Assessment of IAEA exemption quantities on the basis of effective dose

The exemption quantities of the 20 most common radionuclides in use were evaluated according to the methodology applied in establishing exemption quantities by the IAEA in Basic Safety Series 115. The parts of the external dose conversion coefficients of the IAEA for various exposure modes, which affect exemption level significantly, were not based on effective dose of ICRP 60, but on an effective dose equivalent of ICRP 26. The internal effective dose conversion factors of the IAEA were somewhat different from those of ICRP 68. This paper calculated the effective dose conversion coefficients for external exposure, using MCNP4A code to replace those effective dose equivalent conversion coefficients of the IAEA and applied the internal dose conversion of ICRP 68, then combined them into the re-assessment of the exemption quantities. Energy Fluences in an exposed body for 20 mono photon energies ranging from 0.01 to 2 MeV(29 mono photon energies from 1.2 keV to 2 MeV for skin dose equivalent) were calculated using MCNP4A code and the response functions of effective doses for the energies were obtained by applying the effective dose coefficients of ICRP 74. Finally, effective dose coefficients of each radionuclide were calculated, using the response functions above and the nuclear transformation data provided in ICRP 38. When the exemption quantities were calculated by IAEA methodology as it is, the results matched the current IAEA value, admitting 10% of relative error except for P-32. Meanwhile, being evaluated with effective doses assessed in this study, the values of S-35 and Tl-201 were greatly different from IAEA's to a magnitude of an order in addition to the deviation of P-32. The exemption quantities of radionuclides emitting low energy photon, beta, including Tl-201, S-35 will vary with the present IAEA values, if assessed in terms of effective dose coefficients, and it is necessary to revaluate the current IAEA exemption quantity of P-32. (author)