An accident at a nuclear power plant causes the main valves to close and stop the main water flow that cools the reactor. The control rods shut-down of the reactor, but the radioactive fuel rods continues to release energy. The internal pressure and temperature slowly rise to the safety limit of 100 bar causing the pressure relief value to open and saturated steam vapor begins to vent out of the valve.
The exit flow vented is sufficient to keep the pressure constant as long as the reactor core remains completely flooded with saturated liquid. The liquid reserve volume above the core is initially 120 m^3. The temperature of the core, reactor vessel and saturated liquid and saturated vapor remain constant at the saturation temperature at 100 bar 311.1 oC while steam is vented. The exit mass flowrate during this condition is constant at 20 kg/s. Find the elapsed time from when the relief valve first opens to the point when the water level drops below the top of the core = _________ seconds = ________ hours.