The CABRI fast neutron Hodoscope: Renovation, qualification program and first results following the experimental reactor restart

The CABRI experimental pulse reactor, located at the Cadarache nuclear research center, southern France, is devoted to the study of Reactivity Initiated Accidents (RIA). For the purpose of the CABRI International Program (CIP), managed and funded by IRSN, in the framework of an OECD/NEA agreement, a huge renovation of the facility has been conducted since 2003. The Cabri Water Loop was then installed to ensure prototypical Pressurized Water Reactor (PWR) conditions for testing irradiated fuel rods. The hodoscope installed in the CABRI reactor is a unique online fuel motion monitoring system, operated by IRSN and dedicated to the measurement of the fast neutrons emitted by the tested rod during the power pulse. It is one of the distinctive features of the CABRI reactor facility, which is operated by CEA. The system is able to determine the fuel motion, if any, with a time resolution of 1 ms and a spatial resolution of 3 mm. The hodoscope equipment has been upgraded as well during the CABRI facility renovation. This paper presents the main outcomes achieved with the hodoscope since October 2015, date of the first criticality of the CABRI reactor in its new Cabri Water Loop configuration. Results obtained during reactor commissioning phase functioning, either in steady-state mode (at low and high power, up to 23 MW) or in transient mode (start-up, possibly beyond 20 GW), are discussed

Primary activity measurements with 4πγ NaI(Tl) counting and Monte Carlo calculated efficiencies

The radioactive concentrations of 18F, 88Y and 152Eu solutions and the activity of 222Rn gas ampoules are measured using a primary method involving 4πγ NaI(Tl) integral counting with a well-type NaI(Tl) detector and efficiencies computed by Monte Carlo simulations. The simulations use the GEANT code coupled with a routine (sch2for), which generates randomly the decay paths and emissions depending on the decay scheme parameters. The resulting radioactive concentrations of 88Y, 152Eu and 18F are found to agree with those measured with other primary measurement methods, such as 4π (β, e, X)-γ coincidence counting or liquid scintillation counting. Results of the determination of the activity of 222Rn gas ampoules by this method also match the results of an absolute standardisation technique in which radon is condensed onto a cold surface and its α-emissions are detected through an accurately specified solid angle