ML24215A115

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LLC, Response to Sdaa Audit Question Number A-5.4-6
ML24215A115
Person / Time
Site: 05200050
Issue date: 08/02/2024
From:
NuScale
To:
Office of Nuclear Reactor Regulation
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Response to SDAA Audit Question Question Number: A-5.4-6 Receipt Date: 10/20/2023 Question:

Drawings reviewed on the portal (e.g., ED-102539, Rev. 0) include SG tube support spacer and socket head cap screw. Chapter 5 of the SDAA does not include schematics of these components and does not discuss the purpose of these components. Please discuss why these components are not identified in Chapter 5 of the SDAA. In addition, please discuss how the design of these components reduce the potential for tube damage due to loose parts.

A follow-up question was posed on December 8, 2023:

The response to Audit Issue A-5.4-6 states that the SG tube support spacers and socket head cap screws are part of the SG supports in the SDAA. The response describes the purpose of the spacers and socket head cap screws as ensuring that the SG tubes are supported in the area of the RPV with a larger inner diameter. In addition, the response states, The detailed description of every ASME BPVC Section III, Subsection NG, internal structure part is not required in SDAA. No changes to the SDAA were proposed.

Given that the spacers and socket head cap screws ensure SG tube support in the area of the RPV with a larger inner diameter, the staff considers the SDAA design description to be incomplete without a discussion of these components. The staff requests a discussion describing the purpose of the spacers and socket head cap screws be added to the SDAA.

Response

The steam generator (SG) tube support spacer and the socket head screw cap are American Society of Mechanical Engineers (ASME) Boiler Pressure Vessel Code (BPVC)Section III, Subsection NG, Internal Structures. As noted in Standard Design Approval Application (SDAA)

NuScale Nonproprietary NuScale Nonproprietary

Section 5.4.1.5, the design, fabrication, construction, and testing of the SG supports and SG tube supports, including weld materials, does not adversely affect the integrity of the core support structures; the SG tube support spacer and the socket head screw cap are part of the SG supports in SDAA. The detailed description of every ASME BPVC Section III, Subsection NG, internal structure part is not required in SDAA.

The SG tube support spacer bridges the change in reactor pressure vessel (RPV) inner diameter and accommodates the wider inner diameter of the RPV by providing tube support in the flared portion. The SG tube support spacer is a tool ensuring that the SG tubes are supported in the area of the RPV with a larger inner diameter.

Both the spacer and the cap screw are below the SG tubes, so there is no potential for these parts to damage the SG tubes. To prevent damage to other components of the reactor vessel internals, the design of the SG tube support spacer and the socket head cap screw prevents the potential of these components becoming loose parts. The socket head cap screw affixes the spacer block to the Column 21 tube support. The position of the adjacent tube support (i.e.,

Column 20) does not allow space for the cap screw to back out and disengage with the spacer. Additionally, the socket head cap screw is lock welded to the tube support to prevent any rotation.

In response to the follow-up question on December 8, 2023, the attached mark-up to the SDAA incorporates discussion of the spacers and socket head screw caps in Section 5.4.1.2 and adds support bolting materials to Table 5.4-3.

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 5.4-5 Draft Revision 2 The SG design permits periodic inspection and testing of critical areas and features to assess their structural and pressure boundary integrity when the NPM is disassembled for refueling as shown in Figure 5.4-3. The internal surface of SG tubes is accessible over their entire length for application of nondestructive examination methods and techniques that are capable of finding the types of degradation that may occur over the life of the tubes. Individual SG tubes may be plugged and, if necessary, stabilized to prevent adverse interaction with non-plugged tubes. Access to the internal (secondary) sides of tubesheets affords opportunity for inspection, and for removal of foreign objects. Figure 5.4-3 and Figure 5.4-4 contain illustrations of the steam and feed plena inspection ports.

Classifications and Quality Group designations for design, fabrication, construction and testing of SGS components that form part of the RCPB are in Table 3.2-2. Chapter 3 provides detailed information regarding the design basis and qualification of structures, systems, and components based on these classifications and designations. Figure 6.6-1 shows the ASME BPVC Section III, Class 1 and 2 boundaries for the SGS.

Steam Generator Tube Supports and Steam Generator Supports The seamless helical coil SG tubing is supported by a series of austenitic stainless steel tube support assemblies. The geometric design and materials utilized facilitate fluid flow while minimizing the potential for the generation of corrosive products and buildup. The material and geometry choice precludes two of the most significant historical contributors to tube degradation by the tube supports.

Audit Question A-5.4-1, Audit Question A-5.4-6 The tube support assemblies are between each column of helical tubes as shown in Figure 5.4-6. There is a backing strip between the upper riser assembly and the first column of tubes that completes the enclosure of the column 1 tubes and functions as the interface between the upper riser assembly and the tube support.

There is a SG tube support spacer that provides support for the SG Column 21 tube support in the region where the RPV inner diameter flares. There are socket head screw caps that affix the SG tube support spacers to the Column 21 SG tube support.The tube support structure is within the primary coolant environment; therefore, no ingress path exists for general corrosion products from the secondary system to deposit on the primary side of the SG. Optimization of the circumferential spacing of the tube supports provides the minimum possible tube free span lengths while still accommodating the transition of the tubes to the steam and FW tube sheets.

NuScale Final Safety Analysis Report Reactor Coolant System Component and Subsystem Design NuScale US460 SDAA 5.4-39 Draft Revision 2 Audit Question A-5.4-8, Audit Question A-5.4-6 Table 5.4-3: Steam Generator System Component Materials Component Specification Alloy Designation (Grade, Class, or Type)

SGS Piping

  • SGS Main Steam Piping Assembly Pipe SA-312 TP304 SMLS, TP316 SMLS1 Pipe Fittings SA-182 F304, F316 1 SA-403 WP304 SMLS, WP316 SMLS 1 Pressure-Retaining Bolting SB-637 UNS N077182 Piping Supports Supports SA-240 Type 304, Type 3161 Type 405, Type 410S SA-479 Type 304, Type 3161 Type 405, Type 410 Annealed or Class 1 SA-312 TP304, TP304L, TP316, TP316L1 Bolting SA-193 Grade B8, Grade B8M SA-194 Grade 8, Grade 8M SA-564 Type 630 H1100 SG Supports SG Supports, SG Tube Supports SG Backing Strips, Support Bolting SA-240 Type 304 Weld Filler Metals for Piping, Piping Supports, and SG Supports 3XX Austenitic Stainless Steel Weld Filler Metals SFA-5.4 E308, E308L, E316, E316L3 SFA-5.9 ER308, ER308L, ER316, ER316L3 SFA-5.22 E308, E308L, E309, E309L, E316, E316L 3,4 SFA-5.30 IN308, IN308L, IN316, IN316L3 Nickel-Base Alloy Weld Filler Metals SFA-5.11 ENiCrFe-7 SFA-5.14 ERNiCrFe-7, ERNiCrFe-7A, EQNiCrFe-7, EQNiCrFe-7A Inlet Flow Restrictor Components Mandrel with Orifice SA-479 Type 316 Flow Restrictor Flanged Sleeve SA-479 Type 304 Flow Rrestrictor Hardware SA-479 Type 316 Flow Restrictor Collet SA-479 Type 304 Flow Rrestrictor Llocking Pplate SA-240 Type 304 Other SG Components
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