Optimized simulation research of a plastic scintillation fiber array tritium detector in water

Real-time monitoring of tritium in water is critical for nuclear safety, yet current liquid scintillation techniques are limited by poor portability and delayed results. Existing online detectors exhibit limited sensitivity (>10³ Bq L^-1), insufficient for regulatory limits (100 Bq L^-1). In this study, we present the design and simulation-based optimization of an online plastic scintillation fiber (PSF) array detector for tritium detection, using Geant4-based Monte Carlo (MC) simulation. Key parameters (PSF spacing: 0.1-1 mm, length: 50-500 mm, radius: 0.2-0.5 mm) were investigated to maximize detection efficiency. Environmental background from gamma and cosmic muons was suppressed by a combined 2 cm lead (Pb) shielding and low-energy signal filtering, achieving 94 % background reduction. A hexagonal close-packed PSF array with 0.3 mm spacing and 250 mm length achieved balanced photon deposition. Silicon photomultipliers (SiPMs) were evaluated as a replacement for traditional photomultiplier tubes (PMTs), offering a higher photon detection efficiency (0.5 vs. 0.2) and reducing optical crosstalk by 27 % (3.3 % vs. 4.5 %). A modular 3 × 3 detector array (500 mm PSF length) achieved a minimum detectable activity (MDA) of 10 Bq L^-1 within 600 s of acquisition time, meeting Chinese (GB 6249-2011) and European (2013/51/Euratom) standards. This study demonstrates the feasibility of a compact, field-deployable PSF-based detector for real-time tritium monitoring., high-sensitivity tritium monitoring capability, resolving the critical gap between laboratory methods and regulatory requirements.