Abstract: The invention relates to a T-shaped pipefitting element (10) comprising a main tubular branch (10a) having a first end for the connection thereof to a first pipefitting section (7) and a second end for the connection thereof to a second pipefitting section (6), a lateral branch (10b) having an axis which is at an angle to the axis of the main branch (10a), and a free end for connecting to a third pipefitting section (8) of the auxiliary circuit (1). The first, second, and third pipefitting sections (6, 7, 8) of the auxiliary circuit each ensure a different function to the two other sections, that is either the supply of the pipefitting element (10) with a first fluid at a high temperature, the supply of a second fluid to the pipefitting element (10), at a lower temperature than that of the first fluid, or the discharge of a mixture of the first and second fluids. The pipefittings (6, 7, 8) of the auxiliary circuit of the pressurised water nuclear reactor consist of austenitic stainless steel.