Methodological comparison of dose estimation from exposure during boating activities

Abstract

The exposure scenario of an adult individual boating on a contaminated body of water is a plausible situation, given that nuclear power plants release radioactivity into bodies of water as part of normal operation through liquid discharge and through accidents that may occur. When calculating dose rate coefficients from external exposure during boating activities, it has been common practice to make a conservative estimate by halving coefficients from water immersion. To determine the appropriateness of this factor a physically realistic boating scenario was modelled in MCNP6, a Monte Carlo N-Particle code, for three radionuclides of interest to reactor liquid effluents: Co-60, Cs-137, and Mn-54. However, the complexity of this MCNP geometry led to long simulation run-times before acceptable statistics were reached. Simpler modelling geometries and different modelling types were computed for comparison and determination of the acceptability of these methods. To accomplish this, a basic phantom and boat model was created for the point-kernel code QAD-CGGP-A and ran for select organs. Later, MCNP6 calculations of air dose were made in the original model with the phantom removed; these results were converted into expected dose in tissue and were attenuated by a factor representing the loss of tissue shielding after phantom removal. Comparisons were made using reference values taken from the LADTAP II code, as well as Federal Guidance Reports No. 12 and 15. Differences between reference values for boating dose rate coefficients and those coefficients found through the modelling techniques of this research are presented.