Effect of Irradiation Damage on the Deformation Properties of Zr-2.5Nb Pressure Tubes

Abstract

The diametral expansion, elongation, and sag 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. As a result irradiation creep models are needed to predict the deformation behavior of the core components over the reactor life. It is important to know the creep behavior as a function of neutron flux in order to develop creep models over the range of operating conditions in the reactor core. At the edge of the reactor core, the neutron flux is decreasing very rapidly and there is a complex transition in creep behavior from irradiation-dominated creep to thermal-dominated creep. Also, mechanical properties such as tensile strength, fracture toughness, and delayed hydride-cracking are changing in the transition from thermal to irradiation conditions at the edge of the reactor core. Detailed studies have been completed on a Zr-2.5Nb tube irradiated in the NRU materials test reactor at Chalk River Laboratories. Pressure tube 601 was operating for a period of 66 950 h at temperatures ranging from about 547 K at the inlet and 571 K at the outlet. After the tube was removed in 1988 samples were taken for retrospective dosimetry to determine the fast neutron flux along the assembly. It was determined that the tube had been irradiated to a peak fluence of about 6×1025 n⋅m−2 corresponding to a fast neutron flux of about 2×1017 n⋅m−2⋅s−1. The flux profile was mapped and it was clear that the flux dropped rapidly to negligible values at about 0.5 m from the ends of the fueled zone. Samples of pressure tubes were taken for hardness testing and characterization by TEM and XRD analysis at various locations corresponding with different operating conditions (neutron flux and temperature) but at the same time. The creep behavior during operation was obtained by periodic gaging of the pressure tube internal diameter. The results of the microstructure characterization are presented and discussed in relation to the measured mechanical properties (creep and hardness). The microstructure and mechanical properties change significantly in the transition from the unirradiated state up to fluxes of about 1×1017 n⋅m−2⋅s−1.

Effect of Zr+ ion irradiation on the mechanical anisotropy of Zr–2.5%Nb pressure tube material

“…Extensive mechanical testing has been done to characterize the anisotropy of both the flow stress and the thermal creep properties of these tubes in the non-irradiated condition and, to a much lesser extent, in the neutron irradiated condition [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16]. Performing a complete characterisation of the mechanical anisotropy is made difficult by the fact that these pressure tubes are only about 4 mm thick and it is therefore impossible to construct conventional uniaxial test specimens aligned parallel to the radial (thickness) direction of the tube.…”

Orientation sensitivity of focused ion beam damage in pure zirconium: direct experimental observations and molecular dynamics simulations

“…The life is determined by in-reactor property degradation: hydride formation, corrosion/oxidation to irradiation hardening and creep. Radiation damage [23][24][25][26][27][28][29][30] often plays a critical role in all such property degradation [31][32][33][34][35]. Radiation damage has been a subject of textbook [29] and excellent reviews [23][24][25][26][27][28]30].…”

“…The present study deals with microstructural aspects of radiation damage. This can be classified in terms of microstructural changes [24,28, and microstructural dependence [28,[60][61][62]. Radiation damage has been reported to enforce all possible structural changes: creation of vacancies/interstitials and dislocations [36][37][38][39][40][41][42][43][44][45], transmutation of alloying elements [46], dissolution and re-precipitation [47][48][49], amorphization [50][51][52], developments of stresses and lattice rotations [53], radiation-induced segregation (RIS) [54][55][56], voids and void swelling [57,58], etc.…”

“…Radiation damage has been reported to enforce all possible structural changes: creation of vacancies/interstitials and dislocations [36][37][38][39][40][41][42][43][44][45], transmutation of alloying elements [46], dissolution and re-precipitation [47][48][49], amorphization [50][51][52], developments of stresses and lattice rotations [53], radiation-induced segregation (RIS) [54][55][56], voids and void swelling [57,58], etc. On the other hand, both alloy chemistry [21,[27][28][29] and crystallographic orientations [59][60][61] are known to affect the damage kinetics. Examples for the latter exist through Rutherford scattering measurements in both single crystal copper [61] and ceramics [59,60].…”

“…Equally important is the subject of damage (radiation) quantification. This has usually been attempted through either macroscopic [16,[23][24][25][26][27][28][29][31][32][33][34]40,42] or microscopic [16,[23][24][25][26][27][28][29][31][32][33][35][36][37][38][40][41][42][46][47][48][49][50][51][52] characterization: neglecting the in-between domain of mesoscopic measurements. Finally, the modelling of radiation damage appears equally challenging.…”