Among the winners could be China, which has ambitions to turn its growing nuclear technical abilities into a major export. That has raised security concerns in some countries.

The shrinking field is a challenge for the future of nuclear power, and for Toshiba’s revival plans. Its executives have said they would like to sell all or part of Westinghouse to a competitor, but with a dwindling list of potential buyers — combined with Westinghouse’s history of financial calamity — that has become a difficult task.

Toshiba still faces tough questions. The company is also divesting its profitable semiconductor business and plans to sell a stake to an outside investor to raise capital. Most of the companies seen as possible buyers are from outside Japan. Some Japanese business leaders have expressed fears that the sale will further erode Japan’s place in an industry it once dominated.

After writing down Westinghouse’s value, Toshiba said it expected to book a net loss of $9.9 billion for its current fiscal year, which ends on Friday.

“We have all but completely pulled out of the nuclear business overseas,” Toshiba’s president, Satoshi Tsunakawa, said at a news conference. Of the huge loss, he added, “I feel great responsibility.”

Bankruptcy will make it harder for Westinghouse’s business partners to collect money they are owed by the nuclear-plant maker. That mostly affects the American power companies for whom it is building reactors, analysts say. Now, it is unclear whether the company will be able to complete any of its projects, which in the United States are about three years late and billions over budget.

The power companies — Scana Energy in South Carolina and a consortium in Georgia led by Georgia Power, a unit of Southern Company — would face the possibility of new contract terms, long lawsuits and absorbing losses that Toshiba and Westinghouse could not cover, analysts say. The cost estimates are already running $1 billion to $1.3 billion higher than originally expected, according to a recent report from Morgan Stanley, and could eventually exceed $8 billion over all.