The whole reason hydrogen fuses to helium and helium to .... to carbon, silicon, oxygen and ultimately Iron, is that each time, energy is released. E=mc^2 means that a tiny mass loss results in a massive energy output - this is the process we call "nuclear fusion".

So, to drive the process backwards, you must ADD immense amounts of energy.

Now, you suggest a nuclear *fission* "chain reaction".

In a sense, this is what happens in a Supernova. The previous matter of the star is reduced to a degenerate state then randomly re-constituted. Many stable and unstable elements result, but there uis still a net consumption of hydrogen.

Basically, you're trying to push water uphill with a pointy stick!