Durability of potential plutonium wasteforms under repository conditions

Abstract

Separated stocks of UK civil plutonium are currently held as a zero value asset in storage, as there is no final decision about whether they should be treated as a resource for future use as nuclear fuel or as waste. Irrespective of future UK government strategies regarding plutonium, at least a portion of the UK civil plutonium inventory will be designated for geological disposal. In this context, we performed a high-level review of the performance of potential wasteforms for the disposal of separated civil plutonium. The key issues considered were the durability and chemical reactivity of the wasteforms in aqueous environments and the long-term radionuclide release under conditions relevant to geological disposal. The major findings of the review, relevant not only to the situation in the UK but to plutonium disposal in general, are summarized in this paper. The review showed that, in the event of a decision being taken to declare plutonium as a waste for disposal, more systematic studies would be required to constrain the wasteform performance under repository conditions in order to derive realistic source terms for a safety case.

Structural, vibrational, and thermochemical properties of the monazite-type solid solution La1–Pr PO4

“…Monazite has been investigated for more than six decades for numerous reasons, ranging from potential technical applications as luminophors or lasers [1,2,3] to geochronological studies [4,5,6,7,8,9]. It is an important source for thorium, lanthanum and cerium and proposed as a host matrix for long term storage of high-level radioactive nuclear waste [10,11,12,13,14,15,16,17,18,19,20,21,22,23,24]. The immobilization of nuclear waste is a pressing topic in the context of deep geological final repositories.…”

Evaluation of the long-term behavior of potential plutonium waste forms in a geological repository

“…Thus, experimental data on the durability of plutonium waste forms under repository-relevant conditions are generally limited or in many cases absent (cf. [24,25]), since (i) most tests are closed-system tests, (ii) the experimental conditions employed (e.g. regarding solution chemistry and redox conditions) are rather different compared to the conditions in a geological repository in the long-term, and (iii) none of the surrogate elements can mimic all facets of the geochemical behavior of plutonium.…”

Research for the Safe Management of Nuclear Waste at Forschungszentrum Jülich: Materials Chemistry and Solid Solution Aspects

“…[80][81][82][83] Moreover, a variety of single-phase and poly-phase ceramic matrices (based, e.g., on oxides such as pyrochlore and zirconolite, silicates such as zircon, or phosphates such as monazite) have been explored as potential alternative waste matrices for specific waste streams such as separated plutonium from civilian or military sources unsuitable for further use, minor actinides (Am, Cm, Np), or long-lived fission products. [84][85][86][87][88][89][90][91][92][93][94][95][96][97] In these crystalline ceramics, selected in particular for their high chemical durability and radiation stability, radionuclides can be incorporated into the lattice structure of the host phase occupying specific atomic positions, which allows for high loadings of specific radionuclides.…”