>The original nuclear powers are accumulating really old atomic bombs / rocket The US is replacing its nukes: the new nukes have all new parts except the fissi

>The original nuclear powers are accumulating really old atomic bombs / rocket The US is replacing its nukes: the new nukes have all new parts except the fissile material. Russia is ahead of the US here and has finished replacing its Soviet-era nukes in this way up to the limit of what they are allowed to deploy under the START treaties. (I.e., they might have some Soviet-era nukes, but if so, they need to stay in storage for Russia to stay in compliance with its treaty obligations.) US and Russia no longer explode nukes to make sure they still work, which is where simulations using supercomputers come in.