ML25031A421
| ML25031A421 | |
| Person / Time | |
|---|---|
| Site: | HI-STORM 100 |
| Issue date: | 01/31/2025 |
| From: | Holtec |
| To: | Office of Nuclear Material Safety and Safeguards |
| Shared Package | |
| ML25031A418 | List: |
| References | |
| 5021080 | |
| Download: ML25031A421 (1) | |
Text
Request for Additional Information Docket No. 72-1040 Certificate of Compliance No. 1040 Amendment No. 5 to the HI-STORM UMAX Multipurpose Canister Storage System Structural Evaluation:
RAI-St-1 Provide an evaluation for the thermal degradation of concrete subgrade material in space A due to increased temperature for the UMAX storage system.
In response to the RAI St-1, the applicant included the subgrade concrete in the thermal model and provided steady state component temperatures, including the maximum section average temperature of the concrete subgrade from the revised thermal analysis HI-2230586, Revision
- 1. Based on these results, the maximum section average temperature of the concrete subgrade
[PROPRIETARY INFORMATION WITHHELD IN ACCORDANCE WITH 10 CFR 2.390]. The applicant compared this temperature to the temperature limit of 350°F for the Closure Lid plain concrete per the FSAR Table 2.3.7, stating that the plain concrete used in the Closure Lid is the same material used for the subgrade material in space A for the Version MSE VVM, and therefore satisfies the temperature limit established in Table 2.3.7 of the FSAR. The applicant further stated that the plain concrete material in Space A (see Figure 3.4.4) is not designed to meet ACI 349 requirements, and therefore the thermal considerations in Appendix A of ACI 349-01 do not apply.
The staff reviewed the RAI response and considered it to be inadequate due to the following reasons:
The FSAR Table 2.3.7, TEMPERATURE LIMITS, does not list and provide a temperature limit for the subgrade concrete material in space A (i.e. the space between underground storage overpacks). The subgrade concrete has a structural function. It is included in the soil structural interaction (SSI) analysis model, used for tornado missile protection during construction, and is also credited for preventing excessive distortion of the storage overpack under the most severe earthquake (MSE) event to permit future retrievability of a multi-purpose canister (MPC) containing spent fuel. The Closure Lid concrete does not have a significant structural function and the plain concrete properties are instead used in shielding calculations and analysis of mechanical loadings on the Closure Lid. As a result, the applicant did not provide an adequate basis for the 350 F long-term temperature limit for the Closure Lid plain concrete material and its applicability to the subgrade concrete in space A.
Based on statements in FSAR section 8.8.1, it appears to the staff that the temperature limits for the Closure Lid plain concrete in Table 2.3.7 are adopted from the HI-STORM 100 FSAR where the bases for the thermal limits are documented. In the HI-STORM 100 FSAR HI-2002444, Revision 24, Table 1.D.1, Requirements for Plain Concrete, Note 3 states, The 300 F long term temperature limit is specified in accordance with Paragraph A.4.3 of Appendix A to ACI 349 considering the very low maximum stresses calculated and discussed in Section 3.4 of this FSAR for normal conditions. In accordance with this paragraph of the governing code, the specified concrete compressive strength is supported by test data and the concrete is shown not to deteriorate, as evidenced by a lack of reduction in concrete density or durability. to Holtec Letter 5021080
If the bases for the temperature limits of the Closure Lid plain concrete in HI-STORM UMAX SAR Table 2.3.7 are adopted from the HI-STORM 100 FSAR, the 350 F temperature limit used for the HI-STORM UMAX Closure Lid and therefore MSE subgrade concrete in space A does not align with the 300 F long term temperature limit specified in the HI-STORM 100 FSAR, Table 1.D.1, for the plain concrete. Also, the applicant stated in the RAI response that the thermal considerations in Appendix A of ACI 349-01 do not apply to the subgrade concrete in space A, which is inconsistent with the bases used for setting the plain concrete long term temperature limit in the HI-STORM 100 FSAR. Considering the above, it is not clear to the staff the bases for acceptance of the long-term temperature limit of the concrete in subgrade space A for the UMAX system. The staff requests the following information:
a) If the temperature limits in Table 2.3.7 for the plain concrete are adopted from the HI-STORM 100 FSAR, resolve the temperature limit discrepancy between the two HI-STORM systems FSARs and; i) provide bases for the applicability of the long term temperature limit for the Closure Lid concrete to the concrete used for the subgrade in space A; ii) demonstrate the plain concrete used for the subgrade in space A meets the critical requirements for the concrete constituent materials specified in the HI-STORM 100 FSAR, Table 1.D.1 and; iii) demonstrate low stresses in subgrade concrete under normal conditions similar to that shown for the Closure Lid concrete in Note 3 of Table 1.D.1 of the HI-STORM 100 FSAR.
b) If the temperature limits in Table 2.3.7 for the plain concrete are not adopted from the HI-STORM 100 FSAR, provide bases for the 350 F, the long-term temperature limit for the UMAX system Closure Lid concrete and its applicability to the subgrade concrete in space A, based on the applicable industry codes, standards and/or tests. Also, update the UMAX system FSAR, section 8.8.1 as appropriate to resolve any discrepancy.
c) As a result of the long-term temperature increase under this amendment and due to the significant differences in the plain concrete functions and locations between the Closure Lid and the subgrade space A, FSAR Table 2.3.7 should be updated to list the plain concrete in Space A with its temperature limits, and the associated bases for the temperature limits should be provided.
The staff notes that in the RAI response, Table 1, the numbers listed for the margins for Fuel Cladding and Concrete Subgrade do not match the differences between the calculated temperature and the temperature limit. Example for Concrete Subgrade: [PROPRIETARY INFORMATION WITHHELD IN ACCORDANCE WITH 10 CFR 2.390]
The staff needs this information to determine compliance with 10 CFR 72.236(b), (c), (d) and (l).
Holtec Response:
The information requested by the staff is provided below:
a) The temperature limits in Table 2.3.7 for the plain concrete, under normal conditions and short-term events, are meant to align with the temperature limit for HI-STORM 100 concrete established in Appendix 1.D of the HI-STORM 100 FSAR, as indicated in Section 8.8.1 of the HI-STORM UMAX FSAR. Therefore, the 350F limit in Table 2.3.7 has been reduced to 300F for consistency. The long-term temperature limit for the closure lid concrete is to Holtec Letter 5021080
applicable to the concrete used for the subgrade in space A because both concrete volumes experience very low maximum stresses under normal conditions. For the space A subgrade, the stresses under normal conditions arise from the weight of the ISFSI pad above plus the self-weight of the plain concrete material, which amounts to less than 25 psi.
The critical characteristics for the concrete used for the subgrade in space A, namely its density and its compressive strength, are specified in Table 2.3.10 of the HI-STORM UMAX FSAR. Only the temperature limit for plain concrete is adopted from Appendix 1.D of the HI-STORM 100 FSAR. The other requirements listed in Table 1.D.1 are specific to the design and placement of the plain concrete in the HI-STORM 100 lid and cask body.
b) The temperature limits in Table 2.3.7 for the plain concrete are adopted from the HI-STORM 100 FSAR. See response to part (a) for further explanation.
c) FSAR Table 2.3.7 has been updated to include the temperature limits for the plain concrete used for the subgrade in space A with proper bases. All safety conclusions remain unchanged. Further, concrete temperatures presented in Chapter 4 for all normal and short-term conditions of storage continue to remain below the revised temperature limits.
Lastly, Holtec acknowledges the error in Table 1 of the previous RAI response, and it has been entered into companys corrective action program for further evaluation. The corrected version of Table 1 is presented below.
Table 1 Steady-state fuel cladding, CEC shell and concrete temperatures for normal long-term storage of HI-STORM UMAX Version B2
[PROPRIETARY INFORMATION WITHHELD IN ACCORDANCE WITH 10 CFR 2.390].
RAI-ST-2 Provide detailed justification for not reanalyzing the soil-structure interaction (SSI) analyses due to the increased long-term temperatures for the UMAX storage system components and subgrade in space A.
The applicant responded that from the thermal model, the maximum surface temperature of the concrete in space A is well below the previously approved temperature limit of 350F for the plain concrete in the Closure Lid per FSAR Table 2.3.7. The applicant further stated that the plain concrete used in the Closure Lid is the same material used for the subgrade material in space A for the Version MSE VVM. Since the concrete temperature remains below the established FSAR limit, there is no reason to degrade the concrete strength properties and re-perform the SSI analysis contained in calculation/supplement 7A/3 of Holtec Report HI-2125228, Revision 17.
Based on the lower temperatures, the elastic modulus values used to characterize steel components are minimally affected (i.e., less than 3% for CEC shell and less than 1% for Divider Shell). Therefore, a full re-analysis of the SSI model is not warranted.
The staff agrees with the applicants response that a full re-analysis of the SSI model is not warranted, if the applicant provided the requested information in this RAI and accepted by the staff. In the RAI, the staff requested a detailed justification by providing sensitivities of the changes in the input parameters (such as relevant steel and concrete properties) due to temperature to Holtec Letter 5021080
increases on the responses from the MSE SSI analyses (seismic demands) and a comparison to the design margin available in the affected UMAX overpack and other component acceptance limits. The response to the RAI did not provide the requested information. Also, as stated in the staff feedback for the RAI St-1 response, the applicant did not adequately demonstrate: the bases for acceptance of the concrete long-term temperature limit in the subgrade space A, and the impact of long-term temperature increases on the relevant concrete design parameters. The staff needs this information to determine the impact on the safety and retrievability of the package under an MSE event.
The staff needs this information to determine compliance with 10 CFR 72.236(b), (c), (d) and (l).
Holtec Response:
To address the concern regarding the degradation of Space A material properties at high temperature, a sensitivity analysis is performed using the Design Basis Seismic Model (DBSM) for the HI-STORM UMAX Version MSE described in Section 3.4 of the HI-STORM UMAX FSAR. Specifically, the SSI analysis performed in Calculation 7A of HI-2125228 [2.1] has been revisited, and a new sensitivity run has been performed using time history set # 2, which is chosen because it has the largest horizontal ZPA per Table 1 of Calculation 7A. In the sensitivity run, the minimum concrete compressive strength of the Space A material (see Figure 2.4.4 in FSAR) is conservatively reduced by a factor of 2 to account for material strength degradation due to long-term exposure to high temperature (>300 deg. F). Per the thermal analysis supporting Amendment 5 of the HI-STORM UMAX FSAR, the maximum section average temperature for Space A material is only [PROPRIETARY INFORMATION WITHHELD IN ACCORDANCE WITH 10 CFR 2.390]. The 50% reduction in strength is a conservative estimate based on data provided in [2.2]. This approach (i.e., 50% reduction in concrete strength) is also consistent with that used in Amendment 11 of the HI-STORM 100 FSAR [2.3] to assess tornado missile impacts on the cask body at elevated concrete temperatures, which was reviewed and accepted by the NRC staff as documented in the final Safety Evaluation Report [2.4].
The results of this sensitivity run are compared with the original results for Case 2L (i.e., time history set # 2) in Table 1 below. From the results, the maximum MPC guide force and SFP load both increased for the sensitivity run. However, from Table 5 of Calculation 7A in [2.1], the HI-STORM UMAX Version B is evaluated for a bounding impact force on MPC guide plate of 596.41 kip. Therefore, the maximum impact force from the sensitivity run is still below the qualified limit.
Also, the increase in maximum SFP load is less than 2%. Per SFP analysis performed in [2.5],
the minimum safety factor is 2.1. Therefore, there is enough margin to accommodate this increase. There is a slight increase in the vertical acceleration of the closure lid but this increase does not cause the closure lid to dislodge based on the time history simulation. All the other results are lower than previously reported.
to Holtec Letter 5021080
Table 1; Key Results of LS-DYNA SSI Analysis for HI-STORM UMAX VERSION MSE under the Most Severe Earthquake Condition Case Maximum MPC Guide Plate Force (kips)
Maximum SFP Load (kips)
Space A Concrete Maximum Horizontal Acceleration (gs)
Closure Lid Maximum Accelerations (gs)
MPC Maximum Horizontal Accelerations (gs) 2L 394.57 1,061.2 6.22 8.18 (H) 2.46 (V) 7.99 2L-With reduced Space A Modulus 527.00 1,082.3 4.52 4.91 (H) 3.24 (V) 6.17
References:
[2.1]
Holtec report HI-2125228, Structural Calculation Package for the HI-STORM UMAX System, Revision 17.
[2.2]
Carette and Malhotra Performance of Dolostone and Limestone Concretes at Sustained High Temperatures, Temperature Effects on Concrete, ASTM STP 858,1985, p.38-67.
[2.3]
HI-STORM 100 Multipurpose Canister Storage System Amendment Request 1014-11, Holtec International, Docket No. 1014, January 29, 2016.
[2.4]
USNRC Final Safety Evaluation Report, HI-STORM 100 Multipurpose Canister Storage System, CoC No. 1014, Amendment No. 11, November 28, 2018 (ML18355A377).
[2.5]
Holtec report HI-2125239, Structural Analysis of HI-STORM UMAX ISFSI Structures, Revision 2. to Holtec Letter 5021080