SAN ANTONIO -- Despite being under fire by those who say CPS Energy withheld an estimated $4 billion cost increase, its board of trustees in open session did not discuss a specific figure for the expansion of the South Texas Nuclear Project in Matagorda County.

"We’re astounded that they're the ones negotiating for us," said former City Councilwoman Maria Berriozabal, a member of Energia Mia Coalition, a group that opposes the project.

CPS Energy top management Monday briefed the trustees on last week's trip to Japan where they met with Toshiba and the project's other contractors.

"Specifically, we explained that our customers come first," said interim General Manager Steve Bartley.

Otherwise, a higher cost would exceed the current threshold of a 5 percent rate increase every other year.

Bartley told the trustees that the contractors "understood the urgency of our need" and they will revise the estimate that was labeled confidential last month.

"I still want to see the letter. I have not seen it. I've heard about it," trustee Stephen Henning said about the now reported $17 million expansion.

Without confirming that estimate in open session upon advice of CPS Energy attorneys, Bartley said a new lower figure has been promised by Dec. 31.

"It's also a key date for us, a key decision date for us about whether we move forward or not," Bartley said.

In the meantime, at the request of Mayor Julian Castro, CPS Energy staff is working on a contingency plan due on Jan. 15 that could see natural gas becoming a more affordable alternative to nuclear energy.

"Stop this train. We can't afford it," said Berriozabal, whose supports energy efficiencies and renewable energy. "It would be easier to cut our losses right now."

But Castro said he was satisfied CPS Energy was trying to protect the city's current investment in the plant.

"But we also need to be preparing in case on December 31st the final cost estimate comes back and it does not make business sense," he said.

Henning, the longest-running trustee on the CPS Energy Board, said he's optimistic the nuclear plant will be built with or without San Antonio.

"I'm optimistic that Japan will build the plant and they will be a major provider of power in Texas," he said.