ML25216A285
| ML25216A285 | |
| Person / Time | |
|---|---|
| Site: | HI-STORM 100 |
| Issue date: | 08/04/2025 |
| From: | Holtec |
| To: | Office of Nuclear Material Safety and Safeguards |
| Shared Package | |
| ML25216A283 | List: |
| References | |
| 5021081 | |
| Download: ML25216A285 (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 RAIs:
RAI-St-2-2FF Revise FSAR Table 2.3.7, Temperature Limits proposed changes (provided in Attachment 3 to Holtec Letter 5021080) to clarify component description of SES in Space A (see Figure 2.4.4).
The minimum compressive strength of self-hardening engineered subgrade (SES) in Space A (see Figure 2.4.4) per FSAR Table 2.3.2 is 1,000 psi, which is used in tornado missile impact analysis and SSI analysis for the Standard option of the HI-STORM UMAX VVM storage system. As clarified in Attachment 1 to Holtec Letter 5021079, the UMAX Version B1 and Version B2 are not applicable to the Standard option and therefore the associated structural analyses are not affected and updated. Only the MSE option of the HI-STORM UMAX VVM storage system analyses are affected and evaluated for temperature rise in space A SES due to the applicability of UMAX Versions B1 and B2, where SES is a lean concrete mix with a minimum 3000 psi compressive strength per FSAR Table 2.3.10. Therefore, in order to clarify applicability of the specified temperature limits, the component description in FSAR Table 2.3.7 should be revised to SES in Space A for UMAX Version B1 & B2 MSE option (see Figure 2.4.4 and Table 2.3.10).
This information is needed to determine compliance with 10 CFR 72.236(l).
Holtec Response: The component description in FSAR Table 2.3.7 has been revised to SES in Space A for UMAX Version B1/B2 MSE option (section average) (see Figure 2.4.4 and Table 2.3.10) per the staffs request.
RAI-St-2-3FF Add a requirement for an SES in Space A per the FSAR Figure 2.4.4 (i.e.
lean concrete specified in FSAR Table 2.3.10 for the MSE option) to prevent the use of to Holtec Letter 5021081
dolostone as coarse aggregate in a concrete mix, or specify material that are permissible for use in a lean concrete mix.
For the SSI sensitivity analysis in Calculation 7A, Revision 4 of the Holtec Report HI-2125228, the reduction in concrete compressive strength is estimated based on the test data provided in Reference [9], Carette and Malhotra Performance of Dolostone and Limestone Concretes at Sustained High Temperatures, Temperature Effects on Concrete, ASTM STP 858,1985. This paper also concluded that the dolostone aggregate was found to be unstable under a sustained temperature of 150°C (3020F),
which was attributed to the slow oxidation of the pyrite contained in some of the aggregate particles. The resulting expansion causes disintegration of the aggregate and rupture of the concrete. Under similar exposure, concrete made with a limestone aggregate was found to be unaffected.
The critical characteristic like compressive strength and concrete density for subgrade in space A are specified in the FSAR table 2.3.10, however, the NRC staff could not find any material specification for a lean concrete ingredient in the FSAR or any of the drawings. Considering the important-to-safety structural functions of subgrade in space A, potential concrete rupture at sustained high temperature due to dolostone aggregate is not acceptable, and its use in the concrete mix should be prevented.
This information is needed to determine compliance with 10 CFR 72.236(b) and 72.146.
Holtec Response: Chapter 2 of the HI-STORM UMAX FSAR has been revised to add a requirement for SES in Space A for UMAX Version B1/B2 prohibiting the use of dolostone aggregate in concrete mix. This requirement is captured in Note 7 of Table 2.3.7.
RAI-St-3-5FF Clarify and if necessary, update the evaluation of Case - 2L with reduced space A concrete modulus (hereafter called Case 2LR) loads provided in Table 7 for HI-STORM UMAX Version B MSE option soil structure interaction (SSI) seismic analysis in calculation 7A, Supplement 3, Revision 4 (Attachment 4 to Holtec Letter 5021080).
Per Holtec Report HI-2125228, Structural Calculation Package for HI-STORM UMAX System, Revision 18, a sensitivity analysis in Calculation 7A is performed to address to Holtec Letter 5021081
the degradation of Space A lean concrete material properties at high temperature.
This sensitivity analysis run with the reduced concrete modulus of elasticity is performed using time history Set # 2. The results of this sensitivity run indicates that the MPC guide plate and SFP loads have increased as compared to the original results for Case 2L from Table 3. Further, this revised MPC guide load for Case 2LR is compared to the bounding design load for MPC guide from Table 5 (for SONGS) to conclude that the maximum seismic impact force from the sensitivity run Case 2LR is still below the qualified limit.
It is not clear to the NRC staff that if the Case 2LR MPC guide plates load from Table 7 accounts for or not, the increase in load due to the soil parameter variation studies (case 2LL or 2LU) and for the 1/4 gap studies (Case 2LG or 2LGS) as explained in sections 7.1 and 7.2 of the calculation 7A. If not, it appears to the staff that the Case 2LR loads should be increased to account for soil parameters variation and 1/4 gap provided between the guide plates and the MPC, before comparing it to the bounding design load for MPC guide from Table 5.
This information is needed to determine compliance with 10 CFR 72.236 (l).
Holtec Response: The sensitivity analysis identified in the RAI as Case 2LR only considers the reduction in concrete compressive strength due to sustained high temperatures in the concrete material in Space A (refer to FSAR Figure 2.4.4). The separate effects of soil parameter variations and gap variations are not combined with the temperature sensitivity study.
The reason that the effects are not combined is because the temperature sensitivity study (Case 2LR) is a hypothetical scenario in which the bulk temperature of the Space A concrete is conservatively assumed to be above 300 degrees F, leading to a 50% strength reduction of the entire concrete volume. In reality, this is not the case. Based on the results of the thermal analyses presented in HI-2230586 [5FF.1], the peak temperature anywhere in the Space A concrete is below 300 degrees F at the design basis heat load limit (10.87 kW) for HI-STORM UMAX Version B2.
Since the maximum temperature of the Space A concrete is in fact below 300 degrees F, the 50% strength reduction evaluated in Case 2LR is an extremely conservative assumption, which is only considered in isolation and not combined with other parameter studies. This is supported by the findings of Carette and Malhorta in [5FF.2], which show that: to Holtec Letter 5021081
i)
For sustained temperature exposures at or below 150°C (302°F), the reduction in compressive strength is less than 20% for concrete mixes that do not contain dolostone aggregate.
ii)
The strength losses at high temperatures are consistently smaller for leaner concrete (i.e., lower strength). This is important because the design compressive strength of the concrete material in Space A for the HI-STORM UMAX Version MSE (i.e., 3,000 psi per FSAR Table 2.3.10) is significantly less than the tested specimens in [5FF.2], which have compressive strengths between 43 MPa (6,200 psi) to 71 MPa (10,300 psi).
Based on the above, the design temperature limit for the SES (i.e., concrete) in Space A for UMAX Version B1/B2 has been set at 300 degrees F in FSAR Table 2.3.7. This aligns with the temperature limit for HI-STORM concrete established in Appendix 1.D of the HI-STORM 100 FSAR, as previously clarified in Holtecs response to RAI-St-1. Also, paragraph A.4.3 of Appendix A to ACI-349 [5FF.3] allows for higher temperature limits under normal operating conditions if supported by test data that verifies the increased temperatures do not cause deterioration of the concrete. The data provided in [5FF.2]
provides the necessary evidence to support the use of 300 degrees F as the design temperature limit for normal operation, especially considering the low stress state in the Space A concrete under normal conditions.
Lastly, to insure that not only the section average temperature but also the peak temperature of the Space A concrete is firmly below 300 degrees F, the design basis heat load limit for the HI-STORM UMAX Version B2 (MSE option) has been reduced slightly from 11.65 to 10.87 kW as part of this RAI submittal. This change is captured in Table 2.1.15 of the updated HI-STORM UMAX FSAR. The concrete temperatures for HI-STORM UMAX Version B1 are below the 300 degrees F limit with significant margins and therefore, there is no change in the design basis heat load for UMAX Version B1.
[5FF.1]
Holtec Report HI-2230586, Thermal Evaluation of HI-STORM UMAX at SONGS with Inlet Vent Flow Restrictions, Revision 2.
[5FF.2]
Carette and Malhotra, Performance of Dolostone and Limestone Concretes at Sustained High Temperatures, ASTM Special Technical Publication 858, ASTM PCN 04-858000-07, p. 38-67.
[5FF.3]
ACI 349-01, Code Requirements for Nuclear Safety Related Concrete Structures, American Concrete Institute, 2001.
to Holtec Letter 5021081
RAI-St-3-6-FF Confirm that the deformation of the CEC and Divider shell does not prevent MPC retrievability under the revised SSI sensitivity analysis with the reduced concrete modulus of elasticity per calculation 7A Revision 4.
The CEC and Divider Shell components of the UMAX overpack are subject to ovalizing forces under the design basis earthquake event, and have been evaluated in the FSAR section 3.4.4.1.2 based on the stiffness of the subgrade material in space A. The stiffness (modulus of elasticity) of the subgrade material is affected by higher temperatures under this amendment. Therefore, the deformation of the CEC should be evaluated considering the revised SSI analysis results and confirm that the deformation of the CEC and Divider shell does not prevent future MPC retrievability.
This information is needed to determine compliance with 10 CFR 72.236(m).
Holtec Response: For the revised SSI sensitivity analysis with reduced concrete modulus of elasticity, which is documented in Calculation 7A of HI-2125228 [6FF.1], the deformation of the CEC and Divider Shell does not prevent future MPC retrievability.
During the MSE earthquake, the maximum instantaneous change in the inside diameter of the Divider Shell is approximately 0.41 inches. However, the maximum change in the diameter at the end of the MSE event is less than 0.25 inches, as shown in the time history plot below. By comparison, the diametral gap between the MPC shell and the MPC inner seismic restraints is 0.5 inches per Sheet 7 of Licensing Drawing 10017 (see Detail BD). Therefore, notwithstanding the significant conservatism associated with the 50%
reduction in concrete strength (see response to RAI-St-3-5FF), there is no risk to MPC retrievability.
This aligns with expectation since, even after a 50% reduction in concrete compressive strength (from 3000 psi to 1500 psi), the elastic modulus of the subgrade still remains greater than that of the SES material for the standard HI-STORM UMAX ISFSI (which has a compressive strength of only 1000 psi per FSAR Table 2.3.2). This combined with the fact that the standard HI-STORM UMAX ISFSI already has a large margin of safety against ovalization of VVM shells, as discussed in FSAR section 3.4.4.1.2, leads to a similar conclusion for the UMAX Version MSE. This is reiterated towards the end of FSAR section 3.4.4.1.2 (see p. 3-60), which states: The MPC retrievability subsequent to the MSE event is maintained with a large margin.
to Holtec Letter 5021081
Figure 6FF-1: Change in Divider Shell Inside Diameter during MSE Event
[6FF.1]
Holtec Report HI-2125228, Structural Calculation Package for the HI-STORM UMAX System, Revision 19.
SSI ANALYSIS OF HI-STORM UMAX SC PH! DTH I IVE Lt BI change in x-length (in) o 5
10 min=A{
1.68e+01,
-4.14e-01
)
ti) 1.66e+01, 4.09e-02)
Time (s) to Holtec Letter 5021081