TOKYO, Dec 22 (Reuters) - Hokkaido Electric Power Co 9509.T started generating power to sell from a new nuclear reactor on Tuesday, the first new unit in over three years in Japan, and a move that will limit fuel purchases for the firm.

Commercial operations at the 912-megawatt No.3 nuclear generator at its Tomari plant on Japan’s northernmost island started in the late afternoon, after getting the go-ahead from the government, the power firm said in a statement.

Hokkaido Electric has two other nuclear generators at the Tomari plant, each with a total capacity of 579 megawatts, and along with the No.3 unit the plant is expected to meet about 40 percent of the firm’s electricity generation needs.

The start of business at the atomic reactor was the first in Japan since Hokuriku Electric Power Co 9505.T began commercial operations at the 1,206-megawatt No.2 nuclear generator at its Shika plant in western Japan in March 2006.

With the start of the new Tomari unit, Japan has 54 nuclear power generators for commercial use, for a total generating capacity of 48,847 megawatts, the world’s third-biggest nuclear generation capacity after the United States and France. (Reporting by James Topham; Editing by Chris Gallagher)