Is it possible to create a scenario where nuclear power is a practical option for nomads living like in Mongolia?
There's two possible applications of nuclear power. One is to just use it as a heat source. The nomads have limited access to wood, so it's too valuable to burn, and their philosophical principles mean that they can't use animal dung, as the only animal products their philosophy allows are dairy and wool, and not dung. This is a departure from real life, in that vegetarianism is uncommon but not non-existent in Mongolia. In case you're wondering, the use of dung is considered non-vegan. Terry Pratchett in "Lords and Ladies" referred to people banging two subcritical rocks together to "keep warm". The other is to generate electricity. Even though they aren't extremely rich, they have satellite TVs.
There's no barriers on what technology they have, but they are fairly isolated, such that you can't have an electrical grid. In addition, as they're nomadic, the nuclear reactor and fuel can't be too heavy - about the weight and size of a large fridge.
If necessary, the elements and isotopes involved can be different from those found in real life, such as having different half-lives, but the basic concepts involved with nuclear reactions should remain the same. The planet should be millions or billions of years old, not thousands of years old. Ideally, the materials should be simply lying on the surface of the earth, without the need for large-scale mining and refinement operations, but considering that some nomads used to use diesel, it's not a hard requirement. The use of nuclear materials doesn't have to be totally safe - the burning of material inside homes goes on in real life, and has major health impacts. Severe cases of acute radiation poisoning aren't acceptable, but long-term cancer effects are.
For the purposes of this question, solar panels, which are used in real life, don't count as using nuclear power.