Question: where did the worst nuclear disaster in history occur
[{'answer': 'Chernobyl', 'provenance': [{'wikipedia_id': '2589713', 'title': 'Chernobyl disaster', 'start_paragraph_id': 0, 'start_character': 0, 'end_paragraph_id': 0, 'end_character': 9, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}]