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located outside of the containment

  1. 0Utline of other major activities

  1. Steam turbine

Inspections of the steam turbines of NPPs are basically the same as their inspections in FPPs, and they go through the steps of opening, cleaning, checking, maintaining/repairing and restoring. Results of previous periodic inspections and recent operational performance are taken into consideration. The main steps for high pressure and low pressure turbine inspections are described below.

  1. Opening/disassembling

When a series of periodical inspections is started, the steam turbine is slowly cooled down for at least 48 hours with the turbine kept rotating by a rotating gear system, until the metal temperature is decreased to below 150X3 . While the steam turbine is being cooled, its metal covers and insulators are removed, and during the latter half of the cooling period, the foundation bolts of the turbine casings are loosened to allow the

casings to shrink. In the work to lift and remove the turbine casings, the internal structures and the upper halves of the blade rings, great care is taken because of the narrow gaps between the turbine casing and the internal components and attention is also paid to the levelness of lifted items.

Conditions of sub-components of the turbine rotors are checked and gaps between their parts are measured and recorded. After the bearing covers are removed and the shaft couplings are disconnected, the turbine rotors are lifted up and moved to racks provided with rotating mechanisms. Finally the lower halves of the blade rings and internal structures are lifted and removed.

  1. Cleaning, checks and repairs

Conditions of disassembled sub-components and parts are recorded and cleanings, checks and repairs are made if necessary. Items for checks are listed in Table 5.2.2.

  1. Reassembling and test runs

Overhauled components and parts are

Table 5.2.2 Overhaul inspection required by regulations

Steam Turbine

(l)Shell

(2) Shaft, Wheels, Buckets

(3)Diaphragms, Nozzles, Diaphragm Nozzles

  1. Bearings

  2. Main Valves

' Main Steam Stop Valve Steam Control Valve Reheat Steam Stop Valve Intermediate Stop Valve

Overhaul

( a. Removing upper shell, inspection shall be performed with diaphragms and labyrinth packings.

b. Shell flange bolts inspection shall be performed.

Overhaul.

f a. Shaft shall not be removed, the following inspection shall be performed with shaft rotating carefully

  1. Shaft

  2. Wheels

  3. Buckets and their Joint

  4. Shrouds

. (e) Condition of Balance Weight

Overhaul

s a. Diaphragm Inspection etc, shall be performed with the condition that they are fixed on the shaft.

Overhaul

Overhaul

- a. Overhaul Each Valve, Inspection for Strainer, Valve Body, Valve Seat, Valve Stem, Bolts and Nuts shall be

. performed.

NSRA, Japan

5-24