The third and final core was a light water breeder, which began operating in August 1977 and after testing was brought to full power by the end of that year. It used pellets made of thorium dioxide and uranium-233 oxide; initially the U233 content of the pellets was 5-6% in the seed region, 1.5-3% in the blanket region and none in the reflector region. It operated at 236 MWt, generating 60 MWe and ultimately produced over 2.1 billion kilowatt-hours of electricity. After five years (29,000 effective full power hours) the core was removed and found to contain nearly 1.4% more fissile material than when it was installed, demonstrating that breeding had occurred.