Immobilization of Actinides by Hydroxylapatite

1991 ◽  
Vol 257 ◽  
Author(s):  
R. Gauglitz ◽  
M. Holterdorf ◽  
W. Franke ◽  
G. Marx

ABSTRACTIn cooperation with the Ministry of Research and Technology we investigated the influence of hydroxylapatite (HAP) added to the backfill material of a radioactive waste disposal located in a salt dome. The time dependence of the sorption and precipitation of radionuclides has been studied in three different praxisrelevant salt brines under variation of temperature and pH-value.Performing batch experiments uranium and thorium phosphates were precipitated from UO2(NO3)2 and Th(NO3)4 solutions at 75°C, the amounts of the relevant actinide compounds also exceeding that of HAP. The isolated precipitates were investigated by use of X-ray-powder-diffractometry and SEM. For the various uranium systems two mineral phases were obtained. From solution II and also from Q-brine the mineral saléeite Mg(UO2)2 (PO4)2 · 9H2O was formed. From solution III meta-autunite Ca(UO2)2(PO4)2 · 6H2O, a dehydration product of autunite, was precipitated.

2021 ◽  
Author(s):  
Lucas Schwarz ◽  
Paula Bräuer

<p>The political and social debate on nuclear energy in Germany has been characterized for many decades by a high potential for conflict and dissatisfaction. Especially the controversies surrounding the Gorleben salt dome gained international attention and changed the relationship between citizens and political decision-makers from the local to the national level. With the Repository Site Selection Act of 2013 (StandAG, first amendment in 2017) a new approach was chosen to implement a participative, inclusive and transparent search process for the best possible repository for high-level radioactive waste in Germany. In this context, a self-learning process was proclaimed, based on a white (unbiased) map, which should give citizens an active role. However, the first interim report of the Federal Company for Radioactive Waste Disposal and the publication of the colorful map, in which geologically suitable areas were identified on a large scale, already revealed a massive potential for conflict. Many citizens and activists who were already protesting against the Gorleben salt dome criticized in this early phase of the process, the lack of transparency and opportunities to have a say on the possible sitting regions.</p><p>To address this criticism, we want to provide an interactive map as an online platform that presents existing geographic data, that enables people to contribute spatially-located information (geological, on-surface), and thus a possibility for people to interact and participate regarding the possible siting regions. Therefore, we collect existing spatial data that is relevant to the ongoing process, such as possible siting regions (declared by the Federal Company for Radioactive Waste Disposal), nuclear power plants (active/inactive, research facilities, etc.), storage facilities (on-site, central, interim, etc.), historically relevant locations (places of protest, uranium enrichment & processing facilities, etc.) as well as basic data for orientation. We implement two possibilities for participatory interaction: (1) adding spatially-located notes that contain own experiences or local knowledge (e.g. reports, concerns, suggestions) and (2) initiating a platform for a spatially-located discussion. Against the background of transdisciplinary research, in an iterative process, we want to evaluate the participatory value of this application by consulting civic as well as scientific actors. We, therefore, employ focus groups with a transdisciplinary support group of citizens beforehand and surveys after using the application. For this panel we want to present our primary results from a first test with the aforementioned focus groups.</p><p>Aside from testing the suitability of such a mode of participation, we aim to analyze where problems emerge, and which information is necessary and/or might lead to conflict. Finally, we want to gain insight into how such modes of participation influence the quality of dialogue and how it contributes to the overall perception of a procedurally just process.</p>


2019 ◽  
Author(s):  
C. Le Milbeau ◽  
P. Ollivier ◽  
G. Kuippers ◽  
J.R. Lloyd ◽  
A. Albrecht ◽  
...  

2015 ◽  
Vol 79 (6) ◽  
pp. 1287-1295 ◽  
Author(s):  
Adam J. Williamson ◽  
Katherine Morris ◽  
Christopher Boothman ◽  
Kathy Dardenne ◽  
Gareth T.W. Law ◽  
...  

AbstractNeptunium-237 will be present in radioactive wastes over extended time periods due to its long half-life (2.13 × 106years). Understanding its behaviour under conditions relevant to radioactive waste disposal is therefore of particular importance. Here, microcosm experiments were established using sediments from a legacy lime workings with high-pH conditions as an analogue of cementitious intermediate-level radioactive waste disposal. To probe the influence of Fe biogeochemistry on Np(V) in these systems, additional Fe(III) (as ferrihydrite) was added to select experiments. Biogeochemical changes were tracked in experiments with low levels of Np(V) (20 Bq ml–1; 3.3 μM), whilst parallel higher concentration systems (2.5 KBq ml–1;414 μM) allowed X-ray absorption spectroscopy. As expected, microbial reduction processes developed in microbially-active systems with an initial pH of 10; however, during microbial incubations the pH dropped from 10 to ∼7, reflecting the high levels of microbial metabolism occurring in these systems. In microbially-active systems without added Fe(III), 90% sorption of Np(V) occurred within one hour with essentially complete removal by one day. In the ferrihydrite-amended systems, complete sorption of Np(V) to ferrihydrite occurred within one hour. For higher-activity sediments, X-ray absorption spectroscopy (XAS) at end points where Fe(II) ingrowth was observed confirmed that complete reductive precipitation of Np(V) to Np(IV) had occurred under similar conditions to low-level Np experiments. Finally, pre-reduced, Fe(III)-reducing sediments, with and without added Fe(III) and held at pH 10, were spiked with Np(V). These alkaline pre-reduced sediments showed significant removal of Np to sediments, and XAS confirmed partial reduction to Np(IV) with the no Fe system, and essentially complete reduction to Np(IV) in the Fe(III)-enriched systems. This suggested an indirect, Fe(II)-mediated pathway for Np(V) reduction under alkaline conditions. Microbial analyses using 16S rRNA gene pyrosequencing suggested a role for alkali-tolerant, Gram-positive Firmicutes in coupled Fe(III) reduction and Np immobilization in these experiments.


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