Iran Underfeeding The Cascades

As we thought!

Iran, according to “knowledgeable officials” paraphrased by Albright, Shire and Brannan, is underfeeding the cascades:

Based on interviews with knowledgeable officials, however, the feed rate [of 70 grams per hour] may be higher than the optimal value sought currently in each of the eight cascades. Assuming that the lower rate is the actual one, the cascades are estimated to have enriched at this lower optimal level on average almost 90 percent of the time during this one-month period. Although this higher percentage appears to suggest that Iran has made a significant accomplishment, it actually implies that the cascades are operating less efficiently and producing less enriched uranium than expected by Iranian officials in 2006.

If Iran is deliberately underfeeding the cascades, … plant operators [may be] engaged at an intermediate step in a systematic process of increasing the amount of uranium hexafluoride until an optimal feed level is reached. Alternatively, underfeeding may represent operator uncertainty about what may occur in the cascades, including the possibility of large-scale breakage or “crashing” of centrifuges or unexpected interruptions in cascade operations. This caution could be driven by inexperience in operating and controlling a large number of cascades, particularly involving centrifuges subject to excessive vibration.

Under either scenario, Iran still has more to do before it demonstrates that it can reliably operate an enrichment plant. In particular, it must operate its centrifuge cascades with uranium hexafluoride on a sustained basis.

Albright and company also use a smaller date range—April 18 to May 13—that I think is probably more reasonable than my first guess. The suggestion is that Iran may be continuously operating centrifuges, but that the centrifuges are much less efficient that one might expect—maybe less than 1 kg SWU per year.