Repository Media Research Articles

The Value of Visual Disaster Records from Digital Archives and Films in Post-3/11 Japan

This paper explores the value of visual records from natural disasters in assisting reconstruction, including photography, single-shot videos, and documentary movies. It considers three types of visual records related to the Great East Japan Earthquake: 1) raw data, 2) edited educational videos, and 3) commercial documentary films. It also considers the nature of disaster records and their repository medium, including digital data archives, public educational websites, and commercial networks. Furthermore, the authors consider the overlaps between these categories. Raw video records certainly meet the needs of either digital archives or documentary movies. However, commercial documentary movies form a category of their own, as copyright and scripts constrain their exploitation and manipulation. In conclusion, this paper identifies the merit of each type of visual record and argues that both are necessary for the social remembering of disasters and to help reconstruct communities affected by such events. Keywords: digital archives; films; disaster

Uptake of anionic radionuclides onto degraded cement pastes and competing effect of organic ligands

Summary Hardened cement pastes (HCP) present a high affinity with a lot of radionuclides (RN) and can be used as waste confining materials in radioactive waste repository. Indeed, in cementitious media, RN can be removed from solution via (co)precipitation reactions or via sorption/diffusion mechanisms. In this study, the affinity of anionic RN (Cl−, I−, SeO3 2− and CO3 2− chemical forms) with a CEM-I HCP has been studied vs. the degradation of the HCP particles. These RN are considered as mobile in repository media and it is important to have a set of distribution ratio (R d) in cement environment. The R d values have been measured in batch experiments as a function of the pH, used as the degraded state parameter of the HCP suspensions. The R d values increase in all cases, from the unaltered state (pH 13.3) to the altered state of HCP, i.e. until all portlandite is dissolved, corresponding to pH 12.6. Then, R d values decrease until degraded states (pH 12.0), corresponding to the decalcification of the calcium silicate hydrate (C-S-H) phases. The behaviour of anionic RN seems to be correlated to the evolution of calcium concentration and is opposed to the evolution of sulphate concentration in solution which could have a competing effect. Comparison is done with the behaviour of caesium and uranium(VI), which is a cationic RN but has a major negative hydrolysed species at high pH. As awaited, the uranium(VI) behaviour is very different from purely anionic RN one in accord with spectroscopic analyses from literature works. The R d values have also been measured for the organic ligands isosaccharinate (ISA) and EDTA. The uptake of ISA can be important and competing effect with the sorption of SeO3 2− has been evidenced in HCP suspensions as a function of the ISA concentration.

Current state of knowledge of nuclear waste glass corrosion mechanisms: the case of R7T7 glass

The mechanisms of aqueous corrosion of nuclear waste glasses are reviewed. After an initial glass hydration step, a thin reaction zone is created within which a H+ ⇄ alkali metal interdiffusion profile is formed. The hydrated silicate network then dissolves congruently, hydrating all the glass elements. The dissolution kinetics are controlled principally by the H4SiO4 activity in solution, and can be described by a first-order relation. Many glass components, however, including the oxides and hydroxides, are highly insoluble in alkaline media (pH 7–10): the actinides, the rare earths, Fe, Zr, Al and other elements do not enter solution but recombine in situ to form an amorphous surface ‘gel’ layer. Thus dissolution remains nonselective (all the glass elements are hydrated at the same time) but becomes incongruent (not all the elements enter solution). The formation and structural properties of the gel are discussed. The composition of the gel changes as the reaction progresses, approaching the hydrated glass composition as the leaching solution nears saturation. The gel must be taken into account as a diffusion barrier and trap for the species released from the glass. The role of the secondary mineral phases formed during glass alteration is then discussed. Geochemical models show that none of the minerals that have been experimentally identified can control the long-term H4SiO4 activity in the French ‘R7T7’ reference glass, and can thus account for the low residual dissolution rates observed. Finally, the current state of knowledge in the area of glass source term models is assessed for the four repository media under consideration in France.

Will salt repositories be dry?

The National Academy of Science committee that considered geologic disposal of nuclear waste in the mid‐1950s recommended salt as a repository medium, partly because of its high thermal conductivity and because it was believed to be “dry” (perhaps the appropriate thought is “impermeable”). Certainly, the fact that Paleozoic salt deposits exist in many parts of t h e world is evidence for very low rates of dissolution by moving groundwater. The fact that the dissolution rates were so small led many scientists to the conclusion that the salt beds were nearly impermeable. The major source of brine within the salt beds was thought to be fluid inclusions within salt crystals, which could migrate through differential solution toward a source of high heat. The idea that salt was uniformly “dry” was revised when exploratory drilling in the vicinity of the Waste Isolation Pilot Plant (WIPP) in New Mexico encountered brines within the Castile Formation, an evaporite deposit below the Salado Formation. The brine reservoirs were thought to be isolated pockets of brine in an otherwise “impermeable” salt section.