Oxidation of Zircaloy-4 under High Temperature Steam Atmosphere and Its Effect on Ductility of Cladding

Abstract

Zircaloy-steam reaction rate in flowing steam was measured in the temperature range of 900-1,33O"C. T h e reaction rate measured from the weight gain followed a parabolic law above l,OOO"C, but it deviated from the law a t 900 and 950°C. Growth rates of ZrO, layer and Zr02+stabilized a-phase were also parabolic above 1,OOO"C. T h e parabolic rate law constants a r e represented a s follows : Weight gain k,=0.468 e x p (-40,71O/RT) (gZ/cm4 .set) ZrO, k3=0.0215 exp(-35,860/RT) (cm2/sec) ZrO,+stabilized a kc=0.306 exp(-38,970/RT) (cm2/sec). The ductility of zircaloy tubings oxidized in the temperature range of 950-1,33O0C was measured by a ring compression test a t 100°C. It tends to decrease with increasing the amount of oxidation and the oxidation temperature except the case of 9.iO°C, where the specimens become brittle even a t less amounts of oxidation. From these experimental results, it is concluded that the regulation for the amount Of the zircaloy oxidation in the acceptance criteria for LWR's LOCA analyses is cons e r va ti ve.

The effect of oxidation and crystal phase condition on the ballooning and rupture behavior of Zircaloy-4 cladding tube-under transient-heating conditions

“…As shown in Figure 17, the trend of the normalized value k depends on the atmosphere and heating rate in the burst temperature range above ∼1273 K. This trend may be explained by relatively fast oxidation kinetics at burst temperatures in the β-phase region in Zry-4 [12]. Due to the embrittlement Downloaded by [Umeå University Library] at 01:52 06 April 2015 of cladding caused by oxidation, circumferential strain might be suppressed at the heating rate of ∼3 K/s in steam conditions.…”

“…These heating rates, the low heating rate of 3 K/s which is close to a heating rate in a typical postulated LOCA sequence [10,11] and the high heating rate of 30 K/s were chosen to evaluate the effect of heating rate on the ballooning and rupture behavior of the cladding specimen. Steam was introduced into the quartz reaction tube prior to the heat up of the furnace, and the heating of the furnace was started when the TC-2 reached ∼373 K. The steam flow rate was maintained at 5 ± 1 mg/(cm 2 s) during the heat-up phase: this flow rate was considered to be sufficient to avoid a steamstarved condition and to oxidize the entire surface of the 190-mm-long cladding specimen [12][13][14][15]. In order to estimate the effect of oxidation on deformation, the size of the rupture opening and the ballooning and rupture behaviors of cladding tubes under simulated LOCA conditions, the test under argon gas flow condition was also carried out at a heating rate of 3 K/s: this is because it was considered that the amount of oxidation on behavior could be found more easily under low heating rate than high heating rate.…”

Study of oxide and α-Zr(O) growth kinetics from high temperature steam oxidation of Zircaloy-4 cladding

“…A. F. Brown et al [31] used rapid heating by inserting the specimen into the hot zone of a preheated furnaces and did not consider the history effect of non-isothermal heating. Kawasaki et al [2] carried out experiments with preoxidation in pressurized water at 300 C but did not discuss about the effect of initial transient heat up phase. Urbanic et al [19] ascribed the deviations from parabolic rate law occurring during the initial stages of oxidation to the heat-up period required for the samples to reach the desired temperature.…”

“…A comparison of the Arrhenius expression of parabolic rate constants for oxide scale and a-Zr(O) layer growth has been carried out with Leistikow [32], Urbanic [19] and Cathcart [33]. Kawasaki et al [2] did not determine a separate a-Zr(O) growth kinetic equation but a combined oxideþa-Zr(O) apart from oxide layer growth. The comparison is presented in Fig.…”

Simulation Test on Interactions of Zircaloy Claddings Deforming in Fuel Assembly under LOCA Conditions

“…During the heating period, thickness of the layer can attain -10 pm at most'1G' (17) which is equivalent to -1.5% of original wall thickness or -1% metal wall thinning. Increase in oxidation rate generated by tensile straining of substrate metal can be estimated as'") -2O%, which does not significantly alter the oxide thickness growth.…”