I'm not sure if it's still there (I left the area in 1988), but you used to be able to see the flask as it was placed next to the train track running to Heysham 2 power station. Just off the road to the ferry terminal and power station, there was a small bridge over the railway line on a road leading to a caravan site, and you could get a great view of it from the bridge. The most amazing thing was apart from a few scratches on the side, it looked like nothing had even happened to it!
EDIT: looking at google maps, it seems that you can't see it any more. The road was Moneyclose Lane, Heysham where it joins Princess Alexandra Way.
EDIT 2: apparently it's been moved to the visitor's centre: https://www.railscot.co.uk/locations/H/Heysham_Power_Station...