Patent Number: 050531883
Section: claims

1. A reactor system of a boiling water type atomic power plant including a reactor pressure vessel, a primary containment vessel containing the reactor pressure vessel, a main turbine, a main steam piping extending through the primary containment vessel between the reactor pressure vessel and the main turbine, and inside and outside main steam isolation valves provided on the main steam piping inside and outside the primary containment vessel, respectively, at least the outside main steam isolation valve being disposed nearer to a wall of the containment vessel than other valves provided on the main steam piping outside of the containment vessel, at least one of the inside and outside main steam isolation valves being a quick closure valve enabling closure within a period of time of less than 3 seconds required for protection of a turbine at a time of interruption of turbine load, and a volume of the reactor pressure vessel allotted for accommodating steam being sufficient to permit the quick closure valve to quickly close and to mitigate a transient phenomenon associated with a pressure rise in the reactor pressure vessel due to the quick closure of the quick closure valve so as to insure safety and stability of the reactor system. 2. A reactor system as set forth in claim 1, wherein the inside main steam isolation valve is the quick closure valve. 3. A reactor system as set forth in claim 1, wherein the outside main steam isolation valve is the quick closure valve. 4. A reactor system as set forth in claim 1, wherein the reactor pressure vessel, is for a natural circulation reactor. 5. A reactor system as set forth in claim 1, wherein the quick closure valve enables closure within a period of time of about 0.1 second.