Past Events - March 9 2000

Dr. Alistair Miller, manager of AECL's Heavy Water Technologies branch, addressed the CNS Manitoba branch on Heavy Water: Manufacturers Guide for the Hydrogen Century.    Dr. Miller has 34 years experience in heavy water science and technology, having spent most of his career at AECL's Chalk River Laboratories.   He also spent a few years at the Bruce heavy water plant studying and modelling it to improve the production rate.

Amongst Dr. Miller's other passions is the Deep River Science Academy, of which he is the chair of the national board.



Abstract

All you (likely) ever wanted to know about how to produce heavy water. How it has been done?   How it might be done?   Why its production is somewhat difficult?   And, by the way, why we want even to bother?

Deuterium has pedigree (going right back to the big bang), is the isotope that aspires to be almost an element, and impresses the AECB enough that they've made it a proscribed substance!   If you really want to get it cheap, move to Venus.


What is heavy water?
By M.J. Brown

Heavy water is comprised of molecules of two deuterium (D) atoms joined to one oxygen atom.   Protium (P) is the most abundant hydrogen atom, with one proton in its nucleus.   Deuterium is also a naturally-occurring hydrogen atom, with a neutron and a proton in its nucleus (or core).   Deuterium is known as "heavy" hydrogen because it has twice the mass of protium (light hydrogen), since a proton and neutron have almost exactly the same masses.   Deuterium is relatively rare, occurring in about one in 6000 hydrogen atoms on earth.   Tritium (T) is the third type of hydrogen, with two neutrons and one proton in the nucleus.   Tritium is the only radioactive isotope of hydrogen, which decays to helium-3 (non-radioactive) by the emission of a beta particle (an electron).    The half life of tritium is 12.3 years, and thus it is very rare - it is a product of natural solar processes, nuclear reactors and nuclear weapons.

So, why is heavy water important?   Hydrogen atoms are very good at slowing (moderating) the fast neutrons generated by nuclear fissions (splitting atomic nuclei), and slow neutrons are needed to induce further fissions (in most nuclear reactor designs).   Thus water is often used as a moderator because of the high density of hydrogen nuclei.   Light hydrogen nuclei also have a high propensity for absorbing neutrons (the hydrogen atoms become deuterium), so reactors using normal (essentially light) water must use enriched uranium fuel to compensate for the neutron losses.   Enriched uranium has a larger fraction (often 2.5 to 4 %) of splittable uranium-235 atoms than does natural uranium (0.7% U-235).   Heavy hydrogen nuclei are only half as good as light hydrogen nuclei at moderation but have a much lower neutron absorption, so reactors using a heavy water moderator can run on natural uranium.   Thus there is a need to extract the small fraction of heavy water from natural water.

Is heavy water dangerous?   Heavy water comprises a small fraction of normal water, and has the same chemical properties as light water.   The difference is in the reaction rates (kinetics).   Apparently there is no noticeable difference if one had a few percent heavy water in your body, but it would become noticeable above 10%.   A level of 20% heavy water in our systems would be enough to kill us, because of the different reaction rates in the many chemical processes in our bodies.   Perhaps I should write a murder mystery where the poison goes undetected (by the usual chemical forensic work, anyhow).   "Death by Deuterium"? "Murder from Deuterient Excess"? (work with me here)

[CNS Manitoba Home Page

[CNS Home Page]