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Abstracts
measures to reduce the radiation exposure from the exposure pathways to humans in future, and to prevent the occurrence
of relevant environmental contamination.
So far, a great number of data have been acquired and technical methods have been examined for the future
remediation. And using the above-mentioned data, JAEA has been conducting the remediation activities at the related
facilities. Among them, the mill tailings pond, operated since 1965 with the approved volume about 40,000m3, has
deposited mining waste and impounded mine water as a buffer reservoir before it is transferred to the water treatment
facility. It is located at the upstream of the water-source river, and therefore, its presence is a cause for worry to the local
residents. Also, social impact is thought to be extensive in case of an outflow incident of mill tailings, like dam failure by
the earthquake. Thus the highest priority has been put to the pond.
JAEA has planned to conduct the remediation and close the pond in coming couple of years. Some activities have
already begun, and the results have been produced steadily. According to the current plan, the pond will be covered by
the multi-layered capping following dewatering and reshaping of mill tailings. The capping is composed of “radon
barrier” for lowering radon-gas dissipation and dose rate, and “low-permeable protective layer” for protecting the radon
barrier and reducing the amount of permeated rainwater. Natural material, including bentonite and sand, is planned for
use to alleviate the future maintenance. Currently, designing is underway for the upstream half of the pond. Data will be
accumulated after capping to verify its effectiveness, and if proved effective, it will be utilized for the capping of the
downstream half of the pond.
3) 40092 – Radon impact at a remediated uranium mine site in Japan
Yuu Ishimori, JAEA (Japan)
This paper mainly illustrates the radon impact of the closed uranium mine site remediated in 2007. The site
remediated is the waste rock site located on the steep slope of a hill about1.5 km upstream from a residential area along a
main ravine. Major remedial action was to cover these waste rock yards with weathering granite soil. The radon flux
density after remediation was intended to be 0.1 Bqm-2s-1 in consideration with the natural background level around
Ningyo-toge because there is no value of radon flux density regulated in Japan. Our action decreased the radon
concentration in the site to natural background level, approximately from 10 to 40 Bqm-3, although relatively high
concentration in excess of 100 Bqm-3 was observed before remediation. On the other hand, our action did not decrease
the radon concentrations around the site in general. This fact proved that the limited source such as waste rocks affected
the radon concentrations at neighboring area only. The similar tendencies were also observed in other environmental data
such as radon progeny concentrations. In conclusion, these findings proved that our remedial action was successful
against radon. This fact will lead to more reasonable action plans for other closed mine sites.
4) 40243 – Phosphate based remediation techniques: interaction of phosphate with uranium-bound calcite
Chase Bovaird, Dawn Wellman, PNNL (USA)
Despite several decades of studies, effective uranium cleanup strategies remain elusive for contamination in deep
subsurface settings that prevail in a number of Department of Energy sites in the western USA. Numerous strategies have
been proposed, including iron barriers, soluble reductive agents, and microbial stabilization via reduction and
precipitation, but have limited applicability for deep subsurface remediation in an oxidative environment. In-situ
phosphate based remediation techniques can potentially delay the precipitation of phosphate phases for controlled in situ
precipitation of stabile phosphate phases to control the long-term fate of uranium. The basic principles underlying
phosphate stabilization is that aqueous phosphate (PO43-), whether injected as an aqueous solution or solubilized from a
source reacts with heavy metals to form insoluble metal-phosphate minerals. The sorption of uranyl species onto minerals
is dependent on the nature and availability of binding sites, solution composition and pH, and aqueous complexation.
Uranium can be sequestered either through ion exchange or surface complexation, and the rates of release of uranium are
dependent on the sorption mechanism. The Hanford Site in southeastern Washington State is a former nuclear defense
production facility. Uranium has been identified as a contaminant of concern for groundwater and the deep vadose zone.
The vadose zone is comprised of highly alkaline, calcareous sediment. EXAFS analyses at shallow depths suggest that
uranium-rich calcite is one of the major controlling phases. Calcite can also serve as a source of Ca2+ and CO32- ions to
form mobile, aqueous, uranyl-carbonate species [Ca2UO2(CO3)3] under circumneutral to alkaline conditions. Detailed
understanding of the rate and mechanism of the interaction between phosphate and uranium-rich calcite will allow a more
effective design of aqueous phosphate-based infiltration strategies to minimize the mobilization of uranium during
remediation. The objective of this investigation was to evaluate the interaction of phosphate species with uranium-rich
calcite to determine the effects of geochemical conditions on the partitioning of phosphate and its degradation products
with uranium-rich calcite, quantify the release of uranium from uranium-rich calcite based on the identity and
concentration of aqueous phosphate species, and quantify the rate and mechanism of uranium immobilization based on
the identity and concentration of aqueous phosphate species. The information obtained from this line of inquiry is
essential to effectively develop phosphate-based remediation strategies for uranium in calcareous environments.
5) 40220 – Remediation of Old Environmental Liabilities in The Nuclear Research Institute Rez plc
Karel Svoboda, Josef Podlaha, Nuclear Research Institute Rez plc (Czech Republic)
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