EXPERTS’ DISCUSSION ON FOLLOW- UP ACTIVITIES · PDF fileUP ACTIVITIES ON IGSCC OF RBMK REACTORS AUSTENITIC STAINLESS STEEL PIPING IAEA, ... austenitic stainless steel piping welds

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EXPERTS’ DISCUSSION ON FOLLOW-UP ACTIVITIES ON IGSCC OF RBMK REACTORS AUSTENITIC STAINLESS

STEEL PIPING

IAEA, VIENNA, AUSTRIA 27-30 OCTOBER 1998

TC PROJECT RER/9/052 DEPARTMENT OF TECHNICAL CO-OPERATION

DEPARTMENT OF NUCLEAR SAFETY

INTERNATIONAL ATOMIC ENERGY AGENCY

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CONTENTS

1. INTRODUCTION

2. OBJECTIVE

3. PRIORITIES

4. MEASURES REQUIRED TO ADDRESS THE ISSUE

5. CURRENT INTERNATIONAL ASSISTANCE PROGRAMMES

6. PROPOSAL OF FOLLOW-UP ACTIVITIES

7. CONCLUSIONS

APPENDIX I. STATUS UPDATE FOR LITHUANIA

APPENDIX II. STATUS UPDATE FOR RUSSIA

APPENDIX III. REVISED OUTLINES OF FOLLOW-UP ACTIVITIES

ABBREVIATIONS

REFERENCES

CONTRIBUTORS TO DRAFTING AND REVIEW

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1. INTRODUCTION

In 1997, intergranular stress corrosion cracking (IGSCC) was detected in the heat affected zone ofaustenitic stainless steel piping welds in several RBMK NPPs. Similar degradation has beenobserved earlier at a number of vessel type boiling water reactors (BWR) and recognized as ageneric safety issue for reactors operating with BWR type water chemistry, being a new safetyissue for RBMK reactors.

Recognizing the importance of the issue and upon invitation of the Government of Ukraine, theIAEA organized a Workshop on ‘Environment Assisted Cracking of NPP Austenitic StainlessSteel Piping’ in Slavutych, June 22-26, 1998. The objective of the Workshop was to provide aforum for the exchange of experience. The Workshop was organized in the frame of the IAEA TCProject RER/9/052.

The Workshop concluded, that actions to address the issue for RBMK reactors have been initiatedbut still need to be completed. Further exchange of experience and international co-operation inthis area is of a high importance. Follow-up activities to address safety concerns associated withthis issue for RBMK reactors should be established as a matter of urgency.

In order to develop comprehensive well balanced proposals for follow-up activities necessary toaddress the issue of IGSCC that were consistent with the conclusions of the Workshop [1], theIAEA convened an experts’ meeting at its headquarters in Vienna, October 27-30, 1998. Duringthe meeting, experts performed a final review of the Workshop report [1] and developed detailedoutlines for several follow-up activities necessary to address the issue of IGSCC. 16 experts fromcountries operating RBMK reactors, countries involved in the international assistance programmesand the IAEA participated in the meeting.

The basis for the discussion during the meeting was the draft report of the Workshop [1],international experience on the IGSCC issue and the experience accumulated to date in Lithuania,Russia, and Ukraine. Based on the discussion during the meeting this report was developed by theexperts. Section 2 of this report indicates its objective. Section 3 deals with priorities forcompensatory and corrective measures to address the issue. Section 4 provides an overview oftechnical measures to address the issue. Section 5 summarizes the status of ongoing co-operationprogrammes based on information available during the meeting. In Section 6 seven follow-upactivities are outlined and in Section 7 the conclusions of the meeting are given. In Appendix I,update of the status in Lithuania as presented during the meeting is given. Appendix II contains thestatus update for Russia as well as some views of the RBMK designer as provided. In AppendixIII., revised and condensed description of follow-up activities drafted by Russian specialists afterthe meeting is given.

2. OBJECTIVE

The objective of this report is to present the outlines of the safety related activities judged by theexperts participating in the meeting as necessary to address the issue of IGSCC in RBMK reactors.Each outline includes the objective, scope, tasks, milestones, product and participants required toimplement the follow-up activity.

In developing the activity outlines given in this report, safety, technical rationale, and practicalfeasibility were considered. The activities presented in this report represent to the extent possiblethe consensus of the group of experts who participated in the meeting. The implementation of allof the follow-up activities outlined is a matter to be addressed in the frame of the national safety

improvements programmes and bilateral and international co-operation programmes.

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3. PRIORITIES

During the discussion, the following priorities for actions to address the IGSCC issue wereproposed by specialists from countries operating RBMK reactors:

1. Improvement of the reliability of the in-service inspection (ISI) performed on site;2. Implementation/improvement of leak detection systems, improvement of the mechanistic

understanding of the degradation, and comprehensive integrity assessment;3. Improvement of repair techniques;4. Adaptation of corrective measures to regulatory requirements and their on-site application.

It should be noted that some experts participating in the meeting did not agree with these prioritiesand it was not possible to establish consensus during the meeting.

In connection with the priorities given above, it was stated by RDIPE experts that these are basedon the discussion held during the Slavutych Workshop [1], international experience available [7],IAEA recommendations on RBMK pressure boundary integrity [3, 4] and current status ofimplementation of measures at RBMK NPPs.

4. MEASURES REQUIRED TO ADDRESS THE ISSUE

Measures required to address the issue of IGSCC for RBMK reactors can be summarized asfollows.

Improvement of ISI capability and reliability

Improving in-service inspection capability in RBMKs can be accomplished by improving fourareas in ISI:• Developing ISI techniques that improve inspection of welds with limited or no access;• Establishing a regional ultrasonic ISI qualification program;• Transferring ultrasonic technology for inspection of welds repaired using the weld overlay

technique;• Application of automated UT with state-of-art data acquisition systems and software for ISI

results evaluation.

Improvement of leak detection systems capability

This could be achieved through review of performance of existing leak detection systems and theirsubsequent improvements or installation of new leak detection systems.

Comprehensive safety and integrity assessments

A comprehensive safety and integrity assessments should be performed to ensure that all potentialissues associated with IGSCC are addressed. The comprehensive assessments should include thefollowing elements.• A study of leading damage causes which influence different level of damage at specific Units,• Improvement of on-site water chemistry parameters monitoring and control system,• Establishing a comprehensive design, manufacturing and operating history data base,• A comprehensive failure analyses, including laboratory testing using state-of-the-art-

techniques, analyses of on-site and R&D data,• Analyses of possible transients and assessment of loads introduced due analysed transients,

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• Analyses of criteria for integrity assessment and data on their engineering validation,comprehensive integrity assessment based on verified criteria, loads assessment and results ofleading causes of damage.

Improvement of repair techniques

Improving the repair process for IGSCC can be accomplished by improving techniques for on-siteweld edges preparation, transferring automated welding techniques for on-site repair, transfer oftechnology for optimized welding, transfer of technology for overlay welding repair, transfer oftechnology for thermal treatment (solution heat treatment on-site, induction heating).

Corrective measures

Corrective measures include in particular the transfer of technology for mechanical stressimprovement process application, and transfer of technology for water chemistry improvementwith respect to IGSCC (e.g. conductivity, noble metals or other specific addition).The use ofmaterials more resistant to IGSCC should be also considered.

Regarding the approach to the implementation of the measures to address the issue, it was statedthat the issue would be most effectively addressed on a regional basis involving regulators,utilities, plant designers and other technical support organizations

A Russian side proposal formulated after the meeting (text given next in italics) is that a regionalteam involving three working groups should be established:

• Group 1: Representatives of regulatory authorities and technical support organisations;

• Group 2: Representatives of appropriate ministries and organisations of NPP technicalsupport, Chief Designer of RBMK;

• Group 3: Utilities operating RBMK reactors.

All international programs of general activities (as comprehensive root cause analysis, integrityanalysis, inspection qualification requirements harmonisation) and technology transfer whichneeds adaptation to regulatory requirements should be performed by Group 2 efforts co-ordinatedwith Group 1 because there is no sufficient differences in regulatory practice up to now for weldsof austenitic piping.

All programs of direct delivery of equipment to RBMK NPPs should be supervised by Group 3 inco-ordination with Group 2.

Further, the Russian experts noted the following. General safety problems of RBMK NPPs withrespect to design basis accidents have been analysed in the framework of IAEA ExtrabudgetaryProgramme on the Safety of WWER and RBMK NPPs (1992-1998) [2-4], CEC studies on RBMKNPPs safety improvement [5] and numerous bilateral studies.

As prioritized for RBMK NPPs earlier [3, 4] the issues of ISI improvement are one of the mostimportant when pressure boundary integrity is discussed. Following recommendations of [6] onthe role of ISI in proper addressing of IGSCC damages tremendous amount of inspection wasfulfilled by UT during 1997-1998 at all RBMK NPPs [1] and made it possible to have a picture onIGSCC damage levels at specific sites. Increased efficiency of inspection by UT instead ofradiography was demonstrated obviously at Chernobyl NPP Unit 3 where flaws have beenrevealed in 182 welds in addition to 268 flawed welds after radiography [1]. But still there are

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some zones in dia.300 mm piping not accessible for the UT or with limited access. Another aspectof UT improvement is elimination of human factor influence during inspection by application ofautomatic and semiautomatic UT tools/procedures with data recording to PC memory. Taking intoconsideration common features of design of RBMK austenitic piping (piping diameter and wallthickness, geometry of weld edges preparation, base and weld materials, etc.) there is opportunityto establish a Regional Center for personnel training and inspection qualification.

It comes out from the discussion that all RBMK countries have in the current moment very similarrequirements to operation and repair of austenitic piping. The later makes it possible to performadaptation of known technologies in the area of inspection and repair of RBMK austenitic pipingon generic basis for all RBMKs.

Strategies to address IGSCC issues by appropriate technical measures are very similar in allRBMK operating countries as stated in discussion by all RBMK experts from utilities, regulatorsand technical support organizations.

5. CURRENT INTERNATIONAL ASSISTANCE PROGRAMMES

There are several ongoing bilateral and international assistance programmes, some of which aredirectly related to this issue, other indirectly. It is however recognized that much more extensiveand concerted effort would be required to address the IGSCC safety issue in a reasonabletimeframe.

Next, the information provided by individual experts participating in the meeting on the currentsituation regarding IGSCC relevant co-operation programmes is given.

USA International Nuclear Safety Program

Regarding Ukraine, in March 1997, the United States delivered state-of-the-art manual ultrasonicpipe inspection systems to all five nuclear power plants in Ukraine. Also in March, inspectionpersonnel from each plant attended a six-day training course at the Khmelnitsky plant, led by U.S.experts.

In April 1998, specialists from the Pacific Northwest National Laboratory conducted a two-weekworkshop at Khmelnitsky on ultrasonic examination of pipes fabricated from austenitic steel.Representatives from all five Ukrainian plants participated.

The United States is supporting increased training in nondestructive examination. With U.S.support, Energoatom and the National University of Ukraine have established a central trainingand certification facility for nondestructive examination. U.S. and Ukrainian experts aredeveloping a process for certifying technicians as nondestructive examination specialists. Theserequirements conform to international standards. The centre is also developing a procedure forinspection of austenitic welds, 1st draft of which has been completed by mid 1998.

Regarding Russia, the United States delivered both hand-held and remotely operated ultrasonic testequipment to Kursk plant in 1996. Kursk personnel received training in the use of both types ofequipment in October and November 1996.

In January 1999, the United States delivered a manual ultrasonic inspection system to each Russianplant. U.S. specialists trained technicians at each site to use the equipment. The training will becompleted in line with the schedule agreed by both sides.

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The International Nuclear Safety Programme (INSP) also sponsors a programme that is directlyrelated to RBMK maintenance and titled ‘RBMK Maintenance project’. This project has createdan RBMK Advisory Board that sets priorities for maintenance issues related to RBMKs, whichcould also be a central point of contact in coordinating efforts related to IGSCC repair. The USDepartment of Energy point of contact for this project is Gregory Trosman. The project manager isTom Vehec from Pacific Northwest National Laboratory.

Sweden and Lithuania

Within the Lithuanian-Swedish bilateral programme, a broad support is given in the field of ISI toIgnalina NPP. Up to now, concerning IGSCC in downcomers the following support was providedby SIP to Ignalina plant in performance of 100 % ISI on Unit 1:• special manipulator was developed by ABB TRC for application of automated UT with

application of Tomoscan and P-scan data acquisition equipment for UT of the 325 mmpipelines;

• TomoView software for assessment of automated UT results was provided;• implementation of specially developed UT techniques (“KRAB”) and special UT probes for

defect characterization (AMDATA probe) was provided;• root causes analysis and comprehensive material investigation of IGSCC defects was

performed, follow-up activities were planned within development of Reactor Cooling SystemSafety Case which is under development in Ignalina NPP (Safety justification with respect tothe current ISI results, consideration of improved repairing techniques, improvements of LDS,etc.).

Russia

No direct activities to address IGSCC issues via international/bilateral programmes of technicalco-operation and assistance have been realised in 1997-1998 for RBMK NPPs in Russia.

Some previous activities, which were not planned to address directly IGSCC issues, could beuseful to improve current situation. Their current status is as follows:

1)TACIS Project R1.05/94 for Smolensk NPP (equipment for NDE, including means for dia.300mm piping):• January 1996 - endorsement of ST-TOR;• June 1997 - finalising the bid among participating companies;• October 30, 1998 - no contract for NDE equipment delivery have been signed yet.

2)TACIS Project R1.05/95A for Smolensk NPP (implementation of leak detection system):• ST-TOR is not prepared and agreed yet.

3)EBRD Project B-3 for Units 1-4 of Leningrad NPP (Implementation of leak detection system byhumidity monitoring):• equipment is in stage of assembling at Unit 1.

4)EBRD Project A.1.2. for Units 1-4 of Leningrad NPP on ”UT non-destructive examinationequipment”• contract awarded to Tecnatom, Spain• UT equipment to be delivered by December 1998

Ukraine

The equipment for ISI and weld preparation is being supplied through funding by Nuclear Safety

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Account EBRD Grant only. The ultrasonic and visual test equipment (EBRD Project A.1.2. forChernobyl Unit 3) will be provided by Tecnatom, Spain in November 1998.The weld preparationequipment was provided by Furmonoit, UK.

In addition, the Chernobyl plant procured itself automatic welding device from Polisud, France.

6. PROPOSAL OF FOLLOW-UP ACTIVITIES

This section presents seven follow-up activity outlines that were developed during the meeting.These activities are to be implemented on a regional basis wherever applicable, involving expertsfrom all 3 countries operating RBMK reactors (regulatory bodies, plant operators, technicalsupport organizations, and plant designer). It is recognized that a strong co-ordination with theother relevant programmes is required to avoid duplication of effort.

As a first step to initiate these activities, the IAEA should convene for each of them a narrow focusspecialized technical meeting with the objective to develop the activity proposals given in thissection into a detailed workplan for each. Experts participating in these meeting should have adetailed knowledge in the subject discussed and will be expected to form an ‘activity expertsgroup’.

Russian experts pointed out that in addition to these seven activities, which are aimed ataddressing the root cause of the safety issue, there is an urgent need to implement immediatemitigation measures. These include direct supply of equipment for automated non-destructivetesting, automated weld preparation equipment (edge cutting devices), automated weldingequipment and technology for improvement of properties of existing welds to the operating plants.These mitigation measures would reduce the dose to the personnel and improve the quality ofmaintenance and inspection.

It should be noted, that Russian RBMK specialists also developed after the meeting a condensedand partly revised version of the follow-up activities outline. This revised version, which was notdiscussed and agreed upon during the meeting but which contains useful and well structuredinformation is provided in Appendix III.

6.1. Safety assessment

Background

IGSCC is known to be a cracking mechanism capable of producing long cracks that will notnecessarily exhibit LBB behavior. The performance of RBMK systems with extensive IGSCC,either under accident conditions or with continuing growth under normal operating conditions isnot well understood. Furthermore, the existing ISI results have not been well explained in terms ofthe extent of cracking at particular plant and weld types.

Objectives

Identify the overall safety concerns associated with the presence of IGSCC in RBMKs. Considerthe capabilities of safety systems to recover from accidents involving austenitic piping failure. Thiswould include identification of limiting transients. Further consider the value of ”defense in depth”concepts such as LBB to reduce the risk posed by IGSCC. Perform limited LBB analysis toidentify the stability of cracks allowed to remain in service and to determine the leak detectionsystems requirements. Collate existing ISI information and plant operational conditions to explain

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observed behavior and predict possible future development. Identify priorities for ISI and leakdetection systems

Scope

The scope of this activity includes developing requirements and priorities for safety improvements,that allow IGSCC to be managed safely. Identify the relative benefits of possible safetyimprovements to plant or maintenance processes e.g. better leak detection, inspectionimprovements, stress improvement etc. In addition, results from other activities given next willprovide important input and feedback and will be therefore provided to and discussed on a regularbasis in the frame of this activity.

Tasks

1. List possible accident scenarios and comment on relative likelihood.2. Identify safety systems and safety arguments available to make ”defense in depth” arguments

against IGSCC related accidents. Suggest a basis for regulatory review of safety assessment.3. Identify requirements for leak detection systems and targets for ISI effectiveness (including

performance of LBB analysis).4. a) Collection and analysis of ISI experience from each RBMK.

b) Identify conditions that may be leading/have led to IGSCC at each NPP.c) Determine critical factors for IGSCC and likely future trends.

5. Prioritize improvements to ISI implementation, leak detection and other systems.

Milestones

1. Preliminary report (3 months)2. Preliminary report (6 months)3. Preliminary report (12 months)4. Preliminary report (12 months)5. Final report (12 months)

Product

Recommendations on priorities for system/maintenance procedure upgrades.

Participants

RBMK safety expertsRegulatory body expertsRF, UA, LT staff from NPPsPlant design organizations

6.2. Improvement of ISI techniques

Background

In-service inspection of nuclear power plants is a diagnostic tool that helps ensure the structuralintegrity of primary coolant and safety engineered piping systems. In-service inspection detectsdefects that can compromise the safe operation of nuclear power plants. The IAEA organized since1990 a programme to assist countries in Eastern Europe and the former Soviet Union to evaluatethe safety of their nuclear power plants by identifying major design and operational safety issues.As part of the IAEA TC programmes and of this programme, a regional workshop that evaluated

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environmentally assisted cracking of austenitic piping has been organized in June 1998. A panel ofinternational experts that attended the workshop concluded that environmentally assistedintergranular stress corrosion cracking (IGSCC) is a generic safety issue for reactors that operatewith a BWR type water chemistry. IGSCC has recently been detected in RBMK type reactors inLithuania, Russia and Ukraine.

In-service inspection is vital to the proper management of IGSCC. Several specific ultrasonicinspection techniques have been developed in other countries earlier (both Europe and the USA).These inspection techniques have played a valuable role in helping manage piping degradation dueto IGSCC.

This follow-up activity to the ”Regional Workshop on Environmentally Assisted Cracking of NPPAustenitic Piping” proposes that several regional workshops and scientific exchanges be sponsoredthat transfer the following ultrasonic inspection techniques.

• Ultrasonic inspection of weld overlays• Ultrasonic inspection for single side (limited) weld access• Ultrasonic search unit design for welds that have only 20 - 40mm scanning access

Objective

The objective of this engineering study is to organize the relevant experts and conduct a series ofworkshops and scientific exchanges to transfer ultrasonic inspection technology in the followingareas.


Scope

The scope of this activity addresses the transfer of technology through workshops and scientificexchanges. These workshops will concentrate on ultrasonic examination of primary coolant andsafety engineered system piping welds.

Tasks

The following tasks are required to complete this engineering study.

1. Select appropriate experts for the following technical issues in ultrasonic inspection.


2. Conduct three one week workshops to address the specific topics listed above in Task 1.3. Sponsor three one week scientific exchanges to follow-up and reinforce the information

presented during the workshops in Task 2.4. Provide topical reports that summarize the information presented in workshops and the success

of the technology exchange as determined by the follow-up scientific exchanges.

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Milestones

Completion of each of the tasks listed above represents a major milestone. This activity isestimated to require one year to complete. The estimated time duration for each task is listedbelow, however, activity funding levels may significantly alter the estimated duration for the tasks.

1. Select appropriate experts for ultrasonic inspection. This should be complete within twomonths after the start of the activity.

2. Conduct three one week Workshops. This should be complete within six months after the startof the activity.

3. Sponsor three one week scientific exchanges to reinforce and follow-up Workshoppresentation. This document should be complete within three months after completion of theinitial workshop.

4. Topical Reports. The topical reports should be completed within two weeks of the follow-upexchange.

Product

The product from this activity is initial and rapid technology transfer of critical ultrasonicinspection technology to regional experts.

Participants

The following organizations should participate as members of the activity team.

• Representatives from regulatory bodies operating RBMK nuclear power plants.• Ultrasonic inspection specialists from RBMK power plants.• RBMK designer• Appropriate ultrasonic inspection experts from western organizations that have developed

ultrasonic techniques for the following areas.

∗ Ultrasonic inspection of weld overlays∗ Ultrasonic inspection for single side (limited) weld access∗ Ultrasonic search unit design for welds that have only 20 - 40mm scanning access

Relationship to other projects

The US Department of Energy, the European Union and other organizations sponsor projects toimprove the safety culture and safe operation of eastern European nuclear reactors. Thistechnology transfer project leverages the funding and safety improvement efforts. This project alsofosters international collaboration and coordination of both the US and Europe to improve in-service inspection in Eastern Europe.

6.3. ISI systems qualification

Background

In-service inspection of nuclear power plants is a diagnostic tool that helps ensure the structuralintegrity of primary coolant and safety engineered piping systems. In-service inspection detectsdefects that can compromise the safe operation of nuclear power plants. IAEA organized aprogramme to assist countries in Eastern Europe and the former Soviet Union to evaluate thesafety of their nuclear power plants by identifying major design and operational issues. As part of

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this program, IAEA sponsored a regional workshop that evaluated environmentally assistedcracking of austenitic piping. A panel of international experts that attended the workshopconcluded that environmentally assisted intergranular stress corrosion cracking (IGSCC) is ageneric safety for reactors that operate with a BWR type water chemistry. IGSCC has recentlybeen detected in RBMK type reactors in Lithuania, Russia and Ukraine.

In-service inspection is vital to the proper management of IGSCC. International ultrasonicinspection reliability programmes have shown that one of the key elements of ensuring thatreliable in-service inspection is possible involves qualifying in-service inspection processes usingboth performance demonstration and technical justification. IAEA has published recently a reporton ‘Methodology for qualification of in-service inspection systems for WWER nuclear powerplants’, IAEA-EBP-WWER-11 [7]. These guidelines for qualifying in-service inspection processesinclude developing a technical justification as well as experimental trials. The European countriesexperience with respect to the implementation of ENIQ guidelines should be considered as well.

This follow-up activity proposes that a regional engineering study be conducted that developspractical guidelines to address the generic issue of reliable piping examination in RBMK nuclearpower plants.

Objective

The objective of this engineering study is to organize the relevant experts into a activity team todevelop practical qualification criteria and implementation documentation for an ISI qualificationcenter.

Scope

The scope of this activity addresses adapting the qualification guidelines already developed byIAEA into a clear concise report that outlines the technical criteria and implementationrequirements for a regional center for qualification of ultrasonic examination of piping. Thequalification center approach will be based upon a combination of technical justification andexperimental trials. The experimental trials will provide assurance that the combination ofequipment, procedures, and personnel are capable of detecting defects that can potentiallycompromise the structural integrity of primary and safety related piping.

Tasks

The following tasks are required to complete this study.

1. Selection of participants for the activity team2. Develop criteria for selection of location of the regional performance3. Develop Technical Justification Documentation - This document outlines the basis for

determining:• The technical topics that must be addressed in the procedure technical justification.• The rationale for the distribution of pipe diameters and wall thicknesses used in the

trials .• The rationale for defect sizes and numbers of defects used in the experimental trials• The accept/reject criteria for both blind and non-blind trials• Technical Support provided to candidates during testing

4. Develop and document Protocols for demonstration5. Develop and document Specifications for the test specimens6. Develop and document Quality assurance requirements for the ISI qualification center.

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Milestones

Completion of each of the tasks listed above represents a major milestone. This activity isestimated to require two years to complete. The estimated time duration for each task is listedbelow, however, activity funding levels may significantly alter the estimated duration for the tasks.

1. Selection of activity team participants. This task should be complete within three months afterthe start of the activity.

2. Criteria for selection of regional ISI qualification center. This task should be complete withinsix months after the start of the activity.

3. Develop technical justification documentation. This document should be complete within oneyear after the start of the activity.

4. Develop and document protocols for demonstration. This task should be complete within oneyear after the start of the activity.

5. Develop and document specifications for the test specimens. This document should becomplete within nine months, however, the work on the document cannot start until thecompletion of Task 3.

6. Develop and document quality assurance requirements. This document should be completewithin eight months after the start of the activity.

Product

The product from this engineering study is a report that provides detailed engineeringspecifications and complete ISI qualification testing protocols including a complete qualityassurance plan for the ISI qualification center.

Participants

The following organizations should participate as members of the activity team.• Representatives from regulatory bodies operating RBMKs• Plant Design Organization• Representatives from Utilities operating RBMKs• Representatives from RBMK NPP metals control department• Representatives from western organizations that have implemented ISI qualification programs• Representatives from the US International Nuclear Safety Program (INSP), EU, etc.• Representatives from IAEA

Relationship to other projects

The US Department of Energy, the European Union and other organizations sponsor projects toimprove the safety culture and safe operation of eastern European nuclear power plants. Thisengineering study accomplishes two objectives. First, the study outlines the technical requirementsfor a regional center that improves in-service inspection by proving a standard metric fororganizations that conduct ultrasonic in-service inspection of piping in eastern European nuclearpower plants. A regional ISI qualification center is the only economically feasible way to introduceISI qualification into eastern European nuclear power plants. Second, by creating an internationalproject team, the study fosters international collaboration and coordination of both the US andEurope to improve in-service inspection in eastern Europe.

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6.4. Leak detection systems

Background

The LBB concept is based on the assumption that a crack in large diameter high energy piping willgrow through wall and lead to a reliably detectable leak well before a catastrophic break couldoccur. This is demonstrated through the LBB analysis for the candidate piping system. The LBBconcept has been recognised as a viable methodology to demonstrate integrity of the large diameterhigh energy piping. A successful application of the LBB concept enables to exclude specificconsiderations for the dynamic effects associated with primary circuit large diameter piping breaksfor a number of PWRs. It should be noted, that the LBB concept was not successfully applied andapproved for BWR piping to date, mainly due to the concerns associated with the IGSCC. TheIAEA within the frame of its Extrabudgetary Programme on the Safety of RBMK NPPs organisedactivities on the LBB Concept Application to the RBMK NPPs, reports RBMK-SC-034 andRBMK-SC-057. In these reports, the importance of the leak detection system (LDS) waspresented. Reliable leak detection is one of the main pre-condition for a successful LBB conceptapplication. The implementation of a reliable leak detection system would lead to a directimprovement of information about the operational status of the piping. The leak detection systemshould be therefore implemented in the short term at operating plants independently of the wholeLBB concept application. In connection to the ”Regional Workshop on Environmentally AssistedCracking of NPP Austenitic Piping ” the question of applicability and implementation of a leakdetection system was newly discussed.

Objective

A team of relevant experts should be organised to develop the general requirements for applicationof leak detection systems including conditions and methodologies. The document should take intoaccount the general requirements of the LBB and above mentioned documents and IAEA Guidanceon the LBB concept application, IAEA-TECDOC-774 as a basis.

Scope

The scope of this activity is to address possible leak detection system (LDS) implementation toRBMK plants taking into account the typical environmental conditions and specific geometry ofcompartments of various generations of the plants. Extension of the existing leakage surveillancewith sophisticated system should be than proposed.

The conditions and a basis for such implementation should be stated in the document includinggeneral requirements for verification and qualification of such systems.

Tasks

Behind the proposal of work plan mentioned below the two main tasks should be presented as thebasis for the activity

Task 1 - Criteria for postulation of leakage size through wall-flaw (including e.g. evaluation ofmaterial data and crack growth rate);

Task 2 - Assessment and analysis of efficiency of existing system and applicability of systems andmethods of leakage detection including location of the systems their sensitivity and other aspectsas geometry and environmental conditions, etc.

The following subtasks are supposed to be included in the work plan:

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• Preparation of Terms of Reference and time schedule• To build-up the team of experts• Development of Technical Specifications and description of current position• Develop document dealing mainly with conditions for LDS system application (material

properties, classification and sources of leakage, etc.)• Principal methods of leak detection• Requirements for Implementation of LDS• Qualification of LDS• Peer-review of the draft document.• Finalization of the document

Milestones

Each of the Tasks mentioned represents a milestone which should be presented in a time schedulein connection to the Subtask 1. The estimated duration of the Subtask 2 – 6 of the activity shouldnot exceed 12 month.

Product

The product of the work of the team of experts will be a document providing a general guidanceand description of the proposal for application (improvement) of leak detection systems to theRBMK plants.

Participants

The following parties should participate in the team of experts:

• Representatives of design organisations• Representatives of regulatory authorities of countries operating RBMKs• Representatives of Utilities and NPPs operating RBMKs• Representatives of western NPPs, regulatory authorities and Utilities that have implemented

LBB and LDS.• Representatives from similar International Programmes related to this issue• Representatives from IAEA

6.5. Comprehensive integrity assessment

Background

IGSCC is known phenomenon that has been studied extensively in the U.S. and other countriesoperating BWR type reactors. This phenomenon has only recently been observed in RBMK typereactors (1997). RBMK operators and regulatory authorities are still evaluating the extent andseverity of the problem. IGSCC is a corrosion damage mechanism resulting from the combinedaction of tensile stress, a susceptible material condition and a corrosive environment. The tensilestress required for cracking is easily achieved during the welding process without post-weldingheat treatment. The susceptible material condition for austenitic stainless steels is termedsensitization. Sensitization describes a material condition where Cr has been depleted from areasadjacent to the grain boundary with a subsequent increase in brittle phase of Cr carbide Cr23C6.The corrosive environment can be something as benign as oxidizing species (e.g. O2 in water).Different degree of RBMK piping degradation at individual units is not well understood orcharacterized. This follow-up activity proposes a study that will aid in understanding IGSCC crack

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initiation and propagation processes in RBMK piping systems.

One of the ways to mitigate this phenomenon is to maintain strict control of favorable waterchemistry and to limit contaminants. New methodologies are being investigated (Zinc addition,noble metal additions and isolating coatings) and should be evaluated for RBMK application.

Objectives

1. To obtain a comprehensive understanding of leading causes contributing to different level ofdamage, crack initiation and propagation processes for the austenitic materials currently used atRBMKs. This goal should be accomplished through the use of additional comprehensive failureanalyses using state of the art techniques and equipment. The results of the failure analyses andthe updated ISI inspection data will be combined to establish a database for IGSCC in RBMKs.The ultimate objective will be a thorough understanding of crack growth rates and could beused for further risk assessment in order to improve ISI programme.

2. To determine and recommend the optimum water chemistry condition necessary to mitigateinstances of IGSCC in RBMKs.

Scope

Program to set requirements and priorities for safety improvements and allow IGSCC to bemanaged.

Tasks

Tasks of metallurgical and water chemistry issues can run concurrently or separately.

A) Metallurgical regime

1. Select participants for the activity team2. Preparation of a guideline how to handle crack assessment3. Collection and correlation of existing data

• Collect ISI results from each RBMK• Collect water chemistry data• Collect metallurgical data• Collect other relevant data, e.g. about decontamination procedures• Identify conditions that may be leading/have led to IGSCC at each NPP.• Determine critical factors for IGSCC and likely future trends.

4. Additional comprehensive failure analyses to include:• state of the art techniques• detailed crack length and depth measurements

5. Take the results of the failure analyses and combine them with the existing data base to captureall the different crack morphologies and growth patterns/locations.

6. Experimental program establishing a model starting from the beginning and taking into accountthe results of task 3, 4 and 5

7. Recommendations for improvement of ISI on the bases of task 5 and 6 results

Milestones

Completion of each of the tasks listed above represents a major milestone. This activity isestimated to require three years to complete. The estimated time duration for each task is listedbelow, however, activity funding levels may significantly alter the estimated duration and scopefor the tasks.

17

1. Preliminary report (3 months)2. Preliminary report (2 months)3. Preliminary report (12 months)4. Preliminary report (12 months)5. Preliminary report (4 months)6. Preliminary report (18 months)7. Preliminary report (2 months)

The final reports for each task will be presented 3 months after preliminary report.

Depending on the results of the assessment of the current decontamination procedures at RBMKsthe activity on ”Decontamination” should be started.

Product

A comprehensive risk analyses based on the metallurgical aspects of IGSCC in RBMKenvironment. This will be in form of a report.

B) Water Chemistry Issues

1. Select participants for the activity team2. Comprehensive evaluation of current RBMK versus other water chemistry standards3. Reviewing the current data base of RBMK water chemistry. Results should be taken into

account, to be discussed and included in the metallurgical regime.4. Evaluation of water chemistry monitoring practice at RBMKs5. Feasibility study on the use of western water chemistry modifications and RBMK applicability6. Recommendations based upon results of tasks 2, 3, 4 and 57. Identify locations and attributes for monitoring by on site measurements and laboratory testing8. Providing recommendations for total water chemistry regime and modification

Milestones

Completion of each of the tasks listed above represents a major milestone. This activity isestimated to require 18 months to complete. The estimated time duration for each task is listedbelow, however, activity funding levels may significantly alter the estimated duration and scopefor the tasks.

1. Preliminary report (3 months)2. Preliminary report (2 months)3. Preliminary report (2 months)4. Preliminary report (2 months)5. Preliminary report (3 months after task 4)6. Preliminary report (6 months after task 5 completion)7. Preliminary report (12 months)8. Preliminary report (4 months after task 7)


Product

A comprehensive water chemistry evaluation for operation of RBMKs. This will be in form of areport.

18

Participants

The following organizations should participate as members of the activity team.• Countries operating RBMKs

� Representatives from regulatory bodies� Representatives from utilities and plants� Representatives from design organizations

• Representatives from western organizations having relevant experience• Representatives from TACIS and the US International Nuclear Safety Program (INSP)• Representatives from IAEA

Note

In connection with this task, the following note has been pointed out by Russian specialists:proposed division of metallurgical studies and water chemistry issues which is perhaps correct inacademic studies is not of practical value for current situation at RBMKs and emphasis on safetyimprovement on site. It is well known that such complex parameter as electrochemical corrosionpotential (ECP) could indicate clearly situation with potential to IGSCC damages at each NPPUnit. No high temperature ECP measurements have been performed at any RBMK NPP site [1].So as a matter of urgency high temperature water chemistry and corrosion monitoring should beforeseen at reference NPP sites to indicate potential for IGSCC damages of austenitic pipingwelds and give valuable input to understanding of different level of damages at different referenceNPP Units.

IAEA could provide additional input to this project from on-going Coordinated Research Programon high temperature corrosion monitoring WACOL..

6.6. Repair techniques

Background

IGSCC is known phenomenon that has been studied extensively by the U.S. and other countriesoperating BWR type reactors. This phenomenon has only recently been observed in RBMK typereactors (1997). RBMK operators and regulatory authorities worldwide are still evaluating theextent and severity of the problem. When a flaw in an austenitic pipe is revealed during aninspection, decisions will be made to either repair the flaw, or keep the component (flawed) inservice for some time interval. The repair method chosen may remove the flaw entirely or providereinforcement to maintain the original load bearing/carrying ability of the pipe. Four methods ofrepair have been applied to weld repair of austenitic stainless steel piping containing IGSCCindications:

1. Complete removal of the original ”flawed” weld and replacement with a piece of originalpiping, resulting in two new (potentially susceptible) welds being made.

2. A whole section of similar piping (spool piece) low carbon grade or more resistant materialmay be installed. (US BWR and German technology).

3. The defect/flaw may be removed by local repair (excavation and backfilling) with or withoutreinforcement - Chernobyl Unit 3.

4. The flaw may be left in situ and a structural overlay, automatically welded over the originalcircumferential weld may be installed. US-BWR technology.

19

Objectives

To develop a program of improved RBMK repair techniques and essential variables that may havea bearing on IGSCC. This goal should be accomplished through the thorough evaluation of currentand proposed repair schemes and welding optimization schemes for RBMK repairs of IGSCC.This objective may be initiated through the organization of workshops, technical meetings,scientific meetings and seminars

Tasks

1. Evaluate the issues needed to be resolved to incorporate Western repair/welding technologyinto RBMK reactors. This should include both new weld installation and repair (weld overlay)techniques. This can be accomplished through the use of workshops, equipmentdemonstrations, and technical seminars. The information to exchange should include:

• Collection and correlation of existing data• Evaluate all repair welds made for RBMK, IGSCC repairs to date• Collect ISI results on these repairs from each RBMK• Identify any instances of recurring IGSCC in repair welds• Determine critical factors for recurring IGSCC

2. Form a Regional Team to develop draft feasibility study for processes to be used for RBMKrepairs using input from Western Experts and governing regulatory authorities. This could takethe form of 1 or 2 extended Workshops of the necessary experts.

3. Demonstrate the effectiveness of the developed technical feasibility study to provide adequateweld repairs and new welds at a Western manufacturer on RBMK material. This should includedeveloping the following information:

• Residual stress measurement• Degree of sensitization of the repair weld area• Stress improvement/modification techniques• Heat input/Weld weave• Applicability for potential for new material substitutions

4. Purchase appropriate automatic welding equipment and train all RBMK welding operators. (Aminimum of 5 welding set-ups is estimated at $250K-$400K/set-up.)

5. Implement a unified welding repair program at all RBMK sites.

Milestones

Completion of each of the tasks listed above represents a major milestone. The estimated timeduration for each task is listed below, however, activity funding levels may significantly alter theestimated duration and scope for the tasks.

1. 3 months2. 5 months3. 3-4 months4. 6-9 months after Task 3 demonstration5. immediately at the end of Task 4

The final reports for each task will be presented 3 months after completion of Task.

20

Product

A comprehensive set of generic repair procedures (based on good metallurgical and weldingprinciples and adequate inspectability) for IGSCC in RBMK environment. This will be in form ofa report.

Participants




6.7. Decontamination

Background

IGSCC is known phenomenon that has been studied extensively by the U.S. and other countriesoperating BWR type reactors. This phenomenon has only recently been observed in RBMK typereactors (1997). RBMK operators and regulatory authorities worldwide are still evaluating theextent and severity of the problem. IGSCC is a metallurgical phenomenon resulting from thecombined action of tensile stress, a susceptible material condition and a corrosive environment.Since IGSCC repairs and inspection may significantly increase the personnel dose of RBMK stuffdecontamination becomes an important issue for this reactor type. Some decontaminationprocesses have initiated a significant number of IGSCC events, so care is required to ensurecompatibility of the decontamination process with the material and water chemistry requirementsof RBMKs.

Objectives

To exchange information on decontamination principles and procedures at RBMKs which arenecessary to reduce dose rate for both repair and inspection personnel

Scope

Decontamination principles considering ALARA at RBMKs.

Tasks

1. Select participants for the activity team2. Comprehensive evaluation of current decontamination practice worldwide3. Feasibility study on the use of decontamination practices to RBMKs4. Recommendations based upon results of tasks 2 and 35. Initiate a laboratory program (carry out screening tests) to verify compatibility of

decontamination process with RBMK materials and water chemistry

21

Milestones

Completion of each of the tasks listed above represents a major milestone. This activity isestimated to require 21 months to complete. The estimated time duration for each task is listedbelow, however, activity funding levels may significantly alter the estimated duration and scopefor the tasks.

1. Preliminary report (3 months)2. Preliminary report (4 months)3. Preliminary report (3 months after task 2)4. Preliminary report (2 months)5. Preliminary report (6 month)


Product

Comprehensive recommendations for decontamination applicable for RBMKs. This will be inform of a report.

Participants




22

7. CONCLUSIONS

1. Discussion during the meeting was focused on the development of an effective strategy forsafety improvement of RBMK NPPs with respect to IGSCC damage of the heat affected zoneof austenitic stainless steel piping welds. Similar degradation was earlier observed at vesseltype BWRs and the experience accumulated can provide a basis for addressing the issue forRBMKs more effectively.

2. Based on the discussion, seven technical activities to address the issue were proposed. Theseactivities need to be initiated as a matter of urgency. Strengthened co-ordination and improvedexchange of information among the parties involved would contribute substantially to theeffectiveness of related activities.

3. It is recognised, that the proposed activities go in some cases beyond the usual scope of theIAEA programme and therefore have to be addressed in the frame of national safetyimprovement programmes as well as in bilateral and international co-operation programmes.The IAEA should continue to provide a forum for exchange of information, monitor theprogress achieved, and assist in co-ordination of the effort.

4. IAEA should consider making this report available to G-7 Nuclear Safety Group.

23

APPENDIX I. STATUS UPDATE FOR LITHUANIA

CONTENT OF PRESENTATION:

• GENERAL

• UT METHODS AND TECHNIQUES APPLIED AT IGNALINA NPP

• RESULTS OF ISI ACTIVITIES

• RECOMMENDATIONS PROVIDED WITHIN SAFETY JUSTIFICATION OFDY300 PIPING

• DECISIONS TAKEN REGARDING FURTHER OPERATION

• FOLLOW-UP ACTIVITIES

• CONCLUSIONS

GENERAL

• FOLLOWING RECOMMENDATIONS OF MAIN DESIGNER AS WELL TAKINGINTO ACCOUNT RESULTS OF ISI IN OTHER PLANTS OPERATING RBMKEXTENSIVE ISI PROGRAM ON DY300 HAS BEEN PERFORMED BYOPERATING ORGANISATION OF IGNALINA NPP

• CONTRACT HAS BEEN SIGNED BY IGNALINA NPP WITH PROMETEIINSTITUTE TO PERFORM SAFETY JUSTIFICATION OF DY300 PIPING WITHRESPECT TO THE IGSCC PROBLEM

• RESULTS OF ISI REGARDING DY300 HAVE BEEN IMPLEMENTED INTOSAFETY CASE OF IGNALINA NPP RBMK RCS

• FOLLOW-UP ACTIONS HAVE BEEN CONSIDERED WITH RESPECT TO THEFURTHER OPERATION OF DY300 PIPING

24

UT METHODS AND TECHNIQUES APPLIED AT IGNALINA NPP

• ISI OF DY300 PIPING HAS BEEN PERFORMED WITH APPLICATION OF UTAND RT MEANS

• SPECIAL UT TECHNIQUE “KRAB” HAS BEEN DEVELOPED BY CNIITMASWITH APPLICATION METHODOLOGY MCU-5-98

• SPECIAL MANIPULATOR HAS BEEN DEVELOPED BY TRC COMPANYAPPLYING TOMOSCAN AND P-SCAN ISI DATA ACQUISITION EQUIPMENT

• ASSESSMENT OF AUTOMATIC UT RESULTS HAS BEEN PERFORMED BYTRC AND IGNALINA NPP SPECIALISTS BY APPLICATION OF TOMOVIEWSOFTWARE

• AMDATA PROBE HAS BEEN APPLIED TO VERIFY TYPE OF INDICATEDDEFECTS

• STANDARD RT HAS BEEN APPLIED

RESULTS OF ISI ACTIVITIES

• 939 WELDS HAVE BEEN INSPECTED BY APPLICATION OF “KRAB”TECHNIQUE

• 33 WELDS WITH LONGEST INDICATIONS HAVE BEEN INSPECTED WITHAUTOMATIC UT - TOMOSCAN AND P-SCAN DAS

• 82 WELDS HAVE BEEN INSPECTED BY RT

• 38 WELDS (INDICATIONS WHICH LENGTH> 100mm) HAVE BEENINSPECTED BY APPLICATION OF AMDATA PROBE

• 183 WELDS WITH INDICATIONS HAVE BEEN FOUND – LONGESTINDICATION 380 mm , 38 INDICATIONS LONGER THAN 100 mm

25

RESULTS OF ISI ACTIVITIES(CONTINUED)

• TWO WELDS WITH CRACKS AND 16 WITH WELDING INTRODUCEDTECHNOLOGICAL DEFECTS HAS BEEN FOUND BY RT

• 14 WELDS HAVE BEEN INSPECTED BY MANUAL UT “KRAB”, AUTOMATICUT, AMDATA AND RT BEFORE MATERIAL INVESTIGATION TO VERIFY ISIRESULTS

• MATERIAL INVESTIGATION RESULTS OF 14 WELDS INDICATED THATTHERE IS NOW DEVELOPMENT WELDING INTRODUCED DEFECTS AT SITEWELDS

• CRACK TYPE DEFECTS HAVE BEEN CONFIRMED ONLY ON THE WELDSTHAT BEEN MADE DURING MANUFACTURING

RECOMMENDATIONS PROVIDED WITHIN SAFETY JUSTIFICATION OF DY300PIPING

• CONCLUSIONS HAS BEEN PROVIDED BY PROMETEI INSTITUTEREGARDING CAUSES OF IGSCC IN DY300 PIPING

• RECOMMENDATIONS CONCERNING WELDING TECHNOLOGY DURINGREPAIR OF WELDS WITH DEFECTS HAS BEEN ISSUED

• RECOMMENDATIONS CONCERNING ACCEPTABLE SIZE OF CRACK TYPEDEFECTS FOR ONE YEAR OPERATION HAS BEEN ISSUED

• FOUR YEARS ISI PERIOD HAS BEEN RECOMMENDED FOR WELDSWITHOUT INDICATIONS

26

DECISIONS TAKEN REGARDING FURTHER OPERATION

• TECHNICAL DECISION CONCERNING FURTHER OPERATION OF DY300PIPING HAS BEEN REVIEWED AND APPROVED BY THE REGULATORYBODY DURING ISSUING OF THE PERMISSION TO OPERATE INPP UNIT 1AFTER MAINTENANCE

• 24 WELDS HAVE BEEN REPAIRED BY FULL REPLACEMENT OF WELDEDJOINT

• 20 SITE WELDS WITH INDICATIONS LONGER THAN 100 mm ON WHICHCRACK TYPE DEFECTS HAVE NOT BEEN CONFIRMED BY THEAPPLICATION OF UT AND RT MEANS HAVE BEEN ALLOWED FORFURTHER OPERATION WITH FOLLOWING INSPECTION FORESEEN DURINGTHE OUTAGE OF 1999

• WELDS WITH WELDING INTRODUCED TECHNOLOGICAL DEFECTSINDICATED JUST BY RT HAVE BEEN ALLOWED FOR FURTHER OPERATIONWITH FOLLOWING INSPECTION FORESEEN DURING THE OUTAGE OF 1999

DECISIONS TAKEN REGARDING FURTHER OPERATION(CONTINUED)

• 141 WELDS WITH INDICATIONS OF LESS THAN 100 mm INSPECTED BY UTHAVE BEEN ALLOWED FOR FURTHER OPERATION WITH FOLLOWINGINSPECTION FORESEEN DURING THE OUTAGE OF 1999

• REPAIRED WELD SHALL BE INSPECTED WITH APPLICATION OF UTMEANS DURING THE OUTAGE OF 1999

27

FOLLOW-UP ACTIVITIES

• METHODOLOGY OF MANUAL UT APPLIED FOR “KRAB” WILL BEREVIEWED TAKING INTO ACCOUNT RESULTS OF ISI OF DY300 PIPING

• “KRAB” DEVICE WILL BE MODIFIED ADJUSTING IT TO THE ENCODER FORRECORDING TO BE ANALYSED BY TOMOVIEW

• METHODOLOGY FOR AUTOMATIC UT WILL BE MODIFIED TO APPLYAMDATA PROBE FOR CHARACTERISATION OF DEFECTS

• SAFETY JUSTIFICATION REPORT PERFORMED BY PROMETEI INSTITUTEWILL BE REVIEWED TAKING INTO ACCOUNT ISI RESULTS OF 1998

• IGNALINA NPP RCS SAFETY CASE SHALL CONSIDER ISI RESULTS OF DY300 PIPING

CONCLUSIONS

• SUFFICIENT INFORMATION HAS BEEN COLLECTED WITH RESPECT TO THECAUSES OF IGSCC CRACKING OF DY300 PIPING AT IGNALINA NPP

• USED ISI TECHNIQUES SHALL BE DEVELOPED TO INCREASE ABILITIES OFDEFECT CHARACTERISATION

• USED ISI TECHNIQUES SHALL BE DEVELOPED TO INCREASE ABILITIESFOR ASSESSMENT OF DEFECTS DEPTH

• SAFETY JUSTIFICATION SHALL RECONSIDER THE RESULTS OF 1998 ISI OFDY300 PIPING

28

APPENDIX II. STATUS UPDATE FOR RUSSIA

At IAEA Slavutych Workshop of June 1998 there were presented a number of papers by RDIPEspecialists and their colleagues from Russian Utilities and other institutes. After the Workshopthere have been performed additional analyses of available information on various aspects ofIGSCC damages of austenitic piping welds of RBMK NPPs. This enabled RDIPE specialists topropose complex of technical measures to address IGSCC damages of RBMK NPPs piping whichare presented as a chart (Fig.1). The team to perform all types of activities presented at Fig.1 isavailable now in RF Minatom disposal and was in more details presented at Workshop (Appendix3 of Final Report - named herebelow as «App.3», presentation of Mr.Arzhaev).

After the Workshop there were continued ISI and complex material studies of peculiarities ofdamage at different RBMK NPP Units. These results are in process of further analyses now.Approach towards material studies of metal cut from damaged welds was as reported in Slavutychinvolving fractographic and micro roentgen-structural analyses of opened crack surfaces (App.3,presentations of Dr.Abramov (RF) and Prof.Krasovski (Ukraine)). Activities performed sinceSlavutych Workshop give a basis for improvement of Table IV (Chapter 2) of the Final Version ofReport (see Table 1 herebelow for RF RBMK NPPs). It is evident that scope of 1998 year in-service inspection (ISI) at RBMK NPPs austenitic piping dia.300 mm welds was relevant.Information from ISI at some Units will come later in 1998, but total amount of damaged weldsafter 100% ISI at major Units (except Leningrad Unit 3) is not more than 3-10%. These resultscorrespond to the information on mean values of water coolant conductivity at NPP Units andappropriate data by Dr. Andresen&Dr. Ford showing influence of residual stress level andconductivity values (App.3, presentation of Mr.Belous). Further activities on additional waterchemistry parameters measurements are now foreseen to be performed on-site to gather more datawhich will allow to reveal their influence on damage of piping welds at specific RBMK NPP sites.

More efforts have been spent after the Workshop in Slavutych on improvement of automatic leakdetection systems (ALDS) at RBMK NPP Units in RF during the outages of year 1998. After 1998year activities in this area most of primary circuit compartments at RBMK NPP Units will beequipped with two channel ALDS (based on monitoring of humidity and aerosol activity). Butwith respect to IGSCC damages it is needed to fasten additional improvements of ALDS bytechnical means capable of identification throughwall flaw leakage from leaking seal and etc.

Measures foreseen by «RDIPE team» to address IGSCC issues at RBMK NPPs do not includesuch measures as piping material replacement and implementation of hydrogen water chemistrywhich are treated as «long-term» measures by NUREG-0313 (Rev.2F). It is stated in the FinalReport of Slavutych Workshop that introduction of HWC at RBMK NPPs could lead to severecontamination in turbine hall systems. Materials presented in Slavutych by Prof.Speidel(Switzerland) have shown that even low carbon base metal of titanium and niobium stabilizedstainless steels can be damaged in BWR type environment after cold work. So replacement ofexisting piping by manufactured from another base material do not provide 100% guarantee byitself of full absence of IGSCC damages in future. Moreover, according to the regulations (PNAEG-7-008-89 in Russia and appropriate documents acting in the Ukraine and Lithuania) rathercomprehensive set of testing is demanded in order to introduce some new material to be appliedfor primary circuit NPP piping of former USSR design.

On the contrary some «short-term» measures as overlay welding (WOL) and mechanical stressimprovement process (MSIP) applied in many countries (for example, USA, Spain, Finland, etc.)have proofed by experience of near 15 years there effectiveness to mitigate further IGSCCdamages (App.3, presentation of Mr.Gilman ).

29

One of the important feedback of the Slavutych Workshop was that it have been realized byspecialists in RF once more about strong influence of welding process (in terms of weld residualstresses/strains and metal sensitization in HAZ near the fusion line) on further susceptibility ofwelds to IGSCC damages. So it seems practical to make immediate improvement of welding andrepair technology (introducing primarily automatic welding on-site, which is not possible withoutautomatic mechanical devices for grinding weld surface, cutting piping and weld edge preparation,supported secondly by technology transfer of WOL and optimized automatic welding using ofnarrow gap welding, etc.) at all RBMK NPP sites to improve safety as for operation of alreadyexisting welds as well as to give longer life to new welds which appear in increased amount duringtotal replacement of damaged welds by new piece of piping.

But the most valid issue for all further improvements of safety at RBMK NPPs is on-siteapplication of efficient modern UT techniques/means. There are existing primary circuit dia.300mm piping weld zones with limited accessibility and even not accessible currently to application ofUT. It worth to mention here that application of WOL at BWR NPP piping have lead todevelopment of special UT techniques/means for such welds inspection, capable of sizing flawsand revealing sufficient changes in their characteristics (e.g. propagation in wall thicknessdirection during application of WOL repair and in further operation). If efficiency of applied on-site UT techniques/means is guaranteed to exclude long cracks during ISI intervals than it becomespossible to make use of structural integrity assessment of Leak-Before-Break type and demonstratereasonably low probability of Double-End-Guillotine-Break (DEGB) of RBMK dia.300 mm pipingof operating NPP Units.

Of cause mentioned above is relevant first of all to RBMK NPPs in RF. However, in situation withvery similar regulatory requirements and minor differences for welds life assessment in allcountries operating RBMK NPPs approach towards safety improvement presented schematicallyon Fig.1 seems to be applicable and reasonably effective for all population of RBMK NPPs.

30

TABLE 1. RESULTS OF ISI INSPECTION OF DIA 325 MM PIPING ON RUSSIAN RBMK PLANTS

NPP Units ISI Scope

1997/1998

Defects found Repair Left in operation

with flaws

LNPP-1

-2

-3

-4*

10%(UT)/25%(UT)

10%(UT)/25% (UT)

100%(RT) in 1997

10% (UT)/25% (UT)

-

+

+

-

-

+

+(100% welds)

-

-

-

-

-

SNPP-1

-2

-3

100% (UT in 1997/1998)

10% (RT)/100% (UT)

10% (RT)/100% (UT)

+

+ (1998)

+ (1998)

+

+

+

+

+

+

KNPP-1

-2*

-3

-4

100% (RT+UT)/16% ** (UT)

10 (RT)/100% (UT)

10% (RT)/100% (UT)

10% (RT)/25% *** (UT)

+ (1997)

-

+ (1998)

-

+

-

+

-

+

-

+

-

Data for the 1st of October 1998:* - Unit is in process of long-term outage** -planned scope of ISI for 1998 + all welds with previously revealed flaws which have been allowed in operation by analyses*** - planned for 1998.

31

Improvement andValidation of NDEProcedures/Tools

Substantiation of SITechnologies

Application to Welds

Development ofTechnologies and Tools

for SI

Substantiation ofParameters of Solution

Heat Treatment

Application of Tools for:

- Automatic Welding- Automatic Pipe Cutting andWeld Edge Preparation- Grinding

Substantiation of OptimalRegimes of Automatic

Welding

Substantiation of OverlayWelding Repair Technology

ISI and Flaw Root CauseAnalyses

Optimized WeldingRepair Technologies

Development and Application ofStress Improvement Measures

Improvement of Water Che-mistryParameters Monitoring and WC

Organization

Implementation of 3-Channel ALDS

Hightemperature WCParameters Monitoring

Improvement of WCOrganization

H2 Content Monitoringin Case of Deaerator

Mulfuntcion

Implementation ofDeaerated Start-Up

Technology

Assessment of Operating History Data (WC Parameters, Intensity of IGSCCDamage and Unit Specific Rates of Flaw Growth in Operation) and Forecastof Lifetime. Optimization of ISI Programs (Scope, Perio-dicity, etc.) Based

on Operating History and Applied CountermeasuresDevelopment of AnalysisBased on Leak-Before –Break

Concept

Issuing of Safety(Integrity) Analysis Report

Weld Repair and/orSI Countermeasures

Application to Welds

Scope of ISI:- in 1998 25% -100% of

Welds- later according to

Typical ISI Program

ISI Results Assessment, FlawRoot Cause Analyses

Assessment of SafeOperation with Revealed

Flaws(after sizing)

ComprehensiveStress Analysis for

NOC, SSE, Faultedand AccidentConditions

Strength Assessment(PNAE G 002-86)

Fig. 1. Complex of Measures Being Developed and Applied by «RDIPE Team» to Support SafeOperation of Austenitic Piping Welds of RBMK NPPs with Respect to IGSCC Attack

32

APPENDIX III. REVISED OUTLINES OF FOLLOW-UP ACTIVITIES

The information in this Appendix has been prepared and provided by the RBMK specialists fromRussia after the meeting.

Improvement of UT inspection techniques

Main goalTo adapt/develop procedures/tools for UT inspection of dia.300 mm piping weld zones withlimited accessibility and not accessible currently to UT.

Major technical tasks(1) Exchange of information on available procedures /tools for UT inspection of piping zones with

limited accessibility and selection some of them for performance demonstration on weld zoneof dia.300 mm piping.

(2) Production of a set of samples of dia.300 mm piping welds for open and blind trails.(3) Demonstration of efficiency of UT for zones with limited accessibility and currently not

accessible after period of selected procedures/tools adaptation/development on a weld zone ofdia.300 mm piping sample with artificial defects.

(4) Assessment of efficiency of adapted/developed UT procedure/tools by a set of blind trails.(5) Development of recommendations for on-site application at RBMK NPPs.

Expected results(1) Adaptation/development of UT tools/procedures to specific geometry of weld zones of dia.300

RBMK piping with limited accessibility and not accessible now to UT and recommendationfor on-site application at RBMK NPPs.

Demonstration of efficiency of UT inspection for WOL repair zones

Main goalTo demonstrate UT efficiency for WOL, including samples relevant to RBMK dia.300 pipingwelds.

Major technical tasks(1) Exchange of information on available procedures /tools for UT inspection of WOL repair

zones.(2) Production of a set of samples of dia.300 mm piping welds with WOL for open and blind

trails.(3) Demonstration of efficiency of UT for WOL repair zones on samples relevant to RBMK

dia.300 piping welds.(4) Assessment of efficiency of adapted/developed UT procedure/tools by a set of blind trails.(5) Development of report on feasibility of adaptation of WOL inspection techniques to regulatory

requirements in RBMK operating countries and recommendations for on-site application atRBMK NPPs.

Expected results(1) Demonstration to regulatory authorities and utilities in RBMK operating countries of

efficiency of UT inspection methods for welds with WOL repair.(2) Development of TS for Phase 2 activities on WOL repair technology transfer.

33

ISI systems qualification

Main goalTo develop practical performance demonstration criteria and implementation documentation for anISI qualification center (Phase 1. ISI qualification with respect to IGSCC damage of austeniticpiping welds).

Major technical tasks (Phase 1.1)(1) Development of criteria for selection of location of the regional ISI qualification center.(2) Development of recommended technical justification documentation.(3) Development of recommended protocols for performance demonstration.(4) Development of recommended documentation and TS for test specimens.(5) Development of recommended quality assurance requirements for performance demonstration

center.

Expected results(1) Recommendations on technical documentation for ISI qualification.(2) Criteria for selection of location of the regional ISI qualification center and recommended

quality assurance requirements.(3) TS for Phase 1.2 – Regional ISI Qualification Center establishment.

Leak detection systems improvement/implementation

Main goalTo analyse conditions and specific geometry of compartments for different generations of RBMKplants and clarify general recommendations on ALDS improvement/implementation with respectto IGSCC damages.

Major technical tasks(1) Description of design and «as-build» conditions in compartments where MCC components are

situated.(2) Analyses of current status of ALDS implementation at all RBMK NPP Units.(3) Transfer of modern leak detection technology by demonstration for RBMK regional team of

experts (on test rigs of vendors or by selected utilities on-site) for NPP piping: both with andwithout isolation and experience on qualification of ALDS before implementation at NPPs.

(4) Analysis of additional requirements to ALDS with respect to IGSCC damages at RBMK NPPsand necessity for application of LBB type concept (supported by enhanced ISI).

(5) Development of recommendations to ALDS implementations/improvement of specific RBMKNPP Units and TS development for Phase 2 technology transfer on ALDS implementation.

Expected results(1) Recommendations to ALDS implementation/improvement of specific RBMK NPP Units based

on analysis and state-of-the-art ALDS capabilities demonstration.(2) TS for Phase 2 of technology transfer on ALDS implementation/improvement for specific

RBMK NPP Units.

Comprehensive study of degradation mechanism peculiarities

Main goals1. To obtain a comprehensive understanding of leading causes of IGSCC damages at reference

RBMK NPP Units.

34

2. To determine and recommend the optimum water chemistry condition necessary to mitigateinstances of IGSCC in RBMKs.

Major technical tasks(1) Arrangement of additional water chemistry parameter collection/measurement on-site at

reference RBMK NPP Units.(2) Preparation of a guideline how to handle crack assessment(3) Collection and correlation of existing data:• Collect ISI results from reference RBMK Units• Collect water chemistry data• Collect metallurgical data• Collect other relevant data, e.g. about decontamination procedures• Identify conditions that may be leading/have led to IGSCC at reference NPP• Determine critical factors for IGSCC and likely future trends.(4) Additional comprehensive failure analyses to include:• State of the art techniques• Detailed crack length and depth measurements(5) Take the results of the failure analyses and combine them with the existing data base to

capture all the different crack morphologies and growth patterns/locations.(6) Experimental program establishing a model (starting from the beginning and taking into

account the results of task 3, 4 and 5).(7) Recommendations for improvement of general WC guidelines and ISI guidelines.

Expected results(1) Recommendations of optimum water chemistry condition necessary to mitigate instances of

IGSCC in RBMKs.(2) TS for Phase 2 high temperature WC parameters monitoring implementation at all RBMK

NPPs.(3) Comprehensive understanding of leading causes of IGSCC damages at reference RBMK NPP

Units (in a form of a report).

Comprehensive integrity assessment

Main goalTo set requirements and priorities for safety improvements in order to allow IGSCC to be managedsafely.

Major technical tasks(1) List possible accident scenarios and comment on relative likelihood.(2) Identify safety systems and safety arguments available to make “defence in depth” arguments

against IGSCC related accidents. Suggest a basis for regulatory review of safety assessment.(3) Identify requirements for leak detection systems and targets for ISI effectiveness (including

performance of LBB analysis).(4) Determine critical factors for IGSCC and likely future trends.(5) Prioritize improvements to ISI implementation, leak detection and other systems.

Expected resultsRecommendations on priorities for system/maintenance procedure upgrades.

35

Repair techniques

Main goalTo recommend effective repair and welding technologies to mitigate further IGSCC damages.

Major technical tasks(1) Exchange of information on effective repair and welding technologies of austenitic piping

welds.(2) Development of draft feasibility study for repair and welding processes to be used for RBMK.(3) Demonstration of efficiency of repair and welding technologies recommended for application

at RBMK NPPs after feasibility study.(4) Development of TS for application of effective repair and welding technologies at RBMK

NPPs.

Expected results(1) TSs for application of effective repair and welding technologies at RBMK NPPs.(2) TSs for necessary additional equipment delivery to RBMK NPPs.

Decontamination

Main goalTo organize exchange of information on decontamination technologies effective to reduce doserates.

Major technical tasks(1) Comprehensive evaluation of current decontamination practice worldwide(2) Feasibility study on the use of decontamination practices to RBMKs(3) Recommendations for further laboratory studies (if necessary)(4) Initiate a laboratory program (carry out screening tests) to verify compatibility of

decontamination process with RBMK materials and water chemistry

Expected resultsComprehensive recommendations for decontamination applicable for RBMKs (in form of areport).

36

ABBREVIATIONS

ALDS - automatic leak detection systemBWR - boiling water reactor (vessel-type)DEGB - double-ended-guillotine-breakHWC - hydrogen water chemistryIGSCC - intergranular stress corrosion crackingIQ - inspection qualificationISI - in-service inspectionLBB - leak-before-breakMCC - main circulating circuitMSIP - mechanical stress improvement processNDT - non-destructive testingNPP - nuclear power plantPC - personal computerRBMK - reactor of large capacity, channel-typeRT - radiographic testingTS - technical specificationUT - ultrasonic testingWC - water chemistryWOL - repair technology by overlay welding

37

REFERENCES

[1] Report of the IAEA Regional Workshop on Environmentally Assisted Cracking of NPPAustenitic Piping, Slavutych, Ukraine, June 22-26, 1998. IAEA TC Project RER/9/052.RBMK-SC-060, IAEA, Vienna, 1998.

[2] Safety Assessment of Proposed Improvements to RBMK NPPs, IAEA-TECDOC-694, IAEA,Vienna (1993).

[3] RBMK NPPs Generic Safety Issues, IAEA-EBP-RBMK-04, IAEA, Vienna, 1995).

[4] Databases On Safety Issues for WWER and RBMK Reactors, IAEA-EBP-WWER-04, IAEA,Vienna, 1996.

[5] Safety Improvement of RBMK NPPs. CEC Project. Phases I & II.

[6] NRC. NUREG-0313 (Rev.-2F), January 1988.

[7] Methodology for qualification of in-service inspection systems for WWER nuclear powerplants, IAEA-EBP-WWER-11.

[8] IAEA-RBMK-SC-034

[9] IAEA-RBMK-SC-057

[10] IAEA-TECDOC-774

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CONTRIBUTORS TO DRAFTING AND REVIEW

Ms. R. Kilian, Siemens AG, GermanyMr. D. Jungclaus, GRS, GermanyMr. G. Maksimovas, VATESI, LithuaniaMr. Yu. Saburov, Ignalina NPP, LithuaniaMr. A. Arzhaev, RDIPE, RussiaMr. G. Saprykin, RDIPE, RussiaMr. N. Timofeev, RDIPE, RussiaMr. I. Sivokhine, Gosatomnadzor, RussiaMr. E.Brylev, Rosenergoatom, RussiaMr. E.Liszka, Swedish International Project Nuclear Safety, SwedenMr. V. Hryschenko, Ministry for Environmental Protection and Nuclear Safety, NRA, UkraineMr. L. Poulter, AEA Technology, UKMr. T. Taylor, Pacific Northwest Laboratories, USAMr. C. Czajkowski, BNL, USAMr. R. Havel, Czech RepublicMr. Z. Kriz, IAEAMr. J. Reed, IAEA

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