Search

Occasional Topics
OTjapan Measures for Tsunami Striking Nuclear Power Station in Japan
Special Article: The Great Tohoku Earthquake (1)
OTjapan The Tragedy of “To Be” Principle in the Japanese Nuclear Industry
EJAMOT_CN3_Figure1_The_outside_view_of_CEFR OTChinaPlanning and Consideration on SFR R&D Activities in China
< All Occasional Topics

Information
ICMST-Kobe 2014
Nov 2(Sun) - 5(Wed), 2014
Kobe, Japan
Nuclear Regulation Authority Outline of the New Safety Standards for Light Water Reactors for Electric Power Generation
For Public Comment
Outline of New Safety Standard (Design Basis)
For Public Comment
New Safety Standards (SA) Outline (Draft)
For Public Comment
Outline of New Safety Standard(Earthquake and Tsunami)(DRAFT)
Issues
  Vol.5 No.4(Feb-25)
Vol.5 No.3(Nov-25)
Vol.5 No.2(Aug-26)
Vol.5 No.1(May-27)
< Other Issues

Featured Articles
EJAM5-3NT58 "Development of Future Prediction of Animation by coupling of Principle Component Analysis and Singular Spectrum Analysis"
EJAM5-3NT58 Validation of Multifrequency and Window-Multifrequency Techniques using Remote Field Eddy Currents for ISI of FBR Tubes
EJAM5-3NT59 Remote Controlled Robot with expandable features

JSM
Contacts
(EJAM): ejam@jsm.or.jp
(JSM): secretariat@jsm.or.jp
HP: http://www.jsm.or.jp
(in English)

 
Vol.2 No.2 previous GA 14 - AA 19 - 20 - SP3 ( 21 - 22 - 23 - 24 ) - NT 26 - 27 - 28 next Vol.2 No.4
Vol.2, No.3, NT28
 
Review on Conservatism of Guideline for Inspection and Evaluation to BWR internals
 
Tokyo Electric Power Co, Inc.
TOSHIBA Corporation
Hitachi-GE Nuclear Energy, Ltd.
 
1. Technical summary

Classification
3 - B (Evaluation technology for SCC)

"Guideline for Inspection and Evaluation of Reactor Internals" (abbreviated as Guideline, hereafter) by Japan Nuclear Technology Institute (abbreviated as JANTI, hereafter) are published through the deliberation in "Study Group on Guideline". Published Guideline are usually taken into "Rules on Fitness-for-service (FSS code)" of Japan Society of Mechanical Engineers (JSME). FSS code is being endorsed by governmental regulator stage by stage. New maintenance technologies published as Guideline are authorized technically and it is possible to apply to actual nuclear plant if governmental regulator agrees individually.

As for Japanese BWR core shroud, when stress corrosion cracking (SCC) is found by inspection, continuation of the plant operation is decided by the result of integrity evaluation performed according to FSS code that has taken the evaluation procedure specified in Guideline for core shroud[1]. Fig.1 shows the summary concept of the evaluation procedure. When SCC is found, crack growth in future is evaluated by the procedure that Guideline specifies. The next essential inspection time is decided so that the expected remaining cross section is greater than the minimum required area to keep the structural integrity of core shroud. If the result of structural integrity evaluation shows that current remaining cross section is not enough, countermeasure such as repair or replacement is required before restart of plant operation.

EJAM2-3NT28_Fig.1_Concept_of_inspection_and_evaluation_of_core_shroud

Fig. 1 Concept of inspection and evaluation of core shroud

2. Development phase

Phase 3: Publicly-accepted Phase

3. Scope

Scope of this article is consideration through the comparison of actual inspected core shroud SCC growth and growth predicted by the evaluation procedure specified by Guideline for core shroud. Japanese current available data are studied thanks to Japanese BWR utilities.

4. Features

Prediction of core shroud SCC growth by evaluation procedure of Guideline has actually enough conservatism.

As a result of the comparison of actual inspected core shroud SCC growth data and predicted growth by the evaluation procedure specified by Guideline for core shroud, it was confirmed that in every investigated case, predicted core shroud’s SCC growth is much greater than the actually inspected one.

Study Group on Guideline will continue this kind of investigation and will study appropriate modification on current method after validating enough reason as feedback.

5. Examples of Application

Fig. 2 shows a structure of core shroud and weld joint numbers. Following examples of application are described with these weld joint numbers.

EJAM2-3NT28_Fig.2_Structure_of_core_shroud

Fig. 2 Structure of core shroud

Fig.3, 4, 5, 6, and 7 show the comparison of actual inspected SCC growth result and predicted SCC growth evaluated before 1 cycle plant operation. There are 12 figures as result of investigation of all domestic applicable data. In every case we found that prediction by Guideline’s procedure gives greater growth than actual inspected growth.

Results of these investigation show that Guideline’s evaluation procedure can predict SCC growth conservatively enough. Application of Guideline procedure to core shroud is confirmed to be very effective to make rational operating plan for nuclear plant.

 

EJAM2-3NT28_Fig.3_s_SCC_growth_of_outer_side_of_H2_weld_prediction_and_actual_inspection

Onagawa unit 1 (out of H2 weld line)

Fig. 3 SCC growth of outer side of H2 weld (Ring region); prediction and actual inspection

 

EJAM2-3NT28_Fig.4_s_SCC_growth_of_inner_side_of_H4_weld_prediction_and_actual_inspection />

Note) Length of circumferential SCC is defined actual inspected length + 2 × thickness of the sleeve (to increase conservatism)

Hamaoka unit 3 (inner of H4)

EJAM2-3NT28_Fig.4b_s_SCC_growth_of_inner_side_of_H4_weld_prediction_and_actual_inspection

Note) Length of circumferential SCC is defined actual inspected length + 2 × thickness of the sleeve (to increase conservatism)

Shimane unit 2 (inner of H4)

Fig. 4 SCC growth of inner side of H4 weld; prediction and actual inspection

 

EJAM2-3NT28_Fig.5a_s_SCC_growth_of_outer_side_of_H6a_weld_prediction_and_actual_inspection

Onagawa unit 1 (outer side of H6a weld line)

EJAM2-3NT28_Fig.5a_s_SCC_growth_of_outer_side_of_H6a_weld_prediction_and_actual_inspection

Kashiwazaki unit 3 (outer side of H6a weld line)

Fig. 5 (a) SCC growth of outer side of H6a weld; prediction and actual inspection

 

EJAM2-3NT28_Fig.5b1_s_SCC_growth_of_outer_side_of_H6a_weld_prediction_and_actual_inspection

Note*) Averaged value of fixed examination area of 30° - 61°

Hamaoka unit 3 (Outer side of H6a)

EJAM2-3NT28_Fig.5b2_s_SCC_growth_of_outer_side_of_H6a_weld_prediction_and_actual_inspection

Hamaoka unit 4 (Outer side of H6a)

Fig.5 (b) SCC growth of outer side of H6a weld; prediction and actual inspection

 

EJAM2-3NT28_Fig.5c_s_SCC_growth_of_outer_side_of_H6a_weld_prediction_and_actual_inspection
Kashiwazaki unit 2 (Outer side of H6a)

Fig. 5 (c) SCC growth of outer side of H6a weld; prediction and actual inspection

 

EJAM2-3NT28_Fig.6_s_SCC_growth_of_inner_side_of_H7a_weld_Shell_prediction_and_actual_inspection

Hamaoka unit 4 (inner side of H7)

Fig. 6 SCC growth of inner side of H7a weld (Shell); prediction and actual inspection

 

EJAM2-3NT28_Fig.7a1_s_SCC_growth_of_inner_side_of_H7a_weld_Ring_prediction_and_actual_inspection

Onagawa unit 2 (inner side of H7)

EJAM2-3NT28_Fig.7a2_s_SCC_growth_of_inner_side_of_H7a_weld_Ring_prediction_and_actual_inspection

Note *) Averaged value of fixed examination area of 297°- 332°

Hamaoka unit 3 (Inner side of H7)

Fig. 7 (a) SCC growth of inner side of H7a weld (Ring); prediction and actual inspection

 

EJAM2-3NT28_Fig.7b_s_SCC_growth_of_inner_side_of_H7a_weld_Ring_prediction_and_actual_inspection

Hamaoka unit 4 (inner side of H7)

Fig. 7 (b) SCC growth of inner side of H7a weld (Ring); prediction and actual inspection

 
6. Reference
  1. [1]Guideline for Inspection and Evaluation of reactor internals "Core Shroud" (4th revision), JANTI (in Japanese)
7. Contact

Japan Society of Maintenology (ejam@jsm.or.jp)