The PETALE experimental programme

Qualification of reflector materials for GEN-III reactors

Within the framework of a collaboration with CEA Cadarache, PETALE in the CROCUS reactor at EPFL intends to contribute to the validation and improvement efforts of neutron nuclear data in the MeV energy range for stainless steel, particularly in the prospect of heavy reflector elements of pressurized water reactors.

It is a continuation of the PERLE programme at the CEA Eole reactor, which showed that the 56Fe nuclear data were rather well predicted in JEFF-3.1.1. It mainly consists of transmission experiments, where part of the CROCUS water reflector will be replaced by successive sheets of stainless steel alloy and its elemental components – natural iron, nickel, and chromium. The metallic sheets will be set in a watertight box in air, and interleaved with thin dosimeter activation foils. In addition, reflector’s reactivity-worth estimates, in-core spectra characterisations, and sheet activation mapping, when possible, will be performed. While the experiments with the alloy will be used as a reference, the successive experiments with the separated elements aim at targeting and avoiding compensation effects with data assimilation methods.

Figure: Top and side view of the CROCUS reactor with the positioning of the reflector sheets in red (left) and flux per unit lethargy at various locations in the reflector sheets and in the UO2 and Umetal pins (right).

Because of the opposition between the low neutron flux in the dosimeters in the range of interest, requiring irradiations of maximal power and duration, and the operational constraints of the teaching activities at the CROCUS facility, an optimization of the experimental programme was carried out. Reaction rates of interest were maximised, and therefore the sensitivity to target nuclear data, while the integrated power was minimized. The work was performed by propagating uncertainties using the Total Monte Carlo (TMC) approach with ACE files from the TENDL-2017 library and the Serpent2 Monte Carlo code, in association with an acceleration method, Correlated Sampling (CS).

The experimental programme started in September 2019 by the characterisation of neutron spectra in CROCUS, in-core and in the water reflector, without the metal reflector to test methodologies. The reflector experiments are plannned for 2020.

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