SAN ANTONIO -- CPS Energy has launched an internal investigation into the substantially higher cost estimate for nuclear expansion, and as a result has placed two employees on administrative leave.

"The much-higher Toshiba cost estimate is very troubling," Aurora Geis, CPS Energy Board chair, said in a news release Tuesday. "My Board colleagues and I are intensely interested in this matter."

The focus of the probe centers into how and when utility management was aware of the higher-than-expected preliminary cost estimate from Toshiba, the contractor chosen to build Units 3 and 4 at the South Texas Project in Matagorda County, the news release said.

The initial cost for the project was estimated at $13 billion but Mayor Julian Castro said he later learned that the project could cost $4 billion more, prompting City Council to postpone a vote last week on a $400 million bond issue for nuclear development.

Interim CPS Energy General Manager Steve Bartley said the estimate, while preliminary and subject to ongoing scrutiny and challenge, was "not acceptable and will result in CPS Energy exploring other options."

Bartley said the probe is in keeping with the company's long history of service based on the community's trust in the organization.

"Right now, the trust our community has placed in us for many years is being tested," he said. "Our forthrightness has been called into question. That's why it's important that the investigation be completed as expeditiously as possible and, based on the findings, that appropriate action be taken."

Bartley added that CPS Energy officials plan to travel to Japan to meet with top-ranking officials of Toshiba, NRG Energy and others involved in STP expansion to discuss the situation.

"I will make sure all our partners clearly understand our position – STP Units 3 and 4 must be affordable for our customers," he said. "If we can't achieve this goal, then we will have to look seriously at going another direction for a substantial supply of on-demand electricity before 2020."

CPS Energy currently owns 50 percent of the expansion project along with NRG Energy. Both companies have agreed to find another buyer for 20 percent of the project. That will bring CPS Energy's share down to 40 percent.