and the turbine building, and check the states of equipment and systems.

vii )Responses to anomalies

Operators respond to anomalies according to the levels of seriousness of the events. Their responses range from only follow-up activities of monitoring anomalies in equipment or systems identified in surveillances, patrol checks, etc., or determining causes, or temporarily isolating affected equipment, to emergency actions taken in cases of actuation of alarms and automatic protection systems, including confirmation of emergency situations and identification of events, presumption of the cause(s), responding actions in accordance with the emergency procedures, and notification and reporting.

6. Other activities

Operators may perform minor repair work themselves, or request repair work by maintenance personnel if any significant discrepancies are found. They may isolate systems to be repaired, and return them to service after repair work is completed.

4. Plant Shutdown

The reactor power is automatically decreased with the automatic insertion of control rod clusters into the reactor core by the control rod control system when the turbine load decreases from the plant rated power to 15%. Once the reactor power reaches 15%, the operation mode of the rod control system is switched from automatic to manual and the reactor power is gradually lowered to zero. According to the plant operation plan, the reactor is either kept in the standby state with the core at the critical condition, or shut down for a long period. For the long time hot shutdown, the boron concentration in the reactor coolant is increased to and kept at a value which is prescribed in consideration of the xenon decay in the core.

When the plant is shut down to cold conditions for periodical inspections of the plant, the boron concentration in the reactor coolant is increased to a specified value corresponding to refueling outage, or at least to cold shutdown of the plant Subsequently, the reactor coolant system is cooled by the turbine bypass control system at a specified rate, observing the pressure-temperature limitation curve for cool­down. Concurrent with the cooling down of the

NSRA, Japan

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