The RadChartView does not offer Bubble Series. This feature is still not in our development plans and currently this is not supported.
However I think that in some scenarios it would be a feasible solution to use ScatterPointSeries and define a PointTemplate, in which you can place an Ellipse which size is defined by a property of the underlying business item:
One little trick you must apply is set the Width and Height of the ContentPresenter which hosts the Ellipse to be enough to accomodate the largest bubble possible. I have attached a simple app to demonstrate this, and a snapshot of the output that I get when I run the app. In the attached project, the largest possible bubble is 80x80 and this is why I have set this code:
<Setter Property="Height" Value="80" />
<Setter Property="Width" Value="80" />
Give this approach a try and see if you can adopt it to your current project.