Reactor auxiliary cooling system

DRAGS direct reactor auxiliary cooling system... 

Fig. 2.1. Schematic of the LS-VHTR. (DRAGS = direct reactor auxiliary cooling system PRACS = pool reactor auxiliary cooling system.)...

To meet the passive safety requirements of the NGNP, the AHTR uses a reactor vessel auxiliary cooling system (RVACS) similar to that of S-PRISM. It may also use a direct reactor auxiliary cooling system (DRAGS) similar to what was used in the Experimental Breeder Reactor II to supplement the RVACS and reduce the reactor vessel temperature. 

It is also possible to supplement the RVACS heat removal capacity using a direct reactor auxiliary cooling system (DRAGS) based on natural circulation of an intermediate coolant from bayonet heat exchangers in the reactor vessel to air-cooled heat exchangers. This type of DRAGS system was used in the Experimental Breeder Reactor II (EBR-II) with sodium-potasium as the intermediate coolant. There are a variety of potential intermediate coolants, several of which have been used extensively in industry for similar heat transfer applications. 

Primary Reactor Auxiliary Cooling System (PRACS)... 

Four primary reactor auxiliary cooling systems (PRACS) are used A cooling coil is installed in the inlet plenum of each IHX and a heat transfer coil is installed in the mr cooler of ultimate heat sink Coolant is circulated by EM pumps supported by emergency AC power The air cooler consists of a blower, a stack, vanes and dampers The blower is supported by the emergency AC power The vanes and the dampers are operated by the emergency DC power Decay heat removal by natural circulation is possible to mitigate a total blackout event (loss of all AC power)... 

Decay heat removal Primary reactor auxiliary cooling system (PRACS) Steam/water system Active Active N/C operation available Non-safety grade... 

The natural air cooling system in the reactor vessel is designed so that it is capable of removing decay heat without operation of the Primary Reactor Auxiliary Cooling System (PRACS). 

LOF Primary Reactor Auxiliary Cooling System (PRACS) Reactor Vessel Auxiliary Cooling System (RVACS) TOP Mechanical stop of hydraulic drive system of reflector... 

For heat removal from a shutdown reactor, two independent passive systems are provided, which are the reactor vessel auxiliary cooling system (RVACS) and the intermediate reactor auxiliary cooling system (IRACS). The RVACS is completely passive and removes shutdown heat from the surfaces of the guard vessel using natural circulation of air. There is no valve, vane, or damper in the flow path of the air therefore, the RVACS is always in operation, even when the reactor operates at rated power. Two stacks are provided to obtain a sufficient draft. 

The reactor vessel auxiliary cooling system (RVACS) is a system for shutdown heat removal however, to keep the fully passive features, it is continuously operating even at normal operation of the reactor. The intermediate reactor auxiliary cooling system (IRACS) is a sodium loop with an air cooler for shutdown heat removal, arranged in series with the secondary sodium loop (Fig. XIV-2). 

RVACS - Reactor vessel auxiliary cooling system DHX - Direct heat exchanger PRACS - Primary reactor auxiliary cooling system RV -Reactor vessel... 

Reactor vessel auxiliary cooling system (RVACS) and primary reactor auxiliary cooling system (PRACS), see Fig. XV-3. 

The rated thermal output of MONJU [5.63, 5.64] is transported through the primary heat transport system (PHTS) and intermediate heat transport system (IHTS) loops to the steam generators. Shutdown heat removal is normally by forced circulation (FC) provided by pony motors associated with each of the loop pumps. Heat is rejected to air at the air blast heat exchanger of the intermediate reactor auxiliary cooling system (ACS) which branches off from each IHTS loop. Thus the auxiliary cooling system (ACS) of the Monju reactor is coupled with the secondary system which also has the role as decay heat removal system. 

Direct reactor auxiliary cooling system (DRAGS) with immersed DHX in main vessel, intermediate sodium loop and Na-air heat exchangers. 

The secondary cooling system consists of a secondary pump, a once-through SG and piping for each loop. The reactor has two shutdown systems, the primary reactor shutdown system and the backup reactor shutdown system. Either can stop the reactor rapidly independent of the other. The decay heat removal system has four independent loops and employs a direct reactor auxiliary cooling system (DRAGS) to reduce the cost while maintaining reliability. 

Decay heat removal is by a Direct Reactor Auxiliary Cooling System(DRACS) with heat exchangers immersed in the reactor vessel, which improves reliability by a combination of forced and natural circulation, and can remove decay heat without reliance on the outer... 

Twelve sections of the passive reactor auxiliary cooling system (PRACS) are installed in the reactor module around the circumference of 07.0 m. The diameter and height of the PRACS vessel is 0.47 m and about 6 m, respectively. The nominal Pb-Bi coolant flow rate through 12 PRACSs makes 15% of the whole reactor flow rate. The PRACS working fluid is naturally circulated environmental air. About 1.4% of the generated power in nominal conditions is transferred to the environmental air. 

A passive reactor auxiliary cooling system inside the reactor module allows the total removal of decay heat in case of a steam generator trip at temperatures below 1000 K. 

Three reactor auxiliary cooling systems are located at the upper plenum these systems are driven by natural convection. The inherent safety features of the core are enhanced to avoid a core-disruption accident even in anticipated transients without scram (ATWSs). 

A schematic of the reactor and cooling system is shown in Fig. 11.2. Two intermediate reactor auxiliary cooling systems (IRACSs) and one direct reactor auxiliary cooling system (DRAGS) have been applied as a decay heat removal system (DHRS) suitable for the two-loop cooling system and the adopted type of SG. These systems are passive type by natural circulation. 

The DHRS consists of a combination of one loop of DRAGS and two loops of the primary reactor auxiliary cooling system (PRACS). The heat exchanger of DRAGS is dipped in the upper plenum within the RV. The heat exchanger of each PRAGS is located in the primary-side upper plenum of an IHX. AU of these systems can be operated based on a fiiUy passive feature with natural circulation, which requires no active components such as pumps (Yamano, 2010). 

LORL, loss of reactor level LOHS, loss of heat sink RV, reactor vessel GV, guard vessel D/2AC5, direct reactor auxiliary cooling system DHRS, decay heat removal system PRACS, primary reactor auxiliary cooling system AM, accident management. 

S has several safety systems active, passive, and inherent (IAEA, 2003) (see Fig. 20.22). Active shutdown systems are (1) inserting reflectors by using gravitational force and (2) inserting black control rods. The passive safety system of 4S uses natural circulation in RVACS and Intermediate Reactor Auxiliary Cooling System (IRACS). In addition, inherent safety system uses Doppler effect via metallic fuel and large inventory of coolant. 

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