Patent Number: 
Section: claims

1. A hydrostatic packing seal for a system for sealing a shaft of primary motor-driven pump units of nuclear reactors, the hydrostatic packing seal comprising:a rotary active surface attached to the shaft and a floating active surface, wherein the floating active surface is configured to move axially to follow axial displacements of the shaft, and wherein the rotary active surface and the floating active surface face each other and are separated by a water film,wherein said rotary active surface or said floating active surface has at least one surface structured by an array of asperities to prevent the deposition of iron oxide fouling said at least one surface of said rotary active surface or said floating active surface, each asperity having lateral dimensions between 10 nm and 5 μm, a height between 10 nm and 5 μm, and a distance between two consecutive asperities being between 10 nm and 5 μm, said asperities being holes or pillars. 2. The hydrostatic packing seal according to claim 1, wherein the asperities are holes. 3. The hydrostatic packing seal according to claim 1, wherein the asperities are pillars. 4. The hydrostatic packing seal as claimed in claim 3, wherein at least one of the pillars has a form factor less than 2. 5. The hydrostatic packing seal according to claim 1, wherein the asperities are nanometric asperities that have lateral dimensions between 10 nm and 1 μm and a height between 10 nm and 1 μm, with the distance between two consecutive asperities being between 10 nm and 1 μm. 6. The hydrostatic packing seal according to claim 1, wherein the asperities are micronic asperities that have lateral dimensions between 1 μm and 5 μm and a height between 1 μm and 5 μm, with the distance between two consecutive asperities being between 1 μm and 5 μm.