Hybrid Capsule Assembly for Irradiation Testing

1. Hybrid Capsule Assembly for Irradiation Testing Donna P. Guillen and Brian Durtschi Idaho National Laboratory Adam Zabriskie and Heng Ban Utah State University 2011 RELAP5 IRUG Meeting Salt Lake City, Utah June 26, 2011

2. Outline • Genesis of Experiment • Background • Design Requirements • Absorber Block Design • New Material Developed • Specimen Fabrication • Objectives of Irradiation Experiment • Requirements for in-Pile Corrosion Test • Specimen Holder Hardware • Autoclave Tests and Analysis • Recommendations

3. Genesis of experiment Establish a domestic high intensity fast-flux irradiation test capability for nuclear fuels and materials for advanced concept nuclear reactors Provide an interim fast-flux test capability to test nuclear fuels and materials • Could be brought on-line in 5-6 yrs. • Much sooner than building a new fast-flux test reactor Use existing irradiation facility with irradiation volume large enough to irradiate meaningful numbers of test specimens Potential users include Generation IV Reactor Program, Advanced Fuel Cycle Initiative, and Space Nuclear Programs

4. Background Gas Test Loop project • Mission need established 2004 • CD1-A in 2005 authorized resolution of key feasibility issues Original Gas Test Loop Conceptual Design estimated cost was $80M to $100M depending on contingency Challenge - Find a way to make the Gas Test Loop less expensive by using a different cooling approach than pressurized helium Boosted Fast Flux loop concept explored

5. BFFL Design Requirements Fast flux (E > 0.1 MeV) ≥ 1015 n/cm2·s Fast-to-thermal neutron ratio≈ 40 Fuel specimens Up to 3 simultaneous experiments Diameter ~ 1 cm Axial heating rates ≤ 2.3 kW/cm Total heat load ≤ 200kW Maintain test article surface temp. ≤ 500 °C nominal, 1000 °C max. Locate in ATR large flux trap with IPT outer diameter = 9.128 cm (3.593 inches)

6. Absorber Block Design Concept developed to filter out a large portion of the thermal flux component by using a thermally conductive neutron absorber block Use Hf-Al alloy (Al3Hf-Al) to conduct heat away from the experiments Serves a dual role High thermal conductivity of Al Thermal neutron absorption of Hf Limit amt. of pressurized water for cooling Pressurized water systems already exist in ATR If water is not close to experiments, thermalization may be manageable Use booster fuel to augment neutron flux

7. Specimen Fabrication • Cast Al3Hf intermetallic • Al3Hf-Al composite specimens • Al3Hf is brittle, can be easily ground into powder • Grind • Mortar and pestle • Spex mill • Sieve by particle size • <35 μm, 75-105 μm, and 105-149 μm • Mix Al3Hf powder with Al powder • Al3Hf vol%: 20.0, 28.4, 36.5, 100 • Press into pucks • Machine to size

8. Specimen Geometries • Due to brittleness of material, could not machine intermetallic into thin disks • Irradiation specimen geometries designed to accommodate thermophysical property measurements

9. Irradiation Experiment in INL’s ATR Objectives: Thermophysical and mechanical properties of Al3Hf intermetallic and Al3Hf-Al metal matrix composite (MMC) at different temperatures Physical/morphological, metallurgical, and microstructural changes of the Al3Hf-Al composite after different cycles of irradiation Effect of irradiation on the thermophysical and material properties of the Al3Hf intermetallic and Al3Hf-Al composite. Decay products of hafnium (presence of metastable isotopes) Corrosion behavior of the Al3Hf-Al composite B2 position Focus of this presentation

10. Safety Requirements for In-Pile Test with Corrosion Specimens • To assess corrosion behavior of the new material under reactor operating conditions, it must be exposed to the reactor primary coolant • ATR Safety requirements with respect to corrosion specimens: • The irradiation experiment hardware must allow adequate coolant circulation past corrosion specimens • No regions of stagnant water! • The corrosion specimens must maintain integrity during irradiation • No release of particles into coolant!

11. Requirement #1 Irradiation experiment hardware must allow adequate coolant circulation past corrosion specimens

12. New Capsule Design A new type of capsule assembly has been designed for irradiation testing of fuels or materials • Capsules are used to house fuel or material specimens for irradiation testing in a nuclear reactor, such as ATR Traditionally, experiments are designated either as drop-in (static, hermetically sealed from exposure to coolant) or flow-through (all specimens exposed to coolant) • Hybrid capsule design separates flow-through specimens from static specimens to enable testing in a single irradiation position

13. Hybrid Capsule Design This new hybrid design holds fuel or material specimens in two different types of sections, integrated into a single capsule assembly: • static section – specimens remain isolated from the coolant • flow-through section – flow enters/exits through “windows” in the capsule, exposing selected specimens to the reactor primary coolant

14. Advantages of Hybrid Capsule Design • The benefits of this design are the ability to expose a limited number of specimens to the reactor coolant, while simultaneously isolating other specimens from coolant exposure • Enables two types of irradiation tests to be performed with a single irradiation test assembly • Allows enhanced cooling and/or corrosion testing of selected specimens • Modular design facilitates reconfigurability and permits flexibility to add or remove flow-through sections as required by the experiment objectives • Experiments can be performed in one irradiation campaign, rather than over several campaigns, with a substantial saving in costs, time and resources

15. Corrosion Specimen Holder • Vertical orientation of specimens to preclude buildup of debris from reactor coolant • Notched design to securely hold specimens in place • Ramps to entrain flow into flow-through section • Holder maximizes specimen surface area exposed to coolant • Paired “windows” allow coolant to flow in/out, permits circulation and convective cooling of specimens • Constant outer diameter of capsule for ease of reactor insertion/removal

16. Experiment Hardware

17. Basket Configuration

18. Flow Test Experiment • Idaho State University Skyline Lab test loop • Flow test performed to determine pressure drop • System A – solid rod (0.625” dia.) in basket • System B – solid rod with flow through specimen holder (test cap) • Pressure tap holes located ½” above and below test cap

19. Flow-Through Capsule Result • Unexplained pressure drop discrepancy from experiment • Preliminary CFD analysis did not explain result • Further experimentation and simulation needed: • Reproducible result from experiment • CFD analysis spanning full flow range and both geometries

20. Pressure Drop Comparison • Calculate velocity through triform, knowing total flow rate • Suction orifice in a thin wall in the presence of passing flow • Flow exit approx. as single top-hinged flap • Abrupt area change across specimen holder • Thick-edged orifice installed in a transition • Flow splits into parallel branches, then merges again after exiting endcap • ζtot := ζent + ζtriin + ζtriout + ζexit • 23% of flow goes through end cap Pmax=2.32 psi for Impress transducer

21. Possible Explanations • Expected Result – Addition of a parallel flow path should decrease pressure drop • Branch with lower resistance should get more flow • Branch with higher resistance should get less flow • Actual Result – Pressure drop increased with test cap • Plausible explanation for increased pressure drop • Disturbance of flow in annulus near inlets ∆P1=∆P2 Q=Q1 + Q2 ∆P1 ,Q1 test cap Q Q flow inside basket ∆P2 ,Q2

22. Requirement #2 Corrosion specimens must maintain integrity during irradiation

23. Pre-Irradiation Corrosion Testing of Specimens • Pre-irradiation autoclave testing necessary to assess severity of corrosion • Data essential to incorporate flow-through capsules in experiment • Does hydroxide grow underneath particles? • Are particles likely to loosen under hydraulic pressure? • Tested four Al3Hf-Al specimens with different particle size ranges: • 1) <35 μm, 2) 53-75 μm, 3) 75-105 μm, and 4)105-149 μm • Three sets of autoclave tests • Cold pressed material • Hot pressed (damaged) material • Hot pressed material • Examination: • Surfaces by SEM • Cross-sections by metallography No boehmite at aluminide boundary Boehmite presence indicates surface connection

24. Autoclave Procedure • Used to apply an adherent boehmite surface film onto ATR fuel plates before irradiation • Very good test of the stability of the materials and a good indicator of the worst possible behavior in the ATR core • If autoclaving of the material does not result in significant degradation of the material, it is highly probable that it can withstand the less invasive chemical environment during irradiation • Specimens treated in deionized water: • ~12 mm diameter and 1-2 mm thick • 185 ± 15ºC • pH 8.1 (initially), pH 7.15 (following exposure) • 17.5 hrs • 150 psi

25. Fabrication Technique Corrosion Tests Conclusions Cold pressed MMC Use smallest particle size & round particles Hot pressed MMC (damaged) Particles pulled from matrix due to use of acrylic mount (shrinkage) May need to clad or functionally grade material Hot pressed MMC

26. Recommendations To satisfy ATR Safety requirements: • Requirement: The irradiation experiment hardware must allow adequate coolant circulation past specimens • Recommended Action: • Eliminate possibility of regions of stagnant water by redesigning corrosion specimen holder • Requirement: The material must maintain integrity during irradiation • Recommended Actions: • Functionally grade or clad material to avoid potential for release of particles into coolant • Fabricate material using round particles

27. The EndQuestions? Answers?