GOTHENBURG, SWEDEN—Carlo Rubbia, Nobel Prize winner and former Director General of CERN, has spent his more recent career thinking about energy, and he has some strong thoughts on nuclear power. Those thoughts have been driven in part by climate change (nuclear provides the only source of low-carbon electricity that can be deployed anywhere), but they've also been driven by the events at Fukushima.

At least twice during a Nobel Dialog panel, Rubbia said that the sort of risk analyses that we've been doing for nuclear power are simply insufficient. The analyses are based on probabilities: if the failure of a given pump creates an obvious risk, you simply put in a second pump, then a third if necessary. In the end, you get an infinitesimal risk that you can approximate as zero. But Fukushima, Rubbia argued, showed that these calculations simply don't work in the real world.

In its place, Rubbia said that we need to have some form of design that makes safety deterministic—something where, even if things go completely wrong, nothing happens. Nuclear reactions continue at a controlled rate, and all the materials remain contained.

To make that just a touch more challenging, Rubbia also added that we need to completely revamp how we approach nuclear power.

Right now, nuclear power relies on 235U, and the scientist noted that the world's reserves of that are about as limited as fossil fuel reserves are. Rubbia thinks that we need to start using alternatives: thorium, breeder reactors, and other approaches that both greatly broaden the availability of fuel and produce waste that decays back to background levels within a few thousand years. Rubbia said that reactors using these fuels could be designed so that they were probabilistically safe, though he didn't mention any specific technology.

At least one other panelist, Elisabeth Rachlew, was completely on board, saying we should be using thorium and getting rid of boiling water reactors. But throughout the rest of the Nobel Dialog, it became clear that we have a long way to go before any of this is possible. Right now, China and India are just starting construction of test reactors, Norway is putting a bit of thorium in a test reactor, and... well, that's about it.

Even expanding existing nuclear tech is a serious challenge. Former energy secretary (and Nobel Laureate) Steve Chu laid out four challenges that were present in the US but are shared to varying degrees by other countries. These included post-Fukushima safety worries, dealing with waste (which could be done by burning more than the one percent of our fuel's energy content, as we do now), proliferation concerns, and the enormous costs involved in building a plant. We're barely building any nuclear plants today, much less a next generation of them.

But, to Chu, this isn't as much of a problem as some of the other speakers seemed to think it was. He feels there's no need to shut anything down, and he detailed the safety steps the US was taking in the wake of Fukushima. But Chu said, "I don't think we'll need to use fission by the end of this century, for sure." For Chu, nuclear is a key transitional bridge—but a bridge to what?

He's hedging his bets. He figures if electrical storage gets solved, we'll go with solar. If not, we'll have the motivation we need to develop fusion into a viable power source.

This post is part of Ars' coverage of the 2013 Nobel Week Dialogue. It first appeared on the Dialogue's website.