* Republicans want answers about NRC role in Yucca
* Vote on licensing issue continues to be unresolved
* GOP says Democrat Waxman sabotaging their Yucca probe
* Only incremental improvements at Fukushima plant-Jaczko (Updates throughout with comments from commissioners, lawmakers Harper and Waxman)
By Roberta Rampton and Ayesha Rascoe
WASHINGTON, May 4 (Reuters) -Republican lawmakers questioned top officials from the U.S. nuclear regulator on Wednesday over its role in shelving a permanent dump for radioative waste at Nevada's Yucca Mountain.
Storage of nuclear waste is a top issue for regulators in the wake of Japan's Fukushima Daiichi disaster. Officials in Japan are struggling to repair cooling systems needed to bring the reactors under control after bad damage from the March earthquake and tsunami.
Years ago, U.S. lawmakers decided to store waste deep inside Nevada's Yucca Mountain. The plan drew fierce opposition from residents of that state and their Senator Harry Reid. It was ultimately overturned by the Obama administration.
Republicans and some Democrats who want to keep the option open peppered the independent Nuclear Regulatory Commission about its role in shutting down licensing of the site.
A commission vote on the matter has not been officially resolved, even though commissioners voted nine months ago.
"We are working to achieve a majority position," said Gregory Jaczko, chairman of the NRC.
His answers left lawmakers unsatisfied. "Simply shutting the doors on the already spent $12 billion for Yucca is not acceptable, especially with no other alternatives," said Fred Upton, chairman of the House Energy and Commerce Committee, who has launched a formal probe of the issue.
Q+A-Yucca Mountain waste controversy [ID:nN06164783]
ANALYSIS-No easy fix for US nuclear waste [ID:nN21100265]
NEWSMAKER-NRC Chairman Gregory Jaczko [ID:nN06200024]
FACTBOX-NRC commissioners [ID:nN06206336]
INFIGHTING AT NRC?
All commissioners spoke at the hearing except George Apostolakis, who was overseas -- the first time in more than a decade that the House committee had called them together.
The commissioners said they could not reveal how they voted on Yucca, but Republicans Kristine Svinicki and William Ostendorff expressed concerns the matter was unresolved.
Gregg Harper, a Republican from Mississippi, told the NRC it should avoid infighting given its important mandate.
"If ever there was any agency where we could not afford for it to have even a hint of internal issues, it would be the NRC," Harper said.
Commissioner William Magwood, a Democrat, assured reporters after the hearing that the NRC is "getting a lot of work done.
"I think there's always a natural tension between commissioners and a chairman," Magwood said.
Republican William Ostendorff said he was optimistic recent talks could lead to a resolution on the NRC's Yucca position.
"One could certainly leave the hearing believe that we are at loggerheads on every single issue that is before us -- that is not the case," Ostendorff told reporters.
PARTISAN SNIPING OVER PROBE
U.S. Rep. Henry Waxman of California, top Democrat on the Energy and Commerce committee, raised the ire of Republicans when he asked Jaczko about emails obtained during the committee's probe.
The emails from a commission employee assert the decision to stop work on the Yucca license application was illegal and that action on Yucca was delayed for political reasons.
Jaczko, who worked for Senator Reid before being named to the NRC, said his actions were consistent with NRC policy.
"It was in no way a political action," Jaczko said.
Republicans accused Waxman of attempting to sabotage their probe, which began at the end of March.
"It affects and could very well harm the investigation and produce a chilling effect on anyone else we'll be asking for comment," said Representative John Shimkus, who is leading the Yucca probe with Upton.
In a statement, Waxman said Shimkus "has made irresponsible accusations" about Jackzo's actions, and said it was only fair to ask Jaczko for his response.
FUKUSHIMA IMPROVEMENTS "ONLY INCREMENTAL"
Jaczko told lawmakers Japanese authorities are struggling to control the damaged Fukushima nuclear plant.
"While we have not seen or predicted any new significant challenges to safety at the site, we have only seen incremental improvements towards stabilizing the reactors and spent fuel pools," Jaczko said.
The NRC is reviewing the 104 nuclear plants in the United States in the wake of the disaster at the Fukushima plant to see whether safety improvements are needed.
A task force will give its first status report on the investigation at a hearing next week. (Reporting by Roberta Rampton and Ayesha Rascoe; Editing by John Picinich and David Gregorio)