Long time, no speak. Time for a spot of guest blogging at this busy time.

Interesting news from the meetings in Geneva today. Iran has agreed, “in principle”, to have some LEU from Natanz further enriched abroad and fabricated into fuel for the Tehran Research Reactor. (You might remember President Ahmedinijad recently floated the idea of the US supplying fuel for this reactor which is apparently close to running on empty).

Apart from being an interesting confidence-building measure, it’s obvious why Iran might go for this—it needs the fuel. It’s also obvious why the E3+3 like the idea. Julian Borger reports that:

Western officials here say that to restock the TRR, Iran would have to send out up to 1200 kg of LEU. That’s about three-quarters of what they’ve got, and it would be out of the country for a year. When it came back it would be in the form of fuel rods, so it could not be turned into weapons grade material in a quick breakout scenario.

Let’s look at the practicalities of this, because it turns out there might be one potential sting in the tail.

According to NTI, the Tehran Research Reactor (TRR) requires 115.8 kg of 20% enriched fuel. We don’t know the average enrichment of the LEU at Natanz (the maximum is known to be 4.4%), so let’s assume it’s 4% (nice round number and all that). Let’s also assume that the ratio between the product and tails assays is 10, roughly the same as for enrichment from natural uranium to LEU for power reactors. I don’t know for sure this assumption is valid but I believe it is.

If you crunch the numbers (very straightforwardly) then you find that 1040 kg of uranium from Natanz is needed to produce one load of fuel for the TRR. If you assume the average enrichment of the LEU at Natanz is 3.5% then 1390 kg is required. Very much in the right ball park.

My guess (and it is only a guess) is that the enrichment will take place in Russia—at Novouralsk (see page 85 of the 2007 GFMR). Based on what I know about how other states have enriched to 20% or more, Russia probably does not go directly from natural uranium to 20%. I would expect it to enrich first to 3—5% and then to go to 20% in a second stage. If so, using Iranian LEU as feedstock for this second stage should pose few problems beyond, perhaps, a bit of blending to fine tune the enrichment to whatever the Russians normally use, providing that the Iranian material is sufficiently pure.

And here’s the crunch.

Remember the whole molybdenum thing?

The problem gets worse at higher enrichment levels and can cause centrifuges to crash. Although many have assumed than Iran has solved the problem and can produce uncontaminated UF6, we don’t know for sure. But, you can bet that the Russians are going to check this before sticking Iranian LEU into their cascades.

Technical problems could yet derail this interesting initiative…