Radiation and thermal effects on porous and layer structured materials as getters of radionuclides L.M. Wang a,b, * , J. Chen a , R.C. Ewing a,b,c a Department of Nuclear Engineering and Radiological Sciences, University of Michigan, Ann Arbor, MI 48109-2104, USA b Department of Materials Science and Engineering, University of Michigan, Ann Arbor, MI 48109-2104, USA c Department of Geological Sciences, University of Michigan, Ann Arbor, MI 48109-2104, USA Abstract The long term radiation and thermal effects on porous and layer structured materials that may function as getters for radionuc- lides have been evaluated using accelerated laboratory experiments including energetic electron, ion or neutron irradiation, as well as high-temperature thermal annealing. The materials studied include: zeolites, layered silicates (mica and smectite clays), open frame- work structured apatite and crystalline silicotitanate (CST) which is an important synthetic ion-exchange material for the chemical separation of high-level liquid radioactive wastes. In situ transmission electron microscopy during irradiation by energetic electrons and ions has shown that all the studied mate- rials are susceptible to irradiation-induced amorphization. Amorphization can be induced by ionization and/or direct displacement processes. Amorphization may be preceded or accompanied with dehydration, layer spacing reduction and gas bubble formation. In the case of zeolites, CST and some layer silicates, radiation effects are significantly enhanced at higher temperatures. In fact, thermal annealing at high temperatures alone can cause complete amorphization of zeolites. Our experiments have shown that amorphiza- tion or even partial amorphization will cause a dramatic reduction (up to 95%) in ion-exchange and sorption/desorption capacities of zeolite for radionuclides, such as Cs and Sr. Because the near-field or chemical processing materials (e.g., zeolites or CST) will receive a substantial radiation dose after they have incorporated radionuclides, our results suggest that radiation effects may, in some cases, retard the release rate of sorbed or ion-exchanged radionuclides. Ó 2005 Elsevier Ltd. All rights reserved. Keywords: Radiation effects; Zeolite; Getter; Radionuclides; Amorphization 1. Introduction Site restoration activities at DOE facilities and the permanent disposal of nuclear waste inevitably involve understanding the behavior of materials in a radiation field, especially the porous and layer structured materi- als that function as getters for the radionuclides to re- tard migration of those elements [1–3]. Radionuclide decay and the associated radiation and thermal effects may lead to physical and chemical changes that can degrade or enhance important material properties. Alpha-decay of the actinide elements and beta-decay of the fission products lead to atomic-scale changes in materials (radiation damage and transmutation). The radiation exposure due to the release and sorption of long-lived actinides and fission products (e.g., 137 Cs and 90 Sr) may cause changes in important transport properties (e.g., sorption and cation exchange capacity) in geological materials, such as colloidal clays and zeo- lites, along transport pathways. Thus, the effect of radio- active decay on soils and geologic materials during 1359-0286/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.cossms.2005.04.002 * Corresponding author. Address: Department of Nuclear Engineer- ing and Radiological Sciences, University of Michigan, Ann Arbor, MI 48109-2104, USA. Tel.: +1 734 647 8530; fax: +1 734 647 8531. E-mail address: lmwang@umich.edu (L.M. Wang). Current Opinion in Solid State and Materials Science 8 (2004) 405–418