Enriched Uranium

What's big deal, why is there hardly any of it in the world, why is it so hard to get?
Enriched uranium is a type of uranium that has been processed to have increased amounts of uranium-235.  [1] Naturally occurring uranium is made up of three major isotopes, uranium-238, uranium-235, and uranium-234, with the latter two being the relevant ones for enrichment. [1]  There are about 2,000 tonnes of highly enriched uranium in the world, mostly produced for nuclear power, weapons, and naval propulsion, with smaller amounts going to research reactors. [2]  Enriched uranium is expensive and difficult to create, which is why it remains a barrier to countries wishing to develop nuclear weapons. [4]
Currently, the IAEA monitors and controls enriched uranium supplies and processes in its efforts to ensure safety in nuclear power generation and curb nuclear weapons proliferation. [3]
The term "enriched uranium" refers to uranium that has been chemically processed to increase the percentage of uranium-235, one of three major isotopes found in naturally occurring uranium. [1] About 2,000 tonnes of highly enriched uranium are currently in existence, mostly in the form of nuclear power, weapons, and naval propulsion material. [2] The United States and Russia each have about 500 tonnes of highly enriched uranium, while France has about 300 tonnes. [2] Highly enriched uranium is expensive and difficult to enrich, requiring specialized technology and expertise. [3] Another by-product of the enrichment process is depleted uranium, which is considerably less radioactive than natural uranium. [2] The difficulty and expense of enriching uranium is one reason there is a limited supply of enriched uranium in the world. [3] Another reason is that the relatively small amount of plutonium produced by power reactors can also be used in nuclear weapons. [3]