Abstract
In this study, the decay energy productions rate of the SMART reactor core and assemblies were analyzed by using SCALE/Triton depletion sequences. The fuel elements and assemblies were modeled based on technical and operational design data. Time and problem dependent cross sections were generated for the reactor and used in the fuel depletion and decay analysis. The heat generation calculations during operation showed an energy production of 21.6 MW at the beginning of the cycle, the contribution of decay heat to the total reactor power (P/Po) was 6.5% in the BOC and drops to 6.3% toward EOC. Post-shutdown calculations of the decay energy produced per assembly resulted in a decreased from 0.356, 0.369, 0.363 MW at shutdown to 0.261, 0.271 and 0.266 kW after five years, for assembly type A, B, and C respectively.
Decay heat is generated mainly from short-lived fission products; the fast decay of these radionuclides results in an extreme drop in the decay heat generation hours after shutdown. In the first day after reactor shutdown, the ratio of decay heat to total reactor power (P/Po) drops from 6.3% to only 0.53%. System ability to remove this amount of heat from the reactor core during this period is crucial to the reactor safety. Loss of coolant and failure to remove decay heat is a substantial threat to fuel integrity and may lead to overheating and core meltdown.
The reactor core decay heat was calculated for 30 years cooling period; results show that core energy decreases exponentially with time, from 20.8 MW to only 6.8 kW after 30 years. The decay heat as a function of time was calculated and compared to the total reactor power. The energy production of the top 30 heat generating radionuclides and their contribution to reactor decay heat were also estimated.