he containment envelope ( of Western plants ) is supposed to withstand a very large passenger plane striking it, so even a 155 mm shell shouldn't be too much of qa challenge.
I would suspect you have no idea what you are talking abou?
An aircraft is designed for light weight to slice through the air, a shell is designed to penetrate concrete with explosive plasma jets to severe steel let alone a few inches of concrete.
Bottom line - the containment vessel is easily penetrated - and the external cooling systems and ponds are obviou and unprotected.