ML21230A361: Difference between revisions
StriderTol (talk | contribs) (StriderTol Bot change) |
StriderTol (talk | contribs) (StriderTol Bot change) |
||
Line 16: | Line 16: | ||
=Text= | =Text= | ||
{{#Wiki_filter:}} | {{#Wiki_filter:xLPR Loss of Coolant Accident Frequency Estimates xLPR User Group Meeting August 18, 2021 1 | ||
Introduction The approach would be supported by the application of the Extremely Low Probability of Rupture (xLPR) leak-before-break (LBB) analysis tool, developed jointly by EPRI and the NRC Office of Nuclear Regulatory Research for Large Break- (LB) LOCAs. This tool could be used within this generic methodology to inform the probability of LB-LOCAs and that LB-LOCAs may be detected in sufficient time to allow for reactor shutdown before a reactor coolant system (RCS) piping rupture occurs. This approach facilitates the demonstration of no fuel rod burst (that is, no FFRD) and estimates the changes in CDF. | |||
- From: Alternative Licensing Approaches for Higher Burnup Fuel: A Scoping Study on Deterministic and Risk-Informed Alternatives Supporting Fuel Discharge Burnup Extension. EPRI, Palo Alto, CA: 2020. 3002018457. | |||
2 | |||
xLPR Work Scope | |||
* Objective: Perform Probabilistic Fracture Mechanics (PFM) evaluation using xLPR to calculate the probabilities of Loss-of-Coolant-Accidents (LOCAs) as a function of line size | |||
- Use xLPR to benchmark NUREG-1829, Vol. 1, Estimating Loss-of-Coolant Accident (LOCA) Frequencies Through the Elicitation Process | |||
* Validate (or replace) NUREG-1829 LOCA frequency estimates for use in high burnup fuel licensing | |||
- Evaluate the time between detectable leakage and rupture to further inform the fuels licensing effort | |||
* Approach: Project to be performed in phases | |||
- Phase 1 consists of a PFM evaluation of two line sizes as a proof-of-concept and to develop methodology for possible expansion to other line sizes (detailed in this presentation) | |||
- Phase 2 will expand the study to a variety of line sizes 3 | |||
Phase 1 Proof-of-Concept Study | |||
* Focus on the following: | |||
: 1. Methodology for using xLPR to evaluate the probability of LOCAs as a function of line size | |||
: 2. Estimation of the frequency of LOCA events | |||
: 3. Statistics on time between detectable leakage and unstable pipe rupture | |||
* Two lines for initial evaluations were selected considering: | |||
- xLPR computational abilities | |||
- NUREG-1829 LOCA frequency insights (smaller lines have higher freq. of rupture) | |||
- Line size (mid-range of greatest interest to fuels licensing project) | |||
- Input availability | |||
- Degradation mechanisms (i.e., fatigue and primary water stress-corrosion cracking (PWSCC)) | |||
* Scope is limited to Pressurized-Water Reactors (PWRs) | |||
* Base cases for each line include initial postulated flaws, fatigue and PWSCC crack growth (where applicable), and seismic occurrences | |||
* Sensitivity cases were defined considering both inputs known to have influence on xLPR results and assumptions made during input development 4 | |||
Lines Selected for Evaluation | |||
* Emphasis was placed on lines in the 6-10 in. (DN 150-250) range, as this range is of particular interest for fuel fragmentation, release, and dispersal (FFRD) | |||
* Available input sources were reviewed to identify lines for which inputs to xLPR were readily available | |||
- Licensee submittals in the NRCs Agencywide Documents Access and Management System | |||
- EPRI reports | |||
- xLPR documentation | |||
* It was determined that of the two lines evaluated, one should be susceptible to PWSCC and the other only susceptible to fatigue since the population of dissimilar-metal welds is small Stainless Steel Weld Alloy 82/182 Weld | |||
* Nominal pipe size (NPS) 6 (DN 150) | |||
* NPS 12 (DN 300) SCH 140 or 160, resulting in ~10 | |||
* NUREG-1829 category: in. (250 mm) inside diameter | |||
* Direct Volume Injection | |||
* NUREG-1829 Category: | |||
* Represented by Westinghouse Safety | |||
* High Pressure Safety Injection Injection | |||
* Represented by Combustion Engineering Safety | |||
* Population includes both hot leg and cold Injection/Accumulator leg temperature locations | |||
* Cold leg temperature, unmitigated at most plants 5 | |||
Initial Results | |||
* Runs are completed for the two lines selected for Phase 1 - EPRI Technical Update to be published in October 2021 | |||
- Phase 2 work extending the approach to additional lines will begin shortly - | |||
EPRI report with results to be published in 2022 | |||
* As expected, LOCA frequencies are higher for lines susceptible to PWSCC | |||
- When fatigue is the only active degradation mechanism, the number of cases with leakage/rupture is extremely low | |||
* Results show rupture frequencies on similar order of magnitude or lower than NUREG-1829 LOCA frequencies | |||
- Results are conservative as inservice inspection and leak rate detection were not credited | |||
- It is noted that NUREG-1829 expert elicitation considered other degradation mechanisms in addition to those modeled in these xLPR analyses | |||
* Time between leakage and rupture data analysis indicated notable margin for leak-before-break 6 | |||
Lessons Learned | |||
* Performing sensitivity studies on key inputs as well as on inputs for which modeling decisions were made during input development adds confidence to the overall xLPR analysis results | |||
* The xLPR analyses decoupled crack initiation and growth to work within xLPR memory limitations, significantly reducing the number of necessary realizations | |||
* A methodology has been established that is able (with some refinements) to evaluate LOCA probabilities and time between detectable leakage and rupture for other PWR lines 7}} |
Latest revision as of 18:12, 18 January 2022
ML21230A361 | |
Person / Time | |
---|---|
Issue date: | 08/18/2021 |
From: | NRC/RES/DE |
To: | |
Homiack M | |
Shared Package | |
ML21230A354 | List: |
References | |
Download: ML21230A361 (7) | |
Text
xLPR Loss of Coolant Accident Frequency Estimates xLPR User Group Meeting August 18, 2021 1
Introduction The approach would be supported by the application of the Extremely Low Probability of Rupture (xLPR) leak-before-break (LBB) analysis tool, developed jointly by EPRI and the NRC Office of Nuclear Regulatory Research for Large Break- (LB) LOCAs. This tool could be used within this generic methodology to inform the probability of LB-LOCAs and that LB-LOCAs may be detected in sufficient time to allow for reactor shutdown before a reactor coolant system (RCS) piping rupture occurs. This approach facilitates the demonstration of no fuel rod burst (that is, no FFRD) and estimates the changes in CDF.
- From: Alternative Licensing Approaches for Higher Burnup Fuel: A Scoping Study on Deterministic and Risk-Informed Alternatives Supporting Fuel Discharge Burnup Extension. EPRI, Palo Alto, CA: 2020. 3002018457.
2
xLPR Work Scope
- Objective: Perform Probabilistic Fracture Mechanics (PFM) evaluation using xLPR to calculate the probabilities of Loss-of-Coolant-Accidents (LOCAs) as a function of line size
- Use xLPR to benchmark NUREG-1829, Vol. 1, Estimating Loss-of-Coolant Accident (LOCA) Frequencies Through the Elicitation Process
- Validate (or replace) NUREG-1829 LOCA frequency estimates for use in high burnup fuel licensing
- Evaluate the time between detectable leakage and rupture to further inform the fuels licensing effort
- Approach: Project to be performed in phases
- Phase 1 consists of a PFM evaluation of two line sizes as a proof-of-concept and to develop methodology for possible expansion to other line sizes (detailed in this presentation)
- Phase 2 will expand the study to a variety of line sizes 3
Phase 1 Proof-of-Concept Study
- Focus on the following:
- 1. Methodology for using xLPR to evaluate the probability of LOCAs as a function of line size
- 2. Estimation of the frequency of LOCA events
- 3. Statistics on time between detectable leakage and unstable pipe rupture
- Two lines for initial evaluations were selected considering:
- xLPR computational abilities
- NUREG-1829 LOCA frequency insights (smaller lines have higher freq. of rupture)
- Line size (mid-range of greatest interest to fuels licensing project)
- Input availability
- Degradation mechanisms (i.e., fatigue and primary water stress-corrosion cracking (PWSCC))
- Scope is limited to Pressurized-Water Reactors (PWRs)
- Base cases for each line include initial postulated flaws, fatigue and PWSCC crack growth (where applicable), and seismic occurrences
- Sensitivity cases were defined considering both inputs known to have influence on xLPR results and assumptions made during input development 4
Lines Selected for Evaluation
- Emphasis was placed on lines in the 6-10 in. (DN 150-250) range, as this range is of particular interest for fuel fragmentation, release, and dispersal (FFRD)
- Available input sources were reviewed to identify lines for which inputs to xLPR were readily available
- Licensee submittals in the NRCs Agencywide Documents Access and Management System
- EPRI reports
- xLPR documentation
- It was determined that of the two lines evaluated, one should be susceptible to PWSCC and the other only susceptible to fatigue since the population of dissimilar-metal welds is small Stainless Steel Weld Alloy 82/182 Weld
- Nominal pipe size (NPS) 6 (DN 150)
- NPS 12 (DN 300) SCH 140 or 160, resulting in ~10
- NUREG-1829 category: in. (250 mm) inside diameter
- Direct Volume Injection
- NUREG-1829 Category:
- Represented by Westinghouse Safety
- High Pressure Safety Injection Injection
- Represented by Combustion Engineering Safety
- Population includes both hot leg and cold Injection/Accumulator leg temperature locations
- Cold leg temperature, unmitigated at most plants 5
Initial Results
- Runs are completed for the two lines selected for Phase 1 - EPRI Technical Update to be published in October 2021
- Phase 2 work extending the approach to additional lines will begin shortly -
EPRI report with results to be published in 2022
- When fatigue is the only active degradation mechanism, the number of cases with leakage/rupture is extremely low
- Results show rupture frequencies on similar order of magnitude or lower than NUREG-1829 LOCA frequencies
- Results are conservative as inservice inspection and leak rate detection were not credited
- It is noted that NUREG-1829 expert elicitation considered other degradation mechanisms in addition to those modeled in these xLPR analyses
- Time between leakage and rupture data analysis indicated notable margin for leak-before-break 6
Lessons Learned
- Performing sensitivity studies on key inputs as well as on inputs for which modeling decisions were made during input development adds confidence to the overall xLPR analysis results
- The xLPR analyses decoupled crack initiation and growth to work within xLPR memory limitations, significantly reducing the number of necessary realizations