35th Annual EPRI Steam Generator NDE and Tube Integrity ... · 35th Annual EPRI Steam Generator NDE and Tube Integrity workshop Clearwater Beach, FL, USA July 18~20, 2016 ... PWR

© 2016 MITSUBISHI HEAVY INDUSTRIES, LTD. All Rights Reserved.

35th Annual EPRI Steam Generator NDE and Tube Integrity workshop

Clearwater Beach, FL, USA

July 18~20, 2016

K.Namba, T. Hasebe, T.Kinoshita, T. Matsuura, I.Seki

and T. Tsuruta

New and Improved Inspection Techniques

for

Steam Generator Tubes

to

Further Enhance the Safety and Reliability

of

Nuclear Power Plants in Japan


Contents

1

Current situation of nuclear power plants in Japan

Continuous development and improvement of inspection

techniques to enhance safety and reliability

• Multi-functional UT system

• PWSCC depth-sizing using UT techniques

• Improved VT techniques

Conclusions


Contents

2







Conclusions

© 2016 MITSUBISHI HEAVY INDUSTRIES, LTD. All Rights Reserved. 3

Timeline after Fukushima accident

After the Fukushima Daiichi Nuclear Accident caused by the Tohoku Earthquake and Tsunami in

March 2011, the nuclear regulatory system in Japan was reorganized. Shown below is a timeline

summary of events and actions relative to the resumption of NPP operations in Japan.

2011 2012 2013 2014 2015 2016

Overall/

Plant

operation

NRA

assessment

MHI activity

Fukushima accident

NRA established

Plant operation stopped one after another

New regulations ordered

NRA review

• Safety analysis• Mid- and long- term preventative measures• Plant design and construction enhancements to prevent severe accidents

12 PWR plants applied to resume operation

Takahama-3 resumed operation

(Takahama-4 postponed to resume operation)

Sendai-1/2 resumed operation

injunction

Pre-operation inspection for Ikata-3

*Nuclear Regulation Authority (NRA)


Plant situation as of July, 2016

Plant Utility Reactor Status of NRA review/inspection

Sendai-1/2 Kyusyu PWR Review of design enhancements and Pre-operation

inspection completed. Operation resumed.

Takahama-3 Kansai PWR Review of design enhancements and Pre-operation

inspection completed. Operation resumed but

stopped again by District Court order.

Takahama-4 Kansai PWR Review of design enhancements and Pre-operation

inspection completed. Operation is postponed by

District Court order.

Ikata-3 Shikoku PWR Review of design enhancements and Pre-operation

inspection completed. Operation will be resumed in

end of July.

Takahama-1/2 Kansai PWR Review of construction plan completed.

Ohi-3/4 Kansai PWR

Review of application for installment license in

progress.

Mihama-3 Kansai PWR

Genkai-3/4 Kyusyu PWR

Tomari-1/2/3 Hokkaido PWR

PWR plants with applications to resume operation

Genkai-1,Ikata-1 and Mihama-1/2 were decided to be decommissioned.

License renewal over 40 years operation were applied for Takahama-1/2 and

Mihama-3. Takahama-1/2 were already approved.


Plant Utility Reactor Status of NRA review/inspection

Kashiwazaki-6/7 Tokyo BWR

Review of plant design, construction, safety

and reliability for the application of a renewed

operations license, in progress.

Shimane-2 Chugoku BWR

Onagawa-2 Tohoku BWR

Higashidori-1 Tohoku BWR

Hamaoka-3/4 Chubu BWR

Tokai-2 JAPC BWR

Shiga-2 Hokuriku BWR

Oma J-power BWR

Plant situation as of July, 2016 (cont’)

BWR plants with applications to resume operation

Hamaoka-1/2, Tsuruga-1, and Fukushimadaiichi-1/2/3/4/5/6 are to be

decommissioned.


Contents

6







Conclusions


Continuous improvement of Inspection Techniques

As a preventative measure against the potential negative effects of service induced tube degradation

(flaws), and to enhance the safety and reliability of steam generators, it is necessary to develop, and

continuously improve, the applied NDE techniques.

The goal is to achieve the earliest detection and characterization possible in support of root cause

analysis and mitigation.

Moreover, it is important to continuously analyze and assess the results from improved NDE techniques

and to apply that knowledge to inform each aspect of plant operations from design, to construction, to

specific operating parameters.

To achieve improvements in detection and characterization the various flaw types, MHI has developed

highly advanced and effective NDE techniques.

Examples of specifically targeted flaws are PWSCC in the tube sheet region or at the TTS, and wall

thinning either in the free span or near/under tube support plates.

The, methods, technologies, and specific techniques that MHI has developed/improved are:





Continuous improvement of Inspection Techniques

Summary table of UT and VT

Purpose Method Feature

Wear depth sizing

SCC detection

Multi-functional UT • Detectability: 20%t depth

• Sizing accuracy (wear): 5%t

SCC depth sizing PWSCC depth-sizing UT

• Detectability: 20%t

• Sizing accuracy: approximately

10%t (more than 30%t)

Surface

observation of

SCC

VT• Detectability: 5 to 10μm width

SCC can be detected


Contents

9







Conclusions


Multi-functional UT System

Outline of multi-functional UT

Feature

• Detection of outside/inside cracks and wear in straight section locations.

• Simultaneous implementation of straight beam and angle beams techniques.

• Sizing accuracy is enhanced through an algorithm which automatically

compensates for the varying distance of UT sensor to the tube surface as it is

scanned

• Accurate Probe positioning is provided by an accurately controlled probe driver and

built-in ECT coil which identifies landmarks such as tube supports or the TTS.

Sensor for

Axial flaw

Sensor for

Circ. flawStraight UT

sensor for wear

ECT sensor for probe

positioning


Multi-functional UT System

Detectability and Characterization Accuracy

• Detectability (For SCC and wear): 20%t depth for 7/8in. tube

• Sizing accuracy (For wear): 5%t for 7/8in. tube

ThicknessWall loss

Evaluation

: 22%t

Evaluation result of 20% depth EDM notch

Axial distance[mm]

Circ distance[°]

Tip of defect

Outer surface

B scope Corrected C scope

Line 1 Line 3X

Line No

Tube

Flaw

ID OD


Contents

12







Conclusions


PWSCC depth-sizing UT Technique

Sensor for

Circ. flaw

Sensor for

Axial flaw

Feature

• High S/N ratio is achieved by “point focusing” the ultrasonic beam and by reduction

of the echo from tube inner surface.

• Angle beam technique with single element probe is applied and the echo from tip of

defect is used so as to enhance PWSCC detectability from multi functional UT.

Outline of PWSCC depth-sizing UT


PWSCC depth-sizing UT Technique


• Detectability: 20%t for 7/8in. tube

• Sizing accuracy: approximately RMSE 0.13mm (more than 30%t) for 7/8in. tube

Fig.5 Results of UT sizing

0

20

40

60

80

100

0 20 40 60 80 100 Actual depth (%t)

Evalu

ate

d d

epth

by U

T（

%t)

Axial SCC (CCW)

Axial SCC（ CW）

Circ. SCC (DOWN)

Circ. SCC（ UP）

C scope D scope

B scope A scope

Axial SCC data within 22%t

Tip echo


Contents

15







Conclusions


Improved VT Techniques

Camera head with Lens unit for

viewing ahead

Camera head with Lens unit

for side viewing

Description of VT

Feature

• Camera for both ahead and side viewing

• 360 degree articulation

• Accurate probe positioning with well controlled probe driver and ECT coil


Improved VT Techniques

3.0

mm

4.0mm

亀裂欠陥多数

Camera image Sketch Replica


• Detectability: 5 to 10μm width SCC can be detected for 7/8in. Tube

• Comparison with previous methods (replica and sketch of it):

approximately equal to previous methods

Superior SCC

Previous methodsVT

Advantage of VT

• ECT pushers and remote controlled positioning robots can be used to apply the

VT probe greatly reducing radiation exposure. • (The alternative, replicating flaws, requires inspectors much higher radiation exposure)

3.0mm

4.0mm


Contents

18







Conclusions


Conclusions

• Improved UT technologies and techniques were developed to

achieve more accurate characterization and depth sizing of wear

and SCC type flaws.

• Improved VT technologies and techniques were developed to

achieve far more efficient and effective surface inspections with

superior detection and characterization of SCC, and it greatly

reduces radiation exposure as compared to the alternative.

• These more highly enhanced NDE techniques have now proven

to provide increased sensitivity for early detection while vastly

improving flaw characterization accuracy (i.e. flaw orientation as

well as geometric and depth sizing).

• Enhanced NDE techniques like these further contribute to NPP

safety and reliability by providing higher value input to

continuous condition monitoring and operational assessment

programs (CMOA).


35th Annual EPRI Steam Generator NDE and Tube Integrity ... · 35th Annual EPRI Steam Generator NDE and Tube Integrity workshop Clearwater Beach, FL, USA July 18~20, 2016 ... PWR

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