There was no collusion with the DNC, and there was no primary rigging.
The DNC wanted to nominate a Democrat, and Hillary Clinton was the only viable Democratic candidate running for the nomination, so it was logical for the DNC to use their resources to support her.
Bernie Sanders? He’s not a Democrat. He’s a party crasher. I think he did a good thing by running, in that he gave voice to a number of issues that deserved discussion, and he galvanized a bunch of new voters into action. But he wasn’t a Democrat, and he still isn’t. The DNC didn’t owe him a thing.
Collusion is defined as “secret or illegal cooperation or conspiracy, especially in order to cheat or deceive others” (simple Google search). There wasn’t anything illegal in the DNC operations. They didn’t trash, slander, libel, or smear Sanders. They didn’t hurt his campaign. All you can say is that they didn’t provide as much help to Sanders as they provided to Clinton. But they weren’t obligated to.