and it was replenished three times during the lifetime of the first core. Seven years later (when running on its fourth seed) the first core was retired, after having produced 1.8 billion kilowatt-hours of electricity. The second core had increased generating capacity (more than five times) and instrumentation to measure performance, but otherwise used the same seed-and-blanket design. For the second core, the seed volume was 21% of the total core volume. The second core thus required only one seed refueling. It began operating in 1965 and over the next nine years generated almost 3.5 billion kilowatt-hours of electricity. In 1974 the turbine-generator suffered mechanical failure, causing the plant to be shut down. 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. Decommissioning On October 1, 1982, the reactor ceased operations after 25 years. Dismantlement of the facility began in September 1985. In December 1988, the 956-ton (870-T) reactor pressure vessel/neutron shield tank assembly was lifted out of the containment building and loaded onto land transportation equipment in preparation for removal from the site and shipment to a burial facility in Washington State. The site has been cleaned up and released for unrestricted use. While the Shippingport Reactor has been decommissioned, Beaver Valley Nuclear Generating Station Units 1 and 2 are still licensed and in operation at the site. The $98 million (1985 estimate) cleanup of Shippingport has been used as an example of a successful reactor decommissioning by proponents of nuclear power; however, critics point out that Shippingport was smaller than most commercial nuclear power plants, most reactors in the United States are about 1,000 MWe, while Shippingport was only 60 MWe. Others argue that it was an excellent test case to prove a reactor site could be safely decommissioned and a site released for unrestricted