Looking at the number of fatalities (not war related), its possibly far worst than nuclear.
Schoellkopf Power Station - 1 deaths
Vajont Dam - 1917 deaths
Banqiao Dam - 26000 direct deaths + 145000 post disaster deaths
Teton Dam - 11 deaths
Machchhu Dam - 1800 deaths (optimistic estimate)
Lawn Lake Dam - 3 deaths
total deaths: 174,732 deaths
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Kyshtym disaster - Estimated 200 possible cancer fatalities
Chernobyl - 28 direct, 19 not entirely related and 15 minors due to thyroid cancer, as of 2008. Estimated up to 4000 possible cancer deaths.
SL-1 - 3 deaths
Enrico Fermi Nuclear Generating Station - 0 deaths
Lucens reactor - 0 deaths
Jaslovské Bohunice - 2 deaths
THTR-300 - 0 deaths
Surry Nuclear Power Plant - 4 deaths
Fukushima - 1 and 3+ labour accidents; plus a broader number of primarily ill or old people from evacuation stress
total deaths : 4213 deaths