@25, Buster,
You are right about D2O. My lame attempt at humor was hastily thought out and technically incorrect. About graphite reactors, however, I beg to differ. They can be designed properly. One of the Unites States’ first “power” reactors was at Hanford, WA. Designed to produce plutonium for our weapons it sold the “waste” heat to generate electricity. It was a graphite moderated reactor and ran without incident until our need for plutonium was eliminated by the various treaties that limited our stockpile of weapons. Also at Fort St. Vrain in Colorado was an experimental graphite reactor which was shut down because it was too expensive to run and had many outages due to its experimental nature, not for safety reasons. It was gas cooled, using helium. A loss of helium coolant would have meant substituting air which would have served well enough to avoid a meltdown.
The Russian RBMK reactors are another story. However, there are several still in existence and still operating, despite their inherent design flaws. Chernobyl was a disaster only because the graphite core caught fire and launched almost the entire inventory of radioactive fission fragments high into the atmosphere. If Chernobyl had had a containment structure like all American reactors, that fire would never have occurred. Likewise, if the operators had been trained properly instead of kept in the dark by the Soviet’s pathological need for secrecy they never would have tried to run the plant in an unsafe manner and the accident would never have occurred. Likewise, if the plant had an emergency coolant supply like all US reactors it would not have overheated. Likewise if it was made impossible to operate the reactor with all of the control rods out (for a brief time!) the accident would have never occurred. And on and on and on. What would you prefer, a Russian RBMK in Iran (with containment, emergency core coolant, properly trained operators, etc.) or a uranium enrichment facility making bomb grade U-235?
Also, while it is possible to burn U-235 more efficiently in a heavy water reactor by enriching natural uranium, why would you do it? You can also increase the efficiency of your car by burning pure iso-octane, but not by much and the cost of refining gas to the level of a pure substance would be hideously expensive. The whole point of an expensive heavy water reactor is to avoid the even greater expense of enrichment. If you have a heavy water plant, as, I guess the Iranians will soon have, the existence of an enrichment facility can only be for a bomb.
Finally, what’s to prevent the Iranians from shutting down a reactor every month or so to retrieve the bomb grade Pu-239, and just not telling anybody about it. It’s not like they are going to permit UN inspectors or anything like that. Why would they need Pu-239 when they have U-235? A U-235 bomb is much easier to make. Given the choice, I would prefer them to have plutonium rather that uranium for a bomb. More chance for a fizzle, which brings us back on topic. Somewhat.
