I'm concerned about safety not from the engineering side (although not dismissing it), but from the standpoint of an easy access to sufficiently large amount of

I'm concerned about safety not from the engineering side (although not dismissing it), but from the standpoint of an easy access to sufficiently large amount of radioactive material to build a dirty nuke. As the nuclear plants get smaller, the security is going to become a larger percentage of the operating costs and operators will be tempted to skimp in this area.