ML24215A117
Text
Response to SDAA Audit Question Question Number: A-5.4.1-1 Receipt Date: 09/15/2023 Question:
Section 16.1.1 of the SDAA states, These revised GTS [Generic Technical Specifications] were developed consistent with the Improved Standard Technical Specification (ISTS) format and content typified in NUREG-1431, Revision 5 and NUREG-1432, Revision 5.
Revision 5 of NUREG-1431 (Westinghouse plants) and 1432 (Combustion Engineering plants) incorporated changes from Technical Specifications Task Force (TSTF) Traveler TSTF-577, Revision 1, Revised Frequencies for Steam Generator Tube Inspections.
Subsection 5.5.4.d.2 of the proposed GTS states, After the first refueling outage following steam generator (SG) installation, inspect each SG at least every 96 effective full power months
[EFPM], which defines the inspection period.
While TSTF-577 increased the maximum time between inspections and the time to inspect 100 percent of the tubes from 72 EFPM to 96 EFPM for thermally treated Alloy 690 (Alloy 690TT)
SG tubing, a key consideration for the staff in evaluating the inspection interval change was decades of operating experience with similarly designed, operated, and inspected SGs with Alloy 690TT SG tubing at operating pressurized water reactor plants.
TSTF-577 did propose changes to the Westinghouse Advanced Passive 1000 (AP1000)
Standard Technical Specifications (STS) in NUREG-2194, but as noted in the staffs safety evaluation (SE) associated with TSTF-577, those proposed changes will be evaluated in a separate SE.
However, the staff did request additional information related to the TSTF applicability to NUREG-2194 for the AP1000 design. See Request for Additional Information No. 3 in ML21060B434. Specifically, the staff asked how the AP1000 SG design, operating conditions, NuScale Nonproprietary NuScale Nonproprietary
and international experience is bounded by the U.S. Alloy 690TT SG tubing operating experience.
SDAA Section 5.4.1.6.1, Degradation Assessment, states that wear has been identified as the most likely degradation mechanism for the NuScale US460 SGs. Although this has been the case for operating plants with Alloy 690TT SG tubing, it may be determined that degradation of SG tubes in US460 plants differs from the operating plants due to design differences such as the tube shape, reversed secondary/primary coolant location, unique tube support design, or novel inlet flow restrictor. In addition, there may be differences in degradation detection thresholds.
Given the lack of operating experience for the NuScale US460 design, and given that in the first refueling outage, the 100 percent inspection of the SG tubes will only provide a single sampling of wear and degradation growth per tube, the staff sees a challenge in projecting long-term degradation rates after one cycle. Please address the following:
a.
Provide any available information supporting a 96 EFPM inspection interval after inspecting 100 percent of the tubes in each SG during the first refueling outage following SG installation.
b.
Discuss known and potential differences in SG tube inspection data acquisition and analysis capabilities for NuScale US460 compared to the operating PWR plants. In the response provide any available information related to developing and qualifying an inspection technique capable of detecting the degradation mechanisms expected, including any information on probability of detection.
References NUREG 1431, Standard Technical Specifications - Westinghouse Plants, Volume 1, Specifications, and Volume 2, Bases, Revision 5, dated September 2021 (ML21259A155 and ML21259A159, respectively).
NUREG 1432, Standard Technical Specifications - Combustion Engineering Plants, Volume 1, Specifications, and Volume 2, Bases, Revision 5, dated September 2021 (ML21258A421 and ML21258A424, respectively).
TSTF Response to NRC Questions on TSTF-577, Revision 0, Revised Frequencies for Steam Generator Tube Inspections, and Submittal of Revision 1, dated March 1, 2021 (ML21060B434).
NUREG 2194, Standard Technical Specifications, Westinghouse Advanced Passive 1000 (AP1000) Plants, Volume 1 Specifications, and Volume 2, Bases, Revision 0, dated April NuScale Nonproprietary NuScale Nonproprietary
2016 (ML16110A277 and ML16110A369, respectively).
Final SE of Traveler TSTF-577, Revision 1, "Revised Frequencies for Steam Generator Tube Inspections," dated April 14, 2021 (ML21098A188).
Response
(a) NuScale is starting work to have the Electric Power Research Institute investigate the degradation assessment; however, this work will be done to support licensees who build the US460 design. The steam generator (SG) Program will be managed by licensees, not by NuScale; therefore, the licensees SG inspection interval will be based on the degradation assessment that is ongoing.
Part 4 of the Standard Design Approval Application (SDAA) outlines the US460 design SG Program requirements in Section 5.5.4, Steam Generator (SG) Program. Section 5.5.4.d outlines the inspection frequency for SG tubes in the NuScale Power Module (NPM-20).
Because the work to support the 96 effective full power month (efpm) SG tube inspection interval in technical specification 5.5.4 is ongoing, the attached SDAA markup to the technical specifications changes the SG tube inspection interval to 72 efpm.
(b) The licensee of a US460 design plant will develop and qualify the inspection technique capable of detecting expected degradation mechanisms.
Markups of the affected changes, as described in the response, are provided below:
NuScale Nonproprietary NuScale Nonproprietary
Programs and Manuals 5.5 NuScale US460 5.5-5 Draft Revision 2 5.5 Programs and Manuals 5.5.4 Steam Generator (SG) Program (continued) c.
Provisions for SG tube plugging criteria. Tubes found by inservice inspection to contain flaws with a depth equal to or exceeding 40% of the nominal tube wall thickness shall be plugged.
d.
Provisions for SG tube inspections. Periodic SG tube inspections shall be performed. The number and portions of the tubes inspected and methods of inspection shall be performed with the objective of detecting flaws of any type (e.g., volumetric flaws, axial and circumferential cracks) that may be present along the length of the tube, from the tube-to-tubesheet weld at the tube inlet to the tube-to-tubesheet weld at the tube outlet, and that may satisfy the applicable tube plugging criteria. The tube-to-tubesheet weld is not part of the tube. In addition to meeting the requirements of d.1, d.2, and d.3 below, the inspection scope, inspection methods, and inspection intervals shall be such as to ensure that SG tube integrity is maintained until the next SG inspection. A degradation assessment shall be performed to determine the type and location of flaws to which the tubes may be susceptible and, based on this assessment, to determine which inspection methods need to be employed and at what locations.
1.
Inspect 100% of the tubes in each SG during the first refueling outage following initial startup or SG replacement.
2.
After the first refueling outage following SG installation, inspect 100% of the tubes in each SG at least every 7296 effective full power months, which defines the inspection period.
3.
If crack indications are found in any SG tube, then the next inspection for each affected and potentially affected unit SG for the degradation mechanism that caused the crack indication shall be at the next refueling outage. If definitive information, such as from examination of a pulled tube, diagnostic non-destructive testing, or engineering evaluation indicates that a crack-like indication is not associated with a crack(s), then the indication need not be treated as a crack.
e.
Provisions for monitoring operational primary to secondary LEAKAGE.