The three possible fates of neutrons in Uranium metal are ;
They may cause a fission of a U-235 nucleus;
They may be absorbed by a U-238 nucleus , or,
They may escape from the Uranium mass.
Uranium is a naturally occurring radioactive element that has no stable isotopes but two primordial isotopes; Uranium-238, and Uranium-235, that have a long half life and are found in appreciable quantity in the Earth's crust, along with the decay product Uranium-234