replacement works for the steam generator and the … · replacement works for the steam generator...
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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
ge
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.