Methodology for Volume Reduction of Radioactive Metallic Waste - 19491
A decontamination methodology for out-of-core nuclear reactor alloys is being developed to reduce the volume of low- and intermediate-level radioactive metallic wastes. For out-of-core reactor metals contamination is limited to surface oxides. For surface oxide removal a technology based on laser ablation is being explored. This paper presents work performed to identify the key parameters that affect the efficiency of removal of surface oxides from out-of-core reactor metals and alloys. This study examined carbon steel (used for coolant feeder pipes of CANDU{sup R} reactors) as a model reactor material. The morphology and thickness of oxides on a used feeder pipe vary considerably depending on its service life and the location along the pipe. Hence, oxides with different morphologies and thicknesses were first grown by corroding carbon steel coupons under different solution conditions. The oxides formed ranged from thin layers of uniformly distributed mixed Fe{sup II}/Fe{sup III} hydroxides/oxides to dual layers consisting of ferric oxide/oxyhydroxide islands with thickness up to 200 μm on top of the more uniformly distributed mixed Fe{sup II}/Fe{sup III} layer. Removal of these oxides was performed using a 1064 nm pulsed laser. Of the laser parameters tested, the pulse radiance was found to be the most important. Four radiances ranging from 5 to 200 MW/cm{sup 2} were used. At radiances higher than 100 MW/cm{sup 2}, single pulses were sufficient to remove both types of oxides, but also extensively melted the metal substrate. At lower radiances, multiple pulses were required to remove the oxides completely, but caused less damage to the metal substrate. (authors)