Corrosion and Hydrogen Ingress of Pressure Tubes · hydrides present no hydrides present Measured...
Transcript of Corrosion and Hydrogen Ingress of Pressure Tubes · hydrides present no hydrides present Measured...
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
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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