  In this work we present simulation results for a modular tritium in-water
real-time monitor. The system allows for scalability in order to achieve the
required sensitivity. The modules are composed by 340 uncladed scintillating
fibers immersed in water and 2 photosensors for light readout. Light yield and
Birks' coefficient uncertainties for low energy beta particles is discussed. A
study of the detection efficiency according to the fiber length is presented.
Discussion on the system requirements and background mitigation for a device
with sensitivity of 100\,Bq/L, required to comply with the European directive
2013/51/Euratom, is presented. Due to the low energetic beta emission from
tritium a detection efficiency close to 3.3\% was calculated for a single 2\,mm
round fiber.
