ML20139A037
| ML20139A037 | |
| Person / Time | |
|---|---|
| Site: | 07109342 |
| Issue date: | 05/26/2020 |
| From: | Office of Nuclear Material Safety and Safeguards |
| To: | |
| Devaser N | |
| Shared Package | |
| ML20139A033 | List: |
| References | |
| EPID L-2019-LLA-0241 | |
| Download: ML20139A037 (6) | |
Text
SAFETY EVALUATION REPORT Docket No. 71-9342 Model No. Versa-Pac Certificate of Compliance No. 71-9342 Revision 15 Summary By application dated October 7, 2019 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML19280C070), Daher-TLI, (Transport Logistics International, Inc. [TLI] or the applicant) requested revision to and renewal of Certificate of Compliance (CoC)
No. 9342, for the Model No. Versa-Pac package.
The application submits Revision 11 of the safety analysis report (SAR) for the Versa-Pac package which adds a new criticality analysis to support an increased fissile mass limit for 20 weight percent 235U enriched material by limiting the total quantity of hydrogenous material in the package for this content limit to 1 lb. In addition, this new analysis includes an expanded definition of TRISO fuel contents of the package to more clearly describe the permissible contents of this form.
The requested changes to the CoC are to expand and clarify the description of the TRISO fuel, added a table to describe hydrogen restricted contents. In addition, staff made small editorial changes to improve readability of the CoC.
The staff used the guidance in NUREG-1609, "Standard Review Plan for Transportation Packages for Radioactive Material," as well as associated interim staff guidance documents to perform the review of the proposed package changes. Based on the statements and representations in the application, as supplemented, and the conditions listed in the following chapters, the staff concludes that the package meets the requirements of Title 10 of the Code of Federal Regulations (10 CFR) Part 71.
EVALUATION 1.0 GENERAL INFORMATION 1.1 Packaging Description The Versa-Pac packaging consists of two designs, i.e., the VP-55, a 55-gallon drum, and the VP-110, a 110-gallon version. No changes were made to the packaging.
1.2 Contents The applicant requested to modify the CoC to revise the description of TRISO fuel contents, and to include separate fissile mass limits for uranium enriched up to 20 weight percent 235U in the VP-55 with limited hydrogenous packing materials.
The applicant revised the definition of TRISO fuel material to change it from coated thorium/uranium carbide particles pressed within a graphite matrix, to the more detailed definition which limits the material to kernels of uranium oxides, carbides, and/or nitrides, encased in layers of carbon and silicon carbide (SiC). The TRISO particles are of unrestricted size, density, and uranium content per particle, and the particles may be loose or mixed in a graphite matrix and pressed into compacts of varying geometry. Compacts may include a fuel free graphite zone on the periphery.
This change in definition does not alter the applicants conclusion that TRISO material is subcritical in the non-hydrogen-limited content categories previously evaluated. Previous evaluations demonstrated that it was conservative to ignore thorium in the criticality analysis for TRISO materials, and that a polyethylene moderator results in a more reactive system than a graphite moderator. The applicant has shown, and the staff agrees that changing the TRISO content definition to exclude thorium and more explicitly describe the graphite and fuel particle configurations will not affect the results of the previously approved criticality evaluation for TRISO fuel materials in the package.
1.3 Evaluation Findings
The staff has reviewed the revised description of the contents and concludes that the requested changes continue to meet the requirements of 10 CFR Part 71.
2.0 CRITICALITY EVALUATION
The applicant provided an analysis in SAR Section 6.10.8 for uranium enriched up to 20 weight percent 235U in the VP-55 with limited hydrogenous packing materials. The applicant evaluated a range of homogeneous spheres of fissile and moderating materials within the package, assuming up to 1.0 lb. (0.454 kg) hydrogenous packing material homogeneously mixed with other moderators. The applicant modeled the fissile spheres as varying mixtures of uranium metal, water, graphite, and high density polyethylene, similar to the evaluation of package contents for the previously approved package. The difference in the evaluation of the materials with limited hydrogenous packing material is that the high density polyethylene component of the moderator is limited to 1 lb., while other moderators may vary. The applicant varied the size of the moderated sphere within the package to vary the moderation ratio for a given 235U mass.
Material properties are the same as for the previously evaluated packaging and contents models and are summarized in SAR Table 6-4.
The packaging configuration under normal conditions of transport (NCT) and hypothetical accident conditions (HAC), including the worst-case package array configuration, is the same as was previously demonstrated to be the most reactive in SAR Section 6.10.4. The staff agrees that this is acceptable, since no changes were requested to the packaging itself, and the change in contents will not affect the results of the NCT and HAC tests.
For all calculations, the applicant used the CSAS6 sequence of the SCALE 6.1.3 computer code, with KENO VI and the continuous energy ENDF/B-VII cross section library. This is the same code and cross section library used for calculations of the previously approved packaging and contents configuration, which is benchmarked as discussed in SAR Section 6.10.6.
For the single package evaluation, the applicant modeled the package with the moderated fissile sphere in the center of the package, and all other regions of the package fully flooded with water. The applicant also modeled a 12 in. (30 cm) water reflector outside the package, to ensure full reflection. The fissile sphere in the single package model contains 635 grams 235U in uranium enriched to 20 weight percent 235U, which is the highest mass allowed for this material in the package. This single package model is used to demonstrate that the package is subcritical for: 1) a single package fully flooded with water per 10 CFR 71.55(b); 2) a single package under NCT per 10 CFR 71.55(d); and 3) a single package under HAC per 10 CFR 71.55(e). The results of the single package evaluation are summarized in SAR Table 6-200. The maximum calculated keff for the single package is 0.90502, which is significantly below the applicants calculated upper subcritical limit (USL) of 0.9391.
For the evaluation of NCT package arrays, the applicant modeled an array of 360 packages in a triangular pitch. The applicant modeled each package with 635 grams 235U in uranium enriched to 20 weight percent 235U, which is the highest mass allowed for contents with limited hydrogenous packing material in the package. Since the applicant modeled 635 grams 235U per package in an array that corresponds to the lower criticality safety index (CSI) than the applicant is requesting, this NCT array analysis bounds both CSIs for the contents with limited hydrogenous packing material.
The inside of each package in the NCT array is dry, since the applicant demonstrates that there is no water in-leakage under NCT in SAR Section 2.6.8. The only moderators available are 1 lb.
of high density polyethylene and varying amount of graphite, limited only by the capacity of the inside of the package. The applicant modeled the fissile material moderated only by high density polyethylene initially, and then added larger amounts of graphite while varying the size of the moderated fissile mass. The applicant modeled small diameter fissile spheres, and then increased the amount of moderator and the size of the sphere until it touched the inside wall of the package. Then the applicant modeled a varying height cylinder of moderated fissile material with a diameter the same as the inside of the package, with hemispherical regions on the top and bottom of the cylinder. Finally, the applicant modeled the entire inside of the package filled with high density polyethylene and graphite moderated uranium. The results of the NCT array analysis are shown in SAR Tables 6-201 and 6-202. The maximum keff calculated for the NCT array is 0.61291, for the package filled with uranium enriched to 20% 235U moderated by high density polyethylene and graphite.
For the evaluation of HAC package arrays, the applicant modeled two different array sizes corresponding to the two CSIs that are requested for the package contents with limited hydrogenous packing material (CSIs of 0.7 and 1.0 for 605 grams and 635 grams 235U, respectively). For packages with a CSI of 1.0, the applicant evaluated an array of 105 packages with a triangular pitch and eccentric positioning of the moderated fissile sphere, as shown in Figure 6-146, and varying flooding configurations, as shown in Figure 6-147. The applicant modeled the outside of the array fully reflected by 12 in. of water. The most reactive condition identified by the applicant is with interstitial and outer packaging regions modeled without water, and the package cavity filled with a low volume fraction (0.01) of water. The results of the array calculation for 105 packages and a CSI of 1.0 are shown in SAR Table 6-206. The maximum keff reported by the applicant for this configuration is 0.93765, which is less than the USL of 0.9391.
For the HAC package arrays with a CSI of 0.7, the applicant evaluated an array of 144 packages, similar to the configuration shown in SAR Figure 6-146, but with more packages.
The applicant also varied package moderation by water according to SAR Figure 6-147. Similar to the evaluation for 105 packages with a CSI of 1.0, the most reactive condition identified by the applicant for an array of packages with a CSI of 0.7 is with interstitial and outer packaging regions modeled without water, and the package cavity filled with a low volume fraction (0.1) of water. The results of the array calculation for 144 packages and a CSI of 0.7 are shown in SAR Table 6-204. The maximum keff reported by the applicant for this configuration is 0.93736, which is less than the USL of 0.9391.
Since TRISO material is heterogeneous (i.e., small uranium particles suspended in graphite compacts), the applicant also evaluated heterogeneous arrangements of contents within the package. The applicant modeled both the NCT and HAC array configurations with small spheres of uranium suspended in moderator. The moderator consisted of 1 lb. of high-density polyethylene mixed with water (for the HAC array) or graphite (for the NCT array). For the HAC analysis, the particle size was from 0.00625 cm to 0.1 cm. For the NCT array, a single particle size of 0.0425 cm was modeled, since this is the typical size of TRISO fuel kernels. The pitch of fuel particles and size of the cylinder inside the package cavity is varied to find the optimum moderation ratio in each case. Results for the HAC array case are shown in SAR Table 6-207 and demonstrate that the homogeneous representation of package contents is bounding.
Results for the NCT array case are shown in SAR Table 6-208 and show that the maximum keff for this case is slightly higher than the maximum calculated for the homogeneous system evaluated in SAR Section 6.10.8.7 (0.63022 versus 0.61921). However, this keff is significantly less than the applicants calculated USL of 0.9391.
The staff reviewed the configurations modeled by the applicant for the single package and array analyses. The staff agrees that the applicant has identified the most reactive credible condition of the single package and arrays of packages, consistent with the condition of the package under NCT and HAC, and the chemical and physical form of the fissile and moderating contents.
The applicant previously benchmarked the CSAS6 sequence of the SCALE 6.1.3 computer code and ENDF/B-VII cross section library used for the calculations described above in SAR Section 6.10.6. Since the packaging and contents materials evaluated for this amendment are similar to those for the previously approved package, and the code and cross section library are the same, the applicant states that the previous benchmarking analysis applies. The applicant calculated a new USL for uranium enriched up to 20 weight percent 235U in the VP-55 with limited hydrogenous packing materials, based on the USL calculation previously developed based on a trending analysis of keff versus energy of the average lethargy causing fission (EALF). The applicant demonstrated in SAR Section 6.10.8.5.1 that uranium enriched up to 20 weight percent 235U in the VP-55 with limited hydrogenous packing materials remains within the range of applicability for the previous benchmarking analysis. The applicant calculated the USL for the new contents to be 0.9391. The staff agrees that the code and cross section library used by the applicant are appropriate for the analysis, and that the USL determined by the applicant is calculated appropriately.
The staff performed confirmatory calculations using the SCALE 6.2.3 Monte Carlo radiation transport code, with the CSAS6 criticality sequence and the 252-group ENDF/B-VII.1 neutron cross section library. The staffs confirmatory analyses consisted of models of the single package, NCT array, and HAC array, with variation in fuel materials, moderation, and homogeneous versus heterogeneous configurations. Using modeling assumptions similar to the applicants, the staffs independent evaluation resulted in keff values that were similar to, or bounded by, the applicants results.
The staff also performed confirmatory benchmarking calculations. The staff verified that the critical experiments selected by the applicant were applicable to the package with the limited hydrogenous packing materials contents. The staff used the TSUNAMI sequence of the SCALE 6.2.3 code package, with the ENDF/B-VII.1 252-group cross section library, to verify that the experiments selected by the applicant had high integral index (ck) values compared to the package with the requested contents. The staffs results indicate that 88 of the experiments selected by the applicant to benchmark their analysis have ck values above 0.9, which indicates a high degree of similarity. The staff also used the USLSTATS code within the SCALE 6.2.3 package to independently determine a USL for the package evaluated with the SCALE 6.2.3 code and 252-group ENDF/B-VII.1 cross section library. Using a larger set of critical experiments, determined to be applicable using the TSUNAMI code sequence, the staff calculated a USL of 0.9416 based on a ck trending analysis. Although this analysis was performed using a different version of the SCALE code and different set of critical experiments, this indicates that the USL calculated by the applicant is conservative.
2.1 Evaluation Findings
The staff reviewed the applicants requested changes to the CoC, initial assumptions, model configurations, analyses, and results. The staff finds that the applicant has identified the most reactive configuration of the Model No. Versa-Pac package with the requested contents, and that the criticality results are conservative. Therefore, the staff finds with reasonable assurance that the package, with the requested contents, will meet the criticality safety requirements of 10 CFR Part 71.
3.0 MATERIALS EVALUATION The staff reviewed the 235U loading for VP-55 and VP-110 with hydrogen restricted contents and Tri-structural ISOtropic particle fuel (TRISO) fuel contents. The allowable contents (Section 1.1) fulfills the requirements of IAEA 2012 (SSR-6, 501, equivalent to 10 CFR 71.31; 71.43(d) and 71.43(f)).
Additionally, the Versa-Pac may be used to transport TRISO fuels and compacts composed of Uranium Oxycarbide (UCO) kernels encased within layers of SiC to form TRISO particles. The applicant stated that UCO kernels and TRISO particles are of unrestricted size, density, and uranium content per kernel/particle. Further, the applicant stated that UCO kernels and TRISO particles may be loose or mixed in a graphite matrix and pressed into various fuel forms (e.g., annular cylinders, planks, right circular cylinders, spheres, etc.). The applicant evaluated Versa-Pac assuming optimum moderation. The applicant stated that Non-fissile chemical impurities do not increase the reactivity of the system. Therefore, the staff determines that these impurities are acceptable and may be present in any quantity.
3.1 Evaluation Findings
To the maximum credible extent, there are no significant chemical, galvanic or other reactions for each packaging component, among the packaging components, among package contents, or between the packaging components and the contents in dry or wet environment conditions.
he effects of radiation on materials are evaluated. Regarding the potential embrittlement by radiation, the package containment is constructed from materials that meet the requirement of Regulatory Guides 7.11 and 7.12 for embrittlement.
4.0 CONDITIONS The staff made editorial changes to improve the readability of the CoC. The CoC includes the following condition(s) of approval:
Condition No. 3(a) was updated to reflect a new address of the applicant.
Condition No. 5(a)(2) the description was updated to clarify the approved TRISO fuel contents.
Condition No. 5(b)(1) was revised to define the TRISO fuel material as the more detailed definition which limits the material to kernels of uranium oxides, carbides, and/or nitrides, encased in layers of carbon and SiC.
Condition No. 5(b)(2) was revised to include Table 2A which lists the maximum quantities for the uranium enriched up to 20 weight percent 235U in the VP-55 with limited hydrogenous packing materials.
Condition No. 5(b) was revised to include the CSI associated with the materials referred to in Table 2A of the CoC.
The references section has been updated to include reference to this request.
5.0 CONCLUSION
S Based on the statements and representations contained in the application, as supplemented, and the conditions listed above, the staff concludes that the design has been adequately described and evaluated, and the Versa-Pac package meets the requirements of 10 CFR Part 71.
Issued with Certificate of Compliance No. 9342, Revision No. 15, for the Model No. Versa-Pac.