Gamma and dose fields around the primary circuit of a helium-cooled fusion power plant

The Monte Carlo code MCNP-4 has been used to determine the photon flux spectra around two important regions of the primary circuit of the conceptual SEAFP Plant Model 1 (PM-1) fusion power plant. These fluxes have been converted to absorbed dose rates in human tissue by using dose rate conversion factors. Dose rates around a ‘hot-leg’ pipe were found to be low and not significantly above naturally occurring background levels. The dose field surrounding a steam generator were found to be higher than the ‘hot-leg’ pipe, but still well within acceptable limits. Dose rates inside the steam generator shell are considerably higher and would probably require remote and robotic method for inspection and maintenance tasks. The annual occupational radiation exposure to all plant workers was estimated to be approximately 170 man-mSv year−1, which is similar to the levels experienced with modern PWRs, after decades of optimisation.