By Jonathan Saul and Michelle Nichols LONDON/NEW YORK (Reuters) -Ships exporting Ukraine grain through the Black Sea will be protected by a 10 nautical mile buffer zone, according to long-awaited procedures agreed by Russia, Ukraine, Turkey and the United Nations on Monday and seen by Reuters. The United Nations and Turkey brokered the agreement last month after U.N. warnings that the halt in grain shipments caused by Russia’s invasion of Ukraine was stoking severe food shortages and even outbreaks of famine in parts of the world. Since then a number of grain shipments – mainly onboard vessels…