ATOM-PROBE CHARACTERIZATION OF COPPER SOLUBILITY IN THE MIDLAND WELD AFTER NEUTRON-IRRADIATION AND THERMAL ANNEALING

An atom probe field ion microscopy characterization has been performed to determine the copper matrix concentration in a submerged are beltl ine weld of the Midland Unit 1 pressurized water reactor after 4 condi tions: unirradiated, unirradiated and annealed for 168 h at 454 degree s C, neutron-irradiated in a test reactor to a fluence of 1.1 x 10(23) n m(-2) (E > 1 MeV) at a temperature of 288 degrees C, and neutron-ir radiated and annealed for 168 h at 454 degrees C. Atom probe analysis of the unirradiated material revealed a substantial depletion of the c opper in the matrix to 0.119 +/- 0.007 at% Cu from the bulk value of b etween 0.18 and 0.28 at% Cu. Annealing the unirradiated material produ ced intragranular copper-enriched precipitates and reduced the matrix copper level by similar to 25% to 0.088 +/- 0.012 at% Cu. Neutron irra diation also produced copper-enriched precipitates and reduced the mat rix copper level by almost 50% over the stress relieved material to 0. 058 +/- 0.008 at% Cu. Annealing the neutron-irradiated material reduce d the matrix copper level further to 0.050 +/- 0.010+/-at% Cu. These r esults indicate that the annealing treatment coarsens the copper-enric hed precipitates produced during neutron irradiation with a slight dec rease in the matrix copper content. (C) 1997 Elsevier Science B.V.