Japan is considering extending the evacuation zone surrounding the tsunami-damaged Fukushima Daiichi nuclear power facility. The original 12.4-mile evacuation zone was based on the assumption of short-term radiation exposure risks, but the emergency is nearing its fifth week. Tokyo Electric Power Company says workers have begun streaming nitrogen gas into the plant’s No. 1 reactor to reduce the risk of a hydrogen-oxygen explosion. Meanwhile, Japanese officials have dismissed a claim by Massachusetts Democratic Rep. Ed Markey that the No. 2 reactor core had melted through its containment vessel. Markey says he got his information from the U.S. Nuclear Regulatory Commission.