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(2) Major work activities for turbine system

While inspections and checks of the reactor system are performed in the reactor building, in parallel with these, inspections of the turbine system are conducted in the turbine building.

Inspections of the turbine system are performed and also, repairs are made if needed while paying attention to the following items.

  1. Evidence of steam leak trace (especially for joints)

  2. Denting, deforming and bending occurrence

  3. Evidence of contact between rotating parts and stationary parts

  4. Presence of foreign materials

  5. Erosion and wearing occurrence

  6. Attached foreign materials

  7. Changes of color and rusting

  8. Looseness of fastenings, etc.

Before starting overhaul inspections, data on inspection records of the previous inspection time and operating records (casing temperature, bearing temperature, existence of contact during turbine turning, oil leak, rotor elongation and elongation difference, vibration) are organized and checked, and protection of openings and the layout of disassembled parts are also carefully planned.

In addition, as the period allotted to the periodic inspection concerned gets shorter, the turbine overhaul inspection of the turbine system is likely to become a critical path for periodic inspection.

i) Turbine inspection

The upper half sections of the high pressure casing, low pressure casings, and bearings are removed when the turbine internal temperature has reached room temperature, and then clearance measurements at each portion, deflection measurements, centering checks, and disassembly of the thrust bearing are performed.

After that, rotors and lower half sections are taken out and the following inspections are performed in parallel.

  1. Turbine main body inspection (casing level measurement, casing inspection)

  2. Rotor inspection

  3. Rotor coupling inspection

  4. Blade inspection

  5. Nozzle diaphragm inspection

  6. Bearing inspection

  1. Labyrinth packing inspection

  2. Turning device inspection

  3. Control device inspection etc.

In the course of these inspections, removal of impurities, cleaning, nondestructive tests and maintenance as required due to the test results, are conducted along with operational adjustment, and clearance measurements, etc.

ii) Inspection of turbine major valves etc.

In parallel with the turbine inspection, main steam stop valves, steam control valves, combined intercept valves, and turbine bypass valves are disassembled, and care and cleaning of each part, clearance measurements, flaw inspections, valve seat lapping, and actuation tests, etc. are performed. The turbine main body and major valves are assembled while making dimensional measurements of each part, and oil flushing is done after completion of their assembly.

In parallel with the turbine main body inspection, internal inspections of the main condenser and moisture separators and measurements of pipe wall thickness are performed, the integrity of their internal structures are confirmed and their care and cleaning are performed as necessary. The vacuum development test of the main condenser is performed after all of the work activities on the turbine system have been completed to confirm that there is no problem for plant startup.

  1. Other major work activities

i) Inspection and replacement of reactor recirculation pump mechanical seal

Since reactor recirculation pumps are installed in the reactor containment (which is filled with nitrogen gas during plant operation) and their shaft seals are two-stage seals to accommodate the pressure difference of 7 MPa (gage) between their inside and outside, they are usually inspected and replaced during every periodic inspection and check.

A cross-sectional diagram of the reactor recirculation pump is shown in Figure 4.2.4.

The mechanical seal is built in a seal cartridge, and its inspection and replacement are performed as follows.

  1. The reactor recirculation pump inlet and outlet valves are closed, and water in the pump is

NSRA, Japan

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