Jon Wolfstahl has an “analysis”:http://www.carnegieendowment.org/npp/publications/index.cfm?fa=view&id=16509 of recent reports indicating that North Korea shipped UF6 to Libya. He covers a lot of the same issues that I did “here”:http://www.armscontrolwonk.com/index.php?id=418, but includes a sentence which speaks to an important question: how can the Bush administration be so confident that it has all the relevant information about Pakistan’s uranium deposits, mines, etc.?
Jon writes:
bq. In addition, technical experts have confirmed that U-234 content can vary greatly even within the same mine or even within the same sample of ore, raising the possibility that the uranium sample does come from a known source.
I was uncertain as to whether and to what degree U-234 content varies within a country. Jon’s assessment suggests that the uranium in question could well have come from an unknown Pakistani mine. Another possibility is that we know about the mine, but lack the necessary uranium samples.
It’s worth noting that Pakistan does not have a comprehensive IAEA safeguards agreement. “According to the agency,”:http://www.iaea.org/Publications/Reports/Anrep2003/table_A24.pdf Pakistan has three facilities under safeguards. None are mines.
Thanks for the link to Wolfsthal’s article.
I’m really not very current on the question of U-234 content related to mines. However, I can speak to general issues of geological occurrence and isotope and uranium chemistry.
Wolfsthal’s analysis is correct and overlaps with what I posted on WhirledView earlier. His observation that the Pu on the containers could come from overpacks adds to the uncertainty as to origin.
I wasn’t aware that the U-234 content was known to vary within mines, but this would not be surprising. Content of practically everything varies within mines, sometimes within a few tens of feet.
In any case, the U-234 measurement is one-dimensional. It is a single number, which can depend on numerous factors and can be changed in processing, although probably not by much in a conversion to UF6. It’s also a small number and a fairly difficult analysis, so it can be subject to large uncertainties. I wouldn’t consider it enough to identify a mine; I’d probably look for trace elements, although they might disappear in the UF6 conversion.
The question of how many reference samples were available is a good one. I’ll repeat the possibility that uranium from different mines may be mixed at a mill (where the ore is converted to yellowcake). This was common practice in the Soviet Union. The Sillamäe plant in Estonia received ore from Central Asia, Czechoslovakia, Hungary, Romania, Poland, and East Germany, and the relative amounts differed from time to time. A recent article in Science noted that a mill in Kyrgyzstan received ore from as far away as Hungary. Doesn’t make much sense for a capitalist, but that’s the way the Soviets did it.