The United States is buying 32 metric tons of heavy water from Iran, U.S. congressional and administration sources said on Friday.
The purchase will be under $10 million, the congressional sources said.
Heavy water is a form of water that contains a larger than normal amount of the hydrogen isotope deuterium
It is used in certain types of nuclear reactors, where it acts as a neutron moderator to slow down neutrons so that they are more likely to react with the fissile uranium-235 than with uranium-238, which captures neutrons without fissioning. The CANDU reactor uses this design.