Summary
A fatigue management program is only as defensible as the cycle counts behind it, and for most nuclear plants those counts still rest on design-basis assumptions written before the first fuel load. As units move toward license renewal and subsequent license renewal, that inheritance becomes a liability: limiting locations look limiting because the analysis was conservative, not because the metal is spent. Structural Integrity Associates (SIA) has spent more than 30 years helping plants tell the difference, and our engineers hold leading roles in the industry organizations that set how metal fatigue is managed across the fleet.
SI:FatiguePro 4 is the tool that makes the distinction visible. Developed with EPRI and now a mainstay of fatigue management programs at nuclear plants worldwide, it tracks fatigue usage and transients automatically from instrumentation the plant already has. Automated Cycle Counting applies advanced event detection logic to raw instrument data, capturing not only that a transient occurred but how severe it was. Cycle-Based Fatigue recalculates usage from those counted events rather than design transient allowances, and lets engineers add and configure new CBF locations without programming support. Stress-Based Fatigue replaces the single-stress-term methodology of FatiguePro 3.0 with multi-axial stress calculations built on stress histories from plant data, following the fatigue analysis procedures of ASME Subarticle NB-3200.
That methodology matters for reasons beyond accuracy. The multi-axial approach follows EPRI Technical Report 1022876 and directly addresses the NRC concerns about simplified single-stress-term analysis documented in Regulatory Issue Summary 2008-30. Environmentally-Assisted Fatigue is handled in the same framework: for SBF locations, the Fen multiplier is calculated automatically from actual plant data using NRC-approved methodology and industry best practices, while CBF locations accept previously calculated Fen values configured per load pair. A fatigue crack growth module evaluates postulated flaws to support flaw tolerance and ASME Section XI Appendix L evaluations, and improved linear projection shows where margin stands and how fast it is moving.
The payoff arrives at the licensing table. Continuous, current assessment of fatigue usage across critical vessels and piping means plants implementing SI:FatiguePro 4 now face substantially less work at license renewal and subsequent license renewal, because years of accumulated operating history permit less limiting assumptions than a design-basis reconstruction ever could. The software is today’s best answer to the issues raised in RIS 2008-30, RIS 2011-14, and Bulletins 79-13, 88-08, and 88-11. Around it, SIA provides EAF analysis, ASME Code Section III fatigue evaluations, historical cycle counting reconstruction, fatigue management program consulting and handbooks, modification design to extend component life, flaw tolerance and inspection services, and repair support. Explore SIA’s digital solutions portfolio or contact us to scope fatigue monitoring for your units.