Despite White House denials that the U.S. is “considering any proposals that would allow the Iranians to retain any enrichment-related activities,” AP’s George Jahn reports that the United States is considering a “cold standby” proposal for Natanz that would Iran to retain, but not operate, some number of cascades:

Recognizing that Iran would never accept a complete freeze, the powers are considering “a new definition of enrichment,” one diplomat said. Under the proposal, Iran would could keep some of its program intact without actually producing enriched uranium.

[snip

“We purposely left open the possibility that direct talks could happen by being a little less committed to the requirements to have a meeting,” said [another U.S. official who spoke on condition of anonymity]. He alluded to previous demands of an all-encompassing freeze on all enrichment related activities.

[snip]

The United States might accept a version of “cold standby” allowing a set number of centrifuges to remain standing and assembled in series but not running, a diplomat said. Iran, he said, would likely push for keeping the machines operating, if not producing enriched uranium.

If you want a thorough overview of the cold and warm standby options for the centrifuge cascades at Natanz, I highly recommend Matt Bunn’s paper arguing that either would be preferable to an unconstrained Iranian program.

There is nothing wrong with pressing for cold standby from the outset. But what if Iran counter offers a “warm” standby approach where the centrifuges spin empty? I’ve argued before that we should accept warm standby as an interim measure—provided that warm standby is coupled with other arrangements:

To be clear, warm standby would not meet the UN Security Council demand to cease all centrifuge related R&D—Iran, according to the IAEA, would still learn about “the life expectancy and durability of key mechanical components, the failure of materials, the effects of vibrations, electric power requirements…a detailed understanding of the different ways that centrifuges can fail, and information needed for the development of more advanced centrifuge systems.”

That doesn’t mean, however, that warm standby might not be part of a verifiable pause in Iran’s centrifuge program. Under “warm standby” Iran will not learn some things that have bedeviled the Iranian program, including “the relationship between UF6 gas flow, temperature and stress corrosion.”

It would seem to me that, if Iran makes [such an offer], the United States and its European allies should move swiftly to consolidate the suspension, er standby.

Warm standby could be part of a verifiable pause in Iran’s program, if coupled with other measures including renewed adherence to the Additional Protocol and progress on resolving outstanding questions about Iran’s past activities, particularly its P2 centrifuge program.

Warm standby is not a comprehensive or indefinite solution to the problem, but it does present a face-saving measure for Iran to return to negotiations. We should reciprocate, modestly.