To understand the death toll of Chernobyl, we have to dive into radiation theory as well as how death tolls were counted.

First, as a simple answer: 31 people died as a result of the accident, and due to acute radiation syndrome(ARS) within 3 months of the explosion. Acute radiation syndrome occurs when there is a massive exposure over a limited time frame. Exact numbers are debatable, but the NRC estimates that death will occur in 50% of people within 30 days of receiving a 400-450 rem dose. For perspective, a single X-ray will give you 70 millirem to your pelvis. A full body CT scan will give you 1000 mrem, or 1 rem. Most people average around 350 mrem per year in their daily lives.

These 31 people all likely received doses at or above those levels of exposure, which resulted in death due to ARS.

Another report from a United Nations Committee(UNSCEAR) cited additional deaths from trauma and ARS diagnoses to bring the death toll to 54.

An estimated 15 more people died of thyroid cancer in the immediate years following. Thyroid cancer is a particularly high risk to radiation workers exposed to high levels of radiation, and the risk can be reduced by iodine pills(as hinted at in HBO’s Chernobyl).

The next most often cited number you’ll see is the number 4,000 deaths, as cited by an IAEA report. This number comes from diagnoses of thyroid cancers. I cannot personally attest to the lethality of thyroid cancer, I’m just pointing out where the “4000” comes from.

However, even this estimate was contested by scientists and physicians on either side of the debate. Some claimed the data was misrepresented, some felt the estimates were far too conservative.

Perhaps the biggest question mark of the true death toll is the result of the “liquidators.” Declassified Soviet documents prompted first hand accounts of death tolls estimated at 6,000 liquidators, which prompted, again, debates on both sides as either too high or too low. Approximately 600,000 liquidators were conscripted, with an average dose received of 12 rem. Of those workers, approximately 240,000 worked in radioactive or contaminated areas actively.

The Ukrainian government reported a 5% increased cancer rate in the region adults, and 90% in the region children. In 2005, the Ukrainian government was providing survivor benefits to 19,000 families related to the Chernobyl accident.

Vycheslav Grishin of the Chernobyl Union claims “25000 of the Russian liquidators are dead and 70000 disabled, about the same in Ukraine, and 10000 dead in Belarus and 25000 disabled.” This brings the estimate to 60,000 dead.

The high end of the spectrum you’ll see cited is 93,000, although the originators of that statistic, Greenpeace, would argue the number should be much higher.

Death toll estimates are complicated and difficult in modern systems with more or less full transparency. If you factor in Soviet secrecy, the estimates can vary so widely as to seem ludicrous. Changing even a small factor in your assumptions can change an estimate from 4,000 to 93,000.

So now, let’s dive into a bit of radiation theory. A REM(roentgen equivalent man) is a measure of a dose, we’ll be talking about a whole body dose for the purpose of this argument. There are a few thumbrules, but let’s just say for the purpose of this argument that a 100 rem dose increases your chance of acquiring cancer later in life by 10%. So, if you remember, the estimated average exposure of liquidators was 12 rem. This means that of the 240,000, we can expect to see a 1.2% increase in chance of cancer among those workers, or about 2,900 more incidents of cancer. The catch is, that cancer probably won’t come for 10-20 years. However, based on regional estimates, there was a reported 5% increased cancer rate in adults in the decades immediately following Chernobyl. This is fairly significant when applied to the approximately 5,000,000 people previously residing in the area.