Corrosion and HydrogenIngress of Pressure Tubes

V.F. Urbanic,Manager, Corrosion and Surface Science Branch

Meeting with the USNRC and CNSC2002 December

Pg 2

10

100

1.65 1.70 1.75 1.80 1.85 1.90 1.95

1/T(K) x 1000

Hyd

roge

n C

once

ntra

tion

(ppm

)

HYDRIDES

NO HYDRIDES

TSS

ACR

CANDU 6Pickering

& Bruce A

482°F/250°C563°F/295°C617°F/325°C

Source and Consequences of Hydrogen Ingress

• Corrosion Reaction: Zr + 2H2O ZrO2 + 4H

• fraction of hydrogen absorbed by base metal

• hydrides present when Terminal Solid Solubility (TSS) exceeded

• hydrides can potentially lead to fracture issues

• ensure hydrides are not present during reactor operation at power

Pg 3

The Current CANDU Fuel Channel

End Fitting

PHT

Pressure Tube

PHT

AG

ZrO2

ROLLED JOINT PRESSURE TUBE

CalandriaTube

SlidingBearing Spacer

PressureTube

PHT Annulus Coolant GAS (AG)

FeederPipe

FeederPipe

INLET OUTLET

Pressure Tube

Corrosion Reaction: Zr + 2D2O ZrO2 + 4D

Pg 4

Deuterium Buildup Along CANDU Pressure Tube [ Reactor A/9.8 EFPY]

• increased buildup at the tube ends due to coupling between 403SS end fitting and Zr-2.5Nb pressure tube

• gradual rise in measured [D] along pressure tube length due to temperature increase towards the outlet

• hydrides will be present where the solubility limit is exceeded

0

20

40

60

80

100

0 1 2 3 4 5 6

Distance from the Inlet End (m)

Deu

teriu

m C

once

ntra

tion

(ppm

)

Solubility Limit

hydrides present

no hydrides present

Measured Data

Pg 5

Deuterium Measured in Removed Pressure Tubes

• 22 full length pressure tubes examined from various reactors

• [D] increases towards the outlet end

• [D] peaks occur at ~5m from the inlet end

• [D] along the tubes increases with time

0

5

10

15

20

25

30

35

0 1 2 3 4 5 6

3.56 EFPY 4.08 " 4.53 " 6.26 " 6.63 " 7.43 " 8.14 " 8.38 " 8.58 " 8.79 " 9.35 " 9.54 " 9.84 " 14.1 "

Distance from the Inlet End (m)

Deu

teriu

m C

once

ntra

tion

(ppm

)

Reactor A

Pg 6

Reactor D

Deuterium Ingress in CANDU 6 Units after ~ 13.5 Hot Years [95% UCL]

Temperature (ºC)

Deu

teriu

m P

icku

p R

ate

(ppm

/hot

yea

r)

270 280 290 300 3100

1.0

2.0

3.0

4.0

320

Reactor C

Reactor B

Pg 7

Program Support Areas• Variability

- reactor-to-reactor- tube-to-tube

• Increasing ingress rate- EOL predictions

• Reducing D ingress- operating reactors- new/retubed reactors

Pg 8

Temperature Dependence of Oxidation Rate(Halden & NRU tests)

• irradiation programs utilize NRU and Halden test reactors for parametric studies

• ACR temperatures only slightly beyond our current test temperatures

• no significant difference in oxidation rates between H2O and D2O exposures

1

10

1.65 1.7 1.75 1.8 1.85 1.9 1.951/T (K) x 1000

Oxi

datio

n R

ate

(mic

rons

/yea

r)

617°F (325°C) 563°F (295°C) 482°F(250°C)

ACR CANDU 6

Pickering& Bruce A

NRU (H2O)

Halden (D2O)

Halden (D2O)

Pg 9

Parametric Studies in the Halden Test Reactor

• Temperature dependence (model development)

• β-Zr phase decomposition (model development)

• Micro-structure evolution during irradiation (model development)

• Manufacturing variables (extrusion parameters & β—quenching)

• Trace/minor element chemistry (Fe and C)

• Surface treatments (shot peening)

• Dissolved Li and dissolved D2 – (water chemistry)

• Evaluation of prototype material for ACR has started

Pg 10

• Data from Halden irradiationtest program on small Zr/Nb/Fe/Cspecimens (449 days).

• Response Surface Analyses(RSA) from 11 different alloys.

• H ingress in ACR prototypepressure tubes expected to be~40% lower than current C6 tubes

500 1000 1500 2000 2500 3000

Fe concentration (ppm (wt))

0.2

0.3

0.4

0.5

0.6

Deuterium Pickup (mg/dm2)

decreasing [C]C6 PTs

ACR PTs

Influence of Pressure Tube Microchemistry

Pg 11

0

2

4

6

8

10

12

0 5 10 15 20

Oxide Thickness (microns)

Oxi

datio

n R

ate

(mic

rons

/yea

r)

0

2

4

6

8

10

12

0 5 10 15 20

Oxide Thickness (microns)

Oxi

datio

n R

ate

(mic

rons

/yea

r)

Oxidation Rate:

The Pressure Tube Deuterium Ingress Model

Oxidation Kinetics: X=f(t,T,φ,[O])

Deuterium Pickup: D ~ αX

α = % theoretical uptake

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ΦΦ−−γ−

−−+−−

=

o]2O[]2O[

exp*

oexp11*

nX2

oXXexp1C

XPkLk

exp1

LkdtdX

�dt

Zircaloy-2

Zr-2.5Nb

in-flux

in-flux

out-of-flux

out-of-flux

Pg 12

0

20

40

60

80

0 5 10 15 20

Reactor B 89,98 (P)

Reactor B 92,97,00 (S)

Reactor C 90,93,96,98,99 (S)

Reactor D 98 (S)

Reactor E 94 (P)

Reactor E 92,98,01 (S)

Time (hot years)

Deu

teriu

m C

once

ntra

tion

(ppm

) Measured Deuterium Pickup Compared to Model Predictions

95%UCL

95%LCLMean

Candu 6 - 5m from the inlet

Pg 13

Schematic of Current Rolled Joint

Pg 14

Distance from the PT End

Deu

teriu

m C

once

ntra

tion Contribution from

Rolled Joint (galvanic and crevice effects)

Contribution from waterside

corrosion

Deuterium ConcentrationProfile (Schematic)

Distance from the PT End

Deu

teriu

m C

once

ntra

tion Contribution from

Rolled Joint (galvanic and crevice effects)

Contribution from waterside

corrosion

Deuterium ConcentrationProfile (Schematic)

Measuring Ingress Due to Coupling at the Rolled Joint

• measure D profiles frompower reactor rolled joints

• integrate the profiles todetermine the total D at thetube end

• subtract contribution due toingress from watersidecorrosion

• the difference is the D pickedup due to galvanic couplingeffects

• determine the ingress rate asa function of time

Pg 15

0

20

40

60

80

100

120

140

160

0 5 10 15

Amou

nt o

f Deu

teriu

m P

icke

d U

p (m

g)

Time (hot years)

INLETSOUTLETS

Deuterium Ingress at Rolled Joints

• D picked up due to coupling with the 403SS end fitting

• D ingress greater at the outlet end

• ingress rate due to coupling is decreasing with time according to: R(t) =

• model predictions based on declining ingress rates fitted to reactor data

1

at½ + b

Pg 16

PRESSURE TUBE

END FITTING

ROLLED JOINT INGRESS

RATE DECLINING WITH TIME

SPATIAL PROFILE

at1/2 + bR(t) = 1

The Rolled Joint Ingress Model

∂∂

∂∂

Ct

D Cx

(x,t) P(x,t)2

2= + +I

BURNISH MARK

PICKUP ALONG PRESSURE TUBE DUE TO CORROSION

• accounts for ingress from waterside corrosion

• accounts for ingress due to coupling at the rolled joint

• solve the diffusion equation with these contributions

• determine whether TSS is exceeded at the burnish mark during the pressure tube lifetime

Pg 17

Rolled Joint Test Assemblies in CTL-1

•Evaluate full scale rolledjoint designs.

•Determine D ingressprofiles.

•Verify predictive modelsfor D ingress.

•Provide an out-reactorproving ground forCANDU rolled jointcomponents.

Pg 18

Summary

Based on our current understanding of the parameters that influence

corrosion and hydrogen ingress, it is predicted that hydrides will not

be present in ACR pressure tubes during reactor operation over

the pressure tube design life.

Pg 19