RS-24-017, Request for Exemption from Certain Requirements of 10 CFR 72.212 and 10 CFR 72.214 for Dresden Nuclear Power Station – Holtec MPC-68MCBS
| ML24054A031 | |
| Person / Time | |
|---|---|
| Site: | Dresden  |
| Issue date: | 02/23/2024 |
| From: | David Gudger Constellation Energy Generation |
| To: | Office of Nuclear Material Safety and Safeguards, Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| RS-24-017 | |
| Download: ML24054A031 (1) | |
Text
200 Exelon Way Kennett Square, PA 19348 www.constellation.com 10 CFR 72.7 RS-24-017 February 23, 2024 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, D.C. 20555-0001 Dresden Nuclear Power Station Unit 2 and 3 Renewed Facility Operating Licensee Nos. DPR-19 and DPR-25 NRC Docket Nos. 50-237 and 50-249
Subject:
Request for Exemption from Certain Requirements of 10 CFR 72.212 and 10 CFR 72.214 For Dresden Nuclear Power Station - Holtec MPC-68MCBS Pursuant to 10 CFR 72.7, "Specific Exemptions," CEG 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 Dresden ISFSI. Specifically, an exemption is requested for the Holtec 68M Multi-Purpose Canisters with a Continuous Basket Shim (MPC-68MCBS) design basis condition requiring analysis of a postulated non-mechanistic tip-over event using NRC approved methods of evaluation (MOE).
The requested exemption will allow continued storage of loaded storage casks with MPC-68MCBS canisters, as listed in Table 1. Additionally, the exemption will allow future loading of MPC-68MCBS canisters, as listed in Table 2.
The exemption is needed because although Holtec performed a non-mechanistic tip-over analysis with favorable results and subsequently implemented the CBS design variant under 10 CFR 72.48, the NRC issued Severity Level IV violations (Reference 2) that indicated that the design variant should have resulted in 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 approval. It is unknown when an NRC approved MOE for non-mechanistic tip-over analysis of the MPC-68MCBS would be expected. As such, CEG requests approval of this exemption request by April 18, 2024, to support the next loading campaign to include MPC-68MCBS canisters which is scheduled to begin on April 22, 2024.
The attachment to this letter provides the justification and rationale for the exemption request.
Dresden Nuclear Power Station 10 CFR Part 72 Exemption Request February 23, 2024 Page 2 of 2 There are no regulatory commitments contained in this submittal.
If you have any questions or require additional information, please contact Christian Williams at (267) 533-5724.
Respectfully, David T. Gudger Sr. Manager, Licensing Constellation Energy Generation, LLC
Attachment:
Constellation Request for Specific Exemption from Certain Requirements of 10 CFR 72.212 and 10 CFR 72.214 for Dresden Nuclear Power Station cc:
w/ Attachments Regional Administrator - NRC Region III Resident/Senior Resident Inspector-Dresden Nuclear Power Station NRC Project Manager - Dresden Nuclear Power Station Illinois Emergency Management Agency - Division of Nuclear Safety
Attachment CONSTELLATION REQUEST FOR SPECIFIC EXEMPTION FROM CERTAIN REQUIREMENTS OF 10 CFR 72.212 and 10 CFR 72.214 FOR DRESDEN NUCLEAR POWER STATION
CONSTELLATION REQUEST FOR SPECIFIC EXEMPTION FROM CERTAIN REQUIREMENTS OF 10 CFR 72.212 and 10 CFR 72.214 FOR DRESDEN NUCLEAR POWER STATION Page 1 of 8 I.
Description The Holtec International Inc., (Holtec) HI-STORM 100 dry cask storage system is designed to hold, and store spent fuel assemblies for independent spent fuel storage installation (ISFSI) deployment. The system is listed in 10 CFR 72.214 as Certificate of Compliance (CoC) Number 72-1014 (Reference 1). This system is used by Constellation Energy Generation, LLC (CEG) at Dresden Nuclear Power Station (Dresden) in accordance with 10 CFR 72.210, General license issued.
Pursuant to 10 CFR 72.7, Specific Exemptions, CEG 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 Dresden ISFSI. Specifically, an exemption is requested for the Holtec 68M Multi-Purpose Canisters with a Continuous Basket Shim (MPC-68MCBS) design basis condition requiring analysis of a postulated non-mechanistic tip-over event using NRC approved methods of evaluation (MOE).
The requested exemption will allow continued storage of loaded storage casks with MPC-68MCBS canisters, as listed in Table 1. Additionally, the exemption will allow future loading of MPC-68MCBS canisters, as listed in Table 2.
The exemption is needed because although Holtec performed a non-mechanistic tip-over analysis with favorable results and subsequently implemented the CBS design variant under 10 CFR 72.48, the NRC issued Severity Level IV violations (Reference 2) that indicated that the design variant should have resulted in 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 approval. It is unknown when an NRC approved MOE for non-mechanistic tip-over analysis of the MPC-68MCBS would be expected. As such, CEG requests approval of this exemption request by April 18, 2024, to support the next loading campaign to include MPC-68MCBS canisters which is scheduled to begin on April 22, 2024.
The technical justification supporting continued use of the MPC-68MCBS is provided in the following sections.
CONSTELLATION REQUEST FOR SPECIFIC EXEMPTION FROM CERTAIN REQUIREMENTS OF 10 CFR 72.212 and 10 CFR 72.214 FOR DRESDEN NUCLEAR POWER STATION Page 2 of 8 Table 1: List of Affected Canisters Currently Loaded HI-STORM Serial Number MPC Serial Number Location on West ISFSI Pad Date Placed in Storage 100-1520 68-820 82 10 May 2023 100-1521 68-821 67 18 May 2023 100-1522 68-822 68 24 May 2023 100-1523 68-819 53 02 June 2023 Table 2: List of Affected Canisters Scheduled for Loading HI-STORM Serial Number MPC Serial Number Targeted Location on West ISFSI Pad Date Targeted to be Placed in Storage 100-1717 68-837 28 17 May 2024 100-1718 68-838 41 10 March 2025 100-1719 68-839 42 17 March 2025 100-1720 68-840 54 24 March 2025 100-TBD TBD 55 31 March 2025 II.
Background
Dresden currently utilizes the HI-STORM 100 System under CoC No. 72-1014, Amendment No.
8, Revision 1 for dry storage of spent nuclear fuel in specific Multi-Purpose Canisters (MPC)
(i.e., MPC-68M canisters). All design features and contents must fully meet the HI-STORM 100 CoC, operations must occur within the Limiting Conditions for Operations (LCOs), and the site must demonstrate that it meets all site-specific parameters.
Holtec International is the designer and manufacturer of the HI-STORM 100 system. Holtec developed a variant of the design for the MPC-68M known as MPC-68MCBS. The MPC-68MCBS basket, like the previously certified MPC-68M, is made of Metamic-HT, and has the same geometric dimensions and assembly configuration. Improvements implemented through the new variant pertain to the external shims which are between the basket periphery and the MPC shell, and the elimination of the difficult to manufacture friction-stir-weld (FSW) seams joining the raw edges of the basket panels.
The CBS variant calls for longer panels of Metamic-HT. The projections of the Metamic 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. Fixing 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.
CONSTELLATION REQUEST FOR SPECIFIC EXEMPTION FROM CERTAIN REQUIREMENTS OF 10 CFR 72.212 and 10 CFR 72.214 Page 3 of 8 FOR DRESDEN NUCLEAR POWER STATION Holtec performed a non-mechanistic tip-over analysis with favorable results and subsequently implemented the CBS design variants under 10 CFR 72.48. However, the NRC issued Severity Level IV violations (Reference 2) that indicated that these design variants should have resulted in an amendment to the HI-STORM 100 CoC, 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 and HI-STORM Flood/Wind (FW) dry cask storage systems to determine the safety significance of these violations. The conclusions were documented and made public in 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, (Reference 3).
III.
Basis for Approval of Exemption Request In accordance with 10 CFR 72.7, the NRC may, upon application by an interested person or upon its own initiative, grant such exemptions from the requirements of the regulations in this part as it determines authorized by law and will not endanger life or property or the common defense and security and are otherwise in the public interest.
a) Authorized by Law This exemption would allow Dresden to continue to store previously loaded and load additional canisters of the MPC-68MCBS design. The NRC issued 10 CFR 72.7 under the authority granted to it under Section 133 of the Nuclear Waste Policy Act of 1982, as amended, 42 U.S.C. § 10153. Section 72.7 allows the NRC to grant exemptions from the requirements of 10 CFR Part 72. Granting the proposed exemption will not endanger life or property, or the common defense and security, and is otherwise in the public interest.
Therefore, the exemption is authorized by law.
b) Will not Endanger Life or Property or the Common Defense and Security The NRC has performed a safety assessment (Reference 3) to evaluate the loading and storage of the MPC-68MCBS variant without an NRC approved tip-over analysis. This evaluation (detailed below) 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 FW and HI-STORM 100 dry cask storage systems with the continuous basket shim (CBS) fuel basket designs. Based on the NRC safety assessment detailed below and summarized here, the proposed exemption does not endanger life or property or the common defense and security.
CONSTELLATION REQUEST FOR SPECIFIC EXEMPTION FROM CERTAIN REQUIREMENTS OF 10 CFR 72.212 and 10 CFR 72.214 FOR DRESDEN NUCLEAR POWER STATION Page 4 of 8 It is in the publics interest to grant an exemption, since dry storage places the fuel in an inherently safe, passive system, and the exemption would permit the continued storage of already loaded canisters before full compliance. This exemption would also allow upcoming loading campaigns to proceed on time to move fuel into the dry storage condition and maintain the ability to offload fuel from the reactor, thus allowing continued safe reactor operation.
IV.
Technical Justification The MPC-68MCBS basket assembly features the same fuel storage cavity configuration as the certified standard MPC-68M configuration. The manner in which the inter-panel connectivity is established and by which 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 FSW located in the external periphery of the Metamic-HT fuel basket. All other fuel basket design characteristics are unchanged by using the CBS variant.
Regardless of their design, 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 the non-mechanistic tip over accident. The primary design functions of the Metamic-HT fuel basket itself, regardless of shim configuration, 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 The NRC staff used the structural assessment discussed below to confirm there was no loss of confinement integrity and considered 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 FW and HI-STORM 100 storage systems.
Structural and Confinement The hypothetical tip-over accident is the most significant challenge of the structural performance of the basket. The primary safety function is to prevent a criticality event, and as stated below, the criticality assessment determined no safety concerns under hypothetical tip-over including basket failure.
c) Otherwise in the Public Interest
CONSTELLATION REQUEST FOR SPECIFIC EXEMPTION FROM CERTAIN REQUIREMENTS OF 10 CFR 72.212 and 10 CFR 72.214 Page 5 of 8 FOR DRESDEN NUCLEAR POWER STATION The staff assessment (Reference 3) 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 FSAR, there is no requirement to demonstrate structural integrity of the cladding. Retrievability requirements continue to be met since, as stated above, the MPC maintains its 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 below 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 FW and HI-STORM 100 storage systems with the CBS fuel basket designs, (Reference 3).
Finally, the structural assessment considered the handling operations for the dry cask storage systems. The system is either handled with single failure proof devices where a drop is considered non-credible or held to a lift height which has been demonstrated to be acceptable via a drop analysis. The drop analysis shows that there are no significant loads on the basket that would challenge the structural integrity. 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. (Reference 3)
Shielding and Criticality In Reference 3, the NRC 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 concluded [] there is no criticality safety concern for the CBS basket variants for both the HI-STORM 100 and FW casks under the assumption of fuel basket failure.
As documented in Reference 3, the NRC 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 Title 10 of the Code of Federal Regulations (10 CFR) Section 72.106 radiation dose limits. This statement is applicable to the HI-STORM 100 overpack as the bases for the statement also applies to the HI-STORM 100 system.
CONSTELLATION REQUEST FOR SPECIFIC EXEMPTION FROM CERTAIN REQUIREMENTS OF 10 CFR 72.212 and 10 CFR 72.214 Page 6 of 8 FOR DRESDEN NUCLEAR POWER STATION There is no change in the materials used in the CBS variant of the basket compared to the original design of the MPC and basket. Therefore, there is no new material related safety concern.
Safety Conclusion The above analysis demonstrates that structural failure of the CBS basket resulting from a non-mechanistic tip-over event does not endanger life or property or the common defense and security.
As such the safety significance of using an approved non-mechanistic tip-over analysis completed without using NRC approved methods of evaluation, is bounded by the analysis summarized and discussed in this request which assumed structural basket failure during the postulated event.
V. Environmental Consideration The proposed exemption does not meet the eligibility criterion for categorical exclusion for performing an environmental assessment as set forth in 10 CFR 51.22(c)(25) because the exemption does not satisfy the requirement of 10 CFR 51.22(c)(25)(vi). Specifically the request does not involve exemption from any of the following requirements: (A)
Recordkeeping requirements; (B) Reporting requirements; (C) Inspection or surveillance requirements; (D) Equipment servicing or maintenance scheduling requirements; (E)
Education, training, experience, qualification, requalification or other employment suitability requirements; (F) Safeguard plans, and materials control and accounting inventory scheduling requirements; (G) Scheduling requirements; (H) Surety, insurance or indemnity requirements; or (I) Other requirements of an administrative, managerial, or organizational nature.
Dresden has evaluated the environmental impacts of the proposed exemption request and has determined that neither the proposed action nor the alternative to the proposed action will have an adverse impact on the environment. Therefore, neither the proposed action nor the alternative requires any Federal permits, licenses, approvals, or other entitlements.
a) Environmental Impacts of the Proposed Action The Dresden 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 system with the environment is through thermal, shielding, and confinement design functions for the cask system. Based on the safety analysis described above, the following conclusions for the proposed storage of the MPC-68MCBS variant have been verified.
The confinement boundary maintains its structural integrity during accident conditions.
Materials
CONSTELLATION REQUEST FOR SPECIFIC EXEMPTION FROM CERTAIN REQUIREMENTS OF 10 CFR 72.212 and 10 CFR 72.214 FOR DRESDEN NUCLEAR POWER STATION Page 7 of 8 Fuel cladding temperature limits will not challenge NUREG-2215 limits.
Existing radiological evaluations and conclusions for accident conditions in Chapter 5 of the HI-STORM 100 FSAR (Reference 5) remain valid, since, consistent with the above analysis, these evaluations assume localized damage and the majority of the shielding material remains intact.
Further, there are no discussions or analyses in the Dresden Site 72.212 Evaluation report (Reference 4) that would contradict or negate the conclusion made in this request.
There are no gaseous, liquid, or solid effluents (radiological or non-radiological),
radiological exposures (worker or member of the public) or land disturbances associated with the proposed exemption. Therefore, approval of the requested exemption has no impact on the environment.
b) Adverse Environmental Effects Which Cannot be Avoided Should the Exemption be Approved Since there are no environmental impacts associated with approval of this exemption, there are no adverse environmental effects which cannot be avoided should the exemption request be approved.
c) Alternative to the Proposed Action In addition to the proposed exemption request, alternative action has been considered.
Specifically, the existing MPC-68MCBS canister would need to be unloaded and re-loaded into the older design MPC-68M canisters. Future loading campaigns would also need to be delayed until older design canisters can be fabricated and delivered to site.
In addition, the reflooding of the MPCs, removal of fuel assemblies, and replacement into a different MPC would result in additional doses and handling operations with no added safety benefit, since it has been demonstrated that the MPC maintains all its safety functions.
d) Environmental Effects of the Alternatives to the Proposed Action There are no environmental impacts associated with the alternative to the proposed action.
e) Environmental Conclusion As a result of the environmental assessment, the continued storage and future use of MPC-68MCBS at Dresden 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.
CONSTELLATION REQUEST FOR SPECIFIC EXEMPTION FROM CERTAIN REQUIREMENTS OF 10 CFR 72.212 and 10 CFR 72.214 FOR DRESDEN NUCLEAR POWER STATION Page 8 of 8 VI. Conclusion As the safety assessment and environmental review above demonstrate, the HI-STORM 100 system with the MPC-68MCBS canister is capable of performing required safety functions and is capable of mitigating the effects of design basis accidents. Therefore, use of an approved non-mechanistic tip-over analysis completed without using NRC approved methods of evaluation does not present a threat to public and environmental safety.
CEG 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 Holtec HI-STORM 100 MPC-68MCBS systems currently in non-compliance for the term specified in the CoC. The exemption provided herein meets the requirements of 10 CFR 72.7.
References 1
HI-STORM 100 Certificate of Compliance 72-1014 Amendment No. 8, Revision 1, effective 2/16/2016 (ML16041A233) 2 EA-23-044: Holtec International, INC. - Notice of Violation; The U.S. Nuclear Regulatory Commission Inspection Report No. 07201014/2022-201, ML24016A190 3
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 4
Dresden Nuclear Power Station WEST AND SOUTH ISFSI 10 CFR 72.212 Evaluation Report, Revision 15 5
HI-STORM 100 Final Safety Analysis Report, Revision 11.1