Emergency equipment cooling system

As a general rule, sources of heat such as fired heaters and steam reboilers should be shut down as an emergency develops. Cooling systems should continue to operate because they remove heat from the system. Utilities, such as the steam and air supplies, should remain in operation in order to retain control of the equipment that is still in operation. 

In ofT-normal situations, a reactor trip is initiated by rapid insertion (velocity about 2 m/s) of all control rods into the reactor core. In addition, sodium borate solution can be injected into the reactor pressure vessel, thus ensuring subcriticality of the core even in case the control rods fail to operate. In order to deal with the consequences of a loss-of-coolant accident, BWR plants are equipped with an emergency core cooling system similar to that in PWR plants, consisting of high-pressure and low-pressure injection systems and recirculation systems. By the action of these systems, sufficient removal of the decay heat is guaranteed so that no serious overheating of the fuel rods can occur. 

The RBMK-1000 plants are equipped with safety systems which are designed to cope with loss-of-coolant and station blackout accidents. These are, in particular, an emergency core cooling system, an emergency feedwater system, a system for condensation chamber cooling and the emergency power supply. The emer-... 

The plant model includes eight different safety systems that are mostly four-redundant. The safety systems are divided into two separate subsystems Reactor Protection System (RPS) and Diverse Protection System (DPS), which are implemented on different automation hardware. The RPS safety systems are automatic depressurisation system (ADS), component cooling water system (CCW), emergency core cooling system (ECC), service water system (SWS) and residual heat removal system (RHR). The DPS safety systems are emergency feed water system (EFW), and main feed water system (MFW). In addition, the AC power system belongs to both RPS and DPS. The model describes the operation logic of the safety systems, the hardware equipment used to implement each system, and the associated failure modes for each piece of equipment. 

In Siemens/KWU-plants (except Wiirgassen), the core spray system may exist but is not necessary, as they are not equipped with external recirculation lines. Due to this, no large leaks or breaks can occur below the core level. Maximum leak sizes to be postulated in the lower part of the RPV can be controlled in these plants by the emergency core cooling system. 

Now let us consider utility failure as a cause of overpressure. Failure of the utility supphes (e.g., electric power, cooling water, steam, instrument air or instrument power, or fuel) to refinery plant facihties wiU in many instances result in emergency conditions with potential for overpressuring equipment. Although utility supply systems are designed for reliability by the appropriate selection of multiple generation and distribution systems, spare equipment, backup systems, etc., the possibility of failure still remains. Possible failure mechanisms of each utility must, therefore, be examined and evaluated to determine the associated requirements for overpressure protection. The basic rules for these considerations are as follows ... 

The control of the nuclear and chemical reactivity in case of accidents is insured by the emergency shutdown systems. The safety function devoted to the thermal power extraction from the HYPP is directly linked to the control of the chemical reactivity because the kinetics of chemical reactions increases with the temperature. The HYPP must be cooled by emergency systems, water streaming on equipments, spraying systems, and so on. 

When considering the above Ust, remember the time, equipment, or systems used for controlling the process in the normal manner may not be available. Loss of equipment and controls may mean the user cannot cool, purge, or drain the process before or after the emergency. 

As in the case of the emergency cooling systems, the safety-related auxiliary electrical power supply equipment is divided into four independent and physically separated parts, or subdivisions, and the reactor protection system operates on a 2-out-of-4 logic for signal transmission and actuation. 

Cooling of the secondary loop and the electric equipment room is performed by forced open cycle ventilation. The switch board room and the room where Ae coastdown system is situated, are cooled by a heat storage system in the event of loss of power, so that the temperature in each of these rooms is not elevated during loss of power for a long period. As a result, an emergency HVAC system and water cooling system as the final heat sink of the HVAC system are not required. 

To provide for redundancy of emergency cooling systems, the primary circuit is equipped with an auxiliary air cooling system based on multiple small size heat pipes. 

As long as the gas turbine serves as a passive cooling system, it can generate electricity for the NPP electric machinery and systems even after the reactor shutdown in other words, the gas turbine also provides the BN GT plant with a passive source of electricity. Electricity supply redundancy is achieved by placing an accumulator battery and an oil-fired emergency generator in the transportable module of the main equipment. 

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