Well,yeah, we could do that, but then when the nuclear capsules start leaking, it would REALLY ruin your flashlight.
My mining buddies and I used to dream about such things years ago, but even if the physics of such a thing was within the realm of possibility, do you think it would be practical to trust EVERYONE with a nuclear reactor when we can't trust nations with them?
Even a small reactor IS a weapon of mass destruction if it isn't treated right, and we can't even get consumer level LiIon AA batteries for fear that someone will charge them in the wrong charger and do some damage.