ML20139A103
| ML20139A103 | |
| Person / Time | |
|---|---|
| Site: | 07109356 |
| Issue date: | 06/02/2020 |
| From: | John Mckirgan Storage and Transportation Licensing Branch |
| To: | Fowler W NAC International |
| BHWhtie NMSS.DFM/STL 415.6577 | |
| Shared Package | |
| ML20139A101 | List: |
| References | |
| EPID L-2019-LLA-0238 | |
| Download: ML20139A103 (9) | |
Text
SAFETY EVALUATION REPORT Docket No. 71-9356 Model No. MAGNATRAN Package Certificate of Compliance No. 9356 Revision No. 2
SUMMARY
By application dated October 31, 2019, (Agencywide Documents Access and Management System (ADAMS) Accession No. ML19308A203), as supplemented on February 14, 2020 (ADAMS Accession No. ML20054A404), March 12, 2020 (ADAMS Accession No. ML20076C592) and May 8, 2020 (ADAMS) Accession No. ML20136A261), NAC International, Inc., (NAC or the applicant) submitted an application requesting revision of Certificate of Compliance (CoC) No. 9356, for the Model No. MAGNATRAN package. In its application, NAC included revised drawings to incorporate changes made to the canister pursuant to Title 10 of the Code of Federal Regulations 72.48, Changes, Tests, and Experiments during storage for MAGNASTOR canisters; code exceptions to the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel (B&PV) Code; and partial-length non-fuel rods/rodlets loaded in canisters containing damaged and undamaged pressurized-water reactor (PWR).
The application was evaluated against the regulatory standards in Title 10 of the Code of Federal Regulations (10 CFR) Part 71. NRC staff reviewed the application and its supplements using the guidance in NUREG-1617, Standard Review Plan for Transportation Packages for Spent Nuclear Fuel. Based on the statements and representations in the application, as supplemented, and the conditions listed in the CoC, the staff concludes that the package meets the requirements of 10 CFR Part 71.
EVALUATION 1.0 General Evaluation The MAGNATRAN package is canister-based and is part of a dual-purpose system for the storage and transportation of spent nuclear fuel for transporting the MAGNASTOR transportable storage canister (TSC). The MAGNATRAN packaging includes the package body, upper and lower impact limiters, and TSC. The package body consists of the inner and outer shells, lead, and upper forging, lid, bottom plate, bottom forging and solid neutron shield.
The TSC is constructed of a stainless steel cylindrical shell, bottom-end plate, closure lid, closure ring, and redundant port covers. The TSC confines the fuel basket structure and the spent fuel or the Greater-Than-Class C (GTCC) waste basket liner and GTCC waste. The PWR fuel basket design is an arrangement of 21 square, stainless steel fuel tubes held in a right-circular cylinder configuration by side and corner support weldments that are bolted to the outer fuel tubes. The 21 tubes develop 37 positions within the basket for the PWR spent fuel. The fuel tubes support an enclosed neutron absorber sheet on up to four interior sides of the fuel tube. Each neutron absorber sheet is covered by a thin stainless steel sheet to protect the Enclosure 2
neutron absorber during fuel loading and to keep it in position. The neutron absorber and stainless steel cover are secured to the fuel tube using weld posts distributed across the width and along the length of the fuel tube.
The PWR damaged fuel basket assembly holds up to 37 undamaged PWR fuel assemblies, which may include up to four damaged fuel can locations. A damaged fuel can may be placed in each of the four damaged fuel can basket locations around the corner periphery. The arrangement of tubes and fuel positions is the same as in the standard fuel basket, but the design of each of the four corner support weldments is modified with additional structural support to provide an enlarged position for a damaged fuel can at the outermost corners of the fuel basket. Each damaged fuel can location has a nominal 9.80-inch square opening. A damaged fuel can containing a damaged or an undamaged fuel assembly may be loaded in a damaged fuel can location.
NAC requested several changes to the certificate of compliance including:
- Changes to the canister and basket based on acceptance of non-conformances for canister and baskets at the Zion independent spent fuel storage installation.
- Approval of two exceptions to the ASME B&PV Code, one for the Section III, Division 1, Subsection NG-2300, Charpy V-notch testing direction requirement for carbon steel plate material greater than 0.625 inches thick and the other to the post-heat treatment ultrasonic testing (UT) requirements in Section III, Division 1, Subsection NG-2500, for rolled carbon steel plate material greater than 0.75 inches thick.
- Although submitted on Drawing No. 71160-685, Revision 8, NAC requested that the 37-PWR canister shown in item 99 on the drawing not be authorized for transport at this time, since NAC did not provide all the drawings associated with the revised basket for review by the U.S. Nuclear Regulatory Commission.
- Correction of a typographical error on Table 3, Maximum Initial Enrichment Assembly Undamaged Fuel 15 Year Minimum Cool Time, in the certificate of compliance. The last two columns are for fuel burnup greater than 30 MWd/MTU, not less than 30 MWd/MTU.
- Revision of the certificate contents to authorize partial-length nonfuel rods/rodlets and that partial-length rods are permitted in guide tubes provided the guide tube plug devises are installed.
2.0 Structural Evaluation The purpose of this review is to verify that the structural performance of the MAGNATRAN package has been adequately evaluated for the requested design modifications to meet the requirements in 10 CFR Part 71.
The application provides a structural evaluation of the design modifications for five Zion PWR baskets. The five baskets identified in NAC Non-Compliance Report No. NAC-VNCR 805411-18 are all assembled without the shims installed between the fuel tube mounting bosses and the clamped side and corner support weldments at the mounting holes location. As depicted in NAC licensing Drawing No. 71160-575, Rev. No. 11P, the shims are designed to control sliding of the clamped weldment against the fuel tube mounting boss. To demonstrate the structural capability of the package for the original approval, the applicant performed satisfactorily a structural evaluation of the basket assembly for which shims are prescribed in the finite element analysis (FEA) models to limit a boss-to-weldment relative movement to be less than or equal to 1/16 inch.
Basket Components Structural Integrity The applicant evaluates, in Section 2.12.3 of the application, the no-shim configuration of the Zion PWR baskets for the governing cask side drop tests. Using the same ANSYS FEA approach as presented in Sections 2.6.13 and 2.7.9 of the consolidated safety analysis report (ADAMS Package Accession No. ML19196A079), the applicant considered a 0.5-inch gap, in lieu of the original 0.062-inch gap size between the boss on the outer fuel tubes and the support weldments. The analysis results indicate that large factors of safety (FS) for stress remain for the key basket components comprising of fuel tubes, corner weldments, side weldments and the fuel tube boss-to-support weldment clamped connections for both the free side drop tests associated with the normal conditions of transport and hypothetical accident conditions. Based on these evaluation results, the staff finds the assessment by the applicant acceptable because the PWR basket without the weldment shims continues to satisfy the stress design criteria set forth in ASME B&PV Code,Section III, subsection NG and ASME B&PV Code,Section III, Appendix F.
Basket Geometric Stability Using the analysis method similar to that for the original package approval described in the consolidated safety analysis report, Section 2.12.3 of the application presents an evaluation of geometric stability of the Zion no-shim baskets for the governing, 30-ft side-drop accident condition. To observe the dynamic response of the fuel tube assembly and the corresponding pin/slot interface, the applicant modified slightly the LS-DYNA models for PWR basket presented in Section 2.7.13 of the application. As noted in Figure 2.7.13-5, to simulate the no-shim basket modification, the finite-element blocks depicted in the figure are removed. In NAC Calculation Package No. 71160-2147, Basket Evaluation for PWR Square Pin Stability Without Weldment Shims, to address the effect of sliding of the clamped weldments on basket geometric stability, the removed blocks are sized to limit the relative planar displacement to be equal or less than 0.54 inch between the tube boss and the support weldment.
Following the same evaluation scope for the original approval described in the consolidated safety analysis report, the applicant considered three basket orientations: 0-degree, 22.5-degree and 45-degree with respect to the direction of impacted basket without shims. To demonstrate the capability of the no-shim basket to maintain its geometric stability, all fuel tubes joined by the pin/slot connections at tube corners and support weldments were required to stay engaged after the 30-ft side-drop accident. As such, similar to that for the original approval described in the consolidated safety analysis report, the applicant calculated maximum pin/slot movements to ensure that they were less than the allowable movement of 0.429 inch. For the LS-DYNA calculation of the maximum pin/slot movement under the 30-ft side impact, the applicant first considered one of the two inertia-load implementation approaches used in the original approval. Using the same factor of 1.2, each to scale, both the basket mass and the acceleration response computed in the MAGNATRAN impact-limiter analysis, the applicant performed a generic geometric stability analysis of the no-shim basket. The analyses resulted in the maximum pin/slot movements of 0.171 inch, 0.146 inch, and 0.112 inch for the 0-degree, 22.5-degree and 45-degree basket orientations, respectively, which are well below the allowable pin/slot movement of 0.429 inch and therefore, are acceptable.
The applicant did not perform a LS-DYNA basket analysis, however, using the other more conservative inertia-load implementation approach, which considers only a 40% increase of the basket side drop inertia load. Given that an LS-DYNA analysis was performed in the original approval with the 40% inertia load increase in anticipation of a demonstrable FS greater than 1.4 (1 + 0.40 = 1.4), the applicant, nevertheless, provided an estimate of the maximum pin/slot movements for the no-shim basket. This was done by comparing first the LS-DYNA computed maximum pin/slot movements of 0.122 inch, 0.114 inch and 0.087 inch for the basket with shims
to those of 0.171 inch, 0.146 inch, and 0.112 inch for the basket without shims, respectively, for the three basket orientations. This resulted in selecting the largest pin/slot movement ratio of 1.4 (0.171 inch/0.122 inch = 1.4) as a scale factor to conservatively estimate the maximum pin/slot movements for the no-shim basket.
Table 2.7.13-1 of the application lists the maximum pin/slot movements of 0.161 inch, 0.120 inch, and 0.112 inch by the LS-DYNA analyses for the basket with shims for the for the three basket orientations. By applying a scale factor of 1.4, which is the largest, as discussed in the preceding paragraph to those pin/slot movements, the applicant estimated the maximum pin/slot movements of 0.225 inch, 0.168 inch, and 0.157 inch (0.161 inch x 1.4 = 0.225 inch, 0.120 inch x 1.4 = 0.168 inch, and 0.112 inch x 1.4 = 0.157 inch) for the three basket orientations. As noted by the applicant, those conservatively estimated maximum pin/slot movements are well below the allowable pin/slot movement of 0.429 inch.
The staff reviewed the applicants calculations of the maximum pin/slot movement of 0.225 inch for the PWR no-shim basket, which is significantly less than the allowable movement of 0.429 inch. The staff verified the applicants assessment that all of the pin-slot connections remain engaged for all of the cases for the PWR basket without the weldment shims.
Therefore, the staff has reasonable assurance to conclude that the Zion no-shim basket will maintain its geometric stability during the cask 30-ft side drop accident event.
2.1 Materials Evaluation The staffs materials review evaluated the adequacy of drawing changes, the mechanical properties used in the new structural safety analyses, proposed alternatives to the ASME B&PV Code criteria for the damaged fuel cans and fuel basket plates, and revisions to carbon steel coating criteria.
2.1.1 Drawings The staff reviewed the revisions to the MAGNATRAN design-basis drawings associated with the canister and basket changes. The revisions include clarifications to dimensions and tolerances, and they provide additional flexibility in closure operations of the inner and outer port covers.
The staff reviewed the contents of the drawings with respect to the guidance in NUREG/CR-5502, Engineering Drawings for 10 CFR Part 71 Package Approvals, and confirmed that the drawings provide an adequate description of the materials and fabrication requirements, and, therefore, the staff finds them to be acceptable.
2.1.2 Mechanical Properties The staff reviewed the material mechanical properties used in the structural safety analyses and verified that the properties are consistent with those previously reviewed by the staff for both the MAGNATRAN transportation package and the MAGNASTOR dry storage system. The staff also confirmed that these properties are consistent with those listed in ASME B&PV Code,Section II, Part D. The staff further confirmed the validity of the stress-strain curve for the assumed at-service temperature in the calculations (per ASME B&PV Code,Section VIII, Division 2, Annex 3-D). Therefore, the staff finds the mechanical properties to be acceptable.
2.1.3 Codes and Standards In SAR Section 2.1.4.2, the applicant proposed alternatives to ASME B&PV Code Section III, Division 1, Subsection NG requirements for damaged fuel cans and fuel basket components.
2.1.3.1 Damaged Fuel Can For the damaged fuel can, the application proposed two alternatives. First, rather than procuring the structural materials from an ASME-approved organization per the ASME B&PV Code Article NG-2000, the alternative allows the material to be procured from NAC-approved suppliers. Second, rather than meeting the Article NG-8000 requirements for nameplating, stamping and reporting, the alternative allows the damaged fuel can to be marked and identified to ensure traceability in accordance with the NAC quality assurance program (QA) program.
The staff notes that these ASME B&PV Code alternatives have been previously reviewed and approved by the staff for other fuel basket components in the MAGNATRAN CoC. The applicant proposed to extend the alternatives to the damaged fuel can. The staff notes that the NAC QA program meets the requirements of 10 CFR Part 71, Subpart H, and 10 CFR Part 72, Subpart G. As such, the program includes provisions for assuring that purchased material conforms to the procurement requirements, there is objective evidence of quality furnished by the supplier, and that inspections are conducted at the source supplier. The QA program also must have measures for the identification and control of materials, parts, and components.
Therefore, the staff finds the applicants proposal to use NAC-approved suppliers and to use its QA program for the procurement and control of the damaged fuel can structural materials to be acceptable.
2.1.3.2 Impact Testing of Fuel Basket Assembly Plates The applicant proposed an ASME B&PV Code alternative to allow Charpy impact testing to be optionally performed on basket plate specimens that are oriented parallel (longitudinal) to the plate rolling direction. This differs from Article NG-2322.2(a)(4) of the ASME B&PV Code, which requires that specimens be oriented normal (transverse) to the rolling direction. The transverse orientation is generally considered to yield the lowest impact properties (i.e., ductility and toughness) and thus provides the most conservative measurement to compare against the minimum allowable values in the ASME B&PV Code. The applicant stated that, if the longitudinal specimen option is used, the results of the tests must be scaled down to 67% of the measured values before comparing against the code acceptance criteria.
The staff notes that the ASME B&PV Code alternative was proposed to allow the MAGNATRAN package to be used to transport existing MAGNASTOR transportable storage canisters (TSCs) for which the basket plate material was impact tested by the plate supplier using longitudinal specimens. The staffs review and approval of the exemption requests associated with the storage of those MAGNASTOR TSCs is documented in the associated NRC safety evaluation reports (NRC, 2020).
To justify the code alternative, the applicant provided an analysis to show that scaling the longitudinal specimen results down to 67% of their measured values is a conservative means to bound the results from transverse specimens (NAC, 2020). The applicant reviewed observations on the effects of test specimen orientation on Charpy measurements, including historical test results in the technical literature, test results from the MAGNASTOR TSC basket plates that were the subject of the exemption requests discussed above, and additional testing that was performed on the same steel grades that are used to construct the fuel baskets.
Based on those observations, the applicant concluded that (1) a 67% scaling factor on the Charpy results from longitudinal specimens provides a conservative means to bound results of transverse specimens that conform to the ASME B&PV Code and (2) using that scaling factor, the steel plates that were the subject of the MAGNASTOR exemption requests would meet the
ASME B&PV Code acceptance criteria and could be safety transported in the MAGNATRAN package.
The staff reviewed the applicants justification and the technical literature to determine if there is reasonable assurance that fuel baskets tested in accordance with the proposed ASME B&PV Code alternative will fulfill their structural function under normal and accident conditions.
The staff reviewed the applicants analysis on the effects of Charpy test specimen orientation for the steels grades used in the fuel baskets and verified that the proposed 67% scaling reduction factor for longitudinal specimens is a reasonably conservative means to estimate the results from transverse specimens. In addition, the staff notes that this scaling factor is similar to the reduction recommended in NUREG-0800 for pressure vessel steels (NRC, 2018).
NUREG-0800 recommends that, for steel pressure vessel plates in older power plants that were originally tested with longitudinal Charpy specimens, the results of that testing can be reduced to 65 percent of their value to provide a conservative estimate of properties measured with transverse specimens. Based on the applicants study, the NRC guidance, and the staffs independent review of the technical literature on the effects of specimen orientation, the staff finds the applicants proposed alternative to the ASME B&PV Code to be acceptable. Condition No. 12 was added to the CoC to ensure that the applicant revises the SAR to include the proposed 67% scaling reduction factor.
2.1.3.3 Ultrasonic Testing of Fuel Basket Assembly Plates The applicant proposed an ASME B&PV Code alternative to allow fuel basket plates to be examined with UT either before or after the plate normalizing treatment. This differs from the requirements of Article NG-2537 of the ASME B&PV Code, which states that UT must occur after heat treatment. The staff notes that normalizing of low carbon steels is a final processing step whereby the material is heated to high temperatures to convert the steel to the austenite phase, then air-cooled to form a finer, more uniform microstructure of ferrite and pearlite that yields more favorable properties. UT is performed to confirm the absence of flaws with an unacceptable size.
Similar to the Charpy impact testing code alternative discussed above, the applicants proposal is to allow the MAGNATRAN package to be used to transport existing MAGNASTOR TSCs for which the basket plate material was examined before normalizing. The staffs review and approval of the exemption requests associated with the storage of those MAGNASTOR TSCs is documented in the associated NRC safety evaluation reports (NRC, 2020). As documented in those safety evaluation reports, the applicant provided an assessment by a third-party engineering firm on the implications of performing the flaw examination before normalizing.
That assessment concluded that plates examined prior to normalizing should be acceptable because the normalizing process is not expected to be capable of introducing any indications (i.e., potential flaws) into the material. In addition, the applicant described the re-examination of a small number of plates that were originally examined prior to the normalizing treatment. No flaw indications were identified in that material after normalizing. As a result, the applicant concluded that the UT results prior to normalization are indicative of results that would have been observed had the examination occurred after normalization.
The staff notes that the purpose of the ultrasonic examination of the plates is to identify flaws that arise from plate casting, hot rolling, and heat treatment. The platemaking process has the potential to create a variety of indications, such as porosity, cracks, non-metallic inclusions, and surface overlapping, or laps. Because some heat treatment processes can impart significant
stresses in the steel plate that could causing cracking, Article NG-2537 of the ASME B&PV Code requires that UT occur after the final heat treatment.
In its review of the applicants proposed code alternative, the staff considered the potential for the normalizing treatment to initiate cracking or cause existing cracks to grow. The staff notes that the primary drivers of heat treatment cracking are internal stresses caused by (1) large temperature gradients, such as between a water-quenched plate surface and the hot interior and (2) microstructural transformations that involve large changes in volume that may vary from the surface to the interior of the plate. The staff does not consider these sources of stress to be significant for the subject fuel basket plates. First, the normalizing treatment involves heating the plate and allowing it to cool in air, rather than using a rapid quench with water. This minimizes stresses caused by large temperature gradients. Second, the normalized microstructures of the fuel basket steels are expected to be a mixture of ferrite and pearlite.
The formation of this microstructure on cooling does not involve large changes in volume, such as are characteristic of other microstructures (e.g., martensite formed during rapid quenching of alloy steels).
On the basis of the review above, the staff finds that there is reasonable assurance that the proposed UT prior to normalizing will be capable of verifying that the fuel basket plate materials will be free of defects and that the fuel basket subcomponents will be capable of fulfilling their structural function under all normal, off-normal, and accident conditions. Therefore, the staff finds the applicants proposed alternative to the ASME B&PV Code to be acceptable 2.1.4 Coatings In SAR Section 2.3.1, the applicant revised the description of carbon-steel fuel basket components that are coated using an electroless nickel plating process. The applicant added additional description of the coverage of the coating, stating that some areas may not be completely coated due to (1) coating damage during the basket assembly process and (2) difficulties of coating some areas due to the configuration of the basket. For these uncoated areas, the applicant considered these to be minor and not sufficient to affect the operational and structural performance of the fuel basket. Also, to specifically address potential coating damage, the applicant stated that coating repairs may be performed, and that this is considered a special process that must meet the applicants electroless plating requirements for service condition, appearance, and adhesion.
The staff notes that the fuel basket plate coatings are present to improve the resistance of the steel plates to corrosion and the resultant formation of flammable gases when the basket is immersed in water during fuel loading into the TSC. The staff finds the applicants revisions to the description of the coating coverage to be acceptable because small uncoated areas are not considered to be capable of causing sufficient corrosion during the limited time of water immersion to have an effect on the structural performance of the fuel basket or to generate appreciable flammable hydrogen gas. In addition, the fuel loading procedures for the TSC require monitoring of hydrogen concentration during closure welding operations to ensure that flammable conditions do not exist within the TSC. Finally, the staff finds the applicants proposal to control coating repairs as a special process with specific coating acceptance criteria to be an acceptable means of ensuring that repaired areas will be protected against corrosion.
2.1.5
References:
NAC. Supplement to NACs Request for a Revision to Certificate of Compliance No. 9356 for the NAC MAGNATRAN Transportation Package, Calculation Package No. 71160-WP-020, Revision 3, NAC International Assessment of Longitudinal Versus Transverse Charpy Impact Testing for A537 and A516 Materials, Revision 3. March 12, 2020.
NRC. NUREG-0800, Standard Review Plan for the Review of Safety Analysis Reports for Nuclear Power Plants: LWR Edition - Reactor Coolant System and Connected Systems, Branch Technical Position 5-3, Fracture Toughness Requirements, Rev. 3, 2018.
NRC. Safety Evaluation Reports for Exemption Requests Related to the MAGNASTOR Storage Systems at Zion, Catawba, Kewaunee, and McGuire; ADAMS Accession Nos.
ML20098E712, ML20098D960, ML20098D406, and ML20098C984, respectively. April 2020.
6.0 Criticality Evaluation NAC proposed revising the contents for undamaged and damaged PWR fuel assemblies to include nonfuel hardware consisting of partial-length rods or rodlets in addition to the already approved full-length rods. In its criticality evaluation described in the consolidated safety analysis report, NAC excluded nonfuel hardware in its criticality evaluation as nonfuel hardware would displace water and reduce system reactivity. Therefore, the addition of partial-length rods or rodlets for PWR fuel assemblies, excluding under-burned Westinghouse 15x15 fuel assemblies, is bounded by the analysis in the consolidated safety analysis report. The certificate of compliance requires reactor control cluster assemblies in some locations for under-burned Westinghouse 15x15 fuel assemblies.
CONDITIONS The following changes were made to the Certificate:
Condition 5.(a)(3)(iii) was revised to include the following drawings:
71160-500, Rev. 6P Shipping Configuration, Transport Cask, MAGNATRAN 71160-585, Rev. 13 TSC Assembly, MAGNASTOR 71160-685, Rev. 8 DF, TSC Assembly, MAGNASTOR 71160-785, Rev. 4 GTCC TSC, Assembly, MAGNASTOR Conditions 5.(b)(1)(i) and 5.(b)(1)(ii) were revised to authorize transport of partial-length rods/rodlets in the guide tubes provided guide tube plug devises are installed.
The header for the column Burnup in Table 3, Maximum Initial Enrichment Assembly Undamaged Fuel was revised to correct a typographical error. The header was revised to read (GWd/MTU) > 30, rather than (GWd/MTU) < 30.
Condition Nos. 10 through 12 were added.
Previous Condition Nos. 10 and 11 were renumbered to be Condition Nos. 13 and 14.
The References was updated to include the supplements dated October 31, 2019, February 14, March 12, and May 8, 2020.
CONCLUSION Based on review of the statements and representations in the application, the staff concludes that the structural design changes have been adequately described and evaluated and that the package has adequate structural integrity to meet the requirements of 10 CFR Part 71.
Issued with Certificate of Compliance No. 9356, Revision No. 2.