ML24346A185
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Response to SDAA Audit Question Question Number: A-4.4-3 Receipt Date: 06/17/2024 Question:
Please provide the supporting documents in the eRR that support the statements in Section 4.4 that the effects of crud have been accounted for (4.4.4.5 and 4.4.6) and update the FSAR with the basis for how crud was accounted for.
Response
Engineering report ER-100979, Revision 0, Statistical Subchannel Analysis Methodology supports the statements in Final Safety Analysis Report Section 4.4.4.5 and Section 4.4.6 regarding how crud is accounted for. The following is an excerpt from FSAR Section 4.4.4.5 with emphasis:
The fuel stored energy and fuel pin temperature modeling in VIPRE-01 is calibrated against values calculated using the COPERNIC fuel performance code that includes the effects of crud on the fuel rod surface as discussed in Section 4.4.4.6.
The subchannel analysis considers the range of possible axial power shapes within the allowable AO window (Section 4.4.3.4). Impacts that crud may have on AO are protected by the allowed AO window set by the technical specifications.
Therefore, the subchannel analysis methodology bounds the potential effects of crud and no explicit modeling of crud is included in the subchannel analysis.
The basis for how crud is accounted for is included in the FSAR without any revisions. ER-100979 is provided in the electronic reading room as part of this response.
Revised Response - September 2024 Based on feedback received on August 9, 2024 and discussions during the Chapter 4 in-person meeting on September 5, 2024, A-4.4-3 is revised to address concerns related to COPERNIC NuScale Nonproprietary NuScale Nonproprietary
and crud considerations. The following is a roadmap that connects the NuScale engineering validation document to the statement made in the FSAR. The quotes from the FSAR include the revised wording and the red-green markup is in the attached FSAR markup. The roadmap is organized by FSAR statements of fact followed by the corresponding information from validation documentation. Words in bold in the validation document quotes are used to highlight the statements FSAR. The FSAR is not intended to repeat the validation documentation.
((2(a),(c)
FSAR Section 4.4.4.5.2 Subchannel Model The accumulation of crud has a negligible impact on flow resistances through the core. The narrowing of the subchannels as a result of crud buildup is bounded by the flow area reduction uncertainty included in the enthalpy rise engineering uncertainty discussed in Section 4.4.2.7.3.
ER-100979 Rev. 0, Section 3.14 CRUD Considerations (( }}2(a),(c) NuScale Nonproprietary NuScale Nonproprietary
FSAR Section 4.4.4.5.2 Subchannel Model The fuel stored energy and fuel pin temperature modeling in VIPRE-01 is calibrated against values calculated using the COPERNIC fuel performance code that predicts the oxide thickness on the fuel rod surface as discussed in Section 4.4.4.6.
ER-100979 Rev. 0, Section 3.14 CRUD Considerations (( }}2(a),(c)
FSAR Section 4.4.4.5.2 Subchannel Model Crud buildup is limited by inclusion of the oxidation thickness considerations in COPERNIC. The subchannel analysis considers the range of possible axial power shapes within the allowable AO window (Section 4.4.3.4). Impacts that crud may have on AO are protected by the allowed AO window set by the technical specifications. Therefore, the subchannel analysis methodology bounds the potential effects of crud and no explicit modeling of crud is included in the subchannel analysis.
TR-117605-P Rev. 0, Section 4.1.4 Oxidation, Hydriding, and Crud Buildup (( }}2(a),(c) NuScale Nonproprietary NuScale Nonproprietary
(( }}2(a),(c)
FSAR Section 4.4.4.6 Fuel Rod Conduction Conduction of heat through the fuel rod directly impacts thermal margin to CHF for transient analyses. The VIPRE-01 one-dimensional conduction model is used for the fuel rod starting from the centerline of the fuel pellet outward to the cladding surface. VIPRE-01 does not explicitly model the phenomenon associated with fuel rod behavior changes caused by fuel exposure but does account for it by calibrating the VIPRE-01 fuel pin temperatures and stored energy to match or conservatively bound the fuel performance code (COPERNIC) results as described in Reference 4.4-1. Fuel conduction temperature calculations implicitly include the effects of crud deposition on the fuel rods because post-irradiation measurements bound crud in the oxide profile measurement.
TR-0915-17564-P-A Rev. 2, Section 4.4 Fuel Rod Conduction Model Methodology (( }}2(a),(c)
ER-100979 Rev. 0, Section 3.14 CRUD Considerations (( }}2(a),(c) NuScale Nonproprietary NuScale Nonproprietary
(( }}2(a),(c) Supplemental Response - October 2024 FSAR Section 4.4 is revised to address NRC staff feedback received on September 30, 2024. Markups of the affected changes, as described in the response, are provided below: NuScale Nonproprietary NuScale Nonproprietary
NuScale Final Safety Analysis Report Thermal and Hydraulic Design NuScale US460 SDAA 4.4-16 Draft Revision 2 Audit Question A-4.4-3 The accumulation of crud has a negligible impact on flow resistances through the core. The narrowing of the subchannels as a result of crud buildup is bounded by the flow area reduction uncertainty included in the enthalpy rise engineering uncertainty discussed in Section 4.4.2.7.3. The fuel stored energy and fuel pin temperature modeling in VIPRE-01 is calibrated against values calculated using the COPERNIC fuel performance code that includes the effects of crudpredicts the oxide thickness on the fuel rod surface as discussed in Section 4.4.4.6. Crud buildup is limited by inclusion of the oxidation thickness considerations in COPERNIC. The subchannel analysis considers the range of possible axial power shapes within the allowable AO window (Section 4.4.3.4). Impacts that crud may have on AO are protected by the allowed AO window set by the technical specifications. Therefore, the subchannel analysis methodology bounds the potential effects of crud and no explicit modeling of crud is included in the subchannel analysis. Reference 4.4-1 supplemented by Reference 4.4-2 provides details about the methodology used to analyze the thermal and hydraulic response of the fuel and core coolant, including the correlations used for heat transfer, void fraction, and pressure drop. Void fractions for the equilibrium cycle are shown in Table 4.4-4. 4.4.4.6 Fuel Rod Conduction Audit Question A-4.4-3 Conduction of heat through the fuel rod directly impacts thermal margin to CHF for transient analyses. The VIPRE-01 one-dimensional conduction model is used for the fuel rod starting from the centerline of the fuel pellet outward to the cladding surface. VIPRE-01 does not explicitly model the phenomenon associated with fuel rod behavior changes caused by fuel exposure but does account for it by calibrating the VIPRE-01 fuel pin temperatures and stored energy to match or conservatively bound the fuel performance code (COPERNIC) results as described in Reference 4.4-1. The fuel pin temperatures are bounding for any rod type in the core. Use of conservative high and low heat transfer inputs is bounding of crud effects on fuel rod conduction.Fuel conduction temperature calculations implicitly include the effects of crud deposition on the fuel rods because post-irradiation measurements include crud in the oxide profile measurement. Table 4.4-5 provides the peak fuel temperature for the core average linear heat rate and the peak linear heat rate with both values demonstrating significant margin to fuel melting. 4.4.4.7 Fuel Design-Specific Inputs Fuel design-specific information is used in the subchannel basemodel. Spacer grid loss coefficients and friction factor are derived from pressure drop tests. These derivations are applied in the subchannel analysis as described in Reference 4.4-1 and supplemented by Reference 4.4-2.}}