Company nameKansai EPCO

Date of occurrence

4, February, 2008

Unit nameTakahama 3

EventConfirmation of Flaws at the Welds of Primary Coolant
Inlet Nozzle of Steam Generators

International Nuclear Event Scale (INES)

0

Status of report

Interim report

Status when event occurred
During the 18th periodic inspection outage, shot-peening work*1 was scheduled to be performed, as apreventive maintenance of stress corrosion cracking, on the inner surfaces of welds (6 locations of welds
in total) of the primary coolant outlet and inlet nozzles of 3 steam generators (hereafter referred to as“SG”), in considering that stress corrosion cracking events at nickel base alloy 600 welds have occurred inJapan and aboard.
When the eddy current test (hereafter referred to as “ECT”)*2 was conducted on the inner surface of therelevant welds in advance from January 12 to 25 for preparation of this work, significant indications wereidentified at the inlet nozzle weld of each steam generator, i.e., 7 for SG-A (maximum length: about 28mm), 16 for SG-B (maximum length: about 38 mm), and 9 for SG-C (maximum length: about 14 mm)(Multiple imminent indications were evaluated to be continuous.).
In order to identify the depth of flaw, the ultrasonic test (hereafter referred to as “UT”)*3 was conducted for
32 locations in the SG inlet nozzle welds, where significant indications were identified by the ECT. As aresult of the UT, it was evaluated that the wall thicknesses of 11 locations of the inlet nozzle weld of SGs intotal, i.e., 2 for SG-A (maximum depth: about 9 mm), 6 for SG-B (maximum depth: about 15 mm), and 3 for
SG-C (maximum depth: about 9 mm), were less than 75.26 mm which is specified in the application ofapproval for construction plan subject to the Electric Utility Industry Law.
Checks such as observation of metal structure by SUMP method*4 will be conducted to investigate
causes. There was no impact of radioactivity to the environment due to this event.
*1: Shot-peening work
This work is to make tensile residual stress as compressive stress by peening metal balls on metal
surfaces with high velocity.
*2: Eddy current test (ECT)This method detects flaws by the change of electromagnetic induction generated in the materials by
putting an eddy current on the material surface.
*3: Ultrasonic test (UT)The test is to measure the configuration, shape and size of the flaw by observing echoes of ultrasonicwave reflected from the flaw.
*4: SUMP method

JANTI-OTO-008-002 attachment3

The method is to make a photo image by putting film on the surface of the damaged portion, and toobserve it by microscope.

Summary of examination of cause
Under investigation
Cause of event
Under investigation
Measures to prevent recurrenceTo be determined

JANTI-OTO-008-002 attachment3

Takahama Power Station Unit 3
Flaws at Inlet Nozzle Welds of Steam Generators
Location offailure
System Diagram
Reactorcontainment
Pressurizer
Steam generator

Lower barrel(Carbon steel)

To steamturbineFeedwater

Stainless overlay(Stainless steel)Primary coolant
piping weld
(Stainless steel)

ReactorvesselSafe end(Stainless steel)Primarycoolant pumpPrimary coolant piping(Stainless steel)

About 940 mm

Overlay(Nickel base alloy 600)

Tube sheet

View from steam
generator sideo(0 is upper side)Girth weld
(Nickel base alloy 600)

Partition
plate
Primarycoolant
inlet nozzle

Primary coolant
outlet nozzle

Inspected points

Weld

Primary coolant flow

Cross-section drawing
Stainless overlay(Outer side)

Lowerbarrel

Weld(Inner side)

Inspection of Steam Generator-A
ECT results (locations ofsignificant indications)

Locations evaluated to be less than the value
specified in the application for approval of
construction plan as the results of UT

Overlay(Max. length)
No.1: about 28 mm*(Max. depth)
No.1: about 9 mm
* The values areevaluated under thecondition that multiple
imminent ETC
indications arecontinuous.

Girth Weld
Safe end
About 78.0 mm(Specified value in the application forapproval of construction plan : 75.26mm)

Cross-section drawing
Stainless overlay(Outer side)

Lowerbarrel

Weld: The depth of flaw was not detected by ultrasonic test.

Inspection of Steam Generator-B
ECT results (locations ofsignificant indications)

Locations evaluated to be less than the value
specified in the application for approval of
construction plan as the results of UT(Inner side)

Overlay(Max. length)No.11: about 38 mm*(Max. depth)
No.11: about 15 mm* The values areevaluated under thecondition that multiple
imminent ETC
indications arecontinuous.

Girth Weld

Safe end
About 78.1 mm(Specified value in the application for approvalof construction plan : 75.26mm): The depth of flaw was not detected by ultrasonic test.

Inspection of Steam Generator-C
Cross-section drawing
Stainless overlay(Outer side)LowerbarrelWeld

ECT results (locations ofsignificant indications)

Locations evaluated to be less than the value
specified in the application for approval ofconstruction plan as the results of UT(Inner side)

Overlay* The values areevaluated under thecondition that multiple
imminent ETC
indications arecontinuous.

Girth WeldSafe end
About 78.4 mm(Specified value in the application for approval of
construction plan : 75.26mm)

JANTI-OTO-008-002 attachment3(Max. length)
No.2: about 14 mm*(Max. depth)
No.4: about 9 mm

: The depth of flaw was not detected by ultrasonic test.