Validation of a modified FLEXPART model for short-range radiological dispersion and dose assessments in ONERS Decision Support System

Abstract

Online Nuclear Emergency Response System (ONERS) is a GIS based Decision Support System developed for the management of Off-Site Nuclear Emergencies at Nuclear Power Plant (NPP) sites in India. As part of this development, the FLEXPART model is modified to compute atmospheric dispersion using observations from the local meteorological tower for the estimation of concentration and radiological dose over short-range range in realtime. In this work, the modified FLEXPART is validated for dose assessments using gamma dose rate measurements by Autonomous Gamma Dose Loggers installed around the Pressurized Heavy Water Reactor (PHWR) of Madras Atomic Power Station (MAPS) at Kalpakkam site in southeast India. The plume exposure dose is computed in two pathways i) cloudshine dose by incorporating a point kernel algorithm ii) submersion dose by semi-infinite plume method using FLEXPART. Comparison of model estimates with detector data for the 8-day period (01–08 December 2017) covering various atmospheric conditions indicates that the simulated cloud gamma dose rate is in good agreement with observed dose under stable, neutral, and unstable conditions with a coefficient of determination of 0.66, 0.73 and 0.49 respectively. The overestimation of dose under unstable conditions could be due to underestimation of mixed layer height (h) and convective velocity scale (w*) computed using the local similarity approach while using tower data, which needs further insights for improvements.