Abstract

There is uncertainty and disagreement about the question which preventive actions are rationally justified with regard to moderately elevated levels of nuclear radiation. This may have at least four causes: ignorance, insufficient information, inconclusiveness and indeterminability. After the nuclear disaster with the Fukushima nuclear power plant the advice, given by some authorities, to leave Tokyo was largely based on the former two factors: ignorance and insufficient information. By contrast, the uncertainty and disagreement amongst experts about the size of the area to be evacuated was mainly caused by the latter two factors: inconclusiveness and indeterminability. Inconclusiveness concerns the question whether moderately elevated radiation levels cause real and significant health risks that require drastic measures. Indeterminability concerns the problem of rationally weighing disparate benefits and costs of the preventive measures, to wit, expected health benefits versus the costs and burdens of mass evacuation. The International Commission on Radiological Protection (ICRP) recommends that no measures should be taken unless they produce a positive net benefit. Exposure to moderately increased levels of radiation may increase the risk of fatal cancer in the future, while mass evacuation has burdensome and disruptive consequences for the society and for the persons who have to leave their residential and/or working area for a long time. Ordering of mass evacuation seems rationally and ethically justified only if the expected future benefits outweigh the present and future burdens. Small or uncertain future health benefit may be outweighed by large costs and burdens of mass evacuation. Because we have to take into consideration not only public but also individual costs and benefits, it is important to take into account the personal absolute increase in health risk of elevated radiation in addition to relative risk. Unlike relative risk, absolute risk reveals the individual chance of getting a radiation-based disease. The increase in absolute risk – that is, the difference between the chances of getting the disease with and without the exposure to the increased level of radiation – is a useful measure to reveal the personal chance of health benefit from evacuation. This personal benefit must be balanced against the personal costs and burdens. The key question is which levels of radiation absorption and health risks outweigh the burdens of mass evacuation. There seems consensus amongst experts about the justification of mass evacuation in cases of expected individual radiation absorption > 500 mSv over a year. Similarly, experts agree that expected extra radiation absorption < 10 mSv does not justify mass evacuation. But between these two extremes there is a wide range of 50-fold increasing radiation levels in which it is not clear whether the personal and public benefits from mass evacuation outweigh the personal and public costs. This may partly explain why experts and authorities gave conflicting advice about the radius of the area around the Fukushima nuclear power plant within which people had to be evacuated. The uncertainty about the right thing to do with respect to a wide range of moderately elevated levels of radiation seems to be caused not only by inconclusiveness but also by indeterminability, that is, impossibility of determinately weighing disparate costs and benefits.