In the two months since the Fukushima Daiichi Nuclear Power Plant suffered a catastrophic breakdown during an earthquake and tsunami in Japan, what has the United States learned about nuclear safety? How are regulators working to prevent a similar disaster at one of America’s 104 nuclear power plants, about a quarter of which share the same design as Fukushima Daiichi?

This was the topic of discussion at a hearing by the Senate Environment and Public Works Committee yesterday—and for the second time since the disaster in Japan, it summoned all five commissioners of the Nuclear Regulatory Commission to appear and answer questions. The results weren’t exactly comforting, and demonstrated there’s still a long way to go towards a “safe” nuclear power infrastructure in the United States—if that’s even possible.

Spent fuel rods posed a grave threat at Fukushima, as Christian Parenti outlined here. They are packed with radioactive uranium, and are very unstable. They are also generally not well protected. NRC Chairman Gregory Jaczko, when asked by Senator Tom Carper about the spent fuel pools in the United States, admitted that “we have not given that enough attention.”

Jaczko also said that until Fukushima, the NRC had never really considered the possibility that multiple reactors or even multiple plants could fail at the same time, due to some sort of large-scale natural disaster or other event. “Our traditional approach has always been to assume a single incident at a single reactor,” he said. “Clearly Fukushima-Daiichi showed us that we have to consider the possibility of multiple units at a single site, perhaps multiple spent fuel pools being affected at the same time.”

Commissioners also had no answers about how to fix backup power systems that continue to cool nuclear material in the event of a major power outage. The batteries at Fukushima ran for only eight hours—not nearly long enough. In the United States, the standard length is only four hours. “This is something we have to look into and take action on,” said commissioner George Apostolakis. “I’m not sure what that action would be.”

Amidst these less-than-inspiring answers, the NRC commissioners tried to downplay the possibility of similar events happening here anyhow. “The likelihood of something like this happening in the United States is very, very small,” said Jaczko. Senator Barbara Boxer, who chairs the committee, asked commissioner William Magwood to list four or five areas of concern following Fukushima, and he couldn’t provide any. He responded instead that “you can’t predict events that will happen in the future. You have to be able to recover from whatever happens.”

In fairness, the NRC is only sixty days into a ninety-day review of nuclear safety in the wake of the Fukushima disaster, and the real substance will come on July 19 when it releases the results of that short-term review. A longer-term safety review will follow.

But larger questions loom about nuclear regulation. The NRC has frequently been criticized as too close to the nuclear industry. During the 2008 campaign, President Obama called it “a moribund agency…captive of the industry it regulates.” Boxer and Senator Bernie Sanders provided the hearing’s most substantive moments when they grilled the commissioners on this point.

In Vermont, state officials are attempting to shut down the Vermont Yankee nuclear plant by refusing to issue a state certificate of public good so the plant can operate—even though the NRC gave Entergy, the company that owns Vermont Yankee, a twenty-year license in March to continue operations there.

Sanders was incensed at reports that earlier this week, the NRC held a secret vote urging the Justice Department to intervene and force Vermont to allow the nuclear plant to continue operations. Through two rounds of questions, Sanders asked each commissioner if they participated in such a vote, and how they voted. Each commissioner refused to aawer his questions. Jaczko did admit under intense questioning from Sanders that his staff did meet with representatives from Entergy—but not with state officials.

Sanders repeatedly criticized the commissioners, and urged them to step back from the issue. “If the state of Vermont chooses energy efficiency and sustainable energy for its future, instead of an aging and trouble-ridden nuclear power plant, it is not the place of the NRC to prevent us from doing that,” he told them. “The NRC’s mandate is very clear. Its concerns begin and end with safety. It is not supposed to be the arbiter of political or legal disputes between a $14 billion dollar energy company and the people of Vermont.”

Boxer, meanwhile, picked up on a statement from one commissioner that it’s “important [the NRC] hears from both sides” when making regulatory decisions. “Please tell me—don’t you have the ability to decide for yourself if a plant is safe or not safe?” she asked.

“You’re independent. So when I hear you say that there’s a safety issue, you want to hear both sides, that troubles me. I think hearing both sides is fine, but at the end of the day, you have to perform your own inspections,” Boxer said.