NL-24-0199, Request for Specific Exemption
| ML24177A217 | |
| Person / Time | |
|---|---|
| Site: | 07200036, Holtec |
| Issue date: | 06/25/2024 |
| From: | Coleman J Southern Nuclear Operating Co |
| To: | Office of Nuclear Material Safety and Safeguards, Document Control Desk |
| References | |
| NL-24-0199 | |
| Download: ML24177A217 (1) | |
Text
JI!. Southern Nuclear June 25, 2024 Docket Nos.
72-36 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk, Director, Division of Fuel Management Regulatory Affairs Office of Nuclear Material Safety and Safeguards Washington, D. C. 20555-0001 Ladies and Gentlemen:
Edwin I. Hatch Nuclear Plant Units 1 and 2 Request for Specific Exemption 3535 Colonnade Parkway Birmingham, AL 35243 205 992 5000 NL-24-0199 10 CFR 72.7 In accordance with 10 CFR 72.7, Southern Nuclear Operating Company (SNC) requests an exemption from certain requirements in 10 CFR 72.212 and 10 CFR 72.214 for the Edwin I. Hatch Nuclear Plant Independent Spent Fuel Storage Installation. Specifically, an exemption is requested for the use of Holtec 68M Multi-Purpose Canisters (MPCs) with an unapproved Continuous Basket Shim (CBS) design where the terms, conditions, and specifications in the Certificate of Compliance No. 1014, Amendment 11 are not met.
Details supporting the request for exemption are provided in the enclosure to this letter.
Approval of this exemption is requested within six months of the date of this letter.
This letter contains no regulatory commitments. If you have any questions, please contact Ryan Joyce at 205.992.6468.
Respectfully submitted,
~ ~
~an Regulatory Affairs Director Southern Nuclear Operating Company
Enclosure:
Exemption - Holtec CBS Design cc:
Regional Administrator, Region II NRR Project Manager - Hatch Senior Resident Inspector - Hatch RTYPE: PP1.006
Edwin I. Hatch Nuclear Plant Units 1 and 2 Request for Specific Exemption Enclosure Exemption - Holtec CBS Design
Enclosure to NL-24-0199 Exemption - Holtec CBS Design I. Description Southern Nuclear Operating Company (SNC) is authorized to operate the Edwin I. Hatch Nuclear Plant (Hatch) under 10 CFR 50 and holds a 10 CFR 72 general license for storage of spent fuel at the Hatch Independent Spent Fuel Storage Installation (ISFSI) consistent with 10 CFR 72, Subpart K.
The Holtec International Inc., (Holtec) HI-STORM 100 dry cask storage system is designed to store spent fuel assemblies for ISFSI deployment. The system is listed in 10 CFR 72.214 as Certificate of Compliance (CoC) Number 72-1014 (Reference 1 ). In accordance with 10 CFR 72.210, under the terms of its general license, SNC stores spent fuel at the Hatch ISFSI using the HI-STORM 100 dry cask storage system in accordance with CoC No. 72-1014, Amendment 11, Holtec FSAR Hl-2002444 Rev. 16.1 (Reference 2), and Hatch 10 CFR 72.212 Report Rev. 27 (Reference 3).
Pursuant to 10 CFR 72.7, "Specific Exemptions," SNC requests an exemption from the requirements of 10 CFR 72.212(a)(2), 10 CFR 72.212(b)(3), 10 CFR 72.212(b)(5)(i), 10 CFR 72.212(b)(11 ), and 10 CFR 72.214 for the Hatch ISFSI. Specifically, an exemption is requested for the Holtec 68M Multi-Purpose Canisters (MPCs) with a Continuous Basket Shim (CBS) design where the terms, conditions, and specifications in the CoC No. 1014, Amendment 11 are not met.
If approved, the exemption would allow SNC to use MPC-68Ms with the CBS design in the HI-STORM 100 storage system. Specifically, the requested exemption will allow continued storage of loaded storage casks with the CBS design, as listed in Table 1. Additionally, the exemption will allow future loading of MPC-68Ms with the CBS design, currently scheduled for 2025, as listed in Table 2.
Table 1: List of MPC-68Ms with the CBS Design Currently Loaded MPC Serial#
ISFSI Location 799 1F18-B006QA 800 1F18-B006QB 801 1F18-B006QC Table 2: List of MPC-68Ms with the CBS Design Scheduled for Future Loading MPC Serial#
847 848 849 850 851 The exemption is needed because the NRC issued violations (Reference 4) stating that the Holtec 72.48 evaluation for the CBS design was in error and should have concluded that NRC approval was necessary in the form of an amendment to the HI-STORM 100 CoC 72-1014. Specifically, the NRC determined that the non-mechanistic tip-over analysis performed for the CBS design included changes to elements of a previously approved method of evaluation (MOE) as well as the use of a new or different MOE, thus requiring prior NRC E - 1
Enclosure to NL-24-0199 Exemption - Holtec CBS Design approval. SNC loaded three MPC-68Ms with the CBS design prior to the issuance of the Holtec violations and has already purchased and received five MPC-68Ms with the CBS design for future loading. Because Holtec is required to submit a CoC amendment request to the NRC to seek approval of the CBS variant design, such a process will not be completed in time to address the near-term issues of compliance for the casks already loaded and to inform decisions for the future loading of casks, five of which have already been purchased and received. Therefore, SNC requests approval of this exemption in the interim.
II. Background Hatch currently uses the HI-STORM 100 System under CoC No. 72-1014, Amendment No.
11 for dry storage of spent nuclear fuel in MPC-68M canisters. Design features and contents must meet the HI-STORM 100 CoC requirements, operations must occur within the Limiting Conditions for Operations (LCOs), and the site must demonstrate that it meets all site-specific parameters.
Holtec is the designer and manufacturer of the HI-STORM 100 system. Holtec developed a CBS variant of the design for the MPC-68M. The CBS basket, like the previously certified MPC-68M, is made of Metamic-HT, and has the same geometric dimensions and assembly configuration. The new variant contains external shims which are between the basket periphery and the MPC shell, which eliminates the previously used friction-stir-weld seams joining the raw edges of the basket panels.
The CBS variant calls for longer panels of Metamic-HT. The projections of the Metamic-HT panels provide an effective means to secure the shims to the basket using a set of stainless-steel fasteners. These fasteners do not carry any primary loads, except for the dead weight of the shims when the MPC is oriented vertically, which generates minimal stress in the fasteners. The fasteners are made of Alloy X stainless material, which is a pre-approved material for the MPCs in the HI-STORM 100 system. Affixing the shim to the basket has the added benefit of improving the heat transfer path from the stored fuel to the external surface of the MPC.
Holtec performed a non-mechanistic tip-over analysis, with favorable results, and subsequently implemented the CBS design variants under 10 CFR 72.48 which allows licensees to make changes to cask designs without a CoC amendment under certain conditions. However, the NRC issued violations after the CBS design was already in use stating that these design variants required NRC approval through an amendment to the HI-STORM 100 Coe, 72-1014.
A multi-disciplinary NRC team of thermal, criticality, shielding, and structural staff assessed a potential structural failure of the fuel basket during accident conditions for the HI-STORM 100 dry cask storage system to determine the safety significance of these violations. The conclusions were documented and made public in an NRC Safety Determination Memorandum (Reference 5).
Ill. Basis for Approval of Exemption Request In accordance with 10 CFR 72.7, the NRC may grant exemptions that are authorized by law and will not endanger life or property or the common defense and security and are otherwise in the public interest.
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Enclosure to NL-24-0199 Exemption - Holtec CBS Design a) Authorized by Law SNC is requesting an exemption from the provisions in 10 CFR 72 that require compliance with the terms, conditions, and specifications of CoC No. 1014, Amendment No. 11. This exemption would allow SNC to continue to store previously loaded casks and load additional canisters of the MPC-68M with the CBS design at Hatch where the terms, conditions, and specifications in the CoC, are not met. Section 72.7 allows the NRC to grant exemptions from the requirements of 10 CFR 72. This authority to grant exemptions is consistent with the Atomic Energy Act of 1954, as amended, and is not otherwise inconsistent with NRC's regulations or other applicable laws. Additionally, no other law prohibits the activities that would be authorized by the exemption. Therefore, there is no statutory prohibition on the issuance of the requested exemption, and the NRC is authorized to grant the exemption by law.
b) Will not Endanger Life or Property or the Common Defense and Security Issuance of the exemption would not endanger life or property because a tip-over or handling event is administratively controlled, and the containment boundary would be maintained in such an event. SNC relies, in part, on the approach in the NRC's Safety Determination Memorandum. The NRC issued this Safety Determination Memorandum to address whether, with respect to the enforcement action against Holtec regarding the violations, there was any need to take an immediate action for the cask systems that were already loaded with non-compliant basket designs. The Safety Determination Memorandum documents a risk-informed approach concluding that, during the design basis event of a non-mechanistic tip-over, the fuel in the basket in the MPC with CBS design remains in a subcritical condition. In addition, handling procedures used by Hatch comply with CoC No. 72-1014, Amendment 11 Appendix A, Holtec FSAR Hl-2002444 Rev. 16.1, and Hatch 10 CFR 72.212 Report Rev. 27 requirements, including, single-failure-proof lifting mechanisms and lift height restrictions in accordance with applicable codes and standards. Moreover, the combined dose produced by the storage systems on the Hatch ISFSI will not result in annual doses at the ISFSI controlled area boundary in excess of the limits specified in 10 CFR 72.104(a) during normal and anticipated operational occurrences, or in excess of the limits specified in 72.106 during design bases accidents. In the highly unlikely event of a tip-over, any potential fuel damage from a non-mechanistic tip-over event would be localized, the confinement barrier would be maintained, and the shielding material would remain intact. Lastly, the exemption is not related to any aspect of the physical security or defense of the Hatch ISFSI, and therefore, granting the exemption would not result in any potential impacts to common defense and security. A technical justification discussion follows in Section IV that provides additional details demonstrating that the proposed exemption does not endanger life or property or the common defense and security.
c) Otherwise in the Public Interest If approved, the exemption request would allow SNC to use MPC-68Ms with the CBS design in the HI-STORM 100 storage system. Specifically, the requested exemption will allow continued storage of three casks already loaded with the CBS design. Additionally, the exemption will allow future loading of five MPC-68Ms with the CBS design that have already been purchased and received by Plant Hatch.
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Enclosure to NL-24-0199 Exemption - Holtec CBS Design The exemption would serve the public's interest because leaving the three loaded casks with the CBS design undisturbed would ensure that the spent fuel remains in its current, inherently safe, passive system without taking on any additional risk of dispositioning the spent fuel. This exemption would also allow upcoming loading campaigns to proceed on schedule to move fuel from the spent fuel pool (SFP) safely into dry storage, which prevents a reduction in the margin to capacity in the SFP. Each spent fuel bundle adds to the decay heat removal demand on the SFP cooling system. Increased inventory in the SFP could also result in additional fuel moves, and therefore, increase worker doses and the potential for fuel handling accidents that accompany increased fuel handling operations. In addition, moving fuel from the SFP aids in maintaining the ability to offload fuel safely and efficiently from the reactor in the event offloading becomes necessary, thus improving safe reactor operation.
Cask Loading campaigns are budgeted, planned, and scheduled years in advance of the actual performance. Campaigns are scheduled based on the availability of the specialized work force and equipment. These specialty resources support multiple competing activities and priorities. The available windows to complete cask loading campaigns are limited and delays have a cascading impact on other scheduled activities. Use of the already-purchased MPCs allows SNC to continue its loading campaign schedule and plans without introducing unnecessary costs and logistical concerns affecting these specialized resources and equipment.
In conclusion, maintaining adequate SFP margin ensures operational flexibility necessary for sustained safe and efficient operation. Negative logistical and financial impacts outweigh any potential positive impacts of delaying the use of the already-purchased CBS MPCs. Approval of the exemption request supports the continued safe, efficient, and cost-effective operation of Plant Hatch. Therefore, approving the exemption request is in the public interest.
IV. Technical Justification In the NRC's Safety Determination Memorandum, the NRC evaluated the safety impact of loading and storage of the CBS MPCs without an NRC approved tip-over analysis. This evaluation assumed basket failure due to the non-mechanistic tip-over event but "[... ]
concluded that the consequences of a basket failure have a very low safety significance provided the confinement boundary is maintained and the fuel is kept in a dry storage condition. As these conditions are demonstrated to be met during a tip-over event, the staff determined that there was no need to take an immediate action with respect to loaded... HI-STORM 100 dry cask storage systems with the CBS fuel basket designs."
The CBS MPC-68M basket assembly features the same fuel storage cavity configuration as the certified standard MPC-68M configuration. The way the inter-panel connectivity is established and the way the aluminum shims are held in place outside the basket is improved. This improvement is made such that the loose aluminum shims around the basket periphery used in the original MPC-68M design are replaced with integrated aluminum shims that are mechanically fastened (bolted) to basket panel extensions that protrude into the annular region between the basket and the enclosure vessel. The addition of these bolted shims eliminates the need for the friction-stir-weld located in the external periphery of the Metamic-HT fuel basket. All other fuel basket design characteristics are unchanged by using the CBS variant.
The primary design functions of the basket shims are to facilitate heat transfer away from the fuel basket and spent fuel assemblies and to provide lateral support of the fuel basket during E-4
Enclosure to NL-24-0199 Exemption - Holtec CBS Design the non-mechanistic tip-over accident. The primary design functions of the Metamic-HT fuel basket itself are to provide structural support of the fuel assemblies and perform the criticality control design function for the system. The MPC enclosure vessel provides structural support of the fuel basket, assisting in the heat transfer process, and acts as the confinement boundary for the system.
Thermal In the NRC's Safety Determination Memorandum, the staff used a structural evaluation to confirm there was no loss of confinement integrity and to consider the thermal impacts of a postulated non-mechanistic tip-over accident. The staff considered fuel debris that might cause hot spots near the bottom of the MPC (on its side from a postulated tip-over). The staff noted that there might be some local increase in temperatures, but no temperatures that would challenge the MPC confinement based on its stainless-steel material. The thermal review concluded, "[... ] the containment will remain intact, and therefore the non-mechanistic tip-over accident condition does not result in significant safety consequences for the... HI-STORM 100 storage systems."
Structural and Confinement In the NRC's Safety Determination Memorandum, the staff concluded that the MPC, which is the confinement boundary, maintains its structural integrity during a tip-over event, and therefore no water can enter the interior of the MPC during accident conditions. The staff also acknowledged that, consistent with the Holtec FSAR, "there is no requirement to demonstrate structural integrity of the cladding." Retrievability requirements continue to be met because the MPC maintains its structural integrity.
The staff also considered natural phenomena hazards (NPH) and concluded, "[... ]the structural failure of the fuel baskets during these NPH accident conditions is unlikely."
However, even if a basket failure occurs, the criticality evaluation demonstrates that the fuel will be maintained subcritical. "Therefore, the staff concludes that the NPH accident conditions do not result in significant safety consequences for the... HI-STORM 100 storage systems with the CBS fuel basket designs."
Finally, in the structural assessment, the staff considered the handling operations typically used for the dry cask storage systems. The NRC concluded that "[... ] a similar conclusion to that for the non-mechanistic tip-over can be made for dry cask handling accident conditions.
The MPC confinement boundary maintains its structural integrity and no water can enter the interior of the MPC." Handling procedures used by Hatch comply with CoC No. 72-1014, Amendment 11 Appendix A, Holtec FSAR Hl-2002444 Rev. 16.1, and Hatch 10 CFR 72.212 Report Rev. 27 requirements, including, single-failure-proof lifting mechanisms and lift height restrictions in accordance with applicable codes and standards.
Shielding and Criticality In the NRC's Safety Determination Memorandum, the staff assessed the potential for a criticality incident under a complete failure of the basket, which could result in basket material and fuel debris at the bottom of the MPC. The staff relied on documented studies related to the enrichment of uranium needed to achieve criticality in an unmoderated, unreflected environment. The allowable contents have enrichment limits well below that in the studies and would also still have the neutron-absorbing material present. Therefore, the staff E-5
Enclosure to NL-24-0199 Exemption - Holtec CBS Design concluded "[... ] there is no criticality safety concern for the CBS basket variants for... the HI-STORM 100... casks under the assumption of fuel basket failure."
The staff reviewed the shielding impact and concluded,"[... ] as the damage is localized and the vast majority of the shielding material remains intact, the effect on the dose at the site boundary is negligible. Therefore, the site boundary doses for the loaded HI-STORM FW overpack for accident conditions are equivalent to the normal condition doses, which meet the Section 72.106 radiation dose limits." This statement is applicable because the bases for the FW system also apply to the HI-STORM 100 system.
Holtec performed a review of the dose calculation (Hl-2104770R4) for Hatch to assess the impact of the change to the MPC-68M with the CBS design. While the CBS design shims have slightly less material, the total mass of the cask, basket, and MPC materials used to shield the fuel is not changed significantly. Further, the basket supports were not modelled in the dose calculations, so there was no impact to the shielding calculations. Therefore, the Hatch dose calculations continue to be within the regulatory limits of 10 CFR 72.104 and 10 CFR 72.106.
Materials There is one change to the materials in the CBS variant of the basket compared to the original design of the MPC and basket - ASTM B221 Grade 6063 aluminum as an option for basket shim fabrication, in addition to the existing ASTM B221 Grade 2219 aluminum. Holtec determined ASTM B221 Grade 6063 aluminum improves thermal efficiency and safety margins due to the greater thermal conductivity of ASTM B221 Grade 6063 aluminum compared to ASTM B221 Grade 2219 aluminum. Therefore, there is no new material-related safety concern.
Safety Conclusion The non-mechanistic tip-over analysis is bounded by the analysis summarized above which assumed structural basket failure during the postulated event. The analysis demonstrates that structural failure of the CBS basket resulting from a non-mechanistic tip-over event would not endanger life or property or the common defense and security.
V. Environmental Consideration SNC has evaluated the environmental impacts of the proposed exemption request and has determined that the proposed action has no potentially significant impacts on the quality of the human environment. The proposed action does not require any Federal permits, licenses, approvals, or other entitlements.
a) Environmental Impacts of the Proposed Action The Hatch ISFSI is a radiologically controlled area on the plant site. The area considered for potential environmental impact because of this exemption request is the area in and surrounding the ISFSI. The interaction of a loaded HI-STORM 100 dry cask storage system with the environment is through its thermal, shielding, and confinement design functions, which are maintained for the MPCs with the CBS design. In the NRC's Safety Determination Memorandum, the staff concluded, based on the structural analysis review, that the cask confinement boundary function is maintained during the non-mechanistic tip-over accident E-6
Enclosure to NL-24-0199 Exemption - Holtec CBS Design event, and therefore the staff's thermal assessment assumed that there is no loss of confinement integrity.
The change associated with the CBS basket design would not result in any gaseous, liquid, or solid effluents (radiological or non-radiological), radiological exposures (worker or member of the public) or land disturbances that differ from the environmental impacts evaluated in the environmental assessment supporting the CoC 1014, Amendment 11. Therefore, approval of the requested exemption has no impact on the environment.
b) Alternatives to the Proposed Action In addition to the proposed exemption request, alternative action has been considered.
Specifically, the three loaded CBS MPCs could alternatively be unloaded and re-loaded into the older design MPC-68M canisters. This alternative action would result in increased safety risk and increased radiation dose to workers. In addition, future loading campaigns would need to be delayed until older design canisters can be fabricated and delivered to site. Not allowing the planned loadings could affect SNC's ability to manage SFP capacity, reactor fuel offloading, and refueling. It could also negatively impact SNC's ability to manage specialized personnel resources and equipment.
A no-action alternative has been considered, i.e., not submitting an exemption request and awaiting approval by the NRC. Not allowing the use of already-purchased casks would adversely affect SNC's ability to manage SFP capacity, reactor fuel offloading, and refueling.
c) Environmental Conclusion As a result of the environmental assessment, the continued storage and future use of MPC-68Ms with the CBS design at Hatch is in the public interest in that it avoids unnecessary additional operations and incurred dose that would result from the alternative to the proposed action.
VII. Conclusion The HI-STORM 100 system with the MPC-68Ms with the CBS design is capable of performing required safety functions and is capable of mitigating the effects of design basis accidents. Therefore, use of Holtec MPC-68Ms with the CBS design where the terms, conditions, and specifications in the CoC No. 1014, Amendment 11 are not met does not present a threat to public and environmental safety.
SNC has reviewed the requirements in 10 CFR 72 and determined that an exemption to certain requirements in 72.212 and 72.214 are necessary. This exemption request would allow the continued storage and future loading of the already-purchased Holtec HI-STORM 100 CBS MPC systems. The exemption provided herein meets the requirements of 10 CFR 72.7.
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Enclosure to NL-24-0199 Exemption - Holtec CBS Design References
- 1. HI-STORM 100 Certificate of Compliance 72-1014 Amendment No. 11 effective date:
February 25, 2019, as corrected ML19343B024); superseded by Renewed Amendment No. 11 effective date: August 2, 2023.
- 2. HI-STORM 100 Final Safety Analysis Report, Revision 11.1
- 3. Edwin I. Hatch Nuclear Plant Independent Spent Fuel Storage Installation 10 CFR 72.212 Report, Revision 27.
- 4. EA-23-044: Holtec International, INC. - Notice of Violation; The U.S. Nuclear Regulatory Commission Inspection Report No. 07201014/2022-201, ML24016A190
- 5. NRC Memorandum, "Safety Determination of a Potential Structural Failure of the Fuel Basket During Accident Conditions for the HI-STORM 100 and HI-STORM Flood/Wind Dry Cask Storage Systems," dated January 31, 2024, ML24018A085 E-8