Nuclear mattersMedical isotopes no longer require weapons-grade uranium

Published 9 December 2010

Highly enriched uranium (HEU) is used in nuclear weapons, but it is also used to make the radioisotopes that are injected in tiny quantities into people to diagnose and treat disease; indeed, making medical isotopes is a time-honored excuse for enriching uranium, if you want to build nuclear weapons but do not want to admit you are doing so (this is the cover Iran is using for its bomb-oriented enrichment program); South Africa’s Pelindaba reactor is now producing medical treatment-oriented molybdenum-99 (Mo-99) made from low-enriched uranium

Highly enriched uranium (HEU) is risky stuff to have around. You can make nuclear bombs out of it, and there are apparently plenty of would-be bombers who would pay a thief handsomely for the stuff. The United States and its allies promised in Washington, D.C. last April to find ways to cut down on the stuff.

Debora MacKenzie writes that the problem is that we can not get rid of it completely: as well as from the bomb factories of the nuclear powers, there are less well-guarded stocks lying about which we need to make the radioisotopes that are injected in tiny quantities into people to diagnose and treat disease.

At least we thought we could not get rid of it. The United States has just taken delivery of the first shipment of molybdenum-99 (Mo-99) made from low-enriched uranium (LEU). It was made by the South Africa Nuclear Energy Corporation at its Safari-1 reactor at Pelindaba. That was where South Africa built its own nuclear bombs until it renounced them in 1991 — and also where, in 2007, an armed gang apparently tried to steal some of the leftover HEU (see “More questions than answers in South Africa’s nuclear facility attack,” 15 November 2007 HSNW).

The Pelindaba operators thus know the risks of having HEU around — beside which, the United States is giving it $25 million to switch to LEU. Apparently it wasn’t easy.

Normally HEU is bombarded with a stream of neutrons to turn the 235 isotope of uranium into Mo-99. That isotope of uranium is less concentrated in LEU, and the South Africans had to turn it into a powdered alloy to expose it efficiently to the neutrons.

We needed a better source of Mo-99 even without the proliferation risk engendered by having to enrich uranium to get it,” MacKenzie writes. The short-lived molybdenum decays into technetium-99, which is used to help visualize bones and organs in an estimated 100,000 or more medical procedures worldwide, every day. The technetium also does not last long, so we can nott stockpile this stuff — we need constant production.

The nuclear plants that make it have been showing their age, however: the plant in Ontario, Canada that until recently produced more than half the world’s supply has been shut as have Dutch, French, and Belgian ones. Last year Canadian physicists suggested using a particle accelerator to make it instead, without HEU. The South Africans may not be the only ones making HEU-free Mo-99 for long.

MacKenzie notes that not everyone is about to give up the old ways: making medical isotopes is a time-honored excuse for enriching uranium, if you do not have a bomb-making program — at least an admitted one — as an excuse. Iran has insisted it needs further to enrich its LEU to re-fuel its medical isotope plant in Tehran. An agreement between Iran and Western powers earlier this year to swap Iranian LEU for the fuel it needed for isotopes, to stop Iran enriching its own, broke down.

Meetings between the UN Security Council plus Germany and Iran to try and resolve the dispute resumed in Geneva this week. Meanwhile the International Atomic Energy Agency approved an internationally run plant to make and recycle nuclear fuel, yet another way to take enrichment out of national hands. MacKenzie concludes:

One hopes Iran will joyfully embrace the international plant in order not to have to go to all the bother of enriching its own uranium for nuclear fuel anymore. One also hopes it will embrace the South African technology for making medical isotopes, thereby avoiding all that fuss about further enrichment. One does not, however, hold one’s breath.