Control system during maintenance shutdown

4 Control System During Maintenance Shutdown. When the reactor is 

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The 4S employs a reactivity control system with an annular reflector in place of the control rods and driving mechanisms which traditionally require frequent maintenance service. Reactivity is controlled only by the vertical movement of the annular reflector during plant startup, shutdown and power generation, thus eliminating the necessity for complicated control rod operations. Although this reactivity control method using a reflector has been studied in some projects using this method for the core bum-up phase is a new approach. 

An important area where improved reactor-system design and operation have been achieved is in the control of all aspects of coolant chemistry. The major development here has been the identification of the factors controlling movement of corrosion products by the coolant into the reactor core where they are activated, and the subsequent deposition of these radioactive species on out-reactor components causing radiation fields that may interfere with maintenance work during shutdowns. In commercial CANDU reactors the fields from such long-lived radioactivity have been controlled successfully to low values (17). 

Operations personnel should be cognizant of and have control over the detailed status of the plant systems and equipment during shutdown mode. The shift supervisor must be informed of maintenance activities affecting the status of systems and equipment. All work conducted at the plant has to be planned, analysed and executed in a manner that is consistent with the requirements of the shutdown mode. Effective interface between the operation and maintenance groups (including contractors), is essential. 

Wet standpipes are typically designed for use by properly trained occupants to protect the people and contents of the building. These systems have a constant supply of water and are smaller in diameter for occupants use. The loss-control representative of the insurance company attempts to ensure, through the insurance contract, all suppression systems are operating at all times or standby substitute arrangements are in place during periods of shutdown for maintenance and repair. 

Even the best design cannot be expected to anticipate all conditions that may arise during the life of a system. Corrosion inspection and monitoring are used to determine the condition of a system and to determine how well corrosion control and maintenance programs are performing. Traditional corrosion inspection practices typically require planned periodic shutdowns or service interruptions to allow the inspection process. These scheduled interruptions may be costly in terms of productivity losses, restart energy, equipment availability, and material costs. However, accidental interruptions or shutdowns are potentially much more disruptive and expensive. 

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