The system, called Trinity, will simulate nuclear tests (among other things). It's expected to have over 8x as much computing power as a Cray XE6 system (called Cielo) currently used by the NNSA.
"Substantial system acceptances" are expected to occur in late-2015 and 2016. Rival SGI recently won a supercomputer deal wit the U.K.'s Atomic Weapons Establishment.
15% of Cray's float was shorted as of June 13.