The Hubbub Over Iran’s Heavy Water

by Andrew Reimers

More than a year after the P5+1 and Iran agreed to the terms of the Iran nuclear deal, the debate in the U.S. over the deal’s implementation is far from over. In recent months, part of that debate has been focused on what should be done about Iran’s stockpile of heavy water. The ongoing controversy offers an opportunity to discuss the provisions in the deal regarding the country’s heavy water program and to provide some context for the role of heavy water in the history of nuclear proliferation.

As part of the deal, Iran agreed to shut down the Arak heavy water reactor and reduce its stockpile of heavy water to 130 tons. Iran followed through with this agreement by removing the core from the Arak reactor, filling it with concrete, and shipping 32 tons of heavy water to Oman for temporary storage.

In April of this year, the DOE agreed to purchase 32 tons of heavy water for approximately $8.6 million. The Obama administration’s argument in favor of the purchase is that allowing the heavy water to hit the open market would pose a serious risk of proliferation. The opposing argument as articulated by Congressional Republicans is that such an exchange is equivalent to subsidizing both the Iranian nuclear program and Iranian sponsorship of militant groups throughout the Middle East.

Senator Tom Cotton (R-Arkansas) filed an amendment to ban the purchase of Iranian heavy water back in April when the purchase was initially agreed upon, but that move was blocked by Senate Democrats. More recently, House Republicans voted to ban the purchase of Iranian heavy water despite President Obama’s promise to veto such a bill. The chief of Iran’s Atomic Energy Organization has said that Iran will not ship any heavy water to the U.S. until they are confident that the U.S will hold up their end of the bargain.

Heavy Water Reactors and the Production of Nuclear Weapons 

In a nuclear reactor, heavy water can be used as a neutron moderator, meaning it can slow down fast-moving neutrons so that they can sustain a nuclear chain reaction. The upshot is that while light-water reactors typically require fuel that has been enriched to around five percent uranium-235, a heavy water reactor can use un-enriched uranium oxide as fuel. Like with light water reactors, however, the reacted uranium-238 in the fuel is converted to plutonium-239, making such a reactor very useful for producing weapons grade material on the sly.

Heavy water reactors similar to Arak were employed by NPT holdouts such as India, Pakistan and Israel in their pursuit of producing nuclear weapons. In fact, heavy water’s role in the history of nuclear proliferation goes all the way back to the original arms race between the U.S. and Nazi Germany. When the Nazis occupied Norway and took control of the Norsk Hydro plant, the largest heavy water plant in the world at that time, the Allies responded by sending a group of Norwegian commandos to sneak into the facility and destroy its stock of heavy water to prevent the Nazi’s from using it to produce plutonium.

The Obama administration’s decision to purchase Iran’s heavy water doesn’t have as much in common with a James Bond movie as does the sabotage of the Norsk Hydro plant, but the intentions behind both actions are the same – to mitigate the possibility of weapons-grade material ending up in the wrong hands. Thus, while the Congressional Republican’s opposition to the purchase of Iranian heavy water isn’t totally illegitimate, it seems to be based more on partisan politics than on concerns about nuclear proliferation.

Any views expressed are those of the author’s and do not necessarily reflect the views of ANS.

Andrew  ReimersANS member Andrew Reimers is a mechanical engineering Ph.D. student in the Webber Energy Group at the University of Texas at Austin. His research focuses on thermodynamic and economic analysis of power generation and water treatment systems. Andrew blogs about current events related to energy and water at



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