Estimate of feasibility to develop acoustic emission: flaw relationships for inservice monitoring of nuclear pressure vessels

Abstract

The work presented in this report is part of an ongoing program at Pacific Northwest Laboratory to determine the feasibility of continuous inservice monitoring of nuclear pressure vessels, using acoustic emission (AE) to detect and evaluate growing flaws. The major program objectives are to: (1) develop criteria to distinguish flaw growth AE from nonsignificant acoustic signals, (2) develop an AE/flaw growth model as a basis for relating inservice AE to flaw significance, and (3) demonstrate applications of program results through both off-reactor and on-reactor testing. To fulfill the program objectives, laboratory fracture mechanics tests have been performed. These tests were designed to determine the effect of variables such as microstructure, flaw geometry, temperature and mechanical loading upon the AE response during increasing flaw severity. Future tests will more fully simulate reactor pressure vessel behavior. From these tests, two empirical models have been developed to relate AE to fatigue crack growth. One model relates rate of change of AE to stress intensity factor range or the crack growth rate. The other model relates total accumulated AE to stress intensity factor.