Sure, I'm happy to.
On the issue of the effectiveness of one country withdrawing, it depends on the one country. The United States had the lion's share of sanctions that were affecting business activity in Europe and Asia, because we threatened access to the U.S. market if countries and companies didn't co-operate with our efforts. Our ability to threaten banks like HSBC, and major Chinese banks, and companies as diverse as European, Asian, and Indian ones, is what gave a lot of those sanctions power. The U.S.'s ability to withdraw from the JCPOA and reimpose all those sanctions puts back all the problems and costs that Iran cut a deal to get out from under.
If Russia, for instance, which didn't have any unilateral sanctions that had any real impact, were to reimpose, that impact on Iran is much less. For the United States, because of the structure of our sanctions, because of the leveraging of the U.S. economy against Iran and these business interests, I think there's an outsized role provided by the U.S. economy, and thereby by the United States. It's not an inherent legal issue, it's a practical issue of what the ramifications are.
Briefly on the issue of heavy water, from a technical perspective, Iran has zero use now for excess heavy water. The reactor they could have used to produce plutonium has had its innards filled with concrete. They don't have the ability to use that heavy water now. If they were to try to start that reactor, it would take them a couple of years and then four years' worth of production of heavy water and use of the reactor to have enough weapons-grade plutonium.
Heavy water from a technical perspective, in my view, is insignificant. It is important from an enforcement perspective. This is what goes to the issue of what's Iran's resolution. They have not been sending out one barrel at a time of heavy water when they've had these overages. They've been sending out tonnes. The idea is they go in an arc up and then go below the threshold, and then they arc up and then go below the threshold. That's a technical process that's constantly ongoing. The only way they would stop that is by stopping production altogether, which the JCPOA didn't envision.