Nickel solubility limit in liquid lead–bismuth eutectic

Abstract

In the framework of the Accelerator-Driven System (ADS), the Pb–Bi eutectic can be used as spallation target for neutron production. The Pb–Bi flow in contact with the ADS structural steels, T 91 (Fe–9Cr martensitic steel) and 316L (Fe–17Cr–10Ni austenitic steel), can dissolve the main steel components: iron, chromium and nickel. According to literature, in low oxygen containing Pb–Bi, the dissolution rates of 316L depend, at least, on the nickel solubility limit as it dissolves preferentially in the Pb–Bi alloy. Consequently, the determination of this physico-chemical data in the temperature range of the ADS operating conditions (350–450 °C) is needed for the prediction of the corrosion rates in ADS. The nickel solubility limit in Pb–Bi is available in the literature from 400 °C to 900 °C but not for lower temperatures. However, the Ni–Bi phase diagram leads one to suppose that the nickel solubility limit law changes for lower temperatures. Consequently in this study, two experimental techniques have been implemented for the determination of the nickel solubility limit at low temperatures. The first one is performed from 400 °C to 500 °C using the Laser Induce Breakdown Spectroscopy (LIBS). The LIBS technique permits to obtain in situ measurements directly performed on liquid Pb–Bi. This characteristic is very interesting as it allows to monitor on line the concentration of the dissolved impurities in the liquid coolant. However, this technique is still under development and optimization on liquid Pb–Bi medium. The second technique is ICP-AES. This technique, commonly used to analyze alloys composition, is interesting as it permits a global analysis of a Pb–Bi sample. Moreover, the measurement made by ICP-AES is very reliable, very accurate and optimized for such analyses. However, this technique is ex situ; this is its main disadvantage. Experiments using ICP-AES were performed from 350 °C to 535 °C. The two techniques lead to the same solubility limit in their common temperature range. However, the experiment using ICP-AES technique revealed a change in the nickel solubility law for the temperatures lower than 415 °C. Consequently, this study recommends the use of two solubility limits relations, which take into account these results, as well as the literature results: the solubility limits laws of Martynov and Rosenblatt. The nickel solubility limit can thus be expressed as: Log S Ni ( wt. % ) = 5.2 ± 0.12 - 3500 T ( K ) for the temperature range: 330–415 °C. This law is the empirical solubility law obtained in this study at the low temperature range. Log S Ni (wt. % ) = 1.7 ± 0.08 - 1009 T ( K ) for 415–900 °C temperature range. This law is the linear regression made on the overall experimental points available in literature and in this study. According to the Martynov studies, it seems reliable up to 900 °C.