ML23146A097
| ML23146A097 | |
| Person / Time | |
|---|---|
| Issue date: | 06/14/2023 |
| From: | Ali Rezai, David Rudland NRC/NRR/DNRL/NPHP, NRC/NRR/DNRL |
| To: | |
| References | |
| Download: ML23146A097 (1) | |
Text
Industry / NRC Materials Programs Technical Information Exchange
French SCC Issue - Update and NRC Activities
David Rudland Senior Technical Advisor
NRC Headquarters June 14-15, 2023 Outline
- Timeline from ASN/EDF
- Cracking details
- Safety implications
- Staff plans
- Since we went over this issue last year, we will not go through the history in detail
06/14/2023 Industry / NRC Annual Technical Exchange 2 ASN/EDF Timeline
October 2021 December 2021
- Civaux reactor 1 - 2nd ten-year outage:
- Civaux reactor 1: Laborator y analyses Detection of circumferential flaws in concluded that these cracks were close proximity to a weld in the safety due to IGSCC injection system piping
- Anticipated outage for inspection of
- Hypothesis: thermal fatigue Chooz reactors B1 and B2
November 2021 Januar y 2022
- Anticipated outage for
- Penly reactor 1: Laborator y analyses inspection of Civaux reactor 2: concluded that the cracks were due to IGSCC flaws are detected (safety injection system)
- Penly reactor 1-3rd ten-year reactor 1 and 1450 MWe units (N4 type) outage: flaws are detected (safety injection system)
06/14/2023 Industry / NRC Annual Technical Exchange 3 ASN/EDF Timeline
Spring 2022 Autumn 2022
- Implementation of preliminar y inspection program on
- End of inspections on << prioritized priority reactors : reactors >> and repairs
- Reactors identified from reanalysis of previous
- Discussion of the new inspection inspection repor ts (6 reactors) program between ASN and EDF
- Reference reactor (one of each design)
- Those with upcoming10-year outages
- Implementation of Reinforced reactor oversight to secure the ability to quickly detect any leak
Summer 2022 Early 2023
- Following the preliminar y inspection program
- Beginning of the implementation of
- Availability of new NDT method able to accurately the new inspection program, detect and size the defects concerning all reactors in operation,
- Over 110 welds destructive tests performed
- Beginning of the repairs program on the areas that might be susceptible to IGSCC (end of the program by 2025)
- Large flaw found at Penly 2
06/14/2023 Industry / NRC Annual Technical Exchange 4 Original cracking
- Civaux 1 cracking Inside
- The pipe is 300mm in diameter with a wall thickness of 30mm
- Safety injection piping near cold leg
- Stress corrosion cracking (SCC): flaw propagation is intergranular
- Location
- Crack length is 360° (full circumference) and the maximum depth is 5.6mm
- Relatively high hardness (250<HV<290)
- Relatively big first layer of the weld (manual TIG weld )
- Residual stress supports the arrest of through cracking
- Suspected to be due to large thermal stratification loads
06/14/2023 Industry / NRC Annual Technical Exchange 5 New Cracking
- Penly 2 Cracking Crack
- Found after expansion of the inspection plan
- Safety injection piping near hot leg
- Suspected SCC
- 85% deep, 6-inch -long circumferential crack in HAZ
- Little to no thermal stratification Hot Leg
- Weld was repaired twice - suspected driver
- Due to unexpected size and location of cracking, understanding the safety implication to the US fleet is important
06/14/2023 Industry / NRC Annual Technical Exchange 6 Where are these flaws?
Typical Westinghouse four loop ECCS Cold Leg
Crack
Crack
Safety Injection Hot Leg System
06/14/2023 Industry / NRC Annual Technical Exchange 7 Safety Implications
- Could this cracking occur in US fleet?
- If it can, what are the safety implications?
- Cracks are in unisolable section of pipe
- Break can cause LOCA
- Only one ECCS train is affected?
- Can earthquake or startup of ECCS cause failure?
- New cracking was very long and deep
- Staff looked at risk-triplet through their BeRiskSMART process (NUREG/KM-0016)
- What can go wrong/what can go right
- What are the consequences of each
- What is the expected likelihood of each
- Qualitative assessment
06/14/2023 Industry / NRC Annual Technical Exchange 8 Safety Implications, Staff Plans
- Conclusion from BeRiskSMART
- Uncertainties are large with unknown impact of break on plant safety
- Are our plants susceptible? Water chemistry, etc.
- Do we have unknown (undocumented/unrecorded) weld repairs in these locations?
- Even though these systems are susceptible to thermal fatigue, are we inspecting these locations, i.e. are these welds in the risk -informed program?
- What is the impact to the plant if we lose this system?
- Staff concluded that a more quantitative analysis is needed
- Initiated a LIC-504, Integrated Risk -Informed Decisionmaking Process for Emergent Issues.
- Using a Simplified approach with the goal of completion by July 2023.
06/14/2023 Industry / NRC Annual Technical Exchange 9 Safety Implications, Staff Plans
- LIC-504 Plan
- Investigation into the probability of rupture of an unisolable pipe in the safety injection system
- Perform xLPR analyses or use past runs to make a conservative prediction
- Sensitivity studies as necessary
- Investigate the conditional core damage probability resulting from loss of the portion of the safety injection system
- Exercise Standardized Plant Analysis Risk (SPAR) models for a variety of Westinghouse 4 -
loop and 3-loop plants
- Determine risk impact and make recommendation
- Using simplified approach to be completed in 3 months
- Other Actions
- Continue to follow industry actions and report development
06/14/2023 Industry / NRC Annual Technical Exchange 10