Auxiliary Steam Supply System

The nuclear steam supply system (NSSS) of the QP300 consists of a pressurized water reactor, reactor coolant system (RCS) and associated auxiliary systems. The NSSS has retained the general design features of current PWR plant design. 

Figure 1-2 shows the simplified schematic diagram of the SMART nuclear steam supply system (NSSS) and exhibits the safety systems and the primary system as well as auxiliary systems. The engineered safety systems designed to function passively on demand consist of a reactor shutdown system, passive residual heat removal system, emergency core cooling system, safeguard vessel and reactor overpressure protection system. 

The main auxiliaries of the nuclear steam supply system irrelevant to safety are ... 

B class plant users, which represent the whole of the electric users of the nuclear steam supply system (NSSS) and of its auxiliaries, with the exception of the "A" class users. 

The HTR-PM shown in Fig. 3.9 contains two parallel trains of nuclear steam supply system (NSSS) of identical design, each consisting of a 250-MWth pebble bed reactor and a steam generator. The two NSSS systems have independent primary loops but share auxiliary facilities, such as fuel handling system and helium purification system. The two trains jointly supply superheated steam to a common steam turbine power generator rated at 200 MWg. 

The system is totally independent from the main feed water system and is capable of supplying feed water at the rated pressure to the steam generator for decay heat removal. The auxiliary feed water system is designed to be operable under safe shutdown earthquake condition. 

Steam lines of the auxiliary steam system extend from the main steam line they supply steam to heat exchangers of the district heating system, to the process condenser, oil heater and for own needs of the plant. 

As a representative initiating event of an anticipated transient, the loss of external power is commonly postulated, in which a diesel generator is expected to start up and supply electricity for safety demands in a conventional design. Different from this, the LSPR incorporates a fully passive system of decay heat removal without diesel generators - the decay heat can be removed by steam generator auxiliary heat removal system (SGAHRS) through the SGs to the air coolers by natural circulation. 

The HGP, owned by the Supply System, received steam via the steam piping system from the N Reactor. The HGP consists of two 430-MW (electrical) low-pressure turbine generator systems with associated auxiliary equipment normally found in a steam power station. The HGP is operated by the Supply System. The HGP condensers and auxiliary cooling systems were supplied by raw water pumped from the Columbia River and discharged back to the river approximately 90 m (300 ft) upstream from the N Reactor raw water intake structure. 

The decay heat and residual heat could be cooled for about 30 minutes through the natural circulation of primary coolant in the primary system, and through the operation of turbine operation auxiliary water supply pump and the main steam safety valve. Necessary power for the safety protection systems and the turbine-driven auxiliary feedwater systems is supplied from highly reliable batteries to secure the safety of reactor even during the total loss of power. 

The auxiliary steam boiler is an electric package boiler. It supplies the steam required during a cold start of the main steam system and the turbine-generator additionally, it provides the steam for hot water heating. Main steam supplements the auxiliary steam header during start-up, and it supplies the auxiliary steam during normal operation at power. The auxiliary boiler provides the steam during a plant shutdown. 

During reactor operation, the secondary system is operated as a steam condensate system to transfer heat removed from the primary loop to the circulating raw water system. Heat transfer from the primary loop results in boiling on the secondary side of the ten main heat exchangers. This steam then flows to the main 46 steam header atop the 109 Building. Sufficient steam to drive the six drive turbines and to supply auxiliary areas uses flows to the turbine supply header the remainder is condensed in the dump condensers, completing the heat transfer to the circulating raw water system. Secondary coolant pressures, flow rates and Inventory are directly controlled coolant temperatures are dependent variables. 

The control performance of the heat-integrated reactor-column system shown in Fig.. 5.9 deteriorates as the auxiliary rehoiler provides less and less heat to the column. The reason is that uncontrolled variations in the steam pressure of the waste heat boiler affect the heat supplied to the column. When these variations are of the same order of magnitude as the total heat supplied by the auxiliary reboiler, the latter cannot compensate properly for the variations. Part of the prob-... 

The primary circuit includes the equipment of the main circulation circuit, pressurization system and also auxiliary systems connected to the reactor. The fi ee volume above the reactor water level is used as steam-gas pressurizer for which gas is supplied to the pressurizer before reactor startup. The primary circuit operates in a non-boiling mode. 

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