ML20282A527
| ML20282A527 | |
| Person / Time | |
|---|---|
| Site: | 07201032, Holtec |
| Issue date: | 11/03/2020 |
| From: | Leslie Perkins NRC/NRR/DORL/LPMB |
| To: | Manzione K Holtec |
| Perkins L | |
| Shared Package | |
| ML20282A525 | List: |
| References | |
| EPID L-2020-TOP-0018 | |
| Download: ML20282A527 (5) | |
Text
AUDIT REPORT AUDIT REPORT FOR HOLTEC TOPICAL REPORT FOR ALLOWANCE OF HEAT LOAD PATTERNS IN HI-STORM 100 AND HI-STORM FW SYSTEMS PROJECT NO. 5014 (EPID L-2020-TOP-0018)
1.0 BACKGROUND
In a letter dated March 19, 2020 (Agencywide Documents Access and Management System(ADAMS) Package Accession No. ML20101N174), Holtec International (Holtec) submitted Topical Report (TR) HI-2200343, Revision 0, Topical Report for Allowance of Heat Load Patterns in HI-STORM 100 and HI-STORM FW Systems, for U.S. Nuclear Regulatory Commission (NRC) review and approval. Holtec requested the NRC staff review its generic methodology for evaluating the heat load patterns, with the intent of incorporating it for use in the HI-STORM 100 and HI-STORM FW certificate of compliance (CoCs) via a separate, future licensing action.
2.0 REGULATORY AUDIT OBJECTIVES The Topical Report will be used to demonstrate compliance, in part, with Title 10 of the Code of Federal Regulations (10 CFR) Part 72, Licensing Requirements for the Independent Storage of Spent Nuclear Fuel, High-level Radioactive Waste, and Reactor-related Greater than Class C Waste. The NRC staff completed its acceptance review on May 22, 2020, and found that the material presented was sufficient to begin its review (ADAMS Accession No. ML20141L621).
After an initial review, the NRC staff identified some areas requiring further discussion and determined that it was necessary to conduct a regulatory audit to address NRC staff concerns regarding TR HI-2200343 Revision 0. The scope and objectives were defined in an audit plan (ADAMS Package Accession No. ML20244A020). A virtual audit was conducted via Skype on September 9, 2020.
Audit Participants Name Organization Marilyn Diaz-Maldonado NRC JoAnn Ireland NRC Ngola Otto NRC Jason Piotter NRC Leslie Perkins NRC Tae Ahn NRC Ricardo Rodriguez NRC John Wise NRC Kim Manzione Holtec Debu Majumdar Holtec Abrar Mohammed Holtec Enclosure 1
3.0 AUDITED MATERIAL AND DISCUSSIONS The five open items identified in the audit plan are discussed below.
Item #1 Method of Evaluation (MOE) 1a Defining Limitations The NRC staff determined that enhancements to the MOE in the TR HI-2200343, Revision 0, was needed because 1) a broad array of inputs for both heat load patterns and total decay heat were never considered as part of previous approvals of the HI-STORM 100 and HI-STORM FW MOEs; and 2) the range of inputs were not clearly defined.
There were two scenarios discussed as part of the audit:
Scenario 1, which includes heat load patterns in which the total decay heat is less than what has been previously approved for each design.
Scenario 2, which includes heat load patterns in which the total decay heat is greater than what has been previously approved for each design.
The discussion regarding Scenario 1 initially focused on what was meant by significant departure from a previously approved per cell heat load as discussed in the audit plan. The NRC identified that this concern was not specifically focused on defining significant departure, rather that there was no identified objective approach to determine that increasing per cell decay heat values would not produce an unanalyzed condition. This unanalyzed condition is such that it would challenge previous assumptions and effective usage of the computational fluid dynamics (CFD) models to produce accurate temperature and pressure results.
The unanalyzed condition concern also extended to Scenario 2 in that increasing total decay heats over a range not previously considered may render certain assumptions and/or calculations in the MOE, including the numerical models, as invalid. The consideration here is whether or not a systematic and objective approach is employed to verify that the increasing decay heats, above what has been previously approved, do not challenge the range of applicability of the MOE.
Holtecs response to this concern and scenarios focused on the invariance (see also Baseline HI-STORM 100 and HI-STORM FW Thermal Models) of the previously approved CFD models and also the self-limiting materials and pressure limit acceptance criteria. [
].
The NRC staff generally agreed that the acceptance criteria in this instance can be considered self-limiting given that conservative (lower than existing CoC acceptance criteria) values are used, however the calculated values derived from a CFD model need to have a robust pedigree to ensure a reasonable degree of accuracy and allow for meaningful comparisons. Holtec concurred with the discussion regarding the acceptance criteria being self-limiting, however, the
discussion did not extend into identifying specific elements of a reasonable objective approach to provide assurance that the models are operating in their range of applicability, with increasing decay heat.
Disposition Holtec committed to enhancing the discussion within the MOE to demonstrate that the CFD models are able to produce reasonably accurate results for the intended purpose over the range of expected decay heat beyond those that have been previously approved. As noted above, part of this enhancement should include specific elements of a reasonably systematic and objective approach to provide assurance that the models are operating in their range of applicability, with increasing decay heat.
1b Baseline HI-STORM 100 and HI-STORM FW Thermal Models The use of the baseline CFD models submitted by Holtec identified no limitations or exclusions with respect to what changes or alterations that were allowed within TR HI-2200343, Revision 0.
Holtec confirmed during the audit that the two examples CFD models (HI-STORM 100 and HI-STORM FW) submitted as part of TR HI-2200343, Revision 0, are considered as the baseline models that will be used in conjunction with the MOE identified in TR HI-2200343, Revision 0.
Disposition The CFD models were identified as invariant which means that no changes to the models, modeling choices, boundary conditions, or other inputs or numerical manipulations are allowed if used with TR HI-2200343, Revision 0. The only exception to altering the CFD models is the use of mirror symmetry of the existing model formulation and changes to the per cell decay heat values identified for a given candidate heat load pattern.
Item #2 Incorporation by Reference TR HI-2200343 utilizes significant incorporation by reference which requires the NRC staff to piece together the entire MOE being described by the applicant, without clear and specific crosswalks to the information being referenced.
For the purposes of post audit activities, the NRC requested that Holtec provide:
(1) a more thorough crosswalk between TR HI-2200343, Revision 0, and relevant sections of the HI-STORM 100 and HI-STORM FW final safety analysis report (FSAR) including appendices and supplemental calculations that is clear and specific, or (2) update TR HI-2200343, Revision 0, to be a stand-alone document with all relevant information self-contained within the TR, or (3) a combination of (1) or (2).
Holtec agreed that some enhancements were needed to the TR HI-2200343, Revision 0, to address this issue.
Disposition Holtec committed to having internal discussions and making adjustments to the TR contents consistent with those discussions and the options identified in the audit plan and subsequent audit discussions.
Item #3 Screening Evaluation - Limited Calculations The NRC staff identified two concerns related to only using the long-term storage evaluation as a bounding calculation:
(1) higher variability in per cell decay heats that would be allowed with adoption of the TR and potential effects on short-term operations calculations, and (2) a limited data set available to justify that only using the long-term storage condition.
The NRC staff and Holtec discussed the proposed screening evaluation which identifies two screening criteria that are used to determine the relative number of additional operating conditions which must be evaluated to accept a candidate heat load pattern. Specifically, if both screening criteria are met when performing the long-term storage evaluation, then no other storage conditions, including short-term and transfer operations, need to be considered.
The discussion then focused on either adding additional justification for this approach, which assumed that the long-term storage condition evaluation alone is sufficient as a stand-alone bounding calculation or providing additional language in the TR that would require other operating conditions that must be evaluated.
Holtec identified examples where this approach was used in previous CoC amendments and the NRC will consider these items as part of an approved MOE.
Disposition As identified above, Holtec identified examples where this approach was used in previous CoC amendments and the NRC is going to review these items to determine whether they are consistent with the approach cited in TR HI-2200343, Revision 0. These examples will be appropriately considered in the safety evaluation in light of the concerns identified above.
Holtec has committed to identify the specific CoC amendment(s) where this approach was used.
Item #4 Implementation Strategy The NRC staff and Holtec had preliminary discussions during the post submittal meeting on July 17, 2020 (ADAMS Accession No. ML20202A658) on this issue to confirm how the requirements of 72.236, Specific Requirements for Spent Fuel Storage Cask Approval and Fabrication,(a) maximum heat designed to be dissipated, would be met. The NRC staff and Holtec discussed implementation scenarios, as well as how Holtec intended to meet the regulatory and safety functions with respect to other technical disciplines, such as shielding and structural.
The discussion on implementation as it relates to satisfying the regulatory requirement of identifying the maximum decay heat of a system, per 72.236(a), confirmed that this information would be provided during a CoC amendment that incorporates the use of TR HI-2200343,
Revision 0. The discussion also confirmed that it is Holtecs intent to not identify a limiting maximum total decay heat for the system or for individual fuel assemblies.
The technical discussion regarding additional disciplines affected by the implementation of the TR focused on the adoption of TR HI-2200343, Revision 0, via a CoC amendment. Holtec identified that during the CoC amendment, that various sections of the FSAR and/or supporting documentation would make reviewers in those technical disciplines aware that TR HI-2200343, Revision 0, was incorporated and how it would affect those sections as applicable. One example that was identified was the use of Fuel Qualification Tables. Holtec identified that the requirements and procedures for determining that the loaded fuel meets the acceptance criteria and safety goals for shielding or other technical disciplines would not be altered by the incorporation of TR HI-2200343, Revision 0.
Disposition This issue will be revisited separately from the TR HI-2200343, Revision 0, as part of implementation.
Item #5 Notification of Implementation of Thermal Topical Report Since certain elements of the MOE, including aspect of numerical model implementation, will be conducted outside of explicit NRC review and approval through the existing CoC amendment process, the NRC staff believes that it may be appropriate to consider a reporting requirement, submitted to the NRC when TR HI-2200343, Revision 0, is invoked as part of a loading campaign.
Disposition This item was briefly discussed, and it was determined that it was out of scope for the purposes of this audit. This issue will be revisited separately from the TR HI-2200343, Revision 0, as part of implementation.
4.0 REGULATORY AUDIT CONCLUSIONS AND FINDINGS All of the regulatory audit objectives listed in Section 2.0 were covered and all audit items were closed with the exception of the commitments identified above. These commitments as well as any additional items within this audit report necessary to make a safety determination will be further address and dispositioned in the Safety Evaluation Report.