Optimization of Turbulent Timescale of Surface Boundary Layer and Analysis of the Impact on Short-Term Mapping of Airborne Radionuclides for Complex Terrain Using Ar-41 as the Tracer

The well-accepted timescale for mean micro-meteorological surface and upper atmospheric observations for the air dispersion monitoring and modeling over any site is one hour in the nuclear industry. A new study aims to optimize the sub-timescale of time-averaged surface meteorological variables below one hour. This is achieved using high-resolution micro-meteorological data from a reference site with a complex terrain. The study has monitored the 10-s time-averaged micro-meteorological data and turbulent characteristics using a 30 Hz Fast response Scientific Ultrasonic Anemometer at the site with clear-sky weather status. The result of observations of an eventful day for 24 h is presented, herein, after analyzing seven days of primary data. The study found that the mean wind field and temperature during the convective period have a predominant perturbation along the daytime diurnal slope. At night-time, it shows a wave pattern of slope representing fluctuation of the variables. It is observed that the change beyond the 20-min averaging period, viz., for 30 min and 1 h, was modulating the diurnal slope of primary variables significantly. The study optimized the deciding averaging period to 10 min for turbulent flow, including wind components, temperature, derived wind direction, and diffusion classes. The study estimated the spatio-temporal ground level concentration of Ar-41 for 24 h under six sub-timescale simulations, ranging from 5 to 60 min using a Gaussian Puff air dispersion Modeling system, considering a hypothetical daily 1kCi release as activation product from a 100 m stack of a research reactor. The inference helps in near-real-time mapping of spatio-temporal radioactive plumes from the first hour to 24 h in case of a nuclear accident at any complex terrain site. The study also concluded that the sub-timescale under low wind is most influential under a stable atmospheric regime, a forced convective period.