4 of the top 20 super computers in the world, and another 2 in the top 100[1], are operated by the US National Nuclear Security Administration. What do they do?

4 of the top 20 super computers in the world, and another 2 in the top 100[1], are operated by the US National Nuclear Security Administration. What do they do? "One of the primary missions of NNSA is to maintain and enhance the safety, security and reliability of the U.S. nuclear weapons stockpile. NNSA, through its Office of Defense Programs, ensures that the U.S. nuclear arsenal meets the country’s national security requirements and continues to serve its essential deterrence role." [1]: http://www.top500.org/list/2010/11/100 http://www.top500.org/list/2010/11/100 [2]: http://nnsa.energy.gov/aboutus/ourprograms http://nnsa.energy.gov/aboutus/ourprograms