Speaker
Description
Accurate neutron personnel monitoring in nuclear installations requires calibration fields that reproduce workplace spectral characteristics. Existing simulated neutron workplace fields (SWF) are largely optimized for nuclear reactor conditions and offer limited flexibility for representing spectra relevant to spent-fuel handling. This work presents the design and initial validation of a modular Cf-252—based simulated workplace field implemented using a reconfigurable concentric-cube moderator targeting a spent-fuel representative spectrum.
The concentric-cube concept provides a flexible moderator system to reproduce representative spectra for multiple nuclear workplace scenarios, including PWR/BWR power plants, research reactors, spent-fuel, and MOX fuel. Ten moderator configurations were developed for different applications, with estimated total masses ranging from 80 kg to 13 t. For the present study, a spent-fuel design was selected for construction due to its practical mass (~430 kg).
A validated PHITS 3.31 room model using the JENDL-5 nuclear data was employed to evaluate configurations of low-carbon steel, graphite, and PMMA. The choice of materials considered availability and possible restrictions related to safety, health or security. Moderator thicknesses of low-carbon steel (6–58 cm), graphite (10–36 cm), and PMMA (0.5–3 cm) were systematically varied, and spectral agreement with the target distribution was quantified using Hellinger and cosine distance metrics. The selected configuration corresponded to outer cube side lengths of 24 cm (steel), 56 cm (graphite), 58 cm (PMMA) achieved a spectral distance of 0.07 from the representative spectrum, a dose rate of 390 µSv h$^{-1}$ at 75 cm for a 0.563 GBq Cf-252 source as of February 11, 2026.
Experimental validation is underway using DIAMON neutron spectrometry and Bonner sphere measurements combined with spectral unfolding, to assess spectral and dosimetric agreement with the target field. The modular SWF establishes a scalable and reusable calibration infrastructure, improving traceability and offering the infrastructure for intercomparisons of neutron dosimeters.