Company nameKansai EPCO

Date of occurrence

04.December.2007

Unit nameTakahama 2

EventConfirmation of the Flaws at the Inlet Nozzle Weld ofSteam Generator B

International Nuclear Event Scale (INES)

0Status of report

Interim report

Status when event occurred
During the 24th periodic inspection of Takahama Unit-2, eddy current tests (ECT)*1 for the inner surface of
the inlet nozzle weld of steam generators (SG) A, B, and C were performed from November 25, 2007 until
December 3, 2007 as a feed-back of Mihama Unit-2 where some damage was found at the steamgenerator inlet nozzle weld (600 nickel base alloy is used). The ECTs identified significant signal
indications at the inlet nozzle weld of each steam generator, three (3) for SG-A (maximum length: 7 mm),two (2) for SG-B (max. length: 7 mm) and four (4) for SG-C (max. length: 14 mm).
The ultrasonic tests (UT)*2 were conducted to confirm the flaw depth for nine points on the inlet nozzle
weld of steam generator A,B, and C which showed significant signal indication in the ECT. The maximum
depth of the flaw was confirmed to be about 8 mm (the thickness of the nozzle is about 79 mm) which wasevaluated to fall well below the limit value of 75 mm registered in the Application for the Construction
Permit in accordance with the Electricity Enterprise Law.
*1 Eddy Current Test: Flaw detection test in which the eddy current is applied on the surface of thematerial, a flaw can be detected from the variation of the electromagnetic induction generated on thematerial.
*2 Ultrasonic Test (UT): The test method in which configuration, shape and sizes of the flaws can bemeasured by observing the echoes of the incident ultrasonic wave reflected from the test material.

Summary of examination of cause
Under investigation

Cause of event
Under investigation

Measures to prevent recurrence
To be determined

JANTI-OTO-008-002 attachment2

Takahama Nuclear Power Station Unit-2 Periodic Inspection(Flaw at Steam Generator Inlet Nozzle Weld)
Incidence
Location
System Diagram
Steam Generator Replacement
during the 14th Periodic Inspection

Reactor Containment Vessel
Pressurizer
Steam Generator
To SteamTurbineLower Barrel(Low Alloy Steel)Feed-Water

Stainless Overlay(Stainless Steel)Weld(StainlessSteel)

Reactor
VesselSafety End
Stainless Steel)

RCPTubeSheet

Primary Coolant Pipe
(Stainless Steel)

About
940mm

About79mm

Overlay(600 Nickel Base Alloy)

Partition
Plate

View from SG Side
(0° at the top)

Weld Line(600 Nickel Base Alloy)

Inlet Nozzle

Outlet Nozzle

Check Point during This Inspection
Primary Coolant Flow

Inspection of Steam Generator A
Cross-Sectio
StainlessnOverlay(Outside)
Lower
BarrelECT Results (Significant Indication)(Inside)LengthNo. 1 : About 6mm
No. 2 : About 6mm
No. 3 : About 7mm

Depth
Not Detectable
Not DetectableNot Detectable

LengthNo. 1 : About 5mm
No. 2 : About 7mm

Depth
Not Detectable
About 6mm

LengthNo. 1 : About 9mm

Depth
About 6mm

No. 2 : About
No. 3 : About

Not Detectable
Not Detectable

Overlay
Weld
Safe End

Cross-Sectio

Inspection of Steam Generator B

StainlessnOverlay

ECT Results (Significant Indication)(Outside)
Lower
Barrel(Inside)Overlay
Weld
Safe End
About 79mm
(Registered Value in Construction Permit : 75mm)

Inspection of Steam Generator C
Cross-SectionStainless Overlay(Outside)

Lower
BarrelECT Results (Significant Indication)(Inside)OverlayWeld

Safe EndJANTI-OTO-008-002 attachment28mm
4mm

No. 4 : About 14mm

About8mm