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Investors mainly shorted Tokyo Electric Power (9501) on March 17, after TEPCO's share price declined significantly, so did not cause the steep fall in share price from 11th to 17th

An additional 10 million shares were borrowed and shorted on Short Side on March 17, well after TEPCO's share price declined from 2121 on March 11 to 750 on March 17.  Those short sellers that took a position on March 17 were underwater as TEPCO's share price climbed back to above 1000 on the 22nd and 23rd.  Indeed, on March 24, 6 million shares were returned to lenders as some short sellers closed out their trades.  It's unknown as to what price those 6 million shares were originally purchased by shorts, however, so it's not certain that those shares were closed at a loss.

Unfortunately, problems at the nuclear reactor have continued to get worse, and TEPCO's share price has declined below 500.  Shares borrowed has increased back to March 17 levels and remained steady over the prior week.

Reuters reported that two trillion yen (roughly $24 billion) was not going to be enough to allow the company to pay for the cleanup at the nuclear reactor.