ML20262H034
| ML20262H034 | |
| Person / Time | |
|---|---|
| Site: | 07109225 |
| Issue date: | 09/29/2020 |
| From: | John Mckirgan Storage and Transportation Licensing Branch |
| To: | Fowler W NAC International |
| NJDevaser NMSS/DFM/STL 301.415.5196 | |
| Shared Package | |
| ML20262H033 | List: |
| References | |
| EPID L-2020-LLA-0056, USA/9225/B(U)F-96 | |
| Download: ML20262H034 (17) | |
Text
Official Use Only - Security-Related Information UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 September 29, 2020 Mr. Wren Fowler Director, Licensing NAC International 3930 East Jones Bridge Road, Suite 200 Norcross, GA 30092
SUBJECT:
REVISION 70 OF CERTIFICATE OF COMPLIANCE NO. 9225 FOR THE MODEL NO. NAC-LWT PACKAGE
Dear Mr. Fowler:
As requested by your application dated March 24, 2020 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML20087M175), as supplemented August 17 and August 24, 2020 (ML20174A083 and ML20254A327, respectively), enclosed is Certificate of Compliance No. 9225, Revision No. 70, for the Model No. NAC-LWT transportation package.
Changes made to the enclosed certificate are indicated by vertical lines in the margin. The staffs safety evaluation report is also enclosed.
The approval constitutes authority to use the package for shipment of radioactive material and for the package to be shipped in accordance with the provisions of Title 49 of the Code of Federal Regulations (49 CFR) 173.471. Those on the attached list have been registered as users of the package under the general license provisions of 10 CFR 71.17 or 49 CFR 173.471.
If you have any questions regarding this certificate, please contact me or Nishka Devaser of my staff at (301) 415-5196.
Sincerely, Digitally signed by John B.
John B. McKirgan McKirgan Date: 2020.09.29 16:08:16 -04'00' John B. McKirgan, Chief Storage and Transportation Licensing Branch Division of Fuel Management Office of Nuclear Material Safety and Safeguards Docket No. 71-9225 EPID No. L-2020-LLA-0056 Upon Removal of
Enclosures:
- 1. Certificate of Compliance Enclosure 3, this No. 9225, Rev. No. 70 document is uncontrolled
- 2. Safety Evaluation Report
- 3. Registered Users cc w/encls. 1& 2: R. Boyle, Department of Transportation J. Shuler, U.S. Department of Energy c\o L. F. Gelder Registered Users Official Use Only - Security-Related Information
(Transmittal letter and SER): ML20262H034 ADAMS Enclosure 1: ML20262H035 ADAMS Enclosure 3: ML20262H036 OFFICE: NMSS\DFM NMSS\DFM NMSS\DFM NMSS\DFM NAME: NDevaser SFigueroa ARigato TAhn DATE: 09/17/2020 09/18/2020 09/17/2020 09/18/2020 OFFICE: NMSS\DFM NMSS\DFM NMSS\DFM NMSS\DFM NAME: CBajwa ZLi ASotomayor-Rivera TBoyce DATE: 09/18/2020 09/17/2020 09/17/2020 09/22/2020 OFFICE: NMSS\DFM NMSS\DFM NMSS\DFM NAME: RChang MDiaz Maldonado JMcKirgan DATE: 09/24/2020 09/23/2020 09/29/2020 UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 SAFETY EVALUATION REPORT Docket No. 71-9225 Model No. NAC-LWT Package Certificate of Compliance No. 9225 Revision No. 70
SUMMARY
By application dated March 24, 2020 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML20087M175), as supplemented August 17 and August 24, 2020 (ML20174A083 and ML20254A327, respectively), NAC International, Inc., (NAC, or the applicant) requested an amendment to Certificate of Compliance (CoC) No. 9225 for the Model No. NAC-LWT package. NAC requested an amendment to authorize the transport of Enriched Fast Neutron (EFN) rods, Moly targets (Mo-99), and Booster rods utilizing the National Research University/National Research Institutes X (NRU/NRX) (from Canadian research reactor) basket and NRU/NRX caddies, as well as minor clarifications to the CoC.
Following staff review of the associated safety analysis report (SAR), the staff finds that the changes do not affect the ability of the package to meet 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 NAC-LWT is a Type B(U)F-96 radioactive material transportation packaging design. It is authorized to transport several types of contents, including light-water reactor spent fuel, research reactor spent fuel, and high enriched uranyl nitrate liquid in containers specifically designed for the liquid. The NAC-LWT package may be shipped by truck, boat, or railcar and depending on the content, within an international shipping organization (ISO) container.
This application introduces a new NRX/NRU caddy (plug and tube), a new licensing drawing associated with the caddy, and details of the new contents requested in this amendment. The plug used with the caddy are to keep small fragments of material in the caddy when carrying material added to this amendment: EFN rods, Moly targets, and Booster rods. Plugs are not required with NRU/NRX shipments, and the basket used to carry these caddies (same as NRU/NRX) has not been changed.
2 1.2 Packaging Drawings The applicant submitted one drawing that shows the caddy assembly and its configuration within the NAC-LWT package.
LWT 315-40-175, Rev. 2 (Sheets 1 - 2) Caddy Assembly, NRU/NRX 1.3 Contents The applicant requests the addition of new approved contents to the package for use in the previously approved NRU-NRX basket and associated caddy and caddy plug (caddy and plug are also new to this amendment). The new contents requested in this amendment include EFN rods, Moly targets, and Booster rods. Parameter limits of the new contents are now listed in Section 5(b)(1)(xxii) of the certificate and is printed below:
Parameter Short Moly Double Length Moly EFN Boosters Maximum Cask Heat Load (W) 101 101 144 4 Maximum Per Caddy Heat Load (W) 0.3 0.8 8 0.2 Payload Limit (lb/tube) 20
- Rod/Targets (Equivalent) 20 36 36 16 Maximum 235U per rod (g) 1.1 2.41 13 18.1 Minimum Cool Time (yr) 38 8 23 37 Maximum 235U Depletion (%) 94.8 30.4 87.4 2.9 Maximum Enrichment wt% 235U 94 Each NRU/NRX fuel basket can hold up to 18 NRU/NRX caddies loaded with EFN rods, Booster rods, or Moly targets in accordance with the proposed package configuration.
Each NRU/NRX caddy is limited to 36 EFN rods, 16 Booster rods, 20 Short Moly Targets, or 36 double length Moly targets or an equivalent number in rod/target segments or fragments. All materials must be placed in a caddy. One single fuel type may be loaded into one NRU/NRX caddy. EFN and Moly targets may be loaded into a single package. The analysis assumes that Booster rod caddies are not mixed with EFN rod or Moly target caddies in a single package.
Undamaged and damaged material is permitted for transport. Small fragmented rods/targets require the use of the NRU/NRX caddy plug. Larger rod segments are retained axially within the caddy by the NRU/NRX basket tube and basket lid structure and do not require the caddy plug.
2.0 STRUCTURAL EVALUATION The objective of the structural evaluation is to verify that the applicant has adequately evaluated the structural performance of the package (packaging together with contents) and demonstrated that it meets the regulations in 10 CFR Part 71, Packaging and Transportation of Radioactive Material.
The new materials requested in this amendment include EFN rods, Moly targets, and Booster rods. The applicant limited the weight of these new materials to 20 lbs, which is the original weight of material evaluated previously and therefore does not affect the bounding g-loads for normal and accident conditions. As a result, the staff agrees that the basket will continue to perform its intended safety function.
3 The new material is to be carried in caddies that may require a removable cap to retain smaller material within the caddy, as described per the conditions in the certificate of compliance. The caps fit over the plug tubes and are not attached mechanically to them. They are retained in turn by the basket lid and are of welded construction. The applicant evaluated the performance of the caps and demonstrated that the caps are able to withstand standard normal and accident conditions, where the limiting safety factor of all drop scenarios is 8.1 for the top-end drop accident.
The applicant has stated that only 30% of the cladding for EFN rods needs to be intact for criticality purposes under normal conditions of transport (NCT) and hypothetical accident conditions (HAC). No further structural evaluation of the cladding was performed, as the applicant has stated that the cladding will remain intact under NCT and HAC drop conditions.
See Section 7.2 of this SER, Content Integrity, Damaged Fuel, for additional details on cladding integrity.
2.1 Evaluation Findings
Based on review of the statements and representations in the application, the NRC concludes that the performance of the NAC-LWT package while carrying EFN rods, Moly targets, and Booster rods has been adequately described and evaluated to demonstrate that the package will continue to perform its original safety function and meets the structural integrity requirements of 10 CFR Part 71. Specifically, the staff reviewed the structural performance of the packaging under NCT as required by 10 CFR 71.71, and concludes that there will be no substantial reduction in the effectiveness of the packaging that would prevent it from satisfying the requirements of 10 CFR 71.51(a)(1) for a Type B package and 10 CFR 71.55(d)(2) for a fissile material package.
The staff reviewed the structural performance of the packaging under the HAC required by 10 CFR 71.73 and concludes that the packaging has adequate structural integrity to satisfy the subcriticality, containment, and shielding requirements of 10 CFR 71.51(a)(2) for a Type B package and 10 CFR 71.55(e) for a fissile material package.
3.0 THERMAL EVALUATION The objective of thermal evaluation is to verify that the thermal performance of the package design has been adequately evaluated for the thermal tests specified under NCT and HAC, and that the package design meets the thermal performance requirements of 10 CFR Part 71.
3.1 Description of Thermal Design As stated in the SAR, the applicant requested to add EFN rods, Moly targets, and Booster rods, utilizing the NRU/NRX basket and NRU/NRX caddies, as contents in NAC-LWT package. The maximum heat load for a basket slot having this content is less than 8 Watts per basket location, with a maximum package heat load of 144 Watts (for EFN rods). The addition of a caddy plug, for use in the NRU/NRX basket to retain fragments too small to be retained axially within the caddy, has also been requested.
3.2 Material Properties and Component Specifications The specifications and thermal properties of NAC-LWT package main components remain unchanged because there is no change in package thermal design.
4 The staff reviewed the List of SAR Changes (SAR enclosure 3) and the proposed revisions to SAR Sections 1 and 3 and verified that there were no changes to specifications or thermal properties of the main components of the package which directly impact thermal performance.
3.3 Thermal Evaluation under Normal Conditions of Transport (NCT)
The thermal performance of the NAC-LWT package with the newly proposed contents continues to be bounded under NCT by payloads with higher heat loads previously reviewed and approved by NRC staff; therefore, the package continues to meet the requirements of 10 CFR 71.
3.4 Thermal Evaluation under Hypothetical Accident Conditions (HAC)
The thermal performance of the NAC-LWT package with the newly proposed contents continues to be bounded under HAC by payloads with higher heat loads previously reviewed and approved by NRC staff; therefore, the package continues to meet the requirements of 10 CFR 71.
3.5 Evaluation Findings
Based on review of the statements and representations in the application, the staff concludes that the addition of add EFN rods, Moly targets, and Booster rods, utilizing the NRU/NRX basket and NRU/NRX caddies, as contents in the NAC-LWT package has been adequately described and evaluated that the thermal performance of the package meets the thermal requirements of 10 CFR Part 71.
4.0 CONTAINMENT EVALUATION There were no changes made to the packages containment evaluation.
5.0 SHIELDING EVALUATION The objective of the shielding evaluation is to ensure that there is adequate protection to the public and occupational workers against direct radiation from the proposed contents of the NAC-LWT transportation package, and to verify that the package design meets the external radiation requirements of 10 CFR 71.47 and 10 CFR 71.51 for NCT and HAC under exclusive use of transport.
NAC submitted a request to revise the NAC-LWT CoC No. 9225, to permit the transport of 36 EFN rods, 16 Booster rods, 20 Short Moly targets, or 36 double length Moly targets utilizing the NRU/NRX basket and NRU/NRX caddies. Up to eighteen caddies may be loaded into the NAC-LWT. EFN rods, Moly targets, or Booster rods may be loaded as rods/targets, or rod/target fragments. Those fragments too small to be retained axially within the caddy shall have a caddy plug installed after the material has been loaded to ensure the material remains in the caddy.
5.1 Description of the Shielding Design For this amendment request, the applicant stated that NRU/NRX caddies with caddy plugs are going to be used for small fragmented rods/targets to maintain the fuel during transport.
Rods/targets or segments/fragments smaller than 6 inches in length require the use of the caddy plug. Larger rod segments are retained axially within the caddy by the NRU/NRX basket
5 tube and basket lid structure. Undamaged and damaged material is permitted for transport.
According to the applicant, no clad is required to be present to assure that dose rates of the requested payloads remain within safety limit(s). The NRC SER for the NRU/NRX payloads (Revision 58 of the NAC-LWT CoC (ML13059A560)) duplicates the discussion included in the SAR Section 5.3.21 NRU/NRX evaluation and states that the NRU/NRX fuel, which is composed of a metal alloy, is not expected to fail during transport, and will not produce rubble; however, the applicant looked at a damaged fuel configuration that fully collapses the fuel in the basket tubes. Collapsed fuel was modeled at the nominal fuel density. Also, collapsed models do not include fuel clad or end plug material. In particular, the bounding (NRU-HEU) shielding evaluations did not credit a caddy or caddy plug and therefore do not require the use of a caddy or caddy plug.
The NRU/NRX caddy is constructed of aluminum. The aluminum caddy provides geometry constraints to fuel rod movement. The staff found this approach acceptable because these caddies will help to maintain the fuel in place during transport minimizing fuel reconfiguration.
5.1.1 Summary Table of Maximum Radiation Levels Maximum Dose Rates for Booster rods, EFN Rods, and Moly Targets (NRU-HEU Values) are shown in Table 1-2 of SAR enclosure 2 (calculation package 50055-5001):
Transport Dose Rate Location Undamaged Damaged/Compacted Limit Condition
[mrem/hr] [mrem/hr] [mrem/hr]
Side Surface of Cask 2.28 30.3 1000 1 m from Side of cask 0.219 2.23 N/A (Transport Index) 2 m from Truck - 0.064 0.450 10 Radial Dose at Cab of Truck 0.001 0.010 2 Accident Side 1 m 0.463 3.75 1000 5.2 Source Specification The gamma and neutron source for this amendment were generated for Booster rods, EFN rods, and Moly targets in the NRU/NRX basket and compared to fuel contents of the previously evaluated NRU-HEU payload. The evaluated payload properties are listed in Table 1-1 of SAR enclosure 2 (calculation package 50055-5001).
The applicant used the TRITON control module in SCALE 6.1 to generate the gamma and neutron source terms. The staff found the use of TRITON acceptable because each Triton source term includes all necessary dimensions (fuel pin and clad radii, pin and lattice pitch, etc.), material information (exact isotopic compositions, density), and thermal-hydraulic conditions (temperature, void fraction, density) of the fuel and moderator/coolant. This information is provided by the applicant and it is specified in the shielding design.
For this amendment, TRITON source terms were calculated based on maximum depletion (wt% U-235 depleted) for the additional payloads in the NRU-HEU geometry. This means that the masses of U-235 were increased to estimate the sources. Fuel was evaluated at 91%
6 enrichment within the TRTION cases. The staff found this approach acceptable because all materials are highly enriched uranium with thermal fission of U-235 generating higher source terms. The staff reviewed the TRITON outputs and found that there is no significant generation of transuranic elements for this level of enrichment with no significant heat generation by actinides and no significant neutron source. In conclusion, the staffs independent evaluation of the source terms agrees that no significant transuranic isotopes are generated.
5.3 Model Specification 5.3.1 Source Term Determination The applicant estimated the source terms for the Booster rods, EFN rods, and Moly targets by adjusting the NRU-HEU input file to the values appropriate to each of the payload types.
Source terms were estimated by adjusting NRU model burnup by power and burn time adjustments without geometry changes. The short Moly rod requires additional depletion and therefore requires an increase in the number of days in the last modeled cycle. All other additional payloads have reduced depletion, with the Booster rods having the lowest depletion.
SAR Table 6-2 contains the steps taken to estimate the depletion time required, the targeted depletion percentage, and the applied cool time after depletion. In SAR Table 6-2, all gamma sources terms are significantly lower than the NRU-HEU case on a per initial gram U-235 basis since all additional payloads have lower initial U-235 content per caddy than the NRU-HEU payload, and the total gamma sources in the additional payloads is significantly lower than those of the NRU-HEU payload. Only EFN caddies, due to the same depletion percentage, slightly longer cool time, and lower mass, will approach the source term contained in basket tubes loaded with NRU-HEU rods. The applicant used the EFN damaged/compacted dose rates rather than the undamaged dose rates. The staff agrees with the applicants proposed approach since the independent source term analysis confirmed that the EFN damaged/compacted dose rates is bounded by the NRU-HEU dose rates.
5.3.2 Material Properties The fuel material and the geometry properties are presented in SAR Table 4-2.
5.4 Methods A comparison was made between the proposed payloads and the NRU-HEU payload.
For the Booster rods, in an undamaged configuration, the U-235 density in gram/cm for the sum of 16 Booster rods is significantly lower than that of the 12 NRU-HEU fuel rods. At a fixed source density this will result in the undamaged NRU-HEU analysis being bounding. The staff found this comparison acceptable based on crediting a significantly lower depletion percentage, longer cool time, and lower overall fuel mass of the Booster rods, which provides further assurance that NRU-HEU calculated dose rates are bounding for the Booster rods.
For the Moly - Short Targets, the caddy cross section permits no more than 12 Moly targets at a given elevation. Source density per SAR Table 6-2 for the short Moly targets is only 68% that of the NRU-HEU fuel rods while initial U-235 linear density is only 4% higher. The staff found this comparison acceptable because the short Moly target U-235 content in the caddy is only 4% of the permitted NRU-HEU value, and this demonstrates that the NRU-HEU analysis is bounding.
For the Moly Double Length Target, in an undamaged configuration, the U-235 density in gram/cm for the sum of 12 double length Moly targets is lower than that of the 12 NRU-HEU fuel
7 rods. The staff found this comparison acceptable due to crediting the significantly lower fuel mass (17%), with a lower source density (48%), that results from the lower depletion percentage at reduced cooling times, which provides further assurance that the NRU-HEU fuel rods have calculated dose rates which are bounding for the double length Moly targets. In compacted form, the Moly targets have a lower linear U-235 density with shorter height and less source per unit density. Therefore, the staff found that the NRU-HEU compacted evaluation is bounding for the double length Moly targets.
The damaged/compacted dose rates from the NRU-HEU case analysis were considered bounding for the EFN rods (compacted NRU-HEU fuel dose rates are an order of magnitude higher than the undamaged values for NRU-HEU fuel). The staff found this approach acceptable because undamaged EFN rods are similar in cross section to undamaged NRU-HEU rods, and these undamaged EFN rods were evaluated at the same depletion percentage as the NRU-HEU undamaged rods (with only a slight increase in cool time resulting in a slightly lower source density).
For damaged EFN rods, when compacting fuel, the U-235 linear density is almost identical to that of the NRU-HEU rods. However, given the lower source density per initial gram of U-235 (90%) and smaller compacted height for the damaged EFN rods, the NRU-HEU compacted analysis dose rate results are bounding for the damaged/compacted EFN rods. The staff agrees with the applicant since damaged/compacted EFN rods will by bounded by NRU-HEU rods.
5.5 Shielding Evaluation The staff concluded that for the NAC-LWT loaded with NRU/NRX caddy, containing EFN rods, Booster rods, or Moly targets, in an NRU/NRX basket, the dose rates will meet the requirements of 10 CFR 71.47 and 10 CFR 71.51 for an exclusive use shipment. The evaluated payload considered both undamaged and damaged fuel assemblies for both normal and accident operating conditions. The staff conclusions on a payload type basis, are applicable to mixed loading provided bounding constraints, heat load, or dose rates, are considered. The mixed loading statement is applicable to mixing different payloads types in the cask, not a caddy.
The applicant submitted the results of their source terms calculations. The staff reviewed the applicants results of their analyses and examined each gamma spectrum for the additional payloads in comparison with the NRU-HEU case. The staff noted that the NRU-HEU case does not bound every energy bin in comparison with the additional payloads. However, the energy bins in the gamma spectrum for the additional payloads are not important since the probability of occurrence is low and there is a large margin on dose rates for the NRU-HEU case in previous calculations approved by NRC (ML13059A560). Due to this, the staff determined that the proposed additional payloads will be under the regulatory limits. The staff also performed independent confirmatory calculations of the source term evaluation using the applicants data.
The staff finds, based on its review, that for the NAC-LWT loaded with the NRU/NRX caddy, containing EFN rods, Booster rods, or Moly targets, in an NRU/NRX basket, dose rates will meet the requirements of 10 CFR 71.47 and 10 CFR 71.51 for an exclusive-use shipment.
8
6.0 CRITICALITY EVALUATION
6.1 Review objective The objective of the criticality evaluation is to determine if the Model No. NAC-LWT loaded with the proposed new contents continues to meet the regulatory requirements of criticality safety as prescribed in Sections 10 CFR 71.55 and 71.59 under NCT and HAC as prescribed in 10 CFR 71.71 and 71.73. The staff reviewed the criticality safety design of the NAC-LWT with the proposed new contents as presented in the application (ML20087M175). The staff followed the guidance provided in NUREG-1617, Standard Review Plan for Transportation Packages for Spent Nuclear Fuel in its review. The following sections of this SER documents the staffs review and conclusions.
6.2 Criticality safety evaluation 6.2.1 General description of the package design The NAC-LWT packaging system consists of a vessel and two impact limiters. The vessel is made of concentric steel, lead, steel shells. It also includes a neutron shield. Various fuel baskets can be installed in the internal cavity of the vessel for shipment of different radioactive materials as authorized in the CoC. In its application for revision of the CoC (ML20087M175),
the applicant proposes to add irradiated EFN (enhanced fast neutron) rods, Moly targets, and Booster rods as authorized contents. The new contents will be loaded in the package using the fuel baskets for the NRU/NRX reactors and NRU/NRX caddies. Here the term caddy refers to a pipe device as shown in licensing drawing 315-40-175, Revision 2 for the NAC-LWT packaging system. Up to eighteen caddies may be loaded into the NAC-LWT. The criticality safety design of the package relies on limiting the fissile materials per package and the control of the geometric distribution/shape of the fissile materials in the package.
6.2.2 Summary Table of Criticality Evaluations The applicant provided summaries for its criticality safety analyses for the proposed contents in SAR Table 6.7.6-2 through SAR Table 6.7.6-7. These tables also provided the keff value as a function of number of rods or rod segments for each of the proposed contents as defined in Table 1-1 of SAR enclosure 2 (calculation package 50055-5001). The staff reviewed these summary tables and finds that the applicant has provided sufficient information to identify the most reactive package with the proposed new contents. On this basis, the staff finds that the package design meets the regulatory requirements of 10 CFR 71.55.
6.2.3 Criticality Safety Index (CSI)
The applicant identified that the CSI of the package with the proposed content is 100. This means that the package must be transported in an exclusive use mode and only one package can be transported in a conveyance per the requirements of 10 CFR 71.59(c)(3). This CSI has been included in the CoC as a licensing condition.
6.2.4 Specification for Contents The application for revision of CoC No. 9225 requests permission to include Booster rods, EFN rods, and Moly targets as new authorized contents. These Booster rods and EFN rod segments are discharged from the NRU/NRX reactors and the Moly targets are irradiated in reactors to produce the molybdenum-99 isotope. The Moly targets have two different designs, short length
9 or double length. The length is 6.67 cm for the short Moly target and 15.88 cm for the double length Moly target. The U-235 mass is 22 grams per rod for the short length Moly target and 86.76 grams per rod for the double length Moly target rod. But the fissile material masses for both Moly targets are bounded by the ENF rod, which has a U-235 mass of 468 grams per rod.
The applicant provided specifications for these new contents in SAR Table 6.7.6-1.
These new contents must be loaded in the caddies. Up to 18 caddies can be loaded in each NRU/NRX fuel basket. Except for the EFN and Moly targets, only one fuel type may be loaded into one NRU/NRX caddy. EFN rods and Moly targets may be loaded into the same fuel basket in the package provided that only six Moly targets are placed into the six interior basket tubes.
The EFN rods, Booster rods, or Moly targets can be in forms of whole rods or as rod segments/fragments. Each NRU/NRX caddy is limited to load up to 36 EFN rods, 16 Booster rods, 20 Short Moly Targets, or 36 double length Moly targets. For the rod segment payloads, the maximum mass of the rod segments per caddy must not exceed the mass of the Booster rod, EFN rod, or Moly target rod limits. The contents loading configurations must be consistent with NAC Drawing Nos. LWT 315-40-172, LWT 315-40-173, LWT 315-40-174, and LWT 315-40-175. Package configuration is to be in accordance with NAC Drawing No. LWT 315-40-170.
Booster rod caddies may not be mixed with EFN rods or Moly target caddies in a single package. Undamaged and damaged rods are permitted for transport. For Booster rods and Moly rods, there is no need for any cladding material to be attached to the rod or rod segments.
For package with fully loaded ENF rods or rod segments, a 30% of cladding material is credited in criticality safety analyses. Therefore, in a full NRU/NRX basket loaded with ENF fuel, the fuel must retain the equivalent of 30% cladding material in terms of fuel surface area.
In addition, small fragmented rods/targets require the use of the NRU/NRX caddy plug. Larger rod segments are retained axially within the caddy by the NRU/NRX basket tube and basket lid structure.
The staff reviewed the characteristics specified in the application for the spent fuel to be transported using the NAC-LWT packaging system and finds that the specification provides sufficient details for the staff to develop models for confirmatory analyses. On this basis, the staff finds the specification for spent fuel contents is sufficiently detailed, and therefore acceptable.
6.2.5 Criticality Evaluations The applicant performed criticality safety analyses for the package with the proposed new contents. The applicant considered the criticality safety of a single package as loaded to demonstrate that the package meets the regulatory requirement of 10 CFR 71.55(b) as well as a single package under NCT and HAC to demonstrate that the package meets the requirements of 10 CFR 71.55(d) and 71.55(e).
10 Single Package Evaluation The applicant performed analyses for the criticality safety of a single package containing undamaged and damaged Moly targets, EFN rods, and Booster rods in the NAC-LWT.
For packages loaded with Booster rods or Moly targets, the applicant calculated keff values with various pay loads. The rods/targets are analyzed at 94 wt% U-235. This enrichment assumption is consistent with the enrichment limit as specified in the CoC and the description of the physical characteristics for the payloads as listed in SAR Table 6.7.6-1.
For a package fully loaded with the ENF fuel, the applicant evaluated partial cladding loss. As the rods are metal alloy and not expected to disperse significant amounts of fissile material, the cylindrical rod shape was maintained in these evaluations. This calculation addresses extensive clad through-wall damage and clad loss and provides limitations on the additional payloads to allow increased clad loss, or total clad loss, for the payload.
The caddy was modeled with a design basis load of 18 NRU-HEU rods, which contains the largest quantity of fissile material and can be used to bound both EFN rods and Moly targets. The results show that the undamaged NRU rods clearly bound the undamaged Booster rods because the Booster rods have a significantly smaller quantity of U-235.
For similar materials and geometry and the fact that NRU rods have the bounding fissile material mass, the criticality safety analysis results for the package containing the NRU Booster rods is bounding for the packages containing the EFN rods or Moly target payloads.
For the NRU high enrichment fuel, the applicants analysis using similar rod designs demonstrated that partial clad removal increases reactivity because the fuel configuration in the package is under moderated. The applicant analyzed the impact of the different residual cladding thickness to search for the minimal cladding thickness that is required to maintain subcriticality. The results presented in this calculation demonstrate that keff can remain below the upper subcriticality limit (USL) provided the limitation in Table 1-1 are maintained. To assure criticality safety, the minimal residual cladding thickness requirement for the ENF fuel is incorporated in the CoC as a licensing condition.
In addition, the applicant found in its search for the maximum reactivity that a package with a full load of NRU/EFN rods in caddies produces keff exceeding the upper safety limit when assuming unclad materials, and the keff will decrease to significantly below the USL if the six interior basket tubes are empty. Therefore, the applicant developed a new configuration that allows loading of the six interior location empty slots with the Moly targets, which have significantly lower fissile mass.
On SAR page 6.7.6-5, the applicant states: Previous analysis demonstrated that a cask loaded of NRU/EFN rods in caddies produces keff values above the USL when assuming unclad materials. The analysis also demonstrated that a configuration with the six interior basket tubes empty is significantly below the USL. Rather than leaving the interior locations empty the low fissile mass Moly targets are placed into the inner 6 tubes. With a fissile mass of the bounding Moly caddy (containing Double Length Moly targets) being <20% that of the NRU caddy, engineering judgement indicates that results will be below the USL. The staff was initially concerned that the engineering judgment
11 made by the applicant may not be reliable because replacing the six empty tubes with highly enriched Moly targets will have two impacts on the criticality safety of the package: (1) an increase in the quantity of the fissile material and (2) the removal of the neutron flux trap formed by the empty tubes. The staff was especially concerned with the criticality safety of the package with this proposed loading configuration because the package fully loaded with the NRU/EFN rods has already exceeded the USL as stated by the applicant.
In its response to the staffs request for additional information (ML20254A327), the applicant states: In the text following the RAI, the Reviewer quoted an engineering judgment statement from page 6.7.6-5, SAR Section 6.7.6.3.4. NAC did perform the evaluation of the mixed payload and demonstrated that the mixed payload keff was well below the USL. The evaluation included various configurations of the Moly rods to obtain a maximum reactivity mixed payload configuration. The evaluation concluded that spreading out the Moly rods along the length of the tube/caddy to provide maximum interaction with the NRU/EFN rods resulted in increased reactivity versus the more compact configuration for only Moly rods. Results for this evaluation were summarized in SAR Table 6.7.6-6 as stated in SAR Section 6.7.6.3.4. Based on this response, the staff found that the applicants conclusion of criticality is based on calculations rather than engineering judgment and therefore the conclusion is acceptable. Because engineering judgment is typically made by the analysts experience and knowledge, it can be very subjective. However, engineering judgment with solid bases can be acceptable. The staff does not have objection to this use of engineering judgment, since it is justified with analyses.
Evaluation of Package Arrays under NCT and HAC The applicant determined that a single package under both NCT and HAC remains subcritical. The results of the criticality safety analyses show that the keff+ 2 of the NAC-LWT cask with the most reactive configuration under normal and accident conditions is below the USL for package containing the high enrichment ENF rods. The applicant determined that the size of array is one package. Following the procedures prescribed in 10 CFR 71.55(a), based on its calculation, the applicant determined that the criticality safety index (CSI) is 100 because only a single package can remain subcritical.
The staff reviewed the applicants calculation of the CSI and finds that the applicant has appropriately calculated the CSI and the result is acceptable because the applicants calculations followed the procedures prescribed in the regulations and the calculation of CSI is accurate. Because the CSI for the package is 100, the package must be transported in an exclusive mode in accordance to regulatory requirement of 10 CFR 71.59(c)(3).
6.3 Computer model 6.3.1 Computer code and cross section library The applicant used MCNP code version 6.2 and the ENDF/B-VII cross section libraries in these calculations. MCNP is a widely used computer code for criticality safety analyses for various systems. The staff finds that it is also one of the recommended codes in NUREG-1617 and the cross-section library represents the state of the art nuclear data library. On these bases, the staff finds that the computer code and cross section library are appropriate for criticality safety analyses for the NAC-LWT package containing the proposed new contents as defined in
12 Table 1-1 of SAR enclosure 2 (calculation package 50055-5001) and the CoC. The CoC condition provides a reasonable assurance that the correct contents will be loaded as analyzed.
In its criticality safety analyses, the applicant credited the presence of the residual cladding material around the fuel meat for the damaged EFN rod contents in the package containing a fully loaded basket. In the model, the clad was modeled as a 0.02 cm thick layer around the fuel meat (versus a nominal 0.0762 cm clad for <30% of the material credited) and presented the results in Table 6.7.6-4 and Figure 6.7.6-6. The results presented in these two tables show that the reactivity is significantly reduced from the non-clad evaluation with all evaluated cases below the USL of 0.9338 and within the evaluated energy of average lethargy causing fission (EALCF) range (maximum reactivity case has an EALCF of 0.168 eV). As such, for a package containing a fully loaded basket of damaged EFN rods, the contents must include a minimum of 0.02 cm (or 30%) of cladding material attached to the fuel meat to be qualified for shipment.
6.3.2 Material properties The applicant provided material properties for the packaging design in the bills of materials in the various drawings. The body of the caddy is made of aluminum alloy as shown in drawing 315-40-175. The material composition of the EFN rods, Moly targets, and Booster rods are provided in SAR Table 6.7.6-1. The applicant used the material properties as specified in its criticality safety analysis models.
The staff reviewed the material properties used in the criticality safety analysis models and finds that the material properties are consistent with the specifications. On this basis, the staff finds the material properties used in the models are appropriate and acceptable.
6.3.3 Computer Code Benchmark Evaluations The applicant performed benchmarking analyses for the computer code and cross section library. The applicant selected 169 critical experiments, 18 of them are with U-235 enrichment of around 79% and hexagonal geometry, 47 of them are rods with U-235 enrichment of around 79% and square geometry, 97 are plates at 93% enrichment in square arrays, six of them are rods at 17% enrichment with hexagonal arrays and one 360 plate array at 19.77% enrichment.
The Booster rods, EFN rods, and Moly targets are all at 91% enrichment, in solid rod shape, and they will form approximate hexagonal geometry arrays when they are loaded into the caddies, it appears that the majority of the selected critical experiments are not appropriate for this application, particularly the plate shape fuel in a square array and the low enrichment fuel experiments. As such, the staff was concerned that bias and bias uncertainty determined using the selected critical experiments may be skewed.
To address the staffs concern, the applicant performed a trending analysis without the critical experiments that have low enrichments (ML20254A327, email from NAC on August 24, 2020).
The result demonstrated that the keff vs enrichment trending curve is improved slightly, i.e., a reduced bias in keff as a function of enrichment. This is expected because the data as shown in Figure 6.5.6-1 are highly concentrated in two polar clusters. With this new trending in bias, the applicant demonstrated that the keff value remains below the USL. The staff reviewed the new calculation and result and finds the calculations are correct and the results are acceptable.
The applicant provided, in Chapter 6 of the revised SAR, a criticality safety evaluation for the package with the requested content. The staff reviewed these analyses to verify whether these designs meet the transportation package criticality safety requirements of 10 CFR Part 71.
13 6.3.4 Confirmatory Analyses The staff performed confirmatory analysis using the fuel and packaging design parameters. The staff used the CSAS6 sequence of the SCALE 6.1 computer code package and ENDF/B-VII continue energy cross section library. The result of the staffs calculation confirmed the result presented by the applicant in its application. On this basis, the staff finds that applicants criticality safety analyses are reliable and acceptable.
6.4 Conclusion The staff reviewed the criticality safety analyses for the NAC-LWT EFN, Moly targets, or Booster fuel packages presented in the revised SAR. The staff also performed confirmatory analyses for the most reactive configuration using CSAS6 module of the SCALE 6.1 code system with the continuous energy cross section library.
Based on the results of its review and analyses, the staff concludes that the applicant has demonstrated with reasonable assurance that Model No. NAC-LWT package loaded with the EFN, Moly targets, or Booster fuel meets the criticality safety requirements of 10 CFR Part 71 with the following condition:
- For a package with a basket that is fully loaded with EFN rods, a minimum of 0.02 cm thick cladding layer around the fuel meat must be present in the damaged fuel.
7.0 MATERIALS EVALUATION The objective of the materials evaluation is to verify that the applicant has adequately evaluated the performance of the package (packaging together with contents) and demonstrated that the performance of the materials used to fabricate the package meets the regulatory requirements of 10 CFR Part 71, Packaging and Transportation of Radioactive Material.
7.1 Drawing, Weld, Materials Properties, Thermal and Radiation Effects The primary additional materials are stainless steel and aluminum. Both were used previously in compliance with standard Codes (e.g., ASTM). The staff considered the temperature limit for aluminum (less than 200°C) to prevent softening of the material. The applicant stated that temperature(s), with the addition of new package contents, do not reach this temperature limit.
As a result, the seal and O-ring for containment will remain intact. Therefore, the staff finds the thermal stability of component(s) acceptable. The staff reviewed the potential effects of radiation on seal and O-ring stability. The radiation strength did not reach the radiation limit with the addition of new package contents. Therefore, the staff finds the radiation stability of component(s) is acceptable.
7.2 Content Integrity, Damaged Fuel The applicant credited only a limited amount of cladding integrity for full basket/cask loads of EFN rods. Therefore, there are no cladding damage limits except for full basket/cask loads of EFN rods which require the equivalent of 30% clad (fueled surface area). Small fragmented rods/targets require the use of the NRU/NRX caddy plug. Larger rod segments are retained axially within the caddy by the NRU/NRX basket tube and basket lid structure. The staff finds that the cladding integrity credit is acceptable based on complying with the staffs other functional requirements (e.g., shielding) for the transport package.
14 7.3 Corrosion and Chemical Reactions, Drying Adequacy The applicant presented Vacuum Drying System (VDS) procedures. The procedure includes a step to verify that the cavity has no free water by measuring the cavity pressure. In this pressure range of 10 mbar, the staff determined that the amount of hydrogen generated by water radiolysis is well below the ignition point1 (Jung, et al., 2013). Also, the applicant will conduct a helium leak test of the closure lid containment O-ring. Therefore, the staff finds that the drying procedures used are acceptable. Based on this, the staff finds that there will be no corrosion or chemical reactions among components.
7.4 Evaluation Findings
The staff has reviewed the package design description and concludes that the contents of the application meet the requirements of 10 CFR 71.31, 71.33, and 71.35. The staff has previously reviewed the codes and standards used in package design and finds that they are acceptable.
To the maximum credible extent, the applicant complied with the vacuum drying process in the ASTM Standard Guide for Drying Behavior of Spent Nuclear Fuel (ASTM C1553-08). 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.
The effects of radiation or temperature resulting from the new contents on materials were also evaluated. The staff confirmed that any changes in gamma radiation and temperature will have no significant effect on metals and seals.
Based on the review of the statements and representations in the application, the staff finds that the applicant adequately described and evaluated the materials performance of the NAC-LWT package, and they are acceptable. Therefore, the staff concludes that there is reasonable assurance that the NAC-LWT package meets the containment requirements of 10 CFR 71.17.
8.0 PACKAGE OPERATIONS The purpose of the package operations evaluation is to verify that the proposed changes to the operating controls and procedures of the transport package continue to meet the requirements of 10 CFR Part 71.
SAR Chapter 7 provides procedures for package loading, unloading, and preparation of the empty package for transport. SAR Section 7.1.15 provides revised operating procedures for loading the Dry Loading of EFN Rods, Moly Targets and Booster Rods Into the NAC-LWT package.
The staff reviewed the Operating Procedures in SAR Chapter 7 to verify that the package will be operated in a manner that is consistent with its design evaluation. Based on its evaluation, the staff concludes that the combination of the engineered safety features and the operating procedures provide adequate measures and reasonable assurance for safe operation of the proposed dry loading of EFN Rods, Moly Targets, and Booster rods fuel in accordance with 10 CFR 71. Further, the CoC is conditioned such that the package must be prepared for 1 Jung et al., Extended Storage and Transportation: Evaluation of Drying Adequacy, NRC ADAMS Accession No. ML13169A039, 2013.
15 shipment and operated in accordance with the Operating Procedures specified in SAR Chapter 7.
CONDITIONS The following changes have been made to the certificate:
Condition No. 5(a)(3)(ii), Drawings, was updated to reflect the latest revision (revision 2) of drawing No. LWT 315-40-175, (Sheets 1 - 2), Caddy Assembly, NRU/NRX.
Condition No. 5(b)(1)(xxii), has been added to specify parameter limits on the new contents.
Condition No. 5(b)(2)(xx), has been edited to specify that the caddy plug shown in drawing No.
LWT 315-40-175 is not required for NRU/NRX fuel shipments.
Condition No. 5(b)(2)(xxiii), has been added to specify the maximum quantities allowed for the newly approved contents. An additional condition has been included in this condition to specify a minimum of 0.02 cm thick cladding layer around the fuel meat must be present when transporting a basket that is fully loaded with damaged EFN fuel.
Condition No. 5(c), has been edited to include the CSI for the new contents.
Condition No. 20, has been edited to specify the termination date of the previous revision of the certificate (revision 69).
The references section has been updated to include this application supplement.
CONCLUSION Based on the statements and representations in the application, as supplemented, and the conditions listed above, the staff concludes that the Model No. NAC-LWT package design has been adequately described and evaluated, and that these changes do not affect the ability of the package to meet the requirements of 10 CFR Part 71.
Issued with CoC No. 9225, Revision No. 70.