Abstract
This study aims to model the radiological consequences that result from loss of coolant accident in open pool research reactor of 22 MW power. The loss of coolant accident results from rupture in the cooling systems of the reactor and consequently results in decreasing the water level in the reactor pool. Decreasing the water level, that represents the shielding material above the reactor core, results in increasing the dose rate in the top region in the reactor pool as well as the reactor building. LOCA normally results in shutting down the reactor due to the radioprotection system provided in the upper region of the reactor pool. A failure in shutdown systems of the reactor during LOCA is rare but expected and it represents the worst case. So, evaluating LOCA from the radiological point of view must be investigated for the safe shutdown mode as well as the failure of shutdown case. The study also includes occurring LOCA for shutdown reactor taking the decay time into consideration. ORIGEN-S module from scale system was used to estimate the delayed neutrons and gamma rays from the core for the shutdown mode. KENO-VI module from Scale system was used to estimate the prompt neutrons and gamma rays generated from the core for the failure case. Then, MAVRIC/Scale module was used to estimate the dose rate at the top point of the reactor pool for the two cases during LOCA.Studying the dose rate during LOCA aims to determine the water level that verifies the radiological safety limit at the top point of the reactor pool for the two cases. The calculations introduced a relationship between the water level that verifies the permissible radiological limit (WL) and the decay time (DT) in the range between 0 to 30 d.
Highlights
Radiation dose rate at the top point of the open pool type reactor is an important point for evaluating the radiological reactor state because it was provided with radiological alarm system that is capable to trigger the reactor shutdown system in case of rising the dose rate
The radiation dose rate at this point is resulting from two main sources; the radioactive isotopes dissolved in the pool water as well as the neutrons and gamma rays from the reactor core
Since evaluating the dose rate resulting from the dissolved radioactive isotopes in the pool water during normal reactor operation has been studied before [1], this study will focus in determining the dose rate resulting from the reactor core in case of loss of coolant accident (LOCA)
Summary
Radiation dose rate at the top point of the open pool type reactor is an important point for evaluating the radiological reactor state because it was provided with radiological alarm system that is capable to trigger the reactor shutdown system in case of rising the dose rate. The radiation dose rate at this point is resulting from two main sources; the radioactive isotopes dissolved in the pool water as well as the neutrons and gamma rays from the reactor core. The dose rate at this point results from the dissolved radioactive isotopes only and the contribution of the core source is negligible due to the high water level above the reactor core which is sufficient to attenuate the neutrons and gamma rays. Since evaluating the dose rate resulting from the dissolved radioactive isotopes in the pool water during normal reactor operation has been studied before [1], this study will focus in determining the dose rate resulting from the reactor core in case of LOCA
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