"Fissionable material" refers to a substance that can release a large amount of energy when its atomic nucleus is split into smaller parts. It is often used to fuel nuclear power plants or create nuclear weapons. Full definition
As we have seen, the amounts of fissionable material which might be produced through their use would be so small that for any individual unit, or even for units in one country which might number a dozen or more, there would be no real danger in terms of producing material sufficient for use in atomic explosives. (plosin.com)
There is no prospect that for several years such power reactors as described here could be licensed, for the reason that there would not be enough fissionable materials produced in the plants of the Authority. (plosin.com)
It is illegal for a US citizen to possess fissionable material, under NRC regulations, as well as extremely difficult. (politics.stackexchange.com)