The Japanese government will tighten radiation exposure limits for children at schools in Fukushima Prefecture. The Japanese education ministry said it will lower the threshold for cumulative external radiation permitted at schools and kindergartens to a maximum annual exposure of one millisievert. The figure translates to less than one microsievert per hour, Japan’s NHK website reported Wednesday. The previous standards of a maximum 20 millisieverts per year and 3.8 microsieverts per hour were set in April following the accident at the Fukushima Daiichi nuclear power plant. The ministry said the subsequent removal of topsoil from playgrounds has pushed radiation readings at all schools below the 3.8 benchmark. It said it will not require schools to keep children indoors even if radiation levels exceed the new limits, but recommends that they be promptly decontaminated if they go outside. The ministry is to inform Fukushima Prefecture of its decision to change standards on Friday.