Waste Control Specialists and EnergySolutions Inc. engaged in a single-bidder sale process that boxed out other potential buyers and torpedoed the market-leading nuclear waste disposal companies’ defense of a planned $367 million merger that was nixed last month on antitrust grounds, a Delaware judge said in a just-unsealed opinion.

The details surrounding EnergySolutions’ proposed acquisition of its Utah-based competitor came to light Thursday, three weeks after U.S. District Judge Sue L. Robinson of the District of Delaware sided with government attorneys, who argued the deal would illegally create a monopoly in a market that is already difficult to enter. The companies have since cancelled the merger.