ML25183A347
| ML25183A347 | |
| Person / Time | |
|---|---|
| Issue date: | 06/30/2025 |
| From: | Jeffrey Poehler NRC/RES/DE |
| To: | |
| JEFF POEHLER 3014158353 | |
| Shared Package | |
| ML25183A340 | List: |
| References | |
| Download: ML25183A347 (2) | |
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Z AA AB AC AD AE AF AG AH AI AJ AK AL AM AN AO AP AQ AR AS AT Panelist 1 Panelist 2 Panelist 3 Average ImportanceUncertaintyKnowledge ImportanceUncertaintyKnowledge ImportanceUncertaintyKnowledge Recommendation ID title of recommendation Scope, objectives, and/or topic modifications Score Score Score Rationale Score Score Score Rationale Score Score Score Rationale Importanc e (avg)
Uncertaint y (avg)
Knowled ge (avg) error bars Import Uncert.
Know error More research could be used to gain knowledge on a topic expected to be important to safety More research could reduce uncertainty and clarify topic importance More research could improve knowledge but topic not expected to be safety significant Topic expected to have safety significance but likely could be addressed without additional research Topic may have safety significance but sufficient knowledge exists to manage Topic not expected to have safety significance and sufficient knowledge exists H/M/L H/M/L K/PK/UK H/M/L H/M/L K/PK/UK H/M/L H/M/L K/PK/UK APC-1 Investigate long-term creep effects, structural modifications, SGR, loss of prestress, re-tensioning and interactions between original and replacement materials.
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UK Loss of prestress, long-term creep, and material interactions significantly affect structural integrity. While creep and prestress loss mechanisms are well understood in theory, applying this knowledge to aged, in-service structuresespecially under real conditions and during long-term operationis still uncertain and not fully developed.
Retensioning and interactions between original and replacement materials are poorly understood, with very limited data and few studies available, making their effects on long-term structural performance highly uncertain.
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K A methodology is needed to define whether an opening for SGR replacement would affect the overall structural integrity of the reactor building, particularly those that are prestressed. The rating for uncertainty an knowledge are set to L and K because of past reseach efforts.
It is anticipated most of the effort to be computational mecahanics oriented.
H M
UK Long term creep including differential temperature, inelastic creep, reactivation of primary creep, creep under mixed stress state, transient creep during accidental scenarios are not commonly considered in design, specifically in the context of retensioning and detensioning tendons, pressence of small deffect, the impact of plant modifications over time, stress reversals transitioning to tension, poisson's creep effect, radial strain. In 2019, ASME code has added provision for radial reinforcement (Lessons Learned CR3).
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APC-2 Study prestress loss, drying, creep, and shrinkage using reliable models to ensure structural safety under design basis loading including accident conditions.
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PK Reliable models of prestress loss and creep are essential to ensure structural safety under design basis loading including accident condition.
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K Although effects for Large LOCAs have been mitigated through LBB and eLBB, elastic shortening, creep, and shrinkage of the concrete could affect the length of tendons.
Similar to the above, the rating for uncertainty an knowledge are set to L and K because of past reseach efforts. It is anticipated most of the effort to be computational mecahanics oriented.
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PK Creep data commonly available are from short term compression creep experiments. Reliable models should include combinations of various phenomena. Ref. APC-1 rationale.
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APC-3 Analyze degradation mechanisms such as corrosion, ASR, freeze-thaw, carbonation etc.,
as plants age.
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PK These aging mechanisms creates additional complex conditions for post-tensioning structures with limited data.
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K The effects of the degradation mechanisms listed have been examined, but the importance of the topic remains. The susceptibility of a posttensioned containment to ASR is limited to aggregates used for its construction. An understanding of plant specific and/or combined aging effects can be gained and issues resolved for the most part through compuational mechanics (modeling and simulation) efforts.Thus the basis of the proposed rating.
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PK The aging mechanisms are reasonably understood. Early detection and preventive measures can avoid unacceptable degradation. The synergistic degeadation effects for post-tensioned structures are more complex than RC structures.
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APC-4 Use advanced monitoring systems to track deformation, cracking, and structural behavior, preventing unrepairable damage.
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K Advanced monitoring systems enable early issue detection, prevent unrepairable damage, support informed decisions, and extend the safe, cost-effective operation of nuclear plants beyond 80 years. importance high but uncertainty low since it is based on the performance of the structures.
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PK Advanced sensors can monitor and alert when deformations, cracking, and overall behavior would exceed allowed margins potentially dgrading structural integrity. Moreover, for bonded tendon plants monitoring effectiveness relies on ILRT, which mostly now is performed every 15 years. Development of on the fly reporting sensors and methodlogies of deploying and linking to data bases challenge the importance and uncertainty rankings.
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PK Considering LTO >80 years and advancements of technology, modernized monitoring systyems will enable more efficient and safer work environment, improved structural monitoring.
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APC-5 Enhance modeling with data on aging factors to improve predictions and guide interventions.
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PK Enhancing modeling with data on aging factors coupling with advanced monitoing system can improve prediction accuracy, reduces uncertainty, and helps identify when and where interventions are needed.
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K Developping criteria that would alter constitutive laws would be a challege. Easier done in time domain analyses.
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PK What is more important -
reliable and advanced monitoring vs. predictive model? It is both, data acquired by monitoring should be used for improving predictive modeling and simulation for enabling timly prevention or mitigation.
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APC-6 Collect real-world performance data through harvesting of in-service or decommissioned plant structures for validation and benchmarking.
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UK Harvesting real-life data needed to validate models; medium uncertainty; H
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Availability of decommissioned plants and plant owners" willingness to share could induce limitations. Will info gained from intenational sites be of value for use to domestic fleets and NRC for LTO and future licensing?
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UK Harvesting can be an effective way for understanding real life conditions.
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APC-1 APC-2 APC-3 APC-4 APC-5 APC-6 1
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2 Importance Knowledge Session 8 - Civil Structures, Concrete and Components - Aging of Post-tensioned Containments (APC)
High Low Known Unknown
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AA AB AC AD AE AF AG AH AI AJ AK AL AM AN AO AP AQ AR AS AT Recommendation ID title of recommendation Scope, objectives, and/or topic modifications Score Score Score Rationale Score Score Score Rationale Score Score Score Rationale Importanc e (avg)
Uncertaint y (avg)
Knowled ge (avg) error bars Import Uncert.
Know error More research could be used to gain knowledge on a topic expected to be important to safety More research could reduce uncertainty and clarify topic importance More research could improve knowledge but topic not expected to be safety significant Topic expected to have safety significance but likely could be addressed without additional research Topic may have safety significance but sufficient knowledge exists to manage Topic not expected to have safety significance and sufficient knowledge exists H/M/L H/M/L K/PK/UK H/M/L H/M/L K/PK/UK H/M/L H/M/L K/PK/UK 17 18 19