RIC 2009 NRC Research in Support of the NGNP Licensing Strategy

1. RIC 2009NRC Research in Support of the NGNP Licensing Strategy John R. Jolicoeur USNRC/RES/DSA March 12, 2009

2. Outline • NRC Safety R&D Objectives • NGNP and PIRT • Evaluation Model • HTGR R&D • Thermal-fluids • Fuels & Fission Products Transport • Other Research Areas

3. NRC Safety R&D Objectives • Develop staff knowledge, expertise, capabilities and review guidance • Independently confirm technical basis for requirements and criteria • Develop independent analytical capabilities • Confirm/interpret technical information for which there is significant uncertainty • Validate/scope-out technical issues requiring follow-up resolution by an applicant

4. ARRP Structure and Scope(HTGR) In-depth Research Infrastructure Needs Assessment • HTGR-specific, reactor, materials/fuel cycle aspects • Generic aspects (e.g., I&C, human factors, PRA) NRC Research & Development Plans • HTGR-specific, reactor safety review needs emphasis • Generic aspects (e.g., I&C, human factors, PRA)

5. What is NGNP and What is PIRT? • Next Generation Nuclear Plant (NGNP) • An advanced reactor concept for nuclear electricity production and hydrogen cogeneration • Very high-temperature gas-cooled reactor (VHTR) • Phenomena Identification and Ranking Technique (PIRT) • A structured elicitation process to identify safety relevant phenomena and assess their importance • A tool for identifying and prioritizing research needs • Results documented in Phenomena Identification and Ranking Tables

6. Reactor Plant Systems Analysis • Evaluation Models • Normal Operations • Determines the source term for the initial release. • i.e., the generation and distribution of FPs, magnitude and distribution of plate-out & absorbed FPs within He pressure boundary, circulating activity, coolant contaminant & erosion activation products, and dust-born radionuclides. • Initial Release • Models the release of circulating activity including dust mobilization and plate out lift-off; large/rapid reactivity events that result in CFP failures. • Delayed Release • Models the release of FPs from intact & failed CFPs during core heat up and with or without or steam ingress; models FP hold-up and retention within the helium pressure boundary and the confinement.

7. By Function Code Specific NGNP Evaluation Model

8. Thermal-Fluid Technical Challenges Introduction to Thermal-Fluid Technical Challenges • Combined Mode Heat Transfer • Bypass Flow • Maximum Fuel Temperatures • Local Temperature Variations

9. Air Ingress Air ingress through vessel top break: Blue = He / Red = Air

10. CFD Mesh Generated for random close-packed bed near reflector wall CFD Results Pressure Drop Significant under-prediction Implication Wall bypass flows may be larger than expected. Analytical & experimental effort may be needed to resolve. Role of CFD: Example of Ongoing Studies

11. HTGR “TRISO” Coated Fuel Particle Porous Carbon Buffer Layer Dense Inner Carbon Layer UCO or UO2 Fuel Kernel Dense SiC Layer Dense Outer Carbon Layer

12. HTGR Mechanistic S-T and FP Transport Calculation Would Model Many Complex Phenomena Helium Pressure Boundary (HPB) Reactor Building HPB Break UO2, UCO Graphite Dust Fuel Vent Filter? Reactor Bldg Vent M-285(7) 8-27-01

13. MELCOR Development Activities for NGNP • Completed Activities • Pebble-Bed Core Model • Prismatic Core Model • Improved Helium Properties • Point Reactor Kinetics Model • Graphite Oxidation Model • Future Activities • Empirical CFP failure Model • FP diffusion model for CFPs • Reactor Cavity Cooling System Model • Balance of Plant Models (e.g., IHX) • Improved FP lift-off and re-suspension models • Improved numerics for long transients • Lock-exchange model (air ingress)

14. Closing • Research is underway to support the NGNP Licensing Strategy • Cooperative research with DOE / INL • International collaboration