ML19065A027
| ML19065A027 | |
| Person / Time | |
|---|---|
| Site: | Holtec |
| Issue date: | 02/28/2019 |
| From: | Holtec |
| To: | Office of Nuclear Material Safety and Safeguards |
| Shared Package | |
| ML19065A076 | List: |
| References | |
| 5014866 | |
| Download: ML19065A027 (6) | |
Text
Request for Supplemental Information Docket No. 72-1014 Certificate of Compliance No. 1014 Amendment No. 14 to the HI-STORM 100 Multipurpose Canister Storage System Chapter 3 Structural Evaluation RAI 3-1.
Provide an evaluation demonstrating that the DFI will perform its intended function of constraining fissile material during credible accident conditions (e.g., non-mechanistic tip over or seismic event).
Section 2.1.3.1 of the application states that the DFI caps are geometrically constrained to prevent their ejection from the storage cavity during a postulated accident event. However, no analysis is presented in the application to support this claim. The applicant needs to demonstrate that the DFI will adequately perform this behavior.
The staff needs this information to determine compliance with the requirements of 10 CFR 72.236(l).
Holtec Response:
As shown in Figure 2.1.10, the Damaged Fuel Isolator (DFI) consists of two distinct parts, a top cap assembly and a bottom cap assembly, with no physical connection between them. The bottom cap assembly is installed in the basket cell first and lowered to the bottom such that it rests on the MPC base plate. The damaged fuel assembly is then installed in the basket cell and lowered to the bottom such that its bottom nozzle rests inside the DFI bottom cap assembly.
Afterwards the DFI top cap assembly is placed on top of the damaged fuel assembly such that it is in firm contact with the fuel assemblys top end fitting, and the side walls of the DFI top cap assembly are captured inside the basket cell. After all DFIs and fuel assemblies are loaded in the fuel basket, the MPC lid is installed and eventually welded in place.
One of the key design features of DFI top cap assembly is that, when it is installed on top of the damaged fuel assembly and the MPC lid is welded in place, the insertion depth of the DFI top side walls inside the fuel basket cell is greater than the clearance gap between the DFI top cap assembly and the underside of the MPC lid. Thus, based on geometric considerations alone, the DFI top cap assembly cannot be ejected from the basket cell during a postulated accident event, since the MPC lid and its attachment weld have been demonstrated to remain structurally intact and physically in place under all loading conditions. Furthermore, since the DFI top cap assembly is not fixed in place and is able to move with the damaged fuel assembly in the axial direction (relative to the fuel basket), the DFI top cap assembly is not subject to significant loading since the fuel assembly can only make contact with the DFI top and bottom end plates, which in turn are backed by the MPC lid and base plate, respectively.
In terms of its general design, all load bearing members of the DFI, including the interfacing lift points, must be designed to satisfy Level A limits per ASME Code,Section III, Subsection NF ATTACHMENT 2 TO HOLTEC LETTER 5014866
under normal conditions. The most limiting accident conditions are the non-mechanistic tip over and vertical end drop. For these accident loadings, all load bearing members of the DFI must be able to support their amplified self-weight, considering the maximum design basis horizontal and vertical decelerations in Table 3.1.2, without suffering a gross structural failure. A conservative approach is to design all load bearing members of the DFI to satisfy Level D stress limits per ASME Code,Section III, Appendix F.
RAI 3-2.
Provide drawings of the DFI top and bottom caps with dimensions, tolerances, materials of construction and location relative to the basket.
Section 2.1.3.1 of the application states that the DFI caps are prismatic boxes with flat baseplates which fit inside the storage cell space with a small clearance for ease of installation and are geometrically constrained to prevent their ejection from the storage cavity during a postulated accident event. However, it is unclear from this description or the drawings in Figure 2.1.10, what the dimensions, materials, tolerances, etc. are for the DFI caps. These details are needed to assess the ability of the DFI caps to remain in place and constrain fissile material during a credible accident.
The staff needs this information to determine compliance with the requirements of 10 CFR 72.146(a) and 72.150.
Holtec Response:
The DFI is constructed entirely from stainless steel or nickel alloy suitable for use within the high temperature environment of the MPC. Per the detail figure of the DFI, (Figure 2.1.10) the cap walls shall have perforation with a maximum size of 1mm. This allows for gases to permeate the walls while keeping any gross particulate fissile material inside the basket cell.
The height of the DFI is sized dependent upon the fuel assembly geometry. The bottom DFI is installed such that it is flush with the enclosure vessel bottom plate. The bottom of the fuel assembly is in contact with the bottom DFI. The top DFI shall extend far enough into the top of the basket cell such that if the fuel shifts upwards for any reason, the DFI top cap can contact the MPC lid and still remain in the basket cell. During installation, the top DFI will be pushed down on top of the fuel assembly until contact is made.
Section 2.1.3.1 and Figure 2.1.10 were revised to include the DFI material of construction, dimensions and location relative to the basket.
Chapter 4 Thermal Evaluation RAI 4-1.
[PROPRIETARY INFORMATION WITHHELD PER 10 CFR 2.390]
RAI 4-2.
[PROPRIETARY INFORMATION WITHHELD PER 10 CFR 2.390]
ATTACHMENT 2 TO HOLTEC LETTER 5014866
RAI 4-3.
Revise Table 3-1 and its notes in Appendix A, Technical Specifications (TS), for clarification of the heat load limits on the proposed QSHL-2, QSHL-3, and QSHL-4 patterns.
The applicant should revise the last row of Appendix A, TS, Table 3-1 (and its notes), as below, for clarification of the heat load limits on the proposed QSHL-2, QSHL-3, and QSHL-4 patterns:
Keep table entry 42.8 (MPC-68M)Note 7 unchanged (with Note 7 stating: Maximum per assembly allowable heat loads defined in Appendix B Figure 2.4-1.) and add table entry 38.9 (MPC-68M)Note 8 (with Note 8 stating: Maximum per assembly allowable heat loads defined in Appendix B Figures 2.4-2 through 2.4-4.).
The staff needs this information to determine compliance with the requirements of 10 CFR 72.236(f).
Holtec Response:
Last row of Table 3-1 of Appendix A, Technical Specifications is correct as is since the total heat load from the new proposed heat load patterns, QSHL-2, QSHL-3 and QSHL-4 are all below 42.8 kW. Note 7 clarifies that the per assembly loading can be performed per Figures 2.4-1 through 2.4-4. Even when all locations are loaded with full design basis decay heat in Figures 2.4-2 through 2.4-4, the total heat load remains below 42.8 kW. No changes to the TS are therefore necessary.
Chapter 8 Materials Evaluation RAI 8-1 (a) Clarify the condition of the fuel assemblies proposed to be stored utilizing the DFI, given the current design bases and the technical specification definition for damaged fuel assembly.
(b) Clarify whether the DFI provides the ability to handle the fuel assemblies to be stored within it by normal means under both normal and off-normal conditions.
(c) Provide operational descriptions and procedures for use, loading, and unloading of the DFI.
(d) Provide the corresponding revised FSAR page changes, including changes to the operating procedures in Chapter 8 of the FSAR.
The applicant proposes to use the DFI in place of the DFC for damaged fuel assemblies with certain physical defects (e.g., missing or partial fuel rods, a breach in the fuel cladding or a structural failure in the grid strap assembly). The applicant also states that the DFI is to be used only with damaged fuel assemblies that can be handled by normal means and whose structural integrity is such that geometric rearrangement of the fuel is not expected.
ATTACHMENT 2 TO HOLTEC LETTER 5014866
However, the current technical specifications define a damaged fuel assembly as an assembly whose structural integrity has been impaired such that geometric rearrangement of fuel or gross failure of the cladding is expected based on engineering evaluations, or that cannot be handled by normal means. Therefore, it is not clear what is the condition of the fuel assemblies that the applicant is proposing to be stored utilizing the DFI.
The applicant did not provide detailed drawings or operational descriptions and procedures for use of the DFI to explain its design and use. If the applicant intended that the DFI would provide the ability to handle the damaged fuel assembly stored within by normal means, this should be clarified in the RAI response and the FSAR page changes. In addition, the applicant should provide operational descriptions and procedures for use, loading, and unloading of the DFI, including specific changes to the operating procedures in Chapter 8 of the FSAR.
The staff needs this information to determine compliance with the requirements of 10 CFR 72.236(b) and (m).
Holtec Response:
(a) DFIs can only be used with fuel assemblies which can be handled by normal means and whose structural integrity is such that gross cladding failure or geometric rearrangement of fuel is not expected based on engineering evaluations. Fuel stored using DFIs may contain missing or partial fuel rods and/or fuel rods with known or suspected cladding defects greater than hairline cracks or pinhole leaks. Damage to the fuel assembly must be limited such that the normal method for fuel handling can be used.
The definition for DAMAGED FUEL ASSEMBLY lists four conditions which define what constitutes a DAMAGED FUEL ASSEMBLY. The four conditions are:
- 1. Fuel assemblies with known or suspected cladding defects, as determined by a review of records, greater than pinhole leaks or hairline cracks
- 2. Empty fuel rod locations that are not filled with dummy fuel rods
- 3. Missing structural components such as grid spacers, whose structural integrity has been impaired such that geometric rearrangement of fuel or gross cladding failure of the cladding is expected based on engineering evaluations
- 4. That cannot be handled by normal means DFIs can only be used with damaged fuel assemblies which meet conditions 1 or 2. DFIs can not be used to store damaged fuel assemblies which meet conditions 3 or 4. These restrictions are specified in the definition of the DFI in CoC Appendix A and FSAR sections 2.1.3, 2.1.9 and 2.III.1.
(b) DFIs are not used to handle the fuel assembly and do not provide assistance in the ability to handle the fuel assembly during normal or off-normal conditions. The bottom DFI cap is installed in the empty fuel basket location prior to the fuel assembly being loaded. The fuel assembly is loaded into the fuel basket location using normal means of handling. After the fuel assembly is loaded, the top DFI cap is installed into the fuel basket cell location. At no time is the DFI used to handle the fuel assembly. Sections 8.1.3 and 8.1.4 have been revised to include the operational steps used to install the ATTACHMENT 2 TO HOLTEC LETTER 5014866
bottom and top DFI caps into the MPC-68M. Section 8.3.4 has been revised to include the operational step to remove the top DFI cap during unloading of the MPC.
(c) The operational steps for loading and unloading the bottom and top DFI caps are contained in sections 8.1.3, 8.1.4 and 8.3 4.
(d) The revised FSAR pages are included with the response to this RAI.
RAI 8-2 Provide the references used in determining the densities of Metamic-HT and Holtite-A in Table 6.III.3.5.
The applicant presented 2.60 g/cm3 as the density of Metamic-HT in Table 6.III.3.5. The Metamic-HT Qualification Source Book shows ~ 2.7 g/cm3 as the density of Metamic-HT. The applicant presented 7.82 g/cm3 as the density of Holtite-A in Table 6.III.3.5. However, Holtecs Holtite-A: Development History and Thermal Performance Data shows ~ 1.7 g/cm3 as the density of Holtite-A.
The staff needs this information to determine compliance with the requirements of 10 CFR 72.236(c) and (d).
References Holtec International, Metamic-HT Qualification Sourcebook, Report HI-2084122, Holtec Proprietary.
Holtec International, Holtite-A: Development History and Thermal Performance Data, Report HI-2002396, Non-proprietary.
Holtec Response:
The density of Metamic-HT used in the criticality analyses and presented in Table 6.III.3.5 (2.60 g/cm3) has been assumed.
Holtec regrets that the 7.82 g/cm3 presented in Table 6.III.3.5 as the density of Holtite-A is a typographical error. The density of Holtite-A used in the criticality analyses is 1.61 g/cm3. Table 6.III.3.5 of the FSAR has been updated to correct this typographical error. The density of Holtite-A used in the criticality analyses (1.61 g/cm3) has been assumed, and it is consistent with the value provided in Table 6.3.4, which is used in all previous criticality analyses.
Observation O-1 In the initial application for Amendment No. 12, the applicant requested to add a new open loop low pressure drying (LPD) method, and subsequently removed the request. The staff noted that the description of open loop LPD, which is not approved by the NRC, is in the Report HI-2043317, Appendix P. The description of open loop LPD should be removed.
ATTACHMENT 2 TO HOLTEC LETTER 5014866
Holtec Response:
Open loop LPD has been removed from the FSAR. Details documented in the Holtec report HI-2043317 have no pedigree without it being in the FSAR.
ATTACHMENT 2 TO HOLTEC LETTER 5014866