Dose assessment for NPP staff for beyond design basis accident taking into account typical site infrastructure

Abstract

Assessment of radiation effect on nuclear power plant staff was made for beyond design basis accident (4 hours period). The considered accident scenario includes emergency radionuclide emission through containment bypass. Assessment of radiation effect on NPP staff was done on the basis of radionuclide concentration distribution on site considering typical infrastructure. Concentration mapping was calculated by developed program module for COMSOL 3.5a application. The obtained data included average volume radionuclide activities in lower air layer, total inhalation dose, effective dose of external exposure, equivalent and effective dose in thyroid and total effective dose for NPP staff during beyond design basis accident. Doses from radioactive cloud (external exposure) and from inhalation (internal exposure) were estimated for the following radionuclides: 137Cs, 134Cs, 131I, 133I, 90Sr. In the case of selected beyond design basis accident the total effective dose of staff is 61,98 mSv for the first 4 hours after the accident beginning. This number is slightly above the threshold of the allowable annual dose limit for personnel in emergency situations (50 mSv). Taking into account that short-lived iodine radionuclides 131I и133I give the main contribution in the dose (50.23 mSv including 27.23 mSv for thyroid), such emergency actions as respiratory protection and iodine prophylaxis for the staff can significantly decrease the received doses.