With only one month left before a deadline to complete a nuclear deal with Iran, international inspectors have reported that Tehran’s stockpile of nuclear fuel increased about 20 percent over the last 18 months of negotiations, partially undercutting the Obama administration’s contention that the Iranian program had been “frozen” during that period. But Western officials and experts cannot quite figure out why. One possibility is that Iran has run into technical problems that have kept it from converting some of its enriched uranium into fuel rods for reactors, which would make the material essentially unusable for weapons. Another is that it is increasing its stockpile to give it an edge if the negotiations fail. The extent to which Iran’s stockpile has increased […]