Three main steam lines connecting the reactor pressure vessel to the high pressure turbine section serve to transport the steam generated in the reactor to the turbine. Each main steam line inside the containment is allocated a specific number of safety-relief valves for overpressure protection of the reactor pressure vessel. For automatic depressurization, the safety-relief valves are opened either by solenoid pilot valves or by the passive pressure pulse transmitters and diaphragm pilot valves.

The core of the SWR 1000 was reduced in active height and the fuel assembly was enlarged. A consequence of reducing the active core height is that the core can be positioned lower down inside the reactor pressure vessel. This provides a larger water inventory inside the reactor pressure vessel above the core, a feature which facilitates accident control. The fuel assemblies were enlarged resulting in fewer fuel assemblies in the core. This reduces handling times during refueling. Reducing the number of fuel assemblies also reduces the number of control rods, and hence the number of control rod drives as well. The average power density is approximately 51 kW/L.

The reactor pressure vessel has numerous nozzles for connecting the piping of the main steam, feedwater, emergency condenser, shutdown cooling and vessel head spray systems, as well as for accommodating the internal reactor water recirculation pumps, the control rod drives, the core flux monitoring assemblies and the reactor water level, pressure and temperature measuring instrumentation. The four emergency condensers as well as the four standpipes (which connect the passive pressure pulse transmitters and the condensation pots of the reactor pressure vessel level measuring equipment to the reactor vessel) are regarded as being external extensions to the vessel since they are connected to it via non-isolatable lines.

The main auxiliary systems of the SWR 1000 are:

• the residual heat removal (RHR) system;

• the reactor water cleanup system and fuel pool cleanup system;

• the fuel pool cooling system.

Apart from these systems many other auxiliary systems such as waste processing systems, a chilled water system, and HVAC systems exist for normal operation of the plant. The SWR 1000 design concept includes two active systems for low pressure core injection/flooding and residual heat removal. As in earlier plant designs these systems perform the following tasks:

• Cooling of the reactor core during and after normal plant shutdown;

• Water transfer operations before and after refueling;

• Operational heat removal from the core flooding pools and the pressure suppression pool;

• Heat removal from the containment in the event of loss of the main heat sink by cooling the pressure suppression pool and core flooding pool water;

• Low pressure coolant injection into the reactor pressure vessel and simultaneous heat removal in the event of loss-of-coolant accidents.

FIG. XI-1. SWR 1000 — Active and passive safety systems.

FIG. XI-2. SWR-1000 safety concept.