Why estimates differ by tens of thousands of deaths.
A Greenpeace activist carries several of 3,000 wooden crosses to be set up in front of the Soviet-built nuclear power plant in Bohunice on April 25, 1991, to commemorate the nuclear disaster in Chernobyl five years earlier.
When the Chernobyl nuclear reactor exploded in 1986, experts predicted as many as 40,000 extra cancer deaths from the radiation spewed onto parts of what was then the Soviet Union. Friday is the 27th anniversary of the disaster. How many people has Chernobyl killed so far?
We’ll probably never know. That’s partly because even 40,000 cancer deaths are less than 1 percent of the cancer mortality expected in the affected population. Statistically, the deaths are undetectable. Even if they weren’t, science usually can’t say that a particular cancer was induced by radiation rather than something else.
One exception is thyroid cancer, a very rare disease in children that skyrocketed to nearly 7,000 cases in Belarus, Russia, and Ukraine by 2005. There is no doubt that radioactivity from Chernobyl caused them, including about a dozen fatalities. We also know that two people died in the explosion and more than 100 people, mostly firefighters ignorant of the dangers, received doses high enough to cause acute radiation syndrome. Of them, 29 died within a few months, followed by 18 more deaths over the years. The group seems to be at higher risk for blood cancers.
For the rest of the story: http://www.slate.com/articles/health_and_science/explainer/2013/04/chernobyl_death_toll_how_many_cancer_cases_are_caused_by_low_level_radiation.html