Patent Number: 
Section: claims

1. An emergency core cooling system provided for a boiling water reactor plant comprising:three safety divisions for an active safety system, each of said safety divisions including a high pressure core cooling system having no less than 100% of the injection capacity required for cooling a reactor core at a design basis accident, a low pressure core cooling system having no less than 100% of the injection capacity required for cooling the reactor core at the design basis accident, a residual heat removal system, which is commonly used as the low pressure core cooling system, having no less than 100% of a heat removal capacity required for cooling the reactor core and a containment vessel at the design basis accident, and an emergency power supply source for feeding electric power to the high pressure core cooling system, the low pressure core cooling system, and the residual heat removal system; andat least one safety division for a passive safety system including an isolation condenser that cools and safely shuts down the reactor core for no less than 8 hours without replenishing cooling water even when a fire in a first safety division for the active safety system, a single failure in a second safety division for the active safety system and online maintenance in a third safety division for the active safety system occur simultaneously,wherein the active safety system does not include a pre-stage booster pump of which failure can cause a loss of whole function of one safety division. 2. The system according to claim 1, wherein the emergency power supply source provided in each of the safety divisions for the active safety system includes at least one emergency diesel generator. 3. The system according to claim 2, wherein the emergency power supply source includes at least one auxiliary gas turbine generator in each of the safety divisions for the active safety system. 4. The system according to claim 2, wherein the emergency power supply source provided in each of the safety divisions for the active safety system is connected to at least one shared gas turbine generator, said shared gas turbine generator being equipped outside of the safety divisions for the active safety system and shared among the safety divisions for the active safety system. 5. The system according to claim 1, wherein the safety division for the passive safety system further includes a passive containment cooling system. 6. The system according to claim 5, wherein the safety division for the passive safety system further includes a gravity-driven core cooling system. 7. The system according to claim 1, wherein the low pressure core cooling system provided in each of the safety divisions for the active safety system further includes a containment spray system comprising a containment spray header, a containment spray header connecting pipe, and a containment spray injection valve for spraying cooling water into the containment vessel. 8. The system according to claim 1, wherein the residual heat removal system is provided independently of the low pressure core cooling system in each of the safety divisions for the active safety system, said residual heat removal system including a containment spray system comprising a containment spray header, a containment spray header connecting pipe, and a containment spray injection valve for spraying cooling water into the containment vessel. 9. A boiling water reactor plant comprising:a reactor pressure vessel containing a reactor core;a containment vessel containing the reactor pressure vessel;an emergency core cooling system having three safety divisions for an active safety system, each of said safety divisions for the active safety system including a high pressure core cooling system having no less than 100% of the injection capacity required for cooling the reactor core at a design basis accident, a low pressure core cooling system having no less than 100% of the injection capacity required for cooling the reactor core at the design basis accident, a residual heat removal system, which is commonly used as the low pressure core cooling system, having no less than 100% of a heat removal capacity required for cooling the reactor core and the containment vessel at the design basis accident, and an emergency power supply source for feeding electric power to the high pressure core cooling system, the low pressure core cooling system, and the residual heat removal system; andat least one safety division for a passive safety system including an isolation condenser that cools and safely shuts down the reactor core for no less than 8 hours without replenishing cooling water even when a fire in a first safety division for the active safety system, a single failure in a second safety division for the active safety system and online maintenance in a third safety division for the active safety system occur simultaneously,wherein the active safety system does not include a pre-stage booster pump of which failure can cause a loss of whole function of one safety division.