Swelling induced by alpha decay in monazite and zirconolite ceramics: A XRD and TEM comparative study

Zirconolite and monazite matrices are potential ceramics for the containment of actinides (Np, Cm, Am, Pu) which are produced over the reprocessing of spent nuclear fuel. Actinides decay mainly through the emission of alpha particles, which in turn causes most ceramics to undergo structural and textural changes (amorphization and/or swelling). In order to study the effects of alpha decays on the above mentioned ceramics two parallel approaches were set up. The first involved the use of an external irradiation source, Au, which allowed the deposited recoil energy to be simulated. The second was based on short-lived actinide doping with Pu-238, (i.e. an internal source), via the incorporation of plutonium oxide into both the monazite and zirconolite structures during synthesis. In both types of irradiation experiments, the zirconolite samples became amorphous at room temperature with damage close to 0.3 dpa; corresponding to a critical dose of 4 x 10(18) alpha g(-1) (i.e. similar to 1.3 x 10(21) keV cm(-3) Both zirconolite samples also showed the same degree of macroscopic swelling at saturation (similar to 6%), with ballistic processes being the predominant damaging effect. In the case of the monazite however, the macroscopic swelling and amorphization were dependent on the nature of the irradiation. Externally, (Au), irradiated samples became amorphous while also demonstrating a saturation swelling of up to 8%. In contrast to this, the swelling of the Pu-238 doped samples was much smaller at similar to 1%. Also, unlike the externally (Au) irradiated monazite these Pu-238 doped samples remained crystalline up to 7.5 x 10(18) alpha g(-1) (0.8 dpa). XRD, TEM and swelling measurements were used to fully characterize and interpret this behavior. The low swelling and the conservation of the crystalline state of (PU)-P-238 doped monazite samples indicates that alpha annealing took place within this material. (C) 2014 Elsevier B.V. All rights reserved.