The policies of population relocation put in train following the severe nuclear reactor accidents at Chernobyl in 1986 and Fukushima Daiichi in 2011 are examined using the Judgement- or J-value. Here relocation is taken to mean a movement of people that is long-term or permanent. A review is made of a 1992 IAEA/CEC study of the Chernobyl countermeasures, which includes data from which the effectiveness of the 1986 and post-1990 relocations may be judged using the J-value. The present analysis provides endorsement of that study’s conclusion that the post-1990 relocation of 220,000 members of the public could not be justified on the grounds of radiological health benefit. Moreover, application of the J-value suggests that the first Chernobyl relocation is economically defensible for between 26% and 62% of the roughly 115,000 people actually moved in 1986. Thus only between 9% and 22% of the 335,000 people finally relocated after Chernobyl were justifiable, based on the J-value and the data available. Nor does the J-value support the relocation of the 160,000 people moved out on a long-term basis after the Fukushima Daiichi nuclear accident. The J-value results for these very severe nuclear accidents should inform the decisions of those deciding how best to respond to a big nuclear accident in the future. The overall conclusion is that relocation should be used sparingly if at all after any major nuclear accident. It is recognised that medical professionals are seeking a good way to communicate radiation risks in response to frequent requests from the general public for information and explanation in a post-accident situation. Radiation-induced loss of life expectancy, which lies at the heart of the application of the J-value to nuclear accidents, is proposed as an information-rich yet easy to understand statistic that the medical profession and others may find helpful in this regard.