Replacing natural rubber in the 3
inner container clamping system and the inner container cushioning material; 2) Increasing ATRIUM 11 fuel channel thickness from 0.254 to 0.320 centimeters (cm); and 3) Correction for h_poly cross section errors in SCALE.
The current Certificate of Compliance for the TN-B1 package only allows for natural rubber in the inner container clamping system and cushioning material. The change requested will allow other kinds of materials (neoprene, synthetic rubber, or polyethylene) to be used in these components of the package. The hydrogen density of these materials can be higher than that of natural rubber, which was evaluated in previous applications, and may result in a higher system keff.
As presented in the applicants sensitivity study E04-10-004, the applicant modeled the previously evaluated worst case package configuration (package in the hypothetical accident conditions array with ATRIUM 11 fuel contents) with varying polyethylene densities to determine the most reactive density. Synthetic rubber has a maximum density of 1.362 grams per cubic centimeter (g/cm3) and of the additional materials considered in the analysis, polyethylene has the highest hydrogen weight percentage.
Thus, the applicant used a combination of this density and weight percentage to bound all synthetic materials or natural rubbers, as demonstrated in E04-10-004, Table 3. The density of this combination, modeled as polyethene, was varied from 0.08 g/cm3 to 1.362 g/cm3 for the tops and sides of the liner, and 0.16 g/cm3 to 2.724 g/cm3 for the bottom of the liner. The most reactive density was found at 0.28 g/cm3 and 0.56 g/cm3 for a keff plus two times the Monte Carlo calculation uncertainty (2) of 0.9343. This is below the applicants previously calculated Upper Subcritical Limit (USL) of 0.94094.
Included in the applicants model of the worst-case configuration was an ATRIUM 11 fuel assembly channel thickness of 0.320 cm, which is larger than the previously evaluated channel thickness for this fuel type. The applicant had previously determined that the maximum channel thickness results in the highest system keff. The applicant determined a correction factor to account for both the effect of polyethylene and increased fuel channel thickness.
The applicant also determined a correction factor for an error in the h_poly cross section in SCALE, identified by Oak Ridge National Laboratory (ORNL) in a SCALE User Notice dated February 26, 2021. This correction factor is described by the applicant in FS1-0027837 App.D, Section D.3, step 6. The applicant determined the correction factor by calculating keff of the package using the cross-section library containing the known h_poly error, and subtracting it from keff of the package calculated using a corrected cross section library distributed by ORNL.
The applicant calculated the final package keff by adding the correction factors for higher hydrogen density materials and increased channel thickness, and for correction of the h_poly cross section error, to the keff that the applicant calculated for the previously approved package.
For the analyses described above, the applicant modeled the package in the hypothetical accident conditions array using the same configuration and materials as for the previously approved package, with the exception of higher hydrogen density in the inner container and increased channel thickness. While the previous evaluation for the package resulted in a criticality safety index (CSI) of 1.0, the applicant modeled a smaller array size for this evaluation, consistent with a criticality safety index of 1.5. All of the applicants analyses for this array size result in keff values less than the USL of 0.94094.
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For calculation of the correction factors for higher hydrogen density materials in the inner container, increased channel thickness, and h_poly cross section errors, the applicant used the SCALE 6.2.2 code, with the KENO V.a three-dimensional Monte Carlo criticality code and the continuous energy, 252-group, or 56-group ENDF/B-VII.1 cross section libraries. The previous application for this package used SCALE 6.1.3 with the 238-group ENDF/B-VII cross section library. The applicant did not perform additional benchmarking analyses for the SCALE 6.2.2 code, since this code was only used to find differences in keff from previously evaluated configurations in order to determine the keff correction factors.
The staff finds this acceptable for this letter authorization request, since there are unlikely to be significant differences in code bias and bias uncertainty for this system between the two code versions used, and because of the significant conservatism in the difference between the calculated CSI of 1.5 (consistent with a maximum of 33 packages per conveyance) and the requested letter authorization limit of three packages per conveyance.
The staff finds that the criticality analyses provided in the applicants letter authorization request provide reasonable assurance that shipments of up to three TN-B1 packages per conveyance, with inner packaging materials changes and increased ATRIUM 11 fuel assembly channel thickness as described above, meet the criticality safety requirements of 10 CFR Part 71, with a CSI of 1.5, and are acceptable.
The staff also finds that this request has no adverse impact on public health and safety.
Based on the discussion above, the staff found the applicants request for a maximum of two shipments with an increased fuel channel side thickness and new shock isolating materials does not affect the ability of the Model No. TN-B1 package to meet 10 CFR Part 71 requirements.
CONDITIONS
(1) Authorization is for a maximum of 2 shipments to support channeled ATRIUM 11 shipping qualifications.
(2) Up to six channeled ATRIUM 11 fuel assemblies will be shipped in three TN-B1 packages per shipment. Shipments will not include any additional licensed material cargo.
(3) The maximum fuel channel side thickness is increased to 0.320 cm to bound the fabrication tolerances.
(4) Drawing FS1-0042699, Rev. 1.0, allows the use of synthetic rubber, in addition to natural rubber, for the inner container support frame (side face, bottom face and fastening pads). Drawing FS1-0042700, Rev. 1.0, allows the use of rubber, to include the option of natural or synthetic rubber, for the vibro-isolating components; components can be either round or square (40 x 28 mm). Drawing FS1-0042705, Rev. 1.0, allows for strips of rubber between the foam to aid in supporting the fuel channel: the inner container vibration absorber material allows for either polyethylene foam or rubber.
(5) The criticality safety index (CSI) is changed from 1.0 to 1.5.
(6) All other conditions of CoC No. 9372 shall remain the same.
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(7) This authorization shall expire on June 30, 2022.
CONCLUSIONS
Based on the statements and representations in the application dated December 17, 2021, the staff agrees that the use by Framatome of the Model No. TN-B1 package meets the requirements of 10 CFR Part 71, subject to the conditions listed above.
Issued on February 11, 2022.