transient calculations of coolant mixing in vver-440/213 rpv

Fig. 5: Tempreature distribution on the wall of RPV and pipe
ECS INJECTION ABOVE THE CORE
The assumed initial conditions of the next transient: the reactor is in hot shut down condition, i.e.
the main coolant pumps are stopped. There is natural circulation in two loops (2 nd and 6 th loops
are opened), the coolant mass flow rate in these two loops is 40 kg/s. The temperature of the
coolant is 140 o C, the pressure is 0,5 MPa. The ECCS injects water into the 4 th loop and through
the hydro-accumulator nozzles. The mass flow of the injected water is 50 kg/s, the temperature is
35 o C.
The duration of the transient was 60 s. In the calculation buoyancy was taken into account, and
because of the large coolant temperature differences temperature dependent material properties
were used.
For this simulation only the core and the structural elements above the core were modelled in
details. The goal was to simulate the mixing in the upper plenum so this is the reason why the
lower plenum was neglected for this case.
Fig. 6: The model of the core and the upper plenum
The injected water cools down the coolant in the 4 th loop and enters into the vessel in the 23 rd
second. The colder water flows around the perforated reactor pit and passes through the