The use of nuclear and other radioactive material is expanding globally. An increasing number of countries are signalling their intention to employ nuclear power to meet the energy needs of rapidly growing populations, while socioeconomic development is leading to an increased application of medical and industrial radioisotopes. It is critical that rigorous nuclear security systems are established and maintained to accommodate the increased storage, movement and use of such materials. One aspect of nuclear security is nuclear forensics, which is defined by the International Atomic Energy Agency (IAEA) as 'the scientific analysis of nuclear or other radioactive material, or of other evidence that is contaminated with radionuclides, in the context of international or national law'. In Australia, forensic examination of nuclear or other radioactive material is undertaken by ANSTO, whilst the current capability for the forensic examination of evidence contaminated with radionuclides is jointly held by ANSTO and the Australian Federal Police (AFP). This article describes some of the recent activities undertaken by ANSTO and the AFP to maintain and further develop Australia's nuclear forensic science capability and outline future plans to enhance Australia's capability to provide nuclear forensic support to nuclear security.

Seven laboratories used the results of bulk uranium isotopic analysis by either inductively coupled plasma mass spectrometry (ICP-MS) or thermal ionization mass spectrometry (TIMS) for characterization of the samples in the Nuclear Forensic International Technical Working Group fourth international collaborative material exercise, CMX-4. Comparison of the measured isotopic compositions of uranium in three exercise samples is implemented for identifying any differences or similarities between the samples. The role of isotopic analyses in the context of a real nuclear forensic investigation is discussed. Several limitations in carrying out ICP-MS or TIMS analysis in CMX-4 are noted.

The dissolution of the thorium analogue of brannerite (ThTi2O6-I) and U(IV)/U(V) doped Th-brannerite (Th0.97U0.03Ti2O6-II and Th0.955U0.03Ca0.015Ti2O6-III) in aqueous media under atmospheric conditions has been studied to elucidate the effects of pH and uranium valence state on the dissolution rate. The dissolution of I is nearly stoichiometric but slightly preferential release of U occurs for II and preferential release of Ca and U occur for III. The V-shape pH dependence previously observed for U-brannerite only occurs for U (not other matrix elements) for II, indicating that the pH dependence is related to the U oxidation state upon dissolution. The normalised U dissolution rates of III are nearly an order of magnitude higher than those of II for pH values over 3, suggesting brannerite is less durable with U(V) doping. TEM examination of specimens after leaching revealed few surface alteration products, which is consistent with the nearly stoichiometric dissolution of thorium brannerite.

The dissolution in de-ionized water (DIW) at 90 and 150 °C of Cs and Ba from mechanically polished Cs-doped Ba hollandite samples is essentially congruent. The normalized Ba and Cs release rates were <0.001 g/m2/day after 56 days in DIW at 90 °C, and the Ba normalized release rate of a Cs-free sample was 0.01 g/m2/day after 56 days in DIW at 150 °C. Varying the pH between approximately 2.5 and 12.9 affected only the Ba dissolution rates of hollandite by half an order of magnitude. The dissolution rates of all species decrease with increasing leaching time due to the formation of partly impervious surface coatings of Al- and Ti-rich species. These surface coatings were investigated by scanning electron microscopy, and in some cases by cross-sectional transmission electron microscopy and x-ray photoelectron spectroscopy.

Rb-doped Ba-hollandite and synroc-C samples were prepared for aqueous dissolution studies at 90°C in deionized water using MCC-1 protocols. Small amounts of possibly Rb-bearing BaTiO3, hibonite and alumina accompanied the major Rb-doped (0.1 formula units) hollandite phase. The Rb loadings in the synroc samples ranged from 0.89 to 2.67 wt%. Rb leached at <0.2 g/m2/d from hollandite samples and <0.1g/m2d from synroc, with the values decreasing with increasing dissolution time. The variance between the dissolution rates for the different Rb-doped hollandite and synroc samples is discussed, in terms of Rb-bearing minor phases.

Zirconolite-glass and sphene -glass specimens, doped with REE as simulants for trivalent actinides, were leached under two conditions. The first was a solubility test using a powdered sample in deionized water at an SA/V ratio of 200 cm−1, to examine the long-term leaching behavior of the composite materials. The other test was carried out in the presence of moist clay, to assess the degree of surface alteration of the composites in the presence of potential geological repository materials. Both tests were carried out at 90°C. The specimens leached in clay showed signs of preferential attack on the glassy matrix along zirconolite and sphene grain boundaries. EDS results showed no gross changes in composition of the constituent phases as a result of leaching. For the solubility tests, steady state conditions of elemental release were attained within 7 days of leaching, suggesting development of a surface passivation layer hindering movement of reactive species between the surface of the material and the leachant. Calcium, Si and Al releases were similar between composites. Titanium and Ce releases were also similar between composites, and were two orders of magnitude lower than those for Ca, Si and Al. The actinide simulants partitioned into the glass phase and into the crystalline component of the composite materials in approximately similar proportions. Although the surrogates were contained in the less durable glassy phase at these levels, this was not reflected in the release of Ce, for example, which was similar to that for a single-phase zirconolite.

From elastic recoil detection analysis (ERDA) of 2 MeV He ions and secondary ion mass spectroscopy (SIMS), exposure of Synroc-C to D 2 O at 150°C for ~ 30 days produced surface deuteration products of a few nm in thickness, with surface roughness after polishing down to 0.25 μm diamond finish not being of critical importance in the thickness determination. Reaction at 250°C produced more extensive deuteration and general surface alteration, over depths of about a micron. SIMS did not show any surface enhancement of rare earths or Zr on Synroc-C surfaces reacted at 90°C for up to 336 days. Pu-doped SynrocC exposed to deionised water at 70°C showed surface depletion of Pu by alpha-spectroscopy. Zirconolite-rich Synroc showed less surface deuteration than Synroc-C after reaction for 3 weeks at 150°C in D 2 O. Admixtures of 0.001 M of fluoride ions to dilute HCI (pH = 2) produced deposits of anatase, ~ 20 μm thick, on perovskite after a few weeks at 90°C; these deposits were much thicker than those produced by the dilute HCI without the fluoride ions being present.

Aqueous durability has been assessed for fourteen pyrochlore- and zirconolite-rich titanate waste forms designed for the immobilisation of excess Pu. The ceramics used in this study contained about 12 wt% Pu and about 15 wt% of Hf and Gd oxides as neutron absorbers and were fabricated by cold-pressing and sintering or hot isostatic pressing. Total release rates (i.e. unfiltered solution + vessel wall inventory) have been measured withthe MCC-1 test method at 90 °C in deionised water. For all samples, 7-day release rates of Pu are between 4 × 10−5 and about 10−3 g.m−2.d−1, reducing to between about 8 × 10−6 and 3 × 10−5 g.m−2.d−1after more than 300 days of leaching. Release rates of U from the baseline ceramic were found to decrease to values between 6 × 10−4 and 1 × 10−5 g.m−2.d−1after 200 days. Hf leach rates were generally < 5 × 10−6 g.m−2.d−l after more than 7 days. Further, the addition of several % of chemical impurities to the baseline sintered formulations was found to reduce U and Gd releases by about a factor of 10 after 200 days.

A titanate Synroc ceramic for the immobilization of Pu-bearing waste was designed to consist of 70 wt% zirconolite (CaZrTi2O7) + 15 wt% nepheline (NaAlSiO4) + 15 wt% rutile (TiO2). It contained 10 wt% of Pu plus 6 wt% of Gd as a neutron poison. The material was made by our standard sol-gel route, using a mixture of alkoxides and nitrates, followed by stir-drying and calcination. It was fabricated by hot-pressing at 1150–1250°C/20 MPa for 2 hours in a collapsible metal bellows. Though zirconolite was the majority phase, ~20 wt% of perovskite also formed. Some of the Na, intended for nepheline, partitioned into the titanate phases. 84-day differential total leach rates of Pu were in the order of 10–5 g/m2/d at 90 and 200° C. Companion ceramics using molar substitution of Ce for Pu confirmed the idea that Ce is a good simulant of Pu from a solid state chemical view, but that there are limitations in terms of leach rate parallels.