ML24215A080
| ML24215A080 | |
| Person / Time | |
|---|---|
| Site: | 05200050 |
| Issue date: | 08/02/2024 |
| From: | NuScale |
| To: | Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML24215A000 | List:
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| References | |
| LO-169995 | |
| Download: ML24215A080 (1) | |
Text
Response to SDAA Audit Question Question Number: A-3.12.5.9-2 Receipt Date: 12/04/2023 Question:
This question is related to A-3.12.5.9-1. The topic of piping functional capability was discuss as a topic in the agenda of ASME Section III Piping Working Group and Subgroup Component Design During 2023 Boiler and Pressure Vessel Code Week (November 13-17). It was unanimously agreed to that ASME,Section III Code design requirements are to ensure pressure boundary structural integrity and that compliance with ASME Code requirements does address component functional capability. From a regulatory perspective, the staff considers that piping functional capability is ensured by following NUREG-1367 recommendation. NuScale indicated its opposition to meet NUREG-1367. As a result, NuScale is requested to provide an alternative criteria to justify piping functional capability.
Response
NuScale agrees that ASME BPV Code,Section III is intended to ensure pressure boundary structural integrity and the Code does not explicitly address functional capability of piping systems. This point is addressed in NCA-2142(b) where it is stated that, The selection of limits for Design, Service, or Test Loadings to assure operability is beyond the scope of this Section.
However, the use of the ASME BPV Code, 2017 Edition in conjunction with other NuScale design features and design criteria ensures the concerns of NUREG-1367 are adequately addressed and functional capability is assured. The criteria contained in Section 9.1 of NUREG-1367 are discussed separately below, and revised alternative criteria are proposed, which take into account the significant amount of industry discussion related to this issue and changes to ASME BPV Code that occurred after NUREG-1367 was written.
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NuScale proposes the following alternate criteria to specifically address NUREG-1367 recommendations. Further explanation and NuScales compliance are described below each criterion in italics.
Level D nonreversing dynamic loads are combined with SSE.
o Criterion 1 of NUREG-1367 states that all loads must be reversing, which implies that there are no functional capability criteria for non-reversing dynamic loads such as slug-flow water hammer, relief valve discharge, or jet impingement.
However, if the load is combined with SSE, Level D limits are acceptable for functional capability. This approach recognizes the conservatism of loading combinations that combine seismic with other dynamic loads and has been accepted by the NRC in the past (AP600 and AP1000 designs, Reference 1 and Reference 2 respectively). FSAR Table 3.12-1 and Table 3.12-2 show that all non-reversing dynamic loads are combined with SSE in at least one Level D loading combination demonstrating compliance with this alternative criterion.
Dynamic moments calculated using an elastic response spectrum analysis utilize +/-15 percent peak broadening and not more than 5 percent damping.
o Criterion 2 of NUREG-1367 implies that dynamic moments must be calculated using an elastic response spectrum analysis. However, it is common practice for time-history analysis to be used to evaluate dynamic fluid loads and seismic loads in reactor connected piping, and equivalent static analysis utilizing dynamic load factors to be used to evaluate relief valve discharge and jet impingement loads. This alternative criterion does not preclude analysis methods other than elastic response spectra analysis and has been accepted by the NRC in the past (AP600 and AP1000 designs, Reference 1 and Reference 2 respectively).
NuScale complies with RG 1.61 and RG 1.122 when generating in-structure response spectra, which ensures compliance with this alternative criterion.
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The design code utilized is the ASME BPV Code, 2017 Edition.
o Criterion 3 of NUREG-1367 was added to address the failure mode (ratchet collapse) observed in EPRI Piping and Fitting Dynamic Reliability Program component Test #37. The author states that the restriction on weight is due to the lack of test data verifying that higher proportions of weight stress would be acceptable. However, since the publication of NUREG-1367, further investigation of the test #37 results has been performed. In an ASME position paper on the topic (Reference 3), it was judged that the nature of the failure in Test #37 could be primarily attributed to being unpressurized and having an extremely artificial input (long duration low frequency input). However, in an abundance of caution and to specifically address Test #37 concerns, the ASME Code implemented a tighter restriction on allowed Do/t ratios (i.e., less than 40) and a limit on weight stresses of 0.5Sm (or 0.5Sh) if using the B indices and 3Sm (or 3Sh) limit (Reference 3 and Reference 4). Note that the weight stress limit should be thought of as controlling the natural frequency of the system rather than steady state stresses (which was what Test #37 was designed to evaluate), and was implemented to prevent excessive ratcheting even in uncommon piping configurations susceptible to ratchet collapse such as the inverted pendulum (Reference 4). Additional steady state loads, such as jet impingement, would act to stiffen the system. Because NuScale utilizes the ASME BPV Code, 2017 Edition, which includes the applicable limits in NB-3656 and NC/ND-3655, this alternative criterion is satisfied.
The Do/t of the piping does not exceed 50.
o Criterion 4 of NUREG-1367 is retained and not modified. Do/t for NuScales ASME Class 1, 2, and 3 piping does not exceed 50 satisfying this criterion. Note that, as discussed above, the ASME BPV Code, 2017 Edition, includes a more restrictive limit if using the B indices and 3Sm (or 3Sh) limit.
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Service Level D external pressures are considered in Level D loading combinations.
o Criterion 5 of NUREG-1367 states that external pressure cannot exceed internal pressure; however, elsewhere in the document it is stated that this criterion was included as a reminder that this special condition might need to be considered.
NUREG-1367 also states that the Do/t limits of criterion 4 partially address this concern; therefore, it should be noted that NuScales piping includes Do/t ratios significantly under the 50 Do/t limit with all piping being less than a ratio of
((2(a),(c), ECI. NuScales ASME Design Specification for Class 1, 2, and 3 Piping requires the consideration of external differential pressures during all applicable loading conditions including Level D; therefore, this alternative criterion is considered to be satisfied.
References:
1. Westinghouse Electric Company, Mechanical Systems and Components, Chapter 3, Section 3.9, AP600 Design Control Document, Rev. 4. 2. Westinghouse Electric Company, Design of Structures, Components, Equipment and Systems, Chapter 3, AP1000 Design Control Document, Rev. 19. 3. Adams, T.M., et al., ASME Position Paper on Proposed USNRC Rule Making Affecting the ASME Boiler and Pressure Vessel Code, Section III, Division 1 Subsection NB-3600, Subsection NB-3228, Subsection NC-3600 and Subsection ND-3600 Piping Design Rules, March 18, 2004. 4. Minichiello, J, Branch, EB, Adams, TM, Asada, Y, & Barnes, RW. "Background to Recent Revision of the Section III Seismic Piping Rules." Proceedings of the ASME 2002 Pressure Vessels and Piping Conference. Pressure Vessel and Piping Codes and Standards. Vancouver, BC, Canada. August 5-9, 2002. pp. 363-367. ASME. No changes to the SDAA are necessary. NuScale Nonproprietary NuScale Nonproprietary}}