In the past, the agency has questioned whether the Gachin mine, which produces yellowcake uranium for conversion to nuclear fuel, is linked to Iran’s military. The heavy-water plant at Arak could produce plutonium, which can be used in a weapon, and a key concern is that once the plant is operational, it would be all but impossible to destroy it without running the risk of spreading deadly plutonium. Western officials noted that the agreement gave the atomic agency access to the heavy production plant but not the nuclear reactor, which is under construction there.