The verification of spent fuel assemblies is among the ac¬tivities conducted during a safeguards inspection, and several non-destructive assay techniques are being devel¬oped to improve the accuracy of existing methods. Among other techniques, the self-indication neutron resonance densitometry (SINRD) relies on the passive neutron emis¬sion from the spent fuel assemblies. Previous research conducted at SCK•CEN found that the optimal configura¬tion was obtained with the fuel kept in air and surrounded by a polyethylene slab. The SINRD technique was proposed mainly for the direct quantification of the 239Pu mass in spent fuel, whereas this contribution is focused on the potential to detect the diver¬sion of fuel pins from a spent fuel assembly. First, the de¬tector responses of several fission chambers placed in the guide tubes of a PWR 17x17 fuel assembly were calculated with the Monte Carlo code MCNPX. Different fissile materi¬al coatings (e.g. 239Pu, 238U) were taken into account to consider detectors mostly sensitive to thermal and fast neutrons. In addition, the response to ionization chambers was modelled for the detection of gamma-rays. Fuel as¬semblies with material compositions corresponding to dif¬ferent initial enrichment, burnup, and cooling time were modelled to evaluate the sensitivity of the detector re¬sponses to the fuel irradiation history. The detector responses were calculated also for several di¬version scenarios where fuel pins from a complete fuel as¬sembly were replaced with dummies made of stainless steel. The diversions ranged from 15% to 50% of the total pins. The detector responses obtained from the diversion cases were compared to the values for the complete fuel assemblies to determine the capability of SINRD to detect the diversion of fuel pins. Promising results were obtained by combining the responses of the different detector types.
|Number of pages||8|
|State||Published - 1 Jun 2017|
|Event||2017 - ESARDA - European Safeguards Research & Development Association: 39th ESARDA Annual Meeting - Melia, Dusseldorf|
Duration: 3 Apr 2017 → 7 Apr 2017