alt Hacker NewsCumulative total number of deaths from Chernobyl, definitively the worst nuclear disaster in history, ranges from 4000 to 16000 (estimates, via Wikipedia). A dam bursting upstream of a few small towns will kill many more[0].
Do not underestimate excess water.
For comparison the Bhopal disaster (which is much less known in the West) that occurred on 3 December 1984 in Bhopal, Madhya Pradesh, India caused deaths in the range 3928 to 16000.
A government affidavit in 2006 stated the leak caused 558,125 injuries including 38,478 temporary partial injuries and approximately 3,900 severely and permanently disabling injuries.
https://en.wikipedia.org/wiki/Bhopal_disaster