Réacteurs hybrides : Avancées récentes pour un démonstrateur

Introduction1 - Principe et intérêt des réacteur hybrides ou "ADS"2 - Le pilotage et le contrôle des AdS3 - Vers un démonstrateur4 - ConclusionÉcole thématiqueLes réacteurs sous-critiques pilotés par accélérateur font l'objet de nombreux programmes de recherche depuis plus d'une dizaine d'années, avec l'ojectif de tester leur faisabilité tant sur le plan du concept que sur celui d'outils dédiés à la transmutation. De nombreux points clés comme l'accélérateur, la cible de spallation, ou la neutronique du milieu sous-critique ont été activement investigués, ce qui permet déjà d'effectuer des choix technologiques et de concevoir dans un premier temps un prototype de faible puissance (quelques dizaines de MWth) à l'échelle européenne. Les programmes dédiés au pilotage des systèmes sous-critiques ont proposé une procédure pour suivre en ligne la réactivité du système qui sera validée dans les années qui viennent. Les travaux sur les accélérateurs permettent d'établir déjà le schéma d'une machine pour un tel système et les travaux sur leur fiabilité se poursuivent. Une cible de spallation avec fenêtre a été mise en oeuvre au PSI et le design d'une cible sans fenêtre est en cours. Tous ces travaux convergent vers le design d'un ADS de démonstration européen l'ETD/XT-ADS qui pourrait être le projet belge MYRRHA

Calibration and monitoring of the GENEPI neutron source for the MUSE IV experiment

Rapport intern

Analytical investigation and experimental application of the source modulation technique to measure ρ/βeff\rho/\beta_{eff}

In recent years great interest has been displayed, worldwide, for Accelerator Driven Sub critical reactors (ADS) to incinerate the minor actinides generated by the existing energy producing reactors. In sub critical systems, the effective neutron multiplication factor is lower than 1.0 and the neutrons otherwise required to maintain the chain reaction, can be put to other uses, in particular, the destruction of nuclear wastes such as minor actinides (MA). One of the major advantages of such ADS systems is that it can be operated with very high M.A content without jeopardizing the overall safety due to a small effective delayed neutron fraction, a small Doppler temperature coefficient and possibly also a large void coefficient depending on the chosen coolant. This enhanced safety however prerequisites at all time a sufficient subcriticality margin. Reliable reactivity monitoring techniques are hence required to achieve this goal. The MUSE-4 program is a series of low power experiments carried out at the CEA-Cadarache MASURCA facility to investigate the various methods leading to the measurement of the reactivity level and associated kinetic parameters such as the effective delayed neutron fraction. The aim of this paper is to present the results obtained with a method which directly gives the ratio, for a sub critical assembly, between the reactivity ρ and the effective delayed neutron fraction βeff. By combining these results to those obtained with the kp-method for the prompt neutron multiplication coefficient, we have access to the parameters which govern the prompt and the slow kinetics of a sub critical assembly. These parameters can be obtained without reference to any calibration measurement in critical configuration. It opens the way to the control of larger sub critical demonstrators which are operating with fuels which cannot be used in critical reactor, and, thanks to sub criticality, which are characterized by a deterministic safety

First results on Martian carbon monoxide from Herschel/HIFI observations

We report on the initial analysis of Herschel/HIFI carbon monoxide (CO) observations of the Martian atmosphere performed between 11 and 16 April 2010. We selected the (7-6) rotational transitions of the isotopes ^{13}CO at 771 GHz and C^{18}O at 768 GHz in order to retrieve the mean vertical profile of temperature and the mean volume mixing ratio of carbon monoxide. The derived temperature profile agrees within less than 5 K with general circulation model (GCM) predictions up to an altitude of 45 km, however, show about 12-15 K lower values at 60 km. The CO mixing ratio was determined as 980 \pm 150 ppm, in agreement with the 900 ppm derived from Herschel/SPIRE observations in November 2009.Comment: Accepted for publication in Astronomy and Astrophysics (special issue on HIFI first results); minor changes to match published versio

Prompt reactivity determination in a subcritical assembly through the response to a Dirac pulse

The full understanding of the kinetics of a subcritical assembly is a key issue for its online reactivity control. Point kinetics is not sufficient to determine the prompt reactivity of a subcritical assembly through the response to a dirac pulse, in particular in the cases of a large reflector, a small reactor, or a large subcriticality.Taking into account the distribution of intergeneration times, which appears as a robust characteristic of each type of reactor, helps to understand this behaviour.Eventually, a method is proposed for the determination of the prompt reactivity. It provides a decrease rate function depending on the prompt multiplication coefficient Keffp. Fitting a measured decrease rate with this function, calculated once for the reactor, gives the true value of keffp. The robustness of the method is tested. (Elsevier

Observation of water vapor in the stratosphere of Jupiter with the Odin Space Telescope.

International audienceThe water vapor line at 557 GHz has been observed with the Odin space telescope with a high signal-to-noise ratio and a high spectral resolution on November 8, 2002. The analysis of this observation as well as a re-analysis of previously published observations obtained with the SubmillimeterWavelength Astronomy Satellite seem to favor a cometary origin (Shoemaker-Levy 9) for water in the stratosphere of Jupiter, in agreement with the ISO observation results. Our model predicts that the water line should become fainter and broader from 2007. The observation of such a temporal variablity would be contradictory with an IDP steady flux, thussupporting the SL9 source hypothesis

Potential of thorium molten salt reactors : detailed calculations and concept evolution with a view to large scale energy production

PAC