Concerning Heavy water(H3O) in nuclear reactors. Why do some utilize
heavy water vrs. light water(H2O). Are most of the reactors utilizing
heavy water out of the country?
First if all, heavy water is D2O and light water is H2O. D is the
abbreviation for deuterium, the isotope of hydrogen containing one proton
and one neutron in its nucleus. Light hydrogen, H, contains one proton and
no neutrons in its nucleus.
Generally, the reactors that use heavy water are those that use
natural-abundance uranium in the fuel. With these reactors, it is
absolutely essential to conserve neutrons as much as possible, because the
concentration of fissile U-235 nuclei is so low. D2O is used there because
D is less likely to absorb a neutron than H. (When it absorbs a neutron, D
becomes T, tritium, a radioactive isotope of hydrogen. Hen H absorbs a
neutron, it simply becomes D.)
Reactors in the United States use enriched uranium, which does not require
one to be so stingy with neutrons. Canadian reactors often use
natural-abundance uranium, so their reactors are D2O-moderated. I don't
know much about the practices in other countries.
Richard Barrans Jr., Ph.D.
Just a note -- heavy water is not H3O. It is HTO where T is Tritium -- the
isotope of hydrogen that has two neutrons and thus an atomic mas of 3 amu.
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Update: June 2012