The hydrogen explosions, melting fuel rods and radiation leaks at Japan's Fukushima Daiichi nuclear plant are having an immediate impact on perceptions of nuclear power worldwide as many countries are earnestly searching for alternatives to fossil fuels. Safety will be a major concern, particularly as emergency workers in Japan continue battling to keep spent fuel rods stored on site at Fukushima Daiichi from melting down.

Even before the disaster at Fukushima Daiichi could be brought under control and investigated, Germany earlier this week said it would shut down seven of its nuclear power plants built before 1980. This turnaround comes after last year's decision to extend the life of all 17 of the country's nuclear power facilities.

In the U.S. the Nuclear Regulatory Commission (NRC) Thursday said it was canceling next week's meeting to discuss the restart of Progress Energy's Crystal River plant (pdf) on Florida's west coast after the company reported problems with repair work on a containment wall. Crystal River shut down in the fall of 2009 for a planned refueling that included the replacement of steam generators. To install the generators, workers needed to remove concrete in the containment wall, and it was during this work that they discovered a gap in the wall.

Entergy Corp., which last week received NRC approval for a 20-year operating license extension at its Vermont Yankee plant, must in the wake of Japan's crisis obtain final approval from Vermont lawmakers, who last year voted against re-licensing the facility after 2012. Three other Entergy nuclear sites, including New York State's controversial Indian Point, are also up for license extensions.

For an understanding of how nuclear plant safety is assessed and will likely be evaluated moving forward, Scientific American spoke with Najmedin Meshkati, a professor of civil, environmental, industrial and systems engineering at the University of Southern California's Viterbi School of Engineering in Los Angeles. Meshkati expressed concern over the practice of storing spent fuel rods on-site, a product of the risk-based approach to nuclear safety, and what he sees as a conflict of interest at the International Atomic Energy Agency (IAEA).

[An edited transcript of the interview follows.]

What does the incident at the Fukushima Daiichi plant mean for the nuclear industry both in Japan and the rest of the world?
It's too soon to make a judgment on its impact on the "nuclear renaissance" that started in the United States five or six years ago. The most accurate statement I can make is that it's going to seriously hamper the expected growth rate of this movement. On the other hand, it's going to really put more scrutiny on nuclear safety-related issues, which is not bad. In particular the storage of spent nuclear fuel at plant sites should be reexamined.

As we speak, one of the most serious problems happening in Fukushima Daiichi is the spent fuel pool-fire at the fourth reactor. We have likewise been storing spent nuclear fuel at our nuclear plant sites since the country began using nuclear energy. This poses a serious safety problem and a serious security risk of a terrorist attack to get these materials.

What is the alternative to on-site spent fuel storage?
There was a decision in 1982 to have the United States Department of Energy build a permanent nuclear waste repository. In 2002 [President] George W. Bush approved Nevada's Yucca Mountain [about 160 kilometers northwest of Las Vegas] as the site, and to move nuclear waste there. But because of a combination of incompetence, political fighting, bureaucracy in the Department of Energy, and partisan bickering, the site is now in limbo. The only silver lining I see in this dark cloud over Japan is to draw attention to the danger of on-site storage of spent fuel. I hope this revives discussion of Yucca Mountain.

Is it fair to judge the safety of other nuclear power plants based on the extreme conditions that Fukushima Daiichi has had to withstand?
You make say it's an extreme case, and I agree, but just because [prior to this week] there had not been major accidents or fires related to spent nuclear fuel doesn't mean they are safe. When we talk about lessons learned, the most immediate lessons that we have to learn from this catastrophe in Japan is not whether nuclear power is good or bad or whether to continue with nuclear power growth or not. The most immediate lesson we need to learn, and we should implement this yesterday, is a serious look at the state of our on-site spent nuclear fuel pools.

Had there not been spent fuel stored at the Fukushima plant, we would not have had all of the latest problems of the past two or three days. There are four reactors over there that are problematic, but I submit to you that the design of the reactors was excellent. The reactors did not fail or topple or become dislodged because of the earthquake or tsunami. All four reactors have a nice primary containment—which means we should not worry very much at this point about the design of our boiling-water reactors and our pressurized-water reactors.

How is a U.S. nuclear plant's safety evaluated?
For all 65 nuclear sites in the U.S. there are resident NRC inspectors at the different sites. When a nuclear site applies for a license extension or for basically getting a new extension on the life of the reactor, they need to go through a very rigorous risk analysis of their reactor vessel and other hardware. For example, reactor vessel embrittlement [or loss of ductility] is a major issue. There has been some discussion in the United States to change this regulation, making it less rigid and more risk-based.

Another institute that should get a lot of credit for improving our nuclear program since the Three-Mile Island accident is the Institute of Nuclear Power Operations (INPO). They do periodic evaluation and assessment of nuclear power plants around the country in terms of personnel training, human performance and some technical-related issues, and they share this information within the nuclear industry. This has been helpful in improving the nuclear power industry's overall safety. However, there has been some criticism of that. Because they were formed and are primarily funded by the nuclear industry, their information is not shared with outsiders. Not surprising, because they are showing their dirty laundry to this organization.

How does a risk-based approach to nuclear safety work?
You do a quantitative risk analysis, sometimes called a probabilistic risk analysis. The U.S. introduced this approach with the WASH-1400, or the "Reactor Safety Study,"  report produced in 1975 for the Nuclear Regulatory Committee under the leadership of Norm Rasmussen, an M.I.T. professor at the time. [The report considered what might happen during a serious nuclear reactor accident, the radiological consequences of these events, and the probability of these events taking place.]

One of the reasons to use risk-based analysis is to save money and to make regulation more reasonable. The risk-based approach gained some popularity during the administration of George W. Bush. They wanted to get away from the heavy hand of the regulator. But this risk-based approach for safety decision-making is very controversial. People like me question its robustness when quantifying the contributions of human and organizational error to failures in the nuclear industry.

What is the alternative to a risk-based approach?
By comparison, the U.S. Federal Aviation Administration follows an absolute decision-making model, which requires checks of passenger aircraft at prescribed periods. One of these checks comes every 12 to 18 months, after a specific number of flight hours. During this inspection, they take the aircraft to a maintenance hangar, strip it down, and have to replace some parts based on the number of hours of flight.

Does the IAEA get involved with evaluating nuclear plant safety?
I have been very critical for the past 20 years of the International Atomic Energy Agency. In fact, I gave testimony about them to the U.S. Commission on Improving the Effectiveness of the United Nations. At that time, I questioned IAEA's safety-related work. You have to understand that IAEA's primary mission is to be a custodian of the Nuclear Non-Proliferation Treaty. It was meant to safeguard the nuclear technology of any given country and make sure it is not being converted into nuclear weapons. The more recent safety and technology transfer functions of the IAEA are appendages for this organization.

What power does the IAEA have over nuclear plant operations?
IAEA is by its nature a multi-lateral international governmental organization. It is governed by its member states, so it is always on their leash and is not an independent international organization. It has to always, for lack of a better term, appease the member states. At the time of the 1999 Tokaimura nuclear accident in Japan, many people wanted to rank that accident as a 5 or a 6 [on a 7-level scale] on the IAEA's International Nuclear and Radiological Event Scale (INES), but IAEA ranked it as a 4. When Japan's Kashiwazaki-Kariwa Nuclear Plant was damaged by an earthquake in 2007, again the IAEA's assessment of the situation was seen as appeasing the nuclear power industry and the government. That shows you how the IAEA is not very aggressive in promoting safety. When it comes to safety, I respect [the] IAEA but I don't trust their independence.