X-ray and thermal studies of the Na–U–Mo–O system N.D. Dahale * , Meera Keskar, R. Agarwal, K.D. Singh Mudher Fuel Chemistry Division, B.A.R.C., Trombay, Mumbai 400 085, India Received 30 June 2006; accepted 17 October 2006 Abstract In the Na–U–Mo–O system, five compounds with composition Na 2 UMo 2 O 10 , Na 2 U 2 Mo 2 O 13 , Na 2 U 2 Mo 3 O 16 , Na 2 - UMo 4 O 16 and Na 2 U 2 Mo 4 O 19 were prepared by solid state reaction of Na 2 MoO 4 , UO 3 and MoO 3 in the required stoic-hiometric ratio. The compounds were characterized by X-ray powder diffraction, infrared and thermal analysis tech- niques. The XRD data of all the above-mentioned compounds were indexed on the orthorhombic system. All the com- pounds showed thermal stability up to 600 °C in air and decomposed at 950 °C to form Na 2 U 2 O 7 . Infrared spectra of all the compounds show strong spectral bands in the range 700–950 cm 1 due to MoO 2 4 tetrahedra and the UO 2þ 2 group. A pseudo-ternary phase diagram of Na 2 O–UO 3 –MoO 3 was drawn using the quaternary compounds and information available on Na–U–O, Mo–U–O and Na–Mo–O ternary systems. The various phase fields prepared during this work were established by XRD analysis. Ó 2006 Elsevier B.V. All rights reserved. 1. Introduction The liquid metal fast breeder reactor (LMFBR) uses mixed oxide (U, Pu)O 2 as fuel, liquid sodium as coolant and stainless steel 316 as cladding mate- rial. Molybdenum is an important alloying element in structural steel in the sodium circuits of LMFBRs. It is also an important fission product, formed in large quantity (fission yield around 20%) in a nuclear reactor and is present in the irra- diated fuel. When the dissolved oxygen level in liquid sodium exceeds a threshold value, the clad gets corroded due to the reaction of sodium with the cladding components chromium, iron, molyb- denum, etc., and various ternary oxides are formed, imparting high temperature creep strength to the clad. The formation of these compounds may be one of the important factors responsible for the change in behaviour of the nuclear fuel which limit the life of fuel pin. Thus structural and thermal studies on the sodium–uranium–molybdenum– oxygen (Na–U–Mo–O) system are important for understanding the fuel–clad–coolant chemical inter- action in LMFBR [1]. The quaternary systems, alkali metal–U–Mo–O, have been studied by various workers. In the study of the K–U–Mo–O system, Dion and Noel [2,3] prepared and identified new phases, namely, 0022-3115/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.jnucmat.2006.10.020 * Corresponding author. Fax: +91 22 25505345. E-mail address: nddahale@apsara.barc.ernet.in (N.D. Da- hale). Journal of Nuclear Materials 362 (2007) 26–35 www.elsevier.com/locate/jnucmat