Reply #36: 20% is highly-enriched uranium, and Iran is in violation of the NPT.

[bananas]

Fuel-grade uranium is only 3-5%, this is 20%, and it doesn't take much to get it to weapons-grade.
If it's only 19.75%, it is low-enriched.
But Iran is in violation of the NPT anyway.

http://en.wikipedia.org/wiki/Enriched_uranium

Low-enriched uranium (LEU)

Low-enriched uranium' (LEU) has a lower than 20% concentration of 235U. For use in commercial light water reactors (LWR), the most prevalent power reactors in the world, uranium is enriched to 3 to 5% 235U. Fresh LEU used in research reactors is usually enriched 12% to 19.75% U-235, the latter concentration being used to replace HEU fuels when converting to LEU.

Highly enriched uranium (HEU)

Highly enriched uranium (HEU) has a greater than 20% concentration of 235U or 233U.

The fissile uranium in nuclear weapons usually contains 85% or more of 235U known as weapon(s)-grade, though for a crude, inefficient weapon 20% is sufficient (called weapon(s)-usable); some argue that even less is sufficient, but then the critical mass for unmoderated fast neutrons rapidly increases, reaching infinity at 6%235U.<2> For criticality experiments, enrichment of uranium to over 97% has been accomplished.<3>

http://www.armscontrolwonk.com/2620/iran-to-enrich-20-percent-leu

<snip>

70 percent of the work toward reaching weapons-grade uranium took place when Iran enriched uranium gas to 3.5 percent. Enriching it further to the 19.75 percent needed for the reactor is an additional “15 to 20 percent of the way there.”

Once the uranium is enriched above 20 percent, it is considered highly enriched uranium. The uranium would need to be enriched further, to 60 percent and then to 90 percent, before it could be used for a weapon. “The last two steps are not that big a deal,” Albright said. They could be accomplished, he said, at a relatively small facility within months.

It must seem odd for casual readers to see 20 percent and 90 percent U235 lumped together as highly enriched uranium or to be be told that Iran will find it much easier to go from 20 to 90, than from 5 to 20. That’s not how everyday math works, where 5 and 20 are closer to “ten” and 90 rounds to “one hundred.”

For many readers (especially of this blog) the answer is obvious. But for those to whom it is not obvious, Francesco Calogero found a nice way to illustrate the same point to students at a previous ISODARCO meeting. The essential concept is understand enrichment as a process of removing undesirable isotopes (or more specifically, isolating the desirable ones).

So, imagine 1000 atoms of uranium. Seven of them will be the fissile isotope Uranium 235. The rest are useless Uranium 238. (If you are the sort of person who just said, “Hey! What about Uranium 234?” or other nitpicks this post is not aimed at you.)

To make typical reactor fuel, Iran or any other country would removes 860 of the non-U235 isotopes, leaving a U235:U238 ratio of 7:140 (~5 percent).

To make fuel for the TRR, Iran removes another 105 non-U235 atoms from the 140, leaving a ratio of 7:35 (20 percent).

To make a bomb, Iran needs only to remove 27 of the remaining 35 atoms, leading a ratio of 7:8 (~90 percent).

This is simplified illustration, of course, since some of the U235 ends up in the depleted stream as “tails” — but you get the idea.

<snip>

http://en.wikipedia.org/wiki/Nuclear_Non-Proliferation_Treaty

Iran is a party to the NPT, but was found in non-compliance with its NPT safeguards agreement and the status of its nuclear program remains in dispute. In November 2003 IAEA Director General Mohamed ElBaradei reported that Iran had repeatedly and over an extended period failed to meet its safeguards obligations, including by failing to declare its uranium enrichment program.<16> After about two years of EU3-led diplomatic efforts and Iran temporarily suspending its enrichment program,<52> the IAEA Board of Governors, acting under Article XII.C of the IAEA Statute, found in a rare non-consensus decision with 12 abstentions that these failures constituted non-compliance with the IAEA safeguards agreement.<17> This was reported to the UN Security Council in 2006,<53> after which the Security Council passed a resolution demanding that Iran suspend its enrichment.<54> Instead, Iran resumed its enrichment program.<55>