The International Atomic Energy Agency (IAEA) recently reported that Iran had produced up to 1,010 kilograms of low-enrichment uranium, as of November 2008.
Admiral Mike Mullen, chairman of the joints chiefs of staff of the US armed forces opined publicly that this was a sufficient mass from which to extract the fissile portion to build one atomic bomb, and that a nuclear-(one) armed Iran would be a “very, very bad outcome.” Robert Gates, the US Secretary of Defense, viewed the situation as less alarming, stating that Iran was “not close” to fabricating a weapon.
It requires little imagination to anticipate the obvious lobbying stratagems of the many Treasury Department parasites who cast the Persian uranium horde as a dire threat that can only be allayed by offering the nation’s financial jugular to deep penetration by their zealous fangs, and perhaps to also loose some cathartic aerial bombardments upon the Iranians, that like Zeus’s thunderbolts will dissipate an Olympian distemper. Nuclear weapons contractors, Zionists and American militarists are the ultimate automatons of reductio ad absurdum, regardless of the information thrown into them, their concluding outputs are invariably the same: give us more.
So, for now we bypass the mirage of policy discussion regarding today’s Iranian uranium horde, and instead describe some physical facts about Iran’s bomb-making potential.
Uranium is a slightly radioactive, silver-grey metal 70% denser than lead, which appears naturally as oxides in mineral ores. As with a number of other elements, there are several forms of uranium atoms, which are called isotopes. All uranium atoms have 92 electrons (particles with 1 unit of electrical charge, and with negative polarity) and 92 protons (particles with 1 unit of electrical charge, and with positive polarity). Each isotope of uranium has a different number of neutrons (electrically neutral particles) in its nucleus, and this number ranges from 141 to 146.
It happens that the mass of an electron is slight compared to that of a proton or neutron, and the masses of these latter two types of particles is quite close. So, one can characterize the weight of an isotope by the combination of its total proton mass and total neutron mass (this is slightly inexact, but good enough for a general understanding). The number of protons is called the “atomic number,” and the combined number of protons and neutrons is called the “atomic weight.” So, uranium has an atomic number of 92, and an atomic weight, depending on isotope, of between 233 and 238. (See the End Notes for superfluous details).
The natural isotopic distribution of uranium is: U238 at 99.284%, U235 at 0.711% and U234 at 0.0058% (the sum is slightly off 100% due to rounding).
The nucleus of any atom can be ruptured when impacted by a sufficiently energetic sub-atomic particle or quanta of electromagnetic radiation (high energy gamma rays, cosmic rays). This is nuclear fission. Nuclei heavier than an iron nucleus are less tightly bound as they are increasingly massive. It is easier for them to undergo fission.
Because the neutron is electrically neutral, it will not be deflected by an atom’s protons and electrons, so it is a very effective projectile for initiating nuclear fission. While any atomic nucleus can be made to fission by some form of high energy impact, the term “fissionable” is generally used in an engineering sense for those elements that undergo fission when struck by neutrons.
It is interesting that for all naturally occurring isotopes except one, the neutrons initiating fission must have high energy (e.g., 14 MeV). The exceptional isotope is U235, it will undergo fission when impacted by neutrons of low energy (e.g., 1 MeV). Fissioning nuclei can fragment into multiple parts, and emit neutrons of low energy. This is why a mass of U235 can sustain fission chain reactions, while masses of no other natural isotope can.
The term “fissile” is used to designate materials that can sustain fission chain reactions — materials that fission when impacted by low-energy neutrons emitted from prior fission reactions. Aside from the naturally occurring U235, fissile materials are artificially “bred” in nuclear reactors, the main ones being: Plutonium-239 (Pu239), Pu241 and U233. Pu239 is bred when U238 captures a neutron (and rearranges its now heavier nucleus). This same process sequentially produces Pu240 and Pu241. U233 is bred from Thorium-232. There are fifteen actinoid (rare earth) elements from which fissile isotopes can be produced; uranium and thorium are the only naturally occurring actinoids. Fissile uranium and plutonium are the most convenient materials for use as nuclear reactor fuel and in nuclear explosives.
Refining nuclear fuel begins with the extraction of elemental uranium from mineral ores. Since the elemental mass is less than 1% U235, it is put through an enrichment process, which exploits the mass difference between U238 and U235. The enriched portion is reactor fuel with about 3% to 4% U235, while the remainder is slightly more concentrated U238 called depleted uranium (DU). It is important to note that a major investment in both energy and infrastructure is required to be able to produce reactor fuel, a point about massive CO2 emissions that is glossed over by proponents of nuclear power as a “green” technology.
We can see that if Iran now has 1,010 kilograms of reactor fuel, then this mass will contain a portion of U235 equivalent to between 30 kg to 40 kg. If one had this quantity of U235 as a contiguous mass rather than distributed throughout 1,010 kilos (over a ton) of uranium metal, then one could cut and machine the U235 to shape parts (“the pit”) for a fission bomb. Nuclear weapons-grade fuel may be more then 90% U235, and refining reactor fuel to this extent is a lengthy and extraordinarily expensive continuation of the enrichment process that yielded reactor-grade fuel with 3% to 4% U235. So, Robert Gates is quite correct to say Iran is “not close” to having a nuclear explosive (what we normally think of with the phrase “nuclear weapon”).
A state-of-the-art bomb production industry can make an atomic bomb from 10 kg of weapons-grade U235. As the engineering refinement of and control over the implosion and criticality dynamics of the bomb decrease, the quantity of fissile material needed increases. So, an inexperienced weapons design team might have to use 20 kg to 30 kg of weapons-grade U235 to ensure their device would produce “nuclear yield.” The incredibly inefficient Little Boy gun-type uranium bomb dropped on Hiroshima had 64 kg of U235, of which 0.7 kg underwent fission, and only 0.6 grams were transformed into energy (by E = m C-squared). The blast yield of Little Boy was equivalent to that of between 13 to 18 kilotons of TNT. The Fat Man plutonium implosion bomb dropped on Nagasaki had 6.2 kg of Pu239, of which 1.2 kg underwent fission, and under one gram was transformed into energy. Fat Man’s explosive yield was 21 kT. If Iran’s U235 were to be concentrated to weapons-grade material, they would have enough for at least one bomb.
Electricity can be generated from a power reactor that “burns” nuclear fuel. The fission energy released as the motion of fission fragments is captured by the mass of the reactor core, which heats up, and in turn boils water to drive steam turbines that turn electric generators (there are also other types of reactors that exploit the heating of the core). As the mass of reactor fuel burns, it accumulates substances transmuted by nuclear reactions, such as Pu239, Pu241 and other radioactive isotopes. Some of these new substances poison the process of fission chain reactions, because they absorb neutrons. It is this effect, rather than a complete depletion of U235, which limits the utility of a fuel mass. Spent fuel may still be 0.5% U235.
Fissile material bred from uranium fuel in reactors can be harvested (“reprocessed”). An advanced fission weapons program will breed plutonium from uranium, and then enrich the plutonium to a weapons-grade purity of Pu239 or Pu241. This is the kind of program carried on by the major nuclear powers. Iran is nowhere near this. But, it is possible it has done “test tube sized” experiments that attempt to breed and extract trace amounts of plutonium from uranium reactor fuel. Any scientific establishment working to learn how to reprocess spent fuel so as to ameliorate the problems of long-term storage and disposal (and/or to design breeder cycles) will of necessity be working on methods for extracting plutonium.
The practical energy yield or “burn up” from a mass of reactor fuel is characterized by the number of 24 hour days at 1 megawatt output of thermal power per metric ton of uranium metal. Typical numbers for existing reactors are 30,000 to 40,000 MW days per metric ton of fuel mass. Let us say the Iranians acquire or build a reactor with 36,500 MW-day/tonne. This is equivalent to 100 MW-year/tonne (ignoring leap year corrections). Given their 1.01 tonne horde, they could expect an energy yield of 101 MW-year. Now, a megawatt of power is equal to 1,341 horsepower, the power of a moderate train locomotive, an early WW2 airplane engine, a good sized charter fishing boat, and a standby emergency power unit for a campus or moderate industrial site. Nuclear power for supplying electricity to the electrical power grid of a small nation or a national region would more likely flow at a rate of 100 MW to 1 GW (gigawatt, equal to 1000 MW). Our hypothetical 100 MW-year/tonne system would use up the 1.01 tonne fuel supply in 1 year and 3.7 days of continuous 100 MW operation, or in 37 days of continuous 1 GW operation. It is evident that the Iranian uranium fuel supply is only a token of what would be needed to operate a useful civilian power system. The most likely application of the present Iranian uranium reactor fuel supply is in powering a small research reactor that is used to enable experimentation in all aspects of nuclear power technology and reactor fuel management and reprocessing.
Are the Iranians trying to produce an atomic bomb? They should be, given their history of experiencing invasions and warfare (Alexander the Great, Mark Antony, Genghis Khan, Tamerlane, Imperial Russia, the British Empire, Kermit Roosevelt, Jr., Saddam Hussein); their ballistic missile proximity to the Eurasian nuclear powers of Russia, China, India and Pakistan; and to that nuclear-armed Middle East enclave of furious exceptionalism — Israel; their enviable quantities of petroleum and natural gas; and the entrenched hostility of the United States imperialists, miffed at the Iranian refusal to submit to its possessive control and to a cultural deflowering.
The Iranians say they are not building a nuclear weapon, and you cannot disprove their claim on the basis of physical evidence or physics estimates. It does make business sense for Iran to save its petroleum resources for the export market, and to increase that profitability by powering its domestic economy with its own independent system of nuclear power. Also, given the world thirst for oil, it does make sense to develop an alternative now for powering a post-fossil fuel economy. Disbelief of the Iranian characterization of their nuclear energy work is based on political agendas (e.g., Zionism), and simple prejudice aping principled mistrust (e.g., neo-con imperialism). It IS possible the Iranians have not been truthful about their intent, but it is not possible to discern this from physical considerations. And, we must be clear that the Iranians are completely within their rights (by treaties signed) to pursue their nuclear energy work for the purposes they have stated: civilian electrical power.
What is clear is that the physics of bomb-making and the physics of civilian nuclear power are inextricably entwined beyond any possibility of chaste separation that would fully satisfy the political desires of competing states. It is also clear that any nation’s investment in an independent nuclear power system is a de facto national defense program, because the threat of it acquiring nuclear weapons is implicit and physically embedded in the development work for the technology.
What must also become clear is that investment in nuclear energy technology, especially if carried forward to weapons development, is a detriment to the social good because it drains enormous resources that could be used to improve the health and well-being of the public. Some of this public detriment will be due to the ambitions of a national leadership whose machinations for greater power lead to the diversion of national wealth into military programs — and nuclear power is intrinsically a central government and a military program. By the very nature of nuclear material, nuclear fuel and nuclear fuel reprocessing, the central government must control the technology for the sake of security. Civilian nuclear power is at best an attempt by the government to spread the costs of maintaining the nuclear fuel — and nuclear bomb — infrastructure (e.g., a ‘non-bomb’ military application is nuclear-powered warships). This is why the U.S. and Russia have sought, and still seek, client states whose civilian nuclear power systems they would fuel and reprocess (e.g., South Korea).
That Iran does not wish to be such a client state is interpreted by the Washington imperialists as an act of defiance, a declaration of nuclear armament building. This independence on nuclear matters is entirely within Iran’s rights as spelled out in the test ban and non-proliferation treaties. This act of independence may also be an Iranian virtual nuclear weapons program that is a purely psychological illusion, and would be judged successful if the degree of caution and hesitation it introduces into the US approach to Iran outweighs the inevitable increase in US irritation with Iran.
The hostility of large powerful states toward smaller, weaker ones may justifiably motivate some of those lesser states to explore the deterrent potential of nuclear arms. Like the spines of a sea urchin, or the noxious taste of a milkweed (Monarch) butterfly, a small credible capability in nuclear arms may offer significant protection against large unrelenting predators. The entire world can see how gingerly the U.S. treats North Korea, with its puny near-dud atomic bomb (assuming it has another) as compared to, say, Venezuela or Syria or Cuba, which evidently lack nuclear arms.
What is so stupid about US policy regarding nuclear developments in other states is that its ham-fisted belligerence reinforces the fears of small nations that decide to divert resources from economic development to the sprouting of nuclear-armed political spines; and what is so sad is that the objectification of that U.S. hostility and that subject nation’s fear into those armament spines is a heartless tax sapping national wealth that is sorely needed to meet basic human needs. The I Ching might have put it this way: the hostility of the great is the impoverishment of the weak.
The actual physical mass of an atom is the product of its atomic weight — which recall is simply the number of its combined protons and neutrons — multiplied by an “atomic mass unit,” (abbreviated as AMU), which is a precisely defined quantity that we will round for convenience to 1.66/(10 to the 24th power) grams. So, an atom of U238 has a mass of 3.95/(10 to the 22nd power) grams, an exceedingly small mass.
A macroscopic quantity of 238 grams (about half a pound) of pure U238 will contain 6.022 x (10 to the 23rd power) atoms. This last number is called Avogadro’s Number. It is an interesting fact that any pure isotopic mass whose quantity in grams is numerically equal to its atomic weight (the number of combined protons and neutrons in one atom) will contain Avogadro’s Number of atoms.
The numerical value of the AMU is the inverse of the numerical value of Avogadro’s Number.