SAN ANTONIO—Two additional nuclear reactors being considered by San Antonio’s public utility will cost up to $13 billion, according to new cost estimates.

CPS Energy officials want to build the $10 billion to $13 billion reactors at the South Texas Project outside Bay City, saying its the most cost effective way to get additional power. CPS Energy owns 40 percent of the project. New Jersey-based NRG Energy owns the remaining portion, and the utilities would split the cost.

San Antonio ratepayers would be hit with a 5 percent rate increase every other year for the next decade to pay for the expansion, officials said Monday. But that rate projection assumes CPS can sell excess power to other utilities, something critics are wary of.

“We believe the long-term lowest price option is nuclear,” said Steve Bartley, CPS interim general manager. “Even if we decide not to move forward, we will have a need for bill increases over the next 10 years.”