Senator Grassley,chairman of the judiciary committee, will be the one to appoint a special prosecutor for Uranium One. It sounds like he is leaning that way.
Under current law, there is no mechanism for anyone in Congress appointing a special counsel. Congress gave up that ability long ago. The only special prosecutor authorization is in the internal bureaucratic rules of the DOJ, which aren’t ‘laws’ at all. The DOJ decides for itself how and whether to implement its own internal rules.