Replacement Works for the Steam Generator and the … · Replacement Works for the Steam Generator and the Reactor Pressure Vessel Upper Head ... (model 51M) New steam generator ...

Unit 2, Genkai Nuclear Power Plant

Replacement Works for the Steam Generator and the Reactor Pressure Vessel Upper Head

Replacement works for the above components were conducted at Unit 2 of the Genkai Nuclear Power Plant during its 16th scheduled inspection (between March and October 2001). In the following, the details of the replacement works are described.

KYUSHU ELECTIRC POWER CO.,INC.

Outline of the Replacement Work for the Steam Generator of Unit 2 of the Genkai Nuclear Power Plant

Former steam generator (model 51M) New steam generator (model 54F)

Improvement of the steady armsIncrease in reinforcement from a two-arm assembly to a three-arm one

Improvement of the small-radius U-bendHeat-treatment-based reduction of residual stress

Enlargement of the heat transfer area(An increase in the number of tube support plates from seven to eight)

Improvement of the heat transfer tube materialReplacement of alloy MA600 with alloy TT690

Improvement of the tube support platesReplacement of round holes with four-wing-shaped

holesReplacement of carbon steel material with stainless

steel material

Change in the tube plate enlargement work methodUse of a roller in combination with an enlargement

of the tube with rubber was replaced by use of hydraulic pressure in combination with an enlargement of the tube with a roller

Map Showing the Route of Transportation of the Former Steam Generator in the Site

Chigasaki

Solid w

aste

stora

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Radioa

ctive

was

te

dispo

sal b

uildin

gBuil

dings

surro

undin

g

the re

actor

Unit-4

re

actor

Reacto

r au

xiliar

y bu

ilding

Unit-3

re

actor

Turb

ine bu

ilding

Office

build

ing

Switch

yard

Intakes for Unit-3 and Unit-4 reactors

Cask s

torag

e buil

ding

Reacto

r con

tainm

ent

Unit-2

re

actor

Unit-1

re

actor

Turb

ine bu

ilding

Reacto

r aux

iliary

build

ing

Office

build

ing

EL+11

.0m

Switch y

ard

EL+16

.0m

Incinerator building

Solid waste storage

Steam generator storage

Intakes for Unit-1 and Unit-2 reactors

Hokawazuura

Discharge structures for Unit-3 and Unit-4 reactors

Hattaura

Discharge structures for Unit-1 and Unit-2 reactors

EL+11

.0m

Measures Taken to Reduce the Dose during the Replacement Work for the Steam Generator of Unit 2 of the Genkai Nuclear Power Plant

＊ Decontamination of the inner surface of the reactor coolant mainpipe and application of a shielding plug to it after cutting of the pipe

＊ Application of lead shielding onto the outer surface of the reactor coolant main pipe

＊ Use of remote-operated automatic machines (automatic cutting machines, automatic edge preparation machines, and automatic welding machines for piping use)*1

*1 : This includes the effect of operability improvement resulting from training on mockups.

Decontamination of the Inner Surface of the Reactor Coolant Main Pipe and Application of a Shielding Plug to It

MCP physical (blast) decontamination

Shielding plug

Cutting line

Portion to be decontaminated

Cutting line

Shut-off lid

Decontaminating device

Abrasive recovery nozzle

Isolation lid

(Abrasive and compressed air)

Abrasive

(Compressed air)

Abrasive recovery hopper

(Abrasive) Service exhaust duct

(Oxide film)

Separator

Ejector

Shielded drum

Reactor coolant main pipe

Shielding plug

S G

S G

Air tank

Filter

Application of Lead Shielding onto the Outer Surface of the Reactor Coolant Main Pipe

Cutaway view

Shielding material

Reactor coolant main pipe

S G

Use of Automatic Remote-operated Machines

Automatic cutting machine

Automatic edge preparation machine

Automatic welding machine

Fastening fittings

Hydraulic cutting motor

Cutting tool

Tool holderAnchor block Reactor coolant

main pipe

S G

Inside the loop chamber

Welding wire

Ultra-compact camera

Movable carriage

LightReactor coolant

main pipeRail

Welding torch

Power supply

Fixed frame

Feed motor

Gear box

Rotary frame

Tool holder

Anchor block

Hydraulic motor

Reactor coolant main pipe

S G

Outline of the Replacement Work for the Reactor Pressure Vessel Upper Head of Unit 2 of the Genkai Nuclear Power Plant

Former reactor pressure vessel upper head

New reactor pressure vessel upper head

Control rod cluster drive mechanism (CRDM)

Spare nipple

Spare control rod cluster drive mechanism

Part length control rodCluster drive mechanism

Control rod cluster drive mechanism

Removal

Elimination of canopy sealsCRDM housing

Change of materialSUS F316 replacing a material

equivalent to SUS 304

Change of sparesSpare CRDM instead of spare nipples

Change in the nipple materialINCONEL 690 replacing INCONEL 600

Forged monoblock structure

Measures taken to reduce the dose during the replacement work for the reactor pressure vessel upper head of Unit 2 of the GenkaiNuclear Power Plant

＊ Reduction in working hours through the use of the automatic reactor vessel stud hole brushing machine

＊ Reduction in working hours through the use of the fully-automatic reactor vessel stud bolt handling machine

＊ Reduction in working hours through the integration of reactor vessel upper internals

Use of the Automatic Reactor Vessel Stud Hole Brushing Machine

Vacuum suction apparatus

Air supply apparatusApparatus control panel

Suction hose

Brushing machine main body

Reactor pressure vessel upper head flange

Reactor vessel stud bolt hole

Use of the Fully-automatic Reactor Vessel Stud Bolt Handling Machine

Control panel

Reactor pressure vessel

Hydraulic unit

Stud bolt

Tensioning apparatus

Control panel

Guide rail

Integration of Reactor Vessel Upper Internals

Joining ductMovable cable bridge

Missile shield

Ring duct

Measures Taken to Reduce the Dose in Unit 2 of the Genkai Nuclear Power Plant and the Effects Achieved by the Measures Taken

7.6217.55Reduction in working hours through the integration of reactor vessel upper internals

9.2216.50Reduction in working hours through the use of the fully-automatic reactor vessel stud bolt handling machine

0.872.49Reduction in working hours through the use of the automatic reactor vessel stud hole brushing machineReplacement work for

the reactor pressure vessel upper headTrack record value

0.10 man Sv

47.58128.59Use of remote-operated automatic machines (automatic cutting machines, automatic edge preparation machines, and automatic welding machines for piping use)*1

403.83869.98Application of lead shielding on the outer surface of the reactor coolant main pipe

49.98651.15Decontamination of the inner surface of the reactor coolant main pipe and application of a shielding plug to it

Replacement work for the steam generatorTrack record value

0.88 man Sv

After the measure was

taken

Before the measure was

taken*2

EffectDescription

*1: This includes the effect of operability improvement resulting from training on mockups.*2: Values calculated on the basis of exposure track records (dose values) under the assumption that the

dose reduction measures are not taken

Unit: (man mSv)

Measures in Chemical Control Taken to Reduce the Dose in Unit 2 of the Genkai Nuclear Power Plant

・ Early removal of dissolved oxygenAt the startup(at the time of filling RCS with water), vacuum venting machines and gas stripper packages are used to remove dissolved oxygen at an early stage, thereby making the atmosphere reductive to suppress the elution of Ni and Cr from the new steam generator.

・ Control of dissolved hydrogen at a low levelBy keeping the dissolved hydrogen concentration at a lower level during power operation, the amount of Ni on the fuel surface is lowered.

・ Removal of new outer layer cladBy adding H2O2 at shutdown (when the cold shutdown state is reached) to keep the dissolved hydrogen concentration at a lower level, the removal of Ni and Co-58 is accelerated.

Graph Showing the Change in Dose at Scheduled Inspections for Unit 2of the Genkai Nuclear Power Plant

0.71

1.22 1.161.27 1.28

1.06

1.56

1.221.05

1.41 1.55 1.601.76 1.69 1.67

2.09

1.200.86

1.09

0.00

0.50

1.00

1.50

2.00

2.50

3.00

3.50

1st 2nd 3rd 4th 5th 6th 7th 8th 9th 10th 11th 12th 13th 14th 15th 16th 17th 18th 19th

man sV

SGR・VHR

Summary

In the replacement works described above, taking different dose reduction measures suitable to individual work specifics allowed us to achieve greater dose reduction effectiveness.

Recently, factors contributing to an increase in dose associated with inspection and maintenance activities have occurred; in ordinary scheduled inspections, however, taking various dose reduction measures as described above helps to secure dose reduction effectiveness.

We will continue studying new dose reduction measures to further cut down on dosage.

KYUSHU ELECTIRC POWER CO.,INC.