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The Jules Horowitz Reactor (JHR) is designed to be the 100 MW Material Testing Reactor (MTR) which achieves the most important experimental capacity in Europe. It has been conceived to perform several irradiation tests at a time – taking advantage of many positions both in the core and in the reflector. The locations inside the reflector zone may utilize an intense thermal neutron flux to test the properties of fuel materials and to produce radioisotopes for medical purposes. High sample irradiation rates are achieved in the reflector area and a relevant power can be generated here, due to fissile materials inside these fuel test samples: about 60 kW for ADELINE test devices, some 120 kW for MADISON and up to about 650 kW for MOLFI. Then, power transient analyses are requested for these devices, mainly in connection with the reactor shutdowns. Energy deposition in the fuel samples – which are placed in the reflector – has been evaluated considering both normal operation and different reactor shutdown procedures. The analysis has been carried out by dividing the reactor system into two portions: the core as a neutron source and the reflector as a subcritical system. First, core power transients have been simulated by means of DULCINEE point kinetics code. Then, the neutron flux inside the reflector has been evaluated through the Monte Carlo transport code TRIPOLI 4.8, starting from the previously computed source. Both nominal operation and different configurations of control rod insertions have been taken into account. This evaluation provided a description of core-device coupling in terms of flux shape in the reflector. Main focus is on power deposition in samples which is of course affected by flux shape. Thus, point kinetics approach has been applied to the core as a source irradiating the samples that are considered coupled through the parameters evaluated by Monte Carlo. Power transients have been calculated both for energy deposition due to neutron-induced fission reactions and for gamma radiation as well. Results matched technical needs for the cooling loops optimization and the safety scenarios. [ABSTRACT FROM AUTHOR]

Abstract: A preliminary study concerning the responses of a Generation IV (GEN-IV) Lead Fast Reactor (LFR) demonstrator (DEMO) core to externally-induced reactivity perturbations has been carried out with the aim at assessing and comparing the dynamic performances of MOX and metallic fuel alternative options. Reactivity coefficients and kinetics parameters have been calculated for both Beginning of Cycle (BoC) and End of Cycle (EoC) configurations by means of ERANOS deterministic code ver. 2.1 associated with the JEFF-3.1 data library. A simplified lumped-parameter model has been developed to treat both neutronics (point-kinetics approximation) and thermal-hydraulics (average temperature heat-exchange model); the latter have been then coupled to analyze MOX and metallic fuel behaviors following operational transient initiators, such as control rod partial extraction (reactivity insertion), coolant inlet temperature perturbation (simulating a loss of heat sink), and mass flow rate reduction (loss of flow), using the MATLAB/SIMULINK® tool. The analysis of DEMO core sub-system open-loop stability has ultimately been performed. Results have shown that the model is stable and evidences a satisfactory capability of predicting the response to the reactivity perturbations considered. [Copyright &y& Elsevier]

Abstract: Plutonium recycling in new-generation fast reactors coupled with minor actinides (MA) transmutation in dedicated nuclear systems could achieve a decrease of nuclear waste long-term radiotoxicity by two orders of magnitude in comparison with current once-through strategy. In a double-strata scenario, purpose-built accelerator-driven systems (ADS) could transmute minor actinides. The innovative nuclear fuel conceived for such systems demands significant R&D efforts in order to meet the safety and technical performance of current fuel systems. The Integrated Project EUROTRANS (EUROpean research programme for the TRANSmutation of high level nuclear waste in ADS), part of the EURATOM Framework Programme 6 (FP6), undertook some of this research. EUROTRANS developed from the FP5 research programmes on ADS (PDS-XADS) and on fuels dedicated to MA transmutation (FUTURE, CONFIRM). One of its main objectives is the conceptual design of a small sub-critical nuclear system loaded with uranium-free fuel to provide high MA transmutation efficiency. These principles guided the design of EFIT (European Facility for Industrial Transmutation) in the domain DESIGN of IP EUROTRANS. The domain AFTRA (Advanced Fuels for TRAnsmutation system) identified two composite fuel systems: a ceramic–ceramic (CERCER) where fuel particles are dispersed in a magnesia matrix, and a ceramic–metallic (CERMET) with a molybdenum matrix in the place of MgO matrix to host a ceramic fissile phase. The EFIT fuel is composed of plutonium and MA oxides in solid solution with isotopic vectors typical of LWR spent fuel with 45MWd/kgHM discharge burnup and 30years interim storage before reprocessing. This paper is focused on the thermomechanical state of the hottest fuel pins of two EFIT cores of 400MW(th) loaded with either CERCER or CERMET fuels. For calculations three fuel performance codes were used: FEMALE, TRAFIC and TRANSURANUS. The analysis was performed at the beginning of fuel life. Presented results were used for testing newly-developed models installed in the TRANSURANUS code to deal with such innovative fuels and T91 steel cladding. Agreement among codes predictions was satisfactory for fuel and cladding temperatures, pellet-cladding gap and mechanical stresses. [Copyright &y& Elsevier]