Iran: Would Light-Water Reactor Suit Tehran's Needs?

Iran's Bushehr plant under construction is a light-water reactor (Fars) PRAGUE, May 17, 2006 (RFE/RL) -- Diplomats say the EU-3 (Great Britain, France, and Germany) are planning to offer Iran a light-water reactor as part of a package of incentives to persuade Tehran to give up uranium enrichment and efforts to build a heavy-water research reactor. RFE/RL correspondent Jeremy Bransten asked British nuclear physicist Frank Barnaby of the Oxford Research Group what the difference is between the two types of reactor and whether Tehran is likely to be interested.

RFE/RL: What is the main difference between a light-water reactor and a heavy-water reactor?

Frank Barnaby: Both types of reactor produce plutonium and that plutonium can be separated from the spent fuel elements and used to produce nuclear weapons. On the other hand, a heavy-water reactor, generally speaking, is much more efficient at producing plutonium of the type needed for the most effective nuclear weapons. So if you want to produce nuclear weapons, a heavy-water reactor is better. But a light-water reactor is also possible to use.

RFE/RL: Does this mean that all civilian nuclear power plants have light-water reactors?

Barnaby: Canadian reactors, called CANDU reactors, are heavy-water reactors. So not all are, but the vast majority of reactors used for electricity production are light-water reactors. And of course the Russians are building a light-water reactor in Iran at the moment, at Bushehr.

RFE/RL: What do the terms "heavy water" and "light water" mean?

Barnaby: The difference between heavy water and ordinary [light] water is that ordinary water, H2O, uses the normal hydrogen isotope. Heavy water uses deuterium, which is not the normal hydrogen found in nature. So you have to produce deuterium and then combine it with oxygen to produce heavy water.

RFE/RL: Iran is building a heavy-water reactor at Arak, which it says will be used for research and other civilian purposes. Is that a plausible explanation, in your view?

Barnaby: It's a good size for research purposes, maybe a bit on the large side, but a good size. But it does produce plutonium, which could be used for nuclear weapons. So it's dual-purpose, really.

RFE/RL: Why would Iran choose to build a heavy-water plant, if it were truly only interested in research and producing electricity? Is there a rational explanation?

Barnaby: The advantage of a heavy-water reactor from the Iranian point of view is that it can be fueled with natural uranium [which Iran has]. You don't have to enrich the uranium to fuel it. So that is an advantage from the Iranian point of view.

RFE/RL: And light-water reactors, like the Bushehr plant, require enriched uranium as fuel?

Barnaby: Light-water reactors do require enriched uranium fuel to enrichment of about 3.5 percent of uranium 235. But a nuclear weapon requires very highly enriched uranium to 90-plus percent, so there's a big difference there. So the Iranians with a heavy-water reactor would use natural uranium as fuel. But if they went for [a light-water reactor], for research purposes, they would need to have enriched uranium.

RFE/RL: So, to sum up, is Iran's insistence that it is building a heavy-water reactor purely for research and civilian purposes -- possibly because it doesn't want to rely on foreign supplies of enriched fuel -- a plausible explanation to you?

Barnaby: Yes, that is a plausible explanation, certainly.

RFE/RL: But do you believe it?

Barnaby: At the moment, there's no evidence one way or the other, really. There's no "smoking gun" which shows that Iran is going for nuclear weapons. On the other hand, its program could lead to nuclear weapons. So one has to keep a bit of an open mind about it, I suppose.