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The renewed interest for the study of nuclear fission is mainly motivated by the development of GEN-IV reactor concepts, mostly foreseen to operate in the fast neutron energy domain. To support this development, new high-quality nuclear data are needed. In this context, a new experimental setup, the FALSTAFF spectrometer, dedicated to the study of nuclear fission is under development. Employing the double-velocity (2V) and energy-velocity (EV) methods, the fission fragment mass before and after neutron evaporation will be deduced and the correlation between prompt neutron multiplicity and fragment mass will be determined. The first arm of the spectrometer is achieved. It is composed of two SED-MWPC detectors (a combination of a foil to produce secondary electrons and a Multi-Wire Proportional Chamber to detect them) and an axial ionization chamber. The SED-MWPC give access to the velocity (V) via time-of-flight and position measurements. The ionization chamber measures the fragment kinetic energy (E) and the energy loss profile. Preliminary results for spontaneous fission of 252Cf and from the thermal-neutron induced fission experiment on 235U, performed at the Orphée reactor (CEA-Saclay, France), are presented. [ABSTRACT FROM AUTHOR]

The study of nuclear fission is encountering renewed interest with the development of GEN-IV reactor concepts, mostly working in the neutron fast energy domain. To support the fast reactor technologies, new high quality nuclear data are needed. New facilities are being constructed to produce high intensity neutron beams from hundreds of keV to few tens of MeV (Licorne, NFS, nELBE,...). They will open new opportunities to provide nuclear data. In this framework the development of an experimental setup called FALSTAFF for a characterisation of actinide fission fragments has been undertaken. Fission fragment yields and associated neutron multiplicities will be measured as a function of the neutron energy. Based on time-of-flight and residual energy technique, the setup will allow the simultaneous measurement of the complementary fragment velocity and energy. The FALSTAFF setup and the upgrade of the first arm prototype with the new ionisation chamber CALIBER will be presented. The performances of the experimental apparatus is discussed. [ABSTRACT FROM AUTHOR]

In the past years, the fission studies have been mainly focused on thermal fission because most of the current nuclear reactors work in this energy domain. With the development of GEN-IV reactor concepts, mainly working in the fast energy domain, new nuclear data are needed. The FALSTAFF spectrometer under development at CEA-Saclay, France, is a two-arm spectrometer which will provide mass yields before (2V method) and after (EV method) neutron evaporation and consequently will have access to the neutron multiplicity as a function of mass. The axial ionization chamber, in addition to the kinetic energy value, will measure the energy loss profile of the fragment along its track. This energy loss profile will give information about the fragment nuclear charge. This paper will focus on recent developments on the FALSTAFF design. A special attention will be paid to the impact of the detector material thickness on the uncertainty of different observables. [ABSTRACT FROM AUTHOR]

The next generation spallation neutron sources, neutrino factories or RIB production facilities currently being designed and constructed world wide will increase the average proton beam power on target by a few orders of magnitude. Increased proton beam power results in target thermal hydraulic issues leading to new target designs, very often based on liquid metal technologies such as Hg, Pb, or PbBi. Radioactive nuclides produced in liquid metal targets are transported into hot cells, into pumps or close to electronics with radiation sensitive components. Besides the considerable amount of photon activity in the irradiated liquid metal, a significant amount of the Delayed Neutron (DN) precursor activity can be accumulated in the target fluid. The transit time from the front of a liquid metal target into areas, where DNs may be important, can be as short as a few seconds, i.e. well within one half-life of many DN precursors. Therefore, it seems very important to evaluate the DN flux as a function of position and determine if DNs may contribute significantly to the activation and dose rates. The multi-particle transport code MCNPX combined with the material evolution program CINDER’90 is used to predict the DN precursors and construct the DN tables. These DN tables are employed within the generalized geometrical model of the MegaPie spallation target at PSI (Switzerland). We show that the contribution of DNs and prompt spallation neutrons to the total neutron flux is comparable at the very top of the liquid PbBi loop. We also demonstrate that these estimates of DNs within MCNPX are very much model-dependent. No experimental data are available for DN yields and time spectra from high energy fission-spallation reactions. An experiment to perform these measurements is proposed. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]