North Korea is projected by the end of 2020 to have 25 to 50 nuclear weapons, and possibly as many as 60, according to a US think tank’s report on Pyongyang’s nuclear capabilities. David Albright, founder and president of the Institute for Science and International Security, a Washington-based security think tank, said on Tuesday the “worst case” estimate of 60 nuclear weapons would involve the operation of the Experimental Light Water Reactor, a type of thermal-…