From what I know of nuclear physics, (little to none) the radioactive material has decayed too much for use as fuel, and undergoes changes that make it useless until something is done with it. But don't take my word for it
Radioactive waste - Wikipedia, the free encyclopedia Quote:
The back end of the nuclear fuel cycle, mostly spent fuel rods, contains fission products that emit beta and gamma radiation, and actinides that emit alpha particles, such as uranium-234, neptunium-237, plutonium-238 and americium-241, and even sometimes some neutron emitters such as californium (Cf). These isotopes are formed in nuclear reactors.
It is important to distinguish the processing of uranium to make fuel from the reprocessing of used fuel. Used fuel contains the highly radioactive products of fission (see high level waste below). Many of these are neutron absorbers, called neutron poisons in this context. These eventually build up to a level where they absorb so many neutrons that the chain reaction stops, even with the control rods completely removed. At that point the fuel has to be replaced in the reactor with fresh fuel, even though there is still a substantial quantity of uranium-235 and plutonium present. In the United States, this used fuel is stored, while in countries such as the United Kingdom, France, and Japan, the fuel is reprocessed to remove the fission products, and the fuel can then be re-used. This reprocessing involves handling highly radioactive materials, and the fission products removed from the fuel are a concentrated form of high-level waste as are the chemicals used in the process.
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Re-using the waste is an option, but in the end, obviously, you're at the same point, what to do with a bunch of highy deadly stuff.
As to a sign that can be read ten thousand years from now, a good old skull usually scares people. Plus, I'd imagine we'd lock up if we just decided to leave one day, and if we're incapable of locking up, we have bigger problems than worrying about the poor saps 10000 yrs in the future.