WASHINGTON (Reuters) - The U.S. Senate on Friday confirmed geologist Allison Macfarlane, an expert on how to store radioactive waste from power plants, to head the Nuclear Regulatory Commission.

Macfarlane will serve out the year left in the term of Gregory Jaczko, who announced his resignation last month after being publicly criticized by fellow commissioners as being abrasive.

At a hearing in mid-June, Macfarlane pledged to treat her colleagues with respect and ensure the five-member commission operates smoothly.

The NRC, which has about 4,000 staff, is working on sweeping reforms for the 104 aging U.S. reactors in the wake of the Fukushima Daiichi nuclear disaster in Japan, caused by an earthquake and tsunami.

The Senate also confirmed on a voice vote Republican NRC commissioner Kristine Svinicki to a second five-year term at the commission.

(Editing by Eric Walsh)