How safe from terorists are our nuclear plants?

The Nuclear Proliferation Prevention Project at the University of Texas at Austin doesn't think we are very safe.  They think that we would have problems with airplane attacks, rocket-propelled grenades and more than a small handful of attackers.  

Wasn't 9/11 an airplane attack?  Aren't rocket-propelled grenades relatively common in Iraq and Afghanistan? Couldn't terrorists assemble a group of 50 or so fairly readily?

Read more here: http://www.mcclatchydc.com/2013/08/15/199512/all-us-nuclear-reactors-vulnerable.html#storylink=cpy