SEDL / STP / STP1295-EB / STP16193S

Non-Linear Irradiation Growth of Cold-Worked Zircaloy-2

Holt, RA
Atomic Energy of Canada Ltd., Chalk River Laboratories, Chalk River, Ontario

Causey, AR
Atomic Energy of Canada Ltd., Chalk River Laboratories, Chalk River, Ontario

Christodoulou, N
Atomic Energy of Canada Ltd., Chalk River Laboratories, Chalk River, Ontario

Griffiths, M
Atomic Energy of Canada Ltd., Chalk River Laboratories, Chalk River, Ontario

Ho, ETC
Ontario Hydro Technologies, Toronto,

Woo, CH
Atomic Energy of Canada Ltd., Whiteshell Laboratories, Pinawa, Manitoba

Pages: 15    Published: Jan 1996

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Abstract

Accelerating irradiation growth has been reported for several zirconium alloys with a range of metallurgical states during high-temperature tests in fast-breeder reactors (673 to 723 K) for annealed Zircaloys in thermal test reactors at power reactor temperatures (523 to 623 K) and in power reactor core components fabricated from annealed or recrystallized Zircaloy. In the latter case, there was a transition from low to high irradiation growth rates at moderate fluences (about 3 × 10²⁵ n/m², E > 1 MeV, at 580 K) related to the nucleation and growth of basal plane c-component loops.

It was recently reported that the elongation rate of cold-worked Zircaloy-2 pressure tubes also accelerates with increased fluence at about 550 K. This gradual acceleration coincides with a gradual increase in the density of c-component dislocations as a result of the helical climb of those dislocation segments with a predominantly screw character.

New data showing the acceleration of growth of cold-worked Zircaloy-2 at 550 K are presented, and a model is presented for the irradiation growth behavior of cold-worked Zircaloy-2 based on the evolution of the sink strengths of c-component dislocations (net vacancy sinks) and a-type dislocations (net interstitial sinks) as a function of fast fluence. According to the model, the growth rate reaches a maximum when the sink strength of c-component dislocations is approximately equal to that of the a-type dislocations, and hence the growth rate tends to saturate with increasing fluence.