CNL-24-012, Request for Exemption from Various Part 72 Regulations Resulting from Fuel Basket Design Control Compliance
| ML24059A369 | |
| Person / Time | |
|---|---|
| Site: | Watts Bar, 07201032  |
| Issue date: | 02/28/2024 |
| From: | Hulvey K Tennessee Valley Authority |
| To: | Office of Nuclear Material Safety and Safeguards, Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| CNL-24-012 | |
| Download: ML24059A369 (1) | |
Text
1101 Market Street, Chattanooga, Tennessee 37402
CNL-24-012
February 28, 2024
ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, D.C. 20555-0001
Watts Bar Nuclear Plant, Units 1 and 2 Facility Operating License Nos. NPF-90 and NPF-96 NRC Docket Nos. 50-390, 50-391, and 72-1048
Subject:
Watts Bar Nuclear Plant - Request for Exemption from Various Part 72 Regulations Resulting from Fuel Basket Design Control Compliance
References:
- 1. NRC letter to Holtec, U.S. Nuclear Regulatory Commission Inspection Report 07201014/2022-201, Holtec International, dated September 12, 2023 (ML23145A175)
- 2. NRC letter to Holtec, Holtec International Inc. - Notice of Violation; The U.S.
Nuclear Regulatory Commission Inspection Report No. 07201014/2022-201, dated January 30, 2024 (ML24016A190)
Pursuant to Title 10 of the Code of Federal Regulations (10 CFR) 72.7, Specific Exemption, Tennessee Valley Authority (TVA) is reques ting Nuclear Regulatory Commission (NRC) approval of the enclosed exemption request for Watts Bar Nuclear Plant (WBN) from the requirements of 10 CFR 72.212(a)(2), 72.212(b)(3), 72.212(b)(5)(i), 72.212(b)(11), and 72.214.
The regulations require, in part, compliance to the terms, conditions, and specifications of a Certificate of Compliance (CoC) or an amended CoC listed in §72.214. This exemption request from the aforementioned regulations is specific to the conditions of Holtec International, Inc.
(Holtec) Certificate No. 72-1032. CoC No. 72-1032 is issued for the Holtec International Storage Module Flood and Wind (HI-STORM FW) Multi-Purpose Canister (MPC) Storage System which contains the model MPC-37 (used at WBN), including the continuous basket shim (CBS) variant MPC-37CBS.
As documented in Reference 1, during an NRC inspec tion of a Holtec manufacturing facility in December 2022, three apparent violations were identified. As required by 10 CFR 72.48(c)(2)(viii), Changes, tests, and experiments, Holtec failed to obtain CoC amendments pursuant to 10 CFR 72.244 prior to implementing proposed CBS design changes U.S. Nuclear Regulatory Commission CNL-24-012 Page 2 February 28, 2024
to MPCs for four spent fuel cask designs that resulted in a departure from the method of evaluations described in the HI-STORM FW Final Safety Analysis Report used in establishing the design bases. As required by 10 CFR 72.48(d)(1), Changes tests, and experiments, Holtec failed to maintain records of changes that included written evaluations that provided an adequate bases for the determination that changing to the MPC CBS basket variants did not require CoC amendments pursuant to 10 CFR 72.48(c)(2). As required by 10 CFR 72.146(c),
Design control, Holtec failed to subject design changes for the MPC CBS basket variants to design control measures commensurate with those applied to the original design.
As documented in Reference 2, the NRC made final determination and issued a Notice of Violation for the inspection findings. The NRC determined that three Severity Level IV violations of regulatory requirements occurred, and Holtec did not demonstrate objective evidence of plans to restore compliance within a reasonable period of time.
TVA is requesting an exemption from certain requirements in Holtec CoC No. 72-1032 for the HI-STORM FW system. The enclosure to this letter provides the site-specific exemption request for WBN. If approved, the exemption will allow loading of new MPC-37CBS canisters for WBN. TVA requests approval of the enclose d exemption requests by June 1, 2024 in order to avoid delays to the planned spent fuel loading campaign beginning in July 2024.
There are no new regulatory commitments associated with this submittal. Please address any questions regarding this to Stuart L. Rymer, Senior Manager, Fleet Licensing, at slrymer@tva.gov.
Respectfully,
Kimberly D. Hulvey Director, Nuclear Regulatory Affairs
Enclosure:
- 1. Request for Specific Exemption from Certain Requirements of 10 CFR 72.212 and 10 CFR 72.214 for Watts Bar Nuclear Plant
cc (Enclosures):
NRC Regional Administrator - Region II NRC Senior Resident Inspector - Watts Bar Nuclear Plant NRC Project Manager - Watts Bar Nuclear Plant NRC Director - Division of Fuel Management, NMSS Enclosure
REQUEST FOR SPECIFIC EXEMPTION FROM CERTAIN REQUIREMENTS OF 10 CFR 72.212 and 10 CFR 72.214 FOR WATTS BAR NUCLEAR PLANT
I. Request for Exemption
The Holtec International Inc., (Holtec) HI-STORM FW 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 Title 10 of the Code of Federal Regulations (10 CFR) 72.214 as Certificate of Compliance (CoC) No. 1032 (Reference 1). This system is used by Tennessee Valley Authority (TVA) at Watts Bar Nuclear Plant (WBN) in accordance with 10 CFR 72.210, General license issued.
Pursuant to 10 CFR 72.7, Specific Exemptions, TVA requests an exemption from certain 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 WBN. These regulations require, in part, that a licensee store its irradiated fuel in compliance with the terms and conditions of the spent fuel storage casks CoC. Specifically, an exemption is requested for the Holtec MPC-37 multi-purpose canisters (MPC) with a continuous basket shim (CBS) design basis condition requiring analysis of a postulated non-mechanistic tip-over event.
The requested exemption will allow future loading of CBS variant canisters (MPC-37CBS), as listed in the table below.
The exemption is needed because although Holtec orig inally performed a tip-over analysis with favorable results and subsequently implemented the CBS design variants under 10 CFR 72.48, the Nuclear Regulatory Commission (NRC) issued Severity Level IV violations (Reference 2) that indicated that these design variants should have resulted in an amendment to the HI-STORM FW CoC No. 1032. Specifically, the 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 new or different MOEs, thus requiring prior NRC approval. NRC approval of the tip-over analysis MOEs is not expected prior to upcoming loading campaigns using the MPC-37CBS design.
TVA requests approval of this exemption request by June 1, 2024, to support the loading of the next MPC-37CBS canisters beginning July 8, 2024.
MPC SERIAL HI-STORM CoC 1032 FW FSAR NUMBER SERIAL AMENDMENT REVISION NUMBER 0293 0408 0 (REV 1) 2.1 0294 0409 0 (REV 1) 2.1 0295 0410 0 (REV 1) 2.1 0296 0411 0 (REV 1) 2.1 0297 0412 0 (REV 1) 2.1
The technical justification supporting continued use of the MPC-37CBS is provided in the following sections.
CNL-24-012 E1 of 7 Enclosure
II. Background
WBN currently utilizes the HI-STORM FW S ystem under CoC No. 72-1032, Amendment No. 0, Revision 1 for dry storage of spent nuclear fuel in specific MPCs (i.e., MPC-37 canisters). All design features and contents must fully meet the HI-STORM FW CoC, operations must occur within the Limiting Conditions for Operations, and the site must demonstrate that they meet all site specific parameters.
Holtec is the designer and manufacturer of the HI-STORM FW system. Holtec developed a variant of the design for the MPC-37 known as MPC-37CBS. The MPC-37CBS basket, like the previously certified MPC-37, is made of Metamic-HT' and has exactly the same geometric dimensions and assembly configuration. The only 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 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 effect means to fix the shims to the basket using a set of stainless steel fasteners. These fasteners dont 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 FW 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 originally implemented these design variants under the provisions of 10 CFR 72.48.
However, the NRC has issued Severity Level IV violations that indicated that these variants should have been submitted for review and approval, and therefore this exemption request is necessary.
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 are 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 WBN to store previously loaded and load additional canisters of the MPC-37CBS variant 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, which 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.
CNL-24-012 E2 of 7 Enclosure
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-37CBS variant without an approved tip-over analysis. This evaluation (detailed below) assumed basket failure due to the 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.
c) Otherwise in the Public Interest
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 this continued storage of already loaded canisters to bring them back into compliance most quickly and efficiently. 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-37CBS basket assembly features the same fuel storage cavity configuration as the certified standard MPC-37 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 t hat, the loose aluminum shims around the basket periphery used in the original MPC-37 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 welds located in the external periphery of the Metamic-HT fuel basket. All other design characteristics of the fuel basket are unchanged by the use of 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, as well as assisting in the overall heat transfer process, and also acts as the confinement boundary for the system.
Thermal
The NRC staff used the structural assessment to confirm there was no loss of confinement integrity and considered the thermal impacts of a postulated non-mechanistic tip-over accident. The NRC staff considered fuel debris that might cause hot-spots near the bottom of the MPC (on its side from a postulated tip-over). The NRC staff noted that there might be some local increase in temperatures, but no temperatures that would challenge the MPC
CNL-24-012 E3 of 7 Enclosure
confinement based on its stainless steel material. The thermal review concludes, the containment will remain intact and therefore the non-mechanistic tip-over accident condition does not result in significant safety cons equences 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 a hypothetical tip-over including basket failure.
The NRC staff assessment concludes that the MPC, which is the confinement boundary, maintains its structural integrity during a tip-over event and, the staff concludes that the MPC confinement boundary maintains its structural integrity and no water is able to enter the interior of the MPC during accident conditi ons. The NRC staff also acknowledges that consistent with the final safety analysis r eport (FSAR)(Reference 4), the cladding is not relied on for any safety conclusions, 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 NRC 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.
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 acceptable via a drop analysis. The drop analysis shows that there are no significant loads on the basket that would challenge the structural integrity. Therefore, 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. Should the fuel basket fail to maintain its structural integrity during stack-up the fuel will be maintained in a subcritical condition.
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 NRC 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 still present. Therefore, the NRC 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.
Also, the NRC staff reviewed the shieldi ng impact and concluded, as the damaged 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
CNL-24-012 E4 of 7 Enclosure
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.
Materials
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 the MPC maintains all safety functions, and no changes are needed to the operations or allowable contents of the storage system. The MPC-37CBS basket variant meets the criteria outlined in the HI-STORM FW FSAR, and thus meets the necessary requirements of 10 CFR Part 72. Therefore, the MPC-37CBS should be allowed for loading and storage in the HI-STORM FW system.
V. Environmental Consideration
While the proposed exemption does not meet the eligibility criterion for categorical exclusion set forth in 10 CFR 51.22(c)(25), there are no significant environmental impacts associated with the proposed action. The proposed exemption does not:
Increase the probability or consequences of accidents (see no significant hazards consideration provided below);
Change the types of effluents released offsite; Increase the occupational or public radiation exposure; Involve any construction or other ground disturbing activities; Change the footprint of the existing ISFSI, spent fuel pool, or any other supporting structures; Change the physical aspects of the dry or wet fuel storage features at the facility; Have any impacts on aquatic or terrestrial habitats in the vicinity of WBN; Have any impacts on threatened, endangered, or protected species; or Have the potential to cause effects on historic or cultural properties, assuming such properties are present at WBN.
In addition, as discussed below, the proposed exemption meets the first five criteria of 10 CFR 51.22(c)(25), because it involves: (i) no significant hazards consideration; (ii) no significant change in the types or significant increase in the amounts of any effluents that may be released offsite; (iii) no significant increase in individual or cumulative public or occupational radiation exposure; (iv) no significant construction impact; and (v) no significant increase in the potential for or consequences from radiological accidents.
However, the exemption does not satisfy the requirement of 10 CFR 51.22(c)(25)(vi),
because it involves requirements that are not: (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.
CNL-24-012 E5 of 7 Enclosure
a) Environmental Impacts of the Proposed Action
The WBN ISFSI is a radiologically controlled area on site. The area considered for a potential environmental impact as a result of this exemption request is the area in and surrounding the ISFSI.
The interaction of a loaded HI-STORM FW system with the environment is through the thermal, shielding, and confinement design functions for the cask system. As described above, TVA has verified the following conclusions for proposed storage of the MPC-37CBS variant described above.
The confinement boundary continues to have safety factors above 1.0.
Fuel cladding temperature limits re main below the NUREG-2215 limits.
Existing radiological evaluations and conclusions in Chapter 5 of the HI-STORM FW FSAR will remain valid, since there is no change to the shielding evaluation.
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-37CBS canister would need to be unloaded and re-loaded into the older design MPC-37 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, because 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-37CBS at WBN 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.
CNL-24-012 E6 of 7 Enclosure
VI. Conclusion
As the safety assessment and environmental review above demonstrate, the HI-STORM FW system with the MPC-37CBS canister without an approved tip-over analysis continues to be capable of performing required safety functions and is capable of mitigating the effects of design basis accidents and, therefore, does not present a threat to public and environmental safety.
TVA 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 use of the systems currently in non-compliance for the term specified in the CoC.
The exemption provided herein meets the requirements of 10 CFR 72.7.
VII. References
- 1. Holtec International - HI-STORM FW MPC Storage System, Certificate of Compliance No. 1032, Amendment 0, Revision 1, dated April 25, 2016 (ML16112A309)
- 2. NRC letter to Holtec, Holtec International - Notice of Violation; The U.S. Nuclear Regulatory Commission Inspection Report No. 07201014/2022-201, dated January 30, 2024 (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. Holtec International - Final Safety Analysis Report on the HI-STORM FW MPC Storage System, Holtec Report No. HI-2114830, Revision 2.1, dated May 31, 2016
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