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degree of alarm importance in accordance with the plant events and to actuations of the other alarms at the time the alarm is actuated. The alarm notification (whistling, on-off indication) , alarm acknowledgement (on-off indication becomes a steady indication) and resetting (erasing alarms from the screen when the alarm condition is cleared) are actuated on the alarm VDU.

Alarms are also indicated on the large display panel (static screen) as representing alarms for each system and as alarms attached to major parameter displays/major component symbols.

  1. Operator assisting system

The operator assisting system carries out double checks or replaces operators’ acknowledgment tasks through the positive introduction of computer technology, to reduce the work load of operators and potential human error probability.

The functions of the operator assisting system are as follows:

(D OK monitor

Status of component functioning at actuations of reactor trip system, engineered safety features, etc. are checked by computer systems and the results “OK” or “NG” (no good) are displayed on the large display panel (static display division). For the NG result, the NG component symbol is put on the display and operation VDU so that the individual component failing to function is easily confirmed and identified.

  1. Request for related screen display

Touch operations are done in response to alarms actuated on the alarm VDU, the related monitor and operation screen is displayed on the adjacent monitor and operation VDU, and the related operating manual is displayed on the adjacent operating manual VDU. In addition, an accident diagnosis and guidance function is available which diagnoses plant parameters sat the time of an abnormal or accident condition.

  1. Plant operation management

Computer technology is used positively to enhance efficiency of plant operation management work. Some examples are given below.

© Parameter recording on software: Instead of recording the operating history on conventional

recorders (paper records), data are kept on a hard disk of computer system (software records).

(D Tag management: A computerized tag information management system is adopted, instead of the conventional method of putting tags on the controllers on the control boards in the main control room to arouse attention at remote operation from the main control room during maintenance and testing equipment The new computerized information management system uses tag indications on the monitoring and operation VDU.

  1. Daily recording: Plant parameters are printed automatically on a daily printing format.

  1. Reactor shutdown panel outside the main control room

In order to maintain a reactor at the hot shutdown condition and when required, to bring it to the cold shutdown condition, such operations as residual heat removal, primary coolant temperature and pressure control, volume control, boron supply, etc are necessary. Among the systems required for these operations, those to be operated frequently or quickly at hot shutdown can be preferably operated from the reactor shutdown panel located in an appropriate room outside the main control room. In addition, a required minimum number of parameters is also monitored through this shutdown panel.

The reactor can also be tripped by on-site turbine manual tripping, and by opening the reactor trip breakers from the CRDM power room. Furthermore, on-the-spot control and operating of the important equipment is possible and whenever necessary, the reactor can be brought to the cold shutdown condition by a proper manual procedure.

The control and monitoring instruments installed on the reactor shutdown panel (located outside the main control room) are shown in Table 3.6.7.

  1. Emergency support plan

Reflecting lessons learned from the TMI accident, the emergency support facilities are installed in an appropriate area inside the plant site to provide technical support for the main control room, to order important measures to be taken in the plant,

NSRA, Japan

3-78

Chapter 3 Systems of PWR Nuclear Power Plants

Table 3.6.7 Main equipment in emergency shutdown panel outside main control

Item

Equipment

Monitoring Instrumentation

Primary Coolant Thermometer Primary Coolant Pressure Gauge Pressurizer Water Level Gauge Pressurizer Manometer

Steam Generator Water Level Gauge Steam Generator Pressure Gauge

Operating Equipment

Residual Heat Removal Pump Main Steam Relief Valve Primary Coolant Pump Turbine Driven Auxiliary Feedwater Pump Motor Driven Auxiliary Feedwater Pump Charging Pump Boric Acid Pump Pressurizer Back-up Heater Letdown Orifice Isolation Valve

Reactor Auxiliary Component Cooling Pump Sea Water Pump