Irradiated Behavior at High Burnup for HiFi Alloy

Abstract

Irradiation tests of a BWR advanced Zr alloy (HiFi alloy) and Zircaloy-2 (Zry-2) were carried out in a Japanese commercial reactor and the irradiation performances of the materials were investigated. HiFi alloy and Zry-2 showed excellent resistance to corrosion up to 70 GWd/t, and furthermore, HiFi kept lower hydrogen pickup compared with Zry-2. TEM observation showed that the Fe/(Fe+Cr) ratio of Zr(Fe,Cr) 2 type second phase particles (SPPs) for HiFi alloy and Zry-2 tended to decrease as fast neutron fluence increased and to saturate at high fluence. Zr-Fe-Cr SPPs did not completely disappear even for 6 cycles for the irradiated HiFi alloy and Zry-2. In order to clarify the mechanism of hydrogen absorption, an electrochemical technique was used for the oxide film of both materials as part of the out-ofpile test. The relation between the oxide surface potential and the hydrogen pickup fraction was estimated suggesting that the potential difference over the oxide film suppressed hydrogen (proton) diffusion in the oxide film.

Understanding the role of Fe, Cr and Ni in Zircaloy-2 with special focus on the role of Ni on hydrogen pickup

“…The strong preference of Fe to form clusters suggests that once formed these clusters are likely to be energetically stable, thus inhibiting the movement of any clustered oxygen vacancies. This clustering behaviour is a possible explanation for the improved corrosion resistance that has been observed in recently developed Zr-alloys containing higher concentrations of Fe [49].…”

Modelling and experimental analysis of the effect of solute iron in thermally grown Zircaloy-4 oxides

“…Commonly used alloys such as Zircaloy-2, Zircaloy-4, M5 TM and ZIRLO TM include small amounts of iron as it has been shown to increase corrosion resistance [5]. Recent developments in zirconium alloys have been tending towards higher iron content, such as the HiFi (High corrosion resistance and high iron zirconium) alloy developed by Nuclear Fuel Industries Ltd., which demonstrate superior corrosion resistance (mainly in terms of nodular corrosion) [6]. Other reports also suggest that iron can also be beneficial to the general corrosion in zirconium alloys [7].…”

The recovery of irradiation damage for Zircaloy-2 and Zircaloy-4 following low dose neutron irradiation at nominally 358 °C

“…In a different set of samples irradiated in the High Flux Isotope Reactor (HFIR) at a higher flux at 358°C [5], the Zr(Fe, Cr) 2 precipitates were crystalline and exhibited less dissolution, and the lower fraction of iron solute may explain the greater hai loop coarsening and lower irradiation hardening observed in these specimens. The lower hardening observed for the 358°C irradiations of Zircaloy-2 and Zircaloy-4 in HFIR has been shown to be the result of a coarser distribution of hai loops than reported for Zircaloy-4 and Zircaloy-2 irradiations at 260-326°C [1][2][3][4][5][6][14][15][16][24][25][26][45][46][47][48][49][50][51][52][53]. For irradiations at 260-326°C, a higher flux is observed to increase the extent of amorphization of Laves phase precipitates.…”

“…Irradiation hardening is primarily the result of the high number density of small hai loops (4-30 nm diameter) that are formed on the prism planes (f1 0 1 0g) with a Burgers vector b hai ¼ 1 3 h1 1 2 0i [1-3,6-10, [13][14][15][16][24][25][26][27][28][29][30][31][32][33]. These hai loops are nucleated after a neutron fluence of 0.3-1.1 Â 10 24 n/m 2 (E > 1 MeV) and then rapidly saturate to a relatively constant size/number density at a fluence of about 1-5 Â 10 25 n/m 2 , depending on the irradiation temperature [1][2][3][4][14][15][16]. The hai loops are both interstitial or vacancy in nature, and the fraction of loop type is a strong function of irradiation temperature, with the majority being an interstitial type for irradiations at a temperature of 300°C or lower, about 50% interstitial for irradiation at 350°C, and about 30% interstitial for irradiation at 400°C [6,14,30,32].…”

“…Zircaloy-2 contains low alloying levels of Ni, Fe, and Cr additions that are tied up as Laves phase precipitates (Zr(Fe, Cr) 2 ) or as Zintl phase precipitates (Zr 2 (Fe, Ni)) [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16]. Zircaloy-4 contains only low alloying levels of Fe and Cr and contains only Laves phase precipitates [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16]. The neutron irradiation of Zircaloy results in the formation of dislocation loops that are barriers to dislocation motion that result in irradiation hardening .…”