Properties of an Irradiated Heat-Treated Zr-2.5Nb Pressure Tube Removed From the NPD Reactor

Abstract

Some pressure tubes in reactors moderated by heavy water have been made from heat-treated (HT) Zr-2.5Nb. One such tube was removed from the NPD nuclear reactor after 20 years of operation. An extensive program was carried out jointly by AECL and PNC to evaluate the condition and properties of this pressure tube. The investigations include irradiation creep, tensile, corrosion, delayed hydride cracking (DHC), fatigue, and fracture properties. Results show that: (1) the in-reactor elongation rate is much lower and the transverse strain rates are slightly larger than in cold-worked (CW) Zr-2.5Nb tubes; (2) the tensile properties, hydrogen pickup, threshold stress intensity factor for DHC initiation, DHC velocity, and fatigue crack growth rates were similar to those of the CW Zr-2.5Nb material; (3) the fracture toughness of this tube, as measured by curved compact toughness specimens and burst tests, is slightly higher than the CW tubes. The results were also compared with other heat-treated Zr-2.5Nb materials irradiated in the Fugen reactor. The tube was in excellent condition when removed from the reactor and would have been satisfactory for further service.

Evaluation of variables affecting crack propagation by Delayed Hydride Cracking in Zr–2.5Nb with different heat treatments

“…doi:10.1016/j.jnucmat.2011.01.101 rolled pressure tubes (irradiated up to 9.8 Â 10 25 n/m 2 , E > 1 MeV, in the range of 250-290°C) the DHC velocity was three to five times higher than that in unirradiated tubes; this result was attributed to the irradiation hardening [12]. In heat treated PT (500°C for 24 h), after irradiation (4.5 Â 10 25 n/m 2 at 270°C) the increase was about two times [13]. The improved behavior in comparison with the cold worked PT was attributed to the decomposition of b phase produced during heat treatment at 500°C [13].…”

“…In heat treated PT (500°C for 24 h), after irradiation (4.5 Â 10 25 n/m 2 at 270°C) the increase was about two times [13]. The improved behavior in comparison with the cold worked PT was attributed to the decomposition of b phase produced during heat treatment at 500°C [13].…”

“…For this reason, several studies [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] have been conducted in order to elucidate the variable dependence of cracking mechanism.…”

“…Studies in ex-service and irradiated in high flux reactor PTs showed that irradiation increases DHC velocity [12][13][14][15]. In cold 0022-3115/$ -see front matter Ó 2011 Elsevier B.V. All rights reserved.…”

Irradiation Effects on ZR-2.5NB in Power Reactors

“…The only fatigue information for Zr-2.5Nb is from Chow et al [42] who evaluated the fatigue properties of some irradiated (maximum fluence is about 4.7 × 10 25 n·m…”