[en] Vitrification is currently the most widely used technology for the treatment of high-level radioactive waste (HLW) in most countries using nuclear power. Alkali borosilicate and aluminophosphate glass are applied for the immobilization of actinides and fission products depending on the waste streams that arise, respectively. Future waste generation is primarily driven by interest in sources of clean energy and this has led to an increased interest in advanced nuclear power production in many countries, with few exceptions such as Germany, where nuclear power generally is no longer an option for future electric power generation strategies. Therefore, advanced nuclear waste forms are being designed for properly thought-out future nuclear waste management strategies. Potential advanced waste forms can be single-phase or poly-phase crystalline ceramic (mineral) waste forms that chemically incorporate radionuclides and hazardous species atomically in their crystal structures. In this context, phosphates play an important role because many of them show outstanding and desired properties like a high radiation resistance and a high chemical durability. In this chapter, we will focus on phosphates that are currently discussed as potential single-phase ceramic waste forms for the safe disposal of the actinides U, Pu, and the minor actinides Np, Cm, and Am, and in some cases, even for the disposal of fission products like ⁹⁰Sr. The mineral monazite and monazite-type synthetic ceramic phases will be described in more detail; simply because such phases are especially well suited for the permanent incorporation of actinides. Additionally, natural analogues can be used as references that enable a secured estimation of the long-term properties of phases designed in scientific laboratories.

[en] The conditioning of radioactive waste from nuclear power plants and in some countries even of weapons plutonium is an important issue for science and society. Therefore the research on appropriate matrices for the immobilization of fission products and actinides is of great interest. Beyond the widely used borosilicate glasses, ceramics are promising materials for the conditioning of actinides like U, Np, Pu, Am, and Cm. Monazite-type ceramics with general composition LnPO₄ (Ln = La to Gd) and solid solutions of monazite with cheralite or huttonite represent important materials in this field. Monazite appears to be a promising candidate material, especially because of its outstanding properties regarding radiation resistance and chemical durability. This article summarizes the most recent results concerning the characterization of monazite and respective solid solutions and the study of their chemical, thermal, physical and structural properties. The aim is to demonstrate the suitability of monazite as a secure and reliable waste form for actinides. (orig.)

[en] This Volume is the second part of a critical review of the thermodynamic properties of iron, its solid compounds and aqueous complexes, initiated as part of the NEA Thermochemical Database Project Phase IV (TDB IV), and a continuation of Part 1, which was published in 2013 as volume 13a. The database system developed at the NEA Data Bank ensures consistency not only within the recommended data sets of iron, but also among all the data sets published in the series. This volume will be of particular interest to scientists carrying out performance assessments of deep geological disposal sites for radioactive waste

[en] This paper focuses on major phosphate-based ceramic materials relevant for the immobilisation of Pu, minor actinides, fission and activation products. Key points addressed include the recent progress regarding synthesis methods, the formation of solid solutions by structural incorporation of actinides or their non-radioactive surrogates and waste form fabrication by advanced sintering techniques. Particular attention is paid to the properties that govern the long-term stability of the waste forms under conditions relevant to geological disposal. The paper highlights the benefits gained from synergies of state-of-the-art experimental approaches and advanced atomistic modeling tools for addressing properties and stability of f-element-bearing phosphate materials. In conclusion, this article provides a perspective on the recent advancements in the understanding of phosphate based ceramics and their properties with respect to their application as nuclear waste forms.

[en] Highlights: • Comprehensive structural study on metastable Tb- and Dy-monazites. • First published Raman spectra of monoclinic TbPO₄ and DyPO₄. • Data fit well into linear trends of stable lanthanide phosphates. -- Abstract: Metastable Ln-orthophosphates (Ln = Tb, Dy) with monoclinic monazite-type structure were obtained via a precipitation route in aqueous solutions and subsequent thermal treatment. The lattice parameters and fractional coordinates of the atoms in the crystal structures were determined by Rietveld refinement of X-ray diffraction data. The lattice parameters of the metastable monazites obtained here fit well into the linear trends observed for stable LnPO₄ monazites (Ln = La–Gd). Infrared spectroscopic investigations on TbPO₄ and DyPO₄ with monazite structure confirmed the expected shift of the modes to higher wavenumbers with increasing atomic number and decreasing cation radius. Raman spectra of the metastable Tb- and Dy-monazites were obtained for the first time, revealing a typical monazite spectrum for monoclinic TbPO₄, continuing the general linear correlation between the Raman shifts and Ln³⁺ radii observed for the lighter LnPO₄ monazites. In contrast, the Raman spectrum of DyPO₄ was severely biased by fluorescence effects.