BIOPROTA | Publications
13
page,page-id-13,page-parent,page-template-default,ajax_fade,page_not_loaded,,qode-theme-ver-5.1,wpb-js-composer js-comp-ver-4.3.3,vc_responsive

A number of modelling tasks have been undertaken under the BIOPROTA programme to investigate the mathematical and conceptual modelling assumptions of key biosphere processes. More information on these tasks can be found below, along with the reports currently available.

If you are a registered user and would like to download the publications, please click on the pull-down beneath the Publications menu to go to the download page.

Process Modelling

Human Intrusion

The objectives of this study were to review methods and develop an approach to human intruder dose assessment for deep geological disposal facilities for radioactive waste.

 

Smith G M, Molinero J, Delos A, Valls A, Smith K, Conesa A, Xu S, Hjerpe T and Medri C (2012). Human Intruder Dose Assessment for Deep Geological Disposal. Report prepared under the BIOPROTA international programme.

Model Review and Comparison for Spray Irrigation Pathway

The objective of this task was to investigate the calculation of doses arising from interception by growing crops using contaminated irrigation water and the consequent contamination of the food consumed by humans.

 

BIOPROTA (2005): Model Review and Comparison for Spray Irrigation Pathway. A report prepared within the international collaborative project.

Modelling the Inhalation Exposure Pathway

The objective of this task was to investigate further the calculation of doses arising from inhalation of particles suspended from soils within which long-lived radionuclides, particularly alpha emitters, had accumulated.

 

BIOPROTA (2005): Modelling the Inhalation Exposure Pathway. A report prepared within the international collaborative project BIOPROTA.

Model Intercomparison with Focus on Accumulation in Soil

The objective of this task was to discuss the objectives, definitions and results of an assessment model intercomparison. Focus was given to the long-term accumulation of long lived radionuclides in soils. Two often used scenarios were adapted as means of contamination, the well scenario, where contaminated well water is used for irrigation of agricultural land and a river scenario, where contaminated river water floods the agricultural land.

 

BIOPROTA (2005): Model Intercomparison with focus on accumulation in soil. A report prepared within the international collaborative project BIOPROTA.

Carbon-14 in the Biosphere

C-14: Data, Ecosystems and Dose Assessment

It has long been recognised that C-14 is one of the key radionuclides of interest in post-closure assessments for solid radioactive waste disposal facilities and yet uncertainties remain with regard to the behaviour of C-14 in the environment and how these affect long-term dose assessments. Whilst the focus of BIOPROTA is on longer term releases from solid waste disposal, it has long been recognised that information obtained from assessments relating to alternative source terms such as operational discharges from reactors and reprocessing plants, and discharges from pharmaceutical and agricultural sources can provide important information both on the behaviour of C-14 once in the surface environment and on approaches to assessment.

 

This report describes different models and their application to different ecological contexts, the driver being to consider the application of models on the basis of ecosystem understanding complementing the previous focus on detailed process models.

 

K Smith & G Smith (Eds) (2014) C-14: Data, Ecosystems and Dose Assessment. Report of an International Workshop Aix-en-Provence, 1 – 3 April 2014. November 2014

C-14 Dose Assessment, Phase 3

Results of the 2009-2011 C-14 model intercomparison showed that the conceptualisation of the dynamics of the plant canopy atmosphere has a large influence on the calculated plant C-14 concentrations. The major source of uncertainty is related to the identification of conditions under which mixing occurs and isotopic equilibria are established.

 

A phase 3 work programme has been implemented through 2012-13 that aimed to consolidate current understanding in terms of C-14 behaviour in the plant canopy atmosphere and to extend the scope of focus to include aquatic pathways and to provide a mechanism by which a focused research programme can be established to address key modelling uncertainties. Following a workshop held in Stockholm in February 2013, hosted by SKB, a range of potential validation datasets was investigated.

Model Review and Comparison for C-14 Dose Assessment

The objective of this project was to review and discuss modelling of the transport and fate of C-14 and account for the treatment of C-14 processes, pathways and accumulation in the biosphere. Particular attention was given to the appropriate choice between dynamic and equilibrium assessment models.

 

BIOPROTA (2005). Model review and comparison for C-14. A report prepared within the international collaborative project BIOPROTA.

Review of models for Carbon-14 Dose Assessment

Interest in improved dose assessment methods for long-term releases of C-14 to the biosphere gave rise to a model review within the BIOPROTA programme. This qualitative review of models concluded that the major difficulty surrounding the conceptual model for C-14 concerns identifying the conditions under which mixing and isotopic equilibrium may reasonably be assumed. Such system understanding needs to take account of the temporal and spatial scale of the assessment, including the nature of the release from the geosphere. A key issue is the decision as to whether kinetic models are useful and/or necessary, compared with an equilibrium approach. It was also argued that more data are needed for gaseous exchange from surface waters and soils to the atmosphere and how this affects the specific activity in the water and soil compartments, as well as uptake into plants.

 

The overall objective was to improve confidence in dose assessments for long-term releases into the biosphere of C-14 disposed in radioactive waste repositories, focussing upon the soil and plant components of the biosphere. This project compared quantitative estimates of soil, plant and canopy atmosphere C-14 concentrations arising from a scenario with unit C-14 activity in groundwater that is used to irrigate the crops. A FEP analysis, specific to C-14 in soils and uptake into plants has been undertaken and used as the basis for the development of a generic conceptual model.

 

Limer L, Albrecht A,  Marang L, Smith K, Thorne M C, Wiebert A, Xu  S and Smith G (2009). C 14 Long-Term Dose Assessment: Quantitative Model Comparison and Development, Part I.

 

Limer L, Smith K, Albrecht A, Marang L, Norris S, Smith G M, Thorne M C and Xu S (2011). C-14 Long-Term Dose Assessment in a Terrestrial Agricultural Ecosystem: FEP Analysis, Scenario Development, and Model Comparison.

Long-term Dose Assessment for Carbon-14

Several collaborative activities concerned with long-term dose assessment for C-14 have been organised through the BIOPROTA Forum. These activities have contributed to greater confidence and reduced uncertainties in assessments made for disposal of solid radioactive waste containing C-14, such as graphite and reactor operating wastes.

 

The most recent work was extensively reported in Modelling Approaches to C-14 in Soil-Plant Systems and in Aquatic Environments, published by the Swedish Radiation Safety Authority, as SSM report 2014:30, and in C-14: Data, Ecosystems and Dose Assessment, Report of an International Workshop, Aix-en-Provence, April 2014, available at www.bioprota.org. Results demonstrated the continuing potential for improved understanding of processes through collection, collation and sharing of new field and experimental data and its thoughtful application to assessment work. Such work could also benefit, and obtain support from, the assessment of doses due to current releases of C-14 to the environment. To address these developments and to share information on other recent C-14 assessment work, the current workshop was organised.

 

This report describes presentations and discussions held during an international workshop on 28-30 April 2015, hosted by IRSN in Aix-en-Provence, France.

 

Smith K (2015). Long-term dose assessment for C-14: Report of an International workshop.

Chlorine-36 in the Biosphere

A number of tasks have been undertaken on Chlorine-36 in the biosphere as part of the BIOPROTA work programme. Those for which reports are currently available are detailed below.

International Forum on Chlorine-36 in the Biosphere

A forum on the behaviour of Cl-36 in the biosphere was held from 27 – 28 September 2006 at Chatenay-Malabry near Paris and was hosted by ANDRA. The workshop was well attended by 33 participants from nine countries, including operators and regulators. Various participants presented their current models for assessing the radiological impact of Cl-36 ranging from those models using equilibrium concentration ratios those using dynamic specific activity approaches. The chlorine cycle and the behaviour of organic and inorganic chlorine was also discussed.

 

BIOPROTA (2006). Report of an International Forum on Cl-36 in the Biosphere, Châtenay-Malabry, France, 27-28 September 2006.

Chlorine-36 Accumulation in Soil and Crop Uptake

The BIOPROTA programme recently completed a study of Cl-36 behaviour in soils and uptake into plants. Within this study, a significant range of model types and alternative data assumptions were described and compared, demonstrating the degree of understanding of the likely behaviour of Cl-36 in soil and uptake into plants. Quantitative estimates were presented and compared for Cl-36 concentrations in crops based on contaminated water entering surface soil in irrigation water and via upward migration processes from below. Both deterministic and probabilistic assessments were demonstrated and a wide range of sensitivity calculations was also presented. Despite the variations in the models, the results for concentrations in crops were generally within about an order of magnitude of each other. The spread of results obtained in probabilistic calculations did not indicate much greater variation for a given set of site conditions.

 

Limer L, Albrecht A, Marang L, Miquel S, Tamponnet C, Nakai K, Gierzewski P, Thorne M and Smith G (2008). Investigation of Cl-36 Behaviour in Soils and Uptake into Crops.

Chlorine-36 Dose Assessment Uncertainties and Variability

The project extended the work previously undertaken on the behaviour of Cl-36 in soils and uptake into plants to include dose assessment and took into account not only root uptake but also contamination of crops by direct interception of irrigation water. This is so that the relative significance of direct deposition and root uptake can be understood. Special consideration has been given to the assessment of uncertainties, with a clear separation of the contribution to uncertainties arising from:

  • the assessment of Cl-36 concentrations in crops,
  • the assumptions for the potential exposure groups or representative persons, and
  • the dose per unit intake.

 

Limer L, Albrecht A, Bytwerk D, Marang L, Smith G and Thorne M (2009). Cl-36 Phase 2: Dose Assessment Uncertainties and Variability.

Selenium-79 in the Biosphere

Selenium-79 (Se-79) is an important radionuclide in some types of radioactive waste. It is mobile and long-lived and potentially could migrate into the biosphere following release from radioactive waste disposal facilities. Special attributes are its complex chemistry, notably the chemical form is dependent upon the redox state with some compounds being volatile. Selenium is an essential element, but can also be toxic with only a small concentration range between deficiency and toxicity.

 

The data necessary for radiological assessment of Se-79 are scarce and can be unreliable, particularly in relation to its behaviour in the terrestrial soil-plant system.

International Forum on Selenium-79 in the Biosphere

A workshop was held to discuss those attributes of Se-79 of particular relevance to radiological assessments for geological waste repositories. The objective was to provide an open forum for presentation and discussion of the behaviour of selenium in the biosphere, with particular focus on the environmental processes involved in selenium migration and accumulation in the biosphere and how radioecological assessments of Se-79 could be improved.

 

The workshop was held on 5-6 May 2008, hosted by Nagra, Wettingen, Switzerland, and involved both presentation and discussion of data requirements for dose assessment and knowledge and on-going research in the field of Se-79 behaviour in the biosphere.

 

BIOPROTA (2008). Report of an International Forum on Se-79 in the Biosphere, 5-6 May  2008, Wettingen, Switzerland.

Modelling Se-79 in soils and plants

Following from the Se-79 workshop in 2008, a work programme was established which aimed to develop a better understanding of the processes affecting Se-79 accumulation in soils and uptake into plants.

 

The initial phase of work was intended to provide the basis for the development of improved assessment models and to support the selection of parameters for existing models. The project included:

  • Review of the current knowledge (and new research) on Se-79 behaviour in the soil-plant system; Consideration of the Features, Events and Processes (FEPs) of potential relevance to the assessment of doses to hypothetical critical groups arising in the long term due to releases to the terrestrial biosphere from a repository for radioactive waste disposal;
  • Development of an interaction matrix which shows how the FEPs can be combined to create a conceptual assessment model. The intention is to provide a transparent and traceable record of how information has been included, or indeed, excluded, with recorded justification, from the assessment model; and,
  • Identification of data which need to be determined site specifically, as opposed to reliance upon site generic sources.

 

Smith K, Sheppard S, Albrecht A, Coppin F, Fevrier L, Lahdenpera A-M, Keskinen R, Marang L, Perez D, Smith G, Thiry Y, Thorne M and Jackson D (2009). Modelling the Abundance of Se-79 in Soils and Plants for Safety Assessments of the Underground Disposal of Radioactive Waste.

Se-79 Phase II: Improved dose assessment models for Se-79 in the soil-plant system

Phase 2 involved further consideration of those processes considered key to the understanding the behaviour of selenium-79 (Se-79) in soils and uptake into plants, based on new information published. Modelling approaches, conventional and novel for addressing these processes within biosphere assessment models have been described and models applied to a hypothetical scenario description. The objectives were to:

  • examine the quantitative significance of the key FEPs identified in phase 1, for different assessment scenarios;
  • identify the advantages and disadvantages of different modelling approaches;
  • identify the site-specific data needed to support the application of suitable assessment approaches; and
  • identify further research needs.

 

Smith K, Albrecht A, Thorne M, Coppin F, Ikonen A, Perez-Sanchez D, Smith G and Limer L (2012). Se-79 in the Soil-Plant System. Phase 2: Approaches to Modelling.

Uranium-238 Series Radionuclides

U-238 Series Modelling

A project aimed at improving the modelling of U-238 series radionuclides began in 2010. The project aims to:

  • improve understanding of the disequilibrium in the U-238 decay chain within the geosphere biosphere interface and in other potential redox front situations, particularly given the differences in assumed equilibrium distribution coefficients for Th-230 and Ra-226.
  • improve understanding of the radon emanation rate from soils, sediments and the built environment; and
  • to address both the above issues under situations of environmental change, occurring once the contamination is in the environment.

 

The focus is on the upper part of the decay chain (up to and including Ra-226).

 

L M C Limer, Albrecht A, Hormann V, Gallerand M-O, Medri C, Perez-Sanchez D, Smith K, Smith G and Thorne M (2012). Improving Confidence in Long-term Dose Assessments for U-238 Series Radionuclides. 

Radium Workshop

A workshop was held in May 2010, hosted by ANDRA, on the environmental behaviour of radium. Radium-226 (Ra-226) is a member of the uranium-238 (U-238) series decay chain and is found naturally in minute quantities in a wide range of uranium-bearing rocks. Mining and processing of these rocks for a wide range of industrial purposes, gives rise to waste containing, in most cases, elevated concentrations of Ra-226 relative to those normally found in nature.

 

Radium-226 is of particular interest in safety assessments for the geological disposal of spent nuclear fuel, where in-growth of U-238 daughters may lead to additional input to the biosphere over long timeframes. Radium-226 has a long half-life (1,600 years), grows in from even longer lived pre-cursors, has a high radiotoxicity and is relatively physically and biologically mobile. These factors combined mean that Ra-226 is of particular interest in risk assessments for the disposal of spent nuclear fuel and other radioactive wastes.

 

The aim of the workshop was to bring together individuals involved in radioactive waste management with those with experience with legacy sites with the objective of advancing knowledge and understanding of the key processes and fate of radium in the biosphere, specifically relating to the behaviour of radium in soils, uptake into plants and approaches to modelling radium transport in biosphere assessments.

 

The workshop was attended 29 participants from 7 countries, representing a range of operators, regulators, researchers and technical support organisations.

 

Smith K, Smith G and Thiry Y (2010). International workshop on the environmental behaviour of Radium, 24 June 2010, Châtenay-Malabry, France.

Assessment Data

International Workshop on Scientific Basis for Long-term Radiological and Hazardous Waste Disposal Assessments

A variety of environmental impact and human health assessments is used to support decisions on the management and disposal of radioactive and hazardous waste. These assessments have to address a wide range of protection objectives, ecosystems and timeframes. This creates significant challenges to the design of such assessments and in the development of corresponding relevant scientific support.

 

The objective of a workshop, held in Ljubljana, May 2013, hosted by ARAO, was to provide a forum for discussion and comparison of the scientific basis for such assessments, taking into account:

  • assessment endpoints (what actually is calculated as a measure of environmental and / or human health impact?);
  • assessment methodologies for disposal of radioactive and other hazardous waste;
  • the key processes which dominate the release and disposition of radionuclides and other pernicious pollutants within the environment, following disposal;
  • approaches to dealing with environmental change;
  • methods for assessing effects on human health and the environment;
  • assumptions for human behaviour and land use, and how that affects the potential for impacts both on human health and on the environment;
  • approaches to addressing uncertainties, and
  • approaches to addressing low probability events which have high consequences.

 

BIOPROTA (2014). Scientific Basis for Long-term Radiological and Hazardous Waste Disposal Assessments. Report of an International Workshop.

Use of Natural Analogues

Analogue information can increase our conceptual understanding of long term repository behaviour and behaviour of radionuclides in the environment in support of post closure performance assessment. They can also provide quantitative data for Performance Assessment (PA) models and are a communication method to pass on information to a non-specialist audience.

 

The objective of this Task was to review past and present use and understanding of natural analogues relating to biotically-influenced biosphere processes with the intention of promoting considered application of them in future safety assessments and public communication.

 

BIOPROTA (2005). Application of Biotic Analogue Data. A report prepared within the international collaborative project BIOPROTA.

Development of a Database for Key Radionuclides and Process Data

The overall objective of the BIOPROTA Database is to provide data and supporting information relating to key Features, Events and Processes (FEPs) and the behaviour of key radionuclides in the biosphere. Enviros have collated parameter information for inclusion in a database to support BIOPROTA forum members in biosphere modelling exercises.

 

A web-based version of the BIOPROTA database is currently under development. The intention is to make available the information gathered under previous database projects in a web-access system to which sponsors may add additional data in individual project folders.

In situ Study of the Long Term Sorption of Iodine onto Organic Matter

Iodine is generally present in environments as an anion (either iodide or iodate) and is therefore soluble in groundwater and migrates relatively quickly through rock and overburden to low-lying landscape positions such as wetlands where it can be retained by the organic matter of soils (iodine can only be retained in its oxidised form). This reaction with phenols, for example, is well known for I2 or I3-; the question is what controls the oxidation. Organic matter and bacterial activity seem to play an important role). Peat bogs are often located at low-lying landscape positions and are very rich in organic matter and therefore iodine is likely to “accumulate” in peat bogs.

 

An 18 month experimental study has been completed, which aimed to increase understanding of the mechanisms that govern the mobility and transport of iodine in peat bogs, and to acquire values for assessment models such as soil Kd and plant CR (concentration ratio). The study focused on the biogeochemical cycle of iodine in the peat bog including:

  • the transfer of iodine along the carbon cycle in the peat bog (plant uptake, speciation of iodine in the plant, consequences of the biodegradation of the plant material on the availability of iodine in the peat); and, – the role of the redox potential on the migration and the speciation of iodine in the peat bog.
  • the retention of iodine onto the peat; and
  • the relation between the chemistry of organic matter and the retention of iodine.

 

Such an understanding of the mechanisms that govern the fate of iodine in peat bogs will form the basis for a better model of the transfers of this element in these types of ecosystems.

Site Characterisation

The links between site characterisation and the biosphere component of the assessment, including guidance on protocols for obtaining data, have been considered. The objective was to provide advice about the biosphere features of a site which it may be useful to determine because they are especially relevant to the evaluation of radiation exposures over the long term. In addition, advice is also to be prepared concerning the setting up of experiments and field measurements so that the output can be relevantly interpreted for use in radiological assessments.

 

BIOPROTA (2006): Guidance on Site-Specific Biosphere Characterisation and Experimental Research and Field Research Protocols. A report prepared within the international collaborative project BIOPROTA.

 

The next step being considered is to share information on how the obtained data is presented and interpreted, for the purpose of demonstrating an understanding of the site, and for use in developing scenarios for possible site evolution, and for evaluation of these scenarios via conceptual and mathematical models for site behaviour. These models can then be used to justify assumptions for assessment models which address radionuclide migration and accumulation in the biosphere and radiation exposure of humans and other biota.

 

The site characterisation work may also directly supply data for input to existing models for assessing particular scenarios. Following the flow of information and the management of data in the entire process is all part of the challenge, especially if it can be intelligently linked to characterisation for operational phase environmental impact assessments. The experience gained and shared is intended to help make continued site investigation work as effective and efficient as possible.

Continuing Issues in Biosphere Assessments for Radioactive Waste Management

Since its formation in 2002, the BIOPROTA forum has worked to address uncertainties in long-term biosphere assessments of impacts arising from contaminant releases associated with radioactive waste management, identified through consultation with member organisations. Whilst the activities undertaken have gone a long way to addressing many important matters, critical issues continue to arise as disposal projects and related investigations evolve. This workshop on Continuing Issues was therefore organised to provide a forum for sharing experience on approaches to address these issues, and make further progress through development of joint work programmes and activities.
Presentations and discussions took place covering three main areas.

 

  • Scope for model validation based on time series monitoring and related data. This included data for further testing of models for C-14 long-term dose assessment; the use of data from legacy sites, such as areas affected by Mayak PA and Llyn Trawsfynydd, which was the recipient of liquid effluent discharges from the now decommissioned Trawsfynydd nuclear power station. In addition, natural analogue sites were considered, with particular reference to those subject to land-use change.
  • Addressing non-radiological impacts from waste disposal alongside the radiological impacts. The results of the BIOPROTA workshop on comparison of assessment methods for radioactive and hazardous waste, hosted by NRPA earlier in the year, were taken into account.
  • Review and update of the IAEA’s BIOMASS 2001 “Reference Biospheres” methodology. Scope arises for this to be carried forward within BIOPROTA in cooperation with the IAEA as part of the follow-up of the current MODARIA assessment programme.

 

This report describes presentations and discussions held during an international workshop on Continuing Issues in Biosphere Assessments for Radioactive Waste Management held 28 – 29 May 2015 hosted by CIEMAT in Madrid.

 

BIOPROTA (2015): BIOPROTA Workshop on Continuing Issues in Biosphere Assessments for Radioactive  Waste Management.

Comparison of Safety and Environmental Impact Assessments for Disposal of Radioactive Waste and Hazardous Waste

It is clear from presentations that there has been a separate development of the science, management strategies and regulations for radioactive and hazardous waste materials. The idea that the non- radiological hazardous features of radioactive wastes need be considered is not a new concept, but the converse is relatively new, for example, management of asbestos which is found to be radioactively contaminated.

 

Hazardous waste disposal appears to focus on controlled release of leachate from managed landfill to ensure that benchmarks are not exceeded. Hazardous waste landfills tend to have a membrane installed to prevent the release of hazardous material to groundwater, but leachate production occurs and is required to be managed prior to any release to the wider environment. In the case of radioactive wastes, there appears to be a stronger focus on containment. It is acknowledged that there may be some limited contaminant release from radioactive waste disposal facilities, but the intention is contain the wastes until radioactive decay has reduced the hazards to an acceptable level.

 

Assessments for radioactive waste disposal facilities typically extend into the future for at least 1,000 years. For hazardous wastes, assessments are usually for timeframes much less than 1,000 years. The timeframe associated with management of waste natural occurring radioactive materials (NORM) is more variable. Waste from the oil and gas industry is normally of small volume and may therefore be subject to containment in a disposal facility. However, other NORM wastes can be of very large volume and containment is unlikely. NORM is not classified as radioactive waste in all countries.

 

The period of active or passive institutional control at sites varies considerably. The period of institutional control for radioactive waste disposal sites is commonly around 300 years. For hazardous waste sites however, the period of institutional control will vary according to the hazards. For example, in the UK there is no institutional control concept, but the release of a site from a permit would only occur if it can be demonstrated that the site does not pose a risk to people or the environment and that leachate control measures are no longer required. The periods of authorisation and active control have been aligned in the UK for radioactive waste facilities such that both are terminated at the same time. In some countries, a long-term stewardship approach is taken to some NORM sites, which effectively poses an indefinite management requirement on future generations. This appears to be a very different policy from that taken for radioactive and hazardous wastes.

 

This report describes presentations and discussions held during an international workshop on 10-12 February 2015, hosted by the Norwegian Radiation Protection Authority in Asker, Norway.

 

Smith K and Smith G (2015): Comparison of Safety and Environmental Impact Assessments for Disposal of Radioactive Waste and Hazardous Waste: Report of an International Workshop.

Geosphere-Biosphere Interface Zone (GBIZ)

Performance Assessments for disposal of radioactive waste and management of mining and other industrial legacies require an assessment of the likely transfer of radionuclides from underground to the accessible biosphere. It is often the case that systems are not considered as a whole; rather the near field, geosphere and biosphere are treated separately, which results in an overlap or a gap in model domains, commonly referred to as the GBIZ.

An Exploration of Approaches to Representing the Geosphere- Biosphere Interface in Assessment Models

In post-closure radiological safety assessments of geological disposal facilities/geological repositories for radioactive wastes, models are developed and applied for transport of radionuclides through the engineered barriers and surrounding host rock towards the biosphere. Attention in such modelling is generally focused on radionuclides dissolved in groundwater, but transport in the gas phase has also been considered in some relevant cases, as well as the release of radionuclides bound to material being eroded at the surface.

The starting point for this project was the development of an initial briefing note that explored the types of GBI that have been considered within long-term safety assessments. A second briefing note was prepared as input to the second and final workshop on this project, hosted by Andra at Châtenay Malabry, Paris, France, in March 2014. In this second briefing note, a methodology was developed for characterising the geosphere-biosphere interface in a wide range of assessment contexts. The second workshop reviewed this briefing note, ongoing work in the related International Atomic Energy Agency’s MODARIA Project (specifically the work on MODARIA Working Group 6 on climate change and landscape development), and various model development, model application and assessment-related activities being undertaken by the participant organisations.

BIOPROTA (2014) An Exploration of Approaches to Representing the Geosphere- Biosphere Interface in Assessment Models. December 2014

Representation of Environmental Change in the Near-Surface Environment

Post-closure assessment of radioactive waste disposal takes into account the distribution of radionuclides and other contaminants potentially released from underground into the surface environment, or biosphere. Previous activities within BIOPROTA have examined processes relevant to contaminant transfer in the geosphere-biosphere subsystem, leading to production of a generic methodology for how to address those processes. Work within the IAEA-sponsored MODARIA Working Group 6 (WG6) has in parallel been updating methods for addressing environmental change, with a focus on climate-driven changes.

This report summarises the presentations and discussion provided by the 18 participants from 8 countries, representing a range of operators, regulators, researchers and technical support organisations.

 

K Smith & G Smith (Eds) (2014) Representation of Environmental Change in the Near-Surface Environment. Report of an International Workshop London, May 2014 Version 2.0

Modelling processes in the Geosphere-Biosphere Interface Zone (GBIZ)

The objective of this project was to support better account of the treatment of radionuclide transfer through the geosphere-biosphere interface zone, and the related accumulation/dispersion/dilution processes which should be considered in order to provide appropriate confidence in performance assessment results.

International Workshop on the functioning of the GBIZ

An international workshop on the functioning of the Geosphere-Biosphere Interface Zone (GBIZ) was held in September 2011 at Louvain la Neuve, Belgium. Performance Assessments for disposal of radioactive waste and management of mining and other industrial legacies require an assessment of the likely transfer of radionuclides from underground to the accessible biosphere. It is often the case that systems are not considered as a whole; rather the near field, geosphere and biosphere are treated separately, which results in an overlap or a gap in model domains, commonly referred to as the GBIZ. The GBIZ is not a specific feature within a system, but is a region of space that can vary depending on the models being used and the site under assessment.

 

Transfer across the GBIZ is typically represented in a simplistic manner, yet the transfer of radionuclides across the GBIZ could in fact be very complex, involving numerous inter-linked physical, chemical and biological processes that may occur in cyclical or episodic ways. Issues relating to the behaviour of radionuclides and other contaminants within the GBIZ, particularly those that may be affected by changes in redox conditions, was the focus of the workshop.

 

Smith K, Smith G, Vincke C and Thiry Y (2011) International workshop on the Functioning of the Geosphere-Biosphere Interface Zone, 6 – 8 September 2011, Louvain la Neuve, France.

Evaluation of codes for geosphere and biosphere compartmental contaminant transfer modelling

One of the goals of BIOPROTA is the search for opportunities of synergies. A task currently under development within the forum is therefore an inter-comparison of codes and their flexibilities for model development and implementation.

 

The current wealth of models and codes is a sign of healthy independent development by various agencies. Most agencies are moving away form hard coded models, since they allow for little model flexibility, requiring the user to modify the source code in order to adapt the model.

 

Comparing codes, illustrating their capacities, giving examples of their strengths and weaknesses could enhance code refinement and help point towards future development. A workshop on code comparisons was held at ANDRA in September 2005, which provided a platform for knowledge exchange on various codes and set the stage for synergy exploitation in the fields of code, model and data base development.

Assessment of Processes in the Geosphere-Biosphere Sub-system in Post-closure Assessments of Radioactive Waste Repositories

The BIOPROTA forum has long recognised the relevance of having a clear understanding of possible processes for dilution and re-concentration as radionuclides transit between the traditional modelling domains, i.e. from the geosphere to the biosphere. Previous work organised within BIOPROTA has included a steady evolution in the development of understanding and modelling of relevant processes.

 

In particular, a methodology has recently been developed within the BIOPROTA programme, aimed at providing a structured approach to evaluating the geosphere-biosphere sub-system (GBS). There is now a need to consider how readily this approach can be applied, and how well it works, in assessments. These subjects were the focus of the one-day workshop on the 27 May 2015, organised through the BIORPOTA forum and hosted by CIEMAT in Madrid.

 

Smith K, Smith G and Thorne M (Eds) (2015) BIOPROTA Workshop on the Geosphere-Biosphere Sub-system.

Non-Human Biota: Long-Term Assessments

International Forum on Application of Guidance and Methodologies for Assessing Radiation Impacts on Non-Human Biota (NHB) from Radioactive Waste Disposal Facilities (PROBIOTA)

A forum on the application of guidance and methodologies for assessing radiation impacts on non-human biota from radioactive waste disposal facilities was held from 31 January to 1 February 2007 at Lappeenranta, Finland, hosted by Posiva. The workshop was attended by 15 participants from six countries. Presentations were made by participants on developments in international methods for assessing impacts of ionising radiation on NHB and national experience in the application of methods to waste disposal facilities.

 

BIOPROTA (2007).  Report of the ProBiota International Forum on the Application of Guidance and Methodologies for Assessing Radiation Impacts on Non-Human Biota from Radioactive Waste Disposal Facilities. 31 January-1 February 2007, Lappeenranta, Finland.

Non-human biota dose assessment: Sensitivity analysis and knowledge quality assessment

The focus of this project was on those aspects of biota dose assessment specific to the consideration of potential impacts of long-term releases from geological waste repositories. The aim was to evaluate the robustness of (generic) biota dose assessment data in relation to the key long-lived radionuclides applicable to deep geological disposal facilities and to identify important data gaps and uncertainties. A sensitivity analysis was performed and a knowledge quality assessment undertaken.

 

Smith K, Robinson C, Jackson D, De Laz Cruz I, Zinger I and Avila R (2010). Non-human Biota Dose Assessment: Sensitivity Analysis and Knowledge Quality Assessment.

Demonstrating Compliance with Protection Objectives for Non-Human Biota within Post-closure Safety Cases for Radioactive Waste Repositories

Over recent years, a number of methodologies have been developed that enable assessments to be made of the potential impact of releases of radioactivity on the environment through the calculation of dose rates to animals and plants (non-human biota). Most methods include some form of numerical criteria against which the magnitude of assessed doses can be compared. Reach of a screening value implies a need to undertake a further, more detailed assessment, but the extent to which it is possible to derive a more realistic basis for assessment will depend upon the type and scope of the assessment. Even if information is available to undertake a more detailed series of calculations, there remains the issue of what to do in practice, should a breach of a screening value occur since there are currently no standards for environmental protection that can be applied in situations where screening criteria are exceeded. Interpretation of results from dose assessments can therefore be difficult in terms of compliance with protection objectives.

 

It is therefore recognised that there is a need to develop a more structured approach to dealing with situations in which current screening criteria for non-human biota dose assessments are breached.  This is particularly the case for safety assessments for radioactive waste disposal facilities where the prospective and long-term nature of the assessments means that there is limited scope for refinement of assessment input data and parameter values through site-specific measurements.

 

As a contribution to the developing international discussions, and as an interim measure for application where assessments are required currently, a two-tier, three zone framework was proposed, relevant to the long-term assessment of potential impacts from the deep disposal of radioactive wastes. The purpose of the assessment framework, and associated material, is to promote a proportionate and risk-based approach to the level of effort required in undertaking and interpreting an assessment.

 

Smith K, Jackson D and Wood M D (2012). Demonstrating Compliance with Protection Objectives for Non-Human Biota within Post-closure Safety Cases for Radioactive Waste Repositories.

Scales for Post-closure Assessment Scenarios (SPACE)

This report presents the results of a study called SPACE, which was organised through the BIOPROTA Forum to address the issue of averaging scales within long-term non-human biota (NHB) dose assessments for radioactive waste disposal facilities. The overall objective was to advance the understanding of temporal and spatial scales for populations of NHB and their commensurability with current approaches to human spatial and temporal averaging, specifically within the context of long- term safety assessments of releases of radionuclides to the biosphere from radioactive waste repositories.

 

Smith K, Wood M D and Copplestone D (2015). Scales for Post-closure Assessment Scenarios (SPACE).