ML23251A254
| ML23251A254 | |
| Person / Time | |
|---|---|
| Site: | Holtec |
| Issue date: | 09/08/2023 |
| From: | Holtec |
| To: | Office of Nuclear Material Safety and Safeguards |
| Shared Package | |
| ML23251A250 | List: |
| References | |
| 5014968 | |
| Download: ML23251A254 (1) | |
Text
Attachment 3 to Holtec Letter 5014968 1.0.3 Implementation of Topical Reports 1.0.3.1 Thermal Topical Report The NRC has reviewed and approved Topical Report HI-2200343-A [1.0.7]. This report outlines a methodology for developing heat load patterns for each canister. Throughout this FSAR, the areas where the topical report can be applied are identified. However, since the topical report itself is specifically focused on the thermal methodology, this section provides an outline of the approach for implementing that methodology. For additional clarity, a flowchart of the process is included in Figure 1.0.1.
Change Control The NRCs SER [1.0.8] explicitly lays out restrictions on the scope of the review for the topical report. Most notably, limitation 4.2 describes the model reviewed for the scope of the topical report as invariant. However, since this FSAR is subject to the provisions of 10CFR72.48, use of that topical report needs to address the change control process. Note that in all cases, the HI-STORM 100 system being considered must be one of the models listed in Appendix 1 of [1.0.8]
The following explains the steps in the flow chart in Figure 1.0.1 for implementation of the topical report
- Step 1: Site decides the existing CoC heat load patterns do not meet their needs, and develops a new pattern that would meet fuel loading needs
- Step 2: General Licensee and Holtec determine if the HI-STORM 100 system and contents being loaded matches the invariant model in the topical report [1.0.7]
o If yes, then proceed through the qualification process outlined in the topical report, ensure all topical report acceptance criteria (including all temperatures and pressures from Tables 2.1 and 2.2 of [1.0.7]) are met, and rejoin at Step 3 o If no, follow steps 2a through 2d
- Step 2a: Ensure that the variations from the topical report [1.0.7] invariant model (identified in Step 2) are acceptable without prior NRC approval o This process is identical to Holtecs existing 72.48 program and should be documented accordingly, which develops a 72.48 model for that variation o If the 72.48 process indicates that prior NRC approval is required, that application must be made and approved by the NRC prior to use of the HI-STORM 100 system. The topical report methodology [1.0.7] cannot be used until NRC approval is obtained.
- Step 2b: Once the variations have been determined to be acceptable without prior NRC approval under 72.48, the sites candidate heat load pattern should be evaluated by Holtec or the General Licensee in the 72.48 model, which is the invariant thermal model with all 72.48 modifications applicable to the planned loaded canisters applied o The results of this calculation must show that all components have a lower temperature than the FSAR limits and pressures lower than the FSAR limits o The peak cladding temperature (PCT) from this analysis is then compared to the results from Step 2c HOLTEC INTERNATIONAL COPYRIGHTED MATERIAL HI-STORM 100 FSAR Proposed Rev. 22D REPORT HI-2002444 1-6 Page 1 of 4
Attachment 3 to Holtec Letter 5014968
- Step 2c: The candidate heat load pattern is then fully qualified for use by evaluation by Holtec or the General Licensee in the Topical Report [1.0.7] invariant model o This evaluation must show ALL Topical Report [1.0.7] acceptance criteria are met, including all temperatures and pressures from Tables 2.1 and 2.2 of [1.0.7]
o This evaluation must show a higher PCT than Step 2b o If either of these conditions is not met, the candidate heat load pattern must be revised and Steps 2b and 2c are repeated. The original candidate heat load pattern is not eligible for loading.
- Step 2d: The temperature results from both Steps 2b and 2c are compared by Holtec or the General Licensee to the structural evaluations in the FSAR o If FSAR structural evaluations use temperatures that bound the calculated temperatures, no further structural evaluations are needed o IF FSAR structural evaluations use temperatures that do NOT bound the calculated temperatures, an additional 72.48 must be performed to demonstrate the new temperatures are acceptable without NRC approval If the structural evaluation changes are not acceptable under 72.48 than either the candidate heat load pattern must be changed or application made to the NRC and NRC approval obtained prior to use of the topical report
[1.0.7] methodology
- Step 3: Once all the items and acceptance criteria in Step 2a through 2d are satisfied -
Holtec or the General Licensee document the evaluation performed in Step 2c (candidate heat load pattern in invariant model) in sites qualification report and referenced as appropriate in the general licensees 72.212 report. Sites can use Section 5.0 of HI-2200343-A as an example format for this qualification report.
- Step 4: Site chooses fuel to meet the qualified heat load pattern, confirming that the fuel also meets other CoC requirements, such as (but not limited to) fuel types and FQTs (see below shielding discussion)
- Step 5: Site ensures loading procedures have the accurate restrictions for:
o Helium Backfill - HI-2200343-A Section 2.3.6 o Time to boil - HI-2200343-A Section 2.3.8 o Duct Blockage allowable clearance time or temperature monitoring limit - HI-2200343-A Section 2.3.12 Shielding The fuel qualification limits for burnups, enrichments and cooling times (BECTs) are independent of the fuel decay heat limits, and any assembly has to meet both the applicable BECT limits, and any decay heat limit developed through the application of the Topical Report.
No changes are made for now to these BECT limits, and no additional dose calculations are needed for the existing limits. Hence there are no new shielding analyses needed as a consequence of introducing the Topical Report. For further discussions and explanations see the following paragraphs.
Independence of BECTs and decay heat limits Earlier revisions of this FSAR included an explicit link between BECTs and decay heat limits, and this also impacted the way the dose analyses were performed. The link was specified in the HOLTEC INTERNATIONAL COPYRIGHTED MATERIAL HI-STORM 100 FSAR Proposed Rev. 22D REPORT HI-2002444 1-7 Page 2 of 4
Attachment 3 to Holtec Letter 5014968 MPC Design PCT at Sea Level PCT at 1500 feet MPC-32 PWR 711.4oF 723.8oF MPC-68 BWR 697.1oF 718.2oF These results show that the PCT, including the effects of site elevation, continues to be well below the regulatory cladding temperature limit of 752oF. In light of the above evaluation, it is not necessary to place any ISFSI elevation constraints for HI-STORM deployment at elevations up to 1500 feet. If, however, an ISFSI is sited at an elevation greater than 1500 feet, the effect of altitude on the PCT shall be quantified as part of the 10 CFR 72.212 evaluation for the site using the site ambient conditions.
Heat load patterns can be developed in accordance with the thermal topic report (TR) [4.4.3].
Effect of site elevation shall also be evaluated for new heat load patterns and compliance demonstrated with the acceptance criteria specified in the TR.
4.4.5 Maximum Internal Pressure 4.4.5.1 MPC Helium Backfill Pressure For design basis heat load, the helium backfill shall be sufficient to produce the required operating pressure of 7 atmospheres (absolute) during normal storage at reference conditions (See Table 4.0.1). Thermal analyses performed on the different MPC designs indicate that this operating pressure requires a certain helium backfill pressure specified at a reference temperature (70ºF).
The minimum backfill pressure to attain this operating pressure for each MPC type is provided in Table 4.4.11. An upper limit on the helium backfill pressure corresponds to the design pressure of the MPC vessel (Table 2.2.1). The upper limit on the backfill pressure is also reported in Table 4.4.11. To bound the minimum and maximum backfill pressures listed in Table 4.4.11 with margin, a helium backfill specification is set forth in Table 4.4.12. These values support the technical specification of the system for the design basis heat load of the MPC.
In addition the technical specifications allow for using a wider range on the backfill pressure if the heat load of the MPC is less than 28.74 kW. The minimum of this range corresponds to an operating pressure of 5 atm. The heat loads for this condition are provided in Table 2.1.31. If the MPC is loaded such that Table 2.1.31 is satisfied, the lower pressure range in the technical specifications may be used.
It is conservative to backfill the MPC to the higher pressure range regardless of MPC heat load.
Two methods are available for ensuring that the appropriate quantity of helium has been placed in an MPC:
- i. By pressure measurement ii. By measurement of helium backfill volume (in standard cubic feet)
HOLTEC INTERNATIONAL COPYRIGHTED MATERIAL HI-STORM 100 FSAR Proposed Rev. 22D REPORT HI-2002444 4-26 Page 3 of 4
Attachment 3 to Holtec Letter 5014968 SFSC Heat Removal System B 3.1.2 BASES SURVEILLANCE SR 3.1.2 (continued)
REQUIREMENTS As an alternative, for OVERPACKs with air temperature monitoring instrumentation installed in the air outlets, the temperature rise between ambient and the OVERPACK air outlet may be monitored to verify operability of the heat removal system. Blocked air ducts will reduce air flow and increase the temperature rise experienced by the air as it removes heat from the MPC. Based on the analyses, provided the air temperature rise is less than the limit stated in the SR (or calculated as the difference (T) between the average overpack air outlet temperature computed under normal long-term storage condition using topical report HI-2200343-A and ISFSI ambient temperature), adequate air flow and, therefore, adequate heat transfer is occurring to provide assurance of long term fuel cladding integrity. The reference ambient temperature used to perform this Surveillance shall be measured at the ISFSI facility.
The Frequency for aboveground systems per the Completion Time Table in the CoC and 16 hours1.851852e-4 days <br />0.00444 hours <br />2.645503e-5 weeks <br />6.088e-6 months <br /> for underground systems is reasonable based on the time necessary for SFSC components to heat up to unacceptable temperatures assuming design basis heat loads, and allowing for corrective actions to take place upon discovery of blockage of air ducts. For aboveground systems containing MPCs with heat loads less than or equal to the threshold heat loads in Table B.1-1 at the time of inspection, the surveillance frequency of 30 days is appropriate, since the system components and peak cladding temperature limits for 30-day accident are not exceeded and the event is not time limiting.
REFERENCES 1. FSAR Chapter 4
- 2. FSAR Sections 11.2.13 and 11.2.14
- 3. ANSI/ANS 57.9-1992 HOLTEC INTERNATIONAL COPYRIGHTED MATERIAL HI-STORM 100 FSAR Proposed Rev. 22D REPORT HI-2002444 B 3.1.2-9 Page 4 of 4