Gregory Flanders (asker) Jan 26, 2017:

Thank you both so much for the information, greatly appreciated!

Kari Foster Jan 26, 2017:

Reference Here (in the blue box) they are talking about a big (800 m2) exhibition being staged "dans la nef du réacteur G1". I think this would probably support "reactor building" as Claire said.
http://www.sfen.org/en/node/1146
p.s Sorry, this should have gone down as a reference comment rather than a discussion entry...

Tony M Jan 26, 2017:

If it helps The actual place where the fuel rods are, originally the 'atomic pile', is still at least partially referred to as 'pile' in EN — if nothing else, in terms of the 'floor' beneath which sits the actual reactor part being referred to as the 'pile cap'.
And I think the 'nef' would be the vast, cathdera-llike structure above it that allows enough height for the tall fuel reloading machine to be positioned above the comparments for raising and lowering the fuel rods.
This is largely on the basis of my own experience during a visit to the Hinckley Point nuclear power station in the UK, when we actually got to walk (much to my trepidation, I might add!) upon that very 'pile cap', and so I got to hear some of the jargon first hand.
I gues when it comes to decommissioning, this section might be regarded as 'peripheral' (despite being rather important!) simply because it is not in an of itself irradiated.