Comment 60985

By Borrelli (registered) | Posted March 15, 2011 at 13:53:10 in reply to Comment 60982

Main diff between Canadian reactors and basically all other reactors is the moderating medium in which the fuel sits. As Ryan mentioned, Fukushima is a Boiling-Water Reactor which uses so-called "light water" (i.e. normal water).

CANDU reactors get their name from the heavy-water moderator (Canada Deuterium Uranium). Deuterium is an isotope of hydrogen (2H or D) that can replace hydrogen in water (H2O) to get so-called "heavy water" (D20).

The point of using a moderator like water in a reactor is to slow down reactions in the core, but D2O has the added advantage of not absorbing as many neutrons as normal water, thereby allowing CANDU reactors to use un-enriched uranium.

This in itself is a huge design difference--enriching uranium is a complex and expensive task, and using enriched uranium leaves undesirable byproducts like plutonium.

As well, there are safety benefits from using heavy water in CANDU reactors, and I'm not sure I can explain those benefits very succinctly, but here's a good overview:

Comment edited by Borrelli on 2011-03-15 13:55:55

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