RadHtmlChart renders its SVG during the Sys.Application.Init client-side event of the page that hosts it. Thus, the Sys.Application.Load event is the earliest point at which you can obtain its SVG rendering, as shown here: http://www.telerik.com/support/code-library/exporting-radhtmlchart-to-png-and-pdf. This solution relies on the chart being opened in the user's browser so the SVG string can be POST-ed to the server. If you only need to do this on the server you can look into other tools that let you run browsers on the server and obtain their content, like PhantomJS, for example.
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