Safe to use rice cooker after mold grew on rice?
Hot water and detergent might be enough, but after serious mold growth, I'd use a disinfectant. The easiest way to do this would be to disinfect your cooker with bleach, which is very effective at killing mold on non-porous surfaces. After thoroughly washing and rinsing your cooker, make a solution of 10 parts water to 1 part bleach and allow it to soak in your cooker for a few minutes, then dump it out and allow the cooker to air dry.

Using Bleach on Mold (note that the caveat here is that bleach isn't effective for porous surfaces. Anything that you're cooking on should be an acceptable surface for using bleach on.)