Primary reactor auxiliary cooling system

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... 

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 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. 

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. 

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. 

Six-control rod subassemblies made of 90% enriched B4C were used in JOYO MK-II and were located symmetrically in the third row. In 1994, one control rod was moved to the fifth row to provide a position for irradiation test assemblies with on-line instrumentation. Since then, the control rod subassemblies have been loaded asymmetrically. The JOYO cooling system has two primary sodium loops, two secondary loops and an auxiliary cooling system. The cooling system uses approximately 200 tons of sodium. In the MK-II core, sodium enters the core at 370°C at a flow rate of 1 100 tons/h/loop and exits the reactor vessel at 500°C. The maximum outlet temperature of a fuel subassembly is about 570 C. An intermediate heat exchanger (IHX) separates radioactive sodium in the primary system from non-radioactive... 

The SPINNOR and VSPINNOR plants adopt pool type Pb-Bi cooled fast reactors without intermediate heat exchanger. Centrifugal pump is adopted for primary circulation, which is, together with steam generator, placed inside the reactor vessel. Decay heat is removed with the use of a passive reactor vessel auxiliary cooling system (RVACS), as shown in Fig. XXVI-1. 

In addition to the main cooling system there is an auxiliary cooling system to remove decay heat from the core when the reactor is shut down for refueling, or in an emergracy. The auxiliary cooling system which is separated from the secondary sodium system, has an air cooler in parallel with the steam generator. When it is operating, the primary and secondary sodium are circulated by the primary and secondary main circulation pumps driven by pony motors. 

Specifically, a reactor vessel auxiliary cooling system (RVACS) is adopted that can remove 100% of the decay heat passively, even in total loss of the normal heat sink. In the RVACS, heat generated in the core is conveyed to the reactor vessel by natural circulation of the primary coolant, is conducted across the vessel and the guard vessel and is finally transferred to the atmospheric air naturally flowing on the outer surface of the guard vessel. 

Flow proceeds from the lower plenum, through the core. The steam and water are separated the steam is then dried and passed to the turbine. Other flow (see above) returns to the recirculation system. Feedwater is introduced to the annulus between the core shroud and reactor vessel (Fig. 4). The recirculation system piping is a primary pressure boundary for the high-pressure, high-temperature reactor coolant. Type 304 stainless steel was selected for recirculation system piping and numerous other auxiliary systems (such as the reactor water cleanup system, residual heat removal system, core spray, and other emergency core cooling systems) for its corrosion resistance and adequate mechanical properties. Failures of weld heat affected zones... 

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. 

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 major auxiliary systems of SMART consist of a component cooling system (CCS), purification system and make-up system. The function of the CCS is to remove heat generated in the main coolant pumps (MCPs), control element drive mechanisms (CEDMs), pressurizer (PZR), and the internal shielding tank. Feedwater supplied from the condensate pump of the turbo-generator is used as the coolant to remove heat. The purification system purifies the primary coolant and controls water chemistry to provide reliable and safe operation of the reactor core and all equipment in any mode of operation. The make-up system fills and makes-up the primary coolant in case of a primary system leak and supplies water to the compensating tanks for the PRHRS it consists of two independent trains, each with one positive displacement makeup pump, a makeup tank, and piping and valves. 

A. 1005. All water systems of the facility that have not been described previously shall be discussed in this section. These may include the primary purification system, the service water system, the cooling system for reactor auxiliaries and the primary coolant make-up system. In each case, the information provided should include the design bases, a system description, flow and instrumentation diagrams, a safety evaluation, if required, testing and inspection requirements, and instrumentation requirements. 

An integral primary system layout is employed (Fig. 12.4), ie, reactor core, variable frequency submersible coolant pumps, intermediate heat exchanges, safety system heat exchangers, and cold trap filters. The reactor vessel is enclosed in a guard vessel. There are no auxiliary sodium systems in the primary circuit. The reactor core consists of fuel assemblies, boron shield assemblies, and absorber rods. The central part of the core consists of wrap-spaced hexagonal fuel assemblies and cells with absorber rods. The spent fuel is stored in the reactor vessel for up to 2 years, which facilitates spent fuel cooling and eliminates the need for spent fuel storage casks. Assemblies with boron carbide are placed behind the spent fuel to protect the reactor vessel. 

The HPCS system can operate independently of normal auxiliary AC power, plant service air, or the emergency cooling water system. Operation of the system is automatically initiated from independent redundant signals indicating low reactor vessel water level or high pressure in the primary containment. The system also provides for remote-manual startup, operation, and shutdown. A testable check valve in the discharge line prevents backflow from the reactor pressure vessel when the reactor vessel pressure exceeds the HPCS system pressure such as may occur during initial activation of the system. A low flow bypass system is placed into operation until pump head exceeds the nuclear system pressure and permits flow into the reactor vessel. 

The reactor coolant system interfaces with a number of auxiliary systems, principally the ehemical and volume control system, the normal residual heat removal system, the steam generators, the primary sampling system, the liquid radwaste system and the eomponent cooling water system. 

---