First feedback with the AMMON integral experiment for the JHR calculations

The innovative design of the next international Material Testing Reactor, the Jules Horowitz Reactor (JHR), induced the development of a new neutron and photon calculation scheme HORUS3D, based on deterministic and stochastic codes and the European nuclear data library JEFF3.1.1. A new integral experiment, named the AMMON experiment, was designed in order to make the experimental validation of HORUS3D. The objectives of this experimental program are to calibrate the biases and uncertainties associated with the HORUS3D calculations for JHR safety and design calculations, but also the validation of some specific nuclear data (concerning mainly hafnium and beryllium isotopes). The experiment began in 2010 and is currently performed in the EOLE zero-power critical mock-up at CEA Cadarache. This paper deals with the first feedback of the AMMON experiments with reference 3-dimensional core calculations using the continuous-energy Monte Carlo TRIPOLI4 code and the JEFF3.1.1 library. The comparison between experimental and computed reactivity shows that the bias due to nuclear data on the AMMON reactivity is (+376 ± 340) pcm (1σ), which is very satisfactory concerning the a priori nuclear data uncertainty propagation: this result is very important since it made it possible to reduce by a factor 2 the uncertainty associated with the JHR reactivity calculation at the beginning of life of the reactor