In situ monitoring of the hydrogenic fuel inventory in plasma-facing materials (PFMs) is a key issue for the sustainable and safe operation of a magnetically confined fusion device. A laser induced breakdown spectroscopy system has been applied on the linear plasma device PSI-2 to determine the short-term retention of deuterium (D) in the most promising PFM-tungsten (W). Measurements of the fuel content were performed (a) during plasma exposure, providing the dynamic D content in W and (b) after plasma exposure, determining the outgassing of D from W in vacuum. The in situ measurement of D content in W is in the time range of about 100 minutes before plasma termination (during plasma exposure) to 240 minutes after plasma termination (after plasma exposure). The measured surface D content in W drops to 17%–37% of the initial amount (measured before the plasma is switched off), showing a reduction factor of ca. 3–6 within the first 240 minutes.