Duke Energy Progress is negotiating with the N.C. Eastern Municipal Power Authority to buy the stake the authority has in four Duke Progress plants, including the Brunswick and Harris nuclear stations. The $2 billion in debt that the 32 municipal electric companies owed for their purchase of the shares of those plants became an issue in Duke Energy Corp.'s purchase of Progress Energy Inc. in 2012. Some municipalities challenged the merger, hoping to get relief from the debt — and the high rates…