I was on this flight in Y on Sat. DL 295 stopped in Seattle because the 747 we were flying from ATL on had an issue with one of the valves on one of the fuel tanks. The Captain got on the air to explain that they had 2 choices with this flight - either cancel it because of the valve issue, or stop in SEA to refuel before flying over the Pacific to NRT. It was supposed to be less than a hr stop, but for some reason took 2 hrs+.