The confinement and slowing-down of fast tritons in JET deuterium plasmas have been investigated by measuring the 14.1 MeV to 2.45 MeV neutron production ratio which is a direct measure of the triton burnup fraction. The 14.1 MeV neutron production was measured by means of the activation of copper samples, and the 2.45 MeV neutron production was obtained from fission chambers. Data were obtained for different plasma conditions giving burnup fractions in the range of 5 × 10−3 to 13 × 10−3. Comparison with calculations based on classical triton confinement and slowingdown in the JET plasma shows that the data are generally 20% lower than calculated values but still within the overall uncertainties involved