Page "Gaseous diffusion" Paragraph 25

At the time of their construction in the early 1940s, the gaseous diffusion plants were the largest buildings ever constructed.

Large gaseous diffusion plants were constructed by the United States, the Soviet Union ( including a plant that is now in Kazakhstan ), the United Kingdom, France, China, and South Africa.

Most of these have now closed or are expected to close, unable to compete economically with newer enrichment techniques.

However some of the technology used in pumps and membranes still remains top secret, and some of the materials that were used remain subject to export controls, as a part of the continuing effort to control nuclear proliferation.