Comparative study of 131I released during a nuclear accident

Radioiodine-131 (131I) is the most significant environmental contaminant during a short-term nuclear accident. When present in the atmosphere, it concentrates mainly in the thyroid gland through inhalation or ingestion. This can lead to partial or total destruction of thyroid cells, potentially causing hypothyroidism. It therefore negatively affects the thyroid in exposed populations. At high doses, radiation can also cause cellular mutations and increase the risk of thyroid cancer, particularly in children under five years old and those exposed during pregnancy. In such cases, nonradioactive iodine tablets are used to saturate the thyroid and block the absorption of radioactive iodine. This study aimed to quantify and compare total atmospheric emissions of 131I using the ORIGEN-JR code, and to assess the radiological impacts on the environment and humans by estimating and comparing the total effective dose (TED) and committed effective dose equivalent (CEDE) using the HOTSPOT code in the early stages following the Fukushima accident and at the TRIGA Mark-II research reactor in Bangladesh. The simulation results indicate that for the TRIGA MARK-II research reactor, the TED was approximately 379 mSv at a distance of 360 m, with a thyroid CEDE of 19 mSv. For the Fukushima reactor, the TED was approximately 875 mSv at 590 m, with a thyroid CEDE of about 63 mSv. Compared to the IAEA's annual regulatory limits, the TED and CEDE resulting from the Fukushima accident exceeded the permissible thresholds, requiring both evacuation of the population and iodine prophylaxis. Conversely, for the TRIGA MARK-II research reactor, the distribution of iodine tablets is not necessary; however, containment measures remain essential.