The cost of protecting Tokyo Electric Power Co.'s debt shows the likelihood of a default increased to 53 percent after the utility's credit rating was cut to junk status by Standard & Poor's.

The contracts to insure ¥6.85 trillion in bonds and loans of Tepco for five years jumped to as much as 913.5 basis points Tuesday, or ¥91.35 million per year to protect ¥1 billion of the debt, according to data provider CMA. That's pricing in a 53 percent chance of default by 2016, according to data compiled by Bloomberg.

The probability of a company with B-rated debt defaulting during any five-year period between 1975 and 2010 was 19.14 percent, according to S&P's research.