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Name: Eric
Status: other
Age: 20s
Location: N/A
Country: N/A
Date: 1999 


Question:
Hello 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?


Replies:
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.

Bradburn



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