Conversation so far:
what are the short term effects of the chernobyl disaster
The immediate and short-term effects of the Chernobyl disaster include radiation sickness and cataracts.
what are the long term effects of the chernobyl
Late effects of exposure to the Chernobyl disaster are thyroid cancer, especially in children and adolescents, and leukaemia among exposed workers.

Question: when did the disaster occur
Self-contained rewrite: when did the chernobyl disaster occur