Friday, June 02, 2006

Iran: Nuclear Fusion.

As I recalled in one posting last December ("Feasible Fusion Power - I doubt it!"), when I was about 10 years old, I heard that electricity provided by nuclear fusion would come on-stream "in about thirty years". Now, thirty years on it is said that we can probably expect "fusion" to become a practical reality in about 60 years, according to the estimates of scientists from the European Union, France, Japan, South Korea, China and the United States of America. I am surprised, therefore, that Iran has stated that it's nation is set to pursue this holy grail. If they manage to find it, this would be a marvelous accomplishment, and the rest of the world would follow their example, thus obviating the challenge of electricity production that faces all of our nations, in the undoubted wake of hard-won gas supplies, which we in the U.K. are set to import 80% of our current usage by the year 2060. As when I was a child, this is a date comfortably distant from our current conceptions, and the cards may well fall far short of it.
The "nuclear" issue in Iran is complex and looks set to precipitate military conflict. I sincerely hope that there will be no repetition of "Iraq", a war which was ostensibly fought over WMD's (Weapons of Mass Destruction) which were never found, or to topple a barbarous dictator, depending on who's words one was led to believe at its inception. It is interesting that Iran produces the world's third greatest volume of oil, following Saudi Arabia and Russia, and so is provided in that resource even more so than is Iraq. There are also large reserves of oil in Afghanistan; an interesting coincidence of that geological belt of the Earth. The story as I understand it is that there is consensus that Iran is enriching uranium in order to produce nuclear weapons, and the U.S. is telling them to stop it - or else. The Russians have offered to enrich uranium for Iran, but on Russian soil, which would preclude any action against the former.
There is a huge difference in the grade of enrichment required to produce uranium in a form suitable for fabrication nuclear fuel rods and that to make an atom bomb, or the warhead of a nuclear missile, however.
In the case of nuclear fuel, enrichment to only around 3.5% in uranium-235 is necessary. Indeed, natural uranium with its uranium-235 content of just 0.7% can be used if "heavy water" (deuterium oxide, D2O) is used as the coolant and moderator, rather than ordinary "light water" (H2O). However, to produce an atomic weapon, enrichment in uranium-235 to the level of up to 90% is the order of the day, and that is a more difficult process. However, the gas-diffusion or centrifugation apparatus that is used for the purpose of separating the two principal isotopes of uranium-235 and uranium-238 could simply be run for longer, and might well provide the means for making a nuclear device with military intent. Who it might be aimed at is another question. The Iranians claim that they are simply after providing nuclear power for electricity, exactly as the U.K., U.S., Russia and China are intent upon, and why shouldn't they do so as well? Indeed, the former three nations are urging their own nuclear weapons programmes along with a parallel expansion in their nuclear fuel industries.
I have commented before that the world's supply of uranium is a finite resource, which can only be eked out beyond about 50 years worth if fast breeder reactors are employed, which is a difficult technology and hence has not been widely adopted despite the intentions to do so in the 1970's. Instead the world relies mostly on fission powered reactors and hence the need to enrich the uranium fuel in the lighter isotope uranium-235 by gaseous separation of uranium hexafluoride, thus rendering available "depleted uranium" - uranium-238 - for use in tank armaments and warheads of military shells. Depleted uranium is a nasty material in that having torn its way through the side of a tank, and heated up to around 1,000 degrees centrigrade in the process, it then ignites into a fireball in contact with the oxygen inside the tank, and then it is "Goodnight Vienna"!.
Nuclear fusion, however, should not cause such angst. It is often incorrectly claimed that this would be a "clean" form of energy, but indeed the apparatus - the "magnetic bottle" required to confine the plasma of deuterium and tritium nuclei, plus a few electrons ionised from the atoms they originally come from - would become highly radioactive from the attendant neutron irradiation, and would form a high level (in terms of its radioactivity) nuclear waste with the well acknowledged conundrums associated with its disposal, exactly as we now face in providing a solution to the long term disposal of radioactive waste spewed-out by conventional fission powered nuclear reactors. The actual matter of "confinement" is the bugbear that has defeated scientists so far in attaining sutainable nuclear fusion, since there is an apparent tendency (I suspect due to entropy, although I am not entirely certain of this) for the plasma to "leak out" of the bottle, whence the fusion process breaks down.
It is necessary to heat the plasma to around 100 - 300 million degrees centigrade, in order to surpass the critical ignition temperature at which a deuterium nucleus will fuse with a tritium nucleus. Since both carry a positive charge, there is an inherent tendency for the two to repel one another, and this repulsive energy must be overcome; therefore the enormous temperature that is necessary for the process. There is moreover the issue of "fuel" here too. Tritium is a radioactive atom (the nucleus "triton" decays with a half-life of around 12 years) and so it does not exist on Earth in sufficient quantities to power a nuclear fission programme in Iran or anywhere else for that matter. It must be "Bred" from lithium using neutrons in an initial deuterium-tritium fusion stage, and ideally the entire process would become self-sustaining, with lithium fuel being consumed via its conversion to tritium, which then fuses with deuterium and releases more neutrons to breed more fuel. The lithium fuel would be partly employed in the form of a blanket around the reactor by way of increasing the overall tritium yield.
However, there is the opportunity of replacing the blanket of lithium by that other material, uranium, which could be "bred" into plutonium, arguably for nuclear weapons, and so I guess the Iranian proposal to introduce a nuclear fusion progamme could also be interpreted as a nuclear threat even if there is no such intention. However, I doubt the scheme is feasible, and the major political outcome is likely to be a struggle over a significant quantity of the world's oil, and all that may imply.

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