Washington (CNN) -- In the days after the Fukushima Daiichi nuclear disaster in Japan, Gregory Jaczko appeared frequently on television as the calm, steady hand of the U.S. nuclear power industry.
But at a hearing Tuesday on Capitol Hill, critics painted a different picture of the Nuclear Regulatory Commission chairman, saying he ruled by intimidation, yelled at his staff, was manipulative and -- in one key case -- withheld information from his fellow commissioners in order to achieve his goal.
And Congress members dickered over whether another word can be used to describe Jaczko's actions: illegal.
Jaczko is under fire for using administrative procedures to kill a controversial plan to store nuclear waste at Yucca Mountain, Nevada. Fellow commissioners say Jaczko misled them about the consequences of his administrative actions or kept them in the dark entirely.
Last week, a report by the agency's inspector general appeared to clear Jaczko of any legal wrongdoing, saying his decision was supported by the Nuclear Regulatory Commission attorney and was within his discretion as chairman.
But at Tuesday's hearing, members of the inspector general's staff were ambiguous and contradictory.
"Did you find that the chairman of the NRC acted illegally?" California Democrat Henry Waxman asked.
"No. No. No, we didn't, sir," Inspector General Hubert Bell said.
But asked by Pennsylvania Republican Tim Murphy whether Jaczko violated a statute requiring the chairmen to keep commissioners informed, Bell's assistant Joseph McMillan responded: "One could draw that conclusion."
Rep. Joe Barton, R-Texas, drew that conclusion.
"He violated the law," Barton said. "He did not uphold his responsibility under the statute. That is clear layman common sense."
The dispute is only the latest in the 25-year history of Yucca Mountain. In 1987, after the Department of Energy conducted studies of nine potential nuclear waste sites, Congress selected Yucca Mountain, 100 miles northwest of Las Vegas, as the only site for further study for the first national repository.
But the plan faced stiff opposition in Nevada, with Sen. Harry Reid vowing that the site would never open there.
Jaczko, a former top aide to Reid, also opposed Yucca Mountain. After being appointed to the nuclear commission, Jaczko recused himself from matters involving Yucca Mountain for a year, saying at his confirmation hearing that he hoped he could establish his independence during that time.
Later, President Barack Obama appointed him as chairman of the five-member body.
In February 2010, the Obama administration said it would suspend licensing for Yucca Mountain, saying it was "not a workable option."
After that announcement, critics say, Jaczko took steps to stop the Nuclear Regulatory Commission's consideration of the Yucca Mountain application. According to the inspector general report, Jaczko directed agency staff to stop working on a Yucca Mountain review, saying his actions had been reviewed and agreed to by his fellow commissioners.
But, according to the report, "one commissioner was not informed of the language, two were provided some information but did not recognize the impact ... and one commissioner disagreed with the language because he recognized the impact it would have." Jaczko "was not forthcoming with the other commissioners about his intent" to have staff members stop work on Yucca Mountain, the report states.
"Clearly, the commissioners that we spoke to had no understanding" about the consequences of Jaczko's action and were "somewhat agitated" when they found out, McMillan said.
"It appears that Chairman Jaczko has let politics trump science here, that he's manipulated the process," said Rep. Joe Pitts, R-Pennsylvania. "He's misled some of the fellow commissioners about the consequences of the actions that were taken, and I think the credibility of the NRC has been damaged; its reputation has been damaged. There's some real serious questions about the agency's independence and scientific integrity."
Jaczko on Tuesday denied misleading others.
"I believe I was forthcoming with my fellow commissioners," he said in a statement following the hearing. "This was my decision and that has been clear from the start. In leadership positions you have to be prepared to take the heat. I am fully comfortable with the decision because it was entirely within my authority as chairman."
Rep. Ed Markey, D-Massachusetts, said complaints that politics had trumped science were "ironic" given the history of the search for a place to store the nation's nuclear waste. Past congressional leaders had blocked proposals for numerous other sites for political reasons, he said.
"This issue has been nothing but political since the very beginning," Markey said.