Tokyo Electric Power Co.'s bond risk fell to the lowest since the 2011 tsunami wrecked its Fukushima No. 1 atomic plant, as lower fuel costs buoyed earnings of Japan's utilities.

The cost to insure Tepco's debt against default dropped to 140 basis points on Feb. 5, the lowest since a record earthquake struck Japan's northeast region on March 11, 2011, and compared with as high as 1,762 in October 2011, according to CMA prices. The average price for utilities' credit-default swaps worldwide was 92 basis points, CMA data show.

Tokyo Electric said last month its operating profit increased 29 percent in the nine months through Dec. 31 as crude oil prices at six-year low and cost cuts made up for a weaker yen and the absence of nuclear power capacity. The Chubu and Chugoku regional utilities returned to profit while Hokkaido's power provider narrowed its net loss. Bank of Japan Gov. Haruhiko Kuroda said last month that sliding energy costs are positive for the economy, boosting corporate profits and increasing the purchasing power of consumers.