New and Improved Inspection Techniques for Steam Generator Tubes to Further Enhance the Safety and Reliability of Nuclear Power Plants in Japan

Transcription

1 35th Annual EPRI Steam Generator NDE and Tube Integrity workshop Clearwater Beach, FL, USA New and Improved Inspection Techniques for Steam Generator Tubes to Further Enhance the Safety and Reliability of Nuclear Power Plants in Japan K.Namba, T. Hasebe, T.Kinoshita, T. Matsuura, I.Seki and T. Tsuruta July 18~20, MITSUBISHI HEAVY INDUSTRIES, LTD. All Rights Reserved.

2 Contents 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 2016 MITSUBISHI HEAVY INDUSTRIES, LTD. All Rights Reserved. 1

3 Contents 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 2016 MITSUBISHI HEAVY INDUSTRIES, LTD. All Rights Reserved. 2

4 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. Overall/ Plant operation NRA assessment MHI activity Fukushima accident NRA established Plant operation stopped one after another NRA review New regulations ordered *Nuclear Regulation Authority (NRA) 12 PWR plants applied to resume operation Sendai-1/2 resumed operation injunction Takahama-3 resumed operation (Takahama-4 postponed to resume operation) Pre-operation inspection for Ikata-3 Safety analysis Mid- and long- term preventative measures Plant design and construction enhancements to prevent severe accidents 2016 MITSUBISHI HEAVY INDUSTRIES, LTD. All Rights Reserved. 3

5 Plant situation as of July, 2016 PWR plants with applications to resume operation 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 Mihama-3 Kansai PWR Genkai-3/4 Kyusyu PWR Tomari-1/2/3 Hokkaido PWR Review of application for installment license in progress. 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 MITSUBISHI HEAVY INDUSTRIES, LTD. All Rights Reserved. 4

6 Plant situation as of July, 2016 (cont ) BWR plants with applications to resume operation Plant Utility Reactor Status of NRA review/inspection Kashiwazaki-6/7 Tokyo BWR 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 Review of plant design, construction, safety and reliability for the application of a renewed operations license, in progress. Hamaoka-1/2, Tsuruga-1, and Fukushimadaiichi-1/2/3/4/5/6 are to be decommissioned MITSUBISHI HEAVY INDUSTRIES, LTD. All Rights Reserved. 5

7 Contents 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 2016 MITSUBISHI HEAVY INDUSTRIES, LTD. All Rights Reserved. 6

8 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: Multi-functional UT system PWSCC depth-sizing using UT techniques Improved VT techniques 2016 MITSUBISHI HEAVY INDUSTRIES, LTD. All Rights Reserved. 7

9 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 2016 MITSUBISHI HEAVY INDUSTRIES, LTD. All Rights Reserved. 8

10 Contents 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 2016 MITSUBISHI HEAVY INDUSTRIES, LTD. All Rights Reserved. 9

11 Multi-functional UT System Outline of multi-functional UT Feature ECT sensor for probe positioning Sensor for Axial flaw Sensor for Circ. flaw Straight UT sensor for wear 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 MITSUBISHI HEAVY INDUSTRIES, LTD. All Rights Reserved. 10

12 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 B scope Line No Corrected C scope Tip of defect Tube Outer surface Flaw Thickness Wall loss Evaluation : 22%t Axial distance[mm] ID OD Line 1 Line 3X Evaluation result of 20% depth EDM notch Circ distance[ ] 2016 MITSUBISHI HEAVY INDUSTRIES, LTD. All Rights Reserved. 11

13 Contents 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 2016 MITSUBISHI HEAVY INDUSTRIES, LTD. All Rights Reserved. 12

14 PWSCC depth-sizing UT Technique Outline of PWSCC depth-sizing UT 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 MITSUBISHI HEAVY INDUSTRIES, LTD. All Rights Reserved. 13

15 PWSCC depth-sizing UT Technique Detectability and Characterization Accuracy Detectability: 20%t for 7/8in. tube Sizing accuracy: approximately RMSE 0.13mm (more than 30%t) for 7/8in. tube C scope D scope B scope A scope Tip echo Evaluated depth by UT( %t) Axial SCC (CCW) Axial SCC( CW) 20 Circ. SCC (DOWN) Circ. SCC( UP) Axial SCC data within 22%t Actual depth (%t) Fig.5 Results of UT sizing 2016 MITSUBISHI HEAVY INDUSTRIES, LTD. All Rights Reserved. 14

16 Contents 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 2016 MITSUBISHI HEAVY INDUSTRIES, LTD. All Rights Reserved. 15

17 Improved VT Techniques Description of VT Camera head with Lens unit for side viewing Feature Camera head with Lens unit for viewing ahead Camera for both ahead and side viewing 360 degree articulation Accurate probe positioning with well controlled probe driver and ECT coil 2016 MITSUBISHI HEAVY INDUSTRIES, LTD. All Rights Reserved. 16

18 Improved VT Techniques Detectability and Characterization Accuracy 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 亀裂欠陥多数 3.0mm 3.0mm 4.0mm 4.0mm Camera image Sketch Replica VT Advantage of VT Previous methods 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) 2016 MITSUBISHI HEAVY INDUSTRIES, LTD. All Rights Reserved. 17

19 Contents 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 2016 MITSUBISHI HEAVY INDUSTRIES, LTD. All Rights Reserved. 18

20 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) MITSUBISHI HEAVY INDUSTRIES, LTD. All Rights Reserved. 19

21 2016 MITSUBISHI HEAVY INDUSTRIES, LTD. All Rights Reserved. 20