The Coupling of Chemical and Transport Processes in Near-Field Modelling

1986 ◽  
Vol 84 ◽  
Author(s):  
S.M. Sharland ◽  
P.W. Tasker ◽  
C.J. Tweed
Keyword(s):  
Radioactive Waste ◽  
Chemical Equilibrium ◽  
Near Field ◽  
Transport Processes ◽  
Primary Interest ◽  
Field Modelling ◽  
Long Time ◽  
Waste Repository ◽  
Solid Phases ◽  
Chemical Conditions

AbstractNear-field modelling is concerned with the description of the migration, chemical and degradation processes that may occur within an engineered radioactive waste repository and its immediate environs. The object is to gain understanding of such processes in order to predict the long-time evolution of the repository and to assess the degree of containment provided by the proposed engineered construction. The conditions of primary interest to our programme concern the waste contained within a steel canister and buried in a concrete environment within a clay geology. The chemistry of the near-field is controlled in that it is the consequence of the choice of near-field components, but it may be extremely complex. Intrusion of external groundwater and degradation of the chosen materials will lead to variations in the chemistry in both space and time. It is vitally important to understand these changing chemical conditions since they determine the solubility and sorption of any released radionuclides. In this paper, we describe the computer program CHEQMATE (CHemical EQuilibrium with Migration And Transport Equations), which has many applications in modelling various changes in chemistry in the near-field. The program combines an ionic migration code with the geochemical program PHREEQE [1]. The program maintains local chemical equilibrium in the system as the transport processes evolve. The program includes automatic mineral accounting; solid phases are added or removed from the equilibrium as precipitation or dissolution occurs. We illustrate the use of the CHEQMATE program with an example of a coupled chemical and transport problem, particularly relevant to the near-field of a waste repository.

scholarly journals Multibarrier system preventing migration of radionuclides from radioactive waste repository

Nukleonika ◽  
2015 ◽  
Vol 60 (3) ◽  
pp. 557-563 ◽  
Author(s):  
Wioleta Olszewska ◽  
Agnieszka Miśkiewicz ◽  
Grażyna Zakrzewska-Kołtuniewicz ◽  
Leszek Lankof ◽  
Leszek Pająk
Keyword(s):  
Radioactive Waste ◽  
Near Field ◽  
Storage Site ◽  
Radionuclide Migration ◽  
Radioactive Waste Repository ◽  
Geological Barrier ◽  
Radioactive Waste Repositories ◽  
Waste Repository ◽  
Waste Repositories ◽  
Migration Modeling

Abstract Safety of radioactive waste repositories operation is associated with a multibarrier system designed and constructed to isolate and contain the waste from the biosphere. Each of radioactive waste repositories is equipped with system of barriers, which reduces the possibility of release of radionuclides from the storage site. Safety systems may differ from each other depending on the type of repository. They consist of the natural geological barrier provided by host rocks of the repository and its surroundings, and an engineered barrier system (EBS). The EBS may itself comprise a variety of sub-systems or components, such as waste forms, canisters, buffers, backfills, seals and plugs. The EBS plays a major role in providing the required disposal system performance. It is assumed that the metal canisters and system of barriers adequately isolate waste from the biosphere. The evaluation of the multibarrier system is carried out after detailed tests to determine its parameters, and after analysis including mathematical modeling of migration of contaminants. To provide an assurance of safety of radioactive waste repository multibarrier system, detailed long term safety assessments are developed. Usually they comprise modeling of EBS stability, corrosion rate and radionuclide migration in near field in geosphere and biosphere. The principal goal of radionuclide migration modeling is assessment of the radionuclides release paths and rate from the repository, radionuclides concentration in geosphere in time and human exposure to ionizing radiation

The biogeochemical behaviour of U(VI) in the simulated near-field of a low-level radioactive waste repository

2006 ◽  
Vol 21 (9) ◽  
pp. 1539-1550 ◽  
Author(s):  
James R. Fox ◽  
Robert J.G. Mortimer ◽  
Gavin Lear ◽  
Jonathan R. Lloyd ◽  
Ian Beadle ◽  
...  
Keyword(s):  
Radioactive Waste ◽  
Near Field ◽  
Radioactive Waste Repository ◽  
Low Level ◽  
Waste Repository ◽  
Low Level Radioactive Waste

The Geochemical Behaviour of Nickel in the Repository Environment

1994 ◽  
Vol 353 ◽  
Author(s):  
David Savage
Keyword(s):  
Solid Solution ◽  
Trace Elements ◽  
Radioactive Waste ◽  
Performance Assessment ◽  
Solid Solutions ◽  
Near Field ◽  
Solubility Data ◽  
Geochemical Behaviour ◽  
Chemical Conditions ◽  
Selection Of

Abstract59Ni may make significant contributions to calculated doses in performance assessment (PA) studies of geological repositories for radioactive waste, due principally to the adoption of relatively high near-field solubilities. Ni concentration values used in PA are typically 1–6 orders of magnitude greater than those measured in natural groundwaters. This difference is a result of the utilisation in PA of solubility data for pure nickeliferous solids, and in some instances, the selection of solids chemically incompatible with the disposal environment. The geochemical behaviour of Ni is reviewed. It is considered highly unlikely that Ni will form discrete pure solids in the repository near-field, so that partition as a trace element into solid solutions should be considered. Henry’s law behaviour of trace elements is discussed and geochemically-realistic Ni solubility values for HLW and L/ILW disposal scenarios calculated. It is concluded that Ni will behave according to the chemical conditions of the disposal environment, which should be reflected in the choice of solubility data for PA. The adoption of solid solution modelling for other elements of interest to PA should be considered.

The Compilation of Geochemical Data Bases for Performance Assessment of a Planned Repository in the Opalinus Clay in Northern Switzerland

2003 ◽  
Vol 807 ◽  
Author(s):  
Bernhard Schwyn ◽  
Paul Wersin
Keyword(s):  
Radioactive Waste ◽  
Safety Assessment ◽  
Near Field ◽  
Opalinus Clay ◽  
Geochemical Data ◽  
Data Bases ◽  
Northern Switzerland ◽  
Compacted Bentonite ◽  
Waste Repository ◽  
Chemical Retention

ABSTRACTChemical retention of radionuclides in the near field and in the host rock is an important safety pillar within the Swiss concept for a radioactive waste repository. Geochemical databases for solubility limits in cement and bentonite porewater and sorption / diffusion in cement, compacted bentonite and Opalinus Clay were compiled for use in safety assessment calculations. The databases are presented for selected safety-relevant radioelements. In contrast to earlier safety assessment studies Kd values were not truncated at 5 m3 kg−1 and values well above 10 m3 kg−1 (e.g. for actinides) are reported.

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