The primary purpose of the ECCS is to provide coolant makeup to the main circulation circuit. This is required to mitigate the effects of loss-of-coolant accidents or for transients resulting in a loss of main feedwater. The ECCS, Figure 3.1, consists of two subsystems: short-term ECCS and long-term ECCS. The short-term ECCS consists of high pressure accumulators containing emergency coolant and pumped injection from the main feedwater pumps.
This subsystem is activated on signals indicating a break in the main circulation circuit. The purpose of this subsystem is to provide immediate cooling to the failed half of the reactor. The ECCS coolant is therefore
Fig. 3.1 Emergency core cooling system flow diagram [4]:
A - short-term cooling subsystem; B - long-term cooling subsystem; 1 - MCP pressure header; 2 - group distribution header; 3 - ECCS accumulator; 4 - main feedwater pump; 5 - auxiliary feedwater pump; 6 - ECCS pump for pumping water from ACS hot condensate chamber; 7 - ECCS header; 8 - ECCS bypass
Fig. 3.2 Emergency feedwater system flow diagram:
1 - emergency feedwater pump; 2 - feedwater pump; 3 - steam separator; 4 - deaerator
injected into the GDH on the affected side of the reactor. The long-term ECCS consists of six motor-driven ECCS pumps (plus one standby pump) and/or five auxiliary feedwater pumps (plus one standby pump). The primary purpose is to provide the long term reactor coolant inventory control. This coolant is injected into both halves of the reactor.