low-grade uranium ore contains a fraction of a percent (by weight) of uranium; very high-grade ore (as is found in some deposits in canada) can contain up to 20% uranium. if energy is extracted from uranium by fission of 235u (0.72% of naturally occurring uranium), then how large a percentage of uranium in ore is necessary to make a tonne of uranium ore equivalent (in terms of energy) to a tonne of coal? use e for exponent; for e.g. 3x10^8 should be written as 3e8. note that one induced 235u fission releases about 180 mev of energy.