Release of gases from uranium metal at high temperatures Y.S. Sayi a, * , P.S. Ramanjaneyulu a , C.S. Yadav a , P.S. Shankaran a , G.C. Chhapru a , K.L. Ramakumar a , V. Venugopal b a Radioanalytical Chemistry Section, Bhabha Atomic Research Centre, Mumbai 400 085, India b Radiochemistry and Isotope Group, Bhabha Atomic Research Centre, Mumbai 400 085, India Received 13 November 2006; accepted 30 April 2007 Abstract Depending on the ambient environmental conditions, different gaseous species could get entrapped in uranium metal ingots or pellets. On heating, melting or vapourising uranium metal, these get released and depending on the composition, may cause detrimental effects either within the metal matrix itself or on the surrounding materials/environment. For instance, these gases may affect the performance of the uranium metal, which is used as fuel in the heavy water moderated research reactors, CIRUS and DHRUVA. Hence, detailed inves- tigations have been carried out on the release of gases over a temperature range 875–1500 K employing hot vacuum extraction technique, in specimen uranium pellets made from uranium rods/ingots. Employing an on-line quadrupole mass spectrometer, the analysis of released gases was carried out. The isobaric interference between carbon monoxide and nitrogen at m/e = 28 in the mass spectrometric analysis has been resolved by considering their fragmentation patterns. Since no standards are available to evaluate the results, only the reproducibility is tested. The precision (relative standard deviation at 3r level) of the method is ±5%. The minimum detectable gas content employing the method is 5.00 · 10 09 m 3 . About 4 · 10 04 m 3 /kg of gas is released from uranium pellets, with hydrogen as the main constituent. The gas content increases with storage in air. Ó 2007 Elsevier B.V. All rights reserved. PACS: 81.05.Bx; 81.70.Jb; 82.30.Lp 1. Introduction Uranium is an important nuclear fuel material. In the earliest reactors, natural uranium metal was used as the fuel and aluminum as clad. These reactors were designed to produce plutonium. Aluminum was chosen as clad due to its low thermal neutron absorption cross-section and high corrosion resistance. However, due to low melting temperature, it was not used in power reactors. To over- come the problems encountered with aluminum, Mg–Al and Mg–Al–Zr alloys were chosen. Uranium (natural and depleted) is used as fuel in the gas cooled reactors, gas cooled fast reactors and lead cooled reactors. The gas cooled fast reactors with helium as coolant and liquid metal (Pb or Pb–Bi) cooled reactors are suitable both for power generation and for thermochemical hydrogen production. Uranium in alloy form is also employed as fuel in nuclear submarines. The accelerator driven reac- tor systems also use uranium as fuel. In light water reactors (LWR), enriched uranium as UO 2 is used. Uranium metal is produced by different methodologies [1–4]. Based on the expected burn-up aimed at, the fissile atom density has to be increased. This is generally achieved by employing enriched uranium. There are several methods available for the enrichment of uranium. LASER technique is one of the most sensitive and economical methodologies. However, it is in the developing stages in several countries. LASER method employs either molecular or atomic approach, the later judged as better one. In Atomic Vapour Laser Isotope Separation (AVLIS) technique, uranium vapour, produced by heating uranium metal to 2500 K, is subjected to selective ionisation followed by magnetic 0022-3115/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.jnucmat.2007.04.053 * Corresponding author. Tel.: +91 22 25595011; fax: +91 22 25505150/ 1/2. E-mail address: yssayi@barc.gov.in (Y.S. Sayi). www.elsevier.com/locate/jnucmat Available online at www.sciencedirect.com Journal of Nuclear Materials 373 (2008) 75–81