The Busher nuclear power plant in Iran. Photo: IAEA/Paolo Contri
By Dr. Gordon Edwards
All nuclear weapons require a primary nuclear explosive. There are only two materials that are used for that purpose: either Highly Enriched Uranium (HEU) or plutonium of any kind (except plutonium-238).
Highly Enriched Uranium
Highly Enriched Uranium refers to any kind of uranium that has a relatively high percentage (20 percent or more) of uranium-235. Natural uranium — uranium that is mined from the Earth anywhere in the world — has only 0.7 percent uranium-235 and 99.3 percent uranium-238. Uranium-238 is not usable as a primary nuclear explosive material. The mix of U-238 and U-235 found in natural uranium is also not nuclear-weapons-usable, because there isn’t enough U-235.
Uranium enrichment is a process of gradually removing more and more U-238 from the mix, thereby increasing the concentration of U-235, boosting the percentage of U-235 to 3 percent, or 5 percent, or 20 percent, or 90 percent or more.
Any uranium that is over 90 percent U-235 is called “weapons-grade uranium” and is ideal for making atomic bombs. But in fact any uranium that is over 20 percent U-235 is said to be “highly enriched” HEU and can, in principle, be used to make a nuclear explosive device.
[The uranium fuel for the NRU research reactor at Chalk River is between 19 and 20 percent U-235 — just below the magic “cut-off” between Low Enriched Uranium (LEU) and Highly Enriched Uranium (HEU). But the NRU reactor also uses weapons-grade uranium “targets” to produce medical isotopes, and is still importing weapons-grade uranium from the USA. In Chalk River Labs has an import licence pending for that very purpose.]
By agreeing to enrich uranium only to 3.7 percent, the Iranians are foregoing the possibility of producing weapons-grade uranium or even weapons-usable uranium. They are also taking 2/3 of their most advanced centrifuges (used for enriching uranium) out of service — the very centrifuges needed to make HEU.
Plutonium does not exist in nature; it is a uranium derivative that is created inside a nuclear reactor. Specifically, when a uranium-238 atom absorbs a stray neutron inside the reactor it is transmuted into a plutonium-239 atom. Further neutron captures produces other, heavier plutonium isotopes: plutonium-240, -241, -242, et cetera.
All of these reactor-produced plutonium isotopes are usable as a primary nuclear explosive, but the best of the lot (for weapons purposes) is plutonium-239. Any plutonium that has a very high percentage of plutonium-239 is called “weapons-grade plutonium”. Nevertheless, all reactor-produced plutonium is perfectly weapons-usable, regardless of the concentration of plutonium-239. See http://ccnr.org/plute.html .
To get the plutonium out of the irradiated nuclear fuel requires “reprocessing” technology. Reprocessing involves dissolving the solid nuclear fuel assemblies in boiling nitric acid, producing large volumes of liquid high-level radioactive waste, and then chemically separating the small percentage of plutonium from the liquid solution. Once the plutonium has been re-solidified it can then be used as a very powerful nuclear explosive material.
IAEA Director General Yukiya Amano (right) meets with the Deputy for Legal and International Affairs of the Ministry of Foreign Affairs of Iran, Seyyed Abbas Araghchi, at IAEA Headquarters in Vienna, Austria, on 24 February 2015. Photo: IAEA/Dean Calma
Heavy Water Reactors
Commercial nuclear power reactors require a nuclear fuel (usually uranium or plutonium) and a substance called a “moderator” to slow down the neutrons so that the nuclear chain reaction can sustain itself. If ordinary water is used as a moderator, the uranium fuel has to be enriched to about 3 to 5 percent U-235. This is called Low Enriched Uranium (LEU).
However if “heavy water” is used instead of ordinary “light water”, the uranium fuel does not have to enriched at all. Such a reactor, called a Heavy Water reactor, can run perfectly well on natural uranium. In this way plutonium can be produced without the need for any uranium enrichment whatsoever. That plutonium — when extracted from the nuclear fuel waste by reprocessing technology — can then be used as a primary nuclear explosive in nuclear weapons of many different kinds.
By agreeing to forego the pursuit of any reprocessing technology, the Iranians agree not to access the plutonium contained in their irradiated nuclear fuel, thereby making it impossible for them to use that plutonium as a primary nuclear explosive. In addition, their brand-new Heavy Water Reactor (the Arak reactor) will be modified in design so that it cannot be used to make the ideal kind of plutonium for bomb-making — the “weapons-grade” plutonium that is exceptionally rich in plutonium-239.
By eliminating the production of HEU, and foregoing reprocessing technology to extract plutonium, Iran effectively closes the door to nuclear weapons of any kind. They cannot produce any material to be used as a primary nuclear explosive. Unless they smuggle it in from somewhere else, or find a way to produce it clandestinely — but Iran is also willing to accept far-reaching IAEA surveillance on all their nuclear facilities, including unannounced inspections by IAEA authorities. (Pressenza)