PRESIDENT OBAMA should not lament but sigh in relief that Iran has rejected his nuclear deal, which was ill conceived from the start. Under the deal, which was formally offered through the United Nations, Iran was to surrender some 2,600 pounds of lightly enriched uranium (some three-quarters of its known stockpile) to Russia, and the next year get back a supply of uranium fuel sufficient to run its Tehran research reactor for three decades. The proposal did not require Iran to halt its enrichment program, despite several United Nations Security Council resolutions demanding such a moratorium.

Iran was thus to be rewarded with much-coveted reactor fuel despite violating international law. Within a year, or sooner in light of its expanding enrichment program, Iran would almost certainly have replenished and augmented its stockpile of enriched uranium, nullifying any ostensible nonproliferation benefit of the deal.

Moreover, by providing reactor fuel, the plan would have fostered proliferation in two ways. First, Iran could have continued operating its research reactor, which has helped train Iranian scientists in weapons techniques like plutonium separation. (Yes, as Iran likes to point out, the reactor also produces medical isotopes. But those can be purchased commercially from abroad, as most countries do, including the United States.) Absent the deal, Iran’s reactor will likely run out of fuel within two years, and only a half-dozen countries are able to supply fresh fuel for it. This creates significant international leverage over Iran, which should be used to compel it to halt its enrichment program.

In addition, the vast surplus of higher-enriched fuel Iran was to get under the deal would have permitted some to be diverted to its bomb program. Indeed, many experts believe that the uranium in foreign-provided fuel would be easier to enrich to weapons grade because Iran’s uranium contains impurities. Obama administration officials had claimed that delivering uranium in the form of fabricated fuel would prevent further enrichment for weapons, but this is false. Separating uranium from fuel elements so that it can be enriched further is a straightforward engineering task requiring at most a few weeks.