Ž . Journal of Nuclear Materials 252 1998 228–234 Thermophysical property measurements and ion-implantation studies on CePO 4 K. Bakker a, ) , H. Hein a , R.J.M. Konings a , R.R. van der Laan a , Hj. Matzke b , P. van Vlaanderen a a Netherlands Energy Research Foundation ECN, P.O. Box 1, 1755 ZG Petten, The Netherlands b European Commission, Joint Research Centre, Institute for Transuranium Elements, Postfach 2340, D-76125 Karlsruhe, Germany Received 11 August 1997; accepted 3 October 1997 Abstract The thermal properties and the response to fission-product damage of CePO were studied in view of its potential 4 application as inert matrix for the transmutation of transuranium elements in nuclear reactors. The thermal expansion of CePO has been recorded from 293 K to 1323 K using X-ray diffraction. The reduced enthalpy increment of CePO has 4 4 been measured by drop calorimetry from 474 K to 934 K. The laser-flash technique was used to measure the thermal diffusivity between 300 K and 1150 K. Ion implantation studies were performed at 813 K with 72 MeV 127 I ions and at room temperature with 403 MeV 116 Sn ions. The results are not favourable for the use of CePO as inert matrix to incinerate 4 actinides. q 1998 Elsevier Science B.V. 1. Introduction The mineral monazite, a rare-earth phosphate, occurs as an accessory mineral in granitic rocks and is the principal source for the commercial production of cerium and other lanthanide elements. Monazite has the ability to incorpo- rate large amounts of thorium and uranium and remains Ž crystalline despite the high a-decay doses )1 dpa, dis- . placement per atom induced by these elements. a-decay Ž produces a-particles ,5 MeV, producing ,200 dis- . placements in the lattice . The recoil atoms of the a-decay, e.g. 237 Np in the decay of 241 Am, ,100 keV, produce ,1500 displacements in the lattice. For this reason syn- thetic monazite is being considered as a storage medium for transuranium elements like plutonium and americium w x 1–3 . The a-decay resistance and the ability to incorporate Ž . thorium and uranium make synthetic monazite CePO 4 also an interesting support material for uranium-free fuels ) Corresponding author. Tel.: q31-224 564 386; fax: q31-224 563 608; e-mail: k.bakker@ecn.nl. that are considered for the incineration of plutonium and americium, especially in once-through scenarios. While being reactor irradiated, monazite will experience the im- pact of fission products with 70 to 100 MeV energy, one fission event producing ,1 =10 5 displacements. The range of fission products is ,8 mm, compared to ,20 mm for a-particles and ,0.03 mm for recoil atoms. At present no information is available on the influence of irradiation with fission products on the microstructure of CePO . A useful technique to study fission damage is by 4 using high-energy ion beams. This avoids the formation of radioactive species and the need to work in hot cells. The only information that exists about the influence of ions on the microstructure of CePO has been obtained at energies 4 that are much lower than the energies of fission products w x 4,5 . Monazite becomes metamict during irradiation with wx 1.5 MeV Kr ions at doses below 1 dpa 4 . Karioris et al. wx 5 have shown that monazite becomes also metamict when Ž . bombarded with Ar ions 3 MeV . It recrystallizes by annealing at approximately 570 K for 24 h. The stability against fission product impact at fission energy is studied in the present investigation. 0022-3115r98r$19.00 q 1998 Elsevier Science B.V. All rights reserved. Ž . PII S0022-3115 97 00300-0