Stone &amp; Webster's difficulties with constructing conventional power plants were matched by its problems in nuclear construction. By the late 1970s, the company had attained a central role in the nuclear power industry—a significant portion of all nuclear energy in the United States was being generated at plants designed and generated by Stone &amp; Webster. In 1975, the company had been selected to construct the Clinch River Breeder Reactor. However, increasing public opposition to the construction of nuclear plants, lengthy delays brought by challenges before public utility commissions, and corresponding increases in plant construction costs, capped by the incident at Three Mile Island in 1979, brought about a moratorium on the construction of large nuclear plants and the cancellation of many existing orders.