There are several shields before you get near the kettle.
First one is a enviroment shield which contains all the farts etc that the engineers put out.
Then you have the containment shield which is the bit you normally see folk walking on and lots of holes marked out on.
Then you have the core with its shield as well. Which normal mortals never gets to see. A select few get to go in with an impact hardness tester and spend 10 mins twice in thier life with lead underpants checking how much neutron hardening has been occuring to see if the physics boys have ****** up again.