Redesign of Sliding Pressure Startup Procedures

The startup procedures are redesigned in detail, referring to LWRs and FPPs. The coolant flow paths during these procedures are schematically described in Figs. 5.70-5.74 as red lines. 

Main steam stop valve Turbine control valve 

The condensate demineralizer and condensate filter demineralizer clean the condensate system and feedwater system (called the main coolant system in safety design). The reactor is also cleaned with the reactor clean-up system. It should be mentioned that the reactor cleanup system is used for only the startup, and the coolant is purified in the condensate system during the once-through operation as done in FPPs. Also, as in BWRs, the condenser is vacuumized in order to prepare it for start up. 

The recirculation system, including the steam drum, is initially fully filled with water. The water level is generated by dumping part of the water into the condensers. The space above the water level is almost a vacuum. By using this procedure, the recirculation system is filled with only water. Noncondensable gas is not needed to generate a gas phase. Then, starting the circulation pump begins circulation of the coolant in the loop. 

The control rods are carefully withdrawn to start nuclear heating and raise the power. The power rise is kept slow in order to satisfy the limit of temperature rise (55°C/h) as is also applied in LWRs. At the same time, the motor-driven feedwater pumps are started, and the water circulates in the feedwater loop, which is provided to warm the feedwater system during startup. This procedure is necessary to avoid cold shock on the reactor vessel inlet nozzles when the recirculation mode is switched to the once-through mode. 

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