Emergency core cooling system ECCS

Safety. A large inventory of radioactive fission products is present in any reactor fuel where the reactor has been operated for times on the order of months. In steady state, radioactive decay heat amounts to about 5% of fission heat, and continues after a reactor is shut down. If cooling is not provided, decay heat can melt fuel rods, causing release of the contents. Protection against a loss-of-coolant accident (LOCA), eg, a primary coolant pipe break, is required. Power reactors have an emergency core cooling system (ECCS) that comes into play upon initiation of a LOCA. 

Emergency core cooling system (ECCS) disconnected. Apparently this is not necessary for the turbo-alternator power rundown test as planned... 

The containment sump should be designed to permit mixing of emergency core cooling system (ECCS) and spray solutions. Drains to the engineered safety features sump should be provided for all regions of the containment which would collect a significant quantity of the spray solution. Alternatively, allowance should be made for dead volumes in the determination of the pH of the sump solution and the quantities of additives injected. 

The reactor is assisted by the following Emergency Core Cooling Systems (ECCS) ... 

Generic Safety Issue (GSI) C-04 in NUREG-0933 (Reference 1), addresses changes that can be made to the conservative statistical method for the Emergency Core Cooling System (ECCS) evaluation model. 

Systems That Shut Down the Reactor in the Case of Accidents The emergency core cooling system (ECCS) fulfils this purpose. It is a system that refills the reactor fuel channels with light water to remove residual or decay heat from the fuel. The fuel requires heavy water for the reactor to go critical and the light water of the ECCS suppresses criticality. There is no need to add boron to the ECCS water. 

The primary circuit pipelines being cormected to the hot parts of the circuit with nozzles located on the reactor vessel above the core, which limits the outflow in loss of coolant accidents and facilitates reduced requirements to flow characteristics of the emergency core cooling system (ECCS) ... 

System of emergency water supply from the emergency core cooling system (ECCS) pumps and recirculation pumps ... 

As it follows from Fig. X-5, the evolution of this accident for the VKR-MT and a WER-1000 is essentially different. In VVER-1000, the temperature of zirconium claddings increases promptly due to high-temperature heat accumulated in the uranium dioxide pellets and due to heat removal deterioration. The VKR-MT core is practically not heated in the first seconds of the accident process, as the temperatures of micro fuel elements and the coolant in normal operation are different by a few degrees only. Later on, the temperature of micro fuel elements slightly increases due to residual heat up until the start-up of the emergency core cooling system (ECCS) operation. The accident is localized after the core is filled with the ECCS water. As the temperature of micro fuel elements is well below 1500°C, the release of radioactivity to the containment remains at the level of 10. ... 

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 the event of a LOCA, the nuclear reaction in the core would be automatically cut off by the loss of the moderation associated with the coolant, while in the transient case the probability of failure of the shutdown systems is sufficiently low that continued operation at power is not a significant contributor to a core melt situation. For both classes of accident, therefore, the important requirement is the maintenance of a cooling capability sufficient to remove decay heat (see Table 12.7) from the reactor core. The emergency core cooling systems (ECCS) for the PWR and BWR are described below. 

Besides the inherent safety characteristics of SMART, its safety is further enhanced by highly reliable engineered safety systems. These are designed to function passively on demand and consist of a reactor shutdown system, passive residual heat removal system (PRHRS), emergency core cooling system (ECCS), safeguard vessel, reactor overpressure protection system (ROPS) and containment overpressure protection system (COPS). 

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