"This American scientist has seen North Korea’s Nuclear Program up close" PBS NewsHour 2/14/2018

Excerpt

SUMMARY:  How advanced is North Korea's nuclear weapons program?  Just ask the few Western experts who have seen glimpses of the program and its evolution, like Nuclear scientist Sig Hecker, who has visited seven times and given eye-opening access to their facilities.  Science correspondent Miles O’Brien reports on how experts try to access the North’s capabilities.