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Concepts Evolving for Performance Based NDE and Monitoring in ASME Code Section XI Division 2

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CONCEPTS EVOLVING FOR PERFORMANCE BASED NDE AND

MONITORING IN ASME CODE SECTION XI DIVISION 2

Steven R. Doctor

Retired Laboratory Fellow, Emeritus Program, Pacific Northwest National Laboratory, USA

ABSTRACT

The American Society of Mechanical Engineers (ASME) developed a Boiler and Pressure Vessel (B&PV) Code that was adopted for the design, construction, operation, inspection and maintenance of nuclear power plants (NPPs). The ASME Code nuclear sections evolved for the fleet of light water reactors (LWRs) that were built. The recent renaissance and interest in building new and advanced (NPPs) has motivated the ASME B&PV Code developers to review existing code requirements for these new NPPs. ASME B&PV Code, Section XI addresses the issues related to the pre-service and in-service inspection of NPPs.

It was decided that new code requirements should be flexible and capable of addressing all reactor

designs including high temperature gas cooled reactors, small modular reactors, liquid metal reactors, etc. The existing Section XI requirements for LWRs are in Division 1 and it was decided that the new

requirements for new and advanced reactor designs would be placed in Division 2. Division 2 will be based on the reliability and integrity management (RIM) of all reactor structures, systems and

components (SSCs) from the design stage through decommissioning. Division 2 will be performance based for the nondestructive evaluation (NDE) and continuous on-line monitoring that will be required to achieve, demonstrate and document adequate performance for supporting the RIM goals of every SSC. This is a major departure from Division 1 and a number of new concepts must be developed to make Division 2 both practical and effective for its intended purpose. This paper will discuss some of the concepts that are evolving on how to develop performance based NDE and monitoring requirements for all future NPP designs.

INTRODUCTION

The American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel (B&PV) Code has a Section XI ASME (2013) addressing the pre-service and in-service inspection (ISI) of nuclear power plants (NPPs). Section XI was developed as light water reactors (LWRs) were being designed, fabricated and deployed as an important part of the clean electricity generation capability in the United States of America. Since there has been a resurgence of interest in building new NPPs, there has also been an interest in innovative and advanced NPP designs that include small modular reactors (SMRs), high temperature gas cooled reactors, liquid metal and salt reactors, etc. ASME Code developers recognized that the current requirements in many sections of the B&PV Code pertains explicitly to LWRs and that these code sections need to be updated to be relevant to these new NPP designs. Section XI set up a Special Working Group on Reliability and Integrity Management (SWGRIM) to address this need. The SWGRIM has been chaired by Frank Schaaf and he has lead the development of the new Section XI Division 2. Section XI Division 1 contains existing code requirements pertaining to LWRs. The new Division 2 has evolved as the needs changed over time based on the lead NPP that was to be designed and constructed under this new division. Initially the driving force was the Pebbled Bed Modular Reactor (PBMR) that was under development in South Africa and when this program was suspended, the interest moved to the U.S. Department of Energy and an industry alliance program to develop the Next

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moved on to SMRs and then more recently interest from Japan to pursue a liquid metal reactor. Each of these different reactor designs created substantial changes in format and requirements under development in Division 2. Finally, the ASME Code chose an approach to make the Division 2 generic and technology neutral in the sense that the overall approach would address all reactor designs. There would be specified a set of general requirements for the RIM process pertaining to all NPP types. Appendices for each reactor design would be created to define the specifics on how the generic process would be

modified/supplemented to accommodate the unique requirements of each design. There has also been interest in applying the Division 2 to license extension for operating NPPs from 60 to 80 years of

operation and even for non-nuclear complex engineered systems. Since Division 2 is generic and specific applications require appendices be developed for each application, it has been possible to achieve making Division 2 general requirements technology neutral.

In tackling this new approach, it was paramount to build on all of the lessons learned from the 40+ years of LWR operating experience. The key is to not repeat the mistakes of the past but to seek how to make future NPPs safer, more reliable and manage costs to make them cost competitive with other sources of electricity generation.

This paper focuses on the Division 2 Appendix IV that provides the requirements for the qualification of all procedures, equipment and personnel used to monitor and nondestructively examine all of the structures, systems and components (SSCs) to assure that the reliability and integrity goals are met. The challenge for this appendix is the fact that currently all of these new NPP applications are under

development and the specifics needed for establishing a basis for performance based requirements cannot be determined. Many factors such as the SSC materials, designs, operating conditions, critical flaw sizes, flaw locations, inspection intervals, expected or postulated degradation processes, etc. are unknown and they are needed in order to justify quantitative monitoring and inspection performance metrics. Thus, the approach taken for Appendix IV has been to define a systematic and detailed process that will need to be followed. This paper will elaborate on some of the key process concepts that are being discussed in which the committee must reach a consensus to support a technical basis of the process being detailed in Appendix IV.

ASME CODE SECTION XI DIVISION 2 - RIM PROGRAM

The generic requirements contained in Division 2 provides a systematic process for assessing and managing the reliability and integrity of all SSCs that must be included in the RIM program. One of its key features is that it considers all of the monitoring and NDE uncertainties in a consolidated manner rather than the traditional approach whereby as each uncertainty is encountered it is handled

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The generic requirements in Division 2 address the requirements for pre-service examinations to establish a useful and detailed product baseline that insures only high quality/integrity SSCs are placed into service. The pre-service examination requirements pertain to all SSCs. This approach is taken since it is

recognized that the initial application of Division 2 will be for new NPPs for which there is no operating experience and thus, there may be surprises as these NPPs operate and unexpected or unanticipated events occur. These examination processes and the RIM program will be required to be adaptive to operating experience and the unanticipated events as they occur.

APPENDIX IV OF ASME BOILER AND PRESSURE VESSEL CODE SECTION XI DIVISION 2

A white paper Stephens (2014) was prepared and used to justify the rationale and basis for why existing requirements are not adequate to achieve the high performance required to support meeting the RIM goals for each SSC. This white paper basis shows that only performance based requirements for procedures, equipment and personnel would provide the evidence needed to demonstrate that the quality of the monitoring and NDE support meeting the RIM quality and reliability goals. The new ASME NDE program (ANDE), see Turnbow (2015) and ASME ANDE Website (2015), will be an important part of the overall Division 2 Appendix IV process to create quantitative data on performance that’s needed to validate, document and justify how the Appendix IV process is meeting the required reliability and management goals.

One of the major challenges is going to be relating the RIM goals into what needs to be demonstrated for the monitoring and NDE performance process. As an example, the RIM goal for a particular SSC may be a failure probability of 10-7. What does this mean in terms or the probability of degradation detection and sizing accuracy? It is not a simple or direct process to relate SSC failure probability to monitoring and NDE performance metrics. Many factors need to be defined such as:

· Degradation initiation rate · Degradation growth rate · Inspection interval

· Probability of degradation detection as a function of degradation type, size, location, etc.

· Accuracy of degradation sizing as a function of degradation type, size, location, etc. to insure that the proper corrective action can be taken

The RIM program will generate the SSC RIM performance goal and it will be required for the Appendix IV process to convert the RIM goal into meaningful and documented monitoring and NDE performance metrics that will be required to be demonstrated for each SSC.

MONITORING AND NDE EXPERT PANEL

The overall process defined in Division 2 relies on the use of an expert panel to develop the RIM program and to fully document all assumptions, RIM goals, bases, rationale and decisions made for defining the details of the comprehensive living program that covers the NPP from start of design through its entire life cycle including decommissioning. The expert panel membership will need to be documented as to their expertise such that review by independent bodies and regulatory agencies agree that experts in all the needed disciplines are adequately represented on the expert panel. Appendix IV builds on this same strategy and a Monitoring and NDE Expert Panel (MANDEEP) will perform a similar function for the process defined in Appendix IV. There may be some overlap between the RIM expert panel membership and the MANDEEP membership but there are unique skills required for MANDEEP that must be

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specified in Appendix IV for monitoring and NDE procedures, equipment and personnel (PEP). The MANDEEP will require expertise in many areas including:

· Understanding failure goals for each SSC (reliability, integrity and functionality) and relating these to qualification PEP performance metrics

· NPP operating conditions when monitoring and inspections are performed · Material aging related factors and impact on performance metrics

· Materials, fabrication processes and geometries

· Degradation mechanisms and processes both known and postulated · Degradation locations, initiation time frames and growth rates · Critical flaw sizes

· Flaw sizes required to be detected · Fabrication flaws

· Monitoring methods – online methods, surveillance samples, etc.

· Cost benefit considerations related to performance effectiveness and inspection intervals

Regardless of when the MANDEEP begins its process, there will be unknowns and as a result the documentation will require extensively detailed records and technical justification for the decision processes pursued. Since the RIM program is a living process, Appendix IV is also a living process such that as operating experience occurs, if assumptions are found to be invalid or decision bases are

inaccurate then, the performance metrics in Appendix IV will need to be adjusted to verify and validate successfully meeting the updated SSC reliability goals.

The MANDEEP will create comprehensive documentation that specifies all of the important parameters that the monitoring and NDE methods must address along with the specific performance metrics that need to be demonstrated for the procedures, equipment and personnel so that these performance metrics are shown to support the desired SSC reliability goals. This MANDEEP guidance will be utilized as a key input for selecting the demonstration approach to be pursued for implementation.

SELECTION OF THE DEMONSTRATION APPROACH

The demonstration approach will require input from a number of experts skilled in measuring and

quantifying monitoring and NDE performance. This panel of experts may be the MANDEEP or could be another expert panel focused only on how to take the guidance from the MANDEEP and create the detailed strategy for demonstrating the required monitoring and NDE performance metrics. Input will also include the experience and direction from:

· ASME Code Section V Article 14 (ASME (2013a)),

· The under development ANDE program to verify that NDE skills based on a job task analysis have been successfully acquired (Turnbow (2015), ASME ANDE Website (2015)),

· ASME B&PV Code Section XI, Division 1, Appendices VII and VIII (ASME (2013)),

· The Performance Demonstration Initiative (PDI) that implemented the ASME Code Section XI, Division 1, Appendix VIII (Performance Demonstration Initiative Website (2015)),

· The EPRI Steam Generator Management and NDE Program, and

Other experience from international programs such as the European Network for Inspection Qualification (ENIQ). There are many applications of the ENIQ approach and one example being Sweden (Zettervall (2012)) and ENIQ documents can be located at websites such as:

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This demonstration approach panel will provide the performance metric demonstration strategy for both monitoring and NDE inspections. Monitoring is being viewed in a very broad sense due to the needs of measuring operating parameters, degradation drivers, degradation initiation drivers, degradation growth, etc. and thus, monitoring parameters such as:

· Temperature extremes or temperature cycles · Pressure profiles or pressure surges

· Leak detection

· Degradation detection using on-line monitoring with technologies such as acoustic emission, helium leak detection or guided ultrasonic waves and

· Surveillance samples

One of the challenges for the MANDEEP will be to provide guidance on employing continuous monitoring, NDE periodic inspections or a combination of both for making the case that any and all degradation or its precursors or degradation drivers are being addressed in a comprehensive way. The key here is that it is not known what technologies will be employed for a given application, the access considerations and environment, growth rates, degradation locations, the lead time required to manage failures, etc. Thus, it is probable that there may well be a number of monitoring and NDE solutions that could be deployed to meet the RIM goals. Other factors may influence the decision on which scenario is selected based on economics, knowledge of monitoring technology, fuel cycle duration, etc. The

Appendix IV process must be flexible and support/provide the full range of technology options that may be selected for meeting the RIM goals.

It needs to be understood that any and all strategies may be employed for the performance demonstration process. The process requires this flexibility to adequately address existing and evolving monitoring and NDE technologies and their respective level of effectiveness including the probability of detection for known or anticipated degradation processes. All approaches are under consideration to create quantitative performance data including data from modelling, laboratory studies, open demonstrations and blind demonstrations. The key is the accumulation of quantitative performance data for the procedures, equipment and personnel that demonstrate meeting the required RIM goal performance metrics for each SSC. The performance metrics must include tolerances that have to be met in order to address

measurement uncertainties in the quantitative performance data.

There are feedback loops in this approach to address issues that may arise such as:

· If the performance required to manage failure of SSCs cannot be achieved with a chosen approach, then modifications will be needed in other variables such as inspection intervals, alternative monitoring methods or NDE methods

· If surprises occur during operation, then there must be a mechanism built into the process to provide a means for updating and upgrading the monitoring and NDE plan to manage the unexpected.

FUTURE DIRECTION

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CONCLUSIONS

As can be seen in the material presented, there is a significant challenge associated with trying to develop requirements for any reactor design and to cover the full life cycle of a new NPP from the design stage through decommissioning. A process has been described in general terms intended to explain the

concepts being pursued to elaborate on the important process details. It is important to note that there are a significant number of steps in the overall process for which specific requirements are not defined because of the large number of unknowns at this time. Therefore, the requirement is that the user of Division 2 must develop a detailed plan that addresses the knowns and the unknowns and assemble the rationale and documentation for justifying and defending their approach so that independent review by regulators and other interested bodies will be able to assess and determine if the plan is acceptable. There are many unknowns and the potential effectiveness of the approach is linked to the expert panels that must create the guidance for the process to work. Major effort is being devoted to developing the requirements that are needed to define the qualifications for the members of the expert panels and what documentation is need to support the selection of experts. This approach is a major departure for ASME Code but it offers an opportunity for ASME to take a leadership position as new NPPs are being

considered to meet future electrical energy needs.

ACKNOWLEDGEMENTS

The ASME Code Task Team on Performance Based NDE is developing Section XI Division 2 Appendix IV and is chaired by Henry Stephens with the following members: Bruce Allbee, Douglas Henry, Frank Schaaf, Larry Mullins, Mike Turnbow, Stephen Cumblidge, Ned Finney, Tim Roney and Steven Doctor. This paper is the result of the extensive efforts and contributions from all of these dedicated code

members. Steven Doctor was selected and supported by this code committee to develop and deliver this paper.

REFERENCES

ASME. (2013). "Rules for Inservice Inspection of Nuclear Power Plant Components, Section XI." In ASME Boiler and Pressure Vessel Code – An International Code. American Society of Mechanical

Engineers, New York. USA

ASME. (2013a). "Nondestructive Examination, Section V." In ASME Boiler and Pressure Vessel Code An International Code. Amer. Soc. of Mechanical Engineers, New York. USA

ASME NDE/QC Personnel Certification Program (ANDE) website. (2015):

https://www.asme.org/shop/certification-accreditation/personnel-certification/ande

Fleming, Karl N., Fletcher, J., Broom, N., Gamble, R., and S. Gosselin. (2008) “Reliability and Integrity Management Program for PBMR Helium Pressure Boundary Components”, Proc. 4th International Topical Meeting on High Temperature Reactor Technology, HTR2008-58036, Wash. D.C.

Fleming, Karl N. and Kobus Smit. (2008). “Evaluation of Design, Leak Monitoring, and NDE Strategies to Assure PBMR Helium Pressure Boundary Reliability”, Proc. 4th International Topical Meeting on High Temperature Reactor Technology, HTR2008-58037, Wash. D.C.

Performance Demonstration Initiative Program Description at EPRI website:

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Stephens, H. (2014). “Performance-Based NDE Personnel Qualifications.” ASME Pressure Vessel and Piping Conf. Paper No. PVP2014-28427.

Turnbow, M. L. (2015). “ANDE-1 an ASME Nondestructive Examination and Quality Control Qualification and Certification National Standard.” SMiRT 23 Conf. Proceedings. Manchester, UK

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