Safety injection/residual heat removal system

Safety injection/residual heat removal system in RHR mode. 

The AP600 passive safety system includes subsystems for safety injection, residual heat removal, containment cooling, and control room habitability under emergency conditions. Several of these aspects are in existing nuclear plants such as accumulators, isolation condensers as natural-circulation closed loop heat removal systems (in early BWRs), automatic depressurization systems (ADS - in BWRs) and spargers (in BWRs). 

High Safety. Following features make the reactor more safe during its operation double pressure vessel, natural circulation (There is no big sized penetration on the pressure vessel), self pressurizer, gravity boron injection and residual heat removing system with natural circulation etc. 

The Safety Injection and the Residual Heat Removal Systems have been combined and located outside the containment. In order to lower the cost without impairing the safety and reliability, simplifications of the standard well known solutions were examined. 

The use of diverse safety systems and devices based on different principles of operation for example, the electro-mechanical control and protection system (CPS) and the system of soluble poison injection are used for emergency reactor shutdown the residual heat removal system and the channel of aftercooling through the process condenser, and the channel of aftercooling by the third circuit through the cooler of the purification and aftercooling system are used for residual heat removal ... 

The safety system (Fig. 20.21) of SMART includes a shutdown cooling system, residual heat removal system, safety injection system, reactor overpressure protection system, and emergency boron injection tank. Each of the four independent passive residual heat removal systems with 50% capacity can remove the core decay heat through natural circulation at any design basis events. This feature can keep the core undamaged for 72 h without any corrective action by operators in a design basis accident (Kim et ah, 2014). 

Fig. 37. Schematic representation of the in-containment passive safety injection system (PS1S). 1RWST = in-containment refueling water storage tank. PRHR-HX = passive residual heat removal heat exchanger. ADS = automatic depressurization system (four stages). (Westinghouse)...

Residual Heat Removal (RHR) and safety injection systems entirely within the containment building - are all inherent safety characteristics with respect to reactivity control, LOCA, and offsite releases respectively. 

Passive Core Cooling System X Safety Injection, Depressurization and Passive Residual Heat Removal... 

Number of LPSI systems - the number of low-pressure safety injection systems designed to remove residual heat from the reactor core in the case of a considerable loss of coolant, when the coolant pressure drops significantly. Such LPSI systems with a high flowrate may also be used for residual heat removal after normal reactor shutdown. For reactors without an LPSI system, data providers should enter "N/A". 

In case of design basis accidents, the IMR detects abnormal condition and trips the control rods. Since the IMR has no soluble boron system as a chemical shim, control rod worth is enough to maintain cold shutdown conditions. Additionally, in case of a trip failure, stand-by shutdown systems inject borated water to shutdown the reactor. Residual heat is removed by a passive stand-alone direct heat removal system (SDKS). The SDKS works without operator action and external supports and keeps core conditions within the safety criteria. 

In WWERs, residual heat is removed in emergency conditions, and for some of them in shutdown conditions, through heat exchangers of the low pressure safety injection systems. These are cooled by the essential service water system which transfers the heat directly to a spray pond or to a lake, depending on the plant in question. There is no closed loop intermediate cooling system. 

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