978-1-4244-5208-8/09/$26.00 ©2009 IEEE Abstract—In the framework of nuclear waste management, minor actinides could be incinerated in subcritical reactors driven by an accelerator coupled to a spallation target. For safety reason, this so-called Accelerator-Driven System (ADS) requires on-line and robust core reactivity monitoring. In such a system, a simple proportional relationship exists between the reactivity and the ratio of the beam current to the thermal power of the reactor core. This relationship is planned to be exploited as a relative reactivity indicator by the measurement of both the beam current delivered by the accelerator and the core neutron flux. The GUINEVERE experiment facility, which is being built at SCK- CEN in Mol (Belgium), will be devoted to the study of such reactivity measurement techniques. This zero power experiment will consist of the coupling of a subcritical fast core to an external source of 14-MeV neutrons originating from fusion reactions between a deuteron beam and a tritium target. In this case, the target evolution over time and target inhomogeneities preclude from using the beam current for reliable reactivity monitoring and therefore the external neutron source intensity must be monitored directly. This paper presents the systems envisioned to achieve such a monitoring and the results of test experiments. Index Terms—Fission reactor control and monitoring, Diamond, Neutron detectors, Radiation effects. Manuscript received May 19, 2009. This work was supported in part by the 6 th Framework Program of the European Commission (EURATOM) through the EUROTRANS Integrated Project contract # FI6W-CT-2005- 516520, and the French PACEN program of CNRS. J.L. Lecouey (corresponding author, phone: +33 (0)2 31 45 29 65; e-mail: lecouey@lpccaen.in2p3.fr), G. Ban, J.M. Fontbonne, F.R. Lecolley, J.F. Lecolley, N. Marie and J.C. Steckmeyer are with LPC Caen, ENSICAEN, Université de Caen, CNRS/IN2P3, 6 Bd. Maréchal Juin 14050 Caen cedex, France. P. Bergonzo, C. Mer, M. Pomorski and D. Tromson are with CEA-LIST (Recherche Technologique), CEA-Saclay, 91191 Gif sur Yvette, France. A. Billebaud, R. Brissot, S. Chabod, C. Le Brun, E. Liatard, A. Nuttin and H.E. Thyébault are with LPSC, CNRS-IN2P3/UJF/INPG, 53 Avenue des Martyrs. 38026 Grenoble cedex, France. P. Dessagne and M. Kerveno are with IPHC, CNRS/IN2P3/UdS, 23 rue du Loess, 67200 Strasbourg. I. THE GUINEVERE PROJECT N the framework of nuclear waste management, highly radiotoxic minor actinides could be incinerated in subcritical reactors driven by an intense external neutron source provided by an intense high-energy proton beam accelerator coupled to a high atomic number spallation target. For safety reason, this so-called Accelerator-Driven System (ADS) requires on-line and robust core reactivity monitoring. The effective reactivity ρ eff of a sub-critical assembly is given by the following expression [1]: th eff P S C = − ρ (1) Where P th is the power released (or neutron flux) in the reactor core, and S is the number of external source neutrons created per second. The quantity C can be considered a constant. The external source intensity S can be related to the current of the proton beam delivered by the accelerator: p / s N e I S = (2) Where I denotes the beam current, e the elementary charge, and N s/p the number of spallation neutrons created per proton (also assumed to be a constant). Along with other techniques, relationships (1) and (2) could give constant access to a good first order evaluation of any core reactivity change by means of the simple measurements of I and P th . The GUINEVERE (Generator of Uninterrupted Intense Neutrons at the lead Venus Reactor) experiment facility (Fig. 1), which is being built at SCK•CEN in Mol (Belgium), will be partly devoted to the study of such reactivity measurement techniques. This zero power experiment will consist of the coupling of a lead moderated subcritical fast core to an external source of fast (≈14-MeV) neutrons originating from fusion reactions between deuterons and a tritium target located at the center of the reactor core. The deuteron beam will be delivered by GENEPI-3C, an accelerator which will be able to operate either in continuous or in pulsed mode [2]. A bending Monitoring Fast Neutron Sources for Accelerator Driven Subcritical Reactor Experiments Jean-Luc Lecouey, Gilles Ban, Philippe Bergonzo, Annick Billebaud, Roger Brissot, Sébastien Chabod, Philippe Dessagne, Jean-Marc Fontbonne, Maëlle Kerveno, Christian Le Brun, François- René Lecolley, Jean-François Lecolley, Eric Liatard, Nathalie Marie, Christine Mer, Alexis Nuttin, Michal Pomorski, Jean-Claude Steckmeyer, Henry-Emmanuel Thyébault and Dominique Tromson I