ML24215A125
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Response to SDAA Audit Question Question Number: A-5.4.3-1 Receipt Date: 04/10/2023 Question:
The SDAA removed the assumptions used to calculate DHRS cooling performance. SDAA Section 5.4.3.3.4 states, The analyses further show the ability to accommodate fouling, SG tube plugging, and the presence of non-condensible gas, thus precluding the need for high-point vent capability.
Key parameters and assumptions utilized in the DHRS performance analysis should be provided in the FSAR; these include assumptions for reactor pool temperature, heat transfer coefficients, amount of non condensible gas, and other factors that impact cooling performance such as assumptions for future tube plugging.
Response
The US600 Final Safety Analysis Report (FSAR) Section 5.4.3.3.4 provides values used in the decay heat removal system (DHRS) performance analysis for fouling factor, steam generator (SG) tube plugging, and noncondensible gas mass.
In the US460 Standard Design Approval Application (SDAA) FSAR, Table 5.4-5 and Figure 5.4-9 through Figure 5.4-12 provide equivalent information to the information in the US600 FSAR.
The SDAA Table 5.4-2 provides the SG tube fouling factor, and Section 5.4.1.2 defines the allowable SG tube plugging margin.
NuScale Nonproprietary NuScale Nonproprietary
Section 5.4.3.3.4 of the US600 FSAR does not provide heat transfer coefficients. Heat transfer coefficients are both location and time dependent throughout a DHRS cooldown. ((2(a),(c),ECI has been uploaded into the the electronic reading room (eRR). The information needed to complete the review is in this document; NRELAP5 files containing heat transfer coefficients for relevant cases are included in a digital versatile disk (DVD) with LO-140359. ((
}}2(a),(c),ECI On July 20, 2023, there was a clarification call with the NRC. Ryan Nolan indicated that the NRC needs either the noncondensible gas mass in the analyses or an indication of the location of the level switches in relation to the DHRS actuation valves and assurance of how that location will be verified in the design.
NuScale has modified Section 5.4.3.3.2 of the SDAA to include the noncondensible gas mass used in the high inventory steady state case. The location of the level switch in relation to the DHRS actuation valves will be verified against the drawings specified in the American Society of Mechanical Engineers (ASME) design specification documents as part of the Combined Operating License Application. Inspections, Tests, Analyses, and Acceptance Criteria (ITAAC) 02.01.01 requires that Class 1, 2, and 3 piping and Class 1, 2, 3, and CS components comply with ASME Code Section III requirements, which would result in verification of the Design Reports, which include the final engineering drawings for DHRS, with the as-built piping and components. ITAAC 02.01.11 requires verification of the DHRS actuation valves to ensure that they are installed in accordance with the installation specification, which verifies the as-built location against the final engineering drawings for DHRS. Markups of the affected changes, as described in the response, are provided below: NuScale Nonproprietary NuScale Nonproprietary
NuScale Final Safety Analysis Report Reactor Coolant System Component and Subsystem Design NuScale US460 SDAA 5.4-23 Draft Revision 2 5.4.3.3.2 System Noncondensible Gas Audit Question A-5.4.3-1 The DHRS, SGs, and secondary system piping do not include safety-related high-point vent capability. During normal operation, noncondensible gases continuously vent via the MSS. Accumulation of noncondensible gas may occur in the DHRS steam piping below the closed actuation valves when DHRS is not in service. Level sensors located below the actuation valves detect the presence of noncondensible gas to limit the volume of gas that can accumulate in the DHRS piping. The DHRS performance analysis evaluates a conservative mass of noncondensible gas of 0.73 lb per train based on the internal volume of the piping below the DHRSAVs and above the DHRS level sensor and assumed gas conditions. The analysis concluded that the design provides reasonable assurance that the DHRS functions in the presence of a limiting amount of noncondensible gases. 5.4.3.3.3 Flow-Induced Vibration Section 3.9, Mechanical Systems and Components, describes the Comprehensive Vibration Assessment Program for the NPM and includes an assessment the DHRS components exposed to secondary side flow. 5.4.3.3.4 Thermal-Hydraulic Performance As a two phase natural circulation system, DHRS performance is dependent on the following factors: RCS temperature: A higher RCS temperature provides a larger driving temperature difference and increases DHRS heat transfer. water inventory: Water level is high enough to ensure the heat transfer surfaces are wetted, but low enough to ensure adequate surface area in contact with a two-phase mixture for boiling and condensation to be effective. noncondensible gas: Accumulation of noncondensible gas in the DHRS condenser has the potential to impede condensation heat transfer. reactor pool water temperature: Pool water temperature affects the mode of heat transfer on the exterior of the DHRS condenser tubes. pressure losses: A restriction orifice in the DHRS steam piping limits the mass flow rate and heat removal, and dominates the DHRS loop pressure losses. driving head: The elevation difference between the bottom of the DHRS condenser and the bottom of the SG provides the DHRS loop driving head. A thermal-hydraulic analysis, performed with NRELAP5, determines the impact of these above factors on DHRS heat transfer rate using a series of steady state and transient cases. Steady state cases characterize the effect of}}