Delayed gamma radiation simulation in case of loss of water event using Monte Carlo method

Abstract Monte Carlo N-Particle (MCNP) transport code accelerated by AutomateD VAriaNce reducTion Generator (ADVANTG) code was used to simulate the transport of delayed gamma particles emitted from irradiated TRIGA fuel. At the first step, this method was verified on a simple experiment where irradiated fuel was packed inside a transport cask. The calculated dose rate field in the vicinity of the transport cask was compared to the measurements. Due to an acceptable agreement, the method was later used to analyse Loss of Water Event (LOWE) for the JSI TRIGA research reactor main and spent fuel pool. Main results of the analysis show that in the case of LOWE for the reactor pool, the reactor building has to be evacuated since dose rates exceed 2 mSv/h. The highest dose rates are expected at the reactor platform. The radiation from the core is backscattered from the ceiling and affects the dose rates inside the whole reactor hall and control room. In the worst case scenario, the operating personnel can start with corrective actions 10 days after the last reactor operation, when dose rates at the reactor platform drop below 20 mSv/h. If LOWE occurs for the spent fuel pool, the reactor building has to be evacuated. However, the corrective actions by the operating personnel can be started immediately after the accident. This is due to the fact, that the fuel can only be transported into the spent fuel pool after a three-month cooling period inside the main reactor pool, resulting in a lower fuel activity.