Can nuclear waste from power plants be used for any other purpose other than weapons?

If you are referring to the spent fuel assemblies from nuclear power power plants then you have it turned around. Spent fuel assemblies have significant amounts of plutonium which are quite suitable for reprocessing into new fuel. The French have practiced this with their nuclear program for 30 years or so with such success that they reprocess fuel for other countries. The highly radioactive fission products are encased in glass and buried in deep mines. The US had originally intended this for their fuel cycle but the program was cancelled in the 1970's in favor of long term storage (as in Yucca Mountain).

As it turns out in the nuclear world, there are several nuclides of Plutonium just as there are several nuclides of Uranium and, as in the case of Uranium, most Plutonium nuclides aren't suitable for bombs. Spent fuel has a mixture of the Plutonium nuclides that are as hard to enrich as Uranium is and are thus an unsuitable source for weapons grade Plutonium.