ML25121A060
| ML25121A060 | |
| Person / Time | |
|---|---|
| Site: | HI-STORM 100 |
| Issue date: | 04/11/2025 |
| From: | Storage and Transportation Licensing Branch |
| To: | |
| Shared Package | |
| ML25121A058 | List: |
| References | |
| Download: ML25121A060 (1) | |
Text
DRAFT FOLLOW-UP TO FOLLOW-UP TO RAI RESPONSES HI-STORM UMAX AMENDMENT5 Docket No. 72-1040 Structural RAIs RAI-St-2-2FF Revise FSAR Table 2.3.7, Temperature Limits proposed changes (provided in 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).
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 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.
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).
2 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 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).
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).