Development of thick copper coating for nuclear waste container

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Development of thick copper coating for nuclear waste container Legoux, Jean-Gabriel; Poirier, Dominique; Giallonardo, Jason; Vo, Phuong

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Development of Thick Copper

Coating for Nuclear Waste

Container

Presented at NACSC 2016

Edmonton

Jean-Gabriel Legoux

1

_{, Dominique Poirier}

1

_,

Jason Giallonardo

2

_{and Phuong Vo}

1

_{National Research Council of Canada,}

2

_{Nuclear Waste Management Organization,}

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Abstract

Since several years the National Research Council (NRC) is mandated by the Nuclear Waste Management Organization (NWMO) to develop cold sprayed thick copper coating intended to act as a corrosion barrier over a used fuel container developed for deep geological storage of Canada’s spent nuclear fuel. The container consists of a carbon steel structural core covered by a copper corrosion barrier. It has been evaluated that in order to for the copper coating to perform its role of a corrosion barrier it needs to be 3 mm thick. Also to sustain load under Deep Geological Repository (DGR) conditions the adhesion strength higher than 20 MPa and ductility above 15 % elongation should be obtained from the copper coating. This paper will present advances in the Cu coating development for long term corrosion protection of steel container intended for DGR.

Copper is often considered as one of the easy material to be processed by cold spray this statement can be misleading in the case of the deposition of thick Cu coating deposited on massive steel structure. Experimental result on key parameters affecting adhesion will be presented and discussed with emphasis on the case of production massive parts. Particle velocity have shown to play a major role in the development of an adherent coating, up to now proper adhesion of copper over steel has only been obtained while using helium as propelling gas in order to develop particle velocities above 800 m/s. Surface conditions such as

roughness and temperature have also shown great influence on the interfacial fracture

strength. The coating build up rate linked to the ability to move the parts is also playing a major role on the adhesion strength. Finally the thermal history of the part being coated influences adhesion, results of thermal modelling will be described and the development of a

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Outlines

• Application

• Requirements

• Coating development

• Coating optimization

• Surface conditions

• Roughening

• Spray angle

• Buildup rate

• Thermal History

• Summary

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Corrosion Protection of Used Fuel Containers (UFCs)

Mark II

• 2.7 tonnes when filled

• 3 mm thick Cu

• significant reduction in copper contribution costs

• Elimination of creep concern

Mark I

• Over 25 tonnes when filled

• Cu extra thickness required due to

manufacturing considerations

• 1 mm nominal gap between the

copper and steel due to copper

creep consideration  challenging

Inner steel container providing structural

strength

Outer Cu coating for corrosion resistance Outer Cu shell (pierce/draw or extrusion) Inner steel container

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Coating Development - Methodology

Properties Requir. Target

Elongation (%) 10 ≥ 15 Adhesion (MPa) 20 ≥ 60 Porosity (%) n/a ≤ 1

Variables to investigate:

• Feedstock • Substrate • Process parameters • Robot parameters • Post heat treatment

- Powder morphology, composition and size - Surface preparation

- Part temperature - Gas Temperature - Gas pressure

- Gun traverse speed - Step Size

- Standoff distance - Temperature - Time

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Coating Development

– Results I

7

• Particle velocities toward 750

m/s with optimised N

₂

conditions

(850 m/s for He)

• Well within window of deposition

for Cu (~ 400-1100 m/s*) 

dense coatings obtained

• Required adhesion (>60 MPa)

achieved with He bond coat

400 500 600 700 800 500 550 600 650 700 750 800 powder d₅₀ = 42 µm vp (m /s) T_g (°C) P_g = 5 MPa / SOD = 25 mm P_g = 5 MPa / SOD = 100 mm P_g = 3 MPa / SOD = 100 mm

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Coating Development

– Results II

• Annealing is required to recover coating ductility

0 100 200 300 400 500 600 0 10 20 30 40 50 60 70 80 90 100 d50 = 23 µm as-sprayed HV 0.01 Anneal Temperature (°C) 1 h anneal 0 10 20 30 40 0 50 100 150 200 250 1 h at 600°C d₅₀ = 42 µm powder Stress (MPa ) Strain (%) As spray 1 h at 350°C 1 h at 400°C 23 ± 3% ductility Coating cohesive strength (HT@350°C): 67 ± 5 MPa As-spray HT@350°C HT@600°C

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Effect of Annealing on Machining

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Coating Development

– Reference Conditions

• Reference conditions

• 10-70 µm spherical low oxygen copper powder;

• 25.4 mm min. thick A516 grade 70 steel, grit blasted with 24 grit to

remove millscale;

• 100 µm bond coat, applied with He-spray at 5 MPa and 800 °C,

• 3 mm top coat, applied with N

2

-spray at 5 MPa and 800

°C, and

• Post-deposition heat treatment at 350°C for 1 hour.

Properties Requir. Target Obtained

Elongation (%) 10 ≥ 15 23 ± 3

Adhesion (MPa) 20 ≥ 60 67 ± 5

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Coating Validation and Scale-Up

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Coating validation on UFC representative materials and

shapes:

• Larger surfaces

• Curved surfaces

• Hemispherical surfaces

Substrate Handling

Powder feedrate

He gas consumption

Adjustments

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Process Demonstration

Full-scale UFCs Components

Partly coated lower assembly Fully coated lower assembly Machined lower assembly Fully coated

head Head Lower

assembly

Short-sized container

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Process Demonstration

Weld Closure Zone

13

Full-size leading vessel

After coating

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Effect of Surface Preparation

Surface Treatment ID Ra (µm) Grit Blasting with grit 24, pressure of 40 psi GB24 4.8±0.5 Grit Blasting with grit 60, pressure of 60 psi GB60 1.9±0.2

Rough Machining Rough 2.2±0.3

Fine Machining Fine 0.15±0.03

Grinding, 80 sand paper P80 1.5±0.2 Grinding, 180 sand paper P180 0.7±0.1 Grinding, 400 sand paper P400 0.8±0.8 Grinding, 800 sand paper P800 0.19±0.05

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Effect of Surface Preparation

Trial Coating Thickness (mm) Surface Treatments Bond Strength 1 (1501301csB) (1502021csB) ~2.9 ~1.5 GB24* Spontaneous debonding 2 (1501301csB) (1502021csB) ~2.9 ~1.5 GB60* Spontaneous debonding of 2(2.9mm) and 1 samples (1.5mm) 3 (1502022csB) ~ 1 GB60 Spontaneous debonding of 2 samples 5 (1502023csB) n/a, 1 targeted

Rough and Fine Machining Spontaneous debonding 6 (1502031csB) n/a, 1 targeted

P800 and P400 Spontaneous debonding 7 (1502032csB) (1503102csB) ~ 1 ~ 1 GB60 Spontaneous debonding 8 (1503102csB) ~ 1 GB24 4.9 ± 0.9 MPa (A†) 9 (1504152csB)

~ 0.5 GB24 10 ± 1 MPa (A) (5 samples)

• Coatings were

produced using only

N2.

• Only the rougher

surfaces obtained with

coarse grit blasting

enable the production

of thick (3 mm)

coatings

• While using N2 only

the adhesion remains

very limited

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Effect of Spray Angle

on Flat Samples

5 ⁰

10 ⁰

30 ⁰

Coatings were produced on electrodeposited copper at different impinging angle

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Effect of Spray Angle

on Machined Plate

5 ⁰ 10 ⁰ 20 ⁰ 30 ⁰ 10 ⁰

Coatings were produced with

transition zone at different

angle an angle of 10

⁰ enables

the production of a clean

interface and a defect free

coating.

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40 45 50 55 60 Ad h esi o n (M P a)

Effect of Deposited Thickness per Pass

spray run # RPM feed rate surface speed thickness/pass adhesion

min-1 _g/min _cm/s _µm _MPa

1510152 225 160 180 206.9 38.26 1510161 38 12 30 87.2 54.31 1510153 38 74 30 558.9 48.85 1507073 225 75 180 92.7 65.6 45.00 50.00 55.00 60.00 Ad h esi o n (M P a)

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Effect of Feed Rate

Increasing Productivity

Spray conditions 4.9 Mpa, 800 ⁰C

One adhesion pass Process gas helium

Particle feed rate 12g/min

Build up passes Process gas N₂

Particle feed rate 75 g/min

Adhesion 67.9 MPa

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Process Adjustment

Spray Rate

• Need to minimize gas

consumption (mainly He)

• Using smaller

nozzle reduces He flow rate:

5300 LPM → 2100 LPM.

• Particle velocities are similar

• Bond strength is lower.

Surface temperature on

particle impingement was potentially lower with the smaller

nozzle

→ lower gas mass flow.

• Need to control surface temperature.

30 35 40 45 50 55 60 65 60 65 70 75 80 85 90 95

2 prehat passes Lamp preheat Small Nozzle Large Nozzle

Bo n d S tr eng th ( M P a) T emp er atu re (⁰C) Spray conditions

Max Temperature during spraying

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Measuring Surface Temperature During Spraying

• Measurement using an

infrared camera.

• Gun traveling over the sphere

surface

• Without powder

• Nitrogen as the process gas.

It was assumed that the effect

of temperature when using He

would be proportional to what is

measured using nitrogen.

0 10 20 30 40 50 60 70 80 90 100 0 50 100 150 200 T emp er atu re (° C) Time (s)

1 pass large nozzle 600 oC

2 passes preheating small nozzle 800 oC 1 pass after preheating

1 pass small nozzle 600 oC

Different trials show that higher

temperature can be reached if

preheating is applied to the part.

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Thermal Modeling

Acquiring the Heat Transfer Parameters

0 5 10 15 20 25 0 20 40 60 80 100 120 140 -5 5 15 25 35 45 55 H e at tr an sf e r c o e ff ic ie n t Tem p e ratu re ( °C) Steel 516 (200°C, 4.9 MPa) Experimental line 2 Experimental line 1 Tc Modeling result h

Q = h·A· (T

_c

-T

_p

)

Q = heat transferred

H = convection coeficient

A = Surface area

T

_c

= gas temperature

T

_p

= part temperature

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Thermal Modeling

Simulating Real Parts Thermal History

Simulation shows that

rotation rate (surface

velocity) affects the

surface temperature

and thus the thermal

history of the part

being coated

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Thernal Modeling

Design of Sample Holder

Simulation shows that

using a massive sample

holder (22in X 8 in, 1 in

thick) enables to simulate

relatively closely the

thermal history of the

large components.

Validation pull tests on

cylindrical samples have

confirmed the

representativity of the

sample holder.

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Summary

• A cold sprayed thick copper coating has been developed

to fulfill the need of corrosion protection in deep geological

conditions.

• The coating process has been adapted to cope with the

limitation imposed by the size and movement constraint of

used fuel canister.

• These adaptation were made in terms of surface preparation,

• Spray angle

• Coating build-up rate

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