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Hybrid Capsule Assembly for Irradiation Testing

2011 RELAP5 IRUG MeetingSalt Lake City, UtahJune 26, 2011

Donna P. Guillen and Brian DurtschiIdaho National LaboratoryAdam Zabriskie and Heng BanUtah State University

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

Genesis of experimentEstablish a domestic high intensity fast-flux irradiation test capability for nuclear fuels and materials for advanced concept nuclear reactorsProvide 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

BackgroundGas 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 contingencyChallenge - Find a way to make the Gas Test Loop less expensive by using a different cooling approach than pressurized heliumBoosted Fast Flux loop concept explored

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)

0

10

20

30

40

50

60

0 2 4 6 8 10 12

Percent Hafnium

Fast

-to-T

herm

al R

atio

1.025

1.030

1.035

1.040

1.045

1.050

1.055

Fast

Flu

x (1

015 n

/cm

2 /s)

Absorber Block DesignConcept 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

Envelope tube

Coolant annulus

Coolant channels

Helium gas gap

Pressure tube

Experiment locationsHf-Al alloy

heat sink

Envelope tube

Coolant annulus

Coolant channels

Helium gas gap

Pressure tube

Experiment locationsHf-Al alloy

heat sink

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

Specimen Geometries

• Due to brittleness of material, could not machine intermetallic into thin disks

• Irradiation specimen geometries designed to accommodate thermophysical property measurements

Rods 5 mm dia. × 5 mm long

Al3Hf & Al3Hf‑Al CTE, ρ

Disks 5 mm dia. × 0.8 mm thick

Al3Hf-Al α, hardness, SEM, corrosion

Disks 3 mm dia. × 0.3 mm thick

Al3Hf-Al TEM, isotopic analysis, cp

Dogbone-shaped 16 × 4 × 1 mm

Al3Hf-Al Tensile testing

Irradiation Experiment in INL’s ATRObjectives:1. Thermophysical and mechanical

properties of Al3Hf intermetallic and Al3Hf-Al metal matrix composite (MMC) at different temperatures

2. Physical/morphological, metallurgical, and microstructural changes of the Al3Hf-Al composite after different cycles of irradiation

3. Effect of irradiation on the thermophysical and material properties of the Al3Hf intermetallic and Al3Hf-Al composite.

4. Decay products of hafnium (presence of metastable isotopes)

5. Corrosion behavior of the Al3Hf-Al composite

Focus of this presentation

B2position

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:

1. The irradiation experiment hardware must allow adequate coolant circulation past corrosion specimens• No regions of stagnant water!

2. The corrosion specimens must maintain integrity during irradiation• No release of particles into coolant!

Requirement #1Irradiation experiment hardware must allow adequate coolant

circulation past corrosion specimens

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

Hybrid Capsule DesignThis new hybrid design holds fuel or material specimens in two different types of sections, integrated into a single capsule assembly:(1) static section – specimens remain isolated from the coolant(2) flow-through section – flow enters/exits through “windows” in the

capsule, exposing selected specimens to the reactor primary coolant

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

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

Experiment Hardware

Basket Configuration

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

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

0 2 4 6 8 10 12 14 160

2

4

6

8

10

12

Solid rodFlow-through sectionCFD prediction

Flow rate (gpm)

ΔP

(psi

)

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

Q ≈ 9 gpm ∆P (psi)Calculated from Idelchik 1.4

CFD analysis 3.1

Flow test 5.1

Pmax=2.32 psi for Impress transducer

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

Q Q

∆P1 ,Q1

∆P2 ,Q2

∆P1=∆P2

Q= Q1 + Q2

test cap

flow inside basket

Requirement #2Corrosion specimens must maintain integrity during

irradiation

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

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

Corrosion Tests

Cold pressed MMC

Hot pressed MMC (damaged)

Hot pressed MMC

Use smallest particle size & round particles

Particles pulled from matrix due to use of acrylic mount (shrinkage)

May need to clad or functionally grade material

ConclusionsFabrication Technique

Recommendations

To satisfy ATR Safety requirements:1. 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

2. 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

The End

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