XYLENE POWER LTD.

FNR BASEPLATE

By Charles Rhodes, P.Eng., Ph.D.

BASEPLATE:
The FNR baseplate supports the entire weight of the nuclear island. In an ideal world the baseplate would rest on a single chunk of granite in dry soil. The granite would absorb local force concentrations. However, in the real world the FNR is surrounded by soil that sooner or later will become saturated with water, in which case the entire nuclear island in effect becmes a concrete boat.

In a boat, at any particualr depth below grade, the hydraulic pressure is constant. However, the weight of the FNR has downward force concentrations directly underneath the hot wall, the inner structural wall and the outer structural wall.

These force concentrations in combination with uniform external hydraulic pressure at a particular depth, lead to baseplate shear force concentrations in the proximity of the bases of the loaded walls. To absorb these shear force concentrations it is necessary to make the concrete thicker and to increase the amount of reinforcement underneath and in the proximity of these walls. The reinforcement must be particularly dense near the bottom of the baseplate under these walls where the concrete is under maximum tensile stress.

In order to evenly distribute the downward forces related to the structural walls over the bottom of the baseplate, the baseplate needs to be about 6 m thick. The perimeter of the baseplate should extend at least 3 m beyond the outer structural wall, indicating a baseplate diameter of:
52 m + 6 m = 58 m.
 

BELOW GRADE WALL STABILIZATION:
Further, when behaving as a boat there is substantial inward hydraulic radial force on the outer structural wall, immediately above the baseplate. From a theoretical perspective concrete is strong in compression. However, the distance between the major radial shear walls at the air locks is large. To provide additional structural stability it is necesary to introduce thinner below grade radial shear walls spanning the elevation range 4 m to 16 m above the top surfce of the baseplate.

There must be enough vertical reinforcement near the bottom of the outer structural sidewall to absorb the inward radial hydraulic force between successive radial shearwalls. Note that these radial shear walls do not protect the region 0 to 4 m above the baseplate that must remain open to accommodate the NaK dump tanks.
 

This web page last updated February 24, 2026.