ML23052A043
| ML23052A043 | |
| Person / Time | |
|---|---|
| Site: | Callaway  |
| Issue date: | 02/21/2023 |
| From: | Ameren Missouri, Union Electric Co |
| To: | Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML23052A041 | List: |
| References | |
| ULNRC-06796, EPID L-2022-LLA-0132 | |
| Download: ML23052A043 (1) | |
Text
Enclosure 1 to ULNRC-06796 Page 1 of 8 ENCLOSURE 1 RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION to ULNRC-06796 Page 2 of 8 RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION
References:
References are provided at the end of this enclosure.
By e-mail dated January 24, 2023, (Reference 2) the NRC staff requested additional information to support review of the Reference 1 license amendment request (LAR). The requested information is needed to allow the completion of the NRC staff's review of the proposed amendment in terms of regulatory requirements for the protection of public health and safety and the environment. This information is being provided to allow the NRC staff to complete its review.
The NRC staff requested that Ameren Missouri address the following items (in bold text):
Requests for Additional Information:
RAI #1 There appear to be inconsistencies with the allowable storage configurations between the TS requirements and the proposed rules for permissible loading. As described in Section 3.4.3, the rules for the permissible loading preclude potentially more restrictive interface conditions. TS 4.3.1.1.d does not specifically preclude these interface conditions. Thus, the rules for permissible loading appear to be more restrictive than TS 4.3.1.1.d.
Additionally, TS 4.3.1.1.d does not reference the rules for permissible loading, and the storage configuration description of TS 4.3.1.1.d does not perfectly match what would be allowed under the rules for permissible loading. Because the rules for permissible loading are not part of the TS, they are not a TS requirement and are not enforceable.
Please explain why the proposed TS sufficiently describes the allowable storage configuration and precludes the interface conditions described in Section 3.4.3.
Revise the proposed TS to preclude such configurations or provide an analysis of such configurations demonstrating continued compliance with 10 CFR 50.68(b).
Ameren Missouri Response:
Ameren Missouri proposes to modify TS 4.3.1.1 to explicitly include the storage configuration rules identified in Section B-4.0 of Appendix B to HI-2220020, Revision 2, "Criticality Safety Analysis of SFP for Callaway Nuclear Generating Station," (Reference 3). The proposed change adds the rules for storage configurations as TS 4.3.1.1.e which was previously shown as "Deleted" in the Reference 1 LAR. The proposed TS 4.3.1.1, in its entirety, is provided below.
to ULNRC-06796 Page 3 of 8 4.3.1 Criticality 4.3.1.1 The spent fuel storage racks are designed and shall be maintained with:
- a.
Fuel assemblies having a maximum nominal U-235 enrichment of 5.0 weight percent; For fuel with enrichments greater than 4.6 nominal weight percent of U-235, the combination of enrichment and integral fuel burnable absorbers shall be sufficient so that the requirements of 4.3.1.1.b are met.
- b.
keff 0.95 < 1.0 if fully flooded with unborated water and keff 0.95 if flooded with borated water, which includes an allowance for uncertainties as described in Section 9.1 of the FSAR;
- c.
A nominal 8.99-inch center-to-center distance between fuel assemblies placed in the fuel storage racks;
- d.
Partially spent fuel assemblies with a discharge burnup in the "Acceptable Burnup Domain" for Region 2 and 3 storage" of Figure 3.7.17-1 may be allowed unrestricted storage in the fuel storage racks, except for the empty cells associated with a in the checkerboarding configuration Region 1 assembly;
- e.
Rules governing the storage configurations in Regions 1 and 2 are the following: Partially spent fuel assemblies with a discharge burnup in the "Acceptable Burnup Domain for Region 3 Storage" of Figure 3.7.17-1 may be allowed unrestricted storage, except for the empty cells in the checkerboarding configuration, and except in Region 2 locations in a Mixed Zone Three Region configuration in the fuel storage racks; and For cells containing a Region 1 assembly:
1.1 None of the face-adjacent cells may contain a Region 1 assembly; 1.2 A minimum of two of the face-adjacent cells must be empty; 1.3 A maximum of two of the remaining face-adjacent cells may contain Region 2 assemblies. See also Rule 2.3; 1.4 If both of the remaining face-adjacent cells are Region 2 assemblies, then Rule 2.1 is restricted to one Region 1 assembly for those cells.
to ULNRC-06796 Page 4 of 8 For cells containing a Region 2 assembly:
2.1 A maximum of two of the face-adjacent cells may contain Region 1 assemblies. See also Rule 1.4; 2.2 The remaining face-adjacent cells may contain Region 2 assemblies or be empty; 2.3 If two face-adjacent cells contain Region 1 assemblies, then Rule 1.3 is restricted to one Region 2 assembly for those cells.
- f.
New or partially spent fuel assemblies with a discharging burnup in the "Unacceptable Burnup Domain" for Region 2 or 3 Storage" of Figure 3.7.17-1 will be stored in Region 1.
This proposed wording change is reflected in Enclosure 3, which provides the marked-up version of the proposed TS, and in Enclosure 4, which provides a clean, re-typed version of the proposed TS.
Regarding the staff's observation that the originally proposed TS 4.3.1.1.d did not explicitly reflect the storage configuration rules proposed in Section B-4.0 of Appendix B to HI-2220020, Revision 2, and in addition to the changes made for TS 4.3.1.1.e, a change is proposed in the wording of TS 4.3.1.1.d to remove reference to the term "checkerboarding configuration." The proposed TS now specifies that the empty cells being discussed are those associated with a Region 1 assembly. This change eliminates any ambiguity associated with the term "checkerboarding" and any implied configuration associated with the mental model of a checkerboarding pattern. This change is reflected above and in Enclosure 3, which provides the marked-up version of the proposed TS, and in Enclosure 4, which provides a clean, re-typed version of the proposed TS. The proposed changes address the staff's concern by explicitly using language consistent with the supporting analysis given in Reference 3.
The proposed changes address the staff's concern by explicitly stating the storage configuration rules that preserve compliance with the requirements of 10 CFR 50.68(b) in Section 4, "Design Features," of the TS in a manner consistent with 10 CFR 50.36(c)(4).
As a result of the changes proposed above, the Bases for TS 3.7.17, "Spent Fuel Assembly Storage," have been revised to reflect complementary wording and to cite TS 4.3.1.1 as the location of the storage configuration rules vice replicating them at that location. Modifying the TS Bases for TS 3.7.17 helps ensure their consistency and eliminates duplicative information that could lead to contradictory interpretations of the requirements. The proposed Bases for TS 3.7.17 are shown in Enclosure 5. The TS Bases are provided for information only with the final changes processed in accordance with the provisions of TS 5.5.14, "Technical Specification (TS) Bases Control Program."
to ULNRC-06796 Page 5 of 8 The proposed TS 4.3.1.1 continues to support the conclusions reached in Section 4.0, "Regulatory Evaluation," of the LAR submitted in Reference 1. This includes the determination that the proposed change presents no significant hazards consideration under the standards set forth in 10 CFR 50.92(c). In addition, this also includes the determination that the proposed change continues to meet the eligibility criterion for categorical exclusion set forth in 10 CFR 51.22(c)(9).
RAI #2 Section 3.4.6, Combined Qualifications, of the LAR describes the potential ambiguity of using terms such as unrestricted or checkerboard to describe spent fuel pool (SFP) assembly storage configurations. The licensee instead provided a set of permissible loading rules to determine if a cell may contain a Region 1 assembly, Region 2 assembly, or no assembly at all based on the face-adjacent neighbors of that cell. The rules remove any ambiguity associated with uniform or checkerboard descriptions of storage configurations. However, the rules are not sufficient to preclude unanalyzed storage configurations. Figures 1 is an example of a storage configuration which is acceptable according to the rules but does not appear to be analyzed in the nuclear criticality safety (NCS) analysis the licensee provided. The storage configuration seen in Figure 1 is allowed as there are no rules preventing a Region 1 assembly from being flanked on opposite sides by two Region 2 assemblies.
Please explain how these configurations are bounded by the proposed SFP criticality analysis of record or discuss how these configurations would be precluded by the proposed TS requirements.
R2 R2 R2 R2 R2 R2 R2 R2 R2 R2 R2 R2 R1 R1 R2 R2 R2 R2 R2 R2 R2 R2 R2 R2 R2 R2 R2 Figure 1 - Example of an Unanalyzed Storage Configuration Allowed by Rules for Permissible Loading to ULNRC-06796 Page 6 of 8 Ameren Missouri Response:
The example presented in Figure 1 is allowed under the analyses described in Section 3.4, "Spent Fuel Rack Interfaces," in Reference 3, the storage configuration rules presented in Section B-4.0 of Appendix B in Reference 3, and the rules correspondingly proposed for TS 4.3.1.1.e as described in the response to RAI #1. To confirm the validity of this configuration, supplemental analysis was provided by Holtec International in Reference 4 which evaluated a bounding version of the example presented in Figure 1 along with other configurations to demonstrate conservatism of the configurations explicitly analyzed in Reference 3. This supplemental analysis is included in this response as Enclosure 8 (proprietary version) and Enclosure 7 (nonproprietary version).
Note that the configuration presented in RAI Figure 1 is bounded by the configuration presented in Figure 1 of Enclosure 8. The use of a periodic boundary condition effectively replaces the Region 2 assembly in the right-most cell of the middle row with a more reactive, Region 1 assembly.
Section 2, "Additional Region 1 to Region 2 Interface Calculations," in Enclosure 8 presents the results of four additional postulated configurations, including two additional configurations not allowed by the configuration rules. As presented in Table 1 of Enclosure 8, in all allowed cases, the configurations from Reference 3 remain the bounding cases. This confirms the validity of the criteria utilized when selecting the bounding cases in Reference 3, since it shows that when moving away from these criteria, reactivities will be reduced.
RAI #3 The licensees incorrect loading curve analysis does not include an analysis of a multiple misload of underburned Region 1 assemblies. Region 1 assemblies are not necessarily fresh assemblies; therefore, making it more difficult to distinguish between Region 1 and Region 2 assemblies if there is an error in the SFP loading documentation. Typically, a fresh fuel assembly and a burned fuel assembly can be identified by differences in their appearance, thus allowing plant staff to identify any errors in the loading documentation. Because Region 1 assemblies may not be fresh, the appearance of assemblies cannot be used to identify errors in loading documentation, thus a multiple misload of Region 1 assemblies that are more reactive than an assembly requiring 20 years of cooling time to be acceptable for storage in Region 2 is possible. The LAR does not analyze this condition.
Please provide either a bounding analysis of a multiple misload accident involving Region 1 assemblies or provide justification that such a configuration is precluded by means other than visual inspection.
Ameren Missouri Response:
The license amendment request submitted in Reference 1 was developed based on the guidance of Regulatory Guide 1.240, "Fresh and Spent Fuel Pool Criticality Analyses," (Reference 5) which to ULNRC-06796 Page 7 of 8 endorsed the use of NEI 12-16, "Guidance for Performing Criticality Analyses of Fuel Storage at Light-Water Reactor Power Plants," (Reference 6) subject to the identified clarifications and exceptions, as an acceptable method of demonstrating compliance with the requirements of 10 CFR 50.68(b). Consistent with clarification and exception "a." under paragraph 1 in Section C, "Staff Regulatory Guidance," Ameren Missouri did not postulate a scenario in which multiple misloaded Region 1 assemblies was possible. Consistent with NEI 12-16 Section 6.3.5.5: "The administrative controls and processes can influence the credible scenarios that need to be evaluated via analysis to address the multiple misload from a single event." Ameren Missouri has developed and implemented licensee controls consistent with the descriptions in Sections 9.1 and 9.2 of NEI 12-16. While the described visual inspection method is one means of detecting a misloaded condition, the procedural controls that have been implemented are intended to preclude the variety of mechanisms that could result in this condition.
To address RAI #3, Ameren Missouri directed Holtec International to perform additional analyses for the multiple misloaded Region 1 fuel assembly scenario described. This analysis is presented in Section 3, "Additional Misloading Accident Conditions," of Enclosure 8. Using the RAI #3 discussion that fresh fuel is more likely to be identified as incorrectly loaded, the analysis calculated the lowest fuel burnup values that would cause the 10 CFR 50.68(b) acceptance criteria to not be met. The results indicate that this burnup value is substantially smaller than that associated with a once-burned assembly. Based on this analysis and these assumptions, the results show that the regulatory acceptance criteria would not be exceeded.
to ULNRC-06796 Page 8 of 8
References:
- 1.
Ameren Missouri letter ULNRC-06723, "License Amendment Request Regarding Proposed Technical Specification Changes for Spent Fuel Storage (LDCN 22-0015)," dated August 29, 2022 (ADAMS Accession No. ML22242A122)
- 2.
NRR e-mail capture,
Subject:
"Final - Request for Additional Information - Callaway Plant, Unit 1 - LAR for proposed changes to TS for SFP - EPID: L-2022-LLA-0132," dated January 24, 2023 (ADAMS Accession No. ML23026A021)
- 3.
HI-2220020, Revision 2, "Criticality Safety Analysis of SFP for Callaway Nuclear Generating Station," dated October 21, 2022. Previously provided to the NRC as Attachment 6 to of ULNRC-06723 (i.e., Reference 1)
- 4.
HI-2230125, Revision 0, "Supplemental Criticality Safety Analysis of SFP for Callaway Nuclear Generating Station," dated February 14, 2022.
- 5.
Regulatory Guide 1.240, "Fresh and Spent Fuel Pool Criticality Analyses," Revision 0 dated March 2021. (ADAMS Accession No. ML20356A127)
- 6.
NEI 12-16, "Guidance for Performing Criticality Analyses of Fuel Storage at Light-Water Reactor Power Plants," Revision 4 dated September 2019.