A U.S. research institute says that North Korea appears to have restarted the operation of a nuclear reactor at its Yongbyon Nuclear Scientific Research Center. 
 
The 38 North, a North Korea-focused research body affiliated with Johns Hopkins University, said Wednesday that recent commercial satellite imagery indicates new activity at the 5 megawatt plutonium production reactor at Yongbyon after an almost five-month hiatus in operations from late August until mid-December 2014.
 
The 38 North based its speculation on observations at Yongbyon of hot water running from a turbine building, steam from a probable pressure relief valve, and melted snow on the roofs of the turbine-building and the reactor.
 
The institute, however, added that it is too soon to reach a definitive conclusion, saying the facility has been observed over a period of only a few weeks. It said it will continue to monitor the reactor site.