Abstract

The diametral expansion and elongation rates of Zr-2.5Nb pressure tubes in CANDU (CANada Deuterium Uranium) nuclear reactors are important properties that limit their useful life and the maximum power level for reactor operation.

For a given set of operating conditions there is considerable variability in the deformation rates because of the variations in as-fabricated microstructure and chemistry from tube-to-tube — specifically grain size, crystallographic texture, and oxygen content. The as-fabricated microstructure also varies within a given tube, the largest variation occurring along the length, and this is a result of cooling of the tube during the extrusion process. During service in a nuclear reactor, the microstructure evolves further, and this additional change in microstructure is primarily dependent on the rate of radiation damage (determined by the fast neutron flux), the temperature, and the time. Both the fast neutron flux and temperature vary at all points within the pressure tube.

For a given material microstructure, the deformation is a function of the operating conditions: coolant pressure (stress), temperature, and neutron flux. In principle, the deformation rate is a linear function of fast neutron flux, and this is mostly true for fast neutron fluxes of the order of 1017 n.m−2.s−1. Recent analyses of data from pressure tubes measured over long periods of operation in reactor have shown that the steady-state diametral creep rates are not linear with fast neutron flux for fluxes up to about 0.5 × 1017 n.m−2.s−1. A qualitative model has been developed to account for the observed behavior based on the modifying effects of neutron flux and temperature on the microstructure. The model describes the suppression of thermal creep and the transition from thermal to irradiation creep with increasing neutron flux.

References

1.
Griffiths
,
M.
,
Winegar
,
J. E.
,
Mecke
,
J. F.
, and
Holt
,
R. A.
, “
Determination of Dislocation Densities in HCP Metals Using X-Ray Diffraction and Transmission Electron Microscopy
,”
Advances in X-Ray Analysis
 0376-0308, Vol.
35
,
1992
, pp.
593
-
599
.
2.
Holt
,
R. A.
,
Causey
,
A. R.
, and
Fidleris
,
V.
, “
Correlation of Creep and Growth of PTs with Operating Variables and Microstructure
,”
Dimensional Stability and Mechanical Behavior of Irradiated Metals and Alloys
,
British Nuclear Energy Society
,
London
,
1983
, pp.
175
-
178
.
3.
Christodoulou
,
N.
,
Causey
,
A. R.
,
Holt
,
R A.
,
Tome
,
C. N.
,
Badie
,
N.
,
Klassen
,
R. J.
, et al
, “
Modeling In-Reactor Deformation of Zr-2.5Nb Pressure Tubes in CANDU Power Reactors
,”
11th International Symposium on Zirconium in the Nuclear Industry
, ASTM STP 1295,
E. R.
Bradley
and
G. P.
Sabol
, Eds.,
ASTM International
,
West Conshohocken, PA
,
1996
, pp
518
-
537
.
4.
Fidleris
,
V.
, “
The Irradiation Creep and Growth Phenomenon
,”
J. Nucl. Mater.
 0022-3115, Vol.
159
,
1988
, pp.
22
-
42
.
5.
Nelson
,
R. S.
,
Hudson
,
J. A.
, and
Mazey
,
D. J.
The Stability of Precipitates in an Irradiation Environment
,”
J. Nucl. Mater.
 0022-3115 https://doi.org/10.1016/0022-3115(72)90043-8, Vol.
44
,
1972
, pp.
318
-
330
.
6.
Heald
,
P. T.
and
Speight
,
M. V.
, “
Point Defect Behavior in Irradiated Materials
,”
Acta. Met.
, Vol.
23
,
1975
, pp.
1389
-
1399
.
7.
Griffiths
,
M.
,
Davies
,
W. G.
,
Moan
,
G. D.
,
Causey
,
A. R.
,
Holt
,
R. A.
, and
Aldridge
,
S. A.
, “
Variability of In-Reactor Diametral Deformation for Zr-2.5Nb Pressure Tubing
,”
13th International Symposium on Zirconium in the Nuclear Industry
, ASTM STP 1423,
ASTM International
,
West Conshohocken, PA
,
2002
, pp.
796
-
810
.
8.
Matthews
,
J. R.
and
Finnis
,
M. W.
, “
Irradiation Creep Models - An Overview
,”
J. Nucl. Mater.
 0022-3115, Vol
159
,
1988
, pp.
257
-
285
.
9.
Hosbons
,
R. R.
,
Davies
,
P. H.
,
Griffiths
,
M.
,
Sagat
,
S.
, and
Coleman
,
C. E.
, “
Effect of Long-Term Irradiation on the Fracture Properties of Zr-2.5Nb Pressure Tubes
,”
12th International Symposium on Zirconium in the Nuclear Industry
, ASTM STP 1345,
ASTM International
,
West Conshohocken, PA
,
2000
, pp.
122
-
138
.
10.
Griffiths
,
M.
, “
A Review of Microstructure Evolution in Zirconium Alloys During Irradiation
,”
J. Nucl. Mater.
 0022-3115, Vol.
159
,
1988
, pp.
190
-
218
.
11.
Griffiths
,
M.
,
Davies
,
P. H.
,
Davies
,
W. G.
, and
Sagat
,
S.
, “
Predicting the In-Reactor Mechanical Behavior of Zr-2.5Nb Pressure Tubes from Postirradiation Microstructural Examination Data
,”
13th International Symposium on Zirconium in the Nuclear Industry
, ASTM STP 1423,
ASTM International
,
West Conshohocken, PA
,
2002
, pp.
507
-
523
.
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