| 1. |
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| 2. |
- Xu, Shulan, et al.
(författare)
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A regulatory modelling strategy for review of dose calculations
- 2008
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Ingår i: Proceedings of The 12th International High-Level Radioactive Waste managemenent Conference. - : American Nuclear Society. - 9780894480621 ; , s. 466-472
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Konferensbidrag (refereegranskat)abstract
- To be able to carry out review functions regulatory authorities must be able to make critical evaluations of proponent's performance assessment (PA) cases. In Sweden the Swedish Radiation Protection Authority (SSI) aims to have in place its own suite of PA tools. These will be used to address the forthcoming PAs submitted by the Swedish Nuclear Waste Management Company (SKB) for a geological repository for spent fuel (2010). This paper looks at the role and application of the regulator's models to important features of current modelling in SKB 's latest PAs. The SSI modelling tools are applied to demonstrate a possible size of the contaminant area due to leakage of radionuclides from a damaged canister. An improved representation of these processes will enhance our understanding of biosphere functions and provide a better basis for evaluating radiological consequences in the safety assessment.
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| 3. |
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| 4. |
- Klos, Ryk, et al.
(författare)
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Potential for high transient doses due to accumulation and chemical zonation of long-lived radionuclides across the geosphere-biosphere interface
- 2011
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Ingår i: Radioprotection - Revue de la Societé Francaise de Radioprotection. - : EDP Sciences. - 0033-8451 .- 1769-700X. ; 46:6, s. S453-S459
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Tidskriftsartikel (refereegranskat)abstract
- Planning for the disposal of spent nuclear fuel is at an advanced stage in several nations around the world. Licensing of the disposal facility requires correspondingly detailed assessment of the future performance of the facility. With increased site-specific detail available to the assessment, local characteristics play an increasingly important role in determining the potential radiological risk posed by releases to the biosphere. In this paper we go beyond existing reference biosphere models and investigate the potential for specific accumulation mechanisms. The implications for the modelling carried out in long timescale performance assessment are discussed.
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| 5. |
- Marklund, Lars, et al.
(författare)
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Accumulation in the overburden of radionuclides from a leaking nuclear waste repository
- 2008
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Ingår i: American Nuclear Society - 12th International High-Level Radioactive Waste Management Conference 2008. - 9780894480621 ; , s. 473-478
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Konferensbidrag (refereegranskat)abstract
- The spatial distribution of possible discharge areas of radionuclides originating from repositories of high level radioactive nuclear waste was assessed. This was done by using a 3-D transport model. The results indicate "hot-spots" in the landscape where the radionuclides most likely emerge. These hot-spots are highly related to the hydrological network consisting of streams, lakes and wetlands. The geological factors creating this pattern as well as the characteristics that distinguish these areas from others were investigated. Our result suggests that these hot-spots occur in low elevation areas where the quaternary deposits are significantly greater than the average thickness in the area. The most important factors for the locations of the hot-spots are landscape topography and fracture distribution in the bedrock. As a result of the relationship between, fracture zones, topography and streams, the importance of the topography for the discharge area distribution is not contradicted by the heterogeneity in the bedrock as long as the undulation of the groundwater surface is not extremely small. Due to the similarities within deep groundwater discharge areas, one can make site-specific analyses in one area, which have a broad applicability for migration of radionuclides originating from a nuclear waste repository.
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| 6. |
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| 7. |
- McDonnell, J.J., et al.
(författare)
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How old is streamwater? : Open questions in catchment transit time conceptualization, modelling and analysis
- 2010
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Ingår i: Hydrological Processes. - : John Wiley & Sons. - 0885-6087 .- 1099-1085. ; 24:12, s. 1745-1754
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Tidskriftsartikel (refereegranskat)abstract
- The time water spends travelling subsurface through a catchment to the stream network (i.e. the catchment water transit time) fundamentally describes the storage, flow pathway heterogeneity and sources of water in a catchment. The distribution of transit times reflects how catchments retain and release water and solutes that in turn set biogeochemical conditions and affect contamination release or persistence. Thus, quan- tifying the transit time distribution provides an important constraint on biogeochemical processes and catchment sensitivity to anthropogenic inputs, contamination and land-use change. Although the assumptions and limitations of past and present transit time modelling approaches have been recently reviewed (McGuire and McDonnell, 2006), there remain many fundamental research challenges for understanding how transit time can be used to quantify catchment flow processes and aid in the development and testing of rainfall–runoff models. In this Commen- tary study, we summarize what we think are the open research questions in transit time research. These thoughts come from a 3-day workshop in January 2009 at the International Atomic Energy Agency in Vienna. We attempt to lay out a roadmap for this work for the hydrological commu- nity over the next 10 years. We do this by first defining what we mean (qualitatively and quantitatively) by transit time and then organize our vision around needs in transit time theory, needs in field studies of tran- sit time and needs in rainfall – runoff modelling. Our goal in presenting this material is to encourage widespread use of transit time information in process studies to provide new insights to catchment function and to inform the structural development and testing of hydrologic models.
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| 8. |
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| 9. |
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| 10. |
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| 11. |
- Wörman, Anders, 1961-, et al.
(författare)
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Field Study on Discharge of Natural Isotopes from the 238U and 232Th Series through Quaternary Deposit
- 2011
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Ingår i: Proceedings of the 13th International High-Level Radioactive Waste Management Conference (IHLRWMC). - 9780894480850 ; , s. 782-787
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Konferensbidrag (refereegranskat)abstract
- This paper describes tentative results of the transport of natural radionuclides of the Uranium and Thorium series through Quaternary deposits in Sweden. Three drill holes between 10-16 meters deep were made down to bedrock and several radionuclides were measured in the dissolved, adsorbed and mineralogical phases. The isotope composition of the pore water differs from that of the soil minerals, which indicates that the origin of the isotopes is from discharging groundwater from bedrock. Less than 1 % of the isotopes exist in dissolved or adsorbed phases and the remaining fraction in minerals.
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| 12. |
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| 13. |
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| 14. |
- Wörman, Anders, 1961-, et al.
(författare)
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Impact of repository depth on residence times for leaking radionuclides in land-based surface water
- 2006
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Ingår i: Proceedings of the 11th International High Level Radioactive Waste Management Conference, IHLRWM. - 9781604236293
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Konferensbidrag (refereegranskat)abstract
- The multiple scales of landscape topography produces a wide distribution of groundwater circulation cells that control the hydro-geological environments surrounding geological repositories for nuclear waste. The largest circulation cells tend to discharge water into major river reaches, large freshwater systems or the nearby Sea. We investigated numerically the release of radionuclides from repositories placed in bedrock with depths between 100 to 2,000 meters in a Swedish coastal area and found that, leakage from the deeper positions emerges primarily in the major aquatic systems. In effect, radionuclides from the deeper repositories are more rapidly transported towards the Sea by the stream system compared to leakage from more shallow repositories. The release from the shallower repositories is significantly retained in the initial stage of the transport in the (superficial) landscape because the discharge occurs in or near low-order streams with high retention characteristics. This retention and residence time for radioactivity in the landscape control radiological doses to biota and can, thus, be expected to constitute an essential part of an associated risk evaluation.
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| 15. |
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| 16. |
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| 17. |
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| 18. |
- Wörman, Anders, 1961-, et al.
(författare)
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Kinematic model of solute transport in stream networks : Example with phosphate retention in Morsa watershed, Norway
- 2004
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Ingår i: Archives of Hydro-engineering and Environmental Mechanics. - 1231-3726. ; 51:1, s. 41-53
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Tidskriftsartikel (refereegranskat)abstract
- A theoretical description of reactive solute transport in a network of stream channels is derived by convoluting unit solutions based on a physical representation of transport and topographical information of the distributions of solute load as well as pathways. The theory is applied to a generic analysis of the phosphate export in Morsa watershed due to the load from 620 individual households with a local wastewater treatment. Essential factors for the phosphate export is filtering of the water in stream-bed sediments through a distribution of hyporheic flow paths of various lengths. This generic study indicates that a significant portion of phosphate is retained in the hyporheic zones for a long time. The 90% recovery time following a hypothetical remediation action in the households is expected to be in the order of one decade.
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| 19. |
- Wörman, Anders, 1961-, et al.
(författare)
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Scaling of surface water-subsurface water interaction with implication to hydrogeological site evaluations
- 2008
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Ingår i: The 12th International High-Level Radioactive Waste Management Conference (IHLRWM). - : American Nuclear Society. - 9780894480621
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Konferensbidrag (refereegranskat)abstract
- Land surface topography governs the groundwater flow patterns at the regional-to-continental scale and on smaller scales such as in the hyporheic zone of streams. This produces a complicated groundwater circulation pattern that controls releases of radionuclides from a underground nuclear waste repository. Here we utilise a new spectral technique to analytically solve the groundwater flow with account taken to the spectrum of topographical scales on the continent, depth decaying permeability with depth and quaternary deposits. The proposed solution makes it possible to independently analyse the effects on the flow generated by topographical features on various scales. Basically, all topographical scales have the same influence on groundwater exchange with surface water, but the decaying permeability with depth in bedrock causes a predominance of local scales. Discharge of radionuclides from a deep repository placed in bedrock occurs in major rivers and streams where we find the thickest layers of quaternary deposits in post-glacial landscapes. The high sorption affinity in soil implies that radionuclides spend a very long time in quaternary deposits on their travel from an underground repository through bedrock and stream network to the sea.
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| 20. |
- Xu, Shulan, et al.
(författare)
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Application of a Regulatory Performance Assessment Approach for Comparison with the Proponent’s Calculations
- 2006
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Ingår i: Proceedings of the 11th International High Level Radioactive Waste Management Conference, IHLRWM. - 9781604236293 ; , s. 980-985
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Konferensbidrag (refereegranskat)abstract
- To be able to carry out review functions regulatory authorities must be able to make critical evaluations of proponents PA cases. In Sweden the Swedish Radiation Protection Authority (SSI) aims to have in place its own suite of performance assessment (PA) tools. These will be used to address the forthcoming PAs submitted by the Swedish Nuclear Waste Management Company (SKB)for an encapsulation plant (2006) and a geological repository for spent fuel (2008). This paper looks at the role and application of the regulator's models to important features of current modelling in SKB's latest PAs. The SSI modelling tools are applied to a mire system in which radionuclides are assumed to be released from a geological repository. Results are presented which illustrate the importance of a deeper understanding of the geosphere-biosphere interface zone than has been the case in assessments to date.
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| 21. |
- Xu, Shulan, et al.
(författare)
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Effects of compartmental model structure and long-term inflow on model predictions
- 2005
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Ingår i: Radioprotection - Revue de la Societé Francaise de Radioprotection. - : EDP Sciences. - 0033-8451 .- 1769-700X. ; 40:1, s. 477-483
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Tidskriftsartikel (refereegranskat)abstract
- Model predictions of solute transport in a wetland were compared with tracer experimental data to illustrate that the number of compartments in a compartmental model should be selected according to certain rules to accurately describe the transport process. If the input pulse is short, the model structure affects the output significantly. The temporal moments of the residence time distribution was obtained from a general solution of the compartmental model in the Laplace domain derived with an arbitrary inflow pollutograph. The variance of the residence time can be used as a useful tool to analyse the effect of model structure and long-term inflow pollutograph on the response of the model predictions.
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| 22. |
- Xu, Shulan, et al.
(författare)
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Prediction of concentration and model validation
- 2008
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Ingår i: Radioprotection - Revue de la Societé Francaise de Radioprotection. - : EDP Sciences. - 0033-8451 .- 1769-700X. ; 43:1, s. 701-706
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Tidskriftsartikel (refereegranskat)abstract
- In this paper we examine some critical aspects concerning the justification of simplified radioecological models used in safety assessments for geological repositories. We propose a modelling approach for regulatory review of dose and risk calculations for a nuclear waste repository. The SSI modelling tools are applied to explore uncertainties in the size of the contaminant area due to leakage of radionuclides from a damaged nuclear waste canister. We demonstrate that an improved representation of geosphere transport processes will also enhance our understanding of radionuclide migration in the biosphere and provide a better basis for evaluating radiological consequences in the safety assessment.
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