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Chapler 5 Operation and Maintenance of PWR Plants

Axial Neutron Flux Deviation AK3D

Range of Neutron Flux Deviation and Corresponding Axial Offset Range, (at around the initial core life)

Neutron Flux Dev,iation(Al) = PT-PB

Pj Pj Al

Axial Offset (A • 0) = X10Q = —xlOO

Pt+Pb P

Figure 5.1.4 Constant axial offset control relating diagram

  1. Operator Activities during Plant Normal Operation

The following are the main activities performed by operators during the plant normal operation.

  1. )To grasp the performance and conditions of the plant equipment at all times through activities including:

  1. monitoring the state of the plant with instruments and displays;

  2. pre-evaluating the objectives, procedures and results of operations; and

  3. confirming the conditions of components.

  1. )To ensure that important keys and operating records are handed over to the next shift crew and

that the crew are briefed about the plant operating states, when a three- or two-shift operation system is applied to the plant.

  1. To regularly patrol the following facilities and equipment at least once a day and check them directly or indirectly:

  1. the reactor coolant system equipment;

  2. the control rod drive mechanism equipment;

  3. the power supply, the water supply/discharge and the air exhaust systems equipment; and

  4. other specified facilities.

  1. To observe the operational limitations including the reactor thermal limits, pressurizer safety and relief valves set points and the reactor protection circuit set points.

v )To understand the operational requirements of the control rods, the chemical and volume control system, the safety injection system, etc. and to follow them.

  1. To follow instructions of the reactor chief engineer for the reactor operation to ensure the plant security.

  2. ,To investigate the cause of any inadvertent reactor trip occurrence, to take necessary actions and to confirm the reactor safety, and to restart the reactor after approval by the station chief. However, when the cause of a reactor trip is either of the following cases, the operator can restart the reactor without approval of the station chief:

  1. the trip was caused by a ripple effect of an off­site electrical fault, or done intentionally to prevent ripple effects from expanding; or

  2. the reactor was hipped to protect the security of the plant from potential significant effects caused by natural hazards including fires, winds and tidal waves.

Including the operations for the core burnup compensation discussed in 5.1.3 above, various activities must be performed by operators during the plant normal operation as summarized below.

  1. Monitoring and recording of the plant main parameters

The plant main parameters are checked on various indicators and recorders to confirm the plant safety and reliability.

ii ) Burn-up compensation

iii) Treatment of radioactive wastes

This includes operation of gas and liquid waste

5 9

NSRA, Japan

disposal systems, disposal of wastes, operation of the asphalt solidification facility and the incinerator, and packing of miscellaneous noncombustible solids in drums.

  1. Periodical switching over and test run of redundant equipment

Auxiliary components continuously operated during the plant normal operation usually have one or two backup components, so that any loss may not cause loss of the system function. Since uneven operation of components, i.e. large differences in their operating times, is not desirable for extending their lifetimes, operating auxiliary components are periodically switched over to other components. Components not operated in a long while are periodically run to check their operability.

  1. Periodical testing of safety systems

Some systems staying at the standby mode during the plant normal operation are ready to meet plant safe shutdown under any condition. They are used when the plant is normally shut down, or urgently shut down after an accident or emergency occurs. These systems are periodically tested and their operability and reliability is confirmed. Table 5.1.1 shows examples of some periodically tested systems.

  1. Periodical patrols

An important duty of plant operators is to prevent accidents and trouble by monitoring and checking operating conditions of the equipment and detecting anomalies such as fires, leakages of steam, water, oil, and so on at their early stages, and by checking the standby equipment during the plant normal operation. Hence, plant operators periodically patrol in the reactor containment, the auxiliary building

Table5.1.1 Example of periodic test

System name

Test items

Frequency

High pressure injection system

Pump opereation motor operated valve operation test

Once a month during power operation

Low pressure injection system

Ditto

Ditto

Disel genereator

Startup test

Ditto

Auxiliary feed water system

Pump opereation test motor operated valve operation test

Ditto

Containment spray system

Ditto

Ditto