The Bombay Stock Exchange benchmark Sensex which recovered over 300 points in afternoon trade closed down by 272 points at 18168. It had lost over 486 points in opening trade.Brokers attributed the fall to the Japanese Nikkei tumbling by over 10 per cent amid fears of a meltdown at a nuclear power plant.Overnight losses in the US market also dampened the sentiment. National Stock Exchange NIFTY also closed 82 points down at 5500.