This study presents an analysis of the ARIANE GU3 sample, in terms of nuclide inventory, as well as sample rod and assembly decay heat. The validation of a number of CASMO5 and library versions are performed with regards to the measured nuclide inventory, taking into account two dimensional lattice simulations. Uncertainties due to various sources (nuclear data, operating conditions and manufacturing tolerances) are also provided, and are combined with biases into expanded uncertainties. This study is similar to a previous one on the GU1 sample and fit in the framework of code validation, as well as in the estimation of code predictive power for spent fuel characterization.

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The spectrometer ATHENA (Accurate Telescope for High Energy Neutron metrology Applications), in development at the LNE-IRSN, characterizes energy and fluence of fast neutron fields. The detector is a Recoil Proton Telescope and measures neutron energies in the range of 5 to 20 MeV. The system is intended to become a primary standard for both energy and fluence measurements. The most innovative part of ATHENA is made of three CMOS pixel sensors, thinned down to 50 microns thickness, allowing an accurate tracking of the recoil. The use of CMOS sensors and a thick silicon diode increase the intrinsic efficiency of the detector by a factor of ten compared with conventional designs. In this paper, we demonstrate the ability of the detector to measure neutron energies in the range of 5 to 20 MeV. Experimental investigations, using mono-energetic neutron fields produced by the AMANDE facility, indicate a good reconstruction of neutron energies. The present design is still under development. The accuracy of measuring 5 MeV and 14 MeV neutron energies was 15% and 5%, respectively.

The estimation of the neutron fluence at the Reactor Pressure Vessel (RPV) is classically carried out by a two-step approach. The first step is to estimate the full core neutron source term whether the second step of the calculation consists in the transport of neutrons from the core (source term) to the RPV using the neutron fission distribution determined in the previous step. For this purpose, the neutron fission distribution is to be accurately determined at the fuel pin level for the assemblies on the border of the core. To achieve this goal, two methods are evaluated in this study. The first method considered is a full core 2D Monte Carlo calculation using the MNCP6 code. The second method is based on a deterministic approach using the CASMO5 multi-segment option, allowing a full 2D transport calculation at the pin level with an expected accuracy similar to a stochastic method. The comparison of the two methods shows an overall good agreement with differences within the statistical uncertainty for different cores: homogeneous UOX core, mixed UOX-MOX loading and the effect of the hafnium rods used in the assemblies in the periphery of the core. The modelling limitation and the associated calculational time are discussed for the comparison of the two approaches.

The spectrometer ATHENA (Accurate Telescope for High-Energy Neutron metrology Applications) is being developed at the LNE-IRSN and aims at characterising energy and fluence of fast neutron fields. The detector is a recoil proton telescope and measures neutron fields in the range of 5-20 MeV. This telescope is intended to become a primary standard for both energy and fluence measurements. The neutron detection is achieved by a polyethylene radiator for n-p conversion, three 50-µm-thick silicon sensors that use CMOS technology for proton tracking and a 3-mm-thick silicon diode to measure the residual proton energy. The use of CMOS sensors and silicon diode, owing to a large detection solid angle, increases the intrinsic efficiency of the detector by a factor of 10 compared with conventional designs. The ability of the spectrometer to determine the neutron energy was demonstrated and reported elsewhere. This paper focuses on the fluence measurement of monoenergetic neutron fields in the range of 5-20 MeV. Experimental investigations, performed at the AMANDE facility, indicate a good estimation of neutron fluence at various energies. In addition, a complete description of uncertainties budget is presented in this paper and a Monte Carlo propagation of uncertainty sources leads to a fluence measurement with a precision ∼3-5 % depending on the neutron energy.