Design and implementation of a new gamma spectrometry sighting device for gaseous iodine measurements in the VERDON CET-loop
Résumé
Source term assessment under severe accident conditions has been the main objective of several scientific research programmes over the past thirty years or so. But in the recent context of the Fukushima events, a new key issue has been identified the impact of control rod degradation on the release of volatile fission products. Indeed, a higher than expected fraction of gaseous iodine might have been released during the accident due to the reaction of boron with CsI. The VERDON facility, implemented at the LECA-STAR Hot Laboratory of the CEA Cadarache centre, hosted a new test to address this issue and to consolidate the database on the source term assessment of high burn-up UO2 fuel. Prior to that test, the VERDON experimental circuit has been enhanced with a new gamma spectrometry device dedicated to gaseous iodine measurements. Installing such a new device inside the hot cell of the VERDON facility raises a number of specific experimental and operational constraints, e.g. resolution, efficiency, dimensions and robustness of the detector. To match these specifications, the BrilLanCe 380 detector by Saint-Gobain Crystals has been chosen. This paper presents the qualification phase that led to the validation of the MCNP model of the detector, the lead shielding and tungsten screens designing phase preliminary to the implementation on the experimental loop and the first experimental results together with an experiment over calculation comparison which produced a ratio between 0.95 and 1.25 and attested the consistency of those latter.
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