ML25104A116
| ML25104A116 | |
| Person / Time | |
|---|---|
| Site: | Seabrook  |
| Issue date: | 04/14/2025 |
| From: | Division of Operating Reactors |
| To: | |
| References | |
| Download: ML25104A116 (1) | |
Text
Advisory Committee on Reactor Safeguards (ACRS)
Subcommittee Meeting Seabrook Alkali-Silica Reaction (ASR)
Update / Information Briefing Division of Operating Reactor Safety U.S. NRC Region I April 17, 2025
NRC Staff Presenters Nate Mentzer Senior Project Engineer Region I Niklas Floyd Senior Reactor Inspector Region I Travis Daun Senior Resident Inspector, Seabrook Region I 2
Agenda
- NRC Assessment Summary
- Alkali-Silica Reaction (ASR) Background
- Seabrook Aging Management
- NRC Inspection and Assessment of ASR
- Next Steps 3
NRC Assessment Summary
- NRC inspectors determined Seabrook structures remain capable of performing their safety functions as intended, including under limiting conditions
- NRC inspectors will continue to verify NextEra's performance to monitor and take corrective actions to maintain Seabrook structures
- NRC inspectors will continue to verify NextEras performance to meet ASR related license conditions 4
ASR Background
- ASR is a slow, expansive chemical reaction in hardened concrete which occurs in the presence of water, between the alkaline cement and reactive silica found in some aggregates
- The expansion can cause various material impacts 5
- 2009 - 2010: Testing confirmed the presence of ASR
- 2013 - 2016: Large-Scale Test Program
- 2014 - 2015: NRC identified bulk structural deformation in Seismic Category 1 structures
- March 2019: NRC approved and issued both the license amendment request (LAR) and renewed license
- Nov 2020: The LAR was challenged by a local advocacy group, but the licensing action was upheld (with modifications) by the Atomic Safety Licensing Board
Seabrook Aging Management 6
ASR Aging Management Program Building Deformation Aging Management Program Structures Monitoring Program (Demand)
Structural analyses Threshold limits based on load demand vs. capacity Monitoring:
Items from ASR program Crack measurements Seismic gaps Building dimensions (Capacity)
Maximum expansion based on the Large-Scale Test Program results Monitoring:
ASR grids (Crack Indexing and Pin-to-Pin)
Extensometers Equipment Impacted by Building Deformation Aging Management Program Monitoring:
Visual exam of equipment
Seabrook Aging Management Examples of Monitoring ASR at Seabrook:
7 Combined crack indexing (CCI) and pin-to-pin distance Seismic gap widths between buildings Crack gauges and widths Extensometers
Seabrook Aging Management 8
Examples of Modifications:
Fuel Storage Building vertical plates Mechanical Penetration Building corner braces and strong backs
NRC Inspection and Assessment of ASR
- NRC inspectors identified 5 findings of very low safety significance since 2020, and all have been addressed in NextEras corrective action program
- Inspection Report 2024004
- Scope: Re-baseline and re-evaluation of condensate storage tank enclosure; ASR expansion data review
- Results: No findings
- Inspection Report 2025001
- Scope: Corroboration study per ASR License Condition b and f; CIS reactor pit temperature data review; RHR vault rebar strain testing per ASR License Condition d and revised limits
- Results: In-progress 9
NRC Inspection and Assessment of ASR Seabrook ASR License Condition Status a
Assess expansion behavior to confirm it is comparable to the large-scale test program and check margin for future expansion.
First assessment completed.
Subsequent study every 10 years.
b Corroborate, using Seabrook field data, the concrete modulus to expansion correlation used to calculate pre-instrument through-thickness expansion.
Initial study completed.
Follow-up study by May 2035.
c Conduct a volumetric expansion check for control extensometers every six months.
Ongoing d
Develop a monitoring program to ensure that rebar failure or yielding does not occur, or is detected if it has already occurred, if the structural evaluations indicate rebar stress may exceed yield.
Ongoing e
If the ASR expansion rate significantly exceeds 0.2 mm/m (0.02%) through-thickness expansion per year, NextEra will perform an engineering evaluation focused on the continued suitability of the six-month monitoring interval.
Ongoing f
Each core extracted from Seabrook Unit 1 will be subjected to a petrographic analysis to detect internal microcracking and delamination.
Ongoing 10
Next Steps
- NRC will continue inspections under the Reactor Oversight Process that include NextEras ASR-related activities to:
11
- Bring structures into compliance with licensing basis
- Monitor ASR and building deformation
- Complete modifications (physical and/or reanalyze) on affected structures
- Validate thermal and ASR loads in CIS
- Implement ASR related license conditions
References 12 NRC Webpage on Concrete Degradation at Seabrook https://www.nrc.gov/reactors/operating/ops-experience/concrete-degradation.html NRC Webpage on Seabrook License Renewal https://www.nrc.gov/reactors/operating/licensing/renewal/applications.html Documents Available are at https://adams-search.nrc.gov/home:
ASR license amendment request
- NRC staff safety evaluation report: ML18204A291
- ACRS letter: ML18348A951 License renewal application
- NRC staff safety evaluation report: ML18362A370
- ACRS letter: ML18353A954 ASLB hearing decision
- Initial decision: ML20254A339
- Revised license conditions: ML20318A003
End of Staff Presentation 13