Hydrogen Program at AECL

1. Hydrogen Program at AECL Presented by: Matt Krause ERMSAR 2007 Karlsruhe, Germany 2007 June 12-14 UNRESTRICTED

2. Chalk River Mississauga Whiteshell Atomic Energy of Canada Limited • Established 1952 • Commercial Crown Corporation • Owned by Government of Canada • Our Business • Reactor Vendor (CANDU design) • Reactor Maintenance Services • Nuclear Safety/Performance Products & Services • Research & Development Services • Waste Management & Decommissioning

3. Romania Cernavoda 1 unit 1 unit under construction 2 units to come Quebec, Canada Gentilly 2 1 unit Ontario, Canada Darlington 4 units Pickering 8 units Bruce 8 units Republic of Korea Wolsong 4 units China Qinshan 2 units New Brunswick, Canada Point Lepreau 1 unit India RAPS 2 units Pakistan KANUPP 1 unit Argentina Embalse 1 unit CANDU Reactors Worldwide UNRESTRICTED

4. Overview • Hydrogen Risk in CANDU and PWR • Risk Mitigation Strategies and Hydrogen Mitigation R&D at AECL • Dilution • Deliberate Ignition • Pre/Post Inertization • Recombination • Venting • Remaining Knowledge Gaps – International Collaborations UNRESTRICTED

5. Hydrogen Risk in CANDU and PWR • Large Dry Containment Design – basically little differences • CANDU multi-unit stations use a separate Vacuum Building • Main H2 or D2 Sources come from Zr-steam reactions, water radiolysis, and metal corrosion (DBA) • Difference lies in the DBA envelope for CANDU and PWR – LOCA/LOECC UNRESTRICTED

6. Risk Mitigation Strategies • Containment Integrity - Mechanical Loads • Must limit peak pressure and time at pressure • Equipment Survivability – Thermal Loads • Must limit maximum temperature and time at temperature UNRESTRICTED

7. Dilution • Ingredients for Hydrogen Burn: • Fuel and Oxygen • Transport Mechanism • Ignition Source • Only ingredient #1 can be controlled, because #2 is always present and #3 cannot be ruled out • Inerting controls Oxygen, while Dilution controls Hydrogen concentration • Must show that [H2] < 4%, e.g. present CANDU-6 UNRESTRICTED

8. Large-Scale Containment Facility (LSCF) Objectives: Investigate hydrogen mixing behavior in a large-scale facility, under simulated post-accident conditions of high-temperature and high-humidity, using Helium as a H2 simulant Generate experimental data for validation of GOTHIC UNRESTRICTED

9. High-Temperature Room ofLarge-Scale Containment Facility (LSCF) Various Tests have been completed in the high-temperature room: • Well-mixed conditions • Stratified initial conditions • With active condensation on Containment Condensers • Multi-compartment tests UNRESTRICTED

10. Dilution - Results • Adequate mixing ensured during operation of LAC or dousing spray • At question in quiescent containment • Large number of tests showed adequate air entrainment into plumes and jets • GOTHIC captures this effect • Validated accuracy better than ±2% for relevant cases • Input to DDTIndex for assessment of flame acceleration and DDT UNRESTRICTED

11. Deliberate Ignition • Ingredient #3 may occur at any time, i.e. at the most inconvenient time • Solution is to ignite at a convenient time, i.e. near the ignition limit • AECL has tested a variety of igniters over the full spectrum of conditions • Must show igniter qualification and that, when ignited, [H2] < ~8% to avoid high overpressure, e.g. present multi-unit CANDU stations UNRESTRICTED

12. Ignitor Performance • Hot Surface Ignition of H2 • 30% Steam raises ignition temp. by ~75-100°C • But vented combustion overpressure is reduced by steam UNRESTRICTED

13. Vented Combustion • LSVCTF120-m3 volumeconfigurablecombustion andPAR testing • Vented Combustion experiments from 6 to 14% H2, steam, temp., #/location of igniters • PAR performance, qualification, mixing tests UNRESTRICTED

14. Vented Combustion - Results • Steam effect on H2 overpressure and impulse at 10% H2 • GOTHIC capturesthis effect • Validated accuracy better than ±50% UNRESTRICTED

15. Vented Combustion - Results • Peak Pressure de-pends on igniterlocation • GOTHIC calculates highest pressure for central ignition • Igniter location even more critical for tall rooms, due to different up- and downward propagation behavior UNRESTRICTED

16. Recombination • Ingredients for Hydrogen Burn: • Fuel and Oxygen • Transport Mechanism • Ignition Source • Recombiners “manipulate” ingredient #2 and do away with #3 • Greatly reduce limits for #1, designed to operate from 1% to ~7% H2 • Convective flow through PAR helps mix containment and replenish H2 supply to PAR • Must show that H2 reaches PAR, that PAR is qualified, and [H2] < ~8%, e.g. ACR UNRESTRICTED

17. Recombination – AECL PAR • Uses in-house developed proprietary catalyst • AECL has done extensive environmental qualification testing of PAR • Self-start requirement (H2% and temperature) is specific to the containment – and must be determined by the client from safety analysis UNRESTRICTED

18. PAR Testing Facilities Large-Scale Vented Combustion Test Facility (LSVCTF) • 120-m3 test chamber, electrically heated (for operation up to 140°C), insulated and instrumented • Design pressure: 400 kPa • Hydrogen, air, and steam addition systems • A process mass spectrometer to monitor gas composition • Thermocouples to monitor temperature UNRESTRICTED

19. PAR Testing Facilities 6.6-m3Containment Test Facility (CTF) Sphere • Structural-steel test vessel • Instrumented, insulated, and temperature-controlled for operation from ambient temperatures up to 100°C • Rated for internal pressures of 10 MPa • Equipped with systems for the controlled addition of hydrogen, steam, oxygen, and inert gases UNRESTRICTED

20. AECL PAR - Results • Self-start at 1-2% H2, cold, saturated • Self-stop at ~0.5% H2 • Ignition observed at 7-8% in dry atmosphere • Extensive qualification for • Thermal/radiation aging • DBE • VOC and other contaminants • Sprays, Fuel Aerosols UNRESTRICTED

21. AECL PAR - Results • Single, two- and three-chamber tests • Different openings, PAR orientation, initial temperature • In most tests, hydrogen was well-mixed • Exceptions are some of the “dead-end” volume tests UNRESTRICTED

22. PAR Multi-Chamber Mixing Tests UNRESTRICTED

23. Remaining Knowledge Gaps • Validation for lean-mixture combustion, where incomplete combustion is expected. Directional propagation and igniter location effects. • Interaction of PAR operation and containment atmosphere • Quantify EQ effects of H2 burns • New PAR design and application qualification, station-specific and non-nuclear installation support UNRESTRICTED

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25. AECL PAR Model • GOTHIC was used in “CFD-mode” with a 25x25 coarse 2D uniform grid. • Built-in PAR model “burns” a user-specified fraction of the hydrogen flowing through the PAR. Flow through PAR is calculated by the code and depends on buoyancy driving force. • The benchmark specified volumetric H2recombination rate was used to first determine an overall flowrate, which is forced through the GOTHIC recombiner (assumed efficiency of 1.0), using a fan component. • This results in a behavior, that is not expected, I.e. a nearly constant (even increasing) total flowrate through the recombiner, despite a decreasing inlet H2 concentration, and a slow H2 depletion rate. • Final results show the expected layering with a relatively cool, H2-rich layer remaining near the floor. UNRESTRICTED

26. AECL PAR Benchmark Results • Gas velocity field at t=1000s • Symmetric • Stratified, nearly no flow below PARs UNRESTRICTED

27. AECL PAR Benchmark Results • H2 concentration • Stratified, nearly no H2 above PAR inlets <0.1% H2 1.5% H2 UNRESTRICTED

28. AECL priorities for JPA4 WP12-2 CAM • PAR: interest in numerical benchmarks and validation data, but not academic (fundamental) mechanisms • Condensation: no interest, because the GOTHIC condensation models are empirical, while the benchmark investigates boundary layer behavior • Spray: interest in transient spray effect (e.g. local sprays) on pressure, but not in its effects on hydrogen concentration or momentum mixing UNRESTRICTED