Shipping companies aren’t rushing to export millions of tons of trapped grain out of Ukraine, despite a breakthrough deal to provide safe corridors through the Black Sea. That’s because explosive mines are drifting in the waters amid Russia’s war, ship owners are assessing the risks and many still have questions over how the deal will unfold. The goal is to get 20 million tons of grain out of three Ukrainian ports and clear the way for Russian food and fertilizer hampered by wider sanctions. But the deal is running up against the reality of how difficult and risky it will be. The U.N. says the joint center in Istabul that will run the operation is working nonstop to get set up.