In situ purification, alloying and casting methodology for metallic plutonium

Plutonium metal that has been double ER (electrorefined/electrorefining) wa s further purified via zone refining, using a floating molten zone to minim ize the introduction of impurities. The temperature of the molten zone was 750 degrees C, and the atmosphere was 10(-5) Pa. A total of ten zone refini ng passes were made at a travel rate of 1.5 cm/h. There were 19 elements re duced to quantities below the minimum detectable limits (MDL) by zone refin ing, while P, K, and W were significantly reduced. The zone-refined metal w as then used in an in situ distillation, alloying, and casting step to prep are tapered specimens for single-crystal growth experiments. Specifically, Am-241 was distilled from Pu metal by levitating Pu metal with 1 wt% Ga in the melt in a Crystallox vertical electromagnetic levitation crucible at 10 (-5) Pa. The Pu is alloyed with Ga to stabilize the delta phase (fcc symmet ry) upon solidification. The Pu was chill-cast directly from the electromag netic levitation field into 1- cm tapered specimens. A water-cooled ceramic mold was used, and the Pu metal was cooled at a rate of 100 degrees C/min. A microstructure examination of the specimen showed 10 x 25 mu m acicular grains with a density of 15.938 g/cm(3) (+/- 0.002 g/cm(3)). (C) 1999 Elsev ier Science B.V. All rights reserved.