Management of waler trealment chemicals

Figure 5.1.6 Basic concept of secondary water quality control

i.e. maintenance before component or system failures occur, is the predominant approach for NPP maintenance efforts.

Preventive maintenance is divided into two subcategories, condition monitoring maintenance and planned maintenance. Hie former is based on monitoring the conditions of operating equipment to find any deterioration in its performance or any symptoms of potential failures. Planned maintenance is conducted on a periodical basis with prescribed frequencies and is applied to most of the components and systems of a plant during the periods of plant periodical inspections.

Maintenance to repair failed components or systems is called corrective maintenance, and it is applied to equipment, the maintenance of which during the plant operation does not affect the safety, reliability, and continuous operation of the plant.

2. Plant Maintenance

Japanese nuclear industries have accumulated more than 35 years of experiences in the area of maintenance of PWR NPPs, starting with the commissioning of the Mihama No.l Nuclear Power Plant in 1970. Over time, the plant equipment designs have been improved, and plant maintenance management has been optimized based on findings from the experiences with problems in SGs, fuels, reactor core support pins, and piping, so that plant shutdowns due to such causes rarely occur today, resulting in improved plant availabilities. New equipment developed to rationalize plant maintenance work has contributed to shortening the period for periodical inspections and to reducing the radiation dose received by workers as well.

1. Maintenance Management Policy

(1) Categories of maintenance

Maintenance to keep plant equipment operable is broadly divided into two categories, preventive maintenance and corrective maintenance as shown in Figure 5.2.1.

For stable NPP operation, it is necessary to pay attention not only to its normal operation, but also to the maintenance of plant equipment to avoid problems with components and systems during the plant operation. Hence, preventive maintenance,

[Source] Japan Standard Association, JIS Z8115-2000

Figure 5.2.1 Categories of maintenance management

(2) Preventive maintenance and corrective maintenance

The maintenance of NPPs consists of routine checks and periodical inspections performed during the plant periodical inspection periods.

Routine checks include checks of operating conditions of primary components, periodical checks of the operability of engineered safety systems, and checks of components accessible during the plant operation. The periodical inspections are systematically conducted based on a long-term maintenance plan of the plant equipment, referring to operational records and data gained in the routine check activities. The plant equipment is comprehensively checked and repaired to ensure the safe and reliable operation of the plant until the

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NSRA, Japan