A onedimensional
coolant volume was assumed for calculating temperature
change due to decay heat, and its initial temperature was
assumed to be 320 C. Water coolant is pressurized about 155 bar
inside reactor vessel for high intensity heat removal from the nuclear
fuel. During normal operation, high pressure of the coolant
remains constant by the reactor coolant pump. In initial phase of
the accident situation, pressure oscillates in range of 147e170 bar
by the relief valve of the pressurizer connected to the reactor vessel.
For the simplification of the calculation, pressure in reactor vessel
was assumed about 155 bar for the 1-D thermal hydraulic transient
temperature calculation of the coolant.