An engineering-scale pyroprocessing integrated efficiency test was conducted with sodium-bonded, spent Experimental Breeder Reactor II drive fuel elements. The major pieces of equipment used to conduct the test were the element chopper, Mk-IV electrorefiner, cathode processor, and casting furnace. Four batches of the spent fuel (containing 50.4-kg heavy metal) were processed under a set of fixed operating parameters. The primary goal of the test was to demonstrate the actinide dissolution and recovery efficiencies typical of the fixed operating parameters that have been developed for this equipment based on over a decade's worth of processing experience. The total mass balance for the test was 101.28% (slightly more output than input). The uranium mass balance for the test was 100.13%. The test results indicate that 99.3 wt% of uranium in the feed was electrochemically dissolved and 98.4 wt% of the uranium was collected as metal ingots. The complexity of zirconium behavior during electrorefining was confirmed by the test results. More than 85 wt% of the zirconium was electrochemically dissolved during the later stages of the electrorefining process. However, only 33.7 wt% of the zirconium was collected as metal in the ingots. The balance of the zirconium is believed to reside in the cadmium pool. The test also identified that the dross streams from the cathode processor and casting furnace account for ~2.4 wt% of the uranium relative to the feed.