The silly idea of the classic sun model is that the main reaction is H+H --> 2H what of course is absolute nonsense as we do not see an increase of 2H and even more bad: Which process does produce the neutrons ???
The dominant reaction is 4p --> 4He that can run without neutrons. (Something that the nonsensical standard model completely fails to predict!)
I'll call out these Wyttenfacts.
Nice description of proton-proton reaction in the sun in three images:
https://www.forbes.com/sites/s…rogen-into-helium-mostly/
The overall reaction is indeed 4p -> 4He.
However this is done in multiple steps: and the final part from 3He to 4He has two different paths, both of which exist.
p+p -> fusion and then decay into a deuteron, neutrino, and positron does generate D, but is rate limiting. The next step: p + d -> 3He is much more energetically favourable and also much faster, so we do not see a build-up of D.
None of these steps need free neutrons, nor do they generate free neutrons. And the standard model predicts every one of these steps.
THH