SAN ANTONIO -- Mayor Julian Castro said Thursday that he promises changes will be coming to the power structure at CPS Energy.

In an exclusive interview with KSAT 12 News anchor Steve Spriester, Castro talked about his frustration with the utility company and the future.

"I know that a lot of folks look at this situation and they want blood, they want changes to be made right away," Castro said. "Those changes are going to be made. But we're going to do it in a rational, reasonable way."

On Monday, internal investigation results will be revealed into how CPS Energy officials handled a $4 billion oversight on the South Texas Nuclear Project. The CPS Energy Board of Trustees and Castro will find out why the full cost of building nuclear power plants wasn't shared until right before a City Council vote. The mayor believes a shakeup at CPS Energy will likely follow.

"The investigation results will come out on Monday, and after that the board will, in short order, make a determination about personnel issues," Castro said.

As for the project itself, the city and CPS Energy are waiting on the Japanese company Toshiba for a revised cost of going nuclear.

Castro said he is prepared to go with a different energy option if nuclear proves to be too expensive.