Analysis Method for Plant Dynamics

From the beginning of the conceptual study on supercritical water cooled reactors, several plant transient analysis codes have been developed, modified, and applied to them [1-9]. The general name of these codes is Supercritical Pressure Reactor Accident and Transient analysis code (SPRAT). SPRAT mainly calculates mass and energy conservations, fuel rod heat conduction, and point kinetics. The relation among these calculations is shown in Fig. 4.1. SPRAT can deal with flow, pressure, and reactivity induced transients and accidents at supercritical pressure. The flow chart is shown in Fig. 4.2. 

As mentioned in Chap. 2, the fuel assemblies of the Super LWR contain many water rods for neutron moderation. The water rods are cooled by downward flow. 

Oka et al., Super Light Water Reactors and Super Fast Reactors, 

The basic SPRAT was modified to deal with water rods cooled by downward flow [6]. It is called SPRAT-DOWN [7-9], The coolant flow scheme is shown in Fig. 4.3. The fuel channel and the water rod chaimel are modeled as single channels with 20 meshes. At normal operation, 30% of the feedwater is led to the water rod channel through the upper dome and the control rod guide tube. The lower plenum, including the downcomer, is divided into 20 meshes. The upper plenum, including the main steam line, is also divided into 20 nodes. The main feedwater line and the 

Equations (4.2), (4.3), and (4.4) are for the fuel channel, water rod channel, and outside core, respectively. The governing equations are discretized using the upwind difference scheme and the full implicit scheme. The boundary conditions are the feedwater flow rate, the feedwater temperature, and the mrbine inlet flow rate. The characteristic of the turbine control valve, expressed as the change of steam flow rate, is shown in Fig. 4.4 [6]. The feedwater flow rate changes with the core pressure as shown in Fig. 4.5 [6]. 

---