Yesterday, he published those calculation in a paper for the blog ArmsControlWonk. The paper makes clear that if a criticality accident occurred at Fukishima, it could happen again—and while such a possibility poses minimal danger to Japanese citizens outside of the 20km exclusion zone, it means the emergency workers at Fukushima are operating in even more dangerous conditions than anyone realized. “It is important for TEPCO to be aware of the possibility of transient criticalities when work is being done; otherwise workers would be in considerably greater danger,” the paper concludes. “This analysis is not definitive proof but it does mean that we cannot rule out localized criticality.”