Tokyo Electric Power (Tepco) is gauging demand for its first bond offering since the 2011 Fukushima nuclear calamity, with some market participants expecting a sale as early as February, sources familiar the plans said.While the size of the sale has not been decided, potential maturities being discussed are three-, five- and ten-years, bankers and investors told Thomson Reuters DealWatch, asking not to be identified because the information is private. The company is likely to have to pay investors a premium of 1 percentage point above Japanese government bonds, about three times more yield pick up than on other electric utility bonds, they said.The company was in discussions last year with investors to sell as much as 330 billion yen of bonds. A Tepco spokesman said the company still plans to issue bonds by the end of March but declined to comment on specific target dates or sizes.