ML24079A241
| ML24079A241 | |
| Person / Time | |
|---|---|
| Issue date: | 03/21/2024 |
| From: | Gregory Makar NRC/NRR/DNRL/NCSG |
| To: | |
| Makar, G., NRR/DNRL, 301-415-4034 | |
| Shared Package | |
| ML24079A240 | List: |
| References | |
| Download: ML24079A241 (7) | |
Text
U.S. Nuclear Regulatory Commission Public Meeting Summary
Title:
Meeting with the Industry Steam Generator Task Force Meeting Identifier: 20240076 Date of Meeting: February 22, 2024 Location: Webinar Type of Meeting: Observation Meeting Purpose of the Meeting: The purpose of this meeting was for the U.S. Nuclear Regulatory Commission (NRC) staff to discuss steam generator (SG) issues with the industry Steam Generator Task Force (SGTF).
General Details: The industry SGTF met with NRC staff on February 22, 2024, by webinar.
The purpose of the meeting was to discuss a variety of SG issues. The NRC and industry slides are available in Agencywide Documents Access and Management System (ADAMS) under Accession Nos. ML24051A034 and ML24051A123, respectively. This meeting was noticed as a public meeting and the agenda is available in ADAMS under Accession No. ML24022A129.
March 21, 2024 LISTING OF ATTENDEES U.S. NRC MEETING WITH THE INDUSTRY STEAM GENERATOR TASK FORCE February 22, 2024 Participant Affiliation Participant Affiliation Isaac Anchondo-Lopez NRC Nathan Lang Westinghouse Sasan Bakhtiari ANL Sean Kil EPRI James Benson EPRI Paul Klein NRC Cotasha Blackburn Southern Company Jaehee Kwon Doosan Steven Bloom NRC Greg Makar NRC Michael Bodak Constellation Dan Mayes Duke Energy Jasmyn Bone Entergy Josh Morton Energy Harbor Steve Brown Entergy Tim Polich Brent Capell EPRI Connor Rigsby TVA Ronald Carpino Rick Rosas Holtec Russ Cipolla Intertek Miranda Ross NRC James Cirilli EPRI Phil Rush MPR Associates Richard Coe Intertek Ethan Scully Helen Cothron EPRI Jay Smith Westinghouse Bill Cullen EPRI Samuel Snyder Westinghouse James Drake NRC Ryan Spencer TVA Dan Folsom TVA Mike Stark Dominion Energy Michael Frotscher Entergy Leslie Terry NRC Ed Gallagher Kester Thompson FPL Veena Gubbi DEP Rick Trotta Holtec Rich Guill EPRI Artur Wierzbiak Constellation Jerry Humphreys DEP Bill Wiltsey Intertek Andrew Johnson NRC Jonathan Zeitz DEP Craig Kelley Framatome Summary of Presentations: Industry representatives made presentations on recently published Electric Power Research Institute (EPRI) reports, the status of revisions to industry guidelines, recent domestic and international operating experience, and a description of percent degraded area (PDA) calculations.
The NRC staff presented a description of the NRC initial and subsequent license renewal (SLR) guidance on steam generator channel head primary-side inspections.
Additional details of the information exchanged during the meeting is provided below.
Recently published EPRI reports on the following topics were discussed:
o primary-to-secondary leak determination using tritium, o
leak rate estimation methodology for partial through-wall circumferential cracking, o
testing of elastomer compatibility with secondary side filming products, o
impact of hydrazine alternatives on electrochemical potential, o
effect of dispersant application on flow-accelerated corrosion, o
a software tool for estimating foreign object wear, and o
a software model for simulating eddy current signals.
Industry summarized a new report on the evaluation of leak rate estimation methodology for circumferential cracking. Leak rate estimation methodologies are based, in part, on flaw dimensions. The NRC staff noted that a recent request for additional information about a Steam Generator Tube Inspection Report reflects the staffs interest in better understanding how licensees are evaluating circumferential flaw detection capabilities and determining circumferential flaw sizes from eddy current data.
Industry explained that that no changes related to channel head inspection are being made to the Steam Generator Management Program (SGMP) Integrity Assessment Guidelines, which are not specific to license renewal and require channel head inspections for SGs only if they have materials susceptible to primary water stress corrosion cracking (PWSCC).
Industry concluded this is acceptable because there is no technical reason to require inspection of components not susceptible to PWSCC,1 and because plants may have requirements outside of SGMP guidance to perform channel head inspections.
An industry representative summarized recent operating experience at a domestic plant. As a result of tube wear at support plate locations, tube integrity could not be demonstrated based on analysis. During in-situ pressure testing, two of the tubes failed to meet the structural integrity performance criteria. The representative stated that the apparent cause investigation was ongoing, and the SGMP was providing assistance. The NRC staff stated that since the causal analysis is still ongoing it would not be providing detailed comments at this time. However, the staff did offer initial thoughts on the recent operating experience:
o Two tubes failing to meet the structural integrity performance criterion does not meet NRC or industry expectations. Loss of tube integrity due to wear at support structures should not happen.
o The staff thinks it is very important to take the lessons learned from the causal analysis and evaluate them beyond the affected plant to determine if there are broader issues that should be addressed by the SGMP.
o Many U.S. pressurized water reactors (PWRs) have an opportunity to increase the maximum time between inspections, provided tube integrity is technically supported by the unit-specific operational assessment. U.S. PWR operating experience with maintaining tube integrity has been very good. NRC staff will be carefully monitoring future operating experience to determine if this was a plant-specific issue or the beginning of a negative trend.
o After the causal analysis is complete and NRC staff have reviewed the final information, the staff will determine if a generic communication is appropriate.
An international utility concluded tube wear has been caused by pieces of oxide scale that spalled from and then lodged against tube surfaces. Industry described the utilitys activities to confirm the cause, characterize the scale, prevent future occurrences, and SGMP studies to characterize deposits in domestic steam generators.
The subsequent inspection at this plant, and the inspection of another of the same utilitys plants, found additional indications of this type during eddy current inspection. Of the 15 1 The NRC staff considers some of the nickel alloys currently used in channel head components to have low susceptibility to PWSCC; none are considered not susceptible.
indications detected, 6 were estimated by eddy current inspection to be at least 40 percent through wall, 14 were on the cold-leg side of the SG, and all 15 were adjacent to either the second, third, or fourth tube support plate. Microscopy and wear tests confirmed that both units contained scale with a high wear capacity as determined by its high density and wear testing using scale samples and SG tubes.
The utility performed laboratory testing to verify that Advanced Scale Conditioning Agent (ASCA) treatment reduced the thickness of the dense scale layer by increasing the porosity (except when sludge was covering the scale). The utility subsequently performed mechanical cleaning at the tubesheet and tube support plates followed by enhanced ASCA.
In the U.S., the SGMP is characterizing SG deposit flakes spalled from SG tubes that represent a variety of SG designs, locations, operating chemistry, materials of construction, and other attributes. Characterization focuses on factors related to wear: hardness, composition, porosity, and thickness. The collected samples were exposed to sludge removal during multiple outages. Samples were collected before or after chemical cleaning.
The SGMP research to characterize removed flakes and assess the effects of soft chemical cleaning is ongoing, and a technical report is planned.
In response to a question asked previously by the NRC staff, industry presented a summary comparing simplified and geometric formulas for calculating percent PDA for circumferential flaws. Industry stated that the PDA calculation method is not prescribed in SGMP guidelines. An example for a 360-degree, 75 percent through-wall crack resulted in a maximum difference of 1.6 percent PDA, with the geometric method producing the higher PDA. Industry concluded that this difference between calculation methods would apply when comparing a calculated PDA for a detected flaw to the condition monitoring limit curve.
The NRC staff provided an overview of initial license renewal and SLR guidance for inspection of surfaces in SG channel heads. The presentation explained that the guidance includes visual inspection of the divider plate assembly, tube-to-tubesheet welds, channel head interior surfaces, and the tubesheet for all SGs regardless of material. The visual inspections are part of the Steam Generators aging management program (AMP), which is used with the Water Chemistry AMP to manage aging of SG components. A plant-specific AMP (e.g., One-Time Inspection) may also be needed depending on the materials, alternate repair criteria affecting the tube-to-tubesheet welds, and the applicability of bounding industry analyses.
The NRC provided the following in response to questions:
If, according to NRC guidance, a plant-specific program (e.g., One-Time Inspection) is needed to supplement general visual inspection of the channel heads, that inspection must be capable of detecting cracking but not necessarily a volumetric inspection. The staff agreed to include relevant guidance from the One-Time Inspection AMP in the meeting summary (see enclosure).
The channel head inspection maximum interval is increased from 72 months to 96 effective full power months in the draft SLR guidance to be consistent with the latest Steam Generator Program requirements in the Standard Technical Specifications (Revision 5) and Technical Specifications Task Force Traveler 577 (TSTF-577), TSTF Response to NRC Questions on TSTF-577, Revision 0, Revised Frequencies for Steam Generator Tube Inspections, and Submittal of Revision 1 (ML21060B434).
The unconventional design of the NuScale small modular reactor steam generators, with the primary coolant outside the tubes and secondary coolant inside the tubes, does not change the NRC requirements regarding tube inspections. Inspection details are not required at the design stage, but a licensee will be required to perform inspections to maintain tube integrity in accordance with technical specifications based on the same regulations and criteria as plants with conventional nuclear steam generators.
If you have any questions regarding this meeting summary, please feel free to contact Greg Makar by phone at 301-415-4034, or by e-mail at Gregory.Makar@nrc.gov.
Enclosure:
Portions of License Renewal Aging Management Program XI.M32, One-Time Inspection Attachments:
1.
Meeting Notice:
ML24022A129 2.
NRC Slides:
ML24051A034 3.
Industry Slides:
ML24051A123 4.
Package:
ML24079A240 cc: HCothron, EPRI
Package: ML24079A240 Meeting Summary: ML24079A241 Meeting Notice: ML24022A129 NRC Slides: ML24051A034 Industry Slides: ML24051A123
- via econcurrence OFFICE NRR/DNRL/NCSG NRR/DNRL/NRLB/LA NRR/DNRL/NCSG/BC NAME GMakar*
SGreen*
SBloom*
DATE 3/20/2024 3/21/2024 Enclosure ENCLOSURE ONE-TIME INSPECTION AGING MANAGEMENT PROGRAM FOR INITIAL AND SUBSEQUENT LICENSEN RENEWAL (XI.M32)
During the meeting on February 22, 2024, in response to a question from industry about acceptable inspection methods for channel head inspections, the NRC staff stated that additional guidance about the One-Time Inspection Aging Management Program (AMP) would be included in the meeting summary. Table XI.M32-1 (below) from the One-Time Inspection AMP in the Generic Aging Lessons learned report for subsequent license renewal (GALL-SLR report, Volume 2, ML17187A204) provides examples of inspection methods for various aging effects, mechanisms, and parameters monitored.