In reply to HenryJM:
Not all the ice will be gone by the time you get out to Rjukan. You'd be better off starting high at Krokan rather than at Ozzmosis. Apparently it's a bit wet.
Here's some more ideas. Try something different. You can have a real adventure at Kong Vinter. Don't bother with Presenil, there's too much snow.
Try and find a quick way to the start of Sickhausfoss from the contradictory map and written instructions in the heavy water guidebook. Do you start from skruigaten left end or right end?
If the ice is really all gone when you get here then try docteuren (M7) at Bolgen. There's other dry tooling routes too.