Major nuclear accidents don't happen often, so when they do they loom large in our consciousness. We also lack information on how to respond. Consequently, it's not surprising widespread evacuation is the default response. However, a new analysis questions the thinking behind this, suggesting that most of the people evacuated near Chernobyl, and almost everyone around Fukushima, would have been better off continuing to live in their homes.

The immediate aftermath of a major disaster is not a good time to be making considered decisions. While policy-makers are reluctant to err on the side of caution about more long-term threats, such as climate change, they understand the risk in under-reacting to a disaster dominating the nightly news. Consequently, relocating more than 100,000 people living near Fukushima Daiichi was an almost inevitable result in 2011.

However, the passage of time provides opportunities to weigh the evidence when deciding whether to recommend people go back. By late 2015, 85,000 of these people had not returned. Professor Philip Thomas of the University of Bristol has concluded that this was a mistake, one that has been only partially corrected.

To try to establish when evacuations are justified, Thomas has created a measure he calls the J-value, incorporating the risk posed by radiation hazard and the social and health costs of keeping people from their homes. In Process Safety and Environmental Protection, Thomas concludes: “Nearly three-quarters of the 116,000 members of the public relocated after the Chernobyl accident would have lost less than 9 months' life expectancy per person if they had remained in place, and only 6 percent would have lost more than 3 years of life expectancy.”

As the paper continues: “Neither figure is insignificant, but both are comparable with life expectancy differences resulting from the different day-to-day risks associated with living in different parts of the UK.”

To put the dangers in perspective, Thomas points out that London residents lose an average of four and a half months of life to air pollution, while a boy growing up in a poverty-stricken part of the UK can expect to live 8.6 years less than male counterparts from privileged suburbs.

Thomas argues that none of the evacuations from Fukushima were appropriate, and return should have occurred as soon as the leak's size was known. Even for the much larger Chernobyl disaster, only 9-22 percent of the 335,000 permanent evacuees benefited from the move. Moreover, the money saved through not evacuating could improve both quality and length of life.

The same edition has related papers validating the J-value and considering the impact of a theoretical UK nuclear accident, confirming the drawbacks of evacuation. Harder to measure, however, is the psychological impact of living near an accident for people unversed in risk analysis.