DES MOINES - Nine Democratic senators issued a "go-slow" warning to their Senate colleagues Wednesday regarding plans to build nuclear power plants in Iowa.

The group of senators issued an open letter requesting to put off any consideration about nuclear expansion in Iowa until next session while events continued to unfold in Japan. Potential health risks and other ramifications associated with damage to nuclear reactors that was caused by a major earthquake, a tsunami and subsequent aftershocks must be studied.

"We are extremely concerned about proposed legislation that appears to be on a fast track to pave the way for the construction of one or more new nuclear power plants in Iowa," the letter stated. "There is no rush."

The letter was signed by Democratic Sens. Daryl Beall of Fort Dodge, Dennis Black of Grinnell, Joe Bolkcom of Iowa City, Dick Dearden of Des Moines, Bob Dvorsky of Coralville, Gene Fraise of Fort Madison, Jack Hatch of Des Moines, Rob Hogg of Cedar Rapids and Pam Jochum of Dubuque. Democrats hold a 26-24 majority in the Iowa Senate.

Legislative committees in the House and Senate currently are considering similar bills that would help address hurdles that might impede MidAmerican Energy's exploratory effort aimed at building a nuclear power facility in Iowa.

Company officials say they would utilize a series of small modular reactors that represent new-generation technology that do pose the same risks as the facilities in Japan. They say the units that would be built in Iowa would be smaller, self-contained modules that are underground, under water and would not require active controls or human intervention to shut them down should there be a problem.

Senate GOP Leader Paul McKinley of Chariton called Wednesday's letter "extremely premature" because top MidAmerican officials are scheduled to testify before a Senate Commerce subcommittee this afternoon where many of the concerns raised likely will be addressed.

"They will address siting issues, they will address safety issues, and they will address issues of technology," McKinley said.

It appeared the Democrats were "opposing nuclear power simply because it's nuclear power" and "playing politics with the issue," he said.

In their letter, the senators said there are unresolved siting issues, cost impacts, unproven technology and significant safety and financial liability concerns that warrant a more deliberative process than what could be accomplished in the current session's two remaining months.

"MidAmerican is only in the first of what was represented to be a three-year study on the feasibility of constructing a new nuclear power plant in Iowa. When that bill was passed, it was contemplated that Iowa would take at least three years to make any decision about new nuclear power plants," the senators said in their letter.

"We specifically request that we take more time to investigate this decision and not advance this legislation this session," they wrote. "We further propose that a legislative commission be established this year to thoroughly investigate all of the issues, including the need for a nuclear power plant, the costs and impact on utility rates, financing and liability issues, safety and waste disposal issues and renewable energy alternatives."

Iowa has a nuclear power facility operating near Palo, and a nuclear plant is just across the Iowa border in Cordova, Ill.