Stockholm NKS seminar 15-16 January 2019
Dr Claire Cousins: Emergencies, ethics and evolution
The International Commission on Radiological Protection (ICRP) was founded in Stockholm in 1928 and in 2018 celebrated its 90th anniversary there. The initial work of ICRP was focussed on medical workers but since the 1950’s its remit has continued to broaden to include all aspects of radiological protection involving ionising radiation. When ICRP wrote Publications 109 and 111 on the protection of people in emergency exposure situations and living in long-term contaminated areas after a nuclear accident nearly ten years ago, little did it know that the Fukushima Daiichi nuclear power accident would occur so soon afterwards. Much has been learnt from the Fukushima experience and Task Group 93 is updating the two publications in light of this, with the report nearing completion. The ethical dimension of such an accident soon became apparent in addition.
All of the recommendations of ICRP are based on scientific evidence as well as ethical values and balanced judgements. However, ICRP had never written a publication concerning the ethics related to radiological protection. Task Group 94 on this topic was established in 2013 and was published as the ‘Ethical Foundations of the System of Radiological Protection’ Publication 138 in 2018. There is an intention to describe the ethical basis of ICRP publications more explicitly in future publications and to continue the work in a focussed report on the ethics of radiological protection in medicine.
ICRP has many Task Groups working at any one time, and one of these is Task Group 102 on detriment calculation methodology. This is an in-depth review and will include discussion as to whether non-cancer diseases, such as circulatory disease and cataract, should be included in radiation detriment.
Any organisation that has survived for 90 years has undergone significant change and evolution and ICRP is no exception. These changes have included structural and administrative re-organisation, and a drive towards more openness and transparency. As ICRP now heads towards its centenary, its future direction and strategy will need to address current and emerging challenges in radiological protection.
Christian Linde: Overview of the NKS-R program
The NKS-R program is focusing on the area of reactor safety and decommissioning of nuclear installations. The program is offering financial support to 6-8 Nordic collaborations annually, covering the topics of ‘thermal hydraulics’, ‘severe accidents’, ‘reactor physics’, ‘risk analysis and probabilistic methods’, ‘organizational issues and safety culture’, ‘plant life management and extension’, as well as ‘decommissioning’. Most activities within NKS-R involve organisations in Finland and Sweden, which are the two Nordic countries with nuclear power plants in operation, but there are also collaborations with organisations in Norway and Denmark, which both have a long history in nuclear research.
Activities within NKS-R typically involve e.g. experimental and computational studies of phenomena related to reactor safety, model development for risk and uncertainty assessments, and analysis of human and organizational factors. The activities can also involve development of new methods for surveillance and enhancement of safety in daily and long-term reactor operation or within decommissioning and waste management. More than 80 reports from NKS-R activities have been published on NKS website since the last NKS seminar in 2016.
Several representatives from recent and ongoing NKS-R activities have been invited to present at this year’s NKS Seminar. In this overview, some additional NKS-R activities are highlighted in order to illustrate the value of Nordic collaborations within the NKS-R program. It is concluded that the NKSR program provides support with high additionality particularly in smaller R&D projects and pilot projects, and offers the opportunity for network building and valuable collaborations between experts at the leading Nordic research facilities within reactor safety.
A review article of NKS-R was written recently by the NKS coordination group with the ambition to enhance the visibility of the work that is supported by NKS-R to the international community. The article offers an overview of some of the NKS-R activities of the last few years, and exemplifies how value is added by Nordic collaborations. The article was published recently and can be downloaded following the link below.
C. Linde, K. G. Andersson, S. M. Magnússon, F. Physant “Nordic research and development cooperation to strengthen nuclear reactor safety after the Fukushima accident”, Nuclear Engineering and Technology (2018) in press, https://doi.org/10.1016/j.net.2018.11.013
Kasper G. Andersson: Overview of the NKS-B program
The Nordic countries (Denmark, Finland, Iceland, Norway, Sweden, and the Faroe Islands) have for many years shared a regional research and development program on nuclear and radiological safety - NKS. Organisationally, NKS comprises two programs: the NKS-R program on reactor safety issues and the NKS-B program, covering all aspects of nuclear/radiological emergency preparedness, radioecology and measurements. Through the thus established network, each of the Nordic countries has access to invaluable support that can greatly improve their ability to respond quickly, efficiently and cost-effectively to for instance an emergency situation, which might at the same time influence several of the countries in the Nordic region. The networks need to be kept viable, and expanded as needed, and in this context, NKS activities, where Nordic specialists work together on common problems, have proved very useful in the past and will undoubtedly continue to do so in the future. The research and development that has been carried out in NKS activities has generally been of high international standard, e.g., leading to Nordic adaptation as well as generic developments of internationally recognised decision support systems and international frontier development of targeted analysis procedures.
A number of recent activities after the Fukushima accident have been aimed at strengthening emergency management decision support. A problem in this context is that the complex European decision support systems have generally employed deterministic modelling methods, although parametric uncertainties can be large. With respect to long-range atmospheric contaminant dispersion, this problem was addressed for the first time in the NKS-B activity MUD. Using a new computer-intensive methodology inherent meteorological uncertainty can now be quantified, and in a follow-up activity also the impact of source term uncertainties on dose predictions was addressed.
In assessing the contamination of an area after a major nuclear or radiological accident, it should be kept in mind that not all potentially important radionuclides can be measured with gamma spectrometric or dose rate equipment. A number of new techniques for measurement of such radionuclides have been refined and tested in NKS activities, and found to reduce response times considerably.
Decommissioning is currently a hot topic in many countries, also in the Nordic area, with ongoing decommissioning projects in Sweden, Finland, Norway and Denmark. A total of 61 final reports of NKS activities on decommissioning issues are published on the NKS website (www.nks.org), where everything is publicly available for free. For example, in the autumn of 2018, a NKS seminar was held with nearly 100 participants on methods for radioanalytical chemistry for ‘difficult to measure’ radionuclides in decommissioning and waste management.
Other priority areas of the NKS-B programme include laboratory and in situ measurements of radionuclides for a multitude of purposes, radioecological studies of man-made as well as naturally occurring radionuclides in the environment, and efforts to strengthen communication between different organisations and the public in dealing with radiological problems.
A paper from 2018 in the Elsevier Journal of Environmental Radioactivity (see http://www.nks.org/en/this_is_nks/articles) gives an overview of the current NKS-B programme, and particularly focuses on efforts to strengthen Nordic nuclear emergency preparedness after the Fukushima accident.
Jan-Erik Holmberg, Stefan Authén, Ola Bäckström3, Xuhong He, Salvatore Massaiu, Tero Tyrväinen: Site risk of nuclear installations
Currently, multi-unit risks have not typically been adequately accounted for in risk assessments since the licensing is based on unit-specific probabilistic safety assessment (PSA) with focus on a reactor accident. Especially after the Fukushima Daiichi accident in 2011, the interest to develop methods and perform multi-unit PSAs has increased all over the world. NKS-R project SITRON (SITe Risk Of Nuclear installations) has searched for practical approaches for Nordic utilities to assess the site level risk. The project partners are Risk Pilot AB, Lloyds Register Consulting, VTT Ltd., and IFE Halden. The work has been co-financed by SAFIR2018 (The Finnish Research Programme on Nuclear Power Plant Safety 2015–2018), Forsmark Kraftgrupp AB, Ringhals AB, Swedish Radiation Safety Authority (SSM), and Nordic nuclear safety research (NKS).
The starting point of SITRON work has been the fact that the Nordic utilities already have good unit-specific PSAs. Therefore, the question is what additional efforts are needed to obtain a site level risk assessment. Practically, it means two tasks: 1) to identify relevant inter-unit dependences, and 2) to quantify the site level risk. Inter-unit dependences consist of multi-unit initiating events, shared systems, structures and components, dependences in human actions, inter-unit common cause failures, and plant operating state combinations. SITRON provides guidance how to perform the identification of dependences and how to select relevant dependences for quantification (screening). Quantification of site risk can be performed quite straightforwardly, given that the quality of the single-unit PSAs is sufficient.
The SITRON project has also included a survey on the role of Emergency Response Organisation (ERO), often referred to as the Technical Support Centre (TSC) in accident management. Based on responses from four plants in Finland and Sweden, SITRON has investigated different implementations of EROs with respect to possible impact on operational decisions in severe accident and multi-unit scenarios. The human role in severe accidents differs markedly: new decision makers (ERO and TSC rather than main control room); different instructions (guidelines rather than procedures); different decisions (involving trade-offs, novel actions, and strategies contrary to conventional knowledge); inter-unit influences; unreliability of instrumentation; and long time-windows for actions.
Weimin Ma, Anna Nieminen, Anders Riber Marklund: Assessment of Corium Risk of a Nordic BWR
This presentation will summarize the experimental studies at KTH on (1) molten metal penetration in a debris beds, which is concerned with remelting phenomena in a severe accident of light water reactors; (2) oxidation behavior of molten Zr and Fe-Zr droplets falling in a water pool; and (3) melt coolant interactions, including molten jet fragmentation and stratified steam explosion and. The experimental results include the influences of initial temperatures and materials’ properties on penetration depths, hydrogen generation rate from melt coolant interaction, debris morphology, as well as visualization and dynamic load of stratified steam explosion. Relevant analytical works will also be presented.
The second part of this presentation is concerned with assessment of corium coolability, focusing on qualification of simulation tools and performing coolability analysis for prototypical debris beds using the validated tool MEWA. The simulation using the MEWA code for the quenching process of an ex-vessel debris bed of a Nordic BWR indicated that the debris bed is quenched in a multi-dimensional manner if it is flooded from the top. The oxidation of the residual Zr in the corium has a great impact on the coolability of the debris bed due to (i) large amount of reaction heat and the subsequent positive temperature feedback, (ii) the local accumulation of the produced H2. The bottom-flooding and bypass have significant impacts on the quenching process and final state of coolability.
Patrick van Hees: Reliability of fire barriers
Fires in nuclear power plants can be an important hazard for the overall safety of the facility. An important factor in reducing the spread of the fire is the use of fire barriers. However, it is important to be able to quantify the uncertainty of the result of the fire resistance of a fire barrier for fire risk assessment of nuclear power plants.
The scope of the FIREBAN project (sponsored by NKS) is to investigate and assess the reliability of fire barriers in nuclear power plants (NPP) during realistic fire scenarios to support the plant-scale risk assessment. The objective is to establish data and methods to determine the conditional probabilities for failure of fire barrier. The methods used are statistics, literature review, calculation and specific unique designed fire tests. This abstract will focus on one aspect in the project namely the use of calculation methods to determine the uncertainty of a fire barrier when either damage (e.g. cracks), holes (by drilling) or wrong installation of insulation has occurred. Fire barriers e.g. partitions are namely constructed according to specifications taken from manufacturers. However, what happens to the fire resistance rating if the construction is built differently or is altered before it is subject to a fire or changes such as damage or hole drilling has occurred. This study looked at the safety factor inherent in fire resistant structures with regards to the insulation and integrity criterion. This was done using numerical tools such as FDS for the integrity criterion and ABAQUS software for the insulation criterion. No experiment was done during this study. However, the models were validated using experimental data from literature.
It was found that all the tested partitions with increased leakage or reduced insulation had a fire resistance rating too low to fulfill their purpose. This implies that there are no safety factors inherent in fire resistant barriers and that they should be built and kept exactly as specified by the manufacturer in order to give the fire resistance rating acceptable by codes. Also, results showed that it is much more likely that the wall will fail due to the insulation criterion than due to the integrity criterion, if leakage occurs. Finally, in order for the partition to be reliable it is necessary that it is built and remains exactly as tested by the manufacturer. This work showed even the feasibility of using simulation tools for predicting the results of fire resistance tests. This could be very useful especially when considering the high cost of testing whole constructions in fire resistance furnaces. However, more work is needed to be performed in order to accurately model a fire resistance test. Experiments with correct measurement instruments are needed in order to be able to validate properly the models, especially for cavity radiation and heat transfer through leakage area.
Anders Riber Marklund, Elisabeth Tengborn, Joakim Klug, Francesco Di Dedda: Rastep - a versatile tool for decision support in nuclear emergency situations
RASTEP (Rapid Source TErm Prediction) is a software tool developed by LR with support from the Swedish Radiation Safety Authority (SSM) for providing independent decision support to emergency response organizations in case of an accident at a nuclear installation.
The tool is built upon Bayesian Belief Networks and pre-calculated source terms that can be taken from the output of any severe accident code of choice. The decision support will be both based on best available knowledge from PSA L1 & L2 as well as expert judgements that will be pre-loaded into the model. Thereby, the capability to make a relevant prediction within a short timeframe with limited information and personnel available during a real scenario will increase. Results from RASTEP can be easily exported in various formats, including the IAEA information exchange standard IRIX.
As of today, LR has developed both plant specific RASTEP models for operating nuclear power plants in Sweden and plant generic models for the European commission FASTNET project. Recently a new project has also been launched together with the Norwegian Radiation Protection Authority (NRPA) to develop a RASTEP model for spent fuel facilities.
Ideas for future development of the tool include improved capabilities for fine tuning of source terms, functionality for import of plant process parameters as well as improved GUI and uncertainty handling.
Britt-Marie Drottz Sjöberg: Perspectives on interaction with society and associated risks and uncertainties
The presentation focuses on challenges in communicating risks and uncertainties related to nuclear and radiation risks in a social psychological perspective. It involves six themes: objectives for interaction, knowledge and contents, interaction dilemmas between experts and between experts and non-experts, time perspectives, cultural contexts, and societal change. Interwoven into each theme are results from research projects in the fields of risk perception, communication and public participation: one part of the EU-project ARGONA (2006-9) compared circumstances and communication in European countries regarding management of nuclear waste. A Swedish Radiation Authority project (2003) looked at perceptions of extreme time intervals. The AGREE project (2004, Environmental Protection Agency), included studies of safety data sheets and interpretations of specialized concepts, fuzzy words, and omission of information. Examples from interviews with experts in the nuclear waste programmes in Sweden and Finland are included (SKI Report 2004:23, see also Project 2000, in SOS-1, NKS-37) as are experiences within the Social Science Research Programme (2004-10, SKB). The point of departure in this presentation is that science, technology and societal authorities serve citizens and, ultimately humanity, in democratic societies. This starting point highlights that fundamental democratic values and ethical principles are invisible parts of the framework within which interactions between science and society are relevant.
Parties involved in communication on risk and uncertainty act based on their experience, fill different roles and often have different specific objectives in mind. Targeted information efforts and extended communication processes are very different phenomena. Communalities are, however, that they involve various degrees of attention or interest and include parties with different preconceptions and goals. Interest in and understanding of intended messages vary with the perceived importance and a recipient’s degree of familiarity with the matter at hand. Information based on experts’ unique specializations, in combination with varied roles, may produce perceived or real inconsistencies in available messages. Non-experts’ general attitude, degree of familiarity or interest may affect the comprehension of the intended meaning of a message. Time perspectives of risk and uncertainty include as varied perspectives as effects on personal health, conditions for future generations, assumptions related to technological developments, comprehension of physical or technological processes, as well as concerns and wishes regarding types of future societies. The cultural context theme highlights the variation of social conditions that are easily recognizable across countries and regions, as well as the somewhat varying social norms within subcultures that embed and guide experts, decision makers and a variety of public groups. The societal change theme attends to some historic events and trends, and suggests similarities and differences over time regarding information on risks and uncertainties. Current availability of information technology and social media provide promises as well as obstacles to effective communication. Essential challenges today seem to include distinguishing and safeguarding reliable facts from other types of materials and malicious actors, to highlight and strengthen the bond between specialists’ fact-finding and the dynamics of social change, the varying relevance to individuals’ circumstances included. The basic message being that social psychological circumstances influence what is possible and what is achieved in explaining and communicating risk and uncertainty to a higher extent than anyone authority’s or expert’s explanations.
Mark Dowdall, (Jan Erik Dyve, Heiko Klein): NKS ephsogam: early phase source term estimation from gamma spectra
As evidenced by the Fukushima Accident and events during 2017 in relation to 131I and 106Ru, estimation of the release term in the early phases of a nuclear or radiological incident is fraught with difficulties. Provision of an early estimate of quantitative and qualitative information regarding a release establishes a firm foundation for early actions and underpins the ultimate response measures implemented. Early phase monitoring data facilitates the drawing of conclusions regarding the nature of a release, its duration, possible location etc. The EPHSOGAM activity was aimed at the provision of a fit-for-purpose, robust and comprehensive virtual exercise for personnel involved in early phase response extending from interpretation of monitoring data to assignation of a source location and release term.
The activity involved the dissemination of technical materials, derived from simulated incidents, from which participants were required to generate an estimate of the release location, amount of activity released and the temporal development of the incident. The technical data was commensurate with what may be expected to be generated in the early phase of an incident and included meteorological and gamma spectrometric data. Four test scenarios were devised for four different locations and for each of the scenarios, the response at each of three air filter monitoring stations was simulated. Spectra were synthesized for each station and provided in a range of formats. All simulated incidents were assumed to have taken place during a defined time period facilitating the storage of relevant meteorological data for the activity.
A description of the materials provided, their development and the participants responses are provided. The results highlight the complex interplay between a variety of factors affecting the participants abilities with respect to release location and characterization of the release.
Jens Havskov Sørensen, Fredrik Schönfeldt, Robert Sigg, Jan Pehrsson, Bent Lauritzen, Jerzy Bartnicki, Heiko Klein, Steen Cordt Hoe, Anna Maria Blixt Buhr, Jonas Lindgren: Effects of source-term uncertainty and Meteorological uncertainty on plume prediction (NKS-B avesome)
In the early phase of a nuclear accident with possible off-site consequences, e.g. resulting from core melt and breach of containment, accurate prediction of the atmospheric dispersion of radionuclides is of utmost importance. However, two large sources of uncertainty exist: one associated with the meteorological data, and one related to the source term, i.e. the amounts of radionuclides released and the temporal evolution of the release. In the NKS-B project AVESOME (Added Value of uncertainty Estimates of SOurce term and MEteorology), a methodology is developed for quantitative estimation of the variability of atmospheric dispersion modelling resulting from both sources of uncertainty. With modern supercomputing facilities available e.g. at national meteorological services, the proposed methodology is well suited for real-time assessments and implementation in decision support systems (DSSs).
The AVESOME methodology adapts well to the RApid Source TErm Prediction (RASTEP) system, which provides a set of possible source terms and associated probabilities. In the near future, source terms derived within the EU project FASTNET may also become available, describing different release scenarios.
In the presentation, the methodology is described. The resulting implementations in a nuclear DSS (ARGOS) are addressed as well as impacts on real-time emergency management.
Robert R. Finck, Christopher L. Rääf: Ways to reduce uncertainities in mobile search of radioactive material out of regulatory control (NKS-B automorc)
It is unusual that dangerous radioactive sources are lost out of regulatory control, but it has happened and resulted in people being injured. Such events may be caused by accidents, insufficient security of sources or by perpetrators who have acquired radioactive material with the intention to cause harm. Dangerous radioactive material out of control (MORC) must be sought and brought back into safety as soon as possible. Authorities in the Nordic countries have mobile equipment for spectrometric search of lost gamma ray sources. Mobile search is a challenging task where one is trying to identify signals from a possible source while sorting out false alarms from the varying radiation background and quantum noise. Search exercises carried out jointly by Nordic teams over the past two decades have shown the difficulties and uncertainties in localizing missing radiation sources. It is also important to determine if an area that has been searched can be exempted, i.e. that it does not contain any source of radiation above a certain level of activity. In order to do this, it is necessary to know the maximum distance at which a gamma ray source with a certain activity provides a sufficient signal in the measuring instruments to be detected, here referred to as the detection distance. Lund University has developed a computer model, written in Fortran 90, that calculates detection distances for different radionuclides, source strengths, measuring instruments, vehicle speeds, measurement times, detection probabilities and probabilities of false alarms. The accuracy of the model has been tested in two field experiments 2016 (NKS/MOMORC) and 2018 (NKS/AUTOMORC) with participants from all Nordic countries. The results show good consistency between the actual distances used in the setups and the model predictions of the detection distances for gamma ray sources with activities 50 - 1500 MBq. Although not tested for stronger sources due to the difficulty of handling them in the field, there is reason to assume that the model is also correct for highly radioactive sources up to several TBq. In order for the model to function properly, input data is required from careful calibration of the measuring equipment. When calibrated, the model allows one to choose the most optimal combination of instrument settings and vehicle speeds for a particular search assignment and to obtain information about detection distances of gamma ray sources of different activities. The model shows, among other things, that the measurement time, which gives the longest detection distance, depends on the activity of the source being searched. Detection distances increase 3 - 25 percent for non-shielded gamma-ray sources above 1 GBq if the measurement time is increased from 1 s to 5 - 30 s. Best detection distances for searching sources of unknown activities is obtained using floating variable measurement time analysis. Using a mobile 4 L NaI(Tl) spectrometer system at a speed of 50 km/h, the detection distance is between 450 – 530 m for an unshielded 190 GBq 137Cs source, and between 590 and 700 m for an unshielded 190 GBq 60Co source, depending on the measurement time (1 - 30 s). At higher speeds, the detection distances become shorter. Due to attenuation in the air, there is a practical upper limit for detection distances, largely independent of how strong the radiation source is. This limit is for Category 1 radiation sources (extremely dangerous) about 1000 m for 137Cs and about 1500 m for 60Co. Thus, to select settings for mobile search the proposed calculation model facilitates the selection of instrument settings and reduces uncertainty about what can be detected and not detected in a search assignment.
Steen Hoe: Modelling uncertainties and use of uncertain model results in nuclear emergency preparedness
Good prognostic models are useful for several purposes in nuclear emergency management decision support, including rough early phase risk prognoses, estimates of implications of possible solutions for recovery, exercises and competence building. The presentation will focus on how to handle uncertainties introduced for the input to models from the meteorological data and source terms. The Nordic-based decision support system ARGOS will be used for demonstrating how uncertainties can be quantified for of nuclear power plant accidents. Source terms and source terms models from the EU FASTNET project will be mixed with dispersion uncertainty from the Danish Meteorological Institute. It will further be discussed how uncertain modelling results may influence the decision taken in dealing with emergencies. Also ideas for future improvement and maintenance of decision systems used by the Nordic countries will be suggested.
Anneli Hällgren: Ssm:s view on how to secure competence in radiation safety in Sweden
Om 24 September 2018, The Swedish Radiation Safety Authority (SSM) submitted a government assignment report to the Government on the subject how to secure competence in nuclear safety and radiation protection in Sweden over the long term - not only internally at the Authority, but also on the part of other applicable stakeholders on a national level. The assignment was given to the authority in December 2016.
SSM has, by means of communication analyses and horizon scanning, gained situational awareness of needs and potential relating to securing of competence in the field of nuclear safety and radiation protection. Status reports were compiled in co-operation with industry, institutions of higher education and other relevant stakeholders. The focus of the data is on these perspectives: the needs and requirements of licensees and of SSM in terms of competence, higher education programmes, and the potential of academia to maintain scientific expertise. Thereafter, the Authority analysed the situational awareness material and identified weaknesses in the knowledge management framework for securing competence. The Authority also identified sources of funding for research and education in the field, and subsequently suggests approaches to interaction on impending areas of focus. Based on this analysis and the shortcomings identified, this Inquiry suggests measures to ensure that Sweden has access to appropriate competence in the field of nuclear safety and radiation protection. These suggestions are made on the basis of the requirements identified during the investigation: not only the needs of today, but also the requirements of tomorrow.
One main conclusion is, that if today's and tomorrow's competence needs are to be met, the Swedish system for knowledge management in the field of nuclear safety and radiation protection needs strengthening. There are areas of research, critical to society, which are currently underfunded and also education programmes relating to radiation safety that are in jeopardy. Another main conclusion is that national coordination needs to be built as this is a prerequisite for maintaining competencies over the long term.
In the assessment of the Authority, dealing with these problems requires reinforcement of the knowledge management system in the form of the following:
- A comprehensive national strategy with coordinated efforts for achieving a higher level of effectiveness in the knowledge management system
- Increased funding for a critical core of research environments in order to ensure an ongoing and minimum level of scientific expertise; such expertise is to have insight into the activities and practices involving radiation conducted in Sweden. This is in parallel with increased funding for related research environments
- Formalised interaction between stakeholders in the system for central government research funding to guarantee that the relevant research environments are sustained
- Guaranteeing availability of education programmes that are critical to society in the field of nuclear safety and radiation protection
- Several stakeholders should perform informative action and run campaigns for the purpose of attracting students so that they enrol in nuclear safety and radiation protection programmes, and choose occupations in the field.
Kristina Gillin: Uncertainties in nuclear back-end management and the path towards a sustainable decommissioning paradigm
With the list of permanently shut down reactors growing ever longer, nuclear decommissioning is clearly an industry on the rise. But experience to date is showing that decommissioning of nuclear facilities and managing the resulting wastes rarely go according to plan. A nuclear reactor’s scheduled shutdown date often changes. New waste facilities and transport routes tend to be protested. Public and political opinions are unpredictable. Even the regulatory landscape and requirements are associated with great uncertainties, given the long timelines. Major delays have become the norm and complete stops are not uncommon.
It can, therefore, only be concluded that current practices are unsustainable. Which begs the questions: Why? What might a sustainable decommissioning paradigm look like? And how do we get there?
In this presentation, these questions are explored by applying resilience thinking, which has emerged as a leading concept within sustainability research. A range of international examples are drawn upon to illustrate the complex, non-linear nature of nuclear decommissioning and waste management – in turn, demonstrating that nuclear back-end management is a typical complex adaptive system and needs to be approached as such.
By recognizing that nuclear back-end management, at the macro level, actually is a sustainability problem – not an engineering problem – key features of a resilience-based, holistic approach are discussed. These include involving stakeholders in the decision-making, as well as deciding new site land uses before planning decommissioning.
The benefits of a sustainable decommissioning approach are tremendous: increased trust, less waste, lower costs, shorter timeline between productive uses, and reduced risk of long delays or dead ends. Not to mention, the potential for increased safety – both for workers and the public.
In addition, founding decommissioning planning on sustainability principles would be consistent with the nuclear industry’s ambitions to build more reactors in order to help – in the context of sustainable development – in combating climate change.
Martin Amft: Decommissioning in the nordic countries
With its recent decision to shut down the Halden research reactor, Norway is also facing the technical and regulatory challenges that the decommissioning of nuclear facilities entails. Amongst the Nordic countries, Sweden had the largest nuclear program. Hence it gained by now experiences from decommissioning a variety of nuclear facilities, ranging from the almost completed decommissioning of the Ranstad Uranium milling facility and the Studsvik material research reactors to the first dismantling projects in nuclear power reactors. The presentation will give an overview of the current status of decommissioning projects and their particular challenges in Denmark, Finland and Sweden.
The Swedish regulator’s perspective on the foreseeable challenges and possible solutions for conducting up to seven large-scale dismantling and demolition projects nearly in parallel will be discussed. Amongst other things these included the adequate adjustment of the regulatory framework and the development of efficient and effective administrative procedures.
István Szőke: Digital technology aided innovation for planning and cross-cutting issues in nuclear decommissioning
Risk originating from uncertainties in radiological estimates is undoubtedly one of the most important key issues in nuclear decommissioning. Nuclear risks are, in general, very quickly dropping to a negligible level in the very early stage, as part of the decommissioning activities or sometimes classified as POCO operations typically during a transition to decommissioning period. Non-radiological (industrial) hazard conditions (e.g. presence and amount of asbestos) are also very important sources of risk, especially when radiologically contaminated. Radiological waste is a small ratio of the total resulting waste volume. However, in terms of contribution to risk, it is the most critical portion, partly due to the exaggerated public concern for management of radiological material.
Most currently applied methods for radiological risk assessments are based on very traditional techniques providing estimates based on singe values well describing the given state of radiation sources and the environment impacting on exposure. Such methods are equally used in radiological protection, safety demonstration, training and education, and documentation purposes. While updating these current methods is key for modernization of the overall lifecycle management of nuclear and radiological facilities, the need for better methods is more accentuated in the area of nuclear decommissioning, where radiological conditions and uncertainties are very different from the operational phase, and so is the group of people that may be exposed to radiological hazards. One of the issues of highest concern in nuclear decommissioning is initiating work, including human participants, in an environment with unknown (or not adequately know) sources of radiation exposure that may lead to unplanned pause in the work, extensive preplanning activates, and, in some cases, unplanned exposure of humans. Hence, abilities for preparing for some possible contingencies and quick re-planning of activities based on new information is very important for enabling an agile capability for performing decommissioning in a safe and cost-efficient way. In more common words, this means accepting the fact that the exact project outcome and work-plan is not possible to know beforehand and adopt a gradual approach where tasks are performed with allowance for uncertainties and plans for future tasks are continuously adjusted based on new information generated by previous tasks lowering uncertainties for the tasks ahead. While traditional radiation risk estimation methods may be adequate for safe operation of radiological facilities, these techniques are not compatible with an agile process required for safe and cost-efficient decommissioning expected by stakeholders today. In an agile process, radiation risk estimation has to be compatible with a dynamic, highly adoptive, process for a. ensuring the availability of required competence and resources early in time, b. regulatory communication and acceptance – practical application of decommissioning legislation, d. detailed planning of decommissioning and waste management, and e. communication among all the stakeholders of the project. These are perfectly in-line with the outcomes of our Nordic survey (within the NorDec NKS-R project), where participants were asked about key issues related to past and upcoming decommissioning projects in Nordic countries. From the results, it is safe to state that cross-cutting issues related to planning decommissioning activities (both during the transition and later in the implementation phase), where integration of different people and organizations is a key requirement (e.g. utility – regulator, utility – contractors, utility – national waste management, etc.), is an overarching key concern for current practitioners.
This paper aims at presenting innovative concepts enabled by modern information technology and advanced radiation risk assessment methods supporting agile and holistic planning processes in nuclear decommissioning projects, and allowing a highly visual explanation of the connection between assumption on radiological inventory/conditions and their uncertainties with different possible strategies, regulatory framework, training and supply chain needs, waste acceptance criteria, and other requirements.
* The term risk (when used alone, i.e. not radiation risks) is used, in this paper, for project level risks.
Teemu Reiman, Kaupo Viitanen, Carl Rollenhagen: Safety culture change tools in different life cycles of a nuclear power plant
A set of twelve principles of safety culture change were developed in the NKS-R SC_AIM project (Viitanen et al. 2017 [NKS-381], Viitanen et al. 2018 [NKS-405]). The principles summarize the essential good practices of leading safety culture change. The principles represent a systemic approach to leading safety culture change, which is based on a variety of contemporary views of safety science and organizational management. The principles cover topics that include explicating the nature of sociotechnical systems and how culture forms and changes in them, how goals are set in complex, nested and conflicted systems, how various types of interactions can be leveraged for safety culture change, and how different time scales manifest when initiating culture change. The principles can be utilized to support various practical endeavors at safety-critical organizations such as nuclear power plants. For example, the principles can support practitioners in helping steer safety culture change activities, in identifying the leverage points in the system that drive positive change in safety culture, or in identifying the prerequisites that are required for successful implementation of safety culture tools or methods. The presentation focuses on one of the principles, which helps in deciding which safety culture change tools or practices one should or could use during the particular life cycle of the plant: Principle 6: Identify the assumptions embedded within safety culture change tools.
All safety culture change tools are developed and used based on certain assumptions regarding how the tools function and influence the system. These assumptions can include the developers’ views regarding safety culture and its change, models of the organization or perspectives of management and leadership. Because tool development is influenced and steered by these assumptions (either consciously or unconsciously), they get embedded in the tools. Sometimes the assumptions are explicated in tool descriptions or instructions, but often they are not. This may result in a mismatch between the assumptions made during the development of the tools, and the assumptions made by the end-user regarding the tools’ intended function and effect. The mismatch can lead to the end-user utilizing the safety culture change tool in an unintended manner, or otherwise render the tool ineffective. From a wider perspective, assumptions are not only embedded within safety culture change tools and methods, but also within safety culture programs and development targets, safety culture models (either mental or documented) and overall approaches to safety culture improvement.
Due to the embedded assumptions, the end-user needs to be active in reflecting on the tools’ functions, benefits, and potential limitations and prerequisites of implementation. The different requirements set by life-cycles of the nuclear power plant bring in additional complexity. Good safety culture manifests differently in different life-cycles. Also, the challenges differ. For example, a method that has originally been developed for stable operational period may not be usable in a more dynamic project oriented pre-operational phase, or during decommissioning. Examples of safety culture development tools, their embedded assumptions and potential uses will be given in the presentation.
Jixin Qiao: Advances, uncertainties and pitfalls in measurement for decommissioning waste classification --- on the background of the NKS-B radworkshop
In recent years, more and more nuclear reactors and other nuclear installations in Nordic and other countries (e.g., Germany) are under decommissioning or going to be decommissioned. This sets high demands in effective radioactive waste management, which is critically dependent on robust, focused and efficient waste characterization in order to reliably inform all management steps (including waste recovery, treatment/recycling, conditioning, storage and waste disposal) and to ensure the safety of the operators, the general public and the environment.
A range of characterizations techniques may be applied to assess the properties of nuclear wastes, with the choice of approach depending on the compositional complexity and stability of the waste form. Even though there are already some methods and experiences available from the decommissioning of previous nuclear facilities, new challenges in waste characterization are continuously appearing since different nuclear reactors have different design and operational history. Therefore, fit-for-purpose measurement strategies and methods are necessary with focus on specific analytical needs and obstacles.
In this paper, an overview of decommissioning status, advances, uncertainties and pitfall in measurement of decommissioning waste classification in Nordic and other European countries is presented based on the outcome of a recently organized NKS Radworkshop 2018 at DTU Nutech focusing on radioanalytical chemistry in nuclear decommissioning and waste management. It is evident that challenges exist almost in each case for sampling, radiological characterization and radiochemical analysis of hard-to-measure radionuclides. Knowledge/experience sharing, further education of staff and development of new methodologies are needed in the nuclear society to cope with the high demands in the analytical aspects for decommissioning and waste management.
Pål Efsing, Ulla Ehrnsten, Mattias Thuvander, Magnus Boåsen, Sebastian Lindkvist, Kristina Lindgren: Breda – improved methods to enhance the understanding of radiation induced degradation of reactor pressure vessels
From the very beginning of the operation of the current types of light water nuclear reactors, LWRs, the evolution of the mechanical properties of the Reactor Pressure Vessel, RPV steels has been followed by means of surveillance programs. A surveillance program for a RPV ideally consists of all relevant RPV materials, i.e. those that may see neutron irradiation doses beyond 1*1017 n/cm2 over the period of intended operation. Most reactors were initially licensed for a period of 40 years of operation and thus the surveillance programs were laid out for this time period.
Currently many LWR operators foresee extended operation, i.e. operation beyond the original analysis criteria. This includes many of the current reactors in the Nordic countries. Thus there is a need to develop tools to allow for testing of irradiated materials in a way that conservatively use the amount of material available (since there is a limited amount of relevant material) as well as being able to utilize material that has already been tested in previous stages, e.g reconstitution of samples or using miniature specimens. These can also allow for enhancement of the data-base and thus be an integral part of improvement of the understanding. It is also important to correlate the results from the surveillance testing to the actual outcome of the property changes in the real component.
The Swedish nuclear operators has initiated a program to harvest component material aged in one of the RPVs from the decommissioned Barsebäck plant, Barsebäck unit 2. A number of through wall samples has been removed in both the active core region and in an area where the material only is subjected to thermal ageing in the RPV. The objective is to provide material for use in a proposed mechanical and microstructural testing program spearheaded by VTT in Espoo with support from the Finnish SAFIR-program in the new hot-cell facility and adjacent labs. Some element of the high resolution microstructural testing is performed at Chalmers in Gothenburg, and some portions of the mechanical testing, i.e. on material that is unaffected by neutron irradiation at KTH in Stockholm.
The support from NKS has allowed for the formation of a long term foundation to enable exchange and collaboration between the three active service providers and well a net-work for the regulatory institutions in Finland and Sweden as well as the plant operators and owners to collectively gain information that can be used as basis for continued operation of the current nuclear reactor fleet in the Nordic countries.
Justin Brown: Radiation protection of the environment: some thoughts and perspectives
The protection of the environment from the effects of ionizing radiation has received increased attention over the last two decades. The system that the radiological protection community currently uses is based around the concept of reference animals and plants, drawing upon datasets and models related to these entities. This provides a means of relating exposures to dose and dose to effects for the living environment in a structured and consistent manner and has the advantage of fostering close links to the radiological protection framework developed for humans. Nonetheless, the system is not without criticism and recent advocacy of a more ecosystem-based approach has gained traction. There are also challenges in relation to how the datasets and models, that were originally developed to apply to planned exposure situations (such as routine authorized releases of radioactivity), might be adapted to consider emergency and existing exposure situations.
Per Roos: Characterisation of industrial NORM waste including uncertainties (NKS-B CONCORE)
The predominant contributors to the production of Technologically Enhanced Naturally Occurring Radioactive Material (TENORM) and NORM-waste in the Nordic countries are the on- and offshore oil and gas producers. In oil and gas production processes, host rock formation water containing low concentrations of NORM is mixed with seawater containing high concentrations of sulphate. This leads to precipitation of NORM (Ra, Pb, Po)SO4, which is deposited as either scale or sludge in the production equipment. NORM contaminated pipes, tubes, pumps and tanks, etc. are therefore subject to radiological characterization in order to ensure safe reuse or recycling as well as safe NORM waste handling. The procedures and measurement techniques may significantly affect the amount of material that is categorized as NORM contaminated equipment and NORM waste. At present, different procedures are used for categorization by the individual operators in the North Sea. A number of parameters considerably influence the measurement accuracy and may cause false categorization of the materials, for instance abnormal geometry of objects, various density and composition of the scale and sludge, inhomogeneous distribution of NORM, and measurement sensitivity and uncertainty. The presentation gives examples of current methods to characterize NORM contaminated equipment and factors affecting external dose measurements.
Mari Komperød: Risks from naturally occurring radionuclides in the nordic diet
The vast majority of the ingestion dose received by the general population is caused by naturally occurring radionuclides. Nonetheless, natural radioactivity in food receives far less attention than anthropogenic radionuclides.
The Norwegian Radiation and Nuclear Safety Authority (DSA) performed a detailed study of ingestion doses received from radioactivity in the Norwegian diet in 2015, using national consumption statistics and best available estimates of activity concentrations of 16 radionuclides in approx. 50 food categories. The age-weighted mean dose was estimated at 0.010 mSv/y from anthropogenic radionuclides, dominated by 137Cs, whereas the dose from natural radioactivity was estimated at 0.41 mSv/y. 210Po made up the largest contribution from naturally occurring radionuclides, followed by 210Pb, 228Ra, and 226Ra, if disregarding the constant dose from 40K. The dose from ingestion of 222Rn in drinking water from groundwater sources was also significant. Similar data was later used by the Norwegian Scientific Committee for Food Safety to provide an assessment of radioactivity in food in terms of relative risk, both to the average public and specific groups with elevated exposure.
The above work, as well as studies from other countries, have found fish and shellfish to be the food group causing the largest contribution to the average ingestion dose. In addition, concentrations of natural radioactivity vary dramatically between different species of fish and shellfish, according to their dietary niche. Therefore, it is important to use data for the species actually consumed in order to make relevant assessments of ingestion doses.
The objective of the NKS-B project NANOD is to fill the knowledge gaps for important naturally occurring radionuclides in the most consumed species of fish and shellfish in the Nordic region, including farmed fish, with the aim of enabling more accurate dose assessments for seafood and the total diet in Nordic countries. Preliminary data from the NANOD project shows large variation of 210Po levels between species, and also sometimes within the same species. There is a general tendency towards higher concentrations in shellfish. According to national consumption data, there are significant differences both in total seafood consumption and in terms of preferred species in the different Nordic countries. Final measurements and associated dose assessments are to be completed in 2019. According to the FAO, Nordic seafood makes up over 10% of worldwide exports in terms of trade value, meaning such data are also relevant in the global aspect.
T.H. Hevrøy, A.-L. Golz, I. Holmerin, E.L. Hansen, L. Xie and C. Bradshaw: Now we know why there are so few examples of microcosm studies in radioecology
Extensive evidence for the important role of ecological processes in determining net ecosystem effects to anthropogenic stressors has led several authors to call for more consideration of community ecology or an ecosystem approach to radioecology. However, there is still a significant lack of studies using this approach in radioecology research to date. The aim of our studies have been to use multi-species microcosms to investigate ecological processes and/or potential effects of radiation in aquatic communities. The first study we did set out to explore effects of ionizing radiation in a model freshwater ecosystem, including endpoints at both structural and functional levels and as well as ecological interactions. The microcosms were exposed for 22 days to a gradient of gamma radiation with four dose rates in the range from 0.72 to 19 mGy/h. The results showed significant dose related effects on photosynthetic parameters for all macrophyte species, however no significant effects of radiation were observed for the consumers in the microcosms. The ecological processes, and the experimental design itself, were also critical in the understanding of our results. In addition, a second microcosm study was carried out recently to investigate the fate of three radioactive isotopes of micronutrients, Mn-54, Co-57 and Zn-65, which are regularly released into the Baltic Sea from nuclear power plants (NPPs). The microcosms consisted of macroalgae and two grazers, to study both direct and indirect uptake to both algae and grazers, and secondly, the potential effects of eutrophication on the uptake of radionuclides by exposing the microcosms to different nutrient levels. From both microcosm studies, we have gained a great deal of knowledge in the use of microcosms in radioecology. This presentation will discuss both our results, and highlight the main learning points and future recommendations for microcosm studies.
Poster presentation abstracts
Daniela Ene, Rodolfo Avila: Uncertainty and sensitivity analysis in the dose estimates for ESS facility
As part of the environmental impact analysis (EIA) of the ESS facility, assessments of the radiological impacts to humans and non-human biota from releases caused by routine operations and the most severe potential accidental release has been carried out, to comply with requirements from the Swedish Radiation Safety Authority (SSM).
For normal operations the derivation of the Release-to-dose-factors (DF)s and estimation of radionuclide concentrations in the environment, ESS used the PREDO “PREdiction of DOses from normal releases of radionuclides to the environment” methodology. The evaluation of exposures to impacted environmental media considers three main pathways:
- airborne releases of radionuclides through ventilation outlets and diffuse leakages,
- liquid discharges of radionuclides to the sewage system and downstream surface water (rivers and sea),
- migration of radionuclides with groundwater following activation of the surrounding soil.
Source term covering all contributions from the entire ESS facility to releases to the environment were also evaluated and further used for derivation of the annual effective doses by multiplying with the DFs.
Estimation of doses to non-human biota, resulting from the ESS releases and discharges to the environment was also assessed by means ERICA tool.
The models for calculation of the doses, the definition of the ESS reference persons and of the ESS representative ecosystems as well as the obtained results are reported in several ESS internal reports and external publications.
This work will present some studies carried out to assess the uncertainty in DFs estimates for radionuclides and exposure pathways with a potentially significant dose contribution.
The sensitivity analysis was carried out by EASI sensitivity method and by calculating the Spearman rank correlation coefficients. The EASI first sensitivity index quantifies the proportion of the variation in the output that is explained by the variation in each parameter (0%-100%) and assumes that the relationship between the inputs and output are additive. The Spearman correlation factor indicates the degree of influence that each parameter has on the output and also indicates the direction of the relationship and is bounded by [-1,1].
Finally, an assessment of the radiological impacts to humans and non-human biota from releases caused by a potential accidental release will be also presented and driven conclusions outlined.
Ari T. K. Ikonen, Ville Kangasniemi: A model for radionuclide distribution in the main basins of the Baltic Sea – Conceptual framework
The Baltic Sea is an enclosed arm of the North Atlantic Ocean, characterized by high degree of freshwater input and limited oceanic connection that is reflected in the brackish water type hosting relatively distinct biota communities. The sea is also important in many aspects to the people in the region. The area has also received its share of the global fallout from the nuclear tests and very considerable portion of the Chernobyl fallout and, consequently, the radioactivity concentrations in the seawater, sediments and biota, as well as in river waters discharging to the sea, have been monitored relatively extensively for long. There are also a number of nuclear facilities located on the shores of the Baltic Sea, as well as inland within the catchment area, radioactive materials are transported in ships in the area, and some nuclear-powered vessels may travel the waters. There have been various modelling campaigns for different purposes, as well as general assessments (e.g. the NKS-B EFMARE project and the thematic HELCOM assessments of long-term changes in the radioactivity levels) addressing also the radionuclide transport and its implications in the Baltic Sea. Also, there have been both individual safety assessments and international endeavors (e.g. the PREDO projects) regarding the authorized and possible accidental releases from the nuclear facilities. In addition to these, EnviroCase has now opted to invest in increasing the model diversity through establishing yet another radionuclide transport and dose assessment model of the Baltic Sea so that it is flexible to use for a variety of purposes both in commercial and research-cooperative terms. These include further study of the distribution of the radioactivity across the Baltic Sea main basins and the impacts of various sources (atmospheric and aquatic, point and diffuse sources), also through switching source terms and transport processes on and off and by employing hypothetical what-if scenarios; integrated calculation of doses to the humans and the wildlife on the same basis; provision of radioactivity-flux boundary conditions for models specific for more limited coastal areas of special interest (e.g. near nuclear facilities or addressing secondary contamination of specific shoreline areas more remote from point sources); and performing probabilistic simulations as well as sensitivity and uncertainty analyses in respect of the various endpoints of concern (usually, concentrations in the environmental media and foodstuff and/or doses to people and biota). This poster will present a tentative structure of the model, source terms, exposure pathways and result types, identification of key data sources to populate the model (preferably, and seemingly also mostly, in open access), and the way forward including proposals for collaboration.
Vilho Jussila, Billy Fälth, Peter Voss, Björn Lund, Ludovic Fülöp: Synthetic ground motions to support the near-field seismic hazard prediction in Fennoscandia
The relevance of near-field earthquakes to the safety of nuclear power plants (NPP) in Fennoscandia is very high. De-aggregation from probabilistic seismic hazard assessment (PSHA) studies indicate that the prevailing source of hazard for ground accelerations of engineering interest (e.g. PGA>0.5 m/s2), is from mid-magnitude earthquakes in the vicinity of the NPPs. The maximum magnitude (Mmax) is an important factor but the distance range beyond 100km has a small contribution. Conversely, there are very few recordings of Fennoscandian earthquakes in the range of distances of this highest interest. With low activity rates and since earthquakes in Fennoscandia occur widely distributed in the region, the seismic networks with the current station density are also not likely to record mid-magnitude events at short distances.
As the task of estimating ground motions in the near-field of an NPP (0<D<50km) is crucial and since this distance range is poorly covered by seismic measurements, we propose the use of physics-based modeling to create synthetic ground motions. In this work, we present a synthetic ground motion dataset created using the hybrid modeling method developed in earlier NKS projects (2015/2016). In this work we modelled earthquakes with magnitudes of Mw ≈ 4.3, 5 and 5.5, and output ground motions up to 50 km from the hypocenter of the earthquake. For each magnitude, a few possible depths and fault rupture scenarios were modelled based on observed earthquakes in Fennoscandia.
For Mw ≈ 4.0 there are some measurements overlapping with synthetic data. Hence, we have a way to test the accuracy of the models in comparison with the existing measurements and understand the relevance of the model outputs in the Mw=4.5-5.5 magnitude range. At the same time, we compare the synthetic ground motion datasets with the G16 ground motion prediction equation (GMPE) developed for central and eastern North America. In the broader context, we work on an adaptation of the G16 to the Fennoscandian environment. In this study, the synthetic data is used only to guide the extrapolation of the GMPE to short distances and provide comparison for higher magnitudes (Mw=5.5).