Can radioactive waste be used to power a light or a motor?

In theory yes - it is giving off heat which can be applied to thermopiles to make electricity.

In practice, no - too much shielding is required for the power given off and the risks of being broken open are too great. There were protests about launching the space craft with nuclear batteries.

yes you can make power from nuclear waste and the bonus is that you lower the half life and danger of it considerably the more you blend it and use and essentially bring it down to very low levels...the best thing though is that you are using what once would go into a pool of water for a year or two and would then be stored in some far off government waste repository next door to you.the principle behind using nuclear waste for power generation is essentially the same as with any other nuclear powerplant with just a few differences look up fast track reactors and breeder reactors.

Well, it already has given off all the energy that we know how to practically harvest from it. That is why it is considered nuclear waste, and not nuclear fuel.

If you can figure out how to capture a practical amount of energy from it, with practical equipment, you should propose it as much as you can. It can be very valuable.

Potentially. Some satellites, space probes, and devices in very remote locations use radioisotope thermal generators that convert heat from radioactive decay into electricity using thermocouples.

Not considering safety issues, yes, provided it's 'hot' enough.

Check out the 'nuclear batteries' that powered the Voyagers.

Spent fuel generally contains lots of plutonium, which can be reprocessed for use as nuclear fuel.