Both the reactor and guard vessel are hanging vessels (items 1 and 2) with hemispherical bottoms. The interstitial space between the two vessels is accessible by dedicated tools for ultrasonic testing.
The vessel is closed by a 2 m thick cylindrical cover (item 3): a compound of several steel boxes which are filled with concrete. Its function is mainly to bear the components of the primary system inserted into it, and to provide efficient neutron shielding for the structures located above the vessel.
The diaphragm (item 4) is a large cylindrical component separating the 'cold pool' (higher pressure, lower temperature) from the 'hot pool' (lower pressure, higher temperature) of the vessel inner volume. The diaphragm serves as the support structure for the two casings at its periphery (each enclosing one primary pump and two heat exchangers), for the two in-vessel diametrically suspended fuel storages, for the core support plate and for the core barrel.
Like the reactor cover, the diaphragm has dedicated penetrations to bear the primary pumps and heat exchangers, the fuel handling machines, the spallation loop, the in-vessel inspection and in-vessel recovery manipulators.