Finnish Support Programme to the IAEA Safeguards : Annual Report 2019

SUMMARY Radiation and Nuclear Safety Authority (STUK) coordinates and implements Finnish Support Programme to the IAEA safeguards (FINSP). FINPS is financed by Ministry for Foreign Affairs of Finland (MFA). MFA and STUK have made an agreement for implementation of FINSP for the term of three years 2019 – 2021. For 2019 MFA reserved funding of 149 000€. Actual expenditures of the Programme in 2019 was 141 366,89 €. The results of the FINSP are presented in this report. Main goals of the FINSP are the training of the IAEA inspectors and development of the IAEA safeguards methods and concepts. FINSP had two review meetings with the IAEA in 2019. Annual review meeting was held on 26 April and semi-annual review meeting on 22 October, both in Vienna. The goals of the programme were achieved as planned. At the end of the year 2019 FINSP has 15 active tasks and one stand-by task. Of the active tasks three are practically completed and waiting for administrative decision and/or final report from the IAEA. Two new task proposals were accepted in 2019 and one is pending. Two tasks were completed during 2019

Report of STUK Activities in FINSP, IPNDV and GICNT Initiatives in 2021

1 Finnish expertise for a safer world The Treaty on the Non-Proliferation of Nuclear Weapons (NPT) entered into force in Finland in 1970. For fifty years, the treaty has been a key prerequisite for the peaceful use of nuclear energy in Finland, a country that, as a user of nuclear energy, has had solid grounds for preventing the proliferation of nuclear weapons. The Ministry for Foreign Affairs of Finland (MFA) is financing the projects which are related to the non-proliferation, nuclear security and disarmament. The Radiation and Nuclear Safety Authority (STUK) has the technical expertise to offer for the projects. The good cooperation between MFA and STUK deepen the common understanding between the political and technical fields and enable Finland to have the best possible knowledge in international negotiations. Finnish Support Programme to the IAEA safeguards (FINSP) STUK coordinates and implements the Finnish Support Programme to the IAEA safeguards (FINSP). The objective of FINSP is to provide the IAEA support in well managed tasks related to development of safeguards verification methods and safeguards concepts, assisting safeguards implementation in the Member States and provide opportunities and support to the IAEA inspector training. Global Initiative to Combat Nuclear Terrorism (GICNT) Finland coordinated a development of a Joint Statement on National Nuclear Detection Architecture to the 2016 Nuclear Security Summit. This has and will continue to be an important document steering Finland’s contribution to the international nuclear security detection activities. This has enabled an active involvement of STUK experts in both the IAEA and GICNT nuclear security detection activities. International Partnership for Nuclear Disarmament Verification (IPNDV) IPNDV, established by the USA in 2014, is currently on its third phase. Third phase started in the beginning of 2020. The coronavirus pandemic has significantly hampered the implementation of ongoing phase. STUK acts as technical advisor to the MFA on International Partnership for Nuclear Disarmament Verification. This has enabled STUK experts to participate actively in the project since its beginning

In-air and in-water performance comparison of Passive Gamma Emission Tomography with activated Co-60 rods

Abstract A first-of-a-kind geological repository for spent nuclear fuel is being built in Finland and will soon start operations. To make sure all nuclear material stays in peaceful use, the fuel is measured with two complementary non-destructive methods to verify the integrity and the fissile content of the fuel prior to disposal. For pin-wise identification of active fuel material, a Passive Gamma Emission Tomography (PGET) device is used. Gamma radiation emitted by the fuel is assayed from 360 angles around the assembly with highly collimated CdZnTe detectors, and a 2D cross-sectional image is reconstructed from the data. At the encapsulation plant in Finland, there will be the possibility to measure in air. Since the performance of the method has only been studied in water, measurements with mock-up fuel were conducted at the Atominstitut in Vienna, Austria. Four different arrangements of activated Co-60 rods, steel rods and empty positions were investigated both in air and in water to confirm the functionality of the method. The measurement medium was not observed to affect the ability of the method to distinguish modified rod positions from filled rod positions. More extended conclusions about the method performance with real spent nuclear fuel cannot be drawn from the mock-up studies, since the gamma energies, activities, material attenuations and assembly dimensions are different, but full-scale measurements with spent nuclear fuel are planned for 2023

Improved Passive Gamma Emission Tomography image quality in the central region of spent nuclear fuel

Reliable non-destructive methods for verifying spent nuclear fuel are essential to draw credible nuclear safeguards conclusions from spent fuel. In Finland, spent fuel items are verified prior to the soon starting disposal in a geological repository with Passive Gamma Emission Tomography (PGET), a uniquely accurate method capable of rod-level detection of missing active material. The PGET device consists of two highly collimated detector banks, collecting gamma emission data from a 360 degrees rotation around a fuel assembly. 2D cross-sectional activity and attenuation images are simultaneously computed. We present methods for improving reconstructed image quality in the central parts of the fuel. The results are based on data collected from 2017 to 2021 at the Finnish nuclear power plants with 10 fuel assembly types of varying characteristics, for example burnups from 5.7 to 55 GWd/tU and cooling times from 1.9 to 37 years. Data is acquired in different gamma energy windows, capturing the peaks of Cs-137 (at 662 keV) and Eu-154 (at 1274 keV), abundant isotopes in long-cooled spent nuclear fuel. Data from these gamma energy windows at well-chosen angles are used for higher-quality images, resulting in more accurate detection of empty rod positions. The method is shown to detect partial diversion of nuclear material also in the axial direction, demonstrated with a novel measurement series scanning over the edge of partial-length rods.Peer reviewe

Measuring spent fuel assembly multiplication in borated water with a passive neutron albedo reactivity instrument

Abstract The performance of a passive neutron albedo reactivity (PNAR) instrument to measure neutron multiplication of spent nuclear fuel in borated water is investigated as part of an integrated non-destructive assay safeguards system. To measure the PNAR Ratio, which is proportional to the neutron multiplication, the total neutron count rate is measured in high- and low-multiplying environments by the PNAR instrument. The integrated system also contains a load cell and a passive gamma emission tomograph, and as such meets all the recommendations of the IAEA’s recent ASTOR Experts Group report. A virtual spent fuel library for VVER-440 fuel was used in conjunction with MCNP simulations of the PNAR instrument to estimate the measurement uncertainties from (1) variation in the water boron content, (2) assembly positioning in the detector and (3) counting statistics. The estimated aggregate measurement uncertainty on the PNAR Ratio measurement is 0.008, to put this uncertainty in context, the difference in the PNAR Ratio between a fully irradiated assembly and this same assembly when fissile isotopes only absorb neutrons, but do not emit neutrons, is 0.106, a 13-sigma effect. The 1-sigma variation of 0.008 in the PNAR Ratio is estimated to correspond to a 3.2 GWd/tU change in assembly burnup.Peer reviewe

Effect of Gamma-Ray Energy on Image Quality in Passive Gamma Emission Tomography of Spent Nuclear Fuel

Gamma-ray images of VVER-440 and SVEA-96 spent nuclear fuel assemblies were reconstructed using the filtered backprojection algorithm from measurements with a passive gamma emission tomography prototype instrument at Finnish nuclear power plants. Image quality evaluation criteria based on line profiles through the reconstructed image are used to evaluate image quality for spent fuel assemblies with different cooling times, and thus different mixtures of gamma-ray emitting isotopes. Image characteristics at the locations of water channels and central fuel pins are compared in two gamma-ray energy windows, 600-700 and >700keV, for cooling times up to 10 years for SVEA-96 fuel and 24.5 years for VVER-440 fuel. For SVEA-96 fuel, images in the >700-keV gamma-ray energy window present better water-to-fuel contrast for all investigated cooling times. For VVER-440, images in the >700-keV gamma-ray energy window have higher water-to-fuel contrast up to and including a cooling time of 18.5 years, whereas the water-to-fuel contrast of the images taken in the two gamma-ray energy windows is equivalent for a cooling time of 24.5 years. Images reconstructed from higher energy gamma rays such as those in the >700-keV energy window present better water-to-fuel contrast in fuel cooled for up to 20 years and thus have the most potential for missing fuel pin detection.Peer reviewe

Newcomer States and Finnish Safeguards Support Programme to the IAEA

IAEA safeguards is struggling with a financial challenge: regular budget is stagnating while new member states plan to include nuclear energy in their energy mix. These states are called “the newcomer states”. To solve this problem IAEA has initiated an ambitious program to raise awareness about non-proliferation regime and producing and publishing guidance oriented to the professionals in the newcomer states. Finnish Support Programme to the IAEA safeguards (FINSP) supports this mission in two ways. Firstly, FINSP is planning and hosting, together with the IAEA, so called 3S courses to the newcomer states. These courses provide practical level information on the most important aspects needed when a state is taking its steps towards application of nuclear energy. Special emphasis is on operator-regulator interface and implementation of safety, security safeguards, emergency preparedness and public relations. Both the Finnish regulator and the operators have participated in arranging the courses in cooperation. The goal has been to provide a comprehensive view on what is required to run a successful nuclear energy program. So far, two courses have been arranged in Finland, the first in 2012 and the second on 2014. Secondly, FINSP has actively contributed to the development of Safeguards implementation Guides. In 2016 FINSP will participate the outreach activities, which will be organized by the IAEA to make these newly published guides better known in member states

Passive neutron albedo reactivity measurements of spent nuclear fuel

The upcoming disposal of spent nuclear fuel in Finland creates new challenges for nuclear safeguards. Part of the national safeguards concept for geological repositories, developed by STUK — Radiation and Nuclear Safety Authority, is non-destructive assay (NDA) verification of all fuel items before disposal. The proposed verification system is a combination of PGET (Passive Gamma Emission Tomography), PNAR (Passive Neutron Albedo Reactivity) and weight measuring NDA-instruments. PGET takes a pin-level image of the fission products inside of a fuel assembly and PNAR verifies the multiplication of the assembly, a quantity that correlates with the fissile content. PGET is approved by IAEA (International Atomic Energy Agency) for safeguards measurements, but the feasibility of PNAR has not yet been established. A first of its kind PNAR prototype instrument was built in a collaboration coordinated by STUK. This paper concludes the results of the first measurements of spent BWR (Boiling Water Reactor) nuclear fuel with the prototype in July 2019. Based on the measurements, the ability of the PNAR instrument to detect the presence of fissile material in a repeatable manner in a reasonable amount of time was demonstrated. Furthermore, the instrument was able to detect differences in multiplication between partially and fully spent fuel assemblies, and axial differences in multiplication within a single assembly.Peer reviewe

The World’s First Spent Fuel Repository : How to tackle safety, security and safeguards needs?

How to dispose of spent nuclear fuel safely and permanently? This is one of the fundamental questions related to the use of nuclear energy, that has been waiting for an answer since criticality of the first commercial reactors some sixty years ago. Also, in Finland, discussion on the question of nuclear waste was on the public agenda already when the first reactor was commissioned in the late 1970s and nuclear waste management policy and strategy were actively developed on the national level. In 1978, the Finnish Government decided that each producer of nuclear waste is responsible for the management of spent nuclear fuel. This decision was the beginning of a long process, the result of which is the world’s first spent spent nuclear fuel repository Onkalo, where the final disposal of spent nuclear fuel inside the Finnish bedrock is expected to start in 2025. This paper describes from the regulatory perspective how Finland changed the game and how Finland is developing a safe1 and sustainable solution for disposal of spent nuclear fuel. It will explain how this became politically acceptable, how the long-term safety of the solution is being demonstrated and how regulatory challenges related to safety, security and safeguards are being resolved in this first-of-its-kind facility. In broad terms, it will illustrate how the progress in geological disposal has been made possible in Finland and further highlight topical issues that are of interest to professionals and policymakers. The first chapter is focused on public acceptance and development of nuclear waste management policy and strategy in Finland. The second chapter explains how the long-term safety of the final repository has been handled and what the supporting technical solutions are. In the third and final chapter, an overview of safeguards of the disposal process is provided. Safeguards, a prerequisite for peaceful use of nuclear energy, is a topic of utmost importance also in the last leg of the nuclear fuel cycle. The scope of this short paper is rather limited and far from complete, but hopefully it manages to pass on certain lessons: responsible decision-making and a long-term political commitment to the chosen method, together with the research and development of the technical solution and enabling regulatory framework, are the keys for accomplishing the difficult task of disposing of spent nuclear fuel safely and permanently