[en] The production of transuranic actinide fuels for use in current thermal reactors provides a useful intermediary step in closing the nuclear fuel cycle. Extraction of actinides reduces the longevity, radiation and heat loads of spent material. The burning of transuranic fuels in current reactors for a limited amount of cycles reduces the infrastructure demand for fast reactors and provides an effective synergy that can result in a reduction of as much as 95% of spent fuel waste while reducing the fast reactor infrastructure needed by a factor of almost 13.5 [1]. This paper examines the features of actinide mixed oxide fuel, TRUMOX, in a CANDU^R* nuclear reactor. The actinide concentrations used were based on extraction from 30 year cooled spent fuel and mixed with natural uranium in 3.1 wt% actinide MOX fuel. Full lattice cell modeling was performed using the WIMS-AECL code, super-cell calculations were analyzed in DRAGON and full core analysis was executed in the RFSP 2-group diffusion code. A time-average full core model was produced and analyzed for reactor coefficients, reactivity device worth and online fuelling impacts. The standard CANDU operational limits were maintained throughout operations. The TRUMOX fuel design achieved a burnup of 27.36 MWd/kg HE. A full TRUMOX fuelled CANDU was shown to operate within acceptable limits and provided a viable intermediary step for burning actinides. The recycling, reprocessing and reuse of spent fuels produces a much more sustainable and efficient nuclear fuel cycle. (authors)

[en] Core debris retention in the reactor vessel (in-vessel retention) is an important area of research in the field of nuclear power reactor severe accident analysis. The understanding of the behaviour of molten corium, prediction of crust formation in-vessel, and the evaluation of vessel integrity are essential to determining the progression and consequences of a severe accident. In CANDU severe accident analysis, the modelling of corium behaviour and assessment of severe accident progression is performed with the MAAP-CANDU code. The corium behaviour models in the MAAP-CANDU code are assessed and improved through benchmarking exercises which simulate experiments. In this paper, MAAP-CANDU is benchmarked against data obtained from the LIVE (late in-vessel experiments) tests (LIVE-L1 and LIVE-L3), conducted at Forschungszentrum Karlsruhe (now Karlsruhe Institute of Technology) in Germany. The tests involved crust formation within an externally cooled vessel using a corium simulant. This is similar to the late phase of a CANDU severe accident where molten core debris is located at the bottom of the calandria vessel that is surrounded by a water-filled reactor vault or shield tank. A modified version of the MAAP-CANDU code (v4.0.7E) that includes capabilities to model the LIVE tests was used for this assessment. The post-test calculations of the LIVE-L1 and LIVE-L3 tests using MAAP-CANDU were compared with the experimental data (including corium temperature, through-wall heat flux, and crust thickness and temperature). Sensitivity analysis demonstrated that variations in corium properties and heat transfer coefficients can affect calculated melt temperature and crust thickness. The calculations generally agree with the data in most respects, providing some assurance that the various models in MAAP-CANDU used in the simulation of the late phase of CANDU severe accidents are adequate. (author)

[en] The Organisation for Economic Co-operation and Development (OECD)/Nuclear Energy Agency (NEA) Benchmark Study of the Accident at the Fukushima Daiichi Nuclear Power Station (BSAF), which started in 2012 and continued until 2018, was one of the earliest responses to the accident at Fukushima Daiichi. The project, divided into two phases, addressed the investigation of the accident at Units 1, 2, and 3 by severe accident (SA) codes until 500 h, focusing on thermal hydraulics, core relocation, molten corium concrete interaction (MCCI), and fission product release and transport. The objectives of the BSAF were to make up plausible scenarios based primarily on SA forensic analysis, support the decommissioning, and inform SA code modeling. The analysis and comparison among the institutes have brought up vital insights regarding the accident progression, identifying periods of core meltdown and relocation and reactor pressure vessel (RPV) and primary containment vessel (PCV) leakage/failure through the comparison of pressure, water level, and containment atmosphere monitoring system (CAMS) signatures. The combination of code results and inspections (muon radiography, PCV inspection) has provided a picture of the current status of the debris distribution and plant status. All units present a large relocation of core materials and all of them present ex-vessel debris with Unit 1 and Unit 3 showing evidence of undergoing MCCI. Uncertainties have been identified, in particular on the time and magnitude of events such as corium relocation in the RPV and into the cavity floor and RPV and PCV rupture events. Main uncertainties resulting from the project are the large and continuous MCCI progression predicted by basically all the SA codes and the leak pathways from the RPV to the PCV and the PCV to the reactor building and environment. The BSAF project represents a pioneering exercise that has set the basis and provided lessons learned not only for code improvement but also for the development of new related projects to investigate in detail further aspects of the Fukushima Daiichi accident. (authors)

[en] Understanding the accident at the Fukushima Daiichi Nuclear Power Plant is important for safe and timely decommissioning of the reactors. This objective, together with the development of better computer codes for analysis of severe accidents, was the aim of the benchmark study conducted under the auspices of the OECD Nuclear Energy Agency. Through the diversity of the modelling codes and approaches, and the use of parametric studies, it has been possible to identify the more likely scenarios that can fit with the limited data available from the accident. The insights gained from the project will help guide research into severe accident behaviour, improve severe accident computer codes, develop accident mitigation and response at nuclear power plants, support regulatory oversight related to severe accidents, and inform policies on the development and deployment of nuclear technology

[en] A detailed study of several Micromegas detectors prototyped for the COMPASS and CLAS12 experiments is presented. Using a 150 GeV/c pion beam, the discharge probability was measured for several detector variants including bulk and non-bulk Micromegas. A detector equipped with an additional GEM foil as pre-amplification stage was also tested. A resistive coating of the readout strips was found to reduce the amplitude of the discharge by at least two orders of magnitude which was below the detection limit of the experimental setup. The effects of the micro-mesh type and material were investigated as well as the influence of the drift gap. Response in the presence of a 1.5 T transverse magnetic field was also studied. The measurements presented were performed during a RD51 beam test period.

[en] Large samples of Λ, Σ(1385) and Ξ(1321) hyperons produced in the deep-inelastic muon scattering off a ⁶LiD target were collected with the COMPASS experimental setup at CERN. The relative yields of Σ(1385)⁺, Σ(1385)^-, anti Σ(1385)^-, anti Σ(1385)⁺, Ξ(1321)^-, and anti Ξ(1321)⁺ hyperons decaying into Λ(anti Λ)π were measured. The ratios of heavy-hyperon to Λ and heavy-antihyperon to anti Λ were found to be in the range 3.8 % to 5.6 % with a relative uncertainty of about 10 %. They were used to tune the parameters relevant for strange particle production of the LEPTO Monte Carlo generator. (orig.)

[en] Multiplicities of charged hadrons produced in deep inelastic muon scattering off a ⁶LiD target have been measured as a function of the DIS variables x_Bj, Q², W² and the final state hadron variables p_T and z. The p_T² distributions are fitted with a single exponential function at low values of p_T² to determine the dependence of left angle p_T² right angle on x_Bj, Q², W² and z. The z-dependence of left angle p_T² right angle is shown to be a potential tool to extract the average intrinsic transverse momentum squared of partons, left angle k _{perpendicularto}² right angle, as a function of x_Bj and Q² in a leading order QCD parton model. (orig.)