| 1. |
- Bruno, J., et al.
(författare)
-
Modelling experimental results on radiolytic processes at the spent fuel water interface. I. Radiolysis products and U release
- 2004
-
Ingår i: SCIENTIFIC BASIS FOR NUCLEAR WASTE MANAGEMENT XXVII. - 1558997520 ; , s. 397-402
-
Konferensbidrag (refereegranskat)abstract
- Experimental and modelling efforts in the last decade in the frame of nuclear waste management field have been focused on studying the role of the UO2 surfaces in poising the redox state of solid/water systems. For this purpose, an experimental programme was developed consisting on dissolution experiments with PWR spent fuel fragments in an anoxic environment and by using different solution compositions. The collected data so far, indicate that production and fate of radiolysis products follow the same trends independently on the solution composition used in the tests. Hydrogen and oxygen concentrations show an initial increase with time until reaching a constant concentration. The trend observed for hydrogen peroxide is a decrease at short contact times to reach again a constant concentration with time. These steady-states indicate an overall balance of the generated radiolytic species. Modelling work indicates that uranium dissolution is controlled by the oxidation of the spent fuel matrix in 10mM bicarbonate solutions while in the tests carried out at lower or without carbonate concentrations uranium in the aqueous phase is governed by the precipitation of schoepite. These results are determinant to highlight that reducing conditions are restored in the aqueous phase in relatively short periods of time and at short distances away from the dynamic redox spent fuel/water interface.
|
|
| 2. |
- Crawford, James, et al.
(författare)
-
Harmonisation of site characterisation and performance assessment modelling - The relative importance of surface sorption and matrix interaction phenomena
- 2004
-
Ingår i: Scientific Basis For Nuclear Waste Management XXVII. - 1558997520 ; , s. 551-556
-
Konferensbidrag (refereegranskat)abstract
- In the context of geological repositories for nuclear waste disposal, the goal of site characterisation (SC) is to obtain input data that can later be used as a basis for performance assessment calculations (PA). Performance assessment is required to give an indication as to whether the repository will behave as intended over the geological timescales relevant for risk analysis. Processes that may be important in a PA setting for constraining radionuclide transport may not necessarily be dominating, or indeed may not even be observable during SC investigations. In this paper it is shown that the migration of sorbing tracers is governed largely by surface sorption phenomena in typical SC-type field experiments whereas in a PA scenario, matrix interaction instead can be expected to play an overwhelmingly important role. This study uses data and settings that are representative for fractured rocks in Sweden, but the method used and the conclusions may have more general applicability.
|
|
| 3. |
- Dario, Mårten, et al.
(författare)
-
Effects of cement additives on radionuclide mobility
- 2004
-
Ingår i: Scientific basis for radioactive waste management XXVII. - Warrendale, Pa : Materials Research Society. - 1558997520 ; , s. 639-644
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)
|
|
| 4. |
|
|
| 5. |
- Dario, M., et al.
(författare)
-
Effects of technical adsorbents and cleaning agents in a cement matrix - A case study
- 2004
-
Ingår i: Mater Res Soc Symp Proc. - 1558997520 ; , s. 371-376
-
Konferensbidrag (refereegranskat)abstract
- The effects of organic cleaning agents (totally three) and degradation products from solid technical adsorbents (two) on the sorption of Eu on cement and TiO2 were measured with variation of concentration (0.001-10% of the water phase for the cleaning agents, alkaline degradation products corresponding to 0.03-8 mM DOC for the adsorbents) and reaction time (up to 420 d). The effects of the cleaning agents Industrikombi and Prefect Citron were minor. The degradation of the ion exchanger (metaacrylic polymer) had no significant effect on the Eu-sorption. The other adsorbent (filter aid, inert fibre; acrylonitrile polymer) was rapidly degrading at high pH, and the degradation products had a significant reducing effect on the sorption of Eu at added DOC-levels in the mM-range. This category of adsorbent materials should not be incorporated in a cement waste matrix or be stored in a cementitious environment together with radionuclides.
|
|
| 6. |
- Korzhavyi, Pavel A., et al.
(författare)
-
Thermodynamic properties of Pu-O-H compounds and alloys from density functional theory
- 2004
-
Ingår i: SCIENTIFIC BASIS FOR NUCLEAR WASTE MANAGEMENT XXVII. - WARRENDALE : Materials Research Society. - 1558997520 ; , s. 107-112
-
Konferensbidrag (refereegranskat)abstract
- A theoretical approach has been developed that allows one to obtain thermodynamic properties of plutonium-based alloys and compounds from first-principles electronic structure calculations based on density functional theory. The approach is applied to study the defect structure in non-stoichiometric PuO2+/-delta.
|
|
| 7. |
- Källgren, Therese, et al.
(författare)
-
Microstructure development in copper welded by the FSW-Process
- 2004
-
Ingår i: SCIENTIFIC BASIS FOR NUCLEAR WASTE MANAGEMENT XXVII. - Warrendale : Materials Research Society. - 1558997520 ; , s. 483-488
-
Konferensbidrag (refereegranskat)abstract
- To ensure safe storage of nuclear fuel waste, copper canisters are proposed as corrosion barrier. One alternative for sealing the copper canisters is Friction Stir Welding (FSW). During the joining process friction heat and mechanical deformation appear between the rotating tool and the material being welded. Liquid metal will not form, since this is a solid state welding process. Three distinct microstructural zones are developed namely the nugget, the thermomechanically affected zone (TMAZ) and heat-affected zone (HAZ). The nugget is in the centre of the weld, where the pin is located and where severe plastic deformation occurs that leads to recrystallisation. Surrounding the nugget, the TMAZ is only partially recrystallised, due to lower temperature increase and deformation compared to the nugget. The third zone, HAZ, surrounds the TMAZ. The initial nugget can have a classic round aluminium nugget image, when the welding conditions are cold, but the steady state nugget, is wider near the shoulder and shorter in the weld root.
|
|
| 8. |
- Liu, Longcheng, et al.
(författare)
-
Fluid flow and solute transport though a fracture intersecting a canister - Analytical solutions for the parallel plate model
- 2004
-
Ingår i: SCIENTIFIC BASIS FOR NUCLEAR WASTE MANAGEMENT XXVII. - 1558997520 ; , s. 749-754
-
Konferensbidrag (refereegranskat)abstract
- In this paper, we are concerned with a specific scenario where a large fracture intersects, at its center, a canister that contains spent nuclear fuel. Assuming that a nuclide is free to release from the canister into groundwater flowing through the fracture, a detailed formulation of the volumetric flow rate and the equivalent flow rate are made for the parallel plate model. The formulas proposed have been validated by numerical examinations; they are not only simple in forms but also universal in applications where the flow may be taken normal, inclined or parallel to the axis of the canister. Of great importance, they provide a convenient way to predict the average properties of fluid flow and solute transport through a single fracture with spatially variable apertures.
|
|
| 9. |
- Löfgren, Martin, et al.
(författare)
-
A Conceivable Technique of Measuring Sorption Coefficients in Intact Rock Using an Electrical Potential Gradient as the Driving Force for Migration
- 2004
-
Ingår i: Scientific Basis for Nuclear Waste Management Symposium XXVII. - 1558997520 ; , s. 683-688
-
Konferensbidrag (refereegranskat)abstract
- Sorption coefficients are traditionally obtained in batch experiments if the sorbent is strongly or intermediately sorbing. In a batch experiment the rock is crushed and this could increase the surface area as well as induce new and fresh surfaces. Therefore there is some concern whether sorption coefficients obtained in batch experiments represents those of intact rock. Performing sorption experiment by diffusion in intact rock with intermediately and strongly sorbing species seems impossible in practice due to extremely long experimental times. In this paper the possibility of increasing the migration rate in the rock by two of three orders, thus enabling KD measurements of intermediately sorbing species in intact rock, is discussed. The increase in migration rate has already been achieved successfully in so called through electromigration experiments using non-sorbing species. Here a potential gradient acts as the main driving force. In our experiments the migration rate was increased 320 times by using a potential drop of only 9 volts.
|
|
| 10. |
- Moreno, Luis, et al.
(författare)
-
Modelling of solute transport under flow conditions varying in time, using the channel network model
- 2004
-
Ingår i: SCIENTIFIC BASIS FOR NUCLEAR WASTE MANAGEMENT XXVII. - 1558997520 ; , s. 797-802
-
Konferensbidrag (refereegranskat)abstract
- Transport of radionuclides from a repository to the biosphere is calculated in the presence of varying boundary conditions. This may occur in Sweden, for example, during post-glacial rebound. To calculate the transport of radionuclides, the flow field has to be calculated at each time step. An alternative approach is to determine the flow field at certain time intervals; i.e., modelling the dynamic flow system as a sequence of punctuated steady states. This can be done in a rather simple way by using the Channel Network model (CNM), in which radionuclide transport is calculated by particle tracking. Intuitively one would expect such a simple procedure to be permissible and lead to small errors if the time intervals are so short that only small changes in flow rates and flow directions take place. In this paper, the technique is applied to a study case. This describes a repository located at a sub sea level location outside the coastline; where, owing to the land lift that is taking place in Scandinavia the coastline is advancing towards the repository. An important issue to be determined is the minimum number of time intervals that need to be used in order to obtain a reliable solution to radionuclide transport. It is found that the number of time intervals needed is strongly dependent on the variation in the boundary conditions. For the changing conditions used in the example tested, a number on the order of 5-9 time intervals allows a sufficiently good representation of the transport.
|
|
| 11. |
- Moreno, Luis, et al.
(författare)
-
Solute transport in fractured rock. Testing a new and simple aapproach
- 2004
-
Ingår i: SCIENTIFIC BASIS FOR NUCLEAR WASTE MANAGEMENT XXVII. - 1558997520 ; , s. 791-796
-
Konferensbidrag (refereegranskat)abstract
- A new and simple approach for modelling solute transport in fractured rock is presented, based on our previously used Channel Network Model (CNM). In our underlying concept, solute transport in fractured rocks takes place through undulating flat channels in the rock fractures. The channels form a 3-dimensional network. For non-interacting solutes the volume of the channels determines the residence time of a stream of water. For sorbing radionuclides the residence time is mainly determined by the ratio between the Flow Wetted Surface (FWS) and the flow rate in the channel (Q), in addition to the parameters that determine the interaction between the rock and the radionuclides. The main question explored in this paper is whether it is necessary to solve the flow problem for each studied case. From previous investigations, we have found that the flow rates in the channels where the solutes travel are closely related to the transmissivities of the channels. Simulations are presented in which streams of water are allowed to randomly select channels and trace out the paths where the path volume and its FWS can be assessed. The results obtained in this manner for the RTD (Residence Time Distribution) show rather good agreement with those obtained by solving the full flow problem and tracing particles in the network.
|
|
| 12. |
- Sidborn, Magnus, et al.
(författare)
-
Modelling biochemical processes in rocks : Analysis and exploratory simulations of competition of different processes important for ferrous mineral oxidation and oxygen depletion
- 2004
-
Ingår i: SCIENTIFIC BASIS FOR NUCLEAR WASTE MANAGEMENT XXVII. - 1558997520 ; , s. 829-834
-
Konferensbidrag (refereegranskat)abstract
- There are several oxygen consuming processes occurring in deep subsurface fractured rocks. The importance of each process depends on the prevailing conditions and what function it has in the overall oxygen scavenging process. In the present work, some of these processes are studied. The aim is to build a frame of maximum rates for each parallel process. Therefore, several rate-limiting factors are not included. Rate expressions were obtained from the literature and compared for different cases to address under which conditions each process is important. Some of the processes may be considered parallel and independent while others occur in series. The main reactions accounted for are abiotic and biotic pyrite and ferrous iron oxidation and the nonoxidative dissolution of matrix ferrous minerals. In addition, transport processes of oxygen and other substrates within the rock matrix are considered. The main conclusions are that initially, when the diffusion resistance in the matrix is nonexistent or small, reaction kinetics are important. However, in a longer time perspective, diffusion processes limit the oxygen scavenging process.
|
|
