Contribution to the description of the absorber rod behavior in severe accident conditions: An experimental investigation of the AgeZr phase diagram A. Decreton a , P. Benigni b , J. Rogez b , G. Mikaelian b , M. Barrachin a, * , M. Lomello-Tafin c , C. Antion c , A. Janghorban c , E. Fischer d a Institut de Radioprotection et Suret e Nucl eaire, B.P. 3,13115 Saint Paul-lez-Durance Cedex, France b IM2NP, UMR7334, CNRS, Aix-Marseille Universit e, Campus de Saint J er^ ome, Avenue Escadrille Normandie Ni emen e Case 251, 13397 Marseille Cedex 20, France c Laboratoire SYMME, Polytech Annecy Chamb ery e Universit e de Savoie, BP. 80439, 74944 Annecy-Le-Vieux Cedex, France d Universit e Grenoble Alpes, CMTC, SIMAP, 38000 Grenoble, France article info Article history: Received 5 February 2015 Received in revised form 18 May 2015 Accepted 29 May 2015 Available online xxx abstract Most pressurized water reactor (PWR) absorber rods are composed of an AgeIneCd (SIC) alloy inside a stainless steel (SS) cladding, themselves inserted into a Zircaloy tube. During a severe accident, the SIC alloy which melts at 800  C does not practically interact with SS. However, the cladding failure results from its internal pressurization and its eutectic interaction with Zircaloy and occurs at temperatures greater than 1200  C. The subsequent interaction between the SIC melt and the Zircaloy has a strong impact on the quantities of aerosols released into the primary circuit and finally on the iodine chemistry. Accurate knowledge of the AgeZr system is a prerequisite to address this issue. Within this concern, our experimental work is focused both on the investigation of the AgeZr phase diagram and on the deter- mination of the thermodynamic properties of the intermetallic compounds in the system. Two inter- metallic compounds (AgZr and AgZr 2 ) were identified. AgeZr cast alloys with a Ag/Zr ratio of 1:1 elaborated using an arc-melting furnace, once annealed, contained only a single phase AgZr. From metallographic observations, it appears that AgZr 2 likely forms by the peritectic reaction from liquid and the bcc (bZr) phase. The partial enthalpies of solution of silver and zirconium in aluminum were experimentally determined at 723  C in order to determine the enthalpies of formation of the inter- metallic compounds. For silver solution calorimetry in aluminum bath, our measurements were suc- cessful and in agreement with the previous data. Yet, this study shows that liquid aluminum should not be used as a solvent for zirconium below 1000  C. © 2015 Elsevier B.V. All rights reserved. 1. Introduction Most pressurized water reactor (PWR) control rods are composed of AgeIneCd neutron absorber alloy (80 wt. % Ag, 15 wt. % In, 5 wt. % Cd) inside a stainless steel (AISI 304 or 316) cladding. The absorber rod is inserted into a Zircaloy-4 guide tube. In case of an accidental scenario (i.e. loss of cooling), the AgeIneCd absorber alloy starts to melt at about 800  C [1]. This does not affect the core degradation as long as the molten material is contained within the cladding since the liquid absorber material practically does not interact with stainless steel. Failure of the stainless steel control rod cladding takes place as a result of either internal pressurization (high Cd and filling gas vapor pressure) or eutectic interactions with the Zircaloy-4 guide tube (bowing of the rods at high tem- peratures). The released AgeIneCd melt can then interact with the Zircaloy-4 guide tube and chemically dissolve it from 1000  C to 1100  C [2]. At the time of the guide tube burst, almost all cadmium is quickly released due to its high vapor pressure whereas the AgeIneZr-(O) liquid control rod mixtures progressively vaporize if they remain at sufficiently high temperatures before finally flowing out of the hot regions of the core and freezing. Vaporization of silver and indium from these melts during the accidental sequence, the amount released and the nature of the species transported are important for the following reasons. Firstly, the silver and indium * Corresponding author. E-mail address: marc.barrachin@irsn.fr (M. Barrachin). Contents lists available at ScienceDirect Journal of Nuclear Materials journal homepage: www.elsevier.com/locate/jnucmat http://dx.doi.org/10.1016/j.jnucmat.2015.05.039 0022-3115/© 2015 Elsevier B.V. All rights reserved. Journal of Nuclear Materials xxx (2015) 1e8 Please cite this article in press as: A. Decreton, et al., Contribution to the description of the absorber rod behavior in severe accident conditions: An experimental investigation of the AgeZr phase diagram, Journal of Nuclear Materials (2015), http://dx.doi.org/10.1016/ j.jnucmat.2015.05.039