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Castelliti D.,Center Detude Of Lenergie Nucleaire Sck Cen | Castelliti D.,University of Genoa | Lomonaco G.,University of Genoa | Lomonaco G.,National Institute of Nuclear Physics, Italy
Nuclear Engineering and Design | Year: 2016

The MYRRHA (Multi-purpose hYbrid Research Reactor for High-tech Applications) project, started at SCK·CEN since 1999, aims at the construction of a pool-type sub-critical Accelerator-Driven System (ADS) which could also operate as a critical reactor. The primary system, enclosed in the primary vessel, is filled with Lead Bismuth Eutectic (LBE) which acts as primary coolant. The power is then delivered through four heat exchangers to four secondary loops. The secondary cooling fluid is two-phase water operating at relatively low pressure (16 bar). Four aero-condensers act as heat sinks, since MYRRHA design does not foresee any electricity generation. The MYRRHA Primary Heat eXchangers (PHXs) cover a role of fundamental importance in normal operation and accidental conditions, being part of the primary and secondary cooling system and of the Decay Heat Removal (DHR) system. It is thus highly relevant to understand the PHXs behavior under all the potential working conditions. In particular, the stability of the PHXs must be guaranteed under all operating conditions. System code models play an important role in understanding and predicting the behavior of the reactor in all conditions, from steady state to operational and accidental transients, and simulating all the postulated scenarios. A solid PHX design requires a complete assessment of two-phase flow instabilities in the secondary system water tube bundle and the potential implementation of a suitable stabilizing device (orifice) to reduce the impact of the perturbations along the channel. The stability assessment should take in consideration all the possible reactor operational power levels in order to prove the stable behavior under all operational conditions. The tube bundle stability assessment has been carried out by following a similar procedure used for BWR fuel channels, through a specific RELAP5-3D model representing the PHX and able to evaluate the propagation of a density wave in the tube length. A series of suitable boundary conditions, on both primary and secondary side, and perturbation triggers have been foreseen into the model, so to discover all kind of unstable behavior and to dimension the needed orifice to guarantee the flow stability in all operating conditions. The PHX stability analysis is initially performed on the original tube bundle without the adoption of any stabilizing devices, in order to check the natural behavior of the system. The possible adoption and design of an orifice is then conducted on the basis of this preliminary study. The system response against the various types of instabilities, before the introduction of an orifice, is not completely satisfactory: a stable flow is found within certain specific system parameters ranges. After the introduction of a suitable orifice, the system behavior becomes stable under all operating conditions against all types of two-phase flow instabilities. © 2016 Elsevier B.V. All rights reserved. Source

Urso L.,Helmholtz Center Munich | Astrup P.,Technical University of Denmark | Helle K.B.,University of Munster | Raskob W.,Karlsruhe Institute of Technology | And 2 more authors.
Environmental Modelling and Software | Year: 2012

Networks of monitoring stations have been set up in many European countries to detect the passage of a radioactive cloud in the event of a large-scale nuclear emergency. The layout and spatial density of these networks differs according to the needs and criteria defined by national authorities. Germany and the Netherlands decided to set up relatively dense networks for the detection of weak radioactive plumes and, additionally, environmental radioactivity from deposited aerosols. Plausible evaluation criteria are presented here to assess important properties which determine the reliability and efficiency of sections of these networks. As a test case the existing sampling design of the Dutch and German networks with 193 sensors in an area of 200 km around the nuclear power plant near the city of Lingen (Emsland) in the German federal state of Lower Saxony has been selected. For a hypothetical accident scenario 292 radioactive plumes have been simulated which are shaped by recorded weather conditions of the year 2007. To quantify the network performance frequency distributions of the proposed evaluation parameters have been analyzed. Simulation results show that 95% of the plumes are detected within 4 h after the release. Maximal values of the γ-dose rate 1 m above the ground mostly occur near the source within a radius of 5 km. However, under certain weather conditions maximal ground values may also be found more than 50 km away from the source. Within a circle of radius 90 km 98% of the recorded maximal γ-dose rates of the plumes were found by 62% of the 193 sensors. But only in a joint network of German and Dutch sensors all simulated plumes triggered an alarm. This result encourages efforts of close international collaboration, e.g. between EU member states, in network design and operation. Test series which involved the removal of sensors either randomly or in a controlled way showed that the network configuration is fit for the intended purpose of detecting a large majority of plumes. But already a small reduction in the number of sensors would degrade the performance. Whereas the joint network triggers alarms reliably, it fails to detect the true plume maxima. The assessment criteria can be used for a revision of existing networks or for planning purposes in countries such as those applying for EU membership. © 2012 Elsevier Ltd. Source

Konstantinovic M.J.,Center Detude Of Lenergie Nucleaire Sck Cen | Minov B.,Center Detude Of Lenergie Nucleaire Sck Cen | Minov B.,Ghent University
Journal of Nuclear Materials | Year: 2012

In spite of general understanding of the copper precipitation in neutron irradiated Cu-rich alloys, the role of carbon in the precipitation process as well as in the formation of other defects under neutron irradiation, and their overall effect to the dislocation dynamics, are not yet fully elucidated. The mechanical tests are performed in neutron irradiated Fe, Fe-0.1%Cu and Fe-0.3%Cu alloys at three different temperatures, and the results of the yield stress are compared with the internal friction measurements. It is found that the copper precipitation, governed by the neutron irradiation, causes the appearance of carbon redistribution. From the comparison of the yield stress changes at different temperatures and dose, the carbon contribution to the hardening is estimated. © 2011 Elsevier B.V. All rights reserved. Source

Dijulio D.D.,Lund University | Cederkall J.,Lund University | Fahlander C.,Lund University | Ekstrom A.,University of Oslo | And 32 more authors.
European Physical Journal A | Year: 2012

The radioactive isotope 107Sn was studied using Coulomb excitation at the REX-ISOLDE facility at CERN. This is the lightest odd-Sn nucleus examined using this technique. The reduced transition probability of the lowest-lying 3/2+ state was measured and is compared to shell-model predictions based on several sets of single-neutron energies relative to 100Sn. Similar to the transition probabilities for the 2+ states in the neutron-deficient even-even Sn nuclei, the measured value is underestimated by shell- model calculations. Part of the strength may be recovered by considering the ordering of the d5/2 and g7/2 single-neutron states. © The Author(s) 2012. Source

Uyttenhove W.,Center Detude Of Lenergie Nucleaire Sck Cen | Sobolev V.,Center Detude Of Lenergie Nucleaire Sck Cen | Maschek W.,Karlsruhe Institute of Technology
Journal of Nuclear Materials | Year: 2011

A potential option for neutralization of minor actinides (MA) accumulated in spent nuclear fuel of light water reactors (LWRs) is their transmutation in dedicated accelerator-driven systems (ADS). A promising fuel candidate dedicated to MA transmutation is a CERMET composite with Mo metal matrix and (Pu, Np, Am, Cm)O2-x fuel particles. Results of optimisation studies of the CERMET fuel targeting to increasing the MA transmutation efficiency of the EFIT (European Facility for Industrial Transmutation) core are presented. In the adopted strategy of MA burning the plutonium (Pu) balance of the core is minimized, allowing a reduction in the reactivity swing and the peak power form-factor deviation and an extension of the cycle duration. The MA/Pu ratio is used as a variable for the fuel optimisation studies. The efficiency of MA transmutation is close to the foreseen theoretical value of 42 kg TW -1 h-1 when level of Pu in the actinide mixture is about 40 wt.%. The obtained results are compared with the reference case of the EFIT core loaded with the composite CERCER fuel, where fuel particles are incorporated in a ceramic magnesia matrix. The results of this study offer additional information for the EFIT fuel selection. © 2010 Elsevier B.V. All rights reserved. Source

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