DEVELOPMENT OF A STANDARD FOR V&V OF SOFTWARE USED TO CALCULATE NUCLEAR SYSTEM THERMAL FLUIDS BEHAVIOR

1. DEVELOPMENT OF A STANDARD FOR V&V OF SOFTWARE USED TO CALCULATE NUCLEAR SYSTEM THERMAL FLUIDS BEHAVIOR 2010 RELAP5 International Users Seminar September 22, 2010 West Yellowstone, MT Ed Harvego, Richard R. Schultz, Ryan Crane Idaho National Laboratory

2. Committee Overview • Committee charter and objectives • Committee structure • Committee function • Anticipated content of Verification and Validation (V&V) 30 Standard • Relationship to NQA-1 and other Nuclear Standards and Regulations • Summary

3. Proposed Committee Draft Charter The committee… “Provides the practices and procedures for verification and validation of software used to calculate nuclear system thermal fluids behavior. The software includes system analysis and computational fluid dynamics, including the coupling of this software.”

4. Proposed Committee Objectives Develop a standard that: • Defines requirements for verification and validation of computational fluid dynamics (CFD) and system analysis codes used in nuclear applications • Defines requirements for experimental data used for software validation • Is consistent with all Nuclear Regulatory Commission (NRC) regulatory requirements • Is consistent with or complements related consensus standards (existing or under development) • Specifically addresses requirements unique to High-Temperature Gas-Cooled Reactors (HTGRs) • Considers the potential for coupling of CFD and system analysis codes as part of the analysis process • Meets ANSI requirements

5. Committee Structure • Will nominally consist of 8-20 members selected from Industry, National Laboratories, academia, and Government (NRC and/or Department of Energy), and serving a maximum 5 year term • Selection of members will be based on technical qualifications and to ensure balanced representation • Participation on the committee is as an individual technical expert, not as a representative of a particular organization or interest group • A chair and vice chair will be elected for three-year terms by the voting committee membership • Chair is also the committee representative to the Verification and Validation Standards Committee • The secretary is a non-voting appointed position and a member of the American Society for Mechanical Engineers (ASME) staff with no defined term of office

6. Committee Function • Committee members will typically meet two to three times a year to discuss and review progress on development of the standard • Other group or individual meetings may be required to coordinate and/or present results to regulators and/or other consensus standards development organizations • Based on committee deliberations, individual members will research and develop different topics to be included in the standard • Most of the work in writing the standard will be done by individual committee members between meetings • At the discretion of the committee, contributing (non-voting) members may be solicited (within or outside the U.S.) to serve in review and consulting roles • All activities of the committee will of course be subject to availability of funds

7. Anticipated Content of V&V 30 Standard • Definition of operational and accident domains that must be considered for licensing the nuclear reactor • Calculation domain that is to be used to evaluate the system response for licensing purposes • Requirements for the experimental data sets to be used for validation of CFD and/or system analysis software • Requirements for the ensemble of experimental data sets used to populate the validation matrix for the software in question • Application of the software validation standard • Direct reference to appropriate regulatory requirements for each topic addressed in the standard

8. Thermal-hydraulic Analysis Needs for Advanced Reactor Systems • Determined by the operational and accident envelopes of the system • Can only be satisfied if the calculation envelope of the software is demonstrated to either match or encompass the system operational and accident envelopes. System envelope Calculational envelope

9. Definition of Operational and Accident Domains • USNRC Standard Review Plan (NUREG-0800) developed for pressurized water reacotrs and boiling water reactors, but provides the framework for specifying operational and accident domains in HTGRs • Ensure a sufficiently broad spectrum of transients and accidents, or initiating events. • Initiating events categorized according to expected frequency of occurrence and by type. • Anticipated Operational Occurrence (AOO) – one or more times during the life of the nuclear plant • Anticipated transients without scram (ATWSs) – AOOs with failure to scram (beyond design basis) • Postulated accidents – unanticipated accidents that are not expected to occur during the life of the nuclear plant

10. Definition of Operational and Accident Domains – cont. • Grouping of AOOs and postulated accidents by types: • Increase in heat removal by the secondary system • Decrease in heat removal by the secondary system • Decrease in RCS flow rate • Reactivity and power distribution anomalies • Increase in reactor coolant inventory • Decrease in reactor coolant inventory • Radioactive release from a subsystem or component

11. Calculation Domain • Calculation envelope of the thermal-hydraulic software must match or encompass the system operational and accident envelope • Phenomena Identification and Ranking Table (PIRT) process provides a basis for ranking important phenomena associated with each scenario in the operational domain • Software physics models must properly calculate the key phenomena over the entire range of conditions encompassed by the calculation envelope • Basis for assessing the adequacy of the CFD and system analysis software models is experimental data

12. Requirements for Experimental Data and Experimental Data Sets • Proposed standard should provide the processes and procedures for determining the data needed to populate software validation matrices for both system analysis and CFD software • Processes and procedures should address evaluation of both existing experimental data and procedures for defining new data needs • Software validation matrices should include both separate effects experiments for evaluating localized phenomena and integral effects experiments for evaluating global system response • Ideally, experiment validation matrices will include data from experimental facilities at different scales, so that scaling effects can be evaluated to identify any scaling distortions and provide confidence in scaling assessments performed as part of the software validation process

13. Considerations for New Facilities • Assure that the proposed experiment facility captures key phenomena being investigated • Experiment is scaled to provide a direct link between the scaled facility and prototype plant • Adequate high-quality measurements are available to ensure that experimental data uncertainties are quantifiable and acceptably low • Experiment results can be decomposed to the lowest level modeled by the software to ensure that system behavior at the component level is properly being calculated by the governing software physics • Quality assurance meets applicable requirements of ASME Standard NQA-1

14. Application of Software Validation Standard • It is anticipated that the standard will be used by vendors as the basis for verification and validation of software for licensing advanced reactor designs • Standard should conform to current NRC and other regulatory requirements and guidelines, but will provide additional detail on acceptable processes and procedures used to meet regulatory requirements • Standard is being developed in conjunction with ASME V&V 10 and V&V 20 Standards, and should be consistent with and complement these standards • V&V 30 Committee should decide on the detailed scope and intent of this Standard and provide guidance on its use

15. Relationship of V&V 30 Categories to Equivalent Regulatory Requirements and Guidelines for LWRs

16. Relationship of V&V 30 Categories to Other Consensus Standards

17. Relationship of V&V 30 Categories to Other Consensus Standards – cont.

18. Summary • Process initiated for establishment of V&V 30 Committee • Proposed committee organization, function and membership defined • Approval from ASME V&V Standards Committee obtained • Proposed content for standard developed • Path forward to be defined by committee members