ML24226B220
| ML24226B220 | |
| Person / Time | |
|---|---|
| Site: | 07201031 |
| Issue date: | 09/06/2024 |
| From: | Storage and Transportation Licensing Branch |
| To: | |
| Shared Package | |
| ML24226B217 | List: |
| References | |
| Certificate No. 1031, EPID L-2023-LLA-0143, CAC 001028 | |
| Download: ML24226B220 (1) | |
Text
UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001
Request for Additional Information Docket No. 72-1031 Certificate of Compliance No. 1031 Amendment No. 15 Model No. MAGNASTOR
This request identifies additional information needed by the U.S. Nuclear Regulatory Commission (NRC) staff in connection with its review of the application. The NRC staff used NUREG-2215, Standard Review Plan for Spent Fuel Dry Storage Systems and Facilities - Final Report, in its review of the application.
Each question discusses information needed by the NRC staff to complete its review of the application and to determine whether the applicant has demonstrated compliance with the regulatory requirements of Title 10 of the Code of Federal Regulations (10 CFR) Part 72.
Structural Evaluation
RAI-St-1Explain 1) why the values in the proposed final safety analysis report (FSAR) of the allowable yield strength, ultimate strength, and design stress intensity are different for the same material at the same temperature, 2) why yield stress increases with temperature increase (contrary to common material behavior), and 3) why the temperature has no impact to these material properties.
In the proposed FSAR, the value of material yield stress, ultimate strength, and design stress intensity used for multiple capacity checks were changed due to improved high heat loads. These material properties are listed in multiple sections of FSAR, and the values are inconsistent with basic material property behaviors. A few examples are listed below (this is not an all-inclusive list):
- 1. Different yield stress assigned for same material at same temperature.
On page 3.4-44 and 3.4-51:
Sy = 28.4 ksi is listed for yield strength of SA182 Type F304 at 225°F On page 3.4-45, 3.4-47, 3.4-49, and 3.4-50:
Sy = 24.4 ksi is listed for yield strength of SA182 Type F304 at 225°F
- 2. A larger yield stress is assigned for the same material at higher temperature.
On page 3.4-59:
Sy = 27.9 ksi is listed for yield strength of SA182, Type F304 at 215°F On page 3.4-62:
Sy = 26.5 ksi is listed for yield strength of SA182 Type F304 at 155°F
- 3. The same design stress intensity is assigned to different material at different temperatures.
On page 3.4-52, 3.4-64, 3.4-66:
Sm = 20.0 ksi is listed for design stress intensity for SA-240, Type 304, at 200°F and 225°F
Enclosure On page 3.4-54, 3.4-55, 3.4-67, 3.4-69:
Sm = 20.0 ksi is listed for design stress intensity for SA182 Type 304, at 210°F, 225°F, and at up to 300°F
The proposed FSAR needs to be updated to correctly apply the values. When updating the proposed FSAR, the applicant should also correct typos for the material property design temperatures.
This information is needed to determine compliance with 10 CFR 72.24(d)(1) and 10 CFR 72.122(a).
Thermal Evaluation
RAI-Th-1Provide calculations and analysis results of the MAGNASTOR pressurized-water reactor (PWR) configuration during long-term storage and short-term operations that justify the assumption of turbulent flow in the transportable storage canister (TSC) downcomer region as well as bottom and top plenums.
Proposed FSAR section 4.14.1.1.1 states that the helium downcomer region is modeled as turbulent for the TSC models of the PWR configuration. The staff reviewed MAGNASTOR computational fluid dynamics model and noticed that, in addition to the downcomer region being characterized as turbulent flow, the bottom and top plenum are also assumed to be in the turbulent flow regime. To properly characterize and justify the use of turbulent model in these TSC regions, the applicant needs to obtain Rayleigh and Reynolds numbers for helium flow. For proper helium flow regime characterization, both numbers are needed because this is a buoyancy-driven flow. A Reynolds number of at least 2300 and Rayleigh number of at least 1x109 would indicate the flow is in the turbulent regime. Otherwise, the flow would be laminar.
The staff needs this information to have assurance predicted temperatures remain below allowable limits during long-term storage and short-term operations. The staff noticed that the results provided in the amendment application show very small margin against the allowable limit. Predicted temperatures did not include any uncertainty quantification (such as modeling error, numerical, or input error).
This information is needed to determine compliance with 10 CFR 72.236(b) and 10 CFR 72.236(f).
RAI-Th-2Provide calculations and analysis results (including uncertainty quantification) that demonstrate predicted temperature will not exceed allowable limits for the higher heat loads included in the amendment request.
FSAR section 4.14 provides thermal results that show very small margin against the allowable limit for normal conditions of storage. It is not clear to the staff if these predicted temperatures include some type of uncertainty quantification or conservatisms added to the thermal predictions. The staff needs this information to determine the adequacy of predicted thermal results to make sure no thermal limits would be exceeded during normal storage conditions.
2 This information is needed to determine compliance with 10 CFR 72.236(b) and 72.236(f).
Shielding Evaluation
RAI-Sh-1The proposed FSAR states that (page 5.14.9-1) for the reduced the Width LMTC, a significant increase in occupational dose will not be observed, either for uniform or preferential loading patterns.
The proposed FSAR did not provide any justification for this statement even though the dose rate at the side of LMTC will increase by 5 percent and 20 percent along the flats, which is a localized peak. The applicant needs to demonstrate the reasons for not increasing occupational dose due the reduced width for LMTC.
Provide an explanation for not observing any increase in occupational dose rate for both the uniform and preferential patterns. This information is needed to determine compliance with 10 CFR 20.1201 and 10 CFR 72.236(d).
RAI-Sh-2The applicant added two new fuels, CE16-NGF and CE16-HTP, but does not provide a shielding evaluation nor provide any justification that these fuels are bounded by the previously approved CE fuels. Sufficient justification for not evaluating these fuels or why they are bounded by the previously approved fuels needs to be provided, since no additional calculations for the CE16-NGF and CE16-HTP types were provided by the applicant.
Provide justification explaining how the two new fuels, CE16-NGF and CE16-HTP, are bounded by the previous CE fuel. This information is needed to determine compliance with 10 CFR 72.236(d).
RAI-Sh-3Section 5.14 of the proposed FSAR states that the loading patterns (Patterns I, J, K, L, M and N) allow the high heat loads for the loading of PWR fuel with cool times as low as two years. Pattern N has higher heat load. The dose rates evaluated are for the CC3 /CC7 lid/top cask for the fuel assembly. The resulting maximum and average surface dose rates for these patterns are shown in FSAR table 5.14.4-2.
The Pattern N has higher dose rates and bounding.
However, it is not clear from the discussion how decay heat was used to derive source terms for the fuel to be stored in the MAGNASTOR system and why the higher heat source produces higher dose rates.
Based on NUREG/CR-6700 and a study published by Oak Ridge National Laboratory [Reference 1], there is essentially no correlation between decay heat and radiation source terms (neutron and gamma). Therefore, using higher decay heat load will not necessarily result in higher source terms for shielding calculation. The shielding calculations for dose rates and site boundary dose should be made based on the allowable fuel that produces the maximum source terms.
- a. The applicant should demonstrate that the dose rates for the all loading patterns are bounded by the values used for the shielding calculation for the maximum source terms for the MAGNASTOR system.
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- b. Explain how decay heat was used to calculate the bounding source terms and demonstrate that this approach ensures conservative results for the shielding analyses.
The staff needs this information to determine if the MAGNASTOR system design meets the regulatory requirements of 10CFR 72.236(d).
Reference:
- 1. R. Cumberland et. al., A Study on the Relationship between Dose Rate and Decay Heat for Spent Nuclear Fuel Casks, Oak Ridge National Laboratory, June 17, 2020. https://doi.org/10.2172/1649326.
Materials Evaluation
RAI-M-1Address whether the thermal and mechanical properties of the concrete in FSAR chapter 8 used in the thermal and structural evaluations need to be updated to ensure they are valid for the high density concrete for CC8. Please update the thermal and mechanical properties, if needed, to ensure that they are valid for the high density concrete used for CC8.
The staff noted that the Amendment 15 application does not include any updates to the thermal properties for the high density concrete in the FSAR chapter 8 material property tables. For mechanical properties, the Amendment 15 application only shows the higher density of the high density concrete; the mechanical property tables in FSAR chapter 8 do not include updates to any other mechanical properties for the high density concrete relative to the previous version of the application. The staff notes that certain mechanical and thermal properties of concrete may be affected by the higher concrete density. Such changes would affect the structural and/or thermal analyses. The structural and/or thermal evaluations for storage system components should address changes to applicable material property inputs to ensure acceptable performance.
With respect to the effect of concrete density on the modulus of elasticity, the application describes a sensitivity study in proposed FSAR section 3.14.3.2.1 (page 3.14.3-11) to demonstrate that previously calculated concrete cask thermal stresses remain bounding for CC8. The application indicates that this sensitivity study accounts for the difference in the concrete modulus of elasticity corresponding to the higher density concrete. However, the staff identified that the effects of the higher concrete density on the concrete modulus of elasticity are not documented in the mechanical properties tables in chapter 8 of the FSAR, and these tables also do not address the potential effects of the higher concrete density on other mechanical and thermal properties of concrete.
The staff is requesting this information to ensure that the application meets the requirements in 10 CFR 72.236(b) and 72.236(g).
RAI-M-2Specify the thermal properties of the thermal shunts that are used as inputs into the thermal evaluation of their heat transfer performance, if applicable. Update the thermal properties tables in FSAR chapter 8, as needed, to include the thermal properties of the thermal shunts that are used in inputs into the thermal evaluation of their heat transfer function, if applicable.
4 Identify whether the thermal evaluation of the package includes or credits the heat transfer function of the thermal shunts, and if so, please identify the location in the application or the calculation package where the heat transfer function of the thermal shunts is evaluated. If the heat transfer function of the thermal shunts is not evaluated, provide information to demonstrate that such an evaluation is not needed to ensure adequate thermal performance of the storage system.
One of the new fuel loading patterns for the Amendment 15 application includes the use of thermal shunts that are loaded into certain cells in the basket in lieu of spent fuel assemblies. The application states that a thermal shunt is a specially designed stainless-steel weldment designed to occupy specific storage locations in a fuel basket for certain short-loaded preferential loading patterns. The application states that thermal shunts prevent fuel assemblies from being inadvertently loaded into storage locations that are not intended for fuel. The application also states that the thermal shunts provide a heat transfer function.
The application includes a new thermal shunt weldment drawing as Drawing No. 71160-L378 (proprietary) in the Amendment 15 application. The criticality evaluation of the basket with cells containing thermal shunts is addressed on proposed FSAR page 6.1-2 (pdf page 658 in the proprietary proposed FSAR). The staff noted that the Amendment 15 application does not appear to include thermal properties for the thermal shunt materials. Also, the thermal evaluation, as described in chapter 4 of the FSAR, does not appear to specifically address the effect of the heat transfer function of the thermal shunts on the thermal performance of the storage system components.
The staff is requesting this information to ensure that the application meets the requirements in 10 CFR 72.236(b) and 72.236(g).
RAI-M-3Update the Amendment 15 application to reconcile the discrepancy, described below, between footnote d in proposed FSAR chapter 8 page 8.3-2 and the description of the structural evaluation in FSAR section 3.4.3.3.3 (page 3.4-44) regarding the minimum required yield strength at 70 degrees F for the PMTC trunnions:
Footnote d is added to FSAR chapter 8 page 8.3-2 for the Amendment 15 application. Footnote d specifies that a minimum yield strength of 35 ksi at 70 degrees F is required for the trunnions of the PMTC. Footnote d also specifies that a minimum yield strength of 34 ksi at 70 degrees F is required for the trunnions and top forging of the LMTC.
The identification of the minimum required yield strength at 70 degrees F for the PMTC trunnions in the description of the structural evaluation in FSAR section 3.4.3.3.3 (page 3.4-44) appears to be inconsistent with the other parts of the application since the structural evaluation states that the PMTC design requires a special yield strength of 34 ksi for the trunnions (SA182, Type F304) at 70 degrees F, whereas footnote d on page 8.3-2 in FSAR chapter 8 and page 1 of the PMTC body weldment drawing (Drawing No. 71160-656, proprietary) both state that a minimum yield strength of 35 ksi at 70 degrees F is required for the trunnions of the PMTC. Therefore, a correction may be needed to ensure that the application
5 consistently specifies the correct requirement for the minimum yield strength at 70 degrees F for the PMTC trunnions.
The staff is requesting this information to ensure that the application meets the requirements in 10 CFR 72.236(b) and 72.236(g).
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