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An analysis of a data set consisting of 3 years of high time resolution radioxenon stack measurements from the three nuclear reactors at the Forsmark nuclear power plant in Sweden, as well as measurements of atmospheric radioxenon in Stockholm air, 110 km away, is presented. The main causes for the stack releases, such as the function of the xenon mitigation systems, presence of leaking fuel elements, and reactor operations such as shutdown and startup, are discussed in relation to the stack data. The relation between radioxenon releases and reactor operation is clearly illustrated by the correlation between the stack measurements and thermal reactor power. In general, the isotopic ratios of the Stockholm measurements, which are shown to mainly originate from Forsmark releases, agree well with stack measurements, and with a modeled reactor operational sequence. Results from a forward atmospheric dispersion calculation agree very well with observed plume arrival times and widths, and with some exceptions, also with absolute activity concentrations. The results illustrates the importance of detailed knowledge of radioxenon emissions from nuclear power plants when interpreting radioxenon measurements for nuclear test ban verification, and provide new input to this kind of analysis. Furthermore, it demonstrates the possibility to use sensitive radioxenon detection systems to remotely detect and verify reactor operation.

A high throughput system for processing and detection of low levels of radioxenon in soil gas samples has been developed. Processing and analysis of sub-soil noble gas samples puts high demands on the gas separation part of the system since the samples might contain high levels of Rn, CO2 as well as other gases. The gas process is optimized to remove all CO2, H2O and Rn with a high recovery yield of the xenon in the sample to ensure a high sensitivity even for small samples. The system is designed to handle multiple samples per day with a high level of automation and sample traceability to be suitable for use in an on-site inspection (OSI) an important component in the verification of the Comprehensive Nuclear Test Ban Treaty. To ensure a rapid deployment the system could be pre-installed in a flight container.

Over 40 soil gas samples were collected both in post-industrial areas as well as in undisturbed areas in the region of Kvarntorp, Sweden. Radioxenon (133Xe) was detected in 15 samples and radioargon was detected in 7 from 10 samples analysed. The concentration of radioxenon and radioargon in soil gas ranged up to 109 mBq/m3 and 19 mBq/m3, respectively. During sample collection other soil gases such as radon, CO2 and O2 were also measured and soil samples were taken along with dose rate measurements. The field experiment presented here shows that it is possible to detect naturally occurring radioxenon and radioargon in soil gas simultaneously.

Among the most important indicators for an underground nuclear explosion are the radioactive xenon isotopes 131mXe, 133Xe, 133mXe and 135Xe and the radioactive argon isotope 37Ar. In order to evaluate a detection of these nuclides in the context of a nuclear test verification regime it is crucial to have knowledge about expected background concentrations. Sub soil gas sampling was carried out on the oil shale ash waste pile in Kvarntorp, Sweden, a location with known elevated uranium content where 133Xe and 37Ar were detected in concentrations up to 120 mBq/m3 and 40 mBq/m3 respectively. These data provides one of the first times when xenon and argon were both detected in the same sub soil gas. This, and the correlations between the radionuclides, the sub soil gas contents (i.e. CO2, O2, and radon) and uranium concentration in the pile, provide very interesting information regarding the natural background and the xenon concentration levels and can most likely be used as an upper limit on what to be expected naturally occurring.

The radiological environment following a severe nuclear accident can be visualised on building layouts. The direct radiation in an area (or room) can be visualized on the layout by a colouring scheme depending on the dose rate level (for example orange for high gamma dose rate level and purple for an intermediate gamma dose rate level). Following the Fukushima accident, a need for update of these layouts has been identified at the Swedish nuclear power plant of Forsmark. Shielding calculations for areas where access is desired for severe accident management have been performed. Many different sources of radiation together with different types of shielding material contribute to the dose that would be received by a person entering the area. External radiation from radioactivity within e.g. pipes and components is considered and also external radiation from radioactivity in the air (originating from diffuse leakage of the containment atmosphere). Results are presented as dose rates for relevant dose points together with a method for estimating the dose rate levels for each of the rooms of the reactor building.

The goal of this project is to further Nordic understanding of the potential for Level 3 PSA to determine the influences and impacts of off-site consequences, the effectiveness of off-site emergency response, and the potential contributions of improved upstream Level 1 and Level 2 PSAs. This report summarizes the developments from four years of work, but focuses on the finalization of a Nordic Level 3 PSA Guidance Document which has been worked upon mainly during calendar years 2015 and 2016. Other activities that has been conducted, and provided valuable input to the Guidance Document, are an Industrial Survey, a study of potential Risk Metrics, a summary of Regulations & Standards, and two Pilot Studies (one Swedish and one Finnish). The main objective of the pilot studies was to gain practical experience that, together with insights from the other tasks included in the project, could be transferred to recommendations into a final guidance document. During the project, targeted discussions between consultancies, utilities, regulators, and insurance companies on the subject of Level 3 PSA have taken place and at the end of each years working period a seminar has been arranged. The working group has also been engaged in international activities surrounding Level 3 PSA, i.e. the development of the IAEA Level 3 PSA TECDOC and the ANS/ASME Level 3 PSA Standard through the 2016 continuation of the project. All project reports are provided as appendices to this final report.

A cylindrical plastic scintillator cell, used for radioxenon monitoring within the verification regime of the Comprehensive Nuclear-Test-Ban Treaty, has been coated with 425 nm Al 2 O 3 using low temperature Atomic Layer Deposition, and its performance has been evaluated. The motivation is to reduce the memory effect caused by radioxenon diffusing into the plastic scintillator material during measurements, resulting in an elevated detection limit. Measurements with the coated detector show both energy resolution and efficiency comparable to uncoated detectors, and a memory effect reduction of a factor of 1000. Provided that the quality of the detector is maintained for a longer period of time, Al 2 O 3 coatings are believed to be a viable solution to the memory effect problem in question.

Probabilistic Off-site Consequences Analysis, commonly referred to as Level 3 Probabilistic Safety Assessment (Level 3 PSA), has been infrequently performed and is generally poorly represented in the literature in comparison with Level 1 and Level 2 PSA. Due to new nuclear construction projects and the multi-unit accident at the Fukushima Daiichi site, there is a renewed interest in Level 3 in general and what risk insights that can be gained from Level 3 PSA compared to Level 1 and 2. Based on an inquiry from the Nordic Nuclear Safety Research (NKS) and Nordic PSA Group (NPSAG), a consortium of Swedish nuclear risk consultancies (Lloyd's Register Consulting, ÅF, Risk Pilot and Vattenfall) and the Finnish research institute VTT have performed a multi-year study of Level 3 PSA. The objective of the project has been to further develop understanding within the Nordic countries in the field of Level 3 PSA, the scope of its application, its limitations, appropriate risk metrics, and the overall need and requirements for Level 3 PSA. This paper describes the project and its results. During the project, targeted discussions between consultancies, utilities, regulators, and insurance companies on the subject of Level 3 PSA have taken place. Part of the project has also been to participate in ongoing international activities with the International Atomic Energy Agency (IAEA) and the American Nuclear Society (ANS). Other important parts of the project have been to perform an international industrial survey, a study of appropriate risk metrics, and two pilot studies. The main objective of the pilot studies was to gain practical experience that, together with insights from the other tasks included in the project, could be transferred to recommendations in a final guidance document directed to satisfy the needs for the Nordic nuclear power industry. The first pilot study was made by using IDPSA methodology (Integrated Deterministic and Probabilistic Analysis). In this pilot the atmospheric release from the Fukushima accident was studied using weather conditions typical of Japan. The other pilot was performed using a more traditional approach by studying the potential health effects of a release from a generic Nordic plant site considering atmospheric release below, near and above Level 2 PSA regulatory limits, using source terms for the UK EPR (which are publicly available). The end result of the project is a guidance document that aims to provide clear and applied guidance on Level 3 PSA studies toward regulators, utilities, and practitioners based on the conclusions made over the course of the work. During the course of the project a deeper understanding has been developed within the Nordic countries in the field of Level 3 PSA, the scope of its application, its limitations, appropriate risk metrics, and the overall need and requirements for performing a Level 3 PSA. In the short term this experience will be valuable for increasing quality to Level 1 and 2 PSA (e.g. reduced conservatism). In the longer term, the work will set the foundation for performing state-of-the-art Level 3 PSA.

In this work Al2O3 and SiO2 coatings are tested as Xe diffusion barriers on plastic scintillator substrates. The motivation is improved beta–gamma coincidence detection systems, used to measure atmospheric radioxenon within the verification regime of the Comprehensive Nuclear-Test-Ban Treaty. One major drawback with the current setup of these systems is that the radioxenon tends to diffuse into the plastic scintillator material responsible for the beta detection, resulting in an unwanted memory effect. Here, coatings with thicknesses between 20 and 900 nm have been deposited onto plastic scintillators, and investigated using two different experimental techniques. The results show that all tested coatings reduce the Xe diffusion into the plastic. The reduction is observed to increase with coating thickness for both coating materials. The 425 nm Al2O3 coating is the most successful one, presenting a diffusion reduction of a factor 100, compared to uncoated plastic. In terms of memory effect reduction this coating is thus a viable solution to the problem in question.

Elodea canadensis is a submersed macrophytes, widely distributed in stormwater treatment ponds and able to remove heavy metals from water. This study examines the Cd uptake, translocation, and efflux patterns in Elodea. Several experiments were set up in a climate chamber. To study the root and shoot Cd uptake, living and dead roots and shoots were treated with (109)Cd in one- and two-compartment systems. Furthermore, to examine Cd translocation and distribution, either roots or shoots were treated with (109)Cd. Finally, the efflux of Cd from roots and shoots, respectively, to the external solution was studied after loading whole plants with (109)Cd. Results from the two compartment studies show that Cd is accumulated via direct uptake by both roots and shoots of Elodea. The Cd accumulation proved not to be metabolically dependent in Elodea, and the apoplastic uptake in particular was decreased by Cd pretreatment. In one week, up to 23% of the root uptake was translocated to the shoots, while about 2% of the Cd accumulated by shoots was translocated to the roots. Thus, slight dispersion of Cd is possible, while metal immobilization will not be directly mediated via the Elodea plant. The efflux experiment proved that both shoots of dead plants and roots of living plants had a faster efflux than did shoots of living plants. This information is relevant for an understanding of the fate of Cd in stormwater treatment ponds with Elodea.

We report here about measurements of reaction and decay Q values by precise determination of pairs of atomic masses. These were performed with the Penning trap mass spectrometer SMILETRAP. Measurements with Penning traps give reliable and accurate masses, in particular Q values, due to the fact that certain systematic errors to a great deal cancel in the mass difference between the two atoms defining the Q value. Some Q values that are of fundamental interest will be discussed here, for example, a new Q value for the 6Li (n,γ) 7Li reaction, for the β-decay of tritium, related to properties of the electron neutrino mass, and for the neutrino-less double β-decay of 76Ge, related to the question of whether the neutrino is a Majorana particle or not. In case of the latter two we report the most accurate Q values, namely 18,589.8(12) eV for the tritium decay and 2,038.997(46) keV for the neutrino-less double β-decay of 76Ge.

We report here the atomic masses of 3H and 3He determined by using the Penning trap mass spectrometer Smiletrap. The measurements are based on cyclotron frequency determinations of 3H1+ and 3He1+ using H2+ ions as mass reference. The mass values for 3H and 3He are 3.016 049 278 7(25) u and 3.016 029 321 7(26) u, respectively. From these masses a new Q-value of the tritium β-decay was derived resulting in 18.589 8(12) keV, being the most accurate value at present. The Q-value of the tritium β-decay is related to the possible rest mass of the electron antineutrino.

The Penning trap mass spectrometer SMILETRAP is designed for precision mass measurements using the merits of highly charged ions. In this paper we describe the feature of SMILETRAP and give example ...