Auxiliary systems residual heat removal system

Fast boron dilutions caused by a rapid and massive injection of pure water into the core. This could happen, for instance, when restarting a main primary pump after a period of shutdown at low residual power and therefore with no, or low level of, natural circulation and with presence of clear water in the loops due to leakages from the connected auxiliary circuits or condensation processes in the steam generator (see AA 4 and SS 7). It should be taken into account that the natural circulation is blocked when the Residual Heat Removal System (RHR) is in operation. In such conditions, in case of total loss or shutdown of the primary pumps, homogeneous conditions are not guaranteed in all the loops. 

Degradation of instrument air systems can lead to failures in safety related systems, including possible common-mode failures. Failures have occurred in several systems, including auxiliary feedwater, residual heat removal, main steam isolation, BWR scram, service water, emergency diesel generators, containment isolation, and fuel pool seals. 

The only identified loss of electrical supply faults would be a loss of ac power to station auxiliaries (see subsection 5.3.5.3), or a loss of power to the normal residual heat removal system... 

The V-sequence refers to a Loss of Coolant Accident (LOCA) through the Low Pressure Coolant Injection System (LPIS), which in this type of nuclear power plants has a common part with the Residual Heat Removal System (RHRS). The suction pipe of the RHRS connects two of the three hot legs in the primary circuit with the RHRS pumps placed into the Auxiliary Building. It has been assumed that three isolation valves fail in one of these pipelines (two of them are motorized valves) a break near the RHR pump has been postulated as a result of the over-pressurization generated in the pipe. 

The passively actuated air system for emergency cooldown (ASEC) provides residual heat removal to the ultimate heat sink (atmospheric air). ASEC is envisaged for reactor cooldown in case of loss of auxiliary power. Each loop of the secondary circuit has an ASEC subsystem (train) the ASEC is connected at the bypass line of the network heat exchangers. 

The CEFR block is shown in Fig. 14.3 (Xu, 2008). It is mainly composed of a reactor cover, a sodium pool, and internal structures. The reactor cover is an approximately 2-m-thick steel-concrete structure that acts as the reactor upper shielding and provides support for the plug, main pumps, intermediate heat exchangers (IHXs), residual heat removal heat exchangers, and the circuits and pipes of various auxiliary systems. The driving mechanisms of control and safety, the fuel manipulator, and various measurement instruments are all fixed on the small plugs of the plug system. 

No specific auxiliary feedwater system is included in the design residual heat can be removed by a number of non safety systems ... 

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 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. 

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. 

Core Heat Removal Main Feedwater System Auxiliary Feedwater System Residual Heat Removal System... 

In indirect cycle reactors (PWRs), if there is no separate emergency feedwater system, the auxiliary feedwater system is used as a safety system (emergency feedwater system) to remove residual heat from the RCS. The transfer of heat to the ultimate heat sink could be effected through the pressure relief devices of the steam generator or through the condenser. 

In BWRs, the auxiliary feedwater system is usually termed the reactor core isolation cooling system. This system is used to maintain the water level in the reactor vessel in the event of a loss of feedwater in hot shutdown conditions (in such an event residual heat is removed from the reactor core by means of the release of steam through safety relief valves to a suppression pool). Another function of this system is to supply the necessary inventory of reactor coolant in the event of a small loss of coolant during normal operation. 

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