For 35 years, the Energy Department has pursued an all-of-the-above energy strategy — and the critical work done at the National Labs has helped put America at the top of the global clean energy race. This photo from 1979 shows a Lawrence Livermore National Laboratory employee opening the world's heaviest hinged door, which was eight feet thick, nearly twelve feet wide, and weighed 97,000 pounds. A special bearing in the hinge allowed a single person to open or close the concrete-filled door, which was used to shield the Rotating Target Neutron Source-II (RTNS-II) -- the world’s most intense source of continuous fusion neutrons. Scientists from around the world used it to study the properties of metals and other materials that could be used deep inside fusion power plants envisioned for the next century. | Photo courtesy of Lawrence Livermore National Laboratory.