Is nuclear energy safe?

Safety can be compared using health effects per unit of electricity generated. Results depend on the period studied and the effects included in each estimate. The table presents data from the cited studies; the accidents are described below.

Chernobyl, on 26 April 1986, is a level 7 on the INES scale, the maximum. According to UNSCEAR, the accident caused the deaths, within a few weeks, of 30 workers; of the 134 who suffered acute radiation sickness, 28 died within the first three months. The Chernobyl Forum (IAEA, WHO and other UN agencies, 2005) projected about 4,000 eventual deaths among the 600,000 most exposed people — 200,000 emergency and recovery workers from 1986-87, with 2,200 deaths expected in that group alone; 116,000 evacuees; and 270,000 residents of the most contaminated areas — plus about 4,000 thyroid cancer cases in children and adolescents, with at least nine deaths and a survival rate near 99%. UNSCEAR itself is more cautious: beyond the rise in thyroid cancer — more than 6,000 cases documented by 2005 — and an emerging signal of leukemia among the most exposed workers, it states there is no demonstrated increase in solid cancers or leukemia in the broader exposed population, and that such an increase would be very difficult to detect in epidemiological studies given the doses involved. The gap between the Chernobyl Forum's 4,000 deaths and UNSCEAR's caution is not a disagreement over the facts: it is the difference between a lifetime projection using the linear no-threshold model applied forward onto an exposed cohort, and a report of what epidemiological studies have managed to confirm statistically so far.

Fukushima Daiichi, on 11 March 2011, is also a level 7, though with a far smaller release than Chernobyl's, as the INES scale entry explains. There were no acute radiation deaths among workers or the public. The UNSCEAR 2020 Report concludes that, since the UNSCEAR 2013 Report, "no adverse health effects among Fukushima residents have been documented that could be directly attributed to radiation exposure from the accident"; the increase in thyroid cancers found in child screening is attributed to ultrasensitive screening revealing thyroid abnormalities that had not previously been detected, not to radiation. The documented toll of the accident is mostly indirect: Japan's Reconstruction Agency counted 2,348 "disaster-related deaths" in Fukushima prefecture through the end of 2024, deaths recognized as caused by the disaster through the aggravation of an injury or the physical burden of evacuation life; that category lumps together the effects of the earthquake and tsunami with those of the nuclear evacuation, and the source does not separate them.

Three Mile Island, on 28 March 1979, is a level 5: a large part of the core melted, but containment held. Decades of studies by the NRC and independent universities found no deaths or measurable health effects attributable to the radioactivity released. The roughly two million people in the surrounding area received an average dose of only about 0.01 mSv (1 millirem) above background, against about 0.06 mSv (6 millirem) from a single chest X-ray and 1 to 1.25 mSv (100 to 125 millirem) a year of natural background radiation in the area.