[en] The runaway diffusion coefficient, D_r, for the TJ-I tokamak has been deduced using two different methods: in the first, D_r is obtained using a steady state approach for values of the runaway confinement time τ_r deduced from hard X ray (HXR) bremsstrahlung spectra; in the second, D_r is deduced from sawtooth oscillations of HXR flux, and from the soft X ray intensity, recorded simultaneously. Data have been taken in a scan with the toroidal magnetic field B_T. Averaged values obtained for D_r=5-10 m²·s^-1, decreasing with B_T, are in both cases consistent. Assuming that magnetic turbulence is responsible for their transport, from D_r and averaged value of b-tilde/B_T, the magnetic fluctuations level, can be deduced. The thermal conductivity coefficient χ_e, obtained using other diagnostics in TJ-I, is compared with D_r. The results are in good agreement with those obtained in TJ-I using probes, spectroscopic methods, power balance analysis and a coupled analysis for temperature and density pulses. (author). 31 refs, 6 figs