Japan is pledging tighter nuclear safety after an accident at an atomic research facility exposed 33 people to minor excess radiation, though none were injured.

Education Minister Hakubun Shimomura, whose agency oversees such research, said Tuesday the government will tighten oversight of such research. He criticized a "low level of safety awareness" at the facility in Tokaimura, north of Tokyo.

Japan's Nuclear Regulation Authority had rated last week's accident as "Level 1," or third from the lowest level on a 9-level international scale.

Also Tuesday, a zoning reclassification ended a "no-go zone" designation for areas contaminated with radiation from the Fukushima Dai-Ichi nuclear plant, which was damaged by the March 11, 2011 earthquake and tsunami. Most of the area is designated "difficult to return to," and remains off-limits.