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Sample Run - A DVI Line Break

As a sample run, the AP600 was tested for a double-ended DVI line break, the results will be compared against an analysis[4] performed by the Los Alamos National Laboratory using the TRAC code.

To start the run, the user selects from a set of initial conditions (IC) corresponding to various power, flow, and time-of-life conditions. Click at one corresponding to a steady state full power middle-of-life condition, the is started. During operation, the mimic displays the plant condition and the operator controls its operation by using a mouse. The operator can initiate malfunctions that cover all categories analyzed in the plant's Safety Analysis Report and beyond. The severity, delay and ramp time of each malfunction is then entered. The status of every valve or pump in the mimic can be overridden by the operator to simulate a failed on/off situation. Partial failures at fractions of the full capacities are also possible. During execution, the operator can snap a new IC, freeze, back-track, and plot all simulated variables. These features are similar to the instructor's station of a full-scope simulator.

Due to the reduced-node thermal-hydraulics model for the primary coolant, there is no exact location for specifying a break other than its vertical elevation to a reference point. When the system water level drops below the break elevation, the discharge flow turns into two-phase and vapor. This was witnessed by the ARS calculated step changes in figure 3. The reactor was tripped automatically on the signal of low pressurizer pressure, followed by the steam generator feedwater control valves closure.

Figure 3

Subsequently, PRHR isolation valves open, CMT isolation valves open, Main Steam Isolation Valves close, and Reactor Coolant Pumps trip, all are consistent with the TRAC analysis. At about 3 minutes into the event, ADS stages 1 to 3 are opened on low CMT level. Figure 4 shows the primary pressure. The ARS result shows primary pressure is initially higher than that of TRAC. After ADV opening, both depressurized quickly to the containment pressure. The secondary pressure stabilized at the steam dump valve's set point.

Figure 4

At about 350 seconds, the primary pressure is below the containment pressure so the IRWST drain valves open to fill into the RCS.

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