EMPIRICAL EQUATIONS OF CRACK GROWTH RATES BASED ON DATA FITTING OF NEUTRON IRRADIATED STAINLESS STEEL UNDER HIGH TEMPERATURE WATER SIMULATING BOILING WATER REACTOR CORE CONDITIONS

摘要

Various disposition curves and equations of theproperties of austenitic stainless steel are often used toassess the integrity of core structures and components ofboiling water reactors. These disposition curves shouldadequately consider material degradation due to neutronirradiation so as to yield a more precise assessment ofstructural integrity. In this paper, disposition curves ofcrack growth for structural integrity assessment of reactorinternals of boiling water reactors (BWRs) wereinvestigated. Empirical equations of crack growth ratesdue to stress corrosion cracking, ȧ, as a function of stressintensity factors K, and neutron dose F, were developed,based on datasets of neutron irradiated stainless steel,tested under simulated BWR primary coolant conditions.Prior to equation development, digital data of neutron dose,stress intensity factors, and crack growth rates obtainedfrom post-irradiation examinations in the literature werecompiled into each dataset of simulated normal waterchemistry (NWC) and hydrogen water chemistry (HWC)conditions. Empirical equations of crack growth rates weredeveloped from a formula of ȧ=M･Kn on the assumptionthat “M” and “n” show tendencies toward saturation withincreasing F. Data fitting with the least-square method wasapplied to the dataset, and empirical equations of crackgrowth rates for NWC and HWC were developed. Throughstatistical evaluation, the crack growth rates yielded by theequation showed good agreement with the measured dataof NWC, but, not those of HWC. This difference can beattributed crack growth rate data of HWC beingextensively scattered.