Materials corrosion and mitigation strategies for APT, end of FY '97 report: Inconel 718 in-beam corrosion rates from the '97 A6 irradiation

摘要

This report summarizes the results from the 1997 irradiation of the corrosion insert at the LANSCE A6 Target Station. It addresses the corrosion measurements made on the in-beam Inconel 718 probe only. To simulate the environment that materials may be exposed to in a spallation neutron target/blanket cooling loops, samples were irradiated by the proton beam at the A6 Target Station of the Los Alamos Neutron Scattering Center (LANSCE). EIS measurements have demonstrated that the polarization resistance of IN718 decreases from approximately 3 x 10(sup 5) ohms prior to irradiation to approximately 1,000 ohms during irradiation at a proton beam current of 400 (micro)A. From the polarization resistance measurements, corrosion rate as a function of beam current was calculated for several different scenarios of beam/sample interaction. As the beam spot was small relative to the size of the IN718 corrosion probe (2(sigma) = 3 cm vs. 1.3 cm diam. x 15.9 cm length respectively), The first method for calculating corrosion rate used beam profile as a criterion for the area of highest damage. The beam spot intensity profile at LANSCE has been characterized and found to be a Gaussian distribution rotated about a central axis. From this relationship, and R(sub p) as a function of beam current, corrosion rate as a function of radial distance from the center of the beam was calculated for each beam current. Physical evidence from change in thickness measurements made on tungsten rods irradiated at 1 mA during the FY 96 irradiation period suggest that this Gaussian damage profile is an accurate depiction of beam/sample interaction. From this method the corrosion rate of IN718 during irradiation at a beam current of 1.0 mA is calculated to be approximately 0.002 inches per yr (2 mpy). The second method assumed that the predominant contributor to the corrosion current comes from an area defined by 2(sigma). Further, the method assumed that the corrosion rate was uniform over this area. Specifically, the R(sub p) was multiplied by the area (pi)d x 2(sigma) where d was the diameter of the probe and equal to 1.3 cm. From this method the corrosion rate of IN718 during irradiation at a beam current of 1.0 mA is calculated to be approximately 0.001 inches per yr (1 mpy) . The third method to calculate corrosion rate assumed that the distribution of corrosion was uniform across the entire surface. To calculate CR, the measured polarization resistance (R(sub p)) was multiplied by the total probe area (approximately 63.3 cm(sup 2)). From this method the corrosion rate of IN718 during irradiation at a beam current of 1.0 mA is calculated to be approximately 0.0002 inches per yr (0.2 mpy). However, this rate is non- conservative and may be viewed only as a minimum corrosion rate.