Hi Imran,
I guess you expect that the break will be based along the Spline path as if you would use the Spline with the Knife Tool?
The Voronoi Fracture object uses the vertices/points of the Spline (or creates its own vertices/points along the Spline:
Distribution
Points will be produced as follows:
Even: At a uniform distance apart
Step: Dependent on the Spline’s Intermediate Points setting
Count: At random locations
Vertices: On the Spline’s base points
Whatever the points are, the Voronoi Fracture object takes two points and precisely in the middle distance of these points, cuts the object. Since there are more points, more often than now, the cell structure is created.
https://en.wikipedia.org/wiki/Voronoi_diagram
With this, the cuts are more likely to be 90º to a spline than along, roughly said.
Let me know if I got your idea about it wrong.
All the best